bluuebunny/crossref_metadata_2025 huggingface dataset:
Excited States of Gaseous Ions. II. Metastable Decomposition and Predissociation of the CH+ Ion
Authors: Lorquet A. J. , Lorquet J. C. , Wankenne H. , Momigny J. , Lefebvre-Brion H.
Published: February 2004

The slow fragmentation process (τ≃10−7sec) of the CH+ ion in a mass spectrometer can be ascribed to the superposition of several predissociation mechanisms. The potential energy curves of the CH+ ion have been calculated quantum mechanically, and for each intersection, the predissociation lifetime has been estimated on the basis of the Landau—Zener formula. Metastable ions are due to a spin-forbidden predissociation process, allowed by the spin—orbit (Hso), spin—other-orbit (Hsoo) and spin—spin (Hss) operators. These three operators are in some cases sufficient to obtain a lifetime much shorter than 10−7 sec. In order to give rise to a metastable fragmentation, the predissociation process must be slowed down, either by the tunnel effect, or because of a deviation from the Landau—Zener formula. The effect of the collisions on the predissociation processes is discussed. In some cases the mechanism of this effect involves energy transfer, while in others only a symmetry loss occurs. A strictly forbidden predissociation process, for which the matrix elements of Hso, Hsoo, and Hss are equal to zero, can only take place as a collision-induced process. Although they are characterized by a peculiar potential energy curve, exhibiting a shallow basin, the Rydberg states are not involved in the metastable decomposition.
Long-Range Interactions among He and Be Atoms
Authors: Arrighini G. P. , Biondi F. , Guidotti C.
Published: February 2004

Long-range dispersion energies for the atom pairs He–He, He–Be, and Be–Be in their ground states have been calculated in the form E disp=C6/R6+C8/R8+C10/R10+C11/R11+C12/R12, the coefficients Cn being obtained from the appropriate dynamic polarizabilities at imaginary frequencies. The needed polarizabilities of imaginary argument have been calculated within the time-dependent coupled Hartree-Fock approximation. Three-body nonadditive contributions to the interaction energies have been also evaluated.
Measurements of Secondary-Electron Spectra Produced by Electron Impact Ionization of a Number of Simple Gases
Authors: Opal C. B. , Peterson W. K. , Beaty E. C.
Published: February 2004

The energy distribution and angular dependence of secondary electrons generated by the impact of 100–2000-eV electrons on He, N2, and O2 and by the impact of 500-eV electrons on Ne, Ar, Kr, Xe, H2, NO, CO, H2O, NH3, CH4, C2H2, and CO2 have been measured over the 4–200-eV range. The measurements were made in a crossed-beam apparatus with the use of a fixed hemispherical electrostatic analyzer and a rotatable electron gun. The observed spectra were integrated over angle to obtain relative cross sections for secondary-electron production. It was found that the shapes of the spectra of all the gases (except Ar, Kr, and Xe, which contain intense electron emission features in this energy range) were smooth and qualitatively similar, approaching a constant cross section at low secondary energies, and falling off at high secondary energies slightly faster than Es−2, where E8 was the energy of the secondary. The shape of the spectrum was found to be nearly independent of primary energy in He, O2, and N2.
Curve Crossing of the B Σu−3 and Π u3 States of O2 and Its Relation to Predissociation in the Schumann—Runge Bands
Authors: Schaefer Henry F. , Miller William H.
Published: February 2004

Nonempirical quantum mechanical calculations including electron correlation have been carried out for the lowest Σu−3 and Π u3 states of O2. A relatively large basis set is used and 257 Σu−3 and 345 Π u3 symmetry-adapted configurations are included in the first-order wavefunctions. For the B Σu−3 state, the theoretical spectroscopic constants (with experimental values in parentheses) are Te 6.16 eV (6.17), De 0.76 eV (1.01), re 1.64Å(1.60), ω e 679 cm−1 (709), and Be 0.783 cm−1 (0.819). Neither state is well described by a single electron configuration, and the B Σu−3 state is seen to have a normal (non-Rydberg) electron distribution. The calculated potential curves indicate that the repulsive Π u3 curve crosses the inner limb of the B Σu−3 curve. Analogous calculations on the repulsive Π u1 state yield a crossing of the outer limb of the B Σu−3 Since previous interpretations of the predissociation of B Σu−3 have suggested that Π u3 crosses the outer limb, this predissociation is discussed in some detail. It is concluded that spin—orbit coupling is the principal interaction responsible for the predissociation, so that all four repulsive states that dissociate to ground state atoms are expected to predissociate B Σu−3 to roughly the same degree.
Transition Moments, Franck—Condon Factors, and Lifetimes of Forbidden Transitions. Calculation of the Intensity of the Cameron System of CO
Authors: James Thomas C.
Published: February 2004

The factors affecting the intensity of forbidden transitions in diatomic molecules are discussed. It is shown that using Franck—Condon factors to predict relative band intensities is less reliable for forbidden transitions than it is for allowed transitions. The intensity of the 0, 0 and 1, 0 bands of the a 3Π−1Σ Cameron system of CO are calculated using perturbation theory. The intensity arises from spin—orbit mixing of the A 1Π state with the a 3Π state. From the known spin—orbit coupling constant of the a 1Π state and the known intensity of the fourth positive A 1Π−1Σ transition, the oscillator strengths of the 0, 0 and 1, 0 bands are calculated to be 1.63×10−7 and 1.99×10−7. Lifetimes of various rotational levels are shown to range from 2.9 to several hundred milliseconds.
Hyperfine Pressure Shift of Hydrogen in Helium
Authors: Kunik Dan , Kaldor Uzi
Published: February 2004

The hyperfine pressure shift (HPS) of hydrogen atoms in a helium atmosphere is calculated over a wide temperature range (50–700°K). Results are not very sensitive to the exact form of the H–He potential, but depend strongly on the values of the spin density at the hydrogen nucleus at different H–He interatomic separations. Spin densities are evaluated by the spin-optimized self-consistent-field (SOSCF) method and are corrected for the long-range Van der Waals interaction. It is argued that long-range spin density shifts are indeed negative as suggested by several previous calculations, in contrast with a recent five-configuration treatment. Our results are 20%–25% higher than experimental values. Most of the error is attributed to the uncertainties concerning the method of including long-range effects.
Photoelectron Emission Spectroscopy of Solvated Electron Solutions
Authors: Baron Bill , Delahay Paul , Lugo Roberto
Published: February 2004

Instrumentation and methodology were developed for photoelectron emission (PEE) spectroscopy of sodium solutions in hexamethyl phosphoric triamide (HMPA) for irradiation from 1 to 3.7 eV. PEE currents were corrected by the Thomson equation for back scattering in the gas (nitrogen at 200–800 torr) above the solution. The Schottky effect for PEE was smaller than for thermionic emission and decreased with increasing photon energy. PEE spectra exhibited two steps corresponding, respectively, to emission by solvated electron species and metal species. The corresponding thresholds, obtained from Einstein plots, are approximately 1.4 and 2.6 eV. The first threshold is compared with the energy of the 1s state for a simple cavity model. Quantum yields were low, e.g., 10−5 emitted electron per incident photon. Thermionic and PEE currents are correlated.
Correlation Studies on H3+. II. Electron Densities and Expectation Values
Authors: Duben Anthony J. , Lowe John P.
Published: February 2004

Effects of correlation on one-electron distribution and other properties are calculated for the H3+ molecule ion. Effects due to singly substituted and doubly substituted configurations are essentially additive for this closed shell species. The effect of doubly substituted configurations is to shift charge from the molecular center to nuclear regions, mainly outside the molecule. This is rationalized in terms of the many-electron theory of Sinanoğlu. The singly substituted configurations cause a slight electronic contraction similar to that caused by initial atomic—molecular formation. Neglect of singly substituted configurations is not justified when one is seeking improvement of properties beyond the HF-SCF level.
Continuity of the Differential Oscillator Strength through a Dissociation Limit; Application to O2 Schumann—Runge and Herzberg I Systems
Authors: Smith Allan Laslett
Published: February 2004

Using semiclassical methods it is shown that, if the final molecular state in the photodissociation of diatomics has an attractive potential (with no natural or rotational barrier at large R) deep enough to support bound states, then the differential oscillator strength in the photodissociation continuum df/dν≡σ mec2/π e2 (where σ is the photodissociation cross section) may be extrapolated smoothly through the dissociation limit using the continuity relation df/dν↔fv ρ(Ev), where fv is the oscillator strength of a transition to vibrational state v and ρ (Ev)≡dv/d Ev is the density of vibrational states at energy Ev. Applied to the Schumann—Runge (B—X) system of O2, the continuity relation shows that measurements of oscillator strength in the discrete and continuous regions are reasonably consistent; accurate interpolated values of fv for the 17–0 to 20–0 bands are presented. In the Herzberg I(A—X) system, discrete band oscillator strengths determined by Hasson et al. are more consistent with the continuum measurements of Ditchburn and Young than with more recent measurements by Ogawa and by Shardandard. The implications of the continuity relation for the behavior of the photodissociation cross section at threshold are discussed.
Conductivity and Dielectric Relaxation in Concentrated Aqueous Lithium Chloride Solutions
Authors: Moynihan C. T. , Bressel R. D. , Angell C. A.
Published: February 2004

This paper describes a study of the recently recognized phenomenon of conductivity relaxation in liquid electrolytes as it is observed in the system LiCl+water. Advantage has been taken of the supercooling ability of 6–20m solutions in this system to reduce solution temperatures to the vicinity of −100°C and thereby to increase the relaxation time characteristic of the conductance process sufficiently to permit its study with conventional ac conductance bridges operating in the frequency range 0.2–2 000 kHz. Extensive data are presented for four solutions in the concentration range 8.3–11.9m. When the frequency-dependent conductance and capacitance data are analyzed in the dielectric modulus notation developed by Macedo, Bose, and Litovitz, mean relaxation times for conductance are obtained which have a non-Arrhenius temperature dependence identical to that of the dc conductivity. Earlier studies of dielectric relaxation in these solutions, carried out at room temperature and gigahertz frequencies, are re-analyzed and shown to correspond to the high-temperature extension of the same phenomenon examined at low temperatures in the present study. The characteristic migration distance associated with the conductivity relaxation time, assessed using the Nernst—Einstein equation, is of ionic dimensions. The presence of subsidiary higher-frequency relaxations is noted and their origin considered in relation to Goldstein's ubiquitous ``localized motions'' in glasses.
Dynamic Nuclear Polarization by Nitroxide, Perhalocarbon, Semiquinone, and Verdazyl Radicals
Authors: Glazer Robert L. , Poindexter Edward H.
Published: February 2004

Dynamic nuclear polarization has been examined in liquid solutions of 16 different radicals. Hexafluorobenzene was used to gauge the intermolecular hyperfine interaction. The scalar coupling reveals transient complexation between radical and receptor and various bond-forming tendencies. Perhalocarbon radicals show very weak scalar coupling with fluorine nuclei. Verdazyls show strong scalar coupling, with negligible effects from substituents on the outer phenyl rings. Phenoxyl and pyrylyl radicals show a wide range of coupling which is only partly explained by planar complexation. Semiquinones show increasing scalar coupling with increasing chlorination. DNP with aliphatic nitroxide radicals is dominated by the NO group, but aromatic nitroxides show a strong ring substituent effect, exceeding intramolecular hyperfine variation in ESR. It is suggested that DNP can provide unique signatures of substituents on phenyl rings.
Lattice dynamics of polytetrafluoroethylene
Authors: Piseri L. , Powell B. M. , Dolling G.
Published: February 2004

The normal modes of vibration propagating along the unique c axis of stretch-oriented polytetrafluoroethylene at −11, 25, and 40°C have been studied by means of coherent neutron inelastic scattering methods. No significant effects associated with the 19 and 30°C phase transitions have been definitely observed. The results, together with related information obtained from Raman scattering and infrared absorption measurements, have been analyzed in terms of various models of the forces both within and between the polymer chains. The effects of interchain forces on the shapes of the dispersion curves and on the selection rules for radiation scattering and absorption are discussed. It has not been possible to establish a satifactory model for describing all the available data, mainly because of the mathematical complexity involved in treating the dynamical behavior of the coupled chains. The calculations nevertheless indicate that this type of model is capable of providing at least qualitative agreement with experiment. The elastic constant C33 may be estimated from the limiting slope of the longitudinal acoustic branch: we obtain C33=1.50± 0.10 (1012 dyn/cm2), a constant for all three temperatures within experimental error.
Molecular structure and anharmonicity in thallium iodide
Authors: Lowndes R. P. , Perry C. H.
Published: February 2004

Far infrared and Raman spectroscopic investigations of both the orthorhombic and cubic phases of T1I are presented for the temperature range 4–570°K and for the pressure range 0–10 kbar. The results are used to discuss the molecular structure of the orthorhombic phase and the anharmonicity associated with the q ≈ 0 transverse optic mode in the cubic phase. Six Raman active and one infrared active optical modes are observed in the orthorhombic phase whereas group theory predicts six Raman active and three infrared active modes for the generally accepted D2h17 symmetry of this phase. In the cubic phase one infrared active and one second order Raman active modes are observed. Four phonon interactions through the quartic anharmonicity are found to provide the dominant contribution to the anharmonic self-energy of the q ≈ 0 transverse optic mode of the cubic phase, but unlike for T1Cl and T1Br the magnitude of the thermal strain and anharmonic contributions to the total self-energy are approximately equal.
Rates of CO + OH and H2 + OH over an extended temperature range
Authors: Westenberg A. A. , deHaas N.
Published: February 2004

Using a fast flow reactor with a fixed ESR detector and movable NO2 source (for generation of OH by the H + NO2 reaction) it was possible to measure the rate constants for CO + OH → CO2 + H (k1) and H2 + OH → H2O + H (k4) under pseudo-first-order conditions with negligible OH loss by OH + OH → H2O + O. Small losses of OH on the reactor wall were accurately taken into account, and data over an extended temperature range were obtainable. Both reactions show definite curvature in their Arrhenius plots over the range of direct measurement (298–915°K for k1 and 298–745°K for k4). Good agreement is found in comparisons with other well-defined results. In the case of Reaction (4), a definitive experiment was performed to show that by far the dominant reaction path involves breaking the H2 bond, rather than the OH bond as in Reaction (1).
Rate of the reaction OH + OH → H2O + O
Authors: Westenberg A. A. , deHaas N.
Published: February 2004

New measurements are reported on the rate constant for OH + OH → H2O + O (k2) at room temperature. The study was made with a fast flow reactor using a fixed ESR detector and a movable NO2 injector for generating OH by the H + NO2 reaction. Careful attention was paid to accounting for the effect of OH loss on the walls and of the overall stoichiometry at varying H/NO2 ratios. A large number of runs with both H excess and stoichiometric H/NO2 ratios gave k2 = 1.4 ± 0.2 × 1012cm3mole−1 ·sec−1.
Self-diffusion in liquid ammonia and deuteroammonia
Authors: O'Reilly D. E. , Peterson E. M. , Scheie C. E.
Published: February 2004

Coefficients of self-diffusion have been measured by the spin-echo technique for neat NH3 and ND3 from 200 to 298°K. The data are well represented by D=(4.5± 0.2)× 10−3exp [−(2.07± 0.02)/RT] for NH3 and by D=(6.0± 0.3)× 10−3exp [−(2.31± 0.02)/RT] for ND3. The difference in activation energy for self-diffusion between NH3 and ND3 is shown to be consistent with the viscosity measurements of Hutchison and O'Reilly. These results are interpreted by means of a quasilattice model for self-diffusion in the liquid state. Values of the work required to create a molecular vacancy are evaluated from liquid density, isothermal compressibility and the scaled particle theory. The quasilattice model yields pre-exponential factors for self-diffusion that are in reasonable agreement with experiment.
On a semiclassical study of molecular collisions. II. Application to HCl-argon
Authors: Neilsen Walter B. , Gordon Roy G.
Published: February 2004

Extensive calculations on the rotationally inelastic collisions between HCl and argon have been carried out using the semiclassical method described in the preceding paper. By a detailed study of a single system it is hoped to clarify the behavior of an atom-diatomic system during a collision, and the nature of the semiclassical model. This study also elucidates the relations between the different parts of the intermolecular potential and various experiments. We obtain an angle-dependent intermolecular potential by a least squares fit to the available experimental data, and suggest which other experiments will provide useful information about the potential.
Exact solution of the mean spherical model for charged hard spheres in a uniform neutralizing background
Authors: Palmer R. G. , Weeks J. D.
Published: February 2004

The exact solution of the mean spherical model integral equation is found for a system of charged hard spheres in a uniform neutralizing background. This may be considered as a simple example of a fluid with nonadditive hard sphere diameters. Analytic expressions are given for the direct correlation function and for the Laplace transform of the radial distribution function. These, and the thermodynamic properties of the system, are compared with previous solutions of the mean spherical model.
Continuum theory of smectic liquid crystals
Authors: Lee James D. , Eringen A. Cemal
Published: February 2004

The anisotropic physical properties resembling those of fluids and solids of smectic liquid crystals are discussed. Based upon micropolar theory, a set of constitutive equations generalizing the Kelvin-Voigt model has been derived. Material moduli are restricted by material symmetry and physical considerations. The concepts of reference state fundamental to smectic liquid crystals are discussed. Three types of problems, bending, torsion, and wave propagation, are presented. Future studies and experiments are suggested with the hope of creating further confidence in the theory.
Concentration dependent relaxation times in organic radical solids
Authors: Brown I. M.
Published: February 2004

The two-pulse electron spin echo envelope decays have been studied in rigid glass matrices of sulfuric acid and sulfuric acid-d2 containing the randomly oriented radical cations of anthracene and anthracene-d10, respectively. The sources of the time dependent local fields responsible for the shapes of the two-pulse echo envelope decays and the phase memory times have been identified. In the anthracene cation: sulfurie acid system, where the phase memory times are independent of the radical concentration, these local fields arise from spin flips of the protons on the matrix molecules which are a result of spin-spin relaxation within this proton spin system. In the deuterated system, where the phase memory times are strongly dependent on the radical concentration, the time dependent local fields have three sources: (1) the surrounding A electron spins which are flipped by the microwave pulses; (2) the surrounding B electron spins which are flipped as a result of spin-spin and spin-lattice relaxation processes within the electron spin system; and (3) the matrix deuterium spins which are flipped as a result of spin-spin relaxation processes within the matrix deuterium spin system. The electron spin-lattice relaxation times T1 have been measured at 77°K as a function of radical concentration C using an echo method. The data for both systems fit the expression 1/T1= 1.2× 107C2+28(± 5) where T1 is in second−1 and C in mole per liter. The lack of any dependence on the nature of the radical nuclei indicates that the concentration independent term is due to a spin-robit, orbit-lattice mechanism. The concentration dependent term is attributed to either a Wailer mechanism involving a modulation of the electron magnetic dipole-dipole interaction by the lattice vibrations or to the participation of clusters of radicals (pairs or triads) in the spin-lattice relaxation process. The shape of the recovery of the two-pulse echo following an adiabatic fast passage is multiexponential and its exact form is dependent on τ, the interpulse time. This is interpreted as indicating the presence of regions with different radical concentrations which probably form when the matrix solidifies.
On the polarizability theory of optical rotation
Authors: Applequist Jon
Published: February 2004

An equation is derived expressing optical rotation in terms of a set of ``relay tensors,'' which describe the manner in which the external field acting at one unit of a molecule induces a dipole moment in another unit. These tensors can be calculated from the polarizabilities of the units and the geometry of the molecule using either an exact treatment of point dipole interactions or perturbation approximations of any order. The derivation corrects certain previous errors in the calculation of induced electric and magnetic moments. The equation is transformed into alternative forms expressing the rotation in terms of electric and magnetic moments associated with certain sets of molecular normal modes in a manner analogous to Rosenfeld's quantum mechanical equation. One form gives an analytical expression for rotatory dispersion in terms of the polarizability dispersion parameters for individual units. Calculated rotations are given for a simple hypothetical molecule and for CHFClBr, in both cases showing that the lowest order perturbation terms disagree substantially with exact calculations.
Coulombic potential energy integrals and approximations
Authors: Whitten J. L.
Published: February 2004

Theorems are derived which establish a method of approximating two-particle Coulombic potential energy integrals, [φa(1) r12−1 |φb(2)], in terms of approximate charge densities φa′ and φb′. Rigorous error bounds, |[φa(1)|r12−1 |φb(2)]−[φa′(1)|r12−1 |φb′(2)]| ≤slant δ, are simply expressed in terms of information calculated separately for the pair of densities φa and φb′ and the pair φb and φb′. From the structure of the bound, a simple method of optimizing charge density approximations such that δ is minimized is derived. The framework of the theory appears to be well suited for application to the approximation of electron repulsion integrals which occur in molecular structure theory, and applications to the approximation of integrals over Slater orbitals or grouped Gaussian functions are discussed.
Adsorbate interactions on a Pt(110) surface. I. Sulfur and carbon monoxide
Authors: Bonzel H. P. , Ku R.
Published: February 2004

The kinetics of H2S adsorption on a Pt(110) crystal at T = 240°C were investigated by Auger electron spectroscopy. The sticking coefficient of H2S on a clean surface was constant up to θ = 0.6 and estimated near unity while for θ > 0.6 it decreased to about 0.03. A series of LEED patterns characteristic of adsorbed sulfur was observed with increasing sulfur coverage. The adsorption behavior of CO on clean and partially sulfurized Pt(110) surfaces was studied by flash desorption techniques. The resulting desorption energies of CO on the clean Pt surface were 25.1, 28.7 and 31.4 kcal/mole. The partially sulfurized surfaces were characterized by several new CO binding states whose energies decreased with increasing sulfur coverage. A saturated Pt surface with a sulfur coverage of θ ≃ 0.75 did not adsorb any CO. The occurence of sulfur surface phases as defined by changes in the LEED pattern were correlated with the new binding states of CO. Thus the interaction between adsorbed CO and adsorbed sulfur is rather weak and does not lead to a surface reaction. The possible effects of adsorbed sulfur on the catalytic reactivity of Pt(110) are discussed in view of the present results.
Pulse radiolysis studies. XXI. Optical absorption spectrum of the solvated electron in ethers and in binary solutions of these ethers
Authors: Jou F. Y. , Dorfman Leon M.
Published: February 2004

The optical absorption spectrum of the solvated electron has been determined by pulse radiolysis in the pure liquid ethers: tetrahydrofuran, methyltetrahydrofuran, diethyl ether, dimethoxyethane, diglyme, triglyme, and tetraglyme. The absorption maxima are at 4720, 4650, 4350, 4880, 5220, 5440, and 5580 cm−1, respectively. The half-widths of the bands have also been measured. The oscillator strength, determined for the first four ethers is approximately unity. The absorption bands have been determined in binary solutions with ethylenediamine and for tetrahydrofuran-water over the entire concentration range. Calculations using a recent form of a cavity-continuum model have been compared with the experimental results. The model shows agreement with the experimental values for the transition energy for an effective cavity radius of about 4 Å and a coordination number of 6 or 8. Kinetics for the attachment of solvated electrons to pyrene and for the reaction of the solvated electron with the solvent counterion have been investigated in several ethers and absolute rate constants determined.
19F nuclear magnetic resonance in CdF2–ErF3
Authors: Banks E. , Greenblatt M. , McGarvey B. R.
Published: February 2004

The 19F NMR of a single crystal of CdF2:≃ 10% ErF3 has been investigated at 8 and 16 MHz. Weak NMR lines were observed whose shifts relative to the main CdF2 peak were found to be field dependent. These shifts showed axial symmetry about the [111] crystallographic directions with (Δ H/H)∥=−8.73 ± 0.01) × 10−3 and (Δ H/H)⊥=+(5.83 ± 0.10) × 10−3. The small NMR lines are attributed to those lattice fluorides which have one nearest neighbor Er3+ occupying a normal Cd2+ site. The anisotropic portion of the shift is shown to be due to the dipolar contribution of spin on the erbium ion with no unpaired spin in the fluorine p orbitals. Analysis of intensity ratios supports a random distribution of Er3+ among Cd2+ sites with no preferential formation of clusters.
Spectroscopic investigation of van der Waals molecules. I. The infrared and visible spectra of (O2)2
Authors: Long Charles A. , Ewing George E.
Published: February 2004

The infrared and visible spectra of gaseous oxygen have been examined at temperatures around 90°K using a long path absorption cell. At all temperatures the infrared and visible spectra show a broad band which can be assigned as collision-induced absorption. However, at low temperatures small but discrete features appear with integrated intensities dependent on the square of the gas density. These features are assigned to bound state van der Waals molecules of the type (O2)2. The visible absorption of (O2)2 studied corresponds to the Δg1 (ν=0)+1 Δg(ν=1) ←3Σg−(ν=0) simultaneous transition. The part of the spectrum attributed to bound dimers shows a progression of eight fine structure bands superimposed on the broad simultaneous transition absorption. The fine structure has been assigned to combinations of electronic and vibrational transitions involving the stretching mode of the van der Waals bond of (O2)2. In the ground state each oxygen molecule is in the Σg-3(ν=0) state, while in the excited state one oxygen molecule is in the Δg1(ν=0) state and the other is in the Δg1(ν=1) state. The spacings and convergence of the dimer vibrational levels provide a determination of the dissociation energy of the ground and excited dimer states, giving De″=87 and De′=50 cm−1. The infrared spectrum of (O2)2 occurs near the infrared inactive fundamental vibration of O2 and shows three regions of discrete absorption superimposed on the broad collision-induced band. The discrete absorption bands have been assigned to fundamental and combination bands of (O2)2. The combination band features involve hindered rotor transitions associated with the internal rotations of the O2 molecules within the dimer. From an analysis of the infrared vibration-rotation band contour of one of the dimer fundamentals, an average distance of 4.8 Å between the centers of mass of the two O2 molecules was determined for the (O2)2 van der Waals molecule. Applying the usual band analysis formulas to determine the geometry is an uncertain procedure since the data indicate that (O2)2 is weakly bonded and has a floppy structure. It was subsequently not possible to choose among possible linear or nonlinear dimer equilibrium configurations with the present experimental or theoretical information. All the spectroscopic evidence obtained here is consistent with the description of the weak bonding in (O2)2 as due to van der Waals-type interactions. There is no need to suggest a pairing of the electrons in oxygen into some sort of weak chemical bond that might stabilize (O2)2.
Integral equation solutions for the classical electron gas
Authors: Springer J. F. , Pokrant M. A. , Stevens F. A.
Published: February 2004

The hypernetted chain and Percus-Yevick approximations are used to compute the radial distribution functions and the average potential energy for a classical electron gas. The results are compared with Monte Carlo calculations. The Percus-Yevick equation gives poor results above Γ = 1.0; Γ = e2/kTa, where a is the ion-sphere radius. The hypernetted chain equation was solved for 0.05 ≤ Γ ≤ 50. The results agree qualitatively with the Monte Carlo calculations everywhere except at very small Γ, where they agree with the Debye-Hückel approximation. Definite short-range order is predicted for Γ>3.0, but the size of the peak in the radial distribution function is underestimated. The error in the peak size is about 9% at Γ = 50. The average potential energy is in error by less than 2% for 1 ≤ Γ ≤ 50.
Low energy magnetic and electric dipole transitions of the biphenyl crystal
Authors: Hochstrasser Robin M. , McAlpine R. D. , Whiteman J. D.
Published: February 2004

The absorption and fluorescence spectra of biphenyl-h10 and biphenyl-d10 neat crystals, and of lightly and heavily doped isotopically mixed crystals have been studied at 4.2 °K. The first singlet excited state of biphenyl is assigned as 1B3g (33128.2 cm−1 in biphenyl-h10, 33270.4 cm−1 in biphenyl-d10) and transitions to it are found to be consistent with a magnetic dipole mechanism by polarization measurements and calculations. The bulk of the intensity in the B3g1⇄Ag(X) transitions is electric dipole arising from Herzberg-Teller coupling through a mode b2u (9) at 626 cm−1 (h10) and ≈ 593 cm−1 (d10). The next excited state is assigned as 1B2u (M-polarized) and the splitting of the 1B3g and 1B2u states of 746.8 ± 3 cm−1 provides the inter-ring resonance interaction corresponding to the splitting of the 1B2u (D6h) state of benzene through excitation exchange interactions and second-order shifts. The isotopic mixed crystal spectra provide evidence that the width of the biphenyl crystal exciton band (from 1B3g) is less than 4 cm−1. The observation of doublets in the 1B2u excited states of biphenyl-d10 and doublets in the absorption and emission of biphenyl-h10 in biphenyl-d10 suggest that the crystal structure of d10 is changed, at 4.2°K, from the 300°K structure having two centrosymmetric molecules per unit cell. For the first time for organic crystals we report the phonon-induced spectrum: These spectra are electric dipole dipole sidebands of the magnetic zero-phonon transitions.
Low frequency modes in the Raman spectra of polyethylene and paraffins. I. Lattice vibrations and their pressure dependence
Authors: Wu Che-Kuang , Nicol Malcolm
Published: February 2004

Raman spectra of crystalline polyethylene n-C23H43 and n-C44H90 at pressures as high as 40 kbar have been studied at 77 and 298°K, and five bands characteristic of lattice modes have been observed at various pressures. Each of these bands has been assigned to a lattice mode through symmetry arguments and vibrational analysis of unit cell modes, and the pressure dependence of these five lattice frequencies have been calculated and compared with the measured values. Effects of chain folding on the polyethylene spectrum, of end groups on the spectra of n - paraffins, and of chain length on the lattice frequencies are discussed quantitatively. For a test of the present method for lattice frequency calculations, which is based upon Williams' nonbonded atom-atom pair potentials, the lattice vibrational spectrum of naphthalene was reproduced. This method with Williams' V potential also reproduces the measured lattice frequencies of n-C23H43 at 1 atm, but could not explain the pressure dependence of these lattice frequencies equally as well.
Interpretation of dissociative-electron attachment processes for carbon and silicon tetrafluorides
Authors: Wang J. Ling-Fai , Margrave J. L. , Franklin J. L.
Published: February 2004

Appearance potentials and translational energies of the products resulting from several dissociative-electron capture processes have been measured. Hypothetical potential surfaces for CF4− and SiF4− compound states and the possible dissociated products have been shown. The heat of formation of SiF3 (g) has been determined.
Infrared identification of the Pt(N2) and Pt(N2)2 complexes in low temperature matrices
Authors: Green D. W. , Thomas J. , Gruen D. M.
Published: February 2004

Several binary Pt–N2 complexes have been observed in rare-gas matrices and in pure N2 matrices at 14 °K. The N–N stretching mode in the region 2050–2360 cm−1 has been measured as well as changes in the atomic Pt absorption spectrum. Variation of N2 concentration in the rare gases, controlled annealing, and isotopic substitution have led to the assignment of the N–N stretching modes of Pt(N2) and Pt(N2)2. Several other complexes Ptx (N2)y where either x or y is 2 or more could not be uniquely identified. Evidence is presented which strongly indicates that Pt atoms diffuse in Ar matrices more readily than do N2 molecules.
Magnetothermodynamics of Ce2Mg3(NO3)12· 24H2O. II. The evaluation of absolute temperature and other thermodynamic properties of CMN to 0.6 m°K
Authors: Fisher R. A. , Hornung E. W. , Brodale G. E. , Giauque W. F.
Published: February 2004

The design and operation of a magnetocalorimeter for the highly accurate measurement of the enthalpy increase and magnetic properties of CMN over the range 0.0006 to 0.01°K are described. The essentials were as follows: A Pyrex calorimeter equipped with a Pt-9%W noninductively wound heater and carbon thermometers, and containing a very small amount of 3He gas in contact with a spherical sample of CMN suspended as a pendulum. At temperatures above 0.3°K the gas assures very rapid equilibrium. At temperatures below 0.2°K the sample will be isolated by a vacuum, produced by adiabatic demagnetization, which simultaneously cools the sample to very low temperatures. The calorimeter remains at an intermediate guard temperature to block heat leak to the sample and collect it for later accounting. All measurements were corrected for entropy and enthalpy gains due to heat leak and vibration. On the basis of measurements of the magnetic moment of CMN on 64 ``isentropic'' demagnetizations, from 25 000 or 10 000 G to − 30 G, we could find no evidence of magnetic hysteresis when the low field rate was held below 1.5 G/sec under 150G. With an entropy of 0.032 gibbs/mole Ce3+, the magnetization from −30 G to 80% of saturation, near +50 G, leads to an adiabatic susceptibility which was found to remain constant at 85.7±0.2 cm3/mole Ce3+. This extrapolates to a critical field of 60.0 G. The initial susceptibility has been tabulated from 0.001 to 0.04°K. Between 0.007 and 4°K we propose the equation, T=0.3170/(Xo−0.02221)−0.00075 °K, where 0.02221 is the molal temperature independent initial susceptibility. On the basis of heat introduction at zero field the temperature is tabulated from 0.0006° to 0.01°K. Between 0.0006 and 0.0014°K the enthalpy varies as S1.22, leading to the equation, T=1.84 × 10−3 S 0.22 °K. Heat introduction was also used at constant fields of 1000, 2500, and 5000 G. Magnetic work measurements were evaluated on isentropes to determine temperatures and heat capacities on isoerstedic fields of 1000, 2500, 5000, 10 000, and 15 000 G. The various experimental data obtained in this research have defined the CMN temperature scale from 0.0006 to 4.2°K, a seven thousandfold range of temperature. The magnitude of the range may also be expressed by stating that a similar range starting at ordinary temperatures would exceed 2 × 106 °K.
The lower electronic states of nitrite and nitrate ion, nitromethane, nitramide, nitric acid, and nitrate esters
Authors: Harris L. E.
Published: February 2004

CNDO /s –CI calculations are performed for the series of molecules: nitrite ion, nitromethane, nitramide, ethyl nitrate, methyl nitrate, nitric acid, and nitrate ion. The high intensity transitions, which occur near 6.5 eV in these molecules, are assigned to a transition to the 11B2(π0π*) state. The low intensity transitions, which occur below 6.5 eV, are assigned to transitions to 11B1(σ1π*) and 11A2(n 0π*) states. The 11A2(n 0π*) state remains at close to the same energy, 4.5 eV, throughout the series; whereas, the 11B1(σ1π*) state goes to increasingly high energy along the series. In nitrate ion, the 11A1(πD π*) and 21A2(σπ*) states, which lie above 6.5 eV in the other molecules, become degenerate with the 11B2(π0π*) and 11B1(σ1π*) states, respectively. Transitions to the 11A1(πD π*) state, which goes to lower energy across the series, may account for the high energy tail observed on transitions to the 11B2(π0π*) state. The first triplet state is assigned to the 13B1(σ1π*) and 13A2(n 0π*) state in nitrite and nitrate ion. respectively, the 13B1(σ1π*) state in nitromethane and the 13B2(π0π*) state in the nitric esters and nitric acid. The trends in the energies of these states along the series are related to the increasing electronegativity of the donor group attached to the nitro group. The 11,3A1(πD π*) states are characterized as intramolecular charge transfer states, which may be unstable to dissociation into donor and nitro group free radicals.
Photoelectron spectroscopy of high-temperature vapors. III. Monomer and dimer spectra of thallous fluoride
Authors: Dehmer J. L. , Berkowitz J. , Cusachs L. C.
Published: February 2004

The 584 Å photoelectron spectra of the monomer and dimer of thallous fluoride are presented. The observed dimer peaks are compared with semiempirical calculations based on both a planar rhombic and a symmetric linear geometry. The present experiment indicates that the thallous fluoride dimer has a linear F–Tl–Tl–F structure. The chemical bonding in the dimer is discussed. The dimer exhibits covalent bonding characteristics, whereas the monomer exhibits the ionic bonding characteristics typical of all the Group III monohalides.
Force field and tunneling effects in the H–H–Cl reaction system. Determination from kinetic-isotope-effect measurements
Authors: Stern Marvin J. , Persky A. , Klein F. S.
Published: February 2004

An iterative method is used to obtain, within the framework of the transition state theory, sets of force constants from experimental kinetic-isotope-effect data for the reaction system H2 + Cl → [H–H–Cl]‡ → H+HCl. Two sets of force constants, describing quite different transition-state structures, are found to be equally compatible with all available rate data for the reactions of chlorine atoms with H2, HD, HT, DT, D2, and T2. These force fields are compared with force fields derived by semiempirical methods. Measurements of the intramolecular kinetic isotope effect, i.e., the relative rate of production of HCl/DCl in the reaction HD+Cl, are shown to be especially suited for selecting compatible transition-state models.
Dynamics of the triplet state of phthalocyanine complexes of the platinum metals in zero field
Authors: Menzel E. R. , Rieckhoff K. E. , Voigt E. M.
Published: February 2004

The luminescence properties of phthalocyanine complexes of platinum metals with d6 and d8 electron configurations were investigated in dilute solutions between room temperature and 1.6°K. For the first time it was possible to study the magnetic sublevels of the triplet state of aromatic molecules in zero field through optical detection methods alone. It was found that the lowest triplet state of these molecules has three zero field components of unequal splitting which depends on the central metal ion and which ranges from approximately 0.1–-10 cm−-1. Intersystem crossing populates solely the highest triplet component which does not radiate to the ground state, but which, in turn, populates the lower lying triplet components. The spin-lattice relaxation rates of these processes could be estimated to be of the order of 105 sec−1 at liquid helium temperature, and the triplet to ground state (S0← T1) decay rates were obtained. A noticeable solvent dependence of the radiationless rates was observed. The effect of spin-orbit coupling and radiationless energy transfer as a function of the metal ion in the phthalocyanine complexes is discussed. Surprisingly, Pd and Rh phthalocyanine were found to fluoresce as well as phosphoresce from essentially ligand-centered,excited states, an unusual occurrence in open d shell transition metal complexes.
Measurement of the electron affinity of NO2
Authors: Leffert Charles B. , Jackson William M. , Rothe Erhard W.
Published: February 2004

The translational energy dependence of the relative cross section for Cs+NO2→Cs++NO2− has been measured in the threshold region using crossed molecular beams. Good energy resolution in the center of mass is obtained with a time-of-flight technique for the Cs primary beam and by numerical analysis of the remaining c.m. energy spread. The data are well represented by convoluting a c.m. cross section with the experimental energy spreads. This relative cross section has a threshold at 1.39±0.05 eV and yields an adiabatic electron affinity for NO2: 2.50±0.05 eV.
Evaluation of the intermolecular energy between two hydrogen molecules near the van der Waals minimum, from a perturbative procedure
Authors: Kochanski Elise
Published: February 2004

The intermolecular energy between two hydrogen molecules is evaluated from the electrostatic, repulsive, and dispersion contributions, which are supposed to be the leading terms. Calculations have been carried out for four configurations of H2–H2 and the results averaged, these latter values being compared with the available experimental data. Theoretical and experimental results are in fairly good agreement.
Electron transmission spectroscopy: Resonances in triatomic molecules and hydrocarbons
Authors: Sanche L. , Schulz G. J.
Published: February 2004

Compound states of triatomic molecules and simple hydrocarbons are studied using electron transmission spectroscopy. Structures in the derivative of the current transmitted through a gas-filled collision chamber are interpreted as resonances in the electron-molecule cross sections. At low electron energies (0–6 eV) we observe, in N2O, H2S, and C2H4, broad and featureless structures which we identify as shape resonances. In the same energy range, the molecules CO2, NO2, C6H6, and SO2 exhibit narrow structures which form vibrational progressions. In CO2, NO2, and C6H6, these vibrational progressions are identified as shape resonances; in SO2, the interpretation is not clear cut. No low-energy resonances are observed in H2O and in CH4. At higher energies (9–17 eV) we observe sharp structures for H2O, H2S, N2O, CO2, and C2H4 (but not for C6H6 and CH4). These structures form bands, each band consisting of a vibrational progression. The states which are responsible for the bands consist of two Rydberg electrons moving in the field of a particular positive-ion core. These bands are similar to those found previously in diatomic molecules.
Absolute rate constants for the reaction O(3P)+NO2→NO+O2 over the temperature range 230–339°K
Authors: Davis Douglas D. , Herron John T. , Huie Robert E.
Published: February 2004

Using the technique of flash photolysis-resonance fluorescence, absolute rate constants have been measured for the reaction O(3P)+NO2→ NO+O2. Over the temperature range 230–339°K, the rate constant was found to have the value k=9.12± 0.44 × 10−12cm3 molecule−1sec−1, independent of temperature. At stratospheric temperatures, this rate constant is about a factor of two faster than indicated from previous measurements.
J Dependence of the depolarization ratio of the rotational components of the Q branch of the H2 and D2 Raman band
Authors: Holzer W. , Duff Y. Le , Altmann K.
Published: February 2004

The theory on rotational structure of Raman bands predicts-apart from the (2J+1) magnetic degeneracy-an additional J dependence of anisotropic scattering. This implies a J dependence of the depolarization ratio, when measured for the separated rotational components J → J of the Q branch of Raman bands. We report here on experimental results obtained on the transitions J=0, 1, ···, 4 of the Q branch of H2 and D2, which are in full agreement with theory. In particular we demonstrate the completely isotropic character of the O–O transition. Our experimental value for the depolarization ratio of the total vibrational Raman band of H2 agrees well with the one obtained recently by ab initio calculations.
The hydrated proton H+(H2O)n. I. A single crystal neutron diffraction study of the oxonium ion in p-toluenesulfonic acid monohydrate, H3O+CH3C6H4SO3−
Authors: Lundgren Jan-Olof , Williams Jack M.
Published: February 2004

The pyramidal nonplanar conformation of the oxonium ion has been confirmed in the first single crystal neutron diffraction study of a salt containing discrete H3O+ cations in an isolated state, p-toluenesulfonic acid monohydrate (H3O+CH3C6H4SO3−). All H atoms have been located to high precision and the cation has molecular dimensions O–H=1.011(8) (the numbers within parentheses here and throughout the paper are the estimated standard deviations in the least significant digits), 1.013(8), and 1.008(8) Å with H–O–H angles of 110.7(5), 109.2(5), and 111.2(5)°. The oxygen atom is 0.322(4) Å out of the plane of the three hydrogen atoms. Although unrestricted by crystal symmetry, the ion has essentially C3ν symmetry. O–H separations are characteristic of those found in similarly strongly H-bonded systems where the O...O separations are fairly short at 2.53 Å.

The structure was determined using 1732 independent three-dimensional intensities measured using a neutron wavelength of 1.142 Å. The crystals are monoclinic, space group P21/c, with unit-cell dimensions (x ray) a=5.881, b=7.432, c=20.085 Å, and β = 97.95°. The structure was refined by full-matrix least-squares procedures, using anisotropic thermal parameters for all atoms, to an R(F2) of 0.067.