bluuebunny/crossref_metadata_2025_split huggingface dataset:
Abstraction of Hydrogen Atoms by Energetic Recoil Tritium Atoms: Correlation with C–H Bond-Dissociation Energies in Hydrocarbons
Authors: Root J. W. , Breckenridge W. , Rowland F. S. 
Published: January 2005

The yields of HT from ``hot'' abstraction reactions by energetic tritium atoms reacting with various substances RH have been measured in a large excess of C2D4. The energetic tritium atom fluxes are reasonably similar in such systems and permit comparison of absolute HT yields from different R—H bond types. A more accurate comparison is possible when the HT yields are normalized to the yields of either the hot abstraction or substitution reactions with C2D4. The hot HT yields so measured from hydrocarbons show an excellent correlation with the bond-dissociation energies of the C–H bonds involved, with higher yields from weaker bonds. The abstraction of H from CD3CH2CD3 was favored by approximately 1.4, per bond, over H from CH3CD2CH3.
No significant differences were observed in the DT/C2D3T ratios from reaction with C2D4 in the various mixtures with different substances. A preference of 1.27±0.02 was observed for the abstraction of H from C2H4 vs D from C2D4. No isotopic molecule difference was observed between the energetic addition reaction of tritium atoms to the olefinic position in C2H4 vs C2D4.
NMR Determinations of Barriers to Internal Rotation in Halogen-Substituted Ethanes
Authors: Newmark Richard A. , Sederholm C. H. 
Published: January 2005

The theory of Kaplan and Alexander for exchange in nuclear magnetic resonance (NMR) systems has been applied to exchange between three species with any number of nuclei of spin ½, in which all the nuclei in each species are exchanged by the interconversion. A set of explicit equations for the density matrix elements in this case is written down. Computer programs have been written to solve the equations in the two and three spin cases. The results enable the calculation of NMR spectra of highly coupled nuclei undergoing exchange. Absolute reaction rate theory has been used to express the rates of exchange in terms of activation energies. This has been combined with the Kaplan—Alexander theory to determine the free energies of activation for internal rotation in several halogenated ethanes, CFCl2–CFCl2, CF2Br–CCl2Br, CF2Br–CFBr2, CF2Br–CFBrCl, CFClBr–CFClBr, and CF2Br–CHBrCl. Spectra were calculated assuming limiting values for the transmission coefficient, k≪1, k=1. The first case implies free rotation occurs when a molecule is excited to sufficient energy to exceed the barriers. Alternatively, the second case implies that deactivation of the rotational mode occurs in a time comparable with the rotational frequency. The experimental results on CF2Br–CCl2Br can only be explained by the second possibility. The barriers are discussed in terms of the distortion necessary to form the activated complex in which the substituents are eclipsed.
The low-temperature spectrum of the three rotamers of CF2Br–CHBrCl shows two large vicinal HF coupling constants (18 cps) and four small ones (less than 3 cps). The assignment of the rotamers made assuming that the low barrier observed between two of the rotamers does not involve eclipsing two large halogens indicates that the large coupling constants are trans and the four others are gauche coupling constants.
Dielectric and Ultrasonic Relaxation in Glycerol
Authors: Litovitz Theodore A. , Sette Daniele 
Published: January 2005

Measurements of dielectric and ultrasonic relaxation in glycerol are compared over a frequency range of 7.5 to 37.5 megacycles and over a temperature range from 20°C to − 25°C. Reduced dielectric and ultrasonic constants when plotted against viscosity at a constant frequency of 30 megacycles appeared quite similar. The imaginary (or loss) part of the reduced constants exhibited a peak at the same viscosity. Both phenomena exhibited a departure from a single relaxation time theory. This deviation of the dielectric phenomena from the simple theory was attributed in the usual manner to a distribution of relaxation times. The striking similarities in the behavior of the dielectric and ultrasonic phenomena suggests an intimate relation between the two. Thus, if a distribution of relaxation times exists for the dielectric, it should in all probability exist in the ultrasonic process.
Both shear and compressional viscous processes are associated with the acoustic phenomena. It was concluded that if any difference exists in the shear and compressional viscous relaxation times, its effect is masked by a probable distribution in relaxation times for each process.
Calculations indicated that the natural ``rotational jump'' time in glycerol is between ½ and 4 times the ``translational (or viscous) jump'' time.
The Photolysis of Mercury Dimethyl in the Presence of Hydrocarbons
Authors: Rebbert Richard E. , Steacie E. W. R. 
Published: January 2005

Mercury dimethyl was photolyzed in the presence of various hydrocarbons between 28°C and 251°C. The activation energies in kcal per mole for reactions of the type CH3+RH→CH4+Rare: 2-methyl propane−7.4; 2,3-dimethyl butane−6.8; n-butane−8.6; cylcohexane−8.3; 2,2-dimethyl propane−10.4; and toluene−7.3, where it is assumed that the activation energy for the reaction 2CH3→C2H6is zero. The collision theory steric factors are less than 10−3 for all these reactions.
The agreement of the above results with those obtained from the photolysis of acetone is noted.
Studies of Ionization Efficiency. Part III. The Detection and Interpretation of Fine Structure
Authors: Morrison J. D. 
Published: January 2005

The effect of the spread in energy of the ionizing electron beam on the resolution of structural details in ionization efficiency curves has been evaluated, and the possibility of its removal by analytical methods is discussed. It has been shown that the first and second derivatives of the ionization efficiency possess useful properties, and that, when certain assumptions are made about the shape of the ionization probability function for a single process, a new method of measuring ionization potentials can be devised.
Correlation techniques have been employed to enhance materially the signal-to-noise ratio in the output from the ion collector. Detailed measurements of the ionization efficiencies for the inert gases have been made, and the assumptions referred to are justified.
It is shown that the ionization efficiencies for some molecular ions can be correlated with their vacuum ultraviolet and near x-ray spectra. It is found that competition occurs between all possible processes of excitation and ionization at each level of energy. The higher-energy levels of molecules can be studied and, in principle, an unequivocal assignment of bond dissociation energies from mass spectrometric data is possible.
The Reaction of Cyclobutane with Hg 6(3P1) Atoms
Authors: Kantro D. L. , Gunning H. E. 
Published: January 2005

The reaction of cyclobutane with Hg 6(3P1) atoms has been studied in a static system at 30.10±0.01°C, over the pressure range from 2–250 mm. The primary products of the reaction are hydrogen, n-butylcyclobutane, and a saturated C8H14 product which is assumed, from kinetic and mass spectral evidence, to be cyclobutylcyclobutane. In addition, prolonged exposure produced a saturated C12H22 product which is probably a dicyclobutylbutane.
The quantum yields of pressure decrease (φP) hydrogen formation (φH2) and cyclobutane consumption (φC) all reach constant maximum values at cyclobutane pressures greater than approximately 100 mm. These values are φC=0.53, φH2=0.10, and φP=0.16. From the simple stoichiometry of the reaction the quantum yields of n-butylcyclobutane (φBC) and cyclobutylcyclobutane (φC2) formation were calculated. From the data φBC=0.16 and φC2=0.10.
The following mechanism was found to be consistent with the observed characteristics of the reaction: cyclo C4H8+Hg 6(3P1)→cyclo C4H7+H+Hg 6(1S0),H+cyclo C4H8→cyclo C4H7+H2,2 cyclo C4H7→dicyclo C8H14,2 cyclo C4H7→cyclo C8H14,H+cyclo C8H14→cyclo C8H15,cyclo C8H15+cyclo C4H8→cyclo C4H7+cyclo C8H16,where dicyclo C8H14 represents cyclobutylcyclobutane; cyclo C8H14, cyclobutylbutene; cyclo C8H15, cyclobutylbutyl radicals; and C8H16, n-butylcyclobutane. The cyclobutylbutene is considered as an intermediate in the formation of the stable n-butylcyclobutane product.
The Methyl Alcohol Molecule and Its Microwave Spectrum
Authors: Ivash Eugene V. , Dennison David M. 
Published: January 2005

The theory of hindered rotation in methyl alcohol developed by Burkhard and Dennison has been extended to include the second-order Stark effect as well as a detailed discussion of K-type doubling. It has been applied to an interpretation of the microwave spectrum of normal methanol and of two isotopic molecules, C13H3O16H and C12H3O18H3 recently measured by Hughes, Good, and Coles. A very convincing fit between the predicted and observed lines is obtained which serves to determine many of the molecular constants, as well as providing a substantial number of self-consistency checks.
The height of the potential barrier (on the assumption of a sinusoidal potential) is found to be 374.8 cm−1. The CH distance in the methyl group cannot be obtained with any accuracy from the present data but is consistent with the CH distance in methane, namely, 1.093A, and has been taken to have this value. The remaining dimensions are, however, well determined and are: OH distance=0.937A, CO distance=1.434A, COH angle=105°56′, HCH angle=109°30′. The symmetry axis of the methyl group passes between the H and O of the hydroxyl group and lies at a distance of 0.079A from the oxygen. The above values for the barrier height and molecular dimensions do not differ much from those found by Burkhard and Dennison but are believed to be considerably more accurate.
Using the molecular constants, the positions of all the observed microwave lines which can be identified have been calculated. In every case the agreement is good. Those discrepancies which do exist are of an order of magnitude which can be ascribed to higher-order effects not included in the present theory.
The Stark effect, both first and second order, has been computed for all identified lines. In all but one or two cases the agreement with experiment is found to be very satisfactory.
Surface Migration of Water Molecules in Ice
Authors: Murphy E. J. 
Published: January 2005

This paper continues the discussion of data given in a previous paper on the second term in the ``local conductivity'' of ice. It is inferred that the H2O molecules in internal surfaces are engaged in a special kind of random walk, in which the molecule is always attached to the surface by one chemical bond. This is described as bipedal random walk. It occurs with an activation energy of 5.2 kcal/mole (0.23-electron volt per molecule). On the other hand, molecules which jump up into field-free space and return to the surface have to acquire an energy of 11.5 kcal/mole (0.5 ev/molecule). The ratio of the corresponding Boltzmann factors is about 10−5 at 0°C and about 10−8 at −100°C; this implies that the dominant mode of diffusion in internal surfaces in ice is bipedal random walk.
The migration of a water molecule on an ice surface is a special type of diffusion process. The general formulas of the theory of stochastic processes and diffusion become available for the description of the diffusion of water molecules in a surface if the appropriate expression for the diffusion constant D is substituted in the formulas. A new procedure is used to calculate D from the Einstein relation. Instead of using the direct-current conductivity, the second term of the local conductivity is used. The expression for the diffusion constant derived from the model for local conductivity is DL=3.5×10−4 exp(−5.2×103/RT) cm2/sec, where the activation energy 5.2×103 cal/mole, is derived from the second term in the local conductivity of ice. This leads to a rather explicit model of the diffusion process: it may be described as bipedal random walk of the water molecule by the breaking of one bond at a time with an activation energy of 0.23-electron volt associated with each step.
It is pointed out also that the water molecule on an internal surface has a polarizability characteristic of the surface structure.
A Study in the Mechanics of Crystal Growth from a Supersaturated Solution
Authors: Krueger G. C. , Miller C. W. 
Published: January 2005

An experimental investigation of the concentration field during crystallization is made using an improved modification of W. F. Berg's interference technique. Na2S2O3·5H2O is crystallized at 23°C; concentrations between 40 percent and 55 percent. Graphing the positions of the growing faces versus time indicates, in all cases, a uniform rate of growth with occasional abrupt changes. These discontinuities were, in general, correlated with changes in the perfection of the growing face, the disappearance of a region of poor growth being associated with a decrease rate, whereas the appearance of an imperfection led to a higher rate. A minimum of concentration is observed near the face center, corroborating previous investigations with NaClO3. A diffusion coefficient of 1.26×10−5 cm2/sec was calculated for Na2S2O3 corresponding to 0.80×10−5 cm2/sec extrapolated from J. D. R. Scheffer's data.
There is no strict correlation between maximum, minimum, or average concentration at a crystal face and its rate of growth. It appears that the variations in concentration revealed by interferometer maps are to be interpreted as a consequence of solution depletion occasioned by the crystal's growth.
The Temperature Dependence of the Mutual Diffusion Coefficient for Four Gaseous Systems
Authors: Strehlow Roger A. 
Published: January 2005

Diffusion coefficients have been measured for the systems He—A, H2—A, H2—nC4H10, and H2–SF6 over the temperature range 13°C to 150°C. The values were determined by a point concentration analysis, while diffusion proceeded at one end of a Loschmidt-type cell. The analysis was made with a hot-wire technique and utilized the large difference in thermal conductivity to indicate concentration. The generalized equations for calculating D from an experiment with a Loschmidt-type cell are given as well as an analysis of the errors involved in calculating D from these data.
The data were used to calculate binary force constants for the Lennard-Jones 6–12 potential. In the system SF6–H2 these are ε/k=320°K and (r0)12=3.25A. The other three systems fit the theory very poorly. The middle temperature value was about 5 percent low relative to the theoretical curve through the high and low data point. The difficulties of calculating Lennard-Jones force constants from experimental viscosity or diffusion data are discussed.
Nuclear Magnetic Resonance Multiplets in Liquids
Authors: Gutowsky H. S. , McCall D. W. , Slichter C. P. 
Published: January 2005

Multiple magnetic resonance lines have been observed for H1, F19, and P31 nuclei in compounds such as PH3, PF3, F2PO(OH), and BrF5, in the liquid state. The multiplets consisted of two to seven equally spaced narrow components, symmetrically placed about a central frequency, and with splittings from 0.02 to 0.8 gauss. These multiplets arise from a new variety of interaction among the nuclear moments in a molecule. Resonance lines were found to be multiple either when a nucleus interacted with a different species of nucleus or when there was interaction between nuclei of the same species with resonance frequencies separated by a chemical shift. No compounds exhibited multiplets attributable to interactions among structurally equivalent nuclei. Nor were multiplets caused by nuclei whose electric quadrupole moments were coupled to a direction fixed in the molecule.
The number and relative intensities of the components of a multiplet were determined by the number and statistical weights of the various nuclear spin orientations of the nuclei causing the splitting. In a given molecule, the ratio of the multiplet splittings of the two different resonance lines was inversely proportional to the ratio of the gyromagnetic ratios of the interacting nuclei. The splittings were independent of applied magnetic field at 4180 and 6365 gauss; they were independent of temperature over ranges from 55°C to −130°C. In PF5, the one gas examined, the splitting of the doublet fluorine resonance was the same in the gas and liquid phases; also, the doublet was demonstrated to arise from coupling with the phosphorus nucleus, rather than from a chemical shift between the resonances from the apex and meridian fluorines in the bipyramidal structure, as proposed earlier.
All of the above characteristics are accounted for theoretically by assuming the magnetic nuclei interact via magnetic fields inside the molecule. The qualitative aspects are predicted by coupling of the form A12μ1·μ2 between the nuclear moments μ1 and μ2. The coupling constant A12 depends upon the detailed mechanism, which must involve the molecular electrons. Second-order perturbation theory was used to calculate the relative magnitudes of coupling via the electron orbital and the electron spin magnetic moments. The electron spin mechanism was found to give splittings ten to twenty times the orbital. Approximate calculation of the electron spin mechanism in several simpler cases gave good agreement with experiment. The influence upon the splittings of electric quadrupole coupling and spin-lattice relaxation was considered and is discussed briefly.
The Effect of Pressure on Diffusion in Water and in Sulfate Solutions
Authors: Cuddeback R. B. , Koeller R. C. , Drickamer H. G. 
Published: January 2005

Diffusion coefficients are presented as a function of pressure to 10 000 atmospheres for the following systems: THO−H2O  0∘−25∘−50∘;0.1 N H2S35O4  −0.1 N H2SO4    0∘−5∘−25∘−50∘;0.1 N Na2S35O4 −0.1 N Na2SO4   0∘−25∘−50∘;1.0 N Na2S35O4 −1.0 N Na2SO4   0∘−25∘−50∘;0.1 N K2S35O4  −0.1 N K2SO4    0∘−25∘−50∘.The results are interpreted in terms of the activation volume and the tetrahedrally coordinated structure of water. It is found that pressure tends to break down the structure, and in certain regions an increase in diffusion coefficient with pressure is noted.
In the salt solutions the water structure is controlling with some added effects due to solvation and ionic interaction.
Adiabatic Correlation Rules for Reactions Involving Polyatomic Intermediate Complexes and their Application to the Formation of OH(2Σ+) in the H2–O2 Flame
Authors: Shuler Kurt E. 
Published: January 2005

Adiabatic orbital and spin correlation rules applicable to a detailed study of elementary chemical reactions involving nonlinear polyatomic intermediate complexes have been formulated and are presented together with some pertinent correlation tables. These correlation rules and tables permit the determination of the adiabatically allowed term manifold of reaction products from the states of the separated reactants without reference to their detailed electronic configurations. The formulation presented here utilizes group theoretical arguments relating to the symmetry properties of the reactants, the intermediate reaction complex, and the products and is based principally upon the results obtained previously by Mulliken for the resolution of species into those of point groups of lower symmetry. The effects of the change of the (geometrical) configuration of the intermediate reaction complex during reaction and of the electronic-vibrational coupling on these correlations have been considered in detail. It is concluded that strict orbital electronic correlation rules are operative only for reactions where neither the reactants nor the products are polyatomic. For reactions involving polyatomic reactants and/or products, the vibrational-electronic coupling weakens the simple orbital electronic correlations so that detailed vibronic correlations will be necessary. The spin correlation rules, however, are not affected by these interactions and are identical with those given by Wigner and Witmer for atomic and diatomic systems.
These correlation rules are then applied to a study of the reactions H+O2→[HO2]→OH*+OO+H2→[OH2]→OH*+H which may be of importance in the production of electronically excited OH[OH(2Σ+)] in the hydrogen-oxygen flame. The mechanism of these reactions is investigated with special reference to the predissociating OH(2Σ−) state discussed recently by Gaydon and Wolfhard. It is suggested that the interaction of and the consequent radiationless transition between HO2 intermediate reaction complexes is primarily responsible for the formation of OH(2Σ+) in its observed vibrational nonequilibrium distribution with the specific enhancement of the levels v′=2 and 3.
The adiabatic correlations for the special case of association (and dissociation) reactions involving linear polyatomic intermediate complexes and products are considered briefly in the Appendix. It is concluded that vibronic correlations are required for the determination of the product term manifold for these reactions.
The Infrared Spectra of Three Solid Phases of Methyl Ammonium Chloride
Authors: Waldron R. D. 
Published: January 2005

Infrared spectra are presented for three crystalline phases of methyl ammonium chloride which occur at different temperatures. The spectrum of the high temperature structure reveals apparently degenerate vibrational frequencies for the perpendicular bands indicating little or no distortion from a threefold symmetry axis for the methyl ammonium ion. The intermediate and low temperature structures show increasing distortion of the cation as evidenced by increasing splitting of the degenerate absorption bands amounting to about 10–40 cm−1 in the low temperature form, where the torsional vibration about the C–N axis becomes infrared active.
An assignment of frequencies is made in satisfactory agreement with a valence-force normal coordinate treatment and the isotope product rule. A simplified calculation of the height of the potential barrier to internal rotation was made yielding the approximate value, V0=1670 cm−1.
A Semi-Empirical Theory of the Electronic Spectra and Electronic Structure of Complex Unsaturated Molecules. II
Authors: Pariser Rudolph , Parr Robert G. 
Published: January 2005

The theory of electronic spectra and electronic structure, the elucidation of which was begun in the first paper of this series, is further developed and applied to ethylene, butadiene, benzene, pyridine, pyrimidine, pyrazine, and s-triazine.
A realistic and consistent LCAO-MO π-electron theory should allow the σ-electrons to adjust themselves to the instantaneous positions of the mobile π-electrons. This is accomplished in the theory by assignment of empirical values to the Coulomb electronic repulsion integrals and Coulomb penetration integrals which enter the formulas, these values being obtained in a prescribed way from valence state ionization potentials and electron affinities of atoms. Use of the empirical values in the molecular orbital theory reduces the magnitude of computed singlet-triplet splittings and the effects of configuration interaction without complicating the mathematics. From the valence-bond point of view, ionic structures may be said to be enhanced.
The applications to hydrocarbons and heteromolecules which are considered show that the theory can correlate known π-electron spectral wavelengths and intensities very successfully, which, together with the simple structure of the theory, signals that manifold applications of the theory are in order elsewhere.