Abstract

Femtosecond transient absorption spectroscopy of transition states has recently been applied to the study of both Tl-halide¹ and Bi2² gas-phase photodissocation. In our approach a femtosecond UV pump source excites a molecule to a repulsive electronic state, V₀(R). After a variable delay, a femtosecond probe pulse is applied. In this case, the probe pulse is an ~10000 cm^–1 wide white-light continuum pulse, and the photofragments are detected by means of broadband absorption spectroscopy. A complete spectrum corresponding to a given pump-probe delay is thus recorded in a single shot. Changes that are observed in the absorption spectrum as a function of the pump-probe delay provide information about variations δω (R) in the separation between the potential curves, V₀(R) and V₁(R), involved in the probe transition occurring as the interatomic spacing, R, is varied. These time-dependent absorption spectra form the data base for this approach to real-time transition-state spectroscopy.

© 1990 Optical Society of America