bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemiluminescence of metastable tin with fluorine, chlorine, and nitrogen trifluoride utilizing a beam–gas configuration
Authors: Rosano W. J. , Parson J. M.
Published: July 2002

This paper reports the observation of electronic chemiluminescence (CL) from the reaction of metastable Sn with F2, Cl2, and NF3. All three reactions produced CL which was identified as emission from the A 2Σ+–X 2Π system of the tin monohalides and was first order with respect to the scattering gas. All spectra were highly congested suggesting that the product monohalides are produced with a large degree of internal excitation. Attenuation studies of various electronic states of metastable Sn in the beam with H2 show the 1D state to be the major contributor to CL product formation. Absolute CL cross sections were determined for Sn(1D) with F2, Cl2, and NF3 to be 67, >0.07, and 0.006 Å2, respectively, with uncertainties of ∼±60%. The cross section for the F2 reaction is approximately 35 times larger than the corresponding reaction for Sn(3P). The prior model, based on product state densities, predicts an increase of only about 6.5. We propose, in light of recent alignment experiments of Ca p orbitals, that the difference in reactivity of 1D and 3P states is a result of the symmetry of the second p orbital on Sn relative to the F2 molecule. Also, the production of the observed CL states requires a nonadiabatic process. Finally, the CL cross sections for the title reactions were found to increase with increasing collision energy.
The S2 ← S laser photoexcitation spectrum and excited state dynamics of jet-cooled acetophenone
Authors: Warren J. A. , Bernstein E. R.
Published: July 2002

The S2 ← S0 photoexcitation spectrum of jet-cooled acetophenone is presented. The observed homogeneously broadened linewidths indicate S2 lifetimes ≤0.26 ps while the measured emission lifetimes range from 540±30 ns for S2 000 excitation to 130±50 ns for S2 1210 excitation. The dynamics revealed by the spectrum are discussed in terms of the known photochemical and photophysical rates of the excited states of acetophenone. Arguments are presented which identify the emitting state as a known triplet state of acetophenone.
Radiative processes following laser excitation of the A 2Σ+ state of PO
Authors: Wong Koon Ng , Anderson William R. , Kotlar Anthony J.
Published: July 2002

Laser induced fluorescence in the (0,0) band of the A 2Σ+–X 2π system of the PO radical (∼2470 Å) has been used to study the radiative properties of the A state. A laser excitation scan of the (0,0) band and a fluorescence scan of the emission are given. Fluorescence from the B 2Σ+ state to the X state was observed (∼3250 Å) when the A state was pumped by the laser. The branching ratio for emission from the A state to the lower B and X states was indirectly determined. The A state was found to have a very short free radiative lifetime, 9.68±0.47 ns. In the absence of quenching, the excited state decay is found to be primarily due to radiative processes. Upper limits were determined for the quenching rates of Ar and He carrier gases. Relative intensities of emission of the v′=0 progression in the A–X system were also measured. These intensities were used to determine the electronic transition moment function in the region of the equilibrium internuclear distance.
Redox-insensitive molecular force constants
Authors: Brill Arthur S. , Gerstman Bernard S.
Published: July 2002

The differences in force constant and dissociation energy between members of the redox pairs HO–/HO, HS–/HS, and HSe–/HSe are quantitatively explained in terms of the electrostatic and mechanical couplings of a classical model. This model gives an explicit physical description of factors that can cause changes in stretch force constant between oxidized and reduced states to be very small, a condition assumed in theoretical treatments of thermally activated electron transfer.
Pressure effect on reversed micelles in water: An infrared spectroscopic study of aqueous dioleoyl phosphatidylethanolamine
Authors: Wong P. T. T. , Weng S. F. , Mantsch H. H.
Published: July 2002

Infrared spectra of aqueous dispersions of reversed micelles of dioleoyl phosphatidylethanolamine have been obtained at constant temperature (i.e. 28°C) as a function of pressure up to 55 kbar. The changes detected in different infrared spectral parameters indicate that a major structural phase transition occurs at 9 kbar. From a comparison of the barotropic and thermotropic phase behavior of the reversed micelles in water it is concluded that the pressure event at 9 kbar corresponds to a micellar–lamellar transition that encompasses the two thermal events that occur at 5 and −4 °C. It is shown that water (D2O) molecules are unable to penetrate the micelles and form hydrogen bonds with the C=O ester groups of the interface region even at pressures as high as 55 kbar. The absence of correlation field splitting bands in the gel phase at high pressures (up to 55 kbar) suggests that the bent oleoyl acyl chains are closely packed with all chains oriented parallel to each other.
Electron attachment to F2
Authors: McCorkle D. L. , Christophorou L. G. , Christodoulides A. A. , Pichiarella L.
Published: July 2002

The rate constant ka for electron attachment to F2 has been measured at ambient (298 K) temperature T in the buffer gas Ar over the mean electron energy 〈ε〉 range 0.40–2.95 eV; similar measurements were made at T=233, 298, and 373 K in the buffer gas N2 over the 〈ε〉 range 0.04–0.75 eV. The ka(〈ε〉) function attains a maximum value of 1.7×10−8 cm3 s−1 (T=298 K) at ∼0.04 eV and decreases monotonically with increasing 〈ε〉 above thermal energy; the magnitude of ka increases only slightly with increasing T. The ka(〈ε〉) data at 298 K were unfolded and the resultant cross section σa(ε) shows a main maximum at ∼0.0 eV, a shoulder at ∼0.5 eV, and a weak maximum at ∼1.1 eV. Possible electron attachment processes are discussed to account for the energy dependence of σa(ε). Also discussed, in the light of the present measurements, are published experimental and theoretical results on ka(〈ε〉) and σa(ε).
Energy flow and branching ratios between the low-lying electronically excited states of PuF6
Authors: Pack R. T , Rice W. W. , Barefield J. E.
Published: July 2002

Measurements of the rise and decay times, relative intensities, and pressure dependence of the 1.0, 1.9, and 2.3 μm laser-induced fluorescence (LIF) of plutonium hexafluoride (PuF6) excited at 795 nm are reported. Einstein  A coefficients of the transitions are also determined. Then, all these quantities are used to determine many of the rate constants of the kinetics of energy flow and also the relative quantum yields into the low-lying electronically excited states of PuF6. In addition, the data indicate that both radiating and nonradiating states are involved in the relaxation.
Microscopic theory of membrane transport. III. Transport in multiple barrier systems
Authors: Vertenstein Mariana , Ronis David
Published: July 2002

A correlation function expression for the zero wave vector and frequency diffusion permeabilities for membranes having multiple potential barriers is derived for systems linearly displaced from equilibrium. The calculation of these correlation functions is discussed within the context of projection operator theory, and the resulting theory is applied to a model membrane system containing pores similar to those formed by gramicidin A. Stochastic simulations are performed using the BGK model and position dependent diffusion constants are obtained for Na+, Li+, and Rb+ at 300 K. The permeability can be computed from short-time dynamical information, although some commonly made approximations on memory functions are found to be incorrect.
The resonance Raman excitation profile of violaxanthin
Authors: Hoskins L. C. , McCarthy M. C.
Published: July 2002

The resonance Raman excitation profiles for the ν1, ν2, and ν3 vibrations of violaxanthin in acetone, toluene, and carbon disulfide solvents have been measured. The results are interpreted in terms of a three-mode vibrational theory which includes both homogeneous and inhomogeneous broadening effects. Excellent agreement between calculated and observed excitation profiles and visible spectra was found in all three solvents. The broadening mechanism is exclusively homogeneous. The results also indicate that the excited-state vibrational frequencies may be important in the theoretical model.
Interpretation of core-excitation (1s-π*) processes
Authors: Lindholm Einar
Published: July 2002

It follows from recent deductions of the HAM semiempirical MO method from density functional theory and Hartree–Fock, that HAM can be used to calculate electron affinities and core-excitation energies. As an example trans-butadiene is studied. Reasonable agreement with measurements is obtained.
Time-resolved resonance Raman spectrum of chrysene in the S1 and T1 states
Authors: Koshihara Shin-ya , Kobayashi Takayoshi
Published: July 2002

The time-resolved Sn–S1 and Tn–T1 resonance Raman spectra of highly purified chrysene in tetrahydrofuran were observed at room temperature using the third harmonic of a Q-switched Nd:YAG laser as an electronic excitation pulse and a dye laser pumped by the second harmonic of another Q-switched Nd:YAG laser as a Raman probe pulse. We observed the Raman lines attributed to the S1 state at 1549, 1369, 1344, 1110, and 990 cm−1, and to the T1 state at 1528, 1494, 1353, 1199, 1110, 990, 678, 554, 472, and 286 cm−1. The decay time of 1369 cm−1 (S1) line, the formation time of 1528 cm−1 (T1) line, that of 1199 cm−1 (T1) line, and the fluorescence lifetime were obtained to be 35+6−5, 51+19−12, 41+10−7, and 41+− 1 ns, respectively. The observed Sn–S1 and Tn–T1 resonance Raman spectra were compared with the previously reported fluorescence and phosphorescence spectra in Shpolskii matrices, Sn–S1 and Tn–T1 resonance CARS spectra, and Tn–T1 spontaneous resonance Raman spectra. Discussion was made on the geometrical changes in the excited states on the assumption that the changes were not very large for the rigid molecular structure. We came to the following conclusions: (1) The resonance-coupled excited singlet state is different from the ground state in geometry mainly along the normal coordinates of the vibrational modes which have the Sn–S1 resonance Raman peaks at 1549 and 1344 cm−1. (2) The geometry of the resonance-coupled excited triplet state differs from that of the ground state mainly along five coordinates. Four of them correspond to the vibrational bands observed in the Tn–T1 resonance Raman spectrum at 1528, 1353, 1110, and 990 cm−1. The other corresponds to the vibrational bands observed in the Shpolskii spectrum of phosphorescence at 1385 cm−1 in literature. (3) The S1 and T1 states differ along the normal coordinates of the modes which have the Tn–T1 resonance Raman bands at 678, 554,

472, and 286 cm−1.
Theoretical studies of the photoelectron spectroscopy of the fluorinated ethylenes
Authors: Heaton M. M. , El-Talbi M. R.
Published: July 2002

A b initio molecular orbital calculations within the self-consistent field (SCF) method were effected for the complete series of the fluorinated ethylenes. A ‘‘double zeta’’-quality basis set was used with complete geometry optimization. Two methods were employed to correlate these calculated results with experimentally obtained vertical ionization potentials: the use of the orbital energies in accordance with Koopmans’ theorem and the use of the difference between the SCF energy of the molecule and the respective ion constrained to the molecular geometry. In several cases, an average of the Koopmans’ theorem results and the ΔSCF results was employed to approximate the experimental photodetachment energies. Definitive assignments of the molecular orbitals to the experimental bands could not be made on the basis of correspondence of energies. However, the relative ordering of the theoretical energies is considered generally correct. A correspondence also exists between the experimentally determined characteristics of the molecular orbitals, where specified, and the theoretical characteristics as evidenced in the population analyses. The orbital assignments were based upon the latter two factors.
Mössbauer study of short range order in frozen aqueous solutions of Fe(ClO4)2
Authors: Domes H. , Leupold O. , Nagy D. L. , Ritter G. , Spiering H. , Molnár B. , Szücs I. S.
Published: July 2002

Mössbauer spectra of frozen aqueous solutions of Fe(ClO4)2 were measured at T=4.2 K in external magnetic fields up to 5 T. It was found that the [Fe(H2O)6]2+ coordination ions are randomly distorted thereby retaining their C2h symmetry and obeying no significant Eg distortions.
Pressure tuning spectroscopy of binuclear metal cluster compounds
Authors: Carroll T. L. , Shapley J. R. , Drickamer H. G.
Published: July 2002

The effect of pressure has been measured on the absorption spectra of (n-Bu4N)2Re2X8 (X=Cl, Br, I), K4Mo2Cl8, (NH4)4Mo2Br8, and Re2[CCO2 (CH3)3]2X8(X′=Cl, Br). For the rhenium and molybdenum halides in the solid state a distinct shift to lower energy (red shift) was observed for the δ→δ* excitation. In solution the shift of the δ→δ* was red in CH2Cl2 but exhibited a complex behavior in the associated solvents CH3CN and CH3NO2 which we attributed to solvation of the ion. The dipivalate molecules in CH3CN exhibited a red shift as one might expect as they are less solvated. The π→π* excitations in the rhenium bromide and iodide showed a blue shift which increased with pressure. We discuss the observed shifts in terms of the relative importance of intra and intermolecular interactions.
Adiabatic corrections to the potential energy curves of the X 1∑+ state of the isotopic lithium hydrides
Authors: Hadinger G. , Tergiman Y. S.
Published: July 2002

From isotopic spectroscopic data, the internuclear distance dependence of the adiabatic corrections to the potential energy curve has been determined for the ∑ state of a diatomic molecule. Starting from an analytic inversion procedure previously described, the adiabatic corrections can be found in a straightforward way, provided that they can be considered as perturbing terms of the vibration–rotation wave equation. Application to the case of the X 1∑+ state of the lithium hydrides 6LiH, 7LiH, 6LiD, and 7LiD is carried out. The adiabatic corrections ΔUH(R) and ΔULi(R) are obtained and compared with recent results.
Electron attachment rate constants of SOCl2 in Ar, N2, and CH4
Authors: Wang W. C. , Lee L. C.
Published: July 2002

The electron attachment rate constants of SOCl2 in the buffer gases of Ar, N2, and CH4 (150 to 500 Torr) at various E/N (1–15 Td) were measured by a parallel-plate drift-tube electron-swarm technique. Electrons were produced by irradiating the cathode with KrF laser photons. For the SOCl2–Ar mixture, the electron attachment rate constant has a maximum value of 6.2×10−10 cm3/s at E/N=4 Td. For SOCl2 in N2, the electron attachment rate constant is 1.25×10−9 cm3/s at E/N=1.3 Td, and decreases with increasing E/N. For SOCl2 in CH4, the electron attachment rate constant is 4.8×10−9 cm3/s at E/N=1 Td, and decreases with increasing E/N. For every gas mixture studied, the electron attachment rate constant is independent of buffer gas pressure, indicating that the electron attachment to SOCl2 is due to a dissociative process. The electron attachment processes in the studied gas mixtures are discussed.
Calculation of the electron affinity of TeF6
Authors: Rappé A. K.
Published: July 2002

A b initio Hartree–Fock calculations at the valence-double-zeta-plus-diffuse functions level are used to calculate the electron affinity of TeF6 as a function of the Te–F distance. We obtain an electron affinity of 3.1 eV. Our results are compared to previous calculations on chalcogen hexahalides. We find good agreement with experiment and the calculations of Hay on SF6 using analogous methodology.
First observation of the optically inactive modes in the solid 1,4 benzoquinone
Authors: Penfold J. , Tomkinson J.
Published: July 2002

The inelastic incoherent neutron scattering spectrum of 1,4 benzoquinone has been obtained at 20 K, and analyzed to produce an out of plane force field. All out of plane fundamentals are observed for the first time in the solid phase. The optically inactive modes Au occur at 339 and 1027 cm−1. The large shifts in frequency upon vaporization are ascribed to lost hydrogen oxygen contacts.
A diabatic model for photoionization. Application to the inner valence x-ray photoelectron spectrum of acetylene
Authors: Flores-Riveros A. , Ågren H. , Brammer R. , Jensen H. J. Aa.
Published: July 2002

A two-state diabatic model for high-energy photoionization is proposed and applied to the inner valence x-ray photoelectron spectrum of acetylene. The diabatic electronic representation is accomplished by calculating the first order nonadiabatic coupling over the vibrational normal modes. The photoionization overlap amplitudes are expressed in terms of this new basis which is related to the adiabatic representation via an orthogonal transformation. The nonadiabatic (vibronic) coupling leads to a significant redistribution of photoelectron intensity for the totally symmetric states in the inner valence region. This finding resolves previous ambiguities in the analysis of the spectrum.
‘‘Ordered’’ structure in dilute suspensions of charged polymer latices as observed in the vertical planes and in mixtures of heavy and light waters
Authors: Ito Kensaku , Nakamura Hiroshi , Ise Norio
Published: July 2002

The aqueous suspension of various polystyrene-based latices was studied by the microscopic method and the interparticle spacing was determined for 100 pairs of particles with the aid of an image data analyzer. The precision of the data was thereby largely improved. By using mixtures of light and heavy waters, the influence of the specific gravity of the solvent was studied. The spacing 2Dexp in the horizontal plane was almost independent of the specific gravity for latices of diameters smaller than about 5000 Å, indicating that the inequality relation, 2Dexp<2D0 (average spacing calculated from the concentration), observed in an earlier publication [J. Chem. Phys. 78, 536 (1983)] is not an artifact due to the gravitational effects on latices and solvents. The spacing in the vertical plane was also measured in H2O and H2O–D2O mixtures. The 2Dexp values were hardly dependent on the suspension column height. The spacing was measured after the suspension was left undisturbed for a definite period. Up to 11 days, the spacing stayed practically constant and it decreased after a 6 month setting, though very slightly. The ordered regions of various sizes were observed in coexistence with the disordered regions as was found in the previous publication. The spacing was insensitive toward the size of the ordered regions. In spite of the insensitivity of the spacing toward the column height, a concentration gradient was occasionally found along the vertical direction. The information obtained in the present work definitely justifies our previous conclusion on the very nature of interparticle interaction, i.e., the existence of net attractive interaction between similarly charged colloidal particles through the intermediary of counterions.
A model for the asymptotic behavior of loop entanglement in a constrained liquid region
Authors: Lacher R. C. , Bryant J. L. , Howard L. N.
Published: July 2002

A constrained liquid region in a semicrystalline polymer has been modeled by random walk in the slab defined by two parallel planes a distance M units apart in space. Loops (walks beginning and ending on the same plane) play the role of strands of polymer that exit and reenter the same crystal while ties (walks that go from plane to opposite plane) play the role of strands that connect two crystals. A simulation has been designed to investigate the extent to which entanglement of loops may contribute to material properties. Results of the simulation indicate that several measures of entanglement (calculated from the matrix of linking numbers of a left loop with a complete distribution of right loops) approach positive constant values or increase without bound as M increases (while the effect of ties is known to be inversely proportional to M). A model of the simulation, in which random loops are replaced by loops with predictable geometry, yields asymptotic estimates of one such entanglement measure. The results from the simulation and the model agree within 10%.
Moments of the hard sphere correlation function
Authors: Moore S. M. , Raveche H. J.
Published: July 2002

It is shown that the second moment of the hard sphere correlation function is negative. Consequences of this are discussed.
Determination of the atomization energies of the gaseous molecules Nb2O4, Nb2O5, Nb4O9, and Nb4O1
Authors: Balducci G. , Gigli G. , Guido M.
Published: July 2002

The complex gaseous niobium oxide molecules Nb2O4, Nb2O5, Nb4O9, and Nb4O10 were identified for the first time in a Knudsen cell-mass spectrometric study of the vapors in equilibrium over a condensed phase resulting from extensive vaporization of lithium niobate with lithium depletion. These molecules were characterized thermochemically from the study of several all-gas equilibria. The resulting atomization energies are ΔH00,at(Nb2O4) =3322±45 kJ mol−1; ΔH00,at(Nb2O5) =3910±59 kJ mol−1; ΔH00,at(Nb4O9) =7958±82 kJ mol−1; ΔH00,at(Nb4O10) =8595±71 kJ mol−1. The corresponding standard heats of formation are ΔH0f,298(Nb2O4,g) =−909±45 kJ mol−1; ΔH0f,298(Nb2O5,g) =−1252±59 kJ mol−1; ΔH0f,298(Nb4O9,g) =−2889±82 kJ mol−1; ΔH0f,298(Nb4O10,g) =−3281±71 kJ mol−1.
Forces between charged lipid bilayers: A theoretical model
Authors: Graham I. S. , Georgallas A. , Zuckermann M. J.
Published: July 2002

A new theory is developed for a polar electrolyte adjacent to a charged surface. This model explicitly includes the polar nature of the solvent by modeling the electrolyte as a system of point charges and point dipoles, with the number density of ions plus dipoles constrained to be constant. The free energy of the model electrolyte is derived in the continuum limit to yield two coupled differential equations describing the electrolyte. Values of the potential V, polarization P, dielectric constant ε, and local mole fraction of dipoles  f  are evaluated as functions of the distance x from the charged surface. These are compared with the predictions of standard Gouy–Chapman–Debye–Hückel (GCDH) theory. A significant supression of ε(x) is observed close to the surface. This model electrolyte is then used to investigate the behavior of charged lipid bilayers. In particular the pressure between two identical charged bilayers is calculated from the appropriate free energy derivative. GCDH-like behavior is found for separations greater than 15 Å. However, for separations below 15 Å an exponentially decaying short range repulsive force is predicted, with a decay length of ≂1.4 Å. This decay length is of the same order of magnitude as those observed in measurements of short range forces between phospholipid bilayers.
A one order parameter theory for the fluid–solid interface
Authors: Moore S. M. , Raveche H. J.
Published: July 2002

A single order parameter theory for the interface between the flat surface of a single crystal in equilibrium with its melt is developed. Starting with the expression for the free energy as a functional of the nonuniform density, approximations are made which lead to a van der Waals-like formula for the free energy in terms of the order parameter. Expressions for the density profile, interface width, and surface free energy which take into account the crystal structure are derived. Comparison of the theory is made to molecular dynamics simulations.
S-matrix unitarization within reactive perturbation theory
Authors: Horn Thomas R. , Eno Larry
Published: July 2002

We explore the effect of S-matrix unitarization within the framework of reactive perturbation theory. Both exponential and Heitler based schemes are implemented for describing the dynamics on a pair of nonadiabatically coupled one-dimensional potential curves. Reflection and transmission probabilities are determined over a wide range of collision energies and for both low and high system masses. It is found that unitarization is an essential element in correctly describing energy trends in both nonreactive and reactive probabilities. Although exponentiation has been typically the unitarization method of choice, we find that the Heitler method has merit in its own right.
Unitary quantum time evolution by iterative Lanczos reduction
Authors: Park Tae Jun , Light J. C.
Published: July 2002

A general unitary time evolution method for wave packets defined on a fixed ℒ2 basis is developed. It is based on the Lanczos reduction of the full N×N Hamiltonian to a p-dimensional subspace defined by the application of H p−1 times to the initial vector. Unitary time evolution in the subspace is determined by exp{−iHpt}, retaining accuracy for a time interval τ, which can be estimated from the Lanczos reduced Hamiltonian Hp. The process is then iterated for additional time intervals. Although accurate results over long times can be obtained, the process is most efficient for large systems over short times. Time evolution employing this method in one- (unbounded) and two-dimensional (bounded) potentials are done as examples using a distributed Gaussian basis. The one-dimensional application is to direct evaluation of a thermal rate constant for the one-dimensional Eckart barrier.
A rotationally invariant orbital transformation
Authors: Carlacci Louis , McIver James W.
Published: July 2002

A new transformation which predicts molecular orbitals at one molecular geometry from those at another is presented. Unlike other transformations, this one maintains invariance when the geometry change reduces to a pure rotation. The transformation is compared to two others for the internal rotation in ethane using the closed shell canonical Hartree–Fock molecular orbitals and the STO-3G basis. In additon to predicting orbitals that are independent of how the internal rotation is specified, the transformation gives remarkably accurate results.
Internal field correction on infrared spectra of condensed phases
Authors: Akiyama Minoru
Published: July 2002

Infrared spectra observed in condensed phases must be corrected for the effect of the internal electric field. A new equation for such correction was derived by employing the Lorentz internal field model. The previous equation which has been widely used was also derived in order to make clear why the difference occurs, and the validity of the present derivation was pointed out. Moreover, the new equation was applied to the 678 cm−1 band of liquid benzene, and the results were found to be quite reasonable.
Observation of rapid E-to-V energy transfer in the 2.3 μm laser-induced fluorescence of PuF6 containing HF
Authors: Rice W. W. , Barefield J. E. , Pack R. T
Published: July 2002

Following excitation of PuF6 at 800 nm, laser-induced fluorescence (LIF) of PuF6 is observed near 2.3 μm; HF v=1 to 0 emission, arising from near resonant electronic-to-vibrational (E→V) energy transfer, is also observed with the same temporal decay as the PuF6 fluorescence. From the rise and decay times of the PuF6 and HF fluorescence and their relative intensities, all the rate constants involved in this relaxation are determined. The E→V rate constant is found to be (7.5±2.5)×103 Torr−1 s−1, and that for the relaxation of HF (v=1) by PuF6 is found to be (5.7±0.7)×103 Torr−1 s−1.
Charge density in pyroelectric lithium sulfate monohydrate at 80 and 298 K
Authors: Karppinen M. , Liminga R. , Lundgren J.-O. , Kvick Å. , Abrahams S. C.
Published: July 2002

Lithium sulfate monohydrate has been studied at 80 and 298 K by x-ray diffraction. The monoclinic crystal with space group P21 has lattice dimensions at 298 K of a=5.4553(1), b=4.8690(1), c=8.1761(2) Å, and β=107.337(2)°; lattice dimensions at 80 K were reported in our neutron study [J. Chem. Phys. 80, 423 (1984)]. Least-squares refinement based on 3486 (80 K) and 3390 (298 K) independent reflections, assuming a spherical atom model, results in final R( F 2) values of 0.024 (80 K) and 0.026 (298 K). Static deformation and charge density model refinement, based on Hirshfeld-type multipole functions, greatly reduces the residual electron density and gives R( F 2) values of 0.017 (80 K) and 0.016 (298 K). Refinement of the resulting multipole parameters within the Gaussian radial dependence model allows a qualitative estimation of the differences in electron densities between 80 and 298 K. A change of about 0.2 e Å−3 in the deformation density of the O–H bonds in the water molecule over this temperature range is related to the contraction in hydrogen bonding at 80 K. Changes in the sulfate oxygen atom lone-pair deformation densities, caused by contractions in the SO2−4–Li+ contacts between 298 and 80 K, are also found between the two temperatures. X-ray–neutron diffraction deformation density calculations indicate a substantial electron deficiency in the sulfur valence shell. Kappa refinement leads to a point charge model with positive atomic charge close to 1.8 on sulfur, about −1.0 on each sulfate oxygen atom, and −0.8 on the water oxygen atom. Interatomic distances at 80 and 298 K, particularly those based on a Gaussian radial dependence for the deformation density function, are in excellent agreement with the corresponding neutron diffraction values.
Theory of ionization equilibrium: An approximation for the single element case
Authors: Kerley G. I.
Published: July 2002

An approximate solution to the equations of ionization equilibrium for a single element is presented and shown to be very accurate. The Helmholtz free energy is expressed in terms of a simple atomic-like partition function that is summed over all levels and ionization stages of the atom. The result has certain features in common with average atom models.
Influence of ligands on the x-ray absorption near-edge structure of palladium(II) complex compounds
Authors: Sugiura Chikara , Kitamura Michihide , Muramatsu Shinji
Published: July 2002

The palladium LIII absorption and chlorine K absorption spectra from [Pd(NH3)4]Cl2 ⋅ H2O and Pd(OCOCH3)2 have been reported for the first time and discussed in connection with the Pd LIII absorption and Cl K absorption spectra of K2PdCl4, reported previously. The influence of the ligands Cl−, OCOCH−3, and NH3 has been observed in the pallaldium LIII absorption spectra of these compounds. The observed chemical shift of a strong ‘‘white line’’ at the Pd LIII absorption threshold can be explained in terms of the spectrochemical series of the ligands. An intense white line disappears at the Cl K absorption threshold of [Pd(NH3)4]Cl2 ⋅ H2O in contrast to the Cl K absorption spectrum of K2PdCl4.
Monte Carlo simulation on the solvent structure of biopolymers for the study of the effect of hydration on their energy band structure
Authors: Runsheng Chen , Otto P. , Ladik J.
Published: July 2002

The complete solvent structure of a polyalanine fragment in the β-pleated sheet conformation with a repeat unit of two alanine molecules has been determined. In this Monte Carlo simulation, 97 water molecules have been included, their interaction energies and the number of water molecules in the different regions of alanine have been calculated. A water cluster as hydration shell of polyalanine in the β-pleated sheet conformation has been chosen. Then for polyalanine, ab initio crystal orbital calculations have been performed to investigate the effect of the hydration shell on its band structure. The presence of the water molecules caused some band shifts. The width of the conduction band increased by 0.63 eV that is it became more than twice as wide as without the hydration shell. The forbidden bandwidth decreased by nearly 0.8 eV.
Iteratively determined effective Hamiltonians for the adiabatically reduced coupled equations approach to intramolecular dynamics calculations
Authors: Klippenstein Stephen J. , Voth Gregory A. , Marcus R. A.
Published: July 2002

An iterative procedure is proposed for determining increasingly accurate effective Hamiltonians for use in the adiabatically reduced coupled equations approach to intramolecular dynamics calculations [J. Chem. Phys. 84, 2254 (1986)]. The relationships between this iterative determination of the effective Hamiltonian, which is based on an adiabatic approximation, and some other partitioning methods for determining an effective Hamiltonian are discussed. The present iterative procedure provides accurate agreement with the exact dynamics for the two specific model systems studied.
Reaction rate constant of HO2+O3 measured by detecting HO2 from photofragment fluorescence
Authors: Manzanares E. R. , Suto Masako , Lee Long C. , Coffey DeWitt
Published: July 2002

The rate constant for the reaction HO2+O3→OH+2O2 was investigated in a discharge–flow system at room temperature. HO2 was produced from the reaction sequence Cl+CH3OH→CH2OH+HCl and CH2OH+O2→HO2+CH2O. HO2 was detected by the OH(A–X) fluorescence produced from photodissociative excitation of HO2 at 147 nm. A computer modeling of the reaction kinetics occurring in the flow tube was carried out to confirm that contributions from secondary reactions were negligible at low HO2 concentrations. The rate constant was determined from first order decay of HO2 in excess O3. The measured reaction rate constant of HO2+O3 is (1.9±0.3)×10−15 cm3 molecule−1 s−1, which agrees well with published data.
On the intensity dependence of infrared excitation in C3F7I
Authors: Mukherjee P. , Kwok H. S.
Published: July 2002

The question of intensity vs energy fluence dependence in the IR excitation of a polyatomic molecule in the quasicontinuum is addressed. It was found that the energy fluence scaling law breaks down for laser pulses shorter than ∼100 ps for C3F7I. This is consistent with similar results obtained previously for SF6 and C2F5Cl. The reason for the increased intensity dependence is physically due to an increase in the intrinsic small signal absorption cross section of the polyatomic molecules for short interaction times. This increase in the absorption coefficient is not intensity related and is a fundamental property of a dense ensemble of interacting states. The change in the absorption cross section for all molecules studied reveals a nonequilibration of energy relaxation among all the states even for 100 ps pulses. This nonequilibrium situation can be exploited to achieve ps nonstatistical photochemistry.
The electronic structure of the chloroferrocenes
Authors: Driscoll D. C. , Dowben P. A. , Boag N. M. , Grade M. , Barfuss S.
Published: July 2002

We have measured the ionization potentials of gaseous ferrocene and the symmetrically substituted chloroferrocenes, Fe(C5H5−NClN)2 (0≤N≤5) by electron impact techniques. The ionization potential is found to increase in direct proportion to the number of chlorine substitutions. These results indicate that chlorine ring substitutions result in greater overlap of the π-ring orbitals and the metal d orbitals. The binding energies of the unoccupied orbitals of ferrocene and 1,1′-dichloroferrocene have been inferred from photoabsorption studies. The effect of symmetric dichlorination on the splitting of the unoccupied 5e1g ferrocene molecular orbital is described.
A magnetic field study of excited triplet diphenylmethylene
Authors: Graham Daniel J. , Wang Chia-Ling
Published: July 2002

We present a method whereby the excited triplet state of diphenylmethylene can be populated in a spin-polarized manner. The method features sensitization by benzophenone triplet excitons. We ascertain the spin-polarized nature of the excited triplet by observing magnetic field effects on the fluorescence. The observed effects provide information concerning the spin dipolar and intersystem crossing nature of excited diphenylmethylene.
Multiphoton dissociation/ionization of benzene, pyridine, and diazabenzenes. Detection of an atomic carbon transition
Authors: Bolovinos A. , Spyrou S. , Cefalas A. C. , Philis J. G. , Tsekeris P.
Published: July 2002

Multiphoton processes in benzene, pyridine, and the diazabenzenes with ∼10 ns, 0.4–2.5 mJ pulsed laser light in the 336–347 nm range, produced resonantly enhanced molecular ions as well as neutral carbon atoms. The carbon atoms were detected by subsequent two-photon resonant (...2p2 1D2→2hν ...2p3p 1P1) three-photon ionization at 340.93 nm. MPI resonances due to vibrations of the 3p Rydberg state appeared in the spectra of pyrazine and pyrimidine, as well as a probable member of the first singlet→triplet band in pyrimidine.
A test of two approximate two-state treatments for the dynamics of H-atom transfers between two heavy particles
Authors: Klippenstein Stephen J. , Babamov Vasil K. , Marcus R. A.
Published: July 2002

Reactive transition probabilities and Boltzmann-averaged reactive transition probabilities for a slightly off-resonant model H-atom transfer system with an appreciable energy barrier are calculated using the approximate methods of Babamov et al. and of Crothers–Stückelberg. Both are compared with the corresponding quantities obtained from a numerical two-state treatment of the same model system. The method of Babamov et al. is seen to give more accurate results for the transition probabilities at energies below and around the reaction threshold, and much more accurate results for the Boltzmann-averaged probabilities in a wide range of temperatures than the second method. The relative merits of the two formulas are discussed.
Asymmetric rare gas pair potentials from energy density functionals
Authors: Donnamaría María C. , Glossman Mario D. , Alonso Julio A.
Published: July 2002

The Thomas–Fermi density functional theory is applied to calculate repulsive interaction potentials for heteronuclear pairs of rare gas atoms. Our results are compared with other theoretical values as well as with available experimental data.
Photochemistry of acetylene at 193 nm: Two pathways for diacetylene formation
Authors: Seki Kanekazu , Nakashima Nobuaki , Nishi Nobuyuki , Kinoshita Minoru
Published: July 2002

Nanosecond time-resolved absorption spectra of diacetylene were observed in the 193 nm excitation of acetylene to the Ã 1Au(v′3=10) state. The formation of diacetylene was confirmed by comparing it with the spectrum of pure diacetylene. Time behavior of the diacetylene spectrum showed that there are two pathways for diacetylene formation. The first one, which finishes within a laser pulse width of 20 ns (FWHM), is attributed to the reaction of C2H radical. The second one is a slow process of diacetylene formation continuing up to ∼1.5 μs at 50 Torr. This slow process is probably the reaction via an excited triplet vinylidene radical. A Lindemann type unimolecular reaction scheme is introduced to explain the results.
Molecular dynamics of hard spheres. I. Hard spheres in a channel
Authors: Macpherson A. K. , Carignan Y. P. , Vladimiroff T.
Published: July 2002

A molecular dynamics study of the thermodynamics properties, including equation of state, of hard spheres in a narrow channel is presented. Four densities are studied and it is found that the pressure profile is directly correlated to the density profile. Further, the fraction of the total pressure due to collisions in a direction normal to the wall is also correlated to the density profile. The equation of state is that of a hard sphere fluid at a density higher then the fluid and it varies across the channel. The motion of particles near the wall is constrained as found earlier in Monte Carlo studies.
Thermotropic ionic liquid crystals. VII. Calculation of sodium-23 quadrupole coupling constants in lamellar phases of sodium alkanoates
Authors: Phillips M. L. , Jonas J.
Published: July 2002

The 23Na quadrupole coupling constants (QCC) were calculated for a quasicrystalline model of the neat phase of anhydrous amphiphiles. The magnitude of the QCC in short-chain sodium alkanoates and its dependence on the lateral packing area of the polar heads was accurately predicted by assuming the charges to lie in a double-layered square array of interdigitated ion pairs.
Stark, Zeeman, and hyperfine properties of v=0, v=1, and the equilibrium configuration of hydrogen fluoride
Authors: Bass Steven M. , DeLeon Robert L. , Muenter J. S.
Published: July 2002

Molecular beam electric resonance spectroscopy has been done on the v=0 and v=1 states of hydrogen fluoride in external electric and magnetic fields. The v=1 state was populated using a color center laser. v=0, v=1, and equilibrium configuration results have been obtained for the HF dipole moment, fluorine and proton spin rotation interactions, fluorine and proton magnetic shielding anisotropies, both direct and indirect spin–spin interactions, rotational magnetic moment, and magnetic susceptibility. All of these properties can be extrapolated to v=2 with high accuracy and to higher states with reasonable confidence. First and second derivatives with respect to internuclear distance have also been obtained for several of these properties. Comparisons of HF and DF dipole moments indicate significant differences arising from Born–Oppenheimer breakdown.
Dielectric anisotropy of N-methylacetamide in the far-infrared and millimeter-wave region
Authors: Häseler S. , Poglitsch A. , Bechtold G. , Genzel L.
Published: July 2002

Far-infrared and millimeter-wave spectra of polycrystalline and single crystal N-methylacetamide (NMA) samples are presented. The far-infrared measurements taken at approximately liquid helium temperature using polarized light reveal several line splittings and anisotropy effects. Anisotropic dielectric properties are also found in the millimeter-wave region. The effect of relaxation processes in double-well potentials on the anisotropic dielectric tensor is calculated. Thereby an estimation of the dipole moment change between the two wells of the high-temperature phase relaxation in NMA can be given.
Entropy production in the reversible Oregonator oscillatory model: The calculation of chemical entropy production rate in the course of a complete oscillation cycle
Authors: Dutt A. K.
Published: July 2002

Field expanded the five step Oregonator model of the oscillatory Belousov–Zhabotinskii reaction by introducing reversibility into the various steps. The present work involves the calculation of entropy flow (φ[S]) and entropy production (P[S]) in a specially designed reversible Oregonator. Entropy flow due to thermostatic temperature control and the osmotic transport of the reactants (A,B) and product (P) into and out of the reactor has been considered. Entropy production (e.p.) due to mixing of the reactants and product, diffusion of the intermediates (X, Y, and Z), and most importantly the chemical reactions has been considered. An attempt has been made to calculate the e.p. of the model using the results obtained by Field by numerical integration of the appropriate stiff kinetic differential equations. The following new results are obtained: (a) Limit cycle traces of e.p. against concentration of the oscillatory intermediates have been constructed. (b) The model resides on the low e.p. branch for about 97% of the total oscillation period and then switches to the high e.p. branch accompanied by about 105-fold increase of the value. (c) The time average of e.p. is obtained for a complete cycle and is compared with the value at the true unstable steady state.
Comment on: ‘‘H+NO translation-to-vibration/rotation energy transfer: A classical trajectory study’’
Authors: Budenholzer Frank , Hu S. C. , Hwang L. M. , Song Mark
Published: July 2002

Classical trajectories were calculated for H+NO vibrationally, rotationally inelastic scattering at a relative translational energy of 2.3 eV over the 1A′ surface. The results complement an earlier trajectory study by M. Colton and G. Schatz [J. Chem. Phys. 83, 3413 (1985)]. The role of nearly direct hits and complex formation are discussed.
Dipole, quadrupole, and octupole terms in the long-range hyperfine frequency shift for hydrogen in the presence of inert gases
Authors: Greenwood W. G. , Tang K. T.
Published: July 2002

The R−6, R−8, and R−10 terms in the long-range expansion for the hyperfine frequency shift are calculated for hydrogen in the presence of He, Ne, Ar, Kr, and Xe. The R−6 terms are based on the dipole oscillator strength sums. For helium, the R−8 and R−10 terms are based on quadrupole and octupole oscillator strength sums. For the heavier inert gases, the results for the R−8 and R−10 terms are obtained from the sum rules and the static polarizabilities. Upper bounds are also determined for the R−8 and R−10 terms.
On the use of x-ray reflectivity and fluorescence as probes of the longitudinal structure of the liquid–vapor interface
Authors: Thomas Britt N. , Rice Stuart A.
Published: July 2002

The x-ray reflectivity and fluorescence, as functions of angle of incidence and angle of detection, are calculated for several models of the longitudinal density distribution in the liquid–vapor interface. The models studied range from one descriptive of the monotone density distribution in a dielectric liquid–vapor interface to one descriptive of the stratified density distribution predicted for the metal liquid–vapor interface. In addition, we report calculations for the liquid–vapor interfaces of several simple binary alloys, each characterized by varying degrees of surface segregation of the components. Our results suggest that x-ray reflectivity and fluorescence intensity variations with angle of incidence and angle of detection can be sensitive probes of density and composition variations along the normal to the interface for pure metals and alloys.
On the structure and dynamics of water in AlCl3 solutions from H, D, 17O, and 27Al nuclear magnetic relaxation
Authors: van der Maarel J. R. C. , de Boer H. R. W. M. , de Bleijser J. , Bedeaux D. , Leyte J. C.
Published: July 2002

The relaxation rates of 27Al, H, D, 17O, and the relaxation rate of H due to dipolar coupling to 17O were obtained in a series of aqueous AlCl3 solutions. From these data conclusions are reached about bulk water dynamics, the O–H bond distance, and the order within the Al3+ hydration shell. The bulk water dynamics is interpreted by a hydrodynamical model. For comparison viscosity data are presented. It is found that the change in the O–H distance of water molecules adjacent to Al3+ is significant and in agreement with reported theoretical results. The destruction of order within the Al3+ hexaquo complex with increasing concentration is indicated.
Evidence for a rotational rainbow in inelastic hot atom experiments?
Authors: Bowman Joel M. , Gazdy Bela
Published: July 2002

The rotational population of carbon dioxide,after collision with translationally hot hydrogen atoms has been reported recently(ref.1). It is contended that the population distribution can be explained by a rotational rainbow mechanism for the rotational excitation.(AIP) :m
Fluctuations and correlations in molecular dynamics calculations at the coexistence of two phases
Authors: Morales Juan J. , Cuadros Francisco , Rull Luis F.
Published: July 2002

Using long run computer simulations of molecular dynamics (E,V,N) the fluctuations of a two-dimensional system were studied in the melting zone. The system formed by the coexistence of two phases was obtained by rescaling two systems, one from the solid region and the other from the liquid region. Two different algorithms were used to integrate the equations of motion to see the influence on the thermodynamic properties and their fluctuations. In order to estimate the correlations over long times with each algorithm, a method suggested by Smith and Wells, and amplified by Straatsma et al. was used.