On the Kinetic-Energy Distribution of Fragment Ions Produced by Electron Impact in a Mass Spectrometer

Abstract

Distributions of initial kinetic energies have been measured for fragment ions that are produced in the breakup of the excited ions CO⁺, H₂O⁺, NH₃⁺, CH₄⁺, and C₆H₆⁺. These ions were formed by electron impact. The energy of the ionizing electron beam was 400 eV in the case of benzene and 200 eV for the other target gases. The initial‐energy distributions of the fragment ions from H₂O and CH₄ were measured as a function of electron energy over the interval from 100 to 400 eV. No measurable change in the distributions was observed. Evidence presented indicates that the excess‐energy ion pair (masses 15 and 63) are formed simultaneously in the decay of doubly charged benzene ions. Included also in this paper are the details of an analytical method to correct measured energy distributions for kinematic effects and instrumental distortions. In this analysis the distributions of the internal energy converted into kinetic energy of the fragments are characterized by their moments.