Magnetic field effects in reactions of geminate recombination of anisotropic radicals

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Abstract
The general theory of magnetic field effects on geminate recombination of highly anisotropic radicals is developed. The theory takes into account the anisotropic interradical exchange and electrostatic interactions as well as the anisotropy of the reactivity of radicals. The main assumption is that these interactions are strongly localized in the orientational-translational coordinates of the system. The simple analytical expressions for optically-detected magnetic field effects P s and CIDEP P e-amplitudes are deduced. Quite different dependence of P s and P e on the intraradical magnetic interaction strength ω is found in the two regions of ω. In the strong interaction limit ω>τR −1, where τR is the diffusional passing time through the distance of closest approach, P s∼ω3/2 and P e∼ω. In the opposite limit ω<τR −1 the dependences P s. e∼ω1/2 similar to those for isotropic radicals are obtained. The simple analysis shows that Ps sharply depends on the reactivity anisotropy and only slightly on the exchange interaction anisotropy. On the other hand P e depends strongly on the exchange interaction anisotropy. In the absence of attractive electrostatic interactions both P s and P e depend sharply on the anisotropy of initial mutual orientation. The highly anisotropic strong attractive electrostatic interaction essentially modifies the characteristic dependences on ω and on the anisotropy of above mentioned interactions because of the cage effect. The theory proposed is applied to the interpretation of some experimental results.