Rovibrational and dynamical properties of the hydrogen bonded complex (CH2)2S-HF: a combined free jet, cell, and neon matrix-Fourier transform infrared study.

Abstract

Fourier transform infrared spectra of the nu(s) (HF stretching) band of the (CH(2))(2)S-HF complex have been recorded at 0.1-0.5 cm(-1) resolution in a cooled cell, in a supersonic jet expansion seeded with argon and in a neon matrix at 4.5 K. The combination of controlled temperature effects over a range of 40-250 K and a sophisticated band contour simulation program allows the separation of homogeneous and inhomogeneous contributions and reveals significant anharmonic couplings between intramolecular and intermolecular vibrational modes similar to our previous work on (CH(2))(2)S-DF. The sign of the coupling constants is consistent with the expected strengthening of the hydrogen bond upon vibrational excitation of HF which also explains the observed small variations of the geometrical parameters in the excited state. The analysis of sum and difference combination bands involving nu(s) provides accurate values of intermolecular harmonic frequencies and anharmonicities and a good estimate of the dissociation energy of the complex. Frequencies and coupling parameters derived from gas phase spectra compare well with results from neon matrix experiments. The effective linewidth provides a lower bound for the predissociation lifetime of 10 ps. The comparison between effective linewidths and vibrational densities of states for (CH(2))(2)S-HF and -DF complexes highlights the important role of intramolecular vibrational redistribution in the vibrational dynamics of medium strength hydrogen bonds.