Vibrational Interactions in Parisermdash;Parrmdash;Pople Theory. II. Groundhyphen; and Excitedhyphen;State Force Fields

摘要

Expressions are derived for the interaction between ground and excited states to give resonance contributions to the vibrational force field. Two contributions are found: The dominating term reflects largely the change in the bond resonance integral due to bond length variation with some contribution of the electrostatic terms; the other, a relatively small term, is generated by the polarization due to the field generated by a vibrational distortion. Calculations are made for the ground states of a number of aromatics; adequate agreement with experiment is found for benzene and naphthalene.The possible distortion of molecules and the Bornmdash;Oppenheimer approximation are investigated when the resonance interactions become strong. Application is made to the1B1uand3B1ustates of benzene. Distortion and violation of the Bornmdash;Oppenheimer approximation is predicted to occur for the twoB1ustates of benzene.