bluuebunny/crossref_metadata_2025 huggingface dataset:
Close-coupling studies of rotationally inelastic HF–HF collisions at hyperthermal energies
Authors: Alexander Millard H.
Published: February 2003

Earlier close-coupling studies on the HF–HF system [A. E. DePristo and M. H. Alexander, J. Chem. Phys. 66, 1334 (1977)] have been extended to larger channel bases, allowing the determination of converged integral cross sections for excitation out of the lower rotational levels of the bimolecular system. The calculations were confined to collision energies appropriate to supersonic beam experiments (E =0.5–1.5 eV). Two potential surfaces were used, both taken from our earlier fit to ab initio points [M. H. Alexander and A. E. DePristo, J. Chem. Phys. 65, 5009 (1976)]. In the first surface the symmetry of the only anisotropic term included corresponds to the standard dipole–dipole interaction; to which were added, in the second surface, a primarily repulsive anisotropy as well as the long-range dipole–quadrupole interaction. The largest cross sections (40–60 Å2) are associated with R–R processes of the type j1 j2→j1±1, j2∓1 which are dipole-allowed in first order. The magnitudes of these cross sections are little affected by the presence of the shorter-range anisotropic terms, since much of the inelasticity occurs at large impact parameter. Cross sections for processes which are dipole-allowed only in second or higher order are considerably smaller (1–10 Å2), have classical dynamical thresholds at high energy, and are substantially lowered when the additional anisotropic terms are added to the potential, which has the effect of redirecting inelastic flux into the dipole forbidden channels. The cross sections for first order dipole–quadrupole transitions are also small, even in cases of near resonance. By contrast we find sizeable cross sections (7–15 Å2) for transitions which are coupled only by the short range anisotropy, which implies that rotational energy transfer between polar molecules cannot be fully described by models which rely solely on the standard long-range multipole expansion of the potential.
Tests of orbit–lattice interaction models using spin–lattice relaxation data of Er3+, Dy3+, and Yb3+ in Cs2NaYCl6
Authors: Fish G. E. , North M. H. , Stapleton H. J.
Published: February 2003

Measurements of the electron spin–lattice relaxation rate are reported for Er3+, Dy3+, and Yb3+ in the cubic host Cs2NaYCl6. Expressions for the anisotropic direct relaxation rates of the respective Γ8 and Γ6 ground states are given in terms of the eleven coupling parameters of the dynamic orbit–lattice interaction for octahedrally coordinated rare earths. Experimental direct process relaxation data are used to test the predictions of three models: (1) the electrostatic model of Buisson and Borg, (2) a nearest neighbor, effective point charge model, and (3) the nearest neighbor superposition model of Newman and co-workers. None of these proves satisfactory in providing a self-consistent explanation of the data from all three ions.
Resonance enhanced two-photon ionization studies in a supersonic molecular beam: Bromobenzene and iodobenzene
Authors: Dietz T. G. , Duncan M. A. , Liverman M. G. , Smalley R. E.
Published: February 2003

The 1B2(ππ*)←1A1 absorptions of two monosubstituted halobenzenes have been investigated using resonance enhanced two-photon ionization in a pulsed supersonic molecular beam. Detection of the photoions was accomplished by means of a time-of-flight mass spectrometer. The 1B2←1A1 system of bromobenzene has been observed with good sensitivity using this technique, even though the total decay rate of the 1B2 state is greater than 1×1011 sec−1. No ion signal was observed when the same transition was probed in iodobenzene, allowing us to place a lower limit on its decay rate of 4×1013 sec−1.
The infrared spectra of the hydrates of ammonia, NH3⋅H2O and 2NH3⋅H2O at 95 °K
Authors: Bertie John E. , Morrison Mary M.
Published: February 2003

The monohydrate and the hemihydrate of ammonia have been grown from the liquid and characterized by their x-ray powder diffraction patterns at ∼100 °K, which are reported. Infrared spectra of samples mulled in liquid propane, propylene, or Freon 13 at 95 °K are reported from 4000 to 400 cm−1 and a preliminary assignment is made. The previously reported infrared spectra of these compounds are not correct, undoubtedly because the method of preparation did not yield the correct compounds. The spectra are consistent with the reported structures except that limited proton-disorder may occur in the monohydrate and that the lengths of the two types of O–H⋅⋅⋅N bond in the hemihydrate may differ by ∼0.04 Å instead of the reported 0.02 Å. The frequencies of O–H stretching vibrations in O–H⋅⋅⋅N bonds of length 2.775 to 2.84 Å at 100 °K are in the range 2910 to 3125 cm−1.
The line shape of power-broadened microwave transitions
Authors: Schwendeman R. H.
Published: February 2003

By consideration of the steady-state solutions of the density matrix equations for a two-level system including the effects of spatial degeneracy, an expression is derived for the line shape of a microwave transition under conditions of partial saturation. Expressions valid for Δj=0 as well as Δj=±1 transitions are given. The line shape expression, which is a continued fraction, is shown to depend upon a large number of relaxation coefficients. However, it is shown by numerical tests that the dependence on T1 and T2 is roughly an order of magnitude stronger than the dependence on higher order relaxation parameters. The validity of the usual procedure of fitting a power-broadened microwave spectral line to a sum of power-broadened m components is discussed.
Energy selection experiments in glassy matrices: The linewidths of the emissions S2→S and S2→S1 of azulene
Authors: Griesser Hans J. , Wild Urs P.
Published: February 2003

The S2→S0 and S2→S1 fluorescence spectra of azulene have been studied in a low temperature glass using laser excitation into the S2 state. The former emission shows a sharp zero-phonon line pattern, a feature which is characteristic of energy selection experiments. The latter emission consists of broad Gauss-shaped vibronic bands which show the full inhomogeneous matrix width. Solute–solvent interactions which depend strongly on the nature of the excited electronic state restrict the energy selection effect to the resonant electronic transition.
Theoretical analysis of spectral structure: Doorway state coupling schemes
Authors: Cable Ronald , Rhodes William
Published: February 2003

The absorption spectrum of a molecule is analyzed theoretically in terms of a doorway state coupling scheme developed earlier [A. R. Ziv and W. Rhodes, J. Chem. Phys. 65, 4895 (1976)], whereby a set of sequentially coupled states, each having complex energy, is produced. The Green’s function method which is further developed in this paper produces this set of doorway states called the spectroscopic channel basis (SCB) and the spectrum of interaction of each doorway with all remaining states of the system. The latter is referred to as the interaction density spectrum (IDS), and it contains information on the radiative and radiationless decay properties of the doorway state. The IDS is also the (weighted) distribution function for the next doorway state in the SCB chain. The molecule–radiation field nature of the basis states is considered for each stage of the analysis. The method is applied to the (0,0) band of the S2←S0 transition in naphthalene and to the 2B2←2A1 band system of NO2 in order to compare our method with other studies in the literature and to determine practical limits of calculations.
Intramolecular vibrational energy redistribution and the time evolution of molecular fluorescence
Authors: Freed Karl F. , Nitzan Abraham
Published: February 2003

We note the presence of contradictory estimates of intramolecular vibrational relaxation rates in the literature where large molecules in high energy states, corresponding to huge densities of vibrational levels, have been ascribed relaxation rates orders of magnitude smaller than those assigned to smaller molecules with much smaller densities of vibrational levels. This unphysical disparity is explained as arising from vague (or undefined) definitions of intramolecular vibrational relaxation and/or from a consideration of quantities which are not directly measured or measurable. A resolution of a portion of the problem is already well known for electronic relaxation, but the application of those results to a description of the time evolution of the molecular fluorescence, produced during the intramolecular vibrational relaxation of the electronically excited molecules, requires a generalization of the electronic relaxation theory to separate and describe the ’’unrelaxed’’ and ’’relaxed’’ emission spectra. We provide this general theory of the time variation of the emission spectrum for molecules conforming to both the intermediate and statistical limits of intramolecular vibrational relaxation with emphasis placed upon the distinguishability between these two cases. The intermediate case analysis utilizes egalitarian and random coupling type models with essentially identical conclusions from both. The time evolution and relative yields associated with the emission spectra are described for both continuous and short pulse excitation, and reasons are provided for the absence of observation of time varying emission spectra in the experiments of Smalley and co-workers. Quantum beats are possible in principle in the sparse intermediate case. Their observability depends, however, on the detection method. When the emission spectrum can be resolved, beats are expected only in the frequency integrated intensity.
Interaction energies in nematogens
Authors: Warner Mark
Published: February 2003

The effect of steric exclusions between rods in correlating positional with rotational hinderances is used to calculate the mean field a rod sees in a fluid of other rods with which it interacts via anisotropic dispersion forces. The resultant potential involves all Legendre polynomials even within the dipole–dipole approximation. It is also possible to see how specific forces could be incorporated into the derivation to give the often anomalous results seen in Raman scattering. The magnitude of the potential is also estimated using absorption, scattering, and equation of state data. The resultant characteristic energy is somewhat smaller than that required by a recent theory of Flory and Ronca which contains both steric and dispersion effects, and is much smaller than that required by the Maier–Saupe approach which takes no account of steric influences.
Mode dependent enhanced vibrational relaxation in low energy He–1B2 aniline collisions
Authors: Tusa James , Sulkes Mark , Rice Stuart A.
Published: February 2003

Supersonic jet spectroscopy is employed to study the emission spectra resulting from He–1B2 aniline collisions. (AIP)
The conformation of acetaldehyde in its n→3s Rydberg state
Authors: Gordon Robert D.
Published: February 2003

The conformation of acetaldehyde in its n→3s Ryberg state is stated to be s–cis (one methyl hydrogen eclipsed by oxygen). Heath et al.1 stated on the basis of their measurements that it was not possible to tell whether this excited state was a s–cis. The calculations presented here definitely establish the excited state as a s–cis.(AIP)
Local and normal modes: A classical perspective
Authors: Jaffé Charles , Brumer Paul
Published: February 2003

Normal and local mode behavior in molecular systems and the transition between them is explored using nonlinear mechanics techniques. Significant insight into this behavior and into the structure of phase space results from a generalized definition of local and normal modes and the associated identification of normal modes as a (1:1) resonance between local zeroth order oscillators. In addition to qualitative insight, this approach yields a simple formula [Eq. (28)] for the level of excitation at which local modes become possible. Applications to H2O and to the overtone spectroscopy of the dihalomethanes, benzene, and TMS are provided.
Molecular integral of diamagnetic contribution to nuclear spin–spin coupling constant
Authors: Matsuoka O. , Aoyama T.
Published: February 2003

Methods are presented for calculating the molecular integral of the title over the Cartesian Gaussians. They compute four-center field or four-center overlap integrals analytically and then perform the numerical integrations. They are faster and more accurate than the Monte Carlo integration method. The contributions of the title for H2, CH4, NH3, H2O, HF, and CO are also evaluated.
Some interesting new phase diagrams in hydrogen-bonded liquid mixtures
Authors: Wheeler John C. , Andersen G. R.
Published: February 2003

A decorated lattice model of hydrogen-bonded mixtures that exhibits closed-loop coexistence curves and lower critical solution temperatures is shown to exhibit a low-temperature phase separation with an upper critical solution point lying below the lower critical solution point of the closed-loop curve. The model is exactly soluble in terms of the three-dimensional spin–1/2 Ising model and therefore exhibits nonclassical critical behavior. The model also exhibits critical double points at which two coexistence curves merge at a common critical point and the critical exponent β is renormalized to 2β. For a special choice of the parameters the model exhibits a new type of phase diagram in the T–X plane in which the shape of the coexistence curve near the critical solution point is described by the exponent 3β. As a result the phase boundaries appear to approach the critical point nearly as straight lines. Coexistence curves are presented exhibiting the variety of behavior possible in the model, including critical double points and the critical inflection point. We also discuss the possibility of observing the critical inflection point in real mixtures and the behavior to be expected in closed systems in which the overall mole fractions are fixed.
Electrical double layers. I. Monte Carlo study of a uniformly charged surface
Authors: Torrie G. M. , Valleau J. P.
Published: February 2003

This paper reports grand canonical Monte Carlo computations on the diffuse double layer in an ionic system next to a uniformly charged plane surface. The boundary conditions and the grand canonical techniques are discussed. Calculations were carried out for the 1:1 restricted primitive model at several concentrations and over a range of surface charge densities. The results are compared with the modified Gouy–Chapman theory, and some remarks are also possible with respect to the modified Poisson–Boltzmann and the hypernetted chain approaches. At high concentrations and surface charge densities the counterions are packed closely at the surface and begin to show a layered structure. This results in a large electrostatic potential drop, but only very slight charge oscillations are observed in the solution. None of the theories seems able to describe this behavior.
Self-structure factor of hard-sphere gases for arbitrary ratio of bath to test particle masses
Authors: Lindenfeld Michael J.
Published: February 2003

The self-structure factor Ss(k,ω) for test particles of mass different from the mass of the bath particles is considered. For a dilute hard-sphere gas the self-Enskog kinetic equation is solved to high accuracy for Ss(k,ω) by the Gross–Jackson (GJ) modeling procedure. When the variables in the self-Enskog kinetic equation are scaled to customary dimensionless parameters, the peak height and width of Ss(k,ω) vary only about 10% within a large mass ratio range. The GJ solution approaches smoothly the Ss(k,ω) of the Fokker–Planck equation (small bath particle mass). On the other hand, large variation of Ss(k,ω) occurs near the Lorentz limit (large bath particle mass). The optimized Bhatnagar–Gross–Krook (BGK) model of Groome, Dufty, and Lindenfeld shows better quantitative agreement than the usual BGK model but does not predict some qualitative features. Hydrodynamic limits are also discussed in some detail. It is demonstrated that the hydrodynamic limit of Ss(k,ω) for the Lorentz equation does not have the usual Lorentzian line shape.
Viscosity and temperature dependence of the magnetic isotope effect
Authors: Sterna L. , Ronis D. , Wolfe S. , Pines A.
Published: February 2003

The 13C enrichment observed in the first order photolytic decomposition of dibenzylketone (1,3-diphenyl-2-propanone) was studied as a function of solvent viscosity and temperature. The isotope effect is due to electron–nuclear hyperfine interactions in the free radical intermediates of the reaction. The results are explained using a continuum diffusion model and a simplified version of the radical pair theory of Chemically Induced Dynamic Nuclear Polarization (CIDNP). The isotope effect is substantially enhanced at intermediate values of viscosity.
Speed dependence of microwave rotational relaxation rates
Authors: Coy Stephen L.
Published: February 2003

For most molecular systems, rotational relaxation rates depend strongly on absorber speed. The influence of this speed dependence on transient decays in the microwave region and on the measurement of rotational relaxation rates, line positions, and line shifts is described. Measurement of the speed dependence of relaxation rates may be made from the nonexponential behavior of transient decays which are more sensitive to the speed dependence than line shapes. We describe how these transient experiments may be performed using either amplitude modulation or Stark switching, how the data may be analyzed using calculations of nonexponentiality from pressure-dependent sources, and give experimental results for these transitions: OCS J=0−1 and J1–2, H2CO 212−211, NH3 (3,2), and ethylene oxide 431−422. Previous transient experiments need to be re-evaluated in terms of a speed dependent relaxation rate. The speed dependence may make the measured rate an ill-defined population average which cannot be compared to static line width measurements or to calculations.
Laser spectroscopy of the diatomic van der Waals molecule NaNe
Authors: Lapatovich Walter P. , Ahmad-Bitar Riad , Moskowitz Philip E. , Renhorn Ingemar , Gottscho Richard A. , Pritchard David E.
Published: February 2003

We present a thorough spectroscopic study of the van der Waals molecule NaNe. Our molecular beam apparatus, laser scanning system, and frequency reference technique are described in detail. Methods of rotational analysis are discussed. Descriptions of the observed vibration–rotation bands in the A 2Πr–X 2Σ+ and B 2Σ+–X 2Σ+ manifolds are presented. Perturbations in the observed spectra are discussed. Long range analysis techniques are used to determine the vibrational quantum numbering from observed isotopic shifts and to determine excited and ground state potential parameters. We find DeA=145±05 cm−1 at ReA=5.1(1)a0, DeX=8.1(9) cm−1 at ReX=10.0(1)a0, and DeB?3.0(5) cm−1 at ReB?14.4(3)a0.
Coriolis interactions and assignments of the fundamental bands in ethylene oxide and ethylene oxide-d4
Authors: Nakanaga Taisuke
Published: February 2003

The Coriolis interactions among ν5, ν12, and ν15 of C2H4O and those among ν4, ν5, ν12, and ν14 of C2D4O were analyzed to clarify the intensity borrowing phenomena. The signs of the product ζrs(∂p/∂Qr)(∂p/∂Qs) have been determined for all pairs of the above fundamentals. As a result, earlier assignment of ν12 and ν15 of C2H4O has been found to be erroneous. According to the new assignment, the fundamental frequencies of ν12 and ν15 are 822.26 and 808.3 cm−1, respectively. The force field of this molecule was calculated using the new assignment of the fundamental bands.
Laser induced fluorescence and relaxation of singlet molecular oxygen in the liquid phase
Authors: Protz R. , Maier Max
Published: February 2003

The 1Δg state of liquid oxygen was excited by 1.064 μm radiation from a Nd:YAG laser. O2(1Σ+g) was produced by an energy pooling reaction from O2(1Δg). The time dependence of various fluorescence bands from O2(1Σ+g) and from pairs of O2(1Δg) and O2(1Σ+g) was measured and discussed. Rate constants for quenching of O2(1Δg) and O2(1Σ+g) by ground state O2 molecules were determined in the liquid phase (at T=77 K).
Universal formulas for classical transport coefficients: The zero-frequency component
Authors: Allen J. W. , Diestler D. J.
Published: February 2003

An exact universal formula for the zero-frequency component of the classical transport integral, ?(ω) =ℱ∞0dt φ(t) cos ωt, where φ(t) is any equilibrium time-autocorrelation function (TACF), is derived. The analysis is based on the continued-fraction representation of the Laplace transform of φ(t). A sequence constructed from the approximants to this continued fraction is shown to converge to ?(0), if the approximants converge. The derived formula for ?(0) is universal in that it is of the same form regardless of the TACF of interest or of the intermolecular forces or the thermodynamic state of the system. A general relationship between ?(0) and the transport integral ?(0)=ℱ∞0dt K(t) of the ’’memory function’’ K(t) of the corresponding many-variable Langevin equation is also derived. Finally, sequential precursors of the exact universal formula are used to estimate the diffusion coefficient for the Lennard-Jones liquid. These estimates agree with computer simulation data to about 10%–15% over the entire liquid range.
The phase equilibria in thermotropic liquid crystalline systems
Authors: Warner Mark , Flory P. J.
Published: February 2003

The lattice theory of hard rods with anisotropic dispersion forces presented recently is extended to the case where the rods are dispersed in a diluent. Two systems are treated: (i) rods of axial ratio x diluted with solvent molecules having x=1, and (ii) rods of axial ratio xα mixed with homologs of axial ratio xβ. Treatment of the latter system can be regarded as an extension of the Flory and Abe theory for ’’athermal’’ polydisperse systems, in which dispersion forces are inconsequential. Solutions of sufficiently long (x≳20) rods subject to anisotropic dispersion forces are predicted to exhibit complex phase equilibria involving a re-entrant nematic phase (with a critical point) and a triple point, as well as the usual nematic–isotropic coexistence. These deductions should be relevant to thermotropic solutions of rodlike synthetic polymers with phenylene groups or other groups exhibiting anisotropic interactions. Calculations for mixtures of short rods yield more prosaic phase diagrams. It is suggested that such systems (for example, mixtures of the polyphenyls) can provide comprehensive tests of the underlying theory. Mixtures of quinque- and quaterphenyl are specifically considered.
Application of complex coordinate SCF techniques to a molecular shape resonance: The 2Πg state of N2−
Authors: Rescigno T. N. , Orel A. E. , McCurdy C. W.
Published: February 2003

The lifetime and level width of the metastable 2Πg state of N2− are calculated using restricted Hartree-Fock theory.(AIP)
A crossed molecular beam study of the O(1D2)+CH4 reaction
Authors: Casavecchia P. , Buss R. J. , Sibener S. J. , Lee Y. T.
Published: February 2003

A cross molecular beam experiment was performed to study the O(1D2)+CH4 reaction. The results show that hydrogen atom elimination reaction greatly exceeds molecular hydrogen elimination. (AIP)
Shock compression of liquid argon, nitrogen, and oxygen to 90 GPa (900 kbar)
Authors: Nellis W. J. , Mitchell A. C.
Published: February 2003

Dynamic equation-of-state data for liquid Ar, N2, and O2 were measured in the shock pressure range 21–91 GPa (210–910 kbar) by means of a two-stage light-gas gun. The liquids were shocked from initial states near their saturation curves at 0.1 MPa (1 bar) and 80 K. The cryogenic target system is described. The initial liquid densities were obtained by measuring the temperature and pressure of the specimens and calculating the densities from published equations of state. Shock velocities were measured to 0.5–1.1% accuracy with an electronic detection system with subnanosecond time resolution. Impactor velocities in the range 4–7 km/s were measured to 0.1% accuracy with a flash radiographic technique. Mass velocities were obtained by the method of shock impedance matching. The data are discussed in terms of the statistical–mechanical theories of Ross and Ree.
The photodissociation of CH2I2: Production of electronically excited I2
Authors: Okabe H. , Kawasaki M. , Tanaka Y.
Published: February 2003

The primary photodissociation process of CH2I2 leading to the formation of electronically excited I2 (3Π2g) has been studied. The process occurs with yields less than 1% for light of wavelengths below 1320±10 Å. The I2 (3Π2g) initially produced by the Kr (1165, 1236 Å) lines is vibrationally excited up to v′=35. The addition of near atmospheric Ar or N2 deactivated vibrational quanta to v′=0, 1, and 2 but little electronic quenching was observed. The quantum yield of I2 (3Π2g) production is 0.006 at 1236 Å. At 1306 Å little vibrational excitation of I2 (3Π2g) was seen. In addition, very weak I2 emission bands in the 2500–2900 and 4500–4900 Å regions were found in CH2I2 photodissociation by the Kr lamp. The absorption cross sections of CH2I2 in the 1100 to 1500 Å region have been measured and compared with the I2 (3Π2g) fluorescence excitation spectrum. The results show that the I2 emission bands arise mainly from the underlying absorption continua and not from structured features of CH2I2, suggesting that the σ–σ* transitions in the C–I bond are responsible for yielding I2(3Π2g), while Rydberg tranitions are ineffective in forming I2 (3Π2g). The dissociation process CH2I2→hνCH2(? 3B1)+I2 (3Π2g) involves an energy barrier of almost 1 eV, in agreement with other molecular detachment processes. The Kr photosensitized reaction of CH2I2 on the other hand gives rise to the I2 (H) emission in addition to emissions observed in direct photolysis. This state is likely to be 1Σ+u rather than 3Σ+u.
Br*(2P1/2)+H2(v=0,1): Laser studies of the competition between reactive pathways and inelastic energy transfer channels
Authors: Nesbitt David J. , Leone Stephen R.
Published: February 2003

A systematic experimental study has been made on inelastic and reactive processes in the Br*(2P1/2)+H2(v=0,1) system. Laser photolysis and time-resolved infrared detection techniques allow direct observation of the previously unreported E–V equilibrium: Br*+H2(v=0)⇄kVEkEVBr +H2(v=1). A nonlinear kinetic analysis is presented that permits an estimate of the quantum efficiencies for the forward and reverse E–V processes, and provides an explanation for previous discrepancies in measured total Br* quenching rates with H2. In this work the quenching rate constant for Br*by H2 is determined at very low Br* concentrations to be 6.3(±1)×10−12 cm3 molecule−1 sec−1. At higher concentrations of Br*, second order processes involving collisions of Br*with H2(v=1) have been investigated. A substantial fraction of the Br*+H2(v=1) collisions react to form HBr(v=0)+H(2S1/2). It is suggested that the resonant E–V transfer pathway in the entrance channel Br*+H2(v=1) → Br+H2(v=2) may provide an efficient mechanism for potential surface crossing, thereby enhancing the reaction probability.
The vibration–rotational energies of the hydrogen molecular ion HD+
Authors: Wolniewicz L. , Poll J. D.
Published: February 2003

The energies of all the bound vibrational states of HD+ with rotational quantum numbers up to J=5 are calculated using a new variation–perturbation method. Relativistic, radiative, and nonadiabatic corrections are taken into account with an accuracy of the order of 0.001 cm−1.
Spin-dependent effective core potentials for Ni++
Authors: Sabelli Nora H. , Kahn Luis R. , Benedek R.
Published: February 2003

Ni ions assume a divalent charge state in crystalline NiO. To facilitate SCF calculations on NiO clusters, we have derived effective core potentials to represent the Ni++ ion core. Different potentials were obtained for a valence electron with spin parallel and for one with spin antiparallel to the core spin. The potentials were tested in calculations for Ni ions and for a NiO molecule embedded in a matrix of point charges. Comparison is made where possible with previous all-electron calculations and with experiment. The present pseudopotentials afford some prospects for realistic calculations of anion–anion interionic forces in NiO.
Rigorous interface properties for the van der Waals fluid mixture
Authors: Varea Carmen , Valderrama Auster , Robledo Alberto
Published: February 2003

A statistical mechanical treatment for the van der Waals fluid mixture is developed, based on Widom’s potential-distribution theory for nonuniform fluids. For the specific choice of Kac pair interactions, in the van der Waals limit, a set of coupled second-order differential equations determine the density profiles. The solution of these equations and the determination of the interfacial tension are discussed in terms of a mechanical analogy.
A HNC study of asymmetrically charged hard spheres
Authors: Rogers F. J.
Published: February 2003

The hypernetted chain equation (HNC) has been solved for two-component highly asymmetric charged hard spheres and a systematic study of electrolytes ranging up to 20–1 has been carried out in the restricted primitive model. The cation–anion distribution function is found to exhibit complex structure for highly asymmetric electrolytes. Many component solutions of the HNC have been carried out. An application to a 1, 2, 3,-1 electrolyte is discussed.
Lifshitz–van der Waals forces in aerosol particle collisions. I. Introduction: Water droplets
Authors: Marlow William H.
Published: February 2003

Collision rates among water droplets are computed by the application of results of a current paper which gives a rigorous expression for free-molecular collisions between aerosol particles with a singular, attractive contact potential and the extension of that expression throughout the transition regime via Fuchs’ interpolation method. An expression for the Lifshitz–van der Waals attractive potential recently derived by Kiefer et al. is modified to include a physically motivated, frequency-dependent retardation factor and is used with experimental data for water’s frequency-dependent dielectric susceptibility. This expression is employed in the computation of the ratio of the collision rate incorporating the interaction potential to the collision rate omitting the potential for various pairs of water particles of 1, 10, 100, and 1000 nm radii at 0.1, 1.0, and 10.0 atm. pressures. A graph of this ratio for a pair of 200 nm radius particles as a function of pressure is given and shown to display similar pressure-dependent behavior to recent experimental results by Wagner and Kerker on the coagulation rates of DEHS particles of the same size. This appears to be the first explanation of the systematic deviations near to and beyond experimental error of their experimental data from the predictions of Fuchs’ unmodified formula. The ratio is also calculated by dividing the integral over the electromagnetic frequency spectrum in the van der Waals energy into long and short wavelength parts. This is used to estimate the relative importance of these components upon aerosol particle collision rates. By inference they suggest broader patterns of behavior for other particles. Specifically, an explanation is tendered for the source of the large discrepancy between experimental data taken by Graham and Homer and those authors’ theoretical treatment of their data on the coagulation rates of high temperature, free-molecular regime lead aerosol particles. The spectral decomposition of the collision rates also displays interesting behavior, apparently originating from the retardation damping of the modes, which shows that the frequency dependence of the collision rate enhancement by van der Waals forces is strongly dependent upon size. The role of retardation upon the collision rates is computed and shown to increase from unimportance for 1 nm particles to dominance for 100 nm particles, suggesting the need for further work on computational methods which rigorously incorporate retardation in readily computed van der Waals energy formulas.
Monte Carlo calculations for molecular H2 in the fluid phase
Authors: Fiorese G.
Published: February 2003

Using a pair potential deduced from theoretical works, Monte Carlo simulations are performed to compute the thermodynamic properties of molecular hydrogen in the fluid phase. Quantum effects are accounted for by calculating the mean squared force and the mean squared torque. The solidification pressure is determined from a simple criterion of melting. Good agreement is found with experiment, so this potential can be used to successfully describe thermodynamic properties in the fluid phase.
Laser flash photolysis of benzene. III. S
n←S1 absorption of gaseous benzene
Authors: Nakashima Nobuaki , Inoue Haruo , Sumitani Minoru , Yoshihara Keitaro
Published: February 2003

Gaseous benzene was excited by a KrF excimer laser and a transient absorption was observed in the region between 210 and 930 nm. The Sn←S1 absorption spectrum is assigned using time-resolved spectroscopy and the effects of foreign gas. Three peaks have been found and are assigned as follows: 545 nm(1E1u, f∼0.003), 400 nm (1 1E2g, f∼0.02), and 267 nm (2 1E2g, f∼0.08). The observed energies above the ground state are 7.8 eV for the 1 1E2g state and 9.4 eV for the 2 1E2g state. Spectral shapes become sharper and each peak shifts to shorter wavelengths compared with those in cyclohexane solution. The results suggest that the 2 1E2g has a valence character. Other differences between the solution and gas spectra are discussed.
19F nuclear magnetic shielding scale from gas phase studies
Authors: Jameson Cynthia J. , Jameson A. Keith , Burrell Patricia M.
Published: February 2003

By using results of density and temperature studies, 19F nuclear magnetic resonance frequencies measured in 20 gases of known densities are reduced to the zero-density limit at 300 K. From these we obtain differences in shielding between rovibrationally averaged isolated molecules at this temperature. The magnitudes of the corrections linking the shielding in the liquid phase to the isolated molecule at its equilibrium configuration are discussed. These corrections are not necessarily small and are required in deriving an accurate absolute shielding of any molecule from the known absolute shielding of another molecule by observing the NMR chemical shift between the two.
NMR relaxation study of Li+–Ni2+ interaction in aqueous solution
Authors: Hirata F. , Friedman H. L. , Holz M. , Hertz H. G.
Published: February 2003

The NMR relaxation of 7Li+ due to Ni2+ in aqueous solution as a function of magnetic field strength is experimentally determined and is calculated on tha basis of certain models for the ionic interactions. The results can be used to eliminate some models which are consistent with the osmotic coefficient data for aqueous LiCl, NiCl2, and their mixtures.
High resolution 1H solid state NMR studies of polyethyleneterephthalate
Authors: Cheung T. T. P. , Gerstein B. C. , Ryan L. M. , Taylor R. E. , Dybowski D. R.
Published: February 2003

Molecular motions and spatial properties of the solid polymer polyethyleneterephthalate have been investigated using high resolution 1H solid state NMR techniques. The longitudinal spin relaxation time T1ρ of protons (1H) in the rotating frame was measured for a spin locking field ranging from 5 to 20 G. The decay of the 1H magnetization indicated the existence of two distinct T1ρ’s and their field dependence shows that they are associated with two mobile phases of the polymer. The 1H magnetization also relaxes under the dipolar narrowed Carr–Purcell (DNCP) multipulse sequence with two dintinct T1y relaxation times. The ratios T1y’s and T1ρ’s deviate significantly from the expected theoretical values. The combined experiment with magic angle spinning and the DNCP sequence followed by homonuclear dipolar decoupling reveals the individual T1y relaxation of the resolved methylene and aromatic protons. These two species of protons were found to relax with the same T1y’s, thus implying that spin diffusion must have taken place under the homonuclear dipolar decoupling multipulse. The qualitative description of spin diffusion under homonuclear decoupling is given. The combined experiment with spin locking and the DNCP sequence yields the correspondence between the two T1ρ’s and the two T1y’s. The long T1ρ corresponds to the short T1y whereas the short T1ρ corresponds to the long T1y. Communication between the two spatial phases via spin diffusion was also observed in this experiment by monitoring the recovery of the 1H magnitization associated with the short T1ρ after it has been eliminated during the spin locking. The total 1H magnetization is allowed to equilibrate in the laboratory frame for a variable time much shorter than T1 after the spin locking field has been turned off. The spatial relationship between the two phases is discussed.
Surface-enhanced Raman spectroscopy of benzene and benzene-d6 adsorbed on silver
Authors: Moskovits M. , DiLella D. P.
Published: February 2003

The surface-enhanced Raman spectrum of benzene and benzene-d6 adsorbed on a silver film vapor-deposited onto a low-temperature substrate is reported. Many lines which correlate with Raman-inactive and even infrared and Raman-silent modes of the free molecule are observed with high intensity in the spectrum. The local symmetry which would cause those particular, otherwise inactive, vibrations to appear is C3v(σd), which corresponds to a benzene molecule lying flat atop an equilateral triangle of silver atoms so that the normals to three alternate edges of benzene point to the centers of the three atoms. An alternative explanation for the activity of these normally silent modes is presented which does not depend on the adsorption site symmetry but which postulates instead that an unusally steep electric field gradient exists near the surface of the metal which causes modes spanned by the same representations which span the elements of a third rank tensor A to become active. These, together with the vibrations which are normally Raman-active in benzene, are the same vibrations which are Raman-active in C3v(σd). An argument in support of the latter explanation is presented based upon the different response to excitation wavelength of the intensities of those modes which are active as a result of the polarizability tensor, α, as contrasted with those which become active because of A. An unequivocal choice between the two models cannot be made, however, on the basis of the data available.
Inversion of rotationally inelastic differential cross sections under sudden conditions
Authors: Schinke Reinhard
Published: February 2003

An inversion method for rotationally inelastic atom–diatom differential cross sections based on the infinite-order-sudden (IOS) approximation is presented. It consists of two separate steps: (1) The scattering phase shift, which is a function of the partial wave parameter l and the orientation angle γ, is determined by least-squares fitting of the reference cross sections. (2) For fixed orientation γ the R dependence of the interaction potential in obtained from the l dependence of the phase shift using the Firsov technique. This method is applicable in the so-called strong coupling case when rotational rainbow features are dominant and yields information about the anisotropy of the potential surface in the repulsive region. Because of the centrifugal sudden condition, scattering systems with deep potential wells cannot be treated by the present method. Test calculations are performed using theoretical IOS cross sections obtained from a realistic He–Na2 surface as reference data.
Charge transfer transitions within the octahedral uranate group
Authors: Bleijenberg K. C.
Published: February 2003

In this paper the excitation spectra of the luminescence of the octahedral uranate group (UO6−6) are presented for various uranium-doped compounds. The excitation bands have been assigned using the results of theoretical and experimental investigations into the spectroscopic properties of uranium hexafluoride which is isoelectronic with the octahedral uranate group. Charge transfer transitions from orbitals having mainly oxygen 2p character to orbitals having mainly uranium 5f charcter have been observed in the region 2.24–∼4 eV. Charge transfer transitions to orbitals having mainly uranium 6d character have been observed at 4.4 eV and at 5.4 eV.
Normal mode spectra in pure local mode molecules
Authors: Heller Eric J. , Gelbart William M.
Published: February 2003

We define a simple, purely local mode model vibrational Hamiltonian which gives rise to an apparent normal mode spectrum under conditions resembling a symmetric stretch Franck–Condon transition. The model clearly distinguishes the question of the intrinsic separability of the Hamiltonian from the nature of the initial conditions, or ’’pluck’’, implied by the transition moment.
Pure vibrational Raman spectra of simple liquids: O2, N2, CO, CH4, CF4
Authors: Clouter M. J. , Kiefte H. , Jain R. K.
Published: February 2003

Interferometric techniques have been applied in a high resolution study of the polarized Raman components (Q branches) corresponding to the totally symmetric vibrational modes of CO, CH4, and CF4 in the liquid phase. Additional unpublished data for N2 and O2, as well as limited results of dilution studies in liquid argon, are reported. Emphasis is placed upon the measurement of variations in frequency shift and spectral width along the liquid–vapor coexistence line from the triple point to within 0.2 K of the critical point for each pure liquid. The character of the observed linewidth variations exhibits distinct differences from liquid to liquid, especially in the neighborhood of the triple and critical points. A consistent interpretation of the results suggests that a substantial contribution to the N2 and O2 linewidths is associated with the effect of intramolecular vibration–rotation coupling. The CH4 data support the predictions of Hills and Madden (i) that the long wavelength, hydrodynamic, density fluctuations can play an important role in determining the linewidth in the critical region, and (ii) that a transition from fast to slow modulation conditions should be observable as the critical point is approached. CF4 may represent a case where slow modulation conditions hold throughout a large part of the liquid range.
Intermolecular vibrational coupling in crystalline m-dinitrobenzene—Polarized infrared spectra of oriented polycrystalline films
Authors: Katon J. E. , Hanai K. , Tripathi G. N. R.
Published: February 2003

High resolution infrared spectra of oriented crystal films of m-dinitrobenzene have been recorded at about 20 K using polarized radiation. The intermolecular coupling within the unit cell has been observed and is interpreted in terms of the known crystal structure. Symmetry species of the molecular vibrations and their factor group components are determined on the basis of the observed polarization behavior of the crystal bands. Some of the earlier assignments are revised.
Low frequency vibrational spectra, methyl torsional potential functions, and internal rotational potential of propanal
Authors: Durig J. R. , Compton D. A. C. , McArver A. Q.
Published: February 2003

The low frequency Raman and infrared spectra of gaseous propanal have been recorded in the region 300–50 cm−1. A complex far infrared spectrum was observed, and a substantial number of bands are assigned to the asymmetric and methyl torsional modes of both the s-cis and gauche conformers. Analysis of these bands allowed calculation of the torsional potential functions present in this molecule. The results indicated that the potential functions calculated previously for this molecule are inadequate, and that an unusual interaction exists in the s-cis conformer between an in-plane bending mode and the asymmetric torsion. The potential function coefficients for the asymmetric torsion of propanal were calculated (in cm−1) to be: V2=559±7, V3=651±8, V4=−105±4, and V6=−46±6. This potential function has an enthalpy difference between the more stable s-cis and the higher energy gauche conformers of 241±10 cm−1, with the gauche dihedral angles being about ±135 °.
Effective resonant light scattering from adsorbed molecules
Authors: Ueba H.
Published: February 2003

A theory of light scattering from adsorbed molecules is presented based on the general formulation of second order optical processes. The molecular–solid interaction is assumed to be the s-d interaction, which leads to the shift and broadening of the molecular excited state. The physical origin of the anomalous enhancement of the Raman scattering from adsorbed molecules is explained by an effective resonant model so that the electronic resonant level of adsorbed molecule shifts towards lower energies and the effective resonant condition is realized even when the molecule is excited by the off-resonant energy of the isolated molecule. It is also shown that the Raman scattering includes an additional term, which gives rise to the continuum background on which the Raman spectra are superimposed.
Vibrational relaxation in jet-cooled alkyl benzenes. III. Nanosecond time evolution
Authors: Hopkins J. B. , Powers D. E. , Smalley R. E.
Published: February 2003

Spectrally resolved fluorescence time decay measurements have been completed with nanosecond resolution on a series of n-alkylbenzenes laser excited into well-localized ring distortion vibrations in the S1 electronic state. Results indicate that those early members of the series which continue to exhibit some sharp, vibrationally unrelaxed emissions do so because they are intermediate case examples with inadequate density of states to permit dynamical relaxation on a nanosecond time scale. The longer chain, statistical limit molecules show a relaxed fluorescence pattern which displays no residual nanosecond time evolution. Intramolecular vibrational relaxation thus appears to proceed to an essentially complete randomization within a time period shorter than the excitation laser pulse.
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o configuration interaction study of the Rydberg states of O2. I. A general computational procedure for diabatic molecular Rydberg states and test calculations on the 3Πg states of O2
Authors: Saxon Roberta P. , Liu B.
Published: February 2003

Configuration interaction calculations have been performed on the 3Πg symmetry of O2 which establish a general computational procedure for diabatic molecular Rydberg states. Three different calculations which include varying amounts of electronic correlation for the Rydberg and valence states are reported. The interaction potentials for the lowest diabatic Rydberg state from these three calculations are in excellent agreement showing that semi-internal correlation energy of Rydberg states has little effect on the potential curves. The Rydberg state is found to be exceedingly similar to the O2+ 2Πg state to which the 3Πg Rydberg series converges. Energies for the lowest four Rydberg vibrational levels are presented.