bluuebunny/crossref_metadata_2025 huggingface dataset:
Brillouin and Rayleigh scattering studies of the phase transition in chloranil
Authors: Yoshihara A. , Bernstein E. R. , Raich J. C.
Published: February 2003

The nonferroic (constant rotational symmetry) phase transition at ∼93 K in chloranil (C6Cl4O2) is investigated by Brillouin and Rayleigh light scattering. The phase transition is driven by a zone boundary soft mode at the (00 1/2) point which, through various coupling mechanisms, can affect the zone center strains. The major conclusions of these investigations are: (1) the LA-phonon mode propagating along the [010*] direction exhibits a step function anomaly at Tc with an associated transition region in the low temperature phase and a linewidth anomaly. The frequency of this LA mode in the transition region decreases below its low temperature phase value near Tc; (2) the lowest frequency QTA phonon propagating around [010*] has a negative temperature coefficient in the high temperature phase which goes to zero in the low temperature phase; (3) external stress induced relaxation processes can be observed by correlation scattering spectroscopy which are highly polarization, experimental scattering geometry, and stress direction dependent; (4) the relaxation time and intensity of scattered light behave anomalously in the vicinity of the phase transition; and (5) a similar intensity anomaly without a relaxation time anomaly is observed in the absence of external stress applied to the sample. These data are analyzed using a theory developed by Yao, Cummins, and Bruce for improper ferroelastic–ferroelectric phase transitions. The negative temperature slope of the QTA mode in the high temperature phase is thought to be associated with an incipient, unrealized phase instability driven by an optical mode at 16 cm−1 with similar temperature dependence.
Numerical and analytical studies of the long-ranged solutions of the Yvon–Born–Green equation
Authors: Jones Gerald L. , Lee Eok K. , Kozak John J.
Published: February 2003

In this paper we give a detailed description of our numerical studies of the critical behavior of the Yvon–Born–Green (YBG) equation in various dimensions and the conclusions which we believe these studies warrent. A central issue in these studies is the relationship between the convergence of the numerical methods used to solve the YBG equation, the long-ranged nature of the solutions, and possible bifurcations in the solution structure of the equation. An understanding of these relationships is essential to the construction of reliable numerical solutions in the critical region of the YBG equation and is likely to be equally important for a large class of nonlinear integral equations with short-ranged kernels. We give some analytic models and numerical techniques which are effective in exploring these questions. From these studies the following conclusions concerning the critical behavior of the YBG equation are drawn: (1) For d=3 there is a region of density and temperature in which the correlations are long ranged but this range never becomes more than 13 hard-core radii. The compressibility remains finite, though large, in this region. There is no true critical point for d=3 but rather a region of ‘‘near critical’’ behavior. (2) For d=5, 6 there is a (stability) line in the density-temperature plane and, as that line is approached, the range of numerical solutions and the compressibility appear to increase without bound. Inside this stability line solutions cannot be found by the usual numerical techniques. All of the data near the stability line can be fit, quite accurately, with mean-field theory exponents. The thermodynamic behavior of the correlation range and the isothermal compressibility have the scaling (homogeneity) properties of a mean-field or van der Waals-type theory.
Multiphoton induced fluorescence and ionization of carbon monoxide (B 1Σ+)
Authors: Loge G. W. , Tiee J. J. , Wampler F. B.
Published: February 2003

The B 1Σ+ state of carbon monoxide was created by a two-photon absorption of 230 nm laser radiation. The B 1Σ+ state was identified by the positions of the Q branch 0–0 absorption band and the vibrational bands of B 1Σ+ → A 1Π fluorescence occurring after excitation. Collision-induced b 3Σ+ → a 3Π emission in the 350 nm region was also observed. The lifetimes of the B 1Σ+ → A 1Π and the b 3Σ+ → a 3Π emission were obtained as well as the self-quenching rate constants and the CO (B 1Σ)) quenching rate by N2. In addition to the two-photon laser induced fluorescence of B 1Σ+ carbon monoxide, a three-photon resonant (2+1) ionization was observed. Laser power dependence studies indicate that ionization of the B 1Σ+ state was nearly saturated at the laser fluence used, implying that most CO (B 1Σ+) was ionized rather than fluorescing. The measured polarization ratios for circularly to linearly polarized excitation of fluorescence and ionization was much larger than the expected values suggesting that other three-photon processes are occurring and occur more efficiently for linear polarization.
Symmetry selection rules in rotationally inelastic collisions of open-shell diatomic molecules and polyatomic tops: Implications of an irreducible tensor expansion
Authors: Alexander Millard H. , Davis Stephen L.
Published: February 2003

An irreducible tensor formalism due to Grawert is applied to collisions of open-shell diatomics and polyatomic tops. Explicit examination of the reduced T-matrix elements within the infinite-order sudden and first-order Born limits allows the derivation of several general symmetry selection rules for a rotationally inelastic process. In particular, both differential and integral cross sections will vanish unless the symmetry indices of the initial and final states satisfy certain conditions, for the following types of transitions: J=0→J′M′; J,M=0→J′,M′=0; and JM→J,−M. The M=0→M′=0 selection rule represents the extension, to an arbitrary orientation of the quantization axis, of a selection rule we have derived earlier. A comparison with results of fully quantum studies of collisions of NH3 and H2CO with He confirms the predictive accuracy of these rules. We discuss how both the M=0→M′=0 and JM→J,−M selection rules could be directly verified, in experiments involving laser excitation of a particular symmetry level followed by resolution of the fluorescence polarization.
Enhancement of charge-transfer reaction rate constants by vibrational excitation at kinetic energies below 1 eV
Authors: Durup-Ferguson M. , Böhringer H. , Fahey D. W. , Ferguson E. E.
Published: February 2003

A number of molecular ion charge-transfer reactions with neutral molecules have been studied in a flow-drift tube system as a function of average kinetic energy from thermal to ∼1 eV. Varying the buffer gas gives an independent control of the vibrational state distribution of the ions. The reactions include the charge transfer of N2O+, NO2+, SO2+, and H2O+ ions with NO and CO2+ ions with NO, O2, CH4, and Xe. For CO2+ reaction with CH4 and Xe the charge transfer occurs at near the collision rate and has little energy dependence and no measureable vibrational dependence. In every other case, where the rate constants are less than the collision rate constants, large enhancements result from vibrational excitation of the ions. The presence of ion vibrational excitation is demonstrated by the addition of a quenching gas to the flow-drift tube. In the low energy (near-thermal) regime where reaction is presumed to occur via long-lived intermediate complex formation, the reaction rate constants are increased by vibrational energy and decreased by kinetic energy. In the higher energy range where the rate constants increase with increasing kinetic energy, vibrational energy also increases the rate constants and to a comparable extent.
Observation of a new electronic state of carbon monoxide using LIF on highly vibrationally excited CO(X 1Σ+)
Authors: Wolk G. L. , Rich J. W.
Published: February 2003

UV laser-induced fluorescence studies of highly nonequilibrium, vibrationally excited CO molecules, have been employed to characterize a previously unobserved electronic state of CO, the D′ 1Σ+ state. Rotational and vibrational constants have been obtained from excitation spectra of several D′ ← X transitions and these constants have been verified from isotopic spectra (13C16O) of the same transitions. The values obtained here for the D′ 1Σ+ state are ωe=651.4±5.7 cm−1 (one σ), ωexe=20.4±2.5 cm−1, Te=89 438.4 cm−1±3.4 cm−1, Be=0.980 48 cm−1, ∝e=0.026 56 cm−1, Re=1.583 Å. The possible interactions of this newly discovered state with the A 1Π and B 1Σ+ states of CO are discussed in the context of the established electronic spectroscopy of CO.
Large angle elastic scattering from molecules: Vibrational Compton-like scattering
Authors: Bonham R. A. , de Souza G. G. B.
Published: February 2003

The band shape for the electron impact excitation of vibronic levels in molecules is investigated as a function of momentum transfer by use of the first Born approximation of scattering theory. The unresolved vibronic band, including translational excitation, for excitations which leave the molecule in its ground electronic state are reduced to a vibration-rotation (VR) generalized oscillator strength (GOS) and sum rules for it are reviewed. The shape of the VR–GOS is investigated as a function of momentum transfer. Assuming simple harmonic motion, the band shape is found to behave in a manner similar to the Compton peak in electron ionizing collisions although only discrete transitions are considered. At sufficiently high momentum transfer for certain molecules, the 0→1 vibrational excitation is no longer found to be the most probable.
Photodissociation dynamics of Fe(CO)5: Excited state lifetimes and energy disposal
Authors: Whetten Robert L. , Fu Ke-Jian , Grant Edward R.
Published: February 2003

By examining the competition between fragmentation and photoionization of selectively photoexcited Fe(CO)5 in a pulsed jet, we have been able to estimate wavelength dependent upper limits for excited state lifetimes. These range from 0.6 to 1.0 ps over the region from 290 to 310 nm. The nascent CO produced by this dissociation and subsequent multiple fragmentation is detected with rovibronic specificity by two-photon resonant four-photon ionization. Results on dynamics and lifetimes favor a dissociation model involving an unbound lowest ligand field state densely mixed with higher-lying ligand-field and charge transfer states. We also report the observation of highly efficient ion–molecule fragmentation reactions of Fe(II) with cold Fe(CO)5, in which fragmentation branching ratios depend critically on the Fe(II) states produced by preceding resonance-enhanced two-photon ionization of free Fe atoms.
A least-action variational method for calculating multidimensional tunneling probabilities for chemical reactions
Authors: Garrett Bruce C. , Truhlar Donald G.
Published: February 2003

We present a new method for calculating tunneling probabilities for chemical reactions with arbitrary curvature of the reaction path. The computational effort for obtaining a reaction probability at one energy consists of an integral over tunneling amplitudes for paths starting at various points on the reaction coordinate; for each point along the reaction coordinate, a one-dimensional search is performed to find the optimal tunneling path starting at that point; and for each tunneling path, a one-dimensional imaginary-action integral is evaluated. The method is designed to be applicable and practical even for general polyatomic reactions where no other reliable approach is affordable. To ascertain the accuracy of the method we have applied it to a wide range of one- and three-dimensional atom–diatom reactions on analytic potential energy surfaces for which accurate quantum mechanical rate constants are available. The accuracy, as compared to the accurate quantal calculations, is better than any previously available method that is simple enough to be applied to general polyatomic reactions.
Irreversible random and cooperative processes on lattices: Exact and approximate hierarchy truncation and solution
Authors: Evans J. W. , Burgess D. R. , Hoffman D. K.
Published: February 2003

Hierarchial rate equations are presented for processes where events occur irreversibly and, in general, cooperatively ‘‘filling’’ the sites of a lattice (the hierarchy is infinite for an infinite lattice). We comment on the hierarchial connectivity structure and a shielding property of empty sites. Hierachy truncation techniques are developed based on these. We consider, in detail, two irreversible processes on infinite, uniform lattices with nearest neighbor cooperative effects, modeling: (i) reaction at the sites of a 1D polymer chain; and (ii) chemisorption onto the sites of a 2D square lattice. Our truncation procedure recovers previously obtained exact results for the 1D case and provides approximate results for the 2D case. These are compared in various cooperativity regimes including highly autoinhibitory rates (filling in stages) and autocatalytic rates (island formation).
The kinetics of hopping motion of interstitials with chemical reactions in arbitrary time dependent inhomogeneous interactive fields
Authors: Ogurtani Tarik Ö. , Seeger Alfred K.
Published: February 2003

Atomic hopping motions of interstitial species with chemical reactions in an arbitrary time- and space-dependent field have been formulated in terms of a linear but coupled set of differential equations for a general lattice structure. The decoupled form of these equations has been solved exactly using the discrete Fourier k-space transformation supplemented by a Laplace transformation with respect to time. An explicit and compact expression for the Fourier transform of the partial concentration of interstitials is obtained for interactive fields which have absolutely convergent norms in the time domain. Some special cases of general interest such as the simple harmonic, almost periodic, or static inhomogeneous fields are also treated extensively. The power dissipation and the storage terms associated with interstitial hopping motion in harmonic or almost periodic fields are formulated rigorously. The effect of static inhomogeneous bias field due to other imperfections on the relaxation time spectrum is considered in terms of the first-order perturbation theory.
Nonadiabatic approach for resonant molecular multiphoton absorption processes in intense infrared laser fields
Authors: Ho Tak-San , Chu Shih-I
Published: February 2003

A nonperturbative approach for efficient and accurate treatment of the molecular multiphoton absorption (MPA) quantum dynamics in intense infrared (IR) laser fields is presented. The approach is based on the adiabatic separation of the fast vibrational motion from the slow rotational motion, incorporating the fact that the IR laser frequency is close to the frequencies of adjacent vibrational transitions. One thus first solves the quasivibrational energy (QVE) states (or, equivalently, the dressed vibrational states) with molecular orientation fixed. This reduces the computationally often formidable (vibrational-rotational) Floquet matrix analysis to a manageable scale, and, in addition, provides useful physical insights for understanding the nonlinear MPA dynamics. The QVE levels are found to be grouped into distinct energy bands, characterized by the IR frequency, with each band providing an effective potential for molecular rotation. Whereas the interband couplings are totally negligible, the intraband nonadiabatic angular couplings are the main driving mechanisms for inducing resonant vibrational–rotational multiphoton transitions. The utility of the method is illustrated by a detailed study of the sequential MPA spectra for 12C 16O molecule, including state-to-state multiquantum transitions and transitions from initially thermally distributed states as a whole. Results are presented for the case of IR laser intensity 50 GW/cm2 and frequencies ranging from 2115 to 2165 cm−1. Excellent agreement of the MPA spectra obtained by the nonadiabatic approach and the exact Floquet matrix method was observed in all fine details.
Laser induced fluorescence of IO radicals and rate constant for the reaction of IO+NO
Authors: Inoue Gen , Suzuki Makoto , Washida Nobuaki
Published: February 2003

The first observation of laser-induced fluorescence of the IO free radical in the gas phase is reported. The source of ground-state IO (X 3Π3/2) radicals was the photolysis of the O3–HI mixture by KrF (248 nm) and N2O–HI mixture by ArF (193 nm) excimer laser radiation. Laser excitation spectra involving the vibrational levels of the A 2Π3/2 state were measured, using excitation wavelengths varying from 440–470 nm from a YAG-pumped dye laser. The laser excitation spectra of the 2-0 and 0-0 band were observed, while the 1-0 band was not observed due to strong predissociation. The lifetimes of v′=2 and v′=0 levels in the A 2Π3/2 state were shorter than 10 ns. This means that predissociation occurs also in both levels. Each rotational level in the v′=2 and v′=0 levels is affected by predissociation; predissociation occurs more strongly in the higher J levels. The rate constant for the reaction of IO+NO→I+NO2 was measured by the addition of NO to the N2O–HI system. The rate constant obtained is (2.8±0.2)×10−11 cm3 molecule−1 s−1, 1.6 times faster than the value reported by Ray and Watson.
Optical spectra, energy levels, and crystal-field analysis of tripositive rare-earth ions in Y2O3. III. Intensities and g values for C2 sites
Authors: Morrison Clyde A. , Leavitt Richard P. , Gruber John B. , Chang N. C.
Published: February 2003

We report measurements of the oscillator strengths between the Stark-split ground level and numerous excited Stark levels of Nd3+, Sm3+, Er3+, and Tm3+ in the C2 sites of Y2O3. Experimental results are compared with calculations based on the Judd–Ofelt theory of induced electric-dipole transitions, which uses the odd-parity terms in the crystal-field interaction (determined via an effective point-charge model). We also compare our theoretical results with previous measurements of manifold-to-manifold oscillator strengths, excited-state lifetimes, and Judd–Ofelt intensity parameters. Magnetic-dipole contributions to the intensities are included as well. Calculated ground-state g values for all the rare earths with an odd number of f electrons are reported. Comparison of theoretical and experimental results indicates that good agreement is obtained in most cases.
Computer simulation of the photodissociation and recombination of iodine in gaseous krypton using a droplet model
Authors: Lipkus Alan H. , Buff Frank P. , Sceats Mark G.
Published: February 2003

Computer simulations of the photodissociation of an I2 molecule that is physically clustered with Kr atoms are performed. Geminate recombination is observed on the excited A state potential of the iodine atoms, in contrast to previous work. A grand ensemble formulation of the process is developed in which cluster probabilities of the initial configurations are evaluated by Monte Carlo and particle insertion techniques. It is followed by molecular dynamics simulations on the system when the I2 molecule is excited. Excellent agreement with experiment is obtained for the density dependence of the quantum yield of recombination. Analysis of the trajectories reveals that the time evolution of recombinations is approximately exponential, whereas that for escapes reveals a fast immediate component followed by a tail at intermediate times which exhibits approximately exponential decay.
SVL fluorescence spectroscopy and collision-induced intramolecular vibrational energy transfer in 1B1 difluorodiazirine
Authors: Vandersall Mark , Rice Stuart A.
Published: February 2003

SVL fluorescence spectroscopy of 1B1 difluorodiazirine is used to confirm previously measured vibrational frequencies and to allow measurement of collision induced vibrational redistribution in 1B1 difluorodiazirine. The latter is found to have the following properties: (i) The cross section is large, of the order of one percent of the hard sphere collision cross section; (ii) The observed mode-to-mode energy transfer is very selective; (iii) The pathways for energy exchange appear not to be influenced by the symmetries of the initial and final levels; (iv) The data are qualitatively consistent with the predictions of the McDonald–Rice model, but not with the Parmenter–Tang rules.
Classical trajectory studies of energy transfer in Ar–difluorodiazirine collisions
Authors: Rolfe Timothy J. , Rice Stuart A.
Published: February 2003

We report the results of extensive classical trajectory studies of energy transfer in Ar–difluorodiazirine (DFD) collisions. The use of classical mechanics for this purpose leads to some difficulties of interpretation; these are discussed. In the conclusions drawn from the calculations, emphasis is placed on the qualitative results, and no attempt is made to estimate collision cross sections or transition probabilities. The most important results to emerge from our calculations are the following: (i) Classical mechanical simulations of Ar–DFD collisions lead to the conclusion that the induced mode-to-mode energy transfer is very selective, just as is observed. (ii) Despite thermal averaging, some idiosyncratic features of the potential energy surface are reflected in the average energy transfers due to collision (e.g., in the impact parameter dependence of the root-mean-square rotational energy change on collision). (iii) The branching pattern characteristic of collision induced mode-to-mode vibrational energy transfer is likely sensitive to details of the potential energy surface, and not just to its overall structure. We reach this conclusion because the particular pathways of collision induced mode-to-mode energy transfer in the Ar–1B1 DFD system are not correctly reproduced by our calculations, despite the correct prediction of selectivity in mode-to-mode energy transfer.
Molecular dynamics investigation of the crystal–fluid interface. II. Structures of the fcc (111), (100), and (110) crystal–vapor systems
Authors: Broughton Jeremy Q. , Gilmer George H.
Published: February 2003

Structures of atomic layers near crystal–vapor interfaces have been investigated by molecular dynamics techniques. The face centered cubic (111), (100), and (110) interfaces of systems composed of Lennard-Jones particles have been simulated. The properties of the layers reported include densities, potential energies, two-dimensional radial and angular distribution functions, and interlayer spacings.
Adsorption isotherms obtained from thermal desorption data for the system H2/Ni(111)
Authors: Rendulic K. D. , Winkler A.
Published: February 2003

Adsorption and desorption kinetics as derived from flash desorption measurements are used to synthesize adsorption isotherms. It is shown that for the adsorption system H2/Ni(111) detailed balancing is applicable. The isosteric heat of adsorption is found to be temperature dependent in a certain range of coverages. This is a result of two adsorption states being involved. From the variation of the sticking coefficient with temperature, one can conclude that there is a small activation barrier of about 50–100 cal/mol.
On the nature and decay of electronically excited states at metal surfaces
Authors: Persson B. N. J. , Avouris Ph.
Published: February 2003

We present a qualitative discussion of the nature and nonradiative decay of electronically excited states at metal surfaces. Within an Anderson–Newns type of Hamiltonian, we calculate, using the memory function formalism, the effect of the substrate on the energy and shape of the optical absorption or electron energy loss spectra and present illustrative numerical results. The theory is compared with experimental data for excited noble gas atoms on noble metal surfaces.
Direct inelastic scattering of nitric oxide from clean Ag(111): Rotational and fine structure distributions
Authors: Kubiak G. D. , Hurst J. E. , Rennagel H. G. , McClelland G. M. , Zare R. N.
Published: February 2003

The internal state distribution of scattered NO is determined by laser fluorescence excitation spectroscopy when a pulsed, supersonically cooled beam of NO is incident upon the (111) face of a clean Ag single crystal. It is found that the mean rotational energy 〈Er〉 depends linearly on the surface temperature Es(=Ts) and the incident kinetic energy normal to the surface En according to 〈Er〉=a(En+〈Ew′〉)+bEs. The three parameters a, b, and 〈E′w〉 are constants independent of En and Es. Arguments are presented showing that 〈E′w〉 is some measure of the average NO/Ag(111) well depth. For the Ω=1/2 fine structure component we estimate that 〈E′w〉=2850±450 K (245±40 meV), a=0.88±0.009, and b=0.18±0.04 while for Ω=3/2, 〈E′w〉=2080±150 K (180±13 meV), a=0.132±0.005, and b=0.11±0.02. The results are compared to the predictions of one-dimensional impulsive models of gas-surface scattering. These models are able to describe qualitatively the dependence of 〈Er〉 on En and Es but only when trapping fractions that are incompatible with experiment are predicted simultaneously.
Experimental determination of product quantum state distributions in the H+D2→HD+D reaction
Authors: Gerrity Daniel P. , Valentini James J.
Published: February 2003

Rotational and vibrational state distributions of HD formed in the reaction of translationally hot hydrogen atoms with D2 have been measured by CARS spectroscopy under nearly single-collisions conditions. The rotational and vibrational excitation of the HD is small; most of the energy available to the products appears in translation.
Brownian dynamics simulation of macromolecules in steady shear flow
Authors: Dotson Paul J.
Published: February 2003

A nonequilibrium Brownian dynamics technique is used to simulate a dilute solution of polymers in a steady shear flow. Results for the mean square end-to-end length of a Rouse chain agree very well with theoretical results from polymer kinetic theory.
Vibrational relaxation of UF6: Ultrasonic measurements in mixtures with CO
Authors: Bass H. E. , Shields F. D. , Breshears W. D.
Published: February 2003

Ultrasonic attenuation has been measured in mixturs of 5% and 10% UF6 in CO at 273°K. The vibrational relaxation time of UF6 by CO in the mixtures are computed and compared with those of UF6−N2 mixtures. (AIP)
Derivation of an extended geminal model
Authors: Ro/eggen I.
Published: February 2003

An extended geminal model is derived by applying perturbation theory to a matrix representation of the electronic Hamiltonian. The matrix representation is formed by a complete set of orthogonal configuration functions generated from a given finite orbital basis set. By construction, the function defined by the APSG approximation (antisymmetric product of strongly orthogonal geminals) is an element of this set of configuration functions. Considering the nondiagonal part of the Hamiltonian matrix as the perturbation, our model is obtained by a partitioning and reordering of the infinite order Rayleigh–Schrödinger perturbation expansion. The model has a hierarchical structure, is size extensive, and has favorable properties with respect to interpretation. In a test calculation on the water molecule, it is demonstrated that the extended geminal model truncated at the double pair correction level, recovers 100.8% of the correlation energy defined by the corresponding full CI calculation.
Thermodynamic study of gaseous ternary oxide molecules. The europium–vanadium–oxygen system
Authors: Balducci G. , Gigli G. , Guido M.
Published: February 2003

The gaseous ternary oxide molecules EuVO3 and EuVO2 have been identified by high temperature mass spectrometry in the vapors in equilibrium over a mixture of europium and vanadium oxides in a molybdenum cell. From the study of four all-gas equilibria, the stability of these molecules has been derived: D°o,at(EuVO3)=2192.5±16 kJ mol−1, D°o,at (EuVO2)=1504±11 kJ mol−1. The appearance potentials were measured as: 8.1±0.5 and 8±1 eV for EuVO+3 and EuVO+2, respectively.
Toward understanding microemulsion microstructure. II
Authors: Kaler Eric W. , Davis H. Ted , Scriven L. E.
Published: February 2003

Many equilibrium microemulsion phases can solubilize hydrocarbon and water in all proportions in a continuous progression of states without any visibly abrupt transition. At the extremes are solutions of swollen micelles and swollen inverted micelles. Contending pictures of the midprogression microstructures are (1) crowded swollen micelles and crowded swollen inverted micelles, which cannot coexist alone, and (2) bicontinuous structures, parts of which can be micellar. Which is correct? The most extensive published evidence is electrical conductivity, small-angle x-ray scattering (SAXS), and viscosity data on microemulsions made in our laboratory with an alkylaryl sulfonate mixture that is a commercial type of surfactant. We report here complementary data with a comparable pure surfactant and analyze at length the SAXS evidence. We note that the pure surfactant appears to narrow the ranges over which swollen disjoint interacting micelles exist. We conclude that the continuous progression through buildup and breakdown of bicontinuous structures more readily explains all of our data and a number of findings by other investigators.
Chaos in the multiple photon excitation of molecules due to vibration-rotation coupling at lowest order
Authors: Galbraith H. W. , Ackerhalt J. R. , Milonni P. W.
Published: February 2003

We study the multiple photon excitation of a molecule with a triply degenerate near-resonant IR-active mode. The molecule is described by its zeroth-order Hamiltonian as an uncoupled harmonic oscillator-rigid rotor. The molecule-field interaction is dipolar with the field treated semiclassically. The Hiesenberg equations of motion are solved in the classical approximation and chaos is found when the photon absorption exceeds the t=0 angular momentum. The origin of the chaos is due to the nonconservation of the molecule angular momentum.
Mercury halide B(2Σ+) vibrational distributions from dissociative excitation reactions of Hg halides with Xe(3P2) and N2(A,3Σ+u)
Authors: Dreiling T. D. , Setser D. W.
Published: February 2003

The HgX(B 2Σ+–X 2Σ+), X=Cl, Br, I, spectra from the dissociative excitation reactions of N2(A 3Σ+u, v=0, 1) and Xe(3P2) with several mercuric and methylmercury halides have been simulated to assign the HgX(B) vibrational distributions. The distributions from the methylmercury halides could be described as Boltzmann types with temperatures ranging from 1000 K for N2(A)+CH3HgI to 9000 K for Xe(3P2)+CH3HgCl. The distributions from the mercuric halides are non-Boltzmann and the 〈fV〉 are somewhat higher than for the CH3HgX compounds. The initial HgX(B) vibrational distributions are used to discuss the state-to-state quenching mechanisms.
Resonant multiphoton ionization photoelectron spectroscopic study of benzene. Evidence for fast intramolecular vibrational relaxation within the 1E1u state
Authors: Achiba Yohji , Sato Kenji , Shobatake Kosuke , Kimura Katsumi
Published: February 2003

Resonant multiphoton ionization photoelectron measurements were carried out for benzene under collision-free conditions in such a way that the benzene molecule is ionized by four photons through various two-photon allowed vibronic levels of the 1B2u excited state. As a result, single prominent, somewhat broad photoelectron bands were observed in the 0.14–0.36 eV region, arising from Δv=0 ionization transitions. The prominent peak is shifted with increasing photon energy by K=hνl−C, where K is the photoelectron energy, hνl the photon energy, and C a constant. This relationship strongly indicates that the third photon is resonant with a real intermediate excited state. Therefore, the overall ionization process is expressed by (2+1+1). It is concluded that fast intramolecular vibrational relaxation occurs at the third-photon states within the 1Elu (ππ*) state and subsequent ionization takes place from vibrationally relaxed levels. The relaxation within the 1Elu state is supported from the 0–0 energy which was evaluated here for the ionized states from the photoelectron data. It is also suggested that the lifetime of the vibrationally relaxed 1Elu states is the order of 10−11–10−12 s or longer.
Far infrared laser magnetic resonance of singlet methylene: Singlet–triplet perturbations, singlet–triplet transitions, and the singlet–triplet splittinga)
Authors: McKellar A. R. W. , Bunker P. R. , Sears Trevor J. , Evenson K. M. , Saykally Richard J. , Langhoff S. R.
Published: February 2003

We have observed and assigned a number of far infrared laser magnetic resonance spectra of CH2 arising from rotational transitions within the lowest vibrational state of the ã 1A1 electronic excited state and from transitions between such singlet levels and vibrationally excited levels of the X̃ 3B1 electronic ground state. The singlet–singlet transitions are magnetically active, and the singlet–triplet transitions have electric dipole intensity because of the spin-orbit mixing of singlet levels with vibrationally excited levels of the triplet state. By identifying four pairs of singlet and triplet levels that perturb each other we can accurately position the singlet and triplet state relative to each other and determine the single–triplet energy splitting. We determine that T0(ã 1A1)=3165±20 cm−1 (9.05±0.06 kcal/mol; 0.392±0.003 eV), and Te(ã 1A1)=2994±30 cm−1 (8.56±0.09 kcal/mol; 0.371±0.004 eV). A new ab initio calculation of the spin-orbit matrix element between these two states has been of assistance in assigning the levels that perturb each other and has enabled us to calculate the radiative lifetimes of the lowest ortho and para levels of the ã 1A1 state to be about 18 s in each case.
Autocatalysis in isothermal, open systems
Authors: Gray P. , Scott S. K.
Published: February 2003

In open systems, the prototype autocatalytic reaction A+2X → 3X, X → inert may display complex dependences of the stationary-state extents of conversion on flow-rate or residence time even under isothermal, well-stirred conditions. Sustained oscillations corresponding to stable limit cycles are also found. In this note we answer three questions posed by Escher and Ross in a recent paper and draw analogies between their work and earlier studies of our own. (AIP)
Deformable stochastic boundaries in molecular dynamics
Authors: Brooks C. L. , Karplus Martin
Published: February 2003

A new approach to studying localized chemical events in condensed phases is developed. The approach provides a simple and convenient method for reducing the total number of solvent particles explicitly included in simulations of localized processes while decreasing spurious edge effects. Both energy flow across the boundary and density fluctuations in the simulation region are included; this makes it possible to treat nonequilibrium processes, such as thermal gradients and endothermic or exothermic chemical reactions. The essential element of the approach is the introduction of a soft boundary force and a stochastic buffer region. For simple liquids, the boundary force is determined from the solvent equilibrium structure (radial distribution function) and is readily incorporated into conventional molecular dynamics algorithms. The methodology is illustrated by application to liquid argon in spherical and cubical simulation regions; comparison with standard molceular dynamics results show excellent agreement for structural, dynamic, and thermodynamic properties.
Pyroelectric Sr(NO2)2⋅H2O: Room temperature crystal structure
Authors: Abrahams S. C. , Marsh P. , Liminga R. , Lundgren J.-O.
Published: February 2003

Strontium nitrite monohydrate, Sr(NO2)2⋅H2O, is a newly discovered pyroelectric material that crystallizes in the monoclinic system with space group P21 and four formulas in the unit cell. The lattice constants at 295 K are a=12.5831(4), b=8.94941(15), c=4.4860(2) Å, and β=99.111(4)° for λCr Kα1=2.289 753 Å. The integrated intensities of all 6870 reflections within a sphere of reciprocal space having radius (sin θ)/λ≤0.75 Å−1 were measured on a CAD-4 diffractometer with Mo Kα radiation, resulting in 6286 above background. Correction and averaging gave 3158 independent structure factors with an internal agreement factor of 0.0121. The crystal structure was solved from the Patterson function and Fourier series and refined by the method of least squares. The final agreement factor R=0.0129. The four NO−2 ions have a mean N–O distance of 1.252(7) Å and O–N–O angle of 114.0(6)°. The two independent Sr2+ ions have coordination numbers of 10 and 9 with average Sr–N,O distances of 2.70(8) and 2.68(12) Å, respectively. The water molecules have a mean O–H distance of 0.85(5) Å and H–O–H angle of 102.8(7)°: they are connected by hydrogen bonds of average length 2.870(2) and 2.953(2) Å that link to give infinite helices. One hydrogen atom from each water molecule forms a bond with the same nitrite ion resulting in an eight-membered puckered ring.
Interfacial sound modes and heterogeneous catalysis
Authors: Gutkowicz-Krusin Dina
Published: February 2003

The dispersion relation for interfacial sound modes in the presence of a single catalytic reaction at the planar interface between an N-component fluid and a rigid, thermally conducting solid, has been derived. The chemical contribution to the attenuation coefficient of these modes is shown to have nonanalytic dependence on frequency ω and may be written αchemint=α0ω2(1+(ωτs)1/2/2)/(1+ (2ωτs)1/2+ωτs) , where the surface chemical relaxation time τs is proportional to an average diffusion coefficient and inversely proportional to the square of the rate constant for the surface reaction, and α0 depends on the volume and enthalpy changes in this reaction. The experimental study of interfacial sound modes may be an important probe of the kinetics of heterogeneous catalytic reactions.
The measurement of diffusion using deuterium pulsed field gradient nuclear magnetic resonance
Authors: Callaghan P. T. , Le Gros M. A. , Pinder D. N.
Published: February 2003

Diffusion measurements have been made on a variety of molecular systems using deuterium NMR spin echoes in the presence of pulsed magnetic field gradients (deuterium PFGNMR). Consistency is found between self-diffusion coefficients (Ds) obtained separately by proton and deuterium observation in a common molecular species, d1-benzene, and the semiclassical Stejskal–Tanner relation is verified to high precision for j=1/2 and j=1. The influence of rf field inhomogeneity on PFGNMR is examined for j=1/2 and j=1 in theory and experiment and we show that an rf offset angle ΔΘ leads to a zero gradient intercept which depends on cos3 ΔΘ. We obtain the temperature dependence of Ds for D2O and also find the separate proton and deuteron Ds values over the entire mole-ratio range in D2O/H2O mixtures. It is shown theoretically that the presence of rank 2 tensor interactions in the nuclear spin Hamiltonian does not disturb the PFGNMR experiment performed using the solid-echo rf sequence except to introduce a zero gradient intercept. We report the first solid-echo PFGNMR experiment performed on deuterium in the presence of nonzero static quadrupolar interactions. Using the liquid crystal system K-palmitate/D2O we examine the diffusion anisotropy and orientational symmetry in both oriented single crystal and randomly oriented polycrystal samples. Finally we exploit deuterium labeling to obtain the diffusion coefficient of adrenalin in human blood plasma by deuterium PFGNMR.
Branching fraction for I(2P1/2) formation by the F+I2 reaction
Authors: Agrawalla B. S. , Singh J. P. , Setser D. W.
Published: February 2003

The formation of I(2P1/2) from the reaction of F atoms with I2 has been studied by comparing the intensity of the I(2P1/2→2P3/2) transition to that of HF(v=2)→HF(v=0) from the F+CH4 reaction for the same [F]. From the rate constant for F+CH4 an upper limit rate constant for (2P1/2) formation is set as ≤1.8×10−13 cm3 molecule−1 s−1. This corresponds to a branching fraction of less than 0.0004 relative to ground state I(2P3/2) formation for F+I2.
The microwave spectra of CH2DSH and CHD2SH
Authors: Su Chun Fu , Quade C. Richard
Published: February 2003

The microwave torsional-rotational spectra of CH2DSH and CHD2SH have been measured and analyzed over the frequency range 12.5–48.0 MHz. a-, b-, and c-dipole transitions have been assigned for both species which makes it possible to determine the tunneling frequency between the two gauche torsional levels for both species. An internal rotation analysis gives the torsional potential energy coefficients V1=−3.40±0.10 cm−1, V3=456.3±0.5 cm−1 for CH2DSH and V1=4.45±0.10 cm−1, V3=424.5±0.5 cm−1 for CHD2SH with V2 constrained to zero.
Electric dipole intensity parameters for lanthanide 4f → 4f transitions
Authors: Reid Michael F. , Richardson F. S.
Published: February 2003

A general parametrization scheme for the electric dipole intensities of lanthanide 4f → 4f crystal-field transitions is proposed. This parametrization is sufficiently general to accommodate any 4f → 4f intensity mechanism based on the ‘‘one-electron’’ and ‘‘one-photon’’ approximations for lanthanide-ligand-radiation field interactions. It includes as a subset, the familiar Judd–Ofelt–Axe intensity parameters, AtpΞ(t, λ), but introduces additional parameters which are shown to be essential in cases where the lanthanide-ligand pairwise interactions cannot be assumed to be cylindrically symmetric. Expressions are given for calculating the general intensity parameters in terms of two specific intensity mechanisms. Special consideration is given to the effects of ligand polarizability anisotropy on the intensity parameters. A set of ‘‘intrinsic’’ intensity parameters are also introduced. These parameters are defined within the context of the ‘‘superposition’’ model for lanthanide-ligand interactions, and are independent of coordination geometry and lanthanide site symmetry.
Resonant two-photon ionization of fluorene rare-gas van der Waals complexes
Authors: Leutwyler Samuel , Even Uzi , Jortner Joshua
Published: February 2003

Resonant two-photon ionization combined with time-of-flight mass spectrometry was applied for the interrogation of the S0 → S1 electronic-vibrational excitations of van der Waals complexes of fluorene (FL) with rare-gas atoms and N2 in supersonic jets. Energy-resolved and mass-resolved spectra of FL ⋅ Ne, FL ⋅ Arn (n=1–3), FL ⋅ Kr, FL ⋅ Xe, and FL ⋅ N2 were recorded over the energy range 0–800 cm−1 above the electronic origin of S1. The red microscopic spectral shifts of the electronic origins of FL ⋅ R (R=Ar, Kr, and Xe) complexes are dominated by dispersive interactions, being proportional to the polarizability of R. The vibrational level structure of FL ⋅ Rn (R=Ar, Kr, and Xe) complexes exhibits intramolecular vibrational excitations of FL, as well as intermolecular vibrations, which involve the relative motion of FL and R in the complex. The spectra of FL ⋅ Ne and FL ⋅ N2 reveal a rich vibrational structure in the vicinity of the electronic origin, indicating a substantial change of the nuclear configuration upon electronic excitation. Upper and lower bounds on the dissociation energies of FL ⋅ R (R=Ne, Kr, and Xe) and FL ⋅ Ar2 were inferred from the vibrational level structure in the mass-resolved spectra, where the disappearance of the signal of the parent van der Waals ion and the appearance of the ion signal of the fragments mark the onset of the vibrational predissociation process.
Electron spin-echo modulation effects in disordered systems: Structure of traps for H and D atoms in frozen water solutions based on 1H and 2D nuclear modulation data
Authors: Dikanov S. A. , Tsvetkov Yu. D. , Astashkin A. V. , Shubin A. A.
Published: February 2003

Modulation effects induced by matrix protons and deuterons in the primary ESE from H and D atoms trapped in frozen water solutions of sulfuric acid have been analyzed. It has been shown that the nuclear quadrupole interaction in a deuterated sample additionally damps the modulation.
Low temperature spectroscopy of internally hydrogen-bonded 2-(2′-hydroxy-5′-methylphenyl)-benzotriazole in a mixed crystal
Authors: Bocian David F. , Huston Alan L. , Scott Gary W.
Published: February 2003

Low temperature fluorescence and fluorescence excitation spectra of 2-(2′-hydroxy-5′-methylphenyl)-benzotriazole (MeHPB) in a single crystal biphenyl host are reported which exhibit sharp vibrational structure. The spectra are analyzed in terms of seven vibrational modes including three phenyl modes, three normal modes involving N–N and C–N stretching and bending motion, and a low frequency torsional vibration about the central C–N bond. The fluorescence exhibits a normal Stokes shift indicating that excited-state intramolecular proton transfer is precluded in this mixed crystal probably because the MeHPB molecule is held in a nonplanar conformation by molecular packing forces. A model of the MeHPB molecule based on semiempirical molecular orbital calculations is also presented which provides support for these conclusions.
The n
s Rydberg series of 1,3-trans-butadiene observed using multiphoton ionization
Authors: Mallard W. Gary , Miller J. Houston , Smyth Kermit C.
Published: February 2003

The ns Rydberg series of 1,3-trans-butadiene has been observed in a diffusion flame environment using two-photon resonant multiphoton ionization in the 330–269 nm wavelength region. An analysis of the energies for the n=4 to n=12 states yields a series limit of 73 170±23 cm−1 and a quantum defect of 0.91±0.07. This ns series limit has been averaged with the limits of three other Rydberg series to give an ionization potential of 73 154±30 cm−1. The 3s and 4s states show substantial effects of mixing with the core orbitals.
Far infrared spectra, conformational potential function, and barrier to methyl rotation of propionyl fluoride
Authors: Guirgis G. A. , Barton B. A. , Durig J. R.
Published: February 2003

The far infrared spectra of propionyl fluoride CH3CH2CFO in the gaseous and solid states have been recorded from 500 to 40 cm−1. A rather complex spectrum of the gas was observed and a substantial number of bands have been assigned to the asymmetric torsional modes for both the s-cis (oxygen atom eclipsing the methyl group) and the high energy gauche conformers. Analysis of these bands permitted the calculation of the torsional potential function present in this molecule. The potential coefficients for the asymmetric torsional mode were calculated to be: V1=341±24, V2=236±20, V3=390±3, and V4=21±6 cm−1, with an enthalpy difference between the more stable s-cis and the high energy gauche conformers of 434±20 cm−1 (1.24±0.06 kcal/mol). This function gives a potential barrier of 692 cm−1 (1.98 kcal/mol) separating the s-cis from the gauche form and 283 cm−1 (0.81 kcal/mol) separating the two equivalent gauche forms. From a temperature study of the Raman spectrum of the gas, the enthalpy difference between the s-cis and gauche conformers was determined to be 486±45 cm−1 (1.39±0.13 kcal/mol) which is in excellent agreement with the value obtained from the potential function. The barrier to the methyl rotation for the s-cis conformer was calculated from the far infrared data to be 935±2 cm−1 (2.67 kcal/mol). Both the methyl torsion and CFO rock were observed as doublets in the spectrum of the solid which indicates that there are at least two molecules per primitive cell. These results are compared to the corresponding quantities in some related molecules.
Hydrogen cluster ion equilibria
Authors: Beuhler R. J. , Ehrenson S. , Friedman L.
Published: February 2003

The equilibria H3++H2=H5+ and H5++H2=H7+ have been studied using both hydrogen and deuterium in a cooled corona discharge ion source fitted with a very small ion exit aperture. Enthalpies of reaction are in relatively good agreement with results obtained in earlier studies by Hiraoka and Kebarle using a pulse electron impact ion source. Absolute values of equilibrium constants and entropies of reaction are in somewhat poorer agreement. The enthalpy determined for the reaction yielding H5+ was found to be in slightly better agreement with the recent theoretical study of Yamaguchi, Gaw, and Schaeffer than results obtained in earlier examinations. A discussion of potential errors in the experimental determination of these equilibria is presented.