Spin Polarization in Atoms and π-Radicals

Abstract

IN certain radicals, sometimes referred to as σ-radicals^1,2, the contribution to the orbital of the unpaired electron from one or more of the atoms involved includes a relatively high atomic s character, and this is manifested as a large isotropic hyperfine coupling. It is customary to estimate the s character by dividing this isotropic coupling by a calculated value (A⁰) for a spin density of unity in the appropriate orbital². For π-radicals the isotropic hyperfine coupling constants of which are a consequence of spin-polarization or configuration interaction, however, the value is generally related, not to the atomic value, A⁰, but to the value (Q) that would have been obtained had the spin density in the p orbital of the atom concerned been unity.