bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Vibration and Structure of High Polymers. IV. A General Method of Treating Degenerate Normal Vibrations of Helical Polymers and Infrared-Active Vibrations of Isotactic Polypropylene
Authors: Miyazawa T. , Ideguchi Y. , Fukushima K.
Published: January 2005

Polarized infrared spectra of an oriented crystalline film of isotactic polypropylene have been measured in the region 600–300 cm—1. Two parallel bands and three perpendicular bands due to the skeletal deformation modes have been observed. A general method for treating the normal vibrations (with any given phase difference) of infinite helical chain polymers has been restudied. The method has been applied to the infrared active normal vibrations, A and E(⅔π), of isotactic polypropylene. The modified Urey—Bradley force field has been used and the potential constants have been transferred from aliphatic hydrocarbons. The calculated frequencies and potential energy distributions have been used as aids in assigning the infrared bands of isotactic polypropylene in the region 1500–300 cm—1.
Approach to the Metallic State as Obtained from Optical and Electrical Measurements
Authors: Riggleman B. M. , Drickamer H. G.
Published: January 2005

Electrical resistance measurements have been made on I2, Se, AgI, and SnI4. Sublimed single crystals of iodine were studied both parallel and perpendicular to the planes containing the molecules. Perpendicular to the molecular plane one obtains metallic behavior above 160 kbar; parallel to the plane of the molecules above 220 kbar. Selenium becomes metallic at 130 kbar. In the region where both optical gap and resistance measurements could be obtained, the agreement is good. SnI4 becomes metallic above 185 kbar in reasonable agreement with extrapolated optical-gap data. AgI shows apparently ionic conductivity below 70 kbar. At 97 kbar there is a sharp rise in resistance which corresponds quite quantitatively to the observed increase in optical gap. The high-pressure phase is a semiconductor with activation energy of about 0.5 eV, in reasonable agreement with the optical gap for α=0.
Determination of the Diamagnetic Anisotropy Effects of the C–C Bond and C—Halogen Bonds in Nuclear Magnetic Resonance Spectroscopy
Authors: Reddy G. S. , Goldstein J. H.
Published: January 2005

The empirical method previously used to obtain diamagnetic anisotropy effects of ring systems in proton magnetic resonance spectroscopy, based upon C13–H coupling constants, has now been applied to the C–C and C—halogen bonds. The result for the C–C bond, 10.0±1.0×10—6 cm3 mole—1, is somewhat larger, though of the same sign and order of magnitude, as previously reported values. The results obtained are for C—halogen bonds, and are also compared with previous estimates.
Values of the Simon Constants
Authors: Babb Stanley E.
Published: January 2005

The Gilvarry theory of the constants in the Simon melting equation is modified and extended. One novel feature of the model is a melting curve which approaches a finite temperature asymptotically, apparently due to the failure of the Lindemann relationship. Further possible modifications of the theory are discussed.
Relaxation Time in CO2 as a Function of H2 and D2 Concentration at Several Temperatures
Authors: Winter T. G.
Published: January 2005

The frequency of maximum ultrasonic absorption was determined for CO2 with varying small amounts of the impurities H2 and D2 at three different temperatures. Hydrogen was found to be 2.4 times more effective than D2 in quenching the vibration of CO2 at both 47° and 154°C. More unexpectedly, it was found that the rate of shift of the frequency of maximum absorption with impurity concentration is less at high temperature than at low, and this fact is shown to imply that A—B collisions are 15%—20% less effective at the higher temperature than at the lower. The relaxing specific heat determined experimentally was found to be 5%—8% greater than the spectroscopic value over the entire temperature range.
Ultraviolet Absorption of Tetramethyl-1,3-Cyclobutanedione
Authors: Kosower Edward M.
Published: January 2005

The near-ultraviolet spectrum of the cyclic 1,3-dione, tetramethyl-1,3-cyclobutanedione, has maxima near both 3400 and 3000 Å. On the basis of absorption intensity (low), solvent shift (transition energy increases with Z), and position (with respect to cyclobutanone), the two transitions can be explained as n→π1*+π2* (lower transition energy) and n→π1*—π2* (higher transition energy). The assignment is similar to that used by Sidman and McClure for the 1,2-dione, diacetyl. It is pointed out that s-cis-1,2-diones should have low-energy transitions at longer wavelengths than s-trans-1,2-diones, and further, that a cyclic peroxy structure isomeric with the s-cis-1,2-dione might possess sufficient stability for isolation. Evidence from early German literature is cited to show that 1,2-benzoquinone does indeed exist in two isomeric forms; one, a red quinonoid form and a second, a colorless unstable form.
Infrared Spectra of Methylgermane, Methyl-d3-Germane, and Methylgermane-d3
Authors: Griffiths James E.
Published: January 2005

The infrared spectra of gaseous CH3GeH3, CD3GeH3, and CH3GeD3 were observed in the range 4000–400 cm—1. The 12 fundamental frequencies for each molecule are assigned to normal modes and the spectra are discussed in some detail. Teller—Redlich product-rule ratios support the assignments. The height of the barrier hindering internal rotation was found from measurements on twelve combination bands involving the torsional modes to have an average value of 1270 cal/mole. The torsional force constant was estimated to be 0.31×10—12 erg/rad. The corresponding barrier height and torsional force constant for methylsilane were estimated to be 1715 cal/mole and 0.44×10—12 erg/rad, respectively, from published data.

Analyses of the rotational structures of ν7–10 and of ν12 and 2ν12 in the spectrum of CH3GeH3 and of ν7–10 and ν12 in the spectrum of CD3GeH3 afforded values for the band origins, certain rotational constants and ζ7–12 for both molecules.
Bonding Wavefunctions in the Xenon Fluorides
Authors: Bersohn Richard
Published: January 2005

A quadrupole coupling criterion is proposed to evaluate the bonding in the xenon fluorides. Localized valence bonds will give a much higher quadrupole coupling constant for Xe131 than the delocalized linear combinations of p functions used in the polyhalides.
Surface Studies by Spectral Analysis of Internally Reflected Infrared Radiation: Hydrogen on Silicon
Authors: Becker G. E. , Gobeli G. W.
Published: January 2005

An investigation of the adsorption of hydrogen on a large single crystal of silicon has been made by infrared methods in an ultrahigh vacuum system. A broad absorption line at 4.85 μ has been ascribed to a monolayer of atomic hydrogen chemisorbed on clean silicon. The increase in intensity and changes in position and shape of this line produced by hydrogen ion bombardment are reported. The primary purpose of this work was to evaluate the technique of spectral analysis of infrared radiation multiply internally reflected in a semiconductor as a general tool for the study of adsorption on clean semiconductor surfaces. It is concluded that the method can indeed be useful in favorable cases, although formidable experimental difficulties stand in the way of a very general application.
On the Diffusion of Ions in Membranes. II. Generalized Planck—Teorell Equations
Authors: Harris Joseph David
Published: January 2005

The equations given by Planck and Teorell for the fluxes of univalent ions across a uniformly charged membrane are generalized from the case of parallel plane membranes considered by the original authors to the case of membranes of arbitrary shape. It is shown that a change in membrane geometry results solely in the reciprocal membrane thickness being replaced by the vacuum membrane capacitance per unit area when the fluxes are averaged over the outer membrane surface. The generalized equations are in all other respects, in particular in their dependence on the boundary concentrations and potentials, identical with the ones for parallel plane membranes.

Generalized equations for the potential and ionic concentrations within the membrane are also given. Again the functional dependence of these quantities on their boundary values is independent of the geometry.
Analysis of Molecular Weight Changes and Gel Data of Some Irradiated Vinyl Polymers
Authors: Inokuti Mitio , Dole Malcolm
Published: January 2005

The theoretical equations of Inokuti of the preceding paper are applied to the interpretation of data obtained during the irradiation of isotactic and atactic polypropylene, and poly-(1-pentene) and poly-(1-hexene). Inokuti's modified Charlesby—Pinner function calculated for initial values of the Mw/Mn ratio greater than 2 can be made to agree with observation within experimental uncertainties in the case of polypropylene, but in the case of the other two vinyl polymers, the observed discrepancies are probably too great to be explained by experimental error. A G(S) value decreasing at high doses would account for the observed gel data.

It is shown that in the pregelation dose range irrespective of the initial molecular-weight distribution and scission to crosslinking ratio, both Pw,0/Pw and Pn,0/Pn change very nearly linearly with the dimensionless parameter y/yg where yg is the number of crosslinks per initial number-average molecule at the gel point.
Study of Atom—Wall Collisions by Optical Pumping
Authors: Brewer Richard G.
Published: January 2005

Precise hyperfine frequency measurements have been performed on Rb87 atoms contained in hydrocarbon wall coated cells. Frequency detection is achieved optically by hyperfine filtering and transmission monitoring. Atom—wall collisions which perturb the F=2 and F=1 hyperfine levels unequally result in a transition frequency shifted from the free-atom value by about —85 cps. This shift compares favorably with atomic-beam hyperfine measurements of Goldenberg, Kleppner, and Ramsey for Cs atoms contained in hydrocarbon storage boxes. The large Rb87 shifts observed by Alley using a coherent pulse technique are not compatible with these results. Temperature-dependent studies in the region 0° to 72°C reveal that the hyperfine frequency increases approaching the free atom value as the temperature is raised, a decrease in the Rb residence time on the surface being indicated for an increase in temperature. From this information an adsorption energy of 0.1 eV and an average adsorption time of 5×10—11 sec are derived, the latter corresponding to 50 Rb oscillations in the potential well of the hydrocarbon surface. At 72°C the transition frequency is a maximum, and a further increase in temperature up to 105°C produces a frequency decrease, a behavior which correlates with the melting range of the polydisperse hydrocarbon used. This result is interpreted to mean that the adsorption energy and hence the dwell time increase as the polymer becomes more amorphous and is consistent with the idea that the amorphous state contains voids which provide a larger area of contact for a Rb atom than does the crystalline state.
Analysis of Weakly Coupled Nuclear Magnetic Resonance Spectra: Methyl Salicylate
Authors: Freeman R. , Bhacca N. S. , Reilly C. A.
Published: January 2005

The proton magnetic resonance spectrum of methyl salicylate at 60 Mc/sec is sufficiently weakly perturbed for all the strong lines to be assigned on a ``first-order'' basis. The frequency sweep double irradiation method has been used to demonstrate that all the spin coupling constants in the aromatic ring have the same sign. This makes possible the calculation of accurate values of the chemical shifts and spin coupling constants by iterative computer analysis without the need for examining other sign combinations. There is an unexpected long-range coupling (0.4 cps) between the hydroxyl proton and one of the ring protons in the meta position.
Calculations on the Low-Temperature Specific Heat of Selenium and Tellurium
Authors: Kothari L. S. , Tewary V. K.
Published: January 2005

A model of lattice vibrations for linear lattices is proposed in which longitudinal and transverse components of vibrations are considered separately, unlike the model proposed by Tarassov. This model has been applied to interpret the specific heat data for selenium and tellurium obtained by DeSorbo. The agreement with the experimental results is found to be good.
On the Stochastic Theory of Chromatography
Authors: McQuarrie Donald A.
Published: January 2005

Chromatography has been represented as a Poisson process and expressions have been derived for the elution curves of various types of chromatographic systems, such as a column with several kinds of sites, and a column with one kind of site but with various realistic input distributions. The previous stochastic treatments of chromatography have solved exactly only the case of a column with one kind of site with a delta-function input distribution. These various cases have been solved by means of the complex-variable theory of Laplace transforms. The exact expressions are usually complicated and of not much numerical utility. A technique is described by means of which any case can be well approximated by a consideration of only the first few central moments. This has proved to be of great practical use since there exists a theorem of mathematical statistics which allows one to determine moments of complex problems when those of simpler problems are known. This makes it possible to derive easily used expressions for the various elution curves.
Temperature Dependence of the Zeeman Effect in the Nuclear Quadrupole Resonance in Chloranil
Authors: Richardson C. B.
Published: January 2005

The nuclear quadrupole resonance of Cl35 and its Zeeman effect have been observed in chloranil between 78° and 373°K. Effects of thermal expansion appear negligible hence the Bayer theory is used with the measured temperature dependence of the pure quadrupole frequencies and the field-gradient asymmetries to yield room-temperature rigid-body libration amplitudes of 〈θx2〉 = 18×10—3 rad2, 〈θy2〉 = 〈θz2〉 = 0, where x is along the molecular normal. A broad phase transition centered near 100°K is examined. The results suggest that the potential well V(θx) has a double minimum and that the transition occurs when the molecules have sufficient torsional energy to override the barrier.
Electron Spin Resonance in an Irradiated Single Crystal of Tetramethyl Ammonium Chloride
Authors: Tench A. J.
Published: January 2005

An analysis of the electron spin resonance spectrum of γ-irradiated crystals of N(CH3)4Cl shows that the paramagnetic species stable at room temperature is (CH3)3N+. The isotropic coupling constants are found to be 18.0 G for the nitrogen and 26.7 G for the methyl protons. All methyl protons are found to be equivalent. The radical is probably planar and is found to execute restricted rotation at room temperature.
Information Regarding both Molecular-Weight Distribution and Density Distribution in a Polymer Subjected to Density-Gradient Centrifugation
Authors: Hermans J. J.
Published: January 2005

A polymer sample that is subjected to density-gradient centrifugation distributes itself over a band in the centrifuge cell. From results obtained in previous work, equations are derived which relate the magnitude of the fluctuations in molecular weight and apparent partial specific volume to certain integrals over the polymer band. To obtain explicit results, the assumption is made that both the distribution over molecular weight and that over effective density are narrow. It is found that the distribution of the polymer over the band can, in principle, give quantitative information concerning the magnitude of the fluctuations.
Field-Electron and Field-Ion Emission from Single Vapor-Grown Whiskers
Authors: Melmed Allan J.
Published: January 2005

A technique is described for mounting a single vapor-grown whisker on the point of an otherwise ordinary field-emission tip assembly with sufficient bond strength to permit both field-electron and field-ion microscopy. Field-electron emission patterns are shown for clean Au and Pt whisker surfaces. Hydrogen field-ion images of thermally cleaned Pt whisker surfaces and helium field-ion images of field-evaporated Pt whisker surfaces are shown. Imperfections in central {011} planes are sometimes found, but there is no strong evidence that these are axial screw dislocations.
Mercury Photosensitized Reaction of Ethylene at High Temperature
Authors: Arai Shigeyoshi , Shida Shoji
Published: January 2005

The mercury photosensitized reaction of ethylene at high temperature was investigated using gas chromatographic technique. Hydrogen, methane, acetylene, propane, propylene, butane, butene-1, and butene-2 as well as the hydrocarbon products heavier than C4 were observed. Hydrogen and acetylene were formed by the intramolecular decomposition of excited ethylene. The dependence of hydrogen formation on ethylene pressure was in fair accordance with Cvetanović's relationship. The hydrocarbon products except acetylene were mainly produced by the thermal decomposition reactions of larger hydrocarbon radicals. The irradiation of mixtures of ethylene and nitric oxide showed that a part of butene-1 was formed by the reaction of excited ethylene with ethylene. A reaction between excited ethylene and acetylene was also found to occur. In the cadmium photosensitized reaction of ethylene the same products were also observed. In this case a part of the hydrogen was presumably formed by the abstraction reactions of hydrogen atoms.
Nuclear Magnetic Resonance Study of the Phase Transition in Strontium Titanate
Authors: Weber M. J. , Allen R. R.
Published: January 2005

The nuclear magnetic resonances of Sr87, Ti47, and Ti49 in a single crystal of SrTiO3 have been studied in the vicinity of the phase transition at 110°K. The Sr87 resonance exhibited line broadening and a gradual decrease in amplitude below 110°K. This is attributed to quadrupole interactions arising from a noncubic crystalline field and is in agreement with electron paramagnetic resonance experiments. No change in the titanium resonance was observed upon cooling the crystal to the lowest available temperature of 95°K. From estimates of the quadrupole coupling constants, the results suggest that the ionic displacements are small and very little distortion of the titanium—oxygen octahedra occurs during the structural phase transition in SrTiO3.
Validity of the WKB Approximation in the Interpretation of Molecular Beam Scattering Data
Authors: Marchi R. P. , Mueller C. R.
Published: January 2005

The validity of several approximations pertinent to molecular scattering has been investigated. The WKB method was found to be reliable and was used to demonstrate the sensitivity of molecular scattering data to the intermolecular potential.
Influence of Molecular Bonding on the Townsend Ionization Coefficients of Hydrocarbon Gases
Authors: Heylen A. E. D.
Published: January 2005

Measured values of Townsend's α and γ coefficients extending over 30≲E/p0≲ 3000 for methane, ethylene, and acetylene are presented. The α values follow the Townsend equation α/p0=A exp(—Bp0/E) for 35≲E/p0≲300, and the lower limit of E/p0 is set by the experimental conditions. The molecular constants A and B increase with molecular weight and the degree of unsaturation and are in agreement with those obtained from earlier Vs—pd characteristics, provided the latter are obtained under space-charge distortion-free conditions, which was the case for our measurements. Comparison of calculated and experimental α values for ethylene favors a Maxwellian electron energy distribution. Due to the dissociative nature of the bonds, Townsend's γ—E/p curves do not exhibit a photoelectric peak at low E/p, and at high E/p the values are still some 102—104 times smaller than for the common diatomic gases. For a given E/p value, γ decreases with increase in molecular weight. Thus, in general, heavy and complex hydrocarbons are better conductors at high E/p and better insulators at low E/p. Measurements at eαd≳ 106 show up the possible electronegative character of acetylene as compared with methane.
Decomposition of Chemically Activated Ethyl-d3 Radicals. Primary Intramolecular Kinetic Isotope Effect in a Nonequilibrium System
Authors: Current J. H. , Rabinovitch B. S.
Published: January 2005

The rate of decomposition of ethyl-d3 radicals formed by chemical activation was studied at 195° and 300°K over the pressure range from 0.05 to 3.0 mm. The excited radicals decomposed by hydrogen or deuterium atom rupture or were collisionally stabilized. The rate of decomposition was determined relative to the rate of stabilization by complete product analysis. Detailed description is given. The limiting high-pressure rate for hydrogen rupture from energized ethyl-d3 radicals was determined to be 6.5×107 sec—1 at 300°K and 2.5×107 sec—1 at 195°K. The limiting low-pressure rate for hydrogen rupture was found to be 2.0×107 sec—1 at 300°K and 1.0×107 sec—1 at 195°K. The intramolecular hydrogen to deuterium rupture ratio was determined to be ∼2.0 at 300°K and ∼3.0 at 195°K for this nonequilibrium reaction system, and appreciably less than similar ratios determined earlier for the ethyl-d2 system. The disproportionation to recombination ratio for ethyl radicals was found to be 0.14 at 300°K and to be 0.17 at 195°K. The apparent isotopic H/D disproportionation ratio in ethyl-d3, measured at both temperatures, was 1.6 in reasonable agreement with the value of 1.4 of Boddy and Steacie.

Theoretical rates were calculated from a quantum statistical harmonic oscillator formulation of the rate constant. Good qualitative and semiquantitative agreement has been found between the various experimental quantities of this study (as well as a previous one dealing with ethyl-d2 radicals) and magnitudes calculated from a model which has quite a loose activated complex (150 cm—1, C–C–H bends) with the figure axis rotation active, and in which the energized radical has both an active free internal rotation and figure axis rotation.
Approximate Radial Functions for First-Row Transition-Metal Atoms and Ions. II. 4p and 4d Atomic Orbitals
Authors: Richardson James W. , Powell R. R. , Nieuwpoort W. C.
Published: January 2005

Orthogonalized 4p and 4d radial wavefunctions for first-row transition-metal atoms and ions have been computed using a minimum set of Slater-type functions with integral quantum numbers. Configurations of the type 3dx4p, 3dx4p2, 3dx4d and 3dx4d2 were studied. Free parameters were varied to minimize the energy of these electrons in the (fixed) Coulomb and exchange potential field of the inner shells, considered in a previous paper. Various criteria suggest that these functions are reasonably good. The results were generalized to provide estimates of parameters for related configurations.
Role of d-Hybridization in the Pi Molecular Orbitals of Unsaturated Hydrocarbons
Authors: Sovers Ojars , Kauzmann Walter
Published: January 2005

Calculations on the 2pπu state of H2+ suggest that d-type atomic orbitals will make appreciable contributions to the MO's of pi electrons in unsaturated molecules. A symmetry analysis shows that in planar aromatic hydrocarbons only two of the five d orbitals may hybridize with the p orbitals in pi MO systems. The coefficients of the d functions in these MO's were estimated, and their effects on the orbital energies were determined. Resonance energies, charge densities, dipole moments, hyperfine coupling constants, and bond orders were calculated from these modified orbitals, and the results were compared with experiment and with the results of simple Hückel theory. The definitions of charge densities and bond orders must be modified when d orbitals are included. The inclusion of d-hybridization leads one to expect certain effects which are not predicted by the Hückel theory: (a) The simple Hückel theory predicts equal resonance energies for trans- and cis-butadiene. Inclusion of d orbitals makes trans-butadiene more stable than cis-butadiene by about 700 cal. (b) Simple Hückel theory predicts that the square cyclobutadiene molecule will have no resonance stabilization. Inclusion of d orbitals produces a stabilization of about 6 kcal. (c) Simple Hückel theory predicts that phenanthrene has a zero dipole moment. Inclusion of d orbitals leads one to expect a dipole moment of 0.17 D. (d) Simple Hückel theory predicts zero spin densities at certain positions in the pyrene negative ion. Inclusion of d orbitals allows small spin densities to appear at these positions. On the whole, the inclusion of d-orbitals does not greatly alter the interpretation of resonance energies and bond lengths given by the simple Hückel theory. Nor does it shed any light on the problem of the anamolous length of the central bond of naphthalene. The effect of d-hybrids may prove to have an importance in the interpretation of some properties at least as great as that of other refinements of MO theories of aromatic hydrocarbons, such as configuration interaction.
Optical Determination of the Compressibility of Solid Argon
Authors: Smith B. L. , Pings C. J.
Published: January 2005

The compressibility of solid argon was measured in the temperature range 78° to 84°K by a new optical method. A value for the coefficient of thermal expansion was also obtained. The results are kT=(6.65±0.19)×10−11 cm2 dyn−1 at 78°K and β=(1.95±0.07)×10−3(∘K)−1 at 81°K. The experimental method is discussed and the results compared with existing experimental data.
General Relation of Fundamental Molecular Constants between Two Electronic States
Authors: Chen Joseph C. Y.
Published: January 2005

The general relation of fundamental molecular constants between electronic states is investigated in some detail. Formulas stating such relations are found, and the interaction matrix elements, which relate the corresponding electronic states, are examined. Calculations of the quadratic, cubic, and quartic force constants for the hydrogen molecule ion H2+ are carried out, as an example, by utilizing these formulas. The calculated values agree very satisfactorily with those obtained from spectroscopic data.
Kinetics of the Gas-Phase Reaction of CH3I with HI
Authors: Flowers Michael C. , Benson Sidney W.
Published: January 2005

By modification of a Beckmann DB spectrophotometer for use with high-temperature gas systems it has been possible to follow the kinetics of reaction of CH3I+HI which goes quantitatively to CH4+I2 in the temperature range, 260° to 316°C. The kinetics fit the mechanism proposed earlier by Benson and O'Neal very well. I2⇋2 I,(K),I+CH3I⇋ lim 21CH3+I2,CH3+HI⇋ lim 43CH4+I.The rate law for this system is (neglecting 4) d(I2)/dt=k1k3K12(CH3I)(HI)(I2)12/[k2(I2)+k3(HI)].Although this equation can be integrated exactly, the integrated forms are not sensitive to the data, and various expansions must be used. Values for k1 and k3/k2 are found to be in excellent agreement with earlier estimates. From the activation energy E1 and the assumption that E2≤0.5 kcal, the bond energy of CH3I is found to be about 55±1 kcal/mole, in excellent agreement with other estimates. Values are given, in addition, for the individual rate constants, k2, k3 and k4, as well as their Arrhenius parameters.

The A factors for reactions 1 and 4 are shown to be in excess of collision frequencies, indicating steric factors slightly in excess of unity and thus the formation of very loose transition-state complexes. This appears to be typical of iodine-atom or I2-molecule reactions and thus far quite unique.
Vibrational Spectra of Molten Halides of Mercury. II. Trichloro- and Tetrachloromercurate Ions
Authors: Janz George J. , James David W.
Published: January 2005

An investigation by Raman spectroscopy of solutions of molten mercuric chloride containing KCl and NH4Cl as solutes over the composition range 10%—70% added solute is reported. The observed spectra may be completely assigned if HgX2, HgX3—, and HgX4= are recognized as the predominant species in these molten salt mixtures. The vibrational assignment is discussed and the force constants are calculated for these species. From the intensity variations of the strongest Raman lines, 374, 282, and 267 cm—1, the relative concentrations of the above three polyatomic species are deduced as the concentration of the added ligand (Cl—) varies from 0% to 70%. The ionicity of the Hg–Cl bond in HgCl2, and HgCl3—, and HgCl4=, as reflected by the bond force constants, is considered.
SCF Calculations of Spin-Density Distributions in Heteroatom Radicals
Authors: Vincow Gershon
Published: January 2005

Unpaired spin densities for a series of prototype heteroatom radicals (p-benzosemiquinone, o-benzosemiquinone, pyrogallolsemiquinone, and 2,5-dihydroxy-p-benzosemiquinone) are calculated using McLachlan's SCF theory with variation of MO parameters. Agreement with ESR hyperfine splittings is considerably improved relative to that obtained by means of Hückel MO theory.
On the Helix-Coil Equilibrium in Polypeptides
Authors: Applequist Jon
Published: January 2005

The Zimm—Bragg model for helix-coil transitions in polypeptides is discussed. An exact general form for the partition function is derived by Ising's method. Approximations for long chains lead to simple equations describing the transition in the critical region. These are compared for the cases where the minimum size of a nonbonded sequence is one and three residues, respectively, the latter being applicable to α-helical polypeptides. The nature of the helix-coil equilibrium is discussed in terms of the surface representing the populations of molecular states. Fluctuations in degree of bonding are discussed, and shown to be related to the sharpness of the transition. Some experimental data on polypeptides are compared with the theory, and yield values for the heat and entropy of helix formation per mole of residues.
Vapor Snakes in Solid Argon
Authors: Pollack Gerald L. , Broida H. P.
Published: January 2005

Vapor snakes in argon near its triple-point temperature and below are described. An application of conservation of energy gives the ratio of the vapor core of the snake to the thickness of the solid wall as a simple function of the vapor and solid density and heats of fusion and vaporization. For snake growth near the triple point the essential contraction below the crust is due to solidification of the melt on the cold walls. For this case application of volume and mass conservation gives an equation for the velocity of snake growth in terms of the rate of solidification and radius of the snake. Motion picture films are used to measure the radius, wall thickness, and velocity of the snake as well as the rate of solid formation on the walls. The equations are examined and found to be in good agreement with experiment. Other qualitative and quantitative aspects of vapor snakes are described.
Configuration Interaction of the Pr3+ Ion
Authors: Wong Eugene Y.
Published: January 2005

The electrostatic interaction between 4f2 and 5d2 was calculated from the wavefunctions with Slater integrals G1-492 cm—1, G3 = 44.5 cm—1 and G5 = 2.94 cm—1. When this configuration interaction was taken into account the calculated spectrum of Pr3+ was in better agreement with the experimental data.
Infrared Intensities of the C≡C and ≡C–H Bands in Phenylacetylenes
Authors: Brown Theodore L.
Published: January 2005

The integrated infrared intensities of the acetylenic carbon—carbon and carbon—hydrogen stretching bands have been measured for a series of meta and para substituted phenylacetylenes. The C≡C band intensity is very strongly dependent on the substituent, whereas the ≡C–H band is relatively insensitive to substitution. The C≡C band intensity is insensitive to solvent effects; the intensity of the ≡C–H band is increased slightly in basic solvents.

A simple π-electron molecular orbital model for the phenylacetylenes yields results for the dependence of the C≡C band intensity on substituent which are in good agreement with experiment. The analysis shows that most of the intensity in the C≡C stretching band results from transfer of π electronic charge between ring and ethynyl groups during vibration.
Rotatory Diffusion Constants of Stiff-Chain Macromolecules
Authors: Hearst John E.
Published: January 2005

This calculation applies the theory of Kirkwood to the determination of the rotatory diffusion constant of stiff-chain macromolecules. The rotatory diffusion constants of a wormlike coil and of a weakly bending rod are calculated in terms of molecular parameters. The calculation refers only to the mode of relaxation associated with rotation of the entire segment distribution.
Electronic conductivity in Molecular Crystals: An Alternative to the Bloch-Function Approach
Authors: Keller R. A.
Published: January 2005

Bloch functions are not good basis functions for molecular crystals in high electric fields. When the interaction with the electric field is large with respect to next-neighbor interactions, it is better to use wave-functions which are localized over molecular sites as basis functions. A treatment of electronic mobility and diffusion in molecular crystals using quantum mechanical transition probabilities between localized energy levels and considering only nearest-neighbor interactions is developed. The asymmetry of the potential function, caused by the electric field, and the conservation of energy during transport are considered. The mobility is found to be independent of temperature, and the diffusion constant proportional to temperature. The magnitude of the diffusion constant calculated from phonon-induced transitions is quite reasonable (4.6×10—3). Photon-induced transitions do not appear to be important.
United-Atom Configuration-Interaction Treatment of the He–He Repulsion
Authors: Miller R. V. , Present R. D.
Published: January 2005

The repulsive interaction between two normal He atoms is treated by the one-center method, using Slater-type orbitals, for the united-atom configurations 1s22s2 and 1s22pσ2 which are appropriate at smaller and larger internuclear distances, R, respectively. A previous calculation by Huzinaga treated by 1s22pσ2 but not the 1s22s2 configuration. We find the 1s22s2 energy to be below the 1s22pσ2 energy when R < 0.56 a.u. Mixing these two configurations leads to little improvement in the energy; the further admixture of 1s23dσ2 gave a negligible improvement. However, when the basic configuration at small R, 1s22s2, was mixed with the singly excited configuration 1s3dσ2s2, a significant improvement was found (6.2 eV at R=0.5 a.u.). When the singly excited configuration is admixed, the one-electron interaction with the two nuclei contributes to the nondiagonal matrix element and this leads to a greater configuration interaction than for the doubly excited configurations. Although the two-center method gives better results at R=1 a.u., the one-center method with only two configurations appears to be definitely superior for R≲0.6 a.u. when compared with extrapolated energies obtained from the best two-center calculations. With other configurations included, the one-center method should compete with two-center calculations at R=0.75 a.u. Our results tend to confirm the disagreement found between the latest scattering experiments and the most accurate two-center calculations.
Zero-Field Splittings in Molecular Multiplets: Spin—Spin Interaction of Methylene Derivatives
Authors: Higuchi Jiro
Published: January 2005

The electron spin—spin interaction of triplet, quartet, and quintet radicals was investigated. The numerical calculation was carried out for the methylene derivatives by using the simple LCAO—MO's. The calculations are in rough agreement with the two experimental results currently available. The spin—spin interaction energy mainly arises from the spin densities of electrons in the same atom which are perpendicular to each other, and the interatomic contribution is generally small. The effect of a bent bond is considered.
Screening Parameters for Two-, Three-, and Four-Electron Systems
Authors: Considine James P. , Bauman Robert P.
Published: January 2005

A method described earlier for calculating screening parameters in two-electron atoms has been modified and extended to three- and four-electron systems. The angular and distance parameters describing the interelectron potential are fixed by taking them at their most probable values as determined by a distribution function of the form exp (—V/V0), where V0 is the value of the interelectron potential V for these most probable values. This leads to four simultaneous algebraic equations in four unknowns. The accuracy of this simple, empirical treatment is on the order of a few hundredths of an atomic unit.
Relaxation Effects in the Transport Properties of a Gas of Rough Spheres
Authors: Monchick L. , Yun K. S. , Mason E. A.
Published: January 2005

The rough-sphere model is investigated in some detail from the point of view of the formal kinetic theory of polyatomic molecules developed by Wang Chang and Uhlenbeck, and by Taxman. The purpose is to clarify the sources of some discrepancies between the known results for the transport properties of a rough-sphere gas and the results recently obtained by Mason and Monchick in an approximate treatment of the formal kinetic theory, in which the corrections for inelastic collisions are given in terms of relaxation times. It is found that the deviations of the transport coefficients of rough spheres from those of smooth spheres can be understood in first approximation as the result of two effects: an enhancement of the backward and sideward scattering of rough spheres over that for smooth spheres, and an apparent resonant exchange of internal energy when two rough spheres collide. Since these effects are, for the most part, peculiar to rough spheres, it is concluded that the deviations found between the rough-sphere model and the approximate theory are not to be expected for real molecules.
Fluidity and Prefreezing Cluster Formation in Liquid Metals. Aluminum
Authors: Mitra S. S. , Sharma L. P.
Published: January 2005

The viscosity-density relation, (η/ρ)⅓=a+b/T due to Mitra is applicable to normal liquids over wide ranges of temperature, and obtainable accuracy is comparable to that of Andrade's well-known equation connecting the quantities. Liquid metals, however, show anomalous viscosity on approaching the freezing point. Deviation from Andrade's equation in such liquids has been explained by McLaughlin and Ubbelohde as due to the formation of clusters on the approach of the freezing point. It is shown here that a similar analysis is possible starting from Mitra's relation as well. Deviations from Mitra's relation and the prefreezing phenomenon in the viscosity of molten aluminum are examined in terms of the McLaughlin—Ubbelohde theory. Starting from the Mitra relation, cluster parameters for aluminum are evaluated for the first time.
Crystallization Wave Propagation in Supercooled Phosphorus
Authors: Berlad A. L. , Koency J.
Published: January 2005

The propagation, through long tubes, of crystallization waves in supercooled phosphorus is experimentally investigated. The propagating temperature fields associated with such waves are measured and the existence of steady-state fields demonstrated. The crystallization wave propagates as a cloud of crystallites which individually grow and agglomerate during a slushlike interval to finally form the polycrystalline solid.
Modified Sum Rule for the Vibrational Frequencies of Symmetrical Isotopic Molecules
Authors: Machida Katsunosuke
Published: January 2005

A general method of applying the modified sum rule for the vibrational frequencies of symmetrical isotopic molecules has been derived. This rule states that the difference in the sum of the frequency parameters between two isotopic molecules A and A*Δσ=Σλ(A)−Σλ(A*)is the same for the appropriate sets I, II, ... of the symmetry species. The sets I, II, ... are selected in accordance with the interactions between the equivalent atoms involved in the isotopic change from A into A*. Various sum-rule relations are obtained for a given pair of isotopic molecules depending upon the interaction terms of the potential function. The proof of the rule is given by using the property of the transformation from the internal coordinates into the symmetry coordinates. The application of the rule is illustrated for ethylene, benzene, and their deuterated homologs.
C13 Nuclear Magnetic Resonance Spectroscopy. III. Iodobenzene and Methyliodobenzenes
Authors: Lauterbur Paul C.
Published: January 2005

The C13 nuclear magnetic resonance spectra of iodobenzene and six methyliodobenzenes have been obtained and complete assignments have been made. Large deviations from additivity of the shieldings of ring carbon atoms ortho to either the methyl group or the iodine atom are found when the two substituents are ortho to one another, and there is some evidence for a specific interaction with a para methyl group. Long-range magnetic anisotropy effects are believed to be too small to account for the observed anomalously high shielding of carbon bonded to iodine and the unusually low shieldings of carbon nuclei two or three bonds distant.
Inelastic Atomic Scattering. II
Authors: Moskowitz Jules W. , Thorson Walter R.
Published: January 2005

Cross sections for the transitions P322←P122 in an alkali atom in collision with a rare-gas atom have been calculated for thermal impact energies by the use of a modified ``distorted-wave'' approximation. These calculations are part of a continuing comparison study on the effectiveness of several different approximations in predicting intermultiplet transitions. Numerical results agree qualitatively with experiment but this agreement is fortuitous and is not the immediate aim of the calculation. The critical features of such calculations are briefly discussed.
Second Virial Coefficients of Mixed Hydrocarbon Vapors. Principle of Congruence
Authors: Barker J. A. , Linton M.
Published: January 2005

Brønsted's principle of congruence, according to which the excess thermodynamic functions of a liquid mixture of n-alkanes depend only on the average chain length in the mixture, is shown to apply also to the second virial coefficients of gaseous hydrocarbon mixtures.
Field-Emission Observations of Carbon on Tantalum
Authors: Klein Ralph , Leder Lewis B.
Published: January 2005

The carbon—tantalum system, observed with field emission, shows the temperature effects on the solubility and precipitation of the carbide phase. Carbon, once deposited on tantalum, cannot be removed by high-temperature treatment, as in the case of tungsten. With low-carbon contamination the 334 planes appear as dark areas, just as for carbon on tungsten. At temperatures in the region of 950°K, platelets, presumably Ta2C, form and migrate to the [111] zones of the emitter single-crystal tip. The energy of activation of this surface migration process is 54 kcal.
Theoretical Rate of Decomposition of Cyclopropane
Authors: Golike R. C. , Schlag E. W.
Published: January 2005

Slater's original application of his theory was for the isomerization of cyclopropane to propylene. This calculation was based on inadequate spectroscopic data, and hence a recalculation of the Slater parameters was undertaken using more recent and complete spectroscopic data. Since n = 14 is the maximum number allowed by the theory for cyclopropane it was also decided to test the effect of removal of symmetry on this value. It is concluded that a value of n = 21 for the isomerization of cyclopropane-d2 is not demanded by n = 14 for light cyclopropane, but is dependent upon the normal coordinate system; hence removing a major objection to the theory. The value of n is further shown to depend in a sensitive way on the choice of a reaction coordinate. The appropriate values of amplitude factors and frequency factors are given for the various critical modes.
Analysis of ESR Spectra Observed in Irradiated Aromatic Systems
Authors: Ingalls R. B. , Kivelson D.
Published: January 2005

Several structures have been proposed to explain the large hyperfine splittings observed in aromatic systems which have been exposed to ionizing radiation or hydrogen-atom bombardment. The observed extra hyperfine structure was used to obtain electron densities on the various carbon atoms of the cyclohexadienal radical, and McLachlan's treatment was applied to calculate the splitting of the two hydrogen atoms on the single carbon atom of the C6H7 radical. The calculated values are in satisfactory agreement with the 45- to 50-G splitting between lines of the observed triplet. The other proposed structures are shown to be unlikely to produce such large splittings, or not applicable to purely aromatic systems.
Paramagnetic Resonance Spectrum of Fe3+ in Calcite
Authors: Wakabayashi J.
Published: January 2005

The paramagnetic spectrum of an impurity in natural crystals of calcite has been examined and identified as that of Fe3+. The value of g is assumed to be two. Approximate values for | D | and | a—F | are 2.9 and 0.44 Gc, respectively. The value of the cubic field splitting parameter a was not determined.
Shock-Tube Study of Carbon Dioxide Dissociation Rate
Authors: Brabbs Theodore A. , Belles Frank E. , Zlatarich Steven A.
Published: January 2005

The homogeneous dissociation rate of carbon dioxide, diluted with large amounts of argon, was measured in a shock tube by two independent methods: (a) by the single-pulse technique, in which the gas reacts behind a reflected shock, is quenched by a rarefaction wave, and is later analyzed chemically; and (b) by measurements of light intensity in the blue continuum due to CO2(3Π)→CO2(1Σ)+hν. The results of the two experiments agree. The rate is given by d[CO]/dt=k[CO2][M], with k=3×1011T½ exp (—86 000/RT) cm3 moles—1 sec—1. Dissociation evidently does not proceed directly from ground-state CO2 to ground-state CO and O. The mechanism probably involves the intermediate electronically excited state CO2(3Π), the rate-controlling process being associated with its formation.
Diffusion of Lead Ions in Potassium Chloride
Authors: Keneshea F. J. , Fredericks W. J.
Published: January 2005

The diffusion of Pb++ ions in single crystal KCl has been studied over the temperature range, 200°—475°C. A radioactive tracer technique has been used in two types of measurements: diffusion from a deposited surface layer of PbCl2 and diffusion from PbCl2 vapor. For treating the data from the vapor diffusion experiments, a graphical method has been developed which enables D to be obtained as a function of Pb concentration.

The diffusion of Pb in pure KCl obeys the equation D=1.02×10—3 exp (—23 300/RT)/cm2 sec. The behavior of D as a function of concentration supports the Lidiard theory of diffusion by impurity-vacancy complexes. An association free energy for complex formation of 0.49±0.1 eV has been estimated from the data. This is in agreement with the trend shown in theoretically calculated values for other impurities in KCl. An anomalous rate of diffusion has been observed for Pb near the surface of some PbCl2-doped KCl crystals.
Large Statistical Secondary Isotope Effects in Nonequilibrium Reaction Systems. Unimolecular Decomposition of Chemically Activated Ethyl-d1 and Ethyl-d3 Radicals
Authors: Current J. H. , Rabinovitch B. S.
Published: January 2005

Hydrogen atom rupture from chemically activated ethyl-d1 radicals has been studied and is compared with a similar reaction of ethyl-d3 radicals. The activation reactions were D atom addition to ethylene or to trans-ethylene-d2. A very large normal statistical intermolecular secondary kinetic isotope effect of ≳1.5 per D atom substituent was found. The experimental results are in concordance with the theory and conform to the formulation of these effects previously given [B. S. Rabinovitch and J. H. Current, Can. J. Chem. 40, 557 (1962)]. The calculated effect is ∼1.6. These magnitudes per D atom are considerably enhanced over those obtained for butyl radicals. This is expected since the average excess energy of ethyl radical is less.