The sticking of H₂(v = 1, J = 1) on Cu(100) measured using laser-induced thermal desorption

Abstract

The sticking of vibrationally excited H₂ on Cu(100) is measured using molecular beam techniques and stimulated Raman scattering for state preparation. Laser Induced Thermal Desorption (LITD) is developed to measure surface hydrogen coverage by calibration with known H-coverages. We find that LITD can be effectively used to measure adsorbed hydrogen concentrations with a sensitivity of better that 1% of a monolayer. Sticking coefficients of H₂ are determined from the ratio coverage to exposure. Measurements are made for H₂ incident translational energies in the range of 74–189 meV. For the first excited vibrational state, we find and an upper limit of the H₂ sticking coefficient to be 0.065 at E _i = 74 meV and 0.17 at E _i = 189 meV. These limits imply that previous measurements of loss of H₂(v = 1) upon scattering from Cu(100) cannot be predominately a result of dissociative adsorption. The results are broadly consistent with results determined from quantum-state resolved measurements for recombinatative desorption and the principle of detailed balance for H₂ from Cu(111).

Keywords:

• sticking coefficient
• hydrogen
• copper

Acknowledgements

We gratefully acknowledge support of this project under Grant No. CHE-0238224 and CHE-0718886 from the National Science Foundation.