bluuebunny/crossref_metadata_2025 huggingface dataset:
Yields of elementary reactions initiated when HI and DI are activated by 254 nm radiation in 3-methylpentane-h14 and 3MP-d14 at 20–300 °K; H atom trapping
Authors: Perkey Lewis , Willard John E.
Published: February 2004

This paper reports work designed to give a more quantitative understanding of the reactions of hot and thermal hydrogen atoms with hydrocarbons at 298, 77, and 30°K and to explain the absence of trapped H atoms during photolysis of HI in 3-methylpentane-h14 (3MP-h14) glass at 30°K. Quantum yields of H2, HD, and D2 from the photolysis of HI and DI in 3MP-h14 have been determined for samples photolyzed in the liquid state at 298°K and the glassy state at 77 and 30°K. The yields of trapped free radicals and of alkyl iodides and iodine have been determined on samples photolyzed at 77°K. Trapped hydrogen atoms have been produced by photolysis of HI in 3-methylheptane-d18 and methylcyclohexane-d14 glasses, and their production in 3MP-d14 and nonproduction in 3MP-h14 confirmed. Photolysis of HI in 3MP-d14 at 30°K yields H2 as well as HD, indicating that thermalized H atoms are produced, but photolysis of DI in 3MP-h14 at 30°K yeilds no D2. This indicates that all the D atoms produced in 3MP-h14 abstract H from C–H bonds and implies that the reason D and H atoms from the photolysis of DI and HI in 3MP-h14 are not trapped is because the abstraction reaction consumes all of the atoms before they can be trapped. Information on isotope effects in both the liquid and solid phase has been obtained. The data further indicate that: (1) the quantum yield for stabilization of HI (DI) without reaction after having absorbed a photon is about 0.13 at 298°K and 0.5 at 77°K, in either 3MP-h14 or 3MP-d14; (2) the yield of HD from HI in 3MP-d14 or DI in 3MP-h14 at 77 °K is much greater than the yield of trapped radicals, implying that C6D13I(C6H13I) + HD must be formed by a concerted reaction; (3) at 298 °K the reaction D+3MP-h14 competes significantly for thermalized D atoms with the atom scavenging reaction D+DI→D2+I at DI concentrations less than ∼100 mM.
Debye-Waller factors of nickel and chromium
Authors: Pal Satya
Published: February 2004

The temperature variation of the Debye-Waller factors of nickel and chromium has been calculated from the vibrational spectrum derived from the lattice dynamical model of Krebs. The frequency spectra have been computed with the help of Blackman's root sampling technique for a discrete subdivision in the reciprocal space. The theoretical results are in reasonable agreement with the experimental data.
Lifetime of an emitting molecule near a partially reflecting surface
Authors: Chance R. R. , Prock A. , Silbey R.
Published: February 2004

A classical treatment of energy transfer in metal insulator systems is presented. The approach involves the calculation of the radiation field of an emitting molecule near a partially reflecting surface. The modification of the image theory result produces a large correction when the molecule is near the surface. This in turn produces a correction to the calculated lifetime of the molecule as a function of distance from the surface that differs substantially from previous theoretical descriptions of this system and brings the theory into good agreement with experiment.
Dependence of the CH3SiH3 barrier to internal rotation on vibrational coordinates: Testing of models and effect of vibrations on the observed barrier height
Authors: Ewig Carl S. , Palke William E. , Kirtman Bernard
Published: February 2004

The torsional satellite spectrum associated with the J=0→1 rotational transition in several symmetric isotopes of methylisilane is analyzed to yield the internal rotation barrier derivatives ∂V3/∂S1, where S1 is an A1 vibrational symmetry coordinate. Small basis set Hartree-Fock calculations of the same quantities give remarkable agreement with the ``experimental'' values. But we have been unable to construct any simpler model that will reproduce the derivatives corresponding to either the methyl or silyl bend or the CSi stretch. The shielded proton model-and variants which take into account the leftover negative charge as well as non-Coulombic forces-have been tried without success. From the derivatives we calculate a reduction in V3 of 54 cal/mole due to distortion of the equilibrium geometry in the eclipsed configuration. The effect of zero-point motions on the observed barrier height is examined for the first time. It is estimated that the pure harmonic terms arising from just the A1 vibrations contribute about 155 cal/mole, and it is quite possible that the total correction could be 3 or 4 times larger.
Quadrupole moment of CO, N2, and NO+
Authors: Billingsley F. P. , Krauss M.
Published: February 2004

Quadrupole moments obtained by a variety of experiments exhibit a wide range of values even for molecules such as CO and N2. Previous theoretical values were obtained with Hartree-Fock single-configuration wavefunctions. This study reports quadrupole moments obtained with multiconfiguration self-consistent-field wavefunctions chosen by the optimized valence configuration approach of Wahl and Das. The theoretical MC-SCF quadrupole moments are compared with both the experimental and Hartree-Fock values. Vibrationally averaged values of the quadrupole moments were obtained for CO and NO+. The results for the ν=0, J=0 vibrational level are −2.23 and 0.56×10−26 esu cm2, respectively.
Atomic and molecular calculations with the model potential method. I
Authors: Bonifacic V. , Huzinaga S.
Published: February 2004

A new formulation of the model potential method is introduced for atoms and molecules. The model potential consists of a static local potential which simulates the effect of the Coulomb and the exchange of the atomic core electrons and a set of projection operators which prevents the collapse of the valence shell orbitals into the inner cores. A mathematical analysis of the proposed model potential is given as well as numerical results of calculations for the second row atoms Li through Ne. No essential difficulties are expected on obtaining satisfactory results for heavier atoms. Advantages in applying the present method to the all-valence-electron molecular calculations are also discussed.
Geometries of the excited electronic states of HCN
Authors: Schwenzer Gretchen M. , O'Neil Stephen V. , Schaefer Henry F. , Baskin Craig P. , Bender Charles F.
Published: February 2004

Ab initio quantum mechanical electronic structure calculations have been carried out for the ground state and 12 low-lying (< 10 eV) excited states of HCN. A contracted Gaussian basis set of essentially double zeta quality was employed. A new theoretical approach, which should be widely applicable, was applied to the excited electronic states. First one selects a physically meaningful set of orbitals, which, hopefully, will be about equally suitable for all the electronic states of interest. After selecting a single configuration to describe each electronic state, configuration interaction is performed including all configurations differing by one orbital from any of the selected reference configurations. The method appears to be one of the simplest capable of treating several states of the same symmetry. The predicted geometries have been compared with the experimental results of Herzberg and Innes, as well as the appropriate Walsh diagram. The ab initio calculations and the Walsh diagram concur that Herzberg and Innes's assignment of the B̃ 1A″ state, with bond angle 114.5°, is incorrect. Although the theoretical predictions are in several cases at variance with the Walsh diagram, these differences can in most cases be justified in terms of a breakdown of the single configuration picture of electronic structure. One modification of Walsh's diagram is suggested, a change in the shape of the 5a′ orbital binding energy. Without this modification, the Walsh prediction is in serious disagreement with Herzberg and Innes's 141° bond angle for the C̃ 1A′ state. The present theoretical study predicts a bond angle of 141.2° for the third 1A′ electronic state of HCN.
V→T, R energy transfer in HCl- and DCl-rare gas mixtures
Authors: Steele Robert V. , Moore C. Bradley
Published: February 2004

Vibrational relaxation rates have been measured for HCl and DCl in collisions with the rare gases 3He, 4He, Ne, and Ar. For mixtures with 4He and Ar, data are given between 295 and 700°K. The rates vary approximately linearly with T−1/3 indicating that hard collisions cause the relaxation. The value of PHCl–Ar/PDCl–Ar=2 is evidence that nearly all of the vibrational energy is transferred into rotation in collisions with Ar. As the mass of the rare gas decreases, PHCl–M/PDCl–M decreases. PHCl–3He/PDCl–3He=0.6. This indicates an increasing importance of translational motion. Substitution of reasonable parameters into a simple theory of V→T, R energy transfer gives qualitatively the same behavior as the experimental results. The wide range of reduced masses, the isotopic substitution of 3He for 4He, the comparison of HCl and DCl, and the temperature variation make an ideal set of data for testing more complete theories of V→T, R energy transfer in atom-diatom collisions.
Molecular beam study of the K + CF3I reaction: Detailed differential reactive cross section and energy disposal
Authors: Rulis A. M. , Wilcomb B. E. , Bernstein R. B.
Published: February 2004

The reaction of a velocity-selected K beam with a crossed beam of CF3I (from a thermal capillary-array source) has been studied by the velocity-analysis technique. The observed (laboratory) KI product flux (velocity-angle) contour map, obtained at an average incident relative kinetic energy of 2.9 kcal/mole, has been transformed to yield the center-of-mass (c.m.) detailed differential reaction cross section. The c.m. cross section is ``backward'' peaked, but there is a substantial reactive contribution in the forward hemisphere as well. The average energy released into translational recoil of the products is only 8.5 kcal/mole, so that some 70% of the total available energy is partitioned into internal degrees of freedom of the products (cf. only 40% for the analogous reaction of K + CH3I). The present results are interpreted as weighted, orientation-averaged results of Brooks' dual-mode mechanism for the K + CF3I reaction.
Ion-molecule reactions and vibrational deactivation of H2+ ions in mixtures of hydrogen and helium
Authors: Theard Lowell P. , Huntress Wesley T.
Published: February 2004

Ion cyclotron resonance techniques have been used to determine the thermal energy rate constants for the ion-molecule reactions: (H2+)v+H2 → lim k1H3++H,(H2+)v+ He → lim k2HeH+ + H,→ lim kv (H2+)v′ + He lim →He+ + H2 → lim k3HeH+ + H,HeH+ + H2 → lim k4H3+ + He.For a near-Franck-Condon distribution of initial vibrational states in H2+ k1 = 2.08 ± 0.03, k2 =0.13 ± 0.01, k3 < 0.002, and k4 = 1.83 ± 0.06×10−9 cm3/molecule· sec. Collisional deactivation of vibrationally excited H2+ ions is also shown to occur in nonreactive encounters with He atoms. The rate constant kν for this process increases with increasing vibrational quantum number ν and is approximately equal to k2v for H2+ ions in vibrational state ν.
Electronic structure of FeCl4 anions in the Hartree-Fock-Slater model
Authors: Ellis D. E. , Averill F. W.
Published: February 2004

Optical spectra, charge densities, and Mössbauer isomer shift (IS) and quadrupole splitting (QS) parameters are obtained for FeCl4 anions, in the Hartree-Fock-Slater model. These data are compared with experiment, and possibilities of the simple self-consistent-field multiple-scattering approach used are assessed. The relative importance of metal p-d mixing and covalency effects in reducing the effective  values is shown. Conventional overlap distortion estimates of IS and QS parameters are found to be unreliable.
Method for calculating molecular Rydberg states
Authors: Averill F. W. , Walker T. E. H. , Waber J. T.
Published: February 2004

The multiple-scattering X α method is used to construct a potential suitable for Rydberg states and to obtain its eigenvalues. The method is checked by performing atomic calculations for Z ≤ 36 and gives good values. Molecular calculations are carried out with HF or BF3, and good agreement is obtained with experiment. Extensions to larger molecules are suggested.
Translation to vibration energy transfer in O + NH3 and O + CO2 collisions
Authors: Bass James N.
Published: February 2004

Vibrational excitation of NH3 and CO2 in collision with atomic oxygen is investigated for energies of 1–10 eV. A classical hard-sphere model used previously for diatomic molecules is adopted. Four ``diatomic'' models of NH3, in which the H3 complex assumes the role of a single atom, are used to study excitation of the ν2 mode. The results for the four models are very similar despite the model differences. It is shown that excitation of the ν1 and ν2 modes of CO2 can be computed very accurately through construction of the appropriate diatomic molecules. The classical energy transfers for CO2 and NH3 are converted to excitation probabilities of specific quantum states by using the assumption that the time-dependent interaction causing the excitation is a driving force independent of the oscillator coordinate. It is found that multiquantum excitation is important, the more so at higher energies. A scaling technique is used to estimate energy transfer for a more realistic atom-atom interaction. This results in greatly reduced multiquantum excitation for energies less than 5 eV. Excitation of the stiffer modes is also investigated. It is found that while excitation of the NH3ν4 mode is comparable to that of the ν2 mode at higher energies, the other modes may be neglected for the entire energy range studied.
Rydberg states of polyatomic molecules using model potentials
Authors: Betts Timothy C. , McKoy Vincent
Published: February 2004

We have used a simple model potential to calculate the Rydberg series in carbon dioxide, nitrogen dioxide, nitrous oxide, acetylene, propyne, formaldehyde, allene, butadiene, and butene. The model potential for a molecule is taken as a sum of atomic model potentials. The results agree well with experiment and allow us to assign and interpret almost all the Rydberg series in the molecules studied. In addition to various applications we can identify several Rydberg series which are perturbed by interloping valence transitions, e.g., in H2CO and CO2.
Mass spectrometry utilizing collisional ionization of cesium: Maleic anhydride and succinic anhydride
Authors: Compton R. N. , Reinhardt P. W. , Cooper C. D.
Published: February 2004

The translational energy dependence of the relative cross section for production of negative ions by collisions of fast cesium atoms with maleic anhydride (C4H2O3) and succinic anhydride (C4H4O3) has been studied from threshold up to approximately 20 eV (c.m.). Accurate measurements of the threshold energy for the creation of Cs+ and C4H2O3− from collisions of cesium atoms with maleic anhydride yield the electron affinity of maleic anhydride to be 1.4±0.2 eV. A number of fragment negative ions are observed from both compounds and the results are compared with our recently reported electron impact studies. CO2−* ions are observed to be unstable with respect to autodetachment, and the autodetachment lifetimes are measured to be 62±10 and 71±10 μsec for CO2−* from maleic and succinic anhydride, respectively. In both cases the lifetime of CO2−* is independent of the collision energy from threshold up to 15 eV.
Chemically induced dynamic electron polarization. V. A possible theory for alkyl radicals produced in radiolyses
Authors: Wong S. K. , Hutchinson D. A. , Wan J. K. S.
Published: February 2004

This work describes the spontaneous emission and enhanced absorption pattern of the initial spin polarization of alkyl radicals, XH2 and XH3, produced in radiolyses. It is assumed that the various total spin multiplets (electron and nuclear) have different probabilities of formation; this is an extension of our earlier work on the H and D atoms. The mode-spontaneous emission or enhanced absorption-for a given ESR line depends on two factors: first, which total spin multiplet is the more probable and second the sign of the isotropic hyperfine splitting constant.
Study of the theoretical dipole moment function and infrared transition matrix for the X 1Σ+ state of the HF molecule
Authors: Lie George C.
Published: February 2004

The dipole moments as a function of the internuclear distance are obtained from the Hartree-Fock-with-proper-dissociation (H–F PD) wavefunctions for the ground state of the HF molecule from R = 1.25 to 10.0 bohr. The computed vibrationally averaged dipole moment for the v = 0 level is 1.828 D (H+F−), to be compared with the experimental value of 1.827 D. The first and second derivatives of the dipole moment function are computed to be 0.692 D/bohr and −0.680 D/bohr2, respectively, comparing with the experimentally deduced values of 0.805 D/bohr and −0.076 D/bohr2. The infrared transition matrix is reported and compared with the available experimental data. The line strengths for the P and R branches are given for the 0–1, 0–2, 0–3, and 1–2 infrared bands.
Preparation and thermal, structural, and photoelectric properties of glassy and crystalline Te2.0Br0.75I0.25
Authors: Shevchik N. J. , Kniep R.
Published: February 2004

It has been found that mixed crystals of the general composition Te2.0Br1−xIx, where x ≤0.75 form glasses when cooled from the melt. We present the results of the thermal, structural, and photoemission experiments on Te2.0Br0.75I0.25, which is representative of the materials of the general composition above. The radial distribution function of the glassy form determined from x-ray diffraction indicates that the short range order is similar to that of the crystalline phase. Differences in the density of valence states of elemental Te and Te2.0Br0.75I0.25 as determined with uv and x-ray photoemission show that the electronic configuration characteristic of twofold coordinated Te is absent in the mixed crystals. The sharp core level spectra observed in the mixed crystal demonstrates that each type of element is in a similar Coulombic environment.
Phase separation in monolayers of adsorbed ions
Authors: Plesner Igor W. , Michaeli I.
Published: February 2004

Numerical calculations are performed on a dilute electrolyte solution in equilibrium with a charged surface, using the theory developed by Buff and Stillinger. The concentrations of adsorbed cations in the double layer (in the case of a negatively charged surface) are computed as a function of the electrostatic potential in the adsorption zone. It is found that a critical value of the potential exists, such that, for values of the potential more negative than the critical value, a phase transition in the double layer occurs to yield an almost close-packed layer of counterions. The results are discussed in the light of similar effects found in polyelectrolyte theory as well as of experimental results from nuclear relaxation studies. It is demonstrated that in the case of a mixed electrolyte solution (two monovalent cations and a common monovalent anion) the adsorbing surface will selectively adsorb the smallest cation below the threshold potential, even though the larger ion may predominate in the bulk phase. This effect is due largely to the short range (hard sphere) interactions.
Collisions of F(2P1/2) with H2
Authors: Tully John C.
Published: February 2004

The role of spin-orbit and nonadiabatic effects in the reaction of F atoms with H2 is discussed, Ground and excited FH2 potential energy surfaces and the required interactions between them are computed by the diatomics-in-molecules method. Using an approximate semiclassical procedure, thermal rate constants for reaction and quenching of F(2P1/2) are estimated to be 1.2 and 8.4×10−12 cm3 mol−1 · sec−1, respectively. Since the former is about an order of magnitude smaller than previously reported calculations of the rate constant for reaction of F(2P3/2) with H2, these results predict a substantial difference in reactivity between the 2P3/2 and 2P1/2 fine structure states of atomic fluorine.
Electron energy dependence of the energy and angular distributions of O− from dissociative ion pair formation in O2
Authors: Van Brunt R. J. , Kieffer L. J.
Published: February 2004

The energy and angular distributions of O− produced from O2 by dissociative ion pair formation have been measured at selected incident electron energies from threshold to 100 eV. The kinetic energy distributions show well-defined maxima near 2.0 and 3.3 eV with appearance potentials, respectively, at 20.0 and 23.0 eV. The angular distributions are peaked in the forward and backward directions relative to electron beam and exhibit nondipolar structure. The shape of the distributions depends on electron energy, becoming more isotropic with increasing energy. An attempt has been made to explain the behavior of the angular distributions in terms of a superposition of final states using a multipole expansion of the differential cross section which includes the effects of higher-order partial waves.
Breakdown of the dipole-Born approximation for predicting angular distributions of dissociation fragments
Authors: Van Brunt Richard J.
Published: February 2004

A general expression is given for the form of the angular distribution of molecular fragments produced by electron-induced dissociation of diatomic molecules. A model for parametrizing angular distributions is introduced which allows investigation of higher-order multipole corrections to the simple dipole-Born approximation. It is found that higher-order terms are significant and even dominate the form of the angular distribution at electron energies near thresholds involving large momentum transfer. The model is useful in explaining previously observed deviations from the dipolar form and is applied to recent measurements of the angular distribution of O− produced from O2 by dissociative ion pair formation. When the effect of molecular rotation is included, the degree of anisotropy is found to diminish with increasing lifetime of the dissociating state, although general features of the distribution are preserved.
Energy transfer processes in monochromatically excited iodine. IX. Classical trajectory and semiclassical calculations of vibrationally and rotationally inelastic cross sections
Authors: Rubinson M. , Garetz B. , Steinfeld J. I.
Published: February 2004

Classical trajectory calculations were carried out on the system in which I2 in the 3Π0μ+ excited electronic state and certain specific vibrational and rotational levels interact with the inert gases as collision partners. The trajectory results duplicated the effective cross sections for vibrational and rotational energy transfer into specific channels, as well as the mass dependence of the total cross sections for vibrational and rotational energy transfer when a correction was made for quenching. A semiclassical model provided less accurate values for the vibrational deactivation probabilities, but at a considerable saving of computation time.
Viscosity of xenon and ethane in the critical region
Authors: Strumpf Hal J. , Collings A. F. , Pings C. J.
Published: February 2004

The viscosity of xenon has been measured along 10 isochores and the viscosity of ethane along five isochores in the region of the gas-liquid critical point. The viscometer was a torsionally oscillating quartz cylinder, which generates a viscous wave when immersed in a fluid; the resonant properties of the quartz in a viscous fluid can be related to the viscosity-density product of the fluid. The viscosities of both substances exhibit an ``anomalous'' increase which can be fitted to an equation of the form Δη/ηid = A ln[(T−Tc/Tc]+B. This functional form is in agreement with recent theoretical predictions by Sengers, and values of the coefficient A obtained from the data are consistent with theoretical analysis which shows A = −8ν/15π2, where ν is the usual critical state exponent describing the divergence of the long range correlation length. Measured viscosity excesses amount to 15% for xenon and 16% for ethane. The critical temperatures and densities have been determined to be Tc=16.627±0.005°C, ρc=1.11±0.01 g/cm3 for xenon; Tc=32.218±0.005°C, ρc=0.2055±0.002 g/cm3 for ethane.
Symmetry breaking instabilities in illuminated systems
Authors: Nitzan A. , Ortoleva P. , Ross J.
Published: February 2004

Chemically nonreactive and reactive systems (closed and homogeneous) are shown to become unstable to inhomogeneous perturbations beyond given critical intensities of uniform illumination, so that macroscopic inhomogeneities (spatial patterns) arise. We classify symmetry-breaking instabilities into two types: extrinsic length scaling, in which the characteristic length of the developing spatial pattern is determined by the dimensions of the system; and intrinsic length scaling, in which that characteristic length is determined by the dynamics of the system (reaction rates and transport relations). We analyze a variety of nonlinear systems by means of a linear stability analysis. In an illuminated, isothermal, isobaric, two-species system, only extrinsic length scaling is possible; more degrees of freedom, either with increasing number of species or other state variables, are required for intrinsic scaling in the closed system. Next we consider a two-component nonreactive illuminated gaseous system in which diffusion, thermal conduction, and thermal diffusion may occur. We show that if only one component in a thermal diffusion experiment tends towards the hotter region, then extrinsic symmetry-breaking instability is possible. If, in addition, the two species are coupled by reaction (interconversion), then the spatial patterns at the onset of instability are of the intrinsic type. We then include pressure fluctuations in an analysis of a one-component system under steady illumination at a wavelength that is absorbed by the molecules and then converted into heat. We show that such a system may generate and amplify sound waves; that is, the system becomes unstable to spatially periodic pressure (acoustic) variation. This process may be used for the measurement of vibration-translation relaxation rates.
Correlation of the chemical thermodynamic properties of alkane hydrocarbons
Authors: Scott D. W.
Published: February 2004

An internally consistent correlation was made of the extant experimental data on the entropy, heat capacity, enthalpy of formation, and isomerization equilibria of alkane hydrocarbons. Of the data selected as reliable, all 41 values of entropy, 98 out of 100 values of heat capacity, 52 out of 54 values of enthalpy of formation, and all 15 values of enthalpy of isomerization from equilibrium data were fit within the assigned experimental uncertainty. Working formulas, tables, and equations are given whereby thermodynamic properties for selected temperatures between 200 and 1500 K can be calculated for any alkane hydrocarbon with a tractably small number of molecular conformations (say ≤34=81). Compounds with more conformations can be included by use of appropriate substitution methods. Values so obtained for the entropy, heat capacity, and enthalpy of formation at 298.15 K are tabulated for all alkanes C3–C10. Variance-covariance matrices from least squares adjustment of constants provide estimates of the reliability of calculated property values. Gaps are noted in the data base that should be filled to permit improved correlations in the future.
Vacuum ultraviolet spectra of osmium tetroxide and ruthenium tetroxide
Authors: Roebber John L. , Wiener Robert N. , Russell Carol Adam
Published: February 2004

The gas phase absorption spectra of the compounds OsO4 and RuO4 were measured between 2500 and 1050 Å with a Baird 1−m vacuum monochrometer of 1.0 Å bandwidth. Both tetroxides show many electronic absorption bands in this region with diffuse vibrational structure. No spectra of OsO4 or RuO4 have been previously reported below 2200 Å. Absorption maxima for OsO4, which were not previously reported, occur at 48 140, 63 620, 73 960, 85 620, 86 920, 89 160, 90 800, and 91 940 cm−1. The spectrum of RuO4 showed band maxima at 50 660, 64 620, 72 700, 76 420, 79 040, 83 100, 88 860, and 92 080 cm−1. The general appearance and relative strengths of various absorption bands in the spectra of these molecules were similar, with the energy of apparently corresponding transitions shifted to the red in RuO4 by approximately 10 000 cm−1. Most of the strong electronic transitions have been tentatively assigned on the basis of extended Hückel type calculations. The results of these calculations correlated reasonably well with the spectral data obtained. Bands are present in the spectra of both molecules which may be the first members of Rydberg series.
HO2 detected by laser magnetic resonance
Authors: Radford H. E. , Evenson K. M. , Howard Carleton J.
Published: February 2004

Far-infrared absorption spectra of HO2 in the gas phase have been detected at six wavelengths of a water vapor laser magnetic resonance spectrometer. The identification of HO2 as the absorbing molecule is based on a partial analysis of the spectra and on a variety of different chemical methods used to produce the radical. Approximate values of rotational constants and spin doublet separations are derived from the spectra.
Thermal effects of the transformation ice III–IX
Authors: Nishibata K. , Whalley E.
Published: February 2004

The heat and entropy of the transformation ice III–IX has been measured by a differential calorimetric technique as −0.32 cal K−1 mol, compared with the value −0.805 cal K−1 mol expected if ice III were fully disordered and ice IX were fully ordered within the limitations of the ice rules. It seems likely that there is significant disorder in ice IX, as found in a recent neutron diffraction investigation.
Fine and hyperfine structure of ortho-H2, k(4p) 3πu
Authors: Miller Terry A. , Freund Robert S. , Zegarski Bernard R.
Published: February 2004

The MOMRIE (microwave optical magnetic resonance induced by electrons) spectrum has been observed and measured for ortho-H2, k(4p) 3πu, in the lowest four vibrational levels ν = 0−3, and the lowest rotational level, N = 1. The best data are obtained for ν = 1 and 3; the ν = 0 data suffer from severe electric field broadening and the ν = 2 data are affected by a large but undetermined perturbation. Analysis yields values for the spin-orbit and spin-spin coupling constants, the orbital angular momentum and dipolar hyperfine constants, the orbital g factor, and the magnetic and electric susceptibilities. These parameters are then ``corrected'' for the breakdown of the Born-Oppenheimer approximation by the same procedures previously applied to the d(3p) 3πu state. The present results are combined with previous work on the n p 3πu Rydberg series [the c(2p) 3πu and d(3p) 3πu states of H2 and the X ∑1g+ state of H2+] to illustrate the variation of fine and hyperfine structure parameters with the principal quantum number, and the deviation of molecular Rydberg states from the united atom model.
Spatial structures in dissipative systems
Authors: Hanson M. P.
Published: February 2004

A one-dimensional system which exhibits a chemical instability with respect to free diffusion is analyzed numerically. Below a critical size the homogeneous state is stable. Above this size a succession of inhomogeneous states appear, each one stable over a range of values for the dimension of the system. A plot of the rate of entropy production for the system versus the dimension of the system is monotone increasing but with a change in slope at the appearance of the first inhomogeneous steady state. Transitions between inhomogeneous steady states result in a step increase in the rate of entropy production. At least one additional series of steady states is stable for the system. The results are used to present a model for a chemical signal to initiate cell division.
On the coupling operator method
Authors: Hirao Kimihiko
Published: February 2004

The coupling operator method in the general SCF theory is discussed in terms of the projection operator property of the density operator. The advantage of using the density operator is that one can put the arbitrariness of the general SCF orbitals in evidence. We showed how to put the fundamental condition for the optimum orbitals of the general SCF theory into a more general and useful form. The essential point of the coupling operator is how the variational conditions are included as the projections onto the intermanifolds. By using the arbitrariness of the manifold, we indicate how a modified SCF theory is developed, where by choosing an appropriate operator one can get any desired modified orbitals and their associated orbital energies under orbital transformations. The Appendix contains an extension of Koopmans' theorem as an application of the modified SCF theory. Finally the effective Hamiltonian is derived which is valid for almost all of the proposed SCF theory.
Spectroscopic properties of polyenes. II. The vacuum ultraviolet spectra of cis- and trans-1,3,5-hexatriene
Authors: Gavin R. M. , Rice Stuart A.
Published: February 2004

Absorption spectra are reported for cis- and trans-1,3,5-hexatriene in the region between 47 000 and 69 000 cm−1. The observed transitions are compared to those predicted from Pople-Pariser-Parr pi-electron calculations using configuration interaction including both single and double excitations. The ordering of states predicted from calculations based on single excitations appears to be more plausible than that of the more extensive single-plus-double excitation calculations. Vibrational progressions associated with the higher energy ππ* transitions of the trans isomer are almost identical to those reported previously for the lowest energy allowed transition (39 000–47 000 cm−1). The linewidths of the trans isomer transitions are considerably smaller than those for the cis isomer transitions throughout the entire vacuum ultraviolet region. An ionization petential of 8.27 eV is obtained for the trans isomer from a Rydberg series extrapolation. This value compares favorably with the value (8.29 eV) obtained recently from photoelectron spectroscopy. Strong bands which could be assigned unambiguously as Rydberg transitions were not found for cis-hexatriene. However, the shape of the absorption curve in the region 62 000–68 000 cm−1 implies that the ionization potential for cis-hexatriene is probably within 0.1 eV of that for trans-hexatriene.
Impurity quenching of molcular excitons. III. Partially coherent excitons in linear chains
Authors: Hemenger Richard P. , Lakatos-Lindenberg Katja , Pearlstein Robert M.
Published: February 2004

We have extended a model of exciton quenching, previously developed for pure Frenkel excitons, to include the exciton-phonon interaction. We introduce a mathematically tractable exciton density matrix equation that describes the motion of excitons on a finite chain quenched at both ends. From this equation we find that the excitation on the chain as a function of time exhibits several types of kinetic behavior that result from the interplay of coherent, incoherent, and quenching terms. This behavior changes as a continuous function of the strength of the incoherent terms in such a way as to define five kinetic regions, ranging from that of pure Frenkel excitons to that of completely incoherent (hopping) excitons. In each of these five regions the average excitation decay rate constant is proportional to cp, p = 0, 1, 2, or 3, where c is the quencher concentration.
Raman spectra of gases. XIII. Two-quantum torsional transitions in some dihalo- and trihaloethanes
Authors: Durig J. R. , Bucy W. E. , Wurrey C. J.
Published: February 2004

Methyl torsional overtones (Δν=2) have been observed for CH3CHCl2, CD3CDCl2, CH3CHBr2, CH3CCl3, CD3CCl3, CH3CBr3, CH3CCl2F, CH3CF2Br, and CH3CBr2Cl in the Raman effect. From the observed frequency shifts, barriers to internal rotation have been calculated to be 4.13, 4.13, 4.33, 5.43, 5.40, 5.78, 4.42, 5.06, and 5.70 kcal/mole, respectively. Some of these barriers have never been determined for the gas phase. Trends of barrier height as a function of halogen substitution are discussed for chlorine and bromine substitution.
Gas phase recombination of OH with NO and NO2
Authors: Anderson J. G. , Margitan J. J. , Kaufman F.
Published: February 2004

The termolecular recombination of OH with NO and with NO2 is studied for M=He, Ar, and N2 at pressures from 1–10 torr and temperatures from 230–450°K in a flow tube using resonance fluorescence detection of OH radicals. The reactions are in their low pressure, third-order limit. The rate constants for the NO reaction at 295°K are 3.3, 3.4, and 5.8×10−31 cm6 sec−1 in the above order of M gases. For the NO2 reaction the corresponding values are 1.0, 1.0, and 2.3×10−30, all with σ=±20% including estimates of systematic errors. Both recombinations show the expected negative temperature dependence, the Arrhenius activation energies being −1.7 kcal for NO and −1.8 kcal for NO2. These results are compared with all other published data and with RRKM unimolecular calculations.
Generalized Hellmann-Feynman theorems and hypervirial theorems for X α-like methods
Authors: Epstein Saul T.
Published: February 2004

Simple derivations are given of the theorems mentioned in the title. Also, conditions are given under which variational approximations to X α-like methods will satisfy analogous theorems.
Depolarized light scattering near the gas-liquid critical point
Authors: Oxtoby David W. , Gelbart William M.
Published: February 2004

We consider a new mechanism for the depolarization of light by simple fluids that arises only in the gas-liquid critical region. It is shown that the contributions to the integrated scattering intensity can be separated into two distinct kinds: single scatterings off anisotropic clusters of interacting atoms and successive single scatterings off undistorted particles separated by macroscopic distances. Under almost all sample conditions the depolarized spectrum is determined wholly by the former, collision induced effects characterized by the short range, many body fluid structure. Close to the critical point, however, the true double scattering events become dominant and reflect entirely new dependences on wavelength, temperature, and sample size. In the particular case of xenon, we predict — for cell dimensions on the order of a few millimeters and long range correlation lengths (ξ) less than a few hundred angstroms — that the depolarization ratio should increase roughly as ξ2. We also predict a small but observable angle dependence in the integrated depolarized scattering intensity, and we discuss the ``iterated'' (``reducible'') nature of the contributions from three- and four-body structural correlations.
Mean spherical model for the structure of Lennard-Jones fluids
Authors: Narten A. H. , Blum L. , Fowler R. H.
Published: February 2004

The mean spherical model (MSM) has been solved for the 12/6 fluid in four different states which correspond to those of neon, argon, krypton, and xenon at relatively high densities. Structure and correlation functions calculated from the model are in good agreement with results derived from diffraction experiments and molecular dynamics calculations.
Mass spectrometric determination of the heats of formation and atomization energies of the molecules Ge2N and GeSiN
Authors: Muenow David W.
Published: February 2004

Two previously unobserved polyatomic gaseous nitrides, Ge2N and GeSiN, have been identified with a high-temperature mass spectrometer. From second- and third-law analyses of the equilibrium: 2Ge(g)+(1/2)N2(g) =Ge2N(g) and third-law treatment of the isomolecular exchange reaction Si2N(g)+Ge(g)=GeSiN(g)+Si(g), the heats of formation and atomization energies of Ge2N(g) and GeSiN(g) are calculated to be ΔH°f,298=102.3±11 and 92.1±13 kcal mole−1 and ΔH°atoms=189.2±11 and 217.5±16 kcal mole−1, respectively.
Associative ionization in collisions of metastable helium with H and D
Authors: Magnuson G. D. , Neynaber R. H.
Published: February 2004

The exothermic reactions He*+H→HeH++e and He*+D→HeD++e have been studied by merging-beams techniques over a range of interaction energy W from 0.05–10 eV. The He* represents a composite of He(2 1S) and He(2 3S). Data were obtained by observing currents due to the product ions. For each process the relative effective cross section QR (i.e., for the composite He*) as a function of W is the same within experimental error and monotonically decreases with increasing W. The QR are in excellent agreement with theoretical predictions by Miller, Slocomb, and Schaefer for the reaction He(2 3S)+H→HeH++e. Absolute cross sections have also been extracted from the merging-beams data. These are in fair agreement with calculated values but lower than some recent crossed-beam results.
Broadening of hydrogen fluoride lines by H2, D2, and N2
Authors: Meredith Robert E. , Smith Frederick G.
Published: February 2004

Foreign gas broadening of the vibration-rotation lines in the first overtone band of hydrogen fluoride have been investigated. Linewidths broadened by N2, H2, and D2 have been measured for 15 lines in the band at a resolution of approximately 0.1 cm−1. Comparison of the measured widths with predictions based on the Anderson theory show good agreement only for N2 broadening of the lower J transitions. Theory overpredicts all H2 broadened widths and all D2 broadened widths except those for the R(0), P(1), and P(2) lines for the Anderson treatment of close collisions. Better agreement is found with H2 broadening if the Van-Kranendonk treatment of close collisions is used. The general conclusion reached is that the theory cannot be used reliably to predict vibration-rotation linewidths which are dominated by forces of shorter range than dipole-dipole.
Effect of the cluster integrals on three particles on the calculated electron density of a hydrogen plasma
Authors: McIntyre Robert G. , Bruce Rufus E.
Published: February 2004

The effect of the calculation of the cluster integrals on three particles is analyzed and evaluated for a hydrogen plasma where a pairwise-additive hard sphere-Coulomb potential is assumed. The Mayer cluster integral method was used to calculate the Helmholtz free energy which was then applied to the calculation of the electron number density through an iterative technique using a corrected Saha equation. It is seen that the three particle integrals provide a substantial correction to the calculations in the low energy-high density region of the hydrogen plasma.
Debye-Huckel limiting laws based on a generalized Poisson-Boltzmann equation
Authors: MacGillivray A. D.
Published: February 2004

The potential at the surface of a central ion, from which the limiting laws of electrolyte solutions are found, is derived by a method which is simple, rigorous, and valid for a wide class of possible laws governing the dependence of the ion distribution on the potential. This class is characterized by two properties, both very simple and which can very reasonably be expected to be possessed by the actual distribution law, whatever it may be. In particular, the Boltzmann distribution law is not assumed, although of course it is included in the class considered.
Variational perturbation theory investigations on two-electron atomic systems. III. Nonrelativistic results for the state 1s 2s 3S
Authors: Aashamar Kjell , Midtdal John , Lyslo Gudmund
Published: February 2004

The variational perturbation (HSK) procedure has been applied to the two-electron atomic state 1s2s3S. The total nonrelativistic energies and corresponding wavefunctions have been determined with errors less than one part in 1012 and 1–2 parts in 106, respectively, for all Z ≥ 2. The results are presented in tables accompanied by illustrative figures.
Electronic states of B+ produced by electron bombardment of boron trihalides: Some ion-molecule reactions of B+
Authors: Lin Kuo-chin , Cotter R. J. , Koski W. S.
Published: February 2004

Beam attenuation studies of B+ as a function of attenuating gas pressure show that the beam has a composition of 35% 3P and 65% 1S when produced by 70 eV electrons from BF3. As one proceeds in the series from BF3 to BI3, the amount of excited state varies in a regular manner and B+ ions are completely in the ground state when BI3 is used as a target. The composition of the beam could also be varied by varying the electron energy. The results of the attenuation studies were also confirmed by studying the cross section vs beam energy curves for the B+(1S) and B+(3P) reactions with N2O.
Electronic states of doubly ionized ammonia
Authors: Appell J. , Horsley J. A.
Published: February 2004

The ionization potentials corresponding to the formation of the lowest-lying states of doubly ionized ammonia have been measured by double charge transfer spectroscopy, the translational energy analysis of H− ions arising from double charge transfer between 4 keV protons and NH3. SCF–CI calculations have been carried out for the lowest lying states of NH3++ at the equilibrium geometry of the neutral molecule. The assignment of the experimental energy values to given states of NH3++ is discussed. Fairly good agreement between experimental and calculated double ionization potentials is obtained.
Collective oscillation in liquid water
Authors: Heller J. M. , Hamm R. N. , Birkhoff R. D. , Painter L. R.
Published: February 2004

Measurements of the optical properties of liquid water were extended in the vacuum ultraviolet up to an energy of 25.6 eV. The indices of refraction and dielectric functions were obtained by a Kramers-Kronig analysis using reflectances measured in this study between 7.6 and 25.6 eV and reflectances from the literature below 7.6 eV. Our interpretation of the prominent peak in the energy loss function at about 21 eV is that it represents a collective electronic oscillation.
Relaxation rates from time of flight analysis of molecular beams
Authors: Gallagher Robert J. , Fenn John B.
Published: February 2004

In the free jet generated when a gas is expanded from a reservoir at stagnation temperature T0 and pressure P0 into a vacuum chamber, substantial lags can occur in the conversion of internal energy into directed kinetic energy of the expansion. An analytical technique is presented for determining rotational energy relaxation rates from velocity distributions measured on the axis of the free jet at a fixed distance from the sonic throat. The agreement with rates obtained by other methods is good. Some sample experimental and analytical results for carbon dioxide, oxygen, hydrogen, and methane are presented.
Rotational relaxation of molecular hydrogen
Authors: Gallagher Robert J. , Fenn John B.
Published: February 2004

The rotational relaxation rate in molecular hydrogen has been determined experimentally between 300 and 1900°K by time of flight analysis of molecular beams from supersonic free jets. Over their common temperature range from 295 to 1073°K our results are in reasonable agreement with the ultrasonic measurements of Winter and Hill which show a rotational collision number Zr between 300 and 400. In terms of momentum transfer collisions Zr is relatively insensitive to temperature. This observation suggests that rotation-rotation transfers play an important role.
Interaction energy of dissimilar dielectric surfaces
Authors: Craig R. A.
Published: February 2004

A recent calculation of the energy of interaction of a half-space-slab-half-space system is extended to the (ε3−ε2−ε1) geometry.