bluuebunny/crossref_metadata_2025 huggingface dataset:
Density and temperature dependence of self-diffusion and shear viscosity of perfluorocyclobutane in the dense fluid region
Authors: Finney R. J. , Fury M. , Jonas J.
Published: February 2003

The self-diffusion coefficients of liquid perfluorocyclobutane have been measured as a function of temperature and pressure over the density range 1.8⩽ρ/ρc⩽2.9 and the temperature range 0.8⩽T/Tc⩽2.3. The NMR spin-echo technique was employed for the measurement of the diffusion coefficients using a steady magnetic field gradient. Shear viscosities and densities of perfluorocyclobutane have also been determined under the same experimental conditions. Both the diffusion coefficients and shear viscosities are interpreted in terms of the rough hard sphere model of liquids based on the modified Enskog theory. The effective hard core diameter and its temperature dependence are calculated. The Stokes–Einstein relationship with the slipping boundary condition was found to be valid for the liquid studied.
Temperature dependence of the refractive indices of liquids: Deviation from the Lorentz–Lorenz formula
Authors: Beysens D. , Calmettes P.
Published: February 2003

The temperature dependence of the refractive index of liquids is an old problem which has received much attention because experimental results depart significantly from the values inferred from the usual Lorentz–Lorenz formula. Using a sensitive interferometric device, we have very accurately measured the values of (∂n/∂T)p for 15 different molecular liquids, and we give the corresponding deviations from the values predicted by the Lorentz–Lorenz formula. We review the main phenomena able to explain this deviation. Although the Yvon theory gives an expression which well describes our experimental data, it must be considered as an empirical result, since drastic approximations have been made. As both the density correlations and the polarizability anisotropy cannot explain the whole deviation, electronic overlaps and distortions of the molecular framework necessarily affect the refractive index derivatives.
Bimolecular, single collision reaction of ground and metastable excited states of titanium with O2, NO2, and N2O: Confirmation of D(TiO)
Authors: Dubois Lawrence H. , Gole James L.
Published: February 2003

A beam-gas arrangement has been used to study the chemiluminescent emission which results when a thermal beam of titanium atoms (2200–2650 K) intersects a tenuous atmosphere (10−4 to 10−5 torr) of thermal O2, NO2, and N2O molecules (300  K). The visible chemiluminescence extends from 7000 to ∼4000 Å for the titanium–O2 reaction and 7000 to ∼3000 Å for the titanium–NO2 and titanium–N2O reactions. The emission which characterizes the Ti–O2 reaction corresponds predominantly to the B 3Π–X 3Δ and C 3Δ–X 3Δ band systems of titanium monoxide. Some weak emission corresponding to the c 1φ–a 1Δ band system is also observed. The emission from the Ti–NO2 and Ti–N2O reactions is considerably more complicated; however, both reactions are characterized by strong B 3Π–X 3Δ and C 3Δ–X 3Δ emission features. The Ti–N2O reaction also displays strong emission from the D–X 3Δ TiO band system. A detailed analysis of the emission spectrum resulting from the Ti–O2 reaction is presented. Although emission is observed from the seven lowest vibrational levels of the C 3Δ state, only the emission from 0⩽v′⩽4 is the result of a bimolecular process. The v′=5,6 levels are formed in a process second order in oxygen molecules. The temperature dependence of the chemiluminescent spectrum is analyzed. From this analysis, we determine a slope heat for the process which produces the titanium atom whose reaction with O2 leads to the observed chemiluminescence. This slope heat is used to deduce the activation energy for the possible processes which lead to TiO C 3Δ chemiluminescence. We combine this analysis with a comparative study of the chemiluminescence resulting from the Ti–O2 and Ti–N2O reactions and conclude that emission from the Ti–O2 reaction is due overwhelmingly to a metathesis involving excited state titanium atoms. Further analysis demonstrates that the reaction of Ti(5F) excited states is the most likely process leading to the observed C 3Δ–X 3Δ emission. Combining the results of temperature and pressure dependence measurements on the Ti–O2(TiO) chemiluminescent spectrum, we deduce a lower bound of 159.8±3 kcal/mole for the dissociation energy of ground state titanium monoxide. This lower bound is in close agreement with recent mass spectrometric studies. The present study is the first to demonstrate the importance of temperature calibration in single collision chemiluminescent studies and demonstrates the implications of such measurements for accurate mechanistic and thermochemical determinations. Ramifications for previous studies are discussed. Using available spectroscopic data, we generate an RKR potential for the first ten levels of the C 3Δ state of TiO and deduce Franck–Condon factors for the C 3Δ–X 3Δ transition. Based upon these results, a semiquantitative indication of relative (v′) vibrational level populations is presented for the Ti–O2 reaction.
Clausius–Mossotti formula for anisotropic dielectrics
Authors: Urano Kaoru , Inoue Masayoshi
Published: February 2003

The static dielectric constant of a simple anisotropic dielectric model, which consists of anisotropically polarizable molecules, is calculated with the aid of the extended Fröhlich formula, and a molecular Clausius–Mossotti type formula is obtained. The macroscopic Clausius–Mossotti formula for anisotropic dielectrics is also derived. In these calculations the inside field and the reaction field in anisotropic dielectrics have been used, the derivation of which is given in detail.
Determinations of structure and bonding in vitreous B2O3 by means of B10, B11, and O17 NMR
Authors: Jellison G. E. , Panek L. W. , Bray P. J. , Rouse G. B.
Published: February 2003

B10, B11, and O17 NMR were used to study B2O3 glass. B10 NMR was employed to determine the most probable values and the Gaussian widths (σ) of the distributions of the quadrupole coupling constant (Qcc) and the asymmetry parameter (η). The resulting values are Q0cc=5.51 MHz, σQcc=0.21 MHz, η0=0.12, and ση=0.043. These values are consistent with results using B11 NMR. The O17 NMR spectra are obtained and analyzed using two sites: site 1 is characterized by Q0cc=4.69 MHz, σQcc=0.10 MHz, η0=0.58; site 2 is characterized by Q0cc=5.75 MHz, η0=0.4, and ση=0.2. Only small distributions are present for site 1 and for Qcc of site 2. A Townes–Daily calculation was employed, using the boroxol ring model of B2O3 glass, to determine the charge distributions and the B–O–B angle outside the boroxol rings. The results are consistent with a structure composed of randomly oriented boroxol rings.
SCF calculations for hydrogen in a spherical box
Authors: Ludeña Eduardo V.
Published: February 2003

SCF calculations for a hydrogen atom in a spherical box have been performed. The basis functions are products of STO’s and cutoff functions. The variations of the energy and the hyperfine splitting as functions of r0, the sphere radius, have been studied.
The use of Lanczos tridiagonalization in bounding eigenvalues
Authors: Lewchenko V. , Rosenthal C. M.
Published: February 2003

Lanczos tridiagonalization is applied to several problems: the one dimensional quartic oscillator, the two dimensional quartic oscillator, and a finite difference version of the latter. In each case high accuracy upper and lower bounds are established in excellent agreement with previous calculations.
Tests of alkali ion-inert gas interaction potentials by gaseous ion mobility experiments
Authors: Gatland I. R. , Viehland L. A. , Mason E. A.
Published: February 2003

Gaseous ion mobilities are mainly dependent on ion–neutral collision energies in the range 0.03–1 eV and, using a recently developed kinetic theory method, can be directly related to ion–neutral interaction potentials. In this paper, experimental mobilities are used to test recent theoretical calculations based on the electron–gas model of the interaction potentials for the twelve combinations of Li+, Na+, K+, and Rb+ with He, Ne, and Ar. The model potentials are quite good, but some systematic discrepancies with experimental mobilities exist. These discrepancies are analyzed in terms of the relation between the mobility and the ion–atom potential.
On accurate quantum mechanical approximations for molecular relaxation phenomena. Averaged j
z-conserving coupled states approximation
Authors: Goldflam Rudolf , Kouri Donald J.
Published: February 2003

A rigorous formal theory of relaxation phenomena within the framework of the averaged jz-conserving coupled states (jzCCS) (Ajz) approximation is developed. Using the expressions obtained in this paper, the Ajz approximation is shown to yield pressure broadening cross sections which are in exact agreement with full close coupling results for a He+HCl model system. Previous jzCCS approximations to pressure broadening cross sections, which were in complete disagreement with close coupling for all systems studied, are shown to be the result of incorrect labeling of jzCCS T-matrices by total angular momentum J rather than by the effective orbital angular momentum ?. The correctly labeled results are not only found to be highly accurate but also considerably simpler than the expressions resulting from incorrectly labeled jzCCS T-matrices. Expressions are also derived for NMR spin–lattice relaxation cross sections within the Ajz approximation. Because the decoupled dynamical equations may be solved much more easily than the full exact CC ones, it is now feasible for the Ajz pressure broadening and spin–lattice relaxation cross sections to be computed in an iterative procedure. This will enable one to use such experimental data as a tool for determining molecular interactions.
Kinetics of metastable excited state products in a beam–gas chemiluminescent reaction
Authors: Gole J. L. , Preuss D. R. , Chalek C. L.
Published: February 2003

The kinetics of a beam–gas chemiluminescent experiment are investigated. The first observations of collision induced emission from within an excited molecular electronic state are presented. The importance of a ’’loss mechanism’’ whereby metastable molecules are deactivated in wall collision is discussed. Comparisons with beam–beam chemiluminescent experiments are presented and the role of the excited state radiative lifetime is demonstrated.
Electron spin resonance of CrO4 3− in fluoroapatite Ca5(PO4)3F
Authors: Greenblatt M. , Pifer J. H. , Banks E.
Published: February 2003

Electron spin resonance spectra measured in CrO4 3− doped fluoroapatite Ca5(PO4)3F single crystals at liquid helium temperature show the presence of three magnetically nonequivalent chromate (V) tetrahedra indicating that hexagonal (P63/m) fluoroapatite similar to chloro- and hydroxyapatite undergoes a phase transition at low temperature to a phase of lower symmetry. Spin-Hamiltonian parameters determined by an analysis of the electron spin resonance spectra are presented. The ground state of the unpaired d1 electron is found to be dz2.
A shock tube study of the recombination of carbon monoxide and oxygen atoms
Authors: Dean Anthony M. , Steiner Don C.
Published: February 2003

Time resolved emissions from CO2 and the radiative recombination of CO and O (flame-band emission) have been monitored in a variety of N2O/CO/Ar mixtures. These mixtures were studied behind reflected shock waves at temperatures between 2100–3200 K and total concentrations between 2.5–7.7×1018 molecule/cm3. The flame-band detector was calibrated so that absolute concentrations of atomic oxygen could be determined. These data were shown to be consistent with the following mechanism: N2O+M=N2+O+M (I), N2O+O=2NO (II), N2O+O=N2+O2 (III), with kI=4.5×10−10 exp(−226kJ/RT) cm3 molecule−1⋅ s−1 and k2=k3 =7.7×10−11 exp(−117kJ/RT). This combination was also shown to be consistent with earlier data from this laboratory. CO2 was observed to increase linearly with time in these experiments, and an apparent recombination rate constant defined as kapp≡dCO2/dt/([CO] [O] [M]) was measured and found to be a function of pressure. This behavior was attributed to the presence of very small concentrations of hydrogenous impurities. Data at higher pressures were used to estimate the rate constant for the recombination CO+O+M=CO2+M (V) since the effect of impurities was minimized here. It was found that kV= (1.6±0.3) ×10−34 cm6 molecule−2⋅ s−1 between 2100–3200 K. This value is shown to be consistent with recent studies of CO2 dissociation which report ’’normal’’ activation energies.
Two-photon spectroscopy in the gas phase: Assignments of molecular transitions in benzene
Authors: Wunsch L. , Metz F. , Neusser H. J. , Schlag E. W.
Published: February 2003

Ro-vibronic resolved two-photon excitation spectra of benzene, C6H6, and C6D6 have been measured in the region of the S1 ←S0 transition which is parity and symmetry forbidden in two-photon absorption but can be induced by suitable  ungerade  vibrations. Rotational envelopes for the vibronic transitions are calculated for circular and linear polarized light excitation and are in good agreement with experiment. The polarization behavior is shown to change strongly across even a single band contour of a totally symmetric vibronic two-photon transition. The polarization analysis even for a randomly rotating gas phase molecule provides a severe constraint on the possible assignments and hence is an important tool for the assignment of new transitions. About 85% of the observed two-photon excitation spectrum of benzene can thus be assigned. The appearance of combination bands shows that anharmonic mixing plays an important role in the excited state.
Effects of ion speed distributions in flow-drift tube studies of ion–neutral reactions
Authors: Albritton D. L. , Dotan I. , Lindinger W. , McFarland M. , Tellinghuisen J. , Fehsenfeld F. C.
Published: February 2003

The effects of non-Maxwellian ion speed distributions on ion–neutral reaction rate constants measured in drift tubes are examined experimentally and are compared to the predictions of recent theories. The rate constants of strongly kinetic-energy-dependent ion–molecule reactions of O+ with O2, N2, and NO are measured separately in helium and argon buffer gases, in which the O+ speed distributions are expected to be very different. The differences between the helium-buffered and argon-buffered rate constants are often substantial. When different, the argon-buffered values are generally larger than the helium-buffered values at the same mean energy, indicating that the O+-in-argon distribution has a larger high-energy ’’tail’’ than the O+-in-helium distribution. The differences between the two sets of data are compared to predictions from (a) the Monte Carlo trajectory calculations of Lin and Bardsley, and (b) the moment solution of the Boltzmann equation of Viehland and Mason, both described in accompanying papers. The excellent agreement demonstrates that the non-Maxwellian ion speed distributions now pose no problems in the interpretation and application of the kinetic-energy aspects of the rate constants of atomic–ion reactions studied in rare-gas-buffered drift tubes.
Monte Carlo simulation of ion motion in drift tubes
Authors: Lin S. L. , Bardsley J. N.
Published: February 2003

The motion of a swarm of ions in a uniform electric field is studied by simulating the motion of a single ion through many collisions with neutral atoms in order to obtain the drift velocity, average energy, and velocity distribution for the ions. For K+ ions in He at low field strengths, the results agree well with the solutions of the Boltzmann equation by Kumar and Robson; and for K+ in Ar at all field strengths, the computed mobilities demonstrate that the Viehland–Mason moment method can give useful results, especially if carried through to third order. The velocity distributions computed for O+ ions in He and Ar are used in the accompanying paper by Albritton et al. to analyze drift tube measurements of O+ reaction rates. Significant deviations from the Maxwell–Boltzmann form have been found and are seen to have important effects in that application. Velocity distributions have also been obtained for Li+ in He. The sensitivity of ionic mobilities to changes in the ion–atom interaction potential is examined with particular reference to K+ ions in Ar.
Photoionization studies of the Kr2 and Ar2 van der Waals molecules
Authors: Ng C. Y. , Trevor D. J. , Mahan B. H. , Lee Y. T.
Published: February 2003

The photoionization efficiency curves of the Kr2 and Ar2 van der Waals dimers were obtained with the molecular beam technique in the wavelength ranges 850–965 Å (12.848–14.586 eV) and 750–855 Å (14.501–16.531 eV), respectively. The ionization potential of Kr2 was found to be 12.87±0.015 eV (963.7±1.2 Å), which agrees with the value obtained by Samson and Cairns. The ionization potential of Ar2 was found to be 14.54±0.02 eV (852.7±1.2 Å). Using the known ground state dissociation energies of Kr2 and Ar2, the dissociation energy of Kr+2, D0(Kr+2), is deduced to be 1.15±0.02 eV and that for Ar+2, D0(Ar+2), is 1.23±0.02 eV. The photoion yield curves of Kr2 and Ar2 are compared with that of Xe2. Prominent autoionization structure was observed to correspond to Rydberg molecular states which are derived from the combination of a normal and an excited atom in the 4p5ns (or 4p5nd) configuration for Kr and 3p5ns (or 3p5nd) configuration for Ar.
Attenuation and single electron charge-exchange cross sections of He+ on Ne and Ar in the 500–5000 eV energy range
Authors: Eisele Fred L. , Nagy Stephen W.
Published: February 2003

The absolute total charge-exchange cross sections of He+ on Ne and He+ or Ar have been measured using a parallel plate target ion collection method. The first set of collision partners have large but similar ionization potentials and the resulting cross sections agree reasonably well with theory. He+ on Ar collisions appear more complex, involving many interacting states. The resulting cross section does not show good agreement with existing two-state theory. In addition, a lower limit to the total collision cross section of these same two collisions has been determined via incident beam attenuation measurements. For each of these collisions, the cross section was found to decrease monotonically with increasing ion velocity. In the He+ on Ar collision, the measured total and charge-exchange cross sections were observed to coincide at energies above 3 keV.
Measurements of T1 and T2 relaxation cross sections for HDO
Authors: Williams J. R. , Casleton K. H. , Kukolich S. G.
Published: February 2003

Rotational relaxation cross sections for the 220, 221, and superposition states of HDO were measured using a beam maser spectrometer. Scattering gases used were H2O, D2O, HDO (50%), HCl, CH3F, NH3, OCS, CO2, N2, and Ar. For HDO–NH3 scattering, pure state cross sections were much larger than the superposition state cross section. For other scattering gases, pure state cross sections were slightly larger than the superposition state cross section.
Calculations of vibronic magnetic rotational strengths and oscillator strengths in the B1u state of benzene
Authors: Rosenfield Joan Samour
Published: February 2003

Vibronic oscillator strengths and magneto-optical B values are calculated for the 1B1u state of benzene and benzene-d6. The calculations are performed for geometries displaced in the direction of normal coordinates which couple this state with electric dipole allowed states, using the CNDO/S method. Oscillator strengths and the sign of the summed partial B values associated with each vibration agree with experiment. The lack of a high resolution magnetic circular dichroism spectrum prevents more detailed comparisons of B values with experiment.
Perturbation theory for the radial distribution function in the presence of three-body forces
Authors: Ram J. , Singh Y.
Published: February 2003

Perturbation theory is used to consider the effect of the three-body potential on the radial distribution function g (r). We find that the effective pair potential, ueff(1,2) =u (1,2)−kTρℱ g0(1,3) g0(2,3) f (1,2,3) d3, where g0(i,j) is the true pair potential radial distribution function, is an appropriate model for the study of the effect of the triplet potential on the g (r). Dividing the effective pair potential into repulsive and attractive regions, the radial distribution function of the reference potential is evaluated. It is shown, by calculating the total g (r) for the effective pair potential that, to first order, the effect of the triplet potential on the g (r) is accounted for by its effect on the reference g (r). We find that the effect of the triple-dipole potential on the structure of liquids at low temperatures especially near the triple point is substantial.
Intramolecular electron transfer in simple model systems: A propagator study
Authors: Ondrechen Mary Jo , Ratner Mark A.
Published: February 2003

The probability of site-to-site intramolecular electron or hole transfer as a function of time in simple model systems is calculated. Systems studied are the hydrogen molecule, allyl cation, and cyclopropenium ion, in the Hubbard model. We employ the method of electron propagators, using both exact and approximate (molecular orbital and valence bond) ground state wavefunctions. We conclude that the molecular orbital wavefunction affords a good description of the transfer process for a wide variety of systems. The utility of our approach for the calculation of electron transfer rates in which purely electronic effects are dominant is stressed.
The infrared and Raman spectra of solid CH3F and CD3F: Crystal structure inferences
Authors: Chao T. H. , Eggers D. F.
Published: February 2003

Infrared and Raman spectra are reported for solid CH3F and CD3F, and infrared spectra of dilute solid solutions of each substance in the other are also reported, in the region of the internal fundamentals and at temperatures near 80 °K (infrared) and near 130 °K (Raman). The crystal structure, based on the splittings in the spectra, is believed to be centrosymmetric with four molecules in the unit cell, similar to that of methyl bromide and methyl iodide. The possibility of longitudinal optical modes appearing in the Raman spectrum is considered; several reasons lead us to reject this suggestion. Overtones and combinations are assigned, in both infrared and Raman spectra, and shifts between gas and solid phases are discussed.
Scattering of atoms by a stationary sinusoidal hard wall: Rigorous treatment in (n+1) dimensions and comparison with the Rayleigh method
Authors: Goodman Frank O.
Published: February 2003

A rigorous treatment of the scattering of atoms by a stationary sinusoidal hard wall in (n+1) dimensions is presented, a previous treatment by Masel, Merrill, and Miller for n=1 being contained as a special case. Numerical comparisons are made with the GR method of Garcia, which incorporates the Rayleigh hypothesis. Advantages and disadvantages of both methods are discussed, and it is concluded that the Rayleigh GR method, if handled properly, will probably work satisfactorily in physically realistic cases.
On the stability of a fluid toward solid formation
Authors: Lovett Ronald
Published: February 2003

A traditional search for solidlike singlet densities in a system with a fluidlike pair distribution function is undertaken. The analysis is based upon a nonlinear integral equation relating the direct correlation function and the singlet density in contrast with previous analyses based upon similar relations between the singlet and pair number densities. An investigation is also made of the mechanical stability of such a system and it is found that a solidlike solution and mechanical instability appear simultaneously. Numerical analysis shows that the three-dimensional hard sphere system remains stable at all densities but that an additional attractive pair interaction produces a physically reasonable instability.
Dynamic multipoles in molecular crystals
Authors: Luty Tadeusz
Published: February 2003

The lattice energy of molecular crystals is expressed in terms of interactions between effective dynamical multipoles. The multipole moments are characteristic for a given molecule in a crystal; they depend on the arrangement of the molecules in the lattice and can be considered as self-consistent ones. The cohesive energy of the crystal is described as interactions between static multipoles, i.e., those parts of the multipoles which do not depend on displacements of molecules treated as rigid bodies. The remaining parts of the moments, depending on molecular displacements, represent the multipole moments induced by the lattice vibrations. The general equation for lattice vibrations in molecular crystals is derived and the dynamical matrix is expressed by the effective charge distributions and lattice sums. The conception of dynamical multipoles put forward in this paper relates frequencies and infrared intensities of lattice vibrations within the same model.
Intermolecular forces and thermodynamical functions of orthorhombic polyethylene lattice
Authors: Kobayashi Masamichi , Tadokoro Hiroyuki
Published: February 2003

Infrared and Raman data which are related to the intermolecular forces of the orthorhombic polyethylene lattice, the lattice mode frequencies, and the correlation field splittings of the methylene rocking and scissoring modes have been summarized through the temperature range of room to liquid helium temperature. The normal mode frequencies have been calculated for the three-dimensional crystal lattice with the dimensions measured at various temperatures, two values of the setting angle, 48.8° and 42°, being adopted for the calculation. A pairwise intermolecular force field has been assumed and the Buckingham type potential functions V (r) =B exp(−Cr)−Ar−6 (r is the interatomic distance) have been taken into account for the atomic pairs of H–H and C–H with r<4.0 Å. The potential parameters for both kinds of atomic pair have been determined by the least-squares method so as to reproduce the observed frequency data through the wide temperature range, and compared with the values reported previously. The errors involved in the intermolecular force constants thus determined and also in the calculated frequencies due to the uncertainty in the value of the setting angle assumed in the calculation have been estimated by the error-transfer method. For the temperature dependence of the lattice mode frequencies an appreciable amount of discrepancy has still been recognized even after repetition of least-squares fittings. This may be due to the approximation of the pairwise intermolecular potential and also to the anharmonic character of the lattice vibrations. The observed B1u–B2u correlation field splitting of the CH2 rocking, as well as the νa–νb splitting for the ν8 (the CH2 rocking–twisting) branch has been reproduced fairly well by the present calculation. Using the potential functions thus obtained, the thermodynamical functions, the internal energy, the entropy, the Helmholtz free energy, and the heat capacity of the orthorhombic polyethylene lattice have been calculated in the quasiharmonic approximation, giving a good agreement with the experimental results obtained by thermal measurements.
Analysis of translational band observed in gaseous and liquid Kr–Ar mixtures
Authors: Buontempo U. , Cunsolo S. , Dore P. , Maselli P.
Published: February 2003

The translational absorption spectrum of Kr–Ar gaseous and liquid mixtures, arising from the collision-induced dipole moment, has been measured in the 13–300 cm−1 frequency region. From the translational band obtained in the gaseous phase we have derived the intensity and the range ρo of the induced dipole moment. The high frequency part of the spectrum observed in the gaseous phase is similar in shape to that observed in the liquid phase. The low frequency part of the spectrum obtained in the latter case is dominated by the intercollisional interference effect and is discussed in terms of a simple model for the motion of the impurities in the liquid. We have also derived the value of the mean square force 〈F2〉 acting on the impurity dissolved in the liquid matrix.
Dyamics of calf-thymus DNA by single-clipped photon correlation
Authors: Chen F. C. , Yeh A. , Chu B.
Published: February 2003

Time-dependent correlation functions of calf-thymus DNA (Mw=12×106 dalton) and homogenized calf-thymus DNA (Mw=1.5×106 dalton) were measured by means of a 96-channel single-clipped digital photon correlation spectrometer over a range of scattering angles varying from 15° to 120°. Several models as well as the method of cumulants were used to analyze our experimental data which were found to contain at least two decay times. While we agree with earlier findings on the complexity of the time-dependent correlation functions for DNA, our results have led us to different conclusions. For example, we could not find the ’’longest relaxation time.’’ Instead, we observed a simple K2 dependence on the linewidth (Γ) of the low-frequency component of time-dependent correlation functions at small scattering angles, where K is the magnitude of the momentum transfer vector. Furthermore, we were able to identify those low-frequency component (Γ/K2) values with the translational self-diffusion coefficient which had been determined by independent light scattering and ultracentrifugal studies.
Electronic energy transfer between single vibronic levels of C6H6 and C6D6 vapors
Authors: Parmenter C. S. , Setzer B. , Tang K. Y.
Published: February 2003

The collisional transfer of electronic energy from the zero point level of S1, C6D6, to specific levels in S1, C6H6, is studied by observation of resolved fluorescence from mixtures of C6H6 and C6D6 vapors. Strong vibronic effects and high efficiencies are observed. The transfer populates predominately the C6H6 zero point level (ΔE=−203 cm−1) in spite of the near resonance (ΔE=+37 cm−1) of the C6H6 fundamental ν′16 with the initial C6D6 level. The respective cross sections for populating the S1 zero point level and the ν16 fundamental are about 0.6 and 0.1–0.2 of gas kinetic values. Energy transfer by the Förster dipole mechanism cannot account for these efficiencies. Among the possible routes to S1 zero point C6H6 formation in collisions between excited C6D6 and thermal ground state C6H6 molecules, the dominant path is the Δν=0 route C6D6(S1;00) +C6H6(S0;00) →C6D6(S0;00)+C6H6(S1;00). The cross section for this particular state-to-state reaction is about equivalent to the gas kinetic value.
Rotationally inelastic scattering of two HF molecules
Authors: DePristo Andrew E. , Alexander Millard H.
Published: February 2003

For rotationally inelastic HF–HF collisions we have determined fully quantum partial opacities and integral cross sections for the j1=0, j2=0→11, 02, and 22 transitions at total energies of 500, 1000, and 8000 cm−1 and the 11→02 transition at 1000 cm−1. The potential was obtained from a recent fit of an ab initio surface and consisted of a spherically symmetric component and an anisotropic term with dipole–dipole symmetry. The collision dynamics were treated using the recently developed decoupled l-dominant (DLD) and coupled-states (CS) methods as well as within the Born approximation (BA). Comparison with selected full close-coupling calculations indicates that the CS method is very accurate for processes where collisions at small impact parameter play a large role, while the DLD method is to be preferred when large parameter collisions make the major contribution. The BA is, unfortunately, consistently unreliable, overestimating cross sections by more than an order of magnitude except at high energy. Additionally, the BA does not predict correctly the relative ratio of the 11→02 to 11→00 cross sections.
The optical and spectroscopic properties of the sulfate ion in various crystalline environments
Authors: Wu G. J. , Frech Roger
Published: February 2003

The electronic polarizability components of the sulfate ion in LiKSO4, KNaSO4, K2SO4, Na2SO4, and K2Mg2(SO4)3 were calculated from the optical refractive indices using a point dipole model. The values obtained were discussed in terms of the immediate crystalline environment of the sulfate ion. The frequencies of the transverse and longitudinal internal optic modes were measured by polarized Raman scattering experiments and estimated from near-normal incidence reflectivity spectra. The frequency data were analyzed in a molecular dipole model formalism with static crystal field frequencies and molecular dipole moment derivatives of the internal modes of the sulfate ion being reported and discussed.
Electron spin resonance of vanadyl ions in single crystals of strontium formate dihydrate
Authors: Sathyanarayan S. G. , Narayana M. , Sastry G. Sivarama
Published: February 2003

Electron spin resonance and optical absorption studies of vanadyl ions in single crystals of strontium formate dihydrate are reported. VO2+ is found to take up substitutional sites. The spin-Hamiltonian parameters and molecular orbital coefficients indicate covalency in the complex.
Incorporation of electronically nonadiabatic effects into bimolecular reactive systems. I. Theory
Authors: Top Zvi H. , Baer Michael
Published: February 2003

Electronic nonadiabatic interactions are smoothly incorporated into existing exact quantum mechanical methods for treating reactive (or nonreactive) bimolecular systems. A known method for treating reactive systems on a single surface is first given, and then it is shown how to proceed to include electronically nonadiabatic effects. The unexpected result is that the final equations are very similar to those of the one surface case and, therefore, existing methods for treating the single surface case can be directly applied to the many surface case. For the sake of simplicity the study is performed in the frame of the collinear model, but the treatment can easily be extended to three dimensional systems.
Energy dependence of the nonradiative electronic relaxation in camphorquinone vapor
Authors: Avouris Phaedon , Hopewell William D. , El-Sayed M. A.
Published: February 2003

The excess energy dependence of the fluorescence lifetime of gaseous camphorquinone is reported. The non-radiative decay of camphorquinone molecule is deduced from the fluorescence lifetime. (AIP)
Gaussian basis sets for the atoms gallium through krypton
Authors: Dunning Thom H.
Published: February 2003

Hartree-Fock calculations are reported on the atoms gallium through krypton using (13s9p5d) and (14s11p5d) Gaussian basis sets. (AIP)
Rotational energy distributions for homonuclear diatomic beams scattered from solid surfaces: A hard-cube model
Authors: Nichols William L. , Weare John H.
Published: February 2003

Rotational energy distributions of diatomic molecular beams scattered from solid surfaces are calculated with a hard-cube model previously used to compute scattering patterns. The extent of energy transfer between rotational and translational degrees of freedom in a scattering system is examined. Both rotationally cold and hot incident beams are considered. The calculations are all numerical.
Spin Hamiltonians and pair interactions of Co2+ in MgSiF6⋅6H2O, ZnSiF6⋅6H2O, and CoSiF6⋅6H2O
Authors: Francis C. L. , Culvahouse J. W.
Published: February 2003

The spin-Hamiltonian parameters including the orientation of the principal axes have been determined for the two ions in the monoclinic unit cell of the low temperature form of MgSiF6⋅6H2O. The principal values of the g tensor gzz=7.15, gyy=2.73, and gxx=2.17 are close to the values 6.85, 2.7, and 2.1 determined in this investigation for CoSiF6⋅6H2O which has a similar structure. Magnetic interactions determined from pair spectra in the Mg crystal appear to apply to the four nearest neighbor pairs in the monoclinic structure. The values of the pair interactions in the Mg crystal are quite consistent with the magnetic and thermal properties previously determined for CoSiF6⋅6H2O and with the electron paramagnetic resonance linewidths determined here. The magnetic interactions are vastly different for the nearest and the next nearest neighbor despite their almost identical distances, and the interactions of Co2+ pairs are much different for all neighbors in the rhombohedral host ZnSiF6⋅6H2O. It is suggested that these large variations are due to changes in the orientation of the water octahedra which affect the hydrogen bonding between neighboring octahedra.
Hard spherocylinders in an anisotropic mean field: A simple model for a nematic liquid crystal
Authors: Cotter Martha A.
Published: February 2003

A simple model for a nematic liquid crystal is presented, in which the short-range intermolecular repulsions are represented by repulsions between hard spherocylinders, and the (anisotropic) intermolecular attractions are treated self-consistently in the mean field approximation. Using scaled particle theory, an expression for the total configurational free energy is derived and from it the equation of state and other thermodynamic properties of the system in the nematic and isotropic phases are obtained. Extensive numerical results for a model system with a molecular length-to-breadth ratio of three are compared with available experimental data for the common nematogen p-azoxyanisole. Excellent qualitative agreement between theory and experiment is obtained: using reasonable values of the two mean field energy parameters, one can predict the nematic→isotropic transition temperature and the ratio γ= (−ρ/T) [(∂ η/∂ ρ)T/(∂ η/∂ T)ρ] quantitatively (η and ρ are the nematic order parameter and the number density, respectively) while explaining other aspects of the experimentally observed behavior qualitatively. The central question of the relative importance of intermolecular attractions and repulsions in stabilizing nematic order is discussed in the light of these results and of related work by several other authors.
Influence of molecular structure and temperature on trapped electron yields in γ-irradiated hydrocarbon glasses. Trapped electron decay in 2,4-dimethylpentane at ?22 K
Authors: Kimura T. , Bremer N. , Willard J. E.
Published: February 2003

G values (100 eV yields) determined in this work, and taken from the literature, for the production of trapped electrons by γ irradiation of 18 hydrocarbon glasses at 77 K range from 0.02 to 1.1. Small changes in molecular structure of the matrix molecules, such as the differences between 2-methylpentane, 3-methylpentane, and 3-ethylpentane are often accompanied by large changes in G (e−t). It appears that the effects of molecular structure must be attributed either to differences in the concentration of sites which favor trapping in competition with reaction with cations or radicals, or to the influence of molecular structure and matrix structures on tunneling probabilities. The G (e−t) values for six hydrocarbons at 4 K are in each case lower than at 77 K. Electrons produced in 2,4-dimethylpentane (2,4-DMP) glass at 4 K by γ irradiation decay at 22 and 13 K and with the same rate, implying a tunneling mechanism. Electrons produced in 2,4-DMP at 77 K and observed at 77 K decay more slowly, presumably because of the greater average trap depth. No observable electron decay occurs at temperatures <50 K in the other hydrocarbons tested in this region. G (e−t) values for glassy solutions of cyclopentane in methylcyclohexane increase with increasing cyclopentane concentration over the range of 1.5–57 mol%.
The viscosity of five gaseous hydrocarbons
Authors: Kestin J. , Khalifa H. E. , Wakeham W. A.
Published: February 2003

The paper presents new data on the viscosity of CH4, C2H4, C2H6, C3H8, and C4H10 at atmospheric pressure and in the temperature range 25–200°C. The measurements were absolute and were performed in an oscillating-disk instrument. The results fit into the extended law of corresponding states of Kestin, Ro, and Wakeham. The scaling constants σ and ε for each gas which assure such a fit are calculated in the paper.
A systematic treatment of quantum mechanical reaction coordinates
Authors: Witriol N. M. , Stettler J. D. , Ratner M. A. , Sabin J. R. , Trickey S. B.
Published: February 2003

The problem of constructing an orthogonal curvilinear coordinate system which retains the intuitive clarity of the reaction path concept is treated by canonical point transformation. The Hamiltonian describing the collision process is transformed rigorously onto the reaction-coordinate net; no linearization or approximation is employed. Difficulties inherent in earlier work (e.g., triple-valued regions, restriction to regions very close to the reaction path, etc.) do not occur. The transformed momenta and Hamiltonian are obtained in general. A simple, yet useful, example transformation is worked out in detail and applied to a realistic problem, the LEPS potential surface for H+Cl2→HCl+Cl. The example transformation is also used in a comparison of our method with that of Marcus. The canonical mapping of Connor and Marcus is shown to be a special case of the present method. Applications of the procedure to polydimensional surfaces, dissociative reactions, and actual dynamical calculations are discussed.
Configurational packing statistics of polymers near a surface. I. The generalization of the rigid rod case to include both orientation dependence and spatial variation
Authors: DiMarzio Edmund A.
Published: February 2003

The following problem is solved: What is the total number of ways to pack rigid rod molecules together given that the number density f (Ω,r) at each point r and each orientation Ω are specified. This constitutes a generalization of previous work which allowed for only Ω dependence. The problem is first solved for a cubic lattice and then generalized to a continuous variation of both position and orientation. The problem of minimizing the associated free energy is solved. The results are applicable to determination of the adsorption properties of rigid rod molecules near a surface as well as liquid crystal behavior.
The molecular structure of a liquid–vapor interface: Comments on the integral equation approach
Authors: Co K. U. , Kozak J. J. , Luks K. D.
Published: February 2003

A review of attempts to obtain interfacial density profiles by integral equation methods is presented. The first equation of the Yvon–Born–Green hierarchy is solved for ρ(1)(z) for the vapor–liquid interface, using square-well g(2)(r) data input generated by solving the second equation of the Yvon–Born–Green hierarchy. The method used in solving the first equation is discussed. Profiles are presented for three reduced temperatures spanning the vapor–liquid coexistence locus. The properties surface tension and surface excess internal energy are computed using statistical mechanical formulae and the ρ(1)(z) and g(2)(r) data generated.
Model networks of end-linked polydimethylsiloxane chains. I. Comparisons between experimental and theoretical values of the elastic modulus and the equilibrium degree of swelling
Authors: Mark J. E. , Sullivan J. L.
Published: February 2003

Two samples of hydroxyl-terminated polydimethylsiloxane having molecular weights the order of 2×104 and 1×103 g mol−1 were separated into a total of six fractions of relatively narrow molecular weight distribution. Portions of one of the unfractionated polymers and each of the fractions were cross-linked by reacting the hydroxyl chain ends, in the undiluted state, with a tetrafunctional orthosilicate. The resulting networks of end-linked chains were studied with regard to their stress–strain isotherms in elongation at 25°C and their equilibrium swelling in benzene at room temperature. Values of the elastic modulus obtained from the isotherms support theoretical arguments that fluctuations in the network chain vectors reduce the value of the modulus to approximately one-half of the value predicted for affine deformations of chain vectors constrained in their fluctuations by cross-links firmly embedded in the network medium. Values of the equilibrium degree of swelling of the networks calculated on this basis are also in good agreement with experiment. The networks formed by end-linking relatively short chains have small values of the semiempirical constant 2C2 used as a measure of the departure of an observed stress–strain isotherm from the form predicted by theory. Although this observation is consistent with the suggestion that such end-linked networks have a much smaller number of interchain entanglements than do randomly cross-linked networks, other evidence and arguments unfortunately do not support this assumption.
Chain reaction chemiluminescence of alkaline earth catalyzed N2O–CO flames
Authors: Benard D. J. , Slafer W. D. , Hecht J.
Published: February 2003

The combustion of a dry N2O–CO mixture was initiated upon mixing the gases with Mg, Ca, or Sr atoms entrained in a He carrier flow. The flames were supported in a low pressure, fast flow reactor and were marked by intense chemiluminescence corresponding to the metal atom 3P1→1S0 transition and the well known molecular bands of the metal oxides. Additionally, bands in the visible and ultraviolet were observed. By comparison with the similar banded emissions obtained upon mixing active nitrogen with metal–N2O and metal–H2O flames, it was possible to distinguish the chemiluminescence obtained in the dry N2O–CO flames from the nearly identical metal monohydroxide flame bands. The new bands are identical to those previously obtained in arcs and they are shown to correspond to transitions between excited triplet and singlet states of the diatomic metal oxides. Photon yield studies and intracavity resonant absorption measurements further indicate that these systems are prime candidates for development as a three level chemically driven electronic transition laser system.
Franck–Condon factors in studies of dynamics of chemical reactions. I. General theory, application to collinear atom–diatom reactions
Authors: Schatz George C. , Ross John
Published: February 2003

We derive and show the utility of an approximate theory of chemical dynamics based on a generalized Franck–Condon factor. We begin by showing how the general expression for the transition matrix for an electronically adiabatic reaction may be rewritten in terms of a transition between two surfaces through the use of a quasiadiabatic representation. This exact transition matrix may be reduced to a Franck–Condon overlap integral in a variety of ways, and one possible sequence of approximations for accomplishing this reduction is outlined. We neglect terms due to virtual transitions to excited electronic states, make a Born–Oppenheimer approximation, neglect terms involving gradients of the nuclear wavefunction (low kinetic energy approximation), and finally make a Franck–Condon approximation. The overlap is then evaluated for the special case of collinear exoergic atom–diatom reactions for the purpose of studying product state vibrational distributions in these reactions. The evaluation is done approximately by using physical arguments to estimate the general appearance of the reagent and product quasiadiabatic surfaces, and assuming separable solutions to the Schrödinger equation on each surface. The overlap integral is then further approximated by expanding the integrand about the nuclear configuration of maximum overlap. This enables us to obtain a simple analytical result for the product state distribution, using either harmonic or Morse oscillator vibrational wavefunctions. We then use the resulting expressions to study the dynamics of the collinear F+H2(D2) and H(D)+Cl2 reactions. In both applications we find that the Franck–Condon overlap is capable of a qualitatively correct description of the product state distributions, including dependence on reagent translational energy, mass ratios, and various features of the potential energy surface. Furthermore, a physical description of the origin of a dynamic threshold effect in the F+H2(D2) reaction is provided, as is a simple interpretation of the role of potential energy release behavior in the determination of product state distributions.