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arXiv · 0709.1904

Electron-impact rotational and hyperfine excitation of HCN, HNC, DCN and DNC

A. Faure·H. N. Varambhia·T. Stoecklin·J. Tennyson
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Abstract

Rotational excitation of isotopologues of HCN and HNC by thermal electron-impact is studied using the molecular {\bf R}-matrix method combined with the adiabatic-nuclei-rotation (ANR) approximation. Rate coefficients are obtained for electron temperatures in the range 5$-$6000 K and for transitions among all levels up to J=8. Hyperfine rates are also derived using the infinite-order-sudden (IOS) scaling method. It is shown that the dominant rotational transitions are dipole allowed, that is those for which $ΔJ=1$. The hyperfine propensity rule $ΔJ=ΔF$ is found to be stronger than in the case of He$-$HCN collisions. For dipole allowed transitions, electron-impact rates are shown to exceed those for excitation of HCN by He atoms by 6 orders of magnitude. As a result, the present rates should be included in any detailed population model of isotopologues of HCN and HNC in sources where the electron fraction is larger than 10$^{-6}$, for example in interstellar shocks and comets.

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A. Faure, H. N. Varambhia, T. Stoecklin, J. Tennyson. 2007-09-12. Electron-impact rotational and hyperfine excitation of HCN, HNC, DCN and DNC. https://doi.org/10.1111/j.1365-2966.2007.12416.x

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