Fundamental and Overtone Vibrational Transitions in the Raman Spectrum of h.c.p. Solid Hydrogen

Abstract

The use of an argon laser of high intensity has made it possible to observe the vibrational overtone of solid hydrogen and to study the fundamental over a wider concentration range than previously. At ortho concentrations below ~ 15% the Q1(1) line has two components. The dependence on concentration and temperature of the frequency separation and relative intensity of these components is accounted for by the quadrupolar interaction between ortho molecules. Differences in the frequency shifts of the Q1(0) and the Q1(1) and of the Q2(0) and the Q1(1) lines in mixtures of all concentrations are also related to the quadrupolar interactions. The overtone lines show almost no frequency change with concentration. This is explained by a much smaller vibrational coupling due to the isotropic interactions in the ν = 2 than in the ν = 1 state. Confirmation of this is found in the small enhancement of the intensity of Q2(1) relative to Q2(0). The measurement of the frequency of Q2(0) makes it possible to determine the parameters μ1, and μ2, specifying the change in the intramolecular potential by the isotropic interactions, from transitions involving J = 0 states alone.