40min:

YUAN-PERN LEE, Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 30043.

We demonstrate an application of two-color resonant four-wave mixing (TC-RFWM) spectroscopy to detect highly predissociative levels of the C ^{2 +} AND D ² states of CH in a hostile environment of an oxyacetylene flame. The 1-1 band of the C - X transition is detected with the probe and the grating wavelengths in resonance with the A ² - X ² and C ^{2 +} - X ² transitions, respectively. Six branches of the C - X (1-1) system are spectrally resolved for the first time; in total 124 lines detected in this work correspond to excitation of the C ^{2 +} (v = 1) state up to N' = 23. Observed wave numbers are fitted to yield improved spectral parameters of the C ^{2 +} state. The D state was observed by using two grating (probe) beams in resonance with the D ² - B ^{2 -} transition and the pump beam in resonance with a selected B ^{2 -} - X ² transition. A total of 86 lines associated with transitions to the D ² (v = 0) state with rotational quantum number N' up to 16 were detected; parameters for centrifugal-distortion (D, H), spin-rotation interaction ( ), and -doubling (p, q, q₀) of the D ² (v = 0) state were deduced for the first time. The predissociative line width is about 2 cm^-1 for N' = 1 and gradually increases to 7 cm^-1 for N' = 15. Predissociation mechanisms of both the C and the D states are discussed. If time permits, other systems will be briefly described.