Multiple photon excitation and selective reactions of hydrocarbons doped in low temperature crystals

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1. The isolated molecules in low temperature crystals are expected to possess sharp absorption lines due to the decrease of the contribution of the phonon side bands, and thus selective excitation of the molecules may be easy. The vibrational relaxation is expected to be relatively slow in low temperature solids. The objective of the present research is to isolate small polyatomic molecules in low temperature rare-gas crystals and to pursue the photophysical behavior of the isolated molecules.2. The case of oxygen molecules was studied in detail. When the oxygen molecules were isolated in Ar or Kr crystals and irradiated by KrF laser light, absorption lines assigned to the transition from the highly vibrationally excited ground electronic state to a higher electronic state were newly found. Analysis of these line positions and time behaviors gave the potential curve of the upper B electronic state, and also the mechanism and rates of the very slow relaxation of the vibrational states.In the case of hydrogen sulfide and some chlorofluorohydrocarbons, the isolation was only possible when they were diluted to less than 1/10000. These isolated molecules could be dissociated by KrF excimer laser irradiation, but not by infrared TEA carbon dioxide laser irradiation. The latter may be due to the relatively fast vibrational relaxation in the intermediate stages and/or energy mismatch during the infrared multiple photon absorption.