bluuebunny/crossref_metadata_2025 huggingface dataset:
Uniform quality Gaussian basis sets
Authors: Mezey Paul G. , Kari Roy E. , Csizmadia Imre G.
Published: February 2003

A direct optimization technique was applied to determine uniformly balanced, optimum (4s2p), (6s3p), (8s4p), and (10s5p) Gaussian basis sets for the first row atoms. These bases formally correspond to 2G, 3G, 4G, and 5G function representations per symmetry type per shell. The basis sets are throroughly balanced and all satisfy a rather rigorous quality criterion in terms of the local properties of the energy hypersurface over the space of the orbital exponents.
The transition of sulfur to a conducting phase
Authors: Chhabildas Lalit C. , Ruoff Arthur L.
Published: February 2003

Crystalline rhombic sulfur, an excellent insulator, has been converted to a conducting phase in 19 experiments. The cell resistance (initially determined by the boron nitride gasket) drops by at least six orders of magnitude at the transition; the sulfur resistivity itself has changed by a factor of 10−21 compared to its initial value. On the basis of a comparison technique utilizing a two sample cell with either ZnS and S pairs or S and GaP pairs, the transition pressure was shown to be between that for ZnS and for GaP. From interpolation of the forces for the three transitions, the transition pressure of sulfur to a conducting phase was found to be 175 kbars.
19F shielding anisotropies of the fluoromethanes obtained from NMR studies in a smectic liquid crystal solution
Authors: Montana Anthony J. , Dailey Benjamin P.
Published: February 2003

19F magnetic shielding anisotropies of the fluoromethanes have been obtained from studies in a smectic liquid crystal solution using a pulsed FT NMR spectrometer. The value of Δσ obtained for methyl fluoride in the smectic phase is observed to be comparable in magnitude but higher in accuracy than the previous measurements obtained from theoretical, clathrate, molecular beam, and nematic single phase techniques, with the earlier value obtained using the nematic–isotropic two-phase method being obviously in error. The shielding anisotropy measured for fluoroform is found to agree with the prior nematic two-phase value, with the nematic single-phase and clathrate values being considerably lower. The anisotropy measured in this investigation for methylene fluoride was found to be in disagreement with both previous values measured via molecular beam and nematic two-phase techniques. It is shown that on transforming the experimental shielding anisotropy values obtained in this study along the C–F bond direction, that σ11, the shielding component parallel to the C–F bond ,is essentially constant in magnitude for all three systems. In addition, it is also observed that from a knowledge of the signs of the orientation parameters that the absolute signs of the indirect proton–fluorine nuclear spin–spin coupling constants for the fluoromethanes are found to be unambiguously positive.
Internal conversions and relaxation dynamics in the CN radical in solid neon
Authors: Bondybey V. E.
Published: February 2003

In the present work we study the relaxation dynamics of the CN radical in solid Ne following selective excitation of individual vibronic levels of the A 2π and B 2Σ states. We demonstrate experimentally that when the molecule can relax by either vibrational relaxation or by internal conversions into lower lying levels of a nearby electronic state, the latter process is dominant. Neither near resonance nor perfect Franck–Condon overlaps are required for efficient internal conversions to occur. The rates of these conversions show qualitatively the exponential dependence on the size of the energy gap predicted by theory. The CN radical is stabilized in the solid Ne in several distinct trapping sites; its vibrational constants show negligible perturbation by the solid medium.
Laser Stark spectroscopy of the fundamental bands of HNO (ν2 and ν3) and DNO (ν1 and ν2)
Authors: Johns J. W. C. , McKellar A. R. W.
Published: February 2003

The ν2 (N–O stretch) fundamental bands of HNO and DNO and the ν3 (bending) band of HNO in the 6.5 μm region have been studied using the technique of laser Stark spectroscopy. The experiment utilized a Stark cell located inside the cavity of a CO laser, with the short-lived HNO molecules produced in a flow system by the reaction H+NO→HNO. Accurate values for the band origins, rotational constants, and dipole moments were obtained from analyses of 35 transitions in DNO and over 40 in HNO. The Coriolis interaction between the close-lying ν2 and ν3 states of HNO was explicitly included in the analysis, enabling a value for the Coriolis interaction parameter to be derived. A few transitions in the ν1 (N–D stretch) band of DNO near 5 μm were also detected from which a tentative value of the band origin was estimated.
Expansion methods for Adams–Gilbert equations. I. Modified Adams–Gilbert equation and common and fluctuating basis sets
Authors: Matsuoka Osamu
Published: February 2003

Adams–Gilbert (AG) equation for nonorthogonal localized orbitals of a single-determinant wavefunction has been modified so as to enable one to compute wavefunctions of large polyatomic systems by the expansion method. This equation is named as modified Adams–Gilbert (MAG) equation. One solves the AG or the MAG equation by each subsystem and, collecting all the orbitals obtained, one constructs wavefunction of the system. It is shown that when one employs the expansion method, one must actually use basis functions common to all the subsystems (common basis set) to solve the AG equation, while one can employ, by each subsystem, different basis functions appropriate to the subsystem (fluctuating basis set) to solve the MAG equation. An expansion method suitable for solving the AG and the MAG equations has been presented. Application of the method to HF, H2O, and CH4 has revealed that (1) the method proposed is workable, (2) actually so many basis functions are not needed for describing some subsystems, especially for core electrons, and (3) it is necessary to orthogonalize approximately, not necessarily rigorously, the orbitals in the system.
Collision dynamics of three interacting atoms: A method of diatomics-in-molecules
Authors: Micha David A.
Published: February 2003

The interaction of three atoms in a collision process is treated within the Faddeev formalism for three bodies by a method of diatomics-in-molecules (DIM). Many-electron wavefunctions for given electron spin are constructed for each rearrangement channel and are employed to discuss electron exchange. Expansion of scattering equations in these wavefunctions provides a general starting point for calculations. We briefly discuss a Born–Oppenheimer decoupling and a DIM approximation of matrix elements. These developments are exemplified for a system of three hydrogen atoms.
Semiclassical theory of quantum defects: Alkali Rydberg states
Authors: Jaffé Charles , Reinhardt William P.
Published: February 2003

A semiclassical theory of atomic quantum defects is given in terms of a ’’radial action defect’’ derived in the context of Hamilton–Jacobi theory. This derivation leads to the relation δl(E) =πμl(E) between the semiclassical (WKB) phase shift and the semiclassical quantum defect, a result identical in form to that of Seaton for the analogous fully quantum mechanical quantities. The semiclassical theory is used to compute quantum defects for the l=0→3 Rydberg states of Li and the l=0→4 states of Na and K, with good results.
The electronic states of KrF
Authors: Hay P. Jeffrey , Dunning Thom. H.
Published: February 2003

A b initio configuration interaction calculations for the electronic states of KrF are presented. States dissociating to Kr+F(2P), Kr+(2P)+F− and Kr* (3P)+F(2P) are investigated. Spin–orbit coupling is included in a semiempirical manner for the covalent and ionic states. The covalent curves are essentially repulsive in character, while the attractive ionic curves have wells 5.2–5.3 eV deep with calculated Re′s of 2.4–2.5 Å. The lowest 2Σ+ Rydberg state also forms a bound state with calculated values of Re=1.83 and De=1.33 eV. The intense laser emission at 248 nm is found to arise from the transition between the lowest ionic Ω=1/2 to covalent Ω=1/2 states (III1/2–I1/2 in our notation) calculated to occur at 241 nm with a spontaneous lifetime of 7 nsec. The observed emissions at 220 nm and 275 nm are assigned to the IV1/2–I1/2 and II3/2–I3/2 transitions, respectively.
Electro-optical investigation of the effect of space charge on molecular alignment in poly-γ-benzyl-L-glutamate solutions
Authors: Tsuji Kinko , Watanabe Hiroshi
Published: February 2003

In the process of the electro-optical investigation of the concentrated PBLG solutions with various concentrations, semimacroscopic inhomogeneity of the molecular alignment and the dynamic movement of the solution under the dc electric field were observed by use of a polarizing microscope with crossed polarizers. In order to clarify these phenomena in detail, the transient electric birefringence under a long dc electric pulse at various positions in the solutions was measured using a very thin light beam. The typical electric birefringence signal consists of three peaks. The appearance time of the first peak was independent of the position in the solution, but the second peak was propagated from the cathode to the anode. Results were interpreted in conjunction with the effect of the space charge injected from the electrodes on the electrical property of PBLG molecule. Different types of the migration of the space charge were noted.
Quasiclassical studies of rigid rotor–solid surface diffraction scattering
Authors: Ray Charles J. , Bowman Joel M.
Published: February 2003

The quasiclassical trajectory method, previously applied to atom–solid elastic diffraction scattering [C. J. Ray and J. M. Bowman, J. Chem. Phys. 63, 5231 (1975)] is extended to the study of rigid rotor–solid diffraction scattering. The extension of the method allows for the study of rotational inelastic events without recourse to phonon interactions. The results for a 104 meV H2(j=0) beam and 52 meV D2(j=0) beam scattered from the (001) face of LiF are compared with the recent quantal calculations of Wolken [J. Chem. Phys. 59, 1159 (1973)]. The dependence of the D2(j=0) scattering on initial beam orientation is also presented and compared with the recent experimental results of Rowe and Ehrlich [J. Chem. Phys. 63, 4648 (1976)] for the D2+MgO(001) system.
Deuterium isotope effects in the radiation chemistry of glassy and polycrystalline hydrocarbons
Authors: Wilkey D. D. , Fenrick H. W. , Hager S. L. , Bremer N. , Willard J. E.
Published: February 2003

The G value (radicals produced per 100 eV absorbed) of trapped free radicals produced by γ radiolysis of five polycrystalline alkanes (n-pentane, n-hexane, n-octane, cyclohexane, 3-methylheptane and methylcyclohexane) is in each case higher by a factor of 1.6±0.2 in the protiated compound than in the deuterated (≳98 at.% D) compound. This indicates a radiolytic mechanism which favors C–H over C–D bond rupture with similar probability independent of molecular structure or crystallinity. In hydrocarbon glasses containing certain additives, the G values of trapped or scavenged electrons are higher in the deuterated than the protiated matrices. Possible mechanistic origins of these isotope effects are considered.
Gas phase EPR linewidths and intermolecular potentials. V. Quantal derivation
Authors: Fisanick-Englot G. J. , Miller Terry A.
Published: February 2003

A fully quantal derivation of the isolated line broadening parameters applicable to gas phase EPR experiments is presented. Errors inherent in the use of zero field operators are discussed. Under this simplifying approximation line shifts are shown to be identically zero, while the linewidth may be expressed in terms of either Grawert coefficients or isotropically averaged population transfer cross sections. Connection is made to a previously derived semiclassical density matrix formulation. Application of the results to He+F(2P3/2, 2P1/2) broadening will be made in a following paper.
Picosecond photodynamics of intense pulse interactions with molecular populations
Authors: Olson G. L. , Busch G. E.
Published: February 2003

The ultrafast modification of molecular electronic state populations by picosecond duration laser pulses is discussed. The photodynamic interactions operative during the dual pulse irradiation of a saturable absorbing dye are treated by a rate equation approach which allows the temporal changes in the gain and attenuation conditions of the absorber to be predicted. The treatment relies on a knowledge of the molecular absorption and stimulated emission profiles and the existence of homogeneously broadened electronic states of the molecule. The approach is applied to a description of the passive mode-locking capability of certain saturable absorbing dyes at wavelengths substantially different from their absorption maxima.
An analysis of the natural orbital theory of ionization potentials
Authors: Andersen Earl , Simons Jack
Published: February 2003

A perturbation approach is used to analyze the natural transition orbital method proposed by Smith and Day for computing ionization potentials. The results are carried to third order in the electronic interaction and a comparison is made with the diagrammatic method of Cederbaum. Two of the third-order terms included in the natural transition orbital method which contribute to the ’’particle part’’ of the self-energy are found to differ from Cederbaum’s diagrammatic terms by multiplicative factors.
Charge transfer complexes and hyperpolarizabilities
Authors: Levine B. F. , Bethea C. G.
Published: February 2003

We have measured the second order β and third order γ hyperpolarizabilities of the three charge transfer complexes pyridine+I2, pyridine+ICl, and 4-aminopyridine+I2. Using Mulliken’s charge transfer theory we have been able to understand theoretically the large magnitude and absolute sign of these hyperpolarizabilities as well as their interesting and surprising dependence on the strength of the charge transfer interaction.
Rate constants for the reaction of OH radicals with ethylene over the temperature range 299–425 °K
Authors: Atkinson R. , Perry R. A. , Pitts J. N.
Published: February 2003

Absolute rate constants for the reaction of OH radicals with ethylene have been determined, using a flash photolysis–resonance fluorescence technique, over the temperature range 299–425 °K at total pressures of 25–663 torr of argon. The rate constants k2 were observed to be pressure dependent below ∼225 torr total pressure, in agreement with other recent studies. The rate constants were independent of total pressure over the range 225–663 torr of argon, and the Arrhenius expression obtained from data over this pressure range was k2=2.18×10−12 e(770±300)/RT cm3 molecule−1⋅sec−1 with a value at 299 °K of k2= (7.85±0.79) ×10−12 cm3 molecule−1⋅sec−1. This room temperature high pressure rate constant is in good agreement with a recent relative rate determination carried out at atmospheric pressure.
Anisotropic reorientation of planar molecules measured by nuclear relaxation in strongly coupled spin systems
Authors: Vold R. L. , Vold R. R. , Canet Daniel
Published: February 2003

In this paper we describe the use of nuclear magnetic relaxation in strongly coupled spin systems for determining all three rotational diffusion constants of rigid, planar molecules with C2v symmetry. The complete evaluation of the motional parameters rests on the accurate measurement of the cross-correlation terms relating the reorientation of two proton–proton internuclear vectors. This term, as well as more familiar auto correlation terms, may be extracted from an analysis of the recovery of individual lines in the strongly coupled proton spin system following a nonselective 180° pulse. The principles, procedure, and practical considerations of this approach to studies of anisotropic motion are illustrated for the AB2 spin systems of 1,2,3-trichlorobenzene, 2,6-dichloroanisole, and 2,6-dichlorophenol-0-d.
A close coupling calculation for inelastic collisions of protons on H2 molecules at 3.7 eV
Authors: Gianturco F. A. , Tritella P.
Published: February 2003

An an initio computed potential surface for the H3+ system at various geometries is expanded in Legendre polynomials and the ensuing radial coefficients are employed to yield the S-matrix elements from the close coupling expansion of the scattering equations, at the collision energy of recently performed molecular beam experiments. The rotationally inelastic cross sections are obtained for an energy corrected, rigid rotor H2 target and the influence of increasing the basis set size is discussed. The dominant contribution of the charge–quadrupole interaction to the computed observables is examined and an interesting effect is observed on the impact parameter dependence of the 0→2 excitation cross section. All these features are explained in terms of the special nature of the proton interaction with the molecular system and of the dynamics that stem from it.
Quantitative tests of mixed crystal exciton theory. II. Energy denominator study of naphthalene 1B2u resonance pairs
Authors: Ochs Frederick W. , Kopelman Raoul
Published: February 2003

A spectroscopic absorption study is presented of 1-D1C10H7, 2-D1C10H7, and 1,4-D2C10H7 resonance pairs in C10D8, over a concentration range of 0.009% to 5% mole, at 2 °K, with a resolution of 0.5 cm−1. The resulting structure is interpreted in terms of the pairwise exciton exchange interactions, M1/2(a+b), Ma, Mb, Mc, Ma+c, and M1/2(a+b)+c. The energy denominator dependence is interpreted in terms of both exciton quasiresonance and exciton superexchange. The three parameter sets derived by Hong and Kopelman to fit earlier data on neat and isotopic mixed crystals are corroborated by this study, as they were in our previous study on monomers (I). However, it was not possible to narrow down completely the choice of parameters. A discussion is given on the feasibility of deriving a unique dispersion relation (and Green’s function) for the first naphthalene singlet exciton and on its likely precision.
Photodissociation of nitrous oxide cation
Authors: Orth Robert G. , Dunbar Robert C.
Published: February 2003

The cross sections for photodissociation of N2O+ were obtained by ion cyclotron resonance techniques for wavelengths ranging from 220 to 700 nm. The cross section curve for this region showed two peaks, one with a maximum occurring at 340 nm (3.65 eV) having a cross section value of 4.9×10−19 cm2 and the second with a maximum occurring at 240 nm (5.16 eV) having a cross section value of 6.5×10−18 cm2. The peaks are attributed to dissoication from the ? 2Σ+ excited state and the ? 2Π excited state of the ion, respectively. Dissociation from the ? 2Σ+ state was found to yield only one product ion, NO+. For the ? 2Π state the main dissociative product was found to be NO+. The formation of N2+ from this state is apparently an alternative channel, but could not be demonstrated unambiguously. The photodissociation results were found to be consistent with previous studies by photoionization and photoelectron spectroscopy of the dissociative processes from these excited doublet states.
k-independent Rayleigh diffuse line and orientational order in plastic crystals
Authors: Bonnet J. P.
Published: February 2003

A theory of the Rayleigh diffuse line in plastic crystals is proposed. It is shown that the intensity of the diffuse line changes with crystal orientation and that these changes are directly related to the orientational order parameters characteristic of the plastic phase. These results are in agreement with the Kerr effect [T. Bischofberger and E. Courtens, Phys. Rev. Lett. 32, 163 (1974)] and Rayleigh scattering {L. Boyer, R. Vacher, and L. Cecchi [J. Phys. (Paris) 36, (1975)]} measurements made on succinonitrile (cubic plastic crystal).
Kinetic theory of rough sphere fluids: Linear and angular velocity correlation functions
Authors: Mehaffey J. R. , Desai Rashmi C. , Kapral Raymond
Published: February 2003

We present a renormalized kinetic theory for tagged particle motion in a rough sphere fluid which includes the effects of correlated collisions. The kinetic theory is a generalization of a recent theory for monatomic fluids by Mazenko. The correlated collisions create slowly decaying memory in the linear (ψv) and angular (ψω) velocity correlation functions on account of the coupling of the test particle density fluctuations to various moments of the full phase space density correlation function. (These moments are connected with the conserved variables in the system). We use the theory to study ψv and ψω and compare the results with recent molecular dynamics experiments of O’Dell and Berne. The kinetic theory yields the correct long time power law decay for both ψv and ψω without imposing any wave vector cutoff characteristic of the hydrodynamic theories. It also yields useful new insights into various mode couplings responsible for the behavior of ψv and ψω at small and intermediate times. The qualitative features of the computer experiments are reproduced by the theory.
ESR studies of Yang’s biradical
Authors: Mukai Kazuo , Mishina Tadashi , Ishizu Kazuhiko
Published: February 2003

Yang’s biradical (I), its mono- and di-deuterated derivatives, (II) and (III) were generated by PbO2 oxidation in toluene of corresponding bisphenol precursors and investigated by means of ESR spectroscopy. The frozen toluene ESR spectrum of Yang’s biradical (I) at 77 °K has been analyzed, and the g- and D-tensor values have been determined. The results suggest that the threefold symmetry of Yang’s biradical has disappeared in the frozen rigid matrix. Essentially the same g- and D-tensor values are observed for its mono- and di-deuterated derivatives (II) and (III). On the other hand, the toluene solution ESR spectra of these three biradicals at 20 °C appear to correspond to hyperfine interaction with equivalent six, five, and four meta ring protons, respectively. The expected inequivalence of the proton splittings of these biradicals is less than the linewidths.
A pure-rotational collisionally pumped OH laser
Authors: Downey Gale D. , Robinson Dean W. , Smith John H.
Published: February 2003

Laser oscillation is reported on certain pure-rotational transitions in the ground electronic state of the hydroxyl ion, v=0 and v=1. the active medium has been prepared by the O(1D)+H2 reaction in a large excess of rare gas. The transitions on which oscillation occurs have upper states which are energetically resonant with one, or even two, vibrational quanta. The pumping mechanism is assigned as a V→R transfer with ΔJ the order of 12.
Vapor pressures of the isotopic ethylenes. V. Solid and liquid ethylene-d1, ethylene-d2 (c
i
s, t
r
a
n
s, and g
e
m), ethylene-d3, and ethylene-d4
Authors: Bigeleisen J. , Fuks S. , Ribnikar S. V. , Yato Y.
Published: February 2003

A simple chromatographic method is described for the purification of gases. The method can process of the order of 0.5 liter/day and reduce impurities to the ppm level with greater than 90% recovery of feed. Samples of all the deuterated ethylenes have been purified by this procedure over activated alumina columns and their vapor pressures measured over the temperature range 94–180 °K. They are in excellent agreement with the previous measurements on the liquid from the Brookhaven Isotope Chemistry Laboratory. In contrast to the liquid, the deuterated ethylenes show the normal vapor pressure isotope effect in the solid. A new vapor pressure curve for solid C2H4 is derived from the measurements log10P (mm Hg) =9.6921−1011.5/T (94<T<104 °K). The triple point temperatures of the deuteroethylenes have been found to increase with deuteration. A difference is found in the triple point temperatures of the equivalent isomers trans-, cis-, and gem-dideuteroethylene. The results are interpreted in terms of an anharmonic version of the BSVHW model of the solid and liquid applied to the statistical mechanical theory of condensed phase isotope effects. It is found that the force constants associated with the librational motions of the molecule are 50% larger in the solid than the liquid at the triple point. After correction of the temperature dependence of the isotopic vapor pressure data for translation and rotation through a corresponding states method, it is found that agreement with the large body of experimental data can only be obtained by introduction of a plausible temperature dependence to the C–H stretching, CH2 in-plane wagging, and the CH2 torsional modes in the liquid. A force field refined in this manner is in agreement with all the experimental isotopic vapor pressure data within 10−4 in ln(P′/P) over the entire temperature range.
75As Zeeman perturbed NQR in (NH4)2HAsO4
Authors: Milia F. , Blinc R.
Published: February 2003

The electric field gradient tensors have been determined for the two physically nonequivalent 75As sites in (NH4)2HAsO4. The 75As quadrupole coupling constant at room temperature equals 67.2 MHz and the asymmetry parameter η is close to zero. The experimental results agree with a model where the protons are ordered in the O–H⋅⋅⋅O hydrogen bonds to form infinite antiparallel chains of AsO4H dipoles so that the structure may be considered to be antiferroelectric. The 75As NQR frequency increases with increasing temperature, in contrast to antiferroelectric NH4H2AsO4.
An information theoretic derivation of population distributions for vibrational states in laser excited systems
Authors: Huddleston R. K. , Weitz Eric
Published: February 2003

Information theory has been shown to provide a simple means of deriving population distributions in vibrationally excited gases where rapid vibration–vibration energy transfer occurs. The implications of the distributions obtained with respect to temperatures of different modes, decay of vibrational populations, and the possibility of vibrationally induced reactions are discussed.
Molecular beam photodissociation of TlI: Bond energy and state symmetry
Authors: Kawasaki M. , Litvak H. , Bersohn R.
Published: February 2003

A beam of TlI is dissociated with a laser at 299.0 nm. The time of flight of the iodine atoms leads to a bond dissociation energy of 62.1±0.9 kcal/mol. Fragment angular distribution measurements made with a high pressure lamp show that both the 302.5 and the 380 nm bonds of TlI are transitions of mixed parallel and perpendicular symmetries.
A classical mechanical study of the effects of vibration in inelastic He–H2 scattering
Authors: Pattengill M. D.
Published: February 2003

The classical trajectory study method has been used to investigate the effects of H2 vibration on inelastic scattering in the system He+H2. Specifically, earlier calculations which included H2 vibration have been repeated using the rigid rotor approximation. In addition, new calculations, both with and without H2 vibration, have been performed at total collision energies of 5 and 10 eV. It is found that H2 vibration exerts a noticeable effect at energies above 5 eV; however, even at 10 eV, the rigid rotor approximation works well for the most important transitions.
The influence of molecular rotation on vibration–translation energy transfer
Authors: McKenzie Robert L.
Published: February 2003

The role of molecular rotations in the exchange of vibrational and translational energy is investigated for collisions between anharmonic diatomic molecules and structureless atoms. A three-dimensional, semiclassical, impact parameter description is applied with emphasis directed towards the influence of rotational coupling on the net rate of vibrational energy transfer summed over all final rotational states. These results are then related to the predictions of an equivalent collinear collision model, and their comparison allows an evaluation of the collinear approximation. The mechanisms of vibrational energy transfer including rotational transitions are shown to be separable into three classes, with the molecules belonging to each class identified first and foremost by their ratio of fundamental vibrational and rotational frequencies, ωe/Be, and second by the proximity of their initial state to a near-resonant vibration–rotation transition with a small change in angular momentum. While the dynamics of molecules with ωe/Be ratios that are comparable to the range of angular momentum transitions having strong coupling are found to require a complete three-dimensional description, the rates of vibrational energy transfer in molecules with large ωe/Be ratios appear to be well approximated by a collinear collision model.
A simple theoretical model for the van der Waals potential at intermediate distances. I. Spherically symmetric potentials
Authors: Tang K. T. , Toennies J. P.
Published: February 2003

A simple potential model is presented, which uses available ab initio calculated short range SCF Born–Mayer parameters and the perturbation theoretical dispersion terms for the long range potential. In the intermediate region two corrections are shown to be necessary to take account of the divergence of the dispersion expansion and the influence of electron overlap. These corrections can be predicted from the known asymptotic parameters and atomic properties. The resulting potential model, which contains only seven potential parameters, is shown to predict the van der Waals potential parameters R0[V (R) =0], Rm (well location), and ε (well depth) for six rare gas–rare gas atom combinations and six open shell–rare gas atom combinations. The predicted potential shape for Ar–Ar is in excellent agreement (≲3%) with the best experimental determination. The model is used to predict Born–Mayer parameters from measured values of Rm and ε.
On the dynamics of state selected unimolecular reactions: Chloroacetylene dissociation and predissociation
Authors: Sloane Christine S. , Hase William L.
Published: February 2003

Classical trajectories have been used to investigate the dynamics of chloroacetylene dissociation and predissociation. Monte Carlo techniques were used to study dissociation from initial state selected energy distributions. Calculations using different initial distributions show that on a 10−12 sec time scale the HC stretch internal coordinate is decoupled from the remaining internal coordinates. A simulation of chloroacetylene dissociation following S1→S0 internal conversion gives a rate constant in agreement with the RRKM theory. A comparison is made between these results and experimental ones.
ESR and ENDOR study of single crystals of L-asparagine⋅H2O x-irradiated at room temperature
Authors: Close David M. , Fouse George W. , Bernhard William A.
Published: February 2003

The ESR spectra of single crystals of L-asparagine⋅H2O and L-asparagine⋅D2O have been examined. Since these data show a great deal of unresolved hyperfine structure, a detailed ENDOR experiment was undertaken. The ENDOR experiment showed the presence of a single α-hydrogen coupling. By comparing the directions of the principal values (−33.4, −21.1, −10.7 G) of the hyperfine coupling tensor with the equivalent directions expected from various possible free radical models, it was concluded that the dominant free radical observed in L-asparagine⋅H2O at room temperature is CO(NH2) ĊHCH (N+H3)CO−2. The lack of an ENDOR signal from the β-hydrogen and the presence of a rather large β-nitrogen coupling (∼5.0 G) observed by ESR has been adaquately explained by a detailed INDO calculation.
An order analysis of the particle–hole propagator
Authors: Oddershede Jens , Jo/rgensen Poul
Published: February 2003

The particle–hole propagator is examined in terms of orders in electron repulsion. The order analysis is accomplished by expressing the equation of motion for the particle–hole Green’s function in the superoperator formalism and by using the inner projection technique to represent the superoperator resolvent. A particular choice of the projection manifold leads to a propagator which is consistent through third order in electron repulsion and in addition contains terms which are important for the description of the collective motions in medium size systems. Our decoupling approach is compared with a diagrammatic perturbation expansion, and with the higher random-phase approximation, and the self-consistent polarization propagator approximation. The latter two approximations, with two-particle, two-hole corrections, are shown to be consistent through second order in electron repulsion. Finally, we demonstrate that approximate propagator methods give a more balanced description of an excitation process than approximate configuration interaction calculations.
Effect of partial wave parameter identification on IOS opacities and integral cross sections for rotationally inelastic collisions
Authors: Pack Russell T
Published: February 2003

The effect of identification of the partial wave parameter of the Jz CCS and IOS approximations as an orbital angular momentum rather than the total angular momentum is studied. Comparison with accurate close coupling calculations for Ar–N2 and He–CO2 collisions is made, and it is found that this identification results in a marked improvement, both quantitative and qualitative, in calculated IOS opacity functions and integral cross sections for both elastic and inelastic collisions. Use of the correct energy in the cross section formula also makes a marked improvement even though T matrices are computed with an average energy.
Structural data on potassium dioxydifluorobromate (V) KBrO2F2
Authors: Bougon Roland , Joubert Philippe , Tantot Georges
Published: February 2003

The x-ray powder pattern of potassium dioxydifluorobromate KBrO2F2 is given and is indexed in an orthorhombic cell with the parameters a=7.28±0.02, b=6.75±0.02, c=7.87±0.02 Å. A set of force constants calculated from infrared and Raman data is given for both the BrO2F−2 ion and BrO2F.
Thermodynamics in finite time: extremals for imperfect heat engines
Authors: Andresen Bjarne , Salamon Peter , Berry R. Stephen
Published: February 2003

A general description is developed for processes involving work and two heat reservoirs or three heat reservoirs in terms of rates for continuous processes or of cycle averages for periodic processes. The description is applied to heat engines having friction, thermal resistance, and heat losses in order to determine the maximum power and maximum efficiency of such engines. By use of a geometric representation the reversible and irreversible parts of a process are separated as the components of a vector. This leads to the definition of a dimensionless quantity that measures irreversibility and is related in a complementary way to the traditional concept of efficiency. The new quantity appears to be useful in cases where efficiency has no well-defined meaning.
The hydrated proton H+(H2O)n. V. Observation of two diaquohydrogen ions, (D2O⋅D⋅OD2)+, in 5-sulphosalicylic acid dideuterate. A neutron diffraction study
Authors: Attig Rainer , Williams Jack M.
Published: February 2003

The crystal and molecular structure of 5-sulphosalicylic acid dideuterate has been studied using three-dimensional single crystal neutron diffraction data. The triclinic unit cell, space group P1̄, contains two formula units, with dimensions a=7.028(5), b=7.007(5), c=11.678(8)  Å, α=71.49(4), β=94.07(2), and γ=109.35(2) °. A total of 2883 unique reflections were collected and full matrix least-squares refinement on F0 2 yielded an R=0.079. Two almost identical D5O2+ cations were found, and both reside on centers of symmetry, suggesting that the cations are best formulated as (D2O⋅D⋅OD2)+ species. The bridging deuterium atoms have their largest vibrational amplitudes along the O–O direction, which is indicative of a broad–flat anharmonic single-minimum potential energy well. The slight deviations from this direction are correlated with the terminal oxygen atom vibrations. X-ray versus neutron difference density maps show pronounced polarization of the C–H and O–D bonds.
Intermolecular potential surfaces from electron gas methods. II. Angle and distance dependence of the A′ and A″ Ar–NO(X 2Π) interactions
Authors: Nielson Glen C. , Parker Gregory A. , Pack Russell T
Published: February 2003

Angle dependent intermolecular potential energy surfaces for the two states (2A′ and 2A″) that arise from the interaction of ground (X 2Π) state NO with Ar are calculated using the electron gas model to obtain the short range interactions. The average and difference of the two interaction energies are fit to analytic forms convenient for use in scattering calculations and joined smoothly onto the long range van der Waals potential previously determined. The results, which appear to be of useful accuracy, and the applicability of the electron gas model to such open shell–closed shell interactions are discussed.
Monte Carlo study of a phase-separating liquid mixture by umbrella sampling
Authors: Torrie G. M. , Valleau J. P.
Published: February 2003

Recently developed nonphysical sampling methods—umbrella sampling—have been used to obtain the free energy and other properties of a binary liquid mixture exhibiting phase separation with an upper critical solution point. The system is a mixture of two identical Lennard-Jones liquids in which the interactions between the components are characterized by a range parameter σ12 obeying the Lorentz rule, but an energy parameter ε12= (1−α) (ε11ε22)1/2 violating the Berthelot rule. The sampling methods enable one to cover wide ranges of temperature and composition with few Monte Carlo experiments, successfully sampling the metastable regions and obtaining the coexistence curve. The case α=0.25 is studied in detail, and compared with some theoretical predictions. An estimate is made of the minimum value of α required for phase separation at low pressures.
Improved virtual orbitals in the extended basis function space
Authors: Huzinaga S. , Hirao K.
Published: February 2003

A theoretical method is formulated in order to improve virtual orbitals in atomic and molecular Hartree–Fock calculations. It is a natural extension of the former work [S. Huzinaga and C. Arnau, J. Chem. Phys. 54, 1958 (1971)], in which a simple fact is exploited for the betterment of virtual orbitals that the only mathematical requirement on the virtual orbitals space is the orthogonality to the occupied Hartree–Fock orbital space. The formalism is used to calculate excitation energies of atomic He, Li, Be, and Na.
Determination of chalcogen structures on nickel surfaces from orbital energies added to pairwise atomic repulsions
Authors: Anderson Alfred B.
Published: February 2003

A simple theory whose forte has been the determination of structures and energy levels for large nonionic systems is found to be applicable to ionic systems when the effects of self-consistent charge transfer are incorporated. The theory confirms the LEED structural analyses for O, S, and Se on Ni(100) and S on Ni(111) as found by Demuth, Jepsen, and Marcus. Further, the atomic valence ionization energy shifts are in agreement with the surface oxide photoemission spectrum of Conrad, Ertl, Küppers, and Latta.
Photoionization mass spectrometric study of CSe2
Authors: Radler K. , Berkowitz J.
Published: February 2003

The photoionization spectrum of CSe2 has been studied with 0.15 Å resolution. Autoionization from four series of Rydberg states converging on three limits have been analyzed, yielding the following state energies for CSe2+:X2Πg,1/2, 9.524 eV; B2Σu+, 13.6336 eV; and C2Σg+, 15.899 eV. A spin–orbit splitting of 0.266±0.002 eV for the X state is deduced. The symmetry of the Rydberg states is inferred from quantum defects. From the threshold for Se+ formation, a best combination of ΔHf,298(CSe2,g) =+62.0 kcal/mole and D0(CSe) =135±2 kcal/mole is deduced. The onset for CSe+ yields I.P. (CSe) ?10.943 eV. The possible mechanisms for fragmentation are discussed.
Photoionization mass spectrometry and heat of formation of S2O
Authors: Berkowitz J. , Eland J. H. D. , Appelman E. H.
Published: February 2003

Photoionization mass spectrometry of S2O yields an ionization potential of 10.58±0.01 eV, and a 0°K threshold for SO+ production of 13.745±0.006 eV. The heat of formation of S2O is deduced to be −12.75±0.25 kcal/mole.
Electronic structure and oscillator strengths of highly excited states: Resonances in He−, Li, and Be
Authors: Nicolaides Cleanthes A. , Beck Donald R.
Published: February 2003

The calculation of energy levels and widths of certain highly excited states in atoms and molecules is an interesting theoretical problem. This is due primarily to peculiarities of their wavefunctions which result from the (near) degeneracies of such states with Rydberg and continuum series. In this paper we: (a) discuss certain aspects of this problem related to the computation of compact excited-state wavefunctions. The BeI″1s22p2″ 1S and NI 1s22s2p4 4P states serve as examples; (b) present results of a variational treatment of the positions of the 2s22p and ″2p3″ 2P0 resonances in He−(57.3 eV, 60.5 eV) and Li (141.7 eV, 148.5 eV) and an estimate for the He−″2s2p3d″ 2P0 resonances {[(2s2p)  3P03d] 2P0: 61.9 eV, [(2s2p)  1P03d] 2P0: 63.1 eV}. The 2s22p 2P0 levels are in good agreement with recent experimental values (57.2 eV, ∼141.5 eV). A many-body calculation of the Li 1s22s 2S→2P0 two and three electron excitation oscillator strengths yields f2s22p=0.00018, f2p 3=0.0007. These calculations were carried out according to our recently proposed first-order theory of oscillator strengths (FOTOS).
EPR studies of Mo3+ ion in single crystals of NH4Al(SO4)2⋅12H2O
Authors: Radhakrishna S. , Chowdari B. V. R. , Viswanath A. Kasi
Published: February 2003

Electron paramagnetic resonance studies of Mo3+ ion in NH4Al(SO4)2⋅12H2O single crystals are made at X-band frequencies and at room temperature. It is found that there are four magnetically inequivalent complexes of Mo3+ ion in the lattice which exhibit tirgonal symmetry. The angular variation of the fine structure lines is studied in the crystallographic (111) and (100) planes. The z axes of the complexes are found to be along the (111) directions. The spectra are analyzed using the fine structure spin-Hamiltonian and the parameters are found to be g∥=1.974, g⊥=2.009, and D=506.8×10−4 cm−1. Paramagnetic resonance of the polycrystalline samples is also studied and the usual spin-Hamiltonian analysis is made. A model is proposed for the position of the Mo3+ ion in the lattice of ammonium alum.
The adsorption of hydrocarbons on platinum studied by low-energy electron diffraction intensities. The ordered (2×2) overlayers of acetylene and ethylene on the (111) crystal face of platinum
Authors: Stair P. C. , Somorjai G. A.
Published: February 2003

The intensities of the low-energy electron diffraction beams back-scattered from the ordered (2×2) overlayers of acetylene and ethylene on the platinum (111) crystal face are measured by a photographic technique. The intensities are presented in an appendix in the form of normalized diffraction beam intensity versus incident electron energy (I-V curves). Acetylene spontaneously forms the ordered (2×2) adsorbate on platinum at 300 K and low exposure under ultrahigh vacuum conditions. The intensity profiles reveal that this structure is metastable; and upon heating to 350–400 K for 1 hr it undergoes a transformation to a stable structure with the same (2×2) unit cell size. The acetylene transformation is thought to involve a strengthening of the carbon–platinum bond accompanied by an expansion of the carbon–carbon bond length. Ethylene adsorbes on the platinum (111) surface and with electron beam exposure forms an ordered (2×2) surface structure that is identical to the stable acetylene structure as shown by the intensity profiles.
Symmetry-adapted-multiconfiguration SCF wavefunctions via symmetry-restricted annihilation of single excitations. I.
Authors: Yarkony David R.
Published: February 2003

The symmetry-restricted annihilation of single excitations formalism is extended to the case of multiconfiguration wavefunctions. The implications for a completely general computational procedure are discussed.
The long-range interactions of S-state alkali atoms with rare gas and hydrogen atoms
Authors: Proctor Timothy R. , Stwalley William C.
Published: February 2003

The coefficients for the long-range interaction energy expansion for an alkalilike S-state atom with a rare-gas-like S-state atom are evaluated. Proceeding from the results of second-order perturbation theory, we express the multipole interaction energies in terms of series of products of oscillator strength sums. The required alkali sums are calculated from spectral data using hypervirial equations. Rare gas sums are reviewed, and new values of some quadrupole and octupole sums estimated. The theory of asymptotic series is employed to obtain numerical values and associated error bounds for C6, C8, and C10 coefficients for a large number of systems. These results are extensively compared with those of others. In particular, excellent agreement is found with accurate theoretical results for H and Li interactions, and improved agreement is found with Li–rare gas elastic scattering results. Finally, further applications and generalizations are discussed.
An oxidation product in glycine AgNO3
Authors: Rustgi Surendra N.
Published: February 2003

A primary oxidation product in x-irradiated single crystals of glycine silver nitrate at 4.2°K was studied by ESR and ENDOR spectroscopy. The main consequence of the oxidation process is to create an electron deficiency shared by two silver ions and the surrounding carboxylic groups. The delocalized unpaired electron interacts with the two silver nuceli, 107Ag and/or 109Ag, separated by 2.88 Å. The principal values for the g and hyperfine tensors for 107Ag and 109Ag were determined. The highly anisotropic triplet ESR absorption spectrum disappears at 65°K.
Luminescence spectra of solid nitrogen excited by electron impact
Authors: Oehler O. , Smith D. A. , Dressler K.
Published: February 2003

The visible and near-infrared luminescence spectrum of pure solid nitrogen has been reinvestigated. Spectral intensity distributions, decay curves, and the temperature dependence of these characteristics have been measured in a variable-temperature liquid-helium cryostat, using pulsed electron-beam excitation and a photoelectrically recording spectrometer. The parity-forbidden transitions within the ground configuration of trapped atomic nitrogen, 2P→2D and 2D→4S, are observed as dipole radiation which is induced by the dynamical perturbing fields of inter- and intramolecular vibrations. The presence of slowly relaxing, vibrationally excited N2 molecules, 3⩽v⩽13, is confirmed. The vibrational excitation of N2 and electronic excitation of N is ascribed to a common process, namely to the quenching of molecular triplet excitons, N2 A 3Σ, v′≃0, by ground-state atoms, N 4S. This process yields N (2P or 2D) and N2 X 1Σ, v″, at adjacent lattice sites, with initial distributions of v″ populations that show half-widths spanning approximately four quanta, and maxima near v″≃9.