A STUDY OF ACCELERATION REGION PROCESSES IN A DOUBLE-FOCUSING MASS-SPECTROMETER .1.

The ion beam issuing from the Nier-type source of a conventional secto r mass spectrometer is subjected immediately to an accelerating field of the order of 10(4) V cm-1. A variety of processes may occur to a gi ven ion during its flight through the acceleration region, each giving rise to a continuum of mass spectral signals in momentum-to-charge-en ergy-to-charge space. Ion signal intensities are 10(-5) to 10(-6) of t hat of the main beam and are not observed in conventional electron ion ization mass spectra; however, such peaks can make significant contrib utions to ion kinetic energy spectra and are often dismissed as ''inte rference peaks'' or ''artifact peaks''. A description is presented her e of the mathematical considerations governing acceleration region pro cesses, including charge permutation reactions; in addition, accelerat ion region processes are portrayed on an ion incidence map. Experiment al results are presented of the investigation of acceleration region p rocesses which occur in the Argon system in a commercial reverse geome try mass spectrometer. The interpretation of some anomalous ion signal s observed during this work has been facilitated by computer simulatio n.