bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic properties of high purity scandium and the effect of impurities on these properties
Authors: Spedding F. H. , Croat J. J.
Published: February 2004

The magnetic susceptibility of single and polycrystalline Sc has been measured from approximately 1.5 to 300°K. The metal used is believed to be more thoroughly characterized and of significantly higher purity than that used in previous studies. Sc was found to exhibit excellent Curie-Weiss behavior above 70°K. A previously unreported maximum was found at 30°K. The effect of nonmagnetic impurities, including O, H, Fe, Ti, Zr, Hf, Nb, Ta, and Th, on the susceptibility of Sc was found to be quite pronounced. The behavior of dilute Gd and Er impurities in the Sc matrix was also investigated.
Effect of the potential well on vibrational scattering and the validity of SSH theory
Authors: Wagner Albert F. , McKoy Vincent
Published: February 2004

The vibrational de-excitation probability, P 10, is calculated quantum mechanically over a large energy range for models of three collision systems: O2–O2, Cl2–Cl2, and Br2–Br2. The vibrational de-excitation cross section, σ10, is similarly calculated for the Cl2–Cl2 model. P 10 and σ10 are obtained for the Lennard-Jones intermolecular potential and three other ``well-less'' potentials designed to duplicate the scattering of the Lennard-Jones potential. The results emphasize the adiabatic nature of potentials with wells and indicate that the acceleration approximation for the effect of the well is not valid. The curves of P 10 and σ10 as a function of initial translational energy are used to obtain exact collision numbers. These numbers are compared to the results of SSH theory. SSH theory is found to predict collision numbers with reasonable accuracy except at low temperatures. SSH theory is also not suitable for analyzing experimental collision numbers for the well depth potential parameter.
Spectra of the xenon fluorides XeF2 and XeF4 in the far uv region
Authors: Comes F. J. , Haensel R. , Nielsen U. , Schwarz W. H. E.
Published: February 2004

The absorption of gaseous and solid XeF2 and XeF4 has been measured in the region of 50–160 eV. It was possible to reproduce the absorption line shapes observed between 61 and 73 eV by semiempirical calculations based on the one center-one electron model. According to these results, the observed lines could be assigned to transitions from 4d and 4p Xe subshells into ``5p'', 6s, 6p, and 7p levels. The spin orbit splitting of the molecular 4d level has been found to be almost equal to the free atom case. For the first time, a ligand field splitting of core levels is observed. In addition to this, spin orbit and ligand field splittings are measured to occur in the upper levels. The 4d→``5p'' transition in XeF4 suggests a dynamic Jahn-Teller effect. The gross structure of the spectra in both phases is practically identical for both XeF2 and XeF4. The absorption lines of the Rydberg transitions are strongly broadened in the spectra of the solidified gases.
Potential energy curve of the B 1Σu+ state of H2
Authors: Stwalley William C.
Published: February 2004

The serious disagreement between ab initio and Rydberg-Klein-Rees potential energy curves for the B 1Σu+ state of H2 is discussed and explanations suggested. A ``best available'' hybrid potential energy curve for the B 1Σu+ state is then proposed.
Internal state distribution of alkali dimers in supersonic nozzle beams
Authors: Sinha M. P. , Schultz A. , Zare R. N.
Published: February 2004

By spectroscopically analyzing the white light and laser-induced fluorescence excited in a nozzle beam of Na2 molecules, we have measured the population distribution of the (v,J) levels of the ground state. The Na2 molecules are produced in nozzle beams with various stagnation pressures (50–240 torr) of alkali metal and with nozzles of different throat diameters (0.12–0.50 mm). We find at a stagnation pressure of 50 torr and a nozzle diameter of 0.5 mm a Boltzmann distribution characterized by a vibrational temperature of 153 ± 5°K and a rotational temperature of 55± 10°K. Beams under different stagnation conditions have essentially the same internal state distribution. Studies of K2 dimers produced in a nozzle beam with various stagnation pressures (20–300 torr) and a 0.25 mm nozzle throat diameter also show cooling in both vibrational and rotational modes. A search is made for atomic fluorescence arising from the photodissociation of dimers in high vibrational levels of the ground state. No evidence is found for the presence of vibrationally-excited dimers in the nozzle beam.
Oscillator strength of exciton transitions in molecular crystals
Authors: Philpott Michael R.
Published: February 2004

An exact formula is derived for the oscillator strength of exciton transitions in molecular crystals and compared with an approximate one used in earlier calculations. The new formula satisfies a sum rule. Where exciton interactions are weak (small frequency shifts) the two formulas give essentially the same results. However for states experiencing stronger interactions the results differ by as much as a factor of three in one case examined.
Laser induced combination band fluorescence study of vibrational deactivation of ethylene in C2H4-X mixtures
Authors: Yuan Raymond C. L. , Flynn George W.
Published: February 2004

Laser induced fluorescence studies of vibrational deactivation of C2H4 in mixtures with rare gases and diatomic molecules have been made. The experimental results are compared with predictions based on simple vibration-translation and vibration-rotation energy transfer theories. The data is consistent with V-T deactivation of ethylene by light collision partners. For heavy collision partners the experimental results cannot be reasonably described using standard V-T theory. The qualitative trends in the deactivation probability for the heavy collision partners are in the direction predicted by simple, semiempirical V-R calculations.
Van der Waals forces between thin cylinders: New features due to conduction processes
Authors: Davies B. , Ninham B. W. , Richmond P.
Published: February 2004

We discuss the van der Waals force between two long thin conducting cylinders; in particular we show that conduction gives rise to a longer range force than the usual R−5 result for dielectric cylinders. Some difficulties arising in studies of the interaction of long conjugated molecules are discussed and resolved. We further show that at nonzero temperature, there is an entropic contribution to the free energy of even longer range than the ground state interaction. Finally, we note that these forces are not attenuated at long range by retardation.
Complex velocity of sound in chemical systems
Authors: Hayman H. J. G.
Published: February 2004

A series of expressions were obtained for the complex adiabatic compressibility of a liquid chemical system, thus providing corresponding expressions for the complex velocity of sound in the system. The comparatively simple kinetic method used was based on the fact that the rate of an elementary chemical reaction, as well as that of each member of a set of normal modes of chemical relaxation, are proportional to the corresponding affinity. The cumbersome expressions obtained in terms of the rates of the various elementary reactions simplify very considerably when expressed in terms of the relaxation times of the system.
On the H+F2→HF+F reaction. An ab initio potential energy surface
Authors: O'Neil Stephen V. , Pearson Peter K. , Schaefer Henry F. , Bender Charles F.
Published: February 2004

Rigorous quantum mechanical calculations have been carried out to predict the H+F2→HF+F potential energy surface. A double zeta basis set was used, and open-shell self-consistent-field (SCF) calculations were carried out. In addition, electron correlation was explicitly treated using first-order wavefunctions, made up of 555 2A′ configurations. Orbitals were optimized by the interative natural orbital method. From the SCF calculations the barrier height and exothermicity are predicted to be 12.2 and 132.4 kcal/mole, respectively. The configuration interaction (CI) values are 1.0 and 88.3 kcal, in much better agreement with the experimental values, 1.2 and 102.5 kcal. The saddle point is predicted from the CI calculations to occur for a linear geometry, R(H–F)=2.05 Å, R(F–F)=1.57 Å. This corresponds to an H–F separation more than twice as great as in the HF molecule but an F–F separation is only slightly (0.03 Å) longer than in the isolated F2 molecule. A substantial number of calculations were carried out for nonlinear HF2 to determine the anisotropy of the surface. Finally, a brief description is given of electronic structure changes during the reaction.
Nonempirical LCAO MO SCF studies of the low lying states of BeF2
Authors: Gole James L.
Published: February 2004

Nonempirical LCAO MO SCF studies of the low lying excited states of BeF2 are reported. These results provide new insight into the differences between the valence molecular orbitals for covalent and ionic AB2-type molecules. The lowest energy states in BeF2 are predicted to result from transitions involving the highest occupied πg (b2) and πg (a2) molecular orbitals of the ground state to the lowest unoccupied σ̄g (a1) molecular orbital. This is in contrast to the case of CO2 where experiments have confirmed Walsh's prediction that the lowest energy transitions are from the πg (b2) and πg (a2) molecular orbitals to the π̄u (a1) molecular orbital. This predicted change in the ordering of the π̄u (a1) and σ̄g (a1) orbitals for BeF2 and CO2 suggests that the lowest energy transition in BeF2 should be quite weak in absorption since a g to g transition is electric dipole forbidden for the linear molecule. A modification of the Walsh type diagram for highly ionic species of the form X−δ−M+2δ−X−δ is discussed.
Charge-transfer properties of hydrogen bonds. III. Charge-transfer theory and the relation between the energy and the enhancement of dipole moment of hydrogen-bonded complexes
Authors: Ratajczak Henryk , Orville-Thomas W. J.
Published: February 2004

An extension of Mulliken's charge-transfer theory leads to a relation between the enthalpy of formation and the enhancement of the dipole moment for hydrogen-bonded complexes. Extensive experimental data are in accord with this theoretical prediction. It is shown conclusively that the proton transfer effect is not responsible for the enhancement of the dipole moment in these systems.
Localized orbital SCF and CI studies of ground electronic states
Authors: Wilhite D. L. , Whitten J. L.
Published: February 2004

Localized orbitals for molecules are determined by solving an appropriate set of SCF equations based on the assumption that orbitals are qualitatively localized initially. Degrees of orbital delocalization and comparisons with canonical SCF solutions are reported for H2O, NH3, C2H4, and H2CO. Constraints related to prejudging the degree of localization are also investigated. SCF localization arguments are extended to the determination of virtual orbital transformations and configuration interaction calculations of intraorbital and interorbital contributions to the correlation energy are reported. The application of SCF localized orbital techniques to the description of regions of large molecules is discussed with reference to the amide and carboxylate groups of glycylglycine.
Chemically induced dynamic electron polarization. II. A general theory for radicals produced by photochemical reactions of excited triplet carbonyl compounds
Authors: Wong S. K. , Hutchinson D. A. , Wan J. K. S.
Published: February 2004

Electron spin resonance emission was observed from some photochemically produced semiquinone radicals in liquid isopropanol. It is proposed that the dynamic electron polarization is due to the optically spin polarized triplets of the parent quinones and their subsequent hydrogen abstraction reaction with retention of polarization in the resultant semiquinone radicals. Theoretical calculations have been carried out using typical zero field parameters for aromatic triplet molecules and the established assumption that the intersystem crossing rates to the three sublevels are unequal. Calculations reveal significant spin polarization of the triplets randomly oriented in an arbitrary magnetic field. Further treatment shows that when the triplet depolarization via relaxation is comparable to the chemical hydrogen abstraction rate, the resultant radical retains the polarization and is thus in the emissive mode.
Vibrational relaxation of D2 in 3He and 4He mixtures
Authors: Hopkins Barabara M. , Chen Hao-Lin
Published: February 2004

The rates of vibrational relaxation of D2 in 3He and 4He mixtures have been studied by the laser-induced vibrational fluorescence technique. The relaxation rates of HCl/D2/3He and HCl/D2/4He mixtures at 296°K show cross sections of V → T, R energy transfer as σD2−4He = 9.5 ± 1.1 × 10−23 cm2, σD2−3He = 12.5 ± 1.5 × 10−23 cm2. These measured cross sections should provide an ideal test for existing scattering theory calculations.
Non-Hermitian representations in localized orbital theories
Authors: Weeks J. D. , Anderson P. W. , Davidson A. G. H.
Published: February 2004

We consider a non-Hermitian version of Adams' localized orbital equations which is directly analogous to the conventional pseudopotential equation of Austin, Heine, and Sham. This allows the use of the familiar ``pseudizing'' arguments in localized orbital theories and also permits a simple discussion of the relationship between Adams' theory and Anderson's self-consistent pseudopotential theory of localized orbitals. A study of the differences in the Hermitian and non-Hermitian representations shows that the non-Hermitian localized orbital equation has additional localization of the left (adjoint) eigenfunction which may have advantages in practical calculations. An analysis of the secular equation method of going from the localized orbitals to the total system's wavefunction suggests that a non-Hermitian representation again has additional local properties which could prove useful in interpreting and extending semiempirical parameterization methods such as the Hückel theory.
Photodesorption of carbon monoxide from polycrystalline nickel
Authors: McAllister Jerome W. , White John M.
Published: February 2004

The photodesorption of carbon monoxide from polycrystalline nickel ribbons was investigated using light of ultraviolet and visible wavelengths. Ultrahigh vacuum techniques and mass spectrometric detection were utilized in these measurements. The ribbons were prepared both by the high temperature outgassing method and by argon ion bombardment. On the argon-ion-bombarded surfaces carbon monoxide surface coverages were 2–3 orders of magnitude larger than the coverages measured on outgassed surfaces. From both types of surfaces photodesorption was predominately a bulk heating effect, whereas local heating and/or quantum effects were negligible. The validity of this conclusion was demonstrated for a wide variety of pressures, wavelengths, and light intensities.
Statistical mechanics of phase diagrams. II. A simple cell model for the metallic elements
Authors: Young David A.
Published: February 2004

A sphericalized Lennard-Jones Devonshire cell model with a pair potential composed of a hard core plus an attractive square well is used to construct one-component phase diagrams in the pressure-temperature plane. These diagrams show equilibria among the simple cubic (sc), body-centered cubic (bcc), face-centered cubic (fcc), hexagonal close-packed (hcp), and liquid phases. Some of the predicted phase boundaries are similar to those observed experimentally in the metallic elements.
Electron population analysis with generalized x-ray scattering factors: Higher multipoles
Authors: Stewart Robert F.
Published: February 2004

Generalized x-ray scattering factors have been extended to include a 3d Slater-type atomic orbital. The new scattering functions include deformations that represent octapole and hexadecapole atomic charge distributions. These terms are suitable for charge density analysis of atoms with high site symmetry. For a reasonable exponential parameter, the 3d orbital does not introduce significantly different dipole and quadrupole radial scattering factors which have previously been constructed with 2s and 2p Slater-type orbital products. A new monopole term (M-shell scattering factor) is significantly different from the L-shell scattering factor, but it may be difficult to measure the corresponding population parameter from x-ray diffraction data. The valence scattering model is extended to second row atoms by restricting deformation terms to M-shell Slater-type orbitals. Neglect of L-shell deformation in the x-ray scattering analysis of second row atoms may not be appropriate; the matter warrants further study.
Study of the structure of molecular complexes. II. Energy surfaces for a water molecule in the field of a sodium or potassium cation
Authors: Kistenmacher H. , Popkie H. , Clementi E.
Published: February 2004

The previously reported study of the energy surface of a water molecule in the field of an Li+ ion is extended to the surfaces of water in the field of an Na+ or K+ ion. The computations are done in the Hartree-Fock approximation using a large basis set of Gaussian functions. Calculated binding energies and cation-H2O bond distances in the most stable configuration are 35.2, 25.2, 17.5 kcal/mole and 3.58, 4.25, 5.08 a.u. for Li+, Na+, and K+, respectively. A detailed analysis and comparison of the potential energy surfaces are reported by considering a number of cross sections through the surfaces and by decomposing the total energy of the complex into the sum of the energy of H2O in the field of the cation, the energy of the cation in the field of H2O, and the cation-H2O interaction energy.
Penning ionization optical spectroscopy: Metastable helium (He 2 3S) atoms with nitrogen, carbon monoxide, oxygen, hydrogen chloride, hydrogen bromide, and chlorine
Authors: Richardson W. C. , Setser D. W.
Published: February 2004

The generation of triplet metastable helium atoms (19.8 eV) by a hollow cathode discharge coupled to a flow apparatus is described. With this apparatus the Penning ionization reactions of He(2 3S) with six diatomic molecules were investigated at pressures of 1–5 torr of helium and less than 1 mtorr of reagent at 300, 225, and 77°K. The reactions were monitored by analysis of the visible and ultraviolet emission spectra. The following band systems were observed: N2+ (B 2Σu+-X 2Σg+, A 2Πu−X 2Σg+); CO+(B 2Σ+− X 2Σ+, B 2Σ+−A 2Πi, A 2Πi−X 2Σ+); O2+(A 2Πu−X 2Πg, b 4Σg−−a 4Πu); HCl+(A 2Σ+−X 2Π); HBr+(2Σ+−X 2Π) and Cl2+(A 2Πu−X 2Πg). For the last four cases atomic emissions were observed indicating the presence of reaction channels in competition with Penning ionization. The vibrational populations of O2+(A 2Πu), HCl+(A 2Σ+) and HBr+(A 2Σ+) were not in accord with populations expected for vertical transitions from the molecular ground state. However, the N2+(B 2Σu+), CO(A 2Πi), and O2+(b 4Σg−) vibrational populations were very similar to those expected for a vertical ionization. Rotational populations of N2+(B), CO+(B), HBr+(A) and HCl+(A) were found to be very similar to those of the neutral precursor molecule, although at 77°K a non-Boltzmann distribution was observed for high N′ states of N2+(B). The results are discussed in terms of the two state potential model of Penning ionization.
On the variation principle in electron-atom scattering
Authors: Wladawsky Irving
Published: February 2004

The variation principle in electron-atom scattering is analyzed in an attempt to explain the difficulties encountered in even the simplest e-H expansion type calculations. Different variational methods are compared and an approach is introduced which will eliminate the occurrence of spurious singularities found in other methods. This method is applicable to both elastic and inelastic collisions.
Absorption spectrum of CfCl3
Authors: Carnall William T. , Fried Sherman , Wagner Frank
Published: February 2004

The absorption spectrum of thin films of CfCl3 was measured at 298, 77, and 4°K in the range 6000–46 000 cm−1. Interpretation of the results was based on systematic variation of energy level parameters over the actinide series. Electrostatic, spin-orbit, and configuration interaction terms were calculated by diagonalization of the complete interaction matrices and a least squares fitting process involving 27-level assignments. Compared to the energies of the first f→ d transitions observed in lighter actinide trichlorides, the corresponding band in CfCl3 appears to occur at an anomalously low energy.
Crystal and molecular structure of CCl4 III: A high pressure polymorph at 10 kbar
Authors: Piermarini G. J. , Braun A. B.
Published: February 2004

The crystal and molecular structure of a high pressure form of carbon tetrachloride (CCl4 III) was determined at approximately 10 kbar using a diamond-anvil beryllium pressure cell and a modified Buerger-type precession camera. CCl4 III crystallizes in the monoclinic system with a unit cell of the following dimensions: a=9.079± 0.012 Å, b=5.764± 0.003 Å, c=9.201± 0.004 Å, and β=104.29±0.05°. The space group is P21/c with four molecules per unit cell. Observed infrared spectra indicate that the CCl4 molecule exhibits regular tetrahedral symmetry at 10 kbar. By using an approximation to the repulsion energy in a least-squares refinement procedure considering only nonbonded Cl–Cl interactions, an approximate structure was obtained. Subsequent structure factor calculations using a grid-point sampling procedure yielded a final structure with a reliability factor of 9.56%. CCl4 III is isostructural with SnBr4, and contains closest nonbonded Cl–Cl distances of 3.49 Å, significantly less than the normal Van der Waals separation of 3.6 Å. Taking four molecules per unit cell, the calculated density is 2.190 g cm−3. A more compact phase than CCl4 III was predicted in the CCl4 system on the basis of packing efficiency and the predicted phase (CCl4 IV) was subsequently verified by visual observation in microscopic studies at pressures in the 35–40 kbar range and temperatures up to 500°C.
Zero-phonon transitions in O2−, S2−, Se2−, and SeS− molecules dissolved in alkali halide crystals
Authors: Ikezawa M. , Rolfe John
Published: February 2004

Zero-phonon transitions of O2−, S2−, Se2− and SeS− molecules in alkali halide crystals were studied by their emission and excitation spectra at 2°K. Most of the information came from emission spectra, which contain large numbers of zero-phonon lines. These lines usually form a single ground-state progression, but extra progressions also appear in most S2− spectra, and in the spectrum of O2− dissolved in KBr. The spectroscopic constants ν00, ω0″, ω0″x0″ and Δ G1/2″ were calculated for all observed progressions, and the Δ G1/2″ values compared with measured Raman frequencies of the molecules. By measuring the effects of uniaxial stress on the emission spectra it was shown that the optical dipole of the emission transition is parallel to the molecular axis, that the axis is parallel to 〈 111〉 directions for O2− in NaCl, KBr and KI, and parallel to 〈 110〉 directions for all other systems, with the exception of the extra emission of O2− in KBr. This dipole could not be so well characterized, except to say that it must lie in a {100} plane. All the emissions are probably due to a Πu2→Πg2 transition. Stress reorientation in the excited state was measured for O2− in KBr crystals. Stress and strain coefficients were calculated for many zero-phonon emission lines; most of the results are in agreement with a linear theory.
Electron transfer and excitation in collisions of He++ with H
Authors: Rapp Donald
Published: February 2004

Coupled-state calculations have been performed for the collision processes He+  ++H(1s)→He+(nl)+H+, and →He+  ++H(nl), in which 1s, 2s, 2p0, and 2p1 states were included on both centers. In addition, calculations were also performed without the 1s state of He+ to determine the effect of this state on the other transitions. The rectilinear path impact parameter method was used, and cross sections for populating the various channels were determined over the energy range 1–600 keV. The results are compared with recent calculations done for protons incident on H. It was found that there are some major differences between the two collisions, despite the fact that He+ (n=2) has the same energy as H (1s). The cross section for total exchange of an electron from H to He+ + is calculated to have a maximum near 20 keV. At higher energies, electron capture in He+ + +H behaves analogously to electron capture in H++H. However, at lower energies, there is an effective nonresonance in He+  ++H(1s)→He+(n=2)+H+ due to the difference in Coulomb interactions on the left and right sides of this equation, which produces a decreasing cross section below 20 keV. The direct excitation of H to 2s and 2p states by He+ + is analogous to direct excitation of H by H+ when compared at the same velocity.
Application of the Kirkwood theory of transport in polymer solutions to rigid assemblies of beads
Authors: Yamakawa Hiromi , Yamaki Jun-ichi
Published: February 2004

The Kirkwood general theory of irreversible processes in polymer solutions is reformulated to give correct translational and rotatory diffusion coefficients for highly symmetric, rigid molecules which may be represented by rigid assemblies of beads. This provides an elementary description of the physical meaning of the Kirkwood approximation, and gives simple criteria to judge whether Kirkwood's incorrect formulas are or are not exactly valid for a given system. Following the formulation presented here, translational and rotatory diffusion coefficients of rigid rods and rigid rings are also evaluated.
Electron paramagnetic resonance study of S3− formed on magnesium oxide
Authors: Lunsford J. H. , Johnson D. P.
Published: February 2004

Elemental sulfur reacts at 400° with partially hydroxylated magnesium oxide to form a stable paramagnetic species which has been identified as the S3− ion. The 33S hyperfine splitting is characteristic of an aba type molecule with a‖ (a)=20.7 G, a‖ (b)=39.6G, a⊥ (a)=3.7 G, and a⊥ (b)=7.5G. The principal g values are g‖=2.004 and g⊥=2.043. The g and hyperfine tensors suggest that at 77°K the molecule is librating in the plane of the three sulfur atoms. The formation of S3− is accompanied by the evolution of H2S and the loss of another sulfur radical which is believed to be a polymeric form of sulfur, Sn. These observations suggest that the reaction Sn+4OH−→ 2H2S+2S3−+SO4−+Sn-6 may occur at the surface.
Spatial structure and thermodynamic properties of a classical fluid of hard spheres with attractive square wells
Authors: Tago Yoshio
Published: February 2004

The spatial structure and the thermodynamic properties of a classical fluid of hard spheres with attractive square wells are analyzed, based on the Percus-Yevick equation reformulated by Baxter. The equation of state, the isothermal compressibility, the internal energy, the direct correlation function, the radial distribution function, and the structure factor are evaluated over a wide range of temperatures and densities when the width of the attractive square well is half the diameter of the hard core. The temperature- and the density-dependent behaviors of the obtained quantities are discussed. The equation of state is compared with theoretical results obtained by other authors. The pressures calculated via the compressibility equation are in satisfactory agreement with the pressures obtained from computer experiments both at the supercritical temperature kT/ε=3.333 and at the subcritical temperature kT/ε=1.17. Attempts are made to fit the pressures calculated via the compressibility equation to the experimental pressures for gases and liquids. The satisfactory fit between the theoretical and the experimental pressures is shown to be made for rare gases and hydrocargons. The fluid structure is shown to be largely dominated by the repulsive core of the potential when the density is high.
Stability of the metallic state of selenium under pressure
Authors: Wittig J.
Published: February 2004

Selenium is not retained in the metallic state and is hence not a superconductor after the release of high pressure at room temperature. Resistance measurements imply that the semiconductor to metal transformation is readily reversible at a pressure of 130 kbar.
Electron impact ionization studies of ferrocene, cobaltocene, nickelocene, and magnesocene
Authors: Begun G. M. , Compton R. N.
Published: February 2004

Negative and positive ions of ferrocene, cobaltocene, nickelocene, and magnesocene produced by collisions with monoenergetic electrons have been studied. Appearance potentials relative to the ionization potential of krypton have been determined for the products (C10H10M)+, (C5H5M)+, and M+. The ionization potentials derived from the present electron impact studies are in good agreement with recent photoelectron values. In all cases cyclopentadienyl anions were produced at low electron energies; however, their cross sections for formation differed by orders of magnitude. The most striking feature of the negative ion studies was the observation of a long-lived parent negative ion of nickelocene at thermal electron energies, and a second broader compound negative ion resonance at approximately 1 eV. The autodetachment lifetime for the second resonance decreases from 60 μsec at 0.5 eV to 20 μsec at 1.5 eV. Cobaltocene also exhibits two long-lived negative ion states in the energy region below one electron volt which are barely resolvable. Ferrocene forms a short-lived (τ ≳ 2× 10−14 sec) compound negative ion state at ∼0.5 eV. The negative ion results can be qualitatively explained by assuming that the captured electron occupies one of the empty e1g or e2u orbitals of the parent molecule.
Raman spectra of gases. VI. Barrier to planarity in germacyclopentane
Authors: Durig J. R. , Li Y. S. , Carreira L. A.
Published: February 2004

The anharmonic out-of-plane twisting mode of the heavy atom skeleton of germacyclopentane has been observed in the Raman spectrum of the vapor. These data along with the far infrared frequencies for the other out-of-plane ring bending mode have made it possible to calculate the two-dimensional potential surface for these two out-of-plane ring modes without any assumptions as to the magnitude of the barrier to planarity. From this two-dimensional treatment, it is shown that the interconversion between the two twisted configurations is not entirely along the twist axis but the path is actually slightly elliptical and passes through a slightly bent configuration at R2=0. However, it is shown that the twisting and puckering motions are fairly independent. From the two-dimensional treatment, one calculates the barrier to interconversion to be ∼ 1450 cm−1 compared to the less accurate value of 2043 cm−1 calculated using the one-dimensional approximation.
Accurate evaluation of internal energy level sums and densities including anharmonic oscillators and hindered rotors
Authors: Stein Stephen E. , Rabinovitch B. S.
Published: February 2004

The calculation of molecular energy level sums and densities is necessary for the treatment of many physical and chemical problems including reaction rates. An extension of Beyer and Swinehart's algorithm for directly computing harmonic oscillator eigenstate sums and densities is described. With this new algorithm it is possible to compute exact or near-exact energy level sums and densities for degrees of freedom such as free and hindered rotors and anharmonic oscillators so long as the energy levels for each degree of freedom can be specified. Computer calculation by this technique is practical even for large molecules up to all chemically interesting energies and error is confined to small rounding errors. Results by this algorithm are compared to values of energy level sums that have been given in the literature by various alternative approximate treatments and permit more rigorous testing of the latter and assessment of the approximations involved.
Time resolved ESR spectroscopy. I. A kinetic treatment of signal enhancements
Authors: Fessenden Richard W.
Published: February 2004

ESR experiments with time resolution on the order of 1 μsec have been carried out upon aqueous solutions during repetitive pulse radiolysis with a 2.8 MeV electron beam. The ESR spectrometer was operated with no field modulation, and spectra were presented as absorption curves. The radicals ĊH(CO2−)2, ĊH2CO2−, and hydroxycyclohexadienyl, formed in each case by reactions of OH, were studied and each spectrum showed evidence of a nonequilibrium population of spin levels, with the low field lines of the latter two radicals observed in emission. For ĊH2CO2− this emission persists for ∼ 50 μsec. The observed signals are described by enhancement factors V (fractional excess signal) of 0.23, 3.1, and 12.3, respectively. From the short spin relaxation times (1.4 μsec was measured for ĊH2CO2−) it is evident that emission existing at times much greater than this relaxation period must be the result of a continuous regeneration of the population differences by the radical-radical reactions. The form of the kinetic equations for the population of the spin levels is considered and an intrinsic enhancement factor defined (Vt1/2/T1) which takes into account the rate of radical reaction (through the initial second-order half-life t1/2) and the spin relaxation times. This quantity is found to be fundamental to the radical system and is, within experimental error, the same for observations in both steady-state and pulse experiments where the radical lifetimes differ by a factor of ∼ 10. The equations developed successfully describe the time dependence of the observed ESR signals. The intrinsic enhancement factors are large (30–100) and represent ∼ 5%–10% adiabatic character of the recombination when so interpreted. The kinetic theory developed does not require that such large enhancements appear in the NMR spectra of the reaction products.
Drift mobility of holes and electrons in perdeuterated anthracene single crystals
Authors: Mey W. , Sonnonstine T. J. , Morel D. L. , Hermann A. M.
Published: February 2004

The temperature dependence of drift mobilities in perdeuterated anthracene was measured in the range 260–400°K in three crystal directions. Shallow trapping analysis of the temperature dependence allowed determination of the trap-free drift mobilities along the a, b, and c′ crystal axes. Room temperature trap-free mobilities agreed well with those found in normal anthracene, except for the mobility of electrons along the c′ crystal axis which was found to decrease about 10% upon deuteration. Various models for charge carrier transport in anthracene were examined, and it was found that the c′-electron mobility in deuterated anthracene is consistent with the Munn and Siebrand slow-phonon hopping mode while all other components are consistent with the Munn and Siebrand slow-phonon coherent mode.
Magnetothermodynamics of Ce2Mg3(NO3)12· 24H2O. I. Heat capacity, entropy, magnetic moment from 0.5 to 4.2°K with fields to 90 kG along the a crystal axis. Heat capacity of Pyrex 7740 glass in fields to 90 kG
Authors: Giauque W. F. , Fisher R. A. , Hornung E. W. , Brodale G. E.
Published: February 2004

The heat capacity of a 4.023 cm diam spherical single crystal of cerium magnesium nitrate hydrate has been measured with stabilized fields of 0, 1000, 2500, 5000, 10 000, 15 000, 25 000, 40 000, 65 000, and 90 000 G along the a crystal axis, from 0.5 to 4.2°K. The zero of electronic entropy was reached at fields of 90, 65, and 40 kG and the lower temperatures. The isoerstedic entropy changes derived from heat capacity series were interconnected by 28 series of temperatures vs fields on isentropes. Analysis of the heat capacity data indicated that the first excited doublet is 70.5± 1.0 cal/mole Ce3+ above the ground doublet. The splitting factor of the ground doublet was evaluated at gH=1.8385−5.20× 10−12H2± 0.001. An applied magnetic field introduces an internal energy change of 1.39× 10−15H3 cal/mole Ce3+ (H in gauss) to the ground doublet enthalpy separation. The magnetic moment was measured over the same ranges of field and temperature as the heat capacity. Near 0.5°K, and over the range 40 to 90 kG, the total moment reaches definite limits at each field. Subtracting the limiting value of the temperature-dependent moment, 5134−4.36× 10−8H2G·cm3/mole Ce3+, from the total, enabled the evaluation of the differential temperature-independent magnetic susceptibility as, χT ind=2.221× 10−2−1.71× 10−13H2. Thus MlimitT→ 0=5134+2.221× 10−2H−4.36× 10−3H2−5.7× 10−14H3, where H is in gauss. Smoothed correlated values of the heat capacity, entropy, enthalpy, internal energy, magnetic moment and its isoerstedic temperature coefficient, differential isothermal magnetic susceptibility, and the isothermal work of magnetization have been tabulated over the range 0–90 kG and 0.5 to 4.2°K. The heat capacity of 7740 Pyrex glass has been measured over the same ranges.
Laser fluorescence study of vibrational energy transfer in CH3Cl
Authors: Knudtson J. Thomas , Flynn George
Published: February 2004

A laser induced infrared fluorescence technique has been used to measure both vibration to vibration and vibration to translation/rotation energy transfer rates in CH3Cl. The V-T/R rates were measured using H2, D2, CH4, and rare gases as collision partners. Qualitative comparison of these data with V → T and V → R theories indicates that the V → T mechanism dominates for collisions with small reduced masses while the V → R mechanism dominates for collisions with large reduced masses. The V–V rate equilibrating the ν6 and ν3 modes was measured as a function of CH3Cl pressure and was found to be 76 msec−1· torr−1. A lower limit was also obtained for the rate of V–V energy transfer from states near 1000 cm−1 to high lying states near 3000 cm−1.
Equations-of-motion method: Potential energy curves for N2, CO, and C2H4
Authors: Coughran William , Rose John , Shibuya Tai-Ichi , McKoy Vincent
Published: February 2004

We have applied the equations-of-motion method to various states of N2, CO, and ethylene at nuclear configurations slightly distorted from the ground equilibrium geometry. This approach attempts to calculate energy differences instead of absolute energies and is thus relatively insensitive to the accuracy of the assumed ground state wavefunction. By using the experimental behavior of the ground state on distortion, we can generate accurate potential energy curves for the excited states in the region of spectroscopic interest. These curves confirm the spectroscopic behavior of the ∑1u+ states of N2 and the 1Σ+ states of CO where valence and Rydberg states of the same symmetry interact. The results for the T and V states of ethylene agree with experiment and show that the V state is predominantly a highly correlated valence state. Oscillator strengths across an absorption band are also accurately determined in this method. We report the dependence of the transition moment on bond length for the X 1Σ+ → A 1Π transition in CO, which is in excellent agreement with experiment.
Mechanism of shear induced structural changes in liquid crystals-cholesteric-nematic mixtures
Authors: Marsh Dana , Pochan John
Published: February 2004

The reflection spectrum of a mixed nematic-cholesteric liquid crystal has been obtained as a function of mechanical shear. Data are explained in terms of a layered structure consisting of tilted and untilted helical Grandjean texture and a dynamic focal-conic texture for shear rates less than 103 sec−1. The correlated helical structure is shown to tilt under applied shear with slight distortion. At shear rates greater than 103 sec−1, homeotropic texture is generated. The results of this study are consistent with a theoretical model prepared earlier and suggest that the molecular forces maintaining the integrity of the helical structure in cholesteric systems in the Grandjean texture are significantly weakened by incorporation of nematic liquid crystalline materials.
Density effect on the Fermi resonance in gaseous CO2 by Raman scattering
Authors: Wright R. B. , Wang C. H.
Published: February 2004

Raman scattering was used to study the Fermi resonance of ν1 and 2 ν2 bands in gaseous CO2 over the density interval of 15–534 amagat. Both vibrations were found to shift to lower frequency as density was increased. The resonance repulsion of the two bands was also found to increase with increasing density.
Self-consistent-field atomic orbitals for atoms and ions of the second transition series
Authors: Richardson James W. , Blackman Mark J. , Ranochak James E.
Published: February 2004

A systemmatic set of analytic atomic orbitals (AO's) is presented, which spans the atoms and principal ions of the second transition series elements in ground states of the configurations (Kr)4dn,0≤ n ≤ 10. The s and p AO's are expanded in a minimum set of Slater type orbitals (STO's); the chemically and spectrally more significant d orbitals are represented by four STO's. All coefficients and STO exponents have been chosen to minimize the nonrelativistic self-consistent-field total energy. Various computed energies are compared with experiment and with similar quantities obtained from earlier Hartree-Fock results for the corresponding first-row elements. The results indicate that the 4d AO's have sufficient accuracy to make them reliable in studies of spectra and bonding in compounds of these elements.
Vibrational relaxation of HF and DF
Authors: Berend George C. , Thommarson Ronald L.
Published: February 2004

Relaxation times for vibration→rotation, translation deexcitation of HF(v=1) by HF(v=0) and DF(v=1) by DF(v=0) are calculated using quasiclassical trajectory techniques. An empirical interaction potential, formulated so as to give a reasonably accurate description of the hydrogen bonding in these systems, is employed in the calculations. Since the initial rotational states of the collision partners are restricted to the most probable state for each temperature investigated, only qualitative agreement with experiment is obtained. The observed temperature dependencies of the vibrational relaxation times are discussed in terms of their interdependence on the directionality of the hydrogen bonding interaction and initial molecular rotation.
Direct calculation of exciton diffusion coefficient in molecular crystals
Authors: Munn R. W.
Published: February 2004

The exciton diffusion coefficient is calculated directly from the equations of motion for the microscopic exciton density given by Grover and Silbey [J. Chem. Phys. 54, 4843 (1971)]. At high temperatures the diffusion coefficient is obtained purely algebraically, and at low temperatures by solving a single equation. The results are exact in the limit of long times, and validate an approximation made by Grover and Silbey.
Angular momentum dependence of first- and second-order singlet-triplet interactions in polyatomic molecules
Authors: Stevens Charles G. , Brand John C. D.
Published: February 2004

Formulas for the angular momentum dependence of the interaction matrix elements between rotating, nearly degenerate singlet and triplet electronic states are derived for the following conditions: (i) the interaction is first order, involving direct spin-orbit coupling of the states; (ii) the interaction is second order, occurring by a vibronic spin-orbit mechanism with vibronic coupling in the singlet or triplet manifold; and (iii) the interaction is second order, occurring by a spin-rotation mechanism in which the interacting singlet and triplet states are coupled to the manifold of intermediate states by spin-orbit and orbital-rotation coupling. Possible applications of these formulas are discussed.
Nuclear quadrupole interaction studies by perturbed angular correlations
Authors: Haas H. , Shirley D. A.
Published: February 2004

A comperhensive study was made of the applicability of gamma-ray angular correlations to the determination of quadrupole interactions in metals and insulating solids. Dynamic effects were studied in solutions and gases. A total of fourteen gamma-ray cascades were employed. Several nuclear spins were confirmed and the quadrupole moments of ten excited nuclear states were determined or estimated from the data. Quadrupole coupling constants were determined for excited states of the following nuclei in metallic host lattices of the same element: 44Sc, 99Ru, 111Cd, 117In, 187Re, 199Hg. Coupling constants were also measured for the following isotope (lattice) combinations: 99Ru(Zn, Cd, Sn, Sb), 100Rh(Zn, Ru, Cu5Zn8, Pd2Al, PdPb2), 111Cd(In, Hg, Tl, CdSb, Cd3Ag, Zn, Ga, In, Sn, Sb, Bi, AuIn, InBi, In2Bi), 115In(Cd), 117In(Cd, Sn), 131I(Te), 181Ta(HfB2, HfSi2), 204Pb(Cd, In, Sn, As, Sb, Bi, Hg, Tl, PdPb2). Systematic variations of e2qQ with host-lattice structure were observed and host and solute properties were found to be separable to some extent for nontransition metals. The nuclei 111Cd, 115In, 117In, 199Hg, and 204Pb were used to determine a total of fifty quadrupole coupling constants in insulators, including twenty with nonzero asymmetry parameters, which give oscillatory but aperiodic correlation functions. It was strikingly (and exhaustively) demonstrated that good determinations of quadrupole coupling constants could be made following isomeric transitions (IT) (with no elemental transmutation) and beta decay (with elemental transmutation). However, in no case was it possible to derive a coupling constant from a gamma-ray cascade preceded directly by electron-capture (EC) decay, presumably because the sudden creation of a K-hole, and the Auger and ``shake-off'' events that follow, destroy the chemical integrity of the species under study. Relaxation times were determined for a number of liquid samples. Studies of dimethyl-111mCd in various buffer gases showed that the spin memory was lost in one collision with heavy molecules, but that light molecules required several collisions.
One-phonon density-of-states and spatial correlation from the Raman spectrum of molecular crystals: NH4I
Authors: Dultz W. , Ihlefeld H.
Published: February 2004

The missing translational invariance of a disordered crystal is introduced into the second order perturbation theory of the Raman effect. The disorder of the crystal lifts the wave vector conservation of the scattering process so that phonons from the whole Brillouin zone contribute to the light scattering spectrum. Measurements of the temperature dependence of the Raman spectrum allow the study of spatial correlations in the disordered crystal. We measured the low energy Raman spectrum of NH4I in its NaCl-type phase. The random orientations of the ammonium ions of NH4I in the octahedral lattice cell lift the translational invariance of the crystal but do not affect the local point symmetry of the matrix elements. We obtain the one-phonon density of states from the low energy Raman spectrum of NH4I and compare our results with ir and incoherent neutron scattering spectra.
Kinetics of the low temperature deamination of radicals in L-alanine and α-aminoisobutyric acid
Authors: Shields Howard , Hamrick Phillip J. , Smith Clyde , Haven Ysbrand
Published: February 2004

The rate constants for the deamination of radicals in X-irradiated L-alanine and α-aminoisobutyric acid have been determined at temperatures around 150°K. The reactions are first-order with activation energies of 7.5 and 14.1 kcal/mole, respectively, and pre-exponential factors 1× 109sec−1 and 3× 1016sec−1, respectively.