Potential Curves for the Valence-Excited States of Silicon Monoxide. A Theoretical Study

Abstract

Ab initio quantum mechanical calculations have been carried out at 10 internuclear separations for those 72 molecular states of silicon monoxide which dissociate to a Si atom in ³P, ¹D, ¹S, or ⁵S state plus an oxygen atom in ³P, ¹D, or ¹S state. Full configuration interaction calculations were made from a minimal basis set of Slater‐type orbitals, with the restriction that the core orbitals (1s, 2s, 2p Si and 1s O) were fully occupied. The results were strikingly similar to those obtained for CO in an analogous theoretical study. Ten bound states were found to dissociate to ground state Si plus ground state O; five of these states have been observed experimentally in SiO, but eight have experimentally known counterparts in CO. The predicted ordering of states is X ¹Σ⁺, a ³II, ${\mathrm{a\prime \hspace{0.17em}}}^3{\Sigma }^{+}$ , ³Δ, e ³Σ⁻, I ¹Σ⁻, A ¹II, ¹Δ, ⁵Σ⁺, and ⁵II. Molecular orbital configurations are assigned to each of these 10 states. Among 10 higher predicted bound states, the ¹II III state, with calculated D_e=1.32 eV, is perhaps the most likely to be observed experimentally. The tentative assignment of the I ¹Σ⁻ state by Verma and Mulliken is considered unlikely on the basis of the present calculations. The A ¹II potential curve is very flat as it approaches the dissociation limit, but, unlike CO, there is no maximum in this curve for SiO.