This project is in the general area of analytical and surface chemistry and in the subfields of gas phase ion chemistry and mass spectrometry. During the tenure of this three-year continuing grant, Professor Grimsrud and his co-workers will conduct a series of investigations aimed at elucidating the fundamental kinetic and equilibrium processes governing complex ion-ion and ion-molecule reactions at pressures approaching one atmosphere. The goal of this project is to explore the analytical utility of instruments that operate in this pressure regime. %%% The successful attainment of the goals of this project will provide a substantive framework for the rational design and optimal utilization of analytical instruments that operate at significant pressures, particularly those essential to the rapid and reliable characterization of environmentally important trace species.