ENDOR and EPR studies of benzene radical cations in halocarbon matrices: the static Jahn-Teller distortion of the monomer and geometry of the dimer cation

摘要

ENDOR investigations of the benzene radical cation in a CFCl3 matrix at 30K gave evidence for a static Jahn-Teller distortion with the unpaired electron density predominantly in the (2)b(2g) orbital. In this distortion the equivalence of the six protons is lost, with the major spin densities on H-1 and H-4. From ENDOR measurements the isotropic and dipolar couplings were accurately measured (a(iso) = -25.31 MHz (H-1 and H-4) and a(iso) = -5.43 MHz (H-2, H-3, H-5 and H-6)) which agree with those reported earlier from EPR measurements and theoretical calculations. (C6H6)(2)(+.), formed by warming in CFCl3 at 140K and initially present in CF3CCl3, was characterised with ENDOR and assigned to a pi-electron complex. The intermolecular distance was estimated from the measured dipolar hyperfine coupling to be in the range 2-3 Angstrom. (C) 1998 Elsevier Science B.V. All rights reserved. [References: 26]