Thermal Electron Attachment to NF3, PF3 and PF5

摘要

A flowing afterglow Laugmuir probe apparatus was used to measure rate constants(ka) for electron attachment to NF3 and PF5 over the temperature range T =300-550 K. Electron attachment to NF3 is dissociative and produces only F(-) ionic product in the temperature range studied. At room temperature, ka(NF3) 7+/-4 x 10(exp-12)cm3/s. The temperature dependence of ka(NF3) above 340K is characterized by an activation energy of 0.30 +/-0.06eV. Attachment to PF5 is nondissociative in a helium buffer at pressures in the range 53-160 Pa (0.4-1.2 Torr). The rate constant ka(PF5) is 1.0+/-0.4 x l0(exp-10) cm3/s at 300K and is approximately temperature independent over much of the temperature range studied. PF3 does not attach electrons in this temperature range. Upper limits to ka(PF3) were determined (and attributed to impurities): ka < exp(-12)cm3/s at 296K and ka < exp(-10)cm3/s at 550K. The electron attachment rate constants measured in the present work are so small that corrections were required to account for electron/ion recombination contribution to the observed decay of the electron density in the plasma.