bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron escape depths of organic solids. II. The energy dependence of naphthacene and perylene films
Authors: Hino Shojun , Inokuchi Hiroo
Published: February 2003

The energy dependence of the electron escape depth of naphthacene and perylene deposited films has been measured by an overlayer technique. Energy distribution curves of transmitted electrons through deposited organic layers were obtained by differentiating the I–V characteristic curves, and the electron escape depths classified by their kinetic energies were obtained from the above results. Presently obtained escape depth is between 8 and 15 nm for naphthacene and between 30 and 37 nm for perylene. They differ from our previous results, and the reason for this discrepancy is discussed.
Series solutions and the variational principle
Authors: Rioux Frank , Harriss Donald K.
Published: February 2003

The B matrix method of Frost for solution of nonseparable Schrödinger equations is used in combination with the upper bound theorem for linear variation functions to show that series solutions are possible in the general case without explicit evaluation of integrals. The procedures are illustrated with calculations on the hydrogen-molecule ion, with some discussion of the helium atom.
Electron attachment to perfluorocarbon compounds. II. c-C5F8, c-C6F10, c-C6F12, C7F8, and C8F16: Relevance to gaseous dielectrics
Authors: Pai R. Y. , Christophorou L. G. , Christodoulides A. A.
Published: February 2003

Electron attachment rates αw as a function of the pressure-reduced electric field have been measured for c-C5F8 (perfluorocyclopentene), c-C6F10 (perfluorocyclohexene), c-C6F12 (perfluoro-1,2,-dimethylcyclobutane), C7F8 (perfluorotoluene), and C8F16 (perfluoro-1,3-dimethylcyclohexane). The thermal values (αw)ther of the attachment rate for these compounds are 12.8, 12.9, 5.0, 9.2, and 2.4×109 sec−1 Torr−1, respectively. The electron attachment cross sections σa(ε) as functions of the electron energy ε have been determined using the swarm-unfolding technique; they show distinct structure at ε<1.5 eV. The electron attachment properties for the perfluorocarbons (PFCs) studied in this and the preceding paper depend strongly on the molecular structure. Thus (i) open-chain saturated PFCs do not attach electrons as efficiently as the unsaturated PFCs; (ii) for saturated PFCs an increase in molecular size (chain length) increases αw; (iii) the presence of multiple bonds in the molecule dramatically increases the magnitude of αw for the saturated open-chain PFCs, but it has only a small effect for cyclic PFCs; (iv) the cyclic nature of the PFCs seems to increase greatly σa(ε); and (v) for single-bonded cyclic PFCs, substitution of CF3 groups for F atoms increases (αw)ther more than does an increase in molecular size; in double-bonded cyclic compounds increase in ring size increases σa(ε) at thermal energies. The PFCs studied in this and the preceding paper have higher dielectric strengths than SF6. This improvement in dielectric strength can be attributed to their large σa(ε) over a wider energy range (to ∼1.5 eV). Their use as unitary gases and/or as additives to multicomponent gas mixtures is discussed.
Valence and Rydberg excited states of H2S: An SCF-Xα-SW molecular orbital study
Authors: Roberge R. , Salahub D. R.
Published: February 2003

SCF-Xα-SW calculations have been performed for H2S in the ground state, in ionic states resulting from the vertical removal of a valence electron, and in 36 singlet and triplet excited states resulting from the vertical excitation of an electron from the 2b1 or the 5a1 molecular orbitals to various virtual orbitals. Excellent agreement for the transition energies is found both with the experimental ultraviolet and photoelectron spectra and with recent large-scale configuration interaction calculations. The average absolute difference between the Xα-SW and CI results for the 26 cases where both exist is only 0.24 eV. The intrinsic advantages of the Xα-SW method over the traditional LCAO or one-center approaches for the treatment of Rydberg states are delineated. Contour plots of the excited orbitals have been generated and these are used to illustrate some of the conceptual problems related to the Rydberg-valence distinction. Finally, a brief speculative discussion of the possible photochemical implications of the character of the two excited orbitals involved in the first absorption band is given.
Lattice vibrational motion in tetracyanoquinodimethane (TCNQ): A 14N nuclear quadrupole resonance study
Authors: Murgich Juan
Published: February 2003

The mean square angular amplitudes of motion are obtained from the analysis of the 14N nuclear quadrupole resonance thermal averaging in pure TCNQ. The temperature dependence of the mean square angular amplitudes is given. The results are compared with those found at room temperature by x ray by Long et al. [Acta Cryst. 18, 932 (1965)].
On the contribution of angular momentum polarization to gas phase thermal conductivity
Authors: Coope J. A. R. , Snider R. F.
Published: February 2003

The qualitative theory of the Senftleben effects [Coope and Snider, J. Chem. Phys. 57, 4277)], as applied here to the thermal conductivity, is used to stress the generality with which the contribution of angular momentum polarization to the thermal conductivity can be determined from the field dependence of the thermal conductivity.
Numerical SCF method for the calculation of static polarizabilities and hyperpolarizabilities for atoms, He through Ne
Authors: Voegel Thomas , Hinze Juergen , Tobin Frank
Published: February 2003

The static polarizabilities and hyperpolarizabilities for the ground states of first row atoms, helium through neon, have been calculated solving the SCF equations of an atom in an electric field by numerical integration of coupled one dimensional differential equations using the Numerov method in matrix form. The calculated polarizabilities agree within 2% with the values obtained by basis function methods. Heretofore only the hyperpolarizabilities of helium, lithium, beryllium, and neon have been calculated. For helium the hyperpolarizability is in good agreement with previous calculations, whereas for beryllium and neon the values obtained by basis function methods are scattered and significantly lower than the values we obtain. Comparison with experimental results for neon indicates that the Numerical Hartree Fock (NHF) method leads to a better representation of polarized orbitals than the use of basis function methods, which require tedious nonlinear optimization of large basis sets.
First-order diffusive effects in the coagulation of colloidal suspensions
Authors: Baloga Stephen
Published: February 2003

Solutions to an infinite system of reaction–diffusion equations associated with colloidal coagulation are obtained by incorporating first-order diffusive effects into restricted diffusion-free initial value problem solutions. It is shown that this method of approximation yields explicit asymptotically exact solutions for sufficiently small values of time. In addition, the diffusion-corrected solutions are recast in closed form by assuming that the diffusivity of the m-fold aggregates is given by Dm=Dm−δ, where D and δ are positive constants.
Electron spin resonance of polyacetylene and AsF5-doped polyacetylene
Authors: Goldberg I. B. , Crowe H. R. , Newman P. R. , Heeger A. J. , MacDiarmid A. G.
Published: February 2003

The results of an electron spin resonance (ESR) study of trans-polyacetylene, before and after doping with AsF5, are reported. The undoped polymer exhibits a Lorentzian line (g=2.00263) indicative of motional narrowing from a mobile unpaired electron species. Measurement of the intensity indicates a Curie law susceptibility with approximately one unpaired electron per 3×103 carbon atoms in agreement with earlier studies. From these results and comparison with earlier data on the cis polymer, it is suggested that the ESR signal arises from a mobile defect in the π system. Utilizing an apparatus which allows in situ AsF5 doping of a polyacetylene sample in the microwave cavity, we have monitored the ESR signal during the doping process. The spin resonance line narrows and increases in intensity, with no detectable g shift, as the doping proceeds. At high doping levels the line becomes asymmetric with a characteristic Dysonian line shape consistent with metallic behavior.
A normal mode treatment of optical properties of a classical coupled dipole oscillator system with Lorentzian band shapes
Authors: Applequist Jon , Sundberg Kenneth R. , Olson Mark L. , Weiss Lucy C.
Published: February 2003

DeVoe’s classical coupled dipole oscillator model for molecular optical properties is specialized for the case where the individual oscillators have complex polarizabilities with Lorentzian band shapes. The optical properties of this system are derived in terms of a set of eigenvectors and eigenvalues which describe the normal modes of the system. When the real and imaginary parts of the interaction matrix can be diagonalized by the same transformation, the properties are expressed as explicit functions of frequency and do not require a matrix inversion at each frequency. This condition is met by a system in which all oscillators have the same bandwidth. For such a case the computation time is much less than that required by the more general method involving point-by-point matrix inversion. A further simplification is achieved for a system in which a subset of the oscillators have natural frequencies so high that their polarizabilities may be regarded as nondispersive. For this case the order of the eigenvalue problem is reduced to the number of dispersive oscillators. Sum rules are derived for the mixed dispersive/nondispersive system. The normal mode method is illustrated by calculations for a 12-residue right-handed α-helix in which oscillators at 52 000 and 67 600 cm−1 are assigned to each residue. The predicted absorption and circular dichroic spectra are similar to those predicted using Gaussian band shapes for the individual oscillators by the matrix inversion method, while a 40-fold saving in computer time was achieved by the normal mode method.
Picosecond transient spectroscopy of molecules in solution
Authors: Greene B. I. , Hochstrasser R. M. , Weisman R. B.
Published: February 2003

The transient absorption spectra of a number of compounds in solution at room temperature have been measured with picosecond-scale time resolution and unprecedented accuracy and reliability. It is found that the spectra of benzophenone, xanthone, 9-fluorenone, p-benzoquinone, acridine, quinoxaline, t-stilbene all show significant evolution following excitation with the 353 nm third harmonic of a mode-locked Nd:glass laser. These spectral changes provide evidence for previously unrecognized photophysical behavior in the systems studied, including vibrationally nonthermalized triplet states in benzophenone which persist for tens of picoseconds, and formerly unobserved singlet absorptions in acridine, quinoxaline, fluorenone, and benzoquinone. The inadequacy of single wavelength probing techniques in deducing the dynamics of complex molecular systems such as these is demonstrated by the large extent to which spectra of different states overlap. In many cases a reinterpretation of previous single wavelength results is required because of the presence of vibrationally and electronically unrelaxed species. The apparatus used here to obtain the high quality visible transient spectra is described and its performance characterized.
The 2E
g→4A2g phosphorescence spectrum of the Cr3+ ion in K2NaAlF6
Authors: Greenough P. , Paulusz A. G.
Published: February 2003

The low temperature emission spectrum of the Cr3+ ion in the cubic lattice K2NaAlF6 has been measured. A detailed analysis of the vibrational structure observed leads to the conclusion that the 2Eg and 4T2g excited states of the CrF3−6 ion are displaced along the eg, a1g, and possibly the t2g coordinates. A similar analysis of the emission spectrum of K2NaGaF6:Cr3+ is possible, and values of five of the six internal vibrational modes of the CrF3−6 ion have been deduced.
A theoretical study of the predissociation of the c 4Σ−u state of O+2
Authors: Tanakaa) K. , Yoshimine M.
Published: February 2003

Extensive configuration-interaction calculations have been carried out to determine the potential curve for the c 4Σ−u state of O+2. The results show that this state is quasibound with a low potential barrier that could accomodate only few vibrational levels. The lifetimes with respect to the tunneling through the barrier are found to be too short, but the radiative lifetime of 2×10−8 sec for the v=O level is shown to be reliable. Based on these results with available experimental data, a semiempirical curve has been constructed and the mean lifetimes have been determined to be 10−8 and 5×10−11 sec for the levels v=O and 1, respectively. This result clearly explains absence of the v=1 level in emission, and leads to a conclusion that the tunneling should be the dominant mechanism for the predissociation of the c 4Σ−u state of O+2.
Correlation diagrams for rigid and nonrigid four-body systems
Authors: Amar François , Kellman Michael E. , Berry R. Stephen
Published: February 2003

Correlation diagrams are constructed to connect the rotation–vibration energy levels of idealized limiting models for the tetratomic molecule. One limit is the completely nonrigid homonuclear four-atom cluster. Several choices are taken for the other limit: the nearly rigid regular tetrahedron and square, the dimer of two identical homonuclear diatomics, and the ammonialike inverter. A dimensionless parameter, the ratio of two energies, is proposed to characterize the degree of nonrigidity for molecules of arbitrary size or complexity. The parameter is evaluated for several examples.
On the wave vector dependent mutual diffusion of interacting Brownian particles
Authors: Altenberger A. R.
Published: February 2003

The mean field theory of mutual diffusion of interacting, spherical Brownian particles is formulated. The spectrum of light scattered from a dilute macroparticle solution is determined. Wave vector dependent macroparticle mutual diffusion and friction coefficients are determined. Model calculations for the hard-core and square-well macroparticles are performed.
An efficient a
b i
n
i
t
i
o method for computing infrared and Raman intensities: Application to ethylene
Authors: Komornicki Andrew , McIver James W.
Published: February 2003

A new and very efficient method for the calculation of the infrared and Raman spectral intensities of polyatomic molecules using ab initio Hartree–Fock theory is described. The utility of the method is exemplified by an evaluation of the dipole and polarizability derivatives of the ethylene molecule employing a Gaussian basis set of double zeta quality, augmented by two sets of polarization functions. The predicted values of the vibrational intensities and the depolarization ratios are nearly within the experimental uncertainty which indicates that Hartree–Fock theory is capable of correctly describing these phenomena. The new method enables the efficient calculation of these properties by evaluating the dipole and polarizability derivatives as the first and second order contributions to the potential energy gradient of a molecule in the presence of a finite perturbing electric field. The calculations are thus performed at a single nuclear geometry and the molecular integrals are evaluated only once. The efficiency of the method shows great promise in the evaluation of reliable vibrational intensities for a wide range of polyatomic molecules.
Brownian dynamics study of polymer conformational transitions
Authors: Helfand Eugene , Wasserman Z. R. , Weber Thomas A.
Published: February 2003

Conformational transitions of a macromolecule have been studied by computer simulation of the Brownian dynamics of a polymer chain. An activation energy equal to about one barrier height has been found. However, there is a great deal of cooperativity of transitions especially between bonds which are second nearest neighbors.
Effect of an external electric field on the scavenging of geminate ions
Authors: Tachiya M.
Published: February 2003

The probability of recombination of an ion pair in the presence of both scavenger and an external electric field is calculated. (AIP)
Mössbauer effect study of the phase transition in (CH3)2SnF2
Authors: Steenbergen Chr. , van der Kraan A. M.
Published: February 2003

Mössbauer measurements on 119Sn are reported for dimethyltindifluoride below 140° K. A phase transition occurs around 70° K confirming observations reported in ref.(1). (AIP)
Matrix isolated potassium and rubidium halide monomers and dimers
Authors: Schaber H. , Martin T. P.
Published: February 2003

Infrared absorption spectra for matrix is dated potassium and rubidium halides are reported. The spectra were studied by Fourier interferometry. (AIP)
Charge transfer excitation in Ne+–N2O collisions at energies down to 1 eV
Authors: Myers G. D. , Leventhal J. J.
Published: February 2003

The charge transfer excitation in Ne+–N2O collisions is studied for collsion energies down to 1 eV. It is found that as the kinetic energy is lowered the relative emission of N2 as against that of N2O decreases. It is also found that the partial emissions in both N2+ and N2O+ increase as the kinetic energy is lowered. (AIP)
Evidence for atom exchange in OH reactions with carbonyl compounds: 18OH+CO2 → 18OCO+OH; 18OH+CO → 18OC+OH
Authors: Kurylo Michael J. , Laufer Allan H.
Published: February 2003

The exchange reaction of 18OH with CO2 was studied by mass spectroscopy. Mixtures containing H218O, CO2 and an inert gas were photolyzed and the isotopic exchange reactions were studied. (AIP)
Depolarized Rayleigh scattering study of pyridine in cyclohexane
Authors: Whittenburg S. L. , Jonesa) Dane R. , Christensenb) D. H. , Wang C. H.
Published: February 2003

Experimental results are reported of depolarized light scattering studies of pyridine-cyclohexane system. (AIP)
Thermal expansion anomaly of ice VI related to the order–disorder transition
Authors: Mishima O. , Môri N. , Endo S.
Published: February 2003

In order to confirm the existence of an ordering transition in ice VI, an investigation of the thermal expansion was carried out at low temperatures 4.2° K–200° K and high pressure l0.54 kbar. (AIP)
Rate constants for the reaction of O2+(a 4Πu) ions with CH4 at relative kinetic energies 0.04–1.2 eV
Authors: Lindingera) W. , Albritton D. L. , Fehsenfeld F. C.
Published: February 2003

The rate constants for the reaction of O2+ ions with CH4 have been measured at relative kinetic energies of 0.04–1.2 eV. (AIP)
The total absolute electron scattering cross sections for SF6 for incident electron energies between 0.5 and 100 eV including resonance structure
Authors: Kennerlya) R. E. , Bonhamb) R. A. , McMillanc) M.
Published: February 2003

Total electron scattering cross sections are reported for SF6 for incident electron energies between 0.5–100 eV. (AIP)
One term approximation to and direct computation of oscillator strength sums
Authors: Ahlrichs Reinhart , Levy Bernard , Maeder Fabienne
Published: February 2003

A ’’one term approximation’’ (φ,n) is derived and discused for oscillator strength sums S (n) for arbitrary real n. We further propose an approximation to J̃ (φ,n) and apply it in a direct computation of dipole oszillator strength sums of the hydrogen atom for various n.(AIP)
Comments on the cloud chamber study of gas phase photooxidation of sulfur dioxide
Authors: Mirabel P. , Clavelin J. L.
Published: February 2003

The experiments of Marvin and Reiss(1) have been repeated and the rate of production of SO3 by direct use of the nucleation theory has been determined. The results agree quantitavely with those of Ref. (1). (AIP)
Diabatic and adiabatic representations for atomic collision processes
Authors: Delos J. B. , Thorson W. R.
Published: February 2003

A consistent general definition of diabatic representations has not previously been given, even though many practical examples of such representations have been constructed for specific problems. Such a definition is provided in this paper. Beginning with a classical trajectory formulation, we describe the form and behavior of velocity-dependent couplings in slow collisions, including the effects of electron-translation factors (ETF’s). We compare the couplings arising from atomic representations and atomic ETF’s with those arising from molecular representations and ’’switching function’’ ETF’s. We show that a unique set of switching functions makes the two descriptions identical in their effects. We then show that an acceptable general definition of a diabatic representation is provided by the condition P+A=0, where P is the usual nonadiabatic coupling matrix and A represents corrections to it arising from electron translation factors (ETF’s). Two distinct types of diabatic representation result, depending on the definition taken for A. States that undergo no deformation are called F diabatic; those that have no velocity-dependent couplings are called M diabatic. Finally, we discuss the properties of representations that are partially diabatic and partially adiabatic, and we give some rules for the construction of representations that should be nearly optimal for describing many types of collision processes.
Threshold behavior of vibrationally inelastic cross sections
Authors: Lin C. S.
Published: February 2003

Converged cross sections for the vibrational processes (0, j) → (1,j′) for the system para-H2+He are presented at eleven energy values below 1 eV. Pronounced structures in these cross sections, similar to those first observed by McGuire and Toennies but not detected in some other calculations, are studied in detail. It is shown that the rotational coupling and energy gap between the initial and/or final state of a transition and the state just opening up play important roles in the threshold behavior of the cross sections.
Measurement of the U-Kr momentum transfer cross section using crossed molecular beams
Authors: Stern Richard C. , Lang Neil C.
Published: February 2003

The relative laboratory differential cross section for the scattering of atomic U by Kr is determined at a collision energy of 0.10 eV. The cross section is absolutely calibrated by measurement of the fraction of the U beam scattered to 10° LAB and the Kr beam flux. The U–Kr momentum transfer cross section of 46.5+4.4−8.1 Å2 corresponds to an effective U atom radius of 2.43 Å.
Raman spectra of the dimethylether ⋅⋅⋅ hydrogen chloride hydrogen-bonded complex in the gas phase
Authors: Desbat B. , Lassegues J. C.
Published: February 2003

The Raman spectra of the hydrogen-bonded complexes formed between (CH3)2O or (CD3)2O and HCl or DCl have been recorded in the gas phase at room temperature. The Raman profiles of the νClH and νClD stretching vibrations are found to be different from the corresponding infrared ones. It is suggested that, in addition to the rather strong mechanical anharmonicity which couples the νClH and νClH⋅⋅⋅O modes, electrical anharmonicity and coupling with other low-frequency deformation modes of the hydrogen bond, could explain the observed spectral differences. Other band-shaping mechanisms such as Fermi resonances with overtones and combinations involving the ethereal part or rotational broadening seem to be of secondary importance since only small differences are observed on the Raman spectra, respectively, when (CH3)2O is changed by (CD3)2O or when the spectrum of a given complex is taken in the IVV or IVH geometries.
The vibrational and electronic spectra of the mono-, di-, and trianon salts of TCNQ
Authors: Khatkale Murlidhar S. , Devlin J. Paul
Published: February 2003

The vibrational and electronic spectra for the sodium mono-, di-, and trianion salts of TCNQ prepared in vacuo by solvent-free vapor codeposition methods, have been measured. These data, combined with published vibrational assignments for neutral TCNQ and the monoanion salts of TCNQ, have permitted an empirical analysis of the effect of increasing electronic charge on the π- bonding of this conjugated system. Thus, empirical molecular force constants determined from new vibrational assignments, which are somewhat tentative in the case of the di- and trianion, indicate a regular transition of the p-quinoid ring system of TCNQ0 to a benzenoid system for TCNQ3−. Simultaneously, the C≡N and C≡C bonds of the TCNQ wings are considerably reduced in strength while the wing C––C bonds gain double bond character eventually surpassing the original C=C bonds in strength in the case of TCNQ3−. The dianion salt, Na2TCNQ, is colorless while the trianion salt, Na3TCNQ, is golden yellow but there is little evidence in either the visible or infrared spectra to suggest that these salts are other than insulators. The vibrational data are indicative of a severe distortion of the anion in Na2TCNQ and, especially, Na3TCNQ.
The excluded volume effect for self-avoiding random walks
Authors: Wall Frederick T. , Seitz William A.
Published: February 2003

A method is developed to predict the asymptotic behavior of totally self-avoiding walks by utilizing data for random walks of limited orders of nonself intersection. The results shed further light on the exponent, γ, in the equation for the mean square end-to-end separation : <RN2≳∼Nγ, where γ=3/2 in two dimensions and γ=6/5 in three. The prediction of γ is achieved by analyzing the slopes and intercepts of the asymptotes of <RN2≳ for limited order walks. To obtain accurate estimates of the slopes of such asymptotes, a new Monte Carlo sampling method has been developed. Calculations using such Monte Carlo simulation for finite order walks are used to predict the generally accepted self-avoiding behavior.
The differential elastic scattering of CCl4 by Kr
Authors: Bobbio Stephen M. , Sherrod William D.
Published: February 2003

The differential elastic scattering cross section for CCl4+Kr at 0.0857 eV collision energy has been measured. The experimental result resolves the low frequency rainbow structure and has been interpreted using the semiquantal method. An intermolecular potential has been recovered from the calculation and is discussed.
Theoretical determination of molecular structure and conformation. III. The pseudorotation surface of 1,2,3-trioxolane and 1,2,4-trioxolane
Authors: Cremer Dieter
Published: February 2003

The potential surfaces of 1,2,3-trioxolane (primary ozonide) and 1,2,4-trioxolane (final ozonide) have been explored by ab initio MO theory using large augmented basis sets. Extensive optimization of geometry has been perfomed with and without polarization functions. Results indicate that the latter are necessary in order to obtain reliable theoretical predictions with regard to the degree and mode of puckering of the two five-membered rings and with regard to their conformational barriers. Contrary to previous quantum chemical calculations the envelope form (Cs symmetry) of the primary ozonide is found to be the most stable conformation. Pseudorotation is hindered by a barrier of 3.5 kcal/mole which is about half as high as the barrier to planarity (7.7 kcal/mole). Similar barrier heights are calculated for the final ozonide (3 kcal/mole vs 6 kcal/mole), but in this case the twist conformation (C2 symmetry) corresponds to the conformational minimum. The electronic features determining the conformational tendencies of the trioxolanes are analysed in detail using hydrogen trioxide and hydrogen peroxide as alicyclic model compounds.
Theoretical determination of molecular structure and conformation. V. Electronic effects influencing the stability of methyl substituted final ozonides
Authors: Cremer Dieter
Published: February 2003

Restricted Hartree–Fock (RHF) theory is used to explore the conformational surfaces of three methyl substituted final ozonides (FO), namely, 3-methyl-1,2,4-trioxolane (propene FO), cis-3,5-dimethyl-1,2,4-trioxolane (cis-2-butene FO) and the corresponding trans isomer (trans-2-butene FO). A split valence [3s2p/2s] basis and an augmented split valence [3s2p1d/2s] basis is employed. The interconversional processes of the FO ring are studied with a rigid pseudorotor model. Puckered ring conformations are found to be more stable than the planar forms in all three cases. Pseudorotation is hindered by barriers of 3.1 and 5.9 kcal/mole (propene FO), 1.6 and 5.4 kcal/mole (cis-2-butene FO), and 5.7 kcal/mole (trans-2-butene FO). The conformational minima are located at the twist puckered forms (OO half-chair), a result which can be rationalized in terms of lone pair delocalization or σ–π orbital mixing. In agreement with spectroscopic results, the most stable FO conformation is found to possess at least one methyl substituent in an equatorial position. Thus, a favorable interaction between ring and substituent MO’s is guaranteed which leads to a stabilization of the two highest occupied MO’s and back-donation of charge from the ring to the substituent. The difference in the conformational behavior of primary ozonides (PO) and FO’s is shown to result from the different topologies of the two trioxolane rings.
Scaled particle theory for mixtures of nonadditive hard discs
Authors: Tenne Reshef , Bergmann Erich
Published: February 2003

A scaled particle theory for nonadditive hard discs is developed and solved which should have applications in the theory of partial localization of adsorbates. Solutions are given for positively as well as negatively nonadditive hard discs. For positive nonadditivity, the solutions obtained with the Gibbs–Duhem equation show better agreement with the single molecular dynamics calculation available. These solutions again show a demixing phase transition for large nonadditivity and coverage. As in three dimensions, the solutions from the virial equation are superior for negative nonadditivities. We believe that we have discovered a phase transition for large negative nonadditivity: Δcr=−0.365±0.005. For physical reasons, this should be an ordering of the fluid into a crystalline solid phase. The compressibility factor and the free energy have a minimum for equicomposition mixture. The free energy has a kink at the critical coverage ϑcr. This phase transition has also been found for negatively nonadditive hard spheres.
Dipolar narrowed Carr–Purcell measurement of rotating frame spin–lattice parameters in polymers
Authors: Dybowski Cecil , Pembleton R. G.
Published: February 2003

The use of the dipolar-narrowed Carr–Purcell sequence for measuring the spin–lattice contribution to the linewidth under multiple pulse sequences is demonstrated. The relaxation in polyisoprene is exponential with a time constant, T1y, of the order of T1ρ for the sample. The relaxation rate depends on pulse spacing in a manner not predicted by assuming an exponential correlation function for the reorientation.
The far-ultraviolet spectra of CH3SCH2SCH3 and CH3SCH2COCH3
Authors: Olivato P. R. , Viertler H. , Wladislaw B. , Sauvageau P. , Sandorfy C.
Published: February 2003

The far ultraviolet spectra of CH3SCH2SCH3 and of CH3SCH2COCH3 have been measured in the vapor state. The spectra are compared to those of related thioethers and ketones, and are interpreted in terms of valence-shell and Rydberg transitions. In the 41 000–46 000 cm−1 part of the spectrum the σ*←? (lone pair) and 4s←? transitions give clearly separate bands for both compounds. In the 47 000–55 000 cm−1 part of the spectrum of CH3SCH2SCH3 new bands appear which might be related to a split in the 4p levels.
Dimethyl-diacetylene radical cation and its fluorescence spectra in rare gas matrices
Authors: Bondybey V. E. , English J. H. , Miller Terry A.
Published: February 2003

Matrix spectra of the C6H6+ species in solid Ne exhibit a well resolved vibrational structure, which shows a remarkably good agreement with the gas phase fluorescence. The ions in solid Ar are more strongly perturbed and show an interesting line shape asymmetry between the emission and excitation spectra. These are discussed in terms of the ion–host interaction potentials.
Application of the RISM theory to Lennard-Jones interaction site molecular fluids
Authors: Johnson Elijah , Hazoumé Roger Paul
Published: February 2003

It seems that reference interaction site model (RISM) theory atom–atom distribution functions have been obtained directly from the RISM equations only for fused hard sphere molecular fluids. RISM distribution functions for Lennard-Jones interaction site fluids are presented. Results presented suggest that these distribution functions are as accurate as RISM distribution functions for fused hard sphere molecular fluids.
Laser induced fluorescence spectrum of matrix isolated CS+2
Authors: Bondybey V. E. , English J. H. , Miller Terry A.
Published: February 2003

The laser induced fluorescence spectrum of the CS2 cation has been obtained in solid Ne and Ar matrices. The transitions observed originate in the X 2Π state and terminate in the A 2Π state. In the Ne matrix, sharp lines with well resolved vibrational structure are observed. There is only a very small difference between gas-phase and Ne matrix values for the electronic origin and vibrational frequencies, although the latter analysis can be extended somewhat in the matrix. In the Ar matrix only a poorly resolved and strongly shifted CS+2 spectrum is observed. A qualitative explanation for this different behavior is advanced.
ESR–ENDOR study of x irradiated single crystals of α-methyl-D-glucopyranoside
Authors: Madden K. P. , Bernhard W. A.
Published: February 2003

Single crystals of α-Methyl-D-glucopyranoside x irradiated at 77 K contain five free radical species observed by ESR and ENDOR spectroscopy. Four of these have been assigned molecular loci: a primary alkoxy radical at O6, a secondary alkoxy radical at O2, a deprotonated hydroxyalkyl radical at C6, and a radical due to hydrogen abstraction at C5. Structural considerations and mechanisms of formation are discussed.
Sonoluminescence of argon saturated alkali metal salt solutions as a probe of acoustic cavitation
Authors: Sehgal C. , Steer R. P. , Sutherland R. G. , Verrall R. E.
Published: February 2003

Emission from argon saturated aqueous alkali metal salt solutions is observed during insonation at 460 kHz. It is postulated to arise from de-excitation of excited alkali metal atoms formed by free radical reduction processes. In addition to the emission resonance lines, diffuse bands are observed at ∼554 nm and ∼740 nm for Na and K, respectively. The latter are due to emission from alkali metal–argon exciplexes and are known to occur when mixtures of alkali metal vapor and argon are rapidly compressed. An estimate of the cavitational temperatures and pressures is obtained by comparison of experimental emission band parameters with those derived theoretically.
Correction of instrumental distortion by analytical deconvolution of data
Authors: Morton D. C. , Rayborn Grayson H.
Published: February 2003

A general, analytical theorem developed by van de Hulst for inverting the convolution integral is reviewed and illustrated both with synthetic data and with experimental data from time-of-flight measurements. If the undesired influence of an instrument used in an experimental measurement can be represented by the convolution integral, the original undistorted or ’’true’’ distribution may sometimes be recovered in post-processing the data by means of deconvolution. Analytic deconvolution is achieved by using the coefficients from a power series representation of the distorted output distribution and a set of ’’solving polynomials’’ which may be readily derived from the response function of the instrument. The distortion due to the excitation pulse duration in time-of-flight molecular beam data has been removed by application of the theorem. Some possible advantages of this analytical method over conventional deconvolution techniques are discussed.
Infrared intensities and Coriolis interactions in ethylene
Authors: Nakanaga Taisuke , Kondo Shigeo , Saëki Shinnosuke
Published: February 2003

The infrared band intensities of ethylene and ethylene-d4 were measured in the gas phase using the pressure broadening method. From the analyses of Coriolis interactions between ν7 and ν10 and between ν7 and ν12, the relative signs of (∂p/∂Q7), (∂p/∂Q10), and (∂p/∂Q12) have been determined. The obtained band intensities were analyzed by the least squares method with the aid of the results from Coriolis analyses and CNDO/2 calculations. The correct sign combination of (∂p/∂Qi) have successfully been determined. The resulting values of the intensity parameters (∂p/∂Sj) are found consistent with the empirical rule for the sense of the dipole moment derivatives.
Calculations on ionic solvation. III. The electrostatic free energy of solvation of ions, using a multilayered continuum model
Authors: Abraham Michael H. , Liszi János , Mészaros Lajos
Published: February 2003

For the calculation of the electrostatic free energy (and also the entropy) of solvation of an ion, a model is set up in which an ion of given crystallographic radius is surrounded by a series of concentric spherical layers, each with a different relative permittivity, immersed in the bulk liquid. A complete general solution is given for any number of such layers, both for the electrostatic free energy of solvation and the corresponding entropy term. The dielectric saturation effect is taken into account through the different relative permittivities of the layers. The first layer, next to the ion, is considered to have a special role and to have a relative permittivity ε=n2, independent of the dielectric saturation effect of the ion.
Single vibronic level fluoresence from aniline
Authors: Chernoff Donald A. , Rice Stuart A.
Published: February 2003

Gas phase fluorescence spectra of 15 vibronic levels in 1B2 aniline are described. The emission spectra of single vibronic levels in aniline have well separated vibrational structure. A continuum background seen in a few cases is shown to be due to sequence congestion in the absorption spectrum, not to intramolecular vibrational energy transfer.
Magnetic and thermodynamic properties of potassium ferricyanide below 0.4 °K in magnetic fields up to 16 300 G directed along the crystallographic a axis
Authors: Fritz J. J. , Goto T. , Kuntz R. L.
Published: February 2003

Measurements have been made of the intensity of magnetization of potassium ferricyanide at fields up to 1600 G on a series of isentropes with entropies from 0.03 to 1.06 cal mole−1 deg−1. These measurements define a region within which antiferromagnetic ordering of the ions dominates the properties of the salt. They have been combined with previous measurements to give the temperature as a function of magnetic field and entropy and from this the heat capacity at various constant magnetic fields from 0 to 16 300 G at 0.4 °K down to the lowest temperatures obtainable with the given magnetic field. Below 2000 G, the heat capacities show sharp maxima associated with the transition from order to disorder. The heat capacity, entropy and intensity of magnetization of the salt is given at rounded values of the temperature from 0.06 to 0.40 °K for six selected magnetic fields from 0 to 16 300 G.
Theoretical investigations of the metastable triplet state of benzophenone
Authors: Mijoule C. , Leclercq J. M.
Published: February 2003

A one-parameter conformational analysis using open-shell SCF wavefunction gives a C=O bond length (rCO) equal to 1.33 in the lowest 3nπ* state of benzophenone. A study of the correlation between some properties of this state, such as the electric dipole moment or the molecular orbital localizations, and rCO is made. The zero-field splitting (ZFS) parameters D and E of this state are computed. A study of the variation of the spin–spin contribution to D and E with rCO is carried out. On the other hand, the spin–orbit coupling contribution is observed to have a large effect on the D parameter. The final value of D corresponding to the equilibrium rCO distance in the metastable triplet state is found to be equal to −0.141 cm−1, in good agreement with the experimental value (−0.151 cm−1).
Vibrational–rotational relaxation from high vibrational states in He–HD
Authors: Tarr Susan M. , Rabitz Herschel
Published: February 2003

The relaxation behavior of the He–HD system is studied by applying an exponential distorted wave procedure to calculate the cross sections and the rate constants for vibrational–rotational energy transfer in the vibrational manifolds n, 0⩽n⩽5. The rotational states are shown to play an important role in vibrational relaxation by providing many pathways for vibrational–rotational–translational energy exchange. By comparison with breathing sphere calculations it is demonstrated that the near exponential growth in the n→n−1 rates from vibrotor calculations can be attributed not only to the vibrational anharmonicity but also to the decreasing rotational energy spacings as n increases.
Rate constant for the reaction of OH radicals with hydrogen peroxide at 298 K
Authors: Harris G. W. , Pitts J. N.
Published: February 2003

The rate constant for the reaction of OH radicals with H2O2 at 298 K has been determined to be (6.8±1.3) ×10−13 cm3 molec−1 s−1 using the flash photolysis–resonance fluorescence technique.(AIP)
Depletion layer studies in organic films: Low frequency capacitance measurements in polycrystalline tetracene
Authors: Twarowski Allen J. , Albrecht A. C.
Published: February 2003

The study of the electrical properties of (metal 1‖ organic ‖metal 2) cells has not led to a consistent model of their origin. On the one hand, conductivity measurements suggest that many organic materials behave as insulators (low carrier concentrations) while photovoltaic properties of some of these same materials may be rationalized using the concepts of semiconductor physics, suggesting that the organic film has a high carrier concentration. In this paper the voltage dependence of the capacitance of a (Al‖tetracene‖Au or Nesatron) cell is investigated in an attempt to better understand this contradiction. The electrical properties of this cell are explained in terms of a model in which depletion layers are made from a high density of immobile trapped charge. The trapped charge can be mobilized by light and then evidence is found for a Schottky depletion region (∼2000 Å thick) in the tetracene film.
On the choice of buffer gas mixtures for drift-tube studies of ion–neutral reactions
Authors: Viehland Larry A. , Mason E. A.
Published: February 2003

Rigorous and ad hoc theories are presented for choosing a mixture of neutral buffer gases that facilitates the extraction of thermal rate coefficients from the data obtained as a function of temperature and electric field strength in drift-tube mass spectrometers and flow–drift apparatus.
The low frequency Raman spectrum and barrier to planarity of 2-cyclohexene-1-one.
Authors: Carreira L. A. , Towns T. G. , Malloy Thomas B.
Published: February 2003

The low frequency Raman spectrum of gaseous 2-cyclohexene-1-one has been obtained at the full vapor pressure at ∼110°C using the 488 nm line of an argon ion laser at ∼2W power. 2-cyclohexene-1-one has been found to exist with all of the heavy atoms except C5 essentially in a plane. The series of Q-branch transitions in the Raman spectrum between 140–250 cm−1 have been assigned as Δv=2 transitions of a one-dimensional double-minimum oscillator. The vibarational mode is the motion of the CH2 group at the 5 position through the plane of the heavy atoms. The potential function in a reduced coordinate Z [V (cm−1) =27.49(Z4−11.67 Z2)] yields a barrier to planarity of 935±70 cm−1 (2.67±0.2 kcal/mole, 11.2±0.8 kJ/mole).
On the determination of Born–Oppenheimer nuclear motion wave functions including complications due to conical intersections and identical nuclei
Authors: Mead C. Alden , Truhlar Donald G.
Published: February 2003

We show how the presence of a conical intersection in the adiabatic potential energy hypersurface can be handled by including a new vector potential in the nuclear-motion Schrödinger equation. We show how permutational symmetry of the total wave function with respect to interchange of nuclei can be enforced in the Born–Oppenheimer approximation both in the absence and the presence of conical intersections. The treatment of nuclear-motion wave functions in the presence of conical intersections and the treatment of nuclear-interchange symmetry in general both require careful consideration of the phases of the electronic and nuclear-motion wave functions, and this is discussed in detail.
Light scattering by a molecule near a solid surface. II. Model calculations
Authors: Efrima Shlomo , Metiu Horia
Published: February 2003

We use a theory, previously developed by us, to investigate numerically the properties of the light scattered by a molecule adsorbed near a solid surface. We illustrate how the angular dependence and the polarization of the scattered light can be used to infer, in certain limiting cases, the position of the molecule with respect to the surface. The frequency dependence of the scattered radiation is investigated and possible causes for the observed enhancement of scattering by a metallic surface are discussed.
An assessment of the electronic structure of alkylbenzenes
Authors: Bigelow Richard W.
Published: February 2003

The nature and manifestations of the valence orbital interactions between benzene and selected alkyl groups are elucidated through correlations of the gas phase photoelectron spectra with the corresponding ground state orbital eigenvalues obtained according to the semiempirical CNDO/S–CI molecular orbital method. An important result is the finding that alkane orbitals strongly interact with the higher-lying occupied benzene σ orbitals of appropriate symmetry to yield several moderate charge-transfer excitations below 7.0 eV which are predominately of σ→π* character. The oscillator strength for these transitions is found to be strongly dependent on the relative orientation of the benzene and alkane moieties.
Laser excited resonance fluorescence in formaldehyde
Authors: Hardwick J. L. , Till S. M.
Published: February 2003

The 3375 Å line of the Kr+ laser has been used to excite a single rovibronic transition of the ?1A2–?1A1 system of formaldehyde. Fluorescence from the upper level to the ground electronic state forms vibrational progressions in the carbonyl stretch (ν2″), the symmetric in plane bend (ν3″) and twice the out of plane bend (2ν4″), extending over 10 000 cm−1 to the red of the exciting line. The rotational structure has been resolved and effective rotational A constants have been obtained. Vibrational constants and anharmonicities have been calculated.
A model for phase transitions in a bidimensional monolayer of rectangular molecules with a polar head
Authors: Dupin J. J. , Firpo J. L. , Albinet G. , Bois A. G. , Casalta L. , Baret J. F.
Published: February 2003

A model for aliphatic molecules monolayers phase transitions at air–water interfaces is proposed: the molecules are treated as rectangles lying on a square lattice, as in a previous paper. But in this work one extremity of the rectangle is discriminated as the polar head of a molecule by means of an interaction energy different from that between aliphatic chains— (Π−A) isotherms and coexistence curves are calculated in the framework of this model and we point out some improvements brought to the results obtained with our previous model, in particular, a third phase tranisition is given by a polar head orientation.
The electronic transition moment of the B
O+u–X 1Σ+g system of I2 through gain measurements of an I2 optically pumped laser
Authors: Koffend J. Brooke , Bacis R. , Field Robert W.
Published: February 2003

The electronic transition moment of the I2 B O+u–X 1Σ+g system is determined over a range of R-centroid from 2.8–4.6 Å through gain measurements of an optically pumper I2 laser. The technique reported here represents an important new application of optically pumped diatomic lasers allowing accurate determination of relative dipole strength functions from gain measurements. The results are in agreement with the qualitative predictions of Brewer and Tellinghuisen [J. Chem. Phys. 56, 3929 (1972)].