In situ ATR-FTIR spectroscopy has been extended to the study of CO and pyridine adsorptions at crystalline and amorphous Ni-P alloy film electrodes, with an emphasis on the alloying effect of P on their adsorption configurations on Ni sites. The Ni-P films were prepared with initial seeding of a catalytic Pd layer on Si, followed by chemical deposition. Transition from bridge-bonded CO (COB) dominant to linearly bonded CO (COL) dominant adsorption was found with increasing P content, together with a blue-shift in the COL vibrational frequency and an attenuation of the Stark tuning rate Of COL. As for Py on Ni-P electrodes, essentially the N-end-on adsorption was revealed, in contrast to the edge-tilted adsorption on Ni electrode. Modification in the adsorption configurations as compared to that on Ni electrode is ascribed mainly to the site-blocking effect with alloying P, rather than to partial electron transfer between Ni and R (C) 2008 Elsevier Ltd. All rights reserved.