Highly predissociative levels of CH B 2Σ- state detected with two-color resonant four-wave mixing spectroscopy

We demonstrate an application of two-color resonant four-wave mixing spectroscopy to detect highly predissociative levels of CH in the B (2)Sigma(-) State in a hostile environment of an oxyacetylene flame. The probe and grating wavelengths ate in resonance with the A (2)Delta-X (2)Pi and B (2)Sigma(-)-X (2)Pi systems, respectively. We measured 49 previously unobserved rovibronic lines of the 0-0 band and 38 additional lines of the 1-0 band of the B (2)Sigma(-)-X(2)Pi system to access rotational quantum number N' up to 21 and 13 of upsilon' = 0 and 1 in the B (2)Sigma(-) state, respectively. Inclusion of additional line positions measured for the 0-0 and the 1-0 bands yields spectral parameters of the B (2)Sigma(-) State significantly improved over those obtained previously with only nonpredissociative lines; one additional centrifugal-distortion parameter L-upsilon is evaluated significantly. Although power saturation is significant even at smallest practical laser energies, we estimated lifetimes through the power dependence of linewidths. The lifetimes of the highest measurable level of B (2)Sigma(-) (upsilon' = 0 and 1) are 3 +/- 1 (N' = 20) and 8 +/- 2 (N' = 11) ps, respectively. (C) 1998 American Institute of Physics. [S0021-9606(98)00634-5].