Adsorption and thermal reactivity of dimethyl trisulfide on a Au(111) single-crystal surface

We investigated the adsorption and thermal reactivity of dimethyl trisulfide (DMTS, CH₃SSSCH₃) on a Au(111) single-crystal surface. X-ray photoelectron spectroscopy results indicated that at exposure temperatures of 100–300 K, DMTS dissociatively adsorbed as CH₃S and CH₃SS. That the dissociative adsorption rate was independent of exposure temperature suggested that DMTS dissociation on Au proceeded without an energy barrier at >100 K. In contrast, the thermal reactions of the adsorbed CH₃S and CH₃SS varied strongly with formation temperature. Specifically, after CH₃S and CH₃SS formed on Au(111) at 100 K, increasing the temperature resulted in associative desorption of CH₃S as dimethyl disulfide (CH₃SSCH₃) and coupling reaction of CH₃SS to ethane and atomic sulfur. In contrast, after CH₃S and CH₃SS formed at 150 K, increasing the temperature resulted not only in these two reactions but also in production of dimethyl disulfide and atomic sulfur by reaction between CH₃S and CH₃SS. At formation temperatures of 200 and 300 K, the only reaction observed was that between CH₃S and CH₃SS. These results suggest that the surface structure of the adsorbed species formed by DMTS dissociation on Au(111) depended on formation temperature. Specifically, at 100 K, dissociation of DMTS resulted in formation of CH₃S and CH₃SS islands on the Au(111) surface, whereas the two species were randomly adsorbed at higher formation temperatures.