We present measurements of the infrared absorption corresponding to the rovibrational transitions of adsorbed HD. The absorption-line bandwidths at low coverages of HD on porous Vycor glass are more than two times larger than those of adsorbed ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$. Also, we observe the transitions corresponding to δJ=3 and 5, whereas only the allowed δJ=0,±2 are observed for the pure isotopes. Our observations strongly suggest hindrance of the rotational states of HD, which may be attributed to the hybridization of rotations and adsorbed HD phonons resulting from the molecule’s mass asymmetry.

• Received 23 September 1991

DOI:https://doi.org/10.1103/PhysRevB.45.1931