Intensities and the Fano Line Shape in the Infrared Spectrum of HD

The spectrum of gaseous HD at a temperature of 77 K and densities from 1 to 60 amagat has been studied in the regions of the fundamental and first overtone bands. The 1–0 band consists of two components: (1) a collision-induced part, made up of broad Q and S transitions arising from collisions between molecules, and (2) a dipole-allowed part, made up of much sharper P and R transitions due to free molecules. The collision-induced 2–0 band was too weak to be observed in these experiments, but the first overtone R(0) transition was studied. The collision-induced fundamental band shows the expected similarity to the previously observed spectra of H2 and D2. A pronounced asymmetry in the fundamental band P and R transitions may be ascribed to a resonant interference with the underlying collision-induced continuum. Measurements of the intensities of the appropriate R(0) lines yield the following transition dipole moments: (0.49 ± 0.02) × 10−4 D for the fundamental, and (0.21 ± 0.02) × 10−4 D for the first overtone band.