The CO-H interaction on Pt(1Â 1Â 1) studied using temperature programmed vibrational sum frequency generation

We have studied the interaction between CO and H on Pt(1 1 1) 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 ∼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.