Not Completely Innocent: How Argon Binding Perturbs Cationic Copper Clusters

Abstract

Argon is often considered as an innocent probe that can be attached and detached to study the structure of a particular species without perturbing the species too much. We have investigated whether this assumption also holds for small copper cationic clusters and demonstrated that small but significant charge transfer from argon to metal changes the remaining binding positions, leading in general, to weaker binding of other argon atoms. The exception is binding to just one copper ion, where the binding of the first argon facilitates the binding of the second.

IR spectroscopic characterization of the co-adsorption of CO2 and H2 onto cationic Cun+ clusters

“…† We have found that production of Cu n + (n = 1-4) in the presence of only a helium carrier gas yields significant signals for n r 4; the production of larger Cu n + clusters is facilitated by admixing a few % of Ar into the helium carrier gas. Since Ar readily binds to Cu n + clusters, and especially so for the smaller clusters where the total charge is distributed over only a few atoms as was shown in our previous work, 50,60 a competition between complexation of Cu n + with Ar and CO 2 results in a rather complex mass spectrum, with substantial mass overlap for the smaller cluster sizes. This overlap prevents us from completely disentangling depletion and growth for n o 7.…”

“…The binding energy of CO 2 to Cu 10 + in this species amounts to a mere 0.26 eV, which is only a little more than the Ar binding energy of 0.17 eV. 60 Its calculated spectrum is dominated by a strong band at 645 cm À1 , which is associated with the OQCQO bending motion. The bands at lower frequencies are the cluster vibrations, with little involvement of the CO 2 ligand, or the vibrations involving the CO 2 -cluster bond (below 70 cm À1 ).…”

“…For the whole mass range, we observe no significant binding of Cu n + with Ar, indicating that binding of CO 2 is preferred here and that the binding energy thus likely exceeds the 0.2 eV found for Ar. 60 The inset shows two mass spectra zoomed into the region of the Cu 10 + cluster, where the isotopic distributions of Cu 10 + , [Cu 9 , 2CO 2 ] + , and [Cu 10 , CO 2 ] + are visible. Upon resonant IR irradiation at a frequency of 657 cm −1 , the distribution without IR light (top trace) changes such that the intensity of the [Cu 10 , CO 2 ] + distribution reduces, coinciding with an increase of the Cu 10 + bare cluster distribution, as indicated with boxes and arrows in the bottom trace.…”

“…For the whole mass range, we observe no significant binding of Cu n + with Ar, indicating that binding of CO 2 is preferred here and that the binding energy thus likely exceeds the 0.2 eV found for Ar. 60 The inset shows two mass spectra zoomed into the region of the Cu , with k an unknown number of IR photons. In Fig.…”

Benchmarking density functional theory methods for modelling cationic metal–argon complexes

“…For AuArn + with n from 1 to 4, the Eads values are -0.53, -0.68, -0.05 and -0.06 eV (at TPSS level). We note that the adsorption energy of the second adsorbed Ar atom is higher than that of the first; such effect has been seen before for AuArn + and CuArn + complexes [16,50]. A much lower adsorption energy is observed from the third Ar atom onwards, corresponding to weaker bound Ar atoms, with the interaction dominated by dispersion forces instead of a covalent-type of bond.…”