Susanne Elbel

Selective determination of arsenite by flow injection spectrophotometry.

This paper describes the application of the well-known Molybdenum Blue method for selective determination of arsenite in a flow injection system. Selectivity is achieved by on-line separation of the main interferents phosphate, arsenate and silicate using a strong anion-exchange microcolumn located in the aspiration line of injection valve. Arsenite passing through the microcolumn unretained is determined using Molybdenum Blue method following in-line oxidation to arsenate by permanganate. A thorough investigation of optimal experimental conditions for both, the separation of interferents and sensitive detection of arsenite is presented. The method developed permits arsenite to be determined in the concentration range 5-500 microg/l with high precision and reliability. A sample throughput of 20 hr(-1) is achieved. Phosphate, arsenate and silicate do not interfere at concentration levels significantly higher than that of arsenite. The application to real water samples reveals excellent recovery of spiked samples and the absence of matrix interferences.

Photoelectron spectra of the trimethyl compounds of the group V elements. Constant ionisation potentials of the lone pair orbital electrons

The lone pair orbital ionisation potentials of the compounds Me3X (X: N, P, As, Sb) are found to be constant, in contrast to the series Me2Y and H2Y (Y: O, S, Se, Te) whose first i.p. values vary distinctly with Y. This difference is explained on symmetry grounds by changes in hybridization of the lone pair orbitals on the central atoms X. In a qualitative MO model the interactions of the a1 orbitals of Me3X and H3X are discussed. On the basis of this model and semiempirical calculations a consistent interpretation of the photoelectron spectra of the title compounds is proposed.

Photoelectron spectra of group V compounds. The elements: Sb4

Abstract The high-temperature He I photoelectron (PE) spectrum of gaseous Sb 4 is presented and assigned on the basis of the known PE ionisation energies of As 4 and P 4 and from SCC Xa eigenvalues and eigenvectors. Implications for the PE spectra of related antimony compounds are discussed.

Photoelectron spectra of group V compounds. IX [1]. The relative perfluoroalkyl substituent effect

Abstract The gas phase He I p.e. spectra of the series (CF 3 ) 3 E (E = N, P, As, Sb) and (CF 3 ) n AsH 3−n are discussed and compared to those of their methylated analogs. The perfluoroalkyl effect — synonymous with large σ-electron withdrawal — causes a nearly parallel stabilization of all m.o. energies as compared with the respective alkyl counterparts. This property can be used, systematically and generally, as a valuable aid for a more precise interpretation of the p.e. spectra of the parent methyl derivatives. Band superposition due to interfering substituent m.o. energies is diminished without destroying the original orbital energy sequence found for the methyl compounds. Overlapping bands from the ionisation of σ- and π-type skeletal molecular orbitals can be resolved on replacing alkyl by perfluoroalkyl groups. Substituent effects including R = CF 3 , Hal, SiR′ 3 and H are surveyed for the series ER 3 (E = N, P).

Photoelectron spectra of Group 5 compounds. Part IV. A study of the E–X bond in R3EX compounds (R = Me or F; E = N or P; X = O or S)

The He(I) photoelectron (p.e.) spectra of the isoelectronic C3v compounds Me3NO, Me3PO, Me3PS, and F3PS are discussed and assigned by comparison with the p.e. spectra of the parent bases R3P and R3N and with reference to CNDO and EHMO calculations. Bond descriptions for the E–X multiple bonds (σ donation, pπ–dπ back donation) have been critically revised taking into account the variation of the central atom E, of the acceptor X, and of the substituent R, and symmetry arguments. Inductive, hyperconjugative, and d-orbital effects have been determined by the CNDO method.

Photoelectron spectra of polysilanes. Conformational analyses of tetra-and penta-silane

The p.e. spectra of polysilanes SinH2n+2(n= 2,3,4,5) are presented. Whereas assignment is uncomplicated for n= 2 or 3, p.e. spectroscopic conformational analyses are necessary for tetra- and penta-silane. Their p.e. spectra can be simulated by CNDO eigenvalues (Iµ) if various rotamers are taken into account. For this procedure the relation ΔIµi,j≈Δ(ionisation energy)i,j must hold. Comparison of experimental and simulated spectra allows determination of the ratios of rotamers of Si4H10 and Si5H12 present under the p.e. spectroscopic conditions.

Bonding modes in the analogous and isoelectronic group VB/VA compounds As(O)Cl3 and Nb(O)Cl3. An ultraviolet photoelectron-spectroscopic and SCC-Xα study

The He Iα photoelectron spectra of gaseous ‘non-existent’ As(O)Cl3 and of Nb(O)Cl3 have been compared and assigned using the SCC-Xα method. In order to confirm the interpretation, correlations with the known ionization potentials of isomorphous P(O)Cl3 and V(O)Cl3, respectively, are considered. Differences in bonding modes are discussed and illustrated with respect to the SCC-Xα population analyses, to the relative central atomic orbital contributions, to the atomic energy levels and to the experimental ionization energies of the parent AsCl3 and PCl3.

Photoelectron spectra of group 5 compounds. 2, Conformational analysis of diphosphine (P2H4)

The photoelectron spectra of certain hydrazines, disulfides, peroxides, and aminophosphines have been assigned to a unique conformer, being present under normal PE spectroscopic conditions. In contrast, different rotamers could be detected in the PE spectra of hexahydropyridazines and tetrasubstituted diphosphines and diarsines and were assumed for polysilanes. The composition of the rotameric mixture (transgauche) obtained for tetramethyldiphosphine from the relative PE peak areas had to be revised.

Ionization energies and thermal fragmentation patterns of gaseous cyclopolyarsanes and -phosphanes EnRn(E = As or P; R = Me, But, or CF3; n= 3–5): a joint temperature-variable field ionization mass spectrometric and ultraviolet photoelectron spectroscopic study

Ultraviolet photoelectron spectroscopic (u.p.s.) data for gaseous As4But4, As4(CF3)4, and As5Me5 are presented and discussed with respect to the known ionization potentials of the parent cyclopolyphosphanes. Pyrolytically induced fragmentation patterns of representative cyclopoly-phosphanes and -arsanes in the gas phase have been analysed by high-temperature field ionization mass spectrometry (f.i.m.s.) and u.p.s. Evidence for a thermally generated transient phosphinidene P(CF3) from [P(CF3)]n(n= 4 or 5) in the gaseous phase is provided by f.i.m.s., whereas products such as P2 and CF2 from secondary reactions are revealed by u.p.s. The u.p.s. upon thermal fragmentation of Sb(CF3)3 is also presented.

Bonding in and gas-phase pyrolysis of the arsoranes and stibanes EMe3X2(E = As or Sb, X = F or Cl) and SbMe4F: ultraviolet photoelectron and field-ionization mass spectrometric studies

The He I (and partially He II) photoelectron spectra of the gaseous Group 5 molecules AsMe3F2, AsMe3Cl2, SbMe3F2, SbMe3Cl2, and SbMe4F are presented and assigned using the known ionization potentials of SbMe5 and EMe3(E = As or Sb) and simple molecular-orbital models. Calculations have been performed for the series AsH3, AsH5, AsH3F2 using the SCC–Xα method. Upon pyrolysis both AsMe3Cl2 and SbMe3Cl2 undergo unimolecular elimination of HCl in the gaseous phase, indicating the intermediacy of new transient species ‘EMe3Cl2–nHCl.’ However, reductive elimination of MeF is favoured by the gaseous fluorides. These results are strongly supported by high-temperature field-ionization mass spectrometry under similar conditions. Loss of HCl was also observed during solid-state pyrolysis of ionic PMe3Cl2in vacuo.