Dresden 2009 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 62: Surface chemical reactions II
O 62.4: Vortrag
Freitag, 27. März 2009, 12:00–12:15, SCH A01
State resolved measurements of photodesorbed NO from Ag (111) surface — •Daniel Mulugeta1, Kazuo Watanabe1, Dietrich Menzel1,2, and Hans-Joachim Freund1 — 1Fritz-Haber-Institute der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin — 2Physik-Department E20, Technische Universität München, 85747 Garching
The distribution of energy over the various degrees of freedom of photodesorbed molecules contains important information about the dynamics of the desorption event. We have performed state resolved (translation, rotation, vibration) measurements of NO photodesorbed from (NO)2 adsorbed on Ag (111) at 60 K by nanosecond laser pulses (2.3, 3.5 or 4.7 eV) by using (1+1) resonant multiphoton ionization (REMPI) via the A2Σ ←X2Π transition. Both thermal and non-thermal components are observed in state selective time of flight measurements. Rotational and vibration temperatures of about 430 K and 710 K, respectively, were found for NO photodesorbed with a velocity of about 960 m/s, regardless of the photon energy used. The translational energy distributions did not show major change with vibrational excitations. By contrast, the translational temperature showed a systematic increase with increasing rotational excitation. The results are interpreted in terms of an excitation-deexcitation mechanism via transient negative ions.