Butorac, J.; (2011) Femtosecond laser studies of CO and NO on Pd(111). Doctoral thesis , UCL (University College London).

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Abstract

The ultimate goal of any branch of chemistry, including surface chemistry, is to understand the dynamics of reactions. The typical time scale for bond making and breaking is the femtosecond time scale. Femtochemistry has led to enormous progress in the understanding, and even control, of chemical reactions in the gas and solution phases over the past decades. However, a comparable level of sophistication in the analysis of surface chemical reactions has not been achieved due to the complexity of the energy dissipation channels. For this thesis, a new experimental set-up was built with the goal to monitor the femtosecond laser-induced desorption (fs-LID) and femtosecond laser-induced reaction (fs-LIR) of CO and NO co-adsorbed on a Pd(111) surface. In addition, a femtosecond extreme ultraviolet (XUV) source was designed and commissioned. All the femtosecond laser-induced studies were accompanied by temperature programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS). First, fs-LID experiments were performed for pure CO and NO adsorbed on Pd(111) in order to test the apparatus. The CO and NO photodesorption dynamics were compared and the different photoreactivity was explained qualitatively using two theoretical models: electron friction and desorption induced by multiple electronic transitions (DIMET). The power law behaviour was also tested and a new method of fitting proposed. The photodesorption behaviour of CO co-adsorbed with NO on Pd(111) was then studied and compared qualitatively with the photodesorption behaviour of pure CO and NO within the empirical friction model.

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