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1.
Theoretical study of stereodynamics for the reaction O(3P) +D2 (v=0, j=0) to OD+D and isotope effect 下载免费PDF全文
Quasi-classical trajectory (QCT) calculations have been performed to study the product polarization behaviours in the reaction O(3P) + D2 (v= 0, j= 0)→OD + D. By running trajectories on the 3A′ and 3A″ potential energy surfaces (PESs), vector correlations such as the distributions of the polarization-dependent differential cross sections (PDDCSs), the angular distributions of P(θr) and P(ør) are presented. Isotope effect is discussed in this work by a comprehensive comparison with the reaction O(3P) + H2 (v= 0, j= 0) → H + H. Common characteristics as well as differences are discussed in product alignment and orientation for the two reactions. The isotope mass effect differs on the two potential energy surfaces: the isotope mass effect has stronger influence on P(θr) and PDDCSs of the 3A′ PES while the opposite on P(ør) of the 3A″ potential energy surface. 相似文献
2.
The analytical potential energy function of HDO is constructed at first using the many-body expansion method.The reaction dynamics of O+HD(v = 0,j = 0) in five product channels are all studied by quasi-classical trajectory(QCT) method.The results show that the long-lived complex compound HDO is the dominant product at low collision energy.With increasing collision energy,O+HD → OH+D and O+HD → OD+H exchange reactions will occur with remarkable characteristics,such as near threshold energies,different reaction probabilities,and different reaction cross sections,implying the isotopic effect between H and D.With further increasing collision energy(e.g.,up to 502.08 kJ/mol),O+HD → O+H+D will occur and induce the complete dissociation into single O,H,and D atoms. 相似文献
3.
A. Bekstein M. Benhenni M. Yousfi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,61(1):153-159
The ion swarm transport coefficients such as reduced mobility, diffusion
coefficients and reaction rates of three water vapour ion clusters
(H2O)
n
H+ (with n = 1, 2 and 3) in N2 and O2 have
been determined from a Monte Carlo simulation using calculated and measured
elastic and inelastic collision cross sections. The elastic momentum
transfer cross sections have been determined from a semi-classical JWKB
approximation based on a rigid core interaction potential model. The
inelastic cross sections have been deduced from the measured ones in the
case of similar ion cluster. Then, the cross sections sets are fitted using
either the measured reduced mobility at low electric field in the case of
(H2O)
n
H+ in N2 or the zero-field mobility calculated
from the Satoh's relation and the measured ones in N2. From the sets of
elastic and inelastic collision cross sections thus obtained in pure N2
and O2, the ion transport and reaction coefficients for
(H2O)
n
H+ are then calculated in dry air and also
extended over a wide range of reduced electric field in N2 and O2.
These ion data are very useful for modelling and simulation of non-equilibrium
electrical discharges more particularly in humid gases at
atmospheric pressure. 相似文献
4.
Dominique Costa Kamal Sharkas Mazharul M. Islam Philippe Marcus 《Surface science》2009,603(16):2484-2493
The reactivity of the (0 0 0 1)-Cr–Cr2O3 surface towards water was studied by means of periodic DFT + U. Several water coverages were studied, from 1.2H2O/nm2 to 14.1H2O/nm2, corresponding to ¼, 1, 2 and 3 water/Cr at the (0 0 0 1)-Cr2O3 surface, respectively. With increasing coverage, water gradually completes the coordination sphere of the surface Cr atoms from 3 (dry surface) to 4 (1.2 and 4.7H2O/nm2), 5 (9.4H2O/nm2) and 6 (14.1H2O/nm2). For all studied coverages, water replaces an O atom from the missing above plane. At coverages 1.2 and 4.7H2O/nm2, the Cr–Os (surface oxygen) acid–base character and bond directionality govern the water adsorption. The adsorption is molecular at the lowest coverage. At 4.7H2O/nm2, molecular and dissociative states are isoenergetic. The activation energy barrier between the two states being as low as 12 kJ/mol, allowing protons exchanges between the OH groups, as evidenced by ab inito molecular dynamics at room temperature. At coverages of 9.4 and 14.1H2O/nm2, 1D- (respectively, 2D-) water networks are formed. The resulting surface terminations are –Cr(OH)2 and –Cr(OH)3– like, respectively. The increased stability of those terminations as compared to the previous ones are due to the stabilization of the adsorbed phase through a H-bond network and to the increase in the Cr coordination number, stabilizing the Cr (t2g) orbitals in the valence band. An atomistic thermodynamic approach allows us to specify the temperature and water pressure domains of prevalence for each surface termination. It is found that the –Cr(OH)3-like, –Cr(OH)2 and anhydrous surfaces may be stabilized depending on (T, P) conditions. Calculated energies of adsorption and OH frequencies are in good agreement with published experimental data and support the full hydroxylation model, where the Cr achieves a 6-fold coordination, at saturation. 相似文献
5.
Ya-Min Li 《Molecular physics》2013,111(13):1331-1337
This paper reports on the angular momentum polarization of the products of the reaction O(1D2) + H2 via the quasiclassical trajectory (QCT) calculation on the DK (Dobbyn and Knowles) potential energy surface (PES). The four polarization-dependent differential cross-sections (PDDCS) (0, 0), (2, 0), (2, 2), (2, ?1) were calculated at different collision energies. The vector correlation between reagent velocity and product angular moment, the vector correlation between reagent, product velocity and product angular moment were studied. From the calculations, it can be obtained that the OH products are produced mainly in the plane of H–O–H plane. The changes of OH products angular momentum j ′ direction along with the increasing collision energies were ascribed to the existence of a new reaction mechanism. 相似文献
6.
M. A. Khodorkovskii T. O. Artamonova S. V. Murashov D. Michael L. P. Rakcheeva A. A. Belyaeva N. A. Timofeev A. S. Mel’nikov A. L. Shakhmin I. A. Dement’ev 《Technical Physics》2009,54(1):1-6
Signals from ions forming in a supersonic molecular beam consisting of an argon-water vapor mixture are measured as functions
of the exciting electron energy in the range to 120 eV. The thresholds of electron impact excitation of (H2O)
n − 1H+ and Ar
n
(H2O
m
+ clusters are determined for the first time. It is found that the proton-hydroxyl group binding energy decreases considerably
both in the case of water molecule clustering and when mixed Ar
n
(H2O)
m
clusters arise. 相似文献
7.
8.
Structures and luminescence properties of Yb3+ in the double perovskites Ba2YB'O6 (B'=Ta5+, Nb5+) phosphors 下载免费PDF全文
The Yb3+ doped Ba2YB'O6 (B'=Ta5+, Nb5+) were prepared by high temperature solid-state reaction method, their structures were determined by x-ray diffraction and refined by Rietveld method. The diffuse reflection absorption, excitation and emission spectra of Yb3+:Ba2YB'O6 (B'=,Ta5+, Nb5+) were measured at room temperature. Under the excitation of ultraviolet light, these phosphors exhibit broad charge transfer band emissions of TaO6 or NbO6 centre with large Stokes shift. The Yb3+ doped into these hosts are situated at Y3+ sites of cubic symmetry (Oh). The experimental energy levels of Yb3+ in Ba2YTaO6 and Ba2YNbO6 were determined by photoluminescence and diffuse reflection absorption spectra. Their wavefunctions and theoretical energy levels were obtained by diagonalising the Hamiltonian matrix. The experimental energy levels were fitted by Levenberg--Marquardt iteration algorithm to determine crystal field parameters. Then, the magnetic-pole transition line strengths of Yb3+:Ba2YB'O6(B'=Ta5+, Nb5+) from (2F5/2)Γ8- to the low-energy states were calculated. 相似文献
9.
Using molecular-beam relaxation techniques and isotopic exchange experiments, the water-formation reaction on Pd(111) has been shown to proceed via a Langmuir-Hinshelwood mechanism. The reaction product H2O is emitted from the surface with a cosine distribution. The rate-determining step is the formation of OHad in the reaction Oad + Had → OHad. The activation energy for this step is 7 kcal/mole with a pre-exponential factor, v, of 4 × 10?8 cm2 atom?1 sec?1. This value for v lies well below that observed for simple second-order desorption of dissociatively adsorbed diatomic gases, but is roughly of the order of that obtained for the oxidation of CO on Pd(111). The formation of H2O proceeds differently under conditions of excess O2 or H2. In an excess of H2, the kinetics is dominated by the transport of atomic hydrogen between the bulk and the surface as was found for the H?D exchange reaction on Pd(111). In an excess of O2, diffusion of hydrogen into the bulk is blocked by adsorbed oxygen and the hydrogen reservoir available for reaction at the surface is decreased by several orders of magnitude. This results in a drastic reduction of the reaction rate which can be reversed by increasing the partial pressure of H2. 相似文献
10.
The reaction of formamide over the (0 1 1) faceted TiO2(0 0 1) surface has been studied by Temperature Programmed Desorption (TPD) and X-ray Photoelectron Spectroscopy (XPS). Two main reactions were observed: dehydration to HCN and H2O and decomposition to NH3 and CO. The dehydration reaction was found to be three to four times larger than the decomposition at all coverages. Each of these reactions is found to occur in two temperature domains which are dependent upon surface coverage. The low temperature pathway (at about 400 K) is largely insensitive to surface coverage while the high temperature pathway (at about 500 K) shifts to lower temperatures with increasing surface coverage. These two temperature pathways may indicate two adsorption modes of formamide: molecular (via an η1(O) mode of adsorption) and dissociative (via an η2(O,N) mode of adsorption). C1s and N1s XPS scans indicated the presence of multiple species after formamide absorption at 300 K. These occurred at ca. 288.5 eV (-CONH-) and 285 eV (sp3/sp2 C) for the C1s and 400 eV-(NH2), 398 eV (-NH) and 396 eV (N) for the N1s and result from further reaction of formamide with the surface. 相似文献
11.
Guojian Wang Zhoubin Lin Lizhen Zhang Yisheng Huang Guofu Wang 《Journal of luminescence》2009,129(11):1398-1400
This paper reports the spectral properties and energy levels of Cr3+:Sc2(MoO4)3 crystal. The crystal field strength Dq, Racah parameter B and C were calculated to be 1408 cm−1, 608 cm−1 and 3054 cm−1, respectively. The absorption cross sections σα of 4A2→4T1 and 4A2→4T2 transitions were 3.74×10−19 cm2 at 499 nm and 3.21×10−19 cm2 at 710 nm, respectively. The emission cross section σe was 375×10−20 cm2 at 880 nm. Cr3+:Sc2(MoO4)3 crystal has a broad emission band with a broad FWHM of 176 nm (2179 cm−1). Therefore, Cr3+:Sc2(MoO4)3 crystal may be regarded as a potential tunable laser gain medium. 相似文献
12.
13.
R. B. Morgunov E. V. Kurganova T. G. Prokhorova é. B. Yagubski S. V. Simonov R. P. Shibaeva 《Physics of the Solid State》2008,50(4):684-690
Layered single crystals of the (BEDO-TTF)6[M(CN)6](H3O,CH3CN)2 (M = Fe, Cr) compounds with alternating conducting layers of BEDO-TTF and [M(CN)6](H3O,CH3CN)2 are studied. The contributions to the magnetic susceptibility from charge carriers in BEDO-TTF layers and from the subsystem of localized magnetic moments of iron (or chromium) transition metal complexes are separated
for both compounds under investigation. It is revealed that the crystals with [Fe(CN))6]3− anions at a temperature of ∼80 K and the crystals with [Cr(CN))6]3− anions at ∼30 K undergo magnetic transitions which are accompanied by drastic changes in the parameters of the EPR lines
associated with the BEDO-TTF layers and the subsystem of localized spins of transition metal complexes. It is established that the presence of the BEDO-TTF layers in the structure affects the magnetic properties of iron and chromium hexacyanide complexes.
Original Russian Text ? R.B. Morgunov, E.V. Kurganova, T.G. Prokhorova, E.B. Yagubskiĭ, S.V. Simonov, R.P. Shibaeva, 2008,
published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 4, pp. 657–663. 相似文献
14.
在新的全域势能面上, 用准经典轨线方法细致地研究了O(1D)+CD4多通道化学反应的动力学.这个势能面是用交换不变多项式方法基于MRC+Q/aug-cc-pVTZ从头算点拟合得到的.通过计算得到了产物OD+CD3、D+CD2OD/CD3O和D2+DCOD/D2CO的分支比、平动能分布以及角度分布,结果显示理论与实验吻合得较好, 从而说明了这个反应的同位素取代效应很小. 研究表明,O(1D)+CD4反应是经过陷入的抽取机理发生的: 最初主要通过D原子的抽取,并不是之前人们认为的直接C-D键的插入形成CD3OD中间物后再进而解离成各个产物通道. 相似文献
15.
Niina Jalarvo Camilla Haavik Camilla Kongshaug Poul Norby Truls Norby 《Solid State Ionics》2009,180(20-22):1151-1156
The hydrated oxygen deficient complex perovskite-related materials Sr4(Sr2Nb2)O11·nH2O and Sr4(Sr2Ta2)O11·nH2O were studied at high water vapour pressures over a large temperature range by electrical conductivity measurements, thermogravimetry (TG), and X-ray powder diffraction (XRPD). In humid atmospheres both materials are known to exhibit protonic conductivity below dehydration temperatures, with peak-shaped maxima at about 500 °C. In this work we show that the peaks expand to plateaus of high conductivity from 500 to 700 °C at a water vapour pressure of 1 atm. However, in situ synchrotron XRPD of Sr4(Sr2Nb2)O11·nH2O as a function of temperature shows that these observations are in fact coincident with melting and dehydration of a secondary phase Sr(OH)2. The stability of Sr4(Sr2Nb2)O11·nH2O and Sr4(Sr2Ta2)O11·nH2O in humid atmospheres is thus insufficient, causing decomposition into perovskites with lower Sr content and SrO/Sr(OH)2 secondary phases. This, in turn, rationalizes the observation of peaks and plateaus in the conductivity of these materials. 相似文献
16.
Tian-lei Zhang Peng Zhang Zi-long Jia Kai Zhang Xin-yi Miao Zhu-qing Wang 《Molecular physics》2013,111(14):2132-2143
ABSTRACTIn this work, four different channels, represented by H2O???HO2 + HOCl, HO2???H2O + HOCl, H2O???HOCl + HO2 and HOCl???H2O + HO2 have been analysed for water-catalysed formations of H2O2 + ClO to gain insight into the potential impact of the reaction in the atmosphere. The results at the CCSD(T)/aug-cc-pVTZ//MP2/6-311+G(2df,2p) level show that the H2O???HO2 + HOCl reaction is kinetically the most favourable channel among the four channels. Compared to the channel of H2O2 + ClO formations without water vapour, the effective rate constant of H2O???HO2 + HOCl reaction is estimated to be faster than the naked reaction by 2–3 orders of magnitude, indicating that the single water molecule in the H2O???HO2 + HOCl channel exhibits a positive catalytic effect on enhancing the rate of H2O2 + ClO formations. Meanwhile, it is interesting that the transfer process between H2O???HOCl + HO2 and H2O???HO2 + HOCl has an activation energy of 0.6 kcal?mol?1 and can occur easily under tropospheric conditions. 相似文献
17.
H. Klein H. Elchner H.J. Helten H. Kretzer K. Prescher H. Stehle W.W. Wohlfarth 《Nuclear Physics A》1973,199(1):169-185
The break-up reaction p0 + d → p1 + p2 + n has been studied at E0 = 16 MeV in kinematically complete p1-p2 coincidence experiments with special regard to n-p final-state interactions (f.s.i.) and p1-p2 quasifree scattering (q.f.s.). The absolute differential cross section has been measured for n-p f.s.i. c.m. production angles from 60° to 140° and for four pairs of angles with strong contributions due to q.f.s. Calculations with separable nucleon-nucleon potentials based on the Faddeev equations are in good agreement with the data obtained. In general, the shape of the experimental differential cross section is well reproduced. Discrepancies of up to 30 % in the worst cases arise between the absolute values of the theoretical predictions and the experimental data. 相似文献
18.
19.
测量了Tm3+离子不同浓度(0.5at.%, 3 at.%, 5 at.%)掺杂的NaY(WO4)2晶体在800nm激光二极管激发下的上转换发射光谱.结合吸收谱、荧光谱和由Judd-Ofelt理论计算的光谱参数,详细分析了Tm3+:NaY(WO4)2晶体中上转换能量传递机理和离子浓度对上转换发射的影响.讨论了四种影响上转换发光效率的离子间相互作用机理:3H5+1G4→3H6+1D2,3H5+3H5→3H6+3F3,1G4+3H6→3F4+3F3,1G4+3H6→3F3+3F4,并根据Miyakawa-Dexter理论定量计算了各过程的发生概率.论证了交叉弛豫和共协上转换等浓度猝灭效应是影响Tm3+离子蓝色上转换荧光发射效率的主要因素.
关键词:
3+离子')" href="#">Tm3+离子
4)2晶体')" href="#">NaY(WO4)2晶体
上转换
浓度猝灭 相似文献
20.
V. K. Voronkova R. T. Galeev S. Shova G. Novitchi C. I. Turta A. Caneschi D. Gatteschi J. Lipkowski Yu. A. Simonov 《Applied magnetic resonance》2003,25(2):227-247
New compounds, [Cu3Ln2(ClCH2COO)12(H2O)8]·2H2O with Ln = Nd3+ (I), Sm3+ (II), Pr3+ (III), built up of pentanuclear clusters were synthesized and studied by means of X-ray analysis and electron paramagnetic
resonance (EPR). X-ray data show that all compounds are isostructural and the pentanuclear clusteres may be considered as
a linear system with alternating Cu(II) and Ln(III) ions: Cu(2)-L1-Ln-L2-Cu(1)-L2-Ln-L2-Cu(2) with L1 and L2 being bridging fragments and Cu(1) and Cu(2) being structurally nonequivalent copper complexes. EPR studies demonstrate that
in the temperature range of 100–293 K the signals due to only one type of the copper complexes are observed in the spectra
of I–III. AtT<100 K the spectral temperature dependence is nontrivial. AtT<30 K new signals are detected in the spectra of I and II. The temperature dependence of the EPR spectra is interpreted under
the assumption that the parameter of the exchange interaction Cu(2)-Ln considerably exceeds the parameter of the interaction
Cu(1)-Ln. EPR spectra are calculated for the fragments of five paramagnetic centers in the frames of the model taking into
account the nonequivalence of two copper complexes, short longitudinal and transverse paramagnetic relaxation times of the
rare-earth ions at room temperature and the change of the relaxation rates when the temperature decreases. The results of
the calculations show that it is possible to obtain information about the interactions in the system on the basis of the analysis
of the temperature dependence of the EPR spectra of the central copper complex. The parameter of the isotropic part of the
exchange interaction between copper and neodymium ions (for the interaction Cu(2)-Nd) is estimated as about 15 cm−1. A considerable rearrangement of the spin states when the temperature changes is found for all complexes. 相似文献