Illustrative direct ab initio calculations of surface Raman spectra.
Illustrative ab initio calculations of Raman spectra of pyridine (Pyr) and pyridine in metal-molecule complexes with silver (Ag+-Pyr, Ag5+-Pyr) have been undertaken. The Raman spectra were computed numerically in the standard Placzek approximation with the additional feature of a static external electric field, F, perturbation to the system Hamiltonian. F was allowed to change the system equilibrium geometry and symmetry as well as the polarisability, resulting in shifted vibration frequencies and changed Raman intensities. All calculations were done on a Hartree-Fock (HF) level using the 6-31+G* or the Sadlej p-VTZ basis sets for Pyr, and the Stevens Krauss (SBKJC) VDZ ECP basis set for Ag. Raman enhancement factors over 5 orders of magnitude were obtained. The enhancement was analyzed as being due to polarization and charge transfer induced by the metal-molecule contact in the absence of F and in the presence of a strong F as due to increased polarisability derivatives along the surface normal. The use of the present method to qualitatively and quantitatively predict surface Raman spectra is discussed.
Department of Applied Physics, Chalmers University of Technology, SE-41296 Göteborg, Sweden. patrikj@fy.chalmers.se
Patrik
P
Johansson
D008670:Metals / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D011725:Pyridines / Q000737:chemistry*; D013059:Spectrum Analysis, Raman / Q000379:methods*; D014732:Vibration
D008670:Metals; D011725:Pyridines; C023666:pyridine