bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared Spectra of Acetylene and Acetylene Derivatives Adsorbed on Alumina and Silica
Authors: Yates D. J. C. , Lucchesi P. J.
Published: January 2005

An infrared study of adsorbed acetylenes has revealed several features of the nature and orientation of the adsorbed species. Acetylene, deuteroacetylene, methyl acetylene, and dimethyl acetylene are strongly chemisorbed at room temperature on alumina. Weak chemisorption also occurs with acetylene, deuteroacetylene, and methyl acetylene. The strongly held acetylene is held normal to the surface, while the weakly held acetylene is held parallel to the surface. Similar effects occur with methyl acetylene, all of the strongly held molecules being attached to the surface by the acetylenic end. Both the strongly and weakly adsorbed dimethyl acetylene is adsorbed parallel to the surface. The sites responsible for the strong chemisorption of dimethyl acetylene are different from those active in the strong chemisorption of acetylene. With silica, no strong chemisorption occurred at room temperature for either acetylene or dimethyl acetylene. For both adsorbents, the interaction between the OD (and OH) groups of the surface and the adsorbates has been studied. Exchange takes place between the highest frequency OH groups on alumina and the strongly adsorbed C2D2. An OD group at the expected frequency was observed after the exchange had taken place. The remaining two types of OH groups on alumina did not appear to interact with the strongly held species, but only with the weakly held species. With dimethyl acetylene, the silica OD groups interacted to much the same degree as did the two lower frequency alumina OD groups.
Remarks on the Electronic Spectra and Structures of Compounds of Chromium and Benzene
Authors: Berry R. Stephen
Published: January 2005

An orbital level diagram and assignments of electronic spectra are given for the benzene-chromium compounds. These are based principally on symmetry arguments, atomic spectra and dichroism measurements. The problem of the energy involved in distorting benzene rings is also discussed.
On the Approximation of Zero Differential Overlap
Authors: Coulson C. A. , Schaad L. J.
Published: January 2005

The approximation of zero differential overlap is shown unreliable when applied to nonempirical calculations on HF and H2.
Spin-Orbit Interactions in fn Electron Configurations
Authors: Wybourne B. G.
Published: January 2005

Simple relationships can be shown to exist between the spin-orbit matrix elements of different fn electron configurations. These relationships allow a great reduction in the labor of calculating the spin-orbit interaction matrices for fn electron configurations. Several examples are given.
Electron Spin Resonance of an Irradiated Single Crystal of Urea Oxalate
Authors: Rao D. V. G. L. Narasimha , Gordy Walter
Published: January 2005

Free radicals produced in a single crystal of urea oxalate by gamma-irradiation have been investigated with the method of electron spin resonance. Only one species of free radical was observed at room temperature. Analysis of the resonance leads to the conclusion that the free radical has the form RCHOH and is probably[Complex chemical formula]with the electron spin density concentrated mostly on the CH carbon. The radical was found to be very stable: Its ESR pattern was observed, essentially undiminished, for more than a year after the irradiation. The g factor was found to be only slightly anisotropic, with principal values: gu=2.0024, gv=2.0048, and gw=2.0047. Couplings with two H nuclei are believed to be those indicated by H(1) and H(2), with principal elements of coupling, in gauss, of 15.7, 26.5, and 8.1 for H(1), and of 6.2, —0.3, and 8.3 for H(2). With irradiation and observation at 77°K, a different free radical was observed, one with hyperfine structure from only one H, similar to H(2).
Vapor Pressures of the Neon Isotopes
Authors: Bigeleisen Jacob , Roth Etienne
Published: January 2005

The ratio of the vapor pressures of Ne20 and Ne22 have been measured in the temperature range 16–30°K. An accuracy of about 1% in the logarithm of the vapor-pressure ratio has been achieved. The latter is checked by comparisons of (1) triple-point pressures, (2) equilibrium fractionation experiments, and (3) the entropy difference of the condensed phases with thermal measurements.

The Debye temperature for the solid derived from the ratio of the vapor pressures, 74.6°K, is in good agreement with values derived from the Debye-Waller temperature factor and theoretical calculations by Bernardes. The discrepancy between the characteristic temperatures derived from measurements of free energy with those from heat capacities is attributed to the role of the anharmonicity of the lattice.

It is shown that the difference in the thermodynamic properties of solid and liquid neon in the vicinity of the triple point can be attributed to the change in coordination number.
Paramagnetic Defects in Irradiated NH4ClO4
Authors: Cole Terry
Published: January 2005

Analysis of the electron magnetic resonance of x-ray damaged crystals of NH4ClO4 shows that the long-lived defects are NH3+ ions. Isotropic hyperfine splittings are found to be 54.6 Mc for nitrogen and 72.5 Mc for hydrogen. These radicals appear to be planar and execute restricted rotation at room temperature. A second transient defect is identified as ClO3.
Temperature-Dependent Chemical Shifts in the NMR Spectra of Gases
Authors: Petrakis L. , Sederholm C. H.
Published: January 2005

It is found that the chemical shifts of various gaseous compounds, using gaseous methane as a standard, vary with temperature. The slopes of chemical shift versus temperature at 50°C are tabulated for several compounds. This effect is ascribed to excitation of vibrational modes of the molecules, the protons in the excited molecules being differently shielded than the protons in the ground vibrational states. The data are interpreted to yield approximate chemical shifts associated with the excitation of various types of modes. NMR isotopic shifts are discussed on the basis of these data.
Analysis of Polarized Crystal Spectra. The Spectrum of Cobalt(III) Acetylacetonate
Authors: Piper T. S.
Published: January 2005

The analysis of broad bands in the polarized electronic spectra of transition metal ions in crystals is discussed. The band of cobalt(III) acetylacetonate due to the transition 1T1←1A1 is found to be split by the trigonal field into components at 16 200 cm—1 (1A2) and at 17 000 cm—1 (1E). The spectra indicate that the trigonal field of the free molecule is not appreciably distorted in the monoclinic crystal.
Anharmonicity in Unimolecular Reactions
Authors: Thiele Everett , Wilson David J.
Published: January 2005

The in-line vibrations of a linear, symmetric, triatomic molecule having Morse bond-stretching potentials are studied numerically. The significance of the results for unimolecular rate theory is discussed. Harmonic and weakly anharmonic approximations appear to be inadequate.
Nuclear Contribution to the Heat Capacity of Terbium Metal
Authors: Heltemes E. C. , Swenson C. A.
Published: January 2005

The heat capacity of terbium metal has been measured between 0.25° and 1.0°K. The high temperature data can be expressed as C=28R×10−3/T2 cal/mole-deg which is in excellent agreement with the paramagnetic resonance experiments of Baker and Bleaney on terbium ethyl sulfate. The data are compared with a Schottky formula for the heat capacity, assuming equal spacing between the nuclear hyperfine levels with an over-all spacing of Δ=0.45°K, corresponding to the high temperature expression above. The agreement is within experimental error except at the very lowest temperatures obtained. The effective field at the nucleus of the terbium atom can be calculated and is found to be Heff=4×106 gauss.
Extension of Stokes' Law for Ionic Motion to Include the Effect of Dielectric Relaxation
Authors: Boyd Richard H.
Published: January 2005

The suggestion made by Fuoss that dielectric relaxation induced by ionic motion in polar solvents contributes to the frictional force experienced by the ion has been treated theoretically on a macroscopic basis analogous to the Stokes' law treatment of the conventional hydrodynamic friction. An equation previously proposed by Fuoss on a semiempirical basis results from this treatment. Experimental dielectric relaxation times are shown to lead to an effect of the proposed magnitude.
Theoretical Interpretation of Carbon-13 Hyperfine Interactions in Electron Spin Resonance Spectra
Authors: Karplus Martin , Fraenkel George K.
Published: January 2005

A quantitative theory of the isotropic electron-nuclear spin interactions of carbon 13 in pi-electron radicals is presented and applied to the hyperfine splittings observed in the electron spin resonance spectra of these substances. The splittings arise from sigma-pi interactions which polarize both the 1s and 2s electrons. The 1s-orbital spin polarization is shown to contribute a term of negative sign with a magnitude comparable to that from the 2s electrons. For an sp2 hybridized carbon atom that is bonded to three atoms, Xi (i=1, 2, 3), the hyperfine constant aC has the form aC=(SC+ ∑ i=13QCXiC)ρπ+ ∑ i=13QXiCCρiπ,where ρπ and ρiπ(i=1,2,3) are the pi-electron spin densities on atoms C and Xi, respectively. The contribution of the 1s electrons is determined by SC and that of the 2s electrons by the Q's, where QBCA is the sigma-pi parameter for the nucleus of atom A resulting from the interaction between the bond BC and the pi-electron spin density on atom B. Calculations for a planar CHC2 fragment model yield SC= —12.7 gauss, QCHC=19.5 gauss, QCC′C=14.4 gauss, and QC′CC= —13.9 gauss.

The theory predicts both the magnitude and sign of the hyperfine splittings and is readily applied to a variety of compounds. Excellent agreement is obtained with the available experimental data. For the methyl radical, the measured C13 splitting is shown to be consistent with a planar model and limits the deviation from planarity to ≲5°. The theory provides a useful criterion for the validity of approximate wave functions that is illustrated by a comparison of various theoretical treatments for the naphthalene negative ion and triphenylmethyl. The sigma-pi interaction parameters are shown to depend on the bond length, the type of hybridization (including the angles between sigma bonds), and on the nature of the bonding atoms. For pi-electron systems, the results demonstrate that the magnitude of the sigma-pi exchange energy is a small fraction of the total energy. It is also noted that the proton parameter QCHH is somewhat larger in CHC2 than in CH3, which suggests a theoretical justification for some of the variation in the experimental ``QCHH'' required to fit measured proton splittings. The form of the theory is readily extended to the treatment of hyperfine splittings from nuclei other than C13.
Electrical Conductivity of Monocrystalline Cuprous Oxide
Authors: O'Keeffe Michael , Moore Walter J.
Published: January 2005

The electrical conductivity σ of single crystals of cuprous oxide was measured from 25° to 1100°C and at oxygen pressures PO2 from 10—5 to 760 mm. Except at very low PO2 the σ at all T is due entirely to positive holes associated with native defects (cation vacancies). The different activation energies which occur in different temperature regions can be quantitatively interpreted on this basis. For example, in 1.4 mm O2 and T above 750°C, σ=2.3×103 exp(−ε1/kT) with ε1=0.625 ev. This ε1=ε3+(ΔH/2), where ΔH is the heat of solution of an atom of oxygen and ε3 is the activation energy for motion of positive holes in an electric field (ε3=0.295 ev and ΔH=0.63 ev). Polycrystalline cuprous oxide doped with beryllium displayed a conductivity consistent with an increase in vacancies and decrease in free positive holes due to incorporation of Be2+.
Effect of Pressure on the Low-Energy Absorption Peak of Several Phthalocyanines
Authors: Riggleman B. M. , Drickamer H. G.
Published: January 2005

The effect of pressure has been measured on the intense low energy absorption peak in nine phthalocyanines in the solid state. In all cases the peak shifted to lower energies. The shifts were not large, but were very sensitive to the metal ion in the phthalocyanine. In general, the amount of shift was greater for ions having larger polarizability. The shift is attributed to perturbation of the excited π electron state due to dispersion interaction with metal ions in adjacent molecules.
Paramagnetic Resonance Spectra of Chromium III and Manganese IV Hexafluoride Ions: CrF63— and MnF62—
Authors: Helmholz Lindsay , Guzzo A. V. , Sanders R. N.
Published: January 2005

The paramagnetic resonance spectra of the ions CrF63— and MnF62— dilute solution in diamagnetic solids show fluorine hyperfine structure with both isotropic and anisotropic components. The anisotropic coupling constants are of the same order of magnitude as in the case of FeF63—, but have the opposite sign indicating important contributions of π-bonding electrons. Accordingly, the previously estimated degree of σ bonding in FeF63— is certainly too small, and estimates of the fluorine atomic orbital coefficients for the compound are made on the basis of the data presented here. The isotropic effects are to be understood in terms of configurational interactions. The isotropic coupling constants for the two ions have opposite signs and we are at present able to offer no rationalizations of this difference.
Quadrupole Coupling in Lithium Nitrate
Authors: Anderson David H.
Published: January 2005

The value of the Li7 quadrupole coupling constant in a single crystal of LiNO3 has been found to be 35.5±0.2 kc. It is expected that a reliable estimate of the quadrupole moment of Li7 may be made with the observed coupling constant and the point-charge field gradient, because of the good agreement for Na23 in the case of the isomorphous crystal NaNO3. The value found in this manner is ±0.069 b. The LiNO3 crystal was γ irradiated to facilitate the measurements, and a γ-irradiated crystal of NaNO3 was studied for comparison. It appears that the broadening of the Na23 satellite lines in the irradiated NaNO3 results from a relaxation process and not from a wide distribution of static field gradients, and it is concluded that γ irradiation has little or no effect on the Li7 coupling constant in LiNO3. A precise knowledge of the Li7 quadrupole moment would provide a test of the ionic model in LiNO3.
Tetrafluoromethane: P—V—T and Intermolecular Potential Energy Relations
Authors: Douslin D. R. , Harrison R. H. , Moore R. T. , McCullough J. P.
Published: January 2005

Measurements of the gas compressibility of tetrafluoromethane were made in the region, 0–350°, 15–394 atm. From these results, values of the compressibility factor Z=PV/RT, the second, third, and fourth virial coefficients, and the parameters of the Beattie-Bridgeman and Benedict-Webb-Rubin equations of state were derived. The virial coefficients were correlated by the Lennard-Jones (12, 6), Lennard-Jones (28, 7), Stockmayer, and Kihara intermolecular potential energy functions, and numerical values for the molecular parameters were obtained. One of the first tests of the theoretical fourth virial coefficient of the Lennard-Jones (12, 6) potential was made using the experimental fourth virial coefficients of tetrafluoromethane.
Low-Temperature Chemisorption. III. Studies in the Field Emission Microscope
Authors: Ehrlich Gert , Hudda F. G.
Published: January 2005

The dependence of adsorption upon surface structure has been examined with the field emission microscope. Nitrogen adatoms are found on all the planes of tungsten accessible to observation. Their rate of diffusion is fastest over the regions around the 111 pole; the barrier to migration over this area is only 20 kcal mole—1, compared to 35 kcal mole—1 for diffusion over the sharply stepped region surrounding the 100 pole.

A strong structural effect is observed for the weakly bound α state of nitrogen, unstable at T>400°K. This state is concentrated on and around the (111). By contrast, nitrogen molecules held at 79°K in the γ state are distributed without pronounced specificity for surface structure. However, the absence of diffusion in both these states suggests that the nitrogen is held at isolated, discrete sites. The γ state on tungsten somewhat resembles nitrogen adsorbed on nickel; for this system chemisorption is lacking at room temperature, but at 79°K molecules are bound with an energy of at least 5.5 kcal mole—1. At an even lower temperature, T∼20°K, an additional binding state, consisting of nitrogen physically adsorbed on top of the chemisorbed layer, is observed on tungsten. Diffusion out of this state occurs at T∼40°K with the formation of a sharp border, indicating immediate chemisorption of material spilling over the chemisorbed layer.

For the adsorption of carbon monoxide on tungsten no structural specificity appears in the field emission microscope. In addition to the primary chemisorbed state, the presence of weakly bound carbon monoxide is confirmed and it is shown that for neither state does dissociation occur. Both carbon monoxide and nitrogen lower the rate of electron emission from an initially clean tungsten surface. CO raises the work function by 0.5 ev at T∼300°K. In the γ state nitrogen also causes an initial work function increase of 0.1 ev. Nitrogen adatoms, however, are found to lower the work function, in contrast with the results obtained for other dissociating gases, as well as with previous work function measurements on nitrogen itself.
Solid State Photochemical Processes in Sodium Azide
Authors: King G. J. , Miller B. S. , Carlson F. F. , McMillan R. C.
Published: January 2005

Some properties of vacancy color centers produced by ultraviolet light in NaN3 at low temperature are studied by optical absorption and ESPR techniques. Thermal and optical bleaching experiments are discussed which allow one to correlate the optical bands with the ESPR data. The experiments are interpreted in terms of the de Boer model of the F center and the Seitz models of the F2 and F2+ centers. Calculations based on the continuum models for these centers are made and are found to be in favorable agreement with the experimental data. A mechanism for the creation of vacancies and the subsequent formation of the color centers based on photolytic effects is proposed.
Diffusion of Neon Isotopes in Fused Quartz
Authors: Frank R. C. , Swets D. E. , Lee R. W.
Published: January 2005

The diffusion of Ne20 and Ne22 through the walls of high-purity fused quartz hollow cylinders was studied using a mass spectrometer as a detecting device. The diffusion process was found to be relatively simple and fairly well described by Fick's laws. Diffusion coefficients and permeabilities were measured for both isotopes in the temperature range of 440° to 985°C. The D0's for Ne20 and Ne22 were (2.21±0.12) × 10—4 cm2/sec and (2.08±0.17) × 10—4 cm2/sec respectively. The activation energy for diffusion for Ne20 was 11 370±80 cal/g atom and the value for Ne22 was found to be statistically equivalent to this. The best estimate of the ratio of the D0's was 1.05±0.01. Solubilities were calculated by dividing the permeabilities by the diffusion coefficients. The heats of solution for the two isotopes were the same and equal to — 1950±150 cal/g atom. The significance of the isotope effect in diffusion is discussed.
An EPR Study of the Tetrafluorohydrazine-Difluoramino Equilibrium
Authors: Piette L. H. , Johnson F. A. , Booman K. A. , Colburn Charles B.
Published: January 2005

The EPR spectrum of the difluoramino radical (NF2) was observed to be a single broad line at a pressure of 20–40 mm of N2F4 and a temperature of 340–435°K. The peak-to-peak linewidth was observed to be 104 gauss with a g value of 2.010. From the temperature dependence of the line amplitude, the ΔH of dissociation of N2F4 was calculated to be 19.3±1.0.
Effect of Pressure on Crystal-Field Energy and Covalency in Octahedral Complexes of Ni2+, Co2+, and Mn2+
Authors: Zahner J. C. , Drickamer H. G.
Published: January 2005

The effect of pressure has been measured on the absorption spectra of NiCl2, NiBr2, Ni(NH3)6Cl2, CoCl2, CoBr2, MnCl2, and MnBr2. The pressure shifts in every case correspond to increase in crystal field strength. To account for the shifts in a quantitative manner it is necessary to presume that the Racah parameter B decreases with increasing pressure. This can be interpreted as an increase in covalency at high pressure.

From the data on MnCl2 and MnBr2 it is possible to establish limitations on the possible range of values of the parameter ε introduced by Koide and Pryce to describe covalency in transition metal complexes.
Infrared Spectroscopic Study of the Photolysis of Methyl Azide and Methyl-d3 Azide in Solid Argon and Carbon Dioxide
Authors: Milligan Dolphus E.
Published: January 2005

Experiments have been carried out on the photolysis of methyl azide and methyl-d3 azide at high dilution in solid argon (4.2°K) and carbon dioxide (∼50°K). Photolysis of these species in argon and carbon dioxide matrices results in the appearance of a number of new spectral features in the 3300–600 cm—1 region. The spectroscopic data for the photolysis products appear to be consistent with the identification of these species as methyleneimine (CH2=NH) and methyleneimine-d3 (CD2=ND).
Spectrum and Magnetic Properties of Hexagonal DyCl3
Authors: Crosswhite H. M. , Dieke G. H.
Published: January 2005

The absorption and fluorescence spectra of anhydrous DyCl3 were investigated and the levels up to 37 000 cm—1 above the ground state established. Conclusive evidence is presented that the levels below 15 000 cm—1 belong to the 6H and 6F multiplets. The Zeeman effects show considerable nonlinear interactions which follow quantitatively the existing theory. The 12 low levels and their electric and magnetic field splittings are reasonably well represented by the simplified theory with L-S coupling, with the approximate crystal parameters B20=A20〈r2〉 =89.8 cm—1, B40=—40.0 cm—1, B60=—23.3 cm—1, B66=253 cm—1.
``Thermal Conductivity'' and Chemical Kinetics
Authors: Brokaw Richard S.
Published: January 2005

A general expression is derived for the apparent ``thermal conductivity'' of reacting gas mixtures in which a single chemical reaction proceeds at a finite rate. In contrast to cases where reaction rates are either very high or very low, it is found that the ``thermal conductivity'' depends on the geometry and scale of the system—hence the quotes. This expression applies to the three geometries that can be described one-dimensionally: parallel plates, concentric cylinders, and concentric spheres. The results are limited to systems with small temperature differences, such as thermal conductivity cells, wherein reaction rate can be assumed constant. In addition to the scale and geometry, the ``thermal conductivity'' is determined by three types of constants having the dimensions of reciprocal length. Gas phase reaction is characterized by φ, which is proportional to the square root of the chemical reaction rate at equilibrium. (This is the total rate in either direction, not the net rate, which is, of course, zero.) Heterogeneous chemical reaction at the two bounding surfaces is characterized by ψ1 and ψ2, while χ1 and χ2 account for the temperature accommodation. The nature of the ``thermal conductivity'' is discussed for several specific systems. The expression is shown to approximate a numerical calculation of the effect of chemical reaction rate on stagnation point heat transfer. Experimental thermal conductivity data for the N2O4⇄2NO2 system are adequately described in terms of this theory. An upper limit for the rate constant for the bimolecular dissociation of N2O4 is estimated to be 5.3×109 cm3 mole—1 sec—1 at 296°K.
Compressibility of Simple Fused Salts
Authors: Stillinger Frank H.
Published: January 2005

It is pointed out that the isothermal compressibility of monatomic molten salts should nearly equal that for a hypothetical fluid of uncharged ion cores at the same over-all particle density as the salt. The validity of this relation is equivalent to verification of conjectures concerning the number-average correlation function for ion pairs in the melt. When the ion core forces are treated as those acting between rigid spheres, it is readily possible to predict the distance of closest approach for an anion-cation pair from experimentally determined compressibilities. The corresponding distances obtained in this manner for a series of molten halides are consistent with known ion sizes, and furthermore exhibit the proper homologous series trends.
Crystal Spectra of Metal Coordination Compounds. VI. Bis-Salicylaldiminato-Copper (II) and Bis-N-Methyl-Salicylaldiminato-Copper (II)
Authors: Ferguson J.
Published: January 2005

The polarized crystal absorption spectra of bis-N-methylsalicylaldiminato-copper (II) and bis-salicylaldiminato-copper (II) are reported. In each case measurements have been made with two different crystal faces. An analysis of the spectra shows that the ligand field is rhombic (D2h) and the in-plane symmetry axes do not lie along metal-ligand bonds but between them, as reported previously for the corresponding nickel compounds. The effect of copper-copper interaction in the crystal is briefly discussed.
Observation of Free Radical Kinetics in the Cyclohexane-Oxygen System
Authors: McCarthy R. L. , MacLachlan A.
Published: January 2005

Pulsed 6-Mev electrons from a Lineac have been used to initiate free radical reactions in the cyclohexane-oxygen system. The primary radical formed, cyclohexyl, is identified through EPR analysis of the irradiated solid sample at —100°C. In the liquid phase the cyclohexyl-peroxy radical is formed; its decay is observed spectroscopically over a period of 10 msec, and the second-order rate constants calculated. The principal reaction involving the disproportionation of two cyclohexyl-peroxy radicals requires zero (<1 kcal/mole) activation energy. The reaction rate constant is approximately 10—4 that for the diffusion-controlled process.
Organic Semiconductors: Aromatic Hydrocarbon Positive Ions in Solids
Authors: Blomgren G. E. , Kommandeur J.
Published: January 2005

Mixtures of aromatic hydrocarbons with antimony pentachloride in carbon tetrachloride have been studied by the methods of electron spin resonance and visible spectroscopy. The observation of a Tyndall effect and the spectroscopic properties show that the mixtures are colloidal suspensions. The visible spectra are characteristic of aromatic ions and a comparison of ion concentrations measured by visible spectroscopy and spin concentrations measured by spin resonance indicates that the aromatic ions in the solids are the only paramagnetic species present. The solids were found to exhibit high electronic conductivity.
Electron Spin Resonance Studies of Radicals Formed in Irradiated Polytetrafluoroethylene
Authors: Matsugashita Teikichi , Shinohara Kenichi
Published: January 2005

Radicals formed in irradiated PTFE were studied by means of ESR, using reactions with gases. In interpreting the experimental results, it was assumed that the radicals formed in PTFE primarily by irradiation were —CF2–ĊF–CF2— and —CF2–CF2·. The former were found to be stable, but the latter to be very reactive, at room temperature. A large part of the latter is thought to disappear by recombination, and only a small part to be oxidized by oxygen occluded in the polymer to form less reactive oxide radicals —CF2–CF2–O· even in a vacuum vessel. The radicals —CF2–ĊF–CF2— give a double quintet and —CF2–CF2–O·, a triplet in the spectrum. When gaseous oxygen was admitted to the irradiated PTFE, oxygenated radicals were formed. They will be —CF2–(CF–OO·)–CF2— and —CF2–CF2–OO·; the former giving asymmetrical signal termed OI, and the latter a singlet OII. The following reversible reactions were also studied: —CF2–ĊF–CF2—+O2⇌—CF 2–(CF–OO·)–CF2—, and —CF2–CF–CF2—+NO⇌—CF2– (CF–NO)–CF2. Some discussions are given on the reactions between irradiated PTFE and gases.
Transport Properties of Polar Gases
Authors: Monchick L. , Mason E. A.
Published: January 2005

A model is proposed for the calculation of viscosity, diffusion, thermal diffusion, and the translational part of the heat conductivity of dilute polar gases. It is assumed that the molecular-collision trajectories are negligibly distorted by transfer of internal rotational energy, and that the relative orientation of two colliding dipoles remains fixed throughout the significant portion of the collision trajectory around the distance of closest approach. For this model, the Chapman-Enskog theory retains its usual form, but the collision integrals which appear must be averaged over all possible relative orientations occurring in collisions. Collision integrals have been calculated for the Stockmayer (12–6–3) potential, [open phi](r)=4ε0[(σ0/r)12−(σ0/r)6+δ(σ0/r)3],for kT/ε0 from zero to 100 and for δ from —2.5 to +2.5, and averaged over all orientations (assumed equally probable). Sufficient collision integrals are tabulated that the convergence error of the Chapman-Enskog theoretical expressions is not a problem.

Experimental viscosities and dipole moments of a number of polar gases have been used to determine the potential parameters ε0, σ0, and δ, which were then used to calculate other properties for comparison with experiment. The over-all agreement between experiment and this model for polar gases is comparable to that of the Lennard-Jones (12–6) model for nonpolar gases.
Carbon-13 Hyperfine Splitting in the Electron Spin Resonance Spectra of Semiquinones and Cyclooctatetraene
Authors: Strauss Herbert L. , Fraenkel George K.
Published: January 2005

Measurements have been performed on the carbon-13 hyperfine splitting in the ESR spectra of a series of methyl- and chloro-substituted semiquinones and of the cyclooctatetraene anion radical. The splittings were observed from carbon-13 nuclei present in natural abundance (approx. 1%), and the carbon-13 satellites were distinguished from spurious low-intensity lines arising from side-reaction produced radical impurities by means of careful intensity measurements as well as other techniques. The largest observed carbon-13 splitting had a magnitude of 1.7 gauss, and in most spectra smaller splittings were found. The carbon-13 satellites were overlapped by the major lines in the spectra (arising from proton splitting), but after correcting the measured intensities for this overlap, good agreement was found between the predicted and measured intensities in those spectra in which a detailed analysis was possible. In the p-benzosemiquinone ion, a previously observed line of low intensity has been identified as a splitting arising from carbon-13 nuclei, and has been assigned, on the basis of intensity measurements, to the four CH carbon atoms. No splitting was found from the carbon atoms in the CO bonds of this compound, and it was concluded that the splitting is less than 0.6 gauss. Splitting constants tentatively identified with the methyl carbon atoms of the methyl-substituted compounds were in the neighborhood of 1.5 gauss. The splitting in the cyclooctatetraene anion indicates that the three sigma bonds attached to a carbon atom lie in a single plane. The experimental results are in agreement with the theory of carbon-13 hyperfine splittings recently developed by Karplus and Fraenkel. Comparison of theory and experiment indicates that these results provide a very sensitive measure of the pi-electron spin densities in the radicals. The valence-bond theory of the spin-densities in the methyl substituents is shown to be inadequate in its present form, but the molecular-orbital theory appears to give good agreement. This latter agreement is based on certain as yet unjustified assumptions, and therefore both theories require re-examination. The spectrum of the previously observed semiquinone ion formed from 2,5-dihydroxyquinone was interpreted in order to obtain an estimate, in conjunction with other data, of the hyperfine splitting at the carbon-13 nucleus of the carbon atom in a CO bond. The analysis also shows that the two CH carbon atoms in this compound have negative pi-electron spin densities.
Thermal Dissociation Rate of Hydrogen
Authors: Gardiner W. C. , Kistiakowsky G. B.
Published: January 2005

The thermal dissociation rate of hydrogen in xenon-hydrogen mixtures has been studied with shock-wave techniques over the temperature range 3000–4500°K. The observed density profiles were consistent with the rate constant expressions: H2+Xe=Xe+2Hk=1.8×1017T−12exp(−D/RT)cm3mole−1sec−1H2+H2=H2+2Hk=1.8×1020T−32exp(−D/RT)cm3mole−1sec−1H2+H=3Hk=1.2×1018T−12exp(−D/RT)cm3mole−1sec−1.
Effect of Pressure on the Optical Properties of Organic Phosphors
Authors: Gregg D. W. , Drickamer H. G.
Published: January 2005

The effect of pressure to 54 kbar has been measured on absorption spectra, emission spectra, and decay rates of four organic phosphors. For fluorescein and dichlorofluorescein the decay rate increases with increasing pressure. The emission spectrum consists of two peaks which approach each other at high pressure. Thus there appears to be an increased mixing of triplet and excited singlet states at high pressure.

For acridine yellow and orange the absorption spectrum shows a dimer and monomer peak. The dimer peak decreases rapidly in intensity with increasing pressure. At high concentrations the component decay rates are largely independent of pressure. At lower concentrations the decay rate becomes slower at higher pressure. Evidently the emission can be associated with the dimer.
Paramagnetic Excitons in Molecular Crystals
Authors: Sternlicht Himan , McConnell Harden M.
Published: January 2005

The possibility of using electron spin resonance to study paramagnetic excited electronic states of aromatic crystals is explored. Two limiting cases are considered: On the one hand the excitation energy moves from molecule to molecule by a diffusion process; on the other the triplet excitation is described by a Frenkel exciton. In either case intermolecular propagation of the triplet excitation is assumed to proceed through virtual triplet ionization states. The theory of the spin resonance of triplet excitons is developed in some detail. It is shown that there is only a weak dependence of the spectra on the k vector of the exciton wave, except when k is near regions of band degeneracies. Band degeneracies arise from time-reversal symmetry in benzene, naphthalene, and coronene crystals and occur on boundary planes of the first Brillouin zone. A spin Hamiltonian is calculated for these three aromatic crystals for most k vectors which are far removed from regions of band degeneracy. Two-line spectra (with no hyperfine structure), representing an average over the molecular sites in the unit cell, are obtained. Scattering of the exciton wave by lattice vibrations can cause line broadening and also can serve as a mechanism for spin lattice relaxation.
Kinetics of the Photolysis of Sodium Azide
Authors: Dodd Jack G.
Published: January 2005

The evolution of N2 from solid NaN3 during photolysis is shown to result from active sites located as deep as a few hundred lattice constants within the crystallites. These active sites diffuse to the free surface to produce N2, exhibiting a diffusion constant ∼10—15 cm2/sec. The absorption constant of NaN3 for 2537-A radiation is measured to be about 1.8×105/cm, and quantum efficiencies for photolysis are determined to be 0.040 for photolysis of the surface layer and 0.12 for equilibrium nitrogen evolution from a partially decomposed mass. The reaction is shown to be first order with respect to light intensity. A mechanism for photolysis is suggested based upon Thomas and Tompkins' exciton decomposition scheme.
Double-ζ SCF MO Calculation of the Ground and Some Excited States of N2
Authors: Richardson James W.
Published: January 2005

Self-consistent field wave functions for the ground and certain ionized and excited states of the nitrogen molecule, evaluated at the ground state internuclear distance, 1.094 A, are obtained in the molecular orbital (MO) form. The MO's are represented in the usual linear combination of atomic orbitals (LCAO-MO) form, but an expanded basis set is used which contains two each of 2s, 2pσ, 2pπ, and 2pπ̄ Slater-type atomic orbitals of differing nuclear charges. All electronic interactions are properly included and calculated without approximation. The computed total energy of the ground state is —108.785 a.u., which is 21.8 ev above the experimental value but 5.8 ev better than a previous result in which strictly atomic (Slater) orbitals were used in the conventional LCAO form. Excitation and ionization energies obtained by direct calculation of the respective states involved are in reasonably good agreement with experiment, though no better than those same quantities calculated from ground-state orbitals in the usual manner. The wave functions for the various states are analyzed and implications drawn regarding the changes wrought in atomic orbitals by bond formation; relevance to the semiempirical interpretation of quadrupole coupling constants is emphasized. Some conjecture about the correlation energy suggests that the ground-state energy obtained may be only a few electron volts above the true molecular Hartree-Fock energy.
The Polyhedral Clathrate Hydrates, Part 2. Structure of the Hydrate of Tetra Iso-Amyl Ammonium Fluoride
Authors: Feil D. , Jeffrey G. A.
Published: January 2005

The hydrate [i—C5H11]4N+·F—·38H2O belongs to a type of polyhedral clathrate structure in which the water molecules and the anions form the ``host'' structure and the cations are the ``guests''. The structural unit of the hydrogen-bonded clathrate cage is the H40O20 pentagonal dodecahedron. These dodecahedra are regularly associated in the crystal lattice by sharing faces, giving rise, therefore, to other polyhedra. In this hydrate, the other polyhedra are the tetrakaidecahedron and pentakaidecahedron, which form the cages enclosing the cations. A detailed three-dimensional single crystal structure analysis has been completed.
Strength of the N–F Bonds in NF3 and of N–F and N–N Bonds in N2F4
Authors: Kennedy Al , Colburn Charles B.
Published: January 2005

The heat of formation of the difluoroamino free radical is found to be 8.9±2.5 kcal/mole. The NF2–F bond in NF3 is the weakest bond in NF3 in contrast to ammonia where the NH2–H bond is the strongest bond. The strength of the NF2–F bond is 57.1±2.5 kcal/mole while the average NF bond strength in NF2 and N2F4 is 71 kcal/mole. The strength of the N–N bond in tetrafluorohydrazine, as determined from appearance potential data, is 20.7 kcal in excellent agreement with the value 19.8 kcal found by thermal measurements.
s-Tetrazine. II. Infrared Spectra
Authors: Spencer Glenn H. , Cross Paul C. , Wiberg Kenneth B.
Published: January 2005

To aid in the vibronic analysis of the n→π* visible absorption band systems of s-tetrazine vapor, infrared spectra of vapor, solution, and cold, solid film phases of natural and deuterated mixtures of s-tetrazine have been obtained. By use of the product rule and by correlation of the fundamental modes of s-tetrazine with those of benzene and the other azines, it is possible to make tentative vibrational assignments for all seven of the fundamental bands that would be expected to be infrared active in the wavelength region from 2 to 15 μ. However, the low-frequency modes 16a and 16b, Au and B1u, respectively, have not yet been observed, and the lack of knowledge of the frequencies of eight of the nine gerade modes (Raman active only) has prevented any definite assignment of combination bands. The observation of an interesting and peculiar phenomenon—what is believed to be the totally symmetrical mode 6a near 730 cm—1 in the solid film spectra of the various deuterated mixtures—is also reported.
Scintillation Properties of 9-Vinylanthracene
Authors: Heller Adam , Katz Dov
Published: January 2005

9-Vinylanthracene, for which good scintillation properties were predicted, was found to be a high-grade primary and secondary scintillator, capable of replacing the widely used 1,4-bis-(2-(5-phenyl)-oxazolyl)-benzene (POPOP).
NMR Chemical Shift of Hydroxyl and Hydronium Ions
Authors: Musher J. I.
Published: January 2005

The NMR absorption of protons in hydroxyl and hydronium ions is displaced about 10 ppm to low field from the proton-resonance absorption in water. This shift is roughly explained by a model locating all the ionic charge on the oxygen atom for both ions.
Billiard-Ball Collisions in the Reactions of Hot Hydrogen Atoms. Isotope Effect on the Hydrogen Displacement in Methane
Authors: Cross R. J. , Wolfgang R.
Published: January 2005

The nature of collisions leading to reactions of hydrogen atoms of high kinetic energy (in the form of recoil tritium) is investigated. Two extreme models, both originally due to Libby, are examined. One assumes very weak coupling by valence bonds in the molecule attacked, so that the reaction can be represented by a quasi-elastic atom-atom collision (billiard-ball model) and the other assumes strong valence bond coupling (epithermal model). Calculations on the billiard-ball (hard sphere) model of the reaction T*+CH4→H+CH3T leads to an estimate of its relative cross section as a function of energy. An isotope effect for reaction with CH4 and with CD4 is calculated and measured experimentally. Consideration of both the calculations and the experimental results indicate that the billiard-ball model is unimportant in the reactions of gas phase hot hydrogen (as recoil tritium), and that reactions occur nearly exclusively at less than 10–20 ev of kinetic energy, by mechanisms involving strong bond coupling. The possible importance of the billiard-ball model in the reactions of other hot atoms is briefly discussed.
Organic Semiconductors. V. Comparison of Measurements on Single-Crystal and Compressed Microcrystalline Molecular Complexes
Authors: Kronick Paul L. , Labes Mortimer M.
Published: January 2005

Utilizing specialized micromanipulative techniques, measurements of conductivity, activation energy of conduction, and Seebeck coefficient have been performed on charge-transfer complex single crystals. The results are compared with previous measurements on compressed microcrystalline materials.
Nuclear Relaxation in Gases: Mixtures of Methane and Oxygen
Authors: Johnson C. S. , Waugh J. S.
Published: January 2005

Three previously proposed mechanisms of nuclear relaxation in fluids are qualitatively discussed: (1) modulation of intramolecular fields by collisions, (2) transient, and (3) diffusively modulated dipolar interactions with paramagnetic impurities. It is shown that the dependence of T1 for the protons in methaneoxygen mixtures on composition, density, and temperature is adequately described by a superposition of these contributions to 1/T1, and that the magnitudes involved are consistent with a priori estimates. It is suggested that the spin-rotation interaction provides an important relaxation mechanism in both gaseous and liquid methane.
Ultraviolet Spectrum of Dibenzene Chromium Vapor
Authors: Berry R. Stephen
Published: January 2005

The ultraviolet spectrum of dibenzene chromium vapor has been observed under medium resolution conditions. At least three separate band systems are found, at least two of which display progressions of the totally symmetric vibration frequencies. Possible assignments are considered and compared with alternative level structures. It is concluded that the 3de2u level probably lies below the metal a1g orbital, and that term splitting may play a considerable role in determining the order of the excited states.
Proton Magnetic Resonance Spectra of Vinylmethylsilanes
Authors: Hobgood R. T. , Goldstein J. H. , Reddy G. S.
Published: January 2005

Proton magnetic resonance spectra of vinyltrimethylsilane and divinyldimethylsilane in dilute cyclohexane solution, at 40 Mc/sec, have been analyzed and the parameters compared with those obtained for alkylethylenes under similar conditions. The results indicate the presence of dπ—pπ structures in these silanes. Additional anisotropy effects due to the presence of Si may also be involved but are believed not to be solely responsible for the effects observed. All the vinyl coupling constants are considerably greater than those observed in the alkenes, but are comparable to values obtained for molecules containing vinyl-metal bonds.
Analysis of the Absorption Spectrum of YbCl3·6H2O
Authors: Eisenstein J. C.
Published: January 2005

The measurements of Dieke and Crosswhite on the absorption spectrum of YbCl3·6H2O are discussed. Their interpretation of the spectrum is extended by the identification of two of the weaker lines. The entire spectrum is considered on the basis of crystal-field theory, and the possibility of determining the parameters of the crystal-field potential is assessed. It is suggested that this compound may be ferroelectric (or anti-ferroelectric). The spin-orbit coupling constant is determined to be —2924 cm-1.
Ultraviolet Absorption Spectra of Alkali Metal Azides
Authors: Deb S. K.
Published: January 2005

The absorption spectra of thin films of NaN3, KN3, RbN3, and CsN3 have been measured at 295°, 77.3°, and 4.2°K in the wavelength range 1400 to 2200 A. The spectra show three well-defined absorption peaks, which have not been reported previously, and these were identified as the exciton transitions corresponding to n=1, 2, and 3. In thicker films and thin single crystals a new absorption band with multiple structure, having a maximum around 2225 A has been observed in all materials and this has been tentatively identified as due to a transition of low probability to a low-lying excited state of the azide ion. On irradiating the azides at 2400 A a weak fluorescence was observed in all cases.
Construction of Orthogonalized LCAO Wave Functions for the F Center from ENDOR Data
Authors: Gold Albert
Published: January 2005

A simple method for constructing orthogonalized LCAO wave functions for paramagnetic systems from electron spin resonance or electron nuclear double resonance data is presented. It is applied to the calculation of the ground-state wave function of the F-center electron in KCl, taking overlap of heterocentric atomic wave function explicitly into account. This function is built up of 4s and 4p valence functions centered on the six potassium ions nearest the vacancy. It is found that this simple form cannot reproduce the quantitative details of the charge distribution and that the inclusion of additional functions centered on more distant sites is necessary for a complete LCAO description of the center. However, it allows some of the qualitative features of the data to be understood.
An Analysis of the Infrared Absorption Spectrum of Am+3(5f6) in LaCl3
Authors: Gruber John B.
Published: January 2005

The polarized infrared absorption spectrum of single crystals of Am+3(5f6) in LaCl3 has been studied from 0.79 to 16.0 μ. In almost every instance the spectrum is sharp and completely polarized, and appears in definite groupings. Transitions from the ground level, 7F0, to excited levels of the ground term, 7F1, 7F2, 7F3, 7F4, 7F5, and 7F6 have been observed. For the particular point symmetry C3h that is consistent with experiment, magnetic-dipole transitions are observed from the 7F0 level to the 7F1 level, and forced electric-dipole transitions are observed to levels J = 2, 3, 4, 5, and 6.

A theoretical analysis is presented for the crystal-field split 7FJ levels. Using four parameters—A20〈r2〉=206 cm—1, A40〈r4〉=—94.1 cm—1, A60〈r6〉=—93.8 cm—1, and A66〈r6〉=1100 cm—1—excellent agreement is obtained between theory and experiment.
Charge Transfer Spectra of some Gold(III) Complexes
Authors: Gangopadhayay Arun Kumar , Chakravorty Animesh
Published: January 2005

Tetrahalo complexes of Au(III) show two intense bands in the ultraviolet. These are interpreted as charge-transfer bands; the transfer is from halogen p to gold d orbitals. The two bands are associated with pσ→dx2—y2 and pπ→dx2—y2 transitions. The iodo complex undergoes spontaneous reduction; reason for this is discussed. The ethylenediamine complexes of Au(III) also exhibit interesting charge-transfer phenomenon.