Random walks dissociation

Viswanathan R, Raff L M and Thompson D L 1984 Monte Carlo random walk calculations of unimolecular dissociation of methane J. Chem. Phys. 81 3118-21... 

Samuel and Magee250 were apparently the first to estimate the path length /th and time rth of thermalization of slow electrons. For this purpose they used the classical model of random walks of an electron in a Coulomb field of the parent ion. They assumed that the electron travels the same distance / between each two subsequent collisions and that in each of them it loses the same portion of energy A E. Under such assumptions, for electrons with energy 15 eV and for AE between 0.025 and 0.05 eV, they have obtained Tth 2.83 x 10 14 s and /th = 1.2-1.8 nm. At such short /th a subexcitation electron cannot escape the attraction of the parent ion and in about 10 13 s must be captured by the ion, which results in formation of a neutral molecule in a highly excited state, which later may experience dissociation. However, the experimental data on the yield of free ions indicated that a certain part of electrons nevertheless gets away from the ion far enough to escape recombination. 

Figure 21 Schematic drawing of the random-walk diffusion model of Butler et al. [180]. It is shown that molecular intermediates that do not hit an added row may dissociate at a step, bind to an Ag-atom and insert in an added row.

Figure 1 is a schematic representation of Frenkel s notion an atom or ion can get dislodged from its normal site to form etn interstitial-vacancy pair. He further proposed that they do not always recombine but instead may dissociate and thus contribute to diffusional transport and electrical conduction. They were free to Wcuider about in a "random walk" mcuiner essentially equivalent to that of Brownian motion. . . this meant they should exhibit a net drift in an applied field. 

FIGURE 6.7 ABA energies allied with message tapes. Error bars mark averages 1 standard deviation. Quantities are based on the message tapes compiled via random walks and reference to standard tables of dissociation energies. 

However, it has been shown that a simple random walk approximates the behavior of (3) relatively well [21]. Exciton transport competes with exciton decay, which again is taken to occur at a rate measured by spectroscopy [10]. An exciton incident upon a donor-acceptor interface is typically assumed to dissociate immediately into an electron-hole pair either side of the heterojunction, in accordance with experimental findings showing that exciton dissociation in charge transfer pairs is fast. 

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