AVS 50th International Symposium
    Surface Science Wednesday Sessions
       Session SS-WeP

Paper SS-WeP1
High Temperature Catalytic Water Formation Studied with Laser-induced Fluorescence and Cavity Ringdown Spectroscopy

Wednesday, November 5, 2003, 11:00 am, Room Hall A-C

Session: Poster Session
Presenter: S. Hemdal, Goteborg University and Chalmers University of Technology, Sweden
Authors: S. Hemdal, Goteborg University and Chalmers University of Technology, Sweden
A. Johansson, Goteborg University and Chalmers University of Technology, Sweden
M. Forsth, Goteborg University and Chalmers University of Technology, Sweden
M. Andersson, Goteborg University and Chalmers University of Technology, Sweden
A. Rosen, Goteborg University and Chalmers University of Technology, Sweden
Correspondent: Click to Email
Catalytic reactions are successfully studied with Laser-Induced Fluorescence (LIF) and valuable information about mechanisms and reaction paths can be obtained. However, due to the infamous quenching problem absolute concentrations are difficult to measure. Knowledge of exact concentrations of reactants and intermediates are valuable for successfully doing simulations. Cavity RingDown Spectroscopy (CRDS) is a laser absorption method suitable to measure exact concentration of reaction intermediates in trace amounts. In this study we have combined LIF and CRDS to study OH radicals in the water formation reaction desorbing from polycrystalline palladium and platinum catalysts. In CRDS a laser pulse is injected between two highly reflective mirrors that constitute the optical cavity. In each roundtrip some light will leak out and be detected as a function of time. Assuming single exponential decay, the ring down time @tau@ is defined as the time it takes for the intensity of the detected light to decrease to 1/e of its original intensity. By comparing the ring down times for on and off a resonant transition in the OH molecule, the number density can be obtained. The temperature of the catalyst was set to 1500 K, the pressure varied between 7 and 26 Pa and the flow was 100 SCCM. In this study we have successfully detected OH in the H@sub 2@/O@sub 2@ reaction with CRDS and calibrated the LIF profiles. From the CRDS data we have also calculated the rotational temperature of the OH molecule. The quenching rate for OH is also analysed.