An ESR study of benzene radical cation in an argon matrix: evidence for favourable stabilization of B-2(1g) rather than B-2(2g) state

Benzene radical cations were generated in an argon matrix by fast electron irradiation at 16 K. The ESR spectrum measured immediately after irradiatio n results probably from the mixture of the two distorted states; however, i t converts irreversibly to the spectrum of the B-2(1g) state upon annealing . The latter spectrum exhibits major hyperfine coupling with four of six pr otons (the isotropic coupling constant was estimated to be 0.64 mT). The ro le of basic Jahn-Teller distortion and matrix-assisted effects for benzene radical cations trapped in low-temperature matrices is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.