The adsorption of NO on cationic Rh clusters, Rhn + (n = 6−16), was studied by IRMPD spectroscopy using FELIX in combination with DFT calculations. The IRMPD spectra show that NO adsorbs molecularly on an on-top site of Rhn + for all n studied, while for n = 7, 12, 13 and 14 evidence is found for second, bridging, adsorption site. Indeed, the DFT calculations suggest that molecular NO adsorption on a bridge site is more stable than on an on-top site for n = 7. Part of the NO adsorbs dissociatively on Rhn + , and the ratio of dissociative adsorption depends on the size, n. For Rhn + (n = 6, 8, 9), the dissociative form of NO is predicted more favorable than the molecular form by the DFT calculations, but experimentally observed ratios of dissociative adsorption were less than the prediction. The activation barrier existing between the molecular and dissociative adsorption was considered to hinder the NO dissociation. 20 ASSOCIATED CONTENT Supporting Information The supporting information is available free of charge on the ACS Publication website at DOI:_.

No abstract

No abstract

No abstract

Temperature-programmed desorption (TPD) experiments were performed on gas-phase manganese oxide cluster ions, namely, Mn(n)O(m)(+) (n = 3-20) and Mn(n)O(m)(-) (n = 3-18). These cluster ions were prepared by laser ablation of a manganese rod in the presence of oxygen gas, and their composition was investigated using mass spectrometry. The composition of Mn(n)O(m)(±) distribution lies above the m = (4/3)n line. When the cluster ions were heated to 1000 K, Mn(n)O(m)(+) (m = (4/3)n + δ, with δ = -1, 0) and Mn(n)O(m)(-) (m = (4/3)n + δ, with δ = 0, 1) was found to be the predominant species, formed by thermal dissociation. These experimental findings indicate that the nascent manganese oxide clusters comprise robust Mn(n)O(m)(±) (m/n ≈ 4/3) and weakly bound excess oxygen atoms. On the basis of the TPD experiments, the oxygen-molecule release was identified as the main dissociation channel. The temperature dependence of O2 desorption was found to be similar among the clusters with the same oxygen excess or deficiency regardless of the number of Mn atoms. The threshold energy of O2 desorption was estimated for Mn4O(m)(+) (m = 6-11) and compared with bond dissociation energies calculated by density functional theory.

Adsorption of NO molecules on gas phase cobalt cluster ions, Con(+) (n = 4-9), was investigated in thermal equilibrium with He gas at 300 K. The Con(+) clusters, contrary to the isolated clusters in a vacuum, adsorbed NO without undergoing significant dissociation. Thermal desorption spectroscopy of Con(+)(NO)m indicated that Con(+) clusters with n = 4-6 and n = 7-9 can have four and six adatoms chemisorbed, respectively. Reduction of NO occurred, releasing N2 molecules, to form Con(+)Ok(NO)m-k (k = 2, 4, ...). The reaction mechanism involved the exchange of chemisorbed N atoms with the O atom in NO bound to the clusters. The reactivity of Con(+) (n = 4-9) exhibited periodic n dependence, and Co6(+) and Co9(+) was similar to the case of the isolated Co16(+) clusters holding up to eight adatoms reported by Anderson et al. ( J. Chem. Phys . 2009 , 130 , 10992 - 11000 ).

Vibrational spectra of Rh 7 O m + (m = 4−7, 12, 14) were measured in the 300−1300 cm −1 range via infrared multiple photon dissociation (IRMPD) spectroscopy. For the oxygen poor cluster sizes, Rh 7 O m + (m = 4−7), IRMPD spectra were recorded through photodissociation of Rh 7 O m + −Ar complexes. IR spectra for Rh 7 O m + (m = 12, 14) were recorded via the release of an O 2 molecule from Rh 7 O m + producing Rh 7 O m−2 + ; no O 2 loss was observed from Rh 7 O m + (m = 4−7, 8, 10). By comparison with the calculated vibrational spectra of several stable isomers obtained using density functional theory, these IR spectra are assigned to geometrical structures. For m = 4−7, all O atoms are bound to Rh atoms only, with a transition of the Rh core from capped octahedral to capped prismatic between m = 5 and m = 6. For the oxygen-rich Rh 7 O 12 + and Rh 7 O 14 + , molecular O 2 is adsorbed on a bridge site between two Rh atoms. The frequencies of the bands observed bands signal that the O 2 molecules are activated, indicating that rhodium oxide clusters with Rh 2 O 3 composition are still capable to donate electrons to activate O−O bonds in adsorbed O 2 .