query: the set of frequencies produced by an excited state atom is called its

pos: Emission spectrum Emission spectrum The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an atom or molecule making a transition from a high energy state to a lower energy state. The photon energy of the emitted photon is equal to the energy difference between the two states. There are many possible electron transitions for each atom, and each transition has a specific energy difference. This collection of different transitions, leading to different radiated wavelengths, make up an emission spectrum. Each element's emission spectrum is unique. Therefore, spectroscopy can be used

pos: Emission spectrum are emitted. Each of these frequencies are related to energy by the formula: where formula_2 is the energy of the photon, formula_3 is its frequency, and formula_4 is Planck's constant. This concludes that only photons with specific energies are emitted by the atom. The principle of the atomic emission spectrum explains the varied colors in neon signs, as well as chemical flame test results (described below). The frequencies of light that an atom can emit are dependent on states the electrons can be in. When excited, an electron moves to a higher energy level or orbital. When the electron falls

pos: Emission spectrum semi-classical version continues to be more useful in most practical computations. When the electrons in the atom are excited, for example by being heated, the additional energy pushes the electrons to higher energy orbitals. When the electrons fall back down and leave the excited state, energy is re-emitted in the form of a photon. The wavelength (or equivalently, frequency) of the photon is determined by the difference in energy between the two states. These emitted photons form the element's spectrum. The fact that only certain colors appear in an element's atomic emission spectrum means that only certain frequencies of light

pos: Emission spectrum radiation. This is sometimes called the second Einstein coefficient, and can be deduced from quantum mechanical theory. Emission spectrum The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an atom or molecule making a transition from a high energy state to a lower energy state. The photon energy of the emitted photon is equal to the energy difference between the two states. There are many possible electron transitions for each atom, and each transition has a specific energy difference. This collection of different transitions, leading to different radiated

pos: Homogeneous broadening Homogeneous broadening Homogeneous broadening is a type of emission spectrum broadening in which all atoms radiating from a specific level under consideration radiate with equal opportunity. If an optical emitter (e.g. an atom) shows homogeneous broadening, its spectral linewidth is its natural linewidth, with a Lorentzian profile. Broadening in laser physics is a physical phenomenon that affects the spectroscopic line shape of the laser emission profile. The laser emission is due to the (excitation and subsequent) relaxation of a quantum system (atom, molecule, ion, etc.) between an excited state (higher in energy) and a lower one. These states can be

neg: Fluorescence occurs when an orbital electron of a molecule, atom, or nanostructure, relaxes to its ground state by emitting a photon from an excited singlet state: Here formula_3 is a generic term for photon energy with h = Planck's constant and = frequency of light. The specific frequencies of exciting and emitted lights are depended on the particular system. S is called the ground state of the fluorophore (fluorescent molecule), and S is its first (electronically) excited singlet state. A molecule in S can relax by various competing pathways. It can undergo "non-radiative" relaxation in which the excitation energy is dissipated

neg: Saturated absorption spectroscopy Saturated absorption spectroscopy In experimental atomic physics, saturated absorption spectroscopy or Doppler-free spectroscopy is a set-up that enables the precise determination of the transition frequency of an atom between its ground state and an optically excited state. The accuracy to which these frequencies can be determined is, ideally, limited only by the width of the excited state, which is the inverse of the lifetime of this state. However, the samples of atomic gas that are used for that purpose are generally at room temperature, where the measured frequency distribution is highly broadened due to the Doppler effect. Saturated absorption spectroscopy

neg: Dark state to the ground state by emitting a single photon. It can only decay by collisions with other atoms or by emitting multiple photons. Since these events are rare, the atom can remain in this excited state for a very long time, such an excited state is called a metastable state. We start with a three-state Λ-type system, where formula_10 and formula_11 are dipole-allowed transitions and formula_12 is forbidden. In the rotating wave approximation, the semi-classical Hamiltonian is given by with where formula_16 and formula_17 are the Rabi frequencies of the probe field (of frequency formula_18) and the coupling field (of

neg: Doppler cooling be controlled, most frequencies do not affect the atom—it is invisible at those frequencies. There are only a few points of electromagnetic frequency that have any effect on that atom. At those frequencies, the atom can absorb a photon from the laser, while transitioning to an excited electronic state, and pick up the momentum of that photon. Since the atom now has the photon's momentum, the atom must begin to drift in the direction the photon was traveling. A short time later, the atom will spontaneously emit a photon in a random direction, as it relaxes to a lower electronic

neg: Resonance fluorescence lithium is used because it can be closely modeled to a two-level atom as the excited states of the singular electron are separated by large enough energy gaps to significantly reduce the possibility of the electron jumping to a higher excited state. Thus it allows for easier frequency tuning of the applied laser as frequencies further off resonance can be used while still driving the electron to jump to only the first excited state. Once the atom is excited, it will release a photon at the frequency of the absorbed photon within the range of the detuning of the laser

neg: Hollow-cathode lamp to a specific atomic transition by making use of the optogalvanic effect, which is a result of direct or indirect photoionization. By shining the light source into the HCL, one can excite or even eject electrons (directly photoionize) from the atoms inside the lamp, so long as the light source includes frequencies corresponding to the right atomic transitions. Indirect photoionization can then occur when electron collisions with the excited atom eject an atomic electron. formula_3 = atom, formula_4 = photon, formula_5 = atom in excited state, and formula_6 = electron The newly created ions cause an increase in the current

neg: Saturated absorption spectroscopy photodiode reading averaged over many sweeps. In real atoms, there are sometimes more than two relevant transitions within the sample's Doppler profile (e.g. in alkali atoms with hyperfine interactions). This will generate the apparition of other dips in the absorption feature due to these new resonances in addition to crossover resonances. Saturated absorption spectroscopy In experimental atomic physics, saturated absorption spectroscopy or Doppler-free spectroscopy is a set-up that enables the precise determination of the transition frequency of an atom between its ground state and an optically excited state. The accuracy to which these frequencies can be determined is, ideally, limited

neg: Jaynes–Cummings model oscillation associated with an atom-field system of formula_2 quanta will have frequency formula_122. As explained below, this discrete spectrum of frequencies is the underlying reason for the collapses and subsequent revivals probabilities in the model. As shown in the previous subsection, if the initial state of the atom-cavity system is formula_123 or formula_124, as is the case for an atom initially in a definite state (ground or excited) entering a cavity containing a known number of photons, then the state of the atom-cavity system at later times becomes a superposition of the "new" eigenstates of the atom-cavity system: This change

neg: Electromagnetic radiation it excites the atom, elevating an electron to a higher energy level (one that is on average farther from the nucleus). When an electron in an excited molecule or atom descends to a lower energy level, it emits a photon of light at a frequency corresponding to the energy difference. Since the energy levels of electrons in atoms are discrete, each element and each molecule emits and absorbs its own characteristic frequencies. Immediate photon emission is called fluorescence, a type of photoluminescence. An example is visible light emitted from fluorescent paints, in response to ultraviolet (blacklight). Many other fluorescent emissions

neg: Excited state bound to the atom, and the atom will become ionized. After excitation the atom may return to the ground state or a lower excited state, by emitting a photon with a characteristic energy. Emission of photons from atoms in various excited states leads to an electromagnetic spectrum showing a series of characteristic emission lines (including, in the case of the hydrogen atom, the Lyman, Balmer, Paschen and Brackett series.) An atom in a high excited state is termed a Rydberg atom. A system of highly excited atoms can form a long-lived condensed excited state e.g. a condensed phase made completely

neg: Excited state excited state absorption. A further consequence is reaction of the atom in the excited state, as in photochemistry. Excited states give rise to chemical reaction. Excited state In quantum mechanics, an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being raised

neg: Excited state (an atom or molecule) from low-energy excited state to a high-energy excited state with the absorption of a photon is called "excited state absorption" (ESA). Excited state absorption is possible only when an electron has been already excited from the ground state to a lower excited state. The excited state absorption is usually an undesired effect, but it can be useful in upconversion pumping. The excited state absorption measurements are done using pump-probe techniques. However, it is not easy to measure them compared to ground-state absorption and in some cases complete bleaching of the ground state is required to measure

neg: Photoelectrochemical process electrons to a higher energy band. When an excited electron falls back to a lower energy state again, it is called electron relaxation. This can be done by radiation of a photon or giving the energy to a third spectator particle as well. In physics there is a specific technical definition for energy level which is often associated with an atom being excited to an excited state. The excited state, in general, is in relation to the ground state, where the excited state is at a higher energy level than the ground state. Photoexcitation is the mechanism of electron excitation

neg: Jaynes–Cummings model cavity initially in its excited state, while the cavity is initially in the vacuum state. Then the state of the atom-field system as a function of time is: So the probabilities to find the system in the ground or excited states after interacting with the cavity for a time formula_119 are: Thus the probability amplitude to find the atom in either state oscillates. This is the quantum mechanical explanation for the phenomenon of vacuum Rabi oscillation. In this case, there was only a single quantum in the atom-field system, carried in by the initially excited atom. In general, the Rabi

neg: Pound–Rebka experiment is not required to be at exactly the resonant frequency, but must be in a narrow range of frequencies centred on the resonant frequency: a photon with a frequency outside this region cannot excite the electron to the excited state. Now consider two copies of this electron-atom system, one in the excited state (the emitter), the other in the lower energy state (the receiver). If the two systems are stationary relative to one another and the space between them is flat (i.e. we neglect gravitational fields) then the photon emitted by the emitter can be absorbed by the electron in

neg: Jaynes–Cummings model the longer time regime; in that case, the periodic nature of the slowly varying double exponential predicts that there should also be a "revival" of probability at time: The revival of probability is due to the re-phasing of the various discrete frequencies. If the field were classical, the frequencies would have a continuous spectrum, and such re-phasing could never occur within a finite time. A plot of the probability to find an atom initially in the ground state to have transitioned to the excited state after interacting with a cavity prepared a in a coherent state vs. the unit-less parameter

neg: Ramsey interferometry atoms whose Doppler-induced de-phasing has doubled and whose Ramsey fringes have completely disappeared (this is known as the "backward-stimulated photon echo," and its signal goes to zero after integrating over all velocities.) The interaction geometry of two pairs of counter-propagating waves that Bordé et al. introduced allows for improved resolution of spectroscopy of frequencies in the optical range, such as those of Ca and I. Specifically, however, the Ramsey–Bordé interferometer is an atom interferometer that uses this four traveling wave geometry and the phenomenon of atomic recoil. In Bordé's notation, is the ground state and is the excited state. When

neg: Spontaneous emission Spontaneous emission Spontaneous emission is the process in which a quantum mechanical system (such as an atom, molecule or subatomic particle) transitions from an excited energy state to a lower energy state (e.g., its ground state) and emits a quantum in the form of a photon. Spontaneous emission is ultimately responsible for most of the light we see all around us; it is so ubiquitous that there are many names given to what is essentially the same process. If atoms (or molecules) are excited by some means other than heating, the spontaneous emission is called luminescence. For example, fireflies are

neg: Laser opposed to the literal cavity that would be employed at microwave frequencies in a maser. The resonator typically consists of two mirrors between which a coherent beam of light travels in both directions, reflecting back on itself so that an average photon will pass through the gain medium repeatedly before it is emitted from the output aperture or lost to diffraction or absorption. If the gain (amplification) in the medium is larger than the resonator losses, then the power of the recirculating light can rise exponentially. But each stimulated emission event returns an atom from its excited state to the

neg: Population inversion happens due to the presence of the electromagnetic field from a photon, a photon is released in the same phase and direction as the "stimulating" photon, and is called stimulated emission. The rate at which stimulated emission occurs is proportional to the number of atoms "N" in the excited state, and the radiation density of the light. The base probability of a photon causing stimulated emission in a single excited atom was shown by Albert Einstein to be exactly equal to the probability of a photon being absorbed by an atom in the ground state. Therefore, when the numbers of

neg: Resonance ionization from the ground state, the atoms should be efficiently excited and ionized, and each atom should be converted by the photon field of a short-timed pulsed laser to produce a positive ion and a valence electron. In a basic RIS process, a pulsed laser beam produces photons of the right energy in order to excite an atom initially in its ground state, "a", to an excited level, "b". During the laser pulse, the ion population of state "b" increases at the expense of that of state "a". After a few minutes, the rate of stimulated emission from the excited state

neg: Spontaneous emission by the superposition of the wavefunctions of the excited state atom with no photon and the ground state atom with a single emitted photon: where formula_27 and formula_28 are the atomic excited state-electromagnetic vacuum wavefunction and its probability amplitude, formula_29 and formula_30 are the ground state atom with a single photon (of mode formula_31) wavefunction and its probability amplitude, formula_32 is the atomic transition frequency, and formula_33 is the frequency of the photon. The sum is over formula_34 and formula_35, which are the wavenumber and polarization of the emitted photon, respectively. As mentioned above, the emitted photon has a chance

neg: Spontaneous emission which can mix with the excited stationary states of the atom. As a result of this interaction, the "stationary state" of the atom is no longer a true eigenstate of the combined system of the atom plus electromagnetic field. In particular, the electron transition from the excited state to the electronic ground state mixes with the transition of the electromagnetic field from the ground state to an excited state, a field state with one photon in it. Spontaneous emission in free space depends upon vacuum fluctuations to get started. Although there is only one electronic transition from the excited state

neg: Population inversion to the energy gap Δ"E" of the excited state to ground state transition. In this case, the excited atom relaxes to the ground state, and it produces a second photon of frequency ν. The original photon is not absorbed by the atom, and so the result is two photons of the same frequency. This process is known as "stimulated emission". Specifically, an excited atom will act like a small electric dipole which will oscillate with the external field provided. One of the consequences of this oscillation is that it encourages electrons to decay to the lowest energy state. When this

neg: Excited state Excited state In quantum mechanics, an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being raised to an excited state. The temperature of a group of particles is indicative of the level of excitation (with the notable exception of systems that

neg: Zeeman slower moves in a specific direction and encounters a counter-propagating laser beam resonant with its transition, it is very likely to absorb a photon. The absorption of this photon gives the atom a "kick" in the direction that is consistent with momentum conservation and brings the atom to its excited state. However, this state is unstable and some time later the atom decays back to its ground state via spontaneous emission (after a time on the order of nanoseconds, for example in Rubidium 87 the excited state of the D2 transition has a lifetime of 26.2 ns). The photon will be

neg: Nuclear isomer ejected from the atom, a process termed the photoelectric effect. This should not be confused with the internal conversion process, in which no gamma ray photon is produced as an intermediate particle. Nuclear isomer A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons (protons or neutrons). "Metastable" describes nuclei whose excited states have half-lives 100 to 1000 times longer than the half-lives of the excited nuclear states that decay with a "prompt" half life (ordinarily on the order of 10 seconds). The term "metastable" is usually restricted

neg: Photonic molecule The effect is caused by a so-called Rydberg blockade, which, in the presence of one excited atom, prevents nearby atoms from being excited to the same degree. In this case, as two photons enter the atomic cloud, the first excites an atom, annihilating itself in the interaction, but the transmitted energy must move forward inside the excited atom before the second photon can excite nearby atoms. In effect the two photons push and pull each other through the cloud as their energy is passed from one atom to the next, forcing them to interact. This photonic interaction is mediated by

neg: Excimer lamp sufficient concentration of electrons with energies that are high enough to produce the precursors of the excimer molecules, which are mainly excited and ionized rare gas atoms. Excitation of a working gas mixture leads to formation of excited and ionized rare gas atoms: excitation direct ionization stepwise ionization where "Rg*" is an excited electronic state of a rare gas atom, "Rg" is an ionized state of a rare gas atom, "e" is an electron. When the active medium accumulates enough excited rare gas atoms, the excimer molecules are formed by the following reaction: where "M" is a third particle carrying

neg: Excimer Excimer An excimer (originally short for excited dimer) is a short-lived dimeric or heterodimeric molecule formed from two species, at least one of which has completely filled valence shell by electrons (for example, noble gases). In this case, formation of molecules is possible only if such atom is in an electronic excited state. Heteronuclear molecules and molecules that have more than two species are also called exciplex molecules (originally short for excited complex). Excimers are often diatomic and are composed of two atoms or molecules that would not bond if both were in the ground state. The lifetime of an

neg: Gas-phase ion chemistry G is the excited state species (indicated by the superscripted asterisk), and M is the species that is ionized by the loss of an electron to form the radical cation (indicated by the superscripted "plus-dot"). Penning ionization refers to the interaction between a gas-phase excited-state atom or molecule G and a target molecule M resulting in the formation of a radical molecular cation M, an electron e, and a neutral gas molecule G: Penning ionization occurs when the target molecule has an ionization potential lower than the internal energy of the excited-state atom or molecule. Associative Penning ionization can also

neg: Excited state of this concept comes by considering the hydrogen atom. The ground state of the hydrogen atom corresponds to having the atom's single electron in the lowest possible orbit (that is, the spherically symmetric "1s" wavefunction, which, so far, has demonstrated to have the lowest possible quantum numbers). By giving the atom additional energy (for example, by the absorption of a photon of an appropriate energy), the electron is able to move into an excited state (one with one or more quantum numbers greater than the minimum possible). If the photon has too much energy, the electron will cease to be

neg: Electron configuration The energy of a configuration is often approximated as the sum of the energy of each electron, neglecting the electron-electron interactions. The configuration that corresponds to the lowest electronic energy is called the ground state. Any other configuration is an excited state. As an example, the ground state configuration of the sodium atom is 1s2s2p3s, as deduced from the Aufbau principle (see below). The first excited state is obtained by promoting a 3s electron to the 3p orbital, to obtain the 1s2s2p3p configuration, abbreviated as the 3p level. Atoms can move from one configuration to another by absorbing or emitting

neg: Resonance fluorescence Resonance fluorescence Resonance fluorescence is the process in which a two-level atom system interacts with the quantum electromagnetic field if the field is driven at a frequency near to the natural frequency of the atom. Typically the photon contained electromagnetic field is applied to the two-level atom through the use of a monochromatic laser. A two-level atom is a specific type of two-state system in which the atom can be found in the two possible states. The two possible states are if an electron is found in its ground state or the excited state. In many experiments an atom of

neg: Term symbol of the atom. For example, in Ar atom excited from a ground state "…3p" to an excited state "…3p4p" in electronic configuration, "3p" is for the parent ion while "4p" is for the excited electron. In Racah notation, states of excited atoms are denoted as formula_96. Quantities with a subscript "1" are for the parent ion, "n" and "l" are principal and orbital quantum numbers for the excited electron, "K" and "J" are quantum numbers for formula_97 and formula_98 where formula_99 and formula_100 are orbital angular momentum and spin for the excited electron respectively. “"o"” represents a parity of excited

neg: Argon compounds produced during mass spectroscopy have higher intensity when the binding energy of the ion is higher. Transition elements have higher binding and ion flux intensity compared to main group elements. Argides can be formed in the plasma by excited argon atoms reacting with another element atom, or by an argon atom binding with another ion: Doubly charged cations, called superelectrophiles, are capable of reacting with argon. Ions produced include ArCF ArCH, ArBF and ArBF containing bonds between argon and carbon or boron. Doubly ionised acetylene HCCH reacts inefficiently with argon to yield HCCAr. This product competes with the formation of

neg: Internal conversion nucleus) in an excited state. The atom missing an inner electron can relax by a cascade of X-ray emissions as higher energy electrons in the atom fall to fill the vacancy left in the electron cloud by the captured electron. Such atoms also typically exhibit Auger electron emission. Electron capture, like beta decay, also typically results in excited atomic nuclei, which may then relax to a state of lowest nuclear energy by any of the methods permitted by spin constraints, including gamma decay and internal conversion decay. Internal conversion Internal conversion is a radioactive decay process wherein an excited nucleus

neg: Magneto-optical trap of the cooling cycle. The magneto-optical trapping of rubidium 85, for example, involves cycling on the closed formula_8 transition. On excitation, however, the detuning necessary for cooling gives a small, but non-zero overlap with the formula_9 state. If an atom is excited to this state, which occurs roughly every thousand cycles, the atom is then free to decay either the formula_10, light coupled upper hyperfine state, or the formula_11 "dark" lower hyperfine state. If it falls back to the dark state, the atom stops cycling between ground and excited state, and the cooling and trapping of this atom stops. A

neg: Resonance fluorescence for formula_6, the annihilation operator of the field, formula_7 formula_8, where formula_9 and formula_10 are frequency parameters used to simplify equations. Now that the dynamics of the field with respect to the states of the atom has been described, the mechanism through which photons are released from the atom as the electron falls from the excited state to the ground state, Spontaneous Emission, can be examined. Spontaneous emission is when an excited electron arbitrarily decays to the ground state emitting a photon. As the electromagnetic field is coupled to the state of the atom, and the atom can only absorb

neg: Rabi cycle example, for a two-state atom (an atom in which an electron can either be in the excited or ground state) in an electromagnetic field with frequency tuned to the excitation energy, the probability of finding the atom in the excited state is found from the Bloch equations to be: where formula_2 is the Rabi frequency. More generally, one can consider a system where the two levels under consideration are not energy eigenstates. Therefore, if the system is initialized in one of these levels, time evolution will make the population of each of the levels oscillate with some characteristic frequency, whose

neg: Stimulated emission quantum theory, wherein the emission is described in terms of photons that are the quanta of the EM field. Stimulated emission can also occur in classical models, without reference to photons or quantum-mechanics. (See also Laser#history ) Stimulated emission can be modelled mathematically by considering an atom that may be in one of two electronic energy states, a lower level state (possibly the ground state) (1) and an "excited state" (2), with energies "E" and "E" respectively. If the atom is in the excited state, it may decay into the lower state by the process of spontaneous emission, releasing the

neg: Helium dimer at levels below parts per billion. The Hopfield continuum is a band of ultraviolet light between 600 and 1000 Å in wavelength formed by photodissociation of helium molecules. One mechanism for formation of the helium molecules is firstly a helium atom becomes excited with one electron in the 2S orbital. This excited atom meets two other non excited helium atoms in a three body association and reacts to form a AΣ state molecule with maximum vibration and a helium atom. Helium molecules in the quintet state Σ can be formed by the reaction of two spin polarised helium atoms in

neg: Stimulated emission difference in energies between the two states as a photon. The photon will have frequency "ν" and energy "hν", given by: where "h" is Planck's constant. Alternatively, if the excited-state atom is perturbed by an electric field of frequency "ν", it may emit an additional photon of the same frequency and in phase, thus augmenting the external field, leaving the atom in the lower energy state. This process is known as stimulated emission. In a group of such atoms, if the number of atoms in the excited state is given by "N", the rate at which stimulated emission occurs is

neg: Spontaneous emission eigenstates of an atom are properly diagonalized, the overlap of the wavefunctions between the excited state and the ground state of the atom is zero. Thus, in the absence of a quantized electromagnetic field, the excited state atom cannot decay to the ground state. In order to explain spontaneous transitions, quantum mechanics must be extended to a quantum field theory, wherein the electromagnetic field is quantized at every point in space. The quantum field theory of electrons and electromagnetic fields is known as quantum electrodynamics. In quantum electrodynamics (or QED), the electromagnetic field has a ground state, the QED vacuum,

neg: Ion source resultant collisions with other reagent gas molecules will create an ionization plasma. Positive and negative ions of the analyte are formed by reactions with this plasma. For example, protonation occurs by Charge-exchange ionization (also known as charge-transfer ionization) is a gas phase reaction between an ion and an atom or molecule in which the charge of the ion is transferred to the neutral species. Chemi-ionization is the formation of an ion through the reaction of a gas phase atom or molecule with an atom or molecule in an excited state. Chemi-ionization can be represented by where G is the excited

neg: Rydberg state of a distributed ionic core. Even for many electronically excited molecular systems, the ionic core interaction with an excited electron can take on the general aspects of the interaction between the proton and the electron in the hydrogen atom. The spectroscopic assignment of these states follows the Rydberg formula and they are called Rydberg states of molecules. Although the energy formula of Rydberg series is a result of hydrogen-like atom structure, Rydberg states are also present in molecules. Wave functions of high Rydberg states are very diffused and span diameters that approach infinity. As a result, any isolated neutral molecule

neg: Theoretical and experimental justification for the Schrödinger equation for an electron orbiting an atom are those that allow for standing waves associated with each electron. The Balmer series identifies those frequencies of light that can be emitted from an excited hydrogen atom: where R is known as the Rydberg constant and is equal to 13.6 electron volts. The Bohr model, introduced in 1913, was an attempt to provide a theoretical basis for the Balmer series. The assumptions of the model are: In a circular orbit the centrifugal force balances the attractive force of the electron where e is the charge on the electron or proton. The energy of

neg: Nitrogen monofluoride Nitrogen monofluoride Nitrogen monofluoride (fluoroimidogen) is a metastable species that has been observed in laser studies. It is isoelectronic with O. Like boron monofluoride, it has unusual higher than single-bonded fluorine. It is unstable with respect to its formal dimer, dinitrogen difluoride, as well as to its elements, nitrogen and fluorine. Nitrogen monofluoride can be formed by the decomposition of fluorine azide into NF and N. It is also produced when various radical species (H, O, N, CH) react with nitrogen difluoride (NF) to abstract one fluorine atom. Many of the reactions give the product in an excited state that

neg: Dark Ages Radio Explorer universe is neutral hydrogen. This hydrogen has yet to be observed, but there are experiments underway to detect the hydrogen line produced during this era. The hydrogen line is produced when an electron in a neutral hydrogen atom is excited to a state where the electron and proton have aligned spins, or de-excited as the electron and proton spins go from being aligned to anti-aligned. The energy difference between these two hyperfine states is formula_1 electron volts, with a wavelength of 21 centimeters. At times when neutral hydrogen is in thermodynamic equilibrium with the photons in the cosmic microwave background

neg: Wouthuysen–Field coupling is neutral hydrogen. This hydrogen has yet to be observed, but there are experiments underway to detect the hydrogen line produced during this era. The hydrogen line is produced when an electron in a neutral hydrogen atom is excited to a state where the electron and proton have aligned spins, or de-excited as the electron and proton spins go from being aligned to anti-aligned. The energy difference between these two hyperfine states is formula_1 electron volts, with a wavelength of 21 centimeters. At times when neutral hydrogen is in thermodynamic equilibrium with the photons in the cosmic microwave background (CMB),

neg: Pound–Rebka experiment ushered in an era of "precision" tests of general relativity. Consider an electron bound to an atom in an excited state. As the electron undergoes a transition from the excited state to a lower energy state it will emit a photon with a frequency corresponding to the difference in energy between the excited state and the lower energy state. The reverse process will also occur: if the electron is in the lower energy state then it can undergo a transition to the excited state by absorbing a photon at the resonant frequency for this transition. In practice the photon frequency

neg: Exciton static electric dipole moment. At surfaces it is possible for so called "image states" to occur, where the hole is inside the solid and the electron is in the vacuum. These electron-hole pairs can only move along the surface. Alternatively, an exciton may be an excited state of an atom, ion, or molecule, the excitation wandering from one cell of the lattice to another. When a molecule absorbs a quantum of energy that corresponds to a transition from one molecular orbital to another molecular orbital, the resulting electronic excited state is also properly described as an exciton. An electron is

neg: Xenon monochloride known: XeCl and , whereas complex aggregates form in the solid state in noble gas matrices. The excited state of xenon resembles halogens and it reacts with them to form excited molecular compounds. Molecules that are only stable in electronically excited states are called excimer molecules, but may be called exciplex molecules if they are heteronuclear. The exciplex halides constitute an important class of rare gas halides with formula RgX. Rg is the noble gas, and X is the halogen. These molecules are de-excited by emitting a photon whose energy is some Electronvolts. Therefore, the wavelength of produced light produced

neg: General antiparticle spectrometer General antiparticle spectrometer General antiparticle spectrometer (GAPS) is a planned experiment that will use a high-altitude balloon flying in Antarctica to look for antideuteron particles from outer space cosmic rays, in an effort to search for dark matter. Anti-deuterons can be produced by the annihilation of hypothetical weakly interacting massive particles (WIMPs). The goal of the GAPS experiment is to capture anti-deuterons in a target material, to form an exotic atom in an excited state. The exotic atom would quickly decay, producing detectable X-rays energies with pion signature from nuclear annihilation. The GAPS ground test was successfully using a particle

neg: Aurora are also associated with auroras, both discrete and diffuse. Auroras result from emissions of [[photon]]s in the Earth's upper [[Earth's atmosphere|atmosphere]], above , from [[ionized]] [[nitrogen]] atoms regaining an electron, and [[oxygen]] atoms and [[nitrogen]] based molecules returning from an [[excited state]] to [[ground state]]. They are ionized or excited by the collision of particles precipitated into the atmosphere. Both incoming electrons and protons may be involved. Excitation energy is lost within the atmosphere by the emission of a photon, or by collision with another atom or molecule: Oxygen is unusual in terms of its return to ground state: it

neg: Ion source is named after the Dutch physicist Frans Michel Penning who first reported it in 1927. Penning ionization involves a reaction between a gas-phase excited-state atom or molecule G and a target molecule M resulting in the formation of a radical molecular cation M, an electron e, and a neutral gas molecule G: Penning ionization occurs when the target molecule has an ionization potential lower than the internal energy of the excited-state atom or molecule. Associative Penning ionization can proceed via Surface Penning ionization (also known as Auger deexcitation) refers to the interaction of the excited-state gas with a bulk surface

neg: Wave turbulence Wave turbulence In continuum mechanics, wave turbulence is a set of nonlinear waves deviated far from thermal equilibrium. Such a state is usually accompanied by dissipation. It is either decaying turbulence or requires an external source of energy to sustain it. Examples are waves on a fluid surface excited by winds or ships, and waves in plasma excited by electromagnetic waves etc. External sources by some resonant mechanism usually excite waves with frequencies and wavelengths in some narrow interval. For example, shaking container with the frequency ω excites surface waves with the frequency ω/2 (parametric resonance, discovered by Michael Faraday).

neg: Trojan wave packet that it is possible to create a trap which is actually a single atom. Within the atom, the behavior of an electron can be manipulated. During experiments in 2004 using lithium atoms in an excited state, researchers were able to localize an electron in a classical orbit for 15,000 orbits (900 ns). It was neither spreading nor dispersing. This "classical atom" was synthesized by "tethering" the electron using a microwave field to which its motion is phase locked. The phase lock of the electrons in this unique atomic system is, as mentioned above, analogous to the phase locked asteroids of

neg: Overtone guitar string to a flute, will naturally vibrate at a series of distinct frequencies known as normal modes. The lowest normal mode frequency is known as the fundamental frequency, while the higher frequencies are called overtones. Often, when an oscillator is excited — for example, by plucking a guitar string — it will oscillate at several of its modal frequencies at the same time. So when a note is played, this gives the sensation of hearing other frequencies (overtones) above the lowest frequency (the fundamental). Timbre is the quality that gives the listener the ability to distinguish between the sound

neg: Excimer lamp and photon energy of excimer lamp radiation. Excimers are diatomic molecules or complexes of molecules that have stable excited electronic states and an unbound or weakly bound ground state. Originally only homonuclear dimers with a stable excited state but a repulsive ground state were called excimers (exci"ted" dimers). The term excimer has since been extended to mean any multi-atom molecule with a thermally unstable (repulsive or only very weakly bonding) ground state. But sometimes one can meet term exciplex meaning an exci"ted" complex. It is also excimer molecule but not homonuclear dimer. For example, Xe*, Kr*, Ar* are excimer molecules

neg: Rydberg atom of the oscillation in angular momentum (the time to complete the trajectory in figure 8), almost exactly matches the quantum mechanically predicted period for the wavefunction to return to its initial state, demonstrating the classical nature of the Rydberg atom. Rydberg atom A Rydberg atom is an excited atom with one or more electrons that have a very high principal quantum number. These atoms have a number of peculiar properties including an exaggerated response to electric and magnetic fields, long decay periods and electron wavefunctions that approximate, under some conditions, classical orbits of electrons about the nuclei. The core electrons

neg: Forbidden mechanism lower rate. An example is phosphorescent glow in the dark materials, which absorb light and form an excited state whose decay involves a spin flip, and is therefore forbidden by electric dipole transitions. The result is emission of light slowly over minutes or hours. Although the transitions are nominally forbidden, there is a small probability of their spontaneous occurrence, should an atomic nucleus, atom or molecule be raised to an excited state. More precisely, there is a certain probability that such an excited entity will make a forbidden transition to a lower energy state per unit time; by definition, this

neg: Atomic, molecular, and optical physics nucleus. These are naturally in a ground state but can be excited by the absorption of energy from light (photons), magnetic fields, or interaction with a colliding particle (typically other electrons). Electrons that populate a shell are said to be in a bound state. The energy necessary to remove an electron from its shell (taking it to infinity) is called the binding energy. Any quantity of energy absorbed by the electron in excess of this amount is converted to kinetic energy according to the conservation of energy. The atom is said to have undergone the process of ionization. In the

neg: Mechanical resonance Some resonant objects have more than one resonance frequency, particularly at harmonics (multiples) of the strongest resonance. It will vibrate easily at those frequencies, and less so at other frequencies. It will "pick out" its resonance frequency from a complex excitation, such as an impulse or a wideband noise excitation. In effect, it is filtering out all frequencies other than its resonance. In the example above, the swing cannot easily be excited by harmonic frequencies, but can be excited by subharmonics. Various examples of mechanical resonance include: Resonance may cause violent swaying motions in improperly constructed structures, such as bridges

neg: Franz–Keldysh effect formula_30 and above (*), the effective mass equation for the exciton may be written as formula_31 formula_32 then the solution of eq is given by formula_33 formula_34 formula_35 is called the envelope function of an exciton. The ground state of the exciton is given in analogy to the hydrogen atom. then, the dielectric function is formula_36 detailed calculation is in. Franz–Keldysh effect means an electron in a valence band can be allowed to be excited into a conduction band by absorbing a photon with its energy below the band gap. Now we're thinking about the effective mass equation for the

neg: Atom energy level, which thus appear as a single spectral line. The interaction of the magnetic field with the atom shifts these electron configurations to slightly different energy levels, resulting in multiple spectral lines. The presence of an external electric field can cause a comparable splitting and shifting of spectral lines by modifying the electron energy levels, a phenomenon called the Stark effect. If a bound electron is in an excited state, an interacting photon with the proper energy can cause stimulated emission of a photon with a matching energy level. For this to occur, the electron must drop to a

neg: Magnetometer that allows the device to operate is the fact that a caesium atom can exist in any of nine energy levels, which can be informally thought of as the placement of electron atomic orbitals around the atomic nucleus. When a caesium atom within the chamber encounters a photon from the lamp, it is excited to a higher energy state, emits a photon and falls to an indeterminate lower energy state. The caesium atom is "sensitive" to the photons from the lamp in three of its nine energy states, and therefore, assuming a closed system, all the atoms eventually fall into

neg: Population inversion above. The photons are emitted stochastically, and there is no fixed phase relationship between photons emitted from a group of excited atoms; in other words, spontaneous emission is incoherent. In the absence of other processes, the number of atoms in the excited state at time "t", is given by where "N"(0) is the number of excited atoms at time "t" = 0, and τ is the "mean lifetime" of the transition between the two states. If an atom is already in the excited state, it may be agitated by the passage of a photon that has a frequency ν corresponding

neg: Extended X-ray absorption fine structure Linear combination fitting of several different standard spectra can give an estimate to the amount of each of the known standard spectra within an unknown sample. X-ray absorption spectra are produced over the range of 200 – 35,000 eV. The dominant physical process is one where the absorbed photon ejects a core photoelectron from the absorbing atom, leaving behind a core hole. The atom with the core hole is now excited. The ejected photoelectron's energy will be equal to that of the absorbed photon minus the binding energy of the initial core state. The ejected photoelectron interacts with electrons in

neg: Argon compounds argon with hydrogen-rich molecules such as H, HO, CH and CHOH. The X-ray excited argon atoms are in the 4p state. Argon monohydride is unstable in its ground state, 4s, as a neutral inert gas atom and a hydrogen atom repel each other at normal intermolecular distances. When a higher-energy-level ArH* emits a photon and reaches the ground state, the atoms are too close to each other, and they repel and break up. However a van der Waals molecule can exist with a long bond. However, excited ArH* can form stable Rydberg molecules, also known as excimers. These Rydberg molecules

neg: Raman cooling first beam excites the atom to a virtual excited state (for example because its frequency is lower than the real transition frequency), and the second beam deexcites the atom to the other hyperfine level. The frequency difference of the two beams is exactly equal to the transition frequency between the two hyperfine levels. The illustration of this process is shown in the schematic illustration of a two-photon Raman process. It enables the transition between the two levels formula_1 and formula_2. The intermediate, virtual level is represented by the dashed line, and is red-detuned with respect to the real excited level,

neg: Energy level three incomplete outer shells. (See Madelung rule for more details.) For an explanation of why electrons exist in these shells see electron configuration. If the potential energy is set to zero at infinite distance from the atomic nucleus or molecule, the usual convention, then bound electron states have negative potential energy. If an atom, ion, or molecule is at the lowest possible energy level, it and its electrons are said to be in the "ground state". If it is at a higher energy level, it is said to be "excited", or any electrons that have higher energy than the ground

neg: Exotic atom to weak, electromagnetic and gravitational forces, muonic atoms are governed to very high precision by the electromagnetic interaction. Since a muon is more massive than an electron, the Bohr orbits are closer to the nucleus in a muonic atom than in an ordinary atom, and corrections due to quantum electrodynamics are more important. Study of muonic atoms' energy levels as well as transition rates from excited states to the ground state therefore provide experimental tests of quantum electrodynamics. Muon-catalyzed fusion is a technical application of muonic atoms. A "hadronic atom" is an atom in which one or more of the

neg: Energy level state are "excited". If more than one quantum mechanical state is at the same energy, the energy levels are "degenerate". They are then called degenerate energy levels. Quantized energy levels result from the relation between a particle's energy and its wavelength. For a confined particle such as an electron in an atom, the wave function has the form of standing waves. Only stationary states with energies corresponding to integral numbers of wavelengths can exist; for other states the waves interfere destructively, resulting in zero probability density. Elementary examples that show mathematically how energy levels come about are the particle in

neg: Project Excalibur energy state. An isolated atom would normally be found in the ground state, with all of its electrons in their lowest possible state. However, due to the surrounding environment adding energy, the electrons will be found in a range of energies at any given instant. Electrons that are not in the lowest possible energy state are known as "excited", as are the atoms that contain them. Stimulated emission occurs when an excited electron can drop by the same amount of energy as a passing photon. This causes a second photon to be emitted, closely matching the original's energy, momentum, and

neg: Luminophore Luminophore A luminophore is an atom or functional group in a chemical compound that is responsible for its luminescent properties. Luminophores can be either organic or inorganic. Luminophores can be further classified as fluorophores or phosphors, depending on the nature of the excited state responsible for the emission of photons. However, some luminophores cannot be classified as being exclusively fluorophores or phosphors. Examples include transition-metal complexes such as tris(bipyridine)ruthenium(II) chloride, whose luminescence comes from an excited (nominally triplet) metal-to-ligand charge-transfer (MLCT) state, which is not a true triplet state in the strict sense of the definition; and colloidal quantum dots,

neg: Caesium standard directions), leading to a total spin "F"=7/2-1/2=3. In the caesium atom it so happens that the sub-level lowest in energy is the one with F=3, while the F=4 sub-level lies energetically slightly above. When the atom is irradiated with electromagnetic radiation having an energy corresponding to the energetic difference between the two sub-levels the radiation is absorbed and the atom is excited, going from the "F"=3 sub-level to the "F"=4 one. After a small fraction of a second the atom will re-emit the radiation and return to its "F"=3 ground state. From the definition of the second it follows that

neg: Exciton which an electron was moved). The electron in the conduction band is then effectively attracted to this localized hole by the repulsive Coulomb forces from large numbers of electrons surrounding the hole and excited electron. This attraction provides a stabilizing energy balance. Consequently, the exciton has slightly less energy than the unbound electron and hole. The wavefunction of the bound state is said to be "hydrogenic", an exotic atom state akin to that of a hydrogen atom. However, the binding energy is much smaller and the particle's size much larger than a hydrogen atom. This is because of both the

neg: Magnesium argide a change in the d orbital of the magnesium, is very complex with 18 different branches A doubly excited state, where two electrons on the magnesium atom are boosted to 3p sub-orbitals, has a strong binding energy, even higher than in MgAr. Normally an ion would bond an inert gas atom more strongly, as attraction varies as 1/R, compared to 1/R for a van der Waals molecule, and in an ion, the electron cloud shrinks due to the more positive charge attracting it. However in the doubly excited state both of the magnesium atoms are in p suborbitals, which can

neg: Electron atom. Both the electron and electron neutrino can undergo a neutral current interaction via a exchange, and this is responsible for neutrino-electron elastic scattering. An electron can be "bound" to the nucleus of an atom by the attractive Coulomb force. A system of one or more electrons bound to a nucleus is called an atom. If the number of electrons is different from the nucleus' electrical charge, such an atom is called an ion. The wave-like behavior of a bound electron is described by a function called an atomic orbital. Each orbital has its own set of quantum numbers such

neg: Helium compounds repel. However, in some locations such as helium white dwarfs, conditions may be suitable to rapidly form excited helium atoms. The excited helium atom has a 1s electron promoted to 2s. This requires per gram of helium, which can be supplied by electron impact, or electric discharge. The 2s excited electron state resembles that of the lithium atom. Most solid combinations of helium with other substances require high pressure. Helium does not bond with the other atoms, but the substances can have a well defined crystal structure. Disodium helide (NaHe) is a compound of helium and sodium that is stable

neg: Doppler cooling state. If that photon is emitted in the direction of the original photon, the atom will give up its momentum to the photon and will become motionless again. If the photon is emitted in the opposite direction, the atom will have to provide momentum in that opposite direction, which means the atom will pick up even more momentum in the direction of the original photon (to conserve momentum), with double its original velocity. But usually the photon speeds away in some "other" direction, giving the atom at least some sideways thrust. Another way of changing frequencies is to change the

neg: Ramsey interferometry a Ramsey configuration was developed by French physicist and is known as the Ramsey–Bordé interferometer. Bordé's main idea was to use atomic recoil to create a beam splitter of different geometries for an atom-wave. The Ramsey–Bordé interferometer specifically uses two pairs of counter-propagating interaction waves, and another method named the "photon-echo" uses two co-propagating pairs of interaction waves. A main goal of precision spectroscopy of a two-level atom is to measure the absorption frequency formula_1 between the ground state and excited state of the atom. One way to accomplish this measurement is to apply an external oscillating electromagnetic field at

neg: Resolved sideband cooling whose ground state is shown by "g" and excited state by "e". Efficient laser cooling occurs when the frequency of the laser beam is tuned to the red sideband i.e. formula_2, where formula_3 is the internal atomic transition frequency and formula_4 is the harmonic oscillation frequency of the atom. In this case the atom undergoes the transition formula_5, where formula_6 represents the state of an ion whose internal atomic state is "a" and the motional state is "m". This process is labeled '1' in the adjacent image. Subsequent spontaneous emission occurs predominantly at the carrier frequency if the recoil energy

neg: QED vacuum is what leads to spontaneous emission, the transition of an excited atom to a state of lower energy by emission of a photon even when no external perturbation of the atom is present. As a result of quantization, the quantum electrodynamic vacuum can be considered as a material medium. It is capable of vacuum polarization. In particular, the force law between charged particles is affected. The electrical permittivity of quantum electrodynamic vacuum can be calculated, and it differs slightly from the simple of the classical vacuum. Likewise, its permeability can be calculated and differs slightly from . This medium is

neg: Rydberg molecule between the Rydberg electron and the ground state atom. This new kind of atomic bond was theorized in 2002 and is characterized by an electron density distribution that resembles the shape of a butterfly. As a consequence of the unconventional binding mechanism, butterfly Rydberg molecules show peculiar properties such as multiple vibrational ground states at different bond lengths and giant dipole moments in excess of 500 debye. Rydberg molecule A Rydberg molecule is an electronically excited chemical species. Electronically excited molecular states are generally quite different in character from electronically excited atomic states. However, particularly for highly electronically excited molecular

neg: Internal conversion inner shell electron (usually an "s" electron) is said to penetrate the volume of the atomic nucleus. When this happens, the electron may couple to an excited energy state of the nucleus and take the energy of the nuclear transition directly, without an intermediate gamma ray being first produced. The kinetic energy of the emitted electron is equal to the transition energy in the nucleus, minus the binding energy of the electron to the atom. Most internal conversion (IC) electrons come from the K shell (the 1s state), as these two electrons have the highest probability of being within the

neg: Fano resonance scattering by helium and autoionization. The incident electron doubly excites the atom to the formula_1 state, a sort of shape resonance. The doubly excited atom spontaneously decays by ejecting one of the excited electrons. Fano showed that interference between the amplitude to simply scatter the incident electron and the amplitude to scatter via autoionization creates an asymmetric scattering line-shape around the autoionization energy with a line-width very close to the inverse of the autoionization lifetime. The Fano resonance line-shape is due to interference between two scattering amplitudes, one due to scattering within a continuum of states (the background process) and

neg: Resonance fluorescence excited state. Thus double resonance can be used to find the Landé factor, which is used to describe the magnetic moment of the electron within the two-level atom. Any two state system can be modeled as a two-level atom. This leads to many systems being described as an "Artificial Atom". For instance a superconducting loop which can create a magnetic flux passing through it can act as an artificial atom as the current can induce a magnetic flux in either either direction through the loop depending on whether the current is clockwise or counterclockwise. The hamiltonian for this system is

neg: Intersystem crossing the vibrational levels of the two excited states overlap, since little or no energy must be gained or lost in the transition. As the spin/orbital interactions in such molecules are substantial and a change in spin is thus more favourable, intersystem crossing is most common in heavy-atom molecules (e.g. those containing iodine or bromine). This process is called "spin-orbit coupling". Simply-stated, it involves coupling of the electron spin with the orbital angular momentum of non-circular orbits. In addition, the presence of paramagnetic species in solution enhances intersystem crossing. The radiative decay from an excited triplet state back to a singlet

neg: Atomic physics very large numbers of atoms. Electrons form notional shells around the nucleus. These are normally in a ground state but can be excited by the absorption of energy from light (photons), magnetic fields, or interaction with a colliding particle (typically ions or other electrons). If the electron absorbs a quantity of energy less than the binding energy, it will be transferred to an excited state. After a certain time, the electron in an excited state will "jump" (undergo a transition) to a lower state. In a neutral atom, the system will emit a photon of the difference in energy, since

neg: Doppler cooling atoms will always absorb more photons from the laser beam pointing opposite to their direction of motion. In each absorption event, the atom loses a momentum equal to the momentum of the photon. If the atom, which is now in the excited state, emits a photon spontaneously, it will be kicked by the same amount of momentum but in a random direction. The result of the absorption and emission process is a reduced speed of the atom, provided its initial speed is larger than the recoil velocity from scattering a single photon. If the absorption and emission are repeated many

neg: Atom i.e. stationary state, while an electron transition to a higher level results in an excited state. The electron's energy raises when "n" increases because the (average) distance to the nucleus increases. Dependence of the energy on is caused not by electrostatic potential of the nucleus, but by interaction between electrons. For an electron to transition between two different states, e.g. grounded state to first excited level (ionization), it must absorb or emit a photon at an energy matching the difference in the potential energy of those levels, according to Niels Bohr model, what can be precisely calculated by the Schrödinger

neg: Rydberg molecule Rydberg molecule A Rydberg molecule is an electronically excited chemical species. Electronically excited molecular states are generally quite different in character from electronically excited atomic states. However, particularly for highly electronically excited molecular systems, the ionic core interaction with an excited electron can take on the general aspects of the interaction between the proton and the electron in the hydrogen atom. The spectroscopic assignment of these states follows the Rydberg formula, named after the Swedish physicist Johannes Rydberg, and they are called Rydberg states of molecules. Rydberg series are associated with partially removing an electron from the ionic core. Each

neg: Magnesium argide Magnesium argide The magnesium argide ion, MgAr is an ion composed of one ionised magnesium atom, Mg and an argon atom. It is important in inductively coupled plasma mass spectrometry and in the study of the field around the magnesium ion. The ionization potential of magnesium is lower than the first excitation state of argon, so the positive charge in MgAr will reside on the magnesium atom. Neutral MgAr molecules can also exist in an excited state. The spectrum of MgAr can be observed. It resembles that of Mg, however some lines are blue shifted and others red shifted. In