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).