Studies of electron-impact excitation, negative-ion formation, and negative-ion--molecule reactions in boron trifluoride and boron trichloride

Electron attachment processes in BF3 and BCl3 have been studied with both electron swarm and electron beam techniques. Thermal electron attachment rates were determined by the drift-dwell-drift technique to be 〈5 × 105 sec−1 · torr−1 for BF3 and 9 × 107 sec−1 · torr−1 for BCl3. Beam studies showed that F−, F2−, and BF2− were produced from BF3 by electrons of energy near 11.5 eV while Cl− and Cl2− were produced in BCl3 near 1 eV. The SF6− threshold electron impact excitation spectrum of BF3 exhibited no structure, however, a number of peaks were seen in BCl3, the chief one being near 7.6 eV. A low energy peak was observed in BCl3 at ∼ 2.5 eV. The thermal energy SF6−* ion was found to react readily with both BF3 and BCl3, yielding BF4− and BCl3F−, respectively. BF4− was also produced through the reaction F2−/BF3+BF3→ BF4−+F. Thermal energy rate constants for these reactions determined by a pulsed source method were 1.8 × 10−9, 1.6 × 10−10, and 6.1 × 10−11 cm3 molecules−1 · sec−1 in the order above.