, Volume 64, Issue 1, pp 111-118

Resonance enhanced coherent anti-stokes raman scattering and laser induced fluorescence applied to CH radicals: a comparative study

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Resonance enhanced CARS and LIF have been applied to the CH radicals in a microwave excited Ar/H \(_2\) /CH \(_4\) plasma ( \(p = 21\) Pa, \(P_{\rm Mikro} = 2.7\) kW). Both techniques yield similar nonthermal rotational population distributions of CH(X \(^2\Pi_r\) ) in its vibrational ground state ( \(v=0\) ), which can be described by two rotational temperatures, \(T_{\rm rot,1} \approx 600\) K being in the order of the gas temperature for rotational states with \(N \le 7\) , and a considerably higher \(T_{\rm rot,2}\) for the higher rotational states. This result is in good agreement with previous resonance CARS and LIF measurements in similar plasmas. With resonance CARS additional measurements on CH in the \(v=1\) state could be performed yielding a vibrational temperature of 2440 K, the total CH density was about \(1.6 \times 10^{18}\) m \(^{-3}\) . The detection limits of both techniques are determined, in our case about \(2 \times 10^8\) CH radicals per quantum state in the detection volume, and their advantages and disadvantages are discussed.

Received: 29 April 1996 / Accepted: 19 June 1996