bluuebunny/crossref_metadata_2025 huggingface dataset:
An ab initio linear electron correlation functional
Authors: Rassolov Vitaly A.
Published: July 2002

Electron correlation effects are entirely ignored at the single determinant (Hartree–Fock) level. The traditional density functional approach utilizes nonlinear semiempirical density dependent functionals to account for the correlation effects. We show that a natural alternative is a linear correlation operator which modifies the Hartree–Fock Hamiltonian and yields correlation energy for the single determinant wave function. The form of the correlation operator is suggested by the analysis of the energy contributions and from the electron gas correlation hole. Using this operator we calculate the correlation correction to the energies of a number of atoms and atomic ions. This correction is considerably more accurate than standard density functional theory approximations. The new approach might represent an effective way to deal with correlation problems in the framework of linear operators acting in Hilbert space.
Chain dynamics of concentrated polystyrene solutions studied by depolarized photon-correlation and viscosity measurements
Authors: Lai C. S. , Juang J.-H. , Lin Y.-H.
Published: July 2002

Concentrated solutions of nearly monodisperse polystyrene samples in cyclohexane in the theta condition and in the entanglement-free region have been studied by means of the depolarized photon-correlation spectroscopy and viscosity measurements. It is shown that the viscoelastic behavior of the studied systems is described by the Rouse theory and that in agreement with the theoretical analysis the main polymer dynamic process probed by the depolarized Rayleigh scattering is basically the reorientational motion associated with a Rouse segment of the polymer chain, whose relaxation is independent of the scattering angle and the molecular weight. In addition to the main dynamic process, the tail region of a very fast process associated with the sub-Rouse-segmental motions can be observed, whose existence is expected from the theoretical analysis.
A many-particle treatment of the reversible reaction A+B⇔C+B
Authors: Gopich I. V. , Kipriyanov A. A. , Doktorov A. B.
Published: July 2002

A many-particle consideration of diffusion-influenced reversible pseudo-first order reaction A+B⇌C+B is presented. It is shown that the lowest order (in concentration) of the memory matrix is not sufficient for describing the binary kinetics of the reaction. Binary kinetic equations describing both stationary and nonstationary stages of the kinetics have been obtained using diagrammatic representation and selecting the necessary diagrams. Comparison with the fully renormalized kinetic theory is made by considering the contact approximation for reactivity.
Direct formation of solid ammonium chloride particles from HCl and NH3 vapors
Authors: Tao Fu-Ming
Published: July 2002

The possibility of direct formation of particulate ammonium chloride (NH4Cl) from ammonia (NH3) and hydrogen chloride (HCl) gases was investigated by density functional theory and ab initio methods. Equilibrium structures were determined for the clusters constructed, respectively, from one, two, and four units of NH3–HCl in the close-packed form. While a single NH3–HCl unit is a hydrogen-bonded complex, clusters of two and four NH3–HCl units closely resemble the crystal structure of NH4Cl and contain the discrete NH4+ and Cl− ions. The ionic form results from a prompt and complete proton transfer from HCl to NH3 that takes place in the larger clusters where favorable electrostatic interactions are maximized. The implications for nucleation in the pure NH3 and HCl system are discussed.
Conformational properties of polymer chains in the theta region
Authors: Rubio Ana M. , Freire Juan J. , Yong C. W. , Clarke Julian H. R.
Published: July 2002

A configurational bias Monte Carlo algorithm has been employed to investigate the conformational properties of an off-lattice polymer chain model close to the theta point. In particular, we have extended previous results for the chain’s mean size and shape to longer chains, allowing for a more detailed comparison with field renormalization group theory. Moreover, we present the first data of internal energy and specific heat for this type of off-lattice model, showing the approach to the expected theoretical behavior.
Fifth-order two-dimensional Raman spectra of CS2 are dominated by third-order cascades
Authors: Blank David A. , Kaufman Laura J. , Fleming Graham R.
Published: July 2002

We have demonstrated that fifth-order stimulated Raman spectra of the intermolecular modes in CS2 are dominated by cascading third-order processes. Previous studies have successfully discriminated against a sequential cascading process, but did not account for parallel third-order cascades. All of our measured spectra were successfully simulated considering only cascades built directly from our measured third-order spectra. Using an appropriately chosen phase matching geometry we also measured the sequential cascade, which should exist with equal probability to the parallel cascade. When employing a phase matching geometry that provided substantial discrimination against all of the third-order cascades we were not able to measure any signal. We assign an upper limit for the true fifth-order signal of 2% of the cascaded signal.
The accuracy of current density functionals for the calculation of electric field gradients: A comparison with ab initio methods for HCl and CuCl
Authors: Schwerdtfeger Peter , Pernpointner Markus , Laerdahl Jon K.
Published: July 2002

The performance of current density functionals is analyzed in detail for the electric field gradients (EFG) of hydrogen chloride and copper chloride by comparison with ab initio methods and available experimental data. The range of density functionals applied shows good agreement with coupled cluster H and Cl field gradients for HCl, as has been demonstrated previously for other main-group element containing compounds. However, the performance of most density functionals is very poor for the Cu EFG in CuCl (EFG for Cu -0.44 a.u. at the coupled-cluster singles and doubles with perturbative triples [CCSD(T)] level, compared to, e.g., +0.54 a.u. at the B-LYP level). Only the “half-and-half” hybrid functionals give field gradients with the correct sign. The reason for the poor performance of the density functional theory is analyzed in detail comparing density functional with ab initio total electronic densities ρ(r). Due to the conservation of the number of particles, a change in the valence part of the electron density can lead to changes in the core part of the density. Errors in valence electronic properties like the dipole moment and in core properties like the Cu and Cl EFGs may therefore be connected. In fact the errors in both properties show a distinct linear relationship, indicating that if the dipole moment is correctly described by density functionals, the Cu and Cl EFGs may be accurate as well. Furthermore, at the atomic level, electric field gradients are described with reasonable accuracy by current density functionals as calculations for the Cu 2P excited state and the Cu2+ 2D ground state show. A comparison between the different density functionals shows that the incorrect behavior of the electronic density appears to be mainly due to defects in the exchange part of the functional.
The instantaneous normal mode spectrum of a liquid undergoing shear flow
Authors: Lacks Daniel J.
Published: July 2002

The instantaneous normal mode spectrum of a Lennard-Jones liquid undergoing shear flow is determined as a function of shear rate. Shear flow is shown to deplete the density of states at low frequencies and augment the density of states at high frequencies, for both the real and imaginary modes. Shear flow also leads to an increase in the fraction of modes with imaginary frequencies. The implications of these changes are discussed in regard to other system properties.
Microwave spectroscopic study of the SiF3 radical: Spin-rotation interaction and molecular structure
Authors: Tanimoto Mitsutoshi , Saito Shuji
Published: July 2002

The trifluorosilyl radical has been produced by glow discharge in hexafluorodisilane in a free space cell. The rotational spectrum of the radical has been measured from the 330 (N=22−21) GHz region down to the 90 (N=6−5) and 75 (N=5−4) GHz regions. In the lower N transitions the K=1 hyperfine components showed a distinct splitting. From the splitting of the K=1 lines it was concluded that the spin-rotation interaction constant of trifluorosilyl radical has a positive sign, which is different from that of trifluoromethyl. This difference is discussed in terms of the electronic states. The simplified discussion based on the Mulliken–Walsh diagram of the energy level is used to rationalize the difference in the sign of the interaction constants in the two radicals. The Si–F bond length is determined from the rotational constant B0 to be 1.565 Å when the bond angle F–Si–F is assumed to be 109.9° deduced in the matrix infrared spectroscopy. The spin density on the fluorine atoms is derived from the hyperfine coupling constants. The obtained molecular structure is compared with those of related molecules.
Unimolecular dynamics from kinetic energy release distributions. V. How does the efficiency of phase space sampling vary with internal energy?
Authors: Hoxha A. , Locht R. , Lorquet A. J. , Lorquet J. C. , Leyh B.
Published: July 2002

A retarding field technique coupled with a quadrupole mass analyzer has been used to obtain the kinetic energy release distributions (KERDs) for the C2H3Br+→[C2H3]++Br dissociation as a function of internal energy. The KERDs obtained by dissociative photoionization using the He(I), Ne(I), and Ar(II) resonance lines were analyzed by the maximum entropy method and were found to be well described by introducing a single dynamical constraint, namely the relative translational momentum of the fragments. Ab initio calculations reveal the highly fluxional character of the C2H3+ ion. As the energy increases, several vibrational modes are converted in turn into large-amplitude motions. Our main result is that, upon increasing internal energy, the fraction of phase space sampled by the pair of dissociating fragments is shown to first decrease, pass through a shallow minimum around 75%, and then increase again, reaching almost 100% at high internal energies (8 eV). This behavior at high internal energies is interpreted as resulting from the conjugated effect of intramolecular vibrational redistribution (IVR) and radiationless transitions among potential energy surfaces. Our findings are consistent with the coincidence data of Miller and Baer, reanalyzed here, and with the KERD of the metastable dissociation.
Rotationally specific rates of vibration–vibration energy exchange in collisions of NO(X 2Π1/2,v=3) with NO(X 2Π,v=0)
Authors: Islam Meezanul , Smith Ian W. M.
Published: July 2002

Infrared ultraviolet double resonance (IRUVDR) experiments have been performed to investigate the rotational specificity of the vibrational–vibrational (V–V) exchange process, NO(X 2Π1/2,v=3,Ji)+NO(v=0)→NO(X 2Π1/2,v=2,Jf)+NO(v=1), for which the vibrational energy discrepancy corresponds to 55.9 cm−1. Radiation from an optical parametric oscillator was used to excite NO molecules into a specific rotational level (Ji) in the X 2Π, Ω=12, v=3 state. Laser-induced fluorescence (LIF) spectra of the (0,2) band of the A 2Σ+–X 2Π1/2 system were then recorded at delays corresponding to a fraction of a collision. From the relative line intensities, rate coefficients were determined for transfer of the excited NO molecule from the level X 2Π1/2, v=3, Ji to different final rotational levels (Jf) in the X 2Π1/2, v=2 state. Results are reported for Ji=3.5, 4.5, 7.5, 10.5, and 15.5. The data show a significant, though not strong, propensity for J to decrease by one; i.e., for ΔJ=Jf−Ji=−1, especially for the higher Ji levels. This result is interpreted as arising from a combination of (a) the tendency to minimize the energy that has to be accommodated in the relative translation of the collision partners, and (b) the favoring of ΔJ=±1 changes when V–V intermolecular exchange occurs under the influence of dipole–dipole interactions.
Experimental and theoretical investigations of the structure and the stability of the BNSi molecule
Authors: Meloni G. , Viswanathan R. , Gingerich K. A.
Published: July 2002

Theoretical computations were carried out to determine the structure and molecular parameters of the BNSi molecule. The most stable isomer is found to have a BNSi linear geometry. Thermal functions as derived from the theoretical computed molecular parameters were used in the evaluation of the thermodynamic properties of BNSi from high-temperature Knudsen effusion mass spectrometric equilibrium data. From the reactions analyzed by the second-law and third-law methods, the enthalpy of formation, ΔfH0o, and of atomization, ΔaH0o, in kJ mol−1, for BNSi, were obtained as 398±16 and 1078±17, respectively.
Analytical potential energy surface for the GeH4+H→GeH3+H2 reaction: Thermal and vibrational-state selected rate constants and kinetic isotope effects
Authors: Espinosa-Garcı́a J.
Published: July 2002

The potential energy surface (PES) for the gas-phase GeH4+H→GeH3+H2 reaction and its deuterated analogue (GeD4+H) was constructed with suitable functional forms to represent the stretching and bending modes, and using as calibration criterion the experimental thermal rate constants and kinetic isotope effects. The thermal rate constants were calculated using variational transition state theory with semiclassical transmission coefficients over the experimental temperature range, 200–500 K. This surface was then used to analyze dynamical features. From the analysis of the reaction path curvature (kappa), we qualitatively find that excitation of the Ge–H stretch in germane enhances the forward reaction rates and the H2 stretch mode appears vibrationally excited, in accordance with an “early” transition state and an attractive surface. Moreover, as the vibrational modes preserve their characteristic motions (adiabatic behavior) in the forward sense, we quantitatively find that exciting the GeH4 symmetric stretching mode by one quantum increases the rate constants by a factor of from 5.71 to 3.14 when the temperature increases from 200 to 500 K. Interestingly, this quantitative result validates the qualitative analysis based on the reaction path curvature.
Investigation of an H-bonded dimer: Calculations of bonding structures and temperature dependence of the librational substructure of the OH-stretching band
Authors: Laenen R. , Simeonidis K. , Ludwig R.
Published: July 2002

We demonstrate data from time-resolved spectroscopy and quantum statistical thermodynamics of ab initio calculated molecular clusters for 2,2-dimethyl-3-ethyl-3-pentanol (DMEP). The association of the molecules to dimers, only, is supported by the numerical investigation indicating a weak H-bond. This is in agreement with NMR experiments and data from conventional IR spectroscopy. From time-resolved IR spectroscopy of a 2 M DMEP sample diluted in CCl4 in the temperature range from 260 K to 343 K a librational substructure of the proton donor OH-band is suggested from spectral holes and satellite holes in the sample bleaching. With these spectral components we are able to fit the temperature dependent conventional IR-absorption spectrum of the sample in the investigated range from 260 K up to 343 K.
Line mixing in the ν1 and 2ν2 isotropic Raman Q-branch of CO2 perturbed by argon and helium
Authors: Boulet C. , Bouanich J.-P. , Hartmann J.-M. , Lavorel B. , Deroussiaux A.
Published: July 2002

The shapes of the ν1 and 2ν2 isotropic Raman Q-branch of CO2 perturbed by argon and helium have been measured by Stimulated Raman Spectroscopy (SRS) or coherent anti-Stokes Raman Spectroscopy (CARS) techniques. The data have been successfully analyzed with an energy corrected sudden (ECS) approximation model based on basic rates determined independently. Finally comparison of the present data with time resolved double resonance experiments allows us to discuss the physical origin of the two empirical constants which account for the shift and broadening of the branch due to vibrational effects.
Observing the symmetry breaking in the angular distributions of oriented photofragments using velocity mapping
Authors: Rakitzis T. Peter , Samartzis Peter C. , Kitsopoulos Theofanis N.
Published: July 2002

A novel experimental method for extracting the orientation parameter Im[a1(1)(∥,⊥)] from a single photofragment velocity image is presented. The two-dimensional ion image of oriented S(1D2) atoms from the photodissociation of OCS with linearly polarized light reveals an asymmetry in the angular distribution that breaks reflection symmetry with respect to the plane containing the photolysis and probe laser polarizations. This asymmetry is shown to be of the odd functional form sin 2θ, as predicted by theory.
Energy gradients and effective density differences in electron propagator theory
Authors: Ortiz J. V.
Published: July 2002

Efficient calculations of adiabatic electron binding energies require gradients of ground and excited potential energy surfaces. These surfaces may be inferred from reference-state total energies and vertical electron binding energies of the electron propagator. Reference-state total energies from many-body perturbation theory may be derived from electron propagator theory and gradients of these expressions are already known. The missing information for final-state optimization therefore is provided here. Gradients of electron propagator poles (ionization energies and electron affinities) with respect to nuclear positions in the second-order, 2p–h Tamm–Dancoff and nondiagonal, renormalized, second-order approximations of electron propagator theory are derived. Effective electron density difference matrices corresponding to these poles are by-products of the derivations.
Mapping of wave packets in direct fragmentation via pump–probe frequency integrated fluorescence spectroscopy
Authors: Engel V. , Henriksen N. E.
Published: July 2002

We consider femtosecond excitation of a molecule to a dissociative electronic state. The quantum dynamics is recorded via delayed excitation to a higher electronic state and measurement of the total fluorescence from this state detected as a function of delay time. It is shown that the signal can be used to determine the probability density distribution of the outgoing wave packet describing the fragmentation. This, in particular, applies to the case of fragment detection since then the time-dependent signal directly measures the probability flux at a fixed value of the dissociation coordinate. Numerical examples illustrate the procedure.
Molecular parameters for C12 and C13-methanol isotopomers with O-16, 17, and 18
Authors: Duan Yun-Bo , McCoy Anne B. , Wang Li , Takagi Kojiro
Published: July 2002

Torsion–rotational parameters have been determined for C12 and C13-methanol isotopomers CH3OH with O-16, 17, and 18 using a recent formulation [Duan and Takagi, Phys. Lett. A 207, 203 (1995)] of the centrifugal distortion effects from potential parameters for a molecule containing a threefold symmetric internal rotor. The calculated parameters, especially the constants representing interactions between torsion and rotation, are used to interpret the relationships among the terms in reduced Hamiltonian and in the analysis of the observed torsion–rotational spectrum. Molecular parameters are calculated from potential energy surfaces for methanol to check the quality of these surfaces. The calculated parameters are compared with parameters obtained from global fits to large experimental data sets. The good agreement between the calculated centrifugal distortion terms and those derived from fits to spectra demonstrates that the derived formulas provide a useful tool for understanding the physical origins and mass dependence of the molecular parameters.
Structural change of Langmuir and Langmuir–Blodgett films of alkylDCNQI induced by charge-transfer reaction at the air–water interface
Authors: Ikegami Keiichi , Lan Minbo , Nakamura Takayoshi
Published: July 2002

UV-visible absorption spectrum of pure 2-methyl-5-octadecyl-N,N′-dicyanoquinonediimine (C18MeDCNQI) Langmuir films and that of C18MeDCNQI–CuI mixed Langmuir films indicated the occurrence of charge-transfer (CT) reactions at the air–water interface in the latter case. These Langmuir films were deposited onto solid substrates as Langmuir–Blodgett (LB) films by the horizontal lifting method. Polarized UV–visible–IR absorption spectra and x-ray diffraction patterns recorded for the obtained LB films revealed a drastic structural change induced by the CT reactions: An interdigitated bilayer structure was suggested for the pure films, while a monolayer structure for the CT films. Furthermore, the CT degree of the major component of the mixed LB films was estimated at −1, unlike in the case of Cu–DCNQI crystals, for which the CT degree is −2/3.
A fast ab initio model for the calculation of excited electronic states of atoms and molecules in a weakly polarizable environment. I. Theory
Authors: Kunz Christian F. , Hess Bernd A.
Published: July 2002

We report the development of an ab initio scheme designed for the calculation of the electronic ground state and low-lying excited states of an atom or a molecule, perturbed by a weakly interacting environment of discrete, unpolarizable particles acting as a solvent. The model employs an ab initio partitioning ansatz that accounts for the effects of nonlocal exchange–overlap interactions between the solute and the solvent by means of a parametrized exchange–overlap operator and an effective metric in the pair-permutation, pair-additivity approximation, which is known to be valid in regions of small intermolecular overlap. Intramolecular perturbations like spin-orbit effects can be incorporated in the treatment. Due to its fast performance and built-in size-consistency, our model can be employed in the calculation of the electronic states of spectroscopically active fragments with many different settings of the environment.
New energy partitioning scheme based on the self-consistent charge and configuration method for subsystems: Application to water dimer system
Authors: Korchowiec Jacek , Uchimaru Tadafumi
Published: July 2002

The charge-transfer energy in water dimer is analyzed. The analysis is based on self-consistent charge and configuration method for subsystems (SCCCMS). The SCCCMS, as such, is not restricted to any computational schemes and can be applied at Hartree–Fock (HF), post-HF, and density functional levels of theory. In our approach, the interaction energy is decomposed into deformation (DEF), electrostatic (ES), polarization (P), charge transfer (CT), and exchange (EX) [exchange–correlation (XC)] contributions. The CT energy is derived from the energy surface spanned in the populational space. The intermediate results obtained during construction of this energy surface, such as chemical potentials, hardness and softness parameters, are of particular interest in the theory of chemical reactivity and, thus, these values are discussed as well. The influence of basis set and computational method is analyzed. The numerical values of the energy components obtained at the HF level of theory are compared with those of Kitaura–Morokuma (KM) and reduced variational space (RVS) analyses. It is shown that SCCCMS correctly describes the polarization process. The CT contribution is less dependent on the basis set than KM or RVS scheme and is free from the basis set superposition error (BSSE). It is demonstrated that the CT energy is of little importance for the water dimer. In addition, the amount of CT calculated in our scheme is almost identical to that obtained from the supermolecule calculations.
Fluorobenzene and p-difluorobenzene microsolvated by methanol: An infrared spectroscopic and ab initio theoretical investigation
Authors: Buchhold K. , Reimann B. , Djafari S. , Barth H.-D. , Brutschy B. , Tarakeshwar P. , Kim Kwang S.
Published: July 2002

Laser spectroscopy, i.e., resonant two-photon ionization (R2PI), IR/R2PI ion depletion and hole burning spectroscopy have been applied in an experimental study of heterogenous clusters consisting of fluorobenzene (FB) or p-difluorobenzene (pDFB), respectively, microsolvated by up to three methanol molecules. Their infrared ion depletion spectra were taken in the region of the OH and CH stretches of methanol. In these complexes the methanol molecules form subclusters, which are weakly hydrogen bonded to either the aromatic π-system (πOH) or to the fluorine substituent (σF) and a CH group (σCH). In FB⋅(MeOH)1, pDFB⋅(MeOH)1, pDFB⋅(MeOH)2 and one isomer of FB⋅(MeOH)2 the methanol subunits exclusively exhibit σF and σCH H-bonds. A further isomer of FB⋅(MeOH)2 exhibits a πOH type interaction. For FB⋅(MeOH)3 and pDFB⋅(MeOH)3 (1:3) complexes the methanol subcluster may take on either a chainlike or a ringlike conformation. In the chainlike isomer of FB⋅(MeOH)3 the methanol trimer interacts with the chromophore via a πOH H-bond while with the corresponding pDFB cluster a σF H-bond is formed. High level ab initio calculations, still feasible for molecular clusters of this size, have also been carried out to supplement the experimental investigations. These calculations include complete geometry optimizations of FB⋅(MeOH)n (n=1–2) and pDFB⋅(MeOH)1 at the MP2/6-31+G* and B3LYP/6-31+G* levels of theory. The minimum energy structures of the microsolvates together with their harmonic vibrational spectra allow a reliable assignment of the experimentally observed spectra and the determination of structure of the complexes.
Very high rotational excitation of CO in a cooled electric discharge through carbon monoxide
Authors: Cossart-Magos Claudina , Cossart Daniel
Published: July 2002

Infrared emission from CO12 and CO13, excited in the cathode region of a discharge tube immersed in liquid nitrogen, was recorded by Fourier-transform spectrometry at a resolution of 0.005 cm−1. The Δv=1 sequence bands recorded in the 2500–1800 cm−1 spectral interval, indicate the existence of three different rotational populations; (i) molecules in the zero-ground level with Trot≈100 K (responsible for reabsorption of part of the 1–0 emission band); (ii) molecules with Trot≈275 K (maximum intensity for Jmax′≈6 in each band, Tvib≈3000 K for v′=2–4, Tvib≈8600 K for v′=5–13); (iii) molecules with v′ limited to 6, for which R-rotational lines are observed for J′ values between 50 and 120 (Jmax′≈90, non-Boltzmannian population distribution). The full-width at half-maximum (FWHM) of all the observed lines is less than 0.007 cm−1. A Doppler width of 0.005 cm−1 and translational temperature Ttr≈280 K can be deduced. Such high-J levels of the CO molecule had never been observed in the laboratory. In the absorption spectrum of the Sun photosphere, the same lines present FWHM values 5–8 times larger. The best available Dunham coefficients are checked to reproduce the high-J lines wave numbers to at least 0.001 cm−1. Dissociative recombination of the dimer (CO)2+ cation, which is likely to be formed in our experimental conditions, is discussed as a possible mechanism to produce CO fragments with very high rotational excitation, while keeping vibrational excitation limited to v′=6.
Electron correlation in chemical bonds
Authors: Rassolov Vitaly A. , Ratner Mark A. , Pople John A.
Published: July 2002

We study the correlation energy in the H2 molecule as a function of bond distance and the electron coupling parameter that modifies the strength of electron–electron repulsion. For the unscaled electron repulsion we find an unusual complexity of the correlation energy dependence on the bond distance. This complexity remains if the electron repulsion is scaled down. We pay particular attention to the range of bond distances near the H2 equilibrium geometry. We confirm that good performance of the modern exchange–correlation functionals in molecular geometry optimization is due to the cancellation of errors between the exchange and correlation components. These components have different functional dependence on the electron coupling parameter, so the cancellation of errors no longer occurs when the electron repulsion is scaled down. This observation is important if the adiabatic connection theorem is used to construct the exchange–correlation functionals. It is also relevant for the performance of exchange–correlation functionals to study ionic interactions. The performance of the correlation operator in the molecular environment is also investigated and discussed.
Completely inverted ClO vibrational distribution from OClO(2A2 24,0,0)
Authors: Delmdahl R. F. , Bakker B. L. G. , Parker D. H.
Published: July 2002

The gas phase dissociation dynamics of symmetric chlorine dioxide highly photoexcited into its A22 24,0,0 vibronic level has been investigated by monitoring both the kinetic energy release and the angular distribution of the O(3P2) products via velocity map imaging. The resulting O(3P2) kinetic energy profile provides full the vibrational distribution of the formed ClO(X 2Π,v) radicals. The measured O fragment kinetic energy distribution reflects an unprecedented nonstatistical vibrational state population of their diatomic partners, where the excess energy is focused only in the three highest possible ClO vibrational levels v=18–20, with little fragment rotation. The anisotropy of the dissociation process sheds new light on the fragmentation dynamics of this stratospherically relevant triatomic molecule.
Silver nanoparticles on graphite studied by femtosecond time-resolved multiphoton photoemission
Authors: Lehmann J. , Merschdorf M. , Pfeiffer W. , Thon A. , Voll S. , Gerber G.
Published: July 2002

Time-resolved multiphoton photoelectron spectroscopy is employed to study collective excitations and their decay dynamics in silver nanoparticles on highly oriented pyrolytic graphite. Resonant excitation of the surface plasmon in the silver nanoparticles with 400 nm femtosecond radiation allows to distinguish between photoemission from the nanoparticles and the substrate. This extends the method of time-resolved two-photon photoemission spectroscopy to inhomogeneous surfaces and permits to probe the dynamics of a confined electron gas. The multiphoton photoelectron spectra, the polarization dependence of the photoelectron yield and the time-resolved measurements reveal the double excitation of the surface plasmon and allow the identification of two different decay channels of the collective excitation. The multiply excited plasmon transfers its total excitation energy to a single photoelectron or decays into at least two single-particle excitations which share the total energy.
The resonant Auger electron spectrum of C 1s−1π* excited ethene: A combined theoretical and experimental investigation
Authors: Fink Reinhold F. , Sorensen Stacey L. , de Brito Arnaldo Naves , Ausmees Andrus , Svensson Svante
Published: July 2002

The resonant Auger electron spectrum for ethene has been calculated with an ab initio approach using configuration-interaction energies and wave functions for the intermediate core-excited and final states. The transition rates were determined by the “one-center approximation.” The role of vibrational relaxation on the line shapes was described by a moment method which considers the case of symmetric core holes and their localization due to the vibrational relaxation of the core-excited state. The core hole localization is investigated in some detail and is found to be extremely efficient in the C 1s−1π* excited state of ethene. Another property of the core-excited state is found to be the polarization of the valence electron density toward the core hole. We demonstrate this by using three different symmetric configuration interaction representations and one nonsymmetric Hartree–Fock representation for this state. A modified improved virtual orbitals method is described and employed to obtain virtual orbitals which give a compact description of this effect. The theoretical spectra obtained in this way are compared with a measured spectrum and assignment of the structures in the spectrum to electronic configurations is made. We find strong configuration mixing in the higher excited final states which is evidence for the breakdown of the one-particle picture.
Weak bond stretching for three orientations of Ar–HF at vHF=3
Authors: Chuang Cheng-Chi , Higgins Kelly J. , Fu Henry C. , Klemperer William
Published: July 2002

Three new ArHF (vHF=3) states, (3001), (3101), and (3111), have been observed between 11 350 and 11 420 cm−1 by the hot band transitions from (0001) using intracavity laser induced fluorescence. The term values and rotational constants of these levels are: (3001) ν0=11 385.928 98(28) cm−1, B=0.095 546(32) cm−1; (3101) ν0=11 444.258 12(68) cm−1, B=0.090 617(37) cm−1; and (3111) ν0=11 456.076 51(36) cm−1, B=0.091 863(14) cm−1. Observation of the ArHF (3001) state provides the van der Waals stretching frequency for ArHF at v=3, namely 46.8945(4) cm−1=(3001)–(3000). This value shows an increase of 8.208 cm−1 (21%) upon HF v=3←0 valence excitation. The stretching frequency for the T shaped ArHF is (3111)–(3110)=33.7055(5) cm−1. This value is only 7% greater than that observed at v=1. The (vHF101) Σ bend-stretch combination state, corresponding to (νs=1) of the Ar–FH configuration, has not been observed at vHF=0–2. The stretching frequency here is (3101)–(3100)=31.8178(8) cm−1. The soft-mode frequencies reveal strong bend-stretch coupling in the complex. Excellent agreement (within 0.3 cm−1) is found between experiment and prediction from Hutson’s H6(4, 3, 2) potential [J. Chem. Phys. 99, 9337 (1993)], for the three new levels. Large basis set coupled cluster calculations [CCSD(T)] of the Ar–HF intermolecular potential surface, V(R,θ,r), are presented for r=0.6–2.0 Å and θ=0–180° on a grid with 15° spacing. This is an enlargement of the HF valence coordinate of more than double the equilibrium value. The dependence of the intermolecular potential upon the HF valence coordinate, r, is very anisotropic, being maximal for θ=0° and becoming essentially independent of r for θ⩾45°.
Theory for the nonadiabatic multichannel fragmentation of the Na3+ cluster ion following collision with a He atom
Authors: Babikov D. , Gislason E. A. , Sizun M. , Aguillon F. , Sidis V.
Published: July 2002

A general theoretical procedure is developed that treats the fragmentation of a polyatomic cluster ion following excitation by a fast rare gas atom. The process involves multiple electronic states of the cluster ion that are described by the diatomics-in-molecule (DIM) procedure. The interaction of the cluster ion with the rare gas atom is obtained by extending the DIM model and by including three-center interactions. The atom-cluster collision is treated using the semiclassical path procedure and the sudden approximation for the cluster. Finally, the fragmentation is studied using the trajectory surface hopping procedure. The method is applied to the Na3+–He system, which can fragment into three product channels. For each channel doubly differential cross sections are computed and compared with the available experimental data. The calculations give much insight into the fragmentation process of Na3+.
First-order intermolecular interaction energies from coupled-cluster Brueckner orbitals
Authors: Heßelmann Andreas , Jansen Georg
Published: July 2002

It is investigated to which extent the effect of intramolecular electron correlation on intermolecular first-order Coulomb and exchange energies can be accounted for when solely the reference determinant of the Brueckner coupled-cluster-doubles scheme is used to construct the charge density and the density matrices of the monomers. Considering the dimers He2, Ne2, Ar2, NeAr, NeHF, ArHF, (H2)2, (HF)2, and (H2O)2 the Brueckner orbital approximation in general is found to improve considerably upon the results of the Hartree–Fock determinant.
The non-Poissonian collision model for the condensed phase activated rate processes
Authors: Shushin A. I.
Published: July 2002

The non-Poissonian collision model (CM) of energy dissipation (friction) in condensed phase activated rate processes is proposed and analyzed in detail. This model describes the instantaneous change of the velocity distribution of a probe particle caused by the collisions with particles of a medium. In the considered CM the statistics of collisions is assumed to be non-Poissonian. The efficiency of collisions is determined by the transition kernel K(v,v′) in the velocity space which can model both the weak and the strong collision limits including the cases of complete velocity randomization and backscattering (v≈−v′). In the proposed CM simple formulas for the diffusion coefficient D and the rate kr of passage over a barrier are derived in the moderate-to-strong friction limit. They accurately reproduce the known analytical and numerical results. The non-Poissonian CM predicts the interesting phenomenon, the kinetic cage effect, which is observed for the special type of the collision distribution functions corresponding to the nearly periodic collisions and shows itself in the small absolute value of D and kr in the case of backscattering. This effect as well as some other predictions of the proposed CM are discussed in detail.
Spectroscopy of mass-selected gadolinium dimers in argon matrices
Authors: Chen Xiaoyu , Fang Li , Shen Xiaole , Lombardi John R.
Published: July 2002

We report on the absorption, resonance Raman, and Raman excitation profile spectra of mass-selected gadolinium dimers in argon matrices. Two dimer absorption bands were found between 570 and 660 nm. The Raman excitation profile resembles the dimer absorption spectrum very well. Resonance Raman spectra, obtained by excitation into this region with dye laser radiation, give a single progression with up to four Stokes transitions. These data give ωe=138.7±0.4 cm−1 with ωexe=0.3±0.1 cm−1, leading to a spectroscopic dissociation energy of 2.1±0.7 eV.
High resolution pulsed field ionization–photoelectron study of CO2+(X 2Πg) in the energy range of 13.6–14.7 eV
Authors: Liu Jianbo , Chen Wenwu , Hsu C.-W. , Hochlaf M. , Evans M. , Stimson S. , Ng C. Y.
Published: July 2002

The vacuum ultraviolet pulsed field ionization–photoelectron (PFI–PE) spectra for CO2 have been measured in the energy range of 13.6–14.7 eV, revealing complex vibronic structures for the ground CO2+(X 2Πg) state. Many vibronic bands for CO2+(X 2Πg), which were not resolved in previous photoelectron studies, are identified in the present measurement based on comparison with available optical data and theoretical predictions. As observed in the HeI photoelectron spectrum of CO2, the PFI–PE spectrum is dominated by the symmetry allowed ν1+ (symmetric stretch) vibrational progression for CO2+(X 2Πg). However, PFI–PE vibronic bands due to excitation of the symmetry disallowed ν2+ (bending) and ν3+ (asymmetric stretch) modes with both odd quanta, together with the symmetry allowed even quanta excitations, are clearly discernible. The simulation of rotational contours resolved in PFI–PE vibronic bands associated with excitation to the (ν1+=0–1, ν2+=0–2, ν3+=0) vibrational levels has yielded accurate ionization energies for the formation of these vibronic states from CO2(X 1Σg+).
Nonideal rotations in nuclear magnetic resonance: Estimation of coherence transfer leakage
Authors: Jerschow Alexej
Published: July 2002

When spherical tensors are rotated by certain angles, coherence transfer selection rules may apply. For example, a π rotation cleanly inverts the coherence order. A π/2 rotation of a T01 tensor creates only T±11 tensors. In this work estimations are given for the coherence transfer leakage under the action of rotations with small errors in the rotation angle or axis. Although the theory is stated with particular applications to NMR (nuclear magnetic resonance) in mind it is equally applicable wherever nonideal rotations of spherical tensors are considered (e.g., quantum computing and relaxation theory). In NMR it is useful for the estimation of coherence transfer leakage, especially in pulse sequences with many nπ pulses. The results are also applicable to spinors and half-integer representations of the rotation group.
Proof of the decoupling theorem of field theory in Minkowski space. II. Theories involving particles with vanishingly small masses
Authors: Manoukian Edward B.
Published: July 2002

The decoupling theorem of quantum field theory is studied in Minkowski space for theories which on experimental grounds may contain particles with vanishingly small masses. Rules are set up to prove the distributional vanishing property of the renormalized amplitudes when any subset of the underlying masses is scaled to infinity, and any subset of the remaining masses is scaled to zero. By careful estimates, the analysis in Minkowski space may be reduced to a similar one in Euclidean space. All subtractions of renormalization are carried out at the origin of momentum space with the degree of divergence of a subtraction coinciding with the dimensionality of the corresponding subdiagram.
On a computation formula for the representation matrices of U(n)
Authors: Maekawa Takayoshi
Published: July 2002

A d-matrix element of U(n), which is called the semi-highest-weight d-matrix element and plays an essential role for the D-matrix elements, is explicitly determined. By using the result, a formula of computing the D-matrix elements of U(n) is given in terms of lowering operators corresponding to those of Nagel and Moshinsky.
Convergent expansions for glueball masses in strongly coupled 3+1 lattice gauge theories
Authors: O’Carroll Michael , Barbosa Wilson Dantas
Published: July 2002

We analyze the mass spectrum of a strongly coupled (β=2/g2 small) Wilson action lattice gauge theory in 3+1 dimensions. In the subspace generated by the time zero plaquette functions and their complex conjugates we show that there is at least one and not more than four masses. Each mass admits a representation of the form m(β)=−ln β+r(β), where r(β) is a gauge group representation-dependent function analytic in β or β1/2 at β=0. For a gauge group representation with real character there is at least one and not more than two masses of the above form and r(β) is analytic at β=0. Furthermore cn, the nth β=0 Taylor series coefficient of r(β), can be obtained by a finite algorithm.
The eigenvalues of the simplified ideal MHD ballooning equation
Authors: Paris R. B. , Auby N. , Dagazian R. Y.
Published: July 2002

The investigation of the spectrum of the simplified differential equation describing the variation of the amplitude of the ideal MHD ballooning instability along magnetic field lines constitutes a multiparameter Schrödinger eigenvalue problem. An exact eigenvalue relation for the discrete part of the spectrum is obtained in terms of the oblate spheroidal functions. The dependence of the eigenvalues λ on the two free parameters γ2 and μ2 of the equation is discussed, together with certain analytical approximations in the limits of small and large γ2. A brief review of the principal properties of the spheroidal functions is given in an appendix.
Wave equations with the characteristic propagation property
Authors: Torrence R. J.
Published: July 2002

Within the class of second-order linear self-adjoint wave equations in 1+1 dimensions, an explicit construction is given of probably all those with the characteristic propagation property, that is, those whose solutions are without tails.
Joint linearization instabilities in general relativity
Authors: Brill Dieter , Vishveshwara C. V.
Published: July 2002

When Einstein’s equations are supplemented by symmetry conditions, linearization instabilities can occur that are not present in either of the two sets of equations. The general conditions for this joint instability are investigated. This is illustrated with an example where both the Einstein equations and the flatness condition have more linearized solutions than exact solutions. In a minisuperspace model the geometrical reason for these instabilities is shown.
Some rigorous results concerning spectral theory for ideal MHD
Authors: Laurence Peter
Published: July 2002

Spectral theory for linear ideal MHD is laid on a firm foundation by defining appropriate function spaces for the operators associated with both the first- and second-order (in time and space) partial differential operators. Thus, it is rigorously established that a self-adjoint extension of F(ξ) exists. It is shown that the operator L associated with the first-order formulation satisfies the conditions of the Hille–Yosida theorem. A foundation is laid thereby within which the domains associated with the first- and second-order formulations can be compared. This allows future work in a rigorous setting that will clarify the differences (in the two formulations) between the structure of the generalized eigenspaces corresponding to the marginal point of the spectrum ω=0.
Theorems pertaining to Fokker–Planck statistical equilibrium for multidimensional stochastic systems
Authors: Rosen Gerald
Published: July 2002

It is shown that a Fokker–Planck equation ∂P/∂t=−∑ni=1∂[Qi(q)P]/ ∂qi + 1/2 ∑ni, j=1σij  ∂2P/ ∂qi  ∂qj with n≥3 may admit an asymptotic steady-state solution P → Peq(q) that is independent of t only if the necessary condition min{2(1−2/n)[∫(Q ⋅ σ−1  ⋅ Q)n/2 dnq]2/n, [∫Ω‖S‖n/2 dnq]2/n} >2−1+2/nπ1+1/n [Γ((n+1)/2)]−2/nn2 [det(σij)]1/n is satisfied, where S=S(q) ≡∑ni=1∂Qi(q)/ ∂qi and the second integral is over the q-space region Ω≡{q ∈ Rn such that S(q)<0}. In addition, it is demonstrated that the probability distribution P=P(q,t) is localized in q-space as t→∞ if S is bounded from above by a negative constant.
Symmetries of the massive Thirring model
Authors: Ten Eikelder H. M. M.
Published: July 2002

For a Hamiltonian system every non-Hamiltonian symmetry gives rise to a recursion operator for symmetries. Using this method two recursion operators for symmetries of the massive Thirring model are constructed. The structure of the Lie algebra of symmetries generated by these operators is given.
On steady transverse magnetogas flow
Authors: Singh S. N. , Choubey K. R. , Singh B. P.
Published: July 2002

The geometry and solutions for steady transverse magnetogas dynamic flow with arbitrary equation of state when magnitude of the velocity is constant along each individual streamline are investigated.
Boson realization of sp(4, R). II. The generating kernel formulation
Authors: Castaños O. , Kramer P. , Moshinsky M.
Published: July 2002

In a previous paper of this series, the matrix elements were discussed with respect to boson states of an operator K2 required for the boson realization of the sp(4, R) Lie algebra. In the present paper, it is shown that these matrix elements can be obtained from a generating kernel given by the overlap of sp(4, R) coherent states. The results have relevance for the determination of the matrix elements of the generators of the sp(4, R) Lie algebra with respect to the basis of irreps of the positive discrete series for the corresponding group, and are, in principle, generalizable to symplectic algebras of higher dimensions.
Anomalies in supersymmetric nonlinear σ models based on El-type groups
Authors: Moriya Takeshi , Yasui Yukinori
Published: July 2002

The anomalies in exceptional-type supersymmetric nonlinear σ models are investigated. The cohomology rings of Kähler manifolds E6/Spin(10)×U(1), E7/SU(5)×SU(3)×U(1), and E8/SO(10)×SU(3)×U(1) and the Chern classes of the tangent bundles of these manifolds are calculated explicitly. It is shown that the E6/Spin(10)×U(1) model is anomaly-free but the E7/SU(5)×SU(3)×U(1) and E8/SO(10)×SU(3)×U(1) models are anomalous.