Professor Farrar and his research group focus their interests on the reaction dynamics and photochemistry of ionic species. The objective of this research is to elucidate the reactivity of gas phase species important in electrical discharges, reactive ion etching, atmospheric and interstellar chemistry, and planetary atmospheres. The research also focuses on understanding processes involved in the transition from the gas phase to the condensed phases, as probed spectroscopically through size-dependent properties of mass-selected cluster ions. The research employs the techniques of mass spectrometry, laser spectroscopy, molecular beams, and computation.

The principal interest of the group is the application of the crossed beam method to studies of low energy ion-molecule reactions. We are working on state of the art methods that employ imaging techniques for reconstructing product velocity space distributions by taking a snapshot of the spatial distribution in a particular time window. The locus of points of reaction products with a constant center of mass speed is a sphere whose radius increases with time. Imaging the set of nested spheres describing the reaction products by projecting them on a plane allows all product velocity elements to be observed in a single time window. This application of multiplex (Fellgett) advantage will enhance product detection sensitivity by more than an order of magnitude. The schematic diagram indicates the important elements of the imaging method. We expect to apply this method to the study of reactions between ions and simple free radicals. There are virtually no data on such reactions, and we expect that their inclusion in models for planetary atmospheres, for example, will prove to be essential for a quantitative understanding of chemistry in such environments. Our initial efforts will be focused on reactions of methyl and allyl radicals with the anions O^-, OH^-, and O₂-.