Irradiation of small molecules isolated in rare gas matrices by high energy electron beams

Abstract

The matrix isolation technique is used to study radiation chemistry; specifically, rare gas matrices are irradiated with high energy electron beams to (1) spectroscopically probe a high energy electron beam induced reaction, and (2) determine the role of a chemically inert solvent on the electron beam chemistry. In the experiments presented herein, it is shown that the electron beam sensitivity of a component in a mixture may be altered by changing its concentration. A simple two component mixture consisting of small molecular systems like carbon dioxide, and nitrogen dioxide were isolated in chemically inert solvents like solid argon, krypton and xenon, respectively. The net effect of the electron beam exposure, for example, is the conversion of CO2 to CO. When the concentration of CO2 in a rare gas matrix was decreased the efficiency for CO2 decomposition increased. The mechanism for the enhanced decay for CO2 is related to migration and transfer of electronic energy from the rare gas matrix to CO2. A kinetic analysis, formulated for a quantitative evaluation of the process, was used to determined that the rate constant for energy transfer from a Wannier exciton to CO2 is 140 times greater than for transfer back to an argon matrix. The identity of the Wannier exciton as the species transferring energy to the matrix is in part based on energetic considerations. © 1990.