Rates of the reaction C₂ H₃ +H₂ →C₂H₄+H

Abstract

The reaction C₂ H₃+H₂→C₂H₄+H has been studied by different direct ab initio approaches. Accurate rate constants in the temperature range 200–1200 K have been derived by time-independent scattering theory, employing R-matrix propagation on a 2D reduced dimensional G3B3 potential energy surface. Reported experimental reaction rates at room temperature vary over 3 orders of magnitude as they have to be determined indirectly. The computed room temperature rate of 2.1× 10^− 18 cm³ molecule⁻¹ s⁻¹ in this study should remove this ambiguity. At higher temperatures the calculated rates meet experimental rates from direct measurements very well. The use of a reduced dimensionality model is justified by comparing full-dimensional semiclassical tunnelling contributions to those derived on a 2D potential with the same method. The employed semiclassical approach (small curvature tunnelling) yields very similar rates to the scattering approach, thus showing that small curvature tunnelling is a very reliable method to describe reactions like these.

Acknowledgements

Financial support was provided by the European Union Research Training Network, Grant HPRN-CT-2002-00170, ‘Predicting catalysis: understanding ammonia production from first principles’.