bluuebunny/crossref_metadata_2025 huggingface dataset:
Dissociation of Excited Iodine Molecules
Authors: Rabinowitch E. , Wood W. C.
Published: January 2005

By means of a sensitive optical method described elsewhere, we determined the quantum yield of the process I2+hν→I+Iin mixtures of I2 vapor with several hundreds of mms of He, A, H2 and N2, in three spectral regions: (1) In the continuum, i.e., on the short wave-length side of the convergency limit at 4990A; (2) in the band region immediately behind this limit, on its long wave-length side; and (3) in the band region further away from the limit. If the quantum yield is assumed to be γ1=1.00 in the first region, the values γ2=1.14 and γ3=1.10 are obtained for the two other regions, showing that all excited I2 molecules dissociate by collisions with foreign molecules. The quenching of I2 fluorescence by foreign gases is thus practically never due to the dissipation process (1) I2*+X→I2+X but entirely to the dissociation process (2) I2*+X→I+I+X. The process (2) apparently occurs in most cases at the very first kinetic collision of excited iodine with a foreign molecule; only in the case of helium ten or more collisions are necessary to produce dissociation according to (2).
Theory of the Electronic Energy Levels of Simple Hydrides
Authors: Stehn J. R.
Published: January 2005

The conventional extremely simplified form of the Heitler-London theory is applied to the energy levels of the molecules BH, CH, NH, OH, FH. The exchange integrals, determined empirically to make the theory fit the known levels, are found to vary slowly and regularly from one molecule to the next. The energies of states as yet unobserved are predicted.
Inversion of the Partition Function to Determine the Density of Energy States
Authors: Bauer S. H.
Published: January 2005

The density of energy states for a complex system may be deduced from thermodynamic functions when their dependence on temperature is specified. The method is general and depends for its accuracy on the closeness of approximation of the experimentally determined partition function by an appropriate equation. Accurate specific heat data are therefore essential. The degeneracy function is obtained by inverting the Laplace integral defining the sum-over-states; as illustrations, the energy states for an Einstein crystal, and for a modified Debye crystal without and with a transition are discussed. The author was not successful in finding a mathematical expression which fitted the last case sufficiently well to differentiate between transitions of first and higher order.
Optical Activity of the Sugars
Authors: Gorin Everett , Kauzmann Walter , Walter John
Published: January 2005

The optical activities of some pentose sugars have been calculated by using the one-electron theory. The relative signs calculated agree in every case with those experimentally observed while the agreement as to magnitude is satisfactory. Some general considerations concerning the superposition rules are presented. It is shown that the rule is derivable upon the basis of the additivity of the vicinal effects. In addition certain requirements on the structure of the pyranose ring must be fulfilled.
Kinetics of the Oxidation of Hydrogen Sensitized by Nitrogen Dioxide
Authors: Crist R. H. , Wertz J. E.
Published: January 2005

The effect of small amounts of nitric oxide in lowering the explosion limits of the oxidation of carbon monoxide has been studied. The investigation has been extended to the study of the oxidation of hydrogen. The influence of walls, temperature and relative concentration of materials on the reaction rate has been studied. The results are explained on the assumption that NO3 is an important intermediate product in both the carbon monoxide and the hydrogen oxidations. The influence of adsorption by the walls is emphasized.
The Influence of Temperature and Pressure on the Infra-Red Absorption Spectrum of Gaseous and Liquid Hydrogen Chloride up to the Critical State
Authors: West W.
Published: January 2005

The absorption spectra, near 1.7μ, of liquid HCl from — 100°C to the critical temperature of 52°C, and of gaseous HCl from one atmosphere to the critical pressure of 82 atmospheres, have been measured. The spectrum of the gas retains P and R branches about an origin undisplaced from its low pressure value up to just below the critical pressure, although discreet rotational lines are not recognizable after the density of 0.1 g/cc has been reached. At all temperatures, the transition of gas to liquid is accompanied by the replacement of the P—R branched type of spectrum by a single maximum displaced to low frequencies from the gas origin by an amount increasing from 48 to 117 cm—1 as the temperature is lowered from the critical temperature to — 100°. This band is asymmetric, with a tail to the short wave side, and above 20°C shows signs of being resolved into two bands, one in the position of the gas band. It is concluded that liquid HCl contains two types of molecules, one gas-like, the other, with the vibration frequency perturbed by intermolecular action. The variation of the perturbed frequency with temperature is partly consistent with the hypothesis that the perturbation originates in the electrostatic action of neighboring molecules, but the magnitude of the shift is smaller by a constant amount than that produced by inert solvents of the same dielectric constant as liquid HCl. The gas a few degrees above the critical temperature and above the critical pressure also contains some liquid-like molecules.
Infra-Red and Raman Spectra of Polyatomic Molecules XI. Dimethyl Sulfide (CH3)2S
Authors: Fonteyne R.
Published: January 2005

The infra-red spectrum of gaseous dimethyl sulfide has been studied from 1.6 to 26μ, as well as the Raman spectrum of the liquid. A tentative vibrational analysis is given.
Electronic Absorption Spectra in Solution: with Special Reference to the Continuous Absorption of the Halogens
Authors: Bayliss N. S. , Rees A. L. G.
Published: January 2005

The cage theory of liquids has been applied to find the form of potential function that must be added to the U(r) curves of gaseous molecules to give the U(r) curves of dissolved molecules. It is possible to explain the slight displacement of the absorption maximum in halogens dissolved in nonassociated solvents, and also the change in the symmetry of the absorption curve. The large displacement of the maximum in associated solvents is due to a slight compression of the solute molecule by the quasi-crystalline structure of such solvents. The relaxation time of the solvent cage is such that band absorption should persist in solution when normal and excited states are of the same size; but that it should disappear when re′>re″.
Spectroscopic Measurements of Gaseous CN II. Thermal Dissociation of Cyanogen
Authors: White John U.
Published: January 2005

Free CN radicals are formed from cyanogen at high temperature. Their absorption spectrum was observed in a furnace at 1500°K. From the lower limit of the absolute absorption coefficient found in Part I of this paper, their partial pressure and hence the equilibrium constant of the dissociation of cyanogen to free radicals are calculated. A lower limit for the heat of the reaction C2N2→2CN  K1500∘K=1.1×10−12  H0=138.1(±1) kcal.follows directly. f=0.1 is estimated to be the most probable f value for the 2Σ→2Σ transition of CN. The most probable value of the heat of dissociation of cyanogen is calculated from this to be H0=146(±4) kcal. By calculating the partial pressure of CN at about 400°C, the thermal polymerization of cyanogen is explained as the addition of the free radicals formed to cyanogen molecules. From thermodynamic cycles, it is shown that the most probable value of the heat of dissociation of CO is 11.054 volts, and of the heat of vaporization of graphite 169.2 kcal., although 9.797 volts and 140.2 kcal. respectively, for these values cannot be completely eliminated.
Molecular Structure of Nitrogen Dioxide and Nitric Acid by Electron Diffraction
Authors: Maxwell Louis R. , Mosley V. M.
Published: January 2005

New electron diffraction photographs have been taken of NO2 extending the region previously investigated to include larger angles of scattering. An interference ring was found at (1/λ) sin ½θ = 0.49 followed by another ring appearing at 0.94 as determined by visual measurements. The outer portion of the pattern consists of two rather broad rings and two well-defined minima. Theoretical intensities of scattering were computed for various nitrogen valence angles, assuming the positions of the two oxygens to be equivalent. The best fit, and probably the correct structure, gives the angle O–N–O = 130±2° with the N–O distance 1.21±.02A. Photographs were obtained from pure nitric acid vapor at 70°—85°C. The interference maxima were measured visually as far out as the eighth maximum at (1/λ) sin ½θ = 1.83; a prominent minimum was seen at 1.54. Theoretical intensities were computed for various likely models, disregarding the scattering by the hydrogen atom. Good agreement was obtained for a planar model having an NO2 group with the same structure found for nitrogen dioxide. The third oxygen atom O′ is located at a distance of 1.41±0.02A from the nitrogen atom and equidistant from the other oxygen atoms. A model having the nitrogen atom slightly out of the plane containing the oxygen atoms also gave good agreement with the experimental results. This model however is considered less probable in view of Raman spectra data which apparently require a planar structure for O′–NO2.
Force Constants in Some Organic Molecules
Authors: Crawford Bryce L. , Brinkley Stuart R.
Published: January 2005

Consistent normal coordinate treatments, involving force-constants which are related to bond structures and which may be transferred from one molecule to another, are applied to hydrogen cyanide, methyl cyanide, and the methyl halides. The connection with previous treatments of acetylene, ethane, and methyl and dimethyl acetylene is discussed. A method of setting up such a consistent treatment is described, and a table of force constants for a number of bond structures is given. The structural significance of these force constants is briefly discussed.
The Fundamental Frequencies of Certain Halomethanes. II. The Raman Spectrum of Fluoroform
Authors: Glockler G. , Edgell W. F.
Published: January 2005

The Raman spectrum of CHF3 has been determined and the assignment to the six fundamentals has been made by considering the intensities and by comparison with the other haloforms. Checks have been obtained by two independent methods based on the theory of small vibrations. The fundamentals in CHClF2 have been revised to harmonize with the data of CHF3 and they have been empirically correlated in several spectral sequences. Molar heat capacities have been calculated for CHF3, CHClF2, and CHCl2F in the range T=250°K to T=650°K and compared with experimental values where available. The heat capacities have been fitted to empirical equations and a term added to correct to finite pressures by means of the modified Berthelot equation of state. It has been shown that these equations are accurate to 5 percent and are far more reliable than the small amount of thermal data available at present.
Relationship among frequency, temperature of the cooling water and beam current in submillimeter wave gyrotron FU-IV
Authors: Hori Toshihiro , Idehara Toshitaka , Sasagawa Hiroyuki , Kimura Atsushi , Ogawa Isamu , Mitsudo Seitaro
Published: January 2005

The frequency characteristics of the gyrotron FU-IV in free running mode are examined precisely using heterodyne mixing technique. First, the frequency characteristics are measured and the short-term spectral bandwidths and the drifts of the center frequency are found to be less than 10kHz full width at half maximum and about 10MHz during 20min, respectively. Next, an effective water-cooling system reduced the drifts of the center frequency within a range of several MHz. Then, the frequency, the cooling-water temperature, the beam current and the output power are monitored simultaneously to examine the relationship among these parameters. The results indicate that the beam current drift correlate with the frequency drift due to frequency pulling effect as well as the thermal expansion and contraction of the resonant cavity.
ESR Spectra from Paramagnetic Centers in Irradiated KClO4. I. The ClO2 Center
Authors: Byberg J. R. , Jensen S. J. K. , Muus L. T.
Published: January 2005

Accurate spin Hamiltonians for one paramagnetic center in irradiated KClO4 are derived from ESR spectra at five temperatures in the range from −170° to 0°C. The quadrupole interaction gives rise to ``forbidden'' transitions of high intensity. An iterative procedure is used for computation of the principal values of the g tensor as well as the tensors for the magnetic and electric hyperfine interaction. Comparison of the low-temperature spin Hamiltonian for the center with that derived from microwave spectra for the free ClO2 molecule demonstrates that the center is adequately described in terms of a trapped ClO2 molecule as previously suggested by Cole. A pronounced temperature dependence of the spin Hamiltonian indicates a considerable influence of the host lattice.
Millimeter-Wave Rotational Stark Spectra of HNCO, DNCO, and HN3: Dipole-Moment Changes with K
Authors: White Kevin J. , Cook R. L.
Published: January 2005

By employing a parallel-plate semifree-space cell the millimeter-wave rotational Stark spectra of HNCO, DNCO, and HN3 have been observed in the ground vibrational state. Analysis of the Stark effect for the J=3→4 transitions yields the dipole-moment component along the axis of smallest moment of inertia. For these very slightly asymmetric rotors the dipole moment is observed to decrease with increasing K. For HNCO (J=3→4), the dipole moments are found to be (Debye units) K=0, μa=1.613±0.002,    K=2, μa=1.540±0.001,K=1, μa=1.575±0.002,    K=3, μa=1.500±0.002;for DNCO (J=3→4), K=1, μa=1.602±0.003,    K=2, μa=1.580±0.001;and for HN3 (J=3→4), K=1, μa=0.8369±0.0020,  K=2, μa=0.8247±0.0002.The results are discussed in terms of the electronic structures of the molecules.
Acoustic Attenuation in Crystalline Carbon Tetrachloride
Authors: Rasmussen Robert A.
Published: January 2005

The acoustic attenuation in crystalline carbon tetrachloride has been measured using an experimental technique that precludes handling or cutting of the crystals. The measured attenuation was found to be twice the value predicted by the resonance-absorption theory. It is observed that the relaxation rates in liquid and solid carbon tetrachloride are of the same order of magnitude, the attenuation in the liquid being approximately twice that in the solid.
Calculation of the Lifetime of the a 4π State of NO
Authors: Lin Sheng Hsien
Published: January 2005

Both radiative and nonradiative lifetimes of the a 4Π state of NO have been calculated by using the LCAO MO's proposed by Brion et al. The result shows an agreement with the experimental result to an order of magnitude.
Transport Properties of Quadrupolar Gases
Authors: Smith Francis J. , Munn R. J. , Mason E. A.
Published: January 2005

Collision integrals for quadrupolar gases are computed on the assumption of fixed relative orientation per collision, with a 12–6−5 potential model, for a range of reduced temperatures and reduced quadrupole moments. The quadrupole effects on diffusion and viscosity are small, but not completely negligible if one wants accurate values for the parameters of the spherically symmetric component of the potential. These values are needed to obtain quadrupole moments from properties like second virial coefficients, which are more sensitive to quadrupole effects. Thermal-diffusion factors are the most strongly affected of the transport coefficients; the presence of quadrupolar intermolecular forces can wipe out the thermal-diffusion inversion temperatures.
Excitation of the Metastable States of Helium by Electron Impact
Authors: Dugan J. L. G. , Richards H. L. , Muschlitz E. E.
Published: January 2005

Measurements of relative electron-impact excitation functions for production of the metastable 21S and 23S states of helium in the range 25–135 eV have been made by observing the deflection of a beam of excited atoms in an inhomogeneous magnetic field. Effects of imprisonment and scattering of the beam have been eliminated by extrapolating the data to zero pressure, and the effect of photons in the beam separately determined. The ratio of the singlet to triplet functions obtained (including cascade contributions) varies from 0.26 to 2.37 in the energy range studied.
Paramagnetic Relaxation in Liquid-Crystal Solvents
Authors: Glarum Sivert H. , Marshall James H.
Published: January 2005

The influence of a liquid-crystal solvent on paramagnetic relaxation processes involving Zeeman and hyperfine anisotropies is examined. Secular and pseudosecular relaxation mechanisms are reduced by molecular ordering. Secular contributions are most effectively quenched, and, for high degrees of order in viscous media, pseudosecular processes are most important.

ESR studies were made of solutions of vanadyl complexes with six β-diketones in p-azoxyanisole. The linewidths in the spectra depend upon the 51V nuclear spin quantum number M, and vary as A+BM+CM2. As the degree of molecular ordering increases, one predicts and observes that first C and then B change in sign.

It was also found that almost perfect ordering of a solute in an imperfectly ordered liquid crystal can be achieved, provided the solute molecule is sufficiently large and rigidly planar. Implications of ESR observations concerning the structure of liquid-crystal phases are discussed.
Mechanism of the ``Bimolecular'' Hydrogen—Iodine Reaction
Authors: Sullivan John H.
Published: January 2005

The rate of photochemical production of hydrogen iodide in a hydrogen—iodine system irradiated with 5780-Å light was measured and found to be proportional to the square of the iodine atom concentration. Absolute light intensities were determined and rate constants were calculated for the termolecular reaction H2+2I→2HI at 417.9°, 480.7°, 520.1°K. The previously obtained thermal data in the range 633°—738°K were treated considering one of the elementary reactions to be the termolecular reaction and not H2+I2→2HI; the rate constants obtained have the same Arrhenius parameters as those from the photochemical measurements. The bimolecular reaction, H2+I2→2HI, does not occur. Two mechanisms consistent with the photochemical and the thermal data are H2+2I→2HI; H2+I+M=H2I+M, H2I+I→2HI. The specific rate calculated for the termolecular reaction is k=(6.66±0.5)×107 exp (−5310±85/RT) liter2 mole−2·sec−1.
Optical Activity of Single-Strand Oligonucleotides
Authors: Bush C. Allen , Brahms J.
Published: January 2005

The circular-dichroism (CD) spectra of several dinucleoside phosphates containing guanine and cytosine in aqueous solution at −17°C are reported in the range 210–300 mμ. The results differ from previously reported dinucleoside phosphate curves in that the CD bands do not appear in pairs of nearby positive and negative bands. This is in disagreement with the exciton treatment which has been successfully used to interpret other dinucleoside phosphate CD and ORD.

Tinoco's general theory of polymer optical activity is examined in an attempt to explain the nonconservative CD curves we observe. Both the cases of base planes perpendicular to the helix axis and that of the base planes tilted with respect to the helix axis are considered. We conclude that tilting cannot be expected to give large nonconservative rotational strengths. In addition we show by means of a polarizability approximation, that interaction of the far-uv transitions can give rise to rotational strengths such as those we observe, even for the case of base planes perpendicular to the helix axis. This nonconservative contribution is composed of the Kirkwood polarizability term and an analogous term containing the magnetic transition moment and the polarizability perpendicular to the base plane. The contribution also depends on the direction of the electronic transition dipole moment of the transition whose rotational strength is being calculated. We propose that it is through this dependence that the nonconservative effect is not present in the CD of dinucleoside phosphates previously measured but is prominent in the curves reported for dinucleoside phosphates containing guanine or cytosine. The study suggests that the adenosyl—adenosine CD curve, which is conservative, is a special case due to its electronic structure and that the geometry of several dinucleoside phosphates is the same as that of single-strand RNA whose CD curve is nonconservative.
Drift Mobility Measurements in Metal-Free and Lead Phthalocyanine
Authors: Westgate C. R. , Warfield G.
Published: January 2005

The drift mobilities of electrons and holes in metal-free and lead phthalocyanine were measured using a transient space-charge-limited-current method and a time-of-flight method. The mobilities were found to be in the range 0.05–0.1 cm2/V·sec for metal-free phthalocyanine and 0.6–4.0 cm2/V·sec for lead phthalocyanine. Fast trapping of carriers in the bulk and emptying of traps at the surface under illumination were observed.
Analysis of Elastic-Scattering Data in the Semiclassical Approximation
Authors: Greene E. F. , Reck G. P. , Rosenfeld J. L. J.
Published: January 2005

The usefulness and accuracy of several approximations in the semiclassical derivation of the differential elastic scattering cross section are evaluated for the purpose of defining the best way of analyzing experimental data to obtain potential parameters.
Analytical Treatment of Excluded Volume. I. Dimensions of Real Polymer Chains
Authors: Alexandrowicz Z.
Published: January 2005

Excluded-volume interactions in long chains are treated in terms of Gaussian probabilities for intersegmental contacts. Thus for a chain of n segments and end-to-end distance h the energy factor, exp[−βΣΣ lim k>lδ(hlk)],is evaluated by linearly expanding and averaging—sequentially for l=1, 2, ···, n—the interactions of segments l with those following after, k. Accordingly, for each l exp[—βΣkδ(hlk)] into exp[—βΣkfn—l(0lk | h)], where fn—l(0lk | h) is the probability, conditional to h, for a contact among segments l and k. The probability refers to a fictitious chain n in which only the segments from l+1 to n are still interacting (— the ``real section''). Thereafter it is assumed that the contact probabilities can be represented by the Gaussian expressions obtaining for random-flight chains, with the links representing the real section taken as expanded as the most probable end-to-end distance of a corresponding real chain—viz., a chain consisting of r=n—l−1 interacting segments. On this basis an integral equation is derived for the expansion coefficient αn=h*/h*0, h*, and h*0 being respectively the most probable value of the end-to-end distance of chain n, in the presence and absence of interactions. (The integral form of the equation results from the number of interacting segments in the fictitious chains varying from r=n to r=0.) The line obtained for αn2 vs n initially rises like Fixman's but, beyond αn2≈4, diverges from it, the asymptotic limit being αn2∝n0.236 (vs Fixman's ∝n0.33 and Flory's ∝n0.2).

The results also show that the excluded-volume effect is essentially contributed by contacts among segment pairs separated by a vanishingly small fraction of the real chain section, (k—l) *«r*. It seems therefore that the distribution of the internal distances hlk can be treated in Gaussian terms, in spite of the distribution of the end-to-end distance in a real chain being non-Gaussian. On the same grounds it is concluded that a similar treatment of the 2-dimensional chain, leading to αn2∝n0.5, should fail, for in this case (k—l) *≈r*.
Inversion of Low-Energy Experimental He–He+ Elastic Differential Scattering Sections to the 2Σg+ and 2Σu+ Potentials
Authors: Olson R. E. , Mueller C. R.
Published: January 2005

An iterative technique coupled with the two-state theory has been employed to obtain the He–He+ ground state and first excited state potentials from the 10- and 15-eV experimental differential cross sections of Aberth and Lorents. This procedure is adaptable for the inversion of relative data. The resulting ungerade potential displays good agreement with the theoretical calculations of Reagen, Browne, and Matsen in the 0.8- to 2.5-Å region, with the depth of the well found to be 2.34 eV from the 15-eV data. The intermediate regions of both potentials show the dominant term of the power law to be approximately r−4.
Electron Paramagnetic Resonance Studies of the Radiolysis of H2O in the Solid State
Authors: Gunter Thomas E.
Published: January 2005

Free radicals formed by electron irradiation of H2O at 77°K have been studied with the electron paramagnetic resonance (EPR) technique. In particular the spectrum of the OH radical is identified in irradiated CaSO4·2H2O and LiSO4·H2O and in irradiated hexagonal ice. The effective spin Hamiltonian is determined for OH in these crystals. For the ice case, the experimentally determined spectroscopic splitting tensor is shown to be in agreement with a simple theory based on crystal-field theory. The experimentally determined hyperfine splitting of the OH radical is shown to be in agreement with that predicted by an LCAO MO calculation and verified by an EPR study of OH produced by microwave discharges in gases.

In the irradiated sulfates magnetic resonance signals from OH, H atoms, and some form of trapped electron were observed.

Radiation-yield measurements for OH in ice at 77°K are given for the dose range 104 to 109 rad.
Comments on the Influence of Intermediate Excitons and Exchange Forces on the Interaction in Molecular Crystals: The Crystal Structure of Chlorine
Authors: Hillier Ian H. , Rice Stuart A.
Published: January 2005

The reasons for the failure of the Lennard-Jones potential to predict the correct space group of solid chlorine and the molecular orientation within the unit cell are examined. In the analysis given, the contribution of charge-transfer states to the intermolecular binding energy in the ground state is calculated. It is found that these states account for about 25% of the intermolecular interaction, and tend to reinforce the dispersive—repulsive forces in the region of the observed molecular angle of tilt. However, in our approximation these forces fail to account for the observed stability of the orthorhombic structure relative to the cubic structure, the latter being predicted to be more stable if the interaction is a Lennard-Jones potential. The repulsive interactions are calculated using an approximation to the exchange energy. It is concluded that the failure of the Lennard-Jones potential to predict the correct angle of molecular tilt within the unit cell arises from the incorrect form of the repulsive potential. Further, with the binding energies calculated in this paper, the difference between the energies of the cubic and orthorhombic structures is much reduced from that predicted from calculations based on the use of the Lennard-Jones potential.
Theory of the Temperature Dependences of the Hyperfine Interactions in the Methyl Radical
Authors: Schrader David M.
Published: January 2005

The temperature dependences of the hyperfine interactions in the ESR spectrum of the methyl radical are examined theoretically using a semiempirical nonionic valence-bond theory. K-shell polarization and incomplete following of the molecular vibrations by the carbon sigma orbitals are accounted for. The interactions are calculated as functions of the nuclear positions in the out-of-plane bending mode (A2″), and are averaged over the ground vibrational state. By a modest adjustment of semiempirical integral parameters and the degree of the sigma orbital following, four calculated hyperfine coupling constants (H in CH3, D in CD3, 13C in 13CH3 and in 13CD3) are fitted to the values observed at 97°K. The vibrational averaging is then extended to several of the lower excited states. By assuming a Boltzmann population of these states, the interactions are then calculated as functions of temperature from 0°K to 500° for CH3 and from 0° to 700° for CD3 without further parameter adjustment. Thus, by fitting four coupling constants at a single temperature and assuming a definite quantum-mechanical model, we predict the coupling constants over a wide temperature range. The relationship between the temperature dependences of the interactions and the isotope effects is discussed. The contribution of each orbital in the molecule to each hyperfine interaction is calculated, and it is found that the unpaired pi electron plays an insignificant role in the temperature dependence of the proton interaction, but that it dominates the carbon−13 temperature dependence. The calculations indicate that at room temperature the absolute value of the proton interaction in 12CH3 should decrease as the temperature increases by the amount (1.35±0.03)×10−3 G/deg, and the carbon−13 interaction in 13CH3 should increase by (1.29±0.08)×10−2 G/deg. Unfortunately, the only observation of a temperature coefficient is not directly comparable to the theoretical results reported here, since in that measurement water was the solvent. The result was (2.1±0.2)×10−3 G/deg for the proton in 12CH3. In addition to the solvent effect, several other possible sources for the discrepancy are discussed, including vibrations other than A2″, and our use of an approximate normal coordinate for the A2″ mode. Use of a value for the force constant recently suggested by Lester, Andrews, and Pimentel is found to markedly decrease the calculated temperature coefficients.
Collision Theory of Relaxation Processes
Authors: Chen F. M. , Snider R. F.
Published: January 2005

Expressions for the NMR relaxation times T1 and T2 as well as for the chemical shift σ are given in terms of the binary transition operator. These are obtained by solving a Boltzmann equation valid for a dilute monatomic gas. Crude estimates of the anisotropic part of the transition operator and of T1 are obtained for dipolar and spin—rotation interactions. These agree in magnitude with other estimates of these quantities.
Ab Initio Calculations of the Barriers to Internal Rotation of CH3CH3, CH3NH2, CH3OH, N2H4, H2O2, and NH2OH
Authors: Pedersen L. , Morokuma Keiji
Published: January 2005

The barriers to internal rotation of the molecules CH3CH3, CH3NH2, CH3OH, N2H4, H2O2, and NH2OH are calculated by the LCAO SCF MO method using a medium-sized Gaussian orbital basis set. The calculated barriers in kilocalories/mole are CH3CH3 (2.88), CH3NH2 (2.02), CH3OH (1.59), N2H4 (11.05, 6.21), H2O2 (15.94), and NH2OH (9.90, 7.37). In addition, for CH3CH3 and H2O2 the basis set is augmented with p-type orbitals on the hydrogens to investigate polarization effects. With p orbitals on the hydrogens, the ethane barrier was raised to 3.45 kcal/mole and for H2O2 a slight well (0.1 kcal/mole) not present in the smaller basis-set calculation developed between the cis and trans configurations. For CH3NH2 the effect of the nonlinearity of the CH3 symmetry axis and the C–N bond was found to be significant. A population analysis indicates that, in general, as a hydrogen rotates to a position of nearest approach to a lone pair at the other end of the molecule, electron density is lost to the lone pair. Scaling the energy changes the barriers only a slight amount, but changes in the kinetic and potential energies are shown to be larger.
Smoothing and Unfolding the Data of Beam-Collision Experiments
Authors: Ioup G. E. , Thomas B. S.
Published: January 2005

Significant improvement in the resolution of beam-collision experiments has been obtained by applying the techniques of noise removal and deconvolution as developed by Morrison and others. Computational procedures are discussed and some results of the application to experimental data are presented.
Elasticity in Rigid-Disk and -Sphere Crystals
Authors: Stillinger Frank H. , Salsburg Zevi W.
Published: January 2005

Our previously developed product representation for the partition function of rigid molecules under high compression is generalized to include distorted reference lattices. The resulting strain component variations of free energy then permit extraction of elastic constants, both linear and nonlinear. The high-compression elastic behavior of the two-dimensional rigid-disk crystal is explicitly evaluated through triplet cluster contributions. For rigid spheres in three dimensions in the face-centered-cubic lattice, singlet and pair cluster contributions have been evaluated, and the sound velocity ratio is reported for propagation along the 〈100〉 directions. Consideration of singlet and pair contributions for hexagonal packing suggests not only that this structure is more stable than the face-centered-cubic case, but that it exhibits a spontaneous small contraction along the c axis.
Lattice Vibrations of the Solids N2, CO2, and CO
Authors: Ron Arza , Schnepp O.
Published: January 2005

The far-infrared absorptions of the solids N2, CO2, and CO have been investigated. Two bands were observed for each solid below 100 cm−1 and the spectrum observed for CO2 is in good agreement with that reported previously. The frequencies for N2 have been found to be in good agreement with calculations based on the theory described by Walmsley and Pople. The absorption intensities have been calculated from the theory described in the preceding paper. The experimental values available for the intensities are uncertain to within a factor of 3 and the calculated and measured values agree well within this limit. It is concluded that the intensity theory has been shown to be valid to better than within a factor of 2 but a more precise test is contingent on the availability of more accurate experimental measurements. From the lack of agreement between calculated and observed intensity ratios between the absorption bands of the same substance, it is concluded that the quadrupole—quadrupole term is not adequate to describe the angle-dependent part of the intermolecular potential.
Perturbation Calculation of the Energy of the First Excited State (2pσ) of H2+
Authors: Silbey Robert
Published: January 2005

The electronic energy of the 2pσ state of H2+ is calculated by perturbation theory to third order using the Guillemin—Zener wavefunction as a zeroth-order function. The results agree quite well with the exact calculations except for small internuclear distances, as expected.
Magnetic Structure of DyAg
Authors: Arnold G. , Nereson N. , Olsen C.
Published: January 2005

Neutron-diffraction measurements on the intermetallic compound DyAg show that this material is antiferromagnetic below a Néel temperature, TN, of 51°±1°K; this magnetic structure is in agreement with previous susceptibility data. The measured ordered moment on the Dy atom sites is 9.8±0.5 μB which is essentially the full moment to be expected from the free Dy3+ ion. The observed antiferromagnetic structure is in disagreement with predictions derived from the Ruderman—Kittel—Yosida indirect exchange interaction. Molecular field calculations based on TN show that the exchange energy, |Jex|/k, is in the range from 1.5° to 2.2°K.
Seventh Virial Coefficients for Hard Spheres and Hard Disks
Authors: Ree Francis H. , Hoover William G.
Published: January 2005

The seventh virial coefficient B7 is expressed as a sum of modified star integrals instead of the usual Mayer star integrals. The new graphs contain both Mayer f functions and f̃(≡1+f) functions. This simplifies the calculation of B7. That is, instead of the 468 star integrals that appear in Mayer's formulation, only 171 modified star integrals now appear in the evaluation of B7. Furthermore, for D-dimensional particles with a hard core, these 171 integrals are strongly dependent on the number of dimensions D. For hard rods, hard disks, and hard spheres, respectively, at most one, 78, and 164 of these integrals give a nonvanishing contribution to B7. When Monte Carlo integration is used to evaluate these integrals using hard-sphere and hard-disk potentials we obtain the following values of B7: hard spheres, B7/(B2)6=0.0138±0.0004; hard disks, B7/(B2)6=0.1141±0.0005. For hard spheres, the truncated seven-term virial series for the pressure agrees within 10% with the results of the molecular dynamics data throughout the fluid phase. The Padé approximants to the pressure obtained from Bn(n<8) data agree even better (≲5%) with the molecular-dynamics data on the fluid side. Estimated values of B8/(B2)7 obtained from the Padé approximants are 0.005 and 0.063 for hard spheres and hard disks, respectively. Furthermore, for hard disks, the Padé approximants obtained from the seven known values of Bn(n<8) indicate that the virial series shows an unstable phase at ρ=ρ0. If this is in fact true, then the low-density study of the equation of state for hard disks would yield some information on the high-density side. We have also calculated the first seven coefficients Cn of the density expansion of the isothermal compressibility for hard spheres, hard disks, hard parallel cubes, and hard parallel squares. We find that these Cn alternate in sign. For two-dimensional continuum particles with a hard core, the corresponding compressibility series appear to converge faster than the usual virial series of the pressure. We also compare the present values of B7 with the various values of B7 calculated from approximate theories.
Atomic rij Integrals for Many-Electron Wavefunctions
Authors: Karl John H.
Published: January 2005

A general integration scheme is developed for doing multielectron rij integrations. Preliminary calculations on Be indicate that it is practical to obtain variational wavefunctions containing unliked four-electron correlated terms up through at least neon by using this method.
Theoretical Investigations of Gas—Solid Interaction Phenomena. I
Authors: Raff L. M. , Lorenzen Jerry , McCoy B. C.
Published: January 2005

A classical study of gas—solid surface interactions is reported. A two-dimensional, independent oscillator lattice (IOL) is used as a surface model with harmonic potentials connecting each lattice site. Morse-type potential functions are assumed to operate between the incident gaseous atom and each lattice atom. Using Monte Carlo techniques and numerical integration of the 16 differential equations describing the system, energy accommodation coefficients (EAC) and spatial distributions have been calculated for a (He/Ni) system. The dependence of these quantities upon incidence angle, gaseous beam temperature, surface temperature, and various interaction parameters has been investigated. The results indicate that the EAC increases with increasing beam temperature and beam velocity; decreases with increasing lattice force constant; increases with increasing attractive interaction between gas and surface; decreases with increasing incidence angle; and decreases as the surface and gaseous temperatures approach one another. In general, these results are in qualitative to semiquantitative agreement with experiment. The calculated spatial distributions depend strongly upon incidence angle. For perpendicular incidence (θi=0°) a diffuse distribution is predicted. For θi=37.5° the distribution is peaked at an angle subspecular by 18°. As the attractive interactions between gas and surface increase, the maximum is shifted toward the surface normal. Similar behavior is observed with respect to an increase in surface temperature. Comparison with experiment indicates the He scattering to be specular rather than 18° subspecular. The calculated distributions are also too diffuse due probably to the two-dimensional character of the model. The predicted trends with regard to attractive interactions and surface temperature are in accord with observation. The over-all behavior indicates that the ``normal-component model'' of energy transfer is oversimplified and that transfer of energy in the parallel component of motion can be of importance.
Mass-Spectrometric and Theoretical Evidence for NH4 and H3O
Authors: Melton Charles E. , Joy Hubert W.
Published: January 2005

The unusual chemical species H3O and NH4 have been studied using both experimental and theoretical methods. Experimentally the species were investigated by means of a mass spectrometer equipped with two different reactors designed to produce reactive species. The NH4 was produced by surface chemistry techniques, whereas H3O was produced by irradiating water vapor with ionizing electrons. A study of the ionization potential of NH4 by surface ionization techniques gave a value of 5.9 eV. The ionization potential of H3O was measured by conventional techniques and a value of 10.9 eV was obtained. In the theoretical investigation, the physical parameters are given including s-, p-, and d-type orbitals for H3O and s-, p-, and f-type orbitals for NH4. The calculations for NH4 predict a tetrahedral structure with internuclear distances of about 1.06 Å and they predict a planar H3O molecule with bond distances about 1.03 Å. The ionization potentials of H3O and NH4 were estimated to 3.9 and 3.0 eV.
Recoil Tritium Reactions in Methane—Hydrogen Mixtures: CH4—D2
Authors: Root John W. , Rowland F. S.
Published: January 2005

The reactions of recoil tritium atoms have been studied over the full range of mole fractions for mixtures of CH4 with D2 and show total hot yields varying from 53% and 93% as the mole fraction of D2 increased. The specific activity ratio (CH3T)/(CH4):(DT)/(D2) is approximately constant over the entire range, indicating that these reactions occur at similar average energies.

All of the data can be quantitatively explained through the use of the kinetic theory of hot reactions. The moderating ability of CH4 is more than twice that of D2 and confirms the inadequacy of an elastic, hard-sphere model for nonreactive collisions at high energies.
Application of Nonlinear Transformations to the Evaluation of Multicenter Integrals
Authors: Petersson G. A. , McKoy V.
Published: January 2005

The evaluation of multicenter integrals is necessary for ab initio calculations. Expansion techniques give infinite series which must be summed. We have used several nonlinear sequence-to-sequence transformations to obtain more rapidly convergent series. The best of these transformations reduces the time necessary to evaluate some four-center integrals by as much as 75%. This transformation improved the convergence of all of the twenty integrals we have treated.
Dielectric Properties of Adsorbed Gas Molecules
Authors: Gröbner Oswald
Published: January 2005

In this paper the dielectric behavior of gas molecules adsorbed on alumina powder is studied. The method which is used to measure the relative polarizability of adsorbed molecules is described and the results, obtained for the gases N2, CO2, C2H2 as well as for the polar gases Cl2F2C and 1,1-F2C2H4 are discussed.

The capacitance change ΔC of the test condenser filled with the adsorbent is proportional to the total number of adsorbed molecules, N. The polarizability of the molecules determines the slope of the plot ΔC/C versus N. For two gases their relative polarizability is obtained from the ratio of the slopes. With this method the dielectric behavior of adsorbed polar and nonpolar molecules is studied. Furthermore, a distinction is made between weakly and strongly adsorbed molecules. The capacitance change is nonlinear for large amounts of adsorbed molecules. Therefore the polarizability α of the molecules is considered to depend on the number of adsorbed molecules per unit surface, i.e., α = A[1—(N/S)B], where A and B are constants and S is the surface area of the adsorbent. B has the dimension of a surface area per molecule and defines an average distance at which the interaction of neighboring molecules affects their polarizability.
Modulated Double Resonance and Inelastic Collisions
Authors: Gordon Roy G.
Published: January 2005

Microwave, infrared, and optical double-resonance techniques have been developed recently to give highly specific information about rotational, vibrational, and electronic energy transfer in gases. We develop here a quantitative theoretical basis for the understanding of these results in terms of the inelastic collisions between molecules. A general formula is derived for the strength and phase shift of double-resonance-modulated lines produced by collisional transfer, and a number of qualitative trends are explained and predicted.
Computation of the SCF Molecular Orbital Wavefunction in Terms of Localized Orbitals
Authors: Peters David
Published: January 2005

The Hartree—Fock—Roothaan equations are written down and solved for the localized molecular orbitals which describe the chemical bonds and lone pairs of many molecules. The work involves the formulation of a local operator which is concerned with the physical situation in and around the bond in question and which is largely independent of the rest of the molecule. The matrix elements of this operator over the atomic orbitals of the molecule are known, but the explicit form of the operator itself has not been obtained so far.

The theory is applied to two simple examples, the He2 molecule and the BH molecule. The known wave-functions and energies of these two examples are obtained again in a novel way which should be applicable to molecules of any size. These two examples illustrate some, but not all, of the points which arise in the general case.

If it does prove possible to use this method in large molecules, then there is no upper limit to the size of the molecule which can be dealt with at the Hartree—Fock—Roothaan SCF level of approximation.
On the Theory of Excitons in Liquids. II. A Classical Model of Polarization Waves in a Simple Liquid
Authors: Nicolis Gregoire , Rice Stuart A.
Published: January 2005

Recent studies of the localized excited states of condensed matter have been almost exclusively concerned with the properties of crystalline solids. In this paper we construct an analysis of the exciton states of a particular disordered system, namely a simple liquid. We present a model which is an extension of the model previously used by Fano and which allows the construction of a general theory of polarization waves in which the structure of the liquid appears explicitly. Some particular cases of the general form of the dispersion relation of polarization waves are worked out in detail both in the longitudinal and transverse cases. Finally, the possible mechanisms of damping of the exciton waves are briefly discussed.
Ionization Potential and Absorption Coefficient of COS
Authors: Matsunaga F. M. , Watanabe K.
Published: January 2005

Absorption and photoionization coefficients of COS in the region 1070–1700 Å were measured with a resolution of 0.5 Å by photoelectric methods. The absorption curves support the photographic studies of Price and Simpson and Tanaka, Jursa, and LeBlanc. The doublet first ionization potential of the molecule was found to be 11.18 and 11.22±0.01 eV from the convergence limit of a Rydberg series and the photoionization curve.
Radiation Effects on Amino Acids: Valine
Authors: Box Harold C. , Freund Harold G. , Budzinski Edwin E.
Published: January 2005

Single crystals of dl-valine were x-irradiated at liquid-nitrogen temperature. The ESR absorption spectrum was observed as the crystal warmed. After warming to 225°K, a definitive spectrum was obtained which is attributed to the formation of the free radical (CH3)2CHCHCOOH. A transformation of the absorption occurs at room temperature due to the formation of the free radical (CH3)2CCH(NH3+)COO−. This radical was examined by ESR and ENDOR spectroscopy.