Molecular recombination dynamics

VI. Pair Recombination—A Stochastic Approach A. Generalized Encounter Theory An Inelastic Collision Integral Atomic and Molecular Recombination Dynamics... 

Ben]amin I, Barbara P F, Gertner B J and Hynes J T 1995 Nonequilibrium free energy functions, recombination dynamics, and vibrational relaxation of tjin acetonitrile molecular dynamics of charge flow in the electronically adiabatic limit J. Phys. Chem. 99 7557-67... 

To examine the soUd as it approaches equUibrium (atom energies of 0.025 eV) requires molecular dynamic simulations. Molecular dynamic (MD) simulations foUow the spatial and temporal evolution of atoms in a cascade as the atoms regain thermal equiUbrium in about 10 ps. By use of MD, one can foUow the physical and chemical effects that induence the final cascade state. Molecular dynamics have been used to study a variety of cascade phenomena. These include defect evolution, recombination dynamics, Hquid-like core effects, and final defect states. MD programs have also been used to model sputtering processes. 

The first reaction filmed by X-rays was the recombination of photodisso-ciated iodine in a CCI4 solution [18, 19, 49]. As this reaction is considered a prototype chemical reaction, a considerable effort was made to study it. Experimental techniques such as linear [50-52] and nonlinear [53-55] spectroscopy were used, as well as theoretical methods such as quantum chemistry [56] and molecular dynamics simulation [57]. A fair understanding of the dissociation and recombination dynamics resulted. However, a fascinating challenge remained to film atomic motions during the reaction. This was done in the following way. 

C. J. Margulis and D. F. Coker (1999) Nonadiabatic molecular dynamics simulations of the photofragmentation and geminate recombination dynamics in size-selected Ij-(002)11 cluster ions. J. Chem. Phys. 110, p. 5677... 

Nelson, J., Li, X., Long, N.J., and Durrant, J.R. (2004) Molecular control of recombination dynamics in dye-sensitized nanocrystalline TiOj films free energy vs distance dependence. J. Am. Chem. Soc, 126, 5225-5233. 

Batista V S and Coker D F 1996 Nonadiabatic molecular dynamics simulation of photodissociation and geminate recombination of liquid xenon J. Chem. Phys. 105 4033-54... 

Flase W L 1976 Modern Theoretical Chemistry, Dynamics of Molecular Collisions part B, ed W H Miller (New York Plenum) p 121 Gilbert R G and Smith S C 1990 Theory of Unimolecular and Recombination Reactions koadoa Blackwell Scientific)... 

The approach is ideally suited to the study of IVR on fast timescales, which is the most important primary process in imimolecular reactions. The application of high-resolution rovibrational overtone spectroscopy to this problem has been extensively demonstrated. Effective Hamiltonian analyses alone are insufficient, as has been demonstrated by explicit quantum dynamical models based on ab initio theory [95]. The fast IVR characteristic of the CH cliromophore in various molecular environments is probably the most comprehensively studied example of the kind [96] (see chapter A3.13). The importance of this question to chemical kinetics can perhaps best be illustrated with the following examples. The atom recombination reaction... 

Niv M Y, Krylov A I and Gerber R B 1997 Photodissociation, electronic relaxation and recombination of HCI in Ar-n(HCI) clusters—non-adiabatic molecular dynamics simulations Faraday Discuss. Chem. Soc. 108 243-54... 

Using the first-principles molecular-dynamics simulation, Munejiri, Shimojo and Hoshino studied the structure of liquid sulfur at 400 K, below the polymerization temperature [79]. They found that some of the Ss ring molecules homolytically open up on excitation of one electron from the HOMO to the LUMO. The chain-like diradicals S " thus generated partly recombine intramolecularly with formation of a branched Sy=S species rather than cyclo-Ss- Furthermore, the authors showed that photo-induced polymerization occurs in liquid sulfur when the Ss chains or Sy=S species are close to each other at their end. The mechanism of polymerization of sulfur remains a challenging problem for further theoretical work. 

M. Odelius, M. Kadi, J. Davidsson, and A. N. Tarnovsky, Photodissociation of diiodomethane in acetonitrile solution and fragment recombination into iso-diiodomethane studied with ab initio molecular dynamics simulations. J. Chem. Phys. 121(5), 2208-2214 (2004). 

Equation (9.3) has been derived for one-dimensional diffusion and supported by molecular dynamics simulation in the three-dimensional case (Powles, 1985 Tsurumi and Takayasu, 1986 Rappaport, 1984). For the partially diffusion-controlled recombination reaction we again refer to Figure 9.1, where the inner (Collins-Kimball) boundary condition is now given as... 

It must be also considered that the reaction rates of different thermal processes which can occur simultaneously are influenced by the treatment conditions (temperature, heating rate, pressure, static or dynamic atmosphere). This will affect the relative quantities of the products formed and in some cases also their nature, when recombination reactions give rise to secondary degradation products. On account of its sensitivity and resolution power Py-GC/MS will also provide useful information on minor components present in a material, including low molecular weight additives and pigments. 

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