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101.
Titanium cyclopentadienyl (Cp) complexes play important roles as homogeneous polymerization catalysts and have recently received attention as potential anticancer agents. To systematically probe the contribution of the Cp to bonding in organotitanium complexes, Ti K-edge XAS has been applied to TiCl(4) and then to the mono- and bis-Cp complexes, TiCpCl(3) and TiCp(2)Cl(2). Ti K-edge XAS is used as a direct probe of metal 3d-4p mixing and provides insight into the contribution of the Cp to bonding. These data are complimented by Cl K-edge XAS data, which provide a direct probe of the effect of the Cp on the bonding to the spectator chloride ligand. The experimental results are correlated to DFT calculations. A model for metal 3d-4p mixing is proposed, which is based on covalent interactions with the ligands and demonstrates that metal K-pre-edge intensities may be used as a measure of ligand-metal covalency in molecular Ti(IV) systems in noncentrosymmetric environments. 相似文献
102.
The level density of the odd-odd nucleus132 Pr is investigated in the interacting boson-fermion-fermion model (IBFFM) which accounts for collectivity and complex interaction between quasiparticle and collective modes. The IBFFM total level density is fitted by a Gaussian and its tail is also fitted by Bethe formula and constant temperature Fermi gas model. The IBFFM spin-dependent level densities show high-spin reductions with respect to Bethe formula. This can be well accounted for by a modified spin-dependent level density formula. 相似文献
103.
S.?K.?MisraEmail author B.?Endeward M.?Bernardo P.?Brant H.?Thomann 《Applied magnetic resonance》2003,25(2):277-295
We report on the magnetic-field-dependent optically detected magnetic resonance (ODMR) spectra for polycrystalline samples
of the bridged Zr(IV) metallocenes, Me2Si<(Cp2)ZrCl2 ( (dimethylsilylbis(cyclopentadienyl)zirconium-dichloride) and Me2C<(Cp2)ZrCl2 (iso-propylidenebis(cyclopentadienyl)zirconium-dichloride). ODMR spectra at zero magnetic field were recorded by frequency
sweeping a microwave source from 0.1 to 10 GHz with the sample contained in a microwave helix. ODMR spectra at finite magnetic
fields were recorded with the sample contained in either a helix or a slotted-tube resonator with a fixed microwave frequency
and sweeping the magnetic field. For all experiments, the sample and microwave probes were contained in an immersion dewar
cryostat, and the temperature was held at about 2 K. All three zero field ODMR transitions (2|E|, and |D| − |E| and |D|+|E|) were observed in the frequency-swept ODMR spectra recorded at zero and small magnetic fields. The zero-field frequency-swept
spectra allowed the determination ofD andE values uniquely. For frequency-swept small-field ODMR spectra recorded at successively higher magnetic fields, each of the
ODMR line intensities was observed to increase with increasing magnetic field. This intensity increase was observed for all
three ODMR lines, reflecting an increase in the total intensity rather than simply a change in the polarization of the triplet
sublevels. The latter would result in a change in the relative intensities of the ODMR lines but would not change simultaneously
the intensities of all three lines. The ODMR line intensities increase in proportion toB
n, wheren<1. This field dependence is weaker than the expected proportionalB
2 dependence from the Zeeman effect, which likely originates from the magnetic field dependence of the spin relaxation rates
between the triplet sublevels. Magnetic-field-swept ODMR spectra recorded at fixed microwave frequencies in the X-band frequency
range (9.8 GHz) do not show all three expected classic Pake powder pattern line shape profiles, exhibited by the molecules
with their magneticZ, Y, andX axes parallel to the external magnetic field. In particular, the intensity for molecular magneticY-axes parallel to the external magnetic field is completely suppressed. In addition, an external magnetic field dependence
in field-swept ODMR spectra was observed, which results in a linear decrease of the ODMR intensity with increasing strength
of the external magnetic field over and above that would be expected in a polycrystalline spectrum. The data are analyzed
by simulation of the continuous-wave ESR spectrum with the eigenvalues and eigenvectors of the spin Hamiltonian matrix characterizing
the triplet state exhibiting the ODMR spectrum, in conjunction with homotopy, as a function of the orientations of the magnetic
axes of the various molecules in a polycrystalline sample. This approach is useful to interpret the experimentally observed
ODMR transition frequencies andg-values but does not take the amplitudes in the ODMR spectrum. The corrections required to modify the continuous-wave ESR
spectral amplitudes that reproduce the observed ODMR amplitudes are effects associated with the ODMR processes. 相似文献
104.
Ying Wan Katherine A. M. Creber Brant Peppley V. Tam Bui 《Journal of Polymer Science.Polymer Physics》2004,42(8):1379-1397
Hydroxyethyl chitosan and hydroxypropyl chitosan were prepared through the reaction of alkali‐chitosan with 2‐chloroethanol and propylene epoxide, respectively. Fourier transform infrared and 13C NMR measurements were made to examine the substitution on the chitosan unit. According to a comparison of the peak areas between the modified chitosan and unmodified chitosan and the integration of peak areas of 1H NMR spectra, for both modified chitosans, the maximum degree of substitution was less than 25%. The ionic conductivity and mechanical properties of modified chitosan membranes were investigated. In comparison with the unmodified chitosan membrane, hydrated hydroxyethyl and hydroxypropyl chitosan membranes with a higher degree of substitution showed an increase in ionic conductivity of about one order of magnitude; moreover, the crystallinity of hydroxyethyl and hydroxypropyl chitosan membranes was remarkably reduced, and their swelling indices increased significantly. However, these modified membranes did not exhibit significant changes in their tensile strength and breaking elongation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1379–1397, 2004 相似文献
105.
106.
John Canning Brant C. Gibson James R. Rabeau Adrian P. Mancuso Shane T. Huntington 《Optics Communications》2007,273(2):379-382
A simple broadband optical source is demonstrated by using a high numerical aperture air-clad optical fibre to collect broadband emission of blackbody radiation from the fibre during exposure to high intensity electric arcs. 相似文献
107.
Martelli C Olivero P Canning J Groothoff N Gibson B Huntington S 《Optics letters》2007,32(11):1575-1577
A focused ion beam is used to mill side holes in air-silica structured fibers. By way of example, side holes are introduced in two types of air-structured fiber, (1) a photonic crystal four-ring fiber and (2) a six-hole single-ring step-index structured fiber. 相似文献
108.
Cytosine, a nucleobase found in both DNA and RNA, is known to form photoproducts upon UV irradiation, damaging the nucleic acids and leading to cancer and other diseases. To determine the molecular mechanism by which these photoproducts occur, we have measured the resonance Raman spectra of cytosine at wavelengths throughout its 267 nm absorption band. Self-consistent analysis of the resulting resonance Raman excitation profiles and absorption spectrum using a time-dependent wave packet formalism yields both the excited-state structural changes and electronic parameters. From this analysis, we have been able to determine that, at most, 31% of the reorganization energy upon excitation is directed along photochemically relevant modes. 相似文献
109.
Brant C. Jones 《Journal of Algebraic Combinatorics》2009,29(2):229-260
We show that the leading coefficient of the Kazhdan–Lusztig polynomial P
x,w
(q) known as μ(x,w) is always either 0 or 1 when w is a Deodhar element of a finite Weyl group. The Deodhar elements have previously been characterized using pattern avoidance
in Billey and Warrington (J. Algebraic Combin. 13(2):111–136, [2001]) and Billey and Jones (Ann. Comb. [2008], to appear). In type A, these elements are precisely the 321-hexagon avoiding permutations. Using Deodhar’s algorithm (Deodhar in Geom. Dedicata
63(1):95–119, [1990]), we provide some combinatorial criteria to determine when μ(x,w)=1 for such permutations w.
The author received support from NSF grants DMS-9983797 and DMS-0636297. 相似文献
110.
Rowley JD Pierce JK Brant AT Halliburton LE Giles NC Schunemann PG Bristow AD 《Optics letters》2012,37(5):788-790
Optical rectification is demonstrated in (110)-cut ZnGeP(2) (ZGP) providing broadband terahertz (THz) generation. The source is compared to both GaP and GaAs over a wavelength range of 1150 nm to 1600 nm and peak-intensity range of 0.5 GW/cm(2) to 40 GW/cm(2). ZGP peak-to-peak field amplitude is larger than in the other materials due to either lower nonlinear absorption or larger second-order nonlinearity. This material is well suited for broadband THz generation across a wide range of infrared excitation wavelengths. 相似文献