Electron and Ion Processes in Weak Plasmas

\textbf{I. New Plasma Effects Observed in a Flowing-Afterglow Plasma.} In a study of electron attachment to C$_{6}$F$_{5}$Cl in a helium bath gas), we found the first case we know of in which a thermally-detaching ion product (C$_{6}$F$_{5}$Cl$^{-})$ results in competition with a thermally-stable ion product (Cl$^{-})$, at elevated temperatures (500-550 K). We hypothesize that the heavier ions are more confined to the core of the plasma, releasing fresh electrons all the while. A sudden transition is observed in the electron density decay as the C$_{6}$F$_{5}$Cl$^{-}$ concentration dies away. \textbf{II. Electron Attachment to Fluorinated Pyridines.} In this experiment we measured rate constants for electron attachment and electron detachment for C$_{5}$F$_{5}$N and C$_{5}$HF$_{4}$N. From the attachment/detachment reaction rate constants, electron affinities were determined to be EA(C$_{5}$F$_{5}$N) = 0.70 $\pm $ 0.05 eV and EA(C$_{5}$HF$_{4}$N) = 0.40 $\pm $ 0.08 eV. The neutrals are planar, but calculations show the negative ions to have the F or H opposite the N atom to be significantly out-of-plane. Experimental and calculated values show an average decrease in EA of 0.25 eV per substitution of H for F. \textbf{III. Ion-Molecule Reactions at High Temperatures.} We will present data on negative ion-molecule reactions with molecules, obtained in a high-temperature flowing afterglow apparatus at temperatures from 300-1440 K.