The resonance Raman spectrum of CH3I: An application of the MCTDH approach

Abstract

The resonance Raman spectrum of CH3I is investigated employing the multi-configurational time-dependent Hartree (MCTDH) approach. A general scheme for the calculation of Raman excitation profiles within a MCTDH representation is presented. This scheme is based on a previously described iterative diagonalization approach suitable for MCTDH-wavefunctions. An empirical four-dimensional potential energy surface is developed for the electronic ground state of methyl iodide. The vibrational states corresponding to excitations in these four modes are calculated up to an energy of about 4000 cm−1. Accurate MCTDH-calculations for the excited, vibronically coupled 3Q0/1Q1 surfaces are performed on the ab initio potential energy surface of Amatatsu, Morokuma, and Yabushita [J. Chem. Phys. 94, 4858 (1991)]. Based on these dynamical calculations, Raman excitation profiles are computed for the different relative polarizations of incident and scattered radiation. The dependence of the depolarization ratio on the amount of C–I stretching excitation is investigated and interpreted.