CH Vibration Softening and the Dehydrogenation of Hydrocarbon Molecules on Ni(111) and Pt(111)

High-resolution electron energy-loss measurements of ethylene on Ni(111) and cyclohexane on Ni(111) and Pt(111) show an extra CH stretching vibration---not found in free molecules or organometallic compounds---which is strongly broadened and shifted to lower frequencies relative to another, more typical CH stretching vibration. This softened and broadened CH frequency is attributed to a new electronic interaction with the surface which we relate to the mechanism of hydrocarbon dehydrogenation.