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

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.