Abstract
Cross-sections and thermally averaged rate coefficients for vibration (de-)excitation of a water molecule by electron impact are computed; one and two quanta excitations are considered for all three normal modes. The calculations use a theoretical approach that combines the normal mode approximation for vibrational states of water, a vibrational frame transformation employed to evaluate the scattering matrix for vibrational transitions and the UK molecular R-matrix code. The interval of applicability of the rate coefficients is from 10 to 10,000 K. A comprehensive set of calculations is performed to assess uncertainty of the obtained data. The results should help in modelling non-LTE spectra of water in various astrophysical environments.
Highlights
The water molecule is fundamental in a variety of research fields, such as biochemistry, meteorology and astrophysics
Collisions between free electrons and water molecules play an important role in molecular environments as diverse as biological systems, cometary atmospheres and stellar envelopes
The theoretical approach employed in this study is presented in detail in refs. [14,15,16,17]
Summary
The water molecule is fundamental in a variety of research fields, such as biochemistry, meteorology and astrophysics. Because experiments can hardly distinguish between the two stretching excitations (symmetric and asymmetric) of water, vibrational measurements usually provide cross-sections for bending excitation (010) and for the sum of the two stretching excitations (100) and (001) (in normal mode notations) From their compilation of literature data, Song et al [2]. In all previous works for electron collisions with water, vibrational cross-sections were computed for one-quantum transitions only and without considering specific initial and final rotational states. It should be noted, in this context, that Stoecklin and co-workers have recently performed rovibrational state-to-state close-coupling calculations for the quenching of the bending mode (010) of water by (spherical) H2 [12] and helium atoms [13].
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