ELECTRONIC STRUCTURE OF CARBON SUBOXIDE

The CNDO/2 and the extended Hückel molecular orbital (XHMO) methods have been applied to linear and bent configurations of C3O2. The CNDO/2 method was found to give a satisfactory description of the electronic charge distribution in the molecule. It indicates the presence of a large negative charge on the central carbon atom, with a corresponding reduction in the CC π-bond population. These features provide an explanation for the low frequency of the bending vibration about the central carbon atom. The expressions obtained for the highest occupied and lowest unoccupied molecular orbitals are found to explain the dissociations which C3O2 undergoes in the mass spectrum and in photochemical reactions. The variation of the XHMO orbital energies with the apex angle also provides some insight into the low resistance to bending in this molecule, and the resulting orbital energy diagram can be utilized to make predictions concerning the structure of the ions and of some low-lying excited states of the molecule. The CNDO/2 orbital energies appear not to lend themselves to such a discussion.