IR Signature of Size-Selective CO₂ Activation on Small Platinum Cluster Anions, Pt_n ^- (n=4-7)

Infrared multiple photon dissociation spectroscopy (IR-MPD) has been employed to determine the nature of CO₂ binding to size-selected platinum cluster anions, Pt_n ^- (n=4-7). Interpreted in conjunction with density functional theory simulations, the results illustrate that the degree of CO₂ activation can be controlled by the size of the metal cluster, with dissociative activation observed on all clusters n≥5. Of potential practical significance, in terms of the use of CO₂ as a useful C1 feedstock, CO₂ is observed molecularly-bound, but highly activated, on the Pt₄ ^- cluster. It is trapped behind a barrier on the reactive potential energy surface which prevents dissociation.