bluuebunny/crossref_metadata_2025 huggingface dataset:
Internal Conversion in the Photochemical System 1,3-Cyclohexadiene: 1,3,5-Hexatriene
Authors: Srinivasan R.
Published: January 2005

The vapor-phase photochemistry of both 1,3-cyclohexadiene and 1,3,5-hexatriene can be treated as a single system since the photolysis of one gives rise to the other and the remaining products are common to both systems. In the present study, the pressure dependence of the products has been used to demonstrate that a classification of the reactions in this system as those that are common to both photochemistry and thermochemistry and those that occur only in the photochemistry parallels the behavior with pressure. It is argued that the first class of reactions which include 1,3,−cyclohexadiene+hν→benzene+H2→2C2H2+C2H4,→polymerization,1,3,5−hexatriene+hν→[1,3−cyclohexadiene]*→benzene+H2,occurs from a vibrationally excited ground-state molecule which originates from the initially formed excited singlet state by internal conversion. These reactions have been found to decrease with an increase in the pressure of the parent olefin or with the addition of inert gases such as xenon, carbon dioxide, propylene, or ether. Such data when coupled with the calculated lifetimes of the excited singlet states show that collisional quenching of the excited singlet-state molecules is unimportant at pressure below ∼8 mm. The trends observed with an increase in temperature support this general picture.
Kinetic Isotope Effect in Photochlorination of H2, CH4, CHCl3, and C2H6
Authors: Chiltz G. , Eckling R. , Goldfinger P. , Huybrechts G. , Johnston H. S. , Meyers L. , Verbeke G.
Published: January 2005

The relative rates of hydrogen and deuterium abstraction by chlorine atoms from H2–D2, CH4–CD4, and C2H6–C2D6 in direct competition have been studied by a mass spectrometer technique permitting direct determinations of rates. The pair CHCl3–CDCl3 was investigated by a substitution—addition competition with C2Cl4. Data were obtained between 300° and 475°K, and values of kH/kD ranged between 3.64 and 10.9 for CH4/CD4, 2.37 to 2.69 for C2H6/C2D6, 1.58 to 2.26 for CHCl3/CDCl3, and 4.7 to 8.9 for H2/D2. For the family of reactions involving C–H–Cl, an extensive series of model calculations were made by the ``bond-energy—bond-order'' method. The expected variation of activation energy with heat of reaction was computed and compared with experiment. The expected variation of kinetic isotope effect with both temperature and heat of reaction was computed for a range of conditions much wider than these experiments. Simple activated complex theory predicts several strong trends of kinetic isotope effect with heat of reaction. The data, in a general semiquantitative way, follow these predicted trends, but in terms of fine details the data do not fit the theoretical lines. In view of the known simplifications in activated complex theory, this agreement with broad trends is all that anyone should expect.
Multistate Mechanism for Homogeneous Ionic Polymerization. I. The Diastereosequence Distribution
Authors: Coleman Bernard D. , Fox Thomas G
Published: January 2005

A mechanism is proposed to explain the ``stereoblock'' structures which occasionally result from homogeneous anionic polymerizations [cf. J. Am. Chem. Soc. 80, 1768 (1958)]. The mechanism postulates that a growing polymer chain has two reactive states in dynamic equilibrium, both capable of adding monomer, but each with its own stereospecificity. The resulting diastereosequence distribution is calculated and it turns out to be non-Markoffian. It is shown that our ``two-state'' polymerization mechanism yields predictions about the dependence of NMR spectra on polymerization conditions, and as such is capable of experimental test. The case of more than two states is also discussed.
Relative Signs of Nuclear Spin Coupling Constants: A Refinement of the Double-Irradiation Experiment
Authors: Freeman R. , Bhacca N. S.
Published: January 2005

The application of a very weak perturbing radio-frequency field in nuclear magnetic double-resonance experiments in such a way as to irradiate just a single resonance transition is shown to give information about the relative signs of the spin coupling constants in systems of three or more spins. The method is not restricted to near first-order spectra and may be used even when several multiplets overlap. It has been applied to the determination of the relative signs of the couplings in 1,2-dibromopropane, and the results agree with those of Finegold, who used conventional analysis methods. The sign of a long-range coupling is reported.
Statistical Theory of the Error in Approximate Wavefunctions
Authors: Hall George G.
Published: January 2005

The theory of how a probability distribution may be estimated by sampling is applied to the problem of using approximate wavefunctions for quantum mechanical systems and estimating the errors involved. The most probable wavefunction of given mean energy is considered and some of its properties found. The energy variance, which gives a lower bound to the true energy, can be calculated. The theory is applied to the simple harmonic oscillator and the predicted relation between mean energy and variance is compared with the actual relations found using two different types of approximate wavefunction.
Energy Evolution in Pd2H below 1°K
Authors: Fritz J. J. , Maria H. J. , Aston J. G.
Published: January 2005

Energy evolution below 1°K has been observed in β-phase palladium hydride (formal composition Pd2H). The rate of evolution was strongly temperature-dependent below 0.1°K, but became temperature-independent between 0.1° and 1.0°K. It depended upon previous specimen history and was greatly reduced by annealing of the specimen below 50°K. For specimens kept below 1°K, the rate of energy production at a given temperature diminished with a half-life of about 8 h.

The results are explained semiquantitatively as a (spectroscopically forbidden) nuclear-spin conversion in quasi-molecular PdH4 units left behind in small concentrations when the lattice is cooled through the rotational transition (at 55°K) of β-palladium hydride. The temperature-dependence below 0.1°K appears to result from limitation in the rate at which the lattice can remove the change in librational energy associated with the conversion process.
Hydrogen—Helium Ion—Molecule Reactions
Authors: von Koch Helge , Friedman Lewis
Published: January 2005

The reactions producing HeH+ from gaseous mixtures of H2 and He subjected to electron impact in the ion source of a mass spectrometer have been studied. Ionization efficiency curves show practically all of the HeH+ to be formed by reaction of H2+ and He. Phenomenological cross sections were compared with values for the formation of H3+ from the H2+–H2 present in the ion source. The maximum value of the ratio of rate constants for HeH+ and H2+ formation computed from the experimental data was 28% of the theoretical ratio. If the heat of the endothermic reaction between H2+ and He is supplied from internal energy in H2+, then the rate constant should be computed in terms of the fraction vibrationally excited H2+ with sufficient internal energy to meet the needs of the reaction rather than total H2+ in the ion source. An estimate of the population of the excited vibrational state in H2+ produced from H2 by electron impact gives approximately 29% with enough energy to react. The translational energy dependence of the ratio of rate constants reveals a kinetic energy threshold for the HeH+ reaction of about 0.35 eV, but at higher ion kinetic energy there is strong evidence for heat of reaction coming primarily from internal energy in H2+.

An attempt was made to use the HeH+ reaction as a probe to investigate the distribution of excited H2+ produced from CH4 by electron impact. A third-order process giving HeH+ was discovered in this system. Indications of a larger yield of H2+ with sufficient energy to react with He were obtained.
Direct Transformation of Hexagonal Boron Nitride to Denser Forms
Authors: Bundy F. P. , Wentorf R. H.
Published: January 2005

Hexagonal, graphitelike boron nitride may be changed directly into the zincblende cubic form reported earlier or into a new wurtzite form by the application of static high pressures. No catalyst appears to be necessary. At high temperatures, between about 2500° and 4000°K, the zincblende form is favored; at lower temperatures, down to 300°K, the wurtzite form is favored; frequently both forms appear together. The minimum pressure required for the transformations is about 115 kbar at 2000°K; somewhat higher pressures, of the order of 130 kbar, suffice at higher and lower temperatures. The crystallites of the dense phases are small but give good x-ray diffraction patterns from which the crystal structures can be determined.
Temperature and Carathéodory's Treatment of Thermodynamics
Authors: Turner Louis A.
Published: January 2005

It is shown that the existence of functions having the properties of temperature emerges as a consequence of the basic assumptions made by Carathéodory, with omission of the zeroth law. It is unnecessary to introduce the zeroth law and empirical temperature into the arguments which lead to the definition of entropy and thermodynamic temperature.
Mutual Diffusion Coefficient of the Polar Gases: Ammonia and Diethyl Ether
Authors: Srivastava B. N. , Srivastava I. B.
Published: January 2005

The interdiffusion coefficients for the mixtures of polar gases NH3–(C2H5)2O have been measured at five temperatures over a 15°—65°C range by the two-bulb technique of Ney and Armistead. A sensitive differential thermal conductivity analyzer was employed for gas analysis. The experimental D12 values have been utilized to determine the potential parameters for the unlike interactions on the Stockmayer (12:6:3) model. The usual combination rules for the polar—polar interaction have been found to be inadequate.
Electronic Excitation Transfer and Relaxation
Authors: Robinson G. W. , Frosch R. P.
Published: January 2005

One purpose of this paper is to point out that so-called intermolecular resonance transfer, intermolecular nonresonance transfer, and intramolecular electronic relaxation in solid media are simply all special cases of radiationless transitions between nonstationary states of the entire system of molecules plus environment. Intermolecular resonance transfer is also a special case of the pure crystal exciton problem. The theoretical results from a previous paper are applied to radiationless transitions in π-electron systems, and the importance of the Franck—Condon factors is emphasized. One role which the vibrational factors play in these processes is illustrated by the large isotope effects which can arise when the radiationless transition converts a large amount of electronic energy into vibrational energy of the system. Quantitative calculations are made of the radiationless transition probability for 1B2u→3E1u(S1→T2) and 1B2u→3B1u(S1→T1) ``intersystem crossing'' in C6H6. It is further shown that the 3B1u→1A1g(T1→S0) and 1B2u→1A1g(S1→S0) processes and other similar processes are slow because of the small vibrational factors which accompany the large energy gap between initial and final electronic states. Calculations cannot rule out the relative importance of the S1→S0 radiationless transition compared with fluorescence and singlet—triplet nonradiative processes. An empirical method by which the Franck—Condon factors may be ascertained from the electronic-energy gaps in π-electron molecules is presented, and the results are used to estimate radiationless transition probabilities for a number of systems. The enhancement of multiplicity forbidden radiationless transitions by a heavy-atom environment is treated, and, in the case where the environment is a solid rare gas, a third-order mechanism accounts for the observed effect. Temperature effects and other kinds of environmental effects upon nonradiative transitions are also dealt with. It is shown that the use of high-energy excitation may increase, but never decrease, QP/QF, the relative quantum yields of phosphorescence to fluorescence. Radiationless transitions for the interesting case of azulene and the enhancement by a heavy-atom environment of the triplet—triplet emission spectrum of this molecule are discussed. Many needed experiments are suggested throughout the paper.
Microwave Spectrum, Spectroscopic Constants, and Electric Dipole Moment of Li6F19
Authors: Wharton L. , Klemperer W. , Gold L. P. , Strauch R. , Gallagher J. J. , Derr V. E.
Published: January 2005

Transitions between the J = 1 and J = 0 rotational states of Li6F19 have been measured by means of the molecular-beam electric resonance method in the four lowest vibrational states. By this means the rotational constants of Li6F19 were determined. These enabled one to properly assign the rotationally resolved infrared vibration—rotation spectrum of Li7F19 observed by Vidale and to determine the correct vibrational constants. Transitions between the M = 0 and | M | = 1 orientations of the J = 1 rotational state of Li6F19 in the four lowest vibrational states in a strong electric field were measured to high precision, which enabled one to determine the dipole moments accurately and to observe a nonlinear variation of dipole moment with vibrational state. The molecular constants obtained for Li6F19 were: Bv=45.2308111−0.7223089(v+12)+0.0058270(v+12)2±0.0000050 Gc,ωv=964.07−8.895(v+12) cm−1,re=1.563892±0.000050 Å,μv={6.28446+0.08612(v+12)+0.00060(v+12)2}±0.00100 D.
Influence of Structure on Gaseous Products from C11 Recoil Reactions in C6 Hydrocarbons
Authors: Rack Edward P. , Lang Charles E. , Voigt Adolf F.
Published: January 2005

Results are presented on the yields of gaseous products resulting from recoil reactions of C11 in various C6 hydrocarbons: benzene, n-hexane, 2-methylpentane, and 2,2-dimethylbutane. The C11 was produced by the C12 (γ, n)C11 reaction in the target molecule. The radiation time and dose were varied, and iodine was added as a scavenger. Comparison was made with similar results on cyclohexane. In all cases, acetylene is the most abundant product, but as branching in the molecule increases, other products, principally ethylene and ethane, become increasingly important. The results are in agreement with a mechanism involving the insertion of an energetic C11 or C11H group into a C–H bond, followed by bond rupture in the resulting intermediate.
Vibrational Effects in Molecular Exciton Motion Along a Polymer
Authors: Goad Walter
Published: January 2005

Two aspects of the effects of molecular vibrations on exciton motion are considered: First is the reversible evolution of an electronically excited state of a system of molecules, in each of which many vibrational excitations are possible upon electronic excitation. Vibrational structure of the ground state is ignored. The reversible, or coherent, propagation is found to depend on the parameter 2πν2δ—1, where ν2 is the intermolecular coupling energy of individual vibronic levels, and δ is the spacing of vibrational levels. Second is the irreversible effect of vibrational relaxation in individual molecules through interaction with the solvent. The result of a heuristic treatment is that simple diffusive motion occurs if the relaxation time is much smaller than 2πhδ—1, and the diffusion coefficient is calculated. Throughout, we deal with an infinite, linear array of molecules.
Statistical Computation of Configuration and Free Volume of a Polymer Molecule with Solvent Interaction
Authors: Mazur Jacob , Joseph Louis
Published: January 2005

A lattice model of a polymer molecule with excluded nearest-neighbor contacts is of particular interest since it can serve as a model for polymer systems in which the interactions between the polymer and its environment are incorporated. These interactions result in the partial overlapping of polymer segments, and consequently the volume fraction of detached polymer segments exceeds the volume fraction of connected polymer segments. It is found that the contraction in volume per segment is independent of the number of polymer segments n. The mean-square end-to-end distance is found to be approximately proportional to nγ for sufficiently large n, where γ is the mean-square polymer index, in agreement with Wall et al. The value of γ is shown to be considerably lower than the previous estimates of this parameter for a three-dimensional lattice with excluded nearest-neighbor contacts. The decrease in the value of γ from previous estimates is due to the cloverlike structures which result from the addition of a single step to a permissible configuration.
Influence of Vibration—Rotation Interaction on the True Vibrational Wavefunctions
Authors: Jain D. C.
Published: January 2005

A method is suggested for obtaining the true vibrational wavefunctions corrected for vibration—rotation interaction by the application of perturbation theory. For this purpose the harmonic oscillator wave-functions have been considered to be perturbed by the potential V′=[U(r)−V0(r)]+[ℏ2J(J+1)/2μr2],where U(r) is the true potential, V0(r) is the harmonic oscillator potential and [ℏ2J (J+1) /2μr2], the vibration—rotation interaction term.

Expressions are given for the integrals ∫ ψ̄v′J′ψv′′J′′dr  and   ∫ ψ̄v′J′ξψv′′J′′dr,which occur in the transition-moment matrix elements for electronic bands. Similar integrals occurring in the dipole-moment matrix elements for vibration—rotation bands, can also be evaluated by using these wavefunctions.
Collision Lifetimes and the Thermodynamics of Real Gases
Authors: Smith Felix T.
Published: January 2005

The perfect gas law p/kT=n=Σini (where ni is in molecules per cm3) is inadequate for describing real gases because of the interactions during collisions. By a simple intuitive argument, these interactions can be taken into account exactly if you know the collision lifetimes. The product of collision rate and lifetime gives the concentration of transient collision complexes, which must be considered in the perfect gas law along with the stable species. As a result, the complete virial expansion is obtained, in both quantal and classical mechanics. The argument leads further to a new form for the partition function which includes the continuum as well as bound states. From this all the thermodynamic functions can be obtained.
Interactions in Polar Media. I. Interparticle Interaction Energy
Authors: Marcus R. A.
Published: January 2005

Using permanent plus induced charge distributions on particles a Hartree method is used to compute the polar contribution to the interparticle interaction enerby. Each particle may be a single molecule or a coll?ction of molecules, a whole electrode or an entire medium for example. The total interparticle interaction energy is taken to be the sum of this polar term and of an interparticle electron correlation term. The second of these includes effects due to interparticle London dispersion and exchange repulsion forces. A symmetry property associated with a quantum mechanical operator characterizing the induced charge distribution is obtained in a compact way using a projection operator. The polar term is also calculated from classical electrostatics and shown to be the same as the one above. The present work is a generalization of earlier treatments in which the particles were single molecules interacting via permanent and induced dipoles.

An application of this work is the more general formulation of theories associated with polar interactions in condensed phases, such as the theory of electron transfer rates in solution and at electrodes, and the theory of electronic spectral shifts and band broadening of polar solutes in polar media.
Extended Basis-Set LCSTO—MO—SCF Calculations on the Ground State of Carbon Dioxide
Authors: McLean A. D.
Published: January 2005

Extended basis-set SCF—STO—MO wavefunctions for the ground state of CO2 are reported. In particular, the effect of doubling the number of 2pσ basis functions and the effect of changing their orbital exponents has been investigated, together with the effect of addition of 3dσC basis functions. The effect of expanding the π basis set by addition of extra 2pπC basis functions and 3dπO1, O2 basis functions is also shown. A wave-function using the best σ basis set together with the best π basis set used in these calculations would give a molecular energy of approximately 9 eV below that obtained from a `best atom' minimal basis-set calculation. This is to be compared with the estimated Hartree—Fock molecular energy which is approximately 24 eV below the ``best atom'' minimal basis-set value. This highlights the importance of the choice of basis functions and minimization of the total energy with respect to orbital exponents in the case that the number of basis functions out of which MO's can be constructed is limited.

The quadrupole moment of CO2 is computed from two of the wavefunctions reported.
Some Comments on Electrostatic Volumes and Entropies of Solvation
Authors: Whalley E.
Published: January 2005

The volume of solvation of an ion with dipole and quadrupole moments in a cavity in a continuous dielectric has been examined. In highly polar solvents like water, the compression of the cavity due to the electrostatic interaction contributes much more to the electrostatic volume of solvation than does electrostriction of the solvent, if electric saturation is not important. The importance of quadrupole moments on transition states has been emphasized. The compression of the ion has an unimportant effect on the free energy, entropy, or enthalpy of solvation, but the thermal expansion of the cavity containing the ion contributes significantly to the electrostatic entropy of solvation.
Gaseous Diffusion in Porous Media. III. Thermal Transpiration
Authors: Mason E. A. , Evans R. B. , Watson G. M.
Published: January 2005

A previously proposed model for the diffusion of gases in porous media at uniform and nonuniform pressures has been extended to allow for temperature gradients. The porous medium is visualized as a collection of ``dust'' particles constrained to remain stationary in space. As before, by formally treating the ``dust'' particles as giant molecules, it is possible to cover the entire range of intermediate mechanisms from the Knudsen to the normal region by varying the mole fraction of the real gas. For binary systems (a single gas and ``dust''), the phenomenon of thermal transpiration is accounted for by the model in a consistent way for all aspects which are diffusive in character but, as before, needs modification at high pressures by the addition of an expression to account for the viscous backflow. With this modification, an equation is obtained which describes thermal transpiration over the entire pressure range. This equation discloses two new relationships not previously noticed: one between the maximum in the thermal transpiration curve and the Knudsen minimum in the permeability curve, and one between the height of the thermal transpiration maximum and the translational heat conductivity of the gas.

It was found that it was possible to extend the model to include capillaries as well as porous media. This extension disclosed that the relationships applicable to porous media would also describe the analogous behavior that occurs in capillaries with definite geometry. The capillary results reproduce previous semi-empirical and empirical equations of Weber and Liang for thermal transpiration, and the permeability equation of Knudsen. The present equations, however, have fewer adjustable parameters than do the previous equations. A simple connection, not previously mentioned, between Weber's and Liang's equations was also noticed: Liang's equation is really a special form of Weber's equation written in a differential-approximation form.

A remarkable feature of the results, as applied to capillary systems, is that one can calculate rotational relaxation times in gases from the height of the thermal transpiration maxima, which suggests much simpler experimental techniques than those previously employed for the measurement of this phenomenon.
Calculation of Mean Atomic Positions in Vibrating Polyatomic Molecules
Authors: Bartell L. S.
Published: January 2005

A new method is described for calculating effects of anharmonic vibrations on bond lengths and angles in polyatomic molecules. It is shown that the quantum mechanical analog of Newton's second law of motion leads to simple equilibrium conditions from which it is possible to calculate mean displacements of atoms from positions of minimum potential energy. The method resembles the standard first-order perturbation method insofar as it relates mean displacements to mean-square displacements which can be computed from the zeroth-order harmonic problem. It gives a much more direct calculation, however, circumventing the laborious nonlinear transformations between internal and normal coordinates encountered in the perturbation method. Advantages and limitations are discussed.

Applications to several problems are outlined briefly, including isotope effects and effects of temperature on mean molecular structures. The approach, extended to crystal lattices, is shown to account for Grueneisen's relation which correlates thermal expansion and heat capacity. Numerical results of calculations are presented for H2O, D2O, NH3, and ND3, comparing the present method with other methods. Contrary to prevailing opinion, the mean apical angle of NH3 appears to be smaller than that of ND3.
Slater—Condon Parameters from Spectral Data
Authors: Hinze Jürgen , Jaffe H. H.
Published: January 2005

Slater—Condon parameters have been fitted by least-squares methods, as far as spectroscopic data are available, for all the neutral atoms of the first three periods of the periodic system, and for their isoelectronic mono-positive ions, and for the isoelectronic di- and tri-positive ions of the first two periods. Separate evaluations were performed for each configuration, and for pooled data from all configurations. It is concluded that the approximations involved in the Slater—Condon method are at least as serious as the further approximations introduced by pooling of data from several configurations.
Absolute Intensity Measurement for the NO Fundamental at 5.3 Microns
Authors: Schurin B. , Clough S. A.
Published: January 2005

The intensity of the fundamental vibration—rotation band of NO has been measured using the Wilson—Wells—Penner—Weber self-broadening technique. The reported value is 111±7 cm—1/cm atm at 273°K, considerably higher than some previously published values, and in marginal agreement with other less precise previous determinations.
Field-Emission Study of Carbon Monoxide on Tantalum
Authors: Klein Ralph , Leder Lewis B.
Published: January 2005

Adsorbed carbon monoxide shows three states of binding on tantalum. The weakest of these is desorbed at temperatures above 125°K with no observable surface migration. The bonding with the surface is of the van der Waals type. This is in contrast with the second state, which is desorbed above 650°K. The third state is dissociated before desorption to give the oxygen-on-tantalum pattern. Surface migration involving the second adsorbed state occurs with an activation energy of 38 kcal. The work function of a carbon monoxide-covered tantalum surface, obtained by spreading the carbon monoxide on a shadowed tip at 40°K, is 0.8 eV greater than that of the corresponding clean tantalum. Fowler—Nordheim plots of clean and shadowed tips show that at least under these conditions, the infinite-field extrapolation of logi/V2 is proportional to the log of the emitting areas.
On Ionic Catalysis of Hydrogen-Atom Recombination
Authors: Light John C. , Shuler Kurt E.
Published: January 2005

The feasibility of using hydrogen molecular ions, produced in a discharge, for the homogeneous catalysis of H-atom recombination in a second-order process has been investigated. The catalytic cycle involves H3+ and H4+ ions and the efficiency of the H-atom recombination depends critically upon the stability of the H4+ ion complex against unimolecular decomposition. Rate constants for the various elementary reactions have been calculated, and the limiting values of the rate constants for the second-order recombination reaction and for the catalytic efficiency have been determined. It is shown that the detrimental loss of ions through electron—ion recombination can be minimized through sequential pulsed ionization. The results obtained indicate that hydrogen-atom recombination may be catalyzed effectively by molecular ions owing to the large reaction cross section of ion—atom reactions. The possibility of obtaining high catalytic efficiency of H-atom recombination with pulsed molecular ions of the type (XnHm)+ would seem to warrant some extensive experimental studies.
NMR Studies of Hydrated Sodium Tetraborate Minerals. I. Boron—Oxygen Polyion in Borax and Tincalconite
Authors: Cuthbert J. D. , Petch H. E.
Published: January 2005

The quadrupolar splittings of the B11 nuclear magnetic resonance (NMR) signals in single crystals of borax, Na2B4O7·10H2O, and tincalconite, Na2B4O7·5H2O, have been investigated. The electric quadrupole coupling constants, eqQ/h, and asymmetry parameters η of the electric field gradient tensors at the two unique B11 sites in the two crystals were determined to be BoraxTincalconiteeqQ/h487±1 kc/sec2544±4 kc/sec478±1 kc/sec2528±3 kc/secη0.714±0.0030.089±0.0150.473±0.0050.039±0.017.The orientations of the principal axes of the electric field gradient tensors for the above sites and their symmetry-related sites have also been determined.

The picture of the boron—oxygen polyion in borax as given by NMR is in complete agreement with the x-ray results as to numbers and coordinations of boron atoms, symmetry of the polyion and orientation of the planes of the triangularly coordinated boron atoms. The NMR results also indicate that the same boron—oxygen polyion occurs in tincalconite as in borax.
ESR Studies on Irradiated Frozen Aqueous Solutions of Sulfur Compounds
Authors: Henriksen Thormod
Published: January 2005

Radiation-induced ESR centers in frozen aqueous solutions of sulfur compounds have been studied. Special attention has been focused on secondary radical reactions and the relative importance of direct and indirect effects. Solutions were rapidly frozen at 77°K and irradiated in vacuum at this temperature. All ESR spectra were recorded at 77°K. The irradiated samples were heat treated, either for increasing lengths of time at 110°K, or for the same period of time at successively increasing temperatures.

The ESR spectra of aqueous solutions irradiated at 77°K are composed of the ``water resonance'' and a resonance ascribed to radicals in the solute. The latter are found primarily to be induced by the direct action of radiation. This observation implies that H atoms which already have reacted at 77°K have no or very little effect in producing solute radicals.

The remaining ESR centers in water, including OH radicals, are released in the temperature range 100° to 130°K. The spectral changes in this temperature range indicate that recombination processes dominate and only a minor fraction of the ``water radicals'' interacts with the solute. Thus, in a 10% solution of glutathione, about 15% of the ``water radicals'' become effective in producing solute radicals.

The radicals induced in the solute and the subsequent secondary radical reactions seem to be more or less the same as those found when the solute was irradiated in the solid state. For solutions of some simple thiols like penicillamine the secondary reactions yield sulfur radicals above 170°K, in accordance with the results for solid penicillamine. On the other hand, no sulfur resonance appears for solutions of glutathione in spite of the fact that sulfur radicals are formed in the solid state. The resonance of the solution disappears at a lower temperature than that found necessary for the formation of sulfur raducals in solid glutathione.
Analog of n→π Transitions in Mono-Olefins
Authors: Berry R. Stephen
Published: January 2005

The weak absorption of mono-olefins at wavelengths just greater than 2000 Å is ascribed to a transition analogous to the n→π* transition of formaldehyde. The assignment is based on several aspects of the ultraviolet spectra of ethylene and alkyl-substituted ethylenes, on ionization potentials, and on the electron impact excitation of ethylene recently observed by Kupperman and Raff. Several tests of the assignment are suggested and some consequences of such a process, particularly in photochemistry, are mentioned briefly.
Kinetics of the Pyrolysis of Organic Iodides
Authors: Benson Sidney W.
Published: January 2005

An analysis of the data on iodide pyrolysis is made in the light of some recent work together with the newly proposed atom mechanisms for the rapid reactions of RI+HI→RH+I2. It is shown that two mechanisms seem to be rate limiting in the decompositions of alkyl iodides: RI→HI+olefin,I+RI→I+HI+olefin.These are then followed by very rapid reaction of RI+HI, which maintains the HI at a very low stationary state concentration. Mechanism A appears to govern the pyrolyses of i-PrI, EtI, t-BuI and CH3COI, while mechanism B holds for n-PrI, i-BuI and n-BuI. The pyrolysis of sec-BuI appears to involve both A and B as does that of 1,2-C2H4I2. For φCH2I, the mechanism is: I+φCH2I⇋φCH2+I2 (equilibrium),2 φCH2→(φCH2)2 (slow);and for allyl I it is: I+allyl I⇋allyl+I2 (equilibrium),allyl+allyl I→biallyl+I (slow),2 allyl→biallyl (slow).

The I2 in the system brings about a rapid conversion of biallyl to cyclohexene via abstraction of an allylic H atom.

It is shown that the racemization of optically active sec-BuI is not a Walden inversion but a simple reversible abstraction of I: I+RI*⇋ lim 21R+I2,followed by racemization in the back reaction.

Where possible, the data are analyzed quantitatively, and Arrhenius parameters are assigned to the different steps. These are discussed in the light of current data on molecular structure and bond energies.

A unique and somewhat puzzling feature of reaction B is that it appears to go as a concerted step, so that the activation energy is precisely equal to the endothermicity of the reaction. By detailed balancing, the reverse reaction would have no activation energy. This does not occur for alkyl radical attack on n-PrI but appears to be unique to I atoms. If it does occur, it is the first example of a concerted reaction involving free radicals.
Transport Phenomena in Pure and Doped Magnesium Oxide
Authors: Davies Myron O.
Published: January 2005

Ac electrical conductivity measurements have been made on polycrystalline samples of various compositions in the MgO–NiO system. Four activation energies have been obtained with pure MgO: 5.2, 2.7, 3.5, and 0.92 eV. These seem to be the activation energies, respectively, for intrinsic O= conductivity, extrinsic O= conductivity, intrinsic Mg++ conductivity, and extrinsic Mg++ conductivity. Introduction of NiO into the specimens increases the conductivity and decreases the activation energy. The conductivity of the polycrystalline MgO specimens used in this study is larger than literature data for MgO single crystals. This difference results from the large number of grain boundaries present in polycrystals.
Analysis of Molecular Flow in an Isothermal Enclosure
Authors: Carlson K. Douglas , Gilles Paul W. , Thorn R. J.
Published: January 2005

Previously presented analyses of the molecular flow of saturated vapor from a condensed phase in an isothermal enclosure have introduced simplifying approximations early in the treatments. Consequently functions and subtle inconsistencies have appeared which can be recognized, identified, and understood only by returning to the original formulation. A more desirable procedure is to pursue rigorously as far as possible the problem before introducing approximations. The presently described analysis differs from the others in the following respects: (1) The precise system described and the fundamental assumptions employed are defined initially. (2) For a cylindrical (and a generalized) enclosure it is shown that the form p=pe(1—Δ) with pe equal to the equilibrium pressure and Δ a function of the parameters of the cell is a convenient one for the purpose of effecting approximations. (3) The exact physical system corresponding to the classical equation, pe=p[1+(S0/S1)], in which S0 is the area of an orifice and S1 is the evaporating area (both on a spherical surface), has been found to be a spherical enclosure for which Δ can be easily calculated. (4) The single approximation leading to the formulation of Whitman and of Motzfeldt has been found and Δ has been evaluated. An intercomparison is given.
Resonance Fluorescence in Gases and Molecular Crystals
Authors: Hameka H. F.
Published: January 2005

A general theoretical description is derived for the resonance fluorescence of dilute gases and molecular single crystals with special emphasis on optical rotation spectra. The validity of previous theoretical work on dilute gases is confirmed by proving that the damping constants connecting excited states on different molecules are zero. It is shown that the intensities of optical rotation spectra of molecular crystals are much larger than the corresponding quantities for gases. An important theoretical prediction is that the natural line breadth of a resonance fluorescence emission band belonging to an exciton state in a molecular crystal should be larger than the width of the corresponding optical absorption line. The dependence of the intensity of the optical rotation spectrum on the relative orientation of the crystal with respect to the incident beam of light is discussed.
Radii of Gyration for Random-Flight Chains
Authors: Forsman W. C. , Hughes R. E.
Published: January 2005

A new formulation of the radius of gyration of a random-flight chain is presented here. The three independent orthogonal components of the radius of gyration and their associated distribution functions are deduced from the usual model. The properties of the distribution functions are discussed and they are numerially evaluated to a third-order approximation. An alternate empirical distribution function is presented and its properties are analyzed.
Configurational Properties of Random-Flight Chains in Solution and in an Interface
Authors: Forsman W. C. , Hughes R. E.
Published: January 2005

The configurational properties of polymer chains in dilute solution and at an interface are treated in terms of the three independent orthogonal components of the radius of gyration. The distribution functions used are found to satisfactorily represent the dilute solution behavior and are in appropriate form for dealing with the interface. Although the general case cannot be solved, the treatment includes thermodynamically good solvents and solvents at the θ temperature as well as strong and weak polymer—surface interactions.
Adsorption Theory for Flexible Linear Polymer Molecules
Authors: Forsman W. C. , Hughes R. E.
Published: January 2005

A theory is developed for the adsorption of flexible linear polymer molecules at liquid—solid interfaces. Adsorption isotherms are derived for the special cases of sparcely populated surfaces and of heavily covered surfaces, i.e., interfaces in which the polymer segment density is a function only of the distance from the surface. The effects of molecular weight, temperature, and solvent on polymer adsorption are discussed. Comparisons are drawn between the isotherms resulting from small and large polymer—surface interactions.
Spectra and Energy Levels of Eu3+ in LaCl3
Authors: DeShazer L. G. , Dieke G. H.
Published: January 2005

The absorption and fluorescence spectra of Eu3+ in LaCl3 were obtained and analyzed. Crystal-field calculations give good agreement with the observed Stark components for B20 = A20〈r2〉 = 89 cm—1, B40 = —38 cm—1, B60 = —51 cm—1, and B66 = 495 cm—1.
Photo-Ionization and Electron-Capture Processes in Solution: The Flash Photolysis of Ether Solutions of Potassium Metal and of Naphthacene Dianion
Authors: Eloranta Jorma , Linschitz Henry
Published: January 2005

Flash excitation of solutions of potassium in tetrahydrofuran or dimethoxyethane leads to a new substance with a broad infrared absorption. This transforms rapidly to a second intermediate, which finally returns to the original state by a slow first-order process (k = 12.8 sec—1). These changes are interpreted as photodissociation of doubly trapped electrons (e2) followed by fast recombination to a triplet state of e2 and slower return of the triplet to the original singlet. Flashing solutions of naphthacene dianion yields the monoanion and near-infrared bands attributable to e1. The recombination process is second-order (k = 1.5×109 moles—1 sec—1). Much faster electron capture by neutral naphthacene is also observed.
Vacuum-Ultraviolet Absorption Spectra of the Cyclic Ethers: Trimethylene Oxide, Tetrahydrofuran, and Tetrahydropyran
Authors: Hernandez G. J.
Published: January 2005

The vacuum-ultraviolet spectra of trimethylene oxide, tetrahydrofuran and tetrahydropyran show discrete absorption at frequencies higher than 49 000 cm—1. Rydberg series are found to converge to a first ionization potential at 77 980 cm—1 (9.667 eV), 75 960 cm—1 (9.42 eV), and 74 630 cm—1 (9.25 eV), respectively for trimethylene oxide, tetrahydrofuran, and tetrahydropyran. Analysis of the vibronic structure indicates the upper vibrational frequencies are only slightly changed from those of the ground state.
Correlation Energy for Atomic Systems
Authors: Clementi Enrico
Published: January 2005

The correlation energies are estimated for the isoelectronic series of atoms with 2 to 10 electrons in the ground state and in the excited states of the lowest electronic configuration. The obtained values of the correlation energy point out clearly the importance of precorrelation energy, i.e., the energy difference between Hartree and Hartree—Fock energies, the quasi-additivity of 1s, 2s, 2-, ··· intra- and intershell correlation, the relative importance of spin-multiplicity correlation and total angular-momentum correlation, and the Z effects on correlation. The estimate of the correlation energy makes use of energy data for the relativistic energy: the accuracy of the relativistic energy computations is discussed. The 2 to 10 electron correlation energies were used as a basis to estimate the 11 to 18 electron correlation energies and to draw general conclusions on the value of the correlation energy for any atomic system.
On the Infrared Spectrum of Hydrazine Matrix-Isolation Studies of the System NH2NH2:N2 (I)
Authors: Catalano Edward , Sanborn Russell H. , Frazer Jack W.
Published: January 2005

Matrix isolation spectra of the system NH2NH2:N2 were obtained in the region 4000–270 cm—1 at 4.2°K. Spectra taken in this manner are free of complications due to association, over-all rotation, etc. The unusual features of these spectra are that the bands usually assigned to the bending modes which are present in gas-phase spectra at ∼1500–1600 cm—1 are not found; and, that the torsional mode is apparently split. Anomalous behavior for the 6.3-μ gas-phase band was observed.
Charge Transfer in Oxygen, Nitrogen, and Nitric Oxide
Authors: Stebbings R. F. , Turner Ben R. , Smith A. C. H.
Published: January 2005

The cross sections for charge transfer in collisions of N2 and O2 with various atomic and molecular ions have been measured within the energy range 30 to 10 000 eV. Modulated-crossed-beam techniques were used and the relative cross sections so obtained were normalized with the aid of absolute measurements made by Stier and Barnett. Some measurements of charge transfer in NO are also reported.
Comparison of the Crystal Fields and Optical Spectra of Cr2O3 and Ruby
Authors: McClure Donald S.
Published: January 2005

The polarized optical absorption spectrum of Cr2O3 in thin single-crystal plates has been obtained at temperatures from 4.2°K upward. The crystal field at the Cr ions in Cr2O3 has been calculated in the same way as for Cr:Al2O3 since their crystal structures are very similar. The experimental results for Cr2O3 were used to derive empirical values for the quantities 〈r2〉 and 〈r4〉 which appear in the expressions for the cubic and trigonal fields of Cr2O3, and these were substituted into the expression for the trigonal field of Cr:Al2O3. The result is a calculated trigonal field much smaller than is observed. The Cr ion in Al2O3 may therefore be displaced from the Al position as was suggested in a previous study. The details of the Cr2O3 spectrum, particularly the lines, are illustrated and commented upon, but no detailed analysis is presented. The spectrum does show many evidences of exchange coupling, however.
NMR Spectra of Cis and Trans 1,2-Difluoroethylene in the Gas Phase
Authors: Flynn George W. , Matsushima Michiko , Baldeschwieler John D. , Craig Norman C.
Published: January 2005

The proton NMR spectra of cis and trans 1,2-difluoroethylene in the gas phase include a number of peaks of significantly different relative widths. The sharp peaks in the proton spectra can be associated with transitions between states with the largest singlet fluorine spin character if the spin—rotation interaction is assumed to provide the dominant fluorine relaxation mechanism. A comparison of the spectra in the gas and liquid phases then removes the usual ambiguity in the relative sign of JAA′ and JXX′ in these AA′XX′ systems. In both cis CHFCHF and trans CHFCHF, JHH and JFF are opposite in sign.
The Raman Spectrum of Hexafluoroethane
Authors: Rank D. H. , Pace E. L.
Published: January 2005

The Raman spectrum of hexafluoroethane in the liquid phase has been obtained. The polarization of the lines appearing in the spectrum has been measured qualitatively. An assignment of the frequencies has been made from the spectrum.
Dielectric Behavior of Solutions of Electrolytes in Solvents of Low Dielectric Constant I. A Calorimetric Method for Measuring Losses
Authors: Sharbaugh A. H. , Schmelzer C. , Eckstrom H. C. , Kraus C. A.
Published: January 2005

The experimental equipment and method used to determine calorimetrically the energy absorption in a radiofrequency field by several electrolytes in solvents of low dielectric constant is described. The dipole conductivity and the loss factor for these systems are then calculated from the experimental data.
Pressure Broadening in the Infra-Red and Optical Collision Diameters
Authors: Coggeshall Norman D. , Saier Eleanor L.
Published: January 2005

The pressure broadening effects of a number of foreign gases on the infra-red absorption of methane at 7.65μ have been determined. Also the pressure broadening effects of a number of foreign gases on the absorption of carbon dioxide at 4.3μ and 14.8μ have been investigated. The data have been analyzed to obtain optical collision diameters for the various gases and the absorbers. By optical collision is meant any collision which is effective in interrupting the processes of radiation absorption. The data are discussed in terms of the Lorentz theory of pressure broadening and are shown to confirm it. From the results obtained, it is clear that the pressure broadening effects of certain gases on one absorber cannot be reliably extrapolated to predict the effects on another absorber. Also the effects at one wave-length are not in general the same at another wave-length for the same absorber. The optical collision diameter effective for a foreign gas and an absorbing gas at a particular wave-length is a specific function of the two gases and the wave-length. Empirical results on the shape of the curves obtained are presented. The deviation from Beer's law of absorption evidenced by isobutylene at 11.23μ is shown to be not due to pressure broadening.