INTERACTION OF HALIDE AND HALATE IONS WITH COLLOIDAL SILVER AND THEIRINFLUENCE ON SURFACE-ENHANCED RAMAN-SCATTERING OF PYRIDINE WITH NEAR-INFRARED EXCITATION

The interactions between halide and halate ions and colloidal silver s urfaces are studied by surface-enhanced Raman spectroscopy (SERS) with excitation in the near-infrared (NIR) wavelength region. The interact ion strength of halide ions with silver surface decreases in the order I- > Br- > Cl- while the enhancements of the Raman modes of pyridine caused by addition of these ions range in the order of Cl- approximate to Br- > I-. ClO3- and BrO3- ions in silver colloids give rise to SER S bands at about 226 and 158 cm(-1), respectively, while IO3- ions on colloidal silver surface result in two Raman bands at about 750 and 33 4 cm(-1). These results indicate that the interactions of ClO3- and Br O3- ions with silver surface are through their lone pair electrons of Cl and Br. Nevertheless, IO3- ions bond to silver surface through thei r negatively charged O-. The interaction strength of halate ions with silver are measured to be BrO3- > ClO3- approximate to IO3-. The enhan cements of the Raman modes of pyridine caused by addition of halate io ns increase in the order ClO3- < IO3- < BrO3-. These ions contribute n ot only to the electromagnetic enhancement but also to the chemical en hancement in the NIR-SERS. BrO3- ions are able to create about 2.2 and 3.7 Ones more surface active sites on colloidal silver surface than C lO3- and IO3- ions do. (C) 1997 Elsevier Science B.V.