Electron spin resonance line shapes of randomly oriented molecules in septet and nonet states by a perturbation approach

The electron spin resonance line shapes of randomly oriented molecules in septet and nonet states are analyzed in terms of the formulas derived from a perturbation treatment to third-order in the fine-structure energy. The method is applied to a ground-state septet hydrocarbon, 3, 3′-diphenylmethylenebis (phenylmethylene), and a ground-state nonet hydrocarbon, m-phenylenebis[(diphenylmethylen-3-yl)methylene], randomly oriented in mixed polycrystalline powders of benzophenone. It is shown that the g factor and the fine-structure parameters are determined from the line shapes of a K-band spectrum with nearly the same accuracy as in a single-crystal experiment. Extra lines have been observed in addition to the canonical lines corresponding to the external magnetic field along the principal axes of the fine-structure tensor. The appearance of extra lines in the spectra of septet and nonet molecules is discussed relative to the third-order perturbation theory.