15min:
ENERGY AND LIFETIME OF HIGHLY PREDISSOCIATIVE LEVELS OF THE CH C 2 Sigma+ AND D 2 Pi STATES DETERMINED WITH TWO-COLOR RESONANT FOUR-WAVE MIXING SPECTROSCOPY .

YUAN-PERN LEE, XINGHUA LI, AWADHESH KUMAR, CHIH-CHANG SHIAO, 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 Sigma+ AND D 2 Pi 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 Delta - X 2 Pi and C 2 Sigma+ - X 2 Pi transitions, respectively. 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 (v = 1) state up to N' = 23. Observed wave numbers are fitted to yield improved spectral parameters of the C 2 Sigma+ state. The D state was observed by using two grating beams in resonance with the D 2 Pi - B 2 Sigma- transition and the pump beam in resonance with a known B 2 Sigma- - X 2 Pi transition. A total of 86 lines associating with transitions to the D (v = 0) state with rotational quantum number N' up to 16 were detected; spectral parameters of the D 2 Pi (v = 0) state were determined. Linewidth, broadened due to predissociation, up to 6 cm-1 were observed. Predissociation mechanisms of both the C and the D states are discussed.