CS+ (B 2Σ+–X 2Σ+) emission produced from Penning ionization of the CS (X1 Σ+) radical

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Abstract
Emission spectrum resulting from the energy transfer reaction of He (2 3S) with transient CS radical produced through a microwave discharge of Ar/CS2 mixture was observed in a flowing afterglow apparatus. A new CS+ (B 2Σ+–X 2Σ+) band system due to He (2 3S)/CS Penning ionization was identified in the 220–340 nm region. The dominant bands were the (ν′,0) and (0, ν″) progressions, which was consistent with the prediction from calculated Morse potential Franck–Condon factors. Although the observed bandhead wavelengths of the major CS+ (B–X) emission were in good agreement with those predicted from the reported spectroscopic data, the (4,0) band was located at an abnormal position. It was interpreted as a consequence of vibrational perturbation in the B 2Σ+ state. The relative intensities of CS+(B–X), CS+(B–A), CI, and SI emission were estimated to represent that the dominant pathway of the He (2 3S)/CS reaction is Penning ionization.