Hydroquinone molecules were allowed to adsorb on Rh(1 1 1) and Pt(1 1 1) by vapor deposition. The strong interaction between two adjacent hydroxyl groups of neighboring molecules led to the formation of commensurate (root7 x root7)R19.1degrees and incommensurate (root2.56 x root2.56)R16degrees adlayer phases on Rh(1 1 1) and Pt(1 1 1), respectively. The formation processes of HQ adlayers on Rh(1 1 1) and Pt(1 1 1) were very different from each other, possibly due to the difference in lattice parameters of the two metal surfaces. (C) 2004 Elsevier B.V. All rights reserved.