bluuebunny/crossref_metadata_2025 huggingface dataset:
Collisional Deactivation of NH2(Ã 2A1)
Authors: Lenzi M. , McNesby J. R. , Mele A. , Xuan C. Nguyen
Published: February 2004

NH 2 (Ã  2 A 1 ) was produced by photolysis of ammonia in the vacuum ultraviolet. Deactivation rates of this radical were measured by the quenching of fluorescence in NH3, CH4, H2, N2, He, Ne, Ar, Kr, Xe. An estimate of the lifetime of spontaneous radiative decay of 0.8×10−5 sec is suggested. Application of the results to the dynamics of the Jovian atmosphere is reported.
CNDO Calculation of Dipole Moment Derivatives and Infrared Intensities of C6H6 and C6F6
Authors: Bruns Roy E. , Person Willis B.
Published: February 2004

The dipole moment derivatives of C6H6 and C6F6 have been calculated using the complete neglect of differential overlap (CNDO) approximate molecular orbital theory. The calculated set of derivatives with respect to the symmetry coordinates (∂ p/∂ Sj) for the e1u species of C6H6 agrees remarkably well with the unique experimental set of derivatives determined from infrared intensity measurements and the normal coordinate analysis for C6H6 and its deuterated analogues. The success of the benzene calculation suggests that we may have confidence in the CNDO results for C6F6, even though the agreement with the experimental results is much worse. An analysis of the ∂ p/∂ Sj values is given in terms of bond moment derivatives. The failure of the CNDO theory to predict a sufficiently large ``rehybridization moment'' to explain the observed intensity difference between in-plane and out-of-plane bending vibrations is discussed.
RRKM Theory, the CH3NC Paradox, and the Decomposition of Hot-Atom Substitution Products
Authors: Bunker Don L.
Published: February 2004

``Paradox'' and ``contrary to RRKM predictions'' are descriptions that have been applied to secondary unimolecular reactions following hot-atom substitution. These processes are strongly influenced by rotational effects which have until now been ignored. The crudest theoretical construction suffices to account for the curious behavior of CH2TNC in terms of a reasonable (sharply peaked, high energy) excitation function for T-for-H substitution. The reactions of vibrationally energized CH3CF218F, CH218FCF3, and CH3T can also be interpreted, with plausible critical configurations and excitation functions.
Triplet State of Acetylene: Biacetyl Emission from the Mercury Photosensitized Reaction
Authors: Burton C. S. , Hunziker H. E.
Published: February 2004

The question has been studied whether a metastable triplet state of acetylene is formed during its mercury photosensitized reaction, using biacetyl as a probe and employing a modulation-phase shift technique. While no emission is observable in the mercury photosensitized reactions of acetylene or biacetyl alone, in the presence of both compounds biacetyl phosphorescence is generated whose intensity, under suitable conditions of pressure and flow, approaches closely the one of benzene photosensitized biacetyl emission. The phenomenon is not caused by products such as benzene and can be quenched by increasing the acetylene pressure. A mechanism explaining the emission as energy transfer from a metastable acetylene triplet state to biacetyl is proposed, and rate parameters are evaluated by comparing this model with the experimental results. Self-quenching of triplet acetylene occurs at 0.083 times the rate of energy transfer to biacetyl. The excitation energy of triplet acetylene, E, was estimated to be 2.6<E<4.7 eV on the basis of the biacetyl phosphorescence yield and quenching experiments with other triplet states. In addition, the results provide an estimate, viz., 2× 1011 M−1·sec−1, for the biacetyl triplet-triplet annihilation rate constant.
Nonempirical LCAO MO SCF and CI Studies of the Low Lying Electronic State of the HOO Radical
Authors: Gole James L. , Hayes Edward F.
Published: February 2004

Nonempirical LCAO MO SCF and configuration interaction calculations are reported for the ground state and the low lying 2A′ state of HO2. The first excited 2A′ state of HO2 is found to be approximately 17 kcal above the ground state. The correlation diagram for the reaction H+O2⇌OH+O and the importance of the low lying 2A′ state of HO2 are discussed.
Model Calculations on the Influence of Quantum Electrodynamical Effects on the Chemistry of Superheavy Elements. The Chemistry of Element E184
Authors: Fricke B. , Waber J. T.
Published: February 2004

Using a phenomenological model, the influence of quantum electrodynamical effects on the prediction of the chemical behavior of superheavy elements within a relativistic Dirac-Slater calculation was investigated. This influence will be small and nondetectable for elements up to Z = 114. For elements near Z = 164 some changes in the ground state configurations occur but the chemical behavior will not change. Using this heuristic model, it is also possible to calculate elements beyond Z = 175. As an example we have chosen element E184 and are now able to make more valid speculations about the chemical behavior of the element than Penneman and co-workers could.
Ion-Molecule Reactions in Silane
Authors: Henis J. M. S. , Stewart G. W. , Tripodi M. K. , Gaspar P. P.
Published: February 2004

The reactions of primary ions Si+, SiH+, SiH2+, and SiH3+ with SiH4 are observed and reported, along with relative and absolute rate constants for the reactions observed. SiH2+ and SiH3+ are seen to undergo H− transfer reactions with large rate constants. All of the ions also participate in reactions yielding higher molecular weight ions containing two silicon atoms. The rate constants for many of these reactions are also large and suggest that the production of higher silanes from silane in activated systems (discharges, nuclear recoil experiments, etc.) may be due in part to the production of these ions.
Argon Matrix Raman Spectra of Oxygen Difluoride and the Oxygen Fluoride Free Radical
Authors: Andrews Lester
Published: February 2004

The argon matrix Raman spectra of oxygen difluoride and oxygen-18 difluoride at 16°K have been observed; frequencies within one wavenumber of analogous infrared studies were measured. Laser photo-detachment of fluorine atoms has provided significant yields of the OF and 18OF free radicals; the Raman observations confirm the earlier infrared work. Temperature cycling operations and depolarization ratio measurements provide aid in identifying new chemical species and making vibrational assignments.
Parr-Brown Anharmonic Potential Function Applied to CO2, CS2, OCS, HCN, ClCN, and N2O
Authors: Smith D. Foss , Overend John
Published: February 2004

An anharmonic potential function proposed by Parr and Brown has been tested against experimental spectroscopic data for CO2, OCS, CS2, HCN, ClCN, and N2O. The potential function, with only four adjustable parameters for the XYX case and six for the XYZ case is found to give an acceptable model for the general quartic force field of these molecules which contain, respectively, 12 and 19 independent force constants.
Crystal Structure of 2,5-Dimethyl-2,5-hexanediol Tetrahydrate: A Water-Hydrocarbon Layer Structure
Authors: Jeffrey G. A. , Shen M. S.
Published: February 2004

The crystal structure of 2,5-dimethyl-2,5-hexanediol tetrahydrate, C8H18O2 · 4H2O, has been determined at room temperature from diffractometer data with MoKα radiation. The structure is monoclinic, P21/c with two formula units in a cell of dimensions a=6.158(2), b=6.169(2), c=17.854(5) Å, β=101.8(2)°. The parameters were refined anisotropically by least squares to R=0.057 for 1015 reflections. The structure consists of layers of hydrogen bonded hydroxyl and water molecules alternating with layers of hydrocarbon chains. The water hydroxyl layers consist of puckered sheets of edge-sharing pentagons analogous to the water structure found in the pinacol and piperazine hexahydrates. The hydrocarbon chains of the glycol molecules are aligned parallel, analogous to the long-chain hydrocarbons and fatty acids, but spaced further apart. There are no hydrogen bonds between the puckered sheets of pentagons, and therefore the three-dimensional hydrogen bond framework which characterizes the hexahydrates as ``semiclathrates'' does not occur in this tetrahydrate.
Dissociative Excitation of Vacuum Ultraviolet Emission Features by Electron Impact on Molecular Gases. III. CO2
Authors: Mumma M. J. , Stone E. J. , Borst W. L. , Zipf E. C.
Published: February 2004

Vacuum ultraviolet multiplets of CI, CII, and OI have been produced by electron impact on CO2. Absolute emission cross sections for these multiplets have been measured from threshold to 350 eV. The electrostatically focussed electron gun used in this series of experiments is described in detail. The atomic multiplets which were produced by dissociative excitation of CO2 and the cross sections at 100 eV are: OI(2p4 3P−2p33s 3S) 1304  Å−1.04× 10−18cm2± 18%; CI(2s22p2  3P−2s2p3  3P0) 1329  Å−2.67× 10−19  cm2± 21%;  CI(2s22p2 3P−2s2p3 3D0)  1561  Å−7.50 × 10−19  cm2± 30%; CI(2p2 3P−2p3s 3P0)  1657  Å−1.45× 10−18  cm2 ± 23%; CII(2s22p 2P0−-2s2p2 2D)  1335 Å−7.60× 10−19  cm2± 22%; and CII (2s2p2 2D−2p3 2D0)   1324  Å−1.33 × 10−20  cm2± 23%. The dependence of the excitation functions on electron energy shows that these multiplets are produced by electric-dipole-allowed transitions in CO2.
Trimesitylboron−: A Nonplanar Aromatic Negative Ion
Authors: Griffin R. G. , Willigen H. VAN
Published: February 2004

An analysis of the liquid solution ESR spectrum of the negative ion of trimesitylboron is presented together with a discussion of the rigid medium spectrum. Two anomalies in the spectra, the absence of an alkali metal coupling and the positive sign of Δ g = g‖ − g⊥, are pointed out and interpreted in terms of the nonplanarity of the hydrocarbon.
Lower Bounds on Solutions of the Poisson-Boltzmann Equation near the Limit of Infinite Dilution
Authors: MacGillivray A. D.
Published: February 2004

Rigorous existence, uniqueness and lower bound results for solutions of the nonlinear Poisson-Boltzmann equation are obtained. The relationship of these bounds with certain assumptions in Manning's limiting law theory for polyelectrolytes is discussed.
Raman Spectra and Structure of Solid AgNO3 and TlNO3 at High Temperatures
Authors: Balasubrahmanyam K. , Janz G. J.
Published: February 2004

The laser Raman spectra of AgNO3 and TlNO3 have been investigated from the room temperature to an upper limit of about 25°C above their respective melting points (AgNO3, mp 210°C; TlNO3, mp 208°C). Striking results are the observation of the asymmetric shape in the totally symmetric N–O stretching mode (∼1046 cm−1) and the spectral changes accompanying the phase transitions in these solids. While various reasons can be advanced for the asymmetry of the 1046-cm−1 band, the explanation based on the coupling of vibrational modes of adjacent NO3− groups seems most reasonable.
Diffuse Reflectance Spectra of Some Rare Earth β-Diketonates and Esters in the Ultraviolet Region
Authors: Tandon S. P. , Govil R. C.
Published: February 2004

The diffuse reflectance spectra of dibenzoylmethane and acetylacetonates, dibenzoylmethides, ethylacetoacetates, and ethyl-1-methylacetoacetates of La3+, Ce3+, Pr3+, Nd3+, and Sm3+ and the absorption spectra of acetylacetone, dibenzoylmethane, ethylacetoacetate, and ethyl-1-methylacetoacetate in ethanol in the ultraviolet region (195–400 nm) have been reported. The observed bands have been assigned to π→π* transitions.
Valence Electron Studies with Gaussian-Based Model Potentials and Gaussian Basis Functions. II. Discussion of the One-Valence-Electron Molecular Theory and Applications to Li2+, Na2+, and LiH+
Authors: Schwartz Maurice E. , Switalski Jurgen D.
Published: February 2004

A one-electron theory for one-valence-electron molecules is developed. It assumes nuclear-nuclear repulsions to be between net core atomic charges, and that the potential seen by the valence electron is a superposition of atomic model potentials. The atomic model potentials are the core Coulomb potentials modified by Gaussian screened Coulomb potentials, as found in earlier atomic studies. Such model potentials are quite convenient for the use of Gaussian basis functions, which are also taken from the atomic studies, and for which potential energy matrix elements are simply calculated from physically based rules. The theory is applied to the ground states of Li2+, Na2+, and LiH+, using a variety of basis sets. Increasing the basis set flexibility lowers the energy, as in ordinary all-electron variational calculations. Binding energies and internuclear distances from the most extended basis calculations are: Li2+: De=1.23 eV, Re = 5.8 a.u.; Na2+: De=0.97 eV, Re = 6.7 a.u.; LiH+: De = 0.090 eV, Re = 4.5 a.u. These are in excellent agreement with results from more elaborate all-electron quantum mechanical studies, and we thus conclude that our simple, convenient theory simulates the true problem accurately.
Infrared Spectra in Polarized Light of Crystalline Chloroform
Authors: D'Alessio E. A. , Dodero E. , Pomposiello C.
Published: February 2004

High resolution spectra in polarized light of oriented crystalline films of chloroform at 77°K were obtained. The ratio of intensities of Davydov components for different angles of polarization were also determined. Comparison with the oriented gas model approximation allowed the assignment of components to the proper representations of the D2h factor group: all bands were assigned to the infrared active factor group symmetry species B1u, B2u, and B3u corresponding to vibrations along a, b, and c crystallographic axes. Comparison with results of measurements in solid solutions in argon made by King allowed the distinction between crystallographic effect and isotopic shifts.
Infrared Spectra and Normal Coordinate Analysis of Metalloporphins
Authors: Ogoshi Hisanobu , Saito Yutaka , Nakamoto Kazuo
Published: February 2004

The infrared spectra of porphin and its metal complexes with 64Zn, 68Zn, Cu, and Ni have been obtained from 4000 to 100 cm−1. Normal coordinate analyses have been carried out on the D4h model of the porphin complexes with 64Zn, 68Zn, Cu, and Ni. Only the eighteen in-plane vibrations have been calculated. The results indicate that the bands between 1700 and 950 cm−1 are due to CC stretching, CN stretching, CH in-plane bending, CCN in-plane bending or coupled vibrations between these modes, and that the largest contribution of the metal-nitrogen stretching coordinate is found in the vibrations at ≈ 203, 246, and 295 cm−1 of the Zn, Cu, and Ni complexes, respectively. The Urey-Bradley force constants for the corresponding metal-nitrogen stretching modes are estimated to be 0.553, 0.662, and 0.760 mdyn/Å, respectively.
Decay of Quasifree Electrons in Pulse-Irradiated Liquid Hydrocarbons
Authors: Bakale George , Gregg E. C. , McCreary R. D.
Published: February 2004

The decay of the ion current in pulse-irradiated hydrocarbons in a parallel-plate ion chamber has been observed in the nsec-μsec time range during which time the major contribution to the ion current is the quasifree, high mobility electron. At dose rates of 1015 eV cm−3/10−8 sec the electron current decay is exponential with a half-life ranging from ∼5 nsec (cyclopentane) to >400 nsec (n-hexane). At higher dose rates, however, deviation from the exponential decay occurs and second-order decay is approached at the highest doses/pulse (6.5× 1016 eV-cm−3/10−7 sec) studied. This change from pseudo-first-order to second-order kinetics is interpreted as a change in the electron decay from an attachment type process to electron-ion recombination. Absolute rate constants for the electron reacting with several solutes in n-hexane were also determined; these are ks(e−+CCl4) = ks(e−+φ2)=1.0± 0.1× 1012, ks(e−+I2)=2± 1× 1011, ks(e−+H2O)≃ ks(e−+benzene) ≤ 1× 109, and ks(e−+O2, CO2, N2O, SF6) ≤ 2× 108M−1· sec.−1
ENDOR Measurements of Proton Hyperfine Couplings
Authors: Box Harold C. , Freund Harold G. , Budzinski Edwin E.
Published: February 2004

ENDOR (electron-nuclear double resonance) spectroscopy was used to measure hyperfine couplings in radicals in which the unpaired spin density is concentrated mainly on atoms two bond lengths removed from the proton. The measurements were made on radicals produced by x irradiation of single crystals. The anisotropic part of the hyperfine coupling, as a function of the isotropic coupling, was obtained for two types of radicals: (1) neutral radicals obtained by irradiation of certain carboxylic acids and amino acids at room temperature in which the unpaired spin density is localized primarily in a π2p carbon orbital, and (2) radical anions obtained by irradiation of certain carboxylic acids and amino acids at 4.2°K in which the unpaired electron is localized primarily in a π2p carbon orbital on the carboxyl group.
Raman Spectrum of a Single Crystal of Benzene
Authors: Bonadeo H. , Marzocchi M. P. , Castellucci E. , Califano S.
Published: February 2004

The Raman spectrum of a single crystal of benzene at 140°K has been obtained using an argon ion laser source. The single crystals were oriented with the aid of a polarizing microscope. This technique was found suitable for low temperature work. Despite some cracking of the sample, the polarization was defined well enough to make the assignment of most librational lattice modes certain. The internal vibrations were also investigated, and for ν6, ν9, and ν10 the observed peaks have been assigned to their proper factor group species. The agreement between observed frequencies and those calculated in this laboratory is extremely good for the lattice vibrations, and acceptable for the internal modes.
Power Series Expansion of Collision Amplitudes. Electrostatic Potentials
Authors: Lassettre Edwin N.
Published: February 2004

By means of a conformal transformation t= K/(K2+α2)1/2 (where, in physical applications, K is the momentum change of a colliding electron) the complex K plane is mapped onto the complex t plane. With cuts from iα to i ∞ and from −iα to −i ∞, the mapping is one to one. Let I be the ionization potential from a one-electron orbital φi and W the excitation potential from φi to φj. Then if α=(2I)1/2+[2(I−W)]1/2 a region of the K plane, which contains (a) no singular point of the form factor ε=∫ exp(iK · r) φiφj*(dr) and (b) the entire real axis of K, is mapped into the unit circle in the t plane. Hence, when ε is expanded into a power series in t the series converges when t<1 and the region of convergence includes all real values of K. Moreover, the coefficients of the power series in t can be simply obtained from the coefficients of a series for ε in powers of K. This extends to the collision amplitude a result which had previously been obtained for the generalized oscillator strength [E. N. Lassettre, J. Chem. Phys. 43, 4479 (1965)]. The extension is nontrivial since the power series in K for ε contains both even and odd powers while that for oscillator strength contains only even powers of K. A particular series expansion for ε, which takes account of the behavior of ε at both large and small K, can be exploited to obtain a series expansion for an electrostatic potential function. This is possible because the Fourier transform of the potential function is proportional to ε/K2. Hence, an inversion gives the potential function. A particular expansion, which expresses the potential function in terms of a set of generalized moments, is obtained, discussed in detail, and illustrated with some simple examples.
Morse-6 Hybrid Potentials for Pair Interactions of Rare Gas Atoms
Authors: Konowalow Daniel D. , Zakheim David S.
Published: February 2004

Hybrid pair potential functions are constructed from three parts: (1) a short-range exponential repulsion of the form A exp (−λr), obtained from either Self-Consistent-Field or Thomas-Fermi-Dirac calculations; (2) a long-range dipole-dipole dispersion attraction −C6r−6 where the C6 coefficients are obtained from highly accurate semiempirical estimates; (3) a Morse potential A exp (−λr) −B exp (−λr/2), whose B parameter is found by fitting experimental second virial coefficients, and which is used to connect the long- and short-range segments. The bowls of the resulting potentials depend most perceptibly on the nature of the repulsive limb from which they are constructed. Potentials are constructed which describe He–Ne, He–Ar, Ne–Ne, Ne–Ar, Ar–Ar, Ar–Kr, Kr–Kr, and Xe–Xe interactions. The vibrational energy eigenvalues and spectroscopic constants are determined for these potentials. Comparison with the available experimental spectroscopic data and low energy molecular beam results is presented. Our most likely Morse-6 hybrids for ArAr, for example, give good agreement with molecular beam measurements, with the Tanaka and Yoshino spectroscopic measurements, and with the very flexible Barker-Pompe-Bobetic empirical potential.
Nature of the λ Transition and the 56 cm−1 Anomalous Raman Mode in Ammonium Bromide
Authors: Wang C. H. , Wright R. B.
Published: February 2004

The temperature behavior of the Raman spectrum of NH4Br in the 56 cm−1 region is closely associated with the mechanism underlying the order-disorder phase transition. This paper reports the detailed measurement and theoretical analysis of the spectral band shape, polarization, and integrated intensity of this low frequency mode. Above the phase transition temperature (Tλ), the scattering at 56 cm−1 is anomalous due to the fact that it is associated with a zone boundary T A phonon. Below Tλ, the tetragonal distortion of the crystal halves the size of the Brillouin zone and relocates the zone boundary T A phonon to the zone center. One of the new zone center phonons is Raman active (A1g symmetry) and can be observed in the a (cc) b scattering configuration. The intensity and spectral band shape of the A1g mode display unusual temperature behavior. In the vicinity of Tλ, a spectral structure exists in the αcc Raman spectrum (∼3 cm−1 at 230°K). Upon cooling of the crystal below Tλ, the structure disappears rapidly, accompanied by a large growth of the integrated scattering intensity. In addition to the intensity increasing Raman active mode, an intensity decreasing mode appears in the b (aa) c scattering configuration. This mode is not predicted by group theory and is attributed to the scattering from the order parameter for the reason that it is associated with the short-range order that exists above Tλ. A microscopic theory is formulated, relating the intensity behavior associated with the a (cc) b and b (aa) c spectra to the long-range order parameter. It is shown that it is the evolution of the long-range order parameter which governs the increase of the a (cc) b as well as the decrease of the b (aa) c Raman spectral intensity.
Faddeev Approach to the Collinear Three Body Problem with Numerical Results
Authors: James P. B. , North G. R.
Published: February 2004

An integral equation approach is taken to the collinear three body problem in which initially particles 2 and 3 are bound and 1 is incident. The problem is simplified by taking the model of attractive δ-function potentials for the individual pairs of particles. The analytic properties of the Faddeev amplitudes leading to the six final states are studied as an aid to setting up a procedure for solving the equations numerically. Numerical procedures are developed and the results presented for a simple example, which was previously solved analytically by McGuire. This work represents the first step in a program of treating the chemical rearrangement problem by Faddeev methods.
Classical-Limit Quantization of Nonseparable Systems: Multidimensional WKB Perturbation Theory
Authors: Doll Jimmie D. , Miller William H.
Published: February 2004

A general dynamical system of N degrees of freedom is considered as a zeroth order separable part plus a nonseparable perturbation, and explicit formulas are derived for the classical-limit approximation to the eigenvalues through second order in the nonseparable interaction. As a numerical example, the first and second order perturbation energies of the helium atom are calculated semiclassically, and agreement with the exact quantum mechanical values is quite reasonable.
Cross Sections for the Production of CO2+[A 2Πu, B 2Σu+→ X 2Πg] Fluorescence by Vacuum Ultraviolet Radiation
Authors: Lee L. C. , Judge D. L.
Published: February 2004

Fluorescence cross sections for the production of the CO2+[A 2Πu, B 2Σu+→ X 2Πg] bands are presented at several vacuum ultraviolet (vuv) wavelengths between 462 and 715 Å. The cross sections, for incident vuv photons from 600 to 680 Å, are 19 Mb for the production of CO2+ (A 2Πu) and 7 Mb for CO2+(B 2Σu+) and decrease monotonically toward the shorter wavelength region. The relative fluorescence cross sections of the observed sequences are also given for the various incident photon energies.
X-Ray Photoelectron Spectroscopy of Alkali Halides
Authors: Citrin Paul H. , Thomas T. Darrah
Published: February 2004

We have measured ionization potentials for the removal of various electrons from the alkali chlorides and the sodium and cesium halides. These binding energies are compared with the predictions of a simple point charge model with and without corrections for polarization and repulsion. The simple model predicts and the data show that the spacings of the energy levels for a given ion are independent of what crystal it is in and are the same as for the free ion. The point charge model also allows us to calculate the difference between cation and anion energy levels in the same crystal. There is, however, a disagreement between the predicted and experimental values of this difference that ranges from about 1.8 eV for LiCl to −0.2 eV for RbCl. This discrepancy is markedly reduced by inclusion of polarization effects. The point charge model with polarization and repulsion corrections predicts absolute ionization potentials for the alkali and halide ions that differ in a systematic way from those observed. For the sodium halides, the difference between calculated and experimental energies decreases monotonically from about −4 eV for NaF to about 0.9 eV for NaI. The origin of these discrepancies is apparently due to charging of the samples and their trend is directly attributable to the size of the respective bandgaps. We show that the electrostatic model can be used to provide a comparison between experimental binding energies for inner electrons in a crystal and Hartree-Fock calculations for binding energies of inner electrons in free atoms. Finally, using the point charge model we show that the binding energy of an electron on a highly charged ion in an ionic crystal is only slightly different from the binding energy of the same electron in the neutral atom.
Energy-Level Shifts in CaF2–Nd3+
Authors: Toledano J. C.
Published: February 2004

Shifts of the energy levels of neodymium towards lower energies are observed for three oxygen-compensated sites of calcium fluoride. The relation between this effect and the formation of weak covalent bonds involving the f orbitals is recalled. A significant difference of shifts is pointed out between two neodymium sites arising from double oxygen compensation. This difference is accounted for by symmetry considerations determining the possibility for neodymium to establish bonds with the two oxygen ions.
Sufficient Conditions for the Arrhenius Rate Law
Authors: Gibbs Julian H.
Published: February 2004

Kinetics are discussed for a system of identical degrees of freedom each of which is subject to a potential containing a barrier separating minima and is coupled weakly to other degrees of freedom serving as a heat reservoir. Temperature is defined via the assumption that the reservoir does not depart significantly from internal equilibrium. Use is made of an especially detailed form of master equation in which, for each transition in the system-cum-reservoir, account is taken of events in the reservoir as well as in the system. This permits application of the laws of microscopic reversibility and energy conservation to each transition. A generalized form of Arrhenius expression is obtained for the temperature dependence of the net flux between the set of quantum levels essentially contained within either potential well (initial state or final state) and the set of (higher energy) uncontained levels (``activated'' or ``transition'' state). Application of a steady state assumption to transition state concentration (as contrasted with the familiar equilibrium assumption for this) eliminates the latter and provides an equation for the overall net flux over the barrier. The forward and backward components of this flux depend upon ``free energies of activation'' in the familiar exponential fashion. On the other hand the formal expressions obtained for the ``frequency factors'' associated with these forward and backward components are not necessarily identical except under special conditions in which the quantum levels of initial state are equilibrated among themselves and in which similar statements apply (separately) to activated state and final state. Even these special conditions do not require an equilibrium between initial state (or final state) and activated state. Nevertheless they suffice to reduce the general result to one identical, except for a possibly important difference in the form of the ``frequency factor,'' to that of the transition state theory of Eyring.
Vibrational Deactivation of HF(v=1) in Pure HF and in HF-Additive Mixtures
Authors: Hancock J. K. , Green W. H.
Published: February 2004

The laser-excited vibrational fluorescence method has been used to obtain room temperature (294±2°K) vibrational relaxation rates for pure HF and in HF-additive mixtures. Measurement of the quenching of HF(v=1) fluorescence in HF–HF and HF-additive collisions has yielded the following total deactivation rates: HF†Ar<60 sec−1· torr−1, HF†N2=(1.25 ± 0.6) × 102  sec−1· torr−1, HF†D2=(3.7± 0.4)× 103sec−1· torr−1, HF†H2=(2.4 ± 0.3) × 104sec−1· torr−1, HF†CO2=(5.9± 0.2)× 104 sec−1· torr−1, and HF†H2O≈ HF†D2O=(4.1± 0.5)× 106  sec−1· torr−1. The self-relaxation rate for HF was found to be HF†HF=(8.74± 0.1)× 104  sec−1 torr−1 in dilute Ar mixtures and also with other additives. A slower rate (4.4± 0.3)× 104 sec−1· torr−1 has been measured in pure HF and is believed to indicate nonequilibrium of the rotational degrees of freedom during self-relaxation of HF. Observation of 4.3 μ fluorescence from CO2(00°1) and double exponential fluorescent decay from HF–H2 mixtures has led to the following rates for CO2(00°1) and H2(v=1) deactivation: CO2†HF=(5.3± 0.2)× 104  sec−1torr−1, and H2†HF=(6.3± 0.4)× 104  sec−1torr−1. The room temperature data are much faster than predicted from an extrapolation of the available high-temperature shock tube results. The equal, near gas kinetic rates found for HF relaxation by H2O and D2O suggest that strong chemical bonding forces may be responsible for the HF-water relaxation.
Atomic Force Constants in Some First Row Compounds
Authors: Gaughan R. Rysnik , King W. T.
Published: February 2004

By analysis of a vibrational frequency sum rule a set of force constants characteristic of H, C, N, O, and F atoms was found. These quantities, called atomic force constants, have the remarkable property of being independent of the details of molecular geometry or bonding multiplicity. Hence, it is possible to compute the sums of the squares of the normal frequencies of compounds involving these elements without explicit prior knowledge of their structures.
Infrared Spectra of Several New Lanthanide Oxide-Silicate Glasses
Authors: Ferraro John R. , Hazdra J. J. , Boettner W.
Published: February 2004

The preparation and the infrared spectra of 10 new lanthanide oxide-silicate glasses are reported. The three strongest regions of absorptions in the base glass (SiO2/Na2O/CaO) are maintained, although some shifts in frequencies do occur with the addition of lanthanide oxides. The 1050 cm−1 absorption in the base glass, assigned as the silicon-oxygen stretching mode within the SiO4 tetrahedron, shifts toward lower frequency by about 10–25 cm−1; the silicon-oxygen stretching between tetrahedra at 780 cm−1 and the silicon-oxygen bending modes at 475 cm−1 do not show any significant shifts. Evidence is presented that crystallization may occur in these glasses on standing, and this may be connected with the half-filled shell effect in the lanthanide series.
Proton and Fluorine Nuclear Magnetic Resonance Observations on Hypofluorous Acid, HOF
Authors: Hindman J. C. , Svirmickas A. , Appelman E. H.
Published: February 2004

The proton and 19F chemical shifts have been measured for liquid HOF at low temperature, and the proton shift has been measured for the gas at room temperature. The results indicate that the hydrogen and fluorine atoms in the molecule carry charges of approximately +0.5e and −0.5e, respectively.
Electron Spin Resonance Spectrum of the Chlorodisulfanyl (S2Cl) Radical in Inert Matrices at 4.2°K
Authors: Herring F. G. , McDowell C. A. , Tait J. C.
Published: February 2004

A new species, the chlorodisulfanyl radical (ClSS), has been produced by photolysis of dichlorodisulfane (Cl2S2) in inert matrices at 4.2°K. The identification of ClSS rests on the complete simulation of its well resolved electron spin resonance spectrum. A versatile computer program was developed for this purpose. The method of computation is perfectly general and takes into account the noncoincidence of the principal axes frames of the various tensors in the spin Hamiltonian which, apart from the usual g and A tensors, includes a quadrupole coupling tensor and nuclear Zeeman term. The chlorodisulfanyl radical possesses anisotropic g and hyperfine tensors which have principal axes rotated relative to each other by 10° in the molecular plane. In addition to this, the fact that the chlorodisulfanyl radical has been found to have a quadrupole coupling tensor which is of comparable magnitude to the hyperfine interaction tensor leads to a rather complicated ESR spectrum for the randomly oriented species. Our work shows that the chlorodisulfanyl radical is a ``π radical.'' The anisotropy of the hyperfine coupling tensor can be explained by spin polarization of the Cl–S σ bond rather than by contributions from spin density on neighboring sulfur atoms.
Saturated Liquid Properties from the Mie(n, 6) Potential and the Barker-Henderson Perturbation Theory
Authors: Rajagopal K. , Calvin D. W. , Reed T. M.
Published: February 2004

The perturbation theory of Barker and Henderson [J. Chem. Phys. 47, 4714 (1967)] has been used to test various Mie(n, 6) intermolecular pair potentials for their ability to predict liquid properties. The properties studied were the residual energies, entropies, and heat capacities in four saturated liquids: argon, nitrogen, methane, and perfluoromethane. The potential energy function parameters (ε/k, σ, n) used in most cases are those obtained by Klein [Natl. Bur. Std. (U.S.) AECD-TR-67–67] from second virial coefficient data. It is shown that it is possible to obtain a considerable improvement in predicted liquid properties if the parameter n is allowed to vary from the value 12 usually assigned to this parameter.
On Improved WKB (Uniform Asymptotic) Quantum Conditions, Dunham Corrections, the Langer Modification, and RKR Potentials
Authors: Pack Russell T
Published: February 2004

An improvement to the WKB quantum condition for the rotation-vibration levels of diatomic molecules, known empirically to give RKR potentials of increased accuracy and to account for the Dunham correction Y00, is derived using uniform asymptotic methods. The role of the Langer transformation in this problem is also discussed.
Multimode Vibrational Relaxation in Polyatomic Molecules
Authors: Bauer H.-J. , Shields F. Douglas , Bass H. E.
Published: February 2004

The acoustic behavior of polyatomic gas mixtures associated with multimode vibrational relaxation has been calculated. Rapid resonant energy exchange reactions have been assumed which maintain a Boltzmann distribution in each mode during the relaxation process. In this case, energy and temperature relaxation equations have been derived for multiple quanta and multiple mode v-v processes without the invalid assumptions made in previous work. The frequency-dependent and complex heat capacity is expressed in terms of the eigenproperties of the energy relaxation matrix.
Emission Spectra of Deep Impurity States in Solid and Liquid Rare Gas Alloys
Authors: Cheshnovsky Ori , Raz Baruch , Jortner Joshua
Published: February 2004

We have measured the spectral distribution (in the region 1100–2000 Å) of the α excited luminescence from solid and liquid dilute rare gas alloys. Emission was observed from the lowest deep impurity state of xenon in liquid and in solid argon, which provides evidence for medium relaxation resulting in a ``cavity'' formation around the excited impurity in dense rare gases.
Phase Transition within a Phase Boundary
Authors: Kikuchi Ryoichi
Published: February 2004

The excess free energy σ due to the phase boundary has been expressed previously using the bulk properties of the two phases meeting at the boundary as exp(−Aσ/kT)= ∑ ν [p(II)(ν)p(I)(ν)]1/2,where σ is per unit area, A is the cross-sectional area of the boundary, and p(I)(v) is the probability that a configuration v of the lattice plane parallel to the boundary appears in the bulk phase I. The summation goes over all possible configurations of the plane. The present paper applies the above formula to boundaries in the three-dimensional Ising model using the pair approximation. It is shown that an order-disorder transition occurs in σ. The ordered state is identified with the interstitial center boundary calculated before.
Xenon Difluoride: Heat Capacity from 5 to 350°K and Some Derived Thermodynamic Properties
Authors: Osborne Darrell W. , Flotow Howard E. , Malm John G.
Published: February 2004

The heat capacity of a 99.9% pure sample of xenon difluoride, XeF2, was measured between 5 and 350°K by an adiabatic method, and various thermodynamic properties were calculated from the heat capacity. No irregularities in the heat capacity nor solid-solid transitions were observed. At 298.15°K Cp°, S°,(H°−H°0)/T, and (G°−H°0)/T were found to be 75.60±0.08, 115.09±0.12, 51.17±0.05, and −63.92± 0.06 J °K−1· mole−1, respectively. The standard entropy of the gas at 298.15°K calculated from the thermal data is 258.6±1.9 J °K−1 mole−1, in excellent agreement with the value 259.4±0.1 J °K−1 mole−1 from molecular data. For solid XeF2 at 298.15°K the standard entropy of formation is −257.17± 0.12 J °K−1· mole−1, and the standard Gibbs energy of formation is −86.08±0.88 kJ mole−1; the corresponding quantities for gaseous XeF2 are −112.86± 0.1 J °K−1· mole−1 and −73.40±0.89 kJ mole−1, respectively. The equilibbrium constant for the formation of gaseous XeF2 from the elements at various temperatures is calculated and is compared with the experimental results of Weinstock, Weaver, and Knop.
Proton NMR and Piezoelectricity in Tetramethylammonium Chloride
Authors: Gibson A. A. V. , Raab R. E.
Published: February 2004

A proton magnetic resonance investigation has been made on tetramethylammonium chloride between 77 and 567°K. The existence of a new phase is reported, making a total of five known phases, and these are numbered from high temperature down. It is shown that methyl-group reorientation occurs without noticeable tunneling, followed at slightly higher temperatures by pseudoisotropic reorientations of the cations. The correlation times for these motions have been measured in four phases over this temperature range, and expressed by Arrhenius-type relations. Ionic diffusion only occurs in phase I, and then infrequently. This study shows that phase II is piezoelectric, and that in the absence of any solvent it may remain metastable at room temperature. In the presence of small quantities of solvent a transition occurs to the common stable phase III at ∼400°K.
Electric Dipole Moment of Diatomic Molecules by Configuration Interaction. V. Two States of 2Σ+ Symmetry in CN
Authors: Green Sheldon
Published: February 2004

In previous papers we developed techniques for the accurate calculation of dipole moments using moderate-sized (200 configuration) CI calculations. In this paper we consider the modifications necessary to treat higher excited states of a symmetry. It is shown that states below the state of interest must be considered simultaneously to a similar degree of accuracy. Calculations were performed on the 2Σ+ states of CN. For the X 2Σ+ state the SCF, CI, and experimental dipole moments (in debye) are 2.301, 1.465, and 1.45±0.08; for B 2Σ+ the CI and experimental values are −0.958 and −1.15±0.08. Spin hyperfine constants, and in particular spin density at the nucleus, are considered in the context of one-electron operator properties which may be calculated by the same methods used for the dipole moment. SCF and CI values for the spin density are compared with experimental values for several diatomic molecules.
Optical Spectra and Energy Levels of Erbium-Doped Yttrium Orthoaluminate
Authors: Donlan Vincent L. , Santiago Abraham A.
Published: February 2004

The absorption and emission spectra of YAlO3:Er3+ were recorded photographically in the spectral region 12 000–40 000 cm−1. Catalogs of the absorption and emission lines are presented; line strength data are given for the absorption lines. From these spectra, 104 energy levels of YAlO3:Er3+ from 0 to 40 000 cm−1 were deduced and are presented. These comprise the crystal field components of 22 of the 24 Er3+ free ion levels occurring below 40 000 cm−1. A free ion calculation was carried out. The free ion parameters that minimize the rms deviation between calculated and observed centers of gravity are E1=6786.3, E2=32.415, E3=643.27, ζ=2380.7, α =21.721, β =−683.43, and γ=389.03 cm−1. Reasons for the absence of the 2P1/2 and 4G5/2 lines from the absorption data are discussed.
Method for Treating Long Range Interactions in the Noniterative Integral Equation Formalism. Application to Electron-Hydrogen Atom Scattering
Authors: Knirk Dwayne L.
Published: February 2004

It is shown that equations furnished by the noniterative integral equation method can be used to construct a procedure for including the effects of long range potential ``tails'' into a calculation in which the potential has been truncated at rN. In particular, sets of integrals which determine the R matrix may be treated as vectors, and a certain matrix Ω applied to these vectors has the effect of ``projecting'' their values at rN over the potential tail to give corrected values. The Ω matrix, actually an infinite series, carries the iterative structure of the scattering equations and hence formally resembles a Born series development of the integrals involved. A two term approximation Ω1 is considered, and explicit expressions derived for a potential of the form Vij=ΣλCijλr−λ−1. This approximation is applied to the long range r−2 and r−3 potential terms in the close coupled calculations of electron-hydrogen atom scattering and found to give very good results.
Ab Initio and Semiempirical Calculations of the Static Potential for Electron Scattering off the Nitrogen Molecule
Authors: Truhlar Donald G. , Van-Catledge F. A. , Dunning Thom H.
Published: February 2004

Six calculations, three ab initio and three semiempirical, are presented for the static potential (i.e., the interaction potential energy of an electron with the unperturbed charge distribution) of a nitrogen molecule. The ab initio calculations are Hartree-Fock calculations using contracted Gaussian basis sets capable of yielding wavefunctions (1) near the Hartree-Fock limit, (2) near the sp-limit, and (3) at the minimum basis set level. The semiempirical calculations are all within the INDO formalism. We find that the inclusion of d functions in the ab initio calculations is necessary for an accurate description of the anisotropy of the potential. We also find that the INDO calculations give the correct form of the potential at small electron-molecule separation distances but are poor at large distances.
Limiting Form of the Effective Potential for Electron Scattering
Authors: Huo Winifred M.
Published: February 2004

In a previous article [J. Chem. Phys. 56, 3468 (1972)], an effective potential Ṽ f0 for direct scattering is defined such that its Fourier transform, multiplied by −(2π)−1, gives the scattering amplitude. Here we study the behavior of Vf0 at the limit q→ 0, with q the distance between the incident electron and the scattering center. It is found that the limiting form of Ṽ f0 is expressible by an ascending series, the first term being a q−1 term. The coefficient of the constant term is also derived. The applicability of the Born approximation under a number of limiting conditions is considered by means of Ṽ f0. For inelastic scattering, it is found that at a fixed incident energy, deviations from the Born approximation will be observed if the momentum transfer is increased. At a fixed scattering angle, deviations from the Born approximation will also be observed if the energy is increased. However, at a fixed momentum transfer, the Born limit will be approached with increasing energy. A number of calculations on both elastic and inelastic scattering are studied in view of the present results. The derivation in this paper assumes an atomic target but extension to the molecular case is straightforward.
Absolute Total Scattering Cross Sections for 7Li on He, Ne, Kr, and Xe
Authors: Dehmer Patricia , Wharton Lennard
Published: February 2004

Absolute total scattering cross sections were measured for the systems Li–He, Li–Ne, Li–Kr, and Li–Xe over a range of primary beam velocities of 0.75–4.75×105 cm/sec corresponding to a range of kinetic energies of 0.04–0.33 eV for Li–He to 0.02–0.79 eV for Li–Xe. The standard deviations of the cross sections were less than 1.2% of the observed cross section and the maximum systematic errors were between −0.3% and +1.4%. The data were deconvoluted for the effect of target motion and were statistically smoothed. The smoothed data had a standard deviation of 0.2%–0.4% which was about 4 times smaller than the standard deviation of the raw data points and which provided a criterion for judging the adequacy of fits for various model potentials. Model potentials with up to 5 variable parameters were fit to the smoothed cross sections by a least squares method. For Li–Kr and Li–Xe 4 potential parameters were determined simultaneously. These experiments were most sensitive to the potential value over a range of limiting impact parameters. For Li–Kr and Li–Xe this range was 6.5–9.2 Å and 7.8–9.7 Å, respectively, and in this region the potential was determined to an accuracy of 3%–4%, with the error arising primarily from systematic errors in the measurement of the cross section.
Measurements of Temperatures of Vibrationally Excited N2
Authors: Young Stephen J. , Horn K. P.
Published: February 2004

A comparison of the vibrational and rotational temperatures of microwave discharged N2 as measured by the CO tracer and the Penning ionization with He(23S) techniques has been performed in a flow tube apparatus. A vibrational temperature range of 1000–3000°K was covered at a kinetic temperature of ∼350°K. A detailed analysis of each technique is presented. The effect of pressure quenching of the N2+(1−) radiation occurring in the Penning ionization technique and the effect of vibrational temperature gradient across the flow tube in the CO tracer technique are discussed. Because of the good agreement of vibrational temperatures deduced from the two techniques, it is concluded that the Treanor-Teare relationship between the vibrational temperatures of diatomic gases in binary mixture in the V–V quasiequilibrium regime is valid. This work represents the first experimental confirmation of this relationship. The agreement of rotational temperatures implied by the N2+ and CO spectra indicates that the rotational distribution in BN2+(v′) is not significantly distorted from the N2 equilibrium distribution by the heavy He(23S) impact.