Absorption Spectra of Diatomic Molecules in Liquid and Crystalline Rare Gases

Abstract

Examination of absorption spectra of molecules in liquid and crystalline matrices gives information on two fundamental kinds of problems perturbations of molecules by surrounding fields, and effects of impurities on crystals and crystal growth. Rare-gas solid and liquid matrices are ideally suited to such problems since the forces between rare-gas atoms are especially weak, symmetric, short-range, and well known. Experimental studies of growth and observation of pure rare-gas crystals, transparent in a broad range from the infrared to the vacuum ultraviolet, and of low concentrations of diatomic molecules in solid solution with rare gases are described. As an example, the system NO in liquid and crystalline Kr was studied in die range from 2000–5000 A. Even at the smallest concentrations of NO no trace of discrete spectra of the NO γ, system was found. However, a cutoff at short wavelength was observed in the liquid, increasing with increasing NO concentration. This absorption cutoff may be due to the transition from the ground state X ²π to the theoretically predicted ⁴π state. Both spectroscopic and solid state conclusions are drawn from these experiments and experiments on other systems of the same kind.