Charge exchange in slow collisions of Si3+ with H

Low energy electron capture from atomic hydrogen by multi-charged ions continues to be of interest and has wide applications including both magnetically confined$^{ }$fusion and astrophysical plasmas. The charge exchange process reported here\textit{, Si}$^{3+} + H$ -- \textit{Si}$^{2+} + H^{+}$ is an important destruction mechanism of Si$^{3+}$ in photo-ionized gas. The soft X-ray emission from comets has been explained by charge transfer of solar wind ions, among them Si$^{3+}$, with neutrals in the cometary gas vapor. The state selective cross sections are evaluated using the semi-classical molecular orbital close coupling (MOCC) [1] methods. Adiabatic potentials and wave functions for a number of low-lying singlet and triplet states are calculated using the MRD-CI package [2]. Details will be presented at the conference.$\backslash $ [1] M. Kimura and N. F. Lane, At. Mol. Opt. Phys \textbf{26}, 79 (1990). [3] R. J. Buenker, ``Current Aspects of Quantum Chemistry'' 1981, Vol \textbf{21}, edited by R. Carbo (Elsevier, Amsterdam) p 17.