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Electron paramagnetic resonance study of molecular spin multiplets with s>1 Hebden, James Arthur

Abstract

A completely general method has been developed for calculating Electron Paramagnetic Resonance (EPR) transition fields and transition probabilities from the spin Hamiltonian [formula omitted] The method is a generalization of a previously existing, limited technique, and can be applied without any restrictions. A general computer program has also been written based on the method. Using the program, the results of an EPR study on a U.V. irradiated single crystal of para-nitrophenyl azide were fitted to the spin Hamiltonian [formula omitted] The observed and calculated fine and hyperfine transition probabilities were found to be in good agreement. The observed hyperfine splittings, due to the nitrene nitrogen, were analyzed in terms of a 6.5 gauss linewidth, combined with the transition probabilities for the nine theoretical components of the hyperfine resonance fields. Evidence of a ¹⁴N quadrupolar splitting was observed, but not completely analyzed. In addition, evidence was found to indicate that the nitrene impurity is twisted somewhat from the position in the crystal lattice held by the parent azide. The EPR spectra obtained on U.V. irradiation of randomly oriented 1,5- and 1,8-diazidonaphthalene were analyzed, and found to originate from ground triplet state species with |D|= 0.8152±0.0010 cm⁻¹ and 0.7599±0.0010 cm⁻¹, respectively. The theoretical spin densities for the triplet and quintet states of 1,5- , 1,8- and 2,7- naphthalene dinitrene were calculated using the method of intermediate neglect of differential overlap (INDO). Attempts to obtain a consistent picture of multiplet spin densities based on the results of the calculations were largely inconclusive.

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