bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of CH(A 2Δ,B 2Σ−,C 2Σ+) by electron–ion recombination processes in the argon and krypton afterglow reactions of CH4
Authors: Tsuji Masaharu , Kobarai Kazunari , Kouno Hiroyuki , Obase Hiroshi , Nishimura Yukio
Published: July 2002

The CH(A–X,B–X,C–X) emission systems have been observed from the Ar and Kr afterglow reactions of CH4. A significant attenuation of the CH(A–X,B–X,C–X) emissions by an addition of SF6 into the discharge flow suggested that the CH(A,B,C) radicals are excited via secondary electron–ion recombination processes. Since the CH(A–X,B–X,C–X) emissions disappeared by trapping ionic active species in the discharge flow, the responsible active species for the CH(A,B,C) production were found to be Ar+ and/or (Ar+)* in the Ar flow and Kr+ and/or (Kr+)* in the Kr flow. The contribution of Ar+ and Kr+ was examined in the He afterglow, where Ar+ or Kr+ and slow electrons were simultaneously produced by the He(23S)/Ar,Kr Penning ionization. Although intense CH(A–X,B–X,C–X) emissions were observed from Ar+/CH4 where CH+n(n=2–4) were formed, they were absent from Kr+/CH4 where only CH+4 was produced. It was, therefore, concluded that CH+2 and/or CH+3 are important precursor ions for the CH(A,B,C) production. The intensity distribution of CH(A,B,C) and the CH(A,B) rovibrational distributions obtained in the Ar afterglow agreed with those through Ar+/CH4, indicating that Ar+/CH4 plays a significant role for the production of precursor ions in the Ar afterglow or (Ar+)*/CH4 provides the same precursor ions. Since the relative intensity of CH(A,B) and the rovibrational distributions of CH(A) in the Kr afterglow were different from those in the Ar afterglow, different electron–ion recombination processes dominantly take part in the CH(A,B) production.
Liophobic interaction in Baxter’s adhesive fluid
Authors: Jamnik A. , Bratko D. , Henderson D. J.
Published: July 2002

The solvent mediated force between the hard solutes mimicking liophobic colloids in Baxter’s adhesive solvent is studied on the basis of the solution to the Percus–Yevick/Ornstein–Zernike equation for spatial correlations in an infinitely dilute solution. The contact value of the solute–solute potential of mean force remains the same as observed previously in hard sphere fluid but its range increases in the presence of the attractive interaction among the molecules of the solvent. At the critical conditions of the model fluid, the solvation force between the macroparticles tends to vanish in parallel with the increasing compressibility of the fluid. The size dependence of the intercolloidal interaction is similar but slightly more pronounced than found in fluids with pure hard core interaction.
Electron–ion and ion–ion studies of the behavior of CS2 upon core electron excitation
Authors: Hayes Robert G. , Eberhardt Wolfgang
Published: July 2002

We have obtained mass spectra in coincidence with Auger electrons of various kinetic energies which result from the S 2p excitation of CS2. We have also obtained ion–ion coincidence mass spectra of CS2 resulting from the decay of S 2p core electron excitation. These spectra show that the various electronic states of CS2+2, which are produced by Auger processes following the core electron excitation, yield different electronic and vibrational states of the fragmentation products so that the kinetic energy released in the fragmentation is nearly constant. The population of the more highly excited states of CS2+2, corresponding to removal of electrons from the deep valence levels, results in atomization of the system.
Three-body hydrodynamic effects on viscosity of suspensions of spheres
Authors: Thomas Cristina Urdaneta , Muthukumar M.
Published: July 2002

We have calculated for the first time the contribution to the shear viscosity η of a dilute suspension of hard spheres from the full hydrodynamic interactions involving three spheres. Using the multiple scattering theory, we find the third order coefficient k3 in η=η0(1+k1Φ+k2Φ2+k3Φ3 +⋅⋅⋅) to be 6.40 for a suspension of hard spheres and stick boundary conditions. η0 is the viscosity of the solvent and Φ is the volume fraction of particles in the suspension. We conclude that the empirical equations used extensively in the literature are in reasonable agreement with our precise calculations of the hydrodynamic correlations of three spheres.
Interpretation for the anomaly of the C=O stretching band in benzoic acid crystal
Authors: Hayashi Soichi , Oobatake Motohisa , Nakamura Ryoko , Machida Katsunosuke
Published: July 2002

Molecular dynamics simulation has been used to investigate the infrared spectra of ordered and disordered benzoic acid crystals consisting of various proportions of the A and B configurations, whose C–O and C=O bonds are approximately parallel to the a axis, respectively. The simulation reproduced well the splitting and the temperature dependence in intensity for the C=O stretching bands observed. The absorption coefficient of the lower frequency band was simulated as several times larger than that of the higher frequency band in accord with the observed. To interpret this peculiar result of the molecular dynamics simulation, a simple calculation of the band splitting has been made in terms of the transition dipole–transition dipole interaction. It has been shown that the interaction is an essential factor to produce the large difference in intensity and the splitting for the C=O stretching bands. The higher and lower bands are interpreted as due to the A configuration reduced in intensity by the B form, and due to the B form enhanced in intensity by the A form, respectively. Compression effect in the O⋅⋅⋅O distance of the hydrogen bond is also studied in comparison with the observed value.
Continuous-wave supersonic jet diode laser spectroscopy and dynamics of Ar–DCl: Rovibrational analysis of ν1 and ν1+ν12 and the effect of Coriolis coupling in the spectrum of ν1+2ν2
Authors: Wang Zhongcheng , Quiñones Augusto , Lucchese Robert R. , Bevan John W.
Published: July 2002

The ν1 fundamental and ν1+ν12 intermolecular combination bands of the van der Waals dimer Ar–DCl have been observed using a sensitive tunable diode laser continuous-wave (cw) supersonic jet spectrometer. The experimental results are compared with frequency and intensity predictions based on variational calculations using the H6(3) potential of Hutson. A possible assignment of the ν1+2ν02 combination band is proposed on the basis of anomalous intensity predictions from these calculations. The calculations indicate that the R branch of the ν1+2ν02 combination band is much stronger than the P branch due to a strong Coriolis mixing of the ν1+2ν02 and ν1+ν12 states.
Effect of the finite extensibility of polymer chains and of the finite size of added electrolyte ions on polyelectrolyte brushes
Authors: Misra Sanjay , Varanasi Sasidhar
Published: July 2002

Our earlier polyelectrolyte brush theory [Macromolecules 22, 4173 (1989)] was derived by equating the sum of the nonelectrostatic and electrostatic potentials of the polymer segment to an overall parabolic potential shown to exist in the brush by Milner, Witten, and Cates (MWC) [Macromolecules 21, 2610 (1988)]. Here we correct the theory to take into account the finite extensibility of the chains by adopting the non-Gaussian stretch (or entropy) term of Shim and Cates [J. Phys. France 50, 3535 (1989)]. This correction leads to brush heights which will never exceed the chain length; an aspect that was not accounted for in the earlier work of MWC. In addition, the ions of the added symmetric electrolyte are considered to be hard spheres, the size of the cation and anion assuming different values in general. The total electrochemical potential of the ions, therefore, includes a volume exclusion term as well. The ions are assumed to ‘‘view’’ the solvent as a continuum (characterized only by its dielectric constant) and the brush layer as an obstacle course of randomly distributed spherical hard segments. The treatment is made simple by assuming a regime where the volume fraction of ions is much lower than the segment or solvent volume fractions.
The Raman spectra of alkali halide melts: A theoretical description
Authors: Madden P. A. , O’Sullivan K. F.
Published: July 2002

A theoretical description of the light scattering (Raman) spectra of molten salts is presented. Expressions are derived to relate the spectra of the fluctuating polarizability induced by the ion Coulomb field and by the dipole–induced dipole mechanism to the spectra of the mass and charge density fluctuations (i.e., the dynamical structure factors). The theory thereby connects the spectral features seen in light scattering to well known dynamical processes in the ionic melt, such as the charge density wave (plasmon) and the ionic diffusive motion. The validity of this description is confirmed by evaluating the theoretical expression, using dynamical structure factors calculated in computer simulations, and comparing it with spectra calculated directly from the simulations.
Model calculations on the ground vibrational state of Ar–HCN
Authors: Yaron David , Klemperer William
Published: July 2002

The Ar–HCN complex exhibits unusually wide amplitude bending along with large isotope and centrifugal distortion effects. A model in which Ar–HCN tunnels between linear and T-shaped configurations is able to quantitatively account for most of these experimental observations. A parametrized model potential is used and solutions are obtained variationally using a form for the wave function which is arbitrary in the bending angle but Gaussian in the stretching coordinate. The accuracy of the variational solution is checked against results from a two dimensional numerical relaxation procedure. In the final potential, the center of mass separation is about 4.62 Å in the linear, global minimum and 0.86 Å less at the T-shaped configuration. The potential is such that, in the ground vibrational state, the T-shaped region is not classically allowed but the wave function penetrates significantly into this region. This tunneling is the origin of the large isotope effects. The combination of the tunneling with contraction in bond length between the linear and T-shaped structures leads to the large centrifugal effects.
The vibrational spectra of molecular ions isolated in solid neon. VII. CO+, C2O+2, and C2O−2
Authors: Thompson Warren E. , Jacox Marilyn E.
Published: July 2002

When a Ne:CO=100 mixture is codeposited at approximately 5 K with a beam of neon atoms that have been excited in a microwave discharge, several new infrared absorptions appear in the resulting sample deposit. Detailed isotopic substitution experiments support the assignment of these absorptions to CO+, trans-OCCO+, and trans-OCCO−. Analysis of the infrared data has permitted determination of the CO-stretching force constants of the dimer cation and anion and has yielded a preliminary estimate of the valence angles for trans-OCCO−. The role of electron capture in the ‘‘photobleaching’’ of trans-OCCO+ by visible radiation is considered.
The fundamental C–H stretching vibration and associated intermolecular bending hot band of SCO–HCN
Authors: Dayton D. C. , Marshall Mark D. , Miller R. E.
Published: July 2002

Infrared optothermal laser spectroscopy has been used to study the linear SCO–HCN complex. The observed spectrum corresponds to excitation of the C–H stretching vibration out of either the ground state or v=1 of the lowest frequency intermolecular bending state. Ab initio calculations have also been carried out for this system which give, at least for some properties, results which are in good agreement with experiment. A comparison between the SCO–HCN results and those of the linear CO2–HCN complex studied previously, reveals that the shifts in the C–H vibrational frequency upon complex formation are rather similar. This is despite the fact that OCS and CO2 have very different point multipoles, suggesting that the electrostatic part of the interactions are likewise different for these two partners. Nevertheless, a distributed multipole calculation shows that, at the intermolecular separations characteristic of these complexes, the electrostatic interactions are in fact quite similar at the oxygen ends of OCS and CO2, providing an explanation for the similarity between the frequency shifts of these two complexes.
Energy dependent photochemistry in the predissociation of V(OCO)+
Authors: Lessen D. E. , Asher R. L. , Brucat P. J.
Published: July 2002

Photofragmentation of the V(OCO)+ molecular ion in the visible shows sharp resonant absorption features and two distinct dissociation pathways: V+(OCO)+→V++CO2 and V(OCO)+→VO++CO. The photodissociation excitation spectrum reveals two low frequency vibrational modes in the upper state of this molecule at 105 and 196 cm−1. This spectrum indicates that the same photoexcited state in V(OCO)+ is the precursor to both V+ and VO+ products. The branching ratio for VO+/V+ production depends on the excitation energy and upper state vibrational mode. An estimate of the barrier to the production of VO+ of 13 000 cm−1 (37 kcal/mole) above the ground state of V(OCO)+ is made from this data.
The coverage dependence of the sticking probability of Ar on Ru(001)
Authors: Head-Gordon Martin , Tully John C. , Schlichting Hartmut , Menzel Dietrich
Published: July 2002

The coverage dependence of the sticking probability of argon on a cold Ru(001) surface is studied experimentally by thermal-desorption spectrometry, and simulated by classical molecular dynamics with an empirical pairwise-additive potential-energy function. Experimentally, a dramatic linear increase in sticking as a function of Ar coverage is observed between 0 and 0.7 monolayer for a 300 K thermal beam of Ar incident normal to the surface; at higher coverages the sticking probability gradually saturates to approach unity beyond 2 monolayers. The linear regime is reproduced with near-quantitative accuracy by the simulations, with a simple perfect islanding model. The origin of the enhanced sticking lies primarily in efficient energy transfer to the adsorbate, due to perfect mass matching and the deformability of the overlayer. In the simulations at incident energies above 50 kJ mol−1 the sticking on the monolayer diminishes to almost zero, and collision-induced desorption is observed. Additionally, several interesting dynamical effects which have experimental relevance emerge from the simulations, such as prolonged impacts and sticking mediated by attractive interactions at the edge of adsorbate islands.
Full characterization of OH product energetics in the reaction of O(1D2) with hydrocarbons
Authors: Park Chan Ryang , Wiesenfeld John R.
Published: July 2002

The energetics of the OH(X 2Π, 0≤ν″≤4) product arising from the reaction of O(1D2) with the hydrocarbons CH4, C2H6, C3H8, and C(CH3)4 was fully characterized using laser-induced fluorescence (LIF). The product distribution is in sensible accord with earlier more limited LIF and infrared chemiluminescence studies, and the overall yield of OH decreases dramatically in the case of the heavier hydrocarbons as would be expected if dissociation of the collision intermediate was dominated by rupture of the relatively weak C–C bond. The energetics of the O(1D2)/CH4 reaction suggest that it proceeds via an insertion/elimination reaction, while that of O(1D2) with the heavier hydrocarbons appears to involve two parallel mechanisms. The major channel yields vibrationally and rotationally cool OH; by comparison with abstraction of hydrogen by O(3PJ) which preferentially yields vibrationally excited OH, this channel is associated with dissociation of a long-lived complex. The highly excited component of OH population arises from a prompt dissociation of a collision complex prior to statistical distribution of reaction exothermicity among its internal modes.
Decorated fullerenes and model structures for water clusters
Authors: Fowler P. W. , Quinn C. M. , Redmond D. B.
Published: July 2002

Polyhedral cage structures for water clusters (H2O)n are proposed for all even values of n≥20 (except n=22). The geometries are based on tetrahedral decorations of the ‘‘fullerene’’ pseudospherical polyhedra. Each has 12 pentagonal and [(1/2)n−10] hexagonal rings of water molecules linked by hydrogen bonds. The decorated fullerene series may have applications as hypothetical elemental and silicate clusters.
Quantum chemistry by random walk: Exact treatment of many-electron systems
Authors: Anderson James B. , Traynor Carol A. , Boghosian Bruce M.
Published: July 2002

We report an improved Monte Carlo method for quantum chemistry which permits the exact treatment of many-electron systems. The method combines many of the best features of earlier fixed-node, released-node, and positive/negative cancellation methods with new ideas for relocation after node crossing, self-cancellations, multiple cancellations, maximum use of symmetry in promoting cancellations, and rigorous evaluation of energies using importance sampling with trial wave functions. The method is illustrated with applications to the problems of the first excited state of a particle in a two-dimensional box, the two-electron system of excited H2 3Σ+u, and the three-electron system of linear symmetric HHH, the intermediate for the reaction H+H2→H2+H.
Analytical calculation of full configuration interaction response properties: Application to Be
Authors: Koch Henrik , Harrison Robert J.
Published: July 2002

The computation of the frequency dependent linear and quadratic response functions is formulated at the full configuration interaction (FCI) level of theory. It is demonstrated that the frequency dependent polarizability (for real and imaginary frequencies) may be obtained with quadratic dependence on the error in the solution of the response equations. An efficient solution of the FCI response equations for large imaginary frequencies is developed. Initial application is to the Be atom in the standard 9s9p5d basis. Reported results include transition energies and dipole moments for the first few singlet and triplet S, P, and D states, the first polarizability at real and imaginary frequencies, the C6 coefficient, and the static second hyperpolarizability. Comparison to prior theoretical results in this basis, and to experiment, is made where possible. It is the first time that many of these properties have been computed at the FCI level of theory for any system.
Structural defects and ‘‘hot spot’’ formation in a crystalline solid under rapid compression. I. Vacancy clusters and slip bands
Authors: Tsai D. H.
Published: July 2002

Molecular dynamics have been employed in an investigation of the mechanisms of heating of ‘‘hot spots’’ in a model of a crystalline solid. Several types of defects—vacancy clusters of various sizes and geometries in two and three dimensions, and slip bands, grain boundaries, and dislocations in two dimensions have been investigated under rapid and two-stage compression at different temperatures. The results showed that on a molecular scale there were two mechanisms of heating. The first was simply due to the Maxwellian distribution of the kinetic energy, i.e., when energy was added to a system, by heating or by mechanical work, some molecules would be ‘‘hotter’’ than others and would remain hot for a time if the energy exchange among the various degrees of freedom was inefficient. The second mechanism involved the structural relaxation around defects in the solid under load. This process released some potential energy of the defect structure and converted it to the kinetic energy of the atoms around the defects, causing local hot spots. The amount of heating was related to the energy of defect motion during relaxation. The relaxation process, moreover, could propagate to other parts of the structure, so that the hot spot heating could extend to a considerably larger region than the immediate neighborhood of the original defects. These results from the simple model were found to be consistent with experiments. The present report examines the mechanisms of heating associated with vacancy clusters and slip bands. Hot spot heating due to grain boundaries and dislocations under load will be discussed in a subsequent report.
Theoretical study of molten KSi
Authors: Galli Giulia , Parrinello Michele
Published: July 2002

Molten potassium silicide (KSi) has been investigated with a first-principles molecular dynamics technique. The system belongs to the class of I–IV alloys, which have been extensively studied in recent years in view of the anomalous behavior of their structural and thermodynamical properties compared to ideal solutions. A detailed analysis of the ionic trajectories obtained in our computer simulation shows that Zintl-like ions (Si)4−4, present in the solid, tend to lose their identity in the liquid phase and that Si atoms form an extended network with two-, three-, and four-fold coordinated sites. Also, the calculated diffusion constants and power spectra reflect the presence of a different kind of atomic arrangements attained by Si in the melt. The bond between K and Si, characterized in terms of nodal potential energy surfaces, is found to be partially ionic. Accordingly, the computed electronic density of states and electrical conductivity show that the liquid is a semiconductor. Our results can be used to rationalize many experimental findings for molten I–IV alloys.
Role of rotational alignment in molecule–surface interaction for CH3F and OCS
Authors: Broers B. , van der Meer G. J. , Hoogeveen R. W. M. , Hermans L. J. F.
Published: July 2002

The influence of rotational alignment on molecule–surface interaction is studied for CH3F and OCS colliding with a glass surface. Experiments were performed at 285 K with the technique of surface light-induced drift using a flat channel, the alignment being produced through excitation by linearly polarized light. For molecules having rotational energy well below thermal, it is found that the accommodation coefficient for parallel momentum α, which can be related to the trapping/desorption probability, is larger if the angular momentum J is parallel to the surface (‘‘cartwheeling motion’’) than if perpendicular (‘‘helicopters’’). For CH3F the experiments indicate that this difference decreases strongly with increasing K, denoting the component of J along the principal molecular axis. Experiments on OCS confirm this behavior. For molecules having rotational energy well above thermal, however, the reverse behavior is found, viz., α is larger for helicopters than for cartwheels. This is consistent with molecular beam data on the system NO/Pt(111) studied by Jacobs et al. [J. Chem. Phys. 91, 3182 (1989)]. A possible explanation of the observations is given in terms of the role of rotational (de-)excitation in the accommodation process.
Vibrational contributions to third-order nonlinear optical susceptibilities
Authors: Yaron David , Silbey Robert
Published: July 2002

Including vibrational levels in the perturbation theory sum for the third-order nonlinear optical susceptibility γ introduces terms which have a pure vibrational frequency in the denominator. These terms can be rewritten as a sum over Raman amplitudes. Model calculations on a diatomic system with two electronic states show that these terms are negligible, about 3% of the value obtained ignoring vibrations. In polyacetylene, the Herzberg–Teller contribution to the Raman amplitude is much larger than in the diatomic case. Within the tight binding and harmonic oscillator approximations, the sum over Raman amplitudes is 10% of the value for γ obtained ignoring vibrations.
1
4N spin relaxation studies of N2 in buffer gases. Cross sections for molecular reorientation and rotational energy transfer
Authors: Jameson Cynthia J. , Jameson A. Keith , Horst Marc A.
Published: July 2002

Nuclear spin–lattice relaxation times (T1) have been measured as functions of temperature for 14N in N2 gas and in N2–Ar, Kr, Xe, CO, CO2, HCl, CH4, CF4, and SF6 mixtures. The relaxation is dominated by the quadrupolar mechanism so that empirical values of the collision cross sections for molecular reorientation (σθ,2) could be obtained as functions of temperature. The values of σθ,2/Å2 at 300 K are 29.6±0.9 (N2–N2), 33±1 (N2–Ar), 41±2 (N2–Kr), 44±2 (N2–Xe), 32±1 (N2–CO), 59±3 (N2–CO2), 46±1 (N2–HCl), 31±1 (N2–CH4), 59±2 (N2–CF4), and 73±2 (N2–SF6). For all 14N2 –buffer pairs, the temperature dependence of the cross section deviates from T−1, which is not very different from that of the collision cross section (σJ) for changes in the rotational angular momentum vector. This is the first molecule for which the collision cross sections σθ,2 and σJ have both been measured for a series of collision partners. The ratio (σθ,2/σJ) is found to be nearly constant, 2.1±0.2 for the N2 molecule with the ten collision partners. Based on Kouri’s IOS factorization scheme, (σθ,2/σJ)>1 may be true in general. The data for N2 are compared with the theoretical reduced correlation times based on existing mathematical models for molecular reorientation in fluids.
Infrared spectra of water. I. Effect of temperature and of H/D isotopic dilution
Authors: Maréchal Y.
Published: July 2002

The implementation of a cell operating with the technique of Attenuated Total Reflection (ATR) enabled us to obtain good quality IR spectra of water for the whole region above 750 cm−1 (which is the limit of the effect of the cutoff wave number of the crystal) and up to 5000 cm−1. ATR spectra have been recorded as a function of temperature ranging from −5 °C to 80 °C and of H/D molar concentration c(0<c<1). They have been transformed into spectra in ε″, using the Bertie–Eysel iteration procedure. In this paper evolutions of these spectra in ε″ upon variations of these two parameters c and T are investigated and analyzed. It is shown that any experimental spectrum in ε″ of a mixture of normal and heavy water is a superposition of three spectra due to pure H2O, pure D2O, and a spectrum that is only slightly dependent upon isotopic concentration c and is consequently mainly due to HDO. Analysis of this slight dependence upon c allows precise conclusions concerning vibrational interactions for both bending bands δ and stretching bands νs to be reached. Evolution of spectra with temperature unambiguously shows that all spectra at temperature T may be decomposed into a low temperature spectrum and a high temperature spectrum. The coefficient defining this decomposition [Eqs. (11) and (14)] displays a quadratic variation with T. It is the same for H2O, D2O, and HDO within the precision of the experiment. A low temperature spectrum corresponding to a (slightly distorted) H-bond network with no other defects, as well as a high temperature spectrum due to ‘‘defects’’ cannot, however, be determined without any further assumption. Limits for values of the concentration of defects α(T) may nevertheless be established.
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o study of the structure and infrared spectrum of Si2C
Authors: Rittby C. M. L.
Published: July 2002

The Si2C ground state has been reinvestigated using various basis sets at the Hartree–Fock level as well as with the use of many-body perturbation theory to second order. In agreement with previous theoretical investigations, the ground state is found to be a closed-shell C2v symmetry structure, whereas a linear D∞h structure is a transition state. Vibrational frequencies, infrared intensities, and isotopic shifts are presented and found to be in excellent agreement with recent experimental results, supporting a reinterpretation of the infrared spectrum of Si2C.
A triple resonance 19F, 1H, 13C cross polarization magic angle spinning nuclear magnetic resonance investigation of the miscibility in polymethyl methacrylate/polyvinylidene fluoride blends
Authors: Maas W. E. J. R. , van der Heijden W. A. C. , Veeman W. S. , Vankan J. M. J. , Buning G. H. Werumeus
Published: July 2002

The miscibility of blends of polymethyl methacrylate (PMMA) and polyvinylidene fluoride (PVF2) is investigated using triple resonance 1H–19F–13C cross polarization magic angle spinning nuclear magnetic resonance (CPMAS NMR). Two techniques are introduced which give information on miscibility on the molecular level. By transferring magnetization from fluorines to protons, and subsequently from protons to carbons (19F–1H–13C double cross polarization), spectra are obtained in which all PMMA carbon resonances are present, proving the spatial proximity of PMMA and PVF2 chains. In the proton to fluorine cross depolarization experiment, with subsequent proton to carbon cross polarization, proton spin diffusion is studied to estimate the sizes of the domains in which PMMA and PVF2 are intimately mixed. Also the fraction of PMMA and PVF2 that is not intimately mixed can be extracted from these experiments. Four different compositions of the PMMA/PVF2 blend are investigated (with weight ratios 20/80, 40/60, 60/40, and 80/20). A model is proposed to explain the experimental results, and from which the domain sizes can be calculated. It is found that these domain sizes do not differ for different blend compositions. The PMMA/PVF2 ratios in these mixed domains are about the same, except for the PMMA/PVF2 80/20 blend, which is attributed to a dilution effect.
Dynamics in a low-temperature glass: Fast generation and detection of optical holes
Authors: Littau K. A. , Dugan M. A. , Chen S. , Fayer M. D.
Published: July 2002

High-resolution, fast optical hole-burning results are reported for the amorphous system cresyl violet in ethanol glass at 1.3 K. Holes are burned and detected using a novel technique which allows precise detection of narrow (∼0.03 cm−1 ), shallow (∼1%) holes 10 μs to 50 ms after their generation. The technique is described in detail along with careful tests demonstrating the validity of its results. The hole width is observed to increase linearly with time when plotted against log time. Using the four time correlation function description of optical hole burning, the time-dependent increase in hole width (spectral diffusion) is shown to arise from a broad distribution of fluctuation rates in the glass with the probability of having a fluctuation at rate R proportional to 1/R. The 10 μs to 50 ms data is combined with hole-width data spanning the range 100 ms to 10 000 s and with two-pulse picosecond photon echo data. The two-pulse photon echo linewidth is calculated by extrapolating the fluctuation rate distribution obtained from the hole-width data to short times. The results are in excellent agreement with experimental echo results. The combined data from the two sets of hole-burning experiments provides a detailed description of the glass dynamics over nine decades of time, 10 000 s to 10 μs. Together with the two-pulse photon echo results, the data provide information on the glass dynamical behavior over seven decades faster in time as well. The net result is a description of the dynamics in low-temperature ethanol glass on time scales spanning 16 decades.
Counterion condensation and ionic conductivity
Authors: Penafiel L. Miguel , Litovitz Theodore A.
Published: July 2002

The occurrence of counterion condensation is demonstrated through measurements of the incremental ionic conductivity of pH buffered Na polyacrylate solutions. pH values were selected to allow variation of the charge density parameter ξ in the range between 0.4 and 2.8, that is, across ξ=1, the theoretical critical level for counterion condensation. The results show two regions where the incremental conductivity, ΔσP, varies differently with ξ. For ξ<1.3, ΔσP remains relatively constant. A sharp drop in ΔσP is observed between ξ=1.3 and ξ=1.7 corresponding to the onset of counterion condensation. It is suggested that this discontinuity reflects a drastic change in the polyion mobility caused by a structural rearrangement of the macromolecule. For ξ≳1.7, ΔσP decreases with approximately constant slope. This latter behavior agrees qualitatively but not quantitatively with the prediction of the counterion condensation model.
Effects of dipolar disorder on electron transport in molecularly doped polymers
Authors: Borsenberger P. M. , Rossi L. J.
Published: July 2002

Electron mobilities have been measured in mixtures containing two asymmetrical diphenoquinone compounds in a polymer host. The polymers were polystyrene and a polycarbonate. The field dependencies of the mobility, the temperature dependencies of the zero-field mobility, and the temperature dependencies of the field dependencies of the mobility are consistent with predictions of the disorder formalism, due to Bässler and co-workers. In agreement with hole transport in a number of doped polymers, a significant increase in the mobility is observed upon replacing the polycarbonate with polystyrene. The affect is attributed to the elimination of random dipolar fields due to static dipole moments of the carbonyl groups of the polycarbonate.
Ultrafast photodissociation of I3− in solution: Direct observation of coherent product vibrations
Authors: Banin Uri , Waldman Amir , Ruhman Sanford
Published: July 2002

We report the observation of terahertz oscillations in transient transmission measurements following femtosecond UV photolysis of I−3 in ethanol solutions. Transmission signals at 620 nm and at 880 nm, which are above and below the λmax of the known absorption of I−2 oscillate at precisely opposite phase. This and other results presented indicate that though the oscillations we are observing coherent vibration of the I−2 photofragment.
Microwave measurements of manganese quadrupole coupling in cyclopentadienyl manganese tricarbonyl
Authors: Roehrig M. A. , Wallace D. W. , Kukolich S. G.
Published: July 2002

Microwave measurements of rotational transitions in cyclopentadienyl manganese tricarbonyl were made using a Flygare–Balle type pulsed beam Fourier transform microwave spectrometer operating in the 4–14 GHz range. Ninety-six hyperfine transitions were assigned for this prolate symmetric top for the rotational transitions J=2→3, 3→4, 4→5, 5→6, and 6→7. Molecular constants obtained from the analysis of the spectrum are B=828.0333(6) MHz, DJ=0.088(9) kHz, DJK=−0.04(3) kHz, eQqaa(Mn)=68.00(4) MHz, Cbb(Mn)=−5.5(8) kHz. The distortion parameter DJ for CpMn(CO)3 is compared to other DJ values for similar type transition metal complexes.
Detection of stimulated emission pumping via degenerate four-wave mixing
Authors: Zhang Q. , Kandel S. A. , Wasserman T. A. W. , Vaccaro P. H.
Published: July 2002

The stimulated emission pumping (SEP) process has been detected by means of a newly developed zero-background scheme based upon the Doppler-free technique of degenerate four-wave mixing (DFWM) spectroscopy. Rotationally resolved SEP-DFWM spectra recorded for the (02000) vibrational level of CS2 X̃ 1∑+g exhibit signal-to-noise ratios approaching 1000:1.
A molecular dynamics study of the packing structures in monolayers of partially fluorinated amphiphiles
Authors: Shin Seokmin , Collazo Nancy , Rice Stuart A.
Published: July 2002

We report the results of molecular dynamics simulations of liquid-supported monolayers of three partially fluorinated amphiphile molecules, namely CF3(CF2)9CH2COOH, CF3(CF2)6CH2(CF2)3COOH, and CF3(CF2)6(CH2)4COOH. These studies were undertaken to provide information on the interplay between molecular flexibility and the packing structure in a monolayer so as to better interpret the results of recent experiments. The qualitative aspects of the predictions of the simulations are consistent with the recent experimental data for monolayers of CF3(CF2)9CH2COOH [S. W. Barton, A. Goudot, O. Boulassa, F. Rondelez, B. Lin, F. Novak, A. Acero, and S. A. Rice, J. Chem. Phys. 96, xxx (1992)]. In particular, the observed breakup of the homogeneous ordered monolayer into ordered islands with the same collective tilt of the molecules is correctly predicted, and the fact that the collective tilt angle is small is correctly predicted. However, the experimental and theoretical values of the tilt angles are not in quantitative agreement, which we attribute to the inadequacy of the atom–atom potentials used in the simulations. In general, for monolayers of CF3(CF2)9CH2COOH we find that the collective tilt angle predicted is a sensitive function of the area per molecule and is smaller than in monolayers of alkane alcohols and alkane acids. The results of the simulations of monolayers of other partially fluorinated species suggest that the difference in size between the fluorocarbon segments and the smaller head groups or flexible ‘‘spacer’’ CH2 segments can generate subtle changes in the packing structure of a monolayer and the relative stabilities of the untilted and tilted structures.
Memory effects in the self-diffusion of interacting Brownian particles
Authors: Cichocki B. , Felderhof B. U.
Published: July 2002

We study the time-dependent self-diffusion coefficient for suspensions of interacting, spherical Brownian particles. The self-diffusion coefficient exhibits memory effects with a wide range of relaxation times and a long-time tail. An approximate description of the time dependence involving a small number of parameters is proposed. We test the approximation for an exactly solvable model in which the particles interact via a square step or well potential and show that it works satisfactorily.
High Rydberg states of methyl iodide perturbed by nitrogen: A mutual cancellation of shift terms
Authors: Asaf U. , Meyer J. , Reininger R. , Steinberger I. T.
Published: July 2002

The dependence of the positions of both prethreshold and autoionizing high Rydberg states of CH3I on the density ρ of the perturber N2 was measured at room temperature, using synchrotron radiation. Up to ρ=2.2×1020 cm−3 no pressure shift was observed, showing that the scattering shift by the valence electron is compensated by the polarization shift due to the core. From the results, the value A=(1.9±0.3)×10−9 cm was found for the scattering length, in good accord with previous pressure shift and swarm results. The wide range of useful applications of the photocurrent excitation spectra to the study of perturbed transitions is stressed.
A restricted active space self-consistent field and multireference configuration interaction study of the lifetime of the A 3Π state of SO
Authors: Fülscher Markus P. , Jaszunski Michal , Roos Björn O. , Kraemer Wolfgang P.
Published: July 2002

A b initio methods were applied to compute the potential curves for the X 3Σ− and A 3Π states, the transition dipole moment, and the radiative lifetimes of the vibrational levels of the A state of the SO molecule. Extended atomic natural orbital basis sets including up to g-type functions were used. The potential energy curves were computed at the multireference configuration interaction level of approximation. The calculated bond distances and bond energies are 1.498 (1.481) Å and 5.21 (5.36) eV, respectively, for the X state, and 1.694 (1.609) Å and 0.57 (0.64) eV, respectively, for the A state (experimental values within parentheses). Restricted active space self-consistent field (RASSCF) wave functions were used to obtain the transition dipole moments, and the size of the RASSCF active orbital space was increased until stability of the transition moment value was achieved. The calculated transition moment strongly depends on the internuclear distance. The calculated value of the A 3Π, v=0 lifetime is 46.6 μs, while the experimental values are in the range of 36–39 μs. The computed lifetime is a very sensitive function of the relative accuracy of the potential energy and transition moment curves: for example, removing the g-type function on sulphur increases the lifetime to 55 μs.
A frozen-core approximation using reduced core-basis functions
Authors: Matsuoka Osamu
Published: July 2002

A frozen-core approximation (FCA) is proposed using a new orthogonalization method of the valence basis functions to the core orbitals. The orthogonalization is done through corelike basis functions in contrast to the usual Schmidt process in which the valence basis functions are directly orthogonalized to the core orbitals. The FCA using the new orthogonalization is mathematically rigorous and attains saving of the computation using the reduced corelike basis functions. Numerical calculations on diatomic molecules HCl, N2, P2, and Cl2 reproduced well the results of all-electron calculations. Discussion on the proposed FCA is given especially in connection with the model-potential methods of Huzinaga and co-workers.
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o configuration interaction study of excited states of LiNa3 and Li2Na2 clusters: Interpretation of absorption spectra
Authors: Bonačić-Koutecký V. , Gaus J. , Guest M. F. , Koutecký J.
Published: July 2002

The ab initio configuration-interaction (CI) study of excited states of mixed alkali metal tetramers LiNa3 and Li2Na2 accounts for spectroscopic patterns obtained from the depletion spectra of neutral species, reproduces observed excitation energies and intensities for allowed transitions, and permits an assignment of cluster structures. For both mixed tetramers, the rhombic forms with a Li atom or atoms on the short diagonal are the most stable structures and give rise to predicted spectra in full agreement with the measured ones. The exact location of Li atoms seems to be more important in Li2Na2 than in LiNa3 since in the former case, only one isomer reproduces all features of the recorded spectrum.
Ground state properties and optical response of LixNa4−x, x=0–4: An a
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Authors: Dahlseid Tina A. , Kappes Manfred M. , Pople John A. , Ratner Mark A.
Published: July 2002

The ground state properties of LixNa4−x (x=0–4) were investigated using extended basis Hartree–Fock calculations. The existence of substitution isomers was found for the mixed alkali clusters and planar singlet ground states were found for all clusters, including the isomers. The optical response of the clusters was modeled via configuration interaction—singles (CIS) in the hope of helping to interpret the experimental data. CIS results were found comparable to experiment at lower excitation energies, but inadequate at higher energies due to the neglect of doubles and higher excitations. Some exploration of the excited state surfaces of Li4 and of one isomer of Li2Na2 is also reported. Comparisons are made between CIS calculations, experiment, and multireference doubly excited configuration interaction calculations.
Infrared spectroscopy of monolayer CH4 on NaCl(100)
Authors: Quattrocci Laura M. , Ewing George E.
Published: July 2002

Polarized infrared spectra of CH4 adsorbed on NaCl(100) in the temperature range 4–47 K are reported. Coverage-dependent data indicate that there is only one kind of adsorption site. The adsorbate layer is also seen to grow in the form of constant density islands. A partial degeneracy breaking into doublets is observed in both the ν3 and ν4 infrared-active vibrations. Analysis of the ν4 doublet reveals one transition dipole component perpendicular to the (100) face of NaCl and the others in the plane of the face. Isotopic dilution experiments of CH4 in CD4 show that some of the ν4 doublet separation can be attributed to resonant or dynamic adsorbate–adsorbate interactions. The remaining splitting cannot be specifically assigned to any particular interaction but must involve static adsorbate–adsorbate coupling and surface–adsorbate interactions. A structural analysis consistent with the spectroscopic data and the symmetry of slab groups is developed. Two possible adsorbate geometries are considered. A unique determination of the adsorbate geometry will have to await other surface measurement techniques.
First principles computation of thermochemical properties beyond the harmonic approximation. II. Application to the amino radical NH2
Authors: Martin J. M. L. , François J. P. , Gijbels R.
Published: July 2002

The anharmonic potential surface of NH2 has been computed ab initio using the quadratic configuration interaction method and large basis sets. The all-electron augmented coupled cluster surface with the [5s4p2d1f,3s2p] basis set reproduces the experimental fundamentals to within a few cm−1. For this quantitative agreement with experiment, both f functions and core correlation seem to be prerequisite. From our best computed force field, a set of spectroscopic constants has been derived for all important isotopomers of NH2. Using a hybrid analytic/direct summation method recently developed by the present authors, the thermodynamic functions gef(T), hcf(T), S0, and Cp are computed including exact accounts for anharmonicity and rovibrational coupling, and very good analytical approximations to centrifugal distortion and quantum rotation effects. Thermodynamic tables in JANAF style from 100–3000 K, as well as a full set of rovibrational spectroscopic constants, are presented for NH2 and all important isotopomers. The effect of the A 2A1 state is found to become significant around 2000 K.
Dissociation dynamics of HCN(DCN) following photoexcitation at 121.6 nm
Authors: Morley Gregory P. , Lambert Ian R. , Ashfold Michael N. R. , Rosser Keith N. , Western Colin M.
Published: July 2002

The technique of H(D) atom photofragment translational spectroscopy has been applied to the photodissociation of HCN(DCN) at 121.6 nm. Analyses of the H(D) atom time-of-flight spectra reveal the partner CN fragment to be formed predominantly in its A 2Π excited electronic state. Branching into the H/D+CN(B 2∑+) product channel accounts for a few percent of the total fragment yield, but we discern no evidence for any contribution from the product channel yielding H/D atoms in conjunction with ground state CN(X 2∑+) fragments. The majority of the CN (A) fragments are formed in their v′=0 level but with a markedly bimodal rotational state population distribution. This bimodality has been rationalized in the light of the available information regarding the form of the potential energy surface of the excited 1Π state of HCN(DCN) populated following photoexcitation at 121.6 nm.
Excitability and bursting in the chlorine dioxide–iodide reaction in a forced open system
Authors: Dolnik Milos , Epstein Irving R.
Published: July 2002

Responses to single and periodic pulse perturbations have been studied experimentally and numerically for the reaction of chlorine dioxide and iodide ion in a stirred tank reactor. Excitability with transient oscillations was obtained for perturbations by chlorine dioxide or chlorite, while stimulation by iodide produced no excitable response. Periodic stimulations of the reaction by chlorite display bursting behavior. The experimental observations are in agreement with numerical simulations.
State-to-state photoionization of VO: Propensity for large, positive changes in rotational quantum number
Authors: Harrington Joel , Weisshaar James C.
Published: July 2002

State-to-state threshold photoionization cross sections from specific spin–rotation levels N′=7, J′=8.5, v′=3 of C 4∑− VO to specific levels N+J+ of X 3∑− VO+ show a remarkable propensity for large, positive ΔN. Observed transitions span the ranges ΔN=−5 to +7 and ΔJ=−5.5 to +4.5. The adiabatic ionization potential of VO is 7.2386±0.0004 eV. The mean bond length of v+=0, X 3∑− VO+ is 1.561±0.003 Å.