Measurement of Charge-Transfer Rate Coefficients of Diatomic Helium Ion with Selected Atomic and Molecular Species in High Pressure Afterglows.

High pressure, volume dominated glow discharges for use as laser media have gained interest in the past decade as a result of the development of a variety of external ionization and discharge stabilization techniques. In such systems, charge-transfer processes occur by way of bimolecular and termolecular reaction channels at atmospheric pressure, with latter gaining in relative importance due to its dependence on gas pressure. Therefore, it is essential to characterize these termolecular reaction rates and recognize the fact that these reactions must be included among all other processes considering in modeling the high pressure lasers and discharge media. This dissertation reports the measurement of bimolecular and termolecular charge transfer reactions of {rm He}_sp{2}{+} into nonassociative produce channels. In this study, the population of {rm He} _sp{2}{+} was monitored as a function of time by detection of the { rm N}_sp{2}{+}(B to X) transition at 391.4 nm in high pressure afterglows of mixed gases excited by a fast electrical discharge system capable of operation up to 6 atm. Data have been obtained as functions of helium pressure over the range from 900 to 4700 torr and as functions of partial pressure of reactant from 0 to 500 mtorr. From these data, pressure dependent rate coefficients have been extracted and subsequently resolved into contributions from bimolecular and termolecular components for reactions of { rm He}_sp{2}{+} with N_ 2, O_ 2, CO_ 2, Ar, and Xe. The size of the termolecular rates suggests the general importance of three-body ion-molecule reactions in high pressure plasmas such as those found in high pressure gas lasers.