bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum effects in electron transfer reactions with strong electronic coupling
Authors: Stuchebrukhov Alexei A. , Song Xueyu
Published: July 2002

A new complex centroid reaction coordinate method is used to study electron transfer systems with strong electronic coupling. Formal analogy between current problem and the Ising model of one-dimensional spin system is used to develop a useful approximation for the partition function of electron transfer system in all orders of perturbation theory and when quantum effects are present. The reactions in the inverted region are discussed. The range of applicability of the usual nonadiabatic theory is re-examined. It is concluded that quantum solvent modes can effectively reduce electronic coupling in such a way that a nonadiabatic behavior can sometimes be induced in conventionally strongly coupled systems. Such an induced quantum nonadiabaticity is demonstrated in a numerical calculation.
Local chain dynamics of bulk amorphous polybutadienes: A molecular dynamics study
Authors: Kim Eung-Gun , Mattice Wayne L.
Published: July 2002

The local motions of bulk amorphous polybutadienes (PBDs) have been studied by a molecular dynamics simulation. Fully atomistic models of PBDs have been obtained at a realistic bulk density under periodic boundary conditions. Local chain motions are examined for poly(cis-1,4-butadiene) (cis-PBD) and poly(trans-1,4-butadiene) (trans-PBD) well above the glass transition temperature, where the only structural difference is imposed by the different conformational states at the double bond. The local motions are found to be strikingly different in the two polymers. Intramolecular cooperative conformational transitions occur at second-neighbor bond pairs of CH–CH2 in both PBDs. In trans-PBD, both CH2–CH2 and CH=CH triplets undergo cooperative counterrotations. In cis-PBD, CH2–CH2 triplets undergo counterrotations while CH=CH triplets undergo corotations. Intermolecular cooperativity, probed by the local free volume, has little influence on local relaxation processes. The effect of libration on the shape of autocorrelation functions (ACFs) is significant over the entire time range. A universality is found in the time evolution of the Kohlrausch–Williams–Watts exponent regardless of the type and order of the ACF. On the other hand, the single exponential decay regarded as common at short times is only due to the discreteness of conformational states.
Relativistic effects in the electronic structure of the monoxides and monocarbonyls of Ni, Pd, and Pt: Local and gradient-corrected density functional calculations
Authors: Chung Sai-Cheong , Krüger Sven , Pacchioni Gianfranco , Rösch Notker
Published: July 2002

Using a scalar relativistic version of the linear combination of Gaussian-type orbitals density functional method we have computed electronic and spectroscopic properties of the monoxides and monocarbonyls of Ni, Pd, and Pt. All-electron calculations with large basis sets were performed at both the local and the gradient-corrected density functional level. It is found that relativistic effects play a crucial role in Pt compounds, in particular as far as the metal–ligand distance is concerned. At the relativistic level the Pt–O and the Pt–CO distances are shorter than the corresponding Pd–O and Pd–CO bond lengths. Thus the trend in the metal–ligand distances is Ni<Pt<Pd. This is connected to a considerable relativistic strengthening of the Pt–O and Pt–CO bonds. Gradient corrections significantly reduce the computed binding energies, but are much less important for geometry and vibrational frequencies. They cause a more or less similar weakening and lengthening of the bonds which is quite independent of the metal considered.
Structure and properties of the CF1 central force model of water: Integral equation theory
Authors: Duh Der-Ming , Perera Donna N. , Haymet A. D. J.
Published: July 2002

The structure and properties of the CF1 central force model of water are studied using an integral equation theory, which supplements the hypernetted chain approximation with a bridge function. At the temperature 25 °C and density 1.000 g cm−3, both the intra- and intermolecular structure are in excellent agreement with computer simulations of the same model, and thermodynamic properties are in good agreement with experimental values. Comparison is made with the most popular rigid-molecule models of water. The predictions of this theory can be used as input into theories of inhomogeneous aqueous systems.
Molecular dynamics simulation studies of a high resolution Z-DNA crystal
Authors: Lee Hsing , Darden Thomas A. , Pedersen Lee G.
Published: July 2002

We report two 1 ns molecular dynamic (MD) simulations on Z-DNA for which the long-range Coulomb terms are explicitly evaluated by the Particle–Mesh–Ewald method [J. Chem. Phys. 98, 10089 (1993)]. The starting structures were based on the 1 Å resolution crystallographic structure of Gessner et al. [J. Bio. Chem. 264, 7921 (1989)]. The average simulation structures of the DNA compare well to the crystallographic structure; the root-mean-square position deviations for the DNA double-strand heavy atoms are approximately 0.5 Å. Watson–Crick hydrogen bonding patterns are preserved without invoking constraints. These results emphasize the importance of proper treatment of the long-range forces for highly ionic systems.
Vibrational spectroscopy of cocrystallized carbon dioxide and acetylene
Authors: Gough T. E. , Wang T.
Published: July 2002

Fourier transform infrared spectra of acetylene and carbon dioxide cocondensed in a diffusive trapping cell are presented, and interpreted in terms of the stoichiometric phase CO2.(C2H2)2. Simulations show that this novel phase is formed when the degrees of supersaturation of the constituent gases are of comparable values.
Metal oxidation state effect in photoionization of gas-phase metal halides
Authors: Stranges S. , Adam M. Y. , de Simone M. , Decleva P. , Lisini A. , Cauletti C. , Piancastelli M. N. , Furlani C.
Published: July 2002

The full-valence photoelectron (PE) spectrum of SnCl4 excited by synchrotron radiation in the ultraviolet (UV) region is reported here for the first time, and compared with the analogous spectrum of SnCl2 previously published. Electron correlation effects in the different valence spectral regions are experimentally and theoretically analyzed for both tin chlorides. The theoretical results are obtained at ab initio 2h-1p CI level. Total-ion-yield (TIY) spectra excited by synchrotron radiation are obtained for both molecules in the Sn 4d−1 thresholds region for the first time. Sn 4d excited states in the two chlorides are hence identified through the resonant features displayed by the TIY spectra. The assignment is in good qualitative agreement with the excitation energies and oscillator strengths calculated at ab initio CI level. Clear differences exhibited by both PE and TIY spectra reported in this work originate from the different metal oxidation state in the two apparently similar chlorides, or equivalently, from the different involvement of the valence atomic orbitals of tin to form the chemical bonds of the molecule. Inner-valence ionizations in the investigated molecules are shown to be a sensitive probe of the halogen chemical environment, being related to the Sn–Cl bond polarization.
The unimolecular dissociation of HCO: I. Oscillations of pure CO stretching resonance widths
Authors: Werner Hans-Joachim , Bauer Cornelia , Rosmus Pavel , Keller Hans-Martin , Stumpf Michael , Schinke Reinhard
Published: July 2002

The unimolecular dissociation of the formyl radical HCO in the electronic ground state is investigated using a completely new ab initio potential energy surface. The dynamics calculations are performed in the time-independent picture by employing a variant of the log-derivative Kohn variational principle. The full resonance spectrum up to energies more than 2 eV above the vibrational ground state is explored. The three fundamental frequencies (in cm−1) for the H–CO and CO stretches, and the bending mode are 2446 (2435), 1844 (1868), and 1081 (1087), where the numbers in parentheses are the measured values of Sappey and Crosley obtained from dispersed fluorescence excitation spectra [J. Chem. Phys. 93, 7601 (1990)]. In the present work we primarily emphasize the dissociation of the pure CO stretching resonances (0v20) and their decay mechanisms. The excitation energies, dissociation rates, and final vibrational–rotational state distributions of CO agree well with recent experimental data obtained from stimulated emission pumping. Similarities with and differences from previous time-independent and time-dependent calculations employing the widely used Bowman–Bittman–Harding potential energy surface are also discussed. Most intriguing are the pronounced oscillations of the dissociation rates for vibrational states v2≥7 which are discussed in the framework of internal vibrational energy redistribution.
‘‘Pointwise’’ versus basis representations for two-dimensional spherical dynamics
Authors: Sharafeddin Omar A. , Light John C.
Published: July 2002

We compare pointwise representations and nondirect product basis representations for treating quantum dynamics in 2D (θ,φ) spherical polar coordinates. As pointwise representations we have considered a modified discrete variable representation (DVR) and the collocation representation (CR). As basis representations we used spherical harmonics with 2D Gaussian numerical quadratures (FBR) and the spectral collocation representation (SCR). These representations were tested on a simple model potential V(θ,φ) and on a realistic ArH2O potential (at fixed R) and the results were compared. The energies obtained from the pointwise representations considered were substantially less accurate than those obtained from the basis representations for given matrix sizes. The basis representations, especially the FBR, appear to require the least computational effort and to be the most simple and accurate for quantum problems in spherical polar coordinates. This illustrates the difficulties in using pointwise representations for angular problems which do not have good direct product bases.
Theoretical study of the electronic spectrum of antimony oxide employing relativistic effective core potentials
Authors: Alekseyev Aleksey B. , Liebermann Heinz-Peter , Buenker Robert J. , Hirsch Gerhard
Published: July 2002

Potential energy curves and electric dipole transition moments between different electronic states are computed for the antimony oxide molecule employing a relativistic configuration interaction scheme including the spin–orbit coupling interaction. Comparison is made with available experimental data as well as with the corresponding results which were recently reported for the isovalent BiO. A full core relativistic effective core potential proves to be quite effective in describing the antimony inner shells, thereby reducing the amount of computations considerably relative to an all-electron CI treatment. The calculated bond lengths re for the X1 2Π1/2 ground state and C 2Σ−1/2 excited state agree to within 0.01 Å of the respective measured values and good agreement is also found for the vibrational frequencies ωe of a large number of SbO states. The theoretical treatment tends to underestimate transition energy Te values, typically by 1000–2000 cm−1, reflecting the fact that all excited states have more open shells in their leading configurations than does the ground state itself. On the basis of the present calculations it has been possible to confirm a number of earlier assignments for the SbO upper states and also to aid in the experimental detection of several new transitions involving various a 4Π and b 4Σ− species which were not known at the time this work was begun. Theoretical values for the radiative lifetimes of the v′=0 levels of each of the above electronic states have also been obtained, and they are found to agree within at least a factor of 2 in most cases with the recent experimental values obtained by Fink, Shestakov, and co-workers. The lone exception found to date is for the B 2Σ+ state, but it is noted that nonadiabatic interactions between it and the b1 4Σ−1/2 state, as already discussed in an earlier review by Rai and Rai, could be at least partially responsible for this result.
Electric double layer at a metal/electrolyte interface: A density functional approach
Authors: Patra Chandra N. , Ghosh Swapan K.
Published: July 2002

The structure of electric double layer at a metal/electrolyte interface is studied here using a density functional approach for the metallic electrons as well as the ions of the electrolyte. The metal is represented by a jellium and the electrolyte is modeled as an ensemble of charged hard sphere ions. The minimization of the total energy which includes the interaction of metallic electrons with the electrolyte ions yields the electron and the ion density distribution at the interface. The calculated interfacial capacitance compares quite well with the reported experimental results.
Hyperfine structure effects in probing atomic alignment
Authors: Bell I. M. , Quayle C. J. K. , Burnett K.
Published: July 2002

We have performed an analysis of the effect of hyperfine structure in an experiment in which an aligned excited state is probed using linearly polarized light. The state is born with a given electronic alignment resulting from a collisional process. It is probed after a time which is short in comparison to its radiative lifetime but much longer than ω−1hfs, where ℏωhfs is the hyperfine splitting. This means that hyperfine structure has ample time to ‘‘develop.’’ It is therefore essential to take into account both the hyperfine structure of the level and the manner in which the alignment is affected by recoupling to the new basis. Ratios of fluorescent intensities for different laser polarization configurations contain information on the alignment of the system. We show how these may be calculated for a system with several isotopes, some of which have hyperfine structure, and where many components are probed with appreciable strength. A comparison is made with our experimental results for the Hg(6 3P1) level probed on the 6 3P1–7 3S1 transition. The presence of hyperfine structure has a considerable influence on the measurements. It is important to understand such effects if one is to obtain information on the nascent electronic alignment by observation of the fluorescent intensities.
Spectroscopy of mixed early–late transition metal diatomics: ScNi, YPd, and ZrCo
Authors: Arrington Caleb A. , Morse Michael D. , Doverstål Mats
Published: July 2002

Resonant two-photon ionization spectroscopy has been employed to investigate the spectra of the jet-cooled transition metal diatomics ScNi, YPd, and ZrCo, which are isovalent species which possess (or are thought to possess) an X 2Σ+ ground state. Several electronic band systems have been observed for these species in the near infrared, and the analysis of these systems is reported. Ground state vibrational intervals of ΔG1/2″ = 334.5 ± 1.0, 264.4±0.2, and 357.7 cm−1 have been determined for ScNi, YPd, and ZrCo, respectively. The spectroscopic results obtained for ScNi and YPd are compared to theoretical calculations performed by other researchers, and a discussion of the chemical bonding in these species is presented.
Nanoscale shock wave generation by photodissociation of impurities in solids: A molecular dynamics study
Authors: Borrmann Angela , Martens Craig C.
Published: July 2002

The dynamics of shock wave generation, propagation, and decay in an Ar lattice following photodissociation of an I2 impurity are studied using molecular dynamics simulation. A two-dimensional model is treated to allow the modeling of shock wave propagation over larger distances than easily accessible in full three-dimensional calculations. The shock waves are created on atomic length scales by binary collisions between the nascent photofragments and adjacent lattice atoms, and propagate long distances through the crystal in a highly directed, quasi-one-dimensional manner. As a consequence of the I/Ar mass ratio, the I fragments undergo multiple collisions with the adjacent Ar atoms situated along the I–I bond axis, generating pulse trains of shock waves, each with a characteristic initial energy, velocity, and decay rate. The dynamics of the system are interpreted using a simple one-dimensional hard sphere model.
Collisional redistribution in Sr–He spin-changing energy transfer collisions: Final-state alignment
Authors: Ananthamurthy Sharath , Kleiber P. D.
Published: July 2002

We have measured the product alignment resulting from the collisional redistribution of polarized light in Sr–He inelastic spin-changing energy transfer collisions. The experimental results are in good agreement with the predictions of an analytic theoretical model, based on a standard orbital-locking and following approximation, but generalized to this inelastic collision process. The good agreement indicates a clear understanding of the energy transfer dynamics in this case, and suggests that this simple analytic approach may be generalized to a much broader range of collisional phenomena.
Multiconfiguration time-dependent Hartree studies of the Cl2Ne vibrational predissociation dynamics
Authors: Fang Jian-Yun , Guo Hua
Published: July 2002

The vibrational predissociation of a van der Waals complex (Cl2Ne) is studied using a method based on the multiconfiguration time-dependent Hartree approximation. The three-dimensional wave function is first expanded to the time-independent Cl2 vibrational bases and the Hartree approximation is then imposed on the channel wave functions. The wave packets are propagated for a few picoseconds and five configurations are found to give convergent results. The decay lifetimes, product state distributions and the wave packet dynamics are compared with exact results and the agreement is found to be generally satisfactory. It is found that the decay depends sensitively on the quality of the initial resonance wave function and the single configuration TDH gives only a crude approximation of the dissociation dynamics.
Detection of neutral metastable fragments from electron-impact on argon clusters
Authors: van der Burgt P. J. M. , McConkey J. W.
Published: July 2002

We have studied the production of neutral metastable fragments in electron collisions with neutral argon clusters. The fragments are detected using a time-of-flight technique. The time-of-flight spectra show that the metastable fragments appear in two velocity ranges. Kinetic energy distributions are obtained, showing that the faster fragments are ejected with energies from 0.2 to 1.5 eV and that the slower fragments have energies less than 0.2 eV. It is argued that the fragmentation of the clusters involves the excitation and decay of excitons in the clusters.The faster fragments are produced by n=2 excitons, which localize on an excimer or an excited trimer within the cluster and upon dissociation cause the ejection of a metastable atom. The slower fragments are produced by n=1 excitons, which tend to localize on the periphery of the cluster, leading to the ejection of a metastable atom due to weak repulsive forces with neighboring atoms. Four different production mechanisms for neutral metastable fragments are observed.
On the role of conical intersections in photodissociation. III. The case of hydroxylamine
Authors: Hettema Hinne , Yarkony David R.
Published: July 2002

Conical intersections of two states of the same symmetry are usually considered rare and are frequently ignored in the treatment of nonadiabatic processes. This work addresses the veracity of this assumption. The existence of conical intersections of two states of the same symmetry is considered for the four lowest electronically excited states of hydroxylamine NH2OH using configuration interaction wave functions. The existence of ‘‘same symmetry’’ conical intersections is demonstrated and their role in the photodissociation process NH2OH→NH2+OH investigated. Although the ground electronic state has Cs symmetry (with two equivalent hydrogens) it is argued that conical intersections corresponding to nuclear configurations far removed from Cs symmetry play a role in the photodissociation.
Time-resolved laser control of vibrational excitations in molecules
Authors: Tung Nguyen-Dang T. , Chatelas C. , Tanguay D.
Published: July 2002

We show that, on a short time scale, the dynamics of vibrational excitations in multimode ground-state molecular systems, linearly coupled to a laser field, can be expressed as a simple functional of the laser pulse area. The dependence of the vibrational system’s dynamics on a field area leads to simple algebraic equations for this area, in the formulation of the inverse problem associated with the time-resolved control (tracking) of vibrational excitations. The control equation to be solved is quadratic in the area, when the object of the time-resolved control is the total vibrational energy, and linear when the object to be controlled is an average elongation (position tracking), or the average energy of a remotely coupled mode. This yields a control algorithm which requires no iteration and is easy to implement. Numerical tests of the algorithm are performed on the energy and position trackings in simple one-dimensional model systems. An excellent analytical, approximate description of the laser-driven dynamics of these systems is obtained using the concept of Lewis invariant. This analytical description is used as a reference with which the field numerically generated by solving the inverse control problem, using the aforementioned algorithm, can be compared.
Ab initio vibration–rotation-tunneling spectra and dynamics of H2⋅F− and its isotopomers
Authors: Boldyrev A. I. , Simons Jack , Mil’nikov G. V. , Benderskii V. A. , Grebenshchikov S. Yu. , Vetoshkin E. V.
Published: July 2002

Ab initio computations of the potential energy surface (PES) of the ground electronic state of H2⋅F− have been performed as a function of the stretching F–H2 (R) and H2 rotation (θ) coordinates. Minima on the PES correspond to linear H–H–F− structures, while the transition state is T-shaped. The F− to H2 distance increases in the transition state from 2.07 to 3.10 Å, demonstrating strong coupling between the θ and R degrees of freedom. The vibration–rotation-tunneling spectra are calculated by diagonalizing the five dimensional Hamiltonian matrix that describes free rotation of the triatomic (three coordinates) plus the internal θ and R motions. For total angular momentum J=0, the spacing between levels in the tunneling doublets increases from 0.029 to 6.74 cm−1 as the stretching quantum number n corresponding to R motion varies from 0 to 5. The splittings increase even more strongly with the bending quantum number. For J=1, each level in the tunneling doublets is further split by Coriolis forces. K-doubling is found to be an order of magnitude smaller than the tunneling splitting. In the symmetric isotopomers D2⋅F− and T2⋅F−, the tunneling splitting drops by 3 and 4 orders of magnitude compared to H2⋅F−, and thus becomes comparable with the K-doubling for J=1. Finally, incoherent tunneling, appropriate to condensed phase environments, of the H2F− system is also treated.
Solid–fluid equilibria for quadrupolar hard dumbbells via Monte Carlo simulation
Authors: Vega C. , Monson P. A.
Published: July 2002

Solid–fluid equilibrium for the quadrupolar hard dumbbell model has been determined by Monte Carlo simulation for several values of the quadrupole moment and molecular elongation. Several solid structures have been studied including α-N2, a fcc plastic crystal, based centered monoclinic structure providing closest packing for hard dumbbells and two orthorhombic structures. For low elongations, hard dumbbells freeze into a plastic crystal phase when the quadrupole moment is low and into the α-N2 structure when it is large. More elongated dumbbells freeze into a close-packed structure for low quadrupole moment, into an orthorhombic structure for moderate quadrupole moment and into the α-N2 structure for large quadrupole moment. For any elongation and quadrupole moment the stable phase at very high pressures is one of the close-packed structures. The quadrupolar hard dumbbell model gives a qualitatively correct description of trends in the solid–fluid equilibrium for several systems including N2, the halogens, CO2, and acetylene.
Spectroscopy of jet-cooled YCu
Authors: Arrington Caleb A. , Brugh Dale J. , Morse Michael D. , Doverstål Mats
Published: July 2002

Optical spectra of jet-cooled diatomic YCu have been recorded using resonant two-photon ionization spectroscopy in a supersonic expansion of helium. The ground state is shown experimentally to be of 1Σ+ symmetry, with a measured bond length of re″=2.6197(6) Å and a vibrational frequency of 193.21(24) cm−1 for 89Y63Cu. Five excited electronic states are identified as the [10.2]1Σ+ state, the [11.8]3Π0+ state, the [12.0]3Π1 state, the [14.0]1Π state, and, with the help of ab initio theory, the [12.2]1Π state. No evidence whatever for participation of the 3d orbitals of copper in the chemical bonding is found, and the electronic structure of YCu is found to exhibit a striking similarity to that of YH.
Transient nucleation in binary ideal solution
Authors: Kožíšek Z. , Demo P.
Published: July 2002

Influence of solution temperature, composition of the parent phase, heats of fusion and melting temperatures of single components on transient nucleation of binary ideal solution is analyzed. The characteristics of nucleation process, such as nucleation rate, distribution function of nuclei, mean concentration of nuclei of newly forming phase and time lag of nucleation are determined by the numerical solution of kinetic equations. It is shown that mean composition of clusters of new phase at stationary limit (for sufficiently long time) goes to the mole fraction of the saddle point CS only for sufficiently small clusters, but with increasing size of clusters the differences from CS increase. Magnitude and sign of these deviations depend predominantly on temperatures of solution and heats of fusion of single components.
Viscoelastic response of bidisperse melts in the lateral motion model
Authors: Tong Ping , Herman Michael F.
Published: July 2002

A model for stress relaxation of linear chain polymer melts in the linear viscoelastic regime is proposed. This model is developed in the context of the lateral motion model of polymer dynamics, which assumes that polymers diffuse in the melt by sliding laterally along the curvilinear contours of neighboring chains. It is assumed that, in the post-plateau region of the time dependent stress relaxation, the stress is supported by interchain contacts. When each contact breaks, a new contact is formed, since the number of interchain contacts is an equilibrium property. It is also assumed in this model that the new contacts, formed after the application of the strain, support partial stress because the polymer system is not isotropic at the time of the formation of these new contacts. The stress relaxation is evaluated within this model for monodisperse and bidisperse melts using a computer simulation procedure. The results are compared with published experimental data. Very good agreement is found with the experimental results.
Characterization and orientation of adsorbed NO dimers on Ag{111} at low temperatures
Authors: Brown W. A. , Gardner P. , Jigato M. Perez , King D. A.
Published: July 2002

Reflection-absorption infrared spectroscopy (RAIRS) and near-edge x-ray absorption fine structure (NEXAFS) have been used, with isotopic 14NO/15NO mixtures, to determine the structure and orientation of the monolayer species formed by NO adsorption on Ag{111} at 40 to 60 K. The adlayer is composed of NO dimers bonded with the N–N axis in the surface plane and with the molecular plane tilted away from the surface normal by about 30°. This structure provides a simple basis for understanding the facile reaction to adsorbed N2O and O which occurs on heating to 70 to 90 K.
Matrix trapping sites and interactions with LiF monomer
Authors: Redington Richard L.
Published: July 2002

Infrared spectra of the LiF monomer isolated in rare gas and RG/X mixed-matrices are interpreted with the guidance of ab initio molecular orbital (MO) computations performed on FLiArn clusters and on FLiX van der Waals complexes (X=Ar, N2, CO, O2, and CH4). The work suggests there are two distinct trapping subsites for LiF in a single-substitutional vacancy of the Ar fcc crystal. In the primary subsite LiF lies on a tetragonal crystal axis and makes four near-optimal LiAr contacts; in the metastable subsite it lies on a trigonal axis and makes three near-optimal LiAr contacts. The model is supported by its account of the large Ar-induced vibrational frequency shift, spectral doublet, and temperature-dependent infrared (IR) absorption profile of the LiF vibrational fundamental. IR observations of LiF isolated in several RG/X mixed matrices support the existence of FLiX van der Waals complexes isolated in Ar double-substitutional sites of the lattice.
Renner–Teller effect and Rydberg-valence mixing in the N and O K-edge photoabsorption spectra of N2O
Authors: Adachi Jun-ichi , Kosugi Nobuhiro , Shigemasa Eiji , Yagishita Akira
Published: July 2002

We have measured high-resolution angle-resolved ion-yield spectra of the O and N 1s excited N2O molecules (Nt–Nc–O) and investigated them with the help of ab initio quantum chemical calculations. The peak width of the Nc 1s→π* transition is larger than that of the Nt 1s→π* one. This mainly arises from different populations of bending vibrations excited through the Renner–Teller effect, which breaks the degeneracy of the 1s→π* excited states by bending the linear molecule. The angular distribution of fragment ions emitted after the Auger decay is also affected by the Renner–Teller effect. That is, fragment ions significantly lose the information of the Π symmetry of the linear molecule. For the 1s→Rydberg excitations no Renner–Teller effect is observed and the angular distribution is directly related to the Σ and Π symmetries. Furthermore, it is found that the peak intensities of the O and Nt 1s→nsσ Rydberg transitions are unusually large. The N2O molecule has two σ* orbitals, σs*(8σ) and σp*(9σ), below and above the ionization threshold and the 1s→σs* excited states are mixed with the O and Nt 1s–nsσ Rydberg excited states; on the other hand, the Nc 1s→σs* transition is almost dipole-forbidden because of the orbital symmetry.
Surface cosegregation phenomena on bcc(001) alloy surfaces: The effect of nearest and next nearest M–X neighbor interactions
Authors: Uebing Christian
Published: July 2002

In the present work we introduce a three-dimensional lattice gas model for the description of surface cosegregation phenomena on (001) oriented surfaces of multicomponent bcc alloys. It is assumed that the lattice consists of two types of lattice sites M and X. The metal sites M form a body-centered cubic lattice, whose quasioctahedral interstices constitute the nonmetal sublattice. In most cases lattices of 64×64×64 sites of the bcc structure (interstitials plus metal sites) are used. The M sites are accessible to either MA or MB atoms, while the nonmetal sites are either occupied by X atoms or remain empty. Pairwise repulsive nearest and attractive next nearest neighbor interactions between MA–X and MB–X atoms are considered as well as nearest and next nearest neighbor X–X repulsions. The Monte Carlo simulations are performed in the grand canonical ensemble. The simulations indicate that the cosegregation induced formation of the surface compound MBX is basically due to preferential next nearest MB–X neighbor attractions, φMBX(2). Surface compound formation causes an increase of the excess Gibbs free energies of segregation ΔGxsX and ΔGxsM. The Gibbs free energies of segregation can be estimated roughly via a mean field approximation. Upon increasing the strength of the preferential next nearest MB–X attractions surface compound formation is accompanied by a first order phase transition at low temperatures. Depending on the relative magnitude of the nearest neighbor M–X repulsions we observe a strong MB subsurface depletion [φMBX(1)<φMAX(1)<0] or enrichment [φMAX(1)<φMBX(1)<0], the latter has been verified by x-ray photoelectron diffraction (XPD) for the CrN surface compound on Fe–15%Cr–N (001).
A crossed-beam scattering study of CH+4 and CH+3 formation in charge transfer collisions of Kr+ with CH4 at about 1 eV
Authors: Herman Zdenek , Friedrich Břetislav
Published: July 2002

The dynamics of CH+4 and CH+3 ion formation in collisions of Kr+ (2P3/2′1/2) with thermal CH4 has been investigated in a crossed beam experiment at a hyperthermal collision energy of 1.18 eV. The scattering data show that the CH+4 product is formed in a near-resonant exoergic process in which the most probable energy transferred to the target is practically equal to the recombination energy of the Kr+ projectile (resonant energy transfer); in addition a wide band of internal states of CH+4 up to ±0.6 eV is populated in inelastic and superelastic collisions. In contrast, the CH+3 product is formed in dissociative charge transfer, with about one-half of the yield due to nonresonant, endoergic collisions of Kr+ (2P3/2). The other half of the CH+3 product is found to originate in near-resonant exoergic collisions of Kr+ (2P1/2). An estimate is given of the distribution of the total energy deposited in methane by the above processes.
Second-order correlation energy for H2O using explicitly correlated Gaussian geminals
Authors: Bukowski Robert , Jeziorski Bogumil/ , Rybak Stanisl/aw , Szalewicz Krzysztof
Published: July 2002

The second-order pair energies are calculated for the H2O molecule employing explicitly correlated Gaussian-type geminals. The selection of the basis functions is guided by the completeness criteria for Gaussian geminal bases of C2v symmetry and by the recently developed technique [J. Chem. Phys. 100, 1366 (1994)] of crude optimization of nonlinear geminal parameters. Several simplifications have been made in the matrix elements evaluations that substantially reduce the optimization time without sacrificing numerical accuracy. The present results provide the new best upper bound to the second-order correlation energy for the water molecule. These results are compared with those obtained by Kutzelnigg and co-workers using the basis set containing terms linear in the interelectronic distance.
Interatomic potentials of singlet s-Rydberg series of a HgNe van der Waals dimer: Evidence for stabilization by superexchange interaction
Authors: Onda Ken , Yamanouchi Kaoru
Published: July 2002

The interatomic potentials of the singlet Rydberg series of the HgNe dimer 1Σ+ Hg(n1S0)Ne (n=7–9) were determined over a wide range of interatomic distance by the analysis of the optical–optical double resonance (OODR) spectra measured in the present study via the A 3Π0+ and B 3Π1 states. The interatomic potential for n=7 consists of one bound vibrational level (v=0), three quasibound levels (v=1–3) trapped inside a potential barrier, and one weakly trapped quasibound level just above the potential barrier. The dissociation energy (De) of this potential is 50(3) cm−1 and the large potential barrier with a height of 133(2) cm−1 is located at 4.20(3) Å, while the interatomic potentials for n=8 and n=9 consist of a deep bound well, whose dissociation energies (De) are 240(3) and 297(3) cm−1, respectively. From these potentials, it was shown that the principal quantum number dependence (n) of the interatomic potential originates mainly from that of the exchange repulsion between the Rydberg electron of Hg and the attached Ne atom in a similar manner as the triplet Rydberg series of HgNe, 3Σ+ Hg(n3S1)Ne (n=7–10) [K. Onda et al. J. Chem. Phys. 101, 7290 (1994)]. By comparing the potentials of the singlet with the triplet Rydberg series, it was found that an interatomic potential of the singlet state is always deeper than that of the triplet state for the same n. This difference between singlet and triplet was interpreted by a superexchange interaction model [P. N. Anderson, Phys. Rev. 79, 350 (1950)], in which a singlet Rydberg state becomes more stable due to small spin density on the Ne atom induced by the kinetic exchange interaction between the Hg+ ion and the Ne atom.
The infrared spectrum of the N2H+–He ion-neutral complex
Authors: Nizkorodov S. A. , Maier J. P. , Bieske E. J.
Published: July 2002

Rotationally resolved, vibrational predissociation spectra of the HN+2–He complex have been recorded in the region of the N–H stretch (3100–3200 cm−1). The complex appears to be linear. Fitting of the measured lines to the pseudodiatomic expression ν=ν0+(B′ν+B″ν)m +(B′ν−B″ν–D′ν+D′ν) m2−2(D′ν+D″ν)m3 −(D′ν−D″ν)m4 yields the following constants: ν0=3158.419±0.009 cm−1, B″=0.3517±0.0005 cm−1, D″=(5.8±0.5)×106 cm−1, B′=0.3579 ±0.0005 cm−1, D′=(3.9±0.6)×106 cm−1. The data support a proton bound He–HNN+ structure, with a 1.72 Å vibrationally averaged intermolecular bondlength, and an approximate intermolecular stretching frequency of 150 cm−1.
Field-theoretical approach to critical microphase behavior of symmetric crosslinked polymer blends
Authors: Benhamou Mabrouk
Published: July 2002

Critical properties of symmetric crosslinked binary polymer mixtures is studied using the renormalization-group. It is assumed that chains have a low-molecular-weight, in order to have a wide critical regime where a nonclassical behavior is observed. Use is made of a scalar field model of φ4 type, where the order parameter φ is the local fluctuations in the composition. The parameters of the problem are the temperature t∝χ0−χ, the rigidity constant of the gel C, and the coupling constant u. χ is the Flory interaction parameter, χ0=2/N its critical value if the system is uncrosslinked, and N the degree of polymerization. We first show that the set of demixing critical points is a continuous line, in the two-dimensional half-space of parameters −∞<t<+∞ and 0≤C<+∞, defined by the equation, −t≂C1/φ, where φ is a crossover exponent of values φ≂2.501±0.005 and φ=15/4 (exact) at three and two dimensions, respectively. We establish scaling laws, with respect to the relevant parameters which are the wave vector q, t, and C, for any correlation function, in particular, for the structure factor which is simply the two-point correlation function. We formulate these scaling laws in terms of assertions, which show an analogy with those relative to systems governed by finite size scaling; their typical size L corresponds to the critical fluctuations size ξ*≂C−ν/φ of the crosslinked systems. Some preliminary results found previously are recovered.
Formation of NO(A 2Σ+, C 2Πr, D 2Σ+) by the ion–ion neutralization reaction between NO+ and C6F6− at thermal energy
Authors: Tsuji Masaharu , Ishimi Hiroaki , Nishimura Yukio , Obase Hiroshi
Published: July 2002

The ion–ion neutralization reaction between NO+ (X 1Σ+:v″=0) and C6F−6 has been spectroscopically studied in the flowing helium afterglow. In addition to the NO(A 2Σ+–X 2Πr) emission system, which has been found in the previous studies on the NO+/NO−2 and NO+/SF−6 reactions, the NO(C 2Πr–X 2Πr, D 2Σ+–X 2Πr) emission systems are observed in the NO+/C6F−6 reaction. The relative formation rates of NO(A), NO(C), and NO(D) are evaluated to be 1.0, 0.13±0.04, and 0.24±0.04, respectively. Only the v′=0 levels of NO(A,C,D) are formed, indicating that no energy is deposited into the vibration of NO(A,C,D). The rotational distributions of NO(A:v′=0), NO(C:v′=0), and NO(D:v′=0) are expressed by single Boltzmann rotational temperature of 500±50, 300±50, and 400±50 K, respectively. The average fractions of the total available energy deposited into rotation of NO(A), NO(C), and NO(D) are evaluated to be only 1.5±0.1%, 1.4±0.2%, and 1.9±0.2%, respectively. Most of all excess energy is expected to be partitioned into translation of the products. The observed vibrational and rotational distributions are less excited than statistical prior ones, indicating that the reaction dynamics is not governed by a simple statistical theory. The excitation mechanism of NO(A,C,D) in the NO+/C6F−6 reaction is compared with those in the NO+/NO−2 and NO+/SF−6 reactions, which give only the NO(A) state.
Dynamics of hyperthermal Kr++H2O charge-transfer collisions
Authors: Arnold Susan T. , Dressler Rainer A. , Bastian Michael J. , Gardner James A. , Murad Edmond
Published: July 2002

Cross section, time-of-flight (TOF) and luminescence measurements are reported for the Kr++H2O charge-transfer system. Cross section and TOF measurements were carried out in an octopole guided-ion beam apparatus and are reported for collision energies between 0.10–10 eV (c.m.). The charge-transfer cross section has approximately an E−0.5 dependence at low collision energies. TOF measurements of H2O+ products are characteristic of a near-resonant direct charge-transfer mechanism proceeding at long range. A smaller contribution of forward-scattered ions is attributed to the formation of longer-lived collision complexes. The TOF analysis based on the osculating complex model reveals significant energy transfer for orbiting trajectories. Low resolution product ion luminescence spectra (4 nm FWHM), taken at collision energies between 0.1–15 eV (c.m.), are consistent with the TOF measurements. The optical spectra show that H2O+ product ions are formed in Ã-state vibrational levels that are at or below the energy level of Kr+(2P1/2) reactants. No evidence is found for luminescence stemming from Kr+(2P3/2) reactants.
Time-dependent and temperature-dependent aspects of electron distribution functions: H, Ar, and Cs atomic gases
Authors: Krajcar-Bronić Ines , Kimura Mineo , Inokuti Mitio
Published: July 2002

Time-dependent and temperature-dependent aspects of the thermalization of electrons in atomic gases are studied by using the Boltzmann equation. H, Ar, and Cs gases were chosen for the present study because of the characteristic and significantly different dependences of their momentum-transfer cross sections on electron energy; H has a smoothly varying cross section, Ar has a conspicuous Ramsauer–Townsend minimum, and Cs has a resonance-like peak. The effects of these cross section shapes on electron distribution functions and degradation spectra are examined.
Infrared spectra of CF4 adsorbed on ice: Probing adsorbate dilution and phase separation with the ν3 transverse-longitudinal splitting
Authors: Rowland B. , Kadagathur N. S. , Devlin J. P.
Published: July 2002

Infrared spectra have been determined of CF4 adsorbed on nanocrystals of cubic ice at 83 K to a thickness ranging from submonolayer to multilayer with a maximum thickness of ∼ four layers. For the multilayered adsorbate, the band of the CF4 antisymmetric stretch mode, known for its exceptional oscillator strength, appears as a transverse-longitudinal (T-L) doublet, with a splitting of ∼80 cm−1, closely matching that of the plastic solid phase. This doublet splitting is reduced when the amount of adsorbed CF4 is decreased, whether by reduction of the equilibrium vapor pressure or by dilution with CO as a coadsorbate; the response expected for a gradual decoupling of the oscillating dipoles as the local density of CF4 is decreased. A diminished but strong T/L splitting (∼55 cm−1 at 83 K and 72 cm−1 at 25 K) is apparently retained at near monolayer levels of CF4 coverage. Unlike CO, the coadsorbate acetylene was observed to have a relatively minor influence on the T/L splitting despite causing a similar reduction in the total amount of adsorbed CF4, an indication that, unlike CO, acetylene tends to phase separate from the adsorbed CF4 leaving the local CF4 molecular density largely unaffected. The intense absorption by the longitudinal mode, as reported here for the ν3 mode of adsorbed CF4, can be recognized as a Berreman effect from off-normal sampling of thin layers of adsorbates on the curved surfaces of the ice nanocrystals. Such an effect should be common for particulate samples in general that have a coating of a molecular species with an intensely dipole-active vibrational mode. An example of interest may be that of NaNO3 formed by reaction of NO2 or HNO3 at the surface of particles of NaCl as reported by Vogt and Finlayson-Pitts.
Rydberg and charge transfer states of F atoms in neon matrices
Authors: Bressler C. , Lawrence W. G. , Schwentner N.
Published: July 2002

The interaction of an electronically excited F atom with the neon matrix is investigated using absorption, excitation, and fluorescence spectroscopy. Upon vacuum ultraviolet excitation of a neon matrix doped with fluorine atoms, emissions are observed at 12.80, 13.08, and 15.48 eV. The emissions at 13.08 and 15.48 eV have a lifetime of 0.7(0.2) ns and are assigned to the radiative relaxation of the 3s and 3s′ Rydberg F atomic states. The emission at 12.80 eV has a detection limited lifetime less than 0.4 ns and is identified as emission from the Ne+F− charge transfer complex. Absorption and excitation spectra of each of the observed emissions are used to identify the Rydberg absorptions of the F atoms perturbed by the neon matrix at 13.99, 16.27, 16.49, 16.94, 17.22, and 19.02 eV. The Rydberg states belong to ns, ns′, and nd progressions with the same quantum defect as in the gas phase and a blueshift of the vertical ionization energies of 0.8 eV. The Stokes shift of 910 and 790 meV for the 3s and 3s′ states and the large linewidth are attributed to a strong electron phonon coupling with Huang–Rhys factors of about 70. A two-dimensional configuration coordinate model explains the observed absorption, excitation and emission spectra, and the branching ratios of emission from Rydberg and charge transfer states.
Determination of the CC bond dissociation energy in cyanogen
Authors: Francisco Joseph S. , Richardson Steven L.
Published: July 2002

The CC bond dissociation energy (Do) in cyanogen is predicted using many-body perturba- tion (MP) and quadratic configuration interaction theory [QCISD(T)]. The dissociation limit is poorly predicted with many-body perturbation theory. At the QCISD(T)/6-311G(3df)//QCISD(T)/ 6-311G(2d) level of theory, the bond dissociation energy is predicted to be 132.8±2 kcal mol−1, which is in excellent agreement with experiment.
Fluctuation of the number of adsorbed particles analyzed by a virial expansion: Comparison between experiment and theory
Authors: Schaaf P. , Wojtaszczyk P. , Mann E. K. , Senger B. , Voegel J.-C. , Bedeaux D.
Published: July 2002

The irreversible random adsorption of particles on a surface is guided by the available surface function φ. The relative fluctuation σ2/〈n〉 in the number of particles n in a finite region provides one characterization of the distribution of these particles on the surface. We show rigorously that the two quantities are given by the same expression to first order in the surface coverage, for any irreversible adsorption process. This is confirmed in two particular cases: for random sequential adsorption, where values for σ2/〈n〉 from numerical simulations can be compared to an analytic expression for φ, and for Ballistic deposition, where experimental values for deposition under a strong gravitational influence can also be compared to an existing analytical expression for φ.