We have studied the interaction between CO and H on Pt(111) employing Temperature Programmed Vibrational Sum Frequency Generation. Pre-coverage of the Pt(111) crystal with hydrogen redshifts the atop CO stretch vibration by 7-8 cm(-1). Below 180 K an inhomogeneous broadening of the CO stretch vibration is observed. Both effects are attributed to hydrogen induced lateral displacement of atop CO. The inhomogeneous broadening is lifted in a thermally activated process, accompanied with a blueshift of the CO stretch vibration of similar to 1 cm(-1). Corroborated by DFT calculations we suggest that the latter is due to a small tilt of the CO molecule towards the H atom. (c) 2005 Elsevier B.V. All rights reserved.