Dresden 2009 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 62: Surface chemical reactions II
O 62.5: Vortrag
Freitag, 27. März 2009, 12:15–12:30, SCH A01
Direct photochemical formation of N2 from NO dimers on cold Ag(111) — •Ki Hyun Kim1, Kazuo Watanabe1, Dietrich Menzel1,2, and Hans-Joachim Freund1 — 1Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany — 2Technische Universität München, 85747 Garching, Germany
Direct photochemical formation of N2 has been identified for the first time in photoreactions of (NO)2 adsorbed on Ag(111) at ∼ 30 K, induced by UV and visible light. Mass selected time-of-flight signals of N2, N2 O, and NO formed from (NO)2 on Ag(111) by irradiating with 2.3, 3.5 and 4.7 eV laser beams (Nd:YAG laser) were measured. The results show that the translational temperature of the N2 formed from (NO)2 on Ag(111) is ∼ 5700 K, while those of photodesorbed N2 O and NO are ∼ 1200 and 770 K, respectively, independent of incident photon energy. On the other hand the translational temperature of N2 formed from adsorbed N2 O on Ag(111) is only ∼ 1400 K, i.e. much lower than that of N2 formed from (NO)2.
We propose that the formation of fast N2 from (NO)2 on Ag(111) occurs via simultaneous cleavage of the two N-O bonds followed by the formation of an N-N triple bond of N2, and can be regarded as mutual abstraction of the N atom from each nitrosyl in (NO)2. The Ag surface reduces the N-N bond length of (NO)2 to enable the formation of N2 as well as of N2 O; furthermore, the equilibrium surface distance of (NO)2 is considerably shorter than that of N2 which leads to the latter’s high kinetic energy.