A. P. Burtsev

Integral Intensities of Absorption Bands of Silicon Tetrafluoride in the Gas Phase and Cryogenic Solutions: Experiment and Calculation

The spectral characteristics of the SiF4 molecule in the range 3100–700 cm−1, including the absorption range of the band ν3, are studied in the gas phase at P = 0.4–7 bar and in solutions in liquefied Ar and Kr. In the cryogenic solutions, the relative intensities of the vibrational bands, including the bands of the isotopically substituted molecules, are determined. The absorption coefficients of the combination bands 2ν3, ν3 + ν1, ν3 + ν4, and 3ν4 are measured in the solution in Kr. In the gas phase of the one-component system at an elevated pressure of SiF4, the integrated absorption coefficient of the absorption band ν3 of the 28SiF4 molecule was measured to be A(ν3) = 700 ± 30 km/mol. Within the limits of experimental error, this absorption coefficient is consistent with estimates obtained from independent measurements and virtually coincides with the coefficient A(ν3) = 691 km/mol calculated in this study by the quantum-chemical method MP2(full) with the basis set cc-pVQZ.

Interferometric determination of the dispersion of vibrational polarizability and the integrated intensities of fundamental bands of 32, 34SF6 and NF3 molecules

The refractivity of gaseous SF6 and NH3 in the region of the intense absorption bands of these compounds was measured by two-beam, two-color interferometry using a He-Ne laser and a CO2 laser tunable throughout its emission lines. Quantitative data on the profiles of the absorption bands of these gases were also obtained by IR Fourier spectroscopy. By using the joint processing of the results of refractometric and spectral measurements on the basis of the Kramers-Krönig formalism, the dispersion dependences of the vibrational polarizabilities of the given molecules were calculated and the integrated intensities of their fundamental vibrational bands were refined. A table of values of total and vibrational polarizabilities at the emission frequencies of the CO2 laser was compiled.

Collision-induced vibrational polarizability and mixed second refractivity virial coefficients B ab R : an experimental study of the SF 6 -rare gas mixtures

Mixed second refractivity virial coefficients B ab R (ω) are determined in the infrared spectral range from the analysis of the buffer gas-induced intensity redistribution in the ν3 absorption band at ω ≍ 930 cm−1 of 34SF6 perturbed by the rare gases Ar, Kr, and Xe at relative densities up to 140 Amagat. The values of the refractivity virial coefficients are found to be several orders of magnitude greater than those observed in the spectral regions far removed from single-photon resonances. The undamped dynamic dipole—induced-dipole (DID) model is shown to qualitatively correctly reproduce the observed unusual dispersion of the B ab R (ω) functions. A new estimate of the integrated band intensity S(ν3) of SF6 is also obtained.

The temperature dependence of intensity and the function of the transition dipole moment for the induced optical absorption bands of oxygen in the region of the Herzberg photodissociation continuum (200–230 nm)

The values of the binary absorption coefficient μ11 of oxygen in the region of the Herzberg photo-dissociation continuum (200–230 nm) at temperatures from 200 to 110 K are obtained for the first time. It is shown that the induced optical absorption spectrum of oxygen in the region from 200 to 230 nm is composed of two bands with significantly different temperature dependences of μ11: the binary absorption coefficient of the Herzberg III band increases by approximately 50% on cooling from room temperature to 110 K, while the other band shows no pronounced temperature dependence of μ11 in this temperature range. The μ11(T) dependences are calculated theoretically using different functions M(r) of the induced transition dipole moment, namely, a function exponentially dependent on the intermolecular distance and a more complicated function accounting for both the short-range interaction and the long-range interaction due to quadrupole moments averaged over wave functions of various electronic states. It is found that the latter function M(r) better describes the temperature dependence of the Herzberg III oxygen absorption band in the whole temperature range studied and gives a physically justified value for the parameter r0 in the exponential part of the function.

Effect of collisions on the resonance vibrational polarizability of gaseous SF6 and CF4 molecules

The density dependences of the absorption cross sections and refractivity are experimentally studied for the SF6 and CF4 molecules in pure gases in the region of their ν3 infrared vibrational-rotational antisymmetric modes. The dispersions of the refractive index are determined for both compounds by the Kramers-Kronig transformation of the spectral data obtained, and, for the SF6 isotopomers, they are also measured by the method of two-color interferometry. Strong nonlinear dependences of optical parameters and their dispersions on the gas density are observed. The values of second optical virial coefficient BR(ν) obtained for pure SF6 are more than an order of magnitude greater than the values found earlier for mixtures of SF6 with buffer rare gases. The results of calculations of the second virial coefficients of the absorption cross section and refractivity in terms of the DID model of interacting dipoles are in agreement with the experimental data in the band wings. Correlations between the behavior of the spectral dependence of functions BR(ν) and the parameters of model intermolecular potentials used in the calculations are found.

Collision-Induced Absorption of Gaseous Oxygen in the Herzberg Continuum

The values of the binary absorption coefficient for gaseous molecular oxygen in the region of the Herzberg photodissociation continuum (200–230 nm) have been measured in the temperature range 110–295 K. The induced absorption of oxygen in the 200–220 nm spectral region was found to result from two bands with quite different temperature dependence of their intensity: for the Herzberg III band the values of the binary absorption coefficient increase by ~ 50% as the temperature decreases from 295 to 110 K, while for the other band no distinct temperature dependence of the binary absorption coefficient was observed. A transition dipole moment function including both short-range term (overlap of the electron shells of interacting molecules) and long-range term (interaction of the transient quadrupole moments) is proposed to describe the temperature dependence of the binary absorption coefficients in the Herzberg III band.