bluuebunny/crossref_metadata_2025 huggingface dataset:
Mie scattering from thin spherical bubbles
Authors: Aragón S. Sergio R. , Elwenspoek Michael
Published: February 2003

The electromagnetic scattering problem for a thin optically isotropic spherical shell of arbitrary size and refractive index has been solved exactly in closed form. This is the only closed form solution in Mie scattering known to the authors. The standard series solution to the layered sphere problem is shown to be summable and simple exact expressions are obtained for the scattering amplitudes. The Rayleigh–Debye approximation results are also obtained by direct summation of the infinite series. The horizontal depolarization ratio, given a zero value for isotropic shells in the Rayleigh–Debye theory, is given considerable attention and is compared to the Rayleigh–Debye calculation for anisotropic radially oriented segments in the shell. Some comparisons with the Mie scattering from solid spheres are also included. In addition, the deviations of Rayleigh–Debye theory from the exact Mie theory of thin shell scattering are examined in detail as a function of various parameters.
Thermal effects in infrared laser photochemistry and energy transfer experiments
Authors: Bailey R. T. , Cruickshank F. R. , Pugh D. , Guthrie R. , Johnstone W. , Mayer J. , Middleton K.
Published: February 2003

Addition of nonabsorbing inert gas to a cell, in which laser pulses are absorbed by a second low pressure gas, is commonly believed to reduce the peak, axial, translational temperature rise due to the increased heat capacity of the system. It is shown that this interpretation is often incorrect and that the axial temperature rise, as a function of inert gas pressure, passes through a maximum as a consequence of the variation with pressure of the thermal diffusivity and V–T energy transfer relaxation time. In the case of experiments where the laser beam is focused into the cell, the dependence on wavelength of the focal cylinder diameter is shown to have a strong effect on the temperature of and thus on comparative results of experiments using common optical systems at different wavelengths. Results of thermal lens experiments are used to support these conclusions and representative IR laser photochemical data are reassessed, conclusions on ’’hole burning’’ in populations of specific levels being shown to be of doubtful validity.
Statistical-diabatic model for state-selected reaction rates. Theory and application of vibrational-mode correlation analysis to OH(nOH)+H2(nHH)→H2O+H
Authors: Truhlar Donald G. , Isaacson Alan D.
Published: February 2003

The state-selected reaction rates OH(nOH = 0,1)+ H2(nHH = 0,1)→H2O+H are calculated by an extension of variational transiton state theory. The reactant vibrational modes are assumed to correlate diabatically with generalized normal modes of a generalized activated complex. Using the Walch-Dunning-Schatz-Elgersma ab initio potential energy surface, the theory predicts that excitation of H2 is 19–68 times more effective than excitation of OH in promoting reaction at 300 K, where the range of values corresponds to different possible assumptions about the quantal effects on reaction-coordinate motion. These values are in much better agreement with the experimental value (about 100) than is a calculation based on the conventional transition state, which yields 2×104.
Half-field resonance study of triplet exciton exchange dynamics in (O/AsCH3)+(TCNQ)2−
Authors: Chesnut D. B. , Brown M. A.
Published: February 2003

The theory has been derived and experiments carried out on the effect of triplet exciton exchange on the half-field resonance in (O/AsCH3)+(TCNQ)2−. The half-field resonance is a single Lorentzian line which exhibits a line broadening with increasing temperature in agreement with the effect seen at high field; the thermal activation energies at low and high field are 0.127 and 0.116 eV, respectively, but can not be distinguished statistically. The intensity behavior, however, exhibits an activation energy (effective singlet–triplet splitting) of 0.077 eV at low field compared to that observed at high field of 0.090 eV. This difference cannot be atttributed to a thermal modification of the triplet dipole tensor.
The effect of pressure and freezing on luminescence. II. Re(I) metal complexes
Authors: Salman O. A. , Drickamer H. G.
Published: February 2003

The effect of pressure and freezing on the radiative and nonradiative rates from the excited states of two rhenium metal complexes has been investigated in a series of solvents with varying polarity. The radiative rates (kr) depend on the low frequency dielectric constant (ε) of the solvent. A clear demonstration of this dependence is exhibited at the phase transition of the solvent. In polar solvents, kr and ε drop discontinuously while in nonpolar solvents kr and ε show no substantial change. The nonradiative rates (knr) in the liquid and solid phases, depend primarily on the energy gap between the emitting and ground states. The blue shift in energy causes a drop in knr. At the phase transition, both the blue shift in peak energy and the narrowing in ground state potential well affect knr.
Electron-spin relaxation and molecular dynamics in liquids. I. Solvent dependence
Authors: Zager Stephen A. , Freed Jack H.
Published: February 2003

Temperature-dependent ESR relaxation studies of PD-Tempone in a variety of solvents ranging from weakly interacting hydrocarbons to strongly interacting D2O are described. The empirical molar transition energy scale ET, which is a good measure of specific solvent polarity, is found to lead to a useful interpolation method for estimating the solvent dependence of the magnetic tensors required for accurate spin-relaxation studies. The temperature-dependent results are generally well-represented by a modified Stokes–Einstein type of η/T dependence for τR, the rotational correlation time. The ε parameter introduced by Freed and co-workers as an empirical correction to the nonsecular Debye spectral densities is found to correlate with ET, such that it is largest for the weakly interacting hydrocarbon solvents and approaches the Debye limit of ε = 1 for D2O solvent. This is discussed in terms of approximate fluctuating torque and slowly-relaxing local structure models, and the former appears more consistent with experiment. It is also pointed out that ε≳1 would result from the phenomenological feature of viscoelasticity.
Comment on ‘‘Steady, one-dimensional Brownian motion with an absorbing boundary’’
Authors: Naqvi K. Razi , Mork K. J. , Waldenstro/m S.
Published: February 2003

Some comments on Harris’s1 paper regarding the Brownian motion with an absorbing boundary are presented. Harris’s solution of Ni Fokker-Planck equation is discussed. (AIP)
CO
2
+
(Ã–X̃
and B̃–X̃) emissions resulting from the He(2 3S)+CO2 Penning ionization
Authors: Endoh Minoru , Tsuji Masaharu , Nishimura Yukio
Published: February 2003

CO 2 +  (Ã 2Πu–X̃ 2Πg) and CO2+ (B̃ 2Σu+−X̃ 2Πg) emissions produced from the He(2 3S)+CO2 Penning ionization have been observed in a flowing afterglow apparatus. The fluorescence branching ratio of the Ã 2Πu and B̃ 2Σu+ states, and the vibrational populations of the Ã state were determined as a function of helium pressure. The fluorescence branching ratio of the Ã and B̃ states was independent of the helium pressure at 0.5–1.0 Torr. Meanwhile, a significant relaxation was found for the vibrational distribution of the Ã state in the helium pressure range from 0.5 to 5 Torr. The unrelaxed vibrational distribution of the Ã state was determined from the 62 Ã–X̃ bands. The fluorescence branching ratio IA/IB was about four times larger than the initial population ratio of the Ã and B̃ states determined by electron spectroscopy, and the vibrational populations of the Ã state shifted to higher υ1′ levels (υ1′= 3,4, and 5). These discrepancies between the PIOS and PIES results have been interpreted as due to interelectronic state coupling between the B̃ and Ã states.
Electronic structure of tetrafluoro- and tetraoxo-actinide complexes
Authors: Ellis D. E. , Rosén A. , Gubanov V. A.
Published: February 2003

Fully relativistic self-consistent calculations are reported for AcF4 and (UO4)Q complexes, where Ac = Th, U, Np, Pu, using Dirac–Slater local density theory. Energy levels are compared with available photoelectron spectra; the character of low-lying optical transitions is discussed. Using numerical free ion orbitals as a variational basis, we discuss bonding mechanisms and the degree of Ac 5f-ligand 2p covalency. Additional 5f character is found to be distributed across the ligand valence band, in contrast to crystal field models.
Phase transition and dielectric aspects in stoichiometric β-aluminas
Authors: Gouyet J.-F.
Published: February 2003

After recalling the main features of the dipole–dipole–Potts model that we have proposed to explain the phase transitions recently observed in stoichiometric Ag+ and Na+ β-aluminas, we examine its consequences on the temperature dependence of the static dielectric constant in these materials. We used for this purpose a Kosterlitz–Thouless approach. We also discuss the BR–aBr disordering in connection with the validity of the model.
Dynamical study of the H5O+2+H3O−2 neutralization reaction using the polarization model
Authors: Weber Thomas A. , Stillinger Frank H.
Published: February 2003

Computer-generated classical trajectories have been used to simulate reactive collisions between the gas phase ionic species H5O+2 and H3O−2. Two cases have been considered, corresponding, respectively, to the isotopic choices H3 16O−2 and D3 18O−2 for the anion. Two hundred trajectories were constructed for each case, with initial conditions corresponding to zero incident energy. The multidimensional potential energy hypersurface required for the dynamics was supplied by the ’’polarization model.’’ Distributions were calculated for exit angles and for excitation energies of the water molecules produced by the exothermic reaction. Product molecules whose oxygens have anionic origin tend to be ’’hotter’’ than those with cationic origin. Most of the collisions entail simple proton transfer as expected for neutralization; however, approximately 3% exhibit concerted transfer of three protons or deterons. Isotropic labeling of the anion causes little change in the various product distributions, and seems thereby to afford a means to verify present results experimentally.
Revised TIPS for simulations of liquid water and aqueous solutions
Authors: Jorgensen William L.
Published: February 2003

An intermolecular potential function for the water dimer (TIPS2) has been developed and used in Monte Carlo simulations of liquid water in the NPT ensemble at 1 atm and −30, 25, and 75 °C. A simple four-site model is employed for the monomers with one Lennard-Jones term acting between oxygens and Coulomb terms for the intermolecular interactions between the charged sites. The function yields excellent thermodynamic results for the liquid across the temperature range; the average error in the computed densities and energies is 1.2% and a temperature of maximum density is indicated in the vicinity of 25 °C. Futhermore, the structural results are in reasonable agreement with Narten’s x-ray data. Specifically, the oxygen–oxygen radial distribution function shows three well-resolved peaks at 25 °C and a reduction in structure with increasing temperature. The simplicity of the TIPS2 potential,its success in describing liquid water, and the availability of TIPS parameters for hydrocarbons and for various organic functional groups provide a framework for computer simulations of aqueous solutions.
Sn-119 Mössbauer effect study of two Sn-bearing liquid crystalline materials
Authors: Ktorides Petros I. , Uhrich David L. , d’Sidocky Richard M. , Fishel Derry L.
Published: February 2003

A 119Sn Mössbauer, lattice dynamic orientational study, at 77 K, of the smectic B glass phase of the Sn-bearing liquid crystals (LC) p-(11-trimethyltin)undecyloxy-benzilidene-p′-n- butylaniline (Sn-UBBA) and p-(11-trimethyltin)undecyloxy-benzilidene- p′-octylaniline) (Sn-UBOA), and solutions of these liquid crystals in LC of similar structure which do not contain Sn as part of their molecules, is presented. The Sn-bearing liquid crystals were designed and synthesized specifically for this study and their synthesis is described. The samples were aligned by cooling from the melt in the presence of a magnetic field. For the samples of Sn-UBBA and Sn-UBOA, the experimental linewidth appears to depend on the orientational angle ϑ. This is explained as due to the non-negligible sample thickness and the rff versus ϑ variation. These ϑ dependencies were used to extract the absolute fractions for various orientations of Sn-UBBA and then the corresponding Debye temperatures ΘD(ϑ). For the other samples the lattice contribution to the nuclear vibration anisotropy εL was found. A comparison of these parameters suggests that the alignment found in the solutions is similar to the pure LC. Further,the existence of a nematic phase is not important in the alignment of smectics via cooling from the melt in the presence of a magnetic field. The effect of the aligning field intensity on the quality of the alignment is discussed. The ϑ dependence of the apparent line position for pure Sn-UBBA and Sn-UBOA is explained as due to the presence of a weak unresolved doublet, probably induced by the anisotropic enviornment of the Sn nuclei in the LC.
Diffusion in a multiwell potential with spatially varying viscosity
Authors: Reichl L. E.
Published: February 2003

The problem of relaxation of a Brownian particle in a multiwell potential and in a medium with a viscosity which is piecewise constant, but which varies discontinuously in space, is studied using the Smoluchowski equation. Exact solutions are obtained. We find that when one barrier dominates the system the long time relaxation is determined by one eigenvalue, which may be computed using Kramers’ rule applied to the dominant barrier. However, when all barriers are of comparable height, several eigenvalues compete in determining the long time behavior and these eigenvalues depend on the structure and distribution of viscosities of the entire system.
Dielectric relaxation studies in polyvinyl butyral
Authors: Mehendru P. C. , Kumar Naresh , Arora V. P. , Gupta N. P.
Published: February 2003

Dielectric measurements have been made in thick films (∼100 μm) of polyvinyl butyral (PVB) having degree of polymerization n=1600, in the frequency range 100 Hz–100 KHz and temperature range 300–373 K. The results indicated that PVB was in the amorphous phase and observed dielectric dispersion has been assigned as the β-relaxation process. The β relaxation is of Debye type with symmetrical distribution of relaxation times. The dielectric relaxation strength Δε and the distribution parameters β̄ increase with temperature. The results can be qualitatively explained by assuming the hindered rotation of the side groups involving hydroxyl/acetate groups.
Molecular and structural information from 14N–13C dipolar couplings manifested in high resolution 13C NMR spectra of solids
Authors: Hexem J. G. , Frey M. H. , Opella S. J.
Published: February 2003

The dipolar coupling between 14N and 13C is not suppressed by magic angle sample spinning because the relatively large 14N quadrupole interaction shifts the axis of quantization of the 14N spins away from the direction of the applied field. The resulting 13C resonance line shapes are influenced by the sign, magnitude, and asymmetry parameter of the 14N quadrupole coupling tensor; the internuclear distance; the magnitude of the applied magnetic field; and the orientation of the internuclear vector in the principal axis system of the electric field gradient. It is demonstrated that one or more of these parameters can be determined from the 13C NMR data if the others are known by virtue of single crystal studies or molecular symmetry.
Intense field resonance Raman scattering by a molecular continuum: A coupled equations study
Authors: Bandrauk André D. , Turcotte G.
Published: February 2003

Resonance Raman scattering (RRS) via a dissociative molecular electronic state has been studied numerically by a coupled equations approach from low (∼108 W/cm2) to high (10 10 W/cm2) field intensities for the Ar+2 diatomic molecule. Laser induced resonance states found in a previous calculation [A. D. Bandrauk and M. L. Sink, J. Chem. Phys. 74, 1110 (1981)] are shown to be detectable by RRS. The stability of these states is examined in detail at high field strengths and the validity of the rotating wave approximation (RWA) is also verified. It is shown that the semiclassical theory of predissocation is a very useful tool to locate all laser-induced bound states which appear as resonances in the coupled equations formalism.
Perturbation-wave packet studies of vibrational predissociation in collinear X–BC van der Waals complexes: He⋅⋅⋅I2(B 3Π)
Authors: Viswanathan R. , Raff L. M. , Thompson D. L.
Published: February 2003

A time-dependent wave packet method for the investigation of adiabatic vibrational predissociation (VP) of collinear X–BC systems is described. Discrete–discrete and discrete–continuum couplings are introduced into the initial wave function using a first-order perturbation procedure. The system wave packet is evolved in time by an explicit integration procedure and reaction probabilities P(t) as a function of time are computed by integrating the wave packet over the configuration space of the VP products. The VP rate coefficient is given directly by {−∂ ln[1−P(t)]/∂t}. The method has been applied to the vibrational predissociation of He–I2 (B 3Π). Zero and first-order VP rate coefficients and decay half-widths have been computed as a function of initial I2 vibrational state and X-atom mass for both pairwise harmonic and Morse potentials. Comparisons with previously reported distorted wave and quasiclassical trajectory calculations and with measured VP rates show all the methods to be of similar accuracy.
A method of investigating resonance energy transfer in mixed molecular crystals by electric field switching
Authors: Patel J. S. , Hanson D. M.
Published: February 2003

The use of a Stark switching technique to observe triplet state (T1) excitation energy transfer between p-methoxybenzaldehyde (MBA) molecules in a p-dimethoxybenzene host crystal at 4.2 K is described. The results indicate that T1 is a ππ* state and that the rate of energy transfer is very slow, only 3 s−1.
Superhyperfine interactions and their origins for n
d1 ions in rutile-structure oxides
Authors: Madacsi David P. , Stapelbroek M. , Bossoli R. B. , Gilliam O. R.
Published: February 2003

Paramagnetic resonance spectra of 4d1 (Nb4+ and Mo5+) and 5d1 (W5+) ions at substitutional cation sites in single crystals of tetragonal GeO2 have been studied at 92 K. Spin-Hamiltonian parameters obtained from hyperfine and superhyperfine (shf) structures are reported and compared with previously reported results for these ions and for V4+ (3d1), in rutile-structure GeO2, TiO2, and SnO2. Analysis of superhyperfine interactions with these nd1 impurity cations in GeO2 indicates that the unpaired spin is highly delocalized into nearest-neighbor ligand cations. On the basis of an LCAO-MO treatment, delocalization probabilities are inferred from measured shf interactions for these impurities; for each, the isotropic shf interaction is attributed to admixture of the unoccupied ligand-cation 4s orbital into the outer d orbital of the central impurity ion. The anisotropic contribution to the shf interaction is attributed to admixture of 4p ligand-cation orbitals. The results suggest an increase in the probability of delocalization of the unpaired spin onto the nearest-neighbor cations as n increases, however, for the Nb impurity, the degree of delocalization is found to be anomalously high. Extension of this type of analysis to treatment of these impurities in the isomorphs TiO2 and SnO2 is discussed.
Observations of NH infrared chemiluminescence
Authors: Green B. D. , Caledonia G. E.
Published: February 2003

Spectrally resolved NH (3Σ−) vibrorotational band emission has been observed in electron-irradiated mixtures of N2/H2. Evidence is presented suggesting that this radiation arises from the chemiluminescent reaction between N(2D) and H2.
Laser double resonance measurements of vibrational energy transfer rates and mechanisms in HF(v = 2)
Authors: Copeland R. A. , Pearson D. J. , Robinson Jeanne M. , Crim F. F.
Published: February 2003

Overtone vibration-laser double resonance studies of HF(v = 2) yield self-relaxation rate constants for v = 2 and v = 1 of k2 = (19.8±1.0) ×10−12 cm3 molecule−1 s−1 and k1 = (1.46±0.1) ×10−12 cm3 molecule−1s−1, respectively. These experiments indicate that the fraction of HF(v = 2) molecules relaxing via vibration-to-vibration energy transfer is only 0.35±0.10, in sharp contrast to trajectory and scaling calculations which predict the dominance of this pathway over vibration-to-translation, rotation energy transfer.
Absolute rate constants and temperature dependencies for the gas phase reactions of H atoms with propene and the butenes in the temperature range 298 to 445 K
Authors: Harris G. W. , Pitts J. N.
Published: February 2003

We have employed a flash photolysis resonance fluorescence technique to study the rates of reaction of H atoms with propene, 1-butene, cis- and trans-2-butene, and isobutene as a function of temperature. The Arrhenius parameters for the overall reactions in the temperature range 298–445 K have been measured, and it was observed that the variation in room temperature rate constants among these alkenes arises both from differences in the A factors and from variations in the activation energies.
Temperature dependence of the Schottky barrier capacitance in α- and β-zinc phthalocyanine
Authors: Twarowski Allen
Published: February 2003

Capacitance measurements of Schottky barrier devices have proved useful in the past for probing properties of dopant distribution and charge carrier detrapping. In this paper the temperature variation of the Schottky barrier capacitance of cells constructed with either α-zinc phthalocyanine or β-zinc phthalocyanine is compared. The α phase is found to differ markedly from the β phase. The α phase shows a Schottky barrier capacitance down to 150 K, however the slope of the 1/C2 vs V plots is temperature dependent. This temperature dependence is explained in terms of a two-site model for the dopant, oxygen. In this model only one site is active in charge carrier generation. The β phase, on the other hand, shows a hindered response of the charge carriers to the oscillating applied voltage. The dopant density in the β phase film is found to be comparable to dopant densities in α phase film.
Pressure dependence of conductance of the potassium ion in cooled and supercooled water
Authors: Takisawa N. , Osugi J. , Nakahara M.
Published: February 2003

Conductance measurements have been carried out on dilute (10−3–10−2 M) aqueous solutions of KCl at low temperatures of −5, −10, −15, and −20 °C at pressure intervals of 250 bar up to 2 kbar. The limiting molar conductance (Λ0) obtained with the aid of the Fuoss–Onsager equation of conductance has a maximum against pressure at each temperature, and the pressure of the maximum conductance increases very slightly with decreasing temperature. The low-temperature conductances fit well an empirical equation of the critical law form over the pressure range studied; Λ0=A(T/TS−1)γ. The parameter TS decreases with a rise in pressure below 1.5 kbar, but above that TS is almost constant. The pressure dependence of the drag coefficient (Δζ) subtracted by that due to Stokes’ law for perfect slip (4πηR) is obtained for the K+ ion over a wide range of temperature (−10–45 °C) and compared with that predicted by the Hubbard–Onsager (HO) dielectric friction theory. The observed slight decrease in Δζ with pressure at 45 °C can be explained by the continuum HO theory, but the increase in the cooled and supercooled region indicates that the passing-through-cavities mechanism becomes recognizable as the open structure of water is stabilized by lowering temperature.
A SCRF-CNDO/2 study on proton conductivity mechanisms in hydronium perchlorate. Towards a quantum chemical representation of defects and impurities in crystals
Authors: Ángyán J. , Allavena M. , Picard M. , Potier A. , Tapia O.
Published: February 2003

A quantum chemical scheme adapted to study charge separation processes in crystalline molecular/ionic defects is presented. The scheme derives from a generalized self-consistent reaction field theory of surrounding medium effects. Computational implementation has been done at the CNDO/2-INDO approximate level; lattice sums are performed by direct summation techniques. The sums are essential for building the static dielectric response function of the crystal to the field set up by the defect charge density and the Madelung potential created by the surrounding crystal permanent charge density. The scheme has been applied to study some aspects of the proton conductivity mechanism in crystalline hydronium perchlorate. The theoretical results lend support to an experimentally grounded molecular mechanism. The theoretical scheme can easily be extended to describing chemical processes taking place at crystal surfaces.
Critical amplitudes and their relations in a polymer solution: Polystyrene+methylcyclohexane system
Authors: Shinozaki Kenji , Hamada Tatsuro , Nose Takuhei
Published: February 2003

Isothermal osmotic compressibility χ and correlation length ξ near the critical temperature in a polymer solution of polystyrene–methycyclohexane for Mw=9000∼1.26×106 were measured along the critical isochore by laser light scattering. χ and ξ were proportional to M0.48±0.03 and M0.28±0.03, respectively in the region Mw≥5.0×104. The universal ratios of the critical amplitudes were investigated. One of them was almost independent of molecular weight. The scaling laws of the molecular weight dependence of the critical amplitudes proposed previously were examined and were supported by the experiments.
Hydrodynamic interaction effects on isomerization rates in chain molecules
Authors: Ladanyi Branka M. , Hynes James T.
Published: February 2003

The influence of hydrodynamic interaction effects on isomerization rates in chain molecules in solution is studied for a simple model. Attention is focused on the many particle reaction coordinate by which isomerization proceeds. It is found that the rate can be either enhanced or reduced by hydrodynamic interaction effects, depending on activation barrier and conformational properties. In the non-Markovian regime, particle friction and hydrodynamics interaction effects on the rate are diminished, and the transition state theory limit is approached.
Homogeneous nucleation of ethanol and n-propanol in a shock tube
Authors: Peters Franz
Published: February 2003

Condensation of homogeneous nucleation of ethanol and n-propanol is studied in the expansion of a shock tube. For ethanol, the existing range of results is extended and for n-propanol the first shock tube data are given. The results are compared with previous data obtained by different experimental methods. (AIP)
Reaction of Mg(3s3p1P1) with a variety of alkyl C–H bonds: Identical initial MgH(X 2Σ+, v=0) rotational quantum state distributions
Authors: Breckenridge W. H. , Umemoto H.
Published: February 2003

The initial distributions of rotational quantum states of MgH(X 2Σ+, v=0) produced in the reaction of electronically excited Mg(3s3p1P1) with a variety of hydrocarbons containing alkyl C–H bonds have been found to be identical within experimental error. The distribution is peaked at fairly low values of rotational angular momentum (N≂10). This is in stark contrast to the reaction of Mg(1P1) with H2, where very high rotational excitation is observed and has been ascribed to side-on attack of the H–H bond. It is proposed that Mg(1P1) attacks alkyl C–H bonds directly in a relatively narrow cone of angles around the C–H bond axis and that the strength or location of a particular C–H bond has little effect on the dynamical process. Possible reasons for the differences in H2 and hydrocarbon as reactants are discussed, and the hydrocarbon results are compared to those reported by Luntz and co-workers on the reactions of O(3P) and O(1D2) with alkyl C–H bonds.
Rotational effect on SRVL nonradiative transitions: Linewidth and Coriolis coupling
Authors: Kono H. , Lin S. H. , Schlag E. W.
Published: February 2003

In the present paper, we discuss the rotational effect on interval conversion due to the linewidths and the Coriolis coupling in the final electronic state. For a formaldehyde model system, some numerical results of the rotational effect will be reported. It will be seen that the Coriolis coupling plays an important role in small linewidth cases. The numerical results also include the effect of the vibration-rotation coupling through the change of moments of inertia; the change of the geometry shifts between two electronic states due to this coupling is calculated numerically.
Unimolecular reaction paths of electronically excited species. III. Production of CH+3 ions from CH3OH+ as an example of isolated state dissociation
Authors: Galloy C. , Lecomte C. , Lorquet J. C.
Published: February 2003

The CH3OH+ ion dissociates to CH+3+OH as soon as the energy of state B̃ 2A′ is reached. This fragmentation cannot be described by RRKM theory. Ab initio potential energy surfaces at the CI level have been calculated as a function of the CO bond stretching coordinate R and of the COH angle φ for the lowest 2A′, 2A″, 4A′, and 4A″ states. Several zones of strong nonadiabatic interaction have been detected. They correspond to avoided crossings and account for the existence of internal conversions among the different states. In particular, there exists an avoided crossing with a small energy gap between states B̃ 2A′ and Ã 2A′, which is localized in a very restricted range of internuclear distances (R=1.555 Å and φ=69.8°). This avoided crossing plays a very important role because it is the only low-energy de-excitation channel of state B̃. The nonadiabatic coupling matrix elements 〈Ã‖∂/∂q‖B̃〉 have been calculated for coordinates R and φ. They are represented by very narrow Lorentzians and they bring about a very high nonadiabatic transition probability. Thus, the population of the upper electronic states (B̃ 2A′, C̃ 2A″, and D̃ 2A′) detected in the photoelectron spectrum in the 14–18 eV energy range easily cascades down to states Ã 2A′ via this mechanism. Since the zone of nonadiabatic interaction is very narrow, the population starts its evolution on the potential energy surface of states Ã with well-defined initial conditions. In the present case, internal conversion is a much more specific preparation than optical excitation. The reactive flux then branches into two paths. One of them leads directly to the CH+3+OH asymptote and escapes statistical energy redistribution. The other path leads to the bottom of the potential energy surface and gives rise to the RRKM/QET component of the mass spectrum, i.e., leads to the other fragmentations. ‘‘Isolated state decay’’ thus corresponds to dissociation of the nonrandomized fraction of the population and not to isolation, i.e., to lack of radiationless transition to the lower electronic states. The circumstances which give rise to such a behavior are analyzed.
Improved procedure for analysis of electron density redistribution in molecular complexes
Authors: Sokalski W. Andrzej
Published: February 2003

An improved method for theoretical determination of the charge redistribution, i.e., the intramolecular charge shifts, intermolecular charge transfer, and dipole moment enhancement upon complexation, is proposed. This approach consists of counterpoise correction of the basis set superposition error on calculated electron density redistribution in molecular complexes. Ab initio LCAO MO SCF calculations for HF⋅⋅⋅HNH2, H2O⋅⋅⋅HOH, H2O⋅⋅⋅HF, H3N⋅⋅⋅HF, H3N⋅⋅⋅LiF, CO⋅⋅⋅HCN, H2S⋅⋅⋅OCHNH2, H2NHCO⋅⋅⋅HSH, [Mg⋅⋅⋅OH]+ [HO⋅⋅⋅HOH]−, [Be(OH)(NH3)2]+ molecular complexes in different basis set have been performed leading to more consistent results in contrast to sometimes largely overestimated uncorrected values reported previously. In addition, the charge redistribution upon complex formation has been analyzed for some dimers in terms of atomic multipole expansion of electron density and difference molecular electrostatic potentials.
Electron bound states of a dielectric sphere
Authors: Antoniewicz P. R. , Bennett G. T. , Thompson J. C.
Published: February 2003

We have calculated the energy levels for an electron just outside the surface of a dielectric sphere. The electron is bound by dispersion forces which depend on the dimensions of the sphere (or droplet) and on the inner potential of the material of the sphere. Some comments as to relevance of these bound levels to experiments are made.
Wigner phase-space description of a Morse oscillator
Authors: Lee Hai-Woong , Scully Marlan O.
Published: February 2003

Quantum and classical dynamics of a Morse oscillator are investigated in a phase space using the Wigner distribution function. The phase-space description offers a pictorial representation of quantum dynamics in terms of trajectories. Based on the comparison of these trajectories with classical trajectories, a systematic scheme accurately describing quantum dynamics is presented.
Vacuum UV spectrum of C3 trapped in argon at 8 K
Authors: Chang Kok Wai , Graham W. R. M.
Published: February 2003

The vacuum ultraviolet absorption spectrum to 1200 Å has been obtained for the products from the evaporation of graphite at 2700 °C, trapped in argon at 8 K. Based on correlations with the 1Πu–X1Σ+g transition of C3 in the near ultraviolet, the results of 13C substitution, and other observational evidence, it is proposed that a band system originating at 1890 Å be assigned to the 1Σ+u–X1Σ+g transition of C3. Vibrational analysis yields ν1′≂1080, ν2′≂300, and ν3′≂780 cm−1 for the 1Σ+u state.
Coherent Raman scattering in liquid benzene from symmetric ring vibrations in the 1B2u electronic state excited by two-photon absorption
Authors: Guidotti D. , Driscoll T. A. , Gerritsen H. J.
Published: February 2003

In the presence of two-photon absorption in benzene at 5268 Å, we observe coherent anti-Stokes Raman scattering at 993 and 935 cm−1. These energies correspond to symmetric ring breathing vibrations (a1g symmetry) in the 1A1g ground, and 1B2u excited state of benzene, respectively. Raman activity in the latter state is demonstrated for the first time. Its observation is made possible by strong two-photon absorption to the 1B2u level via vibronically assisted transitions, and resonance enhancement of the Raman process by 1B2u–1E1u one-photon transitions. Simultaneously, we observe a resonance enhanced electronic background at the anti-Stokes frequency over a broad, featureless spectrum arising from two-photon transitions to 1B2u. At wavelengths well below the two-photon absoprtion band of benezene, neither electronic contributions nor the 925 cm−1 peak are observed and only the ground state vibrations at 993 cm−1 remain.
Variable-angle sample-spinning high resolution NMR of solids
Authors: Ganapathy Subramanian , Schramm Suzanne , Oldfield Eric
Published: February 2003

We have obtained high-resolution solid-state NMR spectra of a variety of nonintegral-spin quadrupolar nuclei (23Na, 51V, and 55Mn) under conditions of ‘‘magic-angle’’ sample-spinning (MASS) and ‘‘variable-angle’’ sample-spinning (VASS). We show for systems in which the second-order quadrupole interaction dominates the breadth of the (1/2,−1/2) spin transition, that optimum line narrowing is achieved by rapid sample rotation at angles other than the familiar θ=54.7° ‘‘magic-angle.’’ The effect originates in the more complex angle dependence of the second-order quadrupole interaction, rather than the more familiar P2 (cos θ) dependence of dipolar and chemical shift interactions, and theoretical VASS line shapes for a variety of spinning angles, and electric field gradient tensor asymmetry parameters (η), are presented. We show that VASS NMR at low fields generates complex spectral line shapes, which at some angles exhibit well-resolved centerbands and spinning sidebands. We also discuss briefly, with examples, the complexities introduced by the presence of dipolar and/or chemical shift anisotropy interactions in such experiments and investigate the question of the optimum field-strengths for NMR of quadrupolar nuclei. Our results indicate that the VASS NMR technique appears to have considerable utility in obtaining high-resolution NMR spectra of a wide variety of quadrupolar nuclei in inorganic solids, especially those with relatively small (≲5 MHz) quadrupole coupling constants.
A comparison between the Cs3d3/2 photoelectron spectra of gaseous cesium and cesium chloride
Authors: Mathews R. D. , Slaughter A. R. , Key R. J. , Banna M. S.
Published: February 2003

The Cs3d3/2-core regions of atomic Cs and molecular CsCl have been compared. In atomic cesium, two satellites with a combined intensity of 18% of the 3d3/2 peak have been observed at 5.3 and 7.7 eV higher binding energy. Dirac–Fock calculations suggest that they are mostly due to 6s → 7s and 6s → 8s excitation accompanying core ionization. In contrast, no intense satellites have been observed in CsCl, since the Cs6s electron has been partially transferred to the chlorine.
Vibronic intensity parametrization for the UCl2−6 complex in crystals
Authors: Satten R. A. , Schreiber C. L. , Wong E. Y.
Published: February 2003

Oscillator strengths for vibronic bands involving the 260 cm−1 T1u vibration coupled to electronic transitions within the 5f2 configuration of U4+ in [(CH3)4N]2UCl6 were measured at liquid nitrogen temperature and calculated using a Hamiltonian with all symmetry-allowed odd degree vibronic terms up to and including degree seven. The calculation employs complete closure, and good results are obtained for individual vibronic levels in terms of six parameters which are determined by a nonlinear least-squares fit.
Cluster expansion for concentration dependence of cooperative friction coefficients for suspensions of interacting spheres
Authors: Muthukumar M. , Freed Karl F.
Published: February 2003

We presented a general cluster theory for the concentration dependence of the cooperative (mutual) translational and rotational friction coefficients to any order in concentration for a suspension of interacting spheres. The theory involves a generalization of that given for self-friction coefficients because the steady-state limiting hydrodynamics must now be considered in the presence of an external sedimenting force which acts on the spheres. Also, the treatment of the cooperative friction coefficients requires an analysis to demonstrate that no divergent integrals appear in the theory, a major problem with some of the earlier theoretical results. Given these generalizations, the theory has features which parallel that for the self-friction coefficients, and the evaluation of terms of any order in concentration is reduced to quadratures. The sphere–sphere interactions enter through the cluster expansion of the various sphere distribution functions. Each virial coefficient for the cooperative friction coefficients is obtained as an infinite multiple scattering series where successive terms enter with higher inverse powers of the interparticle separations. The general theory is illustrated by presenting analytic calculations for the leading concentration dependent terms in the cluster expansion for the cooperative translational and rotational friction coefficients for hard-sphere interactions. The results for the translational friction are compared with values in the literature, while those for rotational friction have not appeared previously. Explicit formulas are also presented for the calculation of the leading three-body hydrodynamic contributions which have not been given before.
Renormalization group theory of transport properties of polymer solutions. I. Dilute solutions
Authors: Oono Y. , Kohmoto M.
Published: February 2003

The (Gell–Mann–Low type) renormalization group theory is applied to frictional properties of dilute polymer solutions for the first time. The universal ratios such as Flory’s intrinsic viscosity constant, the Flory–Scheraga–Mandelkern parameter, etc., are estimated from the first order ε-expansion theory (ε=4−d, d being the spatial dimensionality). The results are in satisfactory agreement with experimental results in both the nondraining Gaussian and nondraining self-avoiding limits. Preaveraging the Oseen tensor makes the value of the intrinsic viscosity about 10% larger according to the first order ε-expansion calculation.
Ordered structure in dilute solutions of poly-L-lysine as studied by small-angle x-ray scattering
Authors: Ise N. , Okubo T. , Yamamoto K. , Matsuoka H. , Kawai H. , Hashimoto T. , Fujimura M.
Published: February 2003

The small-angle x-ray scattering curve shows a clear peak for aqueous solutions of poly-L-lysine (PLL) of a degree of polymerization of 406 when the polymer concentration is between 0.02 and 0.06 g/m1. In the presence of a large amount of NaBr (0.3 M), the peak disappears. A PLL sample of a degree of polymerization of 13 shows no scattering peak but a broad shoulder at a different scattering vector. Mixing of the two fractions gave a new shoulder at a scattering vector intermediate between the positions of the mother fractions, suggesting that the peak is due to intermolecular ordering. The interparticle distance (2Dexp), calculated by assuming the Bragg equation, decreases with increasing PLL concentration, and increases with increasing salt concentration. The 2Dexp value for the high molecular weight sample is always smaller (by a factor of 2) than the average intermacroion distance (2D0) calculated from the concentration. This suggests that a two-state structure is maintained. This fact and the dependences of 2Dexp on salt concentration and degree of ionization indicate that the macroions attract each other in dilute solutions through the intermediary of counterions.
Dynamics of helical wormlike chains. II. Eigenvalue problems
Authors: Yamakawa Hiromi , Yoshizaki Takenao , Shimada Jiro
Published: February 2003

A general solution of the eigenvalue problem for the representation of the diffusion operator of the discrete helical wormlike chain is presented. The problem is first, to a great extent, decoupled by transforming the basis set introduced previously to a standard representation which is formed by the eigenfunctions of the total angular momentum operator of the entire chain. In order to find the analytical solutions, the size of the problem thus reduced is further reduced by making two approximations: subspace approximation and block-diagonal approximation. The former is equivalent to neglecting the memory term in the projection operator method, and the latter consists of introducing Fourier modes as in the conventional chain. The theory then predicts a number of branches of eigenvalue spectra. In fact, here, eight branches, in general, are derived explicitly. Among these, three are associated with dielectric relaxation, and the remaining five with fluorescence depolarization and nuclear magnetic spin relaxation. (Evaluation of intrinsic viscosity and flow birefringence requires some other branches, as will be shown in later papers.) Numerical computations of some eigenvalue spectra and time-correlation functions are carried out in the following paper.
Phosphorescence from pyridine vapor
Authors: Sushida Kazuyoshi , Fujita Masahisa , Takemura Takeshi , Baba Hiroaki
Published: February 2003

The phosphorescence of pyridine has been observed for the first time. The phosphorescence spectra of pyridine-h5 and -d5 vapors were measured by means of time-resolved emission spectroscopy. Each of the spectra starts at about 340 nm and reaches a maximum at 440 nm (pyridine-h5) or at 430 nm (-d5). The phosphorescence excitation spectra of the pyridines are in good agreement with the corresponding absorption spectra. The phosphorescence lifetimes and quantum yields are 1.4 μs and 5×10−7 for pyridine-h5 and 2.3 μs and 7×10−7 for pyridine-d5. An experiment on T–T energy transfer from the pyridines to biacetyl was made to give further evidence for the phosphorescence of the pyridines.
Laser excitation of excited states of Rb and Cs atoms in an Ar matrix
Authors: Balling L. C. , Wright J. J.
Published: February 2003

Absorption and emission spectra of rubidium and cesium trapped in Ar matrices at 10°K are reported. (AIP)
Comment on hole burning into velocity distribution of thermal electrons due to resonance attachment to O2
Authors: McMahon D. R. A. , Crompton R. W.
Published: February 2003

The comments of Koura1 on the attachment cooling experiments of crampton, Hegerberg and Skullerud2 are answered. Several deficiencies in Koura’s analysis are pointed out. (AIP)
Large van der Waals ions
Authors: Jortner Joshua , Even Uzi , Leutwyler Samuel , Berkovitch-Yellin Ziva
Published: February 2003

Model calculations of the potential surfaces of van der Waals ions, consisting of a benzene cation bound to a rare-gas (R) atom, provide information concerning the reduction of the ionization potentials of benzene in the benzene–R1 complex, relative to that of the bare molecule, and establish the configuration changes accompanying the ionization of benzene–R1 complexes.
Electron structure calculations including CI for ten low lying states of Pb2 and Sn2. Partition function and dissociation energy of Sn2
Authors: Balasubramanian K. , Pitzer Kenneth S.
Published: February 2003

Relativistic calculations including configuration interaction are described for ten low lying states of Pb2 and Sn2. These calculations were accomplished by introducing spin-orbit interaction at the configuration interaction stage in calculations initiated in Λ–S coupling. All the calculations were carried out with relativistic effective potentials which were averaged with respect to spin at the SCF stage and differenced for the spin-orbit operator. The selection of important configurations for the atoms and the molecules is discussed in terms of both Λ–S and ω–ω coupling. Comparisons are made with the available experimental data. With the results of these calculations and recent experimental spectra, it is possible to revise the partition function for Sn2. The partition function is required for the interpretation of mass spectral data on the dissociation energy. The optimum method for the calculation of the partition function where several electronic states are populated is discussed in general terms and then applied to the revision of the dissociation energy of Sn2 with the result 2.04±0.1 eV. An earlier revision for Pb2 needs no further change.
V–V energy transfer to UF6 from laser-pumped SF6 and UV absorption cross sections of vibrationally excited UF6
Authors: Kim K. C. , Freund S. , Sander R. K. , Smith D. F. , Person W. B.
Published: February 2003

Highly vibrationally excited UF6 molecules were produced by V–V energy transfer from CO2-laser pumped SF6. The changes in the ultraviolet absorption of the excited UF6 molecules were investigated in detail as a function of the excitation level in the wavelength region of 220–250 nm. The change in absorbance varies with wavelength and for most cases the vibrational excitation is associated with increased UV absorption cross sections. Exceptions are found near the ground state absorption maxima where vibrational excitation is shown to reduce the UV absorption cross section. This behavior and the UV spectrum of flow-cooled UF6 molecules are discussed in terms of transitions from the ground state to upper dissociative potential energy surfaces in UF6.