Analysis of vibronic-mode coupling in azulene by fully resonant coherent four wave mixing

Abstract

Fully resonant, three laser, coherent Stokes Raman scattering (CSRS) is used to probe the vibrational correlations and couplings associated with the S0−S1 transition of azulene in a low temperature mixed molecular crystal. Unlike incoherent resonant emission, CSRS is not complicated by extra resonances due to relaxed emission. The spectra obtained confirm most of the assignments of the S1 vibronic fundamentals made by incoherent spectroscopies. In addition, however, the vibronic counterpart of the vibrational fundamental at 900 cm−1 is correlated to a previously unobserved vibronic resonance at 842.3 cm−1. Evidence of matrix moderated coupling, including possible site splitting and Fermi resonances involving lattice phonons, is given for the 677, 825, 917, 941, and 900 cm−1 vibrational levels.