bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of Reactive Collisions: Conformal Transformation
Authors: Connor J. N. L. , Marcus R. A.
Published: February 2004

Conformal mapping techniques are applied to the Schrödinger equation for a bimolecular exchange reaction, with all three atoms lying on a line. For the case of a very heavy central mass, the extension of the theory to three dimensions is indicated. An angle-shaped region of the potential-energy surface is mapped onto an infinite strip in order to simplify the theoretical treatment of the boundary conditions. The mapping function is determined with the help of the Schwarz–Christoffel formula, and its properties described. The transformed Schrödinger equation is converted into an integral equation using the method of Green's functions, and integral representations for the reflection and transmission coefficients are obtained.
Shock-Tube Study of the Acetylene–Oxygen Reaction. II. Chemi-ionization during the Induction Period
Authors: Matsuda Shimpei , Gutman David
Published: February 2004

The exponential growth of CH*(A 2Δ → X 2Π) emission and chemi-ion production were simultaneously monitored behind reflected shock waves during the induction period of the C2H2+O2 reaction. Experiments were performed in the temperature range 1479–2282°K using three C2H2+O2+Ar gas mixtures whose C2H2:O2:Ar proportions were 5:5:990, 5:10:985, and 5:30:965. End-on observation was used to monitor CH* emission, and a new saturation-current technique was developed and used to monitor the rate of chemi-ion production. In each experiment the exponential growth constant for ion production was twice that for CH* emission. The results establish that chemi-ionization during the C2H2+O2 induction period is second order in reaction intermediates, which rules out the reaction CH*+C2H2→C3H3++e and is consistent with reaction CH+O→CHO++e as the major chemi-ionization reaction during this early portion of the reaction. An ion–molecule reaction mechanism together with the data obtained in this study is used to demonstrate that the predominance of C3H3+ during the induction period can be explained by such a mechanism.
Low-Pressure Senftleben Effects for Molecular Oxygen
Authors: Coope J. A. R. , Snider R. F. , McCourt F. R.
Published: February 2004

The effect of a magnetic field on the thermal conductivity and viscosity coefficients of paramagnetic Hund's case (b) multiplet Σ molecules, and in particular Σ3 oxygen, is investigated theoretically for the low-pressure region, where the effects are functions of H / p. In this region the fields involved are correspondingly low, so that the total angular momentum J is well defined, and the distribution-function density matrix may be assumed to commute with J2. This fact is exploited in the solution of the kinetic equation. The present treatment makes only very weak assumptions about the nature of the collisions, basically only that the collision (super)operator R is spin independent, which makes it possible to choose a basis in which the R matrix is diagonally dominant. Through detailed analysis of the dependence of all quantities involved on the mean rotational quantum number, N = 〈[N(N + 1)]1/2〉, information about the transport coefficients is obtained in a manner independent of the precise structure of the collision matrix. It is shown that the transport coefficients can be represented as series in powers of N−2, and since N−2 is small, even at liquid-nitrogen temperature, this suggests that the leading terms are the only significant ones. For Σ3 molecules such as oxygen, the even effects show a structure which is a simple superposition of two features of the type found in diamagnetic molecules, one at low field associated primarily with J = N ± 1, and the other at high field, associated primarily with J = N. This formal result depends on very few assumptions about R, whereas the exact positions and intensities depend on the detailed values of the R-matrix elements. The observed 2:1 intensity ratio is consistent with the assumption that R is equivalent within an N shell to a unit superoperator, but this assumption, while sufficient, is not necessary. The odd effects also show a two-feature structure. The high-field feature is again of simple diamagnetic type, while the low-field feature is of reduced intensity, and in general of more complex form.
Dissociation Energy of NaO(g) and the Heat of Atomization of Na2O(g)
Authors: Hildenbrand Donald L. , Murad Edmond
Published: February 2004

The vaporization of Na2O(c) has been studied mass spectrometrically. It was found that the vaporization yields primarily Na(g) and O2(g), with NaO(g) and Na2O(g) being minor vapor constituents. From equilibria involving Na2O(c), Na2O(g), Na(g), NaO(g), and O2(g), it was possible to measure ΔHf298°[NaO(g)] = 24.3 ± 4 kcal/mol and ΔHf298°[Na2O(g)] = − 9.9 ± 3 kcal/mol. These values yield D0°(NaO) = 60.3 ± 4 kcal/mole (2.61 ± 0.20 eV) and D0°(Na2O) = 119.8 ± 3 kcal/mol (5.20 ± 0.15 eV). The appearance potentials of NaO+ and Na2O+ were measured and found to be 6.5 ± 0.7 and 5.5 ± 0.5 eV, respectively. These appearance potentials are suggested to be close to the true ionization potentials of the molecules. Implications of these results regarding some recent beam experiments are briefly discussed.
Inelastic Neutron Scattering from Solid Benzene
Authors: Logan K. W. , Trevino S. F. , Prask H. J. , Gault J. D.
Published: February 2004

Neutron scattering spectra from polycrystalline benzene have been obtained at temperatures between 77 and 270°K. These measurements are compared to recent calculations of spectra using a lattice frequency distribution based on optically determined force constants. The results at different temperatures are discussed, and qualitative agreement between calculated and measured cross sections at lower temperatures is obtained.
Symmetry Properties of the Kinetic Energy Matrix and Their Applications to Problems of Molecular Vibrations
Authors: Dellepiane Giovanna , Gussoni Mariangela , Zerbi Giuseppe
Published: February 2004

In the present paper it is shown that G, the inverse of the kinetic energy matrix in the internal coordinates space, provides all the possible information on the symmetry of molecular vibrations. Namely, once the G matrix of a molecule is known, the point group G of the molecule, the coordinates which provide a basis for a completely reduced representation of G (symmetry coordinates), and the minimal set of independent force constants which must be chosen can be derived. Corresponding computer programs have been written which provide an automatic way for the factorization of the dynamical matrices of large and/or highly symmetrical molecules.
Optical Spectra Line-Shape Representations and Broad Bands in Solids
Authors: Ritter John T.
Published: February 2004

Three methods of analyzing the temperature-dependent optical spectra line shape of a defect center are presented: a representation consisting of a convergent series of n-phonon distributions, a Fourier transform representation, and the moments of line shape. For each of these the calculations proceed from a one-phonon distribution, ρ1(E), which is proportional to the probability of a phonon of energy E being excited. The deriving model is that used for a configurational coordinate model with a removal of the limitation to a single one-phonon energy. Detailed comparisons are made between phonon-broadened line shapes for a defect center coupling to a distribution of phonon energies and CC model parameterizations of the line shapes. Results are that the CC model parameterizes very well the entire line shape for centers with a large Huang–Rhys S factor and the high-energy tail of narrow bands. Parameterization of the smooth tails of bands aids in the separation of overlapping bands. However, the CC parameters (S and effective phonon energy) are not precisely the quantities implied by the CC model.
Electron-Diffraction Investigation of the Molecular Structure of Trifluoramine Oxide, F3NO
Authors: Plato Vernon , Hartford William D. , Hedberg Kenneth
Published: February 2004

The molecular structure of trifluoramine oxide has been investigated by gaseous electron diffraction at a nozzle temperature of 20°C. The results verify the expected C3υ symmetry for the molecule. The N–F bond is slightly longer than the sum of the single-bond radii corrected for electronegativity difference, but the N–O bond is very much shorter and must be regarded as essentially a double bond. The bond angles are not in themselves unusual. However, the positions of the four ligands correspond with remarkable accuracy to the corners of a regular tetrahedron, a fact which strongly emphasizes the importance of nonbonded interactions. The five covalent bonds formed by the nitrogen atom may be understood in terms of a σ system of four bonds comprising 2s–2p hybrids and a π bond obtained by utilizing an empty 3pπ or 3dπ nitrogen orbital with a filled 3pπ oxygen orbital. The electron-diffraction analysis led to the following values for the principal parameters: r(N=O) = 1.158 Å (0.0040), r(N–F) = 1.431 Å (0.0030), r(O···F) = 2.214 Å (0.0130), r(F···F) = 2.206 Å (0.0158), r(X···X) (the average of the nonbond distances) = 2.210 Å (0.0024), l(N=O) = 0.0289 Å (0.0044), l(N–F) = 0.0507 Å (0.0032), l(O···F) = 0.0584 Å (0.0089), l(F···F) = 0.0551 Å (0.0077), ∠ONF = 117.1° (0.89), and ∠FNF = 100.8° (1.12). The distances and amplitudes are ra and la values; the parenthesized quantities are 2σ. When the rotational constant B0 from microwave spectroscopy is taken as a constraint on the diffraction results, the following set of distance and angle values, which differ only very slightly from those above, is obtained: r(N=O) = 1.159 Å (+ 0.0020, − 0.0025), r(N–F) = 1.432 Å (+ 0.0020, − 0.0061), ∠ONF = 117.4° (+ 0.60, − 1.16), and ∠FNF = 100.5 Å (+ 1.44, − 0.75).
Reactions of C+ Ions with Some Methyl Halides
Authors: Wilson Patricia Sullivan , Rozett R. W. , Koski W. S.
Published: February 2004

The reactions of C+ in the ground state with the methyl halides (CH3X) were studied in the 2–200-eV energy region using a tandem mass spectrometer. The cross sections as a function of ion kinetic energy were measured and used to infer reaction mechanism. Hydride ion, halide ion, carbanion as well as halogen atom and CH3 pickup were dominant reactions at low energy. At higher energies dissociative anion pickup was an important mechanism for the formation of ions containing one carbon atom. The polarizability of the C–X bond and the energetics of the process appeared to be the most important factors dictating the course of the reaction.
Ab Initio Calculations of Harmonic Force Constants. IV. Comparison of Different Methods
Authors: Bishop David M. , Macias A.
Published: February 2004

Five different ab initio methods of calculating force constants are considered. The advantages and disadvantages of these methods are brought out by their application to a calculation of the force constant of the hydrogen molecule using a basis set of Gaussian functions. Particular attention is drawn to both the accuracy and time involved in the different methods.
Optical Activity of n–π* Transitions in Polynucleotides
Authors: Bush C. Allen
Published: February 2004

Although the source of most of the large optical activity of polynucleotides may be explained by the interaction of the strong π–π* electronic transitions in the ultraviolet, a number of recent experiments have been interpreted as evidence for Cotton effects due to n–π* transitions in nucleotides. In this study, we propose a method for calculating the rotational strengths of n–π* transitions in polynucleotides. We use the Kirkwood–Tinoco approach, which assumes no electron exchange among the nucleotides in the polymer. The azine n–π* transition is described by an all-valence-electron molecular orbital theory, and the interactions among the nucleotides are calculated by a distributed dipole-charge monopole approximation. The results of a sample calculation on polyadenylic acid, using extended Hückel orbitals to describe adenine, yield oscillator strengths consistent with absorption in the 280-nm-wavelength region. Rotational strengths computed for a polymer of DNA-type geometry are small. This is in agreement with the circular dichroism band of polyadenylic acid at 280 nm. The dependence of the rotational strength on polymer geometry is shown to differ from that of π–π* transitions due to the greater spatial localization of the n–π* transition in the ring.
Small Polarons in Organic and Biological Semiconductors
Authors: Kemeny Gabor , Rosenberg Barnett
Published: February 2004

The band motion (tunneling) of small polarons in thermally activated energy levels of molecules is postulated to be the conduction mechanism is some organic and biological semiconductors. The compensation law is derived from this model. The characteristic temperature is shown to be related to the Debye temperature.
Infrared to Visible Conversion in LiYF4: Yb, Ho
Authors: Watts R. K.
Published: February 2004

A simple model consisting of three simultaneous rate equations is proposed to account for the conversion of infrared excitation to visible emission by LiY0.799Yb0.2Ho0.001F4. All of the parameters appearing in the equations are measured. The time development of the luminescence and the conversion efficiency are calculated and found to be in reasonable agreement with the measurements.
“Complete” and “Partial” Vibrational Inversion in Chemically Pumped Molecular Lasers
Authors: Chester Arthur N.
Published: February 2004

A generalized inversion density is defined and applied to a molecular laser having simultaneous inversion on many different vibrational–rotational transitions. This inversion density is shown to be a measure of the maximum quantum efficiency and the molar flow efficiency of a flowing chemical laser. Calculations are carried out using previously measured vibrational population distributions, and the limiting performance of completely inverted and partially inverted molecular lasers is compared quantitatively.
Crystal Structure of Pinacol Hexahydrate
Authors: Kim H. S. , Jeffrey G. A.
Published: February 2004

The crystal structure of pinacol hexahydrate, C6H14O2·6H2O, has been determined at room temperature from diffractometer data with CuKα radiation. The structure is tetragonal space group P42 / mnm, with two formula units per unit cell of dimensions a = b = 6.398(3) Å, c = 15.926(8) Å. The intensity data were measured with CuKα radiation on a Picker FACS I diffractometer. The parameters were refined anisotropically by least squares to a final R = 0.06 for 294 observed reflections. The hydrogen-bonded water and pinacol molecules form a framework structure which is isostructural with that of piperazine hexahydrate. The water molecules form puckered layers consisting of edge-sharing pentagons. These layers are linked into a three-dimensional framework through the hydroxyls of the pinacol molecules. The pinacol molecules are in voids within this framework structure with twofold orientational disorder. Although this is not a clathrate hydrate, there is a marked structural similarity to that series of compounds.
Theoretical Study of H2+ Ground Electronic State Spectroscopic Properties
Authors: Beckel Charles L. , Hansen Bertle D. , Peek James M.
Published: February 2004

Born–Oppenheimer and adiabatic vibrational–rotational eigenvalues are determined for the (1sσg) 2Σg+ ground state of H2+ by a combination of Runge–Kutta and Adams–Moulton numerical techniques. These eigenvalues are believed to be more accurate than any previously reported. Dunham expansions of the potentials are used to determine Born–Oppenheimer and adiabatic spectroscopic constants; the adiabatic constants are considered to be the best set, theoretical or experimental, available for the ground state of H2+. The ΔG curve for this state has two points of inflection and a positive curvature tail, presumably to be associated with long-range 1 / R4 forces in the molecular ion. The Bυ curve has a shape similar to the ΔG curve; more striking, inflection points occur at essentially the same values of the vibrational quantum number υ. The Dυ curve has a negative slope at υ = 0, but rises rapidly near dissociation. The Hυ values decrease and become negative at large υ values. The sharp rise at high υ in | Hυ |, like that in Dυ, is probably due to the dominance of the centrifugal reaction over the true potential at large nuclear separations R.
Reaction Rate Measurements of O(3P) Atoms by Resonance Fluorescence. I O(3P)+O2+M→O3+M and O(3P)+NO+M→NO2+M
Authors: Slanger T. G. , Black G.
Published: February 2004

Atomic resonance fluorescence techniques have been applied to the determination of O(3P) atoms. The atoms were produced by O2 photodissociation at 1470 Å and then detected by their scattering of 1302–1306-Å oxygen resonance radiation, which was measured photoelectrically. By pulsing the photodissociation lamp, it was possible to make absolute measurements of the O(3P) loss rate. To demonstrate the usefulness of the technique, rate constants at 300°K were determined for two three-body reactions, O(3P)+O2+M→O3+M for M is Ar and N2 (kAr = 4.4 ± 0.6 × 10−34cm6molecules−2·sec−1, kN2 = 7.0 ± 1.0 × 10−34cm6molecules−2·sec−1) and O(3P)+NO+Ar→NO2+Ar. For the latter reaction, a value of 13.5 × 10−32 cm6 molecules−2·sec−1 is obtained, which is precisely twice the accepted value. A possible explanation may involve very rapid reaction of the vibrationally excited NO2 product with a second O(3P) atom.
Infrared and Raman Spectra of Polycrystalline NaBF4
Authors: Bates John B. , Quist Arvin S. , Boyd George E.
Published: February 2004

The infrared and Raman spectra of polycrystalline NaBF4 and the Raman spectrum of an aqueous solution of NaBF4 were measured at 298°K in the region above 200 cm−1. With the exception of ν3, all of the predicted correlation field components arising from multiplet splitting of the BF4− vibrations were identified in the polycrystalline spectra.
Unit Cell Group and the Factor Group in the Theory of the Electronic and Vibrational Spectra of Crystals
Authors: Bertie J. E. , Bell J. W.
Published: February 2004

The unit cell group and the factor group are basic to the theoretical analysis of the vibrations, or electronic transitions, in crystals in the k = 0 approximation. Yet some confusion exists in the literature concerning the definitions of these groups. This paper examines the literature definitions, draws attention to inconsistencies in the literature, and describes the unit cell group and the factor group for the specific cases of the symmorphic space group, P2 / m, and the nonsymmorphic space groups P21 / m and P21 / c.
Deuteron Magnetic Resonance and Relaxation in Ferroelectric KD2PO4, KD2AsO4, and CsD2AsO4
Authors: Blinc R. , Stepišnik J. , Jamšek-Vilfan M. , Žumer S.
Published: February 2004

The temperature dependence of the quadrupole splitting of the deuteron magnetic resonance spectra of KD2AsO4 and CsD2AsO4 has been studied and the electric field gradient tensors at the deuteron sites were determined. The results show that the deuterons are—similar to those in KD2PO4—moving between the two off-center positions in the O–D···O bonds above Tc and are effectively frozen in at one of the two possible sites below Tc. The dynamics of this process was investigated by deuteron spin–lattice relaxation studies. The results show the existence of a “soft” deuteron mode which condenses at Tc, but cannot distinguish between a pure relaxational and an overdamped resonant mode.
Paramagnetic Resonance in Transition-Metal Hexammine Complexes. I The Ni(II)(NH3)6 Complex Ion
Authors: Trapp Charles , Shyr Chin-I
Published: February 2004

Electron paramagnetic resonance studies have been carried out on the complex ion Ni(II)(NH3)6 in the host compounds Zn(NH3)6X2 and Cd(NH3)6X2, where X=Cl, Br, and I. The results support the conclusion that above a certain characteristic transition temperature (Tc) the ligand field in the hexammines is perfectly octahedral. The quenching of the rotation of the ammonia ligands at temperatures below Tc was detected from the sudden transition of the isotropic Ni(II)(NH3)6 single line to three lines characteristic of an anisotropic spectrum. The anisotropic spectrum, which was not found in the previous work on concentrated hexammines, was very clear and the nonoctahedral part of the spin Hamiltonian was determined. The results agree qualitatively with the model of the hexammines proposed by Bates and Stevens, but quantitative agreement is not yet obtainable.
Attachment of Electrons to Substituted Benzenes
Authors: Naff W. T. , Compton R. N. , Cooper C. D.
Published: February 2004

Attachment of slow (0–5 eV) electrons to a number of aromatic species has been studied in a time-of-flight (TOF) mass spectrometer using an automatic retarding potential difference (RPD) electron beam with resolution of ∼ 0.1 eV. Autodetachment lifetimes were measured for parent ions formed by two-body attachment of thermal (∼ 0.03 eV) electrons to the following molecules (lifetimes in microseconds are given in parentheses): C6F5Br (21), C6F5Cl (17.6), C6F5CN (17), C6F5CHO (36), C6H5CN (≈ 5), C6H5NO2 (17.5), C6D5NO2 (22), m-C6H4ClNO2 (47), and perfluoronaphthalene (123). The C10F8− ion and ions of the form C6F5X− had lifetimes exhibiting a systematic increase with the number of vibrational degrees of freedom consistent with the trend observed in a previous study of cyclic fluorocarbons. Cl−, Br− and I− were formed from C6F5X (X==Cl, Br, I) along with C6F5− at incident electron energies below 0.1 eV. Current ratios for X− to C6F5− were found to be approxmaltely 100/1, 3/1, and 1/30, respectively. No nondissociative attachment was observed for C6F5I. Monochlorination of nitrobenzene essentially doubled the autodetachment lifetime and added a new mode of dissociation. Cl− and NO2− ion currents from m-chloronitrobenzene showed almost identical energy dependences with peaks at ∼ 1 eV and ∼ 3.5 eV, corresponding closely to the energy dependence of NO2− dissociation from nitrobenzene. This was taken as evidence that the Cl− and NO2− ion currents result from unimolecular dissociation of the same intermediate negative ion state with the incident electron in a π-electronic orbital. Iodine substitution in nitrobenzene had the effect of elimination of long-lived parent ion formation with dissociative attachment producing I− dominating at thermal electron energy. An SF6 scavenger spectrum of benzaldehyde indicated the presence of a temporary negative ion resonance at ∼ 0.65 eV. Negative ion breakdown curves were also determined for C6H5OH, C6F5OCH3, C6F5NH2, C6H5CN, o-C6H4ClF, m-C6H4ClF, m-C6F4ClBr, and m-C6H4ICl.
Deformation Mechanism for Ice VII
Authors: Yean D. H. , Riter J. R.
Published: February 2004

By using force constants for both the hydrogen bond H···O–H and the chemical bond O–H in harmonic and Morse potential energy functions, we have obtained ratios of potential energy to macroscopic work of compression for H2O and D2O ice VII using the experimental P–V data of Holzapfel and Drickamer. The Morse potentials gave values of this ratio quite close to 1.0 even at the highest pressure, viz., 165 kbar for H2O and 220 kbar for D2O ice VII. These models all yield the result that the protons remain on their original oxygen atoms during compression; i.e., there is no proton migration with formation of “symmetric” hydrogen bonds. The isothermal bulk modulus for pressures in the neighborhood of 22 kbar, for both H2O and D2O ice VII, was estimated to be 235 kbar.
Infrared Spectra of Matrix-Isolated ClF3, BrF3, and BrF5; Fluorine Exchange Mechanism of Liquid ClF3, BrF3, and SF4
Authors: Frey Raymond A. , Redington Richard L. , Aljibury A. L. Khidir
Published: February 2004

The infrared spectra of matrix-isolated ClF3, BrF3, and BrF5 have been investigated in the region from 800 to 33 cm−1. All six fundamentals have been observed in Ar and N2 matrices for ClF3 and BrF3, which are planar T-shaped molecules, and most of them in a Ne matrix. The two lowest-frequency fundamentals, which could not be separated in the gas-phase spectra [H. Selig, H. H. Claassen, and J. H. Holloway, J. Chem. Phys. 52, 3517 (1970)] are clearly visible in the matrix-isolation spectra. Both molecules show only small gas-matrix frequency shifts, and multiplet structure for both molecules suspended in Ar matrices may be understood in terms of isotope and matrix site effects. Several absorption bands found at low matrix-isolation ratios are attributed to dimers and a tentative partial vibrational assignment is presented. Similar dimer structures are assumed for both substances. The structure seems best represented with two F bridges formed using the long-bond F atoms. The structure is favored by the x-ray and NMR data. Re-evaluation of the spectral data for SF4, and comparison with ClF3 suggests reversing the literature assignments of the antisymmetric axial and equatorial S–F stretching vibrations for the SF4 monomer. Then consistent experimental agreement between the closely related ClF3 and SF4 molecules ensues and analogous structures for the matrix-isolated dimers follow. Considered as transient liquid-state species, the dimers demonstrate a highly likely fluorine exchange mechanism involving an intermolecular transfer of the bridging F atoms that can account for the exchange of nonequivalent F atoms which is observed in the liquid state for these systems. The vibrational frequencies of ClF3, SF4, BrF3, and BrF5 are compared and force constants are calculated for ClF3 and BrF3.
Optical and Microwave Studies of Divalent Vanadium in Octahedral Fluoride Coordination
Authors: Sturge M. D. , Merritt F. R. , Johnson L. F. , Guggenheim H. J. , van der Ziel J. P.
Published: February 2004

We have measured the optical absorption spectrum of V2+ introduced as a substitutional impurity into the octahedral site of MgF2 and KMgF3, and its spin resonance spectrum in MgF2 and in uniaxially strained KMgF3. The cubic field splittings are best interpreted in terms of the weak-field formalism of Ferguson and Wood: The parameters of the electron–electron interaction obtained from this formalism show a much more rational trend with increasing covalency than do those obtained from a strong-field analysis. The crystal fields induced by uniaxial strain in KMgF3 are close to those expected from the point charge model. The noncubic splittings of the optical and microwave spectra of V2+ in MgF2 are in reasonable agreement with the ligand field calculations of Ferguson et al., with parameters quite close to those obtained for Ni2+. However, it is found that the ground state splitting in MgF2 is much larger than expected on the basis of the data on strained KMgF3, indicating a large contribution from ions outside the nearest neighbor shell. Finally, there is some indication of a Jahn–Teller interaction (involving the B3g mode of the octahedron) in the 4T2 excited state of V2+ in MgF2, analogous to the well-established case (previously reported) in KMgF3.
Measurement of Sodium Ion Transport in Beta Alumina Using Reversible Solid Electrodes
Authors: Whittingham M. Stanley , Huggins Robert A.
Published: February 2004

The ionic conductivity of the solid electrolyte NaAl11O17 has been measured from − 150 to + 820°C using a novel nonpolarizing solid electrode, reversible to sodium ions. The resistivity at 25°C was found to be 72 Ω-cm, the lowest value reported for any ionically conducting oxide ceramic. The enthalpy of motion is 3.79 kcal/mole, and the transport of sodium ions takes place by an interstitialcy mechanism.
CNDO–SCF–CI Calculations of the Excited Electronic States of 1,3-Butadiene
Authors: Clark P. A.
Published: February 2004

Energies of low-lying excited states of s-cis and s-trans 1,3-butadiene have been calculated using the CNDO–SCF method of Pople, Santry, and Segal, with the inclusion of configuration interaction among the single electron excitations. The results are shown to agree well with available experimental values. An extensive comparison is made between CNDO–SCF and recent ab initio SCF orbital and excitation energies and also excited state energies resulting from CI treatments of the excited configurations of the two theoretical methods. Results obtained from an earlier semiempirical pi-electron calculation are also included for comparison. Charge redistribution in some CNDO excited configurations is investigated.
Vapor-Pressure Test for Intermolecular Potentials
Authors: Chen Chimin Tang , Present R. D.
Published: February 2004

Radial distribution functions g(r) obtained from x-ray and neutron diffraction measurements are used to calculate the vapor pressure of liquid Ar for various empirical potential functions u(r) with parameters chosen to fit gas data. The potentials investigated were the (12,6), (exp-6), Kihara, Kingston, Barker–Pompe, and Dymond–Alder. The results are sensitive to the choice of g(r) and of u(r) and to the potential parameters used with u(r); they are highly sensitive to the threshold behavior of g(r) and also to the slow-collision diameter σ of u(r). The nonadditivity correction to the pressure was calculated from the triple-dipole potential using the superposition approximation. Results are in error by varying orders of magnitude, the (12,6) potential giving the largest disagreement with experiment. The Kingston potential and the Kihara potential with Barker's parameters are consistent with experiment considering the large uncertainties (∼ 300 atm) of the method. The Barker–Pompe and Dymond–Alder potentials give the best vapor pressures, well within these uncertainties. The results suggest that the true value of σ is close to 3.3 Å. The threshold region of g(r) requires more careful experimental investigation.
Photophysical Processes in Polymers. III. Properties of Triplet Energy Traps in 1-Vinylnaphthalene Copolymers
Authors: Fox Robert B. , Price Thomas R. , Cozzens Robert F.
Published: February 2004

Emission spectra of two-component atactic copolymers of 1-vinylnaphthalene with styrene (PVN/S) and with methylmethacrylate have been investigated in a glassy matrix at 77°K. In PVN/S, the rate of intramolecular triplet energy transfer through segments derived from styrene exceeds that of intermolecular triplet transfer from polystyrene to piperylene; the migration occurs through chains having as many as 140 styrene-derived units. Radiative triplet depletion within the 1-vinylnaphthalene-derived segments is manifested by (1) phosphorescence originating from units near the ends of the segments, and (2) delayed fluorescence due to free triplet annihilation within the segment, although some trapping may also take place. In contrast, delayed fluorescence from poly(1-vinylnaphthalene) appears to result from several annihilation reactions, and serves to demonstrate fundamental differences between the homopolymer and copolymer.
High-Pressure Photoionization Mass Spectrometry. Photoionization of Propane at 11.6–11.8 eV. Formation and Reactivity of the (C3H8)2+ Dimer Ion
Authors: Sieck L. Wayne , Searles Stuart , Ausloos P.
Published: February 2004

The major reaction path of the propane molecular ion with propane was found to be the formation of the dimer ion (C3H8)2+ via a termolecular mechanism, C3H8++C3H8→ lim C3H8(C3H8)2++C3H8. In addition, C3H6+ and C3H7+ were also found as minor reaction products at lower pressures. The reactions of the dimeric ions with ethylene and NO were also investigated. The charge exchange reaction, (C3H8)2++NO→NO++ 2C3H8, was found in propane–NO mixtures, suggesting a recombination energy in excess of 9.24 eV. The formation of C3H8NO+ was also detected at higher total pressures. The dimeric ion was also found to transfer H2 to ethylene without affecting the structural integrity of the carbon skeleton, (C3H8)2++C2H4→C6H14++C2H6, indicating that this species exhibits the chemical behavior of a saturated hydrocarbon ion.
Radiationless Processes in Fluorobenzene
Authors: Nakamura Kenichiro
Published: February 2004

The triplet yield of fluorobenzene is studied by the biacetyl emission method. The effect of biacetyl pressure indicates a short triplet lifetime of 130 nsec for fluorobenzene in the gaseous phase. The absence of phosphorescence even in a solid matrix at low temperature is explained by a radiationless process from the triplet state of fluorobenzene. A weak sensitized emission from the first excited singlet state of biacetyl suggests that singlet–singlet energy transfer must be involved. Addition of cis-2-butene quenches the sensitized emission from the triplet state of biacetyl. The triplet yield of fluorobenzene results in a reasonable value of 1.03 for the sum of triplet and singlet yields on excitation at the 0–0 band.
Zeeman Effect in the Electronic Spectrum of Solid CS2
Authors: Hochstrasser Robin M. , Wiersma Douwe A.
Published: February 2004

The lowest-energy A23 ← Σg+1 singlet-triplet transition of CS2 has been studied in the CS2 crystal at 4.2°K. The spectrum consists mainly of progressions in the bending mode ν2′. The following values for the upper state frequencies have been obtained (ν1′ = 677 cm−1, ν2′=309 cm−1) and the unobserved B2 electronic origin has been calculated to be at 24 739 cm−1. Zeeman studies of the 3676-Å band system have been used to assign a very weak component of a vibronic band of this system as a crystal field induced transition to the (A1, B1) pair of spin sublevels of the triplet state A23. The zero field splitting (ZFS) parameter of 36 ± 1 cm−1 thus obtained for the vibronic state is comparable with the one calculated by Hougen [J. Chem. Phys. 41, 363, (1964)] from Zeeman line broadening experiments in the gas phase done by Douglas and Milton [J. Chem. Phys. 41, 357 (1964)] on comparable vibronic bands. The large value of the ZFS parameter can be explained if it is assumed that the A23 and B23 states are quite nearby.
Additional WKB Inversion Relations for Bound-State and Scattering Problems
Authors: Miller William H.
Published: February 2004

New inversion relations for the diatom system (elastic scattering of two atoms by a single potential, or a bound diatomic molecule) are presented. They are exact within the WKB approximation for the relevant quantities and are closely related to the well-known RKR expressions. Explicit formulas are given for bound-state and scattering input.
Raman Scattering from Molecular Crystals. I. Powdered Naphthalene
Authors: Stenman F.
Published: February 2004

The Raman spectrum of powdered naphthalene has been measured at room temperature using 6328-Å He–Ne laser excitation and a double monochromator with photoelectric detection and digital recording. Eighty-six lines are observed, among them all the fundamentals assigned by Hanson and Gee [J. Chem. Phys. 51, 5052 (1969)] from Raman, phosphorescence, and fluorescence spectra. Using narrow slits (0.5–1 cm−1) several asymmetric and multiple lines are discovered and resolved into separate components. Five weak, very broad lines are discovered and interpreted as second-order lines or combinations of intramolecular and lattice vibrations. The width is determined for some of the lines. Intensities are given for all lines.
On a Derivation of a Boltzmann Equation for Homogeneous Systems
Authors: Eu Byung Chan
Published: February 2004

The derivation of a Boltzmann equation for homogeneous systems by Prigogine et al. has been generalized and simplified by an introduction of a binary collision expansion instead of the perturbation expansion of the resolvent operator for the Liouville operator. Such binary collision expansion makes the derivation much simpler than the perturbation expansion. The result, however, agrees with that of Prigogine et al. and the reason for the agreement is briefly discussed.
Interpretation of Alkali–Inert Gas Beam Scattering with the Buckingham–Corner Potential
Authors: Okel J. G. R. , van de Ree J.
Published: February 2004

We have shown that recent measurements of alkali–inert gas beam scattering cross sections can be fit by a four parameter Buckingham–Corner potential with the same accuracy as with previously proposed four to seven parameter models. The Buckingham–Corner model contains a single Born–Mayer repulsive term and two attractive terms, the ordinary Van der Waals attraction and the second term in the London dispersion series. This model gives the correct broadening of the potential well. In addition some of the terms can be calculated theoretically. A fit of the measured total and differential cross sections for the systems Na–Xe and Na–Kr yields a set of form parameters which we assume to be characteristic of the alkali–inert gas interaction. Using these one can deduce well parameter values for each particular combination. Since the fit of the Buckingham–Corner potential is determined from the oscillatory structure of thermal beam measurements, its validity is confirmed only in the attractive region. A possible application of the model to the inert gas–inert gas interaction is discussed.
Magnetic Properties of AlH and N2 from Coupled Hartree–Fock Theory
Authors: Laws Edward A. , Stevens Richard M. , Lipscomb William N.
Published: February 2004

The magnetic susceptibility and nuclear magnetic shielding in AlH and N2 have been calculated using coupled Hartree–Fock theory. The perpendicular component of the AlH susceptibility tensor is predicted to be positive, i.e., paramagnetic. Thus, AlH becomes a second example, in addition to BH, of a gas-phase molecule which has a component which should exhibit the phenomenon of temperature-independent paramagnetism. Results for N2 yield a total susceptibility within 5% of the experimental value. Although the nitrogen nucleus is correctly predicted to be antishielded, the quantitative agreement of the shielding with experiment is not as good as has previously been obtained from coupled Hartree–Fock calculations on other diatomics.
On the Validity of the Master Equation for Internal Relaxation at High Densities
Authors: Keizer Joel
Published: February 2004

The validity of the collisional master equation for the relaxation of molecular internal degrees of freedom in a high-density reservoir of inert particles is examined using the generalized master equation for this system. When the hypotheses of the “Markovian approximation” to this equation are examined, it is found that they are invalidated by correlated collision processes which occur at elevated reservoir densities. At densities where the mean free time is long compared to a characteristic frequency of the internal states and the duration of a collision, the usual multiple collision theory master equation is shown to hold.
14N Nuclear Quadrupole Resonance Study of Hydrogen Bonding in NH3·12H2O
Authors: Eletr S. , O'Konski C. T.
Published: February 2004

The four-line 14N nuclear quadrupole resonance spectrum in the ammonia hydrate NH3·12H2O is reported. The frequencies were unambiguously paired by their Zeeman behavior and each pair is assigned to respective inequivalent sites in the crystal lattice. The temperature dependence was measured between 77°K and the melting point; it is quantitatively interpreted in terms of a motional averaging theory corrected for volume effects. The same theory is applied to previous results on NH3 and ND3, and the quasistatic coupling constants are recalculated. Solid-state shifts of NH3 in the pure ammonia lattice and in the two inequivalent lattice sites of the hydrate are thus obtained and interpreted in terms of the three different hydrogen-bonding situations.
Mechanism of Singlet Molecular Oxygen Formation from Photolysis of Ozone at 2537 Å
Authors: Gauthier M. , Snelling D. R.
Published: February 2004

Emission from O2(1Δg) and O2(1Σg) is observed from photolysis of ozone–oxygen mixtures at 2537 Å. The O2(1Σg) is formed by energy transfer from O(1D) and the relative rates of removal of O(1D) by O2, N2, and O3 are found to be 1:0.7:9.7, respectively. The O2(1Δg) is formed directly by photolysis. Photolysis and the reaction of O(3P) and O(1D) with O3 are discussed as sources of both O2 singlet states.
Mechanism of Volume Viscosity in Molten Bismuth and Lead
Authors: Flinn J. M. , Jarzynski J. , Litovitz T. A.
Published: February 2004

Ultrasonic absorption and velocity have been measured in molten bismuth and lead from the melting point to 650°C. Both liquids were found to exhibit a volume viscosity which increased with increasing temperature. Near the melting point the ratio of volume to shear viscosity was 0.6 and 4.6 for lead and bismuth, respectively. A two-state model using the experimental coordination number is proposed which gives the proper magnitude and temperature dependence of the volume viscosity in these liquids. The theory is also found to be applicable to molten salts.
Collisional Excitation of Vibrational Energy of an Initially Excited Harmonic Oscillator
Authors: Yao S. J. , Yao H. Y. Sun
Published: February 2004

An analytical formula for the phase-averaged vibrational energy transfer to an initially excited harmonic oscillator is presented.
Generalized-Regression-of-Fluctuations Theory as Applied to the Second Viscosity
Authors: Deguent Philippe , Boon Jean Pierre
Published: February 2004

A generalized-regression-of-fluctuations (GRF) theory is developed for the study of the second viscosity, by making use of a generalized transport equation describing the evolution of a dynamical variable in a dense fluid. This method constitutes a generalization of the Mandelstam–Leontovitch model. We obtain a formal expression for the frequency-dependent second viscosity in terms of the kernel of the transport equation. We show that this result is equivalent to the expression obtained from the autocorrelation formalism approach to thermal transport coefficients. This equivalence is easily understood on the basis of the linear response theory; the above result is therefore not restricted to the case of the second viscosity, and constitutes a general exact result within the limits of validity of the theory of regression of fluctuations. We next derive a dispersion equation which is solved for temporal attenuation (light scattering) and for spatial attenuation (ultrasonics) to yield the first sound velocity and the absorption coefficient in both cases. As an example, a simple model is introduced to calculate explicitly the second viscosity, the sound velocity, and the attenuation. Comparison is also made with the single-relaxation-time theory.
Critical Sound Attenuation in the System Ga–Bi
Authors: Puls M. P. , Kirkaldy J. S.
Published: February 2004

Sound attenuation measurements were performed on a liquid Ga–Bi mixture at the frequencies 16.6, 25.5, 37.6, and 49.7 MHz, over a composition range 0.20–0.75 weight fraction Bi and in the temperature range 0.3–9.9°C above the critical temperature of the mixture. The velocity of sound was measured at 25.5 MHz and at each of the above temperatures and compositions. No critical effects were evident in the velocity of sound measurements. Using the results of the velocity and attenuation measurements, the critical temperature and composition of the Ga–Bi system were determined as 263.1°C and 0.60 weight fraction Bi, respectively. The Fixman theory was tested against the attenuation results. The temperature dependence of the Fixman theory could be made to conform to the attenuation results if a value for the Debye short-range correlation length l of 4.5 Å was used. The frequency dependence of the attenuation data was found to be in only rough agreement with the Fixman theory over the temperature interval of the measurements. The composition dependence of the attenuation measurements was compared with the predictions of the Flory–Huggins solution model when combined with the Fixman theory. The experimental attenuation results were found to exhibit broader attenuation maxima with composition than those predicted by the above theory.
Molecular Theory of the Helix–Coil Transition in Polyamino Acids. III. Evaluation and Analysis of s and σ for Polyglycine and Poly-l-alanine in Water
Authors: Gō Mitiko , Gō Nobuhiro , Scheraga Harold A.
Published: February 2004

Previously, the Zimm–Bragg parameters s and σ for the helix–coil transition in polyglycine and poly-l-alanine were calculated in terms of molecular quantities. These calculations are extended here to take into account the effects of water as the solvent and are analyzed to deduce the relative importance of the various interaction terms for the helix–coil transition. The screening effect of the electrostatic interactions by the water molecules which lie between or near two charged atoms is taken into account by using a dielectric constant D = 4.0 for short-range interactions, and by cutting off all interactions of longer range than about 6.0 Å. The calculated values of the parameter σ, which are very sensitive to the value of D, agree well with experimental ones. The origin of the greater stability of the α-helical conformation of poly-l-alanine compared to that of polyglycine is analyzed. The effect on the value of the parameter s, arising from the binding of water molecules to free CO and NH groups of residues in the coil state, is considered. Parameters which express the strength of the binding of water molecules are adjusted so as to make the calculated values of s for poly-l-alanine in water as a function of temperature fit best with experimental values. When the same parameters are used in the calculation of s for polyglycine in water, the theory predicts that polyglycine should be in the random coil form in water in the temperature range of 0–100°C, which agrees with experiment. The values obtained for these parameters are compared with experimental data for binding water molecules to a small-model peptide molecule. Finally, a simple but realistic model of the helix–coil transition, deduced from the calculation of s and σ in terms of molecular quantities, is proposed as a first approximation not only for homopolymers but also for co-polymers.
Metastable Phases in Ferrous Chloride Hydrates
Authors: Ruby S. L. , Zabransky B. J. , Stevens J. G.
Published: February 2004

Surprisingly, a phase diagram for the binary system FeCl2·nH2O has never been published. This is partially due to the difficulty of reaching the equilibrium states from these viscous liquids. The absence of a phase diagram has led to misinterpretations in several Mössbauer studies. Using differential thermal analysis and Mössbauer technique, as well as earlier references, we have constructed a phase diagram. In addition to glass and supercooled liquid regions, it has a metastable crystalline phase.
Microwave Spectrum of Bromostannane, SnH3Br
Authors: Wolf Stephen N. , Krisher Lawrence C. , Gsell Ray A.
Published: February 2004

Pure rotational measurements have been made on nine isotopic species of the unstable symmetric-top molecule bromostannane, SnH3Br, using a microwave spectrometer. The Sn–Br bondlength is 2.4691 ± 0.0003 Å. Quadrupole hyperfine structure due to the bromine nuclei gives values of eQq (79Br) = 350 ± 6 MHz and eQq (81Br) = 291 ± 6 MHz. A centrifugal-distortion constant, DJK = 0.0069 ± 0.0004 MHz affords a best fit to the complex K structure of observed transitions.
Radial Distribution Function for Argon: Calculations from Thermodynamic Properties and the Lennard-Jones 6:12 Potential
Authors: Davis Bruce W.
Published: February 2004

The radial distribution function, g(x), of argon is calculated from thermodynamic data and the Lennard-Jones 6:12 potential. This is accomplished by introducing analytical expressions for the function Y(x) ≡ exp[φ(x) / T*]g(x) − 1 which contain a limited number of adjustable parameters. Three calculations are made. The first uses only the pressure and energy equations and reproduces g(x) accurately for x ≤ 1.5. The other two incorporate the compressibility equation and generally give accurate values of g(x) for x ≤ 2.1 and approximate values for 2.1 ≤ x ≤ 3.