bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of exchange splitting of core levels in x-ray photoemission spectroscopy of hemin
Authors: Chang Jane C. , Kim Y. M. , Das T. P.
Published: February 2003

ESCA experiments provide information on ionization energy differences between core electrons of different spins in a magnetic system, which is related to the exchange interaction between core and the unpaired valence electrons. Using self-consistent charge extended Hückel wavefunctions for hemin, we obtain 7.1 eV for the exchange energy difference between up and down spin 3s electrons of iron. On allowing for the correction by a factor of about 2 from correlation and relaxation effects in the ionized state, the theoretical splitting compares well with the experimental value, 2.4±0.07 eV. The latter is substantially less than in Fe+3 ionic compounds, in agreement with the smaller unpaired spin population on the iron atom in hemin. Comments are made on the relative values of the energies of ionization from iron atom 3s and 3p core states in hemin, relative to ferric and ferrous compounds, the trend of which is in keeping with the charge on the iron in hemin.
Pyroelectric α-Cu(IO3)2. Crystal structure of the transition metal iodates. III
Authors: Liminga R. , Abrahams S. C. , Bernstein J. L.
Published: February 2003

Alpha-cupric iodate, α-Cu(IO3)2, is pyroelectric and piezoelectric at room temperature and crystallizes in the monoclinic space group P21 with two formulas in the unit cell. The lattice constants at 298 °K are a =5.56902 ± 0.00010, b=5.11098 ± 0.00009, c=9.26976 ± 0.00036 Å and β=95.82 ± 0.02 ° (λCuKα1 − 1.540562 Å). The integrated intensities of most reflections within a hemisphere of reciprocal space with radius (sinϑ)/λ?1.02 Å−1 were measured on two different crystals using two different diffractometers, resulting in 1814 Fmeas for one set and 4272 Fmeas for the second set of independent structure factors. The crystal structure was solved using Patterson and Fourier series and refined by the method of least squares, the final agreement factor R becoming 0.063 for the first set, and 0.035 for the second set of Fmeas. The iodate ions form a nearly-regular hexagonal closest-packed array, with Cu2+ in the resulting octahedral interstices. The two independent iodate groups, each with three short I–O distances averaging 1.82 Å, share oxygen atoms to form a three-dimensional framework of corner-sharing polyhedra. One iodate ion forms three additional I–O distances averaging 2.66 Å, the other has four that average 2.95 Å. The CuO6 octahedron is tetragonally distorted, with four bonds averaging 1.97 Å and two apical Cu–O bonds averaging 2.39 Å. The two sets of Fmeas, and the resulting derived structural parameters, are compared using normal probability plot analysis.
Coexistence curve for polystyrene–cyclohexane near the critical point
Authors: Nakata Mitsuo , Kuwahara Nobuhiro , Kaneko Motozo
Published: February 2003

The coexistence curves for the system polystyrene–cyclohexane have been determined with a specially designed differential refractometer, which determines concentrations of the two coexisting phases with a precision of ± 0.01%. The plots of the coexistence curve data represented by log(X+−Xc) and log(Xc−X−) versus the reduced temperature ε = (Tc−T)/Tc yield largely curved lines. The shape of the coexistence curve very near the critical point, however, is asymptotically symmetric. The coexistence curve obtained with an over-all concentration at the critical concentration is represented by the relation X+−X− = Bεβ with β=0.348 and B=0.97 in the temperature region of Tc −T<2.0 °C. The critical point exponent β and the coefficient B vary only slightly depending on the over-all concentration. Although the data give a curved diameter, a precision of the present experiment is not sufficient to determine the asymptotic behavior of the diameter.
The interaction of rare gas atoms with graphite surfaces. II. Adatom–adatom potentials
Authors: Freeman David L.
Published: February 2003

The Gordon–Kim local density method is applied to the calculation of the interaction energy of pairs of neon, argon, and krypton atoms adsorbed on the basal plane of graphite. At the adatom–surface equilibrium separation, the adatom–adatom interaction potentials are found to be from 12% to 20% more repulsive than the gas phase counterparts. At much smaller adatom–surface separations, the adatom–adatom effective potential well depth is only 3% of the gas phase well depth. It is found that the nonadditive contributions to the interaction energy are more important for the smaller rare gas adatoms than for the larger ones. This trend is observed experimentally. It is concluded that rare gas films on graphite are too mobile to be in registry with the substrate.
Formation of supersonic beams of metastable mercury, Hg(6 3P). Kinetics of photoexcitation and intramultiplet quenching in a nozzle
Authors: Haberman J. A. , Wilcomb B. E. , Van Itallie F. J. , Bernstein R. B.
Published: February 2003

A nitrogen-seeded supersonic nozzle-beam source of metastable mercury, Hg(6 3P0),isdescribed.Ground-state(6 1S0)mercuryisexcited with 2537 Å resonance radiation to the 6 3P1 state, which is then converted via intramultiplet quenching to the 6 3P0 state collision with nitrogen (the carrier gas). The mercury beam is accelerated by the N2 seeding gas to a speed of 8×104 cm sec−1. Thus, the present source provides a beam of a single metastable state, Hg(6 3P0), with 4.67 eV of electronic excitation and 0.67 eV of translational energy. The metastable beam has been characterized and the kinetics of the over-all photoexcitation and quenching process studied by a secondary electron (Auger) detector utilizing a potassium surface, and an electron-bombardment ionizer, mass-filter detector. Hg(6 3P0) beam intensities of 4×1012 atoms sr−1⋅sec−1 are obtained, based upon an (assumed) 5% efficiency for the Auger detector.
Ion pair formation in CF4
Authors: Ahnell J. E. , Koski W. S.
Published: February 2003

A careful search has been made for the ion pair process CF4 + e → CF3+ + F− + e in the electron bombardment of CF4 using a coincidence mass spectrometer with near monochromatic electrons. A weak but easily detectable ion pair process was observed with a threshold in the neighborhood of 12 eV. In addition, a low level of CF3+ ions was observed below the ionization potential of CF3. This was attributed to the ionization of excited CF3 radicals.
The isothermal linear and volume compression of pentaerythritol tetranitrate (PETN) to 10 GPa (100 kbar) and the calculated shock compression
Authors: Olinger Bart , Halleck P. M. , Cady Howard H.
Published: February 2003

The isothermal linear and volume compressions of the explosive pentaerythritol tetranitrate (PETN) were measured to 10 GPa using a high pressure x-ray diffraction technique. The fits to the data are a/a0 = 1−2.052×10−2P + 2.230×10−3P2 − 1.041×10−4P3, and c/c0 = 1−2.832×10−2P + 3.295×10−3P2 − 1.458×10−4P3, for P<10 GPa, and ust = 2.16 + 3.007 upt − 0.682 upt2, for upt < 0.95 km/s, and ust = 2.76 + 1.71 upt, for upt ≳ 0.95 km/s, where ust = [PV0/ (1 − V/V0)]1/2, upt = [PV0(1 − V/V0)]1/2, and ρ0 = 1/V0 = 1.774 g/cm3. The shock compression Hugoniot of PETN calculated from the isothermal compression fit is us = 2.24 + 2.95 up − 0.605 up2, for up < 1.00 km/s, and us = 2.81 + 1.75 up, for up ≳ 1.00 km/s, where us is the shock velocity and up is the particle of mass velocity behind the shock wave. The isothermal compression fit and the Hugoniot are initially quadratic because of the rapid change in the strength of repulsive forces between the PETN molecules during initial compression.
Multiphoton ionization spectroscopy: A new state of benzene
Authors: Johnson Philip M.
Published: February 2003

The multiphoton ionization spectra of benzene-h6 and benzene-d6 are reported. A resonance is observed which is tentatively assigned to a theoretically predicted 1E2g state; however, an absolute assignment is not possible. (AIP)
Electron density in Mo/ller–Plesset theory
Authors: Pople John A. , Seeger Rolf
Published: February 2003

The Mo/ller–Plesset theorem states that for the electronic Hamiltonian in the form H = 𝒥pFp+V, where the eigenfunctions of Fp are the Hartree–Fock molecular spin orbitals and the eigenvalues are the one-electron energies, by treating V as a perturbation the first order term in the expansion of the electron density vanishes. In spite of this, some one-electron properties are not given at the H–F level. This Note presents the expression for the second order correction to the electron density.
Coupling constants of the fine and hyperfine interaction in the c 3Πu metastable state of H2
Authors: Jette A. Norman
Published: February 2003

A b initio calculations of the fine and hyperfine coupling constants in the metastable state of molecular hydrogen are extended to internuclear distances of 1.90 and 2.00 a.u. From these results averaged coupling constants for the N=1 rotational state of orthohydrogen and the N=2 state of parahydrogen are obtained over the zeroth vibrational level.
Effect of anisotropy on a Lennard-Jones potential model for certain hexagonal crystals
Authors: Green J. F. , Bolland T. K.
Published: February 2003

The effect of anisotropy on the Lennard-Jones 6-12 potential model prediction for the c-axis elastic behavior of hexagonal graphite is examined. It is found that such anisotropy, as experimentally justified, does not substantially alter the theoretical predictions. In particular, the insensitivity to c-axis shear, common to simple potential models for graphite, is unaffected.
New procedure for generating valence and Rydberg orbitals. II. Atomic photoionization cross sections
Authors: Martin Inmaculada , Simons Gary
Published: February 2003

A previously described procedure for generating approximate valence and Rydberg orbitals from spectral data is extended to continuum states. Formulas for photoionization cross sections are derived, and cross sections are reported for the lithium sequence ions (Li I to Si XII), sodium, and helium. The predicted values are shown to be in good agreement with experimental and polarized-Hartree–Fock values, and results are generally superior to cross sections obtained from the same spectral data by the quantum defect method.
Photodissociation and photodetachment of molecular negative ions. I. Ions formed in CO2/H2O mixtures
Authors: Moseley J. T. , Cosby P. C. , Bennett R. A. , Peterson J. R.
Published: February 2003

A drift tube mass spectrometer and an argon ion laser have been used to study photon interactions with CO−3, CO−3⋅H2O, HCO−3, and HCO−3⋅H2O at discrete photon energies between 2.35 and 2.71 eV. CO−3 photodissociates into CO2+O− with a cross section which varies between 0.3 and 1.0×10−18 cm2 over this energy range. CO−3⋅H2O photodissociates into CO−3+H2O with a cross section near 2×10−18 cm2. HCO−3 and HCO−3⋅H2O have very small (and possibly zero) cross sections for photodestruction on this energy range.
Analysis of the dynamics of a helium discharge by means of the Fourier amplitude sensitivity test
Authors: Peatman Wm. B. , Wu Dan T-c , Barach John P.
Published: February 2003

The development of a method to analyze the chemical dynamics of a repetitively excited chemical system is given along with the analysis of a helium plasma and the implications of the analysis. The method is based upon (1) numerical (Runge–Kutta–Gill) solutions to the coupled differential equations which govern the discharge and (2) the application of the recently described ’’Fourier Amplitude Sensitivity Test’’ (FAST) to the solutions, which enables one to determine the principal dependence of each species on the fundamental rate processes present. The results of this analysis are generally in agreement with previous work but go further in giving a picture of the detailed dynamics.
Structural model for amorphous solid water
Authors: Boutron P. , Alben R.
Published: February 2003

We construct two continuous random network models for amorphous solid water and compute their x-ray and neutron diffraction properties. The results for one type of network accord well with experiment. This implies that there are important relatively long-range, as well as short-range, positional correlations in the solid amorphous phase of water.
Microwave spectrum and ring structure of cyclopropyl cyanide
Authors: Pearson Richard , Choplin Agnes , Laurie Victor W.
Published: February 2003

The microwave spectrum of cyclopropyl cyanide has been re-examined and a centrifugal distortion analysis has been carried out. Also, the two isotopic species containing 13C in the ring have been assigned allowing a substitution determination of the ring structure. Parameters found are r12 = 1.528±0.005 Å, r23 = 1.500±0.002 Å, &C2C1C3 = 58.8±0.3°.
Semiclassical calculations of vibrational energy transfer: Comparison of the harmonic and the Morse oscillator in collinear and perpendicular collisions with a structureless atom
Authors: Schinke Reinhard , Toennies J. Peter
Published: February 2003

Collinear and perpendicular collisions of an atom with a diatom are considered using both the harmonic and the Morse molecular binding potentials. A uniform semiclassical approximation is used to calculate individual vibrational transition probabilities and averaged energy transfers. Differences in individual probabilities and in averaged energy transfers in collinear as well as in perpendicular collisions depend strongly on the reduced mass ratio m. For a large m, the discrepancy between the harmonic and the Morse oscillator is large, while with decreasing m the agreement becomes progressively better. In the collinear geometry more energy is transferred to the harmonic oscillator than to the Morse oscillator, while the reverse holds in the perpendicular geometry. These effects are explained qualitatively by studying the time dependence of the oscillator energy during a classical trajectory.
Resonant structure in electron impact excitation of CO near threshold
Authors: Swanson N. , Celotta R. J. , Kuyatt C. E. , Cooper J. W.
Published: February 2003

Electron impact excitation functions of numerous states in CO have been measured at 45° scattering angle with resolutions of 16–23 meV FWHM. The decay peak of the 10.04 eV resonance can be seen in the results for the a 3Π, a′ 3Σ+, and A 1Π vibrational levels. There was no evidence of resonant excitation of the a′ 3Σ+ state near 8 eV as suggested by Newton and Thomas. Excitation functions of the b 3Σ+, B 1Σ+, C 1Σ+, c 3Π, and E 1Π states, and a previously unobserbed state at 11.26 eV show numerous sharp resonances in the first few eV above threshold. Energy loss spectra in the 8–14 eV loss region show peaks corresponding to known states as well as to unidentified states. No sign of the metastable state at about 9.5 eV seen by Wells, Borst, and Zipf could be detected in direct excitation, but an indirect excitation process involving the A 1Π state is consistent with the data.
Chemically induced dynamic electron polarization. Pulse radiolysis of aqueous solutions of alcohols
Authors: Trifunac A. D. , Thurnauer M. C.
Published: February 2003

The radical pair model of chemically induced dynamic electron polarization (CIDEP) is experimentally verified. Aqueous solutions of alcohols were irradiated with 3 MeV electrons and observed with time resolved electron paramagnetic resonance (EPR) spectroscopy. Relative line intensities of the polarized EPR spectra of radicals from methanol and especially ethylene glycol, alone and in the presence of radicals from compounds containing halogens, illustrates the polarization dependence on the g-factor differences between the radical pair components. The observation of the relative polarization enhancement in the various lines of the multiline EPR spectra illustrates the polarization dependence on the hyperfine terms. Intrinsic enhancements are calculated and are shown to be proportional to the observed enhancement, showing that the radical pair model of CIDEP is qualitatively correct.
Infrared matrix-isolation spectra of acrylyl fluoride rotamers
Authors: Redington Richard L.
Published: February 2003

Infrared spectra of acrylyl fluoride have been studied in the vapor phase and in neon, argon, and nitrogen matrices in the regions 200–4000 cm−1 and all fundamental vibrations have been assigned for the s-cis and s-trans rotamers. Isomerization frequency shifts of 19, 20, and 41 cm−1 are found for certain–OCF modes, though most vibrations show much smaller shifts. Many vapor phase band contours are complex due to the overlap of several modes; the matrix-isolation experiments clarify this data and in some instances provide intense fundamentals that are not detected in conventional sampling. The matrix isolation of large populations of both s-cis and s-trans rotamers suggests that there is a small potential energy difference between these two forms but that a large potential barrier hinders their interconversion. The results are consistent with the magnetic resonance study of Lin and Servis [J. Am. Chem. Soc. 94, 5794 (1972)] and their two data points, together with s-cis and s-trans C–C torsion frequencies, are used to estimate the first four coefficients in the C–C internal rotation potential energy function. Matrix-isolation experiments on 13C acetyl fluoride were performed and a new vibrational assignment found to be necessary for the acyl fluoride group. With this result the –OCF modes of acetyl fluoride and acrylyl fluoride closely parallel one another.
Electron energy loss measurements on p-terphenyl (C18H14) single crystals and vapor
Authors: Venghaus H. , Hinz H.-J.
Published: February 2003

Electron energy loss spectra with 50 keV electrons were taken on p-terphenyl single crystals and vapor from 0–40 eV and 0–25 eV, respectively. The orientation of the main axes of the dielectric tensor is determined by means of symmetry considerations and the energy loss functions Im(−1/εii) (i=x, y, z) are derived from energy loss spectra taken with transferred momentum of the scattered electrons parallel to the tensor main axes. From Im(−1/εii) the main axis elements εii of the dielectric tensor are calculated by Kramers–Kronig analysis. The lower crystal excitations (E≲8 eV) are discussed in terms of excited molecular states, derived from the vapor spectra and taken from optical absorption data given in the literature. Values for the crystal and solution shift of π–π* excitations are obtained.
Electron paramagnetic resonance of Fe3+ ions in (NH4)2SbF5
Authors: Radnell C. J. , Pilbrow J. R. , Subramanian S. , Rogers Max T.
Published: February 2003

EPR studies of (NH4)2SbF5 single crystals doped with Fe3+ show that iron substitutes for antimony in orthorhombic sites and that the spectra remain the same from 77°K to room temperature. Hyperfine splitting from five nearest neighbor fluorines, four ’’planar’’ and one ’’axial’’, is resolved and suggests that the species observed is FeF52−. It is noted that for general orientations of the applied magnetic field the ligand hyperfine structure differs from one Fe3+ fine structure transition to another so that the iron ions cannot be in the plane of the four ’’planar’’ fluorines of the FeF52− species. The large hyperfine splitting for the axial fluorine suggests that it is closer to the Fe3+ ion than are the planar fluorines. The spin Hamiltonian parameters are g = 1.9956±0.0003, ‖D‖ = 690±28, ‖E‖ = 15.2±1.2, ‖a‖ = 32.8±8 and ‖F‖ = 6±3; the fluorine hyperfine constants are ‖A′‖ = 17±4, ‖B′‖ = 15±4 (planar fluorines) and ‖A″‖ = 69±4, ‖B″‖ = 72±4 (axial fluorine) (values are in units of 10−4 cm−1). The fluorine bonding parameters are ‖f′s‖ = 0.50±0.25% and ‖ (fσ − fπ) ′‖ = 0.0±4.5% for the planar fluorines and ‖f″s‖ = 2.46±0.05% and ‖ (fσ − fπ) ″‖ = 9.0±4.5% for the axial fluorine.
Ion kinetic energy distributions from dissociative photoionization of molecular hydrogen
Authors: Ford A. Lewis , Docken Kate Kirby
Published: February 2003

The kinetic energy distributions for the dissociative photoionization of ground and vibrationally excited H2 to the dissociative continuum of the 1sσg state of H+2 are calculated. (AIP)
Dynamics of activated chemisorption: Methane on rhodium
Authors: Stewart Charles N. , Ehrlich Gert
Published: February 2003

Chemisorption of methane has been examined on highly perfect rhodium surfaces by a combination of field emission and molecular beam techniques in order to explore the mechanism of activation. It has been found that dissociative adsorption can be initiated on rhodium at 245 K just by excitation of the gas. Quantitative rate studies as a function of gas temperature have established that the CH4 molecule must overcome an activation barrier of 7 kcal mole−1 for reaction to occur. For gas temperatures 600 < TG < 710 K, the efficiency of chemisorption per impact is at least an order of magnitude smaller for CD4 than for CH4 and a factor of ? 3 smaller for CH2D2. This suggests that translational and rotational motion are not directly involved in passing over the barrier. Vibrational excitation of methane molecules appears to be the significant step in the reaction at the surface. Transition state theory fails to account for the significantly smaller rates observed for CD4 than for CH4. However, Slater’s dynamical model of unimolecular reactions leads to a sizable isotope effect for the rate of dissociation, and the semiquantitative data presently available are best explained by his model.
A comparison of generalized cumulant and projection operator methods in spin-relaxation theory
Authors: Yoon B. , Deutch J. M. , Freed Jack H.
Published: February 2003

The general spin-relaxation theories of Albers and Deutch and of Argyres and Kelley based on different projection operator methods, and the theory of Freed based on generalized cumulant expansions are compared. It is shown that the first two yield equivalent expressions for the time evolution of the spin density matrix. They are also found to be equivalent to a cumulant expansion based on total ordering of the cumulant operators (TTOC), which is different from the partial time ordering method (PTOC) used by Freed. The TTOC method is found to be the more convenient for the frequency domain (i.e., for calculating spectra), while the PTOC method is for time domain analyses. Examples of the use of the TTOC method are given. Useful expressions are given for the case where the lattice may be treated in terms of classical Markov processes, but, in general, it is found that for such cases the stochastic Liouville method is the more useful for computations.
Beam maser measurements of rotational relaxation of H2CO
Authors: Foreman P. B. , Chien K.-R. , Kukolich S. G.
Published: February 2003

Inelastic scattering cross sections for the upper and lower states of J=1 and J=2, K-type doublets of formaldehyde were measured using a beam maser spectrometer. Scattering gasses used were He, Ar, H2, N2, CO2, HCl, NH3, CH3F, and CF3H. Systematic variations in cross sections with the symmetry and dipole moments of scattering molecules are observed. Anderson’s theory of pressure broadening, with slight modification, is used to interpret the data. This model gives reasonably good agreement with most of the observed effects.
A paradox: The thermal rate coefficient for the H+DCl → HCl+D exchange reaction
Authors: Thompson Donald L. , Suzukawa Henry H. , Raff L. M.
Published: February 2003

Previously reported photolysis experiments indicate that the frequency factors associated with the hydrogen-exchange reactions H+DCl μ HCl+D and D+HCl → DCl+H are on the order of 1010 cm3/mol⋅sec. This result indicates that the above processes are associated with very small steric factors, in contrast to what one might be led to expect from recent crossed beam experiments. A series of unadjusted, quasiclassical trajectory calculations have been carried out to compute the thermal rate coefficients and activation parameters for a series of 13 thermal processes of the type A+BC → AB+C, where A=H, D, or Cl and BC=H2, D2, HCl, DCl, or Cl2. In addition, hot-atom yield ratios have been computed from the IRP equation for the reactions D*+DCl → D2+Cl, D*+Cl2 → DCl + Cl as a function of the initial D* laboratory energy. Previously formulated, valence-bond representations were employed for the potential-energy surfaces in all the calculations. The computations yield (1) hot-atom [DCl]/[D2] yield ratios within a factor of 2 of the experimental values; (2) thermal activation energies in satisfactory agreement with experiment for all processes investigated; and (3) frequency factors in reasonable accord with experiment for all the reactions except the hydrogen exchange reactions, where the computed values are a factor of about 103–104 larger than indicated by the photolysis experiments. An investigation of a network of elementary thermal reactions that are apparently occurring in the photolysis experiments indicates that the presently computed thermal rate coefficients for the exchange reactions are too large to be compatible with observed HD and D2 quantum yields. These results make it clear that a serious error exists in either the potential-energy surface, the theoretical scattering calculations, the measured photolysis data, or the interpretation of that data. The agreement of the computed hot-atom yields, rate coefficients, and thermal activation parameters for all reactions except the hydrogen exchange reactions coupled with the results of recent crossed-beam experiments strongly indicate that the error lies in the interpretation of the photolysis data.
Intermolecular 13C kinetic isotope effects in the decarboxylation of oxalic acid in dioxane solution
Authors: Huang Thomas T.-S. , Kidd Richard W. , Yankwich Peter E.
Published: February 2003

Intermolecular 13C kinetic isotope effects in the decomposition in dioxane solution of oxalic acid to carbon dioxide and formic acid were determined at several temperatures between 80 and 132 °C. The isotope effect is normal in sign (k12C ≳ k13C), and approximately 3% in magnitude; the temperature dependence (small over the range of experimental temperatures) may be complex, if real. The method of three-element reaction coordinates (with ν‡1=0) was employed to expose possible properties of the transition state. The reaction coordinate eigenvectors yielding best correspondence to the experimental data consist of C–C bond extension, C–O bond contraction, and either (a) O–H bond extension or (b) contraction of the angle O–C–C to linearize O–C–O, these displacements being sited about the C atom which will appear in carbon dioxide product. The differences in the same region between reactant and transition state force fields which yield calculated results in best agreement with the experimental measurements are F‡C–C = 0.125 F0C–C, F‡C–H = 0.5 F0O–H, F‡C–O = 0.875 F0C–O, and F‡bend = (C‡/C0)F0bend, where C is the product of the bond orders of the stretching coordinates defining the bond angle.
Brillouin scattering in single crystals of γ-oxygen: Determination of the elastic constants at the triple point
Authors: Kiefte H. , Clouter M. J.
Published: February 2003

The technique of high resolution Brillouin spectroscopy has been used to determine the adiabatic elastic constants of oriented single crystals of γ-oxygen at temperatures near the triple point (54.39 K). The values obtained were c11 = 2.5(98), c12 = 2.0(58), c44 = 0.27(5) (in units of 1010 dyn cm−2) with an estimated absolute uncertainty of ±2%. The resulting value for the elastic anisotropy parameter was found to be 1.0(2). Estimates of the relative values of the elasto-optic coefficients were also obtained. It is concluded that γ-oxygen is ’’plastic’’ in nature.
ESR of the triplet molecules CCO and CNN in rare-gas matrices; isotope and matrix effects
Authors: Smith G. R. , Weltner W.
Published: February 2003

CCO and CNN, with isotopic substitution of 13C, 18O, and 15N, were prepared by the reaction of C atoms with CO or N2 and trapped in various matrices at 4 °K. ESR spectra of both 3Σ molecules yielded hyperfine splittings, g values, and zero-field splittings. In solid neon, these parameters for CαCβO, assuming g∥=ge, were g⊥=2.0029(4), D=0.7392(4) cm−1, ‖A⊥(Cα) ‖ = 57(3) MHz, ‖A∥(Cα) ‖ = 17(3) MHz, ‖A⊥(Cβ) ‖ = 26(3) MHz, ‖A∥(Cβ) ‖ = 32(3) MHz. Similar but less extensive data were obtained for CNαNβ where in solid neon, assuming g∥ =g⊥=ge, D = 1.1590(5) cm−1, ‖A⊥(14Nα) ‖ = 35(5), ‖A⊥(14Nβ) ‖ = 19(5), and ‖A⊥(13C) ‖ = 50(5) MHz. D values for isotopic molecules 12C12C16O, 13C12C18O, etc., varied by small but significant amounts (up to about 0.001 cm−1) in Ne and in Ar matrices. These variations could be approximately accounted for by assuming torsional oscillation in the solid. This was supported by a temperature variation study. The observed decrease of Dgas = 0.772 cm−1 for C2O in matrices, particularly large in Kr and Xe, is attributed partially to motional averaging and partially to matrix perturbations of molecular electronic properties. Theory was applied to qualitatively account for the changes in spin–spin, DSS, and spin–orbit, DSO, contributions to the zfs of the molecule in the solids. Matrix effects are expected to increase DSS and decrease DSO (for positive D) so that the dominant electronic effect is the spin–orbit mixing-in of singlet states via the matrix.
A p
r
i
o
r
i low temperature vibrational relaxation rates for He–H2
Authors: McGuire Paul , Toennies J. Peter
Published: February 2003

The recently developed coupled-states approximation has been applied to the He–H2 system for the calculation of the vibrational de-excitation cross sections nj=10→0j′ (j′=0,2,4,6,8,10) for energies from threshold up to Etotal = 0.99 eV. Computations have been carried out for three potential surfaces: (1) Krauss–Mies, (2) Gordon–Secrest, and (3) Gordon–Secrest, modified to include the long-range attraction. The low temperature relaxation rates for each surface are reported and compared to the experimental data from the stimulated Raman technique. V→R energy transfer is found to be very important in the vibrational relaxation process and the modified Gordon–Secrest surface gives the best fit to the experimental data.
Raman scattering from vibrational and electronic states arising from molecular orbitals of the ferricenium ion
Authors: Gächter B. F. , Koningstein J. A. , Aleksanjan V. T.
Published: February 2003

The laser excited Raman spectra of some ferricenium complexes are reported. Small differences exist in the frequency of vibrational modes which involve the iron atom of the ferrocene and ferricenium molecules but the bands of the latter are resonance enhanced. The ferricenium ion has low lying electronic states and the electronic Raman process is allowed. We report here on the observation and interpretation of the E(1/2)g (2A1g) ← E(3/2)g (2E2g) transitions which occur in the 200 cm−1 region. At present we have not found evidence of the occurrence of a Jahn–Teller effect. The results of the electronic Raman measurements are in good agreement with EPR data.
Many-body perturbation theory applied to H2
Authors: Kaldor Uzi
Published: February 2003

Diagrammatic many-body perturbation theory is applied to the H2 molecule using a discrete basis set composed of Gaussian orbitals. Three different zero-order potentials are tried. Corrections through third order are calculated, and higher orders are estimated. The energy obtained is accurate to about 1 kcal/mole. The technique of partial summation of certain classes of diagrams by denominator shifts is investigated. Dipole polarizabilities and transition moments are also calculated, with an accuracy of 5% or better. The use of the geometric approximation to estimate high-order corrections is discussed.
Transport coefficients for a dense fluid of square-well, rough spheres
Authors: Scarfe K. D. , McLaughlin I. L.
Published: February 2003

Transport coefficients are derived for a dense fluid of square-well, rough spheres. This molecular model may be described as a rough spherical core surrounded by a square-well potential. The Chapman–Enskog approach is used to obtain the transport coefficients. The expressions include the ’’first’’ order contributions arising from the deviation of the singlet distribution function from local equilibrium in addition to the ’’zeroth’’ order terms involving the local equilibrium function. The kinetic equation is also derived.
Nonadiabatic effects on vibronic intensities of larger polyatomic molecules in the preresonance regime
Authors: Small Gerald J.
Published: February 2003

The approximations used to simplify the perturbation based theory of nonadiabatic interactions and their effects on vibronic intensities in the preresonance regime are examined for the larger polyatomic molecules. They include employment of a crude adiabatic basis set and certain approximate sum rules.
Calculation of the compressibility coefficients for the alkali and alkaline metals
Authors: Reynolds C. L. , Couchman P. R.
Published: February 2003

Compression data have been used to calculate compressibitliy coefficients for the alkali and alkaline metals, and the coefficients a2 and a3 have been shown to be correlated with a1.(AIP)
Coupled-states approach for elastic and for rotationally and vibrationally inelastic atom–molecule collisions
Authors: McGuire Paul
Published: February 2003

The elastic and inelastic collisions of an atom with a diatomic molecule are treated quantum mechanically in the body−fixed coordinate system. The body−fixed equations of motion are first compared with the usual spaced−fixed ’’close−coupling’’ equations and limiting cases are considered in which the two formalisms become equivalent. The recently developed ’’coupled−states’’ approximation in the body−fixed system is then described in which intermultiplet transitions are neglected and the eigenvalue of the orbital angular momentum operator l̂2 is approximated by h/l (l + 1). Numerically computed cross sections from this approximation are compared to those computed from the standard space−fixed close−coupling equations for the test system He−H2. Agreement to within a few percent is obtained for the integral as well as for the differential cross sections for elastic and for rotationally and vibrationally inelastic scattering in the energy range of 0.9 to 4.2 eV. A coupled−states large basis calculation (j = 0, 2, 4, 6, 8, 10 for n = 0 and j = 0, 2, 4, 6 for n = 1) at 4.2 eV is presented which demonstrates the enormous utility of the method.
Vibrational and triplet excitation by electron impact in benzene
Authors: Azria R. , Schulz G. J.
Published: February 2003

The vibrational excitation of the ν1 mode and the excitation of the first triplet state in benzene exhibit structures which are interpreted in terms of shape resonances associated with excited states of benzene. These excited shape resonances span the energy range 4−11 eV and they decay into a multiplicity of final states.
On the nature of exciton–phonon coupling in crystalline benzene
Authors: Colson Steven D. , Netzel Thomas L. , van Pruyssen Jean M.
Published: February 2003

A new technique for determining the nature of the exciton−phonon coupling in molecular crystals is applied to the S1 (0,0) exciton band. The phonons associated with the origin line of the neat crystal fluorescence are found to derive their intensity by a vibronic mechanism. In addition, the recently proposed ’’localized exciton sideband method’’ is applied to the fluorescence and phosphorescence spectra of pure and isotopic mixed benzene crystals to further test its applicability to molecular crystals. The difficulties expected for the general application of the localized exciton sideband method are discussed in some detail. It is shown that the method can be applied to pure as well as mixed crystals, removing uncertainties about possible impurity induced perturbations of the phonon modes. The correspondence between observed and calculated features in the phonon spectrum is not as satisfactory as in the naphthalene crystal. The strength of the exciton−phonon coupling is found to be similar, but measurably different for the T1 and S1 states of benzene. Furthermore, it is shown that the exciton−phonon coupling for the S1 state is less in the pure than in the isotopic mixed crystal. Thus, even though the pure crystal excitation exchange integrals are as small as ∼2 cm−1, the delocalization of the excitation causes a ∼10% reduction in the phonon coupling.
Hard-cores of molecules of simple fluids
Authors: Bienkowski Paul R. , Chao Kwang-Chu
Published: February 2003

The diameters of hard−cores of molecules of simple fluids (Ar, Kr, Xe) have been deduced from analysis of isothermal compressibility data in light of hard−sphere equations of state. The hard−core diameter σ thus obtained is found to decrease slightly as temperature is increased. The results can be represented in a generalized form in terms of reduced variables σ[(6/π)(?c/?)]−1/3 = 0.549058 − 0.010827 T/Tc with standard deviation of 0.000731.
Structure of Bunsen flames
Authors: Sivashinsky G. I.
Published: February 2003

The structure of Bunsen cone flame tops is studied using the thermal diffusion flame model. Assuming a strong temperature dependence of the reaction rate, the shape of the flame front as well as the temperature distribution at the front are found. It is shown that for the case in which the Lewis number of the limiting component is greater than unity, the front is a smooth surface with a radius of curvature at the flame top substantially exceeding the width of the preheating zone. Towards the flame top, the temperature in the reaction zone increases along with the velocity of the flame relative to the gas. When the Lewis number of the limiting component is less than unity, the temperature at the front decreases towards the flame top, the velocity of the flame relative to the gas drops, and the flame is extinguished at distances close to the top.
Molecular orbital theory of the hydrogen bond. XI. The effect of hydrogen bonding on the n→π* transition in dimers HOH⋅⋅⋅OCHR
Authors: Del Bene Janet E.
Published: February 2003

A b initio SCF−CI calculations with a minimal STO−3G basis set have been performed to determine singlet n→π* transition energies for a series of dimers having monosubstituted carbonyl compounds as proton acceptors and water as the proton donor, represented by the general formula HOH⋅⋅⋅OCHR. In each dimer, the n→π* transition energy is greater than the n→π* transition energy in the corresponding monomer. The dimer transition energy may be approximated as the sum of the n→π* transition energy in the monomer RCHO and the hydrogen bond strength in the corresponding dimer, providing that a single carbonyl group gives rise to the monomer n→π* band. This relationship between the blue shift of the n→π* band and the hydrogen bond strength suggests that the blue shift reflects the additional energy required to break or at least severely weaken the hydrogen bond in the dimer excited state. Only a small blue shift is observed in the water−glyoxal dimers, since in glyoxal, electron excitation occurs from an n orbital delocalized over two carbonyl groups, and the water−glyoxal dimers remain bound in the excited n→π* state.
Moments and distribution functions for polymers using Toeplitz matrices
Authors: Springgate M. W. , Poland Douglas
Published: February 2003

A method is given for calculating the moments and distribution functions for the finite one dimensional Ising model. With the technique presented, as many as 20 or so moments can be calculated as explicit matrix products, thus avoiding the use of numerical differentiation. Previously it was feasible to calculate only the first two moments (giving the mean value and dispersion of the distribution). Using short polypeptide chains as an example where the distribution function is known, it is shown that knowledge of a large number of moments allows very broad, non−Gaussian distributions with more than one maximum to be accurately determined.
Lattice statistics using Toeplitz matrices
Authors: Springgate M. W. , Poland Douglas
Published: February 2003

A new technique is presented for the exact calculation of both low and high density virial coefficients for lattice gases. The virial coefficients are given directly in terms of matrix products using symmetry reduced matrices as elements in a Toeplitz hypermatrix. The technique is applied to the plane−square lattice with nearest neighbor exclusion and next nearest neighbor attraction between particles. Eleven terms are given as explicit functions of the particle interaction energy in both the high and low density virial series; two variants of the basic model are also treated. For the hard core high density series, 14 virial coefficients are calculated exactly.
Absorptive trapping in thin dye layers
Authors: Babcock Walter C. , Simpson William T.
Published: February 2003

Films of organic dyes having thicknesses of ∼200 Å when illuminated in a manner which would give rise to attenuated total reflection spectra show unexpectedly high absorptions. Generally speaking, the phenomenon is interpreted via Maxwell’s macroscopic equations. A surprising feature of the interpretation is that an angle, film thickness, and frequency can be found such that no fraction whatsoever of the incident light is either reflected or transmitted. A special formalism is introduced, which is judged to facilitate a particularly direct interpretation, wherein emphasis is given to the role played by dissipation. The phenomenon as viewed in the framework of this formalism, and with the help of qualitative ideas taken from the microscopic theory, can be further explained: The s− and p−polarized incident beams excite, respectively, lightly damped transverse and longitudinal polariton modes, so that the maximum effect in the two cases comes essentially at the corresponding resonances, ω− and ω+.
Finite element method for bound state calculations in quantum mechanics
Authors: Askar Attila
Published: February 2003

The finite element method, which in other fields has replaced finite difference and variational methods, is applied to the radially symmetric case of the hydrogen atom. The method is shown to have computational advantages over the finite difference and Rayleigh−Ritz methods. (AIP)
Internal energy exchange in molecular collisions with a crystal
Authors: Rowe R. Grant , Ehrlich Gert
Published: February 2003

The angular distribution of the scattered intensity has been measured for beams of molecular hydrogen and its isotopes, colliding with a MgO surface. In the analysis of the spectra, it is not found necessary to invoke phonon excitation. The exchange of energy between internal degrees of freedom and translation gives a good account of the experiments. (AIP)
Circular dichroism of unordered polymers: Extended time dependent Hartree theory for polypeptides
Authors: Rabenold David A.
Published: February 2003

Equations describing circular dichroism (CD) and optical rotatory dispersion (ORD) of a system of unordered polymers in solution are derived via a linear response method in terms of exact states of the system. Origin dependent extrinsic magnetic moment operators are not used. After a multipole expansion of the induced transverse current and a long wavelength expansion of the susceptibilities, the equation of motion of the radiation field’s average vector potential is solved and a definition of the refractive index provides an account of CD−ORD. It is shown that the contribution to the current by the susceptibility characterizing induced electric dipole polarization through intrinsic magnetic dipolar coupling with the curl of the radiation field is identical to the contribution by the susceptibility characterizing induced magnetic dipole polarization through electric dipolar coupling with the radiation field only for isotropic media. Approximate polypeptide susceptibilities are obtained by an extension of the time dependent Hartree scheme. The extension is shown to be necessary when electric and nπ* magnetic dipole transitions are degenerate or near degenerate, for which anomalous dispersion arises and rotational strength is not conserved. The resulting susceptibilities are obtained from the solution to a normal mode problem. The normal modes are determined not only by electric dipolar coupling but also by the coupling of electric quadrupoles with others and with electric dipoles. The time dependent Hartree scheme is then on a comparable level with the matrix scheme, and the two methods are discussed.
Vibrational nonequilibrium in carbon dioxide electric discharge lasers
Authors: Murray Edward R. , Kruger Charles H. , Mitchner Morton
Published: February 2003

An experimental and theoretical investigation of vibrational nonequilibrium in the CO2 electric discharge laser was performed. The vibrational temperature for each vibrational mode of CO2 was measured under a variety of discharge conditions. Measurements indicate nonequilibrium between ν1 and ν2 can be significant. Possible causes for the apparent nonequilibrium which were theoretically examined included anomalously high gain on certain transitions which has been attributed to overlapping hot band contributions, use of different optical broadening cross sections, use of different electron−vibration excitation cross sections, and the effect of uncertainty in all V−V and V−T transfer rates. The most likely cause of the measured nonequilibrium was found to be a lack of strong coupling between the ν1 and ν2 modes.
Monte Carlo calculations for pressure dissociation of H2
Authors: Aviram I. , Goshen S. , Thieberger R.
Published: February 2003

A Monte Carlo method is proposed for the calculation of dissociation of diatomic homonuclear molecules as a function of temperature and density. The procedure is illustrated for hydrogen in the temperature range up to 15000 K. The essentially quantum mechanical processes of dissociation and binding are replaced here by a classical model system of free atoms and molecules whose numbers in the system may vary according to certain probabilistic rules. A choice must be made of the interaction potentials between particles, which are then replaced by equivalent hard−spheres repulsive interactions. The attractive part of the singlet H−H interaction, which is responsible for the bound state of two atoms, is replaced by an intrinsic ’’binding’’ energy attributed to each molecule present in the system. Results show that dissociation starts at densities well below the packing density of molecules.