Resonance enhanced CARS applied to the CH radical

Abstract

Resonance enhanced coherent anti-Stokes Raman scattering (RECARS) is applied to the CH radical produced in a microwave (2.45 GHz) excited Ar CH 4 plasma. The electronic A 2 Δ − X 2 Π 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 v = 2 are measured. In good agreement with earlier LIF measurements in similar plasmas we obtain two rotational temperatures for CH(X 2 Π r), T rot,1 = 671 ± 32 K for N < 8, and T rot,2 = 1400 ± 91 K for N ≥ 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.