Molecular Relaxation by ESR Spectroscopy and Related Phenomena

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In this project supported by the Experimental Physical Chemistry Program of the Chemistry Division, Freed will continue studies of dynamical molecular processes and free radicals in fluids, on surfaces, and in related systems. New electron spin resonance (ESR) relaxation and structural techniques will be employed, and the necessary theoretical frameworks will be developed and extended. Two-dimensional Fourier Transform (2D-FT) ESR, electron-electron double resonance (2D-ELDOR), and Far Infrared (FIR) ESR studies of fast and slow motional regimes will be developed and applied to rotational molecular dynamics in liquids, presenting a multi-frequency approach covering 9-250 GHz. Pulsed ESR methods will be developed at 106 GHz base on a new source appropriate for liquid studies and new quasi-optical methods for FIR-ESR. Other systems investigated will be glass-forming liquids, inhomogeneous fluids such as microemulsions, restricted reorientational dynamics on surfaces, translational diffusion in simple and complex liquids, biradicals in liquids, and radical clusters in solids. NMR spectroscopy has been successfully used in a wide range of applications, from chemical structure determination to medical diagnostic scanning. The related technique of ESR spectroscopy has been much slower to be developed in part because of obstacles caused by the frequencies of radiation which must be used and the shorter relaxation times, that is, the time during which one can measure the molecular effect being observed. This research program will involve the development and improvement of ESR techniques which may help to bring ESR-based methods into more common usage as analytical tools in chemistry, biology, and materials science.