STUDY OF G-ANISOTROPY ASSOCIATED WITH MOLECULAR-MOTION IN THE TRIPHENYLMETHYLPEROXY RADICAL - ENVIRONMENTAL PROBE

ESR spectra of triphenylmethylperoxy radical, Ph3COO·, in γ-irradiated polycrystalline triphenylacetic acid, Ph3CCOOH, were measured at 35 GHz as a function of temperature from 80 to 290 K. Multiple lines observed are due entirely to g anisotropy. Principal values of the g tensor at 80 K are 2.0320, 2.0092, and 2.0035. At 290 K an axial g tensor is observed with g∥ = 2.0175 and g⊥ = 2.0128. At intermediate temperatures new lines appear in the spectrum. All spectral changes with temperature are reversible. The spectra are interpreted with the modified Bloch equations for motional processes. All salient features over the entire temperature range are well reproduced by a motional model involving 120° jumps of the peroxy group about the C-O bond. The jump rates fit an Arrhenius plot and give an activation energy of 9.2 kJ/mol. The possibility of using the peroxy group as an environmental probe of its motional freedom is discussed and several systems where this may be applicable are given. © 1979 American Chemical Society.