Effects of projectile orientation and surface impact site on the efficiency of projectile excitation in surface-induced dissociation: Protonated diglycine collisions with diamond {1 1 1}

Classical trajectory simulations are performed for collisions between protonated diglycine (gly2-H+) and a diamond {1 1 1} surface at incident angles θi of 0° and 45°, with respect to the surface normal, and initial translational energies Ei of 35 and 70 eV. The trajectories are analyzed to determine how the orientation angle of the peptide ion and the surface impact site affect the collisional energy transfer. There are two distinct impact points on the surface on which the peptide ion can collide, hydrogen and carbon atoms, denoted as H- and C-sites. While the impact point plays little to no role in determining energy transfer, for θi = 0° the orientation angle of the peptide has a significant effect on energy transfer. When the peptide ion collides with its backbone vertical to the surface plane and, thus, with a C- or N-terminus approach, the internal energy change is a maximum and the final translational energy and surface internal energy change are at a minimum. When the peptide ion collides horizontally, the opposite occurs. In addition, for vertical collisions more energy is transferred to the peptide ion if the C-terminus first strikes the surface instead of the N-terminus. For non-perpendicular collisions, with θi = 45°, the energy transfer efficiency is less sensitive to the peptide orientation. Peptide orientation becomes more important as Ei is increased.