Doppler-limited spectra of the CH bending overtone of fluoroform

Abstract

The parallel ( A 1) and perpendicular ( E) bands of the CH bending overtone, 2 ν 4, of CHF 3 have been recorded at Doppler-limited resolution at room temperature using a difference-frequency laser spectrometer. The l = 0 component, 2 ν 4 0( A 1), and the l = +2 component, 2 ν 4 +2( E) (accessed by Δ K = −1 transitions), are only weakly perturbed by a mutual l-type resonance near the K′ = 31 and 33 levels, respectively; they can be fit to ≤0.0002 cm −1, approaching the experimental precision. The 2 ν 4 −2( E) component (accessed by Δ K = +1 transitions) is strongly perturbed, principally by anharmonic and Coriolis resonances with 2 ν 3 + ν 4 ±1( E). This perturbing state, though not observed directly, can be well specified by its influence on 2 ν 4 −2. Additional localized resonances, arising from a multitude of possible combinations of lower frequency vibrations, are alos observed in the high K levels of 2 ν 4 −2. These increase the rms deviation of the fit to the Δ K = +1 transitions, but a reliable set of deperturbed constants can be obtained by judicious selection of the data.