bluuebunny/crossref_metadata_2025 huggingface dataset:
Rotation diffusion of aromatic dianions
Authors: Huppert D. , Douglass D. C. , Rentzepis P. M.
Published: February 2003

Rotational diffusion of the major axis of anthracene, tetracene, and pentacene dianions in dimethyl ether at room temperature is measured by picosecond spectroscopy. Data is compared with predictions of three types of models; two based upon the hydrodynamics of a fluid about spheroidal particles, with sticking and slipping boundary conditions, and a third based upon hard-sphere, hard cylinder collisions. The experimental rotational correlation times are proportional to the third power of molecular length. The hydrodynamic model with slipping boundary conditions mimics this observation but predicts magnitudes that are too small. Sticking boundary conditions give the correct magnitude for anthracene but incorrect axis length dependence. The collision model provides roughly correct magnitude and length dependence.
Electron transport in gaseous, critical, and liquid benzene and toluene
Authors: Huang Sam S.-S. , Freeman Gordon R.
Published: February 2003

Electron mobilities μ in the low density gases are independent of electric field strength up to ≳4 Td in benzene and ≳5 Td in toluene. The ratio of the threshold drift velocity (for electron heating) to the speed of low frequency sound in the gas, vd (threshold)/co, is ≳40 in benzene and ≳50 in toluene. The ratios are ≳3 fold higher than those in the saturated cyclic hydrocarbons cyclopentane and cyclohexane. The aromatic molecules have larger inelastic scattering cross sections than do the cycloalkanes for thermal energy electrons. The total scattering cross sections of benzene and toluene each have a minimum for electrons of ∼0.3 eV energy. The value of the total cross section averaged over a Maxwellian energy distribution at 300 K is 82 Å2 for benzene and 87 Å2 for toluene. A plot of μn against density n for the coexistent vapor and liquid is horizontal at n<1×1020 molecule/cm3 in each vapor, slopes negatively to a minimum at n?1−2×1021, increases to a maximum at n?3×1021 (n/nc=1.5), then plunges as the density is increased further. Electron quasilocalization occurs in the dense gas, and localization in the liquid. Quasilocalization is characterized by large negative values of ΔH and ΔS, and a small value of ΔG, over a small temperature range near the vapor/liquid coexistence curve. The magnitudes of ΔH and ΔS and the extent of quasilocalization decrease as a constant density vapor is heated away from the coexistence region. A two state model of electron transport was applied to the results from the liquid phase.
Phase instability and the direct correlation function integral equation
Authors: Lovett Ronald , Buff Frank P.
Published: February 2003

Extensive searches for the equilibrium liquid–solid coexistence line have been based on the identification of this line with the bifurcation points in integral equations such as the lowest order Kirkwood lambda coupling equation, the lowest order Born and Green equation, and a similar relation between the direct correlation function and the singlet density. In applications where these integral equations should be identical, different results have been found. The difference is explained by noting that additional, implicit approximations have always been introduced. A new formulation free of such approximations is given, and it is shown that the general condition for bifurcation to occur is simply expressed in terms of the direct correlation function and has a simple physical interpretation: An approximation free search for bifurcation points will identify points of liquid instability and not points of liquid–solid coexistence.
The binding energy of iodine–rare gas van der Waals molecules
Authors: Blazy Joseph A. , DeKoven Benjamin M. , Russell Timothy D. , Levy Donald H.
Published: February 2003

The product state distribution of the fragment I2* that is produced when an I2–rare gas van der Waals molecule dissociates has been used to measure the binding energies of I2He*, I2Ne*, and I2Ar*. The binding energies D0 for these three van der Waals molecules were determined to be 13.6–14.8, 65–67, and 220–226 cm−1, respectively.
The theoretical foundation of the Lassettre–Dillon relation between the singlet–triplet energy difference and the singlet generalized oscillator strength
Authors: Bonham R. A.
Published: February 2003

A rigorous foundation is presented for the experimentally established relationship between the singlet–triplet energy difference and a certain momentum integral over the singlet generalized oscillator strength proposed by Lassettre and Dillon [J. Chem. Phys. 59, 4778 (1973)]. It is argued that the Lassettre–Dillon relation should improve in accuracy for the higher states of ionization of atoms and molecules.
The electronic chemical potential and the H atom in the H2 molecule
Authors: Palke William E.
Published: February 2003

Properties of the functional relationship between the energy and the natural orbitals and occupation numbers of a system are used to obtain an expression for the chemical potential of the electrons for the case of one or two electrons. These expressions are then used with the principle of equal orbital electronegativity to find the electron density of the hydrogen atom in the H2 molecule; the perturbed atomic potential of which that atom is the ground state is also determined.
Role of symmetry restrictions on valence electron binding energies of CF4
Authors: Müller Jiri , Poulain Enrique , Goscinski Osvaldo , Karlsson Leif
Published: February 2003

A b initio LCAO MO calculations within the Hartree–Fock formalism have been carried out on all ionized states of CF4 and the effects of molecular symmetry restrictions on computed hole state energies are closely examined. It is emphasized that localization, which ordinarily affects core holes, is also of importance for describing inner valence and excited levels with both Hartree–Fock and correlated calculations.
Dynamical effects from resonance Raman and fluorescence studies of the molecular exciton system perylene
Authors: Hochstrasser Robin M. , Nyi Corinne A.
Published: February 2003

The resonance Raman profiles were measured for a perylene crystal exciton state (Au) corresponding to the 0–0 transition of the molecular 1B2u(S1) state. At both 77 and 4.2 °K the profiles of these extremely thin crystals do not coincide with the absorption spectra. This effect is frequency dependent damping perhaps caused by exciton–phonon interactions. The efficiency of resonant scattering relative to excimer emission is used to measure an exciton dephasing time of 6.4×10−14 sec. The luminescence of the population resulting from this loss of coherence was not observed suggesting that these excitons disappear within 5×10−13 sec.
Nanosecond laser photolysis of the benzene monomer and eximer
Authors: Nakashima Nobuaki , Sumitani Minoru , Ohmine Iwao , Yoshihara Keitaro
Published: February 2003

A dilute solution of benzene was photolyzed with a KrF excimer laser. The Sn←S1 and Tn←T1 absorption spectra are measured with time-resolved spectroscopy. The Sn←S1 absorptions in the energy range between 850 and 220 nm were analyzed. The transient absorption band at 500 nm, which was observed previously by several workers disappeared completely upon dilution of the sample, and thus was assigned to be the excimer band. We assigned the other states as follows: 620 nm (1E1u, f∼0.003), 540–325 nm (11E2g, f∼0.04), and 270 nm (21E2g, f∼0.12). The observed energies from the ground state to the 11E2g and 21E2g states 7.8 and 9.2 eV, respectively. The Tn←T1 spectrum showed a single peak at 235 nm (f∼0.35) and a shoulder around 310 nm (f∼0.12).
An ESR study at 77 K of the bromine atom and the ≳N–Br−⋅ σ* radical in x-irradiated N–bromosuccinimide single crystals
Authors: Muto H. , Kispert L. D.
Published: February 2003

Two radicals have been identified from an ESR study of N–bromosuccinimide single crystals x-ray irradiated at 77 K. One is the previously studied σ* radical fromed by an electron attachment to the antibonding orbital of the N–Br bond in N–bromosuccinimide and the other is a bromine atom. Analysis shows that the σ* radical interacts with a neighboring proton to give a large proton superhyperfine coupling of (37, 26, 21)G and it has suggested that the ≳N–Br group is nonplanar. The bromine atom which apparently originates from the cation precursor exhibits a very large g anisotropy of (1.837, 2.384, 2.430) and a bromine 81 coupling of (+510, +183, +209)G. It has been found from the g and hyperfine coupling tensors that the crystal field splitting (Δ=4200 cm−1) is about the same order as the spin–orbit coupling (λ =2456 cm−1) and that the spin densities in the 4p and 4s orbitals are estimated to be close to unity and 0.004, respectively. The geometry of the trapping site has been deduced by comparing the crystallographic coordinates with the principal directions of the g and A tensors.
Reaction coordinate method for quantum tunneling
Authors: de Buda P. , Kostin M. D.
Published: February 2003

A method based on the concept of reaction coordinates is presented for calculating the difference between the first two energy eigenvalues of the Schrödinger equation for a symmetric double-well potential. The method consists of using reaction coordinates to reduce the multidimensional Schrödinger equation to a simpler set of equations, which can then be solved numerically. The method is applied to a two-dimensional problem and the results are compared with those obtained for a special case where an exact solution is available. The agreement is very good.
New infrared absorption bands of cesium vapor
Authors: Zouboulis E. , Bhaskar N. D. , Vasilakis A. , Happer W.
Published: February 2003

We have found a new region of absorption by saturated cesium vapor in the infrared region of the spectrum (1.25–2.5 μ). Most likely candidates for this infrared absorption are cesium dimers in the repulsive triplet state (x 3Σ+u) and higher polymers of cesium (Cs3, Cs4,...).
Time resolved spectroscopy of xenon excimers excited by synchrotron radiation
Authors: Bonifield T. D. , Rambow F. H. K. , Walters G. K. , McCusker M. V. , Lorents D. C. , Gutcheck R. A.
Published: February 2003

Formation and decay rates of the lowest 0u+ and 1u states of Xe2*, excited by monochromatized synchrotron radiation from the Stanford storage ring (SPEAR), have been measured in pure xenon and in xenon–argon mixtures over the pressure range 102 to 104 Torr. The results are interpreted to yield radiative lifetimes (4.6±0.3 and 99±2 nsec, respectively, for vibrationally relaxed 0u+ and 1u molecules), vibrational relaxation rates [7×10−11 and 6×10−12 cm3/sec for Xe2* (1u) in collisions with xenon and argon, respectively], the Xe2* (0u+) three-body formation rate from Xe(3P1) (5.3×10−32 cm3/sec), and rates for 0u+–1u mixing by collisions with xenon and argon.
Iodine at high pressures and low temperatures
Authors: Dunn K. J. , Bundy F. P.
Published: February 2003

Using a cryogenic clamp-type high pressure apparatus, the electrical resistance behavior of iodine was studied for pressures from 80 to 280 kbar and temperatures from 300 to 2.6 °K. The resistivity of iodine approaches metallic values for pressures higher than 130 kbar. No superconductivity is observed in metallic iodine either in the molecular phase below 210 kbar or in the monatomic phase up to 280 kbar.
Spectra and modeling of laser-induced emission from multiple-photon (λ=248.4 nm) irradiation of UF6
Authors: Rice W. W. , Wampler F. B. , Oldenborg R. C. , Lewis W. B. , Tiee J. J. , Pack R. T
Published: February 2003

The laser-induced emission from KrF-laser irradiation of gaseous, room temperature UF6 has been studied as a function of time, wavelength, pressure, and laser fluence. Spectra in the 200–900 nm region are presented at several sampling times. One group of 17 emission peaks in the 650–900 nm range has been assigned to the 3Γ6→1Γ7 transition in UF5. A possible kinetic mechanism is presented that is qualitatively consistent with the time-resolved emission data over the experimental pressures and laser fluences investigated.
Exchange perturbation theory. IV. Calculations on H2+
Authors: Adams William H. , Polymeropoulos E. E.
Published: February 2003

We have applied the two localized-wave-function (LW) exchange- perturbation-theories (EPT) which we have proposed, to the 1sσg and 2pσu states of H2+ with the objective of verifying the insights gained from these EPT’s and of testing their accuracy. The one LW EPT determines a primitive wave function identical to that of the Eisenschitz–London EPT through first order, but which differs from it in all higher orders. The other determines a function identical to that of the Hirschfelder–Silbey EPT through first order and through infinite order, but which differs from it through all intermediate orders. We find that in terms of the perturbation expansion of the interaction energy through third order, our EPT’s are as accurate as the original EPT’s to which they are related. The LW EPT’s have the conceptual asset that their primitive wave functions are least distorted from the zero order wave function in a precisely defined sense. We have also calculated interaction energies using the integrals which define the interaction energies in terms of LW’s, and substituting the LW’s approximated by sums through first, second, and third order. The energies generally increase in accuracy as the LW is summed to higher orders. When each order contribution to the LW is multiplied by a weight which is determined to minimize the interaction energy, and the LW is summed through third order, the interaction energy is in error by 0.07% or less for nuclear separations ranging from 1.0 to 10.0 bohr. An examination of the LW’s shows how the optimization procedure works. Other quantities are calculated which show that the LW EPT’s are systematically refinable methods for the calculation of LW’s as well as for the calculation of interaction energies. This is important because LW’S may be used to calculate distinct ’’physical’’ contributions to interaction energies.
Photodissociation and photodetachment of molecular negative ions. IX. Atmospheric ions at 2484 and 3511 Å
Authors: Hodges Ronald V. , Lee L. C. , Moseley J. T.
Published: February 2003

A rare-gas–halogen laser has been used with a drift-tube mass spectrometer to extend measurements of the photodestruction cross sections of atmospheric negative ions to 2484 Å. Ions studied include O−, O2−, O3−, O4−, CO3−, CO4−, HCO3−, NO2−, O2−⋅NO, and NO3−; hydrates of many of these ions were also studied. As expected, the cross sections for most of the ions were substantially larger at 2484 Å than at wavelengths longer than 3500 Å.
A theoretical method for determining particle distribution functions of classical systems
Authors: Johnson Elijah
Published: February 2003

An equation which involves the triplet distribution function and the three-particle direct correlation function is obtained. This equation was derived using an analogue of the Ornstein–Zernike equation. The new equation is used to develop a variational method for obtaining the triplet distribution function of uniform one-component atomic fluids from the pair distribution function. The variational method may be used with the first and second equations in the YBG hierarchy to obtain pair and triplet distribution functions. It should be easy to generalize the results to the n-particle distribution function.
Recoil ranges of 2.73 MeV tritons and yields of 18F produced by the 16O(t,n)18F reaction in neutron-irradiated lithium compounds containing oxygen
Authors: Kudo Hiroshi , Tanaka Kichizo
Published: February 2003

The 16O(t,n)18F reaction induced by recoil tritons in neutron-irradiated crystalline lithium compounds containing oxygen has been studied with emphasis laid upon the determination of recoil triton ranges. The physical parameters required for quantitative description of successive (n,α) – (t,n) processes have been enumerated. The yields of 18F predicted from the calculation agreed well with the observed ones for a variety of lithium compounds. Mean cross sections, averaged over the triton recoil range, for the 16O(t,n)18F reaction in solids were rather constant [?F= (9.87±0.35) ×10−26 cm2] and were independent of the triton range. The triton ranges in polycrystalline substances can be determined from 18F yield measurements. Ranges derived from the present results include 6.2±0.4 mg cm−2 [Li2O(s)], 7.1±0.6 mg cm−2 [LiOH (s)], and 7.0±0.6 mg cm−2 [Li2CO3(s)].
A coupled-mode model relating Raman line shape to high ionic conductivity
Authors: Nitzan A. , Ratner M. A. , Shriver D. F.
Published: February 2003

A phenomenological model, based on the generalized Langevin equation scheme first developed by Bruesch, Zeller, and co-workers, is employed to calculate the Raman band shapes for metal–halogen stretching modes in ionic conductors of the Ag2HgI4 class. The observed strong broadening of the Hg–I4 stretch mode near 122 cm−1 is explained as arising from coupling to the mobile ion diffusive mode. Below the β→α phase transition, the Ag–I mode is oscillatory, and the coupling effect is negligible on either Ag–I or Hg–I. In the conducting phase, the long time diffusive character of the Ag–I motion results in a strong effective damping of the Hg–I motion, leading to the observed broadening. The coupling effects are strong only when one of the two modes is indeed diffusive, thus explaining the apparent value of the Raman linewidth as a screening device for possible new ionic conductor crystals.
A new method for determining semiclassical tunneling probabilities in atom–diatom reactions
Authors: Altkorn Robert I. , Schatz George C.
Published: February 2003

We present an approximate semiclassical method for determining state to state transition probabilities for reactions which proceed via tunneling which uses a trajectory integrated along purely real and purely imaginary time contours from reagents through the barrier to products. The real and imaginary time portions of the trajectory are connected by introducing separable approximations to the potential near certain translational turning points in the trajectory. For atom–diatom collinear reactions, the use of a vibrationally adiabatic approximation from these turning points to the asymptotic region leads to a very simple expression for the imaginary part of the action involving a nonseparable contribution from a purely real valued portion of the trajectory passing through the barrier along an imaginary time contour, and a separable contribution from a path which follows part of the locus of outer vibrational turning points. At very low translational energies E0, we find that the nonseparable contribution dominates in determining the reaction probability, and there we find very good agreement with the analogous semiclassical complex trajectory (SCCT) results of George and Miller for collinear H+H2. At higher E0, just below the classical threshold for reaction, the separable contribution dominates, and our method reduces to one proposed by Marcus and Coltrin (MC), which also shows good agreement with the SCCT results. Comparison of our results with exact quantum (EQ) results on both the Porter–Karplus and Truhlar–Kuppermann potential surfaces indicates agreement to within better than a factor of 2.5 over a wide range of relative translational energies (0.04<E0?0.23 eV), with the accuracy generally comparable to that of the SCCT, MC, and periodic trajectory (PT) methods. This method is, however, much easier to apply than SCCT (only a real valued portion of a trajectory is used), is capable of determining state to state transition probabilities (in contrast to PT) and is a more dynamical (trajectory oriented) approach than MC. The computational effort associated with this approach is roughly comparable to that of the PT method, which makes it easier than SCCT but harder than MC to implement. Results are also presented for H+H2 using the very accurate Siegbahn–Liu–Truhlar–Horowitz potential, and we examine the influence of using harmonic vs Morse potentials to generate vibrationally adiabatic separable approximations.
An EPR study of the reactivity of peroxy radicals trapped in polytetrafluoroethylene
Authors: Olivier Danièle , Marachi Chokoufé , Che Michel
Published: February 2003

The effect of CO, C2H4, SO2, and 17O2 on the EPR spectrum of peroxy chain radicals (R–CF2–CFOO.–CF2R′) and of peroxy propagating radicals (R″–CF2OO.) of polytetrafluoroethylene (PTFE) has been investigated. The peroxy chain radicals appear chemically stable up to 100 °C while in the same conditions, the peroxy propagating radicals do react. The transformation of peroxy propagating radicals always takes place through the rupture of the C–O bond. In the reaction with SO2, evidence is presented for the formation of R″–CF2–SO2. radical with gxx=1.999, gyy=2.011, gzz=2.005 at 77 K and g∥=2.007, g⊥=2.002 at 300 K. The temperature dependence of the EPR spectra is analyzed in view of the rotational freedom in the polymer. The R″–CF2–SO2. undergoes rotation around the polymer chain axis. From these data the structure of the radical is discussed.
Span components for adsorbed polymer chains
Authors: Lax Melvin , Windwer Stanley
Published: February 2003

An analysis is made of the molecular weight dependence of the span of surface restricted self-avoiding walks. Results for the normal as well as parallel components of the span for some cubic lattices are reported.
The circular dichroism of large helices. A free particle on a helix
Authors: Moore Dexter , Tinoco Ignacio
Published: February 2003

Equations are derived for the circular dichroism and optical rotation of light by a free electron on a helix which is of arbitrary size relative to the wavelength of light. The equations were found to give results in good agreement with measured rotation of microwaves by oriented wire helices. The derivation shows when the usual Rosenfeld approximation for optical activity becomes inadequate.
Direct evidence for formation of radicals in a shock-loaded polymer
Authors: Graham R. A. , Richards Peter M. , Shrouf R. D.
Published: February 2003

We report the first direct evidence for the formation of radicals in shock-loaded polymers. This is obtained from electron spin resonance (ESR) studies of poly(methylmethacrylate) samples subjected to explosive loading and preserved for subsequent examination. (AIP)
Off-diagonal mobility components for electrons and holes in naphthalene
Authors: Walker E. Irene P. , Marchetti Alfred P. , Young Ralph H.
Published: February 2003

The elements of th mobility tensor μac′ and μc′a were measured for naphthalene. The three-segment split-electrode technique was used with 270 nm light (AIP)
Charge-carrier drift mobility analysis for naphthalene
Authors: Munn R. W. , Siebrand W.
Published: February 2003

Electron and hole mobility data for naphthalene are analysed. It is found that simple hopping cannot explain the observed room temperature mobilities.(AIP)
Molecular dynamic simulation of hard spheres near a hard wall
Authors: Grigera J. Raúl
Published: February 2003

The molecular dynamics simulation of 128 hard spheres interacting with a hard wall at 298.16 K with a reduced density d3=0.755 is reported (AIP).
Molecular bonding in LiBe, LiMg, and LiCa
Authors: Jones R. O.
Published: February 2003

Binding energy curves for the 2Σ+ and 2Π states of LiBe. LiMg, and LiCa have been calculated using the density functional formalism. The bonding is characterized by transfer to and s–p polarization of the charge density near the Group IIA atom. The bonding trends show similarities to those evident in earlier calculations for Group IIA dimers.
The orientational correlation parameter and the dipole moment of a water molecule in ice VI
Authors: Johari G. P. , Whalley E.
Published: February 2003

The orientational correlation tensor g on principal axes has been calculated for ice VI. The first and second neighbors and the closure of the four-membered rings were taken account of.The mean value is 2.40 and the square of the anisotropic invariant is only 0.001, so that the permittivity of ice VI is predicted to be isotropic within the uncertainty of the calculations.The dipole moment of a water molecule in the hypothetical fully disordered ice VI is 2.55 D if the internal field is the Lorentz field and is 3.12 D if it is the applied field.
Multiple quantum NMR and relaxation of an oriented CH3 group
Authors: Tang J. , Pines A.
Published: February 2003

NMR relaxation of the n-quantum transitions (n=1,2,3) for an oriented CH3 group by paramagnetic impurities is discussed. The n-quantum spectra are presented, and the effect of the correlation of fluctuations in random fields at the three proton sites on symmetry-breaking relaxation transitions is outlined. Experimental results on acetonitrile dissolved in liquid crystalline EBBA with paramagnetic DTBN are presented together with a discussion on correlations of fluctuation and correlation times.
The photochemistry and infrared spectrum of the isopropyl radical
Authors: Pacansky J. , Coufal H.
Published: February 2003

Irradiation of diisobutyryl peroxide isolated in an argon matrix with ultraviolet light produces the isopropyl radical and carbon dioxide. Further irradiation of the isopropyl radical with ultraviolet light of a shorter wavelength produces an organic acid, ester, and an olefin. Formation of these products is conveniently explained on the basis of an excited radical reacting with carbon dioxide. In addition to photochemical studies, the infrared spectrum of the isopropyl radical is reported for the first time. Infrared and theoretical studies both support that the isopropyl radical exists in more than one conformation in rare gas matrices.
The electronic structure of the germyl anion GeH3−. A comparison with other AH3− species
Authors: Eades Robert A. , Dixon David A.
Published: February 2003

The electronic structure of the germyl anion, GeH3−, has been investigated by ab initio SCF calculations using large Gaussian basis sets. Various levels of basis set contraction for Ge are discussed. The optimum geometry of the ion is found to be C3V with r (Ge–H) =1.61 Å and ϑ (H–Ge–H) =95.9°. The barrier to inversion for GeH3− is 30.0 kcal/mole obtained with a (16,13,7/6,1)/[12,10,4/4,1] basis set. The inversion barrier in SiH3− was also studied and was found to be 26.0 kcal/mole. Vertical electron affinities for GeH3 and SiH3 have been determined from the negative ion wave functions using Koopmans’ theorem. The values are 1.94 eV for GeH3 and 1.65 eV for SiH3. A comparison with the experimental photodetachment results is also presented.
Matrix isolation and laser diagnostic studies of catalytic oxidation of H2 and D2 on platinum
Authors: Tevault D. E. , Talley L. D. , Lin M. C.
Published: February 2003

The reaction of hydrogen (or deuterium) and oxygen on pure polycrystalline platinum surfaces has been investigated in the 10−5 to 10−6 Torr range using the matrix isolation and laser-induced fluorescence techniques. Water, formed with a 1.1±0.2 kcal/mole activation energy, was the only product detected by infrared spectroscopy at catalyst temperatures between 150 and 700 °C. Laser-induced fluorescence experiments were used to observe the production of HO radicals both in argon matrices and in the gas phase. HO production was found to have an activation energy of 31±1 kcal/mole and could only be detected escaping from the surface at catalyst temperatures above 500 °C. The dependence of H2O and HO radical production on the partial pressures of H2 and O2 has been made. Reaction mechanisms are discussed in relation to other studies of the oxidation of hydrogen on single crystal and polycrystalline platinum surfaces.
A remark on phase transitions in insoluble monolayers
Authors: D’León R. Tascón , Moreau M.
Published: February 2003

A simple lattice model is considered in the study of phase transitions in monolayer films of lyotropic molecules. (AIP)
On the basic homogeneity characteristic of atomic and molecular electronic energies
Authors: Parr Robert G. , Gadre Shridhar R.
Published: February 2003

A homogeneity property of electronic energy with respect to atomic number, known to hold to a certain accuracy for neutral atoms, is extended and applied to neutral diatomic and polyatomic molecules. Two alternative hypotheses are examined. Homogeneity of the total energy, W, including repulsions between nuclei, leads to total Hartree–Fock energies at equilibrium proportional to the sum of orbital energies, and a linear first-order differential equation for the energy, for a diatomic molecule having the form R (dW/dR) +(3−k) W=Σεi, where k is the homogeneity parameter (about 7/3). A second, preferred hypothesis is homogeneity of the electronic energy E: ΣαZα(∂ E/∂ Zα)R=kE. It leads to a total energy equation in which appear both the sum of orbital energies and the repulsion between nuclei, and the differential equation R (dW/dR)+(3−k) W=Σεi+(2−k)(ZαZβ/R). The two hypotheses are tested on a number of atomic and molecular species, and their consequences are discussed. A constrained Hartree–Fock method in which the second hypothesis holds exactly is developed and shown to take the form of the extended Hückel method.
A stochastic Langevin dynamics study of correlated ionic motion in one dimensional solid electrolytes
Authors: Jacobson S. H. , Nitzan A. , Ratner M. A.
Published: February 2003

The motion of mobile ions in one dimensional ionic conductors is described by stochastic Langevin dynamics. The interactions of the mobile ions with the framework lattice are approximated by a sum of periodic and random potentials, yielding a set of coupled Langevin equations, which are then solved numerically. The parameters in these phenomenological equations of motion include the potential in which the ion moves and the lattice temperature. Correlated motion is considered by including long range (Coulombic) and short range potentials among the mobile ions. Inclusion of these potentials in calculations describing systems with an integral ratio of total sites to mobile ions (commensurate stoichiometry) shifts the frequency dependent conductivity (increase of maximum frequency, decrease of dc conductivity) in a manner indicating that the mobile ions are driven towards their equilibrium positions. The conductivity then decreases with increasing effective charge. However, when the carrier/site ratio is not integral (incommensurate stoichiometry, e.g., potassium hollandite) the long range ion–ion interaction drives the mobile ions into arrays which are distorted near the vacancies. This lowers the effective potential barrier, and therefore is responsible for increasing the calculated diffusion coefficient and conductivity. As the strength of the ion–ion interactions is increased this cooperative behavior is enhanced. The results for potassium hollandite are in good agreement with x-ray scattering data.
More on the acoustical method of measuring energy and tangential momentum accommodation coefficients
Authors: Shields F. Douglas
Published: February 2003

Additional measurements of the energy (EAC) and tangential momentum accommodation coefficients (TMAC) of He and Ne on polycrystalline tungsten have been made using an acoustic technique previously reported. The measurements were made after the tungsten surface had been exposed to the atmosphere and after it had been flashed in a vacuum at 1240, 1460, 1770, and 2000 K. Three stable, reproducible surfaces were detected. These have been associated with an atomic oxygen film, upper molecular oxygen film, and an unknown film produced by atmospheric exposure. Comparison with molecular beam scattering experiments indicates that TMAC corresponds to the fraction of molecules scattered diffusely from polycrystalline surfaces and EAC to the diffuse fraction from single crystal surfaces.
Quenching of triplet excitons in poly(N-vinylcarbazole) by biacetyl
Authors: Webber S. E. , Avots-Avotins Peter E.
Published: February 2003

Biacetyl is used as a quencher for triplet excitons in poly(N-vinylcarbazole) (PVCz) in 77 K glasses of 2-methyltetrahydrofuran. The phosphorescence of a polymer–biacetyl mixture shows a significant component of biacetyl at times long compared to the biacetyl triplet lifetime (∼2 msec) and delayed fluorescence (∼20–50 msec), showing that some exciton mobility exists after triplet–triplet annihilation has become insignificant. This is interpreted in terms of an exciton trapping model in which shallow and deep traps compete for the mobile triplet exciton. This kinetic model is only an approximation to the complexities of the present system, but it does simulate many of the properties experimentally observed.
The production of CN(X 2Σ+) and C2(a 3Πu) via the infrared multiple photon dissociation of C2H3CN
Authors: Yu M. H. , Levy M. R. , Wittig C.
Published: February 2003

C2(a) and CN(X) radicals have been detected by laser induced fluorescence in the collision-free infrared multiple photon decomposition of C2H3CN. Fluence dependence measurements suggest a common precursor for these radicals while spectrally and temporally resolved data show that the amount of energy that is partitioned among the products is small. The results are consistent with a dominant kinetic scheme, based on RRKM arguments and thermodynamic data, in which C2H3CN decomposes mainly by loss of H2 and/or H. The resulting C3N then fragments to C2(a,X)+CN(X).
Yields of HO2 in the reaction of hydrogen atoms with ozone
Authors: Howard Carleton J. , Finlayson-Pitts Barbara J.
Published: February 2003

Laser magnetic resonance (LMR) studies of the yields of HO2 from the H+O3 reaction are reported. The yields suggest that H+O3→HO2O(3P), accounts for about 3% of the net reaction. (AIP)
Relativistic scattered wave calculations on UF6
Authors: Case David A. , Yang Cary Y.
Published: February 2003

Self-consistent Dirac–Slater multiple scattering calculations are presented for UF6. These are the first such calculations to be reported, and the results are compared critically to other relativistic calculations. The results of all molecular orbital calculations are in good qualitative agreement, as measured by energy levels, population analyses, and spin–orbit splittings. The overall charge distribution is computed to be U+1.5(F−0.25)6. Polarization functions are found to be qualitatively unimportant. A detailed comparison is made to the relativistic Xα (RXα) method of Wood and Boring, which also uses multiple scattering theory, but incorporates relativistic effects in a more approximate fashion. For the most part, the RXα results are in excellent agreement with the present results. Some differences of possible significance are noted in the lower valence and core energies.
Effects of high pressure on molecular electronic spectra. II. Morse potential formulation
Authors: Tompkins Robert C.
Published: February 2003

The effects of high pressure on electronic spectra are treated on the basis of a Morse potential by a method analogous to that used in deriving the well-known Drickamer–Franck–Slichter model. Expressions are presented for evaluating configuration–coordinate parameters from spectroscopic data.
Rayleigh–Bénard instability in n-component reactive fluids
Authors: Gutkowicz-Krusin Dina , Ross John
Published: February 2003

We study the hydrodynamic stability of n-component reactive fluids undergoing a single reversible reaction in the Bénard geometry and the Boussinesq approximation, and take the Soret, Dufour, and cross-diffusion effects to be negligible. The boundaries are assumed to be rigid and perfectly conducting; the dependence of the critical Rayleigh number on the assumed boundary conditions for concentrations is discussed in the limit of fast reactions. In this limit we show that, if the boundaries are impermeable to mass flow (the easiest to achieve experimentally), the critical Rayleigh number, R∞cr, is proportional to the one for nonreactive binary fluids. Apart from multiplicative factors, R∞cr depends only on a single dimensionless parameter δ which vanishes when all the diffusion coefficients are equal. For δ≳0 (<−1) stationary convection may set in only if R∞cr≳0(<0); for intermediate values of δ there exist both positive and negative solutions for R∞cr.
Theory of the time evolution of exciton coherence in weakly disordered crystals
Authors: Abram Izo I. , Hochstrasser R. M.
Published: February 2003

Coherent states in molecular crystals are described as minimum-uncertainty superpositions of all the crystal states that can interact with light, and their amplitude decay due to the presence of disorder is calculated through the time-dependent exciton Greens function. The functional form of the decay is investigated, and different methods for its calculation are compared. The decay obtainable for the k=0 vibrational exciton in α-N2 through direct time-domain approximations provides good agreement with experimental results.
The equilibrium statistical mechanics of the helix–coil transition in torsionally stressed DNA
Authors: Benham Craig J.
Published: February 2003

A theory of helix–coil transitions in torsionally stressed heteropolymeric DNA is developed. Specifically, the polymer is constrained to have a fixed value of total twist in all accessible states, which may differ from its unstressed total twist. This imposed deformation is partitioned between twisting of the helical portions and melting with subsequent twisting in the coil regions. Quadratic free energy densities are associated to torsion in both types of regions. In this theory two parameters influence helix stability—temperature and the magnitude of the imposed twist. Consequently the predicted transition behavior is considerably more intricate than that arising from thermal transitions in unconstrained molecules. In particular, sufficient untwisting can significantly destabilize the helix, even at low temperatures. In this case melting occurs predominantly in AT-rich regions, is complicated. For example, if the imposed twist is altered to decrease helix stability at fixed temperature, the probability of melting of a given monomer unit need not increase monotonically. The predictions of this theory compare favorably with a previous thermodynamic analysis of the same problem.
The barrier to planarity in aminopyrazine
Authors: Kydd R. A. , Dunham A. R. C.
Published: February 2003

The far-infrared spectra of aminopyrazine is reported. The assignments of the spectrum in the range 50–650 cm−1 are given (AIP).
14N and 1H ENDOR studies of x-irradiated single crystals of hippuric acid
Authors: Chacko V. P. , McDowell C. A. , Singh B. C.
Published: February 2003

N-benzoylaminomethyl radical formed by room temperature x-irradiation of single crystals of hippuric acid (N-benzoylglycine) has been identified and its structure established by detailed ENDOR studies at 77 K. Besides proton signals, ENDOR transitions arising from the hyperfine and quadrupole interactions of the 14N nucleus were also detected and a detailed analysis is presented. The assignment of exchangeable protons has been accomplished by use of partially deuterated crystals. Radical identification and spin density distribution have been confirmed by comparison of the experimental results with those obtained from INDO–MO calculations. The radical is most likely formed from oxidized hippuric acid by deprotonation and subsequent decarboxylation.
Brillouin scattering in polyphenyls. I. Room temperature study of p-terphenyl (H14, D14) and biphenyl (D10)
Authors: Ecolivet C. , Sanquer M.
Published: February 2003

We report the results of Brillouin scattering measurements of the elastic constants of two elements from the polyphenyl series : biphenyl (D10) and p-terphenyl (D14, H14). These values are found to differ mainly for C33 : 18.06×109 N/m2 in biphenyl and 26.42×109 N/m2 in p-terphenyl. A simple chain model is given which accounts for this difference whereas elastic constants computed from atom–atom potential parameters are found in moderate agreement with our measured data.
Polymorphism of the smectogen ethyl-p-azoxybenzoate: Far-infrared and Raman study
Authors: Venugopalan S. , Prasad S. N.
Published: February 2003

The far-infrared spectra of the different phases of ethyl-p-azoxybenzoate have been studied in the 30–210 cm−1 range. Distinct differences are observed between the spectra of the two crystalline polymorphs that are stable above and below 102 °C, solid I and solid II, respectively. The spectrum of solid I resembles that of the isotropic phase, while that of the smectic phase is highly broadened. These results are discussed in terms of the structure, molecular conformation, and packing obtaining in the different phases. In the region of the internal modes, the same Raman frequencies are observed in both polymorphs although relative intensity changes occur for several lines. From a comparison of the Raman line shapes corresponding to the N–O and N–N bond stretching vibrations in solid II and solid I, we conclude that in the latter case the reorientations of the azoxy group occur at a rate too slow to affect the vibrational relaxation of these modes.
On dynamic scaling theories of polymer solutions at nonzero concentrations
Authors: Adler Ronald S. , Freed Karl F.
Published: February 2003

A scaling theory is presented for the translational diffusion coefficient of a tagged chain and for the specific viscosity of polymer solutions at nonzero concentration. The derivations employ the full diffusion equation including unaveraged hydrodynamic interactions for the dynamical motion of continuous Gaussian coils with excluded volume. The effects of screened excluded volume and hydrodynamic interactions at nonzero polymer concentrations are introduced through an effective excluded volume strength, v (c), and draining strength, h (c), c being the monomer concentration. For c[η]≲O (1), [η] is the intrinsic viscosity, the hydrodynamics of the polymer solution is treated using effective medium arguments, resulting in exponential forms for v (c) and h (c) (e.g., h (c) =h (0)  exp[constant c[η]]). Towards the concentrated end of the semidilute regime, c[η]≳O (1), a bloblike picture of chain dynamics is seen to appear. An application of the results derived herein is also presented for polyelectrolyte solutions at nonzero concentrations in the presence of added salt.
The use of CNDO/S in spectroscopy. XVI. Multiple photon ICR photodissociation spectra
Authors: Marchese Francis T. , Jaffé H. H. , Seliskar C. J.
Published: February 2003

The theory of two-photon absorption has been implemented within the CNDO/S-CI formalism to calculate two-photon absorptivity of doublet states. The method was utilized to investigate the origins of below threshold optical absorption in ion cyclotron resonance photodissociation spectra of benzene, t-butylbenzene, styrene, and 1-methylnaphthalene. The computations suggest that these below threshold processes may be due to simultaneous two-photon absorption rather than sequential absorption as postulated by Freiser and Beauchamp. Some photodissociation pathways are found to be both mono- and biphotonic in nature. Some wavelength dependent processes found in t-butylbenzene may well be biphotonic and could be competitive with monophotonic absorption below 3.08 eV.
Ion cyclotron resonance studies of radiative and dissociative electron attachment processes at low pressures
Authors: Woodin R. L. , Foster M. S. , Beauchamp J. L.
Published: February 2003

Ion cyclotron resonance spectroscopy is used to measure nondissociative electron attachment rate constants for C6F6 (perfluorobenzene), C7F8 (perfluorotoluene), c-C4F8 (perfluorocyclobutane), and C7F14 (perfluoromethylcyclohexane) at low pressure (<10−6 Torr). Infrared emission is assumed to stabilize excited species leading to long-lived molecular negative ions. Combining the present data with negative ion lifetimes measured at low pressures by time-of-flight methods and electron attachment rates measured at high pressures in swarm experiments allows estimates of radiative lifetimes to be made. These all fall in the range from 0.4 to 1.5 msec, which are typical of infrared radiative lifetimes. Data are also presented for dissociative electron attachment to CCl4, where the rate limiting step is shown to be thermalization of the electron energy distribution. A number of different buffer gases are examined and the ion cyclotron resonance results extrapolate to yield the attachment rate measured in high pressure swarm experiments.
Effects of fluctuation on dissipative structures. III. Analysis of a model sensitive to changes in external constraints
Authors: Iwamoto Kazutoshi , Senō Manabu
Published: February 2003

The effects of fluctuation on a chemical system which contains a subchemical system showing critical phenomena under suitable conditions has been investigated. It is shown that the system shows pulselike oscillations of opposite directions according to the external conditions. The conditions of the transition state where the chemical system reverses the direction of pulse are very severe and, therefore, this chemical system is extremely sensitive to changes in external constraints. Moreover, under the suitable conditions this chemical system shows three different behaviors depending on initial states and very complicated oscillations appear under influence of fluctuations.
A study of the chemiionization process CS2*(n)+CS2→CS3++CS+e− using the molecular beam photoionization method
Authors: Gress M. E. , Linn S. H. , Ono Y. , Prest H. F. , Ng C. Y.
Published: February 2003

Cross sections and branching ratios to various product channels were determined as a function of the CS2 Rydberg level. (AIP)
A quasiclassical trajectory study of collisional excitation in Li++CO2
Authors: Schatz George C.
Published: February 2003

We present quasiclassical trajectory calculations of the state-to-state differential cross sections for vibrational excitation in Li++CO2 collisions and compare our results with analogous results of molecular beam experiments. In the trajectory calculations, the initial and final semiclassical eigenstates of CO2 are numerically determined before and after each collision by using a classical perturbation theory calculation of the good action-angle variables associated with molecular vibrational motion. Two approximations are used to simplify this action-angle analysis. First, an angular motion sudden approximation is introduced into the dynamics to separate angular from vibrational motion in solving the molecular Hamilton–Jacobi equation. Second, the off-diagonal parts of the intramolecular potential are neglected to eliminate Fermi resonant coupling between the bending and symmetric stretch modes. This latter approximation precludes the accurate determination of state-to-state cross sections to certain nearly degenerate states such as (020) and (100), but should still enable the accurate determination of the sums of the cross sections to those states (which is all that is available from experiment). The intramolecular potential is approximated in two different ways, both using pairwise additive potentials. In Surface I, the usual ion-induced dipole long range interaction is added to a sum of He–Ne pair potentials which simulate the short range Li+–C and Li+–O potentials. In Surface II, the sizes of the radius parameters in the short range part of Surface I are changed to correctly reproduce the anisotropy present in the experimentally derived He–CO2 interaction potential. The resulting ratios of inelastic to elastic differential cross sections (for the states (010), (020)+(100) and (030)+(110)) are in reasonable quantitative agreement with the experimental measurements, with errors typically smaller than a factor of two using Surface II at 4.72 eV translational energy and a factor of three at 6.87 eV. Some qualitative features of the angular distributions are actually quite accurately described, including the crossing of the (010) and (020)+(100) ratios near 24° at 4.72 eV and 18° at 6.87 eV, and the similar angular dependence of the (020)+(100) and (030)+(110) cross sections. In addition, a detailed interpretation of many features of the distributions of final vibrational states is developed, including relative propensities for certain types of overtone and combination mode excitation, and the variation in angular distributions as a function of final vibrational state.