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

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Abstract
This work reports the measurement of the excitation transfer reactions of metastable He2(3Σu) helium molecules with Ne, Ar, N2, CO, CO2, and CH4. In this study He2(3Σu) destruction frequencies have been experimentally determined from measurements of the optical absorption of the 4650 Å, 3Σu →3πg 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(3Σu) 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.