Collision-induced absorption (CIA) of radiation occurs due to transient changes in molecular dipole moments during a collision. Transitions that are single-molecule forbidden may be seen in the CIA spectra. This phenomenon is observed in the atmospheres of the outer planets and their satellites; so information on the intensity of absorption is important for analyzing the atmospheric temperature profiles. Both atomic and molecular hydrogen are found in star-forming regions in the interstellar medium, and in the atmospheres of white dwarf stars (particularly DA white dwarfs). In order to calculate CIA spectra of H2-H accurately, it is necessary to determine the interaction-induced dipole quantum mechanically. In this work, new ab initio calculations of the dipole moment of H2-H have been carried out using finite-field methods with Molpro 2012 and Molpro 2015, for various values of the bond length r of H2, the separation R between the center of mass of H2 and H, and the angle between the H2 bond axis r and the vector R connecting the center of mass of H2 to the nucleus of the H atom. We have evaluated the spherical-tensor expansion coefficients for the collision-induced dipole. As found in earlier work, the coefficient D23 converges at long range to the known quadrupolar induction form. In the current work, we have demonstrated for the first time that the ab initio coefficient D45 converges to the hexadecapolar induction term, and that the coefficient D01 agrees closely at long range with the known asymptotic form due to van der Waals dispersion and back induction.

Interaction-induced dipole of a hydrogen molecule colliding with a hydrogen atom

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.