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

1. 由于声子边带的贡献减小，低温晶体中的孤立分子有望具有尖锐的吸收谱线，从而使分子的选择性激发变得容易。在低温固体中，振动弛豫速度相对较慢。本研究的目的是在低温稀有气体晶体中分离小的多原子分子，并追求分离分子的光物理行为。对氧分子的情况进行了详细的研究。当氧分子被分离到Ar或Kr晶体中，用KrF激光照射时，新发现了从高振动激发的基电子态到高电子态转变的吸收谱线。通过对这些线的位置和时间行为的分析，得到了上B电子态的电位曲线，以及振动态缓慢弛豫的机理和速率。对于硫化氢和某些氟氯烃，只有将它们稀释到万分之一以下才能分离出来。这些分离分子在KrF准分子激光照射下可以解离，而在红外TEA二氧化碳激光照射下则不能解离。后者可能是由于红外多光子吸收过程中中间阶段相对较快的振动弛豫和/或能量失配所致。

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.