Picosecond resonance Raman scattering study of methyl viologen reduction on the surface of photo-excited colloidal CdS crystallites.

This manuscript is part of a continuing program to develop spectroscopic techniques for fast, real-time analysis of chemical reactions in liquids, and at condensed phase interfaces. Previous memoranda have shown the value of 10(-8) sec pulsed resonance Raman scattering in capturing the spectra of short-lived chemical intermediate species. In the specific case of conduction band electron transfer from a colloidal crystallite to a surface adsorbed organic molecule, these studies show that transfer and molecular relaxation occur on faster time scales. We therefore now report development of a new Raman laser system for pulsed Raman scattering on the 10(-11) sec time scale. In this study, the colloidal crystallites are slightly smaller than the size necessary to achieve the bulk gap. The electron redox potential in principle is slightly more negative than the flat-band bulk CdS value.