Electronic structures and stabilities of GeC n and Ge2C n in Hückel theory

Some recent results about Ge _p C _n ⁺ ions (p=1, 2;n < 6) produced in laser microprobe mass analyser experiments (LAMMA) show very marked alternations in the emission intensities I(Ge _p C _n ⁺ ) as a function of then andp parities. I(Ge _p C _n ⁺ ) are maxima for evenn. Thus, intensity maxima occur when the total atom numberm of the aggregates is odd for GeC _n ⁺ (m=n+1) and even for Ge₂C _n ⁺ (m=n+2). As a result, GeC _n ⁺ ions seem to behave as C _m ⁺ ions, whereas the behaviour of Ge₂C _n ⁺ ions is quite similar to that of Ge _p ⁺ ions formed in SIMS or vaporization experiments on pure germanium. It is well known (correspondence rule) that the parity effect in the emissions corresponds to alternations in the ion stabilities. These results are analysed from a model built in Hückel approximation with hybridization. Forp=1, the clusters are assumed to be insp hybridization as for C _m ⁺ ions, hence with linear shapes, and forp=2, they would rather be insp ² orsp ³ hybridization as for Ge _p ⁺ ions. Relative stabilities and distributions of the energy levels of the aggregates are then calculated. The relative stabilities given for Ge _p C _n ⁺ by this model show maxima for evenn as in experiments, and we have thus a good agreement between our calculation results and the experimental data. Moreover, we found that Ge₂C _n ⁺ would rather be insp ³ hybridization, that is under three dimensional shapes.     

A theoretical study of internal rearrangements and open channels for fission and mass exchanges in Xe n + clusters

In a previous work the equilibrium geometrical and electronic structures of Xe _n ⁺ clusters had been established using a non-empirical model hamiltonian. The same model is used to determine the energetic barriers between the nearly degenerate isomers; the movement of the neutral atoms around the Xe ₃ ⁺ or Xe ₄ ⁺ ionized linear cores are quite easy (ΔE?0.9 kcal/mole), the changes from a Xe ₃ ⁺ to a Xe ₄ ⁺ core are more difficult (ΔE?2.0 kcal/mole). The energetically possible fissions from a vertical photoionization \(Xe_n \xrightarrow{{h v}}Xe_n^{v + } \to Xe_p^ + + Xe_{n - p} \) forn≦19,p=1–9 and 12–14 and mass exchanges Xe _p ⁺ +Xe _q →Xe _p+m ⁺ +Xe _q?m (m=1,2,3) from relaxed Xe _p ⁺ clusters are given forp+m≦9 and 12–14 andq≦19. Surprisingly the reverse reactions are shown to occur for some values ofp andq. Numerous processes lead to Xe ₁₃ ⁺ , which is especially stable.     

Pressure and isotope effects on the proton jump of the hydroxide ion at 25°C

The limiting molar conductances Λ⁰ of potassium deuteroxide KOD in D₂O and potassium hydroxide KOH in H₂O were determined at 25°C as a function of pressure to disclose the difference in the proton-jump mechanism between an OH^? (OD^?) and a H₃O⁺ (D₃O⁺) ion. The excess conductance of the OD^? ion in D₂O λ _E ^O (OD ^-), as estimated by the equation $$\lambda _E^O (OD^ - ) = \Lambda ^O (KOD/D_2 O) - \Lambda ^O (KCl/D_2 O)$$ increases a little with pressure as well as the excess conductance of the OH^? ion in H₂O $$\lambda _E^O (OH^ - ) = \Lambda ^O (KOH/H_2 O) - \Lambda ^O (KCl/H_2 O)$$ However, their rates of increase with pressure are much smaller than those of the excess deuteron and proton conductances, λ _E ^O (D ⁺) and λ _E ^O (H ⁺). With respect to the isotope effect on the excess conductance, λ _E ^O (OH ^-)/λ _E ^O (D ⁺) decreases with presure as in the case of λ _E ^O (H ⁺)/λ _E ^O (D ⁺), but the value of λ _E ^O (OH ^-)/λ _E ^O (OD ^-) itself is much larger than that of λ _E ^O (H ⁺)/λ _E ^O (D ⁺) at each pressure. These results are ascribed to the difference in the pre-rotation of water molecules, which is brought about by the difference in the intial orientation of the rotating water molecule adjacent to the OH^? (OD^?) or the H₃O⁺ (D₃O⁺) ion.     

Study of compatibility in polymeric system cellulose nitrate-cellulose acetate by reversed-phase gas chromatography

Therm odynamic compatibility in the polymeric system cellulose nitrate-cellulose acetate is studied by reversed-phase gas chromatography. The excess enthalpy ΔH _ji ^E , entropy ΔS _ji ^E , and Gibbs energy ΔG _ji ^E of mixing of the components, and also the Flory-Huggins interaction parameter χ_ji are estimated.     

Coincidence studies of collisionally induced fission of C 60 2+

A direct measurement of collisionally induced fission of C ₆₀ ²⁺ has been performed. We have measured coincidences between various charged fragments resulting from collisions between C ₆₀ ²⁺ and He atoms. The measurements show that C ₆₀ ²⁺ not only emits C₂ units but also breaks up into larger, singly charged parts. In this paper, we report on coincidences between C _n ⁺ (2≦n≦9) and C _m ⁺ (42≦m≦48) fragment ions.     

Heat capacity and thermodynamic functions of cadmium tellurites in the range of 298.15–673 K

The isobaric heat capacity of cadmium tellurites is studied by dynamic calorimetry in the range of 298.15–673 K to derive the equation for the C _p ^○ ～ f(T) dependence, and to determine the thermodynamic functions. The C _p ^○ ～ f(T) dependences exhibit sharp λ-shaped anomalous effects due apparently to secondorder phase transitions.     

Thermodynamic properties of alkaloids lappaconitine and glaucine

Calorimetric methods were used to study the enthalpy of solution of the alkaloids glaucine C₂₁H₂₅NO₄ and lappaconitine C₃₂H₄₄N₂O₈ in 96% ethanol and their heat capacity in the temperature ranges 173–298.15 and 173–423 K. Equations describing the dependences ΔH _sol ^m ～ f( $\sqrt m $ ) (m is molal concentration) and C _p ⁰ ～ f( $\sqrt T $ ) for the compounds under study were derived. The enthalpies of combustion, melting, and formation of C₂₁H₂₅NO₄ and C₃₂H₄₄N₂O₈ were estimated by means of theoretical calculations.     

Thermochemistry of aqueous solutions of nucleic acid bases and their alkylated derivatives

Enthalpy of solution, ΔH _sol ^o , enthalpy of sublimation, ΔH _subl ^o , apparent partial molar volume and heat capacities,V ₂ ^o andC _p,2 ^o were determined for aqueous solutions of thirty alkylated derivatives of uracyl and adenine, eight derivatives of cytosine and guanine. Calculated accessible surface areas and molar volumes are presented, too. The values of enthalpy of solution, enthalpy of sublimation can be useful in the studies on the nature of interaction between these compounds and water molecules. Apparent partial molar volume and heat capacity give a new aspect on hydrophob properties of the examined nucleic acid base derivatives.     

Sampling of aryldiazonium, anilino, and aryl radicals by membrane introduction mass spectrometry: Thermolysis of aromatic diazoamino compounds

Membrane introduction mass spectrometry (MIMS) is used to sample free radicals generated by thermolysis at atmospheric pressure. This is done by heating the solid sample in a custom-made probe that is fitted with a silicone membrane to allow selective and rapid introduction of the pyrolysates into the ion source of a triple quadrupole mass spectrometer. Phenyldiazonium radical (C₆H₅N ₂ ^· ) and some of its ring-substituted analogs, the methoxy anilino radical CH₃OC₆H₄NH^·, and aryl radicals are generated by gas phase thermolysis of symmetrical aryl diazoamino compounds (ArNH-N₂Ar). The radicals are identified by measurement of their ionization energies (IE) using threshold ionization efficiency data. A linear correlation between the ionization energy of the phenyldiazonium radicals and their Brown σ⁺ values is observed, and this confirms the formation of these species and validates the applicability of MIMS in sampling these radicals. The ionization energies of the aryldiazonium radicals are estimated as IE (p-CH₃O-C₆H₄N ₂ ^· ), 6.74 ± 0.2 eV; IE (p-CH₃-C₆H₄N ₂ ^· ), 7.72 ± 0.2 eV; IE (C₆H₅N ₂ ^· ), 7.89 ± 0.2 eV; IE (m-Cl-C₆H₄N ₂ ^· ), 7.91 ± 0.2 eV; IE (p-F-C₆H ₄ ^· N ₂ ^· ), 8.03 ± 0.2 eV; and IE (m-NO₂-C₆H₄N ₂ ^· ), 8.90 = 0.2 eV. The ionization energies of the aryl radicals are estimated as IE (p-CH₃O-C₆H ₄ ^· ), 7.33 ± 0.2 eV; IE (p-CH₃-C₆H ₄ ^· ), 8.31 ± 0.2 eV; IE (C₆H ₅ ^· ), 8.44 ± 0.2 eV; IE (m-Cl-C₆H ₄ ^· ), 8.50 ± 0.2 eV and IE (p-F-C₆H ₄ ^· ), 8.54 ± 0.2 eV. Also, the ionization energy of the p-methoxyanilino radical (p-CH₃O-C₆H₄NH^·) is estimated as 7.63 ± 0.2 eV.     

Thermodynamic modeling of the reaction of polychlorinated biphenyls with sodium methoxide

Thermochemical parameters, like standard enthalpy of formation (ΔH ₂₉₈ ⁰ ), enthalpy increment from 0 to 298 K (H ₂₉₈ ⁰ - H ₀ ⁰ ), standard heat capacity (C _p298 ⁰ ) and its temperature dependence [Cp(T)], and entropy (S ₂₉₈ ⁰ ), were calculated for the gaseous methoxy derivatives formed from polychlotinated biphenyl (PCB) congeners. Thermodynamic modeling and the HSC software were used to evaluate the reactivity of PCB congeners toward sodium methoxide in DMSO, and the calculation results were compared with experimental data.     

Kinetic energy release of clusters after multiphoton ionisation with time of flight and electrostatic analyser techniques

A new technique is presented which allows direct observation of initial kinetic energies in multiphoton ionisation-fragmentation processes of molecules and clusters and provides an unambiguous determination of metastable decay channels. Results are presented for the unimolecular loss of a monomer from clusters (C₆H₆) ₈ ⁺ to (C₆H₆) ₁₂ ⁺ and for the reaction C₆H ₆ ⁺ →C₄H ₄ ⁺ +C₂H₂. We also observe a significant amount of probably collision induced fragmentation processes (C₆H₆) _n ⁺ →(C₆H₆) _n?x ⁺ + (C₆H₆) _x withx much larger than 1.     

Reactivity of positively charged cobalt cluster ions with CH4, N2, H2, C2H4, and C2H2

Reactivity of positively charged cobalt cluster ions (Co _n ⁺ ,n=2?22), produce by laser vaporization, with various gas samples (CH₄, N₂, H₂, C₂H₄, and C₂H₂) were systematically investigated by using a fast-flow reactor. The reactivity of Co _n ⁺ with the various gas samples is qualitatively consistent with the adsorption rate of the gas to cobalt metal surfaces. Co _n ⁺ highly reacts with C₂H₂ as characterized by the adsorption rate to metal surfaces, and it indicates no size dependence. In contrast, the reactions of Co _n ⁺ with the other gas samples indicate a similar cluster size dependence; atn=4, 5, and 10?15, Co _n ⁺ highly reacts. The difference can be explained by the amount of the activation energy for chemisorption reaction. Compared with neutral cobalt clusters, the size dependence is almost similar except for Co ₄ ⁺ and Co ₅ ⁺ . The reactivity enhancement of Co ₄ ⁺ and Co ₅ ⁺ indicates that the cobalt cluster ions are presumed to have an active site for chemisorption atn=4 and 5, induced by the influence of positive charge.     

Collision-induced dissociation evidence for charge separation and “ball-and-chain” propagation in the addition of 1-butene to C 60 2+

The collision-induced dissociation of the adduct ions C₆₀(C₄H₈) ₂ ²⁺ and C₆₀(C₄H₈) ₃ ²⁺ formed by sequential reactions of C ₆₀ ²⁺ with 1-butene has been investigated by using a selected-ion flow tube (SIFT) apparatus. Experiments at 295 ± 2 K in 0.35 ± 0.02 torr of helium indicated that C ₆₀ ²⁺ adds at least five molecules of 1-butene in a sequential fashion with rates that decrease with the number of molecules added. Collision-induced dissociation experiments in which the downstream sampling nose cone of the SIFT was biased with respect to the flow tube indicated that the adduct ions C₆₀(C₄H₈) ₂ ²⁺ and C₆₀(C₄H₈) ₃ ²⁺ dissociate into C ₆₀ ^·+ and (C₄H₈) ₂ ^·+ and (C₄H₈) ₃ ^·+ , respectively. These observations provide evidence for the occurrence of charge separation in the derivatization of C₆₀ dications and support the “ball-and-chain” mechanism first proposed by Wang et al. in 1992 for the sequential multiple addition of 1,3-butadiene to C ₆₀ ²⁺ and C ₇₀ ²⁺ .     

Limiting partial molar volumes of solutions of oleic, linoleic, and linolenic acids in cyclohexane and benzene

High-precision vibration densimetry was used to measure (with an error of less than 5 × 10^?6 g/cm³) the density of dilute solutions (0≤ x ₂ ≤ 0.01 mole fractions) of oleic, linoleic, and linolenic acids in cyclohexane and benzene at 298.15 K. The limiting $\bar V_2^\infty $ and excess V ₂ ^{E, ∞} partial molar volumes of these C_{18: n} fatty acids in the indicated solvents were calculated. Benzene was demonstrated to selectviely influence the volumetric effects of dissolution (V ₂ ^{E, ∞} ) of the linoleic (n _C=C= 2) and linolenic (n _C=C = 3) polyunsaturated acids.     

Primary processes in the thiacyanine dimer-photosensitized reduction of p-nitroacetophenone in water by

Primary processes in the reduction of p-nitroacetophenone (p-NAP) by ascorbic acid (AA) in water photosensitized by thiacyanine dimers M ₂ ^2? have been considered. For M ₂ ^2? , the quantum yields of fluorescence and intersystem crossing to the triplet state (M ₂ ^2? )_T increases in comparison to the monomers M^?. The dimers (M ₂ ^2? )_T enter into the reactions of both one-electron photoreduction by ascorbic acid to give AA^+· and M ₂ ^3? and one-electron photooxidation by p-nitroacetophenone to give p-NAP^?· and the dimeric radical anion M ₂ ^? which dissociates to M^? and M^· within 25–30 μs. The primary oxidative or reductive photosensitization in the ternary systems containing (M ₂ ^2? )_T, p-NAP, and AA affords p-NAP^?· and AA^+·.     

The thermodynamic parameters of oxygen nonstoichiometry defects in lanthanum cobaltite doped with acceptor impurities (Sr and Ni)

The oxygen nonstoichiometry δ of lanthanum cobaltite doped with acceptor impurities (Sr and Ni), La_{1 ? x} Sr_xCo_0.9Ni_0.1O_{3 ? δ} (x = 0.1, 0.3), was studied by high-temperature thermogravimetry over the temperature and pressure ranges 723 K ≤ T ≤ 1373 K and 10^?3 atm ≤ $p_{O_2 } $ ≤ 1 atm. The partial replacement of cobalt with nickel and lanthanum with strontium increased the oxygen nonstoichiometry δ. The partial molar enthalpies $\Delta \bar H^\circ _O $ and entropies $\Delta \bar S^\circ _O $ of solution of oxygen in the solid phase were calculated. Models of point defect formation were suggested and analyzed. The equilibrium constants of formation and concentrations of predominant point defects, ionized oxygen vacancies V _o ^.. , holes Me _Co ^. (Co _Co ^. and Ni _Co ^. ), and electrons Me _Co ^′ (Co _Co ^′ and Ni _Co ^′ ) localized on 3d transition metals, were determined by nonlinear regression from the experimental and theoretical logp $p_{O_2 } $ ?δ dependences.     

Fragmentation of doubly charged ammonia cations NH 3 ++ studied by the photoion-photoion coincidence (PIPICO) method

Doubly charged NH ₃ ⁺⁺ cations were produced by double photoionization of neutral ammonia molecules by using the synchrotron radiation from ACO as a photon source of variable energy in the 35–49 eV energy range. The fragmentation of NH ₃ ⁺⁺ was studied by the photoion-photoion coincidence (PIPICO) method. NH ₃ ⁺⁺ cations were produced in the \(\tilde X^1 \) A ₁ and \(\tilde B^1 \) electronic states of which the onset energies were measured at, respectively, 35.4±0.5 eV and 44.5±0.5 eV. It was shown that the NH ₃ ⁺⁺ ions, initially produced in their \(\tilde X^1 \) A ₁ state, rapidly dissociate (in less than 50 ns), into NH ₂ ⁺ + H⁺. Furthermore, the comparison with results obtained by other methods indicates that NH ₃ ⁺⁺ ions can either be long-lived (τ>10 µs) or slowly dissociating (1 µs<τ<10 µs) or rapidly dissociating (τ<50 ns), depending on their geometry and/or internal energy in their \(\tilde X^1 \) E A ₁ electronic state.     

Analytical photoion spectroscopy applied to dissociative single and double photoionization of diatomic molecules (H2, N2, O2, CO,and NO)

This work reports the principle, advantage, and limitations of analytical photoion spectroscopy which has been applied to dissociative photoionization processes for diatomic molecules such as H₂, N₂, CO, and NO. Characteristic features observed in the differential photoion spectra are summarized with a focus on (pre)dissociation of(i) multielectron excitation states commonly observed in the inner valence regions,(ii) shape resonances, and(iii) doubly charged parent ions. Possible origins for negative peaks in the differential spectra are discussed. This spectroscopy is applied to the reported photoion branching ratios for D₂ (and H₂ at high energies). The main findings are as follows: (1) The direct dissociation of theX ²Σ _g ⁺ (1sσ _g ) state of D ₂ ⁺ , the two-electron excited state¹Σ _u ⁺ (2pσ _u 2sσ _g ) of D₂, and the²Σ _u ⁺ (2pσ _u ) state of D ₂ ⁺ appear clearly in the differential spectrum, as previously observed for H₂. (2) Decay of H ₂ ⁺ (D ₂ ⁺ ) to H⁺ (D⁺) above 38 eV is due to the direct dissociation of highly excited states of H ₂ ⁺ (D ₂ ⁺ ) such as the²Σ _g ⁺ (2sσ _g ) and high-lying Rydberg states converging on H ₂ ²⁺ (D ₂ ²⁺ ). (3) In the ionization continuum of H ₂ ²⁺ (D ₂ ²⁺ ) peculiar dissociation pathways are observed. The differential photoion spectra for O₂ derived from the reported photoion branching ratios are also presented. The (pre)dissociation of theb ⁴Σ _g ^? ,B ²Σ _g ^? , III²Π _u ,²Σ _u ^? , and^2,4Σ _g ^? states of O ₂ ⁺ appears as the corresponding positive values in the spectra in accord with previous observations. Some other dissociation pathways possibly contributing to the spectra are discussed including dissociative double ionization.     

Measurement and Correlation of Excess Molar Enthalpy of Binary Mixtures Containing Butyl Acetate + 1-Alkanols (C1–C6) at 298.15 K

Excess molar enthalpies, ?H _m ^E , for the binary mixtures of butyl acetate + 1-alkanols, namely (methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol), were measured over the whole range of composition at 298.15 K using a Parr 1455 solution calorimeter. The excess partial molar enthalpies, ?H _m,i ^E , were calculated from the experimental excess molar enthalpies using the Redlich–Kister polynomial equation. The sign of ?H _m ^E for all systems are positive because of the disruption of hydrogen bonding and dipole–dipole interactions in the alkanols and esters, respectively. The magnitude of the ?H _m ^E values increases with increasing alkyl chain length. The behavior of ?H _m ^E was analyzed in terms of the length of the alkanol chain, the nature and type of intermolecular interactions and the balance between positive and negative effects on deviations from ideality. The experimental excess molar enthalpy data have also been correlated using the Redlich–Kister and SSF equations and two local composition models (UNIQUAC and NRTL).     

On the stability of Pb n m+ -clusters

The stability of multiply charged Pb _n ^m+ -clusters (n ≤ 3;m=0, 1, 2) was studied by solving exactly for the valencep-electrons a many body Hubbard-like Hamiltonian with intra- and interatomic Coulomb interactions. Particularly we obtain that Pb ₃ ²⁺ has a metastable ground state, in which Pb ₃ ²⁺ has isosceles shape (bond lengthR=3.2 Å, bond angle θ=124°) and a positive binding energyE _B =3.4 eV. The activation barrier against dissociation into Pb ₂ ⁺ + Pb⁺ is 0.13 eV, yielding a very long lifetime. This is in agreement with recent experiments [1] in which the lifetime of Pb ₃ ²⁺ was determined to be at least 10^?6 s. Comparison with self consistent Hartree-Fock calculations shows that the metastability of Pb ₃ ²⁺ is due to electronic correlations within the paramagnetic ground state.