Vibrationally resolved photoelectron spectroscopy of AlO− and AlO2−

Structural Characterization of Nickel-Doped Aluminum Oxide Cations by Cryogenic Ion Trap Vibrational Spectroscopy

Isolated nickel-doped aluminum oxide cations (NiO_m)(Al₂O₃)_n(AlO)⁺ with m = 1-2 and n = 1-3 are investigated by infrared photodissociation (IRPD) spectroscopy in combination with density functional theory and the single-component artificial force-induced reaction method. IRPD spectra of the corresponding He-tagged cations are reported in the 400-1200 cm^-1 spectral range and assigned based on a comparison to calculated harmonic IR spectra of low-energy isomers. Simulated spectra of the lowest energy structures generally match the experimental spectra, but multiple isomers may contribute to the spectra of the m = 2 series. The identified structures of the oxides (m = 1) correspond to inserting a Ni-O moiety into an Al-O bond of the corresponding (Al₂O₃)_1-3(AlO)⁺ cluster, yielding either a doubly or triply coordinated Ni²⁺ center. The m = 2 clusters prefer similar structures in which the additional O atom either is incorporated into a peroxide unit, leaving the oxidation state of the Ni²⁺ atom unchanged, or forms a biradical comprising a terminal oxygen radical anion Al-O^•- and a Ni³⁺ species. These clusters represent model systems for under-coordinated Ni sites in alumina-supported Ni catalysts and should prove helpful in disentangling the mechanism of selective oxidative dehydrogenation of alkanes by Ni-doped catalysts.

Investigation of plasma electrolytic oxidation on valve metals by means of molecular spectroscopy – a review

A review of results of molecular spectroscopic investigations during plasma electrolytic oxidation of valve metals is presented.

Vibrationally Resolved Photoelectron Spectroscopy of BO- and BO2-: A Joint Experimental and Theoretical Study

We report a photoelectron spectroscopy and computational study of two simple boron oxide species: BO- and BO2-. Vibrationally resolved photoelectron spectra are obtained at several photon energies (355, 266, 193, and 157 nm) for the 10B isotopomers, 10BO- and 10BO2-. In the spectra of 10BO-, we observe transitions to the 2Sigma+ ground state and the 2Pi excited state of 10BO at an excitation energy of 2.96 eV. The electron affinity of 10BO is measured to be 2.510+/-0.015 eV. The vibrational frequencies of the ground states of 10BO- and 10BO and the 2Pi excited state are measured to be 1725+/-40, 1935+/-30, and 1320+/-40 cm-1, respectively. For 10BO2-, we observe transitions to the 2Pig ground state and two excited states of 10BO2, 2Piu, and 2Sigmau+, at excitation energies of 2.26 and 3.04 eV, respectively. The electron affinity of 10BO2 is measured to be 4.46+/-0.03 eV and the symmetrical stretching vibrational frequency of the 2Piu excited state of 10BO2 is measured to be 980+/-30 cm-1. Both density functional and ab initio calculations are performed to elucidate the electronic structure and chemical bonding of the two boron oxide molecules. Comparisons with the isoelectronic AlO- and AlO2- species and the closely related molecules CO, N2, CN-, and CO2 are also discussed.

Sequential addition of H2O, CH3OH, and NH3 to Al3O3−: A theoretical study

Photoelectron spectra of two species, Al3O3(H2O)2- and Al3O3(CH3OH)2-, that are produced by the addition of two water or methanol molecules to Al3O3- are interpreted with density-functional geometry optimizations and electron propagator calculations of vertical electron detachment energies. In both cases, there is only one isomer that is responsible for the observed spectral features. A high barrier to the addition of a second molecule may impede the formation of Al3O3N2H6- clusters in an analogous experiment with NH3.

Theoretical Study of Alnand AlnO (n= 2−10) Clusters

The stable structures, energies, and electronic properties of neutral, cationic, and anionic clusters of Al(n) (n = 2-10) are studied systematically at the B3LYP/6-311G(2d) level. We find that our optimized structures of Al5(+), Al9(+), Al9(-), Al10, Al10(+), and Al10(-) clusters are more stable than the corresponding ones proposed in previous literature reports. For the studied neutral aluminum clusters, our results show that the stability has an odd/even alternation phenomenon. We also find that the Al3, Al7, Al7(+), and Al7(-) structures are more stable than their neighbors according to their binding energies. For Al7(+) with a special stability, the nucleus-independent chemical shifts and resonance energies are calculated to evaluate its aromaticity. In addition, we present results on hardness, ionization potential, and electron detachment energy. On the basis of the stable structures of the neutral Al(n) (n = 2-10) clusters, the Al(n)O (n = 2-10) clusters are further investigated at the B3LYP/6-311G(2d), and the lowest-energy structures are searched. The structures show that oxygen tends to either be absorbed at the surface of the aluminum clusters or be inserted between Al atoms to form an Al(n-1)OAl motif, of which the Al(n-1) part retains the stable structure of pure aluminum clusters.

Addition of water, methanol, and ammonia to Al3O3− clusters: Reaction products, transition states, and electron detachment energies

Products of reactions between the book and kite isomers of Al3O3- and three important molecules are studied with electronic structure calculations. Dissociative adsorption of H2O or CH3OH is highly exothermic and proton-transfer barriers between anion-molecule complexes and the products of these reactions are low. For NH3, the reaction energies are less exothermic and the corresponding barriers are higher. Depending on experimental conditions, Al3O3- (NH3) coordination complexes or products of dissociative adsorption may be prepared. Vertical electron detachment energies of stable anions are predicted with ab initio electron propagator calculations and are in close agreement with experiments on Al3O3- and its products with H2O and CH3OH. Changes in the localization properties of two Al-centered Dyson orbitals account for the differences between the photoelectron spectra of Al3O3- and those of the product anions.

Gallium oxide and dioxide: Investigation of the ground and low-lying electronic states via anion photoelectron spectroscopy

The GaO and GaO2 molecules were investigated using negative ion photoelectron spectroscopy. All the photoelectron spectra showed vibrationally resolved progressions. With the aid of electronic structure calculations and Franck-Condon spectral simulations, different molecular parameters and energetics of GaO-/GaO and GaO2-/GaO2 were determined, including the electron affinity of GaO, the vibrational frequency of GaO-, and the term energy, spin-orbit splitting, and vibrational frequency for the first excited A 2PiOmega state of GaO. The GaO2- photoelectron spectra comprised three bands assigned as transitions from the linear X 1Sigma(g)+ ground state of GaO2- to three linear neutral states: the A 2Pi(g), B 2Pi(u), and C 2Sigma(u) + states. The symmetric stretch frequencies of the anion and three neutral states as well as the spin-orbit splitting of the neutral 2Pi states were determined. Electronic structure calculations found the neutral lowest energy linear structure to be only 63 meV higher than the neutral bent geometry.

Products of the addition of water molecules to Al3O3− clusters: Structure, bonding, and electron binding energies in Al3O4H2−, Al3O5H4−, Al3O4H2, and Al3O5H4

Two stable products of reactions of water molecules with the Al3O3- cluster, Al3O4H2- and Al3O5H4-, are studied with electronic structure calculations. There are several minima with similar energies for both anions and the corresponding molecules. Dissociative absorption of a water molecule to produce an anionic cluster with hydroxide ions is thermodynamically favored over the formation of Al3O3-(H2O)n complexes. Vertical electron detachment energies of Al3O4H2- and Al3O5H4- calculated with ab initio electron propagator methods provide a quantitative interpretation of recent anion photoelectron spectra. Contrasts and similarities in these spectra may be explained in terms of the Dyson orbitals associated with each transition energy.