bluuebunny/crossref_metadata_2025 huggingface dataset:
A model calculation of vibration–translation energy transfer
Authors: Altick P. L. , Shin H. K.
Published: February 2003

By employing a simple step potential as the interaction potential in a collision between an atom and a diatomic molecule, we develop a full quantum mechanical treatment of vibrational energy transfer in a collinear collision for which the resulting coupled differential equations can be solved exactly. We find that for all but the weakest coupling strengths, the trend of the solutions to their converged value is not smooth and monotonic but rather shows large oscillations. We also locate a region in the parameter space in which the solutions are a very sensitive function of the coupling strength showing something analogous to ’’resonant’’ behavior.
Numerical solution of semicontinuum models for excess electrons
Authors: Webster B. C. , Carmichael I. C.
Published: February 2003

Numerical solutions of semicontinuum model potentials for excess electrons localized in condensed phases have been obtained in a range of media. These are compared with previous approximate results and with experiment. Transitions to higher excited states are found to be unlikely to contribute significantly to the width of the observed spectra, which still remains unexplained. It is suggested that more sensitive criteria for the appropriateness of a particular model for the species be adopted. The static polarizability is evaluated here, showing current models to be inadequate.
Rovibronic two-photon transitions of symmetric top molecules
Authors: Chen Kuo-mei , Yeung Edward S.
Published: February 2003

Rotational line strengths of two-photon absorption (TPA) processes in symmetric top molecules in the gas phase are developed by angular momentum theory. Experimentally accessible polarization states and frequencies of the photons are considered case by case. For TPA processes of identical photon frequency, parallel linearly polarized photons and same-sense circularly polarized photons form a complete polarization study. In the absence of resonance-enhanced intermediate states, TPA of nonidentical photon frequencies normally does not give new spectral features which are forbidden in identical TPA, because of the highly unfavorable weighting factors involving the intermediate state energies. High resolution studies of TPA, especially in the Doppler-free regime where features can be further resolved, is an alternative and can be more fruitful than polarization study for excited state assignments. A more general selection rule for TPA is that the initial and final states must have identical overall rovibronic symmetry. The Jahn–Teller effect induced, j-type doubling can be probed directly by TPA. As resonance condition is approached, features of different rotational structures (ΔK selection rules) within a two-photon allowed electronic band can occur through a nonadiabatic intermediate state. The polarization ratios for near-resonant TPA, which is useful for both intermediate and final state assignments, are also presented.
A comparison of close coupling and coupled states for low energy spherical top–atom collisions: Ar–CH4
Authors: Heil Timothy G. , Secrest Don
Published: February 2003

Accurate calculations were made for collisions of ground state methane with argon atoms. Methane was treated as a rigid rotor and an empirical interaction potential was used. The calculations were performed at low energies for which only a few rotor states were accessible. The collision energies were of the same magnitude as the attractive well depth of the interaction potential and rainbow oscillations were seen. The coupled states approximation, the statistical coupled states approximation, and the truncated coupled states approximation were then compared with the exact results. These approximations gave good agreement for elastic integral and differential cross sections, but at these low energies, somewhat worse agreement for inelastic cross sections than are found with atom–diatomic collisions. In all cases the small angle differential cross sections were good in the coupled states approximation. A clear failure of the coupled states approximation was found. For the model potential used in the present calculations, a rotational transition which is not forbidden in the close coupling scheme is forbidden in the coupled states approximation. This transition is not energetically accessible in the present calculations.
Highly conducting iodine derivatives of polyacetylene: Raman, XPS and x-ray diffraction studies
Authors: Hsu S. L. , Signorelli A. J. , Pez G. P. , Baughman R. H.
Published: February 2003

Polyacetylene film and bulk samples were prepared by polymerization of acetylene in the presence of a μ- (η1:η5-cyclopentadienyl) -tris (η-cyclopentadienyl) dititanium (Ti–Ti) catalyst in hexane. Conducting films (σR.T.∼25 Ω−1⋅cm−1), or bulk polymer samples (σR.T.∼1 Ω−1⋅ cm−1) were prepared by treatment of the nascent polymer with solutions of iodine in hexane. Raman, x-ray photoelectron, and x-ray diffraction techniques were used to characterize these polyacetylene-iodine derivatives. The measurements are consistent with the presence of iodine in two different forms, I3− and possibly I5−. Although the concentration of the iodine varied in different samples (40%–70% by weight), in all cases the amount of the second species decreases irreversibly upon thermal annealing or the application of high mechanical stresses. X-ray diffraction measurements suggest that iodine species intercalate in sheets parallel to a close packed plane of the polyacetylene. Valence band x-ray photoelectron spectroscopy measurements on an iodinated cis-rich polymer film, show a finite density of states at the Fermi level. This observation suggests metallike conductivity in the sample.
Absolute integrated intensities of the infrared absorption bands of TiCl4
Authors: Person Willis B. , Maier William B.
Published: February 2003

The absolute integrated molar absorption coefficients Ai have been measured for the ν3 fundamental and for the stronger binary combination bands of TiCl4 in the vapor phase. The experimental value for A3, the coefficient of the TiCl4 ν3 fundamental vibration, is 277±42 km mole−1. This value is compared with 320 ±40 km mole−1 predicted from the mean transition movement ‖μz01‖?0.29±0.04 D given by Fox and Person for asymmetric X–Cl stretching vibrations of tetrahedral molecules. Another prediction, based on transfer of effective charges for the Cl atom, yields A3≲125 km mole−1. The implications of these results are discussed.
Distribution functions for Gaussian molecules. I. Stars and random regular nets
Authors: Martin J. E. , Eichinger B. E.
Published: February 2003

Distribution functions P (t) of the reduced squared radius of gyration are presented for linear, circular, and starlike polymer molecules represented in the unperturbed Gaussian approximation. Semiempirical functions of the form 〈s2〉0P(t) =C[1−tanh(a/tβ)]t (3ω1−2)/2exp[ −3λ1Tr(Λ0−1)t /2]where 〈s2〉0 is the mean square unperturbed radius of gyration and t=s2/〈s2〉0 fit the results of numerical quadratures quite well. Only a and β are adjustable parameters; Λ0 is the matrix of eigenvalues of the Kirchhoff matrix that describes molecular connectivity, while λ1 is its minimum eigenvalue with degeneracy ω1. Regular random nets consisting of μ junctions, each with the same functionality or valence f⩾3, have been generated by Monte Carlo methods; the eigenvalue spectra of their Kirchhoff matrices are described. The spectra are remarkably simple and regular in that they are linear functions. Random nets differ sharply in this regard from crystallographic lattices. The distribution functions of the radii of gyration of random networks are calculated to be nearly Gaussian in t; this is also demonstrated analytically. The dimensions of these molecules are extremely small.
Distribution functions for Gaussian molecules. II. Reduction of the Kirchhoff matrix for large molecules
Authors: Eichinger B. E. , Martin J. E.
Published: February 2003

The eigenvalues of the Kirchhoff matrix for a molecule consisting of m chains and μ multifunctional junctions can be calculated from a reduced matrix of dimension μ×μ. Many of the eigenvalues for complicated molecules can be obtained exactly, and the remainder are accessible by numerical methods. We find small eigenvalues for trifunctional networks which can be associated with very slowly relaxing oscillations in gels. In addition, networks have μ high frequency modes, which are located in unique regions of the spectrum.
Dissociation of CO and NO by fast H+, He+, and O+ projectiles
Authors: Wood R. M. , Steuer M. F. , Edwards A. K.
Published: February 2003

In this work we report on studies of the dissociative ionization of CO and NO induced by 1-MeV H+, He+, and O+ projectiles. The time-energy spectroscopy (TES) technique is used to identify the dissociation fragments according to their mass-to-charge (m/q) ratios, and to record kinetic energy spectra for each fragment species. The spectra fragments with 1+, 2+, and 3+ charges show overlapping peaks for which energy assignments are made. In most case, the He+ and O+ projectiles appear to form dissociative states of CO2+ and NO2+ which decay into singly charged fragments. The H+ projectile appears to form CO+ and NO+ which subsequently dissociate into charged and neutral fragments. The dissociative states excited in this experiment are different from those reported in K-shell ionization studies.
Cluster expansion of the wavefunction. Structure of the closed-shell orbital theory
Authors: Hirao K. , Nakatsuji H.
Published: February 2003

A new approach to the closed-shell orbital theory is presented with the formalism of the cluster expansion of the wavefunction. The four independent excitation operators are used to represent the general determinantal wavefunction and also to discuss the stability of the Hartree–Fock solution. This leads to a new concept called the ’’stability dilemma,’’ which is the key not only in understanding the structure of the orbital theory but also for the extension of the orbital model. Only when the stability dilemma is removed, the correlation effect is taken into account within the framework of the orbital approximation. The closed-shell orbital theory including the electron correlation is defined as ‖Φ〉=𝒫 exp[iF]‖0〉, where the F is the excitation operator to generate the variational space and the 𝒫 is the projection operator to remove the stability dilemma. The various orbital theories (some are known but some are new) can be obtained by appropriate choices of the F and 𝒫. It is shown that the above cluster expression makes it possible to analyze and interconnect the various orbital theories in the form of the limited CI based on their own natural orbitals. The complex DODS theory is proposed. This new orbital theory is the most suitable one to include the correlation effect within the orbital model in the closed-shell system.
Cluster expansion of the wavefunction. The open-shell orbital theory including electron correlation
Authors: Hirao K. , Nakatsuji H.
Published: February 2003

A previously developed new approach to the orbital theory with the formalism of the cluster expansion of a wavefunction is applied to open-shell electronic systems in order to include the electron correlation effect within the conventional formalism of the orbital theory. The open-shell orbital theory involving the electron correlation is defined as ‖Φ〉=𝒫 exp[iFK+iFM]‖0〉. The 𝒫 is the projection operator to resolve the stability dilemma and the FK and FM are the excitation operators for closed-shell and open-shell orbitals, respectively. The new orbital theories, which are called Modified SEHF (MSEHF) theory and complex GSO theory, have been proposed with special choices of F and 𝒫. They are analyzed in contrast to the conventional orbital theories such as UHF, SEHF, CMO, and GVB theories in the form of the limited CI based on their own natural orbitals. The MSEHF theory includes the correlation effect effectively in open-shell systems and constitutes a natural extension of the closed-shell SEHF theory (the conventional SEHF theory fails in open-shell systems). The complex GSO theory is the most suitable orbital theory to include the electron correlation effect within the orbital theory (to include spin correlation we have to adopt the symmetry-adapted-cluster (SAC) expansion formalism as shown previously).
Double resonance on the active medium of an optically pumped submillimeter laser: HCOOH
Authors: Dangoisse Didier , Deldalle Alain , Glorieux Pierre
Published: February 2003

The first observation of double resonance on the active molecules of an optically pumped submillimeter laser is reported.(AIP)
The nuclear modulation effect in electron spin echoes for complexes of Cu2+ and imidazole with 14N and 15N
Authors: Mims W. B. , Peisach J.
Published: February 2003

We have studied the nuclear modulation effect in the electron spin echo decay envelope for the complexes Cu2+–ethylenediamine–imidazole and Cu2+– (imidazole)4 with specific attention to the prominent low frequency patterns due to coupling between Cu2+ and the remote nitrogen nucleus of bound imidazole. (Nitrogen nuclei directly coordinated with Cu2+ do not contribute to the effect.) Some experiments were also made with 15N substituted imidazole in order to distinguish between contributions due to the electron nuclear coupling and to the quadrupolar interaction of 14N. Complexes involving Cu2+ and imidazole were selected for study because of their common occurrence in copper proteins. It was found that the remote nitrogen of imidazole is coupled to Cu2+ by a pseudodipolar term which is several times larger than the classical dipolar coupling and which can be represented by assigning an effective radial distance reff=2.9 Å to the nitrogen nucleus in place of the actual physical distance r=4.16 Å. There is also a contact term AI⋅S, where A=1.75 MHz for 14N (A=2.5 MHz for 15N). The magnitude of this contact term is such that, when the electron spin echo experiments are performed in the X-band range (i.e., at fields?3 kG), it almost cancels the Zeeman term for one of the MS=±1/2 manifolds, thus permitting the observation of the zero field quadrupolar frequencies of 14N in the echo envelope. These frequencies are substantially the same as those reported by Hunt, Mackay, and Edmonds (Ref. 21) for the protonated nitrogen in imidazole, thus showing that the imidazole ligands are protonated and that the two complexes studied here carry a net positive charge of 2. Computer simulations of the two-pulse echo envelope have been made in order to obtain an estimate for the pseudodipolar interaction, and in order to establish that the mixture of 14N (or 15N) superhyperfine states is such as to yield modulation patterns of approximately the observed depths.
Crystal structures of the pseudo-one-dimensional magnetic systems, pyridinium manganese (II) chloride monohydrate and quinolinium manganese (II) chloride monohydrate, and the magnetic behavior of the quinolinium salt
Authors: Caputo R. , Willett R. D. , Morosin B.
Published: February 2003

The crystal structures of pyridinium manganese(II) chloride monohydrate (PMC) and quinolinium manganese(II) chloride monohydrate (QMC) both contain bi-bridged linear chains. These chains are hydrogen bonded together to form a two-dimensional network. The magnetic susceptibility of QMC is characteristic of a weak antiferromagnet with a maximum in the susceptibility at 2.0 °K. Analysis of the data in terms of a 1-d Heisenberg linear chain gives an intrachain exchange constant of J/k=−0.36 °K. However, the best model includes significant interchain interactions. Thus, both the structural features and magnetic susceptibility indicate that QMC is a perturbed one-diminsional system. This conclusion is supported by previously reported magnetic susceptibility and ESR data for PMC.
On gradient theories of fluid interfacial stress and structure
Authors: Carey B. S. , Scriven L. E. , Davis H. T.
Published: February 2003

The gradient approximations of the density profile equations obtained from momentum balance (the Yvon–Born–Green theory) and from minimization of the Helmholtz free energy (the van der Waals–Cahn–Hilliard theory) are compared. Tractable equations are obtained by approximating the pair correlation function as that of a homogeneous fluid at densities in the vicinity of the interacting pair. The theories are shown to be insensitive to the particular choice of such approximating pair correlation functions if the third force moments are composition and density independent. The YBG and the VDW–CH gradient approximations yield identical results for such approximating pair correlation functions if the first and third force moments are density and composition independent (in the case of a one-component fluid, only density independence of the third force moment is required). Numerical results are presented for the interfacial properties of a one-component square-well fluid.
Coexisting mobile and localized adsorption
Authors: Knuth Eldon L.
Published: February 2003

A model for coexisting mobile and localized adsorption is developed for arbitrary ratios of characteristic vibrational temperatures to surface temperature. Expressions which facilitate deducing, from measured values of the mean residence time, (a) mole fractions of mobile and localized adatoms and (b) values of the translational–motion potential barrier are presented. Deduced values of the potential barrier, a function of the characteristic lengths of the adatom and the solid structure, are in excellent agreement with those predicted by summing pairwise interactions between a gas atom and the solid atoms.
Thermal ion–molecule reactions in oxygen-containing molecules. Formation of long-lived intermediate ions in acetyl chloride
Authors: Kumakura Minoru , Arakawa Kazuo , Sugiura Toshio
Published: February 2003

The thermal ion–molecule reactions in acetyl chloride have been studied. The dissociation reaction of long-lived intermediate ions (CH3COClH+*) leading to the formation of CH3CO+ was observed. The formation of CH3COClH+ was confirmed from the detection of the metastable ions, and CH3COClH+* results from the reaction of CH3CO+ with acetyl chloride. CH3CO+ reacts with acetyl chloride to form CH3COClH+. In n-propyl acetate–acetyl chloride mixtures, the ion–molecule reactions involving CH3CO+ and CH3COOH+2 have been investigated to clarify the effect of reactant ions on the formation of CH3COClH+*. The reaction channel of CH3CO+ from n-propyl acetate with acetyl chloride to form CH3COClH+ is more probable than that of CH3CO+ from acetyl chloride. CH3CO+ from acetyl chloride led preferentially to the formation of CH3COClH+* in comparison with reactions of CH3CO+ from n-propyl acetate. The measurement of the translational energies of both CH3CO+ ions allows a clear elucidation of the detailed mechanism of dissociation of CH3COClH+* ions formed in the mixtures.
Analysis of the spin-Hamiltonian parameters for Mn2+ in axial sites of the alkali chlorides and fluorides
Authors: Rubio O. J. , Cory W. K.
Published: February 2003

The applicability of the superposition model to the quadrupole spin-Hamiltonian parameters of Mn2+ in axial symmetry sites of the alkali chlorides and fluorides is analyzed. In addition, taking advantage of the EPR spectra of Mn2+ in tetragonal sites of RbCl, the fourth-order parameters b04 and b44 have been determined in order to test the applicability of the superposition model not only for the n=2, but also for the n=4 spin-Hamiltonian parameters. It was found that the sign and value obtained in this work, for the intrinsic parameter ?2 of Mn2+ with Cl− ligands, are in good agreement with those estimated by Newman and Siegel from the ?2 value of Eu2+ ions, if the power law exponent of ?2 is taken to be equal to seven.
Mechanism of thermal electron attachment in N2O–CO2 mixtures in the gas phase
Authors: Shimamori Hiroshi , Fessenden Richard W.
Published: February 2003

The attachment of thermal electrons to nitrous oxide in N2O–CO2 mixtures has been studied at room temperature in the pressure range 5–120 torr. Ionization was by pulse radiolysis and the electron concentration was measured as a function of time by microwave conductivity. Addition of even less than 0.1% CO2 to N2O causes a marked increase in attachment rate. However, this enhancement soon saturates in that further additions of CO2 have less and less effect. Experiments with ternary mixtures including C2H6 showed a further enhancement which was much larger than the additive effects of CO2 and C2H6 alone. These observations can be explained by a two step three-body process producing vibrationally excited N2O−* if the rate constant for stabilization of N2O−* by CO2 is 4×10−30 cm6/molecule2⋅sec. The decrease in effectiveness with increased CO2 pressure is interpreted as the collisional ionization of a complex ion, [N2O⋅CO2]−*. The nonadditive effect of hydrocarbon results from the rapid reactive destruction of such complexes by collision with the hydrocarbon. A detailed quantitative treatment of the proposed mechanism was successful in explaining most features of the data. In a limited set of experiments, allene —N2O mixtures were found to behave much like CO2–N2O.
Photodissociation of atmospheric positive ions. II. 3500–8600 Å
Authors: Smith G. P. , Lee L. C.
Published: February 2003

Using a drift tube mass spectrometer, photodissociation cross sections have been measured for many positive atmospheric cluster ions at ion laser and dye laser wavelengths between 3500 and 8600 Å. Structureless cross sections were observed for the dimer ions O+4, NONO+, N+4, and CO2CO2+, and for cluster ions of O2+. The nature of the electronic states involved is discussed. Evidence of a second dissociative state for O4+ and O2+⋅H2O in the ultraviolet is presented. Upper limits on the cross sections of COCO+ and cluster ions of NO+ and H3O+ below 1×10−19 cm2 were established at many wavelengths.
A generalization of Kramers’ rate formula to include some anharmonic effects
Authors: Pear M. R. , Weiner J. H.
Published: February 2003

Consideration from the Langevin approach of Brownian-motion effects on a particle in a parabolic barrier potential leads to a transmission function which gives the probability that the particle will surmount the barrier. When used in conjunction with an approximate low-temperature normalization condition, the Kramers rate formula, originally derived using the Fokker–Planck approach, is reproduced. The rate formula is then generalized by including anharmonic effects due to the presence of the barrier as they enter in an exact normalization condition. The generalized Kramers formula has a temperature dependence of the frequency factor which is verified by computer simulation for a periodic and double-well potential. Data from computer experiments are fitted using both the original and generalized formulas. The generalized formula is found to be useful in extracting information on the barrier height and friction coefficient from the experimental data.
Infrared spectra of matrix-isolated plutonium oxides
Authors: Green David W. , Reedy Gerald T.
Published: February 2003

The infrared absorption spectra of PuO and PuO2 in both Ar and Kr matrices have been identified. The observed frequencies at 794.25 and 786.80 cm−1 have been assigned to the ν3 stretching modes of Pu16O2 in Ar and Kr matrices, respectively. Normal coordinate analysis of the PuO2 isotopomers, Pu16O2, Pu16O18O, and Pu18O2, in Ar showed that the molecule is linear. The derived stretching force constants are f=5.2476±0.0010 and f ′=0.0034±0.0010 mdyn Å−1. The PuO molecule exists in multiple sites in Ar matrices, but not in Kr matrices. The observed Pu16O vibrational frequency in the most stable site in Ar is 822.28 cm−1 and in Kr is 817.27 cm−1. No absorption peaks were observed that could be assigned to PuO3.
On the evaluation of the van der Waals potentials in ionic crystals
Authors: Shanker Jai , Agrawal G. G. , Singh Ram Pal
Published: February 2003

An application of the Slater–Kirkwood variational method has been made to evaluate the van der Waals dipole–dipole and dipole–quadrupole energies in the four families of ionic crystals, viz., alkali halides, alkaline earth chalcogenides, alkali chalcogenides, and alkaline earth halides. The methods based on the perturbation theory adopted by previous investigators to evaluate the van der Waals potentials are critically discussed. In the present paper we have used an interpolation scheme and semiempirical formulas to estimate the dipole–dipole and the dipole–quadrupole coefficients between a number of different ions with electron configurations close to those of the rare gas atoms. An independent check of the approximate validity of the interpolation scheme has been provided by evaluating the dipole–dipole interaction coefficients between alkali metal atoms. The crystal energies of alkali halides, calculated using the new values of van der Waals potentials, agree closely with the experimental values.
Polarized resonance Raman spectra of hexahalide complexes of transition metals: The effect of electronic degeneracy on the polarization of vibrational Raman scattering
Authors: Hamaguchi Hiro-o
Published: February 2003

Polarized vibrational resonance Raman spectra have been measured for eight hexahalide complexes of transition metals, low-spin d4 OsCl62−, OsBr62−, and low-spin d5 IrCl62−, IrBr62−, and low-spin d6 PdCl62−, PtCl62−, PtBr62−, and PtI62−. Polarization anomaly due to asymmetric Raman tensor was found for the d5 complexes, whereas such was not observed in the cases of the d4 and d6 complexes. The result is analyzed on the basis of a symmetry consideration in vibronic space. Electronic and/or vibrational degeneracy is shown to induce the antisymmetric part of vibrational Raman tensors. It is concluded that the former is primarily responsible for the polarization anomaly found for the d5 complexes. Under resonance conditions, the hot transitions originating from the excited levels of degenerate vibrations can give different Raman tensor patterns from those for the corresponding 1←0 transitions. It is stressed that the selection and polarization rules of vibrational Raman scattering should be discussed in relation to the transition and not to the vibrational mode involved in it.
The coupled-channel method— a Faddeev calculation?
Authors: Preist Trevor W.
Published: February 2003

The coupled-channel method of solving the three-body problem is derived from a Faddeev treatment. This approach clearly indicates the underlying approximations and suggests ways in which calculations can be systematically improved. In particular, the comparison suggests that the treatment of the three-body forces may need to be improved.
Proton magnetic resonance study of lithium ammonium sulfate
Authors: Watton A. , Reynhardt E. C. , Petch H. E.
Published: February 2003

Nuclear magnetic resonance studies have been made of the protons in the ferroelectric salt NH4LiSO4. Absorption line shapes and spin–lattice relaxation times have been measured over the temperature range 77 to 400 K. The results indicate that another phase transition occurs in this material at 133 K, in addition to that previously observed at 284 K. The ammonium ions are found to be weakly hindered in the lattice, undergoing rapid general reorientations over the whole temperature range. The onset of the ionic motion is discussed in terms of simultaneous reorientations around its threefold and twofold symmetry axes.
A molecular beam investigation of the catalytic oxidation of CO on Pd (111)
Authors: Engel T. , Ertl G.
Published: February 2003

A detailed investigation of the steady-state and nonsteady-state reaction CO+1/2O2→CO2 on Pd (111) has been carried out with the molecular beam technique. It could be shown conclusively that the reaction proceeds between two adsorbed species (Langmuir–Hinshelwood mechanism) throughout the temperature and pressure range investigated. For low CO coverages, the activation energy of the reaction was determined to be 25 kcal/mole, whereas at moderate CO coverages, a rearrangement of the oxygen adlayer takes place resulting in a reduction of the activation energy to 14 kcal/mole. It is not possible to formulate a simple kinetic expression for the reaction rate which is valid over the entire range of temperatures and pressures due to changes in the adsorption rate for O2, coadsorption of CO and O2, to diffusion in the adlayer, and to changes in the geometrical arrangement within the adlayer with varying coverage.
Measurement of hyperpolarizabilities of several organic molecules
Authors: Bethea C. G.
Published: February 2003

The second order hyperpolarizability β has been measured for several organic molecules. In this note we present these data and compare the magnitude of β to similar molecules previously measured.
Threshold behavior for collision-induced dissociation of CsCl and Cs2Cl2 by SF6 molecules
Authors: Parks E. K. , Sheen S. H. , Wexler S.
Published: February 2003

Absolute cross sections have been determined for collision-induced dissociation of cesium chloride (monomer and dimer) from collisions with SF6 molecules. SF6 was aerodynamically accelerated in H2 to laboratory energies up to 11 eV. Mass analysis of the product ions indicate the occurrence of the reactions (a) SF6+CsCl→SF6+Cs++Cl−, (b) SF6+Cs2Cl2→SF6 +Cs2Cl++Cl−, (c) SF6+Cs2Cl2→SF6+Cs++CsCl2−. The absolute cross sections for these reactions were determined from threshold to approximately 2 eV above threshold. In this energy region, the cross sections were accurately represented by a power law, σ=A0× (Etot−E0)n/Erel, where Etot is the total energy, E0 the threshold energy, and Erel the relative kinetic energy. Values for A0 for Reactions (a) and (b) are approximately an order of magnitude smaller than for the analogous reactions with Xe, while A0 for Reaction (c) is a factor of 3 smaller. In spite of the molecular character of the projectile the thresholds for Reactions (a) and (b) are very near those observed in the case of Xe. For Reaction (c), however, the threshold is about 1 eV higher. The powers n obtained for the above reactions are all about 1.0 higher than those obtained for the reactions with Xe. This effect, in particular, most likely arises from the SF6 internal degrees of freedom which absorb energy in the collision.
Penning ionization of Ar by He* (1s2s, 3S) in the presence of intense laser radiation: Pronounced laser-modified collisional effects in the emitted-electron energy spectrum
Authors: Bellum John C. , Lam Kai-Shue , George Thomas F.
Published: February 2003

Results of calculations based on quantum-mechanical theory are presented for ionizing collisions of He* and Ar in the presence of a strong electromagnetic field.
Simulation of polymer dynamics. II. Relaxation rates and dynamic viscosity
Authors: Fixman Marshall
Published: February 2003

The stochastic equations of the preceding paper are used to study stress, dielectric, mode and conformational relaxation of chains with threefold symmetric rotation barriers. The modes, qk ∝𝒥bi sinκi where bi is a bond vector, relax independently, insofar as low order time correlation functions are concerned. For stress and dielectric relaxation, most of the theory of mode relaxation in Gaussian chains is directly applicable, with the significant exception that constraints and rotation barriers cause major decreases in relaxation rates from their values for Gaussian chains. This modification suffices to give a large high frequency viscosity limit, which turns out to be a plateau value when a very fast process (of small amplitude in the mode correlations), is incorporated. The rates of passage over barriers show very small effects of chain connectivity, and are well described by Kramers theory. However, the mode relaxation rates show significant dependence on chain length, and approach the conformational relaxation rates quite slowly with increasing chain length.
Correlation effects in the ionization of hydrocarbons
Authors: Cederbaum L. S. , Domcke W. , Schirmer J. , von Niessen W. , Diercksen G. H. F. , Kraemer W. P.
Published: February 2003

The spectral intensity for ionization as a function of binding energy for the valence electrons of ethylene, allene, butatriene, trans-butadiene, acetylene, benzene, methane, ethane, and cyclopropane is computed by a many-body Green’s function method. The results are used to interpret unidentified structures in experimental ionization spectra. For the ionization out of the inner valence orbitals of the unsaturated molecules the spectral intensity is found to be distributed over several lines, in sharp contrast to the ionization out of the inner valence orbitals of the saturated molecules where the greater part of the intensity appears in one main line. The reasons for this behavior are discussed. It is also found that there is a correspondence between the behavior of the spectral intensity in the inner valence region and the satellite structure in the outer valence region. For C6H6, C4H4, and C4H6 interesting satellite lines of considerable intensity are predicted to be situated in the outer valence region accessible with Hei radiation.
Transient diffusion in a system partitioned by permeable barriers. Application to NMR measurements with a pulsed field gradient
Authors: Tanner J. E.
Published: February 2003

A general treatment of time-dependent (transient) diffusion coefficients in a system of parallel planar barriers of arbitrary permeability has been performed, with emphasis on the results expected for NMR pulsed-field-gradient, spin-echo measurements. This is the first such derivation for permeable barriers of any geometry. The calculated distribution functions and diffusion coefficients are in agreement with expectations in most of the limiting cases tried, except that an unexplained dependence of the diffusion coefficients on the magnitude of the field gradient, even at long diffusion times, was found. The application of the results to the interpretation of experimental results is discussed.
Spectroscopy of binary solutions. The benzene–iodine charge-transfer spectrum
Authors: McHale Jeanne , Banerjee Ajit , Simons Jack
Published: February 2003

The theoretical formalism introduced in an earlier publication to treat the spectroscopy of excess electrons in condensed media is generalized to the case of a mixed solvent. With a simple redefinition of the reference state, the theory is shown to be equally applicable to the spectroscopy of neutral species, and is employed to calculate the familiar benzene–iodine charge-transfer spectrum. The zeroth order contribution to the intensity spectrum is seen to involve a direct dipole transition from the donor (benzene) to the acceptor (iodine), whereas the first and second order contributions involve dipole transitions modified by the effects of intermolecular electron ’’hopping’’ and its fluctuations, respectively. Using the so-called hopping (or resonance) and fluctuation integrals as adjustable parameters, the theory is shown to be capable of reproducing the main features of the experimental spectrum.
Rovibronic symmetry correlation in molecular combination and dissociation. I. The Li+Li2?Li3(C2v) system
Authors: Metropoulos Aristophanes , Chiu Ying-Nan
Published: February 2003

A previously developed rotational–vibrational correlation scheme [A. Metropoulos and Y.-N. Chiu, J. Chem. Phys. 68, 5607 (1978)] between two fragments (atomic–diatomic or diatomic–diatomic) and their intermidiate complex is extended to correlations involving also electronic levels with spin. This new correlation scheme, termed rovibronic correlation, is based on the conservation of permutation-inversion and point group symmetries and on the conservation of the total angular momentum. It is applied to the system Li+Li2?Li3. A rovibronic correlation diagram for this system is given.
Electric field quenching of recombination fluorescence in photoionized nonpolar solutions. I. Free electron quantum yield determination
Authors: Bullot J. , Cordier P. , Gauthier M.
Published: February 2003

The field dependence of the relative decrease of fluorescence ΔF/F0 and of the photocurrent, i, is measured for dilute solutions of N,N,N′,N′-tetramethylparaphenylenediamine (TMPD) in 2,2,4-trimethylpentane (TMP) and tetramethylsilane (TMSi). In carefully purified and degassed solutions, irradiated by 5.90 eV photons, at 292 K, and E=45 kV cm−1, one obtains: ΔF/F0=3.9×10−2 in TMP and 11.8×10−2 in TMSi. The data are in good agreement with a model based on Onsager theory for electron escape. It is shown how the combined measurement of ΔF/F0 and i permits the determination of the free electron quantum yield at zero field, Φe0. For TMP:Φe0 =1.4×10−2 and for TMSi:Φe0=6.98×10−2. Finally it is shown that the field dependence of Φe, the free electron quantum yield at E, may be calculated from the experimental data.
Inelastic scattering of positive ions and electrons from water: The 4–6 eV energy loss region
Authors: Edmonson D. A. , Lee J. S. , Doering J. P.
Published: February 2003

Inelastic scattering of positive ions and electrons by water molecules has been investigated with particular emphasis on the 4–6 eV energy loss region. Aside from vibrational excitation of the ground state, no inelastic process was observed below 6 eV with either H+ or H2+ projectile ions although with H2+ impact, singlet–triplet transitions above 6 eV were easily detected. Molecular beam target electron impact experiments using incident energies from 10 to 20 eV showed the previously-observed weak continuum energy loss in the 4–6 eV region. Time of flight measurements established that the continuum signal was from electrons produced in the collision region and not negative ions. An investigation of signals obtained from the apparatus when it was heavily contaminated with water showed a background continuum starting at 3.5 eV energy loss whose intensity varied directly with the recent history of exposure of the apparatus to water vapor and inversely with the collision region temperature. These results, taken together, suggest that there is no bound electronic state of water below 6 eV and that the apparent 4–6 eV energy loss process observed in electron impact experiments actually arises from one or both of two unrelated effects; background scattering of electrons from the water-contaminated apparatus and H− production by dissociative attachment when the incident energy is near 6.5 eV.
Deconvolution of thermal averaging in scattering experiments using integral transform methods
Authors: Smith Neil , Brunner Timothy A. , Driver Richard D. , Pritchard David E.
Published: February 2003

In several distinct types of scattering experiments the velocity distribution of some components of velocity of the primary and/or target particles is a Maxwell–Boltzmann distribution of known width, while other velocity components are known to far better precision. We derive inversion procedures using Fourier and Laplace transforms which permit the detailed microscopic rate constant k (Vrel) to be recovered from the measured quantities. Experiments using the beam–gas arrangement, velocity selection (of one component) by Doppler shift, and experiments conducted in complete thermal equilibrium are considered. Practical applications and limitations are discussed.
Rotational dependence of Fermi resonance in HCN and ClCN
Authors: Mishra K. C. , Mohanty B. S.
Published: February 2003

The problem of rotational dependence of Fermi resonance is studied for the molecules HCN, ClCN, and some of their isotopic derivatives. The parameter δ has been calculated using a twice transformed Hamiltonian. An algorithm has been described to calculate the changes due to second transformation. The results obtained are in good agreement with the empirically obtained values of δ.
Studies of the metastable c 3Πu state of H2: Towards a two-photon amplifier
Authors: Bethune D. S. , Lankard J. R. , Sorokin P. P.
Published: February 2003

Significant populations in the metastable c 3Πu manifold of H2 can be obtained in a pulsed discharge. This manifold potentially could serve as the upper state for two-photon stimulated emission to the autodissociating b 3Σ+u level. To evaluate this possibility, studies of the population densities and quenching times of some of these levels have been made using pulsed laser techniques. A peak density of 1012/cm3 in the c 3Πu manifold was measured, with observed quenching times of approximately 10 nsec. Similar densities were observed in the a 3Σ+g manifold. This state could potentially be utilized to produce one-photon stimulated emission a→b, tunable from 2 to 7 eV. The spectral dependences of both one- and two-photon cross sections were calculated. It was found that the two-photon cross section c→b peaks at 1.3 eV with a value of ∼10−52 cm4 sec while the one-photon cross section a→b peaks at 3 eV with a value ∼3×1018 cm2.
Non-Lorentzian NMR Spectra at low densities
Authors: Sanctuary B. C. , Selwyn L.
Published: February 2003

When the weak coupling approximation is not applicable to the derivation of nuclear magnetic relaxation rates, the transverse and longitudinal components of the magnetization decay nonexponentially. In this paper, the frequency domain is studied for a typical case of gases at low density. This example illustrates the non-Lorentzian behavior expected and gives a clear realization of the rotating frame approximation.
Laser-induced fluorescence of gaseous UF6 in the A–X̃ band
Authors: Oldenborg R. C. , Rice W. W. , Wampler F. B.
Published: February 2003

The A–X̃ band of gaseous UF6 has been studied using the laser-induced fluorescence technique. Excitation and fluorescence spectra are presented for various pressures of UH6 at room temperature. The fluorescence spectra show little change over the pressure range 0.2–20 torr, with a peak wavelength at 421 nm. In contrast, the peak wavelength of the excitation spectra shows a noticeable shift from 391 to 385 nm when the UF6 pressure is increased from 2 to 20 torr. A Stern–Volmer plot of UF6 self-quenching data shows a pronounced nonlinear behavior over this same pressure region. From an analysis of the laser-induced fluorescence spectra, we develop a simple kinetic model for UF6 excited- state dynamics. A standard kinetic treatment of this scheme yields a prediction for the dependence of the fluorescence decay lifetime on total pressure that is in good agreement with experimental results.
Radiative corrections for the vibrational energy levels of the X 1Σ+g state of the hydrogen molecule
Authors: Bishop David M. , Cheung Lap M.
Published: February 2003

Corrections to the vibrational energy levels of the ground electronic state (X 1Σ+g) of H2 due to radiative effects are reported for the first time. They were calculated by using a moment function formula for the Bethe logarithm.
Molecular dynamics of polyglutamic acid studied by perturbed angular correlation of gamma rays
Authors: Martin P. W. , Kalfas C. A. , Skov K.
Published: February 2003

The technique of perturbed angular correlations of gamma rays has been used to study the motion in aqueous solution of two molecular weight species of polyglutamic acid (M.W.=14 700 and 98 000). The rotational correlation times were determined to be τc(14 700) =14+5−3 ns and τc(98 000) =145+45−30 ns. Using a simple model, the mean molecular radii were found to be R (14 700) =19±2 Å and R (98 000) =32±3 Å. Values were also determined for the quadrupole interaction frequencies and asymmetry parameters.
Photodissociation and photodetachment of molecular negative ions. IV. Hydrates of O3−
Authors: Cosby P. C. , Smith G. P. , Moseley J. T.
Published: February 2003

The total photodestruction cross section of gas-phase O3−⋅H2O and O3−⋅2H2O have been measured over a wavelength range of 6300–5120 Å using a tunable dye laser. The cross sections for these ions closely resemble that of O3−, but are progressively smaller, blue shifted, and less structured with the addition of each water ligand. The major product of the O3−⋅H2O photodestruction is O3−. The possibility of other dissociation channels in the hydrate photodestruction and the influence of the water ligands on the O3− absorption spectrum are discussed.
Sodium 4 2D fine structure transition in collisions with rare gas atoms
Authors: Pascale J.
Published: February 2003

The cross sections for the 4 2D5/2→4 2D3/2 fine structure transition in the sodium atom colliding with ground state rare gas atoms are calculated, at thermal energy, in the framework of a semiclassical molecular theory previously reported. For this transition the energy defect of which is extremely small (ΔE?0.035 cm−1), the radial coupling is found localized at large internuclear distances (∼40–65 a.u.), and the rotational coupling is found to contribute significantly to the transition. The calculated cross sections agree with experiment within a factor of 1–2.5.
An efficient, high-power F2 laser near 157 nm
Authors: Woodworth Joseph R. , Rice James K.
Published: February 2003

We have demonstrated high powers (7 MW) and high efficieny (3.5%) in an e-beam excited, molecular F2 laser operating in mixtures of high pressure He and a few Torr of F2. The wavelengths of the three F2 laser lines observed are 156.71, 157.48, and 157.59 nm.
Lifetime saturation of SO2 (3B1) molecules: evaluation of chemical and physical quenching channels in alkanes
Authors: Wampler F. B. , Oldenborg R. C. , Rice W. W. , Karl R. R.
Published: February 2003

Lifetime data at 25 °C for the decay of SO2 (3B1) molecules have been obtained in the presence of high pressures of CH4, C2H6, and C3H8. At high pressures, the physical quenching channel saturates and a kinetic model which incorporates this effect has been applied to the SO2, alkane systems studied. This model permits one to evaluate the partitioning of the total quenching rate constants into their chemical and physical components. The value (in units of 103 torr−1 s−1) of the chemical and physical quenching rate constants (zero pressure limit), respectively, are (0.18 and 4.70), (CH4); (1.66 and 7.70),(C2H6);and (12.5 and 6.5), (C3H8).
The thermodynamic equation of state for insoluble monolayers. II. Ionized films
Authors: Gaines George L.
Published: February 2003

A thermodynamic equation of state for the Π–A curves of insoluble monolayers is extended to ionized surfactant species. It is shown that at infinite dilution on a pure water subphase, the limiting law ΠA=νskT (where νs is the number of ions into which the surfactant dissociates) is obtained. For monolayers spread on salt solutions with a common counterion, it is shown that the adsorption of soluble salt appears explicitly in the equation of state. If the Gibbs dividing surface is placed such that this adsorption is taken as zero, the form of the equation becomes similar to, and can be applied in the same manner as, that used for uncharged films. In some cases, this permits fitting experimental Π–A curves with surface-pressure independent activity efficients. When this is not possible, it suggests that the relative salt and water adsorptions change as the film is compressed. Additional experimental information will be required to evaluate this possibility, and to permit application of the general equation of state for multicomponent systems. The application of this formalism to the surface tension of salt solutions without spread monolayers is also considered briefly.