bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibrational Exciton Splitting, Fermi Resonance, and Crystal Structure of Methyl Iodide
Authors: Kopelman Raoul
Published: January 2005

The splitting of the v5 vibrational band in crystalline methyl iodide has played an important role in the interpretation of vibrational exciton splittings in molecular crystals. According to an earlier interpretation, the site-group splitting was said to be much larger than the factor-group (exciton) splitting, and the effect of isotopic substitution on the exciton splittings was said to be substantial. Evidence is given in this paper to show that this interpretation is questionable and that actually certain features in the v5 structure are most likely caused by Fermi resonance between v5 and the combination band v3+v6. The problem of mixed exciton and Fermi interactions is discussed and it is shown that the factor-group splitting is divided over the Fermi components in a very simple way. The resulting exciton splitting of v5 is 10.5 cm−1 in CH3I and 10 cm−1 in CD3I. The earlier interpretation of the crystal spectrum of methyl iodide had been used as a criterion for the rejection of the otherwise plausible crystal structure (C2v12). Both spectral evidence and packing considerations are now consistent with the existence of isomorphous crystal structures for methyl chloride, methyl bromide, and methyl iodide, having space group C2v12 (Cmc21) with two molecules per primitive unit cell located at Cs sites.
Self-Consistent Perturbation Theory. I. General Formulation and Some Applications
Authors: Diercksen G. , McWeeny R.
Published: January 2005

The self-consistent perturbation theory developed in an earlier paper is formulated more explicitly and applied to various types of perturbation: (i) one-element change of the one-electron Hamiltonian matrix (i.e., of Coulomb or resonance integral), (ii) uniform electric field, (iii) point charge near the system. The applications are to π-electron systems, where the results have considerable chemical interest.
General Quartic Force Field of HCN
Authors: Suzuki I. , Pariseau M. A. , Overend John
Published: January 2005

Anharmonic force constants have been determined by least squares from the vibrational frequencies and rotational constants of HCN and DCN. The contributions of various types of force constant to the xss′ and αs have been calculated, and the estimation of the anharmonic corrections from approximate potential functions is discussed.
Kinetics of Unimolecular Breakdown. VII. Statisticomechanical Aspects
Authors: Levine R. D.
Published: January 2005

The concepts of statistical mechanics are examined from the point of view of application to chemical kinetics. The occurrence of a chemical reaction is considered as an example of an irreversible behavior, and is discussed as due to the combination of system dynamics and experimental conditions. The Lindemann mechanism for thermal unimolecular reactions is discussed on the basis of the relative magnitudes of the various relaxation times.

The significance of the random-phase assumption is discussed on the basis of the uncertainty relation between the occupation number and the phase. A master (Pauli) equation is derived and applied to vibrational relaxation. The construction of classical models for unimolecular fragmentation and the significance of computer simulation studies are considered.
Bipolar Angle Averages and Two-Center, Two-Particle Integrals Involving r12
Authors: Milleur M. B. , Twerdochlib M. , Hirschfelder J. O.
Published: January 2005

The bipolar angle average of a two-center, two-particle function f(ra1, rb2, r12; R) is 〈f〉=(4π)−2 ∫ ∫ fdωa1dωb2.A bipolar angle average weight function L0 is derived from geometrical considerations such that 〈f〉= ∫ r12minr12maxfL0dr12.The L0 is independent of f and has a different, although simple, functional form in each of 42 regions of ra1—rb2—r12 space. However, the 〈f〉 have different functional forms in only four regions of ra1—rb2 space. The expressions which we derive for the bipolar angle average are surprisingly simple and general, requiring only the evaluation of integrals of the form ∫fr12dr12 and ∫fr122dr12. The bipolar angle averages are very useful in the evaluation of two-center, two-particle integrals. Many of our relations are greatly simplified by the use of homogeneous coordinates. Bipolar angle averages are also developed for functions f(ra1, rb1, rb2, r12; R) which involve the additional variable rb1.
Excited-State Perylene—Pyrene Interactions: Relation to the Interpretation of Excimer Emission
Authors: Kawaoka Kenji , Kearns David R.
Published: January 2005

The ``anomalous'' emission properties of perylene—pyrene mixed crystals have been re-examined. The results of this study demonstrate that the unusual character of the mixed-crystal emission spectra is primarily due to reabsorption of ``normal'' monomeric perylene emission, rather than to a very large excited-state perylene—pyrene interaction as previously suggested. Studies of the emission and absorption properties of perylene in liquid solutions containing pyrene indicate, however, that there is a significant excited-state perylene—pyrene interaction. This excited-state interaction shifts the perylene emission over 150 Å to the red, reduces the intensity, and produces a loss of some of the vibronic structure of the perylene emission. Because the lowest excited singlet states of perylene and pyrene are far from degenerate in energy, the excited-state perylene—pyrene interaction cannot be due to a resonance interaction. Preliminary experimental results suggest that the excited-state interaction is of charge-transfer character.
On the Theory of Atom—Diatom Collisions
Authors: Kouri Donald J.
Published: January 2005

The Feshbach approach to scattering theory is used for a theoretical description of the scattering of a rigid rotator and an atom. Coupled equations for the open-channel components of the wavefunction are derived in a total-angular-momentum representation. It is shown that the partial wave amplitudes for either jmi to j′mi′ or j to j′ transitions may be obtained directly from the solution of these coupled equations by different choices of boundary conditions. It is also shown that only the first or second energetically non-accessible rotator state has any effect on the open-channel wavefunctions. The treatment given is exact and may be extended to deal with any finite multipole expansion of the potential of interaction.
Electron Paramagnetic Resonance and Optical Zeeman Spectra of Type II CaF2:Er3+
Authors: Rector C. W. , Pandey B. C. , Moos H. W.
Published: January 2005

A study was made of the EPR and optical spectra of trivalent erbium in Type II crystals of calcium fluoride. The EPR spectrum disclosed the existence of cubic, tetragonal, and trigonal sites in the approximate ratios 15:20:1. The splitting values agreed with those of Ranon and Low.

The optical spectrum consisted predominantly of lines due to 〈100〉 tetragonal sites. This was established by a study of the Zeeman pattern of the lines as a function of rotation about the [1̄10] axis of the crystal. Spectra were taken over a range of 180° in increments of 5° in azimuthal angle. This provided a plot of energy versus azimuthal angle which could be used to establish the site symmetry in a purely geometric fashion.

This technique is of general applicability to problems of nonequivalent sites and provides considerably more information than Zeeman studies restricted to a few crystallographic directions. Spectral lines too weak to be followed in a rotational Zeeman study were assigned by finding ground-state splitting factors associated with their Zeeman patterns or by locating corresponding transitions from excited states of the ground Stark manifold.

For a number of lines, splitting factors were found and by consideration of the polarization of the Zeeman lines and the rotational Zeeman patterns, assignments of representations and crystal quantum numbers were made.
Hyperfine Interactions in the Electron Spin Resonance of Hydrated Electrons
Authors: Fueki Kenji
Published: January 2005

An attempt has been made to interpret the hyperfine structure in the electron spin resonance of hydrated electrons observed at low temperatures. The unpaired electron spin distribution has been calculated with the orthogonalized wavefunction on the basis of the model presented. It has been found that the unpaired electron is mainly localized on the O–H bonds which point toward the center of a cavity and that a sharp peak in the wavefunction occurs in the vicinity of the oxygen nucleus. A calculation has also been made of the linewidth in the ESR spectrum of trapped electrons in deuterium oxide.
Evaluation of Light-Scattering Data of Liquids from Physical Constants
Authors: Deželić Gjuro
Published: January 2005

The Rayleigh ratios and polarization ratios of some liquids are calculated from physical constants. If the molecules are nonpolar and have axial symmetry, the effect of the orientational correlations can be evaluated from Kerr constants. It was found necessary to consider the pressure dependence of Lorentz—Lorenz functions in the theory of light scattering and the Kerr effect of liquids. Theoretical and experimental data are compared and discussed.
Long-Range Interaction of Helium Atoms. A. Calculations
Authors: Kestner Neil R.
Published: January 2005

The interaction of two nonoverlapping helium atoms is evaluated using the many-electron theory of atoms and molecules with a Hirschfelder—Linnett-type of pair function, a Hylleraas intra-atomic correlation function, and a two-term atomic Hartree—Fock orbital. Previous work (previous paper) showed that the ``nonoverlapping'' region is separations over 3.7 Å. In atomic units we find V=−1.353R6−13.25R8−52.45R10−94.45R10for the dipole—dipole (using three variable parameters), dipole—quadrupole (two parameters), quadrupole—quadrupole (one parameter), and dipole—octupole (one parameter) interactions. The accepted correct value of the first coefficient is about 1.47. About 21% of the R−6 coefficient is due to three-electron effects which arise as matrix elements between the two-electron terms in the wavefunction. Neglecting intra-atomic correlation effects we obtain a coefficient of −1.644 for the first term. An error of 25% results if only a one-term atomic orbital is used. The relation of these results to many approximate methods of calculation is also discussed.
Long-Range Interaction of Helium Atoms. B. Study of Approximations
Authors: Kestner Neil R.
Published: January 2005

The higher-order corrections to the calculations of the intermolecular force by the many-electron theory of atoms and molecules are studied and those involving two-electron effects are found to be small. In particular, the corrections to the coefficient of R−6 due to normalization are about 2%. Allowing interatomic pair functions to couple with one another leads to an error of −3.4%. Including all of these effects the coefficient of R−6 is −1.363 in atomic units. The currently accepted value is −1.47. A very approximate study of three-electron correlations in the wavefunction suggests that these may contribute substantially and bring about agreement between the two values.
Thermal-Energy Ion—Neutral Reaction Rates. V. Measured Rate Constants for C+ and CO+ Reactions with O2 and CO2
Authors: Fehsenfeld F. C. , Schmeltekopf A. L. , Ferguson E. E.
Published: January 2005

The rate constants for the charge-transfer reactions of CO+ with O2 and CO2, and the ion—atom interchange reactions of C+ with O2 and CO2 have been measured at 300°K in a pulsed-discharge flowing-afterglow system. These reactions are all efficient, having rate constants ∼10−9 cm3/sec except for CO+ charge transfer to O2 which has a rate constant 2×10−10 cm3/sec.
Spectrum and Structure of the He2 Molecule. IV. Characterization of the Singlet and Triplet States Associated with the UAO's 3dσ, 3dπ, and 3dδ
Authors: Ginter Marshall L.
Published: January 2005

The electronic transitions 3dσf3Σu+, 3dπf3Πu, 3dδf3Δu→3pσc3Σg+ of He2 are described and term values presented for a number of vibrational levels for the 10 components of the singlet and triplet 3d complex. A detailed discussion of the methods of determination of reliable molecular constants in the presence of l uncoupling is presented, and the results applied to the 3d complexes of He2. The following molecular constants (cm−1), which have been corrected for l-uncoupling effects, are reported: StateωexωeBeαere(Å)f3Δu1706.8235.107.2300.2291.0791f3Πu1661.4844.797.1360.2331.0862f3Σu+1635.7744.417.0710.2461.0912F1Δu1706.5935.0657.2300.2251.0791F1Πu1670.5740.037.1560.2351.0847F1Σu+7.0980.2461.0891.
Electron Paramagnetic Resonance of Sulfur Monoxide
Authors: Daniels John M. , Dorain Paul B.
Published: January 2005

Four electron paramagnetic resonance transitions of the SO free radical generated in a gas-phase discharge of SO2 have been observed and assigned. The lines result from electric-dipole transitions between the Zeeman levels of the K = 1, J = 1 → K = 2, J = 1 states of the 3Σ− electronic ground state of 32S16O and 34S16O. The rotational constant B0 and the splitting constants λ and μ have been obtained from the microwave investigation of Powell and Lide. The g values of the electron spin, the orbital, and the rotational magnetic moments of 32S16O as determined from least-squares fitting of the EPR data are gs = 2.00197, gl = 0.00371, and gr = 0.00019. The frequencies of the corresponding transitions for the less abundant species, 34S16O, have been calculated from the isotope corrected 32S16O parameters. The relative intensities and linewidths of the SO spectrum are discussed. The linewidth is attributed to the collision broadening of SO by SO2.
Calculation of Magnetic Shielding Constants of Diatomic Molecules. I. General Theory and Application to HF Molecule
Authors: Zeroka Daniel , Hameka Hendrik F.
Published: January 2005

A general method is derived for the calculation of magnetic shielding constants of diatomic molecules from SCF LCAO MO functions. The method is based on the introduction of gauge-invariant atomic orbitals and is similar with previous calculations of diamagnetic susceptibilities. The only approximation that is used, in addition to the uncertainties in the wavefunctions, is connected with the determination of certain effective average excitation energies. The method is applied to the HF molecule and leads to a value of 4.009×10−5 for the proton shielding constant and of −7.058×10−5 for the second-order paramagnetic term. The agreement with the corresponding experimental quantities, 3.13×10−5 and −7.96×10−5, respectively, is fair. A value of 40.589×10−5 is obtained for the fluorine shielding constant and of −7.570×10−5 for the second-order paramagnetic term. The agreement with the experimental second-order paramagnetic term, −6.79×10−5, is quite satisfactory.
Steady-State Studies in the Conventional Verneuil Process—A Working Model for Burnout
Authors: Pastor R. C.
Published: January 2005

A working model for burnout of additives is presented for the flame fusion growth of crystals (Verneuil process). The case of α—Al2O3:Cr3+ (ruby) is of special interest since the additive (chromium) manifests more than one valence state in the powder, the conventional form of the feed material.
ESR Intensity Relations and Some Gas-Phase Chemical Kinetics of the OD Radical
Authors: Westenberg A. A. , Wilson W. E.
Published: January 2005

The theoretical intensity relations for the quantitative determination of gas-phase OD radical and D atom concentrations by ESR spectroscopy are derived. OD was generated by the fast reaction of D atoms with NO2, and chemical kinetic rate constants for the reactionsOD+OD→D2O+O,OD+CO→CO2+D,were measured at 300°K by following the OD decay in a fast flow system. The values obtained were k2=0.95±0.10×1012 and k4=3.30±0.10×1010 in cubic centimeters mole−1·second−1. Rate constants for the corresponding OH reactions previously measured in this laboratory by the same technique give ratios kH/kD of 1.6 for Reaction [2] and 3.5 for Reaction [4]. These ratios are discussed in terms of the absolute reaction rate theory of isotopic species. It is shown that reasonable assumptions about the activated complexes lead to good agreement with experiment.
Energy-Dependence Measurement of the CH4++CH4=CH3+CH5+ Reaction Cross Section
Authors: Colgate S. O. , Schmidt T. W.
Published: January 2005

From measurements of primary and secondary ions produced by electron bombardment of methane gas in a special mass-spectrometer ion source, analysis yields values of the cross sections for the ion—molecule reaction CH4++CH4=CH3+CH5+. The source is designed to be free of magnetic discrimination, between primary and secondary ion intensities, which has been shown to be prevalent in conventional machines. The cross section is found to be essentially independent of collision energy over the range 3–18 eV, the value being (5.0±0.2)×10−16 cm2. The present result is not in accord with the slow-ion theory of Gioumousis and Stevenson, but suggests the influence of the repulsive as well as attractive part of the potential in the reaction mechanism.
Vapor Pressure of Bismuth
Authors: Fischer Albert K.
Published: January 2005

The total vapor pressure of bismuth as determined in the temperature range 1196°—1268°K by the quasistatic and boiling-point methods is represented by logp(torr) = − (9150.3/T)+7.6327. The bismuth vapor density as found by the transpiration method is 3.05×10−3 g/liter at 1173°K. A combination of the pressure and density data yields an average molecular weight of the vapor at 1173°K of 328 which implies 57 mole % Bi2 and 43 mole % Bi in the vapor, and partial pressures of 0.29 and 0.39 torr for the monatomic and diatomic species, respectively. The standard enthalpies of dissociation of Bi2(g) and of vaporization of liquid to monatomic and diatomic species are 47.8, 50.3, and 52.8 kcal/mole, respectively. The results are compared with those of other workers.
``Hard-Core'' Model of Liquids
Authors: Snider Neil S.
Published: January 2005

Variants of the ``hard-core'' model for liquids were studied. In the hard-core model the interaction between molecules consists of a perfectly rigid repulsive core and finite, negative outer potential. Of primary concern were values of the potential energy per molecule, call it u, for the various model systems. The model systems studied were the lattice gas, hard-core models with long-range outer potentials, and hard-core models at high temperatures. For the cases studied it was found that at high density u is dominated by a term which is a function only of the density n. Furthermore, in several cases this function of density is given either approximately or exactly by —an, where a is a constant. It was noted that certain thermodynamic properties of liquids at high density and low pressure are consistent with a potential energy with a dominant term of the form —an.
Mass Spectrometry of Free Radicals and Vibronically Excited Molecules Produced by Pulsed Electrical Discharges
Authors: Foner S. N. , Hudson R. L.
Published: January 2005

Free radicals and metastable molecules produced by short-duration pulsed electrical discharges have been studied with a mass spectrometer employing a collision-free molecular-beam sampling system. Nitrogen atoms generated by extremely short pulses (0.035-μsec half-width) have been used to study the dynamics of the gas-sampling system. NH free radicals produced by electrical discharges in ammonia were detected in the X 3Σ− ground state and in the a 1Δ electronically excited state. It is estimated that approximately 22% of the NH radicals were in the a 1Δ state. Direct measurement of the ionization potential of NH in the ground state gives I (NH) = 13.1 eV. Vibronically excited nitrogen molecules from a discharge in a N2–He mixture have been observed with excitation energies up to about 9 eV, indicating that either or both of the metastable electronic states, a 1Πg and a′ 1Σu−, are substantially populated by the discharge. Evidence for excitation of N2 X 1Σg+ ground-state molecules to high vibrational quantum numbers has been obtained from the appearance-potential curve of the N2+ ion.
Electric Dipole Moment of the 1A2 Electronic State of Formaldehyde
Authors: Freeman D. E. , Klemperer W.
Published: January 2005

The measurement of the Stark effect of the near-ultraviolet absorption spectrum of formaldehyde vapor is described. The magnitude of the electric dipole moment of the 1A2 (nπ*) state is 1.56±0.07 D and its direction is the same as that of the ground-state dipole moment. The decrease of dipole moment on excitation (0.78 D) is much smaller than predicted from a naive molecular orbital model, but is in good agreement with the value (0.66 D) corresponding to the previously calculated orbitals of Foster and Boys.
Deuterium Nuclear Quadrupole Interaction in FC≡CD, CH3C≡CD, and ClC≡CD
Authors: Weiss V. W. , Flygare W. H.
Published: January 2005

The deuterium nuclear quadrupole coupling constants of CH3–C≡C–D, Cl–C≡C–D, and F–C≡C–D have been determined in order to investigate the effect of substitution on the electron distribution in the C—D bond. The results along the C—D bond yield χD=208±10 kc/sec for CH3–C≡C–D, χD=212±10 kc/sec for F–C≡C–D, and χD=225±18 kc/sec for Cl–C≡C–D. The results show equal deuteron field gradients within experimental error and therefore show that the C—D bond is relatively insensitive to the substitution at the other end of the acetylenic bond.
Method for Separating the Inter- and Intramolecular Contributions to T1 in Liquids When the Pressure Varies. Rotational Correlation Time vs Pressure
Authors: Boss B. D. , Stejskal E. O.
Published: January 2005

It is shown that to separate the intramolecular and intermolecular contributions to the spin—lattice relaxation time T1 in liquids measured as a function of pressure and/or temperature, it is only necessary to perform this separation at a single pressure and temperature if the self-diffusion coefficient D and density are also known as a function of pressure and/or temperature. T1 may be separated by solution measurements in which the liquid under study is dissolved in a solvent identical to it but magnetically inert. The intramolecular part of T1 and, hence, the intermolecular part also are obtained by extrapolation to infinite dilution. Such solution measurements would be cumbersome to perform as a function of pressure and/or temperature. It is argued that the results of such a separation may be extended to other pressures and temperatures if appropriate self-diffusion and density data are available. To examine the usefulness of this idea, the pressure dependence of the rotational correlation time τR for benzene is derived from data already in the literature. Cyclohexane (assumed to be a rigid molecule) is similarly treated except that the separation data were not available and had to be determined. The behavior of τR and D as a function of pressure is compared to the behavior of the viscosity and also to the predictions based on the theories of Debye and Hill. The discrepancies which are observed are discussed in terms of molecular shape and internal reorientation.
Light from the Collision of Excited N2 with NO
Authors: Dugan C. H.
Published: January 2005

When a thermal beam of N2 is excited by electrons of controlled energy and collides with NO, light is observed. The excitation function shows that this light is produced by excited N2 in metastable states. The spectrum is obtained with very low resolution, and it is identified as the transition A 2π—X 2Σ of NO, the γ bands, from low vibration levels. Experiments with other gases are briefly described.
Second-Order WKB Corrections to Rydberg—Klein—Rees Potential Curves
Authors: Davies R. H. , Vanderslice Joseph T.
Published: January 2005

Expressions given in an earlier paper are applied to the X 1Σg+ ground state of hydrogen. The second-order approximations were found to have little effect upon the turning points of the curve, the major correction being an increase in the well depth of 10 cm−1. The method appears to have certain advantages over the Dunham procedure.
Flash Photolysis of H2O2 Vapor in the Presence of D2, Ar, and H218O
Authors: Greiner N. R.
Published: January 2005

The flash photolysis of H2O2 by itself, and in the presence of D2, Ar, and H218O, was studied by the technique of kinetic absorption spectroscopy. The only observable primary products were OH(2Π½) and OH(2Π32). These ground-state levels were populated in a ratio of ∼1:1, respectively, conforming to what is observed with the halogens.

The contribution of Reaction (a) to the primary process was shown in a direct way to be no more than 20% of that of (b). Reaction (c) followed by (d) was shown to make no significant contribution to the OH concentration during the time of our experiments (<200μ sec): H2O2(singlet)→ lim hνH2O(1A1)+O(1D),→2OH(2Π),→H2O(3A1)+O(3P),O(3P)+H2O2 (singlet)→OH(2Π)+HO2 (doublet),OH(2Π)+H2O2 (singlet)→H2O(1A1)+HO2 (doublet).Thus, this technique is a convenient one for directly observing reactions of OH. An upper limit to the rate constant of (e) at room temperature was determined to be 5.8±1.8×10−14 cm3 molecule−1·sec−1.

Conditions for generating vibrationally hot molecules in the primary photolytic step are discussed.
Absorption and Excimer Fluorescence Spectra of Sandwich Dimers of Substituted Anthracenes
Authors: Chandross Edwin A. , Ferguson J.
Published: January 2005

The absorption and fluorescence spectra of seven sandwich dimers of substituted anthracenes are reported. The absorption spectra of dimers of 9-methyl-, 9-chloro-, 9-bromo-, and 9-cyanoanthracene are consistent with a symmetrical sandwich configuration. The resonance splittings are about 400 cm−1 for the 1A1g→1B2u transition (of anthracene) and about 1500 cm−1 for the 1A1g→1B3u transition. The dimers of 9,10-dichloroanthracene and 9,10-dibromoanthracene have absorption spectra consistent with a rotated sandwich configuration; the angle between the molecular axes is 61 deg for the dichloro compound and 73 deg for the dibromo compound. The spectrum of the mixed sandwich dimer of anthracene and 9,10-dichloroanthracene is interpreted on the basis of a ``symmetrical'' sandwich configuration. The 1B3u electronic states are completely mixed by orbital overlap and only one absorption band is observed. On the other hand the spectral features of both monomer transitions to the 1B2u state are present in the spectrum of the dimer. The fluorescence spectra of all the sandwich dimers are of the excimer type and the fluorescence yield, relative to that of the monomer, is decreased markedly by the heavy-atom substituents. The relevance of the experimental results to the theories of the energy levels of dimers and excimers is discussed critically.
Photodimerization of Crystalline Anthracene. The Photolytic Dissociation of Crystalline Dianthracene
Authors: Chandross Edwin A. , Ferguson J.
Published: January 2005

The photodimerization of anthracene dispersed in potassium bromide matrix has been reinvestigated. The hydrocarbon is shown to be present as ordinary crystalline anthracene. Dianthracene, prepared in potassium bromide discs, can be photolytically dissociated at low temperatures to give a new sandwich crystal form of anthracene which has a yellow-green excimer fluorescence. This crystal structure can also be used to explain recent studies of the fluorescence of crystalline anthracene under high pressure.
Radiation Chemistry of Liquid Sulfur Dioxide. II. Radiation-Induced Oxidation—Reduction Reactions in Liquid Sulfur Dioxide Solutions of Sulfur Trioxide and Potassium Iodide
Authors: Rothschild Walter G.
Published: January 2005

Irradiation by 60Co gamma rays of dilute solutions of sulfur trioxide in anhydrous, air-free liquid sulfur dioxide confirms that (1) molecular oxygen is formed by attack of radicals on sulfur trioxide, most likely via O+SO3→SO2+O2, (2) no measurably significant amount of O2 is formed by radical recombination O+O→O2 in the spurs. Irradiation of air-free anhydrous solutions of potassium iodide in liquid sulfur dioxide yields iodine and potassium bisulfate K2S2O7 at constant rates and to high percents of conversion of iodide to iodine. The data are discussed in terms of electron-transfer reactions from the charge-transfer complex iodide anion—sulfur dioxide to the oxygen atom. The possibility of reactions of iodide ion with ionic species which have been suggested to arise in liquid sulfur dioxide during radiolysis is considered briefly. The difference between the radiation chemistry of liquid sulfur dioxide on one hand and those of water and liquid ammonia on the other is believed to be a consequence of the radical scavenging properties of liquid sulfur dioxide.
On the Existence of Conformers of Cyclobutyl Monohalides. III. Assignments of the Fundamentals of Bromocyclobutane and Chlorocyclobutane
Authors: Rothschild Walter G.
Published: January 2005

The infrared spectra of the liquid and the vapor and the Raman spectra of the liquid of bromocyclobutane and chlorocyclobutane are reported. The 30 fundamentals of each halide are assigned and an approximate picture of the motions of those atoms, which are mainly involved in the fundamental modes, is given. There is one-to-one correlation between the fundamentals of bromocyclobutane with the fundamentals of chlorocyclobutane. This signifies that the amount of interaction between different modes is generally of the same order of magnitude in both halides, in contrast to the corresponding cyclopropyl halides. There is little symmetry correlation between the fundamentals of the cyclobutyl halides and cyclobutane; the out-of-plane ring-bending (ring-puckering) mode is an exception. In the Appendix, computer calculations of A- and C-type band envelopes are presented and compared with observations; the computations include vibration—rotation interaction.
Optical Spectra of Divalent Manganese Salts. I. Energy Levels for Cubic and Lower-Symmetry Complexes
Authors: Lohr L. L.
Published: January 2005

An extensive study of the optical absorption spectra of Mn(II) salts is introduced with a re-examination of the nature of crystal-field independent transitions and their dependence upon slight changes in ligand positions. Evidence for an unexpected but significant decrease in metal—ligand bond lengths for the 4A2 state with respect to those for 6A1 equilibrium ground state is obtained both from experiment, in terms of the excitation of totally symmetric displacements, and from approximate calculations. The latter involve both an extended formulation of the nephelauxetic effect and molecular orbital (MO) parameters obtained by a semiempirical LCAO MO scheme. A classification scheme for crystal-field independent transitions, not necessarily in Mn(II) complexes, is introduced, and is based on the type of molecular orbitals, σ, π, or both, appearing in the exchange integrals associated with the transition energies. Low-symmetry effects, especially for the 4E states, are discussed.
Ground-State Energy of Two-Electron Atoms
Authors: Stillinger Frank H.
Published: January 2005

We examine the ground-state energy ε(λ) for two electrons bound to an infinite-mass point nucleus regarded as a function of the complex coupling constant λ for the interelectron interaction. In the units used, the ground states of the homologous series H−, He, Li+, Be++, ···, correspond, respectively, to λ=1, ½, ⅓, ¼, ···, so the λ power-series expansion of ε(λ) is equivalent to the familiar expansion in inverse nuclear charge Z−1. It is argued that the power series has a finite radius of convergence imposed by the existence of a branch point on the positive real axis at λ=λ*≅1.1184 with exponent approximately 6/5. Furthermore, ε(λ*) apparently lies above the continuum limit, but still corresponds to a localized wavefunction.
Determination of Hydrogen-Atom Concentration by Lyman-α Photometry. I. Oscillator Strength of the Hydrogen-Atom 2P,½←2S½ Transition. II. Kinetics of the Reaction of Hydrogen Atoms with Acetylene and Ethylene
Authors: Michael Joe V. , Weston Ralph E.
Published: January 2005

A photometric method of determining hydrogen-atom concentration in the gas phase has been developed. It consists of a hydrogen—neon lamp emitting Lyman-α radiation at 1216 Å, and a nitric oxide-filled ion chamber which serves as the detector. A fast-flow system with a microwave discharge in an H2–He mixture was used as the source of hydrogen atoms. This arrangement permits the determination of H-atom concentrations of 1011 atoms/cc. A photometric calibration curve was obtained by using titration with NO2 as an absolute measure of H-atom concentration.

The oscillator strength of the Lyman-α transition was determined with this apparatus. Depending on the assumed profile of the emission line and the extent of self-reversal in the source, oscillator strengths of 0.4 to 1.1 (compared with the theoretical value of 0.8324) were obtained.

Rates of reaction of H atoms with ethylene and acetylene were determined at various total pressures and concentrations of reactants. Both reactions are first order with respect to each reactant, and the recombination of H atoms contributes very little to their rate of disappearance. The pressure effect on the reaction with ethylene depends on the formation of vibrationally excited ethyl radicals which either decompose to form reactants or are stabilized by collision. The reaction with acetylene appears to be complicated by a pressure-independent reaction path which predominates at low pressures and is most probably the abstraction reaction H+C2H2→H2+C2H.
Vibrational Relaxation Times of Deuterium and Hydrogen. A Comparison of Theory and Experiment
Authors: Parker J. G.
Published: January 2005

A comparison of experimental and theoretical vibrational collision numbers has been carried out for deuterium and hydrogen and also for interactions of those gases with argon and krypton. Agreement is obtained for the latter while definite discrepancies appear for the D2—D2 and H2–H2 interactions. This discrepancy is rather large at the lowest temperatures; however, extrapolation of the experimental data indicates that at temperatures of the order of 10 000°K agreement is attained.

The intermolecular interaction constants used in comparing theory and experiment are shown to be consistent with those derived from measurements on rotational relaxation times for hydrogen and hydrogen—rare-gas mixtures. Using these interaction constants a value of 67 collisions is obtained for the rotational collision number of hydrogen in the limit of very high temperature.
Thermodynamic Properties of a Simple Hard-Core System
Authors: Hoover William G. , Ree Francis H.
Published: January 2005

A simple hard-core system is studied over the entire density range. The model embodies both the simplicity associated with a nearest-neighbor lattice-gas interaction and the realism of a continuous configuration space.

In two dimensions the model system shows no signs of a first-order phase transition. In three dimensions a transition is indicated.
Nonstatistical Energy-Transfer Theory
Authors: Serauskas R. V. , Schlag E. W.
Published: January 2005

Energy transfer between molecules upon collision is of interest to any theoretical formulation of chemical kinetics. Microscopic transition probabilities between specified energy states are extremely difficult to predict theoretically. For collisions involving polyatomic molecules recourse has been made for many years to statistical arguments based on phase space considerations, since detailed dynamic models appear to be virtually intractible. It is shown here, that at least for one experimental system involving vibrational-energy transfer from reacting molecules to a heat bath, statistical calculations grossly overestimate energy transfer efficiencies. Furthermore such statistical models requiring equilibration in the collision complex are difficult to reconcile with the short collision durations observed in molecular-beam experiments. It is proposed here rather, that the actual duration of a collision seriously restricts the amount of energy transfer that can take place both as to time and available phase space. This collision time theory of energy transfer is roughly cast into quantitative form and found to give excellent agreement with at least these experimental data. Qualitative conclusions based on this theory permit an integrated understanding of energy-transfer data from many apparently different sources.
Molecular Beam Measurement of the Hyperfine Structure of 85Rb19F
Authors: Zorn Jens C. , English Thomas C. , Dickinson J. Thomas , Stephenson David A.
Published: January 2005

Radio-frequency transitions between the hfs levels of the J=1 rotational state in 85Rb19F have been observed using a molecular beam electric resonance spectrometer. From these spectra we have obtained values for the constant eq1Q1, which characterizes the interaction between the electric quadrupole moment of the Rb nucleus with the molecular electric-field gradient; for the constants c1 and c2 which characterize the magnetic interaction between the Rb and F nuclei, respectively, and the rotational angular momentum J of the molecule; and for the constants c3 and c4 which describe the magnetic coupling of the two nuclear spins. Measurements have been made on the first-five vibrational states. The results for v=0 are eq1Q1=(−70.342±0.001) MHz,c1=(+0.52±0.02) kHz,c2=(+10.615±0.06) kHz,c3=(+0.80±0.06) kHz,c4=(+0.15±0.05) kHz.Values of these constants for v=1, 2, 3, and 4 are given with somewhat less precision.
Determination of Diffusion Coefficients from Viscosity Measurements: Effect of Higher Chapman—Enskog Approximations
Authors: Storvick T. S. , Mason E. A.
Published: January 2005

Numerical calculations based on the higher Chapman—Enskog approximations show that mutual diffusion coefficients calculated from binary mixture viscosity data agree within experimental uncertainty with the measured D12 values at compositions corresponding to a trace of the heavy component.
Microwave Spectrum of 14N16O17O
Authors: Foster Peter D. , Hodgeson Jimmie A. , Curl R. F.
Published: January 2005

Some 150 hyperfine transitions belonging to the 808→717 and 919→100,10 rotational transitions of 14N16O17O have been observed in the microwave region. The new coupling constants which have been determined are the odd-electron expectation values on oxygen. They are |ψ(0) |2=0.71×1024 cm−3,〈(3r̂a2−1)/r3〉=−4.71×1024 cm−3,and 〈(r̂b−ic^)2/r3〉=5.04×1024 cm−3.The results of the work are combined with previous work on other isotopic modifications of NO2 to give an LCAO MO picture of the odd-electron orbital.
Neutron-Scattering Study of the Intramolecular and Crystalline Modes of Polyethylene
Authors: Safford G. J. , Naumann A. W. , Simon F. T.
Published: January 2005

The neutron spectra and the derived frequency distributions for polyethylene are compared with recent calculations. The skeletal-deformation and -torsion modes appear at 550±50 and 200±10 cm−1, respectively, in agreement with both theory and previous measurements. Five additional weak maxima, observed below 190 cm−1, correlate with predicted intermolecular frequencies and are observed to persist to 350°K (well above the glassy-transition interval) in both a high-density and a strongly branched polyethylene. In contrast, the skeletal torsion and deformation modes broaden and decrease in intensity with increasing temperature and with increasing branching disorder. With annealed samples, the skeletal torsion sharpens with increasing density (i.e., increased order), but the intermolecular modes do not. A spectrum taken normal to the direction of chain alignment in a specimen that had been cold drawn to the yield point showed a sharp, well-resolved, skeletal-torsion mode but no skeletal-deformation mode. This agrees with a previous assignment of the deformation as a longitudinal and the torsion as a transverse mode. The interchain modes were split and shifted in frequency in the drawn sample, presumably because of interchain disordering.

Eight additional weak maxima were observed between 800 and 200 cm−1 in high-density polyethylene. The nature of the molecular motions associated with these modes is uncertain, but it is suggested that they involve coupling with the skeletal modes.
Systematic Use of Solvent Effects in High-Resolution Nuclear Magnetic Resonance
Authors: Freeman R. , Bhacca N. S.
Published: January 2005

It is shown that certain characteristic features of nuclear magnetic double-resonance spectra (the coalescence of spin multiplets or the splitting of single lines into doublets) can also be induced in single-resonance spectra of molecules that contain a pair of strongly coupled nuclei. Degeneracies due to overlap of two groups of resonance lines in one region of the spectrum may cause coalescence or splitting effects in some quite different region of the spectrum. These features are particularly easily recognizable when introduced into the spectrum in a gradual manner by the systematic use of preferential solvent shifts. Expressions derived for the transition frequencies and intensities bear a strong formal resemblance to those used for ``spin-decoupling'' and ``spin-tickling'' double-irradiation experiments. The strong temperature dependence of the chemical shift of the hydroxyl resonance in 2-propyn−1-ol has been exploited to induce the coalescence of certain lines in the spectrum of the methine proton, demonstrating that J(H–C–O–H) and J(H–C≡C–C–H) have opposite signs. This is a case where standard double-irradiation methods would not be applicable because the long-range coupling J(H–C≡C–C–O–H) is vanishingly small. Control over the overlap of the AB region of the ABMX spectrum of 3-fluoro-4-methoxyacetophenone makes it possible to induce splittings in the X spectrum, permitting the subspectra to be identified and the relative signs of the coupling constants to be obtained by inspection. The ortho and meta proton—fluorine coupling are shown to have the same sign, opposite to the sign of the para coupling.
Born—Oppenheimer Separation for Three-Particle Systems. I. Theory
Authors: Hunter G. , Gray B. F. , Pritchard H. O.
Published: January 2005

The Born—Oppenheimer separation for a three-particle system has been re-examined in detail using a variational approach including a scale parameter. Discrepancies arising in earlier work have been resolved. Tables of adiabatic and nonadiabatic coupling terms are presented.
Vibration Spectra of Yttrium and Uranium Hydrides by the Inelastic Scattering of Cold Neutrons
Authors: Rush J. J. , Flotow H. E. , Connor D. W. , Thaper C. L.
Published: January 2005

The vibration spectra of the hydrides and deuterides of yttrium and uranium have been investigated by the energy-gain scattering of cold neutrons. The measured spectra are all split into two bands, one at higher energies, due to the optical hydrogen vibrations, and another at lower energies due to metal—atom vibrations. Values have been obtained for the peaks and widths of the single optical hydrogen bands in YH2, YD2, UH3, and UD3 by the calculation of approximate frequency distributions from the observed neutron time-of-flight spectra. The derived peak frequencies in cm−1 are: YH2, 1025±60; YD2, 725±40; UH3, 970±60; UD3, 710±40. The relative width at half-maximum for the hydrogen band in UH3 is about double that for YH2. The distribution of hydrogen vibrations in hexagonal YH3 and YD3 is considerably broader, and exhibits several maxima, due to hydrogens at different sites in the lattice. The hydrogen modes in all the compounds can be correlated reasonably well with the known crystal structures. The results are in satisfactory agreement with hydrogen frequencies calculated previously from heat-capacity data.
Sum-Frequency-Generated Spectra of Gases and Liquids
Authors: Cohan Norah V. , Hameka Hendrik F.
Published: January 2005

The theory of sum-frequency-generated spectra of gases and liquids is derived for the case of resonance. Our results are in agreement with the previously derived nonresonance theories by Giordmaine and others. It is suggested that the resonance case can be studied by means of an experiment where one of the incident beams comes from a laser source while the other incident beam is ordinary polarized monochromatic light of variable frequency.
Microwave Spectrum of Pivalaldehyde
Authors: Ronn A. M. , Woods R. C.
Published: January 2005

The microwave spectrum of pivalaldehyde [(CH3)3CCHO] has been investigated in the frequency region 9–40 kMc/sec. The ground state, first and second excited states of the t-butyl torsion, and the first excited state of each of the three methyl torsions have been assigned. The barrier to internal rotation of the t-butyl top has been calculated from the splittings in the first excited state to be 1186 cal/mole, from the splittings in the second excited state to be 1176 cal/mole, and from the intensities of the first excited state relative to the ground state to be 1100 cal/mole. The excited states of the methyl torsions show no splittings, but the relative intensities yield barrier estimates of 2600, 3500, and 3800 cal/mole, if one assumes that the three tops are independent. On the basis of certain analogies with previously investigated molecules the lowest of these three barriers is very tentatively assigned to a methyl group which is eclipsed with respect to the oxygen atom. The dipole-moment components were computed from Stark-effect measurements to be μa=2.56 D and μb=0.76 D.
Exothermic Ion—Molecule Reactions
Authors: Moran T. F. , Friedman L.
Published: January 2005

Dissociative charge-transfer reactions between rare-gas He+, Ne+ ions and diatomic N2, O2, CO, NO molecules have been studied as a function of reactant-ion velocity. N+, O+, and C+ fragment ions are the major reaction products observed in these exothermic reactions. Experimental cross sections and corresponding rate constants for thermal-energy ions are in semiquantitative agreement with the theoretical rates calculated from the long-range ion—induced-dipole potential. A reversed-repeller technique was used to probe the kinetic-energy distributions of the ionic reaction products and the experimental (0.2 to 1 eV) distributions so obtained are well correlated with the heats of the respective reactions. The kinetic energies of the product N+ and O+ ions were shifted to lower values when 3He+ was substituted for 4He+ ions in the NO and O2 reactions. This shift in product-ion kinetic energy rules out accidentally resonant charge-transfer processes involving excited product atoms and is consistent with a two-body breakup mechanism of transitory HeN+ and HeO+ at low reactant-ion velocities.
Covalency Effects in Trigonal Distortion
Authors: Englman Robert
Published: January 2005

The trigonal field experienced by a paramagnetic ion owing to its surroundings is studied theoretically, account being taken of covalency effects. In addition to the parameter v, due to the trigonal field of the second-order harmonic acting at the metal ion, there is also the splitting parameter V acting on the corresponding molecular orbitals formed from the ligand orbitals. Covalency mixing then results in an effective splitting parameter that is (in general) different for each configuration in the t and e subshells and which replaces the one-electron splitting parameter used in the absence of covalency. The effect may be particularly marked when V is of opposite sign and larger than v. Under these conditions the Jahn—Teller-type trigonal distortion may also switch over because of covalency.
Mobility of Solvated Electrons in 2-MTHF
Authors: van Voorst J. D. W. , Hoijtink G. J.
Published: January 2005

Solvated electrons in 2-methyltetrahydrofuran prove to have much higher mobilities than alkali ions. This confirms our conclusion drawn in a previous paper that the solvated electrons behave very similarly in MTHF and liquid ammonia.
Molecular Self-Consistent-Field Calculations on B4H4
Authors: Palke William E. , Lipscomb William N.
Published: January 2005

The wavefunction and Hamiltonian matrix for tetrahedral B4H4 have been obtained from an SCF calculation based upon accurate integrals over a minimum basis set of Slater orbitals (H exponent of 1.2). The molecule is bound by 0.43 a.u. relative to 4 BH, the overlap populations are 0.837 for BH and 0.451 for BB, and charges are −0.08 on B and +0.08 on H.