Computer-based numerical analysis applied to E.S.R. spectroscopy.

Abstract

Researches conducted with the help of the electron spin resonance spectroscopy have been very successful so far, in spite of some problems both in resolving power and in sensitivity. In order to overcome these, and to use the technique to its very far limits, we develop here a computer program which process the ESR data post-experimentaly. This work explains how to digitize and record the ESR spectra as well as how this software acts to reveal hyperfine splitting constants, the number of nuclei, and their spins out of complex spectra. This could be done by resolution enhancement (either addition of higher derivatives of the signal or linewidth narrowing by changing the lineshape function) or by CEPSTRAL analysis (modification of the ESR display in order to show out in a clearer may the hyperfine splitting constants). Other aids in the interpratation of spectra are obtained, with the same software, by addition or subtraction of experimental or simulated spectra, by reduction of the noise level and by simulation of spectra correct to second order and including quadrupolar corrections and non-colinear g and A tensors for systems with orthorhombic symmetry. In spite of the fact that the theory presented in the first part might strike one as familiar, we think worthwhile the effort of writting an entirely new computer program, as complete and versatile to use as possible, in order to match the major part of the needs encountered in the analysis of ESR results. Applications of the program have been performed to try to solve some puzzling ESR results. Evidences on the bridged structure of the ?-bromo radical (R2-CC(Br)-R'2) have been found, improvement of the resolution of spectra from spin-trap adduct radicals leads to better fingerprints of these compounds, and simulation of the spectrum from the Acetone radical cation enables us to determine the angle between the molecular bonds