Temperature dependence of the pure rotational band of HD: Interference, widths, and shifts.

Abstract

The far-infrared pure rotational absorption spectra of gaseous HD and HD-X (X=${\mathrm{H}}_{2}$, He, Ne, Ar, Kr, and ${\mathrm{N}}_{2}$) were measured at 195 and 296 K. Values of the allowed dipole-moment matrix elements, the absolute frequencies, the spectral-line-shape parameters (broadening and frequency-shift coefficients), and the interference parameters, for the first four rotational lines, were deduced from the spectra. Theoretical calculations of the interference parameter a and the linewidths were performed, based, respectively, on the theory developed by Herman, Tipping, and Poll [Phys. Rev. A 20, 2006 (1979)] and a semiclassical theory developed by Robert and Bonamy [D. Robert and J. Bonamy, J. Phys. 40, 923 (1979)]. The induced dipole moments for HD-Ne and HD-${\mathrm{N}}_{2}$ were estimated. The analysis includes the present experimental results, together with previous determinations at 77 and 296 K [L. Ulivi, Z. Lu, and G. C. Tabisz, Phys. Rev. A 40, 642 (1989); P. Drakopoulos and G. C. Tabisz, ibid. $bold 36 ---, 5556 (1987)]. The behavior of the temperature dependence of the collisional interference in the pure rotational band for HD and its mixtures is confirmed to be more complicated than predictions of the intracollisional theory.