bluuebunny/crossref_metadata_2025 huggingface dataset:
Collision-induced ion-pair formation of CsCl and Cs2Cl2
Authors: Sheen S. H. , Dimoplon G. , Parks E. K. , Wexler S.
Published: February 2003

Absolute cross sections have been determined for collision-induced ion-pair formation of cesium chloride (monomers and dimers) from collisions with Ar, Kr, and Xe atoms. The rare gas atoms were aerodynamically accelerated in H2, with maximum energies of 6.8, 12.1, and 18.3 eV (in the laboratory frame), respectively. Time-of-flight mass spectrometry permitted the determination of partial cross sections for each ion channel resulting from the collision. For the monomer, the cross secions for the channel leading to Cs++Cl− were similar in magnitude for the three rare gas atoms and were approximately 3×10−16 cm2 at 3 eV above threshold. The rearrangement ionization channel leading to CsM+ (M=Ar, Kr, and Xe) exhibited a step behavior at threshold followed by a very rapid fall off at higher collision energies. Collisions with the dimers produced both Cs2Cl++Cl− and Cs++CsCl−2 but no detectable ions containing the rare gas atoms. The magnitude of the cross sections for the Cs2Cl+ channel varied significantly with the rare gas although the corresponding thresholds were similar. In the case of CsCl−2, however, the magnitudes of the cross sections were similar, but the thresholds varied. A possible explanation for this difference in behavior is given based on simple dynamical models. The cross sections for each product ion from both the monomer and dimer (except for CsM+) exhibited a power-law rise with increasing energy σ=const× (Etot−E0)n/Erel up to about 1–1.15 eV above threshold, where Etot is the total energy, E0 the threshold energy, and Erel the relative kinetic energy. Values of n and E0 were determined for each system. The threshold for each reaction M+CsCl→M+Cs++Cl− was determined most accurately from the peak in the CsM++Cl− excitation function, which occurs (after energy deconvolution) at the threshold for collision-induced dissociation.
High-pressure ultrasonic investigation of the order–disorder transition in ND4Cl
Authors: Garland C. W. , Gorodetsky G. , Zahradnik C.
Published: February 2003

The adiabatic elastic constant c11 has been measured in single-crystal ND4Cl at high pressures. Data were obtained in the range 220–300 K and 0–7 kbar, with special emphasis on the vicinity of the order–disorder transition line. From a comparison with previous measurements, it can be seen that the temperature dependence of c11 in the disordered phase is quite sensitive to deuteration and to pressure while the temperature dependence of the heat capacity is not. This difference in the behavior of the thermal and mechanical properties can not be understood in terms of the compressible Ising model.
Magnetic properties of linear chain systems: Metamagnetism of single crystal Co(pyridine)2Cl2
Authors: Foner S. , Frankel R. B. , Reiff W. M. , Wong H. , Long Gary J.
Published: February 2003

The metamagnetic behavior of the low temperature properties of single crystal Co(pyridine)2Cl2 is discussed. At 1.25 K oriented single crystals exhibit a two-step metamagnetic transition at applied fields ∼0.8 and 1.6 kG along the b-axis, a single transition at ∼0.7 kG for applied fields along the a* axis, and a single transition at ∼4.2 kG for an applied field along the c axis. Just above the transition fields a moment of 2μB/Co atom is measured for B0 parallel to the a* axis or b axis, and 0.4μB/Co atom is measured for the B0 parallel to the c axis. A large field dependent moment is observed at high fields. Many features of this compound closely mirror the behavior of CoCl2⋅2H2O. However, the Co(pyridine)2Cl2 has a much smaller interchain exchange, so that many features can be examined at lower fields. The basic features are consistent with a six-sublattice model for the ordered antiferromagnetic system. Measurements of magnetic moment versus temperature show that Co(pyridine)2Cl2 does not obey a Curie–Weiss law even at relatively high temperatures.
An optical study of the temperature dependent scattering of the a exciton (polariton) of naphthalene
Authors: Robinette S. L. , Small G. J. , Stevenson S. H.
Published: February 2003

High resolution (∼0.1 cm−1) one-photon absorption profiles of the a band of naphthalene at 31 475 cm−1 from pure strain-free mounted (PSF) crystals have been measured between ∼2 and 40 K. Low temperature linewidths (FWHM) as narrow as 0.4 cm−1 have been observed. The a band profile exhibits an asymmetry which increases with the temperature. The high E side is close to Lorenztian at all temperatures (particularly for T≳8 K) and tails more steeply than the low E side. Arguments are presented for the asymmetric line shape being homogeneous so that the T-dependent FWHM are a direct measure of the transverse optical dephasing (T2) of the a exciton. The data and theory are consistent with the exciton–phonon scattering contribution to T2 being due to low frequency (ωeff∼15 cm−1) acoustical phonons. However, existing theories on asymmetric but homogenous exciton line shapes fail to account for the observed asymmetries.
Raman spectra from the internal vibrations of NH+4 ions in NH4Ag4I5
Authors: Gallagher David A. , Klein Miles V.
Published: February 2003

The internal vibrations of NH+4 ions in the fast-ion conductor NH4Ag4I5 have been studied by Raman spectroscopy. Bands due to the four normal modes of NH+4 have been observed along with some second order combination bands. The spectra are similar to those of the high temperature or α phase of NH4I, and at 17 K the spectra of NH4Ag4I5 resemble the spectra of supercooled α-NH4I, or, more precisely, the spectra of a dilute solution of NH+4 in KI.
Angular correlations in linear copolymers from the compositional dependence of their dipole moments. V. Solvent–polymer interactions
Authors: Smith F. H. , Work R. N.
Published: February 2003

Mean square effective dipole moments μ2e per structural unit have been determined at 298 K from a set of poly(4-chlorostyrene, 4-methylstyrene) copolymers, P (4CS,4MS), in p-xylene solutions containing 10 mole % copolymer. Coefficients which are related to local chain conformations have been evaluated from an expansion of the dipole moment ratio R (x) =μ2e(x)/μ2e(1) into a series of linearly independent functions of the mole fraction x of 4 CS units in the copolymer. The coefficient of the quadratic term, F2=1.01±0.06, obtained from these solutions is compared with the value 1.36±0.09, reported previously for the same set of copolymers in the undiluted state at 428 K. Extrapolations based on smoothed temperature coefficients which were derived from measurements in the range 360 to 440 K, yield a value F2=1.15±0.04 for the undiluted copolymers at 298 K. Uncertainties are standard deviations. It is argued that the copolymer method is relatively immune to the usual difficulties of determining dipole moments of molecules in condensed matter because it is framed in terms of ratios of experimental values of effective dipole moments. It is therefore suggested that the observed difference in values of F2 at 298 K reflects a difference in the local chain conformations resulting from the difference in the ’’solvent’’–polymer interactions in the two cases. Approximate values of the Kirkwood correlation factor g=μ2e/μ21 of P4CS, where μ1 is the moment of an equivalent freely orienting 4CS unit, are calculated from our results and compared with values obtained by others. This comparison supports the finding of Burshtein and Stepanova that g of P4CS increases toward unity as the thermodynamic quality of the solvents increase. We suggest that the copolymer method may provide a reliable means of separating a local component from the long range (excluded volume) dimensional changes that occur with changes of solvents.
A new approach to the study of reversible excited-state electron-transfer reactions
Authors: Wight C. A. , Turley T. J. , Demas J. N.
Published: February 2003

Reversible excited-state electron-transfer reactions represent a theoretically and experimentally important class of photochemical reactions. The theory of a new method for studying these sytems is presented. The technique permits simultaneous measurement of the thermal back electron-transfer rate constant (kth) and the probability of detectable excited-state electron transfer per quenching encounter (φet). The method is rapid, inexpensive, and simple to implement; it can work well even when kth is at the diffusion controlled limit. A suitable experimental arrangement is described along with the effects of experimental errors.
The anisotropy in the magnetic susceptibility of poly-γ-benzyl-L-glutamate
Authors: Tohyama Kohji , Miyata Nahonori , Honda Mitsuo
Published: February 2003

It is well known that the helical axis of the poly-γ-benzyl-L-glutamate(PBLG) molecule is oriented parallel to the magnetic field in certain solvents where the solution forms a liquid crystal phase and the PBLG molecules are α helices. This phenomenon is indicative of the existence of magnetic anisotropy in the PBLG molecules. We have measured the anisotropy in the diamagnetic susceptibility of an oriented PBLG film using a high sensitivity torque magnetometer. Also, the distribution function of the molecular axes of PBLG in the film was determined using x-ray diffraction. The value of the anisotropy of the susceptibility for the PBLG molecule was found to be 9.40×10−8 emu/g. The magnetic anisotropy of PBLG and poly-γ-ethyl-L-glutamate molecules is compared.
Calculation of nonlinear electric susceptibilities of aromatic hydrocarbons
Authors: McIntyre Eugene F. , Hameka Hendrik F.
Published: February 2003

We calculate the molecular and space-fixed nonlinear third-order electric susceptibilities of a group of aromatic hydrocarbons. We find large negative susceptibility values for benzoquino- and naphthoquino dimethanes and we recommend that these and similar molecules be further investigated.
The Glauber approximation in molecular scattering. II. Rotational excitation by electron impact
Authors: Gianturco F. A. , Lamanna U. T. , Rahman N. K.
Published: February 2003

The Glauber amplitudes for anisotropic potentials that originate from the local part of the electron–molecule interactions are examined in detail and presented in a final form which is directly suitable for numerical treatment. The various choices for the z axis are also examined and the one now most commonly employed in atomic scattering is selected. The case of rotational excitation from pure quadrupole scattering is examined for a wide variety of Q values and their effects on the form of the corresponding differential cross sections for inelastic transitions are discussed in detail.
Raman line shape study of the ν1 band of chloroform in a polar solvent
Authors: Moradi-Araghi A. , Schwartz M.
Published: February 2003

The polarized and depolarized spectra of CHCl3 in CD3CN (and CDCl3 in CH3CN) were utilized to obtain reorientational and vibrational relaxation correlation functions for the carbon–hydrogen stretching mode. The effect of the polar solvent on molecular reorientation is discussed and compared with earlier studies performed in nonpolar solvents. The recently proposed model of vibrational dephasing has been applied to analyze the isotropic correlation functions obtained for these systems, and an explanation has been proposed to interpret the anomalously greater efficiency of vibrational relaxation for the ν1 mode in CHCl3, compared to that observed in CDCl3.
Lattice dynamics of solid ammonia
Authors: Righini Roberto , Klein Michael L.
Published: February 2003

The zero wave vector k=0 lattice vibrational frequencies of solid NH3 are calculated using atom–atom models for the short range intermolecular forces, a point charge model for the electrostatic interactions, and the correct dispersion interaction for large intermolecular separations. Comparison is made with available infrared and Raman data. An estimate is also made of the anharmonic contributions to the librational modes.
Determination of the density profile in the liquid–vapor interface near the triple point
Authors: Lu Bo Ching , Rice Stuart A.
Published: February 2003

The density profile in the transition region between liquid and vapor Hg has been determined, at room temperature, from a study of the angular dependence of the reflection of Cr Kα x rays. This profile ρ (Z) has a hyperbolic tangent form with width L=5.6±0.5 Å, where L≡−(ρL−ρG)[dρ (Z)/dZ]−1Z=0, with ρL and ρG the densities of liquid and vapor, respectively. The nature of the profile and the value of L are compared with the corresponding quantities obtained from computer simulations of the surface of liquid Ar. For liquid Hg, L is dominated by a static structural contribution fundamentally traceable to the nonzero wavelength of the electrons and their influence on the effective ion–ion potential. For liquid Ar, L is dominated by the contribution from thermal motion. The currently available theory of the liquid metal surface transition zone predicts a value for L which is too small by a factor of 2. This discrepancy, the role of surface capillary waves in broadening the transition zone, and the possible relationship of the structure of the transition zone to the stability of the liquid are discussed.
Matrix radiolysis and photoionization of CFCl3. Infrared spectra of CFCl+2 and the parent cation
Authors: Prochaska Frank T. , Andrews Lester
Published: February 2003

The ’’Freon’’ compound CFCl3 has been subjected to radiolysis and photoionization during condensation with excess argon at 15 K. Infrared spectra of the matrix samples identified stable and free radical products and new absorptions which are attributed to charged species. The molecular ion bands exhibited three different behavior patterns on filtered mercury arc photolysis: The most photosensitive bands, destroyed by 420–1000 nm light, are assigned to the parent cation; several absorptions which photodissociated with 290–1000 nm radiation are due to a molecular anionic species; and new bands reduced by 220–1000 nm light are assigned to the daughter cation CFCl+2. The vibrational assignments were confirmed by carbon-13 substitution.
Study of the stationary state of dissociating dimers in nonisothermal ideal gas phase
Authors: Lengyel S.
Published: February 2003

The binary ideal gas closed system of the dissociating–recombining components dimer A2 and monomer A is studied in nonisothermal stationary state. The stationary form of the internal energy transport equation for this system is div-gradΓ=0, with Γ (T) =ℱTT0λudT where the conductivity coefficient of internal energy flow λu is a function of the variables: temperature, partial pressures in and heat conductivity of the mixture, enthalpy of dissociation, binary diffusion coefficient, and thermal diffusion ratio. A method for calculating the following variables and functions characterizing the steady state is given: equilibrium composition, net reaction rate, component mass fluxes, internal energy flux, reduced heat flow, and chemical contribution to energy transport.
Rotation–vibration symmetry correlation in bimolecular reactions: Building-up principle from molecular fragments
Authors: Metropoulos Aristophanes , Chiu Ying-Nan
Published: February 2003

A rotational–vibrational symmetry correlation scheme between an intermediate reaction complex and the corresponding reactant or product fragments is proposed. The emphasis is on the symmetry of the eigenfunctions at both limits: the fragments at infinite separation and the complex as a molecule. Because of the introduction of rotation, the permutation-inversion group rather than the usual point group is taken as the symmetry group of the rotating and vibrating fragments and its symmetry species are correlated to the point group species of the complex. Correlations are presented for the systems AB–AB, A2–A2, B2–A2, A–A2, and B–A2 at various symmetric configurations without any consideration given to the energetics of the reactions. This general approach makes the scheme useable for a variety of reactions. It also provides the building-up principle for the rotation–vibration states of polyatomic molecules. Application to the O2–O2 dimer formation is discussed.
The origin of surface waves
Authors: Jhon Myung S. , Desai Rashmi C. , Dahler John S.
Published: February 2003

The broken symmetry concept of Goldstone is applied to an inhomogeneous fluid. Specific calculations are performed for the liquid–vapor interface of a simple fluid. The collective variable associated with the breaking of spatial symmetry is the normal displacement of the interface from its equilibrium position. The static correlation function of this variable exhibits long-range order. Associated with this symmetry breaking variable are propagating modes. The dispersion relation for these surface modes is found to be identical with the hydrodynamic result for capillary waves.
Dissociative attachment of halogen molecules by 0–8 eV electrons
Authors: Tam Wing-Cheung , Wong S. F.
Published: February 2003

Dissociative attachment of I2, Br2, Cl2, and F2 have been studied with an electron impact mass spectrometer. In the energy range 0–8 eV the formation of I−, Br−, and Cl− all show a sharp peak at zero energy and two broader peaks at higher energies. Only a single F− peak is observed near zero energy. Using symmetry considerations and correlations to photoelectron spectra, we interpret the negative ion peaks observed in I2, Br2, and Cl2 as due to the 2Πg, 2Πu, and 2Σ+g core–excited resonances, respectively, while the single peak in F2 is due to the 2Σ+u shape resonance.
Coherence vs incoherence in stepwise laser excitation
Authors: Shore Bruce W. , Johnson Michael A.
Published: February 2003

We demonstrate the manner in which solutions of the (coherent) Schrödinger equation for multistep excitation approach those of an (incoherent) rate equation. For a two-level system, coherence produces oscillations about the mean rate-equation values. In more general N-level sequences the two types of solutions agree in the limit described by Ackerhalt and Eberly. We point out instances in which a simple rate equation cannot duplicate results of the Schrödinger equation.
Ligand trajectories for a degenerate Jahn–Teller system
Authors: Judd B. R.
Published: February 2003

The trajectories of the six ligands of the octahedral Jahn–Teller (JT) system T1⊗ (ε+τ2), in which the two modes ε and τ2 possess equal frequencies and are equally coupled to the electronic T1 state, are determined in the limit when the JT interaction is large compared to the kinetic energies of the ligands. They are found to correspond to a fast elliptical motion, characteristic of a classical harmonic oscillator, superposed on a slow circular rotational motion. The eccentricities, magnitudes of the major and minor axes, and directions of the normals to the planes of the ellipses change as the circular paths are followed. Elementary derivations are given for the energies of the rotational bands.
Magnetic properties, Schottky heat capacity, and the nuclear quadrupole splitting of the 8.42 keV excited state of Tm3+ on tetragonal sites in CaF2
Authors: Neogy D. , Chatterji A.
Published: February 2003

A crystal field (CF) calculation of the principal magnetic susceptibilities, the Schottky heat capacity, and the nuclear quadrupole splitting of the 8.42 keV excited state of the Tm3+ ion on tetragonal sites in CaF2 has been carried out in the intermediate coupling approximation. The CF parameters used were those given by Muto who obtained them from the analysis of the absorption spectra of the excited states. Our analysis gives a doublet as the ground state in the Stark pattern of the 3H6 ground manifold which is in contradiction with that stated by Muto. Though the thermal variation of the magnetic anisotropy K∥–K⊥ is similar to that of thulium ethylsulfate (TmES), the sign is positive whereas for the latter it is negative. The behavior of the square of the effective Bohr magneton number (p2eff) is similar to the case of TmES but the magnitude at very low temperatures is much larger since a doublet lies lowest. The Schottky heat capacity Cs shows a peak at 85 K similar to that of TmES but the height of the peak is much lower than that for TmES. The thermal variation of the nuclear quadrupole splitting 〈ΔEQ〉T is seen to be quite different from that of TmES but similar to the case of Tm2O3 except for the magnitudes. Experimental determination of the various quantities is suggested as a check on the CF proposed by Muto.
A one-dimensional model for exciton motional correlation effects in dense triplet exciton systems
Authors: Chesnut D. B. , Bondeson S. R.
Published: February 2003

A model for motional correlation effects of random-walking particles with spin in one dimension is developed. For a system of particle site density ρ, the hard sphere interactions between particles are modeled by considering a single particle moving on a line segment of length ρ−1 undergoing perfectly elastic reflective collisions at the end points of the lattice; the collision rate is used to determine the spin exchange rate. The model is applied to proton spin–lattice relaxation in the MTPA(TCNQ)2 triplet exciton ion radical salt. Using mean theoretical estimates for the anisotropy parameters, a jump rate νj is calculated indicative of an activated process with an activation energy of approximately 0.12 eV ith a preexponential factor of the order of 1.5×10+14 Hz. Limitations and extensions of the model are discussed.
The structures of c
i
s-polyacetylene and highly conducting derivatives
Authors: Baughman R. H. , Hsu S. L. , Pez G. P. , Signorelli A. J.
Published: February 2003

The structures of cis-polyacetylene and polyacetylene–iodine derivatives have been investigated by x-ray diffraction and crystal packing analysis. Results obtained for cis-polyacetylene are consistent with the space group Pnma with one CH per asymmetric unit and a chain symmetry (m1̄)t. Hence, the structure is analogous to that of orthorhombic polyethylene. For a structure with such a concentration of π electrons there is minimal overlap between parallel π orbitals. The π orbitals are almost orthogonal for four of the six closest neighbors of a given chain. Based on x-ray diffraction and spectroscopic results, a model is proposed for the structure of the highly conducting polyacetylene–iodine complexes. According to this model, linear arrays of polyhalide ions (principally in the form of I−3) substitute in positions of displaced polyacetylene chains. At high dopant concentrations, alternate close-packed layers of polyacetylene are separated by a layer consisting of such polyhalide arrays. This model predicts a limiting charge transfer of 0.11 electron on the average per carbon atom in the polyacetylene chain.
Geminal nuclear spin–spin couplings in ABn-type molecular systems
Authors: Hiroike Eiko
Published: February 2003

An approximate formula for the second-order perturbation energy previously obtained by the author is applied to the calculation of geminal nuclear spin–spin couplings in ABn-type molecular systems. It is shown why the electron correlation is unusually important in the geminal couplings. The signs of cis and trans geminal couplings are discussed for the AB6-type molecular systems.
An ESR study of the CH2ClCȮ radical at 77 K in x-irradiated chloroacetamide crystals
Authors: Kalyanaraman B. , Kispert L. D.
Published: February 2003

X-irradiation of chloroacetamide crystals at 77 K yields at least two radicals which are not stable near 300 K. One of these give rise to a four line ESR spectrum due to two nonequivalent protons with the principal hyperfine tensor components for H (1) equal to 268.4, 260.3, and 256.1 MHz and for H (2) equal to 129.9, 109.7, and 109.9 MHz. The principal g values are gmax=2.0674, gint=2.0144, and gmin=1.9909. Comparing the corresponding direction cosines to selected molecular directions obtained from an x-ray crystal structure as well as deuteration studies suggests the species to be the π-radical CH2ClCȮ. The unpaired electron is largely distributed between the oxygen and carbon 2p orbitals whose symmetry axis lies perpendicular to the CCO plane. Crystallographically, the chlorine atom lies nearly in the CCO plane and does not give rise to any resolvable ESR hyperfine couplings. The second radical gives rise to a complex ESR spectrum which has been tentatively assigned as due to ⋅CH2Cl. This radical decays upon warming above 100 K with the resultant formation of ĊHClCONH2.
Light scattering from spheroids in shear flows. I. The orientation correlation
Authors: Cohen Claude , Leal L. Gary
Published: February 2003

The time dependent orientation distribution function for ellipsoids of revolution (a,b,b) in shear flow is obtained as an expansion in terms of the parameter r=[1−(b/a)2]/[1+(b/a)2]. Our results reduce to Peterlin’s steady state results at infinite time (t=∞). Using this distribution, the orientation correlation function and its contribution to the light spectrum of polarized light are calculated. The results for the correlation function as an expansion in r lead also simultaneously to an expansion in the ratio σ of the shear rate to the Brownian rotation diffusion coefficient, σ=γ/D. The expansion procedure is thus valid for reasonably high shear rates in the case of nearly spherical spheroids (r≪1) or for small shear rates but large values of r (‖r‖?1, rods and disks).
Exchangeable proton couplings in free radicals: Radiation products of hydroxyproline HCl
Authors: Ko Ching-Lung , Box Harold C.
Published: February 2003

Free radicals were generated by X irradiation in single crystals of hydroxyproline HCl irradiated at low temperature. Proton hyperfine couplings were deduced from ENDOR measurements on two species, namely, a primary reduction product and a secondary free radical formed in a hydrogen abstraction process. These two radicals are representative of two general types of radicals, one nearly planar and the other markedly pyramidal, in which the unpaired electron interacts with nonexchangeable β protons attached to carbon and exchangeable β protons attached to oxygen. The characteristics of the hyperfine coupling tensors of these protons are discussed.
Theory of elasticity of polymer networks. II. The effect of geometric constraints on junctions
Authors: Erman Burak , Flory Paul J.
Published: February 2003

The effects of junction–chain interactions in a real network are analyzed in terms of a model in which the entanglements restricting fluctuations of the junctions are represented by vertical-wall potential domains. Within these domains the junctions are allowed to fluctuate freely. The domains are assumed to transform linearly with macroscopic strain. The additional stress that arises due to the restrictions on the fluctuations of junction points accounts for the principal departures of experimental stress–strain curves from phantom-network theory. The size of the entanglement domain, which is the only arbitrary parameter introduced, measures the deviations of the real network from phantom network theory. Calculations based on this model show the reduced force to be approximately independent of strain in the compression region (α<1) and to decrease approximately linearly with the reciprocal of the elongation α in tension (α≳1) over the range accessible to experiment.
A Monte Carlo study of the classical octopolar solid
Authors: O’Shea Seamus F.
Published: February 2003

A Monte Carlo simulation of the effect of temperature on the structure of the classical octopolar solid predicts the existence of three phases. The structures are identical with those predicted by the molecular field method but the transition temperatures are significantly different. Results are also given for the energy, specific, and lattice correlation functions as a function of temperature.
Free atom core binding energies from X-ray photoelectron spectroscopy. II. Na, K, Rb, Cs, and Mg
Authors: Banna M. S. , Wallbank B. , Frost D. C. , McDowell C. A. , Perera J. S. H. Q.
Published: February 2003

Gas phase photoelectron spectra of sodium, potassium, rubidium, cesium, and magnesium have been obtained with AlKα radiation. The binding energies measured are: Na 1s (1079.1 eV), K2p (303.2 eV, 300.5 eV), Rb 3p (254.3 eV, 245.4 eV), Cs 3d (745.8 eV, 731.8 eV), and Mg1s (1311.5 eV). Experimental and theoretical values from the literature have been compared with our results. The free atom binding energies were found to be greater than the comparative solid state binding energies; the differences being: Na 5.1 eV, K 3.6 eV, Rb 3.4 eV, Cs 3.4 eV, and Mg 4.8 eV. The multielectron excitation satellites present in the spectra of these atoms are also discussed.
High-temperature vibrational–rotational relaxation in He–H2
Authors: Tarr Susan M. , Rabitz Herschel
Published: February 2003

The vibrational–rotational relaxation of He–H2 at high temperatures is studied by applying a recently developed exponential distorted wave (EDW) technique to calculate inelastic cross sections. Particular attention is given to the role of the high rotational states in vibrational relaxation; transfer through these states is shown to be important at high temperatures. For conditions simulating He–H2 shock tube experiments, a single exponential decay is found to describe the n=0→n′→1 vibrational relaxation for all time. It is shown that this fortunate circumstance, which is important in the interpretation of such experiments, does not necessarily extend to other widely differing experimental conditions.
Electron spin echo modulation studies of silver atom solvation and desolvation in ice matrices
Authors: Narayana P. A. , Becker David , Kevan Larry
Published: February 2003

Electron spin echo modulation patterns have been obtained at 4.2 K and analyzed for desolvated silver atoms produced at 4.2 K by radiolysis of deuterated ice matrices containing AgF and for solvated silver atoms produced by brief warming to 77 K. The analysis shows that desolvated Ag0 is surrounded by eight equivalent deuterons at 3.1±0.1 Å which suggests a tetrahedral model of four waters with their dipoles pointed away from Ag0 (i.e., a solvated Ag+ geometry). Solvated Ag0 appears to be formed by rotation of one or two waters around one of their OD bonds to put one or two deuterons at ∼1.8 Å from Ag0. These close deuterons do not contribute to the echo modulation pattern because the nuclear splitting is larger than the microwave magnetic field, and the remaining six or seven deuterons at 3.1 Å produce the modulation pattern.
Faddeev–UPE theory and the three 4He-atom system: Bound states and zero-energy atom–diatom scattering
Authors: Lim T. K. , Duffy Kathleen
Published: February 2003

Faddeev–UPE theory is applied to the trimer bound states and atom–diatom scattering of 4He. (4He)3 has two bound states while the scattering length of 4He– (4He)2 is 207 Å.
The structure of the HeI2 van der Waals molecule
Authors: Smalley Richard E. , Wharton Lennard , Levy Donald H.
Published: February 2003

The rotational structure of the fluorescence excitation spectrum of the B (v′=10) ←X (v″=0) transition of the van der Waals molecule HeI2 has been measured and analyzed. The analysis indicates that the molecule has a nonlinear equilibrium structure with R′=4.79±0.22 Å and R″=4.47±0.13 Å, where R is the perpendicular distance from the helium atom to a line drawn through the iodine atoms.
On the crystallization of macroionic solutions
Authors: Hastings Roger
Published: February 2003

The Kirkwood theory of solutions of spherical ions is applied to aqueous solutions of macroions plus counter ions and to macroions in strong salt solutions. It is shown that the theory exhibits a mean field phase transition which is interpreted as a transition to the crystalline phase. The theory provides a qualitative explanation of the solidification recently observed in polystyrene sphere and spherical virus solutions. For fixed macroion charge the results are shown to be only weakly dependent upon salt concentration.
Calculation of spin–lattice relaxation during pulsed spin locking in solids
Authors: Rhim W.-K. , Burum D. P. , Elleman D. D.
Published: February 2003

The spin–lattice relaxation time has been calculated for dipolar solids when the spins are locked by an rf pulse sequence with pulses of arbitrary angle and finite width. Expressions are given for the homonuclear case in general and for the heteronuclear case in the δ-function limit. The results for the homonuclear case are experimentally confirmed using solid C6F12. The analysis shows that for small pulse angles, at which the direct spin heating effect is known to be small, the relaxation behavior will be identical to the cw irradiation case.
Free-atom core binding energies from x-ray photoelectron spectroscopy I. Zinc and cadmium
Authors: Banna M. S. , Frost D. C. , McDowell C. A. , Wallbank B.
Published: February 2003

Gas phase photoelectron spectra of zinc and cadmium have been obtained with AlKα radiation. The binding energies measured are: Zn2p1/2 (1052.3 eV), Zn2p3/2 (1029.1 eV), Cd3d3/2 (418.8 eV), and Cd3d5/2 (412.0 eV). Combining x-ray emission data on the solid with free atom optical energy results gives binding energies in close agreement with our values. A decrease of 2.8 eV for Zn2p and 3.3 eV for Cd3d was found in going from the free atom to the metal. This difference is discussed in relation to the various calculations of extra atomic relaxation energies in solids.
Bound atom–diatomic molecule complexes. Anisotropic intermolecular potentials for the hydrogen–rare gas systems
Authors: Dunker Alan M. , Gordon Roy G.
Published: February 2003

Spectra of the van der Waals complexes H2–Ar, Kr, Xe, and D2–Ne have been analyzed to obtain anisotropic intermolecular potentials and transition dipole moments. The Morse-spline–van der Waals functional form is used to describe the potentials. Eigenvalues were computed by solving the close coupling equations, and calculated transition frequencies were fit to the experimental Q1(0) and S1(0) peak frequencies by a least squares technique. For this purpose experimental peaks were chosen from the P and R as well as the N and T branches of the spectra. The absorption was computed for each transition. The total absorption contour for a spectrum was obtained by assuming a Lorentzian line shape for the individual transitions and summing contributions from overlapping lines. The agreement between calculated and experimental absorption contours was excellent. For the Ar, Kr, and Xe complexes it was necessary to include three terms in the angular expansion of the transition dipole moment rather than the usual two terms. These three terms interfere to produce the complex absorption contours observed in some spectra. The anisotropy of the intermolecular potential was not determined completely. Rather, a linear relationship between the repulsive and attractive anisotropy coefficients is found.
Doublet→quartet transitions in nitric oxide as detected by electron-impact spectroscopy
Authors: Frueholz Robert P. , Rianda Ronald , Kuppermann Aron
Published: February 2003

Vibronic bands in NO are investigated using electron beam excitation. The beams had energies of 25, 35, and 50 eV. (AIP)
The adsorption of hard spheres near a hard wall
Authors: Henderson Douglas
Published: February 2003

The formulas of Mandell and of Waisman, Henderson, and Lebowitz for the adsorption of hard spheres near a hard wall are compared and are found to be in good agreement.
Some features of the potential energy surfaces for the F++H2 ion–molecule reaction
Authors: Mahan Bruce H. , Schaefer III Henry F. , Ungemach Steven R.
Published: February 2003

Potential energy surfaces for the F++H2 ion-molecule reaction are studied theoretically.(AIP)
Gas phase 13C chemical shifts and coupling constants in the deuteromethanes
Authors: Alei Mohammed , Wageman William E.
Published: February 2003

13C NMR shifts and coupling constants are reported for 13CH4, 13Cl4, and a mixture of 13CH4 and 13CH3D, 13CH2D2, 13CHD3 and 13CD4. The samples were prepared by reaction f 13CO with either pure H2 or a 1:1 H2:DD2.(AIP)
Spectroscopic properties of polyenes. III. 1,3,5,7-Octatetraene
Authors: Gavin R. M. , Weisman Charles , McVey Jeffrey K. , Rice Stuart A.
Published: February 2003

Absorption and emission spectra of all-trans 1, 3, 5, 7-octatetraene are presented along with fluorescence quantum yields and lifetimes. In solution, a gap of about 3000 cm−1 is found between the first band of the 1 1Ag→11Bu transition and the onset of the emission spectrum. Excitation spectra of concentrated solutions at 77 K show low-lying bands in this gap, the lowest energy band being almost coincident with the highest energy fluorescence band. On the other hand, gas phase fluorescence spectra show no gap between the lowest energy 11Ag→11Bu absorption band and the first fluorescence band. The radiative lifetime in hexane is 220 ns at room temperature and 190 ns at 77 K. The radiative lifetime for the gas phase fluorescence is estimated to be longer than 150 ns. The solvent dependence of the absorption and emission spectra, the fluorescence lifetimes, and the vibrational frequencies observed in solution imply support for the conjecture of Karplus et al. that the lowest excited singlet state is of 1Ag symmetry. The solution data imply that the low-lying state is about 6400 cm−1 below the 11Bu level. On the other hand, the lack of a gap between absorption and emission and the long lifetime found for the gas phase are not compatible with this model.
Excitation and quenching reactions in E-beam excited He/H2O and He/CH3CN systems
Authors: Binns W. R. , Ahl J. L.
Published: February 2003

This paper describes observations made in the afterglow of an electron beam discharge into high-pressure mixtures of He/H2O and He/CH3CN and assesses the laser potential of these systems. Emission spectra and time histories at visible and near uv wavelengths were obtained spectroscopically. OH(A2Σ→X2Πi) emission (306.8?λ?310.9 nm) predominated in the He/H2O system, and CN(B 2Σ+→X 2Σ+) emission (385.0?λ?391.6 nm) predominated in the He/CH3CN system. The suggested pumping reactions operative in these systems are the dissociative charge exchange reactions He2+ + H2O→OH(A)+HeH++He and He2++CH3CN→CN(B)+CH3++2He. The rate constants for these reactions have been determined to be (1.3±0.2) ×10−10 and (1.1±0.3) ×10−10 cm3/s, respectively. The He2+ quenching rate constants for H2O and for CH3CN were found to be (1.2±0.2) ×10−9 and (3.5±0.7) ×10−9 cm3/s, respectively. The OH(A) quenching rate constant for H2O was determined to be (4.2±0.4) ×10−10 cm3/s, and the CN(B) quenching rate constant for CH3CN was found to be (1.4±0.3) ×10−10 cm3/s. The OH(A) yield (number of excited molecules produced/number of He+ ions formed) was found to be 11%; the CN(B) yield was 3%. Maximum laser efficiencies for these systems were calculated and determined to be 0.5% and 0.1%, respectively.
Prior statistical distributions for the collision of an atom with a diatom
Authors: Pollak E.
Published: February 2003

The statistical theories of reaction rates play a major role in the formulation and use of the information theoretic approach in reaction dynamics. The statistical theory is used as the prior theory to which the actual rates should be compared. Since one can formulate many different statistical theories, one is faced with the problem of which to use in the information theoretic analysis. Four different theories are reviewed and analyzed for a collinear reaction. It is shown that of these the theory based on the assumption of equal rates for equal product flux in phase space leads to difficulties. Furthermore, a classical collinear calculation of a reaction on a potential surface with a deep well shows that the product state distribution of a reaction involving a long lived complex is well characterized by the statement of equal probability for equal product density in phase space. The implications of these findings on the information theoretic approach are discussed.
Molecular orbital description of silver clusters: Electronic structure
Authors: Baetzold R. C.
Published: February 2003

Electronic properties derived from calculations of Ag clusters up to 39 atoms in size are compared with bulk properties calculated within the same theoretical framework. Density of states profiles (DOS) determined by extended Hückel theory show a broadening with increasing atoms in this range of sizes. The bulk periodic DOS compare favorably with other calculations. Oscillations in electron affinity, binding energy, and ionization potential for open and closed shells of electrons are observed for Ag clusters using the CNDO method.
Transient visible absorption in infrared saturable absorbing dyes
Authors: Olson G. L. , Busch G. E.
Published: February 2003

An optically generated transient absorbing state in the polymethine pyrylium dyes EK 9860 and 9740 is described. The broadband absorption is produced when solutions of the dyes are irradiated by a 1060 nm picosecond duration pulse. The absorbing state spans the wavelength range from ∼520 to ≳800 nm and is characterized by a molar extinction coefficient of ∼1×104 and by a decay time as short as 13.4 psec (in 9860). The latter result and the 7 psec value previously reported for the recovery of ground state absorption at 1060 nm following excitation at the same wavelength are accommodated by a three level relaxation mechanism. This approach treats the visible absorption as arising from electronic transitions both from the first excited singlet state and from a transient intermediate level. Lack of structure in the transient visible absorption indicates that the transition populates high density bound state manifolds or continuum states.
A reactive collision model for use in kinetic theory
Authors: Xystris Nicolas , Dahler John S.
Published: February 2003

Presented here is a classical model for the reactive collisions A+BC→AB+C that is simple enough to be incorporated into kinetic theory calculations. This model involves a combination of reactive and nonreactive impulsive interactions between the participating particles. For the reactive impulse we use a generalization of the DIPR model proposed by Kuntz, Mok, and Polanyi. The nonreactive part of the interaction includes initial and final rigid-sphere-like repulsions between the reactants and the products, respectively. The angular momenta of AB and BC are taken into account. When the reactive impulse dominates the double differential cross sections reported here agree better with the results of molecular beam experiments than those generated by the latest version of DIPR, as proposed by Kuntz. The scattering is backward.
Kinetic theory of simple reacting spheres
Authors: Xystris Nicolas , Dahler John S.
Published: February 2003

Dilute and dense gas Enskog theory calculations are reported for a fluid composed of simple reacting spheres. Results for the dilute gas provide qualitative confirmation of previous calculations based on the MIRS (multiple interaction, reacting sphere) model. At high densities the viscosity and ’’empirical’’ diffusion coefficients vary almost linearly with the heat of reaction. The diffusion coefficients associated with the collisional transfer or ’’surface reaction’’ contributions to the component mass fluxes depend very strongly on density. For small heats of reaction and large densities this novel mechanism can completely overshadow regular diffusion. The transport coefficients associated with this surface reaction term fall into two categories, those with numerical values which tend to zero for large heats of reaction and those which increase rapidly as the exothermicity rises. The mass fluxes of reaction products belong to the latter category.
Excess electrons in condensed media: Theory of optical absorption spectrum in molecular solutions
Authors: Banerjee Ajit , Simons Jack
Published: February 2003

A theoretical formalism is developed for analyzing the spectra of excess electrons in pure molecular solids and liquids. A perturbation decomposition of the Hamiltonian allows the expression for the band shape I (ω) to be written as a sum of a zeroth order part, proportional to dipole transition matrix elements and corresponding Franck–Condon factors, and perturbation terms containing effects of electron hopping and their fluctuations. By using several physically motivated approximations (e.g., the temporally localized nature of electronic transitions which allows a short-time expansion of the time dependence of operators), the expression for I (ω) can be expressed in terms of solvent structure information and the electron–solvent interaction potential. From the general expressions for I (ω) a simplified model was developed in the special case of systems for which bound-to-bound transitions are dominant. This model has been successfully applied to the spectra of excess electrons in ethanol and anthracene glass, thereby providing some optimism for the potential use of the general formalism derived here.
’’Proximity effect’’ in radiationless transitions
Authors: Wassam W. A. , Lim E. C.
Published: February 2003

The quantum statistical approach to relaxation phenomena was employed in a numerical investigation of the effect of vibronic interaction between the first and second excited states on the radiationless decay rate of the first excited state. It is shown that the vibronically active out-of-plane modes may be the dominant accepting modes for the radiationless transitions of N-heterocyclics with close-lying nπ* and ππ* excited states. The decay rate was found to vary with the strength of nπ*–ππ* vibronic interaction, the nπ* and ππ* separation, the energy gap between the initial and final electronic states of the radiationless process, and isotopic substitution, in a manner which is consistent with experimental observation.
Photoelectron spectroscopy with Zr Mζ (151 eV) radiation. A study of the variation of relative photoionization cross sections of molecules containing first row atoms (C, N, O) with exciting radiation from HeI to Mg Kα limits
Authors: Allison David A. , Cavell Ronald G.
Published: February 2003

Relative perpendicular photoionization intensities for the noble gases Ne and Ar and the molecules CH4, NH3, H2O, CO, N2, and CO2 have been measured with HeI (21.2 eV), HeII (α, 40.8 eV and β, 48.4 eV) resonance lines and Zr Mζ (151 eV) and Mg Kα (1253.6 eV) soft x rays using the same instrument for all measurements. New valence shell spectra of NH3, CO, and CO2 obtained with Zr Mζ radiation are illustrated. The experimental values are compared to values calculated for each radiation by the method of Ellison [J. Chem. Phys. 61, 507 (1974)]. Reasonable success was achieved by the theory which appears to falter most seriously with the inner valence orbitals of dominant 2s atomic character. This failure is most likely due to the improper treatment of the Cooper minimum. Attempts to improve the agreement between observed and calculated relative intensities by inclusion of multiple electron processes (’’shake up’’ transitions) are discussed.
Triplet yield determination for some substituted benzenes: A discussion of the biacetyl method
Authors: Lee San Ardi
Published: February 2003

Quantum yields of fluorescence and of triplet molecule formation have been determined for the xylenes and the ethyltoluenes. Both yields generally decrease with increase in energy of the incident photons, i.e., with decrease in wavelength. Toward the long wavelength limit of the absorption region of each molecule, the sum of the two yields for several of these molecules may exceed unity by as much as 10%–25% unless the biacetyl method for triplet yield determination is modified. If the phosphorescent yield of biacetyl at 435.8 nm is taken as a standard, the results are not acceptable. If a somewhat higher value is used, the data obtained give results which account for all of the absorbed quanta. Various possibilities are discussed but a proper method of determining the triplet yield is still lacking at present.
Self-consistent field energies and wavefunctions for coupled oscillators
Authors: Bowman Joel M.
Published: February 2003

We formulate a self-consistent field description of coupled anharmonic oscillators. The SCF equations are solved numerically for a model problem of two coupled anharmonic oscillators and energy eigenvalues compared with previously published exact quantum and semiclassical ones.