bluuebunny/crossref_metadata_2025 huggingface dataset:
The well-tempered GTF basis sets in calculations on the s2d n, s1d n+1, and d n+2 configurations of the first- and second-row transition metal atoms
Authors: Klobukowski M. , Huzinaga S.
Published: July 2002

Calculations on the lowest states of the excited electronic configurations of transition metal atoms were performed using the recently developed well-tempered Gaussian basis sets. The basis function space for d-symmetry orbitals was augmented using a single exponent from the exponent pool optimized in the ground state total energy minimization. After augmentation, the excitation energies differed from the Hartree–Fock values by 0.04 and 0.01 eV for the first- and second-row transition metal atoms, respectively.
Microwave spectrum, conformation, and low frequency vibrational spectrum of cyclopropylisothiocyanate
Authors: Durig J. R. , Nease A. B. , Berry R. J. , Sullivan J. F. , Li Y. S. , Wurrey C. J.
Published: July 2002

The microwave spectrum of cyclopropylisothiocyanate, c-C3H5NCS, has been investigated in the region from 12.5 to 40.0 GHz. Two sets of a-type R-branch transitions were observed and assigned, on the basis of the rigid rotor model, to the trans and cis conformers. One excited vibrational state for each conformer was also identified and tentatively assigned as the asymmetric NCS torsion. The B and C rotational constants in the ground vibrational state for the trans and cis conformers of c-C3H5NCS were found to be: B=1122.689±0.002, C=1095.619±0.002 MHz, and B=1346.859±0.003, C=1309.166±0.002 MHz, respectively. The values of the A rotational constants for both conformers were not well determined because the measured transitions are not very sensitive to these constants. The dipole moment components were determined for the trans conformer from the Stark effect to be ‖μa‖=3.11±0.02, ‖μc‖=0.62±0.01, and ‖μt‖=3.17±0.01 D and for the cis conformer to be ‖μa‖=3.34±0.01, ‖μb‖=0.27±0.07, and ‖μt‖=3.35±0.01 D. With reasonably assumed structural parameters for the cyclopropyl moiety and bond distances for the isothiocyanate group, the other structural parameters were calculated from the rotational constants by the diagnostic least squares method to be: r(C–N)=1.390±0.016 Å,∢CNC=143.8±4.2 °, and ∢CCN=118.7±0.1 ° for the trans conformer and r(C–N)=1.414±0.017 Å, ∢CNC=144.4±1.1, and ∢CCN=118.6±2.3 ° for the cis conformer. The far infrared spectrum of the vapor was also recorded and the C–N=C bend was observed at ∼104 cm−1 but little evidence could be found for the second conformer in the vibrational spectrum. These results are compared to the corresponding ones in some related molecules.
Diffusion coefficients in anisotropic fluids by ESR imaging of concentration profiles
Authors: Hornak J. P. , Moscicki J. K. , Schneider D. J. , Freed J. H.
Published: July 2002

We report on the use of ESR imaging for determining the translational diffusion constants of typical ESR spin probes in ordered and isotropic solvents. A discussion is given for a Fourier deconvolution method for determining the correct concentration profile if there is more than one hyperfine line in the spectrum of the radical as well as a spatial dependence of the spectrometer sensitivity. A simple but approximate subtraction deconvolution method is also presented. The diffusion constants for 4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPONE) in the nematic and isotropic phases of the liquid crystal p-pentylbenzylidine-p-butylanaline (5,4) were determined. In the isotropic phase the diffusion coefficient is isotropic (D=2.5×10−6 cm2 s−1, at 50 °C), while in the nematic phase it was found to be mildly anisotropic. The diffusion coefficients for motion perpendicular and parallel to the director axis in the nematic phase are respectively, D⊥ =9.0×10−7 cm2 s−1, D∥ =6.4×10−7 cm2 s−1 at 27 °C. This is interpreted in terms of some smectic-like character in the nematic phase of 5,4. Possible improvements in the technique are also discussed.
Quasidegenerate many-body perturbation theory with self-consistently adapted core reference state (SCA QD MBPT). I. Theoretical formulation and its application to the potential energy curve of the ground state of Li2
Authors: Hubač Ivan , Svrček Michal , Balková Anna
Published: July 2002

The alternative version of Brandow’s QD MBPT is formulated, in which the core vacuum state is redefined with respect to a chosen reference state from model space. This is done through a one-particle operator U in such a way that the total electronic Hamiltonian is not changed. The second order of SCA QD MBPT is applied to the study of the potential energy curve of the ground state of Li2. The results are compared with both the highly sophisticated ab initio calculations (MC SCF, CI-SDT) and the experimental results. The convergency properties of the SCA QD MBPT expansion are discussed with respect to a chosen one-determinantal zeroth-order wave function as well as to an applied model space.
Adiabatic limit for the time dependent Coulomb problem
Authors: Pirovano M. V. Ganduglia , Ponce V. H.
Published: July 2002

The dynamic evolution of a hydrogenic state with a time dependent nuclear charge Z(t) is analyzed for the case of weak time dependences ‖dZ/dt‖≪Z. Strong departures from the adiabatic behavior are shown to be produced by discontinuities in the rate of growth dZ/dt of the nuclear charge.
Solutions of the Percus shielding equation
Authors: Wertheim M. S.
Published: July 2002

We consider the Percus shielding approximation (PSA) for the density profile of a hard sphere fluid in the presence of a hard spherical inclusion or plane wall. Two calculations are reported. For an inclusion which is equal to a fluid particle, an equation of state is obtained from the numerical solution of the integral equation by requiring self-consistency. The results are inferior to the predictions of the Percus–Yevick equation. For the case of a plane wall, where the PSA is good, the exact solution of the PSA is found in terms of elementary functions. The recurrence relations for polynomial coefficients in the solution are given in some detail.
Site-selective photochemistry and vibrational analysis of matrix-isolated 1,3,5,7-octatetraene radical cations in different conformations
Authors: Bally T. , Nitsche S. , Roth K.
Published: July 2002

Upon ionization by x irradiation, all-trans 1,3,5,7-octatetraene (OT) gives an electronic absorption (EA) spectrum which indicates the formation of at least five different (peri)planar conformations (‘‘rotamers’’) of OT+̣ next to the parent cation. Some of these undergo specific photochemical interconversions which are discussed on the basis of a complete scheme of OT+̣ rotamers and their connections via single bond-rotation processes. None of these photoreactions lead to any other than the initially observed six species which seem to form a distinguished set within the 20 possible OT+̣ rotamers. By very narrow bandwidth irradiation, interconversions can be induced to take place in a site-selective fashion. The resulting well-resolved difference spectra allow an analysis of the site dependence of the different ion’s first two EA bands. Surprisingly, the extent of this site dependence varies greatly between different OT+̣ rotamers and between different electronic transitions of a given rotamer. Finally, a detailed vibrational analysis of the first two absorption bands of all-trans OT+̣ is given.
Spectral measurements along the path of N ions impinged into dense helium gas (400 Torr and 5.2 K). II. Excimer reactions dependent on stopping power and large emission yields near the termination of the track
Authors: Kimura Kazuie
Published: July 2002

Emission spectra and their decay were measured along the path of 4 MeV/amu N ions impinged into dense helium gas near 5.2 K and 420 Torr. Specific scintillation, dL/dX, and scintillation efficiency, dL/dE, for each emission band were measured separately on total, fast initial-rise (<2 ns), fast decay (<100 ns), and stationary (afterglow) components in order to elucidate the detailed dependence of production and decay of excimers on the stopping power, dE/dX. The curves of dL/dX and dL/dE vs dE/dX are shown to have a bend at 6 MeV mg−1 cm2: Some of the emissions increased abruptly as the stopping power exceeded this value, while the other emissions decreased or their rates of increase were suppressed. This bend point corresponds to the starting point of a rapidly decreasing yield of δ rays. The result shows that helium has a good scintillation response to high-density excitation occurring at the termination of tracks of N ions, in contrast to usual scintillators, where scintillation decreases abruptly with decreasing δ-ray yield. The large yields of emissions at high-density excitation are explained by the direct excitation, induced emission, and cyclic regeneration of excimers by bimolecular reactions between the nonradiative metastable state, a3, in addition to a very low probability of quenching in helium. Furthermore, it is shown that the present results support the tentative assignment made in part I of this report that the new triplet bands centered at 4587 Å result from an excimer–dimer. Also, it is proposed that an excimer–dimer is composed of the a3 and c3, b3, or d3.
The atom in a molecule: A wave function approach
Authors: Rychlewski Jacek , Parr Robert G.
Published: July 2002

Given a homonuclear diatomic molecule AB with an even number of electrons N in the state ψ. What is the state of atom A in the molecule? Using the lemma that 〈ψ‖HA ‖ψ〉/〈ψ‖ψ〉≥E0A where HA is the Hamiltonian for atom A only, having NA =N/2 electrons, and E0A is the ground state energy of A, the following general definition is suggested and quantitatively tested for the hydrogen atom in the hydrogen molecule. Define N-electron functions ψA and ψB by ‖ψ‖2= 1/2 [‖ψA‖2+‖ψB‖2], ψA =ψ[1+F]1/2, and ψB =ψ[1−F]1/2, with ψA, ψB, and ψ all normalized and F a function symmetric with respect to electron interchange. Then  ρ=ρA+ρB and F can be determined to minimize the promotion energy 〈ψA‖ĤA‖ψA〉−E0A. Calculations are performed for the H2 ground state and b3∑+u excited state, as functions R, employing accurate wave functions including correlation. For the ground state at the equilibrium internuclear distance, the promotion energy is found to be 0.0447 a.u. or 28 kcal/mol. The electron density for the atom in the molecule is examined, and extensions to heteronuclear and polyatomic molecules briefly discussed.
Shear viscosity measurements near a critical endpoint
Authors: Rzoska S. J. , Chrapeć J. , Ziol/o J.
Published: July 2002

The coordinates of the critical endpoint in a nitroethane–ethanediol–cyclohexane–methanol solution have been determined and measurements have been made of the shear viscosity in the vicinity of this point. Results can be well approximated with relations used to express the behavior of viscosity in the area of an ordinary critical point.
Transition flow ion transport: Experimental
Authors: French J. B. , Darcie T. E.
Published: July 2002

In previous publications a new theoretical approach to ion transport in neutral gases, based on the integral Boltzmann equation, was reported. The method is applicable to determining the evolution of a source of ions which are electrostatically accelerated through a not necessarily uniform neutral gas target. This paper presents experimental corroboration for two gas target configurations; (1) spatially uniform and (2) free-jet expansion, for protonated dimethyl-sulfoxide ions and nitrogen gas. The theory was in best agreement for the free-jet target and both configurations were used to determine an ion–molecule hard-sphere cross section of 3.6±0.15 Å.
Vibrational analysis of CD3CD2CD3, CD3CHDCD3, and CHD2CD2CD3 in the 100–11 500 cm−1 spectral range
Authors: Gough K. M. , Baudais F. L. , Casal H. L.
Published: July 2002

Raman scattering (100 to 3000 cm−1) and infrared absorption spectra (500 to 11 500 cm−1) of CD3CD2CD3, CD3CHDCD3, and CHD2CD2CD3 are reported and analyzed. The major features of the overtone region can be explained on the basis of coupling between overtones of C–H stretching vibrations and CHD deformation vibrations. Fermi resonance coupling interactions become stronger with increasing overtone number up to ΔvCH=3. This coupling is analyzed for CD3CHDCD3. Implications for C–H stretching frequency and C–H bond length correlation are discussed.
Strongly enhanced infrared vibrational transitions in electronically degenerate states
Authors: Scharf Benjamin , Miller Terry A.
Published: July 2002

Various types of strongly enhanced infrared vibrational transitions, with transition moments comparable to those characteristic of allowed electronic transitions in visible or UV spectra, may ensue in spatially degenerate electronic states of nonlinear molecules. The intimate correlation between the intensity of the enhanced infrared vibrational transitions and the anomalous pure rotational microwave spectra and the Stark effect is elucidated. The rules of Child and Longuet-Higgins with regard to infrared activity and infrared intensity enhancements in electronically degenerate states require revision and extension when properly considering the ramifications of the Jahn–Teller effect and invoking the action of mixed quadratic nuclear potential terms. Significantly, the enhancements of IR transition moments should allow the observation of symmetrical free radicals and molecular ions whose laboratory concentrations are often below the level of detectability for ‘‘normal’’ IR transition strengths. In addition, these effects could lead to multi-enhancement effects in nonlinear infrared and Raman vibrational spectra as well as enhanced radiative and nonradiative vibrational relaxations.
X-ray absorption near edge structure (XANES) of PtCl2−4 in solid and solution environments
Authors: Sham T. K.
Published: July 2002

The LIII,II edge x-ray absorption near edge structure (XANES) of the PtCl2−4 noiety in two different environments, (1) solid K2PtCl4 and (2) K2PtCl4 in aqueous solution is reported. (AIP)
Circular Couette flow of concentrated polymer solutions: Encapsulated finitely extendable nonlinear elastic (FENE) dumbbell model results
Authors: Kaloni P. N. , Brunn P. O.
Published: July 2002

The diffusion equation based on the encapsulated FENE model concept is applied to circular Couette flow. In all cases studied, a nonuniform concentration distribution is predicted, decreasing with increasing distance from the inner cylinder. For highly dilute solutions the degree of nonuniformity increases with increasing shear rate and increasing flexibility. For concentrated solutions the data reported in the literature are used. In contrast to earlier tube flow predictions, all the systems studied behave qualitatively in the same way. Up to the limit of vortex formation the theory presented should be valid. The implications of nonuniform concentration profiles for normal stress measurements are outlined.
Rate constant for the reaction of PO radical with oxygen
Authors: Long S. Randolph , Christesen Steven D. , Force Alan P. , Bernstein Jeffrey S.
Published: July 2002

A CO2 TEA laser is used to generate PO radical by infrared multiphoton dissociation of dimethyl methylphosphonate in an excess of oxygen at total pressures up to 1.4 Torr. The pseudo-first-order reactive decay of PO (v″=0) is followed by laser-induced fluorescence utilizing its A 2Σ+–X 2Π transition. A bimolecular rate constant of 1.4 (±0.2)×10−11 cc/molecule/s is measured for the PO+O2 reaction. Earlier measurements of a much slower rate in flow discharge systems may be complicated by the establishment of equilibrium between the forward and reverse reactions PO+O2↔PO2+O.
Pressure narrowing and the Ornstein–Uhlenbeck process
Authors: Lewis John Courtenay
Published: July 2002

A model for pressure narrowing in collision-induced absorption is developed, using transition probabilities given by the Ornstein–Uhlenbeck process, with Gaussian induced dipole moments. The autocorrelation function for this model can be obtained analytically, and its principal properties readily described. The resultant line shape is a three-parameter function, which exhibits both peak narrowing and base broadening. The transition to the narrowed line shape is found to be gradual. It is found that if angular modulation is ignored, the resultant line shape has a cusp about zero frequency, so that angular modulation contributes not only quantitatively, to the width of the line, but qualitatively, to the line shape. These results are model independent. By including angular modulation, the line shape obtained is also descriptive of the overlap-induced component of the Q branch. The last comprises a generalization of the Levine–Birnbaum line shape to include pressure narrowing.
On contributions from non-Born–Oppenheimer corrections to the calculation of large distance electron transfer rates
Authors: Freed Karl F.
Published: July 2002

Vibronic coupling theory is formulated in an adiabatic Born–Oppenheimer approximation to investigate corrections to the calculation of large distance electron transfer rates arising from Born–Oppenheimer violation terms. Connections with the description of electron transfer in small ions and of radiative and nonradiative decay processes in molecules enable the qualitative assessment of the likely contributions from such terms. A discussion is provided of how certain anomolies in absorption intensities can be used to screen for possible candidates for non-Born–Oppenheimer contributions to large distance electron transfer rates. Peculiar aspects of a crude one-dimensional model treatment of the problem are also noted.
Photoinduced ionization of bovine serum albumin by holographic relaxation methods
Authors: Barish Amy , Johnson Charles S.
Published: July 2002

Holographic relaxation spectroscopy (HRS) has been applied to the study of bovine serum albumin labeled with isothiocyanatoazobenzene (BSA-ABITC) in solutions of low ionic strength. Below 25 mM NaCl two relaxation rates are evident, one of which corresponds to the tracer diffusion rate for BSA while the other increases as the ionic strength is decreased. In the electrophoretic HRS experiment (EHRS), two components having the mobilities μ=2.59×10−4 cm2/V s) and μ=2.21×10−4 cm2/V s) are observed, but in this case the apparent diffusion coefficients are equal. These results are consistent with a model in which the absorption of light by the azobenzene group causes BSA-ABITC to change its net charge. The coupled diffusion of BSA, ionized BSA, counterion, and coions is adequately described by a simple theory based on the model of Lee and Schurr [J. Polym. Sci. 13, 873 (1975)].
Perturbation theory of one-dimensional triangle- and square-well fluids
Authors: Bishop Marvin , Swamy Kandadai N.
Published: July 2002

The Barker–Henderson perturbation theory for free energy is investigated for one-dimensional triangle- and square-well potentials. It is found that the first-order term is equal to that obtained from an expansion of the exact result and that while the macroscopic compressibility approximation for the second-order term is better than the local compressibility approximation, it still does not agree very well with the exact second-order term at higher densities.
Rate constant for the reaction of O(3P) with diacetylene from 210 to 423 K
Authors: Mitchell M. B. , Nava D. F. , Stief L. J.
Published: July 2002

The absolute rate constant for the reaction of O(3P) with diacetylene (C4H2) has been measured as a function of pressure and temperature by the flash photolysis-resonance fluoresence method. At 298 K and below, no pressure dependence of the rate constant was observed but at 423 K a moderate (factor of 2) increase was detected in the range 3 to 75 Torr Ar. Results at or near the high pressure limit are well represented by the Arrhenius expression k1=(1.31±0.12)×10−11 exp[−(678±23)/T] cm3 s−1 over the temperature range 210 to 423 K. The results are compared with previous determinations, all of which employed the discharge flow-mass spectrometry technique. The mechanism of the reaction is considered including both primary and secondary processes. The heats of formation of the reactants, adducts, and products for the O(3P)+C4H2 reaction are discussed and contrasted with those for O(3P)+C2H2.
Electron-impact dissociation of H3O+
Authors: Schulz P. A. , Gregory D. C. , Meyer F. W. , Phaneuf R. A.
Published: July 2002

Fragment cross sections for electron impact dissociation of H3O+ into OH+ and O+, and for dissociation of D3O+ into D2O+ have been measured in a crossed beam appartus for electron energies from threshold to 1000 eV. The cross sections for O+ and OH+ rise abruptly at threshold indicating that the mechanism for dissociation is via production of an electronically excited state of H3O+ and direct dissociation into O+ and OH+. At high energy the cross section has a falloff σ∝ln(E)/E expected in the Bethe-Born approximation. At 200 eV electron energy the cross sections for fragments are: D2O+, σ=6.7±1.8×10−17 cm2; OH+, σ=3.0±0.6×10−17 cm2; O+, σ=7.9±1.6×10−18 cm2. The observed threshold energies for OH+ and O+ production are 14±3 and 19±3 eV, respectively.
Theory of three-photon photoselection with application to the hexagonal point groups
Authors: Cable J. R. , Albrecht A. C.
Published: July 2002

The general problem of the polarization dependence of an orientationally averaged four-photon process in a rigid isotropic medium is examined. The theory is then reduced to the special case of three-photon photoselection (3PP) in which an excited state is first created by the simultaneous absorption of three identical photons and then the system is interrogated by a one-photon probe step (absorption or emission). When the probe signal is measured as a function of both excitation and probing polarizations, five unique transition tensor invariants can be determined. These five invariants provide a characteristic signature of the symmetry of the initial three-photon absorption (3PA). A symmetry analysis is illustrated within the hexagonal point groups where it is demonstrated how the measurement of a single photoselection polarization ratio formally allows, with one exception, a unique symmetry assignment to be made for any three-photon allowed transition. This measurement makes use of circularly polarized excitation with variably polarized probing. The polarized probe step in a 3PP experiment provides information concerning the three-photon transition beyond that available from a simple polarized 3PA study.
High energy chlorine-for-chlorine substitution involving Walden inversion in liquid enantiomers
Authors: Borkar Nitin , Latifi A. Akbar , Rack Edward P.
Published: July 2002

The energetic 38Cl reactions in liquid chloropropionyl chloride are reported. The effects of solvents on the course of 38Cl−for−Cl substitution is studied. (AIP)
Classical and semiclassical aspects of dissipative molecular processes: Radiative and nonradiative vibrational relaxation in polyatomic molecules
Authors: Parson Robert P. , Heller Eric J.
Published: July 2002

The time dependence of spontaneous emission from isolated, highly vibrationally excited molecules is studied from the point of view of the classical and semiclassical mechanics of dissipatively perturbed Hamiltonian systems. A correlation function expression for the time-dependent emission spectrum serves as a starting point for quasiclassical approximations. These in turn lead to an investigation of the classical dynamics of model molecular systems in which small, energy-nonconserving terms have been added to Hamilton’s equations. Numerical calculations show rich dynamical behavior which can be qualitatively understood in terms of the resonance structure of the unperturbed system. For example, trajectories tend to be captured by zones of nonlinear resonance. This ‘‘mode locking’’ produces a characteristic cleanup of an emission spectrum that otherwise is rather congested at these energies. The close connection between spectra and dynamics suggests that the classical dynamics of dissipatively perturbed systems may provide a useful language for interpreting radiative and condensed-phase vibrational relaxation, and possibly some types of intramolecular relaxation phenomena as well.
Rate constant for the reaction SO+BrO→SO2+Br
Authors: Brunning J. , Stief L.
Published: July 2002

The rate of the radical–radical reaction SO+BrO→SO2+Br has been determined at 298 K in a discharge flow system near 1 Torr pressure with detection of SO and BrO via collision-free sampling mass spectrometry. The rate constant was determined using two different methods: measuring the decay of SO radicals in the presence of an excess of BrO and measuring the decay of BrO radicals in excess SO. The results from the two methods are in reasonable agreement and the simple mean of the two values gives the recommended rate constant at 298 K, k=(5.7±2.0) ×10−11 cm3 s−1. This represents the first determination of this rate constant and it is consistent with a previously derived lower limit based on SO2 formation. Comparison is made with other radical–radical reactions involving SO or BrO. The reaction SO+BrO→SO2+Br is of interest for models of the upper atmosphere of the Earth and provides a potential coupling between atmospheric sulfur and bromine chemistry.
Chemi-ionization reactions of barium with chlorine clusters: Observation of Cl−m and BaCl+m products (m=1–15)
Authors: Ross U. , Schulze Th.
Published: July 2002

Chemi-ionization reactions from the collision of Ba with (Cl2) clusters are reported. The scattering yields BaCl+m as well as Cl−m cluster ions. Relative integral cross sections for products with m even or odd depend differently on the collision energy. Over the collision energy range studied of a few eV, channels with odd products predominate, and at higher collision energy constant fractions characterize the observed product pattern. Aspects of the collision mechanism involved are discussed. The analysis suggests these reactions to start within the subsystem Ba+Cl2. The corresponding relative cross section has been determined for Ec.m. ≤2.7 eV.
Perturbed rotational structure in the 18 373 cm−1 band of the fluorescence excitation spectrum of jet-cooled chromyl fluoride
Authors: Gordon R. D. , Beattie I. R. , Brown J. M. , Firth S.
Published: July 2002

The 18 373 cm−1 band in the fluorescence excitation spectrum of jet-cooled CrO2F2 has been recorded with 0.007 cm−1 linewidth. The stronger lines have been assigned to a type c transition, consistent with a B1←A1 vibronic transition analogous to that in CrO2Cl2. Ground-state rotational constants, A″=0.148, B″=0.130, and C″=0.120 cm−1, agree well with electron diffraction predictions. The B1 excited state is significantly perturbed. Evidence includes (i) a decreasing fluorescence yield with increasing J′, such that signals were not observed for J′>3, (ii) the appearance of ‘‘extra’’ lines in the spectrum, leading to perturbing levels strongly mixed with levels of the B1 state, and (iii) anomalous effective rotational constants for the B1 state.
Generalized Massieu–Planck functions: Geometric representation, extrema and uniqueness properties
Authors: Debenedetti Pablo G.
Published: July 2002

Massieu–Planck functions are thermodynamic transforms closely related to the more familiar Legendre transforms. They arise naturally in the theory of concentration and entropy fluctuations in multicomponent systems. Generalization of the Massieu–Planck transform concept gives rise to a one-to-one correspondence between each thermodynamic potential and an associated Massieu–Planck function having the same uniqueness and extrema properties. The specific Massieu–Planck functions arising in fluctuation theory are particular cases of the transforms whose algebraic and geometric properties are presented here.
The effect of rotational Brownian motion on Witten–Sander aggregates
Authors: Hentschel H. G. E. , Deutch J. M. , Meakin Paul
Published: July 2002

The effect of rotational diffusion on the growth of Witten–Sander aggregates is examined. Computer simulations of a model are analyzed where the growing aggregate rotates with a rotational diffusion constant Drot(R∥)∼1/[τrot(R∥/a)δ], while the irreversibly aggregating particles jump with a diffusivity a2/τ0(τ0,τrot are the time constants for translational and rotational jumps and a is the lattice spacing). In the simulations 0.0002<(τ0/τrot)<1600 is varied over seven orders of magnitude. In general the aggregates are anisotropic (despite the inherent symmetry of the model) with longitudinal and transverse length scales R∥ and R⊥. On scales r≪R⊥ the cluster remains fractal, but on scales R⊥≪r≪R∥ the cluster becomes linear. Estimates of the dependence of R∥ on N, (τ0/τrot), and δ are made and compared with the computer data. Both initial and asymptotic behavior are investigated, and several regimes of growth identified.
Clustering and nucleation in supersaturated regular solutions
Authors: Rasmussen D. H.
Published: July 2002

The energetics of cluster formation is evaluated for a supersaturated binary liquid–liquid system. Regular solution thermodynamics are combined with dynamic surface tension evaluation to determine cluster stability. The composition and size of the critical nucleus is predicted for several parent phase supersaturations at a reduced temperature of 0.9. These results while quite similar to the results of Reiss and Shugard are not in total agreement with this prior analysis. The results substantiate the need for a curvature dependent dynamic surface tension in nucleation theory.
Cl2 and HCl emissions in the ArF-laser photolyses of chlorinated compounds: Identification and mechanism of generation
Authors: Kenner R. D. , Haak H. K. , Stuhl F.
Published: July 2002

The ArF (193.3 nm)-laser photolyses of several chlorinated methanes and COCl2 were investigated using the unfocused beam. Cl2 and HCl emissions from highly excited states were observed and identified by use of recently calculated potential energy curves. The emissions were generated by absorption of two ArF-laser photons. It was observed that the first absorbed photon forms an intermediate which subsequently absorbs the second photon to generate the fluorescent molecule. Some intermediates can also absorb a KrF-laser photon to yield Cl2 emission. The intermediates were identified by energy restrictions to be Cl2 with excitation energies below the dissociation limit. In the cases of COCl2 and CCl4 this excitation extends up to the dissociation energy of Cl2(X). Also, vibrationally hot ground state HCl molecules are formed as intermediates. In some cases the intermediates contain the total energy available from the first photolysis step. Energy considerations result in an estimate for the heat of formation of the CHCl radical.
Interfacial tensions near the tricritical points of classical liquids: Experimental evidence for the validity of the prediction of critical scaling theory
Authors: Smith Duane H.
Published: July 2002

It is shown from data in the literature that the predictions of scaling theory for interfacial tensions near tricritical points are valid for classical liquids.
Double energy transfer in rigid glass
Authors: Taen S.
Published: July 2002

The occurrence of two successive energy transfers between two molecules (double energy transfer) has been shown in the phosphorescence from ethanol containing phenanthrene and 1-bromonaphthalene. Both the phosphorescence rise and decay curves of phenanthrene have been observed to consist of rapid and slow components when the wavelength of the excitation light is short enough to be absorbed by 1-bromonaphthalene. On the contrary, the rapid components of the rise and decay curves have been observed to disappear when the excitation light is absorbed by phenanthrene alone. A simple kinetic model has been proposed which can explain the experimental results consistently. The rapid components of the rise and decay curves have been ascribed to the triplet–triplet energy transfer enhanced by the singlet–singlet energy transfer.
Geminate recombination of electrons in liquid methane
Authors: Gee Norman , Freeman Gordon R.
Published: July 2002

A recent molecular dynamics simulation of electron–ion geminate recombination in liquid methane [W. L. Morgan, J. Chem. Phys. 84, 2298 (1986)] is compared with more extensive experimental results. The general form of the dependence upon temperature and density is correct.
Rotational adiabatic switching of asymmetric top molecules
Authors: Patterson Chris W. , Smith R. Scott , Shirts Randall B.
Published: July 2002

We use the principle of adiabatic invariance of the action to find semiclassically the rotational fine structure of asymmetric top molecules. We show that by adiabatically switching the moments of inertia of a prolate or oblate symmetric top molecule, we may determine the asymmetric top energy levels even when crossing a separatrix boundary.
On the effect of the helium ground state wave function on the electron impact triple differential ionization cross section in asymmetric geometry
Authors: Baliyan K. S. , Srivastava M. K.
Published: July 2002

The sensitivity of the triple differential cross sections for the electron impact ionization of helium to the target ground state wave function is investigated at high energies in the asymmetric Ehrhardt geometry. The calculation is done in the modified Glauber approximation using (i) one-parameter Hartree wave function and (ii) three-parameter analytical fit of Byron and Joachain to the Hartree–Fock wave function for the helium ground state. The latter choice leads to somewhat better agreement with the recent absolute data of Jung et al. at 600 eV incident energy. The results are however not very sensitive to this choice.
Fluctuation and rotation in diffusion-influenced monomolecular reactions
Authors: Bashford Donald
Published: July 2002

Different methods of modeling partially absorbing boundaries in diffusion–reaction processes are examined. If the partially absorbing nature of the boundary arises from fluctuations between absorbing and nonabsorbing states, an important parameter is τr, the relaxation time associated with the fluctuations. If τr is much less than the thermal mean free time, a diffusion equation with a radiation boundary condition (RBC) in which the thermal mean free length plays a key role can be used. For the case where τr is much greater than the thermal mean free time, a stochastically switching absorber (SSA) model is presented. For a one-dimensional case it is shown that if τr is much less than the time required for diffusion across the diffusion domain, the RBC model can be made equivalent to the SSA model. A first passage time is calculated for an anisotropic three-dimensional model: two spherical particles connected by a flexible link with one of the particle’s reactivity confined to a circular patch. An approximate analogy is found between the effects of rotation and fluctuation on the first passage time.
A new method of analysis of critical-point singularities from power series expansions: Application to eigenvalue problems and virial series
Authors: Arteca Gustavo A. , Fernández Francisco M. , Castro Eduardo A.
Published: July 2002

A new method is developed for studying real singularities of functions from their power series expansions. It is based on an appropriate calculation of the least-squares deviation of the Taylor coefficients from their asymptotic behavior. Under certain conditions the procedure is shown to lead to the widely used ratio method and it is applied to perturbation-theory problems and virial series. The convergence radii of the Rayleigh–Schrödinger perturbation series for the ground-state energy levels of the plane and linear polar rigid rotators in uniform electric fields are calculated. The occurrence of the singularities in the compressibility factor for hard disks and spheres predicted by the Percus–Yevick and scaled-particle theory is verified. The critical parameters characterizing the Kirkwood ‘‘phase transition’’ near close-packing density and the asymptotic form of the equation of state in the neighborhood of the singularities are verified. Present results elucidate a critical-exponent paradox.
A model Hamiltonian for phase transitions: Application of the continued fraction technique
Authors: Jelski Daniel A. , Wilson Robert S.
Published: July 2002

This paper applies the continued fraction technique previously derived to a model Hamiltonian used to model structural phase transitions. The application is valid in the low temperature limit, and takes advantage of the random phase approximation. The result is quantum mechanical, and it successfully accounts for the displacive transitions in a lattice.
Semiclassical theory in phase space for molecular processes. III. Electronically nonadiabatic transitions in multidimensional systems
Authors: Takatsuka Kazuo , Nakamura Hiroki
Published: July 2002

A theory for electronically nonadiabatic transition in a multidimensional system is presented in the scheme of phase space quantum theory. The previously proposed phase space distribution function called DCF (dynamical characteristic function) is generalized to this case and coupled equations of motion are derived for this new DCF. Semiclassical approximation to these equations is analyzed, and the physical picture is clarified for the propagation of the semiclassical DCF based on wave packets. A sudden approximation applied to a series expansion of solution is shown to produce a multidimensional generalization of the first order Magnus approximation for nonadiabatic transition amplitude. It is also suggested to incorporate the more sophisticated formulas into the propagation of the semiclassical DCF.
Nondegenerate many-body theory and the treatment of conservation principles
Authors: England Walter B. , Silver David M.
Published: July 2002

Projection operators are used to formulate Lipkin’s modified Hamiltonian. By projecting from independent quasiparticle states, a convenient general nondegenerate many-body perturbation theory is generated. A unique feature is that the final results satisfy conservation principles. Practical consequences include ordinary diagrammatic expansions and equations-of-motion for treatments of alternant molecular orbital wave functions.
Higher-order moments in macrotransport processes
Authors: Nadim Ali , Pagitsas Michael , Brenner Howard
Published: July 2002

A novel moment-gradient expansion scheme, expressing the microscale probability density P as an infinite sum of global-space gradients of its corresponding macroscale density P̄ multiplied by coefficients formed from its local and total moments, is employed to derive an asymptotic long-time macrotransport equation from its more detailed microtransport predecessor. Particular emphasis is paid to third- and higher-order gradient terms in the expansion. These are shown to result in non-Gaussian behavior of the macroscale probability density P̄ governing convective–diffusive transport processes.
Formation mechanism of vibrationally excited O2 molecules in the multiphoton absorption of NO2
Authors: Shibuya Kazuhiko , Nagai Hidekazu , Imajo Takashi , Obi Kinichi , Tanaka Ikuzo
Published: July 2002

A pump–probe two-color experiment has been performed to elucidate the formation mechanism of O2 X 3Σ−g in the multiphoton absorption of NO2 over the region 460–540 nm. A probe dye laser was employed to excite O2 X 3Σ−g into the B 3Σ−u state and the UV emission intensity of Schumann–Runge bands was measured under the various experimental conditions. The maximum vibrational level of O2 X 3Σ−g formed is v″max =24 which corresponds to Evib=30 968 cm−1. The rotational distribution of O2 X 3Σ−g (v″=24) was almost of Boltzmann with Trot=1300 K at low pressures. The isotopic 1:1 mixture of N16O2 and N18O2 has been photolyzed to test whether the O2 molecules are formed by unimolecular dissociation or through chemical reactions. From the product branching ratio of 16O2:16O18O:18O2 and the maximum vibrational levels observed, the vibrationally excited O2 molecules are concluded to be mainly generated by the chemical reaction of O(1D)+NO2→O2+NO, ΔH=32 000 cm−1. The O(1D) atoms are formed by a sequential three-photon absorption of NO2, where the initial two-photon absorption occurs through the 1 2B2←X̃ 2A1 transition in a cyclic manner and a certain collision-induced process takes place in a dense system of the predissociative states locating in 11 900–19 400 cm−1 above the dissociation threshold of NO(2Π)+O(3P).
Transition metal–hydrogen complexes in the Mg2NiH4 and Mg2FeH6 crystals described by quantum chemical calculations
Authors: Lindberg Per , Noréus Dag , Blomberg Margareta R. A. , Siegbahn Per E. M.
Published: July 2002

High accuracy quantum chemical calculations (CASSCF and contracted CI) have been performed on the transition metal hydrogen complexes in the Mg2FeH6 and Mg2NiH4 crystals. The effects from the surrounding crystal are simulated by a Madelung field. If the conventional charge of +2 is assumed for the magnesium ions the transition metal hydrogen complexes receive a charge of −4. Good agreement with experiment is then obtained for the bond distance and totally symmetric vibrational frequency for the iron complex. The calculated Fe–H distance in the octahedral FeH4−6 complex is 1.56 Å, which is identical to the value obtained from neutron diffraction data on the Mg2FeH6 crystal. For the nickel compound also the unconventional case of Mg+ has to be considered, yielding a 2− transition metal hydrogen complex. The structure for the NiH4 complex is not as well determined as the iron complex. Experimental data has been interpreted in terms of a planar structure but a tetrahedral structure is not ruled out. Our calculations show that the conformation of the complex depends on the charge it is assumed to have. A 2− complex leads to a square planar structure and a 4− complex leads to a tetrahedral structure.
Rotational spectrum, H, 19F spin–spin and D–nuclear quadrupole coupling constants, and molecular geometry of the sulphur dioxide–hydrogen fluoride dimer
Authors: Fillery-Travis A. J. , Legon A. C.
Published: July 2002

The ground state rotational spectra of three isotopic species 32SO2⋅⋅⋅HF, 32SO2⋅⋅⋅DF, and 34SO2⋅⋅⋅HF of a dimer formed between sulphur dioxide and hydrogen fluoride have been detected and measured using a pulsed-nozzle, Fourier-transform microwave spectrometer. An analysis of observed nuclear hyperfine structure leads to the H, 19F nuclear spin–nuclear spin coupling constants DHFaa =−190(2) kHz and (DHFbb−DHFcc) =−57(4) kHz for 32SO2⋅⋅⋅HF, and to the D-nuclear quadrupole coupling constants χaa =227(3) kHz and (χbb−χcc) =68(13) kHz for 32SO2⋅⋅⋅DF. Rotational and centrifugal constants have been determined for all three isotopic species, with the following values for 32SO2⋅⋅⋅HF: A0=16 502.775(4) MHz, B0=2100.308(1) MHz, C0=1853.642(1) MHz, ΔJ =18.31(2) kHz, ΔJK =−521.78(4) kHz, and δJ =4.37(3) kHz. The rotational constants for the three isotopic species are interpreted in terms of a planar geometry in which hydrogen fluoride forms a cis hydrogen bond to one of the oxygen atoms of SO2. Assuming a linear hydrogen bond and unchanged subunit geometries, it is found that r(O⋅⋅⋅F)=2.818(8) Å and θ=215.1° where θ is the S=O⋅⋅⋅H bond angle. The nuclear hyperfine coupling constants are shown to be consistent with this arrangement.
Infrared spectra of HF complexes with methane, silane, and germane
Authors: Davis Steven R. , Andrews Lester
Published: July 2002

HF complexes with methane, silane, and germane were prepared in noble gas matrices and studied using infrared spectroscopy and Hartree–Fock (SCF) calculations. The spectra indicate that two types of 1:1 complexes were formed, a normal one in which the hydrogen of HF is interacting with one hydrogen of silane or germane, and a reverse complex in which the fluorine of HF is interacting with one hydrogen atom of methane. The IR inactive symmetric C–H stretch in CH4 was observed in the CH4--FH complex as a weak band at 2914 cm−1. In the silane--HF and germane--HF complexes, the Si–H and Ge–H stretches were perturbed approximately 50 cm−1 to higher energy relative to the antisymmetric stretch ν3 in each parent molecule, but the ν1 modes were masked by the strong ν3 parent bands. Higher order 1:2 (AH4:HF) complexes were also observed and support the normal or reverse-type geometry of the 1:1 complexes.
Thermal effects on triplet exciton processes in anthracene crystals
Authors: Yokoi Kohei , Ohba Yujiro
Published: July 2002

Energy transfer and fusion annihilation of the triplet exciton were studied in anthracene crystals using delayed fluorescence. The decay rates of the exciton via monomolecular and bimolecular processes (β and γ, respectively) were measured at temperatures between 90–400 K. As predicted by kinetic analysis including the exciton-trapping effect, the same temperature dependence was obtained on β and γ by eliminating the following thermal effects on the diffusion and fusion-annihilation rates. The energy transfer to traps was diffusion limited, and the diffusion rate decreased by a factor of about 3 on heating from 90 to 400 K. The fusion-annihilation rates between free and trapped excitons, which were about 105 times larger than that between two free excitons, increased as the temperature was raised. The mechanism of the free-trapped fusion must be dominated by some long-range interaction.
The n=2,3 triplet Rydberg states of the HD molecule observed by fast neutral-beam photofragment spectroscopy
Authors: Keiding S. , Bjerre N. , Helm Hanspeter
Published: July 2002

The four states of the 1s3s, 1s3d triplet gerade complex and the metastable 1s2p c 3Π−u state of HD are studied by laser photofragment spectroscopy in a fast mass- and state-selected neutral beam. The spectra are assigned using a model for the l uncoupling in the 3s, 3d complex. Precise experimental molecular constants are obtained for the c state.
Application of the indirect dephasing model to resonance and dispersed fluorescence in the isolated molecular complex
Authors: Hiroike E. , Fujimura Y.
Published: July 2002

The theory of indirect dephasing proposed by Hiroike is applied to studying the mechanism of line broadening in resonance and dispersed fluorescence spectra of molecular complexes in supersonic free jet. In the indirect dephasing model, the width of the luorescence spectra which is characterized by the homogeneous linewidth can be expressed in terms of two parameters, the rate of intramolecular vibrational redistribution (IVR), γ and frequency change induced by the IVR, δω. It is shown that the non-Markovian character introduced into the interaction between the intra- and intermolecular modes reduces the indirect dephasing rate. The theory is applied to calculation of the linewidth of the resonance fluorescence of the tetrazine–Ar molecular complex excited in 6a1 vibronic level. The introduction of the non-Markovian character is necessary to calculate the linewidth of the fluorescence in a molecular complex with a few intermolecular modes such as tetrazine–Ar.
Electron spin resonance detection of Jahn–Teller effect induced phase transition with thermal hysteresis in the copper(II) doped zinc(II)-bis-histidine systems: Free and hindered rotation of histidine molecules in solid lattice
Authors: Rockenbauer A. , Györ M. , Szabó-Plánka T.
Published: July 2002

Anomalous temperature effects of the ESR spectra were found in copper doped zinc (II)-bis-(histidine) powders. In the L-histidine complex, reversible transitions between solid-like and liquid-like spectra were observed at 8 °C by increasing, and at 0 °C by decreasing temperature. In the mixed L-histidine–D-histidine complex, the magnetic parameters of solid-like spectra change strongly around −20 °C. The anomalies were explained by Jahn–Teller effect stabilized square planar geometry around the doping copper centers in the lattice of zinc complex with tetrahedral geometry. The phase transitions can be induced by rearrangements of the water molecules coordinated to the copper ions into their regular positions in the zinc lattice. This molecular displacement can facilitate either uniaxial rotation or torsional oscillation of the histidine molecules in the respective lattices.