bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Mn(II) ions on the growth of ammonium oxalate monohydrate crystals from aqueous solutions: II. Growth kinetics
Authors: Sangwal K. , Mielniczek‐Brzóska E.
Published: February 2003

The experimental results of the effect of concentration of Mn(II) ions on the growth kinetics of different faces of ammonium oxalate monohydrate single crystals from aqueous solutions at a constant temperature and different predefined supersaturations are described and discussed. It was observed that: (1) at a given supersaturation σ, Mn(II) ions lead to a decrease in the growth rates of different faces of AO crystals, (2) the growth of a particular face of the crystals occurs above a critical supersaturation σd but there is also another supersaturation barrier σ* when the rate abruptly increases with σ, (3) the values of σd and σ* increase with increasing concentration of the impurity, and (4) the values of σd depend on the growth kinetics of a face but those of σ* are independent of face growth kinetics. The experimental R(σ) data for different Mn(II) concentrations ci were analysed according to the model involving complex source of cooperating screw dislocations and concepts of instantaneous and time‐dependent impurity adsorption. It was found that: (1) for a given face the differential heat of adsorption Qdiff is higher during instantaneous impurity adsorption than that during time‐dependent adsorption, and (2) the values of Qdiff involved during instantaneous adsorption are related with face growth kinetics but those during time‐dependent adsorption are independent of face growth kinetics.
A joint Japan–China research project for reducing pollution in China in the context of the Kyoto Protocol clean development mechanism (CDM): case study of the desulfurdized bio‐coal briquette experiments in Shenyang and Chengdu
Authors: Hayami Hitoshi , Nakamura Masao , Yoshioka Kanji
Published: February 2003

The Kyoto Protocol agreed on in 1997 allows some flexibility for developed countries in their implementations of their commitments to reduce emissions of CO2 and other global warming gases. In particular developed countries may receive emission credits for facilitating international cooperation for developing clean development mechanisms (CDMs) between themselves and developing countries. CDMs must reduce emissions of global warming gases on a sustainable basis in the developing countries involved. Such CDMs are expected to be an important tool for Japan and other developed countries for achieving their Kyoto Protocol commitments to reduce their CO2 emissions, but assessments and implementations of alternative CDMs require careful international joint research efforts. In this paper, we discuss our on‐going Japan–China joint research to develop and evaluate bio‐coal briquette (biobriquette), a new product to replace coal in some regions of China. Coal is a significant source of air pollution in China. The introduction of biobriquette use in China as a possible CDM for Japan is also discussed. Copyright © 2003 John Wiley & Sons, Ltd.
Reaction thermodynamics of amine‐cured epoxy systems: Validation of the enthalpy and heat capacity of reaction as determined by modulated temperature differential scanning calorimetry
Authors: Swier Steven , Van Mele Bruno
Published: February 2003

The reaction enthalpy and reaction heat capacity of three aromatic epoxy–amine systems have been determined with modulated temperature diffential scanning calorimetry (MTDSC), mostly in quasi‐isothermal conditions, over a wide temperature range (33–140 °C) and for different mixture compositions. The reaction enthalpy is only slightly dependent on the epoxy–amine chemistry, from −111 to −98 kJ/mol epoxy functionality. With the model system phenyl glycidyl ether (PGE)+aniline, the reaction enthalpy of the secondary amine–epoxy reaction step is equal to that of the primary amine–epoxy reaction. Group contributions needed to calculate the reaction heat capacity with an additivity approach are evaluated, and a new value of 37.2 J mol−1 K−1 for the group N(H)(C)(CB) is proposed. With this group contribution, the additivity method predicts almost equal values for the reaction heat capacity of both amine–epoxy reaction steps at 298.15 K (ΔrCp,prim = 15.7 J mol−1 K−1 and ΔrCp,sec = 14.6 J mol−1 K−1), whereas the experimental value of ΔrCp,sec is about three times larger than that of ΔrCp,prim at 100 °C. These results are confirmed experimentally for PGE+aniline as a different temperature dependence of both reaction heat capacities. MTDSC therefore is potentially interesting for differentiating between reactive species in an epoxy–amine reaction, a benefit previously assigned to spectroscopic methods only. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 594–608, 2003
The value of product development lead time in software startup
Authors: Hilmola Olli‐Pekka , Helo Petri , Ojala Lauri
Published: February 2003

This article uses system dynamics simulation to enhance current understanding of the effects of product development lead time improvement in situations where a software company itself is not able to finance its operations with its own cash flow. In these situations, capital markets will provide some rounds of financing for startup at the very beginning, but after a while the company itself should be able to enlarge its operations with its own operational cash flow. However, the delay in the product development process, as well as the decline of R&D productivity within the final product markets, will have their effects. On the basis of the results of this article, it is suggested that the improvement of product development lead time is one of the most important parameters in the software startup environment. In some situations, not only will slightly improved lead time performance require fewer rounds of financing, but also expansion of the company's operations will become less troublesome. Copyright © 2003 John Wiley & Sons, Ltd.
Tailoring the software maintenance process to better support complex systems evolution projects
Authors: Donzelli Paolo
Published: February 2003

When an organization considers the evolution of a software‐intensive system, the selection of the software maintenance process to be adopted must include consideration of the particular technical criteria, such as the application domain, the size and complexity of the final product, the hosting system characteristics, etc, yet be driven by the specific organization's goals, environment and maturity.

By describing and analysing a real project, this paper shows how different approaches and techniques, usually applied in isolation, can be selected, customized and combined to implement a software maintenance and evolution process that better satisfies the goals and meets the constraints of the organization. The project was undertaken to investigate the feasibility of enhancing an aircraft avionics system by integrating new capabilities and, eventually, to identify a quick, low‐cost and low‐risk solution. Copyright © 2003 John Wiley & Sons, Ltd.
Geometry and thermomechanics of structural rearrangements: Ekkehart Kröner's legacy Plenary lecture presented at the 80th Annual GAMM Conference, Augsburg, 25‐28 March 2002
Authors: Maugin G.A.
Published: February 2003

Starting with the influential ideas of E. Kröner on the Non‐Riemannian geometrical theory of defects and a brief review of his works, we show how this legacy has developed into a true mechanics of materials on the material manifold. This synthesis, that essentially combines Kröner's ideas and those of his contemporary, J. D. Eshelby, yields a powerful unification of some of the most fruitful developments of continuum thermomechanics at the end of the XXth century and the beginning of the XXIst. In particular, a general theory of material inhomogeneities emerges which includes the study of the progress, under the action of well defined driving forces, of many microscopic and macroscopic defects or field singularities. In particular, we emphasize the relationship between the notion of material Eshelby stress and the notion of local structural rearrangements that are responsible for many of the macroscopically observed irreversible behaviors of solid‐like matter (e.g., anelasticity, damage, phase transitions, growth). All these phenomena take place directly on the material manifold. That is, their arena and that of the associated driving forces, also called configurational forces, or material forces, require a general setting that emphasizes this material peculiarity. This is the object of the paper in which all types of applications are also mentioned.
On the scattering of point‐generated electromagnetic waves by a perfectly conducting sphere, and related near‐field inverse problems
Authors: Athanasiadis C. , Martin P.A. , Stratis I.G.
Published: February 2003

A spherical electromagnetic wave is scattered by a bounded perfectly conducting obstacle. A generalization of the plane‐wave optical theorem is established. For a spherical scatterer, low frequency results are obtained by approximating the known exact solution (separation of variables). In particular, a closed‐form approximation of the scattered wavefield at the source of the incident spherical wave is obtained. This leads to the solution of a near‐field inverse problem, where both the source and coincident receiver are located at several points in the vicinity of a small sphere. The same inverse problem is also treated from the knowledge of the leading order term in the low‐frequency asymptotic expansion of the scattering cross‐section.
A thermodynamic model of hysteresis in phase transitions and its application to rare earth oxide systems
Authors: Knittel D. R. , Pack S. P. , Lin S. H. , Eyring L.
Published: February 2003

A thermodynamic model of hysteresis in phase reactions based on regular solution theory is developed by invoking metastabilities. The effect of enthalpy and entropy change, pressure, temperature, and interaction energy on the hysteresis curve term is explored. The influence of a variation of the interaction term with temperature and composition is also studied. Observed hysteresis for the phase reactions Tb7O12?7/2Tb2O3+3/4O2 and Pr9O16 ?9/7Pr7O12+2/7O2 is discussed and the theory is applied to each case. The experimental details of data acquisition and the observed hysteresis in the praseodymium oxide reaction are given.
Structure and energy transfer within isolated (O2)2 dimers via high resolution electronic spectroscopy
Authors: Goodman Julie , Brus L. E.
Published: February 2003

Polarized, high resolution 1Δg+1Δg ↔3Σg−+3Σg−(1Ag) and 3Σg−+1Σg+→3Σg−+3Σg− (3B3u) (O2)2 dimer spectra have been observed in solid neon host at 4.2 K. Excited state electronic fine structure components are resolved and assigned. The 1Δg+1Δg transition is both allowed and vibronically induced by b3u antisymmetric O2 stretch quanta. The 1Δg+1Δg geometry is identical to that of the ground 3Σg−+3Σg− state; the 3Σg−+1Σg+ state appears to have slightly different structure. The spectra are entirely consistent with D2h structure, and less likely with D2d structure. The dimer triplet (3B3u) ground state subcomponents lie ∼55 cm−1 above the dimer singlet (1Ag) ground state. The dimer vibrational constants are unperturbed from the O2 in vacuum values. The nearest neighbor vibrational energy transfer time from one O2(1Δg) to another is ∼14 ps, as revealed by zero phonon line splittings in emission. The nearest neighbor electronic energy transfer time of the 1Σg+(v=0) state appears to be 0.6 ps, as revealed by spectral shifts. Both these processes appear to result from electron exchange, and not multipole–multipole interactions. Isotopic substitution experiments show that unfavorable Franck–Condon factors ’’trap’’ the 1Σg+ (v) state on one side of the dimer for v?1. Energy transfer of 1Σg+ (v) from dimers to nearby monomers also occurs. Comparison is made with the calculations of Bhandari and Falicov. Values for the intermolecular exchange integrals are obtained. Gas phase energy transfer is also discussed.
Hydrogen bonding and charge transfer: Interaction of OH radical with rare gas atoms
Authors: Goodman Julie , Brus L. E.
Published: February 2003

Hydroxyl radical in solid Ne at 4.2 K is known to rotate freely, vibrationally relax slowly, and have an essentially unperturbed structure. However, the HO structure and dynamics are profoundly affected by solvation in the heavier rare gases Ar, Kr, and Xe. One Ar atom nearest neighbor increases the OH (A 2Σ+) vibrational relaxation rate by a factor of ?103, and A 2Σ+↔X 2Π spectra consistant with a linear–linear transition in hydrogen bonded ArHO are observed. The Ar–HO (A 2Σ+) well depth is D0?675 cm−1 with ωe?203 cm−1 and ωexe?13.1 in solid Ar host; the Kr–HO (A 2Σ+) well depth is ?1000 cm−1. The Ar–HO hydrogen bond length is shorter by Δre=1.15±0.1 Å in the excited state. The OH (A 2Σ+) (0,0) emission band shifts from 3090 in Ne to 4400 Å in Xe. The theory of hydrogen bond formation in both ground and excited states is discussed, with particular reference to the contribution of charge transfer in various environments. Comparison is made with the spectra of hydrogen halides, and the physical origin of rotation–translation coupling theory is discussed. The role of charge transfer complexes in the gas phase quenching of free radical luminescence by rare gas atoms is also considered.
Hydrogen bonding: The structure of HF–HCl
Authors: Janda Kenneth C. , Steed Joseph M. , Novick Stewart E. , Klemperer William
Published: February 2003

The structure of the hydrogen bonded complex formed between HF and HCl has been determined by molecular beam electric resonance spectroscopy. The molecule HF–HC1 is a slightly asymmetric prolate top. The spectroscopic constants determined from K=0 spectra of several isotopic species are 〈eqQDa〉 for HF D35Cl is 146(15) kHz. The equilibrium atomic arrangement is HF–HCl with the internal proton colinear with the two heavy atoms spaced 2.12 Å from the fluorine atom. The exterior proton is off axis by 50°. The bonding of this complex is discussed with respect to other gas phase complexes and hydrogen halide crystal structures. It appears that a model which involves electron donation from the highest occupied molecular orbital (HOMO), of one submolecule to the lowest unoccupied molecular orbital (LUMO) of the other gives a useful qualitative description of complex formation between closed shell species.
On the mechanism of water cluster-ion formation in nitrogen
Authors: McCrumb J. L. , Warneck P.
Published: February 2003

The reaction mechanism for the formation of H3O+⋅H2O ions in ionized nitrogen containing small amounts of water vapor impurity is found to differ from that established previously by Good, Durden, and Kebarle in that the reaction chain involves not only H3O+, but also N2⋅H2O+ and N2⋅H3O+ ions. The predominant reactions are identified and the associated rate coefficients are estimated.
Temperature dependence of O(1D) rate constants for reactions with N2O, H2, CH4, HCl, and NH3
Authors: Davidson J. A. , Schiff H. I. , Streit G. E. , McAfee J. R. , Schmeltekopf A. L. , Howard Carleton J.
Published: February 2003

Absolute rate constants are reported for the deactivation of O(1D) by five trace atmospheric constituents for the temperature range 200–350 K. O(1D) atoms produced by photolyzing ozone with a frequency quadrupled pulse from a Nd-YAG laser are monitored directly by means of the O(1D) →O(3P) emission at 630 nm. All the gases studied here are thought to deactivate O(1D) primarily through reactive channels. Their rate constants exhibit no detectable temperature dependence. The rate constants are (in units of 10−10 cm3/molecule⋅s) N2O: 1.1,±0.2, H2: 0.99±0.3, HCl: 1.4±0.4, NH3: 2.5±0.5, CH4: 1.4±0.4. The present results and those of our previous studies are compared with rate constants obtained using the time-resolved attenuation of resonance absorption technique.
Observation and analysis of the depolarized Rayleigh doublet in isotropic MBBA and measurement of the de Gennes viscosity coefficients
Authors: Alms G. R. , Gierke T. D. , Patterson G. D.
Published: February 2003

The doublet in the depolarized (IVH) Rayleigh light scattering spectrum was studied in the isotropic phase of p-methoxybenzylidene- (p-n-butyl) aniline, (MBBA). All spectra were found to fit well to the Andersen–Pecora theory for the IVH spectrum in viscous liquids. The value of the rotational–translational coupling parameter R was determined to be 0.36±0.02 for MBBA, independent of temperature over the range 150–230 °C. A direct correspondence is made between the parameters of the Andersen–Pecora theory and the phenomenological theory of de Gennes. From this correspondence we obtain a microscopic equation for the de Gennes ’’a’’ parameter. Using this microscopic evaluation of the de Gennes parameter ’’a’’, we evaluate the de Gennes viscosity parameter ν for MBBA. Using the measured value of R and the values of ν and η we obtain values for the de Gennes viscosity parameter μ for MBBA. We show the value of ν for MBBA can be easily calculated from the slip model of rotational diffusion to good accuracy. Since we know R, the value of μ can also be obtained by the calculation. Finally values of μ are calculated for several liquids for which R is known and the relationship between μ and η is examined.
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o SCF CI calculations on the ground and π–π* excited states of the pyrrole molecule and its positive ion
Authors: Tanaka Kiyoshi , Nomura Tsutomu , Noro Takeshi , Tatewaki Hiroshi , Takada Toshikazu , Kashiwagi Hiroshi , Sasaki Fukashi , Ohno Kimio
Published: February 2003

A b initio SCF π-electron CI calculations are carried out on the ground and lower π–π* excited states of pyrrole and its positive ion. The four singlet states found at 5.9, 6.8, 7.2, and 7.4 eV by experiment are tentatively assigned as the 1B2, 1A1, 1B2, and 1A1 states, respectively. The calculated excitation energies for these four states are 6.0, 6.5, 7.1, and 7.3 eV, respectively. The first excited 1A1 state is a valence type state, whereas the other three states are Rydberg type states. The lowest excited state found at 4.35 eV by experiment is assigned as the 3B2 state, whose calculated excitation energy is 4.27 eV. The three lowest excited states of the positive ion due to π-electron ionization are also investigated. The calculated ionization potentials are 8.10 (2A2), 8.94 (2B1), and 13.33 eV (2B1). They are in good agreement with experimental values of 8.21, 9.20, and 13.0 eV. The lowest two states are represented by la2→∞ and 2b1 →∞, respectively, whereas the second 2B1 state is a mixture of three configurations (1b1→∞), (2b1 2 →3b1∞), and (1a2 2→3b1∞).
Semiclassical eigenvalues for potential functions defined on a finite interval
Authors: Adams John E. , Miller William H.
Published: February 2003

It is shown that the usual WKB quantum condition for one-dimensional potentials should be modified for problems defined on the finite interval (a,b) by adding the ’’correction’’ ΔV (x) = (h/2/8m)[π/(b−a)]2/cos2 {π[x−(a+b)/2]/(b−a) } to the actual potential. Numerical application shows the modified quantum condition to be a considerable improvement over the usual (i.e., unmodified) equation.
Hydrogen–deuterium exchange in acetylene and between acetylene and water
Authors: Pyper J. W. , Liu D. K. K.
Published: February 2003

Calculations of equilibrium constants for reactions C2H2+C2D2=2C2HD and C2H2+D2O=CD2+H2O are reported. These calculations were performed in the harmonic approximation. (AIP)
Comment of fitting a
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o intermolecular potentials for scattering calculations
Authors: Green Sheldon
Published: February 2003

The angular dependence of the interaction between two rigid linear rotors is considered, and on of the two expansions in current use is shwn to be inappropriate. Interpolation of tabulated radial interactions is also discussed, and nuimerical tests are presented which demonstrate the accuracy of Lagrange and spline algorithms as a function of the spacing between points.
Pressure and temperature dependence of the longitudinal proton relaxation times in supercooled water to −87 °C and 2500 bar
Authors: Lang E. , Lüdemann H.-D.
Published: February 2003

The longitudinal proton relaxation times T1 of the water protons have been determined at 100.1 MHz in the temperature range from +20 to −87 °C and up to pressures of 2500 bar. At temperatures below +10 °C, the T1 isotherms exhibit a maximum at pressures between 1.5 and 2 kbar. While at +10 and 0 °C, T1 rises by ∼10% from its atmospheric pressure value, this maximum becomes much more pronounced between −20 and −45 °C. In this region application of pressure increases T1 by ∼100%. The isobars at 2 kbar and above run through a minimum at −76 °C, indicating that at this temperature ωτϑ?1 and that the proton relaxation rate cannot be described by the extreme narrowing condition below ∼−40 °C. The experimental T1 data and the τϑ values derived at 2 kbar could be treated by a sum of two exponentials. While the smaller activation energies derived from this fit of 3.44±0.17 kcal mole−1 is independent of pressure, the higher activation energy decreases from 13±0.65 kcal mole−1 at atmospheric pressure to 9.3±0.5 kcal mole−1 around 1 kbar and then remains independent of pressure to 2.5 kbar. The data are qualitatively discussed in terms of a random hydrogen-bond network.
Rate constants for the reaction of OH radicals with CH2=CHF, CH2=CHCl, and CH2=CHBr over the temperature range 299–426 °K
Authors: Perry R. A. , Atkinson R. , Pitts J. N.
Published: February 2003

Absolute rate constants for the reaction of OH radicals with vinyl fluoride, vinyl chloride, and vinyl bromide have been determined over the temperature range 299–426 °K using a flash photolysis–resonance fluorescence technique. The Arrhenius expressions obtained were k (CH2=CHF) = 1.48×10−12e(775±300)/RT cm3 molecule−1 sec−1, k (CH2=CHCl) = 1.14×10−12e(1045±300)/RT cm3 molecule−1 sec−1, and k (CH2=CHBr) = 1.79×10−12e(805±300)/RT cm3 molecule−1 sec−1, with rate constants at room temperature of (5.56±0.56) ×10−12 cm3 molecule−1 sec−1, (6.60±0.66) ×10−12 cm3 molecule−1 sec−1, and (6.81±0.69) ×10−12 cm3 molecule−1 sec−1 for CH2=CHF, CH2=CHCl, and CH2=CHBr, respectively.
Stark hyperfine structure of hydrogen bromide
Authors: Johnson David W. , Ramsey Norman F.
Published: February 2003

The ν=0, J=1,2 hyperfine spectra of hydrogen bromide have been measured with a molecular beam electric resonance spectrometer at electric fields of 1500–3500 V/cm. The hyperfine structure parameters were determined for H 79.81Br and D 79.81Br. The quadrupole interaction ratios are The distance derivative of the electric field gradient at the site of the bromine nucleus was determined to be d (q/qe)/d ([R−Re]/Re) =1.556(3). The magnetic octupole interaction of the bromine nucleus was negligible ‖ewΩ‖<0.5 Hz. The electric polarizability anisotropy was measured to be (α∥−α⊥) =0.37(9) Å3. The same technique was used for DCl with the result (α∥−α⊥) = 0.23(3) Å3. Numbers in parenthesis are uncertainties in the final figures.
Rotational relaxation of HF
Authors: Sentman L. H.
Published: February 2003

A rotational nonequilibrium model of Hinchen’s HF rotational relaxation experiment has been used to determine the two constants in the Polanyi and Woodall rotational transition probability. Agreement between Polanyi and Woodall’s and Hinchen’s results is demonstrated.
The alkoxy radical, RCH2Ȯ, as a free radical product in x-irradiated single crystals of nucleosides and nucleotides
Authors: Bernhard William A. , Close David M. , Hüttermann Jürgen , Zehner Herbert
Published: February 2003

The RCH2Ȯ radical is formed in x-irradiated 3′-cytidylic acid (3′CMP), 5-chlorodeoxyuridine (ClUdR), 5-bromodeoxyuridine (BUdR), adenosine⋅HCl (AR⋅HCl), and deoxyadenosine monohydrate (AdR⋅H2O) owing to the net loss of hydrogen from O5′ of the primary hydroxylic group. ESR measurements were made between 78 and 100 K on single crystals of 3′CMP, ClUdR, BUdR, and AR⋅HCl and on polycrystalline AdR⋅H2O. The range of principal g values is gmax=2.054–2.093, gint=2.005–2.009, gmin =1.995–2.000. The range of sum of the isotropic β-hydrogen hyperfine couplings is Aβ1iso +Aβ2iso=141–156 G. The g tensors and Aβiso values are used to determine which oxygen nonbonding orbital contains the bulk of the unpaired electron density. The unpaired electron 2p orbital symmetry axis is perpendicular to a plane determined by X(H) ⋅⋅⋅Ȯ–C. Of the two relevant hydrogen bonds in the undamaged molecule, the X–H⋅⋅⋅O bond remains intact whereas the hydrogen in the O–H⋅⋅⋅Y bond is displaced. The equation Aβiso=B0+B2 cos2ϑ, with B0 =0 and B2=101±13 G describes the dependency of the β-hydrogen hyperfine coupling on the torsion angle ϑ, between the unpaired electron symmetry axis and the C–Hβ bond of the RCH2Ȯ radical. Mechanisms of formation, factors in stabilization, and reactions of decay are discussed.
Noncritical interface near a critical end point
Authors: Widom B.
Published: February 2003

The interface between a noncritical phase and a critical or near-critical phase is studied. Its structure and tension are deduced from the van der Waals, Cahn–Hilliard theory with a model free-energy density. The composition profile is found to be such that the composition in the interface approaches that of the noncritical phase on the one side exponentially rapidly, but approaches that of the critical phase on the other side much more slowly, only as an inverse power of the distance. The interfacial tension is calculated along two essentially different paths through the critical end point: one of fixed composition that goes from the three-phase to the two-phase region with varying temperature, the other of fixed temperature but varying composition, lying entirely in the two-phase region. It is predicted that the interfacial tension varies smoothly through the critical end point on both paths; that on the first path it is likely to increase as one goes from the three- to the two-phase region; and that on the second path, as a function of the composition, it has the qualitative shape of a typical critical isotherm. The theoretical implications of these results are discussed, reference is made to the few relevant experiments that have been done, and suggestions are made for further measurements with which to test the theory.
Vibration–rotational and pure rotational laser–Raman spectra of H2, D2, and HD in matrices at 12 K
Authors: Prochaska Frank T. , Andrews Lester
Published: February 2003

The vibration–rotational and pure rotational laser–Raman spectra of H2, D2, and HD were observed in argon, krypton, xenon, nitrogen, and oxygen matrices at 12 K. Transitions arising from the J=0 and J=1 rotational levels were seen for H2 and D2, but from only the J=0 level for HD. Only transitions from the J=0 level were observed for H2 in an oxygen matrix. It is interesting that hydrogen is trapped at all in an inert gas matrix at 12 K; this indicates that hydrogen molecule–inert gas atom interactions are stronger than hydrogen–hydrogen interactions.
Photofragment spectroscopy and potential curves of Ar+2
Authors: Moseley J. T. , Saxon R. P. , Huber B. A. , Cosby P. C. , Abouaf R. , Tadjeddine M.
Published: February 2003

Photofragment energy distributions have been measured for the process Ar+2(2Σ+u)+hν→Ar++Ar using a 3 keV ion beam and cw lasers both coaxial and crossed with the ion beam, polarized, respectively, perpendicular and parallel to the ion beam direction. Measurements were made at 14 wavelengths between 4579 and 7993 Å. Transitions to the dissociative states 2Πg and 2Σ+g are observed, as are the effects of the spin–orbit interaction in Ar+2. The experimental results are used along with theoretical calculations to determine the 2Σ+u, 2Σ+g, and 2Πg potentials. The effects of the spin–orbit interaction on the potential curves, the magnitude and wavelength dependence of the photodissociation cross section, and the angular distributions of the photofragments are considered.
Condensaton of a supersaturated vapor. IV. The homogeneous nucleation of binary mixtures
Authors: Mirabel P. , Katz Joseph L.
Published: February 2003

The upward thermal diffusion cloud chamber was used to measure the supersaturations (i.e., activities) required for the homogeneous nucleation of two binary mixtures, o-xylene–m-xylene and ethanol–water. These measurements were compared to the predictions of the classical theory of homogeneous nucleation. Good agreement was found for o-xylene–m-xylene at all compositions and for alcohol rich mixtures of ethanol and water. However, at high water concentrations, much more alcohol was required than is predicted by theory. The lack of equilibrium surface enrichment of the nuclei was postulated as the reason.
Infrared absorption and the Born–Oppenheimer approximation. II. Vibrational circular dichroism
Authors: Walnut Thomas H. , Nafie Laurence A.
Published: February 2003

A general set of equations is derived for VCD intensities. In order to overcome a vanishing electronic contribution to the rotational strength in the Born–Oppenheimer approximation, these equations include correction terms which provide the necessary correlation of the velocities of the electrons and the nuclei. The summation over all the excited electronic states of the molecule, normally encountered in such correction terms, is formally removed by the introduction of a vibronic gauge function which satisfies a known differential equation. As a special case, this equation is solved for a molecule having an electronic wavefunction comprised of a product of molecular orbitals which are Gaussian and ellipsoidal in form. The resulting VCD expressions for fundamental transitions are identical to those previously derived in the localized molecular orbital model of VCD intensities.
Geometries and energies of the excited states of O3 from a
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Authors: Hay P. Jeffrey , Dunning Thom. H.
Published: February 2003

The geometries and relative energies of the nine lowest states of the ozone molecule have been determined in C2v symmetry from ab initio configuration interaction calculations in a [3s2p1d] contracted Gaussian basis. Calculations were carried out over a two-dimensional grid of points in C2v symmetry to locate the optimum geometrical parameters R and ϑ for each state. For the ground 1A1 state the calculated properties (with experimental values in parentheses) are as follows: Re=1.299 Å (1.271 Å), ϑe=116.0° (116.8°), ω1=1235 cm−1 (1110 cm−1) and ω2=707 cm−1 (705 cm−1). Of the excited states only the lowest 3B2 state is found to have an adiabatic excitation energy (0.92 eV) less than the dissociation energy (De=1.13 eV) and hence to be a likely bound species. The 1B2 state responsible for the strong absorption in the Hartley band (4.7–5.8 eV) is stabilized by asymmetric distortions away from its equilibrium C2v geometry (Re=1.405 Å, ϑe=108°) suggesting unequal bond lengths for this state or else purely dissociative behavior. The ring (21A1) state (Re=1.449 Å, ϑe=60°) is found to lie 1.20 eV above the ground state, while the remaining five states have adiabatic excitation energies ranging from 1.4 to 3.6 eV. The implications for photodissociation of O3 are discussed.
Long-range interactions of ions with atoms having partially filled p subshells
Authors: Gentry W. Ronald , Giese Clayton F.
Published: February 2003

We derive analytic Born–Oppenheimer potential energy functions, including the charge–quadrupole and charge–induced dipole contributions, for the long-range interaction of a positive or negative ion with an atom having a partially filled p subshell. The charge–quadrupole term vanishes at large separations for the 2P1/2 states of p1 and p5, the 3P0 state of p2 and p4, and all states of p3. For 2P and 3P states the potentials at very large separations are characterized by MJ and at smaller separations by ML. The switchover is controlled by the ratio of the spin–orbit energy to the total anisotropy of the interaction potential. Plots of the positive and negative ion interactions with C(3P), O(3P), and F(2P) are presented as illustrations.
Dissociative electron attachment in nitrogen trifluoride
Authors: Sides G. D. , Tiernan T. O.
Published: February 2003

The rate constant for the dissociative attachment of thermal elections (300−350 °K) to nitrogen trifluoride has been measured using a flowing afterglow technique. (AIP)
The structure of a hard-sphere fluid in contact with a soft repulsive wall
Authors: Abraham Farid F. , Singh Y.
Published: February 2003

We present a theory for the structure of a hard-sphere fluid in contact with a soft repulsive wall and show that it agrees very well with Monte Carlo simulations.
Some new electronic states of matrix-isolated diatomic bismuth
Authors: Teichman Richard A. , Nixon Eugene R.
Published: February 2003

Absorption spectra of the diatomic bismuth molecule in argon matrices reveal three hitherto unreported electronic states with band system origins at 12 395, about 15 246, and about 17 736 cm−1. The ωe values for the three states are, respectively, 123, 132, and 145 cm−1. Laser excitations from the red into the ultraviolet produce only a single emission band system for Bi2 in argon or krypton; in argon the emission system origin is at 12 395 cm−1. The ground state ωe value is 151 cm−1, 13% smaller than for the gaseous molecule.
Rate constants for the reaction of O(3P) atoms with CH2–CHF, CH2–CHCl, and CH2–CHBr over the temperature range 298–442 °K
Authors: Atkinson R. , Pitts J. N.
Published: February 2003

Absolute rate constants for the reaction of O(3P) atoms with CH2=CHF, CH2=CHCl and CH2=CHBr have been determined over the temperature range 298–442 °K using a flash photolysis–NO2 chemiluminescence technique. The Arrhenius expressions obtained were k2(CH2=CHF) =8.03×10−12 e−(2025±200)RT cm3 molecule−1 sec−1, k2(CH2=CHCl) =5.58×10−12 e−(1325±200)/RT cm3 molecule−1 sec−1, k2(CH2=CHBr) =9.34×10−12 e−(1660±200)/RT cm3 molecule−1 sec−1, with room temperature rate constants of (2.64±0.27) ×10−13 cm3 molecule−1 sec−1; (5.98±0.60) ×10−13 cm3 molecule−1 sec−1 and (5.65±0.57) ×10−13 cm3 molecule−1 sec−1 for CH2=CHF, CH2=CHCl, and CH2 =CHBr, respectively.
Microscopic boundary layer effects and rough sphere rotation
Authors: Hynes James T. , Kapral Raymond , Weinberg Michael
Published: February 2003

A calculation of the rough sphere angular velocity correlation function is presented which takes into account the presence of both the microscopic boundary layer and outer hydrodynamic regions around the test particle. The boundary layer region is approximately accounted for by the slip boundary condition while generalized hydrodynamic equations (frequency dependent transport coefficients plus fluid spin variables) are used to describe the outer region. The approximate calculation of the slip coefficient and the use of the slip coefficient to account for processes occurring in the boundary layer are discussed in the context of kinetic theory results. Since a description of both regions is incorporated, the present theory contains both microscopic and collective effects. The structure of the result is compared in some detail to a recent renormalized kinetic theory calculation on the same system and various levels of approximation are examined. The results are in good agreement with the molecular dynamics calculations.
Vibron and lattice frequency shifts in the Raman spectra of solid α-N2 and γ-N2 and librational force constants of diatomic molecular crystals
Authors: Thiéry M. M. , Chandrasekharan V.
Published: February 2003

The observed pressure dependence of shifts and splittings of the Raman active vibrational modes in α-N2 and γ-N2 has been successfully reproduced in a calculation using the recent vibron model of Zumofen and Dressler. Different forms of dispersive and repulsive interactions as well as the variations of the potential parameters with bond length are discussed. At the phase transition, the observed drop in the frequency is correctly predicted by softer multiparametric exponential repulsive potential of Raich and Gillis. The observed negative D shift at 1 bar resulting mainly from the large isotropic dispersive interaction indicates that crystal forces acting on the molecule are stretching and not compressive as deduced from most intermolecular potentials. The origin of the large contribution to the librational force constants by these forces is examined and is related to the proper functional dependence of the potential parameters with bond length, generally neglected in lattice dynamic calculations. The observed Grüneisen parameters of librational modes demonstrate the necessity of including quadrupole interactions.
The elastic constants of nematic liquid crystalline terminally substituted azoxybenzenes
Authors: de Jeu W. H. , Claassen W. A. P.
Published: February 2003

The elastic constants K11, K22, and K33 of some members of two homologous series of nematic liquid crystals, the p,p′-di-n-alkyl and p,p′-di-n-alkoxy azoxybenzenes, are reported. Both K11 and K33 become greater with increasing alkyl chain length, while the ratio K33/K11 decreases along the series. For small alkyl chain length we find K33≳K11, for long chain length K33<K11, while for intermediate chain length K33?K11. In all cases K22 is the smallest of the three elastic constants, while K22/K11 is independent of temperature. The variation of K33/K11 with alkyl chain length can qualitatively be attributed to changes of correlation lengths parallel and perpendicular to the director. If the nematic distortion free energy is restricted to terms of the order S2, where S is the order parameter, theory predicts K33=K11. The experiments indicate that this equality holds approximately in some special cases, but in general higher order terms in S must be included to obtain a correct expression for the nematic distortion free energy.
Simulation of polymers by self-avoiding, nonintersecting random chains at various concentrations
Authors: Wall Frederick T. , Seitz William A.
Published: February 2003

Monte Carlo calculations have been carried out on systems of multiple excluded-volume chains for different concentrations on various two- and three-dimensional lattices. For eight-link chains the mean square end-to-end separation and other dimensional parameters have been computed for concentrations up to 95% of bulk. The effect of intermolecular volume exclusion is to decrease the average chain dimensions markedly as the concentration is increased. The limiting values of the shape parameters for bulk polymer appear to correspond to the values for eight-step random walks without step reversals (second order walks). Calculations for 20-link chains on the triangular lattice also approach the second order limit. The radial distribution function projected onto the x axis for eight-link walks on the square planar lattice is given for 95% concentration and is compared to the distributions for single chain second order and self-avoiding walks. A theoretical explanation is offered to account for the approach of the average dimensions of the bulk polymer to the corresponding second order walk values.
New numerical methods applied to solving the one-dimensional eigenvalue problem
Authors: Johnson B. R.
Published: February 2003

Two new numerical methods, the log derivative and the renormalized Numerov, are developed and applied to the calculation of bound-state solutions of the one-dimensional Schroedinger equation. They are efficient and stable; no convergence difficulties are encountered with double minimum potentials. A useful interpolation formula for calculating eigenfunctions at nongrid points is also derived. Results of example calculations are presented and discussed.
The laboratory microwave spectrum of the cyanide radical in its X 2Σ+ ground state
Authors: Dixon Thomas A. , Woods R. Claude
Published: February 2003

The microwave absorption spectrum of the CN molecule in the v=0 and v=1 vibrational states of the electronic ground state has been obtained in glow discharges in nitrogen–cyanogen mixtures at room temperature. Zeeman modulation is used for detection of the signal, and the microwave source is phase locked and digitally programmed by a computer. For each vibrational state the frequencies of the seven strongest hyperfine components of the N=0→1 rotational transition have been extracted from a careful regression analysis of the complex line shapes observed in the digitized spectral data. For the v=0 state the resulting rest frequencies and molecular parameters are in good agreement with, but more precise and accurate than, the values obtained from earlier radioastronomical studies. For the excited vibrational state the present work provides the first determination of the hyperfine parameters. The precision of the results for both states is sufficient to give a reliable measure of the variation of the spin–rotation constant (γ) and the hyperfine constants (b, c, and eQq) with vibrational quantum number.
Temperature dependence of the rate constant for the reaction between carbon monosulfide and atomic oxygen
Authors: Lilenfeld H. V. , Richardson R. J.
Published: February 2003

The rate of the reaction CS+O→CO+S was investigated from 150 to 300 K using a flow-tube technique. The rate was determined both by monitoring the CO formation rate in the presence of excess CS and by measuring the CS reaction rate in the presence of excess O. The reaction S+O2→SO+O could interfere with the first method when CS and O react in the presence of O2. Experimental evidence indicates, however, that the effect of the O2 reaction is not important at room temperature because of a fast chain-terminating reaction for S. The data from both methods fit an Arrhenius form with an activation energy of 6.3±1.2 kJ/mole and a pre-exponential factor of 2.6±0.4×10−10 cm3/molecule s, where the errors quoted are for the 95% confidence level.
Evidence for naive T-cell repopulation despite thymus irradiation after autologous transplantation in adults with multiple myeloma: role of ex vivo CD34+ selection and age
Authors: Malphettes Marion , Carcelain Guislaine , Saint-Mezard Pierre , Leblond Véronique , Altes Hester Korthals , Marolleau Jean-Pierre , Debré Patrice , Brouet Jean-Claude , Fermand Jean-Paul , Autran Brigitte
Published: February 2003

Immunodeficiency following autologous CD34+-purified peripheral blood stem cell (PBSC) transplantation could be related to T-cell depletion of the graft or impaired T-cell reconstitution due to thymus irradiation. Aiming to assess the role of irradiated thymus in T-cell repopulation, we studied 32 adults with multiple myeloma, randomly assigned to receive high-dose therapy including total body irradiation (TBI) followed by autologous transplantation with either unselected or CD34+-selected PBSCs. The median number of reinfused CD3+ cells was lower in the selected group (0.03 versus 14 × 106/kg; P = .002). Lymphocyte subset counts were evaluated from month 3 to 24 after grafting. Naive CD4+ T cells were characterized both by phenotype and by quantification of T-cell receptor rearrangement excision circles (TRECs). The reconstitution of CD3+ and CD4+ T cells was significantly delayed in the CD34+-selected group, but eventually led to counts similar to those found in the unselected group after month 12. Mechanism of reconstitution differed, however, between both groups. Indeed, a marked increase in the naive CD62L+CD45RA+CD4+subset was observed in the selected group, but not in the unselected group in which half of the CD45RA+CD4+ T cells appear to be CD62L−. Age was identified as an independent adverse factor for CD4+ and CD62L+CD45RA+CD4+ T-cell reconstitution. Our results provide evidence that infusing PBSCs depleted of T cells after TBI in adults delays T-cell reconstitution but accelerates thymic regeneration.
tert‐Butylphosphonic Acid: From the Bulk to the Gas Phase
Authors: Mehring Michael , Schürmann Markus , Ludwig Ralf
Published: February 2003

The structure of tert‐butylphosphonic acid in the solid, in solution, and in the gas phase was studied by single‐crystal X‐ray diffraction, 1H and 31P NMR spectroscopic studies in solution, solid‐state 31P NMR spectroscopy, and electrospray ionization mass spectrometry. In addition, density functional theory (DFT) calculations at the B3LYP/6‐31G*, B3LYP/6‐31+G*, and B3LYP/6‐311+G* level of theory for a large number of H‐bonded aggregates of the type (tBuPO3H2)n (Cn, Pn; n=1–7) support the experimental work. Crystallization of tBuPO3H2 from polar solvents such as CH3CN or THF gives the H‐bonded one‐dimensional polymer 2, whereas crystallization from the less polar solvent CDCl3 favors the formation of the H‐bonded cluster (tBuPO3H2)6⋅CDCl3 (1). In CDCl3 the hexamer (tBuPO3H2)6 (C6) is replaced by smaller aggregates down to the monomer with decreasing concentration. DFT calculations and natural bond orbital (NBO) analyses for the clusters C1–C7 and the linear arrays P1–P7 reveal the hexamer C6 to be the energetically favored structure resulting from cooperative strengthening of the hydrogen bonds in the H‐bonded framework. However, the average hydrogen bond strengths calculated for C6 and P2 do not differ significantly (42–43 kJ mol−1). The average distances rO⋅⋅⋅O, rOH, rPO, and rPOH in C1–C7 and P1–P7 are closely related to the hydrogen bond strength. Electrospray ionization mass spectrometry shows the presence of different anionic species of the type [(tBuPO3H2)n‐H]− (A1–A7, n=1–7) depending on the instrumental conditions. DFT calculations at the B3LYP/6‐31G* level of theory were carried out for A1–A6. We suggest the dimer [(tBuPO3H2)2‐H]− (A2) and the trimer [(tBuPO3H2)3‐H]− (A3) are the energetically favored anionic structures. A hydrogen bond energy of approximately 83 kJ mol−1 was calculated for A2. Electrospray ionization mass spectrometry is not suitable to study the assembling process of neutral H‐bonded tert‐butylphosphonic acid since the removal of a proton from the neutral aggregates has a large influence on the hydrogen bond strength and the cluster structure.
Ionische Flüssigkeiten: Innovative Lösungsmittel für die Zweiphasenkatalyse
Authors: Wasserscheid Peter
Published: February 2003

Ionische Flüssigkeiten sind bei niedrigen Temperaturen schmelzende Salze, die eine neuartige Klasse von Lösungsmitteln mit nichtmolekularem, ionischem Charakter darstellen. Durch unterschiedliche Kation/Anion‐Kombinationen können Flüssigkeiten mit sehr unterschiedlichen physikalischen und chemischen Eigenschaften erhalten werden. Durch eine gezielte Auswahl kann das ionische Medium auf die geplante Anwendung hin optimiert werden. Ionische Flüssigkeiten sind als alternative Lösungsmittel für katalytische Reaktionen aus vielen Gründen interessant: Ihre nichtflüchtige Natur bietet verfahrenstechnische Vorteile und ihre außergewöhnlichen Löslichkeitseigenschaften erlauben neue Anwendungen der Zweiphasenkatalyse.