The Ar+–He interaction potential and distribution function effects on swarm measurements of Ar++N2 reaction-rate coefficients using helium buffer gas

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Abstract
Ab initio potentials for the X 2Σ+1/2, A1 2Π3/2, and A2 2Π1/2 states of ArHe+ are tested as to their ability to describe swarm measurements of gaseous ion transport coefficients. Also tested are potentials based on spectroscopic measurements and model potentials chosen specifically so as to match the transport data. Ar+‐ion velocity distributions in a drift tube containing a helium buffer are calculated from the potentials that best match the mobility data, by solution of the Boltzmann kinetic equation. The velocity distributions are used with estimated cross sections for the charge‐transfer reaction Ar++N2 to calculate the effects upon the rate coefficients when the distribution differs from a Maxwell–Boltzmann form. The results indicate that the corrections are small at high buffer gas temperatures (293 K and above) and low to moderate electric‐field strengths, but become larger at low temperature (82 K) and high fields. The smallness of the corrections confirms that previous rate coefficient measurements in a drift tube show a dependence of the Ar++N2 reaction upon the rotational temperature of N2.

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