bluuebunny/crossref_metadata_2025 huggingface dataset:
The A+Bx condensation reaction: Crossed nozzle beams of Br2 and (Cl2)x or (NH3)x clusters
Authors: Behrens Richard , Freedman Andrew , Herm Ronald R. , Parr Timothy P.
Published: February 2003

Nozzle beams of Br2 and Cl2 or NH3 have been crossed in a molecular beam scattering apparatus; the Cl2 or NH3 beam contained (Cl2)x or (NH3)x clusters distributed such that the intensity of a given cluster, Fx, decreased with increasing x for 1⩽x⩽∼50. Mass, angular, and time-of-flight spectra of the scattered neutral species all establish that the A+Bx→ABx* bimolecular condensation reaction is being observed. However, working from the data, it is not possible to distinguish between detection of a long-lived ABx* metastable complex or of a decomposition product formed with low recoil velocity. Product angular distributions are confined to a small region of laboratory scattering angle Θ and peak at small but positive Θ (Θ=0° and 90° defined by cluster and Br2 beam directions, respectively). It is pointed out that this sharp peaking at small Θ is due to a number of experimental factors, including a Jacobian factor varying as sin−2Θ, and should be a universal characteristic of such condensation reactions in crossed beams. In the data it is indicated that there will be a high probability of fragmentation into small daughter ions upon electron bombardment (EB) ionization of an ABx or Bx cluster for the range in x most sensitive to the measurements (∼10⩽x⩽∼50). This in turn implies that the concentration of neutral clusters in the beam can be seriously underestimated if the cluster ion mass spectra produced by EB ionization of the nozzle beam are assigned assuming that fragmentation is inconsequential.
Potential barrier to internal rotation in methyl fluoroform
Authors: Durig J. R. , Bucy W. E. , Wurrey C. J.
Published: February 2003

The Raman and microwave spectra of CF3CD3 are reported and used to obtain a more accurate determination of the potential barrier to internal rotation. The microwave results give a barrier of 3.2±0.2 kcal/mole, however, this is not in accord with the trends for chlorine or bromine substituted ethanes. (AIP)
Internal rotation in ethylamine: A treatment as a two-top problem
Authors: Tsuboi Masamichi , Tamagake Keietsu , Hirakawa Akiko Y. , Yamaguchi Jun , Nakagawa Hisao , Manocha A. S. , Tuazon E. C. , Fateley W. G.
Published: February 2003

The infrared absorption spectra of eight isotopic ethylamine molecules, i.e., CH3CH2NH2, CD3CH2NH2, CH3CD2NH2, CD3CD2NH2, CH3CH2ND2, CD3CJ2ND2, CH3CD2ND2, and CD3CD2ND2, have been examined in the vapor phase in the 300–100 cm−1 region. Several Q-branch peaks were observed for each isotopic species and assigned to the torsional oscillations of the methyl and amino groups of the trans and gauche isomers. The energy levels were calculated on the basis of a coupled two-top system. The analysis yielded a probable potential function for the internal rotation about the C–N bond of the form V (α) = (316.5/2)(1−cosα)−(11.3/2)(1−cos2α)+(713.7/2)(1−cos3α) −(25.0/2)(1−cos4α)+(25.0/2)(1−cos5α)−(3.7/2)(1−cos6α). The difference between the potential energy minima of the trans and gauche conformations is about 230 cm−1, the trans being the more stable form. It has been concluded that the axis of internal rotation of the amino group does not coincide with the N–C bond but is along a line about 4.5° from the N–C bond and in the plane bisecting the NHH triangle.
NMR and NQR study of ClF5 in its solid phases
Authors: Weulersse J. M. , Rigny P. , Virlet J.
Published: February 2003

The 19F NMR line shape and relaxation have been studied in solid ClF5 from the melting point down to liquid nitrogen temperature. The corresponding results, completed by relaxation data concerning 35Cl NMR and NQR, have yielded information about phase transitions and molecular motions. In particular, a new solid–solid transition was found at 117 °K. 35Cl wide-line and 19F high resolution NMR spectra were obtained in the high temperature phase SI, which is shown to be a plastic phase where molecular reorientations (τϑ=8×10−12 sec) are nearly as fast as in the liquid. In addition to the reorientation there is a much slower translational diffusion, the main characteristics of which are derived from 19F T1 and T1ρ measurements using Torrey’s theory. In the low temperature phases SII and SIII, the 19F T1 is due to rotations of the molecules by jumps around their C4 axis (τr=10−8 sec at 110 °K). In solid II the NQR relaxation time T1Q is due to another mechanism which is assumed to be jumps of the C4 axis between two equilibrium positions. The dipolar energy relaxation time TD was also measured; between 123 and 153 °K, the Cl–F dipolar coupling modulated by the chlorine relaxation appears to be the main TD mechanism, for which a theory is described.
Uniform semiclassical approximation to the electron density distribution
Authors: Lee Soo Y. , Light J. C.
Published: February 2003

The single particle reduced density matrices for fermions in a linear potential in one and three dimensions are derived. An idempotent reduced density matrix for a nonuniform field with a single turning point is obtained. The density expression contains the contributions from the direct path and the path with one turning point. When applied to a potential well the corrections from the long-time paths are taken from the theory of Light and Yuan. Only classical quantities of momentum, time, and action enter in the final expression. The density distribution for the nonclassical region is more accurate than that given by the formula of Light and Yuan.
Excitation of ozone formed by recombination. II
Authors: vonRosenberg C. W. , Trainor Daniel W.
Published: February 2003

Experimental measurements of ir emission (2<λ<8 μ) from nascent ozone formed by the three−body recombination O+O2+O2→O3+O2 are reported. This represents an extension of earlier work on the fundamental bands (8<λ<15 μ) and includes these results: (a) 4.7 μ data on the (ν1+ν3) combination band, which quantitatively supports our published fundamental band results; (b) 8 μ signals probably due to vibration–rotation transitions of a bound excited triplet state predicted by theoretical calculations; and (c) 6.6 μ emission, which may be due to 3B2→1A1 (forbidden) emission.
The vibronic representation for collinear atom–diatom collisions: Two-state semiclassical model
Authors: Laing John R. , George Thomas F. , Zimmerman I. Harold , Lin Ying-Wei
Published: February 2003

A unique semiclassical description of atom–diatom collisions is presented in which the vibrational as well as the electronic motion is treated quantum mechanically. The electronic Hamiltonian and the vibrational nuclear kinetic energy operator are diagonalized to yield vibronic potential energy curves, each correlating asymptotically to a specific electronic and vibrational state of the colliding species. The vibronic curves are used in Stueckelberg-like calculations to yield individual S-matrix elements. This theory is applied to a collinear nonreactive model of X+H2 collisions in which X is either F or Br. S-matrix elements are calculated for transitions between the 2P3/2 and 2P1/2 spin–orbit states of the halogen and vibrational states of H2. The results are in very good agreement with rigorous quantum results.
Intermolecular potential between an atom and a linear molecule: The structure of ArOCS
Authors: Harris Stephen J. , Janda Kenneth C. , Novick Stewart E. , Klemperer William
Published: February 2003

The radio frequency and microwave spectrum of ArOCS has been measured by molecular beam electric resonance spectroscopy. ArOCS is a prolate, slightly asymmetric top. The rotational constants and dipole moment components of the ground vibrational state are as follows: A = 6786.014(20) MHz, B = 1509.909(6) MHz, C = 1227.220(6) MHz, μa = 0.2146(10) D, μb = 0.669(2) D. The complex has a nonlinear, T-shaped structure and the vibrationally averaged distances are Ar–C = 3.578(1), Ar–O = 3.601(1), and Ar–S = 4.101 Å. The observed structure is analogous to isoelectronic and isovalent chemically bound systems, and it is shown to be that expected from an interaction of the highest occupied orbital of Ar with the lowest unoccupied orbital of OCS.
New-type correlated wavefunctions for three-body systems with Coulomb interaction
Authors: Cavaliere P. , Ferrante G. , Geracitano R. , Lo Cascio L.
Published: February 2003

Simple correlated wavefunctions are reported for the ground states of three selected Coulombic systems, namely (1) the positronium negative ion e−e+e−, (2) the hydrogen negative ion H−, and (3) the mesic molecular ion pμp. They give quite accurate energy results, and are analytically simple enough to be used widely in applications. Two characteristic features of the proposed wavefunctions are that (1) the correlation between the two particles with the same sign of the charge is explicitly included in the form G= xn3e−γx3, and (2) the variational parameters to be optimized are mostly nonlinear (exponential).
Self-consistent field calculation of the electronic structure of the uranyl ion (UO2++)
Authors: Boring Michael , Wood J. H. , Moskowitz J. W.
Published: February 2003

Using the multiple-scattering Xα method the electronic ground state (1Σ+g) of the UO++2 molecule has been calculated self-consistently. The self-consistent calculations were performed at three U–O bond distances [3.269, 4.269, and 5.269 (a.u.)]. The four highest occupied one-electron levels (σg, σu, Πg, Πu) of the ground state, which have received so much attention in the past, change ordering with decreasing bond distance but are so close in energy that the ordering may be unimportant in determining the absorption spectra. We have also computed the electronic transition energies for the excitations 1Σ+g → 1,3Φg(σ1uφ1u), 1Σ+g → 1,3Δg(σ1uφ1u), 1Σ+g → 1,3Πu, 1,3Φu(π3gδ1u), 1Σ+g → 1,3Δg, 1,3Γg(π3uφ1u), and 1Σ+g → 1,3Φg, 1,3Πg(π3uφ1u). All of these excitation energies fall in the region of the experimental absorption spectrum.
Transient photovoltaic effects in metal–chlorophyll-a–metal sandwich cells
Authors: Tang C. W. , Albrecht A. C.
Published: February 2003

Photovoltaic effects in (Cr‖Chl-a‖Hg) and (Cr‖Chl-a‖Hg/In) sandwich cells under cw and microsecond pulsed excitation have been studied. The (Cr‖Chl-a‖Hg) cell exhibits strong rectification in the dark, whereas the effect in the (Cr‖Chl-a‖Hg/In) cell is weak and in the opposite direction. Upon cw excitation, the photovoltaic current in (Cr‖Chl-a‖Hg) quickly reaches a steady state with no obvious transients. The current flow is in the direction from Cr to Hg though the Chl-a film. The action spectrum of the cw as well as the pulsed photovoltaic currents matches closely the absorption spectrum of the Chl-a film. In contrast, the (Cr‖Chl-a‖Hg/In) cell behaves very differently. Transient photovoltaic currents preceding the steady state currents are seen under cw excitation in spectral regions where the Chl-a film absorbs strongly. The transient current flow is in the direction from Cr to Hg/In, but it quickly reverses direction to reach a steady state current of opposite sign. At wavelengths absorbed only slightly by Chl-a, the transients are not apparent, and only the steady state current is seen (Hg/In to Cr). The action spectrum of the steady state current shows an ’’inverse’’ type behavior revealing a minimum in response where Chl-a absorbs most. Under pulsed excitation, both the sign and the shape of the photovoltaic current pulse is seen to depend on the excitation wavelength. The action spectrum of the pulsed photovoltaic current in the (Cr‖Chl-a‖Hg/In) cell actually shows a ’’reversal’’ effect where the sign of the signal changes with wavelength. External bias voltage can be applied and it influences both the direction of the photocurrent as well as the shape of the action spectrum. The rectifying and the photovoltaic properties of both cells are directly related to the existence of potential barriers at the contact between the p-type Chl-a and the electrodes. These barriers appear to resemble the Schottky barriers used to describe the contacts between metals and inorganic semicondutors. The remarkable difference in the two cells can be explained as being due to the presence of a single barrier at the Cr‖Chl-a contact, in the (Cr‖Chl-a‖Hg) cell, and two opposing barriers in the (Cr‖Chl-a‖Hg/In) cell, one at the Cr‖Chl-a contact, as before, and a stronger barrier at the Chl-a‖Hg/In contact. The action spectra clearly reflect the relative strength of the front and the back barriers and the penetration depth of the excitation light. The appearance of the transient photocurrent spike is apparently due to the electrical polarization of the Chl-a microcrystals by light under the influence of the built-in field at the rectifying contacts. The switching effect in the photovoltaic current in the (Cr‖Chl-a‖Hg/In) cell is seen as a result of such polarization and the consequent mutual biasing of the two opposing contact barriers. The power conversion efficiency of the (Cr‖Chl-a/Hg) cell is better than 10−2% based on monochromatic illumination, a value among the best yet reported for organic cells.
Simple model for surface specific heats
Authors: Naugle D. G. , Allen R. E.
Published: February 2003

Surface specific heats have been calculated with a simple model in which the dispersion curves for the acoustic modes are represented by sine functions, the optical modes are represented by Einstein oscillators, the parameters are fitted to bulk data, and the effect of the surface is estimated from the number of neighbors that the surface atoms are missing. The results are in good agreement with those of detailed lattice-dynamics calculations, indicating that rather accurate calculations are possible for average properties such as the surface specific heat without a detailed knowledge of the surface phonon spectrum.
Study of the sensitivity of coupled reaction systems to uncertainties in rate coefficients. III. Analysis of the approximations
Authors: Cukier R. I. , Schaibly J. H. , Shuler K. E.
Published: February 2003

In Parts I and II of this series [J. Chem. Phys. 59, 3873, 3879 (1973)] we developed a new method of sensitivity analysis for large sets of coupled nonlinear equations with many parameters. In developing this theory and in carrying out the computer calculations involved in this analysis we made a number of approximations. We present here a quantitative analysis of these approximations and, where applicable, develop rigorous error bounds. Our analysis shows that we can specify the approximations which enter into our theory so as to obtain sensitivity measures of known accuracy. On this basis we feel that the techniques developed in this series of papers provide a useful and efficient method of sensitivity analysis of large systems with many parameters.
ESR, ENDOR, and double ENDOR at 300 °K of DL-serine x irradiated at 340 °K, a new radical species
Authors: Hampton Don A. , Moulton Grace C.
Published: February 2003

When DL-serine single crystals are x rayed at 300 °K or below, two stable radicals are observed at room temperature. One of these, IV, is of greater intensity than the other, V, and was previously identified. By irradiating at a slightly elevated temperature, ∼340 °K, the concentration of V becomes more intense than IV. In this work we report on a detailed study of V using ESR, ENDOR, and double ENDOR, all at room temperature. We have determined that V is     and have obtained five hyperfine tensors representing one α-H, two β-H’s, the rotating amino H’s, and a fourth H which is probably in a neighboring molecule. We have also observed the ENDOR transition of the nitrogen. The α-H tensor is somewhat unusual in that the isotropic term (−41.3 MHz) is considerably less than for a 2ρπ electron and of the same sign, but the anisotropic term is approximately the same (+31.9, +3.5, −35.4 MHz). This is consistent with our model since the bonding to the α-carbon is strained and would not be expected to be pure sp2.
Argon matrix infrared spectra of CF3OOF and CF3OOOCF3 and their photolysis products. Spectroscopic evidence for the CF3OO radical
Authors: Smardzewski Richard R. , De Marco Ronald A. , Fox William B.
Published: February 2003

Ultraviolet photolysis of fluoroperoxytrifluoromethane, CF3OOF, in argon matrices at 8 °K produced CF4 and a new species, tentatively identified as the CF3OO radical, with infrared absorptions at 1173.7 and 1094.1 cm−1. This species was also produced, along with CF4, CF3OCF3, and COF2, by photolysis of bistrifluoromethyl trioxide, CF3OOOCF3, at wavelengths below 300 nm. In the latter case, extensive isotopic labeling experiments with CF3 16O16O16OCF3, CF3 16O18O16OCF3, CF3 18O16O18OCF3, and CF3 18O18O18OCF3 led to the observation of four distinct isotopic absorptions for the O–O stretching vibration (1094.1 cm), thus confirming the nonequivalent oxygen atom structure of CF3OO.
Towards a molecular theory of freezing
Authors: Raveché Harold J. , Stuart Charles A.
Published: February 2003

The subject of this article is the fluid–solid transition and, in particular, an analysis of crystallization in terms of quantities which describe the average local arrangements of molecules in a fluid. We determine whether it is possible to predict the existence of crystalline solutions for the local molecular density from a Hamiltonian which is invariant under all translations and rotations. Crystallization is studied using the singlet probability density, the pair correlation function, and the intermolecular potential energy. An integral equation is obtained for these quantities, and we pursue the existence of crystalline (i.e., periodic but nonconstant) solutions for the singlet probability which branch from the fluid (i.e., constant) solution which is the number density. The phenomenon of crystallization, that is, the existence and determination of these solutions, can then be represented as a nonlinear eigenvalue problem. The analysis is applied to hard sphere systems in one, two, and three dimensions. Crystallization to close-packed lattices is found in two and three dimensions when the isotropic media are overcompressed by amounts which depend on the structures to which the fluids crystallize. That is, the fluid persists into a portion of the metastable region. The nature of the crystalline solutions is analyzed in the neighborhood of the branching eigenvalues, and the relation between these special eigenvalues and equilibrium freezing points is discussed. The stability of these crystalline solutions is determined by comparing the values of a free energylike functional on these solutions with its value for the fluid.
The absolute generalized oscillator strength for the Lyman–Birge–Hopfield band of N2 as determined by high energy electron impact spectroscopy
Authors: Wong T. C. , Lee J. S. , Wellenstein H. F. , Bonham R. A.
Published: February 2003

The absolute generalized oscillator strength for the dipole forbidden quadrupole allowed Lyman–Birge–Hopfield band [a 1Πg ← X 1Σ+g] in molecular nitrogen at an energy loss of 9.35 eV is observed by electron impact spectroscopy using 25 keV electrons over the momentum transfer range 0.04?K2?10 a.u. The results agree in the zero angle (zero momentum transfer) limit with the previous observations of Skerbele and Lassettre, but are in disagreement with previous theoretical and experimental results for K2≳0.5.
Electron distributions and ionic binding in series of alkali halide molecules
Authors: Curtiss L. A. , Kern C. W. , Matcha R. L.
Published: February 2003

Electron density maps for series of diatomic alkali halide molecules are determined from near-Hartree–Fock wavefunctions. The charge distributions in these molecules are analyzed in terms of the total-molecular density and density-difference maps. The outermost orbital is found to play a dominant role in the ionic bonding. Finally, the changes in the distributions at various internuclear separations and the relation of density quantities to binding and antibinding regions are discussed.
Measurements of longitudinal and transverse ultrasonic wave velocities in compressed solidified argon and their relationship to melting theory
Authors: Ishizaki Kozo , Spain Ian L. , Bolsaitis Pedro
Published: February 2003

Measurements of longitudinal and transverse ultrasonic wave velocities have been made on compressed, solidified argon for pressures up to 6 kbar (600 MPa) corresponding to melting temperatures in the range 123–206 K. Velocities in the solid phase were measured along isochores to within ∼10−3 K of the melting line. The Lindemann melting parameter, obtained from appropriate physical quantities at the melting line, was constant within the limits of error of the measurement (±2%).
Benzene dimer: A polar molecule
Authors: Janda Kenneth C. , Hemminger John C. , Winn John S. , Novick Stewart E. , Harris Stephen J. , Klemperer William
Published: February 2003

The electric deflection of molecular beams of (C6H6)2, produced by adiabatic expansion, has been measured. The benzene dimer is observed to be a polar species. It is likely that the structure of this species is that of two perpendicular planes, as is observed for nearest neighbors in crystal and liquid benzene.
Normal coordinate treatment of XeO2F2
Authors: Willett R. D. , LaBonville P. , Ferraro J. R.
Published: February 2003

A normal coordinate treatment (NCT) using a modified Urey–Bradley force field (MUBFF) was made for XeO2F2. New analyses were also performed on XeOF4 and XeO3F2. Force constants obtained were compared with force constants from other xenon compounds containing fluorine and/or oxygen atoms. In general, as oxygen atoms are added to XeF2 the bond distance of the Xe–F decreases while the KXeF force constant increases, and the Xe–O bond distances increase while the KXeO force constant decreases.
Calculation of inelastic cross sections for H++Cs → H(n=2)+Cs+
Authors: Valance A. , Spiess G.
Published: February 2003

The cross sections for the processes H++Cs → H(2p and 2s) +Cs+ were calculated in the center of mass energy range 250–2400 eV using a simple pseudopotential formalism for the potential curves and coupling matrix elements and a perturbed stationary state (pss) formulation for the calculation of the cross sections. The results are found to be in reasonable agreement with experiment.
A model study of collision induced dissociation of a diatomic molecule by an atom
Authors: Ford Louis W. , Diestler D. J. , Wagner Albert F.
Published: February 2003

The time-dependent Schrödinger equation for the collinear collision of an atom with a diatomic molecule is solved numerically after the manner of McCullough and Wyatt. The binding potential is taken to be a truncated square well and the interaction is impulsive (hard sphere). For the case in which all three masses are equal final relative momentum distributions and dissociation probabilities are obtained as a function of both the initial relative kinetic energy and the initial vibrational level. For purposes of comparison quasiclassical trajectory analyses of the same cases were performed. Quantum effects on collision-induced dissociation (CID) are seen to be important for this model. A very notable characteristic of the model, observed in both the quantum and classical results, yet not in most experimental results, is that CID is severely vibrationally inhibited, i.e., the probability of CID decreases as the initial vibrational quantum number increases at a fixed total collision energy. Probable causes of this strong vibrational inhibition are examined classically by a detailed trajectory analysis. It is concluded that the collinearity of the model is most likely responsible.
Nonlinear hyperbolic theory of thermal waves in metals
Authors: Wilhelm H. E. , Choi S. H.
Published: February 2003

A closed-form solution for cylindrical thermal waves in metals is given based on the nonlinear hyperbolic system of energy conservation and heat flux relaxation equations. It is shown that heat released from a line source propagates radially outward with finite speed in the form of a thermal wave which exhibits a discontinuous wave front. Unique nonlinear thermal wave solutions exist up to a critical amount of driving energy, i.e., for larger energy releases the thermal flow becomes multivalued (occurrence of shock waves). By comparison, it is demonstrated that the parabolic thermal wave theory gives in general a misleading picture of the profile and propagation of thermal waves, and leads to physical (infinite speed of heat propagation) and mathematical (divergent energy integrals) difficulties. Attention is drawn to the importance of temporal heat flux relaxation for the physical understanding of fast, transient processes, such as thermal waves, and more general explosions and implosions.
ESR study on the spatial distribution of radicals trapped in the heavy ion-irradiated n-eicosane single crystal
Authors: Kimura Kazuie , Ogawa Mariko , Matsui Masao , Karasawa Takashi , Imamura Masashi , Tabata Yoneho , Oshima Keichi
Published: February 2003

Single crystals of n−eicosane were subjected to the irradiation of helium, carbon, and nitrogen ions accelerated with the cyclotron, and the results were compared with those obtained by 60Co γ-ray irradiation. Irradiation was carried out at 77 °K. The nature and the spatial distribution of free radicals produced in the crystals were investigated by an ESR technique. The principal radical is –CH2ĊHCH2– (I) and the minor one, CH3ĊHCH2– (II); the linewidth and decay of these radicals were found to be LET-dependent. The ESR results indicate that radicals are trapped in two regions closely and sparsely; the relative distribution in the two regions is dependent on the LET of radiations used. The mean separation between the radicals trapped in the close proximity was estimated to be approximately 16 Å.
Approximations for the exchange potential in electron scattering
Authors: Riley Merle E. , Truhlar Donald G.
Published: February 2003

Four new exchange potentials (the semiclassical exchange approximation, the asymptotically adjusted free-electron–gas exchange approximation, the second-order free-electron–gas exchange approximation, and the high-energy exchange approximation) are derived. Calculations are performed for elastic electron scattering from helium and argon. The results are compared to one another and to calculations using Hara’s free-electron–gas approximation and the exact nonlocal exchange potential. Three of the approximations to exchange are in good agreement with the exact exchange —except at very low energy— but are much easier to use. Thus they should be very useful in electron–atom and electron–molecule scattering calculations.
Intermolecular forces in gaseous mixtures: He–Ar
Authors: Smith K. M. , Rulis A. M. , Scoles G. , Aziz R. A. , Duquette G.
Published: February 2003

Molecular beam differential scattering measurements on the He–Ar system are reported. The results are used to study the unlike interaction (φ12) in gaseous mixtures. (AIP)
Metric geometry of equilibrium thermodynamics. II. Scaling, homogeneity, and generalized Gibbs–Duhem relations
Authors: Weinhold F.
Published: February 2003

It is shown that the classical Gibbs–Duhem relation can be regarded, in the abstract metric framework proposed recently, as expressing the obvious geometric impossibility of finding r + 1 linearly independent vectors in an r-dimensional space. Certain connections between generalized Gibbs–Duhem relations and permissible scaling hypotheses for thermodynamic potentials are noted.
Photoionization in dielectric fluids: Variation of alkyl composition at the donor site
Authors: Peterson S. H. , Yaffe M. , Schultz J. A. , Jarnagin R. C.
Published: February 2003

The yield of mobile charge carriers obtained by photoionization of solutions containing N,N,N′,N′ tetramethyl-, tetraethyl-, or tetrabutyl-paraphenylenediamine dissolved in tetramethylsilane, 2,2-dimethylbutane, cyclopentane, n-pentane, or n-hexane at room temperature was determined under comparable experimental conditions. The photoionization yield from the ethyl and butyl derivative was found to be as much as 100 times larger than the yield from the methyl derivative in each of the five fluids. The enhanced yield obtained with normal alkyl chains located at the donor site (attached environment) is opposite to the depression of yield obtained with normal alkyl hydrocarbons as solvent (unattached environment). The relative enhancement of photoionization was largest at lower excitation energy and decreased at higher excitation energy. The photoionization yield was found to exponentially increase with increasing photon energy along the lower energy rising edge of ionization up to about 5.5 eV in each fluid. At 5.5 to 5.6 eV, there was an abrupt decline in ionization yield for each donor independent of fluid. The enhanced photoionization from the ethyl and butyl substances enables levels of equal ionization to be attained at as much as 0.25 eV lower photon energy than for the methylated donor in each fluid. The density of electronic states of the fluid which are accessible from excited molecular states of donors have not contributed sufficient structure to the photoionization yield curves to permit identification of band tail states. The shape and breadth of the photoionization yield curves was consistent with an interpretation in which the charge transfer probability was largely determined by electron transfer matrix elements.
Vibrational relaxation of carbon monoxide using a pulse discharge. II. T=100, 300, 500 K
Authors: Powell H. T.
Published: February 2003

A cw probe laser is used to measure the time-dependent gain on vibrational transitions of CO following a weak, pulse discharge at 100, 300, and 500 K. From the time-dependent gain data, vibrational transfer rates are determined for endothermic processes CO(v)+CO(v=0) →CO(v−1)+CO(v=1) over the range v=2–7 at 100 K, v=2–11 at 300 K, and v=2–12 at 500 K. The measured rates exhibit a simple functional dependence on energy defect and temperature which is predicted by theories based on long-range interactions.
Second and third order hyperpolarizabilities of organic molecules
Authors: Levine B. F. , Bethea C. G.
Published: February 2003

We have used the technique of static field induced second harmonic generation in liquids to determine the second order hyperpolarizability β, and the third order hyperpolarizability γ, for a wide range of conjugated and nonconjugated organic molecules. The adequacy of the Onsager local field formulation was tested as was the accuracy of the bond additivity approximation. The large π-electron nonlinearities which are possible in substituted benzene molecules were investigated by measuring a large number of benzene derivatives and subtracting out the σ-electron contributions.
A CIDEP study of p-benzosemiquinone
Authors: Pedersen J. Boiden , Hansen C. E. M. , Parbo H. , Muus L. T.
Published: February 2003

Chemically induced dynamic electron polarization (CIDEP) from photolytically generated p-benzosemiquinone radicals is studied by time resolved steady state experiments. The experimental time resolved intensity curves are fitted to curved derived from theory. Two different polarization contributions are observed with ethylene glycol as solvent. A hyperfine independent initial polarization P∞(I) =−0.107 is due to a triplet mechanism (TM) and a hyperfine dependent polarization (−0.032?P*⩽0.032) is caused by a radical pair mechanism (RPM) due to the radical termination reaction. P∞(I) =−0.034 when isopropanol is used as solvent. The solvent dependence of P∞(I) is consistent with the microscopic theory and the observed values of P∞(I) are indicative of a triplet lifetime in the range 0.1–10 nsec and a zero field parameter ‖D‖≳700 G. The magnitude and hyperfine dependence of P* is in accord with the microscopic theory for an exponentially decaying exchange interaction J (r) with the maximum value J0≳109 rad/sec. The separation at which J (r) is decreased by a factor 105 equals the distance of closest approach (?6.5 Å).
Merging beams study of the D+(H2,H)HD+ and H2+(D,H)HD+ reaction mechanisms
Authors: Lees A. B. , Rol P. K.
Published: February 2003

Lab-energy distributions of HD+ ions formed in the D+(H2,H)HD+ reaction were measured with high resolution for collisions with relative energy W in the range 1 eV⩽W⩽5 eV. In addition to observing the transition from long- to short-lived collision complexes and the relative growth of repulsive interactions, we also observed the possible participation of charge transfer in the entrance channel of the reaction. The charge transfer contribution was suggested by independent study of the H2+(D,H)HD+ reaction, which follows predominantly direct interactions over the range 0.1 eV⩽W⩽10 eV. HD+ ions formed in the H2+(D,H)HD+ reaction have recoil energies in the same range as HD+ ions which appear as a distinct shoulder in the D+(H2,H)HD+ product distributions. For W⩾8 eV, the H2+(D,H)HD+ reaction yields a small fraction of H atoms which may be in an electronically excited state.
Quenching of vibrationally excited nitric oxide by molecular oxygen and nitrogen
Authors: Murphy R. E. , Lee E. T. P. , Hart A. M.
Published: February 2003

Vibrationally excited NO‡(X 2Π, v≳0) was produced by energetic electrons impacting on nitrogen–oxygen gas mixtures. The time decay of the NO‡ fundamental vibration–rotation bands in the presence of varying concentrations of N2 and O2 was measured. The quenching rate constants of NO(v=1) by N2 and O2 were determined to be kO2=2.4±1.5×10−14 and kN2=1.7±0.7×10−16 cm3 sec−1, respectively. Two quenching models are considered, independent and proportional to the vibrational level of the excited NO‡(v). If quenching of NO‡ by O2 is independent of v, the quoted rate constant kO2 becomes 75% larger. Computer intensity calculations of NO‡(Δv=1) are compared to radiometric intensity measurements. Intensity calculations using the uncertainty limits of the experimentally measured kO2 support the reliability of determined rate constants.
Dielectric dispersion in some polymers and polyelectrolytes: A model
Authors: Pollak M. , Pohl H. A.
Published: February 2003

A simple model is investigated for macromolecules which exhibit a giant dielectric constant and a dispersion region at unusually low frequencies. The model postulates a hopping mechanism of carriers along the linear macromolecule. A theory iseory is developed for the dielectric behavior of the model, and its dependence on frequency and on an applied dc bias field. The model does exhibit the experimentally observed large dielectric constant, as well as very long relaxations. Although many modes with different relaxation times are found to exist, only the mode with the longest relaxation time contributes significantly to the ac conductivity at small values of dc bias. The presence of a dc bias shortens the relaxation times for all the modes. In addition, the relative importance of the mode with the longest relaxation time decreases with increasing bias. The real part of the conductivity decreases at all frequencies as the bias increases. The real part of the dielectric constant, however, decreases at low frequencies, but can increase at high frequencies as the bias increases.
Hydrogen–atom scattering: Energy dependence of the total collision cross section for mercury
Authors: Stwalley William C. , Niehaus A. , Herschbach D. R.
Published: February 2003

Total collision cross sections for scattering of H and D atoms from Hg in the energy range 10−5–10−1 a.u. (3×10−4–3 eV) are calculated for an accurate Rydberg–Klein–Rees (RKR) potential based on isotopically-combined spectroscopic data for HgH, HgD, and HgT. Comparison is made with two sets of experiments, a subthermal energy (5×10−3–0.2 eV) study by the Genoa group, and a superthermal energy (0.14–1.7 eV) study at Harvard. The glory oscillations found in both studies and the orbiting resonances found in the subthermal experiments are in good agreement with the calculated cross sections.
On the importance of Ba(3D) as the key reactant leading to BaO(A–X) chemiluminescence in the Ba+N2O reaction
Authors: Wicke Brian G. , Revelli Michael A. , Harris David O.
Published: February 2003

Experiments have been performed to examine the importance of metastable Ba(3D) as the key reactant leading to BaO(A→X) chemiluminescence in the Ba+N2O reaction. It has been found that the steady state concentration of Ba(3D) increases substantially in the reaction of Ba with N2O; in contrast, the Ba(3D) steady state concentration decreases when O2 and NO2 are used as oxidants. By simultaneously monitoring the BaO(A→X) chemiluminescence and the Ba(3D) steady state concentration, it is shown that with the oxidant unchanged, an order of magnitude increase in Ba(3D) has no major effect (±15%) on the BaO(A→X) emission. These results restrict the role played by Ba(3D) in the reaction mechanism leading to A→X chemiluminescence.
Infrared and Raman spectra and structures of matrix isolated thallous halide dimers: Tl2F2 and Tl2Cl2
Authors: Lesiecki Michael L. , Nibler Joseph W.
Published: February 2003

Infrared and Raman spectra are presented for monomeric and dimeric thallous halide species (TlF, Tl2F2, TlCl, and Tl2Cl2) isolated in argon matrices. From these results it is concluded that both the Tl2F2 and Tl2Cl2 molecules have planar rhombic structures rather than linear configurations as previously proposed on the basis of mass spectroscopic, infrared, and photoelectron studies. Entropy calculations and other arguments are presented to resolve this discrepancy. Our structural conclusion for Tl2F2 is in good accord with a very recent electron diffraction investigation of Tl2F2 and the structural parameters and vibrational amplitudes obtained in that work are incorporated with our frequencies in a normal coordinate analysis. Force fields are obtained for both Tl2F2 and Tl2Cl2 and a very large amplitude (31°) is calculated for the out of plane bending coordinate of Tl2F2. Assuming that the bonding in this compound is largely ionic, an average instantaneous vibrational dipole moment of 3.7 D is deduced. This very large value in a ’’nonpolar’’ molecule is in good agreement with a novel electron scattering experiment on Tl2F2 molecular beams in which vibrational dipoles in the range 2–8 D were recently reported.
Rotational energy relaxation in molecular hydrogen
Authors: Rabitz Herschel , Lam S.-H.
Published: February 2003

Theoretical studies of rotational relaxation in para-hydrogen are presented. By using a set of theoretically deduced state-to-state rotational rate constants the master kinetic equations and the relevant fluid mechanical equations are solved numerically. Calculations are performed over the range 100⩽T⩽1100 °K to simulate conditions for free jet expansion, shock tube, and sound absorption experiments. The over-all rotational energy relaxation rates extracted from these calculations are compared with available experimental data and are shown to be in good qualitative agreement. The magnitudes and the temperature dependence of these rates depend critically on the degree and direction of the initial departure from equilibrium as well as the multilevel nature of the relaxation process. The apparent discrepancies in the measured rates from the different experiments are shown to be qualitatively self-consistent in light of the present calculations.
Fast metastable fragments produced by dissociative excitation of carbonyl sulfide
Authors: Van Brunt R. J. , Mumma M. J.
Published: February 2003

Dissociative excitation of OCS by electron impact has been studied using the method of translational spectroscopy. Time-of-flight distributions and excitation functions of the fast metastable fragments have been measured. The results are compared with similar measurements on CO2 and show that a variety of metastable fragments including CO(a 3Π), S(5S), O(5S) as well as long lived high lying atomic and molecular Rydberg fragments can contribute to dissociation.
Angular distribution of N+ from dissociative ionization of N2 near threshold
Authors: Van Brunt R. J. , Kieffer L. J.
Published: February 2003

Translational kinetic energy and angular distributions of N+ from dissociative ionization of N2 have been measured at electron energies close to threshold. For electron energies above 50 eV the energy distributions agree favorably with earlier measurements of Kieffer and Van Brunt. The ion energy distributions at electron energies below 50 eV are dominated by a feature peaked at a kinetic energy below 1 eV in agreement with recent measurements of Locht et al. For electron energies closest to threshold the angular distribution of N+ associated with this feature is consistent with the previously proposed mechanism involving excitation of the C 2Σ+u state followed by predissociation. At higher electron energies the degree of anisotropy increases and then rapidly decreases suggesting a significant contribution from direct excitation to the 4Σ+g repulsive state of N+2 leading to fragments in their ground states.
Optically detected magnetic resonance spectra of the lowest triplet state of 1-iodonaphthalene in durene at zero and high magnetic fields
Authors: Kothandaraman G. , Pratt D. W. , Tinti D. S.
Published: February 2003

This paper describes the results of optically detected magnetic resonance (ODMR) experiments on photoexcited 1-iodonaphthalene (1IN) in a durene host crystal at liquid helium temperatures. The structure observed in both the zero-field (zf) and high-field ODMR transitions is interpreted in terms of a spin Hamiltonian which includes the complete iodine (I=5/2) nuclear quadrupole and hyperfine interactions. Principal values of D (including the absolute signs), P, AI, and estimates of the direction cosine matrices and the components of g are reported. It is concluded from this analysis that (1) the lowest triplet state of 1IN is principally (π,π*) in character but (2) is contaminated by slight admixtures of charge-transfer configurations; (3) the zf parameters of triplet 1IN are considerably perturbed from those of 3B2u naphthalene and presumably reflect the increased importance of second-order spin–orbit contributions to D in the presence of the heavy-atom substituent; and (4) 1IN occupies two magnetically inequivalent sites in the durene lattice which are not substitutional.
Resonance Raman spectra and structure of some complex nitroaromatic molecules
Authors: Kumar Kamal , Carey Paul R.
Published: February 2003

Resonance Raman spectra are reported for several biologically important nitroanilines and nitrophenols. The data provide new insight into intramolecular interactions in highly conjugated nitroaromatics. In certain ortho substituted compounds the data provide evidence for structural changes in going from the ground to the excited electronic state, or states, probed by the resonance Raman experiment. In each compound several Raman bands show variation of intensity with excitation wavelength. For N-methyl-o- nitroaniline excitation profiles for some isolated bands appear to peak at the maximum of the electronic absorption band at 442.0 nm. Experimental intensity profiles are compared to the presently available theories.
Comments on a new class of ionic materials
Authors: Cohen Morrel H. , Jortner Joshua , Thompson James C.
Published: February 2003

We consider the cohesion and electronic structures of a new class of ionic compounds including Na2C18H36N2O6 and NaC18H36N2O6I.
Time dependent variational approach to semiclassical dynamics
Authors: Heller Eric J.
Published: February 2003

Explicitly time dependent methods for semiclassical dynamics are explored using variational principles. The Dirac–Frenkel–McLachlan variational principle for the time dependent Schrödinger equation and a variational correction procedure for wavefunctions and transition amplitudes are reviewed. These variational methods are shown to be promising tools for the solution of semiclassical problems where the correspondence principle, classical intuition, or experience suggest reasonable trial forms for the time dependent wavefunction. Specific trial functions are discussed for several applications, including the curve crossing problem. The useful semiclassical content of the time dependent Hartree approximation is discussed. Procedures for the variational propagation of density matrices are also derived.
The 3d→4s bands of transition metal ions in LiF and NaF
Authors: Chase D. Bruce , McClure Donald S.
Published: February 2003

The absorption spectra in the range 5–10 eV for divalent transition metal ions in the host crystals LiF and NaF are presented. Several features of the spectra show that most of the bands observed are well described as 3d→4s transitions. Thus, the effect of reducing the lattice constant of the host crystal is to increase the transition energy; the intensities of the transitions are low and are dependent on temperature or on the presence of a local charge compensator. The variation of transition energy with atomic number follows that of the free ions. Detailed assignments of the bands are discussed.
Extended, optimized Gaussian bond functions for nitrogen
Authors: Vladimiroff T.
Published: February 2003

Two sets of 1s, 2px, and 2py bond functions are used to describe the nitrogen triple bond. A local minimum in the energy was found at ζs=1.17, ζs′=0.28, ζp=1.11, and ζp′=0.38. The calculated energy, −108.9727 a.u., is comparable to that obtained by a more lengthy calculation using a double set of optimized 3d polarization functions placed on each atomic center. One-electron properties, however, were found to be somewhat inferior.
Solution to the equation describing diffusion with simultaneous energy sinks and sources and the extraction of the diffusion coefficient
Authors: Gates J. V.
Published: February 2003

The solution to a macroscopic diffusion equation is presented in which a quantity diffuses in a media to or from the surface and is absorbed and or generated by multiple distinct first order processes having different rate constants. After some initial time period an experimentally controlled first order process is removed and the system is solved in the presence of diffusion and the remaining processes. A simple normalization method is presented by which the numerical value of the bulk diffusion coefficient can readily be extracted from experimental data, assuming certain conditions are satisfied.
A note on two-dimensional nematic systems
Authors: Kleman M. , Ryschenkow G.
Published: February 2003

Quasi-two-dimensional nematic systems have been achieved with the help of low anchoring energy substrate recently discovered. These 2-D nematics display two particular types of stabilization of order, according to the equilibrium angle of the director with the normal to the substrate. We show theoretically in this article that (i) When this angle is different from zero, stabilization is obtained by the long range fluctuations of this angle. The coherence length of these fluctuations is of the order of the mean distance between defects, which are therefore likely to be equilibrium defects; (ii) when the contact between the nematic and the substrate is homeotropic, stabilization occurs by the highly degenerate fluctuations in ϑ (azimuthal angle), which are now strongly coupled to the fluctuations in φ. These two fluctuations have now the same coherence length, while the coherence length in ϑ, ξϑ, is much larger than ξφ in the case (i).
Frenkel excitons interacting with phonons
Authors: Nakamura Akira
Published: February 2003

Energy eigenvalues of excitons interacting with optical phonons are calculated variationally both for the ground state and for the higher excited states. A perturbation expansion is employed by assuming the (renormalized) exciton transfer energy to be small compared to the energies of optical phonons. It is shown that the ’’unsymmetric narrowing’’ of the exciton bands due to interaction with phonons appears also in higher excited states in the exciton momentum representation. However, in the total (exciton plus phonon) momentum representation, each higher excited state energy band forms a scattering continuum which makes explicit ’’unsymmetricity’’ of the band narrowing indistinguishable. When exciton–phonon coupling is strong enough, exciton band energies lie outside the band of free exciton plus free phonon states. The criterion for this is J/ω<g2/[1+exp(−g2)], with J, ω, and g representing, respectively, half of the free exciton bandwidth, phonon frequency, and exciton–phonon coupling constant parameter.