bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proton Magnetic Resonance Studies in Sodium—Ammonia Solutions
Authors: Hughes Thomas R. 
Published: January 2005

High-resolution techniques have been applied to the measurements of the proton magnetic resonance shifts in sodium-ammonia solutions. Concentrations ranging from R = 1.6×10—4 to 1.7×10—1 were studied, and the temperature was varied from below —70° to above +25°C.
The miscibility gap was noted in the relatively concentrated solutions. In dilute solutions, a triplet, arising from the spin—spin interaction of the nitrogen nucleus on the proton nuclei within an ammonia molecule, was sometimes observed. In order to interpret the data taken on samples having a mole ratio R≤1.15×10—2, a modified form of the Knight shift expression applicable to this system is derived: (ΔHH0)I=−8π3L0ρ(I)χe,theo,where χe, theo = L0μe2/kT. Using this relation, the data taken at —33.2°C are found to offer strong support for the existence of some kind of monomers down to R≤3.41×10—4. The value deduced for the total negative spin density of the electron on the monomer protons is —8.1×1023 cm—3 using the equilibrium constants of Becker, Lindquist, and Alder.
Application of this same formalism to published Knight shift data yields corresponding values for the total electron density associated with the monomer of 9.0×1024 cm—3 on the nitrogen nuclei and of approximately 3.3×1022 cm—3 on the sodium-ion core. The possibility that the electron relaxation occurs on the monomer rather than on the ammonia molecules bordering a singly occupied cavity is also discussed.
Infrared Absorption Spectra of B2O3, B2O2, and BO2 in Solid Argon Matrices
Authors: Sommer A. , White David , Linevsky M. J. , Mann D. E. 
Published: January 2005

The infrared absorption spectra of B2O3, B2O2, and BO2 isolated in solid argon matrices have been investigated in the region 350–4000 cm—1. The visible absorption spectrum of matrix-isolated BO2 was observed in the region 4000–5500 Å. The gaseous species were generated in a high-temperature effusion cell and trapped under conditions of moderate to high dilution in solid argon matrices at approximately 4°K. Bands were found at 1955, 1921, 1899, 1323, and 1276 cm—1 in the infrared spectra of B210O2, B10B11O2, B211O2, and B10O2, and B11O2, respectively. For both B210O3 and B211O3 infrared spectra of the most dilute matrices show seven distinct bands in the region 450–2100 cm—1. Six of these can be readily assigned as fundamentals and their relative intensities explained if the known ``V'' structure of B2O3 is supposed to have a larger apex angle than that determined by electron diffraction, and the correlation of the normal vibrations and selection rules with those for the linear symmetric (D∞h) model is considered. With additional help from the measured B10–B11 isotope shifts and force constant calculations the following complete assignment was obtained (all frequencies in cm—1): B210O3:  2128(A1),733(A1),536(A1);[172](A1),or [260](A1);[476](A2) 2128(B1),1242(B1),471(B1);493(B2);B211O3:  2060(A1),729(A1),518(A1),[172](A1), or [259](A1);[456](A2),2060(B1),1239(B1),454(B1);477(B2);where the bracketed frequencies were not observed directly.
Thermal functions have been computed for B2O3 and compared with the available calorimetric data. Structural parameters and a complete vibrational assignment have been estimated for B2O2. The infrared and green bands observed for BO2 are in agreement with the high-resolution results of Johns. Thermal functions for B2O2 and BO2 have also been computed.
Comparison and Appraisal of Approximation Formulas for Total Elastic Molecular Scattering Cross Sections
Authors: Bernstein R. B. , Kramer K. H. 
Published: January 2005

The Massey—Mohr (MM), Schiff (S), and Landau—Lifshitz (LL) approximations for the total elastic cross section (Q) are intercompared. All can be shown to follow from the same assumption, (i.e., the classical small-angle deflection function, thence the Jeffreys—Born phases via the semiclassical equivalence relationship), sufficing to determine the velocity dependence of Q. Thus, for V=±C(s)/rs, Q(s)=p(s)[C(s)/hv ]2/(s—1) The coefficient p(s) is the same for the S and LL approximations; the ratio pSLL(s)/pMM(s)≥1, (&lt;1.075); it is 1.0709 and 1.0458 for s=6 and 12, respectively.
A numerical calculation for a repulsive (s=12) interaction shows that the SLL formula reproduces the partial-wave calculated Q to within ½%. A graphical presentation suggests the generality of this result; it also indicates the source of bias in the MM approximation. For a ``realistic'' intermolecular potential, (restricting consideration to collisions in the ``thermal'' energy range), the influence of the repulsion is only to produce undulations in Q(v); the correct value of C(6) may be obtained by velocity averaging the ``apparent'' CSLL(6).
Microwave Spectra and Structures of Difluoroethylenes
Authors: Laurie Victor W. , Pence Dallas T. 
Published: January 2005

The microwave spectra of the C12 and C13 species of cis-difluoroethylene-d1 and cis-difluoroethylene-d2 have been investigated in the region of 8–36 kMc. Effective rotational constants for the ground vibrational state have been determined and are combined with previous microwave data to obtain the structural parameters: rCC=1.324 Å, rCH=1.089 Å, rCF=1.335 Å, ∠FCC=122.1°, ∠HCC=124.0°.
The microwave spectrum of vinylidene fluoride has been reinvestigated and the rotational constants for C13 species obtained. These data lead to a structure: rCC=1.315 Å, rCH=1.079 Å, rCF=1.323 Å, ∠FCF=109.1°, ∠HCH=121.8°.
A comparison of the structures with data for vinyl fluoride and ethylene shows that fluorine substitution produces a systematic shortening of both the CC and CF bonds.
Magnetic Properties of Molecules from One-Center Wavefunctions. Theory and Application to the Hydrogen Molecule
Authors: Hoyland James R. , Parr Robert G. 
Published: January 2005

A variational procedure is proposed for the purely theoretical calculation of the diamagnetic susceptibility and nuclear magnetic shielding constants of a molecule, given a one-center electronic wavefunction for it in the absence of a magnetic field. One performs a linear variational calculation, mixing in just those Slater determinants which the field causes to interact with the Slater determinants in the original wavefunction. A simple model is proposed, whereby one can simply estimate the magnetic properties from the original wavefunction. To illustrate the method, the susceptibility of the hydrogen molecule is computed from one simple and one more complex wavefunction expanded about the molecular center.
The diamagnetic susceptibility and proton shielding constant for hydrogen then are calculated from a new single-center wavefunction expanded about one of the protons. The detailed behavior of the computed paramagnetic contribution to the magnetic properties is discussed and the results indicate that these terms are well accounted for by the proposed method. The calculated values for the susceptibility and proton shielding constant are —4.05×10—6 emu (—4.03×10—6 emu experimental) and 2.67×10—5 (2.66×10—5 experimental), respectively. Various other properties of hydrogen as calculated from the proton-center wavefunction are also given.
Comparison of Some Exact and Approximate Results for Gases of Parallel Hard Lines, Squares, and Cubes
Authors: Hoover William G. , Poirier Jacques C. 
Published: January 2005

The first seven virial coefficients for hard parallel lines, squares, and cubes, as derived from approximations of the ring and watermelon type, are compared with the exact coefficients. These approximations give no useful information as to the sign or magnitude of the virial coefficients.
A Cartesian distribution function depending upon only one space coordinate arises naturally for the line, square, and cube molecules. The first four terms of the exact number density expansion of this function are presented and compared with results obtained by iteration from the Percus—Yevick, Kirkwood, and convolution integral equations. The Percus—Yevick equation yields a distribution function which closely resembles the exact result at low densities.
Virial coefficients are obtained from the approximate distribution functions by means of the Ornstein—Zernicke relation and the virial theorem, as well as from a relation between the potential of mean force at zero separation and the virial coefficients. This last relation (which is valid for hard spheres as well as lines, squares, and cubes) has an interesting graphical interpretation and leads to correct values for the third virial coefficient from the Kirkwood equation, but not from the Percus—Yevick or convolution equations.
Theoretical Calculation of Vapor Transport of Solid in the ZnS : HCl System
Authors: Jona F. , Mandel G. 
Published: January 2005

A theory has been previously developed which allows calculation of the rate of diffusion-limited vapor transport of solids in a multicomponent multireaction system which is driven by a small temperature gradient. This theory is applied to the case of ZnS(s) being transported by reaction with HCl(g). All the required parameters, i.e., gaseous diffusion coefficients, thermodynamic data, etc., are either known or independently estimated. The calculated results are found to be in quantitative agreement with the experimental results within the estimated uncertainties in the thermodynamic and diffusion coefficient data over a wide range of initial HCl pressures. Below an initial HCl pressure of 1 atm, it is seen that the experimental rate of transport drops sharply in comparison to the theoretical prediction. This has previously been attributed to kinetic limitations.
It is shown that the assumption of a single binary diffusion coefficient, applying to all pairs of component species, may lead to results in approximate agreement with the more ``exact'' theoretically predicted results.
Relationship between Pi-Electronic Distributions and F19 NMR Shielding in Para-Substituted Fluorobenzenes
Authors: Taft Robert W. , Prosser Franklin , Goodman Lionel , Davis George T. 
Published: January 2005

Experimental results on F19 shielding in p-substituted fluorobenzenes are combined with calculations of pi-electronic charge distribution from MO theory and are used in several procedures devised to test shielding theories. It is concluded that both —R and +R p-substituted fluorobenzenes represent a special case for which there is a reasonable degree of theoretical justification for relating the F19 shielding with the pi charge density of the fluorine atom.
The tests devised for p-substituted fluorobenzenes do not clearly distinguish between the shielding equations of Prosser and Goodman and those of Karplus and Das. Also, the tests do not critically distinguish which of the following may be taken as the better estimator of the pi charge density of the fluorine atom: the shielding parameter based upon unsubstituted fluorobenzene as the standard of comparison or the shielding parameter based upon the meta isomer of the p-substituted fluorobenzene.
Data are presented on F19 shielding of the acid fluoride atom of p-substituted benzoyl fluorides and benzenesulfonyl fluorides. These results show that the special shielding relationship derived for p-substituted fluorobenzenes does not apply.
Mass Spectrometry of Ions in Glow Discharges. IV. Water Vapor
Authors: Knewstubb P. F. , Tickner A. W. 
Published: January 2005

Ions from the negative glow and Faraday dark space of discharges in water vapor have been analyzed with a mass spectrometer. The ions observed are of the form H3O+·(H2O)n with n=0 to 5. It is shown that the observations are altered by the sampling process to an extent which depends on discharge conditions and is sometimes quite large. This effect may be important whenever loosely bound ions are sampled from a plasma.
The sequence of hydration reactions is examined in an approximate manner and it is concluded that the bond strength decreases as successive water molecules add to H3O+, falling sharply beyond n=3. The rate constants for the first few stages of the hydration process appear to increase with the size of the reactant ion.
Analysis of A2B2 High-Resolution NMR Spectra. I. Furan, Thiophene, and Disubstituted Benzenes
Authors: Grant David M. , Hirst Robert C. , Gutowsky H. S. 
Published: January 2005

The features of certain classes of A2B2 spectra are investigated systematically relative to the parameters involved, and these characteristic spectra are given as an aid to future interpretation. The effects upon the spectra of the relative signs of the coupling constants are discussed. Examples are provided by the analysis of spectra for the aromatic protons in furan, thiophene, three symmetrical ortho disubstituted benzenes, two nonsymmetrical para disubstituted benzenes, and a symmetrical 4,4′ disubstituted biphenyl. Better resolution than was obtainable in previous studies permitted a more detailed analysis for compounds cited earlier. In most examples the 24 main spectral lines expected for four spin systems of this symmetry were observed.
It is found that all four of the H–H coupling constants are of the same sign in thiophene, and Jαβ and Jαβ′ in furan. Appreciably different values, 1.55 and 2.85 cps for Jαα and 1.8 and 4.7 cps for Jαβ, are found in furan and thiophene, respectively, while Jββ and Jαβ′ are virtually identical: 3.53 and 3.35 cps, and 0.8 and 1.0 cps. In the substituted benzenes, the values found for J0, Jm, and Jp fall in the ranges 7.4 to 8.8 (9), 1.24 to 3.05 (9), and 0.3 to 0.6 cps (6), the number of cases being given in parentheses. The disubstituted benzenes studied have two nonequivalent ortho or meta coupling constants; they are found to differ by as much as 0.6 cps. The spectra of these substituted benzenes show that the coupling constants J0, Jm, and Jp are all of the same relative sign.
Molecular Geometry and the Vapor Pressure of Isotopic Molecules. The Equivalent Isomers cis-, gem-, and trans-Dideuteroethylenes
Authors: Bigeleisen Jacob , Ribnikar Slobodan V. , Van Hook W. Alexander 
Published: January 2005

The vapor pressures of trans-, cis-, and gem-dideuteroethylenes have been intercompared directly by mercury manometry over the temperature range 120°—180°K. The trans isomer has been compared with ordinary ethylene over the same temperature range. The vapor pressures of cis- and gem-dideuteroethylene are equal to within a few hundredths of a percent. The trans compound has a greater vapor pressure than either the cis or gem compounds (about 0.1% at 130°K and 0.05% at 180°K). At these same temperatures the trans-dideuteroethylene has a vapor pressure 1.2% and 1.6%, respectively, greater than ordinary ethylene.
The difference between the dideuteroethylenes is correlated with differences in molecular geometry. It is shown that the trans is the most volatile of the dideutero isomers, because it has the smallest moment of inertia about the C=C axis. The vapor pressure data are then direct evidence for hindered rotation in the liquid.
Molecular Geometry and the Vapor Pressure of Isotopic Molecules. C2H3D and C12H2=C13H2
Authors: Bigeleisen Jacob , Stern Marvin J. , Van Hook W. Alexander 
Published: January 2005

The isotopic vapor pressure ratio between monodeuteroethylene and ordinary ethylene has been measured in the temperature range 120°—180°K by differential manometry. The inverse isotope effect with C212H3D is less than one-half the effect observed with the dideuteroethylenes. This deviation from the rule of the geometric mean gives further support to the structural theory of isotopic vapor pressure effects and confirms the importance of quantum corrections of the order of (ℏ/kT)4 and higher. Vapor—liquid equilibrium studies of C212H4 and C12H2=C13H2 were made in a packed column under total reflux using C212H3D as an internal monitor to calibrate the column. Whereas C212H3D goes to the top of the column, C12H2=C13H2 concentrates in the boiler. Absolute values of the carbon-13 effect were calculated from the measured relative effects and the manometric data for C212H3D, and the vapor pressure ratios were checked by analysis of the kinetic behavior of the column. A test of the data was made in the framework of the applicable theory. The temperature dependencies of the isotope effects are predicted from the theory within the experimental error. The relative deuterium and carbon-13 isotope effects as well as the differences between the dideuteroethylene isomers are discussed in terms of the structure of the ethylene molecule.
It is shown that there is a large normal A/T2 dependence due to hindered rotation in the liquid. The zero-point energy change on condensation leads to a term of the form B/T and accounts for the higher vapor pressures of the deutero-compounds. The zero point energy changes obtained from the vapor pressure data are in quantitative agreement with theoretical calculations.
A new type of effect is found, namely a perturbation of the internal vibrations by the hindered rotation. This perturbation is different for the different molecules and a strict correspondence is established with the molecular symmetry.
Trapping and Energy Transfer in Atomic Collisions with a Crystal Surface
Authors: McCarroll Bruce , Ehrlich Gert 
Published: January 2005

The condensation of atoms on a solid is examined by calculating the critical energy for trapping of a particle of arbitrary mass and force constant colliding with a linear lattice. In the harmonic approximation and using classical mechanics, the maximum kinetic energy for trapping is found to depend strongly upon the well depth, in qualitative agreement with experiment. For a gas atom colliding with its own lattice (that is, force constant ratio β=1 and mass ratio μ=1) capture occurs at translational energies up to 25 times the binding energy. For β=0.2, this critical energy has diminished to 1.3 times the dissociation energy Q of the homogeneous lattice. The dependence of the critical energy on force constant is not monotonic, however—there is a maximum at β∼0.75. At β=0.75 and μ=1, for example, the incident energy must exceed ∼31Q to prevent trapping.
Most of the energy exchange occurs during the repulsive part of the collision. For this part of the collision interval, the presence of a trapping potential has little effect. However, the energy exchange occurring when the particle rebounds through the attractive part of the potential is sensitively dependent upon the force constant. For β&lt;0.5, the incident particle loses energy equal to ∼0.5 times its binding energy. As β increases, the energy loss diminishes and after β∼0.75 the incident particle actually gains in total energy.
The accommodation coefficient for systems with repulsive interactions only does not show such specificity; for β&gt;0.2 the energy exchange is dictated primarily by the mass ratio. The coefficients calculated for hard-sphere collisions provide an acceptable approximation when β&gt;∼0.5.
Internal Rotation in Completely Asymmetric Molecules. I. A General Theory and Analysis of the Microwave Rotational Spectrum of CH2DCOH, CD2HCOH, and CHOOCH2D
Authors: Quade C. R. , Lin Chun C. 
Published: January 2005

A theory for the internal rotation in molecules where the internal rotor is not a symmetric top has been formulated. The principal feature of the theory is the expansion of the rotational constants for the molecule in a converging series of sinnα and cosnα. This allows for the straightforward evaluation of certain integrals appearing in the development of the theory.
In addition, the theory is applied specifically to CH2DCOH, CD2HCOH, and CHOOCH2D in the analysis of the microwave rotational spectra for these molecules. For CH2DCOH the height of the potential barrier hindering the internal motion is found to be V=410 cm—1, which is consistent with the barrier height for other species of acetaldehyde. To fit the spectra of CD2HCOH and CHOOCH2D a slight rotation of the effective principal axes must be made to obtain a consistent potential barrier.
The results of the calculation indicate that (1) the theory is readily applicable in the determination of the barrier heights of the more general molecules, and (2) investigation of the deuterated-methyl internal rotors could provide information on the structure of the rotor.
Equation of State for Binary Fluid Mixtures
Authors: Hecht Charles E. 
Published: January 2005

The compressibility factor PṼ/RT for a binary fluid mixture is obtained from tabulated values of a reduced equation of state for a general pure substance assuming the law of corresponding states for pure substances.
The binary mixture is treated in zeroth order as a pseudo one-component substance obeying a Lennard-Jones 12–6 intermolecular potential with parameters so chosen that they reproduce the second virial co-efficient of the mixture. In first-order-of-perturbation theory, the difference between the actual intermolecular potentials (assuming all molecular sizes to be equal to that of the pseudo molecular size) and that of the pseudo one-component potential is introduced as a perturbation. The random-mixing assumption need not be made.
Data for a total of 25 mixtures in 7 different binary systems are compared with the theory. The perturbation is seen to be unimportant. Theory holds to within about 15% if reduced densities less than 0.3 are considered.
Kinetics of Addition of HI to Isobutene and Vinyl Chloride
Authors: Bose A. N. , Benson Sidney W. 
Published: January 2005

The addition of HI to i-butene above 200°C proceeds homogeneously and quantitatively to yield i-butane+I2 in accordance with the equation 2HI+i−butene→i−butane+I2.It is shown that the rate-determining step is the formation of the intermediate t-BuI which is present in vanishingly small stationary concentration HI+i−butene→ lim k2t−BuI(slow),  t−BuI+HI→i−BuH+I2(fast).The second-order rate constant k2 is given by (units of liter/mole-sec) logk2=6.50−18 000/4.575T.From the known thermodynamic data the reverse, first-order rate constant k1 is given by (units of sec—1) logk1=12.52−36 400/4.575T.
Comparisons with similar data for EtI and i-PrI show that the substitution of Me groups for H lowers the Eact by about 6 kcal/Me group and also the A factor by about a factor of 5. This can be explained on the basis of a loss of internal rotational entropy in the transition state.
Qualitative observations indicate that C2H3Cl adds HI at a rate intermediate between C2H4 and C3H6. The principle products are C2H5Cl+I2 above 290°C, but sufficient C2H6+HCl appear to vitiate simple kinetic studies. Qualitative observation of the system EtCl+I2 indicate an I-atom-catalyzed elimination of HCl with an Eact∼43 kcal/mole.
Exciton—Phonon Interaction in Crystalline Benzene
Authors: Maria H. , Zahlan A. 
Published: January 2005

The uv crystal spectrum of benzene is investigated in the region 4°—80°K. The intensity of the a-polarized and c-polarized components of the 0–0 band are temperature dependent. The intensity of the a 0–0 component is found to be proportional to the density of phonons with a frequency of 16 cm—1. The half-width of the a and c axis-polarized 0–0 components are also studied as a function of temperature. The half-width of the band at 38 786 cm—1 0–0+925 is similar to that of the purely electronic components, while for the 38990 cm—1 band 0–0+1155, the half-width is temperature independent. The mean phonon-perturbing frequency is 12 cm—1. The a-c 0–0 band splitting is studied as a function of temperature.
Sample line shapes are reported, and the results are discussed briefly on the basis of the theoretical work of Toyozawa.