Faint features of the rotationalS 0(0) andS 0(1) transitions of H2

The complete collision induced absorption spectrum of H₂ - H₂ pairs at a temperature of 77 K, including the faint features due to bound and quasi-bound (H₂)₂ dimers, has been calculated from first principles and compared in detail with recently published laboratory measurements. An empirical anisotropic intermolecular potential energy surface (“F84”), and an ab initio induced dipole moment function due to Meyer were used in the calculations. The close coupled formalism was applied to determine the multiple-component scattering and bound-state wave functions. Comparisons between experiment and theory show very good general agreement: all the faint hydrogen dimer features that are observed are reproduced theoretically. The observed pressure broadening of sharper dimer features could also be partially accounted for in the calculations. The remaining disagreements between theory and experiment in the intensities and positions of the features are very useful for deriving the small modifications required to further improve the F 84 surface, especially in the region of the attractive potential well.