bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarizability and dipole moment changes of the lowest 1ππ* state of azulene; an example of the use of the Stark effect on polar and nonpolar mixed molecular crystals
Authors: Barker J. W. , Noe L. J. , Marchetti Alfred P.
Published: February 2004

The relatively high representative electric fields present at molecular sites in a polar molecular crystal, ∼ 107 V cm−1, make possible the determination of excited-state dipolar and polarizability properties of a guest molecule dispersed in the polar host from a consideration of field induced moments. The determination of the magnitudes and directions of these guest properties is particularly dependent on an analysis interrelating Stark measurements made separately on the spectroscopically accessible states of the guest when dispersed in a polar and in nonpolar host lattice. The azulene-benzophenone, azulene-naphthalene mixed-crystal systems were chosen to demonstrate this method of analysis for the lowest 1ππ* state of azulene. The magnitude of the dipole moment change for azulene dispersed in the nonpolar (zero field) naphthalene lattice Δμzf = 1.21 D, has already been determined. Using this magnitude and the results of Stark measurements on azulene in benezophenone we find that (1) the molecular dipole reverses direction upon excitation, Δ μzf=−1.21 L D and (2) the long axis polarizability is greater in the ground state than in the excited state, Δ αLL=−3.5 Å3. This value compares favorably with the theoretically calculated ΔαLL values of −4.4 Å3 and −3.75 Å3.
Hydrogen transport in lithium hydride as a function of temperature
Authors: Spencer J. N. , Catlett Duane S. , Vogt G. Jerry
Published: February 2004

The exchange process for the reaction between deuterium gas and lithium hydride single crystals has been studied as a function of temperature over the range 400–550°C at 380 torr. The rate of the exchange process was assumed to be diffusion controlled; thus the kinetic data were analyzed by fitting to solutions of Fick's law. A one-dimensional model yields an activation energy range of 22.7 ± 2.8 kcal for the diffusion of deuteride ion. A three-dimensional model gives the activation energy range as 24.3 ± 3.0 kcal.
Study of the structure of molecular complexes. IV. The Hartree-Fock potential for the water dimer and its application to the liquid state
Authors: Popkie H. , Kistenmacher H. , Clementi E.
Published: February 2004

The Hartree-Fock energy of the water dimer has been computed for 216 different nuclear configurations using the basis set given in the first paper of this series. Near the equilibrium configuration, a calculation was carried out using a large Gaussian basis set with optimized orbital exponents for the oxygen 3d - and 4f -type and hydrogen 2p - and 3d -type functions in order to get results close to the Hartree-Fock limit. In the vicinity of the equilibrium configuration the mechanism for binding of the dimer is analyzed with the help of the bond energy analysis formalism. The importance of polarization (internal charge transfer), as pointed out previously by a number of authors, is clearly evident. The computed energies have been used to derive a simple analytical expression that reproduces the Hartree-Fock potential energy surface to a high degree of accuracy. This analytical potential is compared with the empirical effective pair potentials proposed by Rowlinson and Ben-Naim and Stillinger for the description of water in the condensed phase. We report preliminary results for Monte Carlo simulation of the liquid state of water using the computer program of Barker and Watts and our analytical Hartree-Fock two-body interaction potential. At the experimental mass densities we considered 27 water molecules in a cube with periodic boundary conditions at temperatures of 277, 298, and 348°K. The resulting pair correlation functions gO–H(2) (hydrogen bond distribution) and gO–O(2) (oxygen-oxygen distribution) are in agreement with experimental data. It should be strongly emphasized that the properties are computed without any recourse to semiempirical data.
Line shapes for low frequency depolarized (VH) light scattering from fluids. Coupling of rotational and translational motion
Authors: Gershon N. D. , Oppenheim Irwin
Published: February 2004

A generalized theory for depolarized (VH) light scattering from fluids of nonspherical rigid molecules at low frequencies is presented. The dispersion equation for the part of the spectrum which can have fine structures (the autocorrelation function of αk x z) is reduced to a simple quadratic equation given the condition that the internal angular momentum of the molecules decays much faster than the anisotropic polarizability and the transverse linear momentum. The solutions of the quadratic equation and the spectrum of the autocorrelation function of αk x z are similar to those of a linear damped harmonic oscillator. Thus, the depolarized spectrum has different line shapes depending on the experimental situation (e.g., temperature, wave vector, etc.).
Gas-phase EPR linewidths and intermolecular potentials. I. Theory
Authors: Cook Thomas J. , Miller Terry A.
Published: February 2004

A theoretical investigation is presented which relates gas-phase EPR linewidths to the elements of the scattering matrix describing binary collisions. Under the assumption of full rotational symmetry, the EPR linewidths are also related to multipole decay constants and population transfer coefficients. General expressions are developed which are valid for any angular momentum (J) state in which the observed atom may be. Results are explicitly tabulated for all J values less than or equal to 2. As an example, a model van der Waals second-order dipole-dipole potential is presumed to exist between a 2PJ atom and an S-state atom. The EPR linewidths predicted from this model yield differing broadening cross sections for different 2P3/2 transitions. Furthermore a zero cross section is predicted for the 2P1/2 state.
Low density form of the free energy for real matter
Authors: Lebowitz Joel L. , Pena Rafael E.
Published: February 2004

We prove that the thermodynamic free energy per unit volume of an over-all neutral system, composed of electrons and nuclei interacting via Coulomb forces, has the low density asymptotic form kT  Σα=0sραlnρα. Here ρo is the over-all number density of electrons and ρα, α=1,···, s the number density of nuclei of species α. This indicates that, as expected on the basis of nonrigorous arguments, any real physical system will become completely ionized as the density approaches zero (at a fixed nonzero temperature).
Photoionization study of NO2. I. The ionization potential
Authors: Killgoar P. C. , Leroi G. E. , Chupka W. A. , Berkowitz J.
Published: February 2004

The ionization potential of NO2 has been redetermined by photoionization mass spectrometry. The photoionization efficiency curve exhibits autoionization in the threshold region, allowing the assignment of an upper limit on the ionization potential of 9.62 eV. This result combined with the results of other groups brackets the ionization potential between 9.62 and 9.25 eV, most probably closer to the upper limit.
Structure of the hydrated electron
Authors: Weissmann Mariana , Cohan Norah V.
Published: February 2004

We study the short range interactions between an electron and the neighbor water molecules, with a modified version of the CNDO/2 method. The basis set used includes excited atomic orbitals which are fundamental in the study of the system (H2O)n−. Our calculations indicate that the electron is not associated to a vacancy or other type of defect but to a group of water molecules in the normal microscopic structure of ice and liquid water. In ice it can also be considered as an extra electron in an otherwise perfect crystal lattice (an electronic polaron). Our results are consistent with the hydration energy, spectra, and photobleaching experiments.
Unimolecular decomposition of the long-lived complex formed in the reaction F+C4H8
Authors: Parson John M. , Shobatake Kosuke , Lee Yuan T. , Rice Stuart A.
Published: February 2004

The reactions of fluorine atoms with four butene isomers have been studied by the method of crossed molecular beams. Angular distributions and velocity spectra of products formed by substitution of F for CH3 and H have been measured. Relative rates for CH3 and H substitution are in qualitative agreement with RRKM predictions for competitive rates of dissociation of a fluorobutyl complex. Quantitative agreement is possible with minor adjustments in the exothermicities or barriers to dissociation. The kinetic energy distributions of the products, on the other hand, are not in accord with those predicted by statistical theories of unimolecular reactions. The results suggest that the assumption of randomization of internal energy breaks down at least for complex configurations close to the transition state where coupling between separating fragments is still strong enough to allow appreciable nonrandom mixing of translational energy with rotations and vibrations of the larger fragment.
Unimolecular decomposition of long-lived complexes of fluorine and substituted mono-olefins, cyclic olefins, and dienes
Authors: Shobatake Kosuke , Parson John M. , Lee Yuan T. , Rice Stuart A.
Published: February 2004

The reactions of fluorine atoms and substituted mono-olefins, cyclic olefins, and dienes have been studied by the technique of crossed molecular beams. In each case the experimental evidence suggests the existence of a long-lived intermediate complex. Analysis of the angular distribution of products then permits a test of the energy randomization hypothesis of the statistical theories of unimolecular reaction rate. The data obtained strongly imply that for the class of reactions studied energy randomization is not faster then decomposition of the complex.
Laboratory angular dependence and the recoil-energy spectrum of the products of the reaction F+C6D6→ D+C6D5F
Authors: Shobatake Kosuke , Parson John M. , Lee Yuan T. , Rice Stuart A.
Published: February 2004

The reaction of fluorine atoms with perdeuterobenzene has been studied by the method of crossed molecular beams. In this reaction a long-lived intermediate complex is formed. Analysis of the kinetic energy distribution of the products and their angular distribution in space cannot be satisfactorily accounted for by the available statistical theories of unimolecular decomposition. The results of this study can be used to infer that randomization of the internal energy of a molecule is not necessarily rapid relative to chemical reaction.
Detailed analysis of ν5 of CH3I: Fermi and Coriolis resonances with ν3+ν6 and ν2
Authors: Matsuura Hiroatsu , Nakagawa Toru , Overend John
Published: February 2004

The high-resolution infrared spectrum of ν5 of CH3I reported in the previous paper [J. Chem. Phys. 55, 1787 (1971)] has been reanalyzed. By extending the assignment of the observed lines and by taking account of the xy-type Coriolis interaction with ν2 in addition to the Fermi and xy-type Coriolis resonances with ν3+ν6, the rotational constants have been determined to be B 5(unp) = 0.250159 cm−1 and B 3,6(unp) = 0.247631 cm−1 which are now consistent with the microwave results. The l-type doubling constant has been obtained to be q 5(unp)=−2.2× 10−5 cm−1. The Fermi resonance term has been found to depend on the quantum number J.
Laser scattering measurements of droplet growth in binary mixtures. II. H2O and argon H2O and helium
Authors: Vietti M. A. , Schuster B. G.
Published: February 2004

Water droplet growth rates in a Wilson cloud chamber were measured in Ar–H2O and He–H2O media. These rates were determined in the size range 0.45–10.0 μm by detection of oscillations in the intensity of polarized light from a He–Ne laser source scattered at 30° by the droplet population. Pressure and initial temperature were measured in the chamber for use in the computation of three droplet growth theories for comparison to experiment. Experiments were conducted in supersaturations ranging from 1.04 to 3.45.
Population of N2 (B 3Πg) by N2 (A3Σu+) during the nitrogen afterglow
Authors: Hays G. N. , Oskam H. J.
Published: February 2004

The time dependence of the intensity of various emission bands during the decay period of plasmas produced in pure nitrogen was measured using the stationary afterglow method. Two processes involving the N2 (A3Σu+) metastable molecule were found to populate the N2 (B 3Πg) state during the nitrogen afterglow. The first process is the energy pooling reaction N2 (A3Σu+)+ N2 (A3Σu+) → N2 (B3Πg)+N2 (X1Σg+), which also populates the N2 (C 3Πu) and N2 (C′3Πu) states. An approximate value for the reaction rate constant for this process was found to be (1.1−0.5+2)× 10−9 cm3 sec−1 per molecule. Strong evidence was found that N2 (B 3Πg) is also populated by the reaction N2 (A3Σu+)+N2* (X)→N2 (A3Σu+, v′>7)+N2(X)→ N2 (B3Πg)+N2 (X), where N2* (X) is a vibrationally excited ground state nitrogen molecule. The population of the N2 (B 3Πg) energy state by recombination of nitrogen atoms was also observed.
Relaxation processes in water. A study of the proton spin-lattice relaxation time
Authors: Hindman J. C. , Svirmickas A. , Wood M.
Published: February 2004

An experimental study of the proton spin-lattice relaxation time T1 has been made for H2O over the temperature interval from −16 to 145°C. It is found that after correction for spin-rotational interaction, the experimental T1 behavior can be represented by the double exponential form of the rate expression used to treat the relaxation for the quadrupolar nuclei 2H and 17O in water. The oxygen-17 data are used to calculate the intramolecular contribution to the proton T1. The activation energies E1=9.4± 0.8 kcal/mole and E2=3.6± 0.1 kcal/mole for the two contributions to the intermolecular relaxation are in sufficiently good agreement with those for the intramolecular relaxation to indicate that the relaxation mechanism is the same in both cases. This mechanism involves two processes. The data indicate the process dominant at high temperature can be described as a rotational diffusion where the amplitude of angular motion increases with increasing temperature.
Cooperative radiationless relaxation
Authors: Miller Marvin M. , Fong Francis K.
Published: February 2004

The theory of cooperative nonradiative multiphonon relaxation by a multiatom system is developed in the framework of the adiabatic approximation in analogy with the Dicke theory of superradiance. As a concrete example, the nonradiative decay of impurity centers doped in a crystal lattice is considered. The assumptions underlying the theoretical development and the possibility of the experimental realization of this effect are discussed.
Energy transfer upconversion in LaF3:Pr3+
Authors: Zalucha Denis J. , Wright John C. , Fong Francis K.
Published: February 2004

Studies of infrared quantum counter upconversion in LaF3:Pr3+ and LaCl3:Pr3+ have led to the discovery of a process in which a red excitation photon results in the emission of a blue photon. When the 1D2 level of Pr3+ is excited by a cw rhodamine 6-G dye laser, blue fluorescence from the 3P0 level is observed. From the flux dependence and lifetime of the induced fluorescence, we conclude that the observed phenomenon arises from excitation annihilation involving pairs of ions in the 3H6 and the 1D2 states.
Radiation damage produced in single crystals of N-acetylglycine
Authors: Sinclair James , Codella Peter
Published: February 2004

The chemical effects initiated by x irradiation in the simple peptide N-acetylglycine have been examined by electron spin resonance. The paramagnetic fragments produced in the temperature range 77–300 °K have been observed in irradiated single crystals of the peptide. Positive identification of the radicals have been made using isotopically labeled acetylglycines incorporating both carbon-13 and deuterium at selected sites. Proton and carbon-13 hyperfine tensors have been determined for most of the fragments and a reaction scheme is presented which rationalizes the production of the observed species in terms of initially produced anion and cation radicals.
Effects of inelastic processes on the collision distribution in recoil systems
Authors: Malerich C. J. , Spicer Leonard D.
Published: February 2004

The collisional distribution function for recoil hot atom systems is examined to determine the influence of specific inelastic processes on the collision density over the reactive energy range. The inelastic processes considered result from collisional dissociation of target molecules. In the case of recoil tritium reaction with deuterium gas, it was found that the collisional distribution function was lowered due to dissociative collisions. The modified collision density incorporating inelastic events was used in this system to calculate the hot yields of DT as a function of inert gas moderation for comparison with experimental data. Both the magnitude and shape of the experimental yield curve were well represented over the entire range of moderator concentrations.
ESR study of the I atom in HIO3
Authors: Bailey C. Edward
Published: February 2004

A description is given of a paramagnetic center produced in single crystals of iodic acid, HIO3, when irradiated at room temperature with either x or γ rays. This center is interpreted as neutral iodine atoms, I0, trapped in the crystal. ESR studies indicate four different trapping sites that are related by the crystal symmetry. The g values, the hfs tensor, and the quadrupole interaction tensor are presented and discussed.
Random sequential addition of hard atoms to the one-dimensional integer lattice
Authors: Littlewood B. , Verrall J. L.
Published: February 2004

This paper considers the random sequential addition of atoms of different sizes and distinguishable types to the one-dimensional integer lattice (linear chain sites). In such a situation the different processes are competing for space on the lattice, and after a sufficiently long time has elapsed the chain will consist of a linear array of different atoms, in which configuration it will remain forever, since none of the processes is reversible. We present results which enable the proportion of sites occupied by each type of atom to be calculated: (a) numerically from a set of difference equations as a function of the chain length and (b) analytically, for a simplified model and infinite chain length.
Crystal structure of piezoelectric nonlinear-optic AgGaS2
Authors: Abrahams S. C. , Bernstein J. L.
Published: February 2004

Silver thiogallate, AgGaS2, is a representative member of the AIBIIIC 2VI family with chalcopyrite structure. AgGaS2 is strongly piezoelectric and is phase matchable for second harmonic generation. The lattice constants of this tetragonal crystal are a = 5.75722 ± 0.00003 and c = 10.3036 ± 0.0002 Å at 298 °K. The space group is I 42d, with four formulas per unit cell. The integrated intensities of 1978 reflections were measured within a hemisphere of reciprocal space having radius (sin θ)/λ = 1.02 Å−1 using PEXRAD, resulting in 268 symmetry-independent structure factors. The x coordinate of sulfur (0.2908 ± 0.0004) is 0.088 Å less than the value calculated on the assumption of a geometrically regular tetrahedral bond distribution about the B atom. By contrast, four AIIBIVC2V compounds previously reported have x coordinates for the Cv atom either slightly greater than (for ZnSiP2, CdSiP2, and ZnSiAs2), or not significantly different from (for ZnGeP2) that calculated. The experimental Ag–S distance is 2.556 ± 0.001 Å, and Ga–S is 2.276 ± 0.001 Å: the S–Ga–S angle bisected by the c axis is 111.1 ± 0.1°.
Emission spectra of homonuclear diatomic rare gas molecules in solid neon
Authors: Gedanken Aharon , Raz Baruch , Jortner Joshua
Published: February 2004

We report the vacuum ultraviolet 1,3Σu→1Σg emission of vibrationally relaxed Ar2*, Kr2*, and Xe2* in solid neon at 6°K. The inhibition of the formation of Ne2* in solid Ne is attributed to the retardation of vibrational relaxation for this diatomic molecule, which is characterized by a relatively high vibrational frequency.
Dissociation of diatomic molecules. I. Effect of limited numbers of rotational states
Authors: Tregay G. W. , Valance W. G. , MacLean D. I.
Published: February 2004

The rate of dissociation of a diatomic molecule is derived from a simple collision model. The diatomic molecule is treated as a rotating vibrator with a limited number of allowed rotational states in the upper vibrational levels. Limiting the number of rotational levels causes the population of the upper vibrational levels to increase more slowly with temperature than for a harmonic oscillator. This in turn causes the dissociation rate to increase more slowly than predicted by the expression exp(− D/R T), where D is the dissociation energy of the molecule. It is found that the dissociation rate depends strongly on the collisional dissociation probability but the activation energy does not. The model is applicable to situations where there is a Boltzmann translational energy distribution and a nonequilibrium vibrational distribution characterized by a vibrational temperature. The dissociation rates of H2 and HF are considered as specific examples.
Hydrodynamic effect in diffusion-controlled reaction
Authors: Deutch J. M. , Felderhof B. U.
Published: February 2004

A calculation is presented for the effect of the hydrodynamic interaction on the diffusion-controlled rate coefficient for particles that coalesce by diffusion under the influence of an interaction potential. The hydrodynamic effect is found to make a substantial reduction in the rate compared to the Debye model which includes only the effects of diffusion and the forces between the reacting particles. For the case where the particles are hard spheres the reduction is 46%. For ionic species the reduction varies between 25% and 60% depending on the extent of attraction or repulsion.
Chemisorption of H2 on W(211)
Authors: Rye R. R. , Barford B. D. , Cartier P. G.
Published: February 2004

Adsorption, desorption, and work function data for hydrogen adsorption and mixed adsorption of deuterium and ethylene show that multiple binding states exist for hydrogen on the (211) face of tungsten. The desorption spectrum consists of two peaks: β1 with peak maximum at 330°K and β2 with peak maximum at 675°K. Both follow second order desorption kinetics with activation energies of 16 kcal/mole and 35 kcal/mole, respectively. The rate of adsorption into the β1 state is proportional to the fraction of unoccupied β1 sites with a sticking probability of 0.05. Until the β2 sites are nearly filled, adsorption into this state is independent of coverage and occurs with a sticking probability of 0.57. For both states the work function change is linear with coverage, but with a maximum increase of 0.61 eV for the β2 state and a maximum decrease of 0.27 eV for the β1 state. Consideration of the topography of the (211) surface leads to the conclusion that the hydrogen sites on this face are associated with the close packed rows of tungsten atoms and with the troughs between the rows. With these two possible sites both the adsorption kinetics and the results for mixed adsorption of deuterium and ethylene are shown to be consistent with the assignment of the β1 state to the rows and the β2 state to the troughs.
Cyclotron resonance spectra of electrons produced in vacuo by photoejection from metal films and by thermionic emission
Authors: Srinivasan S. C. , Willard J. E.
Published: February 2004

Electrons produced at low steady state concentration by photoionization of metal films, or by thermionic emission, in evacuated tubes in an ESR cavity give a strong electron cyclotron resonance signal. The singlet, at g near 2.0000, is 0.07 G wide; its intensity is independent of temperature, and it broadens at high powers and at gas pressures greater than ≈ 10−5 torr. Unexpectedly, it is always flanked symmetrically by two well-resolved resonance lines separated from it by 5–15 G.
Interpretation of the vapor spectrum of UCl4
Authors: Gruber John B. , Hecht Harry G.
Published: February 2004

Optical spectra of vaporized UCl4 have been re-examined using refined spectroscopic techniques. Improved resolution and extension of the spectral range to include the near and far infrared have allowed us to make assignments on the basis of a tetrahedral crystal field model. Calculations based upon simultaneous diagonalization of electrostatic, spin-orbit coupling, and crystal field effects yield an excellent account of the observed spectral features, including a number of ``hot bands,'' in terms of the following parameters: F2 = 159.1 ± 1.5; F4 = 45.76 ± 0.77; F6 = 2.31 ± 0.08; ζ = 1756± 9;  A4〈r4〉 = − 817.4± 15.5; A6〈r6〉 = − 71.20± 5.52; ν3 = 330 ± 20; ν4 = 110 ± 15 (all units in cm−1). The magnitude of these parameters is discussed in terms of those reported by other workers.
Constrained variation method for excited-state energies of atoms and molecules
Authors: Wang P. S. C. , Benston Margaret Lowe , Chong D. P.
Published: February 2004

In this paper we propose to use the constrained variation (CV) method as an alternative to the conventional Hylleraas-Undheim-MacDonald (HUM) procedure for obtaining wavefunctions and energies of excited states of atoms and molecules. These two methods are compared both analytically and numerically; the results show that when the trial functions are properly chosen the CV method can give energies lower than the HUM method. The 21S state of the helium atom is treated as an example and the following results are obtained: For a Hartree-Fock type trial function, E(HUM) = −2.1431072 a. u. and E(CV) = −2.1431591 a. u., compared to E(Hartree-Fock) = −2.14344 a. u.; for a radial-type trial function, E(HUM) = −2.1440785 a. u. and E(CV) = −2.1440968 a. u., compared to E(radial limit) = −2.14411 a. u.; and for a Coolidge-James-type trial function, E(HUM) = 2.1458011 a. u. and E(CV) = −2.1458011 a. u., compared to E(Pekeris) = −2.145974044 a. u.
Magnetic circular dichroism of spin-forbidden transitions in the Fe3+ high-spin system
Authors: Katô Hajime
Published: February 2004

The magnetic circular dichroism (MCD) of the aqueous solution of potassium trismalonatoferrate (III) is measured at room temperature over the region 400–750 nm. The MCD of the spin-forbidden d-d transitions of high-spin iron (III) complexes is analyzed on the basis of ligand field theory. The electric dipole transition moments are calculated for two cases where d-d transitions are allowed by odd crystal field and by odd vibrations. The MCD analyses prove that the vibrations of T1u mode are effective in promoting transition 6A1g → 4T2g (1). Comparison of the theoretically derived Faraday parameters with the observed MCD shows that the band at 640 nm is the transition 6A1g → 4T2g (1) and that the band at 445 nm is composed of two transitions: transition 6A1g → 4A1g in the higher energy region and transition 6A1g → 4Eg (1) in the lower energy region. The huge MCD of these transitions arises mainly from the C term, which has its origin in the spin degeneracy of the ground state.
De-excitation rates for excited xenon molecules
Authors: Johnson A. Wayne , Gerardo J. B.
Published: February 2004

The time decay of the density of excited xenon molecules (Xe2*) in the lowest bound diatomic states was monitored by observing the photons (1730 ± 100 Å) emitted in transitions to the repulsive ground state. Mutual ionizing collisions of the excited diatomic states are responsible for the initial decay at high excited-state density. The measured rate for this process is (3.5 ± 1.4) × 10−10 cm3 sec−1. At lower excited-state densities, the decay of Xe2* is controlled by spontaneous emission [(20 ± 8) × 106 sec−1], collisional deactivation [(3,3 ± 1.3) × 10−18 cm2], and electronic recombination.
Dielectric tensor and the local electric field in naphthalene
Authors: Munn R. W. , Williams Digby F.
Published: February 2004

The complete dielectric tensor of naphthalene single crystals has been measured by a low-frequency capacitative technique at 295 °K. The principal components are 2.25 ± 0.07, 2.87 ± 0.05, and 3.43 ± 0.08, with the 1 axis making an angle of 28 ± 2.5° with the + a axis. These results are consistent with previous results for anthracene, though different from an earlier set of results used in analysing Hall measurements. The effect of this difference on the results of this Hall analysis is probably small. The measured dielectric tensor has been used to calculate the average local electric field, which resembles that in anthracene but is more anisotropic. The local field has in turn been used to calculate the off-diagonal drift mobility component for electrons and holes from the various experimental diagonal components. An expression has also been derived for the local-field correction required in comparing theoretical hopping Hall mobilities with experiment.
Stefan-Maxwell relations for multicomponent diffusion and the Chapman-Enskog solution of the Boltzmann equations
Authors: Muckenfuss Charles
Published: February 2004

It is established that corrections factors for higher order Chapman-Enskog approximations to multicomponent diffusion coefficients are equal for a given N-component gas mixture. This enables us to invert the mass flux equations for the diffusion forces and obtain the Stefan-Maxwell equations in any Chapman-Enskog approximation. The impedance matrix for these equations is symmetric regardless of whether or not the multicomponent diffusion coefficients are symmetric. Further, the impedance matrix is the same whether one chooses to invert mass flux equations involving symmetric or asymmetric diffusion coefficients.
Electron disappearance in pulse irradiated fluorocarbon gases
Authors: Bansal Krishan M. , Fessenden Richard W.
Published: February 2004

Rate constants for electron attachment to some highly reactive fluorocarbon gases have been determined by microwave conductometric methods. Initial ionization of the gas was by pulse radiolysis with 2.8 MeV electrons. To facilitate measurements on very reactive compounds a method has been developed which is applicable when the electron half-life is < 1 μsec. This method uses the amplitude of the steady-state response of the detector during the pulse and the rate of production of electrons based on measurements on the nonattaching buffer gas alone. This steady-state method was tested on mixtures of CF2Cl2 or SF6 in C3H8 and was shown to agree with direct measurements of the decay of the electron concentration. With propane as the buffer gas the method is applicable where the electron half-life is greater than about 0.5 μsec at 1 torr total pressure. At higher pressures of attaching gas decreases in apparent rate constant were observed which could be attributed to electron reaction before complete thermalization. Values for thermal attachment rate constants (cm3 molecule−1 · sec−1) at 25 °C found in this work are 1.3 × 10−9 for CF2Cl2; 1.2 × 10−8 for cyclo-C4F8, 1.4 × 10−7 for cyclo-C4F6, and 4.9 × 10−8 for C4F8-2. In comparison to these values that for cyclo-C3F6 was determined to be < 3 × 10−14. Perfluoropropylene was found to undergo a transition from three- to two-body behavior at high pressures of buffer gas, and the rate constant values imply a negative ion lifetime near 1 μsec. The limiting value of the two-body rate constant was found to be 3 × 10−10 cm3 molecule−1 · sec−1.
Temperature dependence of Raman-active phonons and nature of the phase transition in lithium and sodium azide
Authors: Iqbal Zafar
Published: February 2004

The Raman spectra of single crystal NaN3 and polycrystalline LiN3 have been recorded in the temperature range 100 to 300 °K. The lattice mode Raman spectrum of NaN3 below Tc [inverted lazy s] 284 °K is consistent with previous reports of a reversible second order rhombohedral to monoclinic phase transition in NaN3. Below Tc the Raman active librational mode at 122 cm−1 splits into two components, with the higher frequency component displaying a large increase in frequency with decreasing temperature. The separation between the two components has been related to the degree of the temperature dependent tilt of the anion with respect to the c axis and to the order parameter of the system. The temperature dependence of the order parameter was found to essentially follow the predictions of conventional mean field theory. In the case of LiN3, the librational modes are found to be accidently degenerate at 300 °K, with a frequency centered at 122 cm−1. However, at 262 °K a phase transition apparently occurs as shown by the onset of splitting of the band at 122 cm−1. The temperature dependence of the librational modes suggests that the phase transition in LiN3 is probably analogous to that in NaN3.
Fourier synthesized excitation of nuclear magnetic resonance with application to homonuclear decoupling and solvent line suppression
Authors: Tomlinson Barrett L. , Hill H. D. W.
Published: February 2004

A method is described for exciting a nuclear magnetic resonance spectrum with a radio frequency source having any desired frequency spectrum. The frequency spectrum of the source is first specified and then Fourier synthesized to define a function which is used to modulate a radio frequency carrier. The NMR spectrum is obtained by Fourier transforming the response of the spin system to this excitation. The technique is applied to the problem of suppressing a strong solvent line while simultaneously observing all other resonance lines in a spectrum and to homonuclear decoupling while observing a complete spectrum.
Electronic energy level and intensity correlations in the spectra of the trivalent actinide aquo ions. I. Es3+
Authors: Carnall W. T. , Cohen D. , Fields P. R. , Sjoblom R. K. , Barnes R. F.
Published: February 2004

The solution absorption spectrum of Es3+ has been measured in the region 10 000–34 000 cm−1. The observed band structure has been interpreted in terms of free-ion energy levels calculated using parameters that are consistent with those obtained in analyses of the specta of earlier members of the 5fN-series. The correlation between observed and computed band intensities has also been examined and shown to be consistent with the energy level scheme adopted.
Time-resolved infrared-microwave double resonance in 13CH3F: Theory and experiment
Authors: Jetter H. , Pearson E. F. , Norris C. L. , McGurk J. C. , Flygare W. H.
Published: February 2004

Infrared-microwave double resonance experiments on 13CH3F are described which lead to a direct measurement of T1, the relaxation time due to population differences for the two transitions J = 3 → J = 4; K = 3 and J = 4 → J = 5; K = 3 in the ground vibrational state. We find T1 = (10.5 ± 0.6) μsec mtorr. Comparing this work with low-power linewidth measurements which measure T2, the relaxation time of the induced polarization, indicates that T1 = T2 for the above two transitions. The theory used to interpret the experiments is developed starting from the density matrix formalism which leads to the electric dipole analog of the Bloch equations in nuclear magnetic resonance. The equations are solved for the conditions appropriate to this experiment which gives the results involving T1 and T2. The theory developed here should be of use in interpreting time-resolved infrared-microwave experiments in the future.
Matrix reactions of alkali metal atoms with ozone: Infrared spectra of the alkali metal ozonide molecules
Authors: Spiker Robert C. , Andrews Lester
Published: February 2004

The 15°K deposition of alkali metal atoms and ozone molecules at high dilution in argon produced very intense bands near 800 cm−1 and weak bands near 600 cm−1 which showed appropriate oxygen isotopic shifts for assignment to v3 and v2 of the ozonide ion. Energetic considerations and alkali metal effects clearly indicated bonding of the metal cation to the ozonide anion. The use of scrambled isotopic ozones showed that the metal cation was symmetrically bound to the ozonide anion in a C2v structure; the symmetric interionic stretching mode was observed at 281 cm−1 for Cs+O3−. The cesium-ozone reaction produced argon matrix fundamentals for CsO at 322 cm−1 and Cs2O at 457 cm−1; simultaneous mercury arc photolysis was required to yield the LiO absorption at 752 cm−1 from the lithium-ozone argon matrix reaction.
Valence excited states of CH. II. Properties
Authors: Lie George C. , Hinze Juergen , Liu Bowen
Published: February 2004

Expectation values of one-electron operators and related molecular properties were calculated for the X2π, a4Σ−, A2Δ, B2Σ−, and C2Σ+ states of CH, using accurate ab initio electronic wavefunctions and potential curves. The calculated dipole moment for the ν = 0 vibrational level of the X2π state is 1.41 D, in excellent agreement with the experimental value of 1.46 ± 0.06 D. Other properties studied include dipole and quadrupole moments and field gradients at the nuclei. There are no known experimental values for these properties. Vibration-rotational wavefunctions were obtained from the calculated potential curves by numerical solution of the radial Schrödinger equation for the nuclear motion. Vibration-rotational analyses were carried out to yield spectroscopic constants which are in satisfactory agreement with known experimental values.
Valence-shell states of PO: An example of the variation of the spin-orbit coupling constants with internuclear distance
Authors: Roche A. L. , Lefebvre-Brion H.
Published: February 2004

Configuration interaction calculations are reported for the excited valence-shell states of PO, using accurate SCF LCAO MO wavefunctions for states of different symmetries. A good representation is found for the C′ 2Δ, C 2Σ−, and F 2Σ+ states. Ab initio calculations for the spin-orbit coupling constants of the 2π states are carried out and show a very large variation with R for the spin-orbit constant A of the first excited 2π state. Consequently in seeking a correspondence between the calculated and observed 2π states, we have considered the possibility that the D′ 2πr regular state corresponds to high vibrational levels of the B′ 2πi inverted state.
Metal intercalation compounds of TaS2: Preparation and properties
Authors: Di Salvo F. J. , Hull G. W. , Schwartz L. H. , Voorhoeve J. M. , Waszczak J. V.
Published: February 2004

We report the preparation of intercalation compounds of 2H–TaS2 with post transition period elements. In general we find that elements to the left of the metalloid line in the periodic table will intercalate TaS2. Crystallographic lattice parameters, the maximum amount intercalated per Ta, magnetic susceptibility, and superconducting transition temperatures are also given.
Hanle effect lifetime measurements on selectively excited diatomic sulfur
Authors: Meyer Keith A. , Crosley David R.
Published: February 2004

Lifetimes for two selectively excited levels of the B3Σu− state of gaseous diatomic sulfur have been measured using the Hanle effect. The ZnI 3075.9 Å line overlaps the P 1(41) absorption line of the (4, 1) band of the B -X transition, and the CdI 3261.1 Å line overlaps the P 1(43) line of the (3, 3) band. We assume a magnetic moment for the B state calculated using a nonzero spin-spin interaction constant to obtain lifetimes of 18.3 ± 1.4 nsec for the ν′ = 4, N′ = 40, J′ = 41 level, and 20.7 ± 1.4 nsec for the ν′ = 3, N′ = 42, J′ = 43 level (quoted errors are 2σ estimates derived from the errors in the experimental data only).
Combining rules for intermolecular potential parameters. I. Rules for the Dymond-Alder potential
Authors: Kong Chang Lyoul
Published: February 2004

A new combining rule for the collision diameters of the Dymond-Alder pair potential function has been introduced. The rule was obtained by considering the long-range repulsive interactions of noble gas atoms, and gives the parameter for an interaction between unlike molecules as a weighted algebraic mean of those for the corresponding like-pair interactions. It is shown that the rule works very well in predicting the second virival coefficients of Ne–Ar, Ar–Kr, and Ar–CH4 mixtures and the binary diffusion coefficients of Ne–Ar, Ne–Kr, Ne–Xe, Ar–Kr, and Ar–Xe mixtures when it is used in conjunction with the previously proposed rule for the potential well-depth parameters, εij = 2εiiεjj/(εii + εjj).
Raman band shape of the N2 molecule dissolved in liquids
Authors: Duff Y. Le
Published: February 2004

We have studied the vibrational Raman band of the N2 molecule dissolved in various solvents. The band shape of isotropic and anisotropic scattering is discussed and compared with the one obtained from N2 gas. A collisional narrowing effect has been observed for the isotropic scattering. For N2 dissolved in SF6 the rotational correlation function is analyzed.
Effect of shape of molecules on transport and equilibrium properties of nonpolar polyatomic gases
Authors: Gupta A. Das , Singh Y. , Singh S.
Published: February 2004

Collision integrals for nonpolar polyatomic gases have been evaluated on the assumption of fixed relative orientation per collision, with a 12–12–6 potential model, for a range of reduced temperatures and shape parameters. The effect of shape of molecules on diffusion and viscosity is small but not negligible. Thermal diffusion factors are most strongly affected; the presence of interaction due to nonsphericity in the shape of molecules can wipe out the thermal-diffusion inversion temperatures. The parameters of the spherical component of the potential have been obtained from the viscosity data for nine gases. These parameters have been used in conjunction with the second viral coefficient data to determine the quadrupole moments and shape parameters of the molecules. The quadrupole moments and shape parameters obtained are very reasonable.
Paramagnetic Ni(IO3)2 · 2H2O. Crystal structure of the transition-metal iodates. I
Authors: Abrahams S. C. , Bernstein J. L. , Elemans J. B. A. A. , Verschoor G. C.
Published: February 2004

Nickel iodate dihydrate, paramagnetic at room temperature and weakly ferromagnetic below 3 °K, crystallizes in the orthorhombic system with space group Pbca and four formulas in the unit cell. The lattice constants at 298 °K are a = 9.14986 ± 0.00008, b = 12.20896 ± 0.00022, and c = 6.58353 ± 0.00013 Å. The crystal structure has been investigated independently in two laboratories. In one, the integrated intensities of 8883 reflections were measured with PEXRAD, within a hemisphere of reciprocal space of radius (sinθ)/λ = 1.02 Å−1. In the other, all independent reflections with (sinθ)/λ ≤ 0.70 Å−1 were measured on a Nonius automatic three-circle diffractometer. The crystal structure was solved by interpretation of Patterson and Fourier series, and refined by the method of least squares, using respectively 824 or 864 symmetry-independent structure factors. The final agreement factor is 0.047 for one set and 0.048 for the other, based on anisotropic temperature coefficients for all atoms except hydrogen, for which isotropic values were used. The structure consists of a network of corner-sharing IO6 octahedra with the Ni ions occupying octahedral interstices at the inversion centers. The water oxygen forms part of the octahedra around Ni, and is not directly bonded to I. The IO6 octahedra are highly distorted, with three I–O distances in the range 1.801–1.820 Å and three more in the range 2.804–2.935 Å. The NiO6 octahedra are almost regular, with Ni–O distances in the range 2.042–2.062 Å and O–Ni–O angles in the range 88.3–89.9°. The hydrogen atoms of the water molecule were detectable, and refinement gave acceptable molecular dimensions. Normal probability plot analysis was used to compare the results of the two independent structural investigations.
Atom trapping on surfaces
Authors: Modak Ashok T. , Pagni Patrick J.
Published: February 2004

The trapping of gas atoms on collision with a solid surface is described using the soft cube model. Fraction trapped is defined as that fraction of an incident flux which has a normal energy less than the gas surface potential well depth, after a single collision with the surface. Sticking coefficient is synonymous with fraction trapped. The functional dependence of the sticking coefficient on the gas and surface atom masses, temperatures and the interaction potential parameters is obtained. Sticking coefficients are predicted over a wide temperature range for xenon, argon, and neon on gold, silver, and platinum, and also for cadmium, gallium, titanium, cesium, silver, and rubidium on tungsten. Good agreement is obtained with experimental results for xenon on tungsten, platinum, and silver and for silver on tungsten. Argon and krypton on tungsten, platinum, and silver obtain reasonable agreement. Potential parameters for xenon, krypton, and argon on tungsten, platinum, and silver are derived from comparison with sticking coefficient data. These parameters are analogous to the gas-gas potential parameters obtained from gas phase transport properties, and though more approximate, may eventually prove to be as useful.
Corrections to the Born-Oppenheimer approximation and electronic effects on isotopic exchange equilibria
Authors: Kleinman Lawrence I. , Wolfsberg Max
Published: February 2004

Corrections to the Born-Oppenheimer electronic energy are calculated for several first and second row diatomic molecules. These corrections are evaluated in the adiabatic approximation at the experimental internuclear distance and thereby constitute the leading terms in the non-Born-Oppenheimer molecular energy. The corrections to the electronic energy are functions of the nuclear masses and are found to produce significant electronic isotope effects on the equilibrium constants of certain exchange reactions. In particular, at 300 °K the electronic isotope effect on the equilibrium constant of the reaction HX + HD = DX + H2 where X is Li, B, N, or F is found to range from 1.029 for Li to 1.101 for B. By partitioning the correction to the Born-Oppenheimer electronic energy into a sum of atomic and overlap terms, the electronic isotope effect is shown to be dependent upon certain characteristics of the molecules, the single most important of which is the X atom electronic angular momentum.
Small molecule behavior and the 3Bg state of biacetyl
Authors: Drent E. , van der Werf R. P. , Kommandeur J.
Published: February 2004

Below excitation energies of 22 500 cm−1 biacetyl behaves as a small molecule as evidenced by the pressure dependence of its phosphorescence and the structure of the excitation spectrum. The sudden transition to large (statistical) molecule behavior at this energy can be explained by the presence of a 3Bg state for which there is also theoretical evidence.
Static distortions of a cholesteric planar structure induced by magnetic or ac electric fields
Authors: Hurault J. P.
Published: February 2004

We discuss the threshold conditions for the nucleation of a static Helfrich distortion of a planar cholesteric structure under a magnetic field or an ac electric field applied parallel to the helical axis. In opposition to the case of nematics, the magnetic threshold in cholesterics is definitely lower than the threshold field for a transition of the Freedericks type. Under ac electric fields, the behavior of the threshold field with frequency is very similar to the one observed in nematics and depends mainly on the sign of the molecular dielectric anisotropy εa. For εa > 0, the threshold field is practically independent of frequency. For εa < 0, the threshold field diverges for a critical frequency proportional to the charge relaxation frequency. All these theoretical derivations seem to be in good agreement with recent experimental results.