bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectra and Structure of Small Ring Compounds. XIX. Vibrational Analysis and the Barrier to Pseudorotation of Germylcyclopentane
Authors: Durig J. R. , Willis J. N.
Published: February 2004

The infrared spectrum of germylcyclopentane in the gaseous state has been recorded from 4000 to 33 cm−1 and that of 1, 1-dideutero-1-germylcyclopentane has been recorded from 4000 to 250 cm−1. The Raman spectra of the two liquids have been recorded and depolarization values determined. The data rule out the planar configuration for the germylcyclopentane molecule and are shown to be consistent with the twisted C2 molecular structure. The 39 normal modes have been assigned on the basis of their depolarization values, infrared band contours, isotopic shift factors, band intensities, and “group frequencies.” The ring-bending mode was found at 113 cm−1 in the vapor phase of the “light” compound. The ring-twisting mode for the d0 and d2 compounds was found at 273 and 269 cm−1, respectively, in the Raman spectrum. The 113-cm−1 band in the light compound was found to be the first of a series of Q branches running to lower frequency. This series has been interpreted in terms of a relatively high barrier to pseudorotation. From midinfrared sum bands a similar series of transitions were obtained for the pseudorotation of the d2 compound. A potential function of the form V = − (2043 / 2) (1 − cos2θ) − (21 / 2) (1 − cos6θ) was found to fit nine observed far-infrared transitions of the ring-puckering mode. The calculated barrier to pseudorotation was 5.9 ± 0.1 kcal/mole for the “light” compound, and the spectroscopically derived parameter mq02 was found to be 18.7 × 10−40 g·cm2. The barrier in the corresponding d2 compound is estimated to be 6.0 ± 0.3 kcal/mole. The barriers are considerably higher than one might expect from existing theories and data on torsional barriers.
5142-Å Transition in Thiophosgene (π* ← n); Rotational Analysis and Excited-State Structure
Authors: Lombardi John R.
Published: February 2004

Rotational structure is observed in the 210310410 vibronic band of the lowest singlet π* ← n transition of thiophosgene (5142 Å). Computer analysis gives three excited-state moments of inertia, from which, assuming a value for the C–S bond length, an excited-state structure may be determined.
Total Elastic Cross-Section Measurements for Argon on Argon
Authors: Baratz Bernard , Andres R. P.
Published: February 2004

Total elastic scattering cross sections for argon on argon are presented as a function of the relative velocity of collision. The “glory” extrema predicted to be present as well as the correct velocity dependence for a potential with long-range 1 / r6 behavior are observed. The data, while not of sufficient quality to be inverted directly, yield constraints on the shape and position of the argon potential well.
Collisional Excitation of Small Molecular Ions
Authors: Cheng M. H. , Chiang M. H. , Gislason E. A. , Mahan B. H. , Tsao C. W. , Werner A. S.
Published: February 2004

We have determined velocity vector distributions for NO+ and O2+ scattered from helium. As expected, the small angle scattering is elastic, but at angles greater than 60°, inelasticity which increases with the scattering angle is apparent. For angles greater than 100°, this inelasticity represents vibrational excitation of the molecule–ion. For initial relative kinetic energies between 4.3 and 25 eV and 180° scattering, the variation of the inelasticity is consistent with a new, corrected version of the classical theory of vibrational excitation. Three methods of calculating the angular variation of the inelasticity are presented and found to be consistent with the experimental data.
Vibrational Excitation in Collisions Involving Oxygen Ion Beams
Authors: Cosby P. C. , Moran T. F.
Published: February 2004

Inelastic energy losses in the collisions of O+ and O2+ ions with neutral molecules have been studied in a beam apparatus designed to direct mass-analyzed low-energy ion beams onto target molecules and scan the energy, mass, and angular distributions of charged reaction products. Maxima in the scattered ion intensities are observed in the O+–O2 and O2+–Ar systems which are energetically displaced from the centroids of elastically scattered ions by amounts corresponding to known vibrational energy spacings in the respective diatomic species. Vibrational transition probabilities obtained from the inelastic energy loss data show multiquantum transitions to be more important as the reactant ion kinetic energy is increased from 10 to 20 eV. For a given reactant ion kinetic energy, higher vibrational transitions predominate at larger scattering angles. The velocity dependences of these transitions are in reasonable accord with calculations that employ a semiclassical impact parameter treatment to estimate collisional energy transfer and time-dependent wavefunctions to evaluate vibrational transition probabilities for a forced harmonic oscillator model.
Calculation of Ion–Molecule Reaction Product Distributions Using the Quasiequilibrium Theory of Mass Spectra
Authors: Buttrill S. E.
Published: February 2004

The quasiequilibrium theory of unimolecular reactions is applied to the calculation of ion–molecule reaction product distributions in ethylene and ethylene–acetylene mixtures. The unimolecular decomposition rates of the ion–molecule reaction complex are computed using the continuous approximation of Vestal et al. [J. Chem. Phys. 37, 1276 (1962)]. The reactions investigated include C3H5++CH3,↗C2H4++C2H4↘C4H7+H, C3H3++CH3↗C2H4++C2H2↘C4H5++H,as well as analogous reactions of the perdeuterated compounds. The calculated and experimental product distributions are in good agreement. When the reaction complex is formed from only partially deuterated reactants, there is an isotope effect favoring loss of hydrogen over deuterium. The theory accurately predicts this effect. The calculation of isotope effects allows very little freedom in the choice of variables such as activation energy or activated complex configurations. The success of these calculations is therefore strong evidence for the validity of the equilibrium hypothesis.
Scattering Cross-Section Measurements for Epithermal Ar on Ag(111) Surfaces
Authors: Calia Vincent S. , Oman Richard A.
Published: February 2004

A series of measurements of scattering cross sections have been made for nearly monoenergetic beams of argon on epitaxial (111) films of silver. Quantitative determinations of the fraction of the incident flow that exits in each solid angle element are compared directly with Oman's calculations for exactly matched situations. Nominal incident energies of 1 and 2 eV were provided by a shock-tube-driven, high intensity molecular beam. The measurements were made both in and out of the plane of incidence, so that a stringent test of the calculations is possible. Agreement was unexpectedly good, further confirming the validity of the calculation method as indicated by earlier agreement with the data of Romney and Anderson as well as those of Miller and Subbarao.
Ab Initio SCF–MO–CI Calculations for H−, H2, and H3+ Using Gaussian Basis Sets
Authors: Csizmadia I. G. , Kari R. E. , Polanyi J. C. , Roach A. C. , Robb M. A.
Published: February 2004

Fixed-center Gaussian-type functions (GTF) have been used as basis sets in an extensive SCF–MO–CI study on H−, H2, and H3+. An accurate description requires 4 or 5 s-GTF on each center, plus at least one set of p-GTF, which are essential for the reproduction of reliable potential curves; d-GTF are, however, of minor importance. A constant p exponent may be used successfully in a wide variety of nuclear configurations. Variational energies of − 1.3397 and − 1.2765 hartree were calculated for the most stable equilateral and collinear geometries of H3+. A potential-energy surface has been computed for the reaction H+ + H2, to an accuracy of about 2 kcal mole−1 over its important regions. In the computation of the proton affinites of H− and H2, little accuracy was lost when a limited basis set was used in SCF calculations.
Magnetic Resonance Line Shapes in Solids: The Rotating Three-Spin Group
Authors: Cobb Thomas B. , Johnson Charles S.
Published: February 2004

The density matrix formalism of spin-exchange theory has been applied to the problem of a rigid equilateral triangle of spin-1 / 2 nuclei undergoing random hindered rotation about the normal to the plane of the triangle. The resulting equations were solved numerically, and spectra are presented for a variety of rates of rotation for both a single orientation and a sum over orientations. These results are compared with recent calculations for coherent rotation (tunneling) of methyl groups, and the experimental situation is briefly discussed.
Electron Spin Resonance Spectra of Monomeric and Dimeric Cation Radicals
Authors: Howarth Oliver W. , Fraenkel George K.
Published: February 2004

Dimer cation radicals of anthracene, naphthalene, 2,3,6,7-tetramethylnaphthalene, and pyrene have been obtained using the technique of Lewis and Singer in which oxidation is carried out with antimony pentachloride in methylene chloride at low temperature. The monomer cation radicals of anthracene, 1,4,5,8-tetramethylnaphthalene, and pyrene were also produced using this technique. In the spectra of the dimers, lines were observed corresponding to the same number of groups of equivalent protons as in the monomer, but each group contained twice the number of protons. The larger of the ring-proton splittings in the dimers were slightly less than one-half the corresponding monomer cation splittings, and were larger than one-half the corresponding monomer anion splittings, but this was not always true of the smallest splittings for a particular compound. The values of the dimer splittings are for the most part in good agreement with the charge-effect treatment of Colpa and Bolton. The methyl-proton splittings in the monomer and dimer cations have been analyzed, and an earlier treatment by Bolton, Carrington, and McLachlan has been corrected. Levy's result for the inclusion of contributions from unpaired electrons on the ring and methyl-group carbon atoms proves useful for the positive ions but is unimportant for the anions. Detailed analysis of the methyl-proton splittings indicates, however, that sufficient discrepancies remain to cause uncertainties about this entire treatment. The structure of the dimers cannot be rigorously determined, but a sandwich in which the two halves are parallel, with one above the other, seems reasonable. The dimer cations appear to be formed more readily than the monomer cations from hydrocarbons that are difficult to oxidize, while the monomer is more easily formed than the dimer for the compounds with smaller oxidation potentials. Steric hindrance may account for the inability to produce the dimer of 1,4,5,8-tetramethylnaphthalene. The theoretical treatment of the stability of the dimers is not yet in a satisfactory state, and it is not fully understood why anion dimers have not been generated. The g values of the dimers may prove useful for obtaining structural information, but again the theory is not sufficiently complete.
On the Determination of Barriers to Internal Rotation
Authors: Ewig Carl S. , Harris David O.
Published: February 2004

A method is presented for determining barriers to internal rotation directly from the spectrum of torsional energy levels without an a priori knowledge of either molecular geometry or the dynamics of the motion. The method is applied to the H2O2 and D2O2 molecules. It is also shown that the neglect of the variation of the effective inverse moment of inertia of threefold rotors can lead to an apparent V6 contribution to the potential function.
Multiphonon Processes in the Nonradiative Decay of Large Molecules
Authors: Freed Karl F. , Jortner Joshua
Published: February 2004

Radiationless transition rates for polyatomic molecules are investigated in the simplest case of the statistical limit, i.e., large energy gaps between the two electronic states. By analogy with the theory of optical line shapes in solids, the “golden rule” rate expression for the nonradiative decay, which is usually written as a double sum over initial and final vibronic states, is equivalently represented in closed form as a single Fourier integral. For the case in which the vibrations are assumed to be harmonic, but may have different frequencies and equilibrium positions in the two electronic states, general closed-form analytic expressions, which include all of the vibrational modes, are obtained for the transition rates. The energy gap law is again obtained in the weak coupling statistical limit along with a proper description of the propensity rules for the promoting mode. For the case of the aromatic hydrobarbons, the effective energy gap is found to be in agreement with Siebrand's analysis, and explicit account is taken of the competition between the C–H modes and the C–C skeletal modes (which have large oscillator displacements) or the out-of-plane modes (which have large frequency changes) for the electronic energy which is involved in the relaxation process. The deuterium isotope effect is again found to be dominated by the modes of highest frequency (C–H or C–D), but corrections due to the C–C modes, which may be measurable, are explicitly included. The theory is also extended to include the role of the host medium as an inert heat bath by considering the intermolecular phonons as potential accepting modes. The approximations employed are compared with those usually made in Boltzmann statistical mechanics, thereby providing greater understanding as to the role of the Franck–Condon principle in the determination of the nonradiative decay rates.
Theoretical Predictions on the Structures of Diimide
Authors: Wong Dorothy Pan , Fink William H. , Allen Leland C.
Published: February 2004

The LCAO MO SCF wavefunctions have been determined for the ground states of the isomeric forms of diimide. Molecular geometries for trans(1Ag)-, cis(1A1)-diimide, and 1, 1-dihydrodiazine were deduced through the most detailed systematic geometry search to date on the diimide molecule. Contrary to the results from semiempirical calculations where cis-diimide has been predicted to be 4.5–8.5 kcal/mole more stable than the trans form, this calculation shows that the trans form is more stable. Furthermore, contrary to the common assumptions, the bond distances and bond angles are found to be different for different isomeric forms, due to the difference in electronic and nuclear repulsive forces. A discussion is made on the ultraviolet and infrared experimental results and comparison is made between the trans-N2H2 closed-shell 1Ag state and the open-shell 3Bg state at the theoretically calculated and the experimentally obtained configurations. The calculated force constants and dipole moment of cis-N2H2 are reported.
Vaporization Thermodynamics of Yttrium Dicarbide–Carbon System and Dissociation Energy of Yttrium Dicarbide and Tetracarbide
Authors: Kohl Fred J. , Stearns Carl A.
Published: February 2004

The Knudsen effusion method was used in conjunction with a double-focusing mass spectrometer to study the vaporization of the yttrium dicarbide–carbon system. Over the temperature range from 2270 to 2550°K the measured vapor pressures for yttrium, yttrium dicarbide, and yttrium tetracarbide were found to be log10PY = (− 2.423 × 104 / T) + 9.45, log10PYC2 = (− 3.286 × 104 / T) + 11.95, log10PYC4 = (− 4.456 × 104 / T) + 14.72, where the units of pressure are newtons per square meter. Experimentally determined enthalpies were combined with published thermodynamic data to yield the atomization energy of yttrium dicarbide and yttrium tetracarbide: YC2(g) = Y(g) + 2C(g)D°0,atom = 1229 ± 17 kJ mole−1, YC4(g) = Y(g) + 4C(g)D°0,atom = 2461 ± 18 kJ mole−1. The heat of formation of solid yttrium dicarbide was calculated as ΔH°298,f = −91 ± 17 kJ mole−1.
Simple Calculation of Polarizabilities, Hyperpolarizabilities, and Magnetic Susceptibilities of Atoms and Ions
Authors: Heinrichs Jean
Published: February 2004

We present calculations of polarizabilities and magnetic susceptibility for the ions and atoms of rare-gas structure. They are based on Kirkwood's variational approximation for second-order perturbations and its extension in the case of the hyperpolarizability. In our detailed calculations we include only the effect of the outermost shell of electrons which is described by means of simple Slater one-electron orbitals. Except for the lightest atoms and ions, the results are in good agreement with available experimental data. The predicted values of ion hyperpolarizabilities are therefore believed to be reliable.
Raman Spectrum and Force Constants of SF4
Authors: Christe Karl O. , Sawodny Wolfgang
Published: February 2004

The laser-excited Raman spectrum of gaseous SF4 has been examined. A previous assignment of the fundamental vibrations has been revised. The force constants and mean amplitudes of vibration have been recomputed.
Role of Diffusion in Oscillatory Electrode Kinetics
Authors: Szpak S. , Rice R. E.
Published: February 2004

The role of diffusion in oscillatory electrode kinetics is studied by examining a conservative system admitting a solution in the form F(x, s) = const. On the basis of this analysis it is shown that a sufficient condition for periodic behavior is the coupling of mass transport with oscillatory electrode kinetics. It is also shown that mass transport may provide a diagnostic criterion for correctness of an assumed model.
Eu
+3
5
D
Resonance Quenching to the Charge-Transfer States in Y2O2S, La2O2S, and LaOCl
Authors: Fonger W. H. , Struck C. W.
Published: February 2004

The 5D emissions of Eu3+ in Y2O2S, La2O2S, and LaOCl quench sequentially with increasing temperature in the simple order 5D3, 5D2, 5D1, 5D0. These 5D quenchings are attributed to thermally activated resonance crossovers from the 5D states to the charge-transfer states (CTS). The activation energies for the 5D quenching place the CTS relative to the 5D states. The 7F→CTS absorption bands also place the CTS relative to the 7F states. The agreement between these two independent CTS placements supports the model of 5D−CTS resonance transitions. Thermally activated 5D→CTS crossovers also account for the two-step 5D2 quenching observed in LaOCl and La2O2S.
Infrared Chemiluminescence from the Reaction of Hydrogen Atoms with SCl2, S2Cl2, SOCl2, SO2Cl2, and OCl2
Authors: Perona M. J. , Setser D. W. , Johnson R. J.
Published: February 2004

The hydrogen chloride infrared emission from the reactions of H atoms with OCl2, SCl2, S2Cl2, SOCl2, and SO2Cl2 has been studied under a variety of conditions. A limited number of experiments with the deuterium atom reactions also are reported. The emission from the highest vibrational level gave an estimate of the first sulfur–chlorine bond dissociation energy for these compounds. The emission intensities, relative to H+Cl2, from the various reactions were measured and were used to estimate relative rate constants, which decline through the series OCl2, Cl2, SCl2, S2Cl2, SOCl2, and SO2Cl2. Qualitative deductions about the energy partitioned to the HCl† product by the different reactions are presented.
Luminescence of Biphenyl and Geometry of the Molecule in Excited Electronic States
Authors: Lim E. C. , Li Y. H.
Published: February 2004

Fluorescence and phosphorescence spectra of biphenyl, biphenyl-d10, and related compounds were studied in n-heptane at 77°K. The fluorescence spectrum of each of these compounds displays a long progression involving odd quanta of a low-frequency vibration, while the phosphorescence spectrum exhibits a short progression involving even quanta of the same vibrational mode. The fundamental frequencies in these progressions are 635 cm−1 for biphenyl, 595 cm−1 for biphenyl-d10, and 626 cm−1 for 4,4′-difluorobiphenyl. From their appearance in Raman spectra (but not in infrared), the ratio of the frequencies in the isotopic species, their dependence on the position of substitutions, and their absence in the fluorescence spectrum of crystalline biphenyl, these frequencies are concluded to be the torsional frequencies in the ground state. The prominence of odd quanta of the torsional mode in fluorescence and even quanta in phosphorescence is shown to be a strong indication that the molecule of biphenyl is planar in the lowest excited states (singlet and triplet).
Classical Theory of Rotational Relaxation in Diatomic Gases
Authors: Brau C. A. , Jonkman R. M.
Published: February 2004

In his well-known theory, Parker assumes that the rotational relaxation of diatomic gases may be described by a single relaxation time which is calculated for the special case of initially nonrotating molecules. In the present theory the evolution of the rotational distribution function is described by a diffusion-equation approximation to the master equation. This equation is linearized and solved for the case of acoustic waves. The results indicate that the absorption and dispersion of acoustic waves cannot be described by a single relaxation time. However, the behavior at very low and very high frequencies can be described in terms of “apparent relaxation times” which differ by approximately 50%. The temperature dependence of the apparent relaxation times is similar to that predicted by Parker, but the magnitudes are larger by approximately a factor of 2.
Surface Tension of Simple Liquids from the Radial Distribution Function
Authors: Shoemaker P. D. , Paul G. W. , de Chazal L. E. Marc
Published: February 2004

Using radial distribution function data available from the literature for liquid argon, krypton, xenon, neon, nitrogen, oxygen, and methane, the authors calculate Lennard-Jones potential function constants from the pressure and configurational energy. They numerically integrate the Kirkwood–Buff–Fowler equations to obtain the surface tension and surface energy of the liquids. These equations are also integrated using literature values of the potential function constants obtained from gas viscosities and second virial coefficients.
Vapor Pressure Isotope Effects of the Deuterated Acetylenes
Authors: Phillips James T. , Van Hook W. Alexander
Published: February 2004

The vapor pressures of the isotopic acetylenes: C2H2, C2HD, and C2D2, have been investigated by mercury manometry. Samples of relatively pure C2HD were prepared for this purpose by low-temperature gas chromatography. The vapor pressure measurements were made from 0.5 to 800 mm pressure (125–190°K) with a precision of ∼0.01 mm. The vapor pressure isotope effects were normal with the isotope effect for C2HD being slightly larger than the rule of the mean value. The data for C2D2 showed a sharp change in the temperature dependence at 147.4°K which has been interpreted as a result of a solid–solid phase transition in C2D2. The experimental results have been considered in the light of the statistical theory of isotope effects in condensed systems. A model calculation made within the framework of this theory is in agreement with the experimental data.
Nuclear Magnetic Resonance Study of Na3P Powder
Authors: Ossman G. W. , Silvidi A. A. , McGrath J. W.
Published: February 2004

NMR spectra of sodium phosphide were obtained. The coupling constant for site 1 is 1.53 ± 0.05 Mc/sec (lower limit) and 1.7 Mc/sec (upper limit); for site 2 it is 0.48 ± 0.05 Mc/sec. These measured coupling constants are inconsistent with an ionic model but are consistent with both Suchet's model and the Z2 = + 1 model, implying a degree of covalent bonding. Asymmetry parameters are zero.
Energy Corrections to the Born–Oppenheimer Approximation. The Best Adiabatic Approximation
Authors: Pack Russell T , Hirschfelder Joseph O.
Published: February 2004

Procedures are presented for solving the previously derived exact coupled Schrödinger equations for the internal motion of a diatomic system, using both nonadiabatic variation methods and adiabatic perturbation methods. A “best adiabatic” (BA) approximation is variationally derived to give the energetically best possible adiabatic vibration–rotation energies and potential-energy curves. The BA electronic wavefunctions are shown to satisfy a set of coupled equations, involving the complete internal Hamiltonian of the system, which leads immediately to a generalization of the noncrossing rule for potential-energy curves. Methods for solving these coupled electronic equations to obtain corrections to the Born–Oppenheimer approximation, valid in the presence of rotational degeneracies, are presented. And finally, some upper-and lower-bound properties of various adiabatic approximations are investigated.
Electron Resonance Powder Spectra for Systems with S > 12
Authors: Mohrmann L. E. , Garrett B. B. , Lewis W. Burton
Published: February 2004

A qualitative interpretation, ignoring nuclear hyperfine effects, of the line shapes and positions of all the lines occurring in the ESR powder spectra for S = 32, 52 systems with rhombic environments is presented. The formulation of the problem assumes the zero-field tensor is dominant in determining the angular dependence of oriented crystal spectra. In favorable cases, g factors and zero-field splitting parameters can be determined, and results from powder spectra are compared with spin-Hamiltonian parameters obtained from a single crystal study of Cr3+: (NH4)2[In(H2O)Cl5].
Vibronic Interactions in the Anions of Benzene and Substituted Benzenes
Authors: Alper Joseph S. , Silbey Robert
Published: February 2004

The Jahn–Teller and pseudo-Jahn–Teller effects involving degenerate and nearly degenerate electronic levels, respectively, are investigated for the anions of benzene and substituted benzenes. Two different transformation methods are discussed. In each the total Hamiltonian for the degenerate case is expressed in second quantized form. In the first method, complex orbitals and coordinates are used and a conanical transformation is employed. The coupling term of the transformed Hamiltonian becomes a small perturbation and the use of a small number of zeroth-order states suffices to give accurate values of the vibronic energy lowering for the lowest state. In the second method, real orbitals and coordinates are used, a different transformation is performed, and second-order perturbation theory is used to calculate the vibronic energy lowering. In both methods, the energy is expressed as a function of a dimensionless coupling parameter. The second method is then applied to the nondegenerate cases. The two transformation methods are compared with each other and with previous calculations. The transformation methods are much simpler computationally and provide comparable accuracy.
Magnetic-Susceptibility Anisotropy of CO and CS
Authors: Gustafson Steve , Gordy Walter
Published: February 2004

The asymmetric frequency shifts in the Zeeman splittings of the first rotational lines of CO and CS have been measured. The magnetic anisotropy evaluated from these shifts is ( − 8.2 ± 0.9) × 10−6 for CO and ( − 24 ± 3) × 10−6 for CS, both in ergs/gauss2·mole. The molecular quadrupole moments are estimated from the anisotropies, and the g factor of CS is shown to be negative.
Chemisorption of Carbon Monoxide on (110) and (100) Nickel Crystal Faces
Authors: Klier K. , Zettlemoyer A. C. , Leidheiser H.
Published: February 2004

Adsorption equilibria, adsorption rates, and exchange rates of carbon monoxide have been investigated on nickel single-crystal faces of the (110) and (100) orientation using radiotracer techniques. On the clean annealed surfaces, carbon monoxide is uniformly bound, is mobile, and occupies an area of 9 Å2 in the saturated layer. The surface equilibria and the kinetic phenomena are both quantitatively accounted for by a theory utilizing the Stockmayer potential and a cell approximation for describing the lateral interaction of the adsorbed molecules. The ion-bombarded nonannealed surfaces are unstable and heterogeneous. The contaminated surfaces adsorb only minute amounts of carbon monoxide. The chemisorption of CO thus provides a useful criterion for the degree of cleanliness of nickel surfaces.
Feenberg–Goldhammer Procedure and Geometric Approximation in Hartree–Fock Perturbation Theory
Authors: Amos A. T.
Published: February 2004

The uncoupled Hartree–Fock procedure plus the geometric approximation is the most economical one for computing second-order perturbation energies of atoms and molecules. The geometric approximation, however, has generally been considered empirical in nature. Here we show that, in fact, it is related to the Feenberg–Goldhammer procedure for improving the convergence of perturbation series.
Helical Twisting Power of Steroidal Solutes in Cholesteric Mesophases
Authors: Baessler H. , Labes M. M.
Published: February 2004

Shifts in the nematic temperature of a compensated cholesteric liquid-crystal solvent, consisting of cholesteryl chloride and cholesteryl myristate, are caused by adding steroidal solutes. A helical twisting power P can be defined which is a molecular property; there is a linear dependence of the inverse of the solute concentration on the helical pitch. The method has the advantages of (1) allowing study of compounds which do not form mesophases themselves and (2) eliminating temperature effects. For a series of fatty acid esters of cholesterol, P decreases with decreasing number of carbon atoms in the ester chain, and shows a zigzag fine structure with P having higher values for odd-numbered carbon-atom chains. P, and therefore the helix, changes rotational senses if the ester chain is replaced by Cl, Br, or OH. Changes are also discussed associated with modification of the 17 side chain or the steroid ring system itself. A model is proposed attributing P to the molecular asymmetry at the 3β position of the steroid ring, which can cause macroscopic twist if two lever arms are present, one of which lacks rotational symmetry.
LCAO–MO–SCF Calculations Using Gaussian Basis Functions. VII. BLi
Authors: Kaufman Joyce J. , Sachs Lester M.
Published: February 2004

Results of LCAO–MO–SCF calculations on BLi using 985p Gaussian basis functions are presented. The calculated EHF as a function of B–Li distance showed a minimum indicative of a stable species, but because of the correlation error this minimum lay completely above the sum of the EHF for B plus the EHF for Li. An estimate of the correlation energy combined with the EHF results indicated that BLi would be bound by approximately 1.2 eV. On this basis it seems quite probable that BLix compounds could be prepared. We conjecture that these would exist as polymeric solids. The gross atomic population shows the Li to be severely electron deficient (only 2.64 electrons) and thus a prime candidate to complex with a species containing a donable electron pair.
Shock-Tube Study of the Oxidation of Carbon Disulfide
Authors: Sheen D. B.
Published: February 2004

The oxidation of carbon disulfide has been studied after shock heating the following mixtures: CS2: O2:Ar = 1:3:96, 1:6:93, 1:9:90, and 5:15:80. A range of initial pressures between 10 and 30 torr, combined with the change of mixture composition and use of reflected as well as incident shocks, resulted in a variation of CS2 and O2 concentrations equal to a factor of 20 in each case. Chemiluminescence accompanying the reaction was recorded at temperatures between 1600 and 2100°K. The assumption that the chemiluminescence is the SO+O recombination emission is consistent with experimental observations of the growth rates of emission intensity and SO absorption. These observations indicate that a direct proportionality exists between the concentrations of SO and O during the early stages of reaction. Induction period measurements and the exponential growth rates for emission are analyzed assuming the following branching-chain-reaction mechanism: CS2, O2→ lim k8SO, O, CS, CS2+O→ lim k9CS+SO, CS+O2→ lim k10aCO+SO, CS+O2→ lim k10bCOS+O, SO+O2→ lim k1SO2+O. The reaction seems to proceed through steps (8)–(10b) and (1), with the oxidation of SO being the single rate-determining step. On this basis a value for the rate constant k1 is given by the expression k1 = (9.7 ± 0.2) × 1013exp(− 29.0 ± 1.0 kcal mole−1/RT) cm3mole−1·sec−1. A few experiments were carried out with COS replacing CS2. The results showed that the oxidation is much slower than in the case of CS2 and goes by a different process. A reaction sequence analogous to that for CS2 can be used to interpret this behavior.
Combined Infrared and Microwave Determination of Torsional Parameters
Authors: Souter Claire E. , Wood J. L.
Published: February 2004

Considerable discrepancies are frequently observed between the values of torsional barriers determined by microwave splitting and those obtained from far-infrared transitions, if the usual rigid-top–rigid-frame model is employed. If a nonrigid model which includes first-order coupling with the internal vibrations is used, the requirement of consistency between the microwave and infrared data permits barrier Fourier coefficients V3 and V6 to be evaluated without any prior choice of a value of Ired, the reduced moment of the top. This has hitherto been the principal source of uncertainty in the determination of barrier parameters. The torsional parameters F, Ired, S, α, and β are also independently evaluated; from these Iα is determined. Comparison of the “self-consistent” and “a priori” values of parameters such as Iα indicates the extent of interaction with other normal vibrations. The limitation of the treatment involved by the neglect of second-order vibrational interaction terms, such as centrifugal distortion, can be assessed in cases where microwave data from torsionally excited states is available. The method is applied to CH3CHO, CD3CHO, and CH3CH = CH2, for which accurate far-infrared spectra have been newly determined.
Tandem-Mass-Spectrometer Study of Solvated Derivatives of OD−. Total Hydration Energy of the Proton
Authors: De Paz M. , Giardini A. Guidoni , Friedman L.
Published: February 2004

Heats of hydration of OD− have been determined by measuring thresholds for collision-induced dissociation reactions of hydrated OD− ions. These data showed similar values of hydrogen bonding energy for OD− and D3O+. Attenuation cross section for various solvated OD− ions were also measured and compared with D3O+ and its solvated derivatives. The relative sizes of solvated hydroxyl and hydrogen ions were found to be within 4% of each other for the unsolvated, mono-, di-, and trisolvated species. The very strong similarity in both ion size and hydrogen bonding energy of the respective positive and negative gaseous ions in the water system was used to divide the sum of the solvation energies of gaseous ions D9O4+ and D7O4−, and thus derive a value of 12.0 ± 0.3 eV for the heat of solution of the proton.
Absorption Cross Section and Photoionization Yield of I2 between 1050 and 2200 Å
Authors: Myer James A. , Samson James A. R.
Published: February 2004

The total absorption cross section and photoionization yield of molecular iodine were measured from 1050 to 2200 Å. Two thresholds were observed in the photoionization yield curve. The first was associated with the ion-pair production I+ + I− and the second to direct ionization of I2. From the appearance potential for ion-pair production and the accurate ionization potential of I2 it was possible to calculate the value of the electron affinity of iodine, namely, 3.073 ± 0.014 eV.
NpT-Ensemble Monte Carlo Calculations for the Hard-Disk Fluid
Authors: Wood W. W.
Published: February 2004

The NpT-ensemble Monte Carlo method previously described, in which the hard-disk interaction is represented by a soft pseudopotential in a reduced configuration space with a fixed periodic enclosure, is used to calculate the equation of state and radial distribution function in the high-density fluid phase. The equation of state agrees within statistical error with the (3, 3) Padé approximant to the six-term virial expansion and, for large enough systems, with Salsburg's analysis of the N dependence. The results also agree with recent Monte Carlo calculations by Chae, Ree, and Ree using the NVT ensemble. Some qualitative results for systems of 48 and 90 disks which lend further support to the now-accepted presence of a solid–fluid phase transition are also presented.
Study of Inhibition and Quenching of Positronium by Iodine and CCl4
Authors: Chuang S. Y. , Tao S. J.
Published: February 2004

Positron annihilation time spectra on various concentration of iodine and CCl4 adsorbed in silica gels have been studied. It is found that iodine acts as a chemical quencher to positronium, and CCl4 acts as an inhibitor to the formation of positronium.
Microwave Spectrum of Chlorine Dioxide. VI. υ2 = 1 State
Authors: Mariella Raymond P. , Curl R. F.
Published: February 2004

Eight rotational transitions of the υ2 = 1 state of chlorine dioxide have been observed and assigned. The spin–rotation constants for the υ2 = 1 state were determined by fitting the hyperfine structure. A theoretical treatment of the vibrational dependence of the spin–rotation constants was developed. Numerical calculations employing an extended Hückel method were carried out, and their results were compared with the experimental results. The rotational constants of the υ2 = 1 state were determined, and the resulting cubic force constants are K122 = + 4.2 cm−1 and K222 = − 9.0 cm−1.
Asymptotic Expansion Method for Franck–Condon Factors of Morse Oscillators
Authors: Chang T. Y. , Karplus M.
Published: February 2004

It is shown that the Franck–Condon factors for Morse oscillators can be obtained by an asymptotic expansion of the necessary integrals. The method gives accurate results for a wide range of vibrational quantum numbers.
Effect of Charge Transfer on Raman Scattering of Hydrogen Halides
Authors: Hanamura Eiichi
Published: February 2004

Many properties of molecules in molecular crystals of hydrogen halides can be shown theoretically to deviate from those of free molecules because of charge-transfer effects. These effects will be discussed in a series of papers. In this paper, the Raman scattering due to intermolecular vibrations is shown to be activated by this charge-transfer process, which can explain the strong Raman scattering due to these intermolecular vibrations as observed by Ito et al.
Application of Bound-State Solutions to the One-Dimensional Barrier Penetration Problem for Boltzmann Systems
Authors: Quickert K. A. , Roy D. J. Le
Published: February 2004

As an alternative to the conventional approach, it is proposed that the problem of Boltzmann particles impinging on an infinite one-dimensional potential barrier may be solved by making use of the bound-state solutions for the corresponding potential well. The method is shown to be rigorous for two simple barrier shapes, a parabolic barrier and a “double anharmonic” barrier; it is shown to be valid for the case of a general infinite barrier in the WKBJ approximation.
Electron-Spin Resonance Studies of Cr3+ in LiNbO3
Authors: Rexford D. G. , Kim Y. M. , Story H. S.
Published: February 2004

ESR studies were performed on a single crystal of ferroelectric LiNbO3 doped with chromium. For the main spectrum, attributed to Cr3+ at the Nb site, all transitions (including forbidden transitions) were identified. The experimental rotation pattern observed at X-band frequency was compared with that computed from the appropriate spin Hamiltonian {H = H̄·ḡ·s̄ + D[Sz2 − 13S(S + 1]} and the best fit ESR parameters obtained: D = 0.411 cm−1 and g = 1.969. In examining these parameters as a function of temperature, the g value was found to be temperature independent, and the variation of D with temperature was attributed to anisotropic lattice expansion. On the main central transition, two additional peaks were observed. EPR parameters (D = 0.21 ± 0.02 cm−1 and g = 1.97) are given for the peak on the high-field side. It is proposed that this peak arises from Cr3+ at the Li site. A discussion of the peak on the low-field side is also given.
Angular Distribution of Photoelectrons. I. Cadmium and Zinc Atoms at 584 and 1048 Å
Authors: Harrison Halstead
Published: February 2004

The distribution of photoelectron trajectories has been measured with unpolarized resonance emission from helium and argon, modulated atomic beams of cadmium and zinc, a sector-focusing photoelectron energy analyzer, and digital counting and demodulation techniques. The autoionizing transitions at 1048 Å to produce Cd+S1/2 and Zn+S1/22 and the direct ionization at 584 Å to produce Cd+D5/22 all result in electron-trajectory distributions which are close to cos2θ with respect to the electric vector of the radiation. Ionization at 584 Å to produce Cd+D3/22 results in an isotropic distribution. For cadmium the ratio of total cross sections to produce D5/22 / 2D3/2is 1.06 ± 0.07.
Hydrogen Density Distribution in Paraelectric Potassium Dihydrogen Phosphate
Authors: Felcher G. , Pelah I.
Published: February 2004

The hydrogen density distribution in potassium dihydrogen phosphate was studied by incoherent elastic neutron scattering. The motions across the hydrogen bond were found to be harmonic in character. The motion along the bond is characterized by a broad density distribution near room temperature. This motion is shown to be strongly anharmonic by comparing the incoherent measurements with the coherent neutron scattering results of Bacon and Pease, and as a consequence of spectroscopic data.
Thermodynamic Properties of Phosphoryl Fluoride from 12 to 240°K. The Zero-Point Entropy of the Solid
Authors: Pace E. L. , Jepson B. E.
Published: February 2004

The heat capacity of phosphoryl fluoride has been measured from 12 to 240°K for a sample with a purity greater than 99.9 mole %. The solid–liquid–vapor triple-point temperature and pressure were, respectively, 233.45°K and 774.06 torr. The heat of fusion was 3086 cal/mole. The heat of vaporization was determined as 5150 cal/mole at a temperature of 236.00°K and a pressure of 880.25 torr. The vapor pressure data were fitted by the equation lnP(torr) = − 487.49218 + 14 223.578 / T + 79.446599 lnT for the solid and by lnP(torr) = 8.05651 − 1206.41 / T for a short temperature range in the liquid phase. An entropy discrepancy, Sspec − Scalc, of 1.33 cal/mole·°K at 236.00°K was found between the spectroscopic entropy of 64.777 cal/mole·°K and the calorimetric value of 63.45 cal/mole·°K. A tentative model to explain the discrepancy has been proposed in which it is assumed that the degree of degeneracy of the several lowest eigenstates of the molecular motion are reduced when the molecule in the solid is subjected to the field of neighboring molecules of a certain symmetry.
Electronic Structure of Ferrous Iron in Hemoglobin Inferred from Mössbauer Measurements
Authors: Eicher H. , Trautwein A.
Published: February 2004

The effect of rhombic perturbation on the low-lying energy levels (calculated for tetragonal point symmetry) of ferrous iron in deoxyhemoglobin Hb(rat, pH = 10) is investigated. The resulting temperature dependent electric-field gradient is compared with experimental values in order to get information about the energy-term scheme. The rhombic perturbation is shown to be small, leading to the splitting of the orbital doublet E5 by less than 400 cm−1. Application is made to the magnetic susceptibility which is calculated by means of the electronic structure inferred from the quadrupole splitting data.
Dielectric Relaxation Studies in Liquids at Microwave Frequencies and Viscoelastic Relaxation Behavior of the Solvents
Authors:   Krishnaji, Srivastava Shyam Lal , Nath Dina
Published: February 2004

Dielectric data of four nearly spherical molecules, viz., tert-butyl cyanide, trimethyl acetaldehyde, nitrochloroform, and nitrobromoform, in solutions of a wide range of viscosity are reported in this paper. The dielectric relaxation time τ and the viscosity ηs have been evaluated. It is found that the plots of logτ vs logηs are not straight lines. The deviation from straight line has been explained on the basis of the concept of dynamical viscosity, and it has been suggested that instead of using the static viscosity one should use the dynamic viscosity while explaining the dielectric data at microwave frequencies. Since no direct method of evaluating the dynamic viscosity at microwave frequencies is available, a linear extrapolation of the dielectric data at low viscosity has been done, and the viscoelastic relaxation time of the solvent Nujol and its mixtures with benzene have been evaluated.
Some Negative-Ion Reactions with CO2
Authors: Paulson John F.
Published: February 2004

The reactions O− + CO2→CO2− + O, O− + CO2→O2− + CO, NO− + CO2→CO2− + NO, O2− + CO2→CO3− + O, and O2− + CO2→CO2− + O2 have been studied with a double mass spectrometer system. The maximum cross sections obtained are about 0.35, 0.2, 0.8, 0.12, and 0.26, respectively, in units of 10−16 cm2. These maxima occur at reactant ion kinetic energies of 8–15 eV.
Melting of Three Organic Compounds at High Pressures
Authors: Akella Jagannadham , Kennedy George C.
Published: February 2004

The melting of napthalene, benzophenone, and p-dichlorobenzene has been determined up to 25 ∼ 30 kbar. The melting curve for benzophenone determined by Bridgman intersects our curve at 4 kbar and at 8 kbar his melting temperature is 8°C higher than ours. The melting temperature versus volume compression curves are nonlinear and are concave towards the temperature axis. The log(Tm / Tm0) versus log(V0 / V) plots are linear for napthalene and p-dichlorobenzene. Benzophenone points show a scatter which is attributed to inaccuracies in the compressibilitity data available for this compound.
Mass Spectrometric Study of the GaAs System
Authors: De Maria G. , Malaspina L. , Piacente V.
Published: February 2004

The vaporization of GaAs has been investigated by means of the mass spectrometric method. The activity values of the components were determined in a composition range of 50–95 at.% Ga at 1283°K. The heteronuclear gaseous species GaAs was detected by the aid of double-oven experiments. Its dissociation energy D°298 = 50.1 ± 0.3 kcal mole−1 was determined using the third-law method. The equilibrium reaction As4⇋2As2 was considered in the study of the vapor over GaAs. Second-law and third-law values D°298 = 77 ± 5 and 73.5 ± 0.3 kcal mole−1, respectively, for the As2–As2 bond were obtained. The value D°298 = 71.0 ± 3.0 kcal mole−1 is proposed as a result of comparison with previous determinations.