MOLECULAR-BEAM OPTOTHERMAL SPECTRUM OF THE NU-1 C-H STRETCHING FUNDAMENTAL-BAND OF CHF2CL

The infrared spectrum of the ν1 CH stretching fundamental of CHF235Cl and CHF237Cl has been measured using a color-center-laser molecular-beam optothermal spectrometer. The high resolution (∼0.0005 cm-) and low rotational temperature (TRot ∼ 14 K) allow the assignment of approximately 500 transitions up to J′ = 16 and K′a = 11 for the excited state of the dominant CHF235Cl isotopic form. The spectrum exhibits perturbations affecting the K′a = 6 through K′a = 9 levels, with the interaction being strong enough at K′a = 7 to observe transitions to the perturbing or "dark" state. A perturbation analysis yields a coupling matrix element of ∼0.02 cm-1 between the two states, with the perturbation determined to be a Fermi-resonance and/or parallel-type Coriolis interaction between the A′ symmetry CH strecthing state and an A′ dark state. The essentially unperturbed K′a = 0-5, 10-11 states have been fit to a Watson-type asymmetrical top Hamiltonian to a standard deviation of 0.00025 cm-1, which is approximately a factor of three larger than the estimated experimental uncertainty. The resulting band origin is 3021.63351(4) cm-1. A smaller set of transitions have been assigned to the CHF237Cl species, yielding a band origin of 3021.3995(10) cm-1. © 1992.