Ab initio potential energy surface and vibration-rotation energy levels of disilicon carbide, CSi2

Abstract

The accurate potential energy surface of disilicon carbide, CSi2, in its ground electronic state X∼1A1 has been determined from ab initio calculations using the coupled-cluster approach in conjunction with the correlation-consistent basis sets up to septuple-zeta quality. The core-electron correlation, higher-order valence-electron correlation, scalar relativistic, and adiabatic effects were taken into account. The potential energy barrier to the linear SiCSi configuration was predicted to be 832cm−1. The vibration-rotation energy levels of the CSi2, 13CSi2, CSi29Si, and CSi30Si isotopologues were predicted using a variational approach. The experimental vibration-rotation energy levels of the main isotopologue were reproduced to high accuracy. In particular, long vibrational progressions in the highly anharmonic SiCSi bending mode ν2 originating from the ground vibrational state of CSi2 are reproduced to within about 2.4cm−1 on average, close to the experimental accuracy.