bluuebunny/crossref_metadata_2025 huggingface dataset:
Time independent methods in semiclassical mechanics: Adiabatic switching
Authors: Jaffé Charles
Published: July 2002

A time independent algorithm based upon Ehrenfest’s adiabatic hypothesis for the construction of the transformation from the physical variables to a set of action-angle variables is presented. At the heart of this algorithm is the recognition that the switching parameter need not be treated as a function of time. The calculations of semiclassical energy levels and dipole matrix elements for the simple quartic oscillator are presented to illustrate this approach.
Spectroscopic identification of the lowest rotation–vibration levels of the (2pσ)2 F 1Σ+g state of the D2 molecule
Authors: Senn P. , Quadrelli P. , Dressler K. , Herzberg G.
Published: July 2002

The previously unobserved lowest vibrational levels of the F state of D2 are detected by the identification of F 1Σ+g–B 1Σ+u bands in infrared emission spectra of electric discharges recorded with a Fourier–transform spectrometer. The rotation–vibration structure of the F state, v=0–5, J=0–5, is in good agreement with accurate ab initio calculations which include the effects of tunneling in the double-minimum potential of the EF  1Σ+g state. For the v=J=0 levels of H2 and D2 the absolute energy error of the ab initio calculation extrapolates, for infinite nuclear mass, to an error of the electronic F state energy of +0.7±0.1 cm−1. This is consistent with Jungen’s recent accurate spectroscopic determination of the ionization potentials of the excited states of H2.
Kinetics of phase separation in the presence of slowly relaxing structural variables
Authors: Binder K. , Frisch H. L. , Jäckle J.
Published: July 2002

The linearized Cahn–Hilliard theory of spinodal decomposition of binary mixtures is generalized to the case where there is a coupling to a slowly relaxing variable (e.g., phase separation of polymer mixtures near a glass transition, etc.). A very simplified model calculation is presented which shows that even in the very early stages pronounced deviations may occur from the simple exponential growth predicted by the standard linear theory. Also the growth rate of the unstable fluctuations is strongly affected: A regime is identified where the initial growth rate is independent of wave number k and controlled by the relaxation rate of the structural variable, rather than given by the standard ‘‘uphill diffusion’’ with diffusivity linearly decreasing with k2. Possible applications of these ideas to real systems are briefly discussed.
Contribution of the fine structure terms to the g values of the biological Fe iii–Fe ii clusters
Authors: Guigliarelli Bruno , Bertrand Patrick , Gayda Jean-Pierre
Published: July 2002

The states of the different spin multiplets which result from the antiferromagnetic interaction in the Fe iii–Fe ii pairs are mixed by the fine structure Hamiltonians relative to each iron atom. The contribution of this effect to the g values of the lowest Kramers doublet is discussed for 2Fe clusters present in different groups of metalloproteins. Special attention is given to iron–sulfur proteins and hemerythrins where models have been developed to discuss the structural implications of the magnetic properties.
Two-photon dissociation of vibrationally excited HD+: The inhomogeneous differential equation approach
Authors: Laughlin Cecil , Datta Krishna K. , Chu Shih-I
Published: July 2002

We extend the inhomogenous-differential-equation (IDE) approach of Dalgarno and Lewis for a detailed study of two-photon dissociation (TPD) of HD+ from high vibrational levels of the 1sσg electronic state. Contrary to the H+2 case, where the TPD cross sections σ(2)L are largest near TPD thresholds and decrease monotonically with increasing photon energy, the HD+ cross sections are characterized by rich resonant and interference structures. We present σ(2)L results for TPD from the initial vi =6, 8, 10, 12, 14, 16, and ji=0 levels as well as from vi=14, ji=0, 2, 4 levels for a wide range of wavelengths of linearly polarized radiation accessible by CO2 and CO lasers. It is found that while there are four TPD pathways, the channel 1sσg(vi ji)→ω 1sσg(v, j=ji±1) →ω2pσu(k, j f=j±1) dominates the two-photon process in most of the cases we have studied. Further, the results show that σ(2)L increases rather rapidly as the initial vibrational quantum number vi increases, indicating that the hereronuclear diatomic molecules in high vibrational levels can be efficiently two-photon dissociated by IR lasers. Consequently molecular structures near the dissociation limit may be conveniently probed by two-photon spectroscopy—as has indeed been demonstrated recently by experiments. Our σ(2)L results thus provide complementary information to the HD+ spectroscopic data obtained recently by Carrington et al.
Anomalous rotational-state distribution of NO A state in UV photodissociation of rare gas–NO van der Waals complexes. Rotational rainbow effect
Authors: Sato Kenji , Achiba Yohji , Nakamura Hiroki , Kimura Katsumi
Published: July 2002

Rotational distribution of NO in the Rydberg A state produced in photodissociation of the Ar–NO and Ne–NO van der Waals complexes have been measured for the first time by using a (1+1) resonant ionization technique in the region 44 350–44 800 cm−1. Two eminent maxima have been observed in the distributions at all the laser energies studied. Dependences of these maxima on the excess energy and the reduced mass have been found to be the same as those of the rotational rainbow peaks in rotationally inelastic scattering. Theoretical formulation is given here for the photodissociation of a triatomic molecule. With a half-collision approximation and a certain assumption about the Franck–Condon factor, the photodissociation cross section has been shown to be proportional to a partial cross section for rotationally inelastic atom–diatom collision. The partial cross sections are calculated by the quantum mechanical close-coupling method with the use of a model potential which mimics the potential for the relevant ArNO system. These calculations strongly support the experimentally observed anomalous rotational-state distribution is a manifestation of the rotational rainbow effect. The upper limits of the dissociation energies of the van der Waals complexes have also been estimated from the highest accessible rotational levels of the photodissociation products.
New Slater-type orbital basis sets for first row transition elements
Authors: Bernardo L. A. G. , Sordo J. A.
Published: July 2002

A comparative study, at the atomic level, of the quality of eight Slater-type orbitals (STO) basis sets has been carried out for the first row transition elements. Two new basis sets are proposed for these elements: the β1 basis set (small-size-type) and the α2 basis set (intermediate-size-type). Both basis sets have been developed according to the so-called δ test [J. A. Sordo and L. Pueyo, Int. J. Quantum Chem. XXVIII, 687 (1985)]. The results suggest that the errors detected by means of the δ test could be responsible for the wrong ordering predicted by 2-ζ (and lower quality basis sets) for the 4s13d10 (2S) and 4s23d9(2D) states in Cu. All the quality tests used indicated that β1 basis sets would be very appropriate for performing economical molecular calculations and that α2 basis sets, with only one STO more than 2-ζ basis sets, would provide atomic results near the Hartree–Fock limit.
The underlayer influence on photoemission and thermal desorption of xenon adsorbed on Ag(111)
Authors: Behm R. J. , Brundle C. R. , Wandelt K.
Published: July 2002

Combined UV and x-ray photoelectron spectroscopy, work function, and thermal desorption measurements are presented for the submonolayer to multilayer adsorption of xenon on a Ag(111) surface. The results compliment the detailed LEED studies of this system by Webb and co-workers. Successive layer-by-layer growth up to at least three Xe layers is seen from the variation of the XPS Xe (3d5/2) intensity as a function of exposure. The thermal desorption of xenon from the first and second layer is compatible with zeroth order desorption kinetics. This is suggestive of desorption from 2D solid Xe islands, in agreement with the first order phase transitions during population of the first and second layer observed by Webb et al. The adsorption energies of the first and second layer are estimated to be E1ad=5.2 and E2ad=4.3 kcal/mol, respectively. The dipole moment per xenon atom in the first layer has the coverage independent value of μ1(Xe)=0.2D. Particular emphasis is put on the discussion of the layer dependent photoemission behavior of xenon. The present work includes the first complete set of UPS and XPS electron binding energies for Xe on one and the same metal. Comparison of the layer values with those of other Xe/metal systems as well as their layer dependent shift provide twofold support for the notion that the electron binding energies (with respect to EF) of adsorbed xenon atoms ‘‘float’’ with the local electrostatic surface potential of the respective adsorption site. This is further supported by some measurements for xenon adsorbed on a sputter-roughened Ag surface. Both the adsorption energy as well as the photoemission behavior of xenon are sensitive towards the surface topography, which in turn can be utilized for the characterization of surface defects induced by sputtering.
Collective dynamics in three body water and sound dispersion
Authors: Wojcik Mark , Clementi Enrico
Published: July 2002

The collective properties of two and two plus three body models of liquid water are studied by molecular dynamics simulation. The three body forces retard the time decay of liquid structure and the diffusion of thermal energy, and also increase the viscosities. Positive dispersion in the sound velocity that is observed in the two body liquid for 0.25≤k≤0.6 Å−1 is even stronger in the three body liquid. From a comparison with various simple liquids it appears that the strength of the longer ranged attractive forces in the intermolecular potential is responsible for this phenomenon. The interpretation of recent experimental neutron scattering data is discussed in the light of the behavior of the simulated liquids and of a generalized hydrodynamics model, and no evidence is found for the existence of a second independent sound mode in water.
Magnetic interactions in HCF and HSiF studied by sub-Doppler spectroscopy
Authors: Suzuki Tetsuo , Hirota Eizi
Published: July 2002

The Ã 1A″(000)–X̃ 1A′(000) band has been observed for HCF and HSiF at sub-Doppler resolution using the intermodulated fluorescence (IMF) technique. The hyperfine structure due to the 19F nuclear spin/overall rotation interaction has been resolved for HCF, yielding the following coupling constants: C″aa =4.19(14) and Caa =−7.71(20) MHz with one standard error in parentheses for the X̃ and Ã states, respectively. In contrast, no hyperfine structure has been observed for HSiF. The Zeeman effect has also been examined for both species by IMF, and the following rotational g factors have been derived: g″aa =−5.69(37)×10−3 and gaa =(5–10)×10−3 for X̃ and Ã of HCF, respectively, and g″aa =−1.47(9)×10−3 and gaa =1.57(11)×10−3 for X̃ and Ã of HSiF, respectively, all in the unit of Bohr magneton with one standard error in parentheses. The two types of molecular constants thus determined have been discussed in terms of electronic Coriolis interaction between the X̃ and Ã states in each of the two molecules.
Solubility of xenon in amino-acid solutions
Authors: Pollack Gerald L. , Himm Jeffrey F.
Published: July 2002

We have measured the Ostwald solubility (L) of 133Xe at 25.0 °C in aqueous solutions of the amino acids: alanine (0–1.8 M), arginine (0–0.9 M), glycine (0–2.1 M), hydroxyproline (0–2.3 M), lysine (0–2.8 M), and proline (0–3.5 M) as well as sucrose (0–2.25 M) and NaCl (0–5.25 M). Over the concentration ranges investigated L decreases, monotonically and approximately linearly, with increasing concentration for amino acids and sucrose. The effect on gas solubility of amino acid in solution can be large, e.g., for 133Xe, we measured L(25.0 °C)=0.1060 in distilled water but L(25.0 °C)=0.055 for a 2.8 M lysine solution. The results can be used to calculate hydration numbers (H), i.e., the number of H2O molecules associated with each solute molecule. The average values of hydration number (H̄) obtained at 25.0 °C are 7.9±0.6 for alanine, 0.2±0.5 for arginine, 8.5±0.6 for glycine, 4.5±0.4 for hydroxyproline, 6.1±1.1 for lysine, 2.0±0.2 for proline, and 3.9±0.7 for sucrose.
Vibronic structure of magnetic circular dichroism (MCD) spectra. II. Perturbational treatment of vibronic coupling effects in molecules with nondegenerate electronic states
Authors: Zgierski Marek Z.
Published: July 2002

Vibronic coupling effects in the MCD spectra of polyatomic molecules with nondegenerate electronic states are studied theoretically. The construction of vibronic wave functions for a molecule in which vibronic coupling can be treated by perturbation theory is discussed in detail. These wave functions are used directly in the calculation of the B term that governs the MCD spectra of the molecules studied. The approach allows the straightforward inclusion of differences in geometries and force fields between magnetically coupled electronic states (non-Condon effects, part I), it takes into account nonadiabatic effects and treats electric and magnetic transition dipole moments on an equal footing. Most of these contributions are neglected in previous treatments. The paper discusses different schemes of magnetic and vibronic couplings between the excited electronic states of a planar molecule for in-plane polarized electric dipole transitions. The theory is used to interpret the vibronic structure of the MCD spectra of anthracene, 9,10-dichloroanthracene and 2,3-dimethylanthracene in the region of the 1La and 1Lb electronic states. This analysis locates the zero-point levels of the hidden 1Lb states in these molecules and yields values for the displacement parameters of the 1400 cm−1 totally symmetric C–C stretching mode in the 1Lb states. It is shown that vibronic interactions via the 1462 cm−1 b1g mode between the 1La and 1Lb and between the 1La and 1Bb states play an important role in shaping the vibronic structure of these MCD spectra, although their main features are determined by non-Condon effects resulting from slightly different C–C bond lengths in the 1La and 1Lb states.
Convergence of direct space exchange lattice sums in polymer band structure calculations
Authors: Delhalle Joseph , Calais Jean-Louis
Published: July 2002

A study of the convergence properties associated with direct lattice summations of the exchange contributions to the quantities needed in a restricted Hartree–Fock calculation for a polymer, leads to a detailed analysis of the analytic and asymptotic properties of the Fock–Dirac density matrix in the LCAO representation. The results, obtained simply by means of Fourier analysis, provide an important characterization of the restricted Hartree–Fock method as applied to chain-like systems. As a by-product we obtain a general proof in direct space that a partially filled band, which influences drastically the analyticity properties of the density matrix in reciprocal space, leads to a logarithmically diverging derivative of the orbital energy at the Fermi level. This in turn gives a vanishing density of states at that level. This result, well known for the electron gas model, is thus an inherent property of the restricted Hartree–Fock approximation.
Generating function methods for macromolecules at surfaces. I. One molecule at a plane surface
Authors: Eichinger B. E. , Jackson David M. , McKay Brendan D.
Published: July 2002

The problem of a macromolecule adsorbed on a single surface is treated by means of a generating function technique. The basic method has the virtues of simplicity and flexibility. The statistical weights that appear in the generating functions for tails, trains, and loops can be calculated with use of a variety of models. The essential physics of the adsorption process, and the occurrence of a critical point, are transparent in this treatment. Illustrative calculations are done for the simplest case, in which tails have unit weight, trains have binding energies proportional to their lengths, and loops are weighted by lattice walk statistics. Methods for treating more realistic models for chains, and for handling their interactions when there is multiple chain adsorption, are discussed.
Role of binding energies in A− ⋅ B and A ⋅ B− complexes in the kinetics of gas phase electron transfer reactions: A−+B=A+B− involving perfluoro compounds: SF6, C6F11CF3, C6F6
Authors: Chowdhury Swapan , Kebarle Paul
Published: July 2002

Exothermic gas phase electron transfer reactions: A−+B=A+B−, where A and B are polyatomic molecules with positive electron affinities, generally proceed at collision rates. However, reactions involving A=SF6 or perfluorocycloalkanes have rates which decrease with the exothermicity of the reaction, becoming very slow at low exothermicity. Earlier work attributed this behavior to the presence of an energy barrier, due to a large geometry change for A− to A. The reaction coordinate used also involves the bond energies A− ⋅ B and A ⋅ B−. These were measured in the present work. It was found that the bond energy in SF−6 ⋅ B is much larger than in SF6 ⋅ B− . This difference increases the energy barrier very significantly and is thus an additional cause for the slow electron transfer. The bond energies for several other complexes like: Cl− ⋅ B, Cl− ⋅ SF6, Cl− ⋅ perfluorocyloalkanes, and Cl− ⋅ C6F6 were measured. These provide insights into the nature of the bonding involved. The work was performed with a pulsed electron high pressure mass spectrometer.
Reaction-path analysis of the tunneling splitting in fluxional molecules: Application to the degenerate rearrangement of hydrogen fluoride dimer
Authors: Hancock Gene C. , Rejto Paul , Steckler Rozeanne , Brown Franklin B. , Schwenke David W. , Truhlar Donald G.
Published: July 2002

The small-curvature semiclassical adiabatic (SCSA) approximation, which is based on a reaction-path Hamiltonian, is used to calculate the tunneling splitting due to the degenerate rearrangement of hydrogen fluoride dimer. The calculation employs a semiempirical potential energy surface which approximates the HF molecules as rigid rotators, and for which accurate tunneling splittings have been previously calculated. The semiclassical method is shown to be accurate within 33%. The internal motion of the dimer along the reaction path and the contributions of the generalized normal mode vibrations to reaction-path curvature in the tunneling region are also discussed.
Static reaction–diffusion structures in folded slow manifold systems
Authors: Sultan Rabih , Ortoleva Peter
Published: July 2002

Static dissipative structures are obtained analytically for multiple time scale systems with folded slow manifolds. We find that the associated free boundary problem displays much of the richness of the full reaction–diffusion system. For a simple one-dimensional structure the pattern is shown to be linearly stable. Spoke patterns in a disk are calculated exactly. Since one type of static pattern in a disk was shown earlier to unfold into a rotating wave, these patterns are also of interest as the basis for the analysis of a class of multiple arm rotors. In a second special limiting case the patterns are shown to be in the form of narrow ‘‘double layers’’ in two-dimensional systems. Double layer patterns in a disk are obtained.
Debye–Waller factor of the solid from the self-diffusion coefficient at the solid–liquid interface
Authors: Bagchi Biman
Published: July 2002

We present a theoretical calculation of the Debye–Waller factors of the solid from the self-diffusion coefficient at the solid–liquid interface. The calculated values are in good agreement with those obtained from the density functional theory of freezing.
Determination of the structure of HCl BF3
Authors: LoBue James M. , Rice Jane K. , Blake Thomas A. , Novick Stewart E.
Published: July 2002

The structure of the weakly bound complex HCl BF3 has been determined by molecular beam electric resonance spectroscopy. The molecule is a near prolate symmetric top with the chlorine atom 3.17 Å above the boron atom, on or very near the BF3 threefold axis. The B–Cl–H angle is close to 90°. The spectroscopic constants for the H35Cl11BF3 isotope are (B+C)/2=1774.117(4) MHz, DJ=5.6(5) kHz, eqQa(35Cl)=+25.761(8) MHz, eqQa(11B)=+2.672(25) MHz, and μa=0.484(5)D.
Superhyperfine interaction of the SiH3 radical with Xe
Authors: Nakamura Kazutaka , Masaki Nobuyuki , Sato Shin , Shimokoshi Kazuo
Published: July 2002

The SiH3 radical formed by the reaction of SiH4 with H in a Xe matrix was investigated by ESR spectroscopy. In addition to the spectra of the radicals SiH3 and SiH5 reported by the present authors [J. Chem. Phys. 83, 4504 (1985)], well resolved new lines were observed superimposed on a broad background signal. These lines were attributed to the superhyperfine structure of a species interacting with xenon nucleus. The magnetic parameters for the species which give rise to the superhyperfine structure were determined.
Stark effect on the 580 nm S1←S transition of isobacteriochlorin using photochemical hole-burning spectroscopy
Authors: Johnson Lawrence W. , Murphy Michael D. , Pope Cecille , Foresti M. , Lombardi John R.
Published: July 2002

High resolution excitation spectra of free base isobacteriochlorin in an n-octane crystal at 4.2 K have been obtained. In the 580 nm region (the 0–0 band of the lowest-lying singlet transition of the trans tautomer) five lines were observed. Using a tunable dye laser two pairs of these lines could be photochemically interconverted, while one line did not burn. With still narrower laser excitation, holes were burned in the four convertible lines which were limited in width by the laser output (0.07 cm−1). Electric fields were applied along each of the crystal axes and Stark splittings of the spectral lines and holes were observed. The splittings are linear over the range 1.21 to 50.0 kV/cm. The magnitude of the total dipole moment change (Δμ) for all lines was found to be 1.64 D; this is much larger (∼7×) than the value measured in free base chlorin. Also, the direction of this vector is a function of the position of the tautomers inner protons; it rotates 90° in going from one trans tautomer to the other. The direction cosines of the Δμ̄’s indicate that free base isobacteriochlorin’s orientation in the n-octane crystal is similar to that of free base chlorin, but with the second exterior reduced double bond rotated about 25° out of the alkane chain plane. Furthermore, the burning pattern of the 580 nm 0–0 bands verifies the earlier hypothesis that these are due to the trans tautomer.
Gaussian curvature in an Ising model of microemulsions
Authors: Hofsäss T. , Kleinert H.
Published: July 2002

We extend Widom’s Ising-like model of microemulsions on a simple cubic lattice by a new term which accounts for the Gaussian curvature energy of the oil–water interfaces. The new term distinguishes between different topologies of the interfaces and plays an important role in determining the microstructure of microemulsions on a scale larger or comparable to the persistence length provided that the microemulsion is dominated at all by curvature energies. We also speculate on its possible role for the breakdown of curvature energies in microemulsions.
Electrolyte friction on charged spherical macroparticles: Beyond the Debye–Hückel limit
Authors: Vizcarra-Rendón A. , Ruíz-Estrada H. , Medina-Noyola M. , Klein R.
Published: July 2002

The contribution to the friction coefficient of a charged spherical polyion diffusing in an ionic solution due to its interactions with the electrolyte ions is calculated, in the absence of hydrodynamic interactions, starting from a formal expression for ζel previously derived by Medina-Noyola and Vizcarra-Rendón. It is shown that such a formal expression can be given a particularly simple form in terms of the equilibrium distribution neqi(r) of the small ions around the tracer, which allows us to study effects ignored in Debye–Hückel level theories. We consider, for example, the effect of a finite size of the small ions and nonlinear contributions to ζel on the polyion charge. We show that the correct Debye–Hückel limit differs from Schurr’s result for ζel, and the source of the disagreement is clearly exposed. The results derived here for ζel are not restricted in the number of species of electrolyte ions or in their charges or mobilities.
Predissociating fundamental vibrations of DCN---DF
Authors: Jackson M. W. , Wofford B. A. , Bevan J. W.
Published: July 2002

Gas phase rovibrational analysis of ν1, ν2, and ν3 vibrationally predissociating fundamentals arising from D–F, D–C, and C≡N stretching vibrations of DCN–DF are reported. The rotational substructure in these fundamentals and a total of five associated hot bands have been assigned, thus providing precisely determined band origin frequencies, distortion, and rotational constants. The following molecular parameters were determined for the three fundamentals (in cm−1): ν0(ν1)=2730.8909(2), ν0(ν2)=2638.1309(1), ν0(ν3)=1943.0046(3), B0=0.111 807(1), D0J =0.1946(4)×10−6, α1=0.001 449(2), α2=−0.003 00(1), α3=−0.000 399(1). The l-type doubling constants q″7 =0.378(3)×10−3 and q7 =0.380(3)×10−3 cm−1 were determined from the observed splitting in ν2+ν17−ν17. Anharmonic cross terms X027 =−0.600(3) and X037 =−0.61(3) cm−1 were also evaluated. Lifetimes of the ν1, ν2, and ν3 excited states were demonstrated to be 5.7(6)×10−10, 5.2(5)×10−9, and 3.0(5)×10−9 s, respectively.
Use of the discrete variable representation in the infinite order sudden approximation for reactive scattering
Authors: Whitnell Robert M. , Light J. C.
Published: July 2002

An infinite order sudden approximation (IOSA) for reactive scattering is derived using the discrete variable representation (DVR). The formal properties of this formulation are examined, and possible formal constraints on the IOS parameters are discussed. The DVR-IOSA is used to calculate reaction probabilities for J=0 H+H2 on the Porter–Karplus surface at energies below 1.1 eV, and the results are compared with more accurate calculations. A model problem where the sudden approximation is known to work well (model H+H2 reacting out of the v=1 state) is also studied within the DVR-IOSA context. These results are used to examine more generally the accuracy of the IOSA for reaction scattering calculations.
Cross sections for rotationally inelastic scattering of H2CO. I. Collisions with polar scattering gases
Authors: van Hulst Niko F. , ter Meulen J. J. , Dymanus A.
Published: July 2002

Rotationally inelastic cross sections for ΔJ=0, ±1, and ±2 transitions in the K−1=1 ladder of formaldehyde (H2CO) in collision with CF3H, CH3F, and NH3 are measured in a beam-maser double-resonance (BMDR) experiment. The dependence on detection angle and relative collision velocity is investigated. At least 80% of the integral cross sections is probed. A striking difference in the angular dependence of the differential cross section for ΔJ=0 and ΔJ=±1 transitions is observed. The cross sections are compared with theoretical predictions in modified Anderson theory and adiabatically corrected sudden approximation. Anderson theory predicts very well the K-doublet cross sections and total inelastic cross sections, but fails to reproduce the state-to-state cross sections for ΔJ≠0 transitions. For ΔJ=±1 and ΔJ=±2 transitions corrected sudden approximation shows a much better agreement both with the cross sections determined in this investigation and with the values from other double-resonance experiments.
Benzonitrile and its van der Waals complexes studied in a free jet. II. Dynamics in the excited state: The effect of changing the degrees of freedom of partner molecules
Authors: Kobayashi Tohru , Kajimoto Okitsugu
Published: July 2002

The dispersed fluorescence spectra of the van der Waals (vdW) complexes consisting of benzonitrile and various partner species were observed in a free jet following a single vibronic level (SVL) excitation. For the vdW complexes with atomic species (Kr and Ar), the fluorescence was found to come from the initially prepared state and/or from the monomer produced by vibrational predissociation. On the contrary, in the case of benzonitrile–molecule complexes (H2O, N2O, and CF3H), only the fluorescence from the relaxed vdW molecule was observed. These features are interpreted in terms of a simple general scheme of predissociation. Vibrational predissociation is considered to be a composite of the four processes: (1) radiative decay of the prepared state; (2) intracomplex vibrational energy transfer producing a relaxed vdW complex; (3) radiative decay of the relaxed vdW complex; and (4) dissociation of the relaxed vdW complex. The difference in fluorescent state between atomic and molecular vdW complexes are caused by the competition among these four processes. The relative importance among these processes is strongly dependent on the state density of the vdW modes which in turn reflects the degrees of freedom of the partner species.
Transient nonequilibrium effects in the attachment of electrons to chlorofluoroethanes
Authors: Ness K. F. , Shizgal B.
Published: July 2002

A study of the transient behavior of a nonequilibrium electron swarm in argon together with a small amount of an electron attaching chlorofluoroethane is carried out. The initial electron distribution function is assumed to be a delta function in energy and the subsequent temporal evolution of the distribution function is determined with the two-term solution of the Boltzmann equation. Owing to the small electron mass relative to the other constituents, the Boltzmann equation reduces to a Fokker–Planck equation. Quite generally, the electron attachment process affects the nature of the electron thermalization and vice versa, that is, thermalization and reaction are coupled processes. The experimental determination of attachment rate coefficients involves the assumption that the attachment process has an insignificant effect on the electron distribution function and that the thermalization to a steady state occurs sufficiently quickly so that the attachment kinetics can be described by the steady state electron distribution. In the present paper, the coupling of the thermalization process and the attachment reaction is studied in detail. The time dependence of the electron energy and the attachment rate coefficient are considered for several chloroflouroethanes which exhibit either attachment cooling or attachment heating. A discussion of these steady state effects is presented in connection with similar concepts in hot atom chemistry.
Rotational dynamics of a solvated dipole: A molecular dynamics study of dielectric friction
Authors: Cross Albert J. , Simon John D.
Published: July 2002

Molecular dynamics has been used to examine the influence of the permanent dipole moment on the rotational diffusion of a diatomic molecule in liquid water. Several runs were made for various values of the dipole moment of the solute ranging from 0 to 20 D. The resultant rotational diffusion times compare favorably with dielectric friction theories up to about 17 D, but for dipole moments larger than this, the time constants are seen to increase much more rapidly than can be explained by dielectric friction theories. This deviation from dielectric friction theory is discussed in terms of a local change in solvation structure.
Dynamic multiple scattering theory of the Huggins coefficient for discrete Gaussian chains. II. Numerical computations of the frequency dependence and steady state limit
Authors: Perico Angelo , La Ferla Roberto , Freed Karl F.
Published: July 2002

Numerical calculations are presented for the frequency dependent Huggins coefficient based on the formal derivation provided in paper I using the dynamical multiple scattering theory for discrete Gaussian chains. The calculations employ fast Fourier transform methods and confirm the analytic complexity of this frequency dependence as previously anticipated from our calculations of the concentration dependence of the normal mode autocorrelation function. The harmonic spring model is considered because this simple limit is amenable to closed form solution, displaying the frequency dependence of the relaxation rates and providing a useful check on the difficult numerical computations for higher numbers n of beads. The steady state Huggins coefficient is also calculated with carefully optimized Gauss–Laguerre quadrature methods which permit extrapolation to n→∞. The calculated steady state value of 0.33 lies below experimental data for theta solutions, and an extensive discussion of the experimental data is provided to understand the discrepancy. One major factor, suggested by Schrag, arises from a strong concentration dependence of the individual bead friction coefficient.
Reactions of cationic silicon clusters with xenon difluoride
Authors: Reents W. D. , Mujsce A. M. , Bondybey V. E. , Mandich M. L.
Published: July 2002

Cationic silicon clusters, Si+1–7, were observed to react bimolecularly and exothermically with xenon difluoride in the ion trap of a Fourier transform mass spectrometer. Three ionic products are observed from Si+n: SiF+, Si+n−1, and SinF+. Subsequent reactions of these products with xenon difluoride were determined as well. SinF+, n=2–6, react with xenon difluoride to form two ionic products: SiF+ and Si+n−1. SiF+m, m=1–3, react with xenon difluoride to form SiF+m+1 and XeF+. All observed products correspond to mono- or difluorination of the clusters by xenon difluoride; in many cases the reaction was sufficiently exothermic that the fluorinated cluster fragmented immediately to produce either Si+n−1 or SiF+. Based upon the observed trends in the product distributions, the extent of mono- vs difluorination of the clusters was obtained. The amount of monofluorination varies from 100% for SiF+m, m=0–3, to 0% for Si+7. By extrapolation, xenon difluoride should difluorinate bulk silicon exclusively. The reaction rates for the bare clusters differ only slightly among themselves. The monofluorinated silicon clusters, in contrast, have significant variations in reaction rate as a group. Substantially lower reaction rates are observed for Si4F+ and Si6F+; this is believed to derive from the greater thermodynamic stabilities of Si+4 and Si+6.
Theory of large angle elastic differential cross sections for complex optical potentials: Semiclassical calculations using partial waves, l windows, saddles, and poles
Authors: Connor J. N. L. , Thylwe K.-E.
Published: July 2002

Four semiclassical (WKB) theories have been used to calculate the large angle elastic scattering for a strongly absorptive complex optical potential modeled on Li+HBr. Two theories—the partial wave and l-window formalisms—use first-order single turning point WKB phase shifts for a large number of discrete (integral) angular momenta. The other two theories involve saddle point evaluations of background and subamplitude contour integrals, together wth WKB calculations of the residues and positions of complex angular momentum poles of the S matrix. There are large numerical discrepancies in the differential cross sections at backward angles between the two real angular momentum and the two complex angular momentum theories. Reasons for these discrepancies are analyzed. The complex angular momentum cross sections are more accurate than those computed from the real angular momentum theories and agree closely with l-window calculations using accurate quantum phase shifts.
(1+ 1) CDAD: A new technique for studying photofragment alignment
Authors: Dubs Richard L. , Dixit S. N. , McKoy V.
Published: July 2002

We report a new technique for measuring photofragment alignment in the gas phase by observing circular dichroism in photoelectron angular distributions (CDAD). This technique is well suited for determining the gas phase alignment of linear molecules. The experiment involves excitation of the photofragment with linearly polarized light followed by photoionization with left or right circularly polarized light. The difference between the photoelectron angular distributions for these two cases is the CDAD spectrum. By measuring CDAD through two different excitation branches, one can obtain the ground state photofragment alignment A(2)0 using a simple analytical formula independent of the photoionization dynamics.
EPR characterization of Er3+ and Yb3+ in single crystals of synthetic perovskite (CaTiO3)
Authors: Boldú O. J. L. , Abraham M. M. , Boatner L. A.
Published: July 2002

Synthetic perovskite (calcium titanate, CaTiO3) crystallizes in the orthorhombic structure with space group Pcmn (Z=4) and with lattice constants a=5.367, b=7.622, and c=5.425 Å. Single crystals of CaTiO3 doped with either Er3+ (4f11 electronic configuration) or Yb3+ (4f13 electronic configuration) were grown by means of a flux technique. A mixed KF–LiF flux and Pt crucibles were employed, and the CaTiO3 crystals were formed by spontaneous nucleation on slow cooling (1.0 °C/h) between 1250 and 875 °C. EPR spectra were observed for both Er3+ and Yb3+ at a frequency of ∼9 GHz and a temperature of ∼15 K. The EPR results establish that both Er3+ and Yb3+ occupy four magnetically inequivalent sites in the CaTiO3 lattice and that these sites become equivalent when the applied magnetic field is oriented parallel to the ‘‘pseudocubic’’ b axis of the host synthetic perovskite crystal. The magnetic axes lying in the plane perpendicular to the b axis were found to make an angle with the a and c faces of the crystal that is equal to 21.0(5)° for Yb3+ and 11.5(5)° for Er3+. Isotopically enriched dopants were employed as an aid in analyzing the spectra, and the spin-Hamiltonian parameters have been determined for both rare-earth impurity ions.
Quenching of NF(b 1Σ) by IF, F2, and I2 from 330 to 572 K
Authors: Young R. A. , Blauer J. , Bower R. , Lin C. L.
Published: July 2002

The collisional quenching of NF(b 1Σ) by F2, IF, and I2 has been studied over the temperature range of 330 through 572 K. The extent of reaction was monitored by measurement of the emission intensity in the b→X transition near 529 nm. A laser-induced fluorescence technique was used to monitor the concentration of the transient species IF and to estimate the gas temperature. Essentially, the data shows that IF and I2 reactively quench NF(b 1Σ) at a gas kinetic rate proportional to T1/2 while F2 quenches less effectively by a factor of 20. At 300 K, the rate constants are 1.2×10−10, 1.4×10−10, and 4.4×10−12 cm3 s−1 for IF, I2, and F2, respectively. These results are correlated with the results of others to give estimates of the product branching ratio for formation of the electronically excited halogen molecules at elevated temperatures.
A study of the reaction Li+HCl by the technique of time-resolved laser-induced fluorescence spectroscopy of Li (2 2P
J–2 2S1/2, λ=670.7 nm) between 700 and 1000 K
Authors: Plane John M. C. , Saltzman Eric S.
Published: July 2002

A kinetic study is presented of the reaction between lithium atoms and hydrogen chloride over the temperature range 700–1000 K. Li atoms are produced in an excess of HCl and He bath gas by pulsed photolysis of LiCl vapor. The concentration of the metal atoms is then monitored in real time by the technique of laser-induced fluorescence of Li atoms at λ=670.7 nm using a pulsed nitrogen-pumped dye laser and box-car integration of the fluorescence signal. Absolute second-order rate constants for this reaction have been measured at T=700, 750, 800, and 900 K. At T=1000 K the reverse reaction is sufficiently fast that equilibrium is rapidly established on the time scale of the experiment. A fit of the data between 700 and 900 K to the Arrhenius form, with 2σ errors calculated from the absolute errors in the rate constants, yields k(T)=(3.8±1.1)×10−10 exp[−(883±218)/T] cm3 molecule−1 s−1. This result is interpreted through a modified form of collision theory which is constrained to take account of the conservation of total angular momentum during the reaction. Thereby we obtain an estimate for the reaction energy threshold, E0=8.2±1.4 kJ mol−1 (where the error arises from uncertainty in the exothermicity of the reaction), in very good agreement with a crossed molecular beam study of the title reaction, and substantially lower than estimates of E0 from both semiempirical and ab initio calculations of the potential energy surface.
Reply to the ‘‘Comment on ‘The relationship between shape resonances and bond lengths’ ’’
Authors: Piancastelli M. N. , Lindle D. W. , Ferrett T. A. , Shirley D. A.
Published: July 2002

The relationship between shape−resonance energies and bond lengths within agiven molecule is explored further.It is contended that some shape−resonance assignments presented by Stohr and Hitchcock (ref.1) are not convincing.(AIP)
Resonance ion dissociation spectroscopy of naphthalene ions prepared in a supersonic expansion
Authors: Syage Jack A. , Wessel John E.
Published: July 2002

Resonance ion dissociation (RID) spectra are reported for cations of naphthalene and 2-methylnaphthalene cooled in a supersonic beam. Discrete vibronic resonances were observed in the ultraviolet region of both ions. A discrete red system was also observed for 2-methylnaphthalene that is subject to strong degenerate vibronic interaction with an underlying quasicontinuum associated with a lower energy electronic transition. This leads to effective power broadening of the RID spectra at moderately low laser intensities. The red two-photon dissociation process of 2-methylnaphthalene was successfully modeled by classical rate equations applied to a four level system, consisting of a ground state, the directly excited state, a lower energy excited state, and a final dissociative state.
Effect of residual interactions on polymer properties near the theta point. II. Higher moments and comparison with Monte Carlo calculations
Authors: Cherayil Binny J. , Douglas Jack F. , Freed Karl F.
Published: July 2002

The three-parameter model of excluded volume is employed to calculate both the moments 〈R2n〉{n=2,3,...} of the end-to-end vector distance of a linear homopolymer and the average square moment 〈R2〉 for a single branch of an f-armed star. These results complement the calculations of 〈R2〉, the radius of gyration RG, the Kirkwood approximation to the hydrodynamic radius RH, and the second virial coefficient A2 for linear chains given in paper I. These calculations are intended to check the self-consistency of the ternary interaction theory against recent simulation data for lattice chains under theta conditions (A2=0) using the fact that higher moments and properties of branched polymers are more sensitive to the presence of ternary interactions. No free parameters are involved in the comparison, and the agreement between theory and numerical data is quite satisfactory. In addition, a general discussion is provided of differences in values of various polymer properties that can result from different methods of regularizing the continuum theory.
Time correlation functions and vibrational energy transfer of the v3ν3 vibration (v3=1–5) of liquid N2O
Authors: Manzanares I. Carlos , Wedlock Michael R.
Published: July 2002

The near infrared spectra of pure liquid nitrous oxide were measured at 190 K. Three overtones (Δv3=3, 4, and 5) of the ν3 vibrational motion were obtained. The signals were digitized and computer deconvoluted. The Fourier transformation of the individual bands was accomplished to obtain the appropriate time correlation function at each level. Vibrational relaxation seems to be the main mechanism of decay. The isolated binary collision model is employed. Contributions to vibrational relaxation from dephasing and energy relaxation are estimated for the fundamental. Experimental results obtained for overtones do not follow the prediction of current dephasing theories. A mechanism of energy relaxation based on transition dipole–transition dipole coupling and near resonant energy transfer is suggested to explain the relaxation times as a function of the vibrational quantum number (v3) excited. With this mechanism, an equation is proposed for the bimolecular rate constant of energy transfer which is a function of v3. The equation correctly predicts the rate constants for all levels from v3=1 to v3=4.
Angle-resolved photoelectron spectroscopic study of the outer- and inner-valence shells of NH3 in the 20–80 eV photon energy range
Authors: Piancastelli M. N. , Cauletti C. , Adam M.-Y.
Published: July 2002

We report here highly resolved photoelectron spectra of the outer- and inner-valence shells of NH3, together with the corresponding angular distribution parameter. The measurements were made in the 20–80 eV photon energy range, using synchrotron radiation as an ionizing source. In the inner-valence region, three spectral features were evidenced, and namely a main component at 27.4 eV and two weaker features at 31.4 and 35.4 eV. The spectral feature at 35.4 eV was not evident in the previous (e, 2e) measurements. Our experimental findings are compared with three different sets of calculations performed by the Green’s function method. The best agreement is found with one of them which predicts three main lines and some low-intensity components. From the angular distribution measurements, we conclude that the nature of the spectral feature at 31.4 eV is different from the one of the main component at 27.4 eV.
Dynamics of Cs2 excited by a synchronously pumped mode-locked dye laser, and the effects of magnetic field
Authors: Katô Hajime , Yokoyama Kazushige , Baba Masaaki , Tamai Naoto , Yamazaki Iwao , Nagakura Saburo
Published: July 2002

When the Cs2 molecule was excited by a dye-laser line of 15 841 cm−1, the fluorescence from the energy-transferred states as well as the resonance fluorescence fromthe optically excited levels, which were assigned to C 1Πu and d 3Πu, were observed. We measured the picosecond time-resolved fluorescence intensity by changing the vapor pressure and the temperature. The decay curves were analyzed by a least-squares curve fitting, and the lifetimes in the collisionless limit and the collision cross sections were determined. From the consideration of the rise and decay rates of fluorescence intensities, the kinetic pathways of the collisional energy transfer were estimated. The intensity of the fluorescence d 3Πu–X 1Σ+g was found to decrease appreciably in the presence of an external magnetic field. The magnetic field effect was estimated to be due to the predissociation induced by an electronic Zeeman interaction between the d 3Πu and c 3Σ+u states.
Depolarization ratios of the resonance Raman bands of soluble t
r
a
n
s-polyacetylene
Authors: Fuso S. , Cuniberti C. , Piaggio P. , Dellepiane G. , Luzzati S. , Tubino R. , Zgierski M. Z.
Published: July 2002

Depolarization ratios for the totally symmetric Raman lines in soluble polyacetylene have been measured for various exciting wavelengths in the resonance region. The origin of the unusually high values of the depolarization ratios and their variations with the exciting wavelength are discussed in terms of two overlapping electronic transitions in the visible region.