bluuebunny/crossref_metadata_2025 huggingface dataset:
Statistical Thermodynamics of Spherical Droplets
Authors: Plesner Igor W.
Published: January 2005

The model employed by Hill for investigating the nature of the transition region between two phases in a one-component system is extended to spherical interfaces. The surface tension and location of Gibbs' dividing surfaces in droplets with a radius of 3 to 25 molecular diameters (the molecules are hard spheres with an attractive potential) are calculated at a reduced temperature of 0.6, providing the numerical basis for investigating the dependence of surface tension on droplet size. It is found that the surface tension in all cases is about 35% of that of a plane interface, but is almost independent of droplet size.

The values of the surface tension relative to that of a plane interface are compared with those obtained from nucleation experiments in jets, using the Becker—Doering theory of nucleation; the agreement is poor, which is not surprising, considering the rather complicated substances used for the experiment.

From the values of the surface tension at the Gibbs surface of tension, the work of formation, W/kT, of a droplet of the size in question can be calculated. Since the method here amounts to finding the critical nucleus in a supersaturated system, this quantity determines a ``critical nucleus for condensation''; from this can be found the ``critical supersaturation'' to be compared with existing cloud-chamber measurements on low-molecular-weight vapors. Assuming that thermal fluctuations will suffice to initiate condensation if W/kT is less than 75, the critical nucleus for condensation is found to contain about 50 molecules, and the corresponding critical supersaturation is found to be S=2.6, in reasonable agreement with most experiments. Some questions concerning the applicability of thermodynamic concepts to microscopic droplets are briefly discussed.
Proton Mobility and Electron Exchange in Aqueous Media
Authors: Horne R. A. , Axelrod E. H.
Published: January 2005

Evidence from several different sources is cited in support of the hypothesis that the iron (II)—(III) electron-exchange reaction involves a Grotthuss-type mechanism closely related to that responsible for the anomalous mobility of protons in aqueous solution. This evidence includes failure of the electron exchange to occur in the absence of water, similarity of the two processes with respect to the deuterium isotope effects, similarity of rate ratios in liquid water and ice, and similiarity of activation energies of the two processes and of their temperature dependence.
Thermal Conductivities of Gaseous H2O, D2O, and the Equimolar H2O—D2O Mixture
Authors: Baker Charles E. , Brokaw Richard S.
Published: January 2005

Measurements have been carried out over the temperature range 380°—525°K using a four-cell hot-wire thermal-conductivity apparatus. At the lower temperatures the thermal conductivities of H2O and D2O are identical, but at the highest temperature the conductivity of D2O is larger by 8–9 parts per thousand. Conductivities of the equimolar mixtures lie midway between the conductivities of the pure components. Results are analyzed to test a recent hypothesis that a resonant exchange of rotational quanta causes the thermal conductivity of a polar gas to seem anomalously low in relation to its viscosity. It is concluded that the interchange of rotational energy between neighboring dipoles may be important, but that exact resonance is probably not required, at least in the case of water vapor.
Out-of-Plane CH2 Bending Potential Functions of Diazomethane, Ketene, and Related Molecules
Authors: Moore C. Bradley , Pimentel George C.
Published: January 2005

The unusually low out-of-plane CH2 bending potential constants of ketene and diazomethane are discussed in terms of a valence bond comparison of their electronic structures to those of ethylene and ammonia. The anharmonic energy levels of the CH2 out-of-plane bending in diazomethane are fitted with an harmonic-quartic potential function. V(γ)=(½(2.74)·Δγ2+0.651·Δγ 4 × 10—13 erg. A model is developed in which potential constants are transferred from the ethylene and ammonia molecules to the two valence-bond structures usually considered for the ketene and diazomethane molecules. The unusually high intensities of the bending overtones are found to be a necessary consequence of this treatment. A further experimental test may be found in the expected large change in dipole moment with vibrational state. The model provides a basis for understanding the potential functions of ketene and diazomethane, and for making qualitative predictions about other molecules such as cyanamide and CF2N2.
Discreteness-of-Charge Adsorption Micropotentials. I. Infinite Imaging
Authors: Barlow C. A. , Macdonald J. Ross
Published: January 2005

The Ershler infinite imaging model for adsorption of ions from electrolytes is discussed in detail. An incorrect derivation of the basic equations for the micropotential is critically examined, and a correct derivation provided. The potential arising from discrete adions and their images is determined exactly based upon a method which heretofore has only been applied to crystal field problems. Finally, the accurate results obtained using a digital computer are compared with the approximate results of other treatments.
Diffusion and Reaction of Water in Additively Colored KCl
Authors: Penley J. C. , Witte R. S.
Published: January 2005

Additively colored KCl single crystals heated in the presence of water vapor developed a colorless region around the surface of the crystal. This bleaching effect is found to be described by a model in which water, or fragments from the dissociation of water, diffuses into the crystal and reacts with the excess potassium to form a colorless, photochemically sensitive reaction product, possibly KH or KOH. Using this model, an order-of-magnitude estimate of the diffusion coefficient of water in colored KCl is D=(7.2±3)×10−6exp[−(0.56±0.07) eV/kT]cm2/h.
Residual Entropy of Ice
Authors: DiMarzio E. A. , Stillinger F. H.
Published: January 2005

We examine the problem of evaluation of residual hydrogen-bond entropy in ice, first noting by way of introduction the results of applying certain well-known approximate lattice theory combinatorial techniques (mean field, Bethe, Kikuchi approximations). Subsequently, a general matrix method is introduced for evaluation of the residual entropy in the square planar lattice analog of ice, in terms of a series of contributions, each of which corresponds to a connected cluster diagram. The leading term in this latter method is the Pauling estimate, and two successive orders of terms are evaluated explicitly to indicate rate of convergence. In the real three-dimensional case the generalization of the matrix method indicates that the Pauling estimate is roughly 1% low.
Statistical Model Including Angular Momentum Conservation for Abnormal Rotation of OH* Split from Water
Authors: Horie Tadao , Kasuga Takashi
Published: January 2005

In order to give an account of extreme, nonthermal populations of the rotational states of the 2Σ+ level of OH split by electron impact from water, a proposal is made for a statistical model which includes the law of angular momentum conservation within it. The interaction volume is taken to be double-walled and spherically symmetric with respect to the center of gravity of the whole system which consists of OH* and H. It is shown that abnormal populations quite similar to typical ones thus far experimentally observed can be derived from the model proposed with the aid of the Franck—Condon principle and a predissociation of OH.
Application of the Space Group to the Molecular Orbital Treatment of Crystalline Iodine
Authors: Rosenberg J. L.
Published: January 2005

The physical model of two-dimensional p-electron delocalization proposed by Bersohn for crystalline iodine is examined. The principal features of the model are adopted, including the Hückel method for writing one-electron orbitals and the restriction to nearest nonbonded neighbor interactions. Crystal symmetry is exploited in defining the matrix integrals. The secular equation is solved exactly for characteristic points in the Brillouin zone for the space group C2vII, and an approximate analytical solution is obtained for the general point. The theory semiquantitatively accounts for the experimental results of nuclear quadrupole coupling, crystal energy, and conductivity.
Bonding in Ion Clusters. I. O4+
Authors: Yang Jae-Hyun , Conway D. C.
Published: January 2005

The O2–O2+ bond energy has been determined to be 0.42 eV from the temperature variation of the equilibrium constant for the reaction: O2+O2+=O4+. The rotational entropy of the O4+ by the ``loose'' cluster model, in which 6 rotational degrees of freedom are assumed, appears to be too large for the observed entropy change, ΔS293°= —20.6 e.u. Approximately half of the bond energy can be ascribed to a simple ion-induced dipole interaction if account is taken of the variation in field strength over the O2 molecule by use of a very simple model. The explanation for the residual bond energy discrepancy might be that the polarizability of O2 is larger than the low-field experimental value at high field strengths such as those ∼3 Å from an ion. The experimental method described is of wide applicability in determining bond energies in ion clusters.
Effects of Electron Transfer on High-Resolution NMR Spectra
Authors: Johnson Charles S. , Tully John C.
Published: January 2005

The 15.1-Mc/sec NMR spectra of isopropylquinone and 2,5-diethoxyquinone in equilibrium with the corresponding semiquinone radicals in pyridine show line positions and intensities that depend on the radical concentrations. These spectra are compared with curves calculated by the density matrix technique with the assumption that modulated isotropic hyperfine interactions provide the only relaxation mechanism. Satisfactory agreement is found for the methyl protons in isopropylquinone from which we estimate that T1>100T2 for the methine protons; however the line shapes for the methyl protons in 2,5-diethoxyquinone suggest that other relaxation mechanisms may be present.
Delta-Function Model for Interaction of Two-Electron Atoms and Ions
Authors: Weber Gunter G.
Published: January 2005

The interaction energy of two-electron atoms and ions in the repulsive range can be calculated by applying a δ-function potential. We describe and justify the δ-function formalism. It is applied to HeHe, Li+Li+, H—H—, Li+He, Li+H—, HeH—. Analogies with well-known methods are shown and the results are compared with those of other theories.
Effect of Surface Coverage and Temperature on the Sticking Coefficient
Authors: Smith Tennyson
Published: January 2005

A theoretical equation is derived that quantitatively describes the peculiar shape of the curves relating the sticking coefficients for the adsorption of nitrogen and carbon monoxide on tungsten as a function of the amount adsorbed and the temperature. The model used to describe chemisorption into a β state with a high binding energy involves a precursor state of low binding energy as assumed by others. However, emphasis is placed on the importance of nonsteady state of the precursor for low coverage and very high coverage. It is found that if the precursor state is actually the α states (for N2 and CO) discovered by Ehrlich, the experimental curves can be predicted within experimental error.
Deviations from the Virial Relationship in Many-Center Variational Functions
Authors: Wasserman Allen L.
Published: January 2005

An equation is derived which relates kinetic and potential energies that have been calculated from unscaled many-center variational functions. The expression finds use in accurately determining diatomic equilibrium nuclear separations and force constants from many-center variational wavefunctions that are not properly scaled.
Growth of Durene from the Melt
Authors: Murphy W. K. , Hormats E. I. , Sears G. W.
Published: January 2005

Microscopic observation of the solidification and melting of durene at small undercoolings demonstrated that the habit face grows by layer spreading. It was also found that certain other unidentified faces grow by layer spreading. The critical supercooling required for an appreciable rate of two-dimensional nucleation on the habit face is consistent with Cahn's analysis of the layer-spreading mechanism for diffuse interfaces. Melting appeared to occur by the reverse of the freezing mechanisms.
Effect of Pressure in the Radiolysis and Photolysis of Methane
Authors: Ausloos P. , Gorden R. , Lias S. G.
Published: January 2005

The photolysis and radiolysis of equimolar CH4–CD4 mixtures were investigated as a function of pressure. The fact that, in the presence of NO, the ethane fraction consists entirely of C2D6, C2D4H2, C2H4D2, and C2H6 in comparable amounts indicates that CH2 and CD2 are produced. The relative yield of these ethanes which are formed by insertion of methylene into methane increases with pressure in both the photolysis and radiolysis. In the radiolysis, the G value reaches a value of 0.35±0.1 at pressures above 15 atm. Information about the effect of pressure on the production of the ethyl ion was obtained by investigating the radiolysis of CH4–C4D10 and CD4—C3H8 mixtures from 1.5 cm to 130 atm. The data indicate that there is a gradual decrease of the ethyl ion yield with increase in pressure while the parent ion yield increases with increase in pressure to a pressure of at least 15 atm.
Statistical Mechanics of Defect-Containing Solids. II. Ionic Crystals
Authors: Allnatt A. R. , Cohen Morrel H.
Published: January 2005

The cluster expansions for the partition function and defect distribution functions derived previously are studied in detail for the case of ionic crystals with the object of calculating activity coefficients, defect concentrations, and defect distribution functions at low defect concentrations. A diagram classification procedure analogous to that in the Mayer theory of ionic solutions is used to obtain nondivergent expansions for defect activity coefficients and distribution functions. The discreteness of the lattice requires some modification of the diagram summation techniques employed in the solutions theory. The theory of association of defects of the sort considered by Lidiard and Teltow is formulated more precisely in terms of the defect distribution functions. The formal multicomponent expressions are studied in more detail for the case of Schottky defects and impurity ions in a sodium chloride lattice. The results parallel those of the Mayer ionic-solution theory, the principal difference being that the Debye—Hückel potential of average force appearing in the final Mayer expressions is everywhere replaced by Ae2 exp(—κRξ)/RD, where A and ξ are structure and concentration dependent and go to unity in the continuum limit.

As an example for the case of activity coefficients, calculations of the contributions from cycle diagrams and terms of next lowest order in concentration have been made for divalent impurity ions and cation vacancies in sodium chloride. The pair correlation function for oppositely charged defects and the degree of association have been calculated for the doped crystal. The theory reduces to that of Lidiard in the limit of zero concentration but differs at finite concentrations. However, calculation of the contribution of ``triangle diagrams'' to the activity coefficients indicates that below 500°C the expansions do not converge rapidly enough to be of value at concentrations of experimental interest because of the low dielectric constant. It was found that in the range of temperature and composition for which the theory converged, the parameters A and ξ differed little from unity.
Analysis of A2B2 NMR Spectra. II. Nonsymmetrical 1,2-Disubstituted Ethanes
Authors: Hirst Robert C. , Grant David M.
Published: January 2005

The features of A2B2 proton magnetic resonance spectra of nonsymmetrical 1,2-disubstituted ethanes are discussed in detail. It s shown that under certain conditions the magnitudes and signs of all the coupling constants may be obtained for this type of A2B2 spectra. Typical calculated spectra along with several experimental spectra are given to illustrate these conditions. With one exception, experimental data are given only for molecules for which all four of the coupling constants are obtained.

It is found that the geminal coupling constants are of opposite sign from the rotationally averaged values for the vicinal couplings. The values of the geminal couplings are approximately those found by other workers in the corresponding monosubstituted methanes. Small vicinal substituent effects on the geminal coupling constants are reported for several of the substituent groups. Assignment of the chemical shift of the particular methylene group is based on the comparison of the A2B2 chemical shifts with the chemical shifts in the related ethyl compounds.
Description of the Distribution of Electrons in the Methane Molecule
Authors: Turner Almon G. , Saturno Antony F. , Hauk Peter , Parr Robert G.
Published: January 2005

A formal scheme is presented for describing the electron distribution in the methane molecule. Purely theoretical electron density contour maps for the ground state of the molecule are displayed, and various aspects of the electronic distribution are discussed. The electronic wavefunction employed is an analytical form composed of atomic orbitals of s through g type centered on the carbon nucleus.

The electronic charge density ρ is expressed as a series of normalized (to 4π) tetrahedral harmonics Tl (θ,φ), which are certain symmetrical linear combinations of spherical harmonics of the given l value. Namely, 4πρ(r,θ,φ)=ΣlAl(r)Tl(θ,φ),where the Al(r) depend only on r, the radial distance from the carbon nucleus. The functions Al(r) are tabulated, and contour maps of ρ are developed. The molecular octupole moment is predicted to be about 1.7×10—24e·cm3.

The distribution of electrons in a single carbon—hydrogen bond is considered from several points of view, with the purpose, among others, of elucidating the question of the sign and magnitude of the ``CH bond moment.''
Calculation of Magnetic Susceptibilities of Diatomic Molecules. IV. Application to LiH Molecule
Authors: de la Vega J. R. , Hameka H. F.
Published: January 2005

A previously proposed method for the calculation of magnetic susceptibilities of diatomic molecules has been applied to the LiH molecule, the result is χ=—9.39×10—6 cgs units per mole. The experimental value is not known. From a measurement of the rotational magnetic moment it is possible to obtain an experimental value for the paramagnetic contribution to the susceptibility for a specific choice of gauge, this value is 7.14×10—6 cgs units which should be compared with our theoretical result 5.48×10—6 for the same quantity.
Molecular Motion and the Moment Analysis of Molecular Spectra. II. The Rotational Raman Effect
Authors: Gordon R. G.
Published: January 2005

The rotational Raman effect is analyzed in terms of moments of its intensity distribution. Each moment may be expressed as an equilibrium property of the molecular distribution in a scattering substance. The first and second moments of rotational Raman spectra are shown to obey the simple proportionality M(1)/M(2)=ℏ/2kT in the high-temperature, or classical limit. This relation is necessary in order that a classical system remain in equilibrium with its black-body radiation. It is the analog for two-photon scattering processes of the Einstein relation for the single photon processes of absorption and emission. The third and higher moments are found to depend on statistical averages of angular derivatives of the intermolecular potential energy, the angular correlation between molecules, and the molecular rotational kinetic energy. The analysis may be applied to the experimental determination of the nonspherical part of intermolecular forces from the rotational Raman effect in compressed gases.
Dipole Moment of 15N16O2
Authors: Esterowitz Leon , Rosenthal Jack
Published: January 2005

Stark effect measurements have been made for the 808→717 rotational transition of 15N16O2. The dipole moment was calculated to be 0.294±0.015 D.
Photochemistry of 1,3-Butadiene : Details of the Primary Processes and Mechanism of Photopolymerization
Authors: Haller I. , Srinivasan R.
Published: January 2005

The photolysis of 1,3-butadiene in the vapor phase was studied in the presence of inert gases such as krypton, diethyl ether, and cyclohexane. In every instance, an increase in the pressure of the added gas led to a decrease in all of the volatile products. The behavior of 1,2-butadiene and 2-butyne were exceptional in that they showed a slight increase in yield when a small quantity of an inert gas was added. But at higher pressures, even in these cases, the yields decreased. A consideration of the radiative lifetime of the first-singlet excited state of 1,3-butadiene suggests that the observed pressure dependence cannot be attributed to a quenching reaction from that state. It seems likely that all of the volatile products in the vapor phase photolysis arise from a vibrationally excited ground state molecule of 1,3-butadiene that is formed by the internal conversion of the electronically excited singlet state. Photolysis of 1,3-butadiene in solution, which is equivalent to photolysis at very high pressures, yielded none of the volatile products that were observed in the vapor phase but only cyclobutene, bicyclo [1.1.0] butane, dimers, and a polymer. The cyclobutene and bicyclobutane are believed to be products of isomerization from the electronically excited state of 1,3-butadiene.

The formation of a polymer in the gas-phase photolysis was found to have an induction period and to depend on the square of the number of photons that were absorbed. In all probability, the polymer is formed in the photolysis of a volatile product(s) of the primary photodecomposition.
Forbidden Electronic Transitions in XeF2 and XeF4
Authors: Pysh Eugene S. , Jortner Joshua , Rice Stuart A.
Published: January 2005

Transition strengths have been measured for the weak 2330 Å band in XeF2 (f=0.002) and for the two weak bands in XeF4 at 2280 Å (f=0.009) and 2580 Å (f=0.003). To investigate the origins of these weak transitions, the possibilities of vibronic and singlet—triplet transitions in XeF2 and XeF4 were examined. Using the Herzberg—Teller theory of vibronic transitions and a molecular orbital treatment of excited electronic states, estimated strengths of the relevant vibronic transitions have been calculated to be f=0.001 for both XeF2 and XeF4. The vibronic band in XeF2 borrows intensity from the symmetry allowed 1A1g→1A2u transition at 1580 Å (f=0.45), while in XeF4 the major contribution to the vibronic band is from the symmetry allowed 1A1g→1Eu transition at 1325 Å (f=0.8). A temperature dependence of the intensity of the 2330 Å band in XeF2 has been observed and found to be less than that predicted by the Herzberg—Teller theory.

The estimated strength of the singlet—triplet transition in XeF2 corresponding to the singlet—singlet transition at 1580 Å is shown to be small (f≦10−4) in spite of a heavy atom effect; the small transition strength persists because of the lack of nearby excited states of the required symmetry. In XeF4 the triplet excited state 3Eu corresponding to the singlet—singlet transition 1A1g→1Eu at 1840 Å (f=0.22) is permitted by group theoretical selection rules to mix with its own singlet state. Using an intermediate coupling scheme the estimated intensity of this singlet—singlet transition is calculated to be f=0.007. The theoretical estimates of the symmetry and spin forbidden transition strengths are used for the assignment of the weak electronic transitions in the xenon fluorides.
Spectroscopic Studies of Vibrational Nonequilibrium in Supersonic Nozzle Flows
Authors: Hurle I. R. , Russo A. L. , Hall J. Gordon
Published: January 2005

Studies have been made of the extent of vibrational nonequilibrium produced in supersonic expansions of undissociated N2 from known initial equilibrium conditions attained behind reflected shock waves. The N2 was shock heated and compressed to reservoir temperatures and pressures in the ranges 2800° to 4600°K, and 24 to 82 atm. It was then allowed to expand through a 15° axisymmetric nozzle coupled to the end of the shock tube. The extent of vibrational nonequilibrium was determined by measurements of local vibrational temperatures using the spectrum-line reversal method. The measurements showed the vibrational temperatures in the expansion flows to be much closer to equilibrium than the Landau—Teller relaxation theory predicts. Observations at two area ratios showed that the flow was not completely frozen in the vibrational sense. The probability of N2 vibrational de-excitation inferred from these measurements is about 15 times greater than that inferred from measurements of vibrational relaxation made behind normal shock waves. Reasons for this apparent difference are discussed in terms of the basic environmental and kinetic differences between shock-wave and nozzle-expansion flows. The validity of the application of Landau—Teller relaxation assumptions and shock-tube measured rates to predict nonequilibrium in expansion flows is thus questioned.
Nuclear Magnetic Resonance Fluorine—Fluorine Coupling Constants
Authors: Ng Soon , Sederholm C. H.
Published: January 2005

The pattern of fluorine—fluorine coupling constants is explained on the basis of two mechanisms for nuclear spin—spin coupling: the ``through-bond'' and the ``through-space'' mechanisms. In the former, the interaction proceeds via the electronic structure in the intervening bonds. It is highly dependent on the electron withdrawing power of the substituents on the carbon skeleton. This contribution to the coupling constant goes to zero when the sum of the electronegativities of the substituents becomes sufficiently high. The latter mechanism is operative when two fluorine atoms are sufficiently close in space for there to be appreciable overlap of their electronic clouds. This ``through-space'' interaction proceeds via an electronic structure where there is no bond per se. Experimental evidence for the existence of both mechanisms is given.
Coriolis Perturbations in the Infrared Spectrum of Ethylene
Authors: Smith W. L. , Mills I. M.
Published: January 2005

Rotational structure has been resolved and analyzed in two of the infrared-active perpendicular bands of C2H4 vapor: the Type b fundamental band, ν10, at 826 cm—1, and the Type c fundamental band, ν7, at 949 cm—1. Many of the individual PP and RR branch lines have been observed. The analysis has been confined to values of the quantum number K≥3, for which energy levels ethylene shows no detectable deviations from a symmetric-top rotational structure. The analysis reveals a Coriolis interaction between ν7 and ν10, and between ν4 and ν10, and values of the Coriolis constants ζ7,10z and ζ4,10y are obtained; these are related to normal coordinate calculations for the appropriate symmetry species, and force constants are derived to fit the observed zeta constants. The band center of ν10 has been revised from the original figure of 810 cm—1 to the new value, 826 cm—1, and the inactive frequency ν4 is estimated to lie at 1023±3 cm—1, in good agreement with the previous estimate of 1027 cm—1.

The change in the value of ν10 leads to a suggested change in the value of the Raman-active fundamental ν6 from 1236 to 1222 cm—1. New combination bands have been observed at 2174 cm—1, assigned as ν3+ν10; and at 2252 cm—1, assigned as ν4+ν6; also rotational structure has been resolved and analyzed in the ν6+ν10 band at 2048 cm—1.

The new data obtained for the C2H4 molecule are summarized in Table XII, with all of the other data presently available on the vibrational and rotational constants.
An Expansion of Binary Collision Phase Shifts in Powers of h
Authors: Curtiss C. F. , Powers Robert S.
Published: January 2005

The phase shifts in binary collisions are expressed as series in increasing powers of Planck's constant, h. The series begins with a term in h—1 and contains all odd powers. Recursion relations are developed which lead to an expression for an arbitrary term in the series. The results apply to an arbitrary interaction potential function, for which any odd number of classical turning points may arise.
One-Center Basis Set SCF MO's. II. NH3, NH4+, PH3, PH4+
Authors: Moccia Roberto
Published: January 2005

One-center-expanded SCF MO wavefunctions are reported for the ground states of NH3 and PH3 in their planar and in their calculated equilibrium configurations and of NH4+ and PH4+ in their calculated equilibrium configurations. The calculated molecular energies and the geometrical parameters of the determined equilibrium configurations agree well with the experimental values.

Good agreement is also obtained for the electric dipole moment and the proton affinity of NH3 while the calculated value of the height of the potential barrier for inversion appears to be too small. For PH3 a good value for the height of the potential barrier is obtained while the calculated electric dipole moment is too large. The calculated proton affinity of PH3 seems to be reasonable. A critical examination of the wavefunctions gives an account of the quality of the several results obtained.
One-Center Basis Set SCF MO's. III. H2O, H2S, and HCl
Authors: Moccia Roberto
Published: January 2005

One-center expanded SCF MO wavefunctions are reported for H2O, H2S, and HCl in their ground states. The wavefunctions refer to the calculated equilibrium configurations which agree well with the experimental data. The corresponding computed molecular energies are —75.922436, —397.58906, and —458.83776 a.u., respectively, which are reasonably close to the experimental values. The energy obtained for H2O is found to be near the estimated Hartree—Fock value.

The computed electric dipole moment of H2O agrees well with the experimental value, while for H2S and HCl larger discrepancies are found.
Intrinsic Viscosity of Coiling Macromolecules
Authors: Ullman Robert
Published: January 2005

The intrinsic viscosity of coiling molecules has been calculated using the Kirkwood—Riseman adaptation of the Oseen approximation. Four different models of chain segment distribution were treated: (a) a Gaussian coil, (b) an excluded volume model of Kurata and Yamakawa, (c) a coil expansion model suggested by Peterlin and (d) an excluded volume model deduced from the machine computation of Wall and Erpenbeck. In all cases the partially free draining coil was treated. The mathematical solution of the problem has been carried out on an IBM 704 computer.
Vibrational Structure of Electronic States of Molecular Aggregates. I. A Variation Approach to Dimeric Systems
Authors: Siebrand W.
Published: January 2005

The vibrational structure of electronic states of molecular aggregates is studied, using a simplified model. In this model the intermolecular electronic coupling is treated by tight-binding theory, and the electron (exciton)-vibration interaction is described in terms of a potential well in which the electron (exciton) is trapped. Both interactions are approximated by constant parameters, which, in typical molecular crystals, are of the order of an internal vibrational energy quantum. These parameters govern the motion of a quasiparticle, consisting of the electron (exciton) together with its well, which is called a polaron (excitaron). Earlier treatments, based on comparable models, are confined to cases in which either the coupling or the well is a small perturbation. In this paper a variation method is developed and applied to molecular dimers. The wavefunctions corresponding to these limiting cases are combined to form a trial function. Eigenfunctions and eigenvalues are derived which behave properly in the limits and join smoothly in the intermediate region. The method provides a suitable basis for quantitative computations. An interesting qualitative feature of the model is the ``thermal dissociation'' of the polaron (excitaron).
Vibrational Structure of Electronic States of Molecular Aggregates. II. Extended Weak-Coupling Theory of One-Dimensional Lattices
Authors: Siebrand W.
Published: January 2005

The model developed in the preceding paper is applied to one-dimensional lattices. The treatment is restricted to weak intermolecular coupling. A perturbation method is developed, in which the exchange term is expanded in powers of the phonon concentration. The expansion is carried through to second order, whereas previous treatments involve only first order terms. This method justifies earlier conclusions that, in the weak-coupling region, the average polaron (excitaron) bandwidth is a decreasing function of temperature. The calculations are extended to higher coupling values by a variation approach, which is a simplified version of the variation method of Paper I. This approach, which amounts to mixing limiting wavefunctions corresponding to equal quantum numbers, accounts for the electron (exciton)—phonon interaction. The more elaborate methods of Paper I become unwieldy here. Preliminary calculations suggest, however, that its conclusion with respect to ``thermal dissociation'' of polarons may be carried over to lattices.
VO2+ and X-Ray Produced V2+ in Tutton Salt
Authors: Borcherts Robert H. , Kikuchi Chihiro
Published: January 2005

The electron spin resonance spectrum of the vanadyl ion (VO2+) in single crystals of Zn (NH4)2(SO4)2·6H2O is studied and the properties of x-ray produced V2+ are compared to those of the V2+ grown directly into the same host lattice. In the unirradiated samples the V–O axis is found to have three possible orientations with populations in the ratio 20:5:1. For the most populous position the spin Hamiltonian parameters at X band are S=½, gx=1.9813, gy=1.9801, gz=1.9331, Ax=0.007120/cm, Ay=0.007244/cm, Az=0.018281/cm, and Q′=7×10—5/cm with the x, y principal axes of the g and A tensor being displaced from each other by 23°20′. Furthermore, the vanadyl hyperfine lines show an additional anisotropic structure of five lines, absent in deuterated samples. The parameters for V2+ at K band in both the as-grown and irradiated crystals are S=3/2, gz=1.9717, gy=1.9733, D=—0.15613/cm, E=—0.02280/cm, and A=—0.00825/cm. A study of the effect of x-ray dose upon the line intensity is made. An impurity model of a vanadyl pentahydrate complex associated with a water moleculy vacancy is proposed.
Molecular Reorientation in Liquids. Deuteron Quadrupole Relaxation in Liquid Deuterium Oxide and Perdeuterobenzene
Authors: Woessner D. E.
Published: January 2005

Temperature-dependence measurements have been made on the deuteron spin—lattice relaxation times for liquid deuterium oxide and perdeuterobenzene. The quadrupole spin—lattice relaxation is expressed in terms of motional models previously developed for magnetic dipole—dipole relaxation. The deuterium oxide data are discussed in terms of microwave, dielectric relaxation, and hydrogen-bonding phenomena. The T1 values follow rather closely a proportionality to absolute temperature divided by viscosity. The effective quadrupole coupling constant is only ⅔ to ¾ of the value derived from microwave data. For perdeuterobenzene, the 1.86-kcal/mole activation energy rules out a dominance of the rotational-inertia effect proposed recently by Steele. The temperature dependence is much lower than that of the absolute temperature divided by viscosity. Possible reasons for this are discussed. By use of proton-relaxation data, a quadrupole coupling constant value of 138 kc/sec is estimated, assuming axial symmetry of the electric-field gradient about the C—D bond.
Empirical Evaluation of the London Potential Energy Surface for the H + H2 Reaction
Authors: Cashion J. K. , Herschbach D. R.
Published: January 2005

An empirical potential surface for the hydrogen exchange reaction is derived from the simplest form of the London approximation (neglecting overlap), by evaluating the Coulomb and exchange integrals from the potential curves for the 1Σg+ and 3Σu+ states of H2. This procedure gives an activation energy of 8.9±1.2 kcal/mole, in good agreement with the experimental value of 8.0±0.5 kcal/mole. The potential surface has a single saddle point, and the H: complex is linear and symmetrical, with a bond length of 0.96 Å. Simple, explicit formulas for the activation energy and the vibrational force constants are also obtained. The results emphasize the important contribution from the triplet repulsion between the end atoms with parallel spins in the complex.
Heat Capacity of MnCl2 from 1.3° to 4.2°K with Magnetic Fields to 50 Kilogauss Parallel to the b Magnetic Axis
Authors: Butera R. A. , Giauque W. F.
Published: January 2005

The heat capacity of single-crystal manganous chloride has been measured in constant magnetic fields stabilized at exactly 0, 5000, 7500, 10 000, 18 000, 25 000, and 50 000 G. The measurements which cover the range from 1.3° to 4.2°K, extend the results of Murray who made measurements to 7.25 kilogauss. All of the measurements have been made with the field parallel to the a crystallographic axis (b magnetic axis) as were those of Murray. Except at fields high enough to approach paramagnetic saturation the heat-capacity curves have double maxima, but at about 8000 G the maxima at the lower temperatures are below 1.3°K, the lowest temperature of observation. The heat capacity maxima in zero field were found to be at 1.815° and 1.945°K. The loci of the maxima curve at the higher temperature has temperature increasing with field as found by Murray; however, near 12 kilogauss and 2.03°K, it has been found that a reversal takes place and the field increases as the temperature decreases. The curves for the loci of both sets of maxima evidently approach zero values of dH/dT at 0°K. The heat capacity maxima are not high compared to those of adjacent temperature regions and we do not believe they can be identified as ``transition points'' but rather are merely regions of somewhat accelerated ordering to some ultimate arrangement of magnetic moments, such as the general type suggested by Wilkinson et al. on the basis of neutron diffraction. A rather novel magnetopressure explosion occurred due to a sudden temperature rise accompanying adiabatic magnetization while a crack in a crystal was filled with liquid helium II. Some comments on possible apparatus damage when high fields are applied to enclosures containing both liquid helium and magnetic materials are included. The entropy change in 7740 Pyrex glass has been determined as a function of magnetic field at 1.370° and 4.205°K.
Initiation of Deflagration Waves at Surfaces of Ammonium Perchlorate—Copper Chromite—Carbon Pellets
Authors: Evans Marjorie W. , Beyer Rodney B. , McCulley Leonard
Published: January 2005

A study was made of the initiation of a deflagration wave at the surface of ammonium perchlorate—copper chromite—carbon pellets in nitrogen at 25 atm. The relationship between energy flux density I and exposure time τI, describing the boundary conditions necessary for initiation, was measured. Integration of the governing partial differential equation using experimentally determined chemical and physical parameters and the boundary conditions gave the temperature T(0, τI) of the initiating surface at the moment τI of cutoff of the energy pulse, and a lower bound for the minimum thermal ignition time τim.

T(0, τI) for ammonium perchlorate with 5% copper chromite was 380±31°C. It was drastically lowered when carbon was added, the amount of lowering being proportional to carbon concentration. It ranged from 300° to 215°C for carbon percentages ranging from 0.5 to 4. For given composition T(0, τI) was independent of flux density over the range 9 to 63 cal/cm2·sec. Initiation occurred substantially before the calculated minimum thermal ignition time τim. The results provide support for the view that thermal ignition of the solid material is not a prerequisite for initiation of a deflagration wave.
Infrared Spectra of NF, NCl, and NBr
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: January 2005

The infrared spectra of FN3, ClN3, and BrN3 suspended in Ar and N2 matrices have been observed at 4° and at 20°K. Ultraviolet photolysis of these systems results in the appearance of absorptions assigned to the free radicals NF, NCl, and NBr. Evidence is presented for the matrix deactivation of NBr to its ground 3Σ— state. Slow photolytic decomposition of NCl and NBr has been observed. Possible mechanisms are discussed for the origin of a green phosphorescence identified as resulting from N atoms trapped in the matrix.
Semiempirical SCF—LCAO—MO Calculation of the Electronic Structure of the Guanine—Cytosine Base Pair: Possible Interpretation of the Mutagenic Effect of Radiation
Authors: Rein Robert , Ladik Janos
Published: January 2005

The π-electronic structure of the guanine—cytosine nucleotide base pair has been investigated in the semiempirical SCF—LCAO—MO approximation.

An examination of the energy levels with respect to the single bases showed that the transition between the highest filled and lowest unfilled π orbitals (n*→n*+1) takes place between the levels originating from two different single bases. This statement follows from considering the n* and n*+1 levels of the base pair as perturbed ones of the guanine, cytosine single bases, respectively. This view is substantiated by the structure of the eigenvectors of the respective states. The transition between these states is associated with a transfer of charge, which in the investigated case involves the transfer of a unit charge from guanine to cytosine.

Since in the charge-transfer state the bases are essentially in an ionic form, a considerable increase in the probability of a single-proton tunnelling, proposed by Löwdin, may be expected. The interpretation of radiation-induced mutations in terms of the charge-transfer state and single-proton tunneling is further discussed.
Intermolecular Forces and the Space Group of Solid Chlorine
Authors: Nyburg S. C.
Published: January 2005

Use of the 6:12 potential for Cl2, and presumably for other halogen molecules, shows that the observed orthorhombic Cmca space group in which they crystallize is not that predicted; both the cubic Pa3 and the hexagonal P6̄m2 would be more stable crystal structures. A molecular model is discussed in which, compared to the free halogen atoms, the molecule has, in addition to concentration of charge at its center, a charge concentration at its outer ends. This model correctly predicts the Cmca space group and the orientation of the molecules in the unit cell. The calculations also show why certain other simple molecules crystallize in Pa3.
Electronic Transitions of Some Polyacene Mononegative and Dinegative Ions
Authors: Buschow K. H. J. , Hoijtink G. J.
Published: January 2005

Absorption spectra of the pentacene mono and dinegative ions in the 5–42 kK region were measured. To determine the relative directions of polarization of the electronic transitions a glassy solution of the dinegative ion was photo-oxidized with plane-polarized ultraviolet light and extinctions of this dichroic solution were measured for plane-polarized light parallel and perpendicular to the vector of the photo-oxidizing light. The experimental spectra are compared with those of the mono and dinegative ions of some other polyacenes. A qualitative interpretation of the spectra is given.
Energy Levels of Am IV in LaCl3
Authors: Conway John G.
Published: January 2005

It has been possible to assign the 10 lowest energy levels of Am IV. By using these assignments and the complete spin—orbit matrices, a fit was obtained with 5f hydrogenic wavefunctions. This fit was then improved by using a fitting program and varying all four parameters. Comparison calculations using hydrogenic wavefunctions are made for Pu I. For Am IV the hydrogenic values are F2=268.6 cm—1 and ζ=2605 cm—1; the corresponding values for Pu I are F2=230.6 cm—1 and ζ=2174.6 cm—1.
Ruby-Laser Excited Photocurrents in Anthracene
Authors: Hasegawa K. , Schneider W. G.
Published: January 2005

Photocurrents in anthracene single crystals excited by the 6943-Å ruby laser line have been studied. At room temperature (and at higher temperatures) the currents are proportional to the square root of the intensity of exciting light, as reported previously. As the temperature is lowered this changes progressively to a linear dependence at —25°C. In the vicinity of 0°C the photocurrent pulses exhibit long decay times following termination of the laser pulse. These are interpreted in terms of carrier-trapping effects. The observed photocurrents are attributed mainly to single photon excitation of localized anthracene ions or trapped carriers. The enhanced currents observed in experiments using preillumination with uv light support this interpretation.
Ultrasonic Absorption Measurements in Single Crystals of Naphthalene and p-Dichlorobenzene
Authors: Yun Seung S. , Beyer Robert T.
Published: January 2005

The attenuation of ultrasonic waves has been measured in single crystals of naphthalene and p-dichlorobenzene at frequencies from 5 to 95 MHz for the former crystal, and 5 to 65 MHz for the latter. The absorption coefficients of the crystals were proportional to the square of the acoustic frequency. The change in absorption coefficient for the temperature range from 30°C down to —70°C was very small to about —40°C; a slight decrease was observed below this point. There was no appreciable change in the absorption coefficient within the limit of experimental error, up to a (uniaxial) pressure of 4.25×106 dyn/cm2 applied in a direction perpendicular to the direction of propagation of the acoustic wave. From these results, it is concluded that any contributions of dislocation damping and thermal conduction in the crystals to the total acoustic absorption were negligibly small.

The sound velocity was determined for these same crystals at room temperature. This velocity was to be found to be a linear function of the temperature, with negative slope, and shows approximately the same temperature coefficient in both cases.
Carbon Monoxide Vibrational Relaxation in Mixtures with Helium, Neon, and Krypton
Authors: Millikan Roger C.
Published: January 2005

The collisional relaxation of CO vibrational excitation for He, Ne, and Kr as collision partners has been determined by observation of infrared emission behind incident shock waves. The data are fit by these equations: CO–He, lne(pτ) = 87T—⅓—19.1 for 580<T°K<1500; CO–Ne, lne(pτ) = 142T—⅓—21.1 for 1400<T°K<3000; CO–Kr, lne(pτ) = 187T—⅓—22.3 for 2100<T°K<7000. These values are for CO infinitely dilute in the second gas at total pressure p atm, where τ is in sec and T in Kelvin degrees. Extrapolation of these data and the CO–H2 data previously available to room temperature yields values that correspond well with those from the quenching of CO vibrational fluorescence for the CO–H2 and CO–He cases. There is wide disagreement in the CO–Ne case. This is traced to an improper extrapolation in the quenching method for obtaining the Ne datum. The collision mass dependence of vibrational relaxation for constant oscillator frequency is briefly discussed.