bluuebunny/crossref_metadata_2025 huggingface dataset:
A new method for the molecular dynamics simulation of hard core molecules
Authors: McNeil William J. , Madden William G.
Published: February 2003

A new method for the dynamical simulation of a hard core fluid is introduced. The method differs from the traditional Alder–Wainwright algorithm in that the effects of collisions are obtained in response to observed core overlaps. The method is in principle more approximate than that of Alder and Wainwright, but extensive tests on a system of 72 hard disks do not show any measurable inaccuracy in the equation of state, the pair correlation function or the velocity autocorrelation function in this system. The principle advantage of the new method is that it is readily extended to potentials with a hard core and an attractive tail. Preliminary calculations on several fluids with a hard core and an attractive tail suggest that some dynamical properties may be unexpectedly sensitive to the detailed form of the attractive part of the intermolecular potential.
The analysis of the surface reactions of ammonia synthesis on iron using infrared spectroscopy. I
Authors: Nakata Toshiko
Published: February 2003

Absorption intensities in IR spectra of molecules adsorbed on a catalyst surface were measured quantitatively at elevated sample temperatures to elucidate the catalytic reaction. Spectra of NH2 and NH, which were formed on the iron surface after its contact with NH3, were measured at 20, 100, 150, 200, 250, and 300 °C in the 3000 cm−1 region with a metal sample dispersed in silica. It is known by our previous work that NH2 gives absorption at 3380 and 3290 cm−1 and NH at 3200 cm−1. The surface concentrations of these determined from their band intensities were plotted against the temperature; NH2 shows a monotonic decrease, while the NH curve, lying well below that for NH2, has a maximum around 150 °C. These changes with temperature were found reversible in the region 100∼200 °C, indicating that the reaction NH2⇄NH+H was in equilibrium. By utilizing this, the heat of reaction of this surface reaction was determined. The necessary relation between the heat and the concentration changes was derived using a simple model for adsorption of species, and the experiment consistent with it was repeated, 2.8±0.2 kcal/mol being obtained. This value is reviewed in connection with other facts. The gas phase above the sample was also observed, ammonia and hydrogen being found in equilibrium with the surface in the range 100∼250 °C.
The flexibility of polyelectrolyte molecules
Authors: Fixman Marshall
Published: February 2003

The electrostatic contribution to the persistence length of polyelectrolytes is calculated on the basis of the worm model and the Poisson–Boltzmann equation. An orthogonal but curvilinear coordinate system appropriate to a curved cylinder is defined, and the Poisson–Boltzmann equation and the electrostatic potential are expanded in inverse powers of the radius of curvature R. The coefficient of R−2 in the charging free energy gives the persistence length. Results are compared with Debye–Hückel calculations, condensation modifications, and the recent calculations on a toroid by Le Bret.
Dielectric constant in fluids of classical deformable molecules
Authors: Ramshaw John D.
Published: February 2003

Classical statistical mechanical description of dielectric fluids is further discussed. Dipole moment correlations of polarizable molecules are discussed.(AIP)
Single vibronic emissions from NO B 2Π (v′ = 7) and O2 B 3Σ−u (v′ = 4) excited by 193 nm ArF laser
Authors: Shibuya Kazuhiko , Stuhl F.
Published: February 2003

Single vibronic emssions of NO B 2Π(v′ = 7)→X 2Π(v\) and of O2 B 3Σ−u (v′ = 4)→X 3Σ−g(v\) are generated following irradiation of NO and O2, respectively, by a 193 nm ArF laser. Both emission processes compete with predissociation of the excited states. The aborption of the laser radiation will be discussed in detail. (AIP)
An investigation of the conformational equilibrium of n-butane in a solvent using Raman spectroscopy
Authors: Rosenthal Lois , Rabolt John F. , Hummel John
Published: February 2003

The trans-gauche energy difference for n-butane dissolved in CH2Cl2 and in CCl4 has been measured by the method of Raman band intensities. In methylene chloride, ΔE was observed to be 537±70 cal/mol, a value indistinguishable from that reported for pure liquid butane. A slightly lower value 438±80 cal/mol was observed for the CCl4 solution.
Reactive cross sections for isotopic variants of the H′+H′′Br abstraction reaction: A classical trajectory study
Authors: Mayne H. R. , Polanyi J. C.
Published: February 2003

Differing dynamics for isotopically related reactions (H′+H\Br→H′H\+Br, with H′ = H, D and H\ = H, D in the present work) must be explicable in terms of different patterns of motion under the influence of the same forces; i.e., kinematic effects. We have identified two prominent kinematic effects in the family of reactions under study. Both effects rendered D+HBr [symbolized (D, H)] and H+DBr (H, D) the extreme mass combinations, but the effects were opposite in sign. The alignment effect increased the reactive cross section for (D, H) compared with (H, D), since the former mass combination had longer in which to align (slower approach) and aligned more rapidly (faster molecular rotation). The rebound effect, by contrast, reduced the reactive cross section for (D, H) relative to (H, D), since in the former case the light central atom tended to rebound to re-form reagents. Either the alignment or the rebound effect could be made to dominate, depending on the choice of potential-energy surface; an increased bending force constant favored the former effect, and an earlier barrier the latter.
The formation of the vinylidene radical as an intermediate in the combination of triplet methylene
Authors: Laufer Allan H.
Published: February 2003

The vinylidene radical (H2C = C) is proposed as an intermediate in the combination reaction of triplet methylene. The conclusion is based upon the distribution of isotopic acetylenes produced from a 1:1 mixture of CD2 and CH2. The path of the reaction and the energetics of the intermediate species are discussed.
An energy-adjusted sudden approximation for inelastic scattering
Authors: Cross R. J.
Published: February 2003

A simple procedure is developed to correct the infinite-order sudden (IOS) approximation for the finite energy separation between states. A phase-shift matrix 〈i‖Δη‖j〉 is computed using the IOS and multiplied by an energy correction factor Bij and then exponentiated to give the S matrix. The correction factor is obtained by calculating an approximate phase-shift matrix for a finite energy separation and dividing this by the approximate form with no energy separation. A simple procedure is given for choosing the energy at which the IOS phase shifts are calculated. Results for He+H2 and Ar+N2 show good agreement with accurate calculations and a substantial improvement over the IOS.
Capillary waves and the inherent density profile for the liquid–vapor interface
Authors: Stillinger Frank H.
Published: February 2003

The statistical mechanical theory of the density distribution through the liquid–vapor interface has been re-examined for single-component monatomic substances. Particles are covered by spheres with radii such that uncovered volume is globally connected throughout the vapor but disconnected throughout the liquid. This approach in turn allows: (1) identification of an ’’outermost layer’’ of particles on the liquid, (2) definition of capillary wave collective coordinates for the surface, and (3) recognition of an ’’inherent density profile’’ for the interface that for T<Tc retains finite width even as the gravitational field strength vanishes. This latter profile is free of any arbitary parameters (such as capillary wave cutoffs), is a nonmonotonic function of normal distance through the interface, and is expected to reflect the diverging bulk-phase correlation lengths as T→Tc.
A calorimetric-equilibrium study of dilute solutions of hydrogen and deuterium in palladium at 555 to 909 K
Authors: Kleppa O. J. , Phutela R. C.
Published: February 2003

The thermodynamic properties of dilute solutions of hydrogen and deuterium in palladium have been studied by a calorimetric-equilibrium method in the temperature range 555–909 K. The new enthalpy data are compared with data for lower temperatures reported in the literature, and are used to obtain analytical expressions for the relative partial enthalpies and heat capacities of hydrogen and deuterium. The derived partial heat capacities are larger than values calculated from the harmonic oscillator model and show distinct maxima in the temperature range 500–600 K. It is possible that this may reflect a localized-mobile transition of the hydrogen atoms.
Numerical comparison of approximate formulas for atomic total energies. Ionization energy test
Authors: Castro Eduardo A. , Fernández Francisco M.
Published: February 2003

A numerical comparison is made of different approximate formulas for total electronic energy. Atomic ionization energies are calculated and results are compared with available experimental data. Similar average deviations are found.
Algebraic proof of the noncrossing rule for the energy levels of the asymmetrical rigid rotator
Authors: Caride A. O. , Zanette S. I.
Published: February 2003

In this note we show that the energy levels of the asymmetrical rigid rotator for an arbitrary fixed value of J do not intersect each other when the eigenvalues of the inertia tensor are allowed to vary continuously between the extreme values characterizing oblate and prolate symmetric tops. (AIP)
Measurement of the molecule–silver separation dependence of surface enhanced Raman scattering in multilayered structures
Authors: Murray C. A. , Allara D. L.
Published: February 2003

We report details and results of experiments in which surface enhanced Raman scattering from molecules is studied as a function of their spacing from a rough silver enhancing layer. Two types of experiments were performed. In the first, an organic monolayer chemisorbed on aluminum oxide is covered with a smooth low Raman cross section polymer spacer layer and rough silver is placed on top of the spacer. The Raman scattering from the monolayer is studied as a function of the spacer layer thickness. As a result of our diffusion and tunneling experiments, we conclude that direct contact of the molecules with scattering from the molecules. We observe an enhancement of roughly 106 for no polymer spacer thickness, and a fall-off of the enhancement by a factor of 10 with each subsequent 35–50 Å spacer thickness. We also observe a similar drop off of the broadband background under the Raman scattering. In the second type of experiment, the Raman scattering from a high Raman cross section polymer is studied as a function of its thickness in similar multilayered structures. The results of these variable thickness experiments are consistent with those of the spacer experiments. We conclude that in our samples, the major cause of surface enhanced Raman scattering is electromagnetic in nature.
The theory of the Fe2+–Fe3+ electron exchange in water
Authors: Tembe Bhalachandra L. , Friedman Harold L. , Newton Marshall D.
Published: February 2003

The rate constant for the Fe2+–Fe3+ electron exchange is formulated as k23= ∫ 0∞g23(r) k̂23(r) 4πr2 dr, a form which also is used to analyze the data for the nuclear spin relaxation in Al3+ induced by collision with Ni2+. It is assumed that the equilibrium pair correlation function g23(r) is the same function of ionic composition and temperature in the two cases and that in the spin relaxation process the local rate constant k̂23(r) has the form that may be deduced from the Solomon–Bloembergen equations. In the case of the exchange reaction the theory of k̂23(r) is developed with respect to the contributions from slow inner shell or outer shell reorganization (activation) dynamics. It is concluded that in the present case these complications are not important and that the controlling dynamics is the crossing from the reactant to the product diabatic Born– Oppenheimer surface. Neither the exchange nor the spin relaxation data can be accounted for if the smallest metal–metal distance in collisions is that given by the closest approach of the envelopes of the M(H2O)6n+ complexes. However, allowing for overlap of the envelopes as one complex pokes into the interstices of the other reduces the distance of closest approach from 6.9 to 4.5 Å. Then one can find Gurney type models for the ion–ion forces in solution such that the model calculations are in good agreement with the experimental exchange and relaxation rate constants and their dependence on temperature and ionic strength, as far as the limited data for the last allow.
Thermodynamic model for tricritical mixtures with application to ammonium sulfate + water + ethanol + benzene
Authors: Kaufman Miron , Griffiths Robert B.
Published: February 2003

Procedures are developed for using composition data in the three-phase region and variations of meniscus heights to determine the parameters needed to relate a classical thermodynamic model for fluid mixtures near tricritical points to actual experiments. In the case of the mixture ammonium sulfate + water + ethanol + benzene, the result is a reasonably good fit to a variety of data, including light scattering measurements of intensity and correlation length. There is some evidence for deviations from the classical theory, but it is not unambiguous.
Dynamic properties of malonic acid in solution from spin relaxation of a 13C labeled methylene group
Authors: Fuson M. M. , Prestegard J. H.
Published: February 2003

The motional properties of malonic acid in dimethylsulfoxide solution have been studied using NMR spin relaxation methods. In particular, the spin coupled 13C resonance of the central methylene of the malonic acid molecule is observed using nonselective pulse techniques. Analysis of recovery curves, which includes consideration of both autocorrelation and cross-correlation spectral densities, allows extraction of the three principle diffusion tensor elements as well as determination of random field contributions arising from intermolecular interactions. We find that the diffusion of malonic acid can be described with an axially symmetric diffusion tensor D⊥ = 2.0×109 s−1 and D∥ = 1.9×1010 s−1. This result is intermediate between the predictions of stick and slip boundary conditions. Experiments conducted in deuterated solvents allow evaluation of the diffusion tensors with minimal interference from intermolecular effects. Use of protonated solvents introduces substantial intermolecular effects. However, these effects can be separated and an essentially identical diffusion tensor measured by concentration of experimental measurements in the early time protions of the relaxation time course. The fact that only a single nucleus is observed in these experiments and the fact that only nonselective pulses are required make these techniques particularly useful in extension to more complex systems.
Electrodynamics at metal surfaces. IV. The electric fields caused by the polarization of a metal surface by an oscillating dipole
Authors: Korzeniewski Gregory E. , Maniv Tsofar , Metiu Horia
Published: February 2003

We compute the electromagnetic field generated by an oscillating dipole located near a metal surface. The dielectric response of the metal is obtained by using the random phase approximation for a jellium model with a surface represented by an infinite barrier. The model includes the role of spatial dispersion (nonlocal response) and of the fact that the dielectric response varies continuously across the interface. These two effects remove the divergence given by the phenomenological electrodynamics (image formula).
Intramolecular vibrational relaxation in hexyl-3 radicals
Authors: Trenwith A. B. , Rabinovitch B. S. , Wolters F. C.
Published: February 2003

Chemically activated hexyl-3 radicals, excited to 43 kcal mole−1, that decomposes to pentene-1(P-11) and butene-1(B-1) are studied. (AIP)
Franck–Condon amplitude for two-photon processes within a displaced harmonic model
Authors: Omae Takayuki , Deguchi Kisaburo
Published: February 2003

An alternate expression of Franck-Condon amplitude is derived which does not contain the infinite summation over the vibrational states given below: Imn = 𝒥∞v = 0(<χgm‖χev≳ <χev‖χgn≳)/(ωr+Egn− Eev). The new Imn is given below: Imn = (Nm/2π) (Nn/2π) ℱ2π0 dϑdϑ′ eimϑeimϑe−inϑ′  e−sA𝒥∞v (av/v!) (b−cv)−1. (AIP)
Comment on ‘‘EPR studies of VO2+ in single crystals of Zn SO4⋅7H2O and certain polycrystalline sulfates’’
Authors: Jain Akhilesh Kumar
Published: February 2003

The author obtained single crystals of ZnSO4⋅7H2O doped woth VO2+ by evaporation at ∼300K and analyses the EPR spectra.(AIP)
Collision induced dissociation of CsI and Cs2I2 to ion pairs by Kr, Xe, and SF6
Authors: Parks E. K. , Inoue M. , Wexler S.
Published: February 2003

Absolute cross sections as functions of collision energy have been determined for collision induced dissociation of cesium iodide monomer and dimer to ion pairs. In these studies a beam of accelerated Xe, Kr, or SF6 projectiles was crossed with a thermal beam of cesium iodide. The partial cross sections for each product-ion channel were determined by time-of-flight mass spectrometry. For the rare gas-monomer collisions, the dependence of each partial cross section on the internal temperature of the CsI was also obtained. Collisions of Xe with CsI produced three-body dissociation as well as the formation of the molecular ions CsXe+ and IXe−. The formation of both the positive and negative molecular ions is primarily a reflection of the similar masses of Cs+ and I−, and was not observed in previously studied systems. For the same reason, Cs2I+ and CsI−2 resulting from collisions of Xe with Cs2I2 were formed with comparable intensities. At energies well above threshold, the total dissociation cross section for the rare gases colliding with CsI or Cs2I2 is large (≳10 Å2). Those for SF6 are approximately a factor of 5 smaller for the monomer, but only slightly smaller for the dimer. No ions containing SF6 were observed. The cross sections for three-body dissociation as well as molecular ion formation are relatively small in the region of the thermodynamic threshold (decreasing in the series Xe, Kr, and Ar). Analysis of the experimental results indicates that dissociation in this region only occurs for CsI molecules having considerable internal excitation, an effect related almost entirely to the projectile-target relative masses. A model which takes into account the coupling of internal motion with relative translational motion is shown to give an excellent description of the dissociation in the threshold region. Collinear trajectory calculations of the rare gases colliding with CsI were also performed in order to determine the threshold for dissociation as a function of the vibrational state of CsI.
Raman study of polar phonons in piezoelectric trioxane crystal
Authors: Kobayashi Masamichi
Published: February 2003

Angular dependence of the Raman bands due to the polar phonons in piezoelectric trioxane crystal was measured at room temperature and at 40 K on single-crystal specimens. At room temperature, two A1 bands due to the (A1)8 (around 960 cm−1) and the (A1)10 (480 cm−1) modes exhibited remarkable angular dispersion giving the LO–TO frequency gaps of 17 and 9 cm−1, respectively. For four internal modes of the E species, E6 through E9, an appreciable amount of the LO–TO splitting, in the range from 4 to 20 cm−1, was detected. A remarkable polariton dispersion was also observed for the (A1)8 mode. These experimental facts indicated that contribution of the long-range electrostatic forces produced by the polar modes was significant even in such a molecular crystal.
On the luminescence of bismuth, cerium, and chromium and yttrium aluminium borate
Authors: Kellendonk F. , van den Belt T. , Blasse G.
Published: February 2003

The excitation and emission spectra of YAl3B4O12 doped with Ce3+ and Bi3+ are reported. The Bi3+ emission spectrum at 4.2 K consists of a zero-phonon line associated with equidistant phonon sidebands. This emission is assigned to the P03→S01 transition. The intensity of the zero-phonon line is due to the mixing of the P03 and P13 levels by the linear term of the crystal field. The energy difference between the 3P0 and 3P1 levels is obtained from the spectra and from the temperature dependence of the decay time. The Ce3+ emission band at 4.2 K is structureless. The energy transfer in Y1−xCexAl3B4O12 (0<x⩽0.3) and Y1−xBixAl3B4O12 (0<x⩽0.23) doped with Tb3+ or Cr3+ is investigated. We found that the concentration quenching at 300 K in the samples with Bi is much more pronounced than in the samples with Ce. Energy migration in the Bi3+ subsystem occurs via the P13 level. In all samples, the transfer to Tb3+ or Cr3+ is not efficient due to the fact that the transfer processes are ’’trapping limited.’’ Furthermore, the temperature dependent characteristics of the Cr3+ ion emission are studied. At 4.2 K a line emission is observed which can be assigned to the E2→A24 transition. At higher temperatures (T>150 K) a broad band emission appears. This emission originates from the thermally populated T24 level. Above ∼450 K the total Cr3+ ion emission intensity starts to quench via the T24 level.
Time evolution studies of triplet toluene by two-color photoionization
Authors: Dietz T. G. , Duncan M. A. , Smalley R. E.
Published: February 2003

Two-color photoionization has been applied to measurement of the time evolution of laser-excited 1B2(ππ*) vibronic levels of toluene. The observed photoionization signals exhibit a biexponential dependence upon the time delay between the pump and ionizing lasers. This photon intensity is shown to be proportional to the population of the excited singlet (S1) and triplet (T†) electronic states. The data is fit to a simple kinetic model which yields the rates of S1 fluorescent decay, S1→T†, and T†→S‡0 intersystem crossings. The measured quantum yield for intersystem crossing was found to agree with previous work. The triplet lifetimes measured are considerably shorter than values reported for collisionally relaxed triplets states due to the steep excess vibrational energy dependence of the nonradiative rate. This excess energy dependence of the triplet decay rate has been measured over a limited range of energy and the observed rates are found not to extrapolate smoothly to the decay rate measured for the vibrationless T1 level. This behavior is rationalized as a dilution of excitation in good accepting modes for the T→S‡0 transition due to increasing dominance of lower frequency, poor accepting modes in the triplet density of states.
Laser induced fluorescence of ions trapped in an ion cyclotron resonance cell: Excitation of CO+X 2Σ, v′′ = 0 and relaxation of CO+A 2Π, v′ = 1
Authors: Danon J. , Mauclaire G. , Govers T. R. , Marx R.
Published: February 2003

An experimental setup has been designed to study laser induced fluorescence of ions produced and trapped in an ICR cell. Fluorescence excited by a tunable dye laser and spontaneous emission may be observed. Production, trapping, excitation, and observation are pulsed and a time resolved signal processing is used in order to identify the different excited species and measure their lifetime. Excitation spectra of CO+A 2Π, v′ = 1←X 2Σ, v\ = 0 in pure CO and (Ar,CO) mixtures are presented. A radiative lifetime τR = 3.5 μs and collisional quenching rates kQ = 7.5×10−10 cm3 molecule−1 s−1 in CO and k′Q = 5.9×10−10 cm3 molecule−1 s−1 in Ar have been determined for the v′ = 1 level of the CO+A 2Π1/2 state.
Interpretation of the intermediate scattering function at short times
Authors: Ackerson B. J. , Pusey P. N. , Tough R. J. A.
Published: February 2003

By considering the intermediate scattering function for simple liquids and suspensions of colloidal particles, we discuss and refute the idea that the short-time collective behavior of such systems is dominated by ’’free-particle’’ motions.
Depolarized Rayleigh–Brillouin scattering from shear waves in supercooled liquid dibutyl phthalate
Authors: Lempert Walter , Wang C. H.
Published: February 2003

Experimental depolarized Rayleigh and Brillouin spectra of liquid and supercooled liquid dibutyl phthalate (M.P. = −35 °C) are reported over the temperature range from −116 to 70 °C. The depolarized spectra exhibit a propagating transverse wave at temperatures as high as −21.5 °C, while the Brillouin spectra exhibit a kink in the longitudinal frequency shift corresponding to the glass transition temperature at approximately −95 °C, and a maximum in the linewidth at approximately 7 °C. A single equation from the recent theory of Wang has been used to fit the experimental depolarized spectra over the entire temperature range and values of the translation rotation coupling constant δ, the orientation relaxation constant Γ, the shear wave relaxation constant η, and the elastic shear wave oscillation frequency Ω have been determined. The depolarized Rayleigh relaxation time τ is shown to obey Arrhenius type behavior with an activation energy of 6.5 kcal mol−1. η, δ, and Ω are shown to constitute an internally consistent set of parameters describing the behavior of the propagating shear wave in a viscoelastic fluid.
Chemical potential and total energy of heavy positive atomic ions in the weak ionization limit
Authors: March N. H.
Published: February 2003

The chemical potential μ (Z,N) of a heavy positive ion with nuclear charge Ze and N electrons is obtained from the Thomas–Fermi theory near the weak ionization limit specified by q = 1−(N/Z) small as           where c = 1/2 (731/2−7). The corresponding form of the total energy E(Z,N) is obtained in terms of the neutral atom energy E(Z,Z) as
A full coupled-cluster singles and doubles model: The inclusion of disconnected triples
Authors: Purvis George D. , Bartlett Rodney J.
Published: February 2003

The coupled-cluster singles and doubles model (CCSD) is derived algebraically, presenting the full set of equations for a general reference function explicitly in spin–orbital form. The computational implementation of the CCSD model, which involves cubic and quartic terms, is discussed and results are reported and compared with full CI calculations for H2O and BeH2. We demonstrate that the CCSD exponential ansatz sums higher-order correlation effects efficiently even for BeH2, near its transition state geometry where quasidegeneracy efforts are quite large, recovering 98% of the full CI correlation energy. For H2O, CCSD plus the fourth-order triple excitation correction agrees with the full CI energy to 0.5 kcal/mol. Comparisons with low-order models provide estimates of the effect of the higher-order terms T1T2, T21T2, T31, and T41 on the correlation energy.
Correlation and the 5F–3F energy separation in Ti
Authors: Fischer Charlotte Froese
Published: February 2003

Multiconfiguration Hartree–Fock studies of the 4s3d3 5F– 4s23d2 3F energy separation in titanium are reported. The f-orbital basis is shown to be important as well as the LS dependent relativistic effects.
Resolvent operator approach to many-body perturbation theory. I. Closed shells
Authors: Banerjee Ajit , Mukherjee Debashis , Simons Jack
Published: February 2003

In this paper, we develop a time-dependent approach to many-body perturbation theory for closed shells based on the resolvent of the Schrödinger equation. We introduce a quantity S(t) = i<φ‖exp [−i(H−E0)t]‖ψ≳/<φ‖ψ≳, where φ and ψ are, respectively, the unperturbed and exact wave functions for the system and E0 is the unperturbed energy. The Fourier transform of S(t), S(ω) = <φ‖(ω+E0− H)−1‖ψ≳/ <φ‖ψ≳, is a matrix element of the resolvent containing the exact function ψ and, thus, has a pole at ω = (E−E0), the correlation energy. Starting from a time-dependent perturbation expansion of S(t) via the Gellman–Low adiabatic theorem, we have obtained a Dyson-like equation: S−1(ω) = S−10(ω)+Σ<φ‖ψ≳ for S(ω). Such a derivation requires judicious grouping of terms of the perturbation series for S(t). It has been shown that specific regroupings of the terms of S(t) into appropriate ’’top’’ and ’’bottom’’ parts and corresponding time-integration procedures yield a Σ which generates the Brillouin–Wigner (BW) or Rayleigh–Schrödinger (RS) energy series. Σ for both the cases are identified as the ’’top’’ parts. The characteristic features of the BW series, namely, the appearance of disconnected and ω-dependent diagrams is to be contrasted with that of the RS series, which contains connected and ω-independent diagrams only, and both emerge naturally as a consequence of the dissection procedure into appropriate top and bottom parts.
Elastic moduli of a liquid–vapor interface
Authors: Baus Marc
Published: February 2003

The elastic moduli introduced by previous authors for a uniform fluid are generalized to the case of a two-phase system. For a planar liquid–vapor interface, we obtained five independent surface moduli, one of which is the surface tension. The presence of four additional moduli results from the fact that at every stage the surface phase is described as a thin layer and not, like in thermodynamics, as a two-dimensional phase.
Electronic excited-state transport and trapping in solution
Authors: Loring Roger F. , Andersen Hans C. , Fayer M. D.
Published: February 2003

A theoretical study of transport and trapping of electronic excitations in a two-component disordered system is carried out. The results are applicable to energy transport in solutions containing randomly distributed donor and trap solute species or lattices with randomly distributed donor and trap impurities. The diagrammatic expansion of the Green function, developed by Gochanour, Andersen, and Fayer to study excited-state energy transport in a one-component system is applied to the trapping problem. The following quantities are calculated from the Green function: the time-dependent probabilities that an excitation is in the donor or in the trap ensembles, the generalized diffusion coefficient, and the mean-squared displacement of an excitation. For Förster transfer, transport properties are shown to depend on the ratio of the Förster interaction lengths RDT0 and RDD0 as well as on the reduced concentrations of donors and traps [CD = 4/3π(RDD0)3ρD, CT = 4/3π (RDT0)3ρT]. The tranport of excitations is found to be nondiffusive. A comparison to other theoretical treatments is presented.
Measurements of relative concentrations and velocities of small clusters (n⩽40) in expanding water vapor flows
Authors: Dreyfuss David , Wachman Harold Y.
Published: February 2003

The concentrations of water clusters (2⩽n⩽40) relative to the monomer concentration in expanding water vapor flows have been determined over a range of source pressures and temperatures by mass spectrometry. The corresponding directed flow velocities and thermal velocity distributions of the monomers and clusters of each size have been determined by mass-filtered time-of-flight (velocity) spectrometry. Relative concentration generally decreases exponentially with n. Translational thermal equilibrium ∼65 K prevails for the monomers and clusters of n≲5 under all source conditions. Translational temperatures of larger clusters generally increase with increasing n. The results suggest a kinetic process in which surviving smaller clusters are formed in three-body collisions and larger ones in two-body collisions.
Intermediate level structure, quantum beats, and nuclear spin effects in the electronic relaxation of the 1B3u (nπ*) state of pyrazine
Authors: van der Meer Barend J. , Jonkman Harry Th. , ter Horst Gerard M. , Kommandeur Jan
Published: February 2003

The P(1) member of the rotational manifold of the 6a10 transition in the 1B3u (nπ) state of pyrazine shows intermediate level structure and quantum beats in its decay. The P(2) member already shows a fast component. The effect of nuclear spin on the relative magnitude of the fast component is shown by partial deuterium substitution.
Comment: On the calculation of low lying resonances in dipolar molecules
Authors: Segal Gerald A.
Published: February 2003

Comments are presented on Krauss and Stevens 1’s configuration interaction calculations of the electronic structure of HCl−. In particular, the discrepancies between Goldstein et al2’s calculations and those of Krauss ans Stevens1 are discussed. (AIP)
Optical activity of the f–f transitions in trigonal dihedral (D3) lanthanide(III) complexes. I. Theory
Authors: Richardson Frederick S. , Faulkner Thomas R.
Published: February 2003

The theory of natural optical activity in the 4f→4f transitions of trigonal dihedral (D3) lanthanide(III) complexes is developed within the framework of a crystal field model. Within this model, both the chiral and achiral components of the crystal field are represented in terms of multipole-point charge and multipole-induced dipole lanthanide–ligand interactions. Electric dipole intensity within the 4f→4f transitions is presumed to arise from interconfigurational mixing between the 4fN, 4fN−1 5d, and 4fN−1 ng configurational states localized on the lanthanide ion, and between the 4fN configurational states of the lanthanide ion and dipolar excitations localized in the ligand environment. Expressions are derived for electronic rotatory strengths, dipole strengths, and dissymmetry factors, and special attention is given to how these quantities are related to the electronic and stereochemical properties of the ligand environment and to the electronic structure of the lanthanide ion. A computational model based on the formal theory is proposed, and qualitative predictions regarding a variety of features to be found in 4f→4f chiroptical spectra are presented.
Vibronic-level dependence of radiative and nonradiative processes in naphthalene vapor
Authors: Ohta Nobuhiro , Baba Hiroaki
Published: February 2003

The vibronic-level dependence of radiative and nonradiative processes in naphthalene vapor has been investigated under collision-free conditions, with particular attention to the effect of molecular rotation and to the contamination caused by simultaneous excitation of levels other than the one under study. Fluorescence excitation spectra, lifetimes, and sensitized biacetyl–phosphorescence excitation spectra were measured by using a pulsed dye laser with a bandwidth of 0.5 cm−1. From the resulting data, the radiative and intersystem-crossing rate constants (kf and kisc,respectively), as well as the fluorescence and intersystem-crossing yields, were determined for 20 single vibronic levels of S1 up to an excess vibrational energy of about 2000 cm−1. The value of kf varies greatly with vibronic level. The levels involving the 8(b1g) vibrational mode have particularly large kf values, and those involving 8(ag), 6(ag), and 4(ag) modes moderately large ones. The observed variation of kf is explained in terms of the transition moment induced by vibronic interaction of S1 with the other singlet states. The value of kisc also varies with vibronic level. A sudden increase and pronounced fluctuation of the kisc value are found at an excess energy of about 1000 cm−1, suggesting the presence of a new crossing channel related presumably to T3. The fluorescence quantum yield measured along the rotational contour of the 8(b1g)01 absorption band shows a rather small variation; moreover, the lifetimes are nearly constant over the contour of the 8(b1g)10 band and of the 0–0 band. The observed variation of the fluorescence yield along the rotational contour is interpreted as due largely to excitation of sequence bands.
Stimulated modulations in triplet spin coherent transients
Authors: Bovy M. W. L. , Glasbeek M.
Published: February 2003

Modulations in coherent transients of photoexcited triplet electron spins in MgO are observed upon the application of a small magnetic field (H≲15G). The results are representative of a magnetic field stimulated dipolar interaction between triplet electron spins and fluctuating I = 5/2 nuclear spins of the 10% abundant 25Mg isotope. Using a memory-function approach, it is shown that the modulation in the spin–echo amplitude decay arises in the limit of ’’slow exchange’’ among hyperfine transitions.
Deuterium hyperfine structure measurements and theory for CD3Br
Authors: Kukolich S. G. , Cogley C. D.
Published: February 2003

Hyperfine structure on the J = 1→0, F1 = 3/2 transitions in CH3 79Br, CH3 81Br, and CD3 79Br was measured with one-cavity and two-cavity beam maser spectrometers. The resolution for the measurements was approximately 2 kHz and most hyperfine structure components were completely resolved. Deuterium quadrupole coupling eQqzz = 178.5±3 khz along the C–D bond and other parameters were obtained. In the theory section, formulas for the hyperfine interaction strengths with three equivalent spins are presented and reviewed. Deuterium quadrupole coupling in other C–D bond systems is discussed.
Optical properties of molecules chemisorbed on the Ni (111) surface
Authors: Robota H. J. , Whitmore P. M. , Harris C. B.
Published: February 2003

The adsorption of a series of molecules on Ni (111) is studied by UV visible spectroscopic ellipsometry. The spectra were analyzed within a simple dielectric model. Chemisorption of molecules on the Ni (111) surface produces a peak in the overlayer optical response at 4.2 eV. This absorption peak is attributed to the selective enhancement of bulk interband excitations resulting from perturbations of the metal orbitals upon chemisorption.
AsF5 intercalated graphite: Conductivity and the anisotropy of the skin depth via NMR spectroscopy
Authors: Resing H. A. , Moran M. J. , Miller Gerald Ray
Published: February 2003

Intercalation of AsF5 into highly oriented pyrolytic graphite (HOPG) produces a compound which is a highly anisotropic, two-dimensional electrical conductor. Despite the high conductivity in the graphite planes, an 19F NMR experiment can detect all of the fluorine in the sample when the c axis of the HOPG is oriented perpendicular to the rf magnetic field B1. It is not necessary to pulverize the sample. The signal intensity is reduced when the c axis is oriented parallel to B1, thereby enabling estimates to be made of the skin depth (∼12 μm) and the in-plane conductivity (∼2.7×105 Ω−1 cm−1).
Saturation of N2F4 by a short CO2 laser pulse
Authors: Lavigne P. , Lachambre J. L.
Published: February 2003

Saturation parameters and absorption characteristics of N2F4 at 10.6 μm is studied using an intense 1.5 ns pump pulse and a low cw CO2 laser probe. It is found that, for short-pulse interaction, a four-level model describe satisfactorily the experimental results at pressure up to 120 Torr. The main parameters of the model are a rotational–rotational exchange constant of 47 ns Torr, a fundamental radiative cross section of 1×10−16 cm2, a contribution of 1/60 of the ground state population to absorption and a residual absorption coefficient equal to 20% of the small signal absorption at low pressure.
A comprehensive light scattering study of a liquid composed of symmetric top molecules
Authors: Chappell Philip J. , Kivelson Daniel
Published: February 2003

We have studied the VH, HH, and VV quasielastic light scattering spectra of the near-symmetric top triphenylphosphite at several scattering angles and over a wide range of temperatures, such that (k 2η/ρmΓ) varied from 0.085 to 3600, where k is the scattering vector, η the shear viscosity, ρm the mass density, and Γ the ’’reorientation’’ frequency. The data have been analyzed in a consistent manner in terms of a generalized hydrodynamic theory in which, in addition to the observed dielectric fluctuations (ε̂) and the conserved hydrodynamic collective variables (n̂,p̂ê,), unspecified ’’slow’’ variables (F̂s, F̂t) are included, where, at k→0, F̂s is a symmetric and F̂a an antisymmetric second rank tensor. Since the theory interrelates the relaxation processes, giving rise to the scattering at different polarizations, the spectra provide enough information to evaluate the considerable number of adjustable temperature-dependent, but ω- and k-independent, transport coefficients involved in the analysis. Of particular interest is our conclusion that three-variable theories |ε̂xz, p̂z, F̂xz|, where F̂xz=F̂xzs, F̂xza or F̂xzs+F̂xza, are incapable of explaining the angular dependence of the VH spectra or of providing parameters which can also fit the central features of the HH spectra. In the successful application of the four-variable |ε̂xz, p̂z, , F̂xza| theory to VH scattering (and correspondingly more complex theories to HH and VV scattering), we focused attention on the transport coefficient C, where (Ck2η/ρm) is the autodecay frequency of the curl of the flow momentum. At high temperatures, in the hydrodynamic regime, we found C≈0, which enabled us to identify F̂xzs and F̂xza with the symmetric (σ̂xzs) and antisymmetric (σ̂xzss) components, respectively, of the stress tensor, i.e., with the flux of a conserved quantity. However, in the viscoelastic regime we found C≠0, small, and varying as η−1; in this case we were, therefore, not able to identify F̂xzs and F̂xza. A still more general theory, in which F̂xza was not necessarily an antisymmetric tensor, would introduce more adjustable parameters than required by our data. Our analysis made use of the independently determined values of η and, in accord with theoretical considerations, yielded values of the translational–rotational coupling parameter R with a relatively constant value 0.4<R<0.5 over the entire, very wide viscosity range.
A discrepancy between experimental and computational evidence for chemical chaos
Authors: Ganapathisubramanian N. , Noyes Richard M.
Published: February 2003

Hudson and Mankin studied the oscillatory Belousov–Zhabotinsky reaction in a flow reactor and found ranges of a few percent of residence time within which behavior was a chaotic mixture of the regular behaviors on either side of that range. Our efforts to model that system computationally indicate that any range of chaotic behavior is less than one part per million of residence time. The discrepancy may mean that the experiments were influenced by the peristaltic pumping or by uncontrolled fluctuations of some other variable. It may also mean that the computational model was too simplified to reproduce the chaotic effects inherent in the real system. The only resolution we can suggest is that random fluctuations in a parameter like residence time may induce chaotic behavior over a range of average residence times that is much wider than the amplitudes of the fluctuations themselves.
Bursting phenomena in a simplified Oregonator flow system model
Authors: Rinzel John , Troy William C.
Published: February 2003

We investigate a model for the Belousov–Zhabotinskii reaction in a continuous flow, stirred tank reactor. The model consists of a system of three ordinary differential equations derived from a more complicated five-dimensional model introduced by Janz, Vanecek, and Field [J. Chem. Phys. 73, 3132 (1980)]. It is basically a simplified, irreversible, batch reactor Oregonator with flow terms and with instantaneous dependence of the stoichiometric parameter f on the amount of brominated organic substance. Over a range of physical parameters (e.g., lower flow rates) the system exhibits ’’bursts’’ of oscillations. As in some experiments [e.g., Marek and Svobodova, Biophys. Chem. 3, 263 (1975)], the observer sees several spikes followed by an interval of quiescence (IQ) which is subsequently followed by a resumption of the spikes, etc. As Janz et al. found, bursting occurs as f sweeps slowly back and forth through values for which the batch reactor subsystem exhibits bistability and hysteresis. The CSTR solution alternates between the batch model’s stable periodic solution, during the oscillatory phase, and the batch model’s stable steady state of low oxidation, during the IQ. Analytically and numerically, we describe these subsystem solutions as functions of f; bistability arises as a subcritical Hopf bifurcation. Also, we estimate quantitatively features of the CSTR bursts, such as IQ duration, and their dependence on parameter values. For other parameter ranges we find qualitatively different bursting phenomena. In one example, the CSTR system is excitable; there is a stable steady state and the response to an adequate perturbation is an excitation burst of several pulses and then a return to the steady state. At considerably higher flow rates, there are repetitive, single-spike bursts with IQ’s of high oxidation; such patterns resemble those calculated by Showalter, Noyes, and Bar-Eli [J. Chem. Phys. 69, 2514 (1978)] and some responses observed experimentally by Schmitz, Graziani, and Hudson [J. Chem. Phys. 67, 3040 (1977)]
Reaction rate constants for O−2(H2O)n ions n = 0 to 4, with O3, NO, SO2, and CO2
Authors: Fahey D. W. , Böhringer H. , Fehsenfeld F. C. , Ferguson E. E.
Published: February 2003

Reaction rate constants for O−2(H2O)n ions with n = 0 to 4 have been measured in a variable temperature flowing afterglow apparatus with a novel ion source configuration. The ions have been reacted with O3,NO, SO2, and CO2. The reaction with O3 is charge-transfer to produce O−3 with simultaneous transfer of water ligands. The reactions with NO and SO2 are ligand switching reactions in which NO or SO2 displaces one or more water molecules clustered to O−2 leaving NO−3 and SO−4 as core ions. In these cases, the reaction rate constants are not decreased measurably by an increase in n. CO2 rapidly displaces H2O in reaction with O−2(H2O) but does not react with O−2(H2O)3,4. Isotopically labelled O−2 ions were used to elucidate several reaction mechanisms. The rapid destruction of O−2(H2O)4 ions by O3,NO, and SO2 insure that O−2(H2O)n ions cannot be dominant small air ions in the earth’s lower atmosphere.
Collisional dissociation of dimers by monomers in rare gases
Authors: Thompson Donald L.
Published: February 2003

Cross sections and thermal rate coefficients for single-collision dissociation in ground-state Rg2 by Rg (Rg = Ne,Ar,Kr, and Xe) were computed using Monte Carlo quasiclassical trajectories. The influence of vibrational and rotational excitation of the dissociation cross sections and rate coefficients was investigated for Ar+Ar2. The following conclusions are reached. At high collision energies the cross section for dissociation of ground-state dimers is given by πR2e (where Re is the equilibrium internuclear separation of the dimer). Initial vibrational excitation greatly enhances dissociation; initial rotation also enhances dissociation but not to the extent that vibration does. The temperature dependence of the rate coefficients for dissociation of ground-state dimers is shown to be well described by k = CT−1/3. The rate of Ar2 dissociation by Ar is found to be orders of magnitude greater than previously reported values.
Spin–orbit coupling constants for the 2E states of CH3O and CH3F+
Authors: Cooper David L.
Published: February 2003

The spin-orbit coupling constants of the free methoxy radical CH3O and methyl fluoridecation CH3F+ are compared. (AIP)
Nonlinear transport processes and irreversible thermodynamics of a mixture of ionized and neutral gases subject to an electric field
Authors: Eu Byung Chan
Published: February 2003

In this paper, the modified moment method is applied to investigate nonlinear transport processes and irreversible thermodynamics of a dilute mixture of nonpolarizable ionized and neutral gases subject to an external electric field. Theories are developed by means of scalar and tensor temperature distribution functions and the extended Gibbs relations are derived in both theories. The latter relations reduce to the equilibrium Gibbs relation as the fluxes vanish at equilibrium. Various nonlinear transport equations are obtained from which nonlinear transport coefficients can be derived. They all reduce to linear transport coefficients as the magnitudes of the fluxes get smaller. Especially, nonlinear diffusion and mobility coefficients are obtained which depend nonlinearly on the electric field strength, and their mutual relationships are found as generalizations of the Einstein relations.