SURFACE ENHANCED RAMAN SPECTROSCOPIC STUDIES OF SURFACE ORIENTATION OF PYRAZINE ADSORBED ON RHODIUM ELECTRODE Li Cui, Bin Ren, De-Yin Wu, Zhong-Qun Tian* Department of Chemistry, State Key Lab. for Phys. Chem. of Solid Surfaces, Xiamen University, Xiamen 361005, China, zqtian@xmu.edu.cn Keywords: SERS, adsorption, rhodium, pyrazine, orientation Abstract: Surface enhanced Raman spectroscopic study of pyrazine adsorbed on a roughened rhodium electrode was carried out. The effect of solution pH value, the pyrazine concentration and electrode potential on the adsorption behavior of pyrazine on the Rh surface has been investigated. Surface enhanced Raman scattering (SERS) spectroscopy is a very powerful technique for studying the orientation and bonding of molecules on metal surfaces with its high spectral resolution. As a high symmetric molecule, pyrazine has been extensively used to probe the properties of surface because of its relative simple molecular structure and widely accepted assignment of its vibrational modes. However, it has been found out that the adsorption configurations of pyrazine on different metal surfaces (Ag, Au and Ni) are quite different [1-3]. Therefore, it is worthwhile to investigate the adsorption behavior of pyrazine on other transition metal surfaces, such as Pt and Rh. In our previous study, a surface pretreatment procedure has been developed to obtain SERS-active Rh surfaces, presenting an enhancement of about 3 orders of magnitude [4]. On such kind of substrate, we are able to investigate the adsorption behavior of pyrazine by Raman spectroscopy. Fig.1 shows the SERS spectra of pyrazine adsorbed on a rhodium electrode in 10 -3 M pyrazine + 0.1 M NaClO 4 . Four pairs of overlapping bands are observed , located at about 1570 cm -1 and 1530 cm -1 ;1212 cm -1 and 1236 cm -1 ;1012 cm -1 and 1040 cm -1 ;628 cm -1 and 654 cm -1 . The overlapping bands have not been reported in SERS spectra of pyrazine on Ni, Au, Ag, Cu electrode surface. By carefully comparing the change of the relative intensity of these overlapping bands, we will see that the intensities of 1570 cm -1 , 1212 cm -1 , 1012 cm -1 and 628 cm -1 (denoted as Peak I) present nearly 400 800 1200 1600 -0.8 V 1232 1209 1564 1529 0 V -0.2 V -0.3 V -0.5 V -0.7 V -0.9 V -0.95 V 50 cps Raman shift/cm-1 400 800 1200 1600 a 1040 1013 1233 1213 1532 1567 1023 1219 1593 50 cps -0.9 V -0.7 V -0.6 V -0.4 V -0.2 V 0 V Raman shift/cm-1 Fig.1 Potential dependent SERS spectra of pyrazine adsorbed on a roughened rhodium electrode in a solution containing 0.001 M pyrazine + 0.1 M NaClO 4 , pH = 7. (a) Potential change from 0 V b 254