Ion Mobility Measurements and their Applications to Clusters and Biomolecules

In this article we describe some of the recent work that has been performed using ion mobility measurements to deduce structural information for polyatomic ions. Determining the structure of a polyatomic ion in the gas phase is a challenging problem, that is usually approached by indirect methods such as dissociation or reactivity studies. Ion mobility measurements have recently emerged as a technique that can provide more direct information about the geometries of large polyatomic ions. The structural information obtained from these studies is not as detailed as information from high-resolution spectroscopic studies, but in many cases the types of spectroscopic studies needed to provide structural information cannot be applied to polyatomic ions in the gas phase. While the use of ion mobility measurements to deduce structural information has grown in the last Ðve years, both the experimental techniques and theoretical methods employed in these studies were largely developed over two decades ago. The mobility of a gas-phase ion is a measure of how rapidly it moves through a bu†er gas under the inÑuence of an electric Ðeld. Mobility measurements are performed in a drift tube, which contains the bu†er gas and usually has a series of electrodes to provide a uniform