bluuebunny/crossref_metadata_2025 huggingface dataset:
Hartree–Fock and correlation energies of expanded metallic hydrogen
Authors: Stanton Richard E.
Published: February 2003

The analysis of the misbehavior of dissociating Hartree–Fock molecules carried out in a previous paper is extended to the theory of crystalline solids, particularly metallic hydrogen. It is shown that at infinite lattice spacing the Hartree–Fock and correlation energies per H atom have the same pathological values that they take on in fully dissociated H2. At large, but finite nearest neighbor distances the Hartree-Fock energies are given by E∞H–F-Nα/R; the parameter α in the Coulomb attraction term varies somewhat from structure to structure, but has nearly the same value as in H2. It is shown that the one-electron energies in the expanded form of metallic hydrogen are monotonically increasing functions of the momentum, just as in normal metals. Explicit results are given for electron energy as a function of momentum in the simple cubic form of metallic hydrogen and for the one dimensional crystal.
Studies on the SCF ground state energy surfaces of HC2 and HC2−
Authors: Pacansky J. , Orr G.
Published: February 2003

A b initio SCF computations are presented for the ground states of HC2 and HC2−. The results indicate that the bonding situation in HC2 and HC2− is similar to CN and CN−, respectively. Qualitatively speaking, the negative ion is formed by addition of the extra electron to the half filled 5σ molecular orbital of HC2 to form a lone pair of electrons. A large positive electron affinity is expected for HC2 on the basis that the 5σ molecular orbital contains an appreciable amount of s character similar to that found for the CN radical. The SCF computed electron affinity is 1.94 eV. The experimental electron affinity is estimated to be 2.5 eV.
Singlet Rydberg states of ethylene
Authors: McMurchie Larry E. , Davidson Ernest R.
Published: February 2003

A configuration interaction scheme is employed to calculate all n=3 Rydberg states of ethylene derived from the excitation of a π electron. This scheme is designed to account for the small amount of correlation energy of the Ryberg electron and to facilitate calculation of term values from a corresponding calculation on the positive ion. With one exception the results are in agreement with the recent spectral assignments of Mulliken. Both the present results and those of other theoreticians illustrate the difficulties of calculating Rydberg states.
On the factorization and fitting of molecular scattering information
Authors: Goldflam Rudolf , Kouri Donald J. , Green Sheldon
Published: February 2003

The factorization of cross sections of various kinds resulting from the infinite order sudden approximation is considered in detail. Unlike the earlier study of Goldflam, Green, and Kouri, we base the present analysis on the factored IOS T-matrix rather than on the S-matrix. This enables us to obtain somewhat simpler expressions. For example, we show that the factored IOS approximation to the Arthurs–Dalgarno T-matrix involves products of dynamical coefficients TLl and Percival–Seaton coefficients fL(jl‖j0l0‖J). It is shown that an optical theorem exists for the TlL dynamical coefficients of the T-matrix. The differential scattering amplitudes are shown to factor into dynamical coefficients qL(χ) times spectroscopic factors that are independent of the dynamics (potential). Then a generalized form of the Parker–Pack result for Σj(dσ/d?)(j0→j) is derived. It is also shown that the IOS approximation for (dσ/d?)(j0→j) factors into sums of spectroscopic coefficients times the differential cross sections out of j0=0. The IOS integral cross sections factor into spectroscopic coefficients times the integral cross sections out of j0=0. The factored IOS general phenomenological cross sections are rederived using the T-matrix approach and are shown to equal sums of Percival–Seaton coefficients times the inelastic integral cross section out of initial rotor state j0=0. This suggests that experimental measurements of line shapes and/or NMR spin–lattice relaxation can be used to directly give inelastic state-to-state degeneracy averaged integral cross sections whenever the IOS is a good approximation. Factored IOS expressions for viscosity and diffusion are derived and shown to potentially yield additional information beyond that contained in line shapes. They are however expected to be dominated by the elastic scattering integral cross section. Factored IOS expressions are also shown to hold for thermal rates and averages and the same spectroscopic coefficients apply. By measuring the line shapes over a range of temperatures, deconvolution methods can be used to obtain the definite energy pressure broadening cross section. This can then yield the inelastic integral cross sections. Computations are given illustrating the use of the factored IOS expressions as fitting functions and for predictions of integral cross sections for the systems CO+He and HCl+He, and of thermal rates for the systems CO+H, HCN+He, N2H++He, and CO, CS, and OCS with H2 (treated as a structureless atom).
Photodissociation of positive ions. I. Photodissociation spectra of D+2, HD+, and N2O+
Authors: Thomas Timothy F. , Dale Fred , Paulson John F.
Published: February 2003

The operation of an apparatus constructed to measure absolute photodissociation spectra of ions and to determine the kinetic energy spectrum of the photoproducts by time-of-flight analysis is described. Photodissociation spectra for the processes D+2+hν→D++D and N2O+→NO++N have been obtained, and the photodissociation cross sections for HD++hν→H++D and HD++hν→D++H have been measured. The photodissociation spectrum of D+2, using an irradiation bandwidth of <0.05 to 0.1 nm, is in reasonable agreement with the structureless spectrum of von Busch and Dunn obtained with a 20 nm bandwidth. The two possible photoprocesses in HD+ were observed to have the same cross sections 2×10−19 cm2 at 589 nm. The photodissociation spectrum of N2O+ over the range 295–342 nm was found to be very sharply structured, with σNO+ =2.6×10−18 cm2 for the largest peak, at 338.5 nm. Fifteen peaks in the N2O+ spectrum were assigned to vibrational progressions in the ? 2Σ←? 2Π1/2,3/2 transition. In making the assignments it was necessary to assume the ions possess from 0 to 2 quanta in the degenerate bending mode, leading to Renner effect splitting in the 2Π state.
Theory of resonant Raman scattering in the strong vibronic coupling limit–a Green’s function approach
Authors: Hong Hwei-kwan
Published: February 2003

A Green’s function approach for resonant Raman scattering is proposed here, which is suitable for both weak and strong vibronic couplings. The formalism is based on the solution of the exact Green’s function in the Longuet–Higgins representation, using the solutions to the static equations in ordinary molecular quantum mechanics as the basis set. The physical meaning of various interaction schemes becomes clear in this representation. In particular the vibronic coupling is based on the interactions between individual zero-order vibronic levels and is carried through to infinite order, whereas the traditional first order results only account for the emission of one single vibrational quantum. Nonadiabatic contributions are also contained in the formulation. The method is applied to the following cases: (1) the change in nuclear equilibrium position due to electronic excitation, (2) vibronic coupling involving two excited states, and (3) the change in nuclear potential (force constants) due to electronic excitation. Numerical results show that the convergence is excellent even for large vibronic coupling and in exact resonance region. Furthermore, all the physical quantities of interest, such as Raman cross sections of fundamentals and overtones, absorption profiles, Franck–Condon factors, quantum yields can be obtained at the same time in this unified approach.
Theory of the magnetic field modulated geminate recombination of radical ion pairs in polar solvents: Application to the pyrene–N,N-dimethylaniline system
Authors: Werner H.-J. , Schulten Z. , Schulten K.
Published: February 2003

Pairs of radical ions generated in polar solvents by photoinduced electron transfer either recombine within a few nanoseconds or separate. The (geminate) recombination process is governed by a hyperfine-coupling-induced coherent motion of the unpaired electron spins which can be modulated by weak external magnetic fields. The process which also generates the well-known CIDNP and CIDEP effects is described theoretically by a stochastic Liouville equation comprising for realistic systems a large set of coupled diffusion equations. For the integration of these equations a finite-difference algorithm with space and time discretization is developed. By comparison with exact solutions of the Liouville equation for model systems, it is demonstrated that an approximate Liouville equation which entails only two coupled diffusion equations for singlet and triplet radical pairs, respectively, suffices to predict the geminate recombination yields accurately. The approximate Liouville equation is employed then to study on the basis of known hyperfine coupling constants, second-order recombination rate constants, diffusion coefficients, and dielectric constants, the solvent, temperature, concentration, and magnetic field dependence of the geminate (singlet and triplet) recombination yields for the system pyrene–N,N-dimethylaniline. The effect of deuteration upon the recombination yield and its magnetic field dependence is also studied. Furthermore, the influence of an exchange interaction acting at small separations of the radicals is investigated for a model system.
An (e,2e) investigation of the (2s2p)  1P autoionized transition in helium. Comparison with an accurate Born calculation
Authors: Dillon Michael A. , Lassettre Edwin N.
Published: February 2003

Intensity ratios related to the shape of an angular correlation function have been obtained in the neighborhood of the (2s2p)  1P autoionized transition in helium using the (e,2e) fast coincidence technique. Subsequent comparison with the interpolated results of an accurate Born calculation reveals a deviation from theory which becomes more pronounced with increasing momentum transfer, ΔP. As ΔP→0 both theory and experiment tend, as expected, to the optical limit.
Photoemission from ferrocene, decamethylferrocene, and decamethylferrocene-bis(7,7,8,8-tetracyano-p-quinodimethane)
Authors: Ritsko J. J. , Nielsen Paul , Miller Joel S.
Published: February 2003

We present the first vacuum ultraviolet photoemission measurements of condensed ferrocene, decamethylferrocene, and the highly conductive charge transfer complex decamethylferrocene-7,7,8,8-tetracyano-p-quinodimethane, at photon energies from 7.7 to 21.2 eV. We compare the electronic spectra of these compounds and discuss substituent effects. The first ionization potentials are 6.1, 5.1, and 5.3 eV, respectively. The charge transfer complex is a semiconductor with its highest occupied states 0.8 eV below EF. The electron scattering lengths in ferrocene and decamethylferrocene are ?60 Å for electrons 0.5 eV above the vacuum level and decrease to ?2.5 Å as the energy is increased to 16 eV. From this result we estimate the electron affinity of solid ferrocene and decamethylferrocene to be about 1 eV.
Nucleation of freezing by charged particles. I. Thermodynamics
Authors: Cole Milton W. , Sluckin Timothy J.
Published: February 2003

We determine the properties of the solid region which surrounds an ion embedded in a compressible atomic liquid. This solid acts as a nucleation center for freezing of the liquid when it is compressed above the melting pressure. Specifically, we evaluate the solid radius, the activation free energy barrier of the ion complex with respect to freezing of the bulk liquid, and the critical overpressure δpc at which the finite radius solid becomes absolutely unstable. We present an alternative approach to the quantity δpc in terms of the spherical solid’s growth in response to an external perturbation.
Ionization reactions of metal hexafluorides with alkali atoms and dimers
Authors: Mathur B. P. , Rothe Erhard W. , Reck Gene P.
Published: February 2003

Ionization reactions are observed in crossed beams, usually of thermal energy, of alkalis and MoF6, WF6, and UF6. Previous studies have indicated large electron affinities for these hexafluorides, and this is confirmed here. Ionization at thermal energies proceeds with the alkali dimers A2 for the three hexafluorides, but with alkali atoms A only for UF6. Several ionization paths are observed, allowing the deduction of molecular energies. A few experiments are done with eV-range beams. Lower limits for the electron affinities are 4.5, 3.3, 4.9, 4.3, and 1.9 eV for MoF6, MoF5, WF6, UF6, and UF5, respectively. Possible mechanisms are discussed.
Evaluation of a new self-consistent approximation for an ionic fluid
Authors: Larsen B. , Stell G. , Wu K. C.
Published: February 2003

Some results are given for the pair distribution functions of a fluid of charged hard spheres in a new self-consistent approximation due to Ho/ye and Stell. Appropriate thermodynamic and contact-value expressions to be used as input in the approximation are developed and compared to available Monte Carlo results; a representative set of resulting distribution functions are also displayed. The approximation appears to be highly successful over a wide range of densities, temperatures, and charge strengths, including the fused-salt regime, where adequate analytic treatments of the structure of ionic fluids have been previously lacking.
Semiclassical calculation of bound states in a multidimensional system for nearly 1:1 degenerate systems
Authors: Noid D. W. , Marcus R. A.
Published: February 2003

The method is devised to calculate eigenvalues semiclassically for an anharmonic system whose two unperturbed modes are 1:1 degenerate, by introducing a curvilinear Poincaré surface of section. The results are in reasonable agreement with the quantum ones. The classical trajectories also frequently show a large energy exchange among the two unperturbed normal modes. Implications for Slater’s theory of unimolecular reactions, which neglects this effect, and for ’’quantum ergodicity’’ are described.
A stochastic theory of translational correlation functions in gases and liquids
Authors: Lindenberg Katja , Cukier Robert I.
Published: February 2003

This paper presents a theory of translational relaxation in hard sphere systems. We construct self-equilibrium time correlation functions for the self-density and for the velocity of a molecule by techniques related to the theory of stochastic point processes. Our stochastic theory yields, at low density, the Boltzmann–Enskog kinetic theory. At intermediate densities we obtain enhancement (t−3/2 decay) and at high density reduction of the velocity autocorrelation function relative to the Boltzmann–Enskog exponential decay in accord with molecular dynamics simulations. The self-diffusion coefficient is correspondingly enhanced and reduced. We also compare our formulation with kinetic theories based on the BBGKY hierarchy. In particular, the relationship of our theory to ring kinetic theory is explored.
Electron paramagnetic resonance in nickel fluosilicate
Authors: Rubins R. S. , Clark Jerry D. , Jani Shirish K.
Published: February 2003

EPR data for NiSiF6⋅6H2O at Ku band and Ka band between 77 and 298 °K were fitted to an isotropic g value of approximately 2.25 with ‖D‖ varying from (0.166±0.005) cm−1 at 77 °K to (0.51±0.01) cm−1 at 298 °K. The values g∥=2.26±0.01 and ‖D‖= (0.125±0.005) cm−1 were obtained from a Ku band measurement at 4.2 °K. The magnitude of the temperature gradient ∂D/∂T had a broad maximum of about 1.8×10−3 cm−1/ °K near 200 °K, decreasing to about 1.5×10−3 cm−1/ °K near room temperature. The spin–lattice relaxation rate was determined from linewidth measurements to vary as T2 above 200 °K. From an expression for the Raman process in the high temperature limit, the Debye Temperature ϑD was deduced to be approximately 107 °K.
Molecular orbital studies of methanol polymers using a minimal basis set
Authors: Curtiss L. A.
Published: February 2003

A b initio minimal basis set LCAO–SCF molecular orbital calculations have been carried out to determine the binding energies and structures of small groups of methanol molecules [(CH3OH)n n = 3,4,5,6] with particular emphasis on aspects relevant to experimental measurements on methanol vapor. Cyclic structures are found to be more stable than the open structures for the trimer and higher polymers. The methanol polymers are very similar to the previously studied water polymers in binding energy and structure. A special stability found for the tetramer in infrared, PVT, heat capacity, and thermal conductivity measurements is consistent with the theoretical results.
Proton magnetic resonance line shape measurements in solid ethane
Authors: Givens F. L. , McCormick W. D.
Published: February 2003

The proton magnetic resonance absorption line shape has been measured for solid ethane in the temperature range from 4 K to the melting point. The linewidth and second moment have been derived from the data. The existence of two solid phases has been confirmed; the solid–solid phase transition temperature was determined to be 89.72 ±0.05 K, and the melting point 90.37±0.05 K. The higher temperature solid phase is characterized by a narrow liquidlike resonance line indicating rapid diffusion. In the lower temperature solid phase the linewidth is much greater and it increases in two stages as the temperature is lowered to 4 K. The second moment of the line has been compared with the result of model calculations and the types of molecular motion inferred. Even at the lowest temperatures the observed second moment is much less than would be appropriate for a rigid lattice; this is interpreted in terms of tunneling of the molecules about their threefold symmetry axes.
Electric relaxation studies of synthetic membrane cells: time-dependent rectification
Authors: Anderson J. E. , Pusch W.
Published: February 2003

We studied electric relaxation across bi-ionic (asymmetric) cells of the form electrode‖solution A‖membrane‖solution B‖electrode. Solutions A and B differ either in concentration or in chemical composition. Response curves were measured at 25 °C as a function of external current and voltage, membrane thickness, and various salts and solution concentration. Cellulose acetate films, between 3×10−4 and 21×10−4 cm thick, were used as membranes. External voltage changes the steady-state ion concentration and the conductivity of the membranes. Conductivity increases with voltage of one polarity, but decreases with the opposite polarity. Ionic concentrations in the membrane require finite time to respond to voltage changes; consequently, the membrane exhibits time-dependent rectification. This is clearly seen in experiments with sinusoidal waveforms. Input and output waveforms are superimposed at high frequencies, where ion redistribution rates are too slow to keep up with voltage oscillations: Here the membrane acts like a constant conductivity. As the ac frequency is reduced and ion redistribution can take place, we see waveform distortion and rectification in the output signal. We measured the voltage response of NaCl/MgCl2 cells to step-current input and the current response of the same cells to step voltage. Our experiments are consistent with a nonlinear relaxation process, where the instantaneous conductivity Λ (t) relaxes toward a conductivity parameter G (V). G (V) is a function derived by Goldman, which relates the steady-state conductivity to the voltage V across the membrane. Bi-ionic cells exhibit both monotonic and oscillating response curves. Following numerical calculations by Cohen and Cooley, oscillating curves are thought to indicate two competing processes. External voltage increases the concentration of ions from one external solution in the membrane, while simultaneously decreasing the concentration of ions from the other solution. The first process increases membrane conductivity; the second lowers it. Superposition of a time-dependent conductivity increase and a time-dependent conductivity decrease produces maxima and minima in response curves. For comparison purposes, experiments on symmetric cells (solution A‖membrane‖solution A) are also reported.
Relaxation kinetics of salol in the supercooled liquid state investigated with the optical Kerr effect
Authors: Ho P. P. , Alfano R. R.
Published: February 2003

The relaxation kinetics of the supercooled liquid salol is investigated using the optical Kerr effect. The Kerr intensity profile versus time is found to decay with two components. The mechanism responsible for this effect is attributed to the nonlinear index of refraction arising from the electronic cloud distortion and molecular reorientational motion of the salol molecules.
An experimental test of the orbiting resonance theory of hydrogen atom recombination at room temperature
Authors: Mitchell D. N. , LeRoy D. J.
Published: February 2003

The percentage of para-hydrogen formed by three body recombination at 296.5 K with helium as the third body has been found to lie between 23.3 and 27.0%. Atom decay profiles were also measured simultaneously, and the third order rate constant obtained from these measurements agreed with other recent work. The implications of these results on orbiting resonance theory are discussed.
Monte Carlo trajectories: Alignment of HBr rotational angular momentum as a function of scattering angle for the reaction H+Br2→HBr+Br
Authors: Blais Normand C. , Truhlar Donald G.
Published: February 2003

A new quasiclassical-trajectory Legendre moment method is applied to calculate the expectation values of several angular-momentum quantities as functions of scattering angle ϑ for the reaction H+Br2→HBr+Br for a relative translational temperature of 2800 °K. The calculated differential cross section is backward peaked. The strongest alignments found are (J′z)2/(J′)2=0.62 at ϑ=135°, (J′z′)2/(J′)2=0.67 at ϑ=100°, and (J′x)2/(J′)2=0.63 at ϑ=95°, where J′ is the magnitude of HBr rotational angular momentum, the z and z′ axes are in the directions of the initial and final relative velocities, and the x axis is perpendicular to the z axis and in the plane of the z and z′ axes. Although the average value of L′/(L′+J′), where L′ is the orbital angular momentum of relative motion, is 0.70, the results differ from statistical-model predictions for the limiting case where L′≳≳J′.
Properties of small ArN−1K+ ionic clusters
Authors: Etters R. D. , Danilowicz R. , Dugan J.
Published: February 2003

A self-consistent formalism is developed that dynamically determines the thermodynamic properties of ionic clusters, based upon a many-body potential, without an a priori designation of the equilibrium structures. The system studied is an aggregate consisting of a single closed shell K+ ion and N−1 isoelectronic argon atoms. The clusters form crystallites at low temperature, with melting transitions at T=8, 19, and 11 K, for N=5, 7, and 13, respectively. They spontaneously disassociate at T=125, 98, 80, and 48 K, for N=3, 5, 7, and 13, respectively. The results confirm experimental evidence that indicates ionic clusters become less stable with increasing N. The crystallite structures formed by these four different systems are isosceles triangle, skewed form, octahedron with the ion in the middle, and icosahedron with the ion in the middle.
Aggregation of proteins in membranes. An example of fluctuation-induced interactions in liquid crystals
Authors: Schröder H.
Published: February 2003

The aggregation of proteins in membranes accompanied by a higher elasticity of the membrane in the vicinity of the proteins and a shift of the crystalline–liquid crystalline phase transition to higher temperatures is shown to be caused by an indirect interaction between the ’’annuli’’ of proteins. In the neighborhood of proteins the order-parameter fluctuations will be decreased, building a region of relative stability, which lowers the free energy of the system. On the base of a linear response approximation an effective potential is defined and an explicit expression for the distance-dependent interaction of two cylindrical model proteins is derived.
Absolute rate parameters for the reaction of atomic hydrogen with carbonyl sulfide and ethylene episulfide
Authors: Lee J. H. , Stief L. J. , Timmons R. B.
Published: February 2003

Absolute rate constants for the reaction of atomic hydrogen with carbonyl sulfide H+OCS→SH+CO (1) and ethylene episulfide H+C2H4S→SH+C2H4 (2) have been determined using the flash photolysis–resonance fluorescence technique. Under conditions where secondary reactions are avoided, rate constants for the carbonyl sulfide reaction over the temperature range 261 to 500 K gave the Arrhenius expression k1= (9.06±1.53) ×10−12 exp(−3850±110/1.987T) cm3 molecule−1 s−1. The corresponding Arrhenius expression for the ethylene episulfide reaction over the temperature range 223 to 423 K is k2= (2.87±0.12) ×10−11 exp(−1880±24/1.987T) cm3 molecule−1 s−1. These results are discussed, comparisons made with previous work, and implications considered for a model of the sulfuric acid aerosol clouds on the planet Venus.
Large amplitude vibrational motion in a one dimensional chain: Coherent state representation
Authors: Dancz John , Rice Stuart A.
Published: February 2003

A study is made of the quantum mechanical motion of a one dimensional finite chain of anharmonic oscillators with free ends. It is shown that, for states which time evolve as coherent states (minimum uncertainty wave packets) of the normal mode vibrations, the motion is equivalent to a classical system with an effective potential interaction determined by convoluting the quantum wave packet and the potential energy. Some examples are discussed, with particular attention given to the Toda and Morse potentials, which are shown to be invariant in form under this convolution. The similarities between the classical Toda and Morse lattices are then utilized to infer the existence of compressional solitary waves in the Morse lattice from the well known soliton solutions of the Toda lattice. Further, for the Morse lattice an analytic expression is found for the first order perturbative correction to the Toda solitons for large amplitude vibrations. We also discuss the relation between the existence of such solitary waves and the rate of vibrational relaxation in molecular systems.
Electronic spectroscopy and dynamics of the low-lying A 3Σ+u, C 3Δu, and c 1Σ−u states of O2 in van der Waals solids
Authors: Goodman Julie , Brus L. E.
Published: February 2003

The 2900–2400 Å absorption of O2 in solid solutions is dominated by the C 3Δu←X 3Σ−g transition, unlike O2 in the gas phase. Isotopically resolved excitation spectra of v=0 C 3Δ1 emission in solid N2 host provide detailed vibrational and electronic C 3Δ spectroscopic parameters. The data establish absolute vibrational numbering for C 3Δ and c 1Σ, in the gas phase as well as in the solid. A progression of perturbations between v C 3Δ2 and v−2 A 3Σ+u is analyzed to show that this host induced interaction is characterized by a 27 cm−1 matrix element. Vibrational relaxation within both singlet and triplet excited states is ’’fast’’ in N2, Ar, and Xe hosts. It is experimentally proven that these spectra occur in isolated O2 monomers. Excited O2 photochemistry appears to occur in Xe host, but not in N2 host. A double resonance experiment of Rebane et al. is reinterpreted.
Mid-infrared spectra of deuterated ices at 10°K and interpretation of the OD stretching bands of ices II and IX
Authors: Bertie John E. , Bates Frances E.
Published: February 2003

The infrared absorption bands due to the OD stretching vibrations of D2O and HDO, and to the D2O rotational vibrations, in the ordered forms of ice, ice II and ice IX, change little between 100 and 10°K. The frequencies and relative intensities of the zero-wave-vector OD stretching vibrations of these phases have been calculated in the harmonic and bond-moment approximations, and explain the main features of these bands. The features are less well resolved than is expected for an ordered molecular crystal, and this ’’hydrogen bonding effect’’ is attributed primarily to Fermi resonance between the fundamental states of the OD stretching vibrations and the isoenergetic continuum of high-order, overtone, and combination states of lower-frequency vibrations. The frequency of the OD stretching vibrations of HDO molecules isolated in H2O ice 1h at 10°K is 2413.5±1 cm−1.
Quantum mechanical theory of a structured atom–diatom collision system: A+BC(1Σ)
Authors: DeVries Paul L. , George Thomas F.
Published: February 2003

The problem of a 2P state atom colliding with a singlet sigma state diatom, which involves multiple potential surfaces, is investigated. Within a diabatic representation for the electronic degrees of freedom (plus spin–orbit interaction), coupled scattering equations are derived in both space-fixed and body–fixed coordinate systems, and coefficients analogous to Percival–Seaton coefficients are exhibited. Approximations to the exact equations, including angular momenta decoupling approximations, are discussed for both the space-fixed and body-fixed formalisms.
Linear response theory and the mechanical energy relaxations of solid high polymer systems
Authors: Eu Byung Chan , Rackovsky S. , Eisenberg A.
Published: February 2003

Linear response theory is applied to mechanical energy relaxation phenomena of polymer solids below the glass transition temperature. The relaxation modulus is related to time-correlation functions of ’’forces.’’ The time-correlation functions are approximately calculated in the paper in the single relaxation time model. The relaxation time is explicitly calculated in the approximation for systems with pendant cyclohexyl groups. The results obtained are examined in the light of experimental data and show that the present linear response theory approach is promising for mechanical spectroscopy of solid polymer systems.
Ionization of xenon atoms in high Rydberg states by collision with molecules
Authors: Foltz G. W. , Latimer C. J. , Hildebrandt G. F. , Kellert F. G. , Smith K. A. , West W. P. , Dunning F. B. , Stebbings R. F.
Published: February 2003

Ionization of xenon atoms in single highly excited states ‖nf≳ (where 25⩽n⩽40) by collisions with CCl4, CCl3F, and SF6 has been investigated. Absolute rate constants for Xe+ production are reported together with the identities of the major negatively charged species produced in the collisions. Cross sections determined from these rate constants are also given. The data lend support to the theoretical model, which views such collisions as being dominated by the interaction between the target molecules and the excited electron, with the Xe+ ion core playing a minor role.
Nuclear corrections to molecular properties. V. Refinements in a
b i
n
i
t
i
o normal-coordinate potential energy and property surfaces for water and their effect on the vibrational analysis
Authors: Ermler Walter C. , Krohn Burton J.
Published: February 2003

A b initio surfaces in reduced normal-coordinate space for water, for the potential energy and components of the dipole moment and second moment of charge about the center of mass, have been refined for use in calculating energies of vibration and expectation values of of these properties in low-lying states of vibration. The two procedural refinements consist of (i) direct fitting of the surfaces to values obtained at a grid of points, where the internal coordinates for each point have been transformed to reduced normal coordinates by an iterative procedure, and (ii) (small) rotation of the axes into coincidence with a vibrationally invariant set at each asymmetric configuration on the grid. The first refinement brings the calculated values of the constants of anharmonicity xij into much closer agreement with experiment. Both refinements generate significant changes in the fitted property surfaces. For several isotopic species of water calculated expansion coefficients are listed for the potential energy in reduced normal coordinates and the dipole moment in internal and reduced normal coordinates; expectation values are also given.
Electron attachment to carbon dioxide clusters in a supersonic beam
Authors: Klots Cornelius E. , Compton R. N.
Published: February 2003

Negative ions have been observed in a time-of-flight man spectrometer with charge-to-man satios corresponding to (CO2)−n with 2⩽n⩽6. It is concluded that these ions are formed by electron attachment to clusters formed in the rapidly expanding CO2 beam from a sonic nozzle. (AIP)
Photoluminescence decay in solid xenon
Authors: Monahan K. , Rehn V. , Matthias E. , Poliakoff E.
Published: February 2003

Photoluminesence bands in solid xenon are studied using synchrotron radiation from SPEAR as excitation source. (AIP)
Legendre moment method for calculating differential scattering cross sections from classical trajectories with Monte Carlo initial conditions
Authors: Truhlar Donald G. , Blais Normand C.
Published: February 2003

We present a method for obtaining continuous differential cross sections for molecular collisions from trajectories with initial conditions selected by Monte Carlo methods. It is a moment method and we represent the differential scattering cross section in terms of the moments of the normalized Legendre polynomials of the cosine of the scattering angle. The method is applied to five examples, for four of which we evaluate the necessary moments exactly. The fifth is a realistic example of an experimentally obtained differential cross section. For the first four cases we can obtain satisfactory convergence with as few as 400 trajectories with the proper choice of the highest order moment used in the expansion. As a working criterion we select as the highest order coefficient the highest order moment whose absolute value is larger than 0.05. Generally, the method does not converge any more rapidly than does the histogram method. It does provide a simple way of deciding the available angular resolution in the differential cross section for a given number of trajectories.
The effect of pressure on the Raman spectra of mercurous chloride and bromide
Authors: Richter P. W. , Wong P. T. T. , Whalley E.
Published: February 2003

The Raman spectra of powdered mercurous chloride and bromide have been measured at zero pressure and up to 16 kbar. At low pressure there are many bands that are forbidden by the crystallographic symmetry I4/mmm, and so the apparent symmetry arises by disorder. One forbidden band was studied under pressure and it increased greatly in intensity. The disorder therefore increases in amplitude with increasing pressure. The disorder is probably related to the structures of the low-temperature phases.
Crossed molecular beams kinetics: BaO recoil velocity spectra from Ba+N2O
Authors: Parr Timothy P. , Freedman Andrew , Behrens Richard , Herm Ronald R.
Published: February 2003

Laboratory (LAB) angular and time-of-flight (TOF) recoil velocity spectra of BaO product produced by crossing a thermal Ba beam with an N2O nozzle beam have been measured in a molecular beam apparatus equipped with an electron bombardment ionizer–quadrupole mass filter ’’universal’’ detector. Product center-of-mass (c.m.) recoil angle and energy distributions have been fit to the data by convoluting the c.m.→LAB transformation over the measured speed distributions of both beams and the bandpass of the TOF analyzer for different N2O vibration and relative collision energies. The results indicate a direct reaction mechanism with substantial internal excitation of the products. Backward scattering of the BaO relative to the initial Ba direction is favored, but the product angular distribution also broadens as the reactant energy increases.
Time-dependent nucleation theory
Authors: Draine B. T. , Salpeter E. E.
Published: February 2003

The theory of time-dependent homogeneous nucleation in a supersaturated cooling gas is investigated both analytically and numerically. The character of the nucleation process (e.g., the critical supercooling when the nucleation rate peaks, and the final cluster size) depends almost entirely on just two dimensionless quantities: the ratio ϑ/T (where T is the temperature, and kϑ is essentially the surface free energy per surface site) and a dimensionless parameter η which measures the number of times monomers collide with a single surface site during one supersaturation ratio e-folding time. Within the framework of classical nucleation theory (assuming the nucleating vapor to be in a carrier gas) an approximate analytical treatment of the regime η≫1 (which includes nearly all terrestrial nucleation experiments) is given, resulting in simple formulas for the critical supersaturation ratio, the mean final cluster size, and the relative dispersion in final cluster sizes. To test the accuracy of the approximations the analytic results are compared with more exact numerical calculations for a number of values of ϑ/T and η; good agreement is found in the limit η≫1. Validity criteria for the use of the results are obtained.
Direct determination of non-Boltzmann vibrational level populations in electric discharges by CARS
Authors: Shaub W. M. , Nibler J. W. , Harvey A. B.
Published: February 2003

The direct measurement of nonequilibrium vibrational level populations of N2 at the center of an electric discharge has been demonstrated by a new diagnostic technique: coherent anti-Stokes Raman spectroscopy (CARS). On the assumption of a Boltzmann equilibrium among only the lowest vibrational levels, a method has been developed and utilized for the direct determination of vibrational populations of all other levels, even in the case of extreme deviations from a Boltzmann equilibrium. Limitations of the method are discussed and illustrated.
The Mössbauer isomer shift in iron (III) sulfate
Authors: Haven Y. , Noftle R. E.
Published: February 2003

The Mössbauer spectra of the rhombohedral and monoclinic modifications of Fe(III) sulfate have been measured. The isomer shift is 0.496 mm s−1 relative to α-Fe for both modifications and the quadrupole splittings are 0.15 and 0.30 mm s−1, respectively. The isomer shift of Fe2(SO4)3 fits on a calibration curve of electron density versus isomer shift proposed by Barrett and Micklitz, and its position is consistent with a high degree of ionic character for the compound. It is proposed to include Fe2(SO4)3 as one of the calibration points for electron density versus isomer shift.
An exactly soluble model of dissociation–recombination
Authors: Gutkowicz-Krusin D.
Published: February 2003

A master equation for a classical collinear model of collisionally induced dissociation and recombination is solved. With the choice of impulsive interaction between diatomic molecules A2 and heat-bath particles M, the results depend strongly on the value of α =arc tan(1+2mA/mM)1/2. It is found that the approach to equilibrium is not, in general, exponential in time for α=π/4, but that the relaxation is exponential for α=0.254π and α=π/3, with, however, different degrees of deviation from the equilibrium approximation. In both of these cases the inequalities kD ?k′D?keqD and kR?k′R=keqR are satisfied, where k′D and k′R are the rate constants calculated when the appropriate reverse reactions are neglected. The rate constants kD and kR are shown to have a weak dependence on the total density of reacting species. In addition, for α=0.254π, a ’’negative activation energy’’ for recombination is obtained at high temperatures.
Excitation of the 3D3 metastable state in mercury by electron impact
Authors: Borst Walter L.
Published: February 2003

The excitation function and cross sections for the production of 5D03 metastable state of mercury by electron impact are discussed. (AIP)
Molecular orbital theory for nonregular polymer chains: Distortions of an infinite chain of hydrogen molecules
Authors: O’Shea S. F. , Santry D. P.
Published: February 2003

A perturbative method is introduced for the theoretical study of lattice distortions in regular polymers. The method is applied to a chain of hydrogen atoms and an estimate of the error entailed in the first order expansion made from a comparison against direct calculations for special lattice distortions. These calculations suggest that the CNDO/2 molecular orbital method predicts the uniformly spaced chain of hydrogen molecules to be the most stable structure for this system.
Transition moments between excited electronic states of N2
Authors: Yeager Danny L. , McKoy Vincent
Published: February 2003

We report the transition moments between the excited states of molecular nitrogen including their dependence on internuclear distance. These moments are calculated using the equations of motion method and can be obtained with only a slight increase in the effort needed to obtain the ground to excited state transition moments. The transition moments along with reliable vibrational wavefunctions should be useful in the analysis of observed band intensities of N2.
Raman studies of librational motion in N2/CO and CO2/N2O mixed crystals
Authors: Witters Kent R. , Cahill J. E.
Published: February 2003

The Raman spectra of N2/CO and CO2/N2O mixed crystals have been measured in the lattice mode region. The spectra of the CO2/N2O mixed crystals exhibit very definite one-mode behavior indicating that the librational states are within the amalgamation limit. In the N2/CO mixed crystals, the Eg and lower frequency Tg modes show one-mode behavior while the higher frequency Tg modes show two-mode behavior. These spectra are shown to be consistent with the established assignments and the librational exciton concept when perturbations in both the site energy and the excitation exchange interactions are considered. The effect of the random sense of the molecules in pure N2O and CO is also discussed from the librational exciton point of view. Two-phonon scattering has been observed in all of the samples and is attributed to librational motion.
Laser magnetic resonance spectroscopy of the ν2 fundamental band of HCO at 9.25 μm
Authors: Johns J. W. C. , McKellar A. R. W. , Riggin M.
Published: February 2003

The ν2 bending fundamental (ν0=1080.76 cm−1) of the formyl radical, HCO, has been studied using CO2 laser magnetic resonance. Fluorine atoms from a discharge in CF4 were reacted with H2CO to form the short-lived HCO, which then flowed through an absorption cell located between the pole faces of an electromagnet and within the optical cavity of a CO2 laser. By means of the Zeeman effect, HCO, vibration-rotation transitions were tuned through resonance with the laser lines. Numerous resonances involving levels with 1⩽N⩽7 and 1⩽Ka⩽3 were assigned, and from analysis of the spectra accurate determinations of the band origin, rotational, centrifugal distortion, spin-rotation, and Fermi interaction parameters for ν2 were made. Fairly large changes in the values of A, ΔK, εaa, and ηaaaa between the ground and v2=1 vibrational states were observed.
Exactly solvable models for vibronic coupling in molecular spectroscopy. II. Totally symmetric harmonic mode
Authors: Gregory A. R. , Henneker W. H. , Siebrand W. , Zgierski M. Z.
Published: February 2003

The treatment of paper I of this series [J. Chem. Phys. 65, 2071 (1976)] is extended to totally symmetric modes. The effect of displacement of vibrational potentials and removal of parity as a conserved quantum number is illustrated through exact model calculations of energy-level diagrams and absorption spectra for the full range of coupling values compatible with the harmonic model chosen.
Raman study of orientational disorder in the molecular charge-transfer crystals naphthalene–TCNB and naphthalene–PMDA
Authors: Macfarlane R. M. , Ushioda S.
Published: February 2003

We have studied orientational disorder in the molecular charge-transfer crystals naphthalene–tetracyanobenzene (N–TCNB) and naphthalene–pyromellitic dianhydride (N–PMDA) by Raman scattering from low frequency intermolecular modes. From the temperature dependence of intensities and linewidths we find strong evidence for an order–disorder transition in naphthalene–TCNB at 63 K in which the center of symmetry is removed. In naphthalene–PMDA, on the other hand, the spectrum is consistent with an ordered structure in which the molecules exhibit anharmonic motion at high temperatures.
Magnetic susceptibility studies of the liquid crystal, N- (p-hexyloxybenzylidene) -p-toluidine (HBT)
Authors: Bahadur Birendra
Published: February 2003

The temperature variation of the magnetic susceptibility (χ) of HBT was studied in isotropic, nematic, smectic B and solid phases. Abrupt changes in χ and Δχ were observed at various phase transitions. An unusual decrease in χ with decreasing temperature was recorded during nematic–smectic B transition.
Semiempirical calculation of diamagnetic susceptibilities of organo–silicon compounds containing carbon–silicon bonds
Authors: Gupta R. R.
Published: February 2003

A semiempirical method for calculating diamagnetic susceptibilities of organo–silicon compounds containing carbon–silicon bonds is reported. Susceptibilities are considered to be contributed by the atoms, bonds, and bond–bond interactions and expressed in terms of parameters. Diamagnetic susceptibilities have been calculated for monomethyl alkyl, dimethyl alkyl, trimethyl alkyl, and tetraalkyl silanes and agree with in 0.75% of experimental values. It can be extended to predict susceptibilities of organic derivatives of metals and metalloids.
Quenching reactions of He(2 3S) and He2(2 3Σ) metastables in the presence of N2 and O2
Authors: Myers G. , Cunningham A. J.
Published: February 2003

Quenching reactions of He(2 3S) and He2(2 3Σ) metastables in the presence of N2 and O2 have been studied in the afterglow period of electron beam excited discharge plasmas at atmospheric pressures. For He(2 3S) both bimolecular and termolecular quenching rate coefficients were determined. For He2(2 3Σ) only bimolecular quenching reactions were observed, and rates for this processes are presented for the first time. In the termolecular quenching of He(2 3S) in the presence of N2 and O2 the product states of this reaction were identified as the He2(2 3Σ) molecular metastable.
Calculation of linear and nonlinear electric susceptibilities of conjugated hydrocarbon chains
Authors: Hameka Hendrik F.
Published: February 2003

We calculated the π electron contributions to the linear and nonlinear static electric susceptibilities of a linear conjugated hydrocarbon chain. We started from the Hückel equations for the π electrons in the presence of an electric field, and we expanded the equation in terms of the electric field by using perturbation theory. We solved the successive perturbation equations analytically, and we derived exact analytical expressions for the energy perturbations up to fourth order. We used these energy perturbations to derive values for χ(1)XX, χ(2)XXX, and χ(3)XXYY where the X axis is along the chain. We found that the molar linear susceptibility χ(1)XX is roughly proportional to the 2.8 power of N and that the nonlinear susceptibility χ(3)XXXX is roughly proportional to the 5.3 power of N. For larger values of N the π electron contributions to the susceptibilities become much larger than the σ electron contributions.