Ion-molecule reactions in zeolites

Zeolites are the first new medium to be developed for the study of matrix-isolated radical cations after nearly two decades of intensive study of these fundamental intermediates in rare-gas and halogenated matrices. The zeolite is a versatile solid-state reactor, which opens a new window onto radical cation reaction mechanisms. Radiolytically generated radical cations and neutral molecules, immobilized at cryogenic temperatures, become mobile at elevated temperatures, and ion-molecule chemistry is observed. An important research goal is the study of ion-molecule reactions in which the reaction partners can be systematically varied. Here is a key example of how zeolites can be exploited to gain new mechanistic information. Radiolysis of dual-loaded zeolites (two adsorbates) can be used to predictably generate one or two (depending on relative concentrations and ionization potentials) radical cation species. Of the possible reactions between radical cation A{sup {sm_bullet}+} and neutrals A and B, the zeolite typically selects only one, e.g., A{sup {sm_bullet}+} + B. Such selectivity greatly simplifies interpretation and analysis of EPR spectra and opens a broad new range of ionic reactions for study.