bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion—Molecule Reactions of Propane Ions with Benzene, 1,3—Butadiene, Hydrogen Sulfide, and Nitric Oxide
Authors: Bone L. I. , Futrell J. H.
Published: January 2005

Reactions of the principal primary ions from propane, C3H8+, C3H7+, C3H6+, C3H5+, C3H3+, C2H5+, C2H4+, C2H3+, and CH3+ with benzene, 1,3-butadiene, nitric oxide, and H2S were investigated in a tandem mass spectrometer. Reaction mechanisms are deduced for these systems and it is suggested that a relatively long-lived reaction complex is involved for most of these reactions. For the reaction of propyl ions with benzene an unstable adduct C9H13+ was observed which could be stabilized by collision and a unimolecular rate constant of 107sec−1 for its decomposition was estimated from its pressure dependence. In the H2S+–C3D8 and C3D8+—H2S systems charge exchange and deuteronation of H2S are competitive reactions, both proceeding via a long-lived intermediate C3D8H2S+ in which extensive isotopic exchange occurs. The results of this study are correlated with recent radiolysis experiments and it is concluded that these two methods for studing gas-phase ionic reactions are complementary.
Partial Interference and Atomic Distribution Functions of Liquid Silver—Tin Alloys
Authors: Halder N. C. , Wagner C. N. J.
Published: January 2005

The x-ray scatterings from liquid Ag–Sn alloys previously measured at temperatures 100°C above the respective liquidus temperatures have been reanalyzed. The total-interference functions (also called structure factors) I(K), where K=4π sinθ/λ, were first refined and then used to calculate the partial-interference functions Iij(K), assuming that they are approximately independent of the atomic concentrations. The least-squares analysis with five different atomic concentrations of Sn, i.e., 18.5, 25, 36.5, 50, and 68.5 at.%, yielded three Iij(K).

The Fourier transform of Iij(K) leads to the partial radial distribution function (RDF)=4πr2ρij(r)/cj, and the reduced distribution function Gij(r)=4πr[ρij(r)/cj—ρ0], where ρij(r) is the partial radial density, cj is the atomic concentration of the j-atoms and ρ0 is the average atomic density. Thus calculated Iij(K) and Gij(r) were used to reproduce the measured I(K) and their corresponding G(r), and a remarkably good agreement was found between the measured and calculated values. Judging from the observed agreement, it can be concluded that for liquid Ag–Sn alloys the partial ISnSn(K), IAgAg(K), and ISnAg(K) are not influenced by the relative abundance of the elements.

The resistivity of the alloys obtained with Iij(K) and the pseudopotential elements Ui(K) agrees well with those measured experimentally.
Use of Corona Discharges for the Study of Ion—Molecule Reactions
Authors: Shahin M. M.
Published: January 2005

Low-pressure positive corona discharges have been developed for studies of ion—molecule reactions at pressures which exceed those used in conventional high-pressure mass spectrometry by several orders of magnitude. The reactions occurring within the discharge are studied by means of a mass spectrometer, sampling the ionic species which arrive at the cathode. Studies made in a system of nitrogen and trace quantities of either water vapor or oxygen have shown the importance of both ion—molecule reactions and charge-exchange processes which occur in atomspheric gases. The cross sections for a number of these processes with ions of near thermal energies have been measured.
Compressibility of Solid Iodine
Authors: Grover R. , Kusubov A. S. , Stromberg H. D.
Published: January 2005

A large discrepancy exists between the recently published, static, x-ray-determined compressibility of solid iodine and previously published shock-wave compression data. In order to resolve this discrepancy, static piston displacement compression measurements have been made on iodine up to 40 kbars. The agreement of these measurements with shock data indicates that compressions calculated from x-ray data on iodine are in error.
Sudden Approximation Applied to Rotational Excitation of Molecules by Atoms. III. Angular Distribution and Energy Dependence of the Inelastic Scattering
Authors: Fenstermaker Roger W. , Bernstein Richard B.
Published: January 2005

The sudden approximation for rotational excitation of diatomic polar molecules by atomic impact is applied, yielding semiclassical angular distributions of rotational transition cross sections and their energy dependence. The results for a model system (intended to approximate TlF–Ar) are not inconsistent with the experimental findings of Toennies. The dominant excitations are those allowed by first-order time-dependent perturbation theory, but the strong coupling (due principally to the large long-range anisotropy in the potential) produces extensive excitation to remote open channels, i.e., those forbidden by low-order perturbation theory. The main prediction of the present work is the presence of a single major peak in each of the various differential polar inelastic cross sections; with increasing collision energy, these maxima trend to smaller angles and increase in peak intensity.
Additivity of Proton Magnetic Resonance Solvent Shifts in the Azine Series
Authors: Laszlo Pierre , Soong John L.
Published: January 2005

Shifts induced by aromatic solvents upon resonances of polar solutes are observed to be additive. Incremental solvent shifts can be ascribed to a proton which has a given relationship with a polar substituent or a heteroatom. There is a dispute as to whether this additivity is merely a consequence of the additivity of substituent effects in any solvent or whether it is an independent phenomenon. Heterocyclic molecules for which additivity in the first sense does not hold are studied. The results are also discussed with respect to the nature of the interaction between the polar solute and the aromatic solvent. It is pointed out that the existing models do not account satisfactorily for both the additive behavior and the observed increments. These empirically derived quantities are quite successful in relating the solvent shifts of a number of compounds; for the ring protons of methyl and polymethyl pyridines, pyridazines, pyrimidines, and pyrazines, the carbon tetrachloride to benzene incremental shifts are −0.07 (ortho-N), 0.44 (meta-N), 0.56 (para-N), and −0.11 ppm per methyl group irrespective of its substitution site.
Experimentally Determined Hückel Coefficients of Aromatic Hydrocarbons
Authors: Griffith O. F. , Poole Charles P.
Published: January 2005

Three theories of hyperfine coupling constants of hydrocarbon radical ions are compared, and the assumptions underlying the theories are discussed. The McConnell and the Colpa—Bolton theories are used to compute experimentally determined Hückel-type coefficients Ci, and tabulations of these values are included. These coefficients should be useful in calculations of various molecular parameters which depend upon molecular orbital results, since they are believed to be more accurate than purely theoretical values. The parameters Q and K are also tabulated and may be used for comparisons between the electronic structures of various radical ions. The enhancement factor Q/QoAv is particularly useful in this respect.
Rigid Disks at High Density. II
Authors: Salsburg Zevi W. , Rudd W. G. , Stillinger F. H.
Published: January 2005

As shown in a previous publication, the Helmholtz free energy per particle (divided by kBT) for a rigid disk system has the following asymptotic form in the limit of the reduced density θ=A0/A→1:F/NkBT∼2ln(λ/a)−2ln(θ−1−1)+C+D(θ−1−1)+···, in which C and D are appropriate numerical constants, λ is the mean thermal de Broglie wavelength, a is the disk diameter, and A0 is the close-packed value of the area, A, of a system of N particles. Moreover, a technique for estimating the value of C was developed. This technique was based upon a product representation for the partition function which considered a sequence of correlated motion of larger and larger sets of contiguous particles. An approximate value of C was previously obtained from all contributions for four or fewer correlated disks. This article extends these calculations to fifth order (contributions of all sets of five particles) with the summary result: C=0.14384–0.013857+0.014322–0.0073211–0.004222+···=0.14384–0.011078+···, in which the first number is the value of C obtained from the one-particle free-area model, and the remaining terms are the corrections from two-, three-, etc., particle correlations. These results are in slight disagreement with the estimate of C obtained by Hoover and Alder from molecular dynamics calculations, namely C≅0.14384–0.06±0.02. The sequential approximation scheme for estimating C is applied to the tunnel model (where the exact value is known) and shows a rapid convergence. An analysis of the most compact clusters or sets also supports the fifth-order estimate of C.
High-Pressure Synthesis of the Stoichiometric Compound FeO
Authors: Katsura Takashi , Iwasaki Bunji , Kimura Shigeyuki , Akimoto Syun-iti
Published: January 2005

A stoichiometric compound, Fe1.000O, was synthesized at high pressures above 36 kbar at 770°C by a reaction between Fe0.950O and metallic iron. The cell dimension of Fe1.000O was determined to be 4.323±0.001 Å at atmosphere pressure.
Configuration Interaction in Molecular-Orbital Theory
Authors: Allinger Norman L. , Stuart Thomas W.
Published: January 2005

The importance of configuration interaction within the framework of a Pariser-Parr treatment of π systems is reviewed and further studied. Three molecules—octatetraene, styrene, and naphthalene—are considered in detail. The energies obtained for the various states are shown to be often quite dependent upon the number of configurations included. Finally, it is argued that, if molecular-orbital configuration interaction is to be of predictive value over a wide range of compounds, then the best general criterion for inclusion of a configuration should be its energy, and that the cutoff point should not be less than 20 eV.
Quantum Mechanics of the H2–H2 Interaction. III. Nonorthogonal SCF—GF Calculations in the One-Configuration Approximation
Authors: Magnasco V. , Musso G. F. , McWeeny R.
Published: January 2005

Short-range intermolecular forces in the H2–H2 system have been approached by a rigorous quantum-mechanical calculation using a wavefunction consisting of one configuration of nonorthogonal group functions constructed from a minimal basis set of 1s Slater orbitals. The need of avoiding, with restricted wavefunctions, the forced orthogonalization of the atomic-orbital basis, which amounts to the relaxation of the strong orthogonality condition in a group-function approach, appears to be essential in order to give the correct angular dependence of the intermolecular energy. About 98% of the potential `barrier' resulting from the minimal-basis-set calculation with complete configuration interaction is accounted for by nonorthogonal group functions which allow only for intramolecular correlation. The even simpler one-determinant wavefunction constructed from SCF bond orbitals gives numerical results within 5% to 10% of the reference value for the intersection and within 3% to 5% for the energy difference between different relative orientations. Both inter- and intramolecular correlations seem therefore to be relatively unimportant in determining the relative orientation of the two molecules in the short-range region. The partitioning of the short-range interaction energy into a Coulomb component (slightly attractive and slowly varying with the dihedral angle) and into a correction or penetration term, which arises from electron interchange between the electron groups when they begin to overlap, shows that the largest part of the interaction and its orientation dependence arise from the repulsion due to negative overlap between the closed-shell charge clouds.
Spin—Lattice Relaxation in Multilevel Systems
Authors: Vold R. L. , Gutowsky H. S.
Published: January 2005

Spin—lattice relaxation behavior is calculated for the six lines of the high-resolution NMR spectrum of an AX spin system in which the A spin has I = ½ and the X, 32. Intramolecular dipole—dipole interactions, quadrupole relaxation of the spin three-halves nucleus, and chemical shift anisotropies of both spins are considered. For simplicity all of the tensor operators are taken to be axially symmetric about the A—X internuclear vector, and random isotropic reorientation of the molecules is assumed. The latter assumption can be removed in a phenomenological manner. Cross terms in the Redfield relaxation matrix elements lead to asymmetric relaxation. In general, none of the lines relax in exponential fashion, unless the quadrupole relaxation of spin X is rapid. The relevance of these calculations to proton saturation recovery experiments on (CD3O)211B–H is discussed. Small differences observed previously in the relaxation of the proton spectrum of this compound are probably due to instrumental effects.
Lowest π, π* Triplet State of Acetophenone
Authors: Lamola A. A.
Published: January 2005

The characteristic short-lived n, π* phosphorescence from acetophenone in hydrocarbon glass is replaced by a long-lived (∼1 sec) phosphorescence in very polar and especially hydrogen-bonding solvents. From the absorption and emission spectra in various solvents together with the ESR spectrum of the phosphorescent state, it is possible to assign the latter as the perturbed 3La state. In nonpolar solvents this state lies between the 1n, π* and 3n, π* states. In all probability, intersystem crossing in acetophenone proceeds from the 1n, π* state to the 3La state. On the basis of lifetime data and polarization studies it is suggested that the 3La→1A transition derives intensity through both mechanisms shown below:[Complex chemical formula]
Infrared Spectrum of Methyl Lithium Monomer in Solid Argon
Authors: Andrews Lester
Published: January 2005

Continued matrix reaction of methyl radical and lithium atoms produces methyl lithium, CH3Li. Isotopic substitutions at all atomic positions verify the molecular identity and indicate that the monomeric species is isolated. The fundamental frequencies, which are slightly lower than those for methyl halides and reasonably near those for solid methyl lithium in mulls, lead to the potential constants kH–C=4.32 mdyn/Å, kH–C–H=0.50 mdyn·Å/rad2, kH–C–Li=0.12 mdyn·Å/rad,2 and kC–Li=0.78 mdyn/Å. The low H–C–Li bending force constant suggests a significant amount of ionic character in the C–Li bond.
Autoionization of Highly Excited Ar+ Ions Produced by Electron Impact
Authors: Newton Amos S. , Sciamanna A. F. , Clampitt R.
Published: January 2005

The (M/q)*=10 peak in the mass spectrum of argon observed at ionizing electron energies of 40 to 120 eV (uncorr.), is shown to consist of approximately equal contributions from: (1) surface-induced transitions of an excited Ar+ ion to Ar2+ at the last ion-source slit, and (2) an autoionization of an excited Ar+ ion after the last ion-source slit. By use of an auxiliary slit beyond the last normal ion-source slit, these two processes were separable, and it is shown that the excited state undergoing surface-induced transitions is a different state than that undergoing autoionization, with the autoionizing state having an A.P. of 0.5±0.2 eV higher than the state undergoing surface-induced transitions. The existence of autoionizing states of Ne+ and Ar2+ was also confirmed.
Time-Dependent Reorientation Probabilities and Molecular Relaxation
Authors: Anderson J. E.
Published: January 2005

This article considers situations in which the probability of molecular reorientation is governed by a secondary, time-dependent process. A ``projection technique'' for computing reorientational correlation functions in these situations is described, together with a ``simple defect'' model of molecular relaxation. The effects of different types of secondary time-dependent processes on the observable correlation time distribution are discussed.
F–F Spin—Spin Coupling in Perfluoro-o-Xylene
Authors: Jonas J.
Published: January 2005

The F–F coupling constants between the ortho-ring fluorines and the fluorines of the CF3 group were measured at different temperatures in perfluoro-o-xylene and some related compounds. The rotationally averaged coupling constants calculated by using the approximate dependence of the JFF upon the dihedral angle between the C–F bond of the CFX2 group and that of the 2-fluorine atom are in good agreement with the observed values. Qualitative conclusions about the conformational behavior of two adjacent CF3 groups were supported by calculations of repulsion energies between the fluorine atoms in these groups using a simple van der Waals repulsive potential. It is proposed that the small temperature dependence of the JFF in the compounds studied is due to intermolecular interactions.
Coalescence Conditions as Constraints in Open-Shell SCF Theory
Authors: Chong D. P.
Published: January 2005

The general coalescence conditions of Pack and Byers Brown are applied to the special case of electron—nucleus coalescence for SCF orbitals in atoms and molecules. Integral coalescence conditions are derived and then used to construct constraints for the variation of the orbitals. The constrained variation leads to new pseudo-eigenvalue equations, which may be solved by combining the methods of parametrization and perturbation.
Quantum Statistics and Slow Neutron Scattering by Gases
Authors: Plummer J. P. , Summerfield G. C. , Zweifel P. F.
Published: January 2005

A surprisingly simple expression in ``closed form'' for the cross section d2σ/dΩdε for the scattering of thermal neutrons (including polarized neutrons) from an ideal quantum gas is derived. This result extends the work of Van Hove on the quantum gas. An expansion is obtained for dσ/dε. The case of elastic scattering is treated separately. From these expressions is obtained a criterion for ignoring the statistics of the scatterer in favor of classical (Boltzmann) statistics. This criterion should have some validity for weakly interacting systems. It is shown that the effects of statistics on the neutron cross section for a helium-4 gas range from 5% or less for the noninteracting gas up to as much as 40% for the interacting system.
F-Aggregate Centers in Sodium Fluoride. I
Authors: Konrad Karl , Neubert Theodore J.
Published: January 2005

Thermal aggregation of color centers in a sample of NaF, x irradiated 67 h at 200°K, was studied by observation of the optical-absorption spectrum during warming. At 200°K, a very intense F′ band (470 mμ) is formed and obscures the M1 band of any M centers which may be present. During warming the F′ band decreases to half-intensity at 280°K but some remains even at 320°K. M centers begin to appear at ∼270°K, preceded by the appearance of a band at 725 mμ which forms and then thermally bleaches. The 725-mμ band is assigned to M+ centers resulting from capture of α centers by F centers. R+ centers (λ=max520 mμ) are also observed to form during warming. Thermal aggregation to yield M centers is not nearly as extensive in NaF as in KCl, nor does the M1 band grow on standing in the dark at room temperature. Bleaching the sample with F-band light at room temperature produced large R1, R2, R+, and M1 bands as well as six smaller bands (576, 604, 630, 736, 870, and 1040 mμ), measured at 65°K. Zero-phonon lines are associated with the R2, R+, 604-, 870-, and 1040-mμ bands. Additional experiments on samples containing M+ centers indicate that the M+ band exhibits a dichroism parallel to that of the M1 band and may be bleached at low temperature by x-ray-released electrons. The M+-band maximum shifts from 726 mμ (273°K) to 736 mμ (80°K) as temperature is decreased, while the half-width (0.18 eV at 80°K) behaves in the usual way.
Proton Magnetic Resonance Coordination-Number Study of AlCl3 in Aqueous Mixtures of Acetone, N,N-Dimethylformamide, Dimethylsulfoxide, Dioxane, Tetrahydrofuran, and Tetramethylurea
Authors: Fratiello Anthony , Lee Robert E. , Nishida Vone M. , Schuster Ronald E.
Published: January 2005

The coordination number of Al(III) in aqueous mixtures of acetone, dimethylformamide, dimethylsulfoxide, dioxane, tetrahydrofuran, and tetramethylurea was measured over a range of solvent concentrations by a proton magnetic resonance technique. At low temperatures, proton exchange is slowed to such an extent in these mixtures that separate resonance signals are observed for bulk water and water molecules in the Al(III) solvation shell. Coordination numbers were measured by direct integration of the two water signals. The measurements show that in aqueous mixtures of acetone and tetramethylurea, and over a small solvent concentration range, dioxane and tetrahydrofuran, only water solvates Al(III). This was indicated by the value of six molecules obtained for the contribution of water to the Al(III) solvation shell in these mixtures. In aqueous mixtures of dimethylformamide and dimethylsulfoxide, wherein separate signals were also observed for the nonaqueous components, both solvents contribute to the Al(III) solvation shell. No evidence for ion pairing was found in any of the mixtures.
Statistical-Mechanical Derivation of the Partial Molecular Stress Tensors in Isothermal Multicomponent Systems
Authors: Snell Fred M. , Aranow Ruth , Spangler Robert A.
Published: January 2005

Commencing with the general equations of molecular dynamics as used by Bearman and Kirkwood, the hydrodynamic equations of motion are derived for each component in an isothermal multicomponent system consisting of sensibly spherical nonreacting molecules. It was the primary purpose of the investigation of which this is a report to attempt to obtain a microscopic statistical basis for the macroscopic phenomenologic development of Snell and Spangler, especially in regard to their new formulation for the partial molecular stress tensors. An expansion of the number densities in pair space of perturbed nonequilibrium states alternate to that used by Bearman and Kirkwood is employed. Our expansion esplicitly recognizes the position vector arguments of both the number densities in singlet space and the local mean velocities of the individual components, as well as for the equilibrium pair correlation function. The quantities are then expanded about the central position vector in a Taylor's series. The results are not only corroborative of the previous phenomenologic development when the flows of the individual components are solenoidal and attention is confined to systems in which the kinetic contribution to the stress tensor is negligible in comparison to the contribution arising from intermolecular interaction, but they also provide a new microscopic theory of hydrodynamical flow in multicomponent systems.
Theoretical Calculation of the Potential Curves of the Be2 Molecule
Authors: Bender Charles F. , Davidson Ernest R.
Published: January 2005

The low-lying electronic states of the Be2 molecule have been examined using MO SCF CI with a basis set of elliptical orbitals. The ground state of the molecule was found to be repulsive in the best calculation. The excited states all seem to be bound with potential curves similar to that predicted for Be2+. Two new techniques for improving the convergence of configuration interaction are introduced and applied to the ground-state calculation.
Polymer Relaxation Times from Birefringence Relaxation Measurements
Authors: Thompson Douglas S. , Gill Stanley J.
Published: January 2005

A theoretical description of the time dependence of induced birefringence in polymers, based on the ``pearl-necklace'' model, is presented, and relations between relaxation and frequency dependence methods are discussed. The relaxation theory is applied to the results of measurements of the longest relaxation time for the DNA from bacteriophage T2. The measured relaxation time, in the limit of infinite dilution, is τ1=0.45 sec. The molecular weight calculated from this value using the theoretical expression for a nondraining coil with excluded volume is in good agreement with the value of the molecular weight obtained from low-shear intrinsic viscosity measurements.
Metastable Transitions Observed in a Time-of-Flight Mass Spectrometer
Authors: Dugger Donald L. , Kiser Robert W.
Published: January 2005

A time-of-flight mass spectrometer has been employed in the investigation of metastable transitions by using a retarding potential technique. Expressions have been developed which permit a simple, nearly quantitative determination of the masses of the daughter ions arising from these transitions. In addition equations are derived which permit the identification of charge exchange reactions, An++B→Ap++B(n—p)+. Most of the metastable transitions observed using magnetic instruments have either been determined or accounted for by this method in n-butane, ethyl acetate, trimethyl phosphate, and dimethylmethylphosphonate. In addition, this approach has the unique feature of permitting the observation of new metastable transitions not observed in magnetic instruments. The limitations of the method are recognized and discussed.
Electron Impact Excitation of the c 3Πu States of H2 and D2 by a Trapped-Electron Method
Authors: Dowell J. T. , Sharp T. E.
Published: January 2005

Electron impact excitation of H2 and D2 within 0.05 eV of threshold is studied with a trapped-electron method. An ac RPD technique is used to achieve energy resolution better than 0.1 eV. A series of trapped-electron peaks is resolved in the 11.7- to 13.5-eV range. These are identified as vibrational levels of the c 3Πu state. In this energy range, excitation of other states (both singlet and triplet) near threshold is found to be weak by comparison. Several peaks observed in the 13.8- to 15.4-eV range could not be assigned to excitation of vibrational levels of a single electronic state.
Energy Levels and Crystal Field of LaCl3:Gd3+
Authors: Piksis A. H. , Dieke G. H. , Crosswhite H. M.
Published: January 2005

The optical-absorption spectra of Gd3+ in single crystals of 2% and 5% GdCl3 in LaCl3 at 1.7° and 77°K are given. The 8S7/2 ground state has no resolved structure in the field-free spectra. Absorption to all Stark components of the 6P and 6I multiplets are observed, as well as for the higher 6D7/2 and 6D9/2 levels. Fluorescence from 6P7/2 and 6I7/2 is observed. A crystal-field analysis gives values of B20=97.4 cm−1, B40=−42 cm−1, B60=−30 cm−1, B66=290 cm−1 for the crystal-field parameters, based on intermediate coupling free-ion calculations for the 6P and 6D multiplets. Hydrogenic ratios of the Slater parameters were assumed.
Correlation Energy of the Two-Electron Atom in a Spherical Potential Box
Authors: Gimarc B. M.
Published: January 2005

Results of calculations approximating the electronic Coulomb correlation energy of the two-electron atom in a spherical potential box are reported and discussed. Although the total electronic energy of such an atom varies rather widely with changes in the radius of the box, the correlation energy seems to be relatively insensitive to such changes except for box radii on the order of or smaller than the atomic radius.
Theory of the Helix—Coil Transition for Synthetic Polynucleotides Forming Branched Helical Structures
Authors: Hijmans J.
Published: January 2005

A theory is developed for synthetic polynucleotides such as dAT, which are capable of forming single-stranded, branched helical structures. The grand-partition function for a dilute solution is expressed in terms of the so-called quasigrand partition function for a strand. Configurations are considered which consist of rings in the random-coil state, connected by helices. Weights are assigned to each configuration according to a similar set of rules as were used by Crothers and Zimm [D. M. Crothers and B. H. Zimm, J. Mol. Biol. 9, 1 (1964)] for unbranched two-stranded complexes. The enumeration of configurations is carried out by means of a graph—theoretical technique. Expressions are derived for the helicity (the fraction bonded pairs), the mean number of base pairs per helix and per ring, the mean numbers of helices and U loops per strand. Our results for self-complementary strands (dAT) are compared with the results of Crothers and Zimm for pairs of complementary homopolymer strands (dG—dC). The slope of our melting curve is found to be proportional to the ½ power of the stacking parameter τ instead of the ⅔-power dependence obtained for unbranched systems.
Infrared and Ultraviolet Spectroscopic Study of the Products of the Vacuum-Ultraviolet Photolysis of Methane in Ar and N2 Matrices. The Infrared Spectrum of the Free Radical CH3
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: January 2005

The vacuum-ultraviolet photolysis of methane in an argon or a nitrogen matrix at 14°K leads to the formation of a sufficient concentration of the methyl radical for observation both of its 1500-Å electronic transitions and of its out-of-plane deformation fundamental, which appears at 611 cm−1 for CH3 trapped in a nitrogen matrix. The value observed for this fundamental of CD3 is in reasonable agreement with the value previously derived from analysis of the 2160-Å band system. Isotopic substitution studies support the assignment of the 611-cm−1 feature to ν2 of CH3. Data are consistent with the previous report of a planar structure. Evidence is presented suggesting that CH3 may rotate in an argon matrix. Although CH2 has not been directly observed, an appreciable concentration of CH2N2 appears in the N2 matrix experiments. Three electronic transitions of CH are observed in the argon matrix experiments, and there is evidence for the production of a small concentration of C atoms.
Infrared and Dielectric Studies of Chloroform as Proton Donor in Hydrogen-Bond Formation
Authors: Khare B. N. , Mitra S. S. , Lengyel G.
Published: January 2005

Infrared absorption bands of free and associated species of deuterochloroform were observed in binary solutions (with triethylamine). Temperature-dependent spectra were used to calculate the equilibrium constants at various temperatures and the heat of formation of the complex molecule. A value of 0.133±3% liter mole−1 was obtained for the equilibrium constant at 25°C. The heat of formation of the deuterochloroform—triethylamine complex was determined to be 4.0 kcal mole−1. The dielectric constant shows a substantial increase over the value predicted by Onsager's theory. This indicated that the associated complex possesses a large dipole moment. In conjunction with the infrared data, the dipole moment of the associated molecule was evaluated as 3.15×10−18±10% cgs units. Similar infrared and dielectric measurements were carried out on deuterochloroform—acetonitrile mixtures. No strong hydrogen bonding was detected by either method.
Heat Capacity of Europium from 5°—300°K
Authors: Gerstein B. C. , Jelinek F. J. , Mullaly J. R. , Shickell W. D. , Spedding F. H.
Published: January 2005

The heat capacities of two samples of Eu have been measured, one in the range 12°—300°K and another in the range 5–300°K. A sharp transition was found in the neighborhood of 88°K, the temperature of the peaks differing by 0.3°K in the two samples, and the height of the peaks differing by roughly a factor of 2. Reasonable values of lattice and electronic contributions yield a magnetic entropy of R ln8 at room temperature in accordance with the ion core being divalent over the entire temperature range measured. This value for the magnetic entropy is not unambiguously determined by our analysis, however. The thermodynamic functions for the two samples agree at room temperature to within 0.2% and are found to be as follows: (H298.15∘−H0∘)/T=26.86 J (g·at. wt·deg)−1,  S298.15∘=77.81 J (g·at. wt·deg)−1.
Ammonia Decomposition in Glow Discharge
Authors: Carbaugh D. C. , Munno F. J. , Marchello J. M.
Published: January 2005

Rate data for the decomposition of ammonia in a glow-discharge flow system were obtained at 1.7 mm Hg and several current levels. Pure ammonia at 25°C was fed continuously to the reactor at different flow rates. The reaction products were observed using both optical spectroscopy and gas chromatography. A reaction mechanism for the rate steps which fits the data well is proposed. The principal feature of the mechanism is the use of two simultaneous reactions for NH2 combination. One leads to N2H4 and the other to NH and NH3.
Study of the Isakovich—Chaban Theory in Viscoelastic Relaxation
Authors: Knollman G. C. , Hamamoto A. S.
Published: January 2005

The recently proposed Isakovich—Chaban phenomenological theory for highly viscous liquids is examined, as it relates to the complex shear modulus for viscoelastic liquids, in the light of experimentation over the sonic frequency regime of liquid relaxation. Two butanediols, glycerol, and two chlorinated biphenyls are studied experimentally at atmospheric pressure to compare shear-relaxation spectra at various temperatures with the theoretical predictions. Similar comparison is made for one of the biphenyls at two temperatures but over a range of static pressure variation. Experimental spectra for polyisobutylene at atmospheric pressure are presented (reduced to a single temperature) to estimate applicability of the theory to polymeric materials. The findings generally indicate very good agreement between theory and experiment, except in a few instances for liquid shear rigidity over the upper frequency portion of the spectrum and for the maximum imaginary modulus component. Isakovich—Chaban theory does not appear to represent quite as well experimental results taken under static pressure variation at elevated temperature as it predicts relaxation spectra under temperature variation at ambient pressure. The theory may relate to certain polymers as well as to liquids, at least judging from the excellent comparison realized in the case of polyisobutylene at atmospheric pressure, where the analytical method even describes qualitatively the low-frequency behavior observed by other investigators.
Photodissociation of NH3 in the Vacuum Ultraviolet
Authors: Okabe H. , Lenzi M.
Published: January 2005

Two photodissociation processes of NH3 producing electronically excited radicals have been studied in the vacuum ultraviolet: NH3→NH2 Ã2A1+H,NH3→NH c 1Π+H2.The intensity of the fluorescence from these radicals, lying in the spectral regions 4000 to 6000 Å and at 3240 Å, respectively, has been measured as a function of wavelength of incident light with a resolution of 7 Å. The fluorescence curves thus obtained were compared with the absorption spectrum of NH3. It is shown that the process (1) may be correlated with the B̃1E′′ (1665-Å bands), D1A2″ (1434-Å bands), Ẽ1A2′′ (1330-Å bands), 1286-Å bands and the continuum (1250 to 1600 Å). On the other hand, the process (2) may be associated with the continua (1250 to 1600 Å and below 1250 Å). The threshold wavelength of Process (2) is 1325±7 Å. The electronic energy a of the first singlet state NH a 1Δ with respect to the ground triplet state X3Σ− is a≤1.6±0.1 eV, which is obtained from the threshold wavelength together with the heat of reaction (3.9±0.1 eV) of NH3→NH X3Σ−+H2, and the electronic of the NH c1Π (3.813 eV) with respect to the a1Δ. Various other primary processes are discussed in conjunction with the absorption spectrum. For incident light of wavelength below 1200 Å the ionization process NH3→NH3++e,and the process (2) both of which may arise from the continuum become predominant. Dissociation processes appear to be subject to the spin conservation rule.
Weinstein Calculations for Excited States
Authors: Goodisman Jerry
Published: January 2005

Weinstein's principle for an energy level, 〈H〉—Q≤Ej≤〈H〉+Q, gives both a lower and an upper bound and is applicable to both ground and excited states. Here, Q2=〈(H—〈H〉)2〉, all expectation values being calculated with respect to the same approximate wavefunction. An iterative method is proposed for solution of the necessary nonlinear equations. In tests on H2+ and H2, it is shown that the iterative method is workable, and that fair lower bounds are obtained. A formal perturbation theory is used to partly explain our results. Comparisons are made with the conventional variation method.
Vibrational Spectra of Molten Salts. III. Infrared and Raman Spectra of Variably Hydrated Zinc Nitrate
Authors: Hester R. E. , Scaife C. W. J.
Published: January 2005

Infrared and Raman spectra of liquids of composition Zn(NO3)2·xH2O, with x having values from ∞ to 1.42, have been obtained. The changing forms of the spectra are reported as functions of both composition and temperature. The composition dependence shows that the nitrate ions become increasingly associated with zinc ions as the water content is decreased, until at very low water content no uncomplexed nitrate ions remain. Near-anhydrous molten Zn(NO3)2 is thus shown to be a nonelectrolyte. All the results can be interpreted in terms of inner-sphere coordinated water molecules being displaced by nitrate ions binding in a monodentate fashion. Below 4H2O per Zn atom the coordination number of Zn must drop below six. The temperature dependence of spectra representing a wide range of compositions shows that different forms of nitrate perturbation caused by water and by zinc are distinguishable.
Oxidation and Pyrolysis of Ethylene in Shock Waves
Authors: Homer J. B. , Kistiakowsky G. B.
Published: January 2005

The oxidation of C2H4 has been studied in a shock tube by monitoring the infrared emissions from CO and CO2 and the visible emission from CH*. The characteristics of this oxidation closely resemble oxidations of C2H2 and C2H2+H2. The induction periods and exponential time constants for the early phase of CO formation are the same for all three oxidations over the temperature range 1500°—2300°K and lead to a common activation energy of 17±1 kcal/mole. Above 1800°K, the C2H4–O2 reaction, in its early stages, consists mainly of the pyrolysis of C2H4, and the concurrent oxidation of pyrolysis products, C2H2 and H2. Later in the reaction, and more prominently so at lower temperatures, the reaction changes in character to a slower direct oxidation of C2H4. The relative rates of CO and CO2 production in both C2H4–O2 and C2H2–O2 reactions are reported as a function of temperature. The pyrolysis of C2H4 has also been studied in the shock tube by an infrared technique and its rates determined between 1950° and 2250°K. The results are in good agreement with previous work and give an activation energy of 52 kcal/mole for the reaction. The oxidation results would indicate that C2H4, above 1800°K, decomposes mainly by a molecular rather than a radical mechanism.
Ground-State Energy of Lithium and Three-Electron Ions by Perturbation Theory
Authors: Seung Shirley , Wilson E. Bright
Published: January 2005

Perturbation theory has been applied to the calculation of the energy of the (1s)22s 2S ground state of the lithium atom and three-electron ion series, with the entire interelectron repulsion potential employed as the perturbation. The wavefunction to first order has been written down in terms of variation perturbation first-order wavefunctions for the three states of the two-electron ion: (1s)2 1S, 1s2s 1S, and 1s2s 3S. From the first-order wavefunction, the second-order and third-order contributions to the energy have been calculated. The results are that the nonrelativistic Schrödinger energy for the ground state of two-electron ions (with fixed nucleus) is given by E(Z)=−1.125Z2+1.022805Z−0.4083–0.0230(1/Z)+O(1/Z2) a.u. The term in Z0 is in agreement with an empirical value within the uncertainty of the latter. The above expression gives an overall energy better for the larger values of Z than any existing direct variation or configuration interaction calculation and shows that the perturbation expansion is quite rapidly convergent, at least for three electrons. New wavefunctions to first order for the 1s2s 1S and 1s2s 3S states of the two-electron ions were obtained by the variation-perturbation procedure at several levels of approximation. In particular, for the 1S functions, steps were taken to ensure that the perturbation part was orthogonal to the unperturbed function and that the correct relationship to the ground state was maintained.
Sublimation of Strontium Sulfide and the Dissociation Energy of SrS
Authors: Cater E. David , Johnson Ernest W.
Published: January 2005

The sublimation of strontium sulfide in the temperature range 1543° to 2122°K was studied by mass spectrometric and vacuum balance effusion techniques. Partial pressures of the vapor species Sr, S, S2 and SrS were derived. Results are compared with those of Marquart and Berkowitz and of Colin, Goldfinger and Jeunnehomme. Best values obtained from second- and third-law calculations based on the dissociation energy of sulfur D0(S2) = 101 kcal/mole give the following heats of reaction: SrS(s)=SrS(g),ΔH0∘=132±4 kcal/mole,SrS(s)=Sr(g)+S(g),ΔH0∘=212±5 kcal/mole,SrS(g)=Sr(g)+S(g),ΔH0∘=80±4 kcal/mole=3.5±0.2 eV,S(s)+Sr(s)=SrS(s),ΔHf,298∘=−108±4 kcal/mole.
Effective Potential Description of the Quantum Ideal Gases
Authors: Lado F.
Published: January 2005

An attempt is made to describe the quantum ideal gases by means of a classical Boltzmann factor using an effective pair potential. We find the n-body distribution function for ideal gases of spin 0 and use the n=2,3 cases, generalized for spin s, with the Born—Green hierarchal relation to obtain an integrodifferential equation for the effective potential. Several numerical solutions for both the Bose—Einstein and Fermi—Dirac ideal gases are presented.
SCF—MO—LCAO—CI Studies of the Pi-Electronic Structures of Acrolein and Glyoxal Using Ohno's Resonance Integral Formula and Constrained to Satisfy Koopmans' Theorem Exactly
Authors: Pilar F. L.
Published: January 2005

The pi-electronic structures of the trans and cis diastereomers of acrolein are studied within the framework of the Pople—Pariser—Parr approximation in which: (1) Resonance integrals are evaluated by a formula originally derived by Ohno, (2) valence-state ionization potentials of non-carbon atoms are chosen by the constraint that Koopmans' theorem is satisfied literally for the first ionization potential of the molecule, and (3) all penetration integrals are neglected. The effects of including nonnearest-neighbor resonance integrals and of using ``fixed'' effective atomic charges in lieu of ``self-consistent electronegativity'' values are investigated. Also examined is the effect of modifying Ohno's resonance integral formula when used for heteropolar bonds. The optimum agreement between calculations and the limited experimental evidence available occurs when ``self-consistent electronegativity'' effective atomic charges are used along with nonnearest-neighbor resonance integrals computed from a modified Ohno formula. Application of the ``best'' acrolein procedures to the glyoxal molecule suggests either that one cannot use the modified Ohno formula to obtain good spectroscopic intervals and reasonable charge densities from a single set of parameters unless the Koopmans' theorem constraint is relaxed or else that the experimental upper limit to the ionization potential is in error by 0.5 eV or more.
γ Radiolysis of Liquids at High Pressures. V. Reaction of the Hydrated Electron with Water
Authors: Hentz Robert R. , Farhataziz  , Milner David J.
Published: January 2005

The γ radiolysis of deaerated aqueous solutions containing 10−2 or 10−3M glucose and 10−5 to 10−4M of H2O2 or NO3− has been studied at ∼20° in the applied pressure range 0 to 6.34 kbar. The behavior of H2O2 and NO3− solutions is essentially indistinguishable. In both the H2O2 and NO3− solutions, G(H2) increases with increase in pressure; at 6.34 kbar, G(H2) decreases with increase in H2O2 or NO3− concentration. However, the pressure dependence of G(H2) is not affected by a change in glucose concentration from 10−2 to 10−3M or by a change in atmospheric-pressure pH from ∼7 to 9. The results are interpreted in terms of an effect of pressure on the competition between Reactions [4] and [5], eaq−+NO3−(or H2O2)→no H or H2,eaq−+H2O→H+OH−,with Reaction [5] followed by H+RH→H2+R. Such an interpretation gives a difference in activation volumes of Reactions [4] and [5] as ΔV4‡—ΔV5‡ ≈ 15.7 ml mole−1 and a specific rate k50 ≈ 25M−1·sec−1 at atmospheric pressure. Assumption that Reaction [4] is diffusion controlled permits estimation of ΔV4‡ ≈ 1.6 ml mole−1, from the pressure dependence of water viscosity. Thus ΔV5‡ ≈ −14.1 ml mole−1. The latter value is used to estimate an absolute value of V̄0(eaq−) in the range −1.7 to either 2.7 or 9.6 ml mole−1 (dependent on the model assumed for the activated complex); such a range for V̄0(eaq−) is in satisfactory agreement with a previous estimate.
Vibration—Rotation Interaction in Symmetric-Top Molecules and the Splitting between A1 and A2 Levels
Authors: Oka Takeshi
Published: January 2005

The main purpose of this paper is to reformulate the theory of vibration—rotation interaction in symmetric-top molecules in a way which is more accessible to practicing spectroscopists than the current contact transformation formalism. Also it is pointed out that the many accurately measured l-type doubling constants can provide information on the cubic as well as the quadratic potential constants. In Sec. I, analytical expressions for the splitting between the A1 and the A2 rovibrational states are derived starting from the Wilson—Howard equation. Although the result agrees with Grenier—Besson's formula, the method of derivation is new in the following three points: (1) The scheme of orders of magnitude of the terms appearing in the rovibrational Hamiltonian has been made in a definite way. (2) Symmetry considerations and the relations between various rovibrational constants have been fully used in the derivation. (3) The standard perturbation method is used instead of the contact transformation. In order to facilitate the understanding of the perturbation procedure, ``interaction diagrams'' are introduced and fully used. In Sec. II, several discussions of the l-type doubling of symmetric rotors are given. First a physical interpretation of the l-type doubling is discussed in Sec. II. A, and then the existence of a close analogy between the treatments of vibration—rotation interaction and vibronic interaction is pointed out in Sec. II. B. The above arguments lead to the conclusion that, because of certain anharmonic vibrational terms, the average structure of a symmetric-top molecule in the first excited state of a degenerate vibration is no longer symmetric. An interpretation of this effect is presented. Finally it is emphasized that the observed l-type doubling constants provide information on the anharmonic potential constants which are not obtainable from α. A numerical example for the NH3 molecule is given and it is shown that the anharmonic vibrational contribution to the l-type doubling is in fact large.
Triplet State of DNA
Authors: Lamola A. A. , Guéron M. , Yamane T. , Eisinger J. , Shulman R. G.
Published: January 2005

Additional proof has been obtained for the fact that the triplet state in DNA and poly dAT resides at the thymine residue by comparing the intensities of the triplet ESR and phosphorescence signals from DNA's from various sources having different (A+T)/(G+C) ratios. The TMP triplet which is not populated from the exited singlet state in dilute neutral solutions can be populated by having the TMP present in high concentrations or through energy transfer from the triplet state of acetone or acetophenone. The triplet state produced in this manner has been characterized by its Δm=2 ESR line, its phosphorescence spectrum, its decay time, and the effect of deuterium substitution on the latter. In all these respects the DNA and poly dAT triplet resembles the neutral TMP triplet (T) more closely than it resembles the ionized (pH 12) TMP triplet (T−). A determination of the acidity constants of the excited states of A and T gives strong evidence against single-proton transfer from the excited singlet or triplet state of T to A. While this cannot be considered final proof that the DNA triplet is that of neutral thymine, this is accepted as the most likely hypothesis.