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. Absorption signals are recorded using near quantum shot noise limited laser absorption methods. The fully resolved absorption spectra of the CH stretch (ν) fundamental band and a partial progression of transitions of the HCF bend plus CF stretch (ν + ν) combination band are observed and show clear evidence of a strong rovibrational coupling between the νK = 2 and ν + νK = 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 ν and ν + ν 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 (ν + ν ← ν) transitions due to vibrationally excited HCF in the CF stretch mode, ν. 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 ν spectroscopic parameters now permit improved predictions for pure rotational and ν fundamental transitions to aid spectral searches for HCF in the laboratory and the interstellar medium.