bluuebunny/crossref_metadata_2025_split huggingface dataset:
Higher Ionization Potentials of Linear Triatomic Molecules. II. CS2, COS, and N2O
Authors: Tanaka Y. , Jursa A. S. , LeBlanc F. J. 
Published: January 2005

Four ionization potentials for the CS2 molecule, three for the COS, and three for the N2O were determined by an analysis of Rydberg series of the respective molecules. Our value for the first ionization potential of CS2 agrees very well with the previous spectroscopically determined value; however, there was disagreement between our value for the first ionization potential of N2O and that determined previously.
Several progressions of absorption bands for each of the molecules were also observed.
Observations of the Thermal Behavior of Radicals in Gamma-Irradiated Ice
Authors: Siegel Seymour , Baum Lillian H. , Skolnik Sol , Flournoy John M. 
Published: January 2005

Ice was subjected to γ radiation at 77°K and the EPR spectra of the radicals produced were examined as a function of temperature. The spectrum consisted essentially of a doublet centered at g=2.008±0.002 and split by 40 gauss; the corresponding spectrum of irradiated D2O consisted of a triplet with approximately 6 gauss between adjacent lines. The doublet decayed rapidly above 100°K leaving a residual broad line which was thermally stable until approximately 145°K. The main spectrum has been attributed to the OH radical and the residual line assigned to the HO2 radical. The decay process of the OH radicals was shown to follow the rate law d(OH)/dt=—k(OH)32 where k=8.5×1012 exp—6000/RT (liter/mole)½ sec—1. The magnitude of the rate constant was shown to be a function of the total irradiation damage experienced by the ice sample.
Stabilization of OH radicals at 77°K was studied as a function of total irradiation dosage; saturation is reached at an OH concentration of 1.8×10—3M or 0.003 mole %. The EPR spectrum of a frozen aqueous NO solution was also observed; it consisted of a broad line centered at approximately g=2.08.
On the Mechanism of the Lewis-Rayleigh Nitrogen Afterglow
Authors: Bayes K. D. , Kistiakowsky G. B. 
Published: January 2005

The relative intensities in the nitrogen afterglow, from 5000 to 11 000 A, have been measured in pure nitrogen and after addition of several foreign gases. Most of the bands in the recently discovered Y — B 3Πg system are overlapped by B 3Πg — A 3Σu+ bands but intensity assignments have been made. Changes in relative intensities accompanying changes in external conditions show that the bands can be classified into five groups of different kinetic origins. The vibrational levels of the B 3Πg and Y states just below De, the energy of two separated ground state nitrogen atoms, are not populated. At low temperature the highest populated levels of the B 3Πg and Y states tend to a limit about 850 cm—1 below De. It is suggested that this is approximately equal to the dissociation energy of the 5Σg+ state of the nitrogen molecule. Some of the emission from the low vibrational levels of the B 3Πg state is associated with the radiation cascade Y→B 3Πg→A 3Σu+, but the rest has a different kinetic origin. The emission from B 3Πg (v=7, 6, 5) is probably the second step in the cascade 3Δu→B 3Πg→A 3Σu+.
Foreign gases modify the vibrational population distribution of the upper levels of the B 3Πg state, each in its characteristic fashion. Some gases quench the emission from the lowest vibrational levels of B 3Πg more effectively than the rest of the spectrum. The quenching of the emission from the higher levels depends on the pressure of nitrogen. A mechanism accounting for most of the afterglow emission is discussed.
Nuclear Magnetic Resonance Spectra of Some Simple Epoxides
Authors: Reilly C. A. , Swalen J. D. 
Published: January 2005

High resolution NMR spectra of four epoxides have been observed at 40 Mcps and analyzed. These epoxides are of the type[Complex chemical formula]where R is a phenyl group (styrene oxide), a cyanide group (glycidonitrile), an acetyl group (1,2-epoxy-3-butanone), and a carboxyl group (glycidic acid). For each molecule the spin-spin coupling constants and nuclear magnetic screening parameters for the A, B, and C protons were derived from the experimentally determined energy levels. The method for obtaining numerical values for the energy levels from the spectra is described fully. ABK and AA′K approximations as well as an iterative ABC method of solution are described and illustrated.
Corresponding coupling constants are found to be about the same in all four molecules with JAB=5.8±0.5 cps, JAC=2.2±0.5 cps and JBC=4.6±0.5 cps. However, the variations from molecule to molecule are considerably greater than the estimated precision of ±0.05 cps. The ABX approximation is shown to be inadequate either for the precise determination of the constants or for the calculation of relative intensities. As compared with the iterated ABC solution, the ABK or AA′K approximation leads to good values for the constants and adequately describes the relative intensities.
Relative Signs of Spin-Spin Interactions in Nuclear Magnetic Resonance. II
Authors: Alexander S. 
Published: January 2005

The spectrum of the allyl group in allyl amine is discussed in detail. The interpretation of the spectra of 1-butene and 3,3-dimethyl-1-butene are also discussed. It is shown how the chemical shifts, spin-spin interactions, and in particular the relative signs of the latter can be determined by numerical methods.
In all three molecules all spin-spin interactions among the vinyl protons have the same sign. One of the three vinyl-methylene interactions is found to have a different sign than the other two. This interaction has the same sign (and approximately the same magnitude) as the methyl-methylene interaction in 1-butene.
Theory of Dilute Polymer Solution. III. Heterogeneous Polymer
Authors: Yamakawa Hiromi , Kurata Michio 
Published: January 2005

The second virial coefficients of osmotic pressure and light scattering of heterogeneous chain polymer solutions are calculated to the double-contact approximation. Two types are assumed for the molecular weight distribution: the Schulz distribution, and the distribution with two deltalike peaks.
Then, the heterogeneity corrections for intrinsic viscosity are evaluated on the assumption of the Schulz distribution. On the basis of the results obtained, a tentative attempt is made at interpreting the proportionality between the intrinsic viscosity at the Θ temperature and the square root of the molecular weight without discarding the hydrodynamic scheme, and the relation between the hydrodynamic and statistical radii of heterogeneous polymer coil is also examined.
Finally, the relation between the second virial coefficient A2 and intrinsic viscosity [η] is discussed somewhat in detail. And it is shown that the initial curvature of the curve of [η]/[η]θ — 1 vs A2Mw/[η]θ is concave upward for ordinary fractionated samples, where [η]θ is the intrinsic viscosity at the Θ temperature, and Mw is the weight-average molecular weight. This statement is verified by comparison with experiment.
Sparking Potential and Molecular Structure of Unsaturated Hydrocarbon Gases
Authors: Crowe R. W. , Devins J. C. 
Published: January 2005

In earlier experiments, we have shown that it is possible to relate sparking potentials of saturated hydrocarbon gases to certain molecular properties. From measurements of electric breakdown in a series of these gases, it has been found that the effective molecular cross section for electron scattering is proportional only to the number of carbon-hydrogen bonds in the molecule and is independent of their disposition. The lack of a contribution by the carbon-carbon bonds has been attributed to a shielding effect.
In the present paper, we describe and discuss the results of a similar investigation of breakdown in unsaturated hydrocarbon gases. It was found that, for a series of olefin gases, the cross section associated with the carbon-carbon double bond is greater than three times that of the carbon-hydrogen bond, while that of the carbon-carbon single bond is essentially zero as it was in the alkane series. An attempt is made to interpret this observation in terms of (1) a decrease in the shielding effect, and (2) the larger spatial configuration of the π-electron orbitals associated with the ethylenic linkage. Variations in the position of the double bond within the molecule has little or no effect upon its contribution to the total cross section.
Breakdown measurements in butadiene-1,3 and benzene indicate that conjugation results in an increase in the effective cross section of each double bond, as might be expected. Evidence of a small but measurable amount of double-bond character was also found in cyclopropane from sparking potential measurements. This is in agreement with the predictions of other investigators.
Proton-Transfer Studies by Nuclear Magnetic Resonance. I. Diffusion Control in the Reaction of Ammonium Ion in Aqueous Acid
Authors: Emerson Merle T. , Grunwald Ernest , Kromhout Robert A. 
Published: January 2005

Rate constants were determined by precise nuclear-magnetic-resonance techniques for the reactions: NH4++H2O−→ lim k4NH3+H3O+;NH3+H3O+−→ lim k-4NH4++H2O;and N lim −H4++NH3−→ lim k6N lim −H3+NH4+in aqueous acid at 25°C. For 0.25–3.00M NH4Cl, k—4 and k6 were 4.3×1010 sec—1M—1 and 1.17×109 sec—1M—1 respectively, independent of NH4Cl concentration. Both rate constants increase on addition of KCl. The rate constant, k4, was 24.6 sec—1 at zero ionic strength and decreased sharply with NH4Cl concentration. The values of KA needed in the kinetic analysis were measured also. The reaction of NH4+ with H2O was investigated also in 50–60 wt % H2SO4-H2O mixtures, where the half-life for isotopic exchange was between two and 20 minutes. The data allowed us to estimate the rate constant (1/τD+1/τR) for the rupture of the H3N···HOH hydrogen bond, by diffusion (D) or rotation (R). The value obtained was 51×1010 sec—1. Using Einstein's theory of Brownian motion, the value of 1/τD was estimated to be 34×1010 sec—1, leaving 17×1010 sec—1 for 1/τR, of which 12×1010 and 5×1010 sec—1 are the contributions due to the rotation of H2O and NH3, respectively. The probability that NH3 rotates during an encounter is therefore fairly small.
The order of magnitude of k—4 and k6 suggests that these reactions are diffusion controlled. Upon applying the Debye-Smoluchowski theory to calculate the frequency of encounters, we found that k—4 is consistent with reaction occurring whenever H3O+ and NH3 are next-nearest neighbors. The steric factor for this reaction appears to be unity. Since the data in strong acid suggest that rotation of a molecule during an encounter is improbable, we conclude that the reactants are oriented during their approach so that the unshared electrons of the NH3 face an acidic hydrogen. To interpret k6, we assume a mechanism in which NH3 and NH4+ become next-nearest neighbors by simple diffusion; the jump to a nearest-neighbor site then requires a somewhat higher activation energy than simple diffusion because NH3 must displace a tightly bonded water molecule. The reaction with rate constant k4 is activation controlled. The negative salt effect on k4 suggests diffusion of charge in the transition state.
Emission Spectra of Erbium in the Scheelite Structure
Authors: Van Uitert L. G. , Soden R. R. 
Published: January 2005

Erbium exhibits luminescent emission from excited states at 15 300, 18 400, and 24 500 cm—1 in calcium tungstate at room temperature and at 77°K. At room temperature, emission from thermally excited states at 18 830, 19 080, and 19 200 cm—1 is also prominent.
At high erbium concentrations, the above spectra are essentially quenched at room temperature and new spectral lines which appear to originate from electronic levels just below the 18 400- and 24 500-cm—1 states are seen. However, at 77°K, emission from the 15 300, 18 400- and 24 500-cm—1 states is again strong and emission associated with levels just below these is no longer observed.
There is no evidence of exchange coupling preferentially quenching the higher-energy emission states as in the cases of Tb3+ and Eu3+. This and the temperature dependencies observed suggest that thermal coupling to the lattice is the main factor responsible for quenching the emission of Na0.5 Er0.5 WO4.
Thermal-Diffusion-Column Shape Factors for the Lennard-Jones (12–6) Potential
Authors: McInteer B. B. , Reisfeld M. J. 
Published: January 2005

The theory of the hot-wire thermal-diffusion column as developed by Jones and Furry involves the shape factors h, kc, and kd, which are functions of the transport properties of the gas. The shape factors have been evaluated numerically for a gas whose molecules interact according to the Lennard-Jones (12–6) potential, given by V(r)=4ε[(σ/r)12−(σ/r)6]. The results are tabulated for a range of kT/ε from 0.8 to 30 for temperature ratios as great as 6 and for ratios of column radii up to 100. These values are more accurate than those previously computed for potentials varying as r—5 (Maxwellian) and for r—∞ (rigid spheres).
The values for the constants are found to give good agreement with experimental data on the system He3-He4.
Molecular Structure of Lithium Chloride Dimer. Thermodynamic Functions of Li2X2 (X = Cl, Br, I)
Authors: Bauer S. H. , Ino Tadashi , Porter Richard F. 
Published: January 2005

Our electron diffraction apparatus has been suitably modified for the study of vapors at high temperatures. A furnace and auxiliary power supply have been constructed, and a serviceable design for a sample container, with a nozzle, has been developed.
Data on two systems have been obtained. The diffraction pattern produced by cesium chloride vapor is that expected for a diatomic molecule; the interatomic distance determined in this experiment checks with the microwave value. In lithium chloride vapor, dimers predominate. Their structure is diamond shape (planar) with Li–Cl=2.23±0.03 ACl–Cl=3.61±0.03 A∠ClLiCl=108∘±4∘.
The dimensions of the lithium halide dimers are compared and their thermodynamic functions tabulated.
Streaming Birefringence of Rigid Macromolecules in General Two-Dimensional Laminar Flow
Authors: Wayland Harold 
Published: January 2005

Quantitative expressions for the direction of the angle of isocline and for the amount of birefringence due to a dilute solution of rigid macromolecules in a general two-dimensional laminar flow are derived. If E is the principal strain rate and Λ0 is the angle between the streamline direction and the direction of the principal strain rate axis, the angle of isocline, measured from the first principal strain rate axis is χ=−(Esin2Λ0/6D){1−(E2/27D2)[sin22Λ0+(24b2/35)]+···],where b=[(a12—a22) / (a12+a22)] is a shape factor for an ellipsoid of revolution of semimajor axis a1 and semiminor axis a2 and D is the rotary diffusion constant for this ellipsoid. The amount of birefringence is Δn=(4π/15)(cGEb/nD) {1−(E2/18D2)[sin22Λ0+(6b2/35)]+···},where n is the mean index of refraction of the solution, c the volume concentration of the macromolecules, and G=g1—g2 is the optical anisotropy of the ellipsoids.
It is seen that if the principal strain rate is not at 45° to the streamline at the point of observation, this will make itself felt in the position of the angle of isocline before it influences the amount of birefringence.
Detailed expressions for the effect of polydispersity show that there is a simple relationship between the birefringence and angle of isocline measured in Couette flow and these quantities measured in general two-dimensional flow only if (a) Λ0=45° in the general flow or (b) the birefringence and angle of isocline values are linear with strain rate.
Approximate Electronic Energy Surfaces from Cuspless Wave Functions
Authors: Wulfman Carl E. 
Published: January 2005

The eigenfunctions of a molecular Hamiltonian in which all Coulomb potentials have been replaced by Hooke's law potentials are easily determined. Their electronic parts are essentially single-particle single-center harmonic oscillator, or Gaussian wave functions originating at the center of nuclear charge. An investigation is made to determine the feasibility of using these cuspless base functions in variational calculations of relative molecular electronic energies. It is found that:
A. Addition of Coulombic or delta-function singularities to the Hooke's law potentials leads to the formation of rigid molecular systems.
B. The Coulomb potentials in 21–26 electron triatomics can be treated as a perturbation upon quadratic potentials.
In agreement with experiment it is noted that:
C. Approximately homonuclear (i.e., nonhydride) 8-, 20-, and 40-electron polyatomics are configurationally unstable.
D. The molecules CO2+, CO2, N2O, NCO—, BO2—, N3—, and NO2+ should all be linear.
E. The molecules NO2—, O3, FNO, F2O, and a number of excited states of the molecules (D) should all be nonlinear.
F. The stable form of nitrous oxide should be N–N–O rather than N–O–N.
A number of general features of the treatment are discussed and several of its limitations are pointed out. A tabulation of coefficients required in Clebsch-Gordan expansions of products of Hermite polynomials is given.
Vapor Pressures of the Neon Isotopes
Authors: Bigeleisen Jacob , Roth Etienne 
Published: January 2005

The ratio of the vapor pressures of Ne20 and Ne22 have been measured in the temperature range 16–30°K. An accuracy of about 1% in the logarithm of the vapor-pressure ratio has been achieved. The latter is checked by comparisons of (1) triple-point pressures, (2) equilibrium fractionation experiments, and (3) the entropy difference of the condensed phases with thermal measurements.
The Debye temperature for the solid derived from the ratio of the vapor pressures, 74.6°K, is in good agreement with values derived from the Debye-Waller temperature factor and theoretical calculations by Bernardes. The discrepancy between the characteristic temperatures derived from measurements of free energy with those from heat capacities is attributed to the role of the anharmonicity of the lattice.
It is shown that the difference in the thermodynamic properties of solid and liquid neon in the vicinity of the triple point can be attributed to the change in coordination number.
Theoretical Interpretation of Carbon-13 Hyperfine Interactions in Electron Spin Resonance Spectra
Authors: Karplus Martin , Fraenkel George K. 
Published: January 2005

A quantitative theory of the isotropic electron-nuclear spin interactions of carbon 13 in pi-electron radicals is presented and applied to the hyperfine splittings observed in the electron spin resonance spectra of these substances. The splittings arise from sigma-pi interactions which polarize both the 1s and 2s electrons. The 1s-orbital spin polarization is shown to contribute a term of negative sign with a magnitude comparable to that from the 2s electrons. For an sp2 hybridized carbon atom that is bonded to three atoms, Xi (i=1, 2, 3), the hyperfine constant aC has the form aC=(SC+ ∑ i=13QCXiC)ρπ+ ∑ i=13QXiCCρiπ,where ρπ and ρiπ(i=1,2,3) are the pi-electron spin densities on atoms C and Xi, respectively. The contribution of the 1s electrons is determined by SC and that of the 2s electrons by the Q's, where QBCA is the sigma-pi parameter for the nucleus of atom A resulting from the interaction between the bond BC and the pi-electron spin density on atom B. Calculations for a planar CHC2 fragment model yield SC= —12.7 gauss, QCHC=19.5 gauss, QCC′C=14.4 gauss, and QC′CC= —13.9 gauss.
The theory predicts both the magnitude and sign of the hyperfine splittings and is readily applied to a variety of compounds. Excellent agreement is obtained with the available experimental data. For the methyl radical, the measured C13 splitting is shown to be consistent with a planar model and limits the deviation from planarity to ≲5°. The theory provides a useful criterion for the validity of approximate wave functions that is illustrated by a comparison of various theoretical treatments for the naphthalene negative ion and triphenylmethyl. The sigma-pi interaction parameters are shown to depend on the bond length, the type of hybridization (including the angles between sigma bonds), and on the nature of the bonding atoms. For pi-electron systems, the results demonstrate that the magnitude of the sigma-pi exchange energy is a small fraction of the total energy. It is also noted that the proton parameter QCHH is somewhat larger in CHC2 than in CH3, which suggests a theoretical justification for some of the variation in the experimental ``QCHH'' required to fit measured proton splittings. The form of the theory is readily extended to the treatment of hyperfine splittings from nuclei other than C13.
Low-Temperature Chemisorption. III. Studies in the Field Emission Microscope
Authors: Ehrlich Gert , Hudda F. G. 
Published: January 2005

The dependence of adsorption upon surface structure has been examined with the field emission microscope. Nitrogen adatoms are found on all the planes of tungsten accessible to observation. Their rate of diffusion is fastest over the regions around the 111 pole; the barrier to migration over this area is only 20 kcal mole—1, compared to 35 kcal mole—1 for diffusion over the sharply stepped region surrounding the 100 pole.
A strong structural effect is observed for the weakly bound α state of nitrogen, unstable at T&gt;400°K. This state is concentrated on and around the (111). By contrast, nitrogen molecules held at 79°K in the γ state are distributed without pronounced specificity for surface structure. However, the absence of diffusion in both these states suggests that the nitrogen is held at isolated, discrete sites. The γ state on tungsten somewhat resembles nitrogen adsorbed on nickel; for this system chemisorption is lacking at room temperature, but at 79°K molecules are bound with an energy of at least 5.5 kcal mole—1. At an even lower temperature, T∼20°K, an additional binding state, consisting of nitrogen physically adsorbed on top of the chemisorbed layer, is observed on tungsten. Diffusion out of this state occurs at T∼40°K with the formation of a sharp border, indicating immediate chemisorption of material spilling over the chemisorbed layer.
For the adsorption of carbon monoxide on tungsten no structural specificity appears in the field emission microscope. In addition to the primary chemisorbed state, the presence of weakly bound carbon monoxide is confirmed and it is shown that for neither state does dissociation occur. Both carbon monoxide and nitrogen lower the rate of electron emission from an initially clean tungsten surface. CO raises the work function by 0.5 ev at T∼300°K. In the γ state nitrogen also causes an initial work function increase of 0.1 ev. Nitrogen adatoms, however, are found to lower the work function, in contrast with the results obtained for other dissociating gases, as well as with previous work function measurements on nitrogen itself.
Effect of Pressure on Crystal-Field Energy and Covalency in Octahedral Complexes of Ni2+, Co2+, and Mn2+
Authors: Zahner J. C. , Drickamer H. G. 
Published: January 2005

The effect of pressure has been measured on the absorption spectra of NiCl2, NiBr2, Ni(NH3)6Cl2, CoCl2, CoBr2, MnCl2, and MnBr2. The pressure shifts in every case correspond to increase in crystal field strength. To account for the shifts in a quantitative manner it is necessary to presume that the Racah parameter B decreases with increasing pressure. This can be interpreted as an increase in covalency at high pressure.
From the data on MnCl2 and MnBr2 it is possible to establish limitations on the possible range of values of the parameter ε introduced by Koide and Pryce to describe covalency in transition metal complexes.