TIME FRAME VIEWPOINT OF RESONANCE RAMAN ENHANCEMENT OF A NONTOTALLY SYMMETRIC VIBRATION

The time frame approach is presented to describe the resonance Raman enhancement of a non-totally symmetric vibration due to vibronic coupling between two nearby electronic states. It is shown that in contrast to the resonance Raman enhancement of a totally symmetric vibration, the resonant contribution to the Raman scattering tensor for a non-totally symmetric vibration arises from the electronic state that is vibronically coupled to the electronic state first reached by the incident light. The second-order differencing method of Kosloff is used to numerically solve the coupled time-dependent Schrödinger equation in an application to pyrazine. In the case where the vibronically coupled states have the same oscillator frequency, it is shown that a unitary transformation of the wave packets leads to an immediate picture of the adiabatic states, as well as provide a qualitative explanation of various factors on the Raman intensity. © 1990 American Institute of Physics.