Improved temperature dependence of rate coefficients for rotational state-to-state transitions in H₂O + H₂O collisions^★

Chemistry Department, Wehr Chemistry Building, Marquette University, Milwaukee, WI 53201-1881, USA
e-mail: dmitri.babikov@marquette.edu

Received: 13 May 2023
Accepted: 17 August 2023

Abstract

Aims. We present an improved database of temperature-dependent rate coefficients for rotational state-to-state transitions in H₂O + H₂O collisions. The database includes 231 transitions between the lower para-states of H₂O and 210 transitions between its lower ortho-states (up to j = 7) and can be employed in cometary and planetary applications up to the temperature of 1000 K.

Methods. We developed and applied a new general method that allows the generation of rate coefficients for excitation and quenching processes that automatically satisfy the principle of microscopic reversibility and also helps to cover the range of low collision energies by interpolation of cross sections between the process threshold and the computed data points.

Results. We find that in the range of intermediate temperatures, 150 < T < 600 K, our new rate coefficients are in good agreement with those reported earlier, but for higher temperatures, 600 < T < 1000 K, the new revised temperature dependence is recommended. The low temperature range, 5 < T < 150 K, is now covered by the above-mentioned interpolation of cross sections down to the process threshold.