Two-color resonant four-wave mixing spectra of the C-2 Sigma(+)-X-2 Pi(1-1) band of CH in a flame

We investigated predissociative transitions C(2)Sigma(+) (v' = 1)-X(2)Pi (v " = 1) of CH in an oxyacetylene flame with the two-color resonant four-wav e 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 spec tral parameters of the C(2)Sigma(+) (v = 1) state; one additional centrifug al distortion parameter L-V is evaluated significantly. These data are comb ined with lines of C-X (0-0) and (2-2) bands to provide improved characteri zation of the C stare 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.