bluuebunny/crossref_metadata_2025 huggingface dataset:
Oscillatory shear induced anisotropic domain growth and related rheological properties of binary mixtures
Authors: Qiu Feng , Zhang Hongdong , Yang Yuliang
Published: July 2002

Numerical simulation based on the modified time-dependent Ginzburg–Landau (TDGL) model has been performed on the domain growth and related rheological properties of binary mixtures under oscillatory shear. The simulation results reveal that the domain growth is anisotropic and depends on the quench depth. It is found that, in the deep quench case, the disclike domain with the normal parallel to the velocity gradient direction is observed, while in the shallow quench case, the rodlike domain with rod axis aligned along the flow direction is observed. The scattering functions for different light incident directions are calculated and suggest that the undulated rodlike morphology is formed in the shallow quench case. This undulated rodlike morphology shows the anomalous rheological response. A plausible interpretation for the anomalous rheological property is proposed based on the deformation of the undulated rodlike morphology under oscillatory shear.
Elastic constants from a microscopic model of bilayer membrane
Authors: Chacón E. , Somoza A. M. , Tarazona P.
Published: July 2002

A simple microscopic model for amphiphilic molecules dissolved in water allows us to obtain within the same scheme the molecular structure of membranes and micelles, the equilibrium thermodynamics for these aggregates and the elastic constants of the membranes. We present a study of vesicles with cylindrical geometry which, joined to previous results for spherical vesicles, gives the saddle-splay modulus and the bending rigidity. Finally, the constraint on the exchange of molecules between the inner and the outer monolayers is included in the model, calculating the nonlocal bending curvature.
Geminate recombination and vibrational relaxation dynamics of aqueous chlorine dioxide: A time-resolved resonance Raman study
Authors: Hayes Sophia C. , Philpott Matthew J. , Reid Philip J.
Published: July 2002

The photochemical dynamics of aqueous chlorine dioxide (OClO) are investigated using time-resolved resonance Raman spectroscopy. Stokes and anti-Stokes spectra are measured as a function of time following photoexcitation of OClO using degenerate pump and probe wavelengths at 390 nm. The temporal evolution of OClO Stokes intensity is found to be consistent with the reformation of ground-state OClO by subpicosecond geminate recombination of the primary ClO and O photofragments. Anti-Stokes intensity is observed for transitions corresponding to the symmetric stretch of OClO demonstrating that upon geminate recombination, excess vibrational energy is deposited along this coordinate. Dissipation of this energy to the surrounding solvent occurs with a time constant of ∼9 ps. Finally, a delay in the appearance of OClO anti-Stokes intensity relative to geminate recombination is observed demonstrating that the excess vibrational energy available to OClO is initially deposited along the resonance Raman inactive asymmetric stretch coordinate with the exchange of energy between this coordinate and the symmetric stretch occurring with a time-constant of ∼5 ps.
Rigid particles in an elastic polymer network: An electrical-analog approach
Authors: Allegra Giuseppe , Raos Guido
Published: July 2002

Within the Gaussian phantom-chain model of a polymer network, we demonstrate and apply the formal analogy between the problem of computing the force constants acting on a set of rigid filler particles and that of computing the capacity of a system of conductors in a dielectric medium. We find that a single spherical particle undergoes a mean-square displacement 〈(ΔX)2〉 from its equilibrium position which is inversely proportional to its radius R. It is thus subject to an isotropic harmonic potential with force constant [3kBT/〈(ΔX)2〉]∝R. Quantitative evaluation of the proportionality constant for typical unswollen networks shows that 〈(ΔX)2〉/R decreases from 10−1 to 10−5 as R increases from 10 nm to 1 μm. The time scale of these fluctuations is independent of R and falls in the range 10−4–101 s. The fluctuations of two neighboring particles are not additive. A distance-dependent “stiffening” of the network is demonstrated through the calculation of the appropriate response and force constant matrices.
Structural and thermodynamic properties of fluid carbon dioxide from a new ab initio potential energy surface
Authors: Steinebrunner Gerold , Dyson Anthony J. , Kirchner Barbara , Huber Hanspeter
Published: July 2002

An intermolecular potential energy surface for the carbon dioxide dimer is calculated fully ab initio using a large basis set and including electron correlation. From this potential the dimer structure and the second virial coefficients are determined. In addition, it is applied in molecular dynamics simulations to obtain the fluid structure, the pressure, the internal energy, the thermal pressure coefficient, and the molar heat at constant volume. The results are compared with those from simulations with a previous ab initio potential. In this way we gain information regarding the sensitivity of each property to the quality of the quantum chemically obtained potential. Equilibration of carbon dioxide simulations must be done with great care due to the very slow energy transfer between the intramolecular vibrations and the other degrees of freedom. This point is addressed in some detail.
A semiclassical approximation model for properties of molecules in solution
Authors: Luo Yi , Norman Patrick , Ågren Hans
Published: July 2002

We propose a simple semiclassical approximation model for frequency-independent properties of molecules in solution using the cavity/dielectric approach. The model is applied to test systems comprising nonpolar, polar, and charged solutes, and is compared with the perturbation expansion method and the self-consistent reaction field theory method. Considering the simplicity of the model, the results compare well with the full self-consistent reaction field theory results, especially for the linear properties. Since the model relies only on gas phase calculations, it can be used for any electronic structure method that is implemented for static properties.
Orientational order–disorder phase transitions in plastic molecular clusters: Projection of three-dimensional distributions onto a two-dimensional surface
Authors: Radev Rossen A. , Proykova Ana , Li Feng-Yin , Berry R. Stephen
Published: July 2002

In addition to the traditional methods of identification of order–disorder transformations in nanoscale clusters containing highly symmetrical molecules, we have developed a simple projection method to recognize such transformations. The three-dimensional orientation distributions of the molecules are projected onto a two-dimensional spherical surface without any loss of information. We have applied the method in the analysis of the phase changes of clusters containing up to 180 tellurium hexafluoride molecules. The molecular configurations are generated by constant energy molecular dynamics simulations of the thermal history of free clusters. We observe two successive transitions as the clusters cool from their melting point. The projection method clearly reveals the mechanism of the structural transformations in the studied clusters: the orientation order of the molecular axes at low temperatures is accompanied by lattice distortion.
Dynamic nuclear polarization of diamond. II. Nuclear orientation via electron spin-locking
Authors: Reynhardt Eduard C. , High Grant L.
Published: July 2002

The polarization of 13C nuclei by means of nuclear orientation via electron spin-locking (Hartmann–Hahn cross-polarization between paramagnetic electrons and 13C nuclei) in a suite of natural diamonds has been investigated at 2.4 GHz and 9.6 GHz. The 13C polarization rate has been found to be independent of the microwave frequency, in agreement with theory. It is shown that since T1ρ(e)≪T1(e) for diamond, the effective polarization rate of 13C nuclei is relatively low. At low paramagnetic impurities (Ce<5 ppm) 13C nuclei in diamond are polarized faster by employing continuous wave microwave radiation to drive the forbidden transitions of the 13C-electron spin system, the so-called solid effect.
Solvation of the Li+–Cl−–Li+ triple ion in the gas phase
Authors: Jarek Russell L. , Denson Stephen C. , Shin Seung Koo
Published: July 2002

Fourier-transform ion cyclotron resonance (FT-ICR) spectrometry was employed to study solvations of the Li+–Cl−–Li+ triple ion with oxygen-donor Lewis bases in the gas phase. The LiClLi+ triple ions were produced in an ICR cell by laser desorption ionization of a lithium chloride/dibenzo-18-crown-6-ether matrix pasted on a Teflon substrate. O-donor Lewis bases include 1,4-dioxane, 1,3-dioxane, tetrahydrofuran (THF), acetone and diethyl ether. All O-donors associate directly with LiClLi+ with the maximum solvation numbers of 3 for 1,4-dioxane, 1,3-dioxane and diethyl ether, and 4 for THF and acetone at room temperature. The rate constants for the stepwise solvations were measured, and the solvent binding energies were determined from van’t Hoff plots. The structures and energetics of LiClLi+ and the 1:1 complexes of Li+ and LiClLi+ with the dioxanes, THF, and acetone were calculated at the Hartree-Fock (HF) level with a 6-311G(d,p) basis set, and those of more highly coordinated LiClLi+ complexes were calculated with a 6-31G(d) basis set. Solvation enthalpies and free energies were calculated, and solvent binding energies were compared with experiments. The mechanisms of stepwise solvations of the LiClLi+ triple ion with dioxanes, THF, and acetone are discussed in light of experimental kinetics and binding energies and theoretical structures and solvation energies.
S
2p
photoexcitation spectra of SO2 at high resolution
Authors: Gedat E. , Püttner R. , Domke M. , Kaindl G.
Published: July 2002

The S 2p photoabsorption spectrum of gas-phase SO2 was studied at high resolution (ΔE≅30 meV) using synchrotron radiation. The spectrum contains excitations to both valence orbitals and Rydberg states. The lowest core-to-valence excitation, S 2p−13b1, was found to be fivefold split, and vibrational subbands originating from the symmetric-stretching mode could be resolved. A Franck–Condon analysis of these five states reveals different geometries depending on the symmetry of the total electronic wave function in the final state. In the Rydberg region, both the spin–orbit splitting (≅1.20 eV) and the ligand-field splitting (≅95 meV) were resolved.
Inelastic multiphonon helium scattering from a stepped Ni(977) surface
Authors: Gaspar Daniel J. , Hanbicki Aubrey T. , Sibener S. J.
Published: July 2002

The multiphonon energy exchange between a neutral He atom and a stepped Ni(977) surface has been measured in order to examine how the presence of a regular array of atomic-scale steps on a surface modifies energy exchange in the classical multiphonon scattering regime. At elevated substrate temperatures, we compare the multiphonon scattering with the predictions of a classical theory that has previously been used by others for assessing energy exchange involving a smooth surface. There is a significant discrepancy between the theoretical predictions and our experimental data, which we attribute to differences between a smooth and stepped surface. Specifically, changes in the vibrational modes and associated surface density of states due to the presence of extended surface defects have a fundamental impact on the details of the energy exchange mechanism.
Electronic spectroscopy and dynamics of the monomer and Arn clusters of 9-phenylfluorene
Authors: Pitts Jonathan D. , Knee J. L.
Published: July 2002

The spectrum of the S1 electronic state of jet-cooled 9-phenylfluorene–Arn, n=0–4, has been measured by two color resonant enhanced multiphoton ionization spectroscopy. The cation ground states of these complexes have also been studied by mass analyzed threshold ionization (MATI) spectroscopy in a 1+1 excitation process with various intermediate states in S1. Ab initio calculations in conjunction with the spectroscopy have determined that the phenyl ring at the 9 position is perpendicular to the plane of the fluorene moiety yielding an overall symmetry of Cs. The Ar complexes for n=1–3 exhibit multiple isomers which are identified in the S1 spectrum and confirmed by MATI spectroscopy. The structure of these isomers is determined by spectral analysis and additivity rules as well as atom–atom calculations using a Lennard-Jones potential. Vibrational dynamics from selected S1 vibronic levels are observed by the appearance of the picosecond or nanosecond time delayed MATI spectra. Vibrational redistribution and dissociation of the clusters are measured with nanosecond and picosecond time resolution. It is found that different isomers of the n=1 cluster show dramatically different rates of redistribution for several vibronic bands.
The rotationally resolved infrared spectrum of the ν1 stretch of the allyl radical
Authors: DeSain J. D. , Thompson R. I. , Sharma S. D. , Curl R. F.
Published: July 2002

Transient infrared (IR) laser spectroscopy near 3100 cm−1 was used to observe the ν1 and ν13 transitions of the allyl radical, with their band origins found to lie at 3113.9779(3) cm−1 and near 3110.5 cm−1, respectively. Detailed assignment and analysis of the ν1 transition identified over 1100 transitions, and yielded improved values for ΔK and ΦK ground state centrifugal distortion constants, as well as a new set of excited state (ν1=1) rotational and centrifugal distortion constants, in addition to determining the band origin. Transitions involving states with quantum number up to Ka=11 and N=27 were identified. Strong perturbations were found in the excited state, included global perturbations of the Ka′=3 branch, extensive perturbations in the Ka′=2 and 4 branches, and very localized perturbations in the Ka′=6 branch. The Ka′=9 and 10 branches also appear to be significantly perturbed. Possible sources for these perturbations are discussed.
Quantum scattering on SN2 reactions: Influence of azimuthal rotations
Authors: Schmatz Stefan , Clary David C.
Published: July 2002

Time independent quantum scattering calculations have been carried out on the SN2 Walden inversion reaction Cl−+CH3Cl(v,k)→ClCH3(v′,k′)+Cl−. The two C–Cl stretching degrees of freedom (quantum numbers v and v′) and the azimuthal angle describing the rotation of the CH3 group (quantum numbers k and k′) are treated explicitly. An infinite order sudden approximation has been introduced using Radau coordinates for the stretching modes. The potential energy surface of Vande Linde and Hase is used. The scattering problem is formulated in hyperspherical coordinates. For the reaction (k=0→k′=0) substitution is observed for initial vibrational excitation with v⩾2. If the system departs from the collinear reaction pathway (initial rotational excitation) the substitution cross sections are strongly decreased. The state-to-state cross sections σvk→v′k′ are large only for transitions with Δk=0. The total reaction cross sections σvk for given v vary only slightly at low values of the azimuthal quantum number k and rise for larger values of k. This is explained by multiple (avoided) crossings of the hyperspherical adiabats.
Analysis of the highly excited vibrational dynamics of HCP using a high-order Fermi resonance Hamiltonian
Authors: Joyeux Marc , Grebenshchikov Sergy Yu. , Schinke Reinhard
Published: July 2002

Based on an ab initio potential energy surface, the features of the quantum spectrum of HCP have been recently discussed in terms of the periodic orbits of the exact classical Hamiltonian [J. Chem. Phys. 107, 9818 (1997)]. In particular, it was shown that the abrupt change in the bending character of the states at the lower end of the Fermi polyads, at about 15 000 cm−1 above the origin, can be ascribed to a classical saddle node bifurcation. The purpose of the present article is to show that the use of a very accurate Fermi resonance Hamiltonian, which was derived very recently from high-order perturbation theory [J. Chem. Phys. 109, 2111 (1998)] can provide a still deeper insight into the highly excited vibrational motion. The principal advantages of the resonance Hamiltonian compared to the exact one rely on the remaining good quantum numbers and classical action integrals, which enable one to consider HCP as a formal one-dimensional system parametrized by the polyad number i and the number v3 of quanta in the C–H stretching motion. It is shown in this article that all the quantum observations can be interpreted and explained in terms of the positions and bifurcations of the fixed points of this one-dimensional system: the shape of the quantum wave functions depends on the stable elliptic fixed points, whereas the dip in the gap between neighboring quantum levels is governed by the unstable, hyperbolic fixed points. The dependance on v3 of the bending character of the lowest states in each polyad i is discussed in some detail, whereas the previous work was fundamentally limited to v3=0. Moreover, the dependence on i and v3 of the form of the dip in the distribution of the gap between neighboring levels is given a clear explanation.
Simulations of high Tc vapor–liquid phase transitions in nanoporous materials
Authors: Saravanan Chandra , Auerbach Scott M.
Published: July 2002

We have performed lattice grand canonical Monte Carlo simulations of benzene adsorption in Na-X zeolite, to determine whether strongly confined benzene molecules exhibit subcritical properties. We observe a phase transition from low to high density of adsorbed benzene, analogous to vapor–liquid equilibrium, at temperatures as high as 300 K and above. By performing thermodynamic integration to construct the coexistence curve, we obtain a critical point for benzene in Na-X at Tc=370±20 K, θc=0.45±0.05 fractional coverage.
The generator coordinate Dirac–Fock method for open-shell atomic systems
Authors: Malli Gulzari L. , Ishikawa Yasuyuki
Published: July 2002

Recently we developed generator coordinate Dirac–Fock and Dirac–Fock–Breit methods for closed-shell systems assuming finite nucleus and have reported Dirac–Fock and Dirac–Fock–Breit energies for the atoms He through Nobelium (Z=102) [see Refs. Reference 10Reference 11Reference 12Reference 13]. In this paper, we generalize our earlier work on closed-shell systems and develop a generator coordinate Dirac–Fock method for open-shell systems. We present results for a number of representative open-shell heavy atoms (with nuclear charge Z>80) including the actinide and superheavy transactinide (with Z>103) atomic systems: Fr (Z=87), Ac (Z=89), and Lr (Z=103) to E113 (eka-thallium, Z=113). The high accuracy obtained in our open-shell Dirac–Fock calculations is similar to that of our closed-shell calculations, and we attribute it to the fact that the representation of the relativistic dynamics of an electron in a spherical ball finite nucleus near the origin in terms of our universal Gaussian basis set is as accurate as that provided by the numerical finite difference method. The DF SCF energies calculated by Desclaux [At. Data. Nucl. Data Tables 12, 311 (1973)] (apart from a typographic error for Fr pointed out here) are higher than those reported here for atoms of some of the superheavy transactinide elements by as much as 5 hartrees (136 eV). We believe that this is due to the use by Desclaux of much larger atomic masses than the currently accepted values for these elements.
Accurate ab initio near-equilibrium potential energy and dipole moment functions of the X 2B1 and first excited A22 electronic states of OClO and OBrO
Authors: Peterson Kirk A.
Published: July 2002

Using highly correlated multireference configuration interaction wave functions with large correlation consistent basis sets, three-dimensional near-equilibrium potential energy functions (PEFs) have been calculated for the X 2B1 and first excited A22 electronic states of the atmospherically important OClO and OBrO radicals. The analytical PEFs have been used in perturbational and variational calculations of the anharmonic spectroscopic constants and vibrational spectra of both species. Excellent agreement with the available experimental data are observed for both species and electronic states, e.g., the vibrational fundamental frequencies in the ground electronic states are reproduced to within about 5 cm−1. For the A 2A2 state of OClO, it is demonstrated that the anomolously strong intensity of the ν3 mode in the UV absorption spectrum is due to strong anharmonic coupling between the stretching vibrations and not to a double minimum in the potential. Three-dimensional electric dipole moment functions have also been calculated for the ground electronic states of both species. These were used to calculate accurate absolute infrared absorption intensities for the fundamentals and low-lying overtones and combination bands of both species.
A nest of structures in dynamics of cellulose diacetate in N,N-dimethylacetamide in quiescent solution state studied by dynamic light scattering
Authors: Kawanishi Hiroyuki , Tsunashima Yoshisuke , Horii Fumitaka
Published: July 2002

In the quiescent state, dynamic light scattering measurements were performed for a polysaccharide, cellulose diacetate (CDA, the degree of substitution 2.40), in a liquid-crystalline promoting solvent N, N-dimethylacetamide (DMAc) in the range from dilute to crossover concentrations. Three modes of motions were detected simultaneously over all concentrations measured. They are in a nest of structures, which are caused by long-range interactions acting between OH groups of glucose units in a highly dielectric-constant solvent DMAc. Denoting these modes as Mode I, II, and III from fast to slow motions, the decay rates Γ of each mode showed the squared scattering-vector dependence at lower angles, i.e., the diffusion nature. In dilute solution, fast Mode I is the translational diffusion of a single CDA chain and others represent the dissipation of locally associated CDA clouds which grow by the interactions specified above. Mode II is related to a coarse cloud formed in a limited time but spread over a wide space A, while Mode III is related to a dense cloud created with a very small space B inside >A. The tentative increase in CDA concentrations in the spaces A and B relaxes to the level of bulk concentration with a large decay rate ΓII for Mode II and a small ΓIII for Mode III. With the increase of c, the number of A and the bulk concentration increase, and the decay rate ΓIII for dissipating B becomes smaller than that in dilute solution. Above the crossover concentration c*, however, the space A becomes close each other and almost all the CDA are packed in A. Then fast Mode I represents the relaxation of concentration fluctuations, or cooperative diffusion, with the length scale as small as a single CDA chain, ξI. Mode II represents another cooperative diffusion, which is originated by the relaxation of concentration fluctuations effective only in A of the correlation length ξII. Mode III is related to the time–space fluctuation in the distribution of A, which emerges as another cooperative diffusion of much larger correlation length ξIII. Mode II was contaminated by a self-diffusionlike (SF) motion, though both were separated into two branches in more concentrated regions. The SF mode is assigned to a reptation motion of CDA, which can be described by the constrained translational motion of a stiff chain in the tube with interacting wall. The dynamical feature of these modes of motions are influenced strongly by strength and nature of long-range interactions between unsubstituted OH groups in glucose residues, or the hydrogen bonds in solvents of high electronegativity.
Confined complex liquids: Passages, droplets, permanent deformations, and order–disorder transitions
Authors: Hołyst Robert , Oswald P.
Published: July 2002

A lamellar phase confined between parallel walls changes its structure when compared with the bulk system. The system is studied here in the Monte Carlo simulations of the Landau–Ginzburg model of a ternary mixture of oil, water, and surfactant. In the case of strongly hydrophilic boundary conditions at the walls, we observe strong topological fluctuations in the form of passages. As we change the distance between the walls we observe the formation of two surfactant layers, then the microemulsion between two layers, and finally four surfactant layers. The transition is marked by the peaks in the average Euler characteristic and in its variance. In the case of strongly hydrophilic boundary conditions at one wall and strongly hydrophobic boundary condition at the other, we observe under dilation a permanent deformation of layers in the middle of the system. In the case of weakly hydrophilic boundary conditions, the system exhibits strong topological fluctuations (passages and droplets) and the lamellar phase which forms is perpendicular to the bounding walls. In this case, edge dislocations form close to the walls. We also simulate an onion vesicle in a cubic pore and edge dislocations in slits, and show that the passages appear near a dislocation core.
State-to-state inelastic scattering from vibrationally activated OH–H2 complexes
Authors: Hossenlopp Jeanne M. , Anderson David T. , Todd Michael W. , Lester Marsha I.
Published: July 2002

State-selective infrared excitation of o-H2–OH via the pure OH overtone transition has been used to induce a half-collision inelastic scattering event between the OH radical and ortho-H2 under restricted initial orientation conditions. The time evolution and final state distribution of the OH products from vibrational predissociation have been evaluated by ultraviolet probe laser-induced fluorescence measurements. The half-collision scattering takes place with ∼3350 cm−1 of energy available to the OH (v=1)+o-H2 products, an energy that exceeds the classical barrier to reaction. The OH (v=1) products are preferentially populated in high rotational levels with a distribution that is consistent with an energy gap law. A significant fraction of the OH fragments are promoted to the excited spin–orbit state in the predissociation process. A strong lambda-doublet propensity is also found, indicating that the OH unpaired pπ orbital is preferentially aligned perpendicular to the rotational plane of the OH products. Finally, the OH rotational and fine structure distributions are compared with those obtained in previous full collision inelastic scattering studies at energies below the threshold for reaction.
Theoretical characterization of divacancies at the surface and in bulk MgO
Authors: Ojamäe Lars , Pisani Cesare
Published: July 2002

Two types of divacancy at the (001) surface of MgO are theoretically studied and compared with the corresponding defect in the bulk: the pit, where a surface magnesium and the oxygen ion underneath are removed, and the tub, where both removed ions are at the surface. All calculations have been performed by means of the EMBED program which adopts an embedded-cluster approach in the frame of the Hartree-Fock (HF) approximation [C. Pisani F. Corà, R. Nada, and R. Orlando, Comput. Phys. Commun. 82, 139 (1994); C. Pisani and U. Birkenheuer, ibid. 96, 152 (1996)]; the semi-infinite host crystal for the study of the surface defects has been simulated with a four-layer slab. The energy released on formation of the divacancy from the two charged isolated vacancies is very high, almost 300 kcal/mol. The tub divacancy is the most stable, both as a neutral and as a singly charged defect. For the paramagnetic center (one electron trapped in the cavity), spin density data are provided and discussed with reference to results from electron paramagnetic resonance experiments and molecular cluster calculations [E. Giamello M. C. Paganini, D. Murphy, A. M. Ferrari, and G. Pacchioni, J. Phys. Chem. 101, 971 (1997)]. It is suggested that the tub divacancy is a common defect, if not the most common, at the highly dehydrated MgO surface.
Zeeman spectroscopy of CaH molecules in a magnetic trap
Authors: Friedrich Bretislav , Weinstein Jonathan D. , deCarvalho Robert , Doyle John M.
Published: July 2002

In a recent experiment [Weinstein et al., Nature 395, 148 (1998)] we magnetically trapped 108 ground-state calcium monohydride molecules, CaH(X 2Σ,v″=0, J″=0). The molecules were prepared by laser ablation of a solid sample of CaH2 and loaded via thermalization with a cold (<1 K) He3 buffer gas. The magnetic trap was formed by superconducting coils arranged in the anti-Helmholtz configuration. The detection was done by laser fluorescence spectroscopy excited at 635 nm (in the B 2Σ,v′=0−X 2Σ,v″=0 band) and detected at 692 nm (within the B,v′=0−X,v″=1 band). Both a photomultiplier tube and a CCD camera were used. Due to the thermalization of molecular rotation, only a transition from the lowest rotational state could be detected at zero field, N′=1, J′=3/2←N″=0, J″=1/2. In the magnetic field this rotational transition splits into two features, one shifted towards lower and one towards higher frequencies. The measured shifts are linear in field strength and indicate a small difference (0.02 μB) in the magnetic moments between the ground and excited states. Here we present a theoretical analysis of the observed magnetic shifts. These are identified as arising from a rotational perturbation of the B 2Σ,v′=0 state by a close-lying A 2Π,v′=1 state that lends the B state some of its A character. We find that the Hamiltonian can be well approximated by a 3×3 matrix built out of elements that connect states from within the Σ-doublet and the Π3/22 manifolds. The interaction parameter describing the Σ−Π coupling in the Zeeman Hamiltonian is determined from the observed shifts and the field-free molecular parameters of CaH given by Berg and Klyning [Phys. Scr. 10, 331 (1974)] and by Martin [J. Mol. Spectrosc 108, 66 (1984)].
Interaction of methanol and water on MgO(100) studied by ultraviolet photoelectron and metastable impact electron spectroscopies
Authors: Günster J. , Liu G. , Stultz J. , Goodman D. W.
Published: July 2002

The coadsorption of methanol (CH3OH) and water (D2O) on the MgO(100)/Mo(100) surface at 100 K has been studied by metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy [UPS (HeI)], and by thermal programmed desorption (TPD). Methanol wets the MgO surface and adsorbs nondissociatively within the first monolayer with the hydroxyl group oriented toward the substrate. In coadsorption experiments, methanol wets a water precovered MgO surface; however, adding water to a methanol precovered MgO surface does not yield a water-only surface. Essentially, a constant fraction of the preadsorbed methanol remains within the topmost surface layer during the buildup of the water multilayer. Temperature-dependent measurements show that the adsorption and desorption dynamics of both water and methanol are governed by intermolecular interactions rather than adsorbate–substrate interactions.
Kinetics of coil–globule transition of poly(methyl methacrylate) in isoamyl acetate
Authors: Nakata Mitsuo , Nakagawa Tomohide
Published: July 2002

The kinetics of coil–globule transition was studied by static light scattering measurements on poly(methyl methacrylate) with the molecular weight Mw×10−6=8.4 and 12.2 in isoamyl acetate. Since the phase separation of the solution occurred very slowly, the mean-square radius of gyration of the polymer could be determined for a long time after quench to far below the θ-temperature 61 °C. The expansion factor α2 observed 30 min after quench to below the coil–globule crossover point, deviated largely from theoretical predictions, and was found to be a transient one. Chain collapse processes were measured in the time range from 30 min to a few thousand min after the quenches to 30 °C and 45 °C for Mw=12.2×106 and to 30 °C for Mw=8.4×106. The expansion factor in each process approached a constant value αeq2 in the time range. The collapse process was expressed as a function of time t(min) by α2=α∞2+{b/(t+c)}p, where b, c, p, and α∞2 were constant, independent of time. In all the three processes the constants had values near p∼0.5, b∼0.4, c∼0.6, and α∞2 was slightly smaller than αeq2. The constant c was introduced to satisfy the initial condition of α2=1 at t=0. This behavior of α2(t) and a comparison with kinetic theories of chain collapse concluded that the chain collapse occurred in a single stage process without formation of chain knots.
Intermolecular bonding and vibrations of phenol⋅oxirane
Authors: Inauen Andreas , Hewel Johannes , Leutwyler Samuel
Published: July 2002

The supersonically cooled hydrogen-bonded phenol⋅oxirane complex was studied using mass- and isomer-selective laser spectroscopic techniques. The S1←S0 vibronic spectrum was measured by mass-selective two-color resonant two-photon ionization. UV/UV-hole-burning experiments prove that the whole observed spectrum is due to only one isomer. High-resolution fluorescence emission spectra yielded five different intermolecular S0 state vibrational fundamentals as 15, 27, 39, 83, and 177 cm−1, which are assigned as the ρ1″, β1″, τ″, β2″, and σ″ modes, respectively, based on ab initio calculations. The analogous S1 state intermolecular vibrations were also assigned, based on frequency and Franck–Condon activity. The observation of the ρ1 and τ intermolecular vibrational transitions in both excitation and emission implies that phenol⋅oxirane is asymmetric (chiral), even though the H-donor is Cs and the acceptor C2v symmetric. Four different ab initio structure optimizations and normal-mode calculations were made, to compare the performance of the self-consistent field (SCF) and Becke–Lee–Yang–Parr (B-LYP) density functional methods, using the 6-31G(d,p) and 6-311++G(d,p) basis sets. The SCF/6-31G(d,p) method and the B-LYP method with both basis sets indeed predict chiral minimum-energy structures. The B-LYP/6-311++G(d,p) and SCF/6-31G(d,p) normal mode frequencies agree well with the experimental S0 state frequencies, with rms deviations of 4%. The MP2/6-31G(d,p) hydrogen bond well depth is De=6.9 kcal/mol and the dissociation energy is D0=5.7 kcal/mol.
Practical formulation of accurate many-body potentials through the perturbative extension of diatomics-in-ionic-systems: Applied to HF clusters
Authors: Ovchinnikov M. , Apkarian V. A.
Published: July 2002

A perturbative extension of the diatomics-in-ionic-systems (DIIS) is formulated as a practical method for describing global many-body potential energy surfaces with accuracy and economy. The method is applied to HF clusters, generalizing the prior accurate DIIS treatment of the dimer [Grigorenko, Nemukhin, and Apkarian, J. Chem. Phys. 108, 4413 (1998)] to arbitrary numbers of HF molecules. The calculated geometries, energetics, and harmonic frequencies of (HF)n, n=2–6 clusters agree in detail with the available data on this well-studied system. The formulation is based on treating intermolecular interactions within perturbation theory. It is shown that second-order perturbation, which includes bimolecular excitations, is necessary and sufficient in describing the many-body potential energy surfaces with spectroscopic accuracy. The approach allows the analysis of H-bonding and its nonadditive induction and dispersion forces in terms of mixings and exchange between ground- and excited states of dimers including intra- and intermolecular charge-transfer states as well as molecular triplet states. The speed of evaluation of the potential scales is the cube of the number of molecules, providing a practical method for dynamical simulations of extended hydrogen-bonded networks.
Slow structural relaxations of glass-forming Maltitol by modulated DSC calorimetry
Authors: Bustin O. , Descamps M.
Published: July 2002

The possibilities offered by the modulated differential scanning calorimetry technique to investigate the glass transition are analyzed and discussed on Maltitol. The technique provides specific tools to follow the structural relaxation in the frequency domain above Tg and in the time domain below Tg. Evidence is obtained that the complex heat capacity can be measured in the course of a routine differential scanning calorimetry (DSC) scan. The enthalpic relaxation can be analyzed which allows us to discuss the fragility degree of the glass former. The smearing effect of the underlying ramp is specifically investigated. It is shown that the method provides estimates both of the Vogel and of the Kauzmann temperatures. It thus offers an attractive way to check for a correlation between dynamics and thermodynamics. The concept of the “nonreversing” component is used and discussed in order to study the slow sub-Tg relaxations.
Kinematics of the three-body dissociation of SO23+, after sulphur 2p photoexcitation of the SO2 molecule
Authors: Lavollée M. , Brems V.
Published: July 2002

An original three-dimensional detector, which allows the precise measurement of the kinetic energy release and angular distributions of charged fragments, has been used to investigate the kinematics of the charge separation reaction SO23+→S++O++O+ after core excitation in the S 2p threshold region. Kinetic energy release distributions and angular distributions are reported at various photon energies. The role of bending and stretching of the molecule in the repartition of the kinetic energies in the dissociative kinematics is demonstrated by means of a simple, parameter free, Coulomb repulsion model. At certain photon energies different geometries of SO23+ have been observed experimentally. An ab initio study, at the multireference single- and double-excitation configuration interaction level, of the potential curves corresponding to the neutral core-excited SO2 molecule is presented. This theoretical approach demonstrates that it is possible to explain this observation from the nuclear dynamics of the neutral core-excited molecule before the Auger decay occurs.
Temperature-dependent absorption strengths for transitions from the ground state to the mutually perturbed A 1Π(v=1) and d 3Δ1(v=5) states of CO
Authors: Wu C. Y. Robert , Chen F. Z. , Judge D. L. , Hua Xin-Min , Caldwell J.
Published: July 2002

High resolution photoabsorption cross section data for the CO 4PG (1,0) band have been obtained under several different temperature conditions. It was found that the absorption strength of the d 3Δ1–X 1Σ+ (5,0) band underlying the 4PG (1,0) band varies with temperature. The ratio of the absorption band strength of the d–X (5,0) band to that of the 4PG (1,0) band has been determined for temperatures at 150 K, 295 K, and 370 K. Adopting the integrated oscillator strength of the 4PG (1,0) from the recent literature we have determined band absorption cross sections for the two bands as a function of temperature. The ratios of the band absorption strengths of the A–X (1,0) and d–X (5,0) bands at different temperatures are compared with those calculated from the mixing coefficients determined by analysis of level shifts in high resolution spectra and lifetime measurements.
Evidence for instantaneous resonant modes in dense fluids with repulsive Lennard-Jones force
Authors: Wu Ten-Ming , Ma Wen-Jong
Published: July 2002

In terms of instantaneous-normal-mode (INM) analysis and a newly defined measure for quasilocalization, we present the evidence for the resonant modes in a model fluid, in which the pair interaction is merely the repulsive portion of the Lennard-Jones potential. We name such a quasilocalized INM as an instantaneous resonant mode (IRM). By examining the potential energy profile beyond the INM approximation, we conclude that the IRMs occur in single-well potentials with strong enough anharmonicity.
Target and trapping problems: From the ballistic to the diffusive regime
Authors: Berezhkovskii A. M. , Bicout D. J. , Weiss G. H.
Published: July 2002

The target and trapping problems refer to the reaction A+B→B. In the target problem a single A particle is fixed in space and surrounded by B’s allowed to move freely, while in the trapping problem the B’s are fixed and the A is able to move. Exact solutions are found for both problems in the ballistic regime, in all dimensions. We show that the solution of the target problem provides a mean-field approximation to the solution of the trapping problem, not only in the diffusive regime, but also for arbitrary noise. This approximate solution works well in the diffusive regime, but not when motion is ballistic, since it breaks down at very early times. We show that the time-dependent rate coefficients in both the target and trapping problems remain finite at t=0 for arbitrarily strong noise intensities. This behavior is in contrast to the diffusion theory prediction that the coefficient diverges at t=0. A recently developed model that discretizes the velocity, allowing only three values, ±v and 0, is used to study the reaction kinetics of both the trapping and target problems in one dimension over the entire range of noise intensities. The solutions are used to study the effects of noise intensity on the mean survival time. We show that in the target problem this time decreases monotonically with increasing noise, while in the trapping problem this time exhibits a turnover behavior. We argue that a similar turnover occurs in the one-dimensional trapping problem when particle motion is governed by a Langevin equation.
Nonseparable transition state theory for nonzero total angular momentum: Implications for J shifting and application to the OH+H2 reaction
Authors: Bowman Joel M. , Shnider Heather M.
Published: July 2002

We report vibration/rotation energies of the OHH2 transition state using the code “Multimode,” for total angular momentum J=0, 1, and 4. Rotation is treated in the adiabatic rotation approximation for J=1 and 4, as well as exactly, i.e., including Coriolis coupling, for J=1. State-dependent rotation constants are obtained using the adiabatic rotation energies from the J=0 and 1 calculations and shown to predict accurately the adiabatic rotation rovibrational energies for J=4. These rotation constants are used in new J-shifting calculations of the thermal rate constant for the reaction OH+H2→H2O+H using results from a previous accurate calculation of the rate constant for J=0 [U. Manthe, T. Seideman, and W. H. Miller, J. Chem. Phys. 99, 10078 (1993); 101, 4759 (1994)]. Comparisons with previous J-shifting and recent centrifugal sudden calculations of the rate constant [D. H. Zhang, J. C. Light, and S-Y. Lee, J. Chem. Phys. 109, 79 (1998)] of this reaction are presented. A modification of the previous centrifugal sudden rate constant is made and shown to yield results that are in good agreement with the new J-shifting calculations. Finally, an assessment of Coriolis coupling is made.
Relaxation of the ionic cloud on the basis of a dressed-ion theory
Authors: Varela L. M. , Rega C. , Perez-Rodriguez M. , Garcia M. , Mosquera V. , Sarmiento F.
Published: July 2002

The dynamic response of a bulk electrolyte or colloid solution to an external field is investigated on the basis of a dressed-ion theory (DIT) in a hydrodynamic point of view. The radial part of the perturbed electric field acting on a given ion is explicitly calculated in terms of the DIT quantities derived from the linear response function calculated from the modified mean-spherical aproximation (MMSA) and its static and frequency-dependent limits are analyzed. In the static case, the asymptotic behavior is analyzed and Onsager’s result is reformulated in terms of the effective charges and effective screening length and in the limit of vanishing concentration Debye–Falkenhagen–Onsager results are recovered. In the frequency-dependent DIT transport theory a relation between the field frequency and the time of relaxation of the ionic atmosphere is shown to be needed in order to get real renormalized charges and screening lengths. A decay of the perturbed electrostatic field as the inverse square root of the field frequency is obtained at high frequency and vanishing concentration along with a model-independent phase factor between the external and internal fields. The radial dependence of the perturbed average potential in the neighborhood of a quasiparticle is also calculated in the static case and several behaviors ranging from classical Derjaguin–Landau–Verwey–Overbeek colloidal stability theory interaction to pure attraction and repulsion are obtained. The results are analyzed in terms of a splitting of the ionic cloud into three different parts each one contributing to the radial dependence of the perturbed potential.
Excited-state site effects in luminescence spectroscopy of SH radicals in krypton matrices: Experiment and simulations
Authors: Grigorenko Bella , Khriachtchev Leonid , Nemukhin Alexandr , Pettersson Mika , Isoniemi Esa , Räsänen Markku
Published: July 2002

The specific features in luminescence spectra of SH radicals in solid krypton differing remarkably from those of SH and OH species in various rare-gas matrices are discussed. Of special interest in Kr matrices are two bands appearing in the SH emission spectra under the A 2Σ+←X 2Π excitation, which center at 375 and 413 nm and possess very different lifetimes, 350 and 750 ns. Along with the experimental findings, we describe the results of the mixed quantum-classical molecular dynamics simulations of the emission spectra performed on the diatomics-in-molecules potential energy surfaces of the ground and excited states of the clusters SH@Krn (n⩾250). The simulations show that both bands in the emission spectra refer to the same (A 2Σ+,v′=0→X 2Π,v″) transition and originate from two different trapping sites in the excited state. The band at the shorter wavelength corresponds to the site with a relatively free movement of SH (A) inside the lattice while the adjacent more intense band at the longer wavelength is associated with the site where one of the matrix atoms is attached to the guest molecule forming a transient complex SH(A)⋅Kr inside the solvation shell.
Competing dissociation between the S–Cl and S–S bonds in the photolysis of S2Cl2 at 248 and 193 nm
Authors: Lee Y. R. , Chiu C. L. , Tiemann E. , Lin S. M.
Published: July 2002

The photodissociation of S2Cl2 at 248 and 193 nm has been studied by translational spectroscopy. Upon excitation at 248 nm, S2Cl2 undergoes predominantly the dissociation channels to form the products, (1) S2Cl+Cl and (2) SCl+SCl. The relative yield of (1)/(2) was determined at ∼3.0:1.0. The S2Cl+Cl products were detected with two separate product translational energy distributions of 〈Et〉=14 and 41 kcal/mol. The slow S2Cl fragment, which is internally excited, undergoes a secondary dissociation to form S2+Cl. Dissociation mechanisms which are consistent with the isotropic recoiling are proposed: the slow component could arise from the ground electronic state while the fast component would more likely originate from a mixed excitation of 1A and 1B states (C2 symmetry). The SCl product with anisotropy parameter β=1.6, on the other hand, should proceed by an excited 1B state. At 193 nm, a three-body formation of S2+2Cl becomes the more efficient process than the simple S–Cl or S–S bond fission. Assuming that the rupture of both S–Cl bonds occurs in a single kinetic step, a P(Et) distribution with 〈Et〉=30 kcal/mol is determined. Because of the measured β=−0.3 for the formation of triple products, a higher 1B state will be involved in the excitation.
Ternary surfactant mixtures in semi-infinite geometry
Authors: Tasinkevych M. , Ciach A.
Published: July 2002

Oil–water-surfactant mixture is investigated near the planar surface by mean-field theory applied to a certain lattice model. Close to the coexistence of the microemulsion with the lamellar phase, the model predicts either surface-induced ordering or surface-induced disordering transitions, depending on the nature of the surface. The new order-parameter, describing the lamellar order, is defined. The Landau–Ginzburg functional based on the new “lamellar order parameter” is introduced. The functional has a form introduced earlier for surface-induced ordering and disordering in simple fluids. Connection of the continuous model to the lattice one is discussed.