Molecular orientation of hydroquinone adsorbed at a platinum(111) thin-layer electrode

Reported are new findings regarding the molecular orientation of hydroquino ne (HQ) adsorbed on Pt surfaces. The packing density of hydroquinone adsorb ed from 1 M HClO4 supporting electrolyte has been measured by use of a Pt(1 11) thin-layer electrode. The packing-density-vs-concentration profiles for hydroquinone, measured by a differential thin-layer electrode method at an ordered Pt(111) surface and at an electrochemically disordered Pt(111) sur face, are identical within an experimental error of about 8%. The profiles from this study are similar to the ones obtained previously at an ordered P t(111) surface by Auger spectroscopy, but they are significantly different from those reported previously for polycrystalline Pt thin-layer electrodes . A procedure based upon displacement of HQ by thiocyanate has been develop ed as an alternative method for determining the packing density of adsorbed HQ. Both methods afford information regarding the molecular state of HQ ad sorbed at the Pt(111) surface, (C) 1999 Academic Press.