Computational study of electronic, spectroscopic and chemical properties of Cun(n=2-8) nanoclusters for CO adsorption

First-principle calculations were carried out to investigate the adsorption of CO over Cun nanoclusters. The structural, spectroscopic and electronic properties like optimized geometries, HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energy levels, binding energy, adsorption energy, vibrational frequency and density of states (DOSs) of the pure Cun nanoclusters, and CunCO complexes in their ground state were thoroughly analyzed. The CO adsorbed on the Cun nanoclusters showed a stretch frequency at 1950-2052 cm-1, which was red-shifted relative to that of gas-phase CO (2143 cm-1). This red-shift was believed to arise from the charge transfer from the Cu metal d states to the CO antibonding 2π* level. The CO adsorption on the Cu nanoclusters was chemisorption in nature with the Cu–C bond length (adsorption height) in the range of 1.85-1.92 Å.