Showing papers on "Hot band published in 1975"

Vibrational analysis of polyene chains. Assignments of the resonance Raman lines of poly (acetylene) and β-carotene

Abstract: The normal frequencies and vibrational modes have been calculated for two models of an infinite polyene chain using a modified Urey-Bradley force field. The vibrational modes giving rise to strong resonance Raman lines have been elucidated on the basis of the results of the calculation.

Spectra and structure of organophosphorus compounds. XIV - Infrared and Raman spectra, vibrational assignment, and the asymmetric potential function for ethylphosphine and ethylphosphine-d sub 2

Abstract: The infrared spectra of gaseous and solid CH3CH2PH2 and CH3CH2PD2 have been recorded from 200 to 3500 cm−1. The Raman spectra of gaseous, liquid, and solid CH3CH2PH2 and CH3CH2PD2 have been recorded from 100 to 3500 cm−1. The gauche and trans isomers have been observed in the fluid phases and only the trans exists in the solid state. A vibrational assignment of the 24 normal modes has been made. Fundamental and hot band transitions have been observed for both the methyl and phosphino torsions. The methyl barrier in the trans d0 molecule was determined to be 3.74±0.05 kcal/mole and 3.14±0.05 for the gauche d0 molecule. The potential function for internal rotation around the C–P bond in CH3CH2PD2 was determined and the following potential constants found: V2=207±6 cm−1, V3=785±5 cm−1, and V6=−25±3 cm−1. The energy difference between the potential energy minima of the gauche and trans conformations is 150 cm−1, the trans being the more stable form. The calculated gauche–gauche barrier is 635 cm−1 (1.82 kcal/...

Quantum mechanical study of electronic transitions in collinear atom—diatom collisions☆

Abstract: Quantum mechanical calculations are reported for model, nonreactive, collinear collision systems composed of the H 2 diatom and the halogen atom X = F, Cl, Br or I. The model involves two electronic potential energy surfaces, obtained in a diatomics-in-molecules formulation, that correspond asymptotically to the two spin-orbit states of X. On each surface the calculations include as many vibrational states of H 2 as are asymptotically allowed, up to a limiting number of five. The first two collision systems, FH 2 and ClH 2 , are characterized by electronic splittings much smaller than any vibrational spacing included in the diatom spectrum, and as a result they show a high degree of vibrational elasticity with essentially all transition activity testricted to spin—orbit switching in the halogen. This pattern is broken for BrH 2 collisions, where the near-equality between electronic and vibrational quanta apparently leads to a resonant exchange of energy between the two modes. The greater spinorbit splitting in iodine (∼ 2 vibrational quanta) results in largely elastic behavior in IH 2 collisions for both vibrational and electronic transitions. A modified Massey criterion is exhibited for some of the FH 2 and BrH 2 transitions.

Vibrational deactivation of O3 molecules in gas mixtures. II.

Abstract: Experimental measurements of the rate constants for vibrational deactivation of O3 by O3, O2, CO2, H2, D2, CH4, N2, He, Ar, SF6, CH3Cl, CH2Cl2, CCl4, and C2H2 are presented. Vibrational relaxation of O3 is shown to follow the sequence (1) rapid V → V intermode coupling between the ν1 and ν3 modes, (2) a slower coupling of the ν1, ν3 modes to the ν2 mode, and (3) V → T relaxation through the O3(010) level. The results are described in terms of a simple analytic model for vibrational relaxation of O3.

The Raman spectrum of (TMA)2UCl6 and (TMA)2SnCl6 crystals and of TMACl in solution

Abstract: The Raman spectrum of (TMA)2UCl6, not reported previously, is presented and the assignments of the observed bands to normal modes of vibration are discussed based on polarized room temperature scans of single crystals. Seventeen of the eighteen fundamental vibrational bands and seven nonfundamental ones are identified. The missing fundamental vibrational band, containing mainly methyl internal symmetric stretching motions, is at least three orders of magnitude weaker than another band composed of the same methyl internal motions. Five totally symmetric nonfundamental bands are resolved near 3000 cm−1. It is suggested that they interact by Fermi resonance with the highly intense totally symmetric methyl stretching vibration. Their proposed assignments imply that one of the nonfundamental bands is an overtone of a combination level, thus involving four vibrational quanta. Another one of these bands is assigned to a combination level involving three different vibrational quanta. Light scattering by three and...

Stark spectroscopy with the CO laser: The dipole moment of H2CO in the v2=2 state

Abstract: Some transitions of the 2ν2←ν2 hot band of H2CO near 5.8 μm have been observed by the laser Stark technique using a 20 cm long intracavity absorption cell with about 4 mtorr total pressure at room temperature. The detection of this weak hot band (partial pressure in the v2=1 state ?8×10−7 torr) illustrates the high sensitivity of intracavity laser absorption spectroscipy. From the measured resonant fields of the transitions, the dipole moment of H2CO in the v2=2 state has been determined. The use of phase sensitive detection at twice the Stark modulation frequency is illustrated; this 2f detection effectively measures the strength of the transient nutation signal in the absorbing gas, and in some cases results in a better signal to noise ratio than does conventional 1f detection.

Vibrational relaxation of the N2O ν1 mode

Abstract: The vibrational relaxation of the ν1 symmetric stretch mode of N2O was studied at room temperature following an overtone excitation via a DF laser. The ν1 and ν3 (asymmetric stretch) fluorescence at 7.8 and 4.5 μ were, respectively, monitored as a function of time. A V–V equilibration time constant of 0.062 μsec⋅atm between the ν1 and ν2 (bending) modes was measured. The vibrational relaxations out of the ν2 and ν3 modes were measured to be 1.3 and 2.1 μsec⋅atm, respectively, with good agreement compared to previous measurements reported in the literature.

Vibrational nonequilibrium in carbon dioxide electric discharge lasers

Abstract: An experimental and theoretical investigation of vibrational nonequilibrium in the CO2 electric discharge laser was performed. The vibrational temperature for each vibrational mode of CO2 was measured under a variety of discharge conditions. Measurements indicate nonequilibrium between ν1 and ν2 can be significant. Possible causes for the apparent nonequilibrium which were theoretically examined included anomalously high gain on certain transitions which has been attributed to overlapping hot band contributions, use of different optical broadening cross sections, use of different electron−vibration excitation cross sections, and the effect of uncertainty in all V−V and V−T transfer rates. The most likely cause of the measured nonequilibrium was found to be a lack of strong coupling between the ν1 and ν2 modes.

Hot band and isotopic structure in the resonance Raman spectrum of bromine vapor

Abstract: The fine structure of the fundamental region of the bromine resonance Raman spectrum is presented. It is analyzed in terms of isotopic splitting of the species 79Br2, 79Br 81Br, and 81Br2. (AIP)

Studies of the inversion and lower level relaxation in pulsed TE CO 2 discharges

Abstract: It has generally been supposed that the rise and fall times of the gain in pulsed CO 2 laser discharges reflect the effective lifetimes of the lower and upper laser levels. Consequently, the ratio of the upper to lower level populations N_{u}/N_{l} should change during the evolution of the gain, and should be a relatively large number at the gain peak. The problems associated with the determination of this ratio using conventional direct gain measurements are discussed, and a new in-cavity technique is described that has sufficient precision to determine the ratio N_{u}/N_{l} as a function of time. The results obtained unambiguously demonstrate that the lower laser level empties rapidly during the rise time of the gain. This conclusion is further reinforced by some measurements concerning the time variation of the gain in the hot band ( 01^{1}1 \rightarrow 11^{1}0 ).

On the information content in a weakly structured absorption band

Abstract: Electronic absorption bands result from transitions between two electronic states. Associated with these states are vibrational and rotational levels. For inorganic complexes embedded in a lattice, the librations associated with the excited states of the solute molecules may give each vibrational level a breadth of up to several hundred wavenumbers. The vibrational levels of the ground state are populated according to a Boltzmann distribution and the resulting electronic absorption band is a superposition of many individual vibronic transitions. Therefore, the usual broad structureless band in most cases is a result of crowding and overlapping of vibrational levels. However, unresolved structure may sometimes be seen. The dangers of assigning weakly structured bands to partially resolved vibrations, lower symmetry, spin-orbit coupling, Jahn-Teller effects, ‘Antiresonances’ or a suitable mixing of all are pointed out. Only by using many different experimental techniques is it sometimes possible to sort out the various ‘effects’. All parameters derived from weakly structured bands are therefore to be viewed with caution.

Kinetics of vibrational exchange in two-component gaseous mixtures in the presence of a resonant laser radiation field

Abstract: The kinetics of nonresonant vibration-vibrational (v-v) exchange in binary mixtures is considered in the presence of a laser field using the harmonic oscillator model and the approximation of single-quantum transitions. An integral representation is obtained for the distributions over the vibrational levels of each component making allowance for the v-v exchange, vibration-translational (v-T) relaxation, and influence of an infrared radiation source. A closed system of equations for the relaxation of the vibrational energy in the modes is derived ignoring the decay processes. The nonequilibrium distribution functions are obtained for the steady-state and quasisteady-state conditions. It is shown that if v1>v2 (v1 is the frequency of the mode excited by the laser field and v2 is the frequency of the mode to which the energy is transferred), the vibrational kinetics of a binary mixture may differ considerably from the kinetics of a single-component medium provided that the strong laser, field acts on the first component and the rate of exchange of the quanta between the modes under consideration is sufficiently rapid. This circumstance makes it possible to utilize a directional v-v exchange for the purpose of efficient "heating" of a mode with a lower vibrational energy. The conditions under which this occurs are determined.

Normal vibrational modes resulting from the lifting of degeneracies in anisotropic crystals

Abstract: The vibrational normal coordinates of internal optic modes originating in molecular normal modes whose degeneracies have been lifted through site group effects are discussed. The normal mode frequencies are calculated in a molecular dipole formalism. The coupling between different Cartesian components of a phonon mode is described with particular attention to the symmetry based sufficiency condition for that coupling to occur.