Jet cooled CN radical beam was formed by cold cathode DC discharge of CH3CNunder molecular beam conditions. The cylindrical cold cathode was placed between the skimmerand the nozzle to prevent the nozzle from being clogged by carbon particles. The pulsed photoncounting LIF measurement was seriously jeopardized by the high intensive scattering laser lightdue to CN(B2Z)’s short lifetime (70ns) and weak fiuorescence. By using an attenuator to reducelaser intensity or a polaroid to reduce the scattering laser intensity, we obtained LIF spectra withgood S/N ratio. With the theoretical simulasd spectra, the effects of laser p0larization on LIFwere discussed and the relative populations of CN rotational and vibrational states were obtained.
