Recombination Kinetics and Spin Dynamics

For the purpose of this work, the rates of longitudinal and transverse Tz relaxation were assumed the same at zero field, such that = Tj, where is the zero field relaxation time. In order to reproduce experimental conditions, a value of 9 and 15 ns was used for cyclohexane and HFB respectively at zero field as determined by Molin and co-workers [15]. To simplify the model, no spin relaxation was allowed 

8 Correlation Between Spin Entanglement and the Spin Relaxation Time 

The spatial configuration of the cations was assumed linear using a variable spacing. The anions were distributed from their respective cations with a standard deviation of 80 A. This is a typical spatial distribution adopted in the literature for treating primary events in non-polar solvents [28]. 

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A. Agarwal, Simulation Studies of Recombination Kinetics and Spin Dynamics in Radiation Chemistry, Springer Theses, DOI 10.1007/978-3-319-06272-3 l, Springer International Publishing Switzerland 2014... 

Simulation Studies of Recombination Kinetics and Spin Dynamics in Radiation Che... 

Two different types of pulsed EPR experiments are possible a spectrum can be measured at a fixed time after the pulse by variation of the field strength B (Eq. 72), or the time profile of a particular spectral line can be measured at constant B to give kinetic information. One vziriation of this kinetic method is to detect the recombination of singlet-state radical ion pairs in liquid hydrocarbons by the fluorescence of the product excited state [142]. This technique is known as fluorescence-detected magnetic resonance (FDMR) and provides information on the spin dynamics of the radical ion pair as well as the chemical kinetics. 

In principle it is not possible to develop an accurate model without an explicit treatment of spin dynamics. Because the reaction rate of a radical pair is partly dependent on its spin state, the recombination kinetics in a spur may depend strongly on the spin correlation of the radicals it contains. In photochemistry it is customary to distinguish between G-pairs (which are initially spin correlated) and F-pairs (which are not), but in a spur all the spins are entangled and this distinction is less meaningful, but nonetheless, this nomenclature will be used in this work, wherever appropriate. One important exception is the radiolysis of water, where the very fast relaxation on the hydroxyl radical destroys any spin effects, such that there is no difference in the reactivity between G-pairs and those whose spins are uncorrelated (F-Pairs). 

The spin-dependent decay of P+H" is complex. It comprises two decay pathways as shown in the kinetics scheme of Fig.3. We will briefly explain how spin-dependent recombination dynamics are responsible for inherent deviations from monoexponentiality in Fig.2 and can fully account for them, as shown by rigorous simulations. On the basis of a brief summary of radical pair dynamics, the effect will be outlined in the following section. 

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