bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of Approximate Translational—Vibrational Energy-Transfer Formulas with Exact Classical Calculations
Authors: Kelley J. Daniel , Wolfsberg Max 
Published: January 2005

The Hamiltonian equations of motion for collinear-colliding diatomic-molecule—atom and diatomic-molecule—diatomic-molecule systems are numerically integrated to obtain vibrational energy-transfer data. The diatomic molecules are taken to be either harmonic or Morse-type oscillators, and the collision potential is either an exponentially repulsive potential or a Lennard-Jones 6–12 potential.
The results of the exact classical three-body calculations are compared to results predicted by classical and semiclassical approximations. The ratios of approximate to exact energy-transfer values are related to the value of a parameter which depends only upon the masses of the particles involved in the collision; this correlation is found to be relatively insensitive to the values of the collision energy and of the potential parameters over wide ranges.
The exact classical energy-transfer data for the four-body systems are compared to the approximate and exact three-body data. The validity of using three-body approximations in treating four-body collisions is discussed.
Gaussian Lobe Function Expansions of Hartree—Fock Solutions for the First-Row Atoms and Ethylene
Authors: Whitten J. L. 
Published: January 2005

Gaussian expansions of ground-state Hartree—Fock solutions for the first-row atoms are determined by a self-consistent-field minimization of atomic energies. Wavefunctions are constructed from a basis set designed primarily for use in molecular calculations which consists only of functions of the form exp(—ar2). Angular dependence is achieved by defining origins for the basis functions at points in space determined in part by the symmetry of the orbital to be expanded.
A use of atomic information in molecular problems is discussed in a SCF treatment of the ethylene molecule.
Quantum-Mechanical Study of Some Three-Center Two-Electron Systems. I. Energy Calculations
Authors: Banyard K. E. , Shull Harrison 
Published: January 2005

Recent work on H3+ has been carried over to an investigation of a series of pseudomolecular ions of the form ZHZ+2Z−1. This was done in the hope of obtaining some understanding of the three-center, two-electron bonds of which the ``bridge'' bond in diborane is one possible example. The two-electron systems, studied here, may be regarded as an approximate representation of a fragment of a more complex molecule. Therefore, noninteger Z values were used in an attempt to make some allowance for the nuclear shielding caused by the presence of other electrons which were otherwise unaccounted for in the present calculations. The effective nuclear charge Z was allowed to take values of 0.8 (0.2) 2.2 and the optimum bond angle ZHZ was studied as a function of Z. For each Z, a study was also made of the angular dependence of the molecular energy for a fixed value of the bond length Z—H. Within a limited basis set the present treatment is a complete configuration-interaction calculation.
The study gave rise to several interesting features, two of which are the sizeable initial decrease in the bond angle as Z is increased and the occurrence of a double minimum in the molecular energy as a function of the bond angle for Z∼1.8. Therefore, for Z=1.8, the dependence of the molecular energy upon the bond angle ZHZ was also investigated for different values of the bond length. Although Part II contains a natural spin—orbital analysis of the wavefunction for each system, it was felt obligatory, at this stage, to offer a tentative interpretation of the present results. This was performed in terms of the movement of charge density components as a function of the bond angle and Z.
Vibrational Analysis of Acetone, Acetaldehyde, and Formaldehyde
Authors: Cossee P. , Schachtschneider J. H. 
Published: January 2005

Normal-coordinate calculations have been carried out for the molecules acetone, acetone-d6, acetaldehyde, acetaldehyde-d4, acetaldehyde-d1, formaldehyde, and formaldehyde-d2. Infrared and Raman spectra for acetone, acetone-d6, and acetaldehyde-d4 were measured and assigned. Together with experimental data and assignments taken from the literature for the other molecules, these yield an almost complete set of fundamental frequencies.
These frequencies were used to derive approximate force fields for these molecules and to investigate the transferability of the force constants. Calculations were carried out with both the Urey—Bradley force field (UBFF) and the valence-force field (VFF) with selected interaction constants. The Urey—Bradley force field is not satisfactory unless it is augmented with some valence-force interaction constants. In the valence-force approximation it is not possible to make an unambiguous choice of the nondiagonal constants. However, a most probable force field is indicated, which on the one hand reproduces the experimental frequencies and on the other hand shows reasonable values for diagonal and nondiagonal force constant.
The CO stretching constant, KCO, and the force constants around the CO group appear to be nontransferable among these molecules. The most probable force field indicates a decrease in the value of KCO in going from formaldehyde to acetaldehyde, to acetone. It is noted that the choice of interaction constants has a great influence on the values of the diagonal force constants and on the normal coordinates. Anharmonicity effects are also found to influence the values of the force constants and may affect the resulting conclusions.
Diffusion in Organic Crystals. II. Lattice and Subgrain-Boundary Diffusion
Authors: Reucroft P. J. , Kevorkian H. K. , Labes M. M. 
Published: January 2005

Self-diffusion studies at extended diffusion anneal times and impurity (phenanthrene) diffusion studies in melt-grown anthracene crystals have shown evidence for a fast subgrain-boundary-diffusion process in addition to a much slower lattice diffusion. Subgrain boundary diffusion is faster by a factor of 106−107, the activation energy being 25% to 66% the value for lattice diffusion.
Phenanthrene diffusion is very similar to self-diffusion in terms of diffusivity magnitude and activation energy. Diffusion anisotropy is more marked for phenanthrene diffusion, diffusivity perpendicular to the ac plane being greater than that perpendicular to the ab plane.
Approximations to Hartree—Fock Perturbation Theory
Authors: Langhoff P. W. , Karplus M. , Hurst R. P. 
Published: January 2005

A detailed examination is made of several approximations to the first-order Hartree—Fock perturbation equation. Four distinct methods are considered: the coupled (Method a) and the uncoupled (Method c) approximation of Dalgarno, a new alternative uncoupled approximation (Method b), and the simplified uncoupled approximation of Karplus and Kolker (Method d). By a comparison of the pertinent equations, it is shown that Methods a, b, and d correspond to each other in the use of a core potential analogous to that appearing in the zeroth-order Hartree—Fock equation, while Method c differs due to the inclusion of an extraneous self-potential term. An alternative analysis based on an orbital basis set expansion of the perturbed function demonstrates that Method c has an energy denominator of the simple Hückel type, while both Methods a and b include important two-electron correction terms. Also, it is found that of the four approximations, only Method c can be obtained as the first-order correction with a zeroth-order many-electron Hamiltonian that has the Hartree—Fock determinant as its eigenfunction; the other techniques are one electron in character, as is the Hartree—Fock method itself.
The significance of the difference in the core potential is demonstrated by test calculations of dipole and quadrupole polarizabilities and shielding factors for the two-, three-, and four-electron isoelectronic series. A variational technique is used with a trial function that has the form of a polynomial times the unperturbed orbital. For the polarizabilities, it is found that Method b is an excellent approximation to Method a, indicating that the self-consistency condition on the Method a solutions has a very small effect. The shielding factors, however, appear to be more sensitive to the self-consistency requirement. Both Method c and Method d introduce larger errors than Method b, with Method c particularly poor for three-electron atoms and ions. The constraint introduced by choice of trial function is shown to be unimportant for polarizabilities, but quite severe for the four-electron atom shielding factors.
A comparison of the complexity of the various techniques shows that the relative computing times for Methods a, b, c, and d are in the ratio of 300 to 60 to 75 to 1. Thus, Method d is simplest by far, although its speed is achieved by some loss of accuracy with respect to Methods a and b.
H2S as a Free-Radical Interceptor in the Gas-Phase Radiolysis and Photolysis of Propane
Authors: Ausloos P. , Lias Sharon G. 
Published: January 2005

The gas-phase photolysis (1236 Å) and the γ-ray radiolysis of C3D8 has been investigated in the presence of varying concentrations of H2S. When 10% or more H2S is added to C3D8, the majority of the D, CD3, C2D3, and C2D5 radicals abstract an H atom from H2S to form HD, CD3H, C2D3H, and C2D5H, respectively. The fully deuterated molecules formed in these mixtures result from the unimolecular elimination of a stable molecule from C3D8 or C3D8+ and from fast bimolecular processes such as ion—molecule reactions
The mechanisms of the radiolysis and the photolysis proposed in earlier studies have been re-examined in the light of the information derived from the C3D8—H2S experiments and of some additional photolysis experiments on CD3CH2CD3—NO mixtures. The results indicate that the modes of decomposition of the neutral excited propane molecule are as follows: C3D8*→C2D6+CD2,→CD4+C2D4,→D2+C3D6,→CD3+C2D5,→D+C3D7.The internally excited C2D4, C2D5, C3D6, and C3D7 species formed in these primary processes decompose to form D, CD3, C2D2, C2D3, and C2D4 unless they are collisionally stabilized.
In the radiolysis of C3D8—H2S mixtures, yields of the free radicals can be adequately accounted for by taking into account the modes of fragmentation of the parent ion and of the excited propane. The C2D5+ ions are shown to react with H2S in part by the deuteron-transfer reaction C2D5++H2S→C2D4+DH2S+.The effect of pressure and the effectiveness of HI as a free-radical interceptor in the radiolysis have been examined.
Electron Paramagnetic Resonance Studies of Photoselected Triplet Molecules. I. Phenoxazine
Authors: Lhoste Jean-Marc , Haug Alfred , Ptak Marius 
Published: January 2005

Paramagnetic resonance of the phosphorescent triplet state was carried out for phenoxazine molecules in rigid glasses at 77°K. The line shapes, in Δm=2 and Δm=1 regions, depend upon the incident light polarization. With complementary results from mixed crystals of diphenylphenoxazine, it was possible to relate the principal-axis system of the tensor describing the zero-field splitting to the molecular-axis system. The zero-field energy levels of the triplet state are of the same order of magnitude as those of aromatic molecules.
Selective excitation of the families of molecules corresponding to stationary values of the resonance field showed that:
(1) the resonant triplet state is mainly populated via one singlet—singlet transition S1←S0,
(2) the dipolar electric transition moment of this excitation is approximately parallel to the nitrogen—oxygen axis of the phenoxazine molecule.
Different aspects of photoselection of magnetoselected phosphorescent molecules are discussed.
Electron Paramagnetic Resonance Studies of Photoselected Triplet Molecules. II. Coronene and Phenanthrene
Authors: Lhoste Jean-Marc , Haug Alfred , Ptak Marius 
Published: January 2005

Photoselective excitation of magnetoselected triplet molecules in glassy rigid matrix at 77°K was used to determine the orientation of the molecular transition moments. Two aromatic molecules were thus selected: coronene which is highly symmetric and phenanthrene which has two different transition moments in its near-ultraviolet absorption spectrum.
Because of the high symmetry of coronene, it was only possible to show that the singlet—singlet transition moments involved in the population of the phosphorescent triplet state lie in the molecular plane.
For phenanthrene, the long-wavelength singlet—singlet excitation is known to have a transition moment parallel to the short molecular axis, the short-wavelength one a transition moment parallel to the long axis of the molecule. Paramagnetic resonance of triplet molecules photoselectively excited in the two bands with convenient filtered light confirmed these orientations.
Spin—Lattice Relaxation in Some Rare-Earth Trichlorides
Authors: Mangum B. W. , Hudson R. P. 
Published: January 2005

Studies of spin—lattice relaxation of the ions Ce3+, Nd3+, Sm3+, Ho3+, and Er3+ present in low concentrations (0.2% to 2%) in the host lattice of LaCl3 have been made in the liquid-helium region by the pulsed-microwave method. The variation of the relaxation time τ with temperature permits separation of the contributions to the relaxation from the two-phonon (resonant and nonresonant) and single-phonon processes.
The substances studied are not ``well behaved''; features such as nonexponential decays and variability of the derived values for the splitting between the ground and first excited levels are discussed. Some of the ions exhibit a significant variation of τ with concentration and Nd3+ shows an interestingly large anisotropy of τ in the Raman process.
Excess Ultrasonic Attenuation and Intrinsic-Volume Viscosity in Liquid Argon
Authors: Naugle Donald G. 
Published: January 2005

The ultrasonic attenuation has been measured in liquid argon by pulse techniques with a single quartz transducer, variable-path-length apparatus. Measurements have been made at temperatures between 84° and 112°K with pressures up to 10 atm. The measured attenuation depends linearly on the square of the frequency over the range 30–70 Mc/sec; however, the measured values exceed the values calculated from the classical Stokes—Kirchhoff expression.
The excess attenuation has been interpreted as evidence for the existence of the volume viscosity in liquid argon. The volume viscosity coefficient has been calculated and the results compared with those of the current theories of liquid-transport phenomena.
Adsorption of Carbon Monoxide on Tungsten. Abundances, Dipole Moments, and Sticking Coefficients
Authors: Bell Anthony A. , Gomer Robert 
Published: January 2005

The relative abundances, relative dipole moments, and absolute sticking coefficients of virgin, alpha, and beta CO adsorbed on tungsten have been determined by a combination of work function vs coverage measurements with step-desorption spectra and sticking-coefficient measurements. The work-function data were obtained in a field-emission tube with an annular CO source, permitting uniform dosing of the tip. The other measurements were performed in a tube in which a CO source illuminated a tungsten ribbon. A movable field emitter serving as detector could be raised in front of this ribbon to receive CO from the latter in desorption or reflection. This arrangement represents a new method of determining sticking coefficients, free from the ambiguities of surface roughness and wall ad- or desorption, usable to 20°K or less.
The dipole-moment ratios were Pα/Pv = −0.68; Pβ/Pv = 0.68 for the initial, and Pβ/Pv = 1.0 for the terminal portion of the beta layer. The relative abundances were total beta/total virgin = 0.55; virgin converted to beta/beta from virgin conversion = 2.1; alpha/total beta = 1.2.
Initial sticking coefficients were close to unity up to 700°K, and decreased rapidly at coverages (relative to the maximum amount of adsorbate retained at that temperature) of 0.6–0.4.
Theory of Formation of Very Thin Oxide Films on Metals
Authors: Boggio Joseph E. , Plumb Robert C. 
Published: January 2005

The growth of oxide on initially oxide-free evaporated aluminum films at room temperature and atmospheric pressure has been studied in parallel experiments, using elliptically polarized light to measure the film thickness and vibrating capacitor measurements to measure changes in the Volta potential. The film thickness reaches 21 Å in 106 sec and varies essentially logarithmically with time in the time range from 102 to 106 sec. The Volta potential is almost constant during the initial stages of growth and then varies approximately logarithmically with time. The observed change of Volta potential, interpreted as resulting from changes in the Galvani potential, is approximately 350 mV in 106 sec of oxidation.
A logical extension of the Mott theory is presented which includes (1) the effect of electronic space charge resulting from equilibration of electrons between the metal and oxide and (2) the electric field in the oxide, both in its role as a barrier to electron penetration of the oxide and in its control over the migration of interstitial aluminum ions. The extended theory predicts a linear relation between V½X (V is Galvani potential difference across the oxide and X is oxide thickness) and ln (oxidation time) whose slope is 3ℏ/(32me)½, m and e being the mass and charge of the electron and ℏ being Planck's constant divided by 2π. The experimentally determined slope has the value 1.32×10−8 V½·cm as compared to the theoretical slope of 1.46×10−8 V½·cm.
Infrared-Reflection Spectra of Molten Fluoride Solutions: Tantalum (V) in Alkali Fluorides
Authors: Fordyce J. Stuart , Baum Ruth L. 
Published: January 2005

Infrared-absorption spectra derived from reflectivity measurements over the range 4000 to 200 cm−1 have been obtained for molten fluoride solutions of electrochemical interest. The results for alkali fluoride melts containing tantalum (V) over the composition range 21.3 KF:21.3 LiF:TaF5 to 2 KF:2 LiF:TaF5 show two strong bands which increase in intensity with increasing tantalum concentration. One band is found at 535 cm−1 and the other is a split (17-cm−1) band centered at 300 cm−1. The band positions are independent of concentration and temperature from the melting point to 800°C. Comparison of these spectra with those for well-characterized solid compounds such as K2TaF7 and CsTaF6 demonstrate that the TaF72— complex ion is the predominant species in these melts.
A study of the influence of cations on the spectra of these melts show that when KF is present TaF72— is the only species observed. In the NaF:LiF solvent, TaF6− also appears.
The spectra of vapors condensed from the various melts studied show interesting contrasts which are related to the vapor—liquid equilibria.
Thermal Transpiration. Rotational Relaxation Numbers for Nitrogen and Carbon Dioxide
Authors: Malinauskas A. P. 
Published: January 2005

Thermal transpiration studies were conducted with the gases Ar, Xe, N2, and CO2 in an effort to test a recently proposed relation between the translational component of the thermal-conductivity coefficient and the maximum transpiration effect that is observed for a particular gas under a given set of temperature and apparatus conditions. The phenomenon was generated by maintaining temperatures of about 290° and 545°K on the opposite ends of 14 0.1-mm i.d. Pyrex glass capillaries arranged in parallel.
The rotational collision numbers for N2 and CO2 which were obtained from the thermal transpiration data were found to be 4.4 and 2.4, respectively, in good agreement with values determined by the more common methods.
Classical Monte Carlo Analysis of Four-Body Reactions: K + C2H5I System
Authors: Raff L. M. 
Published: January 2005

The analysis of the classical four-body problem as applied by Monte Carlo techniques to chemical reactions of the type A+BCD→AB+CD is reported. Using a modified form of a Blais—Bunker interaction potential surface, the model is applied to the reaction of K with C2H5I by approximating the C2H5 radical as being two carbon atoms, one of mass 14 amu, the other of mass 15 amu. Hamilton's equations are solved numerically, and by Monte Carlo averaging over the initial variables for 1060 different trajectories, various attributes of the reaction are calculated; these include the total reaction cross section, the differential reaction cross section, and the distribution of the heat of reaction among the available degrees of freedom of the products. It is found that the total reaction cross section is 15.9 Å2. This result, which is less than that obtained by similar methods for the (K, CH3I) system, is interpreted as reflecting the increased steric hindrance present in the more bulky system.
The differential reaction cross section for C2H5 scattering is peaked at small angles, and an average of about 90% of the available reaction energy finds its way into internal degrees of freedom of the products. These results are in reasonable agreement with the available experimental data. It is also found that the C–C vibrational mode of the ethyl radical is important in absorbing the heat of reaction. On the average it accounts for about 14% of the available energy. Two modes of reaction are observed, one a direct interaction, the second through complex formation. This second mechanism is found to enhance the importance of the organic radical in absorbing the heat of reaction. This is interpreted as being due to the increased opportunity for energy exchange during complex formation.
Vibration—Rotation Spectra of Monomeric HCl, DCl, HBr, DBr, and HI in the Rare-Gas Lattices and N2-Doping Experiments in the Rare-Gas Lattices
Authors: Bowers M. T. , Flygare W. H. 
Published: January 2005

Extensive experiments are performed on trapping of the HCl, DCl, HBr, DBr, and HI molecules in rare-gas lattices. Concentration, deposition rate, and temperature-dependent studies yield the monomer spectra of the molecules. The HCl and DCl monomers in Ar, Kr, and Xe show hindered rotational spectra that is interpreted on the basis of 0h site symmetry. HCl in Ne also appears to rotate. HBr and DBr in Ar shows additional splitting which is attributed to either site splitting due to loss of one of the near-neighbor atoms or site distortion toward D3h symmetry. HBr and DBr in the larger Kr lattice give spectra similar to the HCl spectra. The spectra indicate the predominant local symmetry is 0h and the barriers to rotation in the lattices are given from an interpretation of the spectra. The barriers to rotation are interpreted by extension of an electrostatic model.
Calculations of rotational energy levels have been performed for the linear molecule in a lattice site of D3h symmetry. The perturbed rigid-rotor levels are given as a function of lattice—molecule coupling constants. No experimental evidence was found in these studies for D3h site symmetry.
N2-doping experiments are performed with HCl in the argon lattice. N2 doping (1%—4%) is found to give predominately two sites for the HCl molecule; one site similar to the pure HCl in Ar case and another site in which the rotation is frozen out giving a single transition for HCl. The frozen site is attributed to the nearest-neighbor presence of N2.
Detailed discussions are given in interpreting the spectra in terms of a hindered rotor or a librator. Most of the spectra is interpreted on the basis of a hindered rotor but some spectra such as the N2-doping experiments require the librator analogy similar to CO in Ar and CN− in KCl.
The vibrational shifts of the monomers in the rare-gas lattices are given for all cases studied where the predominant shift is to lower energy. These shifts are also qualitatively explained by localized nonbonded dispersion and overlap repulsion effects.