Interaction of Cu cluster anions (Cu-n, n = 8–11) with oxygen

Abstract

Abstract. The reaction of oxygen with Cu cluster anions consisting of 6-11 atoms was studied by means of Time-of-Flight mass (TOF) spectroscopy and Ultraviolet Photoelectron Spectroscopy (UPS). Using molecular oxygen, we found that a Cu − n cluster (n = 6−11) can react only with one single oxygen molecule, which adsorbs molecularly, implying that the clusters studied here are less reactive towards oxygen chemisorption compared to the smaller clusters (n < 5). This result indicates that chemical properties can alter significantly with increasing cluster size. Depending on the cluster source conditions, different cluster structures and reactivity patterns were found. These results are used to qualitatively describe the chemisorption energetics of oxygen on Cu cluster anions. PACS

Interaction of Pd cluster anions (Pdn -, n < 11) with oxygen

“…For Au, a similar even-odd pattern for the oxygen uptake can be observed in the cluster size regime below 21 atoms [5][6][7]. Cu cluster anions smaller than 5 atoms can dissociate molecular oxygen, whereas larger ones can show non-dissociative chemisorption of oxygen [8][9][10][11]. As a consequence of these unique chemical properties of small clusters, enhanced catalytic activities can often be found for smaller clusters, which are absent for the respective bulk materials.…”

Reactions of Size-Selected Copper Cluster Cations and Anions with Nitric Oxide: Enhancement of Adsorption in Coadsorption with Oxygen

“…As a result, NO can adsorb more strongly onto Cu n O 2 – than onto Cu n – . Furthermore, Cu 8 O 2 – and Cu 10 O 2 – have relatively small electron binding energies in the size range reported ( n = 6–10) , and have larger energy difference between the HOMO (or SOMO) of Cu n O 2 – and the SOMO of NO. This suggests that the 2π* antibonding orbital of NO contributes more to the bonding orbital between Cu n O 2 – ( n = 8 and 10) and NO, so that NO can easily dissociate after adsorption onto these clusters.…”

“…The energies of the highest occupied molecular orbital (HOMO) or SOMO of Cu n – and Cu n O 2 – are estimated from their electron binding energies. The electron binding energies of Cu n O 2 – ( n = 6–10) are 1.7–3.7 eV, , which are larger than those of the corresponding Cu n – . , This indicates that the orbital energy of the HOMO or SOMO of Cu n O 2 – is lower than that of Cu n – , and the bonding orbital between Cu n O 2 – and NO is more energetically stabilized than that between Cu n – and NO. As a result, NO can adsorb more strongly onto Cu n O 2 – than onto Cu n – .…”

Reactivity of Metal Clusters

“…As mentioned above (section ), spin excitations hold a key in determining cluster reactivity of metals with oxygen. In view of the triplet spin of molecule oxygen ( 3 O 2 ), Kima and co-workers performed a comparison of the reactivity of Cu clusters with molecular oxygen and atomic oxygen and showed that atomic oxygen is more reactive for Cu cluster anions. , Similarly, Schnöckel and co-workers found that the reaction rates of odd-numbered clusters obviously increased in the presence of singlet oxygen instead of triplet oxygen in its ground state. Figure gives an example of Al 13 – reacting with molecule oxygen ( 3 O 2 ) and singlet oxygen ( 1 O 2 ), respectively, along with an illustration of the spin conservation in Al cluster reactivity.…”