CO 2 + (ÖX̃ and B̃–X̃) emissions resulting from the He(2 3S)+CO2 Penning ionization

Abstract

CO 2 + (à 2Πu–X̃ 2Πg) and CO2+ (B̃ 2Σu+−X̃ 2Πg) emissions produced from the He(2 3S)+CO2 Penning ionization have been observed in a flowing afterglow apparatus. The fluorescence branching ratio of the à 2Πu and B̃ 2Σu+ states, and the vibrational populations of the à state were determined as a function of helium pressure. The fluorescence branching ratio of the à and B̃ states was independent of the helium pressure at 0.5–1.0 Torr. Meanwhile, a significant relaxation was found for the vibrational distribution of the à state in the helium pressure range from 0.5 to 5 Torr. The unrelaxed vibrational distribution of the à state was determined from the 62 ÖX̃ bands. The fluorescence branching ratio IA/IB was about four times larger than the initial population ratio of the à and B̃ states determined by electron spectroscopy, and the vibrational populations of the à state shifted to higher υ1′ levels (υ1′= 3,4, and 5). These discrepancies between the PIOS and PIES results have been interpreted as due to interelectronic state coupling between the B̃ and à states.