THE PRESSURE-INDUCED ROTATIONAL ABSORPTION SPECTRUM OF HYDROGEN: I. A STUDY OF THE ABSORPTION INTENSITIES

Abstract

The pressure-induced infrared spectrum of H2 and mixtures of H2 with N2, He, Ne, A, Kr, and Xe was measured in the region 300–1400 cm−1 at total gas pressures up to 250 atm at 300° K and, where possible, at 195° K and 85° K. The spectrum shows greatly broadened S lines (ΔJ = + 2) with half widths which decrease as the temperature is lowered. The integrated absorption coefficient of the band is of the form [Formula: see text], where ρƒ is the density of the perturbing gas, except in the case of Xe for which a cubic term, [Formula: see text], is also necessary. The binary coefficient α1 increases by a factor of 28 in going from He to Xe. The theoretical band intensity, calculated on the basis of quadrupole interaction alone, is in good agreement with the experimental value only for Xe as perturbing gas; in other cases the calculated value is appreciably less than the observed value. The shape of the absorption contours suggests that the S lines are overlaid by a continuum increasing in intensity towards lower frequencies. This continuum is interpreted as the counterpart of the QR component in the vibrational band, that is, a collision-induced absorption due to overlap interaction in which the relative kinetic energy of the collision partners changes in the absorption process.