bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics and thermodynamics of the CN molecule. III. Shock tube measurement of CN dissociation rates
Authors: Slack M. W.
Published: February 2003

The dissociation of CN molecules in an argon diluent has been investigated in a shock tube over the temperature range 4400 to 13 000 °K. Observations of CN(B 2Σ+→X 2Σ+) and C2(d 3Πg→a 3Πu)d emission support the following chain as a sufficient decomposition mechanism: CN+M=C+N+M (1); C+CN=C2+N (2); N+CN=N2+C (3); C2+M=2C+M (4); N2+M=2N+M (5); and rate coefficients have been measured for the first four reactions. The measured rate coefficients for reaction (1) were in good agreement with an earlier measurement by Fairbairn and with a theoretical modified phase space estimate by Shui. An initial induction period was identified prior to steady state dissociation, and excess molecular nitrogen was observed to significantly inhibit the CN decomposition chain. Experimental CN and C2 emission records both from the present investigation and from earlier work by Fairbairn and by Patterson and Greene are compared with predicted excited state concentrations obtained by numerical integration of the rate equations. The results of earlier investigations are reinterpreted as limiting cases of the proposed decomposition chain.
Frequency dependence of proton relaxation in liquid crystals
Authors: Fung B. M. , Wade Chas. G. , Orwoll Richard D.
Published: February 2003

The proton spin–lattice relaxation time (T1) of liquid crystalline methyl-deuterated p-azoxyanisole (PAA-d6) was measured at four frequencies as a function of its concentration in perdeuterated PAA. Analysis of the isotope dilution data showed that the intermolecular contribution to the relaxation rate becomes more important at lower frequencies, and in intramolecular contribution has a less pronounced frequency dependence than the intermolecular part.
ESCA and molecular orbital studies of small silver particles
Authors: Mason M. G. , Baetzold R. C.
Published: February 2003

The results of x-ray photoelectron spectroscopy studies of evaporated silver clusters on carbon are reported. The samples were prepared and the particle-size distribution was determined. Spectra have been recorded at coverages from 2.7×1013 to 4×1016 atoms cm−2. The very low coverages yield particle distributions dominated by single-atom centers, whereas the high coverages represent bulk metallic silver. Low-coverage spectra show low binding energy states that are thought to result either from interactions with the carbon substrate or reaction with sulfur contamination. CNDO calculations show low binding energy states to exist for Ag4 on a C16 model substrate. At higher coverages the Ag 4d states broaden and split, and the threshold moves 2.5 eV to lower binding energy. The splitting of the Ag 4d band is attributed to spin–orbit and crystal field effects. The change in threshold can be attributed to the filling and spreading of the Ag 5s states to form the s–p conduction band of the bulk metal. The measured threshold shift of 2.5 eV (Fermi-level reference) is to be compared with 1.5 eV (vacuum-level reference) predicted by extended Hückel calculations. Small shifts in the Ag 3d core levels are also observed and follow the trends predicted by CNDO charge calculations.
Statistical theory of entanglement density in linear polymers and fiber systems. I. General considerations
Authors: Ziabicki Andrzej
Published: February 2003

The problem of entanglement density in systems composed of long chains or threads has been theoretically analyzed. The density of entanglements ν has been defined as the product of the density of physical contacts between interacting elements δ and the effectivity coefficient ε, ν=δ⋅ε. The deterministic concept of an effective entanglement as a definite geometrical configuration has been replaced by the probability εkij that a configuration (ij) subjected to an external local action (k) (motion, tension, etc.) will behave like an entanglement, i.e., will transmit elastic forces from one element to the other. εkij=0 for nonentanglement behavior, εkij=1 for entanglement behavior. Having the probability distribution of configurations and local actions (P̃ij and Pkij, respectively) one can define the average probability of effective entanglement, or the effectivity coefficient ε=Σi,jΣkP̃ijPkij εkij.
The multiphoton ionization spectrum of benzene
Authors: Johnson Philip M.
Published: February 2003

A resonance seen in the multiphoton ionization spectrum of benzene at 391.4 nm is identified as a two-photon resonance with a bound state at 51 085 cm−1. This state has probable symmetry 1E1g or 1E2g as indicated by an active e2g vibration. No other allowed two-photon transitions are seen below this energy. Three-photon resonances with the Rydberg states of benzene are seen and compared to the one-photon absorption spectrum. The great similarity indicates a strong 1A1g component in the two-photon virtual state. Two-photon resonances with the 1B2u state agree with two-photon fluorescence excitation spectra but show no diminution above the energy where fluorescence is quenched.
Effect of incident flux on surface concentrations and condensation coefficients when growth and vaporization involve mobile surface species
Authors: Rosenblatt Gerd M.
Published: February 2003

Kinetic analysis of condensation and vaporization processes which proceed through a mobile, adsorbed precursor state shows that the relative concentration cs/cse of mobile surface molecules depends upon both the vapor saturation ratio P/Pe and the condensation or vaporization coefficient α: cs/cse=α+(P/Pe)(1−α). The result may affect previous treatments of two-dimensional nucleation and of spiral ledge dynamics in which it was assumed that cs/cse =P/Pe. When condensation or vaporization proceeds through a mobile surface layer, condensation coefficients of unity may be approached, but not attained. If surface migration is rapid, the condensation–vaporization coefficient α will change with vapor saturation only if there is a change in the concentration of surface sites at which mobile molecules are incorporated, in the rate constant for incorporation of mobile molecules at these sites, or in the surface residence time. When α is small, the temperature dependence of α yields information on the difference between the activation energy for incorporation and the depth of the molecule–surface potential well. If condensation or vaporization occurs primarily from spiral ledges originating at screw dislocations, condensation and vaporization coefficients will decrease as the system is taken from large oversaturations or large undersaturations towards equilibrium. The slopes of hillocks or pits formed at screw dislocations will decrease concurrently. The results are applied to vaporization and condensation of arsenic and antimony.
Collision and quenching cross sections in the A 2Σ+ state of OH and OD
Authors: German K. R.
Published: February 2003

A pulsed dye laser has been used to excite OH and OD radicals to the A 2Σ+ state and the quenching and vibrational relaxation cross sections have been measured for several different buffer gasses. It was found that the quenching cross sections were reasonably constant within a given vibrational level and tended to increase at higher vibrational levels. The vibrational relaxation cross sections decreased for higher rotational states and were generally smaller for collisions in which V′ changes by two than for collisions where it changes by only one. Finally, the implications of these measurements to the detection of OH in the atmosphere are discussed.
Configuration interaction studies of the HeH+ molecular ion. III. Singlet pi and delta states
Authors: Green T. A. , Michels H. H. , Browne J. C.
Published: February 2003

The method of superposition of configurations is applied to the singlet pi and delta states of HeH+ which correlate to the separated atom states of principal quantum number less than or equal to 3. The calculations are carried out for internuclear separations R in the range 0(0.1)34.5, 35.0(0.5)50.0 a.u. The delta state calculations are also extended to R=65. The work is a continuation of a study of HeH+ for which the singlet sigma states have already been reported. In addition to the energy eigenvalues, matrix elements for radial and angular coupling and the dipole and gradient matrix elements are calculated for all combinations of the singlet sigma, pi, and delta states. Plots and tables of the calculated eigenvalues and matrix elements are presented. Where possible the calculated data are compared with the results of previous work. The results of this work are useful for theoretical collision studies of H++He and H+He+.
The electronic structure of bond-alternating and nonalternant conjugated hydrocarbons: Diphenylpolyenes and azulene
Authors: Yip Kwok L. , Lipari N. O. , Duke C. B. , Hudson Bruce S. , Diamond James
Published: February 2003

The electronic structures of the first four diphyenylpolyenes (stilbene, diphenylbutadiene, diphenylhexatriene, and diphenyloctatetraene) and of azulene are evaluated using the new ’’spectroscopic’’ SCF CNDO/S2 molecular orbital model. In the case of the diphenylpolyenes the higher-energy π and σ ionization potentials and the strong allowed 1Bu optical transitions (in the vicinity of hν=3–4 eV) are predicted to within about 0.1 eV by this model. In addition, the inclusion in our analysis of σ as well as π electronic orbitals permits the detailed interpretation of the electronic origin of all prominent maxima in their ultraviolet photoemission spectra. In the case of azulene, all major peaks in the photoemission and absorption spectra are predicted to within ΔE?0.4 eV. The predicted dipole moment is 2.1 D, as compared with a Pariser–Parr–Pople value of 1.9 D. We conclude that the CNDO/S2 model can describe the electronic structure of nonalternant and bond-alternating alternant hydrocarbons, as well as that of the symmetric alternant hydrocarbons considered earlier.
Augmented random phase approximation applied to H2 excitations
Authors: Kaldor Uzi
Published: February 2003

Diogonal ARPA calculations were carried out for H2. The excitation energies previously calculated by many-body perturbation theory were used as comparison standard. The results are given in a table. (AIP)
Energy transfer in CO A 1Π. II. v′=14
Authors: Melton L. A. , Yao H.-T.
Published: February 2003

Previous measurements of collisional quenching of vibrational levels of CO A 1Π have been extended to v′=14. For He, Ne, Ar, Kr, H2, and D2 the rates decrease with increasing vibrational energy. The results are discussed in terms of transfer to nearby electronic states.
Studies of tetra-(p-fluorophenyl)porphyrins by x-ray photoelectron spectroscopy: Effect of reduction on charge distribution in Fe compounds
Authors: Signorelli A. J. , Hayes R. G.
Published: February 2003

We have studied the x-ray photoelectron spectra arising from nitrogen 1s, fluorine 1s, and metal 2p levels of several compounds of tetra- (p-fluorophenyl)porphine, including the free base and several iron compounds. Using the fluorine 1s level as an internal calibrant, we find that the N 1s binding energies agree well with previous results from this laboratory. The difference in Fe 2p binding energy between Fe(II) and low-spin Fe(III) compounds is 1.6 eV. We show that the difference in the charge on Fe between the two types of compounds is equal to some 0.09 electron charges. Satellite structure, observed adjacent to the N 1s photolines, is also discussed.
Microwave spectra of deuterated forms of bicyclo[2.1.0]pentane and the complete molecular structure
Authors: Mathur S. N. , Harmony Marlin D. , Suenram Richard D.
Published: February 2003

The microwave spectra of six deuterium-labeled species of bicyclo[2.1.0]pentane have been observed and analyzed. These data, along with previously published results for the heavy atoms, permit the evaluation of a complete molecular structure for this polycyclic system. Some pertinent structural parameters include: R (C1H) =1.082±0.003 AÅR (C2H, exo) =1.085±0.007 AÅR (C2H,endo) =1.097±0.009 AÅR (C5H,exo) =1.088±0.002 AÅR (C5H, endo) =1.090±0.003 AÅ‖HC2H=109.4°±0.3 °, and ‖HC5H=116.7°±0.4°. In addition, all methylene groups have been found to be tilted in the exo direction by nearly three degrees.
Multipole operators for an arbitrary number of spins
Authors: Sanctuary B. C.
Published: February 2003

Basis states and operators composed of n, in general, different nuclear spins of integer or half-integer values are explicitly constructed. Various coupling schemes are discussed, and transformations between them derived. Following this, a complete set of irreducible tensor operators T(k){V} is constructed which can be used as a basis for expanding operators which depend on n nuclear spins. It is further shown that decomposition of the tensor’s components T(k)q{V} into a sum of products of two irreducible tensor components involves transformation matrices between different coupling schemes. Various properties and commutation relations of the T(k)q{V}’s are given along with a discussion of their reduced matrix elements.
Antiferromagnetic coupling in ytterbium-diluted dysprosium hexaborides
Authors: Krause Jerry L. , Sienko M. J.
Published: February 2003

A series of dysprosium hexaborides in which dysprosium was progressively replaced by ytterbium have been prepared by high temperature reaction between elemental boron and rare earth oxide. Magnetic susceptibility measurements have been performed by the Faraday method over the range 1.6–300 °K. In the interval 63–300 °K, the susceptibilities follow Curie–Weiss laws with an effective moment per dysprosium of 10.6±0.3 Bohr magnetons. The Weiss constants are relatively small, having values of −21.5, −18.5, −14.0, −11.5, and −7.5 °K in DyxYb1−xB6 at x=1, 0.8, 0.6, 0.4, and 0.2, respectively. Below 60 °K, the materials show antiferromagnetism; Néel temperatures were observed to decrease in the sequence 21, 16, 8, and 2 °K for the first four of the above compositions. Interpretation of results via statistical analysis of two, three, and greater-than-three clusters indicates that when isolated magnetic ions are corrected for, the residual magnetism corresponds to a constant exchange energy J, independent of conduction electron concentration. There is no direct evidence that indirect exchange plays a role in the magnetic interaction.
Measurement of the self-diffusion constant of aqueous calcium nitrate solutions by an NMR spin–echo technique
Authors: Gammell P. M. , Meister R.
Published: February 2003

The self-diffusion constant of concentrated aqueous solutions of calcium nitrate has been measured using an NMR spin-echo technique. Solutions with mole ratios of water to calcium nitrate of 4 (the fused tetrahydrate), 6, 8, and 10 were studied over an extensive temperature range including the supercooled regime. Diffusion data were also obtained on solutions with a water to salt mole ratio of 18.5, 55.5, and 222 over a narrower temperature range. The NMR ’’spin-echo’’ diffusion measurement system which was designed and fabricated in this laboratory incorporated provision for both steady and pulsed gradient diffusion measurements. The system provides a method for improved stability of the widths and amplitudes of the magnetic gradient pulses compared to earlier instrumentation. The improved stability was accomplished with development of a special pulse generator and current control circuitry. The diffusion data were represented over its entire range by the empirical Vogel–Tamman–Fulcher (VTF) equation. The fitting parameters were determined and the values of T0D were found to approach that of water for concentrations higher than R=4. For purposes of comparison with viscosity and conductivity data, fitting of the VTF equation was made for the data taken in the same temperature intervals. Results show an almost Arrhenius behavior for the diffusion process in contrast to the viscosity and conductivity. It appears, from these data, that the water has a mobility which at room temperature is about a factor of 3 higher than the mobility for the other transport properties and which does not tend to ’’freeze out’’ as fast as the glass transition temperature Tg is approached. This high mobility may be attributed to either the motion of the entire water molecule independent of the cation hydration complex, or to the cooperative proton transport where the water is partially dissociated by the strong electrical field of the calcium ions (Grotthuss mechanism).
The effect of N2O laser irradiation on the nitrous oxide–copper reaction
Authors: Bass Henry E. , Fanchi John R.
Published: February 2003

The effect of 10.8 μ radiation from a cw N2O laser on the gas–surface N2O–Cu reaction has been measured. The rate equations for energy transfer, optical excitation, and chemical reactions have been examined and, by adjusting the probability of the latter processes for reaction of ground state and vibrationally excited N2O, reasonable agreement with the experimental results is achieved. The probabilities of reaction were found to be 2×10−7 for the N2O(001) mode, and 3×10−11 for all remaining N2O modes. Although experimental results are not sufficiently accurate to specify these values precisely, they do demonstrate the type of information which can be gained from a detailed analysis of laser chemistry results.
Nuclear magnetic resonance studies of the glasses in the system PbO–B2O3–SiO2
Authors: Kim K. S. , Bray P. J. , Merrin S.
Published: February 2003

The 11B and 207Pb NMR spectra have been used to study the structure of glasses in the system PbO–B2O3–SiO2. The results indicate that the glasses do not contain an appreciable number of BO−3 units, and the network-forming lead atoms play an important role in the compositional behavior of N4 (the fraction of boron atoms in BO4 units). The measured values of N4 are analyzed according to a simplified theoretical equation. It is concluded from the N4 analysis that the Pb+2 ions are shared almost evenly between the boron–oxygen and silicon–oxygen networks.
Determination of the proton affinity from the kinetics of proton transfer reactions. VI. The relative proton affinities of N2, Xe, and CO2
Authors: Fehsenfeld F. C. , Lindinger W. , Schiff H. I. , Hemsworth R. S. , Bohme D. K.
Published: February 2003

The position of equilibrium was investigated with the flowing afterglow technique for the proton transfer reactions N2H++Xe?XeH++N2 at 297, 378, and 800°K, N2H++CO2?CO2H++N2 at 700 and 798°K, and XeH++CO2?CO2H++Xe at 800°K. The equilibrium constants measured at each temperature provided values for the proton affinity differences PA(Xe)−PA(N2) =0.63±0.19 kcal mole−1 and PA(CO2)−PA(Xe) =9.7±1.5 kcal mole−1. Rate constants were also determined for the three reactions proceeding under nonequilibrium conditions.
Proton modulation of the electron spin echo envelope in a Nd3+:aquo glass
Authors: Mims W. B. , Davis J. L.
Published: February 2003

The electron spin echo envelope has been measured at 4.2 °K for a frozen solution of NdCl3 in water and alcohol. Measurements were made at a frequency of 9.134 GHz and at Zeeman field settings of 2400, 3200, and 4000 G. At all these field settings the electron spin echo envelope showed a deep modulation associated with frequencies in the vicinity of ωI and 2ωI, where ωI is the free proton precession frequency. The components at ?ωI were clearly visible in the early portion of the envelopes, but components ? 2ωI tended to predominate towards the end. These results have been interpreted by means of a model in which it is assumed that the protons lie on one or more concentric spheres about the Nd3+ ion. In the simplest form of calculation based on this model the proton distribution was taken to be uniform over each of the spherical shells, and the envelope modulation function was calculated by summing contributions weighted according to the area of elements on the surface and the number of protons in the shell. In an alternative approach, the coordinating protons were assumed to be added in a random and uncorrelated manner on the surface of the sphere (or spheres) and a product formula was used to derive the result. Although the main qualitative features of the modulation envelope could be explained in this way, neither form of calculation was sufficiently exact to interpret the data to within the limits of experimental accuracy. The approximation on which the linear sum calculation is based breaks down in the magnetic field regime concerned here. The product calculation is on the other hand inherently inaccurate because of the assumption regarding the random placement of successive protons. We obtain a best value r1= 3.0 ±0.1 Å for the radius of the first proton shell in the Nd:aquo complex. A more accurate value could probably be obtained by working with a higher microwave frequency and higher values of H0. The significance of these results in relation to the design of electron spin echo experiments in organic and biological materials is discussed.
Simulation of molecular spectra: A linear equation solving method
Authors: Golland Ronald W. , Stillman Arthur E. , Schwartz Robert N.
Published: February 2003

The difficulties in using diagonalizing algorithms in the calculation of molecular spectra are discussed. An alternative method is proposed in which the complex matrix equation is solved directly. The inherent inefficiency of this method is largely bypassed by first reducing the matrix into Hessenberg or triangular form by means of similarity transformations. This method is found to yield accurate line shapes even for matrices for which many diagonalizing algorithms fail.
High-temperature thermodynamics of palladium–hydrogen. I. Dilute solutions of H2 and D2 in Pd at 555 K
Authors: Boureau G. , Kleppa O. J. , Dantzer P.
Published: February 2003

The thermodynamic properties of palladium–hydrogen and palladium–deuterium solutions have been studied by a combined calorimetric–equilibrium method at 555 K for nH/nPd<0.01. For these dilute solutions the relative partial enthalpies and excess entropies of hydrogen are found to vary strongly with compostion, in a way which is not consistent with the known thermodynamic behavior of more concentrated alloys. From the limiting values of the partial enthalpies of solution for hydrogen (−2.27 kcal mol−1) and for deuterium (−1.80 kcal mol−1) we calculate from the Einstein model a vibrational frequency ν̃H for hydrogen in palladium of 695 cm−1, in reasonable agreement with the neutron scattering result for dilute solutions of Kley et al. (∼600 cm−1), but differing significantly from the much lower value of 420 cm−1 for PdH0.6 found by Bergsma and Goedkoop. The difference between the limiting values of the partial excess entropy of hydrogen (5.15 cal K−1⋅mol−1) and of deuterium (6.91 K−1⋅mol−1) is in excellent agreement with the value calculated from ν̃H and ν̃D=ν̃H/√2.
Paramagnetic resonance of Dy3+ in CdF2
Authors: Chang Te-Tse , Cohen Martin I.
Published: February 2003

Paramagnetic resonance of Dy3+ substitutional for Cd in CdF2 was observed at 24 GHz and 4.2 K. The cubic spectrum and the orthorhombic spectrum of samples cross doped with Li, Na, or K were studied. The g factors are as follows: for the Γ7 transition, g=7.4250; for Γ8 transitions in cubic symmetry, g=2.4514; and for Γ8 transitions in orthorhomic symmetry, g1̄10=2.1025, g001=8.6613, and g110=10.1846.
The formation of complexes of the type X2+⋅R in rf rare gas glow discharges
Authors: Coburn J. W. , Kay Eric
Published: February 2003

Complexes of the type X++⋅R (where X is an atom with reasonably low first and second ionization potentials and where R is a rare gas) have been observed in rf rare gas glow discharges. These complexes are believed to be formed by associative ionization of the singly charged ion X+ : X+ +Rm+→X++⋅R+e.
Dynamics of molecular reorientational motion and vibrational relaxation for symmetric top molecules in the liquid phase
Authors: Constant Monique , Fauquembergue Renaud , Descheerder Pierre
Published: February 2003

Detailed studies of the molecular relaxation processes in pure liquid t-butyl chloride (TBC) and t-butyl bromide (TBB) and in solutions in carbon tetrachloride and in n-hexane have been made using several experimental techniques. Single particle reorientational motions perpendicular to the symmetry axis were studied using Raman scattering and a comparison of these results with those obtained from depolarized Rayleigh scattering allowed an evaluation of the importance of correlations in orientation between pairs of molecules in the two systems, also, collision induced scattering was not found to be significant. Additional cross comparisons of related data obtained using infrared absorption and dipolar absorption were made. In all cases, the original experimental data were subjected to Fourier transform analyses so that the time evolution of the resulting correlation functions could be studied. In general, at short times the reorientational motions are inertial, but at long times exponential decay of the correlation functions is observed. The mechanism of vibrational relaxation in TBC and TBB was also studied by analysis of the correlation functions corresponding to the isotropic Raman scattering in the pure liquids and in solution. In addition, an efficient computational model for the theoretical calculation of any orientational vectorial correlation function has been developed. The theoretical correlation functions could be compared directly with those determined experimentally.
The effective direct correlation function: An approach to the theory of liquid solutions
Authors: Adelman S. A.
Published: February 2003

An approach to the theory of liquid solutions based on the concept of the effective solute direct interaction is presented. The Ornstein–Zernike (OZ) matrix equation for an n-component mixture containing p solute components and q=n−p solvent components is rigorously transformed to an effective p-dimensional OZ equation explicitly involving just the solute components. Solvent effects enter the solute OZ equation through a pxp matrix of modified or effective solute direct correlation functions. The osmotic thermodynamic properties of the solution are related to the effective direct correlation function by formulas identical in structure to those which relate the corresponding thermodynamic properties of a pure fluid to the direct correlation function of the fluid. An analysis of the small wave vector k limits of several effective direct correlation functions important in the description of polar–ionic mixtures is given. The effective ion–ion direct correlation function for small k is proportional to a Coulomb potential shielded by a dielectric constant dependent on ion concentration. From the low ion density limit of this result one can recover Debye–Hückel theory. Thus the effective direct correlation function provides a convenient bridge between a first principles approach to electrolyte theory based on a molecular polar solvent and the usual continuum dielectric solvent model. From a similar analysis of the small k forms of the dipole–dipole and charge dipole effective direct correlation functions, one can demonstrate both Debye shielding and dielectric screening of the charge–dipole interactions and Debye shielding of the dipole–dipole interaction.
14N nuclear quadrupole resonance and relaxation measurements of sodium nitrite
Authors: Petersen G. , Bray P. J.
Published: February 2003

Measurements of the quadrupole coupling constant, asymmetry parameter, inverse linewidth parameter T*2, spin–spin relaxation time T2, and spin–lattice relaxation times T1s and T1l are reported for sodium nitrite in the temperature region from 77–467 °K. The relations between the spin–lattice relaxation times and the transition probabilities W+, WΔ, and W− are derived for a spin one system, and the transition probabilities are calculated from the T1 data. The results are compared with other NaNO2 studies and support the work of Avagadro et al. in the temperature region near the ferroelectric phase transition. They also indicate the existence of short-range order above this transition.
Hartree–Fock diamond results illustrating two integral approximations
Authors: Greene R. L. , Euwema R. N.
Published: February 2003

Two different procedures for approximating the smaller two-electron integrals in ab-initio molecular and crystalline Hartree–Fock calculations are discussed and illustrated on diamond. One approximation is due to H. Kashiwagi. The other uses two alternate expressions for the first-order density matrix. The usual expression in terms of the wavefunction basis is used for the integrals involving basis function products with a large pseudocharge. A more approximate expression in terms of the total charge associated with each atom–atom pair is used for integrals involving the smaller basis function products. Crystalline Hartree–Fock diamond results are given to allow comparison of total energies, one-electron eigenvalues, x-ray structure factors, and directional Compton profiles.
Theoretical elastic behavior for hexagonal boron nitride
Authors: Green J. F. , Bolland T. K. , Bolland J. W.
Published: February 2003

Elementary potentials are applied to a study of hexagonal boron nitride. All second- and third-order elastic constants are calculated and compared with the available experimental data. The planar bending constant, important to the semicontinuum theory for layered crystals, is obtained from a simple model.
Photoabsorption cross sections of two-electron atoms by the coordinate rotation method: Application to H− and several states of He
Authors: Rescigno T. N. , McCurdy C. W. , McKoy V.
Published: February 2003

The coordinate rotation method, recently extended by us to treat photoabsorption processes, is used to obtain photoabsorption cross sections for several two-electron atoms. The calculations are performed using standard configuration–interaction methods; the need for atomic continuum wavefunctions is completely avoided in this approach. We have computed the photodetachment cross section of H− and photoionization cross sections for He in its ground and 2 1S states. In all cases, the computed cross sections agree well with results obtained by numerical integration and with available experimental data.
A Monte Carlo study of ion–water clusters
Authors: Mruzik Michael R. , Abraham Farid F. , Schreiber Donald E. , Pound G. M.
Published: February 2003

The procedures developed in this paper have been employed to calculate theoretical free energies of formation of ion–water clusters for comparison with experiment. Gibbs free energies were calculated for the gas phase reaction, ion(H2O)N−1+H2O(vapor)=ion(H2O)N, for the Li+, Na+, K+, Cl−, and F− ions and for N=1–6. The standard state for all calculations was taken as 298 °K and 1 atm. The Monte Carlo method was used to evaluate the appropriate classical expressions of statistical mechanics by employing the intermolecular potential functions recently developed from ab initio Hartree–Fock calculations. Enthalpies, entropies, and structural information were also calculated. Agreement with experiment is sufficiently good to demonstrate the feasibility of this approach.
Reply to ’’Comment on inelastic scattering in atom–diatomic molecule collisions. I. Rotational transition in the sudden approximation’’
Authors: Stallcop James R.
Published: February 2003

A reply is made to the comments by pack in the preceeding Comment and it is argued that the assumptions in paper discussed [Stallcop, J. Chem. Phys. 61, 5085 (1974)] are valid. (AIP)
A polarized single crystal Raman study of the librational phonons in p-diiodobenzene
Authors: Cramer S. P. , Hudson B. , Burland D. M.
Published: February 2003

Single crystal polarized Raman spectra of p-diiodobenzene in the region from 0 to 300 cm−1 are presented for sample temperatures from 2 to 330 K. Eleven of the twelve predicted gerade librational phonons are unambiguously assigned in terms of their space group symmetries. The temperature dependence of the Raman spectra does not show a soft gerade phonon at the nearly second-order phase transition which occurs at 326 K. A significant anharmonicity for molecular motions above the I–I axis is indicated by the observation of overtones and combinations and broadening of these phonons as the temperature is raised from 2 K.
The energy distributions of secondary electrons from Ar, N2, H2O, and H2O with clusters present
Authors: Mathis R. F. , Vroom D. A.
Published: February 2003

Crossed beam measurements have been made of the energy spectra of secondary electrons resutling from collisions of 1 keV primary electrons with N2, Ar, H2O, and H2O with clusters present. Only those electrons emitted normal to the primary beams were detected. A thorough description of the apparatus is given.
Infrared determination of the orientation of molecules in stearamide monolayers
Authors: Chollet Pierre-Alain , Messier Jean , Rosilio Charles
Published: February 2003

The orientation of molecules in the monomolecular stearamide monolayers has been studied by infrared linear dichroism. By comparing the transmission absorption spectra carried out at different angles of incidence with the reflection absorption spectra obtained by depositing the monolayers on a metal substrate, the orientation of the dipole transition moments for a great number of normal vibration modes of the molecules may be determined to within a few degrees accuracy. Given certain assumptions, the orientation of the molecules themselves can then be deduced.
NMR and molecular dynamics in the choline ion
Authors: Graham John D. , Hannon Ralph H.
Published: February 2003

Proton magnetic resonance spectra of three crystalline choline halides have been obtained over a temperature range of 77 to 440 °K. In all of these materials the line shapes are strong functions of temperature with multiple changes observed for each substance. Above 353 °K, the temperature at which a crystal–crystal phase transition occurs, the second moment of 0.9 G2 for choline chloride reflects the presence of isotropic reorientation of the choline ions in the solid. This is just the temperature at which the extremely high radiation sensitivity ceases, suggesting that the existence of this dynamic behavior renders the crystal incapable of supporting the decomposition reaction observed below this temperature. Similar behavior is also observed in choline bromide at a higher temperature. From the temperature dependence of the correlation frequency, activation energies for the motional processes were determined and found to be in the range of 3–4 kcal/mole at low temperature and 12–15 kcal/mole for the high temperature molecular motions. Rigid lattice second moment values of 29 G2 were obtained and reductions of the second moments at higher temperature were employed to characterize the motional processes including the unusual occurrence of self-diffusion in solid choline iodide above 373 °K.
Infrared spectra of matrix-isolated UO+2 and NO−2
Authors: Green D. W. , Gabelnick S. D. , Reedy G. T.
Published: February 2003

The reactions of UO and UO2 with NO and NO2 have been studied by infrared spectroscopy using the matrix isolation technique. Codeposition of vaporized UO and UO2 with NO2 and with NO gases in an argon matrix at 14 K resulted in the production of the UO+2 molecular ion paired with either a NO−2 or NO− anion. Three different reactions have been observed to yield a UO+2 cation product: (1) UO2+NO2, (2) UO2+NO, and (3) UO+NO2. Infrared absorption frequencies in the range 1150–1190 cm−1 have been measured and interpreted as the stretching modes of bent (bond angle = 109°) N16O−2, N16O18O−, and N18O−2 ions paired with UO+2. Infrared absorption frequencies in the range 770–900 cm−1 have been measured and interpreted as the stretching modes of linear U16O+2, U16O18O+, and U18O+2 paired with either NO− or NO−2.
Dielectric and pressure virial coefficients of imperfect gases. VII. CF3H-Ar and CFH3-Ar mixtures
Authors: Copeland T. G. , Cole R. H.
Published: February 2003

Mixed dielectric (Bε12) and pressure (Bp12) second virial coefficients of CF3H–Ar and CFH3–Ar mixtures of 50 °C have been obtained by cyclic expansion and low pressure dielectric measurements. These give Bε12=85 cm6/mole2 for CF3H–Ar and 2 cm6/mole2 for CFH3–Ar, the former being much larger and the latter much less than calculated for spherical polar molecule interactions and Lennard–Jones 12–6 central force parameters derived from Bp12 and interaction viscosity η12. The differences can be accounted for by values of the Buckingham and Pople shape factor of D=−0.18 for CF3H and +0.32 for CFH3; these values are in reasonable agreement with results of Copeland and Cole for the pure polar gases and with estimates from molecular models by Barnes and Sutton.
The effect of shape factor on the quantal collision integrals
Authors: Dutta S. , Rakshit A. B.
Published: February 2003

Quantal collision integrals taking into account the shape factor which represents a nonspherical repulsive part of molecular interactions have been evaluated by using the tabulations of collision integrals for the Lennard-Jones (12:6) potential. The angular part of the interactions has been averaged by assuming that the colliding particles maintain the same relative orientation during an encounter and that all relative orientations have equal probability. The results show that the shape factor has significant influence on the quantal collision integrals. Attempts have been made to interpret the viscosity and thermal diffusion factor data for H2 and D2 gases. Another important result of these calculations is that, contrary to earlier assumptions, it is necessary to consider the effect of shape factor on viscosity for the precise determination of quadrupole moment of these substances from second virial and viscosity data.
Local phase and renormalized frequency in inhomogeneous chemioscillations
Authors: Ortoleva P.
Published: February 2003

Inhomogeneous evolution of a chemically reacting system capable of a homogeneous oscillation is analyzed in terms of a nonsecular perturbation method. This ’’phase diffusion’’ theory takes account of the local phase shifts and frequency renormalization that occurs due to the interaction of reaction and diffusion. The theory is used to show that oscillator like plane waves are stable to small perturbations. Boundary value problems including those for a finite volume impermeable vessel, a ring shaped vessel (periodic boundary condition) and catalytic walls and membranes are shown to lead to stable oscillatory states some of which are inhomogeneous for all times. The structure of the theory allows for clear qualitative interpretations. Several experiments are suggested for the purpose of verification of the theory and the phenomena predicted.
Photoionization mass spectrometric study of formaldehyde H2CO, HDCO and D2CO
Authors: Guyon Paul Marie , Chupka William A. , Berkowitz Joseph
Published: February 2003

Photoionization efficiency curves for H2CO+, HDCO+, D2CO+ and HCO+, DCO+ and CO+ fragment ions are obtained. The ionization potentials of H2CO, HDCO, and D2CO thus determined are, respectively, 10.868, 10.879, and 10.882 eV. The appearance potential of HCO+ fragment is observed at 11.92±0.01 eV, from which the dissociation energy of H2CO+, the proton affinity of CO, and the ionization potential of HCO are inferred. The heat of formation ΔHf00 (HCO+) =196.2±0.5 kcal/mole is obtained, a value lower than any one previous determination. From the abundance ratios measurements the variation of the mass spectrum with photon energy is determined, and hydrogen isotope effects are measured. The observation of a metastable transition (D2CO+)m→DCO++D with a threshold some 2 eV above the dissociation limit is discussed along with the dissociation mechanisms with the help of correlation diagrams. Finally, the finer structure in the photoionization efficiency curves is analyzed in terms of preionized Rydberg series converging to the second and third electronic state of the ion.
A simple empirical function for density computation using the measured refractive index of some selected hydrocarbons
Authors: Hädrich Jürgen
Published: February 2003

Refractive index and density data of gaseous and liquid ethane, propane, n-butane, n-pentane, and liquid n-hexane were fitted to an empirical expression of the Lorentz–Lorenz function proposed by Eisenberg, Reisler, and Minton for application to liquids. This expression takes into account the dependency of the electronic polarizability ?e on density and temperature. This paper presents a way of applying this expression to liquids and gases to compute the density of hydrocarbons with an uncertainty Δρ/ρ?±0.1%.
The vacuum ultraviolet spectra of ethyleneimine and trimethyleneimine
Authors: Clark Patricia A. , Pickett Lucy W.
Published: February 2003

Experimental studies of the vacuum ultraviolet absorption spectrum of ethyleneimine in the region 40 000–60 000 cm−1 yield maxima at 6.32 and 7.15 eV, with oscillator strengths of 0.003 and 0.086, respectively. Trimethyleneimine has in the same region a band maximum at 6.44 eV with an oscillator strength of 0.047. Semiempirical SCF–CI calculations using the CNDO method with Sichel–Whitehead parameters are reported on 3-, 4-, and 5-membered ring compounds in the series of saturated alkanes, ethers, and amines and the predicted transitions are compared with experimental interpretations of the nature of the excitations.
Statistical model calculations of atomic polarizabilities
Authors: Bruch L. W. , Lehnen A. P.
Published: February 2003

The static electric dipole polarizabilities of neutral inert gas atoms are obtained with the Thomas–Fermi (TF) and the Thomas–Fermi–Dirac (TFD) statistical models. The TF model yields an infinite polarizability; the TFD model yields polarizabilities which are much larger than experiment, though the percent error decreases with increasing atomic number.
Structure of the OH stretching vibrational band of formic acid
Authors: Wolff Hans , Müller Harald , Wolff Erika
Published: February 2003

The infrared spectrum of self-associated HCOOH as well as the infrared spectra of the mixed adducts of HCOOH and DCOOH with acceptors of different basicity are analyzed. Contrary to present interpretations involving the coupling of stretching and intermolecular vibrations, Fermi resonance with overtones and combination tones is proven to be the true and single cause for the submaxima in the OH stretching vibrational range.
Two-dimensional spectroscopy. Application to nuclear magnetic resonance
Authors: Aue W. P. , Bartholdi E. , Ernst R. R.
Published: February 2003

The possibilities for the extension of spectroscopy to two dimensions are discussed. Applications to nuclear magnetic resonance are described. The basic theory of two-dimensional spectroscopy is developed. Numerous possible applications are mentioned and some of them treated in detail, including the elucidation of energy level diagrams, the observation of multiple quantum transitions, and the recording of high-resolution spectra in inhomogenous magnetic fields. Experimental results are presented for some simple spin systems.
Scattering of thermal helium beams from high Miller index (stepped) platinum crystal surfaces
Authors: Ceyer S. T. , Gale R. J. , Bernasek S. L. , Somorjai G. A.
Published: February 2003

Helium beams generated by a 300 K source were scattered from single crystal platinum surfaces. The angular distribution of the scattered beam was monitored as a function of azimuthal angle φ and incident angle ϑi. The effect of the presence of atomic steps on the angular distribution of scattered helium atoms was studied on a crystal surface composed of terraces on the average five atoms in width separated by steps of monatomic height. Rainbow scattering is observed when the steps are oriented perpendicular to the incident beam direction indicating strong modulation of the angular distribution by the periodic step potential. Only specular scattering is observed when the incident beam impinges on the crystal along the step edges which indicates minimal effects of the presence of steps on the scattering distribution. These results as well as the absence of diffraction are in good agreement with previous theoretical calculations.
ENDOR studies of methyl radicals in irradiated single crystals of CH3COOLi⋅2H2O
Authors: Toriyama Kazumi , Nunome Keichi , Iwasaki Machio
Published: February 2003

The methyl radicals trapped in single crystals of CH3COOLi⋅2H2O irradiated at 77 °K have been studied by ENDOR. The proton hyperfine coupling tensor was determined to be (−21.30, −20.57, −21.61) G. The absolute sign of the coupling was determined in referring to the nuclear dipole–dipole interaction. The deviation from axial symmetry indicates that the methyl radical undergoes hindered oscillation about the second axis in the radical plane in addition to rapid reorientation about the C3 axis. The superhyperfine coupling tensors were determined for all of the seven neighboring protons within 5 Å from the radical carbon atom. The nearest neighboring CH3 and water protons gave the tensors (3.07. 0.24, 0.26) and (2.01, −1.16, −1.00) G, respectively. The dipolar terms of these neighboring protons and others lead to the conclusion that the methyl radical is trapped in practically the same position with the same orientations as those of the methyl group in the undamaged molecule. The precise analysis suggests that the recoil displacement of the ĊH3 radical along the broken C–C bond is less than 0.3 Å. To facilitate analyses of the spectra, the second order effects on the ENDOR transition frequencies as well as the transition probabilities have been formulated in compact forms.
Determination of interaction force constants for n-alkanes using molecular beam techniques
Authors: Schmidt T. W. , Guillory J. P.
Published: February 2003

Effective interaction force constants ratios, Cij/Cii, for methane-n-alkane mixtures have been determined from time-of-flight measurements using a molecular beam technique. The Cij/Cii ratios were obtained from changes in the velocity distribution due to scattering. Mixed second virial coefficients, B12, were calculated from C12/C11 values assuming a Lennard-Jones potential function model. The C12/C11 values for mixtures of methane with ethane, propane, n-butane, and n-pentane were found to be 1.66±0.15, 2.49±0.12, 3.67±0.31, and 5.09±0.23, respectively, at room temperature. These results agreed well with values calculated from PVT data. C12/C11 values were also determined at temperatures down to −150 °C using the molecular beam technique.
A study of the electronic structures of SN, S2N2, S4N4, NO, and N2O2 and their implications for (SN)x
Authors: Salahub D. R. , Messmer R. P.
Published: February 2003

SCF–Xα–SW calculations have been carried out for SN, S2N2, and S4N4 as well as the analogous oxides NO and N2O2. The electronic charge distribution of the sulfides is remarkably uniform leading to highly polar SN bonds (∼S+1/2N−1/2) in contrast to the oxides where the NO bonds involve less charge transfer and in the opposite direction. The inclusion of d functions on sulfur is shown to have only minor effects on the electronic structure of the sulfides. Contour plots of several of the molecular orbitals are presented. The importance of the polar bonds in S2N2 in determining the structure of metallic polymeric sulfur nitride (SN)x is discussed. Predictions are made on the likelihood of forming (SN)x analogs with a different Group V or Group VI element.
Possible rotational state effects in He–HD total scattering cross sections
Authors: Lang Neil C. , Kinsey James L.
Published: February 2003

Total scattering cross sections for 4He–HD, D2–4He, and D2–3He are reported for relative velocities between 800 and 2400 m/s. The scattering of D2–4He and D2–3He can be described very well by the same isotropic potential. This potential however fails to predict the observed 4He–HD cross sections. It is suggested that this may be evidence of the asymmetry of the He–HD interaction.