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 R_CC=1.271 Å; R_CF=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.