bluuebunny/crossref_metadata_2025 huggingface dataset:
Frictional effects on barrier crossing in solution: Comparison with the Kramers’ equation
Authors: Bowman Robert M. , Eisenthal Kenneth B. , Millar David P.
Published: July 2002

In our efforts to examine the validity of the Kramers’ equation, the rate constants of the excited state isomerization of 1,1′-binaphthyl in n-alkane solvents were measured at room temperature using picosecond spectroscopy. These data, and data measured previously in n-alcohols, were compared with Kramers’ model using two forms for the friction. When a hydrodynamic model for the friction was used, good agreement was found for the alcohol data only. When the isomerization friction is assumed to scale linearly with the friction for overall reorientational motion, we find excellent agreement for both the alcohol and alkane solvents. In addition, the friction in alkanes is found to be considerably larger than that of alcohols of comparable viscosity. This provides a direct indication that the molecular aspects of the solute–solvent interaction play a role in the barrier crossing process.
Spectroscopic characterization of the lowest singlet states of CdNe, CdAr, and CdKr
Authors: Funk David J. , Kvaran Agúst , Breckenridge W. H.
Published: July 2002

We report the characterization of the first excited singlet states of CdNe, CdAr, and CdKr, which correlate with Cd(5s5p 1P1) and the ground-state rare-gas atoms. The van der Waals molecules were created in a free jet supersonic expansion and studied by laser-induced fluorescence, dispersed fluorescence, laser pump/probe action spectra, and spectral simulations. The C 1Π1 states are found to be more strongly bound than their triplet counterparts: 116Cd20Ne (De=89 cm−1, ωe=23.36 cm−1, ωexe=1.80 cm−1, re =3.61±0.05 Å); 116Cd40Ar (De=544 cm−1, ωe=47.97 cm−1, ωexe=1.11 cm−1, re=3.28±0.05 Å); 114Cd84Kr (De=1036 cm−1, ωe=56.72 cm−1, ωexe=0.81 cm−1, Δre(C 1Π–X 1Σ+) =1.16 Å). This is attributed to spatial differences between the atomic p orbital of the singlet vs the triplet excited state of the Cd atom. The D 1Σ0+ states of CdAr and CdKr were found to be repulsive for Franck–Condon accessible internuclear distances. No production of Cd(5s5p 2PJ) states from predissociation of any C 1Π1 molecular state was observed.
Simulations of the premelting of Al(110)
Authors: Stoltze Per
Published: July 2002

The premelting of Al(110) is studied by molecular dynamics simulations using the potential for Al derived from effective medium theory. We find a progressive disordering of the surface region as the bulk melting point is approached. This disorder is mediated by the formation of adatom–vacancy pairs. Based on the calculated radial distribution function and the analytical expression for the energy, it is demonstrated that the thermodynamics of disorder and melting is reflected in the single particle properties by a decrease in the number of nearest neighbors. The Debye temperature for the surface layer as determined from the simulations is θD ∼250 K, compared to θD ∼320 K found for the deeper layers. The thickness of the surface region determined from the Debye temperature is 3–4 layers. From an examination of the properties of some order parameters, we find that the premelting appears anisotropic only for some choices of order parameter. This has implications for the detection of the disorder by a diffraction technique.
Molecular dipole moments and polarizabilities from local density functional calculations: Application to DNA base pairs
Authors: Jasien Paul G. , Fitzgerald George
Published: July 2002

First principles local density functional (LDF) calculations have been performed on a number of molecules to evaluate the use of this method in the theoretical prediction of electrical properties. Calculated dipoles and dipole polarizabilities show good agreement with both experimental and ab initio results based on second-order Mo/ller–Plesset perturbation theory (MP2) calculations. Application to DNA base pairs provides information on the degree of nonadditivity in these interactions, as well as an example of the usefulness of LDF in the calculation of the properties of large molecular systems.
Critical exponents for Anderson localization
Authors: Chang T. -M. , Bauer J. D. , Skinner J. L.
Published: July 2002

We perform numerical calculations on a simple cubic lattice for a standard diagonally disordered tight-binding Hamiltonian, whose random site energies are chosen from a Gaussian distribution with variance ∑2. From phenomenological renormalization group studies of the localization length, we determine that the critical disorder is σc≡∑c/J=6.00±0.17, which is in good agreement with previous results (J is the nearest neighbor transfer matrix element). From our calculations we can also determine the mobility edge trajectory, which appears to be analytic at the band center. Defining an order parameter exponent β, which determines how the fraction of extended states vanishes as the critical point is approached from below, this implies that β=1/2, in agreement with a previous study. From a finite-size scaling analysis we find that π2/ν=1.43±0.10, where π2 and ν are the inverse participation ratio and localization length critical exponents, respectively. This ratio of exponents can also be interpreted as the fractal dimension (also called the correlation dimension) D2 of the critical wave functions. Generalizations of the inverse participation ratio lead to a whole set of critical exponents πk, and corresponding generalized fractal dimensions Dk=πk/ν(k−1). From finite-size scaling results we find that D3=1.08±0.10 and D4=0.87±0.09. The inequality of the three dimensions D2, D3, and D4 shows that the critical wave functions have a multifractal structure. Using a generalized phenomenological renormalization technique on the participation ratios, we find that ν=0.99±0.04. This result is in agreement with experiments on compensated or amorphous doped semiconductors.
Curvature defects in lamellar phases of amphiphile–water systems
Authors: Bagdassarian Carey K. , Roux Didier , Ben-Shaul Avinoam , Gelbart William M.
Published: July 2002

Within the framework of two complementary models, we show that the densities and patterns of defects in amphiphile–water systems with lamellar organization are coupled to the strength of the bilayer–bilayer interactions and hence to the overall surfactant concentration. We consider defects which introduce curvature (i.e., larger head-group area per molecule) while preserving the integrity of stacked bilayers at surfactant volume fractions of several tenths. These features are favored if the molecules comprising the lamellae are preferentially packed with a nonplanar aggregate–water interface: curvature defects lower the local free energy in systems constrained by aggregate–aggregate interactions to lamellar geometry. As the amphiphile volume fraction is increased—and the bilayer–bilayer spacing thereby decreased—we predict phase transitions between lamellar phases of different defect patterns on the bilayer surface, with concurrent decrease in the defect area fraction per bilayer. Specifically, there is a progression from a stripe-like pattern of parallel channels to a random network of line defects to a pore phase, with the latter appearing at the highest amphiphile concentrations but characterized by the lowest density of defects. Connection is made with experimental work which has recently suggested various departures from classical lamellar structure.
Tunable far-infrared spectroscopy of malonaldehyde
Authors: Firth D. W. , Beyer K. , Dvorak M. A. , Reeve S. W. , Grushow A. , Leopold K. R.
Published: July 2002

A tunable far-infrared difference frequency spectrometer has been used to examine the fully protonated form of malonaldehyde in the region near the ground-state tunneling frequency (21 cm−1). An extremely dense and complex spectrum is observed in which the strongest features have been assigned as pure rotational lines involving high values of J and K−1. These transitions, which occur within the individual rotational manifolds of the two halves of the ground-state tunneling doublet, have been analyzed simultaneously with existing microwave data for this species. The value of the ground-state tunneling splitting, determinable indirectly from analysis of vibration–rotation interactions, is 21.584 76(17) cm−1, and is in close agreement with that similarly obtained in previous microwave work. A thorough treatment of the centrifugal distortion in this system significantly extends the range of rotational states whose energies may be reliably calculated, and should therefore be valuable in the future direct measurement of the tunneling frequency. Aspects of the far-infrared spectrum of this species, and of the indirect method of determining the tunneling splitting, are discussed.
Single-mode fibers in fiber-optic quasielastic light scattering: A study of the dynamics of concentrated latex dispersions
Authors: Wiese H. , Horn D.
Published: July 2002

The concentration dependence (range 1–40 %) of the dynamics of monodisperse polymer latex dispersions (particle diameters 41–326 nm) is studied by fiber-optic quasielastic light scattering (FOQELS). The experiments reveal that despite the high turbidity of the samples multiple light scattering has negligible influence on the data when single-mode fibers are employed. This is explained by the diameter of the single-mode fiber core being much smaller than the scattering mean free paths in the dispersions. It is further shown that the autocorrelation functions can be interpreted in terms of the dynamic structure factor of the dispersions. When the particle diameter is raised from 41 to 326 nm the data show that FOQELS probes mutual diffusion for the smaller particles and self-diffusion for the larger ones.
Temperature dependence of vibrational relaxation processes in sulfur crystals: Effect of isotopic impurities
Authors: Becucci Maurizio , Castellucci Emilio , Foggi Paolo , Califano Salvatore , Dows David A.
Published: July 2002

We have studied phonon relaxation processes in orthorhombic sulfur crystals, for several lattice and internal vibrations. Bandwidths were measured as a function of temperature using a tandem Fabry–Perot spectrometer instrument with a limiting resolution of 0.001 cm−1. In order to obtain a basis for the study of the effect of isotopic impurities, we have grown single crystals of isotopically pure 32S. We have measured the bandwidths of six lattice phonons and eight internal vibrons. For most of the bands the width showed a linear variation with temperature in the classical regime, and in these cases we have interpreted the widths in terms of three-phonon decay processes. In some cases, however, a nonlinear temperature variation was observed, which we interpreted in terms of four-phonon and pure dephasing mechanisms. We have measured the widths of the same phonons and vibrons in single crystals of natural sulfur, which contains 4.2% 34S. The widths are in many instances larger when the impurity is present, and the increase is temperature-dependent. This difference is interpreted as being the sum of two contributions. One is temperature-independent, and reflects the simple scattering process, controlled by a harmonic term in the Hamiltonian, in which a phonon is dephased within its own dispersion curve. The second contribution is temperature-dependent, and is interpreted as being due to the same anharmonic processes observed in the pure crystal, scaled by a factor which takes into account the coupling of resonant scattering and anharmonic relaxation processes.
Singly ionized first-row dimers and hydrides calculated with the fully-numerical density-functional program n
u
m
o
l
Authors: Merkle R. , Savin A. , Preuss H.
Published: July 2002

Gradient corrected density functionals yield average errors in the ionization potentials of 0.3–0.8 eV. The average errors in the dissociation energies of the diatomic cations are similar to the corresponding errors of the neutral molecules, i.e., 0.2–0.6 eV. The wrong behavior of the potential curves of the dimer cations at large distances calculated with these functionals does not affect the accuracy of De.
Probing the molecule–surface interaction via inversion symmetry changes in the scattering of state-selected ND3 on graphite (0001)
Authors: Ionov Stanislav I. , LaVilla Michael E.
Published: July 2002

By employing rotationally state-selected ND3 molecular beams, ‖JKMε≳‖inversion≳ =‖1111≳‖−≳, and REMPI detection, it is found that there is a propensity for inversion symmetry change from antisymmetric to symmetric states, ‖−≳ to ‖+≳, as compared to antisymmetric to antisymmetric states, ‖−≳ to ‖−≳, in the scattering of ND3 on a graphite (0001) surface at 130 K. The total probability of inversion symmetry change summed over the post-collisional rotational states is measured as a function of translational energy. We demonstrate that the observed effect is due to molecular self-diffraction on the surface and that it may serve as a new way to probe the molecule–surface interaction. Relying on the infinite order sudden approximation [Gerber et al., J. Chem. Phys. 73, 4397 (1980)], we suggest a procedure for inverting an approximate, corrugation-averaged molecule–surface interaction potential from experimental data on molecular self-diffraction; measurements of the probability of inversion symmetry change for different incident rotational states as a function of translational energy are required. Since we do not possess sufficient experimental data for a full-fledged analysis, computer simulations of the observed energy dependence are carried out with model interaction potentials.
Molecular ordering of organosulfur compounds on Au(111) and Au(100): Adsorption from solution and in ultrahigh vacuum
Authors: Dubois Lawrence H. , Zegarski Bernard R. , Nuzzo Ralph G.
Published: July 2002

Low-energy electron diffraction and reflection-absorption infrared spectroscopy were used to study the monolayers formed by the adsorption of n-alkane thiols [HS(CH2)mCH3] on both (111) and (100) single-crystal gold substrates. Samples were prepared by dosing either from solution (m=15, 17, 18, and 21) or in ultrahigh vacuum (m=0–9). On Au(111), ordered surface structures are obtained which can be indexed as (n√3×√3)R30°, where n varies from 1 to 6. On Au(100), the adsorption of short chain thiols leads to the formation of a c(2×2) overlayer while the longer chain homologs show additional diffraction spot splittings. It is also found that chain length influences both the character of the diffraction seen and perturbs the reactive sticking probability of molecules dosed in UHV. Infrared studies reveal that the polymethylene chains of the monolayers formed on Au(100) are comprised of nearly all-trans conformations and are less canted than the comparable structures formed on Au(111). A simple model is proposed to account for the differences seen on the two surfaces and a mechanism for the adsorption and assembly of organic thiols into ordered monolayer phases on gold is presented.
Excitation function for H+O2 reaction: A study of zero-point energy effects and rotational distributions in trajectory calculations
Authors: Varandas A. J. C.
Published: July 2002

The excitation function of the H+O2 (v=0)→OH+O reaction has been determined from trajectory calculations using the HO2 DMBE IV potential energy surface. Reactive cross sections for thirteen translational energies, corresponding to a total of a quarter of a million trajectories, have been computed covering the range 65≤Etr/kJ mol−1≤550. Various schemes for analyzing the trajectories, three of which aim to correct approximately for the zero-point energy problem of classical dynamics, have been investigated. One of these schemes aims to correct also for known requirements on rotational distributions, e.g., for the fact that by Hund’s rules for the coupling of angular momentum the product OH (2Π) molecule always rotates. It has been found that zero-point energy effects and lowest-J constraints on rotational distributions may have a crucial role, especially close to the threshold energy of reaction. Agreement with recent measurements of absolute reactive cross sections is generally satisfactory but, unlike experiment, no sharp maximum is found on the excitation function in the vicinity of Etr=170 kJ mol−1. Possible reasons for this discrepancy are discussed. There is also good agreement with existing experimental data on the products rotational distribution.
Femtosecond wave packet and chemical reaction dynamics of iodine in solution: Tunable probe study of motion along the reaction coordinate
Authors: Scherer Norbert F. , Jonas David M. , Fleming Graham R.
Published: July 2002

One- and two-color time-domain probing of the resonant dichroic response of iodine in n-hexane following femtosecond B-X excitation at 580 nm is described. The detected signals contain both ground and excited state vibrational coherence contributions to the third-order polarization. The dichroic response can be separated into positive and negative amplitude contributions: B-X absorption and stimulated emission are positive but absorption from the B-state can yield either positive or negative signals depending on the direction of the transition moment. Wave packet motion on both the ground and excited states of iodine is studied with a frequency tunable femtosecond probe. It is shown that the positive signals can be interpreted as B-X dichroic response using the classical Franck principle. The classical Franck principle also provides information about the potential probed in absorption from the B state. From the probe wavelength dependent delay in the signal appearance, it is concluded that the absorptive signal for blue probe wavelengths arises from a repulsive state reached by solvent-induced predissociation of the B state. Dephasing of B state vibrational coherence results from this solvent-induced predissociation of iodine. We discuss the evolving reaction in terms of possible dissociative potential energy curves a1g(3Π) and a′0g+(3Σ−). The time evolution of the bluest probe dichroism signals is representative of continuing atom separation; the experiments have not yet probed large enough internuclear separations to evidence a buildup of dissociated product or momentum reversal, i.e., caging.
Laser cooling of molecular internal degrees of freedom by a series of shaped pulses
Authors: Bartana Allon , Kosloff Ronnie , Tannor David J.
Published: July 2002

Laser cooling of the vibrational motion of a molecule is investigated. The scheme is demonstrated for cooling the vibrational motion on the ground electronic surface of HBr. The radiation drives the excess energy into the excited electronic surface serving as a heat sink. Thermodynamic analysis shows that this cooling mechanism is analogous to a synchronous heat pump where the radiation supplies the power required to extract the heat out of the system. In the demonstration the flow of energy and population from one surface to the other is analyzed and compared to the power consumption from the radiation field. The analysis of the flows shows that the phase of the radiation becomes the active control parameter which promotes the transfer of one quantity and stops the transfer of another. In the cooling process the transfer of energy is promoted simultaneously with the stopping population transfer. The cooling process is defined by the entropy reduction of the ensemble. An analysis based on the second law of thermodynamics shows that the entropy reduction on the ground surface is more than compensated for by the increase in the entropy in the excited surface. It is found that the rate of cooling reduces to zero when the state of the system approaches an energy eigenstate and is therefore a generalization of the third law of thermodynamics. The cooling process is modeled numerically for the HBr molecule by a direct solution of the Liouville von Neuman equation. The density operator is expanded using a Fourier basis. The propagation is done by a polynomial approximation of the evolution operator. A study of the influence of dissipation on the cooling process concludes that the loss of phase coherence between the ground and excited surface will stop the process.
Capillary condensation of helium in narrow slit pores
Authors: Cheng E. , Swift M. R. , Cole M. W.
Published: July 2002

We study the capillary condensation of liquid 4He films inside narrow slit pores with a density functional model and compare the result to the predictions of the Kelvin equation. Our investigation, in the wetting situation, indicates that pores with sizes up to 100 Å are still too small for the macroscopic thermodynamic arguments used to derive the Kelvin equation to be successful. The discrepancy is tentatively attributed to the use of a slab-density model and bulk parameters in the region of very thin films.
Dynamical structure of water in aqueous electrolyte solutions by low-frequency Raman scattering
Authors: Wang Yan , Tominaga Yasunori
Published: July 2002

Depolarized low-frequency Raman spectra of aqueous electrolyte solutions (ACl and BCl2; A=Li, Na, K, Rb and B=Mg, Ca) in the frequency region from −250 to 250 cm−1 have been investigated over a wide concentration range. The spectra were analyzed with one Cole–Cole type relaxation mode and two damped harmonic oscillators. A broad relaxation mode was found below 20 cm−1. For the present aqueous electrolyte solutions, with increasing salt concentration each relaxation time τ becomes longer than that of liquid water τwater. The relaxation time is considered to correspond to the duration time of the tetrahedral structure of bulk water. We have found that the concentration dependence of the ratio τ/τwater is equivalent to the ratio η/ηwater, where η is the viscosity of aqueous solutions.
Ozone photodissociation in the Hartley band: A statistical description of the ground state decomposition channel O2(X 3Σ−g)+O(3P)
Authors: Svanberg Marcus , Pettersson Jan B. C. , Murtagh Donal
Published: July 2002

Ozone photodissociation in the Hartley band O3+hν→O(3P)+O2(X 3Σ−g) is simulated with a statistical model. In the model, energy is partitioned at a decoupling distance which is located at a position with nonzero potential energy on a repulsive and dissociative potential energy surface. Introduction of the repulsive potential on which dissociation takes place, and the choice of decoupling distance is shown to be of crucial importance for the final energy distributions, and in particular it determines the amount of energy left in translation. The model is shown to give good agreement with experimental vibrational and translational energy distributions, while the rotational distributions predicted by the model seem less peaked than experimental data. Vibrational state distributions are calculated for different dissociation wavelengths in the Hartley band (200–310 nm), and they are concluded to deviate substantially from distributions previously used in atmospheric modeling. The statistical approach is compared to impulsive and statistical models, and also related to recent quantum mechanical calculations.
Observation of characteristic, polarity-dependent, Doppler shifts from neutral species in the positive column of a discharge plasma
Authors: Hong Xichun , Miller Terry A.
Published: July 2002

Doppler shifts of emissions from neutral species have been observed for the first time in a positive column of a dc glow discharge. For a detailed study, we have chosen emissions of H2 and its isotopomers in a hydrogen discharge using a high resolution Fourier-transform spectrometer. Experimetal evidence supports the conclusion that the observed shifts derive from momentum transfer during electron-molecule collisions that produce the emissive excited states. A theoretical model has been formulated to relate Doppler shifts to the drift velocity of electrons in the discharge as well as to the momentum transfer of electron-molecule collisions. Predictions based on the model are consistent with the experimental observations.
Photodissociation of ozone in the Hartley band: Fluctuation of the vibrational state distribution in the O2(1Δg) fragment
Authors: Thelen M.-A. , Gejo T. , Harrison J. A. , Huber J. Robert
Published: July 2002

The photodissociation of O3 in the Hartley band has been investigated by high-resolution photofragment translational spectroscopy (PTS). At λdiss=248 nm we determined the quantum yield of the dominant decay channel leading to O2(1Δg)+O(1D) and the fragment vibrational state distribution. The fragment recoil anisotropy (β=1.25±0.15) was found to be independent of the fragment vibrational states. Between λdiss=275 and 295 nm β assumes a value of 1.6±0.2, which exceeds the value expected for a simple impulsive process. Photofragment yield measurements carried out by PTS between 272 and 286 nm revealed a strong fluctuation of the vibrational state distribution with λdiss. Based on the small but distinct structure superimposed on the broad continuum of the Hartley band and the findings of recent 3D wave packet calculations, we propose this fluctuation, a manifestation of wavelength-dependent partial cross sections, to arise predominantly from an interference effect. The latter occurs between the part of the initially prepared wavepacket which propagates directly into the exit channel and a (minor) part which is temporarily trapped by the motion of the bending and symmetric stretching modes in the excited O3 molecule.
Fourier transform infrared observation of the ν7 stretching mode of linear C9 in Ar at 10 K
Authors: Kranze R. H. , Withey P. A. , Rittby C. M. L. , Graham W. R. M.
Published: July 2002

A second stretching fundamental ν7(σu), of the linear C9 carbon cluster has been observed for the first time at 1601.0 cm−1 by means of a Fourier transform infrared investigation of the products of the evaporation of graphite trapped in solid Ar at ∼10 K. Comparison of the measured isotopic shifts of the single 13C and single 12C isotopomers with the predictions of new density functional theory and coupled cluster ab initio calculations carried out as part of this study, conclusively confirms the assignment of the new mode.
The nondestructive detection of the helium dimer and trimer
Authors: Schöllkopf Wieland , Toennies J. Peter
Published: July 2002

A transmission grating is used to nondestructively analyze a low source temperature (6–60 K) beam of helium for small clusters. He2 and He3 are clearly resolved in first order diffraction. The relative ionization and fragmentation probabilities are measured and lend support to a recent mass spectrometer experiment claiming detection of He2.
Recovering a full dimensional quantum rate constant from a reduced dimensionality calculation: Application to the OH+CO→H+CO2 reaction
Authors: Dzegilenko Fedor N. , Bowman Joel M.
Published: July 2002

Two reduced dimensionality theories are used to calculate the thermal rate constant for the OH+CO→H+CO2 reaction. The standard theory employs energy-shift approximations to extract the full six degree-of-freedom quantum rate constant for this reaction from the previous two degree-of-freedom (2-DOF) quantum calculations of Hernandez and Clary [M.I. Hernandez and D.C. Clary, J. Chem. Phys. 101, 2779 (1994)]. Three extra bending modes and one extra ‘‘spectator’’ CO stretch mode are treated adiabatically in the harmonic fashion. The parameters of the exit channel transition state are used to evaluate the frequencies of those additional modes. A new reduced dimensionality theory is also applied to this reaction. This theory explicitly addresses the finding from the 2-DOF calculations that the reaction proceeds mainly via complex formation. A J-shifting approximation has been used to take into account the initial states with non-zero values of total angular momentum in both reduced dimensionality theories. Cumulative reaction probabilities and thermal rate constants are calculated and compared with the previous quasiclassical and reduced dimensionality quantum calculations and with experiment. The rate constant from the new reduced dimensionality theory is between a factor of 5 and 100 times smaller than the statistical transition state theory result, and is in much better agreement with experiment.
Geometric phase effects in the resonance spectrum, state-to-state transition probabilities and bound state spectrum of HO2
Authors: Kendrick Brian , Pack Russell T
Published: July 2002

The general vector potential (gauge theory) approach for including geometric phase effects in accurate 3D quantum scattering calculations in hyperspherical coordinates is applied to low-energy H+O2 collisions using our new more accurate DIM (Diatomics In Molecules) potential energy surface. The newly developed hybrid DVR/FBR (Discrete Variable Representation/Finite Basis Representation) numerical technique is used to include geometric phase effects due to the C2v conical intersection in HO2. The scattering results for zero total angular momentum (J=0) computed both with and without the geometric phase show significant differences in the resonance energies and lifetimes. Significant differences in the state-to-state transition probabilities are also observed. The results indicate that geometric phase effects must be included for H+O2 scattering even at low energies. All 249 vibrational energies of HO2(2A′′) (J=0) are computed both with and without the geometric phase. Due to the localized nature of the bound state wavefunctions, no geometric phase effects are observed in the vibrational energies even in the high-lying states near dissociation.
Scaling of the interfacial tension of microemulsions: A Landau theory approach
Authors: Leitão H. , Telo da Gama M. M. , Strey R.
Published: July 2002

We have calculated the structure and the interfacial tension of microemulsions on the phase inversion path, using a single-order parameter Landau theory. We show that the observed scaling behavior of the interfacial tensions [T. Sottmann and R. Strey, J. Chem. Phys. 106, 8606 (1997)] is described by a simple theoretical model based on the assumption that the ratio of the length scales characterizing microemulsions is a universal function of the reduced temperature, on the phase inversion path. This assumption is based on the results of small angle neutron scattering experiments on this series of systems, at the optimal microemulsion temperature [T. Sottman, R. Strey, and S.-H. Chen, J. Chem. Phys. 106, 6483 (1997)] and on the scaling properties of the Landau free energy on the phase inversion path.
Collisional removal of O2(b 1Σg+,v=1,2) by O2, N2, and CO2
Authors: Bloemink Hannelore I. , Copeland Richard A. , Slanger Tom G.
Published: July 2002

A state-specific two-laser technique is used to investigate the collisional removal of O2 molecules in the b 1Σg+(v=1,2) levels, where we directly excite O2 and then probe the populations by resonance-enhanced multiphoton ionization. We find general agreement with earlier 300 K values for v=1 removal by O2, and show that v=2 removal is slower by a factor of 5.6±0.6 than v=1 removal. Only upper limits are obtained for N2 as a collider. For removal of v=1 in the atmosphere, N2 is unimportant compared to O2, but it might be competitive for v=2. For CO2 as a collider, addressing O2(b 1Σg+) removal in the atmospheres of Mars and Venus, the removal rate coefficients of the vibrationally-excited levels are similar to that for v=0. The significance of the large difference in the v=1 and v=2 rate coefficients for O2 collisions will be discussed as it relates to the modeling of recent earth nightglow observations.
Screening and asymptotic decay of pair distributions in asymmetric electrolytes
Authors: Ulander Johan , Kjellander Roland
Published: July 2002

An accurate description of the screening behavior of asymmetric binary electrolyte solutions is obtained by applying the dressed ion theory to acquire the three leading terms in the asymptotic decay of the radial pair distribution function gij(r) at large distances r. These terms give a surprisingly good representation of the distribution function for quite small r values. A minimum of two asymptotic terms are needed for representing gij(r) at moderately large r in a quite wide concentration range. The relationships between the large r asymptotic behavior of charge–charge, density–density, and charge–density correlations are investigated by means of the dressed ion distribution functions. The role that the dielectric response function of the electrolyte plays for the asymptotic behavior is illuminated and the relationship between this function and the dressed ion charge distributions is given. Ionic effective charges, effective permittivities, and decay lengths and their higher order analogues are calculated for 1:2 electrolytes using the hypernetted chain approximation.
Extensions to quantum optimal control algorithms and applications to special problems in state selective molecular dynamics
Authors: Sundermann Karsten , de Vivie-Riedle Regina
Published: July 2002

We present an implementation of an additional cost in the functional of the recently published iteration methods for quantum optimal control [W. Zhu, J. Botina, and H. Rabitz, J. Chem. Phys. 108, 1953 (1998)] to design optimal laser pulses for population transfer. The additional criterion takes into account the asymptotic switch on and off behavior of experimentally generated laser pulses. Exemplarily, a specially adapted windowed Fourier transform is applied to decompose a complex, highly nonintuitive optimal laser field in a sequence of subpulses to provide laser pulse parameters as helpful information for experimental reconstruction. Numerical calculations for three typical spectroscopic excitation mechanisms show that laser fields obtained with the new functional signify a step towards experimental feasibility.
Effect of solvent fluctuation on the electronic transitions of formaldehyde in aqueous solution
Authors: Naka Kazunari , Morita Akihiro , Kato Shigeki
Published: July 2002

The absorption spectra of nπ* and ππ* transitions in formaldehyde aqueous solution were studied by the reference interaction site model self-consistent-field (RISM-SCF) method. The electrostatic potential fluctuations acting on the solute sites originating from the solvent fluctuations were obtained by calculating the derivative of the solute-solvent radial distribution function analytically, and these were utilized to estimate the spectral bandwidths. The contribution from the solute vibrations was also examined. As a result, a blue shift of 1998 with bandwidth of 2987 cm−1 was obtained for the nπ* transition. The ππ* transition, on the other hand, showed a redshift of 1598 with the bandwidth of 5474 cm−1. The solvent fluctuation effect contributes to the bandwidths by 617 and 137 cm−1 for the nπ* and ππ* transition, respectively. We further analyzed the simulated absorption band shapes using effective charges on the atoms and the charge response kernel calculated for each state.
Levitation effect and its relationship with the underlying potential energy landscape
Authors: Rajappa Chitra , Yashonath Subramanian
Published: July 2002

Positions of potential energy minima for spherical monatomic sorbates in zeolite NaY have been identified for different sizes of the sorbate. It is found that for small sorbates (σ⩽4.96 Å) there are only six adsorption sites per α-cage, which are located close to the inner surface of the α-cage. For larger sorbates, additional sites of comparable energies appear close to the 12-ring window which forms the bottleneck for intercage diffusion. Minimum energy paths between these sites have been computed. These suggest that the barriers for both intracage and intercage site-to-site migrations are comparable and decrease with increase in sorbate size. Earlier simulation studies on the diffusion of monatomic sorbates in zeolites indicated that there is a dramatic change in the nature of dependence of D on sorbate size around 4.96 Å, for zeolite NaY. Therefore, the present results suggest that the dependence of D on sorbate size and the changes in the potential energy landscape are correlated. The sorbate–zeolite system is characterized by a flatter potential energy landscape when the sorbate size is large.
Multiple-collision induced dissociation of trapped silver clusters Agn+ (2⩽n⩽25)
Authors: Krückeberg S. , Dietrich G. , Lützenkirchen K. , Schweikhard L. , Walther C. , Ziegler J.
Published: July 2002

The dissociation energies of singly charged silver cluster cations, Agn+ (2⩽n⩽25), are determined by multiple-collision induced dissociation (MCID) in a Penning trap. The fragment yield is analyzed in terms of a linearized impulsive collision theory for the energy transfer in the multicollisional process and the delayed decay as predicted by the Rice–Ramsperger–Kassel (RRK) model. Previous photofragmentation experiments performed in the size range (9⩽n⩽21) are found to be in good agreement with the present results. Theoretical predictions agree for most clusters sizes.
Free energy of embryo formation for heterogeneous multicomponent nucleation
Authors: Gorbunov B.
Published: July 2002

An approach for calculating the free energy of embryo formation for multicomponent heterogeneous nucleation has been developed. The approach is based on a differential version of the capillarity approximation. It is considered that a liquid droplet is formed due to the deposition of several gaseous compounds onto a nucleus containing a spherical insoluble core and nonvolatile soluble substances. The approach links interfacial free energies of the surfaces, the size of the insoluble core, and chemical characteristics of the substances with the free energy of the embryo formation. The free energy of embryo formation as well as the critical supersaturation are influenced by the ratios of the Henry’s Law constants to the partial pressures of the species. Multicomponent nucleation with a dominant species can be described as a quasibinary nucleation of the dominant species and a virtual species. As an example, the free energy in a binary system of water and acid is considered. It is shown that water+acid nucleation on such nuclei is influenced by the acid, soluble nonvolatile compounds and insoluble substances.
Electronic spectra of carbon chain anions: C2nH− (n=5–12)
Authors: Kirkwood D. A. , Tulej M. , Pachkov M. V. , Schnaiter M. , Güthe F. , Grutter M. , Wyss M. , Maier J. P. , Fischer G.
Published: July 2002

The electronic absorption spectra of mono-hydrogenated carbon chain anions C2nH− (n=5–10) have been measured in the gas-phase and in 6 K neon matrices (n=8–12). The techniques of resonant two-color electron photodetachment in the gas-phase and absorption spectroscopy of mass-selected anions in neon matrix were used. A homologous series is observed, with band system origins shifting from 304 nm for C10H− to 590 nm for C20H−. In conjunction with ab initio calculations the band systems are attributed to a Σ+1←X 1Σ+ transition of linear acetylenic anions. Another near lying electronic transition due to a second isomer is also apparent for C10H− up to C24H−. Comparison with tables of the known diffuse interstellar bands indicates possible matches for the origin bands of the C18H− and C20H− isomers.
Density dependence of solvation properties in polar dumbbell fluids from gaseous to liquid densities
Authors: Takebayashi Y. , Kimura Y. , Ohba M.
Published: July 2002

The solvent density dependence of the solvation energy difference associated with a charge transfer process in a polar dumbbell fluid is studied from the gaslike to the liquidlike densities by means of two types of the integral equation theories and the Monte Carlo simulation. The polar dumbbell fluid model including the Coulombic interaction explicitly has succeeded in a qualitative reproduction of quite a larger density dependence of the solvation energy in the low-density region than that in the higher-density region. The origin of the density dependence has been attributed to the difference in the reaction field response at various densities. At the low density, the reaction field shows a highly enhanced nonlinear response to the solute dipole moment. The nonlinear enhancement is an intrinsic nature in the gaseous dielectric solvation, and is due to the enhanced local density around the solute molecule with increasing the solute charge. On the other hand, the reaction field at the high density responds almost linearly to the solute dipole moment. The analysis based on the integral equation has clarified that the high linearity at the liquid density is closely related to the invariance of the radial distribution between cores in spite of the charging on the solute, which reflects the highly packed structure at the high density. When the solute dipole moment is quite large, we observe the dielectric saturation at the high density, where the enhanced local density around the solute does not result in the increase of the reaction field because of the saturation in the orientational correlation between the solute and solvent dipoles. Even when the solute dipole moment is small enough not to cause the nonlinear response, the reaction field is induced nonlinearly to the solvent density, which is interpreted not only by the local density but also by the contribution per solvent molecule at various densities. This study demonstrates that the following two properties often neglected so far have significant effect on the evaluation of the solvation energy difference at various densities: one is the nonlinearly enhanced field response at the gaseous density, and the other is the density variation of the reaction field induced per solvent molecule.
Double-resonance overtone photofragment spectroscopy of trans-HONO. I. Spectroscopy and intramolecular dynamics
Authors: Reiche F. , Abel B. , Beck R. D. , Rizzo T. R.
Published: July 2002

Using the technique of double-resonance overtone photofragment spectroscopy (DROPS), we have measured rotationally resolved vibrational overtone transitions to the previously unobserved 5v1, 6v1, and 7v1 levels of gas-phase trans-nitrous acid (HONO) in its electronic ground state. Observing the onset of dissociation from different rovibrational states of 5v1 near threshold determines the HO–NO bond energy to be D0=16 772±14 cm−1. Observed spectral splittings and broadening of individual rovibrational transitions provide quantitative data on the rate and extent of collision free vibrational energy redistribution that would result after coherent ultrashort pulse excitation. In parallel with these frequency domain measurements, we determine the unimolecular dissociation rates directly in time for trans-HONO molecules excited to several rotational states near threshold. The combination of time- and frequency-resolved data allows us to estimate the linewidth contributions from the finite dissociation lifetime of the molecule. Our results reveal intramolecular dynamics that are clearly not a simple function of the vibrational energy but rather depend sensitively upon specific couplings and, in turn, on the vibrational character of the individual states excited.
Quantum wave packet dynamics with trajectories: Implementation with distributed approximating functionals
Authors: Wyatt Robert E. , Kouri Donald J. , Hoffman David K.
Published: July 2002

The quantum trajectory method (QTM) was recently developed to solve the hydrodynamic equations of motion in the Lagrangian, moving-with-the-fluid, picture. In this approach, trajectories are integrated for N fluid elements (particles) moving under the influence of both the force from the potential surface and from the quantum potential. In this study, distributed approximating functionals (DAFs) are used on a uniform grid to compute the necessary derivatives in the equations of motion. Transformations between the physical grid where the particle coordinates are defined and the uniform grid are handled through a Jacobian, which is also computed using DAFs. A difficult problem associated with computing derivatives on finite grids is the edge problem. This is handled effectively by using DAFs within a least squares approach to extrapolate from the known function region into the neighboring regions. The QTM–DAF is then applied to wave packet transmission through a one-dimensional Eckart potential. Emphasis is placed upon computation of the transmitted density and wave function. A problem that develops when part of the wave packet reflects back into the reactant region is avoided in this study by introducing a potential ramp to sweep the reflected particles away from the barrier region.
Ab initiostudy of the electron-spin magnetic moments (g-factors) of C2−, CSi−, Si2−, LiC2, NaC2, and LiSi2
Authors: Bruna Pablo J. , Grein Friedrich
Published: July 2002

The electron-spin g-shifts of the title radicals are calculated using second-order perturbation theory, a Breit–Pauli Hamiltonian, and multireference configuration interaction (MRCI) wave functions. The isotropic 〈Δg〉 values (Δg=g−ge) are −830 for C2−(X2Σg+),−6515 for CSi−(X2Σ+), and −7595 for Si2−(12Σg+), in ppm, with ppm=10−6. For the X1A1 ground states of LiC2, NaC2, and LiSi2, they are −315, −290, and −7770 ppm, respectively. Experimental 〈Δg〉 values in Ar matrices, 3900 ppm for LiC2 and 3535 ppm for NaC2, do not agree with calculated results. However, those predicted for the π-type 12B1 excited state of LiC2 and NaC2 (3415 and 3635 ppm, with large parallel components of 9185 ppm for LiC2, and 10 350 ppm for NaC2) are in good agreement with the measured data. Thus, it appears that LiC2 and NaC2 were experimentally prepared, and their ESR spectra measured, in their lowest excited state 12B1. For the 12B1 state of LiSi2, 〈Δg〉 is about 9820 ppm. The latter value is mainly determined by a large g∥-shift of about 28 000 ppm.
A multitype random sequential process
Authors: Mellein B. , Mola E. E.
Published: July 2002

A random sequential process (RSP) can be formulated in two different ways: (I) A linear array of n identical compartments is ceaselessly bombarded by particles which occupy β( β≥2) contiguous lattice sites. These so-called β-bell particles are assumed to make contact in a spatially random manner and to stick only if striking β (adjacent) vacant compartments. (II) A linear array of n identical compartments is sequentially filled by β-bell particles, the occupation process being ‘‘selective,’’ i.e., always being directed to vacant sequences of compartments of lengths at least β. Dynamics of RSP’s has always been formulated in either way and in the case of lattice spaces all the efforts have been addressed so far to allow in the space filling process just one kind of particle. The aim of this paper is to remove that restriction and to consider a lattice space filling problem with various kinds of particles involved. The situations of the two above-described models, making no difference in the one-type case, become distinct in the multitype case. In this paper we will be concerned with the generalization of model II.
Canonical partition function for the hydrogen atom via the Coulomb propagator
Authors: Blinder S. M.
Published: July 2002

The electronic partition function for the hydrogen atom is derived by integration over the recently-available Coulomb propagator. This provides a resolution to an old paradox in statistical mechanics: the apparent divergence of the hydrogen partition function. Electronic excitation does not contribute significantly to the standard-state partition function until temperatures of the order of 5000 K. Thereafter, the continuum, with its immense density of states, makes the dominant contribution. From the discrete and continuum contributions to the partition function, a modification of the Saha–Boltzmann equation for the ionization equilibrium in atomic hydrogen is derived.
Light deflection in Kaluza–Klein gravity
Authors: Lim Paul H. , Overduin J. M. , Wesson Paul S.
Published: July 2002

When general relativity is extended from four to five dimensions, as in the theory of Kaluza and Klein, the relations for the classical tests are modified. The light-deflection problem shows a particularly interesting modification. We derive the general expression for light deflection by a massive body in the five-dimensional theory, and show that it can lead to significantly reduced deflection angles.