bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonexponential decay of CS a 3Π–X 1Σ+ luminescence
Authors: Fournier J. , Deson J. , Vermeil C. , Robbe J. M. , Schamps J.
Published: February 2003

The VUV photodissociation of CS2 embedded in argon or krypton matrices at 5 K yields to the formation of the CS a 3Π radical. A nonexponential decay of the CS (a→X) emission is observed which can be decomposed into three components. The radiative lifetimes of the 3Π0 and 3Π1 sublevels are calculated. The agreement between experimental and ab initio values leads to the conclusion that the three spin–orbit sublevels of the CS triplet state decay independently in low temperature matrices.
X-ray photoemission studies of atom implanted matrices: Cu, Ag, and Au in SiO2
Authors: Young V. Y. , Gibbs R. A. , Winograd N.
Published: February 2003

X-ray photoelectron spectroscopy has been used to study the electronic structure of Cu, Ag, and Au atoms implanted in SiO2. In each case the valence levels shifted to higher binding energy and narrowed compared to the bulk metals, approaching the expected shape of the gas phase free atom spectra. A model is presented which allows calculation of photoemission and Auger energies from atomic spectra, and is shown to accurately predict the observed spectra.
The calculation of vibrational mean square amplitudes of molecular internal coordinates by a perturbation theory technique
Authors: Wolfsberg Max , Peter Eva Au
Published: February 2003

The mean square amplitudes of internal coordinates in a harmonically vibrating molecule are developed to second order in a perturbation theory treatment where the unperturbed problem corresponds to uncoupled coordinate oscillators and the perturbation arises from coupling terms in the kinetic and potential energies. Exact and perturbation theory calculations are compared.
Two-photon spectroscopy of dipole-forbidden transitions. II. Calculation of two-photon cross sections by the CNDO–CI method
Authors: Hohlneicher Georg , Dick Bernhard
Published: February 2003

In the first paper of this series we investigated the applicability of a CNDO/S scheme including double excited configurations for the calculation of excitation energies of larger unsaturated molecules. In this paper we show that the same scheme is very useful for the prediction of two-photon transition probabilities. If the proper expansion is used, the results converge quite well with increasing number of intermediate states. We also show that the inclusion of double excited configurations is not only necessary to obtain better energies for dipole-forbidden transitions to ’’covalent’’ excited states but also to obtain the correct order of magnitude for two-photon cross sections.
Dissociating states of the H−3 system
Authors: Garcia G. Ramiro , Rossi Angelo R. , Russek A.
Published: February 2003

Single determinant Hartree–Fock calculations for the lowest singlet and triplet potential energy surfaces of the H−3 system are presented over a broad range of isosceles triangular configurations of the nuclei. The addition of a diffuse s function to the four-term Gaussian expansion of Huzinaga for H(1s) together with p type polarization functions produces results which are in agreement with experiments on double electron capture by H+3 to form H−3. The present calculations predict that capture to the ground singlet state produces H2+H−, with a dissociation energy in reasonable agreement with the experimental findings. Capture to the triplet state is predicted to resulted in the three body dissociation H+H+H− with small dissociation energy. This is consistent with, but not positively confirmed by, the experimental data.
IR absorption of SF6 excited up to the dissociation threshold
Authors: Fuss W. , Hartmann J.
Published: February 2003

SF6 was pumped by a P20 TEA CO2 laser up to an average energy of 10 000 cm−1 in the absence of collisions and up to 20 000 cm−1 with a certain collisional relaxation. A second CO2 laser, very much attenuated, was used to determine absorption cross sections for frequencies from 915 to 985 cm−1. No coherent effects and no collisionless relaxations were found, in contrast to measurements with a cw laser as a probe. The ν3 band continuously shifts to longer wavelengths, but the shift of the ν2+ν6 band is 10 to 20 times smaller. Many more rotational states of the vibrational ground state are depopulated than expected. To explain it we suggest direct two-photon excitation, for which independent evidence is also presented. Many peaks and holes were found, part of which we assign to high states. Evidence for inhomogeneity of these structures is found by comparison with single laser absorption spectra. Collisional relaxation of unidentified nature and with a time constant of 48±10 ns mbar generates new spectra, indicating large nonequilibrium rotational populations.
Effect of irradiation temperature from 77 to 1.6 K on the optical absorption and scavenging efficiency of localized electrons in aqueous 10 M lithium chloride glasses
Authors: Dolivo G. , Kevan Larry
Published: February 2003

Irradiation of the 10 M LiCl/D2O matrix at 77 K stabilizes the solvated electron species, evis−(λmax∼575 nm) while irradiation at 4.2 or 1.6 K stabilizes two localized electron species evis−(λmax∼680 nm) attributed largely to solvated electrons and eIR−(λmax≳2400 nm) attributed largely to presolvated electrons. Between 4.2 and 1.6 K the evis− spectrum is essentially unaffected but the eIR spectrum is shifted to lower energy at 1.6 K. The electron scavenging efficiencies of bromate, nitrate, and chromate for evis− at 77, 4.2, and 1.6 K and for eIR− at 4.2 and 1.6 K were studied. The total scavenging efficiency for all localized electrons in the glass increases as the temperature is lowered over this range. An apparent low scavenging efficiency for evis− at 4.2 K seems due to competitive tunneling to the scavenger by evis− and eIR−. This interpretation is supported by observations of the scavenging efficiency of nitrate in 10 M NaOH aqueous glass over this same temperature range in which only one main type of localized electron species is observed. The scavenging results support the assignments of e−IR to a presolvated electron with a nonequilibrium orientation of first solvation shell waters and of e−vis to a solvated electron with an equilibrium orientation of first solvation shell waters.
Thermal effects on the optical spectra of a polydiacetylene: Poly{1,2-bis [4- (isopropylcarbamoyloxy) -n-butyl]-1-buten-3-ynylene}
Authors: Eckhardt H. , Eckhardt C. J. , Yee K. C.
Published: February 2003

The reflection spectra of single crystals of the polydiacetylene, IPUDO [R= (CH2)4OCONHCH (CH3)2], were measured between 25° C and 160° C. A nearly reversible thermochromic change is observed together with a variation of hysteresis upon cycling. The latter is attributed to annealing that permits the pendant groups to adopt a conformation which favors the butatriene-type configuration of the polymer at high temperatures. Intensities of the high and low temperature spectra obtained by Kramers–Kronig transforms are in excellent agreement with the spectral intensities of polydiacetylenes which are prototypes for the two configurations.
ESR studies of a nitrogen defect in irradiated potassium azide
Authors: Turner R. C. , Stout F. H. , Trimm T. G.
Published: February 2003

An electron spin resonance study has been conducted on a new paramagnetic defect center in irradiated potassium azide. Irradiation of a single crystal of KN3 with x rays at 77 K resulted in the formation of the defect which was characterized by a single structureless resonance line having considerable anisotropy. Effective g values along the principal axes were measured at 77 K and were found to be 6.16, 1.719, and 0.579 along the crystal [001], [110] and [11̄0] directions, respectively. The rotational spectra could not be fit, however, with a spin one half Zeeman Hamiltonian, leading to the conclusion that only one transition of a spin greater than one half system was being observed. Measurements at temperatures other than 77 K showed a strong temperature dependence of the effective g values which would be consistent with a temperature dependent fine structure term in the spin Hamiltonian. The defect was found to be stable to about 130 K. Isothermal annealing measurements indicated a first order decay with an activation energy of 0.39 eV and a characteristic frequency of about 1012 Hz. Irradiation of a single crystal with ultraviolet light resulted in the formation of a defect with the same effective g values, but a narrower resonance line having hyperfine structure indicative of interaction with a single nitrogen nucleus.
Franck–Condon theory of chemical dynamics. VI. Angular distributions of reaction products
Authors: Vila Carlos L. , Zvijac David J. , Ross John
Published: February 2003

We calculate planar and three-dimensional angular distributions for the products of atom–diatom chemical reactions by means of the Franck–Condon (FC) model. The wave functions on the reactant and product quasiadiabatic surfaces are expanded in partial wave series. A local uncoupling of the different degrees of freedom, as justified earlier, is assumed and consequently the individual members of the partial wave series can be separated into products of angular factors and rovibration–translation factors. To evaluate these factors, we consider the limit of weak and strong potential, and weak and strong kinematic couplings. The center of mass differential cross section is obtained by means of the T matrix formalism, where the T matrix is approximated by a generalized Franck–Condon overlap of the reactantlike and productlike wave functions. We use several further satisfactory approximations, e.g., linearization of the potential in the region of maximal overlap, and semiclassical approximation to the oscillator wave functions, beyond those of the FC model to obtain an analytic expression for the T matrix. For assumed LEPS surfaces of the systems H+H2 →H2+H, H2+F→HF+H and H+Cl2→HCl+Cl, we calculate angular distributions of reaction products in the various coupling limits for ranges of final states. The angular distributions in the strong potential coupling limits have a Gaussian shape peaked about the backscattering angle (π) (the hard sphere deflection angle for the chosen critical configuration) for each of the three reactions studied. In all three cases the 3D angular distribution is narrower than the planar (2D) angular distribution. Our calculations show no difference between the angular distributions of the weak and strong kinematic coupling limits. The angular distribution of the 2D weak potential coupling case are broader than those of the strong potential coupling. For H+H2 we find our results in the strong potential limit to be in qualitative agreement with exact quantum mechanical calculations. The angular distribution for a given product state broadens as the initial relative kinetic energy is increased, in agreement with classical trajectory calculation (F+H2). The angular distribution is also predicted to broaden as the final relative velocity increases, in agreement with experiment (H+Cl2, F+H2). Finally we introduce several simplifying approximations to our analytical model and find that, for exothermic reactions like F+H2, the radial contribution to the T matrix is dominated by certain features of the potential: the barrier width, the slope of the potential on the reactant side, and force constants in the region of maximum overlap. Our analysis provides a basis for the formulation of reduced variables which may be of use in comparing reactions. Finally we discuss some sufficient conditions for the separability of product velocity and angular distributions.
Rotational dependence of the dipole moment of CH3D
Authors: Watson James K. G. , Takami Michio , Oka Takeshi
Published: February 2003

Radio frequency modulated side bands of the C18O2 P (18) laser line were used to perform infrared–infrared double resonance between the first order Stark components of the ν6 rP (10,1) transition of CH3D. The dipole moment in the J=10, K=1 level in the ground state has been measured to be (1.03±0.1) ×10−3 D, which is very different from the previously reported values of around 5.65×10−3 D. This difference has been explained as due to rotational dependence of the dipole moment. Combining the present result with the previous molecular beam measurements by Wofsy, Muenter, and Klemperer, we have obtained the rotational dependence of the dipole moment derived from Stark measurements in the form μStark(J,K) =∓{ (5.657±0.004)−(0.0427±0.0009) J (J+1) +(0.0696±0.0026) K2}×10−3 D. The upper sign would be consistent with ab initio calculations of the signs of the dipole derivatives. A theory was developed to calculate the above coefficients of J (J+1) and K2 for CH3D. It has been demonstrated that they can be completely predicted from the ϑzxy parameter of CH4. The prediction agreed with the observed values within the quoted uncertainties. This theoretical information was indispensable in determining which of the two observed double resonance signals corresponded to the ground state. The apparent contradiction of the present result with that of Ozier, Ho, and Birnbaum, who reported that the dipole moments of CH3D determined from the intensities of R branch spectral lines are independent of J, is explained as due to the fact that the rotational dependence of the dipole moment is different depending on the method of determination. Their measurements are shown to be consistent with the above parameters.
Generalizations of the direct CI method based on the graphical unitary group approach. I. Single replacements from a complete CI root function of any spin, first order wave functions
Authors: Siegbahn Per E. M.
Published: February 2003

The direct CI method is generalized to the class of wave functions, denoted as first order wave functions. With a first order wave function is meant a complete CI expansion in a small internal valence space and single excitations outside this space. The wave function can have any spin. The formalism of the graphical unitary group approach of Paldus and Shavitt is used to reduce the coupling coefficients of the direct CI method to expressions involving the internal space only. The necessary formula tape is therefore reduced drastically in size. An approximate and much faster method is suggested for very large CI expansions, based on the neglect of certain integrals. The method is applied to the singlet–triplet splitting of dioxymethane, CH2O2, which is a proposed intermediate in the ozonolysis of ethylene. The calculations predicts the 1A1 to be the ground state, but the splitting between 1A1 and 3B2 is calculated to be very small, 2.0 kcal/mole, in the best calculations reported here.
Low energy x-ray emission spectra and molecular orbital analysis of CH4, CCl4, and CHCl3
Authors: Perera Rupert C. C. , Henke Burton L.
Published: February 2003

The C–K and Cl–LII,III low-energy x-ray spectra from solid CCl4, CHCl3, and the C–K x-ray spectrum from solid CH4 have been obtained using monoenergetic x-ray excitation and a lead myristate multilayer analyzing crystal. The C–K spectrum of methane and Cl–LII,III spectra of the chloromethanes were also measured in the gas/vapor phase and compared with those measured in the solid phase. The deconvolved spectral components are aligned on a common energy scale with the complementary x-ray emission and photoelectron spectra by identifying the same molecular orbital in all spectra. Such an alignment procedure yields a C-ls ionization energy of gaseous CH4, and solid CCl4 and CHCl3 as 290.0 293.5 and 293.1 eV, respectively; and the Cl-2p3/2 ionization energy of solid CCl4 and CHCl3 as 206.5 and 204.8 eV. Results of the CNDO/2 and MINDO/3 MO calculations have been presented and compared with the available results of the extended Hückel MO method and with the deconvolved spectral components. From the geometry program in the MINDO/3 MO calculation, the C–H bond length in CH4 is 1.102 Å, the C–Cl bond length in CCl4 is 1.751 Å, and the C–H and C–Cl bond lengths in CHCl3 are 1.100 and 1.744 Å, respectively. Comparison with the vapor/gas phase spectra shows essentially the same energies for spectral components in the C–K and Cl–L spectra from CH4 and CCl4, whereas the spectral components in the Cl–L spectra of CHCl3 have energies in the gas phase that are significantly higher than those for the solid phase.
Vibrational averages of x-ray and high energy electron scattering intensities from diatomic molecules
Authors: Epstein Joel , Stewart Robert F.
Published: February 2003

Ground-state vibrational averages of the intensities of x-rays and high-energy electrons elastically scattered by N2 (1Σ+g), CO (1Σ+), BF (1Σ+), and FH (1Σ+) have been calculated. When nonrigid contributions are included, the vibrational averages are accurately computed from generalized x-ray scattering factors at the [2‖2] level. Maximum anharmonic contributions to the average intensities are 0.3%–0.5%. Contributions from nonrigid pseudoatom components are generally smaller by an order of magnitude and are negligible for S greater than 10 Å−1.
Geometric effects on complex formation in collinear atom–diatom collisions
Authors: Fitz D. E. , Brumer Paul
Published: February 2003

Trajectory studies on a variety of collinear collisions systems using a potential surface with a deep well are described. Two distinctly different modes of complex formation, dependent on system masses, are observed. One mode is limited to low translational energies whereas the other persists to high energies. Trajectory plots and simple geometric models are combined to provide a consistent interpretation of these mechanisms and of the observed oscillatory dependence, on system masses, of the reaction and complex formation probabilities.
The valence states of C2: A configuration interaction study
Authors: Kirby K. , Liu B.
Published: February 2003

Potential curves for all 62 valence states of C2 have been computed using configuration interaction wavefunctions within the valence orbital space. The valence orbitals were determined by a multiconfiguration self-consistent-field calculation using a properly dissociating set of configurations for the a 3Πu state. Comparison is made with the experimental spectroscopic constants for ten of these states: Re values are too large by ∼0.05 ao, the bond energies De are too small by ∼0.8 eV, Te values are within ∼0.34 eV, and ωe is generally within ∼70 cm−1. We have identified 19 other possible bound states not yet observed experimentally, and have obtained a good qualitative picture of the positions and shapes of the repulsive states which may be involved in dissociation processes.
Diatomic sulfur: Low lying bound molecular electronic states of S2
Authors: Swope William C. , Lee Yuan-Pern , Schaefer Henry F.
Published: February 2003

We present here the results of self-consistent field (SCF) and configuration interaction (CI) type calculations on thirteen low-lying electronic states of diatomic sulfur. The basis set was one of double zeta quality augmented with polarization functions. The CI space for each electronic state consisted of all configurations constructed from single and double excitations of electrons from the valence orbitals of the Hartree–Fock configuration. There are several significant findings of this study. First, we report the discovery of a previously unobserved and bound 1Πu state which lies approximately 37 000 cm−1 above the ground state. This state dissociates to two ground state sulfur atoms. Second, we provide new predictions of excitation energies and properties for the three states e1Πg, c1Σ−u, and B′3Πu. These states were suspected or known to be bound, but experimentally determined properties were uncertain. Finally, we find that systematic application of a formula of Davidson, which estimates the contribution of unlinked energy terms in a singles and doubles CI calculation, leads to improved predictions of excitation energies.
High resolution electron energy loss spectroscopy of chemisorbed carbon monoxide and oxygen on the ruthenium (001) surface
Authors: Thomas G. E. , Weinberg W. H.
Published: February 2003

The adsorption of CO and O2 on the Ru(001) surface and the interaction between CO and chemisorbed oxygen on this surface have been studied by measuring the vibrational energies of the adsorbed layer with electron energy loss spectroscopy. Adsorbed CO shows two vibrational energies that are assigned to the metal–carbon and carbon–oxygen stretching frequencies of an upright CO with a single metal–carbon bond. Oxygen adsorbed on Ru (001) has a single vibrational energy that can be attributed to a mode of atomic oxygen perpendicular to the surface. The variation of the frequency spectrum of CO with CO coverage and with the coverage of oxygen in coadsorption experiments is discussed in terms of direct interadsorbate interactions and indirect through-bond interactions.
On the comparison of T1 and T2 as determined from zero-field and non-zero-field microwave measurements
Authors: Schwendeman R. H. , Amano T.
Published: February 2003

The application of the recent theories of Liu and Marcus [J. Chem. Phys. 63, 272 (1975)] and Coombe and Snider [J. Chem. Phys. 67, 2659 (1977)] for the experimental determination of the relaxation parameters T1 and T2 from line shape measurements in zero Stark field is examined. In the first part of the paper it is shown that power-broadened absorption lines in zero field may be fit to a single Lorentzian line shape from which a combined parameter qT1/T2 may be obtained. The new parameter q, which is determined by the distribution of populations of the m components of the levels under conditions of partial saturation, is defined and related to results of previous work. In the second part of the paper expressions for T1−1 and T2−1 for the zero-field and non-zero-field cases are derived in terms of time correlation integrals of a random perturbation. It is shown that a close connection exists between T1−1u1 and T2−1 in zero field and certain averages of these quantities over the m states for nonzero field. From the comparisons it is seen that precise values of these parameters may provide additional information about the collision process.
Systematics of high-pressure and high-temperature behavior of hydrocarbons
Authors: Ree Francis H.
Published: February 2003

Hugoniot data of eight different hydrocarbon compounds comprising four different proportions of hydrogen to carbon content have been analyzed using a model. The model assumes that hydrocarbons at high pressure (≳10 GPa) and high temperature (≳1000 K) dissociate into carbon in the diamond phase and hydrogen in a condensed molecular phase. The theoretical Hugoniots of hydrocarbons are evaluated under the assumption that the volume and its ratio to the Grüneisen gamma of the hydrocarbons at any given pressure and 0 K are the weighted sums of the hydrogen and carbon contents. The model gives hydrocarbon Hugoniots that agree remarkably well with the experimental data. Evidence supporting the model and several implications of the model are given.
Absolute rate constant for the reaction OH (v=0)+O3→HO2 +O2 over the temperature range 238–357 °K
Authors: Ravishankara A. R. , Wine P. H. , Langford A. O.
Published: February 2003

The technique of laser flash photolysis–resonance fluorescence has been employed to measure absolute rate constants for the reaction OH (v=0)+O3→HO2+O2 over the temperature range 238–357 K. The results are described by the Arrhenius expression k =1.82+0.35−0.29×10−12 exp[(−930±50)/T] cc/molecule s. Extrapolation of this expression to 225 K, the temperature of the stratosphere in the region where O3 levels are highest, gives a rate constant which is ∼65% higher than the currently recommended value.
Synthesis, characterization, and pressure dependence of conductivity for a partially-oxidized tetra-aza macrocyclic palladium complex
Authors: Mertes Kristin Bowman , Ferraro John R.
Published: February 2003

The synthesis and characterization of the I2 oxidation product of a tetra-aza macrocyclic complex of Pd (II) is described. The product is formulated as [Pd (TAAB)] [I3]2.7 where TAAB is tetrabenzo [b, f, j, n] [1, 5, 9, 13] tetra-azacyclohexadecine. The presence of I3 was confirmed by Raman and far-infrared spectroscopy. Electrical conductivity measurements for pressed powder samples using a diamond-anvil pressure cell showed an unusually large pressure dependence.
Thermodynamics of the lanthanide trifluorides. II. The heat capacity of praseodymium trifluoride PrF3 from 5 to 350 °K
Authors: Lyon William G. , Osborne Darrell W. , Flotow Howard E.
Published: February 2003

The heat capacity of PrF3 was measured by aneroid adiabatic calorimetry from 5 to 350 °K. The following results were obtained for PrF3 (c) at 298.15 °K: the heat capacity Cp°= (92.65 ±0.09) J °K−1 mole−1, the entropy S°= (121.22±0.12) J °K−1 mole−1, the enthalpy (HT°−H0°)= (17 946±18) J mole−1 and the Planck function −(GT° −H0°)/T=(61.02±0.06) J °K−1 mole−1. Recommended thermal functions from 400 to the melting temperature, 1672 °K, are presented in tabular form. The excess heat capacity due to the internal electronic energy levels of Pr3+ in PrF3 is calculated from spectroscopic data and compared with excess heat capacity derived from calorimetric results.
Rayleigh–Brillouin scattering and structural relaxation of a viscoelastic liquid
Authors: Lin Y. -H. , Wang C. H.
Published: February 2003

The linear response theory using a complete set of dynamic variables involving density, velocity, and energy fluctuations is used to analyze the Rayleigh–Brillouin spectrum of a viscoelastic liquid. The result is discussed in the fast and slow relaxation limits. In the former case, the Rayleigh–Brillouin spectrum is identical to that predicted by the classical hydrodynamic equations; whereas in the latter case a new structural central peak is found, in addition to the anomalous dispersion and relaxation effects present in the frequency and linewidth data associated with the Brillouin peak. The evolution of structural relaxation and its effect on the entire Rayleigh–Brillouin spectrum is described. The structural central peak is most pronounced when the frequency dispersion and the linewidth maximum are present. The theoretical result has been used to calculate the Rayleigh–Brillouin spectra of polypropylene glycol at various temperatures. The results of the frequency shift, the spectral linewidth, and the Landau–Placzek ratio are in good agreement with the experiment.
Chemiluminescence of S2 in solid argon
Authors: Lee Yuan-Pern , Pimentel George C.
Published: February 2003

Upon slow warming of previously photolyzed matrix samples of OCS/Ar, CS2/Ar, OCS/Kr, and OCS/SF6 (M/R=100), the B (B″) →X chemiluminescence of S2 is observed as reported earlier. In addition, two new progressions were recorded, a weak progression between 5580–6890 Å and a stronger one between 6680–8750 Å. With OC34S, the 6680–8750 Å progression displayed isotopic shifts that allow deduction of νoo=15 750±10 cm−1, ω″e=699±5 cm−1, and ωexe″=2.6±1 cm−1. Similarly, the weaker 5580–6890 Å progression corresponds to νoo=20 870±30 cm−1, ω″e=724±6 cm−1, and ωex″e=2.9± 1 cm−1, with a less favored, alternative vibrational assignment that gives νoo=21 600±30 cm−1, ω″e=731±6 cm−1 and ωex″e=2.9±1 cm−1. These spectroscopic parameters point to assignments of the c1Σ−u→a1Δg and A′3Δu →X3Σ−g transitions of S2 for the 6680–8750 Å and 5580–6890 Å emissions, respectively. These are the first observations of these transitions of diatomic sulfur, and one of them provides the first direct spectroscopic information illustrating that the c1Σ−u state (To=20 250±200 cm−1) actually lies lower than the A3Σ+u and A′3Δu states, as is the case for O2.
Chemiluminescence in reactions of N+ ions with hydrogen and hydrocarbons. I. Rotational–vibrational product excitation
Authors: Kusunoki I. , Ottinger Ch.
Published: February 2003

Chemiluminescent ion–molecule atom-exchange reactions between N+ ions and H2, CH4, C2H4, C2H6, and C3H8 were studied in a beam–gas arrangement. The collision energy ranged between 1.6 and 150 eVc.m.. The observed product was in all cases NH (A 3Π) radiating into the NH ground state. All reactions proceed nonadiabatically. The NH (A→X) emission spectra obtained were simulated on a computer. This yielded detailed rotational population distributions for both the v′=0 and v′=1 vibrational levels of NH(A), as well as the (v′=1)/(v′=0) vibrational population ratio. At high collision energy the distributions are affected by predissociation, but below 5 eVc.m. in the case of CH4 the observed rotational distribution is that resulting directly from the reactive collision. In this case the dependence of the mean rotational energy on the collision energy strongly suggests a stripping mechanism for the reaction, while the reactions with the heavier hydrocarbons clearly do not proceed by stripping.
Chemiluminescence in reactions of N+ ions with hydrogen and hydrocarbons. II. Dependence of total reaction cross sections on the collision energy
Authors: Kusunoki I. , Ottinger Ch.
Published: February 2003

Chemiluminescent reactions between N+ ions and H2 as well as some hydrocarbons were studied up to ∼450 eVCM collision energy. Emission from NH(A 3Π) and, with hydrocarbons, from CH(A, B, and C) as well as from C and H atoms was observed. Except in the H2 case, the formation of NH(A) in a bimolecular exchange reaction occurs up to 150 eVCM. Below 20 eVCM this reaction appears to proceed by direct interaction between the N+ projectile and an H atom, while at high energies the primary interaction is between N+ and a C atom. The approximately exponential falloff of the cross section for NH(A) formation above 50 eVCM was explained in the case of CH4 using a soft-sphere collision model. A hard-sphere model was used in an attempt to explain the measured ratio of the N++C2H4 and N++CH4 cross sections. Computer trajectory studies revealed the relative importance of various types of collision and led to semiquantitative agreement with experiment.
Methyl group rotation and bonding in solid hexamethyldialuminum, Al2(CH3)6
Authors: Albert Shmuel , Ripmeester John A.
Published: February 2003

Continuous wave proton second moment and line shape studies of the solid state trimethylaluminum dimer, Al2(CH3)6, have shown that all the methyl groups in this compound rotate about their triad axes at 77° K. An activation energy of 840±40 cal/mole was found for this methyl group rotational process from the temperature dependent static and rotating frame spin–lattice relaxation times (T1 and T1ρ, respectively) studies. These observations tend to support the two-electron three-center Al–C–Al bond model for the bridging methyl group carbons.
Induced intensity and band shape of the w 1Δu←X 1Σ+g system in pure solid α-N2
Authors: Kunsch P. L. , Boursey E.
Published: February 2003

The crystal-field induced intensity and the band shape of the w 1Δu←X 1Σ+g transition in pure solid N2 are treated theoretically. The static crystal field generated by the molecular quadrupoles mixes 1Δu and 1Πu states and its magnitude suffices to explain the observed intensity of the transition in the solid. The band shapes can be interpreted as Stokes-type multiphonon structures due to totally symmetric local breathing modes with a weaker librational contribution. The dependence of the Stokes parameter and of the widths of the zero- and one-phonon bands on the intramolecular Franck–Condon factor illustrates that the Stokes-type excitation of phonons is diminished by increased delocalization through intermolecular vibronic resonance.
Potential constants of borane carbonyl
Authors: Jones Llewellyn H. , Taylor Robert C. , Paine Robert T.
Published: February 2003

The vibrational spectra of several isotopic species of BH3CO in neon matrices at 10 °K have been observed. A number of combination bands have also been observed, leading to an assignment of most of the fundamental harmonic frequencies of these isotopic species. A least squares normal coordinate treatment, without constraints, has estimated a set of potential constants. We can conclude that the CO bond in BH3CO is slightly stronger than that of free CO. The interaction coordinates suggest that unimolecular dissociation of the B–C bond proceeds initially toward BH−3+CO+ but reverts to BH3+CO before dissociation.
Production and loss of multiply charged and molecular ions (Kr+, Kr2+, Kr3+, Kr4+, Kr2+) in a krypton hollow cathode discharge
Authors: Howorka F. , Kuen I.
Published: February 2003

The formation of the ions Kr+, Kr2+, Kr3+, Kr4+, and Kr2+ and their losses are studied in a low pressure krypton hollow cathode discharge. From the maintenance voltage as dependent on pressure, the electron impact ionization rate is calculated. The loss processes include single and double electron transfer to the high charge states and volume recombination for Kr+2. The following loss rate coefficients are obtained: Kr2+ (k<5×10−13 cm3s−1), Kr3+ [k= (1.9 ±0.7) ×10−11 cm3s−1], Kr4+ [k? (1±0.7) ×10−10 cm3s−1], Kr+2 [recombination coefficient α = (5.5±3.5) ×10−7 cm3s−1 for Te=1200 °K].
A direct measurement of intramolecular hydrophobic interactions
Authors: Ben-Naim A. , Wilf J.
Published: February 2003

A theoretical argument is used to suggest a new method of processing experimental results to obtain information on pairwise hydrophobic interactions. The experimental data consist of measurements of solkubilities and partition coefficients of some alkylbenzene molecules in water and in n-hexane. From these data one may extract information on the intramolecular hydrophobic interactions, i.e., interaction between two alkyl groups attached to a ’’backbone’’ molecule. Some preliminary results are reported and interpreted.
Local kinetic energy in quantum mechanics
Authors: Cohen Leon
Published: February 2003

The question of local kinetic energy in quantum mechanics is considered by using the phase space formulation of quantum mechanics. We derive the totality of possible quantum mechanical expressions for local kinetic energy and give a subset which satisfy Bader’s criterion. The different definitions that various authors have used are shown to be directly related to particular quasiprobability distributions and correspondence rules.
Brillouin scattering in single crystals of β-carbon monoxide: Determination of the elastic constants at the triple point
Authors: Gammon P. H. , Kiefte H. , Clouter M. J.
Published: February 2003

The technique of high resolution Brillouin spectroscopy has been used to determine the adiabatic elastic constants of oriented single crystals of β-carbon monoxide at temperatures near the triple point. The values obtained at 67.7 K were c11=1.9(01), c12=1.1(46), c13=0.9(51), c33=2.0(95) and c44=0.35(5) (in units of 109 Nm−2) with an estimated uncertainty of ±2%. The similarities to β-nitrogen results are striking; nevertheless, significant differences are noted.
Density functional theory and molecular bonding. III. Iron-series dimers
Authors: Harris J. , Jones R. O.
Published: February 2003

Binding energy curves for low-lying states of the 3d-dimers K2–Cu2 have been calculated using the density functional formalism with a local spin-density approximation for the exchange-correlation energy. Binding energy trends across the series are discussed as a competition between chemical bond formation and the reduction in spin-degeneracy which accompanies it. At the ends of the series, satisfactory agreement is found with available spectroscopic data. Both experimental and calculated binding energies show pronounced minima towards the center of the series, at Mn2 and Cr2, respectively. Discrepancies in binding energy trends are attributed to an incorrect description of s–d transfer inherent in the LSD approximation.
Thermal neutron diffraction from the liquids N2 and O2. Determination of nearest neighbor parameters and angular correlations
Authors: Pedersen Karen Schou , Hansen Flemming Yssing , Carneiro Kim
Published: February 2003

Using a double axis crystal spectrometer, we have determined the structure factor S (κ) of the liquids N2 and O2 up to a maximum wavevector κm=11 Å−1. We derive the parameters characterizing the first nearest neighbor shell and find that the intramolecular bond length is well determined, whereas the width and the volume of the shell is derived with rather large uncertainties. We also demonstrate how our data analysis program may be used to give necessary limits for κm, dependent upon which parameters are to be determined. Finally, we deduce the angular correlations which give a result consistent with the dominant quadrupolar and dipolar interactions in N2 and O2, respectively.
Vibrational de-excitation of CO2*(ν3) by H2 at 200 °K
Authors: Bass H. E. , Causey James , West Karen
Published: February 2003

The fluorescence decay of CO2* (ν3) following laser excitation has been measured in mixtures of 0.10 H2/0.90 CO2, and 0.20 H2/0.80 CO2 vibrational relaxation times are repoted. (AIP)
Laser induced impedance changes in a neon hollow cathode discharge. A mechanistic study
Authors: Zalewski E. F. , Keller R. A. , Engleman R.
Published: February 2003

Irradiation of a neon-supported, uranium hollow cathode discharge at wavelengths between 572 and 672 nm corresponding to optical transitions in neon or uranium causes significant changes in the impedance of the discharge. The behavior of these transitions can be separated into two general classes. (I) For transitions originating in the 1s levels of neon the impedance change is either negative or positive, depending upon the particular state, and the magnitude is proportional to the probability of depletion of these levels by optical pumping. (II) For other neon and all uranium transitions these impedance changes are negative and are proportional to the probability for absorption of laser radiation. Spatial variation of the impedance changes demonstrate the importance of collisions of the metastables with the cathode wall in maintaining the discharge.
Hyper−Raman scattering by chiral molecules
Authors: Andrews D. L. , Thirunamachandran T.
Published: February 2003

A theory of hyper−Raman scattering by optically active molecules is presented. It is shown that scattering intensities depend on the helicity of the incident light: Expressions for the differential scattering intensities are derived taking into account electric dipole and quadrupole and magnetic dipole interactions. A helical box model is used to estimate circular differential scattering intensity ratios and depolarization ratios.
Solid state studies.XIV. Mixed crystal and 13CO isotopic studies on intermolecular vibrational coupling in the ν (CO) region of M2(CO)10, M=Mn,Re
Authors: Arif Mona , Cartner Anthony M. , Kariuki David N. , Kettle Sidney F. A.
Published: February 2003

The ν (CO) Raman spectra of crystalline M2(CO)10 (M=Mn,Re) are interpretable on a molecular basis. Data from mixed Mn/Re crystal and statistical and nonstatistical 13CO-doped crystals of Mn2(CO)10 are used to establish that intermolecular vibrational coupling occurs in these crystals, showing that such a molecular description is not appropriate.
Lyman-α and Balmer-series fluorescence from hydrogen photofragments of H2O vapor
Authors: Wu C. Y. Robert , Phillips E. , Lee L. C. , Judge D. L.
Published: February 2003

Atomic hydrogen Lyman-α and Balmer-series (3–9→2) fluorescence have been observed from photodissociation of H2O, and the production cross sections have been measured. A line emission source provided the primary photons at wavelengths from 400–900 Å. The maximum fluorescence production cross sections for Lyman-α and Balmer-α are 1.72±0.34 Mb at 703 Å and 0.58±0.17 Mb at 672 Å, respectively. The photodissociation is mainly a direct process following absorption of a photon into the continuum state(s). The repulsive potential energy curves corresponding to the respective pseudodiatomic OH–H(n) molecule are constructed according to the Franck–Condon principle. The efficiency for converting H(2S) to H(2P) by H2 collisions, following photodissociation of H2, is determined to be 56±10%, while that by H2O, following photodissociation of H2O, is estimated to be nearly 100%. The present data are important for further understanding of cometary photochemistry.
Depolarized Rayleigh spectroscopy of polystyrene near the glass–rubber relaxation
Authors: Patterson G. D. , Lindsey C. P. , Stevens J. R.
Published: February 2003

Depolarized Rayleigh scattering in polystyrene near the glass–rubber relaxation is studied using photon correlation spectroscopy. The observed correlation functions cannot be fit to a single exponential decay, but the empirical form CH(t)−1=δ+A exp[−2 (t/τ)β] describes the results very well. Average relaxation times 〈τ〉= (τ/β) Γ (1/β) are determined from 100 to 130°C. The apparent activation energy for the change of 〈τ〉 with temperature is over 80 kcal/mole. Depolarized Rayleigh spectroscopy should prove to be a very useful tool in the study of relaxation behavior in polymers.
Positive ion mobilities in gaseous, critical, and liquid hydrocarbons: Density and temperature effects
Authors: Huang Sam S.-S. , Freeman Gordon R.
Published: February 2003

Cation mobilities μ+ in liquid hydrocarbons do not obey Walden’s rule (μ+∝η−1.0). Their relationship with the solvent viscosity η is μ+∝η−1.2±0.1, as found earlier for ions in ethers. Ion migration in liquids made up of nonspherelike molecules is more closely linked to solvent molecular rotation than to shear viscosity. Dipole (permanent or induced) rotation is required during ionic displacement to minimize changes in polarization energy. Diffusion coefficients D of ions in liquid n-hexane are twofold lower than the self-diffusion coefficient of the hexane molecules over most of the liquid range. There is a cusp in the ratio D (molecule)/D (ion) at the critical point. The lower diffusion coefficient of the ion is attributed to its probable dimeric size and to electrostrictive drag. Mobilities in the critical fluids are 4.3, 5.0, and 5.6 (10−3 cm2/Vs) in cyclopentane, cyclohexane, and n-hexane, respectively. In the gas phase along the gas–liquid coexistence curve, the density normalized mobilities μ+n are independent of n up to n/nc?0.8, then increase with n. The increase continues through the critical region and in the liquid phase up to n/nc?1.5; at higher densities μ+n decreases. The ion scattering cross sections of the low density gases have the same velocity dependence in cyclopentane, cyclohexane, and -hexane: σv=Aαv−α, α=2.0. Assuming the ions to be dimeric, the respective values of Aα are 0.01, 0.79, and 1.07 (10−4 cm4 s−2). The scattering potential is more complex than that due to the simple charge induced dipole interaction. The temperature coefficient of μ+ increases with n, probably due to clustering of molecules about the ions at temperatures near the coexistence curve.
A kinetic theory of inhomogeneous fluids: the mean field approximation
Authors: Jhon Myung S. , Desai Rashmi C. , Dahler John S.
Published: February 2003

A kinetic equation is derved, at the mean field level, for a single-component system composed of liquid and vapor phases separated by a planar interface. Three kinetic sum rules are derived and used to verify previously obtained configurational sum rules. The density gradient, which plays a key role in the interfacial dynamics, is discussed and used to construct a surface projection operator. The kinetic equation is then analyzed using this projection operator in conjunction with expansions in terms of momentum and spatial moments. The surface-related terms of the kinetic equation lead to propagating surface modes which exhibit a dispersion identical to that of capillary waves.
A one-dimensional model for demonstrating hydrophobic interaction
Authors: Elkoshi Z. , Ben-Naim A.
Published: February 2003

A one-dimensional model for water, due to Bell, is extended to aqueous solutions of a simple solute. The pair correlation function for two solute particles at adjacent sites is computed as a funtion of the molecular and the thermodynamic parameters of the system. A phenomenon similar to the hydrophobic interaction, observed in real acqueous solutions, may be simulated by this model.
Laser excitation of SF6 in low temperature matrices
Authors: Jones L. H. , Ekberg S. , Asprey L. B.
Published: February 2003

Infrared spectra of SF6 in an Ar matrix at 10°K is reported. The spectrum was excited by CO2 laser.(AIP)
Higher order WKB eigenvalue calculations for van der Waals molecules
Authors: Chan C. K. , Lu P.
Published: February 2003

The miller and good methed2 of higher order WKB approximation is used to calcultate the eigenvalues of van der Waals molecules.(AIP)
On approximate energy differences from average electron densities
Authors: Levy Mel
Published: February 2003

Density functional theory giving eigenstate energies in terms of eigenstate densities is commented upon. It is contended that it can be extended to include molecules as well as atoms.(AIP)
Comments on the theory of dipolar fluids
Authors: Ramshaw John D.
Published: February 2003

The theory of dipolar fluids posbulated by Chan, Mitchell and Ninham is commented upon.(AIP)
Diamagnetic contributions to the nuclear spin–spin coupling constants of several small molecules. An application of Monte Carlo integration methods to molecular one-electron properties
Authors: Lee Wellington S. , Schulman Jerome M.
Published: February 2003

A numerical Monte Carlo integration procedure has been developed for calculation of J1a, the diamagnetic contribution to the nuclear spin–spin coupling constant from an arbitrary molecular charge density. The method is applied first to the HD molecule where several previous values of JHD1a are refined and corrected. A test of Brillouin’s theorem for this unusual sum of one-electron operators is made and the extensive cancellations from different regions of space are examined in detail. Values of J1a are then given for HF, BF, CO, and HCN. It appears that J1a may be the one-electron property most sensitive to the quality of the wavefunction which has been considered to date. Monte Carlo integration may be employed for the calculation of one-electron properties when alternatives to analytic integral evaluation are sought.
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o calculations of the interaction of ions with neutral ligands: I. Pair potentials for Na+/ether, Na+/thioether, and Na+/amide systems
Authors: Corongiu G. , Clementi E. , Pretsch E. , Simon W.
Published: February 2003

Atom pair potentials are obtained from ab initio SCF-LCAO-MO calculations for model complexes of Na+ with a thioether, ethers, and amides. The SCF-LCAO-MO interaction energies for 600 complexes of Na+ with such ionophores were fitted with a simple analytical potential. The analysis of the inter- and intramolecular atom-pair interactions indicates that Na+/ionophore binding is primarily due to the polarization of the model compound in the field of of the sodium ion.
PES of high temperature vapors. VIII. Transition metal dihalides
Authors: Berkowitz J. , Streets D. G. , Garritz Andoni
Published: February 2003

The He i protoelectron spectra of transition metal halide vapors MX2 (M=Mn, Fe, Co, Ni; X=Cl, Br) are presented. The spectra are interpreted by comparing the experimental ionization energies with transition state eigenvalues calculated by the multiple scattering scheme, using a cellular (but not muffin tin) partitioning of space. Satisfactory correlation between theory and experiment is achieved when the calculations are carried out with spin-polarized orbitals. This correlation leads to the conclusion that the metal 3d orbitals contribute predominantly to the uppermost occupied orbitals for MnX2, FeX2, and CoX2, but they are drawn deeper in NiX2 and become corelike orbitals at ZnX2, the full d shell.