Electron attachment and ionization coefficients and electron drift velocities in BF₃ and SiF₄

The drift velocity of electrons (w) in SiF₄ and BF₃ has been measured over the density-reduced electric field (E/N) range 0.5×10^-17 V cm² ≤E/N≤300×10 ^-17 V cm² using a pulsed Townsend experimental technique. The electron attachment (η/N) and ionization (α/N) coefficients have also been measured in SiF₄ and BF₃ over the E/N range 30×10^-17 V cm² ≤E/N≤300×10^-17 V cm² in the same experiment. The electron drift velocities in these two gases exhibit regions of negative differential conductivity (NDC) similar to but smaller in magnitude than those in CH₄ and CF₄. The effective ionization coefficient (ᾱ/N) has been obtained from the η/N and α/N measurements in both gases, from which the high-voltage limiting electric field strengths (E/N)_lim have been found to be 123×10^-17 V cm² for BF₃ and 121×10^-17 V cm² for SiF ₄. The significance of these results in modeling gas discharges for a number of technological applications is indicated.