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

Pyridine-d(5), adsorbed on Au(111), Au(100), and Au(110) electrodes in 0.1 M NaF solution containing pyridine-d(5) (2 mM) have been investigated by in situ IRAS. For the three electrodes, an in-plane ring symmetrical vibration due to vertically adsorbed pyridine was observed around 1558 cm(-1), which was accompanied by a decrease in the in-plane ring asymmetrical vibration at 1309 cm(-1) due to dissolved pyridine. For the low index electrodes, the behavior of the 1309 cm(-1) band intensities corresponding to the total amount of adsorbed pyridine agreed with the previous surface excess results obtained using chronocoulometry. The behavior of the 1558 cm(-1) band intensity for Au(111) and Au(100) was the same as that of the 1309 cm(-1) band, indicating that the N-bonded pyridine was present at all of the adsorption potentials. For Au(111) and Au(100): a new band appeared at 1550 cm(-1) for positive potentials, which was assigned to an in-plane ring symmetrical vibration, as in the 1558 cm(-1) case. We propose that the new band is due to the formation of an ordered domain of the N-bonded pyridine. For the Au(110) electrode, the adsorption behavior agreed with the previous surface excess results obtained using chronocoulometry. (C) 2001 Elsevier Science Ltd. All rights reserved.