Structural and spectroscopic effects of vibronic coupling in the C2F radical

The lowest three (12A′,22A′,12A′′) potential energy surfaces of the C2F radical have been studied at the ab initio level, using Multi Reference Configuration Interaction techniques. For linear geometries, the three surfaces correlate with a 2Π and a 2Σ+ state, which are very close in energy. Only the X2A′ ground state was found to be bent, with RCC=1.271 Å; RCF=1.276 Å; ∠CCF=165°, and a barrier to linearity of 275 cm−1. The spin–rovibronic energy levels up to J=7/2 have been calculated using a recently developed method [Carter et al., Mol. Phys. 98 (2000) 1967]. Almost all of the resulting levels arise from a strong mixture of two out of three electronic states and their assignment is intrinsically ambiguous. A partial characterization, based on the shape of the vibronic wavefunctions, has been made.