bluuebunny/crossref_metadata_2025 huggingface dataset:
Interchange of Charge between Gaseous Molecules
Authors: Rapp Donald , Ortenburger Irene B.
Published: January 2005

The theoretical methods for calculation of charge-exchange cross sections of Gurnee and Magee [J. Chem. Phys. 26, 1237 (1957)] have been applied to the reactions of H atoms with H+, O+, and N+. The agreement with experiment [Fite, et al., Phys. Rev. 119, 663 (1960); Hummer, et al., Phys. Rev. 119, 668 (1960)] is excellent considering the approximations involved in the theory.
Microwave Spectrum, Barrier to Internal Rotation, and Quadrupole Coupling of Acetyl Bromide
Authors: Krisher Lawrence C.
Published: January 2005

The microwave spectra of the two acetyl bromide species, CH3COBr79 and CH3COBr81, have been investigated in the region 12 000 to 33 000 Mc.

The bromine nuclear quadrupole hyperfine splittings were analyzed to give values for the quadrupole coupling constants. The observed coupling constants indicate a considerable deviation from cylindrical symmetry of the electric field gradient about the C–Br bond.

Several of the rotational transitions were further split into doublets due to the hindered internal rotation of the methyl group. The quadrupole hyperfine and internal rotation splittings were found to be essentially independent, and analysis of the latter gives a barrier to internal rotation of 1305±30 cal/mole.
Contribution of Lattice Vibrations to the Order-Disorder Transformation in Alloys
Authors: Wojtowicz Peter J. , Kirkwood John G.
Published: January 2005

The lattice vibrational partition function for a binary crystal is constructed from the normal mode frequencies in the classical nearest-neighbor harmonic approximation. The set of frequencies is computed as a function of the short-range order parameter by the use of the Born-von Karman analysis and second-order perturbation theory. The resulting form of the lattice vibrational partition function closely resembles that of the static configurational partition function so that a reexamination of the statistical thermodynamics, including lattice vibrational effects, proves to be straightforward. The derived thermodynamic quantities are compared with experiment for the case of β-brass. The theoretical heat capacity discontinuity as calculated by the method of Bethe and Kirkwood is increased from 1.7R to 6.1R by the inclusion of the lattice vibrational contribution. The agreement with the experimental value of about 5R is now satisfactory.
Quantum Corrections for Transport Coefficients
Authors: Choi Sang-Il , Ross John
Published: January 2005

The equation of motion of a quantum-mechanical two-particle system is solved without approximation in an expansion in Planck's constant. First-order quantum corrections comprising all contributions to the coefficient of ℏ2 in the expansion are derived for the differential scattering cross section and the kinetic-theory transport coefficients. Numerical results are obtained for a simple model of molecular interactions, and lack of agreement is found with work based on the WKB solution of the Schrödinger equation.
On Molecular Chaos and the Kirkwood Superposition Hypothesis
Authors: Grad Harold
Published: January 2005

We consider properties which are possessed by typical functions of very many variables such as the n-particle molecular distribution function of a dynamical system. We show that such a function ``selected at random'' will in all likelihood approximately satisfy the molecular chaos condition and, to a better approximation, will very likely satisfy the Kirkwood superposition relation.
Theory of ``Melting'' of the Helical Form in Double Chains of the DNA Type
Authors: Zimm Bruno H.
Published: January 2005

Previous theoretical treatments of the transition between the helical and random forms of the desoxyribose nucleic acid (DNA) molecule are extended to include formally the explicit consideration of the dissociation into two separate chains and the consideration of the effects of the ends of the chains. An approximate form for the fraction of base pairs that are bonded is obtained in terms of two parameters, a stability constant for base pairing and a constant representing the interaction of adjacent base pairs. The matrix method of statistical mechanics proves to be adaptable to this problem. Some numerical examples are worked out for very long molecules, for which case it is found that the effect of concentration is small.
Density Correlations, Critical Opalescence, and the Free Energy of Nonuniform Fluids
Authors: Fixman Marshall
Published: January 2005

We show the equivalence of three prior approaches to the theory of critical opalescence: (a) the direct study of the long range behavior of the radial distribution function, due to Ornstein and Zernike, (b), the indirect approach by Rocard, who obtained the local pressure in a system of nonuniform density, and (c), the indirect approach by Debye, who obtained the free-energy density in a system of nonuniform density. The molecular aspects of the theory are relieved to some extent from the confines of regular solution theory. The consequences of the Kirkwood superposition approximation, and its necessary revision, are examined.
Dielectric Relaxation of Polar Liquids
Authors: Glarum Sivert H.
Published: January 2005

The statistical theory of the dielectric relaxation of polar liquids is developed using the fluctuation-dissipation approach to linear dissipative phenomena, and an expression is derived relating the complex dielectric constant to a time-dependent microscopic correlation function. It is found that a finite number of microscopic relaxation times leads to an equal number of macroscopic decay times, and, in the case of a single relaxation time τ0, the decay time is given by T0=[3ε0/(2ε0+ε∞)]τ0,ε0 being the static dielectric constant, and ε∞ being the high frequency dielectric constant. Relaxation times are also determined for systems having two decay times, and for systems characterized by the circular-arc and skewed-arc distribution functions.
Kinetic Theory of Dense Gases
Authors: Hollinger Henry B. , Curtiss C. F.
Published: January 2005

The Boltzmann equation is found to be determined to arbitrary order in the density as a consequence of the molecular chaos assumption. A three-body collision approximation is given explicitly and shown to be identical to that implied by the Bogolyubov assumptions; the relation between the molecular chaos assumption and the Bogolyubov assumptions is discussed. It is shown that the Enskog modification of the Boltzmann equation for dense gases composed of rigid spheres is correct, subject to the molecular chaos assumption. The current disagreement over the correct form for this equation is discussed.
Effect of Binding of Ions and Other Small Molecules on Protein Structure. VIII. On Isomerization of Serum Albumin in Acidic Media
Authors: Cann John R.
Published: January 2005

The complex electrophoretic patterns of BSA in 0.02M NaCl-HCl are due to reaction boundaries arising from a set of rapidly established isomerization equilibria and a slow, apparently irreversible reaction. The slow reaction is of only minor importance for electrophoresis in acetate buffer, although a second irreversible process occurs in this solvent at protein concentrations of 0.2% and lower. This latter reaction accounts for the bimodality of the patterns obtained at low field strength with 0.2% BSA in acetate buffer. Resolution of those peaks corresponding to the rapidly established isomerization equilibria is a consequence of changes in either pH or conductance in the reaction boundary during nonideal electrophoresis. Equilibrium constants can, nevertheless, be computed from extrapolated values of the various electrophoretic mobilities without recourse to area measurements. Our observations suggest the following set of consecutive isomerization equilibria: N+nH+⇄FF+mH+⇄Iwhere, as in the reaction scheme of Aoki and Foster, the F form of the protein has a larger electrophoretic mobility than the N form, whereas that of the I form is intermediate between those of the N and F forms.
Structure of Transport Equations
Authors: Tamor S.
Published: January 2005

The problem of inventing irreversible equations which in some sense approximate the Liouville equation is examined. First a class of solutions of the Liouville equation is defined which have the property of weak convergence to equilibrium. A modified Liouville equation is then constructed which is inherently irreversible and whose solutions constitute an asymptotic approximation to the Liouville equation for those systems which decay to equilibrium. The approximation involves replacing the force term in the Liouville equation by an operator involving the prehistory of the system for a small but finite time. It is found that solutions of this modified equation exist only for time-smoothed distribution functions, and that the smoothing interval must increase slowly with time. This smoothing procedure is essentially the repeated time-smoothing method of Kirkwood.
Cell Method in Grand Canonical Ensemble
Authors: Richardson J. M. , Brinkley S. R.
Published: January 2005

A variational form of the cell theory of multicomponent liquids is formulated on the basis of the grand canonical ensemble. The method can in principle be extended to any desired level of accuracy. More explicit results are obtained for the case in which each cell can contain at most one particle and the correlation between cells is neglected. In addition, a higher order theory is presented in which correlations in the modes of occupancy of cells is treated to the second order. The relation between the radial distribution function and the results of the simpler cell theory is considered.
Emission Spectrum of Trivalent Holmium in the Scheelite Structure
Authors: Van Uitert L. G. , Soden R. R.
Published: January 2005

Fluorescent emission due to holmium can be readily observed in a calcium tungstate host lattice under 3660 A excitation. There are at least eight excited states of holmium which fluoresce in the visible range due to transitions to the 5I8 ground state. These emission peaks show concentration quenching effects which appear to be due to the development of exchange coupling.

A number of emission peaks due to holmium represent transitions which do not correspond to known absorption bands. These peaks are particularly prominent in the emission spectra at high concentrations of holmium.
Trimethylene Oxide. I. Microwave Spectrum, Dipole Moment, and Double Minimum Vibration
Authors: Chan Sunney I. , Zinn John , Fernandez Jose , Gwinn William D.
Published: January 2005

The microwave spectra of four isotopic species of trimethylene oxide have been investigated. Analysis of the spectra indicates that the four-membered ring is essentially planar. From the intensity measurements of the rotational transitions and their vibrational satellites, it was concluded that the energy levels in the ring-puckering vibration are single levels. The Stark effect also provided independent evidence that the ring is not highly puckered. The dipole moment of the molecule was found to lie solely on the C–O molecular axis. A value of 1.93±0.01 Debye was obtained. The existence of a small barrier in the potential function, however, was established by a detailed analysis of the observed vibration-rotation interaction. Quantitative considerations have led to an accurate determination of the barrier height and the general shape of the potential function. The barrier restricting the ring-puckering motion has been found to be 35±5 cm—1. The ground vibrational level is 8±4 cm—1 above the top of the barrier.
Excitation and Negative Ions in H2O
Authors: Schulz G. J.
Published: January 2005

By combining the trapped-electron method with the study of negative ions and positive ions, it is possible to obtain data which can be used for construction of an approximate potential energy diagram of molecules. The experimental methods used are described and the H2O molecule is discussed. The negative ion current peaks at 6.5±0.1 and 8.8±0.1 ev. Kinetic energy measurements on the negative ions show that the latter peak is associated with the same state at infinite separation as the first peak. The inelastic loss processes are essentially in agreement with optical absorption experiments. An inelastic process with a threshold at about 3.4 ev is observed.
Velocity Analysis of Molecular Beams Generated from NaOH Vapors
Authors: Rao V. S. , Schoonmaker Richard C.
Published: January 2005

A molecular beam velocity analysis technique has been employed to determine the molecular composition of vapors in equilibrium with liquid sodium hydroxide in the temperature range 887–996°K. The experimental results are nonreproducible to an extent which far exceeds the expected experimental uncertainties. It is inferred that this anomalous behavior is characteristic of the NaOH system and several possible explanations for the discrepancies are discussed.
Spectrum of Yb3+ in Yttrium Gallium Garnet
Authors: Pappalardo R. , Wood D. L.
Published: January 2005

The optical absorption at various temperatures of an ytterbium-doped yttrium gallium garnet is reported. The effect of a cubic and rhombic crystal field on the splitting of the free-ion levels is calculated. A tentative interpretation of the fine details of the spectrum is given.
Quantum-Mechanical Calculation of Harmonic Oscillator Transition Probabilities in a One-Dimensional Impulsive Collision
Authors: Shuler Kurt E. , Zwanzig Robert
Published: January 2005

Quantum-mechanical vibrational transition probabilities Pi→f(ε) for harmonic oscillators, undergoing impulsive hard sphere collisions along the line of centers with an incident atom with relative kinetic energy ε, have been computed by a machine (IBM-704) solution of the relevant Schrödinger equation. Curves for Pi→f(ε) over a range of ε are presented for initial (i) and final (f) vibrational oscillator states i, f=0, 1, 2, and 3. It is shown that this model of an inelastic collision gives rise to appreciable vibrational transitions v(i)→v(f) with | Δv |>1 (in addition to | Δv |=1) in contrast to the Landau-Teller-Herzfeld adiabatic, first-order perturbation treatment which permits only transitions with | Δv |=1. This result is discussed in relation to the dissociation of diatomic molecules and to the adsorption of atoms on solids. Averaged transition probabilities P̄i→f(T) are computed for an incident beam of particles with a Maxwellian velocity distribution. It is pointed out that such averaged transition probabilities may give a misleading impression of the efficiency of translational-vibrational energy transfer if the Pi→f(ε) show a resonance type of behavior, i.e., a strong dependence of Pi→f(ε) on ε over a small interval of ε.
Scattering of Metastable Helium Atoms in Helium, Neon, and Argon
Authors: Smith G. M. , Muschlitz E. E.
Published: January 2005

Total collision cross sections for the scattering of metastable 23S and 21S He atoms in helium, neon, and argon have been measured using a thermal-energy atomic beam in which a fraction of the helium atoms are excited by electron bombardment. The excited particles are detected by measuring the secondary electron emission from metal surfaces. The cross sections for the scattering of the triplet atoms are larger than for the singlet in each case. For neon the difference is considerably greater than the estimated experimental error, indicating a large difference in the interaction potentials.
Intermolecular Coupling of Vibrations in Molecular Crystals: A Vibrational Exciton Approach
Authors: Hexter R. M.
Published: January 2005

A vibrational exciton theory is developed which parallels in many ways the electronic exciton theory originally put forward by Davydov and amplified by Craig and Hobbins and by Fox and Schnepp. The kernel of the theory is the adoption, following Davydov again, of a transition-dipole—transition-dipole interaction as the potential which perturbs the isolated molecule energies and which thereby couples the motions of pairs of molecules in a crystal. As a result of the quantitative application of this theory, molecular dipole derivatives of several of the parallel modes of methyl chloride are obtained from the correlation field splittings of the corresponding fundamentals in the spectrum of solid methyl chloride. An isotope effect upon correlation field splittings is reported and is accounted for in terms of the same theory. A general method of testing the theory in terms of this isotope effect is suggested. The effect of intermolecular transition dipole coupling on intensities is derived and compared with the ratio of the dipole derivatives obtained from the correlation field splittings to those obtained from absolute intensity studies in the gas phase. The possible use of other bases for correlation field splittings is also discussed.
Temperature Variation of the Linewidth in Nonresonant Microwave Absorption
Authors: Boggs James E. , Deam A. P. , King Joe M.
Published: January 2005

The linewidth parameter Δv/p for nonresonant microwave absorption in CH3Cl and in CHCl2F has been determined at five temperatures between 10° and 150°C from cavity measurements of dielectric dispersion in the gases as a function of pressure at a frequency of 402 Mc. The linewidth is found to be proportional to T—1.5, as opposed to the T—1.0 dependence predicted by Anderson's theory of collision broadening.
Infrared Spectra and Structure of the Isomers of N2F2
Authors: Sanborn Russell H.
Published: January 2005

The isomers of N2F2 have been characterized in the past by their reactivity towards mercury. Investigation of the infrared spectra showed that inactive N2F2 is trans-1,2-difluorodiazine and may be identified by the single strong band centered at 989 cm—1, with PQR structure. Active N2F2 resembles 1,1-difluorodiazine instead of a cis-isomer. This conclusion was reached by considering the mass spectrum, the chemical reactivity, and both the position of the infrared bands and their shapes. 1,1-difluorodiazine may be identified by strong bands at 1524 (PR), 952 (PQR), 896 (PR), and 737 (PQR) cm—1, respectively. Normal coordinate analyses using the Wilson FG-matrix method were performed on both isomers.
Nuclear Hyperfine Interactions in Orbitally Degenerate States of Aromatic Ions
Authors: McConnell H. M. , McLachlan A. D.
Published: January 2005

The dynamical Jahn-Teller effect in the benzene negative ion is investigated by estimating the vibronic eigenfunctions and energies for the lowest energy degenerate and lowest energy nondegenerate vibronic states using Hückel molecular orbital theory and the normal coordinates for the 606 cm—1 and 1595 cm—1 E2g vibrations of benzene given by Whiffen. It is concluded that the lowest energy vibronic state is doubly degenerate, and that this degeneracy is removed by interactions with a polar solvent when this ion is in solution. The solvent interaction produces a time-dependent oscillation or switching of the electronic spin distribution relative to the nuclear framework, which in turn leads to an enhanced broadening of the hyperfine structure through a corresponding fluctuation in the isotropic hyperfine interaction. The calculated linewidths are the same as those reported by Townsend and Weissman if the switching spin distribution is described by a correlation time of the order of 10—9 sec. A similar effect is probably responsible for the anomalously broad proton hyperfine structure reported by Weissman and Townsend in the negative ions of coronene and triphenylene. This effect must also contribute to the linewidth of the hyperfine structure of the negative ion of cyclooctatetraene observed by Katz and Strauss. It is suggested that the enhanced spin-lattice relaxation rate reported by Weissman and Townsend for the negative ion of coronene is due to enhanced spin-orbit interaction, also associated with a degeneracy of the ground vibronic state.
Vacuum Ultraviolet Absorption Spectrum of Phosgene
Authors: La Paglia S. R. , Duncan A. B. F.
Published: January 2005

The spectrum of phosgene was investigated, for the first time, over the region 2000–600 A with a dispersion of about 4.15 A/mm. A number of resolved transitions were found, some with vibrational structure. The vibrational structure was in each case interpreted as a progression in a totally symmetrical frequency. A tentative interpretation of the electronic transitions is given.
Electronic Conduction in Complexes of Aromatic Hydrocarbons with Iodine
Authors: Kommandeur J. , Hall Frances R.
Published: January 2005

Molecular complexes of the aromatic hydrocarbons pyrene and perylene with iodine were found to have an electronic conductivity 10 to 12 orders of magnitude higher than that of the constituent compounds. The specific resistivities measured were 75 and 8 ohm-cm, respectively. The materials behaved like semiconductors and plots of log σ vs 1/T gave activation energies of 0.14 ev and 0.019 ev. No Hall effect could be found, but an upper limit for the mobility of μ≤.01 cm2v—1 sec—1 could be set. Single crystals of the perylene-iodine complex were obtained. The preparation and identification of the complexes are discussed and the results of a phase study on the system of pyrene and iodine are reported.
Electron Spin Resonance in Complexes of Aromatic Hydrocarbons with Iodine
Authors: Singer L. S. , Kommandeur J.
Published: January 2005

Accurate measurements of electron spin concentration in semiconducting molecular complexes of perylene and pyrene with iodine have indicated an exponential temperature dependence in excellent agreement with the activation energy for electronic conduction. The agreement of the magnitudes of the spin concentrations with the carrier concentration estimates obtained from electrical measurements further confirms the identification of the unpaired spins as charge carriers. At low temperatures, small temperature-independent concentrations of trapped spins or free radicals are observed. Spin resonance line shapes, relaxation times, and g-factor anisotropies also have been determined.
Effect of Pressure on the Spectra of Crystalline UF4 and UF3
Authors: Keating K. B. , Drickamer H. G.
Published: January 2005

The effect of pressure has been measured on the crystalline spectra of UF4 and UF3. The UF3, which has a structure analogous to PrF3 and NdF3, behaved much like those compounds, showing a 15% to 40% increase in intensity for different peaks in 50 000 atm. In UF4 certain of the peaks increased in intensity while others decreased. The U4+ ion is almost at a center of symmetry in this crystal. It is indicated that the intensity behavior is reasonable if a significant fraction of the intensity is obtained due to lattice vibrations. Both red and blue shifts are observed on different peaks.
Distortion Correction to the Surface Energy of the {110} Face of Alkali Halide Crystals
Authors: Benson G. C. , Dempsey E. , Balk P.
Published: January 2005

Formulas for the contribution of surface distortion to the surface energy of the {100} and {110} faces of the NaCl-type lattice and of the {110} face of the CsCl-type lattice are obtained by a generalization of a treatment described previously for the {100} face of the NaCl structure. Numerical values of the distortion correction to the surface energy of the {110} faces of all of the alkali halides are presented. These results are discussed in relation to the values calculated previously for the {100} face and to the limited experimental information available.
Linewidths in the Electron Paramagnetic Resonance Spectrum of Gaseous Atomic Hydrogen
Authors: Mazo R. M.
Published: January 2005

A theory of the paramagnetic linewidth in gaseous atomic hydrogen, based on the theory of Baranger, and on an expansion of the spin correlation function in powers of the density is presented. To the approximations considered, the line shape is Lorentzian, the linewidth is proportional to the H atom density, and the relevant cross section involves an interference between the scattered amplitudes from the singlet and triplet potential curves. Comparison with experiment yields a velocity averaged cross section of 28.3×10—16 cm2 at 325°K. This value is compared to other estimates found in the literature.
Dependence of Calculated and Experimental Propane Mass Spectra upon Electron Voltage
Authors: Eyring Edward M. , Wahrhaftig Austin L.
Published: January 2005

Experimental propane mass spectra have been obtained with bombarding electrons ranging in energy from 14 to 500 v. The quasi-equilibrium theory has been used in calculating the same spectra. The grossly simplified version of the statistical theory that satisfactorily predicts the 70-v mass spectrum is inadequate at low voltages, but if half the theoretical number of oscillators are assumed to be effective in the parent-ion and activation energies that bear no simple relation to experimental appearance potentials are employed, a semiquantitative fit of the experimental data is obtained. The description of the decomposition reaction of a molecule-ion in terms of a collection of harmonic oscillators is clearly unsatisfactory. However, the more general form of the quasi-equilibrium theory, in which it is assumed only that the reaction coordinate is separable, does appear to be applicable.
Sum Rule for Transition Probabilities
Authors: Clinton William L.
Published: January 2005

A sum rule is derived for the spontaneous emission transition probability. In particular it is shown that for an atom ∑ m∞Wnm=Zρn(0),where Wnm is the spontaneous emission transition probability, Z is the nuclear charge, and ρn(0) is the electron density of the nth electronic state evaluated at the nucleus.
Composition of the Electronic States of Nd(IV) and Er(IV)
Authors: Wybourne B. G.
Published: January 2005

The eigenvectors of the electronic states of the trivalent neodymium and erbium ions are tabulated for use in calculating the crystal field and Zeeman splittings of the ground and excited states.
Absorption Spectrum and Magnetic Properties of Osmium Hexafluoride
Authors: Eisenstein J. C.
Published: January 2005

This paper is devoted to a discussion of the optical absorption spectrum and the susceptibility of OsF6. It is assumed that two 5d electrons, which move in a ligand field of octahedral symmetry, are responsible for the magnetic and optical properties of the molecule. The calculated positions of the energy levels depend on the strength of the ligand field, the Coulomb integrals and the spin-orbit coupling constant. These quantities are treated as parameters. If they are given appropriate values, excellent agreement with observed energy level positions is obtained. The calculated susceptibility is also in good agreement with experimental values. In order to fit the magnetic data it is necessary to assume that the orbital reduction factor is approximately 0.7.
Quantum-Mechanical Cell Model of the Liquid State. II. Application to the Zero-Point Properties of Close-Packed Crystals
Authors: Hurst R. P. , Levelt J. M. H.
Published: January 2005

The quantum-mechanical cell model previously developed for liquids [J. M. H. Levelt and R. P. Hurst, J. Chem. Phys. 32, 96 (1960)] is adapted and used to evaluate zero-point properties of the noble gases, H2 and D2. Specifically, this theory is applied to determine the heats of sublimation, the zero-point energies and the equation of state for these gases at 0°K. By using the Lennard-Jones (6–12) intermolecular potential constants from second virial coefficients measurements as the only experimental parameters included in the theory, good agreement with the experimentally determined zero-point properties is generally obtained.
Proton Magnetic Resonance Study of Crystalline Potassium Trisoxalatorhodium(III) Hydrate
Authors: Porte A. L. , Gutowsky H. S. , Harris G. M.
Published: January 2005

The broad-line proton magnetic resonance spectrum of crystalline potassium trisoxalatorhodium(III) hydrate, K3Rh(C2O4)34½H2O, has been investigated in the temperature range 77°K—330°K. The spectrum at 77°K indicates that some of the protons in the crystal are not present in water of crystallization and an analysis of this same spectrum indicates that the compound should be formulated as K6[Rh(C2O4)3][Rh(C2O4)2(HC2O4)(OH)]8H2O.This formula is not inconsistent with the chemical reactions that the compound undergoes, and it explains some properties which are not satisfactorily accounted for by the previously accepted formula K3[Rh(C2O4)3]412H2O.The absorption spectrum at 318°K substantiates the analysis of the spectrum at 77°K and it also indicates that the water of crystallization can be grouped into at least three sets, the water molecules in different sets having different degrees of mobility. The proton magnetic resonance data also indicate that the ``monohydrate,'' K3Rh(C2O4)3H2O, is probably K6[Rh(C2O4)3][Rh(C2O4)2(HC2O4)2(OH)]H2O.
Method of Alternant Orbitals for Allyl
Authors: Dearman Henry H. , Lefebvre Roland
Published: January 2005

The π-electron correlation energy and ground-state wave function for allyl are calculated by the method of alternant orbitals. This method accounts for 98.8% of the correlation energy given by the configuration interaction treatment. The atomic orbital spin density matrix obtained with this approximation is also included.
Density Expansions of Correlation Functions for Equilibrium Systems
Authors: Friedman Harold L.
Published: January 2005

A method of deriving density expansions of correlation functions from density expansions of the excess free energy is based on certain thermodynamic relations between derivatives of the grand partition function and derivatives of the excess free energy. The method also depends on using the most general expansion of the interaction energy into components; it is not assumed that this energy is limited to pairwise components. Expansions are obtained for the correlation functions in multicomponent gases and for the correlation functions for solute species in solutions. The method is also applicable to ionic solutions. A mathematical difficulty limits the systems for which these equations are proved to those in which there is a certain flexibility in treating the model.
Radiolysis of Aqueous Solutions Highly Enriched in O18
Authors: Anbar Michael , Guttmann Shmuel , Stein Gabriel
Published: January 2005

Solutions of H2O216,16 in water highly enriched in O18 were irradiated with x rays and protons. The effects of H2O2 concentration, pH, bromide and nitrite ions, on the yield of the isotopic species H2O216,18 and H2O218,18, were investigated. The ``molecular'' H2O2 is formed with a G value of 0.3 in neutral solutions. The formation of H2O216,18 is attributed to the attack of O18H radicals on H2O216,16. The evolved O216,18 may be regarded as a product of a parallel reaction. The yield of O216,18 is dependent on an exchange reaction between HO2 and H2O2. Specific effects due to added NO2— and high concentrations of Br— are discussed.
Oxygen Isotope Fractionation between Calcium Carbonate and Water
Authors: Clayton Robert N.
Published: January 2005

A technique is described for the total extraction of oxygen from calcium carbonate for isotopic analysis. This permits recalculation of previously published data to yield absolute values of equilibrium constants for the oxygen isotope exchange reaction between calcite and water. The equilibrium constant varies with temperature according to the empirical relationship lnK = 2730 T—2—0.00256 over the temperature range 273°—1023°K.
Intramolecular Energy Transfer in Rare Earth Chelates. Role of the Triplet State
Authors: Crosby G. A. , Whan R. E. , Alire R. M.
Published: January 2005

Results of luminescence studies on chelates of La3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Tm3+, Yb3+, and Lu3+ are reported. It is shown that the intramolecular energy transfer efficiency is a sensitive function of the relative positions of the resonance energy levels of the ions and the metastable triplet states of the complexes. In the case of Eu3+ it is demonstrated that, by a proper choice of ligands, it is possible to selectively excite only the lowest resonance level of the two existing resonance levels of this ion. Coupling of the rare earth ions to the ligands is discussed, and a comparison is made between the optical properties of rare earth ions in chelates and in inorganic salts.
Anomalous Relaxation of Hyperfine Components in Electron Spin Resonance. II
Authors: Schreurs Jan W. H. , Fraenkel George K.
Published: January 2005

A detailed study has been made of the linewidth and peak height of each of the five components in the electron spin resonance spectrum of the p-benzosemiquinone ion as a function of microwave power at X-band frequencies. Studies were also made of the spectrum of the peroxylamine disulfonate ion as a function of power. A 20% variation in the linewidths from one hyperfine component to another was found in the p-benzosemiquinone ion spectrum, and a 13% variation in the saturation parameters (T1). The average value for the linewidth parameter at low power for the p-benzosemiquinone ion was found to be (1/T2) = 1.11×106 sec—1, and the reciprocal of the average value of the saturation parameter was found to be about (1/T1) = 0.74×106 sec—1. No variation in linewidths or saturation parameters among the three hyperfine components in the peroxylamine disulfonate ion spectrum was found, and the results were T2 = 2.5×10—7 sec, and T1 = 3.3×10—7 sec. The variation in the linewidth of the p-benzosemiquinone ion can be accurately represented by a quadratic equation in mJ, the field-direction component of the total nuclear spin angular momentum, and the form of this equation is in excellent agreement with the linewidth predicted for a relaxation mechanism arising from an anisotropic intramolecular dipolar interaction between the unpaired electron and the four protons in the molecule, as well as a rotational relaxation of the anisotropic g tensor. Good quantitative agreement between theory and experiment is obtained for the coefficient of mJ2 in the equation for (1/T2) if the rotational correlation time is taken to be τc = 7×10—11 sec, a value which is consistent with the molecular dimensions. The dependence of the saturation parameters on mJ is also in qualitative agreement with the theory, but quantitative discrepancies are found which have not been explained.
Vapor Pressure of Nearly Classical Liquids
Authors: Steele William A.
Published: January 2005

The reduced vapor pressures of liquids which exhibit nearly classical behavior are considered. It is shown that the intermolecular quantum effects upon the parameters of the reduced vapor pressure equations of such liquids are small compared to other variations in these parameters. However, these effects can be reasonably well estimated by considering the changes in vapor pressure upon isotopic substitution in suitable simple systems. Experimental data are analyzed to give quantitative estimates of the quantum effect upon the reduced heat of vaporization, the temperature-independent term in the vapor pressure equation, and the configurational heat capacity of nearly classical liquids.
The Effect of Oxygen Adsorption on Photo- and Semiconduction of β-Carotene
Authors: Rosenberg Barnett
Published: January 2005

The presence of adsorbed oxygen gas increases the magnitude of the surface semiconduction currents in crystalline powder β-carotene by a factor of about 103. The activation energy for the surface semiconduction process is 1.52 ev in argon gas and is decreased to 1.29 ev in oxygen. The room temperature photo-current is increased by a factor of about 25 in oxygen over the value in argon. The activation energy of the photoconduction process is not affected by oxygen. The increase in dark current in an oxygen ambient requires a time of about 2 hr to come to the equilibrium value at room temperature. Radiation is not required to cause the increase. The effect of the oxygen can be reversed completely by heating the β-carotene to 120°C in an inert atmosphere (dry nitrogen or argon). The increase in dark current is linearly proportional to the partial pressure of oxygen in the chamber. The rate of desorption of the oxygen increases with the temperature. The resulting data yield an activation energy of desorption of 0.17 ev. It is suggested that this is the binding energy for the formation of an oxygen-carotene complex, and that the decrease in semiconduction activation energy is correlated to this binding energy. An analysis is given which leads to the conclusion that the mechanism of the current increase with formation of the oxygen complex is twofold; a decrease in the activation energy for semiconduction, and an increase in the mobility of the charge carriers. There is no evidence for a change in the charge creation process. The experimental results are considered to be a partial verification of Platt's theory on the donor-carotene-acceptor complex in photosynthesis since the triplet level of chlorophyll b has a value of 1.43 ev, midway between the value of 1.52 ev for the free carotene semiconduction activation energy and 1.29 ev for the corresponding value of the oxygen-carotene complex. It is also suggested that a possible mechanism for the carotene protection of cells from destructive photo-oxidation may be the formation of the oxygen-carotene complex.
Alkali-Iron Group-Halogen Complexes. Dissociation Energies of KClFeCl2 and CsClFeCl2
Authors: Rao V. S. , Kusch P.
Published: January 2005

A number of complexes between the alkali halides and the divalent halides of the iron group metals have been observed. They are all characterized by a very large rotational magnetic moment of the order of 50 nuclear magnetons for the rotational state of most probable J. The dissociation energies at a temperature of about 1020°K of the two complexes, KClFeCl2 and CsClFeCl2, have been found to be 34.7±1.0 and 24.7±1.0 kcalM—1, respectively. The data from which these results were found were obtained by measuring the relative concentrations of the alkali halide and the complex as a function of temperature while the partial pressure of FeCl2 remained essentially constant. The large difference in the magnetic moments of the two detectable molecular species allows the determination of the relative concentration with considerable accuracy.
Microwave Spectrum of Acetyl Chloride
Authors: Sinnott K. M.
Published: January 2005

The microwave spectrum of ten isotopic species of acetyl chloride are reported. Internal rotation of the methyl group splits some of the rotational transitions into doublets in addition to the chlorine hyperfine structure. Analysis of the internal rotation splitting gives a barrier to internal rotation of 1296±30 cal/mole. From the hyperfine structure, the chlorine nuclear quadrupole coupling constants for Cl35 along the C–Cl bond axis and perpendicular to the plane of symmetry of the molecule were determined to be —58.5 and 21.5 Mc, respectively. The corresponding values for Cl37 were —46.4 and 17.2 Mc. These coupling constants have been interpreted to give information about the double bond and ionic character of the C–Cl bond. The following structural parameters have been determined from the rotational constants of CH3COCl35, CH3COCl37, C13H3COCl35, CH3C13OCl35, CH3CO18Cl35, and CD3COCl35: C–H1.083±0.005 A<CCH110∘21′±10′C–C1.499±0.010<CCO127∘5′±10′C=O1.192±0.010<CCCl112∘39′±30′C–Cl1.789±0.005The observed rotational constants of CH2DCOCl35 show that the equilibrium configuration of acetyl chloride has a methyl hydrogen atom opposite the oxygen atom.
Structure of Alkali Metals in the Liquid State
Authors: Gingrich N. S. , Heaton LeRoy
Published: January 2005

Neutron diffraction patterns have been obtained for the alkali metal liquids; lithium (180°C), sodium (100°C), potassium (65°C), rubidium (40°C, 160°C, 240°C, and 360°C), and cesium (30°C, 300°C, and 575°C). It was found necessary to correct intensities for scattering by a free atom for lithium and sodium but not for the heavier atoms. Atomic distribution curves were computed for all the above cases, and compared with results from x-ray diffraction. Just above melting temperatures the nearest-neighbor distances are for lithium 3.15 A, sodium 3.82 A, potassium 4.64 A, rubidium 4.97 A, and cesium 5.31 A, the number of nearest neighbors is, within one-half atom, about 9.0 to 9.5 atoms in each case. At elevated temperatures with rubidium and cesium, a weak subsidiary concentration of atoms appears between the usual first and second neighbor concentration.
Interaction of a Triplet and a Normal Helium Atom
Authors: Brigman G. H. , Brient S. J. , Matsen F. A.
Published: January 2005

The electronic energy of the system He(1S) and He(3S) was calculated as a function of nuclear separation. This calculation differs from an earlier one by R. A. Buckingham and A. Dalgarno [Proc. Roy. Soc. (London) A213, 327 (1952)] in three ways: (1) the use of a nodeless 2s function, (2) the use of an open-configuration wavefunction (1s1s′) for He(1S) and (3) the use of orbital exponents optimized for each internuclear distance. The energy obtained lies approximately one volt below the earlier calculation but confirms it in all qualitative aspects including the presence of a ``hump'' at R≅4a0.
Theoretical Investigations on the Light Scattering of Colloidal Spheres. IX. Lateral Scattering at 90° from Incident Natural and Linearly Polarized Light
Authors: Pangonis William J. , Heller Wilfried , Economou Nicolaos A.
Published: January 2005

The Mie quantities i∥,i⊥ and their sum are calculated for nonabsorbing spheres for the parameters γ=90°, m=1.05 (0.05) 1.30 and α=0.2 (0.2) 25.6. The experimentally important specific scattered intensity (Iu/I0c)0 is derived from (i∥+i⊥)/2. The periodicities in the prominent (secondary) i (α) oscillations and in the less pronounced primary and tertiary oscillations are briefly discussed.
Theoretical Investigations on the Light Scattering of Colloidal Spheres. X. ``Scattering Ratio'' and Depolarization of Light Scattered at an Angle of Observation of 90°
Authors: Heller Wilfried , Pangonis William J. , Economou Nicolaos A.
Published: January 2005

The scattering ratio σ for nonabsorbing spheres and for an angle of observation γ of 90° is calculated from data given in the preceding publication [J. Chem. Phys. 34, 960 (1961), Paper IX, this issue], for m=1.05 (0.05) 1.30 and α=0.2 (0.2) 25.6. The scattering ratio represents the ratio of the total intensities scattered from a linearly polarized incident beam vibrating once parallel and, subsequently, perpendicular to the plane of observation. In the present instance of spheres, the results are identical with the depolarization in infinitely dilute systems. The experimentally attractive features of σ measurements are pointed out and the precautions to be observed for useful application of the theoretical data are enumerated. The periodicities in the σ (α) curves due to the primary, secondary, and tertiary undulations in the basic i(α) functions are briefly discussed with particular emphasis upon selecting conditions of optimum sensitivity of the method for particle size determinations, characterized by an error of not more than 1–3 A in particle diameter in monodisperse systems.
NMR Spectra of Glycidaldehyde
Authors: Reilly C. A. , Swalen J. D.
Published: January 2005

The NMR spectra of glycidaldehyde were measured at 40 and 60 Mc/sec. [Complex chemical formula] These complicated spectra of four interacting protons were analyzed by two methods: the ABKY approximation and the iterated ABCD solution. The various mathematical techniques developed should prove useful in the analyses of other complicated spin resonance spectra.

The following spin-spin coupling constants, Jij in cycles per second and chemical shifts, δi in parts per million (relative to tetramethylsilane) were found: JABJACJBCJADJBDJCDδAδBδCδD40 Mc/sec5.542.044.90−0.03−0.326.363.0963.1583.3568.92260 Mc/sec5.542.094.87+0.03−0.316.243.0983.1663.3568.922 The first three coupling constants are very close in magnitude to those obtained in other epoxides (in most cases to within 0.5 cps).

The magnitude of the coupling constant between the aldehyde proton (D) and the adjacent proton (C) indicates that the D proton of the aldehyde group is probably on a time average, mainly in a plane perpendicular to the epoxide ring. The proton (D) could be either cis or trans to proton (C), but from a consideration of internal rotation interactions, it is probably in the trans configuration. The JAC and JBC coupling constants are consistent with an ``eclipsed-ethanelike'' model rather than with an ``ethylenelike'' one. The coupling constants across the molecule, JAD and JBD, are an order of magnitude smaller than the other constants. This is in agreement with the approximate attenuation factor of 1/10 for spin-spin coupling through a single bond.
Geometric Basis of Phase Change
Authors: Ginell Robert
Published: January 2005

A consideration of the higher j-mers by association theory shows that starting with the 7-mer and going up to 19-mer, spherically symmetric atoms can pack in an unsymmetrical arrangement in which more bonds exist among the atoms in the array than if the atoms were packed symmetrically. The asymmetric pattern is then the model for the liquid while the symmetric array yields the crystal. The transition from the liquid to the crystal is difficult by homogeneous nucleation because it requires a cooperative effort of, in the neighborhood of 12–15 atoms. Heterogeneous nucleation is, however, simple since by this mechanism the region where the liquid j-mers are more stable than the crystal j-mers is bypassed. Methods of calculating the equilibrium constants and the concentrations of the various species are derived from association theory. The critical value where the formation of higher close-packed j-mers becomes important is when the value of the equilibrium constant exceeds 1.
Changes in the Electronic Transitions of Aromatic Hydrocarbons on Chemical Substitution. II. Application of Perturbation Theory to Substituted-Benzene Spectra
Authors: Petruska John
Published: January 2005

An analysis is made of the changes that occur in the 2600, 2050, and 1850 A transitions of benzene on chemical substitution. Formulas derived by first- and second-order perturbation theory, with coefficients evaluated by molecular orbital theory, are presented and applied to a large collection of intensity-change and frequency-shift data obtained from the literature. Most of these data pertain to the 2600 A transition. The first-order intensity formula derived for the 2600 A transition (taking the excited state to be 1B2u) is found to hold quite well for substituents with monoshift (frequency shift on monosubstitution) less than 1500 cm-1; the first- and second-order frequency-shift formula, for substituents with monoshift less than 2000 cm-1. No attempt is made to analyze the intensity changes observed in the 2050 and 1850 A transitions as these changes are too small, relative to the initial intensity, to be reliably measured for weakly perturbing substituents from existing spectra. The frequency shifts, however, can be measured fairly reliably for these two transitions, and it is shown that the formulas derived on the basis of 1B1u and 1E1u excited states, respectively, hold for methyl substitution at least. Empirical values of the intensity and frequency perturbation parameters for the 2600 A transition are presented for over 30 substituents; values of the frequency perturbation parameters for the 2050 and 1850 A transitions for more than half of these are also presented. The meaning of the parametric values is discussed in the light of theoretical expectations.