bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of the CNDO Method in Spectroscopy. III. Monosubstituted Benzenes and Pyridines
Authors: Del Bene Janet , Jaffé H. H.
Published: February 2004

The modified CNDO method previously reported has been applied to the calculation of a series of monosubstituted benzenes and pyridines, namely, aniline, anilinium ion, benzonitrile, nitrosobenzene, phenol, phenoxide ion, toluene, pyridinium ion, pyridine-N-oxide, 1-hydroxy-pyridinium ion, the aminopyridines, and the cyanopyridines. The calculated values of the transition energies and corresponding oscillator strengths are in good agreement with available experimental data on the electronic spectra of these compounds. An analysis of the lower-energy excited states by means of the calculated results suggests that there is an astonishingly small amount of charge-transfer character associated with the observed ultraviolet bands. The calculations indicate that the changes in charge densities in going from the ground state to the lowest energy π → π* excited state can be related to the Hammett σ's for the substituents.
Electron Spin Resonance Studies of Gamma-Irradiated Glasses Containing Lead
Authors: Kim Y. M. , Bray P. J.
Published: February 2004

Electron spin resonance (ESR) studies have been made of lead borate and lead silicate glasses gamma irradiated and maintained at liquid-nitrogen temperature. In lead borate glasses of low PbO content, a spectrum similar to the five-line spectrum which has been observed in alkali borate glasses was observed, while a different, asymmetric spectrum appeared in glasses of high lead oxide content. This latter spectrum is identified as due to the O− center near one or more Pb++ ions.
Off-Diagonal Hypervirial Theorems as Constraints
Authors: Chong D. P. , Benston Margaret Lowe
Published: February 2004

The method of constrained variation is extended to off-diagonal constraints. We apply the method of linear constrained variation to make approximate wavefunctions satisfy any particular off-diagonal hypervirial theorem. Attention is then focused on atomic transition probabilities. Numerical examples are presented to demonstrate the feasibility of obtaining the same result for the probability of a given transition using the different alternative expressions.
Molecular Structure of CF3PF4 from Infrared Spectroscopy
Authors: Griffiths James E.
Published: February 2004

The structure of CF3PF4, indicated by the complete gas-phase infrared spectrum from 4000 to 33 cm−1, is a trigonal bipyramid in which the CF3 group assumes an equatorial position. The spectrum agrees with selection rules derived from the C2υ point group, or possibly from the C3 point group, and all of the active fundamentals on the basis of a C2υ model were located. Raman spectra of the liquid from −70° to −115°C agree with the infrared results. The relative intensities and the frequencies obtained for the fundamentals of CF3PF4 parallel those of the structurally related CH3PF4 molecule. Although no evidence for a C3υ molecule was recorded, the presence of such a species in a dynamic exchange formalism is not precluded. In fact, the microwave results which favor such a species and the infrared and NMR results, when considered together, indicate an exchange process in which both the CF3 group and the F atoms all participate. The exchange can be thought of as a collision stabilized process.
Effect of Variation of the Bimolecular Rate Constant with Chain Length on the Statistical Character of Condensation Polymers
Authors: Nanda V. S. , Jain S. C.
Published: February 2004

In this paper we investigate the effect of variation of the bimolecular rate constant with chain length on the statistical character of condensation polymers. The problem in general is too complicated to permit even an approximate solution. Nevertheless, for the case where the rate constant varies linearly with chain length, expressions for the various quantities of interest can be deduced. These results, apart from showing certain quantitative features characteristic of the assumed variation, enable us to draw certain general conclusions. Finally we examine some available experimental data in the light of our theoretical results.
Infrared Study of Matrix-Isolated Chlorinated Tetrahedral Molecules
Authors: King S. T.
Published: February 2004

The infrared spectra of CH3Cl, CH3CH2CH2Cl, CH2Cl2, HCCl3, (CH3)–CCl3, FCCl3, BrCCl3, CCl4, and SiCl4 in an argon matrix at 20°K were studied. The chlorine isotopic splitting pattern of the bands in the 500–1300-cm−1 region were recorded, and most of the isotopic frequencies were assigned. Normal-coordinate calculations have been performed on these molecules to establish complete chlorine isotopic splitting patterns of all the fundamental vibration bands. Different isotopic species have different Fermi resonance interactions in the same band system; examples of this were observed in the spectra of FCCl3 and CCl4.
Electronic Structure of Cage Amines: Absorption Spectra of Triethylenediamine and Quinuclidine
Authors: Halpern Arthur M. , Roebber John L. , Weiss Karl
Published: February 2004

The gas-phase electronic absorption spectra of triethylenediamine and quinuclidine have been measured. Each compound shows two strong bands in the regions 1650–2500 Å and 1650–2300 Å, respectively, which have well-resolved vibrational structure, as well as very weak, structured absorption at longer wavelengths (2560–2700 Å for triethylenediamine and 2300–2500 Å for quinuclidine). An essentially complete vibrational analysis of all but one of these bands has been accomplished. The results indicate a substantial change in the equilibrium positions of the nuclei in the excited states relative to the positions in the ground state. For quinuclidine, the most prominent excited state vibrational mode can be correlated with the ground-state mode which corresponds to an approach to planarity of the nitrogen-bearing end of the molecule. For triethylenediamine, ambiguities in the ground-state assignments preclude conclusions about the upper state geometry. By comparisons with the spectra of other amines, the strong electronic bands of triethylenediamine and quinuclidine are assigned as n → p Rydberg transitions. Exciton model calculations of the shift of the first strong band of triethylenediamine relative to the corresponding band in quinculidine predict changes of about 3000 cm−1 to lower energy for an n → 3pz transition and about 1500 cm−1 to higher energy for an n → px y transition. The observed shift of the 0–0 band is 3920 cm−1 to lower energy, which is clearly in accord with z polarization. The weak, longer-wavelength absorption of the cage amines is tentatively considered to arise from sub-Rydberg transitions.
Hyperfine Splitting of the Ground State of Lithium
Authors: Hardcastle D. L. , Gammel J. L. , Keown R.
Published: February 2004

The hyperfine splitting and energy are calculated for both Hartree–Fock (HF) and extended Hartree–Fock (EHF) wavefunctions for the ground state of lithium. The EHF wavefunction is a two-determinant eigen-function of S2 and Sz. A variational principle is used to give three coupled integrodifferential equations that are solved self-consistently. The coupled equations are solved by an iterative numerical integration technique and the resulting energy is better than any similar previous calculation. For the EHF approximation the energy is found to be −14.89496 and the hyperfine splitting constant 〈f〉 is 2.400. For the HF approximation the energy is −14.86544 and the 〈f〉 is 2.097. The results are compared with similar, previous calculations.
Ion–Molecule Reaction Studies from 300° to 600°K in a Temperature-Controlled Flowing Afterglow System
Authors: Dunkin D. B. , Fehsenfeld F. C. , Schmeltekopf A. L. , Ferguson E. E.
Published: February 2004

The flowing afterglow technique for ion-neutral reaction rate constant studies has been modified to cover a range of gas temperature from 82° to 600°K. The experimental apparatus is described and rate constants for six reactions between 300° and 600°K are reported. The reaction of He+ with N2 is found to have a rate constant 1.2 × 10−9 cm/3sec, independent of temperature in this range. The reaction of O+ with CO2 has a rate constant 1.1 × 10−9 cm3/sec at 300°K, decreasing slightly to 8 × 10−10 cm3/sec at 600°K. The reaction of N+ with O2 appears to have a rate constant 6 × 10−10 cm3/sec throughout this temperature range. The rate constant for charge transfer of N2+ with O2 is measured to be 4.7 × 10−11 cm3/sec at 300°K, decreasing to about 2 × 10−11 cm3/sec at 500°K. The rate constant for the reaction of O+ with O2 decreases from 2 to 1.3 × 10−11 cm3/sec, and the rate constant for O+ + N2 decreases from 1.2 × 10−12 cm3/sec to about 6 × 10−13 cm3/sec between 300° and 600°K.
Polymer-Melt Viscosity and the Glass Transition: An Evaluation of the Adam–Gibbs and the Free-Volume Models
Authors: Miller A. A.
Published: February 2004

The Adam–Gibbs and the free-volume theories of polymer-melt viscosity and the glass transition are applied to the infinite polymethylene chain by comparing the exponential terms in the respective viscosity equations: 2.3B / (T − T0) = C / TSc = b / φ. It is shown that the configurational entropy Sc and the free volume φ, which apply in these equations, constitute only a portion of the thermodynamic “excess” liquid entropy and volume. In an alternate form of the A–G equation: C / TSc = Δμz* / RT, if Δμ is identified as 2.3BR, zg* turns out to be equal to the “activation volume” expressed as monomer segments at Tg. In the Adam–Gibbs context, the glass transition is assumed to be characterized by the constant: zg*Scg = 5.5 e.u. On this basis, a value of Sc is derived for polystyrene at Tm which agrees with independent estimates. Values of the A–G and the free-volume parameters are reported for (CH2)∞, polystyrene, and polyisobutylene, and relationships between Sc and φ are presented.
Single-Crystal Spectra of Ferrimyoglobin Complexes in Polarized Light
Authors: Eaton William A. , Hochstrasser Robin M.
Published: February 2004

The polarized absorption spectra of ferrimyoglobin cyanide, ammonia, azide, fluoride, formate, and water (acid ferrimyoglobin) complexes in single crystals are described. Special emphasis is placed on the polarization-ratio (PR) spectrum—the spectrum of the intensity ratio for light absorbed along and perpendicular to the crystal symmetry axis. It is shown that the PR spectrum magnifies spectral effects that are otherwise obscured by wide absorption bands, and it is shown to be a most useful parameter for studying the spectra of those systems that are intrinsically broad and whose spectra do not show any sharpening at low temperature. The results confirm many general features of porphyrin spectra such as the polarization of the B and Q states, the vibronic nature of the Qv state, and the intensity imbalance in the Q0 state. The substances studied span a variety of spectral types, from low-spin, through mixed-spin, to high-spin iron complexes. The high-spin spectra show, in addition to porphyrin bands, charge-transfer bands that are associated with iron dxz and dyz orbitals. The spectra manifest the splitting of these iron dπ orbitals, and some reasons for this are discussed. The Soret (B) bands are also shown to be split. The PR spectrum of the low-spin azide complex uncovered a new excited state, transitions to which were shown to be polarized out of plane. Possible mechanisms for this transition are discussed. The absolute intensity of myoglobin crystal absorption spectra are shown to be unchanged from the solution values, indicating that the heme environment is comparable in the two media. The heme orientation is shown to be identical, within the precision of the subtle variations of the PR spectrum, for all the derivatives studied, with the possible exception of the azide.
Molecular Dynamics. VI. Free-Path Distributions and Collision Rates for Hard-Sphere and Square-Well Molecules
Authors: Einwohner T. , Alder B. J.
Published: February 2004

Free-path distributions and collision rates for systems of hard-sphere and square-well molecules are computed and compared to simple models. Mean free paths for solids and dense fluids are found to be within 2% of those predicted by dividing the kinetic-theory mean free path by the relative probability of two molecules in contact. These mean free paths are much smaller than a mean intermolecular spacing or even the diameter of a free volume. For hard-sphere and hard-disk fluids, free-path distributions are found to be monotone decreasing, nearly exponential, and when scaled by the mean free path, nearly density independent for all fluid densities. This density independence precludes any essential difference in transport mechanisms between dilute and dense fluids based on independent free paths. Scaled free-path distributions for hard-sphere and hard-disk solids are found to agree with those of their fluid counterparts except for long free paths where the smaller free-path distribution for solids reflects their increased molecular localization. The free-volume theory and its simple extensions are shown to be qualitatively inconsistent with the shape of observed free-path distributions in solids. For fluids of square-well molecules, the rate of hard-core collisions is found to be insensitive to the presence of the square well, and so is the free-path distribution as well as selected values of the pair-distribution function. These features are in good agreement with the van der Waals hypothesis, which neglects soft collisions. For dense liquids, hard-core collisions are in the majority, invalidating the hypothesis that soft-core collisions cause a Brownian motion between successive hard-core collisions.
Crystallite Orientation Distribution in Biaxially Oriented Polyethylene
Authors: Krigbaum W. R. , Adachi T. , Dawkins J. V.
Published: February 2004

The procedure of Roe for describing the crystallite orientation in polycrystalline samples having general texture is tested using two samples of biaxially drawn polyethylene. An automated four-circle diffractometer was used to obtain 12 pole figures (4332 fixed points) for the film having stretching ratios 3.0 × 2.0, and 13 pole figures (4693 fixed points) for the film having stretching ratios 1.7 × 1.6. The selection of measurement geometry, procedures for data reduction and correction, and methods for computer calculation of the crystallite orientation distribution are described. While the best representation of the crystallite orientation distribution was obtained from the series of generalized associated Legendre polynomials by retaining terms through l = 12, the characteristic features of the distribution are already evident when the series is truncated at l = 6. Thus, for materials belonging to the orthorhombic crystal class, as few as four or five pole figures suffice to determine the principal features of the crystallite distribution in biaxially oriented samples. The crystallographic b axis is found to be normal to the film plane in both samples examined. The a and c axes are nearly randomly arranged in the film plane for the sample having stretching ratios 1.7 × 1.6, while the 3.0 × 2.0 sample exhibits a combination of this texture and that previously observed for uniaxially drawn polyethylene.
Absorption Spectra of Erbium Tricyclopentadienide at Liquid-Helium Temperature
Authors: Pappalardo R.
Published: February 2004

The absorption spectra of Er(C5H5)3 in 2-methyl tetrahydrofuran have been studied at room temperature, liquid-nitrogen, and liquid-helium temperature. Hypersensitive line groups have been found at ∼19 000 and ∼26 000 cm−1. Large splittings of J = 32 levels have also been observed. A correlation between hypersensitivity and large second-degree terms of the crystalline potential is suggested. Although some line groups in Er(C5H5)3 showed unusually large splittings, no drastic changes in the usual energy-level pattern for 4f11 were found in this volatile, organometallic compound of erbium.
Flux and Speed Distributions of Molecular Beams after Scattering by Metal Surfaces
Authors: Fisher S. S. , Hagena O. F. , Wilmoth R. G.
Published: February 2004

High-intensity, nearly monoenergetic, nozzle-type molecular beams together with a sensitive time-of-flight detection system have been employed to study the scattering of argon and nitrogen from polycrystalline nickel and stainless-steel surfaces. The apparatus has allowed the precise measurement of essentially complete flux and speed distributions of the particles reflected in the plane of the incident beam and the target normal. Incident energy (0.065–0.24 eV), surface temperature (300°–1000°K), angle of incidence, and angle of reflection have been varied. At room temperature, prior to any heat treatment in the apparatus, these unpolished targets exhibit essentially the classical diffuse scattering pattern with almost complete thermal accommodation. With the Ni surfaces tested, outgassing and annealing at approximately 900°K resulted in highly lobular scattered flux patterns for target temperatures between 550° and 950°K. These patterns are accompanied by a marked angular variation of the reflected-particle speed distribution, which differs the more from the fully accommodated Maxwellian distribution the farther the angle of scattering is from the surface normal. These lobular flux patterns are in qualitative agreement with the predictions of the so-called “hand-cube” model, but for the scattered particles the angular variation of the mean speed is smaller, and the angular variation of the relative spread in kinetic energies is greater, than predicted. Stainless steel exhibits similar but less pronounced scattering lobes accompanied by somewhat subdued angular variations of the speed distributions.
Microwave Spectrum of Cyclopropyl Bromide
Authors: Lam Frank M. K. , Dailey Benjamin P.
Published: February 2004

The microwave spectra of four isotopic species of cyclopropyl bromide, namely C3H579Br, C3H581Br, C3H4D79Br, and C3H4D81Br have been analyzed in the frequency region of 19 000–31 000 Mc/sec. The rotational constants obtained are as follows (given in megacycles per second): ABCC3H579Br16 504.9 ± 652579.87 ± 0.032457.68 ± 0.03C3H581Br16 239.6 ± 1602560.49 ± 0.032440.12 ± 0.03C3H4D79Br15 139.2 ± 792527.52 ± 0.042455.93 ± 0.05C3H4D81Br15 046.8 ± 1842502.84 ± 0.052430.73 ± 0.04 Two structures compatible with these data have been obtained for this molecule. Structure I was calculated by assuming for the hydrogen parameters values obtained for cyclopropyl chloride, whereas Structure II was derived with the assumption that all d C–C = 1.080 Å and the ∠H–C–H's are bisected by the ring. Structure IAssumedCalculatedd C–H(trans): 1.086 Åd C1–C2: 1.521 ± 0.004 Åd C–H(cis): 1.074 Åd C1–C3: 1.512 ± 0.007 Åd C–H(sec): 1.078 Åd C3–Br: 1.905 ± 0.007 Å∠C2–C1–H(cis): 116°50′∠H(sec)–C3–Br: 116° ± 50′∠C2–C1–H(trans): 118°56′∠C2–C3–Br: 118°54′ ± 1.0°∠C3–C1–H(cis): 115°20′∠H(cis)–C1–H(trans): 115°59′ Structure IIAssumedCalculatedd C–H: 1.080 Åd C1–C2: 1.518 ± 0.004 Å∠C2–C1–H(cis): 117°37′d C1–C3: 1.507 ± 0.010 Å∠C2–C1–H(trans): 117°37′d C3–Br: 1.899 ± 0.005 Å∠C3–C1–H(cis): 117°6′∠H(sec)–C3–Br: 115°15′ ± 50′∠H(cis)–C1H(trans): 116°∠C2–C3–Br: 119°30′ ± 1.0° The analysis of the hyperfine structures of the spectra gives the following quadrupole coupling constants. For C3H579Br eQqm = 462.3 ± 3.5 Mc/sec, η = −0.23 ± 0.04; C3H581Br eQqm = 391.2 ± 1.0 Mc/sec, η = −0.20 ± 0.02; C3H4D79Br eQqm = 451.0 ± 14 Mc/sec, η = −0.24 ± 0.12; C3H4D81Br eQqm = 404.1 ± 4 Mc/sec, η = −0.08 ± 0.10. The ionicity of the bond was estimated to approximately 22%.
Effusion. IV. Angular Number Distributions of Gaseous CsCl from Right-Circular Cylindrical Orifices into Vacuum
Authors: Wang K. C. , Wahlbeck P. G.
Published: February 2004

Angular number distributions of CsCl(g) effusing from right-circular cylindrical orifices located in the walls of double-oven effusion cells with L / d (ratio of orifice length to diameter) of 0.467 and 1.29 were measured by means of a surface ionization detector. The distributions have been studied as a function of the state of the gas in the effusion cell. A high-pressure limit for molecular flow was found to be approximately at a K (ratio of mean-free path to diameter) value of 1.9 for the longer orifice; the limit for the short orifice was not observed. For the long orifice, as K decreased below 1.9, the probability of effusion in the forward direction decreased. At K larger than 1.9, the angular number distributions were not in agreement with the Clausing theory and fluctuations in the distributions were noted. The results found in this work are compared with those of previous investigators. The effects at K > 1.9 may be explained by introducing specular reflection of molecules from the orifice walls.
Quantum Theory of (H, H2) Scattering: Two-Body Potential and Elastic Scattering
Authors: Tang K. T. , Karplus M.
Published: February 2004

Effective two-body interaction potentials for elastic and reactive H, H2 scattering have been constructed from a semiempirical three-body potential-energy surface. Two limiting approximations were used; in one, (Vu0), the molecule is unperturbed by the incoming atom, and in the other, (Va0), the molecule adiabatically follows the incoming atom. Since van der Waals contributions were not included in the three-body surface, a modified two-body potential, (Vm0), which included long-range (−C / R6) attractive terms, was also considered. Elastic differential and total cross sections were calculated for energies between 0.025 and 1.0 eV and compared with the available measurements. Although more experimental data are needed for a definitive test, the two-body potential (Vm0) appears to give resonably accurate results. As the coefficient C is very small for H, H2, the main effect of the van der Waals term in Vm0 is to reduce the total cross section. Only small differences are found in the elastic scattering from the potentials Vu0 and Va0; this contrasts sharply with the reactive scattering results.
Electronic Energy Relaxation in Toluene Vapor
Authors: Burton Charles S. , Noyes W. Albert
Published: February 2004

Fluorescence and crossover to the triplet state are the only important relaxation paths for toluene excited to the lowest vibrational level of the first singlet state. The fluorescent yield at 2668Å is 0.30 ± 0.07 and this is zero at 2400 Å. The triplet yield (Cundall method) is 0.70 ± 0.03 at 2668 Å and is lower at shorter wavelengths. Probably fluorescence and crossover to the triplet state occur only from the vibrationless level of the upper singlet state under the experimental conditions used. Some other process must become important at short wavelengths, and this process competes successfully with vibrational relaxation. Fluorescence of toluene is quenched by krypton and xenon presumably because of collision-induced crossover to the triplet state.
Allowed and Forbidden Character in the 3715-Å π* ←n System of Benzaldehyde
Authors: Hollas J. M. , Gregorek Edward , Goodman Lionel
Published: February 2004

The 3715-Å system of benzaldehyde-h6, -d1, and -d6 has been observed in absorption in the vapor phase. In spite of some diffuseness two band types have been distinguished by their characteristic rotational contours. Bands showing one main peak in the contour belong to the electronically allowed part of the system, assigned as 1A″(nπ*)←1A′, and those showing two main peaks split by about 9 cm−1 belong to the electronically forbidden part of the system involving activity of nontotally symmetric (a″) vibrations. Assignment of the wavenumbers of the three most strongly active a″ vibrations to approximate normal coordinates is certain in the case of the CHO-torsional vibration but less certain in the cases of the out-of-plane substituent vibration and an out-of-plane ring vibration. Qualitative estimates of intensity borrowed through activity of these three vibrations have been made using undistorted and distorted molecule wavefunctions of the Pople–Santry–Segal type. The calculated n-electron density is highly delocalized (45% in the aromatic ring) and results show that an out-of-plane carbon ring vibration should be the most strongly active of the three, supporting the tentative experimental assignment of the most strongly active vibration to such a mode. Further, the transition moment arising from the activity of this vibration is shown to be predominantly along the long in-plane axis in agreement with experiment. The electronically allowed part of the system is stronger than the electronically forbidden part. Detailed consideration of the allowed intensity show that the largest part arises from delocalization of the n electrons. For this reason the conjugating benzene ring is effective in breaking down the local symmetry of the carbonyl group. Both the allowed and forbidden parts of the system are dominated by progressions involving the C = O stretching vibration. It was shown previously from the polarized excitation spectrum that the most intense progression in the system is polarized perpendicular to the molecular plane and a weaker one is polarized predominantly along the long in-plane axis. These findings are confirmed through correlation with the vapor spectrum.
Semiclassical Theory of Inelastic Scattering: Diagonalization of the Phase Shift Matrix
Authors: Cross R. J.
Published: February 2004

The previously obtained semiclassical phase shift matrix is diagonalized in the classical limit by a simple transformation. In the diagonal representation, the various scattering expressions can be simplified appreciably by the method of stationary phase to resemble the semiclassical expressions for elastic scattering. Analogous equations are obtained for the scattering angle and the collision lifetime. A perturbation method is derived to cover deviations from the classical and sudden-approximation limits.
Restricted Self-Diffusion of Protons in Colloidal Systems by the Pulsed-Gradient, Spin-Echo Method
Authors: Tanner J. E. , Stejskal E. O.
Published: February 2004

The pulsed-gradient, spin-echo technique has been used to study self-diffusion of protons in several colloidal systems in order to examine the usefulness of that technique in determining the extent to which the free movement of molecules in these systems is restricted by the colloidal structures present. The pulsed-gradient experiment is preferred to the steady-gradient experiment because it affords better definition and control over the time during which diffusion is observed. Diffusion times between 1 sec and 10−3 sec have been used. One artificial system of thin liquid layers, three different kinds of plant cells, and one emulsion have been studied. Clear indications of restricted diffusion are found in all the systems. When fitted to theoretical expressions derived for such behavior, the data yielded a description of each system, as seen by the diffusing molecules, adequately in agreement with the known structure and properties. Critiera for recognizing and analyzing restricted diffusion are discussed. Necessary conditions for the successful study of restricted diffusion are also discussed.
Zeeman Studies on Er3+ in GdCl3
Authors: Randazzo Donald J.
Published: February 2004

The absorption spectrum of Er3+ in GdCl3 has been investigated. Extensive Zeeman series have been obtained for three different groups of states with fields applied parallel to the hexagonal axis. It is found that the Zeeman splittings of the Er3+ states depend on the magnetic ordering of the GdCl3 host, and this must be considered in order to get correct Zeeman factors for these states. An attempt was made to represent the effect of the magnetic ordering on the states by a term proportional to the crystal magnetization. A theoretical expression is given for the magnetization of GdCl3 under the different conditions of temperature and field used in the experiments. The Er3+ Zeeman factors obtained with the model are seen to be consistent at all field intensities and to be in reasonable agreement with what one obtains from calculations using the crystal-field parameters of Er3+ in GdCl3.
Transformation Relationships from Center-of-Mass Cross Section and Excitation Functions to Observable Angular and Velocity Distributions of Scattered Flux
Authors: Warnock T. T. , Bernstein R. B.
Published: February 2004

Presented are transformation relationships between center-of-mass differential cross sections (and product internal excitation functions) and laboratory angular and velocity distributions of product flux observable in molecular beam scattering experiments.
Nuclear Magnetic Hyperfine Spectra of H35Cl and H37Cl
Authors: Code R. F. , Khosla A. , Ozier I. , Ramsey N. F. , Yi P. N.
Published: February 2004

The nuclear hyperfine spectra of H35Cl and H37Cl have been studied in the limit of zero external magnetic field by a molecular-beam magnetic resonance spectrometer. Thirteen lines of the H35Cl spectrum were observed in the range 20–230 kHz, and eight lines of the H37Cl spectrum were observed in the range 20–140 kHz. The spectra were analyzed by a zero-field magnetic hyperfine Hamiltonian. For each molecule the proton spin–rotation constant cp and the total tensor spin–spin constant d have been measured, and an upper limit for the magnitude of the scalar part of the electron-coupled spin–spin constant | δ | has been established. The calculated transition frequencies agree with the observed spectra and the independent determinations of the constants for the two molecules are consistent with the first-order theory of isotopic effects. The measured constants for H35Cl are cp = +41.70 ± 0.10 kHz and d = +2.20 ± 0.04 kHz; for H37Cl they are cp = +41.66 ± 0.10 kHz and d = +1.86 ± 0.04 kHz. The upper limits for | δ | in H35Cl and H37Cl are 0.33 and 0.27 kHz, respectively.
Internal Rotation in Propane: Reanalysis of the Microwave Spectrum and Quantum-Mechanical Calculations
Authors: Hoyland James R.
Published: February 2004

Quantum-mechanical calculations are carried out on various conformations of the propane molecule using a Gaussian basis set and the Hartree–Fock–Roothaan formalism. These calculations indicate that internal rotation in propane can be adequately described by a simple equation of the form E(α1, α2) = 12V0 (2 − cos3α1 − cos3α2)−12V1[1 − cos3(α1 + α2)] where α1 and β2 are the two angles describing the rotation of the two methyl groups. The microwave spectrum of propane in the first excited torsional states reported by Hirota, Matsumura, and Morino was analyzed assuming this potential, leading to values for V0 and V1 of 3575 ± 100 cal/mole and 310 ± 40 cal/mole, respectively.
Volume Relaxation in CS2–CCl4 Mixtures
Authors: Barocchi F. , Mancini M. , Vallauri R.
Published: February 2004

Volume relaxation times in CS2–CCl4 mixtures were carried out by means of velocity-dispersion measurement. The results are interpreted in terms of existing theories concerning the behavior of binary mixtures of unassociated liquids.
Matrix-Isolation Study of the Vacuum–Ultraviolet Photolysis of Dischlorosilane. The Infrared Spectrum of the Free Radical SiCl2
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: February 2004

In studies of the vacuum–ultraviolet photolysis of SiH2Cl2 and of SiD2Cl2 suspended in an argon matrix at 14°K, new absorptions appear at 502 and at 513 cm−1 which may be assigned as the two stretching fundamentals of SiCl2. A broad, unstructured absorption is also observed in the region of the ultraviolet spectrum in which features tentatively ascribed to SiCl2 were observed in earlier gas-phase emission studies. The detailed assignment of the observed infrared features is considered, and values of the valence angle, the Si–Cl stretching force constant, and the stretching–interaction force constant are estimated, corresponding to the two possible assignments for the infrared absorptions.
Calculation of the Magnetic Rotation Spectrum of NO in the Near Infrared
Authors: Buckingham A. D. , Segal G. A.
Published: February 2004

The magnetic rotation spectrum for the 3–0 vibration band of NO has been calculated and is compared to the spectra observed by Mann and Hause. With one exception, agreement with experiment is satisfactory.
General Restriction on the Distribution of Ions in Electrolytes
Authors: Stillinger Frank H. , Lovett Ronald
Published: February 2004

The rigorous second-moment condition previously derived for “primitive-model” electrolyte ion atmospheres in equilibrium is generalized to arbitrary mixtures of electrolytes of unrestricted charge species. No special assumptions regarding the nature of solvent dielectric behavior are required, and the condition remains valid even in the presence of specific chemical interactions that lead to complex ion formation.
Use of Green Functions in Atomic and Molecular Calculations. II. The Green Function of the Helium Atom
Authors: Hameka Hendrik F.
Published: February 2004

We derive an analytical expression for the Green function of the helium atom, that is to say for the helium atom where the electron repulsion term (e2 / r12) has been neglected. It is outlined that this Green function may be used as a basis for a numerical iterative procedure to derive the exact eigenfunctions of the helium atom.
Use of Green Functions in Atomic and Molecular Calculations. IV. The Green Function of the Lithium Atom and of the Other Atoms
Authors: Hameka Hendrik F.
Published: February 2004

We derive an analytical expression for the Green function of the lithium atom, that is to say for the lithium atom where the electron repulsion terms (e2 / rij) have been neglected. It is shown that our derivation is easily generalized to all other atoms and ions.
Nuclear Corrections to Electronic Expectation Values: Zero-Point Vibrational Effects in the Water Molecule
Authors: Kern C. W. , Matcha R. L.
Published: February 2004

A variation–perturbation approach is used to determine nuclear corrections to electronic properties of polyatomic molecules. To illustrate the technique, general expressions for the first-order zero-point vibrational corrections are derived and applied to various one-electron properties of the water molecule. These include the electric dipole and molecular quadrupole moments, the diamagnetic susceptibility, the diamagnetic shielding constants, the quadrupole coupling constants, and the Hellmann–Feynman forces. The numerical results, which depend upon the combined use of the LCAO MO CI wavefunctions of Reeves and Boys and of the experimental data of Papous̆ek and Pliva, show that electronic expectation values need to be vibrationally corrected for quantitative comparisons of theory with experiment. For the water molecule, these corrections are typically about 1%, but can be as large as 10%, of the equilibrium values. The net sign of each correction is determined by the symmetric stretching mode in H2O and D2O, and the O–H and/or O–D stretch in HDO. Of particular importance to the proper treatment of the vibrational average is a potential surface containing the proper number of appropriately chosen symmetric and asymmetric configurations of nuclei.
Vibrational Spectra and Structure of Small-Ring Compounds. X. Spectroscopic Evidence for Pseudorotation in Cyclopentane
Authors: Durig J. R. , Wertz D. W.
Published: February 2004

The infrared spectrum of cyclopentane has been examined from 33 to 4000 cm−1. A series of pronounced Q branches with a 5-cm−1 spacing was observed on top of the CH2 deformation. The Q branch frequencies could be reproduced by assuming that the cyclopentane ring was undergoing pseudorotation. The spectroscopically derived parameter mq02 was found to be (11.0 ± 0.2) × 10−40 g·cm2.
Adsorption of Neon on a Xenon Surface
Authors: Barnes Mary W. , Steele William A.
Published: February 2004

Measurements of isotherms and heats of adsorption are reported for neon at submonolayer coverages on a xenon surface which had been prepared by preadsorbing one layer of xenon on a graphitized carbon black substrate. Also, heat capacities of a nominal half layer of neon were measured from 6° to 21°K. These data were used to calculate the absolute entropy of a half-layer of adsorbed neon, and also to locate the critical temperature for two-dimensional condensation in this system. It was found that the neon zero-point entropy was zero within experimental error, and that the critical temperature was 15.3° ± 0.3°K. Theoretical estimates of the energy and partition function of an isolated neon atom on the surface were compared with experiment, as were calculated values of the mutual interaction energy of a pair of adsorbed neon atoms. It was concluded that the neon atoms behave as if they were adsorbed on the points of a lattice congruent with a regular close-packed xenon lattice having sites centered over triangular groups of xenon atoms in the surface. It was shown that the experimental value of the critical temperature is commensurate with this picture, but is definitely anomalous compared to predictions based on other models for the adsorbed film.
γ
Radiolysis of Liquids at High Pressures. VI. Hydrogen-Atom Reactions in Aqueous 0.8N H2SO4 Solutions
Authors: Hentz Robert R. ,   Farhataziz, Milner David J.
Published: February 2004

The competition between Reactions [1] and [2], H + S→no H2, H + RH→H2 + R, in aqueous 0.8N H2SO4 solutions was studied at 20° over the applied pressure range of 0–6.34 kbar by measurement of G(H2) from the gamma-irradiated solutions. With O2 as S, in aerated solutions, relative specific rates k10 / k20 were determined at atmospheric pressure for methanol, glucose, glycerol, ethanol, and isopropanol as RH. From the pressure dependence of k1 / k2 and an estimated ΔV1‡ = 1.6 ml mole−1 for S ≡ O2, values of ΔV2‡ in the range −5.5 to −6.7 ml mole−1 are obtained for the five H donors. The average value ΔV2‡ = − 5.9 ml mole−1 is taken as characteristic for Reaction [2]. Values of k10 / k20 at atmospheric pressure also were determined for four deaerated 0.8N H2SO4 solutions: (1) RH ≡ glucose and S ≡ benzyl alcohol; (2) RH ≡ glucose and S ≡ BrCH2COOH; (3) RH ≡ S ≡ acetone; (4) RH ≡ S ≡ ClCH2COOH. Because little or no pressure dependence of G(H2) and, therefore, of k1 / k2 was observed with these four solutions, ΔV1‡ ≈ ΔV2‡ = − 5.9 ml mole−1. Thus, for a variety of H-atom reactions, which are not diffusion controlled, the value of ΔV‡ is approximately constant. From this result a value of V̄(H) in the range 5.9–10.3 ml mole−1 is estimated. It also is concluded that abstraction of Br or Cl by H occurs, rather than electron transfer, in Reaction [1] with BrCH2COOH or ClCH2COOH as S, respectively. Anomalous results obtained in a deaerated 0.8N H2SO4 solution of glucose and allyl alcohol are discussed.
Configuration-Interaction Study of the H3− System. II. Expanded Basis
Authors: Macías A.
Published: February 2004

A configuration-interaction calculation on the ground state of H3− has been carried out using an orbital basis set made out of 1s, 1s′, 2s, and 2p STO's. The new orbitals were included in the set one type at a time and a large number of calculations was performed to optimize the nonlinear parameters and to keep the wavefunction from becoming too complicated while including the most important configurations that can be formed from each basis set. The best wavefunction obtained from each set was analyzed in terms of natural orbitals (NO). The first two NO's were used to construct simple geminals and study H3− in terms of separated pairs. The Rank 1 functions were used to estimate the Hartree–Fock energy for the system. Electron population analysis was done to gain information about the distribution of electrons in H3−. Information on other four-electron systems (He2 and LiH) was used in the discussion of the results obtained for H3−.
SCF-MO's and Molecular Properties of Methane
Authors: Arrighini G. P. , Guidotti C. , Maestro M. , Moccia R. , Salvetti O.
Published: February 2004

SCF-MO's of the CH4 molecule have been calculated for the experimental geometry by using bases of up to 39 STO's. The best molecular energy obtained is −40.20452 a.u. The ground-state wavefunctions have been utilized to compute some one-electron properties, viz., the electric octupole moment, the electric field gradient at the protons, and the diamagnetic susceptibility. In addition, the electric polarizability and the paramagnetic susceptibility have been evaluated using a perturbed H–F calculation.
Mass Spectrometry of the Vapors over PbCl2 + ACl Mixtures (A = Na, K, Rb, or Cs). II. Electron-Impact Studies
Authors: Bloom H. , Hastie J. W.
Published: February 2004

Ionization-efficiency curves and appearance potentials have been obtained for the positive and negative ions produced by electron-impact ionization of the vapor molecules APbCl3, PbCl2, and ACl where A = Na, K, Rb, or Cs. From the results the ionization processes, ionization potentials, electron affinities, and bond energies for some of the resulting molecules and radicals have been deduced. The concept of electronegativity has been extended to molecules to provide an understanding of the formation of APbCl3 from ACl and PbCl2 in the gas phase.
Molecular Beams of Macroions
Authors: Dole Malcolm , Mack L. L. , Hines R. L. , Mobley R. C. , Ferguson L. D. , Alice M. B.
Published: February 2004

By means of electrospraying a dilute polymer solution into an evaporation chamber, negative macroions can be produced and a molecular beam formed by sampling the gaseous mixture of macroions, solvent, and nitrogen molecules with a nozzle-skimmer system of the Kantrowitz–Gray type. The macroion current can be detected by a Faraday cage after the light ions have been repelled from the beam by negative voltages on a repeller grid. Theoretical repeller voltages which best agree with the observed are those calculated by assuming a macroion velocity within 2% of the estimated supersonic beam velocity of 743 m sec−1. Polystyrene macroions of 51 000 weight-average amu tend to form dimers and trimers in the beam while larger polystyrene macroions of 411 000 weight-average amu appear mostly to be multiply charged single species. The results demonstrate that definite mass/charge states can be formed by the electrospray technique, that a considerable monochromatization of macroion velocities in the beam takes place, and that the macroions become highly concentrated relative to low-molecular-weight solvent and nitrogen ions during the transit time in the supersonic beam.
Rotational Motion in Solution: Hydrogen Halides in Cyclohexane
Authors: Rothschild Walter G.
Published: February 2004

The dipole correlation function and the average kinetic rotational energy of hydrogen fluoride, hydrogen chloride, and deuterium chloride have been computed from the published far-infrared absorption bands [P. Datta and G. M. Barrow, J. Chem. Phys. 43, 2137 (1965)]. The computations show that the dissolved hydrogen halide molecules undergo fast, large-angle rotational diffusional jumps: for instance, the dissolved HF molecules which are in their most populous state have regained their original orientation after a time interval of 0.2 × 10−12 sec following the disturbance of their equilibrium state. The coherence of their rotational motion has completely decayed after about 0.4 × 10−12 sec. A comparison with the dipole correlation function of the classical ensembles of freely rotating molecules shows that the intermolecular forces between HF and cyclohexane become observable only after a time interval of 0.08 × 10−12 sec; the corresponding value for dissolved DCl is 0.14 × 10−12 sec. These time intervals seem to correlate with some “average free volume” in liquid cyclohexane. This was shown by an estimate of the translational and rotational motion of the hydrocarbon from proton spin–lattice relaxation measurements, evaluation of the band shape of its a2u fundamental (522 cm−1), and some simple gas–kinetic considerations. Quantitative estimates of collision-induced absorption between the HF and cyclohexane molecules indicate that dipole–induced-dipole and quadrupole–induced-dipole absorption is appreciable. It is shown that the quadrupole–induced-dipole absorption must be subtracted out in order to obtain good values for the average rotational kinetic energy of the dissolved hydrogen halide molecules.
Ab Initio SCF MO and CI Calculations on the Electronic Spectrum of Benzene
Authors: Buenker Robert J. , Whitten J. L. , Petke J. D.
Published: February 2004

An ab initio SCF MO calculation for the ground state of benzene is reported (total energy equal to −230.3745 hartrees). The set of SCF MO's resulting from this calculation is subsequently employed as the basis for a series of CI treatments investigating the theoretical description of the benzene electronic spectrum. It is found that the inclusion of double and higher excitation configurations in the CI treatment produces significant changes in the calculated results relative to those obtained in the more conventional single excitation CI. Perhaps the most important effects of the higher excitation configurations are observed in the class of excited singlet states; the addition of these configurations causes the B2u1 state to be lower than at least one of the three lowest benzene triplets, in agreement with experimental findings, and also leads to a considerable stabilization of the E2g1 species, making it the second most stable excited singlet in definite contrast with single excitation CI results.
Spin Rotation Constant and Rotational Magnetic Moment of 13C16O
Authors: Ozier Irving , Crapo Lawrence M. , Ramsey Norman F.
Published: February 2004

13C16O has been studied by the molecular-beam magnetic-resonance method in the high-field limit. Two different spectra were observed. These correspond, first, to the reorientation of the carbon-13 nuclear spin with respect to the external field H, and second, to the reorientation of the rotational angular momentum with respect to H. By analyzing these spectra with third-order perturbation theory, it was found that the carbon-13 spin–rotation constant c = − (32.59 ± 0.15) kHz, and that the rotational gyromagnetic ratio gJ = −(0.25691 ± 0.00020) nm. From this measurement of gJ and the known value of the molecular quadrupole moment, the anisotropy constant f of the susceptibility tensor has been determined. It was shown that f / H2 = + (38.9 ± 3.9) × 10−5Hz G−2. By combining the present results for c and gJ with Huo's ab initio calculations of the ground-state electronic properties of the molecule, the average carbon-13 shielding constant σa and the mean diamagnetic susceptibility ξa have been evaluated. These are: σa = 5.0 × 10−6 and ξa = − 203 × 10−31erg G−2·molecule−1. A simple method of determining the sign of c in terms of the sign of gJ by inserting an obstacle into the molecular beam is described.
External Field Dependence of Transport Properties. I. Thermal Conduction in a Fluid of Rough Spheres
Authors: Klein William M. , Hoffman David K. , Dahler John S.
Published: February 2004

A theory of thermal conduction is developed for a gas composed of rotating molecules which is subject to an external electric or magnetic field. This theory of the Senftleben–Beenakker effect is based upon a kinetic equation of the Boltzmann variety and is sufficiently general to include virtually all cases of interest. Application has been made to the rough-sphere model of collisional events and numerical values of the three independent elements of the thermal conductivity tensor obtained. Although the model is rather unrealistic, comparisons with experiment have been made whenever possible. Agreement as to order of magnitude and functional dependence upon field strength is satisfactory but by no means perfect. In these calculations it has been assumed that the molecules either were diamagnetic, e.g., N2, or paramagnetic doublets, e.g., NO. The calculations were extended to high density by invoking a modification of the Enksog theory for a dense gas of smooth spheres. The flux of internal angular momentum caused by a gradient of temperature has been computed.