Electron-, Energy-, and Atom-Transfer

Electron-, Energy-, and Atom-Transfer Reactions between Metal Complexes and DNA H. Holden Thorp... 

ELECTRON-, ENERGY-, AND ATOM-TRANSFER REACTIONS BETWEEN METAL COMPLEXES... 

D. A. Micha. Time-dependent many-electron treatment of electronic energy and charge transfer in atomic collisions. J. Phys. Chem., 103 7562, 1999. 

Micha, D.A. and Runge, K. (1992) Electronic energy and charge transfer in slow atomic collisions A time dependent molecular orbital approach., in Broeckhove, J. and Lathouwers, L. (eds.), Time-dependent quantum molecular dynamics, Plenum Press, New York, pp. 247-265. 

Electronic excitation from atom-transfer reactions appears to be relatively uncommon, with most such reactions producing chemiluminescence from vibrationaHy excited ground states (188—191). Examples include reactions of oxygen atoms with carbon disulfide (190), acetylene (191), or methylene (190), all of which produce emission from vibrationaHy excited carbon monoxide. When such reactions are carried out at very low pressure (13 mPa (lO " torr)), energy transfer is diminished, as with molecular beam experiments, so that the distribution of vibrational and rotational energies in the products can be discerned (189). Laser emission at 5 p.m has been obtained from the reaction of methylene and oxygen initiated by flash photolysis of a mixture of SO2, 2 2 6 (1 )-... 

The first (and still the foremost) quantum theory of stopping, attributed to Bethe [19,20], considers the observables energy and momentum transfers as fundamental in the interaction of fast charged particles with atomic electrons. Taking the simplest case of a heavy, fast, yet nonrelativistic incident projectile, the excitation cross-section is developed in the first Born approximation that is, the incident particle is represented as a plane wave and the scattered particle as a slightly perturbed wave. Representing the Coulombic interaction as a Fourier integral over momentum transfer, Bethe derives the differential Born cross-section for excitation to the nth quantum state of the atom as follows. 

Despite the fact that Bohr s stopping power theory is useful for heavy charged particles such as fission fragments, Rutherford s collision cross section on which it is based is not accurate unless both the incident particle velocity and that of the ejected electron are much greater than that of the atomic electrons. The quantum mechanical theory of Bethe, with energy and momentum transfers as kinematic variables, is based on the first Born approximation and certain other approximations [1,2]. This theory also requires high incident velocity. At relatively moderate velocities certain modifications, shell corrections, can be made to extend the validity of the approximation. Other corrections for relativistic effects and polarization screening (density effects) are easily made. Nevertheless, the Bethe-Born approximation... 

The control that the ene-dithiolate ligand has upon the first ionization energy of these complexes illustrates the importance of this ligation to the reactivity found for molybdoenzymes. The ene-dithiolate ligand acts as an electronic buffer , effectively dampening the harsh electronic changes that would otherwise be expected to take place with changes in the metal formal oxidation states and atom transfer reactions at the active site in these enzymes. 

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