Abstract

Spontaneous resonance Raman (RR)¹ and resonant impulsive stimulated Raman scattering (RISRS)² both contain vibrationally specific information about the structure and dynamics of a resonant excited electronic state, even when that state has a very short (sub-vibrational period) lifetime. Steady-state RR cross sections have a time-domain interpretation in which the laser field transfers part of the initial ground-state wavefunction to the excited state surface, and the spectrum of the spontaneously emitted light provides information on the evolution of that excited-state amplitude on the upper surface. In RISRS, a femtosecond pump pulse drives the initial thermal equilibrium state into a coherent superposition of ground-state vibrational levels, and a delayed probe pulse monitors the resulting perturbation of the chromophore's absorption. This time-domain signal can be Fourier transformed to give a spectrum usually dominated by Franck-Condon active vibrational frequencies of the ground state. However, the Fourier transform of the RISRS signal (FT-RISRS) is by no means equivalent to a RR spectrum, and important qualitative errors of interpretation can result if this assumption is made.³

© 1996 Optical Society of America