Molecular beam translational spectroscopy of physisorption bound states of molecules on metal surfaces. I. HD on Cu(111) and Au(111) single crystal surfaces

A new method for studying resonances in the scattering of molecules from metal surfaces is presented. In the experiment the velocity distribution of specularly scattered molecules with an initially broad distribution is analyzed with a time-of-flight technique and reveals sharp dips and peaks with a width of <0.25 meV attributed to Feshbach resonances. The present results for HD–Cu(111) and HD–Au(111) are analyzed by comparison with a close coupling calculation to provide potential well parameters. The method has been used to study the surface temperature dependence of one of the resonances down to 40 K and provides insight into a possible elementary step in physisorption.