bluuebunny/crossref_metadata_2025 huggingface dataset:
Separation of O, C, and S isotopes by two-step, laser photodissociation of OCS
Authors: Zittel P. F. , Darnton L. A. , Little D. D.
Published: February 2003

Isotopes of O, C, and S have been separated by two-step, laser photodissociation of OCS. The technique utilizes isotopically selective vibrational excitation of OCS in the ν2 (bending) vibrational mode with a line-tuned CO2 laser (λ∼9.4 μm), followed by photodissociation with a KrF excimer laser (λ=249 nm) and chemical scavenging of the sulfur atoms. Enrichment factors ranging from 1.5 to 3.5 were obtained for different isotopes. A sensitive IR absorption apparatus was used to measure absorption of the high energy CO2 laser pulse by OCS as a function of pressure and laser fluence. Average absorptions ranging up to 1.5 photons/molecule were attributed to rapid rotational relaxation and in part to sequential absorption up the ladder of ν2 vibrational levels. The 249 nm photodissociation cross section of OCS was measured as a function of absorbed IR energy. An excitation of one CO2 laser photon per molecule, or two quanta of ν2 vibration per molecule, increased the photodissociation cross section by a factor of 9 over the thermal (295 K) cross section. A rate constant of (4.8±1.0)×105 s−1 Torr−1 was inferred for the exchange of ν2 vibrational energy between isotopic varieties of OCS.
A multiconfiguration self-consistent-field group function method for problems with repeating potentials
Authors: Fink William H. , Banerjee Ajit , Simons Jack
Published: February 2003

An implementation of a conceptual scheme for performing a finite-cluster electronic structure calculation so as to simulate, within the finite cluster, an extended periodic continuation of the cluster is reported. The implementation extends a scheme used previously at a single-determinant wave function level of approximation to a multiconfiguration self-consistent-field (MCSCF) level. The total wave function has the form of McWeeny’s group functions. The MCSCF working equations are cast in the exponential-i-lambda language (EIL) and the energy expressions are cast in notation of the graphical unitary group approach (GUGA). The modifications to the MCSCF working equations necessary to do group function calculations are also developed in the GUGA–EIL notation. A procedure for wave function transfer from one unit of the cluster to another is described. All of this conceptual scheme has been put together in working computer algorithms and applied to two informative, illustrative systems, Be2, and finite hydrogen chains. The results of our computations, while not being definitive, are interesting in being among the first correlated calculations for extended periodic problems.
Collision dynamics of three interacting atoms: The Faddeev equations in a diabatic electronic basis
Authors: Kuruoglu Zeki C. , Micha David A.
Published: February 2003

Starting with all the electrons and nuclei making up a system of three atoms, we introduce a basis of antisymmetrized products of atomic states to define a matrix Hamiltonian partition applicable to atom–diatom collisions. We derive a three-atom generalization of the Faddeev equations in terms of diatomic transition operators. Equations are obtained for three-atom rearrangement transition operators that are then reduced to sets of effective two-body (atom–diatom) equations by introducing separable expansions of the diatomic transition operators. We also discuss the permutational symmetry of identical nuclei and briefly describe how the formalism applies to the H3 and FH2 systems.
Structure of solid water clusters formed in a free jet expansion
Authors: Torchet G. , Schwartz P. , Farges J. , de Feraudy M. F. , Raoult B.
Published: February 2003

Clusters are produced in a free jet expansion of water vapor. Keeping constant the nozzle diameter (d=0.4 mm) and temperature (T=430 K), an increase in inlet vapor pressure from 1 to 5 bar produces an increase in mean cluster size from several tens to several thousands of molecules per cluster. An electron diffraction analysis provides information about the cluster structure and dynamics. A direct observation of diffraction patterns shows that the largest clusters exhibit mainly a crystalline structure, namely, diamond cubic which is the metastable phase of bulk solid water, whereas the smallest ones are amorphous. In order to elucidate the local order in the latter, a comparison is made between the experimental curves and the diffraction functions calculated for various noncrystalline models. The best agreement is obtained with a model which presents distorted rings of three to six H2O molecules, constructed by cooling a liquid water droplet through a molecular dynamics calculation. In particular, this means that the regular dodecahedral structure often referred to in mass spectroscopy is not a realistic model for neutral clusters.
Geometric model of trapped electrons in x-ray irradiated single crystals of rhamnose
Authors: Samskog P.-O. , Kispert L. D. , Lund A.
Published: February 2003

A geometrical model for the trapping site of the electron in x-ray irradiated rhamnose is presented. The electron is trapped in an intermolecular site formed by three hydroxyl groups, two on the carbohydrate and one on a water molecule. The trapped electron decays by cleavage of an OH bond and the liberated hydrogen atom abstracts a hydrogen atom from the carbon atom to which the OH group is attached. A hydroxy alkyl radical is thus formed whose site has been determined. The conclusion is that the electron trap is preexisting in the crystal lattice of rhamnose and no reorientation of the dipoles is necessary to stabilize the electron.
Internal energy dependent radiationless transitions in 1,3,5,-C6F3H+3 and C6F+6
Authors: Dujardin G. , Leach S.
Published: February 2003

From fluorescence quantum yields φF and lifetimes τ measured by the threshold photoelectron–fluorescence photon coincidence (T-PEFCO) method, reported in a companion paper, the radiative kr and nonradiative knr relaxation rates have been determined for energy selected states of 1,3,5,-C6F3H+3 and C6F+6. knr is less than 106 s−1 in the B̃ state energy region of 1,3,5,-C6F3H3+; an exponential dependence of knr as a function of the selected energy was found in the C̃ and D̃ energy regions of this ion. The nonradiative relaxation of fluorescent states of 1,3,5,-C6F3H+3 and C6F+6 involves coupling to high vibrational levels of their ground states. Emission properties, in particular the kr rates, are used to demonstrate the existence of radiationless coupling between the C̃ and B̃ states for both ions. For large vibrational energies in the B̃ 2A2u state of C6F+6, knr increases quasiexponentially with the internal vibrational energy Ev in agreement with results of Maier and Thommen who used a different experimental technique. Below 3100 cm−1, we find that knr no longer depends monotonically on Ev and is sensitive to the particular vibrational mode excited in the B̃ state. Results are given of model calculations of the relative knr rates as a function of specific vibrational levels of C6F6+ in the B̃ state. The results reproduce our experimentally observed mode selective behavior of knr in C6F+6. Comparison with experiment shows that with the increasing values of Ev the excited vibronic state gradually loses its memory of initial mode composition, exhibiting vibrational redistribution to a degree which increases with internal vibrational energy.
Hartree relaxation model of the n=1 exciton in solid Ne
Authors: Derbyshire M. , Etters R. D.
Published: February 2003

A quantum mechanical Hartree calculation of the absorption and emission spectra of 1P1 and 3P1 excitons in solid Ne is presented at pressures 0≤P≲20 kbar. Distortions of the 30 independent lattice vectors in the first 16 shells surrounding the excited atom and two parameters characterizing the system wave function are treated as variational parameters. These results are compared with experiment and with previous classical calculations. The rms fluctuations of the excited and host lattice atoms about their equilibrium sites are also presented.
Vibrational spectroscopy of mixed stack organic semiconductors: Neutral and ionic phases of tetrathiafulvalene–chloranil (TTF–CA) charge transfer complex
Authors: Girlando Alberto , Marzola Franca , Pecile Cesare , Torrance Jerry B.
Published: February 2003

The infrared and Raman spectra for the room temperature, quasineutral, and the low temperature, quasi-ionic, phases of the mixed stack charge transfer complex tetrathiafulvalene–chloranil (TTF–CA) are reported. The analysis of the analogous data for a newly synthesized room temperature phase point to a dimerized segregated stack structure. All the vibrational data are interpreted and exploited through a clear identification of the differences, for the two types of stacks, in the spectroscopic effects due to the vibronic interaction, i.e., the coupling between electron and molecular vibration (e-mv). It is shown that for distorted mixed stack complexes both Raman and infrared spectra can be substantially influenced by the vibronic interaction, whereas the dimerized segregated stack complexes, as already known, display striking vibronic effects only in infrared. The theoretical model which explains the origin of these effects is briefly summarized and its extension to mixed stack structures successfully used to reproduce the infrared vibronic absorption spectrum of the TTF–CA low temperature distorted phase. By this procedure the experimental values of the e-mv coupling constants of TTF and CA units are extracted. A degree of ionicity ρ practically equal to one is determined for the segregated stack phase, whereas the fractional charge for the two mixed stack phases results to be: ρ=0.24±0.1 at 300 K and ρ=0.64±0.1 at 15 K. Some aspects of the neutral to ionic phase transition are discussed in terms of the temperature dependence of the vibrational spectra.
Laser-induced fluorescence spectrum of the CCN radical. II. Excitation of A 2Δi:(010)Π–X 2Πr:(010)Σ− vibronic band
Authors: Hakuta Kohzo , Uehara Hiromichi , Kawaguchi Kentarou , Suzuki Tetsuo , Kasuya Takahiro
Published: February 2003

The laser-induced fluorescence (LIF) spectrum of the CCN radical was observed with a CW dye laser tuned to the P branch head of the vibronic band of A 2Δi:(010)Π–X 2Πr:(010)Σ−. The LIF spectrum consisted of two resonant transitions of nearly equal intensity: A 2Δi:(010)Π–X 2Πr:(v11v3)Σ− and A 2Δi:(010)Π–X 2Πr:(v11v3)Σ+. The observation has provided a further evidence for the assignment of the collision-induced vibronic bands in our previous work [K. Hakuta and H. Uehara, J. Chem. Phys. xx, xxxx (xxxx)]. The analysis yielded a vibronic parameter εω2 for four vibrational states. (AIP)
Dilute and semidilute polymer solutions near an adsorbing wall
Authors: Eisenriegler Erich
Published: February 2003

The variation of the monomer density ρ with distance z from an impenetrable and adsorbing wall is studied for polymer solutions with excluded volume interaction. Both the limits of weak and strong overlap between the polymer chains are considered. For comparison, solutions of ideal noninteracting chains and chains with an excluded volume interaction of the mean-field type are also discussed. The main emphasis is on a temperature region near the adsorption temperature Ta below which a single long chain, fixed with one end close to the wall, condenses a finite fraction of its monomers to the wall. The relation to an n-component field theory in a half-space is used to show that in this temperature region ρ(z) displays crossover scaling behavior involving two macroscopic lengths. The power law exponents for the z dependence in the various regions determined by the two lengths are obtained as well as the qualitative form of the whole profile ρ(z) for various limits of interest.
Staging in polyacetylene–iodine conductors
Authors: Baughman R. H. , Murthy N. S. , Miller G. G. , Shacklette L. W.
Published: February 2003

Evidence is presented for the existence of highly conducting polyacetylene complexes with structures related to high-stage graphite, as well as structures related to first-stage graphite. X-ray diffraction measurements on polyacetylene–iodine complexes indicate equatorial lines at 7.7–8.0 and 13.8–14.3 Å. The shorter spacing arises in part from a structure in which iodine-rich planes alternate with planes of polyacetylene chains. The longer spacing, which disappears upon atmospheric exposure, is consistent with a structure analogous to third-stage graphite in which dopant-rich planes are separated by three close-packed planes of polyacetylene chains. The third-stage complex can be viewed as a perturbation of the structure of undoped polyacetylene, with the region between dopant layers consisting essentially of a one unit cell thickness of the parent polymer structure. Packing calculations for this model, in which a linear column of anions (I3− and/or I5−) displaces either every chain or every other chain in the dopant-rich layer, provide an interlayer spacing which is equal to that observed. Evidence consistent with third-stage structures (with both fractional occupation and complete occupation of the dopant plane) is also found by reexamination of published sorption data, which provides slope changes at close to the calculated limiting compositions for these structures [(CHI0.056)x and (CHI0.13)x]. However, a first-stage structure with alternating dopant arrays and polymer chains in the dopant plane [for which (CHI0.13)x is calculated] provides a better explanation for the second slope change, as well as for the composition obtained under dynamic vacuum, (CHI0.14)x. These results for iodine complexes are compared with those derived for the group VA halide complexes of polyacetylene.
On the relation of Child and Lawton’s harmonically coupled anharmonic–oscillator model and Darling–Dennison couplinga)
Authors: Lehmann Kevin K.
Published: February 2003

Child and Lawton’s1 model for two identifical coupled anharmonic oscillators is further discussed. It is shown that the effective Hamiltonian of that model can be transformed into a special case of the familiar Darling-Dennison resonance Hamiltonian. (AIP)
Comments on ‘‘Temperature dependence of three-body association reactions from 45 to 400 K. The reactions N+2+2N2→N+4+N2 and O+2+2O2→O+4+O2’’
Authors: Mickens Ronald E.
Published: February 2003

Deviations from simple power law fits have been observed at low temperatures for the rate coefficients of certain three-body association reactions. We suggest that such behavior is characteristic of third-order reactions. (AIP)
Model stretching overtone eigenvalues for SF6, WF6, and UF6
Authors: Halonen L. , Child M. S.
Published: February 2003

A four parameter potential model for the stretching modes of XY6 octahedra is shown to give an excellent fit to the published experimental vibrational eigenvalues of SF6, WF6, and UF6. A new technique for the automatic computation of symmetrized local mode basis functions is used to generate eigenvalues, converged to within 1 cm−1, for overtone and combination states up to vtot=v1+v2+v3=6 for WF6 and UF6. Similar convergence for SF6 is possible only up to vtot=4 due to axial momentum transfer arising from the relatively low central mass, which renders a local mode basis less convenient for this molecule. The most striking result for both WF6 and UF6 is that the highest component of the nν3 manifold for n≤6 appears to lie within 1 cm−1 of n multiples of the ν3 fundamental. The continuation of such a pattern up to dissociation would imply that no special anharmonic resonances are needed to account for the infrared multiphoton dissociation.
Density matrix treatment of localized electronic interactions. Separated electron pairs
Authors: Kirtman Bernard
Published: February 2003

The density matrix treatment of localized electronic interactions in large systems is extended to separated electron pair wave functions. We make a local space approximation and carry out a Newton–Raphson linearization which leads to effective SCF equations of relatively small dimensionality. Delocalization is included by rigorously satisfying the orthonormality condition on the natural orbitals as well as the normalization requirement on the pair functions. Both the orbitals and the pair coefficients are fully optimized.
Correlated effective valence shell Hamiltonian for the first-row transition metal atoms
Authors: Lee Yoon S. , Freed Karl F.
Published: February 2003

Ab initio calculations of the effective valence shell Hamiltonians are presented for the 3dn4sm first-row transition metal atoms using quasidegenerate many-body perturbation theory in order to further study the role of electron correlation and relativistic effects in these systems. Prime emphasis is placed here on the individual matrix elements of the effective valence shell Hamiltonian, the true parameters, and in comparing calculated and empirically determined values. The true parameters from second order calculations are supplemented with selected new third order calculations to test the convergence of the quasidegenerate many-body methods with respect to excitation energies and individual true parameters. Valence orbital basis sets can be introduced which lead to good convergence for energies and parameters, but different sets may be necessary for these two purposes. The calculated one- and two-electron true parameters for Ti, V, and Cr compare well with empirical ones, while individual three-electron empirical true parameters are unavailable. Criteria are discussed governing convergence of quasidegenerate many-body perturbation theory for the transition metal atoms.
A molecular dynamics simulation of rotational and vibrational relaxation in liquid HCl
Authors: Levesque D. , Weis J.-J. , Oxtoby David W.
Published: February 2003

We have carried out a molecular dynamics simulation of liquid HCl near its normal boiling point using the C* potential of Klein and McDonald. A wide variety of equilibrium and dynamical properties have been studied, ranging from partial structure factors to velocity, angular velocity, and torque autocorrelation functions. Dipole moment and polarizability tensor correlation functions have been evaulated and compared with experimental data from dielectric relaxation and Raman line shape studies. Vibrational phase relaxation has been simulated; we show that HCl is an intermediate case between the rapid modulation and static broadening limits. The question of correlation between rotational and vibrational relaxation is discussed.
A theory on the electroviscous effect: A method for the estimation of the viscosity of dispersions of charged spherical colloidal particles
Authors: Menjivar Juan A. , Rha ChoKyun
Published: February 2003

A method to estimate the effect of electrostatic interactions on the shear viscosity of concentrated dispersions of charged spherical particles is presented. The secondary electroviscous effect can be related to an effective maximum packing fraction (φM), defined as the particle concentration at which the charged particles attain complete long-range order. The maximum packing fraction (φM) can be determined either theoretically or experimentally. This excluded volume approach quantitatively describes the roles of surface potential (ψ0), particle radius (a), suspending medium ionic strength (I), and particle concentration (φ) on the low-shear viscosity of collodial monodispersions of charged spherical particles. The validity of the proposed theory is suggested by an agreement with existent literature data.
A statistical mechanical theory of the self-diffusion coefficient of simple ions in electrolyte solutions
Authors: Yuan Mou Chung , Thacher Thomas S. , Lin Jeong-long
Published: February 2003

A statistical mechanical theory of the self-diffusion coefficient of ions in solutions of simple electrolytes has been developed. Beginning with a generalized Langevin equation the self-diffusion coefficients of ions may be evaluated at the zero-frequency limit of the Laplace transform of the random force correlation function. We assume that the random force acting on the tagged ion may be separated into contributions from the solvent part, due to the surrounding solvent molecules and an ionic part due to all the other ions. Further, we assume that the evolution of the ionic random force is governed by the Smoluchowski operator. With these assumptions and using the Debye–Hückel pair correlation function, the Onsager limiting law may be derived. Numerical calculations using the HNC pair correlation function shows that our theory can describe experimental data of moderately concentrated solutions adequately.
Dielectric friction and energy dissipation in polar fluidsa)
Authors: Nowak Ernst
Published: February 2003

We consider a continuum model for dielectric friction on charged particles. Approximate results for friction coefficients can be derived in a convenient way by calculating the total energy dissipation in the system. This work is closely related to a theory of Hubbard and Onsager, we show that these authors have neglected a contribution to the energy dissipation, which can be incorporated without major difficulties. In addition, we propose a new type of electrohydrodynamic boundary condition which is a generalization of the familiar hydrodynamic one. The general results are exemplified by studying simple models for moving or rotating ions and polar molecules.
Reactions of He+, Ne+, and Ar+ with CH4, C2H6, SiH4, and Si2H6
Authors: Chatham H. , Hils D. , Robertson R. , Gallagher A. C.
Published: February 2003

The rate coefficients and product-ion distributions for the reactions of He+ and Ar+ with silane and disilane have been measured in a drift tube, typically for collision energies of 0.01–1 eV. The total charge-exchange rate coefficients are found to be roughly independent of E/N, or collision energy, and are about equal to the Langevin values for the reactions of He+ with SiH4 and C2H6 and Ar+ with CH4 and C2H6. The He+ rate coefficients on CH4 and Si2H6, and the Ne+ rate coefficients on SiH4 and Si2H6 are 50% to 80% of the Langevin values, while the Ar+ rate coefficients on SiH4 and Si2H6 are much smaller. Product ions tend to be hydrogen poor with very infrequent breaking of the C–C or Si–Si bonds. Furthermore, hydrogen stripping is more severe for the silanes than the alkanes. These product-ion distributions bear no resemblance to the product-ion distributions of either photoionization or electron collisional ionization.
A theoretical study of coherence effects in charge transfer collisions: Application to Na–Li+
Authors: Orel A. E. , Kulander K. C.
Published: February 2003

We have carried out a theoretical study of charge exchange in the Na–Li+ system and have examined the effects of coherent laser preparation of excited target states. Accurate potential energy curves and nonadiabatic coupling matrix elements were obtained from ab initio, all-electron configuration-interaction calculations. These were used in determining the cross sections over a range of collision energies. Significant differences between coherent and incoherent target preparation were observed in both total and partial cross sections.
Multireference many-body perturbation theory: Application to O2 potential energy surfaces
Authors: Sheppard Maurice G. , Schneider Barry I. , Martin Richard L.
Published: February 2003

A modification of multi-reference many-body perturbation theory is introduced and applied to potential surface calculations of the first 3Σ−g, 1Δg, and 1Σ+g bound states of O2. The modification enhances the convergence and efficiency of both Rayleigh–Schrödinger and Brillouin–Wigner expansions by pre-diagonalizing the primary space and then contracting to a smaller dimension space before calculating perturbative corrections.
Variational calculation of the rotational constants for acetylene and its isotopic derivatives
Authors: Lehmann Kevin K. , Scherer George J. , Klemperer W.
Published: February 2003

A method is presented for calculation of rotational constants for a linear molecule by treating the vibrations variationally, but treating the vibration–rotation coupling perturbatively. The method is applied to the potential energy function for acetylene given by L. Halonen, M. S. Child, and S. Carter [Mol. Phys. 47, 1097 (1982)]. It is found that even though the vibrational energy levels calculated from this potential are in excellent agreement with experiment, the calculated rotational constants are poorly predicted. The calculated ΔB’s are systematically inaccurate by about 5% for C2H2 and 8% for C2D2. This indicates that the potential energy function is inaccurate even near equilibrium.
Effect of nonrandomness on the phonons in mixed InP1−xAsx
Authors: Ahuja Geeta , Gupta H. C. , Tiwari L. M.
Published: February 2003

A concentration dependent model using the effect of nonrandomness has been investigated to demonstrate the two-mode behavior of mixed crystals of the type AB1−xCx having zinc-blend structure. The mixed crystal shows two-mode behavior for all the composition range and the pure crystal behavior at exact x=0 and at x=1.0. The model has been applied to InP1−xAsx to investigate the phonon dispersion curves in the symmetry directions. The results for x=0, x=0.22, x=0.78, and x=1.0 are found to be in agreement with experiment.
Transport properties of ground state nitrogen atoms
Authors: Rainwater James C. , Biolsi Louis , Biolsi Kevin J. , Holland Paul M.
Published: February 2003

Transport properties of dilute monatomic gases depend on the two body atom–atom interaction potential. When two ground state (4S) nitrogen atoms interact, they can follow any of four potential energy curves corresponding to the N2 molecule; the X 1Σ+g, A 3Σ+u, 5Σ+g, and 7Σ+u curves. Transport collision integrals for the 1Σ+g and 3Σ+u states have been calculated by representing the potentials for these states with the Hulburt–Hirschfelder potential. The 5Σ+g state has a large local maximum which requires changes in the computational procedure used previously; a modified Hulburt–Hirschfelder potential has been used to represent the potential for this state. Collision integrals for the 7Σ+u state have been obtained by direct use of a recent theoretical potential for this state. The collision integrals are compared with results obtained in previous studies.
Thermotropic ionic liquid crystals. II. 1H and 23Na NMR study of the smectic mesophase of molten sodium n-butyrate and sodium isovalerate
Authors: Bonekamp J. E. , Eguchi T. , Plesko S. , Jonas J.
Published: February 2003

The 1H and 23Na NMR studies of smectic ionic mesophases of molten sodium n-butyrate and sodium isovalerate are reported over the temperature range of the stability of the liquid crystalline phases. The 1H spin-lattice relaxation times T1 at ν0=9.2, 24.3, and 60 MHz for the anions of both the systems are interpreted in terms of diffusion intermolecular relaxation mechanism. The predicted anion diffusion coefficients are in agreement with those measured directly by spin-echo technique and indicate that the anion diffuses rapidly. In contrast to the T1 relaxation mechanism the results obtained for the proton relaxation times in the rotating coordinate frame T1ρ indicate that the order-fluctuation relaxation mechanism determines the frequency dispersion of T1ρ. The analysis of the T1ρ data provides an approximate measure of the order parameter S as a function of temperature. Fourier transform spectra of the 23Na transitions show that the electric field gradient (EFG) at the Na+ ion is nonaveraged and of such a strength as to produce a second order quadrupole effect in the spectra of the central transition. From the first-order splitting, the quadrupole coupling constant (QCC) is obtained as a function of temperature. The gradual temperature change of QCC demonstrates that only a single liquid crystalline phase exists over the temperature interval of the stability of the smectic mesophase. Using approximate analysis the correlation time τc for the EFG fluctuation is obtained from the 23Na T1 data for the melts of both sodium n-butyrate and sodium isovalerate.
The rotational spectrum of the CD2 radical studied by far infrared laser magnetic resonance spectroscopya)
Authors: Bunker P. R. , Sears Trevor J. , McKellar A. R. W. , Evenson K. M. , Lovas F. J.
Published: February 2003

We report the detection of 17 pure rotation transitions in the ground vibronic state of the CD2 radical using far infrared laser magnetic resonance spectroscopy. Fitting the data using an effective rotational Hamiltonian yields values for the three rotational constants, seven centrifugal distortion constants, the three electronic spin-rotation, and two electronic spin–spin parameters. We also fit this data, and CD2 ν2 band data (published separately), using the semirigid bender Hamiltonian and obtain the effective bending potential function for CD2. Combining this with previous CH2 results enables us to predict the rotation bending energy levels of CHD. We also report here the detection of two further rotational transitions in the ν1 excited vibrational state of CH2.
Rotational cross sections: A new semiclassical perturbed stationary states (PSS) approach
Authors: Jolicard Georges , Bonamy Jeanine
Published: February 2003

We present a new semiclassical PSS approach of rotational cross section calculations, based on the interpolation by spline functions of the nonadiabatic couplings. The method is tested on the pH2+He4 system and a good agreement is obtained with ‘‘exact’’ quantum results.
Resonances in molecular collisions: Importance of mode decoupling in the exit channel of attractive potentials
Authors: Kulander K. C.
Published: February 2003

Two model, collinear triatomic systems are investigated in which the intrafragment vibrational modes are decoupled from the interfragment bond distance in the dissociation channel. Resonances are found in both systems whose amplitudes are predominately outside the interaction region. The consequences of the existence of such resonances on reaction probabilities, dissociation rates, and absorption properties of states near the dissociation limit are discussed.
Equation-of-state data for molecular hydrogen and deuterium at shock pressures in the range 2–76 GPa (20–760 kbar)a)
Authors: Nellis W. J. , Mitchell A. C. , van Thiel M. , Devine G. J. , Trainor R. J. , Brown N.
Published: February 2003

Dynamic equation-of-state data for D2 and H2 were measured in the pressure range 2–76 GPa (20–760 kbar) using a two-state light-gas gun. Liquid specimens were shocked from initial states near the saturation curve at 20 K. Maximum compression was sixfold over initial liquid density at a calculated temperature of 7000 K for D2. The data is discussed in terms of the theory of Ross et al., which includes an effective intermolecular pair potential, molecular vibration, free molecular rotation, and molecular dissociation.
Laboratory measurements in the energy range 0.02–1 eV of the rate constants of ion–molecule reactions involving CS+
Authors: Barassin J. , Thomas R. , Barassin A.
Published: February 2003

The energy dependence of the total rate constant and of the branching ratios of the reactions of CS+ with O2, H2, and CH4 have been determined in the energy range 0.02–1 eV by the drift tube mass spectrometer technique. The reaction CS++O2 proceeds through three primary steps giving OCS+, SO+, and O+2 with branching ratios of 0.7, 0.2, and 0.1, respectively, at low energy (<0.025 eV) and 0.4, 0.1, and 0.5 at high energy (0.38 eV). The secondary ions OCS+ and SO+ do not react with O2. The overall rate constant is energy independent (8±2)10−11 cm3 s−1, but the elementary steps leading to OCS+ and SO+ decrease in rate with increasing energy while the charge transfer reaction increase in rate. The reactions of CS+ with H2 and CH4 form HCS+; the first reaction is found to have an energy independent rate constant of (3.8±1)10−10 cm3 s−1 and the second has a measured rate constant which increases from 5.10−10 cm3 s−1 at the lowest energy studied (0.2 eV) to 1.10−9 cm3 s−1 at 1 eV. HCS+ does not react rapidly with H2 or CH4.
Calculation of the diamagnetic spin-orbit contribution to the nuclear spin–spin coupling tensors in the water molecule
Authors: Galasso V. , Lazzeretti P. , Rossi E. , Zanasi R.
Published: February 2003

The diamagnetic spin-orbit contribution to the nuclear spin–spin coupling constants of water has been calculated employing SCF wave functions of increasing accuracy. The results demonstrate that this term is small in the case of direct O–H average coupling constants. On the other hand, a significant contribution (≂−7 Hz) to geminal H–H coupling constant is found. The theoretical results are slightly affected by the characteristics of the basis set employed in the calculations.
The wetting liquid–vapor interface of a binary liquid mixture
Authors: Beaglehole D.
Published: February 2003

This paper includes gravitational effects in the Cahn squared-gradient model for the wetting liquid–vapor interface, and determines the temperature dependence of the wetting layer thickness for both regular solution and nonclassical free energy functionals.
The binding energy of the ground state of Be2
Authors: Lengsfield B. H. , McLean A. D. , Yoshimine M. , Liu B.
Published: February 2003

Two convergent sequences of multiconfiguration self-consistent field and configuration interaction (CI) calculations have confirmed the predictions of a previous interacting correlated fragments (ICF) calculation and given best values for the De and Re of Be2(X 1Σ+) of 2.04±0.21 kcal/mol and 4.73±0.03a0, respectively. These calculations used a 6s/4p/3d/1f Slater basis set on each atom and correlated only the four 2s electrons. They were shown computationally to be free from basis set superposition and size-consistency errors. A large second order CI calculation yielded a rigorous lower bound to the full four-electron CI binding energy of 1.87 kcal/mol within the present basis set. Arguments are presented that the 1s electronic correlation effect on the binding energy is less than 0.2 kcal/mol. The earlier ICF calculation on Be2 has been repeated and extended to a higher level of fragment correlation using the current basis set. The best ICF results are in close agreement with the second order CI calculations, indicating that the full four-electron CI limit within this basis set has been reached and providing the first computational proof of the convergence of ICF method.
Density functional theory of asymptotic form of electron density in heteronuclear diatomic molecules
Authors: Alonso J. A. , March N. H.
Published: February 2003

Density functional theory is shown to lead to a simple differential equation for the asymptotic form of the electron density in a diatomic molecule. This equation can be solved, if one assumes building blocks which in a heteronuclear diatomic molecule correspond to fractionally charged ions. The resulting expression for the asymptotic electron density can be approximately expressed in terms of the fractional charge and the chemical potentials of the two free atoms. Two models are proposed for estimating the fractional charge.
The cylindrical Poisson–Boltzmann equation. I. Transformations and general solutions
Authors: Benham Craig J.
Published: February 2003

In this paper the cylindrical Poisson–Boltzmann equation in reduced coordinates is transformed into an algebraically nonlinear second order ordinary differential equation, which is a particular case of Painlevé’s third equation. The only singularities of solutions to this equation are movable poles of second order. Series expansions are developed which express the general solution locally about points of analyticity and about a pole. Back transformation yields local solutions to the cylindrical Poisson–Boltzmann equation. The solutions throughout an interval generally require analytic continuation of these local expressions. In addition to developing exact solutions, asymptotic properties are analyzed for the case of an isolated cylindrical polyelectrolyte. Further, an alternative technique of solution is sketched in which the cylindrical Poisson–Boltzmann equation is transformed into the sine-Gordon equation, which may then be solved by standard methods to give a one parameter family of solutions. A bibliography of references to the third Painlevé equation is presented. The application of these results to the analysis of the theoretical behavior of cylindrical polyelectrolytes in ionic solutions will be presented in a subsequent contribution.
Small-angle neutron scattering from H2O/D2O solutions of a sodium alkylbenzenesulfonate having a branched alkyl group
Authors: Triolo R. , Hayter J. B. , Magid L. J. , Johnson J. S.
Published: February 2003

Small-angle neutron scattering results from 0.055 M sodium p(1-pentylheptyl)benzenesulfonate solutions in D2O–H2O solutions of 57% to 100% volume percent D2O are reported. Strong interaction peaks indicate interparticle ordering. Good fits to the results can be obtained taking account of hard-sphere and electrostatic repulsion with the mean spherical approximation. The model used is a spherical micelle, comprising a hydrocarbon core of 11.9 Å radius surrounded by a shell. The thickness of the shell derived from the results is 8.9 Å, implying a rough micellar surface. The measured geometry and change are essentially independent of the contrast between the micelles and the solvent.
Rate theoretical analysis of ion transport in membrane channels with elastically bound ligands
Authors: Schröder H.
Published: February 2003

This presentation consists of two parts. In the first one, a model Hamiltonian for a channel with elastically bound ligands is constructed. In the second one, escape rates are derived from the Hamiltonian and transport properties of the channel are discussed considering diffusion of ions as a random walk between binding sites. Rate theory as traditionally applied considers a potential energy profile as a sequence of rigid barriers. A realistic molecular channel, however, consists of elastically bound atomic groups (ligands) which are subject to temperature induced motion, and which can respond more or less to the presence of an ion. The elastic deformation of the channel gives rise to a correction of the interaction energy between the ion and the channel as a whole. The result is an effective potential for fixed position of the ion. Moreover, due to the finite masses of the ligands and their coupling to the ion in motion, the latter will experience inertia effects, which lead to an effective ion mass. It is shown that the introduction of an effective potential requires a canonical transformation of the generalized momenta. The corresponding Hamiltonian is directly used to calculate the jumping rates over a barrier, with the effective ion mass depending on all ligand masses and the geometry of the channel. In the present case, a model Hamiltonian for a helical arrangement of dipoles as hindered rotators is discussed, followed by an investigation of the diffusion constant for this system.
Line effects in disk-shaped heterogeneous nucleation
Authors: Navascués G. , Mederos L.
Published: February 2003

The classical theory of the heterogeneous nucleation with disk-shaped nuclei is developed and discussed. The nonlinearity of the Pound plot can be understood with the present theory, in which line tension effects play an essential role. Experimental data on the nucleation of zinc depositing on glass is analyzed in the light of the theory; these data can be theoretically fitted for the first time over a full range of temperatures assuming plausible values for the unknown parameters.
CO binding to heme proteins: A model for barrier height distributions and slow conformational changes
Authors: Agmon Noam , Hopfield J. J.
Published: February 2003

A model for the dependence of the potential energy barrier on a ‘‘protein coordinate’’ is constructed. It is based on a two dimensional potential energy surface having as variables the CO–iron distance and a conceptual protein coordinate. The distribution of barrier heights observed in kinetics follows from an initial Boltzmann distribution for the protein coordinate. The experimental nonexponential rebinding kinetics at low temperatures or large viscosities (when the protein coordinates can be assumed ‘‘frozen’’) can be fit with a simply parametrized energy surface. Using the same energy surfaces and the theory of bounded diffusion perpendicular to the reaction coordinate, we generate (in qualitative agreement with experiment) the survival probability curves for larger diffusivity, when the constraint on the protein coordinate is relaxed. On the basis of our results, the outcomes of new experiments which examine the concepts underlying the theory can be predicted.
Simultaneous one- and two-photon processes in the photodissociation of NCNO using a tunable dye laser
Authors: Nadler I. , Pfab J. , Radhakrishnan G. , Reisler H. , Wittig C.
Published: February 2003

Photodissociation of NCNO in the region 660–732 nm shows that direct excitation to a state different than S1 is responsible for dissociation following one-photon absorption at wavelengths <720 nm. Also, throughout the region 660–732 nm, a second photon can easily excite molecules in S1, thereby leading to efficient two-photon photodissociation. It is possible to distinguish between the one- and two-photon processes, which produce rotationally ‘‘cold’’ and ‘‘hot’’ CN radicals, respectively. (AIP)
An ab initio SCF calculation of the polarizability tensor of sulphur dioxide
Authors: Bacskay George G.
Published: February 2003

The principal components of the static electric dipole polarizability have been calculated by an ab initio coupled perturbed Hartree–Fock (CPHF) method. The calculated components are sufficiently accurate so that a choice can be made between the two different sets of experimentally consistent values in favor of the negative anisotropy parameter αxx−ᾱ.
Diffusion controlled reactions of gases with surfaces and state dependent reactivity. II. Diffusion slip and Knudsen corrections
Authors: Monchick Louis , Hess Siegfried
Published: February 2003

An approximate procedure is outlined for incorporating nonequilbrium velocity distributions and free molecular flow effects into the boundary conditions customarily used in diffusion controlled reaction theory. This is applied to the theory of surfaces reacting with gases with state dependent reactivity [S. Hess and L. Monchick, J. Chem. Phys. 77, 307 (1982)], and is found to lead to formulas that are at least qualitatively correct over long ranges of Knudsen number, i.e., that go over into the correct vacuum rate as the mean free path becomes very large.
The evaporation coefficient of trans-diphenylethene at variable undersaturation: A new technique making use of special effusion cells
Authors: van Ekeren P. J. , Jacobs M. H. G. , Offringa J. C. A. , Schuijff A. , de Kruif C. G.
Published: February 2003

In the temperature range 325–340 K the net evaporation coefficient αγ of trans-diphenylethene is measured. We describe a new technique that makes use of special effusion cells for variable undersaturation; the coefficient appears to be pressure independent, and is found to be αγ=1.03±0.03.
Air broadened NO linewidths in a temperature range of atmospheric interest
Authors: Houdeau J. P. , Boulet C. , Bonamy Jeanine , Khayar A. , Guelachvili G.
Published: February 2003

Self- and N2-broadened linewidths of NO in the 5.4 μm band have been measured at 163 and 295 K using high resolution Fourier transform spectroscopy. These linewidths have been calculated using the formalism of Robert and Bonamy. The calculated values are in good agreement with the experimental one. Therefore, the same formalism can be reasonably used in order to calculate O2-broadened widths which cannot be easily measured. Air-broadened linewidths calculations have been performed in the temperature range [163–295 K]. From the results the J dependence of the exponent m(J) which gives the temperature dependence of the widths, according to the power law γ(T)=γ(T0) (T/T0)−m(J) has been established.
Collision energy dependence of vibrational/rotational distribution of BaBr produced in the crossed beam reaction Ba+CH3Br
Authors: Munakata Toshiaki , Matsumi Yutaka , Kasuya Takahiro
Published: February 2003

The energy disposal in the reaction Ba+CH3Br→BaBr+CH3 was studied as a function of collision energy. The collision energy was controlled in the range from 2.9 and 4.9 kcal/mol by variable acceleration of a supersonic CH3Br beam which intersected a thermal Ba beam. The internal states of the nascent BaBr were probed by means of the laser induced fluorescence (LIF). Systematic simulations of the observed LIF spectra revealed that an increase of collision energy brought about a drastic decrease of vibrational excitation. The vibrational quantum of maximum population shifted from 12 to 1 in accordance with a collision energy increment of only 2 kcal/mol. Surprisal analysis of the vibrational population suggests that the collision energy increment causes a transition between two reaction paths, one of which leads to vibrationally excited BaBr of maximum population at around ν″=12, and the other, to internally cold CH3 and statistically excited BaBr.
The dispersive collision dipole in a pair of polyatomic molecules
Authors: Galatry L. , Hardisson Arturo
Published: February 2003

The dipole moment appearing in a pair of polyatomic molecules during a collision, originating from the dynamic correlation of the charges between the two systems, is formulated using two different methods. The first one introduces the electro-optical effect induced in one of the partners by the fluctuating field of the other and by an externally applied field. The second method takes into account the optical rectification processes of one molecule subjected to the fluctuating field of the other. These formalisms may be applied to pairs with any molecular symmetry. An application is made to molecules belonging to the Td group, showing that in such a case the R−7 part of the dispersion polarization may be competitive with inductive effects.
A neutron diffraction study of the zeolite edingtonite
Authors: Kvick Åke , Smith Joseph V.
Published: February 2003

A neutron diffraction study at 294 K of a single crystal of edingtonite (Ba2Al4Si6O20 ⋅ 7H2O; a 9.537(3) b 9.651(2) c 6.509(2) Å; P21212) utilized 1876 diffraction intensities from the Brookhaven National Laboratory high-flux beam reactor. The agreement factor R(F2)=0.055 for conventional anisotropic refinement was reduced to 0.045 for a Gram–Charlier expansion up to fourth order for the thermal factors of the water atoms. The Si–O and Al–O distances correlate inversely with the Si–O–Al angle as in scolecite. There is no indication of substitutional disorder. The barium atom is coordinated to three pairs of framework oxygens (2.89, 2.96, and 3.04 Å) and two pairs of water oxygens (2.79 and 2.79 Å). Two framework oxygens have weak hydrogen bonds to both water molecules [O(4)–OW(1) 2.87, −OW(2) 2.96; O(5) −OW(1) 3.02, −OW(2) 3.02 Å] and the other three framework oxygens are each bonded to a Ba atom. The OW–H ⋅⋅⋅ O angles (163.5°, 165.1°, 173.9°, and 178.0°) are fairly close to 180°, the H ⋅⋅⋅ O distances are long (1.91, 2.02, 2.09, and 2.10 Å) and the observed uncorrected OW–H distances range from 0.928(6) to 0.959(4) Å. Only seven out of the eight water positions are occupied [W(1) 84% occupancy; W(2) 91%]. The average rms displacement of each hydrogen (0.32, 0.29, 0.27, and 0.24 Å) correlates approximately with the hydrogen bond length (2.09, 2.10, 2.02, and 1.91 Å). Third- and fourth-order tensor components in the displacements of the water molecules may result from anharmonic or curvilinear vibrations; however, the effect of the static displacements of the center-of-motion from interaction with unoccupied water sites may also be important.