bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative study of the gradient expansion of the atomic kinetic energy functional–isoelectronic series
Authors: Wang Wen-Ping
Published: February 2003

In previous work, it was shown that, for the ground state of neutral atoms, the truncated gradient expansion of the kinetic energy functional T[ρ] can give very good kinetic energy values when Hartree–Fock densities are used. In this work, we use the Hodges expansion formula: T[ρ]=T0[ρ]+T2[ρ]+T4[ρ], with T0[ρ]=3/10 (3π2)2/3∫ρ5/3dτ, T2[ρ] = (1/72) ∫[(∇ρ)2/ρ]dτ, etc., to calculate the kinetic energies of heliumlike, neonlike, and argonlike atoms and ions. The errors in the values obtained depend significantly on the number of electrons, N, of the system when N is small. As N increases, the error gradually decreases.
Phase transition and rotational excitations in Ni(NH3)6I2
Authors: Eckert J. , Press W.
Published: February 2003

Neutron scattering techniques were used to investigate both the crystal structures and the rotational dynamics of the ammonia groups in Ni(NH3)6I2 above and below the phase transition near 20 K. The phase transition involves orientational ordering of the ammonia groups and is accompanied by a distortion of the crystal lattice from cubic (space group Fm3m) to trigonal symmetry along with a doubling of the primitive cell. A deuterated sample was employed for the structural studies. Its transition temperature was found to be 26.5±0.3 K. Extensive studies of the rotational dynamics of the NH3 groups above the phase transition showed that their motion is best described as one-dimensional rotational diffusion about their trigonal axis. Diffusion constants derived from this analysis as a function of temperature exhibit increasing orientational correlations as the transition temperature is approached. At low temperatures the NH3 groups perform one-dimensional tunneling motions. The resulting splitting of the librational ground state was determined to be 0.0634±0.0014 meV in good agreement with the value derived from earlier specific heat measurements. A further excitation at 9 meV is interpreted as a transition to the first excited librational state.
Dielectric theory for polar molecules with fluctuating polarizability
Authors: Ho/ye J. S. , Stell G.
Published: February 2003

The dielectric properties of a classical system of interacting particles, each bearing a permanent dipole moment and thermally fluctuating polarizability, is considered. It is shown how a useful class of approximations initially defined for a system of nonpolarizable particles can be generalized to include fluctuating polarizability. For the case in which the mean polarization of an isolated particle is linear in applied field (i.e., harmonic fluctuations) it is further shown that the dielectric constant can be explicitly computed in these approximations, which include the mean spherical approximation and the single super-chain approximation (equivalent to the ’’reference’’ version of the linearized hypernetted chain approximation). The resulting ε is identical to that in a corresponding approximation defined for dipolar particles with nonfluctuating polarizability. In the limit of a closed-packed system of nonpolar particles with cubic symmetry, it is found that the resulting approximations for ε all reduce to the Claussius–Mossotti result, which is known to be exact for systems of such symmetry in the case of either fluctuating or constant polarizability. The inclusion of nonlinear effects is discussed briefly; in particular it is noted that a permanent dipole moment is equivalent to a certain limiting case of anharmonic fluctuations.
Stark effects on quasilinear chain excitons in dibromonaphthalene
Authors: Hochstrasser R. M. , Johnson L. W. , Klimcak C. M.
Published: February 2003

Electric field perturbations on the singlet–triplet spectra of 1,4-dibromonaphthalene (DBN) are presented. Studies of the neat crystal exciton (Δμ=0.15±0.02 and 0.16±0.02 D) and of proto in deutero DBN (Δμ=0.12±0.02 and 0.13±0.02 D) gave nonidentical but similar results. The X traps at 4958 and 4960 Å were found to have their dipoles oriented differently than host molecules. The two sublattices of the crystal were found to have significantly different values of Δμ (4952 Å, Δμ=0.16 D; 4937 Å, Δμ=0.06 D). The field dependence of the exciton Stark effect generated an upper limit value of 0.01 cm−1 for the interstack coupling in DBN. Nonlinear field dependent effects are attributed to field induced structural modifications.
Quasiclassical trajectory studies of H+H2 on an accurate potential energy surface. I. Isotope effects
Authors: Mayne Howard R.
Published: February 2003

Quasiclassical trajectory calculations for X+H2(0, 0) and H+X2(0, 0), X=H, D, T at thermal energies have been carried out on the accurate SLTH potential energy surface; Both collinear and three-dimensional results are considered. In three dimensions, the trends in reactivity are those which would be expected from energetic considerations (e.g., exoergicity) but are here explained in terms of simple dynamical effects. Trends in final properties, such as rotational distribution and differential cross sections are presented and explained.
Spectra and structure of gallium compounds. II. Microwave, infrared, and Raman spectra, structure, and vibrational assignment of trimethylaminegallane
Authors: Durig J. R. , Chatterjee K. K. , Li Y. S. , Jalilian M. , Zozulin A. J. , Odom J. D.
Published: February 2003

The microwave spectra of (CH3)3 14N 69GaH3, (CH3)3 14N 71GaH3, (CH3)3 15N 69GaH3, (CH3)3 15N 71GaH3, (CH3)3 14N 69GaD3 and (CH3)3 14N 71GaD3 were recorded from 26.5 to 40.0 GHz resulting in the first gas phase structural determination for a gallane adduct. An rs distance of 2.111±0.002 Å was obtained for the Ga–N bond. With reasonable assumptions for the structural parameters for the methyl moiety and the Ga–H distance the following molecular parameters were determined: r(N–C)=1.47 Å, uGaNC=110.0°, and uNGaH=102.0°. The barrier to internal rotation of the GaD3 moiety was calculated from the relative intensity of the vibrational satellites to be 1.2 kcal/mole. The infrared (200–4000 cm−1) and Raman spectra (50–3500 cm−1) of (CH3)3 NGaH3, (CH3)3 NGaD3, and (CH3)3 15NGaH3 have been recorded for the solid state at low temperature. The spectra have been interpreted in detail on the basis of C3v molecular symmetry. The splitting of the degenerate E modes in the spectra of the solids indicates that the previously determined crystal structure where the hydrogen positions were not determined is not correct for the complete molecule. A normal coordinate calculation has been carried out by utilizing a modified valence force field to calculate the frequencies and the potential energy distribution. The Ga–N stretch was found to be extensively mixed with the NC3 symmetric deformation for the (CH3)3 NGaH3 and for the d3 molecule additional mixing was found with the GaD3 symmetric deformation. The Ga–N force constant was found to have a value of 2.44 mdyn/Å which is considerably larger than the value of the Ga–P force constant (2.0 mdyn/Å) in (CH3)3 PGaH3. These results are compared to similar quantities in several corresponding Group IIIA–VA compounds.
The dependence of rate coefficients and product yields upon fluence, intensity, and time in unimolecular reactions induced by monochromatic infrared radiation
Authors: Quack M. , Humbert P. , van den Bergh H.
Published: February 2003

The influence of the three parameters (with two degrees of freedom) fluence, intensity, and time on rate coefficients and product yields in collisionless Unimolecular Reactions Induced by Monochromatic Infrared Radiation (URIMIR) is discussed in some detail in terms of the recently proposed logarithmic reactant fluence plots. Model calculations for several archetypes of such plots are presented, based on solutions of the Pauli master equation and solutions of the quantum mechanical equations of motion for spectra involving many states at each level of excitation. Linear diagrams, turnups, and turnovers are found and are discussed systematically. Experimental examples re-evaluated from the literature and new measurements on the laser induced decomposition of CF2HCl are reported which nicely illustrate the various theoretical possibilities. Steady state rate coefficients for six molecules are evaluated and summarized. In some situations the intrinsic nonlinear intensity dependence of the steady state rate coefficients and deviations from simple fluence dependence of the product yields both before and at steady state are shown to be important theoretically and experimentally. The role of the reducibility of the rate coefficient matrix is discussed in connection with turnovers and with the strong influence of initial temperature that is found in the laser induced decomposition of CF2HCl.
O(1S) yield from O3 photodissociation at 1700–2400 Å
Authors: Lee L. C. , Black G. , Sharpless R. L. , Slanger T. G.
Published: February 2003

The O(1S) yield from O3 photodissociation is measured in the 1700–2400 Å region using synchrotron radiation as a light source. An upper limit for the yield is set at 0.1% for the entire photon energy range. This small quantum yield indicates that the contribution of O(1S) to atmospheric OH production is not significant.
On the use of pressure broadening data to assess the accuracy of CO–He interaction potentials
Authors: Green Sheldon , Thomas Lowell D.
Published: February 2003

Carbon monoxide and He scattering calculations have been performed using the electron gas and SCF-CI potentials. The cross sections from the SCF-CI potential are marginally in better agreement with experiment than those from the electron gas potential.
Semiclassical quantization of multidimensional systems
Authors: Ramaswamy Ramakrishna , Siders P. , Marcus R. A.
Published: February 2003

Low order classical perturbation theory is used to obtain semiclassical eigenvalues for a system of three anharmonically coupled oscillators. The results in the low energy region studied here agree well with the ’’exact’’ quantum values. The latter had been calculated by matrix diagonalization using a large basis set.
Rational fraction representation of diatomic vibrational potentials. IV. The 2pσu van der Waals state of H2+
Authors: Sonnleitner Stephanie A. , Beckel Charles L.
Published: February 2003

Rational fraction [L/N] representation in nuclear separation R is applied to the Born–Oppenheimer potential V for H2+ 2gσu, a prototype −1/R4 van der Waals electronic state. A [6/10] fraction, least-squares fitted on 0.8⩽R⩽90 Bohr radii, has an rms error of 1.52×10−8 hartrees at fitted points. The [6/10] accurately reproduces the shallow, large R minimum, and yields reasonably reliably the Coulomb pole at R=0. The tests to data on phototype states do not yet reveal any fundamental limitations on the use of [L/N] fractions for representing diatomic molecule potentials.
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o calculations on the 3Σg−, 1Σg+, 3Πg, and 1Πg symmetries of S2: Valence, ion pair, and Rydberg states
Authors: Saxon Roberta P. , Liu B.
Published: February 2003

Configuration interaction calculations have been performed for 3Σg−, 1Σg+, 3Πg, and 1Πg states of S2. The lowest diabatic Rydberg state for each symmetry is presented. Spectroscopic parameters for the bound X 3Σg− and b 1Σg+ states and for the Rydberg states are given. Limited test calculations are reported. The implications of these potential curves for the rate of quenching of S(1S) in collision with another S(1S) are discussed.
RMCS–CI potential surface for H2O→OH+H
Authors: Wright James S. , Shih Shing-Kuo
Published: February 2003

A potential surface is reported for H2O at a fixed bond angle of 105°. The surface covers an extended range, including the dissociation channels OH(2Π)+H(2S) and O(3P)+2H(2S). Using a double-zeta basis set and multireference CI technique, followed by a fitting procedure using rotated Morse curves, the following results were obtained: H2O(1A1)→OH(2Π)+H(2S), ΔE=4.50 eV (expt. 5.47); H2O(1A1)→O(3P)+2H(2S), ΔE=8.03 eV (expt.10.08). A double-zeta + polarization basis set leads to improved results (5.18 and 9.44 eV). The shape of the surface is well described by rotated Morse curves. A simple scaling procedure brings the computed surface into close coincidence (within ∼0.2 eV) with a surface based on an experimental force field. The scaled RMCS–CI approach may be useful for other triatomic systems to provide an accurate surface at a reasonable cost.
On the microscopic origin of Stokes’ law
Authors: Cukier Robert I. , Kapral Raymond , Lebenhaft Julian R. , Mehaffey J. R.
Published: February 2003

The microscopic origin of Stokes’ law for a hard sphere system is examined from two points of view. First, we derive a set of hydrodynamic equations with source terms, which account for the presence of a Brownian particle in the fluid, from the generalized Langevin equation. The friction coefficient can be expressed in terms of averages of the hydrodynamic fields over the Brownian particle. The solution of the source hydrodynamic equations for these averaged fields leads to the slip Stokes’ law result. Second, we consider the problem from kinetic theory and show that the same source hydrodynamic equations are obtained when projections onto hydrodynamic states are made.
Interfacial space charge and capacitance in ionic crystals: Intrinsic conductors
Authors: Macdonald J. Ross , Franceschetti Donald R. , Lehnen Alfred P.
Published: February 2003

The conventional theory of surface charge and distributed space charge in single crystals exhibiting Frenkel or Schottky disorder is generalized in several ways. First we generalize the usual continuum theory of the diffuse double layer in the crystal by adopting a lattice gas model which restricts the mobile charges to a fixed number of lattice sites. The lattice gas activities can be used in both zero and nonzero current situations and are shown to be consistent with a three-dimensional generalization of ordinary Langmuir adsorption. The substantial effects of the resulting limit on concentrations in accumulation regions are examined and shown to be particularly important in high bias situations and in materials in which the bulk equilibrium charge densities are very high. Second, we take explicitly into account the physical separation between the plane of the surface charges, which balance the bulk space charge, and the first normal lattice plane of the crystal and show that under most conditions of interest this separation modifies the earlier surface potential results of Poeppel and Blakely substantially. We also show that the thermodynamically generated equilibrium relation between surface charge density and surface potential is itself just a form of the Langmuir adsorption isotherm applied to occupancy of the kink sites. Finally, we investigate the response of the system when a completely blocking electrode is attached, with the physical separation between the equipotential plane of the electrode and the plane of the electrical centers of the ’’adsorbed’’ surface charges explicitly introduced. Free energy minimization in this situation leads to Langmuir adsorption at the surface. A new equivalent circuit representing the total differential capacitance of the system is derived, and competing effects of adsorption capacitance, diffuse double layer capacitance, and separation capacitances are investigated. An important result is that we find the surface adsorption capacitance to be essentially in parallel rather than in series with the diffuse double layer capacitance. Numerous analytic and numerical results of capacitance versus temperature and applied bias are presented for different limiting surface site concentrations and it is found that the surface potential plays somewhat the role of a diffusion potential, causing the minimum of the diffuse layer capacitance (occurring at the ’’flat-band potential’’) and the maximum of the adsorption capacitance to be displaced from one another in potential. Some of the results of the present work also may be relevant to the theory of adsorption capacitance in unsupported aqueous electrolytes.
Dielectric saturation in dipolar fluids. I. The single-molecule distribution function
Authors: Ramshaw John D.
Published: February 2003

The functional-derivative formalism is used to investigate the form of the equilibrium single-molecule distribution function n(1) in a finite fluid system of rigid polar molecules subjected to a strong external electric field that varies slowly with position. The investigation is based on the assumption that the long-range asymptotic behavior of the direct correlation function is independent of the external field, and is hence the same as in the unperturbed fluid. This assumption implies that n(1) has the form of a single-molecule Boltzmann factor in which the interaction energy is that of a deformable quasidipole with the local Lorentz electric field EL(r1). If the chemical potential μ is held fixed, n(1) is a local function of EL(r1). In a closed system, however, the number of molecules N is held fixed and μ varies with the field. Consequently, n(1) is an inherently nonlocal functional of EL(r), except in the linear approximation where local behavior is regained. The implications of these results for the polarization and higher angular moments of n(1) will be explored in a subsequent article.
The effect of solvent environment on molecular electronic oscillator strengths
Authors: Myers Anne B. , Birge Robert R.
Published: February 2003

A simple expression is derived for the effect of solvent environment on solute oscillator strength. The only parameters required are the refractive index of the solvent and a geometric factor which depends upon the shape of the molecule and the orientation of its transition moment. Whereas classical local field theories predict that oscillator strengths in all molecules should change in the same direction with increasing solvent polarizability, our theory correctly predicts a decrease in the oscillator strength of the π*←π transition of β-carotene and an increase in the oscillator strength of the π*←n transition in pyrazine. The theory is based on perturbation of the ground and excited states of the solute by point–dipole interactions between solvent and solute transition moments. Although our expression is derived for nonpolar solutes in nonpolar solvents, experimental evidence indicates that it may be equally applicable to nonpolar solutes in polar solvents.
Theoretical equations of state for molecular fluids: nitrogen, oxygen, and carbon monoxide
Authors: Kerley Gerald I. , Abdallah Joseph
Published: February 2003

Equations of state for nitrogen, oxygen, and carbon monoxide are derived and compared to experimental data. It is shown how to separate vibrational and rotational degrees of freedom from translational motion in computing statistical averages. Translational contributions can be computed by treating the molecules as spherical particles moving in a potential field which is averaged over the internal degrees of freedom. Agreement with experimental data is good.
Carbon monoxide chemisorption on Ni(100)—direct detection of adsorbate–adsorbate interactions by desorption kinetic measurements
Authors: Yates John T. , Goodman D. Wayne
Published: February 2003

The isotopic exchange between CO chemisorbed on Ni(100) and CO(g) has been studied using thermal desorption spectroscopy. Rapid isotopic exchange occurs at low crystal temperatures, and presumably involves low adsorption energy CO states which are present at high CO coverages on the Ni(100). Exchange is accompanied by rapid equilibration of exchanged CO throughout the entire CO layer.
Isotopic dilution studies of the chloroform–chloroform-d system by Raman difference spectroscopy
Authors: Laane J. , Kiefer W.
Published: February 2003

Raman difference spectroscopy has been used to measure small frequency shifts in the ν1 and ν2 bands of CHCl3 and CDCl3 in various mixtures of liquid chloroform and deuterochloroform. The frequency shifts relative to the pure liquids vary linearly with concentration, and at infinitive dilution are determined to be for CHCl3: Δν1=+0.56 and Δν2=+1.92 cm−1; and for CDCl3: Δν1=+0.33 and Δν2=+1.82 cm−1. The fact that all frequency shifts are positive indicates that an exchange effect between like molecules is responsible for the phenomenon. The ν4 bands show no frequency shifts but narrow substantially in bandwidth upon isotopic dilution. The position of the composite (CHCl3+CDCl3) ν6 band relative to the pure liquids was also measured as a function of concentration. The data confirm that the frequency difference between this band in liquid CHCl3 and in CDCl3 is 1.05 cm−1. The ν6 frequency appear not to be significantly shifted by isotopic dilution.
Further developments and applications of sensitivity analysis to collisional energy transfer
Authors: Eslava Luis A. , Eno Larry , Rabitz Herschel
Published: February 2003

This paper considers the sensitivity of collision cross sections to the variation of intermolecular potential parameters. The study is restricted to the scattering of an atom and a linear rigid rotor, and to an atom and a breathing sphere. Attention is focused upon first order sensitivity coefficients (i.e., the gradient of cross sections with respect to potential parameters) from which an entire family of derived sensitivity coefficients may be obtained. Within this family a special class of coefficients is shown to be particularly important in determining the extent to which a set of measurements is able to define the parameters of an assumed potential. Finally, the global behavior of cross sections in parameter space is examined, and a nonlinear interpolation formula is suggested which utilizes sensitivity information.
Charge transfer of atomic and molecular rare-gas ions with mercury atoms at thermal energy
Authors: Johnsen Rainer , Biondi Manfred A.
Published: February 2003

A drift tube–mass spectrometer apparatus has been used to determine thermal-energy rate coefficients for reactions of the type R++Hg→R+Hg+ and R2++Hg→2R+Hg+, where R denotes an atom of one of the rare gases. Except for He+ ions, charge transfer between atomic rare-gas ions and mercury was found to be immeasurably slow. Both He2+ and Xe2+ exhibited fast charge transfer with mercury; a moderately slow reaction also occurred in the case of Ne2+ ions. Formation of mercury dimer and trimer ions was observed to be quite efficient in xenon–mercury mixtures; rate coefficients for the reaction sequence Hg+→XeHg+→Hg2+→XeHg2+→Hg3+ were estimated to be on the order of 10−31 cm6/sec for the association steps 1 and 3, and about 10−10 cm3/sec for the two-body switching steps 2 and 4.
Lasers based on selenium 1S metastable atoms.
Authors: Powell H. T. , Schleicher B. R.
Published: February 2003

We have investigated the laser performance of the 1S0–1D2 and 1S0–3P1 electric-dipole-forbidden transitions of the ground configuration of selenium atoms using 172 nm photolysis of OCSe to produce large concentrations of Se(1S). With complete dissociation of OCSe the Se(1S) atoms are quenched by photoelectrons and Se(3P) atoms, both undesired products of the photolysis. The quenching by electrons is removed and the laser performance is greatly improved by employing small concentrations of SF6 for electron attachment. At optimized conditions, we have obtained a laser output on both transitions corresponding to 0.3 photons for each OCSe molecule initially in the laser volume. We have also investigated the effects on the lasers of collision broadening and collision-induced emission and have demonstrated XeSe and KrSe collision-induced lasers operating at wavelengths near the Se(1S0–1D2) transition.
Electronic structure for the ground state of TlH from relativistic multiconfiguration SCF calculations
Authors: Christiansen Phillip A. , Pitzer Kenneth S.
Published: February 2003

The dissociation curve for the ground state of TlH was computed using a relativistic ω–ω coupling formalism. The relativistic effects represented by the Dirac equation were introduced using effective potentials generated from atomic Dirac–Fock wave functions using a generalization of the improved effective potential formulation of Christiansen, Lee, and Pitzer. The multiconfiguration SCF treatment used is a generalization of the two-component molecular spinor formalism of Lee, Ermler, and Pitzer. Using a five configuration wave function we were able to obtain approximately 85% of the experimental dissociation energy. Our computations indicate that the bond is principally sigma in form, despite the large spin–orbit splitting in atomic thallium. Furthermore the bond appears to be slightly ionic (Tl+H−) with about 0.3 extra electron charge on the hydrogen.
Energy-density relations and screening constants in atoms
Authors: Levy Mel , Tal Yoram
Published: February 2003

Approximate ratios between energy components of ground state atoms are derived through a synthesis of two limiting theories: the Thomas–Fermi model and the Z−1 expansion. The ratios so obtained are no longer constant (as predicted by Thomas–Fermi theory) but contain some of the periodic character which is observed in the corresponding Hartree–Fock ratios. It is shown that any ratio between E, Vne, and Vee (the total energy, the nuclear–electron attraction energy, and the electron–electron repulsion energy respectively) or between linear combinations of them is well approximated in terms of (aE)1/2 where a=1/(2αZ)2ε0 and α is a universal constant. In the limit Z→∞ each of these ratios approaches a constant as (aE)1/2→3/7 and the Thomas–Fermi prediction is recovered. For low values of Z the agreement with the Hartree–Fock results is much better than predicted solely on grounds of Thomas–Fermi theory (i.e., constant ratios) since some of the periodic information is introduced through the zero order perturbation parameter ε0. Extending this approximate zero order approach we obtain a detailed and rather accurate relation between the total energy and the orbital (rather than total) expectation values of r−1. Namely, E=−1/2Σn21<r−1≳2i where ni is the principal quantum number of the ith orbital. Another result of this procedure is an alternative definition of screening constants, σnl which is numerically compatible with Hartree’s definition. Finally, an expression relating the energies of any two members of an isoelectronic series is derived and used to predict the stability of H−directly from expectation values of He.
The selective preparation of excited vibrational states using the stimulated resonance Raman effect
Authors: DePristo Andrew E. , Rabitz Herschel , Miles Richard B.
Published: February 2003

A nonperturbative treatment of stimulated resonance Raman (SRR) pumping is developed. This theory is based upon the derivation of an effective Hamiltonian for the interaction of the electric field with the molecular electronic–vibrational–rotational states. The resulting reduction in the number of coupled differential equations describing the SRR effect allows for a convenient numerical solution, which is important in intense laser fields. In addition, when the spectral transitions are resonant or sufficiently power broadened, the solutions become analytic. An application of the theory to the I2 system shows the possibility of selectively populating high vibrational levels (v′?10) in the ground electronic state. Most importantly, it is possible to selectively populate all the vibrational levels by suitable variations in the frequencies and proper selection of the intensities and durations of the applied laser fields.
Photoionization of (H2)2 and the clusters of O2 molecules
Authors: Anderson S. L. , Hirooka T. , Tiedemann P. W. , Mahan B. H. , Lee Y. T.
Published: February 2003

Photoionization of (H2)2 and clusters of O2 was investigated in a molecular beam experiment. No evidence was found for the existence of stable (H2)2+. Photoionization spectra of (H2)2 →hυ H3++H+e is quite similar to that of (H2) hν→H2++e, yet the appreciable differences in some features of spectra suggest that there is a competition between the autoionization and vibrational predissociation of vibronically excited (H2)2. From the photoionization thresholds of (O2)n, n=1–5, it is concluded that (O2)2+ is bound by 0.26±0.02 eV, but the additional binding energies for higher clusters of O2+ are much smaller; just about what one would expect from a charge induced dipole interaction.
Vibrational spectra of crystalline disilane and disilane-d6, barrier to internal rotation and some normal coordinate calculations on H3SiSiH3, H3SiNCO, and H3SiNCS
Authors: Durig J. R. , Church J. S.
Published: February 2003

The Raman spectra of gaseous disilane and disilane-d6 as well as the Raman and infrared spectra of their crystalline solids at 20 K have been recorded from 25 to 3500 cm−1. Two quantum torsional transitions of the SiH3 moiety were observed at 233 and 251 cm−1 in the Raman spectrum of gaseous disilane. A barrier to internal rotation of 439±10 cm−1 (1.26 kcal/mol) has been calculated based on these frequencies. The crystalline modification of disilane at 20 K was shown to belong to the monoclinic space group P21/c≡C2h5. There are two molecules per unit cell each of which sits on identical Ci sites. The results of normal coordiante analyses of H3SiSiH3, H3SiNCO, and H3SiNCS are presented and the force fields obtained for the H3Si moieties are compared.
Primary reactions of localized electrons in rhamnose crystals studied by pulse radiolysis and ESR spectroscopy
Authors: Samskog P.-O. , Lund A. , Nilsson G. , Symons M. C. R.
Published: February 2003

The optical absorption spectrum of localized electrons in rhamnose crystals grown from H2O and D2O solutions has been obtained by means of pulse radiolysis. The absorption maximum is at 500 nm, the half-width is 250 nm, and εG=9000 M−1 cm−1 (100 eV)−1 at 293 K. The decay is first order. The rate constants at 293 K and the activation energies are 6.9×107 s−1 and 4.1 kcal/mol in the protonated crystal and 4.3×107 s−1 and 5.4 kcal/mol in the deuterated crystal. The assignment of the optical spectrum has been made by ESR. In the deuterated crystal irradiated and measured at 67 K the electron is trapped and characterized by a single easily bleachable line with g<2.0023. The electron reacts thermally to form a hydroxy alkyl radical at a convenient rate (t1/2?1 h) to be followed by ESR at 77 K in the deuterated compound. The reaction can also be induced by light with λ<700 nm. Reaction mechanisms and the isotope effect are discussed.
Auger spectra of alkanes
Authors: Rye R. R. , Jennison D. R. , Houston J. E.
Published: February 2003

The gas-phase Auger line shapes of the linear alkanes C1 through C6 and of neopentane are presented and analyzed. The general shape of the spectra are characteristic of carbon in a tetrahedral environment with the major feature in all cases occurring at ∼249 eV. The relatively large spectral changes found between methane and ethane results from the direct interaction of the terminal methyl groups in ethane, and the spectra of the higher alkanes are shown to be a composite of contributions from terminal methyl and interior methylene group carbon atoms. Theoretical analysis based on a one-electron approximation is shown to be capable of making a molecular orbital assignment by comparing calculated vertical transitions to features in the Auger spectra of ethane and propane, and, in the case of ethane, of differentiating between the 2Eg and 2A1g assignment of the ground state of (C2H6)+. A one-electron based molecular orbital treatment, however, is shown to partially break down in propane and neopentane. Analysis of neopentane and the observed absence of any noticeable major peak energy shift with increasing molecular size (as predicted by the one-electron treatment) suggests that some Auger final states occur in which both valence holes are localized on the same subunit of the molecule.
Line shape theory for two center cooperative radiative transitions
Authors: Velsko Stephan P. , Oxtoby David W.
Published: February 2003

We derive an expression relating the band shapes of simultaneous transitions to correlation functions involving the relative motions of pairs of molecules. The relationship between the line shapes of simultaneous transitions and the line shapes of the associated single molecule transitions is explored. We apply the theory to simultaneous vibrational transitions in liquids and gases and make suggestions for further experimental and theoretical work.
Statistical treatment of EPR data: The spectra of CF3 and F2NO in SF6
Authors: Morton J. R. , Preston K. F.
Published: February 2003

Isotropic hyperfine interactions and g factors have been determined by a generalized least-squares treatment of measurements made for the spectra of 12CF3, 13CF3, and 14NF2O, 15NF2O in an SF6 matrix. Statistical analysis of the results shows that the slight increase in the 19F hyperfine interaction, observed upon increasing the mass of the central atom, is significant at the 95% confidence level for both CF3 and NF2O. The effect is attributed to a vibrational modulation of the isotropic 19F hyperfine interaction which is dependent upon central-atom mass. Relative signs of the 19F and central-nucleus couplings have also been established for both radicals.
Di-iron and nickeliron
Authors: Moskovits M. , DiLella Daniel P.
Published: February 2003

Resonance Raman progressions assigned to Fe2 and NiFe isolated in solid Ar and Kr are reported. ωe″ and ωe″xe″ for the two molecules are found to be 299.6 and 1.4 cm−1 and 320.0 and 1.32 cm−1, respectively. In addition, an anti-Stokes progression of inordinate intensity was observed for Fe2. On the basis of a laser power study this was suggested to arise from consecutive two-photon absorption processes which are efficient in this case as a result of very long vibrational relaxation lifetimes of the excited vibrational states of the electronic ground state of Fe2. No spectrum of Fe2 was detected in either solid N2 or solid methane, supporting previous reports that Fe2 reacts with these substances to form complexes. With high resolution, each of the bands of the resonance Raman progression of Fe2 is observed to be a multiplet. Some of the multiplet structure results from the expected isotope effect but additional structure is seen because for a particular value of Δv″ there are transition with different initial values of v″.
Argon matrix photolysis and photoionization studies of benzene. Absorption spectrum of benzene cation and benzene dimer cation
Authors: Miller J. Houston , Andrews Lester , Lund Paul A. , Schatz Paul N.
Published: February 2003

Argon/benzene samples subjected to argon resonance photoionization during condensation at 21±1 K revealed a sharp new 552.5 nm product absorption, sharp C−2 bands and a broad 900 nm absorption. The 552.5 and 900 nm absorptions were destroyed and the C−2 bands decreased by mercury arc photolysis, which suggests that the 552.5 and 900 nm absorptions are due to molecular cations. The broad 900 nm absorption is in agreement with an earlier assignment to the intervalence transition in (C6H6)2+. Near agreement between the 552.5 nm absorption energy and the difference between the sharp origins for the first two benzene photoelectron bands invites consideration of the 552.5 nm absorption for C6H6+. A tentative assignment of the sharp, weak 552.5 nm band to the vibronically allowed 2E2g+e2u←2E1g transition of C6H6+ is in accord with deuterium isotopic shifts and predictions from the gas phase fluorescence spectra of fluorine substituted benzene cations. A strong 310 nm band system is attributed to the C6H7 radical which decreases on photolysis to give 288 and 534 nm absorptions that are assigned to the C6H5 radical.
Thermodynamics in finite time: Processes with temperature-dependent chemical reactions
Authors: Ondrechen Mary Jo , Andresen Bjarne , Berry R. Stephen
Published: February 2003

The thermodynamics of two chemical systems obeying Arrhenius law kinetics are studied from the viewpoint of finite time thermodynamics. The first is the determination of the maximum thermodynamic or chemical efficiency of a synthetic process whose heat input appears as preheating to overcome an activation barrier. The second is the determination of maximum power that can be obtained from an exothermic reaction carried out in a continuous flowsystem. The maximum power, achieved with a finite, nonzero flow rate, is a sensitive function of the activation energy of the reaction.
Optical absorption in solid ferric chloride: Implications for intercalated graphite
Authors: Kellerman R. , Ritsko J. J.
Published: February 2003

The optical absorption spectrum of anhydrous solid FeCl3 has been measured over the range 0.5–6 eV by diffuse reflectance spectroscopy. Features at 2.5, 3.65, and 5.25 eV are assigned to u→g charge transfer excitations. Other features at 1.1, 1.4, and 2.1 eV are assigned to g→g charge transfer (2.1 eV) and d–d (1.1, 1.4 eV) excitations. The contribution of FeCl3 to absorption in intercalated graphite compounds is indicated.
On rainbow scattering in inelastic molecular collisions
Authors: Thomas Lowell D.
Published: February 2003

The rainbow structure in the angular distributions of rotationally inelastic cross sections in inelastic molecular collisions are discussed. The possibilities of measurement of certain anisotropic features utilizing such rainbow structures is elaborated upon.(AIP)
Dissociation and exchange in collinear Br2+He,Xe collisions
Authors: Snider Neil
Published: February 2003

Reaction probabilities were calculated from classical trajectories for a collinear model of a bromine molecule colliding with a rare gas atom. For different rare gas atoms the probability for dissociation was found to differ markedly in its magnitude but not in its dependence on total energy E. On the other hand both the magnitude and the E dependence of the exchange probability were found to differ greatly for different rare gas atoms. The probabilities were used to calculate branching ratios Γ. Branching ratio is here taken to mean the rate of dissociation relative to the rate of exchange at the same temperature. The values of Γ obtained from the one-dimensional trajectories were found to be an order of magnitude smaller than the Γ’s obtained from three-dimensional trajectory calculations for the same model. The one-dimensional trajectory results were used to test the assumptions of an approximate theory whereby values of Γ in moderately good agreement with the three-dimensional trajectory results have been calculated without recourse to trajectories. The success of the approximate theory was found to be due to near cancellation of large errors arising from its individual underlying assumptions.
Polarizability calculations with the SCF method. IV. Various conjugated hydrocarbons
Authors: Zamani-Khamiri O. , Hameka H. F.
Published: February 2003

We calculate the third-order nonlinear electrical polarizabilities of a group of 16 conjugated hydrocarbon molecules with 8 to 14 carbon atoms by making use of the Pariser–Parr–Pople method. We find that the results are quite different from values that were derived previously from the Hückel method. The new values of the space-averaged third-order susceptibilities γ are all positive. The largest γ values are predicted for naphthoquinodimethane-2,6 and for the conjugated hydrocarbon chains, in particular, for tetradecaheptaene.
On the low lying singlet states of BeO
Authors: Bauschlicher Charles W. , Lengsfield Byron H. , Yarkony David R.
Published: February 2003

Using a Gaussian basis set of slightly better than double zeta plus polarization quality, MCSCF and CI calculations were performed for the ground and several low-lying singlet states of BeO. The computed separations for X, A, and B states are in good agreement with experiment. The 1Σ− and 1Δ states are predicted to lie ∼40 000 cm−1 above the X state, while the 2 1Π and 3 1Σ+ are predicted to lie 56 000 and 65 000 cm−1 above the X state, respectively.
Excited singlet electronic states of acetylene: c
i
s and t
r
a
n
s structures and energetics
Authors: So S. P. , Wetmore Ross W. , Schaefer Henry F.
Published: February 2003

Molecular electronic structure theory has been used to predict the equilibrium geometries and energies of acetylene in its excited singlet electronic states. A double zeta plus polarization basis set of contracted Gaussian functions was used in conjunction with self-consistent field and large scale configuration interaction wave functions. The first excited singlet state of acetylene is the trans 1Au state, in agreement with the experimental studies of King, Ingold, and Innes. This result is particularly interesting because the lowest triplet state of C2H2 is not the 3Au state but rather the cis 3B2 state. The predicted geometry of the ? 1Au state is re(CC)=1.384 Å, re(CH)=1.096 Å, ϑe(HCC)=121.7 °, in good agreement with available spectroscopic data. The predicted relative energies of the excited singlet states are 5.06 eV (1Au), 5.54 eV (cis 1A2), 6.87 eV (1B2), and 7.29 eV (1Bu). Thus the energetic ordering of the singlet states is Au<A2<B2<Bu, completely different from that predicted for the analogous triplets B2<Bu<Au<A2. Electronic structures are discussed in terms of Mulliken populations and dipole moments predicted for the two cis excited singlet states.
Quasidegenerate perturbation theories. A canonical van Vleck formalism and its relationship to other approaches
Authors: Shavitt Isaiah , Redmon Lynn T.
Published: February 2003

Three forms of quasidegenerate perturbation theory are discussed and compared in terms of a common general formulation based on a similarity transformation which decouples the model space and complementary space components of the Hamiltonian. The discussion is limited to formal, rather than many-body (diagrammatic), aspects. Particular attention is focused on a ’’canonical’’ form of van Vleck perturbation theory, for which new and highly compact formulas are obtained. Detailed comparisons are made with the Kirtman–Certain–Hirschfelder form of the van Vleck approach and with the approach based on intermediate normalization which has been used as the basis for most of the diagrammatic formulations of quasidegenerate perturbation theory.
Critical binding of electron–dipole rotor systems; electronically excited states
Authors: Garrett W. R.
Published: February 2003

Critical binding solutions for the electron–dipole rotor problem are extended to delineate the minimum dipole moments required to support the lowest two electronically excited dipole states. Such dipole states offer a source for threshold photodetachment resonances observed in recent studies involving polar anions.
Vibrations of potassium and cesium thiocyanates crystals. IV. Dispersion relations of lattice modes
Authors: Ti S. S. , Ra O/.
Published: February 2003

A dynamical calculation of the dispersion relations is reported for the orthorhombic crystals of potassium and cesium thiocyanates. A frequency discontinuity is found to occur across the zone center and is briefly explained. The behavior of a lattice mode at difference wave-vector values of a symmetry line and along the different symmetry lines is examined and observed to be appreciably different.
On the charge compensation mechanism in β-alumina
Authors: Wang J. C.
Published: February 2003

Possible charge compensation models for the excess conducting Na+ ions in β-alumina have been investigated with potential energy calculations. The cases studied include an artificial transfer of charge from Al3+ ions in the spinel block to Na+ ions in the conducting plane, the replacement of an Al3+ ion with three Na+ ions, the replacement of an Al3+ ion with a Mg2+ and a Na+ ion, and the interstitial oxygen model in which a VAl–Al–O–Al–VA1 defect compensates two extra Na+ ions. The results favor the last model.
Protonic species in H1.7MoO3
Authors: Taylor R. E. , Ryan L. M. , Tindall P. , Gerstein B. C.
Published: February 2003

The nature of hydrogen in H1.7MoO3 has been investigated with solid state nuclear magnetic resonance. Samples prepared utilizing wet chemical reduction of MoO3 in zinc and HCl, and dry hydrogen spillover on platinized MoO3 have been characterized by proton NMR with and without strong proton decoupling and magic angle spinning. The results of these experiments indicate that there are at least two types of protons in these ’’hydrogen molybdenum bronzes’’ with the relative amounts depending upon the method of preparation. The major protonic species in both samples exhibit a shielding anisotropy which negates its identification as a hydroxyl proton in a hydrogen bond or as a proton belonging to H2O undergoing rapid rotation at room temperature. The NMR spectra of protons in samples prepared by different methods are, in addition, distinctly different at 90 K. Photoelectron spectroscopy indicates that the molybdenum species in both types of samples are identical to within the resolution of the experiment.
Electronic spectra of butadiene and its methyl derivatives: A multiphoton ionization study
Authors: Rothberg L. J. , Gerrity D. P. , Vaida V.
Published: February 2003

The multiphoton ionization (MPI) spectra of trans-1,3-butadiene and three of its methyl substituted derivatives have been recorded using a tunable visible dye laser. The effect of methyl substitution on the electronic structure of butadiene is investigated, resulting in a reassignment of the spectra of these molecules. Quantum defects are found to be independent of principal quantum number, indicating little mixing between Rydberg and core orbitals. The validity of retaining conventional s, p, d, and f descriptions of Rydberg orbitals in these quasilinear molecules is demonstrated. Two electronic states of butadiene, assigned to the 3d and 4s Rydberg states, are observed for the first time in optical spectroscopy. No evidence for an excited 1Ag valence state is found in the MPI spectra.
Collisional relaxation of vibrational energy transients in the methylcyclopropane system. A variable encounter method study
Authors: Kelley D. F. , Kasai T. , Rabinovitch B. S.
Published: February 2003

The variable encounter method has been used to study vibrational energy transients in the isomerization of methylcyclopropane to various butenes. This system was studied with reactor surface temperatures of 800 to 1130 K and average numbers of collisions per encounter with the reactor of 5.6 and 20.0. The reaction rate was treated on the basis of total, rather than individual butene rates, because of butene product interconversion. An exponential model of energy transfer was found to fit to the data with the average down step energy 〈ΔE′〉 decreasing from 1860 to 1415 cm−1 with increase of temperature over the range studied. Incubation times increased from 14 to 19 collisions with increase in temperature, and these times, together with values of the conventional relative collision efficiency β and values of 〈ΔE′〉, are compared with those of other molecules studied by VEM. The calculated transient population distributions and the associated sequential reaction probabilities are also displayed.
Time-resolved study of intramolecular vibrational redistribution in p-difluorobenzene
Authors: Halberstadt N. , Tramer A.
Published: February 2003

Fluorescence spectra were studied for p-DFB vapors excited by 150 ps. pulses from a mode-locked Ar+ laser.(AIP)
Effect of van der Waals molecules on thermal electron attachment in some O2–hydrocarbon mixtures
Authors: Kokaku Yu-ichi , Toriumi Minoru , Hatano Yoshihiko
Published: February 2003

Thermal electron attachment in O2–M(M; C2H6, C3H8 and n-C4H10) mixtures has been investigated using a microwave conductivity technique combined with x-ray pulse radiolysis. Evidence is presented for predominant electron attachment to van der Waals molecules (O2⋅M) at higher pressures. The rate constant of electron attachment to (O2⋅M) is much larger than that to O2 itself. A discrepancy between our previous results at lower pressures and swarm experiment results at higher pressures is explained quantitatively by the van der Waals molecule mechanism.