Electronically nonadiabatic effects

INTERACTIONS OF VIBRATION ALLY-EXCITED MOLECULES AT SURFACES A PROBE FOR ELECTRONICALLY NONADIABATIC EFFECTS IN HETEROGENEOUS CHEMISTRY... 

Fig. 3(b). The stunning agreement between experiment and theory suggests that electronically nonadiabatic effects strongly influence this reaction. 

Top, Z.H. and Baer, M. (1977). Incorporation of electronically nonadiabatic effects into bimolecular reaction dynamics. II. The collinear (H2 + H+,Hj + H) systems, Chem. Phys. 25, 1. 

In all dynamical simulations presented so far, it has been assumed that the electrons stay in their ground state throughout the whole process, i.e. the simulations have been based on the Born-Oppenheimer approximation. Still, at metal surfaces with their continuous spectrum of electronic states at the Fermi energy electron-hole (e-h) pair excitations with arbitrarily small energies are possible. However, the incorporation of electronically nonadiabatic effects in the dynamical simulation of the interaction dynamics of molecules with surface is rather difficult [2, 109, 110]. Hence the role of electron-hole pairs in the adsorption dynamics as an additional dissipation channel is still unclear [4],... 

The formalism and computer eodes developed here for the study of halogen-hydrogen could, without great diffieulty, be extended to die investigation of spin-orbit and electronic nonadiabatic effects in other atom-molecule abstraction reactions. 

The number of coupled equations are 6(N + n) and the quantities calculated are obtained as averages over a number of trajectories which initially have randomly chosen values for the phase angles and the aiming points AX, AF. The trajectories are run on the lower adiabatic potential surface for the interaction between the atom/molecule and the solid. It is possible to include in a simple but approximate manner the effect of electronic nonadiabatic effects if the potential energy surfaces for the excited states are available. This is done by... 

Quantum mechanical effects—tunneling and interference, resonances, and electronic nonadiabaticity— play important roles in many chemical reactions. Rigorous quantum dynamics studies, that is, numerically accurate solutions of either the time-independent or time-dependent Schrodinger equations, provide the most correct and detailed description of a chemical reaction. While hmited to relatively small numbers of atoms by the standards of ordinary chemistry, numerically accurate quantum dynamics provides not only detailed insight into the nature of specific reactions, but benchmark results on which to base more approximate approaches, such as transition state theory and quasiclassical trajectories, which can be applied to larger systems. 

Thus, we have shown that nonadiabatic effects can be important in problems such as electron transfer where excited and ground states may be close together. We believe that future investigations in this area will be fruitful. 

The effects of deviations from the Born-Oppenheimer approximation (BOA) due to the interaction of the electron in the sub-barrier region with the local vibrations of the donor or the acceptor were considered for electron transfer processes in Ref. 68. It was shown that these effects are of importance for long-distance electron transfer since in this case the time when the electron is in the sub-barrier region may be long as compared to the period of the local vibration.68 A similar approach has been used in Ref. 65 to treat non-adiabatic effects in the sub-barrier region in atom transfer processes. However, nonadiabatic effects in the classically attainable region may also be of importance in atom transfer processes. In the harmonic approximation, when these effects are taken into account exactly, they manifest themselves in the noncoincidence of the... 

As mentioned, most calculations we have done so far have concerned molecular systems. However, prior to development of the non-BO method for the diatomic systems, we performed some very accurate non-BO calculations of the electron affinities of H, D, and T [43]. The difference in the electron affinities of the three systems is a purely nonadiabatic effect resulting from different reduce masses of the pseudoelectron. The pseudoelectrons are the heaviest in the T/T system and the lightest in the H/H system. The calculated results and their comparison with the experimental results of Lineberger and coworkers [44] are shown in Table 1. The calculated results include the relativistic, relativistic recoil. Lamb shift, and finite nuclear size corrections labeled AEcorr calculated by Drake [45]. The agreement with the experiment for H and D is excellent. The 3.7-cm increase of the electron affinity in going from H to D is very well reproduced by the calculations. No experimental EA value is available for T. 

In Table II we also compare our total variational energies with the energies obtained by Wolniewicz. In his calculations Wolniewicz employed an approach wherein the zeroth order the adiabatic approximation for the wave function was used (i.e., the wave function is a product of the ground-state electronic wave function and a vibrational wave function) and he calculated the nonadiabatic effects as corrections [107, 108]. In general the agreement between our results... 

L. S. Cederbaum Prof. Jungen, you mentioned that MCQDT takes into account nonadiabatic effects. I would like to point out that this approach only considers those nonadiabatic effects that arise due to the motion of the Rydberg electron. The nonadiabatic effects in the ion core are not considered. These effects can often be substantial. 

If the Born-Oppenheimer approximation is not valid—for example, in the vicinity of surface crossings—nonadiabatic coupling effects (that couple nuclear and electronic motion) need to be taken in account to correctly describe the motion of the molecular system. This is done, for instance, when one needs to describe a jump between two different PESs. In this case, one uses semiclassi-cal theories and the surface-hopping method, which we discuss subsequently. We now discuss in some detail how the region in which nonadiabatic effects become important can be characterized topologically. 

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