bluuebunny/crossref_metadata_2025 huggingface dataset:
The asymptotic properties of second-order density matrices in N-electron atoms and molecules
Authors: Dawson K. A. , March N. H.
Published: July 2002

Asymptotic representations of the density matrix and pair function for atoms and molecules are developed for a number of different limits. These are necessary conditions on any feasible density matrix. We end by discussing the corresponding physical configurations.
Direct solution of the H(1s)–H+ long-range interaction problem in momentum space
Authors: Koga Toshikatsu
Published: July 2002

Perturbation equations for the H(1s)–H+ long-range interaction are solved directly in momentum space up to the fourth order with respect to the reciprocal of the internuclear distance. As in the hydrogen atom problem, the Fock transformation is used which projects the momentum vector of an electron from the three-dimensional hyperplane onto the four-dimensional hypersphere. Solutions are given as linear combinations of several four-dimensional spherical harmonics. The present results add an example to the momentum-space solution of the nonspherical potential problem.
Thermalization–reaction–capture model for low dose active ion bombardment. II. Fast diffusion case
Authors: Mintz Moshe H. , Jo Yangsun , Rabalais J. Wayne
Published: July 2002

A thermalization–reaction–capture model for low dose active ion bombardment which has been treated recently for the diffusionless case has been extended to include fast irradiation-enhanced diffusion in the near-surface region. Analytical expressions are derived for the reduced slopes of the AES or XPS intensities vs ion dose curves for a given ion primary energy and ion/target combination. Comparison of these theoretical reduced slopes with experimental plots yields a nondestructive means for estimating the concentration distributions of the reaction product in the target. In cases when these distributions obey the two extreme possibilities (i.e., the diffusionless case and the fast-diffusion case) the corresponding reaction probabilities may be obtained. Some experimental examples are discussed.
Formation of a long-lived collision complex in alkali diatomic–rare gas collisions and rotational excitation via a mode-specific dissociation
Authors: Al-Imarah F. J. , Bain A. J. , Mehde M. S. , McCaffery A. J.
Published: July 2002

We report an unusual pressure dependence of the gas phase dynamics of alkali diatomics in 1Π excited states in their interactions with certain collision partners. This behavior consists of a change in the relative rates of the ΔJ=+1 and ΔJ=−1 collision-induced transitions, which results in a dominance of rotational excitation at high pressures. This effect occurs only for the e Λ-doublet component of the excited 1Π state. Also observed is a change in the polarization of the parent line such that the polarization ratio increases with increasing pressure. The dependence of this behavior on intermolecular potential, reduced duration of collision, rotational state, and temperature lead us to propose that a long-lived complex or orbiting resonance is responsible for the effects observed. This species appears to be formed during the lifetime of the excited state of the diatomic. Knowledge of the molecule-fixed geometry of the Λ doublets allows us to propose a structure for the long-lived species and to speculate that the observed characteristic rotational excitation results from specific vibrational and rotational predissociation processes within the complex.
The unimolecular reaction of vinyl fluoridea)
Authors: Caballero J. F. , Wittig C.
Published: July 2002

The infrared multiple photon dissociation of CH2CDF proceeds by 3- and 4-center eliminations, in agreement with the predictions of recent ab initio calculations. IR spontaneous emission is detected from HF† and from a species tentatively identified as C2H2† produced from the vinylidene⇄acetylene isomerization which follows 3-center elimination. We are unable to detect emission from DF†, indicating that this vibrationally excited species is not a major product. GC/MS analyses indicate that the 3- and 4-center pathways account for approximately 30% and 70%, respectively, of the decomposition. There is no evidence of an ethylidene intermediate, suggesting that the barrier for 1,2 H migration is higher than predicted by ab initio calculations.
Rotational state dependence of pyrazine fluorescence: Initial decays for the vibrationless 1B3u state
Authors: Lorincz Andras , Smith Duane D. , Novak Frank , Kosloff Ronnie , Tannor David J. , Rice Stuart A.
Published: July 2002

We report new measurements of the rotational state dependence of the initial fluorescence decay of the vibrationless 1B3u state of pyrazine. Through examination of excited state dynamics from a Green’s function point of view the apparently inconsistent data from several sources are reconciled.
Wave packet evolution in isolated pyrazine molecules: Coherence triumphs over chaos
Authors: Novak Frank , Kosloff Ronnie , Tannor David J. , Lorincz Andras , Smith Duane D. , Rice Stuart A.
Published: July 2002

Recent measurements of the rotational state dependence of the initial fluorescence decay of the vibrationless 1B3u state of pyrazine are analyzed from several points of view. The relationship of these analyses to recent ideas dealing with quantum chaos is discussed.
Structure and dynamics of the excited CH–chromophore in (CF3)3CH
Authors: Baggott J. E. , Chuang Mei-Chen , Zare Richard N. , Dübal H. R. , Quack M.
Published: July 2002

The absorption spectra of gaseous (CF3) 3CH (1,1,1,3,3,3-hexafluoro, 2-trifluoromethyl propane) were recorded in the IR between 800 and 12 000 cm−1 by high resolution interferometric Fourier transform techniques and in the visible from 12 000 to 17 000 cm−1 by laser photoacoustic spectroscopy. Instead of single bands in the CH overtone region, complex multiplet structures were observed. Thirty-nine bands were assigned as arising from the interacting CH-stretching and CH-bending manifolds, which account for most of the absorption in the overtone region. The results can be understood quantitatively with an effective, tridiagonal many-level Fermi resonance Hamiltonian. Close agreement is obtained for the positions and intensities of the observed spectral features using only seven spectroscopic parameters. The experimental and theoretical results are summarized in Tables II, III, and IV. The Hamiltonian can be used to calculate and understand the time-dependent redistribution of vibrational energy between the coupled CH-stretching and CH-bending vibrations. The role of broad vibrational band shapes and the possible exponential decay of CH excitation into a background of states from low-frequency vibrations is discussed.
Raman scattering spectra of the triple cation salt Li2NaK(SO4)2
Authors: Kitahama Katsuki , Frech Roger
Published: July 2002

Single crystals of Li2NaK(SO4)2 were grown at elevated temperatures from an aqueous solution of K2SO4, Na2SO4, and Li2SO4⋅H2O. Polarized Raman spectra were measured at room temperature in various scattering geometries and symmetry-based vibrational mode assignments are made. The existence of an apparent surface phase and a bulk phase is deduced from scattering measurements from different regions of the crystal and is discussed.
Excited singlet-state lifetimes of hydrated chlorophyll aggregates
Authors: Alfano A. J. , Lytle F. E. , Showell M. S. , Fong F. K.
Published: July 2002

A time-correlated single photon counting technique, coupled with a red sensitive photomultiplier tube, was used to determine the singlet-state lifetimes and energy transfer mechanisms of Chl a⋅H2O, (Chl a⋅H2O)2, and (Chl a⋅2H2O)n. The use of low concentrations and low incident light fluxes permitted measurements in a regime where nonlinear quenching effects are absent. The lifetimes exhibit a pronounced dependence on aggregate size. The results are examined in terms of exciton interactions in the excited singlet state of the Chl a aggregate. It is shown that in the absence of exciton annihilation effects, the rate of singlet-state decay via radiative coupling and intersystem crossing of a Chl a aggregate containing n equivalent monomeric units is equal to n times that of monomeric Chl a.
Application of the equations-of-motion method to the calculation of the indirect nuclear spin–spin coupling tensors
Authors: Galasso V.
Published: July 2002

The equations-of-motion (EOM) method, developed by Rowe and by Shibuya and McKoy as an approach to calculating excitation energies and transition amplitudes relative to a correlated ground state directly, has been extended to the calculation of the indirect nuclear spin–spin coupling tensors. The theoretical values, calculated at ab initio level taking into account all the four electron–nucleus interactions, of a series of saturated and unsaturated molecules, CH4, C2H6, C2H4, C2H2, CN−, HCN, HNC, and HCNH+, correlate satisfactorily with the available experimental data and with corresponding CHF–CI results. The EOM formalism may be therefore a convenient alternative to the time-consuming CHF–CI procedures in order to get reasonable reproduction of the J tensors, even for molecules which suffer from UHF triplet instability in single configuration CHF calculations.
Pulse expansion deposits and orientational ordering for low temperature matricesa)
Authors: Jones L. H. , Ekberg S. A. , Swanson B. I.
Published: July 2002

Low temperature matrices of SF6 in xenon were prepared by pulsed expansion of premixed gas through a conical 0.5 mm orifice onto a cold window. Infrared polarization studies were made of the orientational ordering exhibited by the ν3 mode at ∼933 cm−1. The orientational ordering was similar to that of big pulse deposits at 40 K and below but less for 50 K deposits. The pronounced polarization observed suggests an anomaly in the refractive index of the matrices prepared by this technique. For deposits at 50 K, aggregation is found to be negligible for pulsed expansion while it is significant for large pulse deposits, and even greater for the slow-spray-on technique.
Size effects in the spin relaxation by bounded diffusion in two dimensional systems
Authors: Korb J.-P.
Published: July 2002

An extension of our previous theory of spin relaxation by translational diffusion in two-dimensional (2D) systems is proposed by considering the very nonuniform radial molecular distribution observed at short intermolecular distance. This increases greatly the absolute values of the spin-lattice relaxation rates T−11 and enhances the size effects on their diffusion (or temperature) dependences. The existence of two maxima in these dependences should facilitate the interpretation of experimental data in 2D heterogeneous systems.
On exact scaling relations
Authors: Eno Larry
Published: July 2002

Exact scaling relations are derived for the matrix elements of an arbitrary operator. While the scaling coefficients in these relations contain the full arbitrary operator, they provide a framework for developments in scaling theory. Various exact collisional scaling relations, which were given recently, are shown to be encompassed by the present analysis. We also discuss the scaling of eigenvalue problems from the new perspective.
Doppler-free optogalvanic spectrum of He2 b 3Πg–f 3Δu transition
Authors: Kawakita Kijuro , Fukuda Kazuhide , Adachi Yukio , Hirose Chiaki
Published: July 2002

Doppler-Free Lamb dip and intermodulated spectra of He2 b 3Πg–f 3Δu transition have been observed by the technique of optogalvanic spectroscopy. The analysis of the triplet splittings of rotational lines yielded the values of spin-orbit (A), spin–spin (λζ and λ⊥⊥) and spin-orbit (γ) coupling constants of AΠ=−6.753±0.26, λζ=3.069±0.37, λ⊥⊥=−4.480±0.03, γ=−0.009±0.02 GHz for the b 3Πg state, and AΔ=−0.073±0.10, λζ=0276±0.27, and γ=0.016±0.03 GHz for the f 3Δu state. The Λ-type doubling in the b 3Πg state was found negligible. The derived values for the b 3Πg state are compared with those for the H2 c 3Πu state which has the optical electron in the same 2pπ orbital as He2 b 3Πg state, and the departure of the electron configuration in the He2 b 4Πg state from the united atom orbital (UAO) is discussed.
An examination of the use of wave packets for the calculation of atom diffraction by surfaces
Authors: Jackson Bret , Metiu Horia
Published: July 2002

We use analytic models, valid for neutron scattering, and numerical calculations to examine a method proposed by Drolshagen and Heller for computing atom diffraction from surfaces. Our main concern is the manner in which the use of narrow packets, causing a partial coherence of the incident beam, might affect the differential intensity. We find that the demands of representing beam coherence correctly conflict with the requirements for the validity of the propagation scheme. We suggest some improvements that should increase the reliability of the method without affecting greatly its remarkable computational and conceptual advantages.
A systematic investigation and characterization of interfacial hydrated n-alkane films by total internal multiple reflection
Authors: Giuliani J. F. , Jarvis N. L.
Published: July 2002

We present the first systematic investigation by the technique of total internal optical reflection of a homologous series of low molecular weight alkanes adsorbed as hydrated films on a glass surface. The detected optical signals for these hydrated alkanes can be shown to depend empirically on the square of their molar refractivity times an optical depolarization scaling parameter. Relative scattering cross-section measurements between a hydrated film of methane and a water film allowed for an estimate to be made of the number of water molecules which surround the methane molecule in the ‘‘cage-like’’ hydrate structure.
‘‘Direct’’ calculation of quantum mechanical rate constants via path integral methods: Application to the reaction path Hamiltonian, with numerical test for the H+H2 reaction in 3D
Authors: Yamashita Koichi , Miller William H.
Published: July 2002

The method recently proposed by Miller, Schwartz, and Tromp for determining Boltzmann rate constants ‘‘directly’’—by the path integral evaluation of a reactive flux correlation function—is developed within the framework of the reaction path Hamiltonian model for a general polyatomic reaction. The expression for the correlation function, the time integral of which is the rate constant, is reduced to a single path integral over only one degree of freedom (the reaction coordinate). Effects of tunneling, ‘‘frictional’’ effects on the reaction coordinate due to coupling to other degrees of freedom, and the effects of recrossing the transition state dividing surface are all correctly accounted for in the approach. Numerical tests of the formulas for the 3D version of the H+H2 reaction (on the Porter–Karplus potential surface) gives excellent agreement with the (known) accurate results for this system.
Raman scattering study of phase transitions in NH4SCN
Authors: Tewari G. D. , Khandelwal D. P. , Bist H. D.
Published: July 2002

The Raman spectra (30–3300 cm−1) of a single crystal and of polycrystalline forms of NH4SCN are presented in the temperature range 135 to −175 °C. The polarization behavior of the Raman bands reveals the antipolar arrangements of SCN− ions in the room temperature phase. Above 86.5 °C the spectra do not show polarization behavior due to the formation of polycrystalline domains. Other changes observed in the entire spectrum at this phase transition are attributed to reorientation of SCN− ions between two equivalent configurations. At the next phase transition around 112 °C the lattice modes of SCN− ions are affected. The characteristics are those of a second-order displacive phase transition. A new phase transition observed at −70 °C is characterized by the strengthening of the hydrogen-bond networks in the lattice.
ODMR and resonance Raman spectroscopy of chlorophyll b on graphite
Authors: Clarke Richard H. , Hanlon Eugene B.
Published: July 2002

Zero-field optically detected magnetic resonance (ODMR) and resonance Raman spectroscopy are used to study the adsorbate/substrate system chlorophyll b on highly oriented pyrolytic graphite. Chlorophyll b was applied to the conductive basal surface of the graphite using Langmuir–Blodgett techniques in which both the chlorophyll–chlorophyll and chlorophyll–graphite spacing could be varied. ODMR data reveal changes in chlorophyll b triplet state dynamic features which in the isolated molecule are determined by spin-orbit coupling mechanisms. The possibility of energy transfer among adsorbed species is also suggested. These results are shown to depend not only upon the distance of the molecule from the surface, but also upon the intermolecular distance of photoexcited adsorbates. The resonance Raman spectrum leads to a plausible orientation of the adsorbed chlorophyll unit with respect to the graphite surface.
The singlet states of styrene. Theoretical vibrational analysis of the ultraviolet spectrum
Authors: Hemley R. J. , Leopold D. G. , Vaida V. , Karplus M.
Published: July 2002

Vibrational analyses of the ground and lowest excited singlet states of styrene are performed using an extended PPP-CI model. Franck–Condon factors calculated from the model are used to analyze the intensity distribution of the ultraviolet absorption bands of the jet-cooled molecule from 34 000–46 000 cm−1. For the weak first absorption system (S1←S0) the small amount of vibrational excitation found experimentally is well described by the theoretical model. The relatively intense second absorption band shows more extended vibrational development. The model predicts that two electronic transitions S2←S0 and S3←S0 contribute to the absorption spectrum in this region and that a large number of vibrational excitations involving carbon–carbon stretching motions are active. For the S1←S0 and S2←S0 transitions a refinement of the theoretical model is performed to calculate the excited state equilibrium geometries from the measured spectra. Because of the large number of vibrations and the evidence for mixing among them in the excited states (Duschinsky effect), the full multimode treatment of the ground and excited state dynamics is required for an analysis of the spectrum.
Absorption of electronically excited Xe2Cl in the ultraviolet
Authors: McCown A. W. , Ediger M. N. , Geohegan D. B. , Eden J. G.
Published: July 2002

The absorption cross section for the lowest-lying, bound excited state (4 2Γ) of Xe2Cl has been measured at several wavelengths in the ultraviolet (UV). Temporally isolating the excited Xe2Cl species in Xe/Cl2 gas mixtures has been accomplished by producing XeCl molecules in the B state by photoassociation [Xe+Cl+ℏω → XeCl(B)] at λ=308 nm. Collisional mixing of the lowest lying ion pair states of the excimer subsequently forms the XeCl species in its C state. Following the formation of Xe2Cl* from XeCl(B,C) by a three-body collision, the long radiative lifetime of the trimer (>200 ns) relative to those for the XeCl B and C levels is exploited to ensure that the triatomic molecule is the predominant species when the experiments are performed. A second UV laser pulse depletes the Xe2Cl(4 2Γ) population by photoexcitation [as evidenced by the sudden suppression of the 4 2Γ → 1 2Γ blue-green (λ∼485 nm) fluorescence] and the absorption cross section is determined from the dependence of the degree of fluorescence suppression on the laser intensity. Contrary to the known Xe+21(1/2)u → 2(1/2)gUV absorption profile, Xe2Cl(4 2Γ) exhibits significant absorption at wavelengths as low as 193 nm, whereas the dimer ion absorption at 248 nm is only a fraction of its peak (λ∼340 nm) value. Photoionization of excited Xe2Cl at wavelengths below ∼275 nm may be responsible for the cross sections measured for photon energies as large as 6.4 eV.
A simple electron gas treatment of the magnetic susceptibility tensor of the lowest 3Σ+u state of H2
Authors: Cina Jeffrey A. , Harris Robert A.
Published: July 2002

The incremental diamagnetic susceptibility tensor of the 3Σ+u state of H2 is obtained using an electron gas theory. This state of the hydrogen molecule is a model for the ground state of a system of interacting closed shell species. Because the energy functional is a gauge independent functional of the electron density, there is no separation of the susceptibility tensor into paramagnetic and diamagnetic portions. The results agree in sign, but not magnitude, with a simple valence bond calculation using London orbitals.
Nonlinear spectroscopy and picosecond transient grating study of colloidal gold
Authors: Heilweil E. J. , Hochstrasser R. M.
Published: July 2002

Measurements of the nonlinear dispersion of χ(3) have been performed on the surface plasmon resonance of aqueous colloidal gold. An analysis of the observed dispersion has revealed that the T1 and T2 lifetimes for the plasmon excitation are extremely rapid (<10−14 s) but the release of heat by the particle electron/thermal reservoir is slower (>2 ps). Picosecond time-resolved transient grating experiments on the same gold sol and organic dye solutions have confirmed that the nonradiative thermal decay of the metal particles occurs on the time scale of tens of picoseconds. The application of these methods to the study of ultrafast nonradiative relaxation mechanisms in molecular systems is discussed.
Auger energy shifts and core level relaxation energies in XeF2, XeF4, and XeF6
Authors: Aksela S. , Bancroft G. M. , Bristow D. J. , Aksela H. , Schrobilgen G. J.
Published: July 2002

The energy shifts in 3d photoelectron and M4N4,5 N4,5 Auger spectra of Xe have been studied for HXeF2, XeF4, and XeF6 molecules in the gas phase. Using the Auger parameter method, the contributions of the initial state chemical and final state extra-atomic relaxation effects to the observed shifts have been estimated. The relaxation part has found to be significant both in the binding energy (up to 1.8 eV for XeF6) and especially in the Auger shifts. The ground state shifts are thus larger than the 3d binding energy shifts reported earlier. Calculated atomic charges are also now in better agreeement with theory and other experimental values.
Application of the superposition model to calculate the zero-field splittings in molecules
Authors: Weltner W. , Van Zee R. J.
Published: July 2002

b 0 2 =D zero-field splitting parameters are calculated for the GdF3 and MnX2 (X=F, Cl, Br) molecules using the superposition model with intrinsic parameters obtained from crystal measurements and interatomic distances from gas-phase electron diffraction, where available.
A study of the quantal time delay matrix in collinear reactive scattering
Authors: AbuSalbi N. , Kouri D. J. , Baer Michael , Pollak Eli
Published: July 2002

The Eisenbud–Wigner time delay matrix is used to study the dynamics of reaction close to vibrationally adiabatic barrier energies. Maxima in the time delay are predicted and are found to be in excellent agreement with vibrationally adiabatic barrier energies determined by quantized pods. The actual time spent in the vicinity of the barriers is estimated by separating out the free particle time. This ‘‘real time’’ is then used to analyze the validity of the adiabatic and sudden approaches to reactive scattering in the 3D H+H2 and D+H2 reactions.
Effect of reactant ion internal and translational energy on the rate constants of the charge exchange reactions: CO2++O2→O2+ +CO2 and O2++O2→O2+O2+
Authors: Derai Renèe , Kemper Paul R. , Bowers Michael T.
Published: July 2002

The rate constants of the charge exchange reactions, CO2++ O2→O2++CO2 and O2++O2→O2+O2+ have been studied as a function of both the internal and kinetic energies of the reactant ion in a tandem ICR spectrometer. Primary ions with known internal energies are formed in the source of the tandem by charge transfer reactions whose energy partitioning has already been determined. The rate constant of the CO2++O2 reaction is found to be 4.4×10−11 cm3 s−1 for ground state primary ions and increases by a factor of 2.9 when CO2+ ions have 1.4 eV of internal energy; this reaction is also found to be much less sensitive to the kinetic energy of the parent ion than to its internal energy. The rate constant for the symmetric charge exchange reaction O2++O2 has been determined for internal energies corresponding approximately to the v=0, 3, and 9 vibrational levels of the O2+ ground electronic state and is found to increase with internal energy, at least at low collision energy.
The silaformyl radical HSiO and its energetically lower-lying isomer SiOH
Authors: Frenking Gernot , Schaefer Henry F.
Published: July 2002

Ab initio investigations with a double-zeta plus polarization basis set extended by configuration interation (single and double excitations) predict that the SiOH isomer is 11 kcal/mol lower in energy than HSiO. The barrier for hydrogen rearrangement is found to be substantial and both isomers should be observed experimentally. Two structures HSiO(A) and HSiO(B) were detected for HSiO with 2A′ symmetry and nearly the same energy but different geometry at the DZ+P SCF level. However, HSiO(A) is clearly favored relative to HSiO(B) at higher levels of theory and might be the only true minimum for HSiO.
Photolysis of hydrogen and fluorine in solid argon. Matrix infrared spectra of (HF)2, (HF) (DF), and (DF)2
Authors: Hunt Rodney D. , Andrews Lester
Published: July 2002

Argon diluted samples of H2 and F2 were codeposited at 10 K, and little reaction was observed. Photolysis produced a strong new 3826 cm−1 band, in agreement with assignment to (HF)2 from HF codeposition experiments, weak HF monomer and trimer bands, and a sharp new 3930 cm−1 band for the H=HF intermediate species. Sample annealing markedly increased trimer, relative to dimer and monomer, and destroyed the intermediate species. Similar experiments were done with D2 and HD; the latter gave a strong 2808 cm−1 absorption for the more stable (HF) (DF) mixed dimer and a weak 3832 cm−1 band for the less stable (DF) (HF) mixed dimer. The ability of the argon matrix cage to quench substantial reaction exothermicity is demonstrated by the preferential stabilization of (HF)2 in these experiments.
Reduction into a rational fraction of a thermodynamic property of the liquid state: Experimental determinations in the case of CO2 and n-butane. Extension to the other properties
Authors: Alba Christiane , Ter Minassian Léon , Denis Armelle , Soulard Alain
Published: July 2002

The expansivity of liquid CO2 and of n-butane is determined as a function of pressure up to 4 kbar, from the melting temperatures up to the critical temperatures. The experimental method is piezothermal. The set of data is processed through a fit with a multipoint Padé approximant using an algorithm due to Werner. This particular technique determines, in its reduced form, the unique rational function relevant to the problem. The expansivity of the whole liquid phase is described in terms of a simple equation with four coefficients which enables calculation of the other thermodynamic properties. The general aspect of the phenomenological equations is discussed in this instance, underlining the particular behavior of the heat capacity as a function of pressure.
On the effective interaction of test multipoles in polar fluids. II. Finite-volume spherical geometry
Authors: Arsenault Guy , Marchildon Louis
Published: July 2002

The effective interaction energy of two test particles immersed in a molecular fluid of finite volume is defined and expressed in terms of the molecular pair correlation function. The specific problem of electric multipoles immersed in a fluid of polar nonpolarizable molecules filling a spherical volume is then analyzed in detail. The long-range part of the effective interaction of the test multipoles is obtained to leading order in 1/V. A comparison is made with similar results obtained in the case of infinite volume.
Electronic transport and paramagnetic properties of acetylene–carbon monoxide copolymers
Authors: Chien James C. W. , Babu G. N.
Published: July 2002

Transport and magnetic properties of acetylene–carbon monoxide copolymers have been studied. The copolymers AC-11, AC-21, and AC-41 have compositions [(C2H2)1(CO)0.15]x, [(C2H2)1(CO)0.1]x, and [(C2H2)1(CO)0.05]x, respectively, and the prefixes p and i designate the pristine and thermally isomerized copolymers. The undoped i-AC-copolymers have unpaired spin concentrations [S⋅] about 10−4 of that in trans-[CH]x, yet the amorphous copolymers have up to ten times the RT conductivity σRT of the crystalline polyacetylenes. These homo and copolymers have the same thermopower coefficient 𝒮 and comparable concentration of intrinsic positive carriers as judged from the log σRT vs log y dependence, where y is the mole fraction of dopant. Undoped p-AC copolymers have σRT lying between that of cis- and trans-[CH]x depending upon the trans content in the copolymers. The unpaired spins in the i-AC-copolymers showed motional narrowing and Curie dependence as in trans-[CH]x in spite of the fact that the average sequence lengths of CH segments between   C=O units in i-AC-11-copolymer is less than the soliton domain width in trans-[CH]x. Heavily doped i-AC-copolymers have σRT within a factor of 2 of similarly doped trans-[CH]x. The σRT of heavily iodine doped p-AC-copolymer has about one-third to one-half of that of cis-[CHI0.1]x. Doping of both p-AC- and i-AC-copolymers with I2 is homogeneous. Some i-AC-copolymers can be doped homogeneously with AsF5 but doping is heterogeneous for the p-AC-copolymers. These doping behaviors are parallel to those reported earlier for polyacetylene. Abrupt increase of σRT of 106–107-fold occurred with about five-fold change of dopant concentration in the vicinity of y∼10−3. There was also a more sharp change in 𝒮 with y. The results cannot be reconciled with models invoking moving domain excitations; a possible mechanism for carrier migration may be vibronically coupled electron tunneling in undoped and lightly doped polymers. The low transport is attributed to carriers being strongly pinned by the Coulomb potential of the counterions. When this pinning potential is screened as dopant concentration increases, the carriers undergo a transition from a ‘‘glassy’’ state to a ‘‘melt’’ state with large increase in carrier mobility. This carrier glass transition or carrier mobility transition is distinct from that transition for the onset of Pauli susceptibility, which is observed at much higher dopant concentrations of few mole percent.
Comment on ‘‘Theory of relaxation in viscous liquids and glasses’’
Authors: Ngai K. L. , Rajagopal A. K. , Rendell R. W. , Teitler S.
Published: July 2002

It is pointed out that Brawer’s description of the Ngai model of relaxation in complex systems is incorrect so his negative conclusions about the model are unfounded. (AIP)
The use of the variational principle in molecular perturbation theory
Authors: Goldman Saul , Kumar Bijoy
Published: July 2002

We have shown how the Variational Principle can be used to optimize the choice of the expansion functional and the reference state potential in molecular perturbation theory. The method was applied to a Stockmayer and to a Lennard-Jones diatomic fluid. For the Stockmayer fluid, the variationally optimized expansion was identical to the Gray–Gubbins–Stell expansion that is based on choosing the potential as the expansion functional, and the unweighted mean of the full pair potentials as the reference state potential. For the Lennard-Jones diatomic fluid, the variationally optimized expansion functional and reference state potential were intermediate between those of the Gray–Gubbins–Stell theory, and those of the reference average Mayer function (RAM) theory.
Kinetic theory of nonlinear transport processes in dilute ionized gases subject to an electromagnetic field
Authors: Eu Byung Chan
Published: July 2002

The modified moment method is applied to study transport processes in a plasma subject to a homogeneous electromagnetic field. Various balance and evolution equations are derived for macroscopic variables chosen, by starting from a kinetic equation. Extended Gibbs relations are also derived as extensions of the extended Gibbs relation for neutral gases. The evolution equations are solved under the adiabatic approximation in the case of the steady state by using an iterative solution method. The first iterative solution yields various linear transport coefficients which reproduce the Chapman–Enskog formulas for the transport coefficients as the magnetic field vanishes, and the second iterative solution gives rise to a set of transport coefficients which depend on the thermodynamic forces as well as the magnetic field. In the sense that they depend on thermodynamic forces they are nonlinear. As the density tends to zero (the rarefied gas limit), the second order transport coefficients vanish as expected for the transport coefficients for rarefied gases.
Resistivity of polydiacetylene gels
Authors: Sinclair M. , Isogai M. , Heeger A. J.
Published: July 2002

We have observed, for the first time, the major change in resistance which results from the collapse of the interconnected gel network at the gel–sol transition. The dc resistivity and ac resistivity (≤10 kHz) were measured as functions of temperature and concentration. At the gel–sol transition, the resistivity increases sharply; in some cases by almost two orders of magnitude. Quantitative analysis of the transport data for detailed comparison with the onset of shear modulus (exponents, etc.) is complicated by the simultaneous occurrence of the rod–coil transition and by a background ionic contribution which leads to finite conductance at concentrations below the critical concentration.
Temperature dependence of the nonexponential decay of photoproduced N,N,N′,N′-tetramethylbenzidine cation radicals in sodium dodecylsulfate micelles: Determination of activation energy distributions and relation to dynamic cooperativity
Authors: Plonka Andrzej , Kevan Larry
Published: July 2002

The temperature dependence of the decay of photoproduced N,N,N′,N′-tetramethylbenzidine cation radicals (TMB+) in sodium dodecylsulfate (SDS) micellar solutions was studied with and without added sodium chloride. The distributions of activation energies g(E) associated with the lifetime distributions f(τ) for the cation radical decay were determined. The f(τ) distributions over a range of 287 to 328 K were determined from the inverse Laplace transform of the radical cation decay curves described by [TMB]/[TMB]0=exp[−t/τ0)α]. The g(E) distributions show a maximum at about 1.5 of the theoretical potential energy maximum for single bond rotation in isolated hydrocarbon chains which is consistent with values estimated for constrained environments. This supports the importance of cooperativity as the origin of time dependent decay of embedded species in constrained environments such as micelles.
Infrared laser spectroscopy of BCl3 in an rf discharge
Authors: Farrow Leonilda A.
Published: July 2002

Infrared laser measurements of the extinction coefficient of a gas in a discharge can be used to determine, in a nonintrusive manner, the rotational and translational temperature and degree of dissociation of the gas, thus enlarging the spectral regions wherein diagnostic measurements of plasma properties may be performed. This is accomplished by obtaining extinction coefficients at 14 CO2 laser lines near 10 μm in a BCl3 rf discharge at two different power levels, as well as under quiescent conditions. All data points are fit to a band model calculation which yields values for upper state rotational constants, band center position, and temperature in the cell as well as total band strength at each power level. The rotational temperature of the gas is found to agree with the cell wall temperature, verifying equilibrium of rotational and translational temperatures. Since these are absolute measurements of band strengths, it was possible to determine a degree of dissociation of ≲15%. The results obtained from this technique are shown to complement those obtained from other plasma diagnostic methods, such as laser induced fluorescence. Since BCl3 is a gas commonly used as a component in the plasma etching of aluminium and aluminium oxide, a more detailed understanding of the chemistry of this reactive plasma system is pertinent to the improved fabrication of integrated circuits.
Experiments concerning phosphorus chemiluminescence
Authors: Harris Dennis G. , Chou Mau Song , Cool Terrill A.
Published: July 2002

A variety of experimental techniques have been employed in a spectroscopic investigation of the strong visible chemiluminescence from the phosphine–nitrous oxide reaction system. Reaction was initiated by a fast electrical discharge in PH3/N2O mixtures over the pressure range 18–666 Torr. The predominant emission is a true continuum extending from a threshold wavelength at 3300 Å to beyond 1 μm. The results are consistent with the possible existence of a chemically formed (PO)2* exciplex molecule as the source of the visible continuum emission, but another molecular emitter containing only phosphorus and oxygen atoms, such as PO2, cannot be ruled out. Because of the possible use of this reaction system for a tunable, visible laser source, laser cavity tests and absorption and stimulated emission tests were carried out; these gave negative results. The photon yield from 3300 to 9000 Å was determined to vary linearly with pressure; a maximum yield of 8.5×10−3 was reached at the highest pressure investigated of 666 Torr. The broad spectral range of emission and low photon yield indicates that the ratio of stimulated emission to spontaneous emission did not exceed 0.02 at any wavelength shorter than 9000 Å.
Chemical reaction networks with finite attractor regions
Authors: Clarke Bruce L. , Jeffries Clark
Published: July 2002

This paper gives a test which establishes that a chemical reaction network has a finite globally attracting region in concentration space for a particular set of rate constants. A second test can establish the same conclusion for all sets of rate constants. If a network passes either test and all the steady states of the system are unstable, there must exist some exotic attractor such as a limit cycle, torus, or chaos either for the set of rate constants used or for all sets of rate constants. A computer algorithm for applying the test is developed.
Fluorescence lifetimes and spontaneous predissociation of I35Cl(B+, v′=1 and 2) as studied by laser excited fluorescence
Authors: Kitamura Mamoru , Kondow Tamotsu , Kuchitsu Kozo , Munakata Toshiaki , Kasuya Takahiro
Published: July 2002

Fluorescence lifetimes of the v′=1 and 2 states of I35Cl(B0+) were measured as a function of the rotational quantum number J′ by selective excitation of the rovibrational levels by a pulsed dye laser. The lifetimes of the rotational levels of the v′=2 state were found to decrease from 3.3 to 0.07 μs with increasing J′ (7–54), whereas the lifetime for the v′=1 state was 4.1 μs, being almost independent of J′. This trend was found to be due to heterogeneous predissociation from the v′=2 state to a repulsive state with Ω=1. A numerical calculation of the predissociation rate constants suggests that the potential energy curve of this repulsive state intersects that of the B0+ state in the vicinity of the outer turning point of the v′=3 state. The homogeneous predissociation known in the v′=3 state was not observed in the v′=2 state.
A thermokinetic model of complex oscillations in gaseous hydrocarbon oxidation
Authors: Wang Xiao-jing , Mou Chung Yuan
Published: July 2002

A three variable thermokinetic model of ignition is devised to describe the gas-phase oxidation of hydrocarbons in CSTR. For a single set of thermokinetic parameters, the model displays steady states, bistability, cool flame oscillation, simple ignition oscillation, and complex ignition-cool flame oscillations, when the reactant pressure P and vessel temperature T0 are varied as control parameters. The predicted P-T0 state diagram compares fairly well with the experimental finding for the system of acetaldehyde/oxygen. The model also predicts interesting bifurcation sequences of complex periodic states. The proposed skeleton model is justified qualitatively by considering detailed kinetics in the oxidation of acetaldehyde.
The gradient expansions of the kinetic energy and the mean momentum for light diatomic molecules
Authors: Allan N. L. , West C. G. , Cooper D. L. , Grout P. J. , March N. H.
Published: July 2002

For eleven neutral diatomic systems and one positive ion we have numerically evaluated the three terms in the gradient expansion of the molecular kinetic energy T=T0+T2+T4. Hartree–Fock–Roothaan molecular densities were used throughout. For the molecules studied T2/T0 ∼0.1, T4/T2 ∼0.2. The contributions to these integrals from different regions of space were examined. We have also estimated the values of the two terms in the gradient expansion of the mean momentum P=P0+P2 and find P2/P0 ∼0.5. Lastly we make contact with earlier work of Mucci and March. D/N2 is found to correlate grossly with T2, where D is the dissociation energy and N the total number of electrons in the molecule.
Detection of resonances in electron–molecule scattering using a modulated supersonic molecular beam
Authors: Polley J. P. , Bailey T. L.
Published: July 2002

Resonance spectra are presented for electron-molecule scattering using supersonic molecular beams. The supersonic beam is crossed at right angles by an electron beam. Results for N2 and CO are presented. (AIP).
Selection rules in rare earth MCD spectra. An experimental confirmation
Authors: Görller-Walrand C. , Behets M. , Porcher P. , Laursen I.
Published: July 2002

The MCD spectra of the 5D1←7F0 and 5D2←7F0 transitions are analyzed for two complexes of the Eu3+ ion with the F− ligand: the LiYF4/Eu3+ (D2d symmetry) and KY3F10/Eu3+ (C4v symmetry). The sign inversion of the 𝒜 terms, predicted theoretically in a previous paper, is confirmed experimentally. It is shown how MCD is able to distinguish unambiguously between the C4v and the D2d coordination symmetries.
Fluorescence lifetimes and excitation spectra of liquid alkanes measured by means of synchrotron radiation
Authors: Shinsaka Kyoji , Koizumi Hitoshi , Yoshimi Toru , Kouchi Noriyuki , Nakamura Yoshio , Toriumi Minoru , Morita Makoto , Hatano Yoshihiko , Asaoka Seiji , Nishimura Hiroshi
Published: July 2002

Fluorescence lifetimes of liquid cyclohexane, bicyclohexyl, cis-decalin, trans-decalin, n-decane, and n-dodecane have been measured at 25 °C by a delayed coincidence single photon counting technique at several excitation wavelengths of SR (synchrotron radiation) pulse between 120 and 180 nm. Excitation spectra of these liquids have been also examined at the wavelength region between 120 and 300 nm. The lifetimes show no dependence on the excitation wavelength of SR used in the experiment. The lifetimes determined are as follows: 1.1±0.1 ns (cyclohexane), 1.8±0.3 ns (bicyclohexyl), 2.4±0.1 ns (cis-decalin), 3.0±0.1 ns (trans-decalin), 3.0±0.1 ns (n-decane), and 4.2±0.2 ns (n-dodecane). Each of excitation spectra of these liquids shows a single broad peak with FWHM of (5–23)×103 cm−1 at the excitation wavelengths between 163 and 185 nm. There is no increase of fluorescence yield in the excitation spectrum with increasing the excitation energy across the ionization potential of each of the liquids. Fluorescence yield at the ionization region seems to be much less than the peak maximum at the subionization region.
Temperature dependence of rate coefficients for ter-molecular association
Authors: Bates D. R.
Published: July 2002

The decrease of the association rate coefficient k with increase in temperature T is much sharper than the norm if readily accessible rotational levels of the complex formed carry so much energy that insufficient remains to excite the vibrational modes of high frequency. It is suggested that this may be the main reason for the reported difference between the T dependence of the k’s for N+2 +2N2 and O+2+2O2 association.
Fractal structures from an evaporation/condensation model
Authors: Meakin Paul , Deutch J. M.
Published: July 2002

Several simple evaporation/condensation models in which all occupied surface sites have the same evaporation probability and condensation occurs on contact with the first occupied site have been investigated using Monte Carlo simulations. In two dimensional simulations these models generate a ‘‘cloud’’ of clusters which at long times are characterized by a fractal-like geometry and an exponential cluster size distribution. The nature of the systems at long times depends on the type of trajectories which the particles follow. Brownian trajectories lead to a cloud of clusters with a fractal dimensionality close to 1.0 (in 2D simulations), whereas linear trajectories generate structures with a fractal dimensionality close to 4/3. In similar one dimensional simulations, there is no evidence for the formation of fractal-like structures at any stage in the evolution of the systems and the equilibrium state consists of a dense region and a completely unoccupied region. The results of three dimensional simulations are inconclusive.
Lattice dynamics and homology of rare gas solids
Authors: Ramamurthy V. , Rajendraprasad S. B.
Published: July 2002

Investigations of the wave vector dependence of theoretical phonon frequencies of neon, argon, krypton, and xenon, deduced by invoking a six constant Clark, Gazis, and Wallis model, reveal that they satisfy a relation, Mν2[sin(πζ/p)]n =Φ(r), a constant which depends on individual rare gas solid with p=1 or 2 and n=−2.018±0.038 at all polarizations except [110]L along the principal symmetry directions and hence their dependence on wave vector q could be separated from that on nearest neighbor distance, r. It is shown that the latter is adequately represented at all wave vectors and polarizations in the Brillouin zone by a homologous relation, Mν2rα =δ(q), a constant with α=−2.818±0.127 in the case of argon, krypton, and xenon and could be exploited to determine the zero point energy which destroys the homology in the case of neon. The physical significance of these empirical relations, the degree of homology that exists among these rare gas solids, influence of zero point energy on their dispersion relations, as well as the accuracy of scaling factors in the evaluation of zero point energy are discussed.
An exact recursion for the occupational degeneracy of dumbbells on a hexagonal lattice space
Authors: Hock J. L. , McQuistan R. B.
Published: July 2002

We derive a ten-term recursion relation that describes exactly the occupational degeneracy for indistinguishable dumbbells distributed on a hexagonal lattice space. The generating functions, normalization, expectation, dispersion, and continuous representation of the associated statistics are also treated. In addition, the occupational degeneracy at saturation is discussed.
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o SCF and CI study of the NH+4⋅H2O complex
Authors: Welti Martin , Ha Tae-Kyu , Pretsch Ernö
Published: July 2002

Interaction energies between a water molecule and an ammonium cation in the gas phase were computed by means of ab initio SCF and CI calculations. The influence of basis set, geometry optimization, and of electron correlation effects on the NH+4 ⋅H2O interaction energy is discussed.
The influence of surfaces on vapor pressures
Authors: Searcy Alan W.
Published: July 2002

An analysis of internal particle equilibrium in J. Chem. Phys. 81, 2489 (1984) is generalized by means of Lagrange’s method of undetermined multipliers to show that a one-component crystalline particle of fixed size and shape is at equilibrium at constant temperature and pressure when the chemical potentials of molecular species, μi, μj, ..., and of vacancies μvi, μvj, ..., for sites i, j,... of different characteristic bond environments fit the relation μi−μvi=μj−μvj =⋅⋅⋅ . The chemical potential differences between molecular species and vacancies is shown to be the chemical potential for the component. The influence of surfaces on vapor pressures is predicted by setting the chemical potential of the component in the particle equal to that of its vapor. The predicted effects of surfaces are larger than those of classical theory but are in reasonable agreement with measurements for liquid drops.