The sclvcnt cage concept of photochemistry is translated into spectroscopic language by an extension of the Bom-Oppenheimer approximation.
The intermolecular perturbation term is taken as the barrier to viscous flow, added to the intramolecular potential. It is shown that novel phenomenological consequences in the spectroscopy of polyatomic molecules cnn be predicted for the inhibition of large amplitude molecular vibrations by the interaction with the solvent cage.
Environmental effects in molecular photochemistry traditionaliy have been discussed in terms of timedependent phenomena in condensed media (fluid solutions, rigid glasses, and crystals). These effects, which have been discussed primarily in terms of kinetics [l], may be given a quantum mechanical basis by tmating solute-solvent interaction with the addition of an intermolecuIar potential perturbation term to the intramolecular potential. Although t-his is an esser;tially new concept, its spectroscopic consequences have been widely observed and studied. Bayliss an:1 RWS [2] applied this concept to halogen spectral chan~,es for the comparison of vapor state and solution :,pectra. Our presentation extends the concept to the case of severe restriction of intramolecular motic;: by intermolecular perturbations especially in rigid matrices. There are pumerous examples of the hindrance of molecular movement in solid inert-hqs matrices. For example, Hdl and Pimentel [3] have studied the inhibition of the cisrrans isomerization of nitrous acid in a solid nitrogen matrix. Similarly, Fimentel et al. found [4] no evidence of inversion of NH, in a solid nitrogen matrix, again indicating a large intermolecular barrier. Mtirchison and Overend [S], and Smith et al. [6] have