Theoretical studies of aliphatic thiols adsorbed on metal surfaces and an UHF method with spin--orbit operators

Abstract

The C-S stretching frequencies of the thiol and the thiolate appear in a similar region in Raman and IR spectra and that of the thiol in lower frequencies in SERS. We have calculated methanethiol and 1,2-ethanedithiol using ab initio methods. Thiolate interacts with water in solution, and forms a water complex. Because this water complex has higher C-S stretching frequency than the isolated thiolate, thiolate in solution has similar frequency with the neat thiol. When the thiol is chemisorbed on metal surfaces, on-top, bridge, and hollow sites are possible. Bridge site adsorption is more stable with the lower C-S frequencies than the on-top site in the present model calculation. A two-component Kramers`` unrestricted Hartree-Fock method (KUHF) has been developed for polyatomic molecules with closed shell and one open shell configurations. The present KUHF program utilizes the relativistic effective core potentials with spin-orbit operators at the Hartree-Fock (HF) level. This is an alternative to the Kramers`` restricted HF method (KRHF). Dissociation curves of HBr, HI, and $CH_3I$ molecules by the KUHF method have been obtained and compared with those from RHF, UHF, and KRHF calculations.