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

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 fol lowing a localized ionization. The use of many-electron states allows a cla ssification of the charge migration pathways through either covalent or ion ic states. Electron correlation is introduced via Coulomb repulsion of elec trons of opposite spins a-la Hubbard. Complete configuration interaction is implemented using the unitary group basis of Paldus. The primary factor de termining charge migration is found to be the local ionization potential. I t is shown that, at lower levels of excitation, the majority of possible in itial states which describe localized ionization at one end of the chain le ad to a preferential dissociation at the other end of the chain. (C) 1999 A merican Institute of Physics. [S0021-9606(99)30111-2].