bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibronic intensities and rotational line strength factors for the three-photon absorption spectrum of ammonia
Authors: Nieman George C.
Published: February 2003

A perturbation theory approach is used to analyze the rovibronic structure of the three-photon resonant absorption of ammonia. The vibronic selection rules are presented in a convenient pyramid mnemonic in terms of irreducible representations of the rotation group and of the D3h point group. The analysis is presented for each possible situation, namely, all three photons are different, two photons are identical and one different, and all three photons are identical. The experimentally important case of three identical photons implies only two polarizations and two vibronic tensor elements for each symmetry type. With both the B̃ and C̃′ systems of ammonia one expects a ratio of 5 to 2 in the absorbance for circularly versus linearly polarized light for the N, O, S, and T branches. For the P, Q, and R branches one expects a 21 to 4 ratio of the weight-1 versus weight-3 tensor contributions to the C̃′ system in linearly polarized light (21 to 6 for B̃). Weight-1 terms are absent with circularly polarized light. These predictions are confirmed experimentally. The complete set of rotational line strength factors for three-photon absorption are given in algebraic form for the first time. The combination of vibronic factors, rotational line strengths, and statistical weights allows one to predict the three-photon absorption spectrum. Such calculated spectra are presented for ammonia at 45 K and they compare very favorably with the experimental spectra for both the B̃ system (a perpendicular band) and for the C̃′ system (a parallel band) in both linearly and circularly polarized light.
Avoided-crossing molecular-beam experiments on fluoroform (CF3H) and fluoroform-d (CF3D)
Authors: Meerts W. Leo , Ozier Irving
Published: February 2003

The avoided-crossing molecular-beam method for studying normally forbidden (ΔK≠O) transitions in symmetric tops has been applied to fluoroform (CF3H) and fluoroform-d (CF3D), thus marking the extension of the method to systems which are not near spherical rotors. In order to reach the high electric fields required while still retaining the necessarily narrow linewidth, the electric resonance spectrometer has been equipped with a new pair of Stark plates capable of providing electric fields up to about 20 kV/cm with a homogeneity of 1 part in 105 over a length of 3 cm. The anticrossing (J,K) = (1,0)↔(1,±1) has been studied for both CF3H and CF3D. In each case, the rotational constant C0 along the symmetry axis has been obtained to 0.002%. From anticrossing spectra observed in combined electric and magnetic fields, the signs of the rotational g factors g∥ and g⊥ have been shown to be negative. From a conventional molecular beam study for each isotopic species, a value of the permanent electric dipole moment accurate to 60 ppm was determined and improved values of g∥ and g⊥ were obtained. The direction of the electric dipole moment is shown by two methods to be +HCF3−. A brief discussion of the difficulties in these methods is given.
Shape resonance effects in the photoabsorption spectra of BF3
Authors: Swanson John R. , Dill Dan , Dehmer J. L.
Published: February 2003

Multiple-scattering model calculations of cross sections for dipole transitions from all occupied orbitals of BF3 to excited bound states and continuum states of electron kinetic energy <30 eV are presented. The photoelectron angular distribution asymmetry parameters β are also given for all occupied orbitals. The boron and fluorine K-shell calculations are in qualitative agreement with, and provide a clear interpretation of, the measured spectra. Two shape resonances are found in the low energy continuum: one of a′1 symmetry, the other of e′ symmetry. The resonances are found to be due to trapping of p waves on the fluorine atoms. This atomic localization as well as the dominance of low-l partial waves outside the molecule put these shape resonances in a class distinct from those observed in diatomic molecules.
Rotational spectrum, structure, and intramolecular force field of the ArClCN van der Waals complex
Authors: Keenan M. R. , Wozniak D. B. , Flygare W. H.
Published: February 2003

The rotational spectrum of the ArClCN van der Waals complex has been assigned using pulsed Fourier transform microwave spectroscopy in a Fabry-Perot cavity with a pulsed supersonic nozzle as the molecular source. ArClCN is T-shaped and the data were fit to the Watson rotational parameters and an exact expression for the Cl and N nuclear quadrupole coupling. The spectroscopic constants for Ar35ClCN are A′′ = 6152.5411(21) MHz, B′′ = 1577.0362(8) MHz, C′′ = 1246.7514(6) MHz, τ1 = −576.0(2) kHz, τ2 = −97.28(8) kHz, τaaaa = −234.8(17) kHz, τbbbb = −55.97(10) kHz, τcccc = −21.60(7) kHz, χClaa = 37.9468(23) MHz, χClbb = −79.5239(20) MHz, χNaa = 1.6403(22) MHz, and χNbb = −3.4571(20) MHz. The centrifugal distortion constants are used to derive the intramolecular force field and a normal coordinate analysis is performed. The Cl nuclear quadrupole coupling tensor indicates that the field gradients in ClCN are slightly perturbed upon complex formation but not enough to proscribe their use in structural determinations of weakly bound complexes.
Theoretical analysis of migration dynamics of solutes between lipid vesicles
Authors: Tachiya M. , Almgren Mats
Published: February 2003

We present a detailed theory of the fluorescence stopped-flow method for the study of solubilization in vesicle solutions, which was recently developed by several workers including one of us.
A molecular theory of Stokes–Einstein behavior. III. Translational Brownian motion in a compressible fluid
Authors: Masters A. J. , Madden P. A.
Published: February 2003

The expressions for the friction coefficient of a diffusing particle, obtained from a completely molecular theory in a previous paper, are solved for a Brownian particle in a compressible fluid. In appropriate limits the exact forms of the hydrodynamic friction coefficients in the slip and stick limits are reproduced. The use of the hydrodynamic results in describing the velocity autocorrelation function (VACF) of a molecule is discussed.
Sum rules for inhomogeneous Coulomb systems
Authors: Gruber Ch. , Lebowitz Joel L. , Martin Ph. A.
Published: February 2003

Using the stationary equilibrium BBGKY hierarchy and some weak spatial decay properties of the correlations, we derive exact sum rules for the equilibrium distribution functions of ionic systems. Our results apply to both homogeneous and nonuniform systems. They show that when there is decay in such systems, then the total excess charge in the vicinity of a given number of fixed ions is zero, and that this excess charge has no dipole nor quadrupole moment. The implications for the static structure factor and for the dielectric tensor are discussed.
The quantum-mechanical second virial coefficients of electron-spin-polarized atomic hydrogen and its admixtures with the isotopes of helium
Authors: Lim T. K. , Larsen Sigurd Y.
Published: February 2003

The quantum-mechanical second virial coefficient of electron-spin-polarized atomic hydrogen H↑ and the second cross virial coefficients of H↑–3He and H↑–4He have been calculated for a range of temperatures using a Lennard-Jones 12-6 potential in each case. Our results indicate that the exchange (spin and quantum statistics) contributions for H↑ drop rapidly with increasing temperature. The Boyle temperature for H↑ occurs at a reduced temperature T*B = 0.25. Those for H↑–3He and H↑–4He are at T*B = 0.53 and 0.74, respectively.
A Monte Carlo study of phase transitions in a fcc octopolar array
Authors: Nosé Shūichi , Kataoka Yosuke , Okada Kenkichi , Yamamoto Tsunenobu
Published: February 2003

Orientational orders of an octopolar array in a fcc lattice are studied by Monte Carlo simulations. Thermodynamic properties and order parameters of several phases are worked out. In particular, the relative stability of each phase is carefully studied through free energy calculations. The results are compared with those obtained from a mean field approximation (MFA). It turns out that an intermediate phase by the MFA is not stable at any temperature and that a single phase transition occurs instead of a double phase transition, contrary to the results from the MFA.
Conformation space renormalization of polymers. I. Single chain equilibrium properties using Wilson-type renormalization
Authors: Oono Y. , Freed Karl F.
Published: February 2003

A conformation space renormalization group is developed to describe polymer excluded volume in single polymer chains. The theory proceeds in ordinary space in terms of position variables and the contour variable along the chain, and it considers polymers of fixed chain length. The theory is motivated along two lines. The first presents the renormalization group transformation as the means for extracting the macroscopic long wavelength quantities from the theory. An alternative viewpoint shows how the renormalization group transformation follows as a natural consequence of an attempt to correctly treat the presence of a cut-off length scale. It is demonstrated that the current configuration space renormalization method has a one-to-one correspondence with the Wilson–Fisher field theory formulation, so our method is valid to all orders in ε = 4−d where d is the spatial dimensionality. This stands in contrast to previous attempts at a configuration space renormalization approach which are limited to first order in ε because they arbitrarily assign monomers to renormalized ’’blobs.’’ In the current theory the real space chain conformations dictate the coarse graining transformation. The calculations are presented to lowest order in ε to enable the development of techniques necessary for the treatment of dynamics in Part II. The theory is presented both in terms of the simple delta function interaction as well as using realistic-type interaction potentials. This illustrates the renormalization of the interactions, the emergence of renormalized many-body interactions, and the complexity of the theta point.
Measuring differential cross sections using the Doppler shift
Authors: Serri J. A. , Kinsey J. L. , Pritchard D. E.
Published: February 2003

We discuss two methods, one of them new, for recovering level-specific differential cross sections in crossed molecular beams experiments from the Doppler profiles of line shapes observed by laser induced fluorescence. The angular resolutions of the two methods are compared and shown to be complementary. An experiment using both methods can have moderately good angular resolution at all scattering angles. In the first method, which has previously been demonstrated experimentally, the Dopper profile is taken with the laser beam parallel to the relative velocity of the collision system. Good angular resolution is obtained between π/4 and 3π/4. In the second method, which is proposed here, the Doppler profile is taken with the laser beam perpendicular to this relative velocity, and the best angular resolution is obtained in the regions 0 to π/4 and 3π/4 to π. This method requires an integral transform to recover the cross section from the Doppler profile. A practical implementation of this transform is presented along with a numerical example showing its relative insensitivity to noise in the profile.
A laser-induced photodissociation study of CH3I+ and CD3I+ at high resolution
Authors: Goss S. P. , Morrison J. D. , Smith D. L.
Published: February 2003

Photodissociation of the molecular ions CH3I+ and CD3I+ has been studied at a resolution of better than 0.3 cm−1 (37 μeV) using a triple quadrupole mass spectrometer and flashlamp pumped tunable dye laser. Calibration of the energy scale is achieved by recording the absorption spectrum of iodine vapor simultaneously with the photodissociation spectra. Several spectra are presented, showing partially resolved rotational structure. To assist with a preliminary analysis, deconvolution is used to improve the effective resolution of the data.
LCAO–MO–SCF calculation of the metal–oxygen bonding in the M2O2 series: M = Li, Na, and K
Authors: Allavena M. , Blaisten-Barojas E. , Silvi B.
Published: February 2003

The geometry and infrared active vibrational frequencies of M2O2 peroxides (M = Li, Na, and K) have been calculated by the SCF method. The pseudopotential method has also been applied to the case of sodium and potassium peroxides and results of both methods are compared. The nature of the metal–molecular oxygen binding and the ability of pseudopotential methods to represent such bonds are discussed.
A retrospective appraisal of the Pople point-dipole model of ‘‘ring-current’’ effects on 1H-NMR chemical shifts in planar, condensed, benzenoid hydrocarbons
Authors: Mallion R. B.
Published: February 2003

A set of well-established, 1H-NMR chemical shift data for 66 nonhindered protons in 16 different condensed, benzenoid hydrocarbons is systematically compared with predictions of (a) the Pople point-dipole ’’ring-current’’ model and (b) nine other distinct ring-current approaches, of varying degrees of sophistication. Provided that it is based on relative ring-current intensities calculated via McWeeny’s (or Pople’s) quantum-mechanical formalism, the point-dipole model gives rise to an empirical correlation with experimental 1H-NMR chemical shifts in a wide range of condensed, benzenoid hydrocarbons which is as good as that obtained when predictions of other, ostensibly more refined, ring-current theories — as well as calculations effected by application of Blustin’s very recent ’’π-bond’’ model — are regressed against the same experimental data.
Theoretical calculation of low-lying states of NaAr and NaXe
Authors: Laskowski Bernard C. , Langhoff Stephen R. , Stallcop James R.
Published: February 2003

The potential curves X 2Σ+, A 2Π, B 2Σ+, C 2Σ+, (4) 2Σ+, (2) 2Π, and (1) 2Δ were calculated for NaAr and NaXe using a self-consistent field plus configuration-interaction procedure. To reduce the computational effort, the core electrons were replaced by an ab initio effective core potential. The molecular wave functions were constructed from a basis of atomic s, p, and d Gaussian-type orbitals. Although higher angular momentum basis functions would be required to precisely determine the weak van der Waals binding at large separations, we feel that these wave functions provide an adequate description of the repulsive region of the potential curves. Our potential curves are considerably less repulsive than the semiempirical ones of Pascale and Vandeplanque and agree well with those deduced from high-energy scattering data by Malerich and Cross. Dipole and transition moments were also computed; these moments should be a considerable improvements over those from the one-electron semiempirical calculation of Pascale.
An atoms in molecules approach to density functional theory
Authors: Guse Michael P.
Published: February 2003

The concept of an atom in a molecule is developed in the context of density functional theory and used to separate the energy of a molecule into intra-atomic and interatomic terms. The intra-atomic kinetic energy may then be calculated accurately in terms of one-electron orbitals while the interaction term is approximated by an explicit functional of the density. This formalism is applied to the molecules H2+ and H2 where it yields a self-consistent picture of a hydrogen atom in a molecule.
Pressure and bulk viscosity in a hard sphere gas
Authors: Eder Otto J. , Lackner Thomas
Published: February 2003

The pressure in a dilute hard sphere gas is calculated, starting from the virial theorem and making use of the ergodic hypothesis. The time development of the system is described within the ’’sucessive uncorrelated binary collision approximation.’’ The results obtained are applied to calculate the time correlation function for the bulk viscosity. As is well known, only the potential part of the time correlation function gives a nonvanishing contribution to the bulk viscosity. It is shown that for hard spheres the time correlation function is just a δ function without an exponentially decaying contribution.
Reversibility and mechanism in a single-crystal phase transformation
Authors: Soltzberg L. J. , Cannon Susan M. , Ho Yon Won , Armstrong Ellen C. , Bobrowski Sophie J.
Published: February 2003

Optical and x-ray diffraction studies of p-di-iodobenzene single crystals undergoing polymorphic phase transformation are strongly indicative of the existence of heterophase domains at temperatures well away from the classical phase equilibrium temperature. Domains of either polymorphic form can exist in a crystal of the other form. These domains seem to have a significant effect on the course of the transformation. Annealing the crystals at temperatures far from the transformation temperatures diminishes or eliminates these domains.
The electronic structure of NiCO: A new prediction for the ground state
Authors: Rives Albert B. , Fenske Richard F.
Published: February 2003

We have performed electronic structure calculations on the NiCO molecular fragment through the configuration interaction level. Our initial motivation was to compare the bonding in the low lying triplet states 3Δ, 3Σ+, and 3Π with that in the lowest closed shell singlet state 1Σ+. In both the σ and the π systems the Ni–CO bond is stronger in the 1Σ+ state than in the others. The σ-bonding difference is a consequence of the occupation of the strongly antibonding Ni 4s-like orbital in the triplet states, whereas in the 1Σ+ state it is unoccupied. The π-bonding difference arises from the greater π-backbonding ability of the more diffuse Ni 3d orbitals present in the 1Σ+ state. Most notably, though, we contradict previously published results by predicting a 1Σ+ ground state rather than a 3Δ ground state. A many configuration wave function is essential in accurately describing the π backbonding as well as producing the correct atomic energy level splittings. It is, for the most part, these two factors which produce the great stabilization of the 1Σ+ state with respect to the triplet states on adding configuration interaction to the Hartree–Fock result.
Calculation of the electric conductivity of the hexagonal lyotropic mesophase
Authors: Photinos P. , Saupe A.
Published: February 2003

The electric conductivity of the hexagonal lyotropic mesophase is evaluated numerically, as a function of the volume fraction. It is assumed that the conductivity is solely due to the mobile ions in the aqueous phase, and that the ion concentration and mobility are uniform throughout the aqueous phase. The conductivities are then evaluated for the principal directions by integrating Laplace’s equation numerically. The calculated values for the anisotropy in the conductivity are compared with experimental findings on flow-induced conductivity anisotropy.
Orientational structure at a vapor–liquid interface: Effect of electrostatic forces
Authors: Thompson S. M. , Gubbins K. E. , Haile J. M.
Published: February 2003

The vapor–liquid interfacial density-orientation profile ρ(z1ω1) gives the probability of finding a molecule at height z1 in the interface with orientation ω1. We present a perturbation theory for this function, using the Mayer f function as the expansion functional. This ’’f expansion’’ has the advantage over the previously used ’’u expansion’’ that at first order it predicts orientational ordering in the surface due to electrostatic forces. The theory is used to study orientational structure in the surface for a model fluid in which the intermolecular potential consists of site–site Lennard-Jones terms plus a quadrupole–quadrupole term. When the quadrupole moment is set equal to zero, the theory predicts that the molecules on the liquid side of the dividing surface prefer an orientation perpendicular to the interface. As the strength of the quadrupole moment is increased, this preference for a perpendicular orientation is reduced, and for moderately strong quadrupoles it is replaced by a preference for an orientation parallel to the surface. These predictions are in qualitative agreement with recent molecular dynamics results.
The dielectric properties of ice Ih in the range 272–133 K
Authors: Johari G. P. , Whalley E.
Published: February 2003

The amplitude of the orientational dielectric dispersion of impure polycrystalline ice Ih has been measured at temperatures down to 133 K in an attempt to find evidence for an ordering transition. The Curie–Weiss temperature is 6.2±1.7 K and so, within the experimental precision, there is no significant evidence that the molecular orientations become more correlated than the ice rules require. From the most recent results on polycrystalline ice, the Curie–Weiss temperature is 15±∼11 K. As this temperature is far below the lowest experimental temperatures, the evidence for an ordering temperature is not firm. The activation energy for dielectric relaxation in the impure ice is 25.5 kJ mol−1 at high temperature and increases at low temperatures. The low activation energy is caused by impurities that generate orientational defects in about the maximum number physically possible, and is mainly the activation energy for diffusion of the defects. At lower temperatures, the impurities produce fewer defects and the activation energy rises because the energy required to produce the defects begins to contribute to it. The low-temperature region in D2O ice with unknown dopants, which has been well studied by Johari and Jones and by Kawada, is due to this effect. An analysis suggests that the low-temperature region would be well worth studying for a sample with known dopants.
Nuclear magnetic and dielectric relaxation of a homologous series
Authors: Schifferdecker M. , Aichmann H. , Nimtz G.
Published: February 2003

Nuclear magnetic and dielectric relaxation behavior of an asymmetric homologous series of the nematic liquid crystalline compound p-alkoxybenzal-p′-ethoxyaniline and of p-octylbenzal-p′propylaniline have been investigated. The nuclear T1 measurements indicate to consider the different molecules of the series in the nematic phase as ellipsoids with dissimilar lengths of the long axis. Applying a 90°–τ–90°90° pulse different decays were observed for the even and the odd members of the series, the differences vanishing below the clear point. They were interpreted by a different chain configuration for the odd and the even members. The dielectric measurements in the microwave range show a strong dependence of the Debye relaxation time on the chain length. The role of the oxygen atom in the chain became evident.
Direct measurement of structural forces between two surfaces in a nonpolar liquid
Authors: Horn Roger G. , Israelachvili Jacob N.
Published: February 2003

The force as a function of separation has been measured between two molecularly smooth surfaces immersed in the liquid octamethylcyclotetrasiloxane (OMCTS) whose molecules are quasispherical of diameter ∼1.0 nm. The force is an oscillatory function of distance, varying between attraction and repulsion, with a periodicity equal to the size of the liquid molecules to within the experimental resolution of ∼0.1 nm. The oscillations decay rapidly with distance: their measurable range is 6–10 molecular diameters and their magnitude exceeds that of conventional van der Waals forces at small distances. The magnitude of the oscillations is insensitive to changes in temperature, but sensitive to the chemical nature of the surfaces, and very sensitive to the presence of water. The results are considered, qualitatively, within the context of current theories of the liquid state near solid interfaces, and some implications for surface chemistry and colloid science are discussed.
Condensation of a supersaturated vapor. V. The nucleating effects of ultraviolet light on vapors containing very low concentrations of o-tolualdehyde
Authors: Katz Joseph L. , McLaughlin Timothy , Wen F. C.
Published: February 2003

The photoinduced nucleation of supersaturated vapors containing low concentrations of o-tolualdehyde has been studied. We have made measurements of the photonucleation spectrum using various host liquids, the steady-state rate of nucleation, the delay time before the start of nucleation, the initial slope of the nucleation rate, the decay of the rate after the light is turned off, the o-tolualdehyde concentration dependence, and the dependence on total pressure and the effect of temperature changes. We show that these measurements are in quantitative agreement with a phenomenological model in which the photoinduced nucleation is initiated by clusters accumulating a small number of photoaffected molecules. Using the vapor concentration, the photon cross section of o-tolualdehyde, and the photon flux, we calculate that a photoaffected o-tolualdehyde concentration as low as 3×107 molecules cm−3 sec−1 (i.e., about 1 part per trillion) is sufficient to cause photoinduced nucleation. This concentration is too small to cause either ordinary heterogeneous nucleation or binary homogeneous nucleation. However, a collision frequency calculation shows that this low concentration of photoaffected molecules is in good agreement with the phenomenological model, since a much smaller number of collisions of photoaffected molecules are then required.
Fourier transform studies of electron spin echo modulation of hemoglobin azide
Authors: Ramakrishna Y. V. S. , Narayana P. A.
Published: February 2003

Electron spin echo modulation studies of hemoglobin have been carried out at 4.2 K at x band. Samples have been prepared from human blood. The modulation has been analyzed in the frequency domain by Fourier transforming the time domain data. The analysis indicates that the modulation arises from 14N of the histidine and of the porphyrin. The superhyperfine frequencies obtained from the Fourier transform results have been interpreted in terms of quadrupole coupling, dipolar and contact coupling with 14N.
Autoionization observed in the O+2(A 2Πu→X 2Πg) and O+2(b 4Σ−g→a 4Πu) fluorescence excitation spectra
Authors: Tabché-Fouhaile Abdallah , Nenner Irène , Guyon Paul-Marie , Delwiche Jacques
Published: February 2003

High resolution O+2 b 4Σ−g and A 2Πu partial photoionization cross sections are obtained in the 450 to 750 Å range using the fluorescence excitation technique. The total photoionization cross section also is measured with the same photon resolution. Most of the fine structure observed in each individual channel is interpreted in terms of electronic and vibrational autoionization. The underlying continuum in the b 4Σ−g cross section shows a strong enhancement at 650 Å (19 eV) photon energy (i.e., 0.8 eV above threshold) and a strong vibrationally resolved structure centered at 620 Å (20 eV). They are interpreted as 3σgεσu resonances associated with 3σg electron ejection, the 19 eV being a shape resonance in the b 4Σ−g continuum, and the 20 eV a bound electronic state associated to B 2Σ−g and strongly autoionized into the b 4Σ−g continuum.
Direct vs complex reaction dynamics for F+OH→HF+O
Authors: Sloan J. J. , Watson D. G. , Williamson J. M. , Wright James S.
Published: February 2003

The exerogicity of the reaction F+H2O→HF+OH is sufficient to give HF(v′?1); however, arrested relaxation infrared chemiluminescence experiments on this system show emission from HF(v′?3). The higher vibrational levels are populated by the secondary reaction F(2P)+OH(2Π)→HF(1Σ+)+O(3P). By a combination of SCF–CI calculations and a rotated Morse curve fitting procedure, it is shown that barrier heights on triplet surfaces which correlate reactants and products of the secondary reaction are too high to provide a reaction path. Instead, the reaction proceeds on a singlet surface to produce an HOF complex, followed by rearrangement and a nonadiabatic transition to the triplet surface. An exit-channel barrier results from the surface crossing. The chemiluminescence data are shown to be in accord with this reaction mechanism.
Radiative lifetimes and two-body collisional deactivation rate constants in Ar for Xe(5p56p),Xe(5p56p), and Xe(5p57p) states
Authors: Horiguchi H. , Chang R. S. F. , Setser D. W.
Published: February 2003

The radiative lifetimes and collisional deactivation rate constants by argon of four Xe(5p 5[2P3/2]6p), three Xe(5p 5[2P1/2]6p), and three Xe(5p 5[2P3/2]7p) levels, hereafter referred to as Xe(6p), Xe(6p′), and Xe(7p) states, have been measured by a time-resolved laser-induced fluorescence technique in a flowing afterglow apparatus. The deactivation rate constants of the 6p levels are in the (0.5–5)×10−11 cm3 s−1 range; however, the rate constants for the 6p′ and 7p levels are much higher with values of (15–40×10−11 cm3 s−1. Product states resulting from two-body collisions between the laser excited Xe(6p, 6p′, and 7p) atoms and ground state argon atoms were identified from the product emission spectra. In addition to intramultiplet relaxation, considerable intermultiplet transfer to the 6s′ levels seems to occur for the Xe(6p) states. Both intramultiplet relaxation and intermultiplet transfer (to the 6d, 5d, and 7s manifolds) are important for the Xe(6p′) and Xe(7p) states. Radiative branching ratios for emission in the 450–1100 nm range were measured for several levels. In some cases these ratios can be combined with radiative lifetimes to provide absolute transition probabilities. The lack of reliable branching ratios for the transitions in the infrared is a serious deficiency which prevents the assignment of absolute transition probabilities and also affects the kinetic interpretations for product formation processes.
Exact calculation of optical rotation for a helicoidal orbital model
Authors: Leuliette-Devin E. , Locqueneux R. , Tillieu J.
Published: February 2003

An exact expression of the optical rotation is derived for helical molecules described by a model of free electrons which are constrained to move on a helix of t turns where t is not necessarily integral. A comparison is made with the results of other authors who have used the same model.
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o SCF calculations on the potential energy surface of potassium cyanide (KCN)
Authors: Wormer Paul E. S. , Tennyson Jonathan
Published: February 2003

The potential energy surface of KCN has been generated by ab initio SCF calculations in the region of equilibrium bond distances. An analytic representation of the surface is presented. The calculations show that the bonding between K and CN is ionic, and that the structure of KCN is triangular, which confirms recent experimental findings. The computed geometry is &KCN = 62.4°, rCK = 5.492a0, and rCN = 2.186a0.
On the interpretation of molecular valence Auger spectra
Authors: Ågren Hans
Published: February 2003

The interpretation of molecular valence Auger spectra by means of ab initio computational methods is discussed. As alternatives to self-consistent-field optimizations of the full Auger spectrum, the feasibility of a procedure based on single ionization potentials and of CI calculations using frozen orbitals is tested. Numerical calculations are performed for the CO, N2, NO, and CO2 molecules, which show especially structure-rich Auger spectra. These spectra are analyzed in detail and they are found to contain three nonoverlapping regions of transitions corresponding to final state vacancies in outer–outer, outer–inner, and inner–inner valence orbitals. It is investigated whether this division of the transitions also is relevant with respect to the magnitude of dynamical relaxation errors in the single ionization potential procedure or with respect to the choice of molecular orbital basis in the CI calculations. CI effects are found to be important for intensities and energies of the Auger transitions in the major energy interval of the spectra. These effects are mainly due to near degeneracies between the main double hole states or between these states and configuration states formed by internal–external double excitations. In particular, configuration states involving π–π excitations are found to give important contributions. The one-center intensity model for Auger transitions is evaluated in the case of an open-shell molecule.
Radiation damage studies of CrO42−-doped alums
Authors: Chowdari B. V. R. , Sekhar Y. Ravi
Published: February 2003

Radiation damage studies on NH4Al(SO4)2⋅12H2O and KAl(SO4)2⋅12H2O single crystals doped with chromate centers are presented. Similar studies on undoped alums are also reported for comparison. EPR and optical absorption results are correlated to identify and characterize the species produced on x irradiation of these crystals. Formation of CrO43− ions seems to be the most interesting feature in the doped crystals. The radicals associated with host lattices are identified as SO3−, O3−, and SO2−. The effect of impurity on the stabilization of these radicals is discussed. Results regarding the growth and decay of all these centers during irradiation and the possible kinetics of radiolysis are presented.
Resonance absorption measurements of atom concentrations in reacting gas mixtures. VI. Shapes of the vacuum ultraviolet oxygen (3S–3P) resonance triplet from microwave sources and empirical calibration in a shock tube
Authors: Pamidimukkala Krishna M. , Lifshitz Assa , Skinner Gordon B. , Wood David R.
Published: February 2003

Spectral line profiles of the atomic oxygen triplet 3S1–3P2,1,0 emitted from microwave discharges in O2–He mixtures containing 0.1% O2 were measured in the 43rd order using a 2 m vacuum Czerny-Turner scanning spectrometer under three different lamp conditions. The profiles varied from nearly Gaussian to highly self-absorbed. The line shapes were accounted for by the amount of light absorbed by ground state oxygen atoms within the lamp. Experiments were carried out to calibrate the microwave discharge lamp for analysis of oxygen atoms using oxygen resonance triplet absorption. Known concentration of O atoms were produced in the temperature range 1950–2600 K in a shock tube by the complete dissociation of dilute (1–20 ppm) mixtures of N2O in Ar and related to the fraction of light absorbed. It was found that the ratios of the intensities of the oxygen components, measured using a low-resolution monochromator, can be used to obtain resonably accurate calibration curves. Kinetic data obtained on N2O dissociation as a part of our calibration experiments in the temperature range 1519–2408 K are also presented; the results are consistent with the correlations of Baulch et al. It was confirmed that O atom concentrations during calibration experiments were determined by stoichiometry, and not by the kinetics of N2O dissociation.
Multiplicity of steady states in heterogeneous catalysis: The case of Langmuir’s nth order kinetics
Authors: Gea J. R. , Ibañez J. L.
Published: February 2003

A description of the multiple steady states to be expected in a catalytic model with Langmuir’s nth order kinetics is given. Multiplicity and the related hysteretic phenomena are linked to the occurrence of a cusp catastrophe in the problem.
Aqualigand dissociation of 5d←4f excited [Ce(OH2)9]3+ in aqueous solution
Authors: Okada Keiko , Kaizu Youkoh , Kobayashi Hiroshi
Published: February 2003

The absorption emission and magnetic circular dichroism spectra of the hydrated Ce3+ ion in La(C2H5SO4)3⋅9H2O single crystal and aqueous solution are reported. The band assignments are discussed. (AIP)
Numerical Hartree–Fock calculations on the first excited state of LiH−
Authors: McCullough E. A.
Published: February 2003

Numerical restricted Hartree–Fock calculations are carried out for the first excited state (1σ2 2σ2 4σ) of LiH−.(AIP)
Structure and motion of the peroxy radical in urea–n-tetracosane complex
Authors: Hori Yasurō , Aoyama Shunzo , Kashiwabara Hisatsugu
Published: February 2003

ESR measurements are reported in single crystals of urea–n-tetracosane complex. The crystals were irradiated by using a 60CO source. The structure of peroxy radicals is discussed.(AIP)
Comment on ‘‘Self-nucleation in the sulfuric acid–water system’’
Authors: Renninger Robert G. , Hiller F. Charles , Bone Roger C.
Published: February 2003

The technique of Doyle [J. Chem. Phys. 35, 795 (1961)] for finding the equilibrium saddle point on the free energy surface of a two-component liquid droplet is criticized. His method is related to modifications of the Laplace equation for the excess pressure inside a droplet and the Kelvin equation for the excess vapor pressure of its constituents. These changes incorrectly account for the variation of surface tension with composition.
Comments on the R(ν̄) spectral representation of the low frequency Raman spectrum
Authors: Nielsen O. Faurskov , Lund P.-A. , Praestgaard E.
Published: February 2003

A few misunderstandings concerning our use of the R (?) spectral representation are clarified. Two different spectral representations for the low frequency Raman spectrum are compared.
Electron transfer energies and dipole moments of alkyl halides and amines from an electrostatic model
Authors: Applequist Jon , Felder Clifford E.
Published: February 2003

Energies of the electron transfer reaction CH3X+RX+→CH3X++RX and dipole moments of molecules RX, where R is an alkyl group and X = Cl, Br, I, or NH2, are calculated for an electrostatic model in which each atom is characterized by a fixed charge and polarizability located at the position of the nucleus. The calculation takes into account the mutual polarization of the atoms in the molecular field. Atom polarizabilities are obtained from previous applications of the atom–dipole interaction model to molecular polarizabilities. Atom charges are assumed to be nonzero only for X and Cα, and these are optimized to fit 13 experimental electron transfer energies from first ionization potentials and 17 gas-phase dipole moments for selected alkyl compounds. Energies of 19 transfer reactions and dipole moments of 29 molecules are calculated, showing satisfactory overall agreement with experiment. The results suggest that the electrostatic interaction of the fixed charges with the polarizable atoms is responsible for the trend toward decreasing ionization potential with increasing size of the R group.
Phase transition at 350 K and dehydration of barium nitrite monohydrate
Authors: Gallagher P. K. , Abrahams S. C. , Wood D. L. , Schrey F. , Liminga R.
Published: February 2003

Ba(NO2)2⋅H2O undergoes a sluggish reversible phase transition on heating to 350 K, followed by water loss to form the hemihydrate at about 425–435 K. The final half-molecule of water is lost by 455 K. Differential thermal analysis, thermogravimetry, differential scanning calorimetry, infrared spectroscopy, x-ray diffraction, and optical microscopic techniques were used. The entropy change of 36 J K−1  mol−1 measured at the phase transition is consistent with five new orientations becoming available to each water molecule above 350 K, accompanied by related reorientations of the two independent NO2− ions as new hydrogen bonds are formed. Both the high temperature monohydrate and the hemihydrate phases are unstable.
On the applicability of the HNC approximation to highly charged polyelectrolytes
Authors: Teubner Max
Published: February 2003

The hypernetted chain approximation is applied to the interaction of two charged colloidal particles immersed in an electrolyte solution and compared to the classical theory of Verwey–Overbeek. The HNC result is asymptotically correct for either small surface potentials or large particle separations. For strongly charged particles, however, it predicts a short ranged attraction which is absent in the classical theory. It is concluded that a similar attraction recently found by Patey [J. Chem. Phys. 72, 5763 (1980)] is an artifact of the HNC approximation.
Nonperturbative approach to collisional dephasing: Application to vibrational dephasing in liquids
Authors: Grimbert Danielle , Mukamel Shaul
Published: February 2003

We develop a theory for the collisional dephasing of spectral lines in the binary collision approximation and in the Markovian (impact) limit of fast collisions. Making use of tetradic and dyadic scattering techniques we derive expressions for the line broadening which are nonperturbative in the potentials of interaction. We present some numerical applications corresponding to vibrational dephasing in liquids which show that for high temperatures, large masses, and short range interactions the nonperturbative corrections may be quite significant and may change the predictions of the binary collision models as to the variation of the dephasing rate with these parameters.
On the optimized cluster theory for continuous potentials
Authors: Madden William G.
Published: February 2003

The optimized cluster theory (OCT) of Andersen and Chandler is reexamined in the light of the recent generalization of the mean spherical approximation (MSA) to continuous potentials. The diagrammatic structure of the ’’renormalized potential’’ arises naturally from this version of the MSA and is found to contain diagrams with f0 bonds between root points. These f0 bonds preclude the topological reduction carried out by Andersen et al. A modification of the renormalized potential is introduced which permits the topological reduction to be performed. The implications concerning the convergence of the OCT are discussed in light of these modifications. It is also shown that the OCT provides an a priori rationale for preferring a perturbative form of the hypernetted-chain approximation to the corresponding form of the Percus–Yevick approximation.
Miller’s unified statistical theory of exchange reactions is (almost) the most probable result for the information given
Authors: Davis Jon P.
Published: February 2003

The author shows that if the a priori probability of a given trajectory having j crossings is uniform over j for all j?1, then the most probable distribution of faj, fbj gives a reaction probability equal to that of Miller’s unified statistical theory to within 6%. (AIP)
Chemical thermodynamic properties and internal rotation of methylpyridines. III. 4-Methylpyridine
Authors: Draeger J. A. , Scott D. W.
Published: February 2003

The ideal gas state thermodynamic properties of 4-methylpyridine have been calculated based on free internal rotation of the methyl group. Selected values are compared with accurate experimental results. (AIP)
Some comments regarding the pressure tensor and contact theorem in a nonhomogeneous electrolyte
Authors: Henderson Douglas , Blum Lesser
Published: February 2003

The pressure tensor of an electrolyte, consisting of charged hard spheres in a dielectric medium near a uniformly charged wall is considered.(AIP)
Comment on simulations of liquid ammonia based on quantum mechanical potential functions
Authors: Jorgensen William L.
Published: February 2003

Monte Carlo simulation of liquid ammonia is reported. An initial potential function of the dimer was generated from minimal basis set calculations. The potential was uniformly scaled by a factor of 1.3 and the energy of the liquid was computed.(AIP)
Spectra and structure of phosphorus–boron compounds. XXI. Microwave spectrum of ethylphosphine–borane
Authors: Durig J. R. , Brletic P. A. , Li Y. S. , Johnston S. A. , Odom J. D.
Published: February 2003

The microwave spectra of CH3CH2PH2 11BH3, CH3CH2PH2 10BH3, and CH3CH2PH2 11BD3 have been recorded in the region 18.0–39.0 GHz and those of CH3CH2PD2 11BH3 and CH3CH2PD2 11BD3 in the range 26.5–39.0 GHz. a-type transitions were observed and R-branch assignments have been made for all isotopes in the ground vibrational state. From the relative intensities of the microwave transitions, the Stark effect, and the experimental rotational constants, it has been determined that the assigned spectra result from the trans conformer which is believed to be more stable than the gauche form at ambient temperature. The dipole moment components for trans-ethylphosphine–borane were determined from the Stark effect to be ‖μa‖ = 4.66±0.01, ‖μb‖ = 1.34±0.03, and ‖μt‖ = 4.85±0.02 D. With reasonable assumptions for the ethyl moiety, the following structural parameters for trans-ethylphosphine–borane were calculated: r(B–P) = 1.914±0.018 Å, r(B–H) = 1.205±0.013 Å, r(P–H) = 1.408±0.016 Å, r(P–C) = 1.823±0.016 Å, ∢BPC = 115.0°±1.1°, ∢PBH = 106.1°±3.4°, ∢CPH = 103.4°±3.7°, and ∢PCC = 115.1°±2.5°. These results are compared to similar quantities in some analogous molecules.
Electronic relaxation induced by the dissociation of van der Waals complexes: Intersystem crossing in 1A
u Ar and He glyoxal complexes
Authors: Jouvet Christophe , Soep Benoit
Published: February 2003

The formation of helium and argon glyoxal complexes has been observed. Their lines and bands have been identified from fluorescence excitation spectra in a supersonic jet. Rapid dissociation of the complexes has been shown for all vibronic levels. Further, it has been shown that this dissociation proceeds either to fluorescent or nonfluorescent levels, depending on the vibronic energy and the complex size. The nonfluorescent state has been identified as the phosphorescent 3Au state.
Dynamic deuterium NMR in liquid crystalline solvents: Ring inversion of cyclohexane-d12
Authors: Poupko R. , Luz Z.
Published: February 2003

The application of deuterium NMR spectroscopy of molecules dissolved in liquid crystalline solvents to study intramolecular dynamic processes is demonstrated using the ring inversion kinetics of cyclohexane-d12. The spectra of C6D12 dissolved in phase V and in hexyloxyazoxybenzene were studied over the temperature range −36 to +115 °C, and were found to exhibit a very pronounced line shape variation with temperature. At low temperatures (<−10 °C) the spectrum consists of two symmetric doublets due to the axial and equatorial sites. The doublet splittings are due to the quadrupole interactions of the corresponding deuterons. Upon increasing the temperature the lines broaden until finally the spectrum transforms into a single doublet with a spacing corresponding to the mean quadrupole splitting of the axial and equatorial deuterons. In an Appendix the line shape theory for two interacting nuclei of spin I = 1 which undergo mutual exchange is presented, and this theory is used to quantitatively interpret the experimental spectra of cyclohexane-d12. The kinetic parameters derived from these results are ΔH≠ = 10.3 kcal/mole, ΔS≠ = +0.5 e.u., and 1/τ(at 300 °K) = 1.5×105 sec−1. The results are compared with corresponding data obtained in isotropic solvents.
The restricted quantum exchange theory of intramolecular T1 and T2 relaxation rates
Authors: Stone James , Thiele Everett , Goodman Myron F.
Published: February 2003

We present a theory for intramolecular vibrational relaxation in polyatomic molecules. The theory postulates the existence of a restriction on the magnitudes of matrix elements connecting zero-order states which favors coupling between vibrational modes. Specifically, the matrix elements are assumed to depend on two parameters, one determining the overall magnitude of coupling, and the other the rate of falloff with increasing quantum exchange. We use this ’’restricted quantum exchange’’ (RQE) hypothesis to derive analytic expressions for T1 (energy-transfer) and T2 (coherence-loss) relaxation rates which depend only on the two coupling parameters, the average molecular frequency, the number of modes, the energy in the molecule, and (for T1) the size of the energy transfer. In the derivation we obtain analytic expressions for the number of pairs of states on an energy shell related to each other by exchange of a fixed number of quantua M. The analysis has been carried out for arbitrary M, allowing us formally to include the effects of all higher order couplings and to show rigorously when they can be eliminated. The resulting T1 and T2 relaxation rates and associated linewidths exhibit saturation with increasing vibrational energy, a property which has been shown to be essential to obtaining reasonable cross sections for multiphoton excitation. We propose on the basis of restricted quantum exchange a simple explanation for the observed narrowing of the linewidths of benzene with increasing vibrational quantum number.