Probing copper and copper-gold alloy surfaces with space-quantized oxygen molecular beam

Tsuda, Yasutaka   ; Gueriba, J. S.*; Ueta, Hirokazu*   ; Dio, W. A.*; Kurahashi, Mitsunori*; Okada, Michio*

The orientation and motion of reactants play important roles in reactions. The small rotational excitations involved render the reactants susceptible to dynamical steering, making direct comparison between experiment and theory rather challenging. Using space quantized molecular beams, we directly probe the (polar and azimuthal) orientation dependence of O chemisorption on Cu and CuAu. We observe polar and azimuthal anisotropies on both surfaces. Chemisorption proceeds rather favorably with the O-O bond axis oriented parallel ( perpendicular) to the surface, and also rather favorably with the O-O bond axis oriented along ( along ). The presence of Au hinders the surface from further oxidation, introducing a higher activation barrier to chemisorption, and rendering an almost negligible azimuthal anisotropy. The presence of Au also prevents cartwheel-like rotating O from further reactions.