We present new results for the dipole moment of hydrogen molecule pairs, obtained from ab initio calculations for 27 relative orientations, 9 bond lengths in all combinations, and up to 24 distances between the centers of mass, considerably extending prior studies of this system. We determined the energy of a pair of interacting H₂ molecules in coupled-cluster calculations with single and double excitations and perturbative triples [CCSD(T)] using Molpro 2015 and 2022. An aug-cc-pV5Z basis was used for the majority of the calculations. We used finite-field methods with six different strengths of an applied static electric field, in order to eliminate hyperpolarization contributions to the calculated dipole moments. We performed full configuration interaction calculations and explicitly correlated coupled-cluster calculations of CCSD(T)-F12 type, and calculations with an aug-cc-pV6Z basis set, to test the accuracy of our results. The results are in excellent agreement with AUTOSURF calculations by Ernesto Quintas-Sanchez and Richard Dawes, who used the CCSD(T)-F12b method with a VQZ-F12 basis.
We have evaluated twenty-two coefficients for the interaction-induced dipoles expanded as a series in the spherical harmonics of the orientation angles of each H₂ molecule of the intermolecular vector. This form is needed for spectroscopic line-shape calculations of collision-induced roto-vibrational absorption and emission.
Collision-induced emission may have contributed to the cooling of the clouds in which the first stars (Population III) formed, thus permitting their continued contraction under gravity and ultimately affecting their size distribution. Collision-induced absorption in the outer stellar atmosphere affects the rate of cooling of very old, very cool white dwarf stars. Determination of the ages of these stars requires information on the H₂-H₂ collision-induced dipoles. Modeling of the temperature profiles of the gas giants in the Solar System and of exoplanetary gas giants also requires information on collision-induced dipoles.

Hua-Kuang Lee

Appearances