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1.
The ratios of the intensities of Raman scattering in the C? CI stretching region for eight combinations of sample orientation and directions of polarization of incident and scattered light have been measured for 15 samples of poly(vinyl chloride) (PVC) containing 0, 5, 10, 15 or 20 pph dioctyl sebacate (DOS) plasticizer which had been drawn uniaxially at 22, 70, 75, 80, or 90°C to draw ratios in the range 1–4.5. The birefringences of the samples were also measured. The Raman data were analyzed to give 〈P2(cosθ)〉cryst and 〈P4(cosθ)〉cryst, the values of the second- and fourth-order Legendre polynomials in cosθ averaged over the distribution of orientations of the crystallites, where θ is the angle between the c axis of a typical crystallite and the draw direction. Comparison of 〈P2(cosθ)〉cryst with the birefrigence showed that the crystallites are more highly oriented than the noncrystalline material in samples containing the higher amounts of plasticizer drawn at the higher temperatures. A value of 13.0 × 10?3 was deduced for the birefringence of fully oriented PVC. The values of 〈P4(cosθ)〉cryst for a given 〈P2(cosθ)〉cryst were found to be higher than predicted by calculations based on two simple models, the pseudoaffine rigid-rod rotation model and the affine rubber elasticity model.  相似文献   

2.
Laser-induced fluorescence spectra for the first allowed electronic transition (22125 cm?1) of methylglyoxal (CH3COCHO) and its perdeutero analog (CD3COCDO) in a supersonic nozzle beam are quantitatively represented assuming that the potential function governing the CH3(CD3) rotation is changed during the transition. In the excited state the potential function is ternary (V1 = 95 (1 + cos 3θ)cm?1) as in the fundamental state (V0 = 134.5 (1 - cos 3θ)cm?1), but the minima are shifted by an angle of π/3. The spectrum of biacetyl (CH3COCH3CO) can be reproduced assuming two uncoupled methyl groups undergoing similar conformational changes during the electronic transition (the estimated potential function is V1 = 117.5 (1 + cos 3θ) cm?1 for each methyl group), in perfect agreement with the most recent assignment of the 0-0 transition. These results are consistent with ab initio calculations for the fundamental and first excited singlet states.  相似文献   

3.
4.
The nature of halogen bonds of the Y?X‐?‐π(C6H6) type (X, Y=F, Cl, Br, and I) have been elucidated by using the quantum theory of atoms in molecules (QTAIM) dual‐functional analysis (QTAIM‐DFA), which we proposed recently. Asterisks (?) emphasize the presence of bond‐critical points (BCPs) in the interactions in question. Total electron energy densities, Hb( r c), are plotted versus Hb( r c)?Vb( r c)/2 [=(?2/8m)?2ρb( r c)] for the interactions in QTAIM‐DFA, in which Vb( r c) are potential energy densities at the BCPs. Data for perturbed structures around fully optimized structures were used for the plots, in addition to those of the fully optimized ones. The plots were analyzed by using the polar (R, θ) coordinate for the data of fully optimized structures with (θp, κp) for those that contained the perturbed structures; θp corresponds to the tangent line of the plot and κp is the curvature. Whereas (R, θ) corresponds to the static nature, (θp, κp) represents the dynamic nature of the interactions. All interactions in Y?X‐?‐π(C6H6) are classified by pure closed‐shell interactions and characterized to have vdW nature, except for Y?I‐?‐π(C6H6) (Y=F, Cl, Br) and F?Br‐?‐π(C6H6), which have typical hydrogen‐bond nature without covalency. I?I‐?‐π(C6H6) has a borderline nature between the two. Y?F‐?‐π(C6H6) (Y=Br, I) were optimized as bent forms, in which Y‐?‐π interactions were detected. The Y‐?‐π interactions in the bent forms are predicted to be substantially weaker than those in the linear F?Y‐?‐π(C6H6) forms.  相似文献   

5.
By measurement of infrared chemiluminescence we have obtained for the branching ratio of the room temperature reaction H + Br2 (1), k*1/k1 = 0.015 ± 0.004 and for H + HBr (2), k*2/k2 ? 0.013. For H + Br2 → HBr(υ· ? 6) + Br (1), the detailed rate constant k* = 6) = 0.014 ± 0.003 relative to k· = 4) = 100.  相似文献   

6.
A two-dimensional network compound [Ce(DMF)4(H2O)][α-BW12O40]·H2O·(HDMA)2 (HDMA = protoned dimethylamine, DMF = N,N-dimethylformamide) was synthesized from α-H5BW12O40·nH2O, Ce(NO3)3·6H2O and DMF and characterized by IR, UV spectra and TG-DTA. The result of the X-ray single crystal diffraction indicates that the crystal is monoclinic, space group P21/n, with unit cell dimensional: a = 1.1983(3), b = 2.4216(5), c = 1.9517(4) nm, β = 92.91(3)°, Z = 4, R 1 = 0.07710, wR 2 = 0.1416. Structural analysis indicates that every [Ce(DMF)4(H2O)]3+ building block is surrounded by three adjacent [α-BW12O40]5? polyanions, meanwhile, every [α-BW12O40]5? polyanion interconnects with three neighboring [Ce(DMF)4(H2O)]3+ subunits, by making use of which two-dimensional network structure can be constructed. The result of thermogravimetric analysis manifests that the title compound has two-stage weight loss and the decomposition temperature of the title polyanionic framework is 560°C. The electrochemical analysis shows the title polyanion has three-step redox processes in the pH = 4–7 media.  相似文献   

7.
The kinetics of albumin adsorption onto a glassy carbon rotating disk electrode in a phosphate buffer, is reported from the time variations of the double-layer capacitance Cd, of the charge transfer resistance Rt and of the Tafel coefficient of the electrochemical reaction b; these three electrical quantities are determined by electrochemical impedance and faradaic current I measurements. The variations of Cd, 1/Rt, b  (RtI)−1 and I can be written under the form: α0 + α1 et/τ1 + α2 et/τ2, where α0, α1, α2, τ1, τ2 characterize a given electrical quantity. We demonstrate that this type of variation validates a two-step adsorption mechanism already proposed, starting from simply taking into account Cd(t). We analyze and discuss comprehensively various possibilities of interpreting the shifts between the time-constants associated with thevarious quantities as well as the correlations between these constants and those associated with physical adsorption phenomena.  相似文献   

8.
The magnesium sulphate complex compounds of general formulae [Mg(H2O)6]2+·2(C6H12N4)·SO4 2?·5(H2O) (1) and Mg(C12H8N2)(H2O)3SO4 (2) have been synthesized, characterised by elemental and thermal analysis, IR, UV?CVIS and fluorescence spectroscopy, and X-ray crystallography. The obtained compounds are air stable at room temperature and well soluble in water. In the structures of the investigated complex compounds the O?CH?O, O?CH?N, and C?CH?O hydrogen bonds exist, and they create N2C 2 2 (8), R 2 2 (8) (compound 1) and N1C 1 1 (6), N1R 2 2 (12) (compound 2) patterns. Their thermal decomposition processes in the investigated atmospheres (air and helium) are different. After the slightly similar dehydratation, the observed transitions and the obtained final products are different (in helium atmosphere the sulphate ion of studied compounds undergoes decomposing what does not take place in air atmosphere). The UV?CVIS spectrum of 2 shows maxima that are typical for ????????* and n??????* transitions, and fluorescence spectrum of the same compound displays its great fluoresce properties. The 1 does not exhibit absorption in the investigated region of electromagnetic spectrum due to the absence of respect chromophore groups. The IR spectrum of 2 shows typical vibrations for chelating amine molecule. An interesting fact is that in 1 the SO stretching vibrations (existing at 1119 and 1182?cm?1) are doubled in comparison to the magnesium sulphate whilst in 2 these vibrations are absent.  相似文献   

9.
A dissociative force field for all-atomistic molecular dynamics calculations has been developed to investigate impact fracture of polymers accompanying dissociation of chemical bonds of polymer main chain. Energy of dimer molecules was evaluated as a function of both bond-length b and bond-angle θ by CASPT2 calculations, whose quality is enough to describe dissociation of chemical bonds. Because we found that the bond dissociation energy D decreases with increasing bond-angle, we employed the Morse-type function VBond(b, θ) = {DVAngle(θ)}[1 − exp{−α(bb0) − β(bb0)2}] where a quartic function VAngle(θ) = k1(θθ0) + k2(θθ0)2 + k3(θθ0)3 + k4(θθ0)4 . This function reproduced well the CASPT2 potential energy surface in a wide range of b and θ. The parameters have been obtained for four popular glassy polymers, polyethylene, poly(methyl methacrylate), poly(styrene), and polycarbonate. © 2019 Wiley Periodicals, Inc.  相似文献   

10.
This paper addresses the general question: what are the significant guest properties selected by this host when interacting with guest molecules in the liquid phase, resulting in cocrystallization of the host and guest? In particular, to what extent do π electrons in a guest molecule effect its potential as a guest? Werner clathrates of the host [Ni(NCS)2(4-ViPy)4] with mixtures of tetrahydrofuran (THF) and cyclic hydrocarbons as guests have been synthesised and their structures elucidated. Clathrate (1): [Ni(NCS)2(4-ViPy)4](1.78 THF)(0.22 cyclohexane), crystallizes in the orthorhombic space groupP bcn a=9.976(6),b=20.630(25),c=19.861 (4) Å,V=4087Å3,Z=4,R=0.087 for 1461 reflections; (2): [Ni(NCS)2(4-ViPy)4](1.76 THF)(0.24 cyclohexene),P bcn ,a=9.987(7),b=20.614(4),c=19.898(4)Å,V=4096Å3,Z=4,R=0.084 for 1304 reflections; (3): [Ni(NCS)2(4-ViPy)4](0.48 THF)(0.52 1,3-cyclohexadiene), tetragonalI41/a,a=16.898(3),b=16.898(3),c=26.463(6)Å,V=7556Å3,Z=8,R=0.120 for 1698 reflections; (4): [Ni(NCS)2(4-ViPy)4](0.36 THF)(1.04 1,4-cyclohexadiene),I41/a,a=16.986(4),b=16.986(4),c=25.896(15)Å,V=7472Å3,Z=8,R=0.103 for 2025 reflections; (5): [Ni(NCS)2(4-ViPy)4](0.35 THF)(1.05 benzene),I41/a,a=17.102(10),b=17.102(10),c=25.498(8)Å,V=7458Å3,Z=8,R=0.118 for 2200 reflections; (6): [Ni(NCS)2(4-ViPy)4](3 benzene), triclinicP1,a=10.432(24),b=11.155(9),c=21.581(7)Å, α=78.70(5), β=82.60(7), γ=74.09(13)°,V=2361Å3,Z=2,R=0.078 for 3427 reflections. Host-guest ratios and, for mixtures of guests, guest1/guest2 ratios, were elucidated by density and NMR. We show that the conformational freedom of the substituted pyridines is not the primary reason for the clathrating ability of Werner hosts. All six structures show no host-guest interaction at the level of van der Waals interactions. As non-bonding interactions are not observed between the host and guest, this study shows that the above host's selectivity by enclathration of particular guest molecules cannot be accounted for by solid state structural analysis.  相似文献   

11.
The chemiluminescence produced by the Ba + Cl2 reaction was recorded as a function of He and N2 pressure. A modified Stern-Volmer treatment of competitive electronic quenching of BaCl* and BaCl*2 emission yielded upper limits to the half pressures p12(He) ? 9.0 ± 3 mtorr and p12 (N2) ? 1.1 ± 0.2 mtorr for quenching of BaCl*2 by helium and nitrogen, respectively. A lower limit of the BaCl*2 radiative lifetime is placed at τR ? 100 μ.  相似文献   

12.
New coordination polymers based on 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (L) with the composition [M2(L)4A(NCS)2] (M2+ = Co2+, Zn2+, Cd2+; A2? = SiF 6 2? , SeO 4 2? ) have been synthesized and characterized by IR spectroscopy and X-ray diffraction. According to X-ray diffraction data, cobalt compounds crystallize in the orthorhombic system with the following unit cell parameters, [Co2(L)4SiF6(NCS)2] · 3CHCl3 · CH3OH: a = 20.568(4), b = 14.568(3), c = 22.929(5) Å, α = β = γ = 90°, V = 6870(2) Å3, space group Pbca (no. 61), R(I > 2σ(I)) = 0.0514; [Co2(L)4SeO4(NCS)2] · 2CHCl3 · 2CH3OH · H2O: a = 13.721(2), b = 21.539(3), c = 22.417(3) Å, α = β = γ = 90°, V = 6625(2) Å3, space group P212121 (no. 19), R(I > 2σ(I)) = 0.0452. The 3D structure of the coordination polymers is composed of wavelike two-dimensional coordination layers [ML2]n connected by bridging anions SiF 6 2? , or Se O 4 2? . The complexes have the same five-bonded topology but different symmetry.  相似文献   

13.
The temperature dependence of the fluorescence and fluorescence excitation spectra of all-trans diphenyl hexathene (DPH) and octatetraene (DPO) in six solvents confirms the S1(1Ag*) and S2(1Bu*) state assignment, and determines their energy difference ΔE. The S1 fluorescence rate parameter kF depends on ΔE, the solvent refractive index n, the S2 (n = 1) fluorescence rate parameter kF20 (2.23 × 108 s?1 for DPH, 2.33 × 108 s?1 for DPO), and the S2-S1 coupling matrix element V (745 cm?1 for DPH, 500 cm?1 for DPO). The S1 fluorescence is induced by 1Bu*-1Ag* potential interaction (PI), via a bu vibrational mode (≈ 900 cm?1), and not by vibronic coupling. The main S1 radiationless transition, rate parameter kR, is thermally-activated internal rotation through an angle θ about the central ethylenic bond(s). The PI distorts the S1 (θ) potential surface and thus influences kR.  相似文献   

14.
The slopes of the ln (absorbance) vs. T?1 dependences for platform/graphite furnace atomization of phosphorus in the presence of Ni2+ or La3+ modifiers are measured, and found to be similar to the theoretical slope calculated for isothermal atomization. It is concluded that in both cases the atomization mechanism is the same and is expressed by P2(gas) ? 2P(gas); P(gas) ? P*(gas). The atomic absorption signal for phosphorus appears and reaches its maximum later when the atomization is carried out from the platform in the presence of modifiers. Hence atomization takes place under nearly isothermal conditions and is much more efficient, thus providing the best conditions for the determination of phosphorus. Treatment of a deteriorated graphite surface with ZrOCl2 solution repairs any defects and improves the sensitivity of phosphorus determination.  相似文献   

15.
Experimental studies of collisions of He2+ ions with Ne, Ar, and Kr atoms have been carried out at laboratory kinetic energies in the range 8 ? E1 ? 10 eV. For each collision pair, relative differential cross sections for elastic scattering, and for the formation of He+ by single charge transfer [e.g., He2+ + R = He+ + (R+)*] were measured. Information concerning the initial states of the charge transfer products was also obtained, from measurements of the kinetic energy distributions of the He+ + He = Ne+(2s 2p62S) ± He+(2S), whereas for the other systems, transfer proceeds via a number of channels. The He+-ion kinetic energy measurements indicated that for He2+. Ar both Ar+ both Ar+ and Ar2+ are formed in transfer, and that for He2+, Kr only Kr2+ (and no Kr+) was formed.The differential elastic scattering patterns were analyzed by means of cross section calculations based on an approximate form of the optical model. These calculations indicated that the pronounced shoulders observed in the σel(θ) versus θ curves arose from scattering from an attractive potential well, in the presence of concurrent inelastic scattering. Using parametrized Morse potentials to represent the ground electronic states of (HeNe)2+, (HeAr)2+, and (HeKr)2+, the corresponding well-depth are estimated to be, respectively: 1.0 eV, 2.1 eV and 2.6 eV.  相似文献   

16.
Zhang Y  Yang W  Tian Z  Yao J 《Talanta》2005,67(3):520-524
Nanoparticles of (R)-1,1′-bi-2-naphthol dibenzoate (R-BND) ranging from 40 to 170 nm were prepared by using the reprecipitation method. The nanoparticles exhibit size-dependent exciton chirality, where the coupling potential V12 of 1Bb transitions increases as nanoparticles grow and simultaneously the exciton chirality peaks exhibit the bathochromic shift. Such size-dependent optical properties can be attributed to the lattice hardening with increased particle size, which leads to a decreased dihedral angel θ between the two naphthyl planes in a R-BND molecule.  相似文献   

17.
The selective laser excitation and induced fluorescence observation technique has been used to study rotationally inelastic collisions of I2*(B 0u+, υ = 15,j) with I2, 3He, 4He, Ne, Ar, H2 and D2. For each collision partner, several initial rotational levels ranging from ji = 12 up to ji = 146 have been excited. For purely rotational transfer within the υ = 15 level, our data are perfectly consistent with energy sudden (eventually corrected) scaling laws. Thus, any thermally averaged rate constant, k(jijf), can be expressed as a function of the basis rate constants k(l → 0). Furthermore, these k(l → 0) are found to follow simple empirical fitting laws. Consequently any k(jijf) can be predicted given a set of two or three fitting parameters. Collisions with relatively heavy particles (I2, Ar and Ne) are well described by using the inverse power fitting law k(l → 0) = b[l(l+1)], where b = 1.7, 1.2 and 1.2×10?10 cm3 s?1 and γ = 1.08, 1.02 and 1.17 for I2*-Ne, I2*-Ar and I2*-I2 collisions respectively. For collisions with light particles (3He, 4He, H2 and D2), k(l → 0) shows a sharp decrease with l which can be accounted for by a hybrid power-exponential fitting law k(l → 0) = b[l(l+1)] exp[-l(l+1)/l* (l*+1)], where b = 0.84, 0.71, 2.77 and 2.78×10?10 cm3 s?1l+ = 20.6, 23.1, 18.8 and 31.4, and γ = 0.66, 0.66, 0.78 and 0.91 for I2*-3He, I2*-He, I2*-H2 and I2*-D2 collisions, respectively. We confirm that the rotational transfer dynamics in heavy molecules is mainly governed by angular momentum exchange.  相似文献   

18.
The reduction of Os3(CO)12 by NaBH4 in tetrahydrofuran has been studied, and the formation of the anionic clusters [HOs3(CO)11]?, [H3Os4(CO)12]? and [H2Os4(CO)12]2? observed. The previously unreported dianion [H2Os4(CO)12]2? was prepared in satisfactory yield, and characterised as the bis(triphenylphosphine)iminium salt. This compound crystallizes in the space group P1, with Z = 1, and cell dimensions of a 11.014(2), b 14.751(3), c 15.168(3) Å, α 123.95(2)°, β 95.77(2)°, γ 98.73(2)°. The structure was solved by a combination of multisolution sign expansion and Fourier methods, and final residuals were R 0.067 and RW 0.066 for 5972 observed intensity data. The dianion comprises a distorted tetrahedron of osmium atoms, each metal also bonding to three terminal carbonyl ligands, which as staggered with respect to the metalmetal bonds. Unlike the cation, the cluster anion is statistically disordered between two centrosymmetrically related sites.  相似文献   

19.
A number of imines (Schiff bases) have been prepared from ketosteroids (estrone, estrone-3-methyl ether, androsterone, epiandrosterone, 5α-cholestan-3-one, 6-ketocholestanol and testosterone) and primary amines (phenethylamine, tyramine and hexanamine). The CD spectra of these compounds have been measured in methanol. Except for the testosterone imines, the azomethine n-π* band (~ 235 nm) exhibited the same sign (but not as high an ellipticity) as the parent ketone's n - π* band (~295 nm). The imines of the estrogens (estrone and estrone 3-methyl ether) gave CD spectra characterized by a negative 1Lb Cotton effect ([θ] ? -1000) near 280 nm and a band near 230 nm ([θ] ? +19,000) which is considered the sum of a positive azomethine n - π* Cotton effect and positive aromatic 1La Cotton effect(s). The 1La band originating in the amine moiety was prominent in the CD of 5α-cholestan-3-one and 6-ketocholestanol phenethylamine imines. When aromatic Cotton effects originating in the amine moiety were detected, they were of the same sign as the n - π* Cotton effect.  相似文献   

20.
Crystals of two modifications of yttrium pivalate solvate Y2Piv6(HPiv )6(HPiv = (CH3)3CCOOH) are synthesized and studied by single-crystal X-ray diffraction analysis. The 3α-modification crystallizes in the monoclinic system, a = 16.394(2) Å, b = 11.948(4) Å, c = 20.352(3) Å, β = 108.73(3)°, Z = 4, space group P21/n, R 1 = 0.105. Crystals of the β-modifications are also monoclinic, a = 21.617(4) Å, b = 36.559(4) Å, c = 29.930(4) Å, β = 104.40(2)°, Z = 12, space group P21/c, R 1 = 0.050. The molecular structures of crystals of the α-and β-modifications consist of the Y22-Piv)4(Piv)2(HPiv)6 dimers. The Y atoms with a distorted antiprismatic coordination surrounding of the O atoms (Y-O 2.23–2.53 Å) are linked by four bridging bidentate pivalate anions and form the structural fragment shaped into a distorted lantern. Monodentate Hpiv molecules participate in the formation of intramolecular hydrogen bonds with Piv ligands. Crystal structures of the α-and β-modifications differ in packing of the Y2Piv6(HPiv)6 dimers and in centrosymmetric nature of the dimers in the structure of the α-modification.  相似文献   

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