bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies of Surface Films by Reflection of Polarized Light. I. A More Rigorous Algebraic Method for Computing Results
Authors: Lucy F. A. 
Published: January 2005

Plane-polarized light is in general elliptically polarized by reflection. Since the molecules in a very thin surface layer are those chiefly concerned in the process of reflection, the ellipticity is very sensitive to the interface conditions such as the presence of thin films. Since light changes phase 360° in a single wave-length, determination of phase changes to within a few minutes of arc should allow film thickness measurements to the nearest angstrom unit. The method has been used for many years to treat problems of wide variety. The instruments and techniques employed have, on the whole, been adequate, but the interpretation of results has often been more or less unsatisfactory. The algebraic relationship between instrument readings and film constants is not exactly known. Reasonably precise graphical solution is tedious. Algebraic solutions have been preferred by most workers.
This paper reports an algebraic method containing fewer approximations than used hitherto and compares results with values found by two prior methods. Drude's original equations give results in rather poor agreement with those of the more precise equations developed in this paper. Results obtained with the equations of Tronstad, on the other hand, agree fairly well in a favorable case.
The Effect of Variations in Surface on the Photolysis of Acetone
Authors: Steacie E. W. R. , Darwent B. deB. 
Published: January 2005

An investigation of the acetone photolysis in the ``continuum'' and in the ``banded'' region has been made in clean quartz vessels and in vessels coated with potassium chloride and with lead. No appreciable change in the C2H6/CO ratio occurs in the coated vessels. This is surprising since biacetyl formation is apparently at least partly heterogeneous, and the ratio would be expected to be sensitive to the condition of the surface.
A few experiments were also made on the mercury photosensitized decomposition of acetone. Very high C2H6/CO ratios were found. It is concluded that this is due merely to higher absorbed intensities for a given incident intensity.
The Reaction of Hydrogen Atoms with the Paraffin Hydrocarbons
Authors: Trost W. R. , Steacie E. W. R. 
Published: January 2005

The reactions of atomic hydrogen produced by a discharge with ethane, propane, and neo-pentane have been investigated. All three reactions proceed at approximately the same rate, with activation energies of ca. 9 kcal., assuming a steric factor of 0.1. It is suggested, however, that the activation energies are in reality somewhat lower than this, with correspondingly smaller steric factors.
In the reaction with neo-pentane considerable ethane is produced. When deuterium atoms are used, this ethane is found to be only slightly exchanged. It is concluded, therefore, that ethane cannot arise by recombination of radicals, and must be formed in one step, presumably from an excited neo-pentane molecule.
Structure of Micelles of Colloidal Electrolytes. III. A New Long-Spacing X-Ray Diffraction Band, and the Relations of Other Bands
Authors: Mattoon R. W. , Stearns R. S. , Harkins W. D. 
Published: January 2005

A newly found x-ray diffraction band, obtained from aqueous solutions of soaps and detergents, gives a Bragg spacing which is independent of concentration and is close to the double-length of the molecule. This is designated as the micelle thickness or M-band. The already known long-spacing band, interpreted here as related to the inter-micellar distance, is designated as the I-band. Its spacing dI increases with decreasing soap concentration. If a hydrocarbon is solubilized in the micelles, these spacings increase by ΔdM and ΔdI. Formerly, ΔdI was supposed to give the mean thickness of the layer of oil dissolved between the ends of the hydrocarbon chains of the soap molecules as a middle layer in the micelle. However, ΔdM seems to be more directly related to this thickness. As measured by dM, the thickness of the micelle remains constant with increasing soap concentration: e.g., the values are 40.8, 41.5, 40.7, 40.2, 39.5, 39.6, 40.2A for potassium myristate at 25°C at the following respective concentrations: 2.3, 4.5, 7.2, 9.8, 12.0, 13.7, and 16.5 percent. The mean ``thickness'' increases from 29.7A for potassium caprylate (C8) to 47.3 for potassium palmitate (C16). By a method explained in the text, the number of molecules in a potassium myristate micelle is calculated as 56 at 9.8 percent by use of the Bragg I-spacing. However, it is probable that a corrected Bragg spacing should be used. A new long-spacing band, designated as an X-band, appears when an I-band is present and oil is solubilized in the micelles. The order of spacing is then dI&gt;dM&gt;dX; e.g., in one case the values are 84&gt;50&gt;27A.
The ``cylindrical'' model of the micelle preferred here differs from the lamellar and in some respects from the spherical model. It exhibits the following characteristics: (1) A micelle consists of one double-layer of soap or detergent molecules. These have their polar ends oriented outward toward the water and their non-polar ends inward toward each other. (2) The thickness of the micelle of a pure soap is essentially twice the length of the soap molecule, independent of concentration. (3) Hydrocarbons solubilize inside the micelle between the two layers of soap molecules and thus make he micelle thicker. (4) The area per soap molecule in the micelle remains practically constant, whether or not solubilized hydrocarbons are present. (5) The width or lateral dimension of the micelle and the number of soap molecules per micelle increase with increasing soap concentration and with solubilization of hydrocarbons. (6) From energy considerations the area of contact between the hydrocarbon chains of the detergent molecules and the water must be as small as is compatible with the other conditions imposed upon its structure.
A Further Investigation of the Mercury Photosensitized Polymerization of Propylene
Authors: Gunning H. E. , Steacie E. W. R. 
Published: January 2005

A reinvestigation has been made of the authors' earlier work on the reaction of propylene with mercury (3P1) atoms at 30°C in a static system, with special concentration on the products of the reaction.
The mechanism C3H6+Hg(3P1)→C3H6*+Hg(1S0)C3H6*+C3H6→2C3H6C3H6*→C3H5+Hwhich was proposed in the earlier work has been confirmed. Some twenty-two different products were identified at low pressures, all of which, with the exception of acetylene, can be explained as the result of interactions of the free radicals present.
The quantum yield of the reaction reaches a maximum of 0.18 at 6.5 mm, and falls to 0.04 at 72 mm.
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.
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.
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&gt;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*.
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.
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.
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.
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.
Classical Small-Angle Scattering from Anisotropic Potentials
Authors: Cross R. J. 
Published: January 2005

A simple, direct method of calculating the small-angle scattering from an arbitrary anisotropic potential is derived. The approximations are valid for large energies or large impact parameters. Two methods are used, both yielding identical results. The first, an impulse approximation, involves integrating the force over the trajectory which would be followed if there were no interaction. The second method involves a perturbation solution of Hamilton's equations of motion. The first method is conceptually simpler, but the second yields a solution of the trajectory and is more easily generalized to include second-order effects.
For scattering of ions and fast neutrals, molecular rotation can be neglected, and a simple expression is obtained for the differential cross section at small angles. This is applied to ion—dipole scattering where the potential is completely anisotropic, being repulsive for half the orientations and attractive for the other half. It is found that the differential cross section behaves exactly like that for a spherically symmetric potential given by μe/2r2. However, when the ion—dipole potential is combined with a repulsive term in the potential, deviations from the behavior of spherically symmetric potentials are found. For scattering at thermal energies, the molecular rotation averages out the anisotropic terms in the potential, introducing further deviations from the behavior of spherically symmetric potentials.
Thermomolecular Pressure Difference Measurements for Precision Helium−3 and Helium−4 Vapor-Pressure Thermometry
Authors: Watkins Reed A. , Taylor William L. , Haubach Walter J. 
Published: January 2005

Thermolecular pressure differences due to thermal transpiration were measured to find the corrections for low-temperature vapor-pressure thermometry using helium−3. The experimental apparatus consisted basically of several stainless-steel, pressure-sensing tubes, each connected to the same pressure container inside a cryostat. The upper, or warm, ends of the tubes were connected to differential pressure gauges outside the cryostat. The gauges measured the differences in warm end pressures between a 0.29-cm radius reference tube and tubes of 0.14-, 0.055-, and 0.0271-cm radii for a variety of cold end temperatures and pressures.
The results for saturated and unsaturated helium−3 and unsaturated helium−4 are identical but greater at the maxima than the values computed from the semiempirical Weber—Schmidt equation, which was based on measurements with unsaturated helium−4. However, experimental data for saturated helium−4 in the low-pressure region were much higher than the Weber—Schmidt equation and the other data. This disagreement was attributed to superfluid film flow. An outline of the derivation of the differential equation describing thermal transpiration is given in this report. Theoretical predictions for the high-pressure region of saturated helium−4 are in agreement with the experimental data. It is concluded that a revision of the Weber—Schmidt equation is needed for precision thermometry.
Energy Distribution of Energetic Atoms in a Gaseous Medium. I. Elastic Scattering of Particles by Spherical Potentials of the Form V(r) = (A1/r
S1) + (A2/r
S2)
Authors: Baer Michael , Amiel Saadia 
Published: January 2005

The energy distribution function n(E) for energetic particles in a gaseous medium is treated (classically) assuming elastic scattering governed by a two-term spherical potential of the form V(r) = (A1/rS1) + (A2/rS2). It is found that in the energy interval from 1 MeV to 1 keV, n(E) differs from that computed for a single-term potential, but it makes almost no difference whether the second (long-range) component is of an attractive or repulsive nature. In the low energy range (&lt;1 keV), if the long-range component is repulsive it almost completely screens the short-range one (which is always assumed to be repulsive). If it is attractive it lowers the values of n(E) in comparison with those obtained with a repulsive long-range term. The calculations also show that n(E) is almost independent of the initial energy of the incoming particles.
The results can be applied to the calculation of the yields of chemical reactions caused by energetic atoms such as fission fragments. One of the implications which emerges is that the yields of the reactions would not be influenced by the initial spectrum of the energetic atoms, since this has practically no effect on n(E) provided that the atoms behave like material points.
Ionization Cross Sections, Charge-Transfer Cross Sections, and Ionic Fragmentation Patterns of Some Paraffins, Olefins, Acetylenes, Chloroalkanes, and Benzene with 40–100-keV Protons
Authors: Collins J. G. , Kebarle P. 
Published: January 2005

The simple and charge-transfer ionization cross sections for Kr, Ne, N2, CH4, C2H4, and n-C4H10 were measured with 40–100-keV protons. The simple ionization cross sections are almost constant in this range, while the charge-transfer cross sections are roughly 40% of the total ionization at 40 keV and decrease to about 10% at 100 keV. The relative ionization cross sections (both simple and charge transfer) of a variety of molecular compounds (see title) were measured with 100-keV protons and found to be linearly related to the polarizabilities.
The mass spectra of a number of hydrocarbons were measured with 50- and 100-keV protons. The mass spectra are qualitatively very similar to spectra obtained with electrons of the same velocity (55 eV for 100-keV protons). This is to be expected from a qualitative extension of the Bethe—Born equation to ionization of molecular electrons. Since the mass spectra change little with velocity the American Petroleum Institute (A.P.I.) fragmentation patterns with 50–75-V electrons are a good guide to ionization by any (singly) charged particle with velocity higher than 108 cm/sec.
Fragments of high appearance potentials and doubly charged ions are considerably more abundant in the 40–100-keV proton spectra than at higher proton energies or in the electron-impact spectra. Conclusions can be made as to the charge-exchange mass spectra produced by particles with velocities in the range 108 cm/sec. These mass spectra are very different from charge-transfer spectra obtained at low primary ion energies. Thus there is little dependence on the recombination energy of the primary ion. The charge-transfer spectra seem not very different from the spectra produced by simple ionization. This means that the distribution of internal energies imparted to the new ion cannot be very different from that in pure ionization.