Potential energy surfaces describing charge transfer

Fig. 10 The three-dimensional potential energy surface describing the motion of protons between N6(A) and 04(T) and between N3(T) and N1(A) shows two critical points in the ground state. The deeper minimum corresponds to the amine/keto structure of AT and a shallow one to the imine/enol structure (A T ). Upon absorption of a UV photon the initaly delocalized excitonic states (1) undergo a rapid localization on f 10 ps timescale for single bases and 100 ps timescale for stacked base pairs to form a charge transfer (CT) states. The subsequent CT states passing through a conical intersection are carried back to the ground state.

For this adiabatic model, the LE to CT interconversion occurs on a single potential energy surface. The methods for describing charge transfers of this type have recently made major progress (see Section III.B). 

Although there are no literature reports on the potential energy surfaces of reactions involving dianions, the proton transfer between doubly deprotonated 1,7-heptanediol and H2O has been investigated at the MP2/6-31- -G(d.p)/HF/6-31-fG(d) level. The surface has a transition state for ion separation that occurs at an 0(CH2)70 HOH distance of = 6.5 A. As described in the Section 3.3, the surface can be adequately modeled by the combination of a proton transfer surface for a singly-charged analog (CHsO" -F H2O) and an electrostatic potential. 

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