RESONANCE-ENHANCED CARS APPLIED TO THE CH RADICAL

Resonance enhanced coherent anti-Stokes Raman scattering (RECARS) is applied to the CH radical produced in a microwave (2.45 GHz) excited Ar/CH4 plasma. The electronic A(2) Delta-X(2)II(r), transition of the CH radical is used to obtain a resonance enhancement of the rotational CARS Lines. With this technique rotational lines up to N = 15 and up to upsilon = 2 are measured. In good agreement with earlier LIF measurements in similar plasmas we obtain two rotational temperatures for CH(X(2)II(r)), T-rot,T-1 = 671+/-32 K for N < 8, and T-rot,T-2 = 1400+/-91 K for N equal to or greater than 8. The vibrational temperature is about 2800 K and the CH density is estimated to be in the range of 10(10) to 10(11) cm(-3).