bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular Beam Time-of-Flight Measurements for the Study of Metastable and Repulsive Electronic States
Authors: Freund Robert S. , Klemperer William 
Published: January 2005

The time-of-flight distribution in an electrically neutral molecular beam has been analyzed, and from it the mass of the constituent molecules has been determined to an accuracy of about 5%. These experiments have been carried out on molecules in metastable electronic states, excited by pulsed electron bombardment and detected by an Auger process. Mass measurements, excitation functions, and electric deflection measurements verify that molecular beams of metastable benzene, toluene, and xylene can be formed.
Molecular dissociation of N2O and CO2 due to electron impact was observed by Auger detection of dissociation products with high translational kinetic energy. The products are identified as metastable N2 and CO, respectively.
Excess Thermodynamic Functions for Binary Mixtures as Calculated from the Percus—Yevick Equation for the Lennard-Jones Potential
Authors: Throop Gerald J. , Bearman Richard J. 
Published: January 2005

Using the Percus—Yevick equation and the Lennard-Jones 6–12 potential for the noble gases, we have calculated the thermodynamic functions for a number of binary mixtures for supercritical isotherms and at densities up to twice the critical density. From these thermodynamic functions, we have calculated the excess functions along the isotherms as a function of density for two mixing processes, one at constant pressure and one at constant volume. The results are presented graphically but the numerical data are available from the thesis of Throop.
For the constant pressure process, we have found that the excess energy, volume, and Gibbs free energy are positive at low densities, increase with increasing density to a maximum, and then decrease to small positive or negative values at higher densities.
The excess functions for the constant-volume process, in the density and temperature ranges of our calculations, are much smaller than the constant-pressure functions for the same density and temperature. The excess energy of the constant volume process is always positive at low densities, passes through a maximum, and becomes negative at high densities. The variation with density of the excess Gibbs free energy is more complicated, and it is usually negative and decreasing with density, although at temperatures near a critical temperature, this function is positive at low densities.
For both of these mixing processes, the excess functions are not quite symmetrical functions of mole fraction, with the constant-volume excess functions being more symmetric.
Internal Rotation in Liquid 1-Fluoro-1,1,2,2-Tetrachloroethane
Authors: Alger T. D. , Gutowsky H. S. , Vold R. L. 
Published: January 2005

Fluorine and proton high-resolution NMR lineshapes have been observed at 56.4 and 60 MHz, respectively, for a 50 mole % solution of 1-fluoro-1,1,2,2-tetrachloroethane in carbon disulfide, between −120° and −14°C. Fluorine spin echoes were obtained at 25.27 MHz and proton spin echoes were obtained at 26.8 and 17.7 MHz. An iterative complete-lineshape-fitting computer program was used with the experimental lineshapes to obtain best-fit exchange rates for interconversion of gauche and trans rotamers. A value of 18.9 ppm was found for the fluorine chemical shift from the low-temperature high-resolution spectrum and was used to fit the lineshapes at higher temperatures, as well as to fit the observed dependence of the fluorine relaxation rate on rf pulse spacing in the Carr—Purcell experiments.
Other parameters required in the analysis, i.e., the energy difference between trans and gauche rotamers and the proton-fluorine coupling constants in each rotamer, were obtained from the temperature dependence of the proton spectrum under conditions of complete averaging (−90°−25°C). The values obtained for the coupling constants are in good agreement with an earlier determination by the same method but over a different temperature range. At −120°C the fluorine resonance consisted of a singlet and a doublet, with splittings in satisfactory agreement with the high-temperature results. The proton spin echoes at −112°C are sensitive to the proton-fluorine coupling constants, and can be calculated satisfactorily with coupling constants obtained from the high-temperature proton lineshape.
Because of the large fluorine chemical shift, four orders of magnitude of the exchange rate were measurable. Exchange rates obtained from all four sets of data fall on the same, linear Arrhenius plot, with frequency factor (7.0±0.5)×1011 sec−1 and activation energy 7.85±0.05 kcal mole−1. The frequency factor is low compared with a value computed by assuming immediate deactivation from the eclipsed transition state, but agrees with a value calculated by assuming that the molecules undergo ``free'' internal rotation before deexcitation to any one of the stable rotamers.
Kinetics of Energy Transfer from the Triplet State in Rigid Solutions
Authors: Kellogg R. E. 
Published: January 2005

Assuming the energy transfer is dependent on the inverse nth power of the donor—acceptor distance (1/Rn), Inokuti and Hirayama derived an expression for the observed decay of donor emission, using flash excitation of a random solid solution, I=I0exp[−t/τ−(2/π1/2)Γ(1−3/n)γ(t/τ)3/n], where τ is the measured lifetime in the absence of an acceptor, γ is linear in acceptor concentration, and n is the distance dependence parameter. This reduces to the Förster result for a dipole—dipole interaction where n=6. The extent to which we can determine n experimentally will allow us to measure the ``purity'' of the dipole—dipole interaction presumed to induce the transfer.
To this effect, a detailed kinetic analysis of triplet—singlet energy transfer in rigid solution has been carried out using triphenylene-d12 as the donor and rhodamine B as the acceptor. A computer fit of the decay data to the above expression was carried out with a nonlinear regression routine that determined I0, γ, and n simultaneously using the least-squares criterion. Over the concentration range of γ=0.26 to 2.1, a value n=6.05±0.17 was determined, indicating no measurable derivation from the behavior predicted by Förster.
In principle, this procedure could be used to identify a quadrupole transition in the acceptor, where a value of n=8 would signify a dipole—quadrupole interaction.
Force Constants of Triatomic Molecules
Authors: Glockler Geo. , Tung Jo-Yun 
Published: January 2005

In the general expression of the potential energy of the triatomic molecule XYZ there are six force constants c1, c1′ (valence bond), c2 (angle deformation), c3, c3′ (angle bond interaction), and c4 (bond-bond interaction), of which only three can be calculated from the three experimentally determined fundamental frequencies. For the isosceles triatomic molecule YX2 the number of force constants reduces to four (c1, c2, c3, and c4). From a study of all the real values of these four force constants, it is seen that they are related to one another by ellipses and straight lines. The graphs of these ellipses indicate the possibility of choosing a certain singular point (near one end of the major axis) which gives the following relation between the force constants: dc4/dc2=0  or  dc4/dc3=0.This condition and the equations usually obtained from the theory of small vibrations permit the calculation of a singular set of four force constants of the isosceles triatomic molecule. When these force constants are applied to isotopic molecules, satisfactory checks between the calculated and experimentally determined frequencies are obtained.
The ellipses showing the relation between the force constants indicate clearly why the simple central force field (c1, c2, c3) or the simple valence force field (c1, c2, c3), containing one interaction constant or crossterm, must yield imaginary values for c2 and c3 in certain cases.
NMR in Hydrate Crystals: Correction for Vibrational Motion
Authors: Pedersen Bjo/rn 
Published: January 2005

A theoretical analysis of the effect of vibrational motion of the water molecule on the line splitting observed in proton magnetic resonance spectra of hydrates is presented. For an assemblage of magnetically equivalent water molecules, the observed line splitting is given by the Pake formula properly averaged over the motion, 〈(3μ/R3) (3 cos2θ—1)〉. The intramolecular stretching and deformation vibrations are assumed to be uncoupled from the rigid body librational vibrations. The intramolecular vibrations affect the (3μ/R3) term only and are given as 0.980 times the value at equilibrium from an anharmonic model of the vibrations. The angular factor is averaged over the librational oscillations assumed to be of small amplitude and harmonic. The resulting expression is a function of the mean-square amplitude of the rocking, 〈θx2〉, and the twisting, 〈θz2〉, oscillations of the H2O molecule. From a simple model of the librational motion the relative magnitude of 〈θx2〉 and 〈θz2〉 is calculated, and an expression is developed for 〈θz2〉 which only contains the potential barrier for rotation of the H2O molecule and the temperature. From the developed formulas it is estimated that, on the average, the uncorrected intramolecular proton—proton distance is about 5% larger than the equilibrium value. This is mainly due to the zero point motion of the H2O molecule; the line splitting is expected to decrease about 5% going from 0°K to room temperature.
The theory presented has been used in interpreting splitting data obtained from Ba(ClO3)2·H2O rotated about the baxis. The set of line splittings are shown not to follow the simple Pake formula, but the data can be satisfactorily interpreted on the basis of the developed formulas with the numerical values of 〈θx2〉 and 〈θz2〉 available in the literature. A reinterpretation of the experimental results by McGrath and Silvidi is given at the end of the paper. The equilibrium intramolecular proton—proton distances in the lattice-bound H2O molecules are derived from literature data in three hydrates and ice. The values obtained are close to the equilibrium distance found in the isolated H2O molecule, 1.51 Å.
Second Virial Coefficient of Linear Polymer Molecules
Authors: Kurata Michio , Fukatsu Masaaki , Sotobayashi Hideto , Yamakawa Hiromi 
Published: January 2005

A variation theory is developed for obtaining a closed expression for the second virial coefficient A2 of linear polymer molecules, which corresponds to the Fixman theory of the excluded volume effect. It is shown that the second virial coefficient of the polymer in good solvents is effectively identical with that of a nonpenetrating sphere whose radius is proportional to the root-mean-square statistical radius 〈S2〉½. In extremely good solvents, A2 becomes a constant independent of molecular weight M. A graphical method is proposed for separate determination of the effective bond length and the polymer—solvent interactions; the method consists of plotting A2M½ against M½. Applications of this method are illustrated by four examples, polystyrene in toluene, isotactic polypropylene in tetralin and in α-chloronaphthalene, and nitrocellulose in acetone. The effective bond lengths obtained are in good agreement with those previously evaluated from the molecular weight dependence of intrinsic viscosity [η], but the polymer—solvent interactions are not. The theoretical value of the ratio A2M/[η] is about 60 in good solvents, which is approximately a half of the ordinary experimental values.
A modification of the variation theory is proposed, which corresponds to Ptitsyn's modification of the Fixman theory and leads to a more plausible value 110 for A2M/[η].
The triple contact term in the perturbation expansion series of A2 is also evaluated. It is found that the expansion of a molecular coil due to the volume effect is somewhat suppressed by intermolecular interactions in the proximity of the second molecule.
Low-Temperature Heat Capacity and Related Thermodynamic Functions of Propylene Oxide
Authors: Oetting Franklin L. 
Published: January 2005

The heat capacity of propylene oxide has been determined from 11° to 300°K in an automatic low-temperature adiabatic calorimeter. The melting point of propylene oxide is 161.22°±0.05°K and the heat of melting is 1561.4±1.7 cal/mole. The absolute entropy at 298.15°K is 46.91±0.15 cal/mole·°K) which includes a residual entropy of R ln 2 for the entropy of mixing of the optical isomers.
The third-law entropy of gaseous propylene oxide at 298.15°K is determined from the entropy of the liquid plus literature data on the heat of vaporization, vapor pressure, and the critical constants. This entropy value is in good agreement with the value determined from statistical thermodynamics using literature data on the fundamental vibrational assignment, the internal rotational barrier, and the entropy of mixing.
Gamma-Induced Divalent Dysprosium in Calcium Fluoride
Authors: Fong Francis K. 
Published: January 2005

Experiments dealing with photochemical and thermal reactions of dysprosium in calcium fluoride are described. Trivalent dysprosium ions doped in calcium fluoride have been reduced by gamma irradiation at room temperature. The efficiency of reduction of Dy3+ in CaF2 is described in terms of the dosage of gamma irradiation and concentration of the dopant ions. The optimum conditions for the photoreduction are given. The absorption band responsible for the reoxidation of the gamma-reduced dysprosium has been determined. It has been established that high densities of gamma-induced defect sites are necessary for the conversion of the majority of divalent ions to the trivalent state, which may be indicative of the tunneling of Dy2+ electrons to hole centers via the gamma-induced defect centers. The tunneling process is also believed to be responsible for the saturation of local and macroscopic concentrations of Dy2+ ions.
The thermal reoxidation of Dy2+ ions is accompanied by bright luminescence, the spectrum of which resembles that of the photoluminescence of Dy3+ ions. The decay of the thermoluminescent emission bands is nonexponential, and the reaction kinetics fit the description of a second-order reaction. The evaluated activation energy (0.33 eV) is indistinguishable from the energy required for the thermal ionization of holes from V1 centers in alkali halides.
Paramagnetic Resonance of Mn++ in NaN3, KN3, and RbN3
Authors: King Gerard J. , Miller Brian S. 
Published: January 2005

The paramagnetic resonance of Mn++ in single crystals of NaN3, KN3, and RbN3 is studied at 9.1 Gc/sec as a function of crystal orientation in the magnetic field. In KN3 and RbN3 containing Mn++ the crystalline electric field is the resultant of a large axial field in the [001] direction plus a small cubic field. The g values for Mn++ in KN3 are g∥ = 1.9961±0.0005, g⊥ = 1.9878±0.0050; and for Mn++ in RbN3 g∥ = 2.0005±0.0005, g⊥ = 1.9971±0.0050. The axial electric field parameter D is —534±3.0 G for KN3 and —278±3.0 G for RbN3 at 25°C. The cubic field parameter a0 is 10±0.5 G for KN3 and 8.7±0.5 G for RbN3. The Mn++ hyperfine coupling constants A and B are —89.7 and —91.1±0.5 G, respectively, in KN3. In RbN3, A and B are —88.0 and —88.9±0.5 G, respectively. The large magnitudes of D, A, and B allow the forbidden ΔM = ±1, Δm = ±1 transitions to be intense. Two inequivalent sites result from the displacement of the Mn++ from a cation site toward a bound nearest-neighbor cation vacancy.
For an unheated crystal of NaN3, the main Mn++ resonance is a single broad line at g = 1.95±0.01. Heating the NaN3 crystal changes this broad line into multiple sets of 30-line spectra. At 25°C these sets of 30-line spectra decay slowly and the original broad line regrows. A similar effect previously found for Mn++ in NaCl has been attributed to mobility of Mn++-cation vacancy complexes. One type of Mn++ spectrum in NaN3 is due to the vacancy-associated complex and another type is due to the dissociated or excited complex. For both types of spectra g∥ = g⊥ = 2.001±0.002 and A≈B = 87±1.0 G. For the dissociated Mn++ complex state the spectrum has axial symmetry about the c axis and D = —240 G. For the vacancy-paired Mn++ spectrum an additional rhombic distortion occurs, and D = —265 and E = +57 G.
The variation of linewidth with temperature is used to show that the KN3 spectra result from charge compensation by vacancy pairing. Additional effects produced by vacancy jumping are noted. Differences between the high-temperature properties of Mn++ in NaN3 and KN3 are related to cation size effects. A low-temperature line broadening of the Mn++ spectrum in KN3 and RbN3 is reported, and the similarity to the Mn++ resonances in solution-grown KCl and KBr is noted.
Gas-Phase Dosimetry by Use of Ionization Measurements
Authors: Meisels G. G. 
Published: January 2005

A basis is provided for the use of ionization measurements to evaluate energy absorption in gas-phase dosimetry when high-energy electrons are employed as the radiation source. It is concluded that total energy absorption can be determined and that stopping powers can be employed to calculate relative energy absorption in various gases. Scattering measurements indicate that irradiation cells should be short. Relative values of the energy required to form one ion pair (W) by 1-MeV electrons are shown to be the same as those reported for lower energy electrons, and the following W values for the partial absorption of 1-MeV electrons are reported with a probable error of about ±2%: C3H8 23.4, n-C4H10 22.9, i-C4H10 23.0, i-C5H12 23.9, C3H6 24.8, 1-C4H8 24.4, trans-2-C4H8 23.9, i-C4H8 24.4, CH3CHO 26.4, (C2H5)2O 23.8, CO 32.2, SO2 30.4, NO 27.5, N2O 32.9, and NH3 26.5.
Chemical-yield measurements on ethylene suggest that the formation of acetylene can be measured with an accuracy of better than ±3%; above 400 Torr and with dose rates in the order of 1015 eV cc—1·sec—1 G(acetylene) = 3.07±0.08.
Significant Structure Theory of Physical Adsorption
Authors: McAlpin J. J. , Pierotti R. A. 
Published: January 2005

The significant structure theory of liquids has been modified to describe the physical adsorption of gases on homogeneous solids. Equations have been derived for the isotherm, the isosteric heat, and the critical properties. Good agreement with experiment is obtained for the systems Ar and Kr on graphite. The lack of mathematical rigor in the foundations of the significant structure theory is compensated for to a certain extent by its good results and its arithmetical and conceptual simplicity. Its departure from a rigorous foundation, however, makes it difficult to make improvements or to understand anomalies.
The third-order dispersion energy correction for molecules adsorbed on a solid as derived by Sinanoğlu and Pitzer was used to determine the two-dimensional lattice energy and the success of the present theory in predicting the heats of adsorption and the critical temperature is a measure of the validity of their work.
Faraday Rotation in Glasses
Authors: Borrelli Nicholas F. 
Published: January 2005

The Verdet constants of a number of glasses have been measured with the object of studying the Faraday effect in glass.
The Verdet constant was measured for three types of glasses: (1) optical glasses, where the Verdet constant correlates well with the reciprocal dispersion; (2) diamagnetic glasses, where glasses which contain high concentrations of ions that have sp—s2 transitions give rise to large Verdet constants; (3) rare-earth glasses, i.e., paramagnetic ions, where Pr3+ and Dy3+ silicate and borate glasses have the largest Verdet constants. These latter rare-earth data were compared to the theoretical expression of Van Vleck and Hebb and to the experimental data on metaphosphates of Berger et al.
Charge-Transfer Exciton States in Aromatic Molecular Crystals
Authors: Choi Sang-Il , Jortner Joshua , Rice Stuart A. , Silbey Robert 
Published: January 2005

In this paper we consider some of the consequences of the mixing of neutral exciton states (neutral excitation waves or Frenkel excitons) with charge-transfer exciton states (ion-pair excitons) in the oriented gas model of aromatic molecular crystals.
The lowest-energy charge-transfer exciton is described by suitable symmetry-adapted functions built on the basis functions of a near-neighbor positive and negative ion pair. It is then shown that the energy of this state is not greatly different from the p states of anthracene and naphthalene, and therefore that the ion-pair exciton and Frenkel exciton states can mix. For the cases of anthracene and naphthalene, such configuration interaction leads to the following contributions to the Davydov splitting of the triplet manifold: Δε=26/ΔE cm−1naphthalene,Δε=31/ΔE cm−1anthracene,where ΔE is the energy difference (in electron volts) between the triplet level and the near-neighbor charge-transfer level. In making the computations, it is necessary to consider carefully the effects of vibronic coupling and of configuration changes in the excited state. It is concluded that charge-transfer excitons can make an important contribution to the Davydov splitting of a triplet manifold. This conclusion is supported by preliminary estimates of the interaction matrix elements for crystalline benzene.
Electronic Structure of Transition Metal Complexes with Nitrosyl Ligand. Mössbauer Effect Investigation
Authors: Danon J. 
Published: January 2005

The Mössbauer effect was investigated with spin-paired diamagnetic pentacyanonitrosylferrate (II) (sodium nitroprusside), spin-paired paramagnetic nitroso-bis-dimethyldithiocarbamates iron (I), and with spin-free pentaquonitrosyl iron (I) complexes.
Information on the nature of bonding in the first two complexes was obtained through detailed interpretation of the isomer shift and quadrupole coupling, measured with polycrystalline and single crystal samples.
Different possible interpretations are discussed for the results with the pentaquo complex.
Simplified SCF Method for σ-Bonded Systems. I. Physical Properties of Hydrogen Halides
Authors: Pohl Herbert A. , Rein Robert , Appel Klaus 
Published: January 2005

Approximate SCF LCAO—MO calculations have been carried out for the ground-state properties of four hydrogen halides; six internuclear distances were considered. In the model only the bonding electrons are considered explicitly. The effect of the inner electrons were taken account of by semiempirical methods. The electron pair is described by a single configurational wavefunction and the MO's are built from 1s and np AO's. The matrix elements are obtained utilizing the Mayer—Sklar, Mulliken, Pariser, and Pople approximations. As a secondary study the effect of the Wolfsberg—Helmholtz parameter K, in the resonance terms is studied.
The calculated binding energies, equilibrium bond distances, dipole moments, vibrational force constants, and breaking forces obey the same trends as in experimental data. Moreover the magnitudes for these calculated quantities are in substantial agreement with experiment. This agreement can be improved for a given physical property of the series by introducing the arbitrary parameter K and optimizing it for one member of the series.
It is concluded that the approximations characterizing the model, all of which had been previously used with π-bonded systems, are equally well applicable to σ-bonded systems.