ON THE APPLICATION OF ASTON BANDS AND APPEARANCE POTENTIAL MEASUREMENTS TO ION COLLISION STUDIES

Abstract

Two techniques are applied to ion collision studies. The first, Aston banding, is native to mass spectrometry, and effectively makes of a simple mass analyzer a double mass spectrometer which separates unambiguously the parent ions from the products. By combining with the mass spectrometer a "high-pass" energy filter, we are able to study ionic collisions which take place in the drift regions both before and after the magnetic analyzer. We describe the methods whereby we measure total cross sections for both charge exchange and collision-induced dissociation and show how we measure the loss and distribution of energy and momentum of the high-velocity product ions. The accelerating potential range for our ion collisions is 0.6 to 2.0 kv.The second technique, the detailed comparison of appearance potential curves, complements Aston banding although it has broader application. We describe how, from the ratio of the A.P. curve of the product to that of the parent, one can determine directly the influence of metastable or long-lived excited ions in the parent ion beam. We further describe how, from the ratio of the differences of slopes, one can determine the relative and sometimes the absolute cross sections associated with these states of the ion which enter into collision with a particular ion kinetic energy. In this paper, the techniques and the conditions under which they are applicable are stressed. In subsequent papers, we shall discuss results obtained with the techniques involving ions coming from Ar, H2, N2, and O2.