Electron capture and excitation collisions of Si2+ ions with He atoms at intermediate energies

We have investigated electron capture and excitation in collisions of Si2+ ions with He atoms in the collision energy range from 0.02-6 keV/u based on a molecular representation. Molecular states are determined by using the multireference single- and double-excitation configuration-interaction method. We have considered electron capture and excitation both by the ground singlet and metastable triplet Si2+ ions. The capture cross section by the ground singlet Si2+ ion increases with increasing collision energy and reaches a value of similar to 1.5 x 10(-16) cm(2), while that by the metastable triplet ion is found to be large with a magnitude of 4 x 10(-16) cm(2) at the highest energy studied. Weak but conspicuous oscillatory structures are found for both cases, which are due to multichannel interference. The present rate coefficient for the ground singlet Si2+ ion impact is found to be much smaller than those of the [Si4+ + He] system studied earlier. [S1050-2947(99)01311-6].