Benzene adsorption on the Rh(111) crystal surface has been studied by HREELS, LEED, and TPD. The vibrational spectra indicate that benzene adsorbs molecularly at 300 K and is π-bonded to the surface with the ring plane parallel to the surface plane. Recent dynamic LEED calculations1 together with the angle-dependent HREELS studies reported here establish a C3υ(σd) bonding symmetry for the c(2√3 × 4)rect-C6H6 structure. Several other ordered benzene overlayers can be formed between 300 and 400 K depending on the benzene coverage. No large changes occur in the chemisorption bonding mode or geometry coincident with the two-dimensional ordering phase transitions in this temperature range. The vibrational spectra show that two molecular adsorption sites can be populated. Benzene adsorption is only partially reversible; less than 20% of the adsorbed benzene desorbs molecularly upon heating. The remaining benzene irreversibly decomposes, evolving hydrogen and leaving a carbon-covered surface. The TPD and HREELS data on Rh(111) and other single-crystal surfaces show correlations between the metal-benzene bond strength, the work function of the clean surface, and the frequency shifts of some of the molecular benzene vibrational modes.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry