bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectroscopic Studies on Organometallic Compounds. V. Fluorine Nuclear Magnetic Resonance Spectra of Some Perfluoroalkyl and Perfluoroacyl Metal Compounds
Authors: Pitcher E. , Buckingham A. D. , Stone F. G. A.
Published: January 2005

The 19F nuclear magnetic resonance spectra of a variety of fluorocarbon derivatives of metals are reported. A large shift to low field is found for the absorption by a CF2 group bonded directly to manganese, rhenium, iron, or cobalt. When a carbonyl group is interposed between the transition metal and the CF2 group, or when a CF2 group is bonded to tin or phosphorus, no large shifts of the fluorine resonances to low fields are observed. It is suggested that these magnetic screening effects are related to the presence in the transition metal derivatives of low-lying excited states in the bonds between the metals and the carbon atoms of the α—CF2 groups, with the result that the paramagnetic contribution to the screening constants of the fluorine nuclei is substantially increased.
Spin Relaxation in Optical Pumping
Authors: Bernheim Robert A.
Published: January 2005

The spin relaxation of optically aligned rubidium vapor has been studied as a function of helium buffer gas pressure. Relaxation times as long as 0.68 sec were observed in helium at ½-atm pressure. The diffusion constant D0 for rubidium in helium at 50°C was evaluated as 0.54 cm2 sec—1. The disorientation cross section σ for rubidium-helium collisions was found to be 6.2×10—25 cm2. A mechanism for spin relaxation in optically aligned alkali vapors is proposed and discussed. It is found that the relaxation arises from the coupling of the alkali electron spin to orbital and rotational motion accompanying the collision. The variation of σ for rubidium in the presence of other inert gases is also discussed.
Double Resonance Spectra of N14 and N15 Ammonium Ion
Authors: Baldeschwieler John D.
Published: January 2005

The double resonance spectra of N14 and N15 ammonium ion are in good agreement with the spectra calculated with a Hamiltonian that is made stationary by transformation to a rotating coordinate system. No effects of cross relaxation are apparent. Terms in the interaction of the strong radio frequency field with the proton magnetic moment, and off-diagonal elements in the nitrogen-proton spin-spin coupling can be neglected. The effects of sweeping magnetic field rather than frequency permit a very accurate measurement of the nitrogen resonance frequency, and the ratio of the N15 and N14 magnetogyric ratios.
Absorption and Self-Luminescence Spectra of Cf3+(5f9)
Authors: Conway John G. , Gruber John B. , Hulet E. Kenneth , Morrow Richard J. , Gutmacher Ralph G.
Published: January 2005

The absorption and self-luminescence spectra of Cf3+(5f9) in LaCl3 has been observed between 3000 and 8500 A. Several of the observed groupings indicate a small crystal-field splitting compared with the spin-orbit splitting. As the basis for a tentative assignment of the reported spectra, a perturbation calculation was made on the LSJ levels of the ground multiplet, 6HJ, where H1526 is the ground level. If we assume ζ=4000 cm—1 and F2=300 cm—1 for Cf3+(5f9), we obtain for the lowest levels a theoretical energy spectrum in reasonable agreement with that observed.
Microwave Spectrum, Structure, Quadrupole Interaction, Dipole Moment, and Bent C–Cl Bonds in 1,1-dichlorocyclopropane
Authors: Flygare W. H. , Narath A. , Gwinn William D.
Published: January 2005

The microwave spectrum of C3H4Cl235,35, C3H4Cl235,37, C3D4Cl235,35 C3D4Cl235,37, C3H3DCl235,35, C3H3DCl235,37 (cis and trans), and C2C13H4Cl235,35 have been investigated. Using the derived rotational constants, a complete structure for the molecule is calculated. The structural parameters are dC–H=1.085 A, dC(2)–C(3)=1.534 A, dC(1)–C(2)=1.532 A, dC–Cl=1.734 A, ∠H–C–H=117°35′, ∠C(2)–C(3)–H2=153°37′±15′, ∠Cl–C–Cl=114°38′. κ for C2C13H4Cl235,35 was very close to zero (±0.0001), and it was not possible to determine its sign unambiguously. Using the negative value instead of the more likely positive value, a slightly different structure was obtained.

High-resolution measurements were carried out on the Cl nuclear quadrupole hyperfine structure in order to obtain the complete quadrupole coupling constant tensor in the C3H4Cl235,35 principal inertial axis system. The values obtained are χaa=—43.545 Mc, χbb=4.100 Mc, χcc=39.445 Mc, all ±0.005 and χab=—51.5±0.3 Mc. The principal quadrupole-coupling constant tensor elements are χα=—76.4±0.3 Mc, χβ=37.0±0.3 Mc, and χcc=39.445±0.005 Mc. The angle between the principal quadrupole axis component along the C–Cl bond and the C–Cl internuclear line is 0±15′. This is strong evidence against bent C–Cl bonds in this compound.

Detailed analysis of the Stark effect in the presence of quadrupole interaction leads to a dipole moment of 1.58 debye.
Double Probe Measurements of Ionization in Active Nitrogen
Authors: Broida H. P. , Tanaka Ikuzo
Published: January 2005

Electron temperatures and ion densities have been measured in nitrogen afterglows in a flow system at short times after the discharge. In pure nitrogen a maximum occurs in the ionization density and in the electron temperature at 5 to 10 msec after the discharge. The position of this maximum coincides with the visible short-duration nitrogen afterglow in which N2+ emission is prominent. Small amounts of added impurity decrease this ion density but cause an increase in the ion density at longer times, reaching a second maximum at 80 to 100 msec after the discharge. These results show that ions and electrons are being produced continuously in nitrogen afterglows and that the rate of production is affected strongly by impurities.
Electron Impact Study of CO Using a Lozier Apparatus
Authors: Fineman Morton A. , Petrocelli Americo W.
Published: January 2005

A Lozier apparatus, modified in that a quasi-monoenergetic electron beam is used, has been employed to study CO. Ionization efficiency curves for both positive and negative ions were collected. From a detailed treatment of these data we deduced the ions produced, the appearance potentials for ions formed with zero kinetic energy, the processes in which they were produced, and the states of excitation of the fragments formed. From an analysis of our results alone, the dissociation energy of CO and the electron affinity of oxygen were determined, and they agreed within experimental error with the spectroscopic value of D(CO) of 11.11 ev and electron photodetachment value for EA(O) of 1.465 ev. Using the accepted values for D(CO) and EA(O), the electron affinity of carbon was determined from two different sets of our data to be between 1.34 and 1.74 ev. The lower value is in better agreement with other experimental determinations and with most of the recent empirical calculations for the EA(C).
Calculation of Electron-Coupled Nuclear Spin-Spin Interactions in Molecules by a Variational Procedure
Authors: O'Reilly D. E.
Published: January 2005

By means of a variational procedure spin-spin coupling constants between nuclei in molecules are evaluated. The Hamiltonian is divided into a part depending on electron spin operators and a part involving only electron orbital angular momenta. A variational function for the first part is constructed by expansion of the wave function in terms of electron spin operators, the first two terms of which are the electron spin densities at the nuclei of interest and succeeding terms contain electric moments of the unperturbed electronic charge distribution of the ground state of the molecule. Retaining terms up to and including the electric dipole moment, a two parameter variational function is used for minimization and an expression for the coupling constant is derived. This result is applied to the hydrogen molecule using valence bond, molecular orbital, and James-Coolidge type wave functions. C13, N14, O17, and F19 coupling constants with protons in CH4, NH4+, H2O, and HF, respectively, are computed with valence bond and molecular orbital functions. The relation of these results to the conventional perturbation theory approach is discussed, particularly in regard to effective ``average energy denominators'' which can be computed by the present procedure. A variational method for electron orbital contributions is briefly considered as well as the calculation of ``long range'' coupling constants.
SCF-MO Wave Functions for the Hydrogen Fluoride Molecule
Authors: Clementi Enrico
Published: January 2005

An SCF-LCAO-MO ground-state wave function is reported for the HF molecule at several internuclear distances. The basis set of Slater-type orbitals (STO's) was chosen so as to obey the following four criteria: (a) be a balanced basis set, i.e., each atom should have a set of STO's equally extended relative to the number and kinds of occupied AO's in the free atom; (b) include in the set STO's for a balanced polarization; (c) optimize the orbital exponents; (d) avoid redundancy in the set. The computed total energy at the internuclear distances of 1.7328 a.u. is —100.05804 a.u. This should be about 0.004 a.u. above the Hartree-Fock energy of the HF molecule. The significance of the STO's in the basis set adopted is illustrated by several parallel computations. The computed equilibrium distance is 1.74 a.u. and the experimental is 1.733 a.u. The dipole moment is computed for several wave functions and the value corresponding to the best wave function is 1.984 D (experimental is 1.74 D), whereas the best computed moment for another wave function is 1.970 D. The significance of this variation is discussed. The dμ/dr is estimated at 1.7 D/a.u. at the equilibrium distance (experimental is 0.954). The overlap population and gross charge Q are computed for several internuclear distances. The significance of the QH is discussed; the best value of QH at the internuclear distance is 0.479.

The ground-state 2Π and the excited-state 2Σ+ for HF are investigated. An SCF computation is made for the 2Π+ excited state at several internuclear distances. Gross charges and overlap populations are given for different internuclear distances for the two ionic states. The reorganization effect due to the removal of one electron is discussed in relation to the total energy, population analysis, and gross charge QH for the ion. A discussion of the computed ionization potential I(3σ) is given at the end of the paper.
Influence of the Excluded-Volume Effect on the Average Square Length of a Normal Alkane-Type Chain
Authors: Hijmans J. , Holleman Th.
Published: January 2005

The model used by Tobolsky for calculating the mean square end-to-end distance of a normal alkane-type chain is modified so as to account for part of the excluded volume effect. All conformations containing cyclohexane-type loops, and most configurations involving pentane-type steric hindrances are excluded. The present model, as compared with that used by Tobolsky, is simpler mathematically and yields values of the average square length of short chains which are closer to the exact ones.
Infrared Studies of Crystal Benzene. V. Reflection Spectrum and Absolute Intensities
Authors: Anderson George R. , Person Willis B.
Published: January 2005

An experimental procedure for obtaining the reflection spectrum in the infrared from solid benzene is described. The results are analyzed according to the method of Robinson and Price to give the index of refraction n and the absorption coefficient κ as a function of frequency. Integration of the latter gives the absolute intensity Γi of the ith fundamental, without requiring a knowledge of the path length. Since the path length is the most uncertain variable in the evaluation of absolute intensities from absorption measurements in condensed phases, the intensity results even from these relatively crude reflection measurements are probably as accurate as those from absorption studies. Comparisons are made with other studies on benzene, and the discrepancies are discussed.
Ground-State Potential Energy of Diatomic Molecules
Authors: Davidson Ernest R.
Published: January 2005

The restrictions placed on the ground-state potential energy of a diatomic molecule by the inequality d2(R2E)/dR2<0 are discussed. This leads to rather weak smoothness conditions on E(R).
Virial Coefficients for Square-Well Potentials
Authors: Barker J. A. , Monaghan J. J.
Published: January 2005

A comparatively simple method for evaluating virial coefficients for square-well potentials is investigated. The method is based on the fact that a square-well function can be expressed as a sum of step functions. Calculations are made for the third virial coefficient and for the fourth virial coefficient. The results for the third virial coefficient are in agreement with published values but the calculated fourth virial coefficients differ from those in the literature. Our values are confirmed by comparison with values derived by an entirely different method which we describe elsewhere. Critical constants are calculated on the assumption that fifth and higher virial coefficients may be neglected at the critical density.
Fourth Virial Coefficients for the 12–6 Potential
Authors: Barker J. A. , Monaghan J. J.
Published: January 2005

A satisfactory numerical method for evaluating fourth virial coefficients for angle-independent intermolecular potential energy functions is developed. The method is based on an expansion in Legendre polynomials which reduces the numerical problem from sixfold integration to triple integration, thus bringing it within the capacity of modern computers. The method is tested by some calculations for square-well potentials and then used to calculate fourth virial coefficients for the Lennard-Jones 12–6 potential. Using the fourth virial coefficients, critical constants for a 12–6 fluid are calculated and compared with experimental values for argon. The calculated and experimental critical temperatures and pressures agree to within 5% and the critical volumes to within 15%.
Thermal Properties Based upon Heat Capacity and Decomposition Pressure of Tetramethylammonium Hydrogen Dichloride. Nature of the Hydrogen Bond in the [Cl–H–Cl]— Ion
Authors: Chang Shu-Sing , Westrum Edgar F.
Published: January 2005

The heat capacity of tetramethylammonium hydrogen dichloride was determined from 5° to 350°K by adiabatic calorimetry and the derived thermodynamic properties were calculated. No thermal anomalies were found. Molal values of heat capacity, entropy, and free-energy function at 298.15°K are 49.07, 60.63, and —31.72 cal mole—1 °K—1, respectively. The decomposition pressure of tetramethylammonium hydrogen dichloride, measured from 340° to 380°K with a Bourdon gauge as the null indicator, can be represented by the equation log10Pmm=—28.4677–1698.5 T—1+15.502 log10T—0.012256 T. Extrapolated values at 298.15° and 410.8°K are 1.8 and 760 mm Hg, respectively. Entropy increments for the decomposition reaction were calculated from the equilibrium data and compared with third-law entropy increment values derived from the thermal data. Excellent agreement was obtained. This provides strong support for the location of the equilibrium position of the hydrogen ion midway between the two chloride ions.
Empirical Method for Estimating Diamagnetic Anisotropy Effects in NMR Spectroscopy, Based upon the Use of C13–H Coupling Constants
Authors: Goldstein J. H. , Reddy G. S.
Published: January 2005

An empirical method is described for the estimation of diamagnetic anisotropy effects in nuclear magnetic resonance spectroscopy, based upon correlations between proton chemical shifts and C13–H coupling constants. This method has been applied to obtain anisotropy effects for benzene, thiophene, acetylene, allene, and chlorine. The results are supported by internal consistency and comparisons with other available estimates.
Note on Magee-Funabashi's Theory of Excitation Migration
Authors: Inokuti Mitio
Published: January 2005

This note concerns a mathematical aspect of Magee and Funabashi's treatment of excitation migration in their linear chain model of coupled systems [J. Chem. Phys. 34, 1715 (1961)]. Their derivation of the rate of excitation migration is subject to the condition that the initially excited member is located sufficiently distant from either end of the linear chain. This restriction can be eliminated by a certain modification of the model and their result is re-derived exactly in the modified model.
Ionization and Dissociation of Hydrogen Peroxide by Electron Impact
Authors: Foner S. N. , Hudson R. L.
Published: January 2005

Mass spectrometric measurements on hydrogen peroxide were carried out with a modulated molecular beam sampling system to eliminate interferences from decomposition products. The mass spectrum of pure hydrogen peroxide differs considerably from previously reported spectra, which did not include an estimate of the H2O+ and O2+ ion intensities because of decomposition problems. Appearance potentials of the ions were measured with the following results: I(H2O2) = 10.92±0.05 ev, A(HO2+) = 15.36±0.05 ev, A(O2+) = 15.8±0.5 ev, A(H2O+) = 14.09±0.10 ev, A(OH+) = 15.35±0.10 ev, and A(O+) = 17.0±1.0 ev. The ionization processes and relevant thermochemical energies are discussed. It is found that the H2O+ and OH+ ions are evolved without excess energy, while the dissociative processes producing O2+ and O+ require excess energy.
Mass Spectrometry of the HO2 Free Radical
Authors: Foner S. N. , Hudson R. L.
Published: January 2005

Mass spectrometric studies on the production, identification, and determination of thermochemical energies of HO2 radicals are reported. Reactions found to produce HO2 radicals, and examined in some detail, were: (1) reaction of H with O2, (2) reaction of H with H2O2, (3) reaction of O with H2O2, (4) reaction of OH with H2O2, (5) photolysis of H2O2, and (6) low-power electrical discharge in H2O2. Of the reactions studied, the low-power electrical discharge in H2O2 provided the most intense and convenient source of HO2 radicals. Ion—molecule reactions, which are negligible in normal operation of our mass spectrometer, are shown to be a potentially serious source of interference in studies of HO2 with conventional mass spectrometers.

The ionization potential of HO2, I(HO)2, and the appearance potential of HO2+ from H2O2, A(HO2+), have been redetermined, and the bond dissociation energies D(H–OOH) and D(H–O2) have been recalculated. The measured values are: I(HO2) = 11.53±0.02 ev, A(HO2+) = 15.36±0.05 ev with an estimated absolute accuracy of ±0.1 ev. The derived thermochemical energies are: D0(H–OOH) = 88.4±2 kcal/mole, D0(H–O2) = 45.9±2 kcal/mole, ΔH00(HO2) = 5.7±2 kcal/mole for the values at 0°K; and D(H–OOH) = 89.6±2 kcal/mole, D(H–O2) = 47.1±2 kcal/mole, ΔH2980 (H–O2) = 5.0±2 kcal/mole for the corresponding values at 25°C. Possible sources of error are examined and their effect on these values is discussed.
Adsorption of Gases on Quartz Single Crystals
Authors: Slutsky L. J. , Wade W. H.
Published: January 2005

Approximate adsorption isotherms of hexane and argon on the crystal face perpendicular to the Y axis of quartz have been obtained, making use of the alteration of the mechanically resonant frequency of a 10-Mc, Y-cut quartz crystal as a measure of the mass adsorbed. The ``area'' of the hexane molecule was found to be 50 A2 and the heat of adsorption at (B.E.T.) monolayer coverage was 1.5 kcal/mole in excess of the heat of liquefaction. A piezoelectric crystal vibrating in a thickness-shear mode appears to constitute a microbalance of sensitivity sufficient to permit measurement, in favorable cases, of isotherms on adsorbents of very low specific area.
Paramagnetic Resonance of Nickel Ions in Double-Nitrate Crystals
Authors: Culvahouse J. W.
Published: January 2005

It is shown that there are two paramagnetic complexes for divalent nickel ions in the double-nitrate crystals. One, which has not been previously described, has a very large-zero field splitting: D = 2.25±0.10 cm—1 for 1% nickel in La2Zn3 (NO3)12·24H2O at 77°K, and it is shown that this complex is due to ions in the same site as that which produces the more anisotropic cobalt spectrum—the Y-ion site. The interaction between cerium ions and nickel ions in the other divalent site—the X-ion site—is shown to be different from the interaction of cerium and cobalt in the same site. The origin of the difference is explained qualitatively.
Population Analyses of the SCF Wave Functions of Ammonia
Authors: Peters David
Published: January 2005

The two published SCF LCAO MO wave functions for NH3 differ in the form of the AO's of the nitrogen atom. The population analysis of these wave functions is reported here and the differences between the two sets of figures reveal the physical results of the two different choices of basis functions.
Formation of Additive V Centers in Disks Prepared from Powdered Alkali Halides
Authors: Glasner Abraham , Ben-Dor Lina
Published: January 2005

The observation of V bands in the absorption spectra of pressed disks prepared from KBr, KCl, and NaCl are recorded. The V centers were produced by two methods: (a) by heating a powdered mixture of the alkali halide and cupric chloride, (b) by heating the alkali halide powder previously soaked in halogen vapor at room temperature. In both cases the powders were heated to about 100°C under reduced pressure; the presence of air interfered with the reaction.
Angular Dependence of the First-Order Transition Density and Spin Density for Many-Electron Atoms
Authors: Bingel Werner A.
Published: January 2005

The spinless first-order transition density between two atomic states with quantum numbers L′,ML′, and L″,ML″ is expanded in spherical harmonics γm,n(r)= ∑ L=|L′−L′′|L′+L′′YL,ML′′−ML′(θ,φ)·rLγL,ML′−ML′′m,n(r).It is shown that the dependence of the expansion coefficients on ML′ and ML″ for fixed L is completely determined by the use of the Wigner-Eckart theorem, so that all (2L′+1) (2L″+1) expansion coefficients of a given order L are known in terms of one of them. The same is true for the expansion coefficients of the first-order transition spin density. These quantities are calculated for all terms of the electron configurations snpm and the results collected in tables.
Infrared Spectra of Gaseous Transition-Metal Dihalides
Authors: Leroi George E. , James Thomas C. , Hougen Jon T. , Klemperer William
Published: January 2005

The infrared spectra of gaseous MnCl2, FeCl2, CoCl2, NiCl2, CuCl2, and CoBr2 have been measured in absorption between 220 and 4000 cm—1. With the exceptions of MnCl2 and CuCl2, the emission spectra of these molecules have also been obtained in this region. The emission from unsaturated vapor indicates that one of the two absorptions observed for each of the dihalides, other than manganous chloride, is attributable to a vibration of a polymeric species. Assuming that the monomeric dihalide molecules have D∞h symmetry, the monomeric absorption is assigned to ν3, the antisymmetric stretching vibration. The M—X bond stretching force constants calculated using the linear model and a simple valence force field are quite similar to those of the corresponding diatomic monohalides. Both sets of constants show a maximum between manganese and zinc.
Electrochromism (Stark Effect) in Solids Due to Isolated Absorbing Centers
Authors: Kumamoto J. , Powers J. C. , Heller W. R.
Published: January 2005

A study has been made of the effect of applied electric fields upon the absorption spectrum of a dye molecule (methyl red) dissolved in a relatively inert, transparent, matrix of high dielectric strength (polystyrene). Theory indicates that the existence of a large dipole moment in either ground or excited state (or in both, if the moment differs in the two states) should lead to a broadening of the absorption band. In contrast, excited states of appropriate type lying close to that involved in the transition should produce a shift to the red. In the present instance the second shift dominates, and one observes, with a field of about one million v/cm, a shift of around 10 Å of the principal band which is centered near 5000 Å. Possible uses of this technique are in evaluating the local field at an absorbing molecule and in estimating dipole moments of various states.
Mobility of Bromine Vacancies in KBr Single Crystals
Authors: Jacobs G. , Vandewiele L. G. , Hamerlinck A.
Published: January 2005

Dielectric loss measurements were made on KBr single crystals doped with sulfide ions, from 0.1 to 1000 cps. The technique is described. The activation energy for a jump of an associated bromine vacancy is 0.94±0.03 ev, whereas 1.02±0.03 ev was found for free vacancies. A dependency of the frequency factor on the thermal treatment was observed.
Centrifugal Distortion of Bond Distances and Bond Angles
Authors: Iwasaki Machio , Hedberg Kenneth
Published: January 2005

A simple method has been developed to estimate the changes of bond distances and bond angles produced by the centrifugal force arising from rotational motions of molecules. The method has been applied to the PCl3 molecule and the predicted effect found to be small but significant in comparison to the effect of vibrational motion. The theoretical results for PCl3 at 300° and 505°K are in good agreement with experimental results from gaseous electron diffraction.
Electron Spin Resonance of the Phenanthrene Negative Ion
Authors: Glarum Sivert H. , Snyder Lawrence C.
Published: January 2005

The electron spin resonance spectrum of phenanthrene negative ion produced by electrolytic reduction in acetonitrile has been measured and analyzed. The smallest proton hyperfine splitting is found to be 0.05 oe larger than in the radical produced by potassium reduction in tetrahydrofuran. Experimental and computed theoretical spectra are compared for the radical generated under both conditions.
Thermodynamics of the Formation and Migration of Defects in Cuprous Oxide
Authors: O'Keeffe Michael , Moore Walter J.
Published: January 2005

The number of gram atoms of excess oxygen y per mole of cuprous oxide has been measured by means of a quartz-fiber microbalance. The combined pressure and temperature dependence is log10 y=0.27 log10PO2—(21.7 kcal) / RT+0.29 with T in °K and PO2 in mm Hg. This relation has been utilized to determine the extent of the cuprite field in the copper-oxygen system. The cation vacancy V+ is formed in Cu2O by the reaction ¼O2→½O=+VCu+. The entropy of formation of the vacancy, computed from ΔS=12S(O=)+S(V+)−14S(O2) is S(V+) = 12.1 cal deg—1. This positive entropy, caused by the lowering of the vibration frequencies of neighboring copper atoms, is the principal factor responsible for the defect structure of cuprous oxide. The new thermodynamic data lead to a quantitative determination of the diffusion parameters for copper in Cu2O.
Free Radicals in Irradiated Nylon
Authors: Shinohara Y. , Ballantine D.
Published: January 2005

Gamma irradiation of undrawn filaments of nylon 6 produces several different free radicals whose concentration, ESR pattern, and lifetimes are affected by irradiation temperature, dose, storage conditions, and crystallinity. A five-peak short-lived species, measured at liquid-nitrogen temperature, predominates at low doses, low irradiation temperatures, and is believed to be a free radical associated with the carbon α to the amide nitrogen. A broad singlet is found at higher doses and is believed to be a radical in a conjugated system which includes the amide group. The experimental results are explained in terms of a free radical which is capable of migrating by a hydrogen-atom transfer process.
Pulse Radiolysis Studies. I. Transient Spectra and Reaction-Rate Constants in Irradiated Aqueous Solutions of Benzene
Authors: Dorfman Leon M. , Taub I. A. , Bühler R. E.
Published: January 2005

The radiation chemistry of aqueous benzene solutions has been studied by the electron-pulse radiolysis technique. Ultraviolet absorption spectra of some of the transient species have been recorded by synchronized flash-absorption spectroscopy. The elementary reactions occurring have been observed by fast photoelectric recording of the transient optical density.

A transient spectrum having a broad absorption with a strong maximum at 313 mμ has been observed. On the basis of both spectrographic and kinetic evidence this spectrum is assigned to the hydroxycyclohexadienyl radical, (OH)C6H6·. The molar extinction coefficient is estimated to be ε3130=3500±800 M—1cm—1. A number of substituted cyclohexadienyl radicals have been observed in aqueous solution as well as in pure benzene and chloro-benzene. A second transient observed in oxygenated aqueous benzene solution shows an absorption shifted to lower wavelengths. This is attributed to the hydroxycyclohexadienyl peroxy radical, (OH)C6H6O2·.

Absolute rate constants have been determined at 23°C for the following reactions: OH+C6H6=(OH)C6H6·(4.3±0.9)×109 M−1sec−1,OH+C6D6=(OH)C6D6·(4.7±0.9)×109 M−1sec−1,(OH)C6H6·+O2=(OH)C6H6O2·(5.0±0.6)×108 M−1sec−1.

The yield of phenol in oxygenated solution was found to decrease continuously with increasing pulse intensity. At the highest intensity used, G(C6H5OH) = 0.19 molecules/100 ev. At the lowest pulse intensity used, G(C6H5OH) = 1.9 molecules/100 ev, which approaches the values found in steady irradiations. Some additional phenol is formed in slow post-irradiation reactions. Diphenyl was identified as a product in the deaerated system by gas chromatographic analysis. Its formation is largely the result of post-irradiation reactions, the initial yield being substantially lower than previously reported.

The mechanism of the radiation chemical reaction in both deaerated and oxygenated solutions is discussed on the basis of the conclusion that the hydroxyl radical enters the ring to form the hydroxycyclohexadienyl radical.
NMR Study of the Protolysis Kinetics in Simple Amino Acids. I. Sarcosine Hydrochloride and its Ester
Authors: Sheinblatt M.
Published: January 2005

The mean lifetime of the amino group τ of acidic aqueous solutions of sarcosine hydrochloride and sarcosine methylester hydrochloride were measured using the NMR technique at 21±1°C. The experimental results show:

(1) 1/τ is first order in respect to both sarcosine and its ester concentration.

(2) 1/τ depends strongly on 1/aH+ in very acidic solutions and becomes almost independent in dilute acid solution. The interpretation is given in terms of an exchange of protons between the amino acid or its ester with a water molecule which is hydrogen bonded to the amino group. The exchange mechanism involves two steps:[Complex chemical formula][Complex chemical formula]Values of the rate constants for sarcosine hydrochloride are: kI′=110(sec−1),  k−I′=3.2×1010(sec−1M),  kH=8.3×109(sec−1);and for sarcosine methyl ester are: kI′=120(sec−1),  k−I′=3.2×1010(sec−1M),  kH=1.9×1010(sec−1).
Radius of Gyration of Polymer Chains. II. Segment Density and Excluded Volume Effects
Authors: Fixman Marshall
Published: January 2005

The segment density ρ(r) at a distance r from the center of mass is evaluated for chains constrained to have a large specified radius of gyration R. It is found that ρ(r)≅(N/2π2)[r2(2R2−r2)12]−1H(2R2−r2),where N is the number of segments and H( ) is the step function. It is argued that this conditional distribution takes better account of large excluded volume effects than a simple scaling of the random flight ρ(r).
Sixth and Seventh Virial Coefficients for the Parallel Hard-Cube Model
Authors: Hoover William G. , De Rocco Andrew G.
Published: January 2005

A procedure for calculating virial coefficients for parallel hard lines, squares, and cubes is outlined, and the sixth and seventh virial coefficients are computed for these models. The essential step in the evaluation of the star integrals lies in the recognition of the fact that only a few ``subintegrals'' contribute to each virial coefficient, relative to the total number of labeled star integrals. Both the sixth and seventh virial coefficients are negative for hard cubes, a fact interesting from the point of view of phase transitions. Approximations to the excess entropy are given for squares and cubes.

The procedure for the star integrals is extended to the calculation of approximations to the pair distribution function and the potential of the mean force. These functions are calculated through the fourth approximation for hard lines, squares, and cubes.

The topological graphs needed for the above investigations, together with the values of the related integrals in one dimension, are displayed.
Effect of Adsorbed Phases on the Electrical Conductivity of Synthetic Crystalline Zeolites
Authors: Stamires Dennis N.
Published: January 2005

The electrical conductivity of Linde synthetic crystalline zeolites type X and type A has been measured as a function of various adsorbed phases in the crystals. The potential energy barrier for the conduction process is decreased by the interaction of the adsorbed molecules with the electrostatic field or the field gradient in the lattice. Polar molecules, such as water and ammonia, exhibit a strong association through ion-dipole interactions with the most mobile cations.

The mechanism of adsorption of various molecules and the self-diffusion of sodium ions in these phases at discussed in terms of changes in the activation energy, free energy, and entropy of the conduction process. The relative importance of the electrostatic, dispersion, and quadrupole contributions to the interaction energy of the adsorbate with the zeolite is described.
Thermodynamics of Small Systems
Authors: Hill Terrell L.
Published: January 2005

It is shown in this paper that the differential equations of macroscopic thermodynamics can be generalized in such a way that they apply as well to small (i.e., nonmacroscopic) systems. Conventional thermodynamic relations then follow from the present treatment as a limiting case (large system). As with macroscopic thermodynamics, there are two main classes of applications: (1) as an aid in analyzing, classifying, and correlating equilibrium experimental data on ``small systems'' such as (non-interacting) colloid particles, liquid droplets, crystallites, macromolecules, polymers, polyelectrolytes, nucleic acids, proteins, etc.; and (2) to verify, stimulate, and provide a framework for statistical mechanical analysis of models of finite (i.e., ``small'') systems. A well-known experimental and theoretical example (in which there are sizable effects of chain length) is the helix-coil transition in synthetic polypeptides and polynucleotides. Unlike macroscopic thermodynamics, thermodynamic functions are different for different environments (open, closed, isothermal, siobaric, etc.). Although it is possible to derive a single set of thermodynamic equations applicable to all environments, it proves useful to give a separate analysis for each environment. Several cases are discussed, and a few simple statistical mechanical models are used for purposes of illustration. The partition function for a ``completely open'' small system can be used without any special technique such as is required when this partition function is applied to a macroscopic system. Solvent effects are discussed and details are given in one case. The present method provides an invariant treatment of the spherical interface of a drop or bubble, independent of any choice of dividing surface. Usually, only mean values of fluctuating extensive variables appear in thermodynamic equations. This is justified in macroscopic thermodynamics because fluctuations are generally unimportant. The situation is different for small systems and we derive, in one case, a hierarchy of thermodynamic equations involving higher moments of the probability distribution of fluctuating extensive properties.
Molecular Chaos and the Boltzmann Equation
Authors: Hollinger Henry B.
Published: January 2005

The form of the Boltzmann equation implied by a general form of the molecular chaos assumption is derived. It is shown that the Bogolyubov hypothesis is a form of molecular chaos, which is compared with other forms of molecular chaos that have been used in derivations of the Boltzmann equation. The determination of the Boltzmann equation for an infinite system of rigid spheres is reduced to the evaluation of integrals that require only two-body collision dynamics; the determination is carried explicitly only to the ternary-correlation approximation.
General Potential-Energy Function for Exchange Reactions
Authors: Wall Frederick T. , Porter Richard N.
Published: January 2005

A general potential-energy function for linear triatomic systems has been developed for use in connection with reaction kinetics calculations. The function is a generalization of the Morse function with a sufficient number of adjustable parameters to permit arbitrary fixing of the location and curvatures of the saddle point of the potential energy surface. The function reduces, of course, to the Morse function when one of the atoms is infinitely distant from the other two. Since the characteristics of the saddle region are adjustable, the function is particularly useful in connection with computations designed to test the effect of different shapes of potential energy surfaces upon reaction probabilities. The function is most readily used for symmetric reactions, but it can be further generalized to cover unsymmetric cases.
Quadricovalent Maximum Overlap Hybrid Orbitals
Authors: Randić Milan
Published: January 2005

Applying the method of Murrell [J. Chem. Phys. 32, 767 (1960)] maximum overlap hybrid orbitals for tetragonal plane (square) and tetrahedral (Td) molecules are constructed. Assuming ligand orbitals being s, p, sp, sp2, and sp3, overlap integrals are obtained from tabulated data for Slater functions. Distribution of s and d character in square snp2d2—n hybridization, and the relative weights of the sp3 and sd3 components in general tetrahedral bond orbitals, for various assumed ligand orbitals and interatomic distances are given. Maximum overlap hybrids, when compared with those based on Pauling's criterion of hybrid strengths, show generally a smaller contribution of d orbitals in the hybridization.
Thomas—Fermi Homonuclear Diatomic Molecule. I. Method of Solution and Atomic Interaction Potential
Authors: Townsend J. R. , Handler G. S.
Published: January 2005

The Thomas—Fermi equation, without exchange, has been solved numerically for the neutral diatomic homonuclear molecule. The method of solution and results of the energy integrations are given. Scaling of the nuclear separation parameter and of the energy units permits calculation of a universal interaction potential applicable to all atomic numbers at all separations. Electronic energies are estimated to have a numerical precision of better than 1 part in 104.
Critical Opalescence of Binary Liquid Mixtures: Methanol—Cyclohexane; Aniline—Cyclohexane
Authors: Debye P. , Chu B. , Kaufmann H.
Published: January 2005

For some liquid mixtures, anomalies—for instance, in the coexistence curve—have been observed. Experiments are reported on the angular dissymmetry of visible light as well as on the temperature dependence of the zero-angle scattering for two liquid mixtures. The mixture methanol-cyclohexane behaves normally, the other, aniline-cyclohexane, shows anomalies.
Intermolecular Bonding in the Solid Halogens
Authors: Bersohn R.
Published: January 2005

The band structure of solid iodine is worked out on the assumption that electron exchange between layers is negligible and that only p functions are used by the iodine atoms. The model is justified by its simple description of the iodine nuclear quadrupole coupling constant, the anisotropy of the electrical conductivity and the optical absorption. Experiments are proposed which would provide a more detailed check of the model; the p bands of gallium and indium can probably be described by a similar tight binding scheme.
Medium Effects in Proton Magnetic Resonance. I. Gases
Authors: Raynes W. T. , Buckingham A. D. , Bernstein H. J.
Published: January 2005

The position of the proton resonance signal of a molecule in a gas is found to depend upon the gas pressure. Four distinct phenomena are considered to contribute to the displacement which the signal undergoes as the density is changed: (a) bulk susceptibility, (b) van der Waals interactions, (c) electric fields, and (d) neighbor-molecule magnetic anisotropy. Theoretical expressions are presented for each of these effects. Experiments were performed on CH4, C2H6, and HCl as pure gases and as mixtures with a variety of foreign gases. For HCl at 30°C, the chemical shift changes by —0.41 ppm as the pressure is raised to 55 atm. Good correlation between theory and experiments is obtained in all cases. Parameters describing the influence of an electric field on the proton screening constant are deduced for C–H bonds and for HCl. The bulk susceptibility contribution is large, van der Waals and neighbor-molecule anisotropy effects are small, and the electric fields from permanent dipoles and quadrupoles and from induced dipoles are all important in some instances.
Reactions of High-Energy, Excited I128 Ions with Gaseous Molecules
Authors: Rack Edward P. , Gordus Adon A.
Published: January 2005

The manner in which molecular additives inhibit the reaction of (n, γ) activated I128 with CH4 was determined in an effort to observe indirectly reactions of I128 with the additives. The data suggest that (1) O2, N2, and CF4 serve only to remove excess I128 kinetic energy; (2) the ionization potential of O2 is greater than 12.16 ev, the potential energy of I+(1D2); (3) the ionization potential of C2F6 is less than 12.16 ev; (4) CH3I, CF3I, n-C3H7I, and C6H6 inhibit the reaction principally as a result of I++additive ion-molecule reactions and/or physical quenching.
X-Ray Study of Phase Transformations in Some Rare-Earth Oxide Systems
Authors: Mozzi R. L. , Guentert O. J.
Published: January 2005

The cubic to hexagonal phase transformation of the systems Nd2O3–Sm2O3 and Nd2O3–CeO2 has been studied by x-ray diffraction methods for zero to 20% atomic substitution of Nd by Sm or Ce. Diffraction patterns were obtained at room temperature after heat treatments between 600° and 1400°C. The patterns indicate that at elevated temperature the oxides containing Ce form a solid solution of the approximate cation composition 75% Nd—25% Ce together with excess Nd2O3. At 1400°C the solid solution was found to be cubic and the excess Nd2O3 to be hexagonal. The oxides containing Sm form solid solutions with cation ratios corresponding to those of the original mixture. They transform into the hexagonal phase via a monoclinic phase which is isomorphous with the B form of Sm2O3. Preferred orientation effects were observed on pressed powder disks of Eu2O3 and Nd2O3 below and above their respective transition temperatures. They support an approximate identification of the monoclinic a, b, and c axes with the cubic [11̄0], [110], and [001] directions and suggest the equivalence of the hexagonal c axis and cubic [111] direction.
Ionization and Fragmentation of Some Molecules by High-Energy Electrons
Authors: Kebarle P. , Godbole E. W.
Published: January 2005

The mass spectra of some 10 representative organic compounds were obtained by using electrons with an energy up to 12 kev. Modifications of the ion source were made to reduce field penetration by the filament potential and emission of secondary electrons in the ion box. The mass spectra showed some small changes from 50 to 1000 ev. The changes were due to decreases in the abundance of ions of low relative intensity. These were ions which could be produced only by a succession of fragmentation processes. The mass spectra remained remarkably constant with further increase of the voltage. The significance of the results for gas phase radiolysis by α particles and β rays is briefly considered.
Viscosity of Critical Mixtures
Authors: Fixman Marshall
Published: January 2005

A theory is given of the sharp viscosity rise in mixtures in the critical mixing region. Good agreement with the experimental dependence of viscosity on composition and temperature is found. The method involves a calculation of the entropy production through diffusion which results when a mixture in a state of composition fluctuation is caused to have a velocity gradient. The long wavelength part of the spectrum of composition fluctuations is intense and very easily distorted by a velocity gradient in the critical region. The return to uniform composition through diffusion dissipates energy, and the loss is interpreted as an excess viscosity. It is shown that this method, which requires no knowledge of the intermolecular potential but only of the long-range part of the radial distribution function, correctly gives the viscosity of a dilute 1–1 electrolyte.
Restriction on the Form of Relaxation-Time Distribution Functions for a Thermally Activated Process
Authors: Macdonald J. Ross
Published: January 2005

When a distribution of relaxation times is associated with thermally activated processes in a material and arises solely from a distribution of activation energies, the form of the relaxation-time distribution may be restricted. In this case, the temperature dependence of some of the parameters which enter into the distribution function will be uniquely determined. The Wagner relaxation-time distribution function may be made entirely consistent with a distribution of activation energies by taking its shape parameter temperature dependent, but the Cole-Cole, Fuoss-Kirkwood, and Davidson-Cole distribution functions can only be made approximately consistent in the separate limits of very wide and narrow distributions of relaxation times. The temperature dependences of their parameters found experimentally for thermally activated processes is compared where possible with that required for the distribution of activation energies situation. A new relaxation-time distribution is proposed which is completely consistent with a distribution of activation energies in an activated process and which can describe a variety of experimental data.
Thermodynamic Significance of Heat of Transport in Interstitial Solid Solutions
Authors: Raleigh D. O. , Sommer A. W.
Published: January 2005

The theoretical relationships involved in thermal diffusion have been re-examined. It has been shown from strictly thermodynamic considerations that in dilute solid solutions the quantity ``heat of transport,'' or Q*, can be expressed as the sum of two distinct contributions.

One of these is the partial molal heat of solution of the solute, referred to pure solute as the standard state. The second is a portion, designated the thermal gradient effect, which exists independent of solubility relationships. The latter has been shown to be obtainable from a plot of log solute activity vs reciprocal temperature when the activity is referred to pure solute as the standard state. Comparison of heat of transport with heat of solution in interstitial solid solutions where data are available indicate that the thermal gradient effect is small in these systems.
3,3-Dimethyl-2-Thiabutane: Chemical Thermodynamic Properties and Barriers to Internal Rotation
Authors: Scott D. W. , Good W. D. , Todd S. S. , Messerly J. F. , Berg W. T. , Hossenlopp I. A. , Lacina J. L. , Osborn Ann , McCullough J. P.
Published: January 2005

Thermodynamic data obtained for 3,3-dimethyl-2-thiabutane (methyl t-butyl sulfide) were used to determine the heights of the barriers hindering internal rotation in the molecule. The chemical thermodynamic properties in the ideal gas state (0 to 1000°K) were calculated from calorimetric, spectroscopic, and molecular structure information. Experimental studies provided the following information: values of heat capacity for the solid (15°K to the triple point), the liquid (triple point to 364°K), and the vapor (360 to 500°K); the triple point temperature; the heat of fusion; thermodynamic functions for the solid and liquid (0 to 355°K); heat of vaporization (330 to 372°K); parameters of the equation of state; vapor pressure (307 to 410°K); and the standard heat of formation at 298.15°K.