bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature dependence of electron attachment to methylene chloride
Authors: Pinnaduwage L. A. , Tav C. , McCorkle D. L. , Ding W. X.
Published: July 2002

Temperature dependence of dissociative electron attachment to methylene chloride in the electron energy range of 0–10 eV was studied in a high-temperature electron swarm apparatus. The measurements were made using N2 and Ar as buffer gases. From the measured electron attachment rate constants, the electron attachment cross sections at 300, 400, and 500 K were determined using an unfolding technique. The maximum electron attachment cross sections at 300, 400, and 500 K were ≈3.1×10−18, ≈8.2×10−18, and ≈1.7×10−17 cm2, and occurred at electron energies of ≈0.8, ≈0.65, and ≈0.55 eV, respectively. The increase in electron attachment to methylene chloride with temperature is attributed to the increase in the vibrational energy of the molecule.
H-bonding in liquid acetamide as studied by x-ray scattering
Authors: Nasr Salah , Ghédira Mounir , Cortès Robert
Published: July 2002

A structural investigation of liquid acetamide was performed at 346 K using x-ray scattering. The data are analyzed to yield the molecular structure factor and the distinct pair correlation function. Two H-bonds per molecule are found on average. The mean N⋯O distance is about 3.03 Å. The liquid structure can be described by some structural units similar to the ones existing either in the rhombohedral or in the orthorhombic crystalline form.
Pure rotational spectrum of CaCH3(X̃ 2A1) using the pump/probe microwave-optical double resonance (PPMODR) technique
Authors: Namiki Kei-ichi C. , Steimle Timothy C.
Published: July 2002

The pure rotational spectrum of calcium monomethyl, CaCH3(X̃ 2A1), was recorded using the pump/probe microwave-optical double resonance (PPMODR) technique. The determined Fermi contact and dipolar parameters are: aF=−1.965(11) and Taa=2.180(18) MHz. The spin-rotation parameters are: εaa=6.702(49) and (εbb+εcc)/2=55.5730(27) MHz. The mm-wave data [M. A. Anderson and L. M. Ziurys, Astrophys. J. 460, L77 (1996)] were reanalyzed to produce a set of fine structure parameters that are consistent with the PPMODR values and for which the standard deviation of the mm-wave data set is greatly reduced. A global fit of the two sets of data was performed to give an improved set of fine and hyperfine parameters for the X̃ 2A1 state. The negative value for aF is inconsistent with a simple σ-bond spin polarization model. A comparison among calcium containing molecules is made using hyperfine and spin-rotation parameters.
Intriguing kinetics for chlorine etching of the Si(100)-(2×1) surface
Authors: Dohnálek Z. , Nishino H. , Kamoshida N. , Yates J. T.
Published: July 2002

The desorption kinetics of SiCl2(g) species from the Cl covered nondefective Si(100)-(2×1) surface is investigated. During temperature programmed desorption, an extremely fast SiCl2(g) desorption with the full width at half maximum of 14 K at 953 K is observed from the superheated Cl saturated Si(100). The coverage-dependent desorption kinetics of SiCl2(g) follows a second order dependence on the coverage of adsorbed Cl and on the coverage of bare Si sites. The activation barrier and preexponential factor of 197±19 kJ/mole and 5×1010±1 s−1, respectively, are obtained from the model. On the Cl-saturated Si(100) surface, an additional high energy kinetic step is necessary to initiate the SiCl2(g) desorption since there are not any bare Si sites. As soon as this process turns on, the desorption of SiCl2(g) occurs catastrophically via the low energy desorption process.
Studies on electronic structures of semiconductors by atomic force microscopy
Authors: Shimizu Masaaki , Watanabe Hiroyuki , Anazawa Kazunori , Miyahara Tomoko , Manabe Chikara
Published: July 2002

We propose a new method of electron spectroscopy. Using an atomic force microscope, we have measured attractive forces between a sample and a metal coated tip with varying applied voltage in dry nitrogen atmosphere. We have then plotted the values as a function of the voltage to obtain a force spectrum. The spectra of Si, ZnSe, and diamond show band gap structures which can be explained by a charge–transfer model. The spectrum of C60 single crystal shows an energy gap of ∼2.0 eV and a highest occupied–lowest unoccupied molecular orbital (HOMO–LUMO) separation of 3.8 eV. These results are in good agreement with the energy gap and the HOMO–LUMO separation obtained by electron spectroscopy, respectively. The spectrum of C60 also reveals the features of density of state, which are in fairly good agreement with those obtained by electron spectroscopy. Application of this method to anthracene and p-terphenyl single crystals allowed us to discuss the natures of valence and conduction bands.
Fractal behavior of galvanic current of dual electrode type of atmospheric corrosion monitor
Authors: Saitou M. , Oshikawa W. , Itomura S. , Tsuzikawa S.
Published: July 2002

Eleven-month series of the galvanic current of dual electrode type devices exposed to the atmosphere are analyzed to make clear the fractal behavior of corrosion. The result indicates that a relation predicted by the scaling theory is strictly consistent with the experimental result and the fractal behavior of corrosion is insensitive to the local details.
Statistics of an ideal polymer in a multistable potential: Exact solutions and instanton approximation
Authors: Mondescu Radu P. , Muthukumar M.
Published: July 2002

We have considered the stationary state of a one-dimensional Gaussian polymer chain of length Nl (N is number of segments, l is the Kuhn length) subjected to a one-parameter class of exactly solvable, symmetric, repulsive potentials with multiple (two or three) minima. We have calculated analytically and numerically the exact Green’s function G(R|R′;L) and the mean-square end-to-end distance 〈(R−R′)2〉, respectively, of the polymer chain. The instanton approximation is translated in polymer physics language and used to analyze the conformation of the polymer chain in its ground state, by evaluating the average number of folds that connect the potential minima. All quantities are functions of the barrier height and of the separation between wells. Our results show that for a given length N, the polymer expands with increasing barrier width until a maximum value of 〈(R−R′)2〉 is reached. Afterwards, the polymer apparently collapses in one of the wells. This behavior defines a critical length N* and may offer the possibility of applications in separation and pattern recognition processes.
Infrared spectrum and ab initio calculations of the CH3CNH+-H2 ionic complex
Authors: Dopfer Otto , Roth Doris , Olkhov Rouslan V. , Maier John P.
Published: July 2002

The infrared photodissociation spectrum of the CH3CNH+-H2 complex has been recorded in the vicinity of the H2 (ν1) and N-H (ν2) stretch fundamentals. The complexation-induced frequency redshifts (Δν1≈64, Δν2=183 cm−1) and the rotational structure of the ν1 band are consistent with a T-shaped proton-bound CH3CNH+-H2 geometry with a vibrationally averaged intermolecular bond length of 1.9 Å. Ab initio calculations at the MP2 level of theory predict a binding energy of 1100 cm−1 for the T-shaped complex, an intermolecular separation of 1.77 Å, and frequency shifts of Δν1=88 cm−1 and Δν2=215 cm−1, in agreement with the experimental data. Whereas the CH3 internal rotation is nearly free (barrier Vb<0.1 cm−1), H2 rotation via a transition state with a linear -H⋯H-H bond is severely hindered (Vb≈1050 cm−1). The lifetime of the ν1 state (>130 ps) greatly exceeds that of the lower lying ν2 state (<30 ps), indicating that the relaxation dynamics are mode-selective and not statistical.
Surface vibrational coherence at the CaF2/air interface: Vibrational wave packet dynamics as a probe of interface inhomogeneity
Authors: Star Dmitry , Kikteva Tanya , Leach Gary W.
Published: July 2002

Vibrational wave packet dynamics from a monolayer-covered surface are reported. These dynamics reflect surface vibrational coherence in a monolayer of amphiphilic molecules deposited at the CaF2/air interface. The induced macroscopic polarization following coherent excitation of adsorbate CH3 vibrational modes displays quantum interference effects (quantum beats) and decays on a time scale dependent on the nature of the interfacial environment. These observations provide a link between the degree of interfacial order and the vibrational coherence lifetime and demonstrate that monitoring interfacial wave packet dynamics represents a new method for characterizing these important chemical regions.
Femtosecond ultraviolet laser-induced desorption of NO from NiO(100)/Ni(100)
Authors: Eichhorn G. , Richter M. , Al-Shamery K. , Zacharias H.
Published: July 2002

We have studied the ultraviolet laser-induced desorption of NO molecules from an epitaxial film of NiO(100) on Ni(100) for pulse durations of 550 fs and at a photon energy of 3.95 eV. For applied laser intensities up to 450 MW/cm2, the highest intensities employed in this work, a linear dependence of the desorption yield on the laser intensity is observed. A desorption cross section of (1.9±0.3)⋅10−17 cm2 is then derived. The molecules are detected with rovibrational state selectivity by (1+1)-REMPI via the A 2Σ+(v′=0,1,2,3)←X 2Π(v″=0,1,2,3) γ-band transitions. The rotational population distributions are nonthermal, with rotational temperatures of about 290 K at low and of about 770 K at high rotational energies. The relative populations in the 2Π1/2 and 2Π3/2 fine-structure states and of the Λ-doublet states are examined for the given set of (v″,J″) quantum numbers. The vibrational states v″>0 are significantly populated approaching vibrational temperatures of 3800 K. Velocity distributions of the desorbed molecules are measured for individual rovibrational states. Bimodal distributions with a distinct rotational-translational coupling are observed. Further, molecules desorbing in the excited fine-structure state 2Π3/2 show a higher velocity than those desorbing in 2Π1/2 The results are compared with earlier ones obtained for the same system with nanosecond desorption pulses at hν=6.4 eV.
Between vapor and ice: Free water clusters studied by core level spectroscopy
Authors: Björneholm O. , Federmann F. , Kakar S. , Möller T.
Published: July 2002

Core level x-ray absorption and photoemission spectra of free water clusters are presented. Core and valence photoemission spectra show a weak but gradual change with cluster size. Comparisons to spectra of the isolated molecule and solid ice indicate that water molecules have a lower average coordination in clusters than in the bulk solid. X-ray absorption spectra reveal spectral characteristics between the free molecule and the bulk. These are compared to similar spectra of the isolated molecule and solid ice, and discussed in connection to calculated structures.
Spectroscopic characterization of excited Ca(4s4dδ 3DJ)RG(3Δ1,2) states (RG=Ar, Kr, Xe): No “heavy-atom” mixing of RG(ndδ) character into the wave functions
Authors: Leung Allen W. K. , Kaup John G. , Bellert D. , McCaffrey John G. , Breckenridge W. H.
Published: July 2002

The excited Ca(4s4dδ 3DJ)RG[3Δ1,2] states (RG=Ar, Kr, Xe) have been characterized spectroscopically by R2PI (resonance-enhanced two-photon ionization) spectroscopy. The main vibrational progressions, assigned to Ca(4s4dδ 3D1)RG[3Δ1]←Ca(4s4pπ 3P0)⋅RG[3Π0−] transitions, have weak subbands 3.7±0.5 cm−1 to the blue which have been assigned to analogous transitions to the Δ23 upper states. For CaAr and CaKr, rotational analysis has confirmed this assignment. The Δ23/3Δ1 splitting is within experimental error the value expected if the molecular spin-orbit coupling constant is derived entirely from the Ca(4s4d 3DJ) atomic contribution. This indicates that there is no “heavy-atom” mixing of RG(ndδ) character into the wave functions of the CaRG(3Δ) states.
Classical flux integrals in transition state theory: Generalized reaction coordinates
Authors: Smith Sean C.
Published: July 2002

Transition state theory (TST) approximates the reactive flux in an elementary chemical reaction by the instantaneous flux passing through a hypersurface (the “transition state”) which completely divides the reactant and product regions of phase space. The rigorous classical evaluation of this instantaneous flux is carried out as a trace in phase space: effectively a multidimensional integral. We present an analysis of the momentum-space component of this flux integral for the case of a generalized reaction coordinate. The classic analysis of the canonical flux by Marcus [J. Chem. Phys. 41, 2624 (1964)] is refined by reducing the determinant which appears in the transition state partition function to a very simple form, facilitating the ensuing integration over coordinate space. We then extend the analysis to provide analytic expressions for the momentum flux integrals in both the energy-resolved, and the energy+angular-momentum-resolved microcanonical ensembles. These latter expressions allow substantial gains in the efficiency of microcanonical variational implementations of Transition State Theory with generalized reaction coordinates.
Time-dependent density functional calculations on the electronic absorption spectrum of free base porphin
Authors: van Gisbergen S. J. A. , Rosa A. , Ricciardi G. , Baerends E. J.
Published: July 2002

Three high-level correlated ab initio studies have recently been performed on the electronic absorption spectrum of free base porphin (FBP), but significant differences between the various assignments of the low-lying bands remain. In view of the importance of FBP as the basic building block of the porphyrins, further reliable results are evidently required and are provided here, using time-dependent density functional theory (TDDFT). Our results strongly support the recent CASPT2 interpretation which is consistent with the traditional interpretation, stating that the intense B band (or Soret band) is due to the two close-lying excitations 2 1B2u and 2 1B3u. As in the CASPT2 paper, we attribute all low-lying bands to pairs of B2u1–B3u1 excitations. The interpretation of the combined B–N band system is discussed in some detail. The effects of basis set, geometry, and choice of exchange-correlation potential are considered as well.
Molecularly chemisorbed intermediates to oxygen adsorption on Pt(111): A molecular beam and electron energy-loss spectroscopy study
Authors: Nolan P. D. , Lutz B. R. , Tanaka P. L. , Davis J. E. , Mullins C. B.
Published: July 2002

High translational energy adsorption of oxygen on the (111) surface of platinum was examined with electron energy loss spectroscopy (EELS) and molecular beam techniques. EEL spectra indicate that over an incident energy range of 0.2–1.37 eV and on a Pt(111) surface held at 77 K, oxygen adsorbs in an associative chemisorbed state—yielding to the dissociated state only after sufficient substrate heating. Simple direct dissociation appears negligible for all incident kinetic energies studied. At near-zero surface coverages, exclusive population of the peroxolike molecular precursor is observed for adsorption at these high translational energies, while both superoxolike and peroxolike forms are detected for low energy adsorption (0.055 eV). This peculiarity represents evidence that translational energy is effective in differentially populating reaction intermediates and provides better quantification of potential energy barriers to dissociation. We estimate the activation barrier for dissociation from the peroxolike precursor to be approximately 0.29 eV. Initial adsorption probability measurements over a wide range of surface temperatures and high incident kinetic energies corroborate a molecular chemisorption mediated mechanism.
Effects of vibration on the polarizability and the first and second hyperpolarizabilities of HF, HCl, and HBr
Authors: Bishop David M. , Norman Patrick
Published: July 2002

We report calculations, using electron uncorrelated and correlated wave functions, of the electronic and vibrational properties which pertain to certain nonlinear optical properties for HF, HCl, and HBr. Our main focus is on vibrational effects (zero-point-vibrational averaging and pure vibration). Analysis of the results obtained at various levels of approximation indicates that first-order perturbation theory is generally adequate for finding the zero-point-vibrational-averaging corrections for these molecules and that complete second-order perturbation theory nearly always gives reliable results for the pure vibrational corrections. Attention is drawn to some differences with previously published results for these properties.
Theoretical study of the electronic ground state of iron(II) porphine. II
Authors: Choe Yoong-Kee , Nakajima Takahito , Hirao Kimihiko , Lindh Roland
Published: July 2002

Ten low-lying electronic states of Fe(II) porphine, 5A1g, 5Eg, 5B2g, 3A2g, 3B2g, 3Eg(A), 3Eg(B), 1A1g, 1B2g, and 1Eg states, are studied with multiconfigurational second-order perturbation (CASPT2) calculations with complete active space self-consistent field (CASSCF) reference functions with larger active space and basis sets. The enlargement of active space and basis sets has no influence on the conclusion of a previous multireference Møller–Plesset perturbation (MRMP) study. The present CASPT2 calculation concludes that the 5A1g state is the ground state. A relativistic correction has been performed by the relativistic scheme of eliminating small components (RESC). For energetics, no significant contribution from the relativistic correction was found. The relative energies and orbital energies are not changed appreciably by the introduction of a relativistic correction. The present result does not agree with all the spectroscopic observations, but is consistent with a magnetic moment study.
Transfer of a pollutant molecule through a water film on a single crystal surface
Authors: Marmier A. , Hoang P. N. M. , Girardet C. , Lynden-Bell R. M.
Published: July 2002

We study the transfer of a CO2 molecule from the gas phase through a thin liquid water film supported on ionic single crystal surfaces NaCl and MgO (001). The free energy profile for the CO2 is calculated at 300 K using constrained molecular-dynamics simulation, and the detailed analysis of the competition between interaction and entropic contributions can help to the understanding of the pollution kinetic process of a water covered solid surface. It is shown that the CO2 solvation and its adsorption directly on the solid surface is easier for a NaCl supported film than for a MgO one.
Relaxation following uniaxial extension of dilute polymer solutions
Authors: Wiest John M.
Published: July 2002

How polymer molecules uncoil and stretch under the influence of an elongational or stretching flow has been the subject of considerable study and discussion. Many experimental studies have been conducted to try to achieve such flows for dilute polymer solutions, but the recent development of filament stretching devices has made it possible to examine the flows unequivocally. Furthermore, these devices allow examination of the processes by which the polymer molecules relax upon cessation of the flow. Here, we present the predictions of the finitely extensible nonlinear elastic chain model (under the Peterlin approximation) for both the stretching and the relaxation. Calculations of conformational, rheological, and optical properties are given. It is found that the process by which the molecules relax, which is governed primarily by segment relaxation and Brownian motion, is quite different from that by which the molecules stretch. Whereas the stretching process passes through several distinct stages, the relaxation process is much more slow and occurs more uniformly. The predictions agree, at least qualitatively, with experimental results.
Vibrational effects on the torsional motion of ethyl radical
Authors: Johnson Philip M. , Sears Trevor J.
Published: July 2002

For molecules such as ethyl radical that have a small torsional barrier, the interaction between the internal rotation and the other normal modes of the molecule can have a substantial effect on the magnitude of the barrier itself. In ethyl this is experimentally demonstrated by a large change in the torsional barrier on vibrational excitation of the methylene group inversion motion. A simple method is applied to ethyl, involving the use of electronic structure calculations to estimate both the electronic and vibrational contributions to the barrier. Good agreement is found with experimental results from the infrared spectrum of the rocking vibration of the ethyl radical.
Infrared laser velocity modulation spectrum of the ν3 fundamental band of HBBr+
Authors: Hunt N. T. , Collet D. , Liu Z. , Davies P. B.
Published: July 2002

The infrared absorption spectrum of the ν3 (B–Br stretching) mode of HBBr+ has been observed using a tunable diode laser and velocity modulation spectroscopy. The ion was formed in an ac glow discharge through a flowing mixture of H2 and BBr3. Thirty-three transitions of H11B79Br+ and the same number of lines of the H11B81Br+ isotopomer have been assigned. The band origins and rotational constants are H11B79Br+: ν0=937.5696(13) cm−1, B0=0.461 822(42) cm−1, and B1=0.459 254(41) cm−1. H11B81Br+: ν0=936.0554(11) cm−1, B0=0.460 330(45) cm−1, and B1=0.457 778(43) cm−1. Ab initio calculations of the band origins and the internuclear distances have been performed using the GAUSSIAN 94 package. The calculated values are in highly satisfactory agreement with the experimental results.
Spatial-partitioning-based acceleration for variational Monte Carlo
Authors: Bressanini Dario , Reynolds Peter J.
Published: July 2002

The problem of inherently differing time scales of core and valence electrons in Monte Carlo (MC) simulations is circumvented in a straightforward and intuitive manner. By appropriately subdividing into equivalent subspaces the high-dimensional (many-electron) space in which Monte Carlo integration is done, it is possible to choose completely independent and appropriate sampling times for each “electron.” This approach trivially satisfies detailed balance. The partitioning of space is applicable to both variational and Green’s function MC. Such a partitioning, however, only provides a significant computational advantage in variational MC. Using this approach we were able to have inner electrons move with reasonably large steps and yet avoid excessive rejection, while outer electrons were moved great distances in few steps. The net result is a large decrease in the sampling autocorrelation time, and a corresponding increase in convergence rate. Results of several standard algorithms are compared with the present acceleration algorithm for the atoms Be and Ne, and the molecule Li2.
Emission by collisional H2–He pairs at temperatures from 2 to 20 kK
Authors: Hammer Dominik , Frommhold Lothar , Meyer Wilfried
Published: July 2002

The dipole surface of H2–He collisional pairs is computed from first principles for 20 intramolecular spacings of the H2 molecule, from 0.6 to 4 Bohr; 11 separations of the H2–He pair, from 2 to 6 Bohr; and five values for the angle subtended by the intramolecular and intermolecular axes. From this dipole surface, the dipole matrix elements are obtained for all possible rotovibrational transitions |vJ〉→|v′J′〉, with v and v′=0,… ,14. Subsequently, the collision-induced emission spectra are computed for frequencies from 100 to 100 000 cm−1, at temperatures of thousands of Kelvin—a range believed to be important for various light sources of high gas densities, such as the atmospheres of “cool” stars, shockwaves, flames, rocket jets, etc. We find that at the lower temperatures considered, radiation is emitted mostly in the fundamental band of H2, while at high temperatures the collision-induced emission spectra extend into the visible, with overtone transitions involving large Δv=v−v′.
Calorimetric indications of a cooperativity onset in the crossover region of dynamic glass transition for benzoin isobutylether
Authors: Kahle S. , Schröter K. , Hempel E. , Donth E.
Published: July 2002

Heat capacity spectroscopy (HCS), dielectric spectroscopy, and shear viscosity data are reported for liquid benzoin isobutylether (BIBE). Dielectric and viscosity peculiarities indicate the crossover region of dynamic glass transition at T=(−8±8) °C where the extrapolated Johari Goldstein β relaxation intersects the main transition trace in an Arrhenius plot. Although HCS does not reach the crossover frequency of order ω=2×106 rad/s, the linear decrease of the square root of cooperativity as calculated from HCS data at lower frequencies indicates a cooperativity onset in the crossover temperature-frequency range. As BIBE belongs to another dielectric crossover scenario as the substances where such an onset could previously be observed, it seems that the cooperativity onset is a general property of the crossover region.
A direct method of calculating sensitivity coefficients of chemical kinetics
Authors: Shen Ji
Published: July 2002

In this paper, a new direct method of calculating the first-order sensitivity coefficients using sparse matrix technology to chemical kinetics is presented. The Gear type procedure is used to integrate a model equation and its coupled auxiliary sensitivity coefficient equations. Because the Jacobian matrix of the model equation is the same as that of the sensitivity coefficient equation with respect to a parameter, it is only necessary to triangularize the matrix related to the Jacobian matrix of the model equation. The FORTRAN subroutines of the model equation, the sensitivity coefficient equations, and their Jacobian analytical expressions are generated automatically from chemical mechanism. This method greatly increases the efficiency of computation by taking advantage of the fact that the auxiliary equations for different sensitivity coefficients are linear and quite similar. Two sets of chemical reactions are used to illustrate this approach: oxidation of formaldehyde in the presence of carbon monoxide and photo-oxidation of dimethyl sulfide. The accuracy and computational efficiency of the new direct method is demonstrated by comparing the results from the new direct method and from the indirect method.
Mathematical modeling of complex oscillatory phenomena during CO oxidation over Pd zeolite catalysts
Authors: Slinko M. M. , Kurkina E. S. , Liauw M. A. , Jaeger N. I.
Published: July 2002

A mathematical model, which simulates the complicated dynamic behavior experimentally observed during CO oxidation over Pd zeolite catalysts is presented. It describes the coupling of reaction rate oscillations, generated by various parts of the inhomogeneous catalytic layer through the gas phase. It can be shown, that the resulting dynamic behavior depends upon the difference between natural frequencies of local oscillators and the strength of coupling, which is defined mostly by the degree of conversion. Chaotic behavior could be identified under the condition of weak coupling for local oscillators with widely different natural frequencies. In the range of strong coupling the phenomenon of phase death has been obtained. A special type of intermittency chaos (“on–off” chaos) was observed in a small region of parameters under the conditions of strong coupling.
Off-lattice Brownian dynamics simulation of wormlike micelles: The dependence of the mean contour length on concentration
Authors: Rouault Yannick
Published: July 2002

A new off-lattice Brownian dynamics simulation potential for wormlike micelles in the framework of equilibrium polymerization is proposed. The system reproduces the complete experimentally observed dependence of mean chain length 〈L〉 with concentration φ for uncharged species: a very slow dependence at very low φ, a 〈L〉∝Φ0.5 in the dilute and semidilute regime, and an enormous growth with concentration at high φ. Besides, it is shown that at high φ the longest chains are swollen by the smallest, suggesting a Russian dolls picture of the system.
Energy disposal in the O(3P)+HCl reaction: Classical dynamics and comparison to experiment
Authors: Ramachandran B.
Published: July 2002

The energy disposal in the O(3P)+HCl(v=2, j=1,6,9)→OH(v′,j′)+Cl reaction is analyzed using the results of fairly extensive quasiclassical trajectory (QCT) calculations on a realistic potential energy surface for the 3A″ state of this system. These results are compared to the experimental observations of Zhang et al. [R. Zhang, W. J. van der Zande, M. J. Bronikowski, and R. N. Zare, J. Chem. Phys. 94, 2704 (1991)]. The experimental and QCT product rotational distributions in the OH (v′=1) manifold, P1(j′), are shown to be very similar in shape, but not magnitude, to the purely statistical “prior” distribution. On the other hand, the rotational distributions in the ground vibrational state of OH, P0(j′), show significant deviations from prior distributions. A careful examination of several reactive trajectories suggests that (a) a direct abstraction mechanism is responsible populating the v′=1 states, (b) secondary encounters with RHCl⩽RHCl‡ and θOHCl>100° are responsible for populating the v′=0, j′⩾11 states, and (c) secondary encounters with RHCl⩾RHCl‡ and θOHCl⩽100° may be responsible for populating the v′=0, j′<11 states. The last observation raises the speculative but intriguing possibility that the state v′=0, j′=11 may represent a phase space boundary between the two types of secondary encounters.
Nonorthogonal localized molecular orbitals in electronic structure theory
Authors: Liu Shubin , Pérez-Jordá José M. , Yang Weitao
Published: July 2002

The concept of nonorthogonal localized molecular orbital (NOLMO) is investigated in this paper. Given a set of the commonly used canonical molecular orbitals, a direct minimization algorithm is proposed to obtain both the orthogonal localized molecular orbitals (OLMO) and NOLMO by using the Boys criterion and conjugate gradient minimization. To avoid the multiple-minimum problem, the absolute energy minimization principle of Yang is employed to obtain initial guesses. Contrary to the early conclusion drawn by Lipscomb and co-workers who claimed that OLMOs and the corresponding NOLMOs are more or less the same, we found that NOLMOs are about 10%–30% more localized than OLMOs. More importantly, the so-called “delocalization tail” that plagues OLMOs is not present in NOLMOs, showing that NOLMOs are more compact and less oscillatory and capable of providing greater transferability in describing the electronic structure of molecules. We also found that main lobes of NOLMOs are slightly larger in size than those of OLMOs because of the normalization requirement. These features establish NOLMOs to be valuable as building blocks in electronic structure theory and for the understanding of chemical bonding. They show the promise for the utilization of NOLMOs—the most localized possible—in the linear scaling approaches of the electronic structure theory for molecules and solids.
Effects of dephasing and vibronic structure on the first hyperpolarizability of strongly charge-transfer molecules
Authors: Wang C. H.
Published: July 2002

The dispersion of the first molecular hyperpolarizability β of strongly charge-transfer chromophores is investigated. The investigation extends the well-known Oudar–Chemla nonresonant two-level model into the resonant regime. An equation for β that includes the effect of dephasing and vibrational structure of electronic states is derived. It is shown that if only the dephasing mechanism is included in the two-level model, the intrinsic hyperpolarizability β0 calculated using the Oudar–Chemla equation from the hyper-Rayleigh scattering (HRS) experimental data will decrease with decreasing the excitation wavelength. The trend is reversed when the vibrational structure is also incorporated. It is concluded that in order to obtain a consistent β0 in the HRS experiment using an excitation wavelength in the resonance regime, it is inadequate to include only the dephasing mechanism. The vibronic structure also plays an important role and needs to be considered in the data analysis in order to obtain a β0 to agree with the off-resonance experimental result.
Band oscillator strengths of the intersystem transitions of CO
Authors: Rostas F. , Eidelsberg M. , Jolly A. , Lemaire J. L. , Le Floch A. , Rostas J.
Published: July 2002

Absorption oscillator strengths of 18 intersystem bands of CO between 1360 and 1620 Å originating from the ground state and involving the a′ 3Σ+, e 3Σ−, and d 3Δ states have been measured using synchrotron radiation as a background source. They have also been calculated using the published molecular parameters provided by the standard spectroscopic perturbation analysis, including the spin-orbit interaction with the nearby A 1Π state. It was found, however, that the model used in that analysis had to be extended in order to take into account the contributions of several vibrational levels of the A state to the intensity of a given singlet–triplet band. The present measurements are in good agreement with the predictions of this extended model. The puzzling discrepancies reported earlier between oscillator strength or rotationally resolved lifetime measurements and standard calculations are now well understood as well as the temperature variation of some of these band-integrated oscillator strengths. Line and band oscillator strengths of the intercombination transitions can now be reliably predicted at all temperatures and used for the measurement of large CO column densities, especially in interstellar molecular clouds, when the allowed bands normally used are saturated.
An extensive study of gradient approximations to the exchange-correlation and kinetic energy functionals
Authors: Chan Garnet Kin-Lic , Handy Nicholas C.
Published: July 2002

We formalize the procedure of functional development, in a general theoretical framework. Expansion in a functional basis set, and fitting via an error functional to a data set, casts functional development as a variational problem to obtain the functional basis-set and data-set limits. Overfitting is avoided by defining the optimum number of parameters. We implement our theory for an investigation of first- and second-order generalized gradient approximations (GGA) to the exchange-correlation and kinetic energy functionals, within an ab initio model. A variety of functional basis sets, including a general finite-element representation, is constructed to represent both one-dimensional and multidimensional GGA enhancement factors. An extensible data set consisting of 429 atomic and diatomic, neutral and cationic species, at stretched and equilibrium geometries, is constructed from Moller–Plesset level exchange-correlation energies, and Hartree–Fock kinetic energies. The range of chemically relevant density and gradient variables is examined. Exhaustive fitting investigations are carried out, to determine the accuracy of the GGA representation of the ab initio models. In the exchange-correlation case we demonstrate that we can reach the functional basis-set and data-set limit, which correspond to a root-mean-square (rms) error of ∼10 mH (6.3 kcal/mol). Changing the functional basis set, higher-order density variables such as the kinetic energy density, multidimensional enhancement factors, and exact exchange yield no significant improvement, and our fits represent an effective solution of the GGA problem for exchange-correlation, at the Møller–Plesset level. In the kinetic energy case, accurate functionals with rms errors of ∼80 mH (50 kcal/mol) are developed. These exhibit a beautifully simple kinetic energy enhancement factor, and are a step towards orbital-free calculations.
Scaling properties of the morphological measures at the early and intermediate stages of the spinodal decomposition in homopolymer blends
Authors: Aksimentiev Aleksij , Moorthi Krzysztof , Holyst Robert
Published: July 2002

The spinodal decomposition of the homopolymer blends has been studied by the numerical integration of the Cahn–Hilliard–Cook equation. We have investigated the time evolution of the morphological measures that characterize quantitatively the interface in the system. For symmetric blends we have found that the Euler characteristic of the interface is negative and increases with time as τ0.75 (connectivity of the domains decreases) regardless of the final quench temperature. The homogeneity index of the interface is constant in this case. This suggests that at the level of the integral geometry quantities (Minkowski functionals), the dynamic scaling hypothesis holds for the evolution of the interface morphology in quenched critical systems. The nonuniversal morphological evolution of the asymmetric blends have been studied. Also, we have shown that the thermal fluctuations can modify significantly the curvature distribution.
Local density approximation and generalized gradient approximation calculations for oxygen and silicon vacancies in silica
Authors: Capron N. , Carniato S. , Lagraa A. , Boureau G. , Pasturel A.
Published: July 2002

Neutral oxygen and silicon vacancies’ energies in silica polytypes (α-quartz, β-cristobalite, and stishovite) have been studied using the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange correlation. While the energies of formation of unrelaxed oxygen vacancies are remarkably constant (9.9 ±0.1 eV) in the three studied systems in GGA, the relaxation behavior is quite different: A strong Si–Si bond is formed in α-quartz, a weak one in β-cristobalite, while no bond at all is formed in stishovite. In α-quartz, peroxyl bridges are formed as the consequences of the relaxation of silicon vacancies. Their energy of formation from O2 (gas) is low (about 2 eV).
Complete basis set extrapolations for low-lying triplet electronic states of acetylene and vinylidene
Authors: Sherrill C. David , Byrd Edward F. C. , Head-Gordon Martin
Published: July 2002

A recent study by Ahmed, Peterka, and Suits [J. Chem. Phys. 110, 4248 (1999)] has presented the first experimentally derived estimate of the singlet–triplet gap in the simplest alkyne, acetylene. Their value, T0(ã 3B2)=28 900 cm−1, does not agree with previous theoretical predictions using the coupled-cluster singles, doubles, and perturbative triples [CCSD(T)] method and a triple-ζ plus double polarization plus f-function basis set (TZ2P f ), which yields 30 500±1000 cm−1. This discrepancy has prompted us to investigate possible deficiencies in this usually-accurate theoretical approach. Employing extrapolations to the complete basis set limit along with corrections for full connected triple excitations, core correlation, and even relativistic effects, we obtain a value of 30 900 cm−1 (estimated uncertainty ±230 cm−1), demonstrating that the experimental value is underestimated. To assist in the interpretation of anticipated future experiments, we also present highly accurate excitation energies for the other three low-lying triplet states of acetylene, ã 3Bu(33 570±230 cm−1), b̃ 3Au(36 040±260 cm−1), and b̃ 3A2(38 380±260 cm−1), and the three lowest-lying states of vinylidene, X̃ 1A1(15 150±230 cm−1), ã 3B2(31 870±230 cm−1), and b̃ 3A2(36 840±350 cm−1). Finally, we assess the ability of density functional theory (DFT) and the Gaussian-3 method to match our benchmark results for adiabatic excitation energies of C2H2.
Thermochemical analysis of core correlation and scalar relativistic effects on molecular atomization energies
Authors: Martin Jan M. L. , Sundermann Andreas , Fast Patton L. , Truhlar Donald G.
Published: July 2002

Core correlation and scalar relativistic contributions to the atomization energy of 120 first- and second-row molecules have been determined using coupled cluster and averaged coupled-pair functional methods and the MTsmall core correlation basis set. These results are used to parametrize an improved version of a previously proposed bond order scheme for estimating contributions to atomization energies. The resulting model, which requires negligible computational effort, reproduces the computed core correlation contributions with 88%–94% average accuracy (depending on the type of molecule), and the scalar relativistic contribution with 82%–89% accuracy. This permits high-accuracy thermochemical calculations at greatly reduced computational cost.
Ion mobility measurements and thermal transpiration effects in helium gas at 4.3 K
Authors: Tanuma Hajime , Fujimatsu Hideko , Kobayashi Nobuo
Published: July 2002

The thermal transpiration effect, which means a significant pressure difference between the two ends of a pipe due to a large temperature difference, has been discussed in ion mobility measurements in helium gas at 4.3 K. A modified Takaishi–Sensui’s empirical formula for the pressure correction is obtained from the experimental results. We propose to use this formula instead of the original Takaishi–Sensui equation for helium gas. By using the new formula, the reduced mobilities of He+4 and Ar+40 ions in He4 gas have been obtained with the measurements of drift velocities at the gas temperature of 4.3 K and comparisons have been made with the recent theoretical calculations by Dickinson et al. [J. Phys. B: At. Mol. Opt. Phys. 32, 4919 (1999)] and Viehland et al., [J. Chem. Phys. 105, 11143 (1996)], respectively, which show fairly good agreements with the experimental results.
A Jacobson–Morozov lemma for sp(2n, R)
Authors: Koçak Hüseyin
Published: July 2002

A variation of the lemma of Jacobson–Morozov on the imbedding of a nonzero nilpotent element of the real symplectic algebra into the split simple three-dimensional Lie algebra is proved. The proof is algorithmic and relies on our earlier work on the theory of normal forms for the real symplectic algebra.
Semiclassical statistical mechanics of two-dimensional fluid mixture of hard disks
Authors: Mishra B. M. , Sinha S. K.
Published: July 2002

High-temperature expansions for the density-independent part of the radial distribution function and the first-order density correction to it are obtained for a two-dimensional binary mixture of hard disks. The ‘‘excess’’ quantum corrections to the second and third virial coefficients and excess free energy are also discussed. It is found that the ‘‘excess’’ quantum effect depends on the concentration and the diameter radio.
Exact temporal evolution for some nonlinear diffusion processes
Authors: Garrido L. , Masoliver J.
Published: July 2002

Exact solutions to Fokker–Planck equations with nonlinear drift are considered. Applications of these exact solutions for concrete models are studied. We arrive at the conclusion that for certain drifts we obtain divergent moments (and infinite relaxation time) if the diffusion process can be extended without any obstacle to the whole space. But if we introduce a potential barrier that limits the diffusion process, moments converge with a finite relaxation time.
Fermionic couplings in Kaluza–Klein theories
Authors: Finkelstein R. , Villasante M.
Published: July 2002

The totally symmetric and totally antisymmetric direct couplings of fermions in d-dimensional space are investigated. Explicit forms are given for d<11. A different way of handling the d-dimensional Dirac algebra is also described.
Markov-type Lie groups in GL(n,R)
Authors: Johnson Joseph E.
Published: July 2002

The general linear group GL(n,R) is decomposed into a Markov-type Lie group and an abelian scale group. The Markov-type Lie group basis is shown to generate all singly stochastic matrices which are continuously connected to the identity when non-negative parameters are used. A basis is found which shows that it in turn contains a Lie subgroup which corresponds to doubly stochastic matrices, which basis, over the complex field, is shown to give the symmetric group for certain discrete values of the complex parameters. The basis of the Markov algebra is shown to give the negative of the corresponding M-matrices with property ‘‘C’’ (for non-negative combinations). These stochastic Lie groups are shown to be isomorphic to the affine group and the general linear group in one less dimension. The basis generates transformations with a natural interpretation for physical applications.
The dequantization programme for stochastic quantum mechanics
Authors: Schroeck F. E.
Published: July 2002

The classical limit ℏ→0 of stochastic quantum mechanics is investigated. An algebra of stochastic classical observables is canonically associated to the algebra of stochastic quantum observables with a product inherited from sequential instruments and also with a Lie commutator. It is shown that the sharp-point limit (limit of no stochasticity), which implies ℏ→0, yields the usual algebra of classical observables.
On the integrability of certain symmetric representations of the Lie algebra of SO0(4,1)
Authors: Bohm A. , Moylan P.
Published: July 2002

A proof of the existence of an essentially self-adjoint extension of a symmetric ∼(SO0(4,1)) Nelson operator, which is constructed out of the generators of a positive mass, arbitrary spin unitary irreducible representation of the Poincaré group, is presented. Our analysis of ∼(SO0(4,1)) and its Lie algebra provides us with an example of an observation of Harish-Chandra: There exist subspaces of the space of differentiable vectors of a representation of a noncompact group which are invariant under the Lie algebra, but the closures of the subspaces are not invariant under the group. The chief results of this paper should hold true for ∼(SO0(n,1)). In particular, we should have a realization of an arbitrary principal series irreducible unitary representation of SO0(n,1) on the direct sum of two identical unitary irreducible representation spaces of the motion group in an n-dimensional Minkowski space, which has one timelike dimension.
Geometric quantization: Modular reduction theory and coherent states
Authors: Ali S. Twareque , Emch Gérard G.
Published: July 2002

The natural role played by coherent states in the geometric quantization program is brought out by studying the mathematical equivalence between two physical interpretations that have recently been proposed for this program. These interpretations are based, respectively, on the modular algebra structure of prequantization, and the reproducing kernel structure of phase space quantization. The arguments are presented in this paper for the particular case where the phase space of the system considered is the cotangent bundle T*M of a homogeneous manifold M, and for didactic reasons, the latter is taken to be a real vector space.
Remarks on some hypergeometric orthogonal polynomials of mathematical physics
Authors: Montaldi E. , Zucchelli G.
Published: July 2002

The main result is a simple evaluation of an integral related to the orthogonality property of hypergeometric polynomials occurring in mathematical physics. Some related formulas for generalized hypergeometric functions are also briefly discussed.
Local linearization stability
Authors: Brill D. , Reula O. , Schmidt B.
Published: July 2002

It is shown that Einstein’s equations are always linearization stable around any finite region of space-time. Let (Ω,g0ab ) be any region of space-time, admitting a compact Cauchy surface with nonempty smooth boundary, and with g0ab a sufficiently smooth solution of the vacuum Einstein equation. It is shown that for any solution g1ab of the linearized equation and any open region U⊆Ω, there exists a smooth one-parameter family gλab of solutions on U such that (gλab‖λ=0 =g0ab ) ‖U and ((d/dλ)gλab =g1ab )‖U. By using a result of Choquet-Bruhat and York [The Cauchy Problem, General Relativity and Gravitation, edited by A. Held (Plenum, New York, 1980), Vol. 1] asserting the smoothness of the map that sends initial data into solutions of Einstein’s evolution equations the proof of the above theorem is reduced to the proof of a similar theorem for Einstein’s constraint equations. The proof of this latter theorem involves the use of the implicit function theorem in Hilbert spaces. This local result on linearization stability asserts, in contrast to the general global case, that linearization about any vacuum solution is locally physically meaningful.