Electron-temperature dependence of the recombination of HCO+ 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 \ensuremath{\alpha}(${\mathrm{HCO}}^{+}$) (${\mathrm{cm}}^{3}$/s)=(2.4\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}7}$[${\mathrm{T}}_{\mathrm{e}}$ (K)/300${]}^{\mathrm{\ensuremath{-}}}$0.69\ifmmode\pm\else\textpm\fi{}0.07 over the range 293 K${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 ${T}_{e}^{\mathrm{\ensuremath{-}}0.5}$ dependence predicted by a simplified theory for diatomic ions.