bluuebunny/crossref_metadata_2025 huggingface dataset:
Single rotational level fluorescence quantum yields, radiative lifetimes, and nonradiative decay rates of S1 D2CO and H2CO(Ã 1A2, 41): Rotational dependence
Authors: Shibuya Kazuhiko , Fairchild Paul W. , Lee Edward K. C.
Published: February 2003

A large number of rotational levels in the 41 (v4′ = 1) manifold of S1 formaldehyde were excited in a multipath absorption/fluorescence cell using a pulsed dye laser. Fluorescence decay times (τfD) of D2CO were measured for a number of rotational levels at 10.8 mTorr so that the apparatus could be calibrated for the measurement of fluorescence quantum yields (ΦfH) of many rotational levels of H2CO at varying pressures (1–120 mTorr). For 10.8 mTorr D2CO, the average values of τfD and ΦfD were 4.8±0.3 μsec and 0.66±0.07, respectively. The zero pressure values of ΦfH for H2CO varied randomly from 0.0063 for J′ = 13, K′ = 7 (Erot = 570.9 cm−1) to 0.32 for J′ = 2, K′ = 2 (Erot = 37.1 cm−1), due to a random variation of the nonradiative decay rates. The J′-population averaged value of ΦfH in a given K′ manifold 〈ΦfH(J′)〉K′ shows a trend to decrease with the increase in the K′ quantum number for K′ = 2–6, but becomes nearly constant for K′ = 6–10. The (J′, K′)-population averaged value of ΦfH is 〈ΦfH(J′, K′)〉 = 0.033 and the average value of radiative lifetimes is τrH = 3.3±1.2 μsec for the 41 level.
Vibrational excitation of HF molecules in a nozzle beam by a cw HF laser in an antiparallel coaxial arrangement
Authors: Ellenbroek T. , Toennies J. Peter , Wilde M. , Wanner J.
Published: February 2003

We have demonstrated that a significant fraction (≳14%) of HF molecules in a given rotational state (j = 2) in a nozzle beam can be excited by a cw HF laser beam directed antiparallel to the molecular beam. The excitation, which is thought to occur near the nozzle orifice, was detected indirectly by observing the decrease in the signal on the mass 21 (H2F+) peak due to (HF)2 dimers in a mass spectrometer viewing the beam. The observed dependence of this effect on the laser lines and the measured dimer spectrum reported in this paper both indicate that the excitation of the monomer is the primary process. An indirect heating of the gas by contact with the laser-heated orifice walls could be ruled out by experiments using the v = 2→1 laser lines, which showed a much smaller effect. Thus, the results are consistent with a three-step mechanism: (1) vibrational laser excitation of the monomers, (2) V–V transfer to the dimers, and (3) predissociation of the metastable dimers. Calculations based on this model and a simplified description of the nozzle beam when fitted to the data provide information on the fraction excited as well as on the efficiency of V–V transfer.
A screened potential molecular-orbital calculation of the π-electron system of porphyrin
Authors: Sekino Hideo , Kobayashi Hiroshi
Published: February 2003

The excitation energies and oscillator strengths of the excited states of metal-free porphin were calculated by the screened potential which incorporates instantaneous polarization effects in the molecular Hartree–Fock field. The spectrum of the lowest excited states was reproduced without any use of empirical parameters. The energies of the lowest triplet 1 3B2u and singlet Q states were reproduced fairly well, while the B states were predicted to lie slightly higher than observed.
Ionic adsorption from a primitive model electrolyte—nonlinear treatment
Authors: Carnie Steven L. , Chan Derek Y. C.
Published: February 2003

In order to investigate the effects of both finite ion size and specific adsorption on the electrical double layer, we consider a restricted primitive model elecrolyte against a uniformly charged nonpolarizable surface, in which the ions adsorb on the wall via Baxter’s sticky potential. Wall–ion interactions are treated in the hypernetted-chain (HNC) approximation and bulk interactions are treated in the mean spherical approximation (MSA). In the HNC/MSA, this model does not exhibit any saturation in the adsorbed surface charge density although one can be produced as an artifact of linearization. The expression for the potential of mean force possesses the term previously identified as responsible for the discreteness-of-charge effect, although there is a quantitative difference due to the absence of a low inner layer dielectric constant in our model. Results for the surface potential and distribution functions are presented for the case of anionic adsorption on the surface.
Molecular dynamics simulations of the structure of rare-earth-doped beryllium fluoride glasses
Authors: Brawer Steven A. , Weber Marvin J.
Published: February 2003

We have simulated the atomic structure of a series of rare-earth-doped beryllium fluoride glasses using the molecular dynamics technique. Compositions include unitary BeF2 and CaF2 glasses and binary BeF2–NaF, BeF2–RbF, and BeF2–CaF2 glasses. Results are presented in the form of radial distribution functions and average coordination numbers about the rare-earth and other cations. In addition, by examining conditional probability distributions, we predict unusual structural features of the glasses such as a significant number of Be ions coordinated by five fluorine nearest neighbors, and the presence of F ions with no Be nearest neighbors. It is also found that the average coordination number of all cations, including Be, increases with an increasing amount of modifier. This result has been observed experimentally for oxides. We show that our runs are sufficiently long that the structural results are not due to insufficient equilibration. The relevance of our results to problems of solubility and crystallization are also discussed. The presence of fivefold coordinated Be is expected to have a dominant effect on glass kinetic properties.
Classical description of the polarizability and dielectric constant of monatomic fluids
Authors: Ho/ye J. S. , Stell G.
Published: February 2003

A simple classical description of the dependence of the pair polarizability upon distance for the monatomics is developed through the extension of the authors’ earlier theory of fluctuating polarizability. The result is shown to yield an analytically tractable theory for the dielectric constant of a fluid of such molecules.
Variational theory of phase separation in binary liquid mixtures
Authors: Foiles S. M. , Ashcroft N. W.
Published: February 2003

It is shown that a double Yukawa potential provides a good physical representation for pair potentials in molecular fluids and that its use greatly simplifies variational calculations based on the Percus–Yevick hard-sphere reference system. The calculations show that for this reference fluid the virial hard-sphere equation of state is preferred to the semiempirical Carnahan–Starling expression. The variational procedure is used to calculate the fluid phase diagrams for two binary noble-gas mixtures.
Theory of the interfacial polarization between isotropic and neutral dielectric bodies
Authors: Galatry L. , Gharbi T.
Published: February 2003

It is shown that, in the case of a planar interface between two different uncharged dielectric bodies, a static difference of potential ΔΦ may be expected across the interface. This quantity is calculated by introducing the nonlinear polarization of the bodies by the surface modes previously used by van Kampen et al. in their theory of the van der Waals attraction between two dielectrics. This leads to a result inversely proportional to the third power of the thickness of the gap between the dielectrics. The proportionality coefficient involves the frequency dependent dielectric constant of the bodies as well as a higher order susceptibility describing their nonlinear (quadratic) polarization. This approach is then found to be consistent with the result of a microscopic model involving the summation of the interatomic dispersion dipole moments appearing in couples involving atoms separated by the interface.
Microwave, infrared, and Raman spectra, structures, quadrupole coupling constants, barrier to internal rotation, and vibrational assignment of 1-chloro-2-methylpropene
Authors: Guirgis G. A. , Li Y. S. , Durig J. R.
Published: February 2003

The microwave spectra of (CH3)2CCH35Cl and (CH3)2CCH37Cl have been recorded from 12.5 and 39.0 GHz. a-type transitions were observed and R-branch assignments have been made for the ground vibrational states for both isotopes. The rotational constants were found to have the following values: for (CH3)2CCH35Cl, A = 8400.77±1.18, B = 2258.18±0.02, C = 1818.72±0.02 MHz; for (CH3)2CCH37Cl, A = 8399.31±0.66, B = 2199.93±0.02, C = 1780.73±0.02 MHz. From a diagnostic least-squares adjustment to fit the six rotational constants and with reasonable assumed carbon–hydrogen distances and angles, the following heavy atom structural parameters were obtained: r(C–C) = 1.507±0.013 Å, r(C = C) = 1.355±0.019 Å, r(C–C1) = 1.750±0.019 Å, ∢C–C = C(cis) = 122.20°±4.50°, ∢C–C = C(trans) = 119.39°±1.84°, and ∢CCCl = 124.24°±2.79°. The quadrupole coupling constants for the (CH3)2CCH35Cl molecule were found to have the following values: χaa = −49.2, χbb = 19.5, and χcc = 29.7 MHz. From an analysis of the internal rotational splittings, the threefold barrier for the cis methyl group was found to be 288±5 cm−1 (0.824 kcal/mole). The infrared (3500–50 cm−1) and Raman spectra (3500–10 cm−1) have been recorded for both the gas and solid states. Additionally, the Raman spectrum of the liquid was recorded and qualitative depolarization values were obtained. All of the normal modes have been assigned based on band contours, depolarization values, and group frequencies. Several torsional transitions for the trans methyl group have been observed in the far infrared spectrum of the vapor, and from these transitions a barrier of 745±60 cm−1 (2.14 kcal/mole) has been calculated for the internal rotation of the trans methyl group. These results are compared to the corresponding quantities in similar molecules.
Angle-resolved photoelectron spectroscopy of CS2 and COS measured with synchrotron radiation
Authors: Carlson Thomas A. , Krause Manfred O. , Grimm Frederick A. , Allen John D. , Mehaffy David , Keller Paul R. , Taylor James W.
Published: February 2003

Angle-resolved photoelectron spectra of CS2 and COS have been taken as a function of photon energy. From these data the angular asymmetry parameter β has been obtained for the five valence orbitals of CS2 and the three least tightly bound valence orbitals of COS. Monochromatized polarized photons produced from synchrotron radiation have permitted studies from near ionization threshold up to 29 eV. The experimental data were used to evaluate previous theoretical calculations which employ a multiple scattering method. The agreement for the least tightly bound orbitals of the nonpolar CS2 molecule were good. There were some problem areas, particularly with the more tightly bound orbitals of CS2 and the polar molecule COS. However, when previous results for CO2 are taken together with the results on CS2 and COS, the calculations in general give a reasonable account of the experimental β values and suggest that the multiple-scattering method will be useful for the study of differential cross sections of polyatomic molecules.
Quasiclassical dynamics of light+heavy–heavy and heavy+heavy–light atom reactions: The reaction X+F2→XF+F(X = Mu, H)
Authors: Connor J. N. L. , Laganà A. , Turfa A. F. , Whitehead J. C.
Published: February 2003

The effect of mass variation on the dynamics of exoergic chemical reactions has been investigated using one and three dimensional quasiclassical trajectories. The reactions studied are the light+heavy–heavy atom reactions X+F2→XF+F(X = Mu, H) and their heavy+heavy–light atom counterparts. For all four reactions, the best extended LEPS potential energy surface No. 2 of Jonathan et al. has been used. Calculations have been performed for the total reaction cross sections, reaction probabilities as a function of impact parameter, product energy disposal, angular distributions, and, for the Mu+F2 and H+F2 reactions, rate coefficients and activation energies. It is found that many features of the reactivity of the three dimensional reactions can be understood in terms of the corresponding one dimensional reactions. The reactivity of all four one dimensional reactions in the threshold region is found to be determined by the heights of their vibrationally adiabatic barriers, which occur in the entrance valley, and not by exit valley properties. Comparison with thermal experimental rate coefficients and activation energies for the Mu+F2 and H+F2 reactions suggests that tunneling is very important for the Mu reaction, and that a potential surface with a different barrier region topology is probably required in order to account for the experimental results.
Laser-induced charge transfer in the HeH+2 and H2+ quasimolecules
Authors: Seely John F.
Published: February 2003

The cross sections for laser-induced charge transfer during the collisions of He+2 and H+ ions with hydrogen atoms are calculated. The electron transfer is into the n = 2 excited levels of the incident ions. Using the exact energy levels and dipole moments of the one-electron diatomic molecule, the cross sections are found to be broad functions of the wavelength of the pumping laser. For a focused laser intensity of 1012 W/cm2 at a wavelength corresponding to the third harmonic of the Nd-glass laser, the calculated charge transfer cross section is greater than 10−15 cm2 for the case of He+2 incident on hydrogen. The photon-induced cross section is largest at low collision velocities where the competing collision-induced reaction is negligible.
Flowing afterflow studies of gas phase magnesium ion chemistry
Authors: Rowe B. R. , Fahey D. W. , Ferguson E. E. , Fehsenfeld F. C.
Published: February 2003

Reaction rate constants have been measured at 300 K for Mg+ ions with O3, HNO3, H2O2, Cl2, CCl4, and Br2, for MgO+ ions with CO, NO, and O3, for MgOH+ ions with HNO3 and H2O2, for MgOD+ ions with D2O, and for MgCl+ ions with CCl4 and HNO3. MgOH+ ions react rapidly with HNO3 to produce NO2+ ions and Mg(OH)2 and hence MgOH+ ions cannot be expected to exist in the stratosphere where HNO3 is abundant. The observed exothermic reactions establish that 1.1<D(MgO+)<3.1 eV, and that the ionization potential of Mg(OH)2 is less than 10.2±0.6 eV and that ΔHf(CCl2 +)<284 kcal mol−1.
A charge flow model for vibrational rotational strengths
Authors: Abbate S. , Laux Leo , Overend John , Moscowitz Albert
Published: February 2003

The valence-optical approach is used to construct a model applicable for the calculation of rotational strengths associated with fundamentals of vibrational transitions. It is shown that the model has the essential property of giving rotational strengths that are independent of the choice of origin.
A study of the reaction of N2+ with SO2 and its dependence on internal energy
Authors: Orth Robert G. , Futrell Jean H. , Nishimura Yukio
Published: February 2003

The reaction of N2+ with SO2 has been studied in a tandem-ion cyclotron resonance mass spectrometer at less than 0.1 eV translational energy as a function of ion source pressure and collision chamber pressure. The internal energy state distribution of the N2+ reactant ions relaxes with increasing N2+/N2 collisions, producing a corresponding change in the branching ratio of the charge-transfer product SO2+ and the dissociative charge-transfer product SO+. With increasing SO2 pressure in the ICR cell, the dissociative charge-transfer channel is quenched. The total rate constant for charge-transfer was determined to be 7.0×10−10 cm3 molecule−1 sec−1; within experimental error, the rate constant is independent of the vibrational excitation of the N2+ ion.
Adsorption of flexible macromolecules. Conformation and dimensions at the θ temperature
Authors: Dejardin P. , Varoqui R.
Published: February 2003

The technique using viscosimetry or flow rate reduction has been used by several investigators to determine the extension from the surface of an adsorbed flexible macromolecule. In this paper, we present a simple interpretation of these measurements. The theory is based on the solution of a modified Navier–Stokes equation which takes into account hydrodynamic interactions for a segment concentration which decreases exponentially with distance from the surface. From the ’’hydrodynamic’’ thickness as a function of molecular weight of polystyrene chains adsorbed onto Pyrex glass at the ϑ temperature, the mean layer thickness as well as the volume fraction in the loop layer is determined.
Second osmotic virial coefficient revisited: Variation with molecular weight and temperature from endothermal to exothermal conditions
Authors: Wolf B. A. , Adam H. -J.
Published: February 2003

Light scattering measurements for six samples of polystyrene (M = 20 400 to 2.5×106) were performed in tert-butylacetate from 0–140 °C. Within this T interval, the second virial coefficients A2 change from negative to positive, pass through a maximum at intermediate temperatures, and get negative again. The M dependence vanishes when A2 = 0 at ϑ+ = 15.5 °C for endothermal, and at ϑ− = 109.5 °C for exothermal conditions. The temperature of athermal behavior increases with M from 42 °C (M = 20 400) to 62 °C (M = 2.5×106). For sufficiently high temperatures A2 grows larger as M is raised, in contrast to the normal situation. There exist strong indications that limM→∞ A2 is generally different from zero, except for theta conditions. The enthalpy part of the second virial coefficient A2,H becomes independent of M at Ξ+ = 31 °C for endothermal solutions and at Ξ− = 90 °C for exothermal. Between these temperatures A2,H decreases as M rises, else it increases. The unperturbed dimensions are the same at ϑ+ and ϑ−. The observations concerning A2(T;M) can be explained theoretically on the basis of the corresponding states principle. For a better understanding of the influence of M, a modified excluded volume treatment is presented; it accounts for the differences in intra- and intermolecular contacts between segments. The interrelation of the chain expansion coefficient and A2 is in agreement with the Zimm–Stockmayer–Fixman equation.
Bimodal rotational quantum state distribution of MgH(X 2Σ+, v = 0) in the reaction of Mg(3s3p 1P1) with H2: Evidence for microscopic branching
Authors: Breckenridge W. H. , Umemoto H.
Published: February 2003

A ’’pump-and-probe’’ technique is employed to determine the initial rotational state distribution of the P1 and P2 branches of MgH. (AIP)
Statistical error in time correlation functions from computer experiments on approximately two-state processes
Authors: Gō Nobuhiro , Kanô Fumiaki
Published: February 2003

Statistical error due to finite time averaging in the calculation of the time correlation function from a computer experiment is analyzed in cases when a record of a computer experiment is approximately a Poisson process. The result indicates that the computer time in units of the main relaxation time can be shorter in these cases by a factor of 2 than in the cases studied by Zwanzig and Ailawadi, i.e., when a record of a computer experiment is approximately a Gaussian process. (AIP)
Millimeter and submillimeter spectra of HCO+ and DCO+
Authors: Sastry K. V. L. N. , Herbst Eric , De Lucia Frank C.
Published: February 2003

Millimeter and submillimeter spectra of HCO+ and DCO+ are reported. (AIP)
Solid state effects in the resonance Raman scattering of [Fe(CN)6]3− as a dopant in Cs2LiCo(CN)6 and Cs2NaCo(CN)6
Authors: Clark H. W. , Swanson Basil I.
Published: February 2003

Resonance Raman spectra have been obtained in the νCN region for pure Cs2MFe(CN)6 and Cs2MCo(CN)6 (M = Li,Na) doped with 10% [Fe(CN)6]3−. The doped systems exhibit a resonance enhancement which follows the 450 nm ligand to the metal charge transfer band for [Fe(CN)6]3− while the pure Cs2MFe(CN)6 salts do not. The enhancement in the doped salts has been attributed to a longer lifetime of the 450 nm electronic state relative to that of the pure salts.
Slow dynamics of entangled polydimethylsiloxane chains observed by proton transverse magnetic relaxation
Authors: Cohen-Addad J. P. , Domard M. , Boileau S.
Published: February 2003

Specific proton magnetic relaxation properties of rotating methyl groups were applied to the observation of the diffusion of long polydimethylsiloxane chains in the molten state. NMR results were interpreted using a freely jointed chain model easily extended to PDMS chains. The magnetization relaxation function was calculated from a multiple step motional narrowing effect associated with normal modes of the polymer chain. Three main features characterize the present NMR study: (i) A NMR submolecule may be defined; it is similar to the average characteristic chain segment determined from viscoelastic measurements. (ii) The terminal chain relaxation time was found to be molecular weight dependent through the zero-shear viscosity only. This result disagrees with the well known Rouse formula; it is in accordance with recent expressions proposed by Doi, Edwards, and Graessley but discrepancies with numerical factors were found. (iii) Although the ’’free draining’’ model used by Rouse to calculate the absolute time scale factor is incorrect, the general shape of the relaxation spectrum associated with this model was found to be correct.
Franck–Condon analysis of the 1 1A
g→1 1B
u absorption in linear polyenes with two through six double bonds
Authors: Granville Mark F. , Kohler Bryan E. , Snow Judith Bannon
Published: February 2003

The vibronic intensity distribution at room temperature and 77 °K of the 1 1Ag→1 1Bu transition for the series of linear polyenes with two through six conjugated double bonds has been measured and analyzed. These inhomogeneously broadened solution spectra can be described reasonably using only two harmonic normal modes of vibration: single and double bond stretches at ∼1200 and ∼1600 cm−1, respectively. Excited state normal coordinate displacements were determined by a least-squares fitting procedure. For both the double and single bond modes the estimated change in bond length upon excitation decreases as the length of the polyene chain increases. The bandwidth of these spectra decreases with increasing polyene length. This is well described by assuming that in solution a range of conformations differing by very small torsions about the terminal single bonds has been frozen in. The Franck–Condon analysis indicates that under these conditions all of the polyenes are approximately planar in the 1Bu state, ruling out the argument that the lack of fluorescence in butadiene and hexatriene is due to the polyene framework being significantly twisted in the lowest energy 1Bu state.
57Fe-Mössbauer studies of the CuxFe3−xO4 spinel system
Authors: Bhaduri Monmatha
Published: February 2003

Mössbauer spectroscopy has been used to examine the effect of increasing copper ion concentration on the iron distribution in CuxFe3−xO4(0⩽x⩽0.9). For x⩽0.37, fast electron exchange among octahedral iron ions occurs as in Fe3O4, suggesting that the itinerant electrons associated with the octahedral Fe2+ ions remain delocalized in the sublattice. At high values of x (x⩾0.59), however, the itinerant electrons become localized in a small fraction of exchange-coupled iron ions. The relative numbers of distinguishable cations making up the complements of the octahedral sites of the copper ferrites are determined.
Piezomodulation spectroscopy of molecular crystals. I. Methods and principles
Authors: Merski J. , Eckhardt C. J.
Published: February 2003

The effects of piezomodulation on the spectra (particularly reflectivity spectra) of molecular crystals for the strong, weak, and no coupling regimes are considered. The stress or strain modulation of the crystal is shown to affect the dispersion energy and exciton resonance interaction. The experimental approach is outlined. Methods of data analysis are described for obtaining differential changes in the real and imaginary parts of the dielectric function, for determining deformation potentials for vibronic transitions, and for applying the Seraphin coefficients. Previous microscopic theory for interaction of excitons with static lattice deformations is adapted for the modulated case. Application of classical dipole theory to model one and two vibronic level systems yields expressions for calculation of the piezomodulated reflection spectrum. Relative contributions to the spectrum are determined for a model polariton stop band by consideration of piezomodulation of the exciton energies, plasma frequency, oscillator strengths, and background dielectric function. Applications of piezomodulation spectroscopy to investigations of molecular and ionic crystals are discussed.
Gaussian basis sets for the transition metals of the first and second series
Authors: Hyla-Kryspin I. , Demuynck J. , Strich A. , Bénard M.
Published: February 2003

Gaussian basis sets consisting of, respectively, (13s, 7p, 5d) and (14s, 8p, 7d) Gaussian functions have been optimized for the transition metal atoms of the first and second series. The optimization criteria and the applicability of these atomic sets for molecular calculations are discussed.
The principle of corresponding states for alkali halides viscosity
Authors: Abe Yoshiyuki , Nagashima Akira
Published: February 2003

The principle of corresponding states has been applied to the viscosity of alkali halide single salts and their binary mixtures. The scaling parameters obtained from the reduced Tosi–Fumi potential were put to use for the reduction of the viscosity values. An empirical universal relationship of η−1∝V⋅T1/2 among the reduced properties η, V, and T was found to be established for alkali halides viscosity. The relationship thus found was further examined for the viscosity of other kinds of liquid, viz., alkali nitrates, liquid metals, hydrocarbons, and rare gases. For either substance, a reasonable conformity was observed.
Structure and stress in spherical microstructures
Authors: Falls A. H. , Scriven L. E. , Davis H. T.
Published: February 2003

An integral theory and gradient theory of inhomogeneous fluid are used to predict the structure of spherical interfaces. The nonlinear integral and differential equations of the theories are solved by using state-of-the-art finite element techniques, coupled with Newton’s method. The numerical method, discussed at some length, is suggested as a potential tool for solving other nonlinear problems of fluid statistical mechanics. Results of integral and gradient theories are compared and found to be in qualitative agreement and, on the strength of this agreement, gradient theory is used to describe and analyze the structure and stress in microscopic spherical drops. Predictions from gradient theory indicate a breakdown of the Young–Laplace equation for drops smaller than about ten molecules wide. However, contrary to the usual estimate of the curvature dependence of surface tension, the surface tension of even very small drops (say, three or four molecules wide) is found to deviate little from the tension of a planar interface.
Study of the tunneling rotations in phase II of solid CH4 with high resolution neutron spectroscopy
Authors: Heidemann A. , Press W. , Lushington K. J. , Morrison J. A.
Published: February 2003

High resolution incoherent neutron scattering experiments were performed to study in detail the temperature dependence and shape of the tunneling spectrum of pure and oxygen-doped CH4 in phase II. The tunnel splittings increase with decreasing temperature below 5 K, in qualitative agreement with a theoretical prediction of Yamamoto et al. A finite linewidth of the tunneling lines of several μeV was observed and is explained by inhomogeneous broadening due to the mixture of nuclear spin symmetry species. A qualitative comparison between the theoretical predictions and the experimental results is presented.
2Σ+ and 2Π states of LiF−
Authors: Hazi A. U.
Published: February 2003

Large and diffuse molecular orbital basis sets have been used to study the electronic states of LiF− arising from the Li+F− asymptotes. The 2Σ+ ground state is bound relative to LiF(X 1Σ+) by 0.33 eV, in agreement with previous calculations. The excited 2Σ+ and 2Π states, which arise from the Li(2P)+F−(1S) asymptote, also remain bound relative to the ground state of LiF as the internuclear distance decreases from 20 to 5a0; however, the corresponding 6σ and 2π orbitals change drastically from a 2p orbital localized on the Li atom to very diffuse ’’dipole’’ states. At R = 2.988a0, the 2 2Σ+ state of LiF− has a binding energy of at least 4.2 meV relative to the neutral molecule. We found no evidence of shape resonances in the electron-scattering continuum of LiF(X 1Σ+), in contrast to previous results obtained with limited basis sets.
Generation of hot and complex charge carriers due to the interaction between excitons and free charge carriers in molecular crystals
Authors: Singh Jai
Published: February 2003

Applying microscopic many-body theory, the consequences of interaction between a free Frenkel exciton and free electron present in molecular crystal are investigated. Two kinds of reactions are possible: (a) a hot electron is created and (b) a complex charge carrier (exciton+electron) is formed. The rate of reaction (a) between singlet exciton and electron in anthracene single crystal is obtained as ∼7×109 sec−1, in agreement with the rate calculated from experiments. The possibility of reaction (b) is attributed to the net attractive potential of interaction between the exciton and electron. Such a potential of interaction is rigorously derived and its quantitative nature is calculated in pure as well as in mixed crystals. It is shown that the complex charge carrier moves throughout the crystal via hopping from one molecule to another. Competitive importance of both reactions (a) and (b) is discussed.
A mass spectrometric study of the vapors above the molten salt systems LiCl–CuCl, KCl–CuCl, LiBr–CuBr, and NaI–CuI
Authors: Bloom H. , Williams D. J.
Published: February 2003

The vapor phase composition over selected fused alkali halide–cuprous halide systems has been examined mass spectrometrically. Second law formation enthalpies and entropies have been calculated for the mixed species identified by ionization efficiency curve analysis to be LiCu2Cl3, Li2CuCl3, KCu2Cl3, LiCu2Br3, Li2CuBr3, NaCu2I3, Na2CuI3, and NaCuI2.
Generalized theory of the reaction field due to a charge or dipole in a prolate or oblate ellipsoidal cavity surrounded by a dielectric
Authors: Felder Clifford E.
Published: February 2003

Formulas are derived for the reaction potential and field due to a fixed charge or point dipole located anywhere within an evacuated prolate or oblate ellipsoidal cavity surrounded by a uniform dielectric. These represent a generalization of a result by Kirkwood and Westheimer for a charge lying on a line joining the two foci of the prolate cavity. In the limit of a spherical cavity, the formulas reduce to those determined previously. The results should be applicable to determination of electrostatic solute energies using more realistic cavity shapes to contain the solute molecules and more flexible placement of solute charges and dipoles within the cavities than was possible with earlier approaches.
Triplet correlations in the Lennard-Jones fluid
Authors: Haymet A. D. J. , Rice Stuart A. , Madden William G.
Published: February 2003

The thermodynamics and the configuration space structure of the Lennard-Jones fluid are studied using a first-principles integral equation theory previously employed to compare calculated and computer simulated pair and triplet correlation functions for a model of liquid sodium. The modified Yvon–Born–Green integral equation is solved by a new application of the quasilinearization (Newton–Raphson) method, which is found to be much more efficient and more stable than a simple iterative (Picard) method. For particular thermodynamic states, predicted values of the pressure and internal energy are compared with the predictions derived from other integral equation theories, semiempirical perturbation theories, and computer simulations. Information contained in the triplet correlation function is revealed graphically as a function both of distance and of angle. The isothermal density derivative of the pair correlation function is calculated and is found to differ measurably from the result obtained using the superposition approximation for the triplet correlation function. An experimental test of higher order superposition approximations is suggested.
Internal energy transfer in molecule–surface collisions
Authors: Foner S. N. , Hudson R. L.
Published: February 2003

The use of a modulated molecular beam mass spectrometer for the first measurements on the internal energy excitation of polyatomic molecules in single collisions with heated surfaces is reported. (AIP)
Vibrational predissociation spectra of (HF)n, n = 2–6
Authors: Lisy James M. , Tramer Andrzej , Vernon Matthew F. , Lee Yuan T.
Published: February 2003

Using molecular beam techniques and a tunable infraredlaser, the vibrational predissociation spectra for (HF)n, n = 2 to 6, in the 3000 to 4000 cm−1 range are presented. The vibrational bands have been assigned to intramolecular HF stretching modes and combinations of intra- and intermolecular modes. The structures of (HF)n, n = 3 to 6, were found to be cyclic, i.e., each HF molecule is both a proton donor and acceptor.
Paramagnetic center in irradiated hydrazinium sulfate (N2H6SO4) crystals
Authors: Gade S. , Johnson B. , Hendrich K. , Knispel R. , Harrell J. W.
Published: February 2003

In hydrazinium sulfate (N2H6SO4) crystals, the predominant radical created by gamma irradiation has been characterized to have the N2H4 structure. The g tensor is approximately isotropic with g = 2.006±0.001 and the 14N hyperfine tensor is nearly axially symmetric with magnitudes of A1 = 29.5, A2 = 6.7, and A3 = 7.0 G. The principal component is nearly perpendicular to the N–N bond. A partial determination of the proton hyperfine splitting was made with values ranging from 14.7 to 4 G.
Glauber generalized oscillator strength for allowed transitions of lithium atom
Authors: Tayal S. S. , Tripathi A. N.
Published: February 2003

Minima and maxima in the generalized oscillator strength (GOS) are studied as a function of momentum transfer for allowed transitions in lithium atom using the Glauber approximation. The results of the present calculations have been compared with the first Born approximation. The results indicate that the Glauber approximation predicts the occurrence of these extrema and their positions shift with energy of the incident particle, in contrast to the results of Born approximation. The total excitation cross sections are also obtained using the Glauber approximation and are compared with the Born calculations and the available experimental data.
Effects of nonresonant ionization on multiphoton ionization line shapes
Authors: Rothberg Lewis J. , Gerrity Daniel P. , Vaida Veronica
Published: February 2003

A kinetics model of multiphoton ionization (MPI) is developed to account for nonresonant ionization and collisional rethermalization effects on MPI. Simple quantitative criteria to describe MPI line shapes are derived. In cases where resonantly enhanced MPI (REMPI) is not an effective spectroscopic tool, it is demonstrated that absorption can deplete ground state levels which would otherwise have contributed to nonresonant ionization. The resulting structured valleys in the ionization current contain spectroscopic and dynamical information which may otherwise be unattainable. The feasibility of depletion of nonresonant ionization (DNRI) as a general technique is investigated and the first experimental observations of DNRI are reported and analyzed.
Theories of ion–molecule association reactions compared with new experimental data on C++H2+H2→CH3++H
Authors: Herbst Eric
Published: February 2003

Rate coefficients calculated from recent statistical theories of ion–molecule association reactions are compared with new experimental data on C++H2+H2→CH+3+H and its deuterium analog. Reasonable agreement is found between experiment and both the modified thermal and phase space theories.
The mechanism for multiphoton ionization of H2S
Authors: Carney Thomas E. , Baer Tomas
Published: February 2003

The resonantly enhanced multiphoton ionization mass spectrum of H2S has been studied as a function of laser wavelength and power. Three mass peaks, due to S+, HS+, and H2S+ were observed at all resonances which were investigated. All three ionic species were found to have different dependences on laser power. The power indexes reflect the increasing number of photons required to form the species, but less than integer differences in the indexes indicate multiple paths for the formation of the various ions. A mechanism which is consistent with these data is one involving a rate-limiting three-photon absorption from the ground state, followed by rapid stepwise absorptions up an autoionization ladder of states above the ionizational potential. Results of a model calculation based on a rate equation description of the autoionization mechanism are in general agreement with the data. A mechanism involving dissociation of parent H2S+ ions by absorption of three or more additional photons could not be ruled out, however.
Absolute electron impact ionization cross section from threshold up to 180 eV for N2O+e→N2O++2e and the metastable and collision induced dissociation of N2O+
Authors: Märk E. , Märk T. D. , Kim Y. B. , Stephan K.
Published: February 2003

Electron impact ionization of nitrous oxide was studied as a function of electron energy up to 180 eV. A double focusing mass spectrometer in combination with an improved electron impact ion source (Stephan et al.) was used, alleviating the problems of ion extraction from the source and the transmission of the extracted ions through the mass spectrometer system. Relative partial ionization cross sections were measured for the process N2O+e→N2O++2e. These cross sections were calibrated absolutely by normalizing the relative cross sections with two different methods. A difference obtained in the absolute cross section values is explained by the delayed unimolecular dissociation process N2O+ to NO++N. Both metastable and collision induced dissociation of N2O+ were studied quantitatively using the well established technique of decoupling the acceleration and deflection electric fields.
UV studies of electron impact excitation of CS2
Authors: Ajello J. M. , Srivastava S. K.
Published: February 2003

We report the first measurements of emission cross sections of CS2 by electron impact over the wavelength interval 110 to 510 nm. Absolute emission cross sections are obtained at 100 eV for all spectral features observed in the interval. The important electronic transitions listed in decreasing order of their emission cross sections at 100 eV are the ionization transitions CS2+(? 2Σu+→? 2Πg) in the middle UV, CS2+(? 2Πu→? 2Πg) in the visible, the dissociative excitation transition CS(A 1Π→X 1Σ+) in the middle UV, and individual carbon and sulfur multiplets in the VUV. Emission cross sections as a function of electron energy (0–125 eV) are reported for several of the important electronic transitions.
Analysis of a
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o effective valence shell Hamiltonian calculations using third order quasidegenerate many-body perturbation theory
Authors: Sheppard Maurice G. , Freed Karl F.
Published: February 2003

A generalization of quasidegenerate many-body perturbation theory is provided which enables the calculation of the Hermitian effective valence shell Hamiltonian ℋv along with the individual one- , two- , three- , and the never-before-calculated four-electron effective integrals of ℋv. Emphasis is placed upon the problems encountered by the use of large valence spaces and the desire to use the same ℋv for all valence states of a given system and all its ions. These stringent requirements, motivated by a desire to investigate the theoretical foundations of semiempirical quantum chemistry, introduce severe difficulties with the quasidegeneracy constraints of the theory. A detailed analysis is presented of methods to handle these problems within a third order formulation which in its simplest form reduces to a symmetrized version of Brandow’s diagrammatic linked-cluster (size consistent) perturbation expansion. An outline of practical ab initio third order ℋv calculations is discussed here and systematically tested in the following paper.
Convergence studies of the effective valence shell Hamiltonian for correlation energies of the fluorine atom and its ions using third order quasidegenerate many-body perturbation theory
Authors: Sheppard Maurice G. , Freed Karl F.
Published: February 2003

The effective valence shell Hamiltonian ℋv, is evaluated through third order quasidegenerate many-body perturbation theory (QDMBPT) for all 46 [2s,2p] valence states of F+7 through F−. The effects of independently varying the orbital basis set, the unperturbed Hamiltonian, and the definition of the valence shell are studied. A generalized of QDMBPT allows the separate evaluation of the many-electron effective integrals which are independent of the number and configuration of valence electrons; hence, one ℋv calculation yields all 46 state energies simultaneously. Methods for dealing wih quasidegeneracy problems associated with large valence shells are numerically tested and proven effective. Guidelines for ℋv calculations on more complicated systems are presented.
Pictures of unbound molecular electrons, including shape-resonant states. Eigenchannel contour maps
Authors: Loomba Dinesh , Wallace Scott , Dill Dan , Dehmer J. L.
Published: February 2003

Eigenchannel wave functions are identified as the continuum analog of discrete-state eigenfunctions familiar from molecular structure calculations. As examples, eigenchannel wave functions are plotted for shape-resonant and nonresonant eigenchannels of N2. Both types of functions show characteristic nodal patterns. The penetration over a narrow energy range of the resonant wave function through a potential barrier into the molecular interior, the key feature of shape-resonant states, is clearly seen for the example of the N2 f-wave-dominated σu shape resonance at 1.2 Ry electron kinetic energy. This visualization of continuum electronic amplitudes should prove to be a significant new tool in the study of continuum electron–molecule dynamics.
Complete basis set correlation energies. II. The beryllium isoelectronic series
Authors: Petersson G. A. , Licht Stuart L.
Published: February 2003

The convergence of natural orbital expansions of the 1s2 and 2s2 intraorbital pair energies of the beryllium isoelectronic series is examined. The observed convergence of the 1s2 pair energies follows the asymptotic form error (N×N)?(ΣNμ = 1Cμ)2 (−225/4608)N−1 to within ∼3% of the MCSCF error (i.e., the absolute accuracy is ∼0.000 25 hartree for N as small as five configurations). The 2s2 pair energies show the expected interference effect—the large negative coefficients of the 2s2→2p2 excitations give small interference factors (ΣNμ = 1 Cμ)2 and hence the convergence of the 2s2 pairs is relatively rapid. However, the constant in the asymptotic form for the 2s2 pair energies appears to deviate significantly from (−225/4608) and the relative accuracy of the extrapolation is only ∼15% unless variations in the constant are determined by perturbation calculations. Nevertheless, the absolute accuracy for the 2s2 pairs is still ∼0.000 31 hartree for the five-configuration extrapolation. The total correlation energy extrapolated from the best CI and perturbation calculations available agrees with experiment to within 0.000 25 hartree for the entire isoelectronic series from z = 3 through z = 10. This is substantially better than previous results without extrapolations.
Pair and isolated ion spectra of Ni2+ in MgTiF6⋅6H2O
Authors: Rubins R. S. , Yung Y. H.
Published: February 2003

EPR measurements were made on single crystals of nickel-doped MgTiF6⋅6H2O in the frequency ranges 23–25 and 34–35 GHz. The isolated ion data were fitted to a conventional spin Hamiltonian with g = 2.248±0.005, D = −(2.301±0.005) cm−1, and ‖E‖ = (0.129±0.001) cm−1 at 4.2 K. The magnitude of D decreased almost linearly with increasing temperature to a value of (2.26±0.01) cm−1 at 394 K. The two most intense satellite lines were fitted to a pair Hamiltonian containing an isotropic exchange term JS1⋅S2 and a truncated dipolar term. Assuming g = 2.245 and D = −2.3 cm−1, the values ‖E‖ = (0.143±0.002) cm−1 and J = +(0.089±0.002) cm−1 were obtained at 4.2 K and the values ‖E‖ = (0.160±0.003) cm−1 and ‖J‖ = (0.088±0.003) cm−1 were obtained at 77 K.
Dynamics of interspecies hydrogen bonding of partially fluorinated compounds and a stable nitroxide radical studied by 1H and 19F relaxation and low-field DNP measurements
Authors: Borah Babul , Bates Richard D.
Published: February 2003

The coupling of –OH protons of (CF3)3COH and C6F5OH interacting with 4-oxo-2,2,6,6-tetramethylpiperidino-oxy (TMPO) free radical is governed by dipolar coupling of the two spins. The magnetic field dependence of the proton relaxation indicates that the interaction is dominated by rotationally modulated diffusion of the interspecies complex with a correlation time of 7×10−11 s in both cases and interaction distances of 2.5 and 2.3 Å, respectively. The dipolar correlation times are longer and the interaction distances are shorter than for the –OH protons in the CF3CH2OH:TMPO interaction. These observations are consistent with the complex formation constants, as determined by ESR measurements, of 4.1±0.4, 4.4±0.4, and 1.9±0.6 m−1 for the (CF3)3COH:TMPO, C6F5OH:TMPO, and CF3CH2OH:TMPO complexes, respectively. Dynamic nuclear polarization (DNP) measurements also indicate that the fluorine atoms in the first two complexes show significant scalar interaction of the fluorines with the unpaired electron on the spin label.
Depolarized dynamic light scattering of a rigid macromolecule poly(p-phenylene benzbisthiazole)
Authors: Crosby C. R. , Ford N. C. , Karasz F. E. , Langley K. H.
Published: February 2003

The rotational relaxation time of poly(p-phenylene benzbisthiazole) (PBT) has been used to characterize its conformation in chlorosulfonic acid solutions. We present a method of extracting the persistence length from the forward depolarized photon correlation data. Using Hearst’s theory for the rotational diffusion coefficient of a wormlike chain, a persistence length of 640 Å is determined. The results also suggest that under certain conditions depolarized photon correlation spectroscopy is a potentially useful method for estimating the polydispersity of a polymer sample.
Raman scattering in lysozyme solutions
Authors: Aliotta F. , Fontana M. P. , Giordano R. , Migliardo P. , Wanderlingh F.
Published: February 2003

Previous measurements on the OH stretching behavior in lysozyme solutions do not agree with each other. A careful measurement is performed using an isotopic substitutional technique in order to improve the precision. It is shown that, taking into account the contribution of the OH groups of lysozyme, elsewhere neglected, the interaction between lysozyme and water does not give any significant contribution to the Raman spectrum of the OH stretching. The conclusion is also supported by depolarization ratio measurements.
Lower order effects in nonlinear two- and three-photon resonance spectroscopies
Authors: Meredith Gerald R.
Published: February 2003

A semiclassical description of the simultaneous processes of two-photon absorption, two-photon excitation, and second harmonic generation in noncentrosymmetric crystals is presented. The results are generalized to include three-photon processes and third harmonic generation in centrosymmetric media. Consequences for molecular crystal excitation spectroscopy are emphasized. Similar results and observations are made for third-order wave mixing in noncentrosymmetric crystals.