Dissociative Electron Attachment inI2Vapor at 295° K

Two-body electron attachment frequencies have been determined for iodine in the presence of helium using microwave cavity techniques where initial ionization is produced by a single light pulse from a hydrogen lamp. The value for the electron attachment coefficient determined from the attachment frequency data is $k=1.8\mathrm{}\times {10}^{-10\mathrm{}}$ ${\mathrm{cm}}^3$ ${\sec }^{-1\mathrm{}}$ at 295°K. The ambipolar diffusion of iodine ions in helium has also been examined at this temperature, and a value for ${\mathrm{D}}_a+p$ of 730 ${\mathrm{cm}}^2$/sec Torr was obtained. Electron-density decay rates observed using a repetitive-pulse technique were higher than those observed using the singlepulse technique for a given iodine vapor pressure. Possible effects on the electron diffusion rate as a result of the presence of negative ions are discussed.