bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular high-Rydberg fragments from CH4 and C2H6 by electron impact dissociation
Authors: Freund Robert S. , Tarr Susan M. , Schiavone James A.
Published: February 2003

In this work we report the observation of polyatomic high-Rydberg molecules which survive for several hundred microseconds. Methane and ethane were excited by electron impact to produce high-Rydberg states of their fragments: CH3 from methane and CH3, C2H4, and C2H5 from ethane. These identifications are proven by measurements of threshold energies and by comparisons to fragmentation patterns for dissociative ionization. Sharp threshold peaks in the excitation functions show the occurrence of direct high-l excitation. The absence of parent CH4 or C2H6 in high-Rydberg states remains unexplained, but may be related to a strong interaction between the Rydberg electron and the core.
Unimolecular processes in vibrationally highly excited cycloheptatrienes. III. Direct k (E) measurements after laser excitation
Authors: Hippler H. , Luther K. , Troe J. , Wendelken H. J.
Published: February 2003

Vibrationally highly excited substituted cycloheptatrienes in their electronic ground states have been prepared by single photon UV laser excitation and subsequent internal conversion. The unimolecular isomerizations of these species have been followed by time resolved UV absorption spectroscopy. The specific rate constants k (E) could be obtained directly at low pressures for methyl-, ethyl-, and isopropyl-substituted cycloheptatrienes. The influence of collisions on the rate of product formation has been elucidated as well. The results are compared with thermal and steady-state photoisomerization experiments. Statistical theories of unimolecular reactions can fully account for all results.
An ESR study of irradiated 1:1 co-crystals of 9-ethyladenine:5,5-diethylbarbituric acid (barbital) at 295 K
Authors: Sagstuen Einar , Close David M.
Published: February 2003

Crystals of the 1:1 complex of 9-ethyladenine:5,5-diethylbarbituric acid have been irradiated with 4.0 MeV electrons at 295 K and examined using electron spin resonance spectroscopy. Three radical species were observed. One of these was identified to be the barbital ethyl-abstraction radical (I) with the main part of the unpaired spin density at C5 interacting with two β protons. A second species is the H adduct at the C2 position of 9-ethyladenine (II). The third radical is tentatively assigned to the corresponding C8 H adduct (III). The relative contribution of each of these radicals to the total resonance is discussed and compared to that for the isolated compounds. It is concluded that the present data give no evidence for horizontal or vertical charge transfer between the bases.
Collision-free lifetimes and quenching of the A 2Σ+ state of HS and DS radicals
Authors: Tiee J. J. , Ferris M. J. , Wampler F. B.
Published: February 2003

The collision-free lifetime of the v=0 level of the A 2Σ+ state of DS has been measured to be 189 ns, and that of HS has been estimated to be ∼0.5 to 2 ns. Absolute quenching rate constants of DS ( A state) by various gases have also been determined.
Trapping by static sinks: An exact result based on fluctuating nonequilibrium thermodynamics
Authors: Keizer Joel
Published: February 2003

The theory of fluctuating nonequilibrium thermodynamics is applied to the trapping of particles by stationary sinks. Earlier treatments of this problem are based on the Smoluchowski theory and have examined the effect of interaction among the sinks. Using a calculation which involves the effects of both diffusion and the rate of trapping, we obtain the static and dynamic structure factors for a system of static sinks with diffusing particles that are replaced at a steady rate. We examine in detail the limiting case of dilute diffusing particles, for which the statistical distribution of sinks remains unperturbed. Using a self-consistent procedure to calculate the trapping rate, we obtain a transcendental equation for the trapping rate constant which agrees with the lowest order density corrections calculated by others. Experiments for testing the density dependence of the trapping rate constant are proposed.
Small-curvature adiabatic approximation for reaction-path reduced-dimensionality effective Hamiltonian
Authors: Skodje Rex T. , Truhlar Donald G.
Published: February 2003

Beginning with the Miller–Handy–Adams reaction-path Hamiltonian, which is applicable to chemical reactions and photodissociation processes, we classify the modes as one reaction coordinate, (f−1) strongly coupled modes, and (F−f) weakly coupled modes. We derive a reduced-dimensionality Hermitian Hamiltonian for f explicit modes such that the (F−f) weakly coupled modes are treated adiabatically and their coupling to the reaction coordinate due to reaction-path curvature is included implicity. The reduction is achieved two ways: one based on a small-curvature-tunneling approximation and one based on a more general semiclassical-path assumption for the weakly coupled modes.
Time-dependent coupled Hartree–Fock calculations of multipole polarizabilities and dispersion interactions in van der Waals dimers consisting of He, H2, Ne, and N2
Authors: Visser F. , Wormer P. E. S. , Stam P.
Published: February 2003

The long-range dispersion interaction coefficients for van der Waals dimers consisting of He, Ne, H2, and N2 have been computed in the time-dependent coupled Hartree–Fock approximation. Static multipole polarizabilities and van der Waals coefficients Cn(n=6,8,10) are presented. The difference between coupled and uncoupled Hartree–Fock results (‘‘apparent’’ correlation) is large in all systems considered and only in the case of Ne the ‘‘true’’ correlation effects are larger. In order to keep the basis set errors in the computed properties smaller than the correlation errors, the basis sets have to be very large. This is demonstrated by using different basis sets for the molecules H2 and N2. The computed van der Waals coefficients for the ten dimers are very accurate, at least the C6 and C8 coefficients, with correlation errors less than 6% for He2, H2–H2, N2–N2, HeH2, HeN2, and H2–N2.
A charge-transfer contribution to the g∥ shift of d7 ions in strong field situations
Authors: Aramburu J. A. , Moreno M.
Published: February 2003

It is shown here that a good insight into the g∥ shift of d7 ions in elongated D4h symmetry requires one to go beyond the crystal field approach and consider the levels arising from a molecular orbital picture. Within this scheme is demonstrated the appearance of a second order contribution to the g∥ shift which depends on the spin-orbit coefficient and the covalency of equatorial ligands. This new contribution can reasonably account for the positive g∥ shift observed for Pd3+ and Rh2+ doped silver halides. Furthermore, the smallness of the spin-orbit coefficient of equatorial ligands in cases such as [Rh(CN)4Cl2]3− or [Fe (CN)4Cl2]5− is consistent with the slightly negative g∥ shift observed for these systems.
Direct cluster expansion method. Application to glyoxal
Authors: Hirao K.
Published: February 2003

The direct cluster expansion formalism for large-scale wave function calculations, based on an integral-list driven procedure, is presented in a new form. The new approach allows us to calculate the correlated ground state wave function and to make the direct determination of excitation energies and various detachment and attachment energies, such as ionization potentials and electron affinities, in the symmetry-adapted-cluster (SAC) and SAC–CI framework. Applications are made to the ground state and low-lying singlet and triplet excited states of glyoxal (CHO)2, and its positive and negative ions. Cluster expansion calculations indicate that correlation effects are very important both in the ground and excited states of glyoxal. The trans conformation is predicted to lie 4.6 kcal below the cis isomer in the ground state. The calculated adiabatic excitation energies are 22 000 cm−1 (3Au), 28 700 cm−1 (3Bg), and 30 400 cm−1 (3Bu). The ordering of the vertical ionization potentials of trans glyoxal is 7ag (n+), 6bu (n−), 1bg (π−), 1au (π+), and the agreement with experiment is fairly satisfactory. It is concluded that the present theory is applicable equally well to the study of the ground state and various excited states.
Irreversible reaction on a polymer chain with range two cooperative effects
Authors: Evans J. W. , Burgess D. R.
Published: February 2003

We consider the kinetics of an irreversible reaction at the sites of an infinite, uniform, 1D polymer chain with first and second nearest neighbor (nn) cooperative effects. The special cases with just nn cooperative effects, and with nn blocking and general second nn cooperative effects have previously been solved exactly. For the latter case, we present several new results for highly autoinhibitory and autocatalytic rates. The general problem cannot be solved exactly but we apply the techniques of the preceding paper, which for this process exploit a shielding property of quadruples of unreacted sites, to obtain approximate solutions. Various cooperativity regimes are considered.
Variational principle for the Kirkwood theory for the dynamics of polymer solutions and suspensions
Authors: Doi Masao
Published: February 2003

The general theory of Kirkwood for the dynamics of polymer solutions and suspensions is reformulated in the form of a variational principle. This formulation is analogous to Lagrangian mechanics and the time evolution equation is derived from a certain scalar functional. The advantage of this formulation is that: (i) it states the essential physics of the Kirkwood theory without using the Riemannian geometry; and (ii) it suggests various new schemes of approximation. Two examples are given to illustrate the usefulness of the formulation, i.e., the dynamics of rodlike polymers and the deformation of an elastic particle in elongational flow.
O2 pressure broadening of the iodine 2P1/2→2P3/2 transition
Authors: Neumann D. K. , Clark P. K. , Shea R. F. , Davis S. J.
Published: February 2003

The pressure broadening coefficient for the I(2P1/2→2P3/2) transition by O2 has been measured using a high resolution Fabry-Perot scanning interferometer. Spontaneous emission from a microwave excited mixture of oxygen and iodine was spectrally resolved using the center spot scanning technique. The broadening coefficient was measured at O2 pressures of 1–10 Torr and found to be 7.5±1.5 MHz/Torr at 300 K.
Reorientational motion, collision-induced scattering, and vibrational relaxation in liquid carbonyl sulfide
Authors: Hegemann B. , Jonas J.
Published: February 2003

The rotational and vibrational behavior of neat liquid carbonyl sulfide under its own vapor pressure is investigated through Raman line shape studies of the symmetric ν1 C=S stretching mode over the temperature range T=183 to 303 K. The reorientational motion is found to be near the diffusional limit. Various methods of determining the reorientational correlation time τθ are compared and their validity discussed. The contribution of collision-induced scattering to the ν1 mode rotational line shape is examined semiquantitatively. It is found that the relative contribution of collision-induced scattering to the overall rotational line shape increases with increasing temperature and decreasing density, whereas the second moment of the collision-induced line shape decreases. Assuming the separability of the collision-induced scattering contribution and the reorientational contribution to the observed line shape, the experimental data are discussed qualitatively in terms of the dipole–induced–dipole (DID) theory of Balucani and Vallauri. The vibrational relaxation mechanism for the ν1 mode is attributed to dephasing and interpreted by Kubo line shape theory. The dephasing is found to be in the ‘‘motionally narrowed’’ regime and discussed qualitatively in terms of attractive dipolar forces.
An NMR relaxation study on the proton transfer in the hydrogen bonded carboxylic acid dimers
Authors: Nagaoka S. , Terao T. , Imashiro F. , Saika A. , Hirota N. , Hayashi S.
Published: February 2003

We have studied the proton spin-lattice relaxation times (T1) of a series of benzoic acid (BAC) derivatives and decanoic acid (DAC) over a wide range of temperature and analyzed the results in terms of the double proton switching along the hydrogen bonds. The proton T1 in the high temperature region are analyzed using the classical jump model and the barrier heights for the proton transfer are determined. The thermodynamic parameters for the equilibria between the two configurations in the solid state are also determined by the FT–IR measurements. It is shown that the energetics and dynamics of the proton transfer in DAC and the para- and meta-substituted BAC are all similar, but they are very different in the ortho-substituted ones. It is suggested that the low temperature behavior of the proton T1 of the dimers of carboxylic acid is due to the tunneling and the asymmetry of the potential brings in a small activation energy.
Equilibrium structure of CO+ from its millimeter wave spectrum. Breakdown of the Born–Oppenheimer approximation
Authors: Bogey M. , Demuynck C. , Destombes J. L.
Published: February 2003

Microwave transitions of CO+ have been observed for several isotopic substitutions, in different vibrational states: 12C 16O+(v=0,1,2,3,4), 12C 18O+(v=0,1), 13C 16O+(v=0,1), and 13C 18O+(v=0). All measured frequencies are fitted together in a one step procedure, leading to a precise determination of molecular constants and equilibrium structure. The vibrational dependence of the 13C hyperfine structure is pointed out, and the ΔC01 and ΔO01 mass scaling coefficients are determined.
EXAFS and Mössbauer studies of iron neutralized Nafion ionomers
Authors: Pan H. K. , Yarusso D. J. , Knapp G. S. , Pineri M. , Meagher A. , Coey J. M. D. , Cooper S. L.
Published: February 2003

X-ray absorption spectroscopy was used together with Mössbauer spectroscopy to study the chemical state and the microstructure of iron neutralized Nafion membranes. The cation oxidation state deduced from the x-ray absorption-near-edge structure (XANES) of the ionomers agrees with that deduced from the Mössbauer isomer shift. Extended x-ray absorption fine structure (EXAFS) results confirm the existence of Fe(H2O)62+ octahedra, with a Fe–O distance of 2.11±0.01 Å in hydrated ferrous ionomers. As water content decreases below 6 wt. %, both coordination number and distances determined from EXAFS are found to decrease. The hydrated ferric Nafion salt contains many isolated Fe(H2O)63+ complexes which convert to a ferric dimer in vacuum-dried ferric salts which has an isomer shift of 0.58±0.02 mm/s relative to iron and a quadrupole splitting of 1.73±0.04 mm/s at 80 K. The dimer is shown to be [(H2O)5Fe–O–Fe–(H2O)5]4+, having an Fe–H2O distance of 2.05±0.02 Å and a rather short Fe–O distance of 1.77±0.02 Å. The Fe–O–Fe bond angle is 155±20°.
Molecular dynamics investigation of the crystal–fluid interface. I. Bulk properties
Authors: Broughton Jeremy Q. , Gilmer George H.
Published: February 2003

Properties of the crystal and liquid phases have been measured for a system of particles interacting through a modified Lennard-Jones potential. Through constant pressure molecular dynamics, we have evaluated the density and internal energy of these phases at a pressure that approximates that of the vapor phase. The free energy of the crystal is obtained with the Einstein crystal as a reference state, and the liquid free energy is measured relative to the ideal gas. The triple point temperature is obtained. Compressibilities and Gruneisen parameters are obtained at zero temperature and the triple point. Dynamic properties of the supercooled liquid state are also calculated. These results are applied in forthcoming publications which calculate surface excess quantities and dynamic properties of the fcc (111), (100), and (110) faces.
Selective adsorption resonances in the scattering of helium atoms from xenon coated graphite: Close-coupling calculations and potential dependence
Authors: Hutson Jeremy M. , Schwartz Carey
Published: February 2003

Accurate close-coupling calculations are carried out for the scattering of helium atoms from a monolayer of Xe on the (0001) face of graphite, using atom-surface potentials based on pairwise additivity and the (known) He–Xe pair potential. Good agreement is obtained with the selective adsorption data of Bracco et al. The potential dependence of the resonance spectrum is explored, and it is found that the data are very sensitive to fine details; two pair potentials which both reproduce the gas phase data well, give significantly different resonance spectra, and the contributions of three-body forces are also shown to be important. The resonance spectra are significantly affected by small changes in the corrugation strength as well as by the laterally averaged potential. The potential dependence becomes even more pronounced as the scattering energy is decreased.
Dynamic light scattering studies of gelatin gels
Authors: Hwang J. S. , Cummins H. Z.
Published: February 2003

Gels formed from very polydispersive gelatin solutions were studied by intensity fluctuation spectroscopy. Single exponential autocorrelation functions were obtained for gelatin gels with and without a crosslinking agent. The elastic continuum model was found to adequately describe all the observed properties. As the concentration increases the cooperative diffusion coefficient Dc of the polymer network decreases in the solution state, but increases in the gel state. For gels without a crosslinking agent, the decay rate of the correlation function was found to remain constant after it reached a terminal value several hours after its temperature was lowered to 20 °C. However, for gels with a crosslinking agent, the decay rate continuously increased and the spatial correlation length became shorter with time.
A non-Gaussian theory of rubberlike elasticity based on rotational isomeric state simulations of network chain configurations. I. Polyethylene and polydimethylsiloxane short-chain unimodal networks
Authors: Mark J. E. , Curro J. G.
Published: February 2003

The present theoretical approach to rubberlike elasticity is novel in that it utilizes the wealth of information which rotational isomeric state theory provides on the spatial configurations of chain molecules. Specifically, Monte Carlo calculations based on the rotational isomeric state approximation are used to simulate spatial configurations, and thus distribution functions for the end-to-end separation r of the chains. Results are presented for polyethylene (PE) [CH−2] and polydimethylsiloxane (PDMS) [Si(CH3)2–O–] chains most of which are quite short, in order to elucidate non-Gaussian effects due to limited chain extensibility. Large values of r were found to be more prevalent in PDMS than in PE, primarily because of the unusually large Si–O–Si bond angle in the PDMS chain, which increases its spatial extension. The use of these distribution functions in place of the Gaussian function for network chains gives upturns in modulus at high elongations, because of the rapidly diminishing number of configurations consistent with the required large values of r, and thus, correspondingly large decreases in the entropy of the network chains. Networks of PDMS should have values of the non-Gaussian increases in modulus significantly different from those for (amorphous) PE networks having the same number of skeletal bonds and stretched to the same relative length.
Numerical study of the bi-variational SCF method as a zeroth order dilated electron propagator
Authors: Mishra Manoj , Goscinski Osvaldo , Öhrn Yngve
Published: February 2003

Eigenvalues of a bi-variationally obtained effective Hamiltonian are studied as the poles of a zeroth order dilated electron propagator. Their role as the zeroth order estimate of resonance energies and widths in the iterative solution of the dilated electron propagator equations is stressed. Applications to the Be atom are presented.
Application of the second order dilated electron propagator to the treatment of Auger and shape resonances of Be
Authors: Mishra Manoj , Goscinski Osvaldo , Öhrn Yngve
Published: February 2003

The adequacy of the bi-variational SCF based second order dilated electron propagator in the treatment of (N+1) and (N−1) electron resonances through calculations on the N-electron target is examined by using it to study the 2P shape and (1s−1) Auger resonances of Be.
A stationary formulation of time-dependent problems in quantum mechanics
Authors: Pfeifer Peter , Levine R. D.
Published: February 2003

A unifying framework is presented which treats time-dependent problems in nonrelativistic quantum mechanics on equal footing with stationary ones. This is accomplished by elevating time t to the role of a dynamical variable and considering evolution in an extended space with respect to a progress variable τ. Among the new objects in the extended space are the time operator as well as operators, such as energy, that are not diagonal in time. The latter bear, e.g., on the question of ‘‘quantum chaos.’’ Only τ-stationary states in the extended space are necessary to recover all of the Schrödinger time evolution. In particular, time-dependent constants of the motion (and these include time-evolved density matrices) elevate to stationary constants of the τ motion. Time-dependent problems, which may also involve time-dependent Hamiltonians, can then be solved by stationary-state methods. Special attention is given to applications based on time-dependent constants of the motion and to maximum-entropy states subject to time-dependent constraints. Two examples (rank-one perturbation, damped harmonic oscillator) illustrate some of these ideas. Scattering theory in the extended space is discussed in two appendices. It furnishes a picture of Hamiltonian τ evolution which promises to embrace also irreversible dynamics.
Diffusion-controlled reactions: A variational formula for the optimum reaction coordinate
Authors: Berkowitz Max , Morgan J. D. , McCammon J. A. , Northrup S. H.
Published: February 2003

The preferred path for a diffusion-controlled reaction depends, in general, upon global properties of the potential surface and the frictional resistance to motion upon this surface. A variational formula for this path is derived. The corresponding Euler–Lagrange equations are examined for two important special cases.
A simple model for the ionization potential, electron affinity, and aqueous redox potentials of small semiconductor crystallites
Authors: Brus L. E.
Published: February 2003

Large semiconductor crystals have intrinsic electronic properties dependent upon the bulk band structure. As the crystal becomes small, a new regime is entered in which the electronic properties (excited states, ionization potential, electron affinity) should be strongly dependent upon the electron and hole in a confined space. We address the possibility of a shift in the photochemical redox potential of one carrier, as a function of crystallite size. As a semiquantitative guide, one might expect a shift on the order of h2/8em*R2 due to the kinetic energy of localization in the small crystallite. We model the elementary quantum mechanics of a charged crystallite using (a) the effective mass approximation, (b) an electrostatic potential for dielectric polarization, and (c) penetration of the carrier outside the crystallite in a cases of small effective mass. Shifts of several tenths of an eV appear possible in crystallites of diameter 50 Å. The carrier charge density reside near the crystallite surface if the effective mass is very small.
Polarized Raman spectra of oriented dipalmitoylphosphatidylcholine (DPPC). I. Scattering activities of skeletal stretching and methylene vibrations of hydrocarbon chains
Authors: Harrand Monique
Published: February 2003

A method of recording polarized Raman spectra of oriented phospholipids obtained from vesicle solution is described. The polarization as well as the observation of the sample between crossed polarizers shows that the molecules of DPPC are oriented nearly perpendicularly to the support. Calculation of the Raman scattering activities has been carried out by means of a simple process based on symmetry properties and additivity of elementary tensors (of C–C bonds or of CH2 groups). Since the molecules are randomly distributed around the z (chain) and Z (sample) axes, the components only depend on the tilting angle. When applied to the skeletal stretching vibrations, the method made it possible to explain the anomaly observed with DPPC (and polyethylene or other phospholipids), i.e., the νs (C–C) and νa (C–C) Raman lines are, respectively, stronger in the ZZ and ZX polarizations, contrary to what is expected when motions of the carbon atoms are considered. The scattering activities were also calculated for the methylene (stretching, rocking, twisting, wagging, and bending) vibrations and comparison with experimental intensities indicates a tilting of the chains of 15°–20°.
An x-ray reflectance study of the liquid–vapor interface of Cs
Authors: Sluis Douglas , Rice Stuart A.
Published: February 2003

We report the results of a study of the angular dependence of the reflection of CrKα x rays from the liquid–vapor interface of cesium. It is shown that the data are consistent with the prediction, by D’Evelyn and Rice, that the liquid–vapor interface of cesium is stratified. Other theoretical models of the liquid–vapor interface are also compared with the experimental data. The Mon–Stroud model is shown to be inconsistent with those data. A model with a monotone density profile only 0.7 atomic diameters wide will fit the experimental data, but it is argued that this model is physically inconsistent, since the restriction of the outermost atoms to lie within ±0.35 diameters of a plane is likely to force stratification of the neighboring liquid for a few atomic diameters.
Radiative transition probabilities, lifetimes, and dipole moments for all vibrational levels in the X 1Σ+ state of the beryllium hydride ion
Authors: Ornellas Fernando Rei , Stwalley William C. , Zemke Warren T.
Published: February 2003

The dipole moment function, vibrationally averaged dipole moment, radiative transition probabilities and radiative lifetimes are computed for all vibrational levels and selected rotational levels of the beryllium hydride molecule ion in the X 1Σ+ state.
Spectroscopic studies of the jet-cooled copper trimer
Authors: Morse Michael D. , Hopkins J. B. , Langridge-Smith P. R. R. , Smalley R. E.
Published: February 2003

Gas phase spectroscopic studies of copper trimer are reported. A band system in the 5430–5225 Å region has been assigned to Cu3 and has been studied by resonant two-photon ionization spectroscopy, spectroscopy by depletion through predissociation, and by radiation repopulation of excited vibrational states in a cold supersonic molecular beam. The spectrum fits well to a 2E″←2E′ transition of a D3h molecule with both states undergoing Jahn–Teller distortions. In this interpretation, the excited state is well described by a weak Jahn–Teller effect, stabilizing the molecule at a configuration in which one Cu–Cu bond length differs from the others by 0.03 Å, with a Jahn–Teller stabilization energy of 9 cm−1. The ground electronic state corresponds to a deep Jahn–Teller situation with the lowest vibronic levels trapped in the distorted configuration. The spectra indicate the tunneling splitting of the lowest vibrational levels in the ground state is 12±7 cm−1. These assignments are based on measured vibrational band positions and may not be unique. Definitive determination of the copper trimer structure will require analysis of rotational fine structure which was unresolved with the laser sources available in this study.
Energies and intensities of the KLL Auger spectra of SiH4, PH3, HCl, and Ar
Authors: Vayrynen J. , Sodhi R. N. , Cavell R. G.
Published: February 2003

The KLL Auger electron spectra of gaseous SiH4, PH3, HCl, and Ar have been measured using TiKα x-ray excitation and, in the case of HCl, by bombardment with 5 keV electrons. The atomic-like spectra have been decomposed into the line components. The experimental relative energies and intensities of the Auger lines and the group intensities deduced therefrom are compared with the theoretical calculations as well as with previous experimental and theoretical predictions. Calculations in this work are based on the intermediate coupling (IC) scheme with final ionic state configuration interaction (FISCI). Intensity calculations have been made both with radial integrals calculated by McGuire and by Walters and Bhalla. Relative energies were calculated using the theoretical values of Fk and Gk from Mann’s tables. Theoretical binding energies and spin-orbit splittings were calculated from tables of Huang et al. A comparison shows that through this series the relative positions of Auger components are well predicted by theory, but the relative intensities of 2s−12p−1(1P1) and 2s−2(1S0) components are lower than theoretical values for PH3, HCl, and Ar. The experimental group intensity of I(KL1L23) is lower and of I(KL2,3L2,3) higher than theoretical predictions.
Single-collision chemiluminescence study of the Ba(1S,3D)+NO2, N2O, O3 reactions
Authors: Cox John W. , Dagdigian Paul J.
Published: February 2003

Chemiluminescence from the reactions of Ba ground state 6s2 1S and metastable 6s5d 3D atoms with NO2, N2O, and O3 has been studied under single-collision conditions. Spectra, chemiluminescence cross sections, and photon yields for production of BaO* are reported. In the Ba(3D)+N2O and Ba(1S, 3D)+O3 reactions, a red feature, not previously reported, has been observed and tentatively assigned as BaO D 1Σ+–A 1Σ+ emission. The dynamics of these reactions and the differences between the Ba and lighter alkaline earth atom reactions are discussed.
Three dimensional quantum mechanical studies of D+H2 → HD+H reactive scattering. V. Cross sections and rate constants from the adiabatic T matrix theory
Authors: Sun J. C. , Choi B. H. , Poe R. T. , Tang K. T.
Published: February 2003

The adiabatic T matrix method is used to carry out a three dimensional quantum mechanical calculation for the reactive scattering of D+H2 on an ab initio potential surface. Total and differential cross sections as well as final state distributions are obtained. When compared with adiabatic distorted wave results, agreement is good except the present total cross section is larger. When compared with trajectory calculations, agreement is also good except for the threshold behavior and the final state distribution. The rate constants obtained from the present total reaction cross sections are in very good agreement with measurements. With the analysis of the center of mass to laboratory transformation for the trajectory calculations and the comparison between those results and present ones, differential cross sections and final state distributions obtained in the present calculation are also seen to be in agreement with the molecular beam experiment.
The origin of cross section thresholds in H+H2: Why quantum dynamics appears to be more vibrationally adiabatic than classical dynamics
Authors: Schatz George C.
Published: February 2003

In this paper, cross sections and J=0 reaction probabilities from the results of quasiclassical trajectory (QCT) and accurate quantum reactive scattering calculations are presented and compared for H+H2 (v=0) and H+H2 (v=1). For both v=0 and v=1, the energies associated with the effective thresholds for reaction in the quantum results are consistent with the adiabatic treatment of bending motions along the reaction coordinate. This is best illustrated by comparing the 3D J=0 reaction probabilities with those from analogous collinear calculations, and with collinear calculations in which the bending zero point energy is added in adiabatically at every point in collinear configuration space. The quasiclassical trajectory cross sections and probabilities, on the other hand, have thresholds which are well below the quantum thresholds, primarily because of reactive trajectories which have little or no energy in bending near the effective reaction bottleneck. This effect is especially important for H+H2 (v=1) and leads to QCT rate constants which are much higher than the quantum ones at 300 K. Classical methods designed to reduce this threshold error are studied, and the most successful of these is one in which the local bending zero point energy is added adiabatically in the full dimensional configuration space. The origin of the threshold error is examined, and it is found that the constraints associated with the uncertainty principle rather than with vibrational adiabaticity are the most important in determining the threshold behavior associated with bending. These constraints lead to the prediction that the vibrationally adiabatic (ground bending state) threshold is the correct one, which means that the quantum threshold appears to be governed by adiabatic theory even when motional time scales are such that the adiabatic approximation is invalid. The classical threshold, on the other hand, is close to the adiabatic threshold only when motional time scales are appropriate.
Vibrational relaxation of CO+(A 2Πi, v′=1) and CO+(B 2Σ+, v′=1) ions in the collision with CO molecules
Authors: Ibuki Toshio , Sugita N.
Published: February 2003

The vibrationally selected CO+(A 2Πi, v′=0,1) and CO+(B 2Σ+, v′=0,1) ions were generated by the photoionization of CO using Ne and He resonance lamps, respectively. The quenching cross sections of the excited ions were found to be very large and exceed gas kinetic values in the B 2Σ+ state. In both excited states it has been observed that the vibrationally excited v′=1 ion relaxes to v′=0 level through the collision with the parent CO molecules. The branching ratio of quenching to relaxation in the v′=1 ions was explained by a cascading relaxation mechanism in which all the vibrational levels underlying the excited v′=1 level contribute to the energy transfer.
Temperature effects in the time-correlator theory of resonance Raman scattering
Authors: Chan C. K. , Page J. B.
Published: February 2003

Within well-defined ‘‘standard’’ assumptions and the time-correlator theory’s separation of resonance Raman (RR) scattering into orders, previously discussed exact relations allow one to calculate mth-order RR profile line shapes directly from optical absorption data at T≠0 K. At T=0 K, the mth-order profiles are identical with the full m-phonon profiles, which are the experimentally measured quantities, while for T≠0 K, the m-phonon profiles include higher-order corrections due to processes which freeze out at T=0 K and which involve virtual phonon excitation–deexcitation in all Franck–Condon active modes. In this paper we show that for one-phonon scattering from a large class of multimode systems, the correction due to a thermally populated mode is small if (1) the mode’s frequency is small compared with the smallest resolvable width in the optical absorption and/or (2) the mode’s electron–phonon coupling is weak. For the multimode system β-carotene in isopentane at T=123 and 298 K, the sum of corrections due to all thermally populated Franck–Condon active modes is found to be negligible, so that even at room temperature, the first-order and one-phonon profiles are essentially identical. Our first-order profile line shapes calculated from optical absorption data for T=123 and T=298 K account well for the observed thermal broadening and are in good overall agreement with the measured one-phonon profiles. A short-time approximation is developed and is shown to give insight into our numerical results—in particular, in the limit of a large number of thermally populated low-frequency modes of comparable electron–phonon coupling strengths, the sum of these modes’ higher-order corrections to the one-phonon profiles is shown to vanish. The negligibility of the higher-order corrections leads to efficient T≠0 K multimode numerical modeling procedures which allow one to conveniently obtain both the optical absorption and RR profiles from a single one-dimensional fast Fourier transform of the absorption time-correlator. Generalizations to mth-order scattering are briefly discussed.
Laser excited fluorescence and infrared absorption spectra of Pr+3: LaCl3
Authors: Rana R. S. , Kaseta F. W.
Published: February 2003

Laser excited fluorescence and infrared absorption spectra of single crystals of praseodymium diluted with anhydrous lanthanum trichloride was examined. A number of new fluorescing levels have been observed, numerous additional crystal field components identified, and a more complete energy level scheme is presented.
CO−2 ions in a low pressure glow discharge of carbon dioxide
Authors: Kumar S. V. Krishna , Venkatasubramanian V. S.
Published: February 2003

CO−2 ions have been detected in the gas phase and measured by a mass spectrometer with a flight time of 30 μs in the positive column of carbondioxide glow discharge. (AIP)
Transient nucleation in condensed systems
Authors: Kelton K. F. , Greer A. L. , Thompson C. V.
Published: February 2003

Using classical nucleation theory we consider transient nucleation occurring in a one-component, condensed system under isothermal conditions. We obtain an exact closed-form expression for the time dependent cluster populations. In addition, a more versatile approach is developed: a numerical simulation technique which models directly the reactions by which clusters are produced. This simulation demonstrates the evolution of cluster populations and nucleation rate in the transient regime. Results from the simulation are verified by comparison with exact analytical solutions for the steady state. Experimental methods for measuring transient nucleation are assessed, and it is demonstrated that the observed behavior depends on the method used. The effect of preexisting cluster distributions is studied. Previous analytical and numerical treatments of transient nucleation are compared to the solutions obtained from the simulation. The simple expressions of Kashchiev are shown to give good descriptions of the nucleation behavior.
Free energy for the heterogeneous systems with spherical interfaces
Authors: Yang Arthur Jing-Min
Published: February 2003

The correct definition for Gibbs free energy is derived for a one component fluid system with a spherical interface. It is obtained by following a reversible path at constant T, P, and N. The process is generalized to discuss the free energies for a liquid drop containing a nucleus and for a multicomponent system containing more than one droplet. The change in Helmholtz free energy for the formation of a liquid drop from supersaturated vapor is also discussed.
Solvation energy of ions in dipolar solvents
Authors: Garisto Frank , Kusalik P. G. , Patey G. N.
Published: February 2003

The solvation energy of hard spherical ions immersed in dipolar hard sphere solvents is investigated as a function of ion diameter. We apply both the mean spherical and linearized hypernetted-chain approximations and show that for ions of physically realistic size both theories give qualitatively similar results. The ion solvation energy is obtained as the sum of two competing terms: UID, the direct ion–solvent interaction energy, which is negative, and UDD, the change in the solvent–solvent interaction energy per ion at infinite dilution. UDD is found to be positive and to make an important contribution to the solvation energy for all ion diameters.
Vibrational excitation in molecule–surface collisions due to temporary negative molecular ion formation
Authors: Gadzuk J. W.
Published: February 2003

Inelastic electron scattering from gaseous and physisorbed diatomic molecules results in greatly enhanced vibrational overtone excitation if the incident electron has the appropriate energy to form a shape-resonance-induced temporary negative molecular ion. It is proposed here that due to the image potential lowering of the electron affinity level of a diatomic molecule in interaction with a metal surface, somewhere outside the surface an incident molecule would find its affinity level degenerate with or lower than the substrate Fermi level at which point a substrate electron could hop onto the molecule, in analogy with gas phase harpooning processes. A negative molecular ion is thus formed which remains until the molecular ion reflects from the surface and the affinity level rises above the Fermi level, thus permitting reverse electron hopping back into the metal. The lifetime of the molecular ion can be controlled by varying both the kinetic energy of the incident molecule and also the substrate work function. In analogy with the electron scattering events, greatly enhanced vibrational excitation of overtones is expected in the molecules of the scattered beam. Induced fluorescence probing of the vibrational state distribution should then yield fundamental information pertaining to the dynamics of charge transfer reactions and nonadiabatic effects in molecule–surface interactions. A theory of this phenomenon is here presented together with the numerical consequences for a model system designed to simulate N2 or NO scattering from standard surface science metal surfaces.
Vibrational dephasing in molecular mixed crystals: A picosecond time domain CARS study of pentacene in naphthalene and benzoic acid
Authors: Duppen Koos , Weitekamp D. P. , Wiersma Douwe A.
Published: February 2003

Multiresonant time-domain coherent anti-Stokes Raman scattering (CARS) experiments have been employed in a study of the decay of vibrational coherences of pentacene doped into naphthalene and benzoic acid. In all cases, the CARS decay is found to be exponential, which indicates that the electronic and vibronic inhomogeneities in this system are strongly correlated. The temperature dependence of vibrational dephasing shows no effect of coupling to the lowest-frequency librational mode of pentacene that is known to dominate electronic dephasing. This surprising result can be understood on basis of a dephasing model where rapid coherence exchange exists between a cold vibrational transition and a corresponding near-resonant librationally hot one. For the 767 cm−1 vibrational transition, oscillations of the CARS signal as a function of delay are shown to arise from interference at the detector with a nearby naphthalene host signal. An inconsistency with a previously reported spontaneous Raman study is resolved by showing that the signal observed there is actually site-selected fluorescence.
Low-frequency Raman spectrum of supercooled water
Authors: Krishnamurthy S. , Bansil R. , Wiafe-Akenten J.
Published: February 2003

We report measurements of the Raman spectrum of supercooled water in the hindered translational region (20–400 cm−1) down to a temperature of −20 °C. The spectra are analyzed after correcting for the effects of Boltzmann factor and harmonic oscillator coupling, i.e., in the reduced R(ν̄) representation of Shuker and Gammon. Spectral deconvolution shows that in addition to the previously observed 0-0-0 bending mode (≂60 cm−1) and the 0-0 stretching mode (≂190 cm−1), there is a weak feature at 260 cm−1 whose intensity increases by almost an order of magnitude as temperature decreases from 40 to −20 °C. A plausible interpretation of the 260 cm−1 band is that it is analogous to the 310 cm−1 band seen in ice I and probably arises because of differing electrostatic interactions in different configurations of coupled H bonds of neighboring H2O molecules. The 0-0 stretching band at 190 cm−1 changes in many respects as temperature decreases from 40 to −20 °C: (i) Its peak intensity increases almost four times; (ii) integrated intensity increases three times; (iii) bandwidth decreases about 30%; and (iv) peak maximum increases linearly from 176 cm−1 at 40 °C to 202 cm−1 at −20 °C. In contrast, the 0-0-0 bending at 60 cm−1 is quite insensitive to changes in temperature. The increase in the intensity of the 190 and 260 cm−1 bands is consistent with the idea that four-coordinated H2O molecules contribute directly to these spectral features and the fraction of such molecules increases with decreasing temperature. This effect on intensity is further enhanced by the strong coupling of the motion of a few four-coordinated water molecules, as seen in the small-angle x-ray scattering data of Bosio et al. We also observe a limiting value to the width of the 190 cm−1 band at temperatures below the melting point, suggesting that the local structure of supercooled water is approaching some limiting structure.
Emission, ground, and excited state absorption spectroscopy of Cr2 isolated in Ar and Kr matrices
Authors: Pellin M. J. , Gruen D. M.
Published: February 2003

Irradiation into either of the two resonance transitions of Cr atoms in Kr matrices results in strong bleaching of the atomic absorptions and simultaneous growth of two Cr2 dimer bands. The lower energy band of Cr2 at ∼470 nm is the well-known 1Σ+u → 1Σ+g transition. The higher energy band at ∼340 nm we assign to the 1Πu ← 1Σ+g transition which occurs at almost the same energy as, and is therefore obscured by, the y7P0 ← a7S transition of normally present Cr atoms in Kr (and Ar) matrices. Laser induced fluorescence from the ∼470 nm band gives a broad, featureless emission presumably because of extensive predissociation after cage relaxation of the excited 1Σ+u state. Emission after excitation of 1Πu ← 1Σ+g transition yields a four member progression with spacing of ∼240 cm−1. The spectrum is consistent with emission from a 3Σg ‘‘trap’’ level to a lower lying 3Σu state, ∼8000 cm−1 above ground. An energy level diagram of the Cr2 molecule is presented which incorporates all of the spectroscopic information available on the dimer.
Excitation spectra of neutral fragments emissions by photodissociation of OCS using VUV photons
Authors: Tabché-Fouhaile A. , Hubin-Franskin M. J. , Delwiche J. , Fröhlich H. , Ito K. , Guyon P. M. , Nenner I.
Published: February 2003

The Rydberg series converging to the B̃ 2Σ+ state of OCS+ are shown to be predissociated by dissociative states leading to CS (A 1Π) and to CO triplet levels. The decay of these excited fragments is observed by their fluorescence in the visible and ultraviolet ranges. The corresponding fluorescence cross section in the 280–630 nm range is roughly estimated not to exceed 3% of the absorption. These dissociative states are very likely involved in the mechanism of resonant autoionization.
Numerical simulation of the coherent anti-Stokes Raman scattering spectrum of CO2
Authors: Papineau N. , Péalat M.
Published: February 2003

A CARS spectrum of natural CO2 under normal conditions of temperature and pressure has been recorded in the 1210–1480 cm−1 range with a resolution of 0.07 cm−1. We have observed the Q branches of the fundamental bands ν1 and 2ν2 of the different species of natural CO2 and several hot bands of the isotopic species 12C 16O2. We have also assigned the O and S lines, for all these bands, and some of the weak P and R lines of the first hot bands. A theoretical calculation of line positions and intensities has been performed taking into account Fermi resonance as well as l-type doubling and Coriolis interaction. For the Q branches we have made a calculation with due account for motional narrowing. The entire spectrum has thus been simulated and the agreement with the experimental spectrum is excellent.
Magnetic vibrational circular dichroism of methyl halides in solution
Authors: Devine T. R. , Keiderling T. A.
Published: February 2003

The magnetic vibrational circular dichroism of four methyl halides in CCl4 solution has been measured. Contrary to expectations based on available theoretical models for MVCD, predominantly B-term MVCD is found for both the A1 and E C–H stretching vibrations. MVCD of these two modes are opposite in sign for each of the CH3X species, and their relative intensity and ΔA/A values vary systematically with halogen mass. Similar results are found in the CH3 deformation region. MVCD of the N–H stretches in NH3 is also presented for sake of comparison.