MANIFESTATION OF INTERACTION OF THE TRANSITION DIPOLE-MOMENTS IN IR-SPECTRA OF LOW-TEMPERATURE LIQUIDS AND SOLUTIONS IN LIQUEFIED NOBLE-GASES

The infrared absorption spectra in the overtone range are studied for liquid SF6, CF4, NF3, and OCS and their solutions in liquid Ar (T = 93 K), Kr (T = 143 K), and Xe (T = 175 K) at concentrations C = (10(-5)- 1) mole fractions (m.f.). In the spectra of low-temperature liquids, t he band shapes of transitions to combined vibrational states in which the strongly IR active nu(3) mode is excited are shown to be completel y determined by the interaction of transition dipole (TD) moments. The formula for the second spectral moment of these bands is derived acco unting for the rt-particle dipole coupling within the first coordinati on sphere. The approach developed is confirmed by the observed linear M(2) dependence on concentration at C > 0.1 m.f. For highly symmetric (T-d or O-h) species, the dimer spectra can be reliably separated from the band shapes observed at low concentrations; we thus found R-SS = 5.22(2) Angstrom for (SF6)(2). In the spectra of NF3 and OCS recorded at the number densities N = (0.3-3) X 10(21) molecule/cm(3), the TD-TD interaction causes band broadening which is linear in N, with the sel f-broadening coefficient independent on solvent and temperature. (C) 1 998 Elsevier Science B.V. All rights reserved.