MO AB-INITIO MCSCF CALCULATION OF THE CHARGE TOPOLOGY IN THE H-ABSTRACTION FROM CH4 BY MGO AND LIO MOLECULES

MCSCF-CAS and SCF ab initio calculations were carried out for the abst raction of H from CH4 by MgO and LiO molecules. Effects of the electro n correlation on internuclear distances, reaction energies, and Laplac ian of the charge density del2rho(r) of the O valence shell were studi ed. An excellent correlation between the values of -del2rho(r) at an e xternal saddle point of this shell and the activation barrier for the H abstraction from CH4 already reported was obtained. In this way, the use of -del2rho(r) has been extended to include the prediction of the chemical reactivity of a reaction involving a homolytic break of a pa ir of bonding electrons. The changes in the charge redistribution in g oing from the reactants to the transition state and to the products wa s also determined in terms of variations of -del2rho(r) at the critica l points of the valence shells.