Abstract: | 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 ν3 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 , , and states of GeC2. © 2018 Wiley Periodicals, Inc. |