Dynamical inhomogeneous broadening and lattice-assisted intramolecular energy transfer in the fundamental A1 vibrations of liquid chloroform Cl-35

Abstract

This report gives extensive isotropic Raman spectral data and their numerical Fourier transformation into the time domain (∼0–20 ps) for the three A1 vibrational fundamentals of Cl-35 isotopically pure chloroform. It was found that the vibrational amplitude correlation decay of the ν1 mode (C–H stretch) at 300 K follows a rapid vibrational dephasing process (inhomogeneous broadening with motional narrowing) that is 1.7 times faster than the concomitant intramolecular energy transfer to the overtone of the C–H bending mode. From the temperature dependence (213 K, 300 K) of the amplitude correlation decay of the ν3 mode (C–Cl deformation) we deduce that it relaxes essentially only by vibrational dephasing and in such a fast modulation regime that the ν3 oscillator is effectively decoupled from the local lattice anisotropies. From the temperature dependence of the amplitude correlation decay of the ν2 mode (C–Cl stretch) we infer a simultaneous vibrational dephasing and lattice-assisted intramolecular energy transfer process, the latter possibly to the overtone of ν3. This paper concludes with some general remarks on the predictability of relative contributions of various types of vibrational relaxation processes to vibrational amplitude correlation decay in molecular liquids and, in an Appendix, gives estimates on the rates of excess phonon depopulation into the lattice as governed by a permanent dipole–transition dipole coupling process for modes ν6, ν3, ν2, and ν5 of liquid chloroform.