Ab initio potential energy surface and vibration-rotation energy levels of germanium dicarbide, GeC2

The accurate ground-state potential energy surface of germanium dicarbide, GeC2, has been determined from ab initio calculations using the coupled-cluster approach. The core-electron correlation, higher-order valence-electron correlation, and scalar relativistic effects were taken into account. The potential energy surface of GeC2 was shown to be extraordinarily flat near the T-shaped equilibrium configuration. The potential energy barrier to the linear CCGe configuration was predicted to be 1218 cm(-1). The vibration-rotation energy levels of some GeC2 isotopologues were calculated using a variational method. The vibrational bending mode (3) was found to be highly anharmonic, with the fundamental wavenumber being only 58 cm(-1). Vibrational progressions due to this mode were predicted for the v1=1, v2=1, and v2=2 states of GeC2. (c) 2018 Wiley Periodicals, Inc.