Minimum energy path dimers

Figure 12.10. Potential-energy functions of the S0 state, the locally excited 1 hit states of guanine and cytosine, the lowest1 rnr state, and the tt-jt charge-transfer state of the WC conformer (a), the conformer B (b), and the conformer C (c) of the CG dimer. The PE functions have been calculated along the linear-synchronous-transit proton-transfer reaction path from the S0 minimum to the biradical minimum. Insets show the potential-energy function of the locally excited 1mr state of guanine calculated along the minimum-energy path for stretching of the NH bond...

In the case where the electron transfer is faster than molecular reorganization (nonadiabatic transfer), the path for electron transfer in the dimer coordinate representation illustrated in Figure 2.2.7 can be decomposed in a vertical activation from the minimum of Vp to the Vp curve, followed by a relaxation to the equilibrium configuration of the product. Accordingly, the Marcus theory of electron transfer [23] introduces the reorganization energy X... 

Almost all neutral dimers form only one stable complex in the gas phase, the neutral complex A-H- B. The energy of the two ions is much higher than that of the two neutral molecules, and the barrier along the proton transfer path between the two minima may also be high. The proton transfer will therefore be a rare event. The situation changes in solution, where both complexes are stabilized by solvation. Some solvents will stabilize the ionic complex more than the neutral one, up to the point that it becomes the global minimum on the proton transfer path. The extent of proton transfer is determined then by the acidity of A-H and the basicity of B. Experimentally... 

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