A theoretical study of the temperature dependence of isotropic hyperfine coupling constants for the ·CH3and ·CH2OH radicals

A theoretical model is described which is based on the assumption that the temperature dependence of hyperfine coupling constants (h.c.c.s) in the E.S.R. spectra of organic free radicals is due to nuclear vibrations. The model is tested on the α-proton h.c.c.s of the methyl and hydroxymethyl radicals and in each case it shows that, although only the lowest vibrational mode contributes to the temperature dependence of the h.c.c.s, other modes do contribute to the vibrationally averaged coupling constant.