Measurement of rotational populations of CH radicals in low-temperature lasmas

Rotational population of CH radicals in A(2)Delta state was measured using a high resolution visible spectrometer in low-temperature helium plasmas with methane injection in materials and plasma (MAP)-II device. The rotational population in the A(2)Delta state is characterized by bi-Maxwellian distributions with different rotational temperatures, T-HOT and T-COLD. The rotational temperatures of both components decreased through collisions with background helium. The dependence of emission intensity on plasma parameters suggests that dissociative recombination of methane ions, which are ionized by charge exchange of methane with helium ions should be taken into account in the discussion of the dissociation processes in CH radicals in the pressure regime from 0.24 to 1.2 Pa in this experiment.