Some theoretical and experimental aspects of gas phase E.P.R. spectroscopy

Abstract

The derivation of an effective rotational Hamiltonian is discussed. Using these general techniques some spin-dependent interactions in Estates of quartet and higher multiplicity are cast into operator equivalent form. As a result the two spin-rotation constants required, in principle, for 4F states are shown to be the same to within experimental error. These results are generalised to cover states of higher multiplicity. A fourth order spin-spin interaction arising in 5E: states is investigated.The rotational energy levels of a molecule in a 2TT electronic state are described, with particular reference to the OH radical, and some higher order A-doubling and hyperfine interactions are cast into operator equivalent form. A comparison is made with effective rotational Hamiltonians used by other workers. A reanalysis of the zero-field A-doubling frequencies for OH is outlined. Other higher order interactions appear to be needed to further improve the fit.The measurement of the gas phase e.p.r. spectrum arising from the 2TT3/2J = 9/2 rotational levels of OH is detailed and the theory of the g-factors in 27T states is given. Values for molecular g-factors determined from an analysis of e.p.r. measurements on seven rotational levels of OH are quoted, and compared with a pure precession model. Effective g-factors are calculated from these molecular g -factors and compared with published experimental results.Some initial experiments investigating the possibility of using pyrolysis to generate radicals for gas phase e.p.r. studies are detailed.

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