A variational method for the calculation of spin–rovibronic energy levels of any triatomic molecule in an electronic triplet state

The triatomic spin-rovibronic variational code RVIB3 has been extended to include the effect of two uncoupled electrons, for both 3Σ- and 3Π (Renner–Teller) electronic states. The spin–orbital–rotational kinetic energy is included in the usual way, via terms ( ). The phenomenological terms are introduced to reproduce the spin–orbit and spin–spin splittings, respectively. Calculations are performed to evaluate the spin–rovibronic energy levels of CCO and CCO for which the Born–Oppenheimer potentials are derived from high-accuracy ab initio calculations.