bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dissociation of Molecular Hydrogen by Electron Impact
Authors: Corrigan S. J. B. 
Published: January 2005

The dissociation of molecular hydrogen by electron impact was studied by observing the rate of pressure decrease in a closed system when the dissociation fragments were trapped on molybdenum trioxide. An onset potential of 8.8 (±0.2) eV was obtained, indicating that a large part of the dissociation must proceed through direct excitation of the repulsive b 3Σu+ state of the molecule. From the onset potential to 95 eV, the upper energy limit of our observations, the dissociation rate increased rapidly at first, then more slowly above 14 eV passing through a flat maximum at 40 eV and then slowly decreasing up to the highest energy investigated.
Reasons are given for supposing that the observed cleanup of hydrogen at high electron energies contains an effect due to dissociative neutralization of molecular ions. With this assumption the cross section for excitation of the molecule to triplet states is derived by subtracting the molecular ionization cross section from the observed total dissociation cross section. In this way we obtain a cross section for dissociation into neutral atoms which has a maximum of 9×10−17 cm2 at an energy of 16.5 eV, followed by a rapid decrease with increasing electron energy.
Vibrational Relaxation in Methane—Oxygen Mixtures
Authors: Parker J. G. , Swope R. H. 
Published: January 2005

Measurements have been made of the relaxation frequency and vibrational specific heat of mixtures of oxygen and methane, with the methane concentration varying from 0.05% to 1.6%. The temperature in all cases was 23°C and the total pressure of the mixture atmospheric. Results of these measurements show that the relaxation frequency does not vary linearly with methane concentration and that the vibrational specific heat is concentration dependent. Theoretical interpretation of these results indicates that there is a strong coupling of the vibration of oxygen to that of methane and that losses due to radiation from the methane are significant. It is further determined that methane is approximately as effective in exciting vibration in oxygen as in itself and that oxygen is considerably less efficient in exciting vibration in methane.
Supplementary measurements were also made on pure methane and methane dilute in gases characterized by their vibrational inertness — N2, Ne, Ar, and Kr. The relaxation time of pure methane was found to be in excellent agreement with values determined by previous investigators. Nitrogen was found to have a measurable effect in shortening the relaxation time of methane; surprisingly, Ne, Ar, and Kr were all found to be more effective than nitrogen.
Spectrum-Line Reversal Measurements of Free-Electron and Coupled N2 Vibrational Temperatures in Expansion Flows
Authors: Hurle I. R. , Russo A. L. 
Published: January 2005

Spectrum-line reversal measurements of the excitation temperature of Na atoms in expansion flows of shock-heated Ar and 1% N2+Ar mixtures are described. The measurements were made in a conical nozzle attached to the end of a conventional shock tube. For expansion flows of pure Ar from reservoir temperatures of 3200° to 4200°K and a reservoir pressure of about 37 atm, the measured Na temperatures (≈2200°K) were considerably in excess of the local-translational temperature (≈400°K). These high excitation temperatures are interpreted in terms of the excitation of Na by free electrons produced from ionization of the Na in the reservoir. On this basis, free-electron temperatures are deduced which indicate freezing of the electron thermal energy at values corresponding to those expected at the nozzle throat. This result suggests a slow rate of transfer of electron thermal energy to the Ar translational mode.
The addition of 1% N2 to the Ar expansions produced large reductions in the measured Na temperatures. The reduced temperatures are shown to correspond to the frozen N2 vibrational temperatures expected on the basis of previous results. These reductions are explained in terms of an efficient transfer of the excess-electron thermal energy to the N2 vibrational mode, the free-electron and N2 vibrational temperatures being thereby coupled and equilibrated during the expansion.
The present results also substantiate the faster vibrational relaxation rates inferred previously from similar expansion-flow studies of pure N2; they further suggest that the simple Landau—Teller rate equation, when used with relaxation times measured in shock-wave flows, is not adequate to describe the vibrational relaxation process under the extreme nonequilibrium conditions associated with nozzle-expansion flows.
Internal Rotation and Kerr Effect in Polymer Molecules
Authors: Nagai Kazuo , Ishikawa Toshihide 
Published: January 2005

A theory of the Kerr effect (the electro-optical birefringence) of dilute polymer solutions is developed. If interactions between polymer molecules are neglected, the molar Kerr constant of polymer molecules is expressed as Km=(2πNA/45kT){(3〈utrγu〉−Tr〈u2γ〉)(kT)−1+[3Tr〈γγ′〉−〈(Trγ)(Trγ′)〉]},where NA is the Avogadro number; k is the Boltzmann constant; T is the absolute temperature; u, γ, and γ′ are the dipole-moment vector and the optical and static polarizability tensors of a polymer molecule, respectively; utr is the transpose of u; Tr denotes the trace of a matrix; and the averages refer to those about a free polymer molecule. In addition to Km, the two quantities 〈r2〉F/〈r2〉 and 〈x2〉F/〈y2〉F are calculated, which, respectively, are considered to be measures of the degrees of deformation and orientation of a polymer molecule by an electric field of strength F. Here r is the absolute value of the end-to-end vector r = (x y z)tr, the field being assumed along the x axis; the averages with and without subscripts refer to those in the presence and in the absence of the field, respectively. Alternative expressions for Km, etc., are derived by assuming the additivity of bond dipole moments and bond polarizabilities.
An application is made to the polyethylene molecule, by using geometrical models proposed by Hoeve and by Nagai and Ishikawa, and also using Denbigh's and Bunn and Daubeny's values for bond polarizabilities. It is found, for example, that the elimination of the GG′ conformation for neighboring bonds, which has been known to increase markedly 〈r2〉, increases only slightly Km.
It is pointed out that the molecular-weight dependence of specific Kerr constants, found by Le Fèvre and his collaborators for a variety of polymer—solvent pairs, should be ascribed to the excluded volume. Thus need for a theory of the effect of the excluded volume on Kerr constants, and for experimental data obtained at the so-called Θ condition, is emphasized.
Bounds on the Configurational Integral for Hard Parallel Squares and Cubes
Authors: Hoover William G. 
Published: January 2005

Upper and lower bounds on the configurational integral for hard parallel squares and cubes are obtained. These bounds are valid over the entire density range and apply to infinite (thermodynamic) systems. Both the upper bound and the lower bound approach the free-volume form at high density.
This strong result proves rigorously that the free-volume form is correct for these systems in the thermodynamic limit.
Calculation of Virial Coefficients. Squares and Cubes with Attractive Forces
Authors: Hoover William G. , Ree Francis H. 
Published: January 2005

A general combinatorial formulation of the star integrals occurring in calculations of virial coefficients is presented. The usefulness of the formulation is demonstrated by the exact calculation of the first five virial coefficients for gases of hard parallel squares and cubes with attractive forces.
For these gases the three-, four-, and five-term virial series are examined, and each series is found to have a critical point. Most of the critical properties of these truncated virial series are sensitive to the number of terms included, but the product PcVc remains nearly constant as more terms are added.
It is shown that any two- or three-dimensional square-well virial coefficient is negative at low temperature. Despite this, the low-temperature contribution of the complete star integral can be either positive or negative.
Mass-Spectrometric Study of Ions at Near-Atmospheric Pressure. II. Ammonium Ions Produced by the Alpha Radiolysis of Ammonia and Their Solvation in the Gas Phase by Ammonia and Water Molecules
Authors: Hogg A. M. , Kebarle P. 
Published: January 2005

A new mass-spectrometric method for the study of solvation of ions and of ion complexes is applied to the ammonium ion.
The major ion in the α-particle radiolysis of NH3 is the clustered ammonium ion NH4+·nNH3. A study of the distribution of these clusters is made at room temperature and in the pressure range 0.05 to 200 Torr ammonia. Clusters up to n=20 can be observed. The intensity distribution of the ions shows that the inner solvation shell contains four molecules. Approximate free-energy changes for inner- and outer-shell solvation are obtained.
Studies of competitive solvation of the NH4+ ion by water and ammonia molecules confirm the inner four shell. Ammonia is preferentially taken up in the inner shell and water in the outer shell. The higher stability of the ammoniated inner shell requires a very small effective NH4+ radius. This requirement leads to an examination of the structure of the NH4+·4NH3 ion.
Reactions of Atomic Oxygen with Acetylene. I. Kinetics and Mechanisms
Authors: Arrington C. A. , Brennen W. , Glass G. P. , Michael J. V. , Niki H. 
Published: January 2005

The room-temperature reaction of acetylene with atomic oxygen has been studied in a moderately fast flow system. The course of the reaction was followed using both the Bendix T.O.F. mass spectrometer and a photometric method. The major products of the reaction were carbon monoxide and hydrogen. Large amounts of atomic hydrogen were also observed.
The following reaction scheme is consistent with our results: (1)  C2H2+O→[C2H2O*]→CH2+CO,(2)  CH2+O→HCO+H,(3) CH2+O→H2+CO,(4)  HCO+H→H2+CO,(5)  HCO+O→OH+CO,(6)  HCO+O→H+CO2,(7)  OH+O→H+O2.The rate of the over-all reaction is determined by the first initial step in which atomic oxygen adds to acetylene to yield an excited complex which then undergoes unimolecular decomposition to give triplet methylene. The rate constant for this initial reaction was measured, at room temperature, as (8.9±2.8)×10−14 cc molecule−1·sec−1. The activation energy was less than 1 kcal mole−1.
Experiments with acetylene-d2 have established that Reactions (2) and (4) constitute the major pathway by which triplet methylene, produced in Reaction (1), is consumed.
One-Center Perturbation Approach to Molecular Electronic Energies. II. Exact Wavefunctions and Energies for H2+-Like Molecular Puffs
Authors: Hauk Peter , Parr Robert G. 
Published: January 2005

The exact solution is given for the problem of the ground state of one electron moving in the potential field V(r) = —Z/r&gt;, produced by an effective nuclear charge Z uniformly spread over a sphere of radius R, with r&gt; the greater of R and the electron's distance r from the sphere center. The lowest eigenvalue and corresponding eigenfunction are tabulated as functions of R and Z.
For the case corresponding to the spherical approximation to H2+ at its equilibrium distance, R = 1, Z = 2, the energy is found to be −1.018502 a.u., in agreement with previous variational calculations of Cohen and Coulson, Howell and Shull, and Houser, Lykos, and Mehler.
One-Center Expansion Wavefunctions for CH3−, CH4, and CH5+
Authors: Rutledge Ronald M. , Saturno Antony F. 
Published: January 2005

One-center expansion (OCE) wavefunctions for the species CH3−, CH4, and CH5+ are presented. These wavefunctions are expressed by configuration interaction of the singly excited states of a closed-shell ground state. The basis set consists of STO's through l=4, belonging to the irreducible representations spanned by the σ-bonding representation. In addition the calculations on CH3− and CH5+ were done as a function of nuclear geometry. These calculations indicate that CH3− has a D3h configuration rather than a C3v configuration. The molecular configuration of CH5+ was indicated to be D3h rather than C4v or C3v.
The ground-state energies of CH3−, CH4, and CH5+ were calculated to be −39.236, −39.859, and −40.036 a.u., respectively. The proton affinity of methane is calculated to be approximately 5 eV.
Electron-Diffraction Study of the Structure and Internal Rotation of Cyclopropyl Carboxaldehyde
Authors: Bartell L. S. , Guillory J. P. 
Published: January 2005

The structure and conformational behavior of cyclopropyl carboxaldehyde in the gas phase have been investigated by electron diffraction. Rotational isomers did not correspond to the trans and gauche isomers observed in a parallel study of the isopropyl derivative, but rather to s-trans and s-cis. The latter isomers were present in nearly equal concentrations. The rotational barrier appears to be greater than 2.5 kcal/mole. Results are interpreted in terms of Walsh's π-electron picture, and various comparisons of cyclopropyl and vinyl groups are made and discussed.
The diffraction experiment yielded normal values for bond angles and amplitudes of intramolecular vibrations. No tendency was detected for the aldehyde to assume a nonclassical structure of the sort postulated for its analog, the cyclopropyl carbinyl cation.
Comparison of Some Calculations on H2O and H2S
Authors: Hake R. B. , Banyard K. E. 
Published: January 2005

For the H2O and H2S molecules, a comparison is made of the values of the molecular energy, molar diamagnetic susceptibility, coherent x-ray scattering factor, dipole moment, 〈1/r〉 and 〈1/r2〉 as calculated by different approximate treatments. The results of a united-atom (UA) calculation, the LCAO—MO—SCF extended one-center expansion (OCE) approach of Moccia, and the LCAO—MO—SCF minimal multicenter expansion (MCE) treatment of Ellison and Shull are compared for H2O. For H2S, UA and OCE calculations are compared. All theoretical values are compared with experiment where possible, and the relative merits of the different approximate treatments are discussed. We also discuss results which might be obtained for H2S from a minimal LCAO—MO—SCF—MCE calculation.
Also for H2S, we report the results of modifications in our earlier UA approach. Although the conclusions drawn in our earlier work remain unchanged by the modifications, we note a pleasing improvement on our earlier values for the force constant, molar diamagnetic susceptibility, and molecular energy.
On the Molecular Kinetic Theory of Cooperative Relaxation Processes in Dipolar Liquid and Crystalline Phases
Authors: Adam Gerold 
Published: January 2005

The correlation-function method is used to describe the dielectric relaxation behavior of liquids and directionally isotropic crystalline phases.
The physical model used is that of a regular mixture of dipole molecules and vacancies on a lattice, i.e., the equivalent of the Bragg—Williams approximation.
To calculate the cooperative transition probabilities, which govern the relaxation correlation function, the effect of vacancies in the neighborhood of the representative dipole is taken into account. The effect of vacancy diffusion is neglected.
The result is a discrete distribution of relaxation times corresponding to cooperative regions with none, one, two, etc., vacancies.
This relaxation spectrum is shown to be narrow in the case of liquids and broad in the case of molecular crystals.
Upon application of the theory to measurements of the dielectric relaxation of crystalline hydrogen and deuterium halides and of liquid bromoalkanes, the fraction of vacancies and an interaction parameter for these substances were obtained.
The values of both quantities were shown to be of the order to be expected from the energy of molecular interactions.
Libration of the OH— Ion in LiOH
Authors: Coogan C. K. 
Published: January 2005

Much discussion and controversy has taken place in recent years on libration of the OH− ion in hydroxide crystals. Recent work on the charge distribution in the OH− ion makes it feasible to calculate the librational frequency and amplitude in LiOH arising from thermal agitation. A simplified model of the libration is chosen which corresponds with the Einstein model for this mode. The calculation is based on the change in lattice energy with rotation of a single OH− ion, involving Madelung, van der Waals, and repulsive terms.
The results indicate considerable anisotropy of libration at thermal amplitudes at room temperature. The calculated frequency thus varies with direction so that ν̃a=342 cm−1 while 〈ν̃〉Av=396 cm−1. At room temperature the calculated rms thermal displacements of the hydrogen atom arising from libration agree well with those derived from the results of neutron-diffraction experiments. The apparent success of this simple model in LiOH suggests that it might be extended to similar layer-lattice hydroxide crystals.
Chemical Kinetics as a Relaxation Process in a Multilevel System. II. General Formulation of the Many-Shot Expansion
Authors: Serauskas R. V. , Schlag E. W. 
Published: January 2005

For a complete understanding of rates in chemical kinetics it is necessary to analyze kinetic processes on the molecular level. For such an analysis one must know the change in the distribution of internal energy as the result of a collision process. It is suggested that this information can be obtained from an analysis of weak-collision terms in a reacting system excited to a nonequilibrium distribution from which it relaxes by way of a many-level process.
The relaxation problem in a nonequilibrium multilevel system weakly coupled to a heat bath can be expressed in terms of a Pauli master equation. It has previously been shown that this relaxation problem can be solved in terms of a many-shot expansion, the leading term being the strong-collision result and further terms being due to weak collisions. In this paper it is shown that this many-shot expansion can be derived from a generalized matrix form of the master equation, as well as by the phenomenological approach used previously. Furthermore, a matrix form for a generalized nearest-neighbor model is analyzed and developed in terms of a series which considers the asymptotic contributions of upward transitions in terms of successively less-probable Markov chains. The input for these computations is a complete set of transition probabilities, for which these methods predict the appropriate laboratory observable. Under certain experimental conditions the laboratory observable is particularly sensitive to the weak-collision terms, and it is in this region that one should be able to obtain information about the effect of collisions on the distribution of internal energy.
Excitation of Molecular Nitrogen by Electron Impact
Authors: Winters Harold F. 
Published: January 2005

Relative cross sections for excitation of the triplet series of molecular nitrogen have been obtained. The cross sections have a maximum within a few volts of threshold as expected for electron exchange collisions. In particular, the C 3IIu state has a sharp maximum within a few tenths of a volt of threshold and then decays sharply.
The A 3Σu+ state has an increasing slope through the Franck—Condon region and then is a strictly linear function of energy for about 1½ V. It subsequently reaches a maximum and starts to decay. This leads to the postulate that the region of increasing slope is caused by the continual excitation of new vibrational levels and that the excitation function of a given vibrational level may be linear to near threshold. This interpretation is shown to be consistent with the experimental data.
Variational Treatment of the HeH+ Ion and the β-Decay in HT
Authors: Wolniewicz L. 
Published: January 2005

The nonrelativistic energies of the HeH+ ion have been computed by the variational method for the ground state and for the first excited 1Σ+ state. The wavefunction employed was a 64-term generalized James—Coolidge expansion. The computed binding energy of the ground state amounts to De=16448.3 cm−1 at the equilibrium separation Re=1.46324 a.u. The excited state is found to be repulsive.
The HeH+ wavefunctions are used to compare quantitatively the theory of β-decay in molecules with experiment. It is shown that for the HT molecule, the theory predicts the dissociation in at least 17.8% of the events while the corresponding experimental number is 6.8%±1.9%.
Theory of the Linear Heisenberg Antiferromagnet. Application to Paramagnetic Excitations in Organic Crystals
Authors: Soos Zoltán G. 
Published: January 2005

We consider a linear array of tightly bound electrons that are exchange coupled to their neighbors. The Hamiltonian, in the Heisenberg model, is H= ∑ j=112N{J(1+δ)S2j·S2j+1+J(1−δ)S2j·S2j−1−12J},where δ is the alternation parameter and the exchange integral J is positive, corresponding to antiferromagnetic coupling. We investigate the solutions for the one-dimensional antiferromagnet, for any |δ|≤1, by transforming the Hamiltonian first to Fermi creation and annihilation operators and then to pseudospin operators similar to the ones used by Anderson in connection with superconductivity. We thus take into account the coherence between antiparallel electrons in a self-consistent manner. We exploit the similarity between the linear antiferromagnet and superconductivity theory to obtain the ground-state energy and the excitation spectrum for arbitrary δ and temperature. We thus obtain a complete thermodynamic description. In particular, we calculate the paramagnetic susceptibility and compare it with experiment.
At 0°K, the solutions we present agree with or improve upon previous calculations, for either the regular (δ=0) or the alternating (δ≠0) antiferromagnet, of the ground-state energy, the excitation spectrum, and the short-range order. Using the finite temperature extension of the theory, we find good agreement between the calculated and the experimental paramagnetic susceptibilities of organic crystals whose structures, so far as spin properties are concerned, may be approximated by either the regular or the alternating antiferromagnet. The temperature dependence of the excitation energies, a many-body effect describing the decrease of coherence between antiparallel electrons with increasing temperature, agrees with the observed behavior of the singlet—triplet energy gap in paramagnetic exciton systems. Thus, we obtain the extension of exciton theory to arbitrary temperature and alternation. The electron pairs forming triplet excitations are, for any alternation, increasingly separated at high temperatures, where, as expected, the electrons behave like a paramagnetic gas.
Calculation of Rydberg Levels in the Nitrogen Molecule
Authors: Lefebvre-Brion H. , Moser C. M. 
Published: January 2005

The energy levels of the lowest members of Rydberg series in N2 have been calculated using LCAO—MO—SCF functions. We have found only one 1Σu+ level around 104 000 cm−1 and this is the first member of a Rydberg series which converges to the X 2Σg+ ground state of N2+. This level can be identified with the p′ 1Σu+ state. Our calculations suggest that, if the Worley—Jenkins Rydberg states have 1Σu+ symmetry (which is not yet absolutely definite) then, no Rydberg series of the type (npπu) 1IIu←X1Σg+ have yet been observed.
Our calculations confirm the configurations previously suggested for the upper states of Worley's third and Hopfield's Rydberg series. The states D 3Σu+, E 3Σg+, z 1Δg, x 1Σg−, and y 1IIg are shown to be the first members of Rydberg series.