Bond Properties and Molecular Conformation from Vibrational Intensity Analysis

Experimental vibrational intensities in infrared spectra can be transformed into quantities characterizing bond properties fol- lowing the formalism of the bond polar parameters model. The theory is briefly presented. An optimized set of bond polar parameters for hydrocarbons is obtained following constraints derived from experimental spectral data and ab initio MO calculations. The set of intensity parameters together with transferable force constants is used in predicting the infrared spectra of individual conformers and equilibrium conformer mixtures of n-butane-do, n-pentane-d, n-pentane-djj and n-hexane-d, The influence of rotational isomerism on infrared intensities in these systems is discussed

Relationship Between Atomic Polar Tensors and Bond Polar Parameters Formulations of Infrared Intensities

The mathematical and physical aspects of the relationship between the atomic polar tensors and bond polar parameters formulations of vibrational intensities in infrared spectra are discussed. The theoretical considerations are illustrated with parallel applications of the two approaches in analysing experimental intensity data for ethane, methyl chloride and H2O

Reference material for radionuclides in sediment IAEA-384 (Fangataufa Lagoon sediment)

Author Posting. © Springer, 2007. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Journal of Radioanalytical and Nuclear Chemistry 273 (2007): 383-393, doi:10.1007/s10967-007-6898-4.A reference material designed for the determination of anthropogenic and natural radionuclides in sediment, IAEA-384 (Fangataufa Lagoon sediment), is described and the results of certification are presented. The material has been certified for 8 radionuclides (40K, 60Co, 155Eu, 230Th, 238U, 238Pu, 239+240Pu and 241Am). Information values are given for 12 radionuclides (90Sr, 137Cs, 210Pb (210Po), 226Ra, 228Ra, 232Th, 234U, 235U, 239Pu, 240Pu and 241Pu). Less reported radionuclides include 228Th, 236U, 239Np and 242Pu. The reference material may be used for quality management of radioanalytical laboratories engaged in the analysis of radionuclides in the environment, as well as for the development and validation of analytical methods and for training purposes. The material is available from IAEA in 100 g units

Reference Material for Radionuclides in Sediment, IAEA-384 (Fangataufa Lagoon Sediment)

The IAEA Marine Environment Laboratory (IAEA-MEL) in Monaco has conducted intercomparison exercises on radionuclides in marine samples for many years as part of its contribution to the IAEA's program of Analytical Quality Control Services (AQCS). An important part of the AQCS program has been a production of Reference Materials (RMs) and their provision to radioanalytical laboratories. The RMs have been developed for different marine matrices (sediment, water, biota), with accuracy and precision required for the present state of the art of radiometrics and mass spectrometry methods. The RMs have been produced as the final products of world-wide intercomparison exercises organized during last 30 years. A total of 44 intercomparison exercises were undertaken and 39 RMs were produced for radionuclides in the marine environment. All required matrices (seawater, biota, sediment) have been covered with radionuclide concentrations ranging from typical environmental levels to elevated levels affected by discharges from nuclear reprocessing plants. The long-term availability of RMs (over 10 years) requires the use of very specific techniques to collect and pretreat large quantities of material (e.g., in excess of 100 kg) in order to ensure sample stability and homogenization of any analytes of interest. The production of a RM is therefore a long process, covering the identification of needs, sample collection, pre-treatment, homogenization, bottling, distribution to laboratories, evaluation of data, preliminary reporting, additional analyses in expert laboratories, certification of the material, and finally issuing the RM. In this paper we describe a reference material IAEA-384, Fangataufa lagoon sediment, designed for determination of anthropogenic and natural radionuclides in the marine environment. This RM has been prepared with the aim of testing the performance of analytical laboratories to measure the activity of these radionuclides in a sediment sample contaminated by elevated levels of fallout from nuclear weapons tests. Participating laboratories were requested to determine as many radionuclides as possible by radiometric (alpha, beta and gamma-spectrometry) as well as by mass spectrometry methods (e.g., ICPMS - Inductively Coupled Plasma Mass Spectrometry, TIMS - Thermal Ionization Mass Spectrometry, AMS - Accelerator Mass Spectrometry)

Combined Experimental and Computational Studies on the Nature of Aromatic C−H Activation by Octahedral Ruthenium(II) Complexes: Evidence for σ-Bond Metathesis from Hammett Studies

Octahedral ruthenium complexes of the type TpRu(L)(NCMe)R [Tp = hydridotris(pyrazolyl)borate; R = alkyl or aryl; L = CO or PMe3] have been shown previously to initiate the C-H activation of aromatic substrates. In order to probe the nature of the C-H activation step, reaction rates have been theoretically obtained for the conversion of TpRu(L)(η2-C, C-C6H5X)Me to TpRu(L)(P-C6H4X) and CH4 where X is varied among Br, Cl, CN, F, H, NH2, NO 2, and OMe. A linear Hammett correlation is calculated with a positive p value of 2.6 for L = CO and 3.2 for L = PMe3. Calculated kinetic data for the aromatic C-H activations indicate that an electrophilic aromatic substitution mechanism is unlikely. While experiments cannot fully replicate the entire range of calculated Hammett plots, reactivity trends are consistent with the calculations that suggest activation barriers to overall metal-mediated arene C-H bond cleavage are reduced by the presence of electron-withdrawing groups in the position para to the site of activation. Previous mechanistic studies, as well as the structure and imaginary vibrational modes of the present transition states, validate that the C-H activation for this family of TpRu complexes occurs through a σ-bond metathesis-type pathway. © 2007 American Chemical Society

COMPUTATION OF VIBRATIONAL SPECTRA OF N-ALKANES

$^{1}$ T. Shimanouchi, H. Matsuura, Y. Ogawa and I. Harada, J. Phys. Chem. Ref. Data, 7, 1323 (1978). $^{2}$ S. Kondo and S. Saeki, Spectrochim, Acta, 20A, 735 (1973).Author Institution: Department of Chemistry, University of Sofia; Department of Chemistry, University of South CarolinaSimultaneous calculations of both frequencies and intensities in vibrational spectra, outside of purely theoretical (quantum mechanical) approaches, have been hampered by difficulties in determining transferable intensity parameters from available experimental data. Objectively, intensity parameters are expected to be less transferable compared to force constants because of the higher sensitivity of band intensities to structural changes. There are, however, a number of series of molecules where intramolecular forces and charge distribution are fairly constant, and therefore transferability of both frequency and intensity parameters is expected. A good example in this respect is the normal paraffins. In this paper we present results on the computation of the infrared spectral curves in $C_{4}, C_{5}$ and $C_{6}$ n-alkanes, based on transferable force constants proposed by Shimanouchi $et al.^{1}$, and local C-H and C-C intensity parameters determined from experimental gas phase infrared intensities of ethane and $propane.^{2}$ The presence of different conformational forms is also considered