bluuebunny/crossref_metadata_2025 huggingface dataset:
Simple mixed hydrides of boron, aluminum, and gallium: AlBH6, AlGaH6, and BGaH6
Authors: van der Woerd Mark J. , Lammertsma Koop , Duke Brian J. , Schaefer Henry F.
Published: July 2002

Equilibrium structures, harmonic vibrational frequencies, and binding energies of the mixed diboranes AlBH6, BGaH6, and AlGaH6 were obtained from ab initio quantum mechanical methods using various basis sets and levels of theory to estimate the effects of electron correlation. Good agreement is found with the experimental IR spectroscopic data on BGaH6. The calculated order of the binding energies with respect to the monomers is AlBH6>B2H6>Al2H6>BGaH6>AlGaH6>Ga2H6. The nature of the bonding in these systems is examined using Bader’s theory of atoms in molecules.
On the low-lying electronic states of the molecule BeN
Authors: Ornellas F. R. , Roberto-Neto O. , Borin A. C. , Machado F. B. C.
Published: July 2002

Using the multireference singles and doubles configuration-interaction approach, this study presents for the first time reliable theoretical evidence of the existence of a new molecular species, BeN. Potential-energy curves, vibrational energy spacings, dissociation energies, dipole moments, and the associated spectroscopic constants are reported for the first ten lowest electronic states. Comparisons with other isoelectronic diatomics are presented. Perturbative effects are expected to play a non-negligible role in the spectroscopy of this molecule due to the closeness of the electronic and vibrational states. The global picture of the electronic states presented will certainly be an important aid to the experimentalist to search for this molecule.
Vibrational-state selective cross sections for the charge transfer H++HCl(X 1∑+)→H(2S
g)+HCl+(A 2∑+,v′)
Authors: Glenewinkel-Meyer Th. , Ottinger Ch.
Published: July 2002

Vibrational-state selective cross sections have been measured for the endothermic charge-transfer reactions H+,D++HCl(X 1∑+)→H,D(2Sg)+HCl +(A 2∑+,v′)−2.67 eV, for collision energies up to 1 keV by means of detecting the spontaneous optical emission of the HCl+(A 2∑+,v′→X 2Πi, v″) band system. Absolute values between 0.25 and 1 Å2 were obtained by calibration against the known cross section for electron-impact ionization of N2 with subsequent emission of the N+2(B,v′→X,v″) transition. The charge-transfer cross sections were also calculated using the Landau–Zener theory. The required model parameters were derived from recent ab initio calculations. The energy dependence and the relative magnitude of the cross sections for the product vibrational levels v′=0–5 were closely rendered by the theoretical curves in the velocity range where the Landau–Zener approach applies, i.e., below 200 km/s (≡200 eV for protons). The absolute magnitude of the calculated cross sections also agrees with the measurements within the experimental error limits.
Clustering and percolation for dimerizing penetrable spheres
Authors: Weist Annemarie Ott , Glandt Eduardo D.
Published: July 2002

Wertheim’s dual density formalism is applied to study the percolation behavior of dimerizing permeable spheres. The model is that of permeable spheres introduced by Blum and Stell as a generalized potential having ideal-gas (randomly centered) spheres as one limit and Percus–Yevick hard spheres as the other. Both thermodynamic results (pressure and site–site pair-correlation functions) and connectivity results (percolation threshold and site–site pair-connectedness functions) are determined for mixtures of dumbbells and spheres as a function of the penetrability factor ε, the bond length L and the fraction x1 of spheres forming dumbbells. A critical bond length L=0.553 was found for which the percolation threshold is independent of the amount of dimerization.
Comparison of theoretical and experimental expansion cloud chamber nucleation rates of n-nonane
Authors: Kobraei H. R. , Anderson B. R.
Published: July 2002

We have applied an extension of a microscopic model to account for the nucleation of n-nonane. We have compared the nucleation rates obtained using the extended model with those of two experimental investigations. The results of the two experimental investigations are consistent. The nucleation rates predicted by the classical theory are inconsistent with experimental data and can vary by as much as 14 orders of magnitude. The extended model yields nucleation rates which are in close agreement with the two experimental works.
An explicit cluster model for binary nuclei in water–alcohol systems
Authors: Laaksonen Ari , Kulmala Markku
Published: July 2002

A new thermodynamical model for the description of critical clusters in water–alcohol systems has been developed. The clusters are divided into an interior layer and a unimolecular surface layer. The surface excess of alcohol in the cluster is the same as in macroscopic liquid. The model is applied to binary nucleation of water and ethanol. The predictions of the model agree fairly well with experimental results.
An effective method for generating nonadiabatic many-body wave function using explicitly correlated Gaussian-type functions
Authors: Kozlowski Pawel M. , Adamowicz Ludwik
Published: July 2002

General formalism for the application of explicitly correlated Gaussian-type basis functions for nonadiabatic calculations on many-body systems is presented. In this approach the motions of all particles are correlated in the same time. The energy associated with the external degrees of freedom, i.e., the motion of the center of mass, is eliminated in an effective way from the total energy of the system. In order to achieve this, methodology for construction of the many-body nonadiabatic wave function and algorithms for evaluation of the multicenter and multiparticle integrals involving explicitly correlated Gaussian cluster functions are derived. Next the computational implementation of the method is discussed. Finally, variational calculations for a model three-body system are presented.
Exact perturbation treatment of the basis set superposition correction
Authors: Sadlej Andrzej J.
Published: July 2002

It is shown that a complete removal of the basis set superposition effect on the interaction properties of a composite system can be understood in terms of constraints imposed on its wave function. This interpretation of the basis set superposition effect is used to build variation methods which account for the constraints imposed by the incompleteness of available solutions for the constituent subsystems. A perturbation analysis of the resulting constrained equations provides an exact method for the evaluation of the basis set superposition contribution to interaction properties. The corresponding perturbation correction is explicitly evaluated for the Hartree–Fock approximation and discussed at the level of different correlated methods.
Theoretical characterization of the potential energy surface for H+N2→HN2. III. Calculations for the excited state surfaces
Authors: Walch Stephen P.
Published: July 2002

In a previous paper in this series [J. Chem. Phys. 93, 2384 (1990)] a global potential energy surface (PES) was presented for H+N2→HN2. In this paper, we report additional calculations which characterize PES’s for the excited 2A″ state, for a bound 2 2A′ state, for HN+2, and for the Rydberg states associated with HN+2. It is anticipated that these excited state PES’s will be important in interpreting and designing experiments to characterize the ground state HN2 species via neutralized ion beam techniques.
Vibrational predissociation lifetime of N2+–He (X, υ=1)
Authors: Bieske E. J. , Soliva A. M. , Friedmann A. , Maier J. P.
Published: July 2002

The B←X spectrum of N+2–He exhibits a hot band which arises from transitions in complexes which have one quantum of the N–N stretching vibration. By measuring the intensity of this peak relative to that of the origin peak as function of the time between ion preparation and laser interrogation we have determined the vibrational predissociation lifetime of the N+2–He complex to be 220±30 μs.
Ring mediated coupling of the internal motions of the amine and methyl groups in p-methylaniline
Authors: Yan Shuxin , Spangler Lee H.
Published: July 2002

The jet-cooled fluorescence excitation spectra of p-toluidine (p-methylaniline), aniline, aniline (ND2), p-toluidine (ND2), and p-fluoroaniline are presented. The spectra strongly suggest that the internal motions of the methyl and amine groups are coupled, the spectral evidence being a splitting of the amine inversion peak. A group theoretical treatment of the problem is presented using molecular symmetry group methods, however, this treatment appears to fail to properly predict selection rules for the methyl torsion. Possible reasons for this failure are discussed. The symmetry of the potential surface along the nonrigid coordinates is also discussed and a model which explains some of the unusual features of the spectra is presented.
The effect of the crystal environment on the metal–ligand interaction and the ligand field spectrum of CrF3−6
Authors: Pierloot K. , Van Praet E. , Vanquickenborne L. G.
Published: July 2002

The octahedral CrF3−6 cluster is studied in two different crystal environments. The available experimental data reveal that the cluster with the largest Cr–F bond distance is at the same time characterized by the largest value of the spectrochemical strength. This paradoxical fact has been shown to be due to the effect of the two different Madelung potentials. In K2NaCrF6, the central Cr ion is situated at a maximum of the Madelung potential; in CrF3, it is situated at a minimum. For the different crystal environments it has also been shown that the increase in covalency, that goes with the introduction of correlation, parallels the covalency that is present already at the Hartree–Fock level.
Isolated resonance decomposition of a multichannel S matrix: A test from the scattering of H+CO=HCO
Authors: Cho Seon-Woog , Wagner Albert F. , Gazdy Bela , Bowman Joel M.
Published: July 2002

We report a full test of the decomposition of a multichannel S matrix in the case of isolated resonances by analysis of coupled-channel scattering calculations for H+CO■HCO with zero total angular momentum on a realistic potential energy surface. The decomposition of S into resonant and a nonresonant matrices [K. W. McVoy, in Fundamentals in Nuclear Theory, edited by A. de-Shalit and C. Villi (International Atomic Energy Agency, Vienna, 1967) and B. Gazdy and J. M. Bowman, Phys. Rev. A 36, 3083 (1987)] developed in the limit of an infinitely narrow isolated resonance is applied to the nine calculated resonances determined in the first 1200 cm−1 of collision energy. These resonances have widths varying from 10−6 to 100 cm−1. Time-reversal, conservation, orthogonality and energy-dependence properties of the resulting decomposed matrices are compared to theoretical expectations. The effect on these comparisons of a six order of magnitude variation in resonance width is examined. The special role of orthogonality properties in setting limits to decay distributions without specific knowledge of resonance location or width is discussed.
Stark effect measurement in dysprosium monoxide: Dipole moments of the [17.1]7 and X8 states
Authors: Linton C. , Simard B.
Published: July 2002

The permanent electric dipole moment of 164DyO in its [17.1]7 and X8 electronic states has been determined in a pulsed molecular beam apparatus by measuring the Stark shifts on the Q(8) and P(8) lines of the (0,1) band of the [17.1]7-X8 system. Electric fields varying up to 14 kV/cm have been employed and the resulting Stark multiplets, containing up to 30 components, have been assigned and analyzed. The magnitudes of the dipole moments have been determined to be μ([17.1]7)=5.007(26) D and μ(X8)=4.507(26) D.
Dissociation dynamics of D2 on rigid and nonrigid Ni clusters
Authors: Fournier René , Stave Mark S. , DePristo Andrew E.
Published: July 2002

We present results of a theoretical study of the dissociation dynamics of D2 on NiN clusters with N=3–13. First, the semiempirical density functional based molecular dynamics/Monte Carlo corrected effective medium method was used to predict the interaction energies of various Ni clusters in this size range. We identified the most stable clusters and found that only N=9 possesses two nearly equally stable isomers with an energy difference of only 0.03 eV. Second, we performed classical trajectory simulations of the reactions in which the Ni atoms were allowed to move. The dissociation cross sections from calculations on the nonrigid clusters were nearly equal to those obtained with the rigid Ni cluster. A particularly intriguing result was that the dissociation cross sections calculated for the two isomers of Ni9 differed significantly, especially at low collision energy. Third, we showed that the dissociation probabilities as functions of the impact parameter and relative translational energy were fit with good accuracy as a simple function of a single variable E⊥, the component of translational energy perpendicular to the surface of the cluster. This indicated that the normal energy scaling of the dissociative sticking probability observed in some gas/surface systems may have an equivalent behavior in gas/cluster systems.
Dynamic simulations of water at constant chemical potential
Authors: Ji Jie , Çaǧin Tahir , Pettitt B. Montgomery
Published: July 2002

The grand molecular dynamics (GMD) method has been extended and applied to examine the density dependence of the chemical potential of a three-site water model. The method couples a classical system to a chemical potential reservoir of particles via an ansatz Lagrangian. Equilibrium properties such as structure and thermodynamics, as well as dynamic properties such as time correlations and diffusion constants, in open systems at a constant chemical potential, are preserved with this method. The average number of molecules converges in a reasonable amount of computational effort and provides a way to estimate the chemical potential of a given model force field.
Thermal fluctuations of a three phase contact line. II. Three fluid phases
Authors: Clarke Andrew S.
Published: July 2002

We describe a phenomenological model for the thermal fluctuations of a three-phase contact line in the case of three fluid phases. The model is an extension of an earlier model for the case of two fluids and one solid. In the previous model only one interface was allowed to fluctuate, and the contact line was constrained to move along the solid surface. In the present case all three two-phase interfaces can fluctuate, and the contact line can move in any direction. Our model includes the effects of line tension, the three surface tensions, and gravity. We investigate the behavior of the fluctuations in the limit of a wetting transition. Since the line tension appears to diverge in the limit of a first order transition, and vanishes in the limit of a second order transition, we consider each of these cases separately. We obtain the mean square fluctuation magnitude analytically if the line tension is identically zero. If the line tension is positive we obtain an integral expression for the mean square fluctuation magnitude, and derive modified exponents for the fluctuation magnitude as a function of contact angle near both a first and second order wetting transition. Our model breaks down if the line tension is negative, just as in the earlier model.
Diffusion-limited reactions in spherical cavities
Authors: Bug Amy L. R. , Grossman Elizabeth L. , Morgan Dane D. , Berne Bruce J.
Published: July 2002

We study a quenching reaction occurring at sinks within a spherical cavity and at the cavity surface. One may think of reactions at these two, distinct locations as two, coupled reactive channels. Reactions of the type D*+A→D+A are studied in the limit of nondilute A, present at both locations, and dilute D, present within the cavity. We use a Monte Carlo algorithm to compute mean rates, pseudo-first-order rates and branching ratios, and compare with results obtained by assuming that the two reactive channels operate in parallel. The ratio of activities of the two channels are varied; static and moving sinks are studied. We discuss an application to the determination of pore structure by NMR (nuclear magnetic resonance).
On frequency shifts in OH stretching vibrations of hydrated cations
Authors: Probst Michael M. , Hermansson Kersti
Published: July 2002

A b initio calculations of force constants up to fourth order and anharmonic frequencies for the uncoupled O–H stretching vibration in hydrates of the ions Li+, Na+, Mg2+, and Al3+ have been performed at the Hartree–Fock level for Mn+(H2O)m and Mn+(H2O)m⋅⋅⋅(H2O)2 complexes, with m=5–7. The dependence of force constants and frequency shifts on ion type, cation–water distances, second hydration shell, hydrogen bonding and coordination number is discussed. In the optimized Li+(H2O)6 system, the OH frequency is downshifted 20 cm−1 compared to the free water molecule, whereas, in the optimized Li+(H2O)6⋅⋅⋅(H2O)2 complex, the downshift is 120 cm−1. The corresponding numbers for the Al3+ hexaaqua complexes are −250 and −1215 cm−1. Frequency shifts with respect to bulk water for the cation–coordinated water molecules have been estimated from the difference between the frequencies of Mn+ (H2O)6⋅⋅⋅(H2O)2 and a (H2O)2⋅⋅⋅H2O⋅⋅⋅(H2O)2 complex. The values are +85 cm−1 for Li+ and Na+, −150 cm−1 for Mg2+, and −1000 cm−1 for Al3+, to be compared with the infrared frequency shifts of +50 for Li+ and Na+, −155 for Mg2+ and −500 cm−1 for Al3+ (experimental aqueous solution values from the literature). The activation energies for water exchange between the hydration shells in the hexaaqua complexes have been calculated for dissociative and associative exchange processes and suggest a dissociative mechanism to be dominant.
Hard, charged spheres in spherical pores. Grand canonical ensemble Monte Carlo calculations
Authors: Sloth P. , So/rensen T. S.
Published: July 2002

A model consisting of hard charged spheres inside hard spherical pores is investigated by grand canonical ensemble Monte Carlo calculations. It is found that the mean ionic density profiles in the pores are almost the same when the wall of the pore is moderately charged as when it is uncharged. Also, a bulklike phase is found to be present at the center of the pores in surprisingly small systems. Finally, the Poisson–Boltzman approximation is discussed in the light of our Monte Carlo results.
Dynamics of ion transfer across a liquid–liquid interface: A comparison between molecular dynamics and a diffusion model
Authors: Benjamin Ilan
Published: July 2002

Most theoretical approaches to ion transfer dynamics across a liquid–liquid interface describe the process as a stochastic crossing of a one-dimensional barrier whose shape is a priori unknown. We describe a molecular model of the ion transfer dynamics across an interface between two immiscible polar and nonpolar liquids. The results of extensive molecular dynamics trajectory calculations for the ion transfer are compared with the solution of a diffusion equation for an ion moving in an external field. The external field used in the equation is obtained from an independent free energy calculation using non-Boltzmann sampling. Near quantitative agreement is found, with discrepancies that may be attributed to solvent–shell exchange dynamics.
Elastic and inelastic neutron scattering study of hydrogenated and deuterated trimethylammonium pillared vermiculite clays
Authors: Fan Yibing , Solin S. A. , Kim H. , Pinnavaia T. J. , Neumann D. A.
Published: July 2002

Neutron scattering has been used to study the basal spacing and vibrational excitations of oriented samples of (CH3)3NH+ –vermiculite and its deuterated form (CD3)3ND+ –vermiculite. Both forms exhibit a basal spacing of 12.71 Å and a rich vibrational spectrum in the energy range 20–140 meV for Q perpendicular and parallel to the c-axis. These results are compared with infrared measurements and inelastic neutron scattering results of trimethylammonium halides over the same energy range. The torsional mode of the methyl group has been found to be split by ∼8 meV due to the top–top interaction between the methyl groups in the trimethylammonium vermiculite.
A kinetic theory of suspensions
Authors: Jorquera Hector , Dahler John S.
Published: July 2002

The Fokker–Planck formalism is used to construct a statistical-mechanical theory of the linear viscoelastic response of a colloidal dispersion of freely rotating spheres. It is assumed that the Newtonian solvent exerts random, fluctuating forces upon the solute spheres and systematic, frictional forces as well. The direct interactions among the spheres are separated into short-ranged, hard-core repulsions and longer-ranged, continuous forces. This model leads to a stress tensor for the suspension of the form σ=σSS+σPP+2σhy, with σPP denoting the contribution due to the translational motions of the suspended particles (P) and their mutual interactions. The term 2σhy arises directly from the frictional, hydrodynamic interactions between the spheres and the solvent and σSS is the stress tensor of the (continuum) solvent perturbed by the presence of the solute spheres. Formulas are obtained for the linear viscoelastic moduli associated with σPP and σhy and explicit procedures are presented for computing the numerical values of these coefficients. The theory is equally applicable to concentrated and dilute suspensions and it clearly can be extended to solute particles with internal (rotational and/or vibrational) degrees of freedom.
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o potential-energy surfaces for Cd(1P)+H2=CdH(X 2Σ+)+H, HCdH(X 1Σ+g), Cd(3P)+H2, and Cd(1S)+H+H
Authors: Boatz Jerry A. , Gutowski Maciej , Simons Jack
Published: July 2002

The outcome of laser excitation of the van der Waals CdH2 complex [which consists of a ground-state Cd(1S) atom bound to an H2 molecule] to its lowest-energy singlet state(s), which connects with Cd(1P)+H2, is examined by calculating ab initio potential-energy surfaces for the above excited singlet states, the corresponding underlying triplet states [connecting to Cd(3P)+H2 ], and the singlet ground state. It is necessary to study such a multitude of states because energetically accessible reaction products such as Cd(3P)+H2, CdH(X 2Σ+)+H, Cd+H+H, and HCdH(X 1Σ+g) connect to various surfaces. In carrying out these calculations, the lowest-energy surface of 1A1 symmetry was evaluated at nearly 1100 C2v geometries using complete-active-space self-consistent-field wave functions with a valence double-zeta and a double-zeta-plus-polarization basis set on cadmium and hydrogen, respectively. The excited singlet and triplet surfaces that correlate with 1P1 and 3PJ levels of Cd plus ground-state H2 were examined in detail along paths that flux prepared by laser excitation of the singlet surface(s) is most likely to follow. Among the photoexcited singlet states, the 1B2 surface is found to provide the most energetically attractive approach path for the excited CdH2 van der Waals complex to access geometries from which HCdH, Cd+H+H, and CdH+H can be formed via intersection and coupling with the lowest 1A1 surface.

The 1B1 surface is found to be weakly attractive, and the excited 1A1 surface to be repulsive at geometries characteristic of the nascent photoexcited species. The underlying triplet surfaces are found to be repulsive (3A1), weakly attractive (3B1), and slightly more attractive (3B2) at such geometries. The repulsive 3A1 surface intersects the 1B2 surface in the latter’s entrance-channel ‘‘streambed’’; the 3B1 state intersects the 1B2 surface closer to where the 1B2 and lowest 1A1 cross. The 3A1 and 1B1 surfaces also intersect in the entrance streambed of the latter. All such triplet–singlet crossings provide paths to Cd(3P)+H2.
Thermal electron mobility and scattering in hexafluoroethane gas
Authors: Gee Norman , Freeman Gordon R.
Published: July 2002

The scattering of thermal electrons is studied in low density C2F6 gas by measuring the electron mobility at low field strengths E/n<2 Td (Td=10−21 V m2/molecule ) at densities 0.2<n/1025 molecule m−3<1.6, and at temperatures 148≤T/K≤500. The field-independent thermal electron mobility μ0 was obtained at E/n<0.7 Td. In the gas away from the gas/solid coexistence curve, nμ0 was independent of density, and decreased monotonically as the temperature increased. The temperature dependence of nμ0 was used to modify values of scattering cross sections reported in the literature. Comparisons of the temperature dependence of nμ0 in CF4 and C2F6 with those in CH4 and C2H6 gases indicate that the molecular sphericity effect found in alkane gases is absent in the perfluoroalkane gases.
Anisotropic repulsive potential energy surfaces from Hartree–Fock calculations for HeCO2 and HeOCS
Authors: Keil Mark , Rawluk Leslie J. , Dingle Thomas W.
Published: July 2002

Hartree–Fock calculations are presented for the repulsive interactions of He with CO2 and OCS. The results are well described by parametrizing the anisotropic potential energy surface as a sum over interactions between He and each atom of the molecule. The interaction of He with the oxygen ends of both molecules is almost identical, thereby reducing the number of potential fitting parameters required. The analytic surfaces obtained yield good agreement with pressure broadening measurements, which probe the anisotropy while being independent of the van der Waals attraction. It is suggested that the sum-over-sites parametrization may be useful in constructing semiempirical surfaces that do include the van der Waals attraction. The sum-over-sites parametrization is also particularly well suited to describing the vibrational dependence of the repulsive anisotropy.
Quantum flux studies of the mechanism of Ca(4s5p 1P)→Ca(4s5p 3P) collisions
Authors: Alexander Millard H.
Published: July 2002

We apply a new method [M. H. Alexander, J. Chem. Phys. 94, 8931 (1991)] for the study of the mechanism of inelastic collisions, to the analysis of spin-changing collisions of Ca atoms in the 4s5p Rydberg state. The method involves the determination of the current density associated with, separately, the incoming and outgoing scattering wave functions in a locally adiabatic basis. This yields a picture of how the incoming flux, initially associated with a given internal state, redistributes itself as a function of the interparticle separation both as the particles approach, and, subsequently, as the particles recede. By proper selection of the initial state, we explore the dependence on orbital orientation of the probability for the spin-changing Ca(4s5p 1P)→Ca(4s5p 3P) process. Further, we show how the distribution of population among the fine-structure levels of the 3P state depends on final-state interactions in the exit channel.
Electronic-state-specific transition metal cation chemistry: Fe++C3H8 and n-C4H1
Authors: Hanton Scott D. , Noll Robert J. , Weisshaar James C.
Published: July 2002

We present total reaction cross sections and product branching fractions for collisions of specific electronic states of Fe+ with the linear alkanes C3H8 and n-C4H10 at two collision energies each, 0.2 and 1.0 eV. Resonant two-photon ionization prepares specific electronic state distributions of Fe+, as described in the preceding paper. A crossed beam experiment using pulsed, time-of-flight mass spectrometry measures total reaction cross sections averaged over known state distributions, from which we extract state-specific cross sections. The three lowest energy electronic terms of Fe+, 3d64s(6D), 3d7(4F), and 3d64s(4D), show remarkably similar reactivity with both alkanes. The relative cross section varies only a factor of 4 in Fe++C3H8 and less than a factor of 2 in Fe++C4H10, in spite of sampling both sextet and quartet spins, 3d64s and 3d7 configurations, and a range of 1.1 eV electronic energy. Product branching between H2 and alkane elimination is insensitive to initial electronic state as well. All reactions are inefficient compared with the Langevin cross section. We propose a model of Fe++alkane chemistry that assumes that all those Fe+ that insert in a C–H bond of the alkane proceed to elimination products. Spin-changing surface hops between diabatic potential surfaces correlating to different reactant asymptotes (i.e., electronic quenching) competes with bond insertion, explaining the low reactivity of the 3d7(4F) term.
State-selected chemical reaction dynamics at the S matrix level: Final-state specificities of near-threshold processes at low and high energies
Authors: Chatfield David C. , Truhlar Donald G. , Schwenke David W.
Published: July 2002

State-to-state reaction probabilities are found to be highly final-state specific at state-selected threshold energies for the reactions O+H2→OH+H and H+H2→H2+H. The study includes initial rotational states with quantum numbers 0–15, and the specificity is especially dramatic for the more highly rotationally excited reactants. The analysis is based on accurate quantum mechanical reactive scattering calculations. Final-state specificity is shown in general to increase with the rotational quantum number of the reactant diatom, and the trends are confirmed for both zero and nonzero values of the total angular momentum.
Time-resolved emission studies of intermolecular triplet excimer formation in fluid solutions of dibenzopyrrole, dibenzofuran, and dibenzothiophene
Authors: Cai Jianjian , Lim E. C.
Published: July 2002

Time-resolved emission studies demonstrate the formation of intermolecular triplet excimers in fluid solutions of dibenzopyrrole, dibenzofuran, and dibenzothiophene at ambient temperature.
Laser multiphoton dissociation–multiphoton ionization and photoelectron spectroscopy of Fe(C5H5)2, Co(C5H5)2, and Ni(C5H5)2
Authors: Niles Stanley , Prinslow Douglas A. , Wight Charles A. , Armentrout P. B.
Published: July 2002

Laser multiphoton dissociation–resonance-enhanced multiphoton ionization (MPD–REMPI) and time-of-flight photoelectron spectra (TOF-PES) of Fe(C5H5)2, Co(C5H5)2, and Ni(C5H5)2 have been obtained in the range 380–390 nm, and the MPD–REMPI of Fe(C5H5)2 and Co(C5H5)2 have been obtained in the range 445–455 nm. The only ions produced by the pulsed dye laser are Fe+, Co+, and Ni+. Transitions observed in the MPD–REMPI spectra are assigned to resonant states of the neutral atoms. Final states of the atomic ions are determined from the TOF-PES spectra. For Ni and Co, there appears to be a propensity for core preservation of the resonant state upon ionization if the resonant state has an electron configuration with an electron in a d-type Rydberg orbital. For Fe, no such propensity is observed.
Photodissociation of BrCH2CH2OH and ICH2CH2OH: Formation and characterization of OH(X 2Π)
Authors: Sapers Steven P. , Hess Wayne P.
Published: July 2002

This work studies the dissociation of BrCH2CH2OH and ICH2CH2OH following laser excitation to the electronic Ã state. The direct subpicosecond dissociation cleaves the C–X bond to produce CH2CH2OH and the halogen atom in either the ground (2P3/2) or excited (2P1/2) state. The initial dissociation produces excited CH2CH2OH in a distribution of internal states, some of which have sufficient energy to undergo secondary, nonphotoinduced dissociation to form OH and C2H4. We probe the OH translational and rotational product states following this secondary dissociation using laser-induced fluorescence in both flow cell and pulsed jet apparatus. Excitation of BrCH2CH2OH at 202 nm produces OH with no vibrational excitation and a non-Boltzmann rotational distribution with an average rotational energy of 8 kJ/mol. Doppler analysis of the rotational line shape shows that a majority of the energy available for the secondary dissociation is partitioned into relative translation of OH and C2H4. Excitation of ICH2CH2OH at 266 nm also produces OH, but at much lower quantum yields due to energetic constraints. We find that the CH2CH2OH radical also absorbs at 266 nm to produce OH. The rotational and translational energy distribution of OH from secondary dissociation of the CH2CH2OH radical is described qualitatively by a simple rotational model.
Semiclassical analysis of vibrational energy transfer in HF–HF and isotopic systems. I. V-T/R and V-V rate constants for the lowest transitions in HF–HF
Authors: Billing G. D. , Zenevich V. A. , Lindinger W.
Published: July 2002

Semiclassical calculations of the V-R/T and V-V rate constants among the lowest vibrational transitions in the HF–HF collisional system in the temperature range 200–3500 K are presented. The interaction potentials used are fits of the functional form used successfully in earlier work to recent large scale ab initio calculations of the energy surface of the hydrogen fluoride dimer in the framework of coupled pair functional and averaged coupled pair functional methods. The semiclassical results are in good agreement with experimental data and differ advantageously from the very recent classical trajectory cross-correlation calculations, which are based on potential fits to the same ab initio points as used in the present paper.
Dynamical inhomogeneous broadening and lattice-assisted intramolecular energy transfer in the fundamental A1 vibrations of liquid chloroform Cl-35
Authors: Rothschild Walter G. , Cavagnat Raymond M.
Published: July 2002

This report gives extensive isotropic Raman spectral data and their numerical Fourier transformation into the time domain (∼0–20 ps) for the three A1 vibrational fundamentals of Cl-35 isotopically pure chloroform. It was found that the vibrational amplitude correlation decay of the ν1 mode (C–H stretch) at 300 K follows a rapid vibrational dephasing process (inhomogeneous broadening with motional narrowing) that is 1.7 times faster than the concomitant intramolecular energy transfer to the overtone of the C–H bending mode. From the temperature dependence (213 K, 300 K) of the amplitude correlation decay of the ν3 mode (C–Cl deformation) we deduce that it relaxes essentially only by vibrational dephasing and in such a fast modulation regime that the ν3 oscillator is effectively decoupled from the local lattice anisotropies. From the temperature dependence of the amplitude correlation decay of the ν2 mode (C–Cl stretch) we infer a simultaneous vibrational dephasing and lattice-assisted intramolecular energy transfer process, the latter possibly to the overtone of ν3. This paper concludes with some general remarks on the predictability of relative contributions of various types of vibrational relaxation processes to vibrational amplitude correlation decay in molecular liquids and, in an Appendix, gives estimates on the rates of excess phonon depopulation into the lattice as governed by a permanent dipole–transition dipole coupling process for modes ν6, ν3, ν2, and ν5 of liquid chloroform.
Many-body calculation of the valence photoemission spectrum of PdN2
Authors: Ohno M. , Decleva P. , von Niessen W.
Published: July 2002

We have performed ab initio two hole one particle (2h1p) CI and algebraic diagrammatic construction [ADC(3)] Green’s function calculations of the valence photoemission spectrum of PdN2. The spectral features obtained by two different reliable methods are similar. However, they disagree with the experimental spectrum of N2/Pd(111) system. The 1π and 5σ ionization peaks are interpreted to be so well separated (1.6 eV) according to the experimental assignment, but the present theoretical result shows that despite a much weaker metal–ligand bonding, they are almost degenerate as in the case of the CO/Ni, CO/Pd, and N2/Ni systems. The basic spectral features and the relative positions of the 1π and 5σ levels do not change much with an increase of the metal–ligand bond length (weaker bonding strength). This shows that further detailed experimental study of the valence photoemission spectrum of the N2/Pd system is needed. The many-body effects such as the breakdown of the quasiparticle picture for the ionization is much stronger in NiN2 that in PdN2, despite the widely held assumption that weak coupling leads to increased many-body effects. It is shown that the change of the valence spectral features of the adsorbate depends on a subtle change of the electronic structure of the substrate metal atom rather than the metal–ligand bond strength.
Sublimation studies of NpO2F2
Authors: Kleinschmidt P. D. , Lau K. H. , Hildenbrand D. L.
Published: July 2002

Using Knudsen effusion mass spectrometry, we have identified the following reaction as the sublimation decomposition mechanism of NpO2F2(s): 2NpO2F2(s)=NpO2(s)+O2(g)+NpF4(g). From second-law analysis of the measured pressures of NpF4(g) over the temperature range 820–985 K the derived enthalpy change at 298 K is 556.8±12.2 kJ/mol and the entropy change is 342.4 ±13.8 J/K mol. From these values and enthalpies of formation and entropies reported in the literature for the other species we calculate the enthalpy of formation of NpO2F2(s) to be −1608±10 kJ/mol and the entropy to be 147±9 J/K mol.
Theoretical study of the size dependence of ionization potential and electron affinity of metallic clusters
Authors: Harbola Manoj K.
Published: July 2002

Ionization potentials (I) and electron affinities (A) of lithium clusters are studied by treating exchange effects exactly within the exchange-only density-functional theory and employing the spherical jellium background model of metallic clusters. In the past, ionization potentials of metallic clusters have been studied by treating the exchange and correlation effects approximately via the local density approximation (LDA). We show that such a calculation leads to ionization potentials which, when extrapolated to large clusters, do not give the correct work function W for the bulk metal as they should. Furthermore, the LDA does not lead to convergent solutions for cluster anions of all sizes. Thus the electron affinities of these clusters cannot be studied within this approximation. On the other hand, by treating exchange effects exactly, solutions for negative ions can also be obtained. We demonstrate that both the ionization potentials and the electron affinities thus obtained extrapolate to the correct value of the work function for the bulk. Furthermore, I and A on the average vary with the size of the cluster as I=W+0.5/(R+a) and A=W−0.5/(R+a), respectively, where R is the radius of the cluster and ‘‘a’’ is a microscopic distance.
Kinetics of multilayer deposition: Models without screening
Authors: Krapivsky P. L.
Published: July 2002

The kinetics of irreversible multilayer deposition on one- and two-dimensional uniform substrates was studied. It was assumed that the distribution of sizes of parking objects, intervals in 1D and disks in 2D, have a small-size and a large-size cutoff, l and L, respectively. The general case when the parking distribution function varies as (x−l)α near the small-size cutoff was studied. It was found that the coverage in each layer approaches to the jamming limit according to a power law as t−ν, with the exponent ν=(α+1+D)−1. The jamming coverages approach the infinite-layer limiting value exponentially as exp(−𝓀/s), with the correlation length s=ln[(α+3)/(α+1)].
Vibrational spectroscopy and predissociation dynamics of the electronically excited HgAr2 triatomic cluster
Authors: Okunishi Misaki , Yamanouchi Kaoru , Tsuchiya Soji
Published: July 2002

Vibronic structures of the Ã–X̃ and B̃–X̃ bands of the HgAr2 triatomic cluster were investigated by laser-induced fluorescence (LIF) spectroscopy. The LIF spectra of the Ã–X̃ and B̃–X̃ bands of HgAr2 were observed free from hindrance of strong A–X and B–X transitions of HgAr by monitoring the fluorescence in the visible region. The analysis of the vibronic structures led to the fundamental frequencies of ω1=26.3(3), ω2=12.0(5), and ω3=28.1(4) cm−1 for the Ã state and ω1=9.2(3) and ω2=23.8(6) cm−1 for the B̃ state, where subscripts ‘‘1,’’ ‘‘2,’’ and ‘‘3,’’ respectively, denote symmetric stretching, bend, and asymmetric stretching modes. A number in parentheses represents an estimated limit of error (σ). It was found that HgAr2 in the B̃ state predissociates to produce HgAr(A)+Ar. The vibrational and rotational distributions of the HgAr fragment in the A state were derived by observing LIF spectra of the E–A band. Based on these distributions, level energies of HgAr2 in the B̃ state were estimated with respect to those of HgAr in the A state, and then, the dissociation energies (De) of HgAr2 to Hg+Ar+Ar were derived to be 374(2), 540(2), and 249(2) cm−1 for the X̃, Ã, and B̃ states, respectively. The vibronic structure of HgAr2 in the lowest Rydberg (Ẽ) state associated with Hg(7 3S1) was investigated by the optical–optical double resonance spectroscopy via the Ã state. The geometrical structure, in which an outer Ar atom is loosely bound to the Rydberg-type HgAr core, that is close to HgAr+, is proposed for the Ẽ state, and a presence of large amplitude motion of the outer Ar atom is deduced from the obtained fundamental frequencies of ω1=102.1(3) and ω2=5.4(2) cm−1, where subscripts ‘‘1’’ and ‘‘2’’ denote a stretching mode of the HgAr core and the Ar–Hg-Ar bending mode.
Nucleation of binary water–n-alcohol vapors
Authors: Laaksonen Ari
Published: July 2002

The previously developed cluster model has been used for thermodynamically consistent nucleation calculations in water–methanol, water–ethanol, and water–n-propanol systems. Besides activity plots for constant nucleation rates, comparisons of nucleation rates with available data points and comparisons of experimental and theoretical temperature dependences are also presented. The predicted nucleation rates are in most cases within 5–6 orders of magnitude from experimental values.
Pyrolysis jet spectroscopy: The S1–S band system of formyl cyanide, HCOCN, and DCOCN
Authors: Clouthier Dennis J. , Karolczak J. , Rae J. , Chan W.-T. , Goddard J. D. , Judge R. H.
Published: July 2002

The Ã 1A″–X̃ 1A′ band systems of HCOCN and DCOCN have been studied in depth using the technique of pyrolysis jet spectroscopy. Ab initio predictions of molecular structures and vibrational frequencies for the ground and excited state were made, to assist in the assignment of the vibronic structure in the laser-induced fluorescence (LIF) spectra. A resolved emission spectrum obtained by laser population of the 81 level of the excited state was analyzed to establish the ground state vibrational frequencies. Both the LIF and resolved emission spectra are consistent with a substantial elongation of the C=O bond on excitation, and smaller changes in the other geometric parameters. The excited state inertial defect, the pattern of bands involving the antisymmetric vibrations, and the ab initio predictions all suggest that the excited state structure is only slightly nonplanar. A rotational analysis of the 910 band of the DCOCN LIF spectrum has provided the first experimental rotational constants for the ground state of formyl cyanide-d1, which should be useful in attempts to observe the microwave spectrum. The uv spectrum of formyl cyanide is found to be remarkably similar to that of propynal.
Pseudolocal phonons in p-terphenyl: pentacene single crystals
Authors: Fleischhauer H.-C. , Kryschi Carola , Wagner Birgit , Kupka Hans
Published: July 2002

The structural nature of the phonon sidebands in the fluorescence and excitation spectra of pentacene guests in p-terphenyl crystals at 4.2 K are investigated using site-selective spectroscopy. The distinct features in the phonon sideband structure were observed to depend significantly on the guest site configuration of pentacene occupying four inequivalent sites in the triclinic p-terphenyl lattice. The sharp peaks dominating the phonon sideband structure are assumed to arise from the pseudolocal phonons. The eigenvalues and eigenvectors of the pseudolocal phonons are calculated carrying out a modified normal mode analysis on the distinct pentacene site configurations including the contribution of all intermolecular atom-pair interactions.
Extended x-ray absorption fine structure studies of dense selenium vapor
Authors: Hosokawa Shinya , Tamura Kozaburo , Inui Masanori , Yao Makoto , Endo Hirohisa , Hoshino Hideoki
Published: July 2002

We have measured the extended x-ray absorption fine structure spectra for dense selenium vapor at high temperatures and pressures up to 1600 °C and 150 bar for the first time. For the experiment, we have developed a high-pressure vessel and a polycrystalline sapphire cell of our own design. We have found that dense selenium vapor under the present experimental condition consists mainly of Se2 and the bond length is much shorter than that of liquid Se. With increasing pressure the bond length slightly increases. When the saturated vapor-pressure curve is approached, the bond is largely elongated.
Analysis of nonequilibrium structures of shearing colloidal suspensions
Authors: Wagner Norman J. , Ackerson Bruce J.
Published: July 2002

The two-particle correlation function is related to the structure factor by an integral transform and serves as an important connection between suspension microstructure, scattering experiments, and macroscopic properties. The nonequilibrium structure factor for a shearing colloidal suspension of spherical particles is expanded in spherical harmonics. Through this expansion, we demonstrate formal relationships between the experimentally accessible static structure factor, bulk stresses, and optical dichroism and birefringence, demonstrating that a limited number of expansion terms are required to characterize the suspension rheology. Low shear limiting theories are expressed in terms of this expansion, demonstrating the utility of the expansion for comparison of experimental measurements of nonequilibrium structure factors to theoretical predictions. Although flow birefringence and the thermodynamic shear stress are calculated as weighted integrals over the nonequilibrium microstructure in the low shear limit, no simple stress-optical coefficient is found. The expansion is proposed as a consistent methodology for analysis of experimental data and presentation of theoretical predictions, providing a means of interpreting rheo-optical data.
Formulas for the solvation force between colloidal particles obtained from the Ornstein–Zernike relation
Authors: Henderson Douglas
Published: July 2002

By considering the Ornstein–Zernike relation for two large spheres in a fluid, in the limit where these spheres are exceedingly large, a formula for the solvation force between the large spheres is obtained. The result conforms with Derjaguin’s approximation. This result is extended to Coulombic systems by plausible arguments. These formulas are applied to large hard spheres in a hard sphere fluid and to charged hard spheres in a fluid of point charges. The results agree with those obtained by other methods.