The adsorption forms of NO on Ir n + (n = 3–6) clusters were investigated using infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory (DFT) calculations. Spectral features indicative both for molecular NO adsorption (the NO stretching vibration in the 1800–1900 cm–1 range) and for dissociative NO adsorption (the terminal Ir–O vibration around 940 cm–1) were observed, elucidating the co-existence of molecular and dissociative adsorption of NO. In all calculated structures for molecular adsorption, NO is adsorbed via the N atom on on-top sites. For dissociative adsorption, the O atom adsorbs exclusively on on-top sites (μ1) of the clusters, whereas the N atom is found on either a bridge (μ2) or a hollow (μ3) site. For Ir5 + and Ir6 +, the N atom is also found on the on-top sites. The observed propensity for NO dissociation on Ir n + (n = 3–6) is higher than that for Rh6 +, which can be explained by the higher metal-oxygen bond strengths for iridium.

The adsorption of an NO molecule on a cationic iridium-doped rhodium cluster, Rh 5 Ir + , was investigated by infrared multiple photon dissociation spectroscopy (IRMPD) of Rh 5 IrNO + • Ar p complexes in the 300−2000 cm −1 spectral range, where the Ar atoms acted as a messenger signaling IR absorption. Complementary density functional theory (DFT) calculations predicted two near-isoenergetic structures as the putative global minimum: one with NO adsorbed in molecular form in the on-top configuration on the Ir atom in Rh 5 Ir + , and one where NO is dissociated with the O atom bound to the Ir atom in the on-top configuration and the N atom on a hollow site formed by three Rh atoms. A comparison between the experimental IRMPD spectrum of Rh 5 IrNO + and calculated spectra indicated that NO mainly adsorbs molecularly on Rh 5 Ir + , but evidence was also found for structures with dissociatively adsorbed NO. The estimated fraction of Rh 5 IrNO + structures with dissociatively adsorbed NO is approximately 10%, which was higher than that found for Rh 6 + , but lower than that for Ir 6 + . The DFT calculations indicated the existence of an energy barrier in the NO dissociation pathway that is exothermic with respect to the reactants, which was considered to prevent NO from dissociating readily on Rh 5 Ir + . The height of the barrier is lower than that for NO dissociation over Rh 6 + , which is attributed to the higher binding energy of atomic O to the Ir atom in Rh 5 Ir + than to a Rh atom in Rh 6 + .

Water splitting is catalyzed by photosystem II, which comprises an inorganic core (CaMn 4 O 5 ) and protein ligands. To understand the evolution of CaMn 4 O 5 after attaching water molecules, an isolated CaMn 4 O 5 + cluster was investigated using vibrational spectroscopy and density functional theory calculations. Computational findings suggest that when a water molecule adsorbs on the Ca atom through the O atom of water, one of the OH bonds forms a hydrogen bond with a μ-oxo bridge, which dissociates into two OH groups. This is consistent with the fact that no isomers with molecularly adsorbed water were experimentally observed.

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Hydrogen is a promising energy resource as a substitute for fossil fuels, and metal alloy hydrides are considered to be good candidates as hydrogen storage materials. In the hydrogen storage processes, hydrogen desorption is as important as hydrogen adsorption. In order to understand the hydrogen desorption features of those clusters, here, single-Nb-atom-doped Al clusters were prepared in the gas phase and their reaction with hydrogen was investigated using thermal desorption spectrometry (TDS). On average, six to eight H atoms were adsorbed in Al n Nb + (n = 4−18) clusters, and most H atoms were released upon heating of the clusters to 800 K. Two types of desorption features of Al n Nb + clusters were found, which related to the flexibility of the clusters. This study demonstrated the potential of Nb-doped Al alloy as an efficient hydrogen storage material with high storage capacity, thermal stability at room temperature, and hydrogen desorption ability upon moderate heating.