Inverse Raman Spectroscopy Measurements of Line-Shift Coefficients in Hydrogen Perturbed by Argon

Abstract

High resolution Raman studies of the Q branch in H2 perturbed by Ar are relevant to combustion diagnostics and for tests of the intermolecular potential. The use of spectroscopic techniques to study combustion requires accurate models for the line shapes, which can range front Lorentzian to Gaussian to more complicated profiles1 depending on the perturber species, perturber concentration, density and temperature. Calculations with these models require estimates of the speed dependence of the line-shift and line-broadening coefficients. Modern theories are now able to predict the shifting and broadening resulting from collisions but are hampered by uncertainties in the interaction potential. One of the most studied potentials is that of H2-Ar, which has the advantage of being theoretically tractable for line shape computations. Furthermore, since the masses of Ar and molecular O2 and N2 are similar, spectral features depending on the perturber’s mass are expected to be similar. We report preliminary measurements of the density shift of the Q branch lines in H2 as a function of rotational state and temperature.