Light atom transfer

LcU ge amplitude vibrational motions of molecules occur at high temperatures, in weakly bound complexes, in chemical reactions, and in many other circumstances. In a subset of these cases the specific (juantuni states and dynamics are important, e.g. light atom transfer reactions, unimolecular decay and isomerization of small molecules, proton transfer in liquids, photodissociation and reactions guided by laser control. 

O.I. Tolstikhin and H. Nakamura, Hyperspherical elliptic coordinates for the theory of light atom transfer reactions in atom-diatom collisions. J. Chem. Phys., 108 8899-8921, 1998. 

Similarly, it should be stressed that vibrational bonding is not limited to light atom transfer systems. Atabek and Lefebvre (35) have given an example for vibrational bonding in non-reactive systems. Poliak (36) and Meyer (37) have studied vibrational bonding in heavy atom transfer reactions. 

Stability is a sufficient condition for breakdown of TST. Interestingly, it is, as seen from the figure, not a necessary condition. As the mass of the middle atom gets higher, stability sets in earlier and TST breaks down at a lower energy. Thus we expect even variational TST to be quite poor for a light atom transfer reaction and very good for heavy atom transfer. 

H. Komweitz, M. Broida and A. Per, "Dynamics of the light atom transfer reaction Q+HQ ClH-i-Q Oscillating reactivi, effect of reagent rotation on reaction cross sections and rotational exdtation of products", /. Phys. Chan., Qn press). 

The second example is the hydrogen atom tunneling in the triatomic molecule HO2 for zero total angular momentum (/ = 0). In this case an analytical DMBE (double many-body expansion) potential function is available [126]. Since the quantum mechanically exact calculation can be carried out, the numerical results based on the present semi-classical theory are compared with the exact results. The exact numerical calculations are carried out in the hyperspherical elliptic coordinates (p, f, r]) [127,128], which are convenient for describing a light atom transfer between two heavy atoms. The coordinate p is called hyperradius, which represents the mass scaled radius of the hypersphere and is defined as... 

Quasiclassical calculations are similar to classical trajectory calculations with the addition of terms to account for quantum effects. The inclusion of tunneling and quantized energy levels improves the accuracy of results for light atoms, such as hydrogen transfer, and lower-temperature reactions. 

The effects of transfer of atoms by tunneling may play an essential role in a number of phenomena involving the transfer of atoms and atomic groups in the condensed phase. One may expect that these effects may exist not only in the proton transfer reactions considered above but also in such processes as the diffusion of hydrogen atoms and other light ions (e.g., Li+) in liquids, tunnel inversion and isomerization in some molecules, quantum diffusion of defects and light atoms in the electrode at cathodic incorporation of the ions, ion transfer across the liquid/solid interface, and low-temperature chemical reactions. 

Formation of bands in solids by assembly of isolated atoms into a lattice (modified from Bard, 1980). When the band gap Eg kT or when the conduction and valence band overlap, the material is a good conductor of electricity (metals). Under these circumstances, there exist in the solid filled and vacant electronic energy levels at virtually the same energy, so that an electron can move from one level to another with only a small energy of activation. For larger values of Eg, thermal excitation or excitation by absorption of light may transfer an electron from the valence band to the conduction band. There the electron is capable of moving freely to vacant levels. The electron in the conduction band leaves behind a hole in the valence band. 

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