Rovibronic states of the X 2Π state of CCO−

For the X 2Π electronic ground state of CCO− three-dimensional potential energy functions have been generated ab initio and used in variational Renner–Teller calculations including electron spin. The spin–orbit constant has been calculated to be −57.8 cm−1, the rotational constant Be=0.3831 cm−1, with ReCO=1.221 Å and reCC=1.308 Å. Rovibronic levels (J=P) for J⩽5/2 are given for energies up to about 4000 cm−1. For the vertical A 2Σ+–X 2Π transition the electronic transition moment amounts to 0.88 debye, yielding a radiative lifetime of 1.1 μs for the A-state.