IN-SITU PHOTOACOUSTIC INVESTIGATION OF THALLIUM UNDERPOTENTIAL DEPOSITION ON POLYCRYSTALLINE COPPER ELECTRODES

Photoacoustic spectrometry (PAS) was used as an ancillary in-situ tech nique for the investigation of underpotential deposition (UPD) of thal lium on polycrystalline copper. The PAS signal generated by 605 nm rad iation was found to increase upon deposition of Tl on Cu. Since underp otential deposition is generally a monolayer event, the limit of detec tion obtained for this technique was estimated to be 0.05 of a monolay er. The PAS results support the conclusion that the second UPD peak is due to a second discrete monolayer rather than a filling-in of vacant sites in the first monolayer. The use of PAS to study the thallium sy stem at pH 12 confirmed that removal of Cu2O from the electrode surfac e occurred at a sufficient rate that it did not interfere with the UPD of thallium.