Ligand geometries and excited states of allene

The distorted geometries of allene found by X-ray diffraction in various transition-metal complexes are used for the excited states of this molecule in a CNDO calculation of transition energies, following a reasoning recently proposed by McWeeny, Mason and Towl. The good agreement between the allene u.-v. spectrum and the calculated values of the transition energies and the comparison with the results of a standard CNDO-CI calculation suggest that the method proposed in the present paper may be applied also to similar cases, where experimentally determined geometries can be attributed to the excited states of molecules.