bluuebunny/crossref_metadata_2025 huggingface dataset:
Conformational barriers to internal rotation and vibrational assignment of cyclopropylcarbonyl fluoride
Authors: Durig J. R. , Bist H. D. , Little T. S.
Published: February 2003

The infrared (3500 to 50 cm−1) and Raman (3200 to 10 cm−1) spectra have been recorded for the gaseous and solid states of cyclopropylcarbonyl fluoride, c-C3H5CFO. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. The asymmetric torsion for the conformer which has the carbonyl group cis to the cyclopropane ring has been observed at 88.5 cm−1 in the far infrared spectrum of the gas with five accompanying hot bands, and the corresponding torsion of the trans conformer was observed at 91.0 cm−1 with two additional hot bands occurring at 90.6 and 90.2 cm−1. From these data the potential function for internal rotation of the asymmetric top has been determined and the following potential constants have been evaluated: V1=−618±6, V2=1970±27, V3=399±6, and V4=−48±10 cm−1. It has been determined that the cis conformer is the predominant form at ambient temperature in the gas phase and the enthalpy difference between the cis and the trans conformers is 222 cm−1 (629 cal/mol) for the vapor. The calculated trans-cis barrier is 1948 cm−1 (5.57 kcal/mol) and the cis-trans barrier is 2168 cm−1 (6.20 kcal/mol). From a temperature study of the Raman spectrum of the liquid an energy difference of 92±20 cm−1 (263 cal/mol) has been determined with the trans conformer being more stable in the liquid phase due to intermolecular interactions. Additionally, an investigation of the vibrational spectrum of the solid state indicates that both conformers persist even to 30 K but the trans conformer is more stable. The number of lattice modes observed in the Raman spectrum of the solid indicates at least two molecules per primitive cell. A complete vibrational assignment is proposed based on infrared band contours, depolarization values, and group frequencies. These results are compared to similar quantities in some related molecules.
Regularities in the two-photon spectra of polysubstituted benzenes
Authors: Rava Richard P. , Goodman Lionel , Philis John G.
Published: February 2003

The regularities in the two-photon 1Lb ← 1A spectrum of polysubstituted benzenes have been studied. Orientation intensity rules are derived which predict the relative two-photon intensities for mono:ortho:meta:para:1,2,3:1,3,5:1,2,4 homosubstitution to be 1:3:1:0:4:0:1, as opposed to the one-photon rule 1:1:1:4:0:0:3. The TP 1Lb spectrum for polysubstituted fluoro- and methyl-benzenes are reported and are in good agreement with these rules. In particular, the theory shows that even in the ortho case where the excited state has A1 symmetry and in the case of Cs symmetry (e.g., 1,2,4 trisubstitution) only the symmetric tensor component, which contributes to the higher symmetry molecules, is nonzero. This prediction is confirmed by polarization experiments. For para-heterosubstitution, the theory requires the two-photon spectrum to be enhanced when the substituents are opposite in their electron donating properties. In contrast, the one-photon spectrum is enhanced when both substituents are either donating or withdrawing.
Electron affinities of SO2 and nitrobenzene
Authors: Fukuda Elaine K. , McIver Robert T.
Published: February 2003

Several ion–molecule reactions have been observed which indicate that the electron affinities of SO2 and nitrobenzene are far greater than the currently accepted values. The reactions were studied by pulsed ion cyclotron resonance (ICR) spectrometry using a trapped ion analyzer cell to store the ions for several hundred ms. Reaction pathways were confirmed by ion cyclotron double resonance and by varying the pressures of the neutral reactants. The relative electron affinity of nitrobenzene and SO2 was determined by measuring the equilibrium constant for the reaction C6H5NO−2+SO2=SO2−+C6H5NO2, ΔG°=−3.0±0.2 kcal/mol. Pulsed ICR bracketing experiments support the following electron affinity values: E.A.(SO2)=2.2±0.1 eV and E.A.(C6H5NO2)=2.1±0.1 eV.
Bound trajectories on the H+H2 surface: A test of the adiabatic model for reaction dynamics
Authors: Costley Jennifer , Pechukas Philip
Published: February 2003

The predictions of the adiabatic model for reaction dynamics are compared with a linear stability analysis of the symmetric stretch and with actual trajectories on the Porter–Karplus H+H2 surface. The results indicate the adiabatic model is accurate only for energies near linear stability. Also, classically bound trajectories in the vicinity of the saddle point are observed and analyzed using methods of nonlinear dynamics.
Theory of resonances in three-dimensional chemical reactions. II. Application to a model atom–diatom reaction
Authors: Shoemaker Curtis L. , Wyatt Robert E.
Published: February 2003

The Feshbach projection operator theory is applied to the study of resonances in model 3D atom–diatom chemical reactions. A resonance formalism based on the Feshbach theory along with the computational techniques described previously are used to solve the Schrödinger equation and interpret the numerical results. Resonance positions are formally explained by the interaction of open channel shape resonances and closed channel ‘‘zero-order resonance states.’’ Illustrations are provided by the numerical results. In particular, resonances occurring near channel thresholds are predicted formally and illustrated numerically. In addition, the role of closed channels is illustrated numerically and is explained in the context of the Feshbach theory. This work represents the first application of the Feshbach resonance theory to three-dimensional reactive molecular collisions.
A single coordinate, arrangement channels approach to reactive scattering
Authors: Top Z. H. , Shapiro M.
Published: February 2003

Collinear exchange reactions of three-atom systems below breakup energies are analyzed. It is shown that the use of a single ‘‘collision’’ coordinate in conjunction with arrangement channels formalism, leads to a set of coupled channels equations whose structure is identical to those encountered in nonreactive inelastic collision problems. In addition, boundary conditions or all channels are satisfied in a natural manner, thus essentially eliminating the need for matching of the various wave function components. The applicability of the single coordinate arrangement channels (SCAC) approach to numerical computations is demonstrated for the H+H2 → H2+H exchange reaction on the Porter–Karplus surface.
Radiative transition probabilities of Er3+ in yttria stabilized cubic zirconia crystals
Authors: Greenberg E. , Katz G. , Reisfeld R. , Spector N. , Marshall R. C. , Bendow B. , Brown R. N.
Published: February 2003

Er3+ doped yttria stabilized cubic zirconia crystals were prepared by the skull melting method. From the absorption maxima in the range 330–1700 nm the eigenvectors for Er3+ were calculated. This was followed by the calculation of the transition matrix elements between each pair of electronic levels. The Judd–Ofelt parameters were obtained by fitting the measured oscillator strengths to their predicted values using the above calculated matrix elements. These, combined with the Judd–Ofelt parameters, yielded radiative transition probabilities. Stimulated cross sections of the laser transitions were calculated and possible laser levels indicated.
Structure and spectra of H2O in hydrated β-alumina
Authors: Bates J. B. , Dudney N. J. , Brown G. M. , Wang J. C. , Frech R.
Published: February 2003

The structure and spectra of hydrated Li and Na β-alumina were investigated using neutron diffraction, infrared absorption, and Raman scattering. The dimensions of the hexagonal unit cell of a hydrated Li β-alumina crystal containing 1.55 H2O molecules per unit cell are a=5.591 Å and c=22.715 Å. The oxygen atoms of the water molecules are located in the conduction plane between the mO, and the aBR sites; the protons, located above the below the plane, form bent hydrogen bonds with the O(4) oxygen ions. The HOH bond angle of water in Li β-alumina is 114° and the ‖O–H‖ bond distance is 0.992 Å. Based on polarized infrared spectra, H2O adopts a similar structure and orientation in Na β-alumina. Spectra of absorbed H2O, D2O, and HDO species show that water molecules dissociate in Li β-alumina to form OH− and H(H2O)+n species. No evidence was found for the dissociation of water in Na β-alumina. The absorption coefficients determined for OH− and H2O in Li β-alumina include local field corrections. A large local field anisotropy at the protons of H2O is responsible for the large ratio of the intensities of ν3 and ν1 observed for water in Li and Na β-alumina.
Light particle states in dense gases and mixtures
Authors: Smith Douglas W. , Hernandez John P.
Published: February 2003

The states available to a light particle in models for gases and gas mixtures are investigated. The models are characterized by atoms (molecules) which mutually interact as hard spheres and which interact with a light particle via a short ranged repulsive interaction. The trends in the densities of states for the light particle, the highest energy for localization, and the number of localized states are pursued as a function of the physical parameters—the particle densities of the constituents, the scattering strengths, the packing fraction, and the relative atomic sizes—using a variational technique and numerical computations. Mean field effects and those due to fluctuations may be isolated. It is noted that these type of calculations provide a context within which experiments, such as those for ortho-positronium annihilation rates in gases, may be analyzed.
WKB for coupled equations and virial coefficientsa)
Authors: Larsen Sigurd Yves , Palma Alejandro , Berrondo Manuel
Published: February 2003

Using semiclassical expressions for eigenphase shifts and bound state energies arising from WKB approximations to the solutions of coupled equations, we show that quantum mechanical formulas for the third virial coefficient (restricted to positive potentials) and for the second virial cofficient (with anisotropic interactions) lead to the known classical results when ℏ goes to zero. The procedure can be extended to the case of higher virials.
Positron lifetime studies on phase transitions of phospholipids
Authors: Jean Y. C. , Hancock A. J.
Published: February 2003

Positron-lifetime measurements have been made on the anhydrous crystalline form of DPPC (DL-α-dipalmitoylphosphatidylcholine) and on bilayer aggregates of 40% water–DPPC systems in the temperature range 23 to 63 °C. The lifetimes of o-Ps atoms for 40% water–DPPC systems vary slowly with respect to temperature starting before the pretransition temperature of the system. The increase of o-Ps lifetime is associated with the pretransition as well as with the main transition of the lipid aggregates. The determination of the phase-transition temperature in terms of the onset temperature and the differential lifetime methods is discussed and compared with the known results obtained by the differential-scanning-calorimetry and the positron Doppler-broadening methods.
Molecular reorientation with internal extended rotational diffusion in liquids
Authors: Shin Kook Joe , Chung Doo Soo , Kim Bong Soo
Published: February 2003

An extended diffusion model is applied to describe the internal rotation about the figure axis of a symmetric top molecule whose overall reorientation is undergoing anisotropic rotational diffusion. An explicit analytical expression for the internal correlation time τ(k)int as a function of the angular momentum correlation time τj is obtained. The overall reorientational correlation time τc in the presence of the internal extended diffusional rotation is also obtained analytically as a function of τ(j). This expression is free from any restriction on the range of validity for τj.(AIP)
Transfer of electronic excitation in collisions of metastable argon atoms with nitrogen molecules. II
Authors: Lishawa C. R. , Allison W. , Muschlitz E. E.
Published: February 2003

The rotational state distributions in the product molecules for collisions of metastable Ar with nitrogen are determined. The fluorescence spectra of N2*C→B emitted at the intersection of supersonic molecular beams of the reactant species is analyzed. (AIP)
Energies and volumes of activation for condensed detonating explosives
Authors: Bardo Richard D. , Hall Thomas N. , Kamlet Mortimer J.
Published: February 2003

The results of Bdzil et al1 regarding the shock decomposition of liquid nitromethane are clarified by emphasizing the need for including in addition to activation energies the volume of activation in the analysis and identification of reactions at high pressure. (AIP)
Chemical rates in detonation reaction zones: Determination of temperature and pressure dependence
Authors: Bdzil John B. , Engelke Ray
Published: February 2003

Bardo et al1 have pointed out that at detonalion pressure the volume of activation of a reaction can have an important effect on the reaction rate. It is shown that both the activation energy and activation volume cannot be determine from the experimental data2. (AIP)
Multiproperty empirical anisotropic intermolecular potentials for ArSF6 and KrSF6
Authors: Pack R. T , Valentini J. J. , Cross J. B.
Published: February 2003

Crossed molecular beam measurements of the total differential cross sections (DCS) for the scattering of Ar and Kr by SF6 are reported. Using anisotropic multiparameter M3SV potential forms and the infinite order sudden approximation (IOSA) to do the scattering dynamics, we determine anisotropic intermolecular potentials by simultaneously fitting the DCS, viscosities, and virial coefficients. Substantial anisotropy is required to fit the observed damping of the rainbow oscillations in the DCS. The results are the first good intermolecular potentials for the ArSF6 and KrSF6 interactions.
Comparative conformational analysis of n-paracyclophanes by molecular mechanics
Authors: Carballeira L. , Casado J. , González E. , Ríos M. A.
Published: February 2003

A molecular mechanical method developed by Boyd et al. has been used to calculate optimal geometries, vibrational frequencies, gas phase thermodynamic functions, heats of formation, and strain energies for the n-paracyclophanes for 5≤n≤10. The results for the geometry and strain energies have been compared with those obtained by Allinger et al. for the same compounds, both methods being found to yield similar degrees of agreement with available experimental data.
Nickel and cadmium phosphates in aqueous solution. Cation–anion complex formation and phosphate–H2O interactions
Authors: Caminiti R.
Published: February 2003

Two highly concentrated phosphate solutions have been investigated by an x-ray scattering technique. The experimental correlation functions show that the main peaks for the nickel phosphate solution are at about 2.05, 2.70, 3.5, and 4.15 Å, and, those for the cadmium at about 2.35, 2.75, 3.55, and 4.3 Å. The presence of hydrated nickel and cadmium complexes in octahedral configuration in our solution is in agreement with the peaks found at 2.05 and 2.35 Å. Water–water interactions from the solvent give the main contributions to the peak at about 2.70 Å. The 3.5–3.6 Å peak in the solutions reveals the formation of inner cation–phosphate complexes of average form Z(H2O)6−x(OPO3H2)+2−x(Z=Ni, Cd), in which oxygens from phosphate groups substitute x water molecules of the hydrated Z(H2O)2+6 ions. Least squares refinements of the structure function i(s) are consistent with a structural unit in which about one phosphate tetrahedron shares a corner with one nickel or cadmium octahedron with Z–O–P angle of 136° and 130°, respectively. The large peak at about 4.2 Å in the correlation functions suggests a hydrogen bonded structure outside the inner coordination sphere of Ni2+ and Cd2+. Some indications have been obtained supporting the presence of hydration water around the phosphate groups.
Salt effects on the phase transition of ionic gels
Authors: Ohmine Iwao , Tanaka Toyoichi
Published: February 2003

An ionized acrylamide gel is found to undergo a discrete phase transition in equilibrium volume upon varying the salt concentration in the solution. The salt concentration required for the transition depends strongly on the valency of the positive salt ion added to the solution. In certain cases the concentration at the transition is many thousand times larger for monovalent ions than for divalent ions. A simple theoretical consideration of the osmotic pressure of the ions can explain the phenomenon.
Rates of collision-induced electronic relaxation of single rotational levels of SO2 (Ã 1A2): Quenching mechanism by collision complex formation
Authors: Holtermann Dennis L. , Lee Edward K. C. , Nanes Roger
Published: February 2003

The electronic quenching cross sections (σQ,M) of SO2 excited to single rotational levels (SRL’s) of the ‘‘B’’ band (J′=9, K′=9) and the ‘‘E’’ band (J′=6, K′=6) were measured from the shortening of the fluorescence decay times by the addition of a variety of nonpolar and polar collision partners (M) at room temperature. σQ,M for the B band SRL varied from 32 Å2 for M=He to 863 Å2 for M=CH3NO2. A similar variation of σQ,M for the E band SRL was also observed. Eighteen observed values of σQ,M are compared to the values calculated from various theoretical models of electronic quenching including collision complex formation. Temperature dependence of the electronic quenching cross section for the collision complex is presented.
Charge transfer to a solvent state. VII. Consistency between the calculated and experimental value for the photodetachment threshold energy of solvated electrons in acetonitrile
Authors: Truong Thu Ba
Published: February 2003

The value of the photodetachment threshold energy Eie−s for solvated electrons in doped CD3CN after UV irradiation at 77 K, as determined by stimulated luminescence technique, agrees well with the calculated value which is derived from the electrochemical data and is based on a solute–solvent cage charge transfer model. For both liquid and solid phases the Eie−s seems to be the same. At least for acetonitrile, the present results indicate that solvated electrons can be identified with the solvent polymer—specifically dimer—anion.
Infrared spectral profile of hydrogen fluoride diluted in deuterium fluoride
Authors: Huong P. V. , Cornut J. C. , Desbat B.
Published: February 2003

A special infrared spectral profile with an intense band and two satellites on each side is observed for hydrogen fluoride hydrogen bonded to deuterium fluoride molecules in the solid state. The sidebands are interpreted as the result of a combination of the FH stretching vibration with the stretching and bending modes of the hydrogen bond⋅⋅⋅F–H⋅⋅⋅F. This interpretation is confirmed by the temperature dependence of the intensity of the sidebands. The experimental result also reveals a strong mechanical anharmonicity in the coupling between the high frequency vibration and the low frequency modes and a strong electrical anharmonicity of the hydrogen-bond vibrations.
Analysis of electron spin echoes by spectral representation of the stochastic Liouville equation
Authors: Schwartz Leslie J. , Stillman Arthur E. , Freed Jack H.
Published: February 2003

Motional effects can easily be incorporated into calculated spin echo decay envelopes by idealizing the effects of the pulses and by using the stochastic Liouville equation (SLE) to govern the time dependence of the density matrix between pulses. The spectral representation of the 90°-τ-180°-τ envelope is: Σl,mal,mexp[−(Λl+Λ*m)τ], where Λl is the lth eigenvalue of the SLE matrix, and al,m are products of relevant components of eigenvectors. The long time (large τ) phase memory time T∞m is equal to (Re Λ1)−1, where Λ1 is the smallest eigenvalue. For an axially symmetric g-tensor case in the slow motional region, T∞m/τR≂ 3‖ℱτR‖−1/2, 2‖ℱτR‖−1/3, and 1, for Brownian, free, and jump diffusion models, respectively, with ℱ≡2βeH0(g∥−g⊥)/3ℏ and τR the rotational correlation time. Analogous results hold for nitroxides having nuclear hyperfine tensors. The echo results are compared with simple methods of measuring τR from cw spectra. The overall shape of the echo envelopes in the slow motional region is exp(−bℱ2τ3/τR) for very short times and exp(−2τ/T∞m) for the longer times. Carr–Purcell (CP) sequences suppress the initial exponential in τ3 and increase the phase memory times as a function of decreasing τ. Detailed analysis of CP sequences can provide information on motional model. The analysis of motional averaging of nuclear modulation effects by our method is also given and it is pointed out that this approach may be useful in studying very slow motions. Despite the simplicity of the methods, we are able to approximately fit experimental data from the Tempone/glycerol–water system in both fast and slow motional regions.
Dichromium and trichromium
Authors: DiLella D. P. , Limm W. , Lipson R. H. , Moskovits M. , Taylor K. V.
Published: February 2003

Resonance and preresonance Raman spectra are obtained from chromium-containing argon matrics. Two progressions are assigned to Cr2 and Cr3, the former with optical constants ω″e=427.5 and ω″ex″e=15.75 cm−1 and the latter with ω″e=313 and ω″ex″e=2 cm−1. When not in resonance two other lines at 123 and 226 cm−1 were observed and ascribed to the bending and asymmetric stretching vibration of Cr3, while the vibration forming the progression was taken to be the symmetric stretch. From this, Cr3 is deduced to be a molecule with C2v symmetry but with an apical angle near 60°, suggesting that it is perhaps a Jahn–Teller distorted D3h molecule.
Electron tunneling in cytochrome c
Authors: Chang Albert M. , Austin Robert H.
Published: February 2003

An upper limit for the extinction coefficient of the charge transfer band in the ferrohexacyanide-ferricytochrome c redox couple has been determined from 800 to 1800 nm. We obtain ε≤0.003 M−1 cm−1 between 800–1400 nm, ε≤0.02 M−1 cm−1 between 1400–1800 nm. Prompt transfer of charge due to excitation in the heme absorption bands occurs with a quantum yield of approximately 10−4. Simple vibronically assisted tunneling theories and appropriate choice of highly localized wave functions have been used to show that tunneling theory can give a reasonable fit to all aspects of charge transfer between cytochrome c and iron hexacyanide, including the small value of the charge transfer band extinction coefficient.
Triplet state of the double molecule 2,2′-biquinoline: A study of the phosphorescence, Raman spectra, and ODMR transitions
Authors: Clarke Richard H. , Mitra Pradip , Vinodgopal K.
Published: February 2003

An investigation of the low temperature phosphorescence and the triplet state zero-field ODMR spectra of 2,2′-biquinoline is presented. In order to characterize the normal modes of the molecule the Raman spectrum of the neat crystal at room temperature has been studied and the observed molecular vibrations assigned. The phosphorescence at 1.9 K in mixed single crystal (benzoic acid) and Shpol’skii hosts show a highly structured vibronic spectrum. The spectra reveal that to a good approximation the molecule retains its trans-planar geometry in the triplet state in these matrices at low temperatures. The zero-field transitions of the molecule in its lowest triplet state were investigated by ODMR spectroscopy on the various optically resolvable sites observed in the phosphorescence. Each of the ODMR transitions exhibit two resonances both of which have well-resolved 14N hyperfine and quadrupolar satellites. On the basis of a hyperfine analysis and the frequencies of the resonances the existence of two close lying triplet states (unresolved in the phosphorescence) was determined. One of these is a localized quinolinelike 3ππ* state while the other possesses a delocalized character.
Charge transfer effects in surface-enhanced Raman scatteringa)
Authors: Adrian Frank J.
Published: February 2003

Surface-enhanced Raman scattering (SERS) due to charge-transfer interactions between the adsorbed molecule and the metal surface is analyzed using the semiempirical Wolfsberg–Helmholz method to relate the molecule–surface interactions and the resulting charge-transfer states to the overlap integrals between the metal conduction-band orbitals and an acceptor or donor molecular orbital of the molecule. Calculations for the model system of ethylene adsorbed on silver, with charge-transfer excitation of an electron from the metal to the antibonding etylene π orbital, show that charge-transfer Raman enhancements of the order of 10 to 1000 are possible if the charge-transfer band is partially resonant with the exciting radiation. Symmetric vibrations usually will be enhanced substantially more than nonsymmetric ones by this mechanism because the vibrational coupling is primarily Franck–Condon rather than Herzberg–Teller. The presence of overtone and combination bands in charge-transfer-enhanced Raman spectra is also possible.
Brillouin and Rayleigh studies of urea single crystals
Authors: Yoshihara A. , Bernstein E. R.
Published: February 2003

Brillouin and Rayleigh scattering techniques have been employed to study the elastic behavior of single crystals of urea over the temperature range 15–300 K. An extensive investigation of the room temperature elastic constants is presented yielding a complete evaluation of their anistropy. The temperature dependence of these elastic modes along the [001] and near the [110] directions is followed to 15 K; no evidence of a structural phase transition has been found. Rayleigh scattering experiments reveal a correlation time in the ms range and an intensity behavior that are temperature dependent but show no anomalies as a function of temperature for a number of directions in the crystal. It is found that scattering intensity and correlation time are caused by the modulation and driving of defects by an external periodic applied stress pulse. Neither the correlation time nor the intensity behavior supports the conclusion that urea undergoes a structural second order phase transition in the temperature range 15–300 K.
Photolytic spectroscopy of simple molecules. IV. Prompt and delayed photolysis of equilibrium mixtures of Cs2, Cs2Kr, and CsKr producing Cs(5 2D) at visible wavelengths
Authors: Davanloo F. , Lee F. W. , Collins C. B.
Published: February 2003

This report belongs to a series concerned with the correlation of photolysis bands observed in electronic transition spectra of simple molecules with their dissociation products. In this work a time-delayed, double resonance technique was used for the study of the state selective photolysis excited at visible wavelengths in a thermal equilibrium distribution of populations of Cs2, Cs2Kr, and CsKr existing at 523 K in the presence of 0.132 amagat Kr. Two independently tunable dye lasers were synchronously pulsed, the first being used to dissociate the constituents of the sample along the various possible channels and the second, delayed pulse being used to identify the products by exciting them selectively into easily detected Rydberg states. The time between photolysis and detection could be varied, starting from a value too short to permit collisional mixing or radiative cascading of the products. Particular attention was paid to the photolytic production of the fine structure components of the second electronically excited state of cesium 5 2D. Not only were the prompt sources from dissociation and predissociation of excited states of CsKr and Cs2Kr confirmed, but new kinetic channels for delayed photolysis were found. Over the visible wavelength range examined in these experiments two delayed processes for the production of Cs(5 2D) atoms were characterized. One appeared to proceed through the intermediate production and dissociation of CsKr(7pΠ) having a lifetime of the order of 100 ns under these conditions. The other seemed to involve a newly observed metastable molecule persisting in the medium for times of the order of 1 μs. It was tentatively identified as Cs2(1Δu) and represented a relatively high level of energy storage.
The vibrational distribution of HgBr (X 2Σ) molecules formed by photodissociation of HgBr2 at 193 nma)
Authors: Cheung Nai-Ho , McGarvey John A. , Erlandson Alvin C. , Cool Terrill A.
Published: February 2003

Laser-induced fluorescence excited from the HgBr (B 2Σ–X 2Σ) bands has been used to determine the vibrational distribution of HgBr (X 2Σ) photofragments of the photodissociation of HgBr2 at 193 nm. The fraction of HgBr molecules initially formed in the B 2Σ state was determined to be 60+15−10%. The remaining 40+10−15% of molecules directly formed in the HgBr (X 2Σ) ground electronic state constitutes an important channel for photodissociation at 193 nm.
Two-photon excitation spectroscopy of a substituted all-trans hexatriene (iso-tachysterol). Spectroscopic assignments of the low-lying 1‘‘1B
u*+’’ and 2‘‘1A
g*−’’ ππ* states
Authors: Pierce Brian M. , Bennett James A. , Birge Robert R.
Published: February 2003

The two-photon excitation spectrum of the substituted all-trans hexatriene, iso-tachysterol, is taken in EPA (77 K). Comparison of this spectrum with the one-photon absorption and fluorescence spectra indicate that the system origin of the 2’’ 1A*−’’g state lies slightly below the 1’’ 1B*+’’u system origin in EPA (77 K). (AIP)
Ground state of the He2+2 molecular ion computed with density functional techniques
Authors: Castro Miguel , Keller Jaime , Ventura Oscar N.
Published: February 2003

Total energy calculations are reported for He2+2 ground state, using the cellular multiple scattering Xαβ method. (AIP)
Photovoltaic properties of Au–merocyanine–TiO2 sandwich cells. II. Properties of illuminated cells and effects of doping with electron acceptors
Authors: Skotheim T. , Yang J.-M. , Otvos J. , Klein M. P.
Published: February 2003

Photocurrent generation in thin films of a merocyanine photosensitizing dye sandwiched between a TiO2 single crystal doped n type and an Au overlayer has been studied using photovoltaic techniques. A theoretical model was developed to explain the observed photovoltaic properties. The model assumes that the principal route for the formation of charge carriers is via singlet excitons diffusing to the merocyanine–TiO2 interface followed by dissociation of the excitons into electron–hole pairs, the electrons being injected into the TiO2 conduction band and the holes into the merocyanine. The model also incorporates field dependence of the quantum efficiency for charge generation. An exciton diffusion length of 79 Å was determined by analyzing the short circuit action spectra using the theoretical model developed. The low fill factor of 0.35 for these cells was attributed to the field dependence of the quantum efficiency and the high series resistance of the undoped merocyanine films. Doping the merocyanine films with iodine was found to increase both the dark conductivity and the steady state photoconductivity, the latter by as much as a factor of 5. This resulted in a quantum yield of 12% for a 500 Å thick film and an increase in the fill factor to 0.44 giving a monochromatic power conversion efficiency of 0.4% at 520 nm. The carrier generation in iodine doped films is shown to result from a bulk process, possibly involving collisions between singlet excitons and acceptor–hole complexes resulting in activation out of the bound states formed by the charge-transfer complex. The quenching of excitons in the immediate vicinity of the metal surface was studied by monitoring the photoconductive response of a 200 Å merocyanine film with varying thickness of perylene sandwiched between the metal and the merocyanine. Perylene was shown to be able to transport the photoexcited holes from the merocyanine to the Au electrode. The quantum efficiency for photocarrier production increased to a maximum of 21% for a 750 Å thick perylene layer.
Electronic polarizabilities of Tl+, Ag+, and Zn2+ ions estimated from refractive index measurements of TlNO3, AgNO3, and ZnCl2 melts
Authors: Iwadate Y. , Kawamura K. , Murakami K. , Igarashi K. , Mochinaga J.
Published: February 2003

Refractive indices of TlNO3, AgNO3, and ZnCl2 ionic melts were measured by a goniometer method using visible light at nine wavelengths. The refractive indices of these pure melts were represented conveniently as functions of both temperature and wavelength by means of a two-dimensional least squares method. According to the obtained formulas, the refractive indices were extrapolated to infinite wavelength so that the electronic polarizabilities of Tl+, Ag+, and Zn2+ ions in each pure melt were evaluated in terms of the Clausius–Mossotti equation to be 4.16, 2.07, and 0.78 A3 at 420 °C, respectively. It was made clear even in the molten state, by correlating the electronic polarizabilities of ions with the ionic radii, that the electronic polarizabilities were unequivocally governed by the electron configuration as well as being affected by the ionic radii.
An approximate adsorption isotherm for physical adsorption. I. Lattice gas
Authors: Woodbury George W.
Published: February 2003

The matrix method of statistical mechanics has been used to obtain an approximate adsorption isotherm for a lattice gas in the presence of a wall which interacts with adjoining sites. The excess number adsorbed per surface site has the form [ρII(z′)−ρIII(z)](1 +∂ ln α/∂ ln z), where the densities ρII and ρIII are two- and three-dimensional (bulk) functions of activity z; α is defined by ρII(α2z)=ρIII(z); and z′ =z⋅α⋅exp(−βεB). Here, εB is the interaction energy of a particle with the wall. Surface viral coefficients were calculated as a test of the theory. For nearest neighbor lattice gases, the first and second coefficients are exact. The third coefficient is exact in the special case of a hard wall, and it is also exact for a hard core gas with coordination number 12 in three dimensions and 6 on the surface layer (corresponding to the geometry of the closest packed spheres). The isotherm was also applied to the continuum model of hard spheres against a hard wall. Virial coefficients indicate results slightly inferior to scaled particle theory.
The quantal collision integrals and transport coefficients of dilute gaseous spin-polarized hydrogen and its admixtures with the isotopes of helium
Authors: Lim T. K.
Published: February 2003

The collision integrals and transport coefficients of spin-polarized hydrogen H↑ and its admixtures with the isotopes of helium are calculated with representative Lennard-Jones interatomic potentials at temperatures below 2 K. Diffractive features are predicted for these systems which are attributable to their extreme quantal characteristics.
Crystal and molecular structure and ESR spectra of the 1:1 salt 5-(1-butyl)phenazinium (NBP)-2,2′-(2,3,5,6-tetrafluoro-2,5- cyclohexadiene-1,4-diylidene)-bispropanedinitrile (TCNQF4)
Authors: Metzger Robert M. , Heimer Norman E. , Gundel Dieter , Sixl Hans , Harms Ralf H. , Keller Heimo J. , Nöthe Dietrich , Wehe Dieter
Published: February 2003

The title compound C28H17F4N6, Mr=513.48, crystallizes in the monoclinic space group P21/c, with a=10.972(2) Å, b=17.557(3) Å, c=13.523(4) Å, β=111.88(2)°, V=2417.36 Å3, z=4, and dc=1.411 Mg m−3. Final refinement yielded residuals of R=0.056 and Rw=0.046. The structure consists of (NBP+)2 and (TCNQF−4)2 dimers stacked in a DDAA sequence along the c axis. The NBP+ and TCNQF−4 ions are planar, with interplanar distances of 3.54(2) Å for a donor pair and 3.15(3) Å for an acceptor pair. The angle between the NBP+ and TCNQF−4 planes is 15.8°. In the ESR experiments, two equivalent species of thermally activated Frenkel triplet spin excitons (TSE), with differently oriented fine structure tensors, are observed. They are located on two TCNQF4 molecular pairs of different orientation. A motion of the TSE in the b direction can be excluded. Additional S=1/2 lines are due to immobile doublet spins on TCNQF−4 radical ions.
The phase behavior of two thiol esters (1̄2̄ S5 and 1̄4̄ S5)
Authors: Gane P. A. C. , Leadbetter A. J. , Tucker P. A. , Gray G. W. , Tajbakhsh A. R.
Published: February 2003

Two examples have been prepared and studied of a class of thiol esters which have been reported to show a new type of smectic phase (smectic X). The structures have been characterized by x-ray diffraction and each compound is found to have a hexagonal B type of phase in which the layers show a strong ripple modulation and a monoclinic G type of phase (smectic X) in which the molecules retain a pseudohexagonal packing and the tilt angle is about 10°. Both types of phase are believed to be essentially crystalline, but the details of the stacking in the G phases have yet to be established.
Dielectric relaxation of poly(vinyl acetate)
Authors: Mashimo S. , Nozaki R. , Yagihara S. , Takeishi S.
Published: February 2003

Dielectric relaxation measurements of undiluted and diluted poly(vinyl acetate) PVAc have been made at temperatures 288<T<366 K over an extremely wide frequency range from 1 μHz to 150 MHz. The complex permittivity can be described quantitatively by the Havriliak–Negami equation ε*=ε∞+Δε[1+(jωτ0)β]−α, 0<α, β≤1. It has been found that the parameter α is given by a linear equation of dipole moment ratio g as α=1.09–0.91g. This observation suggests that α is connected closely with local chain conformations. On the other hand, β is nearly constant ∼0.87 above the glass transition temperature and is independent of effect of the diluent. This suggests that the constant value of β is an inherent characteristic of the relaxation spectrum of PVAc.
The long time properties of diffusion in a medium with static traps
Authors: Grassberger Peter , Procaccia Itamar
Published: February 2003

We investigate the long time behavior of diffusion controlled absorption by randomly distributed static traps without resorting to perturbative calculations. The main idea is that the long time behavior is governed by motions in large trap-free cavities whose probability of occurrence is small but finite. The main result is that in d dimensions, the particle density decays asymptotically slower than any exponential, according to an exp[−td/(d+2)] behavior. This and other predictions are verified with numerical simulations.
Disk plasma oscillations
Authors: Gersten Joel I.
Published: February 2003

Two-dimensional disks of electrons on the surface of a semiconductor are shown to possess a set of discrete oscillation frequencies whose magnitudes depend on the size of the disk as well as on the electron areal concentration and the dielectric properties of the substrate.
A quasiclassical trajectory test for a potential energy surface of the Li+HF reaction
Authors: Alvariño J. M. , Casavecchia P. , Gervasi O. , Laganà A.
Published: February 2003

A three-dimensional quasiclassical trajectory study of the Li→HF→LiF+H reaction has been performed on a recently proposed analytical potential energy surface (PES) fitted to ab initio points. The results of the calculations are compared with the experiment. Previous related work on a semiempirical PES is noted.
Integral elastic-scattering of Kr+ and Xe+ ions in collision with He atoms
Authors: Inouye H. , Tanji-Noda K.
Published: February 2003

Integral elastic-scattering cross sections in collision with He atoms were measured for Kr+ and Xe+ ions with kinetic energies in the range 0.5–3.0 keV formed under various source conditions. Variation of source gas compositions and methods of ion formation had no effect on the cross sections. A possible explanation of the results is that the population distributions of the ions (2P3/2 and 2P1/2) produced in the ion source are quite similar.
Geminate charge recombination in the photoionization of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) in various solvents
Authors: Choi H. T. , Sethi D. S. , Braun C. L.
Published: February 2003

The photoionization of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) dissolved in n-hexane (HEX), 2,2,4-trimethylpentane (TMP), and tetramethylsilane (TMS) is studied using measurements of single-photon photoconductivity. Quantum yields for free carrier production—extrapolated to zero applied field—are reported for the energy range 4.4–7.5 eV. The applied electric field dependence of the quantum yields is measured up to fields approaching 2×107 V/m and interpreted via Onsager’s theory of geminate recombination. The low-field, slope/intercept predictions of the theory are obeyed quantitatively for HEX and TMP as solvent but fail by 25% for TMS. Various distribution functions for the separations of geminate pairs are used to generate predicted field dependence curves, which are compared with the high-field data. A broad distribution of thermalization lengths is definitely required to fit the TMP and TMS data, but the TMS result is suspect because of the observed failure of Onsager theory in that solvent. Thermalization lengths generally increase with increasing photon energy. Estimates of the photoionization (geminate pair) quantum yield are also made. For TMP, the geminate pair quantum yield exhibits maxima at 5.8 and 6.9 eV.
Optical thickness effects in kinetic measurements using chlorine atom resonance fluorescence
Authors: Linevsky M. J. , deHaas N.
Published: February 2003

The production of known concentrations of chlorine atoms by the laser photolysis of Cl2 allows the effect of the optical thickness on fluorescent intensity and base-line chlorine atom decay rates to be evaluated. A simple absorption model leads to an average cross section of (2.8±0.3)×10−13 cm2 for the chlorine resonance transitions in the 134–140 nm region and a correction factor to the observed pseudo-first-order decay constant equal to [(2X0/eX0−1)−1]1/2, where X0 is the initial optical thickness.
Mechanisms of atom-exchange reactions in rare gas atom–diatom collisions: Kr+NeAr, Ar+ArKr, Kr+Ar2, Xe+Ar2
Authors: Raff L. M. , Thompson Donald L.
Published: February 2003

Atom-exchange and dissociation reaction cross sections, angular distributions, and product-energy distributions have been computed for the Kr+NeAr, Kr+Ar2, and Xe+Ar2 van der Waals reactions using Monte Carlo quasiclassical trajectories. Angular and product-energy distributions were also computed for the Ar+ArKr atom-exchange reactions. Detailed collision mechanisms are suggested to explain the cross section ratios for the atom-exchange branching for the two reactions. The trajectory results indicate that the branching ratio is the result of a competition between statistical factors, which tend to favor the more exothermic pathway, and mechanistic factors which tend to favor abstraction of the lighter atom of the reactant diatom through a stripping mechanism.
Ab initio dipole moment functions for the X 2Σ+ and B 2Σ+ states of AlO
Authors: Lengsfield B. H. , Liu B.
Published: February 2003

The dipole moment function for the X 2Σ+ state of AlO has been determined by a convergent sequence of MCSCF and CI calculations. It is nearly constant between R=3.0 and 4.0a0 because of a gradual transition from Al+O− to Al++O−−. This leads to a small vibrational band oscillator strength of f01=(4.0±3.0)×10−7. Several MCSCF models were tested for their ability to describe the charge transfer process, and the best model was used to study the B 2Σ+ state AlO.
A theoretical determination of the electron affinity of methylene
Authors: Feller David , McMurchie Larry E. , Borden Weston Thatcher , Davidson Ernest R.
Published: February 2003

Large basis set configuration interaction calculations yield an electron affinity of 0.42 eV for CH2(3B1). Application of an empirical correction, based on the known deficiencies of the basis set and CI method in atomic calculations, suggests that this estimate should be increased to approximately 0.63 eV. This provides futher evidence in favor of a reinterpretation of the photoelectron spectrum work of Zittel et al., which indicated an electron affinity of only 0.210 eV while giving a 3B1–1A1 energy gap of 19.6 kcal/mol.
The EPR spectrum of Fe(CO)−5 in a single crystal of Cr(CO)6
Authors: Fairhurst S. A. , Morton J. R. , Preston K. F.
Published: February 2003

An anisotropic EPR spectrum observed at 20 K in γ-irradiated single crystals of Cr(CO)6 doped with Fe(CO)5 is ascribed to the radical anion Fe(CO)−5. Measurements of the g-, 57Fe-, and 13C-hyperfine tensors clearly show that the species is an acyl radical Fe(CO)−4CO in which the unpaired spin is principally located in Fe 3dz2 or 3dx2−y2 and in an sp2 hybrid of the unique carbon atom C(1). The Fe–C(1)−O(1) moiety is bent and its plane lies close to the ac crystallographic plane of Cr(CO)6.
The microwave spectrum, dipole moment, and barrier to internal rotation of 3-methyl-2-butenenitrile
Authors: Durig J. R. , Li Y. S. , Rizzolo J. J.
Published: February 2003

The microwave spectrum of 3-methyl-2-butenenitrile was investigated in the frequency range of 18.0 to 39.0 GHz, and the spectrum which has been obtained is characteristic of that of a nearly prolate rotor. Only a-type transitions were observed and R-branch assignments have been made for the ground vibrational state, as well as three vibrationally excited states. The rotational constants in the ground vibrational state were determined to be: A=8379.36±0.66, B=2184.87±0.01, and C=1769.96±0.01 MHz. With seven reasonably assumed structural parameters, a diagnostic least-squares adjustment was used to fit the three rotational constants, and the five remaining structural parameters were obtained: cis, r(C–CH3)=1.503±0.024 Å; trans, r(C–CH3)=1.504±0.029 Å; cis, ∢C=C–CH3=120.6±0.1°; trans, ∢C=C–CH3=120.3±0.1°; and ∢C=C–CN=124.4±0.1°. The dipole moment components were determined from the Stark effect to be ‖μa‖=4.59±0.11 D, ‖μb‖=0.40±0.07 D, and ‖μt‖=4.61±0.13 D. Splittings due to the coupling of internal rotation of the cis methyl group with the overall rotation of the molecule were observed in one of the vibrational satellites, and a subsequent analysis yielded a barrier of 790 cm−1 (2.26 kcal/mol) for the cis methyl group. All of these results are compared to similar quantities in some corresponding molecules.
Molecular theory of curvature elasticity in nematic liquids
Authors: Gelbart William M. , Ben-Shaul Avinoam
Published: February 2003

We extend the generalized van der Waals theory to the case of aligned nematic liquids which are subjected to curvature (i.e., “splay’’, “twist’’, and “bend’’) deformations. The Helmholtz free energy is written as an explicit functional of both the orientational distribution f(Ω) and the spatial variation n̂(R) of the director. The entropy contribution is dominated by the packing statistics of hard anistropic cores and is evaluated by the “y’’ expansion developed earlier to treat liquid-density repulsive reference systems. The energy contribution involves a mean field averaging of the angle-dependent pair attractions, but with explicit allowance made for the excluded volume correlations associated with the impenetrability of the molecular hard cores. Numerical evaluations of the elastic constants are presented for a range of hard core sizes and shapes and of dispersional strengths and anisotropies. The “energy’’ and “entropy’’ contributions are found to be of comparable magnitude, each dominated by terms which go as the square of the usual “P̄2’’ order parameter. But P̄2P̄4 contributions are also significant, accounting for sometimes sizable differences between the splay and bend constants. In particular, the relative magnitudes of these two elastic constants are shown to depend sensitively on the size and shape of the molecular hard core and polarizability. The temperature variations of the elastic constants are similarily accounted for. Finally we derive several recent formulations of curvature elasticity as special cases of the present generalized van der Waals approach.