Adiabatic Proton Transfer Kinetic Isotope Effects

Adiabatic Proton Transfer Kinetic Isotope Effects 

The KIE for adiabatic PT is the ratio of individual rate constants, where each of these is of the form in Eq. (10.4), e.g. H versus D transfer 

the reactant reaction coordinate frequencies 05 in Eq. (10.4) have been assumed equal [4]. From the FER analysis of Eq. (10.5), the explicit form for the 

Further, an equivalent form re-expresses the first part of this in terms of the KIE for the symmetric reaction  

Before proceeding with the KIE analysis for adiabatic PT, it is worth stressing, for comparison with the standard picture, that there are four common experimental observations which are consistent with the standard picture for nonturmeling PT KIEs, and which are thus viewed as supporting that picture (i) the Arrhenius temperature dependence of the KIE (as well as of the individual isotope rate constants) (ii) the KIE - AGrxn behavior described in Section 10.1 (i.e. maximal for the symmetric case) (iii) the KIE range is -2-10 and (iv) the wide applicability of the Swain-Schaad relationship [13, 46] connecting KIE ratios (e.g. kn/kx = These observations have done much to maintain the stan- 

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Adiabatic Proton Transfer Kinetic Isotope Effects... 

In contrast to the subsystem representation, the adiabatic basis depends on the environmental coordinates. As such, one obtains a physically intuitive description in terms of classical trajectories along Born-Oppenheimer surfaces. A variety of systems have been studied using QCL dynamics in this basis. These include the reaction rate and the kinetic isotope effect of proton transfer in a polar condensed phase solvent and a cluster [29-33], vibrational energy relaxation of a hydrogen bonded complex in a polar liquid [34], photodissociation of F2 [35], dynamical analysis of vibrational frequency shifts in a Xe fluid [36], and the spin-boson model [37,38], which is of particular importance as exact quantum results are available for comparison. 

Kieeee, P. M., Hynes, J. T. (2003) Kinetic isotope effects For adiabatic proton transfer reactions in a polar environment, J. Phys. Chem. A 107, 9022-9039. 

When a standard solvent is rq>laced by deuterated one, for example, H2O by D2O, we have the isotope effect by solvent with a complex character. The kinetic isotope effect is characteristic of proton transfer reactions. It depends on the following factors type of the dissociated bond, change in enthalpy, and character of the elementary step of proton transfer (adiabatic or tunneling). For the adiabatic character of the reaction, the isotope effect is maximum for the thamally neutral reaction. The main contribution to the isotope effect is made by the difference in zero energies AE of stretching vibrations of the A—and A—D bonds. The kyjko values are presented below, the effect is due to ASq only for different types of A—bonds (T= 298 K). 

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