FORMATION OF CH(A2-DELTA,B2-SIGMA-,C2-SIGMA+) BY ELECTRON-ION RECOMBINATION PROCESSES IN THE ARGON AND KRYPTON AFTERGLOW REACTIONS OF CH4

The CH(A-X,B-X,C-X) emission systems have been observed from the Ar and Kr afterglow reactions of CH4. A significant attenuation of the CH(A-X,B-X,C-X) emissions by an addition of SF6 into the discharge flow suggested that the CH(A,B,C) radicals are excited via secondary electron-ion recombination processes. Since the CH(A-X,B-X,C-X) emissions disappeared by trapping ionic active species in the discharge flow, the responsible active species for the CH(A,B,C) production were found to be Ar+ and/or (Ar+)* in the Ar flow and Kr+ and/or (Kr+)* in the Kr flow. The contribution of Ar+ and Kr+ was examined in the He afterglow, where Ar+ or Kr+ and slow electrons were simultaneously produced by the He(2(3)S)/Ar,Kr Penning ionization. Although intense CH(A-X,B-X,C-X) emissions were observed from Ar+/CH4 where CH(n)+ (n = 2-40 were formed, they were absent from Kr+/CH4 where only CH4+ was produced. It was, therefore, concluded that CH2+ and/or CH3+ are important precursor ions for the CH(A,B,C) production. The intensity distribution of CH(A,B,C) and the CH(A,B) rovibrational distributions obtained in the Ar afterglow agreed with those through Ar+/CH4, indicating that Ar+/CH4 plays a significant role for the production of precursor ions in the Ar afterglow or (Ar+)*/CH4 provides the same precursor ions. Since the relative intensity of CH(A,B) and the rovibrational distributions of CH(A) in the Kr afterglow were different from those in the Ar afterglow, different electron-ion recombination processes dominantly take part in the CH(A,B) production.