ESR MEASUREMENT OF TRANSLATIONAL DIFFUSION CONSTANTS

ESR spectroscopy can be used to measure the translational diffusion co nstants of spin probes in a variety of media using a capillary method, Following preliminary work, it has been possible to improve upon the accuracy of determining diffusion constants in two ways, Both methods require an experimental measurement of the resonant cavity sampling pr ofile, In the first procedure, this cavity profile is convolved with a trial Gaussian distribution and the result is compared with the exper imental data obtained from the ESR measurements; the diffusion constan t is then determined by graphical optimization. The second method is a graphical one based on a knowledge of the experimental diffusion prof ile and the cavity sampling profile, Both methods have been shown to g ive similar results but the second less rigorous corrected-zero method is generally simpler to apply, For a medium such as water, it takes s everal days to acquire the necessary experimental data but the time ta ken to carry out the experiment can be shortened (or slower rates of d iffusion can be measured) by using a shielded resonant cavity.