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81.
The syntheses, physical characterization and crystal structures of two new molecular copper(II) complexes of composition [Cu(C5H5N)2(C7F5O2)2] (1) and [Cu(C5H5N)2(C7F5O2)2(H2O)] (2) (C5H5N = py = pyridine and C7F5O2− = pfb = pentafluorobenzoate) are reported. Single-crystal X-ray structure determinations revealed that in 1, the Cu2+ ion, which lies on a crystallographic inversion centre, is coordinated to two py molecules and two oxygen atoms from two monodentate pfb anions, resulting in a trans-CuN2O2 square planar geometry. In 2, the Cu2+ ion is also coordinated to two py and two pfb species in addition to a water molecule in the apical site of a distorted CuN2O3 square pyramid. In the crystal packing, both 1 and 2 show segregated aromatic π-π stacking interactions in which (py + py) and (pfb + pfb) ring-pairings are seen, but no (py + pfb) pairings occur. Crystal data: 1: C24H10CuF10N2O4, Mr = 643.88, space group , a = 8.0777 (3) Å, b = 8.0937 (3) Å, c = 10.5045 (5) Å, α = 90.916 (3)°, β = 93.189 (2)°, γ = 118.245 (3)°, V = 603.36 (4) Å3, Z = 1. 2: C24H12CuF10N2O5, Mr = 661.90, space group , a = 7.5913 (5) Å, b = 15.6517 (6) Å, c = 21.1820 (14) Å, α = 95.697 (4)°, β = 94.506 (2)°, γ = 91.492 (4)°, V = 2495.2 (3) Å3, Z = 4. 相似文献
82.
B. Joseph B. Schiavo A. Cognigni G. D’Alì Staiti N.L. Saini 《Journal of solid state chemistry》2010,183(7):1550-1554
Local structure of the nanostructured LaNi5 hydrogen storage alloys, prepared by ball-milling, has been studied using Ni K-edge extended X-ray absorption fine structure spectroscopy. Results indicate that the ball-milling up to 100 h results in the production of nanoparticles characterized by large atomic disorder and slightly reduced unit-cell volume, compared to the bulk LaNi5. High temperature annealing appears to help in partial recovery of atomic order in the ball-milled samples; however, long-time ball-milled samples retain large disorder even after the high temperature annealing. The results suggest that the large disorder and the reduced unit-cell volume might be causing a higher energy-barrier for the hydride-phase formation in the long time ball-milled LaNi5 powders. 相似文献
83.
The International Agency for Research on Cancer determined that bromate is a potential human carcinogen, even at low micro/l levels in drinking water. Bromate is commonly produced from the ozonation of source water containing naturally occurring bromide. Traditionally, trace concentrations of bromate and other oxyhalides in environmental waters have been determined by anion exchange chromatography with an IonPac AS9-HC column using a carbonate eluent and suppressed conductivity detection, as described in EPA Method 300.1 B. However, a hydroxide eluent has lower suppressed background conductivity and lower noise compared to a carbonate eluent and this can reduce the detection limit and practical quantitation limit for bromate. In this paper, we examine the effect of using an electrolytically generated hydroxide eluent combined with a novel hydroxide-selective anion exchange column for the determination of disinfection byproduct anions and bromide in municipal and bottled drinking water samples. EPA Methods 300.1 B and 317.0 were used as test criteria to evaluate the new anion exchange column. The combination of a hydroxide eluent with a high capacity hydroxide-selective column allowed sub-microg/l detection limits for chlorite, bromate, chlorate, and bromide with a practical quantitation limit of 1 microg/l bromate using suppressed conductivity detection and 0.5 microg/l using postcolumn addition of o-dianisidine followed by visible detection. The linearity, method detection limits, robustness, and accuracy of the methods for spiked municipal and bottled water samples will be discussed. 相似文献
84.
The dynamics of photodissociation of acetoxime at 193 nm, leading to the formation of (CH3)2C=N and OH fragments, has been investigated. The nascent OH radicals, which are both rotationally and vibrationally excited, were probed by laser photolysis-laser induced fluorescence technique. OH fragments in both v" = 1 and v" = 0 vibrational states were detected with a ratio of population in the higher to lower level of 0.07+/-0.01. The rotational temperatures of v" = 0 and 1 levels of OH radicals are 2650+/-150 K and 1290+/-20 K, respectively. More than 30% of the available energy, i.e., 115+/-21 kJ mol(-1) is partitioned into the relative translational energy of the fragments. The results of excited electronic state and transition state calculations at the configuration interaction with single electronic excitation level suggest that the dissociation takes place with an exit barrier of approximately 126 kJ mol(-1) at the triplet state (T2) potential energy surface, formed by internal conversions/intersystem crossing from the initially populated S2 state. Using the calculated transition state geometry and its energy, the observed energy distribution pattern can be reproduced by the hybrid model within experimental uncertainties. The presence of an exit barrier is further supported by the observation of N-OH dissociation upon 248 nm excitation, where the relative translational energy of the fragments is found to be approximately 96 kJ mol(-1). The photodissociation dynamics of acetoxime is compared with C-OH dissociation in enols and carboxylic acid and N-OH dissociation in nitrous acid. The observed emission (lambda(max)=430 nm) and the N-OH dissociation dynamics indicate crossing of the initially populated state to an emissive state of acetoxime, which is different from the dissociative state. 相似文献
85.
Fluorescence resonance energy transfer (FRET) is a popular tool to study equilibrium and dynamical properties of polymers
and biopolymers in condensed phases and is now widely used in conjunction with single molecule spectroscopy. In the data analysis,
one usually employs the F?rster expression which predicts (l/R
6) distance dependence of the energy transfer rate. However, critical analysis shows that this expression can be of rather limited validity in many cases. We demonstrate this by explicitly considering a donor-acceptor system,
polyfluorene (PF6)-tetraphenylporphyrin (TPP), where the size of both donor and acceptor is comparable to the distance separating them. In
such cases, one may expect much weaker distance (as l/R
2 or even weaker) dependence. We have also considered the case of energy transfer from a dye to a nanoparticle. Here we find
l/R
4 distance dependence at large separations, completely different from F?rster. We also discuss recent application of FRET to
study polymer conformational dynamics.
Dedicated to Prof J Gopalakrishnan on his 62nd birthday. 相似文献
86.
R. S. Saini Mahabir Nain R. P. Chauhan Nawal Kishore S. K. Chakarvarti 《Indian Journal of Physics》2009,83(8):1197-1200
Radon pollution is an important global problem of radiation hygiene. Radon and its progeny are the major contributors in the
radiation dose received by general population of the world. Keeping this in mind the environmental monitoring of radon, thoron
and their progeny in some dwellings of northern part of Haryana state of India has been carried out. The radon-thoron twin
dosimeter cups were used for the study. The aim of the study is the possible health risk assessment in the dwellings under
consideration. 相似文献
87.
88.
Vavro J Llaguno MC Fischer JE Ramesh S Saini RK Ericson LM Davis VA Hauge RH Pasquali M Smalley RE 《Physical review letters》2003,90(6):065503
We measured thermoelectric power S of bulk single-wall carbon nanotube materials p doped with acids. In contrast to oxygen-exposed or degassed samples, S is very small at the lowest temperatures, increases superlinearly above a characteristic and sample-dependent T, and then levels off. We attribute this unusual behavior to 1D phonon drag, in which the depression of the Fermi energy cuts off electron-phonon scattering at temperatures below a characteristic T0. This idea is supported by a model calculation in which the low temperature behavior of phonon drag is specifically related to the one-dimensional character of the electronic spectrum. 相似文献
89.
90.
G. S. S. Saini Amit Sharma Sukhwinder Singh J. M. Abbas S. K. Tripathi Sarvpreet Kaur C. G. Mahajan H. H. Thanga A. L. Verma 《Journal of Raman spectroscopy : JRS》2007,38(12):1561-1569
We report a resonance Raman study on free‐base tetraphenylporphine (H2TPP) and its chemically prepared diacid dispersed in polymethylcyanoacrylate (PMCA). Photoexcitation of the neutral porphine by laser light leads irreversibly to the formation of the diacid, with the π‐cation radical as intermediate species. Resonance Raman (RR) spectra of the diacid dispersed in the polymer obtained with 441.6 nm in the wavenumber region of 100–1650 cm−1 are recorded. Wavenumbers with other excitation lines are also reported for the diacid species. Some bands assigned to out‐of‐plane vibrational modes and forbidden under ideal D2h symmetry are also observed in the resonance Raman spectra of the diacid. These bands arise from the out‐of‐plane distortions, which reduce the symmetry of the molecule. These findings are supported by the electronic absorption studies of the diacid in the polymer. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献