EXCITATION OF SYMMETRICAL AND ANTI-SYMMETRICAL STRETCHING MOTION IN THE CONTINUUM RESONANCE RAMAN-SCATTERING FROM ABA-TYPE MOLECULES

We theoretically investigate the continuum resonance Raman spectrum fr om symmetric ABA-type molecules using a model of the pseudo triatomic molecule X(=CH2)I-2. The experimental Raman spectrum of this molecule shows pronounced excitation of the asymmetric stretching mode which is in contrast to what is found for other molecules like H2O. We show wi thin time-dependent quantum calculations that this behaviour, in princ iple, gives important information about the excited state potential en ergy surface and in particular about the location of the reaction barr ier relative to the ground-state equilibrium configuration. (C) 1998 E lsevier Science B.V.