Thermal electron attachment to F2

Rate constants have been measured from 300 to 700 K for thermal electron attachment to F${}_{2}$ using two flowing afterglow--Langmuir probe apparatuses. Dissociative attachment yielding F${}^{\ensuremath{-}}$ is observed with a rate constant of 5.0 \ifmmode\pm\else\textpm\fi{} 1.3 \ifmmode\times\else\texttimes\fi{} 10${}^{\ensuremath{-}9}$ cm${}^{3}$ s${}^{\ensuremath{-}1}$ at 300 K, rising to 9.6 \ifmmode\pm\else\textpm\fi{} 2.4 \ifmmode\times\else\texttimes\fi{} 10${}^{\ensuremath{-}9}$ cm${}^{3}$ s${}^{\ensuremath{-}1}$ at 700 K, well below the previously accepted values of McCorkle et al. [D. L. McCorkle, L. G. Christophorou, A. A. Christodoulides, and L. Pichiarella, J. Chem. Phys. 85, 1966 (1986)]. The absolute concentration of F${}_{2}$ reaching the afterglow is verified by measuring the near-collisional rate constant (4.5 \ifmmode\pm\else\textpm\fi{} 1.5 \ifmmode\times\else\texttimes\fi{} 10${}^{\ensuremath{-}10}$ cm${}^{3}$ s${}^{\ensuremath{-}1}$) for Ar${}^{+}$ $+$ F${}_{2}$\ensuremath{\rightarrow}ArF${}^{+}$ $+$ F. Prior attempts to apply $R$-matrix calculations to the F${}_{2}$ $+$ ${e}^{\ensuremath{-}}$ system have failed to explain previously reported thermal and nonthermal attachment rate constants along with high-resolution, low-energy attachment cross sections. The present results are reproduced exceptionally well by $R$-matrix calculations employing previously calculated resonance widths without adjustment.