Brewster Angle Reflectometry (BAR) and spectral photocurrent analysis show that Au nanoparticles are in a resonant state during light-induced hydrogen evolution with unpolarized light near-normal incidence. Keggin-type phosphododecamolybdate (PMo 12 O 403- ) anions were used as reducing and stabilizing agents to form novel Au nanoparticles (Au-NPs). BAR was employed to analyze the resonant optical response after adsorption to the surface of hydrogen terminated p-Si(111):H (1 × 1) and SiO 2 . Proton reduction in 1 M H 2 SO 4 occurs at asymmetric Au-NPs where also multipole field effects influence the plasmonic behaviour. In a comparative discussion, the contribution of surface plasmon polariton excitation to the observed pronounced photocurrent enhancement is outlined. © 2010 Elsevier B.V.