Spectroscopic investigation of size-dependent CO₂ binding on cationic copper clusters: analysis of the CO₂ asymmetric stretch

Photofragmentation spectroscopy, combined with quantum chemical computations, was employed to investigate the position of the asymmetric CO₂ stretch in cold, He-tagged Cu_n[CO₂]⁺ (n = 1-10) and Cu_n[CO₂][H₂O]⁺ (n = 1-7) complexes. A blue shift in the band position was observed compared to the free CO₂ molecule for Cu_n[CO₂]⁺ complexes. Furthermore, this shift was found to exhibit a notable dependence on cluster size, progressively redshifting with increasing cluster size. The computations revealed that the CO₂ binding energy is the highest for Cu⁺ and continuously decreases with increasing cluster size. This dependency could be explained by highlighting the role of polarization in electronic structure, according to energy decomposition analysis. The introduction of water to this complex amplified the redshift of the asymmetric stretch, showing a similar dependency on the cluster size as observed for Cu_n[CO₂]⁺ complexes.