Infrared reflection absorption spectroscopic study of adsorption structure of self-assembled monolayer film of trithiocyanuric acid on evaporated silver film

The self-assembled monolayer film of trithiocyanuric acid (TCA) on evaporated silver films was characterized by using FT-IRAS and ab initio DFT calculation. Three hydrogen atoms in the most stable geometry of TCA tautomers were bonded to nitrogen atoms in the cyanuric ring. Observed IR bands for TCA in KBr disc at room temperature suggested that the TCA has a trithione form as same as in Ar matrix at low temperature as already reported. TCA on silver substrate gave rise to the IRAS bands corresponded to a less stable trithiol form. The calculated frequencies of silver–TCA complex that took a trithiol form with two silver atoms showed in a good agreement with the observed IRAS bands of TCA on silver substrate, on the other hand of silver–TCA complex that took a trithione form did not. The adsorption structure of TCA on evaporated silver film became obvious that TCA adsorbed to the surface through the two sulfur atoms and changed to a trithiol form from trithione form.