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 abstraction of H from CH4 by MgO and LiO molecules. Effects of the electron correlation on internuclear distances, reaction energies, and Laplacian of the charge density del2rho(r) of the O valence shell were studied. An excellent correlation between the values of -del2rho(r) at an external 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 pair of bonding electrons. The changes in the charge redistribution in going from the reactants to the transition state and to the products was also determined in terms of variations of -del2rho(r) at the critical points of the valence shells.