Infrared absorptions and band widths of dilute solutions of CF3H in liquid Ar, N2, and Xe

Abstract

The spectra of fluoroform (CF3H) in the solvents Ar, N2, and Xe have been obtained in the fundamental region (400–4000cm−1) using a low temperature cryostat and a Fourier transform infrared spectrophotometer. Ab initio calculations at the HF/6-31G* level have been performed to obtain the calculated vibrational frequencies of the isolated CF3H molecule and CF3H in the presence of the solvents (Ar, N2, and Xe). Comparison of the frequency shifts of CF2H in solution with respect to the gas phase frequencies is made for the experimental and theoretical results. Lorentzian functions were used to fit the bands and obtain the wavenumber at the peak absorbance and the vibrational band widths. An analysis of the dynamics of relaxation has been made based on the infrared time correlation functions for three of the fundamental modes (ν1, ν3, and ν4). Bandwidths, band moments, and relaxation times were obtained by appropriate fitting of the experimental correlation functions to theoretical models. In liquid argon, the temperature dependence of the second moment (M 2) indicates that rotational relaxation explains the bandwidth of the ν3 mode. For the ν4 mode, the temperature dependence of M 2 can be attributed to rotational relaxation if it is corrected with a Coriolis coupling term. The bandwidths of the ν1 mode do not follow the rotational relaxation model, and probably vibrational relaxation is the dominant mechanism.