Rototranslational absorption spectra of H2-H2 pairs in the far infrared.

Abstract

For the computation of the induced dipole moments, the collisional ${\mathrm{H}}_{2}$-${\mathrm{H}}_{2}$ complex is treated as a molecule in the self-consistent field and size-consistent, coupled electron pair approximations. The basis set accounts for 95% of the correlation energies and separates correctly at distant range. The average of the induced dipole components is obtained for the case of both ${\mathrm{H}}_{2}$ molecules in the vibrational groundstate (v=v'=0) and recast in a simple but accurate analytical form. The analytical dipole expression is used for computations of the spectral moments (sum rules) and line shapes of the collision-induced rototranslational absorption spectra of molecular hydrogen in the far infrared, over a range of frequencies from 0 to 2200 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, and for temperatures from 77 to 300 K, using a quantum formalism. Proven isotropic potential models are input. Numerical consistency of the line-shape calculations with the sum rules is observed at the 1% level. The comparison of the computational results with the available measurements shows agreement within the estimated uncertainties of the measurements of typically better than 10%. This fact suggests that the theory is capable of predicting these spectra reliably at temperatures for which no measurements exist.