Measurements of Recombination of Electrons with HCO+Ions

Recombination coefficients of electrons with HC${\mathrm{O}}^{+}$ ions have been determined with a microwave afterglow/mass-spectrometer apparatus. Afterglow measurements of electron density decays in neon-hydrogen-carbon-monoxide mixtures are correlated with the decay of mass-identified ion currents to the wall of the microwave cavity. At the appropriate partial pressures of hydrogen and carbon monoxide in the mixture, the ion HC${\mathrm{O}}^{+}$ dominates the ion composition and its wall current approximately "tracks" the electron density decay curve. From recombination controlled electron density decay curves, the values $\alpha \left({\mathrm{HCO}}^{+}\right)=(3.3\mathrm{}\pm 0.5) \mathrm{and} (2.0\mathrm{}\pm 0.3)\times {10}^{-7\mathrm{}}$ ${\mathrm{cm}}^3$/sec are obtained at 205 and 300 K, respectively. The implications of these results for models of polyatomic-molecule formation in dense interstellar clouds are briefly discussed.