CHARGE TRANSFER RATE IN COLLISIONS OF H~+ IONS WITH Si ATOMS

摘要

Charge transfer in Si(~3P, ~1D) + 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~+(~4P) formation resulting from H~+ + Si(~3P) 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~+(~2P) formation, resulting from H~+ + Si(~3P) 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.