bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion pair formation and atom abstraction in collisions of Cs and UF6
Authors: Annis B. K. , Datz S.
Published: February 2003

The ion pair formation reaction Cs+UF6→Cs++UF6− and the atom abstraction reaction Cs+UF6→CsF+UF5 have been studied over the relative kinetic energy range 0.2 to 1.3 eV using a seeded nozzle source for UF6. The cross section for ion pair formation was found to increase with the kinetic energy and a value of 32 Å2 was observed at 1.3 eV. Unlike previous results at thermal energies, the angular distributions of CsF provided no indication of complex formation but were found to be peaked in the backward (c.m.) direction. Estimates of the abstraction reaction cross section show it to be the dominant channel in this energy range.
Laser induced fluorescence detection and characterization of ionic and metastable reaction products
Authors: Cook J. M. , Miller Terry A. , Bondybey V. E.
Published: February 2003

Ionic and metastable products of reactions involving metastable inert gas atoms have been detected and characterized by the laser induced fluorescence (LIF) method. The LIF technique has been used to measure product vibrational distributions which can be compared with predictions based on observations of the chemiluminescence produced in these reactions. Good agreement between the LIF measurements and the chemiluminescence predictions has been obtained for A 3Σ+u N2, a 4Π O2+, and a 3Π CO. However, in the case of X 2Σg+ N2+, a surprisingly high v=0 population is detected by LIF. This observation may be explained by either extremely efficient vibrational relaxation or a ’’dark’’ channel for the production of v=0, X 2Σ+g N2+.
Stark effect study of the singlet–triplet absorption of the nitrate ion in NaNO3
Authors: Hochstrasser R. M. , Klimcak C. M.
Published: February 2003

A Stark effect has been observed on the second overtone of the 691 cm−1 vibration at 29 581 cm−1 in the lowest energy absorption spectrum of the nitrate ion in a pure crystal of sodium nitrate. The anisotropy of the effect indicates that the ion does not remain planar in the excited state and has a Lorentz corrected dipole moment of 0.47±0.05 D which is due to a displacement of the nitrogen atom out of the NO−3 plane in the excited state. The absence of a Stark effect with a field directed in the plane of the ion suggests that the excited state is not spatially degenerate as previously suggested. These Stark measurements coupled with Zeeman effect studies from this laboratory indicate that this spectral transition is to an (nπ*)3A1″ state.
The Madelung energy, intermolecular charge transfer, and disorder of HMTTF-TCNQ (hexamethylene-tetrathiafulvalenium-tetracyanoquinodimethane)
Authors: Silverman B. D. , LaPlaca S. J.
Published: February 2003

The Madelung energy of HMTTF-TCNQ (hexamethylene-tetrathiafulvalenium-tetracyanoquinodimethane) has been calculated to be 2.62 eV per donor–acceptor pair with use of a set of CNDO/2 fractional atomic charges. It is suggested that this relatively small value of the electrostatic binding energy is characteristic of incompletely charge transfered 1:1 segregated stack compounds. An examination of the experimental bondlengths of HMTTF-TCNQ also indicates that the material is incompletely charge transferred, in agreement with the results of recent diffuse x-ray scattering measurements. Regions of observed one-dimensional disordered are shown to be close in electrostatic energy to the normal orthorhombic phase. The complete atomic coordinates for the HMTTF-TCNQ structure are given.
Calculation of the matrix shift and center of mass frequency of H2 and D2 dissolved in solid argon, krypton, and xenon
Authors: Vitko John , Coll Cornelius F.
Published: February 2003

Recent experimental and theoretical studies of H2–inert gas dimer spectra have resulted in highly accurate Lennard-Jones pair potentials which include the effects of hydrogen bond stretching. We have used these potentials to calculate the matrix shift Δν and the apparent center of mass frequency νc.m. for H2 and D2 in solid Ar, Kr, and Xe. The static lattice approximation used retains the coupling between the vibrational and the translational motion of the molecule and predicts temperature-dependent values of Δν and νc.m.. Comparison of our results with experiment (where available) yields satisfactory agreement.
Molecular collisions in a laser field: Effect of the laser linewidth
Authors: Lee H. W. , DeVries Paul L. , George Thomas F.
Published: February 2003

The effect of the laser linewidth on molecular collision processes taking place in a laser field is studied, using an approximation scheme that replaces the actual frequency distribution of the field by a finite number of frequencies and weights. The choice of the frequencies and weights is conveniently accomplished by the method of Gaussian quadrature. Close-coupling calculations are performed on model systems, and the results indicate that the neglect of the laser linewidth may be justified in most collision processes in a laser field.
The detection and characterization of the visible emission spectra of lutetium monochloride, monobromide, and monoiodide
Authors: Kramer Jerry
Published: February 2003

Molecular emission has been observed in high pressure electrodeless microwave arc discharges from the monochloride, monobromide, and monoiodide of lutetium. The vibrational analyses of two electronic transitions in LuCl, LuBr, and LuI represent the first spectroscopic data for these molecules. The Lu monohalide band spectra in the visible are composed of two electronic transitions, which are degraded to the red. These transitions are characterized by long vibrational sequences, centered about Δv =0. The term values for LuBr and LuI are shifted to the red with respect to LuCl by ∼1000 and ∼2500 cm−1, respectively, for both transitions. The vibrational analyses reveal that both the upper and lower state vibrational frequencies of these two transitions are different for all three monohalides. This suggests that four different electronic states are involved in these two transitions. Explanations for these two transitions are sought by analogy with the group III (Sc, Y, and La) monohalides and the isoelectronic molecules ZrO and HfO. A comparison has been made between the vibrational frequencies of the Lu and Yb monohalides.
Thermodynamics at nonequilibrium steady states
Authors: Keizer Joel
Published: February 2003

This work continues a discussion of how to extend equilibrium thermodynamics to nonequilibrium steady states. The extension is based on molecular fluctuations of the extensive variables and gives rise to a state function, called the σ function. The σ function reduces to the entropy at equilibrium and can be constructed from a knowledge of the local equilibrium entropy and the molecular fluctuations. The σ function depends on all the variables characterizing a steady state, including fluxes of the extensive variables and reservoir parameters. The theoretical analysis of nonequilibrium fluctuations predicts that the σ function is related to stability and the kinetics around a steady state just like the entropy is at equilibrium. Calculations of the σ function are outlined for several multicomponent systems of experimental interest. Using the fluctuation–dissipation theory, a generalization of the Clausius inequality is obtained. This leads to a class of extremum principles at steady state for Legendre transformations of the σ function.
Raman spectroscopic study of nitrate glasses
Authors: Furukawa Toshiharu , Brawer Steven A. , White William B.
Published: February 2003

Raman spectra have been measured on five series of glass compositions between the nitrates of calcium, cadmium, and magnesium and the nitrates of sodium and potassium. The composition dependence of the spectra can be broadly interpreted in terms of the structure of the glasses. Further, it is observed that for any given divalent cation–degenerate ν3 and ν4 modes tends to remain at constant frequency regardless of composition, while the higher frequency component shifts to higher values as the concentration of divalent cation is increased. A theoretical model is developed which includes both fixed and stochastic perturbations. Two exact theorems about the effect of perturbations on the vibrations of the nitrate anion are proved. Using these theorems as a guide it is shown how the results of some model calculations permit an explanation of the observed band splitting and the frequency dependence of the bands. The observed frequency trends both in glass and molten salt spectra, are largely independent of the detailed geometry of the model.
Photon-induced electron transfer transitions of the solvated electrons
Authors: Funabashi K. , Carmichael I. , Hamill W. H.
Published: February 2003

The role of electron transfer transitions in the absorption spectrum of the solvated electron in liquid water is studied in terms of the generalized line shape function. When the density of trapping sites is greater than one third of the density of solvent molecules, the transition-dipole moment for photon-induced electron transfers was found to be greater than that of the single-site 1s→2p transition. The solvated electron is assumed to be coupled with low-frequency solvent modes and a high-frequency molecular mode. The latter mode is responsible for a small isotope shift in the peak energy. The spectrum consists of contributions from short-distance transfers (’’bound–bound’’) and long-distance (’’bound–free’’) transfers, the latter being the minor component of the total spectrum.
Dynamics and hydrodynamics of suspensions of translational–rotational Brownian particles at finite concentrations
Authors: Freed Karl F. , Muthukumar M.
Published: February 2003

We consider the hydrodynamics of a suspension of rigid particles in a continuum fluid. The motion of the fluid and particles is coupled by the introduction of hydrodynamic boundary conditions. The dynamics of the particles is governed by rigid body translational and rotational classical equations which are derived for the particles in the suspension at finite concentrations. The appropriate random forces are included, making these equations the Langevin equations for translational and rotational Brownian motion for particles in suspensions at finite concentration. For no-slip boundary conditions, the suspension velocity field is first derived to lowest order in the concentration, and the results are applied to spheres to evaluate the suspension zero frequency shear viscosity as η =η0(1+hvsc) where η0 is the pure fluid viscosity and vsc is the volume fraction of the spheres. The constant h equals 5/2 when both translational and rotational Brownian motion is allowed; h=4 if rotations are suppressed; while previous work on stationary suspensions yields h=5/2. A general effective medium theory is introduced to handle suspensions at finite concentrations. A series expansion provides a systematic method for evaluating the corrections to this effective medium theory which arise from correlated disturbances of the fluid velocity field by two or more suspended particles. The zero frequency shear viscosity and friction coefficients for spheres are obtained from the effective medium theory as η =η0(1−hcvs)−1 and ζ=ζ0(1−hcvs)−1, respectively, where ζ0 is the single sphere translational (or rotational) friction coefficient. In the static limit hydrodynamic screening vanishes to all orders in concentration for rigid Brownian spheres.
Theoretical studies of the low-lying electronic states of GaKr, including extrapolation to InKr and TlKr
Authors: Dunning Thom. H. , Valley Marcy , Taylor Howard S.
Published: February 2003

We report ab initio configuration interfaction calculations on the states of the gallium krypton (GaKr) molecule arising from the Ga(2P1/2,3/2,2S1/2) + Kr(1SO) and Ga+(1SO) + Kr(1SO) separated atom limits. The potential energy curves for the states arising from the Ga(2P1/2,3/2) limits, the I 1/2, II 1/2, and I 3/2 states, are found to be repulsive. The potential energy curves for the states arising from the Ga(2S1/2) and Ga+(1SO) limits, the III 1/2 and I 0 states, are both found to be weakly bound; De (III 1/2) = 0.047 eV and D (I 0) = 0.24 eV. The potential energy curves and transition moments obtained in the GaKr calculations have been used to simulate the curves and moments for InKr and TlKr. Using this data the absorption and emission coefficients of all three molecules have been calculated.
Measurements of the O++N2 and O++O2 reaction rates from 300 to 900 K
Authors: Chen Aikwo , Johnsen Rainer , Biondi Manfred A.
Published: February 2003

Rate coefficients for the O++N2 atom transfer and O++O2 charge transfer reactions are determined at thermal energies between ∼300 and ∼900 K in a heated drift tube–mass spectrometer apparatus. At 300 K the values k (O++N2)(=1.2±0.1) ×10−12 cm3/s and k (O++O2) = (2.1±0.2) ×10−11 cm3/s are obtained, with a ∼50% decrease in the reaction rates upon heating to 700 K. These results are in good agreement with heated flowing afterglow results, but the O++O2 thermal rate coefficients are systematically lower than equivalent Maxwellian rates inferred by conversion of nonthermal drift tube and flow–drift data.
Rotational tunnelling in methylpyridines as studied by NMR relaxation and inelastic neutron scattering
Authors: Müller-Warmuth W. , Schüler R. , Prager M. , Kollmar A.
Published: February 2003

Nuclear magnetic resonance (NMR) and inelastic neutron scattering (INS) techniques have been applied to study the phenomenon of methyl group tunnelling of various picolines and lutidines in the crystalline state over a wide range of temperatures. In most of these materials, two maxima—one is field independent—and two different apparent activation energies in the proton spin lattice relaxation rate have been observed. The NMR-T1 results are discussed in terms of Haupt’s model, where nuclear relaxation occurs via successive coupling of the spins with the tunnelling CH3 rotator and the phonon system. The meaning of correlation times and associated activation energies, and the connection between classical and quantum mechanical theory are considered. By INS, the tunnel splittings and the energy differences between the lowest torsional states have directly been determined. For 3,5-dimethylpyridine the tgemperature dependence of the tunnel splitting has been measured; there is agreement between this data and the NMR average tunnel frequency. Potential curves have been derived using tabulated eigenvalues. The INS results confirm Haup’s model.
A new red-edge effect in aromatic molecules: Anomaly of apparent rotation revealed by fluorescence polarization
Authors: Valeur Bernard , Weber Gregorio
Published: February 2003

Measurements of stationary fluorescence polarization at wavelengths of excitation that yield limiting polarizations close to 1/2 and 1/7, respectively, permit the characterization of the rates of in−plane and out-of-plane rotation in aromatic compounds. Propylene glycol solutions of 1- and 2-naphthylamine, some of their derivatives, anthracene, and indole show the expected dependence of the rate of rotation upon limiting polarization, but all of them additionally display on excitation at the red edge of the absorption, a decrease in the rotational rate, which then approaches the rate observed for pure out-of-plane rotations. Differential phase measurements of the polarized components of the fluorescence of 1-naphthylamine confirm this effect. After careful check of the effects of temperature and excitation wavelength upon the emission spectrum and the fluorescence lifetimes, it is concluded that the red-edge rotational anomaly arises from the existence of out-of-plane transition moments in absorption and emission in this spectral region. The physical origin of the effects and their relation to other observed red-edge phenomena are discussed.
Mobility of localized and quasifree excess electrons in liquid hydrocarbons
Authors: Berlin Yu. A. , Nyikos Lajos , Schiller Robert
Published: February 2003

The dependences of excess electron mobility on temperature and conduction state energy in saturated liquid hydrocarbons are measured in order to evaluate the mobilities in the localized and in the quasifree state and the energies of the localized state. These quantities appeared earlier as adjustable parameters of a two-state electron model. Localized electron mobility is described in terms of the motion of a microscopic bubble. The transport of the quasifree electrons is regarded as that of a plane wave scattered by density fluctuations of the liquid. This model, combined with the mobility equation of Cohen and Lekner, finds reasonable agreement with experimental values which vary between 34 and about 400 cm2 V−1 sec−1.
ESR study of radiation-induced radicals in the sugar-phosphate region of nucleotides. III. The alkoxy radical in deoxycytidine 5′-phosphate
Authors: Krilov Dubravka , Velenik Alka , Herak Janko N.
Published: February 2003

The unstable radical at 77 K in a gamma-irradiated single crystal of deoxycytidine 5′-phosphate was analyzed by ESR. A very anisotropic g tensor (g1=1.9997, g2=2.0095, and g3=2.0773) and two approximately equal β-proton couplings with isotropic values of 8.0 G were interpreted to represent a radical of the O–CH2–R form. The radical is formed by the breakage of the phosphate–ester bond. The calculated spin densities on H(5′) and H′(5′) in the INDO MO approximation are in agreement with the observed couplings. The lack of any hydrogen bonding in the radical is believed to bring about much smaller β-proton couplings from those previously observed and assigned to the same radical.
Dispersion forces between noble gas atoms
Authors: Luyckx R. , Coulon Ph. , Lekkerkerker H. N. W.
Published: February 2003

The coefficients of the R−6, R−8, and R−10 terms in the series representation of the dispersion interaction between helium, neon, and argon at distance R are calculated using an elementary variation method.
Intermolecular dynamics of deuterated benzene
Authors: Powell B. M. , Dolling G. , Bonadeo H.
Published: February 2003

Of the 24 distinct intermolecular modes of deuterated benzene, with wave vectors corresponding to the four highest symmetry points R, U, S, and T at the surface of the Brillouin zone, 23 have been observed and identified by means of coherent neutron inelastic scattering experiments. These results complement the zero wave vector data (18 normal mode frequencies) obtained previously by far infrared and Raman scattering methods, and provide a more comprehensive test of any theoretical model of the intermolecular forces in this simplest of aromatic compounds. The results are interpreted in terms of a particular force model involving pairwise interatomic forces, specified by three Buckingham 6-exponential potential functions for C...C, C...D, and D...D pairs respectively, between atoms on different molecules (so-called nonbonding interactions). The agreement between theory and experiment, as regards both the normal mode frequencies and eigenvectors, is reasonably satisfactory, but the existence of more than one set of numerically suitable parameters casts considerable doubt on the uniqueness of the model.
Nuclear electric hexadecapole interactions in solids
Authors: Segel S. L.
Published: February 2003

The quadrupole interactions in a number of solids have been investigated to determine the existence of nuclear electric hexadecapole interactions (HDI). The HDI would manifest itself as a perturbation of the quadrupolar energy levels. The following isotopes in the following compounds have been investigated: 185Re and 187Re in NH4ReO4 and ND4ReO4, 187Re in KReO4, 127I in NaIO4, 209Bi in BiOCl and BiCl3, 93Nb in NbF5 and NbCl5, and 121Sb and 123Sb in SbCl3. The internal consistency of the data is such that it is concluded that no measurable hexadecapole interactions exist in the materials studied.
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o CI calculation of the vibrational structure of the 1(nπ*) transition in formaldehyde
Authors: van Dijk J. M. F. , Kemper M. J. H. , Kerp J. H. M. , Buck H. M.
Published: February 2003

This paper reports an ab initio CI calculation of the radiative 1A1→1A2 transition of H2CO and D2CO. Throughout the calculation the electronic wavefunctions and transition moments are explicitly calculated as functions of the nuclear geometry, contrary to the conventional Herzberg–Teller approach. The evaluation of the vibrational wavefunctions and integrals was made numerically. The results show that the excited state frequency for mode 3 has to be reassigned and that the calculated vibrational structure agrees well with the experimental intensities.
Translational and vibrational energy distributions in metastable laser pumped polyatomic molecules: A quasithermodynamic description
Authors: Shamah Irwin , Flynn George
Published: February 2003

A model is proposed to describe the metastable vibrational population distribution for a laser pumped polyatomic gas which undergoes vibration–vibration energy exchange on a time scale fast compared to vibration–translation/rotation relaxation. Such systems are shown to be characterized by a multiple temperature distribution with temperature relationships governed by the vibrational energy transfer pathway. In the harmonic oscillator limit each vibrational mode is at a single mode temperature, different from the translational/rotational temperature, leading to simple expressions for the steady state thermodynamic quantities. Additional constraint equations allow the complete determination of the temperature distribution and thermodynamic quantities in terms of two initial parameters, input energy and ambient temperature. Examples of multiple temperature distributions are presented for laser pumped CH3F undergoing various relaxation pathways and at a variety of initial conditions. The selection of the hottest vibrational mode is found to depend only on the path, and this mode may not necessarily be the one with the smallest energy spacing nor the one that is actually pumped. The extent of the vibrational enhancement of this mode is dependent on the initial conditions through the conservation equations. A stable multiple temperature condition is found to exist only if a restricted number of energy transfer paths are allowed.
Cross section for single and double ionization of carbon dioxide by electron impact from threshold up to 180 eV
Authors: Märk T. D. , Hille E.
Published: February 2003

Electron impact ionization of carbon dioxide has been studied as a function of electron energy up to 180 eV with a double focussing mass spectrometer. Absolute partial ionization cross section functions have been measured for the processes CO2+e→CO2++2e and CO2+e→CO2+++3e by normalization against the Ar+ ionization cross section. Using nth root extrapolation, the following minimum ionization potentials have been derived from the low energy cross section function: CO2+(X 2Πg) =13.79±0.05 eV and I.P.(CO2++) =37.2±0.5 eV. For the doubly ionized parent molecule, a square law dependence of the cross section has been found from threshold up to some 10 eV above onset. All results obtained are compared with previous determinations where available.
Chemiluminescence and photoluminescence of CuF
Authors: Steele R. E. , Broida H. P.
Published: February 2003

Photon yields, chemiluminescence, and excitation spectra of gas phase reactions of atomic copper with F2, NF3, and SF6 have been obtained between 400 and 1000 nm. Distributions of excited state populations of the products of these reactions and vibrational constants of four previously unreported bands of CuF were measured. A pulsed tunable dye laser was used for excitation of CuF produced in chemical reactions or by thermal dissociation of CuF2. Analysis of rotationally resolved excitation spectra gives a new value of Bo=0.3692cm−1 for the B 1Σ state of CuF. Radiative lifetimes of 7.3 μsec for the A state, 1.2 μsec for the B state, and 0.6 μsec for the C state have been measured through an exponential fit to decays of photoluminescence following laser pulses. Additionally a lifetime of 0.2 to 2 msec for the upper state of the red system has been estimated from relative intensity measurements of the four states observed in chemiluminescence.
Lattice model studies of the effect of chain flexibility on the nematic–isotropic transition. III. Completely flexible chain solutes in rigid rod solvents
Authors: Dowell F. , Martire D. E.
Published: February 2003

A steric, mean field, simple cubic lattice model using DiMarzio lattice statistics for mixtures of completely flexible chain solutes in rigid rod solvents is presented. The chain solutes depress the nematic–isotropic transition temperature of the pure solvent. The slopes of the two-phase coexistence curves in the reduced temperature/mole fraction plane, solute and solvent order parameters, and solute activity coefficients for mixtures of rods and chains of various lengths are discussed and compared with relevant experimental data. The results indicate that although completly flexible chains in this model are too flexible compared with n-alkane solutes, the chain flexibility of the solute is important in determining the ability of the solute to disrupt the nematic order of the solvent.
Electronic to vibrational energy transfer from I(5 2P1/2). II. H2O, HDO, and D2O
Authors: Grimley A. J. , Houston P. L.
Published: February 2003

Time-resolved infrared fluorescence from I* (*=2P1/2) and vibrationally excited water has been observed following pulsed laser dissociation of I2 at 500 nm. The time dependence of the fluorescence signals has been used to determine the rates for the total quenching of I* by H2O, HDO, and D2O as well as for the vibrational self-relaxation of two modes of H2O and D2O. H2O and HDO are roughly 50 times more efficient in quenching I* than D2O. Analysis of relative fluorescence amplitudes shows that the quenching of I* by H2O and HDO is due entirely to an electronic-to-vibrational mechanism which produces two quanta of stretching vibration in the water molecule. The E→V mechanism is also likely to be the dominant mechanism for quenching of I* by D2O.
Theory of lower critical solution points in aqueous mixtures
Authors: Andersen G. R. , Wheeler J. C.
Published: February 2003

Two decorated lattice models of hydrogen bonded mixtures are presented that exhibit lower critical solution temperatures and closed-loop coexistence curves and that account for the strongly asymmetric closed-loop coexistence curves found in many aqueous mixtures. The models are extensions of an earlier decorated lattice model that produces only symmetric closed-loop curves. They incorporate asymmetries in both directional and nondirectional energies as well as the possibility of multiple hydrogen bonding in water. The models are exactly soluble in terms of the spin-1/2 Ising model, and exhibit nonclassical critical behavior at both upper and lower critical solution temperatures. The hydrogen bond energies in the models are in good agreement with those in real systems, and one of the models gives coexistence curves that are in reasonable quantitative agreement with most of the mixtures considered.
Vibronic structure of the second triplet state of 1,3,5-hexatriene
Authors: Frueholz Robert P. , Kuppermann Aron
Published: February 2003

Electron impact spectroscopy is used to study the vibronic structive of the second triplet state of 1,3,5-hexatriene.(AIP)
Nonequilibrium distributions on a lattice from an operator formalism
Authors: Knodel David A. , Hoffman David K.
Published: February 2003

The distribution function for n events at specified set of lattice points is derived in an operator formalism.(AIP)
Silver atom hydration: Electron spin resonance studies of silver atoms formed by radiation in water glasses at 4.2 and 77 K
Authors: Symons M. C. R.
Published: February 2003

Silver atom hydration in acqueous glasses is studied by electron spin resonance. (AIP)
On the solvation shell geometry for silver atom solvation and desolvation in ice matrices
Authors: Kevan Larry
Published: February 2003

Silver atom hydralic in acqueous glasses is studied by electron spin resonance. Shell geometry for Ag atom solvation in ice matrix is explained. (AIP)
Quasielastic neutron scattering experiments near the order–disorder phase transition on NH4Cl single crystals
Authors: Töpler J. , Richter D. R. , Springer T.
Published: February 2003

Quasielastic neutron scattering experiments on NH4Cl single crystals near the order–disorder phase transition were interpreted in terms of a model with statistically independent three- and fourfold rotational jumps. By proper choice of the orientation of the scattering vector, the corresponding jump probabilities could be determined separately. At the phase transition, the fourfold jump rate, which introduces rotational disorder, changes stepwise by a factor of ∼3, whereas the threefold jump rate remains nearly unchanged. The results are consistent with measurements applying the ’’fixed-window method’’ (high resolution experiment at zero energy transfer), and with a number of existing NMR T1 experiments. A model of rotations without a preferred rotational axis could be excluded. Results for the order parameter in the vicinity of the phase transition were also obtained. Good agreement was obtained between the activation energy for fourfold jumps from the experiments and the calculations by Hüller et al.
Quenching of NO+ vibrational radiation by N2 in the upper atmosphere
Authors: Ruderman M. A. , Foley H. M.
Published: February 2003

We estimate the partial cross section for the transfer of vibrational excitation energy between NO+ and N2 molecules to be about 10−16 cm2. This exceptionally large cross-section depends upon both the near degeneracy of the N2 and NO+ vibrations and special features of the molecular orbits caused by the strong long range interaction between the NO+ Coulomb field and the highly polarizable N2. One consequence is that little NO+ vibational radiation (4.3 μ) should be associated with ionizing radiation in the atmosphere up to altitudes above 100 km despite copious NO+ production.
Nuclear double resonance interferometric spectroscopy
Authors: Polak Micha , Vaughan Robert W.
Published: February 2003

A double resonance technique designed to allow study of quadrupolar interactions in nonintegral spin systems is described using both theoretical calculations and experimental data. The interferometric technique involves indirect detection of quadrupolar-broadened satellites by observation of only the central 1/2↔−1/2 transition. Changes in the phase factor of one wavefunction in a multilevel quadrupolar split spin system are monitored by observation of the free-induction decay of the central transition, while a 360° pulse at a second (search) frequency is applied. Particular consideration is given to the accurate reproduction of an inhomogeneously broadened satellite, and several spectroscopic schemes are compared theoretically and tested experimentally using the 23Na satellites in single-crystal sodium nitrate. Emphasis was placed on the important roles of H1 broadening and coherence transfer to the double quantum states.
Unimolecular decay paths of electronically excited species. I. The H2CO+ ion
Authors: Pires M. Vaz , Galloy C. , Lorquet J. C.
Published: February 2003

Potential energy surfaces of the lowest electronic states of H2CO+ have been calculated ab initio and the dissociation paths determined. The most important feature is a conical intersection between the surfaces of the first two excited states, Ã 2B1 and 2A1(1). This conical intersection provides a decay path characterized by a very low activation energy. If the path is followed adiabatically, CO+ ions are obtained. The path is, however, crossed by the potential energy surface of the ground state, X̃ 2B2, and, if a transition to this state takes place, HCO+ ions are produced. The coupling mechanisms are investigated, and a possible explanation of the observed isotopic effects is offered. There is a whole distribution of rate constants for the transfer of population from state Ã 2B1 to state X̃ 2B2; the distribution is found to span several orders of magnitude because of an interference effect between two predissociation mechanisms. The applicability of the quasiequilibrium theory of mass spectra is discussed.
Theory of dynamic depolarized light scattering from nonrigid polymer chains
Authors: Moro Keiji , Pecora R.
Published: February 2003

The depolarized light scattering spectrum from a dynamic, continuous chain model of a macromolecule in solution is calculated. For vanishing chain ’’stiffness’’ the results reduce to those predicted by Ono and Okano for the Rouse–Zimm model. For intermediate degrees of stiffness the contribution of the longer wavelength modes to the spectrum is enhanced.
Intermolecular potential energy surfaces from electron gas methods. III. Angle, distance, and vibrational dependence of the Ar–CO interaction
Authors: Parker Gregory A. , Pack Russell T
Published: February 2003

Angle, distance, and vibrational coordinate dependent Ar–CO intermolecular potentials, suitable for studies of rotationally and vibrationally inelastic Ar–CO collisions, are presented. The short range repulsive interaction is calculated using the electron gas model and tested against accurate ab initio SCF results at a few points; agreement is very good. Semiempirical van der Waals coefficients C6 through C8 for the long range attractive interaction of CO with He, Ne, Ar, Kr, and Xe are also determined. The resulting long and short range potentials are joined together in two different ways to give complete potentials which are smooth and reasonable everywhere and give second virial coefficients in excellent agreement with experiment.
Ferrimagnetism in Fe2F5⋅2H2O
Authors: Jones E. R. , Dawson R.
Published: February 2003

The magnetic susceptibility of Fe2F5⋅2H2O was measured over the temperature range from 5 to 300°K. A ferrimagnetic phase transition was observed at 48.5±0.25°K. At temperatures between 94 and 300°K, Fe2F5⋅2H2O followed a Curie–Weiss law χ =C/(T+ϑ), with ϑ=−138°K and an effective moment of 7.5±0.1 μB. The magnetization was well behaved below the transition and displayed no hysteresis. No evidence of a second low-temperature phase was observed.
Radiationless transitions in azulene: Evidence for the ultrafast S2→S internal conversion
Authors: Hirata Y. , Lim E. C.
Published: February 2003

The energy and isotope dependence of S2→S0 fluorescence of azulene vapor suggest that the S2→S0 internal conversion, already competitive with the S2→S1 internal conversion at zero excess energy, becomes the dominant photophysical process with vibrational excitation of molecules in S2. In azulene-d0, the lifetime of the vibrationless level of the S2 appears to be already governed largely by the S2→S0 internal conversion. The rate of the S2→S0 internal conversion at zero excess energy is estimated to be ∼2.2×108 sec−1 for azulene-d0 and ∼1.0×108 sec−1 for -d8. These are almost three orders of magnitude greater than predicted by the energy gap correlation. The origin of this ultrafast S2→S0 internal conversion is attributed to the large configurational change associated with the transition.
Electron-impact spectroscopy of the alkynes: A comparison of propyne and 1-butyne with acetylene
Authors: Flicker Wayne M. , Mosher Oren A. , Kuppermann Aron
Published: February 2003

The electronic excitation spectra of propyne and 1-butyne have been investigated by the method of variable angle electron-impact spectroscopy. In both molecules, two singlet→triplet transitions were observed with maximum intensities at 5.2 and 5.85 eV. No evidence was found for the existence of any transitions with vertical excitation energy below 5 eV. A number of previously unreported transitions to superexcited states in both propyne and 1-butyne were detected. The relationship of these spectra to those of acetylene is discussed, and the different behavior of valence and Rydberg transition energies in response to alkyl substitution is explained qualitatively in terms of the different excited state charge distributions.
Charge distributions and chemical effects. XVIII. On the relationship between total valence-electron energies and nuclear–electronic interaction energies in atoms and ions
Authors: Fliszár Sándor , Salahub Dennis
Published: February 2003

Valence shell electronic energies EN of atoms and ions, interpreted as multiplet averages, can be calculated accurately within the framework of a theory developed in terms of nuclear–electronic interaction energies Vne. The results point to a constant EN/Vne ratio, both for neutral atoms and charged species.
Photovoltaic effects of metalfree and zinc phthalocyanines. I. Dark electrical properties of rectifying cells
Authors: Fan Fu-Ren , Faulkner Larry R.
Published: February 2003

The electrical properties of thin sandwich cells (M/Pc/Au) have been studied in a quantitative fashion. Here, M is either aluminum or indium (150–400 Å thick), and Pc represents metalfree phthalocyanine (H2Pc) or its zinc complex (ZnPc). The phthalocyanines were ∼3000 Å thick. These devices were assembled by deposition in vacuo, but were studied by recording current–voltage curves in dry air. All showed rectification. Forward bias corresponded to a negative voltage at M. Cells with In contacts adhered quantitatively to expectations for Schottky junctions at the In/Pc boundaries. Cells with Al contacts passed much smaller currents under a given bias, and failed to behave quantitatively like Schottky junction devices. Various pieces of evidence indicate that the Al/Pc junction is spoiled by an interposed zone of Al2O3.
Photovoltaic effects of metalfree and zinc phthalocyanines. II. Properties of illuminated thin-film cells
Authors: Fan Fu-Ren , Faulkner Larry R.
Published: February 2003

Rather strong rectification and photovoltaic effects are observed for sandwich cells in which a thin film (∼3000 Å) of metalfree or zinc phthalocyanine is interposed between an ohmic contact (Au) and a blocking contact (Al or In). The action spectra of the short-circuit photocurrent suggest that only light absorbed near the blocking contact is effective in producing carriers for the external circuit. Cells with indium contacts show performance that is quantitatively consistent with the presence of a Schottky junction at that contact. The quantum efficiency for light incident on the ZnPc phase of an (In/ZnPc/Au) cell can be as high as 14% at 6328 Å. For light actually absorbed in the barrier region, the yield approaches unity. The efficiencies of cells with aluminum contacts are 2–3 orders smaller, apparently because an insulating layer (∼65 Å) of Al2O3 occupies the Al/ZnPc junction. This interfacial insulating film also affects the relation between the short-circuit photocurrent and the light intensity. In cells with In contacts, there is a linear, or nearly linear, current response; but for devices with Al contacts, the photocurrent rises as the cube root of the intensity. The latter dependence can be analyzed in terms of coupled diffusion and second-order decay of light-generated carriers produced near the blocking contact.
High-resolution time resolved spectroscopy of collisionless molecular beams. II. Energy randomization and optical phase relaxation of molecules in crossed laser and molecular beams
Authors: Jones K. E. , Nichols A. , Zewail A. H.
Published: February 2003

This paper outlines new ways for separating the different channels of optical dephasing of molecules in beams. It is shown that both the population loss and the optical phase relaxation rates can be obtained under collisionless conditions (molecular beams). These dephasing rates, which measure directly the homogeneous width of the prepared resonance, can be obtained with an energy resolution of better than one part in 108. Under these conditions the solution of the density matrix equations of motion is given for effusive and nozzle beams which represent a statistically open ensemble. The results, which we applied to our recent measurements of optical T1 and T2, are discussed in different limits of power broadening, beam geometry, detector characteristics, temperature of the oven (or material container), and the transit time the molecules of different velocities spend in the laser beam. Furthermore, we indicate that the treatment of coherent transients in beams utilizing conventional Bloch equations is not valid since there is a loss of optically excited molecules. Finally, we discuss possible differences between small and large molecules when they undergo radiationless (or reactive) processes following the selective laser excitation (∼10 kHz–10 MHz).
Theoretical Compton profile anisotropies in molecules and solids. III. Relationship of parallel–perpendicular anisotropies to charge distributions in alkali chloride molecules
Authors: Matcha R. L. , Pettitt B. M. , Ramirez B. I. , McIntire W. R.
Published: February 2003

Total Compton profiles and anisotropies associated with momentum distribution along vectors parallel and perpendicular to bond axes in alkali chloride molecules are calculated and related to changes in charge distributions accompanying bond formation.
Absorption spectra of heteronuclear group II metal diatomic molecules in solid argon at 10 K
Authors: Miller John C. , Andrews Lester
Published: February 2003

Codeposition of different group IIA and IIB metal atoms in rare gas matrices at 10 K has resulted in the identification of several previously unreported diatomic species from their electronic absorption spectra. Structured absorption bands were observed for ZnHg, CdHg, MgZn and MgCd at 258, 266, 318, and 327 nm, respectively, with average vibronic spacings of 85, 81, 146, and 144 cm−1, respectively, Unstructured absorptions were observed at 267 and 318 nm for Zn/Cd and Mg/Hg combinations. Spectroscopy and bonding are discussed in terms of simple molecular orbital models. The Hg2 dimer is considered in light of the ZnHg and CdHg data.
Low frequency electrical behavior of ferroelectric MASD
Authors: Mansingh Abhai , S. B. Krupanidhi , Prasad E.
Published: February 2003

The low frequency dielectric constant measurements in MASD (Methylammonium Aluminum Sulphate Dodecahydrate) indicate a second order ferro to paraelectric transition. Additional transitions are also indicated at about 145°K and 153°K by very small anomalies in the dielectric constant measurements. The thickness dependent dielectric measurements suggest the formation of a single homogeneous surface layer and the surface capacitance seems to be independent of temperature. Dielectric dispersion (in the frequency range 30–100 KHz) has been observed in the ferroelectric phase and can be attributed to domain wall motions.
Photoionization of CH3OH, CD3OH, and CH3OD: Dissociative ionization mechanisms and ionic structures
Authors: Berkowitz J.
Published: February 2003

The molecules CH3OH, CD3OH, and CH3OD have been investigated by photoionization mass spectrometry from the onset of dissociative ionization to 20 eV. The process forming methyl ion and hydroxyl radical is shown to be direct, rather than statistical. Near threshold, the process involving molecular hydrogen elimination is shown to lead to the structure HCOH+, rather than H2CO+. Removal of an H atom leads predominantly to CH2OH+, although some evidence exists for a CH3O+ structure at higher energy. Similarly, the structure HCO+ is seen to be much more prevalent than COH+, but the latter may be formed with increasing probability at higher energy. Some astrophysical implications regarding the formation of CH2O in dense interstellar clouds are discussed.
The influence of translation distortion on the two quanta vibration–vibration transitions
Authors: Jolicard Georges
Published: February 2003

We study the influence of the translation distortion on the two quanta vibration–vibration transitions by solving the DWA equations to the second perturbation order. We show that these alterations create a new transition path which only uses the linear components with respect to the vibration coordinates in the perturbation potential. This effect appreciably disturbs the two quanta energy transfer when the ratio of the two vibration frequencies is weak.
Absolute rate of the reaction of N(4S) with NO from 196–400 K with DF–RF and FP–RF techniques
Authors: Lee J. H. , Michael J. V. , Payne W. A. , Stief L. J.
Published: February 2003

Rate constants for the reaction of N(4S) with NO have been measured from 196–400 K with two independent techniques both which utilize resonance fluoresence detection for temporal analysis of N(4S). The reaction has been studied at 196, 297, and 370 K by the discharge flow-resonance fluorescence technique (DF-RF) and the measured rate constant is best represented by the temperature independent value of (2.7±0.4) ×10−11 cm3 molecule−1 s−1. The technique of flash photolysis-resonance fluorescence (FP-RF) has been used to study the reaction at 233, 298, and 400 K, and the results are best represented by the temperature independent value of (4.0±0.2) ×10−11 cm3 molecule−1 s−1. Combination of the results suggests a value of (3.4±0.9) ×10−11 cm3 molecule−1 s−1 between 196–400 K. In this work discrimination between O(3P) atom and N(4S) atom fluorescence was necessary, and this was accomplished by inclusion of an O atom resonance line filtering section as an integral part of the resonance lamp. The suggested value for the rate constant is combined with a statistical mechanical evaluation of the equilibrium constant for N(4S)+NO=N2+O(3P) to give a revised estimate for the rate constant of the back reaction. The back reaction is important in the Zeldovich mechanism for thermal production of NO in combustion systems. The rate constant is also theoretically discussed in terms of collision theory.
Diatomics-in-molecules potential surfaces for the triatomic rare gas halides: Rg2X
Authors: Huestis D. L. , Schlotter N. E.
Published: February 2003

Potential energy surfaces have been calculated for the lowest nine electronic states of Ne2F, Ar2F, Kr2F, and Kr2Cl, including spin–orbit coupling. The diatomics-in-molecules (DIM) method used takes advantage of the accurate ab initio potential curves now becoming available for the constituent diatomics. In the case of Ar2F, the DIM results are in close agreement with more elaborate calculations. DIM calculations, for a minimum of effort, supply the potential energy surfaces needed for calculating absorption and emission spectra as well as molecular dynamics.
ESR study of ice irradiated at 4.2 K, a thermally reversible radical
Authors: Johnson Joe E. , Moulton Grace C.
Published: February 2003

Polycrystalline ice was irradiated at 4.2 K with 3 Mev x-rays. ESR spectra were taken continuously from 4.2 K to 200 K. A radical which is thermally reversible, was observed at 4.2 K in addition to the spectra of the hydroxyl radical, the hydrogen atom radical, and the trapped electron. This reversible radical is also present in ice irradiated at 77 K and cooled to 4.2 K, but in smaller amounts. This radical with the same maximum g-value, g=2.08, but a narrower line width, was also observed in polycrystalline D2O irradiated at 4.2 K.
Luminescence and energy migration in Ba2CaUO6
Authors: Krol D. M. , Blasse G.
Published: February 2003

The luminescence of Ba2CaUO6, which has the ordered perovskite structure, is reported. Emission and excitation spectra, quantum efficiency, and decay times were measured at 4.2 K. The temperature dependence of the emission spectra and the decay time were investigated. The results show that, in Ba2CaUO6 energy transfer plays an important role, even at 4.2 K. After excitation in the intrinsic uranate centers, the energy migrates through the lattice till it is trapped at uranate centers near defects. These traps get emptied with increasing temperature. This results in a decrease of the luminescence intensity and the decay time. Furthermore, some results are given on the luminescence of Ba2CaUO6:Eu3+.