Electron Spin Echo Envelope Modulation Analysis of SeO¯3 Radical in (NH4)3H(SeO4)2 Single Crystal

J. Tritt-Goc, J. Goslar, W. Hilczer, S.K. Hoffmann and M.A. Augustyniak Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17/19, 60-179 Poznań, Poland

Received: August 17, 1993

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A detailed computer analysis of the electron spin echo envelope modulations of SeO3 radical in a suitable orientation of (NH4)3H(SeO4)2 single crystal is presented. It was found that the modulations are due to a weak dipolar coupling with nitrogens and protons of the only two neighbouring NH4 groups among the five NH4 groups surrounding SeO¯3 center. Isotropic dipolar coupling constant is 1.7 MHz for nitrogens and 0.9 MHz for protons. It was shown that thermal reorientations of NH4 groups observed by NMR have a negligible effect on the electron spin echo envelope modulation pattern but can be responsible for the same value of aHiso for all protons in a NH4 group. A good fit obtained between experimental spectra and theoretical calculations assuming nondisturbed crystal geometry indicates a small damage of the crystal by X-rays during the radical center formation.

DOI: 10.12693/APhysPolA.84.1131 PACS numbers: 76.60.Lz, 76.30.Mi