Electron-vibrational Bands Research Articles

Engineering of defects in fast neutron irradiated synthetic diamonds

Chemical vapor deposited (CVD) diamonds have been irradiated with fast reactor neutrons at fluencies F = 1·1018 and 3 · 1018 cm-2 and then heated at temperatures up to 1600 °C. The processes of annealing in and annealing out of various complexes of intrinsic defects responsible for vibrational and electron-vibrational bands in the IR absorption spectra have been studied in detail. Some tens of local vibrational modes and zero-phonon lines with rather small width caused by numerous complexes of intrinsic defects were observed in the 400-11000 cm-1 range.

Population of the Metastable A3Σu State of Molecular Nitrogen under Conditions of Plasma Chemical Synthesis of Metal Nitrides

The absolute population of the B3Πg state of molecular nitrogen is calculated from the intensity of electron-vibrational bands of the first positive system. The absolute population of the metastable A3Σu state of nitrogen molecules is calculated based on the solution of the balance equation. It is established that the population of the metastable state of molecular nitrogen increases with a decrease in the pressure and increase in the current intensity of the glow discharge. The results of determining the population of the A3Σu state of nitrogen molecules under conditions of simultaneous excitation of glow and vacuum arc discharges are presented.

Заселенность метастабильного состояния A^3Sigma-=SUB=-u-=/SUB=- молекулярного азота в условиях плазмохимического синтеза нитридов металлов

AbstractThe absolute population of the B ^3Π_ g state of molecular nitrogen is calculated from the intensity of electron-vibrational bands of the first positive system. The absolute population of the metastable A ^3Σ_ u state of nitrogen molecules is calculated based on the solution of the balance equation. It is established that the population of the metastable state of molecular nitrogen increases with a decrease in the pressure and increase in the current intensity of the glow discharge. The results of determining the population of the A ^3Σ_ u state of nitrogen molecules under conditions of simultaneous excitation of glow and vacuum arc discharges are presented.

DPotFit: A computer program to fit diatomic molecule spectral data to potential energy functions

This paper describes program dPotFit, which performs least-squares fits of diatomic molecule spectroscopic data consisting of any combination of microwave, infrared or electronic vibrational bands, fluorescence series, and tunneling predissociation level widths, involving one or more electronic states and one or more isotopologs, and for appropriate systems, second virial coefficient data, to determine analytic potential energy functions defining the observed levels and other properties of each state. Four families of analytical potential functions are available for fitting in the current version of dPotFit: the Expanded Morse Oscillator (EMO) function, the Morse/Long-Range (MLR) function, the Double-Exponential/Long-Range (DELR) function, and the ‘Generalized Potential Energy Function׳ (GPEF) of Šurkus, which incorporates a variety of polynomial functional forms. In addition, dPotFit allows sets of experimental data to be tested against predictions generated from three other families of analytic functions, namely, the ‘Hannover Polynomial’ (or “X-expansion”) function, and the ‘Tang–Toennies’ and Scoles–Aziz ‘HFD’, exponential-plus-van der Waals functions, and from interpolation-smoothed pointwise potential energies, such as those obtained from ab initio or RKR calculations. dPotFit also allows the fits to determine atomic-mass-dependent Born–Oppenheimer breakdown functions, and singlet-state Λ-doubling, or Σ2 splitting radial strength functions for one or more electronic states.dPotFit always reports both the 95% confidence limit uncertainty and the “sensitivity” of each fitted parameter; the latter indicates the number of significant digits that must be retained when rounding fitted parameters, in order to ensure that predictions remain in full agreement with experiment. It will also, if requested, apply a “sequential rounding and refitting” procedure to yield a final parameter set defined by a minimum number of significant digits, while ensuring no significant loss of accuracy in the predictions yielded by those parameters.

Short-wavelength nanosecond-barrier-discharge-pumped emitter operating on lines of argon chloride (175 nm) and chlorine (258 nm) molecules

The emission characteristics of a pulsed-periodic nanosecond-barrier-discharge-pumped source of ultraviolet and vacuum ultraviolet radiation are presented. The source emits into a set of electronic-vibrational bands with maxima at λ = 175 nm ArCl(B→X) and λ = 258 nm Cl2(D′→A′). The emission intensity of ArCl and Cl2 molecules is optimized for the pressure and composition of an argon-freon vapor (CCl4) mixture and also for excitation conditions.

Phonon-assisted optical bands of nanosized powdery SrAl2O4:Eu2+ crystals: Evidence of a multimode Pekarian

A stoichiometric powder composed of nanosized grains of SrAl2O4:Eu2+ was synthesized by combustion method at 500 °C with the subsequent calcination at 1000 °C. The zero-phonon line position, parameter of the Stokes shift, heat release factor and effective phonon energy were studied experimentally and analyzed in the framework of the multimode Pekar–Huang–Rhys model. Experimental data show that the optical 4f–5d transitions in Eu2+ ion exhibit a broad asymmetric electron–vibrational bands with a pronounced structure near the maxima. The form-function of the absorption and luminescence bands are theoretically analyzed in the framework of the model of the linear electron–vibrational interaction assuming strong coupling with the local vibration (estimated Pekar–Huang–Rhys parameter a=2S=10 and frequency ℏω=509 cm−1) and relatively weak interaction with the crystal phonons. The last results in an effective temperature dependent broadening of the discrete lines corresponding to the local vibrations and to a specific shape of the whole phonon assisted band (multimode Pekarian). Providing specific interrelation between the key parameters the calculated absorption and luminescence bands exhibit peculiar temperature dependent structured peaks in a qualitative agreement with the experimental data.

Characteristics and plasma parameters of a short-wavelength low-pressure discharge lamp

We have studied the working optical characteristics and electron kinetic coefficients of a short-wavelength, electric discharge exciplex-halogen UV-VUV lamp employing a mixture of argon and chlorine with a total pressure of P = 0.5–10 kPa. The lamp operates on a system of broadened electron-vibrational bands of ArCl (175 nm) and chlorine (200, 258 nm) molecules, which overlap to form a continuum in the spectral range of 160–260 nm. It is established that the optimum mixtures are those with p(Ar) − p(Cl2) = (2–4)−(0.15–0.30) kPa. The average output power of the short-wavelength radiation is 1–2 W at an efficiency of ∼5%. The electron energy distribution functions (EDFs) and the discharge plasma parameters have been calculated by solving the Boltzmann equation for a gas mixture with the experimentally determined optimum composition in the range of E/P values from 1 to 200 V/(cm Torr), where E is the electric field strength and P is the total gas pressure. Using the obtained EDFs, the electron transport characteristics, specific discharge power losses for the main elementary processes, and rate constants of electron processes are determined.

An exciplex-halogen high-frequency radiation source on mixtures of krypton and xenon with chlorine molecules

The results of optimization of a broadband ultraviolet (UV) radiation source, which is excited with a transverse radio-frequency low-pressure discharge with a planar aperture, are presented. The UV source operates on Kr-Cl2 and Kr-Xe-Cl2 working mixtures. The UV source operates on the system of electron vibrational bands of XeCl* and KrCl* exciplex molecules and chlorine molecules in the spectral range 210–310 nm. The average radiation power reaches 30–50 W at an efficiency of 10–15%.

Rotational contours of electronic and electronic-vibrational bands of carbazole complexes with water cooled in a supersonic jet

The rotational contours of the bands corresponding to electronic and electronic-vibrational transitions of the fluorescence excitation spectrum of jet-cooled carbazole complexes with one, two, and three water molecules have been studied. For the carbazole-(H2O)1 complex, two bands with a spectral shift of 0.57 cm−1 were recorded under exposure to radiation with a spectral width of 0.08 cm−1 at the frequency of the purely electronic transition and some other electronic-vibrational transitions. This is caused by the tunnel effect. The intensities of the shifted low-frequency bands are threefold weaker than those of high-frequency bands due to different values of nuclear spin-statistical weights. In the carbazole-(H2O)2 and carbazole-(H2O)3 complexes, water molecules are combined into a chain by the hydrogen bond, and the two ends of the chain are hydrogen-bonded to the carbazole molecule. The principal axes I A and I B of the moments of inertia in carbazole-(H2O)3 have different orientation compared to the other complexes considered, and this leads to an increase in the intensity of the Q-branch.

Theoretical studies of electron-vibrational 4f N–4f N−1 5d spectra in LiYF 4:RE 3+ crystals

The UV and VUV inter-configuration 4f N –4f N−1 5d spectra of rare-earth ions in insulators consist of broad electron-vibrational bands which sometimes have a resolved fine structure. In the present work, the low-temperature absorption band shapes of the impurity Ce 3+, Pr 3+ and Nd 3+ ions in LiYF 4 crystals have been simulated in the framework of the microscopic theory operating with the real phonon spectrum of the host crystal lattice. The energy levels and wave functions of the ground (4f N ) and excited (4f N−1 5d) electronic configurations of rare-earth ions were obtained from the numerical diagonalization of the Hamiltonian containing energies of electrostatic Coulomb and exchange interactions between electrons, spin–orbit interactions and the crystal field interaction. Crystal field parameters and electron–phonon coupling constants were treated in the framework of the exchange charge model. Form-functions of the spectral bands proportional to the calculated integral intensities of electric dipole transitions are obtained as a sum of convolutions of spectral densities of multiphonon correlation functions and form-functions of zero-phonon lines with the widths determined by distributions of random lattice strains and non-radiative transition probabilities. The calculated values of the Huang–Rhys parameters of crystal field states in mixed 4f N−1 5d configurations vary in the range from 0.1 to 15 and correspond to intermediate or strong electron–phonon interactions. Results of simulations of the spectral envelopes agree satisfactorily with the experimental data available from the literature.

A continuously emitting electric discharge UV lamp

A UV lamp pumped by a dc-current glow discharge in a mixture of helium with iodine vapors inside a quartz discharge tube with an interelectrode distance of 50 cm is described. For the power deposited in discharge (Wel ≤ 200 W), the total power emitted by the lamp in the spectral range 200–350 nm is as high as 27 W with an efficiency of ≤18 %. The lamp service life in the gas-static mode is 400–500 h. The emission is distributed almost equally between the spectral line of iodine atoms λ = 206.2 nm) 0.12 nm wide and the electron vibrational bands of I2(B-X) molecules λmax = 342 nm). The optimal helium partial pressure is 600–800 Pa.

A High-Power Low-Pressure Iodine Lamp Pumped by Glow Discharge

We present the working characteristics of a high-power UV-VUV electric-discharge lamp filled with a working mixture of helium and iodine vapor (He-I2) at a low pressure (0.1–1.5 kPa) and pumped by a dc glow discharge at a power of 15–200 W. The power of the total output UV radiation and the main emission peak at λ = 206.2 nm were studied as dependent on the electric power supplied to the glow discharge and on the partial pressure of helium in the He-I2 mixture. The emission characteristics of the glow discharge plasma were studied in the spectral range from 200 to 350 nm. In this range, the lamp is operating predominantly on a resonance emission line of excited iodine atoms (λ = 206.2 nm, FWHM = 0.10–0.12 nm) and on a system of electronic-vibrational bands of excited iodine molecules with the main peak at λ = 342 nm. The contribution of the resonance emission due to excited iodine atoms to the total UV emission from the glow discharge plasma does not exceed 50%. The optimum partial pressure of helium is within 400–800 Pa. The total UV radiation power of the lamp operating in the optimum regime reaches 25 W at an efficiency of η ≤15%.

New S1 state vibrational and T3, 2, 1 spin–rotational assignments in the vicinity of the acetylene [formula omitted] band

Pulsed supersonic jet spectra of acetylene have been recorded in the vicinity of the A ˜ 1 A u – X ˜ 1 Σ g + V 0 3 K 0 1 band in two mutually exclusive detection channels: ultraviolet laser-induced fluorescence (UV-LIF) and surface electron ejection by laser excited metastables (SEELEM). No eigenstate of the upper state(s) can appear via transitions in both UV-LIF and SEELEM channels. The UV-LIF channel is blind to transitions into eigenstates that have lifetimes longer than a few microseconds, while the SEELEM channel is exclusively sensitive to transitions into electronically excited eigenstates that have lifetimes longer than ∼30 μs. It is observed that intersystem crossing from the à ( S 1) bright state to the dark triplet states is mediated through a single “doorway state” vibrational level of the T 3 electronic state. We have characterized the bright state, the doorway state, and the dark states (singlet as well as triplet) illuminated by the bright state. Rotational transitions that belong to several previously unassigned vibrational-symmetry-allowed but nominally Franck–Condon forbidden S 1 ← S 0 electronic-vibrational bands are detected and assigned in the UV-LIF spectrum. The UV-LIF spectrum reveals that the electronic symmetry of the T 3 state is 3 B u and the K′ value of the observed T 3 ← S 0 vibrational band segment is 1. From the SEELEM spectrum, nine vibrational levels of dark triplet states are observed, spread over only ∼2.42 cm −1. Unique N, K, and e/ f quantum numbers are assigned for all of the observed triplet spin-rovibronic levels. Electronic symmetries for seven of the nine triplet states are determined. Most of the triplet state vibrational levels observed in the SEELEM spectrum belong to the T 1 surface ( 3 B u and 3 B 2) at energy well above the barrier to linearity. Despite the high vibrational state density, the upper levels of all of the assigned spin-rovibronic transitions fall onto surprisingly regular rotational term value plots [ E′ vs. N′ ( N′ + 1)] and the intensities fall onto surprisingly smooth Boltzmann plots. The most remarkable thing about the SEELEM spectrum is its apparent regularity, combined with a vibrational density of states so high that anharmonic and a-type Coriolis coupling among the T 1 and T 2 vibrational levels is essentially complete. The spectroscopically observed density of K-assigned vibrational states is comparable to the calculated symmetry-sorted state density.

On the mechanism of formation and broadening of the electronic and vibrational spectra of vapors of octaethylporphyrin metal complexes

Optical absorption spectra of vapors of metal complexes of octaethylporphyrins known from the literature are analyzed on the basis of notions about sequences as basic elements of the formation of electronic-vibrational bands. According to this analysis, major features of these spectra are explained. These features include considerable half-widths of the electronic-vibrational bands of rarefied vapors, when intermolecular interactions virtually do not affect the broadening; a Lorentzian intensity distribution over the contour of the 0-0 spectral band; long-wavelength shifts of the intensity maxima of bands with increasing temperature; and the origin of a fine structure of the electronic and vibrational spectra at low temperatures. It was concluded that sequential transitions form the basis of the mechanism of formation and broadening of the electronic and vibrational spectra of metal complexes of octaethylporphyrins as representatives of complex biomolecules.

Characteristic features of electronic and vibrational spectra of free polyatomic molecules

The functional relationships between the basic characteristics of individual bands of electronic and vibrational spectra of free polyatomic molecules are ascertained. These basic characteristics are the position of the maximum of an individual electronic-vibrational band, the rate of the temperature shift of the maximum of a band, the half-width of a homogeneously or heterogeneously broadened electronic-vibrational band, the rate of the temperature variation of the half-width of a band, the asymmetry parameter of a heterogeneously broadened band, and the conditions for symmetric or asymmetric distribution of the intensity over the contour of a spectral band. The interrelations between the basic spectral characteristics result from the sequential mechanism of formation and broadening of individual bands of electronic and vibrational spectra of free polyatomic molecules. It is shown that the investigation of the basic spectral characteristics of electronic-vibrational bands and their interrelations allows one to elucidate the nature of the internal motion determining the optical properties of polyatomic molecules.

Sequential spectral lines and intensity distribution in electronic-vibrational bands of free polyatomic molecules

The intensity distribution, the spectral band profile, and the temperature dependences of spectral characteristics of bands in the electronic-vibrational (vibronic) spectra of free polyatomic molecules are studied based on the concept of sequential lines (SLs) as constituent elements of these bands. It is shown that the intensity distribution in a separate electronic-vibrational band is defined by the convolution of an SL profile with the frequency distribution function of sequential transitions. Expressions for the intensity distribution in homogeneously and inhomogeneously broadened electronic-vibrational bands are derived, and specific features of their spectral behavior are determined. Using the latter results, distinguishing features or criteria of the character of broadening of the vibronic spectra of free polyatomic molecules are formulated.

A pulsed-periodic low-pressure volume discharge in a krypton-chlorine gas mixture

The initiation conditions and characteristics of a volume discharge in a krypton-chlorine mixture at low pressures (P≤1.0 kPa) were studied. It is shown that a constant voltage of Uch 1.0 kV applied to a spherical anode-flat cathode system gives rise to a pulsed-periodic discharge with a pulse repetition rate of 1–50 kHz. The current-voltage characteristics of the discharge, the spectra of emission in a wavelength interval of Δ λ=130–350 nm, and oscillograms of the current and the total output emission intensity were studied as dependent on the partial composition and pressure of the krypton-chlorine mixture. It is shown that the discharge is a selective source of emission in the electronic-vibrational bands with λ=257 nm [Cl2(D′-A′)], 222 nm [KrCl(B-X)], and 200 nm [C12**]. The volume discharge in the Kr-Cl2 mixture can be used for the development of pulsed-periodic low-pressure excimer-halogen lamps.

Collapse of vibrational structure in spectra of resonant x-ray Raman scattering

Extreme narrowing, or collapse, of electron-vibrational bands is predicted as a new phenomenon in resonant radiative and nonradiative x-ray scattering (RXS) spectra. It is shown that in the inelastic scattering case, that is, when the potential surfaces of ground and final states are different, a considerable narrowing of the vibronic RXS band results from detuning the excitation photon frequency $\ensuremath{\omega}$ away from the absorption resonance. By fine tuning the frequency, this may under special circumstances also occur in the region of strong photoabsorption. In the case of elastic Rayleigh scattering, that is, when the potential surfaces of ground and final states are identical, the narrowing results in a total collapse to a single resonance by detuning the frequency. The theory predicts how the differencies in vibrational structure of resonant and nonresonant photoemission spectra depends on the excitation frequency. The effect of frequency detuning on complex spectral multilevel structures due to multiplet and spin-orbit splittings is discussed qualitatively. It is shown that the notion of duration time for the x-ray scattering process plays a crucial role in the understanding of RXS spectra.

Development of a two-site Hubbard model for analysis of the electron-molecular vibration coupling in organic charge-transfer salts

A two-site Hubbard model has been utilized for the analysis of the intense electron-vibrational bands in the i.r. spectra of organic charge-transfer (CT) salts with dimerized structures. It is shown that intermolecular charge oscillations in totally symmetric anti-phase vibrations are accompanied by a decrease of the energy of the highest occupied two-electron state of the dimer. This effect is responsible for frequency shifts of the electron-vibrational bands compared with relevant Raman active modes and can be described by dimensionless coupling constants. The absorption coefficient for the bands was found to be proportional to the frequency shift. Calculated values are in agreement with the experimental data on BEDT-TTF based monovalent CT complexes.

A key to the understanding of electron - molecular vibration coupling in organic charge-transfer salts: application of the two-site Hubbard model

A two-site Hubbard model has been utilized for description of the electron - molecular vibration coupling (EMVC) in organic charge-transfer (CT) salts with dimerized structures. It was shown that the intermolecular charge oscillations in the anti-phase totally symmetric vibrations are accompanied by a decrease of energy of the occupied electronic state in the dimer. This effect is responsible for the frequency shift of i.r.-active electron-vibrational bands compared with relevant Raman modes, and can be described in terms of dimensionless coupling constants. The absorption coefficients for the bands were found to be proportional to the frequency shifts. The calculated values are in good quantitative agreement with experimental data for BEDT-TTF-based and TTF-based monovalent CT complexes. .