An advanced molecular-beam surface-scattering apparatus for studies under extreme conditions
Final Report Abstract
This new instrument which uses ion and velocity map imaging to study molecular beam-surface scattering. The surface and the detection plane are perpendicular, allowing the scattering speed and angular distributions to be extracted from a single image. The ability to deconvolute the molecular velocity distribution from the arrival time distribution at the detection laser allows a range of experiments to be performed using a single laser that previously needed tagging experiments with two lasers and molecules with suitable intermediate states. We have used this new instrument to A. Measure the desorption kinetics of CO on Pd(111) and Pt(111) and obtain activation energies of desorption. We also show our first velocity map imaging (VMI) results for water scattering from Pt(111). B. Measure the reaction kinetics for the CO oxidation on Pt(111), Pt(332) and Pd(111). We demonstrate the measurement of CO oxidation rates at step edges and at terraces on a Pt(111) surface. We see that reactions at terraces produce CO2 exhibiting hyperthermal speed and narrow angular distributions, while reactions at steps pro-duce CO2 with thermal speed and broad angular distributions. This settles the long standing “two channel question” in this important reaction. Improved understanding of active sites in catalytic CO oxidation is important to a host of applications including the mediation of pollutants in combustion and the operation of hydrogen fuel cells. C. Measure the reaction kinetics of the H2 oxidation on Pt(111). In spite of the very low number of steps on this surface (0.25 %) we are able to demonstrate that this reactions proceed entirely on steps signifying the importance of surface defects in surface chemical reactivity.
Publications
- Using ion imaging to measure velocity distributions in surface scattering experiments. Journal of Physical Chemistry A Volume: 119 Issue: 50 Pages: 12255-12262; Special Issue: SI; Dec 17, 2015
Harding, DJ; Neugebohren, J; Hahn, H; Auerbach, DJ; Kitsopoulos, TN; Wodtke, AM
(See online at https://doi.org/10.1021/acs.jpca.5b06272) - Ion and velocity map imaging for surface dynamics and kinetics. Journal of Chemical Physics Volume: 147 Issue: 1, Jul 7, 2017
Harding, Dan J.; Neugebohren, Jannis; Hahn, Hinrich; D. J. Auerbach,a,b T. N. Kitsopoulos and Alec M. Wodtke
(See online at https://doi.org/10.1063/1.4983307)
