Dresden 2014 – scientific programme

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O: Fachverband Oberflächenphysik

O 36: Posters: Bio/organic Molecules on Surfaces, Graphene, Solid/liquid interfaces, Metal Substrates, Electronic Structure Theory

O 36.103: Poster

Tuesday, April 1, 2014, 18:30–22:00, P1

Electron-hole pair–vibrational coupling during scattering of HCl/Al(111): TDDFT-MD and model study — Michael Grotemeyer and •Eckhard Pehlke — Institut für Theoretische Physik und Astrophysik, Universität Kiel, 24098 Kiel, Germany

Ab initio simulations using time-dependent density functional theory together with Ehrenfest dynamics for the nuclei have revealed a very efficient energy transfer into substrate electron-hole pair excitations in case of highly vibrationally excited HCl-molecules that scatter at an Al(111) surface. The mechanism of vibrational–electron-hole pair coupling has been traced back to the periodic shift of the LUMO eigenenergy as the HCl bond length oscillates. We present an overview over our results for the energy transfer per vibrational period of the molecule as a function of its initial vibrational excitation energy and molecule-surface separation. The results can be qualitatively recovered by a simple tight-binding model. Notably, the energy dissipation rate goes through a maximum at a certain distance above the surface, i.e. not at very close molecule–surface separations. This is different from the steering mechanism suggested by Shenvi et al. for NO/Au(111) [1]. The coupling mechanism becomes less efficient for low vibrational excitation energy. We suggest this to explain the in comparison to NO small electronic contribution to the v=0 → v=1 vibrational excitation observed experimentally for HCl-surface scattering [2].

[1] N. Shenvi, S. Roy, J.C. Tully, Science 326, 829 (2009).

[2] Q. Ran, D. Matsiev, D.J. Auerbach, A.M. Wodtke, Phys. Rev. Lett. 98, 237601 (2007).