bluuebunny/crossref_metadata_2025 huggingface dataset:
Naphthalene ion photodissociation: Two- and four-photon processes
Authors: Kim Myung S. , Dunbar Robert C.
Published: February 2003

Multiphoton photodissociation processes in the naphthalene molecular ions have been studied both at visible (600–670 nm) and UV (240–350 nm) wavelengths. The optical spectrum obtained is similar to the one for 1-methyl-naphthalene. Based on energetics, the photodissociation in the UV requires sequential absorption of two photons, while that at visible wavelengths needs four photons. Kinetic equations for several mechanistic models are solved by either analytical methods or computer simulation. These simple models can explain the variable dependence of photodissociation rate on light intensity. Also, it is suggested that fast radiative cooling rates are responsible for the very weak pressure dependence of the observed dissociation rates. Finally, calculated results come close to quantitative agreement with observation with the further postulation that optically inert states or structures are in fast equilibrium with the excited ions.
Rate of electron capture by O2 calculated from geminate ion recombination fluorescence data
Authors: Baird James K.
Published: February 2003

Bullot, Cordier and Gauthier1 have suggested that the observed departure in their experiments on aerated solutions, from the onsage theory was due to electron capture by dissolved oxygen. It is shown that their observations are in accord with Tachiya’s form of the Mozumder limiting law for geminate ion scavenging in the presence of an electric field. The rate constant for electron capture by oxygen are derived. (AIP)
Spectrum analysis of U3+:LaCl3
Authors: Crosswhite H. M. , Crosswhite H. , Carnall W. T. , Paszek A. P.
Published: February 2003

The spectrum of U3+:LaCl3 has been analyzed; 53 crystal states of electronic origin have been identified, many of them accompanied by extensive vibronic sidebands having a recognizable structure similar to that for lanthanide-doped LaCl3. Seventeen energy level parameters were varied simultaneously in a least-squares adjustment yielding a mean error of 26 cm−1. Values for the crystal field parameters are: B20=260±64 cm−1, B40=−532±139 cm−1, B60=−1438±113 cm−1 and B66=1025±88 cm−1.
Symmetrized Liouville basis for indistinguishable particles. Application to spectral linewidth
Authors: Liu Wing-Ki
Published: February 2003

Properly symmetrized (with respect to particle exchange) Liouville basis vectors are constructed for symmetry considerations of relaxation phenomena in a gas of identical linear molecules. An explicit expression for a complex collision bracket whose real and imaginary parts correspond to the width and shift of an isolated spectral line is derived in terms of properly symmetrized S matrix elements in the total J representation.
Dynamic dipole polarizability of H2 and HeH+
Authors: Bishop David M. , Cheung Lap M.
Published: February 2003

Isotropic and anisotropic dynamic dipole polarizabilities are calculated for H2 and HeH+. The experimental values for H2, obtained from refractive index data, agree with the theoretical values to within about 0.1%. Previous theoretical–experimental agreement has been of the order of 0.7%. A new approach has been taken with respect to the treatment of the nuclear motion. Some of the problems concerning polarizabilities and nuclear motion are discussed in detail. All the wave functions used contain electron correlation through their explicit dependence on the interelectronic coordinate.
Structural features of the nonionic surfactants stabilizing long-lived bubble nuclei
Authors: D’Arrigo Joseph S.
Published: February 2003

The effects of a wide variety of electrolytes (each at 0.4 M), and one selected organic compound, on bubble production in agarose gels has been studied. Several different commercial preparations of ultrapure agarose were compared for each of the 42 different electrolytes tested, and for phenol (1% v/v in H2O), in order to clearly identify reproducible and significant trends in the chemical data on bubble formation. The anion and cation sequences obtained with regard to the extent of bubble suppression contain many similarities with published data in the physicochemical literature for salting out of identified nonionic surfactants. Moreover, the precise pattern of electrolyte effects on bubble formation yields specific clues as to the structural characteristics of the nonionic surfactants stabilizing bubble nuclei present in different agarose gels. Specifically, the pronounced reduction of bubble number by polyvalent anions and by 1% phenol suggest that the polar portions of these nonionic surfactants represent primarily amide groups. This view was supported by the cation bubble-reduction sequence Na+≳K+≳Li+ consistently observed with the purest agarose preparation tested; this cation sequence indicates that the polar portions of the surfactant molecules are neither weakly acidic nor weakly basic, but essentially neutral as is the dipolar amide group. The above evidence for amide groups is also consistent with the relative position of Mg2+ in all the cation sequences obtained, which repeatedly indicated appreciable (and often strong) salting out in each case. This last result renders it quite unlikely that ether linkages, which commonly occur in artificially produced surfactants, contribute to the hydrophilicity of the nonionic surfactants stabilizing bubble nuclei in the different aqueous (agarose) gels tested. The nonionic surfactants stabilizing long-lived bubble nuclei are probably mostly, if not all, of natural origin.
Local polarization theory for field-induced molecular multipoles
Authors: Oxtoby David W.
Published: February 2003

We outline an approach based on applying concepts from electrostatic theory locally to the electrons of single molecules and demonstrate that it provides a rigorous and computationally practical method for calculating the multipole moments induced in atoms and molecules by nonuniform electric fields. The theory is applied to the simplest case of a hydrogen atom in inhomogeneous fields. We propose the use of this approach to treat the effects of nonuniform fields in liquids.
Comparison of local exchange potentials for electron–N2 scattering
Authors: Rumble John R. , Truhlar Donald G.
Published: February 2003

We consider vibrationally and electronically elastic electron scattering by N2 at 2–30 eV impact energy. We consider static, static-exchange, and static–exchange-plus-polarization potentials, Cade–Sales–Wahl and INDO/1s wave functions, and semiclassical exchange and Hara free-electron–gas exchange potentials. We show that the semiclassical exchange approximation is too attractive at low energy for N2. We show quantitatively by consideration of partial and total integral cross sections how the effects of approximations to exchange become smaller as the incident energy is increased until these differences are about 8% for the total integral cross section at 30 eV.
Dissipative structures in reaction–diffusion systems: Numerical determination of bifurcations in the sphere
Authors: Hunding Axel
Published: February 2003

The steady state spatial patterns arising spontaneously in open nonlinear reaction–diffusion systems beyond an instability point of the thermodynamic branch are studied numerically for a simple kinetic scheme. The set of nonlinear partial differential equations, describing the system, is converted to a (large) set of ordinary differential equations. It is stressed that the resulting system is stiff, and must be solved accordingly. An efficient algorithm is outlined, based on Stiff predictor–corrector formulas and sparse matrix techniques, which yield a gain of a factor 470 in computing time over nonstiff methods. The developed algorithm is used to determine quantitatively the primary and first few secondary bifurcations in the sphere, thus simulating a biological cell or early blastula. Spontaneous gradient formation and ’Chemical hysteresis’, connected to the occurrence of multiple steady states, is encountered. The succession of stable patterns found for increasing size of the sphere is suggested to act as an ideal mechanism underlying the process of mitosis.
Combination rules for two-body van der Waals coefficients
Authors: Diaz Peña M. , Pando C. , Renuncio J. A. R.
Published: February 2003

Combination rules are derived from which dispersion force coefficients for interactions between unlike molecules may be estimated in terms of those for the corresponding like interactions and the static polarizabilities or the sum rules. Relations between the different combination rules and the approximate dynamic polarizability function are examined. Values are calculated for the van der Waals coefficients c6, c8, and c10 of 55 atomic pairs formed from hydrogen, rare-gas, and alkali atoms. Several of the rules give agreement within a few percent when these values are compared with accurate unlike coefficients.
Electronic properties of polyacetylene, polyethylene, and polytetrafluoroethylene
Authors: Kasowski Robert V. , Hsu William Y. , Caruthers Edward B.
Published: February 2003

The extended muffin tin orbitals technique was applied to study electronic properties of polyethylene (PE), polytetrafluoroethylene (PTFE), and polyacetylene (PA). The computed optical gap is 9 and 6.2 eV, respectively, for PE and PTFE whereas it is 1.2 to 1.7 eV for PA depending on the isomeric forms. Three dimensional charge density contours are also presented.
Calculated barriers to abstraction and exchange for CH4+H
Authors: Walch Stephen P.
Published: February 2003

Saddle point geometries and barrier heights have been calculated for abstraction and exchange in CH4+H using POL–CI wave functions with basis sets up to triple zeta valence with double zeta polarization on C and single zeta polarization on H. The saddle point for the abstraction reaction is found to have C3v symmetry (abstraction collinear with a CH bond). The calculated saddle point geometry is closer to products (CH3+H2) than to reactants (CH4+H) and has the CH and HH bonds stretched by 0.38 Å (35%) and 0.18 Å (24%), respectively. The CH bond lengths of the remaining three CH bonds change only very slightly (<0.01 Å) during the reaction, while at the saddle point each methyl CH bond is ∼12.4° out of the plane perpendicular to the C–––H–––H axis and containing the C atom (19.47° for CH4 and 0° for CH3). The calculated barrier height is 15.9 kcal/mole (using the largest basis set). Comparison to comparable calculations for H3 indicates an error of ∼2.4 kcal/mole due to the POL–CI approximation leading to 13.5 kcal/mole as the best estimate of the barrier height. The saddle point for the exchange reaction has a trigonal bipyramidal geometry. The calculated saddle point geometry has rCH=1.41 Å (equal CH bond lengths), while the methyl CH bond lengths change only slightly (<0.01 Å) during the reaction. The calculated barrier height is 36.9 kcal/mole (for the largest basis set). Using the same estimate for the error due to the POL–CI approximation as for the abstraction reaction leads to 34.5 kcal/mole as the best estimate of the barrier height for the exchange reaction.
Thermal diffusion factors for the binary noble gas mixtures
Authors: Taylor W. L.
Published: February 2003

Thermal diffusion factors for the ten binary mixtures of the noble gases have been measured as a function of composition and temperature in a 20-tube trennschaukel. The compositions ranged from approximately 10 to 90 mole% of the lighter component while the average temperature of measurements for equimolar mixtures ranged from approximately 200 to 800 K. The present data, combined with results by previous workers, were correlated to obtain the ’’best’’ representation for the temperature dependences of each system using a large number of correlating functions. Theoretical thermal diffusion factors for four intermolecular potential schemes were calculated and compared to the resulting correlations. In order to avoid the possible uncertainty of the combining rules for potential parameters, those potentials employed were required to have a complete set of parameters for the ten mixtures and the pure species with the mixture parameters derived from one or more physical properties of the gas mixture. The Dymond–Alder potential with mixture parameters obtained from second virial coefficients proved the most satisfactory.
Light induced proton transfer in dihydroxyanthraquinone as studied by photochemical hole burning
Authors: Drissler F. , Graf F. , Haarer D.
Published: February 2003

The low temperature photochemistry of dihydroxyanthraquinone in various host matrices has been studied via photochemical hole burning. It has been shown that the observed photochemistry is due to the rearrangement of protons involving both intra- and intermolecular hydrogen bonds. The model is supported by spectroscopic data on the low temperature photoproduct and by optical experiments on isotopically substituted and deprotonated samples. A brief discussion of the observed homogeneous linewidth links the optical data to possible radiationless deactivation processes (T1) or to optical dephasing processes (T2) on the time scale of several picoseconds.
Intermolecular and intramolecular contributions to proton relaxation in p-methoxy-d3-benzylidene-d1-p-n-butyl-d9-aniline
Authors: Dong Ronald Y. , Bock E. , Lewis John S. , Tomchuk E.
Published: February 2003

A study of the temperature and frequency (4–100 MHz) dependence of the proton spin–lattice relaxation time in the nematic phase of p-methoxy-d3-benzylidene-d1-p-n-butyl-d9-aniline (MBBA-d13) is reported. The intra- and intermolecular contributions to the proton spin–lattice relaxation rate are separated under certain assumptions with the aid of our earlier deuteron T1 study of the same molecule. The frequency and temperature dependences of the intermolecular contribution are compared with two recent theories of intermolecular spin relaxation.
Absorption in cholesteric films and contrast of dichroic liquid crystal displays
Authors: Saupe Alfred
Published: February 2003

The light absorption of cholesteric films in the Grandjean texture is theoretically studied. Calculations are reported for two sets of refractive indices (1.77, 1.53 and 1.50, 1.40), two ratios of pitch to wavelengths (p/λ=3, p/λ=2), and various strengths of dichroism. A numerical procedure is employed for an accurate treatment of the angular dependence of absorption. The data are used to calculate the angular dependence of brightness and contrast for reflective dichroic display devices that are based on switching between Grandjean and pseudoisotropic textures.
Partially deuterated water dimers: Microwave spectra and structure
Authors: Odutola J. A. , Dyke T. R.
Published: February 2003

Radio frequency and microwave spectra for various isotopically substituted water dimers have been studied by molecular beam electric resonance spectroscopy. Resolved radio frequency hyperfine transitions have provided information about the tunneling–rotational levels of water dimer. The microwave spectra have been analyzed with a rigid rotor model to give the following structural information: Roo=2.976 Å (+0.000, −0.030 Å), ϑd=−51(10)°, ϑa=57(10)° and χa=6(20)°. The effects of large amplitude vibrational motion have been estimated and the equilibrium geometry should lie within the above limits. The experimental data is also consistent with χa and φd equal to zero for the equilibrium geometry. The water dimer structure, therefore, has a symmetry plane, a trans configuration, and a linear hydrogen bond within quoted error limits.
Two-photon photochemistry: Angular distribution of photofragments and application to isotope separation
Authors: Chen Kuo-mei , Yeung Edward S.
Published: February 2003

The resonant two-photon dissociation process in a supersonic molecular beam is investigated. Angular distributions of photofragments in such a process are derived via a density matrix formalism. Conservation of angular momentum and bound-continuum Franck–Condon factors determine the angular distributions and the photodissociation cross sections. Criteria which the polarization state of the photon fields and the initial J state of the molecule should meet, to have the largest cross section and good photofragment collection efficiency, are discussed. Applications are foreseen in laser isotope separation.
The velocity autocorrelation function in a dilute hard sphere gas mixture
Authors: Eder O. J. , Kunsch B. , Lackner T.
Published: February 2003

The velocity autocorrelation functions for the different species in a dilute hard sphere gas mixture are calculated by tracing the collision history of the individual hard spheres characterized by their number concentration (nA, nB), mass (mA, mB), and hard sphere diameter (σAA, σBB). Quantities related to the velocity autocorrelation function like the self-diffusion coefficient are calculated and compared to results obtained from the Enskog approximation scheme to the Boltzmann equation.
The polarizability anisotropy of I2 from laser assisted molecular beam spectroscopy
Authors: Callahan David W. , Yokozeki Akimichi , Muenter J. S.
Published: February 2003

The polarizability anisotropy of I2 has been measured in a molecular beam magnetic resonance experiment using laser induced fluorescence for state selection and detection. Stark fields of up to 16 kV/cm produced 50 kHz frequency shifts and α∥−α⊥=6.69±5% Å3.
Vibrational relaxation in the weak coupling limit: The role of molecular symmetry
Authors: Velsko Stephan , Oxtoby David W.
Published: February 2003

We present a set of simple symmetry rules for atomic force correlation functions which determine vibrational relaxation rates in liquids and gases. In addition to greatly simplifying the rate expressions, these rules may provide a basis for understanding vibrational propensity rules in the weak coupling limit.
Effect of matrix on vibrational relaxation: NH and ND X 3Σ− in rare gas solids
Authors: Bondybey V. E. , English J. H.
Published: February 2003

Lifetimes of the v″=1 level of NH and ND in solid rare gases at 4 K are measured. In each matrix, a strong isotopic effect is found with ND relaxation rate a factor of about 100 slower than that of NH. For each isotope a strong dependence upon the host lattice is observed. The rates increase dramatically with decreasing mass of the host matrix, and the relaxation in solid Ne is almost four orders of magnitude faster than in Kr. The rates show only mild temperature dependence.
Perturbation theory and the thermodynamic properties of fluids. I. General theory
Authors: Kerley Gerald I.
Published: February 2003

This paper is the first of three articles describing a new approach to the perturbation theory of liquids and dense gases. The thermodynamic properties are calculated from an expansion about a hard sphere fluid reference system, in which the hard sphere diameter is chosen by a variational principle. The method differs from that of other investigators in the description of the intermolecular forces and in the calculation of corrections to first order theory. The energy of a fluid molecule is defined by a function which depends upon the local configuration of its neighbors. All terms in the expansion are given by averages of this quantity instead of the pair potential. A modified form of the λ expansion is used to derive new expressions for corrections to first order theory, and approximations for these corrections are derived using concepts from macroscopic fluctuation theory. Using these formulas, the expansion can be computed to all orders in the perturbation. The theory is developed in terms of a general set of variables and the corresponding distribution functions which describe the short range structure of fluids.
The rotational spectra of weakly bound dimers of carbon monoxide and the hydrogen halides HX (X=F, Cl, and Br)
Authors: Legon A. C. , Soper P. D. , Keenan M. R. , Minton T. K. , Balle T. J. , Flygare W. H.
Published: February 2003

A microwave spectrometer was used to measure the molecular constants of the dimers and to establish the linearity of the atom arrangement. (AIP)
Direct determination of individual reaction cross sections for the two spin-orbit states Ar+(2P3/2, 2P1/2)
Authors: Tanaka Kenichiro , Durup Jean , Kato Tatsuhisa , Koyano Inosuke
Published: February 2003

The TESICO method was used to study the reactions Ar+(2Pj)+H2(D2)→ArH+(ArD+)+H(D).
Ultrahigh vacuum ESR studies on clean metal surfaces: NO2 on copper
Authors: Nilges M. , Shiotani M. , Yu C. T. , Barkley G. , Kera Y. , Freed J. H.
Published: February 2003

A resonant microwave cavity (Cylindrical Teoll mode) was employed to study NO2 adsorbed on Cu supported on Vycor, on Cu wires of 99.999% purity, and on evaporated Cu films. (AIP)
The emission of CH3O from the reactions of metastable rare gas atoms with methanol
Authors: Sutoh M. , Washida N. , Akimoto H. , Nakamura M. , Okuda M.
Published: February 2003

The uv emission spectra of CH3O (2A1→X2E) observed in the reactions of metastable rare gas atoms (Ar and Kr) with methanol are reported.(AIP)
Comment on ‘‘Phase transitions in lattice gases with linear clusters. I’’
Authors: Heilmann Ole J.
Published: February 2003

The paper by Poland and Swaminathan1 on the lattice gas model is commented upon. It is argued that the occurance of phase transitions is intimately connected to the occurence of a phase transition in the hard core model where only clusters with no surface energy are allowed.(AIP)
A classical trajectory study of xenon atom–chlorine dimer collisions
Authors: Brady John W. , Doll Jimmie D. , Thompson Donald L.
Published: February 2003

Classical trajectory calculations were performed for the collision of xenon atoms with van der Waals dimers of chlorine molecules. Experimental results indicate that much more energy than required for dissociation of the dimer bond is deposited in the molecular vibrations in such processes without disrupting the complex. No energy transfer to the molecular bonds was observed for the trajectory studies, but energy was transferred to van der Waals modes. No long-lived clusters were found in which the energy transfer exceeded the van der Waals well depth. The energy threshold for collision induced dissociation was found to be roughly equal to the van der Waals well depth, in contrast to the large thresholds reported for the molecular beam experiments. It is suggested that possibly the commonly accepted values for the depth of the van der Waals wells in chlorine dimers are too small.
Study of UF6 photodissociation through light scattering of UF5 particles
Authors: Borsella E. , Catoni F. , Freddi G.
Published: February 2003

The process of UF6 photodissociation as function of pressure and excitation wavelength has been investigated through measurements of the light scattered by UF5 particles formed after excitation of UF6 in the range 365–425 nm. The influence of N2 as collisional partner has been studied.
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o and Gordon–Kim intermolecular potentials for two nitrogen molecules
Authors: Ree Francis H. , Winter Nicholas W.
Published: February 2003

Both ab initio MO–LCAO–SCF and the electron-gas (or Gordon–Kim) methods have been used to compute the intermolecular potential (Φ) of N2 molecules for seven different N2–N2 orientations. The ab initio calculations were carried out using a [4s3p] contracted Gaussian basis set with and without 3d polarization functions. The larger basis set provides adequate results for Φ≳0.002 hartree or intermolecular separations less than 6.5–7 bohr. We use a convenient analytic expression to represent the ab initio data in terms of the intermolecular distance and three angles defining the orientations of the two N2 molecules. The Gordon–Kim method with Rae’s self-exchange correction yields Φ, which agrees reasonably well over a large repulsive range. However, a detailed comparison of the electron kinetic energy contributions shows a large difference between the ab initio and the Gordon–Kim calculations. Using the ab initio data we derive an atom–atom potential of the two N2 molecules. Although this expression does not accurately fit the data at some orientations, its spherical average agrees with the corresponding average of the ab initio Φ remarkably well. The spherically averaged ab initio Φ is also compared with the corresponding quantities derived from experimental considerations. The approach of the ab initio Φ to the classical quadrupole–quadrupole interaction at large intermolecular separation is also discussed.
Semiclassical calculation of eigenvalues for a three-dimensional system
Authors: Noid D. W. , Koszykowski M. L. , Marcus R. A.
Published: February 2003

A method utilizing integration along invariant curves on Poincaré’s surfaces of section is described for the semiclassical calculation of eigenvalues for three and higher dimensional systems, supplementing thereby our previous work in two dimensions. The eigenvalues calculated for anharmonically coupled oscillators agree well with the exact quantum eigenvalues.
Near Hartree–Fock calculations on I2 and its positive and negative ions
Authors: McLean A. D. , Gropen O. , Huzinaga S.
Published: February 2003

Potential curves from single configuration SCF calculations near the complete basis set limit are reported for ground state I2(1Σ+), ground state I−2(2Σ+), and the lowest I+2(2Ρ) and I+2(2Σ+) states. Orbitals are expanded in a Slater basis; the Hamiltonian is the usual nonrelativistic one with no spin–orbit and other relativistic effects. The calculations are done to provide a benchmark for model-potential, multiconfiguration, and relativistic and spin-orbit studies. The effect of performing calculations in a symmetry lower than that of the nuclear frame is discussed, and the unusual example of two stable SCF solutions at a given nuclear separation, both computed in the lower symmetry, is demonstrated for I+2(2Π). An experimental value for De(I−2) of 1.07±0.1 eV is derived; compared with the Hartree–Fock computed value of 0.60±0.05 eV. Potential curves are analysed for spectroscopic constants. The Hartree–Fock electron affinity of I2 is 2.17±0.1 eV compared with observed 2.58±0.1 eV. The Hartree–Fock quadrupole moment of the I2 molecule in its ground state is 6.24×10−26 esu cm2.
Model potential SCF calculations on Cl2, Br2, I2
Authors: Gropen O. , Huzinaga S. , McLean A. D.
Published: February 2003

The model potential method proposed by Bonifacic and Huzinaga is tested for Cl2, Br2, and I2. The results are compared with all electron Hartree–Fock–Roothaan calculations, since the method is primarily designed to simulate them, not to reproduce experimental data directly. Overall performance of the method is satisfactory, but the results for I2 may be indicating possible difficulties with increasing nuclear charge.
Theoretical studies of the HeCN+ and NeCN+ molecular ions
Authors: Wilson Stephen , Green Sheldon
Published: February 2003

Self-consistent field calculations are presented for HeCN+ using several basis sets; calculations for HeH+ with the same basis sets are given for comparison. These predict that HeCN+ is stable with a He–CN+ dissociation energy between 1.5 and 2.0 eV. The binding is found to be mainly electrostatic in nature. Rotation and hyperfine spectral constants are predicted. Similar calculations indicate that the isocyanide HeNC+ is not stable. Preliminary calculations on NeCN+ indicate that it is as stable as HeCN+. The possibility of observing noble gas molecular ions in laboratory experiments and in interstellar space is discussed.
New low-temperature crystalline phase of ferrocene: Isomorphous to orthorhombic ruthenocene
Authors: Berár Jean-François , Calvarin Gilbert , Weigel Dominique , Chhor Khay , Pommier Claude
Published: February 2003

A new low-temperature phase of ferrocene Fe (C5H5)2, stable below 250 K, has been characterized by means of x-ray diffraction on powder and differential scanning calorimetry experiments. Lattice of this phase is orthorhombic and its molecular packing is isomorphous to ruthenocence one, so configuration of ferrocene molecules is eclipsed (D5h symmetry). Experimental conditions to obtain this orthorhombic phase are discussed in connection with crystallite size.
The coordination (hydration) of rare earth ions in aqueous chloride solutions from x-ray diffraction. III. SmCl3, EuCl3, and series behavior
Authors: Habenschuss Anton , Spedding Frank H.
Published: February 2003

The inner sphere water coordination of Sm3+ and Eu3+ in concentrated (3.23 m) aqueous chloride solutions was obtained from x-ray diffraction measurements at 25 °C. The average water coordination is 8.8 for Sm3+ and 8.3 for Eu3+. The average RE3+–H2O distances are 2.474 Å for Sm3+ and 2.450 Å for Eu3+. The average RE3+⋅⋅⋅Cl− ion pair distances occur near 4.9 Å. A careful examination of the x-ray diffraction results for ten rare earth chloride solutions indicates that the inner sphere water coordination of the rare earth ions in aqueous solutions decreases from nine to eight due to the decreasing rare earth ionic radii. The ions La3+ through Nd3+ are nine coordinated, those between Nd3+ and Tb3+ are transitional between nine and eight, and those from Tb3+ to Lu3+ are eight coordinated.
Spin–lattice relaxation of reorienting or tunneling deuterated methyl groups
Authors: Tang J. , Pines A. , Emid S.
Published: February 2003

The spin–lattice relaxation of deuterated methyl groups, which is exponential at high temperatures, becomes nonexponential at low temperatures as evidence of the coupling between the Zeeman and tunneling systems. The dominant relaxation is considered to be the quadrupole interaction. Experimental results at liquid nitrogen and liquid helium temperatures support the theoretical model.
The effect of pressure on the Raman spectrum of NH4I
Authors: Heyns A. M. , Hirsch K. R. , Holzapfel W. B.
Published: February 2003

The Raman spectra of NH4I and ND4I are reported at pressures up to 130 kbar and the II–IV transition in this compound is observed to occur at 27(5) kbar at room temperature. The Raman spectral changes which characterize this transition are very subtle and it is concluded that a considerable amount of disorder can still be found immediately above the II–IV transition in the presumably fully ordered phase IV. The behavior of both the N–H stretching modes as well as the librational mode of the NH+4 ions show that at both 298 and 100 K the strength of hydrogen bonding increases when the pressure is raised in phase IV. Two different potentials are used to calculate the barrier heights for the librational motions in NH4I and it is found that anharmonicity is of much less significance in this compound than in NH4Cl and NH4Br. At higher pressures in phase IV the behavior of ν6, however, shows that a volume effect becomes important and this most probably gives rise to the IV–V transition which occurs at 54(4) kbar in NH4I at 298 K and 40(1) kbar at 100 K. The Raman spectra of NH4I (V) are characterized by the appearance of a large number of lattice modes as well as by the disappearance of the LO–TO splitting of ν3 and changes in the relative intensities of the N–H stretching modes. The librational mode ν6 shifts upwards in frequency rather rapidly in NH4I (V) but the N–H stretching modes show only a very slight downward frequency shift. It is not possible to elucidate the structure of NH4I (V), from a consideration of the Raman spectra of powdered samples only, however, similarities and differences between phase V spectra and those of the fictitious phase ’’V’’ of NH4Br, as well as those of other well-known structures of NH+4 compounds are pointed out.
Spectra of Sn2 in argon matrices
Authors: Epting Michael A. , McKenzie Martin T. , Nixon Eugene R.
Published: February 2003

Absorption, fluorescence, and resonance Raman spectra are reported for the diatomic tin molecule isolated in argon matrices. Fluorescence systems provide information on the location of four excited electronic states, including one only 3000–5000 cm−1 above the ground state. A potential energy diagram is proposed for the low lying states and comparisons are made with matrix-isolated Pb2.
Weakly bound complexes of sulfur trioxide: The structure of ArSO3 and the dipole moment of N2SO3
Authors: Bowen K. H. , Leopold K. R. , Chance K. V. , Klemperer W.
Published: February 2003

Microwave and radio frequency spectra of ArSO3 and radio frequency spectra of N2SO3 are measured by molecular beam electric resonance spectroscopy. Both complexes are symmetric rotors. The spectroscopic constants determined for Ar32SO3 are B=1449.089 (5) MHz, DJ=3.6 (6) kHz, and μ=0.2676 (3) D. For Ar34SO3, B=1439.090 (5) MHz. The stretching frequency of the weak Ar–S bond is 61. (5) cm−1, and the force constant is thus 0.059 (10) mdyn/Å. The Ar–S bond length in ArSO3 is 3.350 (1) Å. The Ar–S–O angle is found to be 90.5° (5), thereby indicating no significant out-of-plane distortion of the SO3 moiety. Preliminary assignment of the N2SO3 spectrum yields a dipole moment of 0.46 (1) D. Electric deflection studies show that (SO3)2 and (SO3)3 are polar species, while Xe2SO3 is not.
Chemiluminescence from the Ca(4s3d 1D)+O2 reaction: Absolute cross sections, photon yield, and CaO dissociation energy
Authors: Irvin John A. , Dagdigian Paul J.
Published: February 2003

Chemiluminescence has been observed at 675 to 900 nm from the reaction Ca(4s3d 1D)+O2→CaO*+O under single collision conditions. From the short wavelength limit of the chemiluminescence, the dissociation energy of CaO is found to be 4.11±0.07 eV, in agreement with the lower of two currently disputed values. Absolute chemiluminescence cross sections for emission from CaO(A′ 1Π) and CaO(A 1Σ+) are (3.2±1.4)×10−16 cm2 and (1.1±0.48)×10−16 cm2, respectively, and a lower bound of (5.2±2.5) is given for the total photon yield. The present Ca* source, in which a gaseous discharge is used to excite the atoms, was found to produce the metastable 3P0J and 1D levels very efficiently. Under optimum conditions (different for the two states), up to 85% of the atoms can be converted to the 3P0J levels, and 5% into 1D. A previous laser fluorescence study [L. Pasternack and P. J. Dagdigian, Chem. Phys. 33, 1 (1978)] of the reactions of Ca* with O2 and CO2 is reinterpreted using the lower value of the CaO dissociation energy.
A new semiclassical decoupling scheme for electronic transitions in molecular collisions: Application to vibrational-to-electronic energy transfer
Authors: Lee Hai-Woong , Lam Kai S. , DeVries Paul L. , George Thomas F.
Published: February 2003

A new semiclassical decoupling scheme (the trajectory-based decoupling scheme) is introduced in a computational study of vibrational-to-electronic energy transfer for a simple model system that simulates collinear atom–diatom collisions. The probability of energy transfer (P) is calculated quasiclassically using the new scheme as well as quantum mechanically as a function of the atomic electronic-energy separation (λ), with overall good agreement between the two sets of results. Classical mechanics with the new decoupling scheme is found to be capable of predicting resonance behavior whereas an earlier decoupling scheme (the coordinate-based decoupling scheme) failed. Interference effects are not exhibited in P vs λ results.
Action-angle variables for the quantum three particle system
Authors: Augustin Stuart D. , Demiralp Metin , Rabitz Herschel , Askar Attila
Published: February 2003

This paper uses the newly developed quantum action-angle variable formalism to reduce the Schrödinger equation for the three atom system to the minimum number of coordinates, four. A transformation is also presented which converts the operator to a form amenable to conventional direct numerical integration techniques. Computational considerations relevant to the application of finite elements are discussed, and these are illustrated with a numerical calculation of the quantum energy levels of a rigid asymmetric rotor. The ordinary differential equation which is derived for the last problem permits an unambiguous assignment of the correct expression for the total angular momentum, and the result is different from that used in previous semiclassical calculations.
Electron delocalization in the lowest triplet state of the covalently linked pyrochlorophyllide a dimer
Authors: Clark Robert F. , Clarke Richard H.
Published: February 2003

The light dependent EPR signals are observed for frozen solutions of pyrochlorophyllide a dimers in methanol and toluene. The measurements were taken at 77 °K with a mercury-xenon lamp of 200 W power focused on the samples.
Preliminary solid–solid phase diagram for nitrogen–methane mixtures by x-ray diffraction
Authors: Connolley Donald , Milbrodt Thomas , Stoner Ronald
Published: February 2003

The lattice of molecular centers of solidified mixtures of methane and nitrogen has been determined by x-ray diffraction for a representative sample of temperatures and concentrations. Face centered cubic packing of molecules dominates the solid–solid phase diagram, except for temperatures above 36 K and high molar concentrations of nitrogen, where the hexagonal closest packing characteristic of the β phase of solid nitrogen persists.
Rational fraction representation of diatomic vibrational potentials. III. Application to H2+ 2pπu electronic state
Authors: Beckel Charles L. , Scaggs E. Rodney , Kwong Robin B.
Published: February 2003

Rational fractions [L/N] are used to represent the Born–Oppenheimer potential V for the H2+ 2pπu electronic state. Numerator and denominator polynomials in R are of degree L and N, respectively, with N contrained to be L+3. This state has a maximum at R∼26 a.u. (Bohr radii) and a minimum at 7.9 a.u. Hence, it places rather severe demands on a V(R) functional representation. In spite of this, we find that a [6/9] fitting achieves an rms error at 74 R values in 5⩽R⩽90 a.u. of only 6.44×0−9 hartrees. The [6/9] is reliable for interpolation. It extrapolates at low R to a pole at −1.5×10−6 a.u. with residue 0.92 in place of correct values 0 and 1, respectively. The reliability of the extrapolation near R=0, even though no fitting points below 5 a.u. were used, is probably due to the dominance at intermediate R of the nuclear repulsion over the purely electronic energy.
The infrared spectrum of sodium bifluoride NaHf2 at 295 °K from 2100 to 5700 cm−1
Authors: Bertie John E. , Thomas Dan F. , Thorson Walter R.
Published: February 2003

The infrared transmission spectra of NAHF2 and KHF2 is reported from 2000 cm−1 to 5800 cm−1. The KHF2 and NaHF2 samples were 0.3 mm thick and were grown from 0.25 M HCl solution.(AIP)
Analytic representation of thermodynamic data for the Lennard-Jones fluid
Authors: Ree Francis H.
Published: February 2003

Thermodynamic data for the Lennard-Jones fluid, obtained from Monte Carlo and molecular dynamics calculations, are represented by a simple analytic expression that reproduces Hansen’s expression at high temperatures but extends its applicability to near the triple-point temperature.
On the use of the nuclear–electronic electric field gradient correlation of (CH3)2M moieties in testing nuclear quadrupole moments
Authors: Sham T-K.
Published: February 2003

The model developed by Gupta, Tse and Bancroft3 explains the core level ligand field splittings in photoelectron spectra. Consequently the correlations developed in 1 are regarded incorrect. The problems and modifications are discussed regardig the electric field gradient correlations of (CH3)2 M moieties. (AIP)
Electronic and geometric structure of LI4 and Na4 clusters
Authors: Beckmann H.-O. , Koutecký J. , Bonačić−Koutecký V.
Published: February 2003

The properties of the Li4 and Na 4 clusters are determined utilizing ab initio CI methods. The rhombic and bent square geometries of these alkalai metal clusters are predicted to be the most stable arrangements for the singlet and triplet states respectively. More symmetrical planar square and tetrahedron Li4 and Na4 clusters exhibit pronounced biradical features and are therefore highly unstable. The conjecture is made that the biradical character of some cluster arrangements might be connected with the catalytic activity of geometric irregularities in the surface of catalysator.
Collective theories of supercooled liquids: Supporting polariscopic and kinetic evidence in methylcyclohexane glass above T
g, using a benzene probe
Authors: Leduc J. , Kalantar A. H.
Published: February 2003

At constant temperature, structural relaxation occurs over hours with removal of strain in the viscous liquid, a change in the phosphorescence lifetime of the guest, benzene, and an increase in the viscosity. The lifetime is found to be unaffected by strain. Thus only dynamic relaxation effect(s) may affect the lifetime; the discussion of these shows that none involving internal degrees of freedom of the host or guest can be the cause. Therefore only properties of the supercooled liquid, taken as a whole, can be the cause; this provides strong support for the structure-independent theoretical approaches of Goldstein and Williams to account for relaxation of any viscous liquid near Tg.
Surface enhanced Raman scattering by pyridine on silver island films in an ultrahigh vacuum
Authors: Seki H. , Philpott M. R.
Published: February 2003

Raman scattering of laser light has been observed from submonolayer and higher coverages of pyridine deposited at temperatures down to liquid He temperatures on island films of silver in an ultrahigh vacuum chamber. The coverage was monitored by a quartz crystal microbalance. Spectral intensities were found to be independent of the amount of pyridine deposited, implying that the enhancement occurs only for coverages of the order of one monolayer.
Mild excimers: The spectrum of the dimethyl-tetrazine dimer
Authors: Brumbaugh Donald V. , Haynam Christopher A. , Levy Donald H.
Published: February 2003

The fluorescence excitation spectra of a mixture of DMT in helium is studied.(AIP)
Generation and ESR investigation of YF2 and Y(CN)2 radicals in rare gas matrices
Authors: Knight Lon B. , Wise M. B.
Published: February 2003

The YF2 and Y(CN)2 radicals have been generated and trapped in argon and krypton matrices at 12 K and studied via ESR spectroscopy. Codeposition reactions between Y and X2 were found to produce Y(CN)2 but not YF2 which was generated by the high temperature vaporization reduction of YF3. Comparisons of matrix codeposition results with gas phase reactions monitored by electronic chemiluminescence are discussed. The magnetic parameters for YF2 in argon are: g1=1.997(1), g2=1.989(1), and g3=1.985(1): 19F; A1=98(2), A2=89(2), and A3=75(2) MHz: 89Y; A1=758(3), A2=757(3), and A3=728(3) MHz. The parameters for Y(CN)2 are: g=1.973(2) and A(89Y)=672(3). The existence of low lying excited states and correlations with the Y++ ion are discussed as reasons why the electronic structure of YF2 differs substantially from that of ScF2. The electronic differences are consistent with recent entropy measurements for these two radicals.
Proton–molecule collisional interaction. IV. Core-excited resonances in H+–CO inelastic scattering
Authors: Drolshagen G. , Gianturco F. A. , Toennies J. P.
Published: February 2003

Calculations are performed for purely vibrational inelasticity in proton–CO collisions at energies below 1 eV. A realistic spherical potential and an approximate stretching parameter for the coupling matrix elements between target states are introduced. The appearance of Feshbach-type, core-excited resonances are studied for both the collinear and 3 D situation. The n=0→1 inelastic cross section energy dependence is studied between the first and second thresholds of an harmonic oscillator target description. A strong dependence on the coupling matrix is found for the resonance structures and widths, while an ultrasimple evaluation of perturbative corrections for locating the resonance positions is also discussed. A clustering and broadening of the resonances are found in this system and indicate that experimental detection in the low energy collisional regime may be possible.
Evidence for ultrafast V–E transfer in boron oxide (BO)
Authors: Hanner A. W. , Gole J. L.
Published: February 2003

Boron atoms react with oxygen (O2) and nitrous oxide (N2O) to yield the A 2Π–X 2Σ+ spectrum of BO. These reactions have been characterized from 10−5 to 10−3 Torr and at Ptotal ∼1 Torr in order to study relaxation and the rapid intramolecular V–E transfer BO(X 2Σ+, v″ =17)+X→BO(A 2Π1/2, v′=4)+X where X=O2, N2O, or a combination of these oxidants with argon. At the lowest pressures, a ground state boron atom interacts with a tenuous atmosphere of oxidant gas (beam–gas configuration). These ’’single collision’’ studies are extended in a controlled manner to higher pressure by entraining the metal atoms in argon and subsequently carrying out the oxidation of this mixture. At all pressures the measured A 2Π vibrational populations follow a markedly non-Boltzmann distribution. At pressures as low as 6×10−5 Torr, the formation of BO A 2Π1/2, v′=4 results from both the direct reaction B+RO→BO*+R and the collisional transfer BO(X 2Σ+)+RO→BO(A 2Π)+RO. The spin orbit interaction in BO connects rovibronic levels of X 2Σ+ and A 2Π1/2 facilitating a route for rapid intramolecular energy transfer. This energy transfer leads to the observation of sharp features in the neighborhood of the BO A 2Π–X 2Σ+ (4,0) band which may be correlated with the J′=18.5–21.5 perturbed rotational levels of BO(A 2Π1/2). We characterize this phenomenon determining population distributions, rotational temperatures, and the temperature dependence (boron source) of the chemiluminescence emission. The effects observed in BO demonstrate that a highly vibrationally excited ground state species interacts in the presence of a collision partner with a cross section substantially in excess of that expected for ’’gas kinetic’’ interaction. This behavior may have important implications for the modeling of energy systems as well as the ability to create population inversions requisite for the construction of visible chemical lasers.
A drift chamber study of the formation of water cluster ions in oxygen
Authors: Rakshit Asit B. , Warneck Peter
Published: February 2003

The mechanism of formation of the ions H3O+H2O and H3O+(H2O)2 in ionized oxygen, starting from O2+/O4+ has been investigated with a selected ion-drift chamber mass spectrometer, using lower water vapor pressures than previous studies. With these conditions, the H3O+ ion was not observed indicating that the reaction O2+H2O+H2O→H3O++OH+O2 is endothermic; the ion H3O+(H2O)2 was found to arise mainly from the sequence O2+H2O→O2(H2O)2+→(H2O)3+→H3O+ (H2O)2 rather than by attachment of H2O to H3O+H2O. For the intermediate ion O2(H2O)2+ one must consider the possibility that two different structures exist whose reactions with water vapor give different products.
CF3NO photodissociation dynamics
Authors: Roellig M. P. , Houston P. L. , Asscher M. , Haas Y.
Published: February 2003

The predissociation of CF3NO from 600–680 nm has been studied by monitoring the nascent NO product in real time using a two-photon laser excited fluorescence (TPEF) technique. The observation that the rate of production of NO is equal to the rate of decay of excited CF3NO indicates that no long-lived intermediate is involved in the dissociation. Detection of NO(v″=3) following 600 nm dissociation sets an upper limit of 33 kcal/mole on the C–N bond dissociation energy. The nascent vibrational and rotational distributions estimated from the observed TPEF spectra establish that greater than 95% of the NO product is formed in its ground vibrational state and that all vibrational states are rotationally excited. The rotational excitation is discussed in terms of the dynamics of the dissociation. Possible predissociation mechanisms are considered.