Efficient Calculation of Statistical and Dynamical Reaction Rates for Large Dimensional Molecular Systems


Principal Investigator

Harold W. Schranz

Research School of Chemistry and ANUSF


Terry J. Frankcombe

Department of Chemistry

University of Queensland


s10 - VPP, PC

Knowledge of how quickly chemical reactions occur is an essential ingredient in the rigorous modelling
of combustion, industrial and atmospheric reaction systems. This project focuses on the development of new methods for the accurate prediction of rate constants for chemical reaction. Crucial to this development is a more complete understanding of how and on what timescale energy moves about a molecule (IVR) and between molecules (collisional energy transfer). The current focus is on the role of the intermolecular potential energy and quantum effects on collisional energy transfer in highly excited molecules.


What are the results to date and the future of the work?

Our continuing series of computational studies of the intermolecular potential energy surface and collisional energy transfer of the CO2 + Ar system was extended to an examination of the SO2 + Ar system using a variety of different models of the intermolecular potential surface. Whereas, a strong correlation of energy transfer with the steepness of the intermolecular potential (average force) was found for the CO2 + Ar system, in the SO2 + Ar system there appeared to be no such clear correlation. Further simulation studies are necessary in order to understand the detailed mechanisms involved in the energy transfer. For example, it is possible that the molecular shape may play a role. The linear CO2 molecule and the nonlinear SO2 molecule may involve a differing relative importance of the repulsive and attractive branches of the intermolecular potential yielding differing efficiencies of translational, rotational and vibrational energy flow amongst the collision partners.



Appendix A -





Dependence of average energy transfer <DE> on average force <F> for a range of models of the intermolecular interaction in SO2-Ar collisions.

What computational techniques are used?

Quantum chemical ab initio packages (GAUSSIAN) and density functional theory packages (ADF) were used for calculating points on the intermolecular potential. Given a model of the colliding system (e.g. an excited target molecule and a thermal projectile molecule), described by a global potential energy surface including intra- and intermolecular parts, the classical equations of motion were solved for a specified ensemble of initial conditions before the collision and thereby ending up with a set of final states after the collision is over. Home grown efficient vectorised trajectory codes were employed for this portion of the project and production runs were performed using the VPP and Power Challenge supercomputers. A variety of detailed and averaged quantities were extracted from such studies.


Frankcombe, T.J., Stranger, R., Schranz, H.W., The intermolecular potential energy surface of CO2-Ar and its effect on collisional energy transfer, Internet Journal of Chemistry 1 (1998) 12.

- Appendix A