Infrared absorption spectra of gaseous HD. I. Collision-induced fundamental band of HD in the pure gas and HD–He mixtures at room temperature

The infrared absorption spectra of the fundamental band of HD in the pure gas for densities up to 50 amagat and in HD–He mixtures for different base densities of HD and a number of total gas densities up to 190 amagat have been studied at room temperature. The collision-induced features of the band in the pure gas and in HD–He mixtures are similar to those previously observed for the spectra of H2 and D2 in the pure gases and in their binary mixtures with helium, respectively. In addition, the absorption profiles of the pure gas show the allowed sharp R1(1) transition due to the individual HD molecules. The binary absorption coefficients of the band derived from the measured integrated intensities are 2.32×10−35 and 0.94×10−35 cm6 s−1 for pure HD and HD–He, respectively. An analysis of the profiles of the enhancement of absorption of the band in HD–He 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 ρ of helium and fits to the equation δc = aρ − bρ2(a≫b). This observation and the conclusions derived from it are similar to those obtained previously for H2–He.