Two-Color Resonant Four-Wave Mixing Spectra of the C²<i>Σ</i><i>⁺</i>−X²<i>Π</i>(1−1) Band of CH in a Flame

Abstract

We investigated predissociative transitions C2Σ+ (v‘ = 1)−X2Π (v‘ ‘ = 1) of CH in an oxyacetylene flame with the two-color resonant four-wave mixing technique in which two grating beams are in resonance with the C−X transition and the probe beam is resonant with a selected A−X transition. Six branches of the C−X system are spectrally resolved for the first time; in total 124 lines detected in this work correspond to excitation of the C state up to N‘ = 23. Observed wavenumbers are fitted to yield improved spectral parameters of the C2Σ+ (v = 1) state; one additional centrifugal distortion parameter LV is evaluated significantly. These data are combined with lines of C−X (0−0) and (2−2) bands to provide improved characterization of the C state of CH. For all lines of the C−X (1−1) band, the line widths are nearly identical. Predissociation mechanisms of the C state are discussed.