Photochemistry of Vibrationally Excited HCl in Rare Gas Matrices

Abstract

Most of chemical reactions take place in a liquid or solid environment. Therefore, there exists a great interest in studying such processes, i.e. with matrix isolation spectroscopy. A mixture of HCl rare gas (1-.01%) is frozen out at temperatures between 20 and 70 K. The interaction between the HCl molecule and the rare gas atoms produces a change in the form of the intermolecular potential and creates a barrier. If the molecule dissociates after excitation one of the fragments should overcome the barrier. Thus the dissociation is hindered by the surrounded rare gas atoms and this leads to a decrease in the quantum efficiency in contrast to the gas phase (cage-effect). The aim is to measure the quantum efficiency as a function of excitation energy and to investigate the dynamics of the process. In order to achieve both a better mass selection with respect to HCl monomers, dimers and higher aggregates and an increasing Franck-Condon range in the first repulsive state (A1π), the excitation is split, i.e. an IR excitation from v″=0 → 3.4 in the ground state and a UV excitation to the repulsive state by means of an excimer or tunable dye laser. In order to detect the fragments, excimer or dye lasers are used.