Internal Energy Dependence of the Reaction of NH₃ ⁺ with H₂O; A Tandem ICR Study

Abstract

The Tandem ICR (TICR) is a concept with a great deal of appeal. The concept originated with Smith and Futrell [1] at Utah who constructed the first instrument. The TICR constists of an ion source, a 180° Dempster magnetic mass selector and a differentially pumped ICR cell. All three are positioned between the pole camps of a 12″ electromagnet. The ions are formed in the source, either by direct electron impact or electron impact followed by chemical reaction. They are then mass analyzed and injected through an entrance slit into the ICR cell where their subsequent reactions are studied. The advantages over a conventional ICR are obvious: reaction complexity is greatly reduced with a single primary ion; reactions of product ionsmay be easily studied; ionsmay be formed and thermalized under high pressure source conditions and reacted under low pressure ICR conditions (ions such as Ar₂ ⁺ may be studied this way) and lastly ions with different amounts of internal en.ergy may be formed in the source using charge transfer reactions permitting a determination of absolute reaction rate constants and branching rations and their dependence on internal reaction energy. In this paper we describe briefly the tandem instrument at UCSB and preliminary results of a study of a reaction as a function of ion internal energy.