Theoretical investigation of the effect of a sodium cation on the proton-electron hyperfine coupling constants of the cyclohexadienyl radical and some consequences for the muonium-substituted cyclohexadienyl radical, C(6)H(6)Mu, formed in zeolites

The isotropic hyperfine coupling constants A(iso) for the protons in the cy clohexadienyl radical, C6H7, are calculated using ab initio molecular orbit al methods. Taking all single excitations from a restricted open shell Wart ree-Fock configuration, (CIS), the calculated value for A(iso) at the methy lenic protons is 93.0 MHz. The presence of a sodium cation reduces A(iso) f or the methylenic proton of C6H7 on the same side of the ring as Na+ by 18. 2 MHz. For the other methylenic proton the presence of Na+ enhances the val ue of A(iso) by 30.8 MHz and the C6H7 ring shows significant distortion. (C ) 2000 Published by Elsevier Science B.V. All rights reserved.