On the temperature dependence of the rate in barrierless reactions in solution

We present a theoretical study of the temperature dependence of the relaxation rate in barrierless reactions. It is shown that a small change in the relative positions of the ground and excited potential surfaces can lead to a significant change in the relaxation rate. We suggest that a small shift of the potential surfaces, during the isoviscous temperature variation, may be responsible for the solvent-induced crossover from an apparent negative activation energy to a large positive activation energy observed in recent experiments