UNSTABLE INTERMEDIATES IN X-IRRADIATED CLATHRATE HYDRATES - ESR AND ENDOR OF TETRAMETHYLAMMONIUM HYDROXIDE PENTAHYDRATE (TMNOH)

X-irradiation of tetramethylammonium hydroxide pentahydrate (TMNOH) at 77 K produces trapped electrons, and CH3. and (CH3)(3)N+CH2. radicals . The trapped electrons were detected by bleaching with visible light and by subtraction of spectra from bleached and unbleached samples. Th e decay of the methyl radicals starts at approximate to 100 K and that of the (CH3)(3)N+CH2. radicals at approximate to 150 K. The ESR spect rum measured at 130 K has the best resolution and is a superposition o f contributions from the methyl radicals (13%) and from the (CH3)(3)NCH2. radical (87%). The reversibility of the line shapes with temperat ure variations suggested that the increased resolution observed at 130 K is due to dynamical effects involving the (CH3)(3)N+CH2. radicals. ESR spectra from these radicals can be simulated by assuming that the hyperfine tensor components for the two a protons are averaged by two types of motions: rotation of the CH2 group about the C-2v symmetry ax is and precession or wobbling of this axis. The parameters used in the simulation are g(iso) = 2.0022, two equivalent a protons with axial h yperfine components A(parallel to)(av) = 25.0 G and A(perpendicular to )(av) = 23.0 G, one N-14 nucleus with A(N) 3.9 G, and one remote proto n with A(H,remote) = 4.2 G. The remote proton is identified with a lat tice proton. If the precession model is adopted, the precession angle calculated from the principal values of the hyperfine tensor for the c t protons used in the simulations is 47 degrees. For the wobbling mode l, the wobbling angle deduced is 72 degrees. These results suggest tha t the hydrogen-bonded cage around the guest allows large-scale dynamic al effects even at 130 K.