Time-Resolved Observation of Vibrationally Highly Excited Polyatomic Molecules

Abstract

Vibrationally highly excited molecular states play an important role in a vast class of chemical reactions. For this reason, a spectroscopic detection of these states is of great interest. Various spectroscopic techniques can be used for a time-resolved observation of vibrationally excited state populations. Fluorescence of multiphoton ionization is particularly sensitive. Whenever selected individual states can be separated,state-resolved absorption, fluorescence excitation, or stimulated emission are useful. There exist, however, situations where the densities of states is so large that one cannot realize a resolution of single states, or where neither fluorescence nor multiphoton ionization signals can be detected, Such situations frequently occur with vibrationally highly excited polyatomic molecules in the electronic ground state. In this case, “hot UV-absorption spectroscopy” as developed in our laboratory [1–4] can be used for timeresolved observation of excited state populations. This technique allowed us to study the dynamics of intramolecular processes, such as isomerization [5,6] and bond fission [7,8] under isolated molecule conditions, as well as of collisional intermolecular energy-transfer [9–13]