A study of acceleration region processes in a double-focusing mass spectrometer. Part 1

Abstract

The ion beam issuing from the Nier-type source of a conventional sector 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 given ion during its flight through the acceleration region, each giving rise to a continuum of mass spectral signals in momentum-to-charge—energy-to-charge space. Ion signal intensities are 10 −5 to 10 −6 of that of the main beam and are not observed in conventional electron ionization mass spectra; however, such peaks can make significant contributions to ion kinetic energy spectra and are often dismissed as “interference peaks” or “artifact peaks”. A description is presented here of the mathematical considerations governing acceleration region processes, including charge permutation reactions; in addition, acceleration region processes are portrayed on an ion incidence map. Experimental results are presented of the investigation of acceleration region processes which occur in the Argon system in a commercial reverse geometry mass spectrometer. The interpretation of some anomalous ion signals observed during this work has been facilitated by computer simulation.