bluuebunny/crossref_metadata_2025 huggingface dataset:
Crossed beam electron–electron scattering at 90° and 300 eV
Authors: Block W. F. , Floyd C. , Rhodes R. A. , Wallace B. G.
Published: February 2003

An extensive search of the literature has revealed no evidence that a primary isolation type experiment such as crossed beam electron–electron scattering has ever been performed at low energies. High energy scattering was first performed by a colliding beam technique at a total energy of 600 MeV in 1966. In the usual cathode ray tubes the density of residual gas molecules far exceeds the density of electrons. An analysis of crossed beam scattering equations revealed that if the electron beams intersected each other at an angle of 90° the energy E′ of electrons scattered in the direction of the c.m. velocity vector could range to as high as twice the primary beam energy E. Since electrons scattered from the residual gases would be expected to have energies ?E, it seemed possible to separate the electron scattered electrons from the gas scattered electrons with an energy analyzer. We performed an extensive series of experiments using a parallel plate energy analyzer that revealed no significant results above the rather large background count. The experiments showed how difficult it is to detect the scattering with conventional apparatus. We next constructed an apparatus designed to detect almost all the electron scattered electrons that had energies greater than the retarding potential of a grid. The experiments were performed with beam energies of 300 eV and currents of 1.2 and 1.3 μA. The experimental results were compared to predictions based on Mo/ller’s quantum mechanical model for electron–electron scattering. A computer was programed to numerically integrate Mo/ller’s nonrelativistic c.m. differential cross section equation and the crossed beam equations due to Morse and Bernstein. We found the experimental results to agree well with theory.
Production of CS (a 3Π) in the photodissociation of CS2 below 1600 Å
Authors: Black G. , Sharpless R. L. , Slanger T. G.
Published: February 2003

Photodissociation of CS2 has been studied over the range 1050–2100 Å. While the quantum yield of S(1S) production is ?0.1 throughout this region, high yields of CS(a 3Π) are produced between 1250 and 1400 Å. Assuming that the quantum yield of CS(a 3Π) production in this region is close to unity, a value of (16±3) msec has been deduced for the radiative lifetime of CS(a 3Π), averaged over the three sublevels. Rate coefficients for quenching CS(a 3Π) by CS2, NO, CO, O2, H2, CO2, N2, Ar, and He have also been measured and compared with the values for CO(a 3Π).
Renormalized field theory of polymer solutions. I. Scaling laws
Authors: Schäfer Lothar , Witten Thomas A.
Published: February 2003

The large scale spatial correlations in a dilute solution of long chain molecules are dominated by excluded volume effects. We extend the field-theoretic methods of Des Cloizeaux and De Gennes to describe these correlations. We derive general scaling laws which the experimentally measured correlation functions must obey. The dependence on (scattering) wave number, concentration, and chain length is thereby reduced to a function of two variables. This function may moreover be calculated via well-studied approximations, leaving only an excluded volume parameter and a microscopic length parameter. Using the scaling law, we derive several experimentally observed power laws for parameters such as the radius of gyration, including limiting behavior for small overlap (independent chains), large overlap, and large wave vector.
Radiation-induced oxidation and reduction of iron–cyanide complexes
Authors: Box Harold C. , Lilga Kenneth T. , Budzinski Edwin E.
Published: February 2003

The species [Fe(CN)6]3− was generated by ionizing radiation in single crystals of Na4Fe(CN)6⋅10H2O maintained at 4.2°K. Three different conformations of the complex were obtained giving g tensors whose principal values are the following: 2.68, 2.53, 1.19; 2.74, 2.43, 0.63, and 2.81, 2.28, 1.45. Reduction products are formed in which the unpaired electron occupies an antibonding molecular orbital formed from iron and ligand orbitals.
Chemiluminescence from mixtures of Ba+CO2 and Ba+CO
Authors: West John B. , Poland Helen M.
Published: February 2003

Broad banded chemiluminescence has been detected from the reaction of Ba+CO2 and Ba+CO in a heat pipe. Extending from 500 to 1150 nm, the spectrum of this flame exhibits several prominent peaks. The emitting species has not been identified; however, evidence favors a polyatomic molecule. The observation of such chemiluminescence from apparently endoergic reactions is of interest and importance for the understanding of chemiluminescent processes.
The equation of state of pure water determined from sound speeds
Authors: Chen Chen-Tung , Fine Rana A. , Millero Frank J.
Published: February 2003

The equation of state of water valid over the range 0–100 °C and 0–1000 bar has been determined from the high pressure sound velocities of Wilson, which were reanalyzed by Chen and Millero. The equation of state has a maximum error of ±0.01 bar−1 in isothermal compressibility and is in the form of a secant bulk modulus: K=V0P/(V0−V) =K0+AP+BP2, where K, K0, and V, V0 are the secant bulk moduli and specific volumes at applied pressures P and 0 (1 atm), respectively; A and B are temperature dependent parameters. The good agreement (to within 20×10−6 cm3 g−1) of specific volumes calculated using the above equation with those obtained from other modifications of the Wilson sound velocity data demonstrates the reliability of the sound velocity method for determining equations of state.
Effects of ionic charge on light scattering by macromolecules in solution
Authors: Raman K. , Schor R.
Published: February 2003

Starting with Stephen’s simplified theory, a detailed solution is derived and numerically evaluated for the spectrum of light scattered by a solution of charged macromolecules, in a form that shows explicitly the dependence on the ionic charge parameter. A scheme is outlined for assessing the nature and extent of the deviation of the Debye–Hückel predictions from experimental results.
Spectra and structure of organogermanes. XIX. Microwave, infrared, and Raman spectra of ethylgermane
Authors: Durig J. R. , Lopata A. D. , Groner P.
Published: February 2003

The microwave spectra of GeH3CH2CH3, GeD3CH2CH3, GeH3CH2CD3 for the three most abundant naturally occurring isotopes of germanium, 70Ge, 72Ge, and 74Ge, have been recorded in the range 18.0–40.0 GHz and the spectra have been assigned. Both R- and Q-branch A-type transitions were identified. The dipole moment components were determined from the Stark effect to be ‖μa‖=0.71±0.01, ‖μb‖=0.27±0.01, and ‖μtotal‖=0.76±0.02 D. Barriers to internal rotation of 489±10 cm−1 (1.41±0.03 kcal/mole) for the germyl top and 998±10 cm−1 (2.85±0.03 kcal/mole) for the methyl top have been determined from the analysis of the microwave splitting pattern of the coupled internal rotors of ethylgermane. Thirteen structural parameters were determined from a least squares fit of the 27 moments of inertia. Raman spectra of gaseous and solid GeH3CH2CH3, GeD3CH2CH3, and GeH3CH2CD3 were recorded. A normal coordinate calculation based on thirty internal coordinates and employing 31 internal force constants was carried out and the calculated frequencies fit the observed ones to better than 1%.
Dipole moments of poly(trimethylene oxide) chains
Authors: Mark J. E. , Chiu D. S.
Published: February 2003

Dipole moments of poly(trimethylene oxide) chains [CH2–CH2–CH2–O–]x were determined as a function of degree of polymerization and temperature by means of dielectric constant measurements in the thermodynamically good solvent carbon tetrachloride. The mean-square dipole moment was found to be directly proportional to the degree of polymerization x, or the number of skeletal bonds, thus demonstrating the absence of excluded volume effects on the dipole moment. According to previous studies, the unperturbed dimensions of this chain molecule are unusually small and essentially independent of temperature; this is apparently due to the high degree of conformational randomness in the trimethylene oxide repeat unit in that the two C–C skeletal bonds prefer gauche states whereas the two C–O bonds prefer trans states. The present results indicate that this randomness has a much smaller effect on the dipole moment and its temperature coefficient.
Two-photon absorption measurements in organic liquids via nonlinear light mixing spectroscopy
Authors: Lynch R. T. , Lotem Haim
Published: February 2003

Using the three-wave mixing (3WM or CARS) experiment, the absorptive and dispersive parts of the two-photon absorption (TPA) process in liquid CS2, CHCl3, C6H12 and their mixtures with naphthalene were accurately measured relative to known Raman cross sections of the solvents in the range 35 000<2ω1<45 000 cm−1. The measurement is based on the interference effects between different processes which coherently contribute to the third-order nonlinear susceptibility χ(3) measured in the mixing experiment. It is shown that the parametric mixing measurement is superior to the classical TPA measurements. The TPA cross sections obtained here will be useful for the calibration of classical TPA measurements.
Paramagnetic electronic properties and nodal topology
Authors: Heller Donald F. , Hirschfelder Joseph O.
Published: February 2003

As Riess has showed, there exist restrictions on the nodal topology of electronic wavefunctions possessing permanent orbital paramagnetic moments. These supplement the well-known requirement that such wavefunctions must be complex valued. They are identical to the conditions derived for the existence of quantized vortices. These nodal restrictions thus have nontrivial implications for the magnetic properties of atoms and molecules. Magnetic ’’anomalies’’ characteristic of the existence of orbital magnetic moments are expected to evince themselves in electronic systems capable of supporting vortices (e.g., electron beams, atoms and molecules in magnetic fields, and degenerate electronic states) under appropriate conditions. Indeed, the origins of paramagnetic ring currents and paramagnetic shielding are readily understood from this viewpoint. We briefly consider a few atomic and molecular systems to illustrate the value of this analysis. We demonstrate that, if an electronic system is of known nodal topology, very simple symmetry arguments permit the lowest order magnetic multipole moments to be deduced.
Vibronic perturbations in the electric field spectra of 1,3-diazaazulene and azulene
Authors: Clark Roger , Small Gerald J.
Published: February 2003

The electric field spectra of the 3500 and 4500 Å absorption systems of azulene and 1,3-diaza-azulene in naphthalene host reveal that the a1 fundamental vibrational levels which are known to be vibronically induced exhibit permanent dipole moments which are significantly different from the dipole moment of the zero-point level. It is shown theoretically that, by virtue of an a1 level’s interstate vibronic activity, the same level can derive permanent dipole by (i) borrowing permanent dipole from the electronic state, which couples to the state of interest and (ii) borrowing transition dipole, which connects the two coupled states. Calculations indicate that the latter route is of primary importance for both of the above systems. In addition, the theory is easily used to rigorously compute the crude adiabatic permanent dipole of an electronic state from the experimentally observed adiabatic dipole moments. This is done for the two states above.
Transient effect of electric field on radiation-induced charge carriers
Authors: Chandrasekaran T. , Silverman Joseph
Published: February 2003

The transient transport problem of an isolated ion pair in the presence of an external electric field has been analyzed by solving numerically a modified version of Smoluchowski’s equation. Computations were performed for the case of a delta function initial distribution of electron–cation pairs formed in irradiated cyclohexane for the following strengths: 10, 30, 50, 70, and 100 kV cm−1. Several useful results were obtained from the analysis, such as the surviving fraction of cation–electron pairs as a function of time and field strength, the asymptotic limits of the yields, and the spatial distribution of ion pairs as a function of their orientation to the direction of the external field. The time it takes to reach 95% of the asymptotic limit of the recombined fraction of the initial ion pairs ranges from 32 to 113 psec for fields ranging from 100 to 10 kV cm−1, respectively. The asymptotic yields of the survival fraction obtained for all the electric fields are in good agreement with the free ion yields calculated by using Onsager’s solution of the steady-state problem.
A theory of optical absorption by aggregates of large molecules
Authors: Hemenger R. P.
Published: February 2003

The problem of optical absorption by aggregates of molecules whose wavefunctions do not overlap is formulated and it is shown that there are five exact relationships (sum rules) between the absorption spectrum of the aggregate and the spectra of the constituent molecules. An approximation satisfying these sum rules is developed in which aggregate absorption is given explicitly as a function of the spectra of the constituent molecules. This approximation, which makes use of a complete set of vibrational wavefunctions for the aggregate, is a generalization of the weak and strong coupling models in the sense that it contains each as a limiting case. Moreover, it is far superior to either in both the intermediate and strong coupling cases as shown by comparing it to an exact calculation on a model dimer.
Evidence for a background contribution to the decay rate of concentration fluctuations in ethane + propane near the critical point
Authors: Henry D. L. , Evans L. E. , Kobayashi R.
Published: February 2003

Measurements of the decay rate of concentration fluctuations in the binary liquid–vapor mixture ethane + propane (43.42 mole % ethane) were made along the critical isochore near the critical point using photon correlation spectroscopy. The data are compared with mode–mode coupling calculations for the critical part of the decay rate, and it is shown that a large background term must be included.
A far infrared study of the Ar–HCl van der Waals molecule
Authors: Boom E. W. , Frenkel D. , van der Elsken J.
Published: February 2003

Results of far infrared measurements on the system HCl–Ar at low density and temperature are presented. Distinct spectral features are observed that must be attributed to Ar–HCl van der Waals molecules. Possible explanations of the observed spectra in terms of a simple picture of the internal motion of the complex are discussed. An estimate of the enthalpy of formation is made.
Lifetimes for the d 1Σ+ state of NH and ND
Authors: Hsu Donald K. , Smith W. Hayden
Published: February 2003

The lifetimes for single and blended rotational levels of the d 1Σ+ state of NH and ND have been measured from emission spectra of NH and ND obtained via dissociative electron–molecule excitation. Using phase shift measurements over a range of electron-beam modulation frequencies, a Q-branch lifetime for v′=0 of 46±5 ns for NH and 62±6 ns for ND is derived. The difference in lifetimes provides some support for a predissociation in this state.
Brillouin scattering from liquid benzene at high pressures
Authors: Medina F. D. , O’Shea D. C.
Published: February 2003

Brillouin spectra have been obtained from liquid benzene at temperatures ranging from 25.3 to 75.8 °C and pressures up to 3280 bar. The resulting hypersonic speed can be represented by the following equation v=−4300+12.97T+(6538−12.47T) ρ, where v is the speed in m/sec, ρ is the density in g/cm3, and T is the temperature in °C. The present study does not indicate a departure from complete vibrational relaxation at high pressures.
Collinear classical dynamics on a chemically accurate H+H2 potential energy surface
Authors: Howard Robert E. , Yates Albert C. , Lester William A.
Published: February 2003

Exchange in the hydrogen atom–molecule reaction is investigated via classical collinear dynamics on the Yates–Lester potential energy surface. A threshold kinetic energy of 6.4762 kcal/mole (0.2808 eV) is determined. Exchange probabilities are found to be, in general, slightly less than those obtained using the energy surface of Shavitt, Stevens, Minn, and Karplus. Energy banding is observed and discontinuities in the transition region are attributed to snarled trajectories. Reaction probabilities for all possible combinations of H, D, and T are determined. Isotopic variations in reaction probability are explained in terms of the mass-dependent skew of the potential surface and differences in zero-point vibrational energy.
Comment: The bound 3Σ+u excited level of H+3
Authors: Ahlrichs Reinhart , Votava Christian , Zirz Constantin
Published: February 2003

The energy and wavefunction of the 3Σ+u state of H+3 are computed with a MC−SCF procedure. Using these, the equilibrium geometry, force constants and enthalpy of formation has been derived.(AIP)
Thermoluminescence following vuv photolysis of OCS and CS2 in an argon matrix
Authors: Fournier J. , Lalo C. , Deson J. , Vermeil C.
Published: February 2003

The vuv photodissociation of OCS in an argon matrix at 5 K has been shown to yield S(1S) atoms. The S(1S –1D) emission is observed only during the irradiation and does not appear when CS2 is photolyzed under the same conditions. However, in both cases the thermoluminescence which follows an increase of the matrix temperature is due to the S2(B 3Σu−→X 3Σg−) radiative transition. This substantiates the fact that S atoms do indeed diffuse in an argon matrix already at 6 K. Furthermore, the (a 3Π→X 1Σ+) emission of CS is observed both during the CS2 irradiation and as thermoluminescence. This last observation suggests that C atoms can also diffuse under these conditions at about the same rate as the diffusion rate of N atoms in N2 matrix, measured by Brocklehurst and Pimentel.
Electron paramagnetic resonance of Ag2+ dimers in Na2Zn(SO4)2⋅4H2O single crystals
Authors: Krishnan V. G. , Sastry G. Sivarama
Published: February 2003

Electron paramagnetic resonance studies have been made on Ag2+ ion in Na2Zn(SO4)2⋅4H2O single crystals at 300 K. Ag2+ is obtained by the x irradiation of Ag+ doped samples at ambient temperature and is found to be stable over a period exceeding one year. The EPR spectra indicate the presence of dimeric divalent silver species with the hyperfine structure with two inequivalent silver nuclei. The Ag–Ag has a singlet ground state concluded from the spectra vanishing around 100 K. The major contribution to the fine structure tensor is found to be from spin–orbit coupling.
Temperature dependence of the quenching of vibrationally excited N2 by NO and H2O
Authors: Whitson M. E. , McNeal R. J.
Published: February 2003

A photoionization technique for the detection of vibrationally excited nitrogen (N2*) has been applied to study the quenching of N2* (v=1) by NO and H2O over the temperature range 300 to 993°K using a flow system with microwave excitation of the nitrogen. The rate coefficient for quenching of N2* (v=1) by NO is found to be (2.2±0.9) ×10−15 cm3 sec−1 at 293°K, (3.2±1.3) ×10−15 cm3 sec−1 at 525°K, (6.5±2.5) ×10−15 cm3 sec−1 at 700°K, and (1.6±0.6) ×10−14 cm3 sec−1 at 993°K. These rate coefficients are in reasonable agreement with previous measurements and are the first measurements in the 500 to 993°K range. The rate coefficient for quenching of N2* (v=1) by H2O is found to be (1.2±0.5) ×10−14 cm3 sec−1 at 293°K, (2.5±1) ×10−14 cm3 sec−1 at 523°K, (5.1±2) ×10−14 cm3 sec−1 at 693°K, and (1.1±0.4) ×10−13 cm3 sec−1 at 963°K. These data are also in reasonable agreement with published acoustic, impact tube, and shock tube measurements.
Kinetic model for electron tunneling in frozen irradiated systems
Authors: Bartczak W. M. , Kroh J. , Stradowski Cz.
Published: February 2003

A kinetic model for tunneling of the trapped electron e−t from its trap to a scavenger S has been developed. The probability of the transition of e−t through the three-dimensional potential barrier has been calculated based on the theory of quasistationary states. The transparency of the barrier has been expressed in terms of (1) the distance e−t−S and (2) the energy level in the acceptor molecule. In order to calculate the kinetics of e−t decay, the distribution of e−t−S distances, and the energy levels of electrons in the traps have been taken into account. The model has been numerically applied to the decay of electrons trapped in the glassy 8M NaOH in the presence of NO−3 used as an electron acceptor. The presented model does not allow one to calculate the density of energy levels in the scavenger accesible to electron. Therefore, this parameter has been chosen to provide the best fit of the theory to the experimental data. The observed time dependence as well as scavenger concentration dependence are in a good agreement with those predicted by the theory.
The lowest rotation states of H3+ and symmetry considerations in dissociative e− capture
Authors: Carney G. D. , Porter R. N.
Published: February 2003

Symmetry of the lowest-lying internal states of H3+ and the selection rules governing transitions following electron capture by these states are considered. H3+ is a constituent of interstellar medium and lowest-lying states at temperatures of 3–30°K play a significant role.(AIP)
Oscillations of the D line emission in shock generated sodium halide plasmas
Authors: Gait Paul D. , Berry R. Stephen
Published: February 2003

Oscillations in the sodium D emission line from shock heated NaI vapor have been observed. Interpretation of this behavior is attempted as being due to the atomic population inversions by means of ion neutralization reactions.(AIP)
Possible tests of tricritical behavior in classical multicomponent mixtures
Authors: Papoular M.
Published: February 2003

It is argued that an optical measurement of the interfacial tension tricritical exponent μ=2 would involve a strongly divergent signal in classical multicomponent mixtures, as opposed to the 3He–4He mixture. Similarly a very intense bulk critical opalescence is expected in the former case, corresponding to the response function exponent γτ=2. The principle of an NMR mapping of the ’’α–γ’’ interfacial profile predicted by Widom, is proposed. Finally, a few conjectures are made regarding possible tests of tricritical dynamics in classical mixtures and in metamagnets.
FSGO model for core d electrons: Optimized structures for third row hydrides
Authors: Simons Gary , Talaty Erach R.
Published: February 2003

A quantum mechanical representation of a full M electron shell, employing nine Gaussians in a tripyramidal arrangement, is developed to extend the floating spherical Gaussian orbital (FSGO) method to molecules containing heavy atoms. To demonstrate the computational capabilities of the approach, a series of ab initio calculations including geometry optimizations are reported for CuH, ZnH2, GaH3, GeH4, AsH3, H2Se, and HBr. Excluding CuH, the average difference between predicted and observed equilibrium bond lengths is 0.03 Å; errors in bond angles for AsH3 and HBr average to 2.6°. A set of rules for FSGO orbital exponents, analogous in form to Slater’s rules for STO’s, is deduced, and illustrations of the utility of the rules are given.
Resonance Raman scattering from a multilevel, thermally relaxing system
Authors: Mukamel S. , Nitzan A.
Published: February 2003

We consider light scattering from a multilevel system (e.g., a molecule) interacting with several heat baths. The Liouville space approach is employed and weak incident radiation intensity is assumed, whereas the light scattering process is described in the lowest appropriate order in the interaction between the molecule and the incident and emitted photons. The interaction with other radiation field modes as well as with the thermal baths is treated more fully, such as to account for the correct damping terms and their temperature dependence. The formalism is suited for light scattering from an impurity molecule in both gas and dense phases. The thermal baths induce relaxation within the manifold of excited states as well as transitions to nonradiative channels. Damping due to such transitions (as well as radiative damping) corresponds to interactions with zero temperature baths. The physical interpretation of such a bath depends on the nature of the particular damping process. Thermal relaxation within the excited manifold is induced by interaction with the environment represented by a bath of temperature T. Part of this interaction which is diagonal in the molecular space corresponds to the so-called ’’quasielastic collisions’’ and induces modulations of the molecular energy levels and broadening of the relaxed emission. The remainder, nondiagonal part induces actual transitions between the excited molecular energy levels. The formalism yields in a single calculation expressions for the cross section for both the coherent (Raman) scattering process and the relaxed luminescence and enables us to discuss the effects of different factors such as temperature and quenching processes on the relative yields for these processes. The formalism also allows for interference between different levels of the excited manifold due to coupling of several levels to the same bath, and makes it possible to study the effect of thermal relaxation on these interference phenomena.
Classical trajectory studies of rotational transitions in Ar–CO2 collisions
Authors: Preston Richard K. , Pack Russell T
Published: February 2003

Rotational transitions in Ar–CO2 collisions were investigated using ∼30 000 classical trajectories. Two potential energy surfaces, both using a short range potential calculated with the electron gas method but differing in the way the long range van der Waals attraction was joined to the short range interaction, were used. The resulting integral inelastic cross sections are in excellent agreement with recent molecular beam experiments and show that highly inelastic, large Δj transitions occur frequently. Calculated differential cross sections for the large Δj transitions also agree well with experiment. A disagreement between calculated and experimentally-inferred small Δj differential cross sections is noted and possible explanations of it are discussed.
Energy transfer in collisions of rare gas atoms with CS2: Translational excitation of internal degrees of freedom
Authors: Blais N. C. , Cross J. B. , Kwei G. H.
Published: February 2003

Angle and recoil velocity distributions have been measured for the scattering of CS2 molecules from a crossed beam of rare gas atoms. Both beams were expanded through nozzles and seeded with H2 in order to provide rotational cooling of the CS2 molecules and narrow collision energy distributions, ranging from E=8.1 to 30.7 kJ/mole for Xe+CS2. Angular distributions of CS2 scattered in the plane of the crossed beams were measured by rotating the beam sources about a stationary mass spectrometer. The scattered beam was modulated with a pseudorandom binary sequence and the flight-time distribution of the scattered molecules was calculated from the cross correlated signal with an on-line computer. The measured velocity–angle contour plots show that the translational to vibrational excitation cross section is small compared with the translational to rotational excitation cross section and that the latter is strongly peaked in the forward direction. The CS2 angle and recoil velocity distributions are strongly coupled and the rotational excitation reaches a maximum at intermediate values of the c.m. scattering angle; this, together with the strong forward peaking of the cross section, suggests that a direct mechanism is responsible for the observed energy transfer. Further analysis of the data using only the most probable scattering energy shows that a substantial amount of energy, ranging from maxima of ∼18% for Ne to ∼45–50% for Ar, Kr, and Xe, is transferred from relative translation to rotational excitation of the CS2 molecules; that the fractional energy losses −ΔE/E for Xe+CS2 are comparable for E=17.2 and 30.7 kJ/mole, but considerably less at 8.1 kJ/mole; that both the rotational excitation cross sections and the fractional energy losses at comparable collision energies follow the relations Kr?Xe≳Ar≳Ne; and that the scattering angle for maximum energy loss is smallest for Kr and largest for Ne and Ar and increases somewhat with increasing collision energy.
Configuration interaction effects in the atomic photoelectron spectra of Ba, Sm, Eu, and Yb
Authors: Lee S.-T. , Süzer S. , Matthias E. , Rosenberg R. A. , Shirley D. A.
Published: February 2003

High temperature photoelectron spectra of Ba, Sm, Eu, and Yb were studied using both He i and Ne i resonance lines. In addition to strong lines corresponding to transitions from the primary configurations, correlation satellites were observed in every spectrum. By comparing the spectra excited at different photon energies, the satellite lines found in all Ne i spectra and the He i spectrum of Yb were attributed to admixtures of the configurations 5d 2, 6p 2, etc., into the ground state. Autoionization is believed to occur at the energies of the He iα, He iβ, and Ne i satellite lines for Ba; at the He iα energy for Sm; and at the He iα and He iβ energies for Eu. Autoionization was detected by noting the dramatic increase in satellite intensities and, in some instances, the large deviation of the observed intensity ratios within multiplets from the statistical values. Photoelectron spectroscopy has been demonstrated to have great potential in providing detailed information about electron correlation in both initial and final states.
Theory of dynamic light scattering from large anisotropic particles
Authors: Aragón S. R. , Pecora R.
Published: February 2003

The scattered electric field amplitude autocorrelation function of a dilute solution of large rigid anisotropic particles is computed in the Rayleigh–Debye approximation. The autocorrelation function for cylindrically symmetric particles is an infinite series of decaying exponentials with time constants τ−1l=q2D +l (l+1) Θ⊥ containing both translational and rotational diffusion coefficients. The dynamical terms are weighted by particle form factors and also by experimental geometry factors which are given in coordinate independent form. Explicit formulas for the form factors of spheres, rods, and thin disks are given. The general formulas reduce to the correct expressions for similar optically isotropic scattering systems.
Nuclear magnetic resonance and relaxation properties of solid SF6
Authors: Garg S. K.
Published: February 2003

Line shape and relaxation studies of the low temperature solid phase of SF6 stable below 94 K show the presence of two inequivalent lattice sites, one-quarter of the SF6 molecules being characterized by a barrier to isotropic reorientation of 1.9 and the remainder by a barrier of 2.8 kcal/mole. The chemical shift anisotropy (σ∥−σ⊥) of the S–F bond in SF6 is found to be 300±50 ppm. The sensitivity of line shape to rf field level in the cubic phase between 94 and 135 K is adequately described by the Goldman–Provotorov theory of ’’saturation narrowing’’. The activation energy for translational diffusion in this phase is 9.8 kcal/mole.
Vibrational relaxation of Cl2 by HCl and DCl and self-relaxation of HCl and DCl: A Monte Carlo quasiclassical trajectory study
Authors: Bass H. E. , Thompson Donald L.
Published: February 2003

A Monte Carlo quasiclassical trajectory study of Cl2(v=1) +HCl(DCl) →Cl2(v=0)+HCl(DCl) and self-relaxation of HCl(v=1) and DCl(v=1) has been carried out. The relaxation of Cl2/HCl(DCl) was studied over the temperature range 800–2100°K, HCl/HCl over the range 1600–2600°K, and DCl/DCl at 2100°K. Semiempirical valence-bond potential-energy surfaces were used; the surfaces were obtained by using previously computed parameters and contain no adjustments employing the energy transfer data with which the calculated results are compared. The calculated results are in good accord with experimental results.
Quantum dynamical study of resonance effects in the collinear reaction H2+I→HI+H
Authors: Chapman Frank M. , Hayes Edward F.
Published: February 2003

Collinear quantum mechanical calculations are reported for the endothermic reaction H2+I→HI+H. Resonance structure observed in the scattering results is attributed to the formation of compound (quasibound) states. Perturbation calculations successfully predict the energies of these resonance states. Coupling between the open channels and the closed channel associated with the resonance state is discussed. The lifetime and amplitude of the resonance states associated with a particular closed channel are correlated with the inelasticity or reactivity of the same channel immediately above its threshold. The role of resonance states in enhancing otherwise inefficient reactive pathways is discussed.
Fourier transform Doppler spectroscopy: A new means of obtaining velocity-angle distributions in scattering experiments
Authors: Kinsey James L.
Published: February 2003

A new method is presented for obtaining three-dimensional velocity distributions in scattering measurements. This method, which affords a potential improvement in the rate of signal acquisition of approximately 104 over conventional molecular beam techniques, utilizes Doppler profiles for light absorption, measured as a function of the direction of the incident light. A unique inversion of the set of Doppler profiles into the three dimensional velocity distribution is accomplished by a straightforward Fourier transformation procedure. A numerical example, illustrating the sensitivity and stability of the data-analysis techniques, is presented. New interpretations are obtained for data from gas phase experiments employing the Doppler effect for velocity selection or analysis. These indicate that such measurements can give a much closer approach to information of molecular beam quality than has previously been thought.
Interactions between chemisorbed atoms: Oxygen on W(110)
Authors: Ertl G. , Schillinger D.
Published: February 2003

Experimental LEED data on the 2×1 structure formed on W(110) by oxygen adsorption at coverages ϑ?0.5 are computer simulated by means of the Monte Carlo technique in terms of interactions between nearest and next-nearest neighbor adsorbed atoms. A minimum set of three (properly chosen) interaction energies was found to yield good agreement with experimental results, i.e., the variation of the relative intensity and angular width of the half-order overlayer beams with temperature and coverage. The pairwise interactions are of oscillatory character (i.e., changing sign from repulsive to attractive), have energies in the order of 1 kcal/mole, and fall off within 1–2 lattice spacings. They thus exhibit all the qualitative criteria of indirect interactions between adatoms as treated theoretically in the literature.
Surprisal based predictions of classical integral cross sections for rotational transitions in He+CO2
Authors: Goldflam R. , Kouri D. J. , Preston R. K. , Pack R. T
Published: February 2003

The surprisal analysis of Bernstein and Levine is employed as the basis of an interpolation scheme for fitting and predicting rotationally inelastic cross sections. The thermal prior of Bernstein and Levine is used, and the cross sections for the 5→jf and 19→jf transitions in He+CO2 (computed using classical mechanics) are employed to fix the constants in the surprisal formula. Results of using only the 5→jf transitions as input are studied as to their ability to predict the transitions 19→jf, and vice versa. In addition, all possible transitions are predicted using the two sets of input separately and together. Results for predicted cross sections are sufficiently accurate to be useful for other applications and indicate the usefulness of this approach.
Rotation–vibration analysis by finite difference perturbation technique. Application to 1Σ+ state of NH
Authors: Banerjee Ajit , Grein F.
Published: February 2003

A numerical perturbation method is presented for the solution of the one-dimensional Schrödinger equation by a finite difference approximation. The method is noniterative and has an accuracy similar to the Numerov–Cooley procedure. Rotation–vibration analysis for various multiconfiguration wavefunctions of the b and d 1Σ+ states of NH has been carried out using the above method followed by least square eigenvalue fitting procedures. The results are in very good agreement with known experimental data. The best calculated values of ωe, ωexe, Be, αe, and Re (with known experimental values in parentheses) are for the b 1Σ+ state ωe=3365.3 (3347.0) cm−1, ωexe =65.8 (70.7) cm−1, Be=16.78 (16.73) cm−1, αe =0.6249 (0.6049) cm−1; Re=1.953(1.956) bohr; for the d 1Σ state ωe=2671.8(2665.0) cm−1, ωexe =89.7(71.0) cm−1, Be=14.611 (14.409) cm−1, αe=0.999(0.634) cm−1, Re=2.093 (2.108) bohr.
The electronic structure and positron annihilation characteristics of positronium halides, [X−; e+]. I. Hartree–Fock calculations and stability
Authors: Cade Paul E. , Farazdel Abbas
Published: February 2003

The electronic structure of the atom/positron systems [F−;e+], [Cl−;e+], [Br−;e+], and [I−;e+] are examined by means of restricted Hartree–Fock calculations on the ...ns2np6(nl)+, 2L and...ns2np5 (n+1) sls+, 2P,4P states. A modified version of the numerical MCHF72 program of Froese–Fischer was used in these calculations. Our theoretical investigations suggest that...ns2np61s+, 2S is the ground state of the system. It is shown that X− ions have a substantial positron affinity (e.g. ∼5 eV for F− to 3.3 eV for I−) and arguments based on pair-correlation and many-electron perturbation theory are used to obtain hard lower limit estimates of the binding energy of Ps to the X atom. We thus find that the ground state of [X−:e+] is stable with respect to dissociation into X and Ps with binding energies of at least 1.66, 0.80, 0.19, and −0.45 eV for [F−:e+], [Cl−:e+], [Br−:e+], and [I−:e+], respectively. The details of the positronic orbitals are presented and discussed.
Excitation profiles of the coherent anti-Stokes resonance Raman spectrum of β-carotene
Authors: Carreira L. A. , Maguire T. C. , Malloy Thomas B.
Published: February 2003

The excitation profiles for the ν1 and ν2 vibrations of trans- β-carotene have been studied by means of coherent anti-Stokes Raman spectroscopy (CARS). The experimental profiles are compared to those calculated using the Albrecht theory modified for CARS. In order to obtain meaningful results it was necessary to drastically lower the laser power, specifically the power of ω1, the beam in resonance with the electronic absorption. If the laser power was too high, the intensity of the β-carotene lines did not scale with the square of the power in the pump beam due to saturation effects and, in fact, if the power was high enough the CARS signal was lost in the background emission. Due to the necessity of using low powers, photomultiplier detection was employed. The methods developed made it possible to detect β-carotene in benzene solution at concentrations of ∼5×10−7M, which is considerably lower in concentration than previously observed by CARS.
Quantum mechanical theory of molecular collisions in a laser field
Authors: Zimmerman I. Harold , Yuan Jian-Min , George Thomas F.
Published: February 2003

The effect of a radiation field on (ion)atom–(di)atom collision systems is considered. A detailed derivation is presented for the modified coupled equations that result from adding the field to the coupled channel formalism for nonreactive collisions. A discussion of the coherent state in this context concludes that the number state representation of the field offers a more convenient basis for defining probability channels in the combined system, but that further research on the applicability of the coherent state in more approximate treatments of the system should be carried out. An example of the general formalism is worked out for collinear Br+H2 collisions in the presence of the field, and calculated results are presented. Comparison is made with the results obtained from a vibronic (resonance) model.
Photodissociation of molecular beams of aryl halides: Translational energy distribution of the fragments
Authors: Kawasaki M. , Lee S. J. , Bersohn R.
Published: February 2003

Molecular beams of the aryl halides, 1,5-diiodonaphthalene, 4,4′-diiododiphenyl, 4,4′-dibromobiphenyl, and 9-bromofluorene were dissociated by pulsed laser light at 265, 280, 300, and 321 nm. The measured time of flight distribution of the fragments was converted to a translational energy distribution. This distribution is independent of the wavelength of the light absorbed. The average translational energy of the fragments of the above four molecules is 16.3, 17.4, 11, and 12 kcal/mol, respectively. The I atoms are produced mainly in their ground electronic state. These results are consistent with a model in which the light energy is absorbed by the aromatic system, and the electronic but not the vibrational energy is subsequently transferred to the carbon–halogen bond. Knowing the bond energy one can transform the translational energy distribution into an internal energy distribution of the fragments, which has a Poissonian form. In a typical dissociation 5–10 vibrational quanta are excited in the aromatic rings by the repulsive force of the departing halogen atom. The measured angular distributions of the fragments of 1,4-diiodobenzene, 4,4′-diiodobiphenyl, and 1,5-diiodonaphthalene were fitted with anisotropy parameters β from which lifetimes were extracted. Uncertainties in the β values are such that all we definitely know is that dissociation lifetimes of these and similar iodocompounds are ?2 ps.
Dynamics of adsorption on covered surfaces
Authors: McCreery Jane Hylton , Wolken George
Published: February 2003

A previous model for the interaction of a diatomic molecule with a solid surface is extended to allow the treatment of three atoms interacting with the solid. The effect of an adsorbed atom on the diatom–solid surface potential is examined. The dynamics of adsorption of a hydrogen molecule in the presence of an adsorbed hydrogen atom is studied. For the potential function used, the dissociative sticking probability of the incident molecule decreases for closer collisions with the adsorbed atom.
Approximate natural orbitals via the biorthogonal valence bond method
Authors: Schubert J. G. , Certain P. R. , Norbeck J. M.
Published: February 2003

A method is introduced for determining an initial approximation to the first-order density matrix and natural orbitals of a molecular system within the valence bond formalism. The nonorthogonality problem usually associated with these calculations is avoided by using a dual biorthogonal basis set. Results of test calculations are presented and the feasibility of using this method in large-scale natural orbital CI calculations is discussed.
Theoretical studies of atmospheric triatomic molecules: Accurate SCF vertical spectrum for valence, mixed character, and Rydberg states of CO2
Authors: England Walter B. , Ermler Walter C. , Wahl Arnold C.
Published: February 2003

An accurate SCF vertical spectrum is computed for CO2. Orbital sizes, electric quadrupole moments, and quantum defects are reported for the excited states. The Rydberg MO expectation values are found to be highly transferable. Spectral assignments are made for the Rydberg states based on the closeness of agreement with observed spectroscopic data.
Effects of pressure on Raman-active phonons and distortion of [ZnCl4]2− ions in the Cs2[ZnCl4] crystal
Authors: Wong P. T. T.
Published: February 2003

Pressure dependences of frequencies and Raman intensities of the zone center metal–ligand modes in Cs2[ZnCl4] crystal have been measured and are discussed on the basis of the results from the approximate frequency and intensity calculations. The pressure effect on the distortion of the [ZnCl4]2− ions and the mode anharmonicities have also been studied. The main conclusions are given in Sec. IV of the paper.
Nuclear magnetic resonance in a two-dimensional system
Authors: Avogadro A. , Villa M.
Published: February 2003

The NMR theory for a two-dimensional (2D) system of spins coupled by dipolar interaction and undergoing diffusive motion is presented. The correlation functions (c.f.) of the dipolar coefficients are split in two parts: a ’’slow’’ one and a ’’fast’’ one. The c.f. are also written in a form which allows easy prediction of the angular dependence of the relaxation rates. It is demonstrated that, owing to the diffusion process, the slow part decays at long times as t−1 and the fast one as t−2. Measurements of T2, T1, T1ρ on the protons of nitric acid intercalated in graphite have been performed in the temperature range −153 °C,+18 °C. The prediction of the model was checked both in the solid phases (where ω0τD≫1 with τD= diffusional correlation time) and in the ’’liquid’’ phase (above −20 °C). The measurements at room temperature prove, over several decades of frequency, the logarithmic divergence of the slow part-spectral density for ω→0. Also in the solid phases, the 2D-diffusive model interprets the measurements. Using the experimental results, we can illustrate the angular dependence of the relaxation rates that are predicted by the theory for planar systems in different dynamical situations. The information given by NMR on graphite nitrate are also discussed.
Comparison of final state approximations in the calculation of total and differential photoemission cross sections of neon
Authors: Williams R. Stanley , Shirley D. A.
Published: February 2003

Differential photoemission cross sections for the 1s, 2s, and 2p shells of neon were calculated by several different approximations for photon energies up to 2000 eV. Specifically, plane wave (PW), orthogonalized plane wave (OPW), and Hartree–Fock functions (with and without consideration of relaxation in the final ionic state) were used to compute transition matrix elements in both velocity and length approximations. Plane wave and orthogonalized plane wave continuum functions were found to have very limited applicability to cross section calculations, with both approximations giving spurious local minima and incorrect angular distributions. The reasons for these failures were analyzed, and limits were set on the n, l, and z values for which the PW model yields qualitatively correct total cross sections. Calculations using Hartree–Fock continuum functions agree very well with experiment, emphasizing the necessity of considering atomic potentials explicitly in photoemission processes. Further, the effects of relaxation in the final bound system were investigated. They were small for valence electrons and only slightly more important for Ne 1s core electrons. Applications of these findings to photoemission from molecules and absorbates are discussed briefly.
Anomalous emission in the blue wings of sodium and rubidium lines
Authors: Gait Paul D. , Berry R. Stephen
Published: February 2003

Absorption spectroscopy of the high temperature shock heated vapors of Rb and Na has shown that certain lines of these metals may appear partly in absorption and partly in emission. The lines concerned are the 5890/5896 Å doublet of Na, and the Rb lines at 6298, 6206, 6160, 6071 Å. In all cases the anomalous emission arises in the blue ’’wing’’ of the line. Mechanisms to account for this phenomenon are put forward.