Direct Observation of the Decomposition of Multiply Charged Ions into Singly Charged Fragments

Abstract

A new technique has been developed for the direct observation of the decomposition of multiply charged polyatomic ions. Positive ions or ion pairs and ejected electrons, formed in a uniform electrostatic field by a 1‐keV electron beam, are accelerated in opposite directions to multiplier detectors. The masses of the positive ions are determined by measuring the time interval between electron and ion pulses by delayed coincidence. The formation of positive ion pairs is demonstrated and their masses determined by electron—ion—ion delayed coincidence techniques. The effects of initial kinetic energy on mass‐spectrum peak shapes and travel time correlations between members of an ion pair are discussed. Both of these effects are experimentally observed. The technique has been applied to the study of ionization and fragmentation of CO₂, CF₄, CH₄, and C₃H₆. Numerous decompositions leading to the formation of positive ion pairs are observed. Significant fractions of particular high‐kinetic‐energy fragment ions are formed by these processes.