bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microwave Spectrum of Methyl Nitrate
Authors: Dixon William B. , Wilson E. Bright 
Published: January 2005

The ground-state rotational constants of methyl nitrate show that the five heavy nuclei of the molecule lie in the same plane. The hydrogen atoms of the methyl group are found to be staggered with respect to the nearest oxygen of the NO2 group. Stark effect measurements yield a dipole moment of 3.10±0.05 D.
Satellites arising from excited states of the torsion of the NO2 group were observed. Rough relative intensity measurements yield a frequency of 130±20 cm—1 for this normal mode and a barrier of 9100±2600 cal/mole. This would seem to indicate a significant amount of double-bond character in the CO–N bond.
The barrier to internal rotation of the methyl group, as determined from torsional satellite splittings, is 2321 cal/mole.
A large discrepancy exists between the experimental and statistical entropies, the reason for which is not clear.
Satellites arising from the combination first excited states of the methyl and NO2 torsions have an anomalous appearance on the basis of the single internal rotor theory. A qualitative explanation for this is obtained when the theory is extended to include the torsion of the NO2 group.
First Excited Σg+1 State of the Hydrogen Molecule
Authors: Davidson Ernest R. 
Published: January 2005

A variation calculation on the first excited Σg+1 state of H2 has been carried out using an expansion in elliptical coordinates. All results are reported in Hartree atomic units.
The potential function resulting from this calculation is characterized by having minima at R=1.9 and R=4.3 and a maximum at R=3.3.
The energy obtained at R=1.9 using a 20-term, open-shell, covalent-type wave function was —0.7162 as compared with the ``experimental'' value of —0.7181. Due to convergence difficulties, many more configurations are required to improve this result significantly. At R=4.3, on the other hand, the best result was obtained with an open-shell wave function including nine ionic terms and nine atomic terms. This result of —0.7007 is below the reported ``experimental'' value of —0.6935 because the two lowest (2pσ)2Σg+1 vibrational levels have not been found experimentally. The energy at the top of the barrier was computed to be —0.6844 and probably is as low as —0.6884.
The vibrational levels for this potential function have been computed by a numerical integration technique. The fact that these are in one-to-one correspondence with a combination of the experimental 1s2s and (2pσ)2 levels indicates that both of these sets of levels belong to the first excited state.
NMR Fluorine-Fluorine Coupling Constants in Saturated Organic Compounds
Authors: Petrakis L. , Sederholm C. H. 
Published: January 2005

The spectra of several fluorine-substituted, saturated, organic compounds have been investigated. It has been found that the coupling constants between 1,2 fluorine atoms are usually near zero. The coupling constants between 1,3 fluorine atoms in a free chain are usually between 7 and 10 cps if all of the intermediate skeletal atoms are carbon atoms. If one of the intermediate skeletal atoms is a nitrogen atom, these coupling constants go up to between 10 and 17 cps. The coupling constants between 1,4 fluorine atoms are usually in the range 2–7 cps when a nitrogen atom is in the intermediate skeletal chain. Rings usually reduce all coupling constants below the above stated values.
Several exceptions are found to these generalizations. These generalizations with their exceptions lead the authors to believe that in the case of coupling between fluorine atoms, the main effect is not through-the-bonds, but rather a direct-through-space interaction. It is demonstrated that the restricted rotation about the carbon-carbon bonds has little to do with the near-zero coupling constants, but that these are readily explained on the basis of through-space coupling.
Effect of Temperature on the Intensity and Structure of Bands in the Infrared Spectrum of Rhombic Sulfur
Authors: Neff Vernon D. , Walnut Thomas H. 
Published: January 2005

The infrared spectrum of rhombic sulfur was obtained in the region between 750 and 2000 cm—1. The relative intensities of the bands at 845, 936, 1298, and 1513 cm—1 were measured as a function of temperature and sample orientation from —190° to 85°C.
An expression is given that relates the temperature dependence for an overtone or combination band to the values of the component frequencies. The expression is used in conjunction with the measured temperature dependence to reject some previous assignments and to establish rough values of the component frequencies in the observed overtone and combination bands. A tentative assignment consistent with the rough values found for the component frequencies is made.
In addition, the structure of a band is considered to be the result of combination with acoustic lattice modes, and the temperature dependence of the structure is analyzed from this point of view. The temperature dependence of the intensity of the structure of the band at 845 cm—1 far from the peak agrees roughly with the expression obtained, but the dependence close to the peak does not.
Neutron Diffraction Studies of CaC2, YC2, LaC2, CeC2, TbC2, YbC2, LuC2, and UC2
Authors: Atoji Masao 
Published: January 2005

The complete-matrix least-squares analysis on the neutron diffraction intensities of CaC2, YC2, LaC2, CeC2, TbC2, YbC2, LuC2, and UC2 yielded the C–C distances in the C2 groups, 1.191±0.009, 1.275±0.002, 1.303±0.012, 1.283±0.004, 1.293±0.009, 1.287±0.010, 1.276±0.012, and 1.340±0.007 A, respectively. The statistical averages of the neutron scattering amplitudes obtained from the dicarbide data and those reported previously are 0.488±0.007, 0.796±0.009, 0.832±0.014, 0.482±0.006, 0.756±0.020, 1.262±0.012, 0.73±0.02, and 0.851±0.022, all in 10—12 cm with positive sign, for Ca, Y, La, Ce, Tb, Yb, Lu, and U, respectively.
The paramagnetic scattering analyses revealed that all metal atoms in these dicarbides are in their trivalent Hund ground state, except Ca (divalent), Yb (possible valency of 2.8), and U (possible tetravalent). The scattering data also deduced the screening constants for the 4f electrons in Ce, Tb, and Yb as 39, 43, and 43, respectively, which are compared with those obtained by other methods. The bond numbers for the rare-earth dicarbides are briefly discussed.
Neutron-Diffraction Studies of La2C3, Ce2C3, Pr2C3, and Tb2C3
Authors: Atoji Masao , Williams Donald E. 
Published: January 2005

The neutron diffraction data of the rare-earth sesquicarbides with the Pu2C3-type structure (D5c type), La2C3, Ce2C3, Pr2C3, and Tb2C3, were analyzed using the complete-matrix least-squares method. These sesquicarbides contain the C2 groups with the C–C distances, 1.236±0.009, 1.276±0.005, 1.239±0.003, and 1.240±0.005 A, respectively, for La2C3, Ce2C3, Pr2C3, and Tb2C3. These values are, except for Ce2C3, significantly longer than the C–C distance in CaC2, 1.191 A, but are shorter than the average C–C distance in the rare-earth dicarbides, 1.278 A.
The paramagnetic scattering analyses show that all metal atoms in these sesquicarbides are in their trivalent Hund ground state, except Ce in Ce2C3, whose possible valency is about 3.4. The screening constants for the 4f hydrogenic radial wave functions of Pr and Tb as determined from the diffuse scattering analyses of their sesquicarbides are 40 and 43, respectively. The valency and metallic bonds in these sesquicarbides are briefly discussed.
Structural Requirements of Organic Liquid Scintillators
Authors: Heller Adam 
Published: January 2005

A theory is proposed to explain the relationship between the structure and the scintillation efficiency of organic liquid scintillators.
The requirements for good scintillation properties in given solvent-solute systems are found to be: (a) the existence of pairs of energy levels in the solute which are identical with those involved in the excitation of the solvent and (b) a nonrigid structure in the solute, capable of undergoing conformational changes in the excited state.
It was found that the behavior of liquid scintillators satisfied these requirements. Good scintillation properties were predicted for some hitherto unknown scintillators.
Molecular Weight Distribution of Polymers from Rheological Measurements in Dilute Solution
Authors: Peticolas Warner L. 
Published: January 2005

A method for obtaining the molecular weight distribution of linear polymers from rheological measurements in dilute solution is obtained through the use of the normal-coordinate theory of viscoelasticity as modified by Zimm to include hydrodynamic interactions.
Equations for the frequency-dependence of viscoelastic properties in dilute solutions are shown to the form Φ (ω) = Σpλp-nf(ωλp-m), where Φ(ω) is a measurable, frequency-dependent viscoelastic property. The summation extends over the set of characteristic values λp, which accounts for the relaxation of various normal modes of motion of the molecule as perturbed by hydrodynamic interaction with the solvent; and f(ωλ1-m) is directly related to the molecular weight distribution through an integral equation λ1−nf(ωλ1−m)= ∫ 0∞K(M,ω)W(M)dM,where W(M) is the weight fraction of molecules in range dM at M and K (M, ω) is a kernel dependent upon the quantity measured. Inversion of the above summation has been accomplished for the particular case of characteristic values which obey the inequality, Σpλp-n&lt;2λ1-n, so that f(ωλ1-m) may be obtained directly from the experimentally measured Φ(ω). W(M) is then obtained from f(ωλ1-m) through a solution of the integral equation.
Neutron Diffraction Data for Ta2D and the Probable Arrangement of the Deuteriums in Two of Its Polymorphic Varieties
Authors: Wallace W. E. 
Published: January 2005

Neutron diffraction data are presented for Ta2D at 4°K, 78°K, room temperature, and 53°C. The patterns are indexed assuming a pseudocubic unit cell, the cell edge being 6.74 A at the three lowest temperatures and 3.37 A at 53°C. The enlarged unit cell in the low temperature (β1) form is attributed to ordering of the deuteriums in the tetrahedral interstices. Attempts are made to establish the arrangement of the deuteriums (D's) in the β1 and β2 forms. For the latter, the stable form at 53°C, the intensities can be accounted for in three ways—by random distribution over ⅔ (L group), over ⅓ (S group) or over all of the tetrahedral interstices. From general considerations the first of these is thought to represent the actual situation in β2—Ta2D. In this the D's are distributed over the sites at ½ ¼ 0, ½ ¾ 0, ¼ ½ 0, ¾ ½ 0+000 and +½ ½ ½. Analysis of the β1 pattern shows that despite the fact that this form has a vanishing residual entropy there is no unique configuration of the deuteriums. Instead, to account for the observed intensities one must accept a structure in which each deuterium is statistically occupying more than one site. Assuming each D to be distributed over two sites three satisfactory structures are obtained. These, designated A, B, and C, belong to space groups I4, I4̄, and I41, respectively. Structure A seems the most reasonable of the three and hence is accepted as the one which is probably correct. In it the 8 D's are statistically occupying the 16 tetrahedral sites at ⅛ ¼ 0, ¼ ⅞ 0, ⅞ ¾ 0, ¾ ⅛ 0, ⅝ 0 ¼, ⅜ 0 ¼, 0 ⅜ ¼, 0 ⅝ ¼+000, and +½ ½ ½.
There is an apparent conflict between conclusions based on thermodynamic work and those developed from analysis of the diffraction data for the β2 form as well as for the β1 form. The observed configurational entropies of both forms are much less than those expected for the accepted structures. The discrepancies are thought to be due to local order.
Proton Magnetic Resonance Spectra of 3-Pyridines: The Unsymmetrical Four-Spin ABXY and ABKL Systems
Authors: Kowalewski Valdemar J. , de Kowalewski Dora G. 
Published: January 2005

The high-resolution proton magnetic resonance spectra of four pyridine derivatives of the type[Complex chemical formula](R=Cl, Br, aldehyde and acetyl groups) are studied as ABXY and ABKL systems. Detailed analysis of these methods is made and it is shown that in the 3-pyridines the ABKL treatment gives as good an account of the observed spectra as the ABCD, both methods giving the same values for the molecular parameters vi and Jij.
The analysis of the spectrum of the pyridine-3-carboxaldehyde shows an unexpected coupling of 0.44±0.05 cps between the aldehydic and the beta protons but no interaction with the alpha or gamma protons.
Raman Spectral Studies of Aqueous Solutions of Selenious Acid
Authors: Walrafen G. E. 
Published: January 2005

Photoelectric Raman spectra of aqueous solutions of selenious acid, obtained at various concentrations, and of dilute strongly alkaline and partially neutralized aqueous mixtures of sodium hydroxide and selenious acid, have yielded vibrational frequencies considered to be those of the species H2SeO3, SeO32—, and HSeO3—, respectively. In aqueous solutions of selenious acid, the intensities of two strong bands were found to increase linearly with (stoichiometric) concentration over a wide range of concentrations. This fact suggests essential completeness in the reaction of SeO2 with water, and negligible dissociation of H2SeO3 into its ions, in the solutions for which linearity is obtained.
Polarization studies of the various Raman bands, comparisons of the observed frequencies with those of molecules of known symmetry, intercomparisons of the frequencies of the species SeO32—, HSeO3—, and H2SeO3, and information gained from reported x-ray studies of solid selenious acid have allowed for provisional vibrational assignments on the assumptions of various symmetries.
Mössbauer Spectra of Some Iron Complexes
Authors: Epstein L. M. 
Published: January 2005

Mössbauer spectra were obtained for the following coordination compounds: iron phthalocyanine, ferrocene, iron carbonyl, iron III acetylacetonate, and iron II acetylacetonate dipyridine; for the following complex ion salts iron II trisphenanthroline chloride, iron III EDTA (monosodium salt), iron II EDTA, hemin, ferricium picrate, sodium nitroprusside, and some ferro- and ferricyanides.
The isomer shift (relative to stainless steel) for iron II has the value expected for an inorganic ion only for iron II EDTA. In the other complexes the shifts are about 0.4 mm/sec, except ferrocyanide which is near zero. For iron III only hemin and ferricyanide have unusually small isomer shifts. The large negative isomer shift in sodium nitroprusside suggests iron IV.
Except for ferrocyanide quadrupole splittings occurred in iron of valence 0, II, and IV and were observed for both spin-paired and spin-unpaired complexes. Splittings varied widely, however not exceeding those for inorganic ferrous salts. Sodium ferricyanide showed an unexpected quadrupole splitting. Other iron III complexes gave broad and unsymmetrical spectra.
Magnetic Properties of Hydrogen Fluoride. II. Susceptibility
Authors: Hurst R. P. , Karplus Martin , Das T. P. 
Published: January 2005

A method is outlined for the calculation of the magnetic susceptibility χ from the ground-state wave function of 1Σ molecules. The diamagnetic contribution χd is obtained directly by first-order perturbation theory and the paramagnetic contribution χp is determined by a variational technique based on minimizing the second-order energy in an external magnetic field. When applied to an SCF—LCAO—MO function for hydrogen fluoride, the theoretical result is 〈χ〉Av=—8.74×10—6 erg gauss—2 mole—1, in excellent agreement with the experimental value of —8.6×10—6 erg gauss—2 mole—1. The separate contributions, with respect to the fluorine as origin, are somewhat more in error, with 〈χd〉Av=—9.58×10—6 erg gauss—2 mole—1 (exp: —9.2×10—6 erg gauss—2 mole—1) and 〈χp〉Av=0.855×106 erg gauss—2 mole—1 (exp: 0.609×10—6 erg gauss—2 mole—1, as obtained from the rotational magnetic moment). For the isoelectronic atoms F— and Ne (in which there is only a diamagnetic term), analytic Hartree-Fock functions yield 〈χ〉Av values equal to —12.7×10—6 erg gauss—2 mole—1 (exp: ∼—12×10—6) and —7.48×10—6 erg gauss—2 mole—1 (exp: —6.7 to —7.7×10—6), respectively.
By a comparison of the results obtained with different molecular wave functions for hydrogen fluoride (one-center and two-center approximations), the sensitivity of the magnetic-susceptibility components (especially the paramagnetic terms) to the form of the wave function is clearly demonstrated. This suggests that χ and its components can serve as useful criteria for the accuracy of electron distributions and indicates the need for refinements in the hydrogen fluoride functions. Finally, the availability of a method for the theoretical evaluation of the susceptibility tensor components suggests that additional measurements should be done to improve the experimental values.
Gouy Diffractometry in Thermal Diffusion
Authors: Bierlein James A. 
Published: January 2005

Symmetrical wide-aperture illumination of binary liquid systems undergoing thermal diffusion produces well-defined Gouy diffraction patterns, arising from the interference of conjugate rays passing at equal distance above and below the midplane of the diffusion cell. The optical theory of this phenomenon is formulated; the diffraction phenomena are described by incomplete Airy integrals, tabulations of which are given.
The theory forms the basis for a new method of measuring Soret coefficients. Applied to experimental data for typical electrolyte and nonelectrolyte systems, Gouy diffractometry gives results of high precision which agree well with older values determined by other methods. The new technique has the advantage of providing two separate estimates for the Soret coefficient, affording a check on the internal consistency of the experiments; further, the presence and approximate magnitude of convective disturbances are automatically revealed.
Modified Urey-Bradley Force Field for Condensed Aromatic Rings
Authors: Scherer James R. 
Published: January 2005

A modification of the basic Urey—Bradley force field, which has been shown to reproduce the planar vibrational spectra of benzene and substituted benzenes, is extended to naphthalene. An alternate modification based on MO theory is compared with the simpler Kekulé model, and both models are shown to lead to the same conclusions regarding the vibrational spectra.
A zero-order calculation using thirteen force constants transferred from other molecules agrees remarkably well with the recent Scully—Whiffen and Freeman—Ross assignments. In the B2u species, where these authors have serious differences, the modified UBFF favors the Scully—Whiffen assignment.
A 16-parameter UBFF is refined to the H8 and D8 isotopes, and the vibrational frequencies of all deutero isotopes having Vh, C2v, or C2h symmetry are calculated with this potential function.
Criteria for the Construction of Good Self-Consistent-Field Molecular Orbital Wave Functions, and the Significance of LCAO-MO Population Analysis
Authors: Mulliken R. S. 
Published: January 2005

Criteria for the optimal choice of finite linear combinations of STO's (Slater-type orbitals) adequate to closely approximate SCF (self-consistent-field) MO's are examined in the light of computations on HF and other molecules. First, however, some aspects of the AO (generalized Heitler—London) method are discussed. The concept of induced configuration mixing is proposed as a helpful way of thinking of the higher-order interactions which carry the wave function from that of a ground-state atom pair over toward an SCF-MO form. The concept of valence polarization is suggested as preferable to and/or more general than that of hybridization. When, in the AO method, a molecule is formed from atoms, the AO's of the latter are valence polarized, and if the molecule is heteropolar, also Coulomb polarized. It is noted that both types of polarization are effected in part by the mixing in of highly shrunken excited AO's.
The same concepts are applicable also in the MO method. In an optimal choice of a finite STO basis set for approximating SCF MO's, the principle of balanced truncation, including balanced polarization, should be used; that is to say, an equally generous (or parsimonious) set of primary and of polarizing STO's should be used for each atom, with due respect to the numbers and kinds of occupied AO's in the free atom. The use of flexibilized and polarized SCF AO's (modified SCF AO's, or MAO's) as equivalents to linear combinations of STO's is discussed. In these connections, problems of interpretation and recording of LCAO-MO population analyses obtained using extended STO basis sets are critically examined.
The inherent limitations on the meaning of charges on atoms in a molecule (or of degree of ionic character, or net ionicity) are discussed. It is shown with examples that unacceptable atomic charges are found from an LCAO-MO population analysis made on SCF-MO wave functions approximated using unbalanced STO sets, while acceptable results are obtained with judiciously balanced and sufficiently complete STO sets. Likewise, unbalanced STO basis sets can given unacceptable results for overlap populations. For example, with certain unbalanced sets, there are large apparent π overlap populations in HF and in LiF, where with well-balanced sets a much smaller, but appreciable and probably genuine, amount of π bonding is indicated, confirming evidence from spectroscopic data in the case of diatomic hydrides.
The effects of insufficiently complete and unbalanced STO sets on the computed dipole moments of SCF-MO wave functions are discussed in terms of examples. These indicate that one may expect fairly accurate though slightly too large computed dipole moments for good SCF-MO wave functions. They also indicate that improvement of the latter by limited configuration interaction may give computed values close to experimental values.
Thermodynamics of Iodine Addition to Ethylene, Propylene, and Cyclopropane
Authors: Benson Sidney W. , Amano Akira 
Published: January 2005

The gas-phase equilibrium in the systems C2H4+I2⇌CH2I–CH2I,propylene+I2⇌CH3CHI–CH2I,have been studied in the temperature range 365° to 476°K using a new technique for the determination of di-iodides. In addition, existing data are re-examined for the gas system: cyclopropane+I2⇌CH2ICH2CH2I.Using other available data on the ethylene system which with ours cover a range of 200°K it is possible to obtain for 1,2-C2H4I2: Cp0 = 19.2±2 eu, Sp0 = 83.3±0.5 eu, ΔHf0 = 15.9±0.2 kcal/mole. For 1,2-C3H6I2: Cp0 = 24.1±3 eu, Sp0 = 94.6±1.0 eu, ΔHf0 = 8.6±0.4 kcal/mole. For 1,3-C3H6I2, the values of Cp0 and Sp0 are estimated by additivity rules to be 24.7 eu±1.0 eu and 93.0±1.0 eu, respectively. Based on these estimates and the measured ΔF we find ΔHf0 = 10.6±0.5 kcal/mole. A possibility of slightly lower values for 1,3-diiodopropane is discussed with reference to corrections due to the kinetics of the reaction system as well as the conformations of the molecule.
For use with additivity rules, the following partial contributions are assigned for the C–I bond, C–(I) (H)2(C) group and C–(I) (H) (C)2 group respectively: S0 = 24.9, 42.4, 22.6 eu; and ΔHf0 = 14.1 7.95, 10.7 kcal/mole. The group additivity rule is found to be valid for di-iodides to ±0.5 eu for S0 and to ±0.5 kcal/mole for ΔHf0. On the basis of this rule, thermodynamic values are assigned to a number of alkyl iodides and their C–I bond dissociation energies derived relative to the parent hydrocarbons.
Semiconductive Properties of Tetracyanoethylene Complexes and Their Absorption Spectra
Authors: Kuroda H. , Kobayashi M. , Kinoshita M. , Takemoto S. 
Published: January 2005

The absorption bands characteristic of the solid molecular complexes of tetracyanoethylene are attributed to the charge transfer interaction between tetracyanoethylene and donor molecules.
In the complexes with polycyclic aromatic hydrocarbons the energy gap associated with the semiconductivity agrees well with the energy of the charge transfer excitation in the crystalline state, while the former is much smaller than the later in the complexes with polymethylbenzenes and azulene.