Adsorption of 1,3-dithiol-2-thione-4,5-dithiolate on silver surface studied by surface-enhanced Raman spectroscopy

Adsorption of disodium 1,3-dithiol-2-thione-4,5-dithiolate (Na2dmit) on silver surface has been investigated by SERRS as well as FT-SERS techniques. The results show the dmit2- ion chemisorbs through π-electrons assuming a flat orientation with respect to the surface. FT-SERS signals are very weak when dmit2- is adsorbed on silver colloids whereas very strong signals are observed on chemically deposited silver films. The strong enhancement on silver films is attributed to the larger particle size, suggesting that electromagnetic mechanism is the major factor contributing to enhancement. Ab initio calculations are performed to aid in the interpretation of vibrational spectrum and frequency shifts upon adsorption of Na2dmit.