Charge transfer rate in collisions of H+ ions with Si atoms

Charge transfer in Si(P-3, D-1) + H+ collisions is studied theoretically by using a semiclassical molecular representation with six molecular channels for the triplet manifold and four channels for the singlet manifold at collision energies above 30 eV, and by using a fully quantum mechanical approach with two molecular channels for both triplet and singlet manifolds below 30 eV. The ab initio potential curves and nonadiabatic coupling matrix elements for the HSi+ system are obtained from multireference single- and double-excitation configuration interaction (MRD-CI) calculations employing a relatively large basis set. The present rate coefficients for charge transfer to Si+(P-4) formation resulting from H+ + Si((3)p) collisions are found to be large with values from 1 x 10(-10) cm(3) s(-1) at 1000 K to 1 x 10(-8) cm(3) s(-1) at 100,000 K. The rate coefficient for Si+(P-2) formation, resulting from H+ + Si(P-3) collisions, is found to be much smaller because of a larger energy defect from the initial state. These calculated rates are much larger than those reported by Baliunas & Butler, who estimated a value of 10(-11) cm(3) s(-1) in their coronal plasma study. The present result may be relevant to the description of the silicon ionization equilibrium.