Accurate calculation of the phenyl radical's magnetic inequivalency, relative orientations of its spin hamiltonian tensors, and its electronic spectrum.
The phenyl radical's electronic structure, magnetic inequivalency, spin Hamiltonian tensor components, and the relative orientation of their principal axes are computed by Neese's coupled-perturbed Kohn-Sham hybrid density functional (CPKS-HDF) technique in a moderate amount of time without resorting to expensive post-Hartree-Fock techniques. The g tensor component values are in excellent agreement with those determined experimentally and differ by less than 370 ppm. The computed hydrogen nuclear hyperfine tensors, A(1H), are also found to be in very good agreement with their experimental counterparts. The correlation of the radical's electronic structure with its g and A numerical values corroborates that it has a 2A(1) ground state. In accordance with our previous studies on the equivalency of planar radicals that possess C(2v) symmetry, the in-plane g and A(1H) principal axes should not be parallel to one another. Consequently, the spatially equivalent ortho (1H(2), 1H(6)) and meta (1H(3), 1H(5)) proton pairs should be magnetically inequivalent. This was confirmed in both the present computations and the simulation of the EPR solid-state spectrum. To the best of our knowledge, this is the first aromatic in-plane sigma-type radical whose magnetic inequivalency is studied both computationally and experimentally. To properly interpret the radical's electronic excitation spectra, the spectroscopy-oriented dedicated difference configuration interaction (SORCI) procedure was employed. Aside from a slight overestimation, the method seems to be capable of reproducing the C(6)H(5)* electronic vertical excitation energies in the range of 0-50,000 cm(-1). These vertical excitations, in conjunction with the corresponding orbit and spin orbit matrix elements, were also used to compute the g tensor components, employing the sum-over-states technique. Due to the limited number of computed roots and excited states, the results were marginally inferior to those obtained using the CPKS-HDF method.
Mattar
Saba M
SM
Department of Chemistry and Centre for Laser, Atomic and Molecular Sciences, University of New Brunswick, Fredericton, New Brunswick, Canada E3B 6E2. mattar@unb.ca