PRESSURE-INDUCED INFRARED ABSORPTION OF GASEOUS HYDROGEN AND DEUTERIUM AT LOW TEMPERATURES: I. THE INTEGRATED ABSORPTION COEFFICIENTS

Abstract

The pressure-induced infrared absorption of the fundamental band of hydrogen, in the pure gas and in a H₂–He mixture, and of deuterium was studied in the temperature range from 18 °K to 77 °K. Path lengths up to 13.6 m at 1 atm or somewhat higher were obtained in a multiple-traversal cell cooled by liquid hydrogen or nitrogen. The binary coefficient for hydrogen shows a rise at low temperature, indicating the existence of bound states predicted by theory for the (H₂)₂ complex. The effect is more pronounced for deuterium. For the H₂–He mixture decreases monotonically with temperature, thus showing no evidence of bound states for H₂–He pairs. Fine structure at the maxima of the pressure-induced band in hydrogen and deuterium gives direct spectroscopic evidence of bound states of (H₂)₂ and (D₂)₂ complexes at low temperatures.