Abstract

Photoinduced intramolecular proton transfer in electronically excited states is an important fundamental reaction that often occurs on a subpicosecond time scale. Until now, femtosecond spectroscopy has mainly provided reaction rates of proton and deuterium transfer. The advent of sub-50-fs pulses allows us to excite and monitor coherent vibrational motions that play an important role for the microscopic reaction mechanism. In this paper we report, we believe, the first observation of coherent nuclear motions during and after proton transfer in solution. Low-frequency motions in the first excited state of 2-(2′-hydroxy-5′- methylphenyl)-benzotriazole (commercial name: TINUVIN P, TIN) are directly observed in two-color pump-probe experiments with 25-fs pulses and a qualitative microscopic model of the reaction is presented.

© 1997 Optical Society of America