bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic energies of fragment ions from some hydrocarbons and organic halides in a modified mass spectrometer
Authors: Ossinger A. I. , Weiner E. R.
Published: February 2003

Kinetic energies of ionic fragments have been measured by a new method in a mass spectrometer. Dissociative processes leading to the same products via different pathways have been observed. There is evidence for dissociations from both singly and doubly charged parent ions to yield fragments with excess kinetic energy. Values are given for excess kinetic energies, relative abundances of products from different processes, and the total excess kinetic energy from 100 eV electron impact. The data indicate that several dissociations may occur by a transfer from a bound excited state to repulsive excited states via potential surface crossing.
ĊH3⋅⋅⋅13CO2 pairs in irradiated single crystals of CH313CO2Li⋅2D20
Authors: Toriyama Kazumi , Iwasaki Machio
Published: February 2003

The ĊH3 radical trapped in irradiated single crystals of CH3 13CO2Li⋅2D2O has been found to interact with a 13CO2 molecule, which is formed from the C–C bond breakage as a counterpart. The 13C superhyperfine coupling tensor was determined to be (−4.0, −3.3, −3.5) G. The 13CO2 molecule is located in the direction of the unpaired electron orbital of ĊH3 with the molecular axis perpendicular to it. The spectrum arising from the electron excess center CH3 13ĊO22− was also detected together with the ĊH3 radical. Our results indicate that the ĊH3⋅⋅⋅13CO2 pair is essentially a positive hole center formed from one electron loss followed by the C–C bond breakage.
Rotational relaxation studies of HF using ir double resonance
Authors: Hinchen J. J. , Hobbs R. H.
Published: February 2003

Rotational relaxation effects in HF were observed with double resonance ir experiments. Two single wavelength lasers were employed: a pulsed laser was used to pump a population to a particular vibrational–rotational level, and a stable cw laser was used as an absorption probe to determine the loss or arrival of population in specific J levels. Results are described for both the rotational transfer rates and the temporal behavior of the population distribution over rotational levels after the population was placed in a single level. Rotational transfer rates were found to be three orders of magnitude faster than V–T relaxation and to vary with ΔJ. The data for rotational relaxation were compared with a rate equation model and rate constants for individual relaxation steps were obtained.
An ESR and INDO study of a transient radical in irradiated single crystals of trifluoroacetamide at 77 K
Authors: Chen T. C. S. , Kispert L. D.
Published: February 2003

Immediately following irradiation of trifluoroacetamide at 77 K, an intense 12-line ESR spectrum composed of a triplet of doublets of doublets appears which decays without warming after approximately 6 h. Based on an INDO molecular orbital calculation, the transient radical is attributed to a σ radical containing the –ṄH group with the best agreement being made with the CF3COṄH radical. The ESR parameters are ANy=36.2, ANz=10.08, ANx=7.24 G; AH1y=±20.17, AH1z′=±41.14, AH1x′=±5.35 G; AHorFx=4.51, AHorFz =4.43, AHorFy =4.96 G and gx′′ = 2.0120 gz′′=2.0010, and gy=2.0028. As the transient radical decays, no increase in the ĊF3 concentration is observed; however, the concentration of ⋅CF2CONH2 increases, suggesting fluorine abstraction by the transient species.
Evaluation of libration amplitudes from NMR second moments: Application to three [N(CH3)4]+ halides
Authors: Polak M.
Published: February 2003

We investigate the possibility that moderate discrepancies between observed and calculated NMR second moments reported in the literature may be due to lattice vibration effects. Simplified versions of a previously derived general formula for the libration-affected intramolecular contributions to the second moment are introduced and used for the evaluation of average amplitudes of libration of the tetramethylammonium cation in three of its halide salts. Two possible types of motions are examined: isotropic libration of the cation as a whole and anisotropic librations of the methyl groups around their triad axes. Our comparison of librational amplitudes determined from second moments with those calculated using ir experimental frequencies indicates that the methyls’ librations are the principal source for the reported second moment discrepancies.
Effects of interchain interactions and anisotropy terms on the specific heat of the linear chain antiferromagnet CsMnCl3⋅2H2O
Authors: Iwashita Takashi , Uryû Norikiyo
Published: February 2003

The effects of the interchain interaction and the anisotropy of a crystalline field on the temperature dependence of specific heat in the ordered state of the linear chain antiferromagnet CsMnCl3⋅2H2O are investigated with the use of spin wave theory. It is pointed out that these interaction terms contribute rather important effects to the specific heat and cannot be neglected in explaining the behavior in the low temperature region. Fitting the theoretical specific heat curve with the experimental data has shown that the values of the interaction parameters estimated in the previous analyses of the magnetic susceptibilities and the sublattice magnetization also give satisfactory agreement.
Exciton percolation I. Migration dynamics
Authors: Hoshen Joseph , Kopelman Raoul
Published: February 2003

The exciton transfer, via migration and trapping, in binary and ternary mixed crystals is formulated in terms of percolation theory and the cluster structure for binary randomly mixed crystals. An important limiting case (exciton supertransfer) is derived for long exciton lifetime, relative to jumping and trapping time. The exciton supertransfer case is solved analytically [in terms of the functions derived by J. Hoshen and R. Kopelman, Phys. Rev. B (in press)] and the solutions involve neither physical parameters nor physical constants. Other limiting cases are derived, as well as an algorithm for the general energy transfer case. This algorithm relates the migration and trapping in binary and ternary systems with the trapping-free migration in binary systems. The algorithm involves the use of empirical information, i.e., the parameters describing the exciton dynamics in a pure crystal. The various formulations are valid for concentrations both above and below the critical (’’percolation’’) concentration, with due emphasis on small, medium, and large cluster contributions. Sample calculations are given (for the square lattice with site percolation).
Numerical computations of the Lennard-Jones resonances and ’’relative displacements’’ of the scattered atomic beams from the system He/LiF(001)
Authors: García N.
Published: February 2003

This paper considers the effect of the attractive part of the interaction potential on the scattering of He atoms from a LiF(001) surface. We calculate, in particular, the Lennard-Jones resonances on the intensities and the phases of the scattered amplitudes, using a square well in the front of a hard corrugated surface model. We show that the amplitudes for incident energies smaller than the depth of the well are dominated by the resonances.
Transient nucleation in H2O–H2SO4 mixtures: A stochastic approach
Authors: Shugard W. J. , Reiss H.
Published: February 2003

Transient phenomena in the rate of nucleation are of importance in the interpretation of experimental data on nucleation in the H2SO4–H2O vapor system. Furthermore, fluctuations in the rate of nucleation can actually be measured. In view of these facts, a stochastic approach to the theory of nucleation is developed with eventual application to the H2SO4–H2O system. The central goal of the theory is the evaluation of the distribution of ’’first passage times,’’ for a nucleus, over the relevant free energy barrier. This distribution is calculated from the distribution of a ’’walker’’ on a lattice. However, the distribution of the walker is derived from a ’’master equation,’’ and for this purpose it is demonstrated that walks on lattices and master equations are, in this sense, ’’equivalent’’ even for a lattice which is not translationally invariant. Given the distribution of first passage times, it is possible to compute the transient rate of nucleation, as well as the distribution of fluctuations of the rate about some instantaneous mean. This theory is then applied to the H2SO4–H2O vapor system, and the results indicate that, under many typical experimental conditions, the time to reach the steady state may be quite long (hundreds or thousands of seconds), but that nevertheless, some nucleation should be observed in the laboratory time frame (in agreement with experiment). The character of nucleation as an ’’extreme event’’ is demonstrated by the appearance of a large band gap in the spectrum of relaxation times for the process.
Hydrodynamic behavior of short chain molecules. I. Extension of the Rouse–Zimm theory
Authors: Freire Juan J. , Horta Arturo
Published: February 2003

The Rouse–Zimm formalism of hydrodynamic properties of long chain molecules (polymers) in solution is modified to extend its validity to the case of short chains. The modification introduces: (a) a realistic calculation of averages for the intrachain distances; (b) an exact solution of the eigenvalue equation in matrix form; (c) an approximate representation of short-range interactions (first and second order) by means of springlike forces between nonconsecutive chain segments. The theory is applied to the calculation of limiting viscosity numbers and the Flory–Fox constant of short polymethylene chains (number of segments ?50). Our results are compared with those from other theories.
Hydrodynamic behavior of short chain molecules. II. Limiting viscosity number of n-alkanes
Authors: Freire Juan J. , Horta Arturo , Katime Issa A. , Figueruelo Juan E.
Published: February 2003

Limiting viscosity numbers, [η], have been determined for the n-alkanes (C5 to C40), in two solvents (benzene and carbon tetrachloride), at several temperatures (20–50 °C). The experimental [η]’s are corrected for the effect of the nonzero hydrodynamic volume of the solvent molecules. The corrected [η]’s are used to calculate the variation of the Flory–Fox constant with chain length. The results indicate that the nondraining limit has not been reached with these alkanes. Existing hydrodynamic theories of short chain molecules are compared with these experimental results. Agreement between theory and experiment is found only in the case of the extended Rouse–Zimm formalism of Paper I.
Dynamical theory of migration of an adsorbed atom on solid surfaces
Authors: Kitahara Kazuo , Metiu Horia , Ross John , Silbey Robert
Published: February 2003

A dynamical theory of an adsorbed atom on solid surfaces is developed starting from a Hamiltonian which includes: (1) motion of the adsorbed atom parallel to the surface; (2) the vibration of the adsorbed atom perpendicular to the surface; (3) the lattice vibrations (phonons) of the solid; (4) the coupling between the vibration of the adsorbed atom and its parallel motion; (5) the coupling between the lattice vibrations and the parallel motion of the adsorbed atom; (6) the concerted interaction among the phonons, the vibration, and the parallel motion. Using a canonical transformation, we describe the motion of the adsorbed atom as one of a pseudomolecule formed from the adsorbed atom and the distorted lattice. An equation for the probability of finding the adsorbed atom at a lattice site is derived and the mean square displacement of the motion of the adsorbed atom is calculated. At low temperature, the migration of the adsorbed atom is coherent and the mean square displacement is proportional to the square of time. The adsorbed atom behaves like a free particle with a certain velocity. At high temperature, the migration has diffusional character and the mean square displacement is proportional to time. This is due to the interaction between the parallel motion of the adsorbed atom and phonons as well as to the one between the vibration of the adsorbed atom and phonons. At intermediate temperature, after a certain time, which becomes shorter as the temperature increases, the migration becomes diffusional. The resulting diffusion coefficient consists of two parts: one represents the diffusional character of the migration, and the other its coherent nature. The temperature dependence of the diffusional part is of the Arrhenius type, while that of the coherent part increases as temperature decreases. The coherent part is small when the interaction between the adsorbed atom and the lattice atoms is very strong. Thus the theory gives reasonable trends with respect to the variation of parameters taken into account. Comparison with existing experiments on tungsten and rhodium is briefly made to estimate the order of magnitude of the lattice distortion due to the strong interaction between the adsorbed atom and the lattice atoms.
Rainbow structure and g–u-interference effects in the elastic scattering of low energy protons on deuterium and hydrogen atoms
Authors: Ding A. , Karlau J. , Weise J.
Published: February 2003

Elastic differential cross sections for the scattering of low energy protons (Ec.m.=11–142 eV) on H and D atoms have been obtained. The curves exhibit clearly rainbow structure, g–u oscillations and a type of rapid interference, if coherent scattering of both σg and σu potential curves is taken into account. For comparison, partial wave calculations have been performed using WKB phases and a two-state (1sσg, 2pσu) approximation. The agreement with both experimental results and three-state (1sσg, 2pσu, 2pπu) calculations of Knudson et al. is excellent, which implies that rotational coupling between the 2pσu and 2pπu potential curves can be neglected. It is shown that the reduced phases a=√E/2μN can be described as a single function of the reduced angle τ=Eϑ for all energies and both isotopes. This function agrees with both two-state calculations of the authors and three-state calculations of Knudson et al.
Shift of emission band upon the excitation at the long wavelength absorption edge. III. Temperature dependence of the shift and correlation with the time dependent spectral shift
Authors: Azumi Tohru , Itoh Ken-ichi , Shiraishi Hiroshi
Published: February 2003

The edge-excitation red shift previously observed for quinine and related compounds has been shown to exist also for 8-anilinonaphthalene-1-sulfonic acid. The excitation energy dependent spectral shift observed here and the time dependent spectral shift observed by Chakrabarti and Ware have been interpreted satisfactorily in terms of one and the same mechanism. The previously suggested mechanism of the red shift in which the solute–solvent interaction plays an essential role is thus supported. The solvent reorientation relaxation time has been estimated from two different sets of experimental data, one concerned with the excitation energy dependent shift and the other with the time dependent shift. The estimated relaxation times are shown to be entirely different from the dielectric relaxation times of the solvent.
The perfect-pairing valence bond model for the water molecule
Authors: Chipman Daniel M. , Kirtman Bernard , Palke William E.
Published: February 2003

Optimized orbitals for the water molecule have been obtained within the perfect-pairing valence bond model by an ab inito self-consistent field calculation. Each split pair is optimized by approximating the remaining electron distribution with a localized doubly-occupied orbital sea. In addition, the overlaps between orbitals of different pairs are optimized by considering higher order pair–pair interactions. The expansion of the energy in the cumulative order of intrapair orbital splittings converges rapidly. The total energy obtained is 49.0 kcal/mole below restricted Hartree–Fock, thus accounting for 21.0% of the correlation energy. The orbitals are well localized into a 1s core pair on oxygen, two equivalent O–H bond pairs and two equivalent lone pairs on oxygen. The hybridization of these orbitals differs considerably from what is expected on the basis of ordinary chemical intuition, the split lone pair orbitals being sp0.56 and sp1.83 and the bonding orbital centered on oxygen being sp1.84. No artificial orthogonality restrictions are imposed on the orbitals in this method. The interpair orbital overlaps are typically on the order of 0.0–0.3, rising to over 0.7 for the overlap between the diffuse orbitals of each lone pair! The energy lowering over a valence bond calculation carried out with a strong orthogonality constraint is small (3.4 kcal/mole). However, the nonorthogonal orbitals are the appropriate ones for transferring from one molecule to another and for chemical interpretation in general. Furthermore, the artificial radial nodes that appear in the strongly orthogonal orbitals hamper the perturbation calculation of correlation energies and the application of pseudopotential techniques as well.
Survey of chemi-ionization reactions in accelerated atom–O2 crossed-molecular beams
Authors: Young C. E. , Cohen R. B. , Dehmer P. M. , Pobo L. G. , Wexler S.
Published: February 2003

The chemi-ionization reactions, associative ionization, and rearrangement (reactive) ionization, and the electron transfer reaction have been investigated in the crossed-molecular beam collisions of more than 20 accelerated (by sputtering) metal and nonmetal atoms with O2 molecules. The observations support a generalization on the scope of these chemi-ionization reactions and their relation to electronic structure, namely that associative and rearrangement ionization reactions do not occur for collision partners for which the thermodynamic threshold energy for electron transfer is lower than the thresholds for the chemi-ionizations. On the other hand, rearrangement and associative ionization may be prominent reaction channels when their thermodynamic thresholds are less than that for electron transfer. Relative cross sections for Ce+, CeO+, and CeO2+ formation for collision energies of Ce+O2 up to 50 eV (cm) are presented. A substantial threshold for associative ionization is observed for this system.
Ion–molecule reaction mechanisms: Thermal energy gas phase reactions of 12C+ and 13C+ ions with CH4, C2H4, C2H6, C3H6, C3H8, and CD3CH2CD3
Authors: Smith Richard D. , Futrell Jean H.
Published: February 2003

The results of a tandem Dempster–ICR mass spectrometric study of carbon ion reactions with several hydrocarbons are reported. The reactions of ground state (2P) 12C+ and 13C+ ions at near thermal translational energies (0.1 eV) with methane, ethylene, ethane, propylene, propane, and propane 1,1,1,3,3,3-d6 were investigated. Reaction branching ratios show several reactions with varying degrees of 13C insertion in the ionic products. On progression from smaller to larger neutral reactants the results are characterized by less retention of the reactant ion nucleus in the ionic products. Reaction of C+ with methane gives a product distribution in line with that predicted by Quasiequilibrium Theory (QET) for excited C2H4+ species. However, propylene shows little correlation with QET predictions. Moreover, 13C+ reactions with ethane and propane exhibit reaction channels in which 13C retention in the ionic products is considerably greater than predicted from statistical considerations. It is concluded that the results are best rationalized by a combination of direct processes and an indirect mechanism involving C+ insertion at a C–H bond.
Analytic energy shifts, linewidths, and line profiles in predissociation
Authors: Bandrauk Andre D. , Laplante Jean Pierre
Published: February 2003

C+ and C− predissociations are treated in the linear potential approximation. Using the appropriate Green’s function, analytic expressions are obtained for ΔE and Γ, the energy shifts and linewidth. These parameters are shown to be strongly energy dependent and their effect on predissociation line shapes are illustrated.
Fano line shapes in predissociation
Authors: Bandrauk André D. , Laplante Jean Pierre
Published: February 2003

The absorption line shapes for C+ predissociations are examined in the case of an optically active continuum which gives rise to Fano profiles. Using the model of linear potentials at the crossing point, all relevant parameters are obtained analytically from the appropriate Green’s function. It is shown that the energy dependence of linewidths and energy shifts has important effects on these profiles, introducing sometimes new zeros or peaks in the classical Fano profile.
Electron excitation of the E 3Σg + state of N2 and subsequent collisional deactivation and energy transfer to the C 3Πu state
Authors: Burns D. J. , Golden D. E. , Galliardt D. W.
Published: February 2003

The excitation and subsequent decay of the E 3Σg+ state of N2 has been studied in a delayed coincidence experiment with a pulsed electron beam by monitoring the time and pressure dependence of the second positive C 3Πu→B 3Πg(0,0) radiation at 3371 Å. The rate equations for the populations of the E and C states have been analyzed for the conditions of the experiment and the relevant equations obtained. The analysis shows the 3371 Å radiation detected, at times long compared to the C state lifetime, to be associated with the initial E state population. Analysis of the time and pressure dependence of this long lived radiation yields a value of 3.8×103 sec−1 mtorr−1 for the collisional deactivation rate coefficient for the E state and a value of 1.9×103 sec−1 mtorr−1 for the energy transfer rate coefficient between the E and C states.
Comments on the classical theory of energy transfer. II. Extension to higher multipoles and anisotropic media
Authors: Chance R. R. , Prock A. , Silbey R.
Published: February 2003

The classical electromagnetic theory of the fluorescence emission and energy transfer in layered systems is extended to describe magnetic dipole and electric quadrupole radiation and anisotropic media. A general formulation is developed for energy transfer from various emitter types and orientations to isotropic acceptors. The description is exact within the classical framework and requires none of the usual assumptions as to the nature of the acceptor layer. The theory is further extended to describe one- and two-dimensional acceptors and electric dipole radiation in an anisotropic medium. The latter case is the actual situation in the fatty-acid layer experiments. The coupling to the surface plasmon modes of the acceptor is discussed as it relates to the various systems described here.
Far infrared spectra of ring compounds. XV. The far infrared spectrum of 7-oxabicyclo-[4.1.0]-hept-3-ene
Authors: Malloy Thomas B.
Published: February 2003

The far infrared spectrum of 7-oxabicyclo-[4.1.0]-hept-3-ene has been studied using the Jarrell–Ash 78-900 spectrophotometer at MIT. A series of nine Q branch transitions exhibiting slight negative anharmonicity has been observed beginning at 121.9 cm−1. The fact that the rocking of the oxirane ring with respect to the six-membered ring has a frequency ∼3 times that of the ring-puckering leads to near coincidence between pairs of levels and this is reflected in some irregularity in the positions of the 2→3, 3→4, and 4→5 ring-puckering transitions. In contrast to analogs of bicyclo-[3.1.0]-hexane, where the anharmonicity is substantial and the effect of the quartic term in the potential is quite noticeable, it is possible to account for the data for 7-oxabicyclo-[4.1.0]-hept-3-ene with a harmonic potential with a small cubic perturbation. H=ν0/2(P2+Q2) +CQ3, where P=−id/dQ, Q = dimensionless ring-puckering coordinate, ν0=123.7 cm−1, C=5.49 cm−1.
Relaxation in biological macromolecules: Properties of some exact solutions
Authors: Schwarz Martin , Poland Douglas
Published: February 2003

We develop a modification in the Glauber theory for relaxation in the one dimensional Ising model in order to treat finite chains with two boundaries (ends). We also present an analysis of an exact solution recently obtained by Schwarz and Poland for the reversible unraveling from the ends of a homogeneous multistrand complex with an irreversible final step (chain dissociation). By modification of the Galuber theory, we develop an exact solution for relaxation in finite chains of homopolyamino acids for a specific choice of transition probabilities. For N the chain length and s the Zimm–Bragg helix stability constant, the solution describes the relaxation for arbitrary N from an arbitrary initial value of s (temperature) to a final state at s=1. It is shown that the relaxation process can be factored exactly into a diffusion and an exponential decay term which dominate respectively in the limit of short and long chain lengths, while Glauber’s solution with periodic boundary conditions decays by the exponential term only. We find that, to a good approximation, a universal set of relaxation curves exist for appropriate scaled variables. In contrast to the behavior of polyamino acids, the unwinding of multistrand complexes can be viewed as involving transitions between free energy states with increasing degeneracy as the free energy (paralleling the degree of unwinding) increases. The rate of dissociation is found to be dominated by the rate of passage from the low probability highest free energy level, to the completely dissociated molecule.
Theoretical study of gas–solid energy transfer: An isotropic Debye model
Authors: Lin Ying-Wei , Wolken George
Published: February 2003

We present a model calculation for gas–solid energy transfer in which the solid is approximated as an isotropic Debye solid. For a given initial state of the solid (described by phonon occupation numbers), only states differing from this arbitrary initial state by one phonon (created or destroyed in an arbitrary state) are included in the basis set describing the solid. Using this basis set, a close-coupling calculation is carried out describing energy transfer during a gas–solid collision. Since the scattering calculation does not employ perturbation, all states in the basis set are coupled. Averages over phonon momenta and directions are carried out before the calculation, which results in considerable simplification. Comparisons are made with He+Ag(111) experimental results. Qualitative agreement is good, and quantitative agreement is within a factor of 2. Our model tends to underestimate inelastic effects. The importance of kinematic and geometric considerations is stressed.
Electron-impact spectroscopy of the fluoroethylenes
Authors: Coggiola M. J. , Flicker W. M. , Mosher O. A. , Kuppermann A.
Published: February 2003

The electron-impact excitation spectra of the six fluoroethylenes and chlorotrifluoroethylene have been investigated at impact energies of 60, 40, and either 20 or 25 eV, and at scattering angles from 0° to 80°. The energy and angular dependence of the relative differential cross sections was determined for several features in the energy-loss range 0–16 eV. This information was used to identify transitions as either spin forbidden or spin allowed. In each molecule, the lowest observed inelastic transition is a spin-forbidden excitation with maximum intensity between 4.18 and 4.68 eV. The locations of these transitions, which are analogous to the N→T transition in ethylene, can be used to interpret the results of some photochemical electronic energy transfer experiments. A second weak singlet→triplet transition occurs in vinyl fluoride with a maximum intensity at 6.4 eV. The other features observed in the 6–10 eV energy-loss region of these molecules agree well with optical spectra. In particular, the large positive shift in the N→V transition energy of tetrafluoroethylene is confirmed. However, no such shift occurs in the N→V maximum intensity transition energy of chlorotrifluoroethylene (7.80 eV), indicating that the steric resistance to torsion is probably not the cause of the observed shift in tetrafluoroethylene. Transitions to many superexcited states lying above the first ionization potential are observed in each molecule. Using the term value method, many of these transitions, as well as lower-lying ones, are assigned to Rydberg series. The average term values obtained in this study agree well with those determined from other series of molecules.
Nitrogen self-diffusion in silicon nitride
Authors: Kijima Kazunori , Shirasaki Shin-ichi
Published: February 2003

Self-diffusion coefficients of nitrogen in polycrystalline alpha- and beta-silicon nitride were measured by a gas–solid isotope exchange technique using 15N as a tracer at temperatures in the range 1200–1410°C. The diffusion coefficients for single-crystal grains can be expressed as D (cm2/sec) =1.2×10−12 exp(−55 700/RT) for α-Si3N4 and D (cm2/sec) =5.8×10+6 exp(−185 700/RT) for β-Si3N4. The diffusion of nitrogen along grain boundaries in the reaction-sintered materials was considerably faster than the diffusion through the bulk.
Accurate opacity functions for atom–diatom scattering: Averaged definite parity j
z-conserving approximation
Authors: Shimoni Yair , Kouri Donald J.
Published: February 2003

It is shown that major errors in partial cross sections calculated from the jz-conserving coupled states approximation can be eliminated if the T matrices are labeled by an l-type index rather than by J. Results are reported for the He+H2 system. (AIP)
Geometrical structure of solvated electrons in γ-irradiated 3-methylpentane glass at 77 K from an analysis of the modulation of the electron spin echo decay envelope
Authors: Narayana P. A. , Kevan Larry
Published: February 2003

Deuterium modulation of the electron spin echo decay envelope from trapped electrons in γ-irradiated 3-methylpentane-d14 glass at 77 K has been analyzed to give a solvation structure characterized by 18–21 equivalent nearest neighbor deuterons to the electron at a distance of 3.0–3.2 Å and with an isotropic coupling constant of essentially zero. From the structure of 3-methylpentane it is suggested that there are six to seven first solvation shell molecules around the electron.
The ESR spectrum and structure of BF−3
Authors: Hudson Reggie L. , Williams Ffrancon
Published: February 2003

The isotropic ESR spectrum of BF−3 in γ-irradiated solid solutions of 5 mole% BF3 in tetramethylsilane (TMS) is reported.(AIP)
Potential work: A statistical-mechanical approach for systems in disequilibrium
Authors: Procaccia I. , Levine R. D.
Published: February 2003

A statistical measure of the maximal amount of work available from a system coupled to a reservoir is introduced and applied. The measure is valid for any initial state of the system and for any reservoir and reduces to known particular results in different limits. Any work not extracted due to irreversibility is shown to be compensated by a corresponding amount of heat. The measure of work is interpreted as the information content of the initial state. During a completely irreversible process the initial information content is degraded entirely into entropy of the reservoir (i.e., into heat). For a given change in energy it is shown that systems in thermal disequilibrium are more informative, i.e., yield more work. An explicit example, the work available from the vibrational state distribution of the nascent products of chemical reactions, is provided.
Spectral variation of fixed-molecule photoelectron angular distributions
Authors: Dill Dan , Siegel Jon , Dehmer J. L.
Published: February 2003

We have computed the angular distribution of electrons ejected by electric-dipole interaction from the K shells of CO and N2 molecules held fixed in space, e.g., by adsorption onto a surface. The predicted distributions are very rich in structure, manifesting directly the spectral variation of the orbital momentum composition of the photocurrent. Experimental determination of such distributions will provide a sensitive, detailed probe of molecular photoionization dynamics.
Photon-assisted nonresonant charge exchange: A simple molecular model
Authors: Copeland Drew A. , Tang C. L.
Published: February 2003

A simple two-state molecular theory for calculating the cross section for the photon-assisted charge-exchange collision process A++B+hν→A*+B+ is described. The semiclassical impact-parameter method is applied to such collisions and for simplicity the nuclear trajectory is assumed to be rectilinear. Ignoring the Stark broadening and trajectory distortion of the molecular levels the exact solution of the resulting coupled charge-transfer equations is obtained. A simple model of the required molecular transition moment is discussed and applied to obtain numerical results. The cross section, averaged over the molecular orientation, as a function of the applied field intensity and relative nuclear translational energy is determined. Using parameters characteristic of an atomic system the cross sections for photon-assisted charge transfer are presented for intensities of 109–1011 W cm−2 and relative nuclear energies varying from 10 to 1000 eV. Our results demonstrate that considerable enhancement of the charge-exchange cross section may be possible with the moderate field intensities presently available. 148
Molecular charge transfer reactions of tritium
Authors: Moran T. F. , McCann K. J. , Flannery M. R. , Albritton D. L.
Published: February 2003

Charge transfer cross sections for the T+2 (X 2Σ+g, v′0) + T2 (X 1Σ+g, v″0) reactions have been computed using multistate eikonal and orbital treatments. Differential cross sections for excitation of individual charge transfer as well as the direct scattering channels were computed as a function of scattering angle and integral cross sections have been determined for incident ions with 0.01 to 5.0 keV kinetic energies. Converged cross sections require the inclusion of a large number of product vibrational states in the wavefunction expansion of the system, with the number increasing to over 100 different vibrational channels as the ion kinetic energy is increased to 5 keV. Differential cross sections for the formation of fast neutral products become more intense and concentrated in the forward direction as the vibrational quantum number of either the reactant ion or target molecule is increased. Integral cross sections involving vibrationally excited neutral target molecules and/or incident ions are larger than those for ground state reactants at low kinetic energies where both energy defects and vibrational overlaps exert a strong influence on the reaction mechanism. Large cross sections involving vibrationally excited species at low kinetic energies is a consequence of the larger number of product channels that are energetically accessible as the reactant vibrational state is increased. At high kinetic energies the vibrational overlaps exert a controlling influence on both tthe magnitude of the charge transfer cross sections and product vibrational state distributions.
Thermochemical properties of gaseous Li2 and Li3
Authors: Wu C. H.
Published: February 2003

Using the Knudsen effusion mass spectrometric technique, the gas species Li(g), Li2(g), and Li3(g) have been observed over liquid lithium. The atomization energies of Li2(g) and Li3(g):D0° (Li2) =25.5±1.5 kcal/mole and D0° (Li3) =41.5±4.0 kcal/mole, were derived from the study of the various gaseous equilibria: Li(s,l) →Li(g) (1), 2Li(s,l) →Li2(g) (2), Li2(g) →2Li(g) (3), 3Li(s,l) →Li3(g) (4), 2Li2(g) →Li3(g)+Li(g) (5). The following heats of formation were also obtained: ΔH0° (Li) =38.5±1.0 kcal/mole, ΔH0° (Li2) =51.5±2.0 kcal/mole, ΔH0° (Li3) =73.0±4.0 kcal/mole. The ionization potentials of Li2 and Li3 were determined as 4.86±0.1 and 4.35±0.2 eV, respectively, from which the binding energies D0° (Li+2) =37.7±2.0 and D0° (Li+3) =65.5±4.3 kcal/mole result.
The photoelectron spectra of halogen substituted acetones
Authors: Young V. Y. , Cheng K. L.
Published: February 2003

The HeI photoelectron spectra of fluoroacetone, 1,1,1-trifluoroacetone, 1,1,1-trichlorotrifluoroacetone, 1,1,3-trichlorotrifluoroacetone, 1,1,3,3-tetrafluoroacetone, 1-chloro-1,1,3,3-tetrafluoroacetone, chloropentafluoroacetone, chloroacetone, and 3-bromo-1,1,1-trifluoroacetone have been determined and the vertical ionization energies measured. They have been compared with ionization energies calculated by CNDO/2 and MO assignments of the bands have been made on this basis. A correlation between the oxygen lone pair ionization energy and the number of fluorines substituted was observed. This paralleled a correlation between the width at half-peak height of the lone pair band and the lone pair ionization energy. The carbonyl stretching frequencies were determined and also found to correlate with the oxygen lone pair ionization energy. The linear plot suggested that the oxygen lone pair ionization energies are related to the sum of the effective electronegativities of the substituents. The first chlorine lone pair ionization energy and the carbonyl π were investigated to see if their ionization energies are related to the sum of the effective electronegativities of the substituents. In all three cases, an empirical relationship, IE= α (XA+XB)+β, was found to hold where α and β are constants determined by least squares fit of the data and whose value depends on the type of orbital considered. The values of α and β for the oxygen lone pairs of halogen substituted acetones were found to be 1.24 and 3.91, respectively. For the chlorine lone pairs, the values were found to be 1.16 and 5.89, while for the carbonyl π, they were found to be 1.98 and 3.17, respectively.
Ion molecule reactions in vinyl fluoride by photoionization. Effects of vibrational excitation on major reaction pathways
Authors: Williamson Ashley D. , Beauchamp J. L.
Published: February 2003

Photoionization methods have been used to study the reactions of the molecular ion in vinyl fluoride to yield the ionic products C3H3F2+, C3H4F+, and C3H5+. Quantitative measurements are reported of the effect of the vibrational state of the reactant ion on the product distribution and overall reaction cross section. Reaction cross sections for all three channels decrease with reactant internal energy. The effect on the reaction pathway producing C3H3F2+ is especially pronounced, with 0.18 eV of vibrational excitation being sufficient to reduce the reaction probability by 75%. Deactivation of vibrationally excited reactant ions competes with the reaction and is shown to be an efficient process.
Surface diffusion of individual atoms and dimers: Re on W(211)
Authors: Stolt Kaj , Graham William R. , Ehrlich Gert
Published: February 2003

Quantitative observations of diffusion on the W(211) surface have been made both for rhenium atoms and for rhenium dimers formed from atoms in adjacent [1̄11] channels, using the field ion microscope to reveal the surface on the atomic level. From measurements of the dispersion of individual atomic displacements over the range 290⩽T⩽350 °K, the diffusion parameters for Re atoms are found as D0=2.2(×2.8±1) ×10−3 cm2 sec−1 and ΔE‡m=19.8±0.7 kcal mole−1. The diffusion coefficient of dimers is obtained from observations of center of mass motion over the range 260⩽T⩽350 °K; these yield the parameters D0=4.5(×1.7±1) ×10−4 cm2 sec−1 and 〈ΔE‡〉c.m.=18.0±0.3 kcal mole−1. Rhenium dimers are found in either a straight or a staggered state, with the latter favored. Dimers diffuse by making single atom jumps, in a two step process in which the straight configuration converts to the staggered at the rate a, and the staggered reverts to the straight at the rate b. Quantitative observations of the frequency of occurrence for the two states, combined with diffusion measurements, yield νa=1.1(×2±1) ×1012 sec−1, ΔE‡a =17.5±0.4 kcal mole−1 and νb=2.5(×1.7±1) ×1012 sec−1, ΔE‡b=18.3±0.3 kcal mole−1. This is to be compared with the values ν=5.9(×2.8±1) ×1012 sec−1 and ΔE‡m=19.8±0.7 kcal mole−1 found for jumps of single rhenium atoms. Interactions between rhenium atoms on the W(211) surface are small, on the order of van der Waals forces. Nevertheless, comparison with previous work on iridium dimers reveals a pronounced chemical specificity.
Surface structure of a liquid film
Authors: Rao M. , Levesque D.
Published: February 2003

A molecular dynamic simulation of the surface structure of a liquid film at two temperatures (89 and 84°K) interacting with a Lennard-Jones (6,12) potential is reported. The density profiles normal to the film surface show no significant structure. The surface tension was calculated as 12.2±0.43 dyn/cm compared with the experimental value of 13.45 dyn/cm at 84°K.
Interatomic potentials and transport properties for neon, argon, and krypton
Authors: Nain V. P. S. , Aziz Ronald A. , Jain P. C. , Saxena S. C.
Published: February 2003

Experimental thermal conductivity data generated by Saxena and co-workers for neon (400–2600 K), argon (400–2500 K), and krypton (400–2500 K) are employed in conjunction with some recently proposed interatomic potential functions to assess their relative appropriateness. The ESMSV III for neon, the ESBFW for argon, and the corresponding states BP for krypton best describe these thermal conductivity data. The 11-6-8 is found to be a good correlating potential in each case except krypton above 2000 K. This information together with the kinetic theory is used to predict viscosity and diffusion coefficients.
Coupled states approximation study of inelastic H+–H2 collisions at 3.7 eV
Authors: McGuire Paul
Published: February 2003

Using the diabatic ground state H+3 surface given in analytic form by Giese and Gentry, a coupled-states study of the rotational excitation of H2 (taken as a rigid rotor) by proton impact is made at 3.7 eV. Transitions 0→j′, with j′=0,2,4,...,26, are considered, and one finds a broade distribution in final rotor state j′ which is consistent with recent beam experiments. Despite long-range rotational coupling produced by the charge-quadrupole interaction, the coupled-states method gives a good description of the rotational excitation process as is demonstrated by comparison to standard close-coupling cross sections. Intermultiplet transitions (neglected in the coupled-states approximations) are shown to be less important in the high energy limit.
Absolute rate constant for the reaction of atomic hydrogen with phosphine over the temperature range 209 to 495 K
Authors: Lee J. H. , Michael J. V. , Payne W. A. , Whytock D. A. , Stief L. J.
Published: February 2003

Absolute rate constants for the reactions of atomic hydrogen with phosphine (PH3) have been determined for the first time over the temperature range 209 to 495 K. The method employed was flash photolysis of dilute mixtures of PH3 in He combined with time resolved detection of H via Lyman-α resonance fluorescence. A linear least-squares treatment of the data leads to the expression k= (4.52±0.39) ×10−11 exp (−1470±50)/(1.987T) cm3 molecule−1 s−1. Evidence is presented in support of a hydrogen abstraction mechanism. Implications of these results for the photochemistry of PH3 in the atmosphere of Jupiter are discussed, especially as this relates to the origin of the Great Red Spot.
Entropy and macroscopic disequilibrium. I. Isothermal time evolution with applications to vibrational relaxation
Authors: Procaccia I. , Shimoni Y. , Levine R. D.
Published: February 2003

A practical method for using bulk averaged values of observables for the characterization and prediction of the molecular population time evolution during isothermal relaxation is presented. In practical applications to realistic examples of vibrational relaxation very few bulk averages were required to accurately predict the population distribution even when the initial population was very strongly inverted. The time dependence of the macroscopic observables which are employed as input is conveniently formulated in terms of sum rules. The bulk average values are used as constraints in a maximal entropy procedure for the determination of the population distribution. It is shown that the procedure is of a variational type. Monotonic convergence of the information theoretic predicted distribution to the exact one is guaranteed upon inclusion of additional macroscopic input. The concept of ’’independent moments’’ is introduced for this purpose. Only independent observables are informative, i.e., provide independent data which are required for convergence. The number of informative observables decreases with time and is typically very much smaller than the number of significantly populated molecular energy states. The method is illustrated by comparing its predictions to the results of a numerical solution of the master equation, with a realistic set of rate constants and for different initial conditions. The application of the surprisal analysis to the interpretation, characterization, and compaction of the population distribution is demonstrated. Turning to predictions (’’surprisal synthesis’’), only strongly inverted initial populations required three independent moments, during the initial stages. Over much of the relaxation a single moment (’’vibrational temperature’’) sufficed for an accurate prediction. The limits where the characteristic vibrational temperature is high or low compared to the temperature of the buffer gas are discussed. Special reference is made to rotational relaxation. The rate of internal entropy production due to the irreversible relaxation and the rate of increase of the global entropy are discussed and shown to be positive.
Photoionization processes at threshold. I. Threshold photoelectron and photoionization spectra of CO2
Authors: Batten C. F. , Taylor J. Ashley , Meisels G. G.
Published: February 2003

A threshold photoelectron spectrometer is described. The instrument has a resolution (FWHM) of 14 meV for states reached by direct photoionization, and 90% rejection of electrons from autoionizing events occuring more than 30 meV above direct ionization thresholds. Detailed threshold photoelectron and total photoionization efficiency spectra are presented for three electronic states (2Πg, 2Πu, 2Σ+u) of the CO+2 ion. Vibrational excitation in the symmetric stretching mode is observed for each state with the longest progression occuring for the 2Πu state. Spin–orbit splitting of the 2Πg state is readily visible. Autoionization occurs in the vicinity of most of the 2Πg and 2Πu levels. There is some indication for production of ions with vibrational excitation in the bending mode.
Assignment of vibrational species of pyrazine by the method of microwave induced delayed phosphorescene and polarized phosphorescence
Authors: Matsuzaki Kazuo , Sasaki Masashi , Azumi Tohru
Published: February 2003

An analysis of vibronic bands associated with the phosphorescence of pyrazine in a single crystal of benzene is made from the viewpoints of the polarization and of the relative radiative rate constants for the triplet sublevels. The experimental results in conjunction with theories lead to the unambiguous conclusions regarding the long disputed vibrational assignments for some nontotally symmetric vibrational species.
Catastrophes and fluctuations of polarization in anisotropic dielectrics
Authors: Inoue Masayoshi
Published: February 2003

The static dielectric constants of anisotropic dielectrics are numerically calculated with the aid of the extended Fröhlich formula where the thermal fluctuations of polarization are taken as parameters. The relation between the dielectric constants and the fluctuations of polarization are analytically derived near polarization catastrophes. It is shown that this relation of KH2PO4-type ferroelectrics, in which only one principal values of the dielectric constant goes to infinity, differs from that of isotropic ferroelectrics such as BaTiO3 in the exponent. The critical fluctuations of polarization in KH2PO4 are also calculated using the experimental data on the dielectric constants.
Theory of the chemical bond. III. The radius of convergence of Rayleigh–Schrödinger and implicit perturbation expansions
Authors: Matcha Robert L. , King Stephen C.
Published: February 2003

Simple exact criteria for convergence of explicit and implicit perturbation expansions are developed. An approximate criterion is also given: The difference between the nth eigenvalue of the perturbation matrix in the basis of zeroth order eigenfunctions and the first order correction to the energy must be less in magnitude than the difference between the nth eigenvalue of the zeroth order Hamiltonian and the zeroth order energy.