In situ FTIR study of pyrazine adsorbed on Au(111), Au(100) and Au(110) electrodes

Pyrazine adsorbed on Au(111), Au(100) and Au(110) electrodes in 0.1 M NaF containing 5 mM pyrazine have been investigated by using in-situ infrared spectroscopy. For each of the three electrodes, an in-plane ring symmetrical vibration due to vertically adsorbed pyrazine was observed around 1045 cm(-1) which was accompanied by a loss in the in-plane ring asymmetrical vibration at 1419 cm(-1) due to dissolved pyrazine. For the Au(111), the behavior of the 1419 cm(-1) band intensities corresponding to the total amount of adsorbed pyrazine was coincident with previous results of the Gibbs surface excess investigated by using of chronocoulometry. The behavior of 1045 cm(-1) band intensity as a function of the applied potential was similar to that of the 1419 cm(-1) band for the Au(111) and Au(100). We propose that the tilt orientation is present at negative potentials and the Vertical orientation increases as the potential becomes more positive. For all the electrodes, a new band appeared around 1035 cm(-1) for positive potentials, which was assigned to an in-plane ring symmetrical vibration, as for the 1045 cm(-1) case. We propose that the new band is associated with some adsorption-behavior such as a change in the vertically adsorbed pyrazine orientation. (C) 2000 Elsevier Science Ltd. All rights reserved.