The reactions of methanethiol (CH3SH) on clean, sulfur-covered, and oxygen-
covered Fe(110) have been investigated by X-ray photoelectron spectroscopy,
temperature-programmed reaction spectroscopy, and low-energy electron diff
raction. On clean Fe(110), the S-H bond in methanethiol breaks below 100 K,
affording methylthiolate (CH3Sa) and H-a. Heating to 600 K results in C-S
bond cleavage near 290 K, leading to the evolution of methane and dihydroge
n, and a p(2 x 2) sulfur overlayer. On the oxygen-covered surface (theta(O)
= 0.25 ML), adsorbed methylthiolate and hydroxyl are formed. The amount of
irreversible thiol reaction is essentially the same on the O-covered and c
lean Fe(110) surfaces. The amount of irreversibly bound thiol is reduced by
approximately half on the (2 x 2)-S overlayer (Bs = 0.25 ML). The C-S bond
in methylthiolate is stabilized more by surface sulfur than by surface oxy
gen, based on the methane formation temperature shifts of +55 and +20 K, re
spectively. Oxygen coverages greater than 1 monolayer form an FeO thin film
, weakening the interaction of methanethiol with the surface, further reduc
ing the methane yield which now reacts above 400 K.