Measurement of the rate coefficients for the bimolecular and termolecular de-excitation reactions of He(23S) with Ne, Ar, N2, CO, CO2, and CH4

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Abstract
This work reports the measurement of second and third order excitation transfer reactions of metastable 23S helium atoms with Ne, Ar, N2, CO, CO2, and CH4. In this study He (23S) destruction frequencies have been experimentally determined from measurements of the optical absorption of the 3889 Å, 23S→43P, helium transition in high pressure afterglows of mixed gases excited by intense electron beam discharge. Data have been obtained as functions of helium pressure over the range from 800 to 2000 torr and as functions of the partial pressure of reactant from 14 to 200 mtorr. From this data pressure dependent rate coefficients have been extracted and subsequently resolved into contributions from second order, bimolecular, and third order, termolecular, components. The bimolecular components have been found to agree with tabulated values appearing in the literature. The sensitivity of the method has been sufficient to detect termolecular components as small as 0.3×10−30 cm6/sec and values were found to range from this threshold value for Ne to 8.3×10−30 cm6/sec for CO2. The size of these termolecular rates suggests the general importance of such third order reactions in higher pressure plasmas and afterglows such as those found in e‐beam lasers.