Studies of Electron Impact Excitation, Negative Ion Formation, and Negative Ion-Molecule Reactions in Boron Trifluoride and Boron Trichloride

Abstract

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 ${\text{〈5 × 10}}^5\hspace{0.17em}{\sec }^{\text{−1}}·{\mathrm{torr}}^{\text{−1}}$ for BF₃ and ${\text{9 × 10}}^7\hspace{0.17em}{\sec }^{\text{−1}}·{\mathrm{torr}}^{\text{−1}}$ for BCl₃. Beam studies showed that F⁻, ${\mathrm{F}}_2^{-},$ and ${\mathrm{BF}}_2^{-}$ were produced from BF₃ by electrons of energy near 11.5 eV while Cl⁻ and ${\mathrm{Cl}}_2^{-}$ were produced in BCl₃ near 1 eV. The ${\mathrm{SF}}_6^{-}$ 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 $\text{∼ 2.5}$ eV. The thermal energy ${\mathrm{SF}}_6^{\mathrm{-*}}$ ion was found to react readily with both BF₃ and BCl₃, yielding ${\mathrm{BF}}_4^{-}$ and BCl₃F⁻, respectively. ${\mathrm{BF}}_4^{-}$ was also produced through the reaction ${\mathrm{F}}_2^{-}/{\mathrm{BF}}_3+{\mathrm{BF}}_3\to {\mathrm{BF}}_4^{-}+\mathrm{F}.$ Thermal energy rate constants for these reactions determined by a pulsed source method were ${\text{1.8 × 10}}^{\text{−9}}{\text{,\hspace{0.17em}1.6 × 10}}^{\text{−10}},$ and ${\text{6.1 × 10}}^{\text{−11}}\hspace{0.17em}{\mathrm{cm}}^3\hspace{0.17em}{\mathrm{molecules}}^{\text{−1}}·{\sec }^{\text{−1}}$ in the order above.