bluuebunny/crossref_metadata_2025 huggingface dataset:
Gas-phase electron paramagnetic resonance absorption in nitric oxide. II. The effects of nitrogen-15 and oxygen-17 and 18 substitution
Authors: Jarke Frank H. , Ashford Nicholas A. , Solomon Irvine J.
Published: February 2003

The X-band EPR investigation of the six isotopically related molecules of nitric oxide synthesized from 14N, 15N, 16O, 17O, and 18O has been completed. Perturbation theory applied to Hund’s case (a) representation for nitric oxide yielded excellent agreement with experiment. Linear relationships were found between the g values and the reduced mass, and between the field uncoupling splittings and the reciprocal of the reduced mass, which is indicative of the relationship of these values to the rotational constant, B0. The value of the spin orbit coupling constant was determined to be 123.27 cm−1 in agreement with the value of James and Thibault (Ref. 7), 123.16±0.020 cm−1. The nitrogen-15 hyperfine splitting constant was found to be 38.41±0.19 G. The oxygen-17 hyperfine lines revealed a measurable quadrupole effect and the oxygen-17 hyperfine splitting constant was determined to be 57.6±0.4 G.
Nonadiabatic transitions induced by a time-dependent Hamiltonian in the semiclassical/adiabatic limit: The two-state case
Authors: Davis Jon P. , Pechukas Philip
Published: February 2003

We show rigorously, within the two-state approximation, that in the semiclassical limit h/→0 a nonadiabatic transition induced by an analytic time-dependent Hamiltonian is localized to the vicinity of a complex crossing of the two adiabatic potential curves, with transition amplitude independent of the nonadiabatic coupling and given by a simple formula of A. M.Dykhne.
Vibrational progressions in vibronically induced transitions
Authors: Gregory A. R. , Siebrand W. , Zgierski M. Z.
Published: February 2003

It is shown that progressions of totally symmetric vibrations in vibronically induced spectra do not show the same intensity distribution as comparable progressions in allowed spectra. This is due to cross terms, involving both totally symmetric and inducing mode coordinates, in the Herzberg–Teller expansion. These cross terms express the modulation of the vibronic coupling resulting from differences in interatomic distances between the borrowing and lending states. The effect is universal, as opposed to effects based on normal-coordinate rotation or totally symmetric inducing modes, and enters even in the absence of anharmonic coupling. It leads to anomalous intensity distributions which, moreover, are different for emission and absorption spectra. Quantitative estimates are presented which indicate that it should be readily observable in many molecules.
Diatomic molecules as perturbed Morse oscillators. I. Energy levels
Authors: Huffaker J. N.
Published: February 2003

A formula is obtained for the rotational–vibrational energy levels of a diatomic molecule using a perturbed Morse potential V (r) =Ve[(1−e−aq)2+b4(1−e−aq)4 +b5(1−e−aq)5+⋅⋅⋅], along with additional perturbations describing rotational energy. Results are equivalent to Dunham’s formulas, but have superior convergence properties for analyzing spectra. How to choose the ’’best’’ unperturbed Morse potential and how to evaluate perturbation parameters are briefly discussed. Formulas are applied to the ground state of CO, and results are compared with those for RKR and other potentials.
Rate constants for the reactions OH+H2S→H2O+SH and OH+NH3 →H2O+NH2 over the temperature range 297–427 °K
Authors: Perry R. A. , Atkinson R. , Pitts J. N.
Published: February 2003

Rate constants for the reactions OH+H2S→H2O+SH (k1) and OH+NH3→H2O+NH2 (k2) were determined over the temperature range 297–427 °K by a flash photolysis–resonance fluorescence technique. The Arrhenius expressions obtained were k1= (5.2±0.5) ×10−12 cm3 molecule−1sec−1, independent of temperature (297–424 °K); k2=2.93×10−12 e−(1710±300)/RT cm3 molecule−1sec−1 with rate constants at 298 °K of k1= (5.25±0.53) ×10−12 cm3 molecule−1sec−1 and k2= (1.64±0.16) ×10−13 cm3 molecule−1sec−1. These rate constants are compared and discussed with literature values.
Diffusion of spherical macromolecules at finite concentration
Authors: Anderson John L. , Reed C. Christopher
Published: February 2003

An expression for the concentration-dependent diffusion coefficient is derived which accounts for both hydrodynamic and long-range potential interactions between rigid spherical macromolecules in solution. A self-consistent field approach is taken, based on the Smoluchowski equation for a single Brownian particle in an external force field. The external force contribution to particle flux is replaced by a configurational average which includes the effects of both interparticle forces and hydrodynamic friction for each configuration; this term gives rise to a concentration-gradient-induced migration. The purely diffusive contribution to particle flux is computed from an analysis of two-particle viscous interactions assuming uncoupled pressure fluctuations on each particle. Since only binary hydrodynamic interactions between particles are considered, the resulting expression for the diffusion coefficient is valid only to order φ, the volume fraction of particles in the solution. This expression is evaluated for several types of interparticle potentials. For the hard sphere case, these calculations show fair agreement with published experimental data for diffusion at finite concentrations. The model predicts that tracer and mutual diffusion coefficients for hard spheres should be equal, in agreement with these data. The general relation between diffusivity and particle concentration derived here differs from the classical one, which views the driving force as the gradient in chemical potential. The difference is due to the manner in which the hydrodynamic interactions are averaged.
Crystal field parameters for the pentaphosphates of neodymium and europium
Authors: Karayianis N. , Morrison C. A. , Wortman D. E.
Published: February 2003

Previously reported spectra of the pentaphosphates of neodymium and europium are analyzed by diagonalizing a parametrized Cs(C1h) Hamiltonian in free-ion bases involving the 5 and 7 lowest J multiplets, respectivly, of each ion. By reassigning symmetries to the reported Eu levels according to predictions from scaled crystal field parameters that fit 28 Nd levels to 7.61 cm−1, a fit of 10.43 cm−1 to 46 levels of Eu was obtained. Predicted crystal field parameters for all the lanthanide pentaphosphates are given.
Theory of core-level photoemission correlation state spectra
Authors: Martin R. L. , Shirley D. A.
Published: February 2003

A theoretical framework is given for calculating satellite spectra (sometimes called ’’shakeup’’ or ’’monopole’’ spectra) that accompany core-level photoemission peaks. Photoemission is regarded as a special case of optical excitation in an N-electron system, and the dipole approximation (DA) is used to determine satellite intensities. relationships between the sudden approximation and DA results are noted. Configuration interaction (CI) in the final state is discussed. It is emphasized that the main core-level peak and satellites do not really arise from one- and two-electron excitations, respectively, but from qualitatively identical transitions. The importance of initial-state CI in determining satellite intensities in molecular x-ray photoelectron spectra is pointed out for the first time.
Crystal nucleation in a three-dimensional Lennard-Jones system: A molecular dynamics study
Authors: Mandell M. J. , McTague J. P. , Rahman A.
Published: February 2003

We have observed crystal nucleation in a Lennard-Jones fluid by molecular dynamics. In a 108-particle system cooled slowly below its triple point, crystallization occurs at kT/ε=0.50 and 0.57 for densities Nσ3/V =0.90 and 0.91, respectively. For larger systems (256 and 500 particles) crystallization has also been achieved. The supercooling limit decreases with increasing system size. These results are compatible with classical nucleation theory.
On the asphericity of d electron clouds near transition metal surfaces
Authors: Desjonquères M. C. , Cyrot-Lackmann F.
Published: February 2003

The charge density of d electrons around a bulk atom or low-index facets atoms of fcc Ni, bcc Fe, and hcp Co are studied within the tight-binding scheme using a moment method. The occupation numbers of each orbital are obtained. It is shown that the asphericity of the charge density is increased when going from a bulk to a surface site because the differences between orbital occupation numbers is less than 0.20 ? for a bulk atom but can reach ?0.44 ? for a surface one. The consequences upon preferred adsorption sites are discussed according to the electronic affinity and size of the adatoms.
Molecular theory of surface tension
Authors: Yang Arthur J. M. , Fleming Paul D. , Gibbs Julian H.
Published: February 2003

A molecular theory of surface tension is developed for a liquid–gas interface of a one component system. The Helmholtz free energy, the quantity minimized in the van der Waals approach, is obtained here from a rigorous expansion in powers of derivatives of density ρ and is minimized by the calculus of variations. The coefficient A (ρ) of the term in the square of the density gradient is (kT/6) ℱdr r2C (r,ρ), C being the direct correlation function. In the case in which ρ varies in one direction x only, the solution of the Euler–Lagrange differential equation is analyzed in detail. This describes the cases of a single phase and of two coexisting phases and leads to the equal area Maxwell construction. The effect of an external field on the solution is discussed. The Euler–Lagrange differential equation provides a differential statement of Bernoulli’s theorem. In a three dimensional treatment the stress tensor formula is obtained from the corresponding Euler–Lagrange partial differential equation. A (differential) generalization of the Young–Laplace equation for a spherical interface is also derived. In addition, metastable regions are described and interpreted. The stress tensor for a system in the presence of any kind of conservative force field is also obtained.
Mössbauer study of the formation of metal–metal bonds in planar complexes of iridium
Authors: Aderjan R. , Keller H. J. , Rupp H. H. , Wagner F. E. , Wagner Ursel
Published: February 2003

Chelato-dicarbonyl-iridium(I) compounds of the composition Ir(CO)2LL or Ir(CO)2LCl, where LL stands for a singly-charged bidendate organic ligand and L for a monodendate, neutral organic base, have been studied by Mössbauer experiments with the 73 keV gamma rays of 193Ir. The results indicate that for these compounds the formation of columnar stacks with metal–metal bonds goes along with a reduction of both the magnitude of the electric quadrupole interaction and the electronic charge density at the Ir nuclei. A qualitative explanation for these results is attempted.
Observation of a stripping threshold for the reaction N2++CH4→N2H++CH3
Authors: Wyatt J. R. , Strattan L. W. , Snyder S. C. , Hierl P. M.
Published: February 2003

Chemical accelerator studies on isotopic variants of the reaction N2++CH4→N2H++CH3 are reported. Reaction cross sections, as well as velocity and angular distributions of the ionic products have been measured as a function of initial translational energy over the energy range 0.65–35 eV (center of mass). The results are similar to those recently reported for the reaction of Ar+ with CH4. The excitation function maximizes at about 5 eV (c.m.) and decreases at lower collision energies, appearing to possess a threshold at 0.1 eV. At the higher energies there is a large isotope effect favoring abstraction of H over D. The product velocity vector distribution is strongly peaked forward of the center of mass, indicating that the reaction is predominantly direct over the energy range studied. The spectator stripping model, although providing a reasonable first approximation to the reaction dynamics, overestimates the product translational energy by approximately 0.1 eV. This behavior is presumed to be caused by a basin in the potential energy hypersurface for this reaction. If, however, an N2CH4+ complex is formed at low collision energies, it appears to decompose via reaction channels other than that resulting in N2H+ formation.
Proton magnetic relaxation and internal rotations in tetramethylammonium cadmium chloride
Authors: Tsang Tung , Utton D. B.
Published: February 2003

Proton spin–lattice relaxation times (T1) and second moments (M2), at 14.7 MHz, have been investigated for tetramethylammonium cadmium chloride. Discontinuities in T1 at 104 and 119 K indicate the occurrence of crystallographic transformations. It is proposed that, in the low temperature phase below 104 K, the correlation time for hindered motion of one of the methyl groups is somewhat different from that of the other three. Using this model, the calculated T1 and M2 values are in satisfactory agreement with the experimental data. For the low temperature phase, the activation energies of the tetramethylammonium ion, 2.0±0.3 and 1.6±0.3 kcal/mole (8.4±1.3 and 6.7±1.3 kJ/mole), are considerably lower than the values 5.5–11 kcal/mole observed for the tetramethylammonium halides. In the high temperature phase, the activation energy decreases even further to 0.7±0.2 kcal/mole (2.9±0.8 kJ/mole). This decrease is in accordance with other order–disorder phase transitions involving tetrahedral ions.
Flow light scattering. II. Theoretical results for flow oriented, homogeneous, and isotropic spheroids
Authors: Nakagaki M. , Heller W.
Published: February 2003

The equations developed by A. F. Stevenson on the light scattering by spheroids subjected to hydrodynamic orientation—a theory which takes into account the magnetic dipole and electric quadrupole scattering in addition to dipolar Rayleigh scattering—were generalized so as to include the effect of the scattering angles ϑ and ω as additional variables. The resulting exceptionally lengthy equations were evaluated with the objective of finding the best possible arguments for the determination, by means of the flow light scattering technique, of both exact shape and size (molecular weight) of nonspherical bodies which can be approximated as spheroids. The analytical potential of the flow light scattering technique is compared with that of the standard light scattering technique in resting systems and with that of flow birefringence.
Applications of field theoretical methods to the calculation of infrared band shapes of molecules in strongly interacting solvents. I.
Authors: Paul R. , Fuller G. G.
Published: February 2003

Starting from a finite temperature Green’s function formalism we have developed a diagrammatic method for calculating the complex dielectric constant of a system consisting of diatomic molecules that are strongly interacting with the solvent medium. Perturbative treatments suitable for weak interactions have been replaced by a variational method, and diagrams picked up are summed up to all orders in the solvent–solute interaction potential. A method is presented whereby all the vectorial integrations can be carried out exactly leaving a final quadrature which must be done numerically. It is pointed out that the internal states of the diatomic molecule are coupled to each other via a very complicated cooperative effect induced by the solvent.
Measurement of chemiluminescent reaction cross sections for B+N2O→ BO*+N2 and Ho+N2O→HoO*+N2
Authors: Tang S. P. , Utterback N. G. , Friichtenicht J. F.
Published: February 2003

A crossed atomic–molecular beam apparatus has been used to measure the collisional energy dependences of the total scattering cross section σT and the chemiluminescent reaction cross section σr for holmium and boron atoms interacting with N2O molecules. The laser vaporization of metal foils is used to produce a metal atom beam pulse with energies ranging between ∼0.5 and 4 eV. The target gas of N2O molecules is generated by a room temperature nozzle beam. The chemiexcitation of electronic states of the metal oxides formed in the B+N2O→BO*+N2 and Ho+N2O→HoO*+N2 reactions is assumed to be the source of the observed visible radiation. For the Ho+N2O interaction, σT decreases by about a factor of 3 in the Ho atom energy range from 0.5–3.5 eV, whereas σr increases by about a factor of 2 in the same energy range. For B+N2O, σT is of nearly constant magnitude in the 1–4 eV B atom energy range; however, σr increases by a factor of ten in this energy range. The comparison of results obtained with thin and thick target gases indicates that σr≪σT for both the Ho+N2O and B+N2O interactions.
Surface, subsurface, and bulk exciton transitions of crystalline anthracene
Authors: Philpott M. R. , Turlet J.-M.
Published: February 2003

The polarized reflection spectrum of the first singlet transition of crystalline anthracene at 2 °K is reported for light at near normal angles of incidence on the (001) face. The effect on the spectra of condensing small amounts of gases, transparent in the 400 nm region, has been studied and found to be a useful technique for differentiating surface from bulk exciton transitions. The optical properties of the bulk crystal have been calculated by a Kramers–Kronig transformation of the reflectivity data. The complex refractive index so obtained was used to calculate the effect of surface transitions on the bulk reflection spectrum using equations given by a microscopic theory of surface and bulk exciton states. The agreement between the calculated and experimental spectra is excellent. Model calculations show that the two-dimensional sums of excited state van der Waals interactions are of sufficient range to create a series of excitons localized on surface planes. It is also demonstrated that the reflectivity formulas of thin film optics and the microscopic surface exciton theory are equivalent. The reflection spectra of crystals coated with frozen deposits of air show the presence of a satellite minimum that upon further absorption of gas first grow more prominent at the expense of the original minimum and then are replaced by a single minimum with an even larger red shift. These observations appear to correspond to nucleation, growth, and coalescence of islands of the adsorbed molecules. The higher vibronic transitions are not effected by frozen gas films, except for one peak in the a spectrum that disappears. This peak is located at the position expected of the a-polarized factor group component of the surface state and as such provides new evidence for this assignment. A partial analysis of some of the higher vibronic transitions is presented based on the concepts of single-particle transitions embedded in bands of two-particle states.
Local field models for light scattering and the dielectric constant of nonpolar fluids
Authors: Sullivan Donald E. , Deutch J. M.
Published: February 2003

The resummed molecular theory for the dielectric constant and light scattering in nonpolar fluids developed by previous authors is generalized to account for arbitrary local field models in addition to the Lorentz–Lorenz model. In particular, it is shown that the Onsager–Böttcher and Wertheim models for the dielectric constant may be encompassed by this theory. Expressions for Rayleigh’s ratio in the Born approximation are obtained, providing a molecular derivation of the ’’local field factors’’ for light scattering consistent with these dielectric models. The results are compared with experimental isotropic Rayleigh ratios, indicating that the Wertheim model provides the best agreement. The relation with Einstein’s phenomenological theory of light scattering is discussed.
Nonadiabatic effects in the collision of F(2P) with H2(1Σ+g). II. Born–Oppenheimer and angular momentum coupling in adiabatic and diabatic representations
Authors: Rebentrost Frank , Lester William A.
Published: February 2003

The matrix elements necessary for the description of electronic interactions between the 1 2A′, 2 2A′, and 2A″ surfaces of FH2 are evaluated from Born–Oppenheimer states. It is shown that these couplings are handled most appropiately in a diabatic basis. The transformation between adiabatic and diabatic bases is explicitly obtained.
Energy level analysis of Pm3+:LaCl3
Authors: Carnall W. T. , Crosswhite Hannah , Crosswhite H. M. , Conway John G.
Published: February 2003

A diagonalization of the matrices representing the combined atomic and crystal-field interactions for the 4f4 configuration has provided the basis for interpreting the spectrum of Pm3+:LaCl3. Experimental data were drawn from the literature and were augmented by unpublished absorption and fluorescence results. A method of truncating the large matrices involved is discussed and shown to yield results in excellent agreement with complete calculations. Use of fluorescence branching ratio calculations based on the Judd–Ofelt intensity theory to monitor the interpretation of fluorescence spectra is discussed.
Light scattering and ir measurements in XS2 pryite-type compounds
Authors: Anastassakis E. , Perry C. H.
Published: February 2003

The results of Raman scattering and reflectivity measurements of XS2 (X=Fe, Co, Ni, Cu, Zn) transition metal dichalcogenides are reported. These compounds are expected to exhibit five Raman-active and five ir-active q?0 optical phonons in first-order processes. Measurements of light scattering at T?300 °K revealed at most three phonon modes for the above materials (with the exception of powdered ZnS2). Some overtone scattering was also observed. Measurements of far infrared reflectivity did not yield the frequencies of all five ir-active phonons expected. The results of mixed crystals are also discussed.
Theoretical studies of molecular ions. Ionization potentials of CN− and BO−
Authors: Griffing Karen M. , Simons Jack
Published: February 2003

The 1Σ+→2Σ+ vertical ionization potentials of BO− and CN− and the 1Σ+→2Π vertical ionization potential of CN− are reported for several internuclear distances. The estimated adiabatic electron affinities of BO (2.79 eV) and CN (3.69 eV) are in good agreement with experimental determinations. The 5σ orbital electron density in CN− and BO− is analyzed and compared to that in N2 and CO. Curve crossing behavior in the 2Σ+ and 2Π states of CN is discussed.
Crossed beam study of the rainbow scattering of Hg by I2: Determination of the binding energy of the Hg⋅I2 adduct
Authors: Wilcomb B. E. , Haberman J. A. , Bickes R. W. , Mayer T. M. , Bernstein R. B.
Published: February 2003

Angular distribution measurements of seeded supersonic atomic beams of Hg scattered by a crossed thermal molecular beam of I2 are reported. The experiments have been performed at two average collision energies: ?=0.25 and 0.37 eV. The angular distributions show unresolved rainbow maxima, from which the intermolecular potential well depth has been estimated. Several approximate methods of analysis, assuming realistic potential models and utilizing only the location of the rainbow, have yielded well depths in the range 625–680 K. A more reliable determination of ε has been carried out by an iterative fitting procedure involving calculation of the entire angular distribution(s). For an assumed Lennard-Jones (12,6) potential, the well depth is 670±25 K. This corresponds to a binding energy for the Hg⋅I2 adduct (i.e., the van der Waals molecule) of 0.058 eV or 5.6 kJ mol−1. The absence of fully resolved rainbow structure in the observed angular distributions is evidence for a significant noncentral component in the intermolecular potential (leading to anisotropic quenching and concurrent inelasticity).
Single particle reorientation and pair correlations of methyl iodide solutions studied by depolarized Rayleigh and Raman scattering
Authors: Cheung C. K. , Jones Dane R. , Wang C. H.
Published: February 2003

Concentration and temperature dependent depolarized Rayleigh light scattering spectra were obtained for an important molecular liquid—methyl iodide—using interferometry. The concentration dependent studies yielded reliable single particle rotational-relaxation times. These single particle times were used to test the approximations used to obtain rotational-relaxation times for CH3I from Raman spectra. Having verified the validity of these assumptions for CH3I, depolarized Rayleigh and Raman results were combined to study the concentration and viscosity dependences of pair correlations. Single particle relaxation times obtained from temperature and viscosity dependent studies were used to test various hydrodynamic models of molecular reorientation. The optically isotropic solvent used in the solution work consists of 46% isopentane and 54% CCl4 (by volume).
Light scattering from shear modes in liquid salol
Authors: Enright G. D. , Stoicheff B. P.
Published: February 2003

Depolarized spectra of liquid salol have been observed and analyzed over a range of temperature, from 122 to −22 °C, with the viscosity varying from ∼2 to more than 104 cP. At the lowest temperatures, the spectra exhibit a central line and well-separated Brillouin components, characteristic of light scattering by oscillatory shear waves. As the temperature is raised, the Brillouin components merge with the central line. At the highest temperatures, broad depolarized doublets with intensity minima at the exciting frequency appear, and are ascribed to light scattering from highly damped shear modes. The spectra observed over the entire temperature range are shown to be in good agreement with the ’’two variable’’ theory of Andersen and Pecora.
Phonon bands in disordered systems with both mass and force constant defects: Isotopic mixed ice Ih
Authors: Bellows James C. , Prasad Paras N.
Published: February 2003

An isotopic mixed crystal study is conducted on the 226.5 cm−1 phonon band in ice Ih. The result shows an amalgamation limit for this band with no significant clustering effect and indicates the absence of any isotope selectivity of the hydrogen bonds. The experimentally obtained self-energy when plotted against the mole fraction of the impurity (D2O) yields a symmetric curve pointing out that the additional disorder in the mixed crystals is purely dynamic. The self-energy curve is fitted into a polynomial of the mole fraction of the impurity using regression analysis. The polynomial obtained reveals the importance of both the mass defect and the force constant defect. The result obtained is also shown to provide information regarding the dispersion of this phonon band.
Decoupling scheme for a semiclassical treatment of electronic transitions in atom–diatom collisions: Real-valued trajectories and local analytic continuation
Authors: Komornicki Andrew , George Thomas F. , Morokuma Keiji
Published: February 2003

The semiclassical theory of electronically nonadiabatic transitions in atom–diatom collisions is modified by the introduction of a decoupling approach to the nuclear dynamics. The probability of switching surfaces is calculated locally by integrating in the complex plane over a nuclear coordinate which couples most strongly to the electronic transition. A substantial computational simplification results when this approach is implemented. The power of the method lies in the fact that the potential energy surfaces need be analytically continued locally rather than globally. Thus the trajectories can be maintained on the real axis except for the one point where the surfaces are switched. Computational results are presented and discussed for two model collinear nonreactive systems, F+H2 and Br+H2. It is shown that when the possibility of an E–V resonant energy transfer exists, the vibrational as well as the electronic degrees of freedom must be treated quantum mechanically.
Trapped electrons in crystalline D2O ice at 4°K
Authors: Hase Hirotomo , Kawabata Keisuke
Published: February 2003

The ir absorption band and EPR spectrum of ΔHpp=1.3 G at g?2 observed in irradiated D2O crystalline ice at 4°K have been assigned to trapped electrons. The ir band and EPR spectrum decayed with τ1/2=35 min in pure D2O ice at 4°K. The trapped electrons were not observed in H2O ice at 4°K. Addition of 1.5% H2O in volume in D2O reduced the trapped electron yield to about 60% and shortened τ1/2. Effect of NH4F and AgNO3 doped in D2O ice has been examined. The trapped electrons were stable in 10M LiCl⋅H2O–D2O glass at 4°K. Stability of the trapped electrons in ice has been discussed.
On the accuracy of the ’’decoupled l-dominant’’ approximation for atom–molecule scattering
Authors: Green Sheldon
Published: February 2003

Cross sections for rotational excitation and spectral pressure broadening of HD, HCl, CO, and HCN due to collisions with low energy He atoms have been computed within the ’’decoupled l-dominant’’ (DLD) approximation recently suggested by DePristo and Alexander; these are compared with accurate close coupling results and also with two similar approximations, the effective potential of Rabitz and the coupled states of McGuire and Kouri. These collision systems are all dominated by short-range repulsive interactions although they have varying degrees of anisotropy and inelasticity. The coupled states method is expected to be valid for such systems, but they should be a severe test to the DLD approximation which is expected to be better for long-range interactions. Nonetheless, DLD predictions of state-to-state cross sections are rather good, being only slightly less accurate than coupled states results. DLD is far superior to either the coupled states or effective potential methods for pressure broadening calculations, although it may not be uniformly of the quantitative accuracy desirable for obtaining intermolecular potentials from experimental data.
The three components of the thermomagnetic force in NO and O2
Authors: Al-Ani A. S. , Adair III T. W.
Published: February 2003

The three components of the thermomagnetic force were measured on disks with their surfaces perpendicular to the heat flux. The study was done in the paramagnetic gases NO and O2 for conditions approximating those assumed by recent theory. Comparison has been made with theory as well as previous experimental work.
A molecular theory of interfacial phenomena in multicomponent systems
Authors: Fleming III Paul D. , Yang Arthur J. M. , Gibbs Julian H.
Published: February 2003

The van der Waals theory of surface tensions is generalized to multicomponent systems. The local free energy density consists of a ’’local equilibrium’’ free energy (i.e., equilibrium free energy of a uniform mixture having species densities equal to the local species densities) plus a quadratic form in the gradients of the species densities. The coefficients in this quadratic form depend on the local species densities through the density dependence of the second moment of the local multicomponent direct correlation function. The requirement that the free energy be a minimum yields a system of partial differential equations (one for each component). A particular linear combination of the differential equations is the condition for mechanical equilibrium. It can be interpreted as a microscopic statement of the multicomponent Young–Laplace equation for the pressure variation across a curved interface. For two component systems the theory is a generalization of the treatment of Cahn and Hilliard in that it allows for pressure variations. If the local pressure fluctuations are suppressed, the differential equation for the concentration is very similar to theirs, except that the total density may vary across the interface. Similarly, when the theory is applied to liquid–vapor equilibrium in a binary system, the differential equation for the total number density reduces to that of a single component system when the local chemical potential difference (μ=μ1−μ2) is held constant.
Crystal field parameters for Eu3+ in KY3F10
Authors: Porcher P. , Caro P.
Published: February 2003

The fluorescence spectrum of KY3F10: 1% Eu in powder form was recorded at 77 and 4.2°K between 4600 and 7000 Å, and 89 fluorescence lines arising from levels 5D0, 5D1, 5D2, and probably 5D3 were observed. The spectrum agrees with with a C4v symmetry, and it is possible to determine the irreducible representation of the group associated with the Stark components of 2S+1LJ levels. The set of crystal field parameters agreeing best with the experiment, on a basis of 200 kets ‖7F≳, ‖5D≳, and ‖5G≳ of the 4f6 configuration, is B20=−551 cm−1, B04=−1360 cm−1, B44=+345 cm−1, B60=394 cm−1, and B64=234 cm−1.
On the nonequilibrium distribution of adatoms resulting from dissociative adsorption of a diatomic gas
Authors: Hoffman David K.
Published: February 2003

Kinetic equations governing the distribution of adatoms resulting from irreversible, dissociative adsorption of homonuclear diatoms onto a two-dimensional lattice are derived. Desorption and atomic skating are ignored, which allows the problem to be conveniently formulated from a molecular viewpoint. The rate constant for adsorption is assumed to be of an Arrhenius form with an activation energy which consists of an additive contribution from the interaction of the adsorbing molecule with each adatom on the surface. Special attention is paid to the relationship between the molecular distribution resulting from irreversible adsorption and the equilibrium molecular distribution. The kinetic equations are solved as a power series in the covering fraction; the coefficients involve molecular cluster diagrams similar to those in equilibrium, virial expansions. Comparison of the nonequilibrium and equilibrium covering fraction expansions of the molecular pair distribution functions is made, and an illustrated example is considered for a case where the functions and their expansions can be evaluated exactly. Finally, the effect of the nonequilibrium distribution of adatoms on the configurational contribution to the thermodynamic properties of the adsorbate is discussed.
A generalization of the Wilson charging process to molecular systems in which the motion of both the electrons and nuclei are described quantum mechanically
Authors: García-Sucre M.
Published: February 2003

A generalization of the Wilson charging process to systems is which both the motion of the electrons and the nuclei are described quantum mechanically is presented. For a molecular system of n electrons and N nuclei one shows that the problem of 3n+3N degrees of freedom reduces to one of seven variables plus the calculation of the energy levels of a much simpler system than the original one. Furthermore, if the wave functions involved are all real functions, the problem of 3n+3N degrees of freedom reduces simply to one of six variables for every state of the system.
Foreign gas broadening by water molecule
Authors: Srivastava G. P. , Kumar Anil
Published: February 2003

Microwave spectral linewidths of OCS, BrCN, CH3CN, HCHO, and C2H4O have been measured as broadened by the water molecule on a double modulation microwave spectrograph. On comparing the experimental linewidths with theoretically calculated linewidths on the basis of the Anderson as well as the Murphy–Boggs theory, it is found that the experimental linewidths are higher than the calculated ones, although the strong dipole interactions are involved.
Ultrasonic and hypersonic properties of ionic hydrate melts
Authors: Carpio Ronald , Borsay Frank , Petrovic Cedomir , Yeager Ernest
Published: February 2003

Ultrasonic and Brillouin scattering measurements have been used to establish the relaxation properties of zinc chloride, zinc nitrate, and calcium nitrate hydrate melts in the frequency range 5 MHz to 12 GHz. A distribution of relaxation times is observed for these melts which is generally much broader than for a single relaxation. The width of this distribution decreases with increasing temperature and water content. Deuteration of the hydrate melts produces a significant increment in the low frequency absorption and also an increment in the mean relaxation time. The experimental data have been compared with the Isakovich–Chaban and Montrose–Litovitz theories of viscoelastic relaxation. The mean relaxation times predicted by the I–C theory are generally longer than the experimental values, and the shape of the predicted distribution is different. The data can be closely fitted to the M–L treatment with proper choice of the two adjustable parameters in the theory. A multiple state chemical model is proposed for the hydrate melts. Under such circumstances this model can be reduced to a form which falls within the mathematical framework of the M–L treatment.
Rate constants for the reactions of the OH radical with NO2 (M=Ar and N2) and SO2 (M=Ar)
Authors: Atkinson R. , Perry R. A. , Pitts J. N.
Published: February 2003

Absolute rate constants for the reactions OH+NO2+M→HNO3+M (M=Ar, N2) OH+SO2+M→HSO3+M (M=Ar) have been determined at 298°K, using a flash photolysis–resonance fluorescence technique. Rate constants k1 and k2 were determined over the pressure range 25–648 torr for M=Ar, while a rate constant for the first reaction was also obtained for M=N2 at 25 torr total pressure. The low pressure third order rate constants were determined to be k1(M=Ar) = (1.02±0.10) ×10−30 cm6 molecule−2⋅sec−1 and k2(M=Ar) = (1.64±0.33) ×10−31 cm6 molecule−2⋅sec−1, in reasonable agreement with the literature values. The bimolecular rate constants at 760 torr total pressure were determined to be kbi1= (5.9±0.7) ×10−12 cm3 molecule−1⋅sec−1 (M=Ar), kbi1= (6.4±1.0) ×10−12 cm3 molecule−1⋅sec−1 (M=N2), and kbi2= (6.7±0.7) ×10−13 cm3 molecule−1⋅sec−1 (M=Ar). Extrapolation of the data led to limiting high pressure second order constants of k∞1?8.5×10−12 cm3 molecule−1⋅sec−1 and k∞2?8.3×10−13 cm3 molecule−1⋅sec−1.
Reactive and inelastic scattering of H2+D2 using a London-type potential energy surface
Authors: Brown Nancy J. , Silver David M.
Published: February 2003

Collisions between hydrogen and deuterium molecules are studied using quasiclassical dynamical trajectory calculations with the intermolecular field specified by a London-type potential-energy surface. The occurrence of chemical exchange reactions to form two HD molecules is found to be extremely sensitive to the initial relative orientations of the reactant molecules. Nonreactive collisions are examined for energy transfer processes in terms of average final state energy distribution.
Continuum radiation and potentials of Tl–noble gas molecules
Authors: Cheron B. , Scheps R. , Gallagher A.
Published: February 2003

Continuum emission intensities on the extreme wings of the Tl resonance lines due to noble gas perturbers have been measured as a function of gas temperature. These spectra, due to the B 2Σ1/2−X1/2, B 2Σ1/2−X3/2, and B 2Σ1/2−A1/2 bands, are interpreted with the classical Franck–Condon principle to yield estimates of the B 2Σ1/2, A1/2, X3/2, and X1/2 potentials of Tl–noble gas molecules. As has been noted qualitatively in matrix isolation studies, the Group III elements form unusually stable diatomic bonds with the ’’inert’’ gases, e.g., we find Tl–Xe bound by ∼300 cm−1. The Tl–Xe system is an interesting visible, excimer laser candidate, as the molecular spectra extend very far into the red wings of the resonance lines.
Scaling behavior of the inert gas Brillouin spectra
Authors: Fookson J. E. , Gornall W. S. , Cohen H. D.
Published: February 2003

High resolution Brillouin spectra of the inert gases argon, neon, and helium have been studied at low pressures. Excellent agreement is found with spectral profiles S (k,ω) computed from the Boltzmann equation via kinetic modeling. The results demonstrate the validity of the scaling property of the inert gas spectra when parameterized by one transport coefficient related to the size of the atoms.
Potential model for the elastic scattering of electrons by helium at intermediate energies
Authors: Paikeday Joseph M.
Published: February 2003

Differential scattering cross section of electrons scattered elastically by helium atoms is computed using a model potential constructed from the Hartree–Fock wavefunction of Roothan, Sachs, and Weiss and a three parameter phenomenological potential to account for the effects of long range polarization effects and nonlocal dynamic effects. The results are in good agreement with the recently published experimental data of Bromberg. The calculated values of the partial wave phase shifts agree with those of Ganas, Dutta, and Green and LaBahn and Callaway for angular momentum in the range 0<l<10 within 5%. Results indicate that the model based on the Hartree–Fock wavefunction and a three parameter polarization potential can predict the scattering cross section at intermediate energies within a few percent of the experimental data. On the basis of the computed cross sections in 200–700 eV range, the approximate effective electron helium interaction potential for the quantum mechanical scattering problem is found to be Ve(r) ?<Φ0‖V(r,r1, r 2) ‖Φ0≳−(0.25+0.31r) e−2.8r−αd(1+e−8r)[r4+(1.3+E/350)4]−1. The forward scattering amplitudes calculated from this model and corrected for electron exchange scattering compare favorably with the results of dispersion relation and eikonal optical model theories.
Triplet state radiationless transitions in polycyclic hydrocarbons
Authors: Clarke Richard H. , Frank Harry A.
Published: February 2003

The zero-field EPR transitions and spin sublevel intersystem crossing rates for the lowest triplet states of tetracene, perdeuterotetracene, 1,2-benzanthracene, and 1,2,3,4-dibenzanthracene have been measured in n-alkane solvents at 2°K by optical detection of magnetic resonance techniques. The rates of spin sublevel intersystem crossing are primarily nonradiative, and an analysis of these molecules, as well as the triplet state dynamics of several groups of polycyclic hydrocarbons, is presented with conclusions applicable to planar aromatic organic systems in general. Comparison of the triplet state intersystem crossing rates of the polycyclic hydrocarbons suggests that nonradiative transitions for the individual spin sublevels of the lowest triplet state may be qualitatively understood and predicted by a determination of the symmetry-selected one-center spin-orbit coupling mechanism available to each triplet sublevel.
PES of atomic and molecular bismuth
Authors: Süzer S. , Lee S.-T. , Shirley D. A.
Published: February 2003

HeI photoelectron spectra of Bi and Bi2 were recorded by studying bismuth vapor at 750°C. The spectrum of Bi was found consistent with a j–j coupling description of the ground state. However, relativistic effects seemed to have little influence upon the relative photoionization cross sections of the 3P0,1,2 lines. Satellite peaks 1D2 at 11.49 eV, and possibly also 3D1,2 at 17.12 eV and 3F2,3 at 17.47 eV, were observed. They were assigned to admixtures of the configurations [(6s1/2)26p1/2(6p3/2)2]3/2 and [6s26p6d2]3/2 into the main ground-state configuration [(6s1/2)2(6p1/2)26p3/2]3/2. An autoionization process at the energy of HeIγ radiation (23.74 eV) was suggested by the large intensity of the HeIγ spectrum. The photoelectron spectrum of Bi2 showed three distinguishable bands at 7.53, 8.94, and 9.30 eV corresponding, respectively, to the ionic states 2Πu, 3/2 , 2Πu, 1/2 , and 2Σ+g due to ionization of a (πu6p) or (σg6p) electron. A probable fourth band was observed at 14.87 eV, and was tentatively assigned to 2Σ+u of Bi+2 formed from (σu6s) ionization. The spectrum of Bi2 was found similar to those of lighter Group VA diatomics. A relationship between the equilibrium internuclear distance and the difference between the binding energies of (σgnp) and (πunp) orbitals was established for the Group VA diatomics.
Mode specific excitation of SO2 by resonant energy transfer from laser excited CH3F
Authors: Slater Richard C. , Flynn George W.
Published: February 2003

The rate of rise of the ν3 (7.4 μ) fluorescence in S16O2 and S18O2 has been measured in CH3F/SO2/Ar mixtures subsequent to laser pumping of the 0–ν3 C–F stretching transition in CH3F. The risetimes were analyzed with the aid of a kinetic model which explicitly includes the collisional coupling between nearby vibrational states. The risetime of the S16O2 (ν2) fluorescence near 19 μ has also been measured and found to be almost two orders of magnitude slower than the risetime of the SO2 (ν3) stretching mode fluorescence. These results are consistent with mode specific excitation of SO2 by resonant energy transfer from CH3F and indicate that on the time scale of V–V crossover between CH3F and SO2 the stretching modes in SO2 (ν1 and ν3) are vibrationally hot with respect to the bending mode (ν2) in SO2.
The electronic structure of pyrazine. Configuration interaction calculations using an extended basis
Authors: Wadt W. R. , Goddard III W. A. , Dunning T. H.
Published: February 2003

Extensive ab initio double zeta basis set configuration interaction calculations have been carried out on the nπ* and ππ* states of pyrazine as well as on the low-lying n and π cations. The calculations corroborate the validity of the valence bond (VB) model for the interaction of lone pair excitations proposed earlier by Wadt and Goddard. Good agreement (errors of ∼0.2 eV) with experiment is obtained (except for the higher-lying 1ππ* states that possess significant ionic character). The calculations indicate that the order of increasing ionization potentials is 2Ag(n), 2B1g(π), 2B1u(n), and 2B2g(π). The forbidden 1 1B2g(nπ*) state is predicted to be 1.30 eV above the allowed 1 1B3u(nπ*) state. Finally, the calculations indicate that the adiabatic excitation energies to the 1 3B1(nπ*) and 1 3A1(ππ*) states in pyridine should be nearly degenerate at ∼3.6 eV.
Slip boundary conditions and the hydrodynamic effect on diffusion controlled reactions
Authors: Wolynes Peter G. , Deutch J. M.
Published: February 2003

Approximate calculations of the hydrodynamic effect on diffusion controlled reaction rates yield finite corrections to the Smoluchowski law. However, exact calculations using hydrodynamics with stick boundary conditions have the unsatisfactory feature of predicting a vanishing coagulation rate. In this paper it is demonstrated that this failure of the theory is due to the stick boundary conditions. It is shown that hydrodynamic calculations with slip boundary conditions yield a finite coagulation rate. The exact slip hydrodynamics result indicates a reduction of 29% in the coagulation rate of neutral particles relative to the classical Smoluchowski theory. This is a smaller result than the 46% reduction predicted by the approximate Deutch–Felderhof theory for particles with stick boundary conditions.
Motional characteristics of large molecules from their Raman and infrared band contours: Vibrational dephasing
Authors: Rothschild Walter G.
Published: February 2003

A simple application of Kubo’s line shape theory to the domain of vibrational frequencies is presented, compared with the experiment, and used for predictions. In vibrational modes where vibrational dephasing processes are predominant in determining the shape of the condensed phase band contour, the formalism shows that the vibrational correlation obeys a fast modulation mechanism (’’motional narrowing’’), e.g., in quinoline, tetravinyl tin, and isopropyl alcohol. However, even smaller molecules such as chloroform and methyl iodide show similar characteristics and only in exceptional cases (the uncoupled O–D stretch of D2O in H2O) is the modulation slow. This behavior is a consequence of the short modulation times (order of fractions of a picosecond) in the liquid which determine the phase loss of the vibrational amplitude after a brief period of a quasistatic distribution of molecular environments (’’rigid lattice’’) —times which can be approximately identified with the inverse average collision frequency. In order to compare theory and experiment quantitatively, the model requires that the vibrational second spectral moment must be measured in addition to the vibrational correlation function. Comparisons with vibrational memory functions, obtained from the correlation functions via the modified Langevin equation, corroborate the usefulness of the model.
Infrared absorption of hydrogen and deuterium chemisorbed on nickel
Authors: Nakata Toshiko
Published: February 2003

The infrared spectra of hydrogen and deuterium molecules chemisorbed on nickel surfaces is studied experimentally. Several new bands in this system are assigned to Ni−H and Ni−D bonds. (AIP)