Electron-temperature dependence of the recombination ofHCO+ions with electrons

A microwave-afterglow mass-spectrometer apparatus employing microwave heating of the electrons has been used to determine the dependence on electron temperature $T_e$ of the recombination coefficient of electrons with ${\mathrm{HCO}}^{+}$ ions. By comparison of the observed electron-density decays to the computed behavior of a recombination- and ambipolar-diffusion-controlled afterglow, it is found that the electron-temperature dependence of the recombination coefficients follows a power law of the form α(${\mathrm{HCO}}^{+}$) (${\mathrm{cm}}^3$/s)=(2.4±0.4)×${10}^{\mathrm{-}7}$[${\mathrm{T}}_{\mathrm{e}}$ (K)/300${]}^{\mathrm{-}}$0.69±0.07 over the range 293 K<$T_e$<5500 K. The magnitude of the recombination coefficient is similar to that observed and calculated for simple diatomic ions, while the temperature dependence is somewhat stronger than the $T_e^{\mathrm{-}0.5}$ dependence predicted by a simplified theory for diatomic ions.