On the additivity of atomic and molecular dipole properties and dispersion energies using H,N, O,H2, N2, O2, NO,N2O,NH3 and H2O as models

The zeroth-order theory of intermolecular forces is used to derive additivity relations for rotationally averaged molecular dipole properties and dispersion energy constants by assuming that a molecule is comprised of non-interacting atoms or molecules. Some of the additivity rules are new and others, for example the mixture rule for dipole oscillator strength distributions (DOSDs), Bragg's rule for stopping cross sections and Landolt's rule for molecular refractivities, are well known. The additivity rules are tested by using previously constructed DOSDs and reliable values for the dipole oscillator strength sums S_k , L_k and I_k , and dispersion energy constants C ₆, for H, N, O, H₂, N₂, O₂, NO, N₂O, NH₃ and H₂O as models. It is found that additivity is generally unreliable for estimating molecular properties corresponding to k < -2. Generally for k ≥ -2 and for C ₆, and if the hydrogen molecule is used to represent the hydrogen atom in the additivity rules, the additivity relations yield results that are reliable to within ?20 per cent and the estimates improve substantially as k increases. The effects of molecule formation on DOSDs is examined by comparing the various molecular DOSDs with the sum of the DOSDs for the atoms making up the molecules. Molecule formation results in a net decrease in the amount of dipole oscillator strength for low excitation energies and a compensating net increase for higher energies in a region extending from the absorption threshold to about 100 eV. This is shown to imply that estimates of the stopping average energy I ₀, obtained by using bona fide atomic I ₀ values, are lower bounds to the correct molecular I ₀ results.     

Molecular-statistical approach to a behavior of ferroelectric,antiferroelectric and ferrielectric smectic phases in the electric field

The fundamental theoretical approach derived in A.V. Emelyanenko et al., Phys. Rev. E 74, 011705 (2006) is complemented by a consideration of the influence of the homogeneous electric field on Sm- C _A ^* , biaxial intermediate phases, and Sm-C ^* . The crucial role of the induced polarization is investigated for the first time. The evolution of any tilted smectic phase in the electric field is found to meet the two thresholds. The first threshold corresponds to the unwinding process, and the second one corresponds to the phase transition into the bi-domain structure of Sm-C ^* , where the tilt plane has some contribution either along or against the electric field, while the average direction may still be perpendicular to the electric field. The tilt plane in the monodomain (conventional) structure preceding the second threshold is the same in every unwound phase, and is perpendicular to the electric field. No 3D distortion in Sm- C _A ^* is predicted on application of the electric field. The entire electric-field-temperature phase diagrams including the possibility of existence of the maximal number of tilted smectic phases are plotted and compared with the experimental ones. The numerical calculations in the framework of this fundamental study are done with help of AFLC Phase Diagram Plotter software developed by the author and available at his web page.     

Structure and properties of α‐cyclo[N]thiophenes as potential electronic materials – a theoretical study

Density functional theory (DFT) calculations of ring‐shaped α‐cyclo[N]thiophenes with N = 2 to N = 18 have been performed for ideal structures of high symmetry (point groups C_nv and D_nh) and for optimum energy structures of lower symmetry (D_2d, C_s, C_2v, C_i or C₁). Whereas the first three members of the series behave exceptionally the higher members are typical cyclothiophenes consisting of weakly interacting thiophene rings. In contrast to neutral compounds, cations and dications of cyclothiophenes with N ≥5 exhibit pronounced electron delocalizations along the carbon backbone. However, if the functional B3LYP is replaced by BH cations of large ring‐size cations show polaron‐type charge defects. According to broken symmetry DFT calculations dications with N = 14 and N = 18 have biradical character. These structures correspond to two‐polaron‐type structures rather than to dipolarons. The calculated vertical ionization energies of cyclo[N]thiophene are comparable with those of oligo[N]thiophenes of the same number of thiophene rings but the calculated absolute energies are probably too low at large ring size. Cyclothiophenes absorb light of lower energies than the related oligothiophenes. Cyclothiophenes belong to the strongly absorbing organic chromophores. In case of high molecular symmetry some of the excited states of cyclothiophenes are degenerate. The degeneracy is lifted with lower symmetries but the general absorption feature remains. The theoretical results are discussed with respect to recent experimental findings. Copyright © 2007 John Wiley & Sons, Ltd.     

C60分子电子性质的理论研究

根据C₆₀分子的结构特征,构造了电子的局域波函数,在该函数表象下计算了电子格点之间的跳跃能量.对不等性sp³杂化,通过优化计算,当有效核电荷数Z=1.112时,得到的能隙(最低未占据轨道(LUMO)与最高占据轨道(HOMO)之间的能量差)、能带宽度以及电离能阈值分别为1.70eV,12.19eV和8.13eV.这与实验结果符合得较好.与之相应的电子跳跃能量是：最近邻分别为-2.299eV,-2.113eV;次近邻分别为0.103eV,0.170eV;三近邻分别为 关键词：     

Subthreshold and near threshold K+ meson photoproduction\newline on nuclei

The inclusive K⁺ meson production in photon–induced reactions in the near threshold and subthreshold energy regimes is analyzed with respect to the one–step (γN→K ⁺ Y, Y=Λ,Σ) incoherent production processes on the basis of an appropriate new folding model, which takes properly into account the struck target nucleon removal energy and internal momentum distribution (nucleon spectral function), extracted from recent quasielastic electron scattering experiments and from many–body calculations with realistic models of the NN interaction. Simple parametrizations for the total and differential cross sections of the K⁺ production in photon–nucleon collisions are presented. Comparison of the model calculations of the K⁺ differential cross sections for the reaction γ+C¹² in the threshold region with the existing experimental data is given, that displays the contributions to the K⁺ production at considered incident energies coming from the use of the single–particle part as well as high momentum and high removal energy part of the nucleon spectral function. Detailed predictions for the K⁺ total and differential cross sections from γH², γC¹² and γPb²⁰⁸ reactions at subthreshold and near threshold energies are provided. The influence of the uncertainties in the elementary K⁺ production cross sections on the K⁺ yield is explored. Received: 12 April 1999 / Revised version: 11 September 1999     

Speckle correlations in the light scattered from weakly rough random metal surfaces

Abstract

Diagrammatic perturbation theory and computer simulation methods are used to compute the angular intensity correlation function C(q, k|q′,k′)=([I(q|k) - (I(q|k))] × [I(q′|k′) - (I(q′|k′))]) for p-polarized light scattered from a weakly rough, one-dimensional random metal surface. I(q|k) is the squared modulus of the scattering matrix for the system, and q, q′ and k, k′ are the projections on the mean scattering surface of the wavevectors of the scattered and incident light, respectively. Contributions to C include: (a) short-range memory effect and time-reversed memory effect terms, C ⁽¹⁾; (b) an additional short-range term of comparable magnitude C ⁽¹⁰⁾; (c) a long-range term C ⁽²⁾; (d) an infinite-range term C ⁽³⁾; and (e) a term C ^(1.5) that along with C ⁽²⁾ displays peaks associated with the excitation of surface plasmon polaritons. The diagrammatic methods are also extended to treat the angular intensity correlation function for the scattering of p to p, p to s, s to p, and s to s polarizations of light from a two-dimensional randomly rough surface. These correlations are again described in terms of C ⁽¹⁾, C ⁽¹⁰⁾, C ^(1.5), C ⁽²⁾, and C ⁽³⁾ contributions to C for the two-dimensional surfaces. Short-range memory and time-reversed memory effects are observed in the two-dimensional C ⁽¹⁾ correlations, and peaks associated with the excitation of surface polaritons are observed in the two-dimensional C ^(1.5) and C ⁽²⁾ correlations. Most of the results for the one- and two-dimensional systems are presented for incident electromagnetic plane waves. In addition, results for one-dimensional systems are presented for incident electromagnetic beams of finite width. Some of the results for one-dimensional surfaces are corroborated by means of computer simulation techniques.     

The integrated number of vibrational states in acetylene (12C2H2, 13C2H2, 12C2D2)

A calculated exhaustive set of vibrational state energies in ¹²C₂H₂, ¹³C₂H₂ and ¹²C₂D₂ has been used to analyse the evolution of the integrated number of states with increasing vibrational energy N(E) up to 15000 cm^?1, 12000cm^?1 and 10000 cm^?1 in each isotopomer, respectively. The regular contribution to N(E) was modelled analytically and numerical parameters were fitted. The other expected contribution to N(E), which is of oscillatory nature, was quantified and is discussed using energyand time-dependent theories. Related periods of oscillation and temporal recurrences are interpreted consistently in terms of the constant of the motion N_r = 5v₂ + 3v₂ + 5v₃ + v₄ + v₅ and of an average vibrational quantum. More pragmatically, the vibrational dynamics appear to be dominated by the bending vibrations, i.e., by the slowest oscillators.     

The equilibrium states of A1?xB1+x binary alloys in the hard-sphere and pair-binding model

The equilibrium ordering states of A _1−x B _1+x alloys are investigated analytically and by computer simulation with the hard-sphere and pair-binding model. The alloy energies are calculated for the case where an excess of the B component forms a solid solution or precipitates as pure phase particles. Criteria for pair-binding energies are obtained that define the type of the resulting alloy. The analytical results are presented for an alloy of arbitrary dimensionality and for any number of coordination spheres involved in interatomic interactions. Illustrating examples are given for B2 and L1₀ superstructures and for a two-dimensional square lattice in view of the atomic interaction in the first two coordination spheres.     

II. Electron-impact dissociative excitation of C<Subscript>2</Subscript>H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> and C<Subscript>2</Subscript>D<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

Absolute cross-sections for electron-impact dissociative ionization of C₂ H₂⁺ and C₂ D₂⁺ to CH⁺, C⁺, C₂⁺ , H⁺, CH₂⁺ and C₂D⁺ fragments are determined for electron energies ranging from the corresponding threshold to 2.5 keV. Results obtained in a crossed beams experiment are analyzed to estimate the contribution of dissociative ionization to each fragment formation. The dissociative ionization cross sections are seen to decrease for more than an order of magnitude, from CH⁺ (5.37±0.10) × 10^-17 cm² over C⁺ (4.19± 0.16) × 10^-17 cm², C₂D⁺ (3.94±0.38) × 10^-17 cm², C₂⁺ (3.82±0.15) × 10^-17 cm² and H⁺ (3.37±0.21) × 10^-17 cm² to CH₂⁺ (2.66±0.14) × 10^-18 cm². Kinetic energy release distributions of fragment ions are also determined from the analysis of the product velocity distribution. Cross section values, threshold energies and kinetic energies are compared with the data available from the literature. Conforming to the scheme used in the study of the dissociative excitation of C₂H₂⁺ ( C₂ D₂⁺ )\left( {\rm C}_2 {\rm D}_2^+ \right), the cross-sections are presented in a format suitable for their implementation in plasma simulation codes.     

Influence of the concentration of Ca impurity on the magnetic threshold of the magnetoplastic effect in NaCl crystals

It is found experimentally that the threshold magnetic field B _c for the magnetoplastic effect, i.e., the field at which the depinning of dislocations from paramagnetic impurities in an external magnetic field begins to be observed, increases with increasing concentration C of Ca impurity in NaCl crystals in the range C=(0.5–100) ppm. It is shown that the dependence B _c(C) exhibits a distinct tendency toward saturation. The physical interpretation of the observed dependence rests on the notion that as the impurity concentration C increases, the average size of the impurity complexes increases and, accordingly, the local atomic configuration around the impurity atoms changes according to a definite pattern. In particular, the average number of cation vacancies among the nearest neighbors increases from 1 to 6 as the number N of Ca atoms in the complex increases, and this trend, in turn, should cause the thermal vibration amplitude of the Ca atoms to increase. In other words, the phenomenon in question appears to be physically analogous in its microscopic mechanisms to the previously observed increase of B _c with increasing temperature. The proposed interpretation is further supported by good correlation of the experimental dependence B _c(C) with the calculated function . Fiz. Tverd. Tela (St. Petersburg) 40, 81–84 (January 1998)     

采用Lennard-Jones原子间势研究(C60)N分子团簇的结构演化行为

采用描述原子间相互作用的Lennard-Jones势来描述C₆₀分子间的相互作用,考虑了每个C₆₀分子的一定位置取向,并采用最速下降法计算了IH,fcc,hcp,DH及SC五种典型结构满壳层(C₆₀)_N团簇(N<2000)的能量.结果显示:当尺寸较小(N<20)时,IH结构最稳定;当尺寸处于中等(50<N<300)时,HCP结构最稳定;当尺寸较大(300<N 关键词： 60团簇')" href="#">C₆₀团簇 取向 最速下降法 结构演化     

Nonlinear optical effects for plasma diagnostics

Experimental investigations show that the 1/f noise intensityC and the contact resistanceR can be used to analyse contacts. The simply prepared contacts are fritted by discharging a capacitor, resulting in a multi-spot contact. A model relatesC andR to a number of contact spotsk with radiusa. More impulse-frittings at increasing energies decreaseC andR, thus enhancing the values ofk anda. From experimentalC vsR plots two regions are determined for GaAs: A fritting (a=constant) and A+B fritting (a∝k). Calculated values ofk are in good agreement with the number of peaks or pits formed by etching the semiconductor surface. From experimentalC vsW orR vsW curves, withW the cumulative impulse-fritting energy, the conclusion can be made thatka ³ is proportional toW.     

Effect of Supercollisions on Energy Transfer in Mixtures of Bath Gases and Laser Excited Complex Molecules

Intensities and decay rates of delayed luminescence (DL) initiated by a pulse of N₂ laser were employed to probe collisional relaxation of complex molecules (benzophenone, acetophenone) diluted with bath gases Ar, Kr, Xe, C₂H₄, SF₆, C₅H₁₂. It was shown that vibrational relaxation can be interpreted in terms of two consecutive processes: vibration-vibration (V-V) and vibration-translation (V-T). The results clearly demonstrated that fast component of DL can be used to study V-V energy transfer. It was found that at relatively small internal energy the collisional efficiences of V-V process had the values typical for molecular processes in which supercollisions contribute. The average energies transferred per collision, (ΔE), well correlated with predictions of the simple ergodic collision theory of intermolecular energy transfer.     

Electron-impact ionization and dissociation of C<Subscript>2</Subscript>D<Superscript>+</Superscript>

Absolute cross sections for electron-impact single ionization, dissociative excitation and dissociative ionization of the ethynyl radical ion (C₂D⁺)^+) have been measured for electron energies ranging from the corresponding reaction thresholds to 2.5 keV. The animated crossed electron-ion beam experiment is used and results have been obtained for the production of C₂D²⁺, C²⁺, C₂⁺_2^+ , CD⁺, C⁺ and D⁺. The maximum of the cross section for single ionization is found to be (2.01 ± 0.02) × 10^-17 cm², at the incident electron energy of 105 eV. Absolute total cross sections for the various singly charged fragments production are observed to decrease by a factor of almost three, from the largest cross-section measured for C⁺, over C₂⁺_2^+ and CD⁺ down to that of D⁺. The maxima of the cross sections are obtained to be (14.5 ± 0.5) × 10^-17 cm² for C₂⁺_2^+, (12.1 ± 0.1) × 10^-17 cm² for CD⁺, (27.7 ± 0.2) × 10^-17 cm² for C⁺ and (11.1 ± 0.8) × 10^-17 cm² for D⁺. The smallest cross section is measured to be (1.50 ± 0.04) × 10^-18 cm² for the production of the doubly charged ion C²⁺. Individual contributions for dissociative excitation and dissociative ionization are determined for each singly-charged product. The cross sections are presented in closed analytic forms convenient for implementation in plasma simulation codes. Kinetic energy release distributions of dissociation fragments are seen to extend from 0 to 6 eV for the heaviest fragment C₂⁺_2^+, up to 11.0 eV for CD⁺, 14.2 eV for C⁺ and 11.2 eV for D⁺ products.     

Ground state properties of titaniumdiboride

Abstract

The electronics structure, the charge distribution and the total energy of hexagonal titaniumdiboride are calculated using non-local pseudopotentials in both the local density approximation (LDA) and the generalized gradient expansion approximation (GGA). In the LDA we obtain a = 3.023 Å, c = 3.166 Å and B_o = 271. GPa. For these quantities the GGA values are slightly lower and both compare well with experiment. We also determined selected elastic constants by fitting the total energies to a quadratic surface in the lattice parameters. Using strains that do not break the hexagonal symmetry we obtain C₁₁ + C₁₂ = 777.GPa, C₁₃ = 83. GPa and C₃₃ = 568. GPa. Again slightly lower values are obtained using the GGA. These values agree well with a recent experiment.     

A measurement of the QCD colour factors using event shape distributions at \sqrt{s}=14 to 189 GeV

Measurements of the QCD colour factors and and of the number of active quark flavours in the process at high energy are presented. They are based on fits of +NLLA QCD calculations to distributions of the event shape observables and measured at centre-of-mass energies from 14 GeV to 189 GeV. Hadronisation effects are approximated with power correction calculations which also depend on the QCD gauge structure. In this approach potential biases from hadronisation models are reduced. Our results for individually measured quantities obtained from and C are in good agreement with QCD based on the SU(3) symmetry group where for the energies considered here, and . From simultaneous fits of and with and C we find which is also in good agreement with the QCD expectation. Received: 3 May 2001 / Revised version: 22 June 2001 / Published online: 3 August 2001     

Electron-driven processes for furan,tetrahydrofuran and 2, 5-dimethylfuran

We present the study of electron-induced processes for biomolecules, furan (C₄H₄O) and tetrahydrofuran (C₄H₈O) as well as an industrial relevant molecule 2, 5-dimethylfuran (C₆H₈O) through various total cross sections for impact energies from threshold to 5 keV. We have employed spherical complex optical potential to calculate total cross sections Q_T and total elastic cross sections Q_el. Since these molecules are complex molecules, we have used the group additivity rule which incorporates molecular properties as well as geometry of the target to evaluate these cross sections. Dependence of Q_T and Q_el on number of electrons and correlation of dipole polarisability (α) and ionisation potential (I) with peak of total ionisation cross sections Q_ion is studied and important inferences are noted. The present results for these applied molecules are compared with previous data wherever available. This is the maiden attempt to report Q_el and Q_T for 2, 5-dimethylfuran.     

Buckling of spherical shells adhering onto a rigid substrate

Deformation of a spherical shell adhering onto a rigid substrate due to van der Waals attractive interaction is investigated by means of numerical minimization (conjugate gradient method) of the sum of the elastic and adhesion energies. The conformation of the deformed shell is governed by two dimensionless parameters, i.e., C_s/epsilon and C_b/epsilon where C_s and C_b are respectively the stretching and the bending constants, and epsilon is the depth of the van der Waals potential between the shell and substrate. Four different regimes of deformation are characterized as these parameters are systematically varied: (i) small deformation regime, (ii) disk formation regime, (iii) isotropic buckling regime, and (iv) anisotropic buckling regime. By measuring the various quantities of the deformed shells, we find that both discontinuous and continuous bucking transitions occur for large and small C_s/epsilon, respectively. This behavior of the buckling transition is analogous to van der Waals liquids or gels, and we have numerically determined the associated critical point. Scaling arguments are employed to explain the adhesion induced buckling transition, i.e., from the disk formation regime to the isotropic buckling regime. We show that the buckling transition takes place when the indentation length exceeds the effective shell thickness which is determined from the elastic constants. This prediction is in good agreement with our numerical results. Moreover, the ratio between the indentation length and its thickness at the transition point provides a constant number (2–3) independent of the shell size. This universal number is observed in various experimental systems ranging from nanoscale to macroscale. In particular, our results agree well with the recent compression experiment using microcapsules.     

Initiation of the (<Emphasis Type="Italic">γ, n</Emphasis>) and (<Emphasis Type="Italic">p,n</Emphasis>) nuclear reactions in the picosecond laser plasma at a laser intensity of 2 × 10<Superscript>18</Superscript> W/cm<Superscript>2</Superscript>

The experimental results on the initiation of various (γ, n) and (p, n) nuclear reactions in the picosecond laser plasma are presented. It is demonstrated that the following (γ, n) and (p, n) nuclear reactions can be initiated at a laser intensity of 2 × 10¹⁸ W/cm² with the threshold energies of γ-quanta ranging from 1.67 to 7.56 MeV and the threshold energies of protons ranging from 1.88 to 5 MeV: ⁹Be(γ, n)2α, ¹⁸¹Ta(γ, n)¹⁸⁰Ta, ⁷Li(p, n)⁷Be, ⁶³Cu(p, n)⁶³Zn, ⁴⁸Ti(p, n)⁴⁸V. The method based on the detection of fast neutrons using the 3He counters is employed for the measurement of the number of the initiated (γ, n) and (p, n) nuclear reactions. The measured yield of the (γ, n) and (p, n) nuclear reactions ranges from 5 × 10¹ to 10⁵ reactions per laser pulse.