Excitation and quenching reactions in E-beam excited He/H2O and He/CH3CN systems

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Abstract
This paper describes observations made in the afterglow of an electron beam discharge into high‐pressure mixtures of He/H2O and He/CH3CN and assesses the laser potential of these systems. Emission spectra and time histories at visible and near uv wavelengths were obtained spectroscopically. OH(A2Σ→X2Πi) emission (306.8?λ?310.9 nm) predominated in the He/H2O system, and CN(B 2Σ+→X 2Σ+) emission (385.0?λ?391.6 nm) predominated in the He/CH3CN system. The suggested pumping reactions operative in these systems are the dissociative charge exchange reactions He2+ + H2O→OH(A)+HeH++He and He2++CH3CN→CN(B)+CH3++2He. The rate constants for these reactions have been determined to be (1.3±0.2) ×10−10 and (1.1±0.3) ×10−10 cm3/s, respectively. The He2+ quenching rate constants for H2O and for CH3CN were found to be (1.2±0.2) ×10−9 and (3.5±0.7) ×10−9 cm3/s, respectively. The OH(A) quenching rate constant for H2O was determined to be (4.2±0.4) ×10−10 cm3/s, and the CN(B) quenching rate constant for CH3CN was found to be (1.4±0.3) ×10−10 cm3/s. The OH(A) yield (number of excited molecules produced/number of He+ ions formed) was found to be 11%; the CN(B) yield was 3%. Maximum laser efficiencies for these systems were calculated and determined to be 0.5% and 0.1%, respectively.