Production of CN(B2Σ+) state from dissociative excitation reaction of BrCN with microwave discharge flow of Ar

The mechanism of the dissociative excitation reaction of BrCN with the microwave discharge flow of Ar was investigated based on the CN(B2Σ+–X2Σ+) emission-spectroscopic and the electrostatic-probe measurements. By passing Ar and BrCN through P2O5, the contamination of H2O molecules into the reaction region was reduced to ≈30%, being confirmed by monitoring the reduction of the OH(A2Σ+–X2Π) emission intensity. The variation of the CN(B2Σ+–X2Σ+) emission intensity on the pressure of Ar, PAr, of 0.1–0.3 Torr was compared with that of the density of electrons whose kinetic energy was lower than the ionization energy of BrCN, 11.9 eV. The dissociation of BrCN was found to proceed predominantly via the charge transfer from Ar+ followed by the BrCN+ − e− recombination. When the contamination of H2O molecules in the reaction region was not reduced, the dissociation via the energy transfer from metastable Ar atoms became significant. The present study shows that the contamination of H2O molecules in the reaction system makes significant effect onto the gas-phase plasma process.