QUANTITATIVE VALENCE-BOND COMPUTATIONS OF CURVE CROSSING DIAGRAMS FORA HYDRIDE-TRANSFER MODEL REACTION - CH4-]CH3++CH4(CH3+)

Quantitative calculations of diabatic curve crossing diagrams are appl ied to a model hydride-transfer process, CH4 + CH3+ --> CH3+ + CH4, by means of a multistructure valence bond (VB) technique. The energies o f the various VB structures relevant to the reacting system are follow ed throughout the reaction coordinate, showing that the reaction is be st described as an avoided crossing between the two covalent VB curves , respectively representing the bonding scheme of the reactant and pro duct complexes. The ionic structure characterizing the direct hydride transfer plays a marginal role. It follows that the hydrogen being tra nsferred has a predominant radical character. An alternative more econ omical way of generating curve crossing diagrams is also presented, ba sed on the fast computation of the weights of valence bond structures out of standard MO wavefunctions. This fast procedure is found to give results in qualitative agreement with rigorous VB calculations.