Ab initio potential energy surface and vibrational frequencies of Ã(1A″) HCF

An extensive ab initio MRCI study of the Ã(1A″) surface of HCF is reported that includes characterization of the equilibrium geometry and the barriers to dissociation and linearity. An analytic potential energy surface in the equilibrium region was fitted to the computed energies that allowed the variational calculation of the vibrational fundamentals, overtones and combination bands to ∼6800 cm−1. The computed bend progression is in good agreement with the experimentally observed progression. The spectroscopic constants of HCF in the ground X̃(1A′) and lowest excited ã(3A″) states were also computed using MRCI and coupled cluster techniques.