Recent results from quasiclassical trajectory computations of elementary chemical reactions

Abstract

Recent quasi-classical trajectory (QCT) calculations of the dynamics of some prototypic elementary reactions, from state-resolved differential cross-sections (DCS) to thermal rate constants, are reviewed. The reactions studied are H + H₂, F + H₂, Cl + H₂ and O(¹D) + H₂, for which reliable potential-energy surfaces (PES) are available. The QCT results are analysed in the light of the most recent quantum mechanical (QM) calculations and experimental findings. In general, QCT integral, differential reaction cross-sections and rate constants are found to be in good agreement with their QM and experimental counterparts, indicating that, for the systems considered, the motion of the nuclei during reactive encounters is largely classical and that quantum effects, such as tunnelling, play a relatively minor role in the overall dynamics. The importance of the zero-point energy of the transition state is highlighted as one of the most important deficiencies of the QC treatment. The need for precise QC and quantal simulations of the actual laboratory measurements, in order to identify experimental quantum effects clearly, is emphasized. Finally, the importance of the calculation and measurement of vector correlations in chemical reactions is stressed and some examples are presented.