bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conformation of an Isolated Polymer Molecule at an Interface. II. Dependence on Molecular Weight
Authors: Roe Ryong-Joon 
Published: January 2005

The average conformation of polymer molecules adsorbed from very dilute solution is derived from the partition function Zn pertaining to an isolated molecule with at least one of its segments adsorbed. It is an extension of the treatment in the previous paper in which the generating function Γ (ζ) = ΣZnζn was derived, and from it the partition function Zn, in the limit of very large n, was obtained by the method due to Lifson. In the present paper Zn for finite n is obtained from Γ (ζ) by the use of Cauchy's theorem, the contour integration being evaluated by the steepest-descent method. The numerical result thus obtained agrees well, even for n=5, with the exact results evaluated by direct power series expansion of Γ (ζ) by a computer.
The results show that the conformation of adsorbed polymers can be classified into three distinct types according to the values of the segmental adsorption constant s. When s is large, the molecules lie flat on the surface and various intensive quantities are independent of the chain length n. When s is near the critical point sc, the fraction of adsorbed segments is proportional to n−½, in agreement with the earlier result by Simha, Frisch, and Eirich, but most of the desorbed segments are in the long-chain ends rather than in the internal loops. For very small s, the number of adsorbed segments becomes independent of n, and all the remaining segments are in the free-chain ends, with a negligible probability of loop formation.
The present results apply to the helix—coil transition of DNA with some modifications.
Generalization of Activated-Complex Theory. III. Vibrational Adiabaticity, Separation of Variables, and a Connection with Analytical Mechanics
Authors: Marcus R. A. 
Published: January 2005

In Part I, activated-complex theory was extended by including the possibility of a curvilinear reaction coordinate. A separation-of-variables approximation was made in the neighborhood of the activated-complex region of configuration space. In the present paper a more general yet simpler derivation of the final equation is given. It permits subsequent introduction of analytical mechanics in the above neighborhood in a variety of ways such as separation of variables, vibrational adiabaticity, or a method combining certain features of both, the separable—adiabatic approximation. The relationship of these methods is discussed.
Some numerical quantum- and classical-mechanical results obtained for transmission coefficients of nonrotating atom-transfer reactions (linear complexes), using computers, are interpreted in terms of an adiabatic approximation with reasonable agreement. Attention is also called to a modified WBK expression for the transmission coefficient, which generalizes the usual WBK formula in a simple way.
Pentacoordinated Molecules. VII. The Atomic Polarization and Dielectric Properties of PCl4F, PCl3F2, and PCl2F3 in Solution and in the Pure Liquid State
Authors: Holmes Robert R. , Carter Richard P. 
Published: January 2005

From measurements of the molecules PCl4F, PCl3F2 and PCl2F3 in cyclohexane solution, molar polarizations and refractions are calculated. The atomic polarizations for PCl3F2 (6.6 cc) and PCl2F3 (6.0 cc) approximate that found for PF5 (6.2 cc) and represent from 20%—40% of the induced polarization. The low-frequency bending vibrations of these trigonal bipyramids are shown to be the principal source of the high atomic polarization values. A value of 4.5 cc is estimated for PCl4F.
The temperature dependence of the dielectric constants and densities of the molecules in the pure liquid state also were measured. Application of the Onsager—Kirkwood theory gives dipole moments in good agreement with precise gas-phase values. A similar comparison is made for the moments from the solution study for this series of low dipole halides.
Structure of Sodium Aluminogermanate Melts with Na2O/Al2O3 Ratio Greater Than Unity
Authors: Riebling E. F. 
Published: January 2005

The viscosities and densities of several series of ternary sodium aluminogermanate melts with Na2O/Al2O3 ratios greater than unity have been determined for temperatures between 1050° and 1450°C. The viscosity data suggest that aluminum (III) takes part in network formation in the form of AlO4 tetrahedra for all compositions studied.
The molar-volume data for the 40-mole % Na2O melts and the 53- and 62-mole % GeO2 melts can best be interpreted in terms of a model that involves GeO4 tetrahedra, AlO4 tetrahedra, and v̄Na2O increases that are related to the Al2O3 contents. Molar volumes for 75-mole % GeO2 melts are interpreted in terms of a model that involves GeO6 octahedra. Similar data for the 25-mole % Na2O melts suggest the sudden elimination of GeO2 octahedra and a v̄Na2O minimum with increase of Al2O3 content. This is supported by the expansion coefficient and viscosity results. It is concluded that GeO6 octahedra are stable at 1300°C only within a 10-mole % Na2O semicircular ternary sweep of the 23-mole % Na2O binary point.
Theory of Phenomenological Coefficients in Solid-State Diffusion. I. General Expressions
Authors: Allnatt A. R. 
Published: January 2005

General expressions for the phenomenological coefficients in terms of jump probabilities have been derived for isothermal solid-state diffusion using linear response theory of the Kubo type. The assumptions required are: (a) the system evolves according to the master equation of a Markoff process, (b) a weak assumption about the general form of the perturbation to the transition probabilities in an applied field, (c) the detailed-balance principle as applied to a Markoff process for a system at equilibrium. The Onsager relations are obeyed.
The advantages of using these results as a starting point for detailed calculations compared with conventional methods are briefly discussed and further developments noted.
An appendix discusses the application of the same method to thermal diffusion.
Nuclear Quadrupole Resonance and Bonding in Crystalline Ammonia
Authors: Lehrer S. S. , O'Konski C. T. 
Published: January 2005

Nuclear quadrupole coupling constants (eQq) of 14N have been determined as a function of temperature for each of the isotopic species NH3, NH2D, NHD2, and ND3 in the crystalline state. The temperature dependences are explained, following a theory proposed by Bayer, in terms of an averaging of the electric field gradient (q) by torsional lattice motions. Frequencies and moments of inertia known from other spectroscopic studies of NH3 and ND3 were employed in the calculations, which also led to values for the quadrupole coupling constants without zero-point vibrations. These values turned out to be the same (−3.47 Mc/sec) within 1% for NH3 and ND3, showing that the different field gradients for the various isotopic species in the crystalline solid are well explained in terms of lattice motions.
Comparison of the vibrationless, or ``quasistatic'' values, with the coupling constants of the gaseous molecules (−4.08 Mc/sec) then gave the shift produced by the crystalline field, here called the quasistatic shift. This is large relative to the changes produced by isotopic substitution in the gaseous molecule. Calculations of the electric field and the field gradient produced at a given 14N nucleus by surrounding molecules in the known crystal structure were made to explain the quasistatic shift. Molecules containing the nearest hydrogens were treated as a distribution of four point charges, and the others, to a total of about 100, were taken as point dipoles. Both models were consistent with a crystalline dipole moment evaluated from the gaseous value and the known molecular polarizability, taking into account the reaction field of the lattice. The quasistatic shift was orders of magnitude too large to be accounted for by the direct field gradient of surrounding neighbors; it is better described in terms of a redistribution of electrons in the nitrogen p orbitals by polarization of the molecule in the crystal field.
Kinetics of the Thermal Decomposition of C2F6 in the Presence of H2 at 1300°—1600°K
Authors: Tschuikow-Roux E. 
Published: January 2005

The thermal decomposition of hexafluoroethane in the presence of hydrogen has been studied in a single-pulse shock tube in the temperature range 1300° to 1600°K. The reactants were highly diluted with argon, the composition ratios being Ar:H2:C2F6≃7500:17.4:1. The principal reaction products containing carbon were fluoroform and tetrafluoroethylene. A reaction scheme which accounts for these products is proposed and the first-order rate constant for the primary step C2F6→2CF3 is deduced: k1=4.3×1017 exp(−94 400±4000)/RT sec−1.
Accepting an activation energy of about 1 kcal/mole for the recombination of CF3 radicals leads to D(CF3–CF3)≃93±4 kcal/mole.
Polarization Effects in the Ionic Conductivity of Alkali Halide Crystals. II. Current—Time Dependence
Authors: Allnatt A. R. , Jacobs P. W. M. , Maycock J. N. 
Published: January 2005

The dc polarization of KCl at high temperatures has been investigated for the first time. Current—time curves may be resolved as the sum of a steady-state current and the time-dependent polarization current: the latter may be represented as the sum of two exponential terms. The relaxation times for these two processes are of the order of 40 and 250 sec at around 850°K. The Jaffé (constant-field) theory has been extended to include the case of low fields and the resulting equations have been solved numerically. The calculated relaxation times are an order of magnitude larger than those found experimentally. The reason for this discrepancy is probably the severity of the constant-field approximation.
The polarization is attributed to the slowness of the electrode processes compared to the velocity of the carriers in the bulk crystal and numerical values of the discharge parameter are derived. These are consistent with an activation energy for the electrode process of about 2 eV.
First and Second Triplets of Solid Benzene
Authors: Colson Steven D. , Bernstein Elliot R. 
Published: January 2005

Absorption spectra have been taken of the O2-perturbed first (3B1u) and second (3E1u) triplets of solid benzene at 4.2°K. Spectra of both C6H6 and C6D6 were obtained. The (0–0) bands of the first triplet occur at 29 674±25 cm−1 for C6H6 and 29 851±25 cm−1 for C6D6. For the second triplet they lie at 36 560 cm−1±50 for C6H6 and 36 784±50 cm−1 for C6D6. The result for the first triplet of C6H6 compares very favorably with Evans' gas-phase O2-perturbed spectrum. It is also in satisfactory agreement with Nieman's accurate phosphorescence measurements on isotopic mixed crystals of benzene which place the C6H6 (0, 0) band position in the crystal at 29 657.1 cm−1. Many precautions were taken to eliminate the possibility of mis identification of the second triplet. The observation that the O2-enhanced first triplet and the O2-enhanced bands in the 36 600-cm−1 region always appear together and with approximately the same relative intensities is considered to be the best evidence for the assignment. However, the rather broad structure obtained by the O2-perturbation technique does not allow all the uncertainties in the identification to be completely removed, nor does it allow a detailed study of this interesting state.
A detailed evaluation of the purity of the benzene is made, and a method is described for the preparation of material having ultrahigh spectroscopic purity. Crystals, up to 5 cm in length, of this very highly purified C6H6 and C6D6 were studied at 4.2°K to ascertain if the singlet—triplet absorptions could be seen in the absence of a perturbation. The long crystals showed some sharp and some broad (Δν≈150 cm−1) absorptions starting at 36 947±50 cm−1 in C6H6 and at 37 147±50 cm−1 in C6D6. The broad absorptions correlate reasonably well with the features assigned to the second triplet in the O2-perturbation experiments. The first triplet is too weak to be observed in the long-crystal experiments. The position of the second triplet lies about 3000 cm−1 above that given by the Pariser—Parr calculation. This places the second triplet about nine-tenths rather than half of the distance from the lowest triplet to the lowest excited singlet.
United-Atom Approximation Applied to Argonlike Molecules. II. PH2−, PH3, and PH4+
Authors: Banyard K. E. , Hake R. B. 
Published: January 2005

The united-atom treatment has been applied to the systems PH2−, PH3, and PH4+. For PH3 and PH4+, satisfactory values are obtained for the total molecular energy and ``breathing'' force constants when compared with experiment. The model gives theoretical bond lengths which are in good agreement with the observed values. Coherent x-ray scattering factors are presented for PH3 and PH4+ along with a discussion of the molar diamagnetic susceptibilities. The value of the proton affinity derived here for PH3 is found to be in general agreement with the experimental results.
Except for the considerable improvement in the proton-affinity calculation, the results obtained here are in keeping with the conclusions derived from our earlier work concerning the united-atom study of H2S.
Gas-Phase Radiolysis and Photolysis of Neopentane
Authors: Lias Sharon G. , Ausloos P. 
Published: January 2005

The photolysis of neo-C5H12—neo-C5D12 mixtures has been investigated at 1470 and 1236 Å. From the products formed in the absence and presence of NO or H2S, the occurrence of the following fragmentation processes could be derived: neo−C5H12*→CH4+iso−C4H8CH3+H+iso−C4H8CH3+CH3+C3H6.These modes of decomposition also prevail when neopentane is excited by collision with electrons accelerated by an electrical field applied during radiolysis. At 1236 Å, the relative probabilities of occurrence of Processes (1), (2), and (3) are approximately 1.0, 4.5, and 1.1.
From the isotopic analysis of the products formed in the direct and inert-gas-sensitized radiolysis of neo-C5H12—neo-C5D12 mixtures in the presence of NO, O2, or I2 as free-radical scavengers, it could be derived that the fragment ions C2H3+, C2H5+, C3H5+, and C3H7+ are formed and undergo hydride-ion transfer reactions with neopentane to form C2H4, C2H6, C3H6, and C3H8, respectively. Assuming that this is the only mode of reaction of these ions in the system, ion-pair yields of 0.028, 0.068, 0.062, and 0.015 are obtained for the above listed ions at a pressure of 30 Torr.
The propyl ion, which has a secondary propyl structure, undergoes a hydride transfer reaction with neopentane at a rate which is slower by more than one order of magnitude than the analogous reactions of the ethyl or allyl ions. It is observed that this relatively slow ion—molecule reaction is inhibited when an electric field is applied to the system, probably because of the collection of propyl ions on the cathode. In agreement with mass-spectrometric results, it is suggested that propyl ions are formed mainly as a result of the decomposition of the C5H11+ ion which is formed in the hydride-ion transfer processes.
The C4H9+ ion does not react with neopentane but does, under certain conditions, yield isobutene by an unspecified process. The ion-pair yield of isobutene increases with increasing pressure and with diminishing recombination energy of added inert gas.
In the direct radiolysis, the ion-pair yields of the fragment ions formed with appearance potentials above that of C4H9+ are seen to diminish when the pressure is increased, while, in the inert-gas-sensitized radiolysis, most of these ions increase with an increase of the recombination energy of the inert-gas ions, Xe+, Kr+, Ar+, Ne+.
Absorption Spectrum of Na and K in Rare-Gas Matrices
Authors: Meyer Beat 
Published: January 2005

The absorption spectrum of Na and K in Ar, Kr, and Xe matrices in the region from 2000 to 8000 Å has been studied as a function of temperature and, at 4°K, as a function of concentration. Observations on some spectra of Na in Ne are also included. The first member of the principal series, P212,12∘←S212, can be observed in all matrices. Higher members are weak and can, in most matrices, not be assigned. At alkali concentrations≥0.5%, strong additional absorptions are observed which seem to be due to alkali—alkali interaction.
Most transitions appear blue shifted and have triplet structure. The spectra are sharp in xenon but become increasingly diffuse in lighter rare-gas hosts. The line shape indicates fine structure in most absorption features. During the warm-up, the 2P←2S absorption broadens and shifts to the red. For a given ratio of observation temperature to melting point of host lattice, atomic absorption of the alkali metals seems to have the same linewidth in all of the observed matrices.
Study of Metal-Ion Binding to Nucleic Acids by 31P Nuclear Magnetic Resonance
Authors: Shulman R. G. , Sternlicht H. , Wyluda B. J. 
Published: January 2005

We have measured the 31P NMR in aqueous solutions of RNA (ribonucleic acid) and AMP (adenosine monophosphate) containing Mn2+ and Co2+ ions. Measurements of T1, T2, and Δω, the shift from γIH0, were made as functions of the metal-ion concentration and the temperature. Near-room-temperature linewidths were determined by the slow chemical exchange. At higher temperatures the Co2+ complexes enter the exchange-narrowed region where 31P shifts in the CoAMP system are observed.
The room-temperature value of T1 for CoAMP and CoRNA complexes, the high-temperature shifts of the CoAMP, and the high-temperature values of T2 in the MnAMP all independently determine the strength of the isotropic transferred hyperfine coupling A between the metal ions and the 31P nuclei. Within the experimental accuracy which ranges from ∼5% (for Δω) to ∼50% (for T1 measurements) the values of A agreed with the values derived from 31P NMR measurements in crystals of Mn3(PO4)2 and Co3(PO4)2. From the similarity of A in crystals and complexes, we conclude that Mn2+ and Co2+ bind to the phosphates of AMP and RNA.
Integrated Intensity Measurements on the Fundamental and First Overtone Band Systems of CO Between 2500° and 5000°K
Authors: Breeze J. C. , Ferriso C. C. 
Published: January 2005

Measurements have been made of the total absolute integrated intensities of the 4.7-μ fundamental and 2.4-μ first overtone band systems of CO at various temperatures within the range 2500° to 5000°K. The CO gas sample was studied in emission using a reflected shock wave to raise the sample to the high temperatures. Effects of vibrational relaxation, dissociation, and shock structure have been considered in the data interpretation.
Within the temperature range used in the present experiments, the integrated intensity of the CO fundamental band system remains constant. However, the integrated intensity of the CO first overtone band system shows a small increase with increasing temperature. The temperature dependencies of the two band systems are in agreement with the theoretical temperature dependencies. The present experimental results for CO extrapolated to STP are 289±29 and 2.3±0.3 cm−2·atm−1 for the total integrated band intensities of the fundamental and first overtone band systems, respectively.
Exchange Reactions with Activation Energy. I. Simple Barrier Potential for (H, H2)
Authors: Karplus M. , Porter R. N. , Sharma R. D. 
Published: January 2005

A quasiclassical procedure for the examination of the collision dynamics of atom—diatomic-molecule reactions with activation energy is introduced. By means of Monte Carlo averages over a large number of appropriately chosen three-dimensional classical trajectories, the total reaction cross section (Sr) and other reaction attributes can be determined as a function of the initial relative velocity (Vr) and the initial molecular rotation-vibration state (J, ν).
The method is applied to the exchange reaction resulting from a hydrogen atom and a hydrogen molecule moving on a simple barrier potential of the London—Eyring—Polanyi—Sato type. It is found that Sr is a monotonically increasing function of relative velocity that rises smoothly from a threshold at ∼0.9×106 cm/sec to its asymptotic value of ∼4.5a02 at ∼1.8×106 cm/sec. The zero-point vibrational energy of the molecule contributes to the energy required for reaction, but the rotational energy does not. The reaction probability, which depends on VR, ν, and J, is found to be a smoothly decreasing function of the impact parameter (b) with a maximum of ∼0.6 for b=0 at high velocities. By integration of Sr over the distributions of VR, ν, and J corresponding to temperatures between 300° and 1000°K, a rate constant that can be fitted to an expression of the form K(T)=ATα exp[—Ea°/RT] is obtained, where A, Ea°, and α(α=1.1762) are constants. This temperature dependence is analyzed and contrasted with the results obtained from an absolute rate theory treatment based on the same surface.
A detailed examination of the collision trajectories shows no evidence for a long-lived ``collision complex''; instead the results are best represented by a direct interaction model with an interaction time on the order of that required for the atom to pass unimpeded by the molecule. For reactive collisions, the transition configuration is nonlinear with average angles of 170° for VR=0.93×106 cm/sec and 150° for VR=1.30×106 cm/sec; for nonreactive collisions, the average angle is between 95° and 125°, but has no simple relation to VR.
Precise Measurements in the Infrared Spectrum of Carbon Monoxide
Authors: Plyler Earle K. , Benedict W. S. , Silverman Shirleigh 
Published: January 2005

New measurements have been made in the CO infrared spectrum in both emission and absorption, using a 15,000-line/inch grating spectrograph and a 7200-line/inch vacuum grating spectrograph. High precision in wavelength determinations was obtained by superimposing on the spectra emission lines in higher order of Hg, Kr, and A discharges. The measurements are believed accurate to ±0.02 cm−1. The observed lines in absorption are those of the 2–0 and 3–0 bands of C12O16, between R 30—P 29 and R 9—P 16, respectively; 27 lines of C13O16 and 10 lines of C12O18 have also been measured. In emission from oxy-acetylene and CO–O2 flames, over 300 lines in the 2–0, 3–1, 4–2, and 5–3 bands have been identified between 4360 and 4000 cm−1. The emission bands form heads in the R branch near J=50, and the 2–0 band shows resolved lines out to J=46 in both P and R branches.
The new measurements are in good agreement with earlier results at low quantum numbers, but show discrepancies at high numbers which result in slightly different values for the molecular constants, especially in ye and De. Our constants are in cm−12169.81 lim ωe       13.284 lim xeωe       0.010 lim yeωe       1.93130 lim Be   0.017543 lim α       4.5×10−6 lim γ      5.95×10−6 lim De      0 lim β
The observed isotope shifts of the 2–0 band origin for C12–C13 and O16–O18 are, respectively, 93.27±0.02 cm−1 and 101.03±0.05 cm−1, in good agreement with the calculated values.
The emission spectra permit the determination of rotational ``temperatures'' with an accuracy of ±5 percent and vibrational ``temperatures'' with an accuracy of ±10 percent. Thermal equilibrium between the two modes is observed in the outer cone of the flames, but in the region just above the reaction zone, the rotational temperatures are several hundred degrees higher than the vibrational values or the calculated equilibrium values.