The naphthalene radical cation generated from the corresponding neutral compound by UV-or X-irradiation on H-ZSM-5 zeolite and in frozen CFCl 3 solution has been studied by EPR, ENDOR, and ESEEM spectroscopies. The g and ring proton hyperfine (hf) tensors have been determined and are identical in the two media, within experimental error. The isotropic hf couplings of the two sets of four equivalent protons are |a(1)| ) 16.4 and |a(2)| ) 4.7 MHz (0.587 and 0.167 mT, respectively). Semiempirical calculations of isotropic and dipolar hf couplings are found to be in good agreement with experiment. The hf tensors obtained for the radical cation of naphthalene-d 8 were analogous to those of the protonated compound, scaled by the gyromagnetic ratio, γ H /γ D . The nuclear quadrupole interaction (nqi) tensors of the deuterium nuclei were also determined by ESEEM, being the only resolved method for the present nqi strength.

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X-irradiation of tetramethylammonium hydroxide pentahydrate (TMNOH) at 77 K produces trapped electrons, and CH 3 • and (CH 3 ) 3 N + CH 2 • radicals. The trapped electrons were detected by bleaching with visible light and by subtraction of spectra from bleached and unbleached samples. The decay of the methyl radicals starts at ≈100 K and that of the (CH 3 ) 3 N + CH 2 • radicals at ≈150 K. The ESR spectrum measured at 130 K has the best resolution and is a superposition of contributions from the methyl radicals (13%) and from the (CH 3 ) 3 N + CH 2 • radical (87%). The reversibility of the line shapes with temperature variations suggested that the increased resolution observed at 130 K is due to dynamical effects involving the (CH 3 ) 3 N + CH 2 • radicals. ESR spectra from these radicals can be simulated by assuming that the hyperfine tensor components for the two R protons are averaged by two types of motions: rotation of the CH 2 group about the C 2V symmetry axis and precession or wobbling of this axis. The parameters used in the simulation are g iso ) 2.0022, two equivalent R protons with axial hyperfine components A | av ) 25.0 G and A ⊥ av ) 23.0 G, one 14 N nucleus with A N ) 3.9 G, and one remote proton with A H,remote ) 4.2 G. The remote proton is identified with a lattice proton. If the precession model is adopted, the precession angle calculated from the principal values of the hyperfine tensor for the R protons used in the simulations is 47°. For the wobbling model, the wobbling angle deduced is 72°. These results suggest that the hydrogen-bonded cage around the guest allows large-scale dynamical effects even at 130 K.