bluuebunny/crossref_metadata_2025 huggingface dataset:
The fourth order diagrammatic MB-RSPT calculations of the correlation energy of ten electron systems
Authors: Urban Miroslav , Hubac̆ Ivan , Kellö Vladimír , Noga Jozef
Published: February 2003

The aim of this work is to analyze the correlation energy of the 10-electron systems Ne, HF, H2O, and NH3, using the diagrammatic many-body perturbation theory up to the fourth order. The second and third order contributions are included fully. In the fourth order, attention was directed to the detailed analysis of the inter-relation of contributions which arise from all double excitations, from the renormalization term as well as from quadruple excitations which are due to non-EPV contributions from quadruple excitations diagrams. The connections with other methods are also discussed.
Vacuum–ultraviolet (147 nm) photodecomposition of 1,1,2-trichloro-2,2-difluoroethane
Authors: Yano T. , Tschuikow-Roux E.
Published: February 2003

The 147 nm photolysis of CF2ClCHCl2 has been investigated at 25 °C as a function of reactant pressure, conversion, and nitric oxide as additive. In the absence of NO the observed reaction products are CF2CHCl, CF2CCl2, and the diastereomers of (CF2ClCHCl)2. At constant reactant pressure the quantum yields of the olefin decrease with increasing conversion and there is a corresponding increase in the quantum yield of the C4 product. For fixed values of conversion the olefin quantum yields decrease with increasing reactant pressure and approach limiting values at ∼100 Torr. The addition of NO completely suppresses the formation of the chlorofluorobutanes, while it enhances the olefin quantum yields at higher conversion. These observations are interpreted in terms of reactions of chlorine atoms which result either directly (by near simultaneous expulsion of two Cl atoms), or via the dissociation of an excited Cl2* molecule produced by molecular elimination in the primary process. Chlorine atoms abstract hydrogen from the parent or add to the product olefins. These processes provide the principal source of halo–ethyl radicals in the system. The addition reaction leads to chemically activated radicals with a mean lifetime of τ?0.8×10−8 sec which is commensurate with RRKM-theory predictions. The addition of nitric oxide provides a competing channel for chlorine atom removal by way of their NO-catalyzed recombination. The functional dependence of the olefin quantum yields with conversion in the absence and presence of NO suggests that the major fraction of the principal product, CF2CHCl, derives directly from a primary process, while CF2CCl2 is formed via both, the molecular elimination of HCl and from radical precursors. The limiting quantum yields of CF2CHCl and CF2CCl2 are found to be φ0?0.68 and φ0′?0.19, in the absence of NO, respectively, and φ0,NO?0.56 and φ′0,NO?0.087 in the presence of NO. The extinction coefficient for CF2ClCHCl2 at 147 nm and 25 °C has been determined: ε= (1/PL) ln(I0/It) =404±40 atm−1 cm−1.
Incubation times in the multiphoton dissociation of polyatomic molecules
Authors: Yahav Giora , Haas Yehuda , Carmeli Benny , Nitzan Abraham
Published: February 2003

The incubation period revealed in the multiphoton dissociation of molecules by intense infrared lasers is discussed. It is found experimentally that large excess of added foreign gas affects the incubation period to a much smaller degree than the overall yield. A rate equations model is presented, including both the laser intensity and collisional effects. Exact numerical solution is compared with a simple analytical approximation, based on the passage time moments method. Agreement with experimental results is quite satisfactory, indicating that the role of collisions in the case discussed (tetramethyldioxetane dissociation) is primarily vibrational relaxation of excited molecules.
Molecular orbital theory of cooperative effects in an interrupted chain of hydrogen bonds
Authors: Del Bene Janet E.
Published: February 2003

Ab initio calculations are reported to determine the cooperative nature of hydrogen bonding in open sequential trimers. The calculations were performed by using STO-3G basis set. (AIP)
A multiple pulse proton NMR study of α-oxalic acid dihydrate
Authors: Berglund Bo , Vaughan Robert W.
Published: February 2003

The chemical shift tenson for the water molecule in α-oxalic acid dihydrate was measured using a multiple pulse, NMR technique. The high resolution proton speclia were recorded at room temperature.(AIP)
Entropy of phase transitions in a binary mixture of liquid crystals
Authors: Swift Jack , Mulvaney Brian J.
Published: February 2003

The recently observed behavior of the entropy of the nematic–smectic C transition in a binary liquid crystal mixture is explained by a simple model which relates the transition entropy to the tilt angle of the smectic planes.(AIP)
Comparative study on the convergence of the nuclear spin–spin coupling constant in the H–D molecule
Authors: Rayez-Meaume M. T. , Achard F. , Hoarau J.
Published: February 2003

A numerical estimate is given of the improvement in the determination of nuclear spin–spin coupling constant of HD molecule, using the method of Schwartz? The variation perturbation technique employing the Fermi-contact operator is discussed.(AIP)
Electrical conduction in silver thiocynate
Authors: Tennakone K. , Ariyasinghe W. M.
Published: February 2003

Silver thiocynate is found to be a electrical conductor having a room temperature (30°C) resistivity of 13.7×106 ohm-cm. The temperature variation of the resistivity of silver thiocynate is studied.
Recent analysis of accommodation coefficients of light atoms
Authors: Garcia N. , Celli V. , Manson J. R.
Published: February 2003

Recent calculations on the accomodation coefficient are described. It is shown that as the temperature decreases, T→0, the accomodation coefficient is larger than zero. (AIP)
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o calculation of spin–orbit coupling constant in diatomic molecules
Authors: Trivedi H. P. , Richards W. G.
Published: February 2003

The spin–orbit coupling constant is calculated for several diatomic hydrides and oxides in the Hartree–Fock framework. No approximations have been made. The effect of the two center two electron integrals on the calculated results is discussed.
Effects of a finite coherence on impurity trapping of quasi-free excitons and electrons
Authors: Funabashi Koichi
Published: February 2003

The effects of weak scattering by the medium on the rate of impurity trapping for partially coherent excitons and electrons are studied in 1-D and 3-D lattices. It was found that the cage effect does not alter the asymptotic (t→∞) rate expression for 1-D, but modifies the asymptotic rate in 3-D in such a way that the rate is inversely proportional to the diffusion coefficient in the region of large coherence length and becomes proportional to the diffusion coefficient when the coherence length becomes of the order of the lattice constant. Relevant experiments are discussed.
Nonequilibrium time dependent theory of hot atom reactions. I. Model calculations
Authors: Shizgal B. , Fitzpatrick J. M.
Published: February 2003

The chemical kinetics of hot atoms is studied with a two temperature moment method of solution of the Boltzmann equation. Nonequilibrium time dependent results obtained from the numerical integration of the moment equations are compared with the results obtained with the assumption that the hot atoms are distributed in accordance with a Maxwell–Boltzmann velocity distribution function. The range of validity of the steady state temperature theory is investigated in detail. Extensive calculations of the time evolution of the hot atom velocity distribution function, number density and temperature are presented. These calculations involve the variation of several system variables such as cross sections and mass ratios.
Inelastic scattering calculations in polyatomic systems using an a
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o intermolecular potential energy surface. II. Rotational energy transfer in CO2–H2 collisions
Authors: Sathyamurthy N. , Raff L. M.
Published: February 2003

Results of quasiclassical trajectory studies of CO2 (Ji=0, 16, 30)–H2 (Ji=0, 2) collisions at Etot=0.1, 0.2 eV are reported in terms of state-to-state integral inelastic cross sections, first moments of energy transferred in excitation and de-excitation processes and C values which characterize the variation of the rotational suprisal with energy gap between initial and final states. The magnitude of the first moments are shown to increase with increasing translational energy Ti and with the initial rotational state JiCO2. The value of C decreases with increasing Ti. It is found to be strongly dependent upon JiCO2 but depends only weakly upon JiH2. Comparison of our results with those of Preston and Pack for the CO2–He and CO2–Ar systems reveals that although the qualitative dependence of σ−, σ+, σ, 〈ΔE−〉 and 〈ΔE+〉 upon Ti and JiCO2 is the same in all three systems, there are quantitative differences which reflect the atomic (molecular) size of He, H2, and Ar. Furthermore, the suprisal parameter is distinctly different for all three collision partners (decreases in the order H2, He, Ar) even when the ’’linear sum rule’’ holds, contrary to an earlier proposal by Procaccia and Levine that the surprisal parameter C would be independent of the nature of the collision partner.
The entropy of liquid water from the random network model
Authors: Sceats Mark G. , Rice Stuart A.
Published: February 2003

The random network model (RNM) allows a very simple, yet quantitative estimate of the entropy of liquid water and amorphous solid water. The vibrational and proton disorder contributions are calculated using the prescriptions of the RNM described elsewhere, while the remaining configurational term is calculated using phase space arguments and an appeal to the third law of thermodynamics. The agreement between predicted and observed values of the entropy of the liquid at 0 and 100 °C is excellent.
Theory of molecular dispersion forces and the molecular pair potential under the aspect of liquid crystal ordering
Authors: Schröder H.
Published: February 2003

Dispersion forces play a dominant role in molecular systems, if electrostatic and induction forces are negligible. This is especially the case for strongly anisotropic particles as mesogenic molecules are. For such molecules the representation of the mutual interaction as that one between two pointlike particles is not sufficient. When the molecular dimensions become comparable to the average separation due to the density of the system, the internal molecular structure becomes important, as well as the geometry of the molecules does. On the basis of a general expression for the dispersion self-energy of a molecular system, an effective pair potential which can be held responsible for orientational ordering in liquid crystals is derived, following a hierarchy of necessary approximations. For this purpose a nonlocal polarizability is introduced which allows a treatment of the molecules as spatially extended particles with internal structure. It is shown that anisotropy effects exhibited by the pair potential in general have two different sources, namely form anisotropy and optical anisotropy. The form anisotropy is simply caused by the geometrical arrangement of charges building the ionic skeleton. The optical anisotropy as well as optical activity is due to intramolecular correlation which the polarizability accounts for. The pair potential is formulated with the aid of irreducible molecular tensors, which carry all information about molecular properties and allow a classification according to molecular symmetries.
Transmission and reflectance phonon spectra of corundum single crystals
Authors: Cataliotti Rosario
Published: February 2003

Single crystals of corundum were studied in transmission and reflectance with infrared polarized radiation. All the one-phonon and two-phonon processes were assigned. Additional features, present in the region 7–50 μm, were confirmed as being due to the mixed states of the polariton dispersion.
Superconductivity in graphite–potassium intercalation compounds
Authors: Sano Mizuka , Inokuchi Hiroo , Kobayashi Mototada , Kaneiwa Shinji , Tsujikawa Ikuji
Published: February 2003

Superconductivity transitions were studied in golden graphite−potassium compounds. The transition temperature changes were studied by adding hydrogen to the compound. (AIP)
The application of an effective nuclear charge model to the prediction of valence force constants in planar and pyramidal XY3 molecules. II.
Authors: Ohwada Ken
Published: February 2003

The valence force constants of planar and pyramidal XY3 molecules are calculated on the basis of the effective nuclear charge model previously developed. The calculated results are compared with the experimental force constants which are determined by the normal coordinate analysis. The agreement between the calculated and experimental force constants is moderately good for most molecules under investigation. This implies that the effective nuclear charge model is useful for the prediction of approximate valence force constants in more complicated polyatomic molecules.
Infrared multiphoton decomposition: A comparison of approximate models and exact solutions of the energy-grained master equation
Authors: Barker John R.
Published: February 2003

The approximate ’’thermal’’ model and ’’continuum’’ model have been compared to exact calculations, and neither gives satisfactory results. In particular, the thermal model is based on an inaccurate and unphysical approximation to the correct molecular density of states, as well as a restrictive expression for the absorption cross sections. As an alternative to the approximate models, the exact stochastic method gives exact results and can be implemented using small computers or programmable pocket calculators. The results obtained from this method are exact and precision depends only upon the number of ’’trajectories’’ calculated. It was discovered that the yield versus fluence results from exact numerical integration of the master equation approximately conform to a cumulative log–normal distribution function in decomposition time or fluence. Thus, to a good degree of approximation, computed yield versus fluence results can be expressed simply in terms of a mean and a dispersion parameter. This suggests that the use of probability graph paper and the log–normal distribution function may prove to be a useful means for the presentation and analysis of experimental and computed data. Moreover, deviation from the log–normal distribution may indicate that the simple master equation is not a sufficient description of the experimental results.
Gaussian basis sets for the rare earths
Authors: van Piggelen H. U. , Nieuwpoort W. C. , van der Velde G. A.
Published: February 2003

Extended Gaussian basis sets have been calculated for the neutral and trivalent rare earth atoms. The characteristics of these sets, which are available on request, are reported. The quality of the wave functions is discussed on the basis of a comparison of a number of calculated properties with those of numerical Hartree–Fock calculations. The agreement shown is very satisfactory.
Observations of emissions due to N2+(B 2Σu+), N2(C 3Πu), and N2(C′ 3Πu) molecules in the yellow nitrogen afterglow
Authors: Ung A. Y.-M.
Published: February 2003

Emissions due to N2+(B 2Σu+), N2(C 3Πu), and N2(C′ 3Πu) molecules as well as O(1S) and N(2P) atoms were observed in the yellow nitrogen afterglow. The effects of pressure, transit time between the discharge and the observation vessel, temperature, N-atom concentration, added quencher, and impurities on the emission properties of these species were also studied. Possible excitation mechanisms for these emission systems are discussed.
Localized vs delocalized description of photoelectron spectra
Authors: Sawatzky G. A. , Lenselink A.
Published: February 2003

A model calculation is presented to investigate the conditions under which an excitation of a molecule or solid should be treated in a symmetry restricted or localized manner. The three important quantities in the model, the hole delocalization energy, the response time of the polarizable medium, and the interaction between the hole and the polarizable medium are included as variables. The exact solution is compared to approximations, and ranges of the three above-mentioned quantities are found for which the symmetry restricted or localized solutions yield the best results. It is found that the localized solutions with symmetrization afterwards yield the best results for a surprisingly large range of the three interactions and seems to be the better solution even for describing valence orbital photoelectron spectra.
Trajectory studies of O+H2 reactions on fitted a
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o surfaces. II. Singlet case
Authors: Schinke Reinhard , Lester William A.
Published: February 2003

Classical trajectory calculations of cross sections for the reaction O(1D)+H2(1Σg+;ν′,j) →OH(2Π;ν′,j′)+H(2S) have been performed for collision energies 0.25 kcal/mole ⩽E⩽5.0 kcal/mole using three analytic fits to a recently computed ab initio potential energy surface. The various potentials differ only slightly from each other in the long range region of the entrance channel and are equivalent in all other regions. The differences are of the same order as the assumed error in the ab initio surface. The three potentials have been probed to study the influence of these differences on the scattering results. The total reaction cross sections are sensitive to these changes, especially at very low collision energies, which is the energy regime that determines the total reaction rate constants at room temperature. Since the uncertainty in the available experimental rates is even larger, the validity of a theory–experiment comparison of reaction rate constants is questionable. The vibrational product distribution differs only slightly from the statistical prior distribution indicating that most of the trajectories via the deep well corresponding to the equilibrium geometry of H2O. With increasing energy, the barrier of almost 1 kcal/mole in the collinear geometry can be surmounted, so that gradually more reaction occurs by abstraction and the distribution becomes less statistical. This is even more pronounced, if no barrier is found in the potential surface. This result agrees qualitatively with the findings of Whitlock et al. but not with the study of Sorbie and Murrell where a highly inverted vibrational distribution was obtained using an empirical energy surface. The rotational product distribution is highly nonstatistical with a narrow peak at high rotational quantum number, as found previously in other trajectory studies. The product angular distribution is symmetric with respect to ϑ=90° as expected from reactive trajectories which proceed via a long-lived complex. With increasing energy the barrier to the collinear pathway can be surmounted, such that the angular distribution is slightly shifted towards the backward direction.
Structural phase transition and disorder in tetrathiafulvalenium chloride [(TTF)Clx]
Authors: Williams R. , Lowe Ma C. , Samson S. , Khanna S. K. , Somoano R. B.
Published: February 2003

(TTF)Clx, x=0.67 and 0.70, is a quasi-one-dimensional organic conductor with a room temperature conductivity of ∼ 150 Ω−1 cm−1. At room temperature the structure is tetragonal and consists of chains of uniformly spaced, eclipsed TTF molecules surrounding channels occupied by chloride ions, which form a disordered structure. The chloride substructure becomes ordered and the TTF substructure undergoes a phase transition from tetragonal to monoclinic symmetry at ∼250 °K. The angle β of the monoclinic phase increases continuously as the temperature is decreased from 245 ° to 19 °K. The electrical conductivity shows a sharp decrease at the phase transition which is suggestive of the formation of commensurate charge density waves in the monoclinic phase.
Matrix isolation infrared and Raman spectra of binary and mixed group II B fluorides
Authors: Givan A. , Loewenschuss A.
Published: February 2003

Infrared and Raman spectra of all MF2 and MFX molecules (M=Zn, Cd, Hg; X=Cl, Br) and the infrared spectrum of the fluoroidide HgFI isolated in solid krypton at 20 °K are reported. The MFX species were formed in a vapor mixture of the appropriate MF2 and MX2 dihalides, vaporized, at different temperatures, from separate compartments of a double-oven crucible. The spectra are the first experimental evidence for the existence of the molecular fluorohalides. All three fundamentals of the MF2 molecules and the two stretching mode frequencies of the MFX molecules are assigned. Harmonic force constants are evaluated and isotope effects are used to discuss their geometry. Thermodynamic functions are tabulated for the binary difluorides.
Infrared laser multiple photon ionization
Authors: Avouris Phaedon , Chan I. Y. , Loy M. M. T.
Published: February 2003

The production of ions as a result of the interaction of intense CO2- laser pulses with a variety of organic molecules is reported. The laser frequency dependence of the ionization follows closely the linear infrared absorption spectrum of the respective molecule. The extent of ionization depends very strongly on laser energy fluence. The ion-production process is found to have a strongly collisional character. Various possible mechanisms of laser-induced ionization are discussed, and evidence is presented favoring laser-induced chemi-ionization.
Studies of shear waves and translation–rotation coupling of liquid nitrobenzene in neat liquid and in carbon tetrachloride solution by depolarized Rayleigh scattering
Authors: Lempert Walter , Wang C. H.
Published: February 2003

High resolution depolarized Rayleigh spectra of nitrobenzene in CCl4 have been measured at several concentrations and temperatures. All spectra display a shear wave dip at the zero frequency. They are found to fit well to the form of a two-variable theory in the low frequency regions studied. The various parameters such as the collective molecular reorientation rate Γ, the shear wave relaxation rate q2νs, and the dynamic coupling coefficient R are obtained as a function of temperature and concentration. While the R value is found to be independent of temperature, it changes significantly with the nitrobenzene concentration. Moreover, the R value for pure nitrobenzene is found to be greater than 0.5, higher than any reported previously for a low viscosity liquid. The τRay values are found to follow the classical Stokes–Einstein relation, with zero intercept. The pair orientational correlation affects the Rayleigh relaxation time.
Diffusion modulated donor–acceptor energy transfer in a disordered system
Authors: Auerbach Roy A. , Robinson G. Wilse , Zwanzig Robert W.
Published: February 2003

This mainly theoretical paper treats, in a disordered system, the time-dependence of irreversible donor–acceptor energy transfer in the limit of low acceptor concentrations. The transfer is modulated by diffusion of energetic donor molecules relative to acceptors. Though donor dynamics will be touched upon, the main emphasis of the paper is on the risetime dynamics of the concentration of energetic acceptors in the nanosecond and subnanosecond regimes following excitation of donors with a brief pulse of light. It has been found that the fastest acceptor risetimes occur in the limit of slowest donor diffusion. The reason for this apparent anomaly, which reverses intuition, is that diffusion aids attainment of a steady state, and the steady state donor distribution gives rise to slower acceptor risetimes than transient contributions. The result has been verified in some preliminary experiments where quasidonor diffusion, caused by donor–donor energy transfer, has been retarded by dilution with inert molecules. Faster risetimes also result from shortening the range of the donor–acceptor transfer interaction. A very striking effect on acceptor risetimes can come about from the presence of local order of donors surrounding an acceptor. Providing the peak of the donor radial distribution function is sufficiently close to the acceptor compared with a characteristic transfer distance, acceptor risetimes can be substantially speeded up. Because of the sensitivity of acceptor dynamics to local order and transfer behavior, the possibility is raised of using the acceptor as a ’’probe’’ for these effects in future picosecond and subpicosecond experiments.
QMSCC calculations on the thermal quenching of the uranate luminescence in uranium-doped tungstates with perovskite structure
Authors: Bleijenberg K. C. , Breddels P. A.
Published: February 2003

QMSCC calculations have been performed on the thermal quenching of the uranate luminescence in perovskite-type compounds with compositions A2BW0.997U0.003O6(A2B=Ca2Mg, Sr2Mg, Ba2Mg, Ba2Ca, Ba2Sr or Ba2Ba). Using a three states SCC model the luminescence quenching could be described quantitatively. The model was checked for Ba2MgWO6–U by investigating the luminescence properties of Ba2MgWO6–Eu and Ba2MgWO6–Eu, U.
Experimental evidence that mutual and tracer diffusion coefficients for hemoglobin are not equal
Authors: Hall Richard S. , Johnson Charles S.
Published: February 2003

Photon correlation spectroscopy (PCS) has been used to measure the mutual diffusion coefficient Dm for unliganded hemoglobin in the concentration range 0.86 to 15.7 g/dl. The result corrected to water at 20 °C is Dm=Do[1−(0.0057±.0003)c] where Do= (6.75±0.05) ×10−7 cm2/s and c is in units of g/dl. It is shown that Dm can be used with the phenomenological theory of diffusion to predict the tracer diffusion coefficient Dt and that the predictions agree with the results of diaphragm cell measurements [Keller, et al., J. Phys. Chem., 75, 379 (1971)]. In contrast to this, diaphragm cell measurements of Dm do not agree with PCS measurements, with open capillary and free diffusion experiments [Kitchen, et al., J. Polymer Sci. Sym. No. 55, 39 (1976)], or with ultrafiltration measurements [Probstein, et al., J. Phys. Chem. 83, 1228 (1979)]. The evidence indicates that Dm≠Dt for hemoglobin, and that diaphragm cell measurements of Dm are not reliable for proteins. (AIP)
The laser induced fluorescence spectrum of trapped CD+
Authors: Grieman Fred J. , Mahan Bruce H. , O’Keefe Anthony
Published: February 2003

Preliminary results are presented on the radiative lifetime of the 0,0 vibrational band of the A−X transition. (AIP)
The effect of pressure on refractive index of liquids, calculated up to 100 MPa
Authors: Richard Alfred J.
Published: February 2003

The refractive index of benzene, carbon tetrachloride, n-hexane, n-heptane, n-octane, and n-dodecane has been calculated at 298 K and 632.8 nm for pressures up to 100 MPa. Agreement with the experimental data and recent theory, for benzene and carbon tetrachloride was in the fourth decimal place of refractive index.
Infrared–microwave double resonance spectroscopy of DCCCHO using the 3.51 μm He–Xe laser
Authors: Takami Michio , Suzuki Masao
Published: February 2003

Microwave spectrum of propynal-d1, DCCCHO, was investigated in the v2=1 excited state by an infrared–microwave double resonance method. The 3.51 μm He–Xe laser was magnetically tuned over ±0.1 cm−1 and used as an infrared radiation source. Eighteen pure rotational transitions in the excited state were observed and assigned. The observed spectrum was found to be badly perturbed by other vibrational states. In addition to the transitions within the v2=1 state, ten microwave transitions from the v2=1 to other vibrational states were observed. These intervibrational microwave transitions were discussed in relation to vibrational quasicontinuum states of polyatomic molecules.
Microwave rotational spectrum of methyl azidoformate
Authors: Kakar Ramesh K. , Quade C. Richard , Lwowski Walter , Wilde Richard E.
Published: February 2003

The R branch, a dipole microwave rotational spectra of four isotopic species of methyl azidoformate have been assigned over the range 18–40 GHz. The assignment includes vibrational satellite series as well as the vibrational ground state transitions. The methyl barrier to internal rotation as determined from the E–A doubling data for the first excited state of the methyl torsion is V3=400±10 cm−1. The methyl barrier for the first excited state of another vibrational mode, methyl ground state, is determined to be V3=370±10 cm−1. Only one conformation, that with the azido group and the methyl group cis to the C=O group, was found to be measurably populated at room temperature. A partial vibration–rotation anaylsis has been performed with extremely limited success.
Quantum theory of coherent Raman scattering by optically active isotropic materials
Authors: Bjarnason Jón Örn , Andersen Hans C. , Hudson Bruce S.
Published: February 2003

The fully quantum mechanical theory of coherent Raman scattering developed in a previous paper [J. Chem. Phys. 70, 4130 (1979)] is extended to include magnetic dipole and electric quadrupole interactions. This is done for radiation of arbitrary polarization. The intensities for the scattering of right and left circularly polarized light from an isotropic sample of optically active molecules are shown to differ slightly. The difference, in many cases, is expected to be of the order of 10−3 times the coherent Raman intensity. This is of the same order as circular intensity differentials observed in spontaneous Raman spectra. Because of a high signal to noise ratio as well as other advantages, however, it is proposed that coherent Raman scattering may be superior to the spontaneous process for studying Raman optical activity.
Rayleigh and Raman optical activity: An analysis of the dependence on scattering angle
Authors: Andrews D. L.
Published: February 2003

The differential scattering of left- and right-handed circularly polarized light by optically active molecules is now well established in both theory and experiment. In this paper the dependence of Rayleigh and Raman differential scattering intensities on the angle of scattering is analyzed. It is demonstrated that an experimental study of this angle-dependence should enable magnetic dipole and electric quadrupole effects to be separately evaluated, and provide a useful method for testing electronic and vibrational wave function calculations. Results for circular differential Raman scattering are given in terms of irreducible tensors, allowing the selection rules for polarized and depolarized Raman bands to be applied in a straightforward way. It is also shown how the validity of the two-group model for chiral systems can be experimentally assessed.
The use of CNDO in spectroscopy. XV. Two photon absorption
Authors: Marchese Francis T. , Seliskar C. J. , Jaffé H. H.
Published: February 2003

Two−photon absorptivities have been calculated within the CNDO/S-CI molecular orbital framework of Del Bene and Jaffé utilizing the second order time dependent perturbation equations of Göppert–Mayer and polarization methods of McClain. Good agreement is found between this theory and experiment for transition energies, symmetries, and two-photon absorptivities for the following molecules: biphenyl, terphenyl, 2,2′-difluorobiphenyl, 2,2′-bipyridyl, phenanthrene, and the isoelectronic series: fluorene, carbazole, dibenzofuran.
The mean spherical approximation and effective pair potentials in liquids
Authors: Madden William G. , Rice Stuart A.
Published: February 2003

The mean spherical approximation (MSA) generalized for direct application to fluids with continuous intermolecular potentials. It is shown that, if the intermolecular potential is separated into a purely repulsive core and a weak tail as suggested by Weeks et al., then the generalized MSA includes the strengths of the Percus–Yevick (PY) and hypernetted-chain (HNC) approximations with few of their weaknesses. At liquid state densities and temperatures the MSA pair correlation function is much more accurate than the corresponding PY and HNC pair correlation functions for the Lennard-Jones (12–6) potential. The MSA equation may be inverted to give a semiempirical theory for deriving the pair potential from experimental x-ray diffraction data. It is argued that the resulting pair potentials for liquid Na and liquid K are substantially more reliable than others previously obtained from x-ray data.
Brownian dynamics study of a polymer chain of linked rigid bodies. II. Results for longer chains
Authors: Pear M. R. , Weiner J. H.
Published: February 2003

As an extension of a previous paper, computer simulation results for a polymer chain of linked rigid bodies are presented for chains with between four and fifteen bonds. Previous theoretical results for a three-bond chain are found by computer simulation to apply to longer chains. In particular, a Fixman potential for an N-bond chain is developed as the sum of three-bond Fixman potentials, and transition state rates measured in computer simulation for a four-bond chain compare reasonably well with the theory for a three-bond chain. A further study of the motion of the free end of a chain with one end fixed indicates correlation effects diminish the possibility of a ’’whipping motion’’ of the chain end.
Comparison of reactive and inelastic scattering of H2+D2 using four semiempirical potential energy surfaces
Authors: Brown Nancy J. , Silver David M.
Published: February 2003

Collisions between hydrogen and deuterium molecules are examined using quasiclassical dynamical trajectory calculations with the intermolecular field specified by four semiempirical potential energy surfaces. Three of the surfaces are calculated within the valence bond model with semiempirical evaluation of the integrals, and the fourth is the London type. Various degrees of agreement are observed between these four surfaces and ab initio results. The trajectory calculations are performed at high system energies to permit the possibility of reactions. In addition to nonreactive collisions, four reaction paths are found on each surface with the product species 2H+D2, H2+2D, HD+H+D, and 2HD. The results are analyzed to determine the effect of surface properties on reaction probabilities, average final state properties of the molecules and average final state energy distributions. Dynamical results are found to be strongly dependent on surface characteristics.
O2(b 1Σg+) production and deactivation following quenching of O(1D2) in O3/O2 mixtures
Authors: Amimoto S. T. , Wiesenfeld J. R.
Published: February 2003

The production of oxygen atoms, O(3PJ), following deactivation of photolytically generated O(2 1D2) via was monitored using time-resolved atomic absorption analysis in the vacuum ultraviolet. The measured overall rate constant for O2(b 1Σg+) deactivation by O3, 1.8±0.2×10−11 cm3 molecule−1 s−1, and total yield of ground state O(3PJ) following quenching of O2(b 1Σg+) by O3, 0.61±0.06, are in good agreement with a previous study. These results suggest that the reaction of O2(b 1Σg+) with O3 may play a role in fixing the overall density of oxygen atoms in the stratosphere.
A theoretical study on the water structure for nucleic acids bases and base pairs in solution at T=300 K
Authors: Clementi Enrico , Corongiu Giorgina
Published: February 2003

Monte Carlo simulations are presented for the bases A, C, G, T, and U enclosed in a cluster of forty water molecules and for the base pairs A–T, G–C, and A–U enclosed in a cluster of fifty water molecules. These computations are carried out at a simulated temperature of 300 K. The importance of the temperature effect is shown by carrying the MC simulation for adenine at T=100 K. The intermolecular interactions are computed with atom–atom pair potentials obtained from quantum-mechanical calculations on the water–water and water–base complexes. The identification of the positions and orientations for the water molecules in the first hydration shell is obtained from hydrogen and oxygen atoms probability distribution maps. Relations between the water structure around the bases and base pairs and the water structure in the major and minor groove of B-DNA double helix are preliminarily presented.
Semiclassical calculation for collision induced dissociation. III. Restricted two dimensional Morse oscillator model
Authors: Rusinek Isak
Published: February 2003

A semiclassical procedure previously used for collinear CID calculations is applied to the perpendicular collisions (2D, no rotation, zero impact parameter) of a Morse homonuclear diatomic molecule and an atom, interacting via an exponential repulsive potential. Values of the dissociation probability (Pdiss) are given as a function of total energy (Et) and initial vibrational state (n1=0,1,3,5) for a system with three identical masses. The results are compared with the Pdiss previously reported for an identical one dimensional system. We find: (a) quasiclassical Pdiss that are a good approximation to the semiclassical ones, if CID is classically allowed, (b) vibrational enhancement of CID, and (c) energetic thresholds for dissociation similar to the ones found in the collinear case.
Strong Tl–Xe excimer band emission via electron beam initiated discharges in TlI and Xe mixtures
Authors: Schlie L. A. , Jusinski L. E. , Rathge R. D. , Hamil R. A. , Drummond D. L.
Published: February 2003

Stable glow discharges have been produced by an electron beam ionizing pulse (20 nsec) in TlI/Xe mixtures having densities of approximately 1–4×1016/cm3 of TlI and 1019–1020/cm3 of Xe in order to assess their potential as a medium for a high power Tl–Xe excimer laser system. The use of this thallium salt in place of the pure Tl metal enabled the required operating temperature to be lowered from 820 to 440°C. These e-beam initiated discharges are the first type conducted in metal vapors at these high operating temperatures. The electron beam preionized discharges (60 cm3) produced a factor of 40 enhancement in the Tl–Xe band emission relative to the pure electron beam pumping. Peak power loadings of 3 kW/cm3 were attained for approximately 600 nsec at 2 A/cm2 current densitites for E/N values up to 3×10−17 V⋅ cm2. Higher peak power loadings (31 kW/cm3) were achieved for shorter pulsewidths without the onset of glow-to-arc transitions. Very strong emission was observed from only the Tl atomic lines and the Tl–Xe bands centered at approximately 6000, 4300, and 3650 Å. No emission from excited TlI was ever observed. Monitoring the discharge current gave a TlI attachment rate constant of 1.8×10−10 cm3 sec−1 that was very insensitive to the applied E/N. Available kinetic information is used to develop a plausible model for the dominant kinetic processes involved. The possibility of utilizing the close energy resonance of the Tl and I metastable states to produce lasing at 1.315 μ is discussed. In addition, engineering details of the test cell construction compatible with the required high operating temperatures are presented.
Strong Tl–Hg band emission at 4590 and 6560 Å via electron beam initiated discharges in TlI and Hg mixtures
Authors: Schlie L. A. , Jusinski L. E. , Rathge R. D. , Hamil R. A. , Drummond D. L.
Published: February 2003

Very strong Tl–Hg excimer band emission at 4590 (B 2Σ1/2–X1/2) and 6560 Å (B 2Σ1/2–X3/2) has been observed from stable glow discharges produced in TlI and Hg mixtures via a 20 nsec electron beam pulse. Hg densities up to 5×1019/cm3 and peak TlI densities of 1017/cm3 were used at a maximum operating temperatures of 550°C. Peak power loading of 34 kW/cm3 at 7 A/cm2 and E/N values up to 3×10−16 V⋅ cm2 have been achieved in a 60 cm3 active volume. The discharges are much more stable and repeatable than similar discharges in TlI and Xe mixtures. The Tl–Hg band emission totally dominates the spectrum that also exhibits Tl and Hg atomic emission plus weaker HgI (B 2Σ1/2–X1/2) emission at 4430 Å. A plausible kinetic model for the dominant processes is presented and the potential of this systme as a TlHg laser at 4590 and 6560 Å are discussed.
Molecular dynamics study of two dimensional and adsorbed microclusters
Authors: Weissmann Mariana , Cohan Norah V.
Published: February 2003

Two dimensional and adsorbed microclusters of six, seven, eight, and nineteen rare gas atoms are studied by the molecular dynamics method. The behavior of all these clusters as a function of temperature presents two distinct regions: a low temperature regime typical of the vibrations in a solid and a high temperature or liquid one in which the clusters remain condensed but the particles move in very different ways, depending on the number of atoms and the shape of the cluster. Systems having close shells of neighbors of a central atom (those of seven and nineteen atoms) also show a transition region and at higher temperatures other properties typical of the liquid state. The effect of a weak interaction with a surface becomes important at high temperatures where the clusters evolve to three dimensions as some of the atoms move away from the surface.
Efficient trajectory simulation methods for diffusional barrier crossing processes
Authors: Northrup Scott H. , McCammon J. Andrew
Published: February 2003

The kinetics of many chemical and biochemical processes in solution are governed by the rate at which systems diffuse across energy barriers separating reactant and product states. These rates can be determined by computer simulation of diffusional trajectories by Brownian dynamics techniques. Conventional simulations, in which systems are dynamically unconstrained, sample barrier crossing events inefficiently since the system spends most of its time in low-energy configurations. New techniques, termed activated and branching-activated trajectory methods, are explored which circumvent this problem by constraining trajectories to the barrier top region. The accuracy and efficiency of these new methods are tested by application to a one-dimensional model chemical system. Activated and branching-activated results for the rate constant are found to converge 10 to 25 times more rapidly than the conventional first passage time method, even for a modest barrier height of 2kBT. Application to more realistic multidimensional systems is discussed in an appendix.
A stochastic approach to the theory of intramicellar kinetics. I. Master equation for irreversible reactions
Authors: Hatlee Michael D. , Kozak John J.
Published: February 2003

We develop in this paper a stochastic master equation to describe the dynamics of a certain class of micellar kinetic processes—those in which the reactants are confined to the interior (or, perhaps, the immediate vicinity) of the micellar assembly. At the outset, the problem is formulated in some detail in order to display the theoretical factors involved in accounting both for chemical reaction and physical diffusion (exit/re-entry of solubilized reactants). Then, for definiteness, we confine our attention to the study of irreversible intramicellar reactions where complete compartmentalization of reactants is assumed. For this case, chemical processes of molecularity 1, 2, and 3 are considered, and a solution to the resulting master equation for each process is obtained. Our theoretical predictions are compared with experimental results reported by the groups of Grätzel and Singer and nearly exact, quantitative agreement with the data is found.
The glass transition of BeF2: A Monte Carlo study
Authors: Brawer Steven
Published: February 2003

A Monte Carlo study of the structure, equilibration, and glass transition of a model of BeF2 is described. The system consists of 54 ions in a box of side 8.949 Å. The Ewald sum is approximated by the spherically symmetric part and the repulsive potential is of exponential form. The resulting fluid is motionally hindered at low temperature and has structural features generally attributed to BeF2. The glass structure is found to be a three-dimensional continuous random network of BeF4 tetrahedra linked at the vertices with a broad distribution of Be–F–Be angles. The glass contains a small concentration of defects in the form of one- and threefold fluorine and threefold beryllium. The concentration of such defects in the fluid can be quantitatively related to the rate of structural rearrangements. At the glass transition temperature, diffusion ceases, the specific heat decreases suddenly and other averages show changes in slope as a function of temperature. A structural explanation is given for the change in specific heat. An argument is presented that, near the glass transition temperature, the same time-averaged ionic motions observed in this study will also be observed in the true time-dependent motion of the fluid (such as would be computed in a molecular dynamics simulation). The ionic motion both above and below the glass transition exhibits a long-term memory. Even after an ion moves a distance of 1 Å, there is a large probability of its returning to its starting place. The implications of this memory for studying diffusion and equilibration are pointed out. The glass shows the existence of localized structural rearrangements, in which a few ions undergo periodic hopping motions over 1–2 Å distances during times for which the majority of ions execute (many) simple vibrations of 0.1–0.2 Å displacement about their equilibrium positions. These latter motions do not lead to macroscopic diffusion.
Resonance CARS and CSRS line shapes of Ni(II)-octaethylporphyrin
Authors: Igarashi R. , Adachi Y. , Maeda S.
Published: February 2003

CARS and CSRS of Ni(II)-octaethylporphyrin in benzene solution have been measured in the resonance condition with the first visible absorption (Q) band. The line shape behavior of some nontotally symmetric vibrations has been investigated by changing the pump frequency ω1 in the absorbing region, with the particular elaboration on 1308 cm−1 (A2g) line, which shows the inverse polarization and is most strikingly enhanced in ordinary resonance Raman. The observed line shapes were remarkably different between the CARS and CSRS by the common pumping frequency ω1. The whole result has been consistently interpreted in terms of the vibronic theory of Raman intensity, on the basis of semiclassical perturbation theory by Lotem et al. The effect of concurrent resonances of ω1 and ω3 (or ω2) has been demonstrated in a definite manner.
HTFFR kinetics studies of the Ge/N2O chemiluminescent reaction
Authors: Fontijn Arthur , Felder William
Published: February 2003

The reaction Ge(43P0,1,2)+N2O→GeO(X 1Σ+, a 3Σ+, b 3Π1, A 1Π)+N2 (1) has been studied in a high-temperature fast-flow reactor (HTFFR) at temperatures from 475 to 920 K and pressures from 3 to 55 Torr. The following Ge removal rate coefficients were obtained (in units of ml molecule−1 s−1): k1Ge(3P0)=(1.7±0.3)×10−11exp[−(470±60)/T]; k1Ge(3P1)=(8.1±1.3)×10−12exp[(120±40)/T]; k1Ge(3P2) = (1.2±0.4)×10−11exp[−(200±100)/T]. While these k are considerably higher than those observed in the Sn/N2O reaction, the photon yields, Φ, are two to three orders of magnitude lower and, because of the resulting low chemiluminescence intensity, a complete kinetic expression could be obtained only for Φ(a): Φ(a)=(8.2±6.2)×102{1.3×10−4+0.4×10−21[Ar]}{1+3.3 ×10−15[N2O]}−1exp[−(2800±400)/T]. At [Ar] = (3 to 4)×1017 ml−1, we obtain Φ(b) = (0.23±0.13)(1+2.6×10−15[N2O])−1exp[−(4900±200)/T]; Φ(A) = (0.033±0.025)(1+2.8×10−16[N2O])−1exp[−(3800±380) /T]. At 545 K the following Stern–Volmer coefficients, τkQN2O, for quenching by N2O were obtained (in ml molecule−1), GeO(a): (3.3±0.9)×10−15; GeO(b): (2.6±1.4)×10−15; GeO(A): (2.8±1.4)×10−16. It is shown that reaction (1) is not an elementary reaction and a more detailed mechanism is proposed which, similar to that of Sn/N2O, involves preferential reaction through the 3P1 state and intermediate formation of a GeO* reservoir state from which the emitting GeO states are formed collisionally. The trends in the Group IVA element/N2O reaction kinetics are discussed.