Zeitschrift für Physikalische Chemie, 214, 8, 1137-1149 (2000)  by Oldenbourg Wissenschaftsverlag, München High Resolution Electron Ionization of N 2 O Clusters: Appearance Energies By G. Hanel, T. Fiegele, A. Stamatovic 1 and T. D. Märk 2 Institut für Ionenphysik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria Dedicated to Prof. Dr. Dr. h.c. mult. Jürgen Troe on the occasion of his 60th birthday (Received March 7, 2000; accepted May 7, 2000) Appearance Energy / Electron Impact Ionization / N 2 O Clusters Electron ionization cross sections for (N 2 O) n clusters have been investigated near the threshold with a newly constructed crossed beams apparatus using a hemispherical elec- tron monochromator (HEM) to monochromatize the primary electron beam. Exploratory test measurements including electron attachment studies to CCl4 and CO and appearance energy (AE) determinations for some rare gases (Ar, Kr, Xe) and molecules (N2 ,O 2 ,N 2 O, O 3 ) measured for calibration purposes showed that the accuracy of the energy scale is better than 10 meV exhibiting a good linearity and that AE’s derived for these compounds agree within 20 meV with known photoionization data when using a novel data handling procedure (involving a simultaneous non-linear weighted least-squares fit of two func- tions). Comparison of the presently derived appearance energies with earlier photoionization data shows a distinct difference in corresponding values attributed to different ionization mechanisms. Both data sets can be fitted successfully by a n -1/3 dependence yielding by extrapolation a value for the bulk photoelectric threshold (11.25 eV in the case of the photoionization data). 1. Introduction Electron impact ionization and electron attachment is an important tool in the study of molecules and clusters, in particular concerning the production and identification of the corresponding cations and anions in mass spec- 1 Permanent address: Faculty of Physics Beograd, P.O. Box 368, 11001 Beograd, Yugoslavia. 2 Also adjunct professor at Dept. Plasma Physics, Comenius University, Mlynska dolina, SK-84215 Bratislava, Slovakia. Brought to you by | New York University Bobst Library Technical Services Authenticated Download Date | 6/17/15 5:52 AM