Spin Dynamics and Radical Reactions

Abstract

An electron possesses a spin of magnitude $(\sqrt 3/2)$ ħ, just like a proton. Associated with this is a magnetic moment μ _e that is conventionally written as

$$ {\mu_e}=-g\beta S $$

(9.1)

, where S is the operator for the electron spin. As the minus sign shows, μ _e points in the opposite direction as the spin, owing to the negative charge of the electron. The strength of the magnetic moment, which is about 658 times that of a proton, is expressed in terms of the Bohr magneton β of the electron, β = 9.27 × 10⁻²⁶ J/Gauss, and a number g. This so-called g-factor amounts to 2.0023 for a free electron. If the electron is confined in an organic molecule containing no transition elements, g is only slightly higher or lower, usually by much less than one percent. Its value is characteristic for its surroundings. (Actually, g is a tensor, but in liquid solution rapid molecular motions average out all anisotropy effects.)