Curve crossing techniques solvents

In this review, almost all of the simulations we have described use only classical mechanics to describe the nuclear motion of the reaction system. However, a more accurate analysis of many reactions, including some of the ones that have already been simulated via purely classical mechanics, will ultimately require some infusion of quantum mechanical methods. This infusion has already taken place in several different types of reaction dynamics electron transfer in solution, > i> 2 HI photodissociation in rare gas clusters and solids,i i 22 >2 ° I2 photodissociation in Ar fluid,and the dynamics of electron solvation.22-24 Since calculation of the quantum dynamics of a full solvent is at present too time-consuming, all of these calculations involve a quantum solute in a classical solvent. (For a system where the solvent is treated quantum mechanically, see the quantum Monte Carlo treatment of an electron transfer reaction in water by Bader et al. O) As more complex reaaions are investigated, the techniques used in these studies will need to be extended to take into account effects involving electron dynamics such as curve crossing, the interaction of multiple electronic surfaces and other breakdowns of the Born-Oppenheimer approximation, the effect of solvent and solute polarization, and ultimately the actual detailed dynamics of the time evolution of the electronic degrees of freedom. 

By modelling the TR MFE fluorescence decay curves in low-permittivity solvents using new simulation techniques, it has been shown that the spin-lattice relaxation time can be significantly decreased by this cross-combination effect, depending on the number of radical pairs in the spur. It is hypothesised that this effect acts as an extra source of spin relaxation in hydrocarbons where the recombination fluorescence is slowed down by an electron scavenger, such as hexafluorobenzene. It has also been hypothesised that different spin-lattice relaxation times are to be expected for photolytic and radiolytic pairs. 

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