The NH2 free radical, which is one of the most studied triatomic molecules and is widely used as spin labels in biophysical and biomedical research, has not been reported in mineral lattices. Fourier-transform infrared (FTIR) spectrum supports electron-microprobe analyses that fluorapophyllite on the cavity walls in a phonolite (North Bohemia, Czech Republic) contains ammonium NH4+. Powder and single-crystal electron paramagnetic resonance (EPR) spectra of this fluorapophyllite, with and without γ irradiation, disclose at least four paramagnetic defects, including two previously reported VO2+ centers, the NH2 free radical and an oxygen-associated center. The spin-Hamiltonian parameters of the NH2 free radical have been determined from single-crystal EPR data and show that this molecule is oriented parallel to (and rapidly rotated about) the crystallographic c axis. The NH2 free radical in fluorapophyllite, most likely formed from radiolysis of the NH4+ ion, remains stable after annealing at 300 ° C, but is bleached at 340 ° C.

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