bluuebunny/crossref_metadata_2025 huggingface dataset:
Lattice Energies of the Alkali Halides and the Electron Affinities of the Halogens
Authors: Cubicciotti Daniel
Published: January 2005

The overlap repulsion parameters that occur in the Born-Mayer treatment of lattice energies have been re-evaluated for the alkali halides from recent compressibility data. With these parameters the lattice energies of the alkali halides were calculated. The lattice energies were combined with thermochemical data to calculate the electron affinities of the halogens. The values obtained were: F 80.2; Cl 85.0; Br 79.5; and I 72.5 kcal/mole.
Free Volume Theory for Square-Well Potentials
Authors: Alder Berni J.
Published: January 2005

The thermodynamic functions have been tabulated for molecules interacting with a square-well potential over a wide region of temperature and density by a straightforward application of the free volume theory.
Normal Coordinates of the Planar Vibrations of Pyridine and Its Deuteroisomers with a Modified Urey—Bradley Force Field
Authors: Zerbi Giuseppe , Crawford Bryce , Overend John
Published: January 2005

A Urey—Bradley potential function has been fitted to the observed vibrational frequencies of pyridine, pyridine-2,6-d2, pyridine-3,5-d2, pyridine-4-d1, and pyridine-d5.

As in the case of benzene, it was necessary to include an additional non-Urey—Bradley force constant ρ to describe the aromatic character of the molecule. Our results suggest several minor changes in the vibrational assignment of some of these molecules.
Inhibition of the Argon-Sensitized Radiolysis of Propane by Hydrogen
Authors: Futrell Jean H. , Tiernan Thomas O.
Published: January 2005

Argon sensitizes the radiolysis of propane, presumably by dissociative charge transfer. Hydrogen interferes with the sensitization reaction by serving as a scavenger for Ar+ according to the reaction Ar++H2→ArH++H. Sensitization and self-inhibition by hydrogen are also considered, and approximate values of the sensitization rate constants are derived from a study of the inhibition processes.
Investigation of Bulk Currents in Metal-Free Phthalocyanine Crystals
Authors: Heilmeier George H. , Warfield George
Published: January 2005

The bulk current in many single crystals of metal-free phthalocyanine has been found to exhibit Ohmic behavior up to fields of 104 V/cm and square-law dependence on voltage for higher fields. Photocurrents in these crystals were Ohmic over the entire range. If one interprets these results as space-charge-limited currents (SCLC), trap densities of 1012 to 1014/cm3 are found from the temperature behavior of the I-V characteristic. From the transition between Ohmic and square-law regions, the concentration of free carriers was calculated to be approximately 106 to 107/cm3 in fairly good agreement with that found from Hall measurements. Samples were measured which had both dark and photo currents which varied as V at low fields, but as V1.5–1.7 at higher fields. These observations are interpreted qualitatively in terms of a model in which a layer of higher resistivity than the bulk extends from the contact into the bulk.
Proton Magnetic Resonance Studies in Sodium—Ammonia Solutions
Authors: Hughes Thomas R.
Published: January 2005

High-resolution techniques have been applied to the measurements of the proton magnetic resonance shifts in sodium-ammonia solutions. Concentrations ranging from R = 1.6×10—4 to 1.7×10—1 were studied, and the temperature was varied from below —70° to above +25°C.

The miscibility gap was noted in the relatively concentrated solutions. In dilute solutions, a triplet, arising from the spin—spin interaction of the nitrogen nucleus on the proton nuclei within an ammonia molecule, was sometimes observed. In order to interpret the data taken on samples having a mole ratio R≤1.15×10—2, a modified form of the Knight shift expression applicable to this system is derived: (ΔHH0)I=−8π3L0ρ(I)χe,theo,where χe, theo = L0μe2/kT. Using this relation, the data taken at —33.2°C are found to offer strong support for the existence of some kind of monomers down to R≤3.41×10—4. The value deduced for the total negative spin density of the electron on the monomer protons is —8.1×1023 cm—3 using the equilibrium constants of Becker, Lindquist, and Alder.

Application of this same formalism to published Knight shift data yields corresponding values for the total electron density associated with the monomer of 9.0×1024 cm—3 on the nitrogen nuclei and of approximately 3.3×1022 cm—3 on the sodium-ion core. The possibility that the electron relaxation occurs on the monomer rather than on the ammonia molecules bordering a singly occupied cavity is also discussed.
Raman Spectra of Polyethylenes
Authors: Brown R. G.
Published: January 2005

Raman spectra of normal and deuterated polyethylenes in the solid and liquid states were obtained. Tentative assignments for (CD2)n are made using the Teller—Redlich product rule and Krimm's isotopic frequency rule. Interactions between the CD2 deformation and the symmetrical C–C stretching modes of species Ag, and between the CD2 wagging and the asymmetrical C–C stretching modes of species B2g, are considered. Depolarization ratios for melt spectra successfully identified the symmetric modes only in the neighborhood of the CH2 stretching bands of (CH2)n. The Raman spectrum of molten (CH2)n includes bands at 1080 and 1303 cm—1, at which frequencies ``amorphous'' bands are observed in the infrared spectrum of the solid.
NMR Spectrum of 1,1-Difluoroethylene in the Gas Phase
Authors: Flynn George W. , Baldeschwieler John D.
Published: January 2005

The proton NMR spectrum of CH2CF2 in the gas phase consists of two sharp peaks and a number of broad features. The sharp peaks can be identified as transitions between states with the largest singlet fluorine spin character if the spin—rotation interaction is assumed to provide the dominant fluorine relaxation mechanism. Measurement of the splitting of the two sharp peaks as a function of pressure allows the association of the sharp lines in the gas-phase spectrum with the innermost pair of lines in the spectrum of liquid CH2CF2. This identification of the origin of the lines in an AA′XX′ spectrum removes the usual ambiguity in the relative sign of JAA′ and JXX′. In CH2CF2, JHH and JFF are opposite in sign.
Compliance Matrix and Molecular Vibrations
Authors: Decius J. C.
Published: January 2005

It is shown that treatment of the molecular vibration problem in the form | F—1G—1—λ—1E | =0 has certain advantages when the data from vibrational spectroscopy are to be combined with information from mean amplitudes of vibration or centrifugal distortion toward the end of determining a complete quadratic potential function. The matrix F—1=C is a compliance matrix; its elements presumably have as much physical significance as those of F. Some new isotopic sum rules are formulated, appropriate to the compliance scheme, but they are not nearly so general as those involving the λ's. Linear molecules are discussed, and some numerical examples are given for nonlinear XY2 and XY4.
Classical Model for Vibrational and Rotational Excitation of Diatomic Molecules by Collision. I. Hard-Sphere Collision
Authors: Benson Sidney W. , Berend George C. , Wu James C.
Published: January 2005

The details of inelastic energy transfer between a diatomic, classical, harmonic oscillator, A—B, and a hard-sphere atom C are explored for the simple case of colinear collisions. The influence of the masses MA, MB, and MC on the efficiency of energy transfer is examined in detail. The case of equally matched masses (MB = MC) does not necessarily correspond to high efficiency. It is shown that for colinear collisions not all phase angles of the oscillator can occur at the instant of collision, but that instead certain phase angles are excluded. In the case of a highly excited oscillator in a ``cold'' gas, these excluded phase angles are just those that restrict the energy transfer from the oscillator to small amounts of energy. For a harmonic oscillator, near the dissociation threshold, this implies a small, stepwise deactivation process. It is also shown that even for the hard-sphere case, 100% efficiency of energy transfer is not possible, i.e., there is an activation energy in excess of the energy transferred. This is required as an ``escape energy'' in order to avoid a double collision whose effect would be to reduce the energy transferred. This escape phenomenon is also shown kinetically to favor stepwise energy transfer for quantized oscillators. Some simple cases of rotational-energy transfer are examined.
Absorption Spectrum of Pu3+ in Lanthanum Trichloride and Lanthanum Ethylsulfate
Authors: Lämmermann Hildelore , Conway John G.
Published: January 2005

The polarized absorption spectrum and some Zeeman effect studies were conducted on crystals of lanthanum trichloride and lanthanum ethylsulfate containing 0.1 and 5 mole % of Pu3+ at various low temperatures. The ground-state levels as well as several excited states are well characterized. Attempts at fitting the positions of levels to 5f hydrogenic free-ion states give good agreement for F2=245 cm—1 and ζ=2290 cm—1.
Recombination and Disproportionation Reactions of Monochloroethyl and Trichloromethyl Radicals
Authors: Roquitte B. C. , Wijnen M. H. J.
Published: January 2005

The recombination and disproportionation reactions of CH2CH2Cl and CCl3 radicals have been investigated. Trichloromethyl radicals and monochloroethyl radicals were produced by photolyzing carbon tetrachloride in the presence of ethylene. The main features of the resulting reaction mechanism are given by reactions (1) to (8) CCl4+hν→CCl3+Cl,Cl+C2H4→C2H4Cl,2C2H4Cl→(C2H4Cl)2,2C2H4Cl→C2H4+C2H4Cl2,2C2H4Cl→C2H5Cl+C2H3Cl,2CCl3→C2Cl6,C2H4Cl+CCl3→CCl3C2H4Cl,C2H4Cl+CCl3→CHCl3+C2H3Cl.The following rate constants have been determined k4/k3≤0.1;k5/k3≤0.1;k7/(k312k612)=2.5±0.2,and k8/k7=0.11±0.02.
Constrained Molecular Wavefunctions: HF Molecule
Authors: Mukherji A. , Karplus M.
Published: January 2005

A simple approach for supplementing the usual variational energy criterion for molecular wavefunctions is described. With the requirement that integrals of selected operators agree with the known experimental or theoretical values for the corresponding properties, a constrained variation method is formulated. For an appropriate choice of one-electron operators, the resulting charge distribution can be of greater accuracy than that obtained from an unrestricted variation treatment with the same basis set. Since the method is of most interest for simple wavefunctions, it is illustrated in terms of a modification of the best-limited LCAO—MO hydrogen fluoride function of Ransil. A comparison of the two functions shows that the constrained variation treatment leads to improved results for certain one-electron properties. The calculations also demonstrate the sensitivity of the one-electron expectation values to small changes in the orbital coefficients and the total energy.
Environmental Effects on the Infrared Spectra of NOCl and NOBr Solids
Authors: Hisatsune I. C. , Miller Paul
Published: January 2005

Fundamental infrared absorption bands of NOCl and NOBr solids at liquid-nitrogen temperature exhibit remarkable frequency shifts compared to the gas-phase spectra. Peak frequencies, band shapes, and band multiplicities of the solid spectra are strongly influenced by the nature of the solid matrix. Studies of the reactions of nitric oxide with chlorine and with bromine in the solid state suggest that the observed band multiplicities may be due to the formation of molecular complexes between the nitrosyl halide and the halogen.
Bonding in the Ta6Cl122+ and Mo6Cl84+ Structures
Authors: Crossman Leon D. , Olsen David P. , Duffey George H.
Published: January 2005

Molecular orbitals from d, s, p types of valence orbitals and parametric expressions for energy levels in octahedral Ta6Cl122+ and Mo6Cl84+ were obtained by group theoretical methods. Both cages exhibited electron delocalization and similar bonding energies, even though only the Ta6Cl122+ structure is electron deficient.
Infrared Absorption Spectra of B2O3, B2O2, and BO2 in Solid Argon Matrices
Authors: Sommer A. , White David , Linevsky M. J. , Mann D. E.
Published: January 2005

The infrared absorption spectra of B2O3, B2O2, and BO2 isolated in solid argon matrices have been investigated in the region 350–4000 cm—1. The visible absorption spectrum of matrix-isolated BO2 was observed in the region 4000–5500 Å. The gaseous species were generated in a high-temperature effusion cell and trapped under conditions of moderate to high dilution in solid argon matrices at approximately 4°K. Bands were found at 1955, 1921, 1899, 1323, and 1276 cm—1 in the infrared spectra of B210O2, B10B11O2, B211O2, and B10O2, and B11O2, respectively. For both B210O3 and B211O3 infrared spectra of the most dilute matrices show seven distinct bands in the region 450–2100 cm—1. Six of these can be readily assigned as fundamentals and their relative intensities explained if the known ``V'' structure of B2O3 is supposed to have a larger apex angle than that determined by electron diffraction, and the correlation of the normal vibrations and selection rules with those for the linear symmetric (D∞h) model is considered. With additional help from the measured B10–B11 isotope shifts and force constant calculations the following complete assignment was obtained (all frequencies in cm—1): B210O3:  2128(A1),733(A1),536(A1);[172](A1),or [260](A1);[476](A2) 2128(B1),1242(B1),471(B1);493(B2);B211O3:  2060(A1),729(A1),518(A1),[172](A1), or [259](A1);[456](A2),2060(B1),1239(B1),454(B1);477(B2);where the bracketed frequencies were not observed directly.

Thermal functions have been computed for B2O3 and compared with the available calorimetric data. Structural parameters and a complete vibrational assignment have been estimated for B2O2. The infrared and green bands observed for BO2 are in agreement with the high-resolution results of Johns. Thermal functions for B2O2 and BO2 have also been computed.
Theory of the Effect of Temperature on the Electron Diffraction Patterns of Diatomic Molecules
Authors: Bonham R. A. , Peacher J. L.
Published: January 2005

The effect of temperature on the electron diffraction pattern of a diatomic molecule is considered from the standpoint of the simple kinematic scattering theory utilizing a quartic vibrational potential. The potential is obtained by an expansion of ℏ2J(J+1)/2μr2+Dexp[−2a(r−re)]−2Dexp[−a(r−re)] about its minimum value r0. The second-order wavefunction for the nth vibrational and Jth rotational state of the system has been obtained, and expressions for the electron diffraction quantities rg, le2, and M (s) have been computed. General results for the quantity M (s) utilizing the approximate eigenfunctions of the complete Morse potential and incorporating an approximate treatment of the effect of centrifugal stretching are also presented. Explicit expressions for M (s) for the first three vibrational states as derived by this treatment are given. Appropriate sums over all the vibrational and rotational states have been carried out to obtain the temperature dependence for the above quantities. Estimates of the effect of temperature on the parameters rg and le2 at 300° and 1500°K for representative diatomic molecules are given.
Forces in Molecules. II. A Differential Equation for the Potential-Energy Function
Authors: Clinton William L.
Published: January 2005

A second-order, linear, homogeneous, differential equation for the diatomic molecular potential-energy function, Un(R), is derived. Several aspects of this equation are studied in detail. The solutions of an approximate form of the equation suggest an empirical function that slowly oscillates in the complete interval 0≤R≤∞. This function is fit about the optimum minimum for 23 molecules. An approximate differential equation is derived for the function gij(R)≡Ui(R)—Uj(R), where Ui and Uj are any two potential-energy curves for different electronic states. This equation is valid in an interval for which gij is small—that is, for near degeneracies. An application to two states of H2+ is given.
Spin—Spin Interaction in Methylene
Authors: Sharma Ramesh D.
Published: January 2005

Calculations of the spin—spin interaction for methylene have been carried out. It is predicted that a resonance line should be observed at 3.3×1010 cps in the ESR spectrum of the solid system. It is shown that the splitting of the rotational lines in the electronic spectrum of methylene should be observable with an instrument with a resolving power of ∼0.5 cm—1 in the ultraviolet region of the spectrum.
Theory of the Dielectric Constant of a Nonpolar Fluid
Authors: Isihara A.
Published: January 2005

Taking the dipole interactions of molecules into consideration, a statistical theory of the dielectric constant of a nonpolar fluid is presented. It is assumed that the molecules have a constant polarizability and no higher-order multipole moments. The deviation of the Clausius—Mossotti formula from experiments is expressed in a density series. It is found that coefficient B in the generalized Clausius—Mossotti Eq. (5.1) has a relation to coefficient A. B is determined explicitly as a function of temperature for isotropic spherical molecules with hard-sphere potentials, square-well potentials, and Lennard-Jones potentials. The results are compared with the data of Johnston, Oudemans, and Cole on inert gases.
EPR Spectrum of Irradiated Oriented Polytetrafluoroethylene
Authors: Ovenall D. W.
Published: January 2005

The electron paramagnetic resonance (EPR) spectra of free radicals trapped in oriented samples of polytetrafluoroethylene, after high-energy irradiation in vacuum, are dependent on the angle between the orientation direction and the direction of the magnetic field applied in the EPR experiment. This orientation dependence is considered in the light of recently published data on fluorine-containing free radicals trapped in irradiated single crystals of fluorocarbon compounds. The radical –CF2–ĊF–CF2– put forward to account for the EPR spectra of randomly oriented samples of irradiated polytetrafluoroethylene provides a satisfactory explanation of the principal features of the spectra and their orientation dependence. Several additional weak hyperfine lines have been observed and possible origins of these are discussed.
Comparison and Appraisal of Approximation Formulas for Total Elastic Molecular Scattering Cross Sections
Authors: Bernstein R. B. , Kramer K. H.
Published: January 2005

The Massey—Mohr (MM), Schiff (S), and Landau—Lifshitz (LL) approximations for the total elastic cross section (Q) are intercompared. All can be shown to follow from the same assumption, (i.e., the classical small-angle deflection function, thence the Jeffreys—Born phases via the semiclassical equivalence relationship), sufficing to determine the velocity dependence of Q. Thus, for V=±C(s)/rs, Q(s)=p(s)[C(s)/hv ]2/(s—1) The coefficient p(s) is the same for the S and LL approximations; the ratio pSLL(s)/pMM(s)≥1, (<1.075); it is 1.0709 and 1.0458 for s=6 and 12, respectively.

A numerical calculation for a repulsive (s=12) interaction shows that the SLL formula reproduces the partial-wave calculated Q to within ½%. A graphical presentation suggests the generality of this result; it also indicates the source of bias in the MM approximation. For a ``realistic'' intermolecular potential, (restricting consideration to collisions in the ``thermal'' energy range), the influence of the repulsion is only to produce undulations in Q(v); the correct value of C(6) may be obtained by velocity averaging the ``apparent'' CSLL(6).
Thermochemistry of Cyanocarbons
Authors: Boyd Richard H.
Published: January 2005

The heats of combustion of several cyanocarbons have been measured as well as auxiliary heats of vaporization (from vapor pressures) and solution in order to determine heats of formation. The cyano-olefins, tricyano and tetracyano ethylene have negative stabilization energies indicating electrostatic repulsion between the highly polar cyano groups predominates over electronic delocalization stabilization (—15 and —27 kcal/mole, respectively). In 7,7,8,8-tetracyanoquinodimethan the net effect is stabilization (20 kcal/mole). The electron affinity of 7,7,8,8-tetracyanoquinodimethan has been estimated at 86 kcal from the heats of formation of its aqueous ion-radical salt solutions and an estimate of the hydration energy of the ion radical. Heats of solution of ion-radical salts indicate that the binding energy of ion-radical pairs in the crystal is of the order of 14 kcal/mole-ion radical. The heats of formation of aqueous solutions of the strong organic acids pentacyanopropene and hexacyanoisobutylene compared with calculated values for the unionized forms indicate enthalpies of ionization (acid strength) comparable to mineral acids.
Singlet—Singlet Energy Transfer in Fluid Solutions
Authors: Dubois Jean T. , Cox Mary
Published: January 2005

Further examples of the transfer of singlet-state energy in aerated cyclohexane solutions at 25°C are given. Biacetyl fluorescence was sensitized using diethyl ketone, methyl ethyl ketone, cyclopentanone, chrysene, and phenanthrene. The transfer process is diffusionally controlled and the mechanism appears quite general. Conditions necessary for long-range dipole—dipole interaction are discussed.
Molecular Orbital Studies of Diatomic Molecules. III. The Ground State of the Hydrogen Molecule
Authors: Harris Frank E. , Taylor Howard S.
Published: January 2005

A method of molecular orbital computation described in Papers I and II of this series are applied to the X 1Σg state of hydrogen. The potential curve is reported and the significance of the results is discussed.
Dipole-Moment Function for Diatomic Molecules
Authors: Goodisman Jerry
Published: January 2005

The functional form of the dipole-moment function of a diatomic molecule is investigated in the united-atom and separated-atom limits. The moment goes to zero as R3 for an S or P united atom, and as R5 for a D or F united atom. For separated atoms, the moment goes as R—4 if at least one atom has a quadrupole moment, and as R—7 otherwise. Evidence is given that simply combining the two limiting functional forms is insufficient to represent the actual dipole-moment function.
Semiclassical Analysis of the Extrema in the Velocity Dependence of Total Elastic-Scattering Cross Sections: Relation to the Bound States
Authors: Bernstein Richard B.
Published: January 2005

The phenomenon of extrema in the velocity dependence of the total elastic cross section Q(v) for atom—atom scattering in the thermal-energy region is shown to be a quite general one, whenever the interaction potential consists of both attractive and repulsive parts and the resulting well has a ``capacity'' for one or more discrete levels. The phase shift vs angular-momentum dependence exhibits a maximum; since this maximum is a function of the de Broglie wavelength, the cross section exhibits an undulatory velocity dependence. A semiclassical analysis of the extrema velocities (and undulation amplitudes) is presented. Suitable plots are suggested from which one may deduce certain information on the interatomic potential and the diatom bound states. The following rule is proposed: the observation of m maxima in the elastic atom—atom impact spectrum implies the existence of at least m discrete vibrational levels of zero angular momentum for the diatom.
Infrared Spectroscopic Evidence for the Species HO2
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: January 2005

Infrared absorptions observed following the photolysis of mixtures of HI and O2 in an Ar matrix at 4°K appear to be contributed by HO2 produced in the matrix. Studies on isotopically substituted systems support this assignment. The two oxygen atoms have been shown to be nonequivalent. Approximate force constants and thermodynamic functions for HO2 are tabulated.
Vibrational Energy Transfer in Molecular Collisions Involving Large Transition Probabilities
Authors: Rapp D. , Sharp T. E.
Published: January 2005

The usual calculations of vibrational energy exchange in a diatomic gas make use of first-order perturbation theory and are therefore limited to low transition probabilities. In actual practice, the thermally averaged transition probabilities in most gases are indeed small. However, this is partly because it is the relatively few molecules in the high-velocity ``tail'' of the velocity distribution which account for most of the energy exchange. The actual microscopic transition probabilities in these collisions may be too great to justify the perturbation method for many gases at high temperatures. We have therefore solved the time-dependent Schrödinger equation based on a semiclassical collision, subject to an assumed form of potential, to get exact transition probabilities in a molecular collision. At low velocities, our result reduces to the perturbation result. A thermal average of our transition probabilities should eliminate errors due to use of the perturbation solution in previous calculations. For N2, these errors only become important above 5000°K. For gases with lower vibrational frequencies such as O2, or strong attractive forces such as NO, these effects become important at much lower temperatures.
Determination of Optical Constants from Reflection Bands Using Dispersion Relations
Authors: Schatz P. N. , Maeda Shiro , Kozima Kunio
Published: January 2005

A detailed study has been made of the Robinson and Price (Kramers—Kronig) method for determining optical constants from reflection data collected in regions of strong absorption. This method depends upon the fact that the phase shift at any given frequency can be expressed as an integral involving the reflectivity at all frequencies (0 to ∞). Although in practice reflectivity data are ordinarily available only in the immediate vicinity of a reflection band, a method is presented which can be accurately applied to that situation. The circumstances under which this procedure will be valid are outlined, and some differences from previous methods will be indicated. The following two experimental situations have been considered assuming that the reflectivities have been measured at normal incidence: (1) the sample is not covered by a window, (2) the sample is covered by a window whose (constant) refractive index is greater than the zero frequency refractive index of the sample.
Optical Constants and Absolute Intensities from Infrared Reflection Measurements. The 6.6-μ Band of Liquid CS2 and the 13-μ Doublet of Liquid CCl4
Authors: Barnes D. W. , Schatz P. N.
Published: January 2005

Infrared reflection spectra in the 6.6-μ region of liquid CS2 and in the 13-μ region of liquid CCl4 have been measured using a Perkin—Elmer Model 21 Infrared Spectrophotometer modified for double-beam reflection operation. The measurements were made on samples covered by AgCl windows. The reflection data were analyzed by a new Robinson and Price procedure described in the paper immediately preceding this one. Optical constants (n and K) were obtained throughout the band, and the resulting absolute intensities are in good agreement with values previously obtained from dispersion data. It seems likely that our procedures are capable of giving reliable absolute intensities (5%—10%) for strong bands in condensed phases. This can be accomplished with reflection measurements of an accuracy (1%—2%) which should be obtainable without highly elaborate techniques.
Microwave Spectra and Structures of Difluoroethylenes
Authors: Laurie Victor W. , Pence Dallas T.
Published: January 2005

The microwave spectra of the C12 and C13 species of cis-difluoroethylene-d1 and cis-difluoroethylene-d2 have been investigated in the region of 8–36 kMc. Effective rotational constants for the ground vibrational state have been determined and are combined with previous microwave data to obtain the structural parameters: rCC=1.324 Å, rCH=1.089 Å, rCF=1.335 Å, ∠FCC=122.1°, ∠HCC=124.0°.

The microwave spectrum of vinylidene fluoride has been reinvestigated and the rotational constants for C13 species obtained. These data lead to a structure: rCC=1.315 Å, rCH=1.079 Å, rCF=1.323 Å, ∠FCF=109.1°, ∠HCH=121.8°.

A comparison of the structures with data for vinyl fluoride and ethylene shows that fluorine substitution produces a systematic shortening of both the CC and CF bonds.
Nucleation of Silver on Sodium Chloride
Authors: Walton D. , Rhodin T. N. , Rollins R. W.
Published: January 2005

The nucleation rate of silver deposited from the vapor phase onto a sodium chloride substrate has been studied as a function of substrate temperature and incidence rate. The experiments have been performed in an ultra-high-vacuum system on a substrate cleaved in situ. The results are found to be in agreement with a model of the nucleation process suggested in previous publications. Using the theory, a value of 0.4 eV has been obtained for the adsorption energy of silver on sodium chloride. It is also estimated that the activation energy for surface diffusion is less than 0.2 eV, and that the dissociation energy of the critical nucleus at the lower supersaturations employed is 2.1 eV.
Microwave Spectrum of BaO
Authors: Wharton L. , Klemperer W.
Published: January 2005

Transitions between the J=1 and J=0 rotational states of Ba138O16 have been measured by means of the molecular beam electric resonance technique in the four lowest vibrational states. By this means the rotational constants of BaO were determined to a high degree of accuracy. The previous excellent determination of the rotational constants of BaO by the analysis of optical spectra by Lagerqvist, Lind, and Barrow was confirmed. Additional evidence is found to support the claim that the lower state observed in the optical spectra—the state observed in this investigation—is the ground state, and this state has no net electronic angular momentum. Some of the molecular constants determined were as follows: Bv={9.371952−0.041776(v+12)−0.000120(v+12)2Gc/sec}±14 kc/sec,  re=1.93966±0.00005 Å.
Molecular and Hydrodynamical Effusion of Mercury Vapor from Knudsen Cells
Authors: Carlson K. Douglas , Gilles Paul W. , Thorn R. J.
Published: January 2005

The unilateral flow of saturated mercury vapor through cylindrical channels of stainless steel and a thin-edged orifice into a vacuum has been investigated at source pressures ranging from 10—6 to 1 atm. The results generally agree with the semitheoretical equation derived by Knudsen in a study of the bilateral flow of permanent gases under small pressure gradients, but significant differences exist. For channels with ratios of length to radius of about 60 to 100 and radii of about 0.02 cm, the agreement is within the experimental errors for pressures ranging from the lowest of 10—6 to about 5×10—4 atm. Above this latter value the rate of flow is less than that predicted by the equation, and at pressures near 1 atm the rate tends to approach that value which is expected for a situation in which the channel is filled with the saturated vapor. For the thin-edged orifice the results display the molecular flow and a transition to hydrodynamic flow which is nearly isothermal. For an intermediate value of the ratio (∼5) the results at the lowest pressures are about 6% less than those predicted by molecular flow and show a transition to a flow which tends to approach isothermal hydrodynamic flow and which is greater than molecular flow divided by the transmission probability.
On the Thermodynamics of Solutions. IX. Critical Properties of Mixtures and the Equation of Benedict, Webb, and Rubin
Authors: Ackerman F. J. , Redlich O.
Published: January 2005

Values for the critical properties of gaseous mixtures derived from the equation of Benedict, Webb, and Rubin are not consistently better than those obtained from the equation of Redlich and Kwong.
Crystal-Field Shielding in PrCl3
Authors: Lenander Carl J. , Wong Eugene Y.
Published: January 2005

A calculation of shielding of the crystal field from the 4f valence electrons in Pr3+ due to the polarization of the outer (5s)2(6p)6 shell by the crystal field is reported. The effect is shown to be a principal constituent to the discrepancy of the experimental and theoretical values of the crystal-field parameters.
Dielectric Relaxation in a High-Temperature Dipole Lattice
Authors: Zwanzig Robert
Published: January 2005

The effect of rotational Brownian motion on the dielectric susceptibility of a rigid cubic lattice of permanent point dipoles is calculated. All dipolar interactions are taken into account by means of a high-temperature perturbation expansion. The most significant result is that dipolar interactions give rise to additional new relaxation times increasing dielectric loss at high frequencies.
Electron-Density Distributions in Hydride Molecules. The Ammonia Molecule
Authors: Bader R. F. W. , Jones G. A.
Published: January 2005

An electron-density distribution is determined for the ammonia molecule in its equilibrium configuration by requiring the distribution to exert forces on the nuclei equal and opposite to the nuclear forces of repulsion. The density distribution so obtained is compared with those determined by SCF calculations. All of the density functions are tested by comparing the calculated and observed values for the following molecular properties: (i) the forces on the nuclei, (ii) the dipole moment, (iii) the electric-field gradient at the nitrogen nucleus, (iv) the diamagnetic susceptibility, and (v) the diamagnetic contribution to the nuclear shielding constant.
Theory of Carbon NMR Chemical Shifts in Conjugated Molecules
Authors: Karplus M. , Pople J. A.
Published: January 2005

A molecular orbital theory for carbon-13 chemical shifts in conjugated molecules is formulated. Consideration of the various possible contributions to the shift shows that the local paramagnetic term σpAA is expected to dominate. By a detailed LCAO analysis of σpAA, its variation with the salient features of the electron environment is determined. It is demonstrated that there is a significant local-charge dependence which agrees in sign and order of magnitude with an experimentally established correlation. In addition, the shielding is shown to be a function of the free valence of the atom under consideration and of the polarity of its sigma bonds. A linearized equation for the carbon-13 chemical shift (with respect to benzene) is presented and compared with the available experimental data.
Structure of Hexagonal Silver Iodide
Authors: Burley G.
Published: January 2005

A detailed three-dimensional refinement of the structure of hexagonal silver iodide from room-temperature photographic data showed very little deviation from the ideal wurtzite-type structure. Using anisotropic temperature factors a final R value of 6.6% was obtained. The space group is P63mc, a=4.592, c=7.510, c/a=1.635, μ=0.3747. A general linear relation of the position parameter μ to the c/a axial ratio was found to apply to compounds having this structure type.
Acoustic Isotherms for Nitrogen, Argon, and Krypton
Authors: Lestz S. S.
Published: January 2005

Measurements of the sound velocity in nitrogen, argon, and krypton, and the derived heat capacities, are reported for a pressure range up to 12 atm and at two temperatures: the ice point and 303.7°K. It is believed that the data for nitrogen are more consistent than those reported by other investigators, while comparison data for argon and krypton are practically nonexistent.
Infrared Vibrations of Crystalline Potassium Azide
Authors: Bryant James I.
Published: January 2005

The infrared spectrum of crystalline potassium azide has been investigated over the region from 4000 to 550 wavenumbers by using a grating spectrometer. Selection rules for internal and lattice vibrations and their combinations were calculated by using the ``unit-cell'' method of Bhagavantam and Venkatarayudu. The spectrum was characterized by the splitting of fundamental absorptions and the occurrence of numerous lattice combinations symmetrically spaced about active and inactive fundamentals. From observed lattice combinations, tentative frequency assignments were made for the lattice modes. Polarized spectra indicate that most of these combinations are oriented in the xy plane of the crystal. The spectrum shows good agreement with the accepted crystal structure as described by the space group D4h18—I4/mcm.
Monte Carlo Procedure for Statistical Mechanical Calculations in a Grand Canonical Ensemble of Lattice Systems
Authors: Chesnut Dwayne A. , Salsburg Zevi W.
Published: January 2005

The Monte Carlo method of estimating statistical mechanical averages in the petite canonical ensemble, described by Rosenbluth et al., Wood and Parker (for fluid systems), and Salsburg et al. (for lattice models), has been extended to a general multicomponent lattice model in a restricted grand canonical ensemble. The procedure is applied to the two-dimensional traingular lattice gas with periodic boundary conditions at a supercritical temperature (βε= —ln2), and numerical results are presented for the energy, specific heat, density, isothermal compressibility, thermal-expansion coefficient, and grand partition function (pressure) at Δ=0.1, 0.0, —0.1, —0.2, —0.3, —0.4, —0.6, —0.8 (with B=100); at B=16, 25, 36, 49, 64, 100, 196 (with Δ=0.0); where Δ=βμ—3βε; where ε is the nearest-neighbor interaction; β=(kT)—1, where μ is the chemical potential; and B is the number of sites. These are compared (where possible) with previous (Salsburg et al.) and additional petite-ensemble Monte Carlo results. This comparison emphasizes the different B dependence of intensive properties in these two ensembles and is supplemented by an asymptotic analysis of this difference. Properties in both ensembles display the type of irregular B dependence predicted by Lebowitz and Percus for very small systems. For the larger lattices, properties in the petite ensemble show a stronger B dependence than in the grand ensemble, which is in quantitative agreement with the leading term in the asymptotic analysis. A comparison with the exact analytical results (B= ∞, Δ=0) indicates that the accuracy of the Monte Carlo procedure for the grand ensemble can be reliably estimated by a statistical analysis of partial averages over the Markov chain.
Averaged-Boltzmann-Factor Theories for Nonelectrolyte Solutions
Authors: Salsburg Zevi W.
Published: January 2005

The concept of the one-, two-, and three-liquid approximations to the theory of nonelectrolyte solutions, introduced by Scott in terms of averaged pair potential functions, is extended by defining suitably averaged Boltzmann weighting factors which are composition dependent. These approximations are introduced and treated by means of a perturbation theory similar to that used by Nosonow to obtain a unified presentation of the averaged potential n-liquid approximations.
Stark Energy Levels of Symmetric-Top Molecules
Authors: Shirley Jon H.
Published: January 2005

Calculations have been performed to determine the Stark energy levels of rigid symmetric-top molecules. The continued fraction expression for the eigenvalues of the energy matrix is presented and techniques of evaluation described. Tables of reduced energy levels as a function of electric field are given for all rotational states through J=4. Graphs of these values and the effective dipole moments are included.
Photolysis of Mixtures of Diethyl Ketone and Carbon Tetrachloride
Authors: Gregory Jessie E. , Wijnen M. H. J.
Published: January 2005

The photolysis of mixtures of diethyl ketone and carbon tetrachloride has been investigated at room temperature. The following reaction products were observed: CO, C2H6, C2H4, C4H10, CHCl3, C2H5CCl3, C2Cl6, C2H5 (CH3) CHCOC2H5, and CH3 (CCl3) CHCOC2H5. Primary radicals produced by photolysis of diethyl ketone and carbon tetrachloride are C2H5, CCl3, and Cl. Chlorine atoms react with diethyl ketone to form HCl and CH3CHCOC2H5 radicals. Disproportionation and recombination reactions involving CCl3, C2H5, and CH3CHCOC2H5 radicals are largely influential in the formation of many of the products. The ratios of disproportionation over recombination for CCl3 and C2H5 radicals and for CCl3 and CH3CHCOC2H5 radicals were obtained together with various ratios of other rate constants.
Formation of Fragment Ions from CH3Te125 and C2H5Te125 Following the Nuclear Decays of CH3I125 and C2H5I125
Authors: Carlson Thomas A. , White R. Milford
Published: January 2005

The relative abundances of the fragment ions that result respectively from the nuclear decays of CH3I125 and C2H5I125 (I125 undergoes electron capture to give Te125) have been measured with a specially designed mass spectrometer. The data from both studies are similar and give evidence as follows of the highly destructive nature of the decay: (1) Only about 1% of the Te—hydrocarbon ions appear to remain intact in spite of the fact that these ions would be expected to be collected with high efficiency; (2) In both studies a large number of tellurium ions is found with charges as high as 18 and with an average charge of about 9; (3) Finally, in both studies, the singly, doubly, and triply charged carbon ions are found in greater abundance than the hydrocarbon ions. The cause of this extensive ionization and fragmentation is ascribed primarily to a series of Auger processes that occur subsequently to the formation of inner orbital vacancies in Te125 as the result of electron capture and internal conversion in the decay of I125.
Theory of Dissociation Pressures of Some Gas Hydrates
Authors: McKoy V. , Sinanoğlu O.
Published: January 2005

Dissociation pressures of some gas hydrates have been evaluated using the Lennard-Jones 12–6, 28–7, and Kihara potentials in the Lennard-Jones-Devonshire cell model. The Lennard-Jones 28–7 potential gives the least satisfactory results. The Lennard-Jones 12–6 potential works satisfactorily for the monatomic gases and CH4 but poorly for the rodlike molecules C2H6, CO2, N2, O2, C2H4. This failure may be due to (i) distortions of the hydrate lattice, (ii) neglect of molecular shape and size in determining the cavity potential (iii) barrier to internal rotation of the molecule in its cavity. A crude model for the lattice shows that it is not distorted. The Kihara potential predicts better dissociation pressures for the hydrates of the rodlike molecules. Unlike the previously used Lennard-Jones 12–6 potential, it depends on the size and shape of the interacting molecules. The absence of lattice distortions, improved dissociation pressures through the use of the Kihara potential and the restriction of the motion of the solute molecule to around the center of a cavity makes a large barrier to rotation unlikely. A small barrier may still be present.
Excluded-Volume Effect for Two- and Three-Dimensional Lattice Models
Authors: Domb C.
Published: January 2005

An analysis is undertaken of mean-square sizes of self-avoiding walks enumerated exactly on various two- and three-dimensional lattices. It is suggested that for all three-dimensional lattices the mean-square size tends to an asymptotic relation 〈rn2〉≃A1n6/5+A2, while for two-dimensional lattices the corresponding relation is 〈rn2〉≃B1n3/2+B2n. The constants A1, B1 decrease as the coordination of the lattice increases. Estimates of A1, A2 are given for the fcc, bcc, simple cubic, and diamond lattices, and of B1, B2 for the triangular and simple quadratic lattices.
Microwave Spectrum, Structure, and Quadrupole Coupling Constant Tensor of Ethyl Bromide
Authors: Flanagan Cyprian , Pierce Louis
Published: January 2005

The microwave spectra of 10 isotopic species of ethyl bromide have been measured and assigned, viz., the 79Br and 81Br species of CH3CH2Br, CH3CD2Br, CD3CH2Br, CH313CH2Br, and 13CH3CH2Br. The spectra reported lie in the region of 18 to 31 kMc. The complete structure has been determined by the substitution method, giving the following bond parameters: CC = 1.518 Å, CBr = 1.950 Å, CCBr = 111°2′, CH (methylene) = 1.087 Å, HCH (methylene) = 109°54′, CCH (methylene) = 112°15′, HCBr = 105°25′, CH (methyl) = 1.093 Å, and HCH (methyl) = 108°52′. The principal quadrupole coupling parameters have been determined to be χzz = 541 Mc, χxx = —267 Mc, and χyy = —274 Mc for C2H579Br and χzz = 450 Mc, χxx = —220 Mc, and χyy = —230 Mc for C2H581Br. Through the analysis of second-order effects of quadrupole coupling on hyperfine structure, it was determined that, within experimental error, the CBr internuclear line and the ``z'' principal quadrupole axis coincide, indicating that the CBr bond is not bent. The barrier to internal rotation, recalculated using Lide's splitting measurements, and the above structure is 3684 cal/mole.
Magnetic Properties of Molecules from One-Center Wavefunctions. Theory and Application to the Hydrogen Molecule
Authors: Hoyland James R. , Parr Robert G.
Published: January 2005

A variational procedure is proposed for the purely theoretical calculation of the diamagnetic susceptibility and nuclear magnetic shielding constants of a molecule, given a one-center electronic wavefunction for it in the absence of a magnetic field. One performs a linear variational calculation, mixing in just those Slater determinants which the field causes to interact with the Slater determinants in the original wavefunction. A simple model is proposed, whereby one can simply estimate the magnetic properties from the original wavefunction. To illustrate the method, the susceptibility of the hydrogen molecule is computed from one simple and one more complex wavefunction expanded about the molecular center.

The diamagnetic susceptibility and proton shielding constant for hydrogen then are calculated from a new single-center wavefunction expanded about one of the protons. The detailed behavior of the computed paramagnetic contribution to the magnetic properties is discussed and the results indicate that these terms are well accounted for by the proposed method. The calculated values for the susceptibility and proton shielding constant are —4.05×10—6 emu (—4.03×10—6 emu experimental) and 2.67×10—5 (2.66×10—5 experimental), respectively. Various other properties of hydrogen as calculated from the proton-center wavefunction are also given.
Streaming Birefringence of Polymer Solutions: Asymptotic Behavior
Authors: Čopič Milan
Published: January 2005

The anisotropy of a linear assembly of Gaussian subchains is given for all values of the end-to-end distance of the composite chain. The intrinsic anisotropy is proportional to the square of the end-to-end distance at small end separations and asymptotically approaches the saturation value with increasing end separation. On the other hand, the form anisotropy is proportional to the end-to-end distance at small end separations. It passes through a maximum at almost full extension of the chain and then, due to decrease of the dipole interaction, goes to zero with the third power of the inverse distance between the ends, as the extended chain is further stretched. The streaming birefringence of an infinitely diluted solution of a high polymer has therefore its saturation value at extremely high gradients determined by the asymptotic value of the intrinsic birefringence, because the form birefringence vanishes with the first power of the inverse gradient.
Mass-Spectrometric Study of Ion Profiles in Low-Pressure Flames
Authors: Calcote H. F. , Reuter J. L.
Published: January 2005

A mass-spectrometric technique for determining ion profiles through low-pressure flames (1–6 mm Hg) has been developed. Typical results are presented for hydrocarbon—oxygen flames which show that the dominant ion is H3O+ and that the concentration of C3H3+, the next most abundant ion, reaches a maximum concentration in the flames ahead of H3O+. A large number of other ions are also identified.
Kinetics of High-Polymer Reactions: Effects of Neighboring Groups
Authors: Alfrey T. , Lloyd W. G.
Published: January 2005

A recurring problem in polymer chemistry is the dependence of functional group reactivities on the reacted-or-unreacted status of neighboring groups. This problem has been attacked by means of a closed-loop model and an infinite-chain model. For the latter model, an approximate solution has been developed for the general case, and an exact solution has been shown for the speical case where k1=k2.