Charge migration and control of site selective reactivity: The role of covalent and ionic states

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Abstract
A many-electron description of charge migration along a molecular backbone is discussed. Reference is made to site selective reactivity and the recent experiments of Weinkauf and Schlag on the dissociation of peptide ions following a localized ionization. The use of many-electron states allows a classification of the charge migration pathways through either covalent or ionic states. Electron correlation is introduced via Coulomb repulsion of electrons of opposite spins à-la Hubbard. Complete configuration interaction is implemented using the unitary group basis of Paldus. The primary factor determining charge migration is found to be the local ionization potential. It is shown that, at lower levels of excitation, the majority of possible initial states which describe localized ionization at one end of the chain lead to a preferential dissociation at the other end of the chain.