Electron Spin Resonance in a Gamma-Irradiated Single Crystal of L-Cystine Dihydrochloride

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Abstract
The electron spin resonance of a gamma‐irradiated single crystal of L‐cystine dihydrochloride, HOOC–CH–CH2–S–S–CH2–CH–COOH·2HCl,         –                             –        NH2                      NH2 has been measured at 9 kMc/sec and at 24 kMc/sec for various orientations of the crystal in the magnetic field. The resonance pattern was found to be a doublet, the spacing between the components of which is independent of the crystal orientation as well as of the strength of the static magnetic field. The spectroscopic splitting factor was found to be anisotropic with the principal values: gu=2.003, gv=2.025, and gw=2.053. A model of the free radical, HOOC–CH–CH2–S·,          –        NH2 in which the electron spin density is mainly concentrated in a nonbonding 3 p orbital of the sulfur atom, is proposed. The model accounts very well for the principal values of the g tensor as well as their directions relative to the atomic configuration. It also can give rise to the observed proton hyperfine structure.