<title>Laser Chemistry In Molecular Crystals</title>

Abstract

AbstractThe use of mixed molecular crystals at low temperatures as systems in which to study laser inducedphotochemistry is discussed. As specific examples the photochemistry of s- tetrazine and its dimethylderivative is treated. These molecules have previously been used as guests in host molecular crystals toillustrate solid state laser isotope separation and photochemical hole burning. The results presented hereindicate that the low temperature tetrazine photochemistry may involve the sequential absorption of two photons. With this in mind, we are able to suggest a useful method of finding other materials for isotopeseparation and photochemical hole burning.IntroductionMolecular crystals provide ideal host systems for high resolution spectroscopic studies of substitutionallyincorporated guest molecules. Absorption and emission spectra at liquid helium temperatures can be verysharp,(1) and in many cases the molecules assume known orientations with respect to the host crystal axes.(2)These features of mixed molecular crystal spectra have been successfully exploited to investigate the excitedstates of a variety of organic molecules.In this paper we will discuss a mixed molecular crystal system in which the sharp spectral lines areselectively excited with the intense monochromatic radiation from a tunable dye laser, with the intent ofinvestigating the resulting photochemistry. Laser induced chemistry in mixed molecular crystals, as we willillustrate, promises to yield much valuable information on the mechanisms of photochemical reactions.