Ab initio computation of the broadening of water rotational lines by molecular hydrogen

TL;DR

This paper presents ab initio calculations of water rotational line broadening by molecular hydrogen, comparing theoretical cross sections with experimental data across 65-220 K, highlighting agreements and discrepancies at lower temperatures.

Contribution

It introduces high-accuracy ab initio calculations for pressure broadening of water lines by H2, addressing temperature-dependent behavior with detailed quantum calculations.

Findings

Good agreement with experiments above ~80 K

Discrepancy at lower temperatures possibly due to impact approximation failure

Suggests role of ortho-to-para H2 conversion in observed effects

Abstract

Theoretical cross sections for the pressure broadening by hydrogen of rotational transitions of water are compared to the latest available measurements in the temperature range 65-220 K. A high accuracy interaction potential is employed in a full close coupling calculation. A good agreement with experiment is observed above ~80 K while the sharp drop observed experimentally at lower temperatures is not predicted by our calculations. Possible explanations for this discrepancy include the failure of the impact approximation and the possible role of ortho-to-para conversion of H2.