Ab initio potential energy surface and vibration-rotation energy levels of disilicon carbide, CSi2
Abstract The accurate potential energy surface of disilicon carbide, CSi 2 , in its ground electronic state X ∼ 1 A 1 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 CSi 2 , 13 CSi 2 , CSi 29 Si, and CSi 30 Si 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 ν 2 originating from the ground vibrational state of CSi 2 are reproduced to within about 2.4cm −1 on average, close to the experimental accuracy. Highlights The paper presents results of the accurate state-of-the-art ab initio calculations on the structural and spectroscopic properties of CSi 2 . The study clarifies the importance of various effects which should be taken into account to achieve the ‘spectroscopic’ accuracy for the CSi 2 quasilinear molecule. The results can be useful to theoreticians as a benchmark reference, as well as to experimentalists exploring the structure and vibration-rotation spectra of similar species. Graphical abstract The potential energy surface of disilicon carbide was predicted ab initio . The vibration-rotation energy levels of CSi 2 and its isotopologues were then determined to high accuracy. [DISPLAY OMISSION]
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