Experimental study of the chemisorbed state of ${\mathrm{C}}_2$ ${\mathrm{H}}_2$ , ${\mathrm{C}}_2$ ${\mathrm{H}}_4$ , and ${\mathrm{C}}_2$ ${\mathrm{H}}_6$ on noble-metal surfaces

A systematic study of the near-edge x-ray-absorption fine structure for single-layer coverage of ${\mathrm{C}}_2$ ${\mathrm{H}}_2$, ${\mathrm{C}}_2$ ${\mathrm{H}}_4$, and, for the first time, ${\mathrm{C}}_2$ ${\mathrm{H}}_6$ chemisorbed on Cu(100) and Ag(100) allows the determination of the molecular orientation and bonding strength. The first surface extended x-ray-absorption fine structure at the carbon K edge yields the nearest-neighbor distance to be 1.9(1) Å for ${\mathrm{C}}_2$ ${\mathrm{H}}_2$ and ${\mathrm{C}}_2$ ${\mathrm{H}}_4$ on Cu. A comparison of the σ shape-resonance position in the gas phase, chemisorbed on Ag, Cu, and Pt, is presented.