Pressure shifts in the vibrational Raman spectra of hydrogen and deuterium, 315–85 K

Abstract

The Raman frequencies of the Q(J) lines of the fundamental Raman bands of compressed H₂ and D, were measured with a standard deviation of ±0.02 cm⁻¹ at gas densities from 10 to 100 amagat at several temperatures in the range 315 to 85 K. The frequency shifts are negative and linear in the gas density; they range up to −1.2 cm⁻¹ for H₂ and −0.7 cm⁻¹ for D₂. The linear coefficient for the Q(J) line has the form, a_i + a_c(n_J/n), where n_J/n is the fractional population of the rotational level, J, and a_i and a_c are constants independent of J. The constant a_i is strongly temperature-dependent and is interpreted as the vibrational shift due to isotropic dispersion and overlap forces. On the other hand, a_c is practically temperature-independent and is believed to arise from vibrational coupling through dispersion forces.