bluuebunny/crossref_metadata_2025 huggingface dataset:
Relation of vibrational hyper-Raman intensities to γ-hyperpolarizability densities
Authors: Tisko E. L. , Li X. , Hunt K. L. C.
Published: July 2002

Band intensities for nonresonant vibrational hyper-Raman scattering depend on the derivatives of the β hyperpolarizability, a nonlinear electronic response tensor, with respect to normal mode coordinates. In this work, we derive a new result for the change in β(−ωσ; ω1,ω2) due to small shifts in nuclear positions within a molecule. We prove that the derivative of β(−ωσ; ω1,ω2), taken with respect to the position RK of nucleus K, depends on the nonlocal hyperpolarizability density γ(r,r′,r″,r‴; −ωσ; ω1,ω2,0) of second order, the charge on nucleus K, and the dipole propagator from RK to r‴. Thus γ(r,r′,r″,r‴; −ωσ; ω1,ω2,0) determines the origins of vibrational hyper-Raman intensities on the intramolecular scale. Two observations provide the physical basis for this result: The effective value of β for a molecule in a static applied field is governed by the γ hyperpolarizability density. When a nucleus shifts infinitesimally, the electrons respond to the resulting change in the nuclear Coulomb field via the same nonlocal susceptibilities that characterize their response to an applied electric field.
Ab initio calculations of anharmonic vibrational transition intensities of trans-2,3-dideuteriooxirane
Authors: Bludský Ota , Bak Keld L. , Jo/rgensen Poul , Špirko Vladimír
Published: July 2002

The quartic force field and the cubic dipole moment surface are calculated for trans-2,3- dideuteriooxirane at the self-consistent field and the second order Möller–Plesset levels of theory using a triple zeta plus two polarization functions basis set. Contact transformation theory is used to determine the corresponding anharmonic vibrtional frequencies and intensities. Inclusion of anharmonicity improves agreement of the calculated frequencies and intensities with their experimental counterparts. The anharmonic corrections are much more sensitive to correlation effects for intensities than for frequencies.
A J matrix engine for density functional theory calculations
Authors: White Christopher A. , Head-Gordon Martin
Published: July 2002

We introduce a new method for the formation of the J matrix (Coulomb interaction matrix) within a basis of Cartesian Gaussian functions, as needed in density functional theory and Hartree–Fock calculations. By summing the density matrix into the underlying Gaussian integral formulas, we have developed a J matrix ‘‘engine’’ which forms the exact J matrix without explicitly forming the full set of two electron integral intermediates. Several precomputable quantities have been identified, substantially reducing the number of floating point operations and memory accesses needed in a J matrix calculation. Initial timings indicate a speedup of greater than four times for the (pp‖pp) class of integrals with speedups increasing to over ten times for (ff‖ff ) integrals.
High-resolution infrared study of the translational lattice modes in α-N2 single crystals
Authors: Bini Roberto
Published: July 2002

The analysis of the far infrared spectrum of thin high quality α-N2 single crystals as a function of temperature was carried out by high resolution Fourier-transform infrared spectroscopy. The bandwidths at T=8 K of the two translational modes, correlated to the two-phonon density of states, are considerably smaller than the Raman active modes. This result can be interpreted on the basis of a lower anharmonicity of the translations with respect to the librational modes. The α-N2 is the first molecular crystal where such difference is found. The evolution of the T(1)u linewidth was studied until the α-β phase transition. The relaxation of this mode is essentially dominated by fourth-order decay processes. The study of the frequency shifts of both infrared phonons allowed the contributions relative to different orders of the anharmonic potential to be separated. Finally a careful analysis of the relative intensities of the two phonons was carried out in the α phase.
Effects of monomer geometry and basis set saturation on computed depth of water dimer potential
Authors: Mas Eric M. , Szalewicz Krzysztof
Published: July 2002

The interaction energy for the water dimer has been calculated using supermolecular many-body perturbation theory (MBPT) at the fourth-order level, the coupled clusters method with single, double, and noniterative triple excitations [CCSD(T)], and the symmetry-adapted perturbation theory (SAPT). We argue that the appropriate monomer geometry in such calculations has to be the average geometry of the ground vibrational state rather than the customarily used equilibrium geometry. The use of the former instead of the latter geometry increases the dimer binding energy by about 0.12 kcal/mol in the van der Waals minimum region almost independently of the method employed. Our largest basis set with a balanced account of the intramonomer correlation and dispersion effects gives interaction energy at the second-order MBPT level which is 0.03 kcal/mol lower than the best previous literature value. The final depth at the minimum obtained using SAPT is 5.05 kcal/mol, while the commonly accepted empirical depth is 5.4 ± 0.7 kcal/mol. Taking into account the fact that the empirical result contains a theoretical zero-point energy which is probably overestimated by a few tenths of kcal/mol, our value of the potential depth believed to be accurate to within 0.1 kcal/mol is in a better agreement with experiment than the results of recent large-scale ab initio calculations. The optimized dimer geometry agrees to within 0.001 Å and 2° with the experimental geometry from microwave measurements.
A high resolution neutron powder diffraction study of D2O ice XI
Authors: Line Christina M. B. , Whitworth R. W.
Published: July 2002

The lattice parameters and diffraction peak profiles are presented for KOD-doped D2O ice both in its low-temperature ordered state (ice XI) and as a function of temperature through the transition to ice Ih at 76 K. They are compared with parallel measurements on pure D2O ice. We demonstrate that ice XI is orthorhombic, with lattice parameters a=4.465(3) Å, b=7.859(4) Å, and c=7.292(2) Å at 5 K, as compared with a=4.4974(1) Å and c=7.3236(1) Å for pure ice. The detransformed phase measured at 5 K has a different c-lattice parameter from that of pure ice, with a=4.4971(1) Å and c=7.3182(1) Å. The transformed sample is an intimate mixture of the orthorhombic transformed phase and hexagonal untransformed ice, giving rise to elastic strain effects such that the c-lattice parameter of the untransformed phase is shifted, giving a=4.499(1) Å and c=7.311(1) Å. These strain effects also produce broadening of the diffraction peaks for the transformed phase relative to those of the detransformed and pure phases. We demonstrate that the phase transition from ice XI to ice Ih is first-order. There is a shift in c-lattice parameter of the detransformed KOD ice relative to pure ice above the transition, which decreases with temperature, becoming negligible at 200 K. We suggest that this is due to local ordering in the doped ice.
Bound states of He atoms on Ag(110)
Authors: King J. A. , Brown J. S.
Published: July 2002

The spectrum of bound states of He atoms adsorbed on Ag(110) is calculated, using an interaction potential based on effective medium theory EMT for the repulsive term A exp(−bz) and the Zaremba–Kohn form for the attractive van der Waals dispersion term. The electronic charge density of the host in the selvedge region is modeled by superimposing atomic-charge densities using the Herman–Skillman tables and the prefactor A of the repulsive term is fitted to the exact ground state energy obtained from elastic He scattering data. Comparisons are made with the bound-state spectrum extracted from the measured resonances in the He scattering data and with the results of several other models used in the current literature. An assessment of the role played by higher-order dispersion contributions to the attractive potential is also included.
Cross sections for collisions of low-energy electrons with the hydrides PH3, AsH3, SbH3, SnH4, TeH2, and HI
Authors: Bettega M. H. F. , Lima M. A. P. , Ferreira L. G.
Published: July 2002

We calculated integral and differential cross sections for scattering of low-energy electrons by two groups of hydrides from 10 to 30 eV. The first group is composed by the hydrides of elements in the same column of the Periodic Table and includes PH3, AsH3, and SbH3. The second group is formed by hydrides in the same row and includes SnH4, SbH3, TeH2, and HI. The calculations employed the Schwinger multichannel method with norm-conserving pseudopotentials [M.H.F. Bettega, L.G. Ferreira, and M.A.P. Lima, Phys. Rev. A 47, 1111 (1993)]. Our goal is to find similarities and differences in the cross sections in these two groups.
Formation of autoionizing atomic nitrogen from superexcited states of nitric oxide
Authors: Hikosaka Yasumasa , Hattori Hideo , Hikida Takumi , Mitsuke Koichiro
Published: July 2002

Photodissociation of NO followed by autoionization of an N atom has been studied by two-dimensional photoelectron spectroscopy using synchrotron radiation. In addition to the bands due to molecular ionization, the two-dimensional spectrum shows several characteristic patterns in the photon energy range of 21.5–27 eV which result from autoionization of the Rydberg states converging to N+(1De) into the ionic ground state N+(3Pe). The electronic states of the counter atomic oxygen can be determined from the lower onset energies of these patterns to be 3Pe and/or 1De. Discussion is made about the transition region for the photodissociation reaction, especially being focused on the nature of the primary molecular states and their dynamical aspects including competitive molecular autoionization.
Some reasons not to use spin projected density functional theory
Authors: Wittbrodt Joanne M. , Schlegel H. Bernhard
Published: July 2002

Spin unrestricted calculations using density functional theory can yield wave functions with spin contamination. In conventional post Hartree–Fock calculations (such as Mo/ller–Plesset perturbation theory), spin projection can ameliorate some of the problems caused by spin contamination. However, spin projection can seriously degrade the quality of potential energy surfaces calculated by density functional methods, just as spin projection can yield poor results for Hartree–Fock potential energy surfaces.
Rate statistics and thermodynamic analogies for relaxation processes in systems with static disorder: Application to stretched exponential
Authors: Vlad Marcel O. , Huber David L. , Ross John
Published: July 2002

The paper deals with the relationships between the total rate of a relaxation process occurring in a system with static disorder and the decay rates attached to the different individual reaction channels. It is proven that the models of relaxation constructed on the basis of these two types of rates are equivalent to each other. From an experimentally observed relaxation curve it is possible to evaluate only the density of channels characterized by different relaxation rates and the overall probability distribution of the total relaxation rate. For evaluating the probability density of the individual relaxation rates attached to different channels an approach based on the maximum information entropy principle is suggested. A statistical thermodynamic formalism is developed for the relaxation time of a given channel, i.e., for the reciprocal value of the individual relaxation rate. The probability density of the relaxation time is proportional to the product of the density of channels to an exponentially decreasing function similar to the Boltzmann’s factor in equilibrium statistical mechanics. The theory is applied to the particular case of stretched exponential relaxation for which the density of channels diverges to infinity in the limit of large relaxation times according to a power law. The extremal entropy of the system as well as the moments and the cumulants of the relaxation times and of the relaxation rates are evaluated analytically. The probability of fluctuations can be expressed by a relationship similar to the Greene–Callen generalization of Einstein’s fluctuation formula. In the limit of large rates the density of channels and the probability density of individual rates have the same behavior; both functions have long tails of the negative power law type characterized by the same fractal exponent. For small rates, however, their behavior is different; the probability density tends to zero in the limit of very small rates whereas the density of channels displays an infrared divergence in the same region and tends to infinity. Although in the limit of small rates the density of channels is very large the probability of occurrence of these channels is very small; the compensation between these two opposite factors leads to the self-similar features displayed by the stretched exponential relaxation. The thermodynamic approach is compared with a model calculation for the problem of direct energy transfer in finite systems. The connections between stretched exponential relaxation and the thermal activation of the channels are also investigated. It is shown that stretched exponential relaxation corresponds to a distribution of negative and positive activation energies of the Gompertz-type.
Photodissociation of Kr2F(4 2Γ) in the ultraviolet and near-infrared: Wavelength dependence of KrF (B 2Σ) yield
Authors: Schloss J. H. , Tran H. C. , Eden J. G.
Published: July 2002

The photoabsorption spectrum of the 4 2Γ excited state of Kr2F has been measured in the 280–850 nm region by fluorescence suppression spectroscopy. Both the 9 2Γ←4 2Γ and 6 2Γ←4 2Γ bands, peaking at 320 and ∼710 nm, respectively, have been observed—the latter for the first time. Although the position of the ultraviolet band is consistent with both theory and previous experiments, its spectral width is ∼40% of that measured by Greene and McCown [Appl. Phys. Lett. 54, 1965 (1989)] in absorption experiments in a pulsed discharge. The relative yield of KrF(B) produced in the photodissociation of Kr2F(4 2Γ) was found to be independent of wavelength over the 280–360 nm and 590–840 nm spectral intervals and the mechanism responsible for photodissociation appears to be predissociation of the Kr2F 9 2Γ and 6 2Γ states by potentials correlated with the KrF(D)+Kr and KrF(C)+Kr limits, respectively.
Low temperature multiple quantum nuclear magnetic resonance spin dynamics in one-dimensional quantum spin chains
Authors: Fel’dman Edward B. , Lacelle Serge
Published: July 2002

Time-resolved multiple quantum nuclear magnetic resonance spectral intensity profiles as a function of the order of coherences, n, are calculated analytically for an infinite one-dimensional quantum spin chain with nearest-neighbor dipolar interactions and shown to be symmetric about n=0 for temperatures above tens of μK.
Inherent amorphous structures and statistical mechanics of melting
Authors: Patashinski Alexander Z. , Ratner Mark A.
Published: July 2002

The statistical mechanics of local and global order in a condensed system is studied in a coarsened model in which the atomic arrangements in small volumes may be crystalline or amorphous. The melting behavior of the material is determined by two characteristic energies, the energy of an orientationally disordered locally crystalline state and the energy of a completely amorphous state. If the amorphization energy is high, the material retains local crystallinity even in the melt; then, at higher temperatures there is a crossover to a locally amorphous state. A material with a low-energy noncrystalline local packing exhibits amorphization melting; the phase transition is from an orientationally ordered crystal state to a fully amorphous melt. Strong interactions that are not of a two-body type are suggested to favor the first behavior, and to lead to structural liquids just above the melting point.
Closed form solution of the itinerant oscillator model of molecular libration
Authors: Coffey W. T. , Walsh M. E.
Published: July 2002

It is shown by using self-consistent (so that action and reaction torques are fully accounted for) expressions for the viscous drag and white noise terms in the equations of motion of the fixed axis rotator version of the itinerant oscillator model that the characteristic (secular) equation of the system automatically factorizes. Hence all the correlation functions of the model (which consists of a “cage” of dipolar molecules surrounding a tagged molecule) may be given in closed form. In particular, the orientational correlation functions of the tagged molecule become the products of single particle ones namely those of a free Brownian rotator and a damped harmonic oscillator while the orientational correlation functions of the cage are simply those of the free Brownian rotator. The equations of motion of the system likewise decouple when the restrictions of small oscillations and of rotation about a fixed axis are removed. Thus, irrespective of the form of the interaction potential between the cage and the tagged molecule, the relaxation modes of the system separate into those of the tagged molecule and those of its surroundings which behave as an inertia corrected free Brownian rotator.
A theoretical approach to the tight-binding band structure of liquid carbon and silicon beyond linear approximations
Authors: Lomba E. , López-Martı́n J. L. , Anta J. A. , Ho/ye J. S. , Kahl G.
Published: July 2002

We present a study of the band structure of liquid Carbon and Silicon modelled in a Tight-Binding Hamiltonian approximation by means of an integral equation approximation that includes non-linear corrections. The theoretical predictions are contrasted with Tight Binding Molecular Dynamics simulations in which the energy bands are obtained by direct diagonalization of the Hamiltonian matrix. The results for Silicon are excellent, whereas in liquid Carbon only some of the qualitative features of the band structure are captured by the non-linear corrections. We find that this can largely be understood as an effect of missing three-body correlation functions in the theoretical treatment of the energy bands. This is particularly crucial in the case of strongly directional and short range bonding, as it occurs in Carbon.
A molecular dynamics study of the CO2/NaCl(001) system
Authors: Vigiani Alessandro , Cardini Gianni , Schettino Vincenzo
Published: July 2002

A molecular dynamics study of the adsorption of CO2 on NaCl (100) is presented. The model potential includes short-range Buckingham atom–atom and charge–charge terms for the molecule–molecule interaction and Lennard-Jones atom–atom and charge–charge terms for the molecule substrate interactions. Calculations have been performed for finite patches and for samples with periodic boundary conditions. The adlayer can form domains with the 2×1 herringbone arrangement. The structure of the adlayer as a function of temperature is discussed in terms of various distribution functions. The vibrational properties of the adlayer (internal and external vibrations) are calculated and compared with available experimental data.
Solvation structure and stability of peptides in aqueous solutions analyzed by the reference interaction site model theory
Authors: Kinoshita Masahiro , Okamoto Yuko , Hirata Fumio
Published: July 2002

We report results of numerical analyses on solvation structure and conformational stability of a dipeptide and Met-enkephalin in the extended simple point charge (SPC/E) model water. The reference interaction site model (RISM) theory is fully solved using our robust, highly efficient algorithm. It is shown that water structure near the peptides and the hydration free energy are greatly dependent on the peptide conformations. Stability of Met-enkephalin is examined in terms of the total energy defined as the sum of the conformational energy and the hydration free energy of the peptide. We test several different conformations including that with the minimum energy in gas phase, which takes rather compact form due to an intramolecular hydrogen bond. It is shown that a fully extended conformation has the highest stability in water. Our results are in qualitative accord with the recent nuclear magnetic resonance (NMR) experiments which suggest fully extended conformations with large fluctuations for the solution structure of the peptide. A conformation which is similar to that obtained from the NMR experiments in miceller solutions, is much less stable when it is put in water. Thus, the peptide conformations are greatly sensitive to microscopic solvent environment, and any native treatment of the solvent such as the continuum model will end in failure.
Aspects of sorption and phase behavior of near-critical fluids confined to mesoporous media
Authors: Schoen Martin , Thommes Matthias , Findenegg Gerhard H.
Published: July 2002

The local structure of a Lennard-Jones fluid confined to a mesoscopic slit-pore with structureless (i.e., “smooth”) walls is investigated by computing the local density ρ(z) in grand canonical ensemble Monte Carlo (GCEMC) simulations. For noncritical thermodynamic states of a corresponding bulk fluid, a homogeneous core region exists in the pore characterized by the bulk density ρbulk. Sufficiently close to the bulk critical point, however, the core is depleted, that is its local density ρcore(z) is less than ρbulk. Along a bulk near-critical isotherm T*=1.36≃Tc,bulk* GCEMC data are analyzed in terms of the equations of state μbulk=μ(ρbulk,Tc,bulk) and μcore=μ(ρ̄mid,Tc,bulk), respectively, where ρ̄mid is the average midpoint density of the core fluid. At densities sufficiently above and below the bulk critical density thermodynamic states of core and bulk are the same, i.e. μbulk=μcore. However, if depletion is observed the density dependence of μbulk and μcore is generally different. By applying a mean-field theory to μbulk and μcore depletion is related to a reduced degree of criticality of the core fluid compared with the bulk phase in a self-contained way.
On the gas–gas equilibria of second kind of nonpolar fluid binary mixtures from a hard-sphere EXP-6 molecular model
Authors: Zarragoicoechea G. J. , Scalise O. H.
Published: July 2002

The phase behavior of a molecular-based model of nonpolar binary mixtures is investigated by the application of thermodynamic perturbation theory. The pair potential interaction model is represented as a reference system of equal size hard-spheres perturbed by the exponential-6 potential. It is found that the qualitative behavior of gas–gas immiscibility of second kind is very much sensitive to the hardness of the potential (ratio of the hard sphere diameter to the size parameter of the perturbation). Calculated theoretical phase diagrams are compared with results from Monte Carlo simulations in the Gibbs ensemble performed for this model mixture.
Dynamic properties of heterogeneous surface films: Multiple scattering of capillary waves
Authors: Noskov B. A.
Published: July 2002

The phenomenon of multiple scattering of surface waves by two-dimensional viscoelastic particles is investigated. A method to evaluate the scattering amplitude is proposed and a simple equation which describes a nonlinear dependency of the effective wave number of transverse surface waves on the concentration of a two-dimensional colloid system is obtained. These results are used thereupon to investigate the propagation of capillary waves in a liquid with a heterogeneous surface film. For equilibrium films, effects of multiple scattering due to fluctuations of the surface tension can be neglected. However, for nonequilibrium systems which contain a heterogeneous solidlike surface phase, the nonlinear dependency of the real part of the effective wave number on the concentration of scatterers can be observed. The inhomogeneity of the dynamic surface elasticity can significantly influence the characteristics of surface waves only for condensed films with two-dimensional “bubbles” of the gaseous phase.
Computer simulations of branched alkanes: The effect of side chain and its position on rheological behavior
Authors: Lahtela Maija , Linnolahti Mikko , Pakkanen Tapani A. , Rowley Richard L.
Published: July 2002

Nonequilibrium molecular dynamics simulations have been performed on model fluids representing eicosane isomers in order to investigate the effect of branching and side chain position on fluid rheology. A heterogeneous, united-atom model with 20 Lennard-Jones interaction sites located at carbon centers was used to model the fluids. Vibrations and bond rotations were frozen, but torsional rotation was included. It was found that viscosity increases significantly from the n-alkane structure to a branch on carbon 2, but the movement of the branch along the carbon backbone has a smaller increasing than decreasing effect. The size of the group in a branched position has a more substantial effect upon the viscosity.
Critical parameters for the heliumlike atoms: A phenomenological renormalization study
Authors: Neirotti Juan Pablo , Serra Pablo , Kais Sabre
Published: July 2002

A mapping between the quantum few-body problem and its classical mechanics pseudo-system analog is used to study the critical parameters for the helium isoelectronic sequence. The critical point is the critical value of the nuclear charge Zc for which the energy of a bound state becomes degenerate with a threshold. A finite-size scaling ansatz in the form of a phenomenological renormalization equation is used to obtain very accurate results for the critical point of the ground-state energy, λc=1/Zc=1.0976±0.0004, as well as for the excited 2p2 3P state, λc=1.0058±0.0017. The results for the critical exponents α and ν are also included.
The hard ellipsoid potential model and the limit of rotational energy transfer in molecular collisions
Authors: Agrawal Paras Mal , Tilwankar Shashank , Dabkara Narendra K.
Published: July 2002

The effect of angular momentum conservation constraints on the limit of the rotational energy transfer (RET) in a diatomic molecule due to collisions with an atom has been investigated. The importance of the classical limit of the rotational energy transfer, (ΔE)max, predicted by the hard ellipsoid potential model has been found such that it is comparable to a well known parameter |ΔE|*, given by the two-parameter power-gap (PG) “law” and the RET cross sections computed on the real potentials. Numerical equivalence of (ΔE)max and |ΔE|* for various types of potential surfaces over a wide range of potential parameters, collision energy and the mass of the system has been verified. The feasibility of obtaining the difference of the semimajor and semiminor axes of the hard ellipsoid potential from the scattering data and the PG “law” has also been discussed.
Multicenter integrals of spherical Laguerre Gaussian orbitals by generalized spherical gradient operators
Authors: Chiu Lue-yung Chow , Moharerrzadeh Mohammad
Published: July 2002

Multicenter molecular integrals over the spherical Laguerre Gaussian-type functions (LGTFs), Lnl+1/2(ar2)rlYlm(r̂)e−ar2, are evaluated analytically by using the generalized spherical gradient operator method. Addition theorem to expand the generalized spherical gradient operator, Ynlm(∇), is developed. Integrals are evaluated by transforming the product of the gradient operators instead of the product of LGTFs. The transformation G coefficients for the gradient operators are explicitly given in terms of the vector-coupling coefficients, and they are much simpler to evaluate than the Talmi coefficients which transform the product of LGTFs. The integral formulas obtained are compact and general for LGTFs of unrestricted quantum numbers n, l, and m. They are four-center (as well as three-center and two-center) integrals of two-electron irregular solid harmonic operator, Ylm(r̂12)/r12l+1, where l=0, l=1, or l=2 corresponds to electron repulsion, spin-other-orbit, or spin–spin interaction, respectively. The two-center exchange-type and Coulomb-type integrals are also evaluated. In the case of two-center and three-center, integral formulas are also obtained for the one-electron irregular solid harmonic operator, Ylm(r̂)/rl+1, where l=0, l=1, or l=2 corresponds to nuclear attraction, spin-orbit interaction or electron-spin nuclear-spin interaction, respectively. Integrals of multicenter overlap as well as transition multipole moment operator, rlYlm(r̂), have also been derived. All of the integral formulas are explicitly in terms of the vector-coupling coefficients and LGTFs of the internuclear coordinates, where the analytical derivatives of these integrals with respect to the geometrical variables can be easily obtained.
Temperature dependence and dynamical instability in the Hartley absorption system of ozone
Authors: Johnson Bruce R. , Chang Bor-Yu , Hsiao Chih-Wei , Le Linh , Kinsey James L.
Published: July 2002

Analysis of weak oscillations in the Hartley absorption system of ozone via the equivalent recurrences in the autocorrelation function is found to reveal a clear temperature effect. Previous classical trajectory studies of unstable nearly periodic orbits associated with these oscillations/recurrences are extended to examine the possibility that strong sensitivity to initial rotational conditions is responsible. Using minimum return distance in phase space as an expedient measure for the stability of the orbits, evidence is found for particular destabilization due to in-plane rotations of the ozone molecule. A model for the recurrence temperature dependence is constructed based on this mechanism, and the implications for comparison of theoretical and experimental recurrence intensities are discussed.
Ab initio study for the low-lying electronic states of Al3 and Al3−: The photoelectron spectroscopy of Al3−
Authors: Baeck Kyoung K. , Bartlett Rodney J.
Published: July 2002

The low-lying electronic states of Al3 (2A1,2B1,4A2,4B1,2B2,2A1,4B2,6A2) and Al3− (1A1,3B2,3A1,3A2,3B1,5A2) are studied by coupled-cluster methods with a [6s5p2d1f] basis set. The geometries and harmonic frequencies are calculated by the coupled-cluster single double triple (CCSD(T)) correlation method with frozen core and virtual molecular orbitals. The energetic splittings at CCSD(T) geometries are calculated also by the CCSDT method. The calculated vibrational frequencies of the observed states of Al3 (A12, B12, and A24) and Al3− (A11 and B23) are in excellent agreement with experimental results. Other frequencies of this work are expected to be correct within ±20 cm−1. It is shown that A24–B14(E″4) and B22–A12(E′2) of Al3 as well as B23–A13(E′3) and A23–B13(E″3) of Al3− are pairs of minima and transition states on a potential energy surface of a pseudorotation of the corresponding degenerate states. The vertical excitation energies of additional states of Al3(2E′,4E′,2A1′) and Al3−(1E″,1E′) are calculated by the electron-excitation equation-of-motion CC method and the electron-attachment equation-of-motion CC method. The possible processes of ionizations and vibronic transitions are analyzed based on the calculated results. All features of the recent photoelectron spectroscopic study of Al3− are explained consistently. It is also shown that the photoelectron signals of electron binding energies of 2.65 and 4.4 eV in earlier experiments correspond to the ionization of the ground state of Al3− to higher-lying excited states of Al3. The two states of the resonant two-photon ionization experiment are assigned to the lowest quartet state and the third quartet state, E″4→E′4, without ambiguity. The anticipated features of five more electronic excitations with transition energies of 0.22, 0.69, 0.77, 0.98, and 1.06 eV are discussed.
Analysis of the bound–free emission spectra from the E(0+) and f(0+) ion-pair states of ClF to obtain potentials for the ion-pair and repulsive valence states
Authors: Kokh D. B. , Alekseev V. A. , Setser D. W.
Published: July 2002

The optical–optical double resonance method has been used to excite selected vibrational levels of the E(0+) and f(0+) ion-pair states of ClF. Subsequent bound–free transitions terminating on three repulsive valence states, Y(3Σ0+−), B1(3Π0+), and C(1Σ0++), have been analyzed. The bound–free continua have been modeled to obtain analytical expressions for the three 0+ repulsive potentials and to improve the description for the E(0+) and f(0+) state potentials. One of the repulsive states is Y(3Σ0+−), which is responsible for the predissociation of B(3Π0+). The transition dipole functions also have been assigned for the bound–free transitions. The molecular orbital configurations of the lower states are discussed. Finally, the influence of homogeneous interaction between the E(0+) and f(0+) states on the bound–free spectra from certain vibrational levels is discussed.
Angular momentum influences on vibrational relaxation pathways from 61 benzene
Authors: Waclawik Eric R. , Lawrance Warren D.
Published: July 2002

Vibrational energy transfer from the 61 level of S1(1B2u) benzene has been studied at low collision energies in supersonic free jet expansions for the collision partners H2, D2, N2, CH4, C2H2, and c-C3H6. Three of the four accessible vibrational relaxation channels in S1 benzene are found to be significantly populated: the 162 level, the spectrally unresolved 111 and 161 levels, and the 00 level. A small amount of transfer to the 41 level was observed with H2 as a collision partner. It is found that: (i) transfer to 00 is generally efficient; and (ii) the state-to-state branching ratios change substantially with collision partner. This is quite different from the trends observed for monatomic collision partners, for which transfer to 00 is absent and the state-to-state branching ratios are largely independent of the collision partner’s identity [E. R. Waclawik and W. D. Lawrance, J. Chem. Phys. 102, 2780 (1995)]. It is further observed that the rotational contours of collisionally populated levels change. For a particular collision partner the extent of rotational excitation in the destination level increases with increasing vibrational energy gap. For a particular destination level there is considerable variation in rotational excitation amongst collision partners. The state-tostate propensity differences between monatomic partners and diatomics and small polyatomics are suggested to arise because angular momentum constraints are influencing the vibrational state-to-state branching ratios. 61→00 transfer is most affected: it is observed only when the collision partner can accept energy as rotational motion, and its branching ratio is particularly sensitive to the collision partner identity.
Effects of viscoelasticity of bulk polymer solution on the surface modes as probed by laser light scattering
Authors: Huang Q. R. , Wang C. H.
Published: July 2002

The effects of surface tension, surface dilational modulus, stress relaxation time, and shear stress modulus on the surface laser light scattering (SLLS) spectrum of polymer solutions are investigated. The capillary wave component is significantly affected by both the stress relaxation time and the amplitude of the shear stress modulus. At moderate concentration, before crossing over to the elastic regime, a strong quasielastic component dominates the SLLS spectrum in polymer solution. In the viscoelastic regime, the capillary wave component of the SLLS spectrum is suppressed by the increase of the surface dilational modulus. The decrease of the surface tension gives rise to an effect similar to that caused by increasing the dilational modulus. However, at high polymer concentration in the elastic regime, the dilational modulus has only a negligible effect on the SLLS spectrum, in contrast to the effect of surface tension.
Specific heat and transport “anomalies” in mixed alkali glasses
Authors: Green Peter F. , Brow Richard K. , Hudgens James J.
Published: July 2002

We show that changes in the relative mole fractions of Li2O and Na2O in alkali metaphosphate glasses lead to “anomalies” in the specific heat and structural relaxations. The heat capacity change between the liquid and glassy states, Δcp(Tg), at the calorimetric glass transition temperature, Tg, exhibits a minimum when the mole fractions of Li2O and Na2O are comparable. Moreover, systematic changes in the temperature dependence of the viscosity, η, i.e., changes in the “fragility” of the system, accompany these changes in mole fraction. This observed dependence of the “fragility” on the mixed alkali ion composition occurs in the absence of apparent changes in the covalent network connectivity which normally accounts for this behavior in glasses.
Influence of the interaction on oscillatory behavior in a surface reaction model
Authors: Lemos M. C. , Luque J. J. , Jiménez-Morales F.
Published: July 2002

Bistability and oscillations of temperature and concentrations are observed in a kinetic model, based on the oxidation of carbon monoxide on a solid surface. The macroscopic kinetic equations, which govern the reaction, are obtained by applying a closure approximation of mean-field type. With the aim of studying how the interaction affects the oscillatory behavior in the reaction, we have explicitly considered the interaction between nearest-neighbor adsorbed species, CO–CO, CO–O, and O–O. Interactions favoring CO2 production are analyzed.
Complete kinematic measurement of three-body reaction dynamics: Dissociative photodetachment of O6− at 532 nm
Authors: Hanold K. A. , Luong A. K. , Continetti R. E.
Published: July 2002

Measurement of the translational energy partitioning in the three-body dissociative photodetachment of O6− (O6−+hν→O2+O2+O2+e−) at 532 nm is reported. Using photoelectron and photofragment translational energy spectroscopies in coincidence, a complete kinematic measurement of the three-body dissociation of neutral O6 is obtained. Vibrationally resolved product translational energy distributions are observed. The results provide insights into the structure, binding energy, and dissociation dynamics of O6− and O6 and illustrate a new approach to the study of three-body reaction dynamics.
Interaction induced phenomena in Raman spectra of mesogens
Authors: Yakovenko S. Ye. , Pelzl J.
Published: July 2002

We present the results of experimental studies of light scattering in the isotropic phase of two mesogens, p-n-pentyl-p′-cyanobiphenyl (5CB) and p-n-pentyl-(p′-cyanophenyl)-cyclohexane (5PCH) and in their solutions in CCl4, a globular molecules solvent. Integral intensities of various Raman bands and Rayleigh wing polarized spectra were studied. Dilution experiments have shown that in mesogen systems, due to molecular interactions, intensity of light scattering may be substantially (about 30%) reduced. Isotropic component of the scattered light is influenced by orientation-translational molecular correlations, while for anisotropic component pure orientational molecular correlations are also important. As a result, depolarization ratio in the condensed state may be substantially different from that for the isolated molecule and may vary through the mesomorphic phase transitions.
Ab initio dynamic dipole polarizabilities for O2, its photoabsorption spectrum in the Schumann–Runge region, and long-range interaction coefficients for its dimer
Authors: Spelsberg Dirk , Meyer Wilfried
Published: July 2002

Perturbed states representing the response to an external electric field are obtained in the multireference averaged coupled pair functional formalism based on orbitals which are optimized in a perturbed multireference self-consistent field procedure. For each perturbing operator perturbed wave functions for several frequencies of the perturbing field are obtained simultaneously. From these sets of perturbed states reduced spectra are derived which represent effective oscillator strength distributions. The broad shape of the Schumann–Runge continuum leads to a poor description of the dynamic polarizability for frequencies approaching the first pole when only vertical transitions are considered. To account for this effect the absorption spectrum in the Schumann–Runge region is calculated and the polarizability is described up to the range of anomalous dispersion. The dynamic polarizabilities and the interaction coefficients are found to be in excellent agreement with experimental data where it is available. Significant differencies of up to 20% are observed between our anisotropic interaction coefficients and earlier estimates obtained from semiempirical anisotropic dipole oscillator strength distributions.
Achieving constant pressure in molecular-dynamics simulations with constraint methods
Authors: Wang Jee-Ching , Fichthorn Kristen A.
Published: July 2002

Although constant-pressure molecular-dynamics simulations can be performed through the use of constraint methods, achieving a desired pressure can be difficult. A technique for setting the pressure is proposed in this paper. The pressure is fixed via an automatic, differential pressure controller which provides a first-derivative coupling to external pressure perturbations. This generates neither pressure overshoot during transient periods nor unrealistic fluctuations at equilibrium. The implementation of this algorithm is outlined and discussed. Results of simulations of a Lennard-Jones fluid are presented.
An ab initio study of the mono- and difluorides of krypton
Authors: Hoffman Gerald J. , Swafford Laura A. , Cave Robert J.
Published: July 2002

Results from ab initio calculations at the CCSD(T) level of theory are presented for krypton monofluoride (KrF), krypton monofluoride cation (KrF+), linear, ground-state krypton difluoride (KrF2), the triplet state of krypton difluoride, and the krypton–fluorine van der Waals complex (Kr–F2). These are the first calculations demonstrating that KrF is a bound molecule, in agreement with experimental observation. When corrected for basis-set superposition error, the calculated potential displays quantitative agreement with the attractive wall of the experimentally measured potential curve. Results are also presented for KrF+ and linear KrF2 which yield accurate values for their dissociation energies. The triplet state of KrF2 is found to have a minimum energy below that of separated atoms, and its structure is bent, with a small F–Kr–F bond angle (71 deg). The van der Waals complex, Kr–F2, appears to consist of an unperturbed F2 molecule attached to a krypton atom in the expected T-shaped structure.
Dissociative adsorption of silane on the Si(100)-(2×1) surface
Authors: Brown A. Robinson , Doren D. J.
Published: July 2002

Density functional theory calculations have been used to explore the mechanism of dissociative adsorption of silane (SiH4) on the Si(100)-(2×1) surface. Two reaction paths are described that produce silyl (SiH3) and hydrogen atom fragments adsorbed on the dimer dangling bonds. The energy barrier on the lowest energy path is 12–14 kcal/mol (depending on the details of the theoretical method used), while the barrier on the other path is about 17 kcal/mol. The initial step in both mechanisms is abstraction of a hydrogen atom from silane by an electron-deficient surface atom. It is also possible for the surface to react by forming a bond between the more electron-rich surface atom and the silane Si atom. This latter reaction path has a prohibitively high barrier (39 kcal/mol), and it leads to different products (adsorbed SiH2 and elimination of H2). These results are discussed in the context of Si film growth kinetics, ultrahigh vacuum studies of silane adsorption and other theoretical studies of silicon surface chemistry.
Time-resolved Raman study on the photoinduced intermolecular electron–transfer reaction of biphenyl in alcohols
Authors: Sasaki Yutaka , Hamaguchi Hiro-o
Published: July 2002

Time-resolved Raman spectroscopy has uncovered a new type of photoinduced intermolecular electron–transfer reaction of biphenyl in alcohols. The Raman bands of the first excited singlet (S1) state, the cation radical and the anion radical of biphenyl were simultaneously observed in the time range 0–200 ns after photoexcitation. The two ion radicals exhibit distinct rise and decay behaviors from each other. A kinetic analysis shows that the electron–transfer reaction consists of the following three elementary processes; (i) monophotonic formation of a biphenyl cation radical and a solvated electron via the S1 state, (ii) migration of the electron in the solvent medium, and (iii) anion radical formation resulting from the capture of the electron by a biphenyl molecule in the ground state. The formation of the cation radical from the S1 state is a slow process with a rate not greater than 10−7 s−1.
Smooth landscape solvent dynamics in electron transfer reactions
Authors: Leite Vitor B. P.
Published: July 2002

Solvent effects play a major role in controlling electron–transfer reactions. The solvent dynamics happens on a very high-dimensional surface, and this complex landscape is populated by a large number of minima. A critical problem is to understand the conditions under which the solvent dynamics can be represented by a single collective reaction coordinate. When this unidimensional representation is valid, one recovers the successful Marcus theory. In this study the approach used in a previous work [V. B. P. Leite and J. N. Onuchic; J. Phys. Chem. 100, 7680 (1996)] is extended to treat a more realistic solvent model, which includes energy correlation. The dynamics takes place in a smooth and well behaved landscape. The single shell of solvent molecules around a cavity is described by a two-dimensional system with periodic boundary conditions with nearest neighbor interaction. It is shown how the polarization-dependent effects can be inferred. The existence of phase transitions depends on a factor γ proportional to the contribution from the two parameters of the model. For the present model, γ suggests the existence of “weak kinetic phase transitions,” which are used in the analysis of solvent effects in charge–transfer reactions.
Simulation studies of liquid ammonia by classical ab initio, classical, and path-integral molecular dynamics
Authors: Diraison M. , Martyna G. J. , Tuckerman M. E.
Published: July 2002

The structure of liquid ammonia at T=273 K has been studied using classical ab initio molecular dynamics, classical molecular dynamics, and the path-integral molecular dynamics methods. The three different types of calculation are employed to generate new insights into the ability of theoretical methods to model liquid ammonia effectively. Thus, the limitations of using classical nuclei, simple point charge models, small systems, and gradient corrected density functional theory are assessed through a comparison of the results of the different types of calculations to each other and recent experiments in a consistent manner. Briefly, the experimental intermolecular quantum structure is very well reproduced by the classical approximation while the intramolecular classical and quantum structures exhibit large deviations. The intermolecular ab initio partial radial structure factors of liquid ammonia and the associated radial distribution functions are in better agreement with experiment than the empirical models. However, the empirical models also perform reasonably well.