The adsorption of six-membered hydrocarbon cycles and cyclopentane and the interaction of hydrogen with the adsorbed layer on polycrystalline Pt-foil have been studied. The work function change (Delta phi) was followed by a Kelvin probe and the C/Pt peak ratio was determined by Auger electron spectroscopy. Combining these two techniques made it possible to distinguish between chemisorption via sigma-bonds and pi-complex formation. Benzene and toluene adsorbed first as pi-complex while cyclohexane showed initially a partial aromatization and a pi-complex-like bonding to the surface. Excess hydrocarbon or addition of hydrogen transformed the pi-complex into Q-bonded species. Cyclopentane adsorbed via Q-bonds and showed no significant hydrogen effect. (c) 2005 Elsevier B.V. All rights reserved.