Analysis of bonding properties in molecular ground and excited states by a Cohen-type bond order

A Cohen-type bond-order (I. Cohen, 1972) anal. in terms of orthogonalized at. basis functions is given, which can be used to analyze neglect-of-differential-overlap wave functions of large org. and organometallic mols. For small mols., the results from this method agreed with the results obtained with the same anal. based on ab-initio STO-3G wave functions. For large planar arom. systems, these AVE bond orders are a consistent generalization of the p-bond order. A simple relation between these bond orders and the corresponding covalent bond energies was established. The method can be easily extended to study excited state MC wave functions. Calcns. were done for C2H2, C2H4, C2H6, and Mn2(CO)10. The results indicate that the method can be used to discuss the photochem. of org. and organometallic compds