New Tools for Structure Elucidation in the Gas Phase: IR Spectroscopy of Bare and Doped Silicon Nanoparticles

Structure characterization of metal oxide clusters by vibrational spectroscopy: possibilities and prospects

“…9,31,32 There are several variants of this technique, but they all have in common that they require an intense and tunable IR laser source. 9,33,34 The IR-active fundamental vibrational modes of metal oxide clusters lie below 1700 cm À1 with the more intense M-O stretching and bending transitions typically found in-between 300-1200 cm À1 . This spectral region only became fully accessible to gas phase experiments on clusters with the introduction of IR free electron lasers (IR-FELs) to molecular spectroscopy in 1996.…”

Structure and Chemistry of the Heteronuclear Oxo-Cluster [VPO4]•+: A Model System for the Gas-Phase Oxidation of Small Hydrocarbons

“…Over the last decades the investigation of small cluster systems, in particular metal and metal oxide species, using advanced mass spectrometric methods in conjunction with theoretical studies, proved useful in unfolding insights at a molecular level; this includes reactivity studies of ion/molecule reactions − as well as recent advantages in the development of gas-phase infrared photodissociation spectroscopy. − Due to their large application in heterogeneous catalysis, especially vanadium oxides have been studied exhaustively, and a remarkable reactivity toward small hydrocarbons has been uncovered. ,,,,− With respect to the VPO catalysts, it was conjectured, based on gas-phase as well as surface studies, that the structurally often ill-defined phosphate species work as catalytically innocent linkers between the active vanadium-oxide sites in mixed metal-oxide phosphates . However, this assumption was questioned by several gas-phase studies on the open-shell oxide cation [P 4 O 10 ] •+ , in which the efficient thermal activation of even methane and other small, inert hydrocarbons at ambient conditions by the metal-free oxide was demonstrated with an even higher reactivity of [P 4 O 10 ] •+ toward CH 4 compared to the isostructural, metallic analogue [V 4 O 10 ] •+ . − Further studies aimed at a more systematic investigation of mixed vanadium–phosphorus oxygen cluster ions [V x P 4– x O 10 ] •+ ( x = 1–3). , As shown by a theoretical analysis, these systems possess an oxygen-centered radical which has been found to be crucial in terms of hydrogen-atom transfer (HAT) from methane; for all [V x P 4– x O 10 ] •+ ( x = 1–3) clusters, the structure possessing the lowest energy corresponds to the P–O • isomer, i.e., the spin density is mostly localized at the phosphorus-bound, terminal oxygen atom.…”

Infrared photodissociation spectroscopy of (Al2O3)2–5FeO+: influence of Fe-substitution on small alumina clusters

“…27 The spectrum of Al 2 FeO 4 + ( n = 1) has been published recently by Müller et al 28 Based on our previous studies for monometallic Al- and Fe-oxide clusters, we group the observed IR absorptions into three characteristic spectral regions: (i) 1200–900 cm −1 , (ii) 900–600 cm −1 and (iii) 600–430 cm −1 . 48–52 These regions cover (i) Al–O stretching modes involving the shortest (≤173 pm) Al–O bonds, (ii) Fe–O stretching modes together with medium-length (174–178 pm) Al–O bond stretches and (iii) ring breathing modes as well as stretching and bending modes involving the longest (>180 pm) Al–O bonds.…”