Optical study of the He++N2 charge transfer reaction in a flowing afterglow and in a low-pressure chamber coupled with flowing afterglow

The He++N2 charge transfer (CT) reaction has been studied by optical emission spectroscopy utilizing a conventional flowing afterglow apparatus and a low-pressure apparatus. In the latter apparatus the He+ ions generated by a microwave discharge are expanded into a low-pressure chamber through a nozzle orifice. An intense structured continuum emission as well as the N+2(C 2∑+u–X 2∑+g), N+2(B 2∑+u–X 2∑+g), and N+2(D′ 2Πg–A 2Πu) emission systems has been observed in the 190–320 nm wavelengths region in the both experiments, although the continuum emission detected in the flowing afterglow is electronically quenched and/or vibrationally relaxed by collisions with He atoms. It has been found that the N+2(D′ 2Πg–A 2Πu) emission predominates in the 210–260 nm region, and occupies about a half of that of the total emission in the 200–320 nm region. The relative excitation rate constant for the D′ state has been measured to be 30% of that of the C state, suggesting that the process leading to the D′ state is an important exit channel in the He++N2 CT reaction at (near) thermal energy.