A quantum mechanical and molecular mechanical (QM + MM) direct dynamics classical trajectory simulation is used to study energy transfer and fragmentation in the surface-induced dissociation (
SID) of N-protonated
diglycine, (gly)2H+. The
peptide ion collides with the hydrogenated
diamond [111] surface. The Austin Model 1 (AM1) semiempirical electronic structure theory is used for the (gly)2H+ intramolecular potential and molecular mechanical functions are used for the
diamond surface potential and
peptide/surface intermolecular potential. The simulations are performed at collision energies Ei of 30, 50, 70, and 100 eV and collision angle of 0 degrees (perpendicular to the surface). The percent energy transfer to the
peptide ion is nearly independent of Ei, while energy transfer to the surface increases with increase in Ei. A smaller percent of the energy remains in
peptide translation as Ei is increased. These trends in energy transfer are consistent with previous trajectory simulations of
SID. At each Ei the most likely initial pathway leading to fragmentation is
rupture of the +H3NCH2-CONHCH2COOH bond. Fragmentation occurs by two general mechanisms. One is the traditional Rice-Ramsperger-Kassel-Marcus (RRKM) model in which the
peptide ion is activated by its collision with the surface, "bounces off", and then dissociates after undergoing intramolecular vibrational energy redistribution (IVR). The other mechanism is shattering in which the ion fragments as it collides with the surface. Shattering is the origin of the large increase in number of product channels with increase in Ei, i.e., 6 at 30 eV, but 59 at 100 eV. Shattering becomes the dominant dissociation mechanism at high Ei.