Use of INAA, PIXE and XRF in Homogeneity Testing of New IAEA Reference Air Filters

About 250 sets of polycarbonate (Nuclepore, Costar) membrane filters loaded with two urban air particulate matter (APM) obtained in Vienna and Prague were prepared by filtration of a watter suspension of the above APM materials. The homogeneity of both bulk APM materials and the loaded filters was tested by determining a number of elements by instrumental neutron activation analysis (INAA), proton induced X-ray emission (PIXE) and micro-X-ray fluorescence (-XRF). Relative standard deviations due to inhomogeneity (s _inh ) were below 3% for many elements in the bulk APM materials. In the loaded filters, the s _inh values increased significantly. Nevertheless, for up to 20 elements important in air pollution studies the s _inh values were below 15%, allowing target values with a reasonably low uncertainties (up to 20%) to be derived for the future use of the filters in proficiency testing of laboratories involved in air pollution monitoring.     

Photooxidation of methylnaphthalenes

Studies on the photooxidation of methyl-substituted aromatic hydrocarbons have revealed that whereas electron density is a determinant of endoperoxide formation, steric factors are most important in influencing the stability of the endoperoxide. Additional information on the energetics of the reactions and on the magnitude of the steric interactions was obtained using calculations at the B3LYP/6-311+G* level of theory.     

Variational principles for describing chemical reactions. Reactivity indices based on the external potential.

In a recent paper [J. Am. Chem. Soc. 2000, 122, 2010], the authors explored variational principles that help one understand chemical reactivity on the basis of the changes in electron density associated with a chemical reaction. Here, similar methods are used to explore the effect changing the external potential has on chemical reactivity. Four new indices are defined: (1) a potential energy surface that results from the second-order truncation of the Taylor series in the external potential about some reference, Upsilon(R(1),R(2),.,R(M)()); (2) the stabilization energy for the equilibrium nuclear geometry (relative to some reference), Xi; (3) the flexibility, or "lability", of the molecule at equilibrium, Lambda; and (4) the proton hardness, Pi, which performs a role in the theory of Br?nsted-Lowry acids and bases that is similar to the role of the chemical hardness in the theory of Lewis acids and bases. Applications considered include the orientation of a molecule in an external electric field, molecular association reactions, and reactions between Br?nsted-Lowry acids and bases.     

Nuclear techniques applied to air particulate matter studies

The most important fraction of aerosols with respect to human health is the respirable fraction, which has particles less than 10 m in equivalent aerodynamic diameter (EAD), the so called PM 10 fraction. The collection of these respirable particles and the determination of their trace element composition is the focus of an IAEA Co-ordinated Research Programme (CRP). The IAEA Laboratory participated in this Programme and established collection sites for the air particulate samples on the grounds of the Atominstitute of the Austrian Universities in Vienna and the IAEA Laboratories, Seibersdorf, representing an urban residential site and a rural site. The collected samples as well as samples of simulated air filters (used also for blind controls) and control materials were analyzed sequentially and/or in sections by X-ray fluorescence (XRF), proton induced X-ray emission (PIXE), instrumental neutron activation analysis (INAA), and atomic absorption spectrometry (AAS). Results demonstrate the applicability of the PM-10 sampling approach, provided PIXE and/or INAA are used in the determinations. Reliable results can be obtained that will lead in comparable air pollution data for many regions in the world through CRP.     

Sehwetelbestimmung in Kohlen

Ohne Zusammenfassung     

Hemilability and nonrigidity in metal complexes of bidentate P,PS donor ligands

Hemilability and nonrigidity in a series of mixed P,PS donor ligands has been studied in the complexes [Pd(P,PS)Cl₂], [Pd(η³-C₃H₅)(P,PS)][SbF₆], and [Rh(cod)(P,PS)][SbF₆] (P,PS = Ph₂P-Q-P(S)Ph₂). The effect of bite angle, the rigidity of the ligand backbone, and the role of the ancillary ligands are discussed.     

Approximate density matrices and Husimi functions using the maximum entropy formulation with constraints

The entropy of an electronic system is defined in terms of the Husimi function, a nonnegative distribution function in phase space. The Husimi function is calculated by maximizing the entropy subject to the constraints that the Husimi function give a Gaussian convolution of the desity when integrating over the momentum coordinates and that its second moment with respect to momentum give a sum of Gaussian convolutions of the density and the kinetic energy density. The result is compared with the Wigner function. Equations are given for calculating the density matrix from the Husimi function. The resulting equation for the exchange energy requires a difficult numerical integration. An alternate method is used to obtain the density matrix from an approximate partially collapsed Husimi matrix that gives the maximum entropy Husimi function as its diagonal. The results are exact for the harmonic oscillator ground state. Exchange energies calculated for H and the He isoelectronic series through C⁺⁴ show slight improvements over those calculated using a maximum entropy Wigner function.