Absorption by gaseous and solid HD and solid para-H2 in the far infrared

Abstract

The absorption spectrum of HD at 300 °K, 77.3 °K, and 4.2 °K (solid) has been measured in the frequency range of 40 to 450 cm−1. The spectrum is the sum of a collision-induced part associated with ΔJ = 2 rotational–translational transitions, and an allowed electric-dipole part associated with ΔJ = 1 rotational transitions. The intensity of the induced part of the spectrum has been compared with theoretical predictions; a significant discrepancy between the measured and calculated intensity of the S(0) line in the solid is noted. The intensity of the corresponding feature in solid parahydrogen has also been measured and a similar discrepancy exists.