Andrei P. Burtsev

The vibrational spectrum of the OCS molecule based on the data on spectra of liquid and cryosolutions

The IR absorption spectra of liquid OCS (T = 135(1) K) and of the following solutions—OCS + Ar (T = 90 K), OCS + N2 (T = 90 K), OCS + Kr (T = 130 K), and OCS + Xe (T = 163 K)—are measured in the range 800–7000 cm−1. From 16 to 40 bands corresponding to transitions to vibrational states up to the third order inclusive are interpreted for basic isotope modification and for the isotopically substituted molecules 18O12C32S, 16O13C32S, and 16O12C34S. In the spectra of the liquids, the spectral moments M(1) and M(2) of all the observed bands are determined. The harmonic frequencies ωi and the anharmonicity constants xik are calculated for all the systems, including the liquid. The anharmonicity is found to be constant within the experimental error. A large shift Δω3 is primarily determined by the dipole-induced dipole interaction.

Vibrational spectrum of perfluoroethane

We have obtained IR absorption spectra of a C2F6 gas and a C2F6 cryosolution in Xe (T = 163 K) in the fundamental and overtone ranges. We have interpreted 28 bands of 12C12CF6 and three bands of 13C12CF6. In the spectral ranges that correspond to vibrations that are combinations with ν1, ν7, and ν5, we observe multiplets, which we attribute to interactions of the type of Fermi resonances between the states ν1(A1g) ∼ ν6(A1g), ν7(Eg) ∼ ν6 + ν11(Eg) ∼ 2ν8(Eg), ν5(A2u) ∼ ν8 + ν 11(A2u). We reveal an anomalous intensity distribution in the spectrum of an asymmetric isotopologue. For the basic and isotopic configurations of perfluoroethane, we calculate the coefficients of shapes of vibrations and the intensities of absorption bands. We reveal that the behavior of the groups 12CF3 and 13CF3 is indifferent to the excitation of doubly degenerate stretching vibrations ν7(Eg) and ν10(Eu).

Vibrational moments of fundamental transitions in low-temperature molecular liquids: Determination from the band shape of vibrations in the overtone spectral range

It is shown that the integrated absorption coefficients of strong fundamental bands of some gaseous substances can be determined with an accuracy of 5–10% using experimental data on the spectral moments of bands in the overtone spectral range of these substances in the liquid phase near the melting point. The absorption coefficients are calculated within the framework of the cell model of the liquid state from the contributions of the resonance dipole-dipole interaction to the second spectral moment. The combination and overtone absorption bands of the SF6, CF4, SiF4, NF3, CHF3, CC1F3, CBrF3, OCS, N2O, and CO2 molecules in the liquid state and in solutions in liquefied Xe, Kr, and O2 are recorded. The data in the literature on the intensity of strong IR bands in the gas phase are analyzed. Using an improved experimental technique, additional measurements are performed. It is found that the absorption coefficients determined from the spectral characteristics of the liquids agree well with the coefficients measured in the gas phase.

Efficient optical pumping of the broadband (CO2+N2O) laser medium

Theoretical and experimental study of transverse optical pumping of the high-pressure multi-component (CO2+N2O)-laser medium is carried out. Possibility of high efficiency (15 - 20%) of conversion of the discharge pulsed HF-laser radiation (λ = 2.7 - 3 µm) with the pulse duration <1 µs to the stimulated emission (10 - 11 µm) of the broadband laser medium is shown.

Observation of simultaneous ν1(SF6) + ν3(NF3) and ν2(SF6) + ν3(NF3) transitions enhanced by the resonance dipole-dipole interaction with the ν1 + ν3 and ν2 + ν3 states of the SF6 molecule

IR spectra of the solution of SF6 molecules in liquid NF3 at 84 K have been recorded. In a solvent transmission window of 1500–1750 cm−1, two wide absorption bands with pronounced peaks in the high-frequency part are observed. The profile of these bands is explained by the influence of the resonance dipole-dipole (RDD) interaction of the states of the simultaneous transition ν1(SF6) + ν3(NF3) and ν2(SF6) + ν3(NF3) with the states (ν1 + ν3) and (ν2 + ν3) of the SF6 molecules, respectively. The use of three isotopic modifications 32SF6, 33SF6, and 34SF6 has allowed us to vary the resonance detuning and thus to change the strength of the RDD interaction. With the liquid near the melting point being represented as a close-packed cubic crystal, the profile was calculated and its spectral characteristics were determined. The frequencies of the main peaks coincide with the experimental values accurate to the error.

Lasing of molecular HBr in the four-micron region pumped by a DF-laser

High efficiency optical pumping of 4-μm HBr-laser was performed by the principal 2P9 line (3.836 μm) of pulsed DF-laser. Precise coincidence revealed of this laser transition with R2 line of the fundamental absorption band of the heavy isotopomer of hydrogen bromide was utilized. Lasing within 0.3-15 Torr pressure range was observed in overall (4.017-4.215) μm spectral range, at both off-axis and the collinear pumping geometry (pump fluence of 0.2 - 0.4 J/cm2, pulse FWHM duration ~300 ns). Complex behaviour of HBr-laser emission peak intensity, pulse duration and time delay upon the gas pressure was analyzed. Energy conversion efficiency at P=10 Torr was increased from ~2% to more than 5%, when collinear scheme with better mode-matching was utlized. It is believed that the efficiency may be additionally improved by optimization of HBr-laser cavity losses.

GW-high pressure CO2-N2O laser with optical pumping

To verify experimentally the possibility of effective conversion of multi-line pumping radiation of HF chemical chain laser by the use of a combined active medium on the basis of buffered with inert gas (He, Ar, Kr, Xe) mixture of various isotopomers of CO2 and N2O the energy and spectral characteristics of CO2-, N2O- and combined CO2-N2O lasers with optical pumping were experimentally studied. Pumping of dense mixtures (Ptotal = 11 atm) containing CO2: N2O: (He, Ar) = (0-1):(0-1):10 by cascade P1(8) and P2(7) lines of HF laser with total energy ≈200 J was performed. Specific input energy reached 2 J/cm3 at pump radiation fluence up to 10 J/cm2 and pulse duration of 1 μs. For the separate molecular components CO2 and N2O lasing with energies 4.3 and 8.9 J (input energies 47 and 104 J, respectively) in the spectral regions of (P- and R-) and P-branches was revealed. The CO2-N2O combined laser delivered emission with pulse duration ~ 30 ns in the region of overlap of R- and P-branches of N2O and CO2, respectively (wavelength 10.4 - 10.6 μm), with energy 12 J (200 J/1) equal to the sum of output energies on the individual components.

Increase of efficiency of optical pumping of a broadband CO2 laser amplifier as a result of the use of a multicomponent active medium

The problem of the increase of the energy conversion efficiency of a broadband CO2 laser amplifier with optical pumping by the multi-frequency HF-laser radiation is considered. To improve the utilization of the pumping radiation and to broaden the amplifier bandwidth the use of a buffered with Xe mixture of the isotopomers of carbon dioxide and nitrous oxide as active medium is proposed. Experimentally and by calculation the coefficients of an unsaturated absorption of 14N16O, 12C16O2 and 13C16O2 were determined on 19 lines of the pulsed chemical HF-laser which concentrate up to 60% of its total output energy. The estimations show that the application of a three-component mixture of these molecular gases enables to increase up to 30% the coefficient of the utilization of the pumping radiation at aperture about 10 cm.

Spectroscopic study of nearest-neighbor pairs (dimers) of solute molecules SF6 in liquefied buffer gas

The IR absorption spectra of solutions of SF6 (natural isotopic abundance, concentration range C equals (2 - 9.5) * 1019 molecule/cm3) in liquid O2 (temperature range /80 - 130/K, density range /2.3 - 1.7/ * 1022 molecule/cm3) were studied in the v1 + v3 spectral interval.

Vibrational-resonance self-broadening of IR absorption bands in gaseous fluorides

A new spectroscopic effect of strong self-action was observed for the first time in molecular gases for vibrational transitions to combined states, in which the strongly IR active v3 mode is involved. Transformations of the v3, v1 + v3, v2 + v4 band shapes of 32SF6, 34SF6, 12CF4, 13CF4, 14NF3 upon variation of density (T equals 293 K) were studied for pure gas (p < 70 Amagat) and its dilute mixtures with Ar, Kr, Xe (pmixt < 150 Amagat). A strong linear dependence of the second spectral moment M2 on density for v3 and v1 + v3 bands in pure gases was observed, whereas no effect was found in dilute mixtures and for v2 + v4 band in pure gases.