bluuebunny/crossref_metadata_2025 huggingface dataset:
Decomposition of highly vibrationally excited CDCl3
Authors: Ivanco M. , McRae G. A. , Back R. A. , Goodale J. W. , Lee P. E.
Published: July 2002

Decomposition of highly vibrationally excited CDCl3 was studied in the time domain by measuring laser-induced fluorescence from one of the decomposition products CCl2 or by observing luminescence from CCl2 radical fragments produced in the Ã(1B1) state following IR excitation. It is shown that highly vibrationally excited CDCl3 can be made via two different routes: i/mple optical absorption of an incident 13CO2 laser pulse or through collision-moderated energy pooling coupled with photon absorption. Higher fluence measurements are consistent with the former and support previous claims that the infrared multiphoton decomposition probability for CDCl3 is pressure independent. At a lower fluence the vibrational up-pumping mechanism apparently relies heavily upon collisions, which supports other claims that the decomposition probability is pressure dependent. The results of the present work reconcile these previous disparate claims. Furthermore, there is an indication that the vibrational energy transferred during a collision could be much larger than collision-induced dipole selection rules would allow. In some of the experiments, electronically excited CCl2 fragments are created but only through post-laser-pulse collisions that appear to involve exchanges of very large amounts of vibrational energy. By contrast, no electronically excited CCl2 is produced following excitation with the CO2 laser alone. The experiments also corroborate an earlier prediction that the extent of reaction is governed by adiabatic expansion of the centrally heated zone, even at pressures as low as 0.66 kPa, rather than by diffusion, as is commonly believed.
An electron-spin-resonance study of γ-irradiated barium galliosilicate glasses
Authors: Dutt D. A. , Griscom D. L. , Shaw C. M. , Shelby J. E.
Published: July 2002

Electron-spin-resonance spectroscopy has been used to study the structure of radiation-induced defects in a barium galliosilicate glass compositional series of BaO/Ga2O3=1.0 and 20–80 mol % SiO2. Spin-Hamiltonian parameters derived from computer line-shape simulations have been used to identify three oxygen-associated hole centers: a gallium-oxygen hole center and two variations of silicon-oxygen hole centers. Each of these defects contains an unpaired electron in a nonbonding oxygen p orbital. The compositional dependence of the ESR data is consistent with a gradual change from a Ga-based tetrahedral network to a Si-based tetrahedral network as the silica content is increased.
Coulomb correlation in the H2 molecule: A two-particle density analysis
Authors: Sanders J. , Banyard K. E.
Published: July 2002

The correlation effect in molecules, and its influence on bonding, is difficult to assess in terms of the traditional Coulomb hole, a concept which has been particularly fruitful in atomic studies. As an alternative, we have studied correlation-induced changes in the two-particle density over a preselected molecular plane. The consequences of different components of correlation can be highlighted by choosing specific fixed locations of a ‘‘test’’ or ‘‘reference’’ electron in relation to the nuclear framework. The ground state of H2 is investigated as the initial example. This simple system is especially interesting since it possesses the prototype homonuclear chemical bond. The analysis was aided by using an energetically reliable correlated wave function expressed as a natural expansion. Due to the first natural orbital being effectively a Brueckner orbital, correlation effects were measured here with respect to the first natural configuration. Besides examining the two-particle density changes over the H2 molecular plane, we also defined and determined the corresponding radial and angular ‘‘planar Coulomb holes,’’ ΔR(r12) and ΔA(ε), respectively. Finally, variations in the relative importance of the ‘‘change of density’’ characteristics, arising from each of the three main components of electron correlation, were mapped out as the test or ‘‘fixed’’ electron was moved across the chosen H2 plane. The procedure adopted here is sufficiently general to be applicable to any electron pair within a polyatomic system—in both position space and momentum space.
Exotic states in the E–e Jahn–Teller problem
Authors: Eiermann H. , Wagner M.
Published: July 2002

The Fulton–Gouterman transformation is applied to the dynamical E–e Jahn–Teller problem. This approach leads to an unconventional way of visualizing the exact eigensolutions of the problem. It turns out that in the upper energy region, eigenfunctions with unexpected behavior make their appearance (‘‘exotic states’’). They practically have no distortion in the oscillatory subspace, whereas eigenfunctions of large radial oscillatory displacement are found in their immediate energetic neighborhood. In a rough way, these exotic states may be attached to the upper potential sheet of the ‘‘Mexican hat’’ and furthermore they can be shown to be related to the ‘‘Slonczewski resonances.’’
Symmetry restrictions in diatom/diatom reactions. II. Nonmass-dependent isotope effects in the formation of O+4
Authors: Griffith K. S. , Gellene Gregory I.
Published: July 2002

Nonmass-dependent isotopic enrichment of 17O and 18O has been observed mass spectrometrically in O+4 ions produced by termolecular association reactions of O+2 and O2, where the O+2 was generated by electron ionization. The enhancement is strongly dependent on the energy of the ionizing electrons, decreasing from a near tenfold enhancement at threshold for O+2 production to no enhancement above 40 eV. Additionally, O+2 generated near threshold were found to be significantly less efficient in producing O+4 than O+2 ions generated at higher energies. A permutation-inversion, symmetry analysis of the termolecular association reaction suggests that the results can be understood in terms of a symmetry restriction on the O+2(2Πg) rotational states which can efficiently access the electronic ground state of O+4 upon collisions with O2. The restriction is rooted in the Pauli principle and vanishes when the O+2 ion is isotopically heteronuclear. The possible relevance of the nonmass-dependent isotope enhancement in O+4 to similar enhancements found in stratospheric and laboratory-produced ozone is discussed.
Sequential reactions of SiD+2 with SiD4
Authors: Reents W. D. , Mandich M. L.
Published: July 2002

The thermal (300 K) reaction of SiD+2 with SiD4 proceeds at greater than the Langevin collision rate (21±3×10−10 cm3/molecule s ). The reaction products SiD+3, Si2D+2, and Si2D+4 are produced in a 54:7:39 ratio. Both silicon isotope exchange and adduct (Si2D+6) formation are <1% of the collision rate at silane pressures of 1–4×10−7 Torr. The branching ratio for SiD+3 formation increases with increasing internal energy of SiD+2. Sequential reactions of SiD+3 and Si2D+2 with SiD4 have been previously found to produce terminal species containing five silicon atoms. Si2D+4 reacts with SiD4 only by silicon isotope exchange at 2.0±0.7% of the collision rate (0.20±0.07×10−10 cm3/molecule s ) with no evidence of other reactions (<0.5% of the collision rate). Reaction of SiD+2 with SiD4 does not lead to unconstrained clustering and particle formation in silane plasmas. High level ab initio calculations on this system are reported by Raghavachari in his companion paper. Energies of the critical intermediates and transition states along the reaction surface are compared quantitatively to the experimental results via phase space calculations. The energies agree to within 6 kcal/mol.
Theoretical studies of the complexes of iodine with methanol, ethanol, and acetone
Authors: Khan Arshad
Published: July 2002

The complexes of iodine with methanol, ethanol, and acetone were studied in order to obtain their spectra and geometries. Several possible orientations of I–I were examined to obtain the most stable geometries of the complexes by applying the intermediate neglect of differential overlap self-consistent field (INDO SCF) method and intermediate neglect of differential overlap self-consistent field (INDO SCF) and yielded two stable complexes for each alcohol and one for acetone. Each geometry optimization was followed by an INDO CI (configuration interaction) calculation of theoretical spectrum for comparison with that of the experiment. Excellent agreement between the experimental and the theoretical results further establish the existence of these complexes. The binding energy value of each of these complexes was calculated relative to the separated constituent molecules.
Studies on the influence of nonlinearity in classical activated rate processes
Authors: Straus Jay B. , Voth Gregory A.
Published: July 2002

Computational studies are presented which examine the accuracy of two approximate theories for activated rate processes in condensed matter classical systems. One theory is based on the generalized Langevin equation and the other on multidimensional transition state theory. The specific focus is on studies of effective Hamiltonians which contain nonlinear coupling terms between the reaction coordinate and bath coordinates. Two of these systems phenomenologically describe the activated dynamics of realistic physical problems. The reactive flux correlation function method is used to calculate the numerically exact rate constant and, in turn, compared to the value of the rate constant calculated from approximate analytic theories. In all cases, the value of the rate constant exhibits a dependence on the nonlinearities in the equations of motion. The results suggest that the generalized Langevin equation model and multidimensional harmonic transition state theory may give different predictions for the activated rate constant in nonlinear systems and that both theories should be applied with some care.
Transient nucleation induction time from the birth–death equations
Authors: Shneidman Vitaly A. , Weinberg Michael C.
Published: July 2002

For the set of finite-difference equations of Becker–Döring an exact formula for the induction time, which is expressed in terms of rapidly convergent sums, is presented. The form of the result is particularly amenable for analytical study, and the latter is carried out to obtain approximations of the exact expression in a rigorous manner and to assess its sensitivity to the choice of the nucleation model. The induction time, tind, is found to be governed by two main nucleation parameters, Φ*/kT, the normalized barrier height, and g*, the number of molecules in the critical cluster. The ratio of these two parameters provides an assessment of the importance of discreteness effects. We study the exact expression in both the continuous (g*→∞) and the asymptotic (Φ*/kT→∞) limits. Asymptotic results for tind are compared with those previously reported from simulation studies as well as with tind obtained numerically from the exact expression in the present study. Also, the accuracy of the Zeldovich equation, which is produced in the continuous limit, is discussed for several nucleation models.
Photoabsorption, fluorescence excitation, and lifetimes of the excited states of Br2 at 116–170 nm
Authors: Nee J. B.
Published: July 2002

The photoabsorption and fluorescence excitation of Br2 have been investigated in the wavelength region 116–170 nm. The fluorescence lifetimes of some Rydberg excited states were measured. Perturbations in the excited states are discussed based on the comparison of the absorption and the excitation spectra.
Regularized inversion of diatomic vibration–rotation spectral data: A functional sensitivity analysis approach
Authors: Heo Hoon , Ho Tak-San , Lehmann Kevin K. , Rabitz Herschel
Published: July 2002

We present a stable and accurate inversion method for extracting potentials from spectroscopic data of diatomic molecules. The method, which was developed previously for inverting scattering data, is based on first-order functional sensitivity analysis in conjunction with the Tikhonov regularization, singular system analysis, and an exact transformation technique. Besides being numerically stable, it requires neither explicit functional forms nor special basis function expansions for the potential corrections when solving the corresponding linearized integral equation. Instead, we solve the linear equation directly in terms of the probability densities of the unperturbed vibrotation eigenstates. For illustration, we consider the ground electronic state of the H2 molecule. Inversions have been carried out for simulated data free of noise and for those with noise of magnitude comparable to realistic experimental errors. It is found that in both cases, a relatively large deviation of the starting reference potential from the truth may be tolerated to still accurately recover the intended one. The propagation of the spectral errors is analyzed in detail based on the linearization assumption. The variance of the recovered potential reveals the reliability of various regions of the recovered potential.
Two molecular scale force distributions associated with a planar interface
Authors: Lovett Ronald , Baus Marc
Published: July 2002

The surface tension is a thermodynamic force localized in the interfacial region between two phases. We show that the spatial distribution of this force on a molecular scale can be given a clear thermodynamic definition. In fact, two distinct force distributions are identified, a wall distribution associated with an actual system boundary and an intrinsic distribution associated with an interface unperturbed by (i.e., physically remote from) a wall. While mechanical definitions of the intrinsic distribution are ambiguous on a molecular scale because there is no unique localization of the intermolecular forces, we show that formal density-functional theory admits a natural, operational definition of the intrinsic distribution in terms of a many-body external field. The result is a unified phenomenological definition of these two force distributions from which expressions in terms of the molecular distribution functions are readily developed. The surface tension and location of the surface of tension deduced from the intrinsic force distribution agree with established results. These quantities are also shown to be independent of the details of the structure of a wall as long as the force exerted by the wall is normal to the wall. This verifies at a molecular level the original hypothesis of Young.
More insight into critical wetting in polymer blends
Authors: Jerry Rocco A. , Nauman E. Bruce
Published: July 2002

We have shown that a free energy expression that contains a derivative-dependent boundary penalty term, as introduced by Cohen and Muthukumar [J. Chem. Phys. 90, 5749 (1989)], will extend the region of parameter space over which critical wetting should occur.
High-pressure Raman study of solid deuterium sulfide up to 17 GPa
Authors: Shimizu H. , Murashima H. , Sasaki S.
Published: July 2002

High-pressure Raman studies up to 17 GPa have been made on solid D2S at room temperature. Features of vibron and phonon modes indicate a pressure-induced phase transition near 10 GPa. In the orientationally disordered phase I between 0.5 and 10 GPa, the symmetric stretching mode ν1 shows a red-shift in frequency (dν1/dP=−6.0 cm−1/GPa). By comparing with recent studies of solid H2S, the deuterium isotope effects are investigated for vibrational properties and phase transitions of D2S under ultrahigh pressures.
Depolarized light scattering and dynamic shear compliance of viscoelastic liquids
Authors: Wang C. H.
Published: July 2002

Efforts are made to relate the depolarized light scattering spectral power density to the dynamic shear compliance spectrum of a viscoelastic liquid. Generalized Langevin equations are used to describe the dynamics and coupling of reorientation and translational motions. It is shown that in the presence of the coupling, the depolarized scattering spectrum consists of two components; one is associated with the reorientational motion, and the other with the viscoelastic relaxation of the solution. Methods to obtain the dynamic shear compliance from the depolarized light scattering spectrum are described. It is also shown that in the limit of very slow reorientational motion, the depolarized light scattering spectrum is proportional to the imaginary part of the dynamic compliance spectrum, a result predicted by the Pockels photoelastic law.
Photoelectron spectroscopy of sulfur atoms produced via two-photon dissociation of sulfur dioxide
Authors: Appling J. R. , Harbol M. R. , Edgington R. A. , Goren A. C.
Published: July 2002

The 2+1 resonantly enhanced multiphoton ionization (REMPI) spectrum of sulfur atoms produced by two-photon photodissociation of sulfur dioxide is reported for the wavelength range 252–263 nm. Photoelectron spectroscopy of many resonant ionizations reveals a propensity toward preservation of ion core configuration in formation of ionic species. Several pathways for production of pure populations of excited state 2DJo sulfur ions are documented. Photoelectron angular distributions show contributions from outgoing electrons with a maximum angular momentum lmax=2. Intermediate state alignment from two-photon absorption of ground state 3P0 sulfur atoms is demonstrated.
A time-dependent calculation for vibrational predissociation of H2HF
Authors: Zhang Dong H. , Zhang John Z. H. , Bac̆ić Zlatko
Published: July 2002

Calculations of the total and partial decay widths are presented for the vibrational predissociation of H2HF. The calculation is done for the total angular momentum J=0 of the molecule and for the dissociation process H2HF(v=1)→H2(v=0)+HF(v=0). A time-dependent golden rule wave packet method is employed in the numerical calculation for the decay widths. The lifetime of the complex is determined from our calculation to be about 600 ns for para- and 1600 ns for ortho-H2HF. These values are much larger than the experimentally measured value of 27 ns for ortho-H2HF. The large discrepancy in lifetime for H2HF is in sharp contrast to the excellent agreement in lifetime for D2HF between theory and experiment, though the same potential energy surface is used in both calculations. We also present the rotational state distribution of the fragments H2 and HF following the vibrational predissociation of H2HF. It is found that about 58% of the final rotational population is in j=4 states of H2 for para-H2HF and about 48% is in j=5 states of H2 for ortho-H2HF.
Photofragmentation of CF2I2. Competition between radical and three-body dissociation
Authors: Baum G. , Felder P. , Huber J. Robert
Published: July 2002

The photodissociation of CF2I2 following excitation into the first UV absorption band system has been studied by photofragment translational spectroscopy. Time-of-flight and angular distributions of the dissociation products measured at the photolysis wavelengths 351, 337, 308, and 248 nm reveal the competition between a radical channel that forms the fragment pairs CF2I+I and a three-body dissociation that yields CF2+I+I. These processes are found to occur via B1←A1 type electronic transitions. For the iodine atoms produced in the radical channel the spin–orbit branching ratio I*(2P1/2)/I(2P3/2) increases from I*/I=0.02 at 351 nm to I*/I=0.2 at 337 nm and reaches I*/I=2 at 308 nm. This wavelength-dependent selectivity of the I*/I ratio suggests that the absorption band system is composed of at least two overlapping B1←A1 transitions. Although energetically accessible at 351 nm (where CF2I from the radical channel decays spontaneously to CF2+I), the three-body dissociation is observed first at 308 nm as a minor decay mode and becomes the exclusive decay at 248 nm. The dissociation energy for the formation of CF2I+I(2P3/2) was determined to be D0I≤51.3±2 kcal/mol; in the case of the reaction forming CF2+I(2P3/2)+I(2P3/2) the dissociation energy is D0I+D0II≤63.3±2 kcal/mol.
Coordinate-space formulation of polymer lattice cluster theory
Authors: Baker David , Chan Hue Sun , Dill Ken A.
Published: July 2002

Freed et al. have recently developed a lattice cluster theory of polymer solutions that involves series expansions in momentum space. Here we reformulate the lattice cluster theory in coordinate space. The present treatment has certain useful features. In particular, the terms in the reformulated theory can be obtained readily from existing exhaustive computer enumerations. Also, the Flory–Huggins theory can be shown to arise as the first term in a recentered coordinate-space expansion. Generalization to treat polymers in confined space is straightforward.
Nonplanarity and ring torsion in poly(p-phenylene vinylene). A neutron-diffraction study
Authors: Mao G. , Fischer J. E. , Karasz F. E. , Winokur M. J.
Published: July 2002

Elastic neutron-scattering data from all-hydrogen and selectively deuterated poly(p-phenylene vinylene) (PPV) samples from 296≤T≤616 K are reported. These data, in combination with structure factor refinements, support a nonplanar structural model of the phenylene rings. Increased temperature is accompanied by a gradual rise in both the degree of nonplanarity and in the associated displacements from this mean position. There is also measurable anisotropy in the equatorial thermal expansion coefficients combined with a small 2° drop in the polymer chain setting angle, thereby indicating only a weak approach toward a high-temperature rotator phase. This is in contrast to the pronounced variations seen in polyacetylene and polyethylene, which lack local ring torsional degrees of freedom.
A Heisenberg Hamiltonian for intermolecular exchange interaction: Spin delocalization and spin polarization
Authors: Kollmar Christian , Kahn Olivier
Published: July 2002

We present a Heisenberg Hamiltonian describing the exchange interaction between two molecular units with unpaired electrons. Each unit is represented not only by its open-shell ground state wave function, but also by an admixture of singly excited configurations which account for the spin polarization effect and may lead to negative spin densities in some regions. The states of the two units are then coupled in a valence-bond-type fashion resulting in an exchange coupling constant J expressed in terms of orbitals localized on each unit. It consists of three parts: (a) interaction of the ground state terms; (b) interaction of the spin polarization term of unit A with the ground state term of B; and (c) vice versa. The latter two contributions can be considered as an exchange interaction involving negative spin densities as has been first suggested by McConnell for the intermolecular coupling between alternant hydrocarbons. It is shown that they follow the same simple spin algebra given by the general form of a Heisenberg Hamiltonian as contribution (a) and that they also have a similar structure. The relation between the coupling constant and the spin density is discussed.
Classical Monte Carlo simulations of relaxed trapping site structures in Li atom doped solid Ne
Authors: Fajardo Mario E.
Published: July 2002

Results of classical Monte Carlo simulations of Li atom doped fcc Ne solids are presented. Li atom trapping sites based on four-atom and six-atom vacancies required only minor relaxation of the matrix surroundings to reach equilibrium. Trapping sites based on one-atom and two-atom vacancies were unstable and rearranged to yield crowded versions of the relaxed four-atom trapping site. The lattice strain associated with the crowded trapping sites could be relieved by the incorporation of nearby additional vacancies. These results are all consistent with the intuitive concept of a minimum volume trapping site in a van der Waals guest/host system; for the Li/Ne system apparently at least four Ne atoms must be removed to accommodate a Li atom. In all cases, the energies of the trapped Li atoms were at least ≊0.25 eV above the energy of a Li atom separated from close-packed solid Ne, indicating that Li atoms are indeed unwelcome in solid Ne.
The dynamics of H2 dissociation on Cu and Ni surfaces. Mixed quantum-classical studies with all degrees of freedom
Authors: Grüneich Armin , Cruz Astrid J. , Jackson Bret
Published: July 2002

The dissociative adsorption of hydrogen on metals is examined using models which contain all six molecular degrees of freedom. Fully classical studies are implemented, as well as a mixed approach in which three degrees of freedom are treated quantum mechanically, and three classically. Probabilities for dissociation and rovibrational excitation are computed as a function of incident translational energy for both H2 and D2 on a reactive Ni surface and a less reactive Cu surface. Two sudden approximations are tested, in which either the center of mass translation parallel to the surface or the azimuthal orientation of the molecule are frozen. The quantum and classical results are compared for the above cases.
Matrix isolation spectroscopy of metal atoms generated by laser ablation. III. The Na/Ar, Na/Kr, and Na/Xe systems
Authors: Tam Simon , Fajardo Mario E.
Published: July 2002

The results of matrix isolation experiments of Na atoms generated by pulsed laser ablation of sodium metal are reported. Novel effects previously observed in similarly prepared Li/Rg matrices apparently generalize to the Na/Rg systems. A new spectral feature appears in Na/Ar matrices with peaks near 504, 513, and 523 nm, for which we have coined the name ‘‘violet triplet’’ and assigned to Na atoms in a heretofore unaccessed trapping site. A similar feature in Na/Kr matrices displaying peaks at 528, 537, and 546 nm shares the same name and assignment, correcting previous misassignments in the literature. We have also begun to incorporate ideas about the known inhomogeneous nature of the microstructure of rare gas matrices into our discussions of matrix processes. This refinement of our previous model helps explain certain aspects of the matrix deposition and matrix annealing processes.
Theory of vibrational energy relaxation in liquids: Vibrational–translational–rotational energy tranfer
Authors: Adelman S. A. , Stote R. H. , Muralidhar R.
Published: July 2002

The concepts underlying a theoretical treatment of the vibrational energy relaxation (VER) time T1 of a solute normal mode in a molecular solvent are summarized, and results for T1, valid for VER processes mediated by vibrational–translational–rotational energy transfer, obtained from this treatment are presented. These results are based on the formula T1=βTR−1(ωl), where βTR(ω) is the translational–rotational branch of the friction kernel of the normal mode and where ωl is its liquid phase frequency. βTR(ω) is evaluated as the cosine transform of the autocorrelation function 〈ℱ̃(t)ℱ̃〉0 of the fluctuating generalized force exerted by the solvent on the solute normal mode coordinate conditional that this coordinate is fixed at its equilibrium value and that all solvent molecules are constrained to have their equilibrium geometries. The Gaussian model is utilized to evaluate 〈ℱ̃F(t)ℱ̃〉0 and molecular level expressions for ωl and for the Gaussian model parameters are presented for the infinitely dilute diatomic solution. The expressions involve site density integrals over the coordinates of a single solvent atomic site and over the coordinates of a pair of solvent atomic sites located on the same molecule. The results permit the evaluation of T1 in terms of the atomic masses and gas phase bondlengths of the solute and the solvent molecules, the solute gas phase vibrational frequency, the solute–solvent site–site interaction potentials, and specified equilibrium site–site pair correlation functions of the liquid solution.
High resolution emission spectroscopy of AlCl at 20 μ
Authors: Hedderich H. G. , Dulick M. , Bernath P. F.
Published: July 2002

The high resolution infrared emission spectrum of aluminum monochloride has been recorded with a Fourier transform spectrometer. A total of 1747 rovibrational transitions, v=1→0 to v=8→7, for the most abundant isotopomer 27Al35Cl and 708, v=1→0 to v=4→3, for the least abundant isotopomer 27Al37Cl have been assigned. This new set of infrared data was combined with existing microwave and millimeter-wave data to refine the Dunham Yij constants for the X 1Σ+ electronic ground state. In addition two sets of mass-reduced Dunham Uij constants have been determined from separate fits. In the first fit all of the Uij constants that could be statistically determined were treated as adjustable parameters. In the second fit only the constants satisfying the condition j<2 were treated as adjustable parameters while the values for the remaining constants were fixed to constraints imposed by the Dunham model. Finally, in order to fully utilize the information provided by this extensive data set in an attempt to improve the prediction of energies for higher lying v, J levels of the X 1Σ+ state, the combined data set, consisting of microwave, millimeter, and infrared (IR) data were fitted directly to the eigenvalues of the Schrödinger equation containing a parametrized internuclear potential energy function.
Measurements of the microwave spectrum, Re–H bond length, and Re quadrupole coupling for HRe(CO)5
Authors: Kukolich Stephen G. , Sickafoose Shane M.
Published: July 2002

Rotational transition frequencies for rhenium pentacarbonyl hydride were measured in the 4–10 GHz range using a Flygare–Balle type microwave spectrometer. The rotational constants and Re nuclear quadrupole coupling constants for the four isotopomers, (1) H187Re(CO)5, (2) H185Re(CO)5, (3) D187Re(CO)5, and (4) D185Re(CO)5, were obtained from the spectra. For the most common isotopomer, B(1)=818.5464(2) MHz and eq Q(187Re)=−900.13(3) MHz. The Re–H bond length (r0) determined by fitting the rotational constants is 1.80(1) Å. Although the Re atom is located at a site of near-octahedral symmetry, the quadrupole coupling is large due to the large Re nuclear moments. A 2.7% increase in Re quadrupole coupling was observed for D-substituted isotopomers, giving a rather large isotope effect on the quadrupole coupling. The Cax–Re−Ceq angle is 96(1)°, when all Re–C–O angles are constrained to 180°.
Cation dependence of the ionic dynamics in computer simulated molten nitrates
Authors: Katō Toshiko , Hayashi Soichi , Oobatake Motohisa , Machida Katsunosuke
Published: July 2002

In order to study the cation dependence of the ionic dynamics in molten nitrates, molecular dynamics simulations including vibrational degrees of freedom were carried out for molten LiNO3, NaNO3, and RbNO3. Coulomb pair potential with Born-type repulsion was adopted for the interionic interaction. The simulated diffusion coefficient was smaller for a larger cation, and that of nitrate ions did not change with changing cation species. The mean squared charge displacements showed that the static conductivity decreased considerably as the cation size increased from Li+ to Rb+. The simulated orientational correlation function of nitrate ions decayed more quickly as the cation size increased. Far infrared absorption spectrum simulated from the time evolution of the dipole moment (or the current) of the system showed that the peak shifted to the low energy side and the intensity decreased as the cation size increased. Results of the simulation were compared with the experimental diffusion constants, static and dynamic conductivities, and rotational behavior revealed by Raman spectroscopy. The simulated vibrational correlation functions and the power spectra of NO3− could reproduce the observed cation dependence of the peak frequencies of the ν1(A′1) and ν2(A″2) modes. However, the assumed interionic potentials in the present simulation were found to result in too slow vibrational dephasing of the ν1 mode and too fast dephasing of the ν2 mode as compared with the infrared and isotropic Raman spectra. Strong correlation between radial and angular distributions of cations was found in the first coordination spheres of nitrate ions in the simulated molten nitrates.
Rotational resonance states of Ar–HCl(v=0) by finite range scattering wave function method
Authors: Jang Hyo Weon , Choi Seung E. , Light John C.
Published: July 2002

The low lying rotational resonance states of Ar–HCl van der Waals molecule in the vibrational ground state of HCl are calculated for several total angular momentum states within the model of a rigid rotor-atom system. The necessary scattering calculations are done by the finite range scattering wave function (FRSW) method [J. Chem. Phys. 99, 1057 (1993)] adopting energy independent auxiliary functions which makes the scattering calculations at many energies much more efficient. Discrete eigenvectors and eigenvalues of Hamiltonian matrix are calculated on a finite range via the successive diagonalization-truncation scheme combined with the discrete variable representation (DVR). Analytical eigenfunctions of the asymptotic Hamiltonian operator in a body-fixed frame excluding only the interaction potential, but including all the effective centrifugal potential terms, are used as asymptotic wave functions, which reduces the dynamical range required for the ℒ2 scattering calculations. After a single diagonalization of the Hamiltonian in the finite range ℒ2 representation, resonance parameters are extracted through the energy dependence of Smith’s lifetime matrix. A search algorithm for multiple resonances is used assuming constant background effects and isolated, simple resonances. Several recommendations for the choice of the translational basis functions and the basis set ranges which target specific kinds of resonances with various accuracies are given. Resonance energies and widths (lifetimes and partial decay probabilities) for many predissociating states of Ar–HCl are given with unprecedented accuracy.
Elastic moduli of simple fluids with steeply repulsive potentials
Authors: Heyes D. M. , Aston P. J.
Published: July 2002

We examine the infinite frequency elastic moduli of steeply repulsive inverse power, r−n, potential fluids. Using molecular dynamics simulation we show that these are proportional to n and therefore diverge in the hard-sphere n→∞ limit, which we also prove independently for the case of hard spheres.
A Voronoi polyhedra analysis of structures of liquid water
Authors: Shih Jing-Ping , Sheu Sheh-Yi , Mou Chung-Yuan
Published: July 2002

Molecular dynamics simulations have been carried out for sinple point charge (SPC) water, in normal, compressed, and stretched states. A detailed analysis of local structures using both pair correlation and Voronoi polyhedra distribution, which describes the information about the multiparticle distribution, was reported. We examine the oxygen–oxygen pair correlation function and the distributions of Voronoi polyhedra in response to the variation of density and temperature. The asphericity distributions of Voronoi polyhedra reveals the anisotropicity of local arrangements of water molecules. It is found local pair distributions depend on the asphericities of center molecules. A high value of the asphericity parameter η corresponds to an icelike local structure of tetrahedrally bonded network patch. Loosely bonded structures, with low value of asphericity, have much less hydrogen bonding, and they are more susceptible to density fluctuation. Partition of local structures according to the asphericity of Voronoi polyhedra gives different pair correlation functions which give an identical set of isosbestic points. It is proposed that the Voronoi polyhedra analysis of configurations can be explained by a two-states patch model of water.
Far infrared vibration-rotation-tunneling spectroscopy and internal dynamics of methane–water: A prototypical hydrophobic system
Authors: Dore L. , Cohen R. C. , Schmuttenmaer C. A. , Busarow K. L. , Elrod M. J. , Loeser J. G. , Saykally R. J.
Published: July 2002

Thirteen vibration-rotation-tunneling (VRT) bands of the CH4–H2O complex have been measured in the range from 18 to 35.5 cm−1 using tunable far infrared laser spectroscopy. The ground state has an average center of mass separation of 3.70 Å and a stretching force constant of 1.52 N/m, indicating that this complex is more strongly bound than Ar–H2O. The eigenvalue spectrum has been calculated with a variational procedure using a spherical expansion of a site–site ab initio intermolecular potential energy surface [J. Chem. Phys. 93, 7808 (1991)]. The computed eigenvalues exhibit a similar pattern to the observed spectra but are not in quantitative agreement. These observations suggest that both monomers undergo nearly free internal rotation within the complex.
Spin–orbit autoionization and intensities in the double-resonant delayed pulsed-field threshold photoionization of HCl
Authors: Zhu Y.-F. , Grant E. R. , Wang Kwanghsi , McKoy V. , Lefebvre-Brion H.
Published: July 2002

State-selected delayed pulsed-field threshold photoionization spectra of HCl and DCl are recorded in double-resonant transitions through the F 1Δ, E 1Σ+, and g 3Σ− states of the 4pπ Rydberg configuration. Comparison of observed rotational line strengths with calculated spectra, as well as with available time-of-flight photoelectron spectra, provides useful insight on the influence of spin–orbit and rotational autoionization on delayed pulsed-field threshold photoionization of HCl. Spin–orbit and rotational autoionization are seen to dramatically reduce the ion rotational intensity associated with the upper spin–orbit level of the ion.
Spectral lines and distribution of H+3 in high rotational levels
Authors: Uy Dairene , Gabrys Charles M. , Jagod Mary-Frances , Oka Takeshi
Published: July 2002

Infrared spectrum of the ν2 fundamental band of H+3 in high rotational levels has been studied. Three motives for this study were (i) to provide laboratory data for the observation of astronomical objects in which a large abundance of H+3 exists at high temperature, (ii) to study kinetic energy distribution of H+3 in plasmas and to determine its rotational and translational temperatures, and (iii) to provide information on high rovibrational states for the variational calculations on the intramolecular dynamic of H+3. In order to increase the kinetic temperature, water-cooled plasmas with helium dominated gas mixtures with He/H2∼5/0.6 torr were used. The observed rotational level in the ground state with the highest rotational quantum numbers was J=K=15 which has the rotational energy of 5091.6 cm−1. It was found from the observed relative intensities of the rovibrational transitions and linewidths that H+3 in the plasmas were in approximate thermal equilibrium with both rotational and translational temperature of ∼1000 K. On the contrary, an analysis of the relative intensities of the H+3 spectral lines observed in our previous study of carbocation spectroscopy showed nonthermal rotational distribution. A semiquantitative discussion is given on the observed results.
Predissociation supported high-resolution vacuum ultraviolet absorption spectroscopy of excited electronic states of NH3
Authors: Li Xinghua , Vidal Carl Rudolf
Published: July 2002

Using monochromatic vacuum ultraviolet radiation generated by two-photon resonant sum frequency mixing in a Mg–Kr mixture we have investigated the electronic transition of NH3 in the 67 000–73 000 cm−1 region by detecting the fluorescence from the predissociation fragments of NH3. The spectrum is simplified using a pulsed molecular beam. Vibronic bands of the B 1E″ (29, 210, 211, 212, 2731, 2831) state are clearly identified and relevant molecular constants are deduced. The predissociation in the B̃ 1E″ state is found to be nearly independent of the rotational quantum numbers (J,K) within one vibrational band. The linewidths of different vibronic components of the B̃ 1E″ state are measured. In addition, other absorption bands are presented including previously unobserved weak absorption features.
Collisional relaxation of translational energy and fine-structure levels of the O(3P
j) atom created in the photodissociation of SO2 at 193 nm
Authors: Abe Makoto , Sato Yoshihiro , Inagaki Yousuke , Matsumi Yutaka , Kawasaki Masahiro
Published: July 2002

Collision-induced energy transfer and intramultiplet relaxation processes of O(2p4 3Pj) j=0, 1, and 2 have been studied, using a vacuum-ultraviolet laser-induced fluorescence technique. The O(3Pj) atoms are produced from the photodissociation of SO2 at 193 nm. Doppler profiles of the O(3P2) atoms have been measured as a function of time delay between pump and probe laser pulses. The translational energy and j-level population of the O(3Pj) atoms are thermalized at 300 K after a number of collisions with either He, Kr, Xe, N2, or CO2. A Monte Carlo calculation using the hard-sphere collision model provides the cross sections for relaxation of the translational energy; 21±3 Å2 for He, 25±3 Å2 for Kr, and 25±5 Å2 for Xe. Assuming the principle of detailed balancing among the j levels, the cross sections for the collision-induced intramultiplet transition over the collision energy range 1–6 kcal mol−1 are obtained from the time evolution of the j-level populations: cross sections for the j=2→1 transition are 2.4±1.2 Å2 for Kr and 1.4±0.7 Å2 for Xe.
Microphase and macrophase separation in irreversible reacting chemical binary mixtures
Authors: Schulz Michael , Frisch Harry L.
Published: July 2002

The phase transition of a mixture of A, B and irreversible connected A–B molecules is analyzed for a system in which pure A–B, molecules microphase separate and pure (A,B) mixtures macrophase separate. The possible thermodynamically stable phases (homogeneous, microphase separated, and completely separated) and the different forms of phase transitions are discussed by means of a random phase approximation.
Magnetic circular and linear dichroism saturation studies: Determination of the ‘‘crystal field’’ splitting in krypton and xenon matrix-isolated iron atoms
Authors: Rivoal J. C. , Zoueu J. , Blanchard X. , Nahoum R. , Eyring M. , Pyka M. , Vala M.
Published: July 2002

The site symmetry and magnitude of the crystal field splitting of metal atoms trapped in rare gas matrices may be determined by a combination of the temperature and magnetic field dependence of magnetic circular dichroism (MCD) and magnetic linear dichroism (MLD). General theoretical expressions are derived for the MCD and MLD considering the Zeeman effect and the matrix (i.e., crystal field) as perturbations on the free atom ‖JMJ〉 states. These expressions are applied to the observed MCD and MLD T- and B-saturation curves for Fe atoms isolated in krypton and xenon matrices in the range 0–1.5 T and 2.3–22 K. An octahedral crystal field model accounts well for all four independent sets of data (MCD vs B, MCD vs 1/T, MLD vs B2, and MLD vs 1/T2) for two different, isolated electronic transitions. A crystal field parameter of +0.06±0.05 cm−1 has been determined, corresponding to an overall electronic ground-state splitting of 3.2±2.5 cm−1. This splitting is less than the optical bandwidth and is shown to be consistent with previous studies of rare gas matrix-isolated Fe atoms by Mössbauer and laser-excited emission spectroscopies.
Effects of the order of the energy asymptotes on the calculations of nuclear magnetic shieldings and static polarizabilities
Authors: Fagerström Jan , Oddershede Jens
Published: July 2002

The second-order polarization propagator approximation (SOPPA) has been applied to the calculation of the nuclear magnetic shielding constants and static polarizabilities of CO, N2, F2, and CH4 in order to investigate the effect of decreasing the order (in perturbation theory) of the poles of the propagator, i.e., the energy asymptotes, but still requiring that all response terms to second order must be included. Our results show that the higher than second-order contributions from the poles are of vital importance for the nuclear magnetic shieldings and of less, but not negligible, importance for the static polarizabilities. As the order of the poles is decreased the SOPPA isotropic shieldings approach the results obtained within second-order perturbation theory (MP2), especially for CO, N2, and F2. This behavior is not as pronounced for the C shielding of CH4 and for polarizabilities. For the shieldings we obtain the best agreement with MP2 (and experiments) when the poles are calculated as Hartree–Fock energy differences using frozen ground state orbitals, and for the polarizabilities when the poles are calculated in the random phase approximation and Tamm–Dancoff approximation.
Singularities in the consistent hypernetted chain approximation
Authors: Ferreira P. G. , Carvalho R. L. , Telo da Gama M. M. , Schlijper A. G.
Published: July 2002

We use the consistent set of hypernetted chain (HNC) equations to investigate the stability of liquid and vapor phases of simple fluids. We calculate the phase diagram and discuss the physical (spinodal) and mathematical (termination line) singularities of the theory. The latter delimits a region where the HNC equations have no physically acceptable solutions. Additionally, we confirm that the physical solutions of the HNC equation correspond to local minima of the consistent grand potential which, however, appears to be unbounded from below.
Optical potential coupled to discrete variable representation for calculations of quasibound states: Application to the CO(B 1Σ+–D′1 Σ+) predissociating interaction
Authors: Monnerville M. , Robbe J. M.
Published: July 2002

The optical potential method initially proposed by Jolicard and Austin in the context of the stabilization method is reviewed here and used with the accurate and the efficient discrete variable representation method to obtain the energies and the widths (respectively, the real and the imaginary part of the resonance energies) of rovibrational predissociated states of diatomic molecules. In this method the resonances for an n coupled states problem are obtained by a direct diagonalization of the Hamiltonian matrix in the diabatic representation. This Hamiltonian matrix is directly evaluated in the discrete variable representation using the Fourier grid Hamiltonian method proposed by Marston and Balint-Kurti. In this approach, two optical potentials are tested and used here to impose the asymptotic behaviors of the boundary conditions which are compatible with the resonance states. The method is exemplified for the B 1Σ+–D′1 Σ+ Rydberg–valence predissociating interaction in the CO molecule.
Single chain dynamics in a binary polymer blend
Authors: Genz U. , Vilgis T. A.
Published: July 2002

The dynamics of an individual chain in a binary polymer blend is investigated. A generalized Rouse equation takes into account the coupling to the dynamics of the surrounding polymer matrix. This generalizes Schweizer’s approach to a multicomponent polymer system. The results are applied to a symmetric binary blend. Emphasis is laid on the role of composition fluctuations, which are strongly enhanced close to the phase separation and then show critical slowing down. This has an impact on the dynamics of individual chains. As a result of the treatment, the internal chain motion is expected to be more strongly affected than the center-of-mass motion. A physical interpretation is presented such that the chains are strongly expelled from unfavorable environments. It is discussed how the results are modified if—instead of a mean-field treatment—the theory of critical phenomena is applied to describe composition fluctuations.
Femtosecond studies of interparticle electron transfer in a coupled CdS–TiO2 colloidal system
Authors: Evans J. E. , Springer K. W. , Zhang J. Z.
Published: July 2002

We report the direct femtosecond measurements of the electron transfer process from CdS to TiO2 particles in a coupled colloidal system. The electrons initially created in the conduction band and quickly trapped at the liquid–solid interface in aqueous CdS colloids are found to be transferred to the colloidal TiO2 particles with a time constant of 2 ps, resulting in significantly slower electron–hole recombination. These coupled semiconductor colloids provide a potentially useful system for achieving efficient charge separation, which is important for many chemical reactions involving heterogeneous electron transfer.