Ab initio MO calculations of hyperfine coupling constants of hydronium radical H3O

Hyperfine coupling constants of hydronium radical H3O and methyl radical CH 3 were calculated by means of ab initio molecular orbital calculations. All calculations showed that hydrogen-hyperfine coupling constant of H3O (a(H) ) is positive, whereas that of methyl radical is negative. The absolute val ue of hydrogen-hyperfine coupling constant of the H3O radical \a(H)(H3O)\ w as slightly smaller than that of CH3\a(H)(CH3)\ In the case of CH3, the hyp erfine coupling interaction is induced by spin-polarization mechanism, wher eas that of H3O is caused by direct overlap between Rydberg 3s orbital of t he oxygen and Is orbital of the hydrogen. From the present calculations, it is predicted that both H3O and CH3 radicals are distinguishable from each other by means of electron nuclear double resonance spectroscopy. (C) 2001 Published by Elsevier Science B.V.