HIGHLY PREDISSOCIATIVE LEVELS OF CH-B-(2)SIGMA(-) STATE DETECTED WITH2-COLOR RESONANT 4-WAVE-MIXING SPECTROSCOPY

We demonstrate an application of two-color resonant four-wave mixing s pectroscopy 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 p reviously unobserved rovibronic lines of the 0-0 band and 38 additiona l lines of the 1-0 band of the B (2)Sigma(-)-X(2)Pi system to access r otational quantum number N' up to 21 and 13 of upsilon' = 0 and 1 in t he B (2)Sigma(-) state, respectively. Inclusion of additional line pos itions measured for the 0-0 and the 1-0 bands yields spectral paramete rs of the B (2)Sigma(-) State significantly improved over those obtain ed previously with only nonpredissociative lines; one additional centr ifugal-distortion parameter L-upsilon is evaluated significantly. Alth ough power saturation is significant even at smallest practical laser energies, we estimated lifetimes through the power dependence of linew idths. 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, r espectively. (C) 1998 American Institute of Physics. [S0021-9606(98)00 634-5].