bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of beryllocene
Authors: Margl Peter , Schwarz Karlheinz , Blöchl Peter E.
Published: July 2002

The molecular structure and dynamics of beryllocene are investigated using the Car–Parrinello projector augmented wave method. In the ground state, the molecule prefers a η1–η5-coordinated conformation of CS symmetry. At finite temperature, beryllocene undergoes rapid hapticity changes with a frequency of 1–5×1012 s−1. This occurs by means of two mechanisms, each corresponding to a saddle point of the potential surface elevated 5 and 8 kJ mol−1 above the minimum, respectively. The saddle points have CS and C2h symmetry, respectively. The geometric and electronic structure at finite temperature are discussed.
Analytical derivatives for molecular solutes. III. Hartree–Fock static polarizability and hyperpolarizabilities in the polarizable continuum model
Authors: Cammi Roberto , Cossi Maurizio , Tomasi Jacopo
Published: July 2002

We present the theory of the analytical calculation of the SCF dipole polarizability and hyperpolarizabilities for molecular solutes described within the framework of the polarization continuum model. The formulation refers to a cavity with an accurately modeled molecular shape. Calculations of the components of the α, β, and γ polarizability tensors of some polyatomic molecules, in different molecular conformations are presented and discussed.
State-specific coupled cluster-type dressing of multireference singles and doubles configuration interaction matrix
Authors: Meller J. , Malrieu J. P. , Caballol R.
Published: July 2002

Using the theory of state-specific self-consistent intermediate Hamiltonians, one proposes a new dressing of a multireference (MR) singles and doubles configuration interaction (CI) Hamiltonian matrix which insures size consistency. The method is based on a coupled cluster (CC) type factorization of the coefficients of the triples and quadruples and can be considered as leading to a dressed CI formulation of a state-specific MRCC method. Preliminary application of the new procedure to the H4 model and comparison with other MRCC schemes are presented.
Imaging enhanced energy transfer in a levitated aerosol particle
Authors: Arnold S. , Holler S. , Druger S. D.
Published: July 2002

Energy transfer experiments are carried out at dilute concentrations of donors (10−4 M, coumarine 334) and acceptors (5×10−6 M, sulforhodamine 101) in a levitated microdroplet (diameter, 2a=19 μm), using an aerosol particle fluorescence microscope. Microphotographs in donor and acceptor luminescence show that the transfer mechanism is not of a Förster type, but is mediated by morphology dependent resonances (MDRs) of the microdroplet. The transfer is vanishingly small in the central region of the droplet (r<0.9a), and grows to a pronounced maximum beneath the surface (active region), consistent with the theory of MDR-enhanced energy transfer. The angular intensity profile of the acceptor image, along with current theory, suggests that the energy transfer is a maximum with the donor and acceptor at equal distances on opposite sides of the droplet center, ∼18 μm apart. From photometry we measure an overall ratio of acceptor to total luminescence of 7%. Within the active region the transfer efficiency is above 50%. This yield is ∼1000× that expected from Förster transfer. This effect may be understood from a modification in the photon density of states in this region, which leads to efficient photon emission into MDRs.
The accuracy of the pseudopotential approximation. II. A comparison of various core sizes for indium pseudopotentials in calculations for spectroscopic constants of InH, InF, and InCl
Authors: Leininger Thierry , Nicklass Andreas , Stoll Hermann , Dolg Michael , Schwerdtfeger Peter
Published: July 2002

Small- and medium-core pseudopotentials representing [Ar]3d10- and [Kr]-like cores, respectively, have been adjusted for the In atom, supplementing the energy-consistent three-valence-electron large-core ([Kr]4d10 core) pseudopotential of the Stuttgart group. The performance of these potentials is tested against those of other groups and against experiment, in calculations for the ground-state potential curves of InH, InF, and InCl, both at the self-consistent-field and correlated levels. The role of the core size is discussed, and systematic errors of large- and medium-core pseudopotentials are analyzed.
Fluorescence-dip infrared spectroscopy of tropolone and tropolone-OD
Authors: Frost Rex K. , Hagemeister Fredrick C. , Arrington Caleb A. , Zwier Timothy S. , Jordan Kenneth D.
Published: July 2002

Fluorescence-dip infrared spectroscopy (FDIRS) is employed to record the infrared spectra of the isolated, jet-cooled tropolone molecule (TrOH) and its singly deuterated isotopomer TrOD in the O–H and C–H stretch regions. The ability of the method to monitor a single ground-state level enables the acquisition of spectra out of the lower and upper levels of the zero-point tunneling doublet free from interference from one another. The high power of the optical parametric oscillator used for infrared generation produces FDIR spectra with good signal-to-noise despite the weak intensity of the C–H and O–H stretch transitions in tropolone. The expectation that both spectra will exhibit two OH stretch transitions separated by the OH(v=1) tunneling splitting is only partially verified in the present study. The spectra of TrOH are compared with those from deuterated tropolone (TrOD) to assign transitions due to C–H and O–H, which are in close proximity in TrOH. The appearance of the spectra out of lower (a1 symmetry) and upper (b2 symmetry) tunneling levels are surprisingly similar. Two sharp transitions at 3134.9 cm−1 (out of the a1 tunneling level) and 3133.9 cm−1 (out of the b2 tunneling level) are separated by the ground-state tunneling splitting (0.99 cm−1), and thereby terminate in the same upper state tunneling level. Their similar intensities relative to the C–H stretch transitions indicate that the y- and z-polarized transitions are of comparable intensity, as predicted by ab initio calculations. The corresponding transitions to the other member of the upper state tunneling doublet are not clearly assigned by the present study, but the broad absorptions centered about 12 cm−1 below the assigned transitions are suggested as the most likely possibility for the missing transitions.
NaxAu and CsxAu bimetal clusters: Finite size analogs of sodium–gold and cesium–gold compounds
Authors: Heiz Ueli , Vayloyan Arthur , Schumacher Ernst , Yeretzian Chahan , Stener Mauro , Gisdakis Philip , Rösch Notker
Published: July 2002

Mixed metal clusters of sodium and cesium with gold have been generated in a supersonic expansion from the mixed vapor phase. Their tendency towards binary cluster formation, relative thermodynamic stability, and ionization potentials have been experimentally and computationally investigated. The properties of the NaxAu clusters may be understood within an electronic shell model based on delocalized cluster orbitals, whereas the characteristics of CsxAu are indicative of substantial ionic interactions. Relativistic density functional calculations have been performed to elucidate the cluster electronic structure and to rationalize observed properties which may not be accounted for by the jellium model. The properties of these finite-size clusters are shown to be related to the known bulk intermetallic compounds sodium–gold and cesium–gold (cesium aurid), respectively.
Band structure for an sp3 liquid in the single superchain/effective medium approximation
Authors: Lomba E. , López-Martín J. L. , Kahl G.
Published: July 2002

We present a single superchain/effective medium approximation calculation of the electronic density of states for an sp3 fluid in a tight-binding Hamiltonian approximation, with parameters roughly chosen to represent liquid Hg. Comparison with direct diagonalization of the Hamiltonian using quenched liquid configurations generated by molecular dynamics shows that the performance of the theory is more than acceptable for moderate to high densities. Localization is estimated from the inverse participation ratio calculated from the simulation an in a second order renormalized perturbation theory proposed by Winn and Logan. Analysis of the results indicate that by increasing density the metal nonmetal transition occurs well after the band crossing transition. The major weakness of the theory as far as the density of states is concerned can very likely be coped with by inclusion of nonlinear corrections.
Mode suppression in the non-Markovian limit by time-gated stimulated photon echo
Authors: de Boeij Wim P. , Pshenichnikov Maxim S. , Wiersma Douwe A.
Published: July 2002

It is demonstrated that enhanced mode suppression in stimulated photon echo experiments can be obtained by diagonal time gating of the echo. This technique is especially important when the optical dynamics of the system is non-Markovian. A two-mode Brownian oscillator model is used to analyze the effect of time gating on the stimulated photon echo. The method is demonstrated on a dye solution of DTTCI in ethylene glycol at room temperature. Experimentally, time gating of the echo is accomplished by means of femtosecond phase-locked heterodyne detected stimulated photon echo. The vibrational dynamics in this system are explored by conventional stimulated photon echo experiments. Especially stimulated photon echo-maximum shift measurements are found to be particularly useful.
Simulation and theory of the swelling of athermal gels
Authors: Escobedo Fernando A. , de Pablo Juan J.
Published: July 2002

Results of Monte Carlo simulations are presented for the equilibrium swelling of athermal (hard-core) polymeric gels. The networks investigated in this study are defect-free and exhibit strand lengths that range from small to moderate. It is shown that at equilibrium, increasing pressure and strand length leads to higher solvent holdups by the gel. Computer experiments of swelling of gels in binary solvent mixtures indicate that the gel absorbs preferentially the component having the smaller molecular excluded volume. A simple mean-field theory is also presented to describe the swelling of athermal networks. Agreement between theory and simulations is good.
Ab initio study of chemical species in the BCl3 plasma: Structure, spectra, and decomposition paths
Authors: Baeck Kyoung K. , Bartlett Rodney J.
Published: July 2002

Industrially important plasmas offer a variety of complicated molecular processes that benefit from predictive quantum chemical techniques. Ab initio coupled-cluster and MBPT methods are used to characterize structures, vibrational frequencies, ionization potentials, electron affinities, and excited states for the main fragments in the BCl3 plasma, i.e. BCl3, BCl2, BCl, and their anions and cations for which few experimental results exist. The excited, electron attached, and ionized states are calculated by employing the equation-of-motion coupled cluster (EOM-CC) method. Recent results from a photofragmentation study and an electron collision experiment are analysed based on the calculated results. Some features of the potential energy surfaces of excited states of BCl2 are discussed in order to explain the origin of the experimental fluorescence spectrum. We also consider possible microscopic processes with low energy, such as the formation and destruction of neutral and ionic species, decomposition paths, and the role of each fragment. While decomposition through transient states of BCl3− by electron attachment is the most probable path for low-energy electron attachment, decomposition through excited states of BCl3 can play a role only when there is no other way to make the BCl3+ ion.
A photoionization study of trifluoromethanol, CF3OH, trifluoromethyl hypofluorite, CF3OF, and trifluoromethyl hypochlorite, CF3OCl
Authors: Asher Robert L. , Appelman Evan H. , Tilson Jeffrey L. , Litorja Maritoni , Berkowitz Joseph , Ruscic Branko
Published: July 2002

CF 3 OH , an important and controversial by-product of atmospheric decomposition of CF3CFH2 (HFC-134a) and other hydrofluorocarbons, has been examined by photoionization mass spectrometry. The ionization onset is characterized by a broad Franck–Condon distribution, arising primarily from a substantial elongation of the C–O bond upon ionization. An upper limit to the adiabatic ionization potential (IP) of ⩽13.08±0.05 eV has been established. The appearance potentials (APs) of the first two fragments have been accurately determined by fitting with appropriate model functions as AP0(CF2OH+/CF3OH)⩽13.830±0.005 eV and AP0(CF3+/CF3OH)⩽13.996±0.005 eV. While the exact nature of the lowest-energy fragment (nominally CF2OH+) is not clear, the CF3+ fragment threshold leads unambiguously to ΔHf 298∘(CF3OH)⩾−217.2±0.9 kcal/mol and D298(CF3–OH)⩽115.2±0.3 kcal/mol. With previously derived ΔHf 298∘(CF3O)=−151.8−1.1+1.7 kcal/mol, this yields D298(CF3O–H)=117.5−1.4+1.9 kcal/mol, very close to, or only slightly weaker than the O–H bond energy in water: D298(CF3O–H)–D298(HO–H)=−1.8−1.4+1.9 kcal/mol≈0 kcal/mol. Similarly, with the recently redetermined value for ΔHf∘(CF2O), this implies a 298 K reaction enthalpy for the 1,2-elimination of HF from CF3OH of 2.8−1.1+1.7 kcal/mol. CF3OF and CF3OCl have also been examined by photoionization. CF3OF produces a very weak parent, with an apparent adiabatic IP(CF3OF)⩽12.710±0.007 eV. An analysis of the CF3+ and CF2O+ fragments from CF3OF, when combined with literature data, suggests ΔHf 298∘(CF3OF)=−176.9−1.3+1.8 kcal/mol. The fitted value for the appearance potential of CF3+ from CF3OCl, AP0(CF3+/CF3OCl)⩽12.85±0.01 eV, leads to ΔHf 298∘(CF3OCl)⩾−175.6±1.0 kcal/mol, D298(CF3–OCl)⩽88.4±0.3 kcal/mol, and D298(CF3O–Cl)⩽52.8−1.5+2.0 kcal/mol.
General reptation and scaling of 2d athermal polymers on close-packed lattices
Authors: Nelson Peter H. , Hatton T. Alan , Rutledge Gregory C.
Published: July 2002

A new treatment of the general reptation algorithm, introducing the notion of a transition state, is presented for close-packed lattices. Dynamic and static properties of short N-bead polymer systems on the two-dimensional triangular lattice are obtained from Monte Carlo simulations using this algorithm for systems ranging from dilute to concentrated conditions. Extrapolation of the simulation results to long chain lengths is found to be consistent with simple asymptotic power law scaling relations for 〈Rg2〉, the mean-square dimensions of the polymer; their relaxation time, τR; and the center of mass self-diffusion coefficient, Dc.m.. Empirical formulas of the form 〈RSAW2〉/〈R2〉=αX+exp(−βX) are proposed for the mean-square dimensions, 〈R2〉, of athermal polymers as a function of the scaled density X=(N−1)dν−1ρ; where ρ is the polymer segment density; ν is the power law exponent for the mean dimensions, 〈RSAW2〉, of dilute chains of the same length (N−1); and d is the dimensionality of the system. The fitted constants, α and β, are independent of polymer length and density. These formulas successfully account for properties of 2d athermal polymers, from dilute solution conditions through semidilute conditions to the concentrated regime, for polymers of finite length.
A study of nickel monoxide (NiO), nickel dioxide (ONiO), and Ni(O2) complex by anion photoelectron spectroscopy
Authors: Wu Hongbin , Wang Lai-Sheng
Published: July 2002

We report the first anion photoelectron spectroscopic study of nickel monoxide (NiO), nickel dioxide (ONiO), and nickel-O2 complex, Ni(O2). The adiabatic electron affinity (EA) of NiO is measured to be 1.46 (2) eV. Five low-lying electronic excited states (A 3Π, a 1Δ, B 3Φ, b 1Σ+, c 1Π) are observed for NiO at 0.43 (4), 0.94 (4), 1.24 (3), 1.80 (10), and 2.38 (10) eV above the ground state, respectively. Two isomers are observed for NiO2, i.e., the linear ONiO dioxide and the Ni(O2) complex. The dioxide has a high EA of 3.05 (1) eV while the Ni(O2) complex has a rather low EA of 0.82 (3) eV. Two low-lying excited states are observed for ONiO at 0.40 (2) and 0.77 (3) eV above the ground state, respectively. The vibrational frequency of the ν1 mode of the ground state ONiO (X 3Σg−) is measured to be 750 (30) cm−1. The excited states of the Ni(O2) complex give broad photodetachment features starting at about 1.1 eV above the ground state. Information about the electronic structures of the nickel oxide species and chemical bonding between Ni and O and O2 is obtained and discussed.
An analytical representation of the ground potential energy surface (2A′) of the H+Cl2→HCl+Cl and Cl+HCl→HCl+Cl reactions, based on ab initio calculations
Authors: González Miguel , Hijazo J. , Novoa J. J. , Sayós R.
Published: July 2002

In this work we have studied at an ab initio level the lowest 2A′ potential energy surface (PES) of the HCl2 system. This PES is involved in the H(2S)+Cl2(X 1Σg+)→HCl(X 1Σ+)+Cl(2P) and Cl(2P)+HCl(X 1Σ+)→HCl(X 1Σ+)+Cl(2P) gas phase elementary chemical reactions. The former reaction is an important chemical laser while the second one is the most frequently used prototype of heavy–light–heavy reaction. A large number of points on the 2A′ PES have been calculated at the PUMP2/6-311G(3d2 f,3p2d) ab initio level. The ab initio calculations show the existence of two angular transition states with negligible or very small barriers to collinearity. This and other properties of the PES are in agreement with previous studies. An analytical expression based on a many-body expansion has been used to obtain a satisfactory fit of the 740 ab initio points calculated, with a root-mean-square deviation within the range of the estimated ab initio method error margin. This analytical representation of the 2A′ PES has been used to evaluate the variational transition state theory thermal rate constants of the above-mentioned reactions, including also the Cl+DCl reaction, and quite good agreement has been obtained when comparing with experimental results. The analytical PES obtained in this work is suitable for use in studies on the kinetics and dynamics of the HCl2 system.
Heat capacity of the restricted primitive model near criticality
Authors: Valleau John , Torrie Glenn
Published: July 2002

This concerns the supercritical heat capacity of the “restricted primitive model” of Coulombic systems, one aspect of a more general attempt to study the phase transition and critical behavior of this model using thermodynamic-scaling Monte Carlo techniques. We see no indication of Ising-type divergence of the heat capacity; the strength of the evidence in this regard is discussed.
A quasiclassical trajectory study of H+H2O→OH+H2: Angular distributions and OH angular momentum alignment
Authors: Bradley Kimberly S. , Schatz George C.
Published: July 2002

We present a detailed theoretical study of the H+H2O reaction dynamics using quasiclassical trajectories and two potential energy surfaces, one from Walch–Dunning–Schatz–Elgersma (WDSE) and one from Isaacson (I5). Collision energies of 1.0, 1.4, and 2.2 eV are considered, and both scalar and vector properties of the product distributions are presented. The vector properties include polarization-dependent differential cross sections (PDDCS) and angular momentum alignment parameters for both OH and H2. The WDSE and I5 scalar and vector results are in most respects very similar. However, we find that they differ noticeably with respect to angular momentum alignment, with I5 predicting weak OH alignment, while WDSE shows much stronger alignment with the OH angular momentum vector preferentially perpendicular to the scattering plane. The I5 surface is a more recent and more accurate surface for H3O, so it is extremely encouraging that the alignment predicted by I5 is in quantitative agreement with a recent measurement from Brouard and co-workers. In addition, the I5 differential cross section matches the Brouard results quantitatively, while WDSE does not. Detailed mechanistic information underlying the angular distributions, alignment, and PDDCS results is presented, and we find that the differences between I5 and WDSE alignments are connected to different energy release characteristics of the surface in the corner cutting region.
Additional compact formulas for vibrational dynamic dipole polarizabilities and hyperpolarizabilities
Authors: Bishop David M. , Luis Josep M. , Kirtman Bernard
Published: July 2002

Compact expressions, complete through second order in electrical and/or mechanical anharmonicity, are given for the dynamic dipole vibrational polarizability and dynamic first and second vibrational hyperpolarizabilities. Certain contributions not previously formulated are now included.
A combined experimental and theoretical study of rotational energy transfer in collisions between NO(X 2Π1/2, v=3,J) and He, Ar and N2 at temperatures down to 7 K
Authors: James Philip L. , Sims Ian R. , Smith Ian W. M. , Alexander Millard H. , Yang Moonbong
Published: July 2002

Infrared-ultraviolet double resonance (IRUVDR) experiments have been implemented in the ultra-cold environment provided by a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) apparatus. With this technique rate coefficients of two kinds have been measured for rotational energy transfer in collisions between NO and He, Ar and N2: (a) rate coefficients for total removal from specific states of NO(X 2Π1/2; v=3; J=0.5, 3.5 or 6.5) and (b) state-to-state rate coefficients for rotational energy transfer from these levels to specific final states. Using different Laval nozzles, results have been obtained at several different temperatures: for He as collision partner, 295, 149, 63, 27, 15 and 7 K; for Ar, 139, 53, 44 and 27 K; and for N2, 86 and 47 K. The thermally averaged cross-sections for total removal show remarkably little variation, either with temperature or with initial rotational state. The variation of state-to-state rate coefficients with ΔJ shows three general features: (i) a decrease with increasing ΔJ; (ii) a propensity to favor even ΔJ transitions over odd ΔJ changes; and (iii) at lower temperatures, decreases in J are increasingly favored over increases in J and the distribution of rate coefficients against ΔJ becomes narrower. The experimental rate coefficients for collisions with He and Ar are compared with those from both close coupled and coupled states calculations based on potential energy surfaces determined within the coupled electron pair approximation (CEPA) with a large atomic orbital basis set. The agreement between theory and experiment of both the total and the state-to-state rate coefficients is excellent over the complete range of temperatures covered in the experiments.
Rotational alignment of products from NOCl+Sr chemiluminescent reaction
Authors: Zhan Ji-Ping , Yang He-Ping , Han Ke-Li , Wang Ming-Liang , Deng Wei-Qiao , He Guo-Zhong , Lou Nan-Quan
Published: July 2002

The chemiluminescent reactions Sr+NOCl→SrCl(A,B)+NO are studied under the single collision conditions in a beam-gas arrangement. The product rotational alignment 〈P2(Ĵ′⋅k̂)〉=−0.40±0.05 for SrCl(B) is obtained from Sr+NOCl chemiluminescent reactions. In addition, the electronic state branching ratio and the product vibrational state distribution have been roughly estimated by simulating the chemiluminescent spectra of SrCl. Quasiclassical trajectory (QCT) calculations for the Sr+NOCl reaction as a three-body system have been carried out. The calculated results agree well with the experimental ones.
Formation and dynamics of hot-precursor hydrogen atoms on metal surfaces: Trajectory simulations and stochastic models
Authors: Shalashilin Dmitrii V. , Jackson Bret
Published: July 2002

The results of a theoretical study of H atoms colliding with a Cu(111) surface are presented. The metal is treated as a five-layer slab of 150 atoms, and all dynamics are classical. The formation of trapped “hot-precursor” atoms on the surface is examined, as well as the nature of their motion on the surface and their energy and momentum dissipation. Connections are made with recent Eley–Rideal experiments, for which hot-atom precursors may play an important role. To facilitate future simulations of Eley–Rideal and hot-atom reactions on metals, simple stochastic models are developed to describe hot-atom energy dissipation. A Fokker–Planck equation is used to model the hot-atom energy distribution. Quasi-Langevin terms, which simulate fluctuation and dissipation consistent with this Fokker–Planck description, are developed for the hot-atom equations of motion. These quasi-Langevin terms are different from the hydrodynamic forms used for Brownian-type motion.
An internal coordinate model of coupling between the torsion and C–H vibrations in methanol
Authors: Wang Xiaoliang , Perry David S.
Published: July 2002

The torsional tunneling splittings of the asymmetric C–H stretches (ν2 and ν9) in methanol are inverted with the E level lower in energy than the A level, whereas the symmetric C–H stretch (ν3) is normal with A below E. An internal coordinate model, which treats the torsion and the three C–H stretches simultaneously, accounts for the observed tunneling splittings. The model parameters are the local stretching frequency ω=2934.0 cm−1, the direct local–local coupling λ=−42.2 cm−1, and a single stretch-torsion coupling parameter μ=12.9 cm−1. The torsion-vibration coupling is nonadiabatic in the sense that it is not consistent with a Born–Oppenheimer separation of the torsion from the other vibrations. The fact that the model is based largely on the G6 molecular symmetry suggests that tunneling inversion may be common in torsional molecules. The torsionally mediated couplings among the C–H stretches do not conserve symmetry in the Cs point group and are strong enough to contribute to rapid intramolecular vibrational redistribution (IVR).
Determination of the proton tunneling splitting of tropolone in the ground state by microwave spectroscopy
Authors: Tanaka Keiichi , Honjo Hiroaki , Tanaka Takehiko , Kohguchi Hiroshi , Ohshima Yasuhiro , Endo Yasuki
Published: July 2002

Rotational spectra of tropolone in the ground vibronic state were measured by microwave spectroscopy. Due to the proton tunneling motion, the ground state is split into a doublet, of which the lower and upper components are denoted by 0+ and 0−, respectively. In the frequency region 28–84 GHz, more than 150 pure rotational transitions obeying a-type selection rules were observed for each of the 0+ and 0− states. Additionally, tunneling-rotation transitions connecting the lower (0+) and upper (0−) components of the tunneling doublet were observed by pulsed Fourier transform microwave spectroscopy. Twenty-three P- and Q-branch lines were observed in the frequency region of 10–18 GHz, and analyzed combined with the pure rotational transitions for each of the 0+ and 0− states. The proton tunneling splitting in the ground state, Δ0=29 193.788±0.026 MHz, and the tunneling-rotation interaction constant F=16.456±0.015 MHz, were determined, as well as the rotational and centrifugal distortion constants. The dipole moment along the a axis, responsible for the rotational transitions, was determined to be 3.428±0.050 and 3.438±0.050 D for the 0+ and 0− states, respectively.
Infrared spectroscopy of jet-cooled neutral and ionized aniline–Ar
Authors: Piest Hans , von Helden Gert , Meijer Gerard
Published: July 2002

We report the infrared (IR) absorption spectrum of the jet-cooled neutral aniline–Ar Van der Waals complex together with that of the aniline–Ar cation in the 350–1700 cm−1 range. The spectra are measured using mass-selective ion detection in two different IR–ultraviolet double-resonance excitation schemes, using a free-electron laser as a source of widely tunable, intense IR radiation. A comparison with calculated IR spectra of the bare neutral aniline and of the cation of aniline allows for an unambiguous assignment of all the observed modes. The dissociation limit of the neutral aniline–Ar complex is bracketed between 273 and 329 cm−1, significantly lower than previously estimated.
The variations of the hardness and the Kohn–Sham Fukui function under an external perturbation
Authors: Fuentealba P. , Cedillo A.
Published: July 2002

The equations to study the variation of the hardness and the Kohn–Sham Fukui function under the action of an external perturbation are given. Perturbative equations involving the Unsöld approximation are presented. It is found that the variation of the Kohn–Sham Fukui function depends only on the knowledge of the highest occupied molecular orbital density and a mean energy difference which can be interpreted as the band gap or the finite difference approximation for the hardness. The equation for the variation of the hardness is more involved and it depends on the knowledge of the linear response function and the functional derivative of the exchange-correlation potential. However, a simplified way to calculate the variation of hardness is proposed.
The transition of chemisorbed hydrogen into subsurface sites on Pd(311)
Authors: Farı́as Daniel , Schilbe Peter , Patting Matthias , Rieder Karl-Heinz
Published: July 2002

The activated transition of chemisorbed hydrogen atoms into subsurface sites on Pd(311) has been investigated by means of He-atom scattering, high resolution electron energy loss spectroscopy (HREELS), thermal desorption spectroscopy (TDS) and work function measurements. At 120 K, hydrogen exposure leads to the formation of (2×1)H, (2×1)2H, (2×1)3H and c(1×1) 2H phases, with coverages of 0.25, 0.50, 0.75, and 1 monolayers (ML), respectively. The TDS data show three desorption states: α at ∼170 K, β1 at ∼285 K and β2 at ∼310 K. Chemisorbed H atoms forming the ordered layers desorb in the β2 state, whereas the β1 is originated by H atoms located at subsurface sites. The α state is originated by decomposition of layers of Pd hydride near the surface. In all four phases, long-range order disappears at ∼170 K. Heating to 220 K leads to the migration of 0.25 ML H atoms into subsurface sites only if the coverage of the disordered layer is greater than 0.5 ML. The HREELS data demonstrate that this behavior is caused by the occupation of different adsorption sites as a function of coverage: only fourfold coordinated sites are occupied in the (2×1)H and (2×1)2H phases, whereas threefold coordinated sites are also occupied for Θ>0.5 ML. A surprising result is that the HREELS peaks of the surface hydrogen vibrations still exhibit significant changes once all surface sites are occupied, and saturate only after saturation of the subsurface sites. This effect presumably results from strong repulsion between H atoms adsorbed on threefold coordinated sites and subsurface H atoms located in octahedral sites.
Bonding character of bimetallic clusters AunXm (X=Al, In, Cs)
Authors: Heinebrodt M. , Malinowski N. , Tast F. , Branz W. , Billas I. M. L. , Martin T. P.
Published: July 2002

Bimetallic cluster ions of composition AunXm+ (X=Al,In,Cs) have been studied using time-of-flight mass spectrometry. The mass spectra of gold–aluminum clusters exhibit electronic shell effects for arbitrary composition. Differences in the sequence of shell closings for gold-rich and aluminum-rich clusters can be explained in terms of the differing free electron densities of the two materials. Spectra of gold-indium clusters indicate the formation of electronic shells only for gold-rich species. Among clusters with a higher indium content, the series In+(InAu)n is found to have enhanced stability. This indicates an appreciable charge transfer from gold to indium atoms. Similar spectra are found for the system gold-cesium, where Cs+(CsAu)n are most stable.
Equilibrium behavior of symmetric ABA triblock copolymer melts
Authors: Matsen M. W. , Thompson R. B.
Published: July 2002

Melts of ABA triblock copolymer molecules with identical end blocks are examined using self-consistent field theory (SCFT). Phase diagrams are calculated and compared with those of homologous AB diblock copolymers formed by snipping the triblocks in half. This creates additional end segments which decreases the degree of segregation. Consequently, triblock melts remain ordered to higher temperatures than their diblock counterparts. We also find that middle-block domains are easier to stretch than end-block domains. As a result, domain spacings are slightly larger, the complex phase regions are shifted towards smaller A-segment compositions, and the perforated-lamellar phase becomes more metastable in triblock melts as compared to diblock melts. Although triblock and diblock melts exhibit very similar phase behavior, their mechanical properties can differ substantially due to triblock copolymers that bridge between otherwise disconnected A domains. We evaluate the bridging fraction for lamellar, cylindrical, and spherical morphologies to be about 40%–45%, 60%–65%, and 75%–80%, respectively. These fractions only depend weakly on the degree of segregation and the copolymer composition.
Dipolar relaxation in a many-body system of spins of 1/2
Authors: Nevzorov Alexander A. , Freed Jack H.
Published: July 2002

The method utilized in Paper I [J. Chem. Phys. 112, 1413 (2000)] for treating the density matrix equation for a two-spin system in the presence of the dipolar interaction that is randomly modulated by translational diffusion, is extended to a many-body system of identical spins of 1/2. Generalized cumulant expansions are used, which allow one to take full advantage of the statistical independence of the motions of spins. In the high-temperature approximation (appropriate for dilute solutions), for a single nonselective pulse, the symmetry of the problem allows one to obtain a compact ordered binomial expression for the free-induction decay signal that is related to the two-particle solution, and it still contains the two spin-isochromat components. The latter are evaluated by solving the corresponding stochastic Liouville equation, which allows one to recover in a unified way the two limiting cases including Anderson’s result for statistical broadening in a rigid lattice and the classical Torrey–Bloembergen–Redfield expression for the motional narrowing, as corrected by Hwang and Freed. The line shape expression in the thermodynamic limit, i.e., for large numbers of particles in a macroscopic volume, is obtained. It is found that the many-body dipolar line shapes are very close to Lorentzians over the entire motional range studied, with the linewidths proportional to the spin concentration, as predicted earlier for the limiting cases. Linewidths plotted versus the values of the translational diffusion coefficient clearly show the solid-state limit, the motional-narrowing limit, and the intermediate region. The method is extended to describe the behavior of the many-body system in a solid-echo sequence. This enables one to obtain the homogeneous T2’s over the whole range of motions. A minimum in T2 is found at approximately the same value of translational diffusion coefficient as was found for the two-spin case in Paper I.
The short-time dynamics of molecular reorientation in liquids. I. The instantaneous generalized Langevin equation
Authors: Jang Joonkyung , Stratt Richard M.
Published: July 2002

Up until relatively recently, experimental measurements of the rotational dynamics of small molecules in liquids were largely confined to seeing the effects of rotational diffusion. The molecular character of the process seemed of little relevance. However, newer measurements have begun to look in some detail at the microscopics behind molecular reorientation. We show in this paper that it is possible to understand the short-time dynamics of rotation in liquids at a molecular level by looking at the instantaneous normal modes of the remaining degrees of freedom. With the aid of some other, properly short-time, approximations, the reorientational dynamics can be cast into the form of an instantaneous generalized Langevin equation—one defined for each liquid configuration. One therefore obtains fully molecular expressions for the instantaneous rotational friction and fluctuating torque felt by a solute. The average friction so obtained seems to describe the basic nondiffusional aspects of rotation reasonably accurately and lends itself—as we illustrate in the companion paper—to more detailed investigations into the actual molecular mechanisms behind rotational relaxation. In the course of this work we also show that just as the autocorrelation function for the force on a rigid bond yields an accurate portrayal of the friction needed to study vibrational relaxation, quantitatively accurate results for the rotational friction can be provided by using molecular dynamics to compute the torque autocorrelation function for an orientationally rigid solute.
Size-extensivity correction for the state-specific multireference Brillouin–Wigner coupled-cluster theory
Authors: Hubač Ivan , Pittner Jiřı́ , Čársky Petr
Published: July 2002

We present a simple a posteriori correction for the state-specific multireference Brillouin–Wigner coupled-cluster (MR BWCCSD) theory, which eliminates its size-extensivity error. In the converged amplitudes we drop terms that were identified to be responsible for the lack of size extensivity. We performed MR BWCCSD calculations with this correction on CH2, SiH2, twisted ethylene, F2, and ozone that are all, from the computational point of view, typical representatives of two-reference problems. Comparison with rigorously size-extensive calculations and experiment shows that the size-extensivity error of the corrected MR BWCCSD is only a few tenths of kcal/mol.
A two-step uncontracted determinantal effective Hamiltonian-based SO–CI method
Authors: Vallet Valérie , Maron Laurent , Teichteil Christian , Flament Jean-Pierre
Published: July 2002

We present a new two-step uncontracted spin-orbit configuration interaction (CI) method which automatically accounts for spin-orbit polarization effects on multiconfigurational wave functions by selecting the single excitations having a significant spin-orbit interaction with a chosen determinantal reference space. This approach is in the line of a conventional two-step method, as a sophisticated correlation treatment in a scalar relativistic approximation is carried out in the first step. In the second step, we define a model space which includes a set of reference configurations able to represent all the wanted states along with singly excited configurations selected with the spin-orbit (SO) operator. We then exploit the first-step calculation in order to include correlation effects via an effective Hamiltonian technique and diagonalize the full matrix on the determinantal basis. The method combines the advantages of both one-step and conventional two-step SO–CI methods; it intends to treat efficiently the cases where both relativity and extended CI treatments are needed. The new code EPCISO is tested on the spin-orbit splitting of the P2 electronic ground state of the thallium atom which, in spite of its very simple electronic structure is a well-known difficult case study for SO–CI methods. The EPCISO code yields results in excellent agreement with the experimental splitting value; they are compared to those obtained using the conventional two-step CIPSO code.
Probability density function of the single eigenvalue outside the semicircle using the exact Fourier transform
Authors: Ullah Nazakat
Published: July 2002

It is shown that the probability density function far outside the semicircle is closely related to the form factor of N one-dimensional nucleons. The exact Fourier transform of the probability density function for the Gaussian unitary ensemble is given. Using this transform it is shown that the probability density function P(x) far outside the semicircle is a Gaussian function multiplied by powers of X.
A phase cell approach to Yang–Mills theory. II. Analysis of a mode
Authors: Federbush Paul , Williamson Calvin
Published: July 2002

Properties of a mode announced in a previous paper are proved. This involves some complicated calculations in linear algebra, and observation of the structure of a function of several complex variables.
The covariant effective action in QED. One-loop magnetic moment
Authors: Ostrovsky A. A. , Vilkovisky G. A.
Published: July 2002

The paper starts the program of rewriting quantum electrodynamics in terms of the manifestly covariant and covariantly computed effective action. A general method for obtaining nonlocal terms in the effective action is proposed and the term responsible for the one-loop magnetic moment of the electron is worked out. In contrast to the usual calculation based on Green’s functions, the present calculation nowhere encounters the infrared divergences (including renormalization and restriction to the physical mass shell). Comparison with the method of Green’s functions shows the inadequacy of the latter.
On the construction of Hamiltonians
Authors: Lucey C. A. , Newman E. T.
Published: July 2002

It is shown that, for the system of first-order ordinary differential equations of the form dxa/dt =f a(xb), it is always possible to construct a locally defined nondegenerate symplectic structure Ωab(x), and write the equations as the canonical equations for some Hamiltonian function H(x) such that f aΩab=∇bH. Furthermore, a Lagrangian L(x,ẋ), which is linear in the velocities dxa/dt, can be found, whose variation yields these same canonical equations. Finally we discuss, via the Dirac brackets, how the standard transition from a Lagrangian system to a Hamiltonian system works in this pathological case.
An operator analysis for the Schrödinger, Klein–Gordon, and Dirac equations with a Coulomb potential
Authors: de Lange O. L.
Published: July 2002

An operator analysis is presented that provides a unified treatment of the Schrödinger (S), Klein–Gordon (KG), and Dirac (D) equations with a Coulomb potential. The analysis uses energy shift operators that factorize an appropriate radial equation. This radial equation is based on standard results and a recent formulation of the Dirac–Coulomb problem [J. Y. Su, Phys. Rev. A 32, 3251 (1985)]. The shift operators yield energy eigenvalues and a formula that contains normalized, radial coordinate-space wave functions for the S, KG, and D equations. Formulas that contain expectation values for the S, KG, and D equations are obtained by applying the hypervirial theorem and the Hellmann–Feynman theorem to the radial equation.
The graviton propagator in maximally symmetric spaces
Authors: Turyn Michael
Published: July 2002

Vacuum metric perturbation two-point functions are found for maximally symmetric backgrounds of arbitrary dimension n, using tensor mode functions on the n-sphere and a general gauge-fixing term. The gauge-invariant part of the resulting graviton propagator is isolated, and is fully evaluated for de Sitter spaces in terms of functions of the geodesic separation.
Group theory of the Smorodinsky–Winternitz system
Authors: Evans N. W.
Published: July 2002

The three degrees of freedom Smorodinsky–Winternitz system is a degenerate or super-integrable Hamiltonian that possesses five functionally independent globally defined and single-valued integrals of the motion in both classical and quantum mechanics. This is explained in terms of a forced degeneracy imposed as a consequence of the invariance of the Hamiltonian under a group of symmetry transformations isomorphic to the three-dimensional unitary unimodular group, SU(3). In turn, this degeneracy group is embedded in a larger group of transformations that maps all the bound energy levels among each other, the so-called dynamical group. All the bound state eigenfunctions act as basis functions for a single irreducible representation of the dynamical group. So, in common with the hydrogen atom and the harmonic oscillator, the quantum mechanics of the Smorodinsky–Winternitz system may be completely solved within the framework of group theory alone.
Localized coherent structures of the Davey–Stewartson equation in the bilinear formalism
Authors: Martínez Alonso L. , Medina Reus E.
Published: July 2002

The Davey–Stewartson equation is considered from the point of view of the bilinear formalism of the Kyoto school. Multidromion solutions are constructed in terms of free fermions and their asymptotic properties are characterized. The dynamical properties of dromions are discussed.
The induction coefficients of the Hecke algebra and the Clebsch–Gordan coefficients of the quantum group SUq(N). I. Special Gel’fand basis
Authors: Pan Feng , Chen Jin-Quan
Published: July 2002

A general procedure for evaluating the induction coefficients (IDCs) or the outer-product reduction coefficients of the Hecke algebra Hf(q) of the Af−1 type is formulated based on the linear equation method. Analytical expressions for the IDC’s of Hf(q) are tabulated for f≤4. It is also proved that these IDCs are the Clebsch–Gordan coefficients for the special Gel’fand basis of the quantum group SUq(N).
Grassmann calculus, pseudoclassical mechanics, and geometric algebra
Authors: Lasenby Anthony , Doran Chris , Gull Stephen
Published: July 2002

A reformulation of Grassmann calculus is presented in terms of geometric algebra—a unified language for physics based on Clifford algebra. In this reformulation, Grassmann generators are replaced by vectors, so that every product of generators has a natural geometric interpretation. The calculus introduced by Berezin [The Method of Second Quantization (Academic, New York, 1966)] is shown to be unnecessary, amounting to no more than an algebraic contraction. This approach is not only conceptually clearer, but it is also computationally more efficient, as demonstrated by treatments of the ‘‘Grauss’’ integral and the Grassmann Fourier Transform. The reformulation is applied to pseudoclassical mechanics [Ann. Phys. 104, 336 (1977)], where it is shown to lead to a new concept, the multivector Lagrangian. To illustrate this idea, the three-dimensional Fermi oscillator is reformulated and solved, and its symmetry properties discussed. As a result, a new and highly compact formula for generating super-Lie algebras is revealed. The paper ends with a discussion of quantization, outlining a new approach to fermionic path integrals.
Envelope theory in spectral geometry
Authors: Hall Richard L.
Published: July 2002

It is shown that the discrete spectrum of Schrödinger Hamiltonians of the form H=−Δ+vf may be represented by the semiclassical expression Enl=minr≳0 {K(f)nl(r) + vf(r)}. The K functions are found to be invariant with respect to coupling and shifts: K(Af+B)=K(f). For pure power laws, f(r)=sgn(q)rq, and the log potential, they are also invariant with respect to scale, and have the simple forms (Pnl(q)/r)2 and (Lnl/r)2, respectively. K functions are also derived for sech-squared and Hulthén potentials. If f=g(h), where g is a smooth transformation, then the envelope approximation is expressed in terms of K by the relation K(f)≂K(h). When the transformation g has definite convexity, then the approximation immediately yields eigenvalue bounds for all n and l. The theory is used to prove the log-power theorem Lnl = Pnl(0), which, in turn, generates a simple eigenvalue formula for the log potential.
Classical and quantum integrability of a derivative nonlinear Schrödinger model related to quantum group
Authors: Kundu A. , Mallick B. Basu
Published: July 2002

An ultralocal structure discovered in a derivative nonlinear Schrödinger model enables us to investigate the complete integrability of the classical system through action-angle variables and solve exactly the quantum model by quantum inverse scattering transformation. Exploiting the underlying quantum group related Sklyanin-like algebra an exact lattice version of the model is constructed, and also the deep-rooted reason for the existence of such an ultralocal model is revealed.