Two Adsorption States of C2H4 at Saturation Coverage on Pd(110)-(2x1)-H

The adsorption of C2H4 on Pd(110)-(2x1)-H at 160 K was studied by scanning tunneling microscopy and high-resolution electron energy loss spectroscopy. We found that two adsorbed species coexist at high coverage. The species were characterized by C-C stretching energies of 170 and 153 meV, which were identified as one-dimensional and c(2x2) domains, respectively. The latter species, which appeared only at high coverage, was bonded to the bare surface, which implied the possibility of H atom transition into the subsurface.