The negative ions adsorption on the ion source surface at the resonant electron capture by molecules and measurements of the ion lifetime

Abstract

Using a static sector magnetic mass spectrometer MI-1201B, modified to record negative ions for resonant electron capture by molecules, the ion extraction time from the ionization chamber combined with this apparatus was measured up to several hundred microseconds. It was shown that the values obtained are anomalously great and they arise from the fact that part of the formed in the ionization chamber ions are adsorbed onto the chamber's surface. Those of them that were produced initially in the gas phase, namely the transient negative ions, with a finite lifetime (∼1μs and greater), transform themselves, on the surface, into ‘infinitely living’ (stable) ions. As a result, the contribution of the stable ions to the total ion beam falsifies the ion's lifetime measurements performed with this instrument.