ON THE GROUND ELECTRONIC STATES OF COPPER SILICIDE AND ITS IONS

The low-lying electronic states of SiCu, SiCu+, and SiCu- have been st udied using a variety of high-level ab initio techniques. As expected on the basis of simple orbital occupancy and bond forming for Si(s(2)p (2))+Cu(S-1) species, (2) Pi(r), (1) Sigma(+), and (3) Sigma(-) states were found to be the ground electronic states for SiCu, SiCu+, and Si Cu-, respectively; the (2) Pi, State is not that suggested in most rec ent experimental studies. All of these molecules were found to be quit e strongly bound although the bond lengths, bond energies, and harmoni c frequencies vary slightly among them, as a result of the nonbonding character of the 2 pi-MO (molecular orbital) [composed almost entirely of the Si 3p-AO (atomic orbital)], the occupation of which varies fro m 0 to 2 within the (1) Sigma(+), (2) Pi(r), and (3) Sigma(-) series. The neutral SiCu is found to have bound excited electronic states of 4 Sigma(-), (2) Delta, (2) Sigma(+), and (2) Pi, symmetry lying 0.5, 1. 2, 1.8, and 3.2 eV above the (2) Pi(r). ground state. It is possible b ut not yet certain that the 2 Pi(i) state is, in fact, the ''B state'' observed in the recent experimental studies by Scherer, Paul, Collier , and Saykally. (C) 1998 American Institute of Physics.