Temperature-dependent fermi resonance studies and lineshape simulation by random perturbation model

Abstract

The lineshapes of Fermi diads of thioacetamide and methyl thiourea have been measured at different temperatures in the 120–300 K range. For computation of the lineshape, the dynamic part of the Fermi resonance interaction has been considered as a random perturbation by Redfield's theory. The optical Bloch equations are set up including the Redfield relaxation terms. The steady state solution of these equations lead to the absorption spectrum. The computed lineshape of a Fermi diad is shown to be a superposition of two Lorentzians and an interaction term. The linewidth of the Lorentzians are controlled by the Redfield and 1/ T 2 relaxation terms. The comparison of the computed curves with the observed spectra demonstrates the importance of the dynamic part of the interaction on the lineshape.