bluuebunny/crossref_metadata_2025 huggingface dataset:
Some Remarks on the Semi- and the Nonempirical Values of the Slater-Condon Parameters and the Parametrization for the One-Center Electron Repulsion Integrals in the Semiempirical Molecular Orbital Method
Authors: Anno Tosinobu , Sakai Yoshiko
Published: February 2004

The difference which is present between the semi- and the nonempirical value of a Slater-Condon parameter (SCP) is discussed. It is pointed out that the nonempirical value which is to be compared with its semiempirical counterpart, must be determined with the same least-squares method as that used in the determination of the semiempirical values, by treating the Hartree-Fock (HF) total energy of each state of a configuration as the term value of the respective state, although it is usually determined for each of the states by a direct integration using the HF AO's appropriate to respective states. The data for the atoms and the ions having the electron configurations of 1s22sm2pn type show that the nonempirical value of an SCP thus determined for a particular configuration is more or less the same as that is obtained as the weighted mean of the values of the parameter determined for various states belonging to the configuration by integrations using HF AO's. The difference between the nonempirical value of an SCP thus obtained from the HF total energies and its semiempirical value obtained from the observed term values is analyzed with reference to the correlation energy of the atom in its various states of the configuration. Through this analysis, the semiempirical evaluation of the valence-state energy of an atom is critically considered and prescriptions for obtaining the most appropriate values of the one-center two-electron repulsion integrals in the semiempirical molecular orbital theory are given.
LiH Potential Curves and Wavefunctions for X 1Σ+, A 1Σ+, B 1Π, 3Σ+, and Π3
Authors: Docken Kate K. , Hinze Juergen
Published: February 2004

Ab initio multiconfiguration self-consistent-field calculations are reported for the potential curves and electronic wave functions of the states X 1Σ+, A 1Σ+, B 1Π, 3Σ+, and Π3 of LiH. In this calculation, the outer two electrons are correlated, while the 1σ shell, essentially a K shell on Li, is left uncorrelated. The obtained dissociation energies, with the known experimental values in parentheses, are De(X 1Σ+)=2.411(2.5154) eV, De(A 1Σ+)=1.048 (1.0765) eV, De(B 1Π)=0.017 (0.035) eV and De(3Π)=0.226 eV.
LiH Properties, Rotation-Vibrational Analysis, and Transition Moments for X 1Σ+, A 1Σ+, B 1Π, 3Σ+, and Π3
Authors: Docken Kate K. , Hinze Juergen
Published: February 2004

Using accurate ab initio calculated potential curves and electronic wavefunctions for the states X 1Σ+, A 1Σ+, B 1Π, 3Σ+, and Π3 for LiH, various properties were calculated. These include dipole and quadrupole moment, field gradient at the nuclei, etc. Rotation-vibrational wavefunctions were obtained and a rotation-vibrational analysis was carried out. Some of the properties obtained were averaged over the appropriate rotation-vibrational wavefunctions. In addition electronic transition moments were computed and from this uv and ir line strengths were obtained. In general the agreement with experimental values, where available, is satisfactory.
Diffusion Coefficient in an Ordered Binary Alloy
Authors: Kikuchi Ryoichi , Sato Hiroshi
Published: February 2004

The isotope diffusion coefficient of one of the components in a binary ordered alloy is derived for the vacancy mechanism by the path probability method. By introducing the concept of the transposed lattice and making full use of the symmetry of the system, the derivation is made transparent and simpler than the treatment reported previously. The new derivation leads quite naturally to decomposition of the correlation factor into two components related to the two sublattices; the decomposition leads to a detailed interpretation of the correlation factor. The vacancy availability factor and the effective jump frequency factor are defined and their importance in the diffusion in the ordered phase is pointed out.
Magnetic Field Dependence of I2 B-State Lifetimes
Authors: Capelle Gene A. , Broida H. P.
Published: February 2004

A shortening of I2(B 3Π0u+) fluorescence lifetimes has been observed upon application of a magnetic field and is a function of the vibrational level of the upper electronic state and of magnetic field strengths. A suggested process is predissociation, due to mixing by the magnetic field of a repulsive Ou− state with the B state.
Microwave Dielectric Constant and Conductivity Measurements in the Phthalocyanines
Authors: Abkowitz M. A. , Lakatos A. I.
Published: February 2004

Dielectric constant and loss measurements have been made on α, β, and X metal free and copper phthalocyanine at microwave frequencies. Measurements were carried out on pressed pellets of polycrystalline material. Dielectric constant data is analyzed in terms of a powder dielectric model. The relative dielectric conductivities of these phthalocyanines are examined along with similar measurements on various β transition metal phthalocyanines. Dielectric conductivities of these metal phthalocyanines appear to be consistent with dc conductivities reported in the literature.
Exact Solutions for Dynamics of Finite, Semi-Infinite, and Infinite Chains with General Boundary and Initial Conditions
Authors: Lee Keum H. , Kim Hyunyong
Published: February 2004

The exact analytic solutions in closed form for the dynamics of finite, semi-infinite, and infinite linear chains of identical masses and ideal springs are presented. In addition to the harmonic interaction between nearest neighbors, each particle is harmonically bound to its equilibrium position and is subjected to frictional and other external time-dependent forces. The motion of all the particles is expressed in terms of the given initial conditions and applied forces. In contrast with previous studies on the finite chains, very general (i.e., not necessarily ``periodic'') boundary conditions are used and the resulting solutions contain terms representing all the higher order multiple reflections from the two ends. The properties of the solutions are studied for all possible values of physical constants including the limiting values for uncoupled oscillators. By specializing some results of the present work, those of previous derivations on simpler systems by other authors are recovered. Some useful applications of the results are suggested.
Near Hartree-Fock Calculations on the Ground State of the Water Molecule: Energies, Ionization Potentials, Geometry, Force Constants, and One-Electron Properties
Authors: Dunning Thom. H. , Pitzer Russell M. , Aung Soe
Published: February 2004

Near Hartree-Fock wavefunctions have been calculated for the ground state of the water molecule using both Slater and contracted Gaussian basis sets. Total energies of −76.063 hartree were obtained with a (5s4p1d/3s1p) Slater basis and a [6s5p2d/3s1p] contracted Gaussian basis derived from an (11s7p2d/5s1p) primitive set; these energies are estimated to be within 0.003±0.002 hartree of the Hartree-Fock limit. The Hartree-Fock wavefunctions account for ∼70% of the dissociation energy of water. The Hartree-Fock vertical ionization potentials (in electron volts), 11.1(2B1), 13.3(2A1), and 17.6(2B2), are too low by 1–1.5 eV as expected. With the Gaussian basis set a potential surface was computed and the equilibrium geometry and harmonic force constants were calculated. The calculated bond length, 0.941 Å, and bond angle 106.6°, are in good agreement with the experimental values, 0.957 Å and 104.52°. In spite of the rather good agreement for the geometry, the force constants are in error by 15%–20%. This is attributed to an inadequancy of the Hartree-Fock model. A number of one-electron properties were also computed; they differ only slightly from those reported in earlier work and are in satisfactory agreement with experiment. Plots of the valence (canonical) molecular orbitals are given.
Heat Capacity near the Consolute Point in Solid CH4–Ar
Authors: Greer Sandra C. , Sengers J. M. H. Levelt , Furukawa George T.
Published: February 2004

Measurements are reported of the heat capacity at saturated vapor pressure (essentially Cp) of the system CH4–Ar near its solid-solid consolute point (62°K, 65% Ar). In contrast to the behavior of the heat capacity at binary liquid consolute points, where there are striking anomalies, no large increase was observed for CH4–Ar. An abrupt increase of only about 13% occurred in the heat capacity near the transition. The possibility that the anomaly is suppressed by lattice strain effects is discussed.
On the Energy Losses of Hot Atoms Colliding with Different Molecules
Authors: Alfassi Zeev B. , Amiel Saadia
Published: February 2004

Experimental α values for hot halogen atoms colliding with methyl halides disagree with the calculated values, assuming elastic collisions. This is attributed to the asymmetry of the target molecules which either render the interaction inelastic or are governed by a different scattering potential.
Singlet-Triplet Splitting in Diffusing Radical Pairs and the Magnitude of Chemically Induced Electron Spin Polarization
Authors: Adrian Frank J.
Published: February 2004

A previous theory of anomalous electron spin resonance spectra of free radicals in solution attributes the electron spin polarizations to the combined effects of singlet-triplet mixing by magnetic interactions in a diffusing radical pair and singlet-triplet splitting by the exchange interaction when, and if, the diffusing radicals reencounter each other. This theory is studied in more detail by considering the exchange interaction at all times during the diffusive trajectory of the radical pair, in contrast to the original treatment of approximating it as a rectangular pulse which is nonzero only briefly during the second encounter of the radicals. Time dependent perturbation theory is used to calculate the radical pair wavefunction and the corresponding electron spin polarization to first order in the exchange interaction. The polarization is averaged over all possible diffusion paths of the radicals by averaging the exchange interaction over the distribution of radical pair separations obtained by solution of the diffusion equation with appropriate boundary conditions. These boundary conditions take into account the facts that polarization begins when the radicals separate to a point where the magnetic and exchange interactions are roughly equal, and that the developing polarization is destroyed by spin exchange if the radicals subsequently come too close together. The calculated polarizations are of the right order of magnitude to account for the experimental results, and the dependence of the polarization on the magnetic interactions and the diffusion parameters is essentially the same as predicted by the earlier simpler theory.
On the O2+–C2D2 Reaction: An Endoergic Stripping Process
Authors: Chiang M. M. , Mahan Bruce H. , Maltz Charles
Published: February 2004

We have determined the product velocity vector distributions for the endoergic (ΔE0°=2.23 eV) atom abstraction reaction O2+(C2D2, C2D)O2D+ at a number of values of the initial relative energy. Deuterium atom abstraction occurs at higher energies by a spectator stripping process. An energy threshold for the zero angle reactive scattering process is observed when the energy of the O2+ projectile relative to the abstracted atom is equal to the endoergicity of the reaction. The results show that the spectator stripping process is not to be uniquely associated with exoergic reactions or those which proceed along monotonically decreasing potential energy surfaces.
Strengths and Collision Broadened Widths in the Second Overtone Band of Hydrogen Fluoride
Authors: Spellicy R. L. , Meredith R. E. , Smith F. G.
Published: February 2004

Individual line strengths and self-broadened half-widths have been measured in the second overtone band of hydrogen fluoride. The electric dipole matrix element for the band has been determined from the measured strengths. Its value is: 〈 3|μ(r)|0〉exp=+1.628× 10−21 esu· cm.The m dependence of the measured half-widths agree with the Anderson theory of collision broadening if off resonant collisions are taken into account.
Further Considerations on the Theory of Intermolecular Obstruction in Rubber Elasticity
Authors: Jackson Julius L.
Published: February 2004

An earlier theory which took into account intermolecular obstruction in rubber is reconsidered. On the basis of a revised procedure for counting configurations of polymer chains, a new equation of state is obtained relating stress to strain in uniaxial extension. The new relationship has the same from as a function of the strain but differs in its dependence on f, the fraction of the rubber volume occupied by the polymer chains. When applied to experiments, it leads to higher values of f. In addition, results presented previously only for uniaxial extension are generalized for arbitrary strains.
Semiempirical Scaled Molecular Orbital Theory
Authors: Matheu Federico M. , Ellison Frank O.
Published: February 2004

A new semiempirical scaled molecular orbital theory is developed. The valence MO's are constructed in the usual way as linear combinations of valence AO's. The basis AO's for each atom are defined as eigenfunctions of a prescribed atomic Hartree-Fock Hamiltonian operator; however, the corresponding eigenvalues are made consistent with atomic integrals (one-electron kinetic and electron-nuclear attraction, two-electron Coulomb and exchange) determined by calibration of a semiempirical scaled atomic orbital model to experimental atomic spectra (for neutral, positive, and negative ions). In the molecule, valence AO's belonging to a given atom (or set of equivalent atoms) have an associated independent variable scaling factor. The explicit dependence of matrix elements of the Hartree-Fock Hamiltonian operator upon these scale factors is developed. The total energy of the molecule can then be minimized with respect to simultaneous variations of the scale factors. New approximate and semiempirical expressions are suggested for the non-one-center integrals which are needed in such MO theories. A generalization of Dewar's ``half-electron'' method is utilized which enables smooth application of the model to open-shell as well as closed-shell states. Preliminary calibration and initial tests of the model on various ground and excited states of small molecules and their ions are described.
Rotational-Vibrational Energy Transfer. Dynamics of a Rotating Anharmonic Four-Atom Molecule
Authors: Hung Narl Chow
Published: February 2004

The rotational-vibrational energy transfer in a four-atom linear symmetrical molecule with three Morse bond stretching potentials is investigated. The percentage transfer of rotational energy corresponding to each ER extremum and the time average rotational and vibrational potential energies were computed numerically.
Enthalpies of Mixing in the Binary Liquid Systems Alk(Cl–Br), Alk(Cl–I), and Alk(Br–I)
Authors: Melnichak M. E. , Kleppa O. J.
Published: February 2004

The enthalpies of mixing in the A(X–Y) binary liquid alkali halide mixtures have been measured by high-temperature reaction calorimetry (A denotes Li–Cs; X, Y denote Cl, Br, I). All the considered systems have positive enthalpies of mixing with maximum values which range from about +4cal/mole for Cs(Cl–Br) to about +117 cal/mole for Na(Cl–I). The molar enthalpies of mixing can be represented by the semi-empirical relations, Δ HM≅ N1N2Aδ122.In this expression, N1 and N2 are the mole fractions of the two components; δ12=(d1−d2)/d1d2, where d1 and d2 are the interionic distances characteristic of the two salts; A is a constant which for Li as a common cation is about +125 kcal·Å2/mole; for Na, K, Rb, Cs, A ≈ +250 kcal·Å2/mole. An excellent correlation is found between the positive enthalpies of mixing and calculated values derived from estimates of the London-van der Waals' interaction between second-nearest-neighbor anions. However, the observed values are about 5 times larger than the calculated ones. It is possible that this may be due to use of too low values for the characteristic energy in the London expression.
Re-examination of the Kirkwood-Westheimer Theory of Electrostatic Effects. I. Calculation of the ``Effective'' Dielectric Constant
Authors: Edward J. T. , Farrell P. G. , Job J. L.
Published: February 2004

The value of the ``effective dielectric constant,'' Deff, for an ellipsoidal cavity in the Kirkwood-Westheimer theory of substituent effects upon acid dissociation constants depends critically upon the evaluation of Legendre functions of the second kind, and recalculation of Deff gives results differing considerably from those of the original authors. These results are presented here and in all cases Deff is less than the solvent dielectric constant. Using these Deff values, end-to-end distances in charged chain molecules are shown to be in accord with maximum chain extension.
Two-By-Two Rotation Method Applied to Selected Multiconfiguration Wavefunctions
Authors: Chang T. C. , Grein F.
Published: February 2004

General expressions are derived for the optimization of orbital coefficients by the two-by-two rotation (2× 2) method in the case of multiconfiguration (MC) wavefunctions of pair-excitation type. Computational examples are given for the He and Be atoms. Application to bigger systems is straightforward and simple. The 2× 2 equations for MC wavefunctions containing single excitations have to be derived from case to case. As an example, the all-single-excitation wavefunction for He is considered. The 2× 2 method, although straightforward, is rather lengthy. It presented no convergence difficulties.
Study of Excitation Transfer in a Flowing Helium Afterglow Pumped with a Tuneable Dye Laser. II. Measurement of the Rate Coefficient for the Rotational Relaxation of He2(3p 3Πg)
Authors: Collins C. B. , Johnson B. W.
Published: February 2004

The rotational relaxation of the He2(3p 3Πg) state is examined by optically pumping a flowing helium afterglow with a tuneable dye laser. The population of the J = 8 rotational state is enhanced by optically saturating the R7 component of the transition connecting this state with the metastable He2(2s3Σu+) molecular state. From the lifetime and yield of the Q7 component, the rate coefficient for the rotational relaxation via the forbidden ΔJ = 1 channel is determined to be of the order of 2× 10−11 cm3/sec. It is found that this represents about half of the total rate of rotational relaxation in this state.
High Temperature Enthalpies of Binary Dodecaborides
Authors: Mar R. W. , Stout N. D.
Published: February 2004

The enthalpies of three dodecaborides have been determined from 1300 to 2200°K by a drop calorimetric technique. The enthalpies were fitted with the Shomate function to give Zr0.6Y0.4B12:HT−H298=4.204× 101T+1.260× 10−2T2−(2.528) 106T−1−5.175× 103 cal/mole,ErB12:HT−H298=3.947× 101T+1.357× 10−2T2−(2.706) 106T−1−3.896× 103 cal/mole,UB12:HT−H298=4.232× 101T+1.399× 10−2T2−(2.430) 106T−1−5.713× 103 cal/mole.Minor differences between the enthalpies of these dodecaborides were analyzed and correlated with different electronic conduction contributions, which can be predicted from the valence states of the metal atom. The metal atoms achieve their usual chemical valency by donating two electrons to the boron lattice, and the remainder to a conduction band. The uranium atoms in uranium dodecaboride appear to exist in the +5 and/or +6 states, whereas the +3, +4, and +3 states of erbium, zirconium, and yttrium are most probable.
Loge Localization Analysis of Diatomic Molecules: Li2 and F2
Authors: Hernandez Antonio , Ludeña Eduardo V.
Published: February 2004

The electronic wavefunctions of Das for Li2, and of Das and Wahl for Li2 and F2 have been employed in order to obtain optimum loges for these molecules. Loge probabilities of ascribing two electrons in each one of the atomic core loges V1 and V2 and the remaining n–4 electrons in the molecular bond loge V3 were maximized by varying the radii of the core loges which we have assumed to be spherical and to be centered at the nuclei. The bond loge V3 was taken to be the complementary volume to the core loges. For Li2 we have obtained the following values for the radii R0 and the probability P:R0=1.6846 and P=0.8915 for Das' function; for Das and Wahl's functions we obtained R0=1.6776 and P=0.8866 for Li2 and R0=0.3281 and P=0.4265 for F2. A loge analysis in which four electrons were ascribed to each of the core loges of F2 lead to very low probability values. In view of these results, the localizability of electron groups in these molecules is discussed.
Rate Measurements on OH + NO + M and OH + NO2 + M
Authors: Westenberg A. A. , deHaas N.
Published: February 2004

Measurements of the termolecular rate constants for OH+NO+M→ NHO2+M(k1) and OH+NO2+M→ HNO3+M(k2) in a fast flow reactor with ESR detection of OH decay are reported. The method was to add large excesses of either NO or NO2 to OH generated by the reaction H+NO2→ NO+OH so that pseudo-first-order OH decay resulted. Experiments over a pressure range of 0.5–5 torr for M = He gave the results k1 = 4.7, 2.9, and 1.3×1017, and k2=7.3, 5.7, and 2.1× 1017 cm6 mole−2 · sec−1 at 273, 298, and 395°K, respectively. Data at 298°K for M = Ar were about a factor of 2 lower for both reactions.
Role of Time Delay in Chemical Reaction Rates
Authors: van Santen Rutger A.
Published: February 2004

Using the concept of resonant states, the expressions for the rate of association and dissociation are derived. A density matrix formalism is developed, which enables us to discuss the conditions for which conventional expressions of the reaction rates are valid. It is shown that an Arrhenius type expression is only valid if the widths of the resonant states are larger than π kT, which implies that the decay of resonant states is independent of the way they are formed. As long as this condition and the steady state assumption holds for the concentration of molecules in resonant states, the interference effects of overlapping resonances are found to vanish. The connection with transition state theory is derived. General new expressions valid for all pressures are presented. The role of time delay in them is discussed.
Spectroscopic Studies of the Symmetric O–H–O Hydrogen Bonding in CsH(CF3CO2)2 and KH(CF3CO2)2
Authors: Miller Philip J. , Butler R. A. , Lippincott E. R.
Published: February 2004

The infrared spectra of thin films and the Raman spectra of single crystals of CsH(CF3CO2)2 and KH(CF3CO2)2 and their deuterated analogs are reported. The vibrational assignments are given for all the vibrations involving the very short (O··· O= ∼ 2.40 Å) symmetric O–H–O hydrogen bond. The O··· O stretching mode (∼798 cm−1 for the Cs+ salt; ∼792 cm−1 for the K+ salt) appears to be much less anharmonic than the OHO asymmetric stretching mode, as may be predicted from a Lippincott-Schroeder potential function. This O··· O stretching mode is the first to be reported for the symmetric O–H–O hydrogen bond in a Raman spectrum.
Monte Carlo Estimation of the Free Energy by Multistage Sampling
Authors: Valleau J. P. , Card D. N.
Published: February 2004

A method is described for estimating the free energy and entropy of an assembly of particles. This is done by using Metropolis Monte Carlo techniques to generate energy distributions from which we may calculate the absolute volume of configuration space corresponding to a given energy, and thus the configuration integral. One incidentally obtains the thermodynamic quantities over a wide range of reduced temperature. It is particularly easy to apply the method to particles having hard cores, and calculations are reported for hard spheres with Coulombic forces.
Application of the Debye-Waller Theory to Atomic and Molecular Scattering from Solid Surfaces
Authors: Weinberg W. H.
Published: February 2004

The Debye-Waller theory is applied to atomic helium scattering from various solid surfaces. The theory agrees well with all experimental data currently available with which comparisons may be made, namely, helium scattering from silver, platinum, tungsten, and tungsten carbide surfaces. Qualitative agreement is obtained between the surface Debye temperature of the materials cited above found from the helium scattering data and deduced from LEED measurements. Alternatively, if the surface Debye temperature obtained from LEED data is used in conjunction with the Debye-Waller theory for atomic scattering, the interaction energy between helium and the solid surfaces may be calculated. Very reasonable values of this interaction energy are obtained in this way. The theory is also applied to the interaction of molecular hydrogen and a silver surface, and a gas-surface potential well depth of ∼500 cal/mol is calculated.
Molecular Beam Study of the K+CH3I Reaction: Energy Dependence of the Detailed Differential Reactive Cross Section
Authors: Rulis Alan M. , Bernstein Richard B.
Published: February 2004

A molecular beam study has been carried out on the reaction of a velocity-selected K beam with a crossed beam of CH3I (from a glass capillary-array source). Velocity analysis of the angular distribution of the reactively scattered KI has yielded detailed differential cross sections at three incident relative kinetic energies Ē= 1.77, 2.80, and 3.71 kcal/mole. The center-of-mass (c.m.) differential cross sections were obtained from the lab data by a least-squares computer ``inversion'' program providing for deconvolution of beam velocity distributions. The c.m. cross section is ``backward'' peaked (KI recoiling opposite to the incident K, in accord with the literature) with a very sharp (30%–40% FWHM) recoil velocity distribution which maximizes at 80% of the energetically allowed KI recoil velocity. This distribution shifts systematically to higher velocities with increasing incident collision energy. Averaging over all angles yields an overall product c.m. translational energy distribution which shifts upwards as the incident translation energy is increased. The average energy released into relative product translation varies from 15 to 17.5 kcal/mole over the above range of Ē; the average fraction of the total available energy released is ≈ 0.58. thus incident translational energy is efficiently converted to relative translational energy of product recoil. The detailed differential cross sections at each energy were scaled relative to one another and suitably integrated to yield relative values of the total reactive cross section. The present results confirm previous observations of an increase in reaction cross section with increasing Ē up to ≈ 4 kcal/mole.
Infrared Pressure Broadening in the ν6 Band of Propynal
Authors: Nowak A. V. , Steinfeld J. I.
Published: February 2004

Pressure broadening of individual rotation-vibration lines in the ν6 band of propynal has been measured. The pressure dependence of the extinction coefficient was measured for a line coinciding with the P(12)CO2 laser line at 951.193 cm−1. The line shape was measured directly, using a tunable lead—tin—telluride diode laser, for a different line near 942.8 cm−1. A broadening parameter of (64±25) MHz/torr, corresponding to an optical diameter of (20±4) Å, was found in the first case, and values of (22±4) MHz/torr and (12±1) Å in the second.
Charge Carrier Mobilities in Periodic DNA Models
Authors: Suhai Sándor
Published: February 2004

The drift mobility of electrons and holes has been calculated for various periodic DNA models using LCAO crystal orbitals and applying the variational method of transport theory. Since the energy bands are narrow, inelastic electron-acoustic phonon scattering has been taken into account for all states of the first Brillouin zone including normal and Umklapp processes. The mean free paths of the charge carriers have been estimated too, to test the consistency of the delocalized description. The mobility values obtained for 300°K lie between 30–100 cm2 V−1·sec−1 for models with bandwidths of 0.1–0.3 eV and between 4–20 cm2 V−1· sec−1 for those with bandwidths of 0.02–0.1 eV, respectively. The temperature dependence follows the T−n law with n = 1.5–2 for the former and with n=2–2.5 for the latter group. The calculated mean free paths show real delocalization for the relatively broader bands, but the application of the band model seems to be questionable for the extremely narrow band cases.
Constant Acceleration Approximation in Collision-Induced Absorption
Authors: Miller M. S. , McQuarrie D. A. , Birnbaum G. , Poll J. D.
Published: February 2004

In terms of the constant acceleration approximation, introduced by Oppenheim and Bloom in 1961, the line shapes occurring in collision-induced absorption have a simple form that is suitable for numerical calculation. To test the reliability of the constant acceleration approximation in describing the appropriate time dependent distribution function, we compare a particular line shape in this approximation with the direct computer calculation of McQuarrie and Bernstein. A similar comparison with the experimental results of Bosomworth and Gush is also made. From both comparisons it follows that the constant acceleration approximation, as applied to a short range intermolecular interaction, is poor at all frequencies.
Convergence and First-Order Approximation of the Fugacity Expansions for Physical Adsorption
Authors: Abdallah A. A. , Bakri M. M.
Published: February 2004

Introducing a one-dimensional Mayer-type function for the absorptive potential, the cluster integrals are rewritten as finite sums. Approximating the cluster integrals by their leading terms, expressions are obtained for the specific amount of adsorption, the spreading pressure, and the local densities and pressures inside the surface and the adsorption layers. The equation of state inside the adsorption layer retains, in this approximation, the same form as in the case of the isolated gas. A criterion for the absolute and uniform convergence of the approximated fugacity expansions is obtained.
Simple Model of the Dynamic Jahn-Teller Effect in Six-Coordinated Copper(II) Complexes
Authors: Wilson Douglas G. , Lohr Lawrence L.
Published: February 2004

A model potential is assumed for describing the vibrational degrees of freedom associated with the Jahn-Teller effect in six-coordinated copper (II) complexes. The pseudorotational limit is characterized by a potential that is constant in the region between two concentric cylinders, but becomes infinite elsewhere. The energy spectrum is obtained for both angular and radial excitations. A square-well periodic angular potential is applied as a perturbation, yielding a localization of states. The results are used to describe the temperature dependence of the electron spin resonance spectra of copper (II) complexes with emphasis on the system NaCl:Cu(II) containing the hexachlorocuprate (II) complex.
Statistical Mechanics of Adsorption from Dilute Liquid Solution
Authors: Radke C. J. , Prausnitz J. M.
Published: February 2004

Following the work of Hill, the McMillan-Mayer theory of dilute solutions is used to derive an adsorption ``virial'' equation where the number of solute moles adsorbed is given by a power series in the liquid-phase concentration. The virial coefficients are related to potentials of mean force. The theoretical analysis is used to reduce experimental data for adsorption on carbon for organic solutes from dilute aqueous solution. The adsorption virial equation is readily extended to multisolute systems.
Matrix ENDOR Linewidths of Trapped Electrons in Glassy Matrices at 77°K
Authors: Helbert John , Kevan Larry , Bales Barney L.
Published: February 2004

Matrix ENDOR lines of protons associated with trapped electrons in γ-irradiated glassy matrices of 10M NaOH, methanol and 2-methyltetrahydrofuran at 77°K have been observed. By analysis of the matrix ENDOR line shapes under comparable experimental conditions the linewidth has been related to the spatial extent of the ground state wavefunction of the trapped electron. These experimental results are compared with predictions of the semicontinuum model for trapped electrons and found to be in good agreement.
Theoretical Critical Configuration for Ethane Decomposition and Methyl Radical Recombination
Authors: Hase W. L.
Published: February 2004

A theoretical critical configuration is described which yields calculated rate parameters in agreement with those measured for both the decomposition and recombination reactions in the ethane-methyl radical system. It is shown that if structural effects in the molecule are considered as the reaction co-ordinate is extended, this critical configuration is nearly identical to one determined by using the concept of minimum state density.
Excitation Transfer and Penning Ionization Reactions between Helium Metastables and Carbon Monoxide
Authors: Hurt W. B. , Grable W. C.
Published: February 2004

Absolute intensity measurements have been made of the radiating states of the carbon atom and carbon monoxide ion produced in a flowing afterglow by the reaction, He(2 3S)+CO. These measurements coupled with absorption measurements of the He(2 3S) and CO densities are sufficient for calculating the rate constants for the production of the excited products mentioned above. It is found that of the total reaction rate between He(2 3S) and CO, 4% of this rate corresponds to the production of a dissociated CO molecule with the carbon atom in an excited state and, the remaining percentage of the total rate corresponds to Penning reactions into the three energetically available electronic levels of CO+ with about equal probabilities.
Structure of Methylchlorosilyl Radicals
Authors: Hesse C. , Leray N. , Roncin J.
Published: February 2004

The 29Si coupling constants a have been measured for methylchlorosily radicals in a number of solid matrices. The structure of these radicals deviates more and more from the planar one with the degree of CH3 substitution by a chlorine atom. Correlation found between the change in the value of a29Si coupling constant of a radical and the dipole moment of the molecules of the trapping matrix leads us to the hypothesis of a high value of a29Sipol for the silyl radical.
Reactions of C+ with Ethane, Ethylene, and Acetylene
Authors: Lindemann Ellen , Rozett R. W. , Koski W. S.
Published: February 2004

The ion-molecule reactions of C+(2P) with ethane, ethylene, and acetylene in the gas phase have been investigated over a projectile energy ranging from a few to 100 eV. Ions with one, two, and three carbon atoms and a varying number of hydrogen atoms were observed. The behavior of the cross sections as a function of kinetic energy of the incident ion was used to infer reaction mechanism. The energetics of the processes were the most dominant parameters determining the courses of the reactions.
Torsion-Vibration-Rotation Interactions in Methanol. III. Barrier Height in an Excited Vibrational State of CH3OH
Authors: Lees R. M.
Published: February 2004

A weak Q branch starting with a J =1 line at 26 256.80 MHz has been observed in the microwave spectrum of normal methanol. We have assigned this Q branch to the K=0← 1 E2 transition in an excited vibrational state, on the basis of the Stark effects and the observation of the 11← 00 and 10← 00 E2 lines at 21 900.08 and 48 156.93 MHz, respectively. The excited vibrational state has an energy of 933± 150 cm−1, and is most probably the CH3 in-plane rocking mode. A value for the excited state barrier to internal rotation of 557± 35 cm−1 is required to reproduce the Q-branch origin frequency, if reasonable limits on geometry changes are assumed. This is an increase of 50% over the ground state value of 376 cm−1.
Magnetic Structure of ErAg2
Authors: Atoji Masao
Published: February 2004

A neutron powder diffraction study has been made of the magnetic properties of ErAg2 (the tetragonal body-centered CaC2-type structure) at temperatures between 297 and 1.5°K. At 5.2°K, the onset of an incommensurate, sinusoidal moment alignment takes place (the α structure). The α magnetization wave propagates along the a axis and the α wavelength is 6.345 Å =1.277 a, all in the face-centered lattice description. The x(∥ a) and y(∥ b) components of the α wave amplitude are approximately equal, while the z component is essentially zero. At 3.5°K a commensurate magnetization wave starts to grow (the β structure). The β wave propagates also along the a axis and the β wavelength is equal to the a spacing. In further cooling below 3.5°K, the x component of the α amplitude decreases rapidly and diminishes completely below 1.5°K, while the y component retains its 3.5°K value down to 1.5°K. The maximum x component of the α amplitude is 5.3 μB at 3.5°K and the maximum y component takes the same value at 3.5–1.5°K. No significant variation was observed on the α wavelength at 4.8>T>1.5°K. Regarding the β moment, the x component is predominantly larger than the y component and the z component is undetectably small. The β moment components follow the Brillouin-type magnetization and the moment values extrapolated to 0°K are approximately 6 and 3 μB for the x and y components, respectively. The composite configuration of the α and β waves portrays an antiferromagnetic stacking of the distorted fan-type moment arrays.
Raman Phonon Spectra of Isotopic Mixed Naphthalene Crystals: Librational Exciton Model and the Amalgamation Limit
Authors: Prasad Paras N. , Kopelman Raoul
Published: February 2004

We present an experimental Raman study of lattice modes in neat and mixed (10%–90%) crystals of naphthalene-h8 and naphthalene-d8 at 100°K with 1 cm−1 resolution. The spectral features of the neat crystals are preserved in the heavily doped mixed crystals, with small shifts and broadenings characteristic of an amalgamation limit that assumes weakly coupled excitation bands in the restricted Frenkel-Davydov limit. Rotation-translation interaction does not affect the mixed crystal spectra, thus making the Raman technique uniquely suited for the investigation of the librational (rotational) phonon band structure. The evidence is against localized or pseudolocalized phonons in these isotopic mixed crystals.
Scattering of Thermal Helium Atoms from a Mercury Film Deposited on a Lithium Fluoride Substrate
Authors: Mason B. F. , Williams Brian R.
Published: February 2004

Films of mercury were deposited on a lithium fluoride substrate in an attempt to observe diffraction phenomena in the scattering pattern of helium atoms. No diffraction effects were observed. A large variation of the elastic (00) peak with surface temperature was observed and an attempt was made to use this information in discussing the Debye-Waller effect. A large component of inelastic scattering was observed and reasons have been presented to account for its wide distribution in space. Also studied was the scattering behavior of helium atoms from partially continuous mercury films at various stages in the nucleation process.
Self-Diffusion Coefficients and Rotational Correlation Times in Polar Liquids. IV. Dichloromethane and Pyridine
Authors: O'Reilly D. E. , Peterson E. M. , Yasaitis E. L.
Published: February 2004

Self-diffusion coefficients (D) have been measured in dichloromethane and pyridine from the freezing points to the normal boiling points. The data for CH2Cl2 are represented by D=(2.3± 0.6)10−3exp[−(2.40± 0.15)/RT] cm2sec−1, and the data for C5H5N are given by D=(5.9± 1.5) × 10−3exp[−(3.45± 0.15)/RT] cm2sec−1. Intramolecular proton, deuterium, and chlorine-35 relaxation rates were measured in dichloromethane from 178 to 310°K. The results demonstrate that the rotational correlation time is anisotropic; the proton and chlorine values differ by a factor of 2. The activation energy for relaxation is essentially the same for H, D, and Cl and equal to 1.81± 0.08 kcal mole−1. The present relaxation results and the relaxation data of Kintzinger and Lehn on pyridine are interpreted by means of the quasilattice random flight model generalized to the case of anisotropic rotators. The agreement between the calculated and observed relaxation rates is good for pyridine and fair for CH2Cl2. Calculated pre-exponential factors D0 are 1.8× 10−3 cm2sec−1 for CH2Cl2 and 2.5× 10−3 for C5H5N.
Monte Carlo Calculations of Reaction Rates and Energy Distributions Among Reaction Products. I. F+H2→HF+H
Authors: Wilkins Roger L.
Published: February 2004

A three-dimensional, classical trajectory calculation is made of the collision dynamics of the reaction F+H2(v, J)→HF(v′, J′)+H by means of the London-Eyring-Polanyi-Sato (LEPS) potential energy surface. Monte Carlo procedures are used to start each collision trajectory. A discussion is presented of the temperature dependence of the relative rates of formation of vibrationally excited hydrogen fluoride. By means of this calculation, it can be predicted that 71% of the mean fraction of available energy will become vibration in HF, 10.5% will become rotation in HF, and 18.5% will become translation in the product. The probability that direct chemical reaction between atomic fluorine and molecular hydrogen will lead to the formation of the product HF molecule in the ground vibrational state v′=0 was found to be zero. The ratio k(v′=3)/k(v′=2) appears to be independent of temperature and has a value of 0.49, which is in excellent agreement with available experimental data. The ratio k(v′=2)/k(v′=1) has a slight temperature dependence, which would indicate that the improved or increased inversion could be achieved at low temperatures. Reaction rate constants are presented for reactions directly into specific vibrational and rotational states of the product HF molecule. Translational energy distributions of the products are compared with available experimental data.
Electronic Absorption Spectra of 3-Methyldiazirine and 3-Methyl-d3-Diazirine
Authors: Robertson L. C. , Merritt J. A.
Published: February 2004

The high resolution electronic absorption spectra of 3-methyldiazirine and 3-methyl-d3-diazirine are presented. A vibrational analysis is given for the allowed A″(nπ*1)←1A′ electronic system of each molecule, and a 0–0 band is assigned at 29 201 cm−1 for 3-methyldiazirine and at 29 228 cm−1 for 3-methyl-d3-diazirine. Evidence is also presented for a possible second electronic system to the red of the allowed singlet-singlet system of each molecule. The ν4′ symmetric N=N stretching vibration is the most prominent feature in all the electronic systems.
Photoelectron Spectroscopic Investigation of the Electronic Structure of Nitromethane and Nitrobenzene
Authors: Rabalais J. W.
Published: February 2004

The electronic structure of nitromethane and nitrobenzene has been studied by high-resolution HeI photoelectron spectroscopy and quantum chemical calculations of the INDO type. The spectra of CH3NO2 and CD3NO2 exhibit six ionization bands below 21 eV. The transitions to the ground and first excited ionic states have extensive vibrational structure which has been identified as the symmetric NO2 bending mode. The spectra of C6H5NO2 and C6D5NO2 contain at least 10 ionization bands below 21 eV with resolved vibrational structure only in the transition to the ground ionic state. The most loosely bound MO of nitromethane has been identified as the 5a1 NO2–σ bonding orbital, and that of nitrobenzene as the b1 ring-π orbital. The nonbonding a2 π orbital has been assigned to the second and fourth ionization bands in these respective molecules. Using the MO ordering found here, the 198 mμ absorption band of nitromethane is assigned to the π*(2b1)← σ(5a1) transition and the long wavelength bands of nitrobenzene are assigned to π*← π transitions, one of which involves intramolecular charge transfer from the phenyl ring to the NO2 moiety.
Use of X-Ray Photoelectron Spectroscopy to Study Bonding in Cr, Mn, Fe, and Co Compounds
Authors: Carver J. C. , Schweitzer G. K. , Carlson Thomas A.
Published: February 2004

The photoelectron spectra of some 40 transition metal compounds have been measured using AlKα(1487 eV) and MgKα(1254 eV) x-rays. The compounds included both simple salts (halides and chalcogenides) and hexacoordinated complexes (cyano- and fluoro-) of Cr(III), Mn(II, III), Fe(II, III), and Co(III). From these data we have determined the chemical shifts of the core electrons and related these results to a calculated charge based on Pauling's electronegativities. In addition, multiplet splitting has been obtained for photoionization in the 3s shell and is discussed in terms of the exchange interaction between the partially filled 3s and 3d orbitals. To help in this explanation, calculations were made using both (1) Hartree-Fock solutions of the wavefunctions for free ions and (2) a qualitative evaluation of the behavior of the exchange integral. The value of using x-ray photoelectron spectroscopy for studying chemical bonding for transition metal compounds is amply illustrated.
Optical Emission from O(1D) and O2(b 1Σg) in Ultraviolet Photolysis of O2 and CO2. II
Authors: Clark I. D. , Noxon J. F.
Published: February 2004

Improved optical techniques have been applied to the detection of excited states produced by uv photolysis of O2 and CO2; this has led to a revision of some of the results reported in an earlier paper by Noxon. We now find quenching of O(1D) by CO2 to be somewhat faster than by O2 or N2, in agreement with most other investigations. Improved measurements of O(1D) emission in O2 photolysis have been made but we have been unable to repeat the observation of emission from O(1D) and O(1S) in CO2 photolysis reported earlier.
Optical Spectrum of Nd3+ in Oxidized Calcium Fluoride
Authors: Toledano J. C.
Published: February 2004

The optical spectra of calcium fluoride crystals doped with Nd2O3 or NdOF are analyzed. Four oxygen-compensated sites are identified by their fluorescence lines. One site, assumed to possess C3v symmetry is considered more carefully, and a Stark-level scheme built for 16 multiplets.
Determination of Interatomic Potentials by the Inversion of Elastic Differential Cross Section Data. II. ArH+ at 5 eV
Authors: Klingbeil Ralph
Published: February 2004

A set of phase shifts corresponding to the elastic scattering of protons off of argon is extracted from 5 eV differential cross section data. The phase shifts are inverted to a numerical potential. A critical discussion of the results of other methods used to deduce the ArH+ internuclear potential is given.
Observations Concerning the Nuclear Quadrupole Coupling Constants of the Alkali Halides
Authors: Peters A. W. , Todd J. E.
Published: February 2004

It is shown that a model including antishielding and pπ polarization effects can account for the nuclear quadrupole coupling constant at the halogen nucleus of the alkali halides in both ground and excited vibrational states.
ENDOR Studies in Molecular Crystals. II. Computer Analysis of the Polycrystalline ENDOR Spectra of Low Symmetry Materials
Authors: Dalton Larry R. , Kwiram Alvin L.
Published: February 2004

The quantitative simulation of the electron nuclear double resonance (ENDOR) spectra of low-symmetry, randomly oriented molecules is discussed with particular attention paid to those systems where electron cross relaxation effectively couples the spin packets of the electron paramagnetic resonance (EPR) spectrum. ENDOR transition frequencies are calculated employing the high field approximation; frequency shifts arising from g anisotropy and the SxIx and SyIy terms of the hyperfine Hamiltonian are then evaluated by perturbation theory. ENDOR signal intensities are considered to be determined by transition moments and by electron and nuclear spin relaxation processes. The ENDOR spectra of polycrystalline samples of the x-irradiated aliphatic diacids, HOOC(CH2)nCOOH where n=1 to 8, and the alicyclic diacids, (CH2)mC(COOH)2 where m=2 to 4, have been recorded at 4.2°K and theoretical spectra computed. Reasonably good agreement is observed between experimental spectra and spectra computed assuming complete coupling of the spin packets by cross relaxation and isotropic relaxation rates. These assumptions are compatible with pulsed microwave measurements of electron relaxation rates.