Vacuum UV Photophysics and Photoionization Spectroscopy

Abstract

Vacuum ultraviolet frequencies of the electromagnetic spectrum lie in the region in which air absorbs radiation, so experiments must be carried out in a vacuum. In practice, this region extends from about 180 nm to about 30 nm. Below 110 nm is the windowless region in which a LiF window no longer transmits light. The field of vacuum UV (VUV) photophysics is difficult to review because it is so broad. It encompasses experiments in the gas, liquid, and s<1lid phases. It covers, dynamics, structure, and spectroscopy. To review the field so broadly would clearly be inappropriate. Instead, this review is limited to the major recent advances made in the areas of gas-phase spectroscopy and dynamics. The experiments of interest are those carried out with conventional UV light sources, synchrotron radiation, VUV lasers, and multiphoton ionization. The latter is not technically a VUV source, since the photon energy of interest is achieved by exciting the molecule or atom with two or more photons of lower energy. However, as long as the final states investigated lie in the VUV region, it seems appropriate to include a discussion of these studies. On the other hand, the experiments on ion spectroscopy carried out with IR lasers, are not discussed even though the information obtained by this method is very similar to that obtained by high resolution VUV spectroscopy (e.g. threshold photoelectron spectroscopy).