Vibrations of CO on strained Cu(100) surfaces. A cluster model analysis

The dependence of the vibrational stretching frequency, ωe, of CO adsorbed on compressed or expanded Cu(100) layers has been studied theoretically by means of ab initio cluster model wavefunctions. It is found that even moderate changes in the surface distances result in measurable shifts in ωe(CO) with an almost linear dependence of the ω shift on the CuCu distance. This is primarily due to a change in the back-donation from the surface to CO. It is also found that strain within the Cu layers is much more important that changes in the inter-layer spacing in determining the effect.