Computer Investigations on the Kinetics of Simple Bimolecular Reactions
1. Introduction
This Kinetics of simple bimolecular reactions in 3D liquids is investigated by large scale computer simulations. For most simulations the method of prerecorded trajectory (called also the method of periodic expansion) [1, 2] is applied, which enables us to consider systems of over 108 particles and attain desired accuracy. The irreversible reactions of two kinds have been investigated:
(1) the trapping reaction: A+B -> C+D;
(2) the annihilation reaction: A+A -> B+B, A+A -> D (where D is a dimer).
2. Results and Conclusions
The main goal for (1) was to investigate the influence of the concentration of B on the reaction rate coefficient [3-5]. The simulation has shown that the excess in the rate coefficient is a result of two effects of opposite signs: the interparticle interactions (positive) and the fluctuations in concentrations of reagents (negative). The resulting cumulative effect is weak, except for the ionic systems [5] for which, due to long range B-B repulsion, the excess is positive and over two orders in magnitude higher than for non-ionic liquids. It is shown, by analyzing simple analytical model, that the positive contribution to the excess is strictly correlated with the liquid structure (via. two particle B-B correlation function).
In the second part the long time behavior of the rate coefficient for (2) obtained from the simulation is compared to the rate coefficient predicted within the classical Smoluchowski approach. The deviations are analyzed and compared to the analogous deviations for the trapping process (1). The influence of change of the liquid structure due to dimerization (the second scheme) on the reaction rate is also investigated.
References
[1] J. Gorecki, Mol. Phys. Rep. 10 (1995) 157.
[2] M. Litniewski, J. Chem. Phys. 123 (2005) 124506.
[3] M. Litniewski, J. Chem. Phys. 129 (2007) 034505.
[4] M. Litniewski, Acta. Phys. Pol. B 39 (2008) 1161.
[5] M. Litniewski, J. Chem. Phys. 129 (2008) 104507.