Dynamics of the reactions of C+ with C2H6

Abstract

We present a crossed beam study of the major reactive channels of C++C2H6 in the collision energy range between 0.8 and 1.6 eV. We find that C2H+5 formation proceeds as a direct hydride abstraction reaction with the accompanying CH product scattered in the forward hemisphere. The product recoil energy distribution shows a distinct Gaussian shape that we correlate with the nature of the potential energy surface for transfer of the light hydride ion between two heavy species. C2H+3 formation occurs through two pathways: the first and most important route is direct interaction of C+ with C2H6 to form a new C–C bond with the ejection of CH3 in a collinear interaction that leads to backward scattering of the ionic product. A second, and much less probable pathway involves formation of this product through a transient collision complex living a significant fraction of a rotational period. The condensation product C3H+3 is by far the most abundant C3 product observed in this collision energy range. The sideways-peaked angular distribution for its formation is consistent with a mechanism where the initially formed C3H+6 complex decays in a step in which a molecule of H2 is ejected in a direction perpendicular to the plane of rotation defined by the three carbon atoms. The kinetic energy distribution for this channel is significantly broader than the predictions of statistical phase space theory and underscores the importance of potential energy exit channel barriers in determining product recoil in such elimination processes. We discuss these results in the context of a schematic potential energy surface incorporating thermochemical data and results of ab initio calculations.