bluuebunny/crossref_metadata_2025 huggingface dataset:
Pressure and temperature dependence of the unimolecular decomposition of HO2NO2
Authors: Graham Richard A. , Winer Arthur M. , Pitts James N.
Published: February 2003

The pressure and temperature dependence of the unimolecular decomposition of pernitric acid HO2NO2→NO2+HO2 have been studied in the presence of excess nitric oxide by Fourier transform infrared spectroscopy in a 5800 liter, Teflon-lined chamber over the temperature range 261 to 295°K with N2 or O2 pressures between 1 and 760 torr. The rate constant in the second-order kinetic regime was determined to be 5.2×10−6 exp[−19 900±500/RT] cm3 molecule−1 sec−1 for N2 pressures up to ∼7 torr. The pressure dependence of the reaction between the second-order region and 1 atm pressure was determined for N2 and O2 at 278°K and for N2 at 261°K and fitted to an empirical rate constant expression for use in atmospheric modeling calculations. Extrapolation of the data at 278°K gave a limiting first-order high pressure rate constant of ∼0.018 sec−1. The relative efficiency of O2 as an M gas relative to N2 (1.0) between 1 and 760 torr was 0.83±0.12. The implications of these results for the reaction of HO2 with NO2 and for HO2NO2 kinetics in the stratosphere are discussed.
Thermochemical properties of atoms and molecules in specific quantum states
Authors: Gardiner W. C. , Levine R. D.
Published: February 2003

Procedures are described for computing thermochemical properties in the ideal gas state for atoms and molecules in specific quantum states, and in thermal or nonthermal distributions over specific groups of quantum states. Formulas are given to generate values in the JANAF-compatible format. Applications to electronic states of atoms, vibrational and vibration–rotational states of diatomic molecules, and vibrational states of polyatomic molecules are given as illustrations. It is shown that the choice of procedure for obtaining partition functions has only a minor effect upon the accuracy of the results, the major factors being the energy of the specified state(s) and the accuracy to which the heat of formation of the species itself is known. Procedures are developed for describing systems in which species in specified quantum states are considered together with the same species in a Boltzmann internal distribution, and for expressing the thermochemical properties of state-selected species as polynomials in temperature.
On the selection of sign for the observable dipole moment derivatives
Authors: Aroca R. , Mercau N. , Robinson E. A.
Published: February 2003

The main criteria used in relation to the task of selecting a unique sign set for the experimental dipole moment derivatives, such as isotopic invariance of atomic polar tensors and effective charges ξα, are discussed. It is shown that the selection of a principal axis frame is particularly relevant to this problem. Conclusions are illustrated with a complete discussion of sign sets for CH3X and CD3X (X=F, Cl, Br, I) molecules.
Ultraviolet-laser induced fluorescence of UF6 isolated in argon matrices
Authors: Grzybowski Joseph M. , Andrews Lester
Published: February 2003

Fluorescence spectra of UF6 isolated in solid argon at 12 K and excited at 350.7, 356.4 nm have been studied as a function of concentration. The spectra indicate substantial solute–solute interaction for Ar/UF6 ratios less than 800/1. The most dilute samples, Ar/UF6=1800/1, gave strong sharp progressions in the ν5 (T2g) mode, weaker series in the ν1 (A1g) mode and strong combination progressions of ν1 and ν5 with the ν6 (T2u) mode of the UF6 molecule. At higher solute concentrations, vibrational structure is coalesced into a broad series of bands spaced 200±20 cm−1 apart. The vapor phase, matrix isolation and solid UF6 fluorescence spectra are compared.
Hypernetted-chain equation of state for the two-dimensional Lennard-Jones fluid
Authors: Glandt Eduardo D. , Fitts Donald D.
Published: February 2003

Values of the radial distribution functions and thermodynamic properties for the two-dimensional Lennard-Jones fluid are obtained from the hypernetted-chain (HNC) theory. Results are reported for a wide range of temperatures and densities and are compared with computer simulations and with our earlier Percus–Yevick (PY) values. The HNC radial distribution functions agree with the computer simulations better than do the PY results, but the PY theory yields more accurate thermodynamic properties.
Energy partitioning in the quenching reaction N2(A 3Σ+u, v
i)+N(4S) →N(2P or 2D) +N2(X 1Σ+g, v
f) in solid nitrogen
Authors: Kunsch P. L.
Published: February 2003

The vibrational excitation of N2 observed in the quenching of triplet N2 by a nitrogen atom in a solid matrix is explained by a short-range interaction N2(3Σ+uvi ?0)+N(4S) →N(2D, 2P)+N2(1Σ+gvf ≫0). The golden-rule model gives a simple interpretation of the vibrational distribution vf as a shifted Franck–Condon envelope 〈vi‖vf〉. We treat this system by calculating classical trajectories on an empirical but entirely a priori potential surface of the appropriate N3 states. For that purpose the LEPS formalism for three σ electrons is extended to nine electrons belonging to σ as well as π orbitals. Using a simple surface-hopping method we compare different nonadiabatic pathways. An atom exchange described by a unique diabatic potential seems to be the dominant reaction channel. Agreement between Monte Carlo averaged calculation of the vibrational distribution vf and experiment is surprisingly good considering that no parameter is fitted.
Vibrational analysis of the S2→S1 fluorescence of azulene in a naphthalene mixed crystal at 4.2 K
Authors: Gillispie Gregory D. , Lim E. C.
Published: February 2003

The S2→S1 fluorescence of azulene in a naphthalene mixed crystal has been measured from 740 to 1000 nm at 4.2 K. Of the 25 in-plane fundamentals (exclusive of C–H stretches) of the S1 state, 20 are readily identifiable in emission. A number of other bands are present in the spectrum and these are tentatively identified as S1 out-of-plane vibrations induced by vibronic coupling to σπ* and/or πσ* excited electronic states. An emission previously assigned as T1→S0 phosphorescence is shown to be a combination band of S2→S1 fluorescence. The branching ratio of S2 →S0 fluorescence to S2→S1 fluorescence is approximately 7500 for xenon arc lamp excitation; this is an order of magnitude larger than the value reported for short pulse laser excitation. A summary of photophysical parameters for the low-lying electronic states of azulene, based on the most recent and reliable experimental data, is also presented.
Environmental effects on radiative rate constants with applications to linear polyenes
Authors: Andrews John R. , Hudson Bruce S.
Published: February 2003

An expression for the solvent dependence of the radiative rate constant of a forbidden transition in the presence of vibronic mixing is derived from perturbation theory. The case of nonpolar solvents and nonpolar fluorophores is considered. It is shown that the radiative rate constant, corrected for local field effects, depends on solvent–fluorophore dispersion interactions whose effect is to modulate the energy separation between the vibronically coupled borrowing and lending states. Analysis of radiative rate data for the linear polyenes diphenylhexatriene and trans-retinol gives quantitative agreement with theory. Other linear polyenes with larger separations between their first two excited singlet states are predicted to have radiative rates which do not vary appreciably with solvent polarizability as is observed. The procedure used to derive an expression for the solvent dependence of the radiative rate is not restricted to the linear polyenes but is generally valid.
Near infrared absorptions of neon, argon, krypton, and xenon excited diatomic molecules
Authors: Arai Shigeyoshi , Oka Takefumi , Kogoma Masuhiro , Imamura Masashi
Published: February 2003

Two types of transient absorptions due to excited diatomic molecules have been observed for neon, argon, and krypton irradiated with electron beam pulses in following wavelength regions: 8000 to 8200 Å and 9000 to 10 300 Å for neon, 9500 to 10 000 Å and 11 400 to 13 000 Å for argon, and 9500 to 10 000 Å and 11 600 to 14 000 Å for krypton. The first absorptions located at shorter wavelengths consist of several discrete bands and their lifetimes are longer than those of the second absorptions located at longer wavelengths. In addition, the intensities of the second absorptions are much weaker than those of the first absorptions. We have failed to observe the second absorption of xenon, which may be located at longer wavelengths than the observation limit. The time-dependent changes of absorption spectra suggest the formation of vibrationally and rotationally excited molecules. We attribute the lower state of the first absorption to the lowest triplet state 1u(3Σ+μ) and the upper one to the state 3Πg resulting from a combination of a ground state atom p0(1S0) and any of low-lying Paschen 2p excited atoms. The lower state of the second absorption is attributed tentatively to the lowest excited singlet state O+μ(1Σ+μ), while the upper state may be to 1Πg or 3Σ+gO.
Mean field theory of the hydrodynamics of concentrated polymer solutions
Authors: Freed Karl F. , Metiu Horia
Published: February 2003

A self-consistent theory of the hydrodynamics of concentrated polymer solutions is derived. The lowest order approximation within this theory is equivalent to the result of a diagrammatic summation of the multiple scattering expansion carried out by Freed and Edwards, and it automatically provides the generalization to the case where chain interactions of a nonhydrodynamic nature are also present within and between the chains. The corrections to the Freed–Edwards theory are analyzed to establish the theory’s range of validity. It is explicitly demonstrated that the theory is valid when interchain correlations do not persist over macroscopic distances for times comparable to or greater than the inverse of the probing frequency. A simple heuristic derivation, which highlights the physical content of the Freed–Edwards theory, is also presented to complete and reinforce the conclusions of the mathematical discussion.
Inelastic light scattering studies of the protonic order–disorder transition in SnCl2⋅2H2O
Authors: Satija S. K. , Wang C. H.
Published: February 2003

Raman and Brillouin scattering spectra of SnCl2⋅2H2O in several scattering configurations were studied as a function of temperature, with special emphasis on the phase transition at 218 K. The O–H stretching vibration region was investigated for the first time. A sharp band at 3500 cm−1 has been assigned as the O–H stretching vibration involving the proton not participating in the hydrogen bond formation. The spectral line width of this band shows anomaly near the phase transition temperature and has been interpreted as due to the reorientation of H2O molecules of type II. The low frequency Raman spectra were also studied. The bands at 250 and 320 cm−1 both display a similar striking frequency shift with respect to temperature change. These frequency versus temperature data have been interpreted in terms of the proton population at position 5. The Brillouin spectra obtained at various scattering configurations do not show any anomaly near Tc. Combination of the Raman and Brillouin scattering results leads to the conclusion that the phase transition in SnCl2⋅2H2O is associated with a Debye-type relaxation mode associated with the reorientation of H2O molecules.
Radiative transition probabilities for the A 1Σ+–X 1Σ+ bands of 7LiH
Authors: Zemke Warren T. , Stwalley William C.
Published: February 2003

The recently reported hybrid potential curves of Stwalley et al. [J. Chem. Phys. 66, 5412 (1977)] for the X 1Σ+ and A 1Σ+ states of LiH are combined with the ab initio transition moments of Docken and Hinze [J. Chem. Phys. 57, 4936 (1972)] to calculate radiative transition probabilities between all upper (v′?26) and all lower (v″ ?23) vibrational levels of 7LiH. By far the strongest single band found is the 23–26 band between the highest ’’long-range’’ levels in each potential. A comparison with experimental intensity observations is made; it appears that the experiments are globally in accord with our calculations, but with some detailed differences discussed herein.
Radiative and nonradiative lifetimes for vibrational levels of the A 1Σ+ state of 7LiH
Authors: Zemke Warren T. , Crooks Jon B. , Stwalley William C.
Published: February 2003

Newly calculated radiative transition probabilities for the A 1Σ+→X 1Σ+ (v′–v″) emission bands of 7LiH (preceding paper) are used to calculate the radiative lifetime of the various vibrational levels (0⩽v′⩽26) of A 1Σ+ LiH. For higher levels an estimate of the bound-to-free emission probability is also needed and included. For the highest two levels, A 1Σ+→B 1Π emission is possible and has been included, but makes a negligible contribution to the radiative lifetime. The calculated radiative lifetimes increase with v′ from 28.9 nsec at v′=0 to 36.1 nsec at v′=16 and then decrease to 27.1 nsec at v′=26. They are found to be in good agreement with measured total lifetimes, implying the nonradiative (predissociative) lifetime for the measured levels is ≳10−7 sec, in accord with simple theoretical expectations.
On the l
z-conserving energy sudden approximation for atom–diatom scattering
Authors: Khare V.
Published: February 2003

The utility of a lz-conserving approximation, resulting from only energy sudden approximation to the exact space fixed coupled equations, is investigated for atom–diatom scattering. It is shown that the expressions for various transitions probabilities and differential cross sections may be obtained after evaluating relatively small number of lz-conserving S-matrix elements. Numerical comparisons with IOS and CC results are given for Ar–N2 and Ar–Tlf for a set of previously well studied parameters.
Relaxation processes in matrix isolated C3
Authors: Bondybey V. E. , English J. H.
Published: February 2003

The low value of the bending frequency ν2 in the upper A 1II state leads to efficient vibrational relaxation. The (0,0,0) level of this state populates by efficient intersystem crossing a lower lying triplet state. The vibrational ground state levels involving excitation in the low frequency (∼65 cm−1) ν2 fundamental exhibit severe lifetime broadening due to strong mixing with the lattice modes. The excited ground state levels involving only the stretching frequencies are, on the other hand, sharp.
Solvated electron wavefunctions
Authors: Carmichael Ian
Published: February 2003

Approximate single-parameter variational wavefunctions derived from one-electron models for solvated electrons are compared with their highly accurate numerical counterparts. In a polarized cavity approach the Gaussian function affords the best agreement with the true ground state charge distribution, while the excited state is better represented by a hydrogenic function. At the semicontinuum level the ground state is again well described by the Gaussian function, but neither Gaussian nor hydrogenic distribution offers a reasonable picture of the vertical excited state. Momentum-space wavefunctions along with an analytical solution of the former model are also presented.
Optical emissions of triatomic rare gas halides
Authors: Lorents D. C. , Huestis D. L. , McCusker M. V. , Nakano H. H. , Hill R. M.
Published: February 2003

We report in this paper the observation of optical emissions from triatomic rare gas halide molecules formed in excited high density rare gas–halogen mixtures. The broad-band continuum emissions are identified as transitions between ionically bonded excited states (Rg+2X−) and repulsive covalent lower states that dissociate to ground state atoms. These emissions become predominant at high rare gas densities.
An interpretation of the evolution with temperature of the ν2+ν3 combination band in water
Authors: Fornés V. , Chaussidon J.
Published: February 2003

The near infrared absorption spectra of water around 5000 cm−1 have been obtained at different temperatures, in the range of −50°C to 50°C. The complex band has been resolved into three component bands centered at 5200, 5080 and 4920 cm−1, and having half-widths of 140, 200, and 340 cm−1, respectively. These bands have been associated with the existence of three species of water molecules with hydrogen bond energies distributed around three maxima. From the study of the evolution of the intensities of these component bands with temperature we have determined the energy ΔH° involved in the transition of molecules from one to another of the three energy states, both in liquid water and ice. Any of these values can be taken as a thermodynamic parameter characteristic of water and its variation constitutes a criterium for ascertaining changes in the physical state of water, e.g., changes induced by the proximity of solid surfaces.
Weak Raman bands and the reduced spectrum from vitreous BeF2
Authors: Walrafen G. E. , Samanta S. R.
Published: February 2003

Raman and infrared spectra have been obtained from vitreous BeF2. The sensitivity of the measurements allowed weak features to be seen in the spectra, in addition to bands arising from the main glass structure. The weak features are throught to arise from LO–TO splittings, two-phonon interactions, defects, and the impurities OH and BeO. Features in the reduced Raman spectrum agree well with inelastic neutron scattering data.
Molecular Rydberg transitions. XII. Magnetic circular dichroism of methyl iodide
Authors: Scott John D. , Felps W. Sid , Findley Gary L. , McGlynn Seán P.
Published: February 2003

The absorption spectrum, the derivative spectrum, and the magnetic circular dichroism spectrum of methyl iodide are reported at various pressures in the energy range 48 000–59 000 cm−1 (i.e., the region of the 5p→6s Rydberg absorption bands). A method of determining the magnetic moment (μe) of a given electronic state is outlined, and the relative values of μe for the 5p→6s Rydberg vibronic bands are reported. These values lead to the identification of the four origin bands, the categorization of the pure electronic states with respect to angular momentum (in the linear molecule basis), and the assignment of all four of them. The MCD technique is a powerful tool for the assignment of vibrational bands: The value of μe and the sign of the MCD signature suffice to associate all bands to particular origins and to reveal detailed aspects of the vibronic coupling. Finally, the observed coupling of e vibrational and E electronic states of the symmetric top molecule provides insights into the nature of the vibronic potential.
Solution of the Smoluchowski equation with a Coulomb potential. II. Application to fluorescence quenching
Authors: Hong K. M. , Noolandi J.
Published: February 2003

The rate of fluorescence quenching is derived for the continuum model of a diffusion-controlled reaction, using the exact solution to the Smoluchowski equation with a Coulomb potential derived earlier. The first two terms in the long-time expansion of the reaction rate are formally the same as the result obtained by Smoluchowski for no long-range forces. However, the sum of the hard-core radii in Smoluchowski’s expression is replaced by an effective encounter distance. Our expression for the reaction rate with the Coulomb interaction constitutes an extension of Debye’s steady-state result to the transient case.
Spectroscopic studies of diatomic noble gas halides. IV. Vibrational and rotational constants for the X, B, and D states of XeF
Authors: Tellinghuisen Patricia C. , Tellinghuisen Joel , Coxon J. A. , Velazco J. E. , Setser D. W.
Published: February 2003

The B→X and D→X systems of XeF are recorded by photographing the emission from the low-pressure Xe*/XeF2 and Ar*/XeF2 reactions. A rotational analysis is obtained for the 1–2 band of B–X, for which isotopic blending is negligible. Vibrational parameters for the X, B, and D states are derived from a direct, weighted least-squares fit of all assignments for both transitions. Rotational parameters are deduced from the vibrational dependence of the band shapes and intensities. Some significant results of this analysis are ReX=2.293 å, ReB=2.631 å, ReD=2.51 Å, ωeX=225 cm−1, ωeB=309.0 cm−1, ωeD=350.1 cm−1, and 𝒟eX=1175 cm−1. The Franck–Condon factors for many of the bands in both systems show a strong rotational dependence, which is to be expected in transitions of this type, for reasons discussed herein.
Dielectric relaxations in a few binary mixtures of p-methoxybenzylidene–p′-n-butylaniline and a nematogenic or nonmesogenic compound
Authors: Yano Shinichi , Hayashi Yuzo , Aoki Koichiro
Published: February 2003

Dielectric relaxations in a few binary mixtures, which are in nematic state, of p-methoxybenzylidene–p′-n-butylaniline (MBBA) and other components were studied in the frequency range 300Hz–4 MHz. One of the components added was p-ethoxybenzylidene–p′-cyanoaniline (EBCA), a nematogenic compound, which formed a eutectic mixture with MBBA. Others were p-n-butylaniline and chloroform, nonmesogenic compounds. The low frequency relaxations were observed in all samples. The relaxation time increased by adding EBCA to MBBA, while decreased by adding p-n-butylaniline and chloroform to MBBA. The activation enthalpy for the low frequency relaxation and the activation enthalpy for viscosity of the isotropic phase had a maximum near the eutectic mixing ratio (cE). By examining the above dielectric results by the Meier–Saupe theory, it was concluded that both long range– and short range–intermolecular interactions in nematic phase increase anomalously near cE.
The electronic structure and the optical and photoelectron spectra of carbon subsulfide
Authors: Ginsberg A. P. , Brundle C. R.
Published: February 2003

Carbon subsulfide, the linear molecule S=C=C=C=S, has been investigated by self-consistent field-Xα-scattered wave calculations (overlapping spheres), optical (650–230 nm), and photoelectron [He(I) and He(II)] spectroscopy. The ground state valence level electronic configuration is found to be (6σ+g)2(5σ+u)2(7σ+g)2(6σ+ u)2 (7σ+u)2(8σ+g)2(2πu)4(2πg)4(3πu)4. Comparison of the photoelectron band positions with the calculated ionization potentials, and analysis of their vibrational structure, allows assignments to be made. The experimental ionization potentials (ev) are 3πu(9.09), 2πg(11.24), 2πu(12.87), 8σ+g(14.47), 7σ+u(14.87), 6σ+u(18.2), 7σ+g(19.3), 5σ+u(20.5), 6σ+g(21.9). Agreement between calculated and experimental ionization potentials is very good for the π levels, fair for the 8σ+g and 7σ+u levels and poor for the remaining (low lying) σ levels, although the splittings between the low lying σ levels are correctly calculated. There are two principle features in the optical spectrum, a weak band at 20.7 kcm−1 which is responsible for the orange-red color of C3S2 and a strong uv peak at 38.7 kcm−1. The 20.7 kcm−1 band is assigned as the dipole forbidden 3πu→4πu  (1Σ−g or 1Δg) transition while the 38.7 kcm−1 peak is assigned as the dipole allowed 3πu→3πg  (1Σ+u) and 3πu→9σ+g  (1Πu) transitions. Where comparison is possible, good agreement is found between calculated and observed electronic transitions. A detailed comparison is made between C3S2 and C3O2; to facilitate this an overlapping sphere SCF-Xα-SW calculation was carried out for C3O2. The calculated charge distribution indicates that in C3S2 the sulfur atoms are positively charged while all three carbon atoms are negatively charged, with the central carbon more negative than the end carbon atoms. By contrast, in C3O2 the oxygen and central carbon atoms are negatively charged while the end carbon atoms are positively charged. In agreement with the calculated energy level diagrams C3S2 and C3O2 have similar optical spectra, but the C3S2 absorptions are shifted to lower energy.
Theory of short range interactions and static polarizabilities of alkali halides
Authors: Agrawal G. G. , Shanker Jai
Published: February 2003

An analysis of the static polarizabilities of alkali halides has been presented on the basis of two potential forms for the short range repulsive interactions. The first form is that due to Born and Mayer in which the repulsive energy is considered to depend on interionic separation. The second form is that recently proposed by Narayan and Ramaseshan in which the repulsive potential is expressed as the sum of individual ionic contributions depending on ionic radii. In addition, we have considered the short range attractive forces arising from the van der Waals dipole–dipole and dipole–quadrupole interactions. The polarizability arising from the relative displacement of ions has been calculated. A comparison of calculated and experimental polarizabilites reveals the necessity of introducing an effective charge parameter for ions. The analysis has been extended to predict the strain derivatives of static polarizability and the effective charge parameter. The results obtained are interpreted on the basis of the exchange charge model and the Phillips–Lawaetz ionicity model.
Coupling-strength incoherence and the theory of resonances for a system of several sparse states and quasicontinua
Authors: Druger S. D.
Published: February 2003

The phenomena of unimolecular radiationless decay and vibronic dissipative broadening in large molecules are studied by developing a theoretical treatment of a system of several sparsely spaced zero-order states coupled to a dense set of states that have unlike physical character, thereby extending earlier work on the line shape for a single and a double resonance. Observable quantities, such as the absorption line shape, that involve averages over the dense states are shown to depend on diverse microscopic details of the quasicontinuum states only collectively through the values of a small number of matrix element correlation parameters and matrix element averages. The effects of interstate interactions on the values of the matrix-element correlation parameters and matrix-element averages are examined, and related sum rules are obtained. The physical consequences implied by uncorrelated matrix elements for nearby dense states are studied, and it is shown that relaxing the overly restrictive assumptions of earlier model treatments qualitatively changes the theoretical predictions obtained, generally in the direction of improved agreement with experiment.
Effect of spin polarization on the thermal conductivity of polyatomic gases
Authors: Viehland Larry A. , Mason E. A. , Sandler S. I.
Published: February 2003

Expressions are developed for the thermal conductivity and Eucken factor of a polyatomic gas which include the effects of spin polarization (molecular angular momentum) in terms of experimentally accessible quantities. Comparisons are made of calculations based on these equations with results for the loaded sphere and spherocylinder models, and for nitrogen. Although the effect of spin polarization is small, it is greater than the uncertainty in present experimental thermal conductivity measurements. The numerical importance of spin polarization appears to be greater than the effect of equating the diffusion coefficient for internal energy to the self-diffusion coefficient.
Quenching cross sections for Ar(3P0,2) and Kr(3P0,2) by H2O and D2O
Authors: Sheldon John W. , Muschlitz E. E.
Published: February 2003

Absolute cross sections for the quenching of metastable Ar and Kr atoms by ground state H2O and D2O are reported.
Multiphonon transitions in microcrystalline reflectivity of sodium nitrate
Authors: Nichols Henry , Frech Roger
Published: February 2003

The near normal incidence infrared reflectivity spectrum of a microcrystalline powder is shown to resemble the transmission spectrum in spectral regions sufficiently far from strong fundamental transitions. Weak absorption losses due to multiphonon resonances are superimposed on the structureless diffuse reflectivity background. Microcrystalline reflectivity spectra are measured in Na14NO3 and 90% enriched Na15NO3 and compared with a single crystal transmission spectrum of Na14NO3.
Optical spectroscopy of monolayers of simple molecules adsorbed on copper
Authors: Moskovits M. , McBreen Peter
Published: February 2003

A uv–visible study of monolayers of N2, H, C2H4, and O on polycrystalline copper deposited under ultrahigh vacuum conditions was carried out using a form of polarization modulation spectroscopy. The observed ’’bands’’ are shown to originate both from a trivial modification of the local field in metal irregularities near the surface as well as from bona fide absorptions in the metal–adsorbate surface layer. Some of these bands show vibrational fine structure. Using a simple model which takes into account the direction of polarization of these absorption bands with respect to the surface normal, we were able to deduce the surface geometry of hydrogen and ethylene on the preponderant crystalline face of our deposited copper. Both are found to bridge copper atoms, the latter in the so-called disigma configuration. The position of oxygen on copper could not be deduced with equal confidence; however, a linear CuO geometry was preferred.
The x-ray photoelectron spectrum of atomic sodium
Authors: Martin R. L. , Davidson E. R. , Banna M. S. , Wallbank B. , Frost D. C. , McDowell C. A.
Published: February 2003

The Na(1s) binding energy in atomic sodium has been determined by x-ray photoelectron spectroscopy to be 1079.1(±0.1) eV. The spectrum exhibits a satellite 8.4 eV to the high binding energy side of the primary peak with a relative intensity of 19(±1) %. It is assigned to a 3s→4s excitation accompanying ionization. Ab initio ’’ΔSCF’’ calculations are in good agreement with experiment for both the separation and intensity of the satellite. The unusually large intensity of the shakeup peak compared to those found in the inert gases is discussed. Theoretical Na(1s) binding energies in the series Na, Na2, and Na3, suggest that ∼90% of the binding energy shift between the free atom and the metal (5.1 eV) is due to the extraatomic relaxation in the metal.
Static semiclassical response of a bounded electron gas. II. The finite barrier model
Authors: Lert Peter W. , Weare John H.
Published: February 2003

The semiclassical linear response formalism of a previous publication is applied to the step potential model of a metal surface. Results presented here demonstrate that this model is a significant improvement over the infinite barrier model, though the unperturbed system is too far from self-consistency to yield quantitative accuracy. The conclusion that linear response theory is adequate for many situations is reinforced. Calculations for a model of alkali absorption agree with those of Lang to within 10% for the zero-coverage dipole moment. The surface average potential of Na (001) modeled as a pseudopotential lattice is in semiquantitative agreement with exact results. Exchange and correlation are considered in the ’’local density approximation’’ (LDA).
Experimental study of nucleation in binary mixtures: The nitric acid–water and sulfuric acid–water systems
Authors: Mirabel P. , Clavelin J. L.
Published: February 2003

The upward thermal diffusion cloud chamber was used to study the homogeneous nucleation of the HNO3–H2O and H2SO4–H2O mixtures over a wide range of water activities (i.e., relative humidities). The results were compared with the predictions of theory. Good agreement between the experimental reults and the classical theory of homogeneous nucleation was found for the HNO3–H2O mixture at all compositions. Good agreement was also found for the H2SO4–H2O mixture if one takes into account the formation of sulfuric acid hydrates in the vapor phase.
Effect of asymmetric isotopic substitution on atom–diatom potentials
Authors: Liu W. -K. , Grabenstetter J. E. , Le Roy R. J. , McCourt F. R.
Published: February 2003

A simple and accurate method is proposed for transforming the Legendre expansion of an atom–diatom potential about the diatom center of mass into a new Legendre expansion about a shifted (by isotope substitution) diatom center of mass. It is found that a simple quadrature procedure yields accurate results throughout the range of intermolecular separation of physical interest, while a previously proposed Taylor series expansion procedure gives comparable accuracy only for intermolecular separations greater than the equilibrium separation. Numerical tests of the method are performed for three model atom-plus-rigid diatom systems H2(HD) –He, HCl(DCl) –Ar, and 35ClF(37ClF) –Kr. adequate to determine the residual energy and entropy as well as their volume derivatives. The temperature dependence of the derivatives of the energy and entropy supports the contention that the equation of state is that for segments having a steep repulsive potential of the form ε (σ/r)n with a mean field containing the attractive potential. The independently measured heat capacity combined with (δS/δlnV)T predict the exponent n and this value is corroborated by the internal scaling of the latter derivative. Scaling between compounds of pressure (δS/δV)T and (δU/δV)T is achieved by a two-parameter corresponding-states relation.
On the existence of a nonmonotone surface ion density in liquid metals: Perturbative introduction of discrete ions into jellium
Authors: Allen J. W. , Rice Stuart A.
Published: February 2003

We show that at the surface of a liquid metal oscillations are induced in the positions of ion planes by the Friedel oscillations of the electron density. This conclusion, derived from a discrete ion model via a perturbative pseudopotential analysis, is the same as reached earlier by Allen and Rice in a study of self-consistently relaxed jellium. In the present work the surface of a liquid is modeled by close packed planes of cubic lattices. For either a face centered cubic lattice whose surface has been formed by cleavage perpendicular to the (111) direction, or a body centered cubic lattice cleaved perpendicular to the (110) direction, we find that when rs is less than about 3 only the first lattice plane relaxes; it moves away from the second plane by about 0.5% to 1% of the bulk interplanar spacing. When rs is greater than about 3, we find that the first two planes move nearer to one another than the bulk spacing (by about 0.5% to 1.5%) in such a way that the distance between the second and third lattice planes is greater than the bulk spacing by about 0.3%. This trend holds whether we use the step boundary electron distributions of Lang and Kohn or the author’s relaxed jellium electron distributions. The changes in ion plane positions are in qualitative agreement with the oscillations found for the continuum ion charge distributions of relaxed jellium.
Photolysis of NO trapped in a rigid matrix at 6 K
Authors: Fournier J. , Deson J. , Vermeil C.
Published: February 2003

Nitric oxide embedded in inert solvents has been photolyzed at low temperature (6 K) by different photon energies in the vacuum uv. In argon matrices, two emissions have been identified as the β bands, NO (B 2∏→x 2∏) and as a spin forbidden transition attributed to the M bands. In N2 matrix, only the β bands have been observed. In no case have transitions from Rydberg states been observed.
Applications of fluctuation transport theory
Authors: Weissman M. B. , Ware B. R.
Published: February 2003

It is shown that linearized theories of fluctuation transport cannot be self-consistently applied to most dynamic light-scattering experiments on particles whose characteristic nearest-neighbor spacing is comparable to or larger than the reciprocal of the scattering wave vector. The electrophoretic mobility of concentration fluctuations in protein–counterion solutions without excess salt is shown to have the opposite sign of the protein mobility and to increase through zero as a function of added salt. Effects of coupling between charge and concentration fluctuations are considered, and the magnitude of these effects on the fluctuation mobility is estimated for solutions of bovine serum albumin. Several dramatically anomalous experimental effects are predicted, and relevant published reports of dynamic-light-scattering determinations of fluctuation diffusion coefficients and electrophoretic mobilities are compared with the predictions of fluctuation transport theory.
A CNDO/S assessment of the electronic structure of p-benzoquinone and tetrafluoro-p-benzoquinone
Authors: Bigelow Richard W.
Published: February 2003

The semiempirical molecular orbital CNDO/S spectral parameterization of Del Bene and Jaffe has been used to further characterize the electronic structure of p-benzoquinone and tetrafluoro-p-benzoquinone. This study demonstrates that CNDO/S calculations provide a quantitative basis for the understanding of the effects of fluorine substitution without reflecting the large 2–3 eV shift to lower energy of the σ orbitals, commonly referred to as the ’’perfluoro-effect.’’ Specifically, the predicted TFPBQ ground state orbital ordering and excited state energy shifts, relative to PBQ, are in accord with arguments based upon photoelectron spectral data and correlation with the absorption properties of structurally related molecules.
Electron mobilities and ranges in methyl substituted pentanes through the liquid and critical regions
Authors: Ryan T. G. , Freeman G. R.
Published: February 2003

Density normalized penetration ranges bGPd of secondary electrons and mobilities μe of thermal electrons vary in similar manners as the temperature of the solvent hydrocarbon is increased toward the critical. These quantities pass through maxima in 3,3-dimethylpentane, 2,2,4-trimethylpentane, and 2,2,4,4-tetramethylpentane, but not in 3-methylpentane. In 2,3-dimethylbutane μe has a small maximum just below the critical point while bGPd reaches a short plateau. As the molecules in a series become more spherelike, the maxima grow and the temperature at which they occur moves farther below the critical. Changes of the range and mobility are caused by changing scattering properties of the fluids. The decrease of μe on the high temperature side of the maximum is attributed to a decrease of mobility in the conduction band μ0h rather than to an increase in electron trap depth that might have been caused by the greater density fluctuations that occur as the critical region is approached. The results support the earlier conclusion that the major part of the secondary electron range bGP is attained while the electron has only a few tenths of an eV energy and is skittering through the liquid in the conduction band. The mobilities in all the liquids are independent of field strength up to 30 kV/cm, except in 2,2,4,4-tetramethylpentane under conditions where the drift velocity exceeds 14 km/s. The mobilities in the five critical fluids are all between 19 and 31 cm3/V s, a factor of 1.6, whereas those in the liquids at 293 K range over a factor of 130. This demonstrates the importance of short range forces in governing electron behavior in dense matter.
Decay rates of Ar(4s,3P2), Ar(4s′,3P), Kr(5s,3P2), and Xe(6s,3P2) atoms in argon
Authors: Kolts J. H. , Setser D. W.
Published: February 2003

The decay rates of Ar(3P2), Ar(3P0), Kr(3P2), and Xe(3P2) metastable states in argon carrier gas have been measured in a flowing afterglow apparatus. From analysis of the dependence of the pseudo-first-order decay constants upon pressure, the diffusion, two-body, and three-body rate constants have been assigned for each metastable state in Ar. The rate constants found for Ar(3P2) agree with the values accepted in the literature for these processes. The two-body rate constants for Kr(3P2) and Xe(3P2) are a factor of 4 lower than for Ar(3P2). The three-body rate constants for Kr(3P2) and Xe(3P2) are reduced by factors of 10 and 100, respectively, relative to the Ar(3P2) rate constant. The reduction in three-body constants for Kr(3P2)+2Ar and Xe(3P2)+2Ar is consistent with the reduced binding energy of KrAr* and XeAr*. The diffusion and three-body coefficients for Ar(3P0) are equal to those for Ar(3P2), but the two-body rate constant is 2.5 times larger than for Ar(3P2). The results for each of the three processes are discussed in terms of physical models.
Dielectric behavior of solid phase OHMBBA
Authors: Arora V. P. , Agarwal V. K. , Mansingh Abhai
Published: February 2003

Dielectric measurements have been made in the solid phase of OHMBBA [N- (2-hydroxy-4-methoxybenzylidene) -p-butylaniline] in the frequency range 60 Hz to 1 KHz and in the temperature range −40 to +20 ° C. The results indicate a Debyetype dispersion with symmetric distribution of relaxation strength (Δε=ε0−ε∞) and the Cole–Cole distribution parameter vary with temperature and show peaks at about −14 °C and dips at about 0 °C. The results below 0 °C can be explained, as in metastable solid phase MBBA. [(V. K. Agarwal, V. P. Arora, and A. Mansingh, J. Chem. Phys. 66, 2817, (1977)], by considering the rotation of methoxy groups; but in OHMBBA the rotation is considerably slowed down due to intermolecular hydrogen bonding. Above about 0 °C the results can be explained by assuming the rotation of the molecule as a whole about its long axis.
Optical absorption and photoconductivity spectra of localized electrons in x-irradiated aqueous 10M lithium chloride glasses at 4.2 K: Support for two types of localized electrons each with overlapping bound–bound and bound–continuum transitions
Authors: Rice Stephen A. , Dolivo Gilles , Kevan Larry
Published: February 2003

Irradiation of the 10M LiCl/H2O and 10M LiCl/D2O matrices at 4.2 K has shown that the localized electron species, e−vis (λmax∼680 nm) and e−ir (λmax≳2400 nm) observed previously by pulse radiolysis at 77 K, can be stabilized. Photobleaching and addition of nitrate as an electron scavenger show that e−ir does not appear to interconvert to e−vis. Thus e−ir does not appear to behave as a presolvated electron which is convertible into a solvated electron (i.e., e−vis) as observed in alcohols and other organic glasses. The wavelength dependence of the photoconductivity generated in these irradiated glasses was also measured. The photocurrent peaks at higher energy than the respective optical spectra for both e−vis and e−ir, hence both bound–bound and bound–continuum transitions are suggested for both species. The trap depth of e−vis appears to be two or more times deeper than that of e−ir, and the photoconductivity quantum efficiency of both species is 0.1−1 at 4.2 K at their respective photoconductivity maxima, ∼400 and 1400 nm.
Reflection spectra of natural faces of crystalline anthracene
Authors: Syassen K. , Philpott M. R.
Published: February 2003

Polarized reflection spectra, taken at 1.5 K, off faces (001), (201̄), (1̄01), (110), (1̄1̄1), and (1̄1̄2) of vapor grown anthracene crystals are reported for the wavelength range 400–350 nm. This range spans most of the first singlet electronic transition of the crystal. The faces (001), (201̄), and (1̄01) contain the crystallographic b axis and, according to the Fresnel formulas, should have identical normal incidence b-polarized reflection spectra. However, the spectra of the (201̄) and (1̄01) faces do not show the reflection minima assigned to surface transitions that are prominent within the stop band of the 0–0 transition on face (001). On the other hand, the higher vibronic transitions of (001), (201̄), and (1̄01) appear to be identical for b polarization in agreement with the Fresnel formulas. The absence of surface transitions on (201̄) and (1̄01) is attributed to coupling between surface and volume excitons. Spectra of faces (1̄1̄2), (1̄1̄1), and (110) display no feature attributable to surface transitions. A resonance prominent in the b-polarized spectra off (001), (201̄), and (1̄01) persists in the spectra of the other faces even when the Coulomb exciton lies at higher energy. This feature is tentatively assigned to a two-particle process in which a volume polariton and lattice phonon are simultaneously created.
Self-consistent field theories of the polymer excluded volume problem. IV. The linear polymer
Authors: Kosmas Marios K. , Freed Karl F.
Published: February 2003

The previous abstract formulation of self-consistent field (SCF) theories of polymer excluded volume is extended and generalized to provide a SCF theory for the moments of the end-vector distribution such as 〈R2n〉. The nonlinear integrodifferential equations of the SCF theory are considered for a linear polymer where the SCF’s, V2n, are shown to be spherically symmetric, and the dominant part of V2n is obtained and shown to be self-consistent. The 〈R2n〉 are obtained and have asymptotic long chain limits conforming to the Flory–Edwards power laws. Contributions from fluctuations about the SCF are considered and are shown to alter the total number of chain configurations but not to change the long chain limits for 〈R2n〉 for n≳0. A discussion is presented of the relationship of the SCF results to those obtained by use of the renormalization group method.
Thermodynamic fluctuations in phospholipid bilayers
Authors: Doniach S.
Published: February 2003

A simplified statistical mechanical model of the solid–fluid melting transition of wet lipid bilayers is developed which allows for calculation of thermodynamic fluctuation effects. The model is used to estimate the lowering of the free energy barrier for transbilayer ion permeability due to enhanced lateral compressibility near the melting point. The calculation is used to fit permeability data for dipalmitoyl phosphatidyl choline vesicles and the fit provides evidence that the bilayer is quite close to a critical temperature at which the melting transition would go from first to second order.
On the contribution of intramolecular zero point energy to the equation of state of solid H2
Authors: Chandrasekharan V. , Etters R. D.
Published: February 2003

Experimental evidence shows that the internal zero-point energy of the H2 molecule exhibits a relatively strong pressure dependence in the solid as well as changing considerably upon condensation. We show that these effects contribute about 6% to the total sublimation energy and to the pressure in the solid state. Methods to modify the ab initio isolated pair potential to account for these environmental effects are discussed.
The selective dissociation of SF6 in an intense ir field: A molecular beam study on the influence of laser wavelength and energy
Authors: Brunner F. , Proch D.
Published: February 2003

We report the results of a molecular beam study on the energy fluence and wavelength dependence of the dissociation probability of SF6. We find surprisingly high values at power densities which rule out an essential contribution of power broadening but rather stress the importance of efficient absorption in the lower levels. No loss of isotopic selectivity is observed for power densities up to 108 W/cm2 in the P (20) line at 944.2 cm−1.
Vibrational energy relaxation and exchange in liquid N2–CO–OCS mixtures
Authors: Brueck S. R. J. , Osgood R. M.
Published: February 2003

The laser induced fluorescence technique has been applied to the vibrational dynamics of liquid N2 doped with small (∼1–100 ppm) quantities of CO and OCS. For N2–CO mixtures, the vibrational energy is shown to equilibrate among the CO and N2 molecules on a time scale rapid compared to vibrational decay processes. These decay processes are dominated by radiative effects for both N2 (radiative lifetime 60 s and CO (radiative lifetime 0.023 s). OCS(00°1) vibrational decay is much more rapid (∼2±0.5 ns) and has been measured by infrared saturation techniques. In N2–CO–OCS mixtures, the OCS acts as a rapid deactivation center for vibrational energy and the rate limiting processes are the vibrational exchange rates between the initially excited N2 and the CO and OCS dopants. The measured rate constants are KN2*,CO*=2.7±0.6×10−15 cm3 s−1, KN2*,OCS*=1.0±0.2×10−15 cm3 s−1, and KCO*,OCS*=4.6±0.8×10−12 cm3 s−1, where KX*,Y* refers to vibrational transfer from X to Y. The N2*→CO* rate constant is identical with previous gas phase measurements and is shown to be inconsistent with a simple isolated binary collision model of a liquid.