bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamic properties of a hard sphere fluid with temperature dependent effective hard sphere diameter
Authors: Wilhelm Emmerich
Published: February 2004

The residual thermodynamic quantities for a rigid sphere fluid with temperature dependent hard sphere diameter have been calculated with an analytical equation of state (Carnahan-Starling). The incorporation of the coefficient of thermal expansion of the effective hard sphere diameter, l=(dσ/dT)σ−1, results in the appearance of internal energy U* and heat capacity CV*. These and other quantities are reported for a wide range of fluid density. By using parameters pertaining to liquid argon, CV* was calculated for the corresponding hard sphere fluid over a large temperature interval (Tt<T<0.9Tc) and then compared to experimental data of argon. The agreement is regarded as being satisfactory.
On the recognition of identical graphs representing molecular topology
Authors: Randić Milan
Published: February 2004

A procedure that can establish the identity of apparently different graphs is given. When certain instructions are followed, any adjacency matrix can be brought by permutations of rows and columns to a prescribed standard form, which is defined by a unique numbering of vertices. Identity of two graphs may then be established by a direct comparison of the transformed adjacency matrices. This approach is simple and practical. Furthermore, the associated unique numbering of atoms in a molecule may in itself be of significance for chemical nomenclature. Several molecular graphs describing polycyclic hydrocarbons illustrate the numbering procedure. The systematic generation of all structures having any prescribed number of vertices and edges is possible by adopting the present scheme of numbering of graphs. This is illustrated for systems having four and five vertices (atoms).
Some features of vibrational relaxation of a diatomic molecule in a dense medium
Authors: Nitzan Abraham , Mukamel Shaul , Jortner Joshua
Published: February 2004

In this paper, we consider some experimental implications of a theory [Mol. Phys. 25, 713 (1973)] of vibrational relaxation of a guest molecule in a host matrix induced by multiphonon processes. We have explored the dependence of the vibrational relaxation rate on the guest molecular frequency, on the temperature, on the gross features of the spectrum of a monatomic and a polyatomic host matrix, and on the presence of molecular impurities. The recent experimental results of Legay, Abouaf-Marguin, and Dubost on the vibrational relaxation of CO in solid rare gases and of the 970 cm−1 vibration of NH3 in solid nitrogen are adequately interpreted in terms of the present theory.
On some aspects of the inertia defect in planar molecules
Authors: Müller A. , Mohan N. , Rai S. N.
Published: February 2004

Some new relations involving the inertia defect Δ in different vibrational states are given. The utility of such data in fixing a unique force field for XY2(C2v), XY3(D3h), and XY4(D4h) type molecules has been discussed. The parametric study and the extremal properties of Δvib for XY2(C2v) type molecules are also presented. It is shown that in cases where the bonded mean amplitudes do not provide the unique solution for the force constants, the Δ values in different states can be used. The experimentally determined values of Δvib(0) for many XY2(C2v) type molecules are found to be in the neighborhood of their maximum ones, which corresponds to the constraint ζ13y=0 or L21(A1)=0 (upper triangular L matrix).
Mass spectrometric study of gas-phase clustering reactions: Hydration of the monovalent bismuth ion
Authors: Tang I. N. , Castleman A. W.
Published: February 2004

Gas-phase hydration equilibria of the monovalent bismuth ion were investigated over the temperature range 10–160°C using high-pressure mass spectrometry. The hydration enthalpies and entropies for the clusters, Bi+(H2O)n, n ≤ 6, were derived from appropriate van't Hoff plots. A comparison of the stability of bismuth-ion hydrates with corresponding lead-ion hydrates reveals further evidence of chemical bonding in these heavy metal-ion clusters. The distribution of these metal ions, present in the atmosphere as the radon progeny, is assessed on the basis of the measured thermodynamic properties. In addition, the implication of the data to the molecular aspects of heteromolecular nucleation is discussed.
On the probability density of quantum mechanics
Authors: Kostin M. D.
Published: February 2004

The Schrödinger equation is used to derive a nonlinear equation for the probability density of N independent spatial variables. It is shown that under certain conditions the equation is linear. In these cases a linear equation is then derived for the N-dimensional spatial distribution function of quantum statistical thermodynamics.
Ion-solvent cluster in the vicinity of an electrode: Semiempirical SCF model including image forces
Authors: Rösch Notker , Hofacker G. L. , Sabin John R.
Published: February 2004

A formalism is developed for an LCAO—MO—SCF calculation of a molecule in the field of its image charge as it approaches a metal surface. The CNDO approximations are then made, and the method is applied to the problem of a solvated sodium ion approaching a metal surface. The results of the calculation are discussed and compared with experimental quantities where possible.
The kinetic theory of polyatomic liquids. II. The rough sphere, rigid ellipsoid, and square-well ellipsoid models
Authors: Theodosopulu Mary , Dahler John S.
Published: February 2004

The generalized moment method presented in the first paper of this series is applied here to three model systems. These models—rough spheres, rigid ellipsoids, and square-well ellipsoids—have been selected not only because they are more tractable than others from a computational point of view but also because they mimic with varying degrees of success several characteristics of real polyatomic fluids. Formulas are derived for the transport coefficients and relaxation times descriptive of the establishment and maintenance of a steady state of transport of energy and of linear and angular momentum. To the approximation of Enskog these phenomenological coefficients can be expressed in terms of integrals of the same type as occur in the dilute gas theory. The integrands of these (which are trivial to evaluate in the rough sphere case) are complicated by the fact that they include the polyatomic generalization of the equilibrium pair distribution function. The formulas given here also include contributions (based upon the theories of Severne, of Prigogine, Nicolis and Misguich, and of Davis) from dynamical correlations that are not included in the Enskog approximations. These are more difficult to evaluate numerically.
Multiconfiguration self-consistent-field calculation of the dipole moment function of CO(X 1Σ+)
Authors: Billingsley F. P. , Krauss M.
Published: February 2004

The dipole moment function for the 1Σ+ ground state of CO in the vicinity of the equilibrium internuclear distance has been calculated by the optimized valence configurations (OVC) multiconfiguration self-consistent-field method. The results are compared with existing Hartree-Fock and configuration interaction treatments of this molecule at single points and also the dipole moment function deduced from experimental infrared intensities. At the experimental equilibrium separation, the calculated dipole moment is −0.167 D (C−O+) which is in reasonable agreement with the microwave value of −0.112 D (C−O+). The vibrationally averaged expectation value of the dipole moment based on the computed moment function and accurate vibrational wavefunctions is −0.151 D (C−O+) which is in better agreement with the observed microwave quantity and illustrates that the effect of vibrational averaging is not negligible in systems such as CO that possess small permanent dipole moments. A general prescription for constructing OVC wavefunctions for diatomic molecules is also presented.
Interionic vibrations and glass transitions in ionic oxide metaphosphate glasses
Authors: Exarhos Gregory J. , Miller Philip J. , Risen William M.
Published: February 2004

The far infrared spectrum of each ionic metal-metaphosphate glass, (MPO3)n (M = Li, Na, K, Rb, Cs) and [M(PO3)2]n (M = Ca, Sr, Ba), contains a broad absorption band whose peak frequency, ω0, and halfbandwidth, Δω1/2, are strongly dependent on the mass and charge of the glass-modifying cation. Each such band, which appears as the envelope of the optical phonon spectrum of the crystalline form of the material, is assigned to a density of coupled oscillator pseudo phonon states, which assignment is shown to be consistent with experimental linear vibrations of ω0 with Δω1/2 and of ω02 with < A >, the integrated absorbance, within the complete set of glasses. The net effect of coupling the oscillators in the vitreous (disordered) system is equivalently treated as a single damped harmonic oscillator. The damping coefficient, b = μΔω1/2, is constant in each series as is the complex part of the refractive index at ω0, κ(ω0), and the Lorentzian band is used to compute the force constant, F, b, and < n >T, < q2 >0, and < q2 >T, the excitation quantum number and mean square amplitudes at temperatures 0 °K and T, for each glass. A relationship between Tg and the vibrations is derived: Tg = F(< q2 >0/k) + < n >Tghcω0/k by which the experimental linear relationship between Tg and F for each series is understood to relate variations in Tg to those in zero point vibrational energy. Reexpressed, this shows that the energy required to pull the anion site away from the cation permitting the glass transition to ensue, F(< q2 >Tg – < q2 >0), is a constant for each series of metaphosphate glasses.
Normal coordinate treatment and Raman intensity analysis of crystals. I. Lithium nitrate
Authors: Kumar S. P. , Padma V. A. , Rao N. Rajeswara
Published: February 2004

Intensity formulas are derived for the Raman lines in the polarization spectra of crystalline LiNO3. Using the spectra taken by Miller et al., the L elements and force constants of the crystal are computed.
Interpretation of the vibrational spectra of small ring systems II. Perfluorocyclobutane
Authors: Harris W. C. , Yang D. B.
Published: February 2004

The vibrational spectra of gaseous and solid perfluorocyclobutane have been interpreted in terms of a planar molecule with D4h symmetry in view of the observed mutual exclusion between the infrared and Raman frequencies. A vibrational assignment for perfluorocyclobutane is presented and based upon the observed infrared and Raman band contours, depolarization ratios, relative band intensities, and positions. A comparison of the ring-puckering potential functions and skeletal structures of cyclobutane, 1,1-difluorocyclobutane, trimethylene oxide, and 3,3-difluoroxetane suggests the inversion barrier is reduced significantly upon introduction of a CF2 group in the cyclic systems. The apparent trend toward planarity appears to continue in 1,1,2,2-tetrafluorocyclobutane and perfluorocyclobutane. The factors that may dictate the equilibrium structures of small ring molecules are considered in view of the data presently available.
Fast passage in rotational spectroscopy: Theory and experiment
Authors: McGurk J. C. , Schmalz T. G. , Flygare W. H.
Published: February 2004

The theoretical and experimental analysis of fast passage phenomena in rotational spectroscopy is described in the pressure broadened limit. The phenomenon of Stark sweeping fast passage is carefully distinguished from the phenomena of transient absorption and transient emission that were treated earlier. We show that the observed response at the detector after Stark sweeping a molecular resonance through a fixed oscillator is a combination of off-resonance absorption and the beat between the fixed oscillator and the emission from the fast passage induced polarization.
Raman scattering by the hydroxyl ion in KCl and KBr
Authors: Peascoe Judith G. , Fenner W. R. , Klein Miles V.
Published: February 2004

Raman studies have been performed on KCl:OH− and KBr:OH− crystals between 2 K and room temperature. They provide additional information about previously measured infrared bands near 30 cm−1, 300 cm−1, and 3600–4000 cm−1. The 300 cm−1 band, its weak satellites, and its combination bands with the O–H stretching mode can be seen in Raman spectra only below 100 K. All these bands have T2g symmetry, consistent with libration of the O–H bond about <100> equilibrium directions. From the intensity of the combination bands relative to one component of the main stretching band a numerical value of the matrix element <θ> of the librational coordinate was determined and found to be consistent with a picture of angular harmonic oscillation of the hydroxyl ion with its center of mass fixed. The 30 cm−1 bands share the intensity and symmetry properties of the 300 cm−1 bands. A librational picture was applied to them also. The measured <θ> yielded a large moment of inertia (18 amu-Å2) that implies that this low frequency librational motion involves displacement of the center of mass as well as rotation of the O–H bond direction. The same conclusion resulted from a fit to the Devonshire theory for the combined motion. The fitted moments of inertia were in the range 14–18 amu-Å2, and the dimensionless barrier parameter k was about 45 for KCl:OH− and 85 for KBr:OH−. At higher temperatures the depolarized components in the O–H stretching region suggested strongly damped free-rotor-like behavior. Its onset coincided approximately with thermal population of levels that are essentially unbound in the Devonshire potential. The cause of the damping was assigned to greatly increased phonon emission and absorption that accompanies large-angle rotations of the off-center hydroxyl ion.
Hot band transitions to the triplet state in anthracene and pyrene crystals
Authors: Whitten W. B. , Arnold S. , Swenberg C. E.
Published: February 2004

The low energy end of the S0→T1 absorption spectrum has been measured in anthracene and pyrene crystals from 220 to 330°K. A transition is found in both of these systems at an energy approximately 400 cm−1 below the 0–0 energy. The temperature dependence of this absorption reveals it to be excitation of a hot vibrational level of the ground state. Polarized excitation measurements have been carried out on the hot band absorption in anthracene, and it is found that the polarization ratio between light polarized parallel and perpendicular to the b axis is the same as that for the 0–0 transition. In addition it is found that there is no measurable shift (within 4 cm−1) in the position of the hot band maxima for the two polarizations. Within the framework of strong and weak coupling and the Born-Oppenheimer approximation only weak coupling is found to fit all the experimental facts.
Triplet states of biacetyl and energy transfer as revealed by opto-acoustic spectroscopy
Authors: Kaya K. , Harshbarger W. R. , Robin M. B.
Published: February 2004

Using the technique of opto-acoustic spectroscopy, it is first demonstrated that radiationless decay from S1 of biacetyl when excited at wavelengths longer than 4430 Å involves a very slow (knr ∼ 103 sec−1) T1→S0 step, whereas beyond this wavelength a second fast channel opens: T2→S0. Addition of oxygen makes the apparent T1→S0 relaxation very fast. In mixtures of biacetyl and benzene, monitoring the slow component of the heat released from the biacetyl T1 state while irradiating at wavelengths absorbed by benzene shows that energy transfer from benzene directly to the Tn manifold of biacetyl occurs from the onset of 1B2u absorption to 2440 Å rather than throughout the band. In pyridine-biacetyl mixtures, the lowest n→π* state of pyridine transfers to the triplet manifold of biacetyl, but the lowest π→π* state does not.
H
3
+
: Geometry dependence of electronic properties
Authors: Carney G. D. , Porter R. N.
Published: February 2004

As the first step to the ab initio calculation of the vibration-rotation spectrum of the H3+ ion, we present results of configuration-interaction calculations of the potential-energy surface and the geometry-dependent electric dipole and quadrupole moments for the ground electronic state. Interpolation on the potential-energy surface, required for setting up the Hamiltonian matrix for nuclear motion, is facilitated by use of generalized Morse functions and Fourier analysis. An analysis of the equilibrium geometry and harmonic force constants is based upon the present and previous calculations. We conclude that H3+ has its potential minimum in an equilateral geometry with bond distances of 1.65 a.u. and harmonic frequencies ωA=3471 cm−1 and ωE=2814 cm−1.
Description of diatomic molecules using one electron configuration energies with two-body interactions
Authors: Anderson Alfred B. , Hoffmann Roald
Published: February 2004

It has recently been shown that the vibrational potential energy for a diatomic molecule α-β may be written exactly in the form (i) W(R) = Wβ(R)+WNPF(R), where Wβ(R) is the electrostatic interaction energy between nucleus α and the free atom β and WNPF(R) is the electrostatic interaction energy between nucleus α and the ``Non-Perfectly-Following'' electronic charge density redistributions arising when atoms α and β form the molecule α-β with the internuclear distance R. In this paper it is shown that WNPF(R) may be approximated, within a constant near equilibrium, by the extended Hückel configuration energy, taken as a simple sum of orbital energies, WEH(R), yielding an approximate molecular energy W*(R) according to the formula (ii) W*(R) = Wβ+WEH(R). Comparisons are made between W*(R) and the experimental W(R) for first and second period diatomic molecules. Equation (ii) overcomes the deficiency present when either Wβ(R) or WEH(R) alone is used to estimate equilibrium internuclear distances, although equilibrium force constants may be derived from Wβ(R) if the equilibrium distances are known.
Vibrational relaxation of NO X 2Π(v = 1) in the temperature range 100–300 °K
Authors: Stephenson John C.
Published: February 2004

Laser-excited fluorescence measurements have given rate constants for the vibrational deactivation of NO(v=1) by NO, He, and N2, and for the V–V exchange between CO(v=1) and NO(v=1) in the temperature region 100–300°K. Relaxation was caused entirely by bimolecular collisions. Deactivation rates of NO(v=1) by H2O, D2O, NO2, CH4, C2H4, C2H6, and C4H10, and of N2(v=1) by NO and CO(v=1) by NO2 and N2O4 were measured at T=298°K.
Semiclassical treatment of electronic transitions in molecular collisions: Collinear H++D2→HD++D
Authors: Lin Ying-Wei , George Thomas F. , Morokuma Keiji
Published: February 2004

A semiclassical treatment is presented for the dynamics of the collinear reaction H++D2→HD++D as occurring by transition from the ground to the first excited singlet electronic state of the HD2+ system. The potential energy surfaces corresponding to the two singlet states of the same symmetry have an avoided intersection for real values of nuclear coordinates, and the surfaces are analytically continued to the complex intersection. Complex-valued classical trajectories are integrated on the analytically continued surfaces, and an electronic transition is effected by a trajectory switching surfaces continuously at the complex intersection. From the complex action calculated along appropriate trajectories, the classical limit of S-matrix elements is calculated for transitions from the ground vibrational state of D2 to the ground and first excited vibrational states of HD+ for initial relative translational energies in the range 3–6 eV. These two vibrational states of HD+ differ in that the energy of the ground state lies below the asymptotic real intersection point of interest of the two surfaces while the first excited state lies above the real intersection point. Furthermore, transition points, which are points in time when a trajectory switches surfaces, occur close together in pairs for the transition to the ground vibrational state of HD+, whereas transition points are well separated for the transition to the first excited vibrational state of HD+. The differences of the transitions to these two vibrational states of HD+ result in different dynamical behavior of the trajectories leading to these transitions and require different expressions for the classical limit of the S-matrix elements.
Ion-rare gas interactions on the repulsive part of the potential curves
Authors: Kim Yung Sik , Gordon Roy G.
Published: February 2004

Interactions of the rare gas atoms with some alkali and halide ions are treated using the model presented in our previous paper [J. Chem. Phys. 56, 3122 (1972)]. In the calculation of the interactions of an atom and an ion, the electron density of the combined system is assumed to be equal to the sum of the two separate electron densities. The Coulombic energy contribution to the interaction energy is calculated directly from the charge distribution of the nuclei and the assumed electron density. The non-Coulombic part of the interaction energy is calculated from the electron density by integrating the uniform electron gas energy expression over the local electron density. The calculated potential curves agree very well with available experimental results over the entire repulsive wall. At larger distances, the model fails, because in its present form it does not include induction forces.
Ion-ion interaction potentials and their application to the theory of alkali halide and alkaline earth dihalide molecules
Authors: Kim Yung Sik , Gordon Roy G.
Published: February 2004

Interaction potentials of many ion pairs are calculated using the model presented in our previous paper [J. Chem. Phys. 56, 3122 (1972)]. In the calculation of the interactions of two ions, the electron density of the combined system of the ions is assumed to be equal to the sum of the two separate ionic electron densities. The Coulomb energy contribution to the interaction energy is calculated directly from the charge distribution of the nuclei and the assumed electron density. The non-Coulombic part of the interaction energy is calculated from the electron density using the electron gas energy expression in terms of the local electron density. The ions treated are the alkali, the alkaline earth, and the halide ions. The calculated ion-ion interaction potentials are applied to the theory of alkali halide and alkaline earth dihalide molecules. The predicted molecular bond energies, bond lengths, and vibration frequencies agree quite well with existing experimental data.
Radiationless singlet deactivation in isolated large molecules. I Naphthalene, naphthol, and naphthylamine
Authors: Hsieh J. C. , Huang Cheng-Schen , Lim E. C.
Published: February 2004

Fluorescence lifetimes of naphthalene, β-naphthol, and β-naphthylamine have been measured under collision-free conditions in the vapor. The lifetimes were then combined with the measured quantum yield (for naphthalene), or with the estimated radiative decay rate (for β-naphthylamine), to deduce the nonradiative decay rate of the molecule as a function of excitation energy. The results indicate that (1) the nonradiative decay probability increases, first slowly then very rapidly, as the excess vibrational energy in the lowest excited singlet state (S1) is varied over a range of nearly 20 000 cm−1, and (2) a plot of nonradiative decay rate versus excitation energy exhibits a break at photon energy corresponding to the second excited singlet state of a molecule. Observation (1) is interpreted in terms of two different pathways of radiationless transition that compete in the singlet deactivation of the molecules. It is argued that, in the region of low excess energies, the intersystem crossing to the triplet manifold dominates over the internal conversion to the ground state owing to a more favorable Frank-Condon factor. As the excess vibrational energy is increased the internal conversion, which is expected to display greater energy dependence than the intersystem crossing, becomes increasingly more important and it finally becomes the dominant pathway of nonradiative decay at high excess energies. This model of competing radiationless transitions is shown to be consistent with the observed deuterium isotope effect on the nonradiative decay rate of naphthalene vapor. Observation (2), which confirms our earlier results [J. Chem. Phys. 58, 1247 (1973)], suggests that S2→S1 internal conversion leads to changes in vibrational distribution, which is substantially maintained during the time scale of radiationless decay of S1. Thus, the intramolecular vibrational energy redistribution, leading to the randomization of vibrational levels, does not appear to be a fast process even for large molecules with high density of states.
Rotational friction coefficients for spheroids with the slipping boundary condition
Authors: Hu Chih-Ming , Zwanzig Robert
Published: February 2004

Friction coefficients for the uniform rotation of prolate and oblate spheroids in a viscous fluid, with the slipping boundary condition, are computed numerically and reported in tabular form.
Lattice vibrations of boron trihalide crystals
Authors: Binbrek Omar S. , Krishnamurthy Narasingarao , Anderson Anthony
Published: February 2004

The infrared and Raman spectra of polycrystalline samples of BCl3, BBr3, and BI3 at 80 and 18 K have been recorded. In the intramolecular region, isotopic and crystalline field splittings are observed in substantial agreement with earlier work. In the lattice region, no far-infrared absorption has been found, in accordance with predictions from a group theoretical analysis based on the known structures of these isomorphous crystals. The three observed Raman lattice modes are assigned according to these procedures, and their frequencies are compared with those derived from calculations of the lattice statics and dynamics of these crystals. It is found that a four-parameter model using the rigid molecule approximation and simple pairwise interaction potentials between X–X and B–X atoms is capable of giving acceptable values of the zone center frequencies while simultaneously satisfying the static equilibrium conditions for these crystals.
Luminescence and radiationless transitions from single vibronic levels of the isolated pyrazine molecule in the S 1(n,π*) state
Authors: Frad A. , Lahmani F. , Tramer A. , Tric C.
Published: February 2004

Luminescence spectra, fluorescence, and phosphorescence yields were measured for pyrazine excited to six different vibronic levels of the S 1(n,π*) state in pure pyrazine vapor and in gaseous pyrazine-SF6 mixtures. The vibrational analysis of the fluorescence spectrum is given. As the total gas pressure increases from 10−2 to several torr, the fluorescence yield decreases and reaches a constant pressure-independent value almost identical with that observed in condensed phases. The amount of this effect depends on the energy of the excited vibronic level. The phosphorescence yield, equal to zero at the low-pressure limit, increases with gas pressure. The deviation from the Stern-Volmer law for the fluorescence quenching is explained by the nonexponential decay of the fluorescence, evidenced by direct measurements of the decay curves. The results are discussed in terms of the kinetic and quantum-mechanical models of radiationless transitions in intermediate-size molecules.
Use of an ``ordered'' electron spin state as a probe in molecular spectroscopy: Optically detected adiabatic demagnetization in excited triplet states in zero field
Authors: Brenner H. C. , Brock J. C. , Harris C. B.
Published: February 2004

An ``ordered'' electron spin ensemble in molecular excited triplet states has been created by adiabatic demagnetization in the rotating frame. The ``ordered'' state can be viewed as an explicit spin sublevel population distribution dependent upon the triplet's local field. The state is created isentropically from the initial value of the triplet's spin alignment and is investigated by a series of optically detected spin-echo experiments in which the phosphorescence intensity is made to reflect quantitatively the order remaining in the ensemble. Experimental results on the 3ππ* state of 1,2,4,5-tetrachlorobenzene in a durene host are presented. In this system the order persisted for a time approaching the triplet lifetime and was independent of temperature over the range investigated. The results of these initial experiments suggest that the ordered state can be used to monitor many features associated with excited triplets such as the communication between localized triplet states at different energies, migration of triplet excitons, and as a general probe of the dynamics of any process that alters the excited state's environment. Several specific experiments are outlined to illustrate these principles.
Study of the structure of molecular complexes. VII. Effect of correlation energy corrections to the Hartree-Fock water-water potential on Monte Carlo simulations of liquid water
Authors: Kistenmacher H. , Popkie H. , Clementi E. , Watts R. O.
Published: February 2004

The two-body Hartree-Fock potential for water-water interactions previously used to describe small water clusters and used in Monte Carlo studies of liquid water has been used to assess the effect of neglecting the correlation energy correction. A number of semiempirical corrections based on the London, Kirkwood, and Wigner formulas were used. They have an energy spread such that they encompass the expected magnitude of the exact correlation energy correction. Short range correlation interactions were included using a modification of the functional of density proposed by Wigner and the corresponding long range interactions were given by a term proportional to r−6 with coefficients due to both London and Kirkwood. After adding the corrections to the Hartree-Fock potential the various potentials were compared by generating a number of potential energy surfaces. Following this the water-water potentials were used in a Monte Carlo simulation of liquid water to calculate thermodynamic and structural data. After comparing the results with experimental data it is seen that the Hartree-Fock potential gives a realistic representation of the structure of liquid water but predicts poor thermodynamic data. Correlation energy corrections reduce the discrepancies significantly and it is probable that the remaining error is attributable to many-body effects. The potentials are sufficiently accurate that certain discrepancies in the interpretation of scattering data for liquid water can be indicated.
Determination of thermal transport properties from thermal transpiration measurements. III. Polar gases
Authors: Tao J. C. , Revelt W. , Sandler S. I.
Published: February 2004

The results of capillary thermal transpiration measurements for nitrogen, oxygen, carbon monoxide, methane, methyl chloride, hydrogen sulfide, and sulfur dioxide over a (mean) temperature range of 408.6 to 501.3°K are reported. The problem that arises in interpreting the data to obtain thermal transport information is carefully considered. While this difficulty is not completely resolved, our data for the nonpolar gases are combined with our earlier results and used to compute smoothed values of the rotational relaxation numbers and Eucken factors for the temperature range 165–500°K.
Calculation of singlet and triplet excitation energies, ionization potentials, and electron affinities of closed-shell systems by many-body Rayleigh-Schrödinger perturbation theory
Authors: Kvasnička Vlado , Hubač Ivan
Published: February 2004

A method for the calculation of singlet and triplet excitation energies, ionization potentials, and electron affinities by the many-body Rayleigh-Schrödinger perturbation theory is elaborated. In this method the excitation energies, ionization potentials, and electron affinities are given by an infinite sum of terms, each of which may be interpreted using the diagrammatic technique. Application of this method to systems described by a π-electron PPP-Hamiltonian is carried out.
Diabatic capture in dissociative attachment
Authors: Crawford Oakley H. , Koch Brian J. D.
Published: February 2004

Diabatic capture is shown to account for low energy dissociative attachment in alkyl bromides (RBr) and hydrogen halides. It is argued that low energy negative ion electronic resonances do not exist in these systems. The theory is tested by computations based on a one-electron model, and agreement with experimental results is achieved for the hydrogen halides. Molecules (HF and RBr, in particular) which have a dipole moment greater than 1.625 D must have a positive vertical electron affinity. Information about the relation between the neutral molecule and negative ion potential curves is deduced using an isotope effect for HCl, HBr, and HI. The alkyl bromide and hydrogen halide negative molecular ions are all suggested to be stable when in isolation. Electron energy loss by vibrational excitation is discussed.
Iterative solutions of the close-coupled equations that appear in the problem of rotational excitation of a rigid rotor
Authors: Nanbu K.
Published: February 2004

A method to solve iteratively the close-coupled equations that appear in the theory of scattering of an atom by a rigid rotor is proposed. It is a natural extension of the distorted-wave approximation method (DWA). The total cross sections obtained by the present method agree well with those of Johnson and Secrest. Iterative solutions converge rapidly. As for computer execution time, it depends upon the number of coupled equations. If only the open channels are taken into consideration, it takes only 20–30% more for the present method than for the DWA method. However, if the closed channels are also taken into consideration, it takes 90–100% more than for the DWA method.
Magnetic studies on μ4-oxo-hexa-μ-chlorotetrakis [(pyridine) - copper (II)]
Authors: Drake Robert F. , Crawford Van H. , Hatfield William E.
Published: February 2004

The magnetic susceptibility of μ4-oxo-hexa-μ-chlorotetrakis[(pyridine)copper(II)] has been measured in the temperature range 1.7−294°K. The data may be explained on the basis of simple Heisenberg exchange theory with J=7.65 cm−1, g=2.25, and zJ1 (the intercluster exchange parameter)=−4.0 cm−1.
Adsorption of hydrogen on nickel single crystal surfaces
Authors: Christmann K. , Schober O. , Ertl G. , Neumann M.
Published: February 2004

Adsorption of hydrogen on Ni(111), (100), and (110) surfaces was studied by means of LEED; energy loss spectroscopy, flash desorption, and work function measurements, as well as by the technique of laser-induced thermal desorption. Noticeable variations of the LEED intensities for Ni(111) and (100) indicate the formation of disordered adsorbed layers, whereas with Ni(110) the formation of ``streaked'' diffraction patterns and (at high coverages) of a 1×2 structure were observed. Hydrogen adsorption causes a strong damping of the intensity of the surface plasmon excitation and the appearance of an electron loss peak around 15 eV. Flash desorption experiments revealed for Ni(111) and Ni(100) the existence of β1 and β2 states, the former being only filled after completion of the β2 state. Desorption from the β2 state follows a second-order rate law for Ni(111) and Ni(100), but is of first order with Ni(110). Maximum increases of the work function Δ φ by 0.195, 0.170, and 0.530 eV were observed with Ni(111), (100), and (110), respectively. Adsorption isotherms Δ φ=f(pH2) for Ni(111) and Ni(100) may be closely described up to medium coverages on the basis of a model that assumes second-order desorption and first-order adsorption kinetics. The validity of this model was further proved by measurements of the variation of coverage with time. The adsorption isotherms for Ni(110) have a unique shape indicating the occurrence of two-dimensional condensation due to attractive interactions in the adsorbed layer. Isosteric heats of adsorption at low coverages of 23 kcal/mole for Ni(111) and Ni(100) and of 21.5 kcal/mole for Ni(110) were evaluated. With Ni(110) the onset of condensation is characterized by an increase of Ead by about 2 kcal/mole. A steplike decrease of Ead at medium coverages accompanies the formation of the β1 states.
Temperature dependence of vibrationally assisted electronic absorption band shapes of impurities in solids
Authors: Kelley C. Stuart
Published: February 2004

The detailed temperature dependence of the half-width, peak intensity, and wavenumber of the peak of the absorption band shape is calculated for a vibrationally assisted electronic transition in an impurity in a solid. The quantum mechanical vibrational interaction between the impurity and the lattice is linear, and the convolution approach with a single vibrational mode is used. Results are compared to those of the nonconvolution approach. The nonconvolution-approach results consistently overestimate the half-width and peak intensity of the convolution results; but the basic temperature dependences are the same. In the convolution approach, the wavenumber of the peak increases with increasing temperature, while it is temperature independent in the nonconvolution approach.
Monte Carlo classical dynamical study of the Cl + Cl2 and I + I2 systems: Vibrational relaxation and atom-exchange reactions
Authors: Thompson Donald L.
Published: February 2004

The Monte Carlo quasiclassical trajectory method is used to investigate the atom-exchange reactions and the vibrational relaxation in the systems Cl + Cl2 and I + I2. The Cl + Cl2 system is examined over the temperature range 500–1500°K and initial vibrational states ν = 0, 1, 3, 7, and 14, and the I + I2 system is examined over the temperature range 700–1500°K and initial vibrational levels ν = 0, 1, 7, 10, 12, and 14. London equation potential-energy surfaces are employed; the energy barrier to linear configuration atom exchange is zero for Cl + Cl2 and about 5.9 kcal/mole for I + I2. The rates of atom exchange for both Cl + Cl2 and I + I2 are calculated as a function of temperature and initial vibrational state. Vibrational relaxation rate coefficients are calculated for individual transitions ν→ν′ for both reactive and nonreactive collisions. It is found that both nonreactive collisions and atom-exchange reactions contribute to the vibrational relaxation.
Photodissociation of NaBr, Nal, and KI vapors and collisional quenching of Na* (3 2P), K* (4 2P), and K* (5 2P) by foreign gases
Authors: Earl Boyd L. , Herm Ronald R.
Published: February 2004

Fluorescence from excited alkali atoms (A*) may be produced by photodissociation of alkali halide (AX) vapor. Fluorescence efficiencies have been determined as a function of the photodissociation wavelength, λ0, for Na* (3 2P) from NaBr and for K* (4 2P) and K* (5 2P) from KI. Employing the Stern-Volmer relation, cross sections, Qq, for the collisional quenching of the A* electronic excitation may be determined from the attenuation of the A* fluorescence that is observed upon introduction of a foreign gas. Because A* may be produced with different average speeds by varying λ0, this method permits the determination of the dependence of Qq on relative collision speed, g. Employing this method, Qq was determined to decrease monotonically with increasing g for Na* (3 2P)+Br2 (AX = NaBr) and K* (4 2P)+C2H4, CF3Cl, and SO2 (AX = KI). Moreover, values of Qq were determined at a particular g value for K* (4 2P)+I2 and K* (5 2P)+I2, HCl, and DCl. Alternatively, premixing the quenching gas in a large (∼ 100-fold) excess of Ar thermal moderator (Ar failed to quench any of these A* levels) makes possible the measurement of Qq for a thermal distribution in g. Thermal results (800–900°K) obtained by this method are reported for the quenching of Na* (3 2P) (AX=NaI), K* (4 2P), and/or K* (5 2P) by N2, CF3Cl, H2, H2O, CH3OH, CF4, CH4, C2H6, C2H4, and SO2. In general, for any particular quenching gas, Qq[K* (5 2P)] > Qq[Na* (3 2P)] ≳ Qq[K* (4 2P)]. The difference between K* (52P) and K* (4 2P) [or Na* (3 2P)] is sometimes quite large; for CH4, for example, Qq[K* (5 2P)]/Qq[K* (4 2P)] > 60. For I2, however, the trend is dramatically reversed with Qq[K* (5 2P)]/Qq[K* (4 2P)]=0.2. Effects of isotopic substitution were also examined; no difference in Qq was measured for H2 vs D2, H2O vs D2O, C2H4 vs C2D4, or HCl vs DCl. However, for K* (5 2P), Qq(CH4)/Qq(CD4) ≈ Qq(C2H6)/Qq(C2D6) ≈ √2. All of these results are discussed in terms of the likely forces between the reactants and the possibility of a change-transfer intermediate.
13C-spin-lattice relaxation behavior of acetonitrile and acetone
Authors: von Goldammer E. , Lüdemann H.-D. , Müller A.
Published: February 2004

Spin-lattice relaxation times of all carbon atoms in acetonitrile and acetone were measured at various temperatures. Spin-rotation coupling constants of acetonitrile were determined, and for the methyl carbon atom the following values were found: c⊥=4.5 kHz, c‖= −39 kHz. Considerable contributions of anisotropic-chemical shift relaxation to the nitrile carbon relaxation was detected at lower temperatures with a chemical shift anisotropy of Δσ≈450 ppm. The relaxation behavior of acetone was also studied in aqueous mixtures. Existence of microheterogeneities in the acetone rich concentration range has been concluded from the carbonyl relaxation in D2O, where a considerable contribution from intermolecular proton-carbon interaction was found.
Mechanism of condensation. II. Condensation of molecular beams of sodium chloride on clean and contaminated surfaces of oriented single crystals of NaCl
Authors: Schoonmaker R. C. , Tu L. C.
Published: February 2004

With large supersaturation ratios, unit coefficients have been measured for condensation of normal-incident molecular beams of sodium chloride on clean (100) oriented single crystal surfaces of NaCl. Since α=1 for the composite molecular beam, individual coefficients for condensation of NaCl(g) and Na2Cl2(g) must have unit values under the conditions of these experiments. Over the range investigated, α is independent of molecular beam flux and surface temperature. A large flux of nitrogen on the surface during molecular beam deposition has no effect on α. Nonunit values of α correlate with the presence of relatively small amounts of hydrocarbons in the residual gas. The results of the present work on condensation on clean surfaces under ultrahigh vacuum differ from those previously reported for condensation of sodium chloride under high vacuum. A mechanism of condensation is proposed. Discrepancies between the present and previous results for condensation of sodium chloride are discussed.
Theoretical analysis of the vibrational structure of the electronic transitions involving a state with double minimum: E, F 1 Σg+ of H2
Authors: Lin C. S.
Published: February 2004

It is shown that the convergence problem encountered in the numerical integration of the vibrational Schrödinger equation for an electronic state with a double-minimum potential does not exist in the analytical expansion method. For the B 1 Σu+, C 1πu, and E, F 1 Σg+ states of H2, the expansion method gives consistently and progressively better energy eigenvalues than the numerical integration. method. Franck-Condon factors for the transitions B1Σu+ − E,F1Σg+ and C1 Πu − E,F1Σg+ were computed, and the vibrational structure of the case B1Σu+ − E,F1Σg+ is discussed in some detail.
EPR investigations of Eu2+ in orthorhombic sites of NaCl
Authors: Aguilar G. , Muñoz P. S., E. , Murrieta S. H. , Boatner L. A. , Reynolds R. W.
Published: February 2004

Spin-Hamiltonian parameters describing the EPR spectrum of Eu2+ in orthorhombic sites of NaCl single crystals have been determined at 77 and 300 K. Previously undetermined absolute signs of the parameters were deduced from observations of relative line intensities at liquid helium temperatures. The sign of the second-order spin-Hamiltonian parameter b20 was found to be positive and is therefore in agreement with the sign reported by Nair et al. for Eu2+ in KCl. Previously proposed models for the orthorhombic Eu2+ defects in alkali halides are discussed.
Application of the variational least squares method to inelastic scattering
Authors: Abdallah Joseph , Truhlar Donald G.
Published: February 2004

The anomaly-free, minimum-norm, and variational least squares methods for algebraic variational inelastic quantum mechanical scattering calculations are all applied to the same example. The zero-order variational least squares method, which is completely free of spurious singularities, is found to be an accurate and useful method. Some alternative versions of the variational least squares method are pointed out.
127I Mössbauer studies of some fluorosubstituted organo iodine compounds
Authors: Lazarus Marc S. , Thomas T. Darrah
Published: February 2004

From the measured 127I Mössbauer spectra, we have determined the isomer shift, quadrupole coupling constant, and recoilless fraction for CH3I, CF3I, C6H5I, o-, m-, and p-C6H4FI, and C6F5I. From relative intensities of the peaks, there is evidence for either orientation or Goldanskii-Karyagin effects in CH3I, CF3I, and φI. The isomer shifts and quadrupole coupling constants give values for the numbers of p and s holes, from which the charge and hybridization of iodine in these compounds is calculated. Except for C6F5I, the charges correlate well with the pKa of corresponding carboxylic acids. It is suggested that the anomalous behavior of this compound arises from the formation of a charge transfer complex in the solid. From a comparison of NQR and Mössbauer data for CI4 and CF3I, an explanation is suggested for the anomalous decrease of chlorine NQR frequencies in the series of compounds CFn Cl4−n (n = 0→3). The problem of deriving meaningful Mössbauer parameters from complex spectra taken with thick absorbers is discussed.
Corrections to the Born-Oppenheimer approximation and electronic effects on isotopic exchange equilibria. II
Authors: Kleinman Lawrence I. , Wolfsberg Max
Published: February 2004

If nonadiabatic effects are neglected (the adiabatic approximation), the potential energy for the motions of the nuclei of a molecule is the sum of the Born-Oppenheimer electronic energy and the adiabatic correction (diagonal nuclear motion correction). This adiabatic correction has been evaluated at the experimental equilibrium internuclear separation for a number of first- and second-row diatomic hydrides and deuterides. The electronic wavefunctions which have been used in these calculations are LCAO MO SCF functions which range in quality from so-called minimum basis set functions to so-called near-Hartree-Fock functions. The explicit R dependence of the LCAO coefficients has been taken into account. The adiabatic corrections to the electronic energy are functions of the nuclear masses. With the assumption of the distance independence of the adiabatic correction, the calculations here can be used to evaluate the effect of the adiabatic correction on the equilibrium constants for the isotopic exchange reactions HX+HD=DX+H2. For the HX systems on which calculations were done here, these correction factors range, with good single configuration wavefunctions, from 0.963 to 1.113 at 300°K.
Shifts in vibrational constants from corrections to the Born-Oppenheimer approximation: Effects on isotopic exchange equilibria
Authors: Kleinman Lawrence I. , Wolfsberg Max
Published: February 2004

The adiabatic correction to the Born-Oppenheimer approximation has been evaluated as a function of internuclear separation for the diatomic molecules in the isotopic exchange reaction HX+HD=DX+H2, where X=D, Li, or Cl. The sum of the isotope-dependent adiabatic correction and the isotope-independent Born-Oppenheimer electronic energy is the effective potential energy for nuclear motion if nonadiabatic effects are neglected. The resulting shifts, from the Born-Oppenheimer values, of the equilibrium internuclear separations and of other vibrational constants are calculated. It is found that these shifts are so small that they have negligible effect on calculated values of the isotopic exchange equilibrium constants. The only important contribution of the adiabatic correction to the equilibrium constants arises from the fact that the ΔE of the isotopic exchange reactions between translationless, rotationless, vibrationless reactants and corresponding products no longer equals zero.