bluuebunny/crossref_metadata_2025 huggingface dataset:
Crossed-beam investigation of translational energy effects in oxygen atom reactions
Authors: Clough P. N. , O’Neill G. M. , Geddes J.
Published: February 2003

The reactions of oxygen atoms with I2, CS2, and OCS have been investigated using crossed molecular beams, for two mean collision energies (∼5 and ∼30 kJ mol−1). The reaction O+I2→IO+I exhibits an unexpected change in behavior from long-lived complex formation at low energy to a backwards-scattering rebound mechanism at higher energy. Translational energy is very effective in overcoming the small activation barrier to the O+CS2→SO+CS reaction, but appears ineffective in promoting the analogous reaction O+OCS→SO+CO, which has a higher activation energy.
Transport properties of concentrated polymer solutions: Hydrodynamic screening theory of viscous friction in a suspension of spheres
Authors: Mou Chung Yuan , Adelman S. A.
Published: February 2003

A new hydrodynamic method for computing the transport properties of concentrated polymer solutions is proposed. The method is developed in detail for the case of N impermeable spheres of radius R suspended in a solvent of viscosity η0 and is applied in this paper to the calculation of the concentration, ρ0, dependent translational friction coefficient ζ[ρ0] of a typical sphere in the suspension. In the following paper the method is applied to compute the concentration dependent viscosity η[ρ0] of the suspension. The theory is based on the following key ideas. The microscopic steady state Navier–Stokes equation, which depends on the instantaneous N-sphere configuration, is reduced by averaging to a coupled hierarchy of effective hydrodynamic equations which depend, respectively, on the coordinates of 0, 1, 2,..., etc., spheres. The first member of the hierarchy, which governs the macroscopic flow, involves η[ρ0] and an inverse screening length κ, which accounts for screening of hydrodynamic interactions in the suspension. The parameters κ and η[ρ0] are found to depend upon the difference between local and macroscopic velocity fields and field gradients near a sphere. This difference is determined by solving the second equation in the hierarchy. The second equation is rendered tractable by a closure of the hierarchy which is tantamount to assuming that the flow with one sphere fixed is governed by the same screened hydrodynamics which describes the macroscopic flow. This mean field closure gives self-consistent equations for η[p0] and ζ[ρ0]. For the case that the spheres are modeled as point perturbers, solution of the self-consistency problem yields at low concentrations ζ[ρ0] =6πη0R[1+4.5φ], where φ=4πρ0R3/3 is the volume fraction of the solute. For a realistic treatment of the finite size of the spheres which includes excluded volume effects and the effect of local velocity gradients, one finds at low concentrations ζ[ρ0] =6πρ0R[1+6.769 φ]. This result is in good agreement with the two sphere calculations of Pyun and Fixman, who find ζ[ρ0] =6πη0R[1+6.157φ]. At higher concentrations, the results for ζ[ρ0] are in fair agreement with results derived from sedimentation experiments. The discrepancy between theory and experiment is attributed to neglect of attractive forces between the spheres and neglect of the concentration dependence of the sphere–sphere correlation functions.
Transport properties of concentrated polymer solutions: Hydrodynamic mean field theory of the viscosity of a sphere suspension
Authors: Mou Chung Yuan , Adelman S. A.
Published: February 2003

The hydrodynamic mean field theory of the preceeding paper [C. Y. Mou and S. A. Adelman, J. Chem. Phys. 69,xxx(1978)] is applied to analytically calculate the concentration ρ0 dependent viscosity η[ρ0] for a suspension of spherical particles of radius R. One finds that η[ρ0]=η0[1+5/2φλ], where η0 is the solvent viscosity, φ=4π/3 ρ0R3 is the solute volume fraction, and where λ=2/3φ−1{5/2φ−1+[(1−5/2φ)2 +3φ]1/2}. To order φ2, η[ρ0]=η0[1+5/2φ +K (5/2φ)2] where the order φ term is the Einstein shift and where the Huggins constant K=0.70. This result for K is in good agreement with previous theoretical estimates. The full form of η[ρ0] is compared with the experimental results of Cheng and Schachman for 2700 Å polystyrene latex spheres. Agreement between theory and experiment is fair. The discrepancy is attributed to neglect of concentration dependence in the sphere–sphere pair correlation functions and neglect of attractive intermolecular forces in the present theory.
Molecular beam photoionization study of acetone and acetone-d6
Authors: Trott Wayne M. , Blais Normand C. , Walters Edward A.
Published: February 2003

High resolution photoionization efficiency curves have been obtained for CH3COCH3+ and CD3COCD3+ using supersonic molecular beam sampling. As a result of adiabatic cooling during the nozzle expansion, sufficient concentrations of (CH3COCH3)2, (CD3COCD3)2, (CH3COCH3)3, and (CH3COCH3)4 were formed to permit the study of their photoion yield curves as well. Appearance potential curves have been determined for CH3CO+, CD3CO+, and (CH3COCH3) ⋅CH3CO+ fragments. The measured ionization potentials of acetone and acetone-d6 monomers are 9.694±0.006 and 9.695±0.006 eV, respectively. Transitions to higher vibrational levels in CH3COCH3+ are seen at 320, 695, and 930−1370 cm−1 above threshold. The effect of perdeutero substitution is to reduce these frequencies to 260 and 660–1100 cm−1. Appearance potentials of CH3CO+ and CD3CO+ fragments are observed at 10.52±0.02 and 10.56±0.02 eV, respectively. The measured ionization energies for (CH3COCH3)n, n=1–4, are found to decrease linearly as a function of 1/n. Observed ionization thresholds for (CH3COCH3)2, (CH3COCH3)3, and (CH3COCH3)4 are 9.26±0.03, 9.10±0.03, and 9.02±0.03 eV, respectively. Within experimental resolution, the ionization potentials of (CH3COCH3)2 and (CD3COCD3)2 are identical. The appearance potential of the process (CH3COCH3)2 → (CH3COCH3) ⋅CH3CO++CH3+e− is found to be 10.08±0.05 eV. By consideration of appropriate thermodynamic cycles, a lower bound for the acetone dimer ion binding energy is calculated to be 0.538 eV (12.4 kcal/mole) and the desolvation energy of (CH3COCH3) ⋅CH3CO+ is estimated to be 0.544 eV (12.5 kcal/mole).
X-ray and neutron diffraction study of liquid antimony trichloride at 80°C
Authors: Triolo R. , Narten A. H.
Published: February 2003

X-ray and neutron diffraction experiments with liquid SbCl3 at 80°C are described and discussed. The liquid consists of discrete molecules with an Sb–Cl distance of 2.35 Å and a Cl–Sb–Cl angle of 96°. The diffraction data are analyzed to yield structure functions for intermolecular atom pair interactions. The radial distribution functions obtained from these curves yield directly some valuable insight into the nature of the strong spatial correlations present in liquid SbCl3.
Sensitized phosphorescence studied by the site selection technique
Authors: Fünfschilling J. , Wasmer E. , Zschokke-Gränacher I.
Published: February 2003

Sensitized phosphorescence of 1-iodonaphthalene (energy donor) and perfluorated naphthalene (energy acceptor) has been studied in solid solutions at 4.2 K. The donor is excited by a laser in a site selection experiment. We observe that the site selection is conserved during the triplet energy transfer. This is consistent with a modification of Dexter’s theory of sensitized phosporescence that includes the site energy distribution of the donor and acceptor molecules.
Velocity dependence of the absolute cross sections for the chemi-ionization of Ar, Kr, and Xe on impact of 21S and 23S helium atoms
Authors: Woodard M. R. , Sharp R. C. , Seely Mikell , Muschlitz E. E.
Published: February 2003

Measurements of the velocity dependence of the absolute cross sections for the chemi-ionization of Ar, Kr, and Xe on impact of thermal energy metastable helium atoms in the relative velocity range 1–3 km sec−1 have been made using a single velocity-selected beam, collision-chamber method. Separate measurements for both 23S and 21S helium atoms are obtained through the use of a He discharge lamp to quench the singlets from the beam. The metastable atom electron ejection efficiencies are separately measured in the same apparatus. The results are compared with the relative measurements of other workers. The constants are evaluated in a two-parameter exponential function representing the coupling width for decay of the discrete electronic state of the incoming channel into the continuum electronic state of the outgoing channel, which give the best fit to the experimental data for the He* (23S) –Ar and He* (23S) –Kr systems.
Statistical thermodynamics of phase equilibria in microemulsions
Authors: Talmon Yeshayahu , Prager Stephen
Published: February 2003

The statistical thermodynamics of microemulsions is investigated on the basis of a model which represents microemulsion structure as a random geometry of interspersed oil and water domains generated by a Voronoi tesselation, with the surfactant adsorbed at the boundary. The resulting one-parameter free energy function predicts two- and three-phase equilibria bearing a strong resemblance to experimental observations on certain alkyl aryl sulfonate–oil–brine microemulsion systems.
Potential energy of Ag+ ion in RbAg4I5
Authors: Takeuchi T. , Choi Sagn-il
Published: February 2003

The potential energy of a silver ion along possible paths in RbAg4I5 has been calculated. The calculation includes the interaction of a silver ion with point charges and dipole moments of the fixed framework ions (Rb+’s and I−’s) has well as the Born–Mayer repulsive potential energy. The potential energy barriers and vibrational frequencies along the paths are found to be in reasonable agreement with available experimental data.
Calculation of intermolecular exchange potentials using the Bonham series representation of the Born–Oppenheimer exchange amplitude
Authors: Huo Winifred M.
Published: February 2003

Using the Bonham series representation of the Born–Oppenheimer exchange amplitude, three approximations to the exchange integral are deduced, the electron gas approximation, the constant 〈Q2〉 approximation, and a nonlocal approximation. In the second approximation the kinetic energy operator is replaced by its expectation value and the exchange integral is reduced to a multicenter overlap integral. The nonlocal approximation involves a simple ’’interactionless’’ Green’s function and the exchange integral is again reduced to the sum of multicenter overlap integrals, except that the wavefunctions involved are distorted by the operation of the Green’s function. Both the constant 〈Q2〉 and the nonlocal approximation have the advantage of expressing the exchange integral as an analytic function of the intermolecular separation and are particularly suited for the study of anisotropy of intermolecular potentials. Calculations of the exchange potential between 1sA–1sB and 1sA–2pσB have been carried out to test the validity of these methods. The most reliable R dependence is provided by the nonlocal approximation. The singlet–triplet splitting of the 1sA–2pσB pair is also studied. The anisotropy and asymptotic behavior of the splitting are deduced.
Kinetic theory of reactive pair dynamics in liquids
Authors: Shin K. J. , Kapral Raymond
Published: February 2003

The kinetic theory of chemical reactions in dense fluids is extended to calculate the dynamics of a reactive pair of particles. Given an initial pair distribution, the probability that the pair of particles will remain unreacted is calculated. Explicit solutions are obtained by taking into account repeated ring events and the results are shown to be a generalization of Fick’s law calculations for this problem. Other classes of dynamical events which lead to a coupling of the diffusive motion of the pair are examined in a more formal way and their physical significance is discussed. The applicability of the theory to the analysis of recombination reactions in liquids is discussed.
Fluctuations at chemical instabilities
Authors: Mangel Marc
Published: February 2003

We consider the effects of fluctuations on chemical systems that have multiple steady states. The systems of interest have two stable steady states and one unstable steady state (a kinetic saddle point). As parameters vary, two or three of the steady states coalesce. We consider experiments beginning near the deterministic separatrix and formulate a stochastic first exit problem. The deterministic separatrix is surrounded by a band. We calculate the first exit probability u (x) and mean exit time T (x) from this band, conditioned on initial position. Fluctuation formalisms connecting the Langevin equation and deterministic kinetic equations are discussed. We use the diffusion approximation so that u (x) and T (x) satisfy (backward) diffusion equations. Approximate solutions of the diffusion equations are constructed by an asymptotic method that involves various incomplete special functions. Two applications are discussed: (1) the spontaneous asymmetric synthesis model of F.C. Frank; (2) fluctuation effects on substrate inhibited reactions in open vessels.
Electron attachment and compound formation in flames. VII. Electron attachment in flames containing phosphorus and potassium
Authors: Miller William J.
Published: February 2003

The addition of phosphorus to a series of potassium-seeded H2/O2/N2 flames results in the formation of negative ions accompanied by a decrease in free electron concentrations. The ions have been identified mass spectrometrically as PO2−. Equilibrium constants for the reaction HPO2+e=PO2−+H have been measured by determining the ratio [PO2−]/[e] in four flames of known temperature and composition. Analysis of the results via both second and third law methods yields ΔH °298=−6.1±6 kcal mole−1 for the above reaction and ΔHf,298 (PO−2) =−146 ±6 kcal mole−1. The electron affinity of PO−2 from these results is 85±6 kcal mole−1 (3.7±0.3 eV).
Spectra and structure of small ring compounds. XXXIX.a) Barrier to interconversion in selenacyclopentane
Authors: Durig J. R. , Natter W. J.
Published: February 2003

The Raman spectrum of selenacyclopentane in the gaseous phase was observed from 25 to 4000 cm−1. A series of Q branches at 231, 238, and 244 cm−1 has been assigned to transitions of the radial ring mode of an extremely hindered pseudorotator with a planar intermediate. Based on their relative intensities, these bands have been assigned as the 1←0, 2←1, and 3←2 radial transitions, respectively. For the two out-of-plane ring modes, we have calculated a potential surface of the form V (q,φ) =Aq4 +Bq2+Cq2 cos2φ+Dq4 cos2φ+Eq4 cos4φ. The barrier to planarity for the twisted conformer is found to be of the same order as in one-dimensional treatment.
Homogeneous nucleation in associated vapors. II. Formic and propanoic acids
Authors: Russell Yvonne G. , Heist Richard H.
Published: February 2003

Homogeneous nucleation measurements have been made on formic and propanoic acids. The temperature dependence of the critical supersaturation was measured and found to agree well with that predicted by the Katz–Saltsburg–Reiss theory for nucleation in associated vapors.
Charge transfer in graphite nitrate and the ionic salt model
Authors: Loughin S. , Grayeski R. , Fischer J. E.
Published: February 2003

Fractional charge transfer is studied from both chemical and electronic property standpoints in graphite intercalated with nitric acid. NO2 byproduct is analyzed quantitatively by optical absorption, and H2O byproduct is observed qualitatively, consistent with 2HNO3 →N2O5+H2O; N2O5→NO2+ (oxidizes graphite) + NO3− (intercalates). The compond is found to contain one NO3− per four neutral HNO3. Metallic reflectivity data is consistent with one free hole per 5 total intercalated entities, indicating that each charge transferred from graphite to acid results in a free hole, as required by the ionic salt model.
Quantum dynamics of the F+H2 reaction: Resonance models, and energy and flux distributions in the transition state
Authors: Latham Susan L. , McNutt Joe F. , Wyatt Robert E. , Redmon Michael J.
Published: February 2003

Theoretical analysis is provided of quantum collinear scattering calculations on the F+H2 reaction. Modeling the 0→2 and 0→3 reaction probability curves by altering the vibrational energy correlation diagram illustrates the significance and necessity of wells in the v=2 and v=3 potential curves. Variation of the average vibrational energy and vibrational entropy in the interaction region clarifies the function of temporarily populated high lying vibrational levels during the reaction. Maps showing the probability density, flux, and phase of the scattering wavefunction clearly depict the quantum nature of the reaction dynamics. The vibrational entropy and average vibrational energy increase dramatically in the region of the potential surface where multipole quantum whirlpools are formed.
Calculation of ir band profiles of diatomic molecules dissolved in liquids
Authors: Sanctuary B. C. , Richon Dominique
Published: February 2003

Using a memory function approach, ir band profiles are calculated for diatomic molecules dissolved in a solvent of orientable molecules. The motivation is to extract the solvent correlation function from the solute spectrum. The approach is tested by fitting the theory to experimental data for CO and DCl. The agreement is encouraging, indicating that theory should provide a basis for testing models for liquid dynamics.
Universal basis sets for electronic structure calculations
Authors: Silver David M. , Wilson Stephen
Published: February 2003

The concept of a ’’universal’’ basis set for electronic structure calculations is explored by presenting energy results obtained when basis sets are transferred from one atom to another. The calculations are performed using the diagrammatic techniques of many-body perturbation theory. A single universal basis set is shown to give uniformly accurate descriptions of the matrix Hartree–Fock and correlation energies of the He, Be, and Ne atoms.
Low-energy electron interactions with organic molecules: Negative ion states of fluorobenzenes
Authors: Frazier J. R. , Christophorou L. G. , Carter J. G. , Schweinler H. C.
Published: February 2003

An electron transmission technique has been employed to determine the positions of the three π-negative ion states (configurations π12π22π23π41, π21π22π23π15, and π21π22π23π16) of benzene and fluorobenzenes in the vapor phase. These are 1.13 (1.35), 1.13 (1.35), (4.80) eV for benzene; 0.82 (0.91), (1.40), (4.66) eV for fluorobenzene; 0.53 (0.62), (1.41), (4.51) eV for p-difluorobenzene; (0.77), (0.77), (4.48) eV for 1,3,5-trifluorobenzene; 0.34, (0.50), (1.29), (4.51) eV for 2,3,5,6-tetrafluorobenzene; <0.15 (0.36), (1.19), (4.53) eV for pentafluorobenzene; and (0.42), (0.42), (4.50) eV for hexafluorobenzene. The numbers in parentheses are the vertical attachment energies, and those not in parentheses are the 0→0 transitions. On the basis of these data, the first π-electron affinities (E.A.) of the isolated molecules of these compounds are equal to −1.13, −0.82, −0.53, ≳−0.77, −0.34, ?−0.15, ≳−0.42 eV for benzene, fluorobenzene, difluorobenzene, 1,3,5-trifluorobenzene, 2,3,5,6-tetrafluorobenzene, pentafluorobenzene, and hexafluorobenzene, respectively. The present results, therefore, suggest that the π-electron affinity of C6F6 is <0.0 eV, although C6F6 is known to have a positive (+1.8 eV) E.A. and although the parent ion, C6F6−*, is known to form with a very large electron attachment cross section at ∼0.0 eV and to be long lived (∼12 μsec). These findings are reconciled, discussed in connection with previously published data, and are theoretically treated. They extend our understanding of the negative ion states of substituted benzenes.
Tunable laser photodissociation of HgI2: Quantum yield for formation of excited I(5 2P1/2) atoms
Authors: Hofmann Hubert , Leone Stephen R.
Published: February 2003

Tunable laser, infrared fluorescence techniques are used to study the detailed photodissociation dynamics of the linear triatomic molecule HgI2. The quantum yield of excited I(5 2P1/2) atoms has been measured in the first long wavelength absorption band of HgI2 from 265 to 320 nm. From quantitative measurements of the yield of excited I atoms, it is shown that the total absorption cross section in this region is actually composed of two distinct components. These components correspond to states leading to both excited and ground state I atoms according to the processes HgI2→HgI+I or I*. From the time decay of the excited I* atoms as a function of HgI2 pressure, the collisional deactivation rate of I* by the parent HgI2 molecule has been obtained. This quenching rate constant is 4.5±0.2×10−10 cm3 molecule−1 s−1 at T=453 K, which is essentially a gas kinetic rate.
An ESR study of x-irradiated diacetylene single crystals at 77 K
Authors: Hori Y. , Kispert L. D.
Published: February 2003

Single crystal monomers of the bis(p-toluene sulfonate) ester of 2,4-hexadiyne-1,6-diol x irradiated at 77 K give rise to an intense ESR spectrum at 77 K consisting of triplets of doublets of doublets. The principal hyperfine tensor components of the triplet equal 19.7, 15.7, and 13.1 G, while the hyperfine tensor components of the doublets are equal to (4.5, 3.2, 2.6 G) and (3.2, 2.5, 2.0 G), respectively. The principal g values are equal to 2.0020, 2.0023, and 2.0029. Based on an INDO calculation the ESR spectrum appears to be due to the radical (oligomer) –C(CH2OR′) –C=C=C=CH2OR′. A small concentration of a triplet species was also observed.
Optical time of flight spectroscopy: A method for the direct state selective measurement of photofragment recoil energies
Authors: Campbell J. D. , Yu M. H. , Mangir M. , Wittig C.
Published: February 2003

The ir photolysis of C2H3CN, producing C2[a 3πu(v=0)] via sequential photodissociation processes, is studied using laser induced fluorescence to measure the time of flight spectrum of the recoiling C2 photofragments. This technique measures the recoil velocity distribution for particular energy states, and can be applied to the study of a number of elementary processes. The average recoil energy of the C2 photofragment is 1.1±0.3 kcal/mole, and this includes contributions from recoil along the reaction coordinate as well as rotational motion in the precursor.
Simple molecular orbital treatment of diatomic force constants
Authors: Zerner Michael C. , Parr Robert G.
Published: February 2003

From the molecular orbital theory for diatomic molecules, the virial theorem, and the Heisenberg equation of motion, expressions are derived for off-diagonal matrix elements of the one-electron Hamiltonian for a limited basis set of atomic orbitals that display exact zero differential diatomic overlap. The resulting expressions are combined to yield analytic equations for the force constants ke and higher derivatives of the diatomic potential energy surface. These expressions depend only on the density matrix of a single calculation near enough to the equilibrium geometry. Under the approximation that all nonvanishing Coulomb interactions are given by classical electrostatics, a simple formula for the force constant is obtained which has mean square error of 3% for a number of first- and second-row diatomic molecules. If reasonable approximations are made for the density matrix and the equilibrium separation Re is estimated by a ’’tangent sphere’’ model, the following simple equations are obtained: keR3e=η/2(1+nAζB+nBζA) (two atoms with an s,p basis), keR3e=η/2[1+nbζa +1/2ζb(na+ζa)] (hydrides), keR3e=η/2[1+1/2(nAζB+nbζA)] (hydrogen molecule).

Here, η is the number of bonds, n the principal quantum number, and ζ the orbital exponent of the valence electrons as, for example, given by Slater’s rules. These equations yield predictions generally within ±10% of the experimental values.
The cyanide stretching vibrations in 1−D tetracyanoplatinate conductors
Authors: Ferraro John R. , Basile Louis J. , Williams Jack M. , McOmber J.I. , Shriver D. F. , Greig D. R.
Published: February 2003

The Raman spectra and infrared spectru of 1−D tetracyoursplatinate conductors is discussed.(AIP)
R-matrix solution of coupled equations for inelastic scattering
Authors: Stechel Ellen B. , Walker Robert B. , Light John C.
Published: February 2003

The R-matrix propagation method for solving the close coupled equations for inelastic scattering is presented. The method is shown to be fast, accurate, and stable without the need for stabilizing transformations. We demonstrate the use of this method for two model close coupling problems, and investigate the rate of convergence of the solutions.
An analytic function describing the H+C2H4?C2H5 potential energy surface
Authors: Hase William L. , Mrowka Gerald , Brudzynski Richard J. , Sloane Christine S.
Published: February 2003

A b initio SCF calculations, using the unrestricted STO-3G and 4-31G approximations, were carried out to determine the minimum energy path for H-atom addition to ethylene, the angular width of the H-atom addition entrance channel, and the reaction path for H-atom migration between the carbon atoms. The accuracy of the calculations is discussed. Using spectroscopic, thermodynamic, and the ab initio information, an analytic function is derived for the H+C2H4? potential energy surface. The analytic function is highly flexible and can be adjusted to fit more accurate quantum mechanical results as they become available.
Adiabatic polarization potentials for electron scattering by N2 and CO
Authors: Truhlar Donald G. , Van-Catledge F. A.
Published: February 2003

Interaction potentials including effects of target charge polarization by the incident electron are calculated for electron scattering by N2 and CO. The method used is molecular orbital theory with intermediate-neglect-of-differential overlap (a modified INDO/1s calculation). The calculations provide new insight into the shape and anisotropy of the potential.
Spin-dependent magneto-optical rotation for free radicals and for singlet–triplet transitions
Authors: Brown Samuel H. , Chiu Ying-Nan
Published: February 2003

Magneto-optical (Faraday) rotation of free radicals involving spin-forbidden singlet-triplet transitions is investigated. To facilitate the transition unusual spin-dependent radiative transition operators are used. These operators for polarized light are derived from the Breit–Pauli approximation to the Dirac’s relativistic theory. A comprehensive list (Sec. I) of them are given along with their origin, meaning, and derivation (Appendix). The general formula for self-interference or mutual interference among these transition operators to give rise to optical rotation is given [Eqs. (6) and (7)]. Specific attention is given to the largest three spin-radiative operators arising from the field–field interaction between the radiation field and (1) the field due to spin–own-orbit interaction H6, (2) the field of spin magnetic quadrupole H8, and (3) the correction term for small spinor components H9. It is shown (Sec. III) that the self interference of H6, H8, and H9 gives rise to temperature-dependent magneto-optical rotation where the magnetic field is manifested through the energy difference between the magnetic spin sublevels in an external field (Tables I and II). Similarly it is shown (Sec. IV) that the mutual interference between spin–orbit-assisted electric-dipole transition operator H1 and H6, H8, H9 will also give a temperature-dependent Faraday effect (Tables III and IV). However, when the operator H4 for direct radiative interaction with external magnetic field is introduced, it is shown (Sec. V) that the interference of spin–orbit-assisted H4 with H6, H8, and H9 will give rise to temperature-independent Faraday effect (Table V). Most of these effects are operative in oriented as well as in random molecular systems and all do not require the molecule to be spatially inherently asymmetric. Formulas for these new terms given in Tables (I–V) may be compared with the known formulas of Kramers and Hougen rederived by using the present formalism (Sec. II).
Bifurcation analysis of nonlinear reaction–diffusion systems: Dissipative structures in a sphere
Authors: Billing Gert Due , Hunding Axel
Published: February 2003

The steady state spatial patterns arising in open nonlinear reaction–diffusion systems beyond an instability point of the thermodynamic branch are studied for a simple kinetic scheme derived from glycolysis. Bifurcation theory is used to derive analytic expressions for patterns within a sphere. The results indicate that a gradient of substance may arise spontaneously from a homogeneous distribution within a cell or a blastula, thus establishing a prepattern. Finally, the derived solution scheme is shown to simplify considerably if rotation matrices are introduced into the formalism.
Electronic spectroscopy of 1,3,5,7-cyclooctatetraene by low-energy, variable-angle electron impact
Authors: Frueholz Robert P. , Kuppermann Aron
Published: February 2003

The electron-impact energy loss spectrum of 1,3,5,7-cyclooctatetraene has been measured at electron impact energies of 30, 50, and 75 eV, and scattering angles varying from 5° to 80°. Three transitions with maxima at 3.05, 4.05, and 4.84 eV are identified as singlet → triplet excitations. The significance of the lowest lying of these triplet states in the quenching process of dye laser solutions (in particular rhodamine 6G) is discussed and an exciplex mechanism for triplet quenching is suggested. Singlet→singlet transitions are observed at 4.43, 6.02, and 6.42 eV. These spin-allowed transitions have been observed optically and are assigned as ? 1A1 →1A2, ? 1A1→1E, and ? 1A1→1E excitations. Three new, singlet → singlet transitions are observed at 6.99, 8.41, and 9.05 eV and are tentatively assigned as the ? 1A1→1B2, ? 1A1→1E, and ? 1A1 →1E, π→π* excitations. Several superexcited features between 10 and 15 eV have been observed and are believed to involve excitations to autoionizing Rydberg states.
Photofragment spectroscopy of ozone in the uv region 270–310 nm and at 600 nm
Authors: Fairchild C. E. , Stone E. J. , Lawrence G. M.
Published: February 2003

Both O(3P) and O(1D) atom fragments are observed in the photofragment spectroscopy of O3 in the Hartley band absorption region 270–300 nm. The quantum yield for O(3P) is 0.1 at 274 nm. The dissociation partner for O(3P) is O2(X3Σ−g) and that for O(1D) is O2(a 1Δg). The O2(X 3Σ−g) fragment is populated in a range of vibrational levels, v?0−10. For the O2(a 1Δg) fragment, all energetically accessible vibrational levels are populated at each energy of bombardment. In the Chappuis bands at 600 nm the O2(X 3Σ−g) photofragment is produced principally with v=0, 1. Photofragment angular distributions are measured in the uv for both O atom dissociation products at each wavelength of bombardment. A theoretical angular distribution for O(1D) is derived and the resultant prediction is in good agreement with the experimental results.
Polarized fluorescence spectrum of triphenylene in a n-heptane single crystal. Evidence for deformed molecules
Authors: Lamotte Michel , Risemberg Salomon , Merle Anne-Marie , Joussot–Dubien Jacques
Published: February 2003

The polarized fluorescence spectrum of triphenylene as a guest in a n-heptane single crystal has been studied at 4 K. The transitions in the fluorescence spectrum are analyzed in terms of known ir and Raman active vibrations in the ground state. A small matrix induced deformation of triphenylene, leading to an in-plane change of geometry is proposed. Polarization data are analyzed in terms of this model.
Chemisorption of CO on (101̄1) titanium studied by XPS, UPS, FDMS, and AIB
Authors: Fukuda Yasuo , Lancaster Gerald M. , Honda Fumihiro , Rabalais J. Wayne
Published: February 2003

Chemisorption of CO on the clean (101̄1) face of a titanium single crystal has been investigated by the techniques of x-ray and uv photoelectron spectroscopy (XPS and UPS), flash desorption mass spectrometry (FDMS), and active ion bombardment (AIB). CO is dissociatively chemisorbed at room temperature to form oxide- and carbidelike species. The (101̄1) face of Ti is very active; the sticking probability for CO is unity below 0.6 L (1 L=10−6 Torr sec) and the surface is saturated at 2 L exposure. Approximately 1% of the chemisorbed CO is desorbed upon heating to 300°C by a mechanism which does not follow simple first-order kinetics. The C and O remaining on the surface at 300°C form titanium carbides and oxides which migrate into the bulk of the crystal between 300 and 500°C. AIB with 500 eV CO+ produces carbides and oxides that are identical to the species on the surface at 300°C. High kinetic energy AIB results in complete dissociation of the CO+ into atoms, thus confirming that chemisorbed CO is dissociated on the (101̄1) face of Ti.
Velocity dependence of angular distributions in gas/solid–surface collisions: Relationship to the interaction potential
Authors: Brady John W. , Doll J. D. , Thompson D. L.
Published: February 2003

The angular and velocity distributions for gas/solid-surface collisions are examined. It is shown that the envelope of the scattered phase-space distribution is quite sensitive to the gas/surface interaction potential.
Raman spectroscopic studies of the OH stretching region of low density amorphous solid water and of polycrystalline ice Ih
Authors: Sivakumar T. C. , Rice Stuart A. , Sceats Mark G.
Published: February 2003

Extensive experimental studies of the OH stretching region of the Raman spectra of polycrystalline ice Ih and low density amorphous solid water (H2O (as)) are reported. Analysis of these spectra, using insights from theoretical calculations, leads to the following conclusions: (i) The overall span and distribution of features in the spectra result from strong intermolecular coupling of OH oscillators. This coupling is so strong that the solids cannot be considered to be composed of weakly perturbed water molecules, and the identification of features of their spectra with molecular vibrations is not useful. (ii) At the low end of the OH stretching region there is a totally symmetric mode—that is the amplitudes of motion on all oscillators are in phase, but these amplitudes vary erratically from site to site in the solid. The temperature dependence of the shift in frequency of this mode is likely all accounted for by thermal expansion, the temperature dependence of its FWHM is accurately described as due to scattering by optical phonons with effective frequency 200 cm−1. (iii) The earlier proposed interpretation of the Raman spectrum of H2O(as) by Venkatesh, Bates and Rice [J. Chem. Phys. 63, 1065 (1975)] is withdrawn. Their interpetation was based on the assumptions that they had observed the spectrum of high density H2O (as), which we now believe to be incorrect, and that the solid could be considered an assembly of weakly perturbed water molecules, which we now believe to be untenable.
Reactive cross section as a function of collision energy. I. H(D)+Br2→HBr(DBr)+Br
Authors: Hepburn J. W. , Klimek D. , Liu K. , Polanyi J. C. , Wallace S. C.
Published: February 2003

Reactive scattering cross sections are measured for H(D)+Br2→HBr(DBr)+Br by crossing a beam of hydrogen atoms with a beam of Br2.(AIP)
Infrared spectra from 300 to 10 cm−1 of structure II clathrate hydrates at 4.3 °K
Authors: Bertie John E. , Jacobs Stephen M.
Published: February 2003

The far infrared transmission spectra of the structure II clathrate hydrates of cyclopropane, oxetane, 1,3-dioxolane, tetrahydrofuran, and cyclobutanone at 4.3, 50, and 100 °K have been recorded. The features have been assigned to translational vibrations of the water molecules and rotational vibrations of the enclathrated guest molecules. The ring puckering vibration of cyclobutanone may contribute to the spectrum, but no evidence was seen of that of oxetane. The density of translational vibrational states of the water molecules is similar to, but shows more pronounced features than, that of the structure I hydrates. The force constants for rotational displacements of the guest molecules arise mainly from steric forces, as is the case in the structure I hydrates. The force constants for 1,3-dioxolane are anomalously high in spite of the fact that the Arrhenius activation energy for reorientation of 1,3-dioxolane in the hexakaidecahedral cage is not.
The free energy of vacancy pairs
Authors: Cook Robert , Shuldiner Alan
Published: February 2003

The configurational free energy change ΔA2/kT associated with the introduction of pairs of vacancy defects into a two-dimensional triangular lattice with nearest neighbor interactions is calculated by lattice dynamics in the classical high temperature limit. It is found that second and third nearest neighbor vacancies yield the greatest decrease in the free energy.
Diffusion of F− ions in CaF2
Authors: Jacucci G. , Rahman A.
Published: February 2003

It is shown that in a recently reported model of the dynamics of CaF2, the decay with time of the Fourier transform, 〈exp(ik⋅u(t)) 〉, of u(t), the F− displacement, for various wave vectors k can only arise from diffusive motion occurring between the simple cubic anion sites of the fluorite structure. Most of the jumps (∼80%) occur between near neighbor sites (i.e., they are in the 100 direction). The motion of F− ions can be understood in terms of a spontaneous creation of anti-Frenkel pairs which diffuse and eventually get annihilated. At the temperature of this calculation (1590 K) the average number of such pairs at any instant is found to be 7.9 in an assembly of 216 anions. A detailed breakdown of the nature of various types of atomic jumps arising out of the dynamics of these pairs is also presented.
F and G intensity sum rule applications: the CHxD4−x molecules
Authors: de Barros Neto Benício , Bruns Roy E.
Published: February 2003

Numerical analyses based on the F and G intensity sum rules show that recently published experimental values for the fundamental vibrational intensities of CH4, CH3D, CH2D2, CHD3, and CD4 are internally consistent within experimental errors. Effective charge values for the carbon and hydrogen atoms obtained using the intensity sums for all these isotopically related molecules are almost in exact agreement with reported values obtained from the polar tensors of CH4 and CD4. The G sum rule allows a determination of the signs of the dipole moment derivatives using the fundamental intensity sum for CH4 (or CD4) and the polar tensor values for CD4 (or CH4).
Relation of the Lauer–Fong formula to the SCC model: Application to Sm+2 5d?5D crossovers
Authors: Fonger W. H. , Struck C. W.
Published: February 2003

In single-h/ω models in any number of coordinates, the transition nuclear factor is known to be the Huang–Rhys–Pekar Wp function for the operator 1 and certain combinations of Wp functions for the operators z and ∂/∂z. Since Wp satisfies a linear recursion formula, the z and ∂/∂z combinations can be written in different but equivalent ways. The Wp functions in these nuclear factors can be approximated under Poisson b1 and Stirling conditions (both defined in text). The Lauer–Fong formula is the ∂/∂z-operator rate for the one-coordinate model (equal-force-constants SCC model) with the Wp combination written in a particular 5-Wp form and with the five Wp functions Stirling approximated. The Fong–Wassum formula is the analogous formula under Poisson b1 conditions. The application of the Lauer–Fong formula to the quenching of Sm+2 5D states in KCl, SrF2, BaBr2, and BaCl2 is re-examined. A necessary correction is made which increases the transition electronic factors for Sm+2 5d?5D nonradiative crossovers by four orders of magnitude.
Optical and dielectric functions of liquid glycerol from gas photoionization measurements
Authors: Birkhoff R. D. , Painter L. R. , Heller J. M.
Published: February 2003

In the vacuum ultraviolet spectral region, all solids strongly absorb electromagnetic radiation. Thus, optical properties of liquid surfaces must be obtained from reflectance measurements on a sample exposed to near vacuum rather than from a conventional closed-cell arrangement. In the first application of a new reflectance method which measures photon intensities before and after reflection by gas ionization, we have redetermined the optical functions of glycerol. The new data agree generally with those published before in the region of overlap and extend to a higher energy, 24.4 eV. Although the reflectance between 12 and 18 eV is slightly higher than reported previously, the interpretation of dielectric data calculated from the reflectance is unaltered. The plasmon energy now appears to the at 22 eV instead of the value of 20.4 eV measured earlier.
7Li NMR study of a co-ionic conductor: Lithium/sodium β-alumina
Authors: Highe A. , Vaughan R. W.
Published: February 2003

Room temperature 7Li spectra are reported for β-alumina samples with varying amounts of lithium substituted for sodium. A large dependence of the 7Li satellite (±3/2↔±1/2) position on lithium content was observed. A 91 percent-exchanged sample exhibited a thermally averaged lithium electric-field gradient of near-axial symmetry (η=0±0.04) with e2qQ=17.0±0.2 kHz. Field-dependent structure in the 1/2↔−1/2 transition was also observed.
The isotropic intermolecular potential for H2 and D2 in the solid and gas phases
Authors: Silvera Isaac F. , Goldman Victor V.
Published: February 2003

A semiempirical pair potential for molecular hydrogen and deuterium has been derived by fitting to solid state data. The potential is bounded to conform asymptotically to short- and long-range theoretical results. In the solid, many-body effects are accounted for by including a spherical form of the nonnegligible Axilrod–Muto–Teller three-body forces. The potential can be used to successfully describe isotropic properties in the solid and gas phases.
Tunneling states and nuclear spin conversion in solid CH3D
Authors: Lushington K. J. , Morrison J. A.
Published: February 2003

Total neutron cross section measurements have been made on condensed CH3D over the temperature region 0.75<T<100 K. The neutron wavelength was sufficiently long (4.7 Å) so that, in the low temperature region, the cross section was proportional to 〈I (I+1) 〉, the mean squared proton nuclear angular momentum per molecule, where I = total nuclear spin. 〈I (I+1) 〉 was determined to an accuracy of 1% or better and was only found to change significantly in the region T<10 K where conversion between nuclear spin symmetry species becomes appreciable. In contrast to the example of CH4, the rate of conversion appears to be rather insensitive to the amount of O2 impurity. For pure CH3D, the rate of conversion is rapid and is shown to correspond closely to the rate of thermal relaxation observed in calorimetric measurements on the solid at low temperatures. Estimates of low-lying tunneling states are made from the complementary calorimetric and neutron cross section results. There is a slight indication that the energy levels dilate in the region T<1.6 K, as has been predicted to occur in solid CH4. It is concluded that the unexpectedly rapid conversion between nuclear spin symmetry species in CH3D is a consequence of an accidental degeneracy between an A and an E tunneling level in each of two manifolds. Analysis of the thermodynamic data shows that the lowest temperature phase (phase III) of solid methane is not fully orientationally ordered.
Pyroelectric Na(H3O) [I(OH)3O3]: Room temperature crystal structure
Authors: Abrahams S. C. , Bernstein J. L.
Published: February 2003

Na(H3O)[I(OH)3O3] is pyroelectric at room temperature and crystallizes in the space group R3 with lattice constants at 298 °K of a=6.04272(6) and c=13.23165(2) Å for CuKα1 =1.54062 Å. There are three formulas in the unit cell. The integrated intensities of 2081 structure factors, within two-thirds of a sphere of reflection with (sinϑ) λ?1.2 Å−1, were measured on a CAD-4 diffractometer with Nb-filtered MoKα radiation. The crystal structure was solved by Patterson and Fourier series methods and refined by the method of least squares with 1102 symmetry-independent Fmeas. The final agreement index R =0.015 for a model in which all atoms undergo anisotropic thermal vibration except for the hydrogens, which were refined with isotropic temperature factors. The I(OH)3O3−2 ion is octahedral, with I–O distance of 1.844(2) Å and I–OH distance of 1.920(2) Å. Strong hydrogen bonds of 2.544(1) Å connect oxonium and I(OH)3O3−2 ions in sheets normal to the polar axis. Weaker intersheet hydrogen bonds of 2.697(2) Å connect the OH− surfaces of one sheet to the O− surfaces of adjacent sheets.
The sound velocity in metastable liquid water under atmospheric pressure
Authors: Trinh Eugene , Apfel Robert E.
Published: February 2003

Ultrasonic sound velocity data in supercooled water are analyzed in the light of present theories. Preliminary evidence for a minimum in the sound speed versus temperature curve is shown to be consistent with available data for other thermodynamic properties. A simple two-state mixture model combined with experimental data may be used to yield similar evidence. Sound speed data in superheated water are used to determine other thermodynamic parameters in the 100 to 170 °C temperature range under atmospheric pressure.
Vibronic coupling effects in the photoelectron spectrum of ethylene
Authors: Köppel Horst , Domcke W. , Cederbaum L. S. , Niessen W. von
Published: February 2003

The vibrational structure of the first band in the photoelectron spectrum of ethylene is calculated taking into account the vibronic coupling between the ground state and first excited state of the ion. The vibronic Hamiltonian describes linear coupling to the totally symmetric vibrational modes ν1–ν3 as well as to the non-totally symmetric torsional mode ν4. The energies and coupling constants entering the calculation are computed by ab initio Hartree–Fock and many-body methods. Qualitative agreement between the theoretical and the experimental spectrum is found. By slightly readjusting some of the parameters, the experimental spectrum can be reproduced accurately. It turns out that nonadiabatic and intensity borrowing effects are small. The vibronic coupling results mainly in a pronounced anharmonicity of the adiabatic potential energy surface. In particular, a nonplanar equilibrium geometry is found for the ionic ground state, the equilibrium torsional angle being ∼25°. Although the corrections to the Franck–Condon principle are small, the calculation of the vibrational structure is greatly complicated by the nonseparability of the totally symmetric and the non-totally symmetric vibrations. A decoupling procedure is presented which approximately makes possible the separate treatment of the modes. The results obtained with this procedure are in good agreement with the full vibronic treatment for ethylene.
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i rates of phonon-assisted v–v transfers among CO and N2 molecules in N2 matrices
Authors: Zumofen G.
Published: February 2003

The method of computing matrix shifts, splittings, and sideband intensities of the vibrational fundamental bands in solid N2 and CO has been extended to the calculation of resonant and off-resonant v–v transfer rates. The contribution of mechanical anharmonicity, i.e., vibron–phonon coupling through third- and higher-order terms in the potential, is found to be negligible for phonon-assisted transfer rates, similar to the situation in ir and Raman sideband intensities. Electrical anharmonicity, i.e., the modulation of vibron resonance energies by phonon-type motions, produces off-resonant v–v rates which are larger than those due to mechanical anharmonicity by two orders of magnitude. Analytical expressions have been derived for the quantitative determination of rates based on static multipole–multipole interactions, and contributions by repulsive exchange forces have been calculated numerically. The calculated rates are consistent with observations in a system of CO diluted in N2 and they explain the observed temperature behavior of endothermic v–v processes in pure solid N2 where two and more phonons are involved. It is found that molecular librations dominate over translational motions in all of these phonon-assisted rates, even in the repulsive contributions.