Infrared absorptions and band widths of dilute solutions of CF3H in liquidAr, N-2, and Xe

The spectra of fluoroform (CF3H) in the solvents Ar, Nz, and Xe have been o btained in the fundamental region (400-4000 cm(-1)) using a low temperature cryostat and a Fourier transform infrared spectrophotometer. Ab initio cal culations at the HF/6-31G* level have been performed to obtain the calculat ed vibrational frequencies of the isolated CF3H molecule and CF3H in the pr esence of the solvents (Ar, N-2, and Xe). Comparison of the frequency shift s of CF2H in solution with respect to the gas phase frequencies is made for the experimental and theoretical results. Lorentzian functions were used t o fit the bands and obtain the wavenumber at the peak absorbance and the vi brational band widths. An analysis of the dynamics of relaxation has been m ade based on the infrared time correlation functions for three of the funda mental modes (v(1), v(3), and v(4)). Bandwidths, band moments, and relaxati on times were obtained by appropriate fitting of the experimental correlati on functions to theoretical models. In liquid argon, the temperature depend ence of the second moment (M-2) indicates that rotational relaxation explai ns the bandwidth of the v(3) mode. For the v(4) mode, the temperature depen dence of M-2 can be attributed to rotational relaxation if it is corrected with a Coriolis coupling term. The bandwidths of the v(1) mode do not follo w the rotational relaxation model, and probably vibrational relaxation is t he dominant mechanism.