THE INFRARED SPECTRUM OF LIQUID HD

$^{1}$N. H. Rich et al., Can. J. Phys. 61, 1648 (1983); 62, 1665, 1673 (1984). $^{2}$A. Crane and H. P. Gush, Can. J. Phys. 44, 373 (1966).Author Institution: National Research Council of Canada, Herzberg Institute of Astrophysics; National Research Council of Canada, Herzberg Institute of Astrophysics; Department of Physics, Memorial University of NewfoundlandWe have measured the spectrum of liquid hydrogen deuteride in the region of the fundamental band ($3500-4000 cm^{-1}$) and of the pure rotational R(0) transition ($80-90 cm^{-1}$). The experiments were performed using a Bomem DA3.002 spectrometer and a 1 cm path; the liquid was followed along the gas-liquid coexistence line from 18 to 35 $^{\circ} K$. Of special interest are the effects of interference between the permanent dipole moment of HD and the transient dipoles induced during molecular collisions. These effects have been studied in the gas $phase,^{1}$ and were also observed in solid $HD.^{2}$ We observe a pronounced anomalous dispersion (Fano) lineshape for the $R_{1}(0)$ transition around $3715 cm^{-1}$, whereas the $R^{0}(0)$ transition around $88 cm^{-1}$ is only slightly asymmetric. A weak, sharp absorption feature was observed in the liquid at 18 $^{\circ} K$ on the high frequency side of the broader Fano $R_{1}(0)$ profile; this feature resembles the beginning of the stronger sharp feature observed in the $solid.^{2}