Collision-induced absorption in the rototranslational band of dense hydrogen gas

Measurements of the H-2-H-2 collision-induced absorption spectra at temperatures of 297.5 and 77.5 K are reported in the frequency range from 1900 to 2260 cm(-1) at gas densities ranging from 51 to 610 amagat. Ab initio calculations of the absorption are carried out for comparison with the measurements. In these calculations, for the lower temperature close-coupled equations describe the H-2-H-2 scattering in the presence of a weak electromagnetic radiation field; the anisotropy of the H-2-H-2 interaction is accounted for. For the room temperature calculations, the isotropic potential approximation is employed. Agreement of measured and calculated spectral shapes is observed. However, in the far wing, at large frequencies (greater than or similar to2000 cm(-1)), discrepancies of measured and calculated spectral intensities are observed which are somewhat larger than the combined, estimated uncertainties of theory and measurement. These differences remain unexplained at this stage. (C) 2003 American Institute of Physics.