CHARGE-TRANSFER RATE IN COLLISIONS OF H+ IONS WITH SI ATOMS

Charge transfer in Si(P-3, D-1) + H+ collisions is studied theoretical ly by using a semiclassical molecular representation with six molecula r channels for the triplet manifold and four channels for the singlet manifold at collision energies above 30 eV, and by using a fully quant um mechanical approach with two molecular channels for both triplet an d singlet manifolds below 30 eV. The ab initio potential curves and no nadiabatic coupling matrix elements for the HSi+ system are obtained f rom multireference single- and double-excitation configuration interac tion (MRD-CI) calculations employing a relatively large basis set. The present rate coefficients for charge transfer to Si+(P-4) formation r esulting from H+ + Si((3)p) collisions are found to be large with valu es 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 fro m H+ + Si(P-3) collisions, is found to be much smaller because of a la rger 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 presen t result may be relevant to the description of the silicon ionization equilibrium.