On the role of ion bombardment parameters in AES sputter depth profiling of Ta2O5/Ta with Ar+ and Xe+

Summary In order to study the influence of the ion bombardment parameters on the achievable depth resolution of AES sputter depth profiles, 500 Å thick Ta₂O₅-layers produced by anodic oxidation of polished polycrystalline Ta-substrates were sputter depth profiled with Ar⁺- and Xe⁺-ions in a Scanning Auger Microprobe. The 90%–10% interface widthsz were measured for bombarding ion energies from 0.5 to 5 keV and angles of incidence of 15°, 33° and 56°, respectively.z reduces from 48 Å for Ar⁺-bombardment at = 15° andE = 5 keV to 20 Å when bombarding at = 56° andE = 1 keV. The corresponding values for Xe⁺-bombardment are 31 Å and 18 Å. The influence of the ion bombarding energy and angle on the interface broadening is discussed by means of a simple model. From corresponding evaluations the maximum transportation length of layer species into the substrate is found to be proportional toE ^0.5.

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Zum Einfluß der Ionenbeschußparameter auf die Tiefenauflösung bei der AES-Sputtertiefenprofil-analyse von Ta₂O₅/Ta mit Ar⁺ und Xe⁺

     

SIMS yields from glasses; secondary ion energy dependence and mass fractionation

SIMS studies of glasses indicate that calibration of positive monatomic ion yields via relative sensitivity factors (RSF) is significantly dependent both on the kinetic energyE _k and on the massM _t of the analyzed ions. Due to elemental differences in the energy distributions of the sputtered ions, relative emissivities at highE _k are radically different from those at the tops of the distributions. While the RSF values of cations from glasses range within ca. 3 powers of ten, atE _k above ca. 40 eV the range remains within a factor of ten or less, and further change of relative elemental sensitivities withE _k is slow. At low exit energy the LTE formalism is reasonably well obeyed. At highE _k , a trend is noted towards a relative suppression of the ion yields of lowvalent elements.Measurements of isotope fractionation in secondary ion yield were performed on 17 elements sputtered from glasses. The mass factor (defined by the proportionality of the yield toM _i ^– ) is found to range from near-zero to2.5, dependent on the element and onE _k . For most elements a drops steeply at lowE _k , but generally a slow rise is noted at higher energies. The behaviour of appears to be to some extent connected with the shape of the energy distribution curve. The dependence of onE _k and on elemental parameters can qualitatively be described in terms of a simple phenomenological model.     

Massenspektrometrische Bestimmung thermodynamischer Aktivitäten in Dreistoffsystemen

Zusammenfassung Das für Zweistoffsysteme angegebene Auswerteverfahren zur Ermittlung der freien Zusatzenthalpie G ^E und der chemischen Zusatzpotentiale _i ^E aus massenspektrometrischen Daten wird auf Dreistoffsysteme erweitert.

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Mass spectrometric determination of thermodynamic activities in ternary systems

A method for the evaluation of the excessGibbs free energy G ^E and the excess chemical potentials _i ^E from mass spectrometric data, previously derived for binary systems, is applied to ternary systems.

     

Formation of a Hydroxo-bridged Dinuclear Ru(III)/Ru(III) Complex from N-Methylimidazole and [Ru Cp(CH 3CN) 3] +

The reaction of [RuCp(CH₃CN)₃]PF₆ with 1 equiv of N-Me-imidazole results in the quantitative formation of [RuCp(¹N-N-Me-imidazole)(CH₃CN)₂]PF₆ (1) featuring a ¹N rather than a ¹C bound N-Me-imidazole ligand. According to DFT/B3LYP calculations, ¹N coordination of N-Me-imidazole is preferred over ¹C coordination by 25.5kJ/mol. Upon exposure to air 1 reacts with oxygen and water to afford the novel hydroxo-bridged dinuclear complex of [Ru₂Cp₂(¹N-N-Me-imidazole)₂(-OH)₂](PF₆)₂ (2) featuring a metal-metal single bond. The dimeric nature of 2 was confirmed by a single-crystal X-ray structure analysis.     

Salt Effects on Volumetric Properties of Some n-Alkoxyethanols (C1Em, m = 1, 2, and 3) in Aqueous Solutions at 298.15 K

Accurate density measurements over the whole composition range were made at a temperature of 298.15 K under ambient pressure for the mixtures of ethylene glycol monomethyl ether (2-methoxyethanol, C₃H₇O₂; C₁E₁), or diethylene glycol monomethyl ether (2-(2-methoxyethoxy)ethanol, C₅H₁₂O₃; C₁E₂), or triethylene glycol monomethyl ether [2-{2-(2-methoxyethoxy)ethoxy}ethanol, C₇H₁₆O₄; C₁E₃) in aqueous salt solutions having a common anion with a view to examining the cationic effect on the volumetric properties. To gain insight into the mixing behavior, results of the density measurements were used to estimate excess molar volumes, V_m^E, apparent molar volumes, V_{, i}, partial molar volumes, , excess partial molar volumes, V_m,i^E, and their limiting values at infinite dilution, V_{, i}, V_m,i, and V_m,i^E,, respectively. Aqueous solutions of the chlorides of lithium, sodium, potassium, and calcium in a concentration range to ca. 1 mol-kg^–1 were chosen for investigation as this concentration is used most frequently in applied chemistry. All mixtures except that containing lithium chloride show a decrease in the magnitude of V_m^E with the addition of a salt when compared to salt-free mixtures. Comparison of the derived volumes at infinite dilution suggested modification of the water structure as well as an electrostatic interaction between the ionic species and an alkoxyethanol molecule.     

Mechanisms of anion formation in O2, O2/Ar and O2/Ne clusters; the role of inelastic electron scattering

Measurements are reported on the formation of negative ions in O₂, O₂/Ar and O₂/Ne clusters aimed at establishing the mechanisms of anion formation and the role of inelastic electron scattering by the cluster constituents on negative ion formation in clusters. In the case of pure O₂ clusters the main anions we detected are of two types: O^–(O₂) _n0 and (O₂) _n ^1– . The yields of O^–(O₂) _n showed maxima at 6.3, 8.0 and 14.0 eV and the data suggest O^– as their precursor; the maxima at 8 and 14 eV are due to the production of O^– via symmetry forbidden dissociative attachment processes in O₂ at these energies which become allowed in clusters. The yields of (O₂) _n ^– showed a strong maximum at near-zero energy (0.5 eV) and also at 6.3, 8 and 14 eV. With the exception of the near-zero energy resonance, the (O₂) _n ^– anions at 6.3, 8 and 14 eV are attributed to nondissociative attachment of near-zero energy secondary electrons to O₂ clusters. The slow secondary electrons result predominantly from scattering via the O ₂ ^– negative ion states of incident electrons with energies in their respective regions. Similar results were obtained for the mixed O₂/rare gas clusters except that now a feeble and distinctly structured contribution in the yields of O^–(O₂) _n , (O₂) _n ^– (and Ar(O₂) _n ^– ) was observed at energies >10 eV. These anions are believed to have the lowest negative ion states of Ar*^– (Ne*^–) as their precursors.     

Metallorganische Verbindungen der Lanthanoide, 60. Mitt.: Synthese und Röntgenstrukturanalyse von Cyclooctatetraenyl(methylcyclopentadienyl)-(tetrahydrofuran)yttrium(III)

Summary The reaction of (C₈H₈)YCl(THF) with NaC₅H₄CH₃ in tetrahydrofuran leads to (C₈H₈)Y(C₅H₄CH₃)(THF). The X-ray structural analysis shows the compound to be orthorhombic witha=1157.5 (2),b=1553.2 (5),c=1718.9 (6) pm, space group Pbca,Z=8, andD (calcd)=1.48 g/cm^–3. The structure was solved from 1643 observed reflections withF _o4 (F _o) and refined to a finalR factor of 0.058. The expected sandwich structure is bent according to the ring centroid-Y-ring centroid angle of 149° caused by theTHF molecule coordinated to Y.

Herrn Prof. Dr. E. Hengge mit den besten Wünschen zum 60. Geburtstag gewidmet.     

Fragmentation of the valence electronic states of NF3 studied by threshold photoelectron–photoion coincidence spectroscopy

The valence threshold photoelectron spectrum of NF₃ is reported for the first time in the literature, and threshold photoelectron–photoion coincidence (TPEPICO) spectroscopy has measured, state-selectively, the decay dynamics of the valence states of NF₃⁺ in the range 13–23 eV. Vacuum–UV radiation from the Daresbury synchrotron source dispersed by a 1 m Seya-Namioka monochromator photoionises the parent molecules. Electrons and ions are detected by threshold electron analysis and time-of-flight mass spectrometry, respectively. TPEPICO spectra are recorded continuously as a function of photon energy, allowing coincidence ion yields of the fragment ions and the breakdown diagram to be obtained. A comparison of the integrated threshold photoelectron and the total ion signals as a function of energy suggests that, in the range 16–19 eV, autoionisation via Rydberg states of NF₃ makes a significant contribution to the production of threshold electrons. The 50% crossover energy for production of NF₂⁺ from NF₃⁺ is determined to be 14.10±0.05 eV. The first onsets for NF₂⁺ and NF⁺ production are 13.95±0.05 and 17.6±0.1 eV, respectively. The majority of the Franck–Condon region of the ground state of NF₃⁺ is stable with respect to dissociation to NF₂⁺, whereas the unresolved states and most of the state dissociate exclusively to NF₂⁺. The and states dissociate to NF⁺. Translational kinetic energy releases have been measured in NF₂⁺ and NF⁺ at the energies of the Franck–Condon maxima of the valence states of NF₃⁺. The results are compared with models assuming statistical and impulsive dissociation. The Ã/ states of NF₃⁺ dissociate directly from the excited-state potential energy surface to NF₂⁺, whereas the higher-lying state probably dissociates off the ground-state surface following rapid internal conversion. It is not possible to correlate unambiguously the formation of NF⁺ with either F₂ or 2F, although on energetic grounds the latter products are more likely. Assuming that the neutral products are 2F, no information is obtained whether the two N–F bonds break simultaneously or sequentially.     

Submonolayer-Deposition of Mass-Selected Au+ and Au n + (n = 3 and 7) on HOPG and Amorphous Carbon

Ions of gold monomer and clusters emitted from a liquid metal ion source were mass-selected, and deposited on cleaved HOPG (highly oriented pyrolytic graphite) surfaces and on amorphous carbon thin films at room temperature with the impinging energy E _i from 0 to 500 eV. The coverage of deposited ions were 1/100 and 1/1000 monolayers on HOPG surfaces and 1/3 monolayers on carbon films. Scanning tunneling microscopy of the HOPG surfaces deposited with low impinging energy (E _i<50 eV) revealed that large clusters with diameters ranging from 2 to 5 nm and height of 1–2 layers were present instead of isolated monomers and original clusters. When E _i was higher than 100 eV, HOPG surfaces were damaged and only bumpy surfaces were observed by STM. Transmission electron microscopy of Au⁺-deposited carbon films showed the formation of clusters with diameter 0.5–20 nm, depending on the E _i and the time elapsed after deposition.     

Substituent effects in mass spectra of monosubstituted benzils

The mass spectra of a series of thirteen m- and p-substituted benzils have been determined at several ionising voltages below 20 eV and at 70 eV. At ionising voltages up to 5 eV above the ionisation potentials the benzil molecular ions decompose entirely by two pathways to give substituted and unsubstituted benzoyl ions. Fractional intensities of the molecular ion (F_M), substituted (F_X) and unsubstituted (F_H) benzoyl ions were obtained for each benzil as a function of energy from measured ionisation efficiency curves, and ionisation and appearance potentials for all major ions determined from the ionisation efficiency curves by a semilogarithmic method. Various correlations of ion intensity and energy parameters with δ⁺ and δ constants are examined; these are generally poor. Fair correlations are obtained between log (F_X/F_H) or (AP – AP) and δ or δ⁺, and these are interpreted in terms of the expected effect of substituents on the stabilities of the product ions in the decompositions. A good correlation is observed between log (F_X/F_H) and AP · AP; this suggests that substituents affect F_X/F_H mainly by changing the activation energies for the competing decompositions of the molecular ions. The competitive shift has a marked effect on these appearance potentials so that in this system AP – IP is not a good measure of the activation energy for the primary decompositions.     

The fragmentation of some alkyl thio-phosphate esters by electron-impact

The mass spectra of the following compounds have been studied: and the fragmentation pathways established with the aid of accurate mass measurements, metastable transition and appearance potential determination. The mass spectra show that the sulphur-containing compounds (II to IV) give a stronger molecular ion that that of compound I. A further significant difference is the low intensity, in the mass spectra of II to IV, of the fragments relative to the processes that occur in I, probably because the electron removed upon ionisation belongs to the sulpher atom in compounds II to IV and to the oxygen in compound I. The isomeric compounds, (III and IV) show quite different mass spectra, The radicals containing only Phosphorus and oxygen have an ionisation potential close to 9 eV and the presence of sulphur considerably lowes this value. The measured ionisation potentials of compounds I to IV are respectively, 10·7₀, 9·5₅, 9·2₀ and 9·0₀eV. The heats of formation of compounds II and III have been estimated as ?176 and ?118 Kcal mole^?1, respectively.     

Excess Chemical Potentials and Partial Molar Enthalpies in Aqueous 1,2- and 1,3-Propanediols at 25°C

Excess chemical potentials and excess partial molar enthalpies of 1,2- and 1,3-propanediols (abbreviated as 12P and 13P), ^E _i, and H ^E _i (i = 12P or 13P) were determined in the respective binary aqueous solutions at 25^°C. For both systems, the values of ^E _i are almost zero, within ±0.4 kJ-mol^–1. However, the excess partial molar enthalpies, H ^E _i show a sharp mole fraction dependence in the water-rich region. Thus, the systems are highly nonideal, in spite of almost zero ^E _i. Namely, the enthalpy-entropy compensation is almost complete. From the slopes of the H ^E _i against the respective mole fraction x _i we obtain the enthalpic interaction functions between solutes, H _i–i ^E, (i = 12P or 13P). Using these quantities and comparing them with the equivalent quantities for binary aqueous solutions of 1-propanol (1P), 2-propanol (2P), glycerol (Gly), and dimethyl sulfoxide (DMSO), we conclude that there are three composition regions in each of which mixing schemes are qualitatively different. Mixing Schemes II and III, operative in the intermediate and the solute-rich regions, seem similar in all the binary aqueous solutions mentioned above. Mixing Scheme I in the water-rich region is different from solute to solute. 12P shows a behavior similar to that of DMSO, which is somewhat different from typical hydrophobic solute, 1P or 2P. 13P, on the other hand, is less hydrophobic than 12P, and shows a behavior closer to glycerol, which shows hydrophilic behavior.     

Theoretical study of the structure and stability of the heme dimer (FeC34H32N4O4)2 and its ion (FeC34H32N4O4) 2+

The electronic and geometric structures and the dissociation energies of the isolated molecule of heme dimer (heme)₂ = (FeC₃₄H₃₂O₄N₄)₂ and its ion (heme) ₂ ⁺ = (FeC₃₄H₃₂O₄N₄) ₂ ⁺ in the states with different multiplicities have been calculated by the density functional theory B3LYP method with the Gen-1 = 6-31G*(Fe) + 6-31G(C,H,N,O) and Gen-2 = 6-311++G*(Fe) + 6-31G*(C,H,N,O) basis sets. The computation results are compared with the analogous calculated data on monomeric heme and hemin⁺, as well as the previously considered dimeric ferriporphyrin X molecule and ion FeC₃₄H₃₁O₄N₄) ₂ ^{0, +} . In the heme dimer cation (heme) ₂ ⁺ , which is identified in mass spectra, the rings are linked with each other by a pair of Fe carbonyl bridges Fe⋯O_b = C(OH) and a pair of hydrogen bridges OH_b⋯N. According to the calculations, the most favorable state for (heme) ₂ ⁺ is the sextet in which five unpaired electrons are approximately uniformly distributed over the metal atoms, whereas the states with higher multiplicities 8 and 10 are, respectively, 0.15 and 0.20 eV higher on the energy scale. For the neutral dimer (heme)₂, the quintet is favorable in which each of the two Fe atoms has two unpaired electrons, and the states with the higher multiplicities 7 and 9 are only 0.10–0.15 eV higher. The calculated energies of dissociation D of the dimers into monomers point to a rather high stability of the (heme) ₂ ⁺ (D ∼ 1.4 1.4eV) and to a low stability of the neutral dimer (heme)₂ (D ∼ 0.3 eV). The R(Fe⋯O_b) distances in the bridges in (heme) ₂ ⁺ are 0.2–0.4 ? shorter than in (heme)₂. The trends in the behavior of the energetic and structural characteristics of the dimers (R(Fe-N), displacements of Fe atoms from the porphyrin ring plane, character of ring distortions, etc.) associated with the involvement of the and AOs of Fe atoms in bonding, as well as the spin density distribution over the Fe atoms and the rings, are analyzed as a function of the multiplicity and charge of the system. Differences in the character of interaction of the heme and ferriporphyrin dimers with molecular oxygen are discussed. Original Russian Text ? O.P. Charkin, N.M. Klimenko, D.O. Charkin, S.H. Lin, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 7, pp. 1166–1174.     

Reaction of 1,2-dibromoethane with primary amines: formation of N,N′-disubstituted ethylenediamines RNH-CH2CH2-NHR and homologous polyamines RNH-[CH2CH2NR]n-H

The reaction of primary amines RNH₂ (R: Me, Et, iPr, tBu and Ph) with 1,2-dibromoethane gave N,N′-disubstituted ethylenediamines R-NH-CH₂CH₂-NH-R (1) in yields ranging from 10% (1a; R=Me) to 70% (1d, R=tBu; 1e, R=Ph). Piperazines and N-substituted polyethyleneimines were identified (¹H NMR, ¹³C NMR and EI-MS) as side products of the reaction and isolated by fractional distillation. The piperazines 2 are formed in yields of 3-10% and can be separated from the diamines 1 in all cases, except for R=Me and Ph. The polyamine homologues RNH-[CH₂CH₂NR]_n-H (3-5) were isolated in yields ranging from 0.1% (n=4, R=iPr) to 14% (n=2, R=iPr). The yields of 1 increase with the size of the substituent R, no obvious trend exists for the yields of the side products.     

Delayed fluorescence from the lowest 1B+3u state of anthracene,due to hetero-triplet—triplet annihilation of 3anthracene* and 3xanthone*

The P-type delayed fluorescence (DF) S_i→S_o of aromatic compounds results from the population of excited singlet states S_i by triplet—triplet annihillation (TTA) of molecules in their lowest and metastable triplet state T₁ : T₁ + T₁

S_i + S_o; S_i may be any excited singlet state whose excitation energy E(S_i ? 2 E(T₁). TTA of unlike molecules A and B (hetero-TTA) may lead to excited singlet states either of A or of B. In particular, if E(T_A¹) < E(T₁^B), hetero-TTA may lead to excited singlet states S_k^A which are not accessible by TTA of 2 T₁^A. In the present paper we report the first example of the detection of the DF from a very short-lived upper excited singlet state S_k^A which has been populated by hetero-TTA. The systems investigated are liquid solutions of A = anthracene-h₁₀ or anthracene-d₁₀ or 9,10-dimethylanthracene and B = xanthone in 1,1,2-trichlorotrifluoroethane at 243 K. S_k^A is the lowest ¹B_3U⁺ state (B_b state) of anthracene.     

Über die Darstellung der 7R-Oxirane von 5Z- und 5E-10-Oxo-19-norcholecalciferol

Summary The two title compounds12b and13b have been prepared by direct oxidation of the corresponding 10-oxo-19-norcolcalciferol derivatives3c and4c withMCPBA. The generation of12b and13b by treatment of the ⁷ epoxidized ethylisoxazolin adducts of 5Z- and 5E-cholecalciferol8a,8b and9a,9b with Mo(CO)₆ failed, since besides the retroaldol cleavage of the heterocycle a deoxygenation of the oxirane with retention of configuration to the ⁷ double bond occurs.

     

Ligand-structure effect on electrochemical reduction of copper(II) complexes

Summary Half-wave potentials for a one-electron reduction of copper(II) complexes containing polydentate ligands can be calculated using the equationE _1/2=E ⁰(Cu^2+/+)+ _{i j} E _i where E _i are contributions related to the electronic and steric properties of the ligands. The values of 18 E _i contributions are presented and explained, and the effect of the solvents on the half-wave potentials is exemplified.Dedicated to Prof. Dr. Viktor Gutmann to his 70th birthday     

Electron bombardment induced fragmentation of size selected neutral (D2O) n clusters

The fragmentation behaviour of size selected neutral (D₂O) _n clusters withn4 after ionization with 70 eV electrons is subject of this work. Size selection by scattering the cluster beam from a He target beam in combination with a quadrupole mass filter and time resolved measurements at specific laboratory angles enables us to determine the neutral precursor masses of the detected ions. The measured fragment pattern is dominated by deuterated ions of the form (D₂O) _n–x D⁺ withx1. The dimer fragmentation which leads with a probability of 62.5% to the D₃O⁺ ion and with 37.5% to D₂O⁺ can be explained by fast intracluster ion-molecule reactions of charged monomer fragments reacting with the partner molecule. For larger clusters the fragmentation process can be rationalised by the creation of an initially highly excited D₃O⁺ (D₂O) _x complex which is stabilized by evaporating additional monomer units with the main fragment channel (D₂O)D⁺ forn=3 and (D₂O)₂D⁺ forn=4. With increasing cluster size an increasing tendency of evaporation of more than one water monomer unit has been observed.     

Radiolysis and corrosion of238Pu-doped UO2 pellets in chloride brine

Deaerated 5 M NaCl solution is irradiated in the presence of UO₂ pellets with α-radiation from²³⁸Pu. Experiments are conducted with²³⁸Pu doped pellets and others with²³⁸Pu dissolved in the brine. The radiolysis products and yields of mobilized U and Pu from the oxidative dissolution of UO₂ are determined. Results found for radiolysis products and for the oxidation/dissolution of pellets immersed in Pu containing brine are similar to results for Pu doped pellets, where the radiation chemical processes occur only in the liquid layer of some 10 σm thickness adjacent to the pellet. The yield of radiolysis products is comparable to earlier results, that of mobilized U from the pellets is < 1% of the total amount of oxidized species. Thus, the radiation chemical yield (G-value) for mobilized hexavalent U is < 0.01 ions/100 eV. In spite of the low radiation yield for the corrosion, the rate of UO₂dissolution is higher than expected for the concentrations of long-lived oxidizing radiolysis compounds found in the solutions.     

Cp2ZrCl2-catalyzed hydroalumination of norbornene derivatives withi-Bu2AlCl

Cp₂ZrCl₂-catalyzed (Cp = ⁵-C₅H₅) hydroalumination of substituted norbornenes withi-Bu₂AlCl was conducted, yielding higher cycloalkylhaloalanes with high yields.Institute of Organic Chemistry, Ural Branch, Russian Academy of Sciences, 450054 Ufa. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2791–2798, December, 1992.