A NON ADIABATIC THEORY FOR ULTRAFAST AND CATALYTIC TRANSFER OF ELECTRONS AT LOW TEMPERATURE

摘要

Electron transfer (ET) between weakly interacting molecules is a ubiquitous elementary process of chemical reactions generally well described by the Marcus theory as a thermally activated process. In the vicinity of the inversion point where the activation energy becomes small, ET is faster and should occur by quantum tunnelling at low temperature. Then, the standard adiabatic approximation used in the Marcus theory looses its validity and improvements are needed. We construct a non-adiabatic theory of ET using the complex amplitudes on each molecule of the electronic wave-functions as Kramers variables. The effective dynamics of ET is then described by a nonlinear equation with dissipative terms and colored Langevin forces globally modeling the interaction with the thermalized environment. Far from the inversion point, our model reproduces essentially the standard Marcus results but close to it, a correct description of the quantum tunnelling of the electron in its deformable environment requires to take into account nonlinearities and damping. We analyze quantum ET on the base of the recently proposed nonlinear concept of Targeted Transfer which extends but also qualitatively modifies the well-known concept of linear resonance and tunnelling. In addition, we predict and numerically confirm spectacular catalytic effects if ET occurs in the presence of a third molecule chosen very special. Then even in situations with a large energy barrier, where a direct ET between donor and acceptor cannot occur at low temperature, a weak coupling with an extra appropriately tuned (catalytic) site can trigger selectively an ultrafast ET at low temperature. New perspectives on ET and more generally on selective quantum transitions in complex systems are opened and seems to be highly relevant for biosystems (e.g. the photosynthetic reaction center).