bluuebunny/crossref_metadata_2025 huggingface dataset:
Parametric sensitivity of system stability in chemical dynamics
Authors: Hedges Richard M. , Rabitz Herschel
Published: July 2002

A combined stability–sensitivity analysis is implemented to probe the details of the solutions of systems of ordinary differential equations arising in chemical dynamics. The dynamical Green’s function matrix is calculated and then diagonalized to yield the stability eigenvalues and eigenvectors. The latter eigenvectors prescribe the combinations of state variables (respectively, concentrations in kinetics or coordinates and momenta in classical mechanics) giving rise to the stable or unstable motion as indicated by the associated eigenvalues. In addition, the sensitivities of the eigenvalues and eigenvectors are calculated. This approach provides pertinent information regarding the response of system stability to the relevant physical parameters. Model problems from homogeneous chemical kinetics and classical molecular dynamics are studied using this analysis. The additional information available is discussed in comparison with other approaches to stability analysis.
The study of the evolution of some self-organized chemical systems
Authors: Bourceanu G. , Moroşanu G.
Published: July 2002

Starting from a self-organized chemical model with three chemical variables endowed with replication properties, we first get a model that includes the new species X4 with autocatalytic properties. Then we get another model where the additional species X5 appears leading to a model with six chemical variables. We prove that all these models are self-organized.
A time-of-flight study of H+ fragments produced by low-energy electron bombardment of the hydrogen halides
Authors: Kittams B. K. , Hsieh K. C. , McIntyre L. C.
Published: July 2002

Time-of-flight and kinetic energy distributions were obtained for H+ fragments resulting from electron bombardment of HF, HCl, HBr, and HI at electron energies between 21.2 and 51.2 eV. Several distinct features were observed in these spectra for each molecule and the corresponding threshold electron bombarding energies were obtained. Some of these features are proposed to originate from dissociation of HX+ which is excited by removing an inner σ-shell electron in the corresponding molecule. Results from recent (e,2e) experiments support this proposal.
ESR study on rotational motions of some free radicals in the supercooled and glassy organic solvents
Authors: Ohta Nobuaki , Kuwata Keiji
Published: July 2002

Rotational motions of solute molecules in supercooled and glassy media were investigated with the temperature-dependent ESR spectra of the organic nitroxides and chlorine dioxide in some organic solvents. The rotational correlation times (τR’s) of the solutes were estimated by the method of Freed et al. for the nitroxides and by the spectral simulations based on the stochastic Liouville method for chlorine dioxide. From comparison between τR’s of the solutes and the dielectric relation times of the solvents or some equations which provide τR’s of molecules in supercooled liquid, it was concluded that a solute molecule rotates almost independently from motions of solvent molecules. The solvent-dependent parts of τR’s of the solute molecules obtained in the various combinations of the solute and solvents can be treated as perturbation for the rotational motion of a solute molecule. Nonlinear dependence of τR’s of the solutes on the relaxation times calculated from Stokes–Einstein’s relation shows such situation can be caused from inertial motion of a solute molecule.
New raising and lowering operators for highly anharmonic coupled oscillators
Authors: Kellman Michael E.
Published: July 2002

New raising and lowering operators A+, A are proposed for vibrations in the highly anharmonic regime (roughly corresponding to the zone of overlapping nonlinear resonances and the transition to classical chaos). All matrix elements 〈ν+k‖0‖ν〉 of p and powers xλ of x=2Ce−aq between bound states ‖ν〉 of the Morse oscillator can be written exactly in terms of powers of the new operators, (A+)k and (A)k, and a supplementary operator α̂. In terms of α̂, A+, A, the momentum and coordinate operators take a form similar to that of the harmonic oscillator in terms of a+, a. It is shown that it is the operator α̂ that is crucial for representing the novel qualitative behavior of dynamical operators in the highly anharmonic regime. It is therefore suggested that the operators α̂(A+)k and α̂(A)k be used in place of the conventional (a+)k and (a)k in fits and dynamical models for systems of coupled anharmonic vibrations.
Vapor–solvent shift of the lowest frequency vibration of p-benzoquinone and toluquinone and the consequences for the vibrational and electronic spectral assignments
Authors: Trommsdorff H. P. , Wiersma D. A. , Zelsmann H. R.
Published: July 2002

Far-infrared (20–230 cm−1) absorption spectra of p-benzoquinone-h4,-d4 and of toluquinone have been measured. In the vapor phase, the lowest frequency vibration of these three compounds is found at 88.9, 87.5, and 82.3 cm−1, respectively. In the condensed phase the frequency increases by approximately 20 cm−1. These measurements clarify assignments, based on this vibrational mode, of the visible absorption spectrum as well as of other vibrations. It is proposed that intermolecular forces are responsible for the large frequency shift and that the observed width in solution (≂24 cm−1) is homogeneous, reflecting rapid relaxation processes of this large amplitude low frequency bending mode.
Unique labelling of J states in finite symmetry
Authors: Yeung Y. Y. , Newman D. J.
Published: July 2002

Tables are given which provide a method of generating a unique labelling scheme for all finite point group irreducible representations subduced from the representations of D(J) of SO3. A method is also given for determining the explicit basis states corresponding to this unique labelling, and some examples are given for cubic and D2d symmetries. The circumstances in which such basis states may be employed as approximate crystal field eigenstates are discussed.
Free radicals formed by reaction of silane with hydrogen atoms in rare gas matrices at very low temperatures
Authors: Nakamura K. , Masaki N. , Sato S. , Shimokoshi K.
Published: July 2002

The radicals formed by the reaction of SiH4 with H produced by the photolysis of HI in the matrices of Xe and Kr were investigated by electron spin resonance (ESR) spectroscopy at the temperatures between 4.2 and 100 K. The radicals observed were identified as SiH3 and SiH5. The newly observed radical SiH5 is considered as the intermediate of the reaction SiH4+H→SiH3+H2. The radical had two conformers; both were observed in a Xe matrix, while only one was observed in a Kr matrix. The ESR parameters of these radicals were determined by numerical deconvolution of the observed spectra. The hyperfine coupling of 29Si in silyl radicals isolated in Kr was determined accurately by the present method of the radical formation. The value obtained was 189.5 G instead of 266 G previously reported.
SiLiF: The competition between electronic effects favoring singlet and triplet ground states. A case study
Authors: Colvin Michael E. , Schaefer Henry F. , Bicerano Jozef
Published: July 2002

Electronegative substituents such as F favor closed-shell singlet, while electropositive substituents such as Li favor triplet ground electronic states in carbenes and silylenes. Therefore, SiLiF presents a very instructive case study of the competing electronic effects involved. We have examined the minima on the lowest-lying 1A′, 1A″, and 3A″ potential surfaces of SiLiF, using self-consistent-field and configuration interaction methods with a basis set at the double zeta plus polarization level. Two minima, one with a wide and the other with a narrow bond angle θ (LiSiF), have been found for each of the three electronic states, in analogy with SiHLi. The most stable minimum at all levels of approximation is the narrow-angle triplet (3A″ I). It lies below the second most stable minimum, the narrow-angle closed-shell singlet (1A′ I), by 10.5 kcal/mol at the CISD level of theory. This result is similar to the singlet–triplet separation in SiHLi at the same level of theory (10.7 kcal/mol), demonstrating that the electropositive Li atom prevails against the electronegative F. The harmonic vibrational frequencies and the results of a Mulliken population analysis are also presented for each minimum.
Ultraviolet absorption cross sections of infrared laser excited UF6
Authors: Kim K. C. , Freund S. M. , Sorem M. S. , Smith D. F.
Published: July 2002

Ultraviolet absorption cross sections of ν3 vibration-excited UF6 molecules were measured in the wavelength region between 230 and 280 nm. The state-selective excitation was accomplished by 16 μm laser pumping of the ground vibrational state of flow-cooled UF6. Maximum changes in the absorption cross sections were observed toward longer wavelengths in the wings of the two charge transfer bands located at 220 and 260 nm. The results are discussed in terms of a transition from the ν3 vibrationally excited state to an upper dissociative potential surface. The change in the UV absorption cross section was also monitored as a function of the IR laser frequency and the sample gas temperature. The IR excitation spectrum follows qualitatively the low resolution contour of the ν3 Q branch. The magnitude in the absorption change is dependent on the fraction of molecules being accessed by the IR laser. The characteristic relaxation time for the ν3 excitation was estimated to be about 0.25 μs Torr at 100 K.
Comparison of different theories for slow-tumbling axial nitroxide ESR hyperfine centers in polycrystalline-amorphous substances
Authors: Lee Sook , Tang Sheng-Zhang
Published: July 2002

The electron spin-resonance ESR hyperfine spectra computed by the Freed numerical–theoretical method have been critically compared with the recent analytical–theoretical results for axially symmetric nitroxide ESR centers undergoing isotropic orientational diffusion motion in polycrystalline-amorphous substances. Consistent with the new analytical–theoretical results, the dependencies of slow-motional line broadening and line shift on the associated orientational correlation time τ of the parallel-edge ESR centers determined from the Freed theoretical spectra are found to be τ−1/2 within numerical computational limits. In addition to this τ dependence, the absolute magnitudes of the slow-motional line broadening and line shift are in reasonable agreement between the two theories. Except for the occurrence of some unexplainable extra lines in the Freed theoretical spectra, their overall powder-pattern structures are consistent with those computed by the analytical–theoretical results.
Raman spectrum of ferroelectric PbHPO4
Authors: Ohno N. , Lockwood D. J.
Published: July 2002

The Raman spectrum of ferroelectric PbHPO4 (TC∼310 K) has been measured at temperatures between 10 and 320 K in the frequency region 10–3200 cm−1. Mode assignments have been made, which are consistent with the m(Cs) point-group symmetry of the ferroelectric phase. From examination of the correlation field splittings, it is concluded that the distortion of the PO4 tetrahedron is relatively small. The Raman study confirms the acentric structure of the paraelectric phase as proposed from neutron and x-ray diffraction data. No drastic change in the Raman spectrum occurs at TC. A soft mode with A′(Bu)-type symmetry is observed, which softens from 77 cm−1 at 10 K to 50 cm−1 at 300 K. The A″(Au)-type tunneling mode is tentatively assigned to a line at 164 cm−1. A low-frequency wing appears near 200 K and its intensity grows with increasing temperature reaching a maximum around 290 K. The presence of the wing feature indicates the phase transition is of an order–disorder type.
Comparison of electron spin resonance and electron spin echo spectra of chlorophyll-a cation radical in frozen vesicle and glassy solutions
Authors: Ohta Nobuaki , Narayana M. , Kevan Larry
Published: July 2002

Electron spin resonance (ESR) and electron spin echo (ESE) studies of chlorophyll-a (Chla) cation radical (Chla+) produced by photoirradiation and chemical oxidation have been carried out in frozen dl-α-dipalmitoylphosphatidylcholine (DPPC) vesicular and methylene chloride–methanol glassy solutions. The nitrogen modulation patterns are different between the two systems which must reflect a difference in the local structure of the pyrrole ring in Chla+. Fourier transformation of the ESE modulation spectra of Chla+ shows several modulation frequencies of nitrogen nuclei in the pyrrole rings of Chla+ which appear to differ somewhat between the two types of frozen solutions.
Calculations of induced moments in large molecules. V. A study of intermolecular interactions and a functional group analysis of some amides, through the investigation of their polarizabilities and hyperpolarizabilities. A comparative study
Authors: Waite J. , Papadopoulos M. G.
Published: July 2002

The calculated polarizabilities α and hyperpolarizabilities γ of some amides are reported. The effect on these properties of methylation, bonding and nonbonding interactions, and isomerism, has been analyzed. Some aggregates of formamide have been considered and the cooperative character of the intermolecular interactions is demonstrated. The effective properties (α and γ) of several functional groups, associated with the examined amides, were studied using an appropriate index. The established order for the relative polarizabilities of the considered functional groups is: NH2OC<HCH3N<(CH3)2N<NHCH3OC<N(CH3)2OC while the relative hyperpolarizabilities follow the order: HCH3N<(CH3)2N<NH2OC<NHCH3OC<N(CH3)2OC. The computations have been performed by employing the CHF-PT-EB-CNDO method. This procedure gave, for the considered amides, polarizability values which are in satisfactory agreement with experimental data (theoretical and experimental values differ on average by 9.4%).
Detection and characterization of the NO(L′ 2Φi) state at 6.6 eV
Authors: Taherian M. R. , Cosby P. C. , Slanger T. G.
Published: July 2002

By using the techniques of stimulated emission pumping combined with fluorescence dip spectroscopy it has been possible to characterize the metastable NO(L′ 2Φ) state. The spectroscopic parameters are: Te =53 675.51 (47) cm−1, ωe =1000.0 (6) cm−1, ωexe =10.090 (64) cm−1, Be =1.1163 (39) cm−1, αe =0.016 85 (53) cm−1, Av =−42.567 (161)−0.196 (160) [v+1/2] cm−1, re =1.4222 (25) Å. The state is produced by initially populating NO(B′ 2Δ5/2, v=3, J=7.5) with 157.630 nm radiation from an F2 laser. While observing the B′–X fluorescence emission, a Raman-shifted dye laser is tuned through the appropriate spectral region (950–1300 nm), and intensity decreases are observed at the positions of the J=6.5, 7.5, and 8.5 rotational levels of the 2Φ state (as well as other states). The first four vibrational levels have been detected in this manner, with the numbering being confirmed by the recent matrix isolation detection of v=0 by Chergui et al. Perturbations in the v=1 level of the B′ 2Δ state, postulated by Huber as being due to the L′ 2Φ state, are shown to involve the v=9 level. Data for 14N16O and 14N18O at the B′(1)−L′(9) perturbations are used in the evaluation of the spectroscopic constants.
Photoelectron generation and transfer to cytochrome c studied by nanosecond transient absorption spectroscopy
Authors: Cartling Bo , Holtom Gary R. , Spiro Thomas G.
Published: July 2002

A reaction scheme is proposed and shown to be useful for time-resolved spectroscopy of cytochrome c reduction on the nanosecond timescale. It is based on photochemical generation of hydrated electrons from ferrocyanide by a pulsed UV laser and the reduction of cytochrome c by the hydrated electrons. The reaction scheme is such that the system nearly regenerates itself, and it can be modified for more complete regeneration. Results by two types of nanosecond transient absorption spectroscopy are presented. Both methods utilize pulses of the fourth harmonic, at 266 nm, from a Nd:YAG laser for the photolysis. One technique is based on a gated vidicon detector for identification of the transient species. The other uses a transient recorder for kinetic measurements at a higher time resolution. The observed results are in close agreement with those obtained by a kinetic analysis including all coupled reactions and using previously determined values of the quantum yields and rate constants. The approach utilizing photochemically generated hydrated electrons as reductants might be useful in several other systems for studies of transient states involved in redox transitions.
Beams of doubly ionized molecules from a tandem accelerator
Authors: Galindo-Uribarri A. , Lee H. W. , Chang K. H.
Published: July 2002

We report the observation of 3–4 MeV beams of several species of small doubly charged molecules (10B11B++, 10B++2, 11B12C++, 9Be14N++, 12C13C++, 12C13CH++, 12C14N++, 12C2H++, 12CH++2, 9Be16O++, 10B16O++) emerging from a tandem accelerator. These observations significantly increase the number of such molecules known. All are probably produced in metastable states with lifetimes longer than 1 μs. Substantial fluxes (>108 molecules per second was shown for CN++) of these doubly charged molecules were obtained and they were identified by observing the fragmentation of molecular ions after passing through a carbon foil. In some cases the molecules are observed to decay in flight. An efficiency of 10−4 in producing mass 25 molecules (12C13C++ +12C2H++) has been measured. Advantage is taken of the existence of ‘‘atomic interference free’’ mass regions, where no atomic negative ions are formed, therefore allowing the production of pure molecular beams. Some implications of this work for accelerator mass spectrometry (AMS) are discussed. An application of doubly positive charged molecules in a search for doubly negative charged molecules was made, establishing an upper limit of 1:1010 of 10B11B−−/10B11B− and of 1:109 of 12C13C−−/12C13C−.
Translation-rotation invariance for N-particle systems: Internal coordinates and search for stationary points in reduced spaces
Authors: Banerjee Ajit , Jensen James O. , Simons Jack
Published: July 2002

Using the translational and rotational invariance of the energy, we show that for an N-body system there exists a subset of 3N−6 Cartesian coordinates such that the derivatives of the energy of a given order with respect to the members of this subset form an independent and complete set. That is, all other derivatives can be calculated knowing these independent derivatives. We further show that this subset of coordinates can be chosen to be a bonafide set of internal coordinates. Since these coordinates are a subset of the 3N Cartesian coordinates, they are orthonormal and uniform. Applications have been made of such internal coordinates in algorithms which search for stationary points on potential energy surfaces. It is shown that the surface walking algorithms are exactly separable for these coordinates. Thus the problem can be reexpressed in terms of (3N−6) Cartesian variables without the annoying zero eigenvalues of the Hessian (of the energy) matrix corresponding to the translational and rotational eigenvalues.
Multiplet splitting (broadening) of the Ru LII, III edge white lines in the x-ray absorption near edge spectra of Ru(NH3)6Cl3
Authors: Sham T. K.
Published: July 2002

It is shown that the linewidth broadening of the Ru LII, III edge white lines of Ru(NH3)6Cl3 can be accounted for on the basis of final state multiplet splitting. The spread in the final state exchange energy has been calculated to be ∼0.5 eV, which is in reasonable accord with the observed broadening.
A time-resolved EPR study of short-lived triplet states: Host and temperature dependences of triplet properties of phthalazine
Authors: Terazima Masahide , Yamauchi Seigo , Hirota Noboru
Published: July 2002

The triplet properties of phthalazine are investigated by means of the time-resolved EPR technique with laser excitation in various hosts over a wide range of temperature. The host and temperature dependences are interpreted satisfactorily in terms of the vibronic mixing between the 3nπ* and 3ππ* states. From the host dependences of the EPR parameters the zfs of the pure 3nπ* state of phthalazine is deduced to be Xn =0.027 cm−1, Yn =−0.058 cm−1, and Zn =0.031 cm−1. The fraction of the 3nπ* character of the T1 state is estimated to be ∼0% in ethanol, benzoic acid (BAC), and 1, 4-dichlorobenzene (DCB), 14% in 1, 2, 4, 5-tetrachlorobenzene (TCB), 60% in biphenyl (BP), and 84% in durene. The temperature dependences of the zfs, linewidth, phosphorescence spectrum, and lifetime are investigated and the results are explained using a continuum model. From the simulation of the temperature dependence of the triplet lifetime in the DCB host the decay rate constant of the second excited triplet (3nπ*) state is estimated to be 2.5×104 s−1. A drastic increase of the decay rate at higher temperatures suggests the presence of a higher 3nπ* state with a decay rate constant of ∼106 s−1. Possible causes for the lack of phosphorescence and fast radiationless decay are also discussed.
Infrared and far-infrared laser magnetic resonance spectroscopy of the GeH radical: Determination of ground state parameters
Authors: Brown John M. , Evenson K. M. , Sears Trevor J.
Published: July 2002

The GeH radical has been detected in its ground 2Π state in the gas phase reaction of fluorine atoms with GeH4 by laser magnetic resonance techniques. Rotational transitions within both 2Π1/2 and 2Π3/2 manifolds have been observed at far-infrared wavelengths and rotational transitions between the two fine structure components have been detected at infrared wavelengths (10 μm). Signals have been observed for all five naturally occurring isotopes of germanium. Nuclear hyperfine structure for 1H and 73Ge has also been observed. The data for the dominant isotope (74GeH) have been fitted to within experimental error by an effective Hamiltonian to give a set of molecular parameters for the X 2Π state which is very nearly complete. In addition, the dipole moment of GeH in its ground state has been estimated from the relative intensities of electric and magnetic dipole transitions in the 10 μm spectrum to be 1.24(±0.10) D.
Perturbation theory of electrolyte solutions
Authors: Boyle E. J. , McQuarrie D. A.
Published: July 2002

First-order perturbation theories of Barker, Henderson, and Leonard, and Chandler, Weeks, and Andersen are applied to model ionic solutions. The results for osmotic coefficient are compared to one another and to hypernetted chain calculations. If the intermolecular potential of the model ionic solution contains no discontinuity, the results of each perturbation theory agree with one another, but are systematically smaller than the results of hypernetted chain calculations. If the intermolecular potential of the model ionic solution contains discontinuities, Chandler–Weeks–Andersen theory more closely matches the results of hypernetted chain calculations than does Barker–Henderson–Lenard theory.
Fractal to Euclidean crossover and scaling for random walks on percolation clusters. II. Three-dimensional lattices
Authors: Argyrakis Panos , Kopelman Raoul
Published: July 2002

We perform random walk simulations on binary three-dimensional simple cubic lattices covering the entire ratio of open/closed sites (fraction p) from the critical percolation threshold to the perfect crystal. We observe fractal behavior at the critical point and derive the value of the number-of-sites-visited exponent, in excellent agreement with previous work or conjectures, but with a new and improved computational algorithm that extends the calculation to the long time limit. We show the crossover to the classical Euclidean behavior in these lattices and discuss its onset as a function of the fraction p. We compare the observed trends with the two-dimensional case.
A study of the unimolecular decompositions of the (C3H6)+2 and (c-C3H6)+2 complexes
Authors: Tzeng W.-B. , Ono Y. , Linn S. H. , Ng C. Y.
Published: July 2002

The major product channels identified in the unimolecular decompositions of C3H+6⋅C3H6 and c-C3H+6⋅c-C3H6 in the total energy [neutral (C3H6)2 or (c-C3H6)2 heat of formation plus excitation energy] range of ∼230–450 kcal/mol are C3H+7+C3H5, C4H+7+C2H5, C4H+8+C2H4, and C5H+9+CH3. The measured appearance energy for C4H+7(9.54±0.04 eV) from (C3H6)2 is equal to the thermochemical threshold for the formation of C4H+7+C2H5 from (C3H6)2, indicating that the exit potential energy barrier for the ion–molecule reaction C3H+6+C3H6→C4H+7+C2H5 is negligible. There is evidence that the formations of C4H+7+C2H4+H from (C3H6)+2 and (c-C3H6)+2 also proceed with high probabilities when they are energetically allowed. The variations of the relative abundances for C4H+7,C4H+8, and C5H+9 from (C3H6)+2 and (c-C3H6)+2 as a function of ionizing photon energy are in qualitative agreement, suggesting that (C3H6)+2 and (c-C3H6)+2 rearrange to similar C6H+12 isomers prior to fragmentation. The fact that C6H+11 is found to be a primary ion from the unimolecular decomposition of (c-C3H6)+2 but not (C3H6)+2 supports the conclusion that the distribution of C6H+12 collision complexes involved in the C3H+6+C3H6 reactions is different from that in the cyclopropane ion–molecule reactions. Using the ionization energies (IE) of (C3H6)2(9.33±0.04 eV) and (c-C3H6)2(9.61±0.04 eV) determined in this study, the calculation of the bond dissociation energies for C3H+6⋅C3H6 and c-C3H+6⋅c-C3H6 gives 0.43 and 0.14 eV, respectively. The measured IE of C3H6 is 9.738±0.003 eV and that of c-C3H6 is 9.721±0.011 eV.
Rotational disorder in crystalline pyrene as a model for layered aromatic structures
Authors: Boeyens Jan C. A. , Levendis Demetrius C.
Published: July 2002

The lattice energy surface of crystalline pyrene, as a model of layered aromatic structures, is analyzed numerically as a function of molecular reorientation. Cooperative effects are simulated by concerted rotation of neighboring molecules and the preservation of translational symmetry. The potential energy surface calculated by intermolecular atom–atom potentials corresponds to those of more rigid binary units like metallocenes and π-molecular compounds of the charge-transfer type. Common features in physical properties and low-temperature phase transitions with crystal fracture, observed for all these compounds, are readily accounted for in terms of domain disorder, calculated for the room-temperature structures. Because of the high molecular symmetry, rotationally disordered arrangements 60° apart are difficult to distinguish crystallographically and the predicted order–disorder transition for pyrene has only been characterized spectroscopically.
Perturbation approximation to the structure factor of two-dimensional fluids with repulsive pair potentials
Authors: Bonissent A. , Bruch L. W.
Published: July 2002

The first order approximation of the perturbation theory of Andersen, Weeks, and Chandler is used to estimate the pair distribution function of two-dimensional fluids interacting with inverse power law repulsive pair potentials. The wave number of the maximum in the liquid structure factor and the width of the maximum are followed as a function of density and power law index. Calculations are also reported for the expectation value of the inverse cube of the interparticle distance, a quantity entering in the theory of the depolarizing fields of adsorption dipoles.
A comment on the consistency of truncated nonlinear integral equation based theories of freezing
Authors: Cerjan Charles , Bagchi Biman , Rice Stuart A.
Published: July 2002

We report the results of two studies of aspects of the consistency of truncated nonlinear integral equation based theories of freezing: (i) We show that the self-consistent solutions to these nonlinear equations are unfortunately sensitive to the level of truncation. For the hard sphere system, if the Wertheim–Thiele representation of the pair direct correlation function is used, the inclusion of part but not all of the triplet direct correlation function contribution, as has been common, worsens the predictions considerably. We also show that the convergence of the solutions found, with respect to number of reciprocal lattice vectors kept in the Fourier expansion of the crystal singlet density, is slow. These conclusions imply great sensitivity to the quality of the pair direct correlation function employed in the theory. (ii) We show the direct correlation function based and the pair correlation function based theories of freezing can be cast into a form which requires solution of isomorphous nonlinear integral equations. However, in the pair correlation function theory the usual neglect of the influence of inhomogeneity of the density distribution on the pair correlation function is shown to be inconsistent to the lowest order in the change of density on freezing, and to lead to erroneous predictions.
Validity of the Ruff–MKW boiling point method: Vapor pressures, diffusion coefficients in argon and helium, and viscosity coefficients for gaseous cadmium and zinc
Authors: Wahlbeck P. G. , Myers D. L. , Truong V. V.
Published: July 2002

The Ruff–MKW boiling point method is used to determine equilibrium vapor pressures greater than 660 Pa (5 Torr). Samples are vaporized from a Ruff cell, which has a capillary exit, in the presence of an inert gas. Viscosity coefficients and gaseous interdiffusion coefficients may be determined also. This is a second study of the method using Cd(l) and Zn(l) as samples. For the first study with CsCl(l), see J. Chem. Phys. 81, 915 (1984). Vapor pressure data are in good agreement with previous data and gave a third-law ΔsubH0(298) for Cd(s) of 111.95±0.42 kJ/mol and for Zn(s) of 130.65±0.48 kJ/mol. Analyses of the diffusion coefficients gave atomic diameters of 4.06×10−10 m for Cd and 3.46×10−10 m for Zn; these values are somewhat larger than previously measured values. In these experiments when the equilibrium vapor pressures were greater than 13 000 Pa (100 Torr), the need to consider heat transfer from the furnace to the vaporizing sample was noted, i.e., sample cooling occured due to rapid vaporization. Validity of the MKW analysis was found.
Sudden representation and sudden approximation quantal generalized master equation
Authors: Chan C. K. , Kouri D. J.
Published: July 2002

The application of the sudden approximation in the derivation of a quantal generalized master equation (GME) is examined. Two different types of physical systems are considered. One is a composite system comprised of a fast primary system and slow bath compared to the time the former is coupled to the latter. The other is a composite system comprised of a slow primary system and fast bath. The resulting sudden GME’s for both cases contain non-Markovian memory kernels. In the second case, the memory kernel can be further approximated by a Markovian form. The resulting Markovian-sudden GME is identical to the GME obtained by using the adiabatic elimination method for removing the (fast) stochastic bath coordinates. Using a representation of the Schrödinger propagator for the density operator analogous to the recently developed (energy) sudden representation of the Schrödinger propagator for the wave function, the exact GME is recast into a form such that when the memory kernel and the inhomogeneity term of the equation are expanded in a perturbation series, the zeroth order equation is in the sudden approximation form. Finally, a harmonic oscillator coupled linearly to a bath of harmonic oscillators is used as an illustration. The behavior of the bath correlation functions in the Markovian and the sudden limits is examined. The reduction of the exact GME to the sudden approximation form is also considered.
Many-body perturbation theory for effective Hamiltonians using nonorthogonal basis sets
Authors: Ng Betty , Newman D. J.
Published: July 2002

A diagrammatic many-body perturbation approach using nonorthogonal basis sets is used to derive explicit expressions for an Hermitian effective Hamiltonian matrix. Approximate overcompleteness is shown not to lead to any difficulties provided that an exact inverse of the overlap matrix is obtained. Applications of the formalism to crystal-field calculations are discussed in detail.
Analysis of torsional spectra of molecules with two internal C3v rotors. XXIII. Microwave, infrared, and Raman spectra, barriers to internal rotation, and vibrational assignment of 3,3,3-trifluoro-2-methylpropene
Authors: Guirgis G. A. , Durig J. R. , Li Y. S.
Published: July 2002

The microwave spectrum of 3,3,3-trifluoro-2-methylpropene, H2C=C(CH3)CF3 has been recorded from 18.5 to 39.0 GHz. Only a-type transitions were observed and R-branch assignments have been made for the ground vibrational state as well as for three vibrational excited states of the CF3 torsion and one excited state of the CH3 torsion. The rotational constants for the ground vibrational state were found to have the following values: A=3549.25±0.35, B=2465.82±0.05, and C=1978.25±0.02 MHz. The dipole moment components were determined from the Stark effect to be ‖μa‖=2.44±0.01, ‖μb‖=0.59±0.09, and ‖μt‖=2.51±0.03 D. From an analysis of the internal rotational splittings, the threefold barrier for the methyl group was found to be 603±19 cm−1 (1.72 kcal/mol). This value is consistent with the value of 610±4 cm−1 (1.74 kcal/mol) obtained from the far infrared spectrum where the fundamental was assigned at 160.9 cm−1, but only if kinetic coupling between the perfluoromethyl and methyl torsion is taken into account. The CF3 torsional mode was observed at 55.9 cm−1 from which a threefold periodic barrier of 743±7 cm−1 (2.12 kcal/mol) was calculated. No appreciable potential coupling was found between the two C3v rotors. The infrared (3500 to 30 cm−1) and Raman spectra (3500 to 10 cm−1) have been recorded for both the gas and solid states. Additionally, the Raman spectrum of the liquid was recorded and qualitative depolarization values were obtained. All of the normal modes have been assigned based on band contours, depolarization values, and group frequencies. These results are compared to the corresponding quantities in some similar molecules.
Quantum mechanical study of multiphoton excitation of the nonrotating OCS molecule
Authors: Milfeld Kent F. , Wyatt Robert E.
Published: July 2002

A quantum mechanical approach based upon Floquet theory is used to study IR multiphoton excitation of the nonrotating OCS molecule within the frequency and power range of the cw CO2 laser. Using a classical field interacting with a quantum molecule in the dipole approximation, the effects of laser frequency and power are investigated by computing long-time average transition probabilities, total energy absorption, and time-dependent probabilities. While multiphoton excitation is found to occur at the most intense CO2 laser line [P(24)], high-order excitation dominates near the weaker P(16) line, some 10 cm−1 higher in photon energy. Also, various types of time averaging and approximate dipole interactions are investigated.
A study of the charge and potential distribution at the semiconductor/electrolyte interface for the condition of degeneracy
Authors: Gerischer Heinz , McIntyre Robert
Published: July 2002

We have calculated the differential surface capacitance for two different semiconductors MoSe2(0001) and WSe2(0001), as a function of applied potential, for the condition of degeneracy. The calculated curves are compared with the experimentally measured capacitance for the systems, MoSe2(0001) in propylene carbonate containing 0.1 M LiClO4, for a range of crystal conductivities, and WSe2(0001) in acetonitrile containing 0.2 M (C3H7)4N BF4. As expected the experimental values are significantly lower than the calculated values, since the measured capacitance is the total capacitance for the system which is described by the surface capacitance of the semiconductor in series with the Helmholtz capacitance. Calculations based on this model, using the data for the Helmholtz capacitance for a mercury electrode in the same electrolyte, are shown to be in good agreement with the measured values. The results are discussed with particular reference to the screening distance for the semiconductor surface charge in the degenerate region.
Electronic mechanism for desorption
Authors: Hellsing Bo
Published: July 2002

The electronic mechanism in the thermal desorption process is discussed. It is pointed out that the nature and importance of this mechanism depends strongly on the character of the adsorbate–substrate interaction. The transition rate between bound states, which is a key quantity in the process of desorption, differs by orders of magnitudes for a simple chemisorption system from one theoretical approach to another. A calculation in the spirit of the electron–phonon problem, based on self-consistent electron-structure determinations, is described. From it, it is concluded that there exist chemisorbed species, for which the electron-hole pair mechanism may dominate in the process of desorption.
A class of exactly soluble three-body problems
Authors: Crandall R. , Bettega R. , Whitnell R.
Published: July 2002

A class of three-body problems characterized by masses m, m, M and ‘‘helium-like’’ Hamiltonian H=−(1/2m)(∇21+∇22) −(1/2M)∇23 +V3(r12)+V2(r13)+V1(r23), where V1, V2 are attractive but V3 is repulsive, is shown to admit of complete analytic solution for arbitrary values of m, M. Qualities of the resulting system depend strongly on the natural parameter m/M. For M≫m we identify a ‘‘helium’’ model for which M is a nuclear mass, while for m≫M we obtain a ‘‘hydrogen molecular ion’’ model for which each mass m is a relatively fixed ‘‘proton’’ site. Exact expectation calculations are used to identify geometrical features of the three-body wave functions in these asymptotic mass regions.
The ideally polarizable interface: Integral equations
Authors: Rosinberg M. L. , Blum L. , Lebowitz J. L.
Published: July 2002

The integral equations used in the microscopic theory of the electric double layer are extended to the case of an impermeable interface separating two conducting media (ionic solutions or plasma). This system is a model for an ideally polarizable interface. Exact relations are given for the contact values of the one particle density function, and also for the pair correlation functions. We solve numerically the Poisson–Boltzmann (PB), the hypernetted chain (HNC), and mean spherical (MSA) approximations, and compare the results to the exact solution of the one component plasma in two dimensions.
Product vibrational state distributions of thermal energy charge transfer reactions determined by laser-induced fluorescence: N++CO→CO+(v=0–2)+N
Authors: Hamilton Charles E. , Bierbaum Veronica M. , Leone Stephen R.
Published: July 2002

The nascent vibrational state distribution of the N++CO→CO+(v=0–2)+N charge transfer reaction is measured at thermal energy. The reaction is carried out in a flowing afterglow and the vibrational state populations are determined by laser-induced fluorescence on the CO+(A 2Π−X 2Σ+) system. The nascent vibrational state distribution for the N++ CO reaction is (0.71±0.05)v=0:(0.27±0.04)v=1:(0.02±0.01)v=2. The observed vibrational distribution suggests that neither a long-range Franck–Condon mechanism nor an energy resonant process adequately describes the charge transfer reaction. A dual channel mechanism of the reaction is considered, in which a fraction of the reactive collisions proceed by a long-range Franck–Condon mechanism while the remainder proceed via a long-lived NCO+ intermediate. The intermediate may lead to the observed extent of CO+ vibrational excitation either through statistical partitioning of the energy or by dynamical changes in the CO bond length through specific molecular orbital occupancies.
Scattering of atoms by a stationary periodically rough hard wall in (n+1) dimensions
Authors: Lakhtakia Akhlesh , Varadan Vijay K. , Varadan Vasundara V.
Published: July 2002

A rigorous treatment of the scattering of atoms by a stationary periodic hard wall in (n+1) dimensions is presented using the T-matrix approach. The normalized Fourier expansion of the surface field used in this formalism is shown to be computationally superior to the GR method of Garcia and the technique used by Goodman. This improvement comes because the surface field representation used here allows one to bypass the restrictions of the Rayleigh hypothesis.
Dynamics of weakly bending rods: A trumbbell model
Authors: Nagasaka Kyosuke , Yamakawa Hiromi
Published: July 2002

Some dynamic properties of weakly bending rod-like polymers are studied on the basis of a trumbbell model which consists of two frictionless bonds and three beads with constraints on bondlengths and with a bending potential between the bonds. The diffusion equation is formulated by imposing the constraints in the diffusion limit (Smoluchowski level), considering fluctuating hydrodynamic interaction. All evaluation is carried out analytically, though only near the rod limit, i.e., to terms of O(α−1) with α the bending force constant. The mean translational diffusion coefficient Dt (at long times) and the dynamic intrinsic viscosity [η] are evaluated by the projection operator method and by the time-correlation function formalism, respectively. The former and the steady-state intrinsic viscosity are evaluated also in the rigid-body ensemble approximation, and it is found that this approximation is very good near the rod limit. Some other features of Dt, including its dependence on time, are also discussed. The results for [η] are equivalent to those of Roitman and Zimm, who have solved the problem numerically for the trumbbell as the Kramers-type chain in the free-draining case; [η] relaxes by end-over-end rotation and bending near the rod limit. However, a comparison of theory with experiment for storage and loss moduli for light meromyosin leads to an estimate of the persistence length too large compared to its known reasonable value.
Comment on: ‘‘Effect of temperature on nondissociative electron attachment of perfluorobenzene’’
Authors: Chen E. C. M. , Wentworth W. E. , Limero T.
Published: July 2002

The rapid decrease in the phenomenological rate of electron attachment to perfluorobenzene with increasing temperature, reported by Spyrou and Christophorou [J. Chem. Phys. 82, 1048 (1985)] can be attributed to electron detachment rather than a change in the rate constant for electron attachment. Using previously published data for the temperature dependence of the electron capture detector response [N. Herdandez-Gil, W. E. Wentworth, T. Limero, and E. C. M. Chen, J. Chromatogr. 312, 31 (1984)], the electron affinity of C6F6 has been calculated to be 0.86±0.03 eV. On the basis of this value the rate constant for electron detachment will become significant at high temperatures in an electron swarm.
Collisional quenching of photoexcited iodobenzene ions: Effect of collision-partner size and deuteration
Authors: Dunbar Robert C. , Ferrara Joseph
Published: July 2002

Energy transfer from vibrationally excited iodobenzene ions to the neutral collision partners hydrogen, methane, and cyclohexane was studied by pressure quenching of two-photon photodissociation in the ICR spectrometer. At a wavelength of 579 nm (600 nm for methane) it was found that hydrogen required 210 collisions, methane 35 collisions, and cyclohexane 4.3 collisions to quench the photoexcited ion below the one-photon threshold at 3000 cm−1. The corresponding deuterated neutrals gave the same extent of quenching at corresponding pressures, implying a collisional efficiency 1.4 times greater for D2 than for H2, 1.1 times greater for CD4 than CH4, and 1.05 times greater for C6D12 than C6H12. The results indicate substantial participation of vibrational degrees of freedom of the neutral in the energy transfer process, but are not consistent with full energy equilibration during each collision. Compared with available results for neutral–neutral collisional quenching, the ion–neutral quenching is comparable for H2, and somewhat more efficient for the larger quench gases.
Bonding in d9 complexes derived from EPR: Application to CuCl2−4, CuBr2−4, and CdCl2:Cu2+
Authors: Aramburu J. A. , Moreno M.
Published: July 2002

In this work are reported the theoretical expressions for the [g], hyperfine, and superhyperfine (shf) tensors of a d9 square-planar complex within a molecular orbital (MO) scheme. These expressions include contributions arising from crystal field and charge transfer excitations calculated up to third and second order perturbations, respectively. This makes the present framework more general than those previously used. Through those expressions we have derived from the experimental EPR and optical data the MO coefficients corresponding to the valence b1g(x2−y2), b2g(xy), and eg(xz,yz) levels and also the core polarization contribution K to the hyperfine tensor for the systems CuCl2−4, CuBr2−4, and CdCl2:Cu2+. The 3d charge obtained for CuCl2−4 is equal to 0.61, 0.83, and 0.85 for the antibonding 3b1g, 2b2g, and 2eg levels, respectively. These figures are much closer to the Xα results by Bencini and Gatteschi [J. Am. Chem. Soc. 105, 5535 (1983)] than to those by Desjardins et al. [J. Am. Chem. Soc. 105, 4590 (1983)]. The σ and π covalency for CuBr2−4 are both higher

than for CuCl2−4 in accord to the lower electronegativity for bromine. However, only for the antibonding 3b1g level of CuBr2−4 have we obtained an electronic charge lying mainly on ligands. The covalency of CdCl2:Cu2+ is smaller than that found for CuCl2−4, a fact associated to a higher metal–ligand distance for the former. Evidence of this statement are also given from the analysis of crystal-field spectra and isotropic shf constant. The values of K derived for CuCl2−4 (128.1×10−4 cm−1), CuBr2−4 (103.6×10−4 cm−1), and CdCl2:Cu2+ (123.9×10−4 cm−1) point out the dependence of K on the equatorial covalency but also on the existence of axial ligands. The [g] tensor of CuBr2−4 is dominated by the charge transfer contribution while the crystal field one is negative. Finally an analysis of the importance of each one of the involved contributions to the spin-Hamiltonian parameters is reported for the three systems, together with the results obtained through a full diagonalization within crystal field and charge transfer states.
High resolution optogalvanic spectroscopy of He 3 1,3D–2 3P transitions
Authors: Fukuda Kazuhide , Fujimaki Shigehiko , Adachi Yukio , Hirose Chiaki
Published: July 2002

He 3 1,3D–2 3P lines have been investigated by optogalvanic spectroscopy in the hollow cathode discharge of He to reveal the presence of the 3 1D2–2 3P2 component which is predicted at 0.0764 cm−1 above the 3 1D2–2 3P1 line appearing at 17 018.137±0.004 cm−1. The assignment of the latter has also been experimentally established by the present study through the use of optogalvanic double resonance methods. The spin-orbit interaction of the 3 1D2 level with the 3 3D2 level is responsible for the appearance of the 3 1D2–2 3P2 line. The relaxation processes among the 3 1D, 3 3D, and 2 3P levels have also been briefly discussed on the basis of the observations of mysterious dips on the double resonance signals and of a broad background signal on Doppler-free intermodulation spectrum.