bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Structures of PCl4F, PCl3F2, PCl2F3, and PF5: Infrared and Low-Temperature Raman Vibrational Spectra
Authors: Griffiths James E. , Carter Richard P. , Holmes Robert R.
Published: January 2005

Molecular structures of PCl4F, PCl3F2, PCl2F3, and PF5 are derived from vapor-state infrared spectra (2000–250 cm—1) and low-temperature liquid-state Raman displacements (Δν=50–1200 cm—1) together with qualitative polarization measurements. All of the compounds appear to have a basic trigonal bipyramidal framework.

The spectra of PCl4F are best interpreted in terms of a C3v structure in which the fluorine atom occupies an axial site; in PCl3F2 (D3h point group) the fluorine atoms also assume axial positions. For PCl2F3, the symmetrical D3h structure is shown to be incorrect. Available evidence supports the C2v structure in which the fluorine atoms appear in one equatorial and two axial sites. Phosphorus pentafluoride is found to have a regular trigonal bipyramidal structure.

Complete vibrational assignments are made in terms of the normal modes and thermodynamic functions are evaluated for PCl5, PCl3F2, and PF5.
Heat Capacity of Yb from 15°—350°K
Authors: Gerstein B. C. , Mullaly J. , Phillips E. , Miller R. E. , Spedding F. H.
Published: January 2005

The heat capacities of two samples of Yb have been measured in the range 15°—350°K. The results of measurements on both samples agree to within experimental error below 200°K but diverge by as much as 2% at 350°K, the difference being associated with difference in impurity content. The following values are found for the thermodynamic functions at 298.15°K: S298.15°=59.88 J(g at. wt deg)—1, (H298.15°—H0°)/T=22.51 J(g at. wt deg). The thermodynamic functions are tabulated from 0° to 1373.15°K. A third-law calculation to check vapor-pressure measurements is made, and the results are discussed.
Determination of the Structure of Liquid Ammonia by X-Ray Diffraction
Authors: Kruh R. F. , Petz J. I.
Published: January 2005

X-ray diffraction measurements show that in liquid ammonia each molecule is surrounded on the average by about 11 other molecules. There is evidence that hydrogen-bonded approaches occur at a mean distance of 3.56 Å, and that the short-range spectrum of intermolecular distances resembles that of crystalline ammonia. These results are used to interpret the volume changes occurring upon dissolution of alkali metals in liquid ammonia.
Observation of Divalent Dysprosium in CaF2 by Paramagnetic Resonance
Authors: Sabisky E. S.
Published: January 2005

The paramagnetic resonance spectra of Dy2+ in the cubic field of CaF2 were investigated at liquid-helium temperatures at frequencies of 9 to 27 kMc/sec. The nonmagnetic ground doublet (E) is strongly perturbed by two adjacent triplet states (T1 and T2) and transitions within the E state are made allowed. The T1 triplet state which is separated by 4.9 cm—1 from the ground state doublet has a g value along the [001] direction of 9.66±0.02 for the outer splitting. The observed splittings of the E and T1 states are in good agreement with the calculated values using the reported ratio of the cubic field parameters.
Generalized Pippard Equations
Authors: Garland Carl W.
Published: January 2005

The Pippard equations for α, CP, and βT near a λ-point transition have been generalized in terms of stress—strain variables. The resulting equations, which interrelate αi, sijT, and CP near a λ point, are tested with data on quartz near its α—β transition. A consequence of the new equations is the prediction that C′=(c11–c12)/2 should be constant for cubic crystals near a λ point; this prediction is compared with experimental data on ammonium chloride.
Conformation and Internal Rotation of Nitroaromatic Amines in Solution as Detected by Proton Magnetic Resonance
Authors: Heidberg Joachim , Weil John A. , Janusonis Gaile A. , Anderson Judith K.
Published: January 2005

The 60-Mc/sec proton magnetic resonance spectra of N-methyl-2,4,6-trinitroaniline (I) and of N-methyl-2,6-dinitroaniline (II), as well as of the analogous N-diphenylamino compounds, show that the 3- and 5-phenyl protons are inequivalent at low temperatures in solution, but act as equivalent at sufficiently high temperatures. The N-unsubstituted anilines and N,N-dimethyl anilines corresponding to I and II show no such inequivalence. The coalescence with temperature of the AB quartet of the picryl protons in the picrylaniline (I) and diphenylpicrylhydrazine in dichloromethane solution could be described quantitatively by the line-shape equations for two coupled protons exchanging with each other. The analysis yielded the lifetimes of the ground state configurations of these molecules, with Arrhenius activation energies of 14.5±0.3 and 12.5 ± 0.2 kcal/mole and frequency factors of 1.4×1015 and 6×1010 sec—1, respectively, for the intramolecular exchange process. A model for these observations, including Hückel MO calculations, is presented in terms of the barrier to rotation about the amino nitrogen-ring carbon bond, the orientation of the nitro groups ortho to the amino group, and hydrogen bonding between the amino group and these nitro groups.

The chemical shift and spin—spin coupling parameters for these compounds and for the 2,4-dinitro analogs are tabulated and compared. The chemical shift values exhibit regularities in excellent agreement with the model introduced.
X-Ray Diffraction Study of Solid Argon
Authors: Barrett C. S. , Meyer Lothar
Published: January 2005

Lattice constants for face-centered cubic argon determined on a precision x-ray diffractometer were found to be 5.3118 Å at both 4.2 and 15°K, 5.3187 at 21°K, 5.4033 at 64°K, with estimated errors of ±0.0005 Å, and 5.458 at 81°K. Least-squares fitting to a polynomial expression gives, for T≥21°K, a=5.29980+ 5.6389×10—4T+1.4231×10—5T2+3.552×10—8T3 (an expression not intended to be used below 21°K). Lattice constants for the close-packed hexagonal phase that sometimes coexists with the cubic may be taken as ahex=0.7071 acubic and chex=1.633ahex throughout the temperature range of solid argon. Evidence of rapid diffusion was seen near the melting point; at lower temperatures, cold work produced strain hardening. Agreement with published density measurements is good; values from some prior x-ray work lie slightly below these values.

Techniques were developed which permit plastic deformation and annealing of specimens to produce fine-grained strain-free samples suited to powder diffractometry. When grain growth could not be avoided (above about 65°K) a method of single crystal diffractometry was used.
Concerning the Roots of a Polynomial which Contains a Perturbation Parameter
Authors: Hollingsworth C. A. , Schumacher David P.
Published: January 2005

Methods are presented for the calculation of the roots of a polynomial equation in terms of a perturbation parameter. The roots are expressed in the form λi=λi0+λi1ξ+λi2ξ2+···, where λi is the ith root, and ξ is the parameter. The methods use recurrence relationships by which λi(k+1) can be obtained from λik.
On the Ionic Hydration Polyhedra in the Crystal Structure of Sodium Hydroxide Tetrahydrate and the Hydrogen Bonding of the Hydroxide Ion
Authors: Beurskens Gezina , Jeffrey G. A.
Published: January 2005

The crystal structure of NaOH·4H2O is compared with that of KF·4H2O, described in the preceding paper, in terms of the hydration polyhedra of the ions. The marked difference in structure corresponds with a difference in the hydrogen-bond environment of the F— and OH— ions. The environment of the latter is consistent with the formation of five strong acceptor hydrogen bonds and a very weak donor hydrogen bond which completes an octahedral coordination. A similar environment is found in the structures of the mono- and heptahydrates.
Assignment of Hyperfine Splittings in Electron Spin Resonance Spectra by Linewidth Analyses
Authors: Bolton James R. , Fraenkel George K.
Published: January 2005

A method is developed for the assignment to nuclear positions of the hyperfine splittings in the electron spin resonance spectra of free radicals in solution. The procedure is applicable to the splittings from the nuclei of atoms with a nonvanishing pi-electron spin density, and it is thus useful for 13C and 14N splittings, but cannot be employed for proton splittings. The technique used depends on linewidth effects. It is shown that one contribution to the linewidths is approximately proportional to the square of the spin density on the atom containing the nucleus of interest (the local spin density), and that, under appropriate conditions, splittings from nuclei at positions with high spin density show greater linewidth effects than those from positions with low spin density. The technique is applied to two of the 13C splittings from nuclei present in natural abundance in the spectrum of the anthracene negative ion radical.
Analytical Self-Consistent-Field Functions for Ions Crn+
Authors: Synek Miroslav , Stungis George E.
Published: January 2005

Analytical SCF functions were calculated for ions Crn+ (n = 1, 2, 3, 4, 5). The cusp condition is identically satisfied. The nodal condition for the radial functions Piλ(r) is satisfied unusually accurately; an occasional deviation never exceeds 0.00006.
Centrifugal Distortion Effects and Structure of Hydrazoic Acid from the Millimeter Wave Rotational Spectra
Authors: Winnewisser Manfred , Cook R. L.
Published: January 2005

The rotational spectra of two 15N-substituted species of hydrazoic acid have been investigated. The values of the rotational constants are: H15N14N14N:  A0=619 916   Mc/sec,B0= 11 667.54 Mc/sec,C0= 11 427.86 Mc/sec,H14N14N15N:  A0=616 868   Mc/sec,B0= 11 641.76 Mc/sec,C0= 11 405.08 Mc/sec.With the aid of the rotational constants for H14N3 and D14N3 the following structural parameters were obtained: r(N1–H) =0.975±0.015 Å,r(N1–N2) =1.237±0.002 Å,r(N2–N3) =1.133±0.002 Å,∠HN1N2=114∘ 7.8′±30′.An important part of this study was the investigation of the centrifugal stretching behavior exhibited by HN3 and its isotopic species. It has been found that even at low J the introduction of P6 distortion terms for higher K—1 transitions is essential to accurately account for the observed rotational frequencies.
Morphology of Thermally Evaporated Zinc Cleavage Surfaces
Authors: Ruff A. W.
Published: January 2005

The process of thermal evaporation has been studied on (0001) cleaved zinc surfaces. The effects on the evaporated surface structures due to zinc vapor understauration, impurities, and crystal dislocations were investigated. For undersaturation ratios between 0.29 and 0.006, evaporation proceeded primarily from localized surface regions resulting in shallow conical evaporation pits. The number density of these evaporation pits was in good agreement with the dislocation density determined by chemical etching. It was concluded that the step sources responsible for the evaporation pits were dislocations terminating at the surfaces. The theory of evaporation from dislocation sites predicts a critical undersaturation similar to that observed experimentally. The interferometrically measured evaporation-pit slopes increased with vapor undersaturation in agreement with the theory of Cabrera and Levine near the critical undersaturation. The data extended further into the region of higher undersaturations. The effects of surface impurities were studied by admiting oxygen into the evaporation cell. For a constant vapor undersaturation, the evaporation pit slopes increased at the higher oxygen pressures. This increase could be explained qualitatively as a result of adsorbed impurities.
Energy Levels of Er3+ in LaF3 and Coherent Emission at 1.61 μ
Authors: Krupke William F. , Gruber John B.
Published: January 2005

The analysis of the absorption spectrum of Er3+ in LaF3 is extended into the ultraviolet region to 2000 Å. A number of fluorescence lines recently observed in the region from 3000 to 25 000 Å is also reported. Based on the best over-all agreement between the predicted ``free-ion'' 4f11 SLJ states and 21 experimentally observed levels for Er3+ in LaF3, one finds a set of atomic wavefunctions for the ion based on F2 = 435.7 cm—1, F4 = 67.21 cm—1, F6 = 7.388 cm—1, and ζ = 2350.8 cm—1. Laser experiments are described and the details of coherent emission found at 1.61 μ are presented.
Raman Spectra of Polycrystalline Methyl Iodide
Authors: Ito Mitsuo
Published: January 2005

The Raman spectrum of polycrystalline methyl iodide has been studied at 77° and 195°K, and the difference between the Raman and infrared spectra has been discussed. All of six frequencies due to lattice vibrations have been found, and their assignments have been given. The heat capacity of crystalline methyl iodide at various temperatures has been calculated from the spectral data obtained and compared with the observed values of crystalline methyl bromide.
Ultrasonic Absorption in Liquid Sodium—Potassium Alloys
Authors: Jarzynski J. , Litovitz T. A.
Published: January 2005

Ultrasonic absorption measurements were made in sodium—potassium alloys at temperatures from 20° (or mp) to 150°C. The measured absorption was found to be higher than the classical absorption. In liquid sodium the bulk viscosity is attributed to structural relaxation and the ratio of bulk/shear viscosity is 3. In the alloys, in addition to structural relaxation, a second relaxation loss was observed at temperatures below 80°C. This loss was greatest for an alloy of composition near 33 at.% of K, and is attributed to the slow adjustment of the equilibrium 2Na+K⇌Na2K.
Crystal Growth and Color Centers of Alkaline-Earth Halides
Authors: Fong Francis K. , Yocom P. Niel
Published: January 2005

Single crystals of CaF2, SrCl2, BaBr2, and BaClF have been grown. Color centers have been developed in calcium fluoride by treatment with Ca vapor at 850°C and by gamma irradiation at room temperature. It has been observed that additive colorability of the salt depends on the rate of cooling from the additive-coloring temperature. The gamma-irradiated samples display a host of color centers, the formation of which appears to be dependent upon the dosage of the irradiation. Below 105 rad, no coloration of the crystal is achieved by the irradiation. At higher dosages, bands due to yttrium and oxygen impurities become evident, whereas at the very high dosage of 5×107 rad, a multibanded spectrum with very intense infrared absorption is obtained. These bands are believed to be indicative of the formation of defect centers by high-dosage irradiation. Unlike the bands associated with chemical impurities, these bands are relatively unstable. They are readily bleached by heat and light, the bands in the infrared being the most unstable. Color centers have also been observed in strontium chloride, barium bromide, and barium chlorofluoride. Whereas only one band has been observed for strontium chloride, more have been observed for barium bromide and barium chlorofluoride, which may presumably be due to their noncubic symmetries. Bands produced by gamma irradiation in these crystals are unstable, and all bleach readily under ordinary room conditions.
Evaporation Mechanism of CdS Single Crystals. II. Diffusion Controlled Evaporation of Cadmium- and Sulfur-Doped CdS
Authors: Somorjai G. A. , Jepsen D. W.
Published: January 2005

Excesses of cadmium and sulfur over that of stoichiometry are found to lower the evaporation rate of CdS single-crystal c faces in the temperature range 700°—740°C. Initial rates for highly doped crystals are an order of magnitude lower than the steady-state evaporation rate. An initial induction period (0.1–6 h) is followed by a rapid upturn and subsequent attainment of the steady-state rate. This transient behavior is accompanied by drastic changes in crystal conductivity. Experiments indicate that excesses of cadmium or sulfur in the bulk, diffusing to the surface, cause the effect. A theory for evaporation controlled by the out diffusion of excess cadmium or sulfur is derived which, under proper conditions, yields a very convenient determination of the diffusion constant. There is evidence of the presence of precipitated Cd in the heavily doped crystals. The actual diffusing species in these experiments is presumed to be sulfur vacancies.
Gaussian Correlation Functions: Two-Electron Systems
Authors: Lester William A. , Krauss Morris
Published: January 2005

The correlated molecular orbital method is applied to the He isoelectronic sequence and H2 using a Gaussian basis set to explore the possible use of Gaussian basis function in wavefunctions containing explicit electron correlation for larger systems. The wavefunctions are analyzed in terms of the change in the electron-pair distribution and a comparison of the Coulomb holes is made for the atomic cases. The dependence of the correlation improvement on the accuracy of the orbital functions is discussed.

General formulas for Gaussian correlation integrals also are included.
Microwave Spectrum of the SO Radical
Authors: Powell F. X. , Lide David R.
Published: January 2005

Five microwave transitions of the SO free radical in the gas phase have been measured and assigned. The lines result from electric dipole transitions between rotational levels in the 3Σ— ground state which are strongly perturbed by the interaction of the electron spin. The molecular constants determined from the analysis are B0=0.71791 cm—1, λ=5.276 cm—1, and γ=—0.0052 cm—1. The electric dipole moment has been determined as 1.55 D from the Stark effect. Wavefunctions and intensities are discussed. A combination of microwave and optical data gives Be=0.72072 cm—1 and re=1.48095 Å for the ground state and λ=3.5 cm—1 for the excited B 3Σ— electronic state. The spectrum was studied in a flow system in which SO was generated by the reaction of oxygen atoms with OCS or other materials. The apparatus is described in detail.
X-Ray Characteristic Temperatures of Some II—VI Ionic Compounds
Authors: Baldwin T. O. , Tompson C. W.
Published: January 2005

The characteristic temperatures and thermal expansion coefficients of MgO, CaO, MgS, CaS, and BaTe have been measured by observing Bragg reflections as functions of temperature in the temperature range from 100° to about 1000°K. The compounds selected were those for which the simple cubic approximation should be most applicable, and interpretation of the data was based upon the Debye approximation for a solid. For at least one of these materials, evidence was found at high temperatures for a temperature dependence of ΘM nearly equal to that predicted by the explicit dependence of ΘM on volume, while at low temperatures ΘM was a much more rapid function of temperature. For MgO the absolute value of ΘM was found to agree fairly well with the published specific heat values, after correction for the difference in averaging over the vibrational spectrum, although it was found to be somewhat larger than a value obtained from earlier x-ray measurements. Expansion coefficients for MgO and CaO were in agreement with other determinations. Neither characteristic temperatures nor expansion coefficients were found in the literature for the other materials.
Theory of Rydberg Series in Polyatomic Molecules: H2O
Authors: La Paglia S. R.
Published: January 2005

The characteristic features of the Rydberg transitions in a polyatomic molecule are examined with emphasis on their extravalence-shell nature. It is made plausible that in molecular orbital perturbation theory the corresponding Hartree—Fock atomic orbital of principal quantum number n is a zero-order approx-imation to the Rydberg orbital. Calculations without integral approximations are carried out for the low-lying states of H2O. The ASP—SCF—LCAO—MO treatment of the H2O ground state provides the core. The mean singlet—triplet absorption spectrum of H2O is fairly well reproduced by the calculation. The calculated oscillator strength of B1(3s)←A1, 1×10—2, and the calculated symmetry-induced splitting of the 3p Hartree—Fock atomic orbital in C2v symmetry into B1 and A1 components, 2200 cm—1, are also in satisfactory agreement with experiment, 3×10—2 and 1500 cm—1, respectively.
Vapor Pressure of Neptunium
Authors: Eick H. A. , Mulford R. N. R.
Published: January 2005

The vapor pressure of liquid neptunium metal in the temperature range 1700° to 1950°K, as determined by the Knudsen effusion technique, may be described by the equation logp(atm) = — (20 610±1280)/T+(5.10±0.70). The experimental heat and entropy of vaporization are ΔH°1800=94.3±5.9 kcal/mole, and ΔS°1800=23.3±3.2 cal/mole·deg, and the extrapolated normal boiling point of the metal is 4175°K.

The neptunium specimen contained 0.56 wt. % plutonium-239, and the partial pressure of that species over the solution may be described by the equation logp(atm) = — (19 051±538)/T+(3.29±0.30).
Vaporization Studies on the Mixed Trioxides of Antimony and Arsenic
Authors: Norman J. H. , Staley H. G.
Published: January 2005

In a Knudsen-cell study of a premelted sample of As2O3 and Sb2O3, the vapor species As4O6, As3SbO6, As2Sb2O6, AsSb3O6, and Sb4O6 were observed. For the disproportionation of one of these mixed species to its neighbors in the above list of compounds, a zero heat of reaction was found. The entropies of reaction were nearly indistinguishable from the entropies derived from statistical considerations of the replacement of one metal with another.
Normal Coordinate Analyses of Hydrogen-Bonded Compounds. II. Dimeric Formic Acid and Acetic Acid
Authors: Kishida Sanae , Nakamoto Kazuo
Published: January 2005

Normal coordinate analyses have been made both for dimeric formic acid and acetic acid, including their deutero analogs. The Urey—Bradley force constants of the dimers have been compared with those of the corresponding monomers to study the effect of hydrogen bonding on individual bonds. Theoretical band assignments have been made for all the in-plane vibrations based on the potential energy distribution. The results reveal the nature of vibrational couplings which have hitherto been assumed only on an empirical basis.
Collision-Induced Microwave Absorption in Compressed Gases. III. CO2—Foreign-Gas Mixtures
Authors: Maryott A. A. , Kryder S. J.
Published: January 2005

Measurements of the increase in dielectric loss accompanying the addition of various foreign gases (He, H2, Ar, N2, CH4, C2H6, and SF6) to CO2 have been made at a frequency near 24 GHz and a temperature of 25°C. This loss is attributed to the dipoles induced in the foreign gas by the molecular quadrupole field of CO2. Excluding mixtures with He and H2, for which the effect is very small, the value of the quadrupole moment of CO2 derived from these losses is about 4.4×10—26 esu in all cases. This is in good agreement with the directly measured value of 4.1×10—26 esu reported by Buckingham and Disch.
Some Excited States of the Hydrogen Molecule. II. 1Πg(1s2pπ), 3Πg(1s2pπ), 1Δg(1s3dδ), 3Δg(1s3dδ), 1Δu(1s3dδ), 3Δu(1s3dδ)
Authors: Browne J. C.
Published: January 2005

Complete theoretical potential curves for the bound 1Δg(1s3dδ) and 3Δg(1s3dδ) states of H2 and for the long-range portions of the repulsive 1πg(1s2pπ), 3πg(1s2pπ), 1Δu(1s3dδ), and 3Δu(1s3dδ) states of H2 are reported. Comparison of these results plus results from Paper I of this series to the conventional perturbation theory computations for the long-range interactions of those states shows that the conventional perturbation results may be misleading if ``valence'' and ``overlap'' forces are not considered. The computed total energies at Re for the 1Δg(1s3dδ) and 3Δg(1s3dδ) states are —0.6570143 (—0.65778), and —0.6571785 (—0.65872 a.u.), respectively. The values in parentheses are experimental values. Spectroscopic constants and expectation values for some one-electron operators for the 1Δg(1s3dδ) and 3Δg(1s3dδ) states are also presented. Two-center and one-center wavefunctions yielding comparable energies for the 1Δg(1s3dδ) state are compared through expectation values for a series of one-electron operators.
Variational Solutions to the Brillouin—Wigner Perturbation Differential Equations
Authors: Meath William J. , Hirschfelder Joseph O.
Published: January 2005

Variational techniques for the Brillouin—Wigner (BW) perturbation theory, analogous to the Hylleraas and Sinanoğlu principles in Rayleigh—Schrödinger (RS) theory, are derived. A practical method of applying this approach to BW theory, which does not require the knowledge of the exact BW wavefunctions, is discussed. Using this method one obtains an upper bound to the exact total energy for systems in the lowest energy state of a given symmetry. Finally, a convenient matrix method of applying the variational principles is suggested and degenerate BW theory is discussed briefly.
Electron-Impact Studies of Aromatic Hydrocarbons. II. Naphthacene, Naphthaphene, Chrysene, Triphenylene, and Pyrene
Authors: Wacks Morton E.
Published: January 2005

The systematic survey of ionization-dissociation processes of fused-ring aromatic compounds initiated previously is continued. Mass spectra and appearance potentials of the singly and doubly charged molecule ions are reported. The observed ionization energies of naphthacene (6.95 eV), naphthaphene (7.53 eV), chrysene (8.01 eV), triphenylene (8.19 eV), and pyrene (7.72 eV) are compared with available spectroscopic data, with values obtained from molecular orbital calculations, with the available empirical and semiempirical methods, and with other electron-impact data.
Z-Center Energy Levels
Authors: Johnson Wilbur V. , Scott Allen B.
Published: January 2005

One of the centers proposed to account for Z-band absorption in alkali halide crystals consists of an electron trapped at the divalent cation. A calculation of the absorption energy has been made using the method of Simpson. This method, though not free of objections, has been surprisingly successful in predicting F-band absorption maxima.

For Ca++ in KCl and NaCl, the absorption maxima were found to lie at 3.92 and 3.70 eV, respectively, for Sr++ at 9.00 and 8.70 eV. These locations are far removed from the Z bands, which lie near 2.0 eV in both crystals. While the numerical accuracy of the calculations is not high, the possibility of a Z-type center absorbing in the far ultraviolet is raised; this has a bearing on recent thermodynamic arguments concerning the nature of Z centers.
On the Appearance of Unlinked Clusters in SCF–CI Calculations
Authors: Yaris Robert , Musher Jeremy I.
Published: January 2005

The unlinked clusters which have appeared in SCF–CI calculations are shown to be introduced by the particular choice of normalization usually employed. If the appropriate change in the normalization is made, the contributions from unlinked clusters are eliminated. The same change in the normalization also improves the energy for a partially correlated CI wavefunction.
Quenching of the 2537-Å Resonance Radiation of Mercury
Authors: Yarwood A. J. , Strausz O. P. , Gunning H. E.
Published: January 2005

Cross sections for the quenching of the 2537-Å resonance radiation of mercury have been obtained by direct measurement of the resonance fluorescent intensities in an improved Zemansky-type apparatus. The data were evaluated on the basis of Zemansky's calculation (a) of the imprisonment time from Milne's theory, as well as using Holstein's experimentally verified formula (b) for the imprisonment decay constant, developed on modern imprisonment theory. The cross section values derived by (a) with the Samson ``equivalent opacity,'' by (b), and those obtained by Biberman from a numerical solution of the Holstein—Biberman transport equation all agree within 23%.

The trend observed in the measured cross section values of a number of substances including paraffins, olefins, silane and methyl silanes, alcohols, N2O, and some other inorganic molecules provides further evidence for the electrophilic character of Hg 6(3P1) atoms.
NMR Studies of Asymmetric Ethanic Rotators: 1,2-Disubstituted Propanes
Authors: Finegold H.
Published: January 2005

The NMR spectra of several 1,2-disubstituted propanes, particularly 1,2-dichloropropane and 1,2-dibromopropane, are examined in detail in various media. A range of vicinal J couplings is obtained from the computational analyses of solution systems selected to afford an extensive cross section of rotational averaging over the possible conformers. An expression is then given relating the conformational free-energy difference to theoretical couplings of ``frozen'' structures and experimentally evaluated couplings of ``fluid'' structures. This permits the approximate determination of the gauche and trans vicinal couplings for the frozen conformations of a 1,2-disubstituted propane. These are —1.5 cps for the gauche and +15.5 cps for the trans coupling, in very good agreement with the findings of Gutowsky, Belford, and McMahon for other ethanic molecules studied by variable temperature techniques. Ranges of free energies are graphically related to computed couplings obtained from experimental spectra. The stereospecificity of the sign of the long-range couplings in these structures is deduced and predictions are made of the previously unreported signs of the reportedly observed long-range couplings in other related structures. Experimental measurements and predictions of the signs of long-range couplings are made for some 2,2-disubstituted propanes studied to evaluate the role of substitution in determining the magnitudes and signs of the long-range couplings in the 1,2-disubstituted propanes. Geminal J couplings computed from these spectra show novel solution effects. Experimental chemical shift differences are accounted for by considering the neighbor-anisotropy contributions in model structures.
Carbon Dioxide Dissociation at 3500° to 6000°K
Authors: Davies William O.
Published: January 2005

The dissociation rate of CO2 has been measured for temperatures of 3500° to 6000°K. The rate of disappearance of CO2 behind shock waves in CO2–N2 and CO2–Ar gas mixtures was monitored by observing the infrared radiation from the CO2 4.3-μ fundamental vibration band. The dissociation rates expressed in the classical collision theory for 1% CO2 in both Ar and N2 are kAr = (9.71) (10—14) (D/kT)4.38 exp (—D/kT) and kN2 = (3.27) (10—14) (D/kT)4.72 exp (—D/kT) where D = 5.5 eV is the CO2 dissociation energy, k is the Boltzmann constant, and T is the absolute temperature. The same data fit to an Arrhenius equation yields the rate constants kAr = (4.79) (10—13) T½ exp (—3.24 eV/kT) and kN2 = (4.07) (10—13) T½ exp (—3.23 eV/kT). The dissociation rate is not altered within the experimental error by (a) increasing the CO2 concentration up to 10%, (b) adding either CO of H2O to the gas for concentrations of these gases up to 2%, (c) making the dissociation measurement at different wavelengths or pass bands within the 4.3-μ band, or (d) making the dissociation measurement by observing the radiation from the CO2 2.7-μ combination bands.
Behavior of Fused-Ring Aromatic Hydrocarbons at Very High Pressure
Authors: Aust R. B. , Bentley W. H. , Drickamer H. G.
Published: January 2005

The effect of very high pressure has been studied on the electronic structure of some fused-ring aromatic hydrocarbons. The material most thoroughly studied is pentacene. Observations include optical absorption of the low-energy peaks and electrical resistance. The optical absorption peaks of tetracene and pentacene shift red at a rate which increases with density. Azulene peaks shift first blue, then red. The dipole moment of the excited state increases with increasing pressure. The electrical resistance decreases rapidly with increasing pressure, as a result of the decrease in activation energy for carrier production. Single-crystal pentacene becomes metallic at 270 kbar. The fused powder exhibits metallic behavior at somewhat higher pressures.

At pressures above about 180–200 kbar and temperatures above 180°—190°K an irreversible transition takes place in pentacene involving resistance increase and, at higher pressure, a transformation from metal to semiconductor. The low-energy optical absorption peaks have largely disappeared. It is proposed that this is a cross linking between adjacent molecules. A similar phenomenon is observed in violanthrene. The very sharp irreversible rise in resistance in single-crystal graphite above 150 kbar and 180°K may be an analogous cross-linking transformation.
Equilibrium in the Deuterium Exchange of Acetylene and Water
Authors: Pyper James W. , Long F. A.
Published: January 2005

The isotopic-exchange equilibrium between acetylene gas and deuterated water vapor has been experimentally studied over a wide range of deuterium content in the temperature range from 5° to 85°. The equilibrium constant K7 for the gas-phase reaction C2H2+D2O=C2D2+H2O is 0.473±0.008 at 25°. The thermodynamic parameters for the reaction are ΔH°=0.29 kcal/mole and ΔS°=—0.56 eu at 25°. The equilibrium constant for the disproportionation reaction C2H2+C2D2=2C2HD has also been measured and is found to have a constant value of 3.95±0.10 for the temperature range 5° to 85°. The exchange constant K7 has been calculated from the available spectroscopic data for the relevant acetylene and water species and the theoretical values agree with the experimental values to within 10%. The observed data for both the exchange and disproportionation reactions are consistent with those for similar systems.
Direct Determination of the Crystal Structure of Cornetite, Cu3PO4(OH)3, by the Monte Carlo Method
Authors: Fehlmann M. , Ghose Subrata , Finney J. J.
Published: January 2005

The crystal structure of the peacock-blue mineral cornetite, Cu3PO4(OH)3, orthorhombic, with a0=10.845, b0=14.045, c0=7.081 Å, space group Pbca, has been determined. The phase problem has been solved by the direct determination of the heavy atom positions through the application of the Monte Carlo and optimal shift methods. Subsequent three-dimensional Fourier synthesis revealed all the light atom positions. The atomic parameters have been refined, using three-dimensional data, by the method of full-matrix least squares.

Two of the three independent copper atoms have essentially fivefold tetragonal pyramidal coordination, the coordination plane being curved in a boat shape towards the fifth ligand. The third copper atom has a highly distorted tetragonal bipyramidal coordination. Cornetite contains two sets of dimeric cupric complex ions. The first set [Cu2(OH)4O2] is formed by two different copper coordination planes sharing an edge, and the second [Cu2(OH)4O4] by two tetragonal pyramids, related by a center of symmetry, sharing a pyramidal edge. The [Cu2(OH)4O2] dimers are stacked upon each other along the c axis in a zigzag fashion, so that each dimer has two (OH) groups common with two other dimers above and below it. The dimeric chains thus formed are held together in a three-dimensional network, through isolated [Cu2(OH)4O4] dimers, PO4 groups, and O–H···O bonds.
Initiation of Lead Azide by High-Intensity Light
Authors: Roth Julius
Published: January 2005

Radiation from an argon flash-bomb is used to initiate detonation in lead azide aggregates. Optical methods are employed to measure initiation delay as a function of energy absorbed by the azide. It is found that the product of the rate of energy absorption and the initiation delay is constant. This is interpreted in terms of a thermal initiation mechanism as follows: Absorption of flash-bomb radiation causes a continuing increase in azide surface temperature; above a critical temperature Tc, exothermic decomposition of the azide becomes very rapid and leads to thermal explosion and detonation in very short times. Typical initiation delays are of the order of 1 μsec and Tc∼900°K. Reaction-rate parameters calculated on the basis of this model, using measured initiation delays, are in good agreement with those obtained from thermal decomposition studies without explosion. It is shown that, for the experimental conditions used, purely photochemical reactions are unimportant.
Evolution of Molecular Systems and the Separation of Electronic and Nuclear Motions
Authors: Micha David
Published: January 2005

A time-dependent approach to the study of molecular systems is used to analyze the interaction between the electronic and nuclear motions. The set of coupled evolution equations for the nuclei, resulting from this treatment, is solved in a first-order perturbation approximation to obtain the decoupling of electronic and nuclear motions and to give conditions for its validity. A comparison is made with an adiabatic approximation treatment of the evolution equations and with the Born—Oppenheimer approximation, paying attention to the initial suppositions and to the restrictions in the different cases.
Absorption, Fluorescence, and Energy Levels of Ho3+ in Hexagonal LaCl3
Authors: Dieke G. H. , Pandey B.
Published: January 2005

The absorption and fluorescence spectrum of Ho3+ in LaCl3 has been obtained between 2600 and 12 000 Å and the energy levels established. The Stark components are virtually complete, except for the high-lying levels where, because of crowding and weak absorption, the interpretation becomes uncertain. The observed crystal field splittings for the low-lying levels agree reasonably well with calculated ones if B20=122, B40=—45, B60=—28, B66=280 cm—1. Zeeman effects for fields parallel and perpendicular to the axis have been obtained and used for the classification. Approximately 180 absorption and 380 fluorescence lines have been obtained. A considerable number of the former show resolved nuclear hyperfine structure. The mechanism for energy transfer between excited states has been cleared up.
Paramagnetic Resonance of Rare-Earth Ions in YCl3 and LuCl3
Authors: Garton G. , Hutchings M. T. , Shore R. , Wolf W. P.
Published: January 2005

The principal g values of the ground-state doublets of Dy3+, Er3+, and Yb3+ in monoclinic YCl3 and LuCl3 have been measured using EPR at 9.6 kMc/sec and 4.2°K. The results show little variation between the two host lattices, indicating their use for the interpretation of the bulk properties of the concentrated trichlorides. The principal g values of Ce3+ and Nd3+ in YCl3 have also been measured. It is found that the g values may be accounted for to a first approximation by a distorted octahedral cubic crystal field.
Correlation of Activation Energies and Bond Energies in CF3 Reactions
Authors: Carmichael Halbert , Johnston Harold S.
Published: January 2005

Rate constants and activation energies have been measured for deuterium abstraction from CD4, (CH3)3CD, and Cl3CD, to give, respectively: 10—12.6 exp(—12.1/RT), 10—11.3 exp(—7.4/RT), 10—12.0×exp(—9.0/RT) cc/molecules·sec with activation energies in kilocalories. By means of the London—Polanyi—Eyring—Sato LPES method of evaluating potential energy surfaces (with the one adjustable parameter fitted to the activation energy of the reaction CF3+CH4) and by means of activated complex theory, the predicted kinetic quantities (Arrhenius A, kH/kD, and other activation energies) were calculated for the two series involving both H and D: H3C–H, C2H5–H, (CH3)2CH–H, (CH3)3–H; H3C–H, H2ClC–H, HCl2C–H, Cl3C–H. The results are compared with observed values from the literature and from this study. The observed trend of E with bond energy for the series was compared with that predicted by the LPES method and that predicted by the one-parameter Polanyi—Semenov rule. For the general family of reactions of CF3 on substituted hydrocarbons RH, the following evaluation of the predictive value of the LPES method is made: Arrhenius E, not predicted but used to select the one adjustable parameter; Arrhenius A, predicted within a factor of 10 when full N-atom model is used and predicted very poorly when simple three-atom model is used; kH/kD, excellent prediction over wide range of temperature if large tunneling correction is made; E trend with —ΔH, good prediction, but no better than the vastly simpler Polanyi—Semenov rule.
Effect of Pressure on the Properties of TCNQ and Its Complexes
Authors: Aust R. B. , Samara G. A. , Drickamer H. G.
Published: January 2005

The effect of very high pressure has been measured on the properties of TCNQ (tetracyanoquinodimethane) and three complexes. For all three complexes the electrical resistance at 296°K decreased with increasing pressure to about 140–150 kbar, beyond which pressure there was a very large rise accompanied by much drifting upward with time. This transformation was irreversible. At 78°K no rise was noted at high pressure, but if a sample was heated at high pressure the transformation initiated about 180°K.

It was found that the absorption peaks in the visible region had almost completely disappeared in the transformed material although the 280-mμ peak remained. The resistance of TCNQ was too high to permit electrical studies, but samples taken to high pressure also showed disappearance of absorption peaks in the visible. These and other related observations indicate that the TCNQ molecules are reacting, probably through the C≡N bond. The type of reaction seems in many ways similar to that obtained in pentacene and single-crystal graphite and discussed in a previous paper.
Interaction Effects on Lifetimes of Atomic Excitations
Authors: Hutchinson D. A. , Hameka H. F.
Published: January 2005

The apparent lifetime of an excited atom in a p state is investigated when another atom, in an s ground state, is present. The dependence of the lifetime on the distance RAB between the two atoms is obtained. It is found that the results for a p0 state differ somewhat from those for the p±1 states. (The axis of quantization is taken as the line joining the two atoms.)
Angular Momentum Distribution and Emission Spectrum of OH (2Σ+) in the Photodissociation of H2O
Authors: Carrington Tucker
Published: January 2005

When water vapor absorbs light of wavelength less than 1350 Å, an electronically excited OH fragment may be produced. This process has been observed, using wavelengths 1216, 1236, and 1302 Å, and the rotational and vibrational excitation of the product OH 2Σ+ has been determined from its emission spectrum. Most of the energy beyond that necessary to produce electronically excited OH goes into rotation of that molecule. Roughly one-third of the OH molecules have one quantum of vibrational energy, and in these molecules too, the highest energetically allowed rotational levels are strongly populated.

Knowledge of the energy and rotational angular momentum of the OH allows estimation of the kinetic energy and orbital angular momentum of the H as it flies away from the center of mass. This is interpreted in terms of two-body forces at large distances, with the most probable dissociation corresponding to an orbiting interaction.
Calculation of Thermodynamic Properties of Fused Salts from a Rigid-Sphere Equation of State
Authors: Yosim S. J. , Owens B. B.
Published: January 2005

A rigid-sphere equation of state developed by Reiss, Frisch, and Lebowitz was used as a starting point for the development of expressions for the absolute entropy, entropy of fusion, heat capacity, and compressibilities of molten alkali halides. The absolute entropy of 2 moles of rigid spheres, compressed to the volume of the fused salt, was found to be equal to that of the molten salt. The entropy of compressing these rigid spheres from the molar volume of the liquid to the volume of the solid was in good agreement with the entropy of fusion of fused alkali halides. The heat capacity calculated by the differentiation of the expression for the absolute entropy, at constant pressure of the liquid, was also in good agreement with experimental values. However, the agreement between the calculated compressibility and the experimental results was not good.
NMR Study of Rotational Barriers and Conformational Preferences. II. d11-Cyclohexane
Authors: Bovey F. A. , Hood F. P. , Anderson E. W. , Kornegay R. L.
Published: January 2005

The rate of conformational isomerization of cyclohexane has been measured over the temperature range —75.0 to —47.0° by observation of the NMR spectrum of C6HD11, which is much simpler than that of cyclohexane itself and is amenable to exact kinetic treatment. The line broadening arising from D—H coupling was eliminated by double resonance. It is found that ΔF‡ is equal to ΔH‡ within experimental error for the chair-to-chair reaction and is 10.5 kcal (206.0°K) (10.2 kcal for the chair-to-boat process); ΔS‡ for the chair-to-chair process is thus about zero and for the chair-to-boat process is about +1.4 eu.
United Atom Treatment of H2+
Authors: Levine Ira N.
Published: January 2005

The exact second-order united atom perturbation energy for the ground state of H2+ is evaluated. The result shows that for small internuclear distance R, the second-order perturbation energy goes as R3.
Fluorescence Quenching and Energy Transfer in Monomolecular Films Containing Chlorophyll
Authors: Tweet A. G. , Bellamy W. D. , Gaines G. L.
Published: January 2005

Quenching of the fluorescence of chlorophyll a in monomolecular films by copper pheophytin a, a non-fluorescent chlorophyll derivative, has been measured as a function of quencher concentration. For some measurements the monolayers consisted entirely of chlorophyll plus an admixture of quencher (0.001–0.2 mole fraction). For other measurements, the pigments were dissolved in monolayers of the inert diluent oleyl alcohol. The fluorescence quenching data were analyzed in terms of the inductive resonance transfer mechanism of Förster for the chlorophyll—quencher interaction. For the dilute layers, where a single-transfer calculation is satisfactory, the range of the chlorophyll—quencher interaction in the Förster theory is 40 Å. This result is in fortuitously good agreement with values of 38–41 Å derived from optical absorption and emission spectra also measured in dilute monomolecular layers. For the undiluted monolayers, where interactions among chlorophyll molecules are much more important, the single-transfer model is not applicable. The fluorescence quenching data have been analyzed in terms of diffusion of localized excitations. Values of approximately 13 Å for the range of the chlorophyll—quencher interaction and 20–23 Å for the chlorophyll—chlorophyll interaction were derived from this analysis. These results are to be compared with values of 11–12 Å and 18 Å, for the two interaction ranges, respectively, calculated from the optical properties. It is pointed out that a collective excitation representation would be more appropriate for describing the undiluted monolayers.
Anisotropic Proton Hyperfine Interaction in the CH Bond
Authors: Higuchi Jiro
Published: January 2005

The anisotropic proton hyperfine interaction of the CH fragment is investigated in connection with the properties of the CH bond in aromatic hydrocarbon radicals or ions by the use of the LCAO—MO's determined by the condition of minimum energy. The dependence of the hfs on the bond angle is not as great as that expected from a simple consideration of the s—p hybridizations in the CH bond.
Computer Analysis of NMR Spectra: Magnetic Equivalence Factoring
Authors: Ferguson Raymond C. , Marquardt Donald W.
Published: January 2005

An extension of the NMR analysis method of Swalen and Reilly is described. The Hamiltonian matrix is factored to reduce it to minimal dimension by taking advantage of magnetic equivalence. Significant improvements are obtained in computation speed, computer program capacity, and convenience of use. Other extensions of the method provide a thorough statistical assessment of the resulting parameter estimates, and permit a solution even when some of the energy levels do not participate in any of the assigned transitions. The method has been tested by analyzing the 60-Mc/sec proton resonance spectra of propane (A6B2) and isobutane (A9B). The chemical shifts, downfield from internal tetramethylsilane, and the coupling constants are: CH3CH2CH3; δ(CH3) = 0.912±0.005 ppm, δ(CH2) = 1.350±0.005 ppm, J = 7.35±0.02 cps: (CH3)3CH; δ(CH3) = 0.900±0.005 ppm, δ(CH) = 1.738±0.005 ppm, J = 6.73±0.05 cps.