Rotational quenching of H2CO by molecular hydrogen: cross-sections, rates, pressure broadening

TL;DR

This study calculates detailed rotational quenching rates of H2CO with H2 across 10-300 K, revealing significant differences from previous He-based estimates and aligning with experimental pressure broadening data.

Contribution

It provides the first comprehensive quantum calculations of H2CO-H2 collision rates and pressure broadening cross sections over a wide temperature range.

Findings

Quenching rates differ markedly from scaled He rates.

Critical densities are lower than previously estimated.

Results agree with low-temperature experimental data.

Abstract

We compute the rotational quenching rates of the first 81 rotational levels of ortho- and para-H2CO in collision with ortho- and para-H2, for a temperature range of 10-300 K. We make use of the quantum close-coupling and coupled-states scattering methods combined with the high accuracy potential energy surface of Troscompt et al. (2009a). Rates are significantly different from the scaled rates of H2CO in collision with He; consequently, critical densities are noticeably lower. We compare a full close- coupling computation of pressure broadening cross sections with experimental data and show that our results are compatible with the low temperature measurements of Mengel & De Lucia (2000), for a spin temperature of H2 around 50 K.