Dissociation of polyatomic ions at surfaces: The influence of mechanical and electronic energy transfer

Dynamics of dissociative scattering: Hyperthermal energy collisions of state-selected OCS+ on Ag(111)

“…The scarcity of scattered positive ions is consistent with the observation of Koppers et al for CF 3 ϩ incident on Ag͑111͒; there, the authors noted that the intensity of scattered positive ions was 2 orders of magnitude lower than the intensity of scattered negative ions. 24 The electron affinities for potential scattered products are 1.26 eV for C, 1.46 eV for O, 2.08 eV for S, 0.205 eV for CS, 1.125 eV for SO, and 0.46 eV for OCS. 38 The time-offlight mass spectrum of Fig.…”

“…These states can be populated either by resonant or Auger neutralization; 24,47-49 however, resonant neutralization will dominate at the low collision energies employed in this study. 24,49 Neutralization into the lowest lying affinity level of OCS ϩ will produce bound, ground state OCS(X 1 ⌺) immediately prior to impact with the surface. Additionally, there are a number of bound excited states ͑e.g., 3 ⌸), that may be populated in the neutralization event.…”

“…22, 23 Kleyn and coworkers attributed the fragmentation of CF 3 ϩ on clean and barium-covered Ag͑111͒ to a complex mechanism involving both impulsive dissociation and DA steps. 24,25 Although many mechanisms have been proposed for the dissociation of small molecular ions at surfaces, electronic dissociation mechanisms are rarely discussed in the scattering of large polyatomic ions. Furthermore, whereas the impulsive dissociation of a diatomic molecule necessarily happens in half a vibrational period (ϳ10 Ϫ14 s͒, mechanical dissociation is thought to occur on a much longer time scale for larger molecules.…”

“…In the literature, the delayed unimolecular dissociation mechanism is frequently termed surface-induced dissociation ͑SID͒; [26][27][28][29][30][31][32] whereas the prompt dissociation associated with small molecules has of-ten been called collision-induced dissociation ͑CID͒. 3,[8][9][10]24,25 Herein, we adopt the terminology, ''delayed SID'' and ''prompt SID,'' to clearly identify the different mechanistic time scales. To facilitate the unambiguous discussion of molecular dissociation at surfaces, these two impulsive mechanisms and the electronic mechanisms discussed above, are explicitly listed in Table I.…”

Dynamics ofCN−ion emission during hyperthermalN2+Deng1, Souda2 2002Phys. Rev. B2000View full textAdd to dashboardCite

“…8 As for dissociative negative ion formation, the dissociation process can be categorized into two mechanisms: mechanical dissociation and electron-transfer induced dissociation. 9 Mechanical dissociation refers to impulsive transfer of kinetic energy into rovibrational energy during collision that subsequently ruptures the molecular bond. Electron-transfer induced dissociation involves population of a repulsive electronic state of a molecule by an electron.…”