IR Intensities of CO Molecules Adsorbed on Atop and Low-Coordinate Sites of Pd Nanoparticles: Analysis Using Natural Perturbation Orbitals

The natural perturbation orbital (NPO) computational method was applied to the analysis of infrared (IR) intensities of CO molecules adsorbed on the surfaces of Pd nanoparticles. Enhancement of the IR intensities for a CO bonded to a single low-coordinate metal adsorbed on the metal surface (lowcoordinate model) was compared with those for a CO bonded directly to the metal surface (atop model). This enhancement was ascribed to the mixing between occupied and virtual orbitals induced by molecular vibrations. The occ-virt term, representing this mixing, was efficiently decomposed into contributions from three NPO pairs (sigma(z) - sigma(z)*, pi(x) - pi(x)*, and pi(y) - pi(y)*) for each model. The main contributors were the pi(x) - pi(x)* and pi(y) - pi(y)* pairs, which were localized around CO in the atop model, but delocalized throughout the Pd cluster in the low-coordinate model. This variance in orbital delocalization comes from differing interactions between Pd and CO in the atop and low-coordinate models.

Automated summary

The NPO computational method was applied to analyze the IR intensities of CO molecules adsorbed on Pd nanoparticles, revealing different interaction mechanisms between CO and metal surfaces under different adsorption models.