Regensburg 1998 – scientific programme

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O: Oberflächenphysik

O 11: Poster (I)

O 11.81: Poster

Monday, March 23, 1998, 19:30–22:30, Bereich C

Investigations of heterogeneous CO oxidation using sum frequency generation — •Uwe Metka, Helmut H"arle, Hans-Robert Volpp, L"uko Willms, and J"urgen Wolfrum — Physikalisch Chemisches Institut der Universit"at Heidelberg, INF 253, D-69120 Heidelberg

Infrared-visible sum frequency generation (SFG) spectroscopy was used to detect CO molecules adsorbed on a platinum surface during heterogeneous CO oxidation at temperatures from 293 to 350 K and at a pressure of 1 mbar. SFG is a second-order nonlinear optical process in which a tunable infrared laser beam is mixed with a visible laser beam to generate a sum frequency signal. In the electric dipole approximation this process is only allowed in a medium without centrosymmetry. Therefore in the gas/Pt system the signal is dominated by a contribution from the surface layer, where inversion symmetry is necessarily broken. Thus the detected CO SFG signal originates principally from adsorbed molecules. A mode-locked Nd:YAG laser system with an optical parametric system was used for the optical measurements. The SFG experiments were carried out in a reaction chamber in which in situ cleaning of the platinum crystal via heating and argon ion sputtering in ultra-high vacuum was possible. The Pt crystal could be cooled using liquid nitrogen and resistively heated up to 1500 K. Investigations were done under reactive flow conditions to allow comparison of the experimental results with numerical simulations.