bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Chemical Reactions on the Bimolecular Rate Constant
Authors: Kostin M. D.
Published: January 2005

The dependence of the bimolecular rate constant on the reaction rate, degree of anisotropic scattering, mass ratio, and other parameters is investigated by considering the Boltzmann equation for a dilute homogeneous reacting gas. For highly anisotropic elastic scattering, a differential form of the Boltzmann equation is derived and a solution obtained, which yields an analytical expression for the rate constant. It is found that the correction to the standard reaction-rate formula is significant for highly anisotropic scattering, small mass ratios, and large reaction cross sections.
Adsorption and Occlusion of Gases by the Low-Temperature Forms of Ice
Authors: Ghormley J. A.
Published: January 2005

Water vapor condensed on a surface at −196°C in the presence of O2, N2, Ar, or CH4, forms a condensate which, on warming, evolves gas in three temperature ranges. The rate of gas evolution first goes through a maximum between −196° and −125°C probably from release of adsorbed gas due to decrease in surface area of the amorphous ice. A second peak in the gas evolution rate appears in the same temperature range as the formation of cubic ice between −120° and −110°C. The remainder of the occluded gas comes out between −70° and −40° (at 15° rise/min) where cubic ice transforms to the hexagonal form. Nitrogen adsorption isotherms indicate surface areas as high as 241 m2/g for amorphous ice prepared at −196°C, and annealing measurements suggest areas as high as 500 m2/g for lower-temperature preparations. Water—oxygen mixtures subjected to a microwave discharge, then condensed at −196° and allowed to warm, evolve as much as 97% of the product oxygen between −70° and −40°C.
Isotope Effects in the Diffusion and Solubility of Hydrogen in Nickel
Authors: Ebisuzaki Y. , Kass W. J. , O'Keeffe M.
Published: January 2005

The solubility and diffusivity of hydrogen and deuterium in a single crystal of nickel have been measured in the range 490°—690°K. The theory of isotope effects has been developed in the harmonic approximation. It is shown that the experimental results can be quantitatively accounted for in terms of the derived expressions. The theory is tested by calculation of the pre-exponential factor for diffusion (D0) using only the data for the relative diffusivities of hydrogen and deuterium. The calculated value is in excellent agreement with experiment if it is assumed that direct jumps of hydrogen from one octahedral site to another are involved.
Diffusion and Solubility of Hydrogen in Single Crystals of Nickel and Nickel—Vanadium Alloy
Authors: Ebisuzaki Y. , Kass W. J. , O'Keeffe M.
Published: January 2005

A method of obtaining very precise data on the solubility and diffusion of hydrogen in single crystals of metals is described. Results for the permeability, solubility, and diffusivity of hydrogen in pure nickel and a nickel −4.4 at. % vanadium alloy are presented. For pure nickel the diffusion coefficient is D=(5.22±0.18)×10−3exp [−(9.56±0.04) kcal/RT] cm2sec−1 and the solubility in atom fraction H/Ni is S=(3.26±0.17)×10−3exp[−(3.60±0.06) kcal/RT]. The nickel—vanadium alloy is more permeable to hydrogen because of a lower heat of solution of hydrogen (2.09±0.05 kcal/mole) in the alloy.
Heat Capacity of Polyethylene from 2.5° to 30°K
Authors: Tucker J. E. , Reese W.
Published: January 2005

Heat-capacity measurements for three samples of polyethylene of varying density are reported for the range 2.5° to 30°K. In this range that heat capacity is strongly density-dependent, being linear in the crystallinity. Extrapolation to the cases of completely amorphous and completely crystalline material have been made and a table giving the heat capacity of these hypothetical materials is presented. In the lowest temperature range the heat capacities of all of the samples and of the extrapolated amorphous material do not show a cubic temperature dependence, but rather indicate an excess heat capacity similar to that found in some other amorphous materials. The extrapolated crystalline material does not display an excess heat capacity, but rather has a cubic temperature dependence to approximately 9°K. It is found that a simple continuum model represents the heat capacity of polyethylene quite well at low temperatures.
Structure of Liquids. III. An X-Ray Diffraction Study of Fluid Argon
Authors: Mikolaj P. G. , Pings C. J.
Published: January 2005

X-ray diffraction measurements were made on argon at 13 states in the general critical region on a density—temperature grid covering the range 0.280 g/cc⩽ρ̄⩽0.982 g/cc and −130°C≤T≤−110°C. Features of the intensity patterns vary rather simply with density and only weakly with temperature. Computed values of the radial distribution functions show similar dependence on T and ρ̄. The first three maxima in the distribution functions are at average locations of 3.90, 7.51, and 10.9 Å.
Mass-Spectrometric Studies of Negative Ions in Acetone
Authors: de Souza B. C. , Green J. H.
Published: January 2005

The negative-ion mass spectra of acetone have been studied as a function of pressure (to 0.075 torr) with a high-pressure ion source. The number of fragment ions and their abundance was found to be much less than that for the corresponding positive-ion spectra. Secondary ions presumably resulting from ion—molecule reactions make a significant contribution to the spectra at high pressure. Probable mechanisms for formation of some of the observed ions are suggested from the nature of the spectra. In addition to the acetone spectra, some preliminary work on simple ketones is described.
Correlation between the Luminescence Behavior of Octahedral Chromium(III) Complexes and the Ligand-Field Strength
Authors: Schläfer Hans L. , Gausmann Hans , Witzke Horst
Published: January 2005

An empirical rule for the type of luminescence (fluorescence only, fluorescence and phosphorescence, phosphorescence only) to be expected, which depends on the position of the respective ligands in the spectrochemical series, has been found for octahedral chromium (III) complexes. This correlation is discussed in terms of the shape and intersection of potential-energy surfaces.
Statistical Mechanics of a Simple Entanglement
Authors: Prager Stephen , Frisch H. L.
Published: January 2005

It is shown that the statistical mechanics of an entanglement produced by looping a polymer chain around an infinitely long straight bar can be treated exactly, essentially because successive turns of the chain around the bar can be considered as constituting a Markoff process. The elastic response of such a loop to a force exerted on one of its segments is nonlinear and surprisingly complex.
Sedimentation Coefficients of Linear and Cyclic Wormlike Coils with Excluded-Volume Effects
Authors: Gray Horace B. , Bloomfield Victor A. , Hearst John E.
Published: January 2005

The sedimentation coefficient for the Kratky—Porod wormlike coil is calculated with the effects of excluded volume taken into account. The statistical length of native DNA is found to be 900 Å. The hydrodynamic diameter of the Watson—Crick helix is 26–27 Å. Sedimentation coefficients are calculated to decrease by about 13% on going from a cyclic native DNA to a linear molecule of the same molecular weight.
Microwave Spectrum, Structure, Dipole Moment, and Quadrupole Coupling Constant of Germyl Cyanide
Authors: Varma Ravi , Buckton Keith S.
Published: January 2005

The symmetric-top spectra of 10 isotopic species of GeH3CN have been observed and measured. From the rotational constants obtained the following structural parameters have been derived: r(C–N)=1.155±0.001 Å and r(Ge–C)=1.919±0.001 Å, assuming r(Ge–H)=1.529 Å and a tetrahedral distribution about the Ge atom. From an analysis of the splittings observed in the 1→2 transitions of GeH3CN a quadrupole coupling constant for the nitrogen nucleus of −5.0±0.1 Mc/sec has been obtained. Analysis of the Stark effect gives a dipole moment of 3.99±0.05 D.
Excitation of Luminescence from KI:Tl at 5°K
Authors: Kaufman R. Gilbert , Hadley Wayne B.
Published: January 2005

Emission and excitation spectra of single and double thallous ion fluorescence are measured in KI:Tl 0.06 mole %) at 5°K. Spectra are also measured of the emission during x irradiation, of the emission stimulated after irradiation, and of the phosphorescence after irradiation. There are differences between the stimulated emission, which is entirely the result of recombination of electrons and holes, and the x-ray-induced emission. Two possible interpretations of the differences are discussed and the suggestion favored that hot electrons produced in the radiation shower excite optically available states of the thallium ion.
Ionization of Liquids by Radiation. III. Field Dependence of the Conductivity
Authors: Hummel Andries , Allen A. O.
Published: January 2005

The conductivity of hexane under 1500-kV x rays was studied at fields up to 40 kV/cm. Conditions were attained under which the theoretical proportionality to dose rate and to plate separation was strictly obeyed. Data are also reported for diethyl ether and 1,4-dioxane, and for hexane irradiated by 2.4-keV electrons from 37Ar. Onsager's formula for probability of escape of a single ion pair describes the behavior of the conductivity of low-dielectric-constant liquids under high-energy x rays, but fails when applied to the results from 2.4-keV electrons, where an appreciable probability exists of escape of more than one ion pair from a group.
Stochastic Models for Second-Order Chemical Reaction Kinetics. Time Course of Reactions
Authors: Darvey I. G. , Ninham B. W.
Published: January 2005

A detailed study is given of the time course of a stochastic model for the reversible second-order chemical reaction A+B⇄C+D. The solutions are obtained by perturbation theory for a range of values of the rate constants of the reaction and the techniques developed may be applied to a variety of other reactions. The main conclusion of this study is that fluctuations in the number of molecules of every component present in the system at any time are negligible even for small systems.
Performance of a New Photoelectric Detection Method for Optical Spectroscopy. II. Application to Laser Raman Spectroscopy
Authors: Griffiths James E. , Pao Yoh-Han
Published: January 2005

The application of a new ac photoelectric detection method to laser Raman spectroscopy is described. Chlorine isotope fine structure in HCCl3, CCl4, SiCl4, GeCl4, and SnCl4 is well resolved and the relative intensities of the individual isotope lines revealed an unusual liquid-state interaction in SiCl4. Such interactions are absent at room temperature in the other molecules of this type.

Spectra of CS2, ν1 and ν2, and the ν2 line of 12C6H6 and 12C513CH6 are also presented. A survey scan of the Raman spectrum of the SnCl4 using narrow slit openings demonstrates some of the advantages of the present detection method.
Delayed Fluorescence Due to Triplet—Triplet Annihilation: A Theoretical Study
Authors: Krishna V. G.
Published: January 2005

A mechanism for delayed fluorescence is considered in which the interaction of two molecules in their triplet states is followed by nonradiative transitions to a dissociative singlet state. The energies of the bimolecular states formed from the 3La states of some aromatic hydrocarbons are calculated. The rates of nonradiative transitions from the singlet and triplet bimolecular states are shown to be much faster than the rate of the quenching of triplets in solutions. It is also shown that nonradiative transitions from the quintet bimolecular state may compete favorably with triplet quenching.
Impurity Effects on Heterogeneous Nucleation from the Vapor: Selenium on Glass
Authors: Kressner Bernhardt E. , Hudson John B.
Published: January 2005

It has long been recognized that impurities adsorbed on the substrate can have a marked influence on the kinetics of heterogeneous nucleation. However, the detailed nature of these effects has not been demonstrated heretofore. In the present work, impurity effects have been characterized for the nucleation of selenium vapor onto Pyrex glass. It is shown that the degree of surface contamination not only affects the critical supersaturation required for nucleation, but may cause a nucleated phase of other than equilibrium structure. It is also shown that the degree of material accommodation for selenium on Pyrex is affected by surface contamination. These results are discussed in terms of the changes in substrate and nucleus interfacial energies accompanying impurity adsorption, and in terms of the possible masking of ordering influences exerted by a clean substrate.
Surface-Induced Transitions in Highly Excited Noble-Gas Ions and Quasimetastable Peaks in the Mass Spectra of the Noble Gases
Authors: Newton Amos S. , Sciamanna A. F. , Clampitt R.
Published: January 2005

The appearance of some quasimetastable peaks in the mass spectra of the noble gases is shown to be due to a surface-induced transition of the type: X(q)+*→ lim SX(q+1)++e−in which X is any of the noble gases and S represents a metal surface. In argon, peaks arising from this type of transition at the ion-source first slit, focus slit, and last slit, respectively, have been observed and characterized as to (1) their behavior with the voltage effective at each respective slit, (2) their kinetic energy as measured by the metastable-ion-suppressor cutoff behavior, and (3) their appearance potential. These peaks are postulated to arise from ions in Rydberg levels of high principal quantum number at an excitation level near the next higher ionization potential. Possible mechanisms for the transition are discussed.
Electronic Structure and Geometry of Hydrogen Cyanide
Authors: Pan Dorothy C. , Allen Leland C.
Published: January 2005

The geometry and charge distribution of HCN in its ground state has been determined by means of many-electron, self-consistent-field molecular-orbital wavefunctions. LCAO MO SCF calculations and ones which split the AO's with linear variation coefficients yield properties and total energies reasonably close to the molecular Hartree—Fock limit. A linear molecule with bond distances correct to 1% of the microwave spectroscopy values is obtained. Walsh's orbital-energy diagrams are found to be almost independent of angle but with nearly compensating variations and for this molecule Walsh's orbital-energy summation criterion leads to a bent ground state. This result, however, is easily understood in terms of the relatively high ionic character of the H–CN bond. An empirical molecular bind energy correlation scheme based on diatomic molecular Hartree—Fock solutions is employed to analyze the difference between the computed (7.10 eV) and the experimental (13.53 eV) binding energy values.
Matrix Elements of z/r3 and (3z2—r2)/r5 in a Slater Basis for Linear Systems
Authors: McLean A. D. , Yoshimine M.
Published: January 2005

Methods are given, which are adequate for computation of all matrix elements of the operators z/r3 and (3z2—r2)/r5 in a Slater basis set for linear systems with an arbitrary number of nuclei. The one-center integrals are evaluated analytically. The remainder are evaluated using a two-dimensional numerical quadrature after having modified the integrand to remove any infinities in those cases where they occur. With reasonable grids, these procedures are adequate for the evaluation of the force on, and the electric field gradient at, the nuclei in linear systems with an accuracy of four to five decimal places (in atomic units). This is all that is, in general, justified by the accuracy of the wavefunction.
Near-Molecular Hartree—Fock Wavefunction for CH3+
Authors: Kari R. E. , Csizmadia I. G.
Published: January 2005

Ab initio LCAO MO SCF calculations have been performed on CH3+ with a C–H bond length of 1.95 Bohr a.u., using Gaussian-type functions (GTF) as the basis set. By successive increases in the size of the basis set (N) of GTF's (N=12, 20, 28, 36, 40) it was possible to approach the molecular Hartree—Fock limit within 0.03 Hartree a.u. The best calculated total energy was −39.21726 hartrees while the Hartree—Fock limit has been estimated to be −39.243 hartrees for the above C–H distance.

The variation of the geometry of CH3+ indicated that the molecule is planar in its ground state and has an extensive electron delocalization. The charge distribution was such that there was approximately 0.13 positive charge on the carbon atom and 0.29 positive charge on each of the three hydrogen atoms. Due to its symmetry, the planar molecule possessed zero dipole moment but it assumed finite values in pyramidal conformations. The total electron density as well as the near Hartree—Fock molecular orbital densities are presented in the form of contour maps.

Within the framework of a single Slater determinantal wavefunction, estimations for some of the low-lying electronic excited states of CH3+ have been made.
Role of Singlet Excited States of Molecular Oxygen in the Quenching of Organic Triplet States
Authors: Kawaoka Kenji , Khan A. U. , Kearns David R.
Published: January 2005

The quenching of triplet-state molecules by molecular oxygen is examined theoretically. Two different quenching processes are considered: namely, (i) quenching by transfer of electronic excitation energy from the triplet state of the donor molecule to oxygen, resulting in a ground-state donor molecule and an electronically excited singlet-state oxygen molecule; and (ii) quenching by enhancement of intersystem crossing in the donor molecule, resulting in a vibrationally excited donor molecule in its ground electronic state and a ground-state molecule. The relative importance of these two quenching processes is determined almost entirely by Franck—Condon factors, rather than by electronic factors. From our analysis we conclude that quenching by transfer of electronic excitation energy from the triplet-state molecule to oxygen is usually 100–1000 times faster than quenching by enhanced intersystem crossing.

Exchange interactions appear to be less important in promoting the radiationless transitions than do interactions involving charge-transfer virtual states. The absolute value of the quenching rate calculated for the energy transfer process satisfactorily accounts for the experimental observations on the oxygen quenching of triplet-state molecules in solution. These theoretical results give strong support to the previous suggestion that quenching of triplet-state molecules by oxygen leads to the production of electronically excited singlet-state (1Σg+ or 1Δg) oxygen molecules.
Bond Lengths in the α-Ga2O3 Structure and the High-Pressure Phase of Ga2−xFexO3
Authors: Marezio M. , Remeika J. P.
Published: January 2005

The crystal structure of α-Ga2O3, which is isostructural with α-corundum, has been refined from single-crystal x-ray diffraction data. The bond lengths have been determined to an accuracy of about 0.01 Å.

The bond lengths in the GaO6 octahedron are 2.077 and 1.921 Å. The short Ga–O distance corresponds to the oxygens forming the unshared face of the octahedron, whereas the long one corresponds to the shared face.

Under high pressure and high temperature Ga2−xFexO3 undergoes a phase transition. The room-temperature, room-pressure phase is orthorhombic. In this structure the gallium ions have coordination numbers 4 and 6 while the iron ions have coordination number 6 only. The high-temperature, high-pressure phase is isostructural with α-corundum so that all cations have coordination number 6.
Raman Spectral Studies of Intermolecular Coupling in Aqueous Selenious Acid Solutions
Authors: Walrafen G. E.
Published: January 2005

Polarized argon-ion laser and unpolarized mercury-excited photoelectric Raman spectra, and infrared spectra, were obtained for aqueous selenious acid solutions ranging in concentration from ∼1–13M at 25°C. Relative integrated Raman contour intensities, and Raman and infrared contour frequencies were obtained. Relative integrated Raman—Gaussian-component intensities, and Raman and infrared Gaussian-component frequencies were also obtained by means of a special-purpose analog computer.

Relative integrated Raman contour intensities obtained with unpolarized excitation were found to fit an equation of the form I=aM2+bM for valence and deformation contours where I is the intensity, and M the stoichiometric H2SeO3 molarity. Relative integrated Raman intensities of Gaussian valence components from unpolarized spectra were also found to show the quadratic concentration dependence.

Frequencies from polarized and unpolarized valence contours, as well as frequencies of Gaussian valence components from unpolarized Raman spectra, also indicated quadratic concentration dependences. Frequency differences between polarized and unpolarized valence contours, and between Gaussian valence components from unpolarized Raman spectra indicated quadratic concentration dependences as well.

The quadratic intensity dependences were described by the term coupling intensification, because the molar intensities were found to increase in general with M, i.e., I/M=aM+b. The quadratic frequency dependences were described by the term coupling frequency shifting. The quadratic frequency differences constitute a splitting and they were termed coupling splitting. The use of the term coupling refers to intermolecular in-phase and out-of-phase coupling between H2SeO3 vibrations. The predominant coupling mechanism was found to involve hydrogen bonding through water between the coupled H2SeO3 molecules, as evidenced by the persistence of the characteristic out-of-phase coupled component at all concentrations.
Drift Velocities of Slow Electrons in Methane, Ethane, Ethylene, Propylene, Acetylene, and 1-Butene
Authors: Bowman C. R. , Gordon D. E.
Published: January 2005

A double-shutter drift tube was used to measure the drift velocities of electrons in methane, ethane, ethylene, acetylene, propylene, and 1-butene for low E/P values. The data were analyzed to obtain values of the momentum transfer cross section as a function of electron energy in the interval 0.010 to 0.063 eV. Cross sections were obtained by fitting a power series in electron velocity to the slope of electron-drift-velocity data in the thermal equilibrium range where electron velocities can be represented by a Maxwellian distribution.
Vapor Pressures of the Methylacetylenes, H3CCCH, H3CCCD, D3CCCH, and D3CCCD
Authors: Van Hook W. Alexander
Published: January 2005

The vapor pressures of the four deutero—protio isomers of methylacetylene of C3v symmetry have been measured over the temperature range 167° to 255°K (∼1 mm C3H4 to ∼1000 mm C3H4) by mercury monometry. Methyl-d3-acetylene shows an inverse vapor-pressure isotope effect which amounts to about 1.6% per deuterium atom at 167°K falling to 1.2% per deuterium atom at 255°K, while methylacetylene-d displays a normal effect of about 2.0% at 167°K which falls to an inverse effect of 0.2% at 255°K. The crossover temperature is near 226°K. The effect observed for D3CCCD is slightly less than the sum of the effects of D3CCCH and H3CCCD.

The data are interpreted in the light of the statistical theory of isotope effects in condensed systems. A model calculation is made in the framework of this theory in the harmonic-cell approximation using reasonable force fields. It is shown, as in the previous study on ethane, that anharmonicities in the lattice frequencies must be postulated in order to rationalize the vapor-pressure effects observed for the deutero methyl compounds. The vapor pressure of the deutero methynic compound appears unusual and it will be shown that the data indicate considerable molecular association in the condensed phase, and that the amount of this association is temperature dependent. This last point is in agreement with the results of an independent NMR investigation and with spectroscopic studies.
Kinetics of Hydrogen Halides in Shock Waves: HCl and DCl
Authors: Jacobs T. A. , Cohen Norman , Giedt R. R.
Published: January 2005

Decomposition rates of HCl and DCl, diluted in an Ar bath, were studied behind incident shock waves over the temperature range 2800° to 4600°K, by application of infrared emission techniques. Within a factor of 2, the dissociation rate constants (cubic centimeters·moles·second units) were found to be as follows. HCl: k1=1021.83T−2 exp (−102 170/RT); DCl: k1=1021.90T−2 exp (−103 200/RT). Evidence is presented to show that a superior match is achieved between experimental and computed time derivatives for HCl and DCl when an activation energy of about 70 kcal is taken for the dissociation step; in this case, a k1=1012.82× exp (−70 000/RT) is found for HCl and DCl.
Perturbational Calculations of the Nuclear Spin—Spin Coupling Constant for the Hydrogen Fluoride Molecule
Authors: Kato Yoshifumi , Saika A.
Published: January 2005

Most of previous perturbational calculations of nuclear spin—spin coupling constants either made the mean excitation energy approximation or took account of only a few lower excited states. We have examined these approximations by including higher excited states, taking as an example the hydrogen fluoride molecule, for which several molecular-orbital wavefunctions are available. Contributions from the orbital and spin dipolar terms besides the Fermi contact term are also calculated with due regard to two-center integrals. The present results indicate that the calculated values of the coupling constant are extremely sensitive to the wavefunctions employed, and the estimates by these approximate wavefunctions available at present cannot be fully trusted as yet.
Accurate Wavefunctions for Fe3+ and Its Excited Configurations
Authors: Synek M. , Rainis A. E. , Peterson E. A.
Published: January 2005

The accurate analytical self-consistent-field wavefunctions were calculated for the Fe3+ ground state, and for the Fe3+ excited configurations with two and three open shells of different symmetries. All the expansion basis sets were selected so as to satisfy precisely the cusp condition. The deviations from the tail nodal extinction for the radial functions Piλ(r) never exceeded 0.00010. Our wavefunctions for Fe3+ are the most accurate ones available. For the two- and three-open-shell states of Fe3+ the calculated wavefunctions and total energies are presented for the first time. The experimental energy levels were available for comparison with one of the excited states calculated.
Flash Photolysis of Methane in the Vacuum Ultraviolet. II. Absolute Rate Constants for Reactions of CH with Methane, Hydrogen, and Nitrogen
Authors: Braun W. , McNesby J. R. , Bass Arnold M.
Published: January 2005

By means of kinetic spectroscopy, the concentration of CH has been measured in the flash photolysis of methane. Measurements were made by following the attenuation of C 2Σ+←X 2Π Q branch at 3143 Å, where the disappearance of CH is of the first order in CH. Experiments were conducted with pure methane, methane+H2, and methane+N2. The reactions and the corresponding rate constants in mole−1 cm3 sec−1 are CH+CH4→C2H4+H,k=1.5×1012;CH2+H2→CH3,k=6.2×1011;CH+N2→products,k≃4.3×1010;CH+CH→C2H2,k≃1.2×1014.
Reactions between Vacancies and Impurities in Magnesium Oxide. II. Mn4+-Ion and OH−-Ion Impurities
Authors: Glass A. M. , Searle T. M.
Published: January 2005

Reactions between cation vacancies and Mn4+- and OH−-ion impurities in MgO are studied as a function of temperature using optical techniques to determine the concentrations of reaction components. The emission spectrum of the Mn4+ ion in both cubic and noncubic sites in single crystals of MgO is reported, and several new features of the OH−-ion absorption spectrum are discussed. The experiments have enabled the identification of the spectral lines due to Mn4+ and OH− in isolated and associated sites. Calculation of the OH−-ion eigenfrequencies for ions in various sites, using a point-charge model, are found to be in good agreement with the experimental results. Finally, observations of the x-ray-induced V′ center (the Seitz V1 center) absorption are found to be consistent with the results of impurity-ion—vacancy interaction.
Study of the Hydrogen Bonding in the Adenine—Thymine, Adenine—Cytosine, and Guanine—Thymine Base Pairs
Authors: Lunell Sten , Sperber Gunnar
Published: January 2005

The motion of the protons in the hydrogen bonds of the guanine—cytosine base pair has recently been studied by Rein and Harris, using a semiempirical LCAO MO SCF method. These investigations are extended to the adenine—thymine base pair and the ``rare'' base pairs adenine—cytosine and guanine—thymine. The total electronic energy of the ground states of the neutral base pairs and their positive and negative ions has been calculated for about 100 different configurations of the protons in the hydrogen bonds. The potential-energy surfaces obtained are reported together with the equilibrium distributions between different tautomeric forms of the base pairs.
Motion of a Weakly Coupled Exciton Wavepacket
Authors: Bierman Arthur
Published: January 2005

The rate of spreading of a weakly coupled exciton wavepacket in an infinite one-dimensional crystal with nearest-neighbor coupling at 0°K is calculated. An initial state consonant with the Franck—Condon principle is assumed. This rate is found to be time independent and is given by the expression (√2W/h̄) (Σm | Sm0 |6)1/2, where the symbols are defined in Eqs. (5).
Hydrogen Atom Scattering: Velocity Dependence of Total Cross Section for Scattering from Rare Gases, Hydrogen, and Hydrocarbons
Authors: Fluendy M. A. D. , Martin R. M. , Muschlitz E. E. , Herschbach D. R.
Published: January 2005

An apparatus for scattering experiments with thermal energy hydrogen atom beams is described. The atoms are generated by dissociation of H2 in a tungsten-tube furnace at ∼2700°K, modulated by a mechanical chopper, and velocity selected by deflection in an inhomogeneous magnetic field. After passing through a scattering chamber containing the target gas, the atoms strike a platinum strip bolometer which functions as a catalytic recombination detector (capable of detecting an H beam of ∼5×1010 atoms cm−2· sec−1). Measurements of the velocity dependence of the total collision cross section in the range 3 to 11×105 cm/sec (equivalent to 0.05 to 0.5 eV) are given for scattering of H atoms from the rare gases, H2, CH4, C2H2, C2H4, C2H6, and C(CH3)4. The results show that throughout this range attractive r−6 interactions are still predominant for Xe, C2H4, and C(CH3)4 whereas repulsive interactions are dominant for most of the other gases. The data are compared with calculations based on the Lennard-Jones (n, 6) potential and with empirical correlations of van der Waals force constants.
Nuclear Magnetic Relaxation in Ionic Solution. II. Relaxation of 23Na in Aqueous Solutions of Various Diamagnetic Salts
Authors: Eisenstadt Maurice , Friedman Harold L.
Published: January 2005

The β coefficients in the equation T1−1—T10−1=Σβscs, which represents the nuclear relaxation rate of 23Na+ in dilute aqueous solutions at 25° as a function of solute molarity, have been determined for a variety of ionic solutes and separated into cationic and anionic contributions. For many species β is simply expressed in terms of viscosity and volume effects. Large additional contributions to β are found for a group of symmetrical, singly charged oxy and fluoro anions of which ClO4=, studied in the previous paper, is typical. The same is true for ions such as SO4= and PO4−3 for which extra interaction (such as association) with Na+ has been deduced from other types of measurements. For some solutes, including sucrose, nonlinear contributions to T1−1 dominate at concentrations as low as 0.2M. In the case of SO4= the observed nonlinearity may be attributed to ion association, in which case a dissociation constant (molar scale) of 0.2, in agreement with the result of Davies may be deduced from the data if his activity-coefficient approximation is used.

The temperature dependence of T10−1 is found to be markedly different from that for a group of relaxation and transport coefficients (e.g., proton T1 and viscous flow), all of which have nearly common behavior. It is concluded from this that the strength of the 23Na+–H2O quadrupolar interaction that determines T10 is temperature dependent. By contrast, the temperature dependence of the β for the 23Na+–ClO4− interaction exhibits the common behavior.

Approximate values of the β coefficients for the relaxation of 79Br− and 127I− are extracted from linewidth measurements on aqueous solutions of their salts reported by Hertz and Richards and co-workers. With allowance for differences in nuclear properties they are of similar magnitude and range as those for 23Na+. Structure-breaking cations give large β coefficients in these systems just as structure-breaking anions do with 23Na+.
Electron Spin Resonance of an Irradiated Single Crystal of Ammonium Trifluoroacetate
Authors: Srygley Fletcher D. , Gordy W.
Published: January 2005

The electron spin resonance of γ-irradiated single crystals of ammonium trifluoroacetate (CF3COONH4) has been investigated at 300° and at 77°K. Free radicals of two types were detected at 300°K. One of these is proved to be CF2COONH4 and the other tentatively identified as CF3CO2. The nuclear couplings of the two F's of the former are equivalent and axially symmetric with A∥=188 G and A⊥=14 G. These couplings indicate spin densities of 0.12 in a 2p orbital of each F. No hyperfine structure is observed for the CF3CO2. This is interpreted to mean that the spin density is concentrated on the oxygens. At 77°K the negatively charged radical (CF3COONH4)− was found. Its spectrum was observed to change into that for CF2COONH4 as the temperature was raised. Different coupling tensors are observed for each of its three F's. The principal elements of the couplings indicate 2p spin densities of 0.11, 0.13, and 0.13 on the three F's.
Origin of Rotational Barriers. II. Methylamine and Improved Wavefunctions for Hydrogen Peroxide
Authors: Fink William H. , Allen Leland C.
Published: January 2005

LC(Hartree—Fock) AO MO SCF wavefunctions have been constructed for CH3NH2 and MO SCF wavefunctions beyond this level of approximation for H2O2. Analysis of these solutions along with wavefunctions determined previously for CH3CH3 and CH3OH makes possible several conclusions concerning the origin of rotational barriers: (1) Study of a sequence of molecules, including particularly those of low symmetry, is required for detailed understanding. (2) The origin may be found within the framework of the Hartree—Fock approximation. (3) Decomposition of the total energy into one- and two-electron components elucidates the barrier origin and provides a physical picture of the barrier mechanism as a delicate balance between the interactions of lone pairs, bonds, and protons.
Molecular-Orbital Representation of Repulsive Potential Surfaces: An Analysis of the Neon Dihydride Wavefunction
Authors: Kapral Raymond
Published: January 2005

A variety of wavefunctions are constructed for the neon dihydride molecule. The Hartree—Fock wavefunction is decomposed into its constituent valence-bond structures and the effects of the orbital constraints are analyzed. The constraints imposed by writing this wavefunction as a single determinant may render the molecular-orbital method incapable of distinguishing between attractive and repulsive potential surfaces.
Hyperpolarizabilities of Some Polar Diatomic Molecules
Authors: O'Hare J. M. , Hurst R. P.
Published: January 2005

The energy E of a polar diatomic molecule in a uniform external electric field F is expressible as E=E0−piFi−(2 !)−1αijFiFj−(3 !)−1βijkFiFjFk−···,where E0 is the energy of the molecule out of the field, pi is the permanent dipole moment, αij is the dipole polarizability tensor, and βijk is the first hyperpolarizability tensor. In this work, theoretical results are presented for αij and βijk for some diatomic molecules. The zero-order wavefunctions used in these calculations are extended basis Hartree—Fock functions of the Roothaan type. The values of αij and βijk are obtained via an uncoupled Hartree—Fock scheme. The results for αij are compared with previous uncoupled and coupled self-consistent-field calculations. The present scheme improves upon the previous uncoupled calculations and compares favorably with the results obtained in self-consistent-field calculations. Finally, these polarizabilites and hyperpolarizabilites are found to be quite sensitive to the quality of the zero-order wavefunctions.
Thermal Conductivity of a Gas of Rotating Diamagnetic Molecules in an Applied Magnetic Field
Authors: McCourt F. R. , Snider R. F.
Published: January 2005

The effect of an applied magnetic field on the thermal conductivity of a gas of rotating diamagnetic molecules is determined with the rotational states treated quantum mechanically. The anisotropic part of the thermal conductivity tensor λ is given in terms of square-bracket integrals and the ratio of the magnetic field H to the equilibrium pressure p of the gas. The square-bracket integrals to be determined are expressed in terms of reduced relative and center-of-mass velocities. The ratio of the saturation values of the anisotropic thermal conductivity when the applied field is parallel to and perpendicular to the temperature gradient is found to be ⅔. Also, a transverse heat flux or Righi—Leduc effect for gases is discussed briefly, and shown to vanish at infinite and zero fields, attaining a maximum somewhere between.
General Expression for the Interchange Theorem of Double Perturbation Theory
Authors: Tuan Debbie Fu-Tai
Published: January 2005

The general expression for the interchange theorem in double perturbation theory is derived from the perturbation expansion. It gives a compact relation between two different formulations of the double perturbation energy ε(n,m). This relation will allow the exchange of integrals involving higher-order perturbed wavefunctions related to a complicated perturbation, by integrals involving higher-order perturbed wavefunctions related to the simpler perturbation. They can be applied, without qualifications, to the nondegenerate unperturbed state in any double perturbation problem. For cases where the unperturbed Hamiltonian and the more complicated perturbation are Hermitian, two more useful expressions of the interchange theorem are also obtained. These latter relations permit one to obtain the perturbation energy to (2n+1)th order with respect to the complicated perturbation from the knowledge of the wavefunction perturbed through the nth order. All the expressions of the interchange theorem we have obtained are valid to all orders with respect to both perturbations. They include Dalgarno's interchange theorem as the special lower-order cases.
Dissociation Energy of TiO(g) and the High-Temperature Vaporization and Thermodynamics of the Titanium Oxides. II. Trititanium Pentoxide
Authors: Wahlbeck Phillip G. , Gilles Paul W.
Published: January 2005

Vapor-pressure and mass-spectrometric measurements on Ti3O5(s) contained in tungsten crucibles show that for the congruent vaporization, Ti3O5(s)=3 TiO(g)+2 O(g),logK=−(1.504±0.011)×(105/T)+39.99±0.59.The vapor-pressure measurements were obtained in the temperature range 1837°—2040°K and are used with auxiliary values to obtain ΔH298° = 713.85±5.25 from the second-law treatment, ΔH298° = 717.42±3.10 kcal/mole from the third-law treatment, ΔS298° = 212.16±2.71 (second-law), and ΔS298° = 213.98 eu (third-law). Derived values based on the third-law result and on numerous auxiliary values are: D0∘(TiO)=167.38±2.30 kcal/mole,7.26±0.10 eV,D0∘(TiO2)≦292.06 kcal/mole,12.67 eV.Earlier work and discrepancies are discussed, and suggestions are made for future efforts.
Vibrational Properties of Excitons in Molecular Crystals
Authors: Takeno Shozo
Published: January 2005

A general theory is developed for the interaction of exctions with molecular vibrations in pure and impure molecular crystals. A study is made of a model Hamiltonian which describes the interaction of Frenkel excitons with harmonic oscillators, with particular attention paid to the case in which exciton bandwidth is fairly narrow. Equations of motion for molecular excitons are obtained in the form of Dyson equations using the method of double-time Green's function. By solving the Dyson equations, it is shown that the vibrational energies of excitons in pure and impure molecular crystals, which can be classified into zero-phonon and one-phonon energies, are very different for different combinations of the energies of molecular vibrations and the exciton bandwidth. For example, a series of vibronic exciton bands is obtained for a pure crystal when the energies of phonons are larger than the exciton bandwidth while for an impure crystal, under certain circumstances, molecular vibrations can induce a delocalization of exciton impurity states in the opposite case. A study is then made of the role of phonons in the exciton energy transfer in a pure molecular crystal. It is shown that the effect of exciton—phonon interactions is to reduce the exciton bandwidth from free exciton value while there can exist a phonon-assisted energy transfer with emission or absorption of a single phonon, which has a long-range oscillatory interaction form similar to the Ruderman—Kittel interaction. A brief discussion is also given of the transfer of energy associated with an exciton impurity state to host molecules.
Spectrum of Nd3+ in Lanthanide Oxide Crystals
Authors: Henderson J. R. , Muramoto M. , Gruber John B.
Published: January 2005

The ultraviolet, visible, and near-infrared spectra of single-crystal Nd2O3 and La2O3:Nd3+ observed at 10°, 80°, and 290°K, were analyzed. Over 300 absorption lines were assigned from the five crystalline Stark levels of the ground I9/24 state to over 20 excited J manifolds in each crystal. In thick crystals, transitions to many excited levels from the higher Stark levels of the I9/24 state were observed. The spectral assignments are compared with calculations of ``free-ion'' energy levels and with the assignments of Y2O3:Nd3+. The parameters E1, E2, E3, and ξ are calculated for the three oxide crystals, and comparisons between observed and calculated energy levels are made. The significance of these parameters in comparison with those for Nd3+ in other crystals is discussed, and the effects of configuration interaction are pointed out.
Infrared Spectra of Charge-Transfer Complexes. VII. The Solid Benzene—Bromine Complex
Authors: Person Willis B. , Cook Courtney F. , Friedrich H. Bruce
Published: January 2005

The infrared spectrum of the solid benzene—Br2 complex has been measured to give the changes in frequency and an estimate of the changes in intensity from the pure benzene and pure Br2 crystals. The complex was usually prepared by condensing a 1:1 mixture of benzene and bromine vapor onto a cold plate, but other techniques were also tried, and partial studies are reported. These spectra show definitely that neither the benzene nor bromine molecules in our samples are located on a site possessing a center of symmetry. From the analysis of the spectrum of the complexed benzene, a site symmetry of C3v is deduced. This apparent contradiction of the results of the x-ray studies of Strømme and Hassel is discussed and reconciled. The frequency shifts and intensity changes on complex formation are discussed in some detail.
Electronic Spectrum of Single Crystals of Ferricytochrome-c
Authors: Eaton William A. , Hochstrasser Robin M.
Published: January 2005

The absorption spectrum of crystalline horse-heart ferricytochrome-c was investigated. Measurements were made on single crystals at room temperature from 3700 to 7600 Å using a microspectrophotometer. Molar extinction coefficients for light parallel and perpendicular to the fourfold c crystallographic axis are given.

The Soret band (4100 Å) and main visible band (5300 Å) were found to have the same polarization, while the weaker band at 5650 Å is polarized differently. These transitions are discussed in terms of the molecular orbital theory for simple metalloporphyrin complexes. Assuming the Soret and main visible bands correspond to transitions to an Eu state, the angle that the normal to the porphyrin plane makes with the c axis is calculated from the polarization ratios to be 72°. Using this angle the isotropic extinction coefficients calculated from the crystal data agree well with the extinction coefficients for these bands in solution.

The weak band at 6950 Å is polarized out of the porphyrin plane and is tentatively ascribed to the promotion of an electron from the porphyrin a2u(π) orbital to the iron a1g(dz2) orbital. The intensity of this band has been shown to be dependent on the conformation of the polypeptide. The proposed mechanism for this transition indicates two different ligand-heme configurations in ferricytochrome-c which are consequent upon the two ``conformational isomers'' postulated by Schejter and George.

It is concluded that hemoproteins provide a near perfect example of an oriented gas of chromophores.
Low-Energy Electron-Diffraction Study of the Clean (100), (111), and (110) Faces of Platinum
Authors: Lyon H. B. , Somorjai G. A.
Published: January 2005

The structures of the (111), (100), and (110) crystal faces of platinum were studied as a function of temperature in the range 300°—1769°C (melting point). The (111) and (100) substrates are stable while the (110) face shows faceting above 600°C. Several surface structures were found to exist on the stable platinum substrates. These have well-defined temperature ranges of stability. There are two types of surface structures, ordered and disordered. Both types appear to be the property of the clean platinum substrates. The ordered structures appear during annealing, after ion bombardment at lower temperatures (<900°C). They exhibit long-range order and their stability ranges overlap on a given substrate. These structures are believed to be due to ordered arrays of vacancies in the substrate plane which, under proper conditions, show remarkable stability. A high, nonequilibrium concentration of defects at the surface may be necessary to induce their formation.

The disordered surface structures appear at high temperatures, above the stability range of most of the ordered structures. They are characterized by ringlike diffraction features which develop gradually as a function of increased heating time or temperature. The formation of these structures is irreversible and they can only be removed by ion bombardment. Near the melting point, the ring patterns remain the only diffraction features of the presumably greatly disordered surfaces.

The ratio of lattice parameters assigned to the diffraction rings on each substrate indicate that they can be due to domains of (111) surface structures. These hexagonal structures appear on all of the platinum surfaces, are freely rotated in the substrate plane, and show an ∼11% contraction with respect to the inter-planar spacing in the ordered (111) face. The disordered close-packed-hexagonal structure seems to be the stable high-temperature surface phase of platinum.
New Model for Classical Fluids. II
Authors: Wertheim M. S.
Published: January 2005

A model for classical fluids given previously has been extended in two ways. An approximate Helmholtz free energy is obtained by using the equation of state of hard spheres to continue a virial series truncated after N+1 terms into the whole density—temperature plane. The model given earlier corresponded to N=1. A modified version of the model is given, which contains an additional function of the excess entropy. It is shown that the two versions of the model constitute truncation after one and two terms of an expansion of the thermodynamic function which transforms from the model free energy to the exact free energy. The expansion is made around the line of zero excess pressure, suggesting that the modified model is appropriate for liquids. It is formulated entirely in terms of experimentally accessible thermodynamic quantities. Comparison with experimental data for argon favors the modified version.