bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature-Dependent Optical Activity Due to Quantized Molecular Rotation and Optical Rotation by Oriented Molecules
Authors: Chiu Ying-Nan
Published: February 2004

Classical works on optical rotation have dealt with random systems for which all molecular orientations are equally probable. We have considered here optical rotation by quantum mechanically rotating molecules. The contributions to optical rotation from the individual rotational levels of a symmetric- and a spherical-top molecule have been derived. These may be asymmetric molecules belonging to the C3, D3, or T point group. The contributions are weighed by the Boltzmann distribution over the rotational levels, thus giving rise to temperature dependence. Such dependence will be significant at low temperatures. It is shown that, the same as for classical random systems, the optical rotation by quantized rotors comes from the interference of an electric multipole of a given rank with a magnetic multipole of the same rank. However, because of the dependence on the rotational energy level K, for the rotation of infrared “light” which is close to the frequency of a rotational transition, the optical rotation may arise purely from the quantized rotation of symmetric-top molecules that are not necessarily asymmetric. The difference in behavior between a symmetric-top molecule with rotational angular momentum K and a linear molecule with electronic angular momentum Λ is discussed. In the limit of equally probable orientations and in the dipole approximation, it is shown that the results for quantized rotors reduce to the classical expression of optical rotation. Whereas for rotating molecules optical rotation normally requires asymmetry and interference between one electric and one magnetic multipole of the same rank, for oriented molecules, optical rotation may come purely from molecular arrangement requiring no asymmetry of the individual molecule, and may come from arbitrary interference mechanisms. We have considered the optical rotation by molecules uniformly oriented in solid matrices or in weakly interacting molecular crystals. We have derived the optical rotation from the following interference mechanisms: electric dipole–electric dipole (E1E1), electric dipole–magnetic dipole (E1M1), electric dipole–electric quadrupole (E1E2), magnetic dipole–magnetic dipole (M1M1). The angles of rotation have been expressed in terms of the Euler angles of orientation of the individual molecule with respect to the incident polarized light and in terms of the scattering tensor matrix elements over the molecular states. The conventional rotatory strength proportional to the matrix element of the pseudoscalar, R·M, was shown to come from the orientation-independent term in the E1M1 interference mechanism. The possible contributions, of these various mechanisms and various scattering tensors, to optical rotation by oriented molecules belonging to a few simple groups are illustrated in tabular form.
Evaluation of Three-Center Nuclear Attraction Integrals
Authors: Kleinman B.
Published: February 2004

The three-center nuclear-attraction integral, with exponential-type orbitals, is evaluated. The result is a relatively simple expression having a finite number of terms. This permits the four-center two-electron integral 〈ϖα(A, 1), ϖβ(B, 1) | r12−1 | ϖγ(C, 2)ϖδ(D, 2)〉 to be expressed as a linear combination of a finite number of one-electron integrals.
Crystal-Field Theory Investigation of Bis(N, N-Dialkyldithiocarbamato) Ferric Halides
Authors: Ake Robert L. , Loew Gilda M. Harris
Published: February 2004

The crystal-field model is used to describe ferric ion in the five-coordinated bis(dialkyldithiocarbamato) halide complexes. All seven compounds investigated have quartet ground states. A fit to experimental zero-field splittings is obtained naturally and provides eigenfunctions and eigenvalues which can be used to calculate magnetic properties. The calculated electric-field gradient, due to a large lattice term, and magnetic moment, showing little temperature variation, are both in accord with experiment. The magnetic-field energies of the four A24 states are calculated as a function of the molecule's orientation in the static magnetic field. The angle- and field-dependent wavefunctions together with a Gaussian line shape function are used to construct low-energy absorption spectra which are displayed by the computer. These calculated spectra are in agreement with the experimental curves.
Further Studies of Reactions of Hot Hydrogen with Hydrocarbons
Authors: Baker R. T. K. , Silbert M. , Wolfgang R.
Published: February 2004

A further quantitative examination of the reactions of recoil tritium with hydrocarbons has been made. Reaction probabilities for various types of processes have been determined as a function of neon moderation. Data have been analyzed using the kinetic theory of hot reactions. This theory has been extended to indicate the relative mean energies and overlap of the excitation functions for the several possible reactions. The following conclusions are indicated by our data: (1) Reactivity integrals I and energy loss parameters α increase with increasing complexity of the reactant molecule. This appears to be associated with the greater ability of larger molecules to absorb the excess energy of hot tritium atoms. (2) Abstraction appears to occur at higher average energies than displacement. Since abstraction is known to be dominant at lower energies, this means that it can also occur efficiently at higher energies than displacement. These findings accord with a previously postulated stripping mechanism for abstraction and with the observed effect of bond energy on this process. (3) Displacement reaction is restricted to a relatively narrow energy range in methane but can extend to higher energies in higher hydrocarbons.
Electron Correlation and Separated Pair Approximation in Diatomic Molecules. II. Lithium Hydride and Boron Hydride
Authors: Mehler Ernest L. , Ruedenberg Klaus , Silver David M.
Published: February 2004

By use of the variational principle, nearly optimal antisymmetrized products of separated geminals have been determined for lithium hydride, boron hydride, and their separated atoms. The geminals are determined in terms of their natural orbitals, which are represented as expansions of Slater-type atomic orbitals. By comparison of the fully optimized wavefunctions of the hydrides at their equilibrium distances with the corresponding wavefunctions for the separated atoms, it is shown that the inner shells are essentially invariant upon molecule formation and that the detailed correlation structure of the inner geminal can be neglected for the determination of difference properties. From a partitioning of the geminal expansions into a principal part and a correlation part, a corresponding partitioning is obtained for the total wavefunction and the energy. With the help of this partitioning the detailed correlation interactions are analyzed and the sources of intrapair correlations are exhibited. Comparisons are made with previous calculations in terms of this analysis. A method is developed for obtaining potential curves from many-parameter wavefunctions in which the wavefunction is reoptimized at a few selected values of the internuclear separation. Moreover, at these few points, the correlating natural orbitals of the inner shells can be omitted during the course of the minimization. From the fact that the parameters are smooth and slowly varying functions of the internuclear distance, an interpolation scheme is proposed for determining the entire potential curve. From these potential curves the spectroscopic constants are calculated on the basis of the Dunham analysis.
ESR of 17O-Labeled PO32− Ion Trapped in a Single Crystal of Na2DPO3·5D2O
Authors: Schlick S. , Silver Brian L. , Luz Z.
Published: February 2004

The ESR spectrum of an x-irradiated 17O-enriched Na2DP17O3·5D2O single crystal is reported. The results show unambiguously that the radical formed is PO32−. The values and directions of the principal components of the 17O and 31P hyperfine tensors were determined and were used to derive values for the atomic-orbital coefficients in the 6a1 molecular orbital containing the odd electron. The relative orientation of the two magnetically inequivalent PO32− radicals in the unit cell in deuterated crystals was found to differ markedly from that in the isotopically normal crystal.
Absolute Differential Cross Sections of Elastically Scattered Electrons. III CO and N2 at 500, 400, and 300 eV
Authors: Bromberg J. Philip
Published: February 2004

Absolute differential cross sections of electrons elastically scattered by CO and N2 have been measured at 500, 400, and 300 eV. At scattering angles greater than 12° there is no significant difference between the two isoelectronic molecules. At small angles the cross sections for CO increase at a slightly faster rate than for N2, reflecting the presence of a dipole moment for the heteronuclear CO molecule.
Gd3+ ESR Spectra in Cubic and Trigonal Sites of BaF2
Authors: Boatner L. A. , Reynolds R. W. , Abraham M. M.
Published: February 2004

Accurate spin-Hamiltonian parameters for Gd3+ in cubic and trigonal sites of BaF2 have been determined at 300, 77, and 4.2°K. Previously undetermined signs of the crystal-field constants were established. Unusual linewidth and intensity variations were observed in the BaF2:Gd3+ trigonal spectrum.
Trapping and Damping of Molecular Exciton States
Authors: Schmidt P. P.
Published: February 2004

In this paper we show that for an exciton mode coupled to a vibronic state of an impurity or to a different electronic final state of a host molecule (through an intersystem crossing or internal conversion) where the final state is damped, the damping causes a broadening of the initial exciton mode. The damping is considered in terms of Senitzky's theory of the damped quantum oscillator for molecular vibrations and in terms of his theory of the damped two-level system for the molecular electronic states. The damping constants found in the Senitzky-type damping theory are related to Green functions. Thus, it is possible to relate the exciton linewidth (or lifetime) to well-defined energy conversion processes within a molecule. The final energy-loss step—to the thermal bath—can still be treated by means of an arbitrary damping constant.
Noncubic EPR Spectra of Gd3+ in CdF2
Authors: Smith S. R. P. , Cole T.
Published: February 2004

Spectra of Ge3+ with orthorhombic symmetry have been observed in CdF2 crystals containing both Gd3+ and Na+ as impurity ions, where the charge-compensating Na+ ions occupy nearest-neighbor Cd2+ sites. The orthorhombic field parameters are D = 116 ± 1 MHz, E = 42 ± 1 MHz, and the cubic field parameter is B4 = − 2.444 ± 0.005 MHz. The variation of the intensity of the orthorhombic spectrum with heat treatment has been observed. Also, a complicated spectrum has been observed in CdF2 containing both Gd3+ and Y3+; it is suggested that this spectrum can be interpreted in terms of the exchange coupling between Gd3+ ions and trapped conduction electrons.
Molecular Orbital Studies of Hydrogen Bonds: Dimeric H2O with the Slater Minimal Basis Set
Authors: Morokuma Keiji , Winick Jeremy R.
Published: February 2004

Ab initio LCAO–MO–SCF calculation for the dimeric H2O system is carried out with a minimal Slater basis set with exponents optimized for H2O. The most stable linear dimer is found to have an O···H distance of 1.80 Å, with the proton-acceptor molecule perpendicular to the donor molecule and bent by 54° trans with respect to the end OH bond of the donor. The stabilization energy calculated is about 6.55 kcal/mole. The changes in the length and the stretching force constant of the donor O–H bond are also discussed. A population analysis shows that the stabilization at a larger O···H distance (>2.3 Å) is essentially electrostatic, while at a smaller distance, the charge transfer becomes increasingly important.
Isotope Effect as a Function of Alpha-Particle Energy in the Ionization of Hydrocarbon Gases
Authors: Jesse William P.
Published: February 2004

In this work the isotope ratio, i.e., the ratio of the ionization produced by a given alpha particle in a deuterated hydrocarbon gas to the corresponding ionization in an undeuterated hydrocarbon gas, was investigated as a function of alpha-particle energies in the range 5.8–1.6 MeV. Alpha particles from 244Cm, 210Po, and 147Sm were employed. Particles reduced energies were also obtained by passing alpha particles through thin mica windows. The isotope effect was larger in the hydrocarbons investigated than for our previous experiments for ionization by beta particles from 63Ni. For the hydrocarbons methane, ethane, acetylene, and ethylene there was found to be a very small increase of the order of 1%–3% in the isotope ratio as one decreased the alpha-particle energy from 5 to 1.6 MeV. A tentative explanation of this change with alpha energy has been advanced.
Molecular Vibration Spectra from Field-Emission Energy Distributions
Authors: Flood Dennis J.
Published: February 2004

A calculation is presented which predicts the effect of an inelastic interaction between field-emitted electrons and adsorbed molecules at a metal–vacuum interface. The derivative of the total energy distribution of the field-emission current should yield information on the infrared absorption spectra of the adsorbed molecules. A numerical estimate of the size of the effect indicates that changes on the order of 1% of the total current should occur.
EPR Spectrum and Heat of Dissociation of the Perylene Dimer Cation
Authors: Chiang T. C. , Reddoch A. H.
Published: February 2004

The EPR spectrum of the perylene dimer cation, obtained by dissolving (perylene2)+ ClO4− in CH2Cl2 and in CH3CN, is reported. The proton coupling constants in CH2Cl2 are 1.913, 1.492, and 0.212 G, while the g value at − 80°C is 2.002601. The heat of dissociation in CH2Cl2 is estimated to be 8.6 kcal/mole.
Theory of the Collision-Induced Rotational Spectrum of Tetrahedral Molecules
Authors: Ozier Irving , Fox Kenneth
Published: February 2004

The general theory of induced absorption resulting from binary collisions has been extended and applied to the pressure-induced far-infrared spectrum of a gas of tetrahedral molecules. The molecular octopole moment is related to the integrated intensity resulting from the modulation of the octopole-induced dipole moment by the rotational motion of the molecules. Translational effects are not considered. The intensity resulting from the overlap moment is estimated and found to be negligible. The quantum-mechanical analysis is presented using both unsymmetrized and symmetry-adapted wavefunctions. The results are compared, and the limitations of the unsymmetrized approach are discussed. The techniques developed in the symmetrized treatment are generally useful in integrated-intensity calculations for molecules with a high degree of symmetry and will be discussed in detail. The analysis is applied to recent room-temperature far-infrared data on CH4, CD4, and CF4. The octopole moments deduced from the experimental spectra agree well with those obtained by other techniques. The general features of the spectrum are derived from the theory. The theoretical predictions concerning these features are found to agree well with experiment. The variation of the shape and integrated intensity of the theoretical spectrum with temperature over the range 110–500°K is also discussed.
Semiclassical Treatment of the Optical Model
Authors: Roberts R. E. , Ross John
Published: February 2004

Semiclassical scattering theory is applied to the optical model for two different complex potentials. For the case of a Lennard-Jones interaction, the results for the imaginary part of the phase shift are in excellent agreement with the exact calculation of Marriott and Micha. The use of a modified wavenumber approximation yields useful estimates. For a complex exponential potential, the semiclassical and quantum expressions for the opacity function at zero impact parameter are identical.
Orbital Populations and π Backbonding in Some Organohalostannanes: The Interpretation of Tin Mössbauer and Ligand NQR Data
Authors: Williams D. E. , Kocher C. W.
Published: February 2004

Tin Mössbauer isomer shifts and quadrupole splittings are reported for 23 compounds. Equations are derived and applied which enable the tin hybrid orbital populations for tetravalent tin compounds of the type AmSnB4−m to be determined from the above data. Critical tests of the theory are proposed. A minimum value of 5.8 mm sec−1 is obtained for the quadrupole splitting due to one p electron by comparing Mössbauer-derived with ligand NQR-derived populations. The two sets of populations are also used to obtain π backbonding orbital populations in organohalostannanes. The results show that tin sp3 orbitals are more important than d orbitals for π backbonding.
Kinetic Theory of Thermal Molecular Flow between Coaxial Cylinders and Concentric Spheres
Authors: Wu Yau
Published: February 2004

According to the revised theory of thermal transpiration in a Knudsen gas, the macroscopic properties in a thermal molecular system has been solved exactly. Based on the exact anisotropic velocity distribution functions the density, pressure, temperature, and isotropy distributions between coaxial cylinders and concentric spheres in a thermal molecular regime are integrated in closed forms.
Linear Constrained Variational Procedure for LCAO–SCF Wavefunctions
Authors: Weber Thomas A.
Published: February 2004

A variational procedure is developed for the determination of LCAO–SCF wavefunctions which are subjected to a set of linear constraints. The procedure gives wavefunctions from the solution of an eigenvector-type problem using a self-consistent iterative technique.
Self-Consistent-Field Atomic Wavefunctions from Efficient Nested Basis Sets
Authors: Weber Thomas A. , Handy Nicholas C. , Parr Robert G.
Published: February 2004

Constrained self-consistent-field wavefunctions are reported for the ground-state neutral atoms, He–Ne, in which each atomic orbital is a linear combination of Slater-type orbitals. A more efficient use of the basis set chosen reduces the number of parameters to be optimized while maintaining the energy equal to within five significant figures to the energy of the fully optimized basis set. The reduction in the number of independent linear and nonlinear parameters is achieved by forcing a certain long-range behavior and a nuclear cusp condition. In one set of calculations the orbitals are forced to behave asymptotically as φi ∼ exp[−r(− 2εi)1/2], where εi is the orbital energy. In the second set of calculations, the orbitals are also forced to exactly obey the nuclear cusp condition.
Closure Procedure for Two-Photon Absorption Intensities
Authors: Stoner T. R. , Gruber J. B.
Published: February 2004

A derivation of a sum identity is presented which is an extension of the Thomas–Reiche–Kuhn sum rule for oscillator strengths. A derivation of the probability amplitude for two-photon absorption by a one-electron quantum system is sketched, and an application for the sum identity is suggested in the approximate evaluation of the perturbation sum which appears in the expression for the amplitude.
Scintillation Efficiencies at High Solute Concentrations: Possible Energy Transfer from S3 States of Excited Aromatic Solvents
Authors: Horrocks Donald L.
Published: February 2004

At normal solute concentrations (3–10 g/liter) the relative scintillation efficiency of a solution is dependent upon the particular solvent; 1,2,4-trimethylbenzene>p-xylene>toluene>benzene. The relative scintillation yields seem to follow the same general trend as the efficiency of internal conversion of S3 → S1 of the aromatic solvent. At high solute concentrations (>150 g/liter) the relative scintillation efficiency of these solutions was independent of the particular aromatic solvent. It was assumed that the fluorescence was produced by a process which involved energy transfer before the S3 → S1 internal conversion. A possible mechanism involves the transfer of energy from the S3 state of the solvent to an excited state of the solute, F3. The relative scintillation efficiency of concentrated solutions would then be dependent upon the internal conversion efficiency for the process F3 → F1.
Ultrasonic Absorption in Liquid Oxygen and Nitrogen
Authors: Victor Alfred E. , Beyer Robert T.
Published: February 2004

Ultrasonic absorption measurements were made in liquid oxygen and nitrogen at 50 MHz as a function of temperature from 66–86°K. The values obtained are approximately 20% higher than those obtained previously and 60% higher than those calculated from classical theory. When liquid oxygen was subjected to a field of 10 kG, the values of α / ν2 obtained were within 4% of the zero-field values. The excess absorption observed in the zero-field case is attributed to the bulk viscosity.
Interaction of Microwave Radiation with a Polar Gas under Conditions of Power Saturation
Authors: Quade C. R.
Published: February 2004

The propagation of microwave radiation through a gas-phase dielectric under conditions of power saturation is considered. It is shown that the nonuniform polarization gives rise to additional modes of electromagnetic oscillation. The amplitudes of the induced electric field are estimated and shown to be small. The results of the calculation substantiate that Harrington's method of averaging the power distribution in determining the power density distinction function φwg is correct for application to microwave spectroscopy.
Influence of Brownian Rotations and Energy Transfer upon the Measurements of Fluorescence Lifetime
Authors: Spencer R. D. , Weber G.
Published: February 2004

The depolarization of the fluorescence of solutions by either Brownian rotations or intermolecular energy transfer may be simply described by a system of first-order linear differential equations containing as only parameters the rate of fluorescence emission and the rate of transport of the excitation from one orthogonal component of the emission to another. The steady-state solution has the form of Perrin's equation describing the depolarization by Brownian rotations, and the time-dependent depolarization following a unit light impulse is that originally described by Jablonski. The solution for sinusoidal excitation is novel in that: 1. It shows the difference in lifetime between the polarized components of the emission to be a sensitive function of the ratio of the modulation frequency ω to the emission rate λ. For ω/λ > 1 the difference between the polarized lifetimes may become many times greater than that observed after a unit light impulse. 2. It permits the determination of both the rate of transport of the excitation and the limiting polarization of the fluorescence from observations at one fixed temperature and viscosity. 3. It allows the definition of conditions under which the true or exponential decay of the fluorescence may be measured. Experimental tests of the theory by phase fluorometry are described: These include observations upon dilute solutions in media of limited viscosity where Brownian motion is the only cause of depolarization and observations upon concentrated frozen solutions where depolarization is due to energy transfer alone.
Separation of Xenon Isotopes in the Thermal Diffusion Column
Authors: Roos W. J. , Rutherford W. M.
Published: February 2004

Thermal diffusion column coefficients were measured for the separation of the isotopes of natural xenon, a mixture of nine stable species, in a 7.32-m hot wire column at wire temperatures of 790 and 1073°K. For the two remixing coefficients good agreement was found between experiment and the theory of the thermal diffusion column. Measured values of the initial transport coefficient, however, were in poor agreement with theory when the theoretical calculations were based on measurements of the thermal diffusion factor of xenon taken from the literature. The agreement was considerably improved by the use in the theory of isotopic thermal diffusion factors evaluated from a corresponding states correlation of data for other noble gases. On this basis the average ratio of the experimental initial transport coefficient to the corresponding theoretical value was found to be 1.10 ± 0.07.
Low-Energy Electron Reflection Spectrometry for Thin Films of n-Hexane, Benzene, and Ice at 77°K
Authors: Hunter Linda M. , Lewis David , Hamill William H.
Published: February 2004

A simple low-energy electron-reflection spectrometer is described. It constants of a 10−9 torr chamber fitted with an electron gum, an ultrathin film of vacuum evaporated sample, supported on a metal block at 77°K, and a Faraday cup to measure the backscattered electron current, I. Plots of I vs the incident electron energy eV exhibit some structure, more clearly exhibited by plots of dI / dV vs V which show clearly defined peaks and appear to correspond to near-resonant energy losses. For benzene these peaks are matched by spectroscopically measured electronic energy levels, including triplets. For an ice film there is a strong peak at 4.2 eV which, supported by several other recently reported measurements using other devices, is attributed to the B13 state of H2O. For n-hexane the two lowest peaks occur at ∼ 3.9 and ∼ 4.6 eV.
Transition Probabilities in Molecular Collisions: Computational Studies of Rotational Excitation
Authors: Levine R. D. , Shapiro M. , Johnson B. R.
Published: February 2004

Exact numerical solutions are presented for the coupled-state formulation of a rigid-rotor–structureless-atom collision, and are compared with qualitative ideas and semiquantitative decoupling approximations for the system. The advantages of using an adiabatic basis for the internal states of the system are demonstrated, in distorted-wave-type computations and in accounting for the direct part and the resonance energies in slow inelastic collisions, in the absence of curve crossing. The diabatic regime is also considered, and a diabatic basis is used for a curve-crossing problem. For these slow, head-on collisions, the Franck–Condon factors are not exponentially small, and significant (>10−1) transition probabilities are possible.
Vibrational Relaxation of Anharmonic Oscillators with Vibration–Vibration and Vibration–Translation Energy Exchanges
Authors: Hsu C. T. , Maillie F. H.
Published: February 2004

The vibrational relaxation of a system of anharmonic oscillators with high initial vibrational energy into a low-temperature heat bath was studied. It was assumed that the vibration–vibration quasisteady population distribution was instantly established, and during the longer time scale the level population distribution was controlled by a continuous equilibrium vibration–vibration exchange-dominated process or by a vibration–translation exchange-dominated process. Although large differences occurred in upper level populations of the two processes, no significant difference was found in the de-excitation rate. The effect of an-harmonicity did enhance the de-excitation rate in the early stage of the relaxation process. This rate fell off quickly to a value close to the excitation rate obtained for the harmonic oscillator. No large order of magnitude differences in the de-excitation rates of this investigation and previously established excitation rates were found.
Ab Initio LCAO–MO–SCF Calculations on Formic Acid, Formate Ion, and Protonated Formic Acid
Authors: Hopkinson A. C. , Yates K. , Csizmadia I. G.
Published: February 2004

The site of protonation of formic acid as well as the proton affinities of the formate ion and formic acid have been estimated using ab initio LCAO–MO–SCF calculations with Gaussian basis sets. The three carbonyl protonated formic acid conformers were found to be more stable than the hydroxy protonated isomer for all basis sets. In agreement with experimental observation, the large basis set calculations gave the cis–trans conformer to be the most stable.
ESR Study of an Irradiated Crystal of l-Alanine: Two New Proton–Deuteron Exchange Reactions
Authors: Itoh Koichi , Miyagawa Ichiro , Chen C. S.
Published: February 2004

Two new proton–deuteron exchange reactions in an irradiated crystal of alanine were discovered with the use of α-deutero-l-alanine. It was shown that both exchanges took place between the radical and its adjacent molecule (or molecules): Exchange I took place between the α hydrogen of the radical and a methyl hydrogen of the molecule, and exchange II between a methyl hydrogen of the radical and the α hydrogen of the molecule. Both exchange rates were much higher than the rate of the previously reported one for irradiated alanine (exchange III). Activation energies for exchange I and exchange II were found to be 17.0 ± 1.0 kcal/mole and 21.0 ± 1.5 kcal/mole, respectively.
Vibration Spectra of Hydrogen Bonds by Neutron Energy-Loss Spectrometry
Authors: Collins M. F. , Haywood B. C. , Stirling G. C.
Published: February 2004

A neutron spectrometer with a beryllium-filter detector has been used to obtain vibration spectra of a selection of hydrogen-bonded compounds in the range 400–1400 cm−1. The neutron technique preferentially observes hydrogen motions, thus providing a less ambiguous assignment of modes than is possible in optical spectroscopy. Data are reported here for KHF2, CsHCl2, CsDCl2, NaHCO3, KH(CF3COO)2, and KH(CCl3COO)2. In the first three compounds the results provide confirmation of existing infrared and Raman assignments, and in the latter three cases the locations of the bending modes are indicated.
Hydrogen Abstraction by Hot CF3 Radicals
Authors: Fass Richard A. , Willard John E.
Published: February 2004

The quantum yields of CF3H from the reactions of hot CF3 radicals and thermal CF3 radicals resulting from the photolysis of CF3I at 2537 Å and of CF3Br at 1850 Å in gaseous CH4, C2H6, and C3H8 have been investigated. Reactions of hot CF3 radicals with hydrocarbons appear to be dependent on the translational energy of the radicals when these are produced from CF3I at 2537 Å, and dependent on vibrational energy when the radicals are produced from CF3Br at 1850 Å. Translationally thermalized CF3 radicals from 2537-Å activation show unusual reactivity with I2 relative to C3H8, which is attributed to a low vibrational excitation. This is quenched by CF3I with a collision number of 30–100. Vibrationally excited CF3 radicals produced from CF3Br at 1850 Å show a selectivity for H abstraction vs D abstraction and secondary vs primary bond attack similar to that of thermal atoms, whereas translationally hot CF3 radicals produced from CF3I at 2537 Å are much less selective. The reaction of hot CF3 radicals from CF3Br at 1850 Å with C3H8 is obscured by the reaction with HBr produced by thermal bromine atoms.
Absorption and Laser-Excited Fluorescence of Matrix-Isolated CuO
Authors: Shirk James S. , Bass Arnold M.
Published: February 2004

Absorption and laser-excited fluorescence spectra of CuO trapped in variousmatrices have been observed. The matrix data and previously observed gas-phase data are consistent withν00 (martix)ν00 (gas)5ν (martix)(cm−1)(cm−1)(cm−1)(cm−1)C23 550B(2Σ?)20 49020 953624A(2Π?)3 9004 460605(2Π1/2 − 2Π3/2 = 275)X(2Π)00665(2Π1/2 − 2Π3/2 ≃ 200)for the lowest states of CuO. It is shown that the matrix-isolation technique can beused to “tune” an absorption into coincidence with a laser line in order to observefluorescence. The vibrational relaxation of CuO in a solid matrix requires on the order of 105 vibrations.
Statistical Mechanics of Rodlike Particles. II. A Scaled Particle Investigation of the Aligned→Isotropic Transition in a Fluid of Rigid Spherocylinders
Authors: Cotter Martha A. , Martire Daniel E.
Published: February 2004

Expressions for the equation of state and the chemical potential are derived as functions of density and temperature for both a perfectly aligned and a completely isotropic fluid of rigid spherocylinders through consideration of the reversible work W(α, λ, ρ) necessary to add a scaled spherocylinder of radius α and cylindrical length λ at an arbitrary fixed point in the fluid. A first-order aligned→isotropic transition is obtained and the transition densities, free volume fractions, and entropy change determined at various values of the radius and cylindrical length of the spherocylinders. Although the densities of the two phases and the density change at the transition depend on the radius of the particles, the entropy change and the free volume fractions of the two phases at the transition depend only on the length-to-breadth ratio x, indicating that the transition results from packing effects alone. The behavior of the expansivity and the compressibility of the system near the transition is also determined. The results of this treatment strongly suggest that the molecules of nematogenic compounds do not behave like inflexible rods, but rather must exhibit appreciable flexibility in the nematic as well as the isotropic phase. Some light is also shed on the problem of the relative importance of attractive and repulsive forces in determining the stability of nematic mesophases.
Magnetic Characteristics of CuFecl4, AgFeCl4, and TlFeCl4 Near the Néel Temperatures
Authors: Jones E. R. , Hendricks M. E. , Finklea S. L. , Cathey L. , Auel Theo , Amma E. L.
Published: February 2004

The magnetic susceptibility and Mössbauer spectra of the compounds: CuFeCl4, AgFeCl4, and TlFeCl4 have been measured. These data can be interpreted for the Ag and Tl compounds as Ag(I) and Tl(I) with Fe(III). In contrast, CuFeCl4 must be interpreted as Cu(II) and Fe(II). The magnetic susceptibility of AgFeCl4, TlFeCl4, and CuFeCl4 follows a Curie–Weiss law to low temperatures with Curie–Weiss constants of 53, 31, and − 14.1°K, respectively. All three become antiferromagnetic with Néel temperatures of 13.1 ± 0.2, 11.2 ± 0.2, and 20.5 ± 0.3°K, respectively. The isomer shifts relative to a copper matrix source of AgFeCl4, TlFeCl4, and CuFeCl4 were found to be + 0.11, + 0.11, and + 0.92 mm/sec, respectively, whereas the quadrupole splittings were found to be 0.16, 0.00, and 0.60 mm/sec, in the same order. The Fe(II) seems to be in a significantly lower symmetry environment than the Fe(III), probably due to the different geometrical demands of Cu(II) compared to Ag(I) and Tl(I).
X-Ray Diffraction Study of Liquid Silicon Tetrachloride
Authors: Rutledge Carl T. , Clayton Glen T.
Published: February 2004

The angular intensity distribution of x rays scattered from liquid SiCl4 has been measured at temperatures of − 65 and + 23°C by use of theta–theta reflection diffractometry. Molecular nearest neighbors reside in two well resolved shells of radii 3.9 and 6.8 Å. There are about 4.25 and 7.5 molecules in the respective shells at the lower temperature, and about 3.75 and 7.0 at the higher temperature. This agrees well with the macroscopic density of the liquid. The inner shell of neighbors is interpreted as resulting from short range orientational effects due primarily to molecular shape.
Spectral Behavior of Hydrogen-Bonded Systems: Quasiparticle Model
Authors: Fischer S. F. , Hofacker G. L. , Ratner M. A.
Published: February 2004

The spectral behavior of protons forming hydrogen bonds in a solid is investigated. The ionic defect H3O+ in the ice crystal is used as a basic model. Strong interaction with optical phonons (wagging vibrations) is considered to infinite order by construction of a quasiparticle analogous to the small polaron. We predict for the absorption profile a broad peak with some fine structure at the low-frequency side. Temperature dependence, red shifting, and mass dependence of the spectrum are discussed.
Temperature Dependence of Intersystem Crossing in Crystalline Anthracene
Authors: Stacy W. T. , Swenberg C. E.
Published: February 2004

Blue-light-excited delayed fluorescence is used to study the temperature dependence of monomolecular intersystem crossing in crystalline anthracene. The associated rate constant k is found to obey an equation of the form k = k1 + k2exp(− E / kT), where E = 900 ± 100 cm−1 and k2 / k1 = 800 ± 200. A calculation of the relevant Franck–Condon factors using the method developed by Siebrand gives good agreement with experiment. At temperatures less than 90°K, the delayed fluorescence appears to be dominated by trapping effects similar to those reported in red-light-excited measurements.
19F Spin–Rotational Interactions in 1- and 2-Trifluoromethylnaphthalenes in the Liquid State
Authors: Bull T. E. , Jonas J.
Published: February 2004

The temperature dependences of the 1H and 19F spin–lattice relaxation times in 1- and 2-trifluoromethylnaphthalenes, and also in benzotrifluoride have been measured by the adiabatic fast passage method. The effects of dilution in toluene-d8 on 1H and 19F T1's in the molecules studied have also been investigated. It has been found that the 19F relaxation rates in 2-trifluoromethylnaphthalene and benzotrifluoride are determined by spin–internal-rotation coupling and independent of intermolecular torques within the temperature region studied. An approximate relationship between the angular velocity correlation time and the barrier to internal rotation of the CF3 group has been proposed. The estimated barriers to rotation, 0.2 and 0.4 kcal/mole in benzotrifluoride and 2-trifluoromethylnaphthalene, are in agreement with those calculated by using approximate potential functions. Since there is a steric interaction between the CF3 group and the hydrogen at the 8 position in 1-trifluoromethylnaphthalene, the spin–internal-rotation coupling is quenched to a large extent, and the spin-rotational mechanism is mainly due to the spin–over-all-rotation coupling.
Calculation of the Refractive Index of Crystalline Anthracene in the Dipole Approximation
Authors: Philpott Michael R.
Published: February 2004

The refractive indicies of crystalline anthracene are calculated near the long-wavelength edge of the first singlet transition using a classical theory of molecular excitons and the dipole approximation. Dipole sums and isolated molecule data from previous Davydov splitting calculations are used to test whether theories which predict numbers close to the experimental splitting also yield reasonable values of the refractive index. Agreement between the calculated and experimental indices is poor. This implies the existence of high-energy transitions of considerable total intensity above 6 eV which are the source of a considerable background polarization in the crystal. Intense transitions at high energy occur in many hydrocarbons and, by means of a collective (cooperative) interaction, could be responsible for a major part of the Davydov splitting of the lowest singlet transitions of moderate intensity (f≃0.1). This point is discussed in detail together with other factors influencing the size of the Davydov splitting in molecular crystals.
Composition Dependence of the Thermal-Diffusion Factor of a Dusty Gas
Authors: Annis B. K. , Malinauskas A. P. , Yun K. S.
Published: February 2004

The composition dependence of the thermal-diffusion factor αT of a dust–gas mixture is derived. In the case of monatomic gas, (αT)−1 is shown to vary linearly with mole fraction, but nonlinear contributions arise in the case of a polyatomic gas as a result of inelastic gas–gas collisions. Application of the result to a description of thermal transpiration in terms of the “dusty-gas” model yields a correction to the previously derived equation for thermal transpiration and may have a significant effect on the determination of rotational collision numbers from thermal transpiration measurements.
Applications of Diatomics-in-Molecules Theory. IV. Dimers of LiH
Authors: Tyndall John R. , Companion Audrey L.
Published: February 2004

Ellison's semiempirical diatomics-in-molecules method, applied to the study of dimeric LiH systems, yields predictions of two conformations stable with respect to isolated diatomic systems. A metastable D2h diamond structure (comparable to alkali-metal halide dimers studied by Berkowitz) with a Li–H separation of 3.36 Bohr units lies 13.8 kcal/mole lower in energy than the system Li2 + H2 and 28.4 kcal/mole lower than 2 LiH. A stable C2υ structure (analogous to previously predicted disphenoid Li4 molecules) with perpendicular diatomics Li2 and H2 separated by 2.66 Bohr units, lies 26.7 kcal/mole lower than Li2 + H2 and 41.3 kcal/mole lower than 2 LiH. Fundamental vibrational frequencies and certain characteristics of potential surfaces are presented for both stable species. The properties of four unstable linear dimers are examined.
Reaction H+C2H4: Comparison of Three Experimental Techniques
Authors: Barker John R. , Keil David G. , Michael J. V. , Osborne David T.
Published: February 2004

The reaction H+C2H4 has been studied as a function of He pressure at room temperature with three independent experimental techniques, and rate constants have been obtained in both the excess ethylene and excess hydrogen-atom environments. The products of the reaction are CH3, CH4, and C2H6. An experimental value for the third-body recombination coefficient for H+CH3+M has been obtained. The over-all stoichiometry of the reaction has been experimentally determined and is found to vary as a function of the initial reactant concentrations. A reaction mechanism is proposed which accounts for all of the experimental data obtained.
Frenkel Excitons in a Vibrating Molecular Crystal
Authors: Fischer Sighart , Rice Stuart A.
Published: February 2004

This paper is concerned with a study of the interaction between collective electronic excitations and collective vibrational excitations in a molecular crystal. A strong coupling theory is developed and is used to calculate the vibrational structure of the collective excitation in the Frenkel limit. The frequency dependence of the self-energy of the excitation and dispersion in the optical phonon branch of the vibrational spectrum are included in the analysis. The line shapes in the absorption spectrum of a molecular crystal are considered for the two limiting cases of exciton–phonon coupling—namely weak and strong coupling. One of the topics considered in detail is the damping of the zero phonon transition.
Collisional Deactivation of Vibrationally Excited 2-Pentyl Radicals
Authors: Georgakakos J. H. , Rabinovitch B. S. , McAlduff E. J.
Published: February 2004

Collisional deactivation of chemically activated 2-pentyl radicals having ∼44.3 kcal mole−1 vibrational energy has been studied in the low-pressure turnup region for the bath gases H2 CH4, and CF4. A stochastic analysis of the data yielded information about 〈ΔE〉, the average amount of energy transferred per collision and β∞j, the practical high-pressure relative collisional efficiency of inert gas j. The approximate values of 〈ΔE〉 for H2, CH4, and CF4 are 1.2, 3.0, and 4.5 kcal mole−1, respectively. These correspond to average values of β∞j = 0.20, 0.64, and 0.85, respectively. The preferred collisional transition probability model for H2 is not definite, but an exponential form gives best fit; a stepladder or, more probably, a Gaussian model seems in order for the most efficient gas.
Matrix-Isolation Studies of the Infrared Spectra of the Free Radicals CCl3 and CBr3
Authors: Rogers Ernest E. , Abramowitz Stanley , Jacox Marilyn E. , Milligan Dolphus E.
Published: February 2004

CCl3 has been stabilized both by the reaction of lithium atoms with CCl4 in an argon matrix at 20°K and by the vacuum-ultraviolet photolysis of HCCl3 or of DCCl3 in an argon or a nitrogen matrix at 14°K. The analogous techniques have been found to lead to the stabilization of CBr3. The product spectra obtained in the lithium-atom experiments are considerably simpler than those obtained in the previous studies of the reaction of lithium atoms with matrix-isolated CX4. In the vacuum-ultraviolet photolysis experiments, DCCl2, HCBr2, and CBr2 have also been observed. The absorption frequencies and contours obtained for ν3 of CCl3 and of CBr3 are independent of the method used to produce these species, suggesting that lithium atoms and their reaction products do not appreciably perturb the degenerate stretching mode of either CCl3 or CBr3. Despite yields of these species comparable to those previously reported, absorptions at 674 and at 582 cm−1, previously attributed to ν1 of CCl3 and CBr3, respectively, are completely missing from the present experiments. No other absorption attributable to ν1 of either species has been detected. It is concluded that a pyramidal (C3υ) structure for CCl3 and for CBr3 has not been established.
Probability Density Functions of the Radii of Gryation of Short Random Flight Chains
Authors: Hoffman Robert F. , Forsman W. C.
Published: February 2004

Distribution functions for the one-dimensional radii of gyration were calculated for random flight chains of 2, 4, and 10 statistical segments, and were compared with approximate distributions calculated with the “long-chain” eigenvalues. The correct distributions are broader and flatter than their long-chain counterparts and have larger moments. The true distributions are not well represented by the long-chain approximation when the number of statical segments t is less than 10. But, considering the rate at which the two distributions approach each other with increasing t, we feel confident that the long-chain eigenvalues would be adequate for t ≥ 100. Indeed, for many practical considerations, one might take the long-chain distributions as reasonable approximations to the correct ones, even for t ≥ 10.
Gaussian-Type Functions for Polyatomic Systems. III
Authors: Huzinaga Sigeru , Arnau Catalina
Published: February 2004

A new set of combined Gaussian-type orbitals (CGTO) is presented for Li through Ne for the use in the molecular calculation. The accuracy is comparable to that of the double-zeta Slater-type orbitals.
Field Ionization from H2 Layers
Authors: Jason A. , Halpern B. , Inghram M. G. , Gomer R.
Published: February 2004

Field ionization from hydrogen layers adsorbed at 4.2°K on tungsten emitters has been studied in sealed-off tubes and by means of a mass spectrometer which could probe small regions of the tip. At 4.2°K and 2 × 10−7 torr, ion currents of ∼10−9 A could be obtained at F ≅ 1 V/Å; the low field indicates that the dwell time of H2 in the ionization region is much longer than in gas-phase field ionization, while the high current obtained at this pressure shows that supply occurs by diffusion of H2 from the emitter shank. The mass spectrometric experiments indicate that H2+ predominates at F ≤ 1.1 V/Å, but that H3+ and H+ are formed at higher fields. Plots of lni vs 1 / F indicate that at low fields molecular tunneling controls the over-all rate of field ionization, while at higher fields supply of H2 is rate limiting.
Relaxation Phenomena in Electrolytic Solutions
Authors: Fritsch K. , Montrose C. J. , Hunter J. L. , Dill J. F.
Published: February 2004

Sound velocity and absorption measurements were made in a number of aqueous electrolytic solutions, principally the 2–2 valent sulfates. Ultrasonic pulse measurements were used in the frequency region 30–900 MHz, and the technique of Brillouin light scattering was employed in a number of measurements between 6000 and 7000 MHz. In several of the solutions studied, the ultrasonic data indicate the existence of two relaxation processes with relaxation times lying in the range 5 × 10−9–2 × 10−10 sec. These two relaxations, considered together with the previously observed long relaxation time process, can be interpreted in terms of the Diebler–Eigen model of ionic association which predicts three relaxation processes. The shortest relaxation time process was identified with the diffusion controlled approach of the hydrated ions. The calculation of the appropriate reaction rate constants using data by other workers below 50 MHz and the present data above 50 MHz was carried out. The results are compared with earlier results based on data taken below 200 MHz.