bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of High Pressure on the Lattice Parameters of Diamond, Graphite, and Hexagonal Boron Nitride
Authors: Lynch R. W. , Drickamer H. G.
Published: January 2005

The effect of pressure to several hundred kilobars has been measured on the lattice parameters of diamond, graphite, and hexagonal boron nitride. The linear compressibility of diamond is independent of pressure. The a axis of graphite (characteristic distance in the plane) is considerably more compressible than diamond at low pressure but above about 160 kbar is much less compressible than diamond. The c axis of graphite is much more compressible than the a axis. Assuming van der Waals forces between the graphite planes and using the lattice sums of Girifalco and Lad, it is possible to describe the compressibility of graphite to very high pressure from low-pressure data. Hexagonal BN is much like graphite, with both a and c axes somewhat more compressible than the corresponding parameters of graphite.
Electron Paramagnetic Resonance of Divalent Manganese in Ammonium Chloride
Authors: Forman A. , van Wyk J. A.
Published: January 2005

The electron paramagnetic resonance of divalent manganese in NH4Cl has been studied at X-band frequencies. Several unexpected features of the spectrum are observed because the microwave quantum used is very close to the smaller of the two electronic zero-field splittings. The entire spectrum can be explained by assuming there is a vacancy in the nearest-neighbor NH4+ position to each manganese ion.
Photoionization of Propylene at 1236 Å. Reactions of C3D6+ with Added Alkanes
Authors: Gorden R. , Doepker R. , Ausloos P.
Published: January 2005

C3H6–C3D6–O2 mixtures have been irradiated at 1236 Å (10 eV) in the presence and absence of an applied electrical field with the purpose of obtaining information about the ion—molecule reaction mechanism. On the basis of a number of observations, it was concluded that the product, propane, can be ascribed to the reaction C3mH6m++C3H6→C3mH6m−2++C3H8 (m≥2). When alkanes (RH2) whose ionization energy is larger than 10 eV are added to C3D6—O2 mixtures, the following H2−-transfer reaction occurs: C3D6++RH2→CD3CDHCD2H+R+ . Relative rates of the reaction of C3D6+ with various alkanes have been determined and compare favorably with values obtained in a recent radiolytic study in which cyclopentane-d10 was used as a source of C3D6+ ions.

The optimum experimental conditions, under which meaningful saturation ion currents can be obtained in the photoionization apparatus, are discribed. On the basis of measurements of the saturation ion current in NO and propylene at 1236 Å, values of 0.197 and 0.208 were obtained for the photoionization efficiencies of C3H6 and C3D6, respectively. The latter measurements made it possible to express the products in the number of molecules formed per ion pair as well as in the number of molecules formed per quantum absorbed.
Rate of Interconversion of Electronic and Vibrational Energy
Authors: Lin Sheng Hsien
Published: January 2005

Radiationless transitions are treated from the viewpoint of the nonstationary character of the Born—Oppenheimer approximation. It is shown that the theory explains the fast rates of internal conversion and highly variable rates of intersystem crossing, accounts for the temperature dependence and selection rules of radiationless transitions, and explains the deuterium effect and external heavy-atom effect on the radiationless transitions.
Quantitative Observation of Slow and Fast Exchange in EPR Spectra of Organic Free Radicals
Authors: Miller Terry A. , Adams Ralph N. , Richards Peter M.
Published: January 2005

We have measured effects of electron exchange on the EPR spectrum of the organic free radicals DTBN and DNB/DNB·− in both the low-concentration and high-concentration regions. At low concentrations exchange broadens the individual hyperfine lines while at high concentrations exchange narrows the single, merged line. Existing theories are used to calculate the rate constant from both the low-concentration and high-concentration data, and consistent results are obtained. Such quantitative agreement has not been previously reported, to our knowledge. In the region of very high concentration, however, intermolecular dipole—dipole interactions contribute to the line breadth making it more difficult to determine the rate constant.
On Brownian Motion in a Fermi Fluid
Authors: Davis H. Ted , Dagonnier R.
Published: January 2005

Using the quantum-mechanical Boltzmann equation we study the motion of a heavy ion (mass M) moving through a Fermi fluid of light particles [mass m, γ=(m/M)½≪1] under the influence of an electric field. We find, contrary to the classical case, that the condition γ≪1 is not sufficient to ensure that the ion undergoes Brownian motion (i.e., its motion is characterized by a Fokker—Planck equation). The condition γξ≪1 must hold, where ξ2 is the ratio of the Fermi energy to the temperature. When ξ is too large the ion will suffer large momentum changes upon colliding with the fermions and hence its motion will not be describable by a Fokker—Planck equation.

In liquid 3He there is a temperature region (4°>T>1°K) in which a heavy ion experiences what we call quantum-mechanical Brownian motion; the Fokker—Planck equation still holds but the friction coefficient contains quantum-mechanical effects. Using our formula for mobility and the mobility data of Meyer we estimate the effective mass of an ion in liquid 3He to be about 20 times the mass of an 3He atom. This is in agreement with the recent measurements of Dahm and Sanders in liquid 4He. They have found the effective mass to be between 20 to 40 4He atoms. However, since only binary scattering events are accounted for in our mobility formula, its application to liquid 3He should be taken with reservation.
Thermal Energy Ion—Neutral Reaction Rates. I. Some Reactions of Helium Ions
Authors: Fehsenfeld F. C. , Schmeltekopf A. L. , Goldan P. D. , Schiff H. I. , Ferguson E. E.
Published: January 2005

A flowing, steady-state afterglow system has been utilized to measure room-temperature ion—neutral reaction rates. A description of the apparatus and technique is given. Measured rate constants for He+ reactions with O2, N2, CO, NO, and CO2 are reported, as well as upper limits for the reactions of He+ with H2, Ne, and Ar, and an estimate for the reaction of He2+ with Ne and N2.

The reactions of He+ with O2, N2, CO, NO, and CO2 are all rapid, the rate constants all being ≈10−9 cm3 sec−1, implying essentially a reaction per collision.
Lattice Parameters of Nine Oxides and Sulfides as a Function of Pressure
Authors: Clendenen R. L. , Drickamer H. G.
Published: January 2005

The lattice parameters of seven oxides and two sulfides have been measured as a function of pressure to several hundred kilobars. FeO, CoO, NiO, MnO, and MnS have the NaCl structure or slight distortions thereof. The data can be fit by a Born—Mayer equation. For FeO, CoO, and NiO the crystal-field stabilization term contributes 5% to 15% of the total attractive pressure. FeS2 (pyrites) has a cubic structure which can be related to the fcc lattice. Its compressibility is much less than MnS and more comparable to the oxides. The binding is appraently covalent.

SnO2, MnO2, and TiO2 all have the same tetragonal structure. For SnO2 and MnO2 the c axis actually expands with increasing pressure at low pressure, then passes through a maximum and ultimately contracts. The compressibilities of these two compounds are low at low pressure and increase at pressures beyond the maximum in c. TiO2 behaves more normally. It is apparent that central forces, and therefore ionic binding, contribute little to the cohesion of these crystals.
Metastable Peaks in the Mass Spectra of N2O and NO2
Authors: Newton Amos S. , Sciamanna A. F.
Published: January 2005

Metastable states in N2O+ and NO2+ have been observed, the product ion of the metastable dissociation being NO+ in each case. In N2O+ (m), with a half-life of ≤0.2×10−6 sec, the total kinetic energy given to the fragments NO+ and N was found to be 1.05±0.05 eV. In NO2+ (m) two processes are found, one of half-life 0.7±0.1×10−6 sec which leads to a total kinetic-energy release of 1.12±0.10 eV, and a second of half-life 2.5±0.5×10−6 sec which leads to a total kinetic-energy release of 0.51±0.10 eV. The effect of pressure on peak height shows the metastable peak from N2O+ to possess a unimolecular component, which, under proper conditions of operation, can be made to predominate over a normally intense collision-induced dissociation peak. The metastable peaks from NO2+ both arise from unimolecular dissociation processes.
ESR Linewidths in Solution. IV. Experimental Studies of Anisotropic and Spin—Rotational Effects in Copper Complexes
Authors: Wilson Raymond , Kivelson Daniel
Published: January 2005

The linewidths of copper acetylacetonate in toluene and in chloroform have been measured as a function of temperature (T), viscosity (η), and magnetic field. The contributions arising from motional modulation of the anisotropic dipolar and g tensors have been calculated in terms of independently determined magnetic parameters and a single adjustable parameter, the hydrodynamic radius r (r=3.857 Å in chloroform and 3.357 Å in toluene). The remaining or residual linewidth is independent of nuclear quantum number M and only slightly dependent on the applied magnetic field; it is linear in T/η. A theory of spin relaxation through spin—rotational interaction has been discussed in Article II of this series; the predicted linewidth arising from this spin—rotational interaction accounts very well for the residual linewidth in terms of the single adjustable parameter r already determined. The spin—rotational linewidth is proportional to Σ(gi−2.0023)2, which, in turn, is proportional to the spin—orbit coupling constant squared; the comparison of the residual linewidths of vanadyl and copper acetylacetonate indicate that this dependence is in fact satisfied by the residual linewidths.
Proton Resonance Shift of Water in the Gas and Liquid States
Authors: Hindman J. C.
Published: January 2005

Temperature-dependence measurements have been made on the chemical shift of the proton of a water molecule in the liquid state and in the gas state at varying pressure. The problem of relating these experimental data to the intermolecular forces leading to cohesion and to hydrogen-bond formation between water molecules is considered in detail. It is shown that a consistent treatment of the chemical shift, thermal, and dielectric data for water can be given based on a two-state model involving an equilibrium between a hydrogen-bonded ``icelike'' fraction and a ``monomer'' fraction whose interaction with the lattice arises entirely from London dispersion forces.

Using semiempirically derived values of the chemical shift and energy associated with the condensation of water vapor to ``monomer,'' the magnitude of the shift associated with the transformation to ice is calculated. It is then shown that, on the assumption that the hydrogen bond is electrostatic in character, the ``polar'' contribution to this shift can be related through the appropriate shielding equations to the dipole moment of the water molecule in ice. The magnitude of the dipole moment derived from these relationships is found to be in excellent agreement with values derived from dielectric data.

The possibility that the shielding changes may in part be due to processes other than the breaking of hydrogen bonds is considered. It is shown that the model leads to the conclusion that the chemical shift in the transformation of ice to water at 0°C could be entirely accounted for either by a stretching of the hydrogen bonds or a small amount of bending of the bonds. It is noted that if some bond breaking does occur, as required by the fact that water is a liquid, then the amount of stretching and/or bending will be limited.
13C Hyperfine Splittings in the Electron Spin Resonance Spectra of HCO and FCO
Authors: Cochran Edward L. , Adrian Frank J. , Bowers Vernon A.
Published: January 2005

The radicals H13CO and F13CO have been prepared in an argon matrix at 4°K by the addition of an H atom and an F atom, respectively, to CO enriched to 52% in 13C. The electron spin resonance spectra of these radicals contain large 13C hyperfine splittings in addition to the previously observed proton and fluorine hyperfine splittings. In HCO the principal components of the 13C hyperfine splitting tensor are: Ax(C)/h=365.7, Ay(C)/h=427.9, and Az(C)/h=338.9 Mc/sec. These results give an approximate value of 125 deg for the HCO bond angle and a value of 0.45 for the unpaired electron density on the carbon atom. The isotropic part of the 13C hyperfine splitting in FCO (some unusual complications made it impossible to determine the anisotropic terms) is A(C)/h=802.5 Mc/sec, where A(C) has the same sign as the fluorine hyperfine splitting constant. This result indicates that FCO is more sharply bent than HCO, the bond angle having an approximate value of 110 deg.
Improvement of Uncoupled Hartree—Fock Expectation Values for Physical Properties
Authors: Tuan Debbie Fu-Tai , Epstein Saul T. , Hirschfelder Joseph O.
Published: January 2005

It is shown that if one uses the uncoupled Hartree—Fock method as a zero-order approximation for calculating atomic and molecular second-order properties (either static or dynamic), then the first-order corrections to this approximation are determined solely by quantities already available from the zero-order calculations. No new equations need be solved.
Vibrational Relaxation of Diatomic Molecules
Authors: Benson Sidney W. , Berend George C.
Published: January 2005

A one-dimensional model is explored and rigorous solutions are obtained to the classical equations of motion yielding transition probabilities between low-lying vibrational levels of diatomic molecules. Results are listed for four halogens, O2, N2, and CO colliding in pure gases and O2 with Ar or He as a collision partner. Selecting a single variable ``a'' (the range term of the Morse potential function), excellent agreement was found with the available experimental data over a 30-fold temperature range. The validity of the Landau—Teller theory is discussed; in particular, the effect of the consideration of an attractive potential and the simplification involved in its explicit treatment. Transitions involving double quantum jumps are considered. Some preliminary results of a two-dimensional model are discussed.
Vibrational Relaxation of Hydrogen
Authors: Kiefer John H. , Lutz Robert W.
Published: January 2005

The laser schlieren technique has been applied to a shock-tube study of hydrogen vibrational relaxation. Mixtures of 30%, 50%, and 70% normal hydrogen in argon have been investigated in the range 1100°—2700°K. The results yield an expression for relaxation in pure hydrogen, PτH2–H2 = (3.9±0.8) × 10−10 exp[(100.0±2.6) / T⅓] atm·sec (1100°—2700°K), and allow an approximate determination of the relaxation time for hydrogen dilute in argon, PτH2–Ar = 4.1 PτH2–H2 (1500°—2700°K).

These results are in adequate agreement with previous data and the theoretical calculations of Salkoff and Bauer. However, they are in serious disagreement with both the correlation of Millikan and White and the SSH theory.
Intermolecular Potentials and the Infrared Spectrum of the Molecular Complex (H2)2
Authors: Gordon R. G. , Cashion J. K.
Published: January 2005

The infrared absorption spectrum of the molecular-hydrogen complex H4 has been calculated. The model assumed is that of two spherically symmetric, freely rotating hydrogen molecules bound by a weak inter-molecular potential. Two types of induced-dipole transitions are considered; the first arises from electronic overlap and is directed mainly along the intermolecular axis, while the second results from a dipole induced in one molecule by the electric-quadrupole moment of the other. Calculations are made for three different intermolecular potentials. For all three the results are in excellent agreement with the hydrogen spectrum observed by Watanabe and Welsh. The dependence of particular spectral features on the shape of the potential is discussed, and also the feasibility of discriminating between various potential models experimentally by improving the spectral resolution. A calculation of the bound levels of (HD)2 and (D2)2 complexes indicates that at least the sharpest features of their absorption spectra should be observable under the resolution already achieved by Watanabe and Welsh.
Theoretical Investigations of Reactive Collisions in Molecular Beams: K+CH3I and Related Systems
Authors: Raff L. M. , Karplus M.
Published: January 2005

A three-dimensional, quasiclassical analysis of the K+CH3I reaction and related reactions is performed. Hamilton's equations of motion are solved to obtain collision trajectories from which the reaction attributes are determined by Monte Carlo averaging over appropriately selected sets of initial conditions. Four different functional forms for the potential energy of interaction of the reacting species are examined. Comparisons are made of the total reaction cross section, the rotational and vibrational state distribution of the product molecule, the reaction energy distribution, the differential reaction cross section in both center-of-mass and laboratory coordinates, the distribution of the final angular momentum between the molecule and the relative orbital motion, the degree of polarization of the final rotational angular momentum of the molecule, the behavior in the transition region, and the effect of mass changes on the reaction. Although most of the calculated results are not subject to direct experimental verification at present, the theoretical laboratory cross section can be compared with measured values. It is found that three of the surfaces studied yield a laboratory differential cross section for K+CH3I in reasonable correspondence with the available experimental measurements, which are insufficient as yet to permit any distinction between these surfaces. Analysis of the behavior in the transition region shows that the reaction on these surfaces proceeds through a simple collision mechanism in which the three particles interact for only a very short time. The very different results obtained from a special surface in which a collision complex is formed are given for comparison.
Infrared Lattice-Vibration Spectra in NiF2, CoF2, and FeF2
Authors: Balkanski M. , Moch P. , Parisot G.
Published: January 2005

The optically active vibration modes of iron group divalent fluorides have been investigated by reflection measurements on single crystals and by optical-transmission studies on sintered powders containing fluorides diluted in polyethylene. The obtained spectra are compared with the theoretical predictions for optical absorption due to photon—phonon interaction. For some spectra Kramers—Krönig inversion was performed, allowing more precise measurements of the optically active normal-modes frequencies and providing an evaluation of the oscillator parameters.
Detection of Long-Lived Excited States of Molecules by Penning Ionization
Authors: Čermák V.
Published: January 2005

A method for the detection of excited neutral long-lived particles by ionization of properly chosen molecules with different ionization potential was developed and applied to the study of long-lived excited states of H2, N2, CO, and O2. Results in H2 and O2 confirm previous findings. In N2 a new state was found which releases in the transition to the ground state an energy of ∼11.4–11.6 eV. Also determined was its separated excitation function. This state is formed partly through a resonance capture of an exciting electron and subsequent decomposition of the unstable negative excited molecular ion N2−*. In CO a new long-lived excited state at ∼10 eV was detected, and the existence of another, higher lying, state was suggested.
NMR Study of Electron Transfer Rates and Spin Densities in p-Xylene and p-Diethylbenzene Anions
Authors: de Boer E. , MacLean C.
Published: January 2005

Electron transfer reactions between a diamagnetic molecule and its paramagnetic anion modify the NMR spectrum in two different ways. First, the NMR lines are broadened and secondly, the lines are shifted. The line broadening may provide information on rates of electron exchange; the line shift is related to the spin density at the proton.

The magnitude and the sign of the spin densities are quantities of great interest from a quantum-chemical point of view. It is useful, therefore, to provide methods for measuring spin densities. Usually they are derived from hfs parameters in ESR psectra. In this paper it is shown how they may be detected by the NMR line shifts. A special advantage of the NMR method is that the sign of the spin density is also easily available, because it is directly related to the direction of the line shift.

Basic equations that describe both line broadening and line shifts are derived in this paper. The theory has been applied to p-xylene and p-diethylbenzene. Rates of electron transfer of p-xylene have been obtained from the broadening of the NMR lines. A combination of ESR and NMR has been used to obtain the values of the spin densities at the sites of the methyl and methylene protons; contrary to predictions in the literature, the sign is negative. An explanation for this is given on the basis of MO theory.
Motional Narrowing in One-Dimensional Triplet-Exciton Systems
Authors: Soos Zoltán G.
Published: January 2005

Motional narrowing of the hyperfine interaction for a localized, diffusional model of one-dimensional triplet excitons is shown to lead, at low temperatures, to Lorentzian lines, with half-width ωobsωobs=[ωp2/(2ωjωr)12]  (ωj≫ωp,ωr>ωobs).ωp is the half-width of the Gaussian envelope of the hyperfine pattern of an exciton in the absence of motion, ωi is the exciton jumping rate along the chain, and ωr represents all other, slower randomizing processes. The Lorentzian line shape is in agreement with experiment, and the jumping rate ωj agrees with previous calculations. These results give further evidence that a localized, diffusional description of triplet excitons is appropriate at low temperatures.
Glow-Discharge Shock Tube for Studying Chemiluminescent, Surface-Catalytic, and Gas-Phase Reaction Rates; Temperature Dependence of NO–O and CO–O Chemiluminescence
Authors: Hartunian R. A. , Thompson W. P. , Hewitt E. W.
Published: January 2005

The ordinary glow-discharge tube has been used extensively to study both surface and gas-phase recombination rates, as well as chemiluminescent reactions, typically at room temperature. The combination of a glow-discharge flow tube with a shock-tube driver to provide a considerable extension of atom fluxes, temperatures, and densities for the study of these kinetic processes is described. In operation, the ordinary glow-discharge-tube situation appropriate to the particular process under study is first established and, then, a shock is propagated into the predissociated gas by a driver upstream of the rf region. Typically, the shock strength is less than that which causes further dissociation. Under these conditions, the effect of the shock is to compress, heat, and accelerate to high speed those species already in the glow tube. The high temperature and compression provide a means for studying the temperature dependence of gas-phase recombination processes and chemiluminescent reactions, while the high-speed flow, in increasing the atom flux, provides a means for studying surface-catalysis phenomena occurring on a short time scale (<1 msec). Application of the present technique to determine the temperature dependences of the NO–O and CO–O chemiluminescent reactions is described in considerable detail.
Carbon Dioxide as an Electron Trap in 3-Methylpentane at 77°K
Authors: Johnson Philip M. , Albrecht A. C.
Published: January 2005

The narrow paramagnetic resonance in a photolyzed 3-methylpentane system at 77°K, previously assigned tentatively to the ``solvated'' electron, is characterized and assigned to the carbon dioxide radical anion. The ionization potential of CO2− is bracketed between 2.3 and 2.9 eV. A hyperfine splitting of 122 G is obtained for the species 13CO2−, and a value of −0.32 is calculated for the coefficient of the 2s atomic orbital in the 4a1 (C2v) molecular orbital of CO2−.
Electron Attachment and Detachment. I. Pure O2 at Low Energy
Authors: Pack J. L. , Phelps A. V.
Published: January 2005

Electron attachment and detachment coefficients are reported for pure oxygen from analyses of the current waveforms observed in drift-tube experiments. The results are consistent with the identification of the negative ion as O2− with an electron affinity of 0.43±0.02 eV. The two-body collisional detachment coefficient for O2− in thermal equilibrium with the gas increases from 9×10−17 cm3/sec at 375°K to 1.4×10−14 cm3/sec at 575°K. The three-body attachment coefficient for thermal electrons increases from 2.0±0.2×10−30 cm6/sec at 300°K to 2.8±0.5×10−30 cm6/sec at 530°K. The O2− ions are found to survive at least 3×108 elastic collisions without de-excitation and so are believed to be in their lowest vibrational state. At low oxygen densities the current of detached electrons is separated from the negative-ion current by applying a high-frequency voltage to the control grid. At high oxygen densities the electrons and negative ions cross the tube in a narrow pulse at a drift velocity determined by the equilibrium concentrations of electrons and ions.
Dioxygen Monofluoride: Infrared Spectrum, Vibrational Potential Function, and Bonding
Authors: Spratley Richard D. , Turner J. J. , Pimentel George C.
Published: January 2005

Photolysis of F2 and O2 suspended in solid N2, Ar, or O2 produces infrared absorptions of an oxyfluoride other than OF2 and O2F2. Isotopic labeling, concentration dependence, diffusion behavior, and normal coordinate analysis permit assignment of these bands, at 1499.7, 586.4, and 376.0 cm−1, to O2F. On diffusion at low temperatures, this molecule forms only loosely bound aggregates, (O2F)n, though it is a free radical. Normal coordinate analysis shows that the O–O bond of O2F is a double bond, like those in O2 and in O2F2 and that the OF bond is much weaker than those in OF2. Thus, O2F resembles O2F2 in its bonding.
Some Aspects of the Photochemistry of Benzene
Authors: Noyes W. Albert , Mulac W. A. , Harter D. A.
Published: January 2005

Three methods of measuring absolute gas-phase-emission yields from benzene are described. Two of the three proved to have large possible errors due to scattered light. One was used to give a value of Q2537=0.18 at a pressure of 10 torr at 25°C. This is in agreement with one value in the literature and slightly lower than the other although all three agree within the limits of error prescribed by the various authors. There is no significant variation with pressure but there is a marked wavelength effect. Below 2500 Å the emission decreases rapidly and it is essentially zero at 2400 Å and below in agreement with the findings of Poole. Variation at wavelengths longer than 2537 Å may exist but seems to be small. By implication the emission yield of biacetyl vapor as determined by Almy and Gillette is probably accurate within the errors specified by those authors. By use of these data it is shown that there is now excellent agreement on the extent of cross-over of excited-singlet benzene molecules to the triplet state by at least two methods. Some process competes with emission and crossover from the singlet state and the extent of this process increases with frequency. Benzene and oxygen react photochemically with a small yield to give an unstable peroxide.
Molecular Ions in Radiation Chemistry. I. Formation of Aromatic-Amine Cations in CCl4 by Resonance Charge Transfer at 77°K
Authors: Shida Tadamasa , Hamill William H.
Published: January 2005

Gamma-irradiated polycrystalline CCl4 at 77°K provides evidence that positive charge migrates and is trapped by the matrix itself. The trapped positive hole absorbs at about λmax=400 mμ in pure CCl4 or dilute solid solutions of aromatic amines. The solvent band is depressed by aromatic amines or other additives which act as hole traps with appearance of the corresponding amine cation absorption. After γ irradiation the residual 400-mμ band photobleaches at 77°K with increase in solute cation absorption. Brief heating to 143°K gives the same result. A kinetic treatment which assumes that the only labile species in the system is migrating positive charge can explain the experimental results in a satisfactory way. The kinetic analysis gives a rough estimate of total available positive charge created per 100 eV of absorbed energy as 1.9. Several aromatic amines have been used as test substances and their optical absorption spectra recorded.
High-Temperature Equation of State
Authors: McQuarrie D. A. , Katz J. L.
Published: January 2005

An equation of state is obtained in closed form for a gas composed of molecules with a Lennard-Jones (n, 6) potential. It is derived by expanding the partition function in powers of n−1 and expanding the attractive part of the potential in powers of T−1. The resulting equation is of the form P/ρkT=A+B/T+ClogT where A, B, and C can be simply expressed in terms of known hard-sphere quantities such as the compressibility factor and the radial distribution function as functions of density. The equation contains no adjustable parameters and reliably reproduces PVT data up to densities of 40 mole/liter and reduced temperatures as low as 3.
Isotope Effects on Franck—Condon Factors. V. Electronic Transitions of Isotopic O2, N2, C2, and H2 Molecules
Authors: Halmann M. , Laulicht I.
Published: January 2005

Arrays of Franck—Condon factors for vibrational quantum numbers up to v′ and v″=14 were computed using Morse potentials, for the Schumann—Runge bands of 16O2, 16O18O, and 18O2, for the first positive and the Vegard—Kaplan band systems of 14N2 and 14N15N, for the Swan bands of 12C2 and 12C13C, and for the Lyman bands of H2 and D2. The isotope effects on vibrational transition probabilities are large at the minima between the loci of the Franck—Condon parabolas and smallest at the loci of the maxima.
Mass-Spectrometric Studies of Reactions in Flames. II. Quantitative Sampling of Free Radicals from One-Atmosphere Flames
Authors: Milne Thomas A. , Greene Frank T.
Published: January 2005

Direct mass spectrometric sampling studies of one-atmosphere flames are described. A simple model of the sampling process is summarized which accounts for the effects and results obtained. Stable product analysis and evidence for appreciable temperature dependence of fragmentation patterns are shown. Quantitative sampling of the free radicals H, O, OH, and Cl from the burnt gas region of one-atmosphere flames is demonstrated, with direct observation of excess free-radical concentrations in the reaction zones of these flames.
Oxygen and Nitric Oxide Quenching of Positronium in Liquids
Authors: Lee John , Celitans G. J.
Published: January 2005

The value of the long lifetime for positron annihilation in a number of organic liquids is markedly reduced by the presence of dissolved oxygen or nitric oxide. If the change in long lifetime is interpreted as a quenching reaction of triplet positronium formed in these liquids, the reaction with oxygen or nitric oxide is found to obey bimolecular kinetics with quenching rate constants in the range 1010−1011M−1sec−1, about twice those for oxygen quenching of molecular excited states in these same liquids. These reactions also exhibit the usual features of diffusion controlled reactions having inverse viscosity dependence and low activation energy. The interpretation of these and other properties of positronium in liquids is made by postulating solvent-cage trapping of the triplet positronium. These considerations severely limit the amount of information which may be obtained by study of these reactions in liquids.
On Polymer Dynamics
Authors: Harris R. A. , Hearst J. E.
Published: January 2005

The properties of a polymer solution in which the polymer dynamics contain both bending and spring forces are determined in the free-draining limit. All properties may be determined in closed form in terms of a few fundamental parameters by use of a correlation-function technique.
Studies of Hydroxyl Radical Kinetics by Quantitative ESR
Authors: Dixon-Lewis G. , Wilson W. E. , Westenberg A. A.
Published: January 2005

Reactions of the OH radical with OH, H2, and CO have been studied at room temperature in a fast flow system at pressures of the order of 1 mm. The very fast reaction between H atoms and NO2 was used as the source of OH. Electron spin resonance techniques were employed to examine the decay of OH concentration along the flow tube, using NO gas as the calibration standard. Rate constants at 300°K were found to be, in cubic centimeters per mole·second units OH+OH=O+H2O,k2=1.55±0.12×1012,OH+H2=H2O+H,k4=3.9±0.2×109,OH+CO=CO2+H,k5=1.15±0.05×1011.

Combination of the last two of these with published results at higher temperatures leads to k4=3.9±0.2×109exp{[(5200±300)/R][(1/300)−(1/T)]},k5=1.15±0.05×1011exp{[(600±300)/R][(1/300)−(1/T)]},or in simple Arrhenius form k4=2.3×1013exp(−5200/RT),k5=3.1×1011exp(−600/RT).
Lower Electronic Levels of the Radicals SiH, SiH2, and SiH3
Authors: Jordan Peter C.
Published: January 2005

This paper describes a semiempirical quantitative theory of the low-lying electronic states of SiH, SiH2, and SiH3. The method used is that developed by Jordan to treat phosphorus hydrides. Best agreement with available experimental data is obtained when the valence state has a small percentage of d character and the d orbital is somewhat contracted by polarization. The ground state of SiH2 is predicted to be 1A1 with a bond angle of 95°. The three lowest-lying excited states of SiH2, 3B1, 1B1, and 1A1 are also bent. SiH3 is predicted to be planar.
Determination of Hydration Numbers of Cations in Aqueous Solution by Means of Proton NMR
Authors: Swift T. J. , Sayre W. G.
Published: January 2005

A technique was developed for the determination of the primary hydration numbers of cations in aqueous solution. The method was devised to be applied in particular to the study of those ions for which the average lifetime of water molecules in the primary hydration sphere is less than ∼10−4 sec.

The new technique is based on the kinetics of exchange of water molecules with hydrated manganous ions in solution and makes use of the relationship between this exchange and the proton nuclear magnetic resonance relaxation time T2 for such solutions. This relaxation time was found to be dependent on the nature and concentrations of added diamagnetic salts in a manner which could be related to the primary hydration numbers of the added cations.

An empirical relationship was derived and tested as a function of concentration, temperature, anion and for cations of known primary hydration number, and the relationship was found to be satisfactory in all cases. The precision of the technique is estimated to be ±0.2 of a hydration unit.

The empirical relationship was derived and tested with the ions Al3+, Be2+, H+, and NH4+. Ions to which the technique was subsequently applied included Mg2+, Ca2+, Sr2+, Ba2+, Zn2+, Cd2+, Hg2+, and Pb2+. The rather low numbers found for these ions are interpreted as a reflection of the role of the solvent structure of water in the determination of the structures of hydrated ions.
Studies in Configuration Interaction. I. Matrix Elements between Spin-Coupled Functions
Authors: Cooper I. L. , McWeeny R.
Published: January 2005

Rules are presented for the derivation of matrix elements of all one- and two-body operators between arbitrary spin-coupled functions arising from arbitrary orbital configurations. The coupling scheme used is essentially that employed in valence bond theory, but the results are completely general, including, for example, the matrix elements of spin-dependent operators which couple functions with different spin eigenvalues. In later papers these rules will be applied to various spin-coupling problems.
Crossed-Molecular-Beam Measurements of the Total Cross Sections of Ar–N2, Ar–Ne, Ar–He, and Ar–H2 at Thermal Energies
Authors: Landorf R. W. , Mueller C. R.
Published: January 2005

Total cross sections have been measured for the scattering of Ar beams from perpendicular intersecting beams of N2, Ne, He, and H2. The beams were at 300°K and contained Maxwellian velocity distributions. The slit system approximated ideal slits, and the scattering-center density was calculated from rate-of-flow measurements and a modification of the usual beam-intensity equations. In addition, beams of He and H2 were scattered from an intersecting beam of Ar. Beam reversal reduced the angular-resolution correction to less than 1%. The background scattering of the primary beam could be estimated without recourse to pressure-gauge readings. Comparison of the experimental results was made with the Schiff—Landau—Lifshitz formula and calculations with the partial-wave WKB approximation with an assumed Lennard-Jones (12, 6) potential. The L-J total cross sections do not agree with the experimental results for Ar–He and Ar–H2 systems. The L-J angular-resolution corrections do not bring the beam-reversal measurements in line with the measurements with Ar as the scattering gas.
Fluids with Weak Long-Range Forces
Authors: Hauge E. Hiis , Hemmer P. C.
Published: January 2005

We consider a classical system of particles interacting via a pair potential consisting of a strong short-range repulsion us(r) and a weak long-range potential of the form ul(r)=γ3 F(γr), where the range γ−1 is long compared with the range of us. The systematic expansion of the thermodynamic quantities in the ratio of the two ranges has been developed previously and is briefly reviewed. The expansion breaks down when the inverse compressibility of the fluid vanishes. Explicit calculations of the equation of state for special choices of the two parts of the intermolecular potential are presented and compared with the corresponding experimental results for argon. It is also shown that to first order in the expansion parameter the specific heat cv has a maximum near the critical isochore.
Cluster Expansion for the Ising Model
Authors: Farrell R. A. , Morita T. , Meijer P. H. E.
Published: January 2005

A binary alloy system with nearest-neighbor interaction which forms a rigid lattice is the (ideal) Ising system. The present paper is an application of the theory of classical fluids, as developed by Morita and Hiroike, to such systems. The partition function for the Ising system is made formally equivalent to that for a binary fluid as discussed by Morita. Then, using the methods of graph theory, a high-temperature expansion is obtained for fixed long-range order parameters. By performing a partial summation, one finds that the free energy is given in terms of connected diagrams which are composed of βJ bonds, and black circles Mn. The quantities Mn are evaluated by noting that the diagrammatical expressions for these quantities appear in the expansion of the grand potential of a soluble problem.

The method is illustrated in the case of an AB alloy or the ferromagnetic Ising system which form cubic lattices. Chang's result is easily obtained. The extension of this method to higher terms and its application to other alloy systems are retained for a forthcoming paper.
Time-Dependent Hellmann—Feynman Theorems for Variational Wavefunctions
Authors: Epstein Saul T.
Published: January 2005

Conditions are given under which optimal variational wavefunctions will satisfy various time-dependent Hellmann—Feynman theorems.
Computed High-Temperature Rate Constants for Hydrogen-Atom Transfers Involving Light Atoms
Authors: Mayer S. W. , Schieler L. , Johnston Harold S.
Published: January 2005

The procedure of Johnston and Parr for computing the potential energy and structure of a triatomic linear activated complex containing hydrogen as its central atom has been combined with the Eyring—Polanyi rate-constant expression to calculate rate constants at 1000° to 4000°K of gas-phase hydrogen-atom transfers for every possible reaction between the ground states of the atoms H, Li, Be, B, C, N, O, F, Na, Cl, Br, I, and any of the diatomic hydrogen compounds of these elements. The relation between activated complex theory and collision theory for reactions of this sort is examined in detail. The usual form of activated complex theory breaks down for reactions of low activation energy and high temperature, and the conditions for this failure in terms of bending vibrational amplitude are given. For these cases rate constants are evaluated by hard-sphere collision theory. Although calculated activation energy and other parameters differ from one reaction to another, these differences become unimportant at very high temperature. Almost all calculated rate constants have a value within a factor of 4 of the single value 2×1013 cc/mole·sec at 2500°K.
High-Resolution NMR Spectra of Polycyclic Hydrocarbons
Authors: Memory J. D. , Parker G. W. , Halsey James C.
Published: January 2005

The McWeeny theory has been used to calculate the shielding parameters for polycyclic hydrocarbons up through four rings. These results are presented along with experimental values, some of which come from new analyses of 100-Mc/sec NMR spectra of these compounds, and semiquantitative agreement is observed. The Jonathan—Gordon—Dailey semiempirical equation for spin—spin coupling constants is also subjected to further test by new data. Absence of inter-ring spin—spin coupling is reconfirmed.
Long-Range Scattering from Anisotropic Potentials: Dipole—Dipole Scattering
Authors: Cross R. J. , Gordon R. G.
Published: January 2005

Total cross sections were calculated for collisions of polar molecules. They were found to be determined chiefly by the rotationally inelastic collisions occurring at large impact parameters and to be highly sensitive to the amount of energy transferred from translation to rotation. The calculations were done by using either the Born approximation or a semiclassical method based on time-dependent perturbation theory to obtain the scattering matrix for large impact parameters (both methods yield the same results). Scattering at smaller impact parameters was handled using a generalized Massey—Mohr treatment. The cross sections were found to be large and strongly dependent on the rotational states. Averaged cross sections were calculated for Boltzmann distributions of rotational states. These depend, as expected, on both the rotation constants and on the rotational temperature. Cross sections for linear dipoles such as alkali halides scattered by CH3I are around 4000 Å2. Cross sections for two symmetric tops are much higher. The averaged velocity derivative is quite different from that found for atom—atom scattering. A calculation of the second-order elastic scattering was done for the case where the rotational energy levels of the two molecules are badly mismatched. Comparison is made with several other treatments which use the sudden approximation or some sort of averaged potential. The methods developed here are also applicable to scattering of polarized beams or to the calculation of small-angle inelastic scattering.
ESR Studies of the Interaction of Nitrogen and Oxygen Atoms with Polystyrene
Authors: Greyson J. , Ingalls R. B. , Keen R. T.
Published: January 2005

Freeze-dried polystyrene ``fluffs'' were found to react with gaseous oxygen or nitrogen atoms to yield free-radical products which were observed by ESR spectroscopy. Both oxygen and nitrogen atoms apparently add into the polymer at a rate significantly slower than that which has been observed for hydrogen-atom addition.
Phase Transition of a Hard-Core Lattice Gas. The Square Lattice with Nearest-Neighbor Exclusion
Authors: Ree Francis H. , Chesnut Dwayne A.
Published: January 2005

We consider an M×N periodic system of hard squares each of which prohibits the occupation of its nearest-neighbor sites by the other squares. An appropriate unitary transformation factors the matrix required in evaluating the grand canonical partition function into a direct sum of submatrices. Each submatrix belongs to a distinct irreducible representation of the dihedral group of order 2M. For an M×∞ system, only the submatrix belonging to the one-dimensional symmetric representation A1 must be considered. To investigate the possible existence of an order—disorder transition for a system infinite in both dimensions, detailed calculations are carried out with the M×∞ systems (M=2, 4, 6, ···, 18). All eigenvalues λi+ and eigenvectors of the submatrix are evaluated with eight-digit accuracy, and the various thermodynamic variables are expressed exactly in terms of the eigenvalues and eigenvectors. The result indicates that an order—disorder transition takes place continuously without any sharp break in a density (ρ)- vs-activity (z) plot, or a pressure (P)- vs-ρ plot. The transition point is characterized by the following set of numbers: zt=3.7966±0.0003, ρt/ρ0=0.73552±0.00001 (ρ0≡the close-packed density), and Pt/kT=0.7916±0.0001. Within numerical accuracy of the data, Pt/kT is equal to zt/(1+zt). The compressibility ρ−1dρ/dP appears to become infinite at the transition point, while the ratio λ1+/λ2+ of the two largest eigenvalues of the submatrix becomes unity. For a semi-infinite system in the neighborhood of zt, these two quantities exhibit, respectively, a maximum and a minimum given for large M by [(kTρ/ρ0)dρ/dP]max≃(0.0798±0.0001) lnM+(0.0910±0.0009) and [λ1+/λ2+]min≈exp[(6.25±0.04)/M]. We find that the activity z at [λ1+/λ2+]min converges rapidly to zt, thus providing a good means of locating the transition point. From the study of the eigenvalue spectrum over all densities, it appears that the transition point zt, the ordered (z>zt), and the disordered (z<zt) phases are, respectively, characterized by asymptotic degeneracy of order ∞, 2, and 0 in the modulus of the largest eigenvalue. The ordering of the hard-square lattice is investigated by introducing a radial distribution function g(l, ρ) (l is lattice spacing). The calculations of g(l, ρ) are carried out for the 4×4, 8×8, and 8×∞ systems. A long-range order parameter L(ρ) {≡liml→∞[g(l, ρ) −1], l: even} is introduced. For a two-dimensionally infinite system, all coefficients in the low-density expansion of L(ρ) vanish identically, while the first five terms of the high-density expansion of L(ρ) are computed. Therefore, the transition to an ordered state presumably takes place at density between 0 and ρ0.
Nuclear Magnetic Resonance Study of Electron-Coupled Internuclear Interactions in Thallium Chloride
Authors: Clough S. , Goldburg W. I.
Published: January 2005

Measurements are reported of the electron-coupled nuclear exchange and pseudodipolar interactions in thallium chloride single crystals. The interaction parameters are obtained by combining second-moment data for the nuclear magnetic resonance lines of the two abundant thallium isotopes with measurements of the heat capacity of the whole system of spin—spin interactions. Spin-decoupling experiments in which the 205Tl nuclear spins are decoupled first from the 203Tl spins, and then from the 203Tl and chlorine spins, help to determine the relative importance of Tl–Tl and Tl–Cl interactions. The results show that the Tl–Cl interaction is unmeasurably small, consistent with a calculation due to Yosida and Moriya. The exchange coupling constant between neighboring thallium nuclei is found to be 1.4 G. The pseudodipolar coupling has the opposite sign from that of the dipole—dipole interaction and is of approximately equal magnitude. The sign is that predicted from a simple two-electron model. From the relative magnitudes of exchange and pseudodipolar terms, we infer that the wavefunctions of the valence electrons on the thallium atoms have about 35% s character.
Vibronic Effect on the Mean-Square Amplitudes of Internuclear Distances in a Tetrahedral Molecule
Authors: Uehara Hiromichi
Published: January 2005

A quantitative relation has been derived for the mean-square amplitudes of internuclear distances in a tetrahedral XY4 molecule when vibronic interactions are present. The calculation has revealed that, first, the mean-square amplitude lY—Y increases by the presence of vibronic interactions and second, the effect is large when the frequency of the degenerate vibration ν2 is low.