A mass spectrometric study of the vaporization of cerium tribromide under Knudsen and Langmuir conditions

The molecular and ionic vaporization of cerium tribromide from the effusion cell (Knudsen conditions) and the open surface of a CeBr₃ single crystal (Langmuir conditions) were studied by high-temperature mass spectrometry. The CeBr₃ and Ce₂Br₆ molecules and the CeBr₄⁻ and Ce₂Br₇⁻ negative ions were observed as vapor constituents. The partial pressures of the molecules in saturated vapor and the ratio between the vaporization coefficients of monomers and dimers under free vaporization conditions were determined. The enthalpies and the activation energies of sublimation in the form of monomers and dimers were measured. Ion–molecular equilibria with the participation of negative ions were studied. The enthalpies of formation of molecules and ions in the gas phase were obtained.     

Electron ionization mass spectrometric study of isomeric cyclohexyl-N-phenylanilines

Electron ionization mass spectra of N-, 2-, 3-, and 4-cyclohexyl-N-phenylaniline isomers have been obtained and investigated. Molecular ions of the 2–4 isomers are the base peaks demonstrating their high stability relative to the N-isomer in which the molecular ion intensity is about 76%. The characteristic primary fragmentation pattern for each isomer is proposed and discussed. Further fragmentations of some of the primary fragment ions is also discussed.     

Aggregation of fullerene (C_(60)) nanoparticle:A molecular-dynamic study

We present the results of molecular dynamics simulations of net positively charged fullerene nanoparticles in salt- free and salt-added solution. The aggregation of fullerene （C60）-like nanoparticle and counterion are studied in detail as a function of temperatures and a finite salt concentration. Our simulations show that the strong conformation changes as temperature changes. The net positively-charged nanoparticles do not repel each other but are condensed under proper temperatures. If salts are added, the aggregated nanoparticles will be disaggregated due to the Debye screening effect.     

57Fe conversion electron Mössbauer spectrometric study of boron and carbon ion implanted irons

Amorphous layers produced at the surface of iron by B⁺ and C⁺ implantation (50 kV, 1×10¹⁸ ions cm⁻²) were analyzed by CEMS. The CEM spectrum of B⁺ implanted layer was composed of broad doublet and sextet. Spread hyperfine field distribution, P(H), indicates the formation of extremely disordered FeB layer. Annealing at 400°C brought about precipitation of FeB, which was converted to Fe₂B by annealing at 500°C. The P(H) for C⁺ implanted iron was resolved to 3 subpeaks with H values of 11.0, 18.0 and 22.5 T. The amorphous FeC phase was strongly correlated to crystalline Fe₅C₂ and Fe₂C, which precipitated at 300°C and were transformed into Fe₃C at 500°C. The amorphous layer disappeared by annealing at 600°C.     

超薄Fe(4(A))膜磁特性极化中子反射研究

利用分子束外延薄膜生长技术,制备了200 (A)V/4 (A) Fe/900 V/MgO(100)薄膜样品,通过X射线反射和极化中子反射两种测量手段获得了薄膜的表面、界面及各层膜厚的相关结构信息.中子反射结果表明,Fe原子磁矩在室温下约为1.0±0.1μB,随着温度的降低,Fe原子磁矩增加,在10 K时达到1.5±0.1μB.利用指数定律拟合磁矩随温度的变化情况,外推得出4(A)铁薄膜样品的居里温度约为310±30 K.

Abstract：

Uhrathin Fe film 200 (A)V/4 (A)Fe/900 (A)V/MgO(100) has been prepared by molecular beam epitaxy (MBE). The structure parameters, such as the surface and interface roughness and the thickness of each layer, were obtained by X-ray and neutron reflectivity measurement. The magnetic properties of the thin Fe layer were investigated by polarized neutron reflectometry at different temperature. The result shows that the magnetic moment of an Fe atom is about 1.0 ± 0.1 μB at room temperature and increases to 1.5 ±0.1 μBat 10 K. The Curie temperature of the thin Fe film is estimated to be 310 ± 30 K.     

Knudsen cell mass spectrometric investigation of the PbO-ZrO(2)-TiO(2) system

Knudsen effusion mass spectrometry (KEMS) was used for direct determination of lead oxide activity as a function of temperature in various regions of the PbO-ZrO(2)-TiO(2) system. From the results, the enthalpy, Gibbs free energy and entropy of formation of PbTiO(3) (PT), PbZrO(3) (PZ) and Pb(Zr,Ti)O(3) (PZT) were evaluated. In addition, the single phase widths of Pb(Zr(0.5)Ti(0.5))O(3) and PbTiO(3) perovskite structures were determined at 1100 K. The reaction rate of PZT synthesis in vacuo was followed by direct measurement of the change of PbO activity with time. Lead oxide activity in stoichiometric Pb(Zr(0.5)Ti(0.5))O(3), PbTiO(3) and Pb(0.968)(Zr(0.5)Ti(0.5))O(2.968) (3% lead deficient) at 850 degrees C was found to be 0.40, 0.45 and 0.1, respectively. PZT, PT and PZ powder samples prepared by a solid state procedure were also measured, all revealing lead deficiency. Copyright 1999 John Wiley & Sons, Ltd.     

A(SLq(2)) at Roots of Unity is a Free Module over A(SL(2))

It is shown that when q is a primitive root of unity of order not equal to 2 mod 4, A(SL_q(2)) is a free module of finite rank over the coordinate ring of the classical group SL(2). An explicit set of generators is provided.     

The quark condensate from K(e(4)) decays

We show that, independently of the size of the quark condensate, chiral symmetry correlates the two S-wave pipi scattering lengths. In view of this constraint, the new precision data on K(e(4)) decay allow a remarkably accurate determination of these quantities. The result confirms the hypothesis that the quark condensate is the leading order parameter.     

Mass spectrometric study of the repolymerization of (SN)x

A mechanism for the repolymerization of (SN)_x, is proposed on the basis of mass spectral studies (ion abundances and appearance potentials) on its vapor, and the previously postulated mechanism of polymerization of S₂N₂ from S₄N₄. Thermal decomposition of the polymer leads to acyclic (SN)_x, x ⩾ 2, which is the essential element for repolymerization, and also to cyclic combination products of SN radicals.Obviously, if only acyclic components are present, they need only combine. Cyclic products present in the condensate will slowly decompose to SN. The decomposition will be accelerated by the presence of polymeric chains, since SN will react with the polymer and integrate therein.     

Laser ablation of a silicon carbide target: a time-of-flight quadrupole mass spectrometric study

Laser ablation of a SiC target was attempted to investigate the formation mechanisms and expansion dynamics of ionic species including silicon carbide cluster ions in the plume. Time-of-arrival distributions of ions were analysed to obtain their mean velocities and spatial distributions. Laser-plume interaction was examined by illuminating the plume with a UV laser pulse. Si₂C was found to be the major photodissociation product of silicon carbide cluster ions. PACS 82.40.Ra; 79.20.Ds; 79.20.La     

Formation of macrocyclic oligoferrocenes: a matrix-assisted laser desorption/ionization mass spectrometric study

Oligomeric ferrocenes were investigated simultaneously by matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOFMS). The oligomers were obtained by the reaction of tetrahydro-4,4,8,8-tetramethyl-4,8-disila-s-indacene-3a,7a-diyldilithium (Li(2)L) with FeCl(2).1.5 THF (THF = tetrahydrofuran). Depending on the reaction conditions up to ten linear-chain and eleven cyclic ferrocene oligomers with masses between 1139 and 5071 Da could be detected unambiguously. The most abundant macrocycles contained ten and seven iron atoms when the reactions were carried out at -20 and 25 degrees C, respectively. The chains had cyclopentadienes as end groups and formally resulted from replacing one iron of a cycle by two hydrogens, which corresponds to a mass difference of 54 Da. Copyright 1999 John Wiley & Sons, Ltd.     

High-resolution mass spectrometric study of pure helium droplets,and droplets doped with krypton

Mass spectra of doped and undoped helium droplets are presented. The high resolution of the time-of-flight spectrometer (m/Δm ≅ 5000) makes it possible to fully resolve small helium cluster ions from impurities and to unambiguously identify abundance anomalies in the size distribution of He _n ⁺. The yield of He₄ ⁺ shows the well-known enhancement relative to other small cluster ions when the expansion changes from sub- to supercritical, provided the electron energy exceeds a value of 40 ± 1 eV, the threshold for formation of electronically excited ions. Upon doping with krypton, pure Kr _n ⁺ cluster ions containing up to 41 Kr atoms are observed. The spectra exhibit abundance anomalies at 13, 16, 19, 22 & 23, 26 and 29, in agreement with spectra obtained by ionization of bare krypton clusters that are formed in neat supersonic beams. Mixed clusters He _m Kr⁺ indicate closure of a solvation shell at m = 12.     

Laser ablation of polysulfone films: a laser ionization TOF mass spectrometric study

2 . Major peaks were assigned to direct fragments and recombination products ejected from the PS surface. The arrival profiles of these ablation products varied from product to product and were fitted by using a shifted Maxwell–Boltzmann distribution with a center-of-mass flight velocity [(1.4-5.6) ×10⁵ cm/s] and a Knudsen layer temperature (350–3810 K). Two types of ablation products, whose velocities and temperatures showed different dependences on laser fluence, were found to exist. Dynamical aspects in the decomposition of the polymer chain, the ejection of various fragments, and their expansion are discussed on the basis of a photothermal ablation model, where a heated surface layer with a temperature gradient along its depth plays an important role. Received: 11 August 1998/Accepted: 12 August 1998     

High-Resolution FTIR Spectrum of the nu(9) Band of Ethylene-D(4) (C(2)D(4))

The spectrum of the nu(9) fundamental band of ethylene-d(4) (C(2)D(4)) has been measured with an unapodized resolution of 0.004 cm(-1) in the frequency range of 2300-2400 cm(-1) using a Fourier transform infrared spectrometer. A total of 549 transitions have been assigned and fitted using a Watson's A-reduced Hamiltonian in the I(r) representation to derive rovibrational constants for the upper state (v(9) = 1) up to five quartic terms with a standard deviation of 0.00087 cm(-1). They represent the most accurate rovibrational constants for the nu(9) band so far. About 30 transitions of K(a)(') = 0, one transition of nu(9) which were identified to be perturbed possibly by the nearby nu(11) and nu(2) + nu(12) transitions, were not included in the final fit. The nu(9) band of C(2)D(4) was found to be basically B-type with an unperturbed band center at 2341.836 94 +/- 0.000 13 cm(-1). Copyright 2000 Academic Press.     

A nuclear mass formula based onSU(4) symmetry

It is argued that mass anomalies at the N≈Z line are associated with SU(4) isospin-spin symmetry. Drawing on these arguments, a Weizsäcker-type nuclear mass formula is investigated which has the eigenvalue of the quadratic Casimir operator of SU(4) as a Wigner term. This SU(4)-based mass formula yields a better agreement than the one with the usual Wigner term |N—Z|/A. In addition, the SU(4) eigenvalue expression adequately replaces the usual pairing term of the Weizsäcker formula giving a lower overall rms deviation than the latter.     

Structure of premixed flames of propylene oxide: Molecular beam mass spectrometric study and numerical simulation

The knowledge of the combustion chemistry of oxygenated fuels is essential for the development of detailed kinetic mechanisms suitable for the combustion processes involving biofuels. Moreover, epoxidized olefins, are increasingly used as chemical intermediates or as bulk chemicals. Nevertheless, a dearth of data for their reactivity in the oxidative environment can be observed in the current literature. This study reports the experimental and the model characterization of the flame structure of propylene oxide at stoichiometric and fuel-rich conditions at atmospheric pressure. To this aim, the species mole fractions in three premixed flames stabilized on a flat-flame burner have been quantitatively measured by using the flame sampling molecular beam mass spectrometry. Three chemical kinetic mechanisms retrieved from the current literature involving propylene oxide chemistry have been validated against the novel experimental data. In general, the predictions appeared to be in satisfactory agreement with measurements except for acetaldehyde and ketene. The rate of production analysis in the flame has shown that the discrepancies observed for these species are related basically to the incorrect ratio between the rates of primary reaction pathways of propylene oxide destruction.     

Boson realization of YangiansY(sl(2)) andY(sl(3))

Studying the algebraic structure of the YangiansY(sl(2)), andY(sl(3)) we present their boson realizations. In the case ofY(sl(2)) we give the realization by using 1-canonical boson pair and two parameters and in theY(sl(3)) with 2-canonical boson pairs, two parameters and subalgebrasl(2). Substituting the realization ofU(sl(2)), we can obtain the pure boson realization by 3-canonical pairs and three parameters.Presented at the 4th Colloquium Quantum Groups and Integrable Systems, Prague, 22–24 June 1995.     

A Multi-Parameter Reduced Deformation of U(sl(r))

A multi-parameter reduced deformation of U(sl(m+n)) is constructed. This deformation has both the usual reduced q-analogue of U(sl(m+n)) and the reduced q-analogue of U(sl(m,n)) as its special quotients.