bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic H abstraction of surface H on Si: An Eley–Rideal mechanism?
Authors: Koleske D. D. , Gates S. M. , Jackson B.
Published: July 2002

The abstraction kinetics for atomic hydrogen (Hat) removal of chemisorbed D and atomic deuterium (Dat) removal of chemisorbed H are studied on single crystal Si surfaces. The surface H and D coverages are measured in real time by mass analyzing the recoiled H+ and D+ ion signals. On both Si(100) and Si(111) surfaces, the abstraction reactions are efficient, and have very low activation energies ≂0.5–1 kcal/mol. For abstraction from surfaces containing only monohydride species, the abstraction reaction probability is ≂0.36 times the adsorption rate of Hat or Dat. For the same Hat and Dat exposures, the reaction rates for Hat removal of adsorbed D and Dat removal of adsorbed H are nearly identical. All observations are consistent with a generalized Eley–Rideal abstraction mechanism, and a two-dimensional quantum-mechanical model is used to calculate reaction probabilities for these reactions. According to the model, the activation energies are due to enhanced abstraction rates from excited vibrational states of the adsorbed Si–H or Si–D bond. With SiH2 and SiH3 species present on the surface, the removal rate of H using Dat is decelerated, suggesting that the higher hydrides have a lower cross section for abstraction.
Experimental absolute differential cross section for the excitation of the lowest triplet state of [1.1.1]propellane by electron impact
Authors: Allan Michael
Published: July 2002

Absolute differential cross sections for collisions of low-energy electrons with [1.1.1]propellane were measured. Presented are the energy dependence of the elastic cross section at 90° in the range 0.5–16 eV, energy dependence of the cross section for the excitation of the 3A2″ lowest triple state at 90° up to 6 eV above threshold, and the angular dependence of the inelastic cross section at energies 1.5, 2.6, and 5.0 eV above threshold. The data is compared with the results of a recent ab initio scattering calculation [C. Winstead, Q. Sun, and V. McKoy, J. Chem. Phys. 97, 9483 (1992)]. The calculated cross section is found to be about two times larger than the experiment in absolute magnitude and to reproduce qualitatively correctly the main experimental features both in the energy and the angular dependence.
Comment on ‘‘A theoretical stochastic model for the A+1/2B2→O reaction’’ [J. Chem. Phys. 9
8, 10017 (1993)]
Authors: Sholl David S. , Skodje Rex T.
Published: July 2002

We examine an approximate theory for the A+1/2B2→O surface reaction presented by Mai et al. [J. Chem. Phys. 98, 10017 (1993)]. This theory predicts kinetic oscillations in the vicinity of a kinetic phase transition. We show, using Monte Carlo simulations, that these oscillations are an artifact of the approximations in the theory. We demonstrate that these approximations fail near the phase transition. The theoretically predicted onset of oscillations actually corresponds to the position of the kinetic phase transition.
MIE scattering from anisotropic thick spherical shells
Authors: Hahn David K. , Aragón Sergio R.
Published: July 2002

A theory of the electromagnetic scattering from spherical shells composed of radially oriented optically anisotropic scattering elements is presented. The theory is valid for arbitrary shell size and index of refraction but is limited to moderate shell thickness compared to the shell radius. The theory includes the effect of the shell thickness to second order, thereby extending previous work by Lange and Aragón [J. Chem. Phys. 92, 4643, (1990)]. Exact closed form solutions could be obtained for some, but not all of the terms in the expansion. Extensive comparisons with exact numerical computations based on infinite series of non-integral order Bessel functions are included, as well as comparisons with the exact closed form expressions of the first order theory. The relationship of the second order theory to the Rayleigh–Debye approximation is examined and it is shown that, in contrast to the first order case, there are Mie corrections to the effects of the optical anisotropy on the scattering amplitudes. These results are useful in the interpretation of light scattering experiments from phospholipid vesicle dispersions.
Coherent anti-Stokes Raman spectroscopy of infrared multiphoton excited molecules
Authors: Deliwala Shrenik , Goldman Jay , Chen Kuei-Hsien , Lü Cheng-Zai , Mazur Eric
Published: July 2002

Time-resolved coherent anti-Stokes Raman spectroscopy is used to obtain the rovibrational energy distributions in polyatomic molecules following infrared multiphoton excitation. In addition to presenting new results on SF6, we review previously obtained data on SO2 and OCS. The data yield new details about infrared multiphoton excitation and intramolecular vibrational energy relaxation. In particular they show the significance of collisions in redistributing vibrational energy following excitation. The results also clearly show stronger intermode coupling and higher excitation in systems with increasing numbers of atoms per molecule.
Swelling effects in semidilute block copolymer solutions
Authors: Mayes Anne M. , Barker John G. , Russell Thomas P.
Published: July 2002

Small-angle neutron scattering is used to investigate swelling effects in disordered block copolymer solutions in the semidilute regime. Results are compared with Leibler’s mean-field analysis for incompressible copolymer melts rescaled by Olvera to account for chain swelling. Semidilute solutions of two copolymers in toluene are considered: poly(styrene-b-methyl methacrylate) and poly(methyl methacrylate-b-methyl methacrylate-d8). The copolymers are found to exhibit the predicted scaling behavior for the characteristic crossover distance (or blob size) as a function of copolymer concentration, φ. However, the shift in the position of the scattering maximum, q*, is seen to have a weaker dependence on concentration than that predicted theoretically. For both systems investigated the peak position scales approximately with concentration as q*∼φ0.05.
The effect of phase separation on short- and intermediate-range order in high-silica Li2O–SiO2 glasses
Authors: Ellison A. J. G. , Price D. L. , Dickinson J. E. , Hannon A. C.
Published: July 2002

Wide-angle neutron diffraction measurements have been performed on single-phase and phase-separated high-silica glasses in the system Li2O–SiO2. The structure factors of the single-phase glasses vary modestly with increasing Li2O concentration compared to the changes observed when Na2O or K2O is added to SiO2, and vestiges of the intermediate-range order characteristic of v-SiO2 are retained to 33 mol % Li2O. The structure factors of single-phase and phase-separated glasses are identical to within 1%–2%, indicating that phase separation results in very minor disruptions to local atomic arrangements. When combined with evidence obtained from previous studies, these data indicate that single-phase high-silica glasses in this system contain compositional heterogeneities analogous to those produced by phase separation.
Brownian dynamics of weakly bendable macromolecules: Effects of bending fluctuations on electric dichroism
Authors: Fukudome Kiyohiro
Published: July 2002

The expression of the steady-state value of electric dichroism (ED), over the entire electric field strength, for semistiff linear polymers with an electric polarizability along the chain has been derived by a normal mode approximation on the basis of the Brownian dynamics. Only a flexibility parameter, L/P defined as the contour length L to the persistence length P, is introduced into the expression without any assumption of the configuration. Our ED theory predicts that, with the increase in an L/P value, the steady state value is decreased over a low-to-medium field strength range but remains to be unchanged at infinitely high fields. The expression of the ED relaxation after the removal of an electric field is also derived, when the field strength is low. The off-field relaxation decays multiexponentially not only due to rotational diffusion but also due to bending diffusion. The contribution of the bending to the decay amplitude is increased with increasing L/P. The flexibility strongly affects the transient state, i.e., the rotational and bending relaxation times and their amplitudes rather than the steady state.
Trajectory studies of the reaction F−+HCl→HF+Cl−. I. Reaction rate constant
Authors: Wei Jianmei , Meng Qin , Su Timothy
Published: July 2002

Ab initio calculations at the MP4/6–31G** level in conjunction with experimental data were used to derive an analytical potential energy function for the reaction F−+HCl→HF+Cl−. A Monte Carlo-classical trajectory method was used to estimate the thermal energy reaction rate constants at various temperatures. The results showed that the reaction efficiency decreases sharply as temperature increases. At room temperature, the calculated reaction rate constant is in excellent agreement with the experimental result. Reaction rate constants were also calculated as a function of relative translational energy at internal (vibrational and rotational) temperatures of 50, 300, and 3000 K. It was observed that the rate constant exhibits a similar relative translational energy dependence as the temperature dependence. Calculated results show no internal temperature dependence of the reaction rate constant.
Integral equations for interaction site fluids: The influence of connectivity constraints and auxiliary sites
Authors: Lue Leo , Blankschtein Daniel
Published: July 2002

We examine two central features of two well-known integral equations for interaction site fluids: (i) the Chandler–Silbey–Ladanyi equations, and (ii) the site–site Ornstein–Zernike equation. The first feature involves the influence of connectivity constraints. Specifically, we identify the restrictions imposed on the site–site correlation functions arising from the constraints of connectivity between sites within a molecule. We find that when the Chandler–Silbey–Ladanyi (CSL) equations, a set of diagrammatically proper integral equations, are combined with a general approximate closure, they do not necessarily satisfy these connectivity constraints. On the other hand, the site–site Ornstein–Zernike (SSOZ) equation, combined with a simple fluid closure, does satisfy these constraints. These findings profoundly affect the long-range behavior of the correlation functions and the dielectric constant of the bulk fluid. These findings are also important for the development of computational methods to obtain accurate numerical solutions of the CSL and SSOZ equations.

When theories do not satisfy the above-mentioned connectivity constraints, we find that the resulting correlation functions do not satisfy the local neutrality constraints, which is a necessary requirement for any theory to properly predict the fluid dielectric constant. Instead, the correlation functions satisfy the constraints applicable to ionic fluids, that is, the Stillinger–Lovett moment conditions. This leads to the prediction of an infinite fluid dielectric constant. The second feature which we examine involves the influence of auxiliary sites on the prediction of the site–site total correlation functions. We prove that the addition of certain types of auxiliary sites does not affect the correlations between real sites when the Chandler–Silbey–Ladanyi equations are combined with a general approximate closure. The predictions of the SSOZ equation, combined with a general approximate closure, have been shown to depend on the presence of auxiliary sites. However, in the case of the Percus–Yevick closure for systems characterized by hard-sphere interaction sites, we are able to prove that the SSOZ equation does not exhibit this dependence for certain types of auxiliary sites.
Dynamics of crystalline acetanilide: Analysis using neutron scattering and computer simulation
Authors: Hayward R. L. , Middendorf H. D. , Wanderlingh U. , Smith J. C.
Published: July 2002

The unusual temperature dependence of several optical spectroscopic vibrational bands in crystalline acetanilide has been interpreted as providing evidence for dynamic localization. Here we examine the vibrational dynamics of crystalline acetanilide over a spectral range of ∼20–4000 cm−1 using incoherent neutron scattering experiments, phonon normal mode calculations and molecular dynamics simulations. A molecular mechanics energy function is parametrized and used to perform the normal mode analyses in the full configurational space of the crystal i.e., including the intramolecular and intermolecular degrees of freedom. One- and multiphonon incoherent inelastic neutron scattering intensities are calculated from harmonic analyses in the first Brillouin zone and compared with the experimental data presented here. Phonon dispersion relations and mean-square atomic displacements are derived from the harmonic model and compared with data derived from coherent inelastic neutron scattering and neutron and x-ray diffraction. To examine the temperature effects on the vibrations the full, anharmonic potential function is used in molecular dynamics simulations of the crystal at 80, 140, and 300 K. Several, but not all, of the spectral features calculated from the molecular dynamics simulations exhibit temperature-dependent behavior in agreement with experiment. The significance of the results for the interpretation of the optical spectroscopic results and possible improvements to the model are discussed.
Sampling of semiclassically quantized polyatomic molecule vibrations by an adiabatic switching method: Application to quasiclassical trajectory calculations
Authors: Huang Jingrong , Valentini James J. , Muckerman James T.
Published: July 2002

We apply the adiabatic switching (AS) method to determine the polyatomic classical motions that correspond to selected vibrational quantum states on multidimensional, anharmonic potential energy surfaces, and use these semiclassically quantized motions as initial conditions for quasiclassical trajectory (QCT) calculations of state-to-state reaction dynamics. Specifically, we calculate the classical motion corresponding to the quantum mechanical zero-point vibration of deuterated methane, CD4, and run QCT calculations on the H+CD4→HD(v′,j′)+CD3 reaction. The distribution of CD4 vibrational zero-point energy (ZPE) associated with the AS-sampled motions is compared with that from normal-mode-sampled motions. The spread of total zero-point energy in the AS calculations is much narrower than with normal-mode sampling, and the ZPE’s are appropriately shifted to lower energy due to anharmonic effects. Reverse adiabatic switching is used as an indirect check of the quantum numbers of the adiabatically sampled motion, but numerical limitations made this test inconclusive. The AS method thus appears to be superior to normal-mode sampling, but this superiority cannot be demonstrated conclusively for the fully anharmonic CD4 potential. However, the AS method is shown to perform very well for transformation from one CD4 harmonic potential to another and for transformation from an harmonic to an anharmonic, but decoupled potential in which CD4 is described by Morse oscillators. Evidence is presented that suggests the AS calculations are limited by numerical inaccuracies or intrinsic features of the potential energy surface, both of which are unavoidable. H+CD4→HD(v′,j′)+CD3 QCT calculations of state-to-state dynamics using CD4 with no ZPE, the ZPE from AS sampling, and the ZPE from normal-mode sampling are reported and compared.
Theory of spectral line shape. III. The Fano operator from near to far wing
Authors: Roney P. L.
Published: July 2002

In this third part of a theory of spectral line shape, applicable to conditions of atmospheric transmission, an evaluation of the frequency dependence of the complete Fano collision operator has been made using the collision time theory developed earlier. This results in a considerable reduction of the terms in the Fano operator. An analysis of the spectral line wing shows that there are two different regimes: the near wing and the far wing. These regimes are demarcated by a turning point at a frequency displacement of kT/h. In the very far wing, beyond the turning point, the behavior of the Fano operator changes and the effects of binary collision overlap and photon absorption into the binary collision complex become important. The line wing behavior is corroborated qualitatively by experimental results for carbon dioxide near 4.2 μm.
The magnitude and location of the surface tension of curved interfaces
Authors: Baus M. , Lovett R.
Published: July 2002

A thermodynamic definition is given for the spatial distribution of the force in a curved interface that manifests itself macroscopically as the ‘‘surface tension.’’ A general thermodynamic characterization of a curved interface requires a complete knowledge of this force distribution. While a thermodynamic description in terms of a ‘‘surface tension’’ acting on a ‘‘surface of tension’’ is always incomplete, we identify circumstances under which this description is useful and we show how, in these circumstances, the ‘‘surface tension’’ and the location of the ‘‘surface of tension’’ can be derived from the force distribution. Using external field methods, we derive molecular level expressions for the force distribution in planar, cylindrical, and spherical liquid–vapor interfaces in terms of the intermolecular pair potential and the one- and two-particle distribution functions.
Electrolytes at charged interfaces: Integral equation theory for 2–2 and 1–1 model electrolytes
Authors: Booth Michael J. , Eaton Andrew C. , Haymet A. D. J.
Published: July 2002

The structure and thermodynamics of both 2–2 and 1–1 model electrolytes at a charged interface have been determined. The solvent is modeled as a structureless dielectric continuum. The structure is calculated from the ‘‘singlet’’ version of the Ornstein–Zernike integral equation, using as input the structure of the bulk electrolyte from a recent integral equation theory. The approximation in the theory is the wall–ion bridge function, which is investigated for two levels of approximation. Surface thermodynamic quantities calculated from this structural information are compared with the classical Gouy–Chapman–Stern approximation for the interfacial region, computer simulations, and selected experimental data. Higher order structure predicted by the integral equations indicates that caution should be used when interpreting results of the classical approximation.
Theoretical study of the bonding of NO2 to Cu and Ag
Authors: Rodríguez-Santiago Luis , Branchadell Vicenç , Sodupe Mariona
Published: July 2002

The structure, binding energies, and vibrational frequencies have been determined for CuNO2 and AgNO2 in different coordination modes. Calculations have been performed using ab initio theoretical methods that include electron correlation and methods based on the density functional approach. Three structures are found to be stable minima on the potential energy surface: the C2v bidentate η2–O,O, a Cs monodentate η1–O and the C2v monodentate η1–N structures. For both CuNO2 and AgNO2 systems the η2-O,O coordination is found to be the most stable structure. The computed dissociation energies of CuNO2 and AgNO2 are 56 and 47 kcal/mol, respectively.
Sensitivity analysis of multiple chemical equilibria: Sensitivity coefficients and response equilibria
Authors: Fishtik Ilie , Nagypál István , Gutman Ivan
Published: July 2002

For general multiple chemical equilibria it is shown that both the Hessian determinant and the sensitivity coefficients may be presented as sums of contributions coming from two distinct classes of reactions, which we call Hessian and non-Hessian response equilibria (HEQs and NHEQs, respectively), and pairs thereof. This approach is shown to be equivalent to another one in which the Hessian determinant and the sensitivity coefficients are treated in terms of contributions coming solely from HEQs and their pairwise interactions. The results obtained in this work hold irrespective of the type of kinetics (linear or nonlinear) by means of which the equilibrium state is achieved.
A comparative study of chain conformation at the surface of poly(β-benzyl-L-aspartate) and poly(γ-benzyl-L-glutamate) films with high resolution electron energy loss spectroscopy
Authors: Leclerc G. , Pireaux J. J. , Caudano R. , Hönings C. , Knopp B. , Höcker H.
Published: July 2002

High resolution electron energy loss spectroscopy (HREELS) is used to study spin-coated films of two polyaminoacids, poly(β-benzyl-L-aspartate) (PBA) and poly(γ-benzyl-L-glutamate) (PBG). The experimental results show that the side chains of these two polymers take a very different conformation at the surface: This is confirmed by infrared spectroscopy (ir) and differential scanning calorimetry (DSC) which are more bulk sensitive techniques. This effect is further attributed by computer graphics facilities (BIOSYM) to a larger flexibility of the side chain of PBG as compared to PBA.
(SF6)N clusters, 100≲N≲3000, produced in a SF6+Ne gas expansion: Size, temperature, and solid phase transition
Authors: Torchet G. , de Feraudy M.-F. , Raoult B.
Published: July 2002

In this paper, the phase behavior of SF6 clusters is examined experimentally and is discussed in the context of the previous work. SF6 clusters made of 100 to 3000 molecules are produced in a free jet expansion of a Ne+SF6 mixture. Cluster structures are identified by means of electron diffraction methods and ascertained by molecular dynamics (MD) simulations. On warming up the clusters, diffraction patterns display the transition from the monoclinic (low temperature) to the body centered cubic (high temperature) bulk structure, finite size effects appearing in the form of intermediate patterns that correspond to neither structure. MD simulations have shown that these intermediate patterns are due to a progressive rearrangement of the cluster surface prior to the cluster core transition, a process which leads to the observed temperature spread of the transformation. Taking advantage of the sensitivity of diffraction patterns to cluster temperature, SF6 clusters are used to probe the free jet expansion, particularly the cooling efficiency of the carrier gas and the warming effect caused by the crossing of the frontal shock wave. It is found that upon increasing the SF6 mole fraction, clusters become larger and warmer, the high-temperature structure being achieved when the expanding mixture is nearly saturated in SF6, which corresponds to a maximum cluster size. When cold clusters are allowed to cross the frontal shock wave, they warm up and acquire the cubic structure, without any appreciable evaporation. Using line height measurements in the cubic patterns, it is shown that the variation of the Debye–Waller factor, in a large range of sizes, is mainly due to a size effect. Finally, the temperature at which the transition to the cubic structure occurs is found to be constant for clusters made of more than about 1300 molecules; however, it decreases when the clusters get smaller. This result has been confirmed by recent molecular dynamics simulations.
Quartet excited halogen atoms produced in the electron pulse irradiation of rare gases containing halogenated compounds
Authors: Kuramasu T. , Ohyama H. , Yoshikawa S. , Terazawa N. , Ishikawa Y. , Arai S.
Published: July 2002

Quartet excited halogen atoms F*(2p4 3s,4PJ), Cl*(3p4 4s,4PJ), Br*(4p4 5s,4PJ), and I*(5p4 6s,4PJ), where the J’s are 5/2, 3/2, and 1/2, were found to be produced in the electron pulse irradiation of Ne or Ar containing one of SF6, CCl4, CClF3, CBrF3, CBr2F2, and CF3I. The population distribution ratios at the stage of production were 1.0(J=5/2):0.41(J=3/2):0.06(J=1/2) for F* in Ne containing SF6, 1.0(J=5/2):0.27(J=3/2):0.14(J=1/2) for Cl* in Ne containing CCl4, 1.0(J=5/2):0.29(J=3/2):0.2–0.3(J=1/2) for Br* in Ne containing CBr2F2, and 1.0(J=5/2):0.13(J=3/2):0.54(J=1/2) for I* in Ar containing CF3I. The observed ratios considerably differ from those calculated from the Boltzmann distribution law. F*(4P5/2), F*(4P3/2), and Cl*(4P5/2) are mainly produced by the reactions of lowest triplet excited diatomic molecules of neon with SF6 and CCl4. Cl*(4P3/2) and Cl*(4P1/2) are produced in a rapid process and deactivated into lower Cl*(4P5/2). Several reaction channels probably contribute to the formation of Br*(4PJ) and I*(4PJ). Rate constants for reactions of triplet excited diatomic molecules of neon or argon with these parent molecules were determined from observed absorption decay curves for Ne2* or Ar2* in the presence of parent molecules.
Optical spectroscopy and ground state dynamics of methyl groups
Authors: Gebhardt V. , Orth K. , Friedrich J.
Published: July 2002

We investigated dimethyl-s-tetrazine (-h6 and -d6) in a n-heptane (-h16 and -d16) lattice with hole burning techniques. Stark experiments definitely show that the two methyl groups in dimethyl-s-tetrazine (DMST) are inequivalent. Hence, the respective rotational tunneling dynamics can be different. This is clearly seen in the behavior of DMST-d6 in both lattices n-heptane-h16 and -d16: Hole burning produces three pairs of sideholes symmetrically shifted from the laser frequency. The tunneling dynamics of the central hole as well as of the sideholes is governed by two relaxation times which differ by about one order of magnitude. Due to the narrow temperature range accessible, an unambiguous assignment of the microscopic tunneling relaxation process is not possible. On the other hand, DMST-h6 relaxes via a Raman process above 3 K and via a direct process below. In the Raman-active regime the tunneling rates for both host lattices fall on top of each other in agreement with theory. There are, however, features in the tunneling dynamics which are not yet understood. For instance, in the temperature regime where the direct process prevails, host deuteration speeds up the tunneling relaxation by an order of magnitude. In addition, the sidehole pattern of DMST-h6 is quite different from DMST-d6: Only one pair is observed.
Theory of hyperfine coupling constants of solvated molecules: Applications involving methyl and ClO2 radicals in different solvents
Authors: Fernández Berta , Christiansen Ove , Bludsky Ota , Jo/rgensen Poul , Mikkelsen Kurt V.
Published: July 2002

A multiconfiguration self-consistent reaction field method is presented for calculating isotropic hyperfine coupling constants of solvated molecules. The solvent model is based on generalizations of Kirkwood’s model for describing solvation effects. Isotropic hyperfine coupling constants are calculated for the methyl and ClO2 radicals in different solvents.
Approximate size-consistent treatments of Heisenberg Hamiltonians for large systems
Authors: Guihery Nathalie , Amor Nadia Ben , Maynau Daniel , Malrieu Jean Paul
Published: July 2002

A truncation of the Heisenberg Hamiltonian CI matrix is proposed in order to treat large molecules or clusters. The criterion for the selection of the model space is energetic. To correct the size-inconsistency error due to the truncation of the CI matrix, the diagonal part is dressed by the spin configurations of the outer space. This correction remains simple despite its self-consistent character and gives accurates energies. Using a geometry-dependent Heisenberg Hamiltonian for conjugated hydrocarbons, it provides reliable geometries at low computational cost. Test calculations on linear polyenes are compared with the results of the full matrix diagonalization, and the large linear polyene C32H34 and the cyclic C32H32 polyene are studied.
Effect of dynamical asymmetry on the viscosity of a random copolymer melt
Authors: Kumaran V.
Published: July 2002

The variation of the viscosity as a function of the sequence distribution in an A–B random copolymer melt is determined. The parameters that characterize the random copolymer are the fraction of A monomers f, the parameter λ which determines the correlation in the monomer identities along a chain and the Flory chi parameter χF which determines the strength of the enthalpic repulsion between monomers of type A and B. For λ≳0, there is a greater probability of finding like monomers at adjacent positions along the chain, and for λ<0 unlike monomers are more likely to be adjacent to each other. The traditional Markov model for the random copolymer melt is altered to remove ultraviolet divergences in the equations for the renormalized viscosity, and the phase diagram for the modified model has a binary fluid type transition for λ≳0 and does not exhibit a phase transition for λ<0. A mode coupling analysis is used to determine the renormalization of the viscosity due to the dependence of the bare viscosity on the local concentration field. Due to the dissipative nature of the coupling, there are nonlinearities both in the transport equation and in the noise correlation.

The concentration dependence of the transport coefficient presents additional difficulties in the formulation due to the Ito–Stratonovich dilemma, and there is some ambiguity about the choice of the concentration to be used while calculating the noise correlation. In the Appendix, it is shown using a diagrammatic perturbation analysis that the Ito prescription for the calculation of the transport coefficient, when coupled with a causal discretization scheme, provides a consistent formulation that satisfies stationarity and the fluctuation dissipation theorem. This functional integral formalism is used in the present analysis, and consistency is verified for the present problem as well. The upper critical dimension for this type of renormalization is 2, and so there is no divergence in the viscosity in the vicinity of a critical point. The results indicate that there is a systematic dependence of the viscosity on λ and χF. The fluctuations tend to increase the viscosity for λ<0, and decrease the viscosity for λ≳0, and an increase in χF tends to decrease the viscosity.
Spectroscopic properties of the bound n=3 states of H+2
Authors: Sonnleitner Stephanie A. , Beckel Charles L. , Peek James M.
Published: July 2002

Spectroscopic properties are determined for the six bound electronic states of H+2 that correlate as nuclear separation R → ∞ with a proton and a hydrogen atom in an n=3 state. Two antibonding orbitals 5gπg and 6hσu have significant potential wells and an infinite number of bound vibrational states due to strongly attractive pole–dipole leading multipole terms. Vibrational–rotational eigenenergies are reported for three angular momentum J values for each bound state. Coefficients up to a6 are listed for Dunham power-series expansions of the vibrational potentials V(R) about the equilibrium separations Re. The higher a coefficients come almost entirely from the nuclear Coulomb repulsion only for the 3dδg state, the one state that is lowest of its symmetry type and is therefore not perturbed from below. Dunham Yij are determined also; the leading vibrational Y10, rotational Y01, and anharmonicity ‖Y20‖ constants are very small due to the very broad potential wells and large values of Re for all six n=3 electronic states. For five of the six states, Y00 is negative and therefore the vibrational quantum number ve at the potential minimum is ≳−1/2. The wavelength range of the bound–bound (n=3)↔(n=2)H+2 transitions is 3800–9700 Å; many unidentified diffuse interstellar bands have been reported in this range.
Effects of vibronic coupling on the local Frenkel states in doped naphthalene crystals
Authors: Eilmes A. , Zgierski M. Z.
Published: July 2002

Effects of vibronic coupling on charge transfer induced local Frenkel exciton states (CTILFES) in doped naphthalene crystals are discussed. Two simple coupling models are proposed, one suitable for neat and the other for doped crystals. The results suggest that the difference between the stabilization energy of the local state and its vibrational replica may be attributed to the vibronic interaction with charge transfer states.
Electron transfer reactions in clusters: The effect of polar solvents on the (2p3s) Rydberg state of azabicyclo-octane
Authors: Dion C. F. , Bernstein E. R.
Published: July 2002

(1+1) mass resolved excitation spectra are reported for the (2p3s)←(2p)2 Rydberg transition of azabicyclooctane (ABCO) van der Waals clusters. The solvent molecules employed in this study are mostly polar. The polar solvent cluster spectra are red shifted from those of the bare molecule ABCO by more than 500 cm−1 in most cases. This large increase in the interaction energy of the ABCO molecule Rydberg state in polar solvent clusters with respect to that of the ground state ABCO cluster is due to an exchange delocalization or electron transfer interaction for the excited state cluster. The ABCO Rydberg state electron is delocalized into the available (virtual) orbitals of the polar solvent molecule. Relaxation dynamics are measured for the generation of the electron transfer state of the cluster. This behavior is similar to that characterized for other cyclic amines in polar solvent clusters.
Heterogeneously catalyzed hydrolysis of chlorine nitrate: Fourier-transform ion cyclotron resonance investigations of stratospheric chemistry
Authors: Schindler Thomas , Berg Christian , Niedner-Schatteburg Gereon , Bondybey Vladimir E.
Published: July 2002

High resolution Fourier-transform ion cyclotron resonance (FT-ICR) mass spectroscopy is used to investigate reactions of large ionic water clusters H+(H2O)n and X−(H2O)n (n=1−100, X=O or OH). Reactions of the clusters with chlorine nitrate, important ‘‘reservoir compound’’ involved in the stratospheric ozone chemistry, are investigated to evaluate the importance of heterogeneously catalyzed reactions for ozone depletion. It is found that reactions of both cationic and anionic clusters result in effective hydrolysis of chlorine nitrate and return of the more active hypochlorous acid, HOCl into the gas phase. The chemistry of clusters is discussed, and its validity and relevance as a model for ‘‘real life’’ processes in the so-called polar stratospheric clouds (PSC’s) is assessed.
Pressure tuning of solvent viscosity for the formation of twisted intramolecular charge-transfer state in 4,4′-diaminodiphenyl sulfone in alcohol solution
Authors: Hara Kimihiko , Bulgarevich Dmitry S. , Kajimoto Okitsugu
Published: July 2002

The effect of solvent shear viscosity on the formation of twisted intramolecular charge-transfer (TICT) state in the excited state for 4,4′-diaminodiphenyl sulfone (DAPS) in three linear alcohol solvents has been investigated by measuring the picosecond fluorescence lifetime as a function of pressure. At lower pressures the kinetics of the TICT-state formation is controlled by solvent relaxation. While with increasing pressure, the reaction path shifts toward the ‘‘high viscosity regime’’ in which the reaction proceeds through the nonrelaxed path independent of solvent coordinate on the free energy surface of the S1 excited state. This behavior could be called as ‘‘pressure tuning effect’’ of solvent viscosity. The power law parameter (α) is used as a measure of the viscosity dependence. For the high viscosity regime, α=0.2 can be attributed to the intrinsic viscosity dependence for barrier crossing.
Far-wing excitation study of the reactions in the Hg–H2 collisional quasimolecules. I. Transit-state selectivity in HgH formation and three-body dissociation
Authors: Ohmori K. , Takahashi T. , Chiba H. , Saito K. , Nakamura T. , Okunishi M. , Ueda K. , Sato Y.
Published: July 2002

Laser-pump/probe and double-beam absorption/dispersion approaches have been applied to the far wings of the Hg 3P1–1S0 resonance line broadened by collisions with H2. Absolute reduced absorption coefficients of the Hg–H2 quasimolecules have been determined as a function of the wave-number shift Δ from the resonance-line center both in the red and blue wings. Decay probabilities of the excited Hg*(3P1)–H2 quasimolecule into the reactive channel (hGH formation) or into the elastic channel (Hg*(3P1) formation) have been determined as a function of Δ both for the red-wing excited Ãi and blue-wing excited B̃ states. The rest of these decay probabilities have been attributed to three-body dissociation Hg(1S0)+H+H. These results indicate that (a) the Ã-state surface serves more effectively in HgH formation than the B̃-state surface by a factor of about 2.3; but (b) three-body dissociation, in turn, proceeds far more efficiently on the B̃-state surface than on the Ã-state surface. Discussions about the energy barriers and the orbital correlations for HgH formation are presented, based on the Δ dependence of these decaying probabilities.
Conformational dynamics of the CO:CO2 complex in argon matrices. I. Thermodynamical considerations derived from the observed kinetics
Authors: Raducu V. , Gauthier-Roy B. , Dahoo R. , Abouaf-Marguin L. , Langlet J. , Caillet J. , Allavena M.
Published: July 2002

In a previous work, experimental evidence for different conformations of the weakly bonded CO:CO2 complex has been given in argon matrices, from the analysis of FTIR absorption spectra. A spontaneous interconversion occurs between a high frequency form (HF A and B lines: The CO frequency is shifted toward high frequencies upon complexation) and a low frequency form (LF line: The CO frequency is shifted toward low frequencies upon complexation) which has been characterized at different temperatures between 5 and 12 K. Above 12 K, the HF doublet only remains. In an attempt to explain the observed phenomena, concentration, matrix, and isotopic effects are studied, as well as the reverse conversion which is ten times faster than the direct one. A thermodynamical analysis of the conversion is performed. From the temperature behavior of the equilibrium constant K, we can suppose that the conversion exhibits two regimes: A low temperature one below 8 K and a high temperature one between 8 and 12 K. A reasonable explanation could be that three conformations are involved: A more stable one corresponding to the narrow low frequency line (probably the T shape observed in molecular beam experiments) and two closely related less stable conformations which give rise to the A and B lines of the high frequency doublet. The energy differences between these conformations are small: ΔH=−140 J mol−1 and −337 J mol−1 between the LF form and the HF B and A forms, respectively. A subtle mechanism, involving a concerted exchange between the CO molecule of the complex and a nearest argon atom, is proposed to explain the experimental observations.
A Fermi Golden Rule, Liouville-space approach to the study of intramolecular electron transfer rate in solution
Authors: Lami Alessandro , Santoro Fabrizio
Published: July 2002

We consider the problem of the calculation of the intramolecular electron transfer (ET) rate for molecules in solution and focus on the case of rapid, almost activationless processes. We assume that the weak-coupling, nonadiabatic limit holds and utilize the Fermi golden rule expression for the ET rate, avoiding the introduction of phenomenological data. The Fermi Golden Rule is elaborated in the Liouville space formalism taking into account at second order the coupling to the bath of instantaneous normal modes (INM) of the solvent as well as to the intramolecular bath responsible for relaxation in the isolated molecule. The couplings among the principal modes (the ones more directly involved in the ET process), mainly intramolecular, are taken into account exactly. The main inputs are weighted densities of states which can be, at least in principle, calculated. For those concerning the solvent we take advantage from the recent progresses in the INM approach to the description of the short time dynamics. We compute the ET line shape (i.e., the ET rate as a function of the electronic energy gap E) for some model cases, with one, two or more principal modes, investigating the influence of the solvent and of the temperature. The ET rates show a complex, but not dramatic, dependence on the solvent and are quite sensitive to the energy gap E. The temperature dependence is generally weak. The results seem to be in general agreement with recent experimental data on molecular systems exhibiting rapid ET.
Ab initio potential energy surfaces and nonadiabatic couplings involved in Be4++H2 electron rearrangement
Authors: Errea L. F. , Gorfinkiel J. D. , Kryachko E. S. , Macı́as A. , Méndez L. , Riera A.
Published: July 2002

We present the main characteristics of the energy and coupling surfaces for the BeH24+ quasimolecule, that are relevant to the dynamics of electron capture in Be4++H2 collisions in the 50 eV amu−1<E<1 keV amu−1 energy range. To construct the wave functions, we implemented a block-diagonalization method using the many electron description standard (MELD) program, which was recently modified to calculate nonadiabatic couplings.
Multireference configuration interaction calculations of electronic g-tensors for NO2, H2O+, and CO+
Authors: Lushington G. H. , Grein F.
Published: July 2002

Electronic g-tensors parametrize the Zeeman splitting observed in the EPR spectra of radicals. In this work, we report g-tensor calculations for NO2, H2O+, and CO+ at the multireference CI level. Deviations of the tensor elements (g-shifts) from the free-electron value are computed via a perturbation expansion, complete to second order in relevant Breit–Pauli terms. The g-shifts we obtain for these molecules are as follows: NO2: Δgxx=3571, Δgyy=−10296, Δgzz=−537; H2O+: Δgxx=−249, Δgyy=15733, Δgzz=4105; CO+: Δg⊥=−2383, Δg∥=−181 [all values in parts per million (ppm)]. These results are in reasonable agreement with gas phase experimental data. Larger g-shifts are typically within 20% of experiment, whereas smaller g-shifts generally differ by no more than several hundred ppm. Basis set effects and gauge dependence are examined in the case of CO+. For this molecule, a good valence description is vital for achieving accurate Δg-values and small gauge-dependence. Polarization functions are of some use in these calculations, but diffuse functions have little effect on the gauge dependence of a cationic radical such as CO+. Vibrational effects are also examined for CO+. The vibrationally averaged g⊥-shift only differs from the equilibrium value by 83 ppm.
Laser induced fluorescence spectra and carbonyl wagging potential energy functions for the S1(n,π*) excited states of tetrahydrofuran-3-one and tetrahydrothiophen-3-one: Correlation between inversion barrier and angle strain for cyclic ketones
Authors: Sagear Paul A. , Lee S. N. , Laane Jaan
Published: July 2002

The jet-cooled fluorescence excitation spectra of the S1(n,π*) states of tetrahydrofuran-3-one, CH2OCH2CH2C¯=O, and tetrahydrothiophen-3-one, CH2SCH2CH2C¯=O, have been recorded and analyzed. The carbonyl inversion bands, which arise from double-minimum potential energy functions in the excited states, were fit with functions of the form V=ax4−bx2 or V=cx2+d exp(−fx2). The furanone was found to have an inversion barrier in the S1(n,π*) state of 1152 cm−1 (13.8 kJ/mol) while the thiophenone has a barrier of 659 cm−1 (7.9 kJ/mol). The two molecules have their potential energy minima for the S1(n,π*) state at carbonyl wagging angles of 26° and 20°, respectively. The results here, together with previous data for several other cyclic ketones, demonstrate that the inversion barrier increases with the ring angle strain at the ketone carbon atom.
Monte Carlo computer simulation of small clusters of methane, ethane, and their mixture
Authors: Vishnyakov Aleksey , Piotrovskaya Elena M. , Brodskaya Elena N.
Published: July 2002

Monte Carlo simulation results for small clusters of ethane, methane and methane–ethane equimolar mixture are reported. The radial profiles of local density, energy, electric potential and normal component of Irving–Kirkwood pressure tensor were calculated. The local orientational distribution of the molecules of ethane was considered. It was shown that in the surface layer of small drops diatomic molecules prefer to align parallel to the surface, and the fraction of such molecules increases with the decrease of the droplet size. The surface potential and the surface tension were estimated. The values of the surface potential of clusters of ethane were found to be in good agreement with the conclusion of the modern theory about a quadrupolar contribution to the surface potential.
Optothermal spectroscopy of the dissociating lowest electronic singlet states of s-tetrazine and dimethyl-s-tetrazine in a molecular beam
Authors: Kerstel E. R. Th. , Becucci M. , Pietraperzia G. , Castellucci E.
Published: July 2002

We report the spectra of the 000 bands of s-tetrazine and dimethyl-s-tetrazine in a seeded molecular beam, using optothermal detection. The S/N of the optothermal s-tetrazine spectrum is about 1000 times higher than that of the LIF spectrum recorded with the same machine. The depletion nature of the signals unequivocally establishes that both molecules dissociate before reaching the detector (i.e., within ∼0.5 ms) following excitation to the S1 state. The s-tetrazine spectrum is fit to an asymmetric rotor Hamiltonian that includes the observed interchange of the a and b inertial axis in the excited state. The rotational constants and the homogeneous line broadening of 215(10) MHz (FWHM) observed here are in good agreement with, but more accurate than, those obtained in earlier sub-Doppler (saturation) gas-cell and free-jet spectra. The spectrum of dimethyl-s-tetrazine is analyzed for the m=0 free-rotor states only. Its rotational lines require a Lorentzian component of 34(2) MHz, corresponding to an excited state lifetime of 4.7 ns. The relative efficiency of the dissociative and radiative decay channels is evaluated. Despite the fact that we believe we have sufficient sensitivity, we failed to observe the s-tetrazine T1 state at 735 nm, which may be evidence of its nondissociative character.
Jet spectroscopy of p-methoxyaniline and intramolecular vibrational relaxation dynamics in the p-alkoxyaniline series
Authors: Wategaonkar S. , Doraiswamy S.
Published: July 2002

The vibronic spectroscopy of p-methoxyaniline (p-anisidine) in the S1 and S0 states has been studied using laser induced fluorescence in a supersonic jet apparatus. The band origin is found at 31 581 cm−1. Vibrational modes 6a, 6b, 1, I, and 10b are found to be active in the excitation and emission spectrum and their frequencies are 395, 565, 821, 668(v=2), and 499(v=2) cm−1 in the excited state and 426, 642, 845, 472(v=2), and 525(v=2) cm−1 in the ground state, respectively. The intramolecular vibrational relaxation (IVR) dynamics discerned from the single vibronic level fluorescence (SVLF) spectra is compared with p-aminophenol and p-ethoxyaniline, the other two members of the p-alkoxyaniline series. It is postulated that the IVR dynamics in this series is dependent on the changes in the electronic structure in the excited state rather than the increase in the density of states alone.
Rovibrational and rotational autoionization dynamics of Rydberg electron wavepackets in H2: A time-dependent multichannel quantum-defect theory approach
Authors: Fielding H. H.
Published: July 2002

The rovibrational and rotational autoionization dynamics of a Rydberg electron wavepacket in para-H2 has been investigated using time-dependent multichannel quantum-defect theory (MQDT). In the case of rovibrational autoionization, rotational channel interactions are shown to introduce a phase shift to the electron wavepacket proportional to the strength of the configuration interaction. In the case of pure rotational autoionization, the electron wavepacket is observed to remain trapped in the Coulombic potential of the rotating molecule following rotational relaxation, thus increasing the autoionization lifetime.