Infrared absorption spectra of gaseous HD. IV. Analysis of the collision-induced fundamental band of the pure gas

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Abstract
Studies of the infrared absorption spectra of the HD fundamental band in the pure gas, reported for the room temperature in Paper I of this series, have now been extended to temperatures 77 and 196 K. The spectra of the band were recorded for a number of gas densities up to 50 amagat. In addition to the usual collision‐induced broad features of the infrared fundamental band of a symmetric diatomic gas, these spectra at 77 and 196 K show the dipole‐allowed sharp R1(0) and R1(1) transitions owing to the individual molecules. Derived binary absorption coefficients of the collision‐induced band are (1.15±0.06) ×10−35 and (1.71±0.07) ×10−35 cm6 s−1 at 77 and 196 K, respectively. An analysis of the absorption profiles of the band at 77 and 196 K and those of the band at 298 K reported in Paper I was carried out, and the characteristic half‐width parameters δd and δc of the short‐range overlap‐induced transitions and δq (and δq′) of the long‐range quadrupole‐induced transitions are derived. The contributions of the overlap‐ and quadrupolar‐interactions to the absorption intensity of the band are separated by the method of profile analysis. The magnitude parameter λ and the range ρ of the overlap‐induced dipole moment for the HD–HD collision pairs are determined by obtaining the best fit of the calculated overlap part of the binary absorption coefficient as a function of temperature to the experimental values. Derived overlap parameters are λ=5.60×10−3, ρ=0.25 Å, and μ (σ) (the overlap‐induced dipole moment at the Lennard–Jones intermolecular diameter σ) =3.1×10−2 ea0.