31 Nonstationary Electronic States...

Accession Number
    YB795-0004
 
Document Delivery
    The Genuine Article Number: YB795

Authors
    Weinkauf R., Schlag EW., Martinez TJ., Levine RD.

Title
    NONSTATIONARY ELECTRONIC STATES AND SITE-SELECTIVE REACTIVITY

Source
    Journal of Physical Chemistry. 101(42):7702-7710, 1997 Oct 16.

ISSN
    0022-3654

KeyWords Plus
    Born-oppenheimer approximation. Transfer matrix-elements.
    Mass-spectrometry. Large molecules. Energy-transfer. Multiphoton ionization.
    Charge separation. Laser desorption. Nuclear-dynamics. Peptide cations.

Abstract
    An efficient route to the site-selective reactivity of electronically excited states
    of multicentered molecules is discussed. In the first stage the migration of the
    electronic excitation occurs. This can operate over an extensive range without
    extensive draining of energy into the nuclear frame. Only in a second stage,
    once the optimal site has been reached, does the excess energy become
    available for bond breaking or isomerization at the new, optimal, site. This
    two-stage mechanism, where electronic excitation (or the charge) is the
    scout, avoids the pitfall of conventional large molecule kinetics. (In that view,
    known as the quasi equilibrium theory, the electronic excitation is first
    converted to nuclear modes. But then there are so many available vibrational
    states that the probability for the excitation energy to become localized at
    the necessary site, is too small and the resulting reaction rate is too slow.) By
    confining the site search to the electronic manifold, it becomes a highly
    efficient process. The recent novel experiments of Weinkauf et al. on
    (positive) charge migration and dissociation of peptide ions are suggested as
    an example of the considerations above where there is a facile migration of
    the positive charge followed by reactivity at the selected site. The peptide is
    modeled as beads on a chain. Interbead and intrabead coupling are
    discussed in terms of adiabatic and diabatic states. We find a multistep
    mechanism (unlike superexchange): a charge-directed reactivity (CDR) model.
    Such efficient ranging could also take place in other chain structures and
    suggests that there will be examples where electronic processes set the time
    scale for the chemical change. [References: 73]

Language
    English

Publication Type
    Article

CC Categories
    Physical chemistry/chemical physics.

Subset
    Current Contents/Physical, Chemical & Earth Sciences

Institution
    Reprint available from:
    Levine RD
    HEBREW UNIV JERUSALEM
    FRITZ HABER RES CTR MOL DYNAM
    IL-91904 JERUSALEM
    ISRAEL

    Weinkauf R.
    HEINRICH-HEINE-UNIVERSITAET DUESSELDORF
    INST PHYSICAL CHEMISTRY & ELECTROCHEMISTRY I
    40204 DUESSELDORF
    GERMANY

    Martinez TJ
    UNIV ILLINOIS
    DEPT CHEM
    URBANA, IL 61801
    USA
    GERMANY