bluuebunny/crossref_metadata_2025 huggingface dataset:
An ab initio cluster study of chemisorption of atomic Cs on Ga-rich GaAs (100) (2×1), (2×2), and β(4×2) surfaces
Authors: Schailey R. , Ray A. K.
Published: July 2002

Chemisorption properties of atomic Cs on the Ga-rich GaAs (100) (2×1), (2×2), and β(4×2) surfaces are investigated using ab initio self-consistent restricted open shell Hartree–Fock total energy calculations with Hay–Wadt effective core potentials. The effects of electron correlation have been included using many-body perturbation theory through second order, with the exception of β(4×2) symmetry, due to computational limitations. The semiconductor surface is modeled by finite sized hydrogen saturated clusters. The effects of surface relaxation and reconstruction have been investigated in detail. We report on the energetics of chemisorption, charge population analysis, highest occupied molecular orbital-lowest unoccupied molecular orbital gaps, and consequent possibilities of metallization. The most stable chemisorbed site is found to be the trough site for the Ga9As9H25 cluster, with the adatom at a distance of 3.796 Å from the surface at the MP2 level. The highest occupied molecular orbital-lowest unoccupied molecular orbital gap, in this case is reduced by 0.724 eV due to Cs adsorption. At the Hartree–Fock level, the most stable chemisorbed site is also the trough site for the Ga19As15H39 cluster, with a reduction in the gap of 1.403 eV.
The hyperfine interactions in CsF
Authors: Cederberg J. , Ward J. , McAlister G. , Hilk G. , Beall E. , Olson D.
Published: July 2002

The molecular beam electric resonance technique has been used to examine the hyperfine spectrum of CsF to determine the nuclear quadrupole interaction of the cesium nucleus. A total of 95 transitions in vibrational states v=0−5 and rotational states J=1−8 have been included in a fit to determine the cesium nuclear quadrupole and spin–rotation interactions, the fluorine spin–rotation interaction, and the tensor and scalar parts of the spin–spin interaction. Vibration and rotation dependencies of these constants have been determined, allowing correction for zero point vibration effects. This experimental Cs nuclear quadrupole coupling constant when combined with the electric field gradient calculated using a relativistic coupled cluster method yields a nuclear quadrupole moment of the Cs nucleus equal to eQ=−3.43098 mbarn. The vibrational dependence of the coupling constant is smaller than the theoretical estimate. The coupling constants we have determined are the following: eQCsqCs=1245.598(10)−14.322(25)(v+1/2)+0.080(14)(v+1/2)2+0.0040(22)(v+1/2)3−0.00209(59)J(J+1)+0.00048(40)(v+1/2)J(J+1), cCs=0.66177(14)−0.01509(28)(v+1/2)+0.000550(94)(v+1/2)2, cF=15.08163(84)−0.1744(14)(v+1/2)+0.00234(41)(v+1/2)2−0.000093(13)J(J+1), c3=0.92713(53)−0.00917(93)(v+1/2)+0.00097(29)(v+1/2)2, c4=0.62745(30)−0.00903(22)(v+1/2). All values are in kHz units, with one standard deviation uncertainty estimates in the last two digits shown in ( ).
Infrared spectroscopic observation of the argon isomer distribution in evaporative ensembles of I−⋅ROH⋅Arm (R=methyl, ethyl, isopropyl) clusters
Authors: Nielsen Steen B. , Ayotte Patrick , Kelley Jude A. , Johnson Mark A.
Published: July 2002

Vibrational predissociation spectra of argon-solvated iodide–alcohol clusters (I−⋅ROH⋅Arm, ROH=MeOH, EtOH, i-PrOH) are reported in the OH stretching region (3200–3400 cm−1). The spectra display multiple peaks associated with the ionic H-bonded OH stretching fundamental, which vary according to the extent of argon solvation. At small m, the number of peaks reflects the total number of attached argon atoms, such that peaks associated with fewer argons persist (with a small blue shift) in the spectra of the larger clusters, while new peaks appear red shifted by about 12 cm−1 with each additional argon. The effect saturates in a manner that depends on the particular alcohol (mmax=6 for MeOH, 5 for EtOH, and 4 for i-PrOH). We interpret these observations to indicate the presence of multiple isomers in the evaporative ensemble, which are distinguishable according to the different arrangements of argon atoms among two effective binding sites.
Dynamic multipole polarizabilities and reduced spectra for OH, application to the long-range part of the two lowest potential surfaces of the OH–CO complex
Authors: Spelsberg Dirk
Published: July 2002

The formalism of the two-center expansion of the long-range interaction potential is extended to molecules which may be in a degenerate state. As a consequence of this degeneracy the common long-range interaction coefficients have to be replaced by “long-range interaction matrices.” The formalism is applied to the OH–CO complex and leads to an accurate description of the long-range part of its potential surfaces. The reduced spectra that represent the dynamic polarizabilities of the subsystems are obtained in the single excitation multi-reference averaged coupled pair approach. They also serve to calculate the interaction matrices.
Solvent effects on the polarizabilities and hyperpolarizabilities of conjugated polymers
Authors: Luo Yi , Norman Patrick , Macak Peter , Ågren Hans
Published: July 2002

Solvent effects on the static polarizabilities and hyperpolarizabilities of conjugated polymers have been studied by means of a semiclassical solvation model using results from ab initio calculations. The solvent-induced changes of the static polarizabilities show maxima at fairly short oligomer lengths, with the main axial contribution decreasing rapidly to a zero value at the geometrically nondistorted polymer limit. Different saturation behaviors of the static polarizabilities of conjugated oligomers in gas phase and in solution are observed. It is concluded that the dipole–dipole interaction is responsible for the solvent-induced property changes of the oligomers.
A combined instantaneous normal mode and time correlation function description of the infrared vibrational spectrum of ambient water
Authors: Ahlborn Heather , Ji Xingdong , Space Brian , Moore Preston B.
Published: July 2002

A formal connection is made between the vibrational density of states (DOS) of a liquid and its approximation by way of instantaneous normal modes (INMs). This analysis leads to a quantum generalization of the INM method (QINM), and to the possibility of evaluating the classical DOS exactly. Further, INM approximations to spectroscopic quantities (e.g., infrared absorption and Raman scattering) follow in a consistent manner by evaluating the appropriate golden rule expressions for harmonic oscillators, using the INM or QINM DOS in place of the true DOS. INM and QINM methods are then applied along with traditional time correlation function (TCF) methods to analyze the entire infrared (IR) spectrum of ambient water. The INM and TCF approaches are found to offer complimentary information. TCF methods are shown to offer an unexpectedly accurate description of the O–H stretching line shape. Further, the 19-fold enhancement in liquid phase absorption compared to the gas phase is also reproduced. INM and QINM methods are used to analyze the molecular origin of the water spectrum, and prove especially effective in analyzing the broad O–H stretching absorption. Further, it is argued that a motional narrowing picture is qualitatively useful in analyzing INM approximations to spectroscopy.
Vibrorotational Raman and infrared spectra of polar diatomic molecules in inert solutions. II. Rotational spectroscopy of HCl in liquid SF6
Authors: Padilla A. , Pérez J. , Calvo Hernández A.
Published: July 2002

The non-Markovian spectral theory presented in the preceding paper is applied to the calculation of the pure rotational spectroscopy of HCl in liquid SF6 and its comparison with available experimental far-infrared and anisotropic S-branch results. A quantitative and qualitative study of memory and interference effects on the overall infrared and anisotropic Raman spectra has been carried out. The relation of these effects to the time scales of the dephasing processes and the strong cancellation effects between interbranch and intrabranch mixing are especially stressed. The statistical parameters required for the theoretical calculation of the profiles have been obtained from a microscopic extended cell model for the liquid.
Infrared laser jet spectroscopy of the ν6 fundamental band of W(CO)6: Rotational structure and octahedral splitting
Authors: Hansford G. M. , Loroño M. , Davies P. B.
Published: July 2002

Infrared laser absorption spectroscopy in conjunction with a cold molecular beam of W(CO)6 has yielded the rotationally resolved spectrum of this spherical top molecule near 2000 cm−1. Octahedral splitting has been resolved for the first time and is analyzed using the highly spherical top data system (hTDS) developed at Dijon. In addition, a perpendicular band of the symmetric top molecule W(12C 16O)5 13C 16O was observed in natural abundance. The spectroscopic parameters derived for this molecule, together with electron-diffraction data, provided a value for B0 of the dominant isotopomer, and a check on the consistency of the analysis of the spectra.
Multichannel quantum defect analysis of the double resonance photoionization series of H2O
Authors: Child M. S. , Glab W. L.
Published: July 2002

A new analysis is presented of the recent photoionization spectrum of H2O, excited by double resonance via several rotational sublevels of the (100) vibrational level of the C̃(1B1) state. Evidence for a previously unsuspected strong f series indicates significant d orbital contamination of the nominal p orbital in the intermediate state. This is the first report of an f series in the Rydberg state of any asymmetric top. Previous d series analyses of single-photon photoionization spectra terminating on the (100) level of H2O+ are also corrected and extended to a wider range of excited rotational electronic states. The d series appears to contain absent lines, indicative of predissociation. Some lines remain unassigned, but there is no systematic evidence of either s or p series.
S
1
–S
2
vibronic coupling in trans-1,3,5-hexatriene. II. Theoretical investigation of absorption and resonance Raman spectra
Authors: Woywod Clemens , Livingood William C. , Frederick John H.
Published: July 2002

No direct absorption or emission signals of the 2 1Ag state of trans-1,3,5-hexatriene (THT) have been detected so far. However, the ab initio calculations of the three valence singlet states of THT presented in the preceding paper (paper I) put the vertical excitation energy of the 2 1Ag state ca. 0.5 eV below that of the 1 1Bu state. This result indicates possible strong vibronic coupling effects on the spectroscopy of the bright 1 1Bu state. We construct a quantum-mechanical three-state eight-mode model Hamiltonian operator for the microscopic description of the ultrafast S2→S1 internal conversion dynamics following optical excitation of the 1 1Bu state based on the ab initio potential energy information for the S0, S1, and S2 states of THT compiled in paper I. This dynamical model is shown to yield a reliable description of the absorption, preresonance and resonance Raman (RR) spectroscopy of the 1 1Bu state of THT. The homogeneous linewidth of 155 cm−1 FWHM observed for the origin band of the 1 1Ag→11Bu transition can be reproduced with an optical dephasing time T2 of 90 fs. The strong enhancement of 1 1Bu RR bands involving the almost Franck–Condon inactive tuning mode ν9 as well as the observed rapid 1 1Bu population decay indicate that the S1 and S2 states are probably nearly degenerate, the 2 1Ag energy may also be slightly higher than that of the 1 1Bu state vertically. However, the parameter set that yields a realistic description of the RR spectroscopy and population dynamics within the eight-mode vibronic coupling model needs to be modified in order to reproduce the high-resolution 1 1Bu absorption profile, i.e., a significant reduction of the ab initio interstate coupling constants is required. A convergence of the two different parameter sets can be expected if the Hamiltonian is extended by the 28 weakly coupled modes that are considered by a phenomenological relaxation term in the present model.
Raman spectrum and bonding of matrix isolated GeO2
Authors: Friesen Markus , Junker Markus , Schnöckel Hansgeorg
Published: July 2002

A suitable experimental method for the synthesis of molecules like O=Ge=O, which cannot simply be generated by heating of the well known solids, is provided by matrix isolation technique. In solid noble or other inert gases Ge atoms react with O2. The formation of the CO2-like GeO2 species was monitored by IR spectroscopy some time ago. In order to determine the complete force field the Raman spectrum has now been recorded. Bonding in this species is discussed on the basis of experimental findings and ab initio calculations which have been performed in addition. These results reveal, that multiple bonding in the system GeO/GeO2 is completely different from that in the molecules CO and CO2.
Subspace iteration techniques for the calculation of resonances using complex symmetric Hamiltonians
Authors: Sommerfeld T. , Tarantelli F.
Published: July 2002

We investigate and compare the performance of the Arnoldi and block-Davidson approaches for the calculation of selected eigenstates of complex symmetric Hamiltonians arising in the study of resonances. In the context of the block-Davidson scheme, both the “natural” complex symmetric subspace projection and the unsymmetric orthogonal projection are studied. The latter is found to possess the best convergence properties in realistic examples, clearly outperforming the other methods.
The application of a VUV Fourier transform spectrometer and synchrotron radiation source to measurements of: II. The δ(1,0) band of NO
Authors: Imajo T. , Yoshino K. , Esmond J. R. , Parkinson W. H. , Thorne A. P. , Murray J. E. , Learner R. C. M. , Cox G. , Cheung A. S.-C. , Ito K. , Matsui T.
Published: July 2002

Line-by-line photoabsorption cross-sections of the NO δ(1,0) band were measured with the VUV Fourier transform spectrometer from Imperial College, London, using synchrotron radiation at Photon Factory, KEK, Japan, as a continuum light source. The analysis of the NO δ(1,0) band provides accurate rotational line positions and term values as well as the photoabsorption cross-sections. The molecular constants of the C(1) 2Π level are found to be T0=54 690.155±0.03 cm−1, Bv=1.944 06±0.000 62 cm−1, Dv=(5.91±0.42)×10−5 cm−1, AD=−0.0187±0.0050 cm−1, p=−0.0189±0.0037 cm−1, and q=−0.015 21±0.000 20 cm−1. The sum of the line strengths for all rotational transitions of the NO δ(1,0) band is determined as 4.80×10−15 cm2 cm−1, corresponding to a band oscillator strength of 0.0054±0.0003.
The decomposition of C60 on nickel clusters
Authors: Parks E. K. , Kerns K. P. , Koretsky G. M. , Nieman G. C. , Riley S. J.
Published: July 2002

The adsorption of C60 on nickel clusters Nin in the n=8–31 size range is studied at elevated temperatures. Above 800 °C, decomposition of C60 is seen on clusters containing oxide impurities by the loss of CO and/or CO2 molecules. The extent of decomposition depends on cluster size and C60 coverage, which affect the charging of the metal core by electron transfer from the metal to the C60. Both decreased cluster size and increased C60 coverage reduce the electron transfer per C60 molecule, weakening the C60–Nin bond and decreasing the rate of decomposition. In spite of this effect, C60 appears to decompose more readily on small nickel clusters than on bulk nickel surfaces. While decomposition is only observed for clusters having adsorbed O atoms, the oxygen may actually inhibit decomposition by withdrawing electronic charge from the metal, likewise weakening the C60–Nin bond.
The dispersion curves of the three phonon modes of xenon, krypton, and argon monolayers on the Pt(111) surface
Authors: Bruch L. W. , Graham A. P. , Toennies J. P.
Published: July 2002

The dispersion curves of all three phonon modes, the shear horizontal (SH), longitudinal (LA), and perpendicular (S) vibrations of the two-dimensional monolayer inert gas solids of xenon, krypton, and argon on Pt(111) have been measured by inelastic helium atom scattering (HAS). Previous HAS measurements of xenon on other substrates revealed, in addition to the S mode, only a single dispersive mode which deviated strongly from the expected behavior of the LA branch, to which it had been assigned. The new measurements now identify this mode as the SH mode and all three modes are in excellent agreement with calculations based on the inert gas pair potentials determined from gas and bulk solid data. Possible mechanisms for the excitation of the SH branch, which should couple only very weakly to HAS on the basis of symmetry considerations, are discussed.
Refinements on solvation continuum models: Hydrogen-bond effects on the OH stretch in liquid water and methanol
Authors: Cappelli Chiara , Mennucci Benedetta , da Silva Clarissa O. , Tomasi Jacopo
Published: July 2002

We present a study on the IR vibrational shifts of the OH stretch mode for water and methanol when passing from gas to liquid phase. Both a purely continuum solvation model (here the polarizable continuum model) and its semicontinuum extensions, obtained explicitly considering small clusters of H-bonded molecules of liquid, have been tested. The definition of such clusters as the new quantum mechanical system to be coupled to a continuum description of the remainder liquid has allowed us to take into account both the “local permanent specific” interaction due to the H-bond and the long-range effects present in all liquids. The analysis mainly focused on harmonic approximations and has been extended to include mechanical anharmonicities in order to have a more reliable comparison with the experiments. Finally, careful attention has been paid to the analysis of the “intrinsic” parameters of continuum models (i.e., the shape and size of the molecular cavity containing the QM system) and to their effects on the vibrations.
The electronic origin and vibrational levels of the first excited singlet state of isocyanic acid (HNCO)
Authors: Berghout H. Laine , Crim F. Fleming , Zyrianov Mikhail , Reisler Hanna
Published: July 2002

The combination of vibrationally mediated photofragment yield spectroscopy, which excites molecules prepared in single vibrational states, and multiphoton fluorescence spectroscopy, which excites molecules cooled in a supersonic expansion, provides detailed information on the energetics and vibrational structure of the first excited singlet state (S1) of isocyanic acid (HNCO). Dissociation of molecules prepared in individual vibrational states by stimulated Raman excitation probes vibrational levels near the origin of the electronically excited state. Detection of fluorescence from dissociation products formed by multiphoton excitation through S1 of molecules cooled in a supersonic expansion reveals the vibrational structure at higher energies. Both types of spectra show long, prominent progressions in the N–C–O bending vibration built on states with different amounts of N–C stretching excitation and H–N–C bending excitation. Analyzing the spectra locates the origin of the S1 state at 32 449±20 cm−1 and determines the harmonic vibrational frequencies of the N–C stretch (ω3=1034±20 cm−1), the H–N–C bend (ω4=1192±19 cm−1), and the N–C–O bend (ω5=599±7 cm−1), values that are consistent with several ab initio calculations. The assigned spectra strongly suggest that the N–C stretching vibration is a promoting mode for internal conversion from S1 to S0.
Simulated phase behavior of reversibly assembled polymers
Authors: Fodi B. , Hentschke R.
Published: July 2002

We perform molecular dynamics simulations to model the self-organization and phase behavior of reversibly aggregated linear model polymers. In our model the monomers interact via a Lennard-Jones-type potential with anisotropic attraction. In addition to the usual Lennard-Jones parameters the monomers are characterized by a unit vector assigning an orientation to each monomer. Our model potential allows one to control the monomer coupling and thus the aggregate flexibility. We examine the dependence of the polymer length distribution and the orientational as well as the translational ordering on monomer density, chain flexibility, and temperature.
(
N
2
O
)
2
⋅
SO
2
:
Rotational spectrum and structure of the first van der Waals trimer containing sulfur dioxide
Authors: Peebles Rebecca A. , Kuczkowski Robert L.
Published: July 2002

The trimer (N2O)2⋅SO2 has been studied by Fourier transform microwave spectroscopy. The rotational constants for the normal species are A=1369.1014(11) MHz, B=1115.5816(11) MHz, and C=730.5790(4) MHz. Five isotopomers of the complex have been studied, allowing a determination of its structure. The configuration aligns the centers-of-mass of the three monomers in an approximate equilateral triangle. The monomers twist relative to this plane so that the two N2O’s are intermediate between T-shaped and crossed rather than the usual slipped-parallel planar. The SO2 is oriented so that its oxygens are straddling one N2O (similar to the N2O⋅SO2 dimer), while its sulfur is closest to the oxygen end of the other N2O. The dipole moment of (15N2O)2⋅SO2 was measured, giving μa=0.606(1) D, μb=1.256(2) D, μc=0.058(2) D, and μtotal=1.396(2) D. A semiempirical model has been used to predict the trimer structure, and comparison is made with this model as well as with the dimer N2O⋅SO2.
Two-body correlations in two-dimensional classical solids and their role in first-order perturbation theories
Authors: Serrano-Illán J. , Velasco E. , Navascués G. , Mederos L.
Published: July 2002

A highly accurate theoretical approach, based on exact and quasiexact sum rules, is presented for the averaged two-body correlation function of the hard-disk solid. Excellent results are obtained as compared to computer simulations for this function. However, when these results are used as the basis for a first-order perturbation theory, the phase diagram of the two-dimensional square-well model potential is only reproduced qualitatively, showing that higher-order correlation terms play a non-negligible role in two dimensions.
Inelastic collision processes of CH4 and C2H6 molecules at highly corrugated surfaces studied by the molecular beam scattering technique
Authors: Kondo Takahiro , Tomii Takashi , Hiraoka Tomomi , Ikeuchi Toshiyuki , Yagyu Shinjiro , Yamamoto Shigehiko
Published: July 2002

Inelastic collision dynamics of alkane (CH4 and C2H6) molecules at highly-corrugated surfaces is studied by the molecular beam scattering technique. For the azimuthal direction such as the [110] or the [100] of the impinging molecules on a LiF(001) surface, a wide variety of surface corrugation can be realized. Angular distributions of the reflected molecules realized in our experiment are found to qualitatively agree with those predicted by such simple classical collision models as hard cube [R. M. Logan and R. E. Stickney, J. Chem. Phys. 44, 195 (1966)] and washboard [J. C. Tully, J. Chem. Phys. 92, 680 (1990)] models. The surface corrugation experienced by C2H6 molecules is found much less than that experienced by CH4 molecules, due to the effectively large size of a C2H6 molecule. The surface corrugation decreases as the kinetic beam energy of the impinging molecules increases. This is caused by the difference in energy dependence of the repulsive potential energy surface of Li and F ions which independently interact with the incoming molecules.
Solid–liquid phase transition of Lennard-Jones fluid in slit pores under tensile condition
Authors: Miyahara Minoru , Kanda Hideki , Shibao Mutsumi , Higashitani Ko
Published: July 2002

The effect of equilibrium vapor-phase pressure onto freezing of a simple fluid in a nanopore is examined. We employ a molecular dynamics (MD) technique in a unit cell with imaginary gas phase, which has the benefit of easy determination of equilibrium vapor pressure. The method is shown to give consistent results with those by the grand canonical Monte Carlo (GCMC) method, and to have better feature of smaller degree of hysteresis between freezing and melting. The MD simulations showed liquid–solid phase transitions, at a constant temperature, with the variation in the equilibrium vapor-phase pressure below the saturated one. Thus-determined solid–liquid coexistence lines exhibited significant dependence of the freezing point against small changes in the bulk–phase vapor pressure, which implies the importance of tensile effect on freezing in nanopores. The capillary effect on the shift in freezing point was successfully described by a simple model based on continuum and isotropic assumption, even in a pore as small as 2 nm in width.
The passage of small molecules through a water film supported by MgO(100): Transfer times from molecular dynamics simulations
Authors: Toubin C. , Hoang P. N. M. , Picaud S. , Girardet C.
Published: July 2002

The passage of small pollutant molecules (HCl, CO2) through a thin water film supported on a MgO substrate at 300 K has been studied by constrained classical molecular dynamics simulations. The calculated free energy profile of the pollutants exhibits two minima, one at the gas/liquid film interface, and the other inside the film near the ionic substrate. Lifetimes of the pollutants in these two sites have been characterized by unconstrained simulations. The residence times in these sites are in the range of a few tens of picoseconds. The transfer times from one site to the other, and the times spent by the pollutants in the liquid and at the liquid/gas interface (∼ one hundred ps) are always twice longer for CO2 than for HCl. This difference is interpreted in terms of correlated dynamics of HCl and H2O due to hydrogen bond interactions with water. The duration of the hydrogen bond Cl–H⋅⋅⋅O increases significantly (∼2 ps) at the film surface with respect to its value inside the film (<1 ps).
CCNN: The last kinetically stable isomer of cyanogen
Authors: Ding Yi-hong , Li Ze-sheng , Huang Xu-ri , Sun Chia-chung
Published: July 2002

The dissociation and isomerization stability of the linear cyanogen isomer CCNN, a formally charge-transfer species comprising C2− and N2+, is theoretically investigated by means of ab initio methods, including the Hartree–Fock (HF), the Mo/ller–Plesset perturbation theory from second through fourth order (MP2, MP4SDQ, MP4SDTQ), the configuration interaction with singles and doubles (CISD), the quadratic configuration interaction with singles and doubles (QCISD) as well as with triples [QCISD(T)], and the density functional theory (DFT) including Beck’s three parameter hybrid methods with the Lee–Yang–Parr correlation functional (B3LYP) and with the Perdew–Wang 91 correlation functional (B3PW91) methods. At the QCISD(T)/6-311G(3df)//QCISD(T)/6-311G(d) level with QCISD/6-311G(d) zero-point vibrational energy (ZPVE) correction, the barriers from CCNN to the NNC three-membered ring structure with exocyclic C–C bonding and to the dissociation products C2 and N2 are predicted to be 42.1 and 51.8 kcal/mol, respectively. The QCISD(T)/6-311G(3df) potential energy surface of C2N2 indicates that CCNN may be kinetically more stable than the other two well-studied isomers CNCN and CNNC. Thus, although CCNN is thermodynamically less favorable due to its high energy, it is still experimentally observable. Moreover, a barrier of 5.5 kcal/mol is predicted for the reverse association reaction between C2 and N2 to produce CCNN at the QCISD(T)/6-311G(3df)//QCISD(T)/6-311G(d)+ZPVE level, while both B3LYP and B3PW91 methods erroneously predict a barrierless association process. Finally, the possible strategy for the formation of CCNN in laboratory and in interstellar space is discussed in detail. The calculated results may provide a useful guide for future laboratory and interstellar identification of the last kinetically stable isomer of cyanogen, CCNN.
Multiple dynamical pathways in the O+SiH4 reaction studied by the crossed molecular beam method
Authors: Lin Jim J. , Lee Yuan T. , Yang Xueming
Published: July 2002

In this report, the O+SiH4 reaction is investigated using crossed molecular beam techniques. Multiple pathways have been observed for this reaction. Angular resolved time-of-flight spectra have been measured for all reaction products in a single set of experiments. Different product angular distributions were measured for various product channels, indicating that multiple reaction pathways with distinctive dynamics are present. An intriguing triple product channel, SiO+2H2, has also been clearly identified. However, the role of O(3P) vs O(1D) in the reactions remains to be clarified in further experimental investigations. This study provides a good example of multiple dynamical pathways in a complicated reaction, which opens enormous opportunities in investigating the dynamics of chemical reactions that are important in combustion and atmospheric chemistry.
Confirmation of classical nucleation theory by Monte Carlo simulations in the 3-dimensional Ising model at low temperature
Authors: Wonczak S. , Strey R. , Stauffer D.
Published: July 2002

We examine and visualize cluster formation, nucleation, and growth by Monte Carlo simulations in the three-dimensional Ising model at T/Tc=1/4, i.e., far from the critical temperature. Homogeneous nucleation rates as a function of supersaturation are obtained. From the slope of nucleation rate curves, model-free values for the critical cluster size are calculated, which agree with predictions of the Gibbs–Thomson relation for cubic nuclei. In fact, examining the shape of the critical clusters more closely, we find them to be cubical rather than spherical. Accordingly, the work of nucleus formation is accurately given by the classical nucleation theory, at least for the 3D-Ising model at the relatively low temperatures examined here. Furthermore, from the simulations subcritical equilibrium cluster number distributions are determined, which also agree with predictions for the exponential part of the classical nucleation theory.
Some simple type D solutions to the Einstein equations with sources
Authors: Torres del Castillo G. F. , Plebański Jerzy F.
Published: July 2002

Starting from a particular metric of the Kerr–Schild form, we find solutions to the Einstein equations coupled to a Weyl field, to an electromagnetic field, to a nonlinear (Born–Infeld) electromagnetic field, to a Yang–Mills field, and to a cosmological constant. These solutions can be superposed to construct others with any combination of the sources considered.
Spectrum doubling and double-valuedness
Authors: Stacey Richard
Published: July 2002

The effect of making the lattice Dirac operator the square root of the Laplacian is investigated. The doubling of the fermion spectrum is then matched by that of the boson spectrum, unless bosons are restricted to a double-spaced sublattice. Fermion spectrum doubling is found to be a necessary consequence of the double-valuedness of the square root.
Differential characters: The Dirac monopole as an example
Authors: Coquereaux Robert
Published: July 2002

Choosing the Dirac monopole as an example, the theory of differential characters is sketched and the quantization condition is recovered in a new way without considering singularities and without using a global formulation of gauge fields (i.e., without using fiber bundle techniques).
On the energy–time conjugation in quantum physics
Authors: Bailly F.
Published: July 2002

The energy–time conjugation is discussed in terms of mutually Laplace conjugated positive variables. The quantum statistical distribution functions in the energy are thus put into correspondence with ‘‘draw’’ distributions in the time, represented by sums of Dirac δ distributions. Time averages on correlation functions correspond to ensemble averages in energy. Conversely energy coupling of systems can be represented by a special operation on the δ distributions in time. For this aim, the connection of distributions is introduced, which enables one to take into account in some ‘‘multiplicative’’ way their simultaneous and cooperative effects. The Appendix is entirely devoted to the definition and properties of these connections and to some aspects of their algebra that make them suitable for treating some fundamental problems bound to the necessity of accounting interactive effects of singularities.
Formulation of Noether’s theorem for Fokker-type variational principles
Authors: Herman Warren N.
Published: July 2002

A formulation of Noether’s theorem is given for Fokker-type variational principles describing directly interacting particles. Many-body as well as two-body interactions depending at most on the particle positions and velocities are considered. Invariance up to a divergence of the action integral under infinitesimal transformations, as usual, leads to divergences that equal linear combinations of the Lagrangian derivatives. Conservation laws can be obtained when the Lagrangian derivatives vanish. The use of the formulation, which is independent of any specific transformations, is illustrated by rederiving the form of the conserved quantities following from the invariance of general two-body Fokker-type variational principles under the infinitesimal transformations of the Lorentz group and of the Galilei group; such conservation laws were previously derived using a method that, although exploiting the symmetries of the action integral, did not directly connect the divergence of the conserved quantities with linear combinations of the Lagrangian derivatives. Other applications and extensions are discussed.
The De Donder condition and the Poincaré group in quantized general relativity
Authors: Belinfante Frederik J.
Published: July 2002

The De Donder coordinate condition for an unquantized metrical field is discussed first. While the coordinate transformations allowed by this condition do not form a group in the ordinary sense, it is possible in an infinite number of ways to make these transformations elements of a group of metric-dependent coordinate transformations. In the unquantized theory, the question what coordinate transformations the De Donder condition will allow remains not generally answered, but it is not of primary importance, because the imposition of the De Donder condition in the unquantized theory is at best a question of convenience. The question is more important in the quantized ‘‘altered theory’’ of gravity, in which the De Donder condition serves for selecting the physical part of a theory that without this condition would also describe unphysical states. There are as many ‘‘altered’’ quantum theories of gravity, as there are affine orbits in the space of coordinate systems. Each orbit has its own altered theory, and in each separate altered theory with its own De Donder condition the only coordinate transformations that make sense are the affine ones, or, with proper boundary conditions imposed, Poincaré transformations. The coordinate transformation between two frames in which the De Donder condition is valid, either weakly or strongly, must be an affine (or Poincaré) transformation, if the coordinates are required to be c numbers.
Noncoordinated basis and Schild’s solution
Authors: Palou P. , Stela J. , Mas L.
Published: July 2002

In this paper we show the paradoxical consequences which appear in Schild’s solution, as seen from a noninertial frame (NIF). We propose a treatment for the noninertial frame which resolves the ambiguities.
How to construct integrable Fokker–Planck and electromagnetic Hamiltonians from ordinary integrable Hamiltonians
Authors: Hietarinta J.
Published: July 2002

Integrable Hamiltonians with velocity-dependent potentials, including those of Fokker–Planck-type H=1/2(p2x+p2y)+Kxpx+Kypy, are constructed from integrable Hamiltonians of type H=1/2(p2x+p2y)+V(x,y) using certain canonical and noncanonical transformations. Some of the Hamiltonians obtained this way are integrable only for zero energy. Candidates for the Φ potential, which is of interest for Fokker–Planck models, are constructed in several cases.
On the space-times admitting a synchronization of constant curvature
Authors: Bona Carlos , Coll Bartolomé
Published: July 2002

A synchronization S on the space-time is a foliation by spacelike hypersurfaces. We study here the vector fields, tangent to S, which are Killing fields for the induced metric on every instant of S but which are not necessarily Killing fields of the whole space-time metric; they are called S-Killing vector fields. We analyze the multiplicity of the maximal symmetry or complete integrability case, that is the case for which the space-times admit a synchronization S with the maximum number of S-Killing vector fields. In particular, the important case where S is umbilical is treated in detail.
Formulation of the inverse problem for the reduced wave equation in momentum space
Authors: Weston V. H.
Published: July 2002

The direct and inverse problem associated with the reduced wave equation expressed in momentum space (Fourier transform space of the spatial variable) is considered. It is shown that the right inverse of the scattering operator associated with complex scattered field amplitude T(k′,k) exists for the case where the index of refraction n(x) is real and satisfies certain smoothness conditions. A quadratic integral equation involving only T(k′,k) is obtained that represents a necessary and sufficient condition for T(k′,k) to be a complex scattered field amplitude associated with a real index of refraction. For the actual physical inverse problem where only on-shell (‖k′‖=‖k‖) values of T(k′,k) are known, the inverse problem involves solving this nonlinear system for off-shell data from on-shell data. Several other nonlinear systems that can be used are derived. Once T(k′,k) is known for k′,k, n(x) is readily obtained.
Cartan ideal, prolongation, and Bäcklund transformations for Einstein’s equations
Authors: Bilge A. H. , Gürses M.
Published: July 2002

Einstein’s equations in the Newman–Penrose formalism for vacuum, vacuum with cosmological constant, and electrovacuum fields are expressed as Cartan ideals. Two different prolongations of these ideals are obtained. These two types of prolonged ideals generalize previous prolongations for vacuum fields to vacuum with cosmological constant and electrovacuum fields. Some Bäcklund transformations are obtained for vacuum, vacuum with cosmological constant, and electrovacuum fields. These Bäcklund transformations include the generalized Kerr–Schild (GKS) transformation, and a two-parameter generalization of the GKS transformation. GKS transformations are studied in detail. Expressions for the transformation of Newman–Penrose quantities are given and algebraic properties are discussed. It is shown that the GKS transformation cannot give algebraically general and asymptotically flat vacuum and electrovacuum space-time metrics.
On the hydrogen-oscillator connection: Passage formulas between wave functions
Authors: Kibler M. , Ronveaux A. , Négadi T.
Published: July 2002

Recent works on the hydrogen-oscillator connection are extended to cover in a systematic (and easily computarizable) way the problem of the expansion of an R3 hydrogen wave function in terms of R4 oscillator wave functions. Passage formulas from oscillator to hydrogen wave functions are obtained in six cases resulting from the combination of the following coordinate systems: spherical and parabolic coordinate systems for the hydrogen atom in three dimensions, and Cartesian, double polar, and hyperspherical coordinate systems for the isotropic harmonic oscillator in four dimensions. These coordinate systems are particularly useful in physical applications (e.g., Zeeman and Stark effects for hydrogenlike ions and coherent state approaches to the Coulomb problem).
Direct and inverse scattering in the time domain for a dissipative wave equation. II. Simultaneous reconstruction of dissipation and phase velocity profiles
Authors: Kristensson G. , Krueger R. J.
Published: July 2002

The one-dimensional inverse scattering problem for inhomogeneous lossy media is considered. The model problem involves electromagnetic wave propagation in a medium of unknown thickness with spatially varying conductivity and permittivity. Two inversion algorithms are developed in the time domain using data obtained from normally incident plane waves. These algorithms utilize reflection data from both sides of the medium, and one of them also uses transmission data. These algorithms are implemented numerically on several examples, one of which includes the effects of noisy data. The possibility of using one-sided reflection data and no transmission data is reviewed and analyzed.
A general method of generating and classifying Clifford algebras
Authors: Li Deming , Poole Charles P. , Farach Horacio A.
Published: July 2002

A general construction program is given for the generation of higher-order Clifford algebras of various signatures together with their faithful representations in terms of Pauli-type operators. The analysis is based upon several isomorphism theorems that provide a simpler understanding of the standard classification scheme of these algebras, and an improved signature index notation is suggested that identifies each of the five types of Clifford algebras
Conformally Ricci-flat perfect fluids
Authors: Van den Bergh N.
Published: July 2002

Classes of inhomogeneous perfect fluid solutions can be obtained by requiring that the associated Weyl tensor corresponds to a nonflat vacuum solution of Einstein’s field equations. It is shown how one derives from this assumption useful information on the Newman–Penrose variables. Some particular classes of shear-free perfect fluid solutions are discussed, which all turn out to be locally rotationally symmetric.
Fractional approximation to the vacuum–vacuum amplitude of a φ4-potential theory in zero dimensions
Authors: Chalbaud Eduardo , Martín Pablo
Published: July 2002

Here, the vacuum–vacuum amplitude with a φ4-potential in terms of the fractional approximation to the partition function of a zero-dimensional field theory is presented. This fractional approximation has been obtained from both the power series and the asymptotic expansion. The power series diverges, nonetheless the fractional approximations are excellent. All the approximations from first to seventh degree are presented, with maximum errors from 0.6% to 1.6×10−5%, respectively.
On a particular transcendent solution of the Ernst system generalized on n fields
Authors: Leaute B. , Marcilhacy G.
Published: July 2002

A particular solution, a function of a particular form of the fifth Painlevé transcendent, of the Ernst system generalized to n fields is determined, which characterizes both the stationary axially symmetric fields, the solution of the Einstein (n−1) Maxwell equations, and one class of axially symmetric static self-dual SU(n+1) Yang–Mills fields.
Variational principles and orthogonal polynomials
Authors: Case K. M.
Published: July 2002

It is known that there is a close relationship between the theories of scattering and orthogonal polynomials. Here variational principles analogous to those of scattering theory are shown to hold for problems involving difference equations such as those for orthogonal polynomials. Some applications are indicated.
Spinors and space-times
Authors: Bugajska Krystyna
Published: July 2002

Dirac spinors for vector space-times Rs,t are considered as real spinors of appropriate extended vector spaces Rs′,t′. This extension is determined by the condition Rs′,t′≂RCs,t. The catalog of reality, chirality conditions allowed for Dirac spinors by the analysis of corresponding Clifford algebras and their left minimal ideals are completed.
The action of a general gauge field theory: Minimum or stationary
Authors: Bishop N. T.
Published: July 2002

Unless both the Cartan–Killing metric (Cα β) and the space metric (gij) are positive definite, a solution of the field equations always represents a stationary value of the action and never a minimum or maximum. In the Euclidean case, with (Cα β) positive definite, the action is a strict local minimum at a solution of the field equations. The validity of imposing certain gauge conditions is also discussed.
The propagator of the time-dependent forced harmonic oscillator with time-dependent damping
Authors: Cheng Bin Kang
Published: July 2002

By using the Caldirola–Kanai Hamiltonian and by applying Feynman polygonal paths, exact evaluation of the propagator of one-dimensional time-dependent forced and damped harmonic oscillator, based on the work of Montroll in deriving the propagator of the harmonic oscillator with time-dependent frequency, is possible. The results are compared with previously found results.
Non-Abelian Berry’s phase, accidental degeneracy, and angular momentum
Authors: Segert Jan
Published: July 2002

The non-Abelian Berry’s phase effect for a family of operators H0+k⋅V is considered, where H0 is rotationally invariant, V is a vector operator, and k varies over the unit vectors in R3. The parameter space is the two-sphere. The time evolution in the adiabatic limit is given by a connnection on a fiber bundle over the two-sphere. All connections consistent with the rotational symmetry are classified, and the time evolution is explicitly calculated for a nondegenerate Hamiltonian, as well as for a Hamiltonian with a double degeneracy. In the nondegenerate case, the connection is uniquely determined by the symmetry. In the doubly degenerate case, the connection is in some instances not determined by the symmetry. The case of approximate degeneracy is also discussed. A possible experimental test of this effect using optical pumping is described elsewhere.
Colliding gravitational plane waves with noncollinear polarization. I
Authors: Ernst Frederick J. , García D. Alberto , Hauser Isidore
Published: July 2002

An Ehlers transformation on the Ernst potential for the Nutku–Halil solution [Phys. Rev. Lett. 39, 1379 (1977)] provides a new solution of the Einstein field equations describing colliding gravitational plane waves with noncollinear polarization, the first of an infinite sequence of solutions that can be generated using techniques described in this paper.
Factorization of the wave equation in higher dimensions
Authors: Weston Vaughan H.
Published: July 2002

The factorization of the wave equation into a coupled system involving up-and down-going wave components is obtained for the case where the field quantities are multivariate functions of spatial variables, but the velocity c is a function of the z variable only. The form of the reflection operator is derived and the quadratic differential-integral equation satisfied by its kernel is obtained.
Group theoretical basis of some identities for the generalized hypergeometric series
Authors: Beyer W. A. , Louck J. D. , Stein P. R.
Published: July 2002

It is shown that Thomae’s identity between two 3F2 hypergeometric series of unit argument together with the trivial invariance under separate permutations of numerator and denominator parameters implies that the symmetric group S5 is an invariance group of this series. A similar result is proved for the terminating Saalschützian 4F3 series, where S6 is shown to be the invariance group of this series (or S5 if one parameter is eliminated by using the Saalschütz condition). Here Bailey’s identity is realized as a permutation of appropriately defined parameters. Finally, the set of three-term relations between 3F2 series of unit argument discovered by Thomae [J. Thomae, J. Reine Angew. Math. 87, 26 (1879)] and systematized by Whipple [F. J. Whipple, Proc. London Math. Soc. 23, 104 (1925)] is shown to be transformed into itself under the action of the group S6×Λ, where Λ is a two-element group. The 12 left cosets of S6×Λ with respect to the invariance group S5 are the structural elements underlying the three-term relations. The symbol manipulator macsyma was used to obtain preliminary results.