Evidence d'un lieu privilegie de transfert de charge dans un spectrographie de masse de type mattauch-herzog

Abstract

Trajectories of charge-exchange ions are calculated in a spark source mass spectrograph. It is assumed that the charge-exchange process M n +→M p + takes place inside the magnetic fringing field extending across the so-called “field-free space” of the Mattauch—Herzog geometry. The calculations involve a line shift versus the expected value M − n/ p 2, given by S = √2 · f · X · ( n− p)/ p, f being the relative intensity of the virtual field representative of the fringing field, and X the projected ion path before charge-exchange occurs. S does not depend on the instrument dispersion or on the ion mass, and is in good agreement with experimental data. This result provides evidence of a privileged location for the charge-exchange process. Hence a collision-induced process is questionable.