Search for the quantum delocalization of hydrogen on solid surfaces

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Dynamics of hydrogen as the lightest atom is inherently quantum-mechanical in nature, and its adsorption state on a metal surface has been proposed to be delocalized over the surface. The purpose of the present project is to explore the possibility of quantum delocalization of hydrogen adsorbed on pure metal and alloy surfaces. In order to achieve this, we have developed a new technique of zero-point vibrational spectroscopy using the ^1H(^<15>N,αy)^<12>C resonance nuclear reaction. Since the conventional spectroscopic techniques measure the excitation from the ground to the first-excited state, characteristics of the vibrational ground state are not yet clarified experimentally to date. With this zero-point vibrational spectroscopy combined with other experimental and theoretical methods, we have found the following results:1. The zero-point vibrational energy of H on Si(111) in the perpendicular and parallel directions is 123.4±4.6 and 44.6±6.2 meV, respectively, which are consistent with harmonic potentials.2. The zero-point energy obtained for Pt(111)-H is 80.8ア3.9 and 62.1$ア6.0 meV for perpendicular and parallel directions, respectively, which indicate that the stretching mode is harmonic, while the bending mode is strongly anharmonic.3. The potential energy surfaces for H on Pt(111) obtained from first-principles electronic structure calculation are strongly anharmonic, which are qualitatively consistent with the experimental results. 4. The zero-point energy of H adsorbed on Pt(lll)-2x2-Sn is 75 and 57 meV for perpendicular and parallel directions, which are similar to the values measured for Pt(111)-H.