Measurement of the rate coefficients for the de-excitation reactions of He2 (3Σu) metastables with Ne, Ar, N2, CO, CO2, and CH4

Abstract

This work reports the measurement of the excitation transfer reactions of metastable He₂(³Σ_u) helium molecules with Ne, Ar, N₂, CO, CO₂, and CH₄. In this study He₂(³Σ_u) destruction frequencies have been experimentally determined from measurements of the optical absorption of the 4650 Å, ³Σ_u →³π_g helium transition in high pressure afterglows of mixed gases excited by intense electron beam discharges. Data have been obtained as functions of helium pressure over the range from 1500 to 2500 torr and as functions of the partial pressure of reactant from 14 to 200 mtorr. From this data pressure independent rate coefficients have been extracted which describe the effective bimolecular rates of reaction. These bimolecular rate coefficients have been found to range from 4.4×10⁻¹¹ cm³ sec⁻¹ for reactions with Ne to 95 ×10⁻¹¹ cm³ sec⁻¹ for reactions with CO₂. Reaction probabilities have been found to be generally larger than for the corresponding reactions of He(2³S) metastable atoms, approaching unity for the reaction of He₂(³Σ_u) with CO₂. Other measured values of ionization probability ranged from 0.3 and 0.4 for N₂ and Ar, respectively, to 0.6 for CO and CH₄.