The X1Σ+ ground state of kh near the dissociation limit

Fluorescence excited in the A¹Σ⁺ -X¹Σ⁺ system of ³⁹KH by the 4880 Å argon-ion laser line gives information about the ground state as far as the last bound rovibrational level. This is identified as J = 6 in v = 23, and, assuming a limit midway between J = 6 and J = 7, D_e(KH) = 14776 ± 4 cm⁻¹.     

Thermodynamic properties of ethanol and water— III. Description of the different excess functions (gE,hE, cEP) using an empirical model

Published values of the thermodynamic excess functions (g^E, h^E, c^E_P) are used to fit the temperature-dependent parameters of an empirical g^E model. A modified Redlich-Kister approach with six concentration-dependent coefficients is chosen as a model equation for the excess Gibbs energy. The temperature dependence of the coefficients is defined in such a way that the result is a quadratic dependence of the molar excess heat capacity c^E_P as a function of the temperature. The fitting is carried out over the temperature range 25–150°C using the maximum likelihood method combined with the Gauss-Newton procedure (Anderson et al.). The h^E and c^E_P data, in particular, are clearly reproduced much better than when a fit based only on VLE data is used.     

Evaluation of the valency of Fe,Cr, Cu,Sb doping ions in Pb(Zr0.95Ti0.05)O3 ceramics

The valency of the ions Fe, Cr, Cu, Sb, incorporated in PZT 95/5 ceramics, is evaluated from the viewpoint of a correlation between the mean radius of the ions at the octahedral site and the two parameters: the temperature of the antiferroelectric-ferroelectric phase transition, and the volume of the unit cubic cell. It is found that Fe and Cr enter as Fe²⁺ and Cr²⁺ at the B site. Experiments suggest that Cu is incorporated at the B site as Cu⁺ and Cu²⁺ and that Sb enters partly at the A site as Sb³⁺ and mainly at the B site as Sb⁵⁺.     

The orbital description of the potential energy curves and properties of the lower excited states of the BH molecule

The electronic wavefunctions for the ground (X¹ Σ⁺) and the low-lying excited states (a³Π, A¹Π, ³Σ⁺) of the BH molecule have been calculated as a function of internuclear distance using the ab initio generalized valence bond method (GVB) with optimization of spin coupling (SOGI). The potential curve of the A¹Π state in the zero rotational level is found to have a hump of 0.150 eV at R = 3.8₉a_o (experimentally a hump of unknown size is found at 3.9 ± 0.4 a₀); a smaller hump at larger R (0.02 eV at R = 4.9₂a₀) is also found for the calculated a³Π state. The presence of such humps is found to result from the recoupling of orbitals that must occur as R is decreased from ∞ to R_e and is comparable in origin to the activation barrier in a radical exchange reaction (e.g., H₂ + D ? HD + H). The calculated binding energies of the BH states are 3.272 eV (X¹ Σ⁺), 2.216 eV (a³ Π), and 0.502 eV (A¹ Π). The ³Σ⁺ state is unbound although it does exhibit a small unbound minimum. The dipole moment, quadrupole moment, and electric field gradient are calculated as a funtion of R. The shapes of the potential curves and the properties are interpreted in terms of simple qualitative considerations of the GVB orbitals.     

Solution of the complex eigenvalue Schrödinger equation for the rydberg series of inner hole excited autoionizing states. The Be 1s 2s 2 n p (n=2–5)3 P 0 and1 P 0 series

In the state-specific theory of autoionizing states, the square-integrable wavefunction of complex coordinates corresponding to the complex eigenvalue is separated into terms contributing to the stability of the state and terms contributing to its decay. The choice and optimization of the function spaces describing these terms are different. In this work, taking the inner hole excited Be 1s 2s ² n p Rydberg series as an example, we compute the asymptotic correlation and the concomittant energy shifts and widths by expanding the open channels in terms ofback-rotated generalized Laguerre polynomials and by diagonalizing a complex Hamiltonian matrix where the coordinates of the operator and of the occupied and virtual orbitals are real. Interchannel coupling is determined by mixing the independently optimized asymptotic pair correlation functions via the diagonalization of the total matrix. We found that, as expected, the Auger widths of both³ P ⁰ and¹ P ⁰ series converge as a function ofn to the value of the previously determined width of the Be⁺ 1s 2s ^{2 2} S state. We also computed the oscillator strengths of the transitions Be 1s ² 2s ^{2 1} S→1s 2s ² n p ¹ P ⁰, which had previously been calculated within the time-dependent Hartree-Fock approximation. Forn>2, the discrepancy is large.     

The influence of uncompensated solution resistance on the determination of standard electrochemical rate constants by cyclic voltammetry,and some comparisons with a.c. voltammetry

a digital simulation analysis is presented of the deleterious effects of uncompensated solution resistance, R_us, on the evaluation of standard rate constant, k^s_ob, by cyclic voltammetry. The results are expressed in terms of systematic deviations of “apparent measured” rate constants, k^s_ob(app), evaluated in the conventional manner without regard for R_us, from the corresponding actual values, k^s_ob(true), as a function of R_us and other experimental parameters. Attention is focused on the effects of altering the electrode area and the double-layer capacitance on the extent of the deviations between k^s_ob(app) and k^s_ob(true), and on comparisons with corresponding simulated results obtained from phase-selective a.c. impedance data. The extent to which k^s_ob(app) <k^s_ob(true) for small R_us values was found to be similar for the cyclic and a.c. voltammetric techniques. The latter method is, however, regarded as being preferable under most circumstances in view of the greater ease of minimising, as well as evaluating, R_us for a.c. impedance measurements. The influence of solution resistance on k^s_ob measurements with microelectrodes and without iR compensation is also considered.     

Three-dimensional derivative spectrochimatograms in high-performance liquid chromatography and their implications for peak homogeneity validation

The full ultraviolet spectra generated by a photodiode-array detector are transformed to the nth derivative (dⁿA/dλⁿ). The bipolar, three-dimensional data matrix (dⁿA/dλⁿ, λ, t) is presented with computer-aided graphics as an extension of the spectrochromatogram concept to aid peak validation. Existing display algorithms are modified to yield several presentations which reveal the full topography of the elution profile. These include rotation in three-dimensional space and inspection of the positive and negative data planes. A novel contour-plot representation is proposed to enable the derivative spectrochromatographic data to be presented in a two-dimensional format. Two planes of data (i.e., positive and negative amplitudes of (dⁿA/dλⁿ) in the (λ, t) plane) can be displayed as required for derivative data presentation. The technique is used to assess the homogeneity of overlapping peaks of ethynyloestradiol and norethisterone.     

Électrochimie dans le carbonate de propylène: II. Utilisation du système Ar+/Ar− des hydrocarbures aromatiques alternés comme référence de potentiel indépendante du solvant

The standard potentials of Ar⁺/Ar and Ar/Ar^? redox couples of some mono- and poly-nuclear aromatic hydrocarbons have been measured in propylene carbonate. It appears that: (a) the difference E⁰(Ar⁺/Ar)?E⁰(Ar/Ar^?) is constant in various solvents for a given hydrocarbon; (b) in a medium, the sum E⁰(Ar⁺/Ar)+E⁰(Ar/Ar^?) is independent of the hydrocarbon. These results confirm that the Ar⁺/Ar^? system can be used as a solvent-independent reference for potential comparisons.     

Rotational relaxation in the Ar—N2 system

The first (Z⁽¹⁾) and second (Z⁽²⁾) approximations to the rotational number of the Ar—N₂ system are compared for a range of temperatures. Although Z⁽¹⁾ and Z⁽²⁾ differ by a significant amount their difference remains nearly constant as a function of temperature. The effects of mass and potential parameter variations on the rotational relaxation time are also studied. When the mass of the incoming atom is decreased Z⁽²⁾ goes through a minimum while Z⁽¹⁾ steadily increases.     

Field shifts in hafnium II

By means of classical interference spectroscopy, using enriched isotope samples, the isotope shift between¹⁷⁸Hf and¹⁸⁰Hf has been measured for 33 transitions in the Hf II spectrum. For the pure Russell-Saunders terms 5d ²6s ⁴ F and² F the parametric analysis yields a field-shift difference of 17(2) mK produced by the second-order interaction of the electrostatic operator and the field-shift operator. Semi-empirical calculations based on the non-relativistic Hartree-Fock method reproduce this value as well as the experimental field shifts if a factor of 1.68(6) is used to scale theab initio electron densities at the nucleus. The corresponding factor for the Hf atom is much smaller. This leads to a re-evaluation of screening ratios for Hf and to a more accurate value of the nuclear parameter λ^178,180 (Hf)=0.072(4) fm².     

Intra- and inter-atomic auger processes in collisions of low energy He++, He+, He* (23,S, 21 S) and Li+ with Li covered W(110) surfaces

Electron spectra from He⁺⁺, He⁺ and Li⁺ (10 to 1500 eV) ions colliding under grazing incidence with Li covered W (110) surfaces are reported. The results are compared with those obtained from thermal collisions of (2³ S; 2¹ S) metastable He atoms. In these collisions 1s vacancies are either produced during the collision event (energetic He⁺ (Li ⁺) collisions) or are brought into the collision (slow He⁺⁺ (He⁺, He*) collisions). Population of the 2s orbitals by two electrons produces states which decay by intraatomic Auger processes: we observe autoionization of He** (2s ²) and Li** (1s 2s ²) as well as autodetachment of He^?* (1s 2s ²). Alternatively the 1s-holes in the projectile or target (Li) can be filled by Auger processes involving one or two surface electrons. The processes leading to electron emission are studied as a function of the Li coverage in the submonolayer region (0≦Θ_Li≦1Ml) and as a function of the projectile energy. It is concluded that with one or two 1s vacancies present in the projectile the double capture of two surface electrons constitutes an important process responsible for electron emission of low work function surfaces.     

Influence of charge-compensating ions on the luminescence of vanadium-activated sulfates

Samples CaSO₄V⁵⁺, Me³⁺ show mainly unassociated-vanadate emission if Me³⁺ is smaller than the Ca²⁺ ion and mainly associated-vanadate emission if Me³⁺ is about as large as the Ca²⁺ ion. Samples MgSO₄V⁵⁺, Me³⁺ show efficient yellow emission at room temperature.     

Relativistic all electron configuration interaction calculation of ground and excited states of the gold hydride molecule

We present relativistic configuration interaction calculations with the spin-free no-pair hamiltonian on the gold hydride molecule, treating the ground state as well as the eleven lowest excited states. The calculations provide a picture of the bonding in theX ¹Σ⁺ ground state consistent with previous work on this species using four-component spinors: compared to non-relativistic calculations, the dipole moment is reduced by a factor of two, hybridization (and thus participation ofd orbitals at the bonding) is greatly enhanced, the bond length is shortened by 20 pm, and the dissociation energy is increased by 50%. Comparison of the spin-averaged potential curves of the excited states with experiment suggests a reinterpretation of theC ¹Σ⁺ as the 0⁺ fine structure component of 2³Π and the prediction of a weakly bound³Σ⁺ state with weak transitions to the ground state in the range of 2.9–3.1 eV.     

Influence of excluded volume on the conformational property of tail-like chain on the simple cubic lattice

The influence of excluded volume on the conformational property of linear tail-like chain with one end attached to a flat surface is investigated by means of dynamic Monte Carlo method. Conformational properties such as mean-square end-to-end distance 〈R²〉, mean-square radius of gyration 〈S²〉 and mean asphericity parameter 〈A〉 are calculated for random walking (RW) and self-avoiding walking (SAW) tail-like chains on the simple cubic lattice. We find that the EV has nearly the same effect on 〈R²〉 as on 〈S²〉: (1) 〈R²〉_SAW/〈R²〉_RW≈〈S²〉_SAW/〈S²〉_RW∝n^0.204±0.05, where n is the chain length, and (2) the limiting value of 〈R²〉/〈S²〉≈7.7 for both chains. The distribution P(R) of the SAW tail-like chain can be expressed as a R⁴ correction of that of the RW one. We find that the value 〈A〉 of the SAW tail-like chain is bigger than that of the RW tail-like chain for all chain lengths, and the limiting values are 0.446±0.006 and 0.403±0.005 respectively.     

Crystal-field calculation of the 3d multiplets of the binuclear Ni(II) monothiocarboxylates

The electronic spectra of the dimers (Ni(RCOS)₂)₂ and (Ni(RCOS)₂)₂ · C₂H₅OH are calculated by crystal-field theory in terms of different polyhedra of coordination around the two Ni²⁺ ions. The necessary radial parameters are taken from other clusters of Ni²⁺ after a detailed study of their intercluster transferability. The calculations are organized in two blocks. In the first one, the Ni²⁺Ni²⁺ interaction is neglected and the clusters Ni^AS₄, Ni^BO₄, and Ni^BO₅ are considered. In the second block, this interaction is explicitly taken into account as a point-charge perturbation produced by one of the two metal ions on the 3d states of the other one. Accordingly, we deal with the Ni^AS₄Ni^B, in which the Ni^B acts as a pointlike ligand of charge q, and with the Ni^BO₄Ni^A and the Ni^BO₅Ni^A, where the Ni^A is the punctual ligand. The calculation shows that the optical spectra and magnetic moments of these dimers can be best reproduced if $\text{q ? 0}$, i.e., when the metal-metal electrostatic interaction is negligible. The agreement with the experiments quickly disappears as q grows. This calculation supports the interpretation of Melson et al. (Inorg. Chem.9, 1116 (1970)) according to which the 3d electronic distribution of the Ni²⁺ ions in these dimers is probably controlled by their nearest neighbors rather than by the metal-metal interaction.     

Zur Thermodynamik der Mischungen von n-Alkoholen mit Kohlenwasserstoffen

A method is presented which allows to describe the concentration dependence of the excessGibbs free energyG ^E as well as its variation with temperature in mixtures of n-alcohols with various hydrocarbons. The number of data required is reduced to one experimental point of the excessGibbs free energy for each system. The theoretical treatment is based on the work ofFlory ^{1, 2} and ofRenon andPrausnitz ³. The excess volume due to mixing and association is neglected, but differences in the size of the various species are taken into account. This procedure yields a thermodynamic correlation between the excessGibbs free energy and the enthalpy of mixingH ^E of alcohol-hydrocarbon solutions and results in a comprehensive formalism including nonassociated mixtures.     

Synthesis of 13C4-labelled oxidized metabolites of the carcinogenic polycyclic aromatic hydrocarbon benzo[a]pyrene

Polycyclic aromatic hydrocarbons (PAHs), such as benzo[a]pyrene (BaP), are ubiquitous environmental contaminants that are implicated in causing lung cancer. BaP is a component of tobacco smoke that is transformed enzymatically to active forms that interact with DNA. We reported previously development of a sensitive stable isotope dilution LC/MS method for analysis of BaP metabolites. We now report efficient syntheses of ¹³C₄-BaP and the complete set of its ¹³C₄-labelled oxidized metabolites needed as internal standards They include the metabolites not involved in carcinogenesis (Group A) and the metabolites implicated in initiation of cancer (Group B). The synthetic approach is novel, entailing use of Pd-catalyzed Suzuki, Sonogashira, and Hartwig cross-coupling reactions combined with PtCl₂-catalyzed cyclization of acetylenic compounds. This synthetic method requires fewer steps, employs milder conditions, and product isolation is simpler than conventional methods of PAH synthesis. The syntheses of ¹³C₄-BaP and ¹³C₄-BaP-8-ol each require only four steps, and the ¹³C-atoms are all introduced in a single step. ¹³C₄-BaP-8-ol serves as the synthetic precursor of all the oxidized metabolites of ¹³C-BaP implicated in initiation of cancer. The isotopic purities of the synthetic ¹³C₄-BaP metabolites were estimated to be ≥99.9%.     

On the electronic structure of the Ni4+2 ion and its relation to the metal-metal bonding in binuclear Ni(II) complexes

In an attempt to improve the understanding of the electronic structure of the Ni²⁺ thiocarboxylates, we have analized, as a zeroth-order approximation, the electronic structure of the Ni⁴⁺₂ dimer in vacuo. Two small-size Slater-type orbitals (STO) basis sets have been used in order to study basis effects, referring particularly to the details of the d-d interactions. All the electrons have been included and all the molecular integrals have been computed accurately. All the multiplets of the {Ar₂}σ²_gσ²_gπ⁴_gπ⁴_uδ^x_gδ^4?x_u (x = 0 to 4) configurations have been calculated at different values of the Ni²⁺Ni²⁺ distance, R, ranging from 3.20 to 5.20 a.u. in the smaller basis calculation and from 3.20 to 4.20 a.u. in the larger basis calculation. Inclusion of configuration interaction (CI) limited to the δ^x_gσ^4?x_u (x = 0 to 4) configurations yields a ³Σ^?_g as the lowest multiplet. This CI reduces R_e from 2.03 to 1.76 Å, an effect also encountered in much more extensive CI calculations on Ni₂. The bonding in Ni⁴⁺₂ is discussed in terms of the R dependence of the orbital energies; σ, π, and δ interactions seem to make important contributions to the bonding, in view of their orbital splittings and stabilizations with respect to the free-ion values. The present results are compared with previous nonempirical studies on the Ni₂ and Ni⁺₂, as well as with empirical relationships among different molecular constants. The relevance of the results on Ni⁴⁺₂ to the question of the metal-metal interaction in {Ni(RCOS)₂}₂ compounds is difficult to discuss with certainty, but, mainly from the theoretical geometry obtained, it is argued that the Ni²⁺Ni²⁺ interactions might have a very small contribution to the selling of the electronic structure of the thiocarboxylates.     

CEPA calculations on open-shell molecules

Ab initio calculations at SCF and CEPA levels using large Gaussian basis sets have been performed for the two lowest electronic states,X ² Σ⁺ andA ² Π, of HeAr⁺. Spin-orbit coupling (SOC) effects have been added using a semiempirical treatment. The resulting potential curves for the three statesX,A ₁, andA ₂ have been used to evaluate molecular constants such as vibrational intervals ΔG(v + 1/2) and rotational constantsB _v as well as — by means of a Dunham expansion — equilibrium constants such asR _e , ω _e ,B _e etc. Comparison with the experimental data from UV emission spectroscopy shows that the calculated potential curves are slightly too shallow and have too large equilibrium distances:D _e = 242 cm^?1 andR _e = 2.66 Å compared to the experimental values of 262 cm^?1 and 2.585 Å, respectively, for theX ²Σ⁺ ground state. However, the ab initio calculations yield more bound vibrational levels than observed experimentally and allow for a more complete Dunham analysis, in particular for theA ₂ state. The experimental value of 154 cm^?1 for the dissociation energyD _e of this state is certainly too low; our best estimate is 180±5 cm^?1. For theA ₁ state our calculations are predictions since this state has not yet been observed experimentally.     

Two-photon absorption of dissociating TLI in strong laser fields

In a strong laser field (I=2 GW/cm²) TlI is dissociated by a two-photon process and the Tl fragment is detected state specifically. The yield of Tl 6p ² P _3/2 (Tl*) is measured as a function of the dissociation wavelength (480 nm–540 nm). If the dissociation wavelength is close to two-photon transitions of the Tl atom from 6p ² P _3/2 to np² P _1/2,3/2 or mf² F _5/2,7/2,n=10 ... 15,m=7 ... 12 dips in the yield are observed. These dips show a significant asymmetric broadening, compared to a free atomic transition and the observation is interpreted as an absorption process of the transient state of dissociating TlI during the laser pulse. By applying the Landau-Zener approximation for the potential crossing of dressed molecular states, we are able to describe the broadening and the power density dependence of the observations. Simulations show that the asymmetry is determined by the difference potential of the electronic states which are coupled by the laser field.