Quantum state-resolved studies of sticking and elastic scattering of H₂ from Cu(100)

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Kim, Jonghyuk

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The sticking and elastic scattering of vibrationally excited H2 from Cu(100) were studied using Laser Induced Thermal Desorption (LITD), laser spectroscopy, and molecular beam techniques. The scattering of H2 from Cu(100) has been the subject of numerous experimental and theoretical stud ies. There is general agreement between theory and experiment for elastic scattering results but not in sticking or inelastic scattering measurements. LITD is developed to measure the H/Cu(100) coverage and to deter mine the sticking coefficients. For the ground vibrational state, the H2 sticking coefficient is 1.2±0.4×10−4 at Ei = 74 meV and ≤ 2.5±0.6×10−4 at Ei = 189 meV. For the first excited vibrational state, the upper limit of the H2 sticking coefficient is 0.065 at Ei = 74 meV and 0.17 at Ei = 189 meV. The kinetic energy transfer during the elastic scattering of H2(v = 1,j = 1) from Cu(100) increased rapidly from ∆E = 3.1±.16 meV at Ei = 74.7 meV to ∆E = 29.5±.04 meV at Ei = 122 meV and ∆E = 54.3±.25 meV at Ei = 189 meV. This trend is hard to explain using classical mechanics and may show an electronic friction effect. The survival probabilities in the elastic scattering branch were dropped from 0.97 to 0.56 with increasing incident kinetic energies.