bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of interactive noise on the driven Brusselator model
Authors: Kruel Th.-M. , Freund A. , Schneider F. W.
Published: July 2002

We examine the effects of interactive noise, i.e., noise which is processed by the system, on the Brusselator, a nonlinear oscillator. The Brusselator is investigated for three types of motion: periodic, quasiperiodic, and chaotic. Fluctuations are imposed on the system variables (Type V noise). The average fluctuation amplitudes are chosen between 10 and 10 000 ppm (1%) and they are Gaussian distributed. The simulated time series are analyzed by autocorrelation functions, Fourier spectra, Poincaré sections, one-dimensional maps, maximum Lyapunov exponents, and correlation dimensions. As a result, noisy periodic and quasiperiodic motion can be distinguished from deterministic chaos if the fluctuation amplitude is sufficiently small. The generic structure of the attractor can be recognized when Lyapunov exponents or correlation dimensions are extrapolated to zero fluctuation amplitude. Quasiperiodic attractors in the Brusselator are obscured even by small amounts of noise. Chaos in the Brusselator, on the other hand, is found to be robust against noise. For periodic motion we show that points close to a bifurcation exhibit a stronger sensitivity towards noise than points far away. In the log–log plots for the correlation dimension we observed break points for noisy periodic and quasiperiodic motion. They separate the noise from the purely deterministic part of the motion. For increasing noise levels the break points move to higher length scales of the attractor. Break points were not found for chaos in the Brusselator nor in the Lorenz and Rössler models. In the Brusselator very large noise levels beyond 1% obscure the deterministic structure even of a chaotic attractor so that any clear distinction between chaos and noise induced (statistical) aperiodicity is no longer possible. Implications on experimental systems are discussed.
Theoretical and experimental investigation of the reaction BH+D2→BHD2
Authors: Caldwell N. J. , Rice J. K. , Nelson H. H. , Adams G. F. , Page M.
Published: July 2002

The rate of the association reaction, BH+D2→BHD2 is determined both theoretically and experimentally. In the theoretical calculations, potential-energy surface information is obtained using multiconfiguration self-consistent-field and large-scale multireference configuration-interaction calculations with large correlation consistent basis sets. The preferred direction of approach is found to be along a non-least-motion pathway for which the BH and DD bonds come in nearly parallel to one another. The small computed activation energy of 2.6 kcal/mol for this highly exothermic reaction is found to arise almost exclusively from changes in zero-point vibrational energy. The experimental measurements of the BH disappearance rate are made at temperatures from 298 to 597 K and are shown to be only weakly dependent on total pressure over the range of 1–100 Torr. As a test of the proposed mechanism, we observe the growth of BD and find the BD appearance rate constant to be in excellent agreement with that for BH disappearance. The measured reaction rates are compared to the results of canonical variational transition-state theory calculations of the association rate and are found to be in excellent agreement.
Electrons trapped in single crystals of sucrose: Induced spin densities
Authors: Box Harold C. , Budzinski Edwin E. , Freund Harold G.
Published: July 2002

Electrons are trapped at intermolecular sites in single crystals of sucrose X irradiated at 4.2 K. The coupling tensors for the hyperfine couplings between the electron and surrounding protons have been deduced from electron-nuclear double resonance (ENDOR) data. Electron spin densities at nearby hydroxy protons are positive, whereas spin densities at the more remote protons of carbon-bound hydrogen atoms are negative. The origin of these negative spin densities is discussed.
Ab initio oligomer calculations of dynamic properties of polyacetylene
Authors: Cui C. X. , Kertesz M. , Dupuis M.
Published: July 2002

The electronic and dynamic properties of all-trans polyacetylene have been calculated on the basis of oligomer calculations on H–(CH)10–H and H–(CH)22–H at the ab initio 6-31G level. The calculated ir and Raman intensities are in good agreement with the experimental relative intensities.
Investigation of collision-induced transitions for CH3Br by radio-frequency–infrared double resonance
Authors: Scappini Flavio , Di Lonardo Gianfranco , Mäder Heinrich
Published: July 2002

The highly sensitive method of radio-frequency–infrared double resonance spectroscopy inside the cavity of a CO2 laser has been applied to the study of collision-induced transitions of CH379Br and CH381Br in the four level scheme. Various types of radio-frequency transitions corresponding to A1–A2 and pure quadropole resonances were observed as a result of collision population transfer between different rotational levels. Thus, collision-induced dips have been measured in the pure gas and in mixtures with polar carbonyl sulfide (OCS) and nonpolar (He, Ar) foreign gases. Clamping experiments were also done, using a second radiation in a six level triple resonance configuration to investigate collision selection rules. The intensity ratios of the collision-induced dips to the corresponding three level double resonance signals were measured for a number of transitions in the ground and in excited vibrational states. Collision selection rules in the pure gas and in mixtures with polar and nonpolar foreign gases are discussed.
Dynamics and spectroscopy of PH2(Ã 2A1)
Authors: Nguyen Xuan Chieu , Margani Alessandro
Published: July 2002

The radiative lifetimes and quenching rate constants due to parent molecules PH3 of PH2(Ã 2A1;0v′20; Ka=0 and K′a=1) have been selectively measured for v2=0,1,2,3, and 4 using the laser induced fluorescence technique. The data found in this work do not confirm those reported in literature. Laser induced fluorescence spectra of PH2(Ã 2A1;060) have been observed for the first time. These new data and observations do not support the hypothesis of a predissociation of PH2(Ã 2A1) starting up at v′2=4 proposed by some authors. The Renner–Teller coupling between Ã 2A1 and the higher vibrational levels of X̃ 2B1 seems to be the origin of the lengthening of the radiative lifetimes of PH2(Ã 2A1;0,v2=1 and 2,0; K′a=1) with respect to those found for the corresponding vibrational levels with Ka=0. Evidence of collision induced vibrational relaxation of PH2(Ã 2A1,v′2=4→v2=3) has also been observed.
The spectrum of photoexcited Nd3+ ions in LaCl3
Authors: Pelletier-Allard N. , Pelletier R. , Shertzer J.
Published: July 2002

Nine new levels of the 4f 3 configuration of trivalent neodymium in lanthanum chloride have been identified through absorption experiments on the photoexcited ions. Transitions from the ground state to the μ=5/2 levels are forbidden by the selection rules; by populating the metastable levels (μ=1/2 and 3/2), absorption transitions to the μ=5/2 levels are observed. A least squares fit has been carried out for the 127 known levels of Nd3+:LaCl3 using a Hamiltonian with 20 adjustable parameters.
CN B→X emission in electron-stimulated desorption from alkali halides: Population analysis via nonlinear models
Authors: Xu Jun , Mendenhall Marcus H. , Tellinghuisen Joel
Published: July 2002

Excitation of crystalline KBr, KCl, and LiF with electrons of energy 60–1000 eV produces weak emission in the 360–420 nm region, identified as the B→ X electronic transition in the CN radical. The emission is attributed to CN molecules that leave the surface of the crystal in their electronically excited B 2Σ+ state. The resulting spectra, which are rotationally unresolved, are analyzed by novel nonlinear fitting procedures to yield information about the vibrational and rotational population distributions. For CN(B) produced via electron-stimulated desorption from LiF, the vibrational populations approximate a temperature of 1500 K, while the rotational abundances can be represented as a sum of two Boltzmann distributions having temperatures of 660 K (81%) and 90 K (19%). For ESD from KBr, the rotational distribution is adequately represented as a single Boltzmann at ∼ 590 K.
Dielectric relaxation in polar and viscoelastic fluids
Authors: del Castillo L. F. , Dávalos-Orozco L. A.
Published: July 2002

The generalized evolution equations for the polarization vector and the total stress tensor (viscous plus Maxwell’s electric stress tensors) are obtained in the framework of extended irreversible thermodynamics. The coupling of these equations represents the mutual influence between mechanical and dielectric properties of a viscoelastic and dielectric fluid. The dipolar memory and the associated correlation functions are discussed in order to give an understanding in the current way of thinking based on linear response theory. A comparison with studies of polarization charge diffusion is included as a particular result obtained from the generalized constitutive equations. Calculations of the complex electric susceptibility and the complex viscosity for the linear and incompressible case are presented.
Chemical potentials from integral equations using scaled particle theory. I. Theory
Authors: Pfund David M. , Lee Lloyd L. , Cochran Henry D.
Published: July 2002

A new method is presented for calculating chemical potentials using integral equation theories. The method uses a multistep charging process which allows attractive and repulsive contributions to the chemical potential to be determined separately. The hybrid mean spherical approximation is used to provide needed correlations about the test particle. A novel application of particle scaling is used to determine the repulsive, or cavity formation contribution to the chemical potential. A formal definition is given for the effective hard core diameter of a softly repulsive solute molecule. A simple Kirkwood charging process is used to determine the attractive, or solvent–solute binding contribution to the chemical potential. The use of an integral equation theory for estimating the test particle correlation functions allows chemical potentials and solvent–solute bindings to be determined in nonideal mixtures at supercritical conditions.
Chemical potentials from integral equations using scaled particle theory. II. Testing and applications
Authors: Pfund David M. , Lee Lloyd L. , Cochran Henry D.
Published: July 2002

Presented are the results of testing the method for estimating chemical potentials which was described in paper I. The method, which is based on scaled particle theory, provides accurate chemical potentials in mixtures of softly repulsive particles when used with the Rogers–Young integral equation. Calculated excess Gibbs energies agreed with simulations to an average of −0.67% for 2:1 diameter ratio mixtures. The method provides approximate results in Lennard-Jones mixtures when used with the hybrid mean spherical approximation integral equation theory. Results for supercritical isotherms reproduce simulation data to an average of −3.0%. For subcritical isotherms, vapor results are exact while liquid results are qualitatively correct. The method used with the integral equation theory correctly predicts the effect of energy ratio on the Henry’s Law constant. The predicted effect of size ratio on the constant has an incorrect slope at subcritical temperatures when the solvent density is near the value for a saturated liquid. The incorrect slope results from inaccuracies in the predicted correlation functions for the fluid surrounding the test particle. The method allows estimates to be made of the work of cavity formation and of the strength of solvent–solute binding in near-critical mixtures.
Infrared diode laser spectroscopy of the GeH radical in the 2Π1/2 state
Authors: Akiyama Yasunobu , Tanaka Keiichi , Tanaka Takehiko
Published: July 2002

The vibration–rotation spectrum of the GeH radical for the fundamental band in the 2Π1/2 spin state was observed using an infrared diode laser spectrometer. The GeH radical was produced by ac glow discharge in the mixture of GeH4, He, and H2. The signals were detected by the discharge modulation method. In total 94 GeH lines were identified for five isotopic species, and were simultaneously analyzed to determine effective molecular constants in the 2Π1/2 spin state.
Stimulated echo time domain electron nuclear double resonance
Authors: Cho H.
Published: July 2002

The observation of nuclear spin coherences in a pulsed electron nuclear double resonance (ENDOR) experiment is reported. The coherences are detected indirectly as time-dependent modulations of the electron spin stimulated echo envelope. A theoretical description of these double resonance coherence experiments for spin systems coupled by nonsecular interactions is developed, and is employed to calculate the expected time domain signals assuming indirect detection of the nuclear coherences. The resolution and sensitivity of this technique is compared with other, related ENDOR techniques, and the prospects for more sophisticated time domain experiments are briefly assessed.
Dissociative electron attachment in NO
Authors: Sambe Hideo , Ramaker David E.
Published: July 2002

Previously reported experimental data on dissociative electron attachment (DEA) in NO are reinterpreted. The negative-ion yield resulting from DEA in NO has peak intensities at electron energies around 8 and 9 eV. It is demonstrated that the 8 and 9 eV peaks are due to O− ions and long-lived N− ions, respectively. It is also shown that the O− ions are produced via the single repulsive state, NO−(1π−12π2)1Δ. The possibility that two or more NO− repulsive states might be involved is ruled out. It is further argued that the long-lived N− ions are produced via electron attachment to an excited state of NO, rather than to the ground state. The responsible excited state is believed to be the metastable NO(1π−12π)4Π state.
Nuclear spin–lattice relaxation of methyl groups via multiphonon processes
Authors: Jin Bih-Yaw , Silbey Robert
Published: July 2002

The empirical correlation between the logarithm of tunneling splittings and the temperature at which the spin–lattice relaxation time is minimum for methyl groups in different molecular crystals is explained successfully by taking multiphonon processes into account. We show that one-phonon transitions dominate in the low barrier limit. However, in the intemediate barrier range and high barrier limit, it is necessary to include multiphonon processes. We also show that the empirical correlation depends only logarithmically on the details of the phonon bath.
Surface photochemistry: Adsorption and dissociation of CH3Cl on clean and K-promoted Pd(100) surfaces
Authors: Solymosi Frigyes , Kiss János , Révész Károly
Published: July 2002

The photochemistry of adsorbed CH3Cl on clean and potassium-dosed Pd(100) surfaces has been studied by illumination with low-intensity UV light from a high-pressure Hg lamp. The effects of illumination were established by post-irradiation thermal desorption, Auger and photoelectron spectroscopic measurements. Evidences are presented for photodissociation of the C–Cl bond to give surface bound methyl group coadsorbed with chlorine. The thermal decomposition of the surface methyl is accompanied by desorption of methane, and small amounts of ethane and ethylene. The presence of preadsorbed potassium greatly enhanced the extent of photodissociation of the C–Cl bond. The efficiency of potassium adatoms depended on its amount, i.e., on the work function of the coadsorbed systems. From the study of the wavelength dependence it is concluded that in the photodissociation of CH3–Cl the optical excitation of the substrate to produce photoelectrons plays a dominant role.
A localized-basis monoexcited configuration interaction technique for extended systems
Authors: Karadakov Peter , Calais Jean-Louis , Delhalle Joseph
Published: July 2002

It is demonstrated that the monoexcited configuration interaction matrix, constructed from the localized (or Wannier) orbitals for an one-dimensional extended system with translational symmetry can be used to define a series of finite-dimensional matrices whose lowest eigenvalues and eigenvectors converge to the lowest eigenvalues and eigenvectors of the infinite-dimensional full monoexcited configuration interaction problem. As an illustration, the developed monoexcited configuration interaction approach is applied to the π-electronic model of cyclic polyenes (annulenes) in the framework of the Pariser–Parr–Pople approximation. A standard parametrization scheme has been found to yield a value of ∼2.42 eV for the lowest singlet excitation energy of an infinite polyene, which is in good agreement with the experimental estimate of ∼2 eV.
Diffusion-controlled reactions: Upper bounds on the effective rate constant
Authors: Blawzdziewicz J. , Szamel G. , Van Beijeren H.
Published: July 2002

For a diffusion-controlled reaction in a static, reactive bed of nonoverlapping spherical traps, upper bounds on the effective reaction-rate constant have been obtained from a variational principle of Rubinstein and Torquato. The bounds remain finite for all volume fractions and arbitrary distributions of traps. We have obtained two kinds of bounds: one kind depends on the trap volume fraction only; the other includes, in addition, a nearest-neighbor-distance distribution of the traps. The bounds have been explicitly evaluated, in the latter case using the distribution corresponding to the hard-sphere equilibrium ensemble.
Resonant two photon dissociation dynamics of HD+ in intense infrared laser field
Authors: Datta Banani , Bhattacharyya S. S.
Published: July 2002

The intensity dependent line shapes of resonant two photon dissociation process in HD+ from the 1sσg (v=6, J=0) are obtained at three different intensities (1.53×1010, 1.53×1012, and 6.12×1012 W/cm2 ) in the wavelength range 16 000–17 200 Å using the resolvent operator formalism. The discrete state v=11, J=1 (1sσg) is the intermediate resonant state. The position of the resonance on the wavelength scale depends strongly on intensity. It is shown that for sufficiently strong fields the earlier semiperturbative theory formulated in analogy with Fano’s theory of atomic autoionization breaks down near resonance due to saturation of the strongly coupled resonant transition. Also, when the dissociative transitions to both the electronic states 1sσg and 2pσu are considered simultaneously, the line shape is altered from that obtained by the superposition of the line shapes of these two transitions separately. The conditions under which a unique time independent transition rate is ill defined are discussed. For such situations the time dependent transition probabilities can be obtained from the effective Fano asymmetry parameters, and line shifts and widths of the ground and resonant states. The limiting transition rates for such cases for short and long pulse times are also shown.
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o study of the electronic spectrum of a Cs11O3 cluster
Authors: Wang Ping , Ermler Walter C.
Published: July 2002

Geometries and electronic states of the cesium suboxide cluster Cs11O3 are investigated by means of ab initio Hartree–Fock calculations. Relativistic effective core potentials are employed to represent core electrons in the atoms while Gaussian-type orbital basis sets are used to describe the valence electrons. Interatomic distances are optimized for the ground electronic state. The work function of Cs11O3 is calculated as 0.65 eV, in excellent agreement with an experimentally determined value of 0.7 eV for bulk cesium suboxide. Mulliken populations of negatively charged and neutral Cs11O3 clusters are calculated and indicate that upon ionization the emitted electron exits a molecular orbital encompassing the outermost cesium layer of the cluster.
Approximate algebraic solution to the forced highly excited rotor: Application to I*2 rotationally inelastic scattering
Authors: Maricq M. Matti
Published: July 2002

A comparison between coupled states and classical path calculations is used to elucidate the power gap law for energy transfer observed in rotationally inelastic scattering of B 3Π0+uI2 by heavy atoms and the deviations from that law that occur for scattering by light mass species. An operator algebra is developed to describe raising and lowering of the eigenstates of j2 for highly excited rotational states. It forms the framework for a closed form solution of the forced rotor evolving under the Hamiltonian H=Ω/ℏ⋅j2+V(θ,t). Transition probabilities are given by Bessel functions of the frequency component of the applied torque corresponding to the local rotational energy level spacing. This implies an oscillatory dependence of probability on ‖Δj‖ up to a ‖Δj‖max, beyond which it decreases dramatically. Integration of the oscillatory distribution in jf over impact parameter and degeneracy averaging yield the observed power law dependence of cross section on ‖Δj‖ along with the deviations from this law for light mass collision partners. The similarity of the present theory and results to previous work on vibrational relaxation of I*2 is discussed.
(H2O)2(g): Monomer/dimer vibrational frequency shifts in Bopp–Jancsó–Heinzinger- and Matsuoka–Clementi–Yoshimine–Lie-type flexible potentials
Authors: Slanina Zdenĕk
Published: July 2002

Harmonic vibrational analysis of the water dimer is reported for four BJH- and four MCYL-type flexible water–water potentials. The calculated monomer/dimer frequency shifts correspond reasonably well to the available observed terms, the BJH-type flexible potentials (with the gas-phase intramolecular potential) yielding a slightly better agreement.
Effect of isotopic substitution on the visible absorption spectrum of ozone
Authors: Anderson Stuart M. , Maeder John , Mauersberger Konrad
Published: July 2002

Absorption spectra for 16O3 and 18O3 have been recorded to study the vibronic structure of the Chappuis band. The isotope shifts indicate that the strongest features involve transitions to two electronically excited states characterized by adiabatic energies ≊750 cm−1 apart, with the higher one near 16 400 cm−1. The vibrational structure can be associated with a relatively simple progression in this higher state (ω1 and ω2≊1210 and 640 cm−1, respectively), and one isolated band associated with the lower state. Alternatively, an autocorrelation analysis indicates major recurrences near 31 and 41 fs for 16O3, and correspondingly longer times for 18O3. Minor recurrences at longer times are also present, but all are significantly shorter lived than those associated with the Hartley band. The results are discussed in the context of ab initio calculations and recent experimental and theoretical work involving visible and ultraviolet absorption spectra of ozone.
External noise, density fluctuations, and divergences in steady state reaction–diffusion systems
Authors: Molski Andrzej , Keizer Joel
Published: July 2002

The effect of an external, stochastic particle input on density fluctuations at nonequilibrium steady states in diffusion–reaction systems is studied using the fluctuation dissipation theory. The following reactions are analyzed: unimolecular decay A→P; one-species bimolecular annihilation A+A→P; and two-species bimolecular annihilation A+B→P. Two mechanisms of particle input are considered: (i) random creation of individual particles, (ii) random creation of geminate pairs. For three-dimensional systems the variance of the particle number in an arbitrary spherical volume is calculated. In one and two dimensions the reaction A+B→P does not achieve a homogeneous steady state if the input of A’s is not correlated with the input of B’s. The origin of this effect is discussed.
Perturbation theory of angular molecules interacting through the Kihara potential
Authors: Vega Carlos , Lago Santiago
Published: July 2002

A perturbation theory for angular molecules interacting through the Kihara potential is proposed. The theory is applied to a model of propane and the different approximations of the theory are checked by comparing the theoretical with previously obtained simulation results. We also obtained vapor–liquid equilibria of propane by fitting the potential parameters with the theory. Good agreement between theoretical and experimental results was obtained. Thus, the Kihara potential which is much simpler than the site–site model for this kind of molecule is able to represent the equilibrium behavior of angular nonpolar molecules.
The thermodynamic properties of the niobium–hydrogen system measured by reaction calorimetry
Authors: Luo W. , Kuji T. , Clewley J. D. , Flanagan Ted B.
Published: July 2002

Calorimetric enthalpies for reaction of hydrogen with niobium in the α-, and (α+α′)-, α′-, (α′+β)-, (α+β)-, β- and (β+δ)-phase regions are reported. The free energies and entropies are reported for those regions where the equilibrium pressures can be measured. The enthalpies for reaction with (1/2)H2(g) in the plateau regions for (α+β) and (α+α′) are −47.4 and −42.8 kJ/mol H, respectively. The magnitude of the calorimetric (absorption or desorption) enthalpy for the (β+δ) plateau region is 17.3 kJ/mol H which is about 3 kJ/mol H smaller than the literature value based on a van’t Hoff plot of the decomposition pressures. This difference arises because of the large hysteresis in this system and because of the irreproducibility in the plateau pressures; neither factor affects the present calorimetrically determined enthalpies.
Charge and electrical potential distributions in a nonequilibrium inhomogeneous electrolyte solution. A statistical mechanical approach. I. Single binary electrolyte. Theory
Authors: Raineri Fernando O. , Friedman Harold L.
Published: July 2002

A molecular theory of the liquid junction between two different solutions of the same single binary electrolyte is derived from the statistical mechanical theory of linear response to thermal perturbations. The new theory employs a certain salt representation of the electrolyte solution that involves the transport numbers of the ion constituents. In this representation the solution is formally treated as a binary mixture of nonelectrolytes. The theory leads to expressions for the profiles (distributions through the junction) of charge, electrical potential, and number densities of the ion constituents in terms of the transport numbers and static equilibrium correlation functions formulated at the Born–Oppenheimer level. The implications of the new theory for the liquid junction potential (LJP) at this level remain to be developed. A simple approximation reduces the calculation of these profiles to the McMillan–Mayer level where only the ion–ion equilibrium correlation functions are required. The LJP derived at this level depends on the specific interactions between ions through the short-range part of the ion–ion direct correlation functions. If these interactions are absent (point ions) or if their effect mutually cancels (as in the restricted primitive model) we recover the LJP of classical electrochemistry, a result that is not trivially derived from a molecular theory. Calculations are presented to illustrate the predictions of the theory concerning the charge profile.
Creation and dynamics of molecular states prepared with coherent vs partially coherent pulsed light
Authors: Jiang Xue-Pei , Brumer Paul
Published: July 2002

The mixed state of an isolated molecule, which results from one-photon absorption using a pulsed laser of arbitrary coherence, is obtained using a simple model for a partially coherent laser source. The relative effect of the pulse time τ, source coherence time τcoh, and field correlation time τc on the prepared state and on its subsequent molecular dynamics are described. Numerical computations on several properties are provided and support obtained for the analytical result showing that under certain circumstances the falloff of the survival probability of the created molecular state depends primarily on the pulse time τ.
Association reactions at low pressure. IV. The HC3N+/HC3N system
Authors: Sen Atish D. , Huntress Wesley T. , Anicich Vincent G. , McEwan Murray J. , Denison Arthur B.
Published: July 2002

The reactions between HC3N+ and HC3N, and between HC5N+ and HC3N have been examined at pressures from 1×10−7 to 1×10−3 Torr by ion cyclotron resonance mass spectrometry. The reaction between HC3N+ and HC3N has both a bimolecular reaction path and a termolecular reaction path. The overall bimolecular reaction rate coefficient was found to be 1.3×10−9 cm3 s−1. The primary product, HC5N+, represents 90% of the product ions, while the minor products HC6N+2 and H2C6N+2 each represent 5%. The termolecular association rate coefficient was 3.7×10−24 cm6 s−1 with He as the third body. From double resonance experiments the mean lifetime of the collision complex was determined to be 180 μs. HC5N+ was found to react with HC3N and form the adduct ion H2C8N+2 through both bimolecular and termolecular channels. The bimolecular rate coefficient was 5.0×10−10 cm3 s−1 and the termolecular rate coefficient was observed to be 1.2×10−22 cm6 s−1 with HC3N as the third body. With He as the stabilizing molecule, the termolecular rate coefficient was 6.0×10−24 cm6 s−1. The mean unimolecular lifetime of the collision complex was estimated to be ≥15 μs and the mean radiative lifetime for the radiative association channel was found to be ≥89 μs. HC5N+ was found to be formed with excess internal energy and did not react by bimolecular association until relaxed by several nonreactive collisions with HC3N.
Fine-structure mixing within the Zn(4 3P
J) multiplet by collisions with the noble gases
Authors: Han X. L. , Kelly J. F.
Published: July 2002

Measurements of rate coefficients for intramultiplet state transfer of Zn(4 3P1→4 3PJ′) by collisions with the rare gases are presented. The state-to-state binary rate coefficients are derived from least-squares fittings of the time-resolved triexponential behavior of the 4 3P1 fluorescence. These rate coefficients were studied systematically over a temperature range of 690–1100 K in order to characterize the velocity dependence of the collisional coupling. The systematic behavior of the rate coefficients with varying temperature and noble gas species is qualitatively consistent with a nearly adiabatic coupling limit for noncrossing levels.
Detection of atomic nitrogen by third harmonic generation
Authors: Celii F. G. , Thorsheim H. R. , Butler J. E.
Published: July 2002

The four-wave mixing technique of third harmonic generation (THG) was used to detect gas-phase atomic nitrogen atoms. Ground state N(4S03/2) atoms were produced in a microwave discharge and monitored via 120 nm radiation which was generated by a 360 nm pulsed dye laser beam focused into the post-discharge region. The THG excitation features were blue-shifted from the 3s 4PJ→2p3 4S03/2 atomic resonance lines. Both the frequency shift and VUV intensity were sensitive to the N(4S03/2) concentration as expected for the THG process. Absolute concentration was determined using standard flow reaction calibration and yielded a minimum sensitivity of 3×1013 cm−3. Similar THG detection schemes for atomic nitrogen metastable states (2p3 2D0j and 2p3 2P0J) are discussed. The third harmonic generation technique possesses a number of potential advantages for in situ optical diagnostics.
Rotational spectrum and structure of the complex Ar–CH3CN
Authors: Ford R. S. , Suenram R. D. , Fraser G. T. , Lovas F. J. , Leopold K. R.
Published: July 2002

The microwave spectrum of the weakly bound complex Ar–CH3CN has been observed using a pulsed-nozzle Fourier-transform microwave spectrometer. The spectrum is characteristic of an asymmetric rotor with nearly free internal rotation of the methyl group. Spectroscopic constants for the ground internal rotor state, in megaHertz, are 3:[RW3:A=9323.7769(22),:B+C=3439.5578(15),:B–C=326.6860(12)].
Test of a pairwise additive ionic potential model for silica
Authors: Della Valle Raffaele Guido , Andersen Hans C.
Published: July 2002

Lattice dynamics calculations have been performed for crystalline SiO2, using the two-body potential model developed by Tsuneyuki et al. [Phys. Rev. Lett. 61, 869 (1988)]. The computed phonon frequencies agree reasonably well with experiment. Minor deficiencies suggest that the Si–O force constant obtained from the model is too weak.
Kinetic energy release in thermal ion–molecule reactions: The Nb2+–(benzene) single charge–transfer reaction
Authors: Gord James R. , Freiser Ben S. , Buckner Steven W.
Published: July 2002

We have adapted the techniques originally developed to measure ion kinetic energies in ion cyclotron resonance (ICR) spectrometry to study the single charge–transfer reaction of Nb2+ with benzene under thermal conditions in a Fourier transform ion cyclotron resonance mass spectrometer (FTICRMS). The partitioning of reaction exothermicity among the internal and translational modes available is consistent with a long-distance electron-transfer mechanism, in which the reactants approach on an ion-induced dipole attractive potential and cross to a repulsive potential at a critical separation of ∼7.5 Å when electron transfer occurs. The reaction exothermicity, 5.08 eV, is partitioned to translation of Nb+, 0.81±0.25 eV, translation of C6 H6+, 1.22±0.25 eV, and internal excitation of C6 H6+ to produce the la2u electronic state, which is ∼3 eV above the ground state of the ion. We have also studied the kinetics of the reaction of Nb2+ with benzene and determined the rate constant, k = 1.4×10−9 cm3 molecule−1 s−1, and the efficiency, 0.60, of the process. These also support the proposed charge–transfer mechanism. In addition to the charge–transfer pathway, which accounts for 95% of the reaction products, Nb2+ is observed to dehydrogenate benzene to form Nb2+ (benzyne). This process implies D(Nb2+ –benzyne)≥79 kcal/mol.
Structure function of linear polymers in the ideal and excluded volume regime
Authors: Bishop Marvin , Saltiel Craig J.
Published: July 2002

Monte Carlo simulations employing the pivot algorithm are used to generate ideal and excluded-volume chains on two- and three-dimensional lattices. The second, fourth, sixth, and eighth moments of the average monomer–monomer separation are calculated from the resulting configurations. The coefficients in the expansion of the structure factor are computed from universal ratios of these. The values found for excluded-volume chains are smaller than the ideal chain values and the differences are greater in two dimensions than in three dimensions.
Fluctuations and phase diagrams in ternary mixtures
Authors: Teubner Max
Published: July 2002

A binary or liquid ternary mixture has two independent densities, say x1 and x2. There are three independent fluctuations in these densities, namely 〈(δx1)2〉, 〈(δx2)2〉, and 〈δx1 δx2〉. It is demonstrated that there exists a homogeneous linear relation between these fluctuations, if the mixture coexists with a second phase. The coefficients of this relation are simple geometric quantities of the phase diagram. If the mixture coexists with two other phases, there exist two such linear relations. In this case the fluctuations can be determined up to a common factor from the phase diagram alone.
Dependence of vibrational energy transfer and bond dissociation on initial excitation and phases in O2(0)+O2(v)
Authors: Shin H. K.
Published: July 2002

The dependence of vibrational energy transfer and bond dissociation on the initial vibrational energy and initial phases in the collision of two oxygen molecules O2(0)+O2(v) has been studied using classical trajectory procedures. When the initial vibrational energy of O2(v) is not large, the energy gained by O2(0) is mainly through the V→V pathway, but as the initial excitation increases the contribution of translational motion becomes important. For the highly excited O2(v), most trajectories lead to T→V energy transfer, and for such molecules dissociation probabilities are found to increase linearly with the initial excitation. The dissociation of O2(v) is sensitively dependent on the initial vibrational phase. For v=1, the resonant energy exchange probability is a linear function of the collision energy.
Dynamical calculations for the H+para, ortho-H2 reactions at low temperatures: Effect of rotational energy of reagent H2 molecule
Authors: Takayanagi Toshiyuki , Masaki Nobuyuki
Published: July 2002

The reactive probabilities for the H+H2( j=0,1)→H2( j ′=0,1)+H reactions are calculated at low translational energies using a simplified Jz -conserving coupled-states method. Both the LSTH and the PK2 potential energy surfaces are used. The energy where the Wigner threshold behavior appears is affected both by the existence of van der Waals well included in the potential surface and by the rotational state of H2. Thermal rate constants at low temperatures are calculated for the title reactions, and the calculated values are compared with the experimental results in solid phase reported by others. The effect of rotational energy of reagent H2 molecule on the rate constants is discussed.
Pressure broadening data as a test of a recently proposed Ar–H2O interaction potential
Authors: Green Sheldon
Published: July 2002

An interaction potential for H2O–Ar that was recently determined from spectra of the van der Waals complex [R. C. Cohen and R. J. Saykally, J. Chem. Phys. 94, 7991 (1990)] is used with accurate molecular scattering calculations to predict line broadening parameters for the 183 and 380 GHz transitions of water vapor. Theoretical values are about 15% higher than experiment.
Construction of effective Hamiltonians for time-dependent phenomena from variational principles
Authors: Echave Julián , Fernández Francisco M. , Campanaro Mónica , Micha David A.
Published: July 2002

We develop a variational method for constructing the effective Hamiltonian that best propagates the state of a system, based on the minimization of a temporal error functional. As an illustrative example the procedure is used to derive the effective Hamiltonian in the time-dependent self-consistent-field method. The present variational approach is particularly useful to build the best effective Hamiltonian that is a linear combination of the generators of a Lie algebra. We explicitly consider systems having classical analogs with many degrees of freedom and calculate transition probabilities for a simple semiclassical model of the collinear collision between an atom and a diatomic molecule. We show that our variational approach is more general and accurate than the widely used local harmonic approximation.
Critical-scaling theory for ternary systems with ‘‘polar’’ tielines
Authors: Smith Duane H. , Lim Kyung-Hee , Ferer M.
Published: July 2002

As used in the previous literature, critical-scaling theory for ternary (or pseudoternary) systems requires that the tielines be parallel, i.e., that one of the concentrations appears to be a field variable, rather than a density variable as it is known to be. However, for many chemical systems, the tielines in the conventional weight-fraction phase diagram are not parallel; instead, extensions of the tielines radiate from a single point (or are assumed to do so). For such cases, we show that there are two coordinate transforms (one to polar coordinates, the other to a second set of triangular coordinates) that convert one of the compositions from a density variable to a ‘‘hidden variable.’’ The latter transformation makes the tielines parallel. An association model that produces such parallel tielines is discussed, and the ability of critical-scaling equations to describe conjugate phase compositions in the system of transformed triangular coordinates is examined for a real ternary system, ethanol/n-hexane/water.
1
P
1 level decay in high pressure krypton
Authors: Audouard E. , Laporte P. , Subtil J. L. , Reininger R.
Published: July 2002

The 1P1 decay in high pressure krypton (densities 1×1020–5×1020 cm−3 ) has been investigated using selective photoexcitation. At densities above 4×1020 cm−3, the decay occurs fully through the 3P1 level. 1P1 blue or red excitation lead to identical results with evidence of a long lived reservoir effect with a rate constant associated with 1P1→3P1 transfer of ≊0.2×10−32 cm6 s−1. The kinetic scheme includes formation of short distance g symmetry excimers followed by 1g dissociation into the 3P1 state. At low density the results strongly support the hypothesis of a competing O+g(1P1) infrared excimer decay into the relaxed 1u(3P2) state.
Structure and melting of a bilayer oxygen film on graphite
Authors: Morishige Kunimitsu
Published: July 2002

X-ray diffraction measurements of oxygen physisorbed on graphite have been taken over the temperature range 32–52 K and the coverage range 0.13–0.27 molecule/Å2. The results strongly suggest the model that bilayer oxygen at low temperatures consists of two independent layers of O2 molecules, a top layer of a centered rectangular lattice above a bottom layer of a hexagonal lattice incommensurate with the substrate. On warming, the top layer first melts at ∼38 K abruptly and then the bottom layer melts immediately after that. The resulting fluid II, which is a composite phase of a liquid giving rise to a very broad peak centered at 2θ=28.5° and a phase giving rise to a broad peak around 2θ=32°, is stable over the wide temperature range 38–47 K and eventually changes to the pure liquid. The structure of this composite phase remains unresolved, although the diffraction pattern shows evidence of long-range order retained in this phase.
Tristability in the iodate–As(III) chemical system arising from a model of stirring and mixing effects
Authors: Ganapathisubramanian N.
Published: July 2002

The iodate–As(III) system which exhibits bistability in an ideal continuous flow stirred tank reactor (CSTR), exhibits tristability when subjected to the mixing model of Kumpinsky and Epstein [J. Chem. Phys. 82, 53 (1985)]. The cross flow between the major and minor reactors influences the system’s lower hysteresis limit more than its upper hysteresis limit.
The atomic correlation operator method
Authors: Chaumet Martin , Fulde Peter
Published: July 2002

Atomic correlation operators are introduced which provide a method of selecting configurations for the description of correlations. When the calculations are done to lowest order in the residual interactions their accuracy can be checked by comparing them with Mo/ller–Plesset perturbation calculations. A subset of the atomic correlation operators generates interatomic correlations. When the latter are treated better than by lowest-order perturbation theory the computational results can be compared with those of a coupled-electron-pair approximation (zero) calculation. The method is tested by applying it to CH4.
Tunneling within localized states in nitrosyl myoglobin
Authors: Nascimento Otaciro Rangel , Neto Ladislau Martin , Wajnberg Eliane
Published: July 2002

The temperature (T) dependence of the spin lattice relaxation time of nitrosyl myoglobin (MbNO) was measured in the range from 9 to 310 K. Both powdered and solution samples exhibit an unexpected dependence. Experimental data is well fitted by a Tn function with n=2.2±0.3 in this large temperature range. This result is interpreted within the tunneling localized states model associated with the existence of conformational equilibrium in MbNO.
Absolute vibrational differential cross sections of water vapor by 30 and 50 eV electron impact
Authors: Furlan M. , Hubin-Franskin M.-J. , Delwiche J. , Collin J. E.
Published: July 2002

Direct vibrational excitation of water vapor has been investigated by use of electron impact spectroscopy. Absolute vibrational differential cross sections have been measured for the bending (010) and stretching (100,001) modes of the electronic ground state at 30 and 50 eV impact energies and in the angular range from 10° to 60°. Our experimental data are compared to theoretical results available in the literature.
The description of elementary organoaluminum fragments: AlCHx (x=1,2,3)
Authors: Jin Su Qian , Xie Yaoming , Schaefer Henry F.
Published: July 2002

High-level quantum mechanical methods have been applied to several fundamental organoaluminum species of the general formula AlCHx. In connection with basis sets as large as triple zeta plus double polarization plus f function (TZ2P+f), self-consistent-field (SCF) and configuration interaction including all single and double excitations (CISD) methods have been applied. Predictions of molecular structures, vibrational frequencies, infrared intensities, and dipole moments for the various stationary points (three for AlCH, four for AlCH2 and five for AlCH3) have been made. Aluminum–carbon systems strongly avoid multiple bonding. The best candidates for an observable Al■C double bond are the trans bent HAl■ĊH isomer (which is predicted to lie 45 kcal/mol above the :Al–ĊH2 global minimum for the tetra-atomic system) and the HAl■CH2 isomer (44 kcal/mol above :Al–CH3).
A theoretical study on ionization of ethylene with analysis of vibrational structure of the photoelectron spectra
Authors: Takeshita Kouichi
Published: July 2002

A b initio calculations have been performed to study the vibrational levels of the low-lying ionic states, 2B3u , 2B3g, 2Ag, 2B2u, and 2B1u of ethylene. The equilibrium molecular structure and vibrational modes of these states are presented. The theoretical ionization intensity curve including the vibrational structure is also presented and compared with the photoelectron spectra of C2H4 and C2D4. A number of new assignments of the photoelectron spectra are proposed.
Selected versus complete configuration interaction expansions
Authors: Illas F. , Rubio J. , Ricart J. M. , Bagus P. S.
Published: July 2002

Full CI (FCI) and selected multireference CI (MRCI) calculations have been carried out for the first row atoms (B to F) and hydrides (BH to FH). The multireference selected CI calculations were carried using the CIPSI algorithm (CIPSI stands for configuration interaction by perturbative iterative selection). An analysis of the relationship between variational and perturbational correlation energy contributions is also reported. By diagonalizing a matrix corresponding to a CI expansion selected from the full MRCI space, 99% of the total FCI correlation energy is obtained. The contribution of a large number of generated determinants to the correlation energy can be accounted for by second order perturbation theory. This contribution to the correlation energy is one order of magnitude smaller than the error with respect to the FCI value. The calculations were carried out using two different basis sets. The first one is based on the atomic natural orbital (ANO) contraction, and the second follows the segmented contraction scheme. Both sets contain 4s3p1d contracted functions for atoms B to F and 2s1p for the H atom.
Fourier transform emission spectroscopy of BeF2 at 6.5 μm
Authors: Frum C. I. , Engleman R. , Bernath P. F.
Published: July 2002

The high resolution infrared emission spectrum of BeF2 was observed. The fundamental antisymmetric stretching mode ν3 and numerous hot bands involving ν1 and ν2 were found near 1550 cm−1 by Fourier transform spectroscopy. Eight vibration–rotation bands were rotationally analyzed and the spectroscopic constants are reported. The equilibrium beryllium fluorine distance (re) was found to be 1.372 9710(95) Å in BeF2.