Properties of the absorption spectrum due to the Gamma;1+ → Γ4− transition

We present results for the absorption spectrum due to a localized Γ₁⁺ → Γ₄^? transition that take into account the properties of the linear electron- phonon (e-p) interactions transforming as Γ₁⁺, Γ₃⁺ and Γ₅⁺ in the excited electronic state, in the cases of strong and weak e-p interaction coupling. We show that in the strong e-p interaction coupling limit the asymmetric shape of the structured band is due to the commutation relations of the e-p interaction matrices. Moreover, in the weak coupling limit we present an expression for the spectrum line shape obtained by taking into account the time ordering of the e-p interaction matrices and the phonon propagators at all times. It is shown in the latter case that the densities of phonon states corresponding to the electronic excited state are different from those corresponding to the ground state, and the e-p coupling constants are redefined due to the Jahn-Teller interactions.     

A high-resolution study of the OH-stretch fundamental of methanol

The OH-stretch fundamental of CH₃OH has been observed with 0.025 cm^?1 resolution between 3430 and 3940 cm^?1 and the resulting spectrum deconvoluted using the procedure of P. A. Jansson. Approximately 600 lines have been assigned to a total of 67 P- or R-branch series and some 30 excited state levels have been determined. Of these, 14 belong to the lowest torsional state with n = 0, 13 to n = 1 and 3 to n = 2. A nonlinear least-squares fit to these levels varying the major parameters used by Y. Y. Kwan and D. M. Dennison in their analysis of the normal state produces an rms deviation between observed and calculated levels of 0.51 cm^?1. Variation of all the parameters including those of the smaller Kirtman perturbation terms produces only a slight improvement in the fit. Both analyses yield a barrier height of 411 cm^?1 in the excited vibrational state as compared to the normal state value of 373 cm^?1. A number of unexplained anomalies appear in the spectra including large and irregular changes in the coefficient of J² + J for different torsion-rotation states.     

High-temperature infrared spectrum of HCN near 3300 cm−2

The infrared absorption of HCN near the fundamental band at 3311 cm^?1 has been measured at temperatures up to 1200 K. Transitions involving high rotational states (up to J = 62) have been measured. These give an improved value for the sextic centrifugal distortion term H₀. Many hot-band transitions have been observed and assigned to transitions originating in vibrationally excited states up to 4000 cm^?1 above the ground state. These measurements give new data on vibrational states involving moderately high bending quantum numbers and indicate that new terms are needed to fit the ro-vibrational energy levels.     

Electron-lattice coupling of F centers: Particular case of NaI: F

Absorption and magnetic circular dichroism studies of the F centers in NaI reveal a strong electron-lattice coupling with the vibration modes of Γ₁⁺ symmetry in comparison with those of Γ₃⁺ and Γ₅⁺ symmetry. On the other hand, the F electron exhibits in its first excited state a large spin-orbit coupling, in agreement with the value previously calculated. These results are confirmed by the Raman spectra which show a predominant intensity for the Γ₁⁺ modes, particularly for the resonant mode at 113 cm^?1.First and second-order Raman spectra have been calculated using a “quasi-resonant” theory in which the vibrations of the ions up to the fifth shell have been taken into consideration. We have been able to determine from these calculations absolute values for the contributions of the different types of vibration modes to the broadening of the F-absorption band.     

Far-infrared absorption of MgO: Fe2+ in magnetic fields

We have measured the far-infrared absorption of iron-doped MgO in the wavenumber region 10–200 cm^?1 and in magnetic fields up to 6 T. Absorption peaks found at 107.0 and 110.5 cm^?1 are assigned to magnetic dipole transitions between the spin-orbit Г_5g groundstate (J = 1) and the Г_3g, Г_4g excited states (J = 2) of the Fe²⁺ -ion at a cubic site. The observed magnetic field dependence shows that Г_4g is the higher excited level, so that the crystal field order of the levels is not changed by the reduction of the spin-orbit splitting attributed to a dynamic Jahn-Teller effect. An additional absorption peak at 33.4 cm^?1 is found to split in magnetic field.In iron-doped KMgF₃ absorption peaks at 52 and 87 cm^?1 that have previously been attributed to the same transitions of Fe²⁺ are found to remain unshifted and unsplit in magnetic fields up to 6 T.     

Laser excited luminescence spectra of zirconia

Luminescence spectra of ivory zirconia (Zr0₂) excited by an argon-ion laser (19,436–21,839 cm^?1) reveal a complex pattern consisting of both sharp and diffuse peaks in the 16,000–19,000 cm^?1 region. The intensity behavior of these features depends markedly on the excitation frequency. The sharp luminescence peaks of the 18,140–18,600 cm^?1 region are attributed to phonon-mediated de-excitation of excited states of the impuriity-doped ZrO₂ lattice. The more diffuse luminescence bands of the 17,700–18,000cm^?1 region may be associated with the electron traps observed in glow experiments and/or with higher-order phonon processes.     

Vibronic spectra of matrix-isolated lead sulfide

Vibronic spectra are reported for lead sulfide in argon, krypton and SF₆ matrices at low temperatures. Emission stimulated by laser line irradiation of PbS is observed from the v′ = 0 level of three electronic states lying at about 14 500, 18 500 and 21 500 cm^?1 above the ground state. Emission is also observed from an excited state of Pb₂S₂ at about 17 000 cm^?1. In addition, the laser radiation gives rise to the vibrational Raman spectrum of PbS in argon at 423.2 cm^?1 and to a very weak Raman band at 297 ± 2 cm^?1 which we attribute to Pb₂S₂.The effects of temperature on the matrix spectra, of matrix material on the band origins, and of matrix concentration on the vibrational relaxation process, and the apparent degrees of coupling among the electronic states have all been examined. The electronic absorption spectrum of PbS in Ar is reported and the matrix data are compared with available information on gaseous PbS.     

The two-dimensional anharmonic oscillator: The CCC bending mode of C3O2

Newly observed data on the rotational constants of carbon su?ide in excited vibrational states of the low-wavenumber bending vibration ν₇ have been successfully interpreted in terms of the two-dimensional anharmonic oscillator wavefunctions associated with this vibration. By combining these results with published infrared and Raman spectra the vibrational assignment has been extended and a refined bending potential for ν₇ has been derived: this has a minimum at a bending angle of about 24° at the central C atom, with an energy maximum at the linear configuration some 23 cm^?1 above the minimum. From similar data on the combination and hot bands of ν₇ with ν₄ (1587 cm^?1) and ν₂ (786 cm^?1) the effective ν₇ bending potential has also been determined in the one-quantum excited states of ν₄ and ν₂. The effective ν₇ potential shows significant changes from the ground vibrational state; the central hump in the ν₇ potential surface is increased to about 50 cm^?1 in the v₄ = 1 state, and decreased to about 1 cm^?1 in the v₂ = 1 state. In the light of these results vibrational assignments are suggested for most of the observed bands in the infrared and Raman spectra of C₃O₂.     

Infrared and microwave high-resolution spectrum of the ν3 band of ozone

The vibration-rotation band ν₃ of ozone has been recorded with a high-resolution (0.012 cm^?1) spectrometer, and microwave absorption spectra of ozone have been identified in the excited vibrational states (100) and (001). A strong Coriolis interaction has been observed. More than 1200 spectral lines have been identified in the ν₃ band, using a Watson-type Hamiltonian, including all the sextic centrifugal distortion terms. Band constants and an atlas listing line wavenumbers, intensities, and assignments are given, from 1007 to 1072 cm^?1. It is shown that transitions with high values of the quantum numbers K_?1 (≥11) contribute to significant absorption.     

Dye laser site selection spectroscopy on U6+ luminescent molecular centers in LiF-U3O8 crystals

The polarized excitation and emission spectra of the U⁶⁺ molecular centers giving the most intense emission lines at 18 940 cm^?1 and 19 285 cm^?1 are presented and analyzed in detáil. From the polarization experiments, it is shown that the symmetry of the centers is C_4v and that the symmetries of the observed electronic states are Γ₂, Γ₁ and Γ₅. Finally, an electronic model is proposed which associates the emission and excitation lines of the U⁶⁺ centers in the visible region to transitions between the fundamental state $\text{Γ}{}_1\text{(6p}{}^6\text{,}{}^1\text{S)}$ and the states of the excited configuration $\text{6p}{}^5\text{(}{}^2\text{P}\text{3}\text{2}\text{) 7s}$.     

Two-phonon Raman scattering in GaAs

The second-order Raman Spectrum of GaAs has been measured at room temperature by using an argon ion laser with Brewster's angle configuration. A number of critical points have been interpreted by considering neutron inelastic scattering work and detailed critical-point analysis in Ge. The Γ₁ component is the strongest in the spectrum where overtone scattering is dominant. Combination scattering has been observed in the energy region between 300 and 350 cm^?1for both Γ₁ and Γ₁₅ components. The second-order Raman spectrum is compared with the two-phonon overtone Raman intensity, calculated from neutron diffraction data. In the low frequency region, the Raman spectrum shows directly the one-phonon density of states of the TA phonon.     

Recombination population of excited states of the hydrogen atom in an He-H<Subscript>2</Subscript> plasma

The population of excited states of the hydrogen atom in an afterglow plasma produced by a pulsed discharge in helium (40 Torr) with a small admixture of hydrogen ([H₂] ≈ 10¹² cm^?3) has been studied spectroscopically. The contribution from electron-ion recombination Γ ₃ ^rec to the production rate of atoms H(n = 3) has been separated. On the basis of an experiment in which the response of the spectral line intensities to the perturbation of the electron temperature in the afterglow phase was observed, the dependence Γ ₃ ^rec (T _e ～ T _e ^?(0.9–1.0) has been obtained in the region kT _e = 0.026–0.064 eV.     

Correspondences of the vibrational frequencies of the ground and electronic excited states of quinoxaline as revealed by the Raman intensities

The intensities of the Raman lines of quinoxaline were measured at different excitation wavelengths. The matrix element ratios of the vibronic couplings between the two lowest electronic excited states of the molecule were evaluated from the Raman intensities of the b₁ vibrations, and they were compared with the matrix element ratios obtained from the vibrational frequencies of the ground and electronic excited states of the molecule. It was suggested that the ground state frequency of the b₁ vibration at 867 cm^?1 decreases greatly to 425 cm^?1 in the lowest $\text{nπ}{}^1$ excited state.     

Far infrared absorption of Fe2+ in KMgF3

Far infrared absorption in cubic KMgF₃ doped with Fe²⁺ is reported . A line is observed at 87cm^?1, which is assigned to the (Γ_5g → Γ_3g, Γ_4g) transition in the Fe²⁺. The reduction in the spin-orbit coupling from the free ion value has been predicted by Ham, Schwarz and O'Brien.     

Spectroscopy of 7Li in stopped pion absorption reactions

The structure of excited levels in the ⁷Li isotope is studied via inclusive and correlation measurements in the stopped π^? meson absorption reactions ¹⁰B(π^?, t)X and ¹²C(π^?, dt)X, respectively. The experiment is conducted using a low-energy pion beam at the LAMPF meson factory. Analysis of the missing mass spectra reveals ⁷Li states with the resonance parameters (E _x , Γ) (4.7, 0.1), (6.6, 0.9), (7.3, 0.1), (9.1, 2.8), and (9.6, 0.4) MeV. A highly excited state with E _x ≈ 11.2 MeV (i.e., an isobar analog of ⁷He) is observed in the ¹⁰B(π^?,t)X reaction. An excited state with E _x = 10.3 ± 0.1 MeV and γ = 1.8 ± 0.4 Mev is observed for the first time in the ¹²C(π^?,dt)X reaction.     

Optical absorption due to paraexciton of Cu2O

In Cu₂O a new absorption line is observed at 97 cm^?1 below the n =1 of the yellow exciton (triply degenerate orthoexciton) under a strong magnetic field at 4.2 K. The line is assigned as a transition to a nondegenerate spin triplet state Γ⁺₂ (paraexciton). An analysis including the effects due to the n =1 of the green exciton yields 364 cm^?1 as the exchange energy, and 2.68 and ?1.02, or 1.02 and ?2.68 as the g-factors of the conduction and valence bands forming the yellow exciton.     

Neutron-induced molecular defect O<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> in beryllium orthogermanate

Be₂GeO₄ polycrystalline samples preliminarily irradiated by fast neutrons (E ～ 1 MeV, Φ = 4.5 × 10¹⁷ cm^?2) were studied by photoluminescence spectroscopy using synchrotron radiation pulses for excitation. The neutron-induced luminescence band observed at 1.7 eV in the spectra of the irradiated samples is assigned to the radiative relaxation of a molecular ion O ₂ ^? . The luminescence of these defects in the Be₂GeO₄ structure is effectively excited by 4.7-and 5.2-eV photons. At low temperatures (10 K), the profiles of the photoluminescence and excitation bands have a fine structure characteristic of electron-vibration interactions. The vibration frequencies for the ground state (v₁ = 161 cm^?1) and two excited states (v₂ = 672 cm^?1 and v₃ = 887?1451 cm^?1) were measured. Potential curves of the energy states of the O ₂ ^? center are constructed in terms of the Morse model using the experimental data. The optical spectrum fine structure is shown to be predominantly due to intrinsic vibrations of the molecular defect.     

Spin-dependent phonon Raman scattering in CdCr2Se4

Influences of ferromagnetic ordering on the phonon Raman scattering are studied for CdCr₂Se₄ through the intensity measurements of Raman spectra between 25 and 300 K with various wavelengths of excitation light (488.0–676.4 nm). Spin-dependent enhancements of Raman cross section are observed for optical phonon lines D(168 cm^?1) and F(238 cm^?1) with excitation wavelengths of about 630 and 550 nm, respectively. This kind of phenomenon in spinel-type chalcogen chromites seems to originate in spin-dependent intermediate interactions in the excited states of specific electronic transitions with which the incident or scattered light is resonant.     

Submillimeter wave spectrum and molecular constants of N2O

The submillimeter wave spectrum of the N₂O molecule has been investigated within the 375–565 GHz frequency range with a sensitivity better than 10^?8 cm^?1. The measured frequencies include 161 lines with intensities γ ? 10^?6 cm^?1 belonging to 22 spectroscopically different species of the molecule (specifically, the ground and some excited vibrational states of the five most abundant isotopic species of the molecule in natural abundance) with a statisticall and systematic error of the order of magnitude 10^?8. Rotational and two centrifugal stretching constants could be determined for each spectroscopic species. For each isotopic species observed, we have made a general analysis of the spectrum in different vibrational states bearing in mind resonance effects. The total number of the rotational and rovibrational constants obtained exceeds 40.     

Measurement of excited state number densities of oxygen and nitrogen in a non-equilibrium plasma

Number densities of several excited states of atomic oxygen and nitrogen have been measured in the decaying non-thermal plasma of a θ-pinch afterglow. The spatial variation of the electron density and temperature as functions of time after initiation of main bank discharge have also been measured to facilitate a comparison of the excited state number densities with model calculations. Measurements of the atomic oxygen excited states indicate that quintet to triplet spin exchange collisions and doubly excited states must be included in the model. The measured populations of the excited atomic nitrogen states agree well with those calculated at high density (N_e≈ 10¹⁴ cm^?3), but disagree badly at lower densities (N_e ≈ 10¹² cm^?3). The discrepancies seem to be real since they are larger than expected measurement uncertainty.