bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared double resonance of fluoroform-d with a tunable diode laser
Authors: Harradine D. , Foy B. , Laux L. , Dubs M. , Steinfeld J. I.
Published: February 2003

An infrared double-resonance experiment has been carried out on fluoroform-d. The ν2←0 and ν5←0 fundamentals have been reanalyzed at a resolution of 0.001 cm−1. From excited-state absorptions in the ν2+ν5←ν5 and 2ν5←ν5 bands, we obtain values for the anharmonicity constants x25=−1.0 cm−1, x55=−0.23 cm−1, and g55=0.13 cm−1. Both of the xk5 values are in good agreement with Dennison’s rule estimates of Kirk and Wilt. Collision-induced double-resonance signals indicate propensity rules for rotational state changes ΔJ=±1, ΔK=±3n, where n may take integer values as large as 6 or 8. The rotational relaxation rates are three to five times hard-sphere gas kinetic for polar collision partners (CDF3 itself or CH2F2), but only one-fifth gas kinetic for helium collisions. These results are used to assess proposed models for multiple infrared photon dissociation in CDF3 and for submillimeter-wave optically pumped laser action in this gas.
The additivity of NMR isotope shifts
Authors: Jameson Cynthia J. , Osten H.-Jörg
Published: February 2003

One of the most interesting and useful aspects of the isotope effect on nuclear magnetic shielding is the proportionality of the shift to the number of substituted atoms in equivalent positions. In this paper we show the quantitative basis for the additivity of isotope shifts in NMR, using the CX4−nYn (X,Y=H,D,T) system and the linear triatomic systems CO2, NNO, and OCS as examples. We also predict small deviations from additivity and find that these deviations are consistent with those observed for 14N shifts in the NH4−nD+n homologous series. Furthermore, we determine the mass dependence of the one-bond isotope shift.
The NMR isotope shift in polyatomic molecules. Estimation of the dynamic factors
Authors: Jameson Cynthia J. , Osten H.-Jörg
Published: February 2003

In a continuing study of the factors which determine the isotope shifts in NMR we consider here substitution of end atoms in molecular types in which the bond angle deformation does not play a significant role. We show that in molecules of the type AXn the rovibrational correction to shielding of nucleus A can be obtained directly from the isotope shift without dynamical calculations. We propose a method for estimating 〈Δr〉, knowing only the equilibrium bond length, the masses, and the rows of the Periodic Table of the atoms in the bond. We test this on diatomic molecules for which we are able to calculate 〈Δr〉 directly from the spectroscopic constants and examine its dependence on bond order. We apply the estimation method to polyatomic molecules for which we have completed a full dynamical calculation using the best available force fields. We use the estimated 〈Δr〉 for other molecular systems and obtain estimates of the shielding derivatives from the observed isotope shifts. The results compare well with derivatives that are known for related electronic environments.
Vibrational autoionization in PF3: Doing violence to the propensity rule
Authors: Berkowitz J. , Greene J. P.
Published: February 2003

The photoionization spectrum of PF+3 in its threshold region displays two prominent progressions of autoionization peaks. When these are analyzed, together with earlier photoabsorption studies and a photoelectron spectrum, they lead to the conclusion that vibrational autoionization is occurring, with Δν≤−13. This conclusion stands in sharp contrast with the current theory of vibrational autoionization, which predicts a propensity rule Δν=−1. Other examples from the recent literature are summarized, to suggest that a more general theory of vibrational autoionization is required.
Quasiclassical trajectory study of the reaction O(3P)+HCl → OH+Cl. The effects of vibrational excitation, rotational excitation, and isotopic substitution on the dynamics
Authors: Persky Avigdor , Broida Michael
Published: February 2003

Three dimensional quasiclassical trajectory calculations were carried out for the nearly thermoneutral reaction of oxygen atoms O(3P) with hydrogen chloride molecules (HCl and DC1), for reaction temperatures of 300 and 700 K, employing two LEPS potential energy surfaces. Calculations for 300 K were performed for various initial vibrational states of the reagents HCl(ν=0, 1, 2, and 4) and DC1(ν=0 and 1). Calculations for 700 K were carried out for the ground vibrational state ν=0. The effect of rotational excitation on reactivity was investigated by calculating reaction cross sections for specific initial rotational states for the reaction O+HCl(ν=0, J=0–19) for collision energies of 6.0 and 10.0 kcal/mol. The rate of the O+HCl reaction was found to be enhanced by more than two orders of magnitude (factors of 150 and 390 for the two surfaces used) for O+HCl(ν=1), and by more than three orders of magnitude for O+HCl(ν=2), as compared to O+HCl(ν=0). The influence of rotational excitation on reactivity was found to be very different for the two surfaces used, and a possible explanation is suggested. The results of the trajectory calculations are compared with experimental results of rate constants and kinetic isotope effects and with results of other trajectory calculations for this system.
The high resolution infrared spectrum and molecular structure of the superacid H2F+ by velocity modulation laser absorption spectroscopy
Authors: Schäfer Eckhard , Saykally Richard J.
Published: February 2003

The gas phase infrared spectrum of the fluoronium ion (H2F+) was recorded with Doppler-limited resolution between 3080 and 3520 cm−1 by velocity modulation laser absorption spectroscopy of a hydrogen plasma containing 5% HF. One hundred and nine of the observed transitions were assigned to the symmetric stretch (ν1) and 217 to the asymmetric (ν3) stretch. A least squares analysis of ν3 transitions up to J=11 and Ka=6 and ν1 transitions up to Ka=4 with Watson’s S-reduced Hamiltonian yielded rotational constants and centrifugal distortion constants for the vibronic ground state and for the two excited states. Small Coriolis interactions between ν1 and ν3 levels were observed, but were not treated explicitly. The band origins for ν3 and ν1 are 3334.6895(26) and 3348.7078(36) cm−1, respectively. The r0 structure of H2F+ was determined as: rHF=0.9577 Å <HFH=114.55°.
Direct absorption spectroscopy of jet-cooled polyenes. I. The 1 1B+u←1 1A−g transition of t
r
a
n
s, t
r
a
n
s-1,3,5,7-octatetraene
Authors: Leopold D. G. , Vaida V. , Granville Mark F.
Published: February 2003

The direct absorption spectrum of the 1 1B+u←1 1A−g transition of jet-cooled trans,trans-1,3,5,7-octatetraene is reported here for the 35, 120–42, 600 cm−1 region. The alleviation of vibrational sequence band congestion in the jet spectrum results in an order-of-magnitude decrease in the observed breadth of the origin band and a comparable sharpening throughout the spectrum, enabling the redetermination of vibronic band positions, relative intensities, and widths. Vibrational assignments for the seven observed active modes are discussed, and results are compared to the predictions of previously reported vibronic structure calculations.
Determination of surface parameters of metals by means of image analysis of morphological instability in electrodeposition
Authors: Makino Tohru , Aogaki Ryoichi , Niki Eiji
Published: February 2003

A new method to determine surface parameters of metals, viz., surface energy γ and surface diffusion coefficient Dad of metal adatoms is proposed and experimentally established. This method is based on the image analysis for the change of metal surface morphology due to electrodeposition. First, potentiostatic and galvanostatic electrodepositions are performed in the same electrolyte solution. In these experiments, average sizes of the crystal particles formed on the electrode surfaces are measured at a given deposition time. With the values obtained, computer calculations are carried out to make two kinds of Dad–γ plots corresponding to the galvanostatic and potentiostatic cases, respectively. From their intersection, the surface energy γ and the product DadC*ad of diffusion coefficient Dad and adatom concentration C*ad are determined. Each value of Dad and C*ad is easily separated by the data of C*ad measured by electrochemical technique for electrodeposition. As a result, it is found that the value of γ is kept constant at the high cathodic potentials while there is one maximum at the lower potentials, which seems to correspond to the point of zero charge (pzc) of an electrocapillary curve of mercury electrode system. The dependence of γ in the high cathodic region on the bulk concentration is also investigated. Consequently, it is concluded that surface energy γ is proportional to 3/2 power of the bulk concentration.
Application of morphological instability to the analysis of physical parameters of a metal surface: Adsorption effect of hydrogen on galvanostatic electrodeposition
Authors: Makino Tohru , Aogaki Ryoichi , Niki Eiji
Published: February 2003

Using a newly developed method with which surface parameters of metals such as surface energy and surface diffusion coefficient of adatoms can be measured from the change of surface morphology, the effect of hydrogen adsorption on the crystal sizes formed in galvanostatic electrodeposition was studied. As a result, the reasons for the eccentric formation of minute, powdery crystals accompanied with hydrogen evolution was derived as follows: Since surface diffusion of metal adatoms is strongly hindered owing to saturated adsorption of hydrogen atoms, the supersaturation of the adatoms is violently promoted. Many small crystals resulting from nucleation growth, therefore, continuously appear at high growth velocity. At the same time, the surface energy of the crystals also increases and its value is mainly determined by saturatedly adsorbed hydrogen, so that the tendency for rapid formation of minute crystals are the more accelerated. On the other hand, when hydrogen adsorption can be disregarded, crystals grow more slowly and have relatively larger sizes. The transition from a hydrogen-nonadsorbed state to a hydrogen-adsorbed state is rather discontinuous; immediately after the electrode surface is saturatedly covered with hydrogen, the crystals suddenly reduce their sizes.
Electrophoretic mobility of a porous sphere through gel-like obstacles: Hydrodynamic interactions
Authors: Lumpkin O.
Published: February 2003

An approximate calculation of the electrophoretic mobility of a uniformly charged porous spherical particle in a random suspension of long rod obstacles, a possible model for a gel, is described. The calculation, which treats hydrodynamic interactions, but ignores particle obstacle collisions, predicts, in accord with observation, that the logarithm of the relative mobility is closely proportional to particle radius squared, to the obstacle density, and is also dependent on the ionic milieu. At low obstacle densities, the predicted relative mobility depends on the square root of the obstacle density. Comparisons with experiment suggest that a gel model which neglects cross linking is probably too simplistic.
Relativistic integrals over Breit–Pauli operators
Authors: Simas Alfredo M. , Smith Vedene H.
Published: February 2003

The treatment of kinetic energy in the relativistic Breit–Pauli Hamiltonian is considered. It is shown that although this Hamiltonian is seemingly correct to order c−4 (where c is the speed of light), it cannot be corrected to order c−6 by simply including a p6 term in the relativistic expansion. If a formalism including the full relativistic kinetic energy operator is used, it is demonstrated that the integrals involved can be easily done in momentum space.
Clustering time dependence in molecular dynamics: A kinetic model
Authors: Lippmann D. , Schieve W. C. , Canestaro C.
Published: February 2003

A multichannel kinetic model of clustering is developed consistent with previous MD simulation of nucleation. The kinetic constants are estimated and the results agree well with new isothermal MD data on the growth of small clusters. For 17 particle clusters, the monomer addition approximation to the multichannel model is found to be in serious error in describing the temporal growth.
K-shell binding energy of Mg and Ca
Authors: Beck Donald R.
Published: February 2003

Including many body, relativistic, and radiative effects, a theoretical value of 1311.47 eV has been obtained for the binding energy of Mg, and a value of 4047.84 eV for Ca. Two experimental values, 1311.4 and 1311.3 eV have been reported for Mg. Continuing our systematization of the effects of correlation upon this property, we note that the nonsatisfaction of Brillouin’s theorem for the final state plays an important role.
Quantization with operators appropriate to shapes of trajectories and classical perturbation theory
Authors: Uzer T. , Marcus R. A.
Published: February 2003

Quantization is discussed for molecular systems having a zeroth order pair of doubly degenerate normal modes. Algebraic quantization is employed using quantum operators appropriate to the shape of the classical trajectories or wave functions, together with Birkhoff–Gustavson perturbation theory and the Weyl correspondence for operators. The results are compared with a previous algebraic quantization made with operators not appropriate to the trajectory shape. Analogous results are given for a uniform semiclassical quantization based on Mathieu functions of fractional order. The relative sensitivities of these two methods (AQ and US) to the use of operators and coordinates related to and not related to the trajectory shape is discussed. The arguments are illustrated using principally a Hamiltonian for which many previous results are available.
On the evaluation of analytic energy derivatives for correlated wave functions
Authors: Handy Nicholas C. , Schaefer Henry F.
Published: February 2003

It is shown that to obtain the (2n)th and (2n+1)th energy gradients, it is only necessary to solve equations of the difficulty of the nth order coupled perturbed equations for the orbital and configuration interaction (CI) parameters. For example, to find analytic second and third energy derivatives for CI wave functions, it is only necessary to solve the first order coupled perturbed equations and some related equations, for the effects of orbital rotations. Similar results apply for gradients of energies derived using perturbation theory.
Asymptotic expansions for autocorrelation functions with Gaussian memory
Authors: Denner V. , Wagner M.
Published: February 2003

Mori’s integro-differential equation for equilibrium correlation functions is investigated for a Gaussian memory. For this type of memory the first four moments of the autocorrelation function are reproduced exactly. So far, however, the underlying Mori equation has only been solved numerically. In this paper analytic short-time and long-time expansions are derived by the aid of which the behavior of the autocorrelation function can be described in the whole time domain. The analysis shows that there exists a critical parameter τc which separates the regime of oscillatory from that of nonoscillatory decay of the autocorrelation function. Finally, the Gaussian memory results are compared with those of an exponential memory.
Determination of the 14N quadrupole coupling tensors and the 13C chemical shielding tensors in a single crystal of L-asparagine monohydrate
Authors: Naito A. , McDowell C. A.
Published: February 2003

The 14N quadrupole coupling tensors for the Nα and Nδ nitrogen nuclei in a single crystal of l-asparagine monohydrate were completely determined using proton enhanced 14N NMR. The quadrupole coupling constants and asymmetry parameters were evaluated to be e2Qq/h=1.152 MHz and η=0.220 for the Nα nitrogen nucleus, and e2Qq/h=−2.677 MHz and η=0.337 for the Nδ nitrogen nucleus. It was found that the direction of the largest absolute principal value of the quadrupole coupling tensor for the Nδ nitrogen nucleus was perpendicular to the NH2 plane (sp2 plane) and that for the Nα nitrogen nucleus was parallel to the Cα–Nα bond. The 13C chemical shielding tensors for all four chemically different nuclei (Cα, Cβ, Cγ, and COO−) were determined and assigned to the molecule in the unit cell on the basis of the 13C–14N dipolar splittings. It turned out that the directions of the most shielded value of the chemical shielding tensors for the Cγ and COO− carbon nuclei were perpendicular to their sp2 plane, and that of the least shielded value of the chemical shielding tensor for the COO− carbon nucleus was parallel to the Cα–COO− bond. The direction of the intermediate value of the Cγ chemical shielding tensor makes an angle of 7.7° with the Cγ–Oδ bond. The lengths of the Cα–Nα and Cγ–Nδ bonds were calculated to be 1.513 and 1.364 Å, respectively, by analyzing the 13C–14N dipolar coupling tenors. These values agree well with those determined by neutron diffraction studies.
A XANES investigation of the bonding of divalent lead in solids
Authors: Rao K. J. , Wong J.
Published: February 2003

XANES (X-ray absorption near-edge structure) spectra of divalent lead compounds have been studied at both the Pb LIII and LI edges using synchrotron x rays from CHESS (Cornell High Energy Synchrotron Source). The combined LIII and LI near-edge spectral features strongly support a sp3d2 hybridization scheme in covalently bonded yellow PbO. The absorption features associated with the spectra of ionic halides (PbF2, PbCl2, and PbI2) and the oxysalts [Pb(NO3)2, PbSO4, and PbCrO4] have been shown to be consistent with crystal field splittings of the final states using group theoretical arguments. The XANES spectra of a series of PbO–PbCl2 glasses have also been studied to elucidate the nature of bonding and confirm the local structure derived from x-ray diffraction experiments. Shape resonance features associated with LIII and LI edge XANES have also been discussed. This investigation illustrates the novel use of XANES spectroscopy in studying the bonding of nontransition metal ions.
Spectroscopy and dynamics of the dipole-bound state of acetaldehyde enolate
Authors: Mead Roy D. , Lykke Keith R. , Lineberger W. C. , Marks J. , Brauman John I.
Published: February 2003

Ultrahigh-resolution photodetachment spectroscopy of acetaldehyde enolate negative ion has revealed ∼50 narrow resonances near threshold, corresponding to excitation to a diffuse state in which the electron is weakly bound by the field of the molecular dipole. A complete analysis of rotational transitions between the ground valence state and the excited dipole-bound state has been carried out, yielding spectroscopic constants and geometries for both states. In analogy to Rydberg states, the structure of the ‘‘neutral core’’ of the dipole-bound state is like that of the neutral radical. The dependence of autodetachment lifetimes upon the rotational quantum numbers of the dipole-bound state has been measured. Bound levels of the dipole-bound anion state are readily electric-field detached. The selection rules and dynamics of autodetachment from the dipole-bound state are discussed.
Submillimeter spectra and molecular constants of 6LiH, 7LiH, 6LiD, and 7LiD
Authors: Plummer Grant M. , Herbst Eric , De Lucia Frank C.
Published: February 2003

The fundamental J=1←0 rotational transitions of 7LiH in its two lowest vibrational states and of 6LiH in its ground vibrational state have been measured. In addition, the J=2←1 transitions of 7LiD in its two lowest vibrational states and of 6LiD in its ground vibrational state have been studied. The measured submillimeter transition frequencies have been combined with previous millimeter data on 6LiD and 7LiD into a data set which has been successfully analyzed according to the theories of Herman, Asgharian, and Watson, which treat the problem of Born–Oppenheimer breakdown.
Higher electronic states of XeO
Authors: Scott W. F. , Walker W. C.
Published: February 2003

XeO is prepared in an Ar matrix by photolysis of Ar:Xe:O2 and Ar:Xe:CO2 films. Excitation spectra for XeO(d 1Σ+–α 1Σ+) and O(1S–1D) emission yield evidence for absorption by XeO at 8.6 and 10.1 eV and energy transfer from CO to XeO.
Picosecond dynamics and photoisomerization of stilbene in supersonic beams. II. Reaction rates and potential energy surface
Authors: Syage J. A. , Felker P. M. , Zewail A. H.
Published: February 2003

Using picosecond excitation in a supersonic jet, we present a full account of our earlier report on the dynamics of state-selective photoisomerization of t-stilbene. Collisionless isomerization in this case indicates the twisting of the molecule about the ethylene bond away from the trans configuration Central to this reaction is the question of vibrational energy redistribution or IVR. From direct (single vibronic level) time-resolved measurements, relative fluorescence quantum yields from relaxed and unrelaxed states, and a thorough vibrational analysis from excitation and dispersed fluorescence spectra (previous paper), the following conclusions are reached: (i) The IVR yield is state selective being more extensive from combination modes than from fundamental modes of similar energy. The IVR yield becomes very significant above ≊900–1000 cm−1. The rate is much faster than the reaction at all energies studies. (ii) The barrier to isomerization is observed at 3.3±0.2 kcal/mol (1100–1200 cm−1). The radiative lifetimes, measured from the 0° level fluorescence decays, are 2.7±0.1 ns (h12) and 2.5±0.1 ns (d12). (iii) The observed isomerization rates in the isolated molecule are approximately an order of magnitude less than the calculated RRKM rates and observed solution phase rates. (iv) The apparent non-RRKM behavior in the isolated behavior is explained by considering the nature of IVR and by adopting a diabatic representation of the reactive surface (i.e., an allowed surface) using a Landau–Zener–Stueckelberg model. (v) Finally, we compare t-stilbene with other related isolated molecules and to solution phase t-stilbene results in order to assess the role of mode mixing and the nature of the reactive surface.
Nonlinear Raman study of line shapes and relaxation of vibrational states of isotopically pure and mixed crystals of benzene
Authors: Trout T. J. , Velsko S. , Bozio R. , Decola P. L. , Hochstrasser Robin M.
Published: February 2003

New experimental results on vibrational dynamics in crystalline benzene are presented. High resolution CARS measurements on a number of Raman active modes are presented for crystals of natural isotopic composition and for a 12C6H6 isotopically pure crystal. This is the first measurement of vibrational linewidths of an isotopically pure crystal. This study indicates that the naturally occurring 13C substituted isotopic impurities make a large quantitative contribution to the Raman linewidths. The residual low temperature linewidths of the pure crystal are consistent with mode specific energy relaxation. The effect of the 13C impurities on these lines is caused by near resonant scattering or trapping of vibrational excitons. In addition, the site energy dispersion due to disorder has been measured directly for the 991 cm−1 mode in a dilute mixed crystal. Also the relative contributions of scattering and trapping to the linewidths of the Ag and B2g factor group components of the 991 cm−1 band have been assessed.
Dynamics in nonentangled concentrated polymers solutions. III. Exact calculations of the frequency dependent relaxation times and normal mode autocorrelation function to first order in concentrations
Authors: Perico Angelo , Buscaglia V. , Freed Karl F.
Published: February 2003

We investigate approximations to a full dynamical theory of the concentration dependence of the viscoelasticity of polymer solutions in order to alleviate the impediments which arise by virtue of the frequency dependence of the individual polymer mode relaxation rates within the effective medium theory. The problem is considered for the simplest situation under which these frequency dependences appear, namely, in the leading concentration correction for the dimensionless relaxation rates δ̂a(ω). These δ̂a(ω) are evaluated numerically for short chains by use of fast Fourier transform methods. The exact δ̂a(ω) are compared with the previous static approximation and are used to calculate the concentration dependent normal mode autocorrelation function Za(τ). The steady state δ̂a(ω) provide an average relaxation rate approximation to Za(τ) with a form in good agreement with low concentration viscoelastic data.
Electrical double layers. VI. Image effects for divalent ions
Authors: Torrie G. M. , Valleau J. P. , Outhwaite C. W.
Published: February 2003

The effect of image forces on the behavior of primitive model double layers is investigated by means of Monte Carlo computer simulation and modified Poisson–Boltzmann theory for two types of systems containing divalent ions. For the symmetric 2:2 electrolyte the fractional change in the diffuse layer potential caused by image forces differs from the previously studied 1:1 case both by being much larger in the 2:2 system and by decreasing once the surface charge is increased beyond a certain point. For 2:1 electrolytes a small charge separation is found at an uncharged surface and the structural effects associated with it can be significant if image forces are present.
Laser induced thermal desorption from surfaces
Authors: Lucchese Robert R. , Tully John C.
Published: February 2003

Nonresonant laser induced desorption of adsorbed molecules from surfaces has been simulated using the stochastic trajectory technique. An NO molecule is initially bound to a cold LiF(100) surface. Rapid heating of the surface is then simulated via random forces applied to the edges of the 32 atom surface slabs. When the rate of heating is rapid compared to the rates of thermalization of the degrees of freedom of the molecule, it is found that the mean energies of the translational, rotational, and vibrational degrees of freedom of the desorbing molecule are significantly lower than those corresponding to the temperature of the surface at the instant of desorption. Additionally, the angular distribution of the desorbing molecules is found to peak towards the surface normal, and the rotational angular momentum vector is preferentially aligned parallel to the surface plane. These results shed light on recent experimental observations.
Fractal chemical kinetics: Simulations and experiments
Authors: Anacker L. W. , Kopelman R.
Published: February 2003

We relate the effective order X of the elementary binary reaction, A+A→ products, on a fractal, to the spectral dimension. For ds<2: X=1+2/ds. We regain the calsssical value (X=2) for the cubic lattice but get X=3 for the linear lattice. Supercomputer simulations (transient and steady state) and exciton fusion experiments are in quantitative agreement with the above. For percolating clusters X=2.5 and for the Sierpinski gasket X=2.45. Relevance to heterogeneous kinetics is discussed.
Lattice vibrations of ices Ih, VIII, and IX
Authors: Tse John S. , Klein Michael L. , McDonald Ian R.
Published: February 2003

We report the results of molecular dynamics calculations on ice Ih, and the proton ordered ices VIII and IX based on the SPC intermolecular potential, which was parametrized to the properties of liquid water. Particular emphasis is placed on the calculation of vibrational frequency spectra and comparison is made with incoherent inelastic neutron scattering data for ice Ih. The calculated longitudinal acoustic modes agree well with experiment but the transverse acoustic and optic modes are too soft, as are the librational modes. These conclusions are confirmed by comparing individual phonon frequencies for deuterated ice Ih with the measured phonon dispersion curves. Frequency spectra are presented for ice VIII and ice IX.
Bonding and ionization energies of N–F and P–F compounds
Authors: Berkowitz J. , Greene J. P. , Foropoulos J. , Nesković O. M.
Published: February 2003

NF3, N2F4, NF2, PF3, P2F4, PF2, and PF2I have been studied by photoionization mass spectrometry. Modified or confirmatory values have been obtained for the heats of formation of NF+3, NF+2, and NF+ and the ionization potentials of NF3 and NF2. The stepwise bond energies are deduced to be D00(NF) =3.27±0.02 eV; D00(FN–F) =2.85±0.02 eV; and D00(F2N–F) =2.47±0.01 eV. Heats of formation at 0 K have been measured for PF+2 (89.6±0.5 kcal/mol), PF+ (≤214.8 kcal/mol), and PF2I (−142.3±1.0 kcal/mol). The directly measured ionization potential of PF2 is 8.85±0.01 eV. The stepwise bond energies are found to be D00(PF)
The rate of nucleation in a vapor–liquid transition determined from hydrodynamic fluctuation theory
Authors: Lovett Ronald
Published: February 2003

A Fokker–Planck description, based upon hydrodynamic fluctuation theory, of homogeneous nucleation of liquid drops in a vapor phase is reformulated as a one-dimensional time-independent scattering problem. This result is then coupled with an elementary analysis of the interactions between distinct fluctuations to determine the concentration of nuclei produced in a nucleation experiment. An extended comparison between the assumptions of this formulation and those of the classical formulation is given.
X-ray diffraction study of Na+ ions coordination in sodium borate glasses
Authors: Paschina G. , Piccaluga G. , Magini M.
Published: February 2003

X-ray diffraction measurements were performed on glasses of the type Na2O–B2O3 and Li2O–B2O3, in which the maximum content of Me2O is 0.3 mol per 1 mol of B2O3. By subtracting the radial distribution functions of the Li2O–B2O3 samples from those of Na2O–B2O3 glasses having the same molar ratios, difference curves were obtained in which peaks coming from the distribution of nearest neighbor atoms around Na+ ions were observed. The quantitative analysis showed that the environment of Na+ ions is not a regular polyhedron. About 5.0–5.5 O atoms surround Na+ ions; on the average 3.4–3.6 O atoms are 2.40–2.44 Å distant from Na+ ions while 1.5–2.0 other O atoms are at a distance of 2.75–2.80 Å.
Orientational ordering in solid parahydrogen and orthodeuterium
Authors: Sprik Michiel , Klein Michael L.
Published: February 2003

The low-temperature pressure-induced orientational ordering transition in solid parahydrogen (p-H2) and orthodeuterium (o-D2) is investigated using a model consisting of quantum rotors on a rigid fcc lattice. A correlated variational wave function of the Jastrow type is used to describe the zero-point orientational fluctuations which inhibit ordering into a Pa3 structure. Using the bare electrostatic quadrupole–quadrupole interaction, the predicted ordering pressure for o-D2 is about half the experimental value; realistic intermolecular potentials, with anisotropic exchange repulsion, yield even lower estimates. Hence, at high pressure the hydrogen molecule appears more isotropic (spherical) than indicated by the model potentials used here. Possible explanations for this are discussed, a likely candidate being the assumption of a rigid lattice and hence the neglect of translation-rotation coupling.
Hydrogen bond statistics and dynamics in water: Self-diffusion and dielectric relaxation
Authors: Bertolini Davide , Cassettari Mario , Ferrario Mauro , Salvetti Giuseppe , Grigolini Paolo
Published: February 2003

Dynamical properties of water up to the supercooled region are analyzed by explicitly taking into account the dynamics of the hydrogen bonds. The H-bond dynamics is described by means of a stochastic variable η exploring different states according to the number of H bonds established by the tagged molecule with its neighbors. Application of the ‘‘reduced’’ model theory leads to a master equation for the long-time diffusional properties of water, depending only on meaningful physical quantities that are obtained either from experiments and computer simulations or on the ground of physical considerations. Dielectric relaxation and self-diffusion behaviors are successfully reproduced and also recent results from incoherent neutron scattering can be rationalized.
Enhancement of intramolecular vibrational energy transfer through rotational coupling
Authors: Clodius William B. , Shirts Randall B.
Published: February 2003

The classical effects of rotation on vibrational energy transfer have been analyzed using a model based on H2O and its deuterated analogs. This model examines the coupling of the two stretching modes when rotation in the plane is allowed but the bending mode is frozen. It is found that the effects of rotation can be significant but the nature of the effects depends on the details of the system. For example, an angular momentum of 30 ℏ greatly increases energy transfer for H2O but decreases energy transfer for D2O. An explanation for this difference in behavior is derived from the effect of rotation on the 1 : 1 vibrational resonance.
Measurements of the interfacial tension between nematic and isotropic phase of some cyanobiphenyls
Authors: Faetti S. , Palleschi V.
Published: February 2003

The interfacial tension γeq between nematic and isotropic phases of some cyanobiphenyls has been measured by using the sessile drop method. Values of γeq ranging from 0.7×10−2 to 1.8×10−2 erg/cm2 are obtained. In a recent paper we measured the optical reflectivity coefficients at the nematic–isotropic interface of 7CB. By using these coefficients and the measured value of γeq we can obtain the experimental value of the intrinsic thickness of the nematic–isotropic interface of 7CB. This thickness is compared with the one predicted by the Landau–De Gennes theory. A satisfactory agreement between experimental and theoretical values is found.
Uranium isotope effects in some ion exchange systems involving uranyl–carboxylate complexes
Authors: Kim Hwan Young , Kakihana Masato , Aida Masao , Kogure Kazumi , Nomura Masao , Fujii Yasuhiko , Okamoto Makoto
Published: February 2003

Isotope fractionation between uranyl complexes in aqueous solution and uranyl ions in cation exchange resin was experimentally studied. The isotope separation coefficients ε of the uranyl complex systems determined by a chromatographic method were (0.25±0.1)×10−4 (uranyl–chloride system), (0.88±0.1)×10−4 (acetate), (1.03±0.1)×10−4 (glycolate), (1.42±0.15)×10−4 (lactate), and (2.18±0.2)×10−4 (malate) at 25 °C. IR spectroscopic measurements were conducted on the uranyl complexes of which isotope effects were determined. It was found that the separation coefficients are linearly proportional to the shift of the asymmetric stretching vibration ν3 of O=U=O in uranyl complexes. The observed relation is ε=4.62×10−6 (960−ν3/cm−1). A theoretical treatment indicated that approximately one third of the observed isotope effects could be attributed to the asymmetric stretching vibration.
Fourier transform methods for calculating action variables and semiclassical eigenvalues for coupled oscillator systems
Authors: Eaker Charles W. , Schatz George C. , De Leon N. , Heller E. J.
Published: February 2003

Two methods for calculating the good action variables and semiclassical eigenvalues for coupled oscillator systems are presented, both of which relate the actions to the coefficients appearing in the Fourier representation of the normal coordinates and momenta. The two methods differ in that one is based on the exact expression for the actions together with the EBK semiclassical quantization condition while the other is derived from the Sorbie–Handy (SH) approximation to the actions. However, they are also very similar in that the actions in both methods are related to the same set of Fourier coefficients and both require determining the perturbed frequencies in calculating actions. These frequencies are also determined from the Fourier representations, which means that the actions in both methods are determined from information entirely contained in the Fourier expansion of the coordinates and momenta. We show how these expansions can very conveniently be obtained from fast Fourier transform (FFT) methods and that numerical filtering methods can be used to remove spurious Fourier components associated with the finite trajectory integration duration. In the case of the SH based method, we find that the use of filtering enables us to relax the usual periodicity requirement on the calculated trajectory. Application to two standard Henon–Heiles models is considered and both are shown to give semiclassical eigenvalues in good agreement with previous calculations for nondegenerate and 1:1 resonant systems. In comparing the two methods, we find that although the exact method is quite general in its ability to be used for systems exhibiting complex resonant behavior, it converges more slowly with increasing trajectory integration duration and is more sensitive to the algorithm for choosing perturbed frequencies than the SH based method. The SH based method is less straightforward to use in studying resonant systems, but good results are obtained for 1:1 resonant systems using actions defined in terms of the complex coordinates Q1±iQ2. The SH based method is also shown to be remarkably accurate in determining high energy eigenvalues (about three-quarters of the dissociation energy).
Kinetic theory of rotational relaxation in liquids: Smooth spherocylinder and rough sphere models
Authors: Evans Glenn T. , Evans David R.
Published: February 2003

The orientational correlation times for the single particle and the collective second rank Legendre polynomial are calculated for a dense fluid using Enskog kinetic theory. The rotating molecules are modeled as smooth spherocylinders and rough spheres. For rough sphere molecules, the dynamic part of the collective orientational time j2 is sensitive to anisotropies in the contact radial distribution function (rdf). Spherocylinder models exhibit dynamic as well as static contributions to j2 in that j2−1 is nonzero even if the rdf is isotropic. Like the smooth ellipsoid models, orientational correlation times derived from Enskog theory underestimate the friction on a molecule rotating in a liquid. Predictions of kinetic theory agree best with the results from molecular dynamics on smooth, hard spherocylinders.
EPR of Mn2+ in polycrystalline dolomite
Authors: Shepherd Robert A. , Graham W. R. M.
Published: February 2003

The EPR spectrum at 9.1 GHz of the M=1/2↔-1/2 transition for Mn2+ in polycrystalline dolomite has been studied using a detailed computer simulation of the line shapes in the powder pattern spectrum. The accuracy of the analytical procedure was verified for the spectrum of Mn2+ in calcite, yielding magnetic constants which were in excellent agreement with previous polycrystalline and single crystal results. The EPR parameters obtained for Mn2+ in dolomite are g=2.0020(2), A=−9.48(2) mT for Mn2+ substituted in the Ca lattice site and g=2.0028(2), A=−9.25(2) mT, D=14.60(5) mT for substitution at the Mg site.
Vibrational energy transfers from the v=1 level of HBr, HCl, and DF to the v=1 level of CO, NO, N2, and to the 001 level of CO2 and N2O: A rate constant calculation based upon long-range multipolar forces
Authors: Seoudi B. , Doyennette L. , Margottin-Maclou M.
Published: February 2003

Rate constants for far-from-resonance V–V transfers in HX–M and DF–M systems, with X=Cl and Br and M=CO, NO, N2, CO2, and N2O, have been calculated from the semiclassical method of Dillon and Stephenson: the transfer probability is calculated from an exponential form of the scattering operator, and long-range multipolar forces are assumed, involving not only interactions between vibrational transition moments but also interactions between permanent moments, the effect of which is to make the multiquanta rotational transitions efficient. The formalism, developed by these authors for HX–CO2 systems, i.e., for the case of a dipole–dipole vibrational interaction and a dipole–quadrupole rotational interaction, has been extended to other cases involving a dipole–quadrupole vibrational interaction or a dipole–dipole rotational interaction, in order to treat systems such as HX–N2 or HX–N2O systems. The computations have been performed for temperatures between 300 and 900 K. The comparison between calculated and experimental values shows that, as expected from the analysis of the experimental results, long-range multipolar forces play certainly a preponderant role in these transfers, all the more as the temperature is lower. The limits of the model are discussed.
Energy pooling reactions in the oxygen–iodine system
Authors: Lilenfeld H. V. , Carr P. A. G. , Hovis F. E.
Published: February 2003

The rate constant for the energy pooling reactions O2(1Δ)+O2(1Δ)→O2(1Σ)+O2(3Σ) and O2(1Δ)+I(2P1/2)→O2(1Σ)+I(2P3/2), were studied in the temperature range between 200–400 K. The room temperature rate constant for the former reaction was found to be (2.7±0.4)×10−17 cm3 molecule−1 s−1 and for the latter reaction was found to be (8.2±1.6)×10−14 cm3 molecule−1 s−1 in reasonable agreement with the previous determination by other workers. The temperature dependencies of both reactions are small over the range of interest.
A molecular beam study of electronic to electronic, vibrational, and rotational energy transfer in the collision of two step laser excited sodium with N2
Authors: Jamieson G. , Reiland W. , Schulz C. P. , Tittes H. U. , Hertel I. V.
Published: February 2003

The quenching of excited Na* (4d,5s,4p,4s) by N2 has been studied in a crossed atomic and molecular beam apparatus at thermal collision energies. The sodium atoms are excited by two laser beams of different wavelengths to either the 42D5/2 or 52S1/2 state, via the intermediate 32P3/2 state. For both excitation schemes optical relaxation processes lead to a population in the 42P3/2 and 42S1/2 states of several percent. The relative densities of the excited states have been calculated from rate equations using stationary conditions. The measured energy transfer spectra show high scattering intensities at low kinetic energies together with some structure at medium energies. This structure can be partially disentangled using the results of the previously studied Na*(32P3/2)+N2 quenching process. The main conclusion is that collisional deexcitation to the Na(3s) ground state is negligible, whereas among the higher levels the collisional energy transfer cross sections are between 0.5 and 7.5 times the magnitude of the 3p–3s quenching cross section and they are strongly forward peaked in the same way. Relative values for the differential quenching cross sections are reported.
Rate constants and branching fractions for xenon halide formation from Xe(3P2) and Xe(3P1) reactions
Authors: Lin Daimay , Yu Y. C. , Setser D. W.
Published: February 2003

The rate constants for XeF(B,C), XeCl(B,C), and XeI(B,C) formation from reactions of Xe(3P1) and Xe(3P2) with NF3, N2F4, NF2, CCl4, and CF3I have been measured relative to XeCl(B,C) formation from the reactions with Cl2. The XeCl(B,C) formation rate constants from Cl2 are assumed to equal the total Xe(3P2) and Xe(3P1) quenching rate constants. The dependence of the XeX* formation rate constants upon reagent for Xe(3P1) and Xe(3P2) are similar with the polyatomic reagents having considerably smaller XeX* product formation rate constants than does Cl2. The previous claim from this laboratory that the XeF(B,C) formation rate constant from NF3 was approximately equal to the total quenching rate constant is revised downward in this work.
The density matrix, density, and Fermi hole in Hartree–Fock theory
Authors: Dawson K. A. , March N. H.
Published: February 2003

In density matrix and density functional theory, one is concerned with methods that bypass explicit calculation of antisymmetric wave functions but nevertheless take full account of the Fermionic nature of the problem. The purpose of this paper is to examine two quite different approaches which achieve this aim. The first of these involves general many-electron theory and subsequent closure yielding an integrodifferential equation for the density matrix. Despite the interesting nature of this equation, analytical progress is hampered by its nonlinearity. Hence we have considered an alternative more practical variational procedure which, for some simpler systems, has the additional merit of yielding closed differential equations for the density.
Microwave–optical double resonance of DNO in the Ã 1A″ (000) state
Authors: Petersen J. C. , Amano Takayoshi , Ramsay D. A.
Published: February 2003

The microwave–optical double resonance technique has been used to observe rotational transitions in the Ã 1A″(000) state of DNO. Thirty-four rotational lines, including 101–000, 28 a-type, and three b-type transitions were observed in the frequency region from 3 MHz to 90 GHz. Most of the observed lines are found to be perturbed by a few to a few hundred MHz. Perturbations are found in transitions with K′a =0, 1, 2, and 3, and ‘‘extra’’ levels associated with the 93 levels of the excited state have been observed. Improved values have been obtained for the rotational constants B and C and for the centrifugal distortion constants δJ and δK.
The highly excited C–H stretching states of CHD3, CHT3, and CH3D
Authors: Voth Gregory A. , Marcus R. A. , Zewail A. H.
Published: February 2003

Unlike many other molecules having local modes, the highly excited C–H stretching states of CHD3 show well resolved experimental spectra and simple Fermi resonance behavior. In this paper the local mode features in this prototype molecule are examined using a curvilinear coordinate approach. Theory and experiment are used to identify the vibrational state coupling. Both kinetic and potential terms are employed in order to characterize the coupling of the C–H stretch to various other vibrational modes, notably those including D–C–H bending. Predictions are also made for CHT3 and the role of dynamical coupling on the vibrational states of CH3D explored. Implications of these findings for mode-specific and other couplings are discussed.
Photodissociation of cyanogen: Angle and velocity distributions of state resolved fragments
Authors: Eres Djula , Gurnick M. , McDonald J. D.
Published: February 2003

The disposal of excess energy above the dissociation threshold into internal excitation and translation in a photochemical decomposition of C2N2 has been determined by utilizing a technique by which measurements of the recoil velocity distribution for particular rotational states are possible. Simple phase space theory calculations appear to give a fairly good interpretation of the rotational energy distributions in a particular vibrational state, while the vibrational energy disposal is definitely nonstatistical with only about 63% of the total population predicted by statistical calculation in the first vibrational state and no excitation observed in the v=2 state. Our experimental results support the previous predictions of high translational energy disposal ( fT=75%) compared to a low or moderate product internal state excitations ( fR=18.6%, fv=6.4%). We also measure the dissociation energy of C2N2 to be 133±1 kcal/mol rather than the previously reported 128±1 kcal/mol.
The ‘‘Fraunhofer theory’’ of rotational inelastic scattering of He on small molecules
Authors: Faubel M.
Published: February 2003

The well-known Fraunhofer approximation provides a simple and direct qualitative physical explanation for the diffraction oscillations and the oscillation phase shift phenomena observed in differential rotational state to state scattering cross sections for He on a number of small molecules. This approximation has been further developed to yield a simple analytical expression for the angular dependence of the inelastic cross sections. For the experimentally and theoretically well investigated systems He–N2 and He–CH4 the Fraunhofer formula is found to reproduce the measured cross sections to within better than a factor of 2. For the investigated collision energy Ecm ≊30 meV (≊3 kJ/mol) the deformed sphere interaction potential model used in the Fraunhofer approximation appears to be closely related to the zero crossing equipotential line of the full interaction potential. The relationship to the cluster model of molecules composed of atomic hard spheres is discussed. The dependence of the rotational excitation on the interaction potential is shown to be primarily a dependence on the equilibrium positions of the atoms in the molecule.