A Study of the Orientatlon and Bonding of Thiophene on Clean Mo ( 100 ) Using Angle - Resolved Ultraviolet Photoelectron Spectroscopy

We have examined the bonding and orientation of thiophene on Mo(100) following chemisorption at 180 K. At these temperatures, thiophene adsorbs predominantly molecularly, and a shift in the binding energy of peaks due to molecular a-orbitals in the photoelectron spectrum suggests that at least part of the bonding of the thiophene molecule to the surface involves these orbitals. Measurements of the variation in intensity of thiophene photoemission peaks as a function of angle of incidence of the radiation suggest that the molecular plane is tilted at 25 & 5 O with respect to the surface normal. These observations suggest a bonding configuration in which thiophene chemisorbs into a fourfold site. This geometry explains the regiospecific hydrogen abstraction seen for thermal decomposition of thiophene on Mo( 100) in which the a-hydrogen is preferentially removed.