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O: Oberflächenphysik

O 17: Adsorption II

O 17.3: Vortrag

Dienstag, 28. März 2006, 11:45–12:00, TRE Phys

Energy resolved quadrupole alignment of H₂ desorbing from Cu(100) — •Carsten Thewes, Marco Rutkowski, and Helmut Zacharias — Physikalisches Institut, Westfälische Wilhelms-Universität, 48149 Münster

Measurements of the energy dependent quadrupole alignment for associative desorption of H₂ from Cu(100) were performed. The analysis includes different rotational states in the vibrational ground state v”=0 and the first vibrationally excited state v”=1. State selective detection of the desorbing molecules is realised by the (VUV+UV)-REMPI techniques. For the excitation step in the B¹Σ_g⁺ ← X¹Σ_u⁺ Lyman bands of H₂ photon energies around 110 nm are used. In v=0 the angular momenta J=1,2,3,4,5 and 8 while in v”=1 measurements for J”=2,3,4 could be detected. The acquired energy dependent alignment factor A₀⁽²⁾ shows a preferentially positive value between 0,2 and 0,4, thus helicopter motion of the desorbing molecules is observed. A₀⁽²⁾ increases at low kinetic energies close to the respective translational barrier of the two states, i.e. around 300 meV and 200 meV for v”=0 and 1, respectively. For higher energies (1100 meV for v=0, 800 meV for v”=1) a decrease of the quadrupol alignment is observed, as expected. Based on theoretical calculations of the quadrupole alignment [1] possible reaction mechanisms will be discussed.

[1] M.F. Somers, D.A. McCormack, G.J. Kroes, R.A. Olsen, E.J. Baerends and R.C. Mowrey; J. Chem. Phys., 117, 6673 (2002)