Electron motion in the gases CF4, C2F6, C3F8, and n-C4F10

The drift velocity w of electrons has been measured in the perfluoroalkanes n-CNF2N+2 (N=14) over the density-reduced electric field (E/N) range 0.03×10-17 V cm2E/N500×10-17 V cm2 using a pulsed Townsend experimental method. The present measurements of w are the first to be obtained for C2F6, C3F8, and n-C4F10 at low E/N values. The electron-drift-velocity measurements in C3F8 and n-C4F10 are dependent on gas pressure at high E/N values, even after allowing for nonequilibrium and boundary corrections to the measured electron swarm transit time. This is the first observation of a pressure dependence in the electron drift velocity in these gases and is believed to be due to changes in the electron energy distribution function f(,E/N) with gas pressure resulting from increases in the density-normalized electron attachment coefficient /N with gas pressure. The perfluoroalkanes CF4, C2F6, and C3F8 exhibit regions of pronounced negative differential conductivity (NDC) similar to but smaller in magnitude than that in CH4. Possible mechanisms leading to the observation of NDC effects in these molecular gases are discussed.