Rotational excitation of HC3N by H2 and He at low temperatures

被引：0

作者：

Wernli, M. ^{[1
]}

Wiesenfeld, L. ^{[1
]}

Faure, A. ^{[1
]}

Valiron, P. ^{[1
]}

机构：

[1] Laboratoire d'Astrophysique, Observatoire de Grenoble, Université Joseph-Fourier, Boîte Postale 53, 38041 Grenoble Cedex 09, France

来源：

Astronomy and Astrophysics | 2007年 / 464卷 / 03期

关键词：

Aims. Rates for rotational excitation of HC3N by collisions with He atoms and H2 molecules are computed for kinetic temperatures in the range 5-20 K and 5-100 K; respectively. Methods. These rates are obtained from extensive quantum and quasi-classical calculations using new accurate potential energy surfaces (PES). The HC3N-He PES is in excellent agreement with the recent literature. The HC3N-H2 angular dependence is approximated using 5 independent H2 orientations. An accurate angular expansion of both PES suitable for low energy scattering is achieved despite the severe steric hindrance effects by the HC3N rod. Results. The rod-like symmetry of the PES strongly favours even ΔJ transfers and efficiently drives large ΔJ transfers. Despite the large dipole moment of HC3N; rates involving ortho-H2 are very similar to those involving para-H2; because of the predominance of the geometry effects. Except for the even ΔJ propensity rule; quasi classical calculations are in excellent agreement with close coupling quantum calculations. As a first application; we present a simple steady-state population model that shows population inversions for the lowest HC3N levels at H2 densities in the range 104-106 cm-3. Conclusions. The HC3N molecule is large enough to present an original collisional behaviour where steric hindrance effects hide the details of the interaction. This finding; combined with the fair accuracy of quasi classical rate calculations; is promising in view of collisional studies of larger molecules. © ESO 2007;

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摘要：

Journal article (JA)

引用

页码：1147 / 1154

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