Dissociative ionization of molecules by electron impact. I. Apparatus and kinetic energy distributions of D+ ions from D2

A crossed beam apparatus for the study of electron impact dissociative ionization of molecules is described. D+ time-of-flight and energy spectra are presented for impact of electrons on D2, from energies near dissociative threshold to 300 eV. In addition to the group of D+ ions peaking near 8 eV kinetic energy from dissociative ionization via the 2Σ+u state of D+2, groups of ions of lower kinetic energy peaking near 5, 2, and possibly near 1 eV are observed. These ions appear to be due to excitation of states of D2 or D+2 lying near to or above the 2Σ+u state of D+2.