Issue Number 26 GAS SURFACE NEWS December 1999 Editors Note GSDList and Thank you to all those who replied to the survey earlier this year on the Web Page future of Gas-Surface News. We have received enough support to suggest that publishing on the Web would be viable so this is the last issue posted This issue of the out to the entire address list. We will continue with the policy of asking Newsletter is also available Institutes to pay subscriptions so that all in that Institute who are interested on the Web site. To test may have access to GSNews at no extra charge. This policy also allows your ability to read and very small groups and individuals who are not part of a group, to receive the download check Newsletter free. In order to spread the costs fairly, however, it is still http://www.phchem.uni- important to increase our subscriptions base. 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If you do not have access to the Web, please remember to tick the Surface News Mailing list. box to receive a copy by post. Just send your message to [email protected] I look forward to hearing from you all and meanwhile – enjoy this issue and essen.de. please invite any new members of your group to join the mailing list. The next issue is planned for early April. (Continued on back page....) I N S I D E T H I S I S S U E 2 Research Reports- Leiden Inst of Chemistry, University of Leiden (Mischa Bonn, Prof. Dr Aart Kleyn) 4 Current Research - L.I.S.E. Facultés Universitaires Notre-Dame de la Paix in Namur (Petra Rudolf) 9 Meeting Reports 15 Papers for Publication 17 Job Vacancies and Announcements 23 Diary Page 24 Continuation from Page 1 and Reply Slip – EVERYONE MUST REPLY TO CONTINUE SUBSCRIPTION Editor–Sue Free. Cambridge University Chemistry Dept, Lensfield Road, Cambridge, CB2 1EW, UK. Tel/Fax +44 1223 336536. [email protected]. Web Page containing contact list and other announcements – http://www.phchem.uni-essen.de/gsd/ Gas-Surface News Research Report Very Small and Very Fast: Studies of Surface Structure and Dynamics Leiden Institute of Chemistry, Leiden University P.O. Box 9502, 2300 RA LEIDEN The Netherlands With the move of Aart Kleyn from the FOM- the reaction is taking place. In these so-called Institute in Amsterdam to head the “Surface and pump-probe experiments, one femtosecond laser Catalysis” Group at the Leiden Institute of pulse (pump pulse) is used to switch the reaction Chemistry in Leiden, the scope of the research on, and a second (the probe pulse) is used to there has broadened considerably. It was, of investigate changes in the electronic absorption course, quite broad to begin with: Ben spectrum: The products exhibit different absorption Nieuwenhuys has supervised, for many years, a lines from the reactants, and the transition from one group doing research focused on both supported to the other can be observed. Interestingly, one catalysts, -real catalysts in reactors -and on surface makes use of the finite speed of light in such science investigations on model catalytic systems. experiments: the probe pulse is guided over a mirror Present topics include "non-linear processes on that can be moved back and forth. Increasing the surfaces, STM investigations of multicomponent path length of the probe pulse by 1 µm causes a surfaces and catalytic oxidation reactions on delay of 3.33 fs (speed of light: c = 3x108 m/s), so multicomponent catalysts. A recent overview was that spectroscopic images of the system can be presented in GSN 18 {April 1997}. Aart is now taken at pre-selected times, simply by moving that further introducing molecular beams into the mirror back and forth. The beautiful experiments by Leiden Group. Zewail and co-workers not only identified transition states and reaction intermediates for model What is more, with Aart’s arrival in Leiden, an reactions, but also clarified the mechanism for some amplified femtosecond (1 fs = 10-15 s) laser important chemical reactions. These experiments system, which was being used in Leiden for the were all carried out in the gas phase, in pulsed study of ultrafast processes in liquids, became molecular beams. available for experiments on surfaces due to the retirement of a senior staff member of a When one wants to transfer the same techniques to neighboring group. Aart then asked the investigate the dynamics of reactions at surfaces, undersigned, at that time working as a post-doc in there are a few complicating factors. First of all, one the group of Martin Wolf with Prof. Ertl at the has to get a UHV system leak-tight and Fritz-Haber-Institute in Berlin, to join his group in characterization equipment operative and Leiden to set up a new experiment to investigate simultaneously get the femtosecond laser system to the dynamics of surface reactions directly by work. Anyone who has worked in either surface means of time-resolved surface spectroscopy. I science or optics knows that to get one going is hard have already been working on that type of enough. Recent years, however, have seen a steady experiment in Berlin. increase in the reliability of commercial laser systems, and indeed, there have recently been Ahmed Zewail, at the California Institute of several studies successfully combining the two. Technology recently won the Nobel in Chemistry for his ground-breaking work using femtosecond A second complication is that the electronic levels lasers to investigate chemical reaction dynamics. are strongly smeared, shifted and broadened, when Zewail and co-workers were the first to a molecule or atom is close to a metal surface. This demonstrate the possibility of real-time is caused by the strong electronic coupling between monitoring the reactants turning into products as the electrons of the molecules on the surface and the Page - 2 - Gas-Surface News metal electron gas. The absence of well-defined (UCLA, Berkeley) for conventional (not time- resonances makes it hard to investigate such a resolved) SFG spectroscopy.[4] Time-resolved SFG system using electronic transitions in the visible or could provide an additional wealth of information UV to probe the reaction dynamics. A third on catalytic systems under reactive conditions. complication arises when one realizes that a monolayer of molecules at the surface is hard to We have a few vacancies for PhD students and detect optically, since it is optically very thin. The post-docs for this project. Those who are interested optical thickness of a system is defined as the should contact us. absorption cross section per sample unit length multiplied by the sample thickness. It is Mischa Bonn impossible to see changes in absorption due to the reaction when one sees no absorption to begin Leiden Institute of Chemistry with because there is only one layer of molecules. Leiden University P.O. Box 9502 The latter two problems can be overcome by the 2300 RA LEIDEN very elegant technique of time-resolved Sum- The Netherland Frequency-Generation (tr-SFG). The technique of [email protected] tr-SFG is essentially femtosecond RAIRS (Reflection Absorption InfraRed Spectroscopy): It allows one to record the vibrational spectrum of [1] J.A. Prybyla, H.W.K. Tom and G.D. Aumiller, adsorbates with very high sensitivity (signals from Phys. Rev. Lett. 68, 503 (1992). coverages below 10-3 monolayers of CO have [2] M. Bonn, S. Funk, Ch. Hess, D. N. Denzler, C. been observed) and very high time resolution Stampfl, M. Scheffler, M. Wolf and G. Ertl, Science (~100 fs). In analogy to the Zewail experiments, 285, 1042 (1999). the surface reaction is switched on by a pump [3] A. Bandara, J. Kubota, K. Onda, A. Wada, S.S. pulse, and the time evolution of the adsorbate is Kano, K. Domen and C. Hirose, J. Phys. Chem. B followed by means of time-resolved SFG. If we 102, 5951 (1998). take the desorption of NO from Ru(0001) as an [4] X. Su, P.S. Cremer, Y.R. Shen and G.A. example of a simple surface reaction, we know Somorjai, Phys. Rev. Lett. 68, 503 (1992). that the frequency of the N-O stretch vibration will change from 1825 cm-1 at the surface to 1876 cm-1 in the gas-phase. The temporal evolution of the vibrational frequency will give us information on how long it takes for molecules to desorb, after excitation of the substrate. It has already been demonstrated that important information on reaction dynamics and energy flow at surfaces can be obtained from such experiments [1, 2], specifically with time-resolved (in that case: picosecond) SFG [3].