Low Magnetic Field Dependence of the 31P Chemically Induced Dynamic Nuclear Polarization in the Photolysis of a Benzoyl Phosphonate. Role of S−T- Mechanism

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 1999-05, Vol.103 (18), p.3430-3437
• Main Authors: Ananchenko, Gennady S, Purtov, Peter A, Bagryanskaya, Elena G, Sagdeev, Renad Z
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp9839955

The chemically induced dynamic nuclear polarization (CIDNP) upon the photolysis of 2,4,6-trimethylbenzoylphosphonic acid dimethyl ester in solvents of different viscosities has been studied in high and low magnetic fields. The reaction was carried out in the presence of an effective radical scavenger, bromotrichloromethane, which allows the study of only the geminate contribution to the CIDNP. The theory proposed earlier, considering S−T- transitions in the level crossing region in the balance approximation, has been modified by taking into account the reaction with scavengers, anisotropy of the exchange interaction, and the reactivity of radicals and has been used for the description of the CIDNP field dependencies obtained. Good agreement of theoretical and experimental results is achieved with the following set of parameters:  J 0 = −450 ± 100 mT, λ = 0.7 ± 0.1 Å, f (steric factor) = 0.08 ± 0.02, τ r (correlation time of modulation of the exchange interaction and reactivity anisotropy) = 7 ± 2 ps (in CH3CN), 25 ± 3 ps (in dioxane).