bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical-Shift Anisotropy and Nuclear Quadrupole Coupling Constant of 14N in Methyl Isocyanide
Authors: Yannoni Costantino S.
Published: February 2004

H–{14N} spin tickling has been used to determine for the first time a 14N chemical-shift anisotropy (ΔσN). The measurement was made on C1H314NC partially oriented in a nematic liquid-crystal solvent, and the result is + 360 ± 73 ppm. The 14N nuclear quadrupole coupling constant was also measured and is + 272 ± 2 kHz, only 57% of the gas-phase value. Using a simple valence model of CH3NC to supply the orbital parameters, Pople's chemical-shift theory yields a value of ΔσN = + 675 ppm. e2qNQN / h was calculated to be + 880 kHz using the results of an all-electron SCF calculation in a Townes–Dailey treatment modified to reflect expansion of the nitrogen atomic orbitals in the molecule. Considering the level of approximation used in both calculations, the agreement with experiment is satisfactory. The problem of knowing the molecular geometry of CH3NC in the nematic phase is discussed along with the related difficulty of determining a reliable value for the anisotropy in the NH indirect coupling tensor.
Spin Susceptibilities of Organic Systems on a Narrow-Band Model
Authors: Fedders Peter A. , Kommandeur Jan
Published: February 2004

A narrow-band model is used to explain the temperature dependence of the spin susceptibilities of organic free-radical solids. It is shown that for temperatures in excess of the bandwidth the spin susceptibility is half the expected Curie susceptibility, while at low temperatures exponentially vanishing susceptibilities are obtained through the splitting of the bands due to the asymmetry of the crystal structure. A consideration of the effects of nuclear motion on the band structure leads to a “Curie–Weiss” law behavior at high temperatures, with a quite different interpretation of the Weiss constant. The results of the calculations are compared with available experimental data for DPPH (diphenylpicrylhydrazil), PAC (picrylaminocarbazyl), and D(NO2)2 [bis(p-nitrophenyl)picrylhydrazyl]. Very good agreement with experiment is obtained. Further applications of the narrow-band model are discussed.
Theory of the Rare-Gas-Induced Q Branch in HCl Vibration–Rotation Spectra at High Pressures
Authors: Herman R. M.
Published: February 2004

A theory for the rare-gas-induced Q branch in the HCl fundamental vibration–rotation band at high pressures is developed. The interaction responsible for the phenomenon arises from the displacement of the center of attraction (repulsion) to the rare-gas atom from the center of mass in HCl. The short-range behavior of this interaction is studied, and it is concluded that the displacements between centers in short- and long-range interactions are equal. Based on this conclusion, the absorption intensity distributions for HCl–Ar and HCl–He mixtures at 400 amagat, 195°K are computed, as well as that for the HCl–Ar mixture at 450 amagat, 300°K. Certain general aspects of the calculations reveal the reasons behind various observed characteristics of Q-branch induction, while the results of explicit calculations of absorption intensity contours show substantial quantitative agreement with experiment. Among other things the over-all magnitude of the Q branch, its dependence on rare-gas species, and its dependence on temperature are successfully accounted for in the present analysis. The principal discrepancies arise from underestimation of the widths of the various components of the absorption intensity distributions.
Low-Frequency Modes in Molecular Crystals. VI. Methyl Torsions and Barriers to Internal Rotation of C(CH3)4, C(CD3)4, Si(CH3)4, Ge(CH3)4, and Sn(CH3)4
Authors: Durig J. R. , Craven S. M. , Bragin J.
Published: February 2004

The far-infrared spectra of C(CH3)4, C(CD3)4, Si(CH3)4, Ge(CH3)4, and Sn(CH3)4 have been recorded from 300 to 33 cm−1. The f1 torsional modes were observed at 281, 206, 177.5, 134, and 101.5 cm−1 and the a2 torsional modes were assigned to bands at 221, 157, 163.5, 134, and 101.5 cm−1 for the C(CH3)4, and C(CD3)4, Si(CH3)4, Ge(CH3)4, and Sn(CH3)4 molecules, respectively. The corresponding CH3 torsional barriers were calculated to be 4.3, 4.6, 2.0, 1.3, and 0.8 kcal/mole. These barriers are shown to be consistent with those reported for the similar trimethyl molecules but are considerably higher than the barriers previously reported for these molecules from PMR studies.
Trigonometric Interpolation Method for One-Dimensional Quantum-Mechanical Problems
Authors: Meyer R.
Published: February 2004

A rapidly converging difference method, based on harmonic analysis, is described. It can be applied to periodic or nonperiodic bound-state problems of the general Sturm–Liouville type. Numerical examples for the Mathieu problem and for the harmonic oscillator show considerable accuracy. Advantages and disadvantages of the method are discussed in a comparison with Harris's matrix transformation technique and with direct integration methods. The set of difference equations representing a quantum-mechanical problem constitutes a symmetric matrix eigenvalue problem which is approximately equivalent to the algebraic problem obtained by using a finite trigonometric basis. Basis functions associated with the difference method are related to the Dirichlet kernel. In an approximation which corresponds to the difference method, these basis functions can be treated in a similar way as Dirac's δ function.
Exciton–Phonon Interactions in Molecular Crystals
Authors: Grover M. K. , Silbey R.
Published: February 2004

The interaction of Frankel excitons with optical phonons in molecular crystals is studied by means of a Green's function method in which the use of a canonical transformation allows most of the exciton–phonon interaction to be treated nonperturbatively. The self-energy of the Green's function is then expanded in terms of the intermolecular potential. An expression is obtained for the absorptive part of the dielectric function of the exciton–phonon system. Comparison is made with experiment and also with earlier theories, some of the limitations of which are pointed out.
NO3 Radical: “Soft” Lattice Preparation and Pure ESR Spectrum at 88°K
Authors: Martin T. W. , Swift L. L. , Venable J. H.
Published: February 2004

The NO3 radical is generated by the direct photolysis of ceric ammonium nitrate in aqueous nitric acid solutions. When produced in aqeuous HONO2–HOClO3 mixtures frozen to form a good glass or “soft” lattice at 88°K, the pure ESR spectrum of NO3 is uncomplicated by lattice distortions. Under these conditions we found the radical to be planar with true axial symmetry having the following computed parameters: g‖ = 2.0041 ± 0.0003, g⊥ = 2.0207 ± 0.0003, and σ(12ΔHpp) = 5.16 Oe. Some problems of NO3 photochemistry are explained. The use of this technique to generate a variety of more stable free radicals is discussed. The first comparative evidence is given that radicals with nearly equal electron affinities, such as OH and NO3, nevertheless show unique and selective reactivity differences toward the same substrates.
Symmetry Rule for Predicting the Structures of Molecules. II. Structure of X2Yn Molecules
Authors: Pearson Ralph G.
Published: February 2004

Using the second-order Jahn–Teller effect as a criterion, molecular shapes are predicted for molecules with the formulas X2Y2, X2Y4, and X2Y6. The method is remarkably successful, the only failure being the inability to predict the correct angle of rotation about single bonds. However, this is a necessary failure.
Total Ionization Times in Shock-Heated Noble Gases
Authors: Merilo Mati , Morgan Edward J.
Published: February 2004

Total ionization times in shock-heated argon, krypton, neon, and xenon have been calculated, taking into account atom–atom collisions, electron–atom collisions, and recombination. Excellent agreement is found with the experimental results obtained for argon, neon, and some experiments on xenon. The highly inconsistent results obtained by some investigators for xenon have probably been due to high impurity levels and inadequate testing times in the shock tube.
Shock-Tube Study of Carbon Monoxide Dissociation Using Vacuum-Ultraviolet Absorption
Authors: Appleton John P. , Steinberg Martin , Liquornik David J.
Published: February 2004

The dissociation kinetics of carbon monoxide diluted in argon and in mixtures of oxygen in argon have been investigated over the temperature range 8000–15 000°K behind reflected shocks using light absorption at 1176 Å. An induction period, 5–100 times longer than the vibrational relaxation time of carbon monoxide, was observed in the carbon monoxide–argon mixtures prior to the establishment of the steady-state dissociation rate for the over-all process, CO+M→ lim kd(M)C+O+M. Rate coefficients were determined for Ar, CO, and O as the collision partner, M. The steady-state dissociation rate coefficient, kd(Ar), was found to be well represented by the expression kd(Ar) = 2.8 × 103 ± 0.08T−2.86 ± 0.14 × exp − (1.29 × 105 / T) cm3sec−1, with kd(CO) ≲ 2kd(Ar) and kd(O) = 15 kd(Ar). Induction time measurements reported here are in excellent agreement with the previous measurements of Fairbairn and in reasonable accord with the transient behavior of mechanisms in which either of the following reactions: CO + C(or O)→CO* + C(or O) or CO + C→C2 + O, may be involved in the transient buildup of the steady-state intermediates CO* or C2. The measured induction times, τ, of this and the previous studies are best correlated by the relationship [τ2(CO)(M)]−1 = 4.97 × 10−19 ± 0.18exp − [(132 400 ± 3300) / T] cm6sec−2. Mechanisms are advanced to account for the measured induction behavior and steady-state dissociation rates.
EPR of O2 Impurity in Solid N2
Authors: Graham G. M. , Harvey J. S. M. , Kiefte H.
Published: February 2004

The EPR spectrum of O2 impurity in solid N2 has been observed at K band and at X band. The results are consistent with the specific-heat results for this system and indicate that the Σ3 state is split in zero field by 105 ± 15 GHz. A small temperature-dependent splitting of the upper doublet is indicated by the results, and the possibility of using O2 as a probe to investigate the motions of molecular solids is pointed out.
X-Ray Compton Profiles of Benzene, Cyclohexane, and Oriented Polyethylene
Authors: Weiss R. J.
Published: February 2004

The Compton profiles of liquid benzene, liquid cyclohexane, and oriented polyethylene were measured with MoKα x rays. The electron momentum distributions in all cases are considerably more extended in momentum space than those (a) calculated from the Coulson and Duncanson type of hybrid orbitals or (b) measured with the angular correlation of positron–electron annihilation radiation. In addition, a high momentum “tail” is observed in the Compton profile suggestive of electron–electron correlation. The measured anisotropy in the electron momentum density of oriented polyethylene is small.
Vibrational Spectra of Single Crystals. Polymorphic Solids of Cyclohexane-d12
Authors: Brown Chris W. , Obremski Robert J. , Lippincott Ellis R.
Published: February 2004

Single crystals of the two polymorphs of cyclohexane-d12 were grown using miniaturized high-pressure instrumentation. The infrared spectrum of a single crystal of solid I supports a cubic crystal structure with Th2 space group symmetry for this solid modification. Polarized infrared spectra of a single crystal of solid II and the infrared and laser-excited Raman spectra of a polycrystalline film were also measured. The splitting of the fundamental vibrational bands and the polarized infrared data are compatible with the previous results on cyclohexane-d0 and confirm an orthorhombic D2h crystal structure.
Semiempirical Extended Hartree–Fock LCAO Crystal Orbital Method
Authors: Ladik J. , Martino F.
Published: February 2004

The extended Hartree–Fock method in its semiempirical LACO form has been extended for the treatment of the delocalized π electrons of a finite linear chain containing an arbitrary number of π orbitals within the elementary cell. The formalism leads to two coupled matrix equations. A method for numerical solution of these equations is outlined in the paper.
Thermal-Energy Dissociative Attachment of I2; Deduction of the Curve Crossing Point from Experimental Measurements
Authors: Shipsey Edward J.
Published: February 2004

O'Malley's theory has been applied to the reaction of thermal energy electrons with I2 molecules. The best fit to the experimentally measured temperature dependence of the attachment coefficient is given by an I2−−I2 crossing at 0.066 ± 0.007 eV above the I2 minimum. This occurs very close to the υ = 2 vibrational energy level.
Quantum-Mechanical Solution of the Collinear Atom–Diatomic Collision with a Linear Interaction Potential
Authors: Diestler D. J.
Published: February 2004

The method of Shuler and Zwanzig is extended to treat the collinear collision of an atom interacting with a diatomic molecule by a linear finite-slope repulsive potential having an adjustable attractive step. The interaction potential has two parameters, one governing the strength of the repulsive portion and the other the strength of the attractive portion. Results for the system in which all particles have equal mass are presented for five different combinations of the potential parameters. In two of the cases the potential is strictly repulsive and in the other three it has an attractive well in addition to the linear repulsive wall. The presence of the attractive well causes resonances in the probability curves at certain energies corresponding to the formation of metastable “complexes.”
Transient Photoconductivity in Poly(N-vinylcarbazole)
Authors: Pai Damodar M.
Published: February 2004

Transport of holes through thin films of poly(N-vinylcarbazole) was studied using transient photoconductivity techniques. The photogeneration depends on the electric field with quantum efficiency of generation approaching a value of 0.1 at an applied electric field of 108 V/m. The motion of carriers cannot be characterized by a drift mobility but can be fully represented by an “effective transit time” given by (Teff)−1 = (mτ0)−1exp(γE1/2 − ε0 / kT), where m = d / d0 (d being the thickness of the film and d0 a characteristic length), τ0 is a characteristic release time from a localized state, E is the applied electric field, ε0 is an activation energy, k is the Boltzmann constant, and T is the absolute temperature. This relationship suggests a model in which holes jump from one localized state to the next one, the “effective transit time” being the sum of release times from the localized states. Bulk trapping occurs at low fields, and the release from these traps depends on both temperature and electric field.
Production of n = 3 and n = 4 States of Atomic Hydrogen by Electron Impact on H2
Authors: Weaver L. D. , Hughes R. H.
Published: February 2004

Absolute cross sections for the production of Hα (n = 3 → 2) and Hβ (n = 4 → 2) emissions by electron impact on H2 have been measured in the energy ranges 20–400 eV and 30–400 eV, respectively. Time-resolved spectra were taken for 50-, 75-, and 110-eV impact in which the s-state decays could be definitely identified since the decay times agreed with theory. All decays could be fit with a two-mode decay scheme, the second mode having a lifetime somewhat longer than the d-state theoretical lifetime. The possibility of Stark mixing of certain states is discussed. Cross sections for the production of atoms in the 3s and 4s states are estimated for 50, 75, and 110 eV. The 3s → 2p contribution to Hα and the 4s → 2p contribution to Hβ are about 24% and 14%, respectively, at these energies.
Visible Spectra of Argon Matrix Isolated Phthalocyanines: Pair Interactions
Authors: Lucia E. A. , Verderame F. D. , Taddei G.
Published: February 2004

The 5000–8000-Å transmission spectra of H2PC and CuPC embedded in an argon matrix at 5°K at molar ratios of 4000:1 are very similar to their spectra in liquid solution. The predominant CuPC species in the matrix are isolated molecules, but a strong sideband in more concentrated mixtures (1000 Ar:1 CuPC) is attributed to interacting pairs. Coupling of transition dipoles was invoked to correlate the observed spectrum with several CuPC “dimer” configurations. Computer calculations based upon nonbonded atom–atom potentials were conducted to find the most probable relative orientations of two neighboring solute CuPC molecules. H2PC does not appear to show the effects of pairs even in extremely dilute solutions. A strong doublet which is very similar to that in liquid solution persists in the matrix.
Optical Spectrum of Single-Crystal Nd2S3
Authors: Henderson James R. , Muramoto M. , Gruber John B. , Menzel Roland
Published: February 2004

Rare-earth sesquisulfide crystals have been grown by the Czochralski method. The crystals as grown are opaque n-type semiconductors. Diffusion of sulfur into semiconducting crystals at 1200°C produces transparent insulators having the same crystal structure, lattice parameters, bandgap, and optical spectrum as the semiconductors. Electrical conductivity can be controlled over 12 orders of magnitude by heating crystals in an atmosphere of sulfur. Assignments of Nd3+ J levels observed in the spectrum of insulator-type Nd2S3 are made with the aid of a calculation of free-ion wavefunctions and energy levels. A crystal-field calculation based on Oh symmetry describes the details of the observed spectrum. Even at 4°K observed 4f → 4f transitions in Nd2S3 are broader than in other Nd3+ salts and are shifted about 300 cm−1 to the red of the Nd2O3 spectrum.
Vibrational Effects on the Hyperfine Interactions of Aromatic Radicals in Solution
Authors: Reddoch A. H. , Dodson C. L. , Paskovich D. H.
Published: February 2004

Measurements of the temperature dependence of the proton hyperfine coupling constants of a number of aromatic radicals in solution together with some measurements of the proton-to-deuteron coupling constant ratio are reported. These and data from the literature show the effects of out-of-plane CH vibrations. A relationship between the two types of measurements is demonstrated. Such vibrations lead to a small hyperfine coupling between the proton and spin densities on carbons adjacent to the one to which it is bonded. The implications of this effect are discussed.
Birefringence of Solutions of Rigid Particles in Steady and Oscillatory Flow
Authors: Thurston G. B. , Munk Petr
Published: February 2004

Theories of flow birefringence in steady and oscillatory shear flow for spheroidal particles are compared. It is shown, that proper normalization of birefringence functions make them identical for both flows at low gradients and frequencies. The deviations at high gradients and frequencies increase with increasing particle axial ratio. The theory for polydisperse particles is developed. From the limiting behavior at low and high gradients and frequencies it is possible to find various averages of the relaxation times of the particles and hence some description of the polydispersity. The differences between steady and oscillatory flow behavior for a monodisperse system persist even for the polydisperse case thus giving the possibility of indirectly checking some aspects of the monodisperse theory. Experiments on microcrystalline alumina (Baymal), tobacco mosaic virus, and bentonite are in essential agreement with theoretical predictions.
Reaction of CHO+ with C3H6 as a Function of Ion Translational Energy
Authors: Futrell Jean H. , Tiernan Thomas O.
Published: February 2004

The reactions of CHO+ ions derived from acetaldehyde source molecules on propylene have been studied using an in-line tandem mass spectrometer. Rate constants for the formation of propyl ions and for the unimolecular dissociation of propyl ions into C2H3+(+CH4) and C3H5+(+H2) as a function of ion translational energy were estimated from experimental data and reaction parameters. Comparison of the results with rates of decomposition of excited propyl ions calculated from the quasiequilibrium theory of mass spectra lead to the conclusion that the initial interaction of CHO+ with propylene takes place via proton stripping rather than complex formation.
Bromine Nuclear Quadrupole Resonance in Ferroelectric Hydrogen Bromide
Authors: Kadaba P. K. , O'Reilly D. E.
Published: February 2004

Bromine-79 and bromine-81 nuclear quadrupole resonance frequencies have been observed for HBr (below 70°K) and DBr (below 85°K). The observed frequencies decrease with temperature more rapidly than those calculated from the Bayer theory, and the lines broaden rapidly with increase in temperature above 45°K for HBr and above 65°K for DBr. The line broadening is interpreted as due to a 90° flip process of the molecules in the ferroelectric solid III. The correlation times and activation energy for this process are in good agreement with those calculated from dielectric dispersion data for DBr. The bromine-79 resonance is 4 times broader in DBr than in HBr at low temperatures. A quantitive explanation of this effect has not been found. A doublet fine structure in the resonance of H79Br at low temperatures is interpreted as due to two kinds of chemically inequivalent molecules in the unit cell.
Deuteron Magnetic Resonance of the Solid Phases of Deuterium Sulfide
Authors: O'Reilly D. E. , Eraker J. H.
Published: February 2004

The deuteron magnetic resonance of D2S was examined from 77°K to above the liquid–solid transition at 187°K. In solid III of polycrystalline D2S, e2qQ / h = 142 ± 9 kHz and η ≈ 0.1 independent of temperature. Solid II yields e2qQ / h = 88 ± 4kHz and η = 0.30 ± 0.01. In solid I a very sharp deuteron resonance line is observed for which spin–lattice relaxation times (T1) have been determined. For solid III, the lattice is rigid and e2qQ / h is 91% of the gas-phase value. Solid II is characterized by orientations of the S–D bonds by an approximately 90° flip motion with concomitant change of the direction of the bisectrix of the DSD angle and the direction of the D–D vector. This result is consistent with the previously observed dielectric constant and proton second moments in this phase. In solid I the averaging of the quadrupolar splitting is complete and the molecular reorientation is isotropic with a rotational correlation time (τ2) of 4 × 10−13 sec just above the solid II–I phase transition (133°K). Previous proton resonance measurements are interpreted in terms of presently available data on the solid phases of hydrogen sulfide.
Analytic Approach to the Theory of Phase Transitions
Authors: Weeks John D. , Rice Stuart A. , Kozak John J.
Published: February 2004

An approximation to the first equation of the Kirkwood coupling parameter hierarchy and other model equations for the singlet distribution function are cast into the standard Hammerstein form of nonlinear integral equation. We give a criterion for the existence and uniqueness of solutions of this equation involving the first negative eigenvalue of the kernel, which allows us to establish temperatures and densities where the solution is unique. Multiple solutions of the nonlinear equation are associated with instability of the single phase and thus signal a phase transition. A necessary condition for the existence of other solutions of small norm is given by a bifurcation equation. These new solutions are associated with the freezing transition, and the periodic singlet density of the solid falls naturally out of the theory. The bifurcation equation can be related to the Kirkwood instability criterion, but, in contrast to this, predicts no transition for a system of hard rods when a model kernel is used. This model, in an approximate numerical calculation, also predicts no transition for a system of hard spheres, in apparent agreement with Meeron's recent suggestion that systems with purely repulsive forces have no phase transitions.
Percus–Yevick Equation Applied to the Melting Problem with Application to Argon
Authors: Kerber Ronald L.
Published: February 2004

For the melting transition, the solid is represented by an anharmonic model and the liquid is described by the Percus–Yevick approximation. The behavior of the liquid at high densities is studied on the isotherms kT / ε = 1.3, 1.8, and 2.0, where k is the Boltzmann's constant, T is the temperature, and ε is the well depth of the Lennard-Jones 12–6 pair potential. No solutions of the Percus–Yevick equation were found for ρσ3 above 1.3, where ρ1 is the particle density and σ is the radial parameter of the Lennard-Jones potential. The liquid structure is found to be very different from the solid structure near the melting line. The liquid pressures are about 50% low for experimental melting densities of argon. This discrepancy gives rise to melting pressures up to twice the experimental values.
Atomic and Molecular Pseudopotential Studies Using Gaussian Orbitals
Authors: Simons Gary , Mazziotti Alexander
Published: February 2004

The Hellmann model potential is employed for the first time in atomic and molecular calculations with a Gaussian basis set. The use of Gaussian functions allows for the simple application of the pseudopotential method to large molecular systems while maintaining the accuracy exhibited by Slater-type-orbital calculations. A new model potential specifically designed for Gaussians, V(r) = C1r2 + C2, is proposed and used to examine a series of two-valence-electron atoms. A number of diatomic molecules are studied with both the Hellmann and Gaussian model potentials. Bond lengths, vibrational frequencies, dipole moments, and dissociation energies are calculated, and the results are generally in good accord with experimental data. The Phillips–Kleinmann pseudopotential formalism is used to examine the model potentials and analyze the atomic and molecular results.
γ
Radiolysis of Liquids at High Pressures. VIII. Primary Yields at 8.7 kbar and Reactions of the Hydrated Electron with H2O and H3O+
Authors: Hentz Robert R. , Knight Ronald J.
Published: February 2004

Pressure invariance of the primary yields of water radiolysis (previously established for pressures up to 6.4 kbar) was shown to extend to 8.7 kbar in γ radiolysis of both neutral and 0.8N H2SO4 solutions. G(H2) was measured in γ radiolysis of the following deaerated solutions at 25° and pressures in the range 0–8.85 kbar: (a) 3 × 10−5M NaNO3 and 0.05M glucose (slightly alkaline); (b) 10−3M NaNO3, 2.3 × 10−4M HClO4, and 0.05M glucose. In solution (a) G(H2) is determined by a competition for eaq− between the diffusion-controlled Reaction [3], eaq−+NO3−→no H or H2, and Reaction [1], eaq−+H2O→H+OH−. In solution (b) the competition is between Reactions [3] and [2], eaq−+H3O+→H+H2O. All H are converted to H2 by reaction with glucose. With the assumption that pressure dependence of k3 is determined approximately by that of water viscosity, kinetic analysis of the results gives ΔV1‡ = − 14.3 ml mole−1 and ΔV2‡ ≈ 0 ml mole−1. From the value of ΔV2‡, the absolute partial molal volume of eaq− (based on a value of −5.4 ml mole−1 for H+) is estimated to be in the range 0–11.3 ml mole−1. With an estimated electrostriction contribution of −3 ml mole−1, the electron cavity volume is in the range 3–14 ml mole−1, as compared to about 100 ml mole−1 in liquid ammonia.
Excitation Energy Transfer in Alkanes. I. Exciton Model
Authors: Partridge Roger H.
Published: February 2004

The molecular exciton theory of sigma bonds, which was set up previously to explain the vacuum-ultraviolet absorption spectra of alkanes, is applied here to the primary radiation chemical reactions of linear and branched alkane polymers. From this a number of theoretical predictions are made, the most important being that very efficient excitation energy transfer will occur along the CC bonds of the polymer main chains without causing main chain scission but that excitation energy in CH bonds will be localized in pairs of these bonds and give rise here to a high rate of scission. These predictions are examined in detail in the following two papers, using experimental data.
Excitation Energy Transfer in Alkanes. II. Experimental Demonstration
Authors: Partridge Roger H.
Published: February 2004

A very efficient energy-transfer process is reported here which occurs in alkane molecules during irradiation with an efficiency which is strongly dependent on molecular chain length. The energy transfer is detected by addition of small amounts of suitable additives that ionize or dissociate into fragments which can be detected by visible and ultraviolet absorption measurements. Such energy transfer has hitherto usually been explained on a positive charge-transfer model but the evidence here strongly suggests that excitation energy transfer is in fact the dominant mechanism and that some reassessment of the other model may be needed. Energy transfer occurs predominantly along the molecular chains, over distances at least ∼1500 Å in long chain alkanes.
Nuclear Relaxation in Solids due to Molecular Rotation at Low Temperatures
Authors: Wallach Daniel , Steele William A.
Published: February 2004

A quantum-mechanical treatment of nuclear spin–lattice relaxation due to molecular rotation in the solid is presented. It is shown that at low temperatures, where this treatment is valid, the rate of relaxation is directly proportional to the rates of transitions among the torsional levels and to the extent to which those transitions alter the expectation value of the diple–dipole Hamiltonian. The form of the expression for T1 is analogous to the usual form obtained by a correlation function approach, in the limit ω0τc ≫ 1, if the inverse of the correlation time is identified with an appropriate average transition rate among torsional levels. It is predicted that at very low temperatures the apparent activation energy of the correlation time should be much smaller than the height of the barrier to rotation.
Asymptotic Properties of Atomic Form Factors and Incoherent Scattering Functions
Authors: Goscinski O. , Lindner P.
Published: February 2004

By use of the cusp condition for electronic wavefunctions the exact asymptotic behavior of the atomic form factor is determined. The relation between the pair distribution function and the incoherent scattering function for large wave vector is pointed out.
Study of the Glory Effect for Atomic Collisions in the Hyperthermal Energy Region
Authors: Neumann W. , Pauly H.
Published: February 2004

The velocity dependence of the total collision cross section for the systems Li–Hg, Na–Hg, K–Hg, Rb–Hg, Cs–Hg, and Na–Cs has been measured for energies between several electron volts and several hundred electron volts. Due to the high angular resolution of the apparatus it was possible to resolve in all cases the glory undulations, which are analyzed in order to determine potential parameters. The influence of the finite angular resolution of the apparatus on the observed glory structure is discussed.
Behavior of Macromolecules on the Phase Boundary. II. Conformational Statistics of the Linear Chain in a Pore
Authors: Pouchlý J.
Published: February 2004

The pseudodiffusion equation with a term added by the author to describe the effect of the field of force has been employed in the calculations of the partition function and equilibrium concentration of a dilute solution of linear polymer in pores, the walls of which are formed by a swollen gel and are therefore partly permeable to chainlike macromolecules. The effect of surface forces near the walls of the pores has also been considered. In this way, Casassa's equilibrium theory of gel permeation chromatography (GPC) formulated for pores with inert impermeable walls has been generalized. To simplify the calculations, a quasistationary approximation has been proposed and employed. The equilibrium concentration difference between a pore and the bulk phase of solution is a result of two antagonistic phenomena; i.e., of the decrease in the number of conformations in the walls of the pore, and of attractive adsorption forces. Its sign depends on the values of the following expressions: (d / b)2(φA / kT), φA / φG, and (ν − 1)d / (L − d), where d is the thickness and φA is the potential of the layer of adsorption forces, b is the length of the chain segment, φG is the potential characterizing the interaction of the linear polymer with the gel, L is the radius of the pore, and ν is the geometric characteristic of the pore (ν = 1 for a plane-parallel pore, ν = 2 for a cylinder, ν = 3 for a sphere).
Infrared and Ultraviolet Spectra of the Products of the Vacuum-Ultraviolet Photolysis of Silane Isolated in an Argon Matrix
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: February 2004

The vacuum-ultraviolet photolysis of silane and of the various deuterosilanes isolated in an argon matrix at 4 or at 14°K leads to the production of several reactive species. Infrared and ultraviolet spectroscopic evidence is presented indicating that Si2, SiH, SiH2 and SiH3 are stabilized in these experiments. A previously unobserved transition of Si2, tentatively identified as the D(3Πu) − X(3Σg−) transition, is reported. Observation of the bending vibration absorption of SiH2 at 1008 cm−1 has confirmed that the lower state of the previously observed electronic transition of singlet SiH2 is the ground state of this species. The stretching vibrations of SiH2 have also been observed near 2000 cm−1. Infrared absorptions at 925, 996, 1955, and 1999 cm−1 have been tentatively assigned to SiH3. The removal of one or more H atoms from SiH4 leads to an appreciable lengthening of the remaining Si–H bonds. Disilane and incompletely characterized products of its photolysis contribute significantly to the infrared spectra observed at 14°K.
Ionization Potential and Structure of Olefins
Authors: Demeo D. A. , El-Sayed M. A.
Published: February 2004

The method of photoionization has been used to measure the ionization potential of a number of simple, cyclic, exocyclic, bicyclic mono- and diolefins. These data are compiled with others from the literature of related systems, and the results are compared. In mono-olefins, the ionization potential of the olefinic π electron is found to decrease as the size of the molecule increases, the change being largest with the first methyl substitution to ethylene. As the size of the σ system of a monofolefin increases, the energy of both the neutral molecule and the ion decreases by the extra bonds formed as well as by strengthening the π system as a result of mixing it with the ionic form due to hyperconjugation. Both factors stabilize the ion more than they do the neutral molecule. The fact that cyclic and exocyclic olefins have ionization potential comparable to that observed for straight chain olefins of comparable size again strongly indicates that the stabilization of the ion by the electrons in the σ bonds (rather than by hyperconjugation) is an important factor in determining the ionization energy of π electrons in olefins. The effect of a second olefinic group greatly depends on whether or not strong interaction between the two groups occurs, but is independent of whether a chain or cyclic system is studied. Conjugation is found to decrease the I.P. values by ∼0.5 eV. Due to the increase in the effective nuclear charges of the atoms in the ion, resonance and Coulombic-type interactions stabilize the ion upon conjugation more than they do the neutral species. Nonconjugated dienes have slightly lower I.P. than the corresponding monofolefins by an amount that depends on the separation and geometry of the diene. The effect of a second olefinic system in a bicyclic diene can be as great as that produced by the classic type of conjugation in favorable cases, such as in norbornadiene. In these systems, increasing the ring size increases the number of bonds, thus lowering the value of the I.P., but also increases the separation between the double bonds, which raises the value of the I.P. 1,4,7-cyclononatriene (crown) has an I.P. value which is 0.6 eV lower than that in benzene, but higher than trimethyl-substituted benzene. This result is explained by the fact that strong conjugation is present in the crown but is not as effective as it is in the phenyl ring.
Experimental Test of the Two-Parameter Theory of Dilute Polymer Solutions: Poly-p-methylstyrene
Authors: Tanaka Genzo , Imai Shozaburo , Yamakawa Hiromi
Published: February 2004

In order to test the two-parameter theory of dilute polymer solutions, light-scattering and intrinsic-viscosity measurements were carried out on fractions of poly-p-methylstyrene in toluene, dichloroethane, cyclohexane, and methyl ethyl ketone at 30°C, and in diethyl succinate at temperatures ranging from 16 to 60°C. The theta temperature for this polymer in diethyl succinate was found to be 16.4°C. With the data for the statistical-radius expansion factor αS and the interpenetration function Ψ appearing in the second virial coefficient, validity of a theory of these quantities was examined using the two criteria introduced previously: (1) consistency in the values of the excluded-volume parameter z determined from αS and Ψ, and (2) linearity between z and the square root of the molecular weight. It was found that the Yamakawa–Tanaka theory of αS and the Kurata–Yamakawa theory of Ψ were a self-consistent pair of intramolecular and intermolecular theories of interaction which satisfied both of the two criteria. The data for the viscosity-radius expansion factor αη indicated no existence of the draining effect, and there was no satisfactory theory of αη. An empirical relation between αη and z was obtained, where values of z were calculated from observed values of αS using the Yamakawa–Tanaka equation. It was found that at small z, αη3 = 1 + C1z + ···, with 1.05 < C1 < 1.55. This is a theoretical problem to be solved. Based on the empirical relation between αη and z, the equation for the Stockmayer–Fixman viscosity plot was revised. Values of the polymer–solvent interaction parameter B determined from viscosity plots using the revised equations were in good agreement with those from mean-square radii and also from second virial coefficients.
Dilute-Solution Properties of Polar Polymers: Poly-p-chlorostyrene and Poly-p-bromostyrene
Authors: Noguchi Yasuhiro , Aoki Akihiro , Tanaka Genzo , Yamakawa Hiromi
Published: February 2004

Light-scattering and intrinsic-viscosity measurements were carried out on fractions of poly-p-chlorostyrene and poly-p-bromostyrene in toluene at 30°C. Unperturbed dimensions were estimated from the Berry plots of second virial coefficients and also from the Stockmayer–Fixman plots of intrinsic viscosities. Values of the binary-cluster integral β per monomeric unit were determined by the two methods proposed in the previous paper; one is based on the use of the Yamakawa–Tanaka equation for the statistical-radius expansion factor, and the other the modified Stockmayer–Fixman plot. The results by the two methods were in excellent agreement with each other. The differences in β between poly-p-chlorostyrene and poly-p-methylstyrene, and between poly-p-bromostyrene and poly-p-methylstyrene in toluene, were analyzed using the theory of dilute solutions of polar polymers developed by Yamakawa and Rice on the basis of the cavity field and reaction field arguments. The agreement between theory and experiment was found to be satisfactory. The difference in β between polystyrene and poly-p-methylstyrene in toluene is also discussed. It is suggested that a complete theoretical calculation of the whole β should be based on the theory of simple liquids.
Intramolecular Interactions in the Water Molecule: The Stretch–Stretch Interaction Force Constant of Water Molecules in Hydrogen-Bonded Systems
Authors: Fifer R. A. , Schiffer J.
Published: February 2004

A calculation is described for determining water molecule Frr force constants from observed HOD, H2O, and D2O vibrational frequencies. The calculations for water in the vapor and in the hydrates MnCl2·2H2O, FeCl2·2H2O, CoCl2·2H2O, and CuCl2·2H2O indicate a large increase in Frr with hydrogen bonding. Various contributions to Frr are considered, and its increase is attributed to an enhancement of the effective charge on water hydrogens with increased hydrogen bonding.
Spectroscopic Reassignment and Ground-State Dissociation Energy of Molecular Iodine
Authors: LeRoy Robert J.
Published: February 2004

Reanalyzing some early bandhead data for I2[B 0u+(3Π)], an improved value of the ground-state dissociation energy is found to be D0 = 12 440.9 ± 1.1 cm−1, differing significantly from the previously accepted value of Verma, 12 452.5 ± 1.5 cm−1. This result implies that the final state of one of the uv resonance series reported by Verma must have a rotationless potential maximum some 13.1 ± 1.4 cm−1 high. It is further shown that the original electronic assignment of this state as ground-state X 0g+(1Σ) is implausible. A reassignment as 0g+(3Π) is proposed, and the nature of the 0g+(3Π) potential is considered.
Molecular Constants and Internuclear Potential of Ground-State Molecular Iodine
Authors: LeRoy Robert J.
Published: February 2004

A reanalysis of the spectroscopic data for ground-state iodine yields improved rotational constants and vibrational energies which are used to compute a new RKR potential. Polynomial representations of the vibrational energies and rotational constants are presented which fit all the data to within the respective experimental precision of Verma and of Rank and Baldwin. New approaches are introduced for separately obtaining the rotational Bυ and Dυ constants and for estimating error bounds for computed RKR turning points.
Possible O8+–O12+ Structures Obtained by Use of Classical Electrostatic Theory
Authors: Conway D. C.
Published: February 2004

The interaction energy in the series O2–O6+ through 3O2–O6+ is approximated as the sum of the van der Waals interactions between the neutral species and the following electrostatic interactions: monopole–quadrupole, quadrupole–quadrupole, and (monopole+quadrupole)–induced dipole+induced dipole–induced dipole. Two planar O6+ structures and charge distributions obtained by the CDO–IBM method were used in the O8+ computations. The computed dissociation energy De(O2–O6+) is certainly too large for the O6+ structure with the larger charge on the central O2. The De values computed for the O6+ structure of smaller charge are as follows: De(O2–O6+) = 3.42, De(O2–O8+) = 3.26, and De(O2–O10+) = 3.12 kcal/mole. Although these values are larger than the experimental ΔH° data, they are in reasonable agreement considering the uncertainties in the van der Waals potential and the quadrupole moments and the lack of data concerning the higher moments and polarizabilities, e.g., the quadrupole polarizability. The O8+–O12+ have been studied at T < 100°K. The barriers to internal rotation by the attached O2 molecules are computed to be 1.2 kcal, much larger than RT for T < 100°K.
Dynamics of the Reaction of Ar+ with D2
Authors: Chiang M. , Gislason E. A. , Mahan B. H. , Tsao C. W. , Werner A. S.
Published: February 2004

We report measurements of the velocity vector distributions of the ionic products of collisions of Ar+ with D2 and He for relative energies between 2.26 and 9.1 eV. The ion ArD+ is produced by a direct interaction mechanism which gives considerable forward scattering. The nonreactive scattering of Ar+ by D2 is intense, nearly elastic, and very similar to the scattering of Ar+ by He. Differential reactive cross sections are determined, partially deconvoluted, and compared with results from several other laboratories.
Surface Rainbows: A Similitude between Classical and Diffractive Scattering of Atoms from Crystalline Surfaces
Authors: McClure J. Doyle
Published: February 2004

A preliminary account is given of sharp “rays” and related intensity structure revealed by high-resolution classical calculations of atomic scattering from an ordered monolayer. Factors related to use of structural features of the intensity maxima for investigation of atom–surface interaction fields are discussed.
Polarized Absorption Spectra of Carbazole Single Crystal
Authors: Chakravorty S. C. , Ganguly S. C.
Published: February 2004

Absorption spectra of carbazole polarized parallel to a and b crystallographic axes have been obtained for first and second singlet systems. Vibrational fundamentals observed for the first excited state consist of A1 species which indicates that the first electronic transition is along the short axis of the molecule (A1 → A1). Polarization study, however, reveals that the transition is along the short axis together with some out-of-plane component. An attempt to explain the out-of-plane component has been made on the basis of a slight nonplanarity of the molecule in the crystal lattice. From the relative intensity of the first two absorption systems in solution and crystal phase and with the knowledge of molecular orientation in the crystal lattice, it has been concluded that the second-lowest electronic transition is along the long axis of the molecule (A1 → B2).
Galvanomagnetic Data and the Sign of the Carriers Located at Point K in the Brillouin Zone of Graphite
Authors: Spain Ian L.
Published: February 2004

Schröeder et al. have recently proposed from magnetoreflection experiments that electrons occupy states near point K in the Brillouin zone of graphite, whereas previous studies had assigned holes at this point. Analysis of galvanomagnetic data indicates that majority carrier behavior favors the new assignment. Minority carrier behavior for natural and synthetic crystals is discussed.
Dependence of Vicinal H–H Coupling Constants in Substituted Ethanes on the Potential Function Characteristics to Internal Rotation. Application to A2B2 PMR Spectrum of Nonsymmetrical 1,2-Disubstituted Ethanes
Authors: Lin Wei-chuwan
Published: February 2004

Based on rotational averaging, a theory governing the change of the vicinal coupling parameters L and N in the A2B2 PMR spectra of nonsymmetrical 1,2-disubstituted ethanes, as evidenced in the studies of substituent effect and solvent effect, has been developed in terms of the potential function characteristics to internal rotation about the C–C bond. By taking the average over the entire period of dihedral angle with respect to an appropriate potential function for internal rotation of the compound, a refined Karplus equation for the vicinal H–H coupling constant as a function of dihedral angle, J = A cos2φ + B cosφ + C, could yield the expression for L / A and/or N / A in terms of hyperbolic Bessel functions which describes an explicit functional dependence of L and/or N on both the ethane barrier and the maximum dipole interaction potential between the two bonds C–X and C–Y. These expressions enable one to determine the physical parameters related to internal rotation upon measurement of L and/or N from NMR spectrum. The determined energy difference between rotamers for several 1,2-disubstituted ethanes were found in good agreement with the literature values. Solvent effect on the A2B2 PMR spectrum was discussed on the light of the theory. The NMR experimental relation N∓13| L | = A was derived from the above expressions. This latter relation enables one to tell whether the trans or the gauche isomer is more stable for the given compound from measurement on N and L with respect to the neat sample or in the medium of various solvent, and it also enables one to evaluate the value of A for each given compound.