Collision-induced infrared absorption spectra of the fundamental bands of hydrogen deuteride and hydrogen

The infrared absorption spectra of the fundamental band of HD in its binary mixtures with He, Ne, Ar, Kr, and Xe for different base-densities of HD and a number of total gas densities up to 190 amagat were recorded at room temperature with a one meter transmission type high-pressure absorption cell. The collision-induced features of the band in these mixtures are similar to those observed for the corresponding spectra of H₂ in its binary mixtures. The binary and ternary absorption coefficients of the band have been derived from the measured integrated intensities. An analysis of the profiles of the enhancement of absorption of the band in all the five mixtures has been performed by assuming appropriate line shapes, and the three half-width parameters, δd and δc of the overlap transitions and δq of the quadrupolar transitions are obtained. The half-width δc of the intercollisional interference dip of the Q branch increases with density ρb of the perturbing gas and satisfies the equation δc = αo + αρb for all the binary mixtures. -- An interesting finding in the enhancement spectra of the fundamental band of HD in HD-Kr and HD-Xe mixtures is the first observation of a narrow line at the R₁(1) position whose intensity increases with the rare gas density. This line is interpreted as due to a constructive interference between the allowed dipole of HD and the collision-induced dipole of the colliding pair HD-Kr or HD-Xe and the effect is referred to as “intracollisional interference.” -- The collision-induced absorption spectra of the fundamental band of HD in pure gas were recorded for gas densities up to 50 amagat at 77 and 196 K on a two meter high pressure absorption cell and at 298 K on the one meter absorption cell. The binary and ternary absorption coefficients of the band have been derived from the experimental profiles. The contribution to the intensity of the band from the short-range overlap induction was obtained from the analysis of the absorption profiles. For the HD-HD molecular pairs, the overlap parameters λ and ρ which give, respectively, the magnitude and range of the overlap dipole moment, and µ(α), the overlap-induced dipole-moment at the Lennard-Jones intermolecular diameter σ, were determined by obtaining the best fit of the calculated overlap part from the theory of Van Kranendonk (1958) to the experimental values of the overlap parts. The collision-induced absorption spectra of the fundamental band of H₂ in the pure gas was reinvestigated for densities up to 60 amagat at temperatures 77, 196 and 298 K and the over- lap parameters for the H₂-H₂ collision pairs were derived by adopting a procedure similar to the one used for the fundamental band of HD in the pure gas