bluuebunny/crossref_metadata_2025 huggingface dataset:
State-specific photochemistry of SiCl4 condensed on Si(100) with synchrotron radiation
Authors: Chen J. M. , Lu K. T. , Lee J. M.
Published: February 2003

State-specific photochemistry for SiCl4 adsorbed on Si(100) at ∼90 K following the Cl 2p and Si 2p core-level excitations has been investigated by photon-stimulated ion desorption, resonant photoemission, ion energy distribution, and soft x-ray absorption spectral measurements. The Cl+ photon-stimulated ion desorption spectrum and Cl L-edge x-ray absorption spectrum for condensed SiCl4 exhibit a clear dissimilarity unlike the other fragments, viz. SiCl3+, SiCl2+, SiCl+, and Si+. The Cl+ desorption yield shows a significant enhancement following the Cl 2p→8a1* excitation, while the Si 2p→8a1* excitation leads to the scarce enhancement of the Cl+ yield. The Cl+ ion energy distributions via the Cl 2p→8a1* excitation are shifted to higher energy (0.3–0.4 eV) compared to those via the Cl 2p→9t2* and Si 2p→8a1* excitations. The enhancement of the Cl+ desorption yield at the Cl(2p)−18a1* resonance is attributed to the higher ion escape energy. These results provide an insight into the comprehensive understanding of the state-selective fragmentation of molecules via core-level excitation.
Secondary echoes in three-frequency nuclear quadrupole resonance of spin-1 nuclei
Authors: Sauer K. L. , Suits B. H. , Garroway A. N. , Miller J. B.
Published: February 2003

We demonstrate, theoretically and experimentally, that the irradiation of a powder sample containing spin-1 nuclei by two of the three characteristic nuclear quadrupole resonance (NQR) frequencies can result in several echo signals at the third NQR frequency. One of these echoes, the principal echo, has the same shape and time of occurrence as an echo produced after a pair of single-frequency excitations. The other echoes are not equivalent to any single-frequency echo. These secondary echoes are the focus of this paper. The time of occurrence and shape of the secondary echoes are determined by the correlation of the distribution in one transition frequency to the distribution in a second transition frequency. This correlation is in turn determined by the correlation between the distributions of the electric field gradient components, which is itself determined by the types and concentrations of crystalline defects present. We present the optimal conditions to observe such secondary echoes and compare theory with experiment using N14 (I=1) in powder samples of sodium nitrite and RDX.
Variation with the intermolecular distance of properties dependent on the electron density in cyclic dimers with two hydrogen bonds
Authors: Gálvez O. , Gómez P. C. , Pacios L. F.
Published: February 2003

The variation with the intermolecular distance of geometries, energies, and other properties dependent on the electron density ρ(r) are studied in three cyclic dimers linked by two hydrogen bonds: formic acid and formamide homodimers and the heterodimer formamide/formic acid complex. Topological features, energy densities and integrated atomic properties provided by AIM theory are calculated with ρ(r) obtained at B3LYP/6-311++G(d,p) optimized geometries for a number of intermonomer distances covering large separations, equilibrium, and short distances. The variation with these distances of properties studied allows to characterize the nature of the interaction in A–H⋯B (A=N, O and B=O) hydrogen bonds. Whereas at large distances the attraction is purely electrostatic, quantum effects associated with redistributions of ρ(r) mainly around H and B atoms dominate the interaction in the neighborhood of equilibrium. Mutual penetration of the electron densities of these atoms leads to considerable reductions of their atomic volumes and associated polarization effects as well as energetic stabilization of atom A. Although the interaction in this range of intermonomer separations displays noncovalent features, when the dimers move at distances shorter than equilibrium, characteristics typical of covalent interactions begin to appear while the systems leave the planar structures presented until then. This work complements our previous study [O. Galvez, P. C. Gomez, and L. F. Pacios, J. Chem. Phys. 115, 11166 (2001)] of dimers with one single hydrogen bond.
Liquidlike structures in dilute suspensions of charged liposomes
Authors: Haro-Pérez C. , Quesada-Pérez M. , Callejas-Fernández J. , Casals E. , Estelrich J. , Hidalgo-Álvarez R.
Published: February 2003

Electrostatically stabilized aqueous dispersions of both slightly and highly charged liposomes have been analyzed by quasielastic light scattering. The obtained static structure factor S(q) revealed a liquidlike ordering due to long range electrostatic interactions. The fit of S(q) assuming a Derjaguin–Landau–Verwey–Overbeek interaction potential within the Debye–Hückel approximation, the Ornstein–Zernike equation and the hypernetted chain approximation, as a closure relation, allowed obtaining an effective charge value. Simultaneously, alternative charge values were estimated from electrophoretic measurements, turning out to be very close to the effective ones. This study also suggests that the charge seems to be unequally distributed over the vesicles in the case of liposomes formed by mixtures of charged and uncharged lipids. Size polydispersity was also considered.
Phonons in colloidal systems
Authors: Penciu R. S. , Kriegs H. , Petekidis G. , Fytas G. , Economou E. N.
Published: February 2003

Rich phonon spectra were observed experimentally by Brillouin spectroscopy in liquid, glassy, and crystalline state of colloidal systems of low and high elastic constant contrast. The nature of these phonons was elucidated by theoretical calculations of the single sphere scattering cross section, the energy density distribution, the light scattering intensity, and determination of the band structure by the multiple scattering method. Besides the ordinary acoustic phonon, localized optic-like modes, mixed modes, and Bragg induced modes were identified. Their relation to the physical state of a colloidal suspension sensitively depends on the micromechanical mismatch between particle and surrounding medium and the coherence of the crystalline structure. Polycrystalline colloidal suspensions show distinct acoustic excitations in the high wave vector–low frequency region.
Stimulated Stokes downconversion in liquid and solid parahydrogen
Authors: McCall B. J. , Huneycutt A. J. , Saykally R. J. , Lindsay C. M. , Oka T. , Fushitani M. , Miyamoto Y. , Momose T.
Published: February 2003

We report the results of our preliminary investigations into the suitability of condensed-phase parahydrogen as a Raman-shifting medium for infrared cavity ringdown laser absorption spectroscopy. We have observed the conversion of ∼10-ns pulses of 532-nm radiation into first-, second-, and third-order vibrational Stokes radiation in bulk liquid and solid parahydrogen after a single 11-cm pass. Unexpectedly, we find that liquid H2 yields more efficient conversion than solid H2 with certain focal geometries, and that in the case of the solid, a collimated or loosely focused pump geometry is more efficient than a tight focus.
Use of voltage pulses to detect spin-polarized tunneling
Authors: Yamada T. K. , Bischoff M. M. J. , Mizoguchi T. , van Kempen H.
Published: February 2003

The present letter describes a method to make a spin-polarized scanning tunneling microscopy tip by applying voltage pulses between a W tip and a magnetic sample. This spin-polarized tip has the similar characteristics as an Fe-coated W tip, which was confirmed by observations of antiferromagnetically coupled ferromagnetic Mn(001) layers (>3 ML) grown on an Fe(001) whisker at 370 K. Furthermore, we demonstrate that these voltage pulses can vary the tip magnetization direction.
Layered Cu-based electrode for high-dielectric constant oxide thin film-based devices
Authors: Fan W. , Saha S. , Carlisle J. A. , Auciello O. , Chang R. P. H. , Ramesh R.
Published: February 2003

Ti–Al/Cu/Ta multilayered electrodes were fabricated on SiO2/Si substrates by ion beam sputtering deposition, to overcome the problems of Cu diffusion and oxidation encountered during the high dielectric constant (κ) materials integration. The Cu and Ta layers remained intact through the annealing in oxygen environment up to 600 °C. The thin oxide layer, formed on the Ti–Al surface, effectively prevented the oxygen penetration toward underneath layers. Complex oxide (BaxSr1−x)TiO3 (BST) thin films were grown on the layered Ti–Al/Cu/Ta electrodes using rf magnetron sputtering. The deposited BST films exhibited relatively high permittivity (150), low dielectric loss (0.007) at zero bias, and low leakage current <2×10−8 A/cm2 at 100 kV/cm.
Nanometer-scale composition measurements of Ge/Si(100) islands
Authors: Floyd Margaret , Zhang Yangting , Driver K. P. , Drucker Jeff , Crozier P. A. , Smith David J.
Published: February 2003

Quantitative, nanometer-scale spatial resolution electron energy-loss spectroscopy (EELS) was used to map the composition of coherent islands grown by molecular-beam epitaxy of pure Ge onto Si(100). The Ge concentration XGe decreased, and the Ge/Si interface became more diffuse as the growth temperature increased from 400 to 700 °C. Integrated island volumes measured by atomic force microscopy (AFM) increased linearly with Ge coverage θGe, with slopes greater than 1. This result confirmed that island growth is faster than the Ge deposition rate due to Si interdiffusion. The linearity of the island volume versus θGe curves implied that XGe was independent of island size. XGe measured by EELS and AFM agree well with each other and correctly predicted the minimum dome size observed at each growth temperature.
Resonance Raman spectra of Cu-etioporphyrins I, I-m
e
s
o-d4, and IV
Authors: Mendelsohn R. , Sunder S. , Verma A. L. , Bernstein H. J.
Published: February 2003

Resonance Raman spectra obtained using the Ar+ and tunable Rhodamine 6G dye lasers are presented for the position isomers Cu−etioporphyrin I and IV in dilute (10−4 M) solution. The spectra show significant differences in several vibrations enabling the molecules to be distinguished. Several anomalously polarized (ρl ≳ 3/4) vibrations are observed which show dispersion of the depolarization ratios. The dispersion of ρl is interpreted as arising from reduction of chromophore symmetry from its idealized D4h. The solution data for Cu−etioporphyrin I and Cu−etioporphyrin IV are consistent with C4h symmetry and C2v symmetry, respectively, thereby demonstrating the sensitivity of resonant Raman scattering to slight perturbations of the chromophore due to peripheral substituents. Resonance Raman data are also presented for the deuterated analog Cu−etioporphyrin I (meso−d4). Several shifts in the vibrational modes are observed and possible vibrational assignments are discussed.
Molecular beam investigation of the effect of inner-shell electrons in molecular collisions
Authors: Winicur Daniel H. , Fraites James L.
Published: February 2003

Differential elastic scattering cross sections were obtained at thermal energies using crossed molecular beams for metastable Kr*, Ar*, Ne*, and He* scattered by ground−state krypton. Potential well depths are calculated from the location of the observed rainbow maxima and are compared to those for the analogous alkali atoms Rb, K, Na, and Li scattered by krypton. The effect of the inner−shell electrons on molecular collisions is deduced. At high electron shell levels, the (n−1) electron decreases the strength of the interaction during a collision whereas at low shell levels, the interaction strength is increased by the (n−1) electron. s and p electrons are shown to affect the interaction strength differently at the lowest shell level.
A
b i
n
i
t
i
o study of the electronic structure and hyperfine coupling in simple hydrocarbon radicals. I. Test of the calculation method on methyl and vinyl
Authors: Ellinger Y. , Rassat A. , Subra R. , Berthier G.
Published: February 2003

Nonempirical calculations of the energy, proton, and carbon−13 hyperfine splittings for methyl (ĊH3) and vinyl radicals (H2C=ĊH) in their equilibrium geometry are presented. The spin−restricted SCF method and first−order double−perturbation theory including all spin−adapted monoexcited states with three unpaired electrons have been used. The basis set consists of Gaussian−type orbitals contracted in a double−zeta form. The orbital exponents of the hydrogen functions have been simultaneously varied using a scaling procedure in order to simulate a minimum Slater hydrogenoid orbital. The sensitivity of SCF energies and hyperfine splittings to variations in values of the orbital exponent ζH have been investigated. The lowest total energy is obtained for ζH=1.15. Although calculated hydrogen hyperfine splittings increase with ζH, neither the zeroth−order nor the first−order spin density, computed from canonical MO’s or quasilocalized equivalent MO’s can be correlated to ζ3H. A structural analysis of the contributions of the various excited states reveals that the intrabond CH→CH* excitation yields about 90% of the first−order spin density at the proton in each case. This quantity depends most critically on the nuclear effective charge of the hydrogen atom through the value of the CH* antibonding MO at the nucleus. For vinyl, the splittings computed using the unoptimized exponents (ζH=1.0) are aHα=+7.52 G; aHcis =+37.56 G; aHtrans=+23.20 G, and aĊ=+123.52 G; aCα=−4.53 G.
Hypersonic velocities and compressibilities for some molten nitrates
Authors: Knape H. E. Gunilla , Torell Lena M.
Published: February 2003

The spontaneous Brillouin scattering has been used to measure the hypersonic velocity and its temperature dependence in a temperature range covering about 100 °C above the melting point in the nitrates: LiNO3, NaNO3, KNO3, RbNO3, CsNO3, and AgNO3. The investigations were performed in a frequqncy interval below any relaxation frequency in LiNO3 and NaNO3, while in KNO3 and AgNO3 the investigations were performed above some relaxation frequency according to comparisons with ultrasonic data. The measurements in CsNO3 and RbNO3 do not indicate any dispersion of the sonic velocity within the investigated frequency range and no conclusions can be drawn about relaxation effects as these molten alkali nitrates have neither been investigated hypersonically nor ultrasonically before. The measured hypersonic velocities were used for calculating the adiabatic and isothermal compressibilities as well as the specific heat at constant volume.
Collective oscillation in liquid normal tetradecane and normal heptadecane
Authors: Heller J. M. , Birkhoff R. D. , Painter L. R.
Published: February 2003

The optical properties of the liquids normal tetradecane (C14H30) and normal heptadecane (C17H36) were determined for photon energies from 4 to 25 eV. Near normal incidence (15 °) reflectance measurements were analyzed by a Kramers–Kronig method to yield the optical parameters n and k, the refractive index and extinction coefficient, respectively. The dielectric properties and the energy loss function were calculated. Structure from optical data in the liquid state is compared with vapor data for normal paraffin hydrocarbons and with solid data for the 26- and 36-normal paraffins. Evidence of collective excitation of electrons in the n-alkanes is compared with plasma resonances previously identified in the insulating liquids water, glycerol, tetramethyltetraphenyltrisiloxane (DC-704), and trimethylpentaphenyltrisiloxane (DC-705).
High-temperature thermodynamic properties of MnS by the dynamic Knudsen–torsion effusion method
Authors: Viswanadham Puligandla , Edwards Jimmie G.
Published: February 2003

The vaporization and thermodynamics of MnS were investigated from 1536–1693 K by Knudsen effusion and dynamic-torsion effusion. The principal vaporization reaction was confirmed to be MnS(s) = Mn(g)+(1/2)S2(g). Equations representing vapor pressures as functions of temperature were derived. Third-law ΔH °m (298 K) of the principal vaporization reaction was 563.7±0.3 kJ from torsion effusion and 562.8±0.2 kJ from Knudsen effusion. A vapor analysis from the combined Knudsen and torsion effusion results revealed the average molecular weight of effusing vapor was 62.5±8.3 at 1600 K. Results were compared with those from previous investigations and with the enthalpy calculated from a thermodynamic cycle. Efficacy of the dynamic torsion effusion method was tested by observing the torsion effusion pendulum in three ways, at different parts of its oscillation, and comparing the results. The method gave results in excellent agreement with Knudsen effusion results and was effective in detecting and analyzing extraneous torques on the torsion pendulum.
Continuum hydrodynamic interactions and diffusion
Authors: Phillies George D. J.
Published: February 2003

The Oseen tensor is not an adequate characterization for the contribution of hydrodynamic interactions to the homodyne (’’self-beat’’) spectrum of light scattered from a dilute macromolecule solution. Physical constraints on the possible form of the true cross diffusion tensor DT(R), which describes hydrodynamic interactions in macromolecule solutions, indicate that hydrodynamic interactions do not by themselves contribute to the homodyne spectrum. However, if the macromolecules in a solution interact directly as well as hydrodynamically, the direct and hydrodynamic interactions couple to contribute jointly to the mutual diffusion coefficient of the solute molecules, and thence to the spectrum of the quasielastically scattered light. Tracer diffusion techniques may be used to study the cross-diffusion tensor. Comparison with the available experimental data indicates that the joint contribution of direct and coherent hydrodynamic interactions to diffusion need not be large, even in extremely concentrated solutions.
A quantum kinetic theory of moderately dense gases. II. Coupled integral equations
Authors: Olmsted R. D. , Curtiss C. F.
Published: February 2003

The triplet Wigner distribution function developed in a previous paper leads to a closed set of coupled integro–differential equations for the pair and singlet Wigner distribution functions. These equations are simplified by a perturbation technique which assumes that the distribution functions differ only slightly from their equilibrium forms. The equations are expanded and only terms at most linear in the gradients of the physical properties are retained. Separating the equations on the basis of a density expansion, a set of equations is obtained, the solution of which is sufficient to determine the first density corrections to the transport coefficients.
Electronic quenching and vibrational relaxation of the OH (A 2Σ+, v′=1) state
Authors: Hogan P. , Davis D. D.
Published: February 2003

Rate constants for electronic quenching and vibrational relaxation of the v′=1 manifold of (A 2Σ+) OH by Ar, H2, N2, and He have been obtained by a laser fluorescence method. The quenching rate constants for v′=1 are not appreciably different from those which have been measured for v′=0. The relaxation rate constants are a factor of 3 larger than the quenching rate constants for Ar and H2, and 5 times larger for nitrogen. (AIP)
EPR studies of x-ray irradiated KH2AsO4 and KH2PO4-type ferroelectrics and antiferroelectrics
Authors: Dalal N. S. , Hebden J. A. , McDowell C. A.
Published: February 2003

EPR has been used to characterize the hyperfine couplings and electronic structure of a new paramagnetic center (H2AsO4)2− in x-irradiated ferroelectric crystals of pure KH2AsO4 and mixed KH2PO4–KH2AsO4, and antiferroelectric mixed crystals of NH4H2PO4–NH4H2AsO4, NH4H2PO4–KH2AsO4, and ND4D2PO4–KD2AsO4. This center is formed by the capture of an electron by proton deficient AsO3−4 units in these crystals. The assignment of the center is supported by EPR studies on the temperature dependence of the proton superhyperfine structure of these crystals. The present study also corrects an earlier identification of this center in NH4H2PO4–KH2AsO4 as a hole-type ionic defect center AsO2−4. Our results also provide a direct experimental basis for the currently accepted model of electrical (protonic) conduction in these crystals and help to resolve an earlier controversy regarding conductivity measurements on sulfate-doped ammonium and potassium salts. In conjunction with x-ray photoelectron spectroscopic studies, the EPR results on doped crystals also provide interesting results on electron-capture processes in single crystals. The present work also provides an explanation of some anomalous trends of the hyperfine coupling variation in other XO4-type radicals.
Inference of cross sections from rate constants measured in drift tubes
Authors: Russ C. , Barnhill M. V. , Woo S. B.
Published: February 2003

The feasibility of inferring ion–molecule reaction cross sections from rate constants measured in drift tubes is demonstrated. In order for the rate constants to be of value for such a purpose, the dynamic range and statistical uncertainties of the laboratory data must meet fairly stringent requirements. These requirements are stated and illustrated with numerical examples. Rate constants recently reported in the literature are close to meeting the requirements. Examples also show that the drift tube rate constants can be used to infer threshold energies for ion–molecule reactions to better than 15 mV at thermal energies, if a sufficiently accurate ion–neutral speed distribution is known and rate constants of sufficient dynamic range and accuracy are available.
Crystal dynamics of KCN and NaCN in the disordered cubic phase
Authors: Rowe J. M. , Rush J. J. , Vagelatos N. , Price D. L. , Hinks D. G. , Susman S.
Published: February 2003

The lattice dynamics of KCN and NaCN in their disordered cubic phase has been studied by coherent inelastic neutron scattering and infrared reflection measurements. Acoustic phonon branches for cyanide single crystals were measured in the [001] direction, with more limited measurements taken in the [110] direction. The one-phonon scattering generally appeared as weak peaks superimposed on a large background of non-one phonon scattering, particularly as measurements were extended to higher energy. No peaks clearly assignable to optical phonons were observed in the neutron measurements but the infrared reflection spectra for polycrystalline pellets were analyzed to derive TO and LO phonon energies (at q=0) of 17.0±0.6 and 28.5±2.5 meV. These measurements (and a comparison with the rather easily measured acoustic and optical phonons in a KBr crystal of similar volume) indicate that phonons do not exist as well-characterized excitations in the cyanides at higher frequencies and finite wave vectors. The unusual character of these results is attributed to the dynamical disorder of the cyanide ions in the fcc crystal and is compared with recent phonon measurements in the analogous fcc phase of ND4I. The [001] transverse acoustic branches of both KCN and NaCN show unusually low frequencies below q=0.5, which are consistent with recent elastic constant results and with the very large Debye–Waller factors derived from previous neutron diffraction results, and further suggest that the phase transitions in the cyanides are ’’driven’’ by a soft shear mode.
Methyl group deuteron quadrupole coupling parameters in solid toluene-d8, o
r
t
h
o- and p
a
r
a-xylene-d10
Authors: Barnes R. G. , Harper W. C. , Torgeson D. R.
Published: February 2003

Quadrupole coupling constants and asymmetey parameters have been determined for the methyl group deuterons in toluene-d8, C6D5CD3, and in ortho- and para-xylene, o-C6D4 (CD3)2 and p-C6D4(CD3)2, at 77 K. The coupling constant values are equal within experimental uncertainty, whereas the asymmetry parameters are not. The considerable disparity in effective asymmetry parameters observed in these three compounds shows that significant differences must arise in the rigid bond coupling constants of the individual methyl group deuterons.
Sorption in inhomogeneous slabs
Authors: Frisch H. L. , Bdzil J. B.
Published: February 2003

We find the exact, short time asymptotic behavior of the diffusion controlled sorption of a Fickian penetrant into an inhomogeneous slab. We also investigate the long time uptake of such a penetrant into an inhomogeneous slab when the inhomogeneity can either be treated as a small perturbation or when it is bounded from above by means of a variational principle. We discuss and compare the kind of information provided by permeation and sorption studies for a simple type of inhomogeneity.
Crystal structure of ammonium hydrogen malonate
Authors: Chapuis Gervais , Zalkin Allan , Templeton David H.
Published: February 2003

Ammonium hydrogen malonate, NH4HC3H2O4, is monoclinic, space group C2/c, with cell dimensions at 22 °: a=11.214(3), b=8.647(3), c=11.507(4) Å, β=107.29(2)  °; Z=8, Dx= 1.510(3) g cm−3, Dm=1.51(1) g cm−3. The structure was determined from x-ray diffraction data collected with an automatic diffractometer for 794 independent nonzero reflections, and the model was refined to R=0.040. The two carboxyl groups lie in planes which are nearly perpendicular. They are linked by strong symmetrical hydrogen bonds [O–O = 2.488(3) and 2.476(3) Å], so that each can be regarded as half-ionized. Average bond lengths are C–O = 1.29, C=O = 1.23, C–C = 1.51, C–H = 1.05, N–H = 0.99 Å. The ammonium ion participates in four N–H⋅⋅⋅O hydrogen bonds with lengths from 2.80 to 2.99 Å.
Molecular beam kinetics: Exchange reactions of deuterium atoms with hydrogen halides
Authors: McDonald J. D. , Herschbach D. R.
Published: February 2003

A crossed-beam study finds the reactions of D atoms with HCl, HBr, and HI give large yields of DCl, DBr, and DI, corresponding to reaction cross sections of the order 1–10 Å2. This demonstrates that the exceptionally small steric factors or transmission coefficients previously inferred from analysis of chain reaction mechanisms are low by several orders of magnitude. The reactively scattered deuterium halides recoil predominantly into the backward hemisphere with respect to the incident D atoms. In each case, the reaction exoergicity is ∼1 kcal/mole and the mean initial collision energy is 9 kcal/mole (with the D beam at 2800 °K, the hydrogen halide at 250 °K). The most probable final relative translational energy of the products is ≳4 kcal/mole for the HCl and HBr reactions and 7 kcal/mole for the HI reaction. The magnitude of the reaction cross sections and the predominant backward recoil and translational energy of the products are consistent with recent classical trajectory calculations based on semiempirical potential surfaces.
Interpolated values of spectroscopic constants of asymmetric alkali molecules and molecular ions
Authors: Cavaliere P. , Ferrante G. , Lo Cascio L.
Published: February 2003

With a very simple interpolation procedure, a number of fundamental spectroscopic constants (ground-state energies, equilibrium distances, force constants, and frequencies) for asymmetric alkali molecules and alkali molecular ions are estimated, starting from the corresponding values of the symmetric molecules and ions. For the quantities for which there are data available in the literature, good agreement is found both with experimental data and theoretical calculations. In general, the estimated spectroscopic constants may be considered sufficiently reliable to be safely used in applications such as the construction of potential-energy curves.
Primary photochemical processes in the vacuum-uv photolysis of fluoroethylene
Authors: Guillory William A. , Andrews George H.
Published: February 2003

The vacuum-ultraviolet (VUV) photolysis of fluoroethylene (FE) has been performed in Ar, N2, Kr, CO, and CO-doped argon matrices between 8 and 24 K. Excitation into various portions of the broad π*←π absorption (λm=1665 Å) was effected with N and Br resonance lamps while σ*←σ and/or Rydberg absorptions were excited with the 1216 Å H-resonance line. The major elementary processes which occur as a result of photoexcitation are: H2C=CHF+hν → C2H2+HF (1) and H2C=CHF+hν → C2H2F⋅+H (2); where (1) is molecular elimination and (2) a radical producing process. Photoexcitation with the Br and H resonance sources also produces fluoroacetylene (FA) via H2C=CHF+hν → C2HF+(HH) (3), to a very small extent. Based on relative infrared intensities (1) ? (2) ≫ (3) at all the exciting frequencies. The results of concurrent studies involving the difluoroethylenes suggest that (1) and (2) probably occur via internal conversion and intersystem crossing, respectively.
Complex-valued classical trajectories for tunneling and well-defined paths
Authors: George Thomas F.
Published: February 2003

A paper by Hirschfelder, Christoph, and Palke has suggested analogies between quantum streamlines and complex−valued classical trajectories in a semiclassical treatment of tunneling in reactive molecular collisions. This Comment points out that there are basic differences between trajectories and the streamlines and that care must be taken ataching any physical significance to complex−valued trajectories or in relating them to quantum mechanical quantities such as streamlines. (AIP)
Nonstatistical emission from metastable autoionizing states of Oi
Authors: Dehmer P. M. , Chupka W. A.
Published: February 2003

Emission intensities are reported for multiplet components of three metastable autoionizing OI 3P0 levels with nanosecond lifetimes—the 2s2p5 3P0, 3s″ 3P0, and 3d′ 3P0 states. Emission intensities for the 3s″ 3P0 and 3d′ 3P0 states are nonstatistical, i.e., the observed intensities for components of the multiplets do not correspond to the theoretical statistical absorption intensities. Autoionization, prohibited for these states in a pure Russell−Saunders coupling scheme, proceeds via weaker spin−orbit or spin−spin interactions, primarily through direct interaction with available continua. Previous autoionization studies of all of these states showed that the autoionization intensities are nonstatistical only for the 2s2p5 3P0 and 3s″ 3P0 states. These results are explained in terms of a competition between autoionization and emission based on a comparison of the true lifetimes of the states and the radiative lifetimes calculated from the absorption oscillator strengths. When the autoionization and emission lifetimes are comparable, both decay channels show nonstatistical behavior; when one decay channel dominates, only the minor decay channel shows nonstatistical behavior. The nonstatistical nature of the decay is discussed in terms of selective autoionization of certain total angular momentum levels of the decaying 3P0 states; however, additional theoretical work is required to establish the origin of this effect.
Coupling coefficients for hexagonal close-packed solids
Authors: Chandra Ramesh , Gupta N. P.
Published: February 2003

The expressions of coupling coefficients from 1 to 34 neighbors of an ideal hcp lattice and 1 to 41 neighbors of real hcp lattices have been derived. The splitting of neighbors with changing axial ratio values (c/a) has been studied with a TDC−12 computer. Both expressions of coupling coefficients and number of neighbors for various axial ratios have been reported.
Theory of angular momentum decoupling approximations for rotational transitions in scattering
Authors: Secrest Don
Published: February 2003

A systematic method is discussed for decoupling the internal angular momentum of molecules involved in a collision from their relative angular momentum. This leads to a large class of rotational approximations of varying degrees of complexity and accuracy. These approximations may be used directly for computing rotational transitions or they may be used for reducing the rotational complexity involved in accurate vibrational calculations. It is shown how this approach may be used to study the infinite−order sudden approximation and how that approximation may be extended to more complex potentials. It is shown also how one may use results of the jz−conserving approximation to obtain more complete information on the scattering matrix. The present approach may be used to deduce new angular momentum decoupling approximations and analyze such approximations arrived at through other considerations.
Density of methoxybenzylidene butylaniline about the isotropic–nematic phase transition
Authors: Gulari Esin , Chu B.
Published: February 2003

We have measured the density and determined the coefficient of expansion of MBBA about its isotropic−nematic transition temperature using a Mettler/Paar density meter. Our results show essential agreement with those of Press and Arrott using a buoyancy method. The small difference (<0.3°C) between the actual transition temperature and the virtual critical temperature differs from that determined by light scattering studies which yield values of about 1°C. Further examination on the nature of the virtual critical temperature is suggested.
Short−range order fluctuations in the isotropic phase of a liquid crystal MBBA
Authors: Gulari Erdogan , Chu B.
Published: February 2003

We have measured the polarized (I∥) and the depolarized (I⊥) scattered light intensities by fluctuations of the orientational order parameter as a function of two scattering angles over a range of temperatures close to and above the isotropic−nematic phase transition of para−methoxybenzylidine para−n−butylaniline (MBBA). The coherence length χ was found to diverge as ε−0.50±0.01, in essential agreement with the last results of Stinson and Litster and the theoretical predictions of de Gennes, where ε = (T − Tc*)/Tc* and Tc* is a pseudocritical temperature slightly below Tp. We have also measured the temperature dependence of the extinction coefficient of MBBA using the 632.8 nm wavelength of He−Ne laser light and observed that (limKμ0) 1/I∥ or ⊥ after attenuation correction diverges as εγ with γ = 0.85±0.05 which differs from γ = 1 as reported by previous studies. K represents the magnitude of the momentum transfer vector.
Evaporation and condensation for general gas–liquid surface scattering
Authors: Lang H.
Published: February 2003

The Onsager matrix for the liquid−vapor phase change of a monatomic gas in the presence of a Knudsen layer is calculated for a general gas surface sscattering law. The linearized Boltzmann equation is solved by the variational technique. The driving forces are the macroscopic pressure and temperature jumps. The calculated phenomenological coefficients show the influence of the reflection probability of the molecules on the surface and satisfy Onsager’s symmetry relation and the inequalities which follow from the fact that the entropy production rate in nonequilibrium is positive definite. In particular, the influence of the evaporation coefficient and the thermal accomodation coefficient is given. Simpler expressions are given for a generalized Maxwellian boundary condition.
Satellite structure in the x-ray photoelectron spectra of the K shell of transition metal compounds
Authors: Carlson Thomas A. , Carver James C. , Vernon G. A.
Published: February 2003

Satellite structure has been measured in the x−ray photoelectron spectra for FeCl3, FeBr3, K3Fe(CN)6, and K4Fe(CN)6. Specifically, comparisons were made of the satellites found in photoelectron spectra of the 2p and 1s subshells of iron. To interpret the data, calculations are presented on electron shake up and shake off, and multiplet splitting as a function of the location of the inner shell vacancy in iron. It is demonstrated, theoretically, that satellite structure found in the photoionization of the K shell of iron must be due to electron shake up and not multiplet splitting. From experimental data on FeCl3 and FeBr3, the conclusion is reached that the satellite structure formed as the result of photoionization in the 2p shell is due primarily to electron shake up.
Dissociative field ionization of H2 and HD
Authors: Hanson Gary R.
Published: February 2003

Distributions in kinetic energy of the atomic ions resulting from field ionization of H2 and HD are reported. For fields of 1.4−2.6 V/Å, the distributions of H+ from HD are characterized by a series of peaks which cannot be ascribed to field induced resonance states. This structure can be understood by examining the motion of vibrationally excited molecular ions in the high electrostatic field necessary for field ionization during the period immediately following field ionization. The stability of a molecular ion in such fields is a strong function of the angle between the molecular ion axis and the field. Thus, not all molecular ions produced with sufficient vibrational energy to dissociate, if properly oriented, do in fact dissociate in a time comparable to the first one−half vibrational period. Such ions dissociate after a time of the order of (3/2), (5/2), or (7/2), ..., vibrational periods, depending on the time required for the field to induce rotation of the molecule ion to the unstable orientation. These dissociations, periodic in time, result in periodicities, i.e., peaks, in the kinetic energy distribution of H+ from HD. Because the energy differences between these peaks vary as the square of the electrostatic field, they can be used as a sensitive method of field calibration. The effect of these molecular processes on the kinetic energy distributions of the other atomic ions resulting from the dissociation of H2 and HD are discussed.
Millimeter- and submillimeter-wave spectrum and molecular constants of cuprous chloride
Authors: Manson E. L. , De Lucia Frank C. , Gordy Walter
Published: February 2003

Monomeric cuprous chloride (CuCl) has been produced an an intermediate reaction product of copper and chlorine gas at 1000°K. Rotational transitions of 63Cu35Cl, 65Cu35Cl, 63Cu37Cl, and 65Cu37Cl have been measured in the millimeter and submillimeter wave region. Transitions have been observed in 7 different vibrational states and for J as high as 32→33. Analysis of the data yields the following Dunham and equilibrium coefficients for 63Cu35Cl: Y01 = 5343.72266(100) MHz, Y11 = −30.37285(120) MHz, Y21 = 0.06021(46) MHz, Y31 = −0.061(50) kHz, Y02 = −3.89432(77) kHz, Y12 = 0.00234(47) kHz, Y03 = −0.0006220(10) Hz, Be = 5343.768(20) MHz, ωe = 417.599(42) cm−1, ωexe = 1.617(6) cm−1; for 65Cu35Cl: Y01 = 5284.98184(100) MHz, Y11 = −29.87340(120) MHz, Y21 = 0.05889(46) MHz, Y31 = −0.059(50) kHz, Y02 = −3.80917(77) kHz, Y12 = 0.00227(47) kHz, Y03 = −0.0006017(10) Hz, Be = 5285.026(20) MHz, ωe = 415.297(42) cm−1, ωexe = 1.599(6) cm−1; for 63Cu37Cl: Y01 = 5158.15294(100) MHz, Y11 = −28.80453(120) MHz, Y21 = 0.05610(46) MHz, Y31 = −0.056(50) kHz, Y02 = −3.62854(77) kHz, Y12 = 0.00214(47) kHz, Y03 = −0.0005594(10) Hz, Be = 5158.195(20) MHz, ωe = 410.284(42) cm−1, ωexe = 1.561(6) cm−1; for 65Cu37Cl: Y01 = 5099.41148(110) MHz, Y11 = −28.31388(120) MHz, Y21 = 0.05483(46) MHz, Y31 = −0.054(50) kHz, Y02 = −3.54636(77) kHz, Y12 = 0.00208(47) kHz, Y03 = −0.0005405(10) Hz, Be = 5099.453(20) MHz, ωe = 407.941(42) cm−1. ωexe = 1.543(6) cm−1. The Dunham potential constants for cuprous chloride are a0 = 244588.0(480) cm−1, a1 = −3.21936(32), a2 = 6.908(26), a3 = −11.68(23), and the equilibrium internuclear distance is re = 2.051177(8) Å.
Perturbation theory for short-range atomic interactions. I. Numerical results
Authors: Certain Phillip R. , Merkel Robert R.
Published: February 2003

Numerical results for various perturbation series for atomic interactions at short range are presented for the energy, dipole moment, and dipole polarizability of one−electron diatomics. Although third−order energy results are accurate at short range, there is appreciable error in the other property values. The convergence of the series is considered in a companion paper.
Improved upper bounds on Knudsen permeabilities through a bed of spheres
Authors: Strieder William , Vallejo Rodolfo
Published: February 2003

In a previous publication, a variational upper bound on the permeability of a porous medium to Knudsen flow was presented. The bounds were calculated for a model pore structure generated from randomly placed, freely overlapping solid spheres. In this paper, the improvement of these bounds is discussed.
Absolute infrared intensities and band shapes in pure solid CO and CO in some solid matrices
Authors: Jiang George J. , Person Willis B. , Brown Kenneth G.
Published: February 2003

The infrared absorption spectra of carbon monoxide in argon matrices have been studied over a wide range of CO concentrations. The absolute infrared intensities of pure crystalline CO and of CO in argon matrices have been measured. The technique of using the second moment to determine the baseline of the absorption band has been tested and found to improve the data. The absolute integrated molar absorption coefficient of pure solid CO was found to be A=58.1±5.50 km mol−1 (1 km/mole=100 cm/mmole) and that for CO in the argon matrices is 66.5±2.4 km mol−1. The two values are believed to be the same within experimental error. Studies were also made of CO trapped in different matrices, including SF6, C6H6, and CCl4. The absolute intensity of CO increases from the gas phase (A=58.0 km mole−1) to the pure solid phase (A=58.1) or to the solid matrices (66.5−114 km mol−1, depending on the matrix) apparently due for the most part to the electric field effect. The band shapes have been analyzed to obtain the second and fourth moments and hence the intermolecular torques and dipole time−correlation functions. The large values for the torques and slow decay of the correlation function with time from one system to another suggest that the CO molecules have either greatly hindered rotation or no rotation at all in the pure solid and in the solid matrices.
Interfacial tensions of three fluid phases in equilibrium
Authors: Widom B.
Published: February 2003

It is suggested that it may be a general thermodynamic law that when three mutually saturated fluid phases are in equilibrium, the three interfacial tensions σ satisfy the triangle inequality σmax < σmed + σmin, where σmax is the largest of the three, σmed the median, and σmin the smallest. An argument for the inequality is given, and systems in which to test it experimentally are suggested. The quantitative law by which the interfacial tensions vanish as the three fluid phases become identical at a tricritical point is derived by an adaptation of an earlier argument on the vanishing of the interfacial tension on approach to the tricritical point in phase−separated 3He−4He mixtures.
Reaction of C2H+ with H2
Authors: Smith G. P. K. , Carlson R. D. , Cross R. J.
Published: February 2003

Using a crossed beam technique, the product angular and velocity distributions have been measured for the reaction of C2H+ with D2 and the reaction of C2D+ with H2. The case where the product is the acetylene ion is discussed and reactions mechanisms are proposed. (AIP)
Infrared spectra of matrix isolated alkali metal perchlorate ion pairs
Authors: Ritzhaupt Gary , Devlin J. Paul
Published: February 2003

The infrared spectra of the vapors over alkali metal perchlorate salts at temperatures in the 400−450° range have been measured by isolation of molecular beams of the vapor species in various matrices at 12°K. The data indicate that at these temperatures the dominant vapor species are the monomeric ion pairs, M+ClO−4, though the LiClO4 vapor, in particular, may contain a large percentage of dimers. Observation of the monomer ion−pair spectra for argon matrices shows a strong splitting of the ν3(f) and ν4(f) threefold degeneracies with the magnitude of the ν3(f) splittings in the same range (200 cm−1) as previously reported for M+NO−3 monomers and, therefore, suggestive of a strong distortion of the tetrahedral perchlorate structure. The appearance of three distinct widely spaced ν3 components indicates a bidentate or bidentate−like cation−perchlorate pairing and may require an examination of the bases for the conclusion that the pairing is unidentate in M+NO−3 and M+ClO−3 ion pairs. The perchlorate ion distortion is reduced by as much as a factor of six in H2O and NH3 matrices, much as observed for the nitrates, apparently as a result of cancellation of the cation charge via electron transfer from the matrix molecules.
Mechanism and types of explosive behavior in hydrogen–fluorine systems
Authors: Sullivan John H. , Feber Roy C. , Starner John W.
Published: February 2003

The experimental data of Kapralova et al. [Kinet. Catal. (USSR) 10, 23 (1969)] have been modeled on a computer to show that two chain−branching reactions occur, H2* + F2 → HF + H + F (1), HF* + F2 → HF + 2F (2). The asterisks indicate a vibrationally excited molecule. Rate coefficients derived for these reactions depend slightly on the computational model. For a model that is adiabatic and in which HF(0) is not absorbed on the wall, 6×104 < k1 < 2×105 and 5×106 < k2 < 7×106 cm3/mol−s when all vibrationally excited molecules of HF and H2 are included in HF* and H2*. For a model that includes flow of heat out of the reacting gas and also diffusion of HF(0) to the wall, the coefficients are 6×104 < k1 < 1×105 and 2×106 < k2 < 5×106 cm3/mol−s. The computations show that quenched reactions take place during the time of experimental manipulation, so that the stability of H2−F2−O2 and H2−F2−O2−M mixtures can be due in large measure to the HF produced during mixing. Double explosions and oscillatory reactions can also occur.
Ion clustering reactions in carbon monoxide
Authors: Horton Robert L. , Franklin J. L. , Mazzeo Blas
Published: February 2003

Ion−molecule reactions in carbon monoxide have been studied in a drift tube ion source of a quadrupole mass filter. Pressures to approximately 0.35 torr and temperatures from 174−280°K were employed. CO+ was found to add up to three molecules of CO. The first and second of these appear to be attached irreversibly, probably by true chemical bonds. Small amounts of water present as impurity contribute to the formation of several product ions, the most important of which is at m/e 46, which we interpret to be the formic acid ion. Rate constants of seven reactions have been determined at each temperature. No equilibria were detected.
Temporary negative ions and electron affinities of benzene and N-heterocyclic molecules: pyridine, pyridazine, pyrimidine, pyrazine, and s-triazine
Authors: Nenner I. , Schulz G. J.
Published: February 2003

Electron transmission spectroscopy is used to study shape resonances (temporary negative ions) in benzene and some isolectronic N−heterocyclic molecules (pyridine, diazines, and s−triazine), in the energy range 0−6 eV. The lowest shape resonance in each of these molecules exhibits vibrational structure which is interpreted in all cases as the totally symmetric C−C stretch mode. The ground vibrational level of this lowest shape resonance is accessible by electron impact only in benzene and pyridine. Thus, their electron affinities can be determined from the present experiment (−1.15 eV for C6D6 and −0.62 eV for C5H5N). Only excited vibrational levels are accessible in the diazines and s−triazine, indicating that the electron affinities for these molecules have positive values. For benzene, pyridine, and some other aromatic hydrocarbons, we compare the electron affinities established in the gas phase with the polarographic potentials established in the liquid phase and we find a linear relationship. Using this correlation in conjunction with the measured values of the polarographic potentials, we estimate the electron affinities for pyridazine (0.25 eV), pyrimidine (0 eV), pyrazine (0.40 eV) and s−triazine (0.45 eV).
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o calculations of the effective spin–spin constants of the 3Σ excited states of the N2 and CO molecules
Authors: Sink M. L. , Lefebvre-Brion H. , Hall J. A.
Published: February 2003

Using a π3π′ single configuration description for the 3Σ states, good agreement with experiment has been found for the λ values of both the 3Σ+ and 3Σ− states of the N2 and CO molecules. To obtain such agreement in a nonempirical calculation, it is necessary to include two−center spin−spin integrals in the calculation of the direct spin−spin part of the effective constants.