Oxide Bond Energies Research Articles

A guided ion beam investigation of UO2+ thermodynamics and f orbital participation: Reactions of U+ + CO2, UO+ + O2, and UO+ + CO.

A guided ion beam tandem mass spectrometer was employed to study the reactions of U+ + CO2, UO+ + O2, and the reverse of the former, UO+ + CO. Reaction cross sections as a function of kinetic energy over about a three order of magnitude range were studied for all systems. The reaction of U+ + CO2 proceeds to form UO+ + CO with an efficiency of 118% ± 24% as well as generating UO2+ + C and UCO+ + O. The reaction of UO+ + O2 forms UO2+ in an exothermic, barrierless process and also results in the collision-induced dissociation of UO+ to yield U+. In the UO+ + CO reaction, the formation of UO2+ in an endothermic process is the dominant reaction, but minor products of UCO+ + O and U+ + (O + CO) are also observed. Analysis of the kinetic energy dependences observed provides the bond energies, D0(U+-O) = 7.98 ± 0.22 and 8.05 ± 0.14eV, D0(U+-CO) = 0.73 ± 0.13eV, and D0(OU+-O) = 7.56 ± 0.12eV. The values obtained for D0(U+-O) and D0(OU+-O) agree well with the previously reported literature values. To our knowledge, this is the first experimental measurement of D0(U+-CO). An analysis of the oxide bond energies shows that participation of 5f orbitals leads to a substantial increase in the thermodynamic stability of UO2+ relative to ThO2+ and especially transition metal dioxide cations.

Following laser-induced plasma stoichiometry with atomic absorption spectroscopy

Atomic absorption spectroscopy was used to measure the absolute vanadium and titanium masses present as neutral atoms in the plume formed by laser ablation of a titanium alloy sample. At delays between two and twenty microseconds, the absolute masses and temperatures were measured with time-resolved Boltzmann plots under pure helium and an 80:20 He/O2 mixture. The Boltzmann plots, which include the ground term (in contrast to emission-based measurements), produced high-quality estimates of the plasma composition. Under helium, the metal vapors persisted beyond the longest ∼20 μs delays measured. The V:Ti stoichiometry was approximately as expected from the nominal sample composition at all times under He. However, under He:O2, the atomic vapor disappeared entirely in under 10 μs and the stoichiometry became more enriched in vanadium at increasing delays. This enrichment is interpreted in terms of the difference in first oxide bond energies of the two metals. There was evidence of loss of metal even under helium within the investigated 20 μs window.

Principal component analysis of the main factors of line intensity enhancements observed in oscillating direct current plasma

Enhancement of emission line intensities by induced oscillations of direct current (DC) arc plasma with continuous aerosol sample supply was investigated using multivariate statistics. Principal component analysis (PCA) was employed to evaluate enhancements of 34 atomic spectral lines belonging to 33 elements and 35 ionic spectral lines belonging to 23 elements. Correlation and classification of the elements were done not only by a single property such as the first ionization energy, but also by considering other relevant parameters. Special attention was paid to the influence of the oxide bond strength in an attempt to clarify/predict the enhancement effect. Energies of vaporization, atomization, and excitation were also considered in the analysis. In the case of atomic lines, the best correlation between the enhancements and first ionization energies was obtained as a negative correlation, with weak consistency in grouping of elements in score plots. Conversely, in the case of ionic lines, the best correlation of the enhancements with the sum of the first ionization energies and oxide bond energies was obtained as a positive correlation, with four distinctive groups of elements. The role of the gas-phase atom-oxide bond energy in the entire enhancement effect is underlined.

On Mercury(I) Oxo Compounds — Quasi‐Relativistic Computational and Experimental Studies

AbstractAbout 60 molecular species composed of up to 10 mercury atoms and of oxygen atoms and/or of some other elements or groups (such as halogen, OH2, OH, H, alkali, NO3) have been investigated quantum chemically. Different density functional approaches and theab initioSCF‐MP2 method were applied, comparing different basis sets and different atomic core sizes. It is important not to treat the Hg 5s, p, d as inactive core shells, and to use sufficiently many polarization functions.The shape of the 〉O‐Hg‐Hg‐O〈 units is not favorable concerning the formation of lattices composed of HgI, O and OH only. Despite its bulkiness, the OHgHgO units can easily come into contact with each other and then disproportionate. This is prevented in the so‐called ternary M‐HgIoxides by the embedded oxometallate (oxoacidic) anions. Furthermore, the HgIand HgIIoxide bond energies are less favorable towards the stability of HgIoxo compounds, as compared to Hg halidic or oxoacidic compounds. Both points are not promising concerning the search for HgIoxides/hydroxides, although the preparation of such compounds, including spacer groups, by topochemical reactions can still not be excluded.So far, experimental efforts towards the synthesis of such a new class of compounds have only demonstrated that HgIIis strictly preferred over HgIin the formation of solids of binary Hg‐O or ternary A‐Hg‐O composition (A = electropositive metal such as alkali, in contrast to M = transition or semi‐metal). This is so even if compounds containing ‘electron rich Hgδ—atoms’ (i.e. A‐Hg amalgams) are oxidized under mild conditions.

Guided ion beam studies of the reactions of Crn+ (n=1–18) with CO2: Chromium cluster oxide bond energies

The kinetic energy dependence of the reactions of Crn+ (n=1–18) with CO2 are studied in a guided ion beam mass spectrometer. The primary product ions are CrnO+, which then decompose by sequential loss of chromium atoms as the kinetic energy is increased. Simple collision-induced dissociation to form the Crn−1+ product ions is also observed. Large cluster ions, n⩾9, form the CrnCO2+ adduct at low kinetic energies. For many cluster sizes, the cross section for the primary reaction, Crn++CO2→CrnO++CO, exhibits an interesting bimodal energy behavior that is discussed in some detail. Crn+–O bond energies are measured and found to compare well with measurements obtained from guided ion beam studies of the Crn++O2 systems. The trends in this thermochemistry are discussed and compared to bulk phase oxidation values.

Guided ion-beam studies of the reactions of Fen+ (n=1–18) with CO2: Iron cluster oxide bond energies

The kinetic energy dependence of the reactions of Fen+ (n=1–18) with CO2 are studied in a guided ion-beam mass spectrometer. The primary product ions are FenO+, which then decompose by sequential loss of iron atoms as the kinetic energy is increased. Simple collision-induced dissociation to form the Fen−1+ product ions is also observed. Large cluster ions, n⩾9, form the FenCO2+ adduct at low kinetic energies. The cross section for the primary reaction, Fen++CO2→FenO++CO, exhibits an interesting bimodal energy behavior that is discussed in some detail. Fen+–O bond energies are measured and found to compare well with previous measurements obtained from guided ion-beam studies of the Fen++O2 systems. The trends in this thermochemistry are discussed and compared to bulk phase values.

Reactions of fourth-period metal ions (Ca+−Zn+) with O2: Metal-oxide ion bond energies

Reactions of Ca+, Zn+ and all first-row atomic transition metal ions with O2 are studied using guided ion beam techniques. While reactions of the ground states of Sc+, Ti+, and V+ are exothermic, the remaining metal ions react with O2 in endothermic processes. Analyses of these endothermic reactions provide new determinations of the M+–O bond energies for these eight elements. Source conditions are varied such that the contributions of excited states of the metal ions can be explicitly considered for Mn+, Co+, Ni+, and Cu+. Results (in eV) at 0 K are D0(Ca+–O)= 3.57±0.05, D0(Cr+–O)=3.72±0.12, D0(Mn+–O)=2.95±0.13, D0(Fe+–O)=3.53±0.06 (reported previously), D0(Co+–O)=3.32±0.06, D0(Ni+–O) =2.74±0.07, D0(Cu+–O)=1.62±0.15, and D0(Zn+–O)=1.65±0.12. These values along with literature data for neutral metal oxide bond energies and ionization energies are critically evaluated. Periodic trends in the ionic metal oxide bond energies are compared with those of the neutral metal oxides and those of other related molecules.

Influence of oxide bond energies on the kinetics of chemical dissolution of anodic oxides on valve metals

The influence of M-O bond energies on the kinetics of the chemical dissolution of anodic oxide films on valve metals was analysed and the different profiles of atomic defects in these oxides were deduced. Four different equations describing the dissolution behaviour of such oxides were derived and the respective examples justifying each equation were also introduced. For many oxides, M-O bond energy was found to vary linearly with the activation energy of the dissolution. It was also found that the dissolution rate increases with increase of the initial thickness of the oxide. The dissolution processes were followed by using potential and capacitance measurements.

Oxide bond energies for the calibration of matrix effects in secondary ion mass spectrometry

Analyses of trace and major elements in Group III-V compound matrices by secondary ion mass spectrometry (SIMS) have shown that practical ion yields are related linearly to the matrix composition. The affinity of the matrix to oxygen appears to be the critical factor in this relationship. A direct relationship between the slopes of calibration lines, determined for elements in the same column of the periodic table, and the first ionization potential of the respective elements has also been shown.