Ultraviolet photoelectron spectroscopic and thermal desorption studies of the chemisorption and decomposition of benzene, cyclohexadiene, cyclohexene and cyclohexane on W(100)

Abstract

The chemisorption and decomposition of the cyclic hydrocarbons, viz. benzene, 1,4 (and 1,3) cyclohexadiene, cyclohexene and cyclohexane on a W(100) surface at 300 K have been investigated using ultraviolet photoelectron spectroscopy and thermal desorption studies. The hydrocarbons all decompose on the surface to give an adsorbed layer of hydrogen and the same molecular species. Increase in exposure to the hydrocarbon results in a monotonic increase in the surface concentration of the molecular fragment, while the surface concentration of the adsorbed hydrogen, in the case of the unsaturated hydrocarbon, first increases and then decreases so that at saturation coverage only the molecular species remains on the surface. On heating the adsorbate covered surface the molecular species decomposes and hydrogen is found to be the only observable desorption product while the surface is left with an adsorbed layer of carbon. The nature and bonding of the molecular fragment are also discussed.