Effectiveness of the infrared reflection-absorption spectroscopy (IR-RAS) using transparent electrodes made of Ga-doped ZnO as metal substrates has been demonstrated. For a merocyanine dye with and without a metallic cation, differences in the IR-RAS spectrum have been clearly observed, even when the quantity of the material is restricted to the monolayer level. Referring to the visible transmission spectra of the samples, which can be measured thanks to the transparency of the substrates, chelation of the metallic cation by the carboxyl group belonging to a dye molecule and the keto group belonging to an adjacent dye molecule has been regarded as a promising candidate for the J-aggregation driver. (C) 2009 Elsevier B.V. All rights reserved.