bluuebunny/crossref_metadata_2025 huggingface dataset:
Static structure and ionic transport in molten AgBr and AgCl
Authors: Tasseven Ç. , Trullàs J. , Alcaraz O. , Silbert M. , Giró A.
Published: July 2002

The static structure of molten AgBr and AgCl have been calculated using the hypernetted chain theory of liquids (HNC) and molecular dynamics simulations (MD) with effective potentials based on the functional form originally proposed by Vashishta and Rahman [Phys. Rev. Lett. 40, 1337 (1978)] to study α-AgI. The HNC and MD are in good agreement among themselves as well as in good qualitative agreement with experiment. MD simulations have been also used to calculate the time correlation functions and ionic transport properties of these melts. The results for the velocity autocorrelation functions suggest, in both cases, a mechanism for diffusion akin to that we suggested for molten AgI and CuX (X=Cl, Br, I) [J. Phys. Condens. Matter 2, 6643 (1990)] even though the cations velocity autocorrelation function is no longer purely diffusive. The results for the diffusion coefficients resemble the type of behavior found in superionic melts, as if the transition to a superionic state is finally realized in AgCl and AgBr on melting. The results for the specific ionic conductivities are in good agreement with experiment if it is assumed that the ions, in their transport, carry with them their full complement of electrons.
Spectroscopy of high n Rydberg states of the triatomic deuterium molecule D3
Authors: Müller U. , Majer U. , Reichle R. , Braun M.
Published: July 2002

We report first investigations of high principal quantum number Rydberg states of the neutral triatomic deuterium molecule. The experiments were performed using a fast neutral beam photoionization spectrometer recently developed at Freiburg. A fast beam of metastable D3 molecules was created by charge transfer of a D3+ beam in cesium. Rydberg states of D3 were analyzed by pulsed-laser excitation using two-photon resonance-enhanced ionization, electric field ionization and autoionization. Our data identify the 2p 2A2″(N=K=0) state of D3 to be metastable with a lifetime of about 1 μs. The spectral lines following excitation in the ultraviolet spectral range were assigned to s-type and d-type Rydberg-series converging to vibrational ground state, symmetric stretch excited and degenerate mode excited D3+ ion states. By a combination of vibrationally diagonal and non-diagonal transitions, we determined the ionization potential, the symmetric stretch and degenerate mode vibrational frequencies of the 2p 2A2″ state in D3. The data give insight into the influence of the coupling between the Rydberg electron and the ion core on the potential energy surface.
Collision induced deactivation of the bending mode v=1 vibrational level of the excited Ã 2A1 and ground X̃ 2B1 electronic states of PH2 by rare gases
Authors: Nguyen Xuan Chieu , Margani Alessandro , Mastropietro Marcello
Published: July 2002

Collisional deactivation of the vibrational level v=1 of the bending mode by rare gases has been studied for both the excited Ã 2A1 and ground X̃ 2B1 electronic states of PH2. Quenching constants have been determined. While a non-SSH behavior has been observed in the dependence of the relaxation probability upon the mass of the collision partner in the ground state denoting a possible predominance of an intramolecular V–R energy transfer process, the cross sections fit quite well the Parmenter and co-workers’ potential well depth correlation rule for both the electronic states indicating that their interactions with the quenchers occur for both of them under the influence of long range attractive forces.
Two-component plasma in a gravitational field
Authors: Téllez Gabriel
Published: July 2002

In this paper we study a model for the sedimentation equilibrium of a charged colloidal suspension: the two-dimensional two-component plasma in a gravitational field which is exactly solvable at a special value of the reduced inverse temperature Γ=2. The density profiles are computed. The heavy particles accumulate at the bottom of the container. If the container is high enough, an excess of light counterions form a cloud floating at some altitude.
Binding energies of Ti+(H2)1–6 clusters: Theory and experiment
Authors: Bushnell John E. , Maître Philippe , Kemper Paul R. , Bowers Michael T.
Published: July 2002

Formation of Ti+(H2)n clusters (n=1–6) has been studied by both temperature-dependent equilibrium measurements and density functional theory (DFT). The successive binding energies (BDEs) were measured to be 7.5±0.5, 9.7±0.6, 9.3±0.7, 8.5±0.4, 8.2±0.4, and 8.7±0.4 kcal/mol for n=1–6, respectively. The relatively low value of the n=1 BDE is due to a curve crossing from the Ti+[a4F(sd2)] ground state to the Ti+[b4F(d3)] first excited asymptote with the addition of the first ligand. The first BDE is 10 kcal/mol when measured with respect to the excited state asymptote. This series of almost constant BDEs is unlike any other M+(H2)n series. The present DFT calculations show these relatively constant BDE values for the Ti+(H2)n clusters are due to an electronic occupation which allows the Ti+ ion to interact equally with up to six H2 ligands. Bond lengths, geometries, and vibrational frequencies from the DFT calculations are reported here for all clusters. The influence of basis set size and computational method on the first two clusters was also examined. It was determined that a multireference wave function was required to describe these first two clusters accurately. A possible crossing to the lowest doublet potential energy surface was examined for Ti+(H2)4 and found to be endoergic.
Further studies of the methyl nitrite cis→trans isomerization
Authors: Martı́nez-Núñez Emilio , Vázquez Saulo A.
Published: July 2002

Classical trajectory calculations have been performed to get more insights into the dynamics of cis→trans isomerization of methyl nitrite. Harmonic (diagonal and nondiagonal) and anharmonic potential energy surfaces with parameter values based on the available experimental data and our own ab initio results have been used in these computations. The ab initio calculations have been carried out at the MP2 and QCISD levels of theory, employing the 6-311++G** basis set. Coupling of vibrational modes is analyzed in detail. The influence of molecular rotation and isotopic substitution on the isomerization rate is investigated. Mode specific effects are clearly exhibited for the diagonal-harmonic potential, but they are significantly reduced by inclusion of anharmonicity or interaction terms in the potential function. It is found that modes that exhibit specificity are coupled with the reaction coordinate and with other vibrational modes that couple with the reaction coordinate as well. A comparison of rate coefficients computed for several deuterated species show an unexpected secondary isotope effect.
Nuclear quadrupole spin–lattice relaxation due to molecular reorientations in crystals with orientational disorder
Authors: Meriles C. A. , Pérez S. C. , Brunetti A. H.
Published: July 2002

p -chloronitrobenzene (PCNB) and p-chlorobromobenzene (PCBB) crystallize in the centrosymmetric space group P21/c with two molecules per unit cell. The space lattice will have an equal number of points with molecules facing in opposite directions. As a consequence, these compounds exhibit an orientational rigid disorder. In this work, we have measured the temperature dependence of the chlorine nuclear quadrupole spin–lattice relaxation time (T1), linewidth, and resonance frequency for both compounds for temperatures higher than 80 K. Both compounds exhibit an inhomogeneously broadened line shape and a “normal” Bayer-type temperature dependence of the resonance frequency. The analysis focuses on the identification of the dominant relaxation process at high temperatures (T>240 K in PCNB and T>260 K in PCBB). It is shown that T1(T) reflects the existence of 180° molecular reorientations through a modulation of the crystalline contribution to the electric field gradient.
Quantum-tunneling versus thermally activated electron transfer in ohmic and non-ohmic heat baths
Authors: Tang Jau , Hsien Lin Sheng
Published: July 2002

The dependence of electron transfer rates on temperatures and energy gaps is investigated using more realistic spectral density for solvent fluctuation, such as ohmic, sub-ohmic, super-ohmic dissipation, and the Debye models. We will systematically examine the entire range of temperature and energy-gap dependence, covering the quantum-tunneling regime, the classical Marcus regime, and the intermediate crossover regime.
H+N
2
O
collision dynamics: Branching ratios for T–V energy transfer and the effect of N2O vibrational excitation on the reaction kinetics
Authors: Neil W. S. , Li J.-Y. , Sloan J. J. , Kong F.-A.
Published: July 2002

We report time-resolved Fourier transform spectroscopic measurements on the kinetics of the reaction of vibrationally excited N2O with hydrogen atoms. Vibrationally excited N2O is formed by T–V energy transfer in collisions with hydrogen atoms having 2.3 eV of translational energy. Although the T–V process is capable of exciting the N2O to vibrational levels up to 18 500 cm−1, collisions in which the relative translational energy is greater than 11 000 cm−1 result in rapid reaction to form either NH(X 3Σ)+NO(X 2Π) or OH(A 2Σ+)+N2(X 1Σ+). N2O which is vibrationally excited to energies between 6000 and 11 000 cm−1, reacts with thermal hydrogen atoms, with a rate constant which is about 1.7×10−10 cm−3 molecule−1 s−1. N2O vibrationally excited to levels below 6000 cm−1 [the height of the barrier to reaction forming OH(X 2Π)+N2 on the ground-state surface] is lost very slowly, presumably by deactivation, with a rate constant which is about four orders of magnitude slower than the reaction. The results indicate that increasing the vibrational energy of the N2O by 11 000 cm−1 increases the cross section for the reaction with hydrogen atoms by about seven orders of magnitude.
Density fluctuations in irreversible adsorption processes: Hard ellipses in two dimensions
Authors: Adamczyk Zbigniew , Weroński Pawel/
Published: July 2002

Density fluctuations in 2D systems of irreversibly adsorbed particles were studied. Analytical expressions were derived connecting the magnitude of these fluctuations (characterized by the reduced variance σ̄2) with the available surface function φ and the isotropic pair correlation function g0. Limiting expansions in terms of power series of the dimensionless coverage θ were also derived. The range of validity of these expressions was determined by performing numerical simulations based on the random sequential adsorption (RSA) model. Calculations of g0(r), g0(s), φ, and σ̄2 were performed for hard circles and hard ellipses characterized by aspect ratio k=2 and 5. It was deduced that the simulation results can well be accounted for by the theoretical predictions stemming both from the RSA and equilibrium models.
Mode-coupling theory of self-diffusion in diblock copolymers. II. Model calculations and experimental comparisons
Authors: Guenza Marina , Schweizer Kenneth S.
Published: July 2002

The predictions of polymer-mode-coupling theory for self-diffusion in entangled structurally and interaction symmetric diblock copolymer fluids are illustrated by explicit numerical calculations. We find that retardation of translational motion emerges near and somewhat below the order–disorder transition (ODT) in an approximately exponential and/or thermally activated manner. At fixed reduced temperature, suppression of diffusion is enhanced with increasing diblock molecular weight, compositional symmetry, and/or copolymer concentration. At very low temperatures, a new entropic-like regime of mobility suppression is predicted based on an isotropic supercooled liquid description of the copolymer structure. Preliminary generalization of the theory to treat diblock tracer diffusion is also presented. Quantitative applications to recent self and tracer diffusion measurements on compositionally symmetric polyolefin diblock materials have been carried out, and very good agreement between theory and experiment is found. Asymmetry in block local friction constants is predicted to significantly influence mobility suppression, with the largest effects occurring when the minority block is also the high friction species. New experiments to further test the predictions of the theory are suggested.
Geometric phases and quantum dynamics in spin–orbit coupled systems
Authors: Schön Jörg , Köppel Horst
Published: July 2002

The quantum dynamics of vibronically interacting systems with additional effects of spin–orbit coupling is studied theoretically. The combined effects of spin–orbit and vibronic coupling lead to geometric phases which can vary smoothly between the case of uncoupled potential energy surfaces (vanishing geometric phase) and the limiting case pertinent for conically intersecting surfaces (geometric phase equals π). The impact of these phases on the nuclear energy levels and wave functions is revealed by companion studies for two and three coupled potential energy surfaces including and suppressing the geometric phase effects. For free pseudorotation the resulting effective angular momentum can take any noninteger value. The stationary wave functions exhibit a corresponding smooth transition between the limiting cases of integer and half-odd integer angular momentum. For localized wave packets with high angular momentum the geometric phase increases in the same way as found when treating the nuclear coordinates as classical variables. For delocalized wave packets destructive interference leads to a complete loss of symmetry and, for longer times, to a different overall shape of the wave packet. The effects can be relevant also when the nonadiabatic coupling to the higher potential energy surface is negligible.
Measurement of the Raman spectrum of liquid water
Authors: Carey David M. , Korenowski Gerald M.
Published: July 2002

The Raman spectrum from water was obtained for a range of conditions from ambient to above the critical point, 256 bar and 400 °C. A fluorescence-free sapphire high-pressure Raman cell was employed with which the Raman spectra from water were examined between 30 and 4000 cm−1. Computer deconvolution of the Raman OH-stretching contours allowed the hydrogen bond strength to be determined from the integrated component intensity ratios by use of the van’t Hoff relationship. This procedure yielded a hydrogen bond enthalpy of 2.53±0.10 kcal/mol which is in excellent agreement with previously reported values.
The pulsed electron–electron double resonance and “2+1” electron spin echo study of the oriented oxygen-evolving and Mn-depleted preparations of photosystem II
Authors: Astashkin Andrei V. , Hara Hideyuki , Kawamori Asako
Published: July 2002

A “2+1” electron spin echo method has been applied to measure the angular orientation of the radius-vector RDZ joining the redox-active tyrosine residues YD and YZ in membrane-oriented Mn-depleted preparation of photosystem II. The angle between RDZ and the normal to the photosystem II membrane was determined to be 100°±2°, where the angle of 0° corresponds to the direction from YD towards the stromal side of the membrane, along the membrane normal. A pulsed electron–electron double resonance method has been used to obtain similar information for YD and Mn cluster in oriented sample of oxygen-evolving photosystem II. The angle between the radius-vector from YD to the Mn cluster, RDMn, and the membrane normal was found to be 110°±2°.
Phase transitions in two-dimensional monolayer films on the (110) face-centered-cubic crystal surface
Authors: Patrykiejew A. , Sokołowski S. , Zientarski T. , Binder K.
Published: July 2002

The results of Monte Carlo simulation of two-dimensional films formed on the (110) face of a face-centered-cubic crystal are presented. Systems with different corrugation of the gas–solid potential and different size of adsorbed atoms are discussed. It is demonstrated that even small changes in the gas–solid potential corrugation considerably affect the inner structure of the low-temperature ordered phases and the location of the order–disorder phase transition.
Relativistic effects in silicon chemistry: Are the experimental heats of formation of the silicon atom and SiH4 compatible?
Authors: Collins Charlene L. , Grev Roger S.
Published: July 2002

We have investigated the effects of relativity on the atomization energy of silane, SiH4, to attempt to resolve an earlier discrepancy between theory and experiment. Using a spin-free no-pair Hamiltonian that is based on a second-order Douglas–Kroll transformation, we find that relativity reduces the atomization energy of SiH4 by 0.7 kcal mol−1: a small change, but sufficient to bring theory and experiment into agreement when we include experimental uncertainties. Excitation energies in the silicon atom, S5(sp3)–3P(s2p2), and the atomic cation, P4(sp2)–2P(s2p), which involve a reduction in the number of s-electrons, increase ∼1.2 kcal mol−1 when we include relativity. These excitation energies show an even larger increase, about 2.5 kcal mol−1, when we include core correlation. By contrast, the ionization potential, which involves no change in the number of s-electrons—electron configurations s2p2 in the neutral atom and s2p in the cation—changes ∼0.2 kcal mol−1 when we include relativity. These predictions are consistent with the notion that s-electrons are the most affected by relativity, and that changes in the amount of s-character are related, qualitatively, to differential relativistic effects.
Investigation of the chemical nature of two-dimensional polymerized octadecyltrimethoxysilane Langmuir films by inelastic electron tunneling spectroscopy
Authors: Brousseau J.-L. , Vidon S. , Leblanc R. M.
Published: July 2002

High resolution vibrational spectra of Langmuir films of octadecyltrimethoxysilane (C18TMS) have been obtained by Inelastic Electron Tunneling Spectroscopy (IETS) in order to identify chemical modifications of C18TMS occurring at the air–water interface when the pH of the subphase is changed. The Langmuir films have been transferred onto an aluminum electrode by the Langmuir–Schaefer technique at three different acidic pH: 1.3, 3.3, and 3.8. The former was expected to promote the formation of polysiloxane polymers, while the latter was presumed to considerably slow down the condensation reaction, although the hydrolysis is effective. These assumptions found a direct proof in the vibrational fingerprint of C18TMS. Finally, we show that IETS is the most appropriate technique for the vibrational study of such films.
A theoretical study of the isotope effects on the fluorescence excitation spectrum of 5-aminotropolone
Authors: Paz Juan J. , Moreno Miquel , Lluch José M.
Published: July 2002

A combined ab initio+nuclear dynamics study is performed to theoretically analyze the intramolecular H-atom transfer process in 5-aminotropolone in both the ground (S0) and first excited (S1) singlet electronic states. A complete active space self-consistent field (CASSCF) method is used to optimize the geometries. Energies are then corrected through the second order Mo/ller–Plesset perturbation theory. These results are used to build up reduced bidimensional energy surfaces so that the nuclear wave functions for the nuclear motions in both electronic states are obtained. In particular we have analyzed the six isotopomers that result from deuteration of the amino and hydroxy groups of 5-aminotropolone. It is found that for symmetric structures (−OH/−NH2, −OH/−ND2, −OD/−NH2, and −OD/−ND2), the two lowest vibrational levels in both S0 and S1 appear as a quasidegenerated tunneling doublet. The tunneling splitting in S0 is much lower so that the doublet at the origin, seen in the fluorescence excitation spectra of 5-aminotropolone, can be entirely assigned to the S1 state. In agreement with the experimental findings, this splitting greatly diminishes when the transferring hydrogen is substituted by a deuterium, whereas deuteration of the amino group produces only a modest decrease of such a splitting. A quite different result is found for the nonsymmetric isotopically substituted structures (−OH/−NHD and −OD/−NHD), as the isotope induced asymmetry, combined with the high energy barrier in the S0 potential energy surface, leads to a complete localization of the two lowest vibrational wave functions in S0. On the other hand, for S1 the asymmetry and energy barriers are low enough so that an important degree of delocalization of the two lowest vibrational wave functions is found. These results are again in agreement with the presence of an isotope induced quartet in the fluorescence excitation spectra of these species.
Tunneling currents in long-distance electron transfer reactions. IV. Many-electron formulation. Nonorthogonal atomic basis sets and Mulliken population analysis
Authors: Stuchebrukhov Alexei A.
Published: July 2002

In this paper we further develop the formulation of the method of tunneling currents for the description of the tunneling transition in long-distance bridge-mediated electron transfer reactions introduced in our previous work [A. A. Stuchebrukhov, J. Chem. Phys. 104, 8424 (1996); 105, 10819 (1996)]. Here we present a full many-election treatment of the problem in the case when the atomic basis set employed for the description of the medium is nonorthogonal. In this formulation we introduce many-electron Mulliken population operator and derive a set of kinetic equations describing evolution of different atomic states during the tunneling transition. The analysis of the kinetic equations naturally leads then to a concept of electron density fluxes, or currents, between atoms of the medium propagating the tunneling electron. Explicit formulas expressing interatomic tunneling currents in terms of the coefficients of expansion of molecular orbitals of donor and acceptor diabatic electronic states in the atomic basis set are derived. Specific effects due many-electron nature of the system and non-orthogonality (overlaps) of the atomic states are discussed.
Ab initio studies on the electronic excited states and photodissociation of O3 anion
Authors: Cui Qiang , Morokuma Keiji
Published: July 2002

Extensive ab initio calculations have been performed for the low-lying electronic states of O3− to elucidate the mechanism of photodissociation processes. The identity of the mysterious state implied by the recent experiment of Continetti et al. has been discussed based on the current calculations. Calculations reveal that B22 is a truly bound state favoring a strongly bent geometry with ∠O–O–O∼90.0°, and crosses with the X 2B1 at a similar angle. Therefore, if O3− is produced in a highly bent geometry, B22 might be preferentially populated. The large transition dipole moment and the vertical excitation energy for B22→2A1 also suggest that B22 may be electronically excited efficiently to A12 at the wavelength of 523 nm. The computed energetics of B22 and B12 and the corresponding dissociation limits may explain the larger maximum kinetic energy release (KER) observed in the second experiment of Continetti and the smaller O2–O− bond energy derived from the experiment of Hiller, if we assume that B22 is the parent state in both cases. Furthermore, meta-IRC (intrinsic reaction coordinate) calculations suggest rather different final state distribution of the photofragments from B12→2A2 and B22→2A1 processes, in qualitative agreement with the experimental observations. Although the vibrationally excited ground state O3− might also produce rotational hot, vibrational cold photofragments through the angular dependence of the seam between the two diabatic excited A″2 states, the exact effect of parent vibrational excitation requires future dynamics calculations. At the current stage, our calculations strongly support that the B22 electronic state has been accessed in the second experiment of Continetti et al.
Dynamics of linear and branched alkane melts: Molecular dynamics test of theory for long time dynamics
Authors: Kostov Konstantin S. , Freed Karl F. , Webb Edmund B. , Mondello Maurizio , Grest Gary S.
Published: July 2002

Molecular dynamics (MD) simulations of united atom models for alkane melts are compared with a recently developed theory for calculating the memory functions of flexible polymers. The theory is based upon an approximate solution of the diffusion equation without hydrodynamic interactions. The polymer dynamics are described by using time correlation functions which are expressed in terms of a set of equilibrium averages and the approximate eigenvalues and eigenfunctions of the diffusion operator. For flexible enough chains with sufficiently high molecular weight, the hydrodynamic interactions are screened, and the simplified solvent model used by the theory is expected to be adequate. The only parameter not defined by the MD simulations is the bead friction coefficient ζ. In the limit of weak hydrodynamic interactions (Rouse dynamics), ζ can be determined from the molecular diffusion coefficient by applying the Rouse relation D=kT/NζR. Given this choice of ζR, the time correlation functions computed from the theory are compared with those obtained directly from the MD simulations. Excellent agreement with the simulations is found for all correlation functions and all times for the decane dynamics, provided the theory employs one scale factor to increase ζR and, hence, to compensate for the inadequacy of the Rouse relation. The same picture holds for hexadecane and triacontane (C30H62) but with smaller scale factors. Scaling becomes unnecessary for C44H90 which is long enough for the crossover to Rouse dynamics for D to be almost complete. Very good agreement (after appropriate scaling of ζR) also emerges between theory and simulations for several branched alkanes with carbon numbers C25-C30. Computations for hexadecane at different temperatures show that the scale factors may be weakly temperature dependent.
Simple finite field method for calculation of static and dynamic vibrational hyperpolarizabilities: Curvature contributions
Authors: Kirtman Bernard , Luis Josep M. , Bishop David M.
Published: July 2002

In the static field limit, the vibrational hyperpolarizability consists of two contributions due to: (1) the shift in the equilibrium geometry (known as nuclear relaxation), and (2) the change in the shape of the potential energy surface (known as curvature). Simple finite field methods have previously been developed for evaluating these static field contributions and also for determining the effect of nuclear relaxation on dynamic vibrational hyperpolarizabilities in the infinite frequency approximation. In this paper the finite field approach is extended to include, within the infinite frequency approximation, the effect of curvature on the major dynamic nonlinear optical processes.
Structure, bonding, and energetics of C72− isomers
Authors: Dolgounitcheva O. , Zakrzewski V. G. , Ortiz J. V.
Published: July 2002

Several isomers of C72− were studied with electron correlation methods and augmented, correlation-consistent basis sets. All are thermodynamically stable with respect to dissociation into C5− and C2− anions. Isomerization energies are less than 5 kcal/mol at the highest level of theory. Vertical and adiabatic electron detachment energies are positive for the D3h form of C72−. Linear, carbene, bridged-chain, and chain-ring isomers are considered as well. Feynman–Dyson amplitudes connecting dianionic and anionic states reveal extensive delocalization of the least bound electrons.
Quantum calculations of inelastic and dissociative scattering of HCO by Ar
Authors: Qi Jianxin , Bowman Joel M.
Published: July 2002

Quantum inelastic scattering calculations of Ar+HCO are reported using a new global potential, based on ab initio calculations. The infinite-order sudden approximation is used to describe the slow CO-axis rotation of HCO (which is approximately the top A axis), together with a coupled-channel treatment of the H-atom rotation about the A axis (with associated quantum number K), and the HCO vibrations. Pure ΔK transitions are examined for K=0, ΔK=1, 2; K=1, ΔK=−1, 1; and K=2, ΔK=−1, −2, for several low-lying vibrational states. Overall, the pure ΔK-changing cross sections are large and approximately the same for these vibrational states. However, for the same ΔK, the smaller initial K gives a larger inelastic cross section, and negative ΔK results in larger cross sections than positive ΔK. For vibrationally inelastic scattering, the present results are qualitatively in agreement with previous calculations, which used a standard sum-of-pairs (Lennard-Jones) Ar–HCO interaction potential [B. Pan and J. M. Bowman, J. Chem. Phys. 103, 9661 (1995)]. But quantitatively, the present vibrationally inelastic transition cross sections are roughly ten times smaller than these earlier ones. We attribute this to the use of the empirical interaction potential surface in those calculations. The coupling between the H-atom rotation and some vibrational modes can have a significant effect on the magnitude of the inelastic cross section. This is shown in detail for the transition from the initial state 4νb. The initial state-specific average energy transfer is also calculated, and ranges from −5 to 15 cm−1. Dissociation cross sections are also calculated for several initial states and one orientation angle of the CO axis. The contribution of resonance and nonresonance states to dissociation is assessed.
Rate constants for the reaction of Ar+ with O2 and CO as a function of temperature from 300 to 1400 K: Derivation of rotational and vibrational energy effects
Authors: Midey Anthony J. , Viggiano A. A.
Published: July 2002

Rate constants for the charge-transfer reactions of Ar+ with O2 and CO have been measured in a high temperature flowing afterglow from 300 to 1400 K. Comparisons between our results and the previous flow drift tube studies of Dotan and Lindinger at 300 K illustrate the effects of internal excitation on the reactivity. The rate constants measured for both systems agree favorably with the drift tube results from 300 to 900 K. Rotational and translational energy decreases charge transfer equally, consistent with previous experiments, indicating a long-lived collision complex forms during the reaction. The flowing afterglow rate data deviate from the drift tube results above 900 K as a result of populating vibrationally excited states of the neutral reagents. Charge transfer from the thermally populated spin-orbit excited state of Ar+ with O2 and CO only slightly enhances the rate constants at 1400 K. Populating the v″>0 levels reduces the threshold for accessing excited state products, and the rate constants for vibrationally excited states are much larger than for v″=0. The data suggest most of the enhancement comes from v″>2.
Bond fluctuation model of polymers in random media
Authors: Dua Arti , Cherayil Binny J.
Published: July 2002

Conventional descriptions of polymers in random media often characterize the disorder by way of a spatially random potential. When averaged, the potential produces an effective attractive interaction between chain segments that can lead to chain collapse. As an alternative to this approach, we consider here a model in which the effects of disorder are manifested as a random alternation of the Kuhn length of the polymer between two average values. A path integral formulation of this model generates an effective Hamiltonian whose interaction term (representing the disorder in the medium) is quadratic and nonlocal in the spatial coordinates of the monomers. The average end-to-end distance of the chain is computed exactly as a function of the ratio of the two Kuhn lengths for different values of the frequency of alternation. For certain parameter values, chain contraction is found to occur to a state that is chain length dependent. In both the expanded and compact configurations, the scaling exponent that characterizes this dependence is found to be the same.
State-to-state vibrational relaxation from levels at state densities up to 2.3 states per cm−1 in p-difluorobenzene
Authors: Mudjijono  , Lawrance Warren D.
Published: July 2002

Collision-induced vibrational energy transfer has been studied from three vibrational levels at intermediate state density in S1 p-difluorobenzene in a supersonic free jet expansion. Transfer was studied from the 51 (Evib=818 cm−1; ρvib=0.6 per cm−1), 292 (Evib=876 cm−1; ρvib=0.6 per cm−1), and 5182 (Evib=1179 cm−1; ρvib=2.3 per cm−1) levels. The collision partners include a range of monatomics, diatomics, and polyatomics for 51 and 292. Hydrogen was the collision partner for 5182. For 292, transfers involving multiple changes in vibrational quanta are important, and generally such transfers dominate. This behavior is different from that observed at low state densities but is analogous to what has been observed previously at intermediate state densities in p-difluorobenzene [Mudjijono and W. D. Lawrance, J. Chem. Phys. 108, 4877 (1998)]. There is a suggestion in the data for c-propane and ethane that transfer to vibrational modes of these collision partners is occurring. 51 shows very inefficient relaxation. With the exception of N2, there is no evidence in the spectra for significant transfer via channels involving multiple changes in vibrational quanta. The state-to-state branching ratios for transfer from 5182 were essentially in quantitative agreement with those expected based on transfer from 82. It appears that the in-plane mode ν5, and combinations involving low frequency modes with ν5, behave qualitatively differently to the lower frequency, out-of-plane modes. The lower frequency, out-of-plane modes change their state-to-state relaxation preferences with increasing vibrational state density, with multiple quantum changes becoming preferred, while the higher frequency in-plane ν5 retains the state-to-state preferences seen at low state densities.
Gaussian-3 (G3) theory for molecules containing first and second-row atoms
Authors: Curtiss Larry A. , Raghavachari Krishnan , Redfern Paul C. , Rassolov Vitaly , Pople John A.
Published: July 2002

Gaussian-3 theory (G3 theory) for the calculation of molecular energies of compounds containing first (Li–F) and second row (Na–Cl) atoms is presented. This new theoretical procedure, which is based on ab initio molecular-orbital theory, modifies G2 theory [J. Chem. Phys. 94, 7221 (1991)] in several ways including a new sequence of single point energy calculations using different basis sets, a new formulation of the higher level correction, a spin–orbit correction for atoms, and a correction for core correlation. G3 theory is assessed using 299 energies from the G2/97 test set including enthalpies of formation, ionization potentials, electron affinities, and proton affinities. This new procedure corrects many of the deficiencies of G2 theory. There is a large improvement for nonhydrogen systems such as SiF4 and CF4, substituted hydrocarbons, and unsaturated cyclic species. Core-related correlation is found to be a significant factor, especially for species with unsaturated rings. The average absolute deviation from experiment for the 148 calculated enthalpies of formation is reduced to under one kcal/mol, from 1.56 kcal/mol for G2 theory to 0.94 kcal/mol for G3 theory. Significant improvement is also found for ionization potentials and electron affinities. The overall average absolute deviation of G3 theory from experiment for the 299 energies is 1.02 kcal/mol compared to 1.48 kcal/mol for G2 theory.
Response to “Comment on ‘Frequency-dependent equation-of-motion coupled cluster hyperpolarizabilities: Resolution of the discrepancy between theory and experiment for HF?’ ” [J. Chem. Phys. 109, 3293 (1998)]
Authors: Rozyczko Piotr B. , Bartlett Rodney J.
Published: July 2002

In a recent comment on our paper, Hättig et al. claim that Eq. (1) of our paper on the equation-of-motion coupled-cluster (EOM-CC) method for frequency dependent polarizabilities is (1) “incompatible with, the so-called ‘generic definition’ of EOM-CC properties and converges to the wrong full configuration limit;” (2) causes our calculations to violate time-reversal symmetry; (3) that we unjustifiably ignore renormalization terms; and (4) that our estimates of relaxation effects are suspect due to Eq. (1) being invalid. In the following we prove Eq. (1) and demonstrate that all subsequent criticism of our paper are spurious.
A cluster size nanofilter with variable openings between 2 and 50 nm
Authors: Schöllkopf Wieland , Toennies J. Peter , Savas T. A. , Smith Henry I.
Published: July 2002

A variable size nanoscale particle sieve with openings between 2 and 50 nm has been used for determining, selecting, and manipulating the size of large liquid helium clusters in the range from 7×103 to 3×106 atoms. The variable openings of the sieve are obtained by rotating a nanofabricated free-standing transmission grating with a 100 nm period and 50 nm wide slits around an axis parallel to the slits. The new nano-sieve can be applied to clusters of various species as well as to large molecules with sizes down to 2 nm.
Microwave measurements and calculations on the molecular structure of tetracarbonyldihydroruthenium
Authors: Lavaty T. Greg , Wikrent Pollyanna , Drouin Brian J. , Kukolich Stephen G.
Published: July 2002

The microwave rotational spectra for seven isotopomers of tetracarbonyldihydroruthenium were measured in the 4–12 GHz range using a Flygare–Balle type microwave spectrometer. The measured transition frequencies could be fit to within a few kilohertz using a rigid rotor Hamiltonian with centrifugal distortion. The rotational constants for the most abundant isotopomer are A=1234.2762(4), B=932.7016(6), and C=811.6849(6) MHz. The dipole moment is aligned with the c axis of the complex. The 21 measured rotational constants were used to determine the following structural parameters: r(Ru–H)=1.710(23) Å, r(Ru–C1)=1.952(21) Å, r(Ru–C3)=1.974(28) Å, ∠(H–Ru–H)=87.4(2.4)°, ∠(C1–Ru–C2)=160.6(4.3)°, ∠(C3–Ru–C4)=101.4(1.5)°, and ∠(Ru–C1–O1)=172.6(7.6)°. The axial carbonyl groups are bent slightly toward the hydrogen atoms. These structural parameters are in excellent agreement with the substitution coordinates determined from the Kraitchman equations, and with the structural parameters calculated using density functional theory. There was no previous structural data on this complex. The results of the microwave data and theoretical calculations both indicate C2v molecular symmetry, and show that the H atoms are separated by about 2.36 Å. These results indicate that this complex is clearly a “classical dihydride” rather than an η2-bonded, “dihydrogen” complex. Fairly large deuterium isotope effects were observed for the Ru–H bond length and H–Ru–H angle. The r0, Ru–D bond lengths were observed to be 0.03(2) Å shorter than the r0, Ru–H bond lengths. The D–Ru–D angle is 1.1° less than the H–Ru–H angle indicating that the anharmonicity effects are comparable for the bond lengths and for the interbond angle. The new results on this complex are compared with previous results on the similar dihydride complexes, H2Fe(CO)4, and H2Os(CO)4.
Self-interaction-corrected band structure calculations for intracavity electrons in electro-sodalite
Authors: Blake Nick P. , Metiu Horia
Published: July 2002

The zeolite sodalite is a crystalline compound consisting of cages. The windows connecting the cages are large enough to allow small molecules to be absorbed. The material studied here, called sodium electro-sodalite (SES), is prepared by absorbing one Na atom in each cage. Because of the large electric fields inside the cages, each alkali atom is ionized and the donated electron is shared among several ions. A noninteracting electron model, used in earlier work, calculated the absorption spectrum and the temperature dependence of the Al and Si NMR shifts and found good agreement with experiment. The model predicted that the material is a metal. However, recently published low-temperature magnetic susceptibility measurements show that the ground electronic state is antiferromagnetic. This is incompatible with a noninteracting electron model. In this paper we study the electronic properties of this material by using various levels of spin–density functional (local density approximation, local spin–density approximation, generalized gradient spin–density approximation, and self-interaction corrected generalized gradient spin–density approximation) and unrestricted Hartree–Fock calculations. While all calculations show SES to be a narrow band material, only the unrestricted Hartree–Fock (UHF) and self-interaction corrected (SIC) density functional calculations lead to an antiferromagnetic ground state. The resulting Wannier functions are used to calculate the exchange constant for the antiferromagnetic Heisenberg spin–Hamiltonian. The Néel temperature predicted by UHF is 47 K while the self-interaction-corrected generalized gradient spin–density approximation gives a Néel temperature of 42 K.
Managing singular behavior in the tracking control of quantum dynamical observables
Authors: Zhu Wusheng , Smit Martina , Rabitz Herschel
Published: July 2002

Singularities can arise in the external field obtained by tracking control of quantum mechanical systems. Whether or not the trajectory is disturbed by the presence of a singular point is shown to mainly depend on the average momentum along the trajectory at the moment of passing the singular point. If the singularity occurs on a turning point, the tracking will be quite unstable since the direction taken by the trajectory is very sensitive to field errors. The theoretical analysis of these situations yields detailed conclusions about the impact of field singularities in quantum tracking control. A rank index is defined to characterize nontrivial singularities, and the rank is shown to play an important role in determining the tracking quality while passing over a singular turning point where the field has a unique solution. A special class of nontrivial singularities is identified by the ability to remove the singularity under a proper limiting process. These insights into the nature and influence of singularities in tracking control of quantum systems are beneficial for developing numerical schemes and for designing controls.
Electronic structure of poly(1,10-phenanthroline-3,8-diyl) and its K-doped state studied by photoelectron spectroscopy
Authors: Miyamae Takayuki , Ueno Nobuo , Hasegawa Shinji , Saito Yutaka , Yamamoto Takakazu , Seki Kazuhiko
Published: July 2002

Ultraviolet photoelectron spectra were measured using synchrotron radiation for thin films of poly(1,10-phenanthroline-3,8-diyl) (PPhen) and its potassium-doped state. Upon potassium doping of PPhen, two new states, which could be assigned to bipolaron bands, appear in the originally empty energy gap. The electronic structure of the neutral and potassium-doped states was theoretically analyzed using single-scattering approximation combined with semiempirical molecular orbital calculations.
Isotropic collision-induced scattering by CF4 in a Raman vibrational band
Authors: Godet J.-L. , Elliasmine A. , Le Duff Y. , Bancewicz T.
Published: July 2002

Light-scattering intensities and depolarization ratio data have been recorded at room temperature for gaseous tetrafluoromethane in the collision-induced band of the Raman vibrational line ν1=908 cm−1. For the first time, binary isotropic intensities of the ν1-Raman band are reported in absolute units for Stokes frequency shifts up to 110 cm−1. From comparison with theoretical semiclassical computations of the dipole-multipole spectrum contributions, evaluations of the first derivatives of the successive dipole-multipole polarizability tensors are provided. These results are coherent with those obtained from corresponding depolarized intensities. Moreover, the agreement with ab initio quantum-chemistry calculations of the CF4 multipolar polarizabilities is satisfactory.
Direct observation of the femtosecond nonradiative dynamics of azulene in a molecular beam: The anomalous behavior in the isolated molecule
Authors: Diau Eric W.-G. , De Feyter Steven , Zewail Ahmed H.
Published: July 2002

Using femtosecond-resolved mass spectrometry in a molecular beam, we report real-time observation of the nonradiative, anomalous dynamics of azulene. We studied both S2 and S1 state dynamics. The motion of the wave packet in S1 involves two time scales, a dephasing time of less than 100 fs and a 900±100 fs internal conversion. We discuss the dynamical picture in relation to the molecular structures and the conical intersection, and we compare with theory.
Structural studies of alkali methylidyne radicals: High resolution spectroscopy of NaCH and KCH (X̃3Σ−)
Authors: Xin J. , Ziurys L. M.
Published: July 2002

High resolution spectroscopic measurements have been carried out for alkali methylidyne radicals. The pure rotational spectra of NaCH and KCH, along with their deuterium isotopomers, have been recorded in the frequency range 328–529 GHz using millimeter/submillimeter direct absorption techniques. These molecules were created in a dc discharge by the reaction of metal vapor and CH4 or CD4. These data indicate that KCH and NaCH are linear molecules with 3Σ− ground electronic states arising from a π2 configuration. Spectroscopic constants for KCH and NaCH have been determined from the data, including rotational, spin–spin, and spin–rotation parameters, as well as bond lengths. In comparison with other alkali and transition metal-bearing molecules, these results suggest some degree of covalent bonding in the alkali methylidynes, with carbon atom undergoing sp hybridization.
Computer simulation of wetting and drying of spherical particulates at a liquid–vapor interface
Authors: Bresme Fernando , Quirke Nicholas
Published: July 2002

We investigate the behavior of model particulates of nanometer size at a liquid–vapor interface. The particulate undergoes wetting and drying transitions, defined by its penetration in the liquid and vapor phases, respectively. We have analyzed the dependence of the wetting and drying of this particulate in terms of the fluid–particulate interaction strength and range, and particulate radius. We have also considered the limit of a particulate of infinite radius, where the model becomes equivalent to a system consisting of a fluid in contact with a planar wall. We have explored the effect that the curvature of the substrate has on the wetting and drying transitions. The wetting transition in our model is very sensitive to the size of the particulate (curvature of the substrate), whereas the drying transition is essentially independent. Small particulates are less stable at the liquid–vapor interface than larger ones, and they exhibit enhanced solubility. Our results suggest that curved surfaces can be wetted more easily than planar substrates. As expected, long range attractive interactions enhance wetting, but our simulations show that this enhancement is larger in curved surfaces than in planar ones. The description of the wetting behavior of the particulates using Young’s equation breaks down for the smallest particulates considered. We have computed the line tensions for our model using a methodology introduced previously [F. Bresme and N. Quirke, Phys. Rev. Lett. 80, 3791 (1998)]. They are found to be negative and of the order of ≈10−12 N.
Direct observation of surface diffusion of large organic molecules at metal surfaces: PVBA on Pd(110)
Authors: Weckesser Jens , Barth Johannes V. , Kern Klaus
Published: July 2002

The bonding and surface diffusion of 4-trans-2-(pyrid-4-yl-vinyl) benzoic acid (PVBA) on Pd(110) was investigated by variable temperature scanning tunneling microscopy at sample temperatures between 300 and 450 K. PVBA is a large organic molecule designed for nonlinear optics applications. At low coverages single PVBA molecules are randomly distributed at the surface where they bind diagonally to three neighboring Pd-rows, leading to four equivalent adsorption configurations. The “dog-bone” molecular structure could be resolved. The molecules’ surface diffusion is strictly one-dimensional along the close-packed [11̄0]-direction of the surface Pd atomic rows and obeys an Arrhenius law with an activation barrier of 0.83±0.03 eV and an attempt frequency of 1010.3±0.4 s−1.