bluuebunny/crossref_metadata_2025 huggingface dataset:
A general procedure for classical variational rate calculations for three-body exchange reactions
Authors: Martin David L. , Raff L. M.
Published: February 2003

A general procedure for the variational minimization of the classical flux across a dividing surface for any three-dimensional reaction of the type A+BC→AB+C has been developed. The dividing surface is expresed in terms of a linear combination of internal coordinates (LCIC) that span the entire hyperspace of the potential surface. This LCIC-variational method has been applied to the H+H2 and H+I2 reactions. For the H+H2 exchange, it is found that even a truncated LCIC expansion for the dividing surface yields minimum variational rate coefficients that are never more that 26% in excess of the classical trajectory (CT) results. With the DS defined in terms of a full LCIC expansion, the computed variational rates are found to converge to the corresponding CT values. The H+I2 reaction is found to be a more demanding test due to the presence of a potential well in the entrance valley combined with a barrier that is relatively independent of approach angle. For this system, a full LCIC-variational calculation yields a minimum rate coefficient that is a factor of 2.26 greater than the CT value. For the H+H2 system, the computed variational activation energy is in exact agreement with the trajectory result, but the frequency factor obtained variationally is 11.6% in excess of the CT value. It is shown that the computation of the variational rate at five temperatures requires only 4% of the computer time required for corresponding trajectory calculations. When the LCIC-variational procedure is combined with a CPST calculation, it is shown that exact classical rate coefficients, activation energies, and frequency factors may be computed with greater statistical accuracy and with very large reduction in computer time. In the case of the H+H2 exchange, the combined LCIC–CPST method is found to give rate coefficients at five temperatures in agreement with trajectory calculations with a factor of 18.4 overall reduction in computer time and a decrease of a factor of 4 in the statistical error.
Laser photodissociation of O3+ and the energetics of ozone and its ions
Authors: Hiller J. F. , Vestal M. L.
Published: February 2003

Absolute cross sections for the production of O+ from O+3 have been determined at intervals of 1 nm or less through the range from 560 to 730 nm. The results are interpreted as implying an upper limit on the threshold for this process of 1.860±0.005 eV. This value, together with recent values for the adiabatic ionization potential of ozone, implies an upper limit for the bond dissociation energy of neutral ozone of 0.761±0.007 eV. This bond dissociation energy is in excellent agreement with our earlier result derived from photodissociation measurements on O3− but in serious disagreement with the literature value of 1.05±0.02 eV determined calorimetrically.
Trimer formation, atom exchange, and dissociation in argon dimer collisions
Authors: Thompson Donald L.
Published: February 2003

Cross sections and rate coefficients are presented for the reactions that occur in argon dimer–dimer collisions. Quasiclassical trajectories are used to compute cross sections as a function of the initial relative translational energy and rate coefficients as a function of translational temperature and initial argon dimer internal excitation for trimer formation and the dissociation reactions.
Influence of vibrational and translational energies on energy transfer in Ar+HCl (J = 0, 2, 6, and 12)
Authors: Thompson Donald L.
Published: February 2003

The influence of initial relative translational energy on pure-rotational energy transfer in various vibrational states of HCl in collisions with Ar has been studied by using quasiclassical trajectory calculations and a model potential-energy surface. The vibrational states v = 0, 3, and 6 and initial rotational states Ji = 0, 2, 6, and 12 were studied over the collision energy range 0.1 to 1.0 eV. The results show that pure-rotational energy transfer is not, in general, a strong function of the vibrational state in which the energy transfer takes place. It is found that there is a difference in the dependence of the cross section on the initial relative translational energy for low Ji and high Ji.
Calculation of activity coefficients from a novel numerical solution of the Poisson–Boltzmann equation and application to 23Na NMR of sodium polystyrene sulfonate
Authors: Delville Alfred , Gilboa Haggai , Laszlo Pierre
Published: February 2003

Interaction of sodium cations with polystyrene sulfonate (PSS) is studied. The Poisson–Boltzmann equation, modified in order to incorporate ion–ion correlation, is solved numerically using a cell model. Outstanding agreement is found between the calculated and measured activity coefficients γ± for systems consisting of NaPSS+NaCl, KPSS+KCl, CaPSS+CaCl2, and the more complex system, the quarternary mixture NaPSS+CaPSS+NaCl+CaCl2. A complementary study by sodium-23 NMR provides a reliable estimate of the fractions of bound, atmospherically condensed, and free sodium ions for NaPSS in the presence of added NaCl, HCl, MgCl2, and MnCl2. We find a nice correlation (ρ = 0.93, N = 16) between the observed 23Na line broadenings and the calculated electrostatic field gradients for these various cases.
The reactions of Ba+ ions with O2 and H2O
Authors: Murad Edmond
Published: February 2003

The reactions of Ba+ with O2 and with H2O and of Al+ with O2 have been studied in a double-mass spectrometer system. Primary ions were formed by surface ionization. Thresholds were observed for Ba+(O2, O)BaO+ and for Al+(O2, O)AlO+ which were in agreement with values derived from thermochemical data. The results obtained for Al+(O2, O) AlO+ are in agreement with D°0(Al+–O) = 1.69±0.1 eV. The reactions of Ba+ were complicated by the presence of an excited state Ba+(2D3/2, 5/2), and corrections had to be made for the contribution of this species to the reaction. The corrected results for Ba+(O2, O)BaO+ are in agreement with D°0(Ba+–O) = 4.1±0.2 eV. Ba+(H2O, H)BaOH+, which is exothermic, behaves somewhat like an endothermic reaction, and has small cross sections at ECM<1 eV. The population of the excited states in the beam and their contributions are briefly discussed. Atmospheric implications are also briefly discussed.
A molecular dynamics study of dephasing in solid N2 and O2
Authors: Guissani Y. , Levesque D. , Weis J. J. , Oxtoby D. W.
Published: February 2003

We have carried out a theoretical study of the isotropic Raman vibrational band shape in high temperature molecular solids. We employ a new vibrational exciton formalism to determine the line shape in the weak coupling limit for solids with several inequivalent lattice sites. We demonstrate that resonant vibration–vibration coupling can lead to mixing of the contributions from various lattice sites, so that it is no longer possible to associate a particular band in the spectrum with a single lattice site; the effect of V–V coupling on relative band intensities can be particularly large. We have used a molecular dynamics simulation to study the vibrational line shape of solid β-N2. The relative contributions of different parts of the potential are discussed. We have also simulated the isotropic Raman line shape of solid γ-O2, which has a lattice structure with eight molecules per unit cell in two inequivalent lattice sites. The shifts, widths, and intensities of the two Raman bands that result are calculated using an atom–atom Lennard-Jones potential and are compared with recent experiments.
An EPR spin label study of the glass forming liquid dibutyl phthalate
Authors: Spielberg Johanan I. , Gelerinter Edward
Published: February 2003

Spectra from a small nearly spherical probe and a large nearly cylindrical probe are studied as a function of temperature from 130–370 K. These spectra are used to calculate a rotational correlation time τ and the temperature dependence of τ is matched, at higher temperatures, to existing viscosity models such as the energy activation, Vogel–Fulcher, and Grest–Cohen models. The glass temperature is observed at ∼ 180 K and the data indicate a reduction in translational diffusion, but not rotational diffusion, as the glassy state is reached. We also observe that the spherical probe tumbles isotropically while the cylindrical probe tumbles anisotropically. In the latter case, the tumbling can be represented by an axially symmetric rotational diffusion tensor whose axis coincides with the long axis of the molecule. Finally, we present a phenomenological model for the temperature dependence of τ which fits the data well at all temperatures.
Resolution of interference effects in the rotational excitation of NO (N = O) by Ar
Authors: Andresen P. , Joswig H. , Pauly H. , Schinke R.
Published: February 2003

Pulsed nozzle sources are used to analyze the rotational excitation of NO by Ar. Integral cross sections are determined and compared with the results of a coupled-state calculation. (AIP)
The effects of collision energy and ion vibrational excitation on proton and charge transfer in H2++N2, CO, O2
Authors: Anderson S. L. , Turner T. , Mahan B. H. , Lee Y. T.
Published: February 2003

The effects of vibrational excitation of reagent ions and collision energy on the proton and charge transfer reactions of H2+ and D2+ with N2, CO, and O2 have been investigated using a method combining photoionization and a radio frequency guided ion technique. For proton transfer the H2++N2 results are quite similar to the H2++Ar system; proton and charge transfer channels are closely coupled for kinetic energies above 3 eV. In contrast, for H2++CO, the vibrational dependence of proton transfer is quite weak. For the H2++O2 case, evidence is seen for direct competition between the charge and proton transfer process. A simple model for charge transfer is used to assess the importance of energy resonance and Franck–Condon effects. In these simple molecular systems, the energy defect is found to be most important to charge exchange, although Franck–Condon factors play a substantial role.
Optimized Gaussian basis set for second row transition metals
Authors: Friedlander Marvin E. , Howell James M. , Snyder Grace
Published: February 2003

A Gaussian basis set consisting of 12 s-type, 8 p-type, and 7 d-type functions have been optimized for the second row transition metals (Y–Cd). Orbital energies along with the coefficients and exponents are presented for the neutral, monopositive, and dipositive atoms. Three additional s-type functions were used to represent occupied 5s orbitals, when necessary.
A new self-consistent-field valence bond method. II. The effective spin Hamiltonian
Authors: Kuwajima Satoru
Published: February 2003

The effective spin Hamiltonian is introduced as a practical tool of valence bond (VB) calculation on nonorthogonal orbitals. The effective spin Hamiltonian obtained in the SCF VB method proposed previously is examined in detail for conjugated π systems (linear polyenes and monocyclic systems) within the Pariser–Parr–Pople (PPP) model. It is found that the Heisenberg spin Hamiltonian with only the nearest-neighbor exchanges is a reasonable first approximation; this means that the well-known classical VB treatment, the simplified VB treatment developed by Slater, Pauling, and others, is justified theoretically as far as the PPP model systems are concerned. The next-nearest-neighbor exchanges are found to be not negligible from the quantitative standpoint. In the case of monocyclic systems, the ring (or cyclic) permutations, the permutations making a full circle round the ring, emerge with a coefficient a little larger than those of the next-nearest-neighbor exchanges; the VB calculation taking them into account yields the ground-state energy exhibiting the Hückel rule. The SCF VB calculation with a Heisenberg spin Hamiltonian was further carried out on linear polyenes (all-trans form, PPP model) of up to 14 π electrons. The calculated ground-state energy, which is expected to be fairly accurate in this specific case, becomes lower than that of the single and double excitations CI (SDCI) calculation for polyenes of more than ten π electrons. The first excited 1Ag state was also calculated and the calculated excitation energy decreases rather steadily with increasing polyene-chain length in contrast to the SDCI results and in agreement with observations and more accurate CI results.
Energy transfer in molecular crystals: Nondipolar Coulomb exciton transfer interactions in crystalline naphthalene and anthracene
Authors: Schlosser Donald W. , Philpott Michael R.
Published: February 2003

Several approximations to the nondipolar Coulomb exciton transfer interaction are compared using crystalline naphthalene and anthracene as examples. It is found that nondipolar interactions calculated with the atomic multipole model are a good approximation to nondipolar interactions calculated with the exact two-center integrals. In contrast, the atomic monopole and molecular multipole models give poor results. The scaling of the calculated nondipolar interactions with respect to the point dipole–dipole interaction is investigated and it is found that, with the proper choice of scaling factor, the nondipolar interactions are largely independent of the wave function used to generate them. Because the nondipolar interactions decrease very rapidly with increasing intermolecular distance, the sum of the nearest-neighbor interactions is a good approximation to the total interaction. Inclusion of nondipolar interactions in calculations of the exciton energies, oscillator strengths, and factor group splittings of the crystals leads to substantially better agreement of theory and experiment.
Potential of a sphere in an ionic solution in thin double layer approximations
Authors: Chew W. C. , Sen P. N.
Published: February 2003

The three-dimensional problem of a charged spherical particle immersed in an ionic solution is solved asymptotically. The small parameter used is δ/a, where δ is the Debye screening distance and a the radius of the particle. The solutions to the Poisson–Boltzmann equation are obtained inside the double layer and outside the double layer. They are matched together asymptotically to obtain a solution whose error is of order δ2/a2 smaller than the expression kept. A uniform solution valid in all the regions is also obtained. Comparison with numerical solution to the problem, which is usually tedious, shows excellent agreement.
Study of static and dynamic structure of β-quinol-methanol clathrate by 13C high-resolution solid-state NMR and proton T1 measurements
Authors: Matsui S. , Terao T. , Saika A.
Published: February 2003

13C high-resolution solid-state NMR spectra and proton spin-lattice relaxation times T1 have been measured for β-quinol clathrate with trapped methanol molecules over a wide temperature range of 4.2–363 K. Above the transition point (∼67 K), a single and axially-symmetric 13C chemical shift tensor is observed for the trapped methanol, demonstrating that the molecules reorient themselves among three potential minima in the cavity. Its anisotropy allows us to obtain a temperature-dependent angle ϑ between the CO bond and the crystallographic c axis. Analysis of the T1 results gives the motional parameters (Ea = 0.7±0.2 kcal/mol, τ0 = 3.7×10−12 s for C3- reorientation and Ea = 2.4±0.1 kcal/mol, τ0 = 4.5×10−14 s for inversion about the cavity center) and the position of the methanol molecule in the cavity. Each 13C absorption line for both methanol and quinol is found to split into three below the transition point. This splitting indicates that the methanol molecules are settled down in any of the six orientations and simultaneously the quinol lattice is distorted from the space group R3̄ below the transition point. From the methanol 13C chemical shift tensor, the direction and the librational frequency of the settled CO-bond axis are determined. Ordering of the methanol dipoles, methyl tunneling motion, and residual C3-reorientation below the transition point are also discussed.
Time-dependent perturbation theory for inelastic scattering
Authors: Cross R. J.
Published: February 2003

We show by numerical integration that the first-order, time-dependent, Magnus approximation agrees with the first-order, exponential, distorted-wave approximation to within a few percent, provided that the trajectory used for the time-dependent calculation is characterized by the arithmetic mean of the initial and final velocities and the arithmetic mean of the initial and final orbital angular momenta. Calculations are done for rotational energy transfer from an exponentially repulsive potential characteristic of He+H2 and for a Lennard-Jones potential characteristic of Ar+N2.
A time-independent quantum mechanical theory for multiphoton dissociation of diatomic molecules
Authors: Whaley K. B. , Light J. C.
Published: February 2003

A nonperturbative expression for the rate of dissociation from the ground vibrational state of a diatomic molecule in the presence of an infrared laser field is derived using R-matrix techniques. No rotating wave approximation and no metastable levels are introduced. The result is applied to a model system and to HF to obtain the dependence of multiphoton dissociation rate upon laser frequency and intensity. Dissociation is predicted at fields of order 1013 W/cm2.
Quenching of Na(3p2P) atoms by N2 and CO molecules at low temperatures
Authors: Tanarro I. , Arqueros F. , Campos J.
Published: February 2003

Quenching cross sections of Na(3 2P) by N2 and CO molecules at temperatures below 400 K have been measured by studying the dependence of the 3 2P lifetime on gas pressure. An original pulsed laser configuration has been employed to excite Na atoms. Lifetimes have been measured by the delayed coincidence method. From comparison of the present result with previous ones a linear dependence of quenching cross section on reciprocal mean kinetic energy can be inferred.
Matrix isolation studies of the reactions of silicon atoms. I. Interaction with water: The infrared spectrum of hydroxysilylene HSiOH
Authors: Ismail Zakya Kafafi , Hauge Robert H. , Fredin Leif , Kauffman James W. , Margrave John L.
Published: February 2003

This study focuses on the interactions and reactions of silicon atoms and molecules with water. Initially, a silicon–water adduct (Si:OH2) is formed, as noticed from the red shift of the ν2 bending modes of H2O, HDO, and D2O. This silicon “hydrate’’ complex rearranges spontaneously through hydrogen tunneling to give HSiOH and HSiOD as final products of the reaction of Si with H2O and HDO. Photolysis of Si:OD2 with λ⩾400 nm is necessary for the production of the deuterated insertion product DSiOD. All silicon hydroxy–hydrides undergo a photolytic decomposition reaction when strongly irradiated to give silicon monoxide and molecular hydrogen or two hydrogen atoms. Band assignments for trans-HSiOH, trans- and cis-HSiOD, and DSiOD have been made. It appears that the cis-isomer converts to the more stable trans-isomer when the matrix is heated. The SiOH bond angle has been calculated for a planar structure of Cs symmetry using the Redlich–Teller product rule and the torsional frequencies for HSiOH, HSiOD, and DSiOD. Normal coordinate analyses have been carried out using the measured frequencies for six isotopomers, namely, HSiOH, HSiOD, DSiOD, HSi 18OH, HSi 18OD, and DSi 18OD. Thermodynamic properties have also been calculated for this new species.
Matrix isolation studies of the reactions of silicon atoms. II. Infrared spectrum and structure of matrix-isolated fluorosilylene: HSiF
Authors: Ismail Zakya Kafafi , Fredin Leif , Hauge Robert H. , Margrave John L.
Published: February 2003

Silicon spontaneously reacts with HF and DF to form the molecules HSiF and DSiF in solid argon. Photolysis of the matrix during deposition greatly enhances the yield of these products. Frequencies for the three infrared active modes of HSiF and DSiF have been accurately measured. The force field of this triatomic molecule has been fully determined through normal coordinate analyses. Thermodynamic functions for the fluorosilylene have been calculated.
Vibrational anharmonicity constants for UF6: The ν3 transitions at 16 μm
Authors: Krohn B. J. , Kim K. C.
Published: February 2003

Assignment of nine hot-band Q branches in the ν3 (16 μm) region of the diode laser spectrum of UF6, and measurement of their wave number displacements from the origin of the fundamental band, provide values of effective anharmonicity constants x34, x35, and x36. The relationship x3j = −aω0j, where a = (1.28±0.08)×10−3 and ω0j = normal-mode wave number for j = 4, 5, or 6, has been used to compute spectra in good qualitative agreement with observed spectra between T = 170 K and room temperature.
A matrix isolation study of the benzene bromine atom complex
Authors: Engdahl Anders , Nelander Bengt
Published: February 2003

Thermally generated bromine atoms have been trapped in argon matrices containing varying concentrations of benzene. The UV and IR spectra of the matrices have been recorded. Evidence for the formation of a bromine atom benzene complex has been obtained. The spectra indicated that the symmetry of the complex is lower than C6v.
C(K
V
V) Auger line shape of chemisorbed CO
Authors: Koel B. E. , White J. M. , Loubriel G. M.
Published: February 2003

Using x-ray excitation, the C(KVV) Auger spectrum for CO chemisorbed on Ni(100) has been measured and deconvoluted to provide the undistored line shape. This line shape is compared with spectra for gas phase CO and Fe(CO)5(g). The magnitude of Ueff, a final state interaction term, is shown to be near zero for chemisorbed CO, indicating that significantly different relaxation/screening processes occur in this case as compared to gas phase CO and metal carbonyls. Charge–transfer screening of the core hole in the Auger initial state is proposed to account for the small value of Ueff.
Direct current electric field induced second harmonic generation in flexible molecules and polymers
Authors: Khanarian G.
Published: February 2003

We calculate the dc electric field induced second harmonic generation of flexible molecules and polymers. We employ the bond additivity approximation for the dipole moment and the first and second hyperpolarizabilities μ, β, and γ, respectively, and the rotational isomeric state approximation and matrix multiplication methods of Flory. Illustrative calculations are presented for poly(oxyethylene dimethyl ether) versus chain length and for poly(p-nitrostyrene) versus tacticity.
A comparison of the simulated a
b i
n
i
t
i
o molecular orbital (SAMO) method with the method of transferability of atomic potentials
Authors: Duke Brian J. , O’Leary Brian
Published: February 2003

A comparison between two methods of calculating molecular wave functions, the simulated ab initio molecular orbitals (SAMO) method and the method of transferability of atomic potentials (AP), is presented. (AIP)
Comment on the influence of the dielectric constant upon the noncoincidence of the isotropic and anisotropic Raman frequencies
Authors: Mirone Paolo
Published: February 2003

The formula for the difference between the isotropic and anisotropic components of a Raman band for polar liquids given by McHale is discussed. Comments on the role of dielectric constant are presented. (AIP)
Response to ‘‘Comment on the influence of the dielectric constant upon the noncoincidence of the isotropic and anisotropic Raman frequencies’’
Authors: McHale Jeanne L.
Published: February 2003

A reply to P. Mirones comments on the role of dielectric constant in the description of the noncoincidence of the isotropic and anisotropic Raman frequencies in polar liquids is presented. (AIP)
Localization and delocalization: Distinction between through space and through bond interactions
Authors: Surján Péter R. , Mayer István , Kertész Miklós
Published: February 2003

We propose a special perturbation formalism based on the local Brillouin theorem to study the effects causing delocalization (’’tails’’) of bond orbitals. Assuming a given one-electron Hamiltonian, an explicit recursion relation is derived for the tails to any order. It permits to distinguish between the ’’through space’’ effects caused by the direct interaction of bonds, and the ’’through bond’’ ones which appear in higher orders. Application of the results to SCF-type theories indicates that only through space interactions like vicinal ones are orientation sensitive.
Ab initio HF–CI calculations of the electronic ‘‘band structure’’ in the Fe2 molecule
Authors: Shim Irene , Gingerich Karl A.
Published: February 2003

In this study we present all electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations of 112 electronic states resulting from interaction between two Fe atoms. The basis set used was of double zeta quality, in general, but the 3d orbital was represented by a triple zeta function. The CI calculations of the ground state included sixtuple excitations from a reference configuration. The calculations were performed to the same degree of accuracy for all the 112 low-lying states. The ground state is a 7Δu state with the configuration (3dσg)1.57(3dπu)3.06(3dδg)2.53 (3dδu)2.47(3dπg)2.89(3dσu)1.49 (4sσg)2.00. The equilibrium distance is calculated to be 4.54 a.u. (2.40 Å), and the vibrational frequency to be 204 cm−1. The chemical bond between the iron atoms is a single bond, and it is almost entirely due to the 4sσg molecular orbital. The ’’band’’ of the 112 low-lying states make a large contribution to the partition function, resulting in a lowering of the experimental dissociation energy of the Fe2 molecule. Our mass spectrometric measurements essentially confirm the previous results by Lin and Kant. The experimental dissociation energy D0° of Fe2 has been determined as 18±4 kcal mol−1 or 75±17 kJ mol−1. The corresponding standard heat of formation is 180.5±4 kcal mol−1 or 755±17 kJ mol−1.
Calculations of induced moments in large molecules. III. Polarizabilities and second hyperpolarizabilities of some aromatics
Authors: Waite J. , Papadopoulos M. G. , Nicolaides C. A.
Published: February 2003

We report the results of calculations of the average polarizability α and second hyperpolarizability γ for benzene, naphthalene, and three different configurations of biphenyl, phenanthrene, anthracene, and pyrene. The computations were performed employing a scheme whose main elements are McWeeny’s coupled Hartree–Fock perturbation theory, the CNDO approximations, and a small, properly optimized, extended basis. The mean error for the average polarizabilities is 7%. The error for the second hyperpolarizability of naphthalene is within the experimental uncertainty.
Tracer diffusion in polyatomic liquids. III
Authors: Chen S.-H. , Davis H. T. , Evans D. F.
Published: February 2003

Tracer diffusivities are reported for argon, krypton, xenon, methane, carbon tetrachloride, and tetraalkyltins (methyl, ethyl, n-propyl, and n-butyl) in normal octane, decane, and tetradecane for temperatures ranging from 25 to 160 °C. The diffusivities were measured by the Taylor dispersion method. With temperature-dependent solvent diameters fitted from the tracer diffusivity of one of the solutes, a rough-hard-sphere theory predicts well the observed tracer diffusivities of all the other solutes in n-octane and, at high temperatures, n-decane (60–160 °C) and n-tetradecane (100–160 °C). The data are well correlated by either the Arrhenius equation, a free-volume formula, or the Dμp-correlation.
A study of the formation of high molecular weight water cluster ions (m/e<59 000) in expansion of ionized gas mixtures
Authors: Beuhler R. J. , Friedman L.
Published: February 2003

Mass spectrometric determinations have been made of size distributions of cluster ions produced by expansion of ionized mixtures of water and various carrier gases. Measurements span a range up to mass to charge ratios of 59 000. Dilute water–nitrogen carrier gas mixtures producing cluster masses up to 12 000 gave size distributions which are first order in water concentration. This observation is explained by the relatively large value of the ion–dipole associative collision cross sections which determined the rate of growth of cluster ions in the mass range studied. Studies in different mass carrier gases show that cluster ion size distributions are largely determined by the cross section for, and number of, associative collisions taking place during the expansion process. Estimates of associative collision efficiency have been made for water and alcohol cluster ion growth on expansion. Evidence has been obtained for steric inhibition of efficient alcohol collision processes compared to relatively efficient water clustering.
Some properties of large amplitude motion in an anharmonic chain with nearest neighbor interactions
Authors: Collins Michael A. , Rice Stuart A.
Published: February 2003

We consider the classical and semiclassical dynamics of a one-dimensional atomic lattice with periodic boundary conditions. Using quasicontinuum approximations, we derive the form of the perfectly periodic vibrational modes of the chain for a cubic and a Lennard-Jones nearest neighbor interaction potential. These long wavelength traveling waves are trains of solitons, rather than harmonic modes, even at low energy. A semiclassical quantization procedure is used to obtain the energy level spectrum for a model anharmonic Xe lattice. The lower eigenenergies are near the harmonic values even though the corresponding classical motion is solitonlike. We show that at high energy the soliton character of the vibrations leads to a breakdown in their stability. This is related to the onset of classical chaos.
Dispersive contributions to the linear dichroism of chromophores oriented by association to biopolymers or in anisotropic solvents: Associate induced linear dichroism (AILD)
Authors: Schipper Pieter E. , Nordén Bengt
Published: February 2003

Anisotropic chromophores (A) oriented in anisotropic media such as liquid crystals or stretched films, or by association with flow oriented biopolymers (e.g., DNA) will, in addition to their intrinsic orientation linear dichroism (LD) exhibit a component of LD characteristic of the dispersive coupling to the electronic states of the orienting agent (B). We may refer to this dispersive component as associate induced linear dichroism (AILD) to distinguish it from the corresponding component for dissociated A-B systems (DILD). The form of the AILD component is investigated using perturbation theory, and it is shown to be both strong and long range, falling off with the inverse cube power of the A-B separation.
Variations of splittings of vibronic Jahn–Teller states in asymmetrically deuterated benzenes
Authors: Scharf Benjamin , Vitenberg Rachel , Katz Benjamin , Band Yehuda B.
Published: February 2003

Measurements of the Rydberg absorption spectrum converging to the first ionization threshold of asymmetrically deuterated benzenes are reported. Evidence of splittings of the 0 → 0 bands in the R′ series upon reduction of the nuclear symmetry to D2h or C2v by deuteration is revealed. No such effect is present in the R series. The 0 → 1 bands of ν18(e2g) in the R′ series exhibit a much smaller splitting. A theoretical analysis predicting all of the facets of these phenomena is presented. These observations enable an independent assignment of the R and R′ series previously obtained on the basis of splitting in the hot band structure of the R′ series due to quadratic Jahn–Teller activity of the out-of-plane mode ν20(e2u) which cannot be linearly J–T active. These results conform with the direct observations of splittings of Jahn–Teller degeneracy obtained in benzene Rydberg series converging to the second ionization threshold upon asymmetric deuteration.
Surface plasmon enhanced Raman spectra of monolayer assemblies
Authors: Knoll Wolfgang , Philpott Michael R. , Swalen J. D. , Girlando Alberto
Published: February 2003

This paper describes the systematics of using plasmon surface polariton (PSP) fields to enhance the Raman spectra of monolayer assemblies deposited on silver metal gratings by the Langmuir–Blodgett deposition technique. The intensity of the incident light is enhanced by grating coupling to the PSP mode, likewise, the intensity of the outcoupled Raman light is enhanced by emission via radiative PSP modes. It is shown how the various spectral regions corresponding, e.g., to C–C and C–H stretching vibrations are individually enhanced by selecting the appropriate scattering angle for the light collected from the grating. Results are presented that demonstrate how the gaps in the PSP dispersion curve at the center and the boundary of the Brillouin zone can be shifted to preselected frequency ranges using assemblies of different thickness. It is also shown that the dispersion gap width and intensities of the Raman vibrational bands depend on the number of monolayers making the assembly.
Site selective spectroscopy and defect chemistry of CaO
Authors: Porter Laura C. , Wright John C.
Published: February 2003

The site selective spectroscopy of CaO:Eu3+, CaO:Er3+, and CaO:Pr3+ has been studied. The Eu3+ doped system has a cubic and an orthorhombic site which vary with concentration in a manner that can be quantitatively described by a simple defect equilibrium model. The Er3+ and Pr3+ spectra do not have transitions from the cubic site because electric dipole transitions are forbidden but there are strong transitions from the orthorhombic site. The Pr3+ system exhibits efficient relaxation between levels separated by 4000 cm−1 and efficient up-conversion. Both processes are attributed to the presence of states other than those in the 4f2 electron configuration.
An ESR study of 77 K alkoxy and hydroxyalkyl radicals in x-ray irradiated trehalose single crystals
Authors: Samskog P.-O. , Kispert L. D. , Lund A.
Published: February 2003

Four different alkoxy radicals were identified by ESR studies in x-ray irradiated single crystals of trehalose. The radical sites are O′2(I), O2(II), O′3(III), and the probable ring oxygen O5(IV). All alkoxy radicals exhibit one or two β-proton couplings. An additional coupling to a γ proton for radical II is observed. The difference in the gmax value for the alkoxy radicals is discussed in terms of the type of hydrogen bonding involved. Two hydroxyalkyl radicals VI and VII were also produced at 77 K. Storage of crystals for one week results in decay of radicals I and II. Alkoxy radical II transform into a C6-centered hydroxyalkyl radical V.
System-bath decomposition of the reaction path Hamiltonian for polyatomic scattering: Quantum perturbative treatment
Authors: Miller William H. , Schwartz Steven
Published: February 2003

An approach to quantum mechanical reactive scattering in polyatomic molecular systems is described. The formulation is based on the reaction path Hamiltonian of Miller, Handy, and Adams [J. Chem. Phys. 72, 99 (1980)]. The essential physical idea is that the reaction coordinate in even polyatomic systems may be coupled strongly to only a few (one or two) of the vibrational modes orthogonal to it, and rather weakly coupled to the (perhaps many) remaining modes. This leads naturally to a ’’system-bath’’ decomposition of the reaction process, and this paper shows how this is carried through for the reaction path Hamiltonian. If only one transverse mode is included with the reaction coordinate to form the ’’system,’’ for example, then the overall model is that of a collinearlike reaction, whose dynamics are treated accurately, taking place in a (harmonic) ’’bath’’ to which it is weakly coupled.
Effect of reaction exothermicity on the fate of long-lived collision complexes: The reaction C3H+4(C3H4,H)C6H+7 in propyne and allene
Authors: Lifshitz C. , Gleitman Y.
Published: February 2003

The reaction C3H+4(C3H4,H)C6H+7 has been studied in propyne and allene by photoionization mass spectrometry (PIMS). In contrast to allene where the reaction cross section decreases with increasing internal energy, the reaction cross section in propyne is independent of internal energy. The results are explained by model RRKM calculations.
Dynamics of energy transfer during charge-exchange in symmetric diatomic systems
Authors: McAfee K. B. , Szmanda C. R. , Hozack R. S. , Johnson R. E.
Published: February 2003

The measured, efficient energy transfer between vibration and translation during charge exchange in N2+ on N2 collisions is compared with a model which exploits the near u-g character of the electronic-exchange interaction. The dynamics of the concurrent electronic and vibrational-exchange process taking place during collisions are considered. The measurements and analysis indicate that significant vibrational exchange can occur in concert with small center-of-mass deflections, and changes of an even number of vibrational quanta are strongly favored at center-of-mass angles (<1°) and velocities about 3×106 cm/s (∼0.013 a.u). The dominant vibrational transitions are induced by the nonspherical component of the charge distribution of the N2 molecule at potential curve crossings for which the electron-exchange frequency is a multiple of the vibrational frequency.
Optical activity of higher order in a medium of randomly oriented molecules
Authors: Wagnière G.
Published: February 2003

It is shown that, in an optically active medium, if sum or difference frequency generation or four-wave mixing occurs, the response to left and right circularly polarized light should be different. Similar effects are studied where, in analogy to the Faraday effect, the optical activity is induced by an external static magnetic field.
The avoided crossing region of the CsH X 1Σ+ potential energy curve
Authors: Yang Sze Cheng
Published: February 2003

Measurements of the laser induced fluorescence spectrum of CsH from the B 1Σ+ state to the X 1Σ+ state are reported. The Rydberg–Klein–Rees potential of the X 1Σ+ state is determined up to v″ = 24, a vibrational level very close to the dissociation limit. The dissociation energy of the X 1Σ+ state is estimated to be D0 = 14 360±30 cm−1 or De = 14 805±30 cm−1. The highest energy level of X 1Σ+ state observed in this experiment is v″ = 24, J″ = 16. It is found to be quasibound by 14 cm−1±30 cm−1. Both the vibrational spacings and the rotational constants show anomalous behavior as a function of the vibrational quantum number v″. This behavior is explainable in terms of the ionic–covalent avoided crossing. The Rydberg–Klein–Rees potential curve shows a sharp change of slope at v″≃20, and gives detailed information on the avoided crossing region. The avoided crossing point is determined to be Rc=5.33 Å and the energy gap of the A 1Σ+ and X 1Σ+ adiabatic potentials at RC is found to be ΔV(Rc)=5020±30 cm−1. Comparisons with scattering experiments and theoretical calculations are made. The relevance of the spectroscopic measurement in the avoided crossing region to the dynamical process of charge transfer reactions is emphasized.
Collisional effects on the rotational and rotation–vibration Raman spectra of HD compressed by argon
Authors: Marsault-Herail F. , Echargui M. , Levi G. , Marsault J. P. , Bonamy J.
Published: February 2003

Rotation and rotation–vibration Raman spectra of HD compressed by argon were recorded at room temperature (72 to 695 amagat) and 175 K (95 to 364 amagat). At low densities, an important motional narowing in the Q branch conceals the vibrational broadening, while this last mechanism becomes the main contribution to the bandwidth when pressure is sufficiently increased. Discussion of the results in the impact limit is given for the low density range where a linear density dependence of the rotational linewidths is observed. The validity of second order calculations in a semiclassical approach is discussed. The case of the HD–Ar system is compared to that of pure HD for which new data complete previous experimental studies.
Ionic dynamics in the LiCl–KCl system at liquid state
Authors: Lantelme Frédéric , Turq Pierre
Published: February 2003

The mixing effects in the fused system LiCl–KCl are studied by molecular dynamics simulation. The predominant contribution of the Coulombic interaction is clearly detected, its nonlinear variation gives rise to the main part of the excess internal energy. This change reflects the structural ionic arrangement; at high potassium concentration a significant decrease of the Li+–Cl− distance is observed. The anion–cation radius ratio has a marked effect: the lithium ions remain fourfold coordinated by chloride ions throughout the concentration range while the potassium ions are about sixfold coordinated. It is shown that the ion motion proceeds from two main mechanisms: an oscillatory displacement in the force field of the surrounding particles which tends to restore the electroneutrality and a collective mode which concerns the ion and its ionic atmosphere. This approach is described by the generalized Langevin equation and may open a better understanding of the transport processes at liquid state. It provides a link between the structure and the dynamical properties, the strong Li+–CL− interactions leading to a significant decrease of the Li+ mobility when the potassium concentration increases.
Rotational viscosity γ1 of nematic liquid crystals
Authors: Kneppe H. , Schneider F. , Sharma N. K.
Published: February 2003

The rotational viscosity coefficients γ1 are measured with the rotating field method as a function of temperature in the nematic phases of 4-methoxybenzylidene-4′-n-butylaniline, 4-n-pentyl-, and 4-n-octyl-4′-cyanobiphenyl, of the eutectic mixture of two 4-n-pentylphenyl 4-alkoxybenzoates and of the eutectic mixture of the two isomers of 4-methoxy-4′-n-butylazoxybenzene. Equations are proposed which describe the temperature dependence very well. The Leslie coefficients αi are calculated from the γ1 values and recently measured shear viscosity coefficients.
Solubility of xenon in liquid n-alkanes: Temperature dependence and thermodynamic functions
Authors: Pollack Gerald L. , Himm Jeffrey F.
Published: February 2003

Measurements of the Ostwald solubility as a function of temperature L(T) are reported for 133Xe gas in liquid n-alkanes. All the alkanes from n-C5H12 through n-C20H42 were investigated and the temperatures ranged from 10.0 to 50.0 °C. The experimental method is recently developed and has some unique aspects. From the temperature dependent results the chemical potential Δμ20(T), the enthalpy ΔH̄20, and the entropy ΔS̄20 of solution were determined. Values for Δμ20(T) ranged from 2546 cal/mol for n-C7H16 at 50.0 °C to 1811 cal/mol for n-C14H30 at 10.0 °C. The range of ΔH̄20 was from −2818 cal/mol for n-C5H12 to −2117 cal/mol for n-C20H42, and the corresponding range in ΔS̄20 was −16.90 to −13.58 cal/mol K. A Barclay–Butler plot of the thermodynamic functions and a plot of the dependence of solubility on the Hildebrand solubility parameter for this system are displayed. All of the data obtained in this experiment may be given to better than 0.8% by the empirical relation Δμ20=−RT ln x2=−0.0637nT+2.575×10−2T2, in which x2 is the mole fraction of solute in the solvent at 1 atm partial pressure and T is the absolute temperature. Because the solute is an inert monatomic gas and the solvents are a single homologous series of nonpolar liquids, the results show some interesting simple physical interpretation.
Far-infrared spectrum and x-ray diffraction of polycrystalline structure I clathrate hydrate of xenon at 4.3 K
Authors: Bertie John E. , Jacobs S. M.
Published: February 2003

The far-infrared absorption spectrum of the structure I clathrate hydrate of xenon at 4.3 K is reported, with the x-ray powder diffraction pattern of the same compound at 110 K. The cubic lattice parameter is 11.84±0.02 Å at 110 K. The spectrum is similar to that of the isomorphous cyclopropane hydrate, confirming the previous conclusion that the latter is due to the translational vibrations of the disordered water lattice. The results also show, by comparison with the lattice parameters and spectra of the hydrates of cyclopropane, ethylene oxide, and trimethylene oxide, that a large guest molecule lowers the vibrational frequencies of the water molecules by 2.5% to 3% while increasing the lattice parameter, and therefore the lengths of the hydrogen bonds, by 0.5% to 1%.
Theoretical studies of ion neutralization: A tight binding linear chain model
Authors: McDowell H. Keith
Published: February 2003

A tight binding semi-infinite chain is used to model the neutralization of ions impinging on a solid surface. Starting from the equations of motion for the appropriate annihilation operators of site-centered orbitals, two approaches to computing the neutralization probability are developed. The first approach is based on using the well-known molecular orbitals of such a chain. We conclude that this method, in general, is dependent on one’s ability to obtain molecular orbitals for an extended solid system. The second approach developed is based on a Langevin-type model in that we separate out a primary zone where the collision of the ion with the surface occurs and treat the remainder of the chain by using a memory kernel. We conclude that this method offers hope for treating realistic systems. Numerical computations are carried out using both approaches for specific choices of the parameters of the model. Exact agreement between the methods is obtained. In addition, the neutralization probability is found to oscillate as a function of the incident ion energy. This behavior is analyzed in some detail as a function of the parameters of the model.
Potential parameters for the K(4P)–rare gas Π interaction
Authors: Düren R. , Hasselbrink E. , Tischer H.
Published: February 2003

The results of scattering experiment to determine K–rare gas interactions in excited states, are presented for Ne, Kr and Xe. (AIP)
Critical exponents for surface interacting self-avoiding lattice walks. II. The square lattice
Authors: Ishinabe Takao
Published: February 2003

Critical exponents for the two-dimensional version of adsorption of a polymer chain at an interface are estimated as δa≃1.9 and ζ≃1.5 from the exact enumeration of self-avoiding walks up to 21 terms on the square lattice, where δa and ζ are defined from the respective dependences of the free energy and the thickness of adsorption layer on monomer–surface interaction; ζ is to be estimated to be about unity for three-dimensional lattices. These values are different from the scaling predictions of de Gennes: δa=4 and ζ=3 in two dimensions, and ζ=1.5 in three dimensions. An assumption in the scaling treatment is examined by using the exact enumeration data in order to explain the discrepancy.
Dissipative structures in coupled cells: Experiments
Authors: Stuchl Ivan , Marek Miloš
Published: February 2003

A system of coupled cells with mutual mass exchange and reaction is widely used as a model of heterogeneous catalytic reactors, catalytic reactions at the surface of a solid catalyst, in models of cell growth in morphogenesis, modeling of physiological systems, etc. A model hexagonal structure of seven thermostatted, flow-through, well-stirred reaction cells with mutual mass exchange between the cells was constructed and tested experimentally. The Belousov–Zhabotinsky reaction of oxidation of malonic acid by acidic bromate with ceric–cerous ion catalyst was used in experiments. Two stable stationary states can exist in a single flow-through cell in a well-defined range of inlet concentrations of malonic acid. When a string of up to seven cells is coupled by mutual mass exchange between neighboring cells, various combinations of ’’upper’’ and ’’lower’’ stable stationary states in individual cells—dissapative structures—can exist. The stability of dissipative structures to perturbations in Ce4+ and Br− ion concentrations was studied, and transitions between individual structures were followed.