Mechanism of dissociative excitation of BrCN in electron cyclotron resonance plasma flow of He

The dissociative excitation reaction of BrCN induced by the products of the electron cyclotron resonance (ECR) plasma flow of He was studied based on the electrostatic-probe measurements and on the optical emission spectra of the B2Σ+ − X2Σ+ transition of CN radicals. The partial pressures of He and BrCN were 3 and 1 mTorr, respectively, and the partial pressure of H2O, PH2O, was in the range of 0.0-0.6 mTorr. The electron density, ne, showed a negative dependence on PH2O as (2.63 ± 0.13) × 1012 − (0.23 ± 0.10) × 1012 m−3, and the electron temperature, Te, a positive dependence, (2.38 ± 0.36) − (4.51 ± 0.15) eV. The CN(B2Σ+ − X2Σ+) emission intensity showed a negative dependence on PH2O. Based on a kinetic analysis of these PH2O dependencies, the decomposition of BrCN does not proceed via electron impact; instead, decomposition proceeds via the processes involving He+ and/or He metastable atoms.