Thermal-energy charge transfer, quenching, and association reactions of doubly charged ions in the rare gases

A drift-tube mass-spectrometer apparatus has been used to determine thermal-energy (300 K) charge transfer rate coefficients for reactions of the type Rₐ²⁺+Rb→Rₐ⁺+Rb+* and Rₐ²⁺+Rb→Rₐ⁺+Rb²⁺+e^- (transfer ionization), where $R=He,{{0ex}{0ex}}Ne,{{0ex}{0ex}}Ar,{{0ex}{0ex}}Kr,{{0ex}{0ex}}and{{0ex}{0ex}}Xe$. Rate coefficients for ions in the low-lying, metastable excited states ($¹S$ and $¹D$) as well as the ground state ($³P$) have been determined and, in some cases, deexcitation (quenching) coefficients for $¹S$ and $¹D$ ions have been measured. Reactions with an exoergicity ${Δ}E{~}4$ eV are found to be fast, approaching the limiting Langevin rate, while for ${Δ}E<2 and >7$ eV the rates fall off dramatically, in some cases dropping to the radiative value (${{{~}}10}^{{-}14}$ ${cm}³$/sec). The equilibrium constant for the three-body association reaction ${Xe}²⁺+ 2 Ne{(XeNe)}²⁺$ + Ne has been determined at 300 K.