bluuebunny/crossref_metadata_2025 huggingface dataset:
On the equivalence of semiclassical and Born total cross sections. Penning ionization of H(12S) by He(21S)
Authors: Huo Winifred M.
Published: February 2003

The equivalence of total cross sections calculated in the Born approximation and the semiclassical straight-line trajectory method is shown to hold for a potential of arbitrary symmetry if a set of conditions is satisfied. This is used to support a previous argument [W. M. Huo, J. Chem. Phys. 66, 3572 (1977)] on the applicability of the Born approximation to near resonant energy transfer at thermal energies. As an example, the Penning ionization of H(12S) by He(21S) is calculated in the Born approximation using electron impact data.
Structure of the HNCH2CO2− radical trapped in α glycine single crystals
Authors: Iacona C. , Michaut J. P. , Roncin J.
Published: February 2003

Single crystals of α glycine were γ irradiated and then photolyzed at 77 K. The structure of the HNCH2 CO2− radical so formed and its position in the crystal have been determined by single crystal ESR measurements. The factors controlling the reactivity of this radical in the matrix at 173 K are suggested.
Differential scattering of spin ± (1/2) polarized neutrons by chiral systems. I. Theory
Authors: Cox J. Neal , Richardson Frederick S.
Published: February 2003

A theoretical model is developed for treating the scattering of longitudinally polarized neutrons by a chiral array of nuclei. The model is restricted to consideration of nonmagnetic scattering systems comprised of ’’spinless’’ nuclei, and only forward scattering is considered. The differential scattering of spin ± (1/2) polarized neutrons is presumed to arise via a ’’spin–orbit’’ coupling mechanism in which the spin of the neutron is coupled to the orbital (vibrational) motions of the nuclei in the neutron–nuclei interaction region. Only low-energy neutron scattering by vibrational excitations (or deexcitations) is considered. Neutron–nuclei interactions are described in terms of (1) neutron absorption–emission processes; (2) neutron reflection processes; and (3) neutrons moving through the (long-range) Coulombic field of the nuclei. General expressions are developed for the differential scattering amplitudes of spin ± (1/2) polarized neutrons interacting with nuclei undergoing chiral vibrational motion.
Rotational tunneling in hexamine nickel halides by inelastic neutron scattering
Authors: Press W. , Prager M.
Published: February 2003

A splitting Δ=8.0 μeV of the librational ground state of the NH3 molecules in Ni (NH3)6Br2 has been observed directly by inelastic neutron scattering at T=5 K. In Ni (NH3)6Cl2 the tunnel lines cannot be well resolved. A splitting Δ?0.1 μeV has been estimated at T=9 K.
Microwave spectrum of methyldiborane
Authors: Penn R. E. , Buxton L. W.
Published: February 2003

The microwave spectra of eight isotopic modifications of methyl diborane (CH3B2H5) are reported. A convenient and general computational scheme for the application of Pierce’s ’’method of second differences’’ is described and used to determine the rs B⋅⋅⋅B distance of 1.773(5) Å. Several experimental results suggest a decrease in this distance of about 0.007 Å upon B2H5-group perdeuteration. The dipole moment is 0.566(6) D with 0.562(5) D and 0.06(3) D a and b components, respectively. The threefold methyl group torsional barrier is 4.28(9) kcal/mole.
Infrared studies of one-dimensional conductors of the cation-deficient type: M1.75[Pt(CN)4]⋅1.5H2O where M=K, Rb, or Cs
Authors: Ferraro John R. , Basile Louis J. , Williams Jack M.
Published: February 2003

Infrared studies of one-dimensional conductors of the cation-deficient type M1.75[Pt(CN)4]⋅1.5H2O, where M=K, Rb, or Cs are reported. Results are compared with those previously reported for the anion-deficient conductors as well as between the starting materials, unoxidized K2[Pt+2(CN)4]⋅3H2O and fully oxidized K2[Pt+4(CN)4Br2]. It is observed that some of the infrared-active vibrations are sensitive to the oxidation state of Pt. The trends are explained in terms of an increase in metal–CN π-back bonding, and a decrease in the metal–carbon sigma bonding. Spectral data are included for the organic guanidinium tetracyanoplatinate 1-D conductor.
An analysis of the A 1Σu+–X 1Σg+ band system of 7Li2
Authors: Kusch P. , Hessel M. M.
Published: February 2003

A new analysis of the A 1Σu+–X 1Σg+ band system of 7Li2 has been made. The analysis extends from v′=0 to v′=25, from v″=0 to v″=14, and up to J=78. The dissociation energy of the A state is found to be 8940 cm−1, considerably less than any earlier estimate of that energy. The RKR potential curves for the A and X states are given, together with the Franck–Condon factors for the A–X transition.
The wave equation of a nonlinear triatomic molecule and the adiabatic correction to the Born–Oppenheimer approximation
Authors: Bardo Richard D. , Wolfsberg Max
Published: February 2003

The wave equation for a nonlinear polyatomic molecule is formulated in molecule-fixed coordinates by a method originally due to Hirschfelder and Wigner. Application is made to a triatomic molecule, and the wave equation is explicitly presented in a useful molecule-fixed coordinate system. The formula for the adiabatic correction to the Born–Oppenheimer approximation for a triatomic molecule is obtained. The extension of the present formulation to larger polyatomic molecules is pointed out. Some terms in the triatomic molecule wave equation are discussed in detail.
Application of the scaled particle theory to the problem of hydrophobic interaction
Authors: Ben-Naim A. , Tenne R.
Published: February 2003

We consider a process in which m simple solute molecules are brought from fixed positions at infinite separation from each other to a close-packed configuration where they are confined to a spherical region of a suitable diameter. The process is carried out at a given temperature and pressure. The free energy, entropy, and the enthalpy changes accompanying this process are computed by using a combination of experimental and theoretical sources; the latter part is based on the scaled particle theory. The results of our computations are, in most cases, consistent with previous conclusions that have been reached by other methods, applied to the same problem.
Chemistry of nuclear recoil 18F atoms. IX. High-pressure investigation of 1,1,1-trifluoroethane
Authors: Manning Ronald G. , Mo Siu-Hong , Root John W.
Published: February 2003

Nuclear recoil 18F reactions in CH3CF3 have been investigated throughout the effective pressure range 0.3–170 atm. The principal reaction channel is F-to-HF abstraction for which the combined yield from thermal and energetic processes in the presence of 5 mol% H2S additive is 84.4%±0.1%. Organic-product-forming channels include F-for-F, F-for-2F and F-for-H atomic substitution and F-for-CH3 and F-for-CF3 alkyl replacement with respective primary absolute yields of 4.21%±0.10%, 0.26%±0.03%, 5.75%±0.14%, 1.04%±0.03%, and 1.33%±0.04%. With the exception of the F-for-2F channel substantial portions of the organic primary products contain sufficient internal excitation to induce secondary decomposition. At low pressures the average fractional decompositions following single substitution (F-for-X) and alkyl replacement (F-for-R) reactions are 0.80±0.03 and 0.27±0.04. Alkyl replacement products are fully stabilized through collisional deactivation at pressures below ∼13 atm. At 170 atm only 0.60±0.05 of the single-substitution products have undergone collisional stabilization, representing 0.50±0.04 of the species capable of decomposition. Experiments with CH3CF3/C3F6 mixtures demonstrated average reaction energy differences for F-to-HF and organic-product-forming processes in CH3CF3 vs olefinic addition in C3F6.
Variational energy functionals involving one-electron operators
Authors: Levy Mel
Published: February 2003

A variational energy functional for isoelectronic changes is derived which requires only the one-electron operators in the Hamiltonian and knowledge of an eigenstate of one member of the isoelectronic series. Approximate equations are deduced from the main equation. The approximate functionals involve electron densities and first-order reduced density matrices. Numerical examples are presented for the helium isoelectronic series.
The magnetic structure of metamagnetic Co(pyr)2Cl2
Authors: de Jonge W. J. M. , van Vlimmeren Q. A. G. , Hijmans J. P. A. M. , Swüste C. H. W. , Buys J. A. H. M. , van Workum G. J. M.
Published: February 2003

The zero-field magnetic structure of Co(pyr)2Cl2 is obtained by means of nuclear magnetic resonance. The low temperature crystallographic structure must be described by the α structure. Field induced phases are proposed, and the resulting magnetizations are compared with experiment.
Entanglement probabilities for a harmonically bound macromolecule
Authors: Wiegel F. W.
Published: February 2003

We discuss a general scheme to derive various statistical properties of a macromolecule whose repeating units interact with a straight line and which is entangled with that line. In the case of harmonic forces an exact expression is found for the probability that a ring shaped macromolecule is n-times entangled with the line. For more general interactions, the low and high temperature limits of the entanglement probabilities are discussed briefly.
Light scattering from orientational and density fluctuations in liquid 1,2,5-thiadiazole
Authors: Jones Dane R. , Wang C. H. , Christensen D. H. , Lund P.-A.
Published: February 2003

The orientational and density fluctuation spectra of liquid 1,2,5-thiadiazole were determined by the light scattering technique. The viscosity and density of the pure liquid were also measured as a function of temperature. Results of concentration dependent studies of 1,2,5-thiadiazole in an optically isotropic solvent having the same viscosity as the pure liquid show that the pair orientational correlation is very small. The experimentally determined reorientational relaxation times were found to be close to the prediction of the slip model for rotational diffusion. The sound velocity of the pure liquid was found to decrease linearly with increasing temperature. The sound dispersion was found negligible in the GHz frequency region.
New self-consistent approximations for ionic and polar fluids
Authors: Ho/ye J. S. , Stell G.
Published: February 2003

A general approximation scheme for the pair correlation function of fluids at equilibrium is discussed, and two new specific approximations that come out of it—one for polar fluids and one for ionic fluids—are introduced. The approximation scheme, developed for hard-core particles, is based upon the replacement of the actual structure of the Ornstein–Zernike direct correlation function c (12) outside the core by a form that can be wholly characterized in terms of its poles in Fourier space. The locations and residues of the poles are constrained by thermodynamic self-consistency; the approximate scheme is designated as the self-consistent Ornstein–Zernike approximation (SCOZA) scheme.
NH+4 ion motions in diammonium hydrogen phosphate
Authors: Watton A. , Reynhardt E. C. , Sandhu H. S. , Petch H. E.
Published: February 2003

Proton second moments and relaxation times in the laboratory frame T1 in (NH4)2 HPO4 were measured over the temperature range 77–430 K. The relatively high activation energies associated with the different motions of the nonequivalent NH+4 groups are attributed to hydrogen bonding between the NH+4 groups and the surrounding nearest neighbor oxygens. It is suggested that angular oscillations of the NH+4 groups result in the unrealistically short interproton distance of 1.47 Å determined by x-ray diffraction. The second moment results above 215 K could be explained satisfactorily if the standard interproton distance of 1.68 Å is assumed. Below 215 K the lineshapes and second moments strongly suggest a doubling of the number of nonequivalent ammonium groups. Good agreement was obtained between second moment and relaxation results.
Rotational excitation of H2 in collision with He
Authors: Lin C. S. , Secrest Don
Published: February 2003

Converged close coupling cross sections for the vibrationally and rotationally inelastic processes for the system H2+He are reported. (AIP)
Orientational dependence of spin–lattice relaxation in nematic liquid crystals
Authors: Tarr C. E. , Vosman F. , Whalley L. R.
Published: February 2003

We have extended the calculation of Ukleja, Pirs, and Doane on the spin–lattice relaxation in nematic liquid crystals to calculate the orientational dependence of the rotating frame relaxation rate T−11ρ. This calculation, including the effect of cutoff in the collective order modes, is compared to the experimental data for MBBA.
Accurate charge densities and two-electron intracule functions for the heliumlike ions
Authors: Thakkar Ajit J. , Smith Vedene H.
Published: February 2003

Integral formulas necessary to compute charge densities and intracule functions from explicitly correlated wavefunctions of the form ψ (r1, r2, r12) = (4π)−1ΣNk=1ck(1 ±P12)  exp(−αkr1−βkr2−γkr12) are derived. They are applied to such wavefunctions recently computed by us for the ground states of the heliumlike ions from H− through Mg10+. An analysis of the resulting distribution functions is given. A simple method for obtaining reasonable approximations to an intracule function from its moments is developed.
Collisionless CO2 laser-induced photodissociation of sulfur hexafluoride in a molecular beam experiment
Authors: Brunner F. , Cotter T. P. , Kompa K. L. , Proch D.
Published: February 2003

Many polyatomic molecules exhibit an anomalous absorption behavior when exposed to high-power infrared laser radiation. This has been studied in a molecular beam experiment, where vibrational superexcitation and dissociation of SF6 molecules under collisionless conditions was induced by a CO2 laser over a wide range of laser flux densities. By mass spectrometric detection it was possible to identify vibrational excitation in molecules which were not dissociated. The results provide unambiguous insight into the laser energy dependence of the primary dissociation and show the highly isotopically selective nature of these processes.
Concentration dependence of correlation times from proton NMR relaxation in hydrous melts
Authors: Girard C. , Braunstein J. , Bacarella A. L. , Benjamin B. M. , Brown L. L.
Published: February 2003

Proton spin–lattice relaxation times (T1) for hydrous melts of Ca(NO3)2 containing 2.8, 4.0, 8.0, and 16.O moles H2O/mole salt (55.5 to 2.32 moles H2O/l) at temperatures between 290 and 390 K are analyzed in terms of intramolecular and intermolecular contributions. Rotational correlation times for water (τrot) are estimated from the relaxation rates in the high temperature (narrow line) region using intermolecular correlation times (τinter) estimated from melt viscosities or from diffusivities of protons or of dilute solute ions (Cd2+). The ratio τinter/τrot increases from about 2.5 in pure water to about 17 in the viscous melt Ca(NO3)2-2.8 H2O, suggesting a much greater medium effect on translational than on rotational motion. An empirical relation was found that quantitatively correlates the dependence of the relaxation rate, varying over three orders of magnitude, with viscosity (or water diffusivity) and the volume concentration of water at all of the compositions and temperatures investigated.
Optical nonlinearities of various substituted benzene molecules in the liquid state, and comparison with solid state nonlinear susceptibilities
Authors: Oudar J. L. , Chemla D. S. , Batifol E.
Published: February 2003

The second- and third-order hyperpolarizabilities of various mono- and meta-disubstituted benzene derivatives have been measured in the liquid state by simultaneous use of static-field induced second-harmonic generation and tunable four-wave mixing. For the vector part of the second-order optical nonlinearity comparison is made between liquid-state and solid-state experimental data.
Variationally optimized T matrices for elastic scattering
Authors: Lurie B. N. , Rosenthal C. M.
Published: February 2003

Trial T matrices depending only on the wave vector difference ki−kf have been employed to obtain optimum elastic scattering amplitudes. These amplitudes are the values assumed by a variational functional evaluated at the optimum trial T and thus have a more complex dependence on ki and kf than the trial T. By way of illustration, two examples are presented: scattering from an attractive Yukawa potential, and scattering from an attractive well. In both instances the results compare very favorably with other methods of solution.
Diagrammatic perturbation theory: N2 X 1Σ+g
Authors: Wilson Stephen , Silver David M.
Published: February 2003

The diagrammatic many-body perturbation theory is used to calculate the correlation energy of the nitrogen molecule in its electronic ground state. Using the algebraic approximation, the energy is evaluated through third order, including all many-body effects. [2/1] Padé approximants and variational upper bounds are constructed. For one of the perturbation expansions considered, the [2/1] Padé approximant leads to the recovery of 79.5% of the empirical correlation energy, while the variational upper bound recovers 72.0%. Three-body effects are examined in some detail. The relationships with previous work on N2 are discussed.
The electronic structure of rare gas halide excimers
Authors: Krauss M.
Published: February 2003

The rare gas halide excimer states are analyzed in terms of an electrostatic model that includes mixing between the ionic excimer and neutral ground configurations. The energy splitting between the 2Σ and 2Π excimer states is strongly affected by this configuration mixing. A Rittner type energy expression is derived and parameterized for the KrF* excimer energy curves, which are found in good agreement with the ab initio curves of Dunning and Hay. Perturbation expressions are also derived for the dipole and transition moments of this system. The long-range formulas are compared with the available ab initio literature. These expressions are then applied to a qualitative analysis of the transition moments of KrF*. The 2Σ+→2Σ+ transition is found to be dominant, in agreement with the ab initio results. The transition moment can actually be viewed as a small admixture of the large ionic dipole moment. Since the dipole moment varies as R and the mixing coefficient as exp(−αR), it is apparent that the transition moment will vary rapidly as a function of R and also of the vibrational quantum number.
Recoil- and field-enhanced diffusion
Authors: Axelrod A. , Corbett J. W.
Published: February 2003

A quantum mechanical description is presented of diffusion that is enhanced by the presence of a constant force field (field-enhanced diffusion) or by the recoil energy obtained by collisions with bombarding particles (recoil-enhanced diffusion). One- and three-dimensional equations are given, the one-dimensional one being particularly pertinent to channeling situations. Methods for calculating relevant transition rates are examined; these are used to illustrate the similarities between the two enhancements.
Electronuclear basis for three-dimensional electronic nonadiabatic chemical reactions
Authors: Miller Donald L. , Wyatt Robert E.
Published: February 2003

The quantum mechnical theory of electronic nonadiabatic atom–diatomic molecule reactive collisions in three dimensions is discussed with emphasis on the reaction F(2P3/2,2P1/2)+H2(1Σ+g,v,j). It is known that the first two excited electronic adiabatic surfaces of the FH2 system are very close to the ground state surface at large F–H2 distances. Only the ground state surface, however, can lead to reaction at subdissociative energies. The importance of considering the exchange of flux between these surfaces is discussed. An electrorotational basis set {ΩJMα} is formulated for use in a quantum mechanical, reactive scattering calculation for systems of this type. These basis functions are formed by starting with good total angular momentum (nuclear plus electronic) kets in the space-fixed frame. Then, these functions are written in terms of the body-fixed natural collision (NCC) coordinates, and the Euler angles that orient the body frame with respect to the space frame. One feature of the {ΩJMα} setting them apart from other basis sets typically used in scattering calculations is that they cannot be factored into products of nuclear and electronic parts. It is then shown how the ΩJMα may be written in terms of adiabatic electronic basis functions used in the ’’diatomics-in-molecules’’ (DIM) treatment of atom–diatom systems. By writing the {ΩJMga} in terms of DIM basis functions, matrix elements of the type 〈ΩJMα′‖Ĥel‖ΩJMα〉 are evaluated as linear combinations of pure electronic matrix elements of Ĥel in the DIM basis. Four nonmixing parity types are found for the ΩJMα. Plots of selected matrix elements 〈ΩJMα′‖Ĥel‖ΩJMα〉 as functions of the reaction coordinate s and vibrational coordinate ρ are presented for F+H2. Matrix elements of T̂rot (the nuclear rotational kinetic energy operator expressed in NCC) are also evaluated in the electrotational basis. The method of conversion from the electrotational basis to an adiabatic electronic basis is formulated. This transformation should be useful after the system passes the zone where electronic transitions are significant.
Laser excitation spectra of the CO+2 molecular ion A 2Πu→X 2Πg fluorescence
Authors: Bondybey V. E. , Miller Terry A.
Published: February 2003

The molecular CO+2 cations were generated in the X 2Πg ground state by the Penning ionization reaction with neon metastable atoms. The vibrational and rotational distribution of the product ions was observed by the laser fluorescence method. These experiments demonstrate the possibility of using this technique to detect polyatomic ions in various environments, including flames, plasmas, etc. (AIP)
Methyl group tunneling effects on 1H NMR line shapes of solids at low temperatures
Authors: Ripmeester J. A. , Garg S. K. , Davidson D. W.
Published: February 2003

Methyl group tunneling side bands have been observed in the proton NMR line shapes of solid dimethyl ether, propane, propane-2, 2d2, and dimethyl sulfide at low temperatures. The line shape theory after Apaydin and Clough was used to derive tunneling frequencies. Assuming a threefold, sinusoidal potential barrier for methyl group rotation, application of the Hecht and Dennison relation yields barrier heights of 3.85, 3.58, 3.60, and 3.51 kcal/mole, respectively, for dimethyl ether, propane, propane-2, 2d2, and dimethyl sulfide.
Chemiexcitation of the 3P metastable states in lead atoms
Authors: Gabai A. , Rokni M. , Shmulovich J. , Yatsiv S.
Published: February 2003

We report excitation of the 3P1 and 3P2 metastable states of the ground configuration of lead atoms by the homogeneous oxidation by oxygen of acetylene or cyanogen containing tetramethyl lead (TML). The population of the excited states is monitored by absorption spectroscopy. Our results indicate that the reactions excite a considerable fraction of free lead atoms to these metastable states. Evidence is presented that the population of the metastable states in the oxyacetylene reaction is due to chemiexcitation.
Vacuum ultraviolet photolysis of sulfur hexafluoride and its derivatives in argon matrices. The infrared spectrum of the SF5 radical
Authors: Smardzewski Richard R. , Fox William B.
Published: February 2003

Vacuum ultraviolet photolysis at 1048, 1067 Å of sulfur hexafluoride and its derivatives, SF5X (where X=Cl, Br, and SF5) in dilute argon matrices at 8 K produced two new infrared absorptions at 811.6 and 552.1 cm−1 which were also observed in the argon matrix reactions of fluorine atoms with SF4 molecules. Both features were assigned to the SF5 radical, a new species of C4v symmetry. A weaker absorption at 682.4 cm−1 was tentatively assigned to the SF3 radical, while, in the sulfur–fluorine experiments, secondary reactions produced the known SF−5 anion. The photolytic production of significant yields of SF4 and XF indicated the presence of a simultaneous molecular photoelimination process which, in the case of SF5Br, afforded the direct observation of the BrF fundamental at 650.5 cm−1.
Photon assisted field ionization
Authors: Niu Bill H. C. , Beacham James R. , Bryant Paul J.
Published: February 2003

An enhancement of the field ionization current was observed when the tungsten tip was illuminated by an external light source. Enhanced ionization occurs for photon energies of lower value than the work function of tungsten. Results indicated that holes are created below the Fermi level by the interaction of photons with the tungsten tip. Hence, the critical distance for which field ionization can occur is reduced. This study provides a method which is complementary to photon assisted field emission to study the electronic states at a metal surface.
The infrared multiphoton photochemistry of methanol
Authors: Bialkowski Stephen E. , Guillory William A.
Published: February 2003

CO2 TEA laser has been used to initiate the multiphoton dissociation of CH3OH, both pure and with NO added as a free radical scavenger. The decomposition of CH3OH at the high power density of the focused laser radiation results in molecular and free radical initiated products. Decomposition through molecular intermediates appears to proceed via CH3OH+nhν→CH2O*+H2 and CH2O* →CO+H2, and comprises ∼90% of the consumed CH3OH in ∼3000 laser pulses. The radical initiated process CH3OH+nhν→CH3 +OH ultimately results in the stable products C2H4, C2H2, and CH4 to an extent of ∼10% of the CH3OH consumed. Luminescence from the focal zone is due to emission from OH†, CH†, C†2, and possibly CH2O†. Stable products as well as the visible luminescence due to the electronically excited diatomic radicals are followed as a function of pressure, time, and addition of the free radical scavenger gas NO. Both major photodecomposition routes appear to be non-Boltzmann.
Relaxation in biological macromolecules and application of theory to the investigation of secondary structure of DNA
Authors: Chay Teresa Ree
Published: February 2003

Using a statistical mechanical approach we have shown that, in the case of large perturbations, the fraction of helicity at time t can be factored into two terms—a chain length dependent term which is a function of the dispersity of macromolecules and a sigmoidal term which depends on the nucleation parameter, σ, but not on chain lengths. The analytic expression for the fraction of helicity obtained from our approach is very similar to that obtained by Trifonov et al. for an irreversible conformational transformation. Our approach, however, uses one less parameter than that of Trifonov et al. and, moreover, is applicable to the reversible as well as irreversible cases. We have applied our theory to the denaturation of DNA under the action of formaldehyde and found excellent agreement between the theory and experiment.
The vacuum uv absorption spectrum of O2 from its metastable states b 1Σ+g and a 1Δg
Authors: Katayama D. H. , Ogawa S. , Ogawa M. , Tanaka Y.
Published: February 2003

The absorption spectra of 16O2 and 18O2, excited by a transformer discharge, have been photographed with a 6.65 m vacuum spectrograph in the 1280–1620 Å region. The spectra were obtained in the first and second orders of a 1200 grooves/mm grating. New bands have been observed and assigned to the n=3 and 4 members of the Rydberg series npπu 1Σ+u←b 1Σ+g. The 4pπu 1Σ+u (v=1) level is overlapped and perturbed by a 1Πu state. Rotational analyses have been made for all the well resolved bands of 16O2 and 18O2. The vibrational quantum number assignments were based on the isotope shifts of 18O2 relative to 16O2. Rotational and vibrational constants for the upper states of the bands analyzed are reported and a discussion is given of these states in relation to the Rydberg states of O2 converging to the ground state of O+2. In addition, a new diffuse band at 1611.8 Å is discussed in terms of previously reported bands from the a 1Δg state.
Fragmentation of aliphatic chlorocarbons under low-energy (≲10 eV) electron impact
Authors: Johnson J. P. , Christophorou L. G. , Carter J. G.
Published: February 2003

The fragmentation of ten aliphatic chlorocarbons (CHCl3, 1,1,1-C2H3Cl3, 1,1,2-C2H3Cl3, 1,1-C2H4Cl2, 1,2-C2H4Cl2, C2Cl4, C2HCl3, 1,1-C2H2Cl2, cis-1,2-C2H2Cl2, and trans-1,2-C2H2Cl2) under low-energy (0–10 eV) electron impact has been investigated with a time-of-flight mass spectrometer. Three types of fragment negative ions were observed: Cl−, Cl−2, and (M–Cl)− (parent molecule, M, less one Cl atom)−; for C2Cl4 the parent ion, C2Cl4−*, was also observed at ∼0.0 eV and found to be metastable with an autodetachment lifetime of 14±3 μsec. The Cl− ion was by far the most abundant. The intensities of Cl2− and (M–Cl)− with respect to Cl− depended very strongly on the number and relative positions of the Cl atoms in the molecule. The yield of Cl2− was, as a rule, very much lower when the two Cl atoms in the Cl2− ion originated from the same C atom. The measured Cl− currents as a function of electron energy were corrected for the finite width of the electron pulse, and the resultant unfolded functions exhibited distinct resonances whose relative intensity depended strongly on molecular structure. They indicated the existence of at least five such resonances below ∼2 eV for both the chloroethanes and the chloroethylenes studied. The average positions of the observed resonances are 0.18, 0.54, 0.8, 1.06, and ∼1.45 (?) eV for the chloroethanes and 0.19, 0.53, 0.75, 0.95, and ∼1.35 eV for the chloroethylenes. The spacings and energy dependences of the intensities of the observed resonances seem to preclude the involvement of vibrational levels, and the similarity in their positions for the two groups of molecules (chloroethanes and chloroethylenes) seems to suggest that they are associated with orbitals dominated by the p-orbitals of the Cl atoms. The C=C π-orbital is clearly involved in the formation of the long-lived C2Cl4−* ion. The relative magnitudes and energy dependences of the Cl−, Cl2−, and (M–Cl)− ions have been partially rationalized on the basis of the energetics involved in the production of the respective ions. Comparison of the present results with existing electron-swarm data is satisfactory; based on the swarm data, absolute cross-section values for the Cl− ions of some of the compounds studied have been obtained.
Rotationally inelastic scattering of K on NH3 observed by a time-of-flight technique
Authors: Kusunoki I.
Published: February 2003

A new experimental technique for obtaining time-of-flight spectra of a scattered molecular beam is reported. Both the primary (K) and the secondary (NH3) beam were velocity selected and had very narrow angular spreads, resulting in high-resolution TOF spectra. Both beams had thermal energy, and the TOF spectra of the scattered potassium atoms were obtained at five different LAB angles and four different primary beam velocities. The spectra show that more than 50% of the scattering is inelastic . The mean energy transfer ranges between 15.6 and 40.4 meV, which corresponds to about 20%–40% of the relative total kinetic energy. The inelastic scattering is due to rotational excitation of NH3. A modified hard-sphere model for this process leads to an average angular momentum transfer of 2−3 h/. The effect of the long range potential is discussed.
A method for the calculation of the distribution functions of dielectric relaxation times, using a deconvolution technique, applied to simulated experimental spectra
Authors: Salefran J. L. , Bottreau A. M.
Published: February 2003

The authors use the deconvolution technique for research into distribution functions of the relaxation times of a substance. They propose a new method of smoothing and of interpolation and extrapolation of the experimental data. They recommend the use of a rectangular integration window which allows the acquisition of a good resolving capacity while taking into account experimental errors. The method of calculation used enables also the differentiation of the different types of distribution (Debye, Cole and Cole, and Cole and Davidson). The advantages of this method are illustrated by numerous examples.
A theoretical study of the optical absorption band shape for xenon hexafluoride
Authors: Ehlhardt William J. , Lohr Lawrence L.
Published: February 2003

The classical Franck–Condon approximation is used together with the Monte Carlo integration technique to calculate the optical absorption band shape arising in xenon hexafluoride from the pseudo-Jahn–Teller active t1u bending mode. The potential energy function for this mode has the Devonshire form for the hindered rotational motion of a diatomic molecule in a cubic site and is characterized by three parameters. Results are presented using values of these parameters as determined by Pitzer and Bernstein for the 1A1g electronic ground state and as estimated by us from the crystal-field model of Wang and Lohr for the 1T1u and 3T1u electronic excited states.
Electron traps in irradiated alkaline glasses at 77 K studied by stimulated luminescence
Authors: Truong T. B.
Published: February 2003

The results of stimulated luminescence studies at 77 K on photoionized tryptophan or tyrosine in alkaline ices or on γ-irradiated alkaline ices reveal that (1) the luminescence emission results from neutralization of bleached electrons with parent cations whose concentration is much more dilute (10−5–10−3M) than that of the alkaline ions (10M); (2) spatial heterogeneous distribution of OH− exists prior to irradiation in alkaline ices. There are zones where OH− concentration is higher than in others; (3) complementary to the optical absorption and ESR techniques, the stimulated luminescence method can serve to identify negative species other than solvated electrons stabilized in alkaline ices, namely, H− and possibly O=.
Steady state spatial structures in dissipative systems: Numerical algorithm and detailed analysis
Authors: Kubí?ek M. , Marek M.
Published: February 2003

A one-dimensional reaction–diffusion system for a model chemical network was studied. The location of bifurcation points was determined analytically. By applying the general parameter mapping numerical technique, the dependence of the solutions on the length of the system was calculated. Both symmetric and asymmetric spatial concentration profiles exist. For boundary conditions of the second kind the solution for a larger interval can be composed from the solutions for the elementary interval; spatially repeated order structures can thus be formed.
Numerical Hartree–Fock calculations for N2, FH, and CO: Comparison with optimized LCAO results
Authors: Christiansen Phillip A. , McCullough E. A.
Published: February 2003

The restricted Hartree–Fock equations for the ground states of N2, FH, and CO were solved numerically in prolate spheroidal coordinates. The series expansions employed converge rapidly, the maxium error in our orbitals being about 10−5 or less. The errors in our energies are smaller than 5×10−4 hartree. Comparisons of the energies, dipole quadrupole moments, and cusp ratios of our wavefunctions with the best available matrix LCAO results are presented. Our solutions, in most cases, significantly improve the cusp ratios and for N2 and CO lower the total energies by more than 10−3 hartree. Orbital density difference plots indicate the existence of significant errors in the LCAO orbitals, which are most apparent in the internuclear region.
Primitive radiation damage: Succinamic acid
Authors: Ko Ching Lung , Box Harold C.
Published: February 2003

Two oxidation products and two reduction products are observed in single crystals of succinamic acid x irradiated at 4.2 °K. The reduction products are formed by electron addition to carbonyl oxygens. One oxidation product results from decarboxylation; the other from loss of a CH2 hydrogen. The products were identified from ENDOR measurements of their proton hyperfine couplings.
Antiferromagnetic resonance of organic free radical, polycrystalline 1,3-bisdiphenylene-2- (p-chlorophenyl) -allyl
Authors: Yamauchi Jun
Published: February 2003

The antiferromagnetic phase transition of an organic free radical, 1,3-bisdiphenylene-2- (p-chlorophenyl) -allyl, was confirmed by the antiferromagnetic resonance (AFMR). The long range ordered state of the unpaired electron spins was elucidated in detail. The AFMR absorptions were obtained in polycrystalline specimen using a conventional X-band spectrometer. The AFMR theory of a two-sublattice model with an orthorhombic anisotropy was applied to the results obtained. The antiferromagnetic resonance parameters C1 and C2 were determined to be 2.25×106 and 7.84×106 (Oe2) at the absolute zero of temperature, respectively. The degree of an orthorhombic anisotropy was thus determined to be C2/C1=3.5. Assuming the exchange field, which was moderately estimated in terms of the exchange parameters obtained from susceptibility measurements, the anisotropy field amounts to be 17 Oe. The antiferromagnetic spin flop field Hc was also determined to be 1500 Oe at the absolute zero of temperature. Both of the anisotropy and the spin flop fields are in excellent agreement with those obtained from torque measurements. It is clarified that a reliable determination of the parameters in the antiferromagnetic state is possible from polycrystalline samples of organic free radicals.
On the subject of displaced thresholds
Authors: Marchand P. , Veillette P. , Marmet P.
Published: February 2003

It is shown that the name ’’displaced threshold’’ for displaced features in ejected electron experiments is misleading and leads to confusion in the interpretation of electron impact data.
High pressure studies of the effect of viscosity on fluorescence efficiency in crystal violet and auramine O
Authors: Brey L. A. , Schuster G. B. , Drickamer H. G.
Published: February 2003

The dependence of the fluorescence efficiency of the dyes crystal violet and auramine O on solvent viscosity at room temperature has been investigated using pressure to alter the viscosity. Pressures to 11 kbar on four polar solvents were utilized to obtain a 5 order of magnitude viscosity range. We confirm the η2/3 dependence of fluorescence intensity on viscosity shown for crystal violet by Förster and Hoffman [T.H. Förster and G. Hoffman, Z. Physik. Chem. NF, 75, 63(1971)] and observe the same dependence for auramine O over a smaller range of viscosities with a large deviation at low viscosity. The effect of increasing solvent viscosity on the peak shift and half-width change is briefly discussed in terms of a configuration coordinate model.
Kinetic theory of gas phase microwave experiments. I. A two level approach
Authors: Coombe D. A. , Snider R. F.
Published: February 2003

The response of a polyatomic gas to microwave radiation—including both steady state (pressure broadening) and time dependent (coherence transients) effects—is described theoretically. The treatment is based on solutions of a quantum Boltzmann equation and employs kinetic theory methods which have previously been used in the explanation of the field dependence of transport phenomena (Senftleben–Beenakker effects). Such methods allow for a proper description of the rotational aspects of a real molecular system, in contrast to standard approaches which effectively model the molecular system as having only two nondegenerate energy states. In the present work the magnetic quantum number degeneracies of two rotational levels connected by microwave radiation are specifically considered, and the resulting vector (and tensor) nature of the motions is emphasized throughout. The relaxation processes involved are related to matrix elements of the (rotationally invariant) collision superoperator occuring in the quantum Boltzmann equation.
Kinetic theory of gas phase microwave experiments. II. The j=0 to j=1 transition in diatomics
Authors: Coombe D. A. , Snider R. F.
Published: February 2003

The kinetic theory approach to gas phase microwave experiments, as presented in the previous paper, is further illustrated by treating the j=0 to j=1 transition in diamagnetic diatomics (or linear polyatomics) in some detail. The small dimensionality of this particular two level system allows a relatively exact treatment, i.e., within the restrictions imposed by being a two level system, and by the rotating wave approximation. Estimates of the relaxation times involved in such a system are given using the distorted wave Born approximation. General steady state and transient solutions to the system of moment equations are presented, which include the effects of unequal populations in the ’’m’’ states of the j=1 level. The physical nature of the ’’fourth moment’’ associated with this latter effect are emphasized throughout.
Kinetics studies of Ne–N2 by proton excitation
Authors: Chen C. H. , Judish J. P. , Payne M. G.
Published: February 2003

Charge transfer processes in Ne–N2 mixtures excited by weak proton beams are studied through the time-resolved fluorescence spectra of N+2(B2Σ+u→X2 Σ+g). Our experimental data give indirect evidence of the existence of Ne+3. We also report the first measurements of overall quenching rates for atomic and molecular neon ions at room temperature. The fluorescence spectra of Ne–N2 and the ratio of the fluorescence efficiency to that of He–N2 are also obtained.
119Sn Mössbauer spectroscopy of tetrahedral tin (IV) molecular solids: SnH4, SnD4, Sn(CH3)4, SnCl4, SnBr4, SnI4, and related compounds
Authors: Herber R. H. , Leahy M. F.
Published: February 2003

The temperature dependence of the 119Sn recoil-free fraction has been determined for a number of tetrahedral Sn(IV) compounds and related molecules in order to test further the assumptions of the effective vibrating mass (EVM) model as applied to Mössbauer effect studies. For a number of model compounds, including SnCl4, SnBr4, SnI4, (C6H5)4Sn, and (C6H5)2SnCl2 the temperature dependence of lnfa in the high temperature limit is sufficiently linear to permit an assignment of a Raman active mode in the lattice mode region of the (low temperature) vibrational spectra to an intermolecular, intraunit cell vibration of the molecules against each other. In the case of (CH3)4Sn, SnH4, SnD4, and (C6H5CH2)4Sn, the Mössbauer data in the high temperature limit cannot be fitted to a simple linear temperature dependence due to pronounced motional anharmonicity over the whole accessible temperature range. The effect of isotopic substitution on the Mössbauer hyperfine parameters has been examined over the temperature range 4.2⩽T⩽100 °K. Low temperature Raman spectra in the lattice-mode region are reported for the compounds examined in this study.
Self-consistent, nonorthogonal group function approximation for polyatomic systems. I. Closed shells
Authors: Mehler Ernest L.
Published: February 2003

The wavefunction of a closed shell system in the orbital product approximation is reformulated into a product of nonorthogonal group functions, and a variational method based on local energy functionals is developed for the determination of the orbital equations. The orbitals are expanded in terms of local bases, and a double iterative procedure based on Roothaan’s method is used to compute the self-consistent solutions of the equations. The use of local energy functionals and nonothogonal groups permits the replacement of the usual system of equations by several systems of lower dimensionality. In addition, the number of electron interaction integrals required for the solution of the orbital equations is reduced, leading to a simplification in the calculation of the required matrix elements. This method is applied to hydrogen fluoride and lithium hydroxide, and calculations from a number of wavefunctions with differing group function structure are compared with the Hartree–Fock results.
Method of averaging wavefunction corrections. Inelastic results
Authors: Malik David J. , Weare John H.
Published: February 2003

The previously introduced generalized distorted wave method is extended to multichannel scattering. The method is applied to the collinear collision problem of an atom and a diatom with an exponential repulsive interaction. Results are included which show the method is superior to the third order distorted wave Born series for a wide range of energies, masses, and potential values and for comparable computational effort. The method is also compared with another separable kernel procedure based on the Schmidt method (Weinberg’s quasiparticle method). Some numerical comparisons in elastic scattering are included for the square well and Yukawa potentials. The results obtained by both methods are an improvement over the Born expansion in regions where the series converges and diverges.
Variation of chemical shielding with intermolecular interactions and rovibrational motion. I. 19F nuclei in BF3, CF4, SiF4, and SF6
Authors: Jameson Cynthia J. , Jameson A. Keith , Cohen Sheila M.
Published: February 2003

The chemical shifts due to rotational and vibrational motion in CF4, SiF4, BF3, and SF6 are obtained by extrapolation of 19F resonance frequencies to zero density. The second virial coefficients of chemical shielding, σ1(T), are obtained at the same time from the slopes. It is found that the σ1 values for these molecules do not depend on temperature nearly as strongly as was previously reported.
Measurement of the rate coefficients for the de-excitation reactions of He2 (3Σu) metastables with Ne, Ar, N2, CO, CO2, and CH4
Authors: Lee F. W. , Collins C. B.
Published: February 2003

This work reports the measurement of the excitation transfer reactions of metastable He2(3Σu) helium molecules with Ne, Ar, N2, CO, CO2, and CH4. In this study He2(3Σu) destruction frequencies have been experimentally determined from measurements of the optical absorption of the 4650 Å, 3Σu →3πg helium transition in high pressure afterglows of mixed gases excited by intense electron beam discharges. Data have been obtained as functions of helium pressure over the range from 1500 to 2500 torr and as functions of the partial pressure of reactant from 14 to 200 mtorr. From this data pressure independent rate coefficients have been extracted which describe the effective bimolecular rates of reaction. These bimolecular rate coefficients have been found to range from 4.4×10−11 cm3 sec−1 for reactions with Ne to 95 ×10−11 cm3 sec−1 for reactions with CO2. Reaction probabilities have been found to be generally larger than for the corresponding reactions of He(23S) metastable atoms, approaching unity for the reaction of He2(3Σu) with CO2. Other measured values of ionization probability ranged from 0.3 and 0.4 for N2 and Ar, respectively, to 0.6 for CO and CH4.
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o calculations of the minimum energy path in the doublet surface for the reaction N(4S)+O2(3Σ−g) →NO(2Πu) +O(3P)
Authors: Benioff Paul A. , Das G. , Wahl Arnold C.
Published: February 2003

A b initio MCSCF+CI calculations of the minimum energy path in the doublet surface for the N(4S)+O2(3Σ−g) →NO(2Πu)+O(3P) reaction were carried out using a 4-31 G basis set. The minimum path was calculated to pass through a bent N–O–O 2A′ transition complex with a barrier of 21.7 kcal/mole. A high barrier was found for the doublet C2v approach of N(4S) to O2(3Σ−g). Two distinct regions of orbital transformations, given by the MCSCF calculations were found along the minimum energy path.
Relaxation of the mercury 6 3P and 6 3P1 states
Authors: Stock M. , Smith E. W. , Drullinger R. E. , Hessel M. M.
Published: February 2003

The relaxation of 6 3P0 mercury atoms excited by a laser pulse was measured for densities ranging from 2×1017 to 8×1018 cm−3. The decay of the 253.7 nm resonance line was also measured for densities ranging from 5×1016 to 1018 cm −3. The decay coefficients were analyzed to yield rate coefficients for three body molecular formation, the 3P1→3P0 collision rate and a collisional quenching rate for the 3P0 state. Small loss rates due to diffusion and radiation were also observed and found to be consistent with theoretical estimates of these quantities.