Ab Initio Potential Energy Surface and Vibration-Rotation Energy Levels of Silicon Dicarbide, SiC2

The accurate ground-state potential energy surface of silicon dicarbide, SiC2, has been determined from ab initio calculations using the coupled-cluster approach. Results obtained with the conventional and explicitly correlated coupled-cluster methods were compared. The core-electron correlation, higher-order valence-electron correlation, and scalar relativistic effects were taken into account. The potential energy barrier to the linear SiCC configuration was predicted to be 1782 cm(-1). The vibration-rotation energy levels of the SiC2, (SiC2)-Si-29, (SiC2)-Si-30, and (SiCC)-C-13 isotopologues were calculated using a variational method. The experimental vibration-rotation energy levels of the main isotopologue were reproduced to high accuracy. In particular, the experimental energy levels of the highly anharmonic vibrational nu(3) mode of SiC2 were reproduced to within 6.7 cm(-1), up to as high as the v(3) = 16 state.