Effects of vibrational excitation of target N2 molecule in charge–transfer reaction of He+ with N2 at thermal energy

Abstract

The effects of vibrational excitation of target N2 molecule in the charge-transfer (CT) reaction He++N2(X:v″)→N2+(C)+He has been studied at thermal energy using a flowing–afterglow method. The vibrational distribution of N2(X:v″⩾0), produced from a microwave discharge of Ar/N2 or He/N2 mixtures, was determined using N2+(B–X) emission resulting from the He(2 3S)/N2(X:v″) Penning ionization. Although the initial vibrational distribution of N2+(C) produced from the He+/N2(X:Nv″=0=100) reaction was Nv′=3:Nv′=4=100±5:28±2, it was Nv′=3:Nv′=4:Nv′=5:Nv′=6=100±5:60±3:41±2:49±2 in the He+/N2(X:Nv″=0:Nv″=1:Nv″=2:Nv″=3=91±5:100±5:100±5:18±1) reaction. The N2+(C:v′=3) level, which is the most favorable level in the thermal He+/N2(X:v″=0) reaction, is still favored in the He+/N2(X:v″⩾0) reaction. This indicates that the deviation from the energy-resonance rule becomes large by the vibrational excitation of N2(X:v″). The rotational distributions of v′=3 and 4 were similar between the He+/N2(X:v″=0) and He+/N2(X:v″⩾0) reactions, demonstrating that V→R transfer is insignificant for N2(X)→N2+(C) ionization in the He+/N2(X:v″⩾0) reaction.