The structure and spectrum of SiC2.

Second order polarization propagator calculations indicate that the blue/green bands attributed to SiC2 in the atmospheres of certain carbon stars arise from a triangular (C2v) form of the molecule. It appears that this form is separated from a linear (C∞v) form by only a very small barrier, and that spectra from both forms might be observable. The potential for the movement of Si around the C2 fragment, the spectral lines, oscillator strengths, and lifetimes are discussed. We find, as observed previously, that only in a correlated calculation is the triangular geometry the preferred ground state conformation. Also the excitation properties change markedly with correlation. [ABSTRACT FROM AUTHOR]