bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polarization of the Luminescence of Phenanthrene
Authors: Azumi T. , McGlynn S. P. 
Published: January 2005

The polarization of the luminescence emitted when a randomly oriented array of phenanthrene molecules is excited with polarized light is discussed. Considerable attention is devoted to various correction methods in an effort to establish a correct zero-polarization base line.
The polarization of the fluorescence excitation spectrum, the fluorescence spectrum and the phosphorescence spectrum of phenanthrene have been determined. The polarization of the fluorescence spectrum validates Platt's assignment of the first four singlet electronic states of phenanthrene as 1Lb, 1La, 1Bb, and 1Cb in order of increasing energy. The possible occurrence of one or two other electronic states in the same energy interval, as suggested by Zimmermann and Joop, is discussed. The phosphorescence emission is primarily polarized out of plane. The results further suggest that either two perturbing singlet states are mixed into the lowest triplet state, or that two perturbing triplet states are mixed into the singlet ground state by spin-orbital coupling; the Platt assignment of 3La for the lowest triplet state is supported. It has been found that polarization measurements are of considerable help in vibrational analysis, and may in certain cases uniquely determine vibrational types. A vibrational analysis of the fluorescence spectrum, phosphorescence spectrum and 1Lb absorption band is presented.
ESR Studies of Free Radical Decay in Irradiated Polyethylene
Authors: Cracco Francis , Arvia A. J. , Dole Malcolm 
Published: January 2005

A study has been made of the temperature and rates at which molecular hydrogen is evolved and free radical decay occurs when semicrystalline polyethylene, irradiated at liquid-nitrogen temperature, is warmed to room temperature. Hydrogen evolution and free radical decay roughly parallel each other. The temperature of half reaction is the same as the temperature of the gamma-maximum in the mechanical dispersion temperature curve. At constant temperature over the temperature range —71° to 41°C, the free radical decay is first order and the free radical concentration seems to decrease to a limiting value at each temperature. The first-order decay constants are approximately constant with temperature. The data are interpreted in terms of free radicals decaying in spurs. If a constant activation energy of 15 kcal mole—1 is assumed, the frequency factors decrease with rise of temperature. This decrease is interpreted on the basis of a decreasing probability of reaction for those free radicals that escape reaction at low temperatures, but react at higher and higher temperatures. An alternative model based upon the release of free radicals from traps as the temperature is raised is also discussed.
The reaction rate constant for free radical decay calculated from D—H exchange experiments agrees with that deduced from the ESR measurements. It is also concluded that the persistent free radical in polyethylene irradiated to moderate doses is the allyl free radical.
Proton Magnetic Resonance Spectra of 2-Pyridines. The Strong-Coupled AA′KL System
Authors: Kowalewski Valdemar J. , de Kowalewski Dora G. 
Published: January 2005

The 60-Mc/sec spectra of 2-chloro, 2-cyano, 2-bromo, and 2-acetyl pyridines are studied and analyzed as ABKL and AA′KL systems. The results are compared with the exact ABCD solution given by a computer. It is shown that if one of the coupling constants is greater than the corresponding chemical shift, the AA′KL approximation can give a good account of the frequencies of the lines of the experimental spectrum, but not so good for the intensities. The molecular parameters calculated with both approximate methods differ only some hundredths of a cycle per second from the values given by the computer.
An iterative method based on the use of average group frequencies and average splittings and improved by the use of the principle of least squares is fully described.
Chemisorption of Hydrogen on Cobalt
Authors: Abeledo Carlos R. , Selwood P. W. 
Published: January 2005

The change in saturation magnetization of small particles of cobalt upon adsorption of hydrogen has been measured. It has been found that the average hydrogen atom chemisorbed decreases the magnetization by about 0.5 Bohr magnetons. This result, together with previous results on the effect of hydrogen chemisorbed on nickel, suggests the existence of surface states associated with the adsorbed atoms and the surface metal atoms.
Simultaneous measurement of the magnetization of cobalt and adsorption of hydrogen in a low-field ac permeameter have shown that hydrogen chemisorbs on, and changes the magnetization of, cobalt at temperatures up to 500°C.
Motion of F Centers in KCl and KI
Authors: Gravitt J. C. , Gross G. E. , Benson D. K. , Scott A. B. 
Published: January 2005

The drift velocity of F centers in KCl and KI as a function of temperature is determined. The electric field producing this motion in the colored portion of the crystal is measured directly. The electric field in the uncolored region is found to be appreciably higher than the field in the colored portion.
The thermal ionization energy for F centers is found to be 2.4 eV for KCl and about 2.0 eV for KI.
Kinetics of the Gas-Phase Addition of HI to C2H4 and the Pyrolysis of Ethyl Iodide
Authors: Benson Sidney W. , Bose A. N. 
Published: January 2005

The addition of HI to C2H4 yields C2H5I at low temperatures and C2H6+I2 at higher temperatures. From 289° to 331°C the rate law is mixed—second order with C2H6+I2 as products. The rate is independent of added I2 and has a specific rate constant k2 (units, liter/mole-sec): logk2=8.52−(28900/4.575T). The pyrolysis of C2H5I from 330° to 392°C goes by a first-order process to C2H4+C2H6+I2. The first-order rate constant is given by (units, sec—1): logku=13.66−(50000/4.575T).
If it is assumed that both processes have the same rate determining step, namely the reversible dissociation of C2H5I, they yield an equilibrium constant in good agreement with independently calculated values of Keq for this dissociation. Under these conditions k1, the specific rate constant for the unimolecular split of C2H5I into C2H4+HI is given by ku/2. Arguments are presented to show that this common path involves the four-center molecular transition state rather than a radical disproportionation. The latter, however, may account for as much as 20% of the pyrolysis at 392°C.
Mass Spectrometry of Ions in Glow Discharges. III. Nitrogen and Its Mixtures with Hydrogen and Oxygen
Authors: Knewstubb P. F. , Tickner A. W. 
Published: January 2005

Ions in the negative glow and positive column of a dc glow discharge in nitrogen have been examined at a pressure of 0.4 mm and a current density of 0.03 mA/cm2. Mixtures of nitrogen with hydrogen (0.9%) and with oxygen (0.5% and 20%) were also used.
In addition to N2+ and N+, the ions N3+ and N4+ are prominent in the negative glow in pure nitrogen. They appear to be formed by N++2N2→N3++N2, N2++2N2→N4++N2, both of which proceed to an extent dependent on field strength.
With added hydrogen the ions N2H+ and NH4+ become important. N2H+ appears to be formed by at least two processes. The concentration of NH4+ is greatest in the tail of the negative glow where vibrational excitation is a possible factor and the residence time of ions is relatively long.
In the presence of oxygen the ions NO2+ and N2O+ appear, as well as O2+, but the most prominent oxygen-containing ion is NO+. The mechanism of formation of these ions is not definitely assigned but charge-transfer reactions may be important, as well as ion-molecule reactions which depend to some extent upon vibrational excitation, or upon residence time in the discharge.
Self-Diffusion and Impurity-Controlled Proton Relaxation in Liquid Ethane
Authors: Gaven J. V. , Stockmayer W. H. , Waugh J. S. 
Published: January 2005

Self-diffusion in liquid ethane, under its own vapor pressure, has been studied over most of the liquid range between the triple point and the critical point by means of the spin-echo technique. The activation energy for self-diffusion increases markedly from approximately 0.5 kcal/mole at 100°K to 3.5 kcal/mole at 300°K. The Stokes—Einstein relation is not well satisfied with either a constant molecular radius or a radius proportional to the cube root of the molar volume. The results are well correlated by a free-volume expression in which the free volume, defined as an actual volume minus the volume of the hypothetical liquid at 0°K, replaces temperature as the independent variable. The value of the hypothetical 0°K liquid volume resulting in best fit of the experimental data is less than that determined by extrapolation of the liquid specific volume to 0°K or that based upon best fit of experimental liquid viscosity data, but it is between a value based on a hard-sphere radius determined from gas viscosity and one derived from the second virial coefficient.
Proton spin-lattice relaxation measurements on the liquid ethane sample over a similar temperature range indicate that the relaxation is controlled by mutual diffusion of ethane and small amounts of dissolved oxygen, although the situation is somewhat complicated by temperature dependence of the distribution of oxygen between the two phases.
Absolute Infrared Intensities in Crystalline Benzene
Authors: Hollenberg J. Leland , Dows David A. 
Published: January 2005

The infrared spectra of polycrystalline benzene and fully deuterated benzene have been examined under high resolution. All ``u'' fundamentals (except ν16 of C6D6) have been observed and most crystal multiplets have been resolved, many to the full extent predicted. Accurate frequencies at two low temperatures are presented.
Absolute intensities have been measured at two temperatures for all fundamentals observed. An interference method has been used to measure sample thickness. The results are compared to existing data on three phases of benzene. The sum of all integrated intensities for a given molecule is empirically found to be independent of state of aggregation, and a sum rule expressing this fact is derived and criticized.
Evaluation of Lattice Sums in the Calculation of Crystal Spectra
Authors: Hexter R. M. 
Published: January 2005

Transition dipole—transition dipole exciton interaction lattice sums are shown to be amenable to evaluation by the general procedure of Nijboer and de Wette [Physica 23, 309 (1957)]. The practical evaluation of lattice sums in certain cubic and tetragonal crystals is then discussed, with emphasis upon the importance of the manner in which the spectrum of a molecular solid is obtained. The particle size of a polycrystalline sample is shown to strongly affect the value of the lattice sum. For single crystals, the orientation of the crystal and its transition moment directions with respect to the electric vector of the exciting field is of importance. Specific formulas relating crystal field splittings to dipole derivatives (in vibrational spectra) and to oscillator strengths (in electronic spectra) are given and tested with a variety of vibrational transitions of various cubic crystals as well as with the deformation mode of N3— in the tetragonal alkali azides. The oscilator strength of the 1∏←1Σ+ transition of CO is calculated to be 0.148, using some recent data on this spectrum obtained by Dressler. Splittings in the related transition in solid N2 are also discussed.
The results indicate that several conclusions in earlier calculations based upon dipole coupling models have been in error due to inadequate summation procedures. The results also indicate that ``exciton packets'' extend to the boundaries of the crystallites of which a polycrystalline sample is composed. Limitations to the general applicability of the summation procedures presented here are also discussed.
Effect of Pressure on Cyanine Spectra
Authors: Samara G. A. , Riggleman B. M. , Drickamer H. G. 
Published: January 2005

The effect of high pressure has been measured on the electronic spectra of a number of cyanine dyes dissolved in cellulose acetate. In general, a red shift was observed with pressure, which varied in magnitude with the chain length and electronegativity of the end group. The results are discussed in terms of Olszewski's resonance barrier model.
The peaks tended to broaden with increasing pressure, and to decrease in height. There was no significant change in the total area under the peak.
For a few cyanines the spectra of the crystals were also measured to study the effect of pressure on the Davydoff splitting. The degree of splitting increased with increasing pressure as was to be expected. There was a redistribution of intensity among the different branches with increasing splitting.
Kinetic Theory of Dense Fluids. XII. Electronic and Ionic Motion in Liquid He4I and Liquid He3
Authors: Davis H. T. , Rice Stuart A. , Meyer Lothar 
Published: January 2005

The mobilities of positive and negative charge carriers in liquid He3 and He4I are calculated and the resultant agreement with experiment is excellent. The negative carrier is taken to be an electron. Due to electrostriction and density fluctuations the effective mass of the electron is of the order of 100 electron masses. In addition, the disorder of the liquid leads to incoherences in the scattering of the electron from atomic pseudopotentials. The positive carrier is taken to be He2+. An extension of the theory of Rice and Allnatt, using the ideas introduced by Mazo and Kirkwood, leads to a formula for the mobility in terms of a quantum-mechanical temperature. Electrostriction increases the density about an ion and the dissipation arises about equally from the short-range repulsive forces and the Coulomb and van der Waals attractive forces. Both calculations involve only basic considerations and there are no adjustable parameters in the theory.
The computed effective mass of the negative carrier in He3 at 3.00°K and 2-atm pressure is 105 electron masses: The observed effective mass is 97 electron masses. For the negative carrier in He4I at 4.2°K and 1-atm pressure the computed and observed effective masses are 149 and 128 electron masses, respectively. In the case of the positive ion, the observed mobility at 2.2°K and 1-atm pressure in He4 is 5.6×10—2 cm2 V—1 sec—1 while the computed value is 5.2×10—2 cm2 V—1 sec—1.
The reader is referred to the Note added in proof for new comments and alternative interpretation of the electron effective mass.
Hydrogen—Deuterium Kinetic Isotope Effect, an Experimental and Theoretical Study over a Wide Range of Temperature
Authors: Sharp Terry E. , Johnston Harold S. 
Published: January 2005

An experimental study of the kinetic isotope effect for the reactionCF3+CHD3–|→F3C–H–CD3→F3CH+···→F3C–D–CHD2→F3CD+···has been carried out between 300° and 700°K, and also the Arrhenius parameters k=A exp (—E/RT) were obtained for the individual reactions. An especial effort was made to avoid systematic errors, and the precision obtained was good.
These data were combined with those of Tschuikow-Roux who studied the essentially same reaction between 1000° and 1800°K, and a detailed test was made of activated complex theory utilizing the method of London—Polanyi—Eyring—Sato with corrections for quantum mechanical tunneling. Sato's parameter was evaluated from activation energy of an analogous reaction so that kH/kD and A provided an unambiguous, nonadjustable test of theory. Because reactants were identical for both reactions, all the kinetic isotope effect depended on differences in the two activated complexes. The vibrational frequencies of the two nine-atom models of the complex were evaluated by a computer, programmed to E. B. Wilson's FG-matrix methods, and the effect of replacing the full nine-atom model by simpler five-, four-, or three-atom models was tested.
The Arrhenius A factor was enormously sensitive (factor of 103) to number of atoms assigned to the model; the three- or four-atom models gave A factors much too high, but the five- or nine-atom models with tunneling corrections were in fairly good agreement with experiment from 300° to 1800°K.
It is judged that if one evaluates a potential-energy surface, carries out a full vibrational analysis, and applies a reasonable tunneling correction, then one has in activated complex theory an expression analogous in logic and in usefulness to the perfect-gas theory; that is, broad over-all predictions can be made (in spite of readily identified conceptual flaws) but fine points will always be missed. Any quantitative value in the simplified versions of the theory is open to grave doubt.
Frequency Counting in Lattice Dynamics
Authors: Hwang Jenn-Lin , Wang Chen-Show 
Published: January 2005

A method for determining the frequency distribution of crystal lattices on the basis of Born—von Kárman theory is proposed. This is a full account of the previous work, and a generalization to the case of three-dimensional crystal lattices is described.
The procedure for obtaining the frequency distribution involves the following stages:
(1) One must solve the secular equation for determining the squared circular frequency ω2 along the edges of an appropriate part of the first Brillouin zone in the reciprocal lattice in the same manner as did Houston.
(2) One must find, in addition, a few important contours of constant frequency on the surface of the zone as accurately as possible.
(3) On the basis of (1) and (2), one can calculate or trace the desired contours of constant frequency on the surfaces by the proposed interpolation scheme [Eq. (1) or Eq. (2)].
(4) The contours of constant frequency in the inner planes can be calculated or traced by the proposed interpolation scheme described in Sec. IV.
(5) The volume V(ω2) enclosed by the surface of constant frequency means the number of modes of vibrations whose frequencies are less than ω2, and its magnitude may be computed by the proposed numerical or mechanical mean of integration described in Sec. V.
(6) V(ω2) thus calculated is fitted in an analytical form, and at this time the results of van Hove's analysis for singularities may be taken into account to obtain the actual shape of frequency distribution in the vicinity of singularities. A differentiation of V(ω2) with respect to ω2 yields the frequency distribution.
Applications to the two-dimensional and three-dimensional simple cubic lattices are made, and an excellent agreement with the exact frequency distributions calculated by Montroll and Rosenstock is obtained. The present method is thought to be far easier to handle than the conventional ones.
Field Desorption of Barium from Tungsten
Authors: Utsugi H. , Gomer R. 
Published: January 2005

The field desorption of Ba has been studied over a range of fields and coverages in an attempt to determine the mechanism of desorption and the charge of the desorbing species. It was found that adsorption seems to be polar but not ionic and that desorption of Ba++ occurs under our conditions. If this interpretation is correct α≅60 Å3 for the polarizability of adsorbed Ba results, close to the value for the free atom. The accessible field-temperature range is restricted by the onset of field-dependent surface diffusion, which was also investigated. It was found that positive fields have more effect on the activation energy Ed and pre-exponential term of the diffusion coefficient than negative ones. While a ½ αF2 dependence of Ed is compatible with the limited data obtained for negative fields, no simple behavior was found for positive ones, Ed going through a minimum of 0, accompanied by a drastic reduction in pre-exponential term. A tentative explanation in terms of a compensation effect is advanced.
Values for the zero field heat of adsorption were obtained over a wide coverage interval and agree well with those of Moore and Allison where overlap occurs.
Luminescence Decay Times: Concentration Effects
Authors: Yguerabide Juan , Burton Milton 
Published: January 2005

The optical properties (e.g., absorption spectrum, fluorescence spectrum, luminescence decay) of solutions of 2,5-diphenyloxazole (PPO) and p-terphenyl in benzene and cyclohexane are reported as functions of solute concentration. The absorption spectra of the solutions, when plotted as extinction coefficient vs wavelength, are unaffected by scintillator concentration, but the fluorescence spectrum of PPO solutions is affected in both intensity and shape. The luminescence decay of all solutions studied is nonexponential and can be resolved into the sum of two exponential decays. The fluorescence spectra and decay curves are affected by oxygen.
The interactions between excited and unexcited molecules and between unexcited molecules themselves and the effect which these interactions have on the optical properties of luminescent solutions are examined. The experimental results can be adequately explained by a mechanism which involves formation of transient dimers by an interaction between excited and unexcited molecules in addition to excitation of solute domains of unexcited solute molecules. It is shown that cage effects by themselves cannot account for the luminescent properties of the systems studied.
High-Pressure Mass Spectrometric Study of Reactions of Rare Gases with N2 and CO
Authors: Munson M. S. B. , Field F. H. , Franklin J. L. 
Published: January 2005

Studies have been made in a mass spectrometer at ionization chamber pressures of about 160 μ on mixtures of rare gases, R=He, Ne, Ar, Kr, and Xe, with N2 or CO. The ions R2+, ArN2+, KrN2+, XeN2+, ArCO+, KrCO+, XeCO+, N4+, and C2O2+ were observed in these mixtures as a result of reactions of excited rare-gas atoms. The addition of Ar to N2 enhances the formation of N4+ by reactions initiated by excited states of Ar; the addition of Ar or Kr to CO promotes the formation of C2O2+ through reactions initiated by excited states of Ar and Kr. Rate constants were determined for the reactionsArN2++N2=N4++Ark=1×−10cc/molecule−secKrCO++CO=C2O2++Krk=3×10−10cc/molecule−secat a repeller field strength of 50 V/cm. Other combinations of rare gases with N2 or CO show no such promotional effect on the formation of N4+ or C2O2+. Ratios of the rate constants for the formation of RN2+ and R2+ in rare-gas-nitrogen mixtures and for the formation of RCO+ and R2+ in rare-gas-carbon monoxide systems were also determined. At high pressures of N2 or CO alone the formation of N4+ or C2O2+ is observed, and the reaction is a bimolecular chemi-ionization involving highly excited N2 or CO. At still higher pressures these ions are formed by termolecular ion—molecule processes.
At sufficiently high electron energies there are formed in binary mixtures of N2 or CO with different rare gases the following ions: RC+, RN+, C2O+, CO2+ and N3+. The N3+ and RN+ ions are formed by the reaction of excited nitrogen molecule ions with R and/or N2, and the relative rates of these reactions were determined.
No compound ions between He or Ne and N2 or CO were observed under any of the conditions of these experiments.