Intermolecular Potentials and the Infrared Spectrum of the Molecular Complex (H2)2

Abstract

The infrared absorption spectrum of the molecular‐hydrogen complex H₄ has been calculated. The model assumed is that of two spherically symmetric, freely rotating hydrogen molecules bound by a weak inter‐molecular potential. Two types of induced‐dipole transitions are considered; the first arises from electronic overlap and is directed mainly along the intermolecular axis, while the second results from a dipole induced in one molecule by the electric‐quadrupole moment of the other. Calculations are made for three different intermolecular potentials. For all three the results are in excellent agreement with the hydrogen spectrum observed by Watanabe and Welsh. The dependence of particular spectral features on the shape of the potential is discussed, and also the feasibility of discriminating between various potential models experimentally by improving the spectral resolution. A calculation of the bound levels of (HD)₂ and (D₂)₂ complexes indicates that at least the sharpest features of their absorption spectra should be observable under the resolution already achieved by Watanabe and Welsh.