bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hypervirial Functions and the Positive Powers of the Radial Coordinate Operator in He and H—
Authors: Gordon Sidney L. 
Published: January 2005

Ground-state He and H— trial functions are scaled to satisfy the hypervirial relations generated by the family of hypervirial operators Wn=r1np1. These one-parameter hypervirial functions are used to calculate expectation values of the positive powers of the radial coordinate operators, rt, for t=1 through 20. Accurate values of 〈rt〉, for this range of t, are calculated using 20-term Hylleraas functions. A comparison of results shows that simple hypervirial functions of the form exp[—K(r1+r2)] scaled to satisfy the hypervirial relations generated by W2, give a good over-all calculation of 〈rt〉 for both He and H—.
The hypervirial theorem is used to develop a variety of expectation value relationships for one- and two-electron central force problems in the Appendix.
Activation Energy for the Sublimation of Gallium Nitride
Authors: Munir Zuhair A. , Searcy Alan W. 
Published: January 2005

Gallium nitride was found to sublime congruently from a torsion—effusion cell when the ratio of orifice area to sample area was about 1/30 and incongruently to yield nitrogen gas and liquid gallium when this ratio was about 1/100 or less. A mass-spectrometer investigation revealed no measurable concentrations of gallium nitride vapor molecules. The heat of activation for the reaction 2GaN(s)=2Ga(1)+N2(g) was calculated to be 39 kcal at 1300°K from the temperature dependence of the effusion data.
The rate of the reaction 2GaN(s)=2Ga(g)+N2(g) was measured by a torsion—Langmuir method. From the temperature dependence of sublimation the heat of activation for this reaction was calculated to be ΔH1300‡=218.6 kcal compared to 173 kcal for the equilibrium reaction, and the entropy of activation was calculated to be 74.3 cal/deg.
Static and Dynamic Frequency Shifts in Electron Spin Resonance Spectra
Authors: Fraenkel George K. 
Published: January 2005

A detailed theoretical analysis has been made of the factors which affect the positions of the hyperfine lines in electron spin resonance spectra. The deviations from the usual high-field-approximation formulas are found to depend on the relaxation and line-broadening interactions [H1(t)] as well as on the well-known corrections to the high-field approximation that result from the exact solution of the time-independent static Hamiltonian [Ho]. The time-dependent processes H1(t) make a direct dynamic contribution to the frequency shifts, and in addition they alter the frequency spectrum of the static Hamiltonian. This latter effect arises because the dynamics of the system are properly determined by the total Hamiltonian Ho+H1(t), not just by the time-independent part Ho. The theory is developed in terms of the Redfield—Abragam relaxation-matrix formulation, but simple models are also treated by a limited but more easily handled procedure based on the modified Bloch equations.
The most interesting results predicted by the theory occur when there is a large alternating linewidth effect arising from modulations of the isotropic hyperfine splittings. Usually, the dynamic frequency shifts are less than the linewidths, but, when there is a large alternating linewidth effect, the dynamic shift is large compared to the width of the narrow lines in the spectrum even though it is still small compared to the width of the broad lines. The alternating linewidth phenomenon also changes the static frequency shift, e.g., in the case of two nuclei of spin I=1 it causes the mean relative static shift in the positions of the sharp lines to be a factor of 3 greater than in the absence of an alternating linewidth effect. The theory indicates that experimental studies of the frequency shifts and linewidths in appropriate systems should make it possible to determine both the magnitude of the mean-square fluctuations in hyperfine splittings and the correlation time characteristic of the fluctuating motions. The experimental determination of these two quantities, which appear only as adjustable parameters in previous theories, should make it possible to obtain considerable information about the inter- and intramolecular factors which influence the instantaneous structure of free radicals.
It has been rigorously shown that, when the width variations among a group of degenerate or nearly degenerate transitions are small, the net shift is determined by the average value of the shifts, both static and dynamic, of all the components involved in the set of degenerate transitions. Unresolved shifts from proton splittings (or from other nuclei with spin I=½) usually cause all the hyperfine lines to be shifted by the same amount, independent of whether or not the width variations are small. Normally, the shifts arising from the effects of tumbling motions on the intramolecular, anisotropic, electron—nuclear, magnetic-dipole interactions are small, as are those arising from the cross term between the dipolar and g-tensor interactions.
Microwave Absorption and Molecular Structure in Liquids. LX. Intramolecular Relaxation Mechanisms in Aromatic Ethers and Several Related Molecules
Authors: Anderson James E. , Smyth Charles P. 
Published: January 2005

The dielectric constants and losses of 11 aromatic ethers and related compounds in dilute benzene solution have been measured at wavelengths between 1.25 and 50 cm at temperatures from 20° to 60°. The substances measured are dibenzyl ether, benzyl phenyl ether, dicyclohexyl ether, 2-nitrophenyl phenyl ether, m-diphenoxybenzene, 4-bromophenyl phenyl ether, 4-biphenyl phenyl ether, phenoxathiin, thianthrene, triphenylphosphine, and triphenylchloromethane. The dielectric relaxation times calculated from these data indicate that most of the seemingly small values obtained result from combination of short, coupled, ring rotations with over-all molecular rotation.
Comparison of the dipole moment values calculated for twenty-three substituted phenyl ethers with the observed values gives no evidence of the large mesomeric moments seemingly necessary to make mesomeric charge shift a generally important factor in lowering the relaxation times of these molecules. The low relaxation time found for phenoxathiin probably results from combination of dipole orientation by a ``butterfly motion'' of the nonplanar molecule with orientation by over-all molecular rotation.
Mechanism of the Acetylene—Oxygen Reaction in Shock Waves
Authors: Glass G. P. , Kistiakowsky G. B. , Michael J. V. , Niki H. 
Published: January 2005

The oxidation of acetylene has been studied using sufficiently high gas densities and concentrations of inert gas to keep the reaction isothermal and reduce boundary-layer effects. The induction periods and exponential time constants of the oxidation have been measured using the observations of: (a) chemiluminescence and gas conductivity in incident and in reflected shock waves, and (b) total ionization and product formation using a time-of-flight mass spectrometer in reflected shock waves. The results are internally consistent, and the time constants τ are best represented by the following equation: log10(τ[O2])=−11.29+17 000/4.58Tin units of seconds·moles/liter. Induction periods are about eight times longer. The following reaction mechanism is most consistent with the data: H+O2=OH+Ok1=1/(4τionization[O2]),O+C2H2=OH+C2Hk2,OH+C2H2=H2O+C2Hk3,C2H+O2=2CO+Hk4,C2H+O2=CO2+CHk5.
Reaction (1) is rate-controlling, the above-defined value of k1 agreeing well with the work of others. The time constants τ for CO, CO2, and H2O are identical, indicating that they are all formed in the branching chain reaction, but those of ionization and luminescence are half as large. Diacetylene formation is observed in acetylene-rich mixtures. Experiments with added CO indicate that Reaction (5) is initially the main source of CO2.
The reactionC2H+O=CH(A2Δ)+CO  k6explains the observed chemiluminescence well.
Experiments with the mass spectrometer show that C3H3+ is the first ion observed. Other experiments suggest that the simple reaction CH(A2Δ)+C2H2=C3H3++e— k7 is not responsible for the ionization. Other possible mechanisms for the formation of C3H3+ are discussed.
Relative Signs of the Nuclear Spin Coupling Constants in Propylene Oxide and Indene Oxide
Authors: Elleman Daniel D. , Manatt Stanley L. , Pearce Claude D. 
Published: January 2005

The 60-Mc/sec high-resolution NMR spectrum of propylene oxide was analyzed as an ABCD3 nuclear spin system in the conventional iterative manner utilizing in addition double resonance to decouple the D3 (methyl group) protons from the ABC protons. A fit was obtained by two sets of parameters whose main difference was that either both long-range couplings JBD and JCD are positive with respect to the other couplings or only JCD is negative. By use of a weak perturbing rf field to irradiate a particular resonance transition it was determined that JCD has a different sign than the other couplings.
The 60-Mc/sec spectrum of the protons of the five-membered ring of indene oxide (II) was analyzed as an ABCD system with the aid of triple-irradiation experiments in which the long-range couplings of the A, C, and D protons with the aromatic ring protons were destroyed by a large rf irradiation applied at the resonance position of the aromatic protons while a second weaker perturbing irradiation was applied at particular lines in the ABCD spectrum. The results of these experiments determined the energy level scheme and suggested that if this spectrum is truly first order then all the coupling constants in the four spin system are positive except JCD. However, complete iterative analysis using the Swalen and Reilly program showed the spectrum of II was definitely not first order and that JAD is almost zero and JBC very small. The following sets of parameters were found for I and II. JABJACJADJBCJBDJCDδAδBδCδDI+3.88+2.57+5.15+5.37+0.52−0.362.8492.5892.2791.214II+2.90+1.32−0.01+0.12+3.11−18.224.1393.9833.1422.879 The spin—spin couplings are in cycles per second and chemical shifts in parts per million downfield from tetramethylsilane.
Stereochemically the H–C–C–C–H couplings in II and the positive H–C–C–C–H coupling in I are similar, i.e., the protons on the oxirane ring are related in what can be considered a ``trans'' manner to the carbon—carbon bond joining the methyl or methylene group to the oxirane ring. The results from the rigid molecule II suggest that this particular long-range coupling involving four saturated bonds is positive when the protons are in an ``anti—trans'' relation or furthest away and near zero when the protons are in a ``syn—trans'' relation or nearer. The magnitudes and signs of the H–C–C–C–H couplings found in I and II are discussed in some detail and compared with other reported similar long-range couplings.
The description of the field-frequency lock spectrometer used in this work is given. With this system it was possible to detect excursions of the field-frequency setting of the order of 1–2 parts in 1010.
Mass-Spectrometric Study of Ions at Near Atmospheric Pressures. I. The Ionic Polymerization of Ethylene
Authors: Kebarle P. , Hogg A. M. 
Published: January 2005

An apparatus is described which allows the mass-spectrometric analysis of ions produced by the alpha-particle irradiation of gases in the pressure range 5–200 Torr. The ions emerge from the field free ionization chamber by effusion. This method of sampling should give an (approximate) picture of the steady state ionic concentration. A simplified kinetic treatment based on the steady state assumption can explain the experimental results.
The mass spectrum of ethylene at 40 Torr pressure is very complex. It extends beyond the highest mass (215) measured. The major ions are CnH2n−1+.
A simplification of the reaction system is achieved with a dilution—charge-exchange technique. The ethylene spectrum obtained from 1% ethylene in xenon gives the ionic polymerization initiated by C2H4+. The most abundant series is (C2H4)n+. Xenon is deactivating the excited addition products.
Low ionization potential impurities or reaction products, present in less than parts-per-thousand concentration, can still change the ionic population profoundly. This is of significance to conventional radiolysis work.
Temperature increase from 20°—60°C has little effect on the ethylene spectra. Other gases or gas mixtures show large changes because of cluster rearrangement.
Transition Probabilities of the Nuclear Pure Quadrupolar Relaxation of 35Cl in Paradichlorobenzene
Authors: Pissanetzky Sergio 
Published: January 2005

A measurement of the transition probabilities W1 and W2 for the pure quadrupolar relaxation of 35Cl in paradichlorobenzene is interpreted in terms of the Woessner—Gutowsky theory.
A supposition about two-torsional oscillation frequencies contributing simultaneously to the relaxation is found to produce a good agreement with experiment at a temperature of 77°K. This is shown to be a transition temperature, because at lower temperatures the relaxation is governed principally by the oscillation of lower frequency, while at higher temperatures it is governed by the oscillation of higher frequency.
Pulse Radiolysis Studies. VII. The Absorption Spectra and Radiation Chemical Yields of the Solvated Electron in the Aliphatic Alcohols
Authors: Sauer Myran C. , Arai Shigeyoshi , Dorfman Leon M. 
Published: January 2005

The absorption spectra of the solvated electron in five aliphatic alcohols have been determined by the pulse radiolysis method. For the alcohols: ethylene glycol, methanol, ethanol, n-propanol, and isopropanol, the absorption maxima show a red shift with decrease in the value of the static dielectric constant. The absorption maxima for these alcohols are, respectively, 5800, 6300, 7000, 7400, and 8200 Å. The molar extinction coefficient at the maximum and the oscillator strength of the broad absorption band has been determined for each alcohol.
The radiation chemical yields of the solvated electron in these irradiated alcohols as determined by pulse radiolysis are, respectively, 1.2, 1.1, 1.0, 1.0, and 1.0 per 100 eV.
The correlation between the transition energy for optical excitation of the solvated electron and the dielectric behavior of the liquid is discussed in terms of the theory.
Ground States of Conjugated Molecules. I. Semiempirical SCF MO Treatment and Its Application to Aromatic Hydrocarbons
Authors: Chung Alice L. H. , Dewar Michael J. S. 
Published: January 2005

The π-bonding energies and resonance energies for a series of monocyclic polymethines (CH)n, and several benzenoid and nonbenzenoid hydrocarbons are calculated by the Hückel, Pople, and SPO methods. Special attention is paid to the formulation and definition of such energy terms. For simplicity equal bond lengths are assumed in each case; in the case of the polymethines, the planar configurations of regular polygons are taken.
The calculated π-bonding energies of 11 benzenoid hydrocarbons are combined with experimental heats of formation and an assumed carbon—hydrogen bond energy to obtain estimates of the bond energy of a carbon—carbon σ bond in an aromatic ring. The values obtained for the eleven compounds agree very closely, implying that a good estimate of the heat of formation of such hydrocarbons can be obtained by adding the σ-bond energies to the calculated π energy. This approach is used to estimate resonance energies of the aromatic hydrocarbons.
The resonance energies of the polymethines are found to alternate strongly, regardless of the choice of methods used; the values are uniformly larger for rings with 4n+2 π electrons than for rings with 4n π electrons. In the Pople and SPO cases, bond alternation is predicted for all the rings with 4n carbon atoms as well as for those with 4n+2 carbon atoms starting at n=4.
For certain nonbenzenoid hydrocarbons the calculated resonance energies are only in fair agreement with experimental findings. For most, agreement is satisfactory.
Virial Coefficients for the Hard-Core Gas in Two Dimensions
Authors: Hemmer P. C. 
Published: January 2005

The fourth virial coefficient for a gas of hard disks is calculated by means of the virial theorem. The exact result is B4/b3=2–93/2π+10π−2, where b is the second virial coefficient. The numerical value for B4/b3 of 0.532232 confirms previous estimates obtained by Monte Carlo integration.
The weights of all four-point irreducible clusters are also recorded.
Paramagnetic Resonance of the Phosphorescent States of Quinoline and Isoquinoline
Authors: Vincent James S. , Maki August H. 
Published: January 2005

Paramagnetic resonance measurements are reported in solid solutions of quinoline, and of isoquinoline in durene under irradiation with ultraviolet light at 77°K. The fine structure of the magnetic resonance spectrum observed at 9.2 Gc/sec may be described by the spin Hamiltonian H=βH·g·S+DSz2+E(Sx2−Sy2), with S = 1. D, E, and the principal values of g are reported for each molecule. The principal axis systems of the zero-field tensors D are found to be displaced from the molecular axis system of durene in the host crystal in both the quinoline and isoquinoline doped crystals. The D axis systems are found to be rotated about an axis perpendicular to the molecular plane of durene. The principal axis systems of D and g are found to be the same within experimental error for the quinoline phosphorescent state. Hyperfine structure is observed in both molecules, and is assigned to coupling with protons in the 1, 4, 5, and 8 ring positions in quinoline, and in the 1, 4, 5, and 8 ring positions in isoquinoline. The normalized spin density at these positions is approximately equal to 0.23 in both molecules, assuming that the hyperfine coupling tensors for doublet-state π radicals are applicable to triplet-state molecules.
The phosphorescent states of quinoline and isoquinoline are interpreted to result from π—π* excitations. The decay constants of the isomers were found to be 0.80±0.02 and 0.95±0.1 sec, respectively.
Preliminary measurements on the phosphorescent state of cinnoline are consistent with the interpretation of this as an n—π* triplet state.
Spectra and Energy Levels of Er3+ in YCl3
Authors: Rakestraw J. W. , Dieke G. H. 
Published: January 2005

Yttrium chloride is monoclinic with C2 point symmetry at the site of a Y3+ ion. The point symmetry is approximately octahedral. The absorption and fluorescence spectra of Er3+ in YCl3 are used to find the energy levels of Er3+. The Zeeman effect and the excitation of fluorescence are studied. Assuming a cubic field, the Stark splittings of the Z and Y groups are used to obtain the crystalline field parameters: A4〈r4〉=175. cm−1,  A6〈r6〉=10.4 cm−1.
The cubic field gives approximate agreement with the experimental data and explains the clustering of Stark components which is characteristic of rare-earth ions in YCl3. The total Stark splitting of the free ion levels of a rare-earth ion is larger in YCl3 than in LaCl3. The centers of gravity of the excited levels of Er3+ are higher in LaCl3 than in YCl3, and this shift increases with increasing wavenumber.
Molecular Vibrations of Quinones. III. Preparation and Infrared Spectra (Solution and Vapor) of p-Benzoquinone-d1, p-Benzoquinone-2,5-d2, p-Benzoquinone-2,6-d2, p-Benzoquinone-18O2, and p-Benzoquinone-d4-18O2
Authors: Ziffer Herman , Charney Elliot , Becker Edwin D. 
Published: January 2005

Three specifically deuterated quinones, p-benzoquinone-d1, -2,5-d2, and -2,6-d2, have been prepared by a scheme involving (1) the formation of the dibenzyl ether of the appropriate bromohydroquinone, (2) reaction of this bromoether with n-butyl lithium, (3) introduction of deuterium by solvolysis of the lithium derivative in D2O, (4) cleavage of the ether with sodium in liquid ammonia, and (5) oxidation of the specifically deuterated hydroquinone by chromic oxide in buffered acetic acid. Infrared spectra have been obtained for the three compounds both in solution (4000–75 cm−1) and in vapor phase (4000–300 cm−1). The band contours of the vapor spectra are analyzed and discussed.
In addition, p-benzoquinone-18O2 and quinone-d4-18O2 have been prepared by exchange of quinone and quinone-d4 with H218O. Solution spectra (4000–300 cm−1) are reported.
Luminescence of Solids Excited by Surface Recombination of Atoms. V. Quantitative Dependence of Luminescence Response on Oxygen- and Nitrogen-Atom Densities
Authors: Sancier K. M. 
Published: January 2005

The quantitative relationship between luminescence response and atom density was investigated for the lumophor CaO:Sb:Cl excited by surface recombination of nitrogen or oxygen atoms. Atom densities were determined by electron spin resonance employing molecular oxygen as a standard of spin density.
Luminescence response is essentially linearly proportional to nitrogen-atom density for total nitrogen pressures of 0.007 to 0.29 Torr. Luminescence response to oxygen atoms, determined at a total oxygen pressure of 0.016 Torr, is linearly proportional to oxygen-atom density when account is taken of the decreased response caused by oxygen-atom exposure. However, for certain operating conditions of the discharge, enhanced luminescence response occurred at oxygen-atom densities less than 3×1013 atom/cc; also, no significant decrease of response occurred with exposure to oxygen atoms at densities less than 0.4×1013 atom/cc. The enhanced response and the absence of a decreased response upon continued exposure are attributed to electronically excited oxygen species, probably O(1D) or O(1S). Equal densities of nitrogen and oxygen atoms produced about the same luminescence response.
Mercury-Sensitized Photolysis of Propylene Primary and Radical Reactions
Authors: Heller Carl A. , Gordon Alvin S. 
Published: January 2005

A description is given of the mercury-sensitized photolysis of propylene and mixtures of propylene with H2, D2, and propylene-d6 at 26°C using 253.7 and 184.9-nm light. There are at least five primary steps: C3H6*→H+C3H5,  C3H6*→CH3+C2H3,  C3H6*→cyclopropane,  C3H6*→CH4+C2H2,  C3H6*→H2+(C3H4).The ratios of the primary reaction rates depend upon wavelength of the light and deuteration of the propylene. Addition of hydrogen atoms to the propylene double bond gives 5% n-propyl radicals.
We find no evidence of vinyl—vinyl radical combination to form butadiene. The cross-combination ratio of isopropyl and allyl radicals is 6½.
Isotopic Mixing in CO Chemisorbed on Tungsten. A Kinetic Study
Authors: Madey T. E. , Yates J. T. , Stern R. C. 
Published: January 2005

When 12C18O and 13C16O were adsorbed together on tungsten, rapid isotopic mixing to form 12C16O and 13C18O occurred at temperatures above 850°K. These temperatures correspond to the desorption temperatures of the more strongly held adsorbed CO species (β states). No evidence was found for dissociation of CO into mobile adsorbed C and O atoms. A four-center bimolecular exchange intermediate on the surface is postulated. This is consistent with a model for molecular CO chemisorption on tungsten, which involves surface bonding through both the carbon and oxygen.
The rate constant for the bimolecular surface-exchange reaction is 1.9×10−10 exp(−30 000/RT) cm2/molecule·sec.