Comparison of rate coefficients for rydberg electron and free electron attachment

New experimental results on attachment reactions involving free electrons at sub-meV resolution allow for the first time a conclusive comparison of measured rate coefficients for Rydberg electron attachment with those calculated from the measured free electron cross sections on the basis of the quasi-free electron model for Rydberg electron collisions. Using classical velocity distributions for the highn Rydberg electrons and our measured free electron attachment cross sections, we calculate Rydberg electron attachment rate coefficientsk _n for the two cases SF₆ and HI for Rydberg binding energies |E _n | of 0.1–40 meV. We find a significant increase ink _n towards lower binding energies, especially for HI, which is due to the deviation of the free electron cross section from the limitings-wave behaviour ₀E ^–1/2. The increase at |E _n |2 meV is in qualitative agreement with our highn Rydberg data (n80) if -mixing due to residual electric fields is taken into account. For low , Rydberg rate coefficientsk _n(|E _n |) are significantly larger than free electron rate coefficientsk _e (E=|E _n |), while for circular orbits (=n–1) they agree. On average, attachment reactions of Rydberg electrons in low orbits proceed with an effective collision energy substantially smaller than the binding energy |E _n |.     

Exact solutions of the rigid rotor in the electric field

We first present a new constraint condition on the confluent Heun function H_C(α, β, γ, δ, η;z) (β, γ ≥ 0, z ∈ [0, 1]) and then illustrate how to solve the rigid rotor in the electric field. We find its exact solutions unsolved previously through solving the Wronskian determinant. The present results compared with those by the perturbation methods are found to have a big difference for a large parameter a. We also present 2D and 3D probability density distributions by choosing different angular momentum quantum numbers l. We observe that the original eigenvalues with degeneracy (2 l + 1) are split into the (l + 1) state with approximate eigenvalues l(l + 1) for small a but large l.     

l-Lactat-Durchflu?elektrode mit immobilisierter Lactat-Oxidase

Zusammenfassung Eine leicht zu handhabende l-Lactat-Durchflußelektrode mit immobilisierter Lactat-Oxidase wird beschrieben. Sie ist Bestandteil eines dreikanaligen O₂-sensitiv-enzymatischen Meßsystems für l-Lactat, Pyruvat und -d-Glucose. Der l-Lactat-Sensor weist eine schnelle Einstellzeit, geringe Streuung um die errechnete Regressionsgerade und einen für die klinisch-chemische Analytik adäquaten linearen Anzeigebereich auf. Meßkurven werden demonstriert. Auf den Chemismus anderer üblicher elektrochemisch-enzymatischer Meßverfahren von l-Lactat wird hingewiesen und auf die klinische Bedeutung der l-Lactat-Bestimmung Bezug genommen.

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l-lactate flow-through electrode with immobilized lactate oxidase

Summary An l-lactate flow-through electrode with immobilized lactate oxidase is described that is easy to handle. It is part of a three-channel O₂-sensitive enzymatical measuring system for l-lactate, pyruvate and -d glucose. The l-lactate sensor features a short response time, little variation about the regression line computed and a linear indicating range adequate for clinical-chemical analysis. Measurement diagrams are demonstrated. The chemism of other conventional electrochemical-enzymatical measuring methods for l-lactate is mentioned, and reference is made to the clinical importance of l-lactate determination.

     

Characterization of the Retro-[3+2] Reaction of Protonated 2,3′-Bisindolylmethanes by Electrospray Ionization–Tandem Mass Spectrometry

Twelve 2,3′-bisindolylmethanes with various substituents were investigated using electrospray ionization quadrupole time-of-flight tandem mass spectrometry in positive ion mode. A retro-[3+2] reaction was observed in the collision-induced dissociation spectra of protonated 2,3′-bisindolylmethanes for the first time. The mechanism of retro-[3+2] reaction was concerted or stepwise. For the concerted pathway, carbon–carbon bonds of a protonated compound simultaneously cracked and the m/z 208 ion ([C₁₅H₁₀D₂N]⁺) was observed with hydrogen–deuterium exchange labeling. The stepwise pathway goes through 1,3-hydrogen migration twice and the m/z 208 ion ([C₁₅H₁₀D₂N]⁺) and m/z 207 ion ([C₁₅H₁₁DN]⁺) were detected with deuterium labeling. In the deuterium-labeled tandem mass spectrum for one compound, only the peak at m/z 208 was present at high abundance, suggesting that the concerted pathway is more likely. In addition, the substituents have no obvious trends on the ratios of the product intensity to the base intensity, further supporting the concerted pathway.     

Anion intercalation and exchange in Al(OH)3-derived compounds

Precipitation of Al³⁺ at pH = 10 in excess Li₂CO₃ leads to an anion exchanging compound, [Al₂Li(OH)₆]⁺₂CO²⁻₃. This compound exhibits, compared to [Mg₃Al(OH)₈]⁺₂CO²⁻₃, a higher degree of size selectivity in anion exchange. The structure of the [Al₂Li(OH)₆]⁺ layers is gibbsite-like, with a (110) diffraction feature at d = 4.35 Å indicating a pronounced Al³⁺ ordering. As claimed originally by Serna et al., the structure is [Al₂Li(OH)₆]⁺A^z−_1/z rather than [Al₂(OH)₆]Li⁺A^z−_1/z, with the Li⁺ coordinated in the octahedral positions left vacant by Al³⁺. This emerges from the details of a lithium-leaching process, which proposedly leads to a novel compound, [Al₂H(OH)₆]⁺A^z−_1/z.     

水合Pb(OH)~+在高岭石(001)晶面的吸附机理(英文)

采用密度泛函理论广义梯度近似平面波赝势法,结合周期平板模型,探讨了水体环境中Pb(OH)+在高岭石铝氧八面体(001)晶面的吸附行为和机理,确定了吸附配合物的结构、配位数、优势吸附位和吸附类型.结果表明,Pb(II)与高岭石铝氧(001)面的氧原子形成单齿或双齿配合物,其配位数为3-5,均为半方位构型.高岭石表面存在含"平伏"氢原子的表面氧(Ol)位和含"直立"氢原子的氧(Ou)位,后者更易与Pb(OH)+单齿配位,该吸附配合物具有较高的结合能(-182.60 kJ·mol-1),为优势吸附物种;高岭石表面位于同一个Al原子上的"OuOl"位可形成双齿配合物.表面Ol与水分子配体形成氢键,对配合物的稳定性起到关键作用.Mulliken布居和态密度分析表明,高岭石单齿配合物中Pb―O成键机理主要为Pb 6p轨道与Pb 6s―O 2p反键轨道进行耦合,电子转移到反键轨道.双齿配合物"Pb―Ol―H"共配位结构中,受配位氢原子影响,Pb―Ol成键过程成键态电子填充占主导地位.     

Analysis of the Rydberg structure in the vapor-phase electronic absorption spectrum of (η7-cycloheptatrienyl)(η5-cyclopentadienyl) chromium

Parameters of the Rydberg transitions in the vapor-phase absorption spectrum of (η⁷-C₇H₇)(η⁵-C₅H₅)Cr were analyzed in detail. A correspondence between the three Rydberg series in the short-wavelength region of the spectrum and low-frequency Rydberg bands was established. Vibronic structure of the observed transitions to the lowest Rydberg s, p _x,y , p _z , and d _xz,yz levels was interpreted. The long-wavelength and short-wavelength series, respectively characterized by quantum defect (σ) values of 1.26 and 0.82, were unambiguously assigned to the Rydberg p _x,y and d _xz,yz excitations, respectively. Transitions from the 3d _z 2 orbital to theR(n−1)f,Rnd _z 2, andRnp _z levels can contribute to the series characterized by a σ value of 1.04. The assignment was made of Rydberg bands in the spectral region corresponding to the principal quantum number (n) values of 5, 6, and 7 (in this region, interpretation of the spectral pattern is complicated because of the band shifts and broadening). Atn>5, changes in the σ values of the Rydberg excitations with increase in then value are due to configuration interaction. The electronic-excited states, which can be responsible for the observed changes in the Rydberg parameters, were determined. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1677–1684, September, 1999.     

Spectrophotometric Determination of Nitrogen Dioxide <Nitrite>

Abstract

A highly sensitive spectrophotometric method has been developed for the determination of nitrogen dioxide (nitrite as NO_z ^?) by reacting manganese dioxide in 1:20 perchloric acid. An amount of manganese dioxide (MnO_z) equivalent to the concentration of nitrogen dioxide becomes soluble due to the reduction of Mn (IV) to Mn (II) by nitrite in acidic medium. The soluble Mn (II) ion is filtered to remove excess of MnO₂ and is oxidized to permanganate ion by periodic acid in presence of phosphoric acid. The violet colored solution shows maximum absorbance at 525 nm. The sensitivity of the method is 0.08 ppm based on 0.0044 absorbance, and Beer's law is obeyed in the concentration range of 0.2 to 10.0 μg/mL of NO₂ ^?. Molar absorbance is found to be 2442 at 525 nm.

In the present investigation NO₂ ^? was treated with excess of MnO₂ in 1:20 perchloric acid where NO₂ ^? reduces equivalent amount of Mn (IV) to Mn (II) and becomes soluble. The soluble Mn (II) was heated to boiling and 25 mg (approx.) periodic acid is added and cooled. The volume of each solution is made to 50 mL in volumetric flask. Reagent blank is prepared in similar way except sodium nitrite solution. The absorbance is measured at 525 nm against reagent blank.     

Excitonic Bands in the Spectra of Some Organic-Inorganic Hybrid Compounds Based on Metal Halide Units

Summary.  The optical absorption, photoluminescence, and photoconductivity spectra of some compounds of the formulas [R(CH₂) _n NH₃] _x M _y X _z , [R(CH₂) _n NH(CH₃)₂] _x M _y X _z , [R(CH₂) _n S(CH₃)₂] _x M _y X _z , [R(CH₂) _n SC(NH₂)₂] _x M _y X _z , and [R(CH₂) _n SeC(NH₂)₂] _x M _y X _z (R = organic residue; M = Bi(III), Pb(II), Sn(II), Cu(I), Ag(I) etc; X = I, Br, Cl; n, x, y, z = 0, 1, 2, 3, …) are briefly reviewed, and some new results are reported. The position, intensity, and shape of the excitonic bands depend on the dimensionality and size of the inorganic network as well as on the nature of the M, X, R, and onium moieties. Received June 23, 2000. Accepted August 1, 2000     

On the Sanibel coefficients in the expansion of spin-projected slater determinants

Every Slater determinant D may be uniquely analyzed in terms of spin components D_l = O_lD which are pure spin eigenfunctions, so that S²D_l = l(l+1)D. Every component D_l = O_lD may in turn be written as a sum of symmetric combinations of Slater determinants, T_k = [α^μ?kβ^k‖α^kβ^ν?k], and the coefficients c in the expansion O_lD = ∑_k c T_k are known as the “Sanibel coefficients.” By using the relation S²D_l = l(l+1)D, a recursion formula for the coefficients c is derived, which is then explicitly solved in the special case when S_z has the pure quantum number m = 0.     

Atomic bonding of neutral and cationic Mn clusters

By using the spin-polarized DV-X-LCAO method, electronic states of neutral and cationic Mn _N clusters (N=25) are calculated to study atomic bonding of Mn clusters. For the neutral Mn₂ cluster, the equilibrium interatomic distance is much larger than that of the bulk crystal. The 3d-derived states are nearly half-filled, and the 4s-derived states are almost fully occupied,i.e. the electronic configuration is close to that of the isolated atom. These indicate that the Mn₂ cluster is bound by the van der Waals force. The same situation is true for the larger neutral clusters while the equilibrium interatomic distance becomes smaller and thes-d mixing becomes larger. For the cationic clusters, the behaviors tend to become metallic. The equilibrium interatomic distances are smaller and thes-d mixings are larger than those of the corresponding neutral clusters. However, the Mn ₂ ⁺ and Mn ₄ ⁺ clusters still remain the van der Waals characters. Contrary to these clusters, the Mn ₅ ⁺ cluster, whose interatomic distance is smaller than that of the bulk crystal, shows strong metallic bonding. These results seem to correspond to the magic number observed on the mass spectroscopy of cationic Mn clusters.     

Charge monotonicity of atomic systems and radial expectation values

A functionf(r) is monotone of orderp if itspth-derivativef ^(p)(r) fulfils that (–1) ^p f ^(p)(r)0. So, e.g. the monotonicity properties of orderp=0, 1, 2 describe the non-negativity (p=0), the monotonic decreasing from the origin (p=1) and the convexity (p=2) of the function, respectively. Here, the monotonicity properties of the electron functiong _n (r; )=(–1) ^{n (n)} (r)r ^– , 0, of the ground state of atomic systems are analysed both analytically and numerically. The symbol (r) denotes the spherically averaged electron density. First of all, the condition which specifies, if exists, a value _np such thatg _n (r; _np ) be monotone of orderp is obtained. In particular, it is found that ₀₁=max {r(r)/(r)}, ₀₂=max {q ₀(r)}, ₁₁=max {r(r)/(r)} and ₁₂=max {q ₁(r)}, whereq ₀(r) andq ₁(r) are simple combinations of the first few derivatives of (r). Secondly, numerical calculations of the first few values _np in a Hartree-Fock framework for all ground-state atoms with nuclear chargeZ54 are performed. In doing so, the pioneering work of Weinstein, Politzer and Srebrenik about the monotonically decreasing behavior of (r) is considerably extended. Also, it is found that Hydrogen and Helium are the only two atoms having the functions (r), –(r) and (r) with the property of convexity. Thirdly, it is analytically shown that the charge functionr ^– (r) with [(1+4Z ²/I)^1/2–1]/2, I being the first ionization potential, is convex everywhere. Finally, the above mentioned monotonicity properties are used to obtain rigorous, simple and universal inequalities involving three radial expectation values which generalize all the similar ones known up to now. These inequalities allow to correlate various statical and dynamical quantities of the atomic system under study, due to the physical meaning of the radial expectation values. It is worth to remember that some of these expectation values may be experimentally measured in experiments of (e, 2e)-type.     

Isotope shift measurements in titanium I

The use of an effusive beam of titanium atoms crossed with a CW single-mode tunable dye laser has allowed the high-resolution, Doppler-free study of the isotope shifts between⁵⁰Ti,⁴⁸Ti and⁴⁶Ti, for seven 3d ² 4s ² a³ F _J 3d ² 4s 4p z ⁵ D _J , visible transitions of Ti I. The measurements show without ambiguity the existence of a non-negligible field shift. Using the values of the nuclear radii of titanium (coming from muonic X-ray measurements), it is possible to determine the respective values of the field and mass shifts.     

Theoretical studies of the g factors and local structures of the Ni3+ centers in Na2Zn(SO4)2·4H2O and K2Zn(SO4)2·6H2O crystals

The local structures and the g factors g_i (i = x, y, z) for Ni³⁺ centers in Na₂Zn(SO₄)₂·4H₂O (DPPH) and K₂Zn(SO₄)₂·6H₂O (PHZS) crystals are theoretically studied by using the perturbation formulas of the g factors for a 3d⁷ ion with low spin (S = 1/2) in orthorhombically compressed octahedra. In these formulas, the contributions to g factors from both the spin-orbit coupling interactions of the central ion and ligands are taken into account, and the required crystal-field parameters are estimated from the superposition model and the local geometry of the systems. Based on the calculations, the Ni-O bonds are found to suffer the axial compression δz (or Δz) of about 0.111 Å (or 0.036 Å) along the z-axis for Ni³⁺ centers in DPPH (or PHZS) crystals. Meanwhile, the Ni-O bonds may experience additional planar bond length variation δx (≈0.015 Å) along x- and y-axes for the orthorhombic Ni³⁺ center in DPPH. The theoretical g factors agree well with the experimental data. The obtained local structural parameters for both Ni³⁺ centers are discussed.     

l-DOPA production by immobilized tyrosinase

The production of l-DOPA using l-tyrosine as substrate, the enzyme tyrosinase (EC 1.14.18.1) as biocatalyst, and l-ascorbate as reducing agent for the o-quinones produced by the enzymatic oxidation of the substrates was studied. Tyrosinase immobilization was investigated on different supports and chemical agents: chitin flakes activated with hexamethylenediamine and glutaraldehyde as crosslinking agent, chitosan gel beads, chitosan gel beads in the presence of glutaraldehyde, chitosan gel beads in the presence of polyvinyl pyrrolidone, and chitosan flakes using glutaraldehyde as crosslinking agent. The last support was considered the best using as performance indexes the following set of immobilization parameters: efficiency (90.52%), yield (11.65%), retention (12.87%), and instability factor (0.00). The conditions of immobilization on chitosan flakes were optimized using a two-level full factorial experimental design. The independent variables were enzyme-support contact time (t), glutaraldehyde concentration (G), and the amount of enzyme units initially offered (U _C). The response variable was the total units of enzymatic activity shown by the immobilized enzyme (U _IMO). The optimal conditions were t=24 h, G=2% (v/v), and U _C=163.7 U. Under these conditions the total units of enzymatic activity shown by the immobilized enzyme (U _IMO) was 23.3 U and the rate of l-DOPA production rate was 53.97 mg/(L·h).     

Solubility and Enhanced Tension of Solute in Solution

Abstract

In solution, solute molecules B are coupled by attractive forces between them and all other molecules present; and these other molecules enhance the tension in the coupling force between solute molecules an amount π_B, the osmotic pressure of the solution solute. Two equilibria determine the n ^o _B moles of pure solute which dissolve in n ¹⁰ _A moles of pure liquid solvent. If at T the solute is solid and in excess, then 1) the n _B ^lsat moles of B in the n^l _A moles of A in a solution saturated with B are in thermodynamic equilibrium with the solid solute at the same T and p and 2) the n _B ^lsat moles of B and n^l _A moles of A may also be in chemical equilibrium with the moles of new molecular or ionic species formed in the solution. Solute molecules dissolve until the chemical potential of the solution solute, p^l _B(T p, x_B ^lsat), equals the chemical potential of pure solid solute at the same T and p, μ _B ^so(T, p). When the solution is saturated with B and the mole fraction of B is x_B ^lsat = n _B ^lsat/σj n ¹ _j, then the vapor pressures of the solid solute at T and p, the solution solute at T and p, and the pure undercooled liquid solute at T and p-π _B ^lsat are identical. If at T the n _B ^lo moles of pure solute and the n^l _A moles of pure solvent are liquids, then if molecules of B are allowed to dissolve in A while molecules of A are dissolved in B, the resulting solutions may 1) contain only molecules of A and B or 2) contain A and B which also react to form other ionic and molecular species. The two solutions may be identical or they may differ. In all cases, however, the mole ratio of n^l _Bn^l _A in both solutions must be identical.     

Ewald summation of multipolar interactions at an arbitrary order on a two-dimensional lattice

There exist problems in condensed-matter theory that require evaluating infinite Bloch sums of multipolar potential r^?l?1Y_l,m(θ,φ) on a periodic lattice. For an arbitrary multipolar order l, tractable formulas are given for summing such interactions on a two-dimensional Bravais lattice and evaluating their Bloch sums at a point outside as well as inside the plane of the lattice. The approach used is the Ewald method, which consists of separating the original series in rapidly converging sums in reciprocal and real spaces. Computational aspects of the present formulation are briefly reviewed. © 1993 John Wiley & Sons, Inc.     

Stereoselective Michael Addition of Carbonyl Compounds to ( E )-β-Nitrostyrene Catalysed by N -Toluensulfonyl-l -proline Amide in Ionic Liquids

Summary. N-Toluensulfonyl-l-prolin amide was tested as catalyst in the enantioselective Michael addition of carbonyl compounds to (E)-β-nitrostyrene in nine ionic liquids under different reaction conditions. The reaction rates and enantioselectivities were strongly dependent on the ionic liquids. Change of enantioselectivity was observed too and it is attributed to both the cation and the anion of ionic liquid. The best yields (up to 98%) and enantioselectivity (70% ee) of product were obtained in a basic ionic liquid [bmim]BF₄ at room temperature.     

Hosoya index of unicyclic graphs with prescribed pendent vertices

The Hosoya index z(G) of a (molecular) graph G is defined as the total number of subsets of the edge set, in which any two edges are mutually independent, i.e., the total number of independent-edge sets of G. By G(n, l, k) we denote the set of unicyclic graphs on n vertices with girth and pendent vertices being resp. l and k. Let be the graph obtained by identifying the center of the star S _n-l+1 with any vertex of C _l . By we denote the graph obtained by identifying one pendent vertex of the path P _n-l-k+1 with one pendent vertex of . In this paper, we show that is the unique unicyclic graph with minimal Hosoya index among all graphs in G(n, l, k).      

Application of the theory of design of experiments in examination and elimination of the matrix effect

Summary A method of experimental optimization of an analytical procedure aimed at elimination of the matrix effect is proposed which is based on the theory of design of experiments. The criterion functions Q are formulated, which are expressed by regression coefficients in the empirical mathematical model approximating the relationship between a quantity R and the concentrations of sample components. R denotes, for example, the measured signal (e.g. absorbance, emission intensity), the concentration of a component being determined read from the calibration graph, or the error of determination. The quantities Q depend, in general, on the conditions of analysis which can be expressed by the factors z ₁..., z _M (e.g., in AAS — observation height, gas flux, concentrations of the auxiliary substances in a sample, etc.). It is assumed that the extreme of a function Q corresponds to the optimum conditions of analysis. In this paper the relationship between a quantity Q and the factors z is approximated by the polynomial model. The regression coefficients in this model are estimated on the basis of the results of an experiment carried out according to the composite rotatable design. The extreme of the model is found mathematically. Various criterion functions Q are discussed. An example concerning determination of Mg and Ca in AlCl₃ reagent by AAS is presented.

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Anwendung der Theorie der Versuchsplanung zur Untersuchung und Eliminierung des MatrixeffektsBestimmung von Mg and Ca in AlCl₃ mit Hilfe der AAS

Zusammenfassung Ein auf der Theorie der Versuchsplanung beruhendes Verfahren zur experimentellen Optimierung einer analytischen Methode mit dem Ziel der Eliminierung des Matrixeffekts wird beschrieben. Die Kriteriumfunktionen Q werden formuliert, die durch Regressionskoeffizienten in einem mathematischen Modell ausgedrückt werden, das der Beziehung zwischen einem Wert R und den Konzentrationen der Bestandteile angenähert ist. Hierbei bedeutet R z. B. das gemessene Signal (Extinktion, Emissionsintensität), den von der Eichkurve abgelesenen Konzentrationswert oder den Fehler der Bestimmung. Der Wert Q hängt im allgemeinen von den Analysenbedingungen ab, die durch die Faktoren z ₁... z _M (bei der AAS zum Beispiel die Beobachtungshöhe, der Gasstrom, die Konzentration von Hilfssubstanzen usw.) ausgedrückt werden können. Es wird angenommen, daß der Extremwert einer Funktion Q den optimalen Analysenbedingungen entspricht. Die Beziehung zwischen Q und den Faktoren z wird durch ein Polynommodell angenähert. Die Regressionskoeffizienten in diesem Modell werden aufgrund von Versuchsergebnissen bestimmt. Der Extremwert des Modells wird mathematisch berechnet. Verschiedene Kriteriumfunktionen Q werden diskutiert. Als Beispiel wird die Bestimmung von Mg und Ca in AlCl₃ mit Hilfe der AAS beschrieben.