High-resolution infrared spectroscopy of HCF in the CH stretch region

We present the results from a high-resolution infrared study of jet-cooled singlet monofluorocarbene (HCF) in the CH stretch region near 2600 cm^-1. Absorption signals are recorded using near quantum shot noise limited laser absorption methods. The fully resolved absorption spectra of the CH stretch (ν₁) fundamental band and a partial progression of transitions of the HCF bend plus CF stretch (ν₂ + ν₃) combination band are observed and show clear evidence of a strong rovibrational coupling between the ν₁K_a ^' = 2 and ν₂ + ν₃K_a ^' = 3 manifolds, including the observation of "dark state" transitions. A detailed perturbation analysis of a c-type Coriolis interaction is carried out for these two coupled vibrational states, providing experimental determination of precise rovibrational constants. A combined ground state combination difference fit of the transitions to the ν₁ and ν₂ + ν₃ vibrational states in this study with previously reported LIF Ã(0,0,0) ← X̃(0,0,0) data has been done to increase the accuracy of the ground state rotational constants [M. Kakimoto et al., J. Mol. Spec. 88, 300-310 (1981)]. Moreover, we report, for the first time, hot band (ν₁ + ν₃ ← ν₃) transitions due to vibrationally excited HCF in the CF stretch mode, ν₃. The high-resolution results for all vibrational frequencies and rotational constants are in good agreement with and significantly extend the analysis of the rovibrational manifold of HCF. The present ground state and ν₃ spectroscopic parameters now permit improved predictions for pure rotational and ν₃ fundamental transitions to aid spectral searches for HCF in the laboratory and the interstellar medium.