Dimethyl disulfide on Cu(111): From nondissociative to dissociative adsorption

Adsorption of dimethyl disulfide (CH₃SSCH₃) on Cu(111) was investigated using the density functional theory method. This computational work clarifies some hitherto unclear issues about nondissociative adsorption of CH₃SSCH₃. In addition, the work charts the reaction pathways and relevant transition states about CH₃SSCH ₃ dissociation. Briefly, our results show that trans-CH ₃SSCH₃ is 0.5 eV more stable than its cis-isomer in gas phase, and the domination of the trans-isomer in population is maintained for CH₃SSCH₃/Cu(111) as its adsorption energy of 0.42 eV is 0.23 eV higher than that of the cis-isomer. Our calculations also clarify that trans-CH₃SSCH₃ nondissociatively chemisorbed on the top sites of Cu(111), with the S-S bond aligning along the nearest Cu-Cu bond. The details of these and other adsorption properties are further elaborated with our computational electronic structures and simulated scanning tunneling microscopic images. In addition, our reaction dynamics analysis shows that the dissociation of trans-CH₃SSCH₃ to form CH₃S/Cu is barred by an activation barrier of 0.21 eV, but since it is exothermic by 1.1 eV, the dissociation can proceed although the surface temperature cannot be too far below room temperature. This explains the experimental findings that intact trans-CH₃SSCH₃ is the only product for CH ₃SSCH₃/Cu(111) at 5 K and implies that the experimentally observed CH₃SSCH₃ dissociation at 150 K was probably influenced by other factors such as the presence of intrinsic surface defects.