Structure and Properties of Fe4 with Different Coverage by C and CO

Cryo spectroscopy of N2 on cationic iron clusters

Infrared photodissociation (IR-PD) spectra of iron cluster dinitrogen adsorbate complexes [Fe_n(N₂)_m]⁺ for n = 8-20 reveal slightly redshifted IR active bands in the region of 2200-2340 cm^-1. These bands mostly relate to stretching vibrations of end-on coordinated N₂ chromophores, a μ_1,end end-on binding motif. Density Functional Theory (DFT) modeling and detailed analysis of n = 13 complexes are consistent with an icosahedral Fe₁₃ ⁺ core structure. The first adsorbate shell closure at (n,m) = (13,12)-as recognized by the accompanying paper on the kinetics of N₂ uptake by cationic iron clusters-comes with extensive IR-PD band broadening resulting from enhanced couplings among adjacent N₂ adsorbates. DFT modeling predicts spin quenching by N₂ adsorption as evidenced by the shift of the computed spin minima among possible spin states (spin valleys). The IR-PD spectrum of (17,1) surprisingly reveals an absence of any structure but efficient non-resonant fragmentation, which might indicate some weakly bound (roaming) N₂ adsorbate. The multiple and broad bands of (17,m) for all other cases than (17,1) and (17,7) indicate a high degree of variation in N₂ binding motifs and couplings. In contrast, the (17,7) spectrum of six sharp bands suggests pairwise equivalent N₂ adsorbates. The IR-PD spectra of (18,m) reveal additional features in the 2120-2200 cm^-1 region, which we associate with a μ_1,side side-on motif. Some additional features in the (18,m) spectra at high N₂ loads indicate a μ_1,tilt tilted end-on adsorption motif.

Multistep reactions of water with small Pdn clusters: A first principles study

Multistep dissociative chemisorption reactions of water with Pd 4 and Pd 7 clusters were studied using density functional theory. The adsorption energies and referred adsorption sites from water molecule ( H 2 O ) to partially dissociative ( H 2+ O and OH + H ), then to fully dissociative ( O + H + H ) configurations are carefully determined. It is found that the adsorption energies of three dissociative reactions are 5–6 times larger than that of water molecule. Atop sites of Pd 4 and Pd 7 clusters are found to be the most stable sites for the adsorbed H 2 O molecule. For the coadsorption cases of partially and fully dissociated products, H 2 and OH molecules preferably tend to bind at the low coordination (atop or bridge) sites, and O and H atoms prefer to adsorb on the high coordination (hollow) sites. It is also found that the most favorable adsorption sites for the molecular adsorbates ( H 2 O , H 2 and OH ) are adjacent to the Pd atoms with the largest site-specific polarizabilities. Therefore, site-specific polarizability is a good predictor of the favorable adsorption sites for the weakly bound molecules. The different directions of charge transfer between the Pd clusters and the adsorbate(s) is observed. Furthermore, the processes of the adsorption, dissociation, and the dissociative products diffusion of H 2 O are analyzed.