bluuebunny/crossref_metadata_2025 huggingface dataset:
Uniform semiclassical quantization of regular and chaotic classical dynamics on the Hénon–Heiles surfacea)
Authors: Jaffé Charles , Reinhardt William P.
Published: February 2003

Qualitative arguments (made substantially more quantitative in the accompanying article by Shirts and Reinhardt) are put forward which indicate that the apparently chaotic dynamics on the Hénon–Heiles surface display sufficient regularity on a short to intermediate (but not long) time scale to allow use of standard EBK quantization techniques, taking advantage of the remnants of manifold structure that these remarks imply. A complete uniform semiclassical quantization is carried out using the time independent technique of the Birkhoff–Gustavson normal form, recently introduced in the context of semiclassical quantization by Swimm and Delos.
Approximate constants of motion for classically chaotic vibrational dynamics: Vague tori, semiclassical quantization, and classical intramolecular energy flow
Authors: Shirts Randall B. , Reinhardt William P.
Published: February 2003

Coupled nonlinear Hamiltonian systems are known to exhibit regular (quasiperiodic) and chaotic classical motions. In this and the preceding paper by Jaffé and Reinhardt, we find substantial short time regularity even in the chaotic regions of phase space for what appears to be a large class of systems. This regularity is demonstrated by the behavior of approximate constants of motion calculated by Padé summation of the Birkhoff–Gustavson normal form expansion and is attributed to remnants of destroyed invariant tori in phase space. The remnant toruslike manifold structures are used to suggest justification for use of Einstein–Brillouin–Keller semiclassical quantization procedures for obtaining quantum energy levels even in the absence of complete tori and to form a theoretical basis for the calculation of rate constants for intramolecular mode–mode energy transfer. These results are illustrated in a thorough analysis of the Hénon–Heiles oscillator problem. Possible generality of the analysis is shown by brief consideration of classical dynamics for the Barbanis Hamiltonian, Zeeman effect in hydrogen, and recent results of Wolf and Hase for the H–C–C fragment.
On heterogeneous catalysis near magnetic phase transitions of the catalyst
Authors: Hentschel H. G. E. , Procaccia I.
Published: February 2003

Experiments on adsorption/desorption rates of gases from surfaces of bulk and thin film catalysts show anomalous behavior close to the magnetic phase transition of the substrate. The qualitative behavior of these anomalies, including the appearance of cusps and kinks in Arrhenius plots, their shift from Tc in the case of thin films, and their pressure and isotope dependence are accounted for by a simple model involving renormalized interactions which can be treated accurately in the critical region. Critical exponents are found. A novel prediction concerning a strong pressure dependence for the anomalies in the desorption rates is discussed. The activation energies far above and below Tc are found to be different, in agreement with experiments. In addition, the anomalies in the equilibrium coverages are treated.
UV photoelectron spectroscopy of several one- and two-component organic photoconductors
Authors: Karl Norbert , Sato Naoki , Seki Kazuhiko , Inokuchi Hiroo
Published: February 2003

Solid state photoelectron spectra have been measured at several UV wavelengths for vapor-deposited films of the organic photoconductors phenothiazine, anthracene, and carbazole and for the 1:1 donor:acceptor complexes of phenothiazine, carbazole, and acridine with the common acceptor pyromellitic dianhydride (PMDA). Differences in photoemission threshold energies of the one-component photoconductors are used to estimate hole trap depth energies for systems where one of the compounds is doped with another one. Further, the photoemission threshold values are used for predicting the energy differences of charge transfer transitions in donor:acceptor crystals with a common acceptor. The reliability of this kind of estimation for the above mentioned substances is tested. In addition, by comparing the threshold values obtained for the D:A complexes with those of the neat donors, it is found (in confirmation of an earlier result) that complex formation with PMDA tends to increase the ionization threshold of the respective donor by 0.2–0.3 eV.
ESR of sulfur substituted purines and nucleosides: Hydrogen atom and alkoxy radicals at 20 Ka)
Authors: Kim Hack-soo , Alexander Chester
Published: February 2003

Single crystals of the sulfur-substituted adenosine analog, 6-methylmercaptopurine riboside have been irradiated by x rays and studied by electron spin resonance techniques at 20 K. Three resonances have been identified. The radical R1 exhibited a 506±2 G hyperfine doublet splitting and was identified as trapped hydrogen atoms. Radical R2, a secondary alkoxy radical at O′3 identified previously at 77 K, was shown to be stable at 20 K. Radical R3 exhibited doublet splittings of 21±3 G and 4 to 12 G and g-value principal values of 2.0019, 2.0077, and 2.0429, and was identified as a secondary alkoxy radical at O′2. The presence of trapped hydrogen atoms in coincidence with the O′2 and O′3 hydrogen abstraction radicals at 20 K is an indication of direct hydrogen abstraction as a primary radiation event in this crystal.
Infrared spectrum of the methanol dimer in matrices. Temperature and irradiation effects in solid nitrogen
Authors: Schriver L. , Burneau A. , Perchard J. P.
Published: February 2003

Four different open chain forms of methanol dimer have been identified in nitrogen matrices through temperature and IR irradiation effects. Each form is characterized by two OH stretching vibration frequencies, one (D1) close to the monomer frequency (3664 cm−1) and corresponding to the oxygen perturbed (electron donor) oscillator, and the other (D2) around 3500 cm−1 due to the hydrogen perturbed oscillator. Concentration ratios between two of these species (A: 3655 and 3519 cm−1; B: 3651 and 3504 cm−1) depends reversibly on temperature: the A form is predominant below 8 K while the B form is mainly observed above 10 K; this thermal process is fast. Moreover, the A or B concentration increases by IR irradiation at the expense of the C and D forms (C: 3659 and 3496 cm−1; D: 3654 and 3489 cm−1). This photoisomerization leads to a steady state with predominance of A or B, according to the temperature: its rate, relatively slow, has been quantitatively compared for OH and OD methanols. Since these processes are not observed for methanol in argon matrix, it is suggested that they are favored by the presence of nitrogen around the dimer.
Kinetic rates in the oxygen–iodine system
Authors: Fisk G. A. , Hays G. N.
Published: February 2003

Rate constants governing the following processes were determined at 298 K from optical emission data collected using a flow-tube apparatus: O2(1Δ)+O2(1Δ)→k1O2(1Σ)+O2(3Σ), O2(1Δ)+I*k7→O2(1Σ)+I, I+O2(1Δ)k4→I+O2(3Σ), I*+O2(3Σ)k9 →I+O2(3Σ). Results, in units of cm3 molecule−1 s−1, are: k1=2.0×10−17, k7=8×10−14, and k4+Keqk9=3×10−14, where Keq is the equilibrium constant for the process I+O2(1Δ)⇄I*+O2(3Σ). The quenching probabilities for O2(1Σ) on glass and halocarbon wax were found to be about 2×10−2 and 1×10−3, respectively. The quenching probability for O2(1Δ) on halocarbon wax was found to be about 3×10−5.
Rotational relaxation in supersonic beams of hydrogen by high resolution photoelectron spectroscopy
Authors: Pollard J. E. , Trevor D. J. , Lee Y. T. , Shirley D. A.
Published: February 2003

The rotational relaxation of n-H2, p-H2, HD, and n-D2 in a free jet expansion was studied by means of rotationally resolved photoelectron spectroscopy using a collimated supersonic molecular beam. Rotational state distributions were determined from the relative intensities of the Q branch rotational components for a wide range of stagnation pressures with nozzle temperatures from 300 to 700 K. Significant deviations from a Boltzmann distribution were observed for those cases in which the degree of rotational relaxation was substantial. HD was found to relax after undergoing only one-tenth of the number of collisions required to relax H2 or D2. The state-to-state rate constants method of Rabitz and Lam was used to model the relaxation of p-H2 and was confirmed to be quite effective in accounting for the experimentally observed population distributions.
Pyridine radical cation and its fluorine substituted derivatives
Authors: Bondybey V. E. , English J. H. , Shiley R. H.
Published: February 2003

The spectra and relaxation of the pyridine cation and of several of its fluorinated derivatives are studied in low temperature Ne matrices. The ions are generated by direct photoionization of the parent compounds. Of the compounds studied, laser induced B̃→X̃ and B̃→Ã fluorescence is observed only for the 2, 6-difluoropyridine cation. The analysis of the spectrum indicates that the ion is planar both in the X̃ and B̃ states. The large variety in the spectroscopic and relaxation behavior of fluoropyridine radical cations is explained in terms of their electronic structure and of the differential shifts of the individual electronic states caused by the fluorine substitution.
Medium high-resolution CARS applied to the ring puckering progressions in the C–H stretching region of trimethylene oxide and several deuterated analogs
Authors: Fietz H. , Beckmann A. , Kiefer W. , Wieser H.
Published: February 2003

The application of medium high-resolution CARS to the problem of ring puckering is demonstrated with selected C–H stretching vibrations of trimethylene oxide and several deuterated analogs. The strong Raman lines resulting from totally symmetric modes are resolved and assigned to sequences of components for which Δvp=0 (vp the puckering quantum number). While in general the agreement between infrared and Raman peak positions is good, the higher resolution has revealed possible small perturbations of puckering levels in the excited state of the second mode resulting from Fermi resonance-type interactions.
Hydration of lithium β-alumina
Authors: Dudney N. J. , Bates J. B. , Wang J. C.
Published: February 2003

The hydration reaction of Li β-alumina has been studied using infrared measurements of large single crystals equilibrated at controlled water vapor pressure (2–80 kPa) and temperature (250–450 °C) conditions. The equilibrium H2O concentrations in the conduction plane can be carried continuously and reversibly up to a saturation limit of about 1.8 H2O per unit cell. Values of the enthalpy and entropy for the hydration reaction at 300–450 °C were determined to be ΔH=−102 kJ/mol and ΔS= −167 J/mol K. In Li β-alumina, some of the H2O dissociates to form OH− ions and H+ ions which are bound to lattice oxygen ions; the enthalpy for the dissociation reaction is ∼10 kJ/mol. In addition to OH−, H3O+ and H5O+2 species have been identified from the observed change in the equilibrium concentration with the water vapor pressure. The relative concentrations of the different types of OH− species depend on the sample age. The hydration enthalpy for Na β-alumina of ∼−84 kJ/mol was determined from a similar study.
Correlated ionic motion in solid electrolytes: Tests of Smoluchowski dynamics and conductivity relations
Authors: Jacobson Solomon H. , Ratner Mark A. , Nitzan A.
Published: February 2003

The conductivity of a one-dimensional model for solid electrolytes of framework type is calculated using both the Langevin and Smoluchowski equations. The Smoluchowski conductivity is generally larger than that from the (more general) Langevin approach; they become identical only in the strong damping limit. The inversion of computed or observed carrier densities to obtain an effective potential is generally straightforward for one dimension, but the derivation of the conductivity from this potential is easy only in the strong-damping extreme. The vibrational spectra of most ionic conductors indicate that the quantititve validity of the Smoluchowski equation is dubious for them.
High pressure measurements in phospholipid bilayers using adiabatic compression
Authors: Russell Ned D. , Collings Peter J.
Published: February 2003

Results of high pressure adiabatic compression experiments on dilute dispersions of three members of the phosphatidylcholine and three members of the phosphatidylethanolamine series are reported. The pressure range examined extends up to 1 kbar, over three times the range previously investigated. These measurements reveal important new information about the gel to liquid crystal coexistence curve and also indicate that unexpected changes in the latent heat occur at high pressure.
Equilibrium properties of hard-sphere fluid mixture in the semiclassical limit
Authors: Singh U. N. , Sinha S. K.
Published: February 2003

High-temperature expansions for the density independent part of the to it are obtained for a hard-sphere binary mixture. The ‘‘excess’’ quantum corrections to the excess properties, such as excess second and third virial coefficients and excess free energy, are also reported. It is found that the excess quantum effect depends on the concentration and the particle diameter ratio.
Wetting transitions: First order or second order?
Authors: Teletzke G. F. , Scriven L. E. , Davis H. T.
Published: February 2003

A generalization of Sullivan’s recently proposed theory of the equilibrium contact angle, the angle at which a fluid interface meets a solid surface, is investigated. The generalized theory admits either a first-order or second-order transition from a nonzero contact angle to perfect wetting as a critical point is approached, in contrast to Sullivan’s original theory, which predicts only a second-order transition. The predictions of this computationally convenient theory are in qualitative agreement with a more rigorous theory to be presented in a future publication.
Surface tensions of simple liquids
Authors: Wu Shinn-Tyan , Yan Genn-Shan
Published: February 2003

Surface tensions of neon, argon, krypton, and xenon liquids are calculated from triplet point to critical temperature. Compared with experiments the theory over estimates surface tensions by about 10%. It is discovered that the accuracy of pair interaction potential can be quite important in the calculation.
On the virial equation for the osmotic pressure of linear polyelectrolytes
Authors: Vlachy V.
Published: February 2003

The paper discusses the virial equation for the osmotic pressure of a polyelectrolyte solution. The formal relationship between the osmotic coefficient and distribution functions can be straightforwardly integrated if the correlation between simple ions is neglected. This assumption is proved to be equivalent to the approximation inherent in the Poisson–Boltzmann equation. In the resulting expression, the osmotic coefficient is determined by the concentration of the counterions adjacent to the polyion. In addition, the counterion–counterion contribution to the osmotic coefficient is found to be independent of the polyelectrolyte concentration, and equal to λ/2. The comparison with the Monte Carlo calculations yields the conclusion that the Poisson–Boltzmann equation overestimates the counterion–counterion, and underestimates the counterion–polyion contribution to the osmotic coefficient.
EPR study of shock and thermally induced reaction in solid copper tetramine nitrate
Authors: Owens F. J.
Published: February 2003

Electron paramagnetic resonance studies of copper tetramine nitrate, subjected to explosive shock loading and analyzed after recovery, indicate that the Cu(NH3)2+4 complex is completely converted to Cu(NH3)2+2. The same reaction could also be induced by isothermal heating of the material for 1 h at +160 °C. The intrinsic linewidth of the Cu(NH3)2+2 complex in the shocked material was larger by a factor of 3 compared to the linewidth of the spectrum produced by isothermal decomposition. The perpendicular g shift was also slightly different. These differences are attributed to shock-induced defects in the material. When a foil flyer plate electric gun is used to shock CTN, the conversion to Cu(NH3)2+2 was not observed, but evidence of a new spectrum was obtained.
Green’s function Monte Carlo for few fermion problems
Authors: Arnow D. M. , Kalos M. H. , Lee Michael A. , Schmidt K. E.
Published: February 2003

The Green’s function Monte Carlo method used for obtaining exact solutions to the Schrödinger equation of boson systems is generalized to treat systems of several fermions. We show that when it is possible to select eigenfunctions of the Hamiltonian based on physical symmetries, the GFMC method can be used to yield the lowest energy state of that symmetry. In particular, the lowest totally antisymmetric eigenfunction, the fermion ground state, can be obtained. Calculations on several two- and three-body model problems show the method to be computationally feasible for few-body systems.
A study of spatially nonuniform solutions of the first BBGKY equation
Authors: Feijoo Laura , Rahman Aneesur
Published: February 2003

We investigate the existence of periodic nonuniform solutions of the first BBGKY equation under the assumption, first introduced by Kirkwood and Monroe, that the pair correlations in the solid can be described by the radial distribution function of a disordered metastable phase at the same temperature and density. The calculated one-particle distribution function is used to obtain the equation of state of three systems, namely, hard spheres, rubidium, and Lennard-Jones. The consequences of the central approximation are discussed in the light of our results.
Lattice dynamics of alkaline-earth oxides
Authors: Kushwaha Manvir S.
Published: February 2003

The crystal dynamics of some alkaline-earth oxides (MgO, CaO, SrO, and BaO) have been studied in the framework of a seven-parameter bond-bending force model (BBFM). The BBFM incorporates seven disposable parameters, which have been fixed by making use of the experimental data on elastic constants and neutron scattering and/or infrared (IR) measurements. The phonon dispersion relations have been computed at all the irreducible wave-vector points in the first Brillouin zone. The complete phonon spectra have been used to calculate the phonon density of states, which are further used to derive the temperature (T) dependence of the Debye-characteristic temperature (θD). Theoretical phonon dispersion curves along three symmetry directions and the θD–T curves have been compared with the available experimental data. It is observed that the model calculations are in a reasonably good agreement with the existing experiments. Few assignments have also been proposed for the SrO spectra by using the critical-point–phonon analysis for which not sufficient neutron and IR measurements exist.
Studies of liquid water by computer simulations. II. Static properties of a 3D model
Authors: Kataoka Yosuke , Hamada Hidetaka , Nosé Shūichi , Yamamoto Tsunenobu
Published: February 2003

A 3D model for water is presented and its static properties are thoroughly studied by Monte Carlo simulations over a wide region of temperature and density. Various kinds of molecular distribution functions are derived and from their temperature and density dependences are revealed the structure of the liquid state in detail. Relevant thermodynamic quantities are estimated as functions of temperature and pressure (or density) and main features of the observed anomalous properties of liquid water are reproduced semiquantitatively. The mechanical instability is found as the limit of supercooling and ascribed to the origin of the divergent singularities observed in supercooled water.
The rotational spectrum and hyperfine structure of the methylene radical CH2 studied by far-infrared laser magnetic resonance spectroscopy
Authors: Sears Trevor J. , Bunker P. R. , McKellar A. R. W. , Evenson K. M. , Jennings D. A. , Brown J. M.
Published: February 2003

Thirteen pure rotational transitions of CH2 in its X̃ 3B1 ground vibronic state have been measured and assigned using the technique of far-infrared laser magnetic resonance (LMR) spectroscopy. The energy levels thus determined led to the prediction and subsequent detection by microwave spectroscopy of a further rotational transition 404–313, at lower frequency (∼70 GHz). The analysis of these observations yields precise rotational constants as well as spin–spin, spin-rotation, and hyperfine interaction parameters for gas phase CH2. Its rotational spectrum may enable interstellar CH2 to be detected by radio astronomy. Two rotaional transitions within the v1=1 excited vibrational state have also been identified in the LMR spectrum. Future observations of vibrationally excited CH2 may afford a means of determining the singlet–triplet splitting in methylene, and studies of CD2 and CHD will result in improved structural determinations.
Radiative lifetime and collisional quenching of carbon monochloride (A 2Δ) in an alternating current glow discharge
Authors: Gottscho Richard A. , Burton Randolph H. , Davis Glenn P.
Published: February 2003

Glow discharges are widely employed in semiconductor processing but are relatively poorly understood owing to, in part, a lack of reliable, quantitative diagnostics. Laser-induced fluorescence promises to be a useful in situ, nonintrusive probe for species concentrations and gas-phase temperatures, but requires the determination of fluoresence yields (i.e., radiative vs nonradiative decay rates) as a function of the plasma state and molecular rotational quantum number. In this work, carbon tetrachloride plasmas, which are used in the dry etching of such materials as Al, Si, GaAs, and InP, are examined using the laser-induced fluorescence technique. The quantum yield φ of CCl A 2Δ→X 2Π fluorescence is determined as a function of pressure, flow-rate, power, electrode temperature, and feedstock composition. Total pressure and addition of Cl2 to the feedstock are found to be most important in reducing the quantum yield; other plasma parameters and addition of O2, He, Ar, or N2 are found to be of secondary importance. The radiative lifetime of carbon monochloride CCl, A2Δ (v=0) is found to be 105±3 ns and to be independent of rotational quantum number up to J=45.5. The weak dependence of CCl laser-induced fluorescence on most plasma variables makes it nearly ideal as a simple, direct, and quantitative temperature and concentration diagnostic.
Quasiclassical trajectory studies of rigid rotor–rigid surface scattering. I. Flat surface
Authors: Bowman Joel M. , Park Seung C.
Published: February 2003

Rotationally inelastic transition intensities are calculated for a model N2 rigid rotor–rigid flat surface at initial collision energies of 104 and 3800 meV and for many initial beam orientations. The interaction potential is a Morse function modulated by a term which depends on the rotor orientation angle. The calculations are based on the quasiclassical trajectory method and a distorted trajectory perturbation theory. At the low collision energy the rotational excitation is mediated by the attractive part of the potential and by the repulsive part at high energies. The collision dynamics is direct in both energy regimes, however, quite complicated in the former one. Rotational rainbows are clearly observed for the high energy collisions.
Vibrational energy transfer from OH to other gaseous hydrides
Authors: Glass G. P. , Endo H. , Chaturvedi B. K.
Published: February 2003

Vibrational energy transfer from OH (v=1, 2) to a number of simple hydrides (CH4, NH3, H2O, HCl, H2, D2) has been investigated using a discharge flow apparatus attached to a sensitive EPR spectrometer. Strong similarities between the rate of vibrational energy transfer from OH and the rate of V–V transfer from HCl have been observed. These similarities have been discussed in terms of the mechanism of the energy transfer process.
Multiproperty empirical interatomic potentials for ArXe and KrXe
Authors: Pack R. T , Valentini J. J. , Becker C. H. , Buss R. J. , Lee Y. T.
Published: February 2003

Crossed molecular beam measurements of elastic differential cross sections (DCS) for the scattering of Ar and Kr by Xe are reported. Empirical multiparameter M3SV interatomic potentials for the ArXe and KrXe interactions are determined by simultaneously fitting the DCS, the viscosities, and virial coefficients; the results are the most accurate potentials yet reported for these systems.
Dielectric saturation and dielectric friction in electrolyte solutions
Authors: Stiles P. J. , Hubbard J. B. , Kayser R. F.
Published: February 2003

Electrohydrodynamic equations developed by Hubbard and Kayser to account for the combined effects of dielectric saturation and dielectric friction on ionic motion in polar solvents are solved numerically to yield ionic conductances. Dielectric saturation is incorporated into this continuum treatment through a phenomenological relationship between the electric permittivity and field strength. The results of the analysis are critically tested by comparison with experimental conductance data.
The phase-change behavior of hydrogen in niobium and in niobium–vanadium alloys
Authors: Futran Mauricio , Coats Steve G. , Hall Carol K. , Welch David O.
Published: February 2003

A study was made of the phase-change behavior of hydrogen in niobium and in niobium–vanadium alloys. A lattice-gas model calculation for hydrogen in pure niobium in which no adjustable parameters are used predicts a critical point temperature of 460 K as compared with the experimental value of 443 K. More importantly, the shape of the coexistence curve corresponds quite closely to the shape of the coexistence curve found experimentally. The model is extended to the case where hydrogen is dissolved in the alloys Nb0.94V0.06, Nb0.85V0.15, and Nb0.75V0.25. The resulting phase diagram predicts a depression in the critical point temperature with increasing vanadium concentration in qualitative agreement with experiment. When the model is corrected to include the effect of trapping of hydrogen by vanadium atoms, the results are in quantitative agreement with experiment.
The vapor phase dissociation of ammonium salts: Ammonium halides, ammonium rhodanide, ammonium nitrate, and ammonium bicarbonate
Authors: de Kruif C. G.
Published: February 2003

Vapor pressures as a function of temperature of the ammonium salts are measured by means of a simultaneous torsion effusion and mass-loss effusion technique. From a theoretical analysis, which is given first, it is shown that the enthalpies of sublimation and the degree of dissociation b in the vapor phase are related to the measured quantities. The degree of dissociation appears to be a weak function of temperature and is evaluated by b(NH4F, 288.91 K)=0.97; b(NH4Cl, 352.02 K)=0.85; b(NH4Br, 380.06 K)=0.51; b(NH4I, 385.03 K)=0.39; b(NH4CNS, 313.78 K)=0.61; b(NH4NO3, 351.89 K)=0.66; b(NH4HCO3, 270.56)=0.85. It is assumed that NH4HCO3 dissociates into NH3, H2O, and CO2. At the given temperatures, total vapor pressure is 0.40 Pa.
Langevin model of the rotational motion of molecules: Two-dimensional rotator in a cubic potential
Authors: Gerling Rainer W. , de Raedt Bart
Published: February 2003

The rotational motion of a linear molecule in a potential of cubic symmetry is treated in the framework of the Langevin equation. The corresponding Langevin equation is solved numerically. From these numerical data, time-dependent correlation functions are extracted and compared with the results of other models. It is found that the harmonic approximation is good for potential barriers higher than about eight times the thermal energy. Earlier models describe the static behavior very well, but they do not describe dynamic properties correctly. For potential barriers comparable to the thermal energy, the Langevin equation seems to provide the most realistic description.
UV absorption and circular dichroism calculations of three Drosophila virilis satellite DNA’s: Use of linear response polarizability theory
Authors: Ito Hirotoshi , I’Haya Y. J.
Published: February 2003

Assuming the Fano–DeVoe-type of model Hamiltonian which is capable of involving usual cases of copolymer systems, the polymer polarizability tensor has been derived in terms of the electronic state wave functions for identical and nonidentical constituent monomers. A prescription is presented as to how to simply involve the polarizability tensors of sugar–phosphate residues into the total polymer polarizability tensor. Within the dipole–dipole approximation, a detailed computational procedure is given for obtaining the polymer polarizability tensor from monomer spectroscopic data. The calculations of UV and CD band shapes have been carried out on highly repeating DNA’s such as Drosophila virilis satellite DNA’s I, II, and III, i.e., poly[d(CAAACTA)]⋅poly[d(TAGTTTG)], poly[d(TAAACTA)]⋅poly[d(TAGTTTA)], and poly[d(CAAATTA)]⋅poly[d(TAATTTG)].
Laser flash photolysis of benzene. VII. Fluorescence decay in the channel 3 region
Authors: Takagi Yoshihiro , Sumitani Minoru , Nakashima Nobuaki , O’Connor Desmond V. , Yoshihara Keitaro
Published: February 2003

The benzene vibronic level 7101611120 (Q12), which lies about 2000 cm−1 above the channel 3 threshold, was selectively pumped with tunable UV laser radiation. The resulting single vibronic level fluorescence was exponential with a lifetime of 42±10 ps. A small amount of fluorescence from the thermalized S1 level was also detected.
Polarization model for high temperature and high density water droplets
Authors: Demetros George , David Carl W.
Published: February 2003

Monte carlo simulations are carried out on droplets of 64 water molecules in spherical gas phase droplets at high temperatures and densities. (AIP)
Competition between atomic and molecular chlorine elimination in the infrared multiphoton dissociation of CF2Cl2
Authors: Krajnovich D. , Huisken F. , Zhang Z. , Shen Y. R. , Lee Y. T.
Published: February 2003

Infrared multiphoton dissociation of CF2Cl2 has been reinvestigated by the crossed laser-molecular beam technique using a high repetition rate CO2 TEA laser. Both the atomic and molecular chlorine elimination channels were observed: (1) CF2Cl2→CF2Cl+Cl and (2) CF2Cl2→CF2+Cl2. No evidence was found for secondary dissociation of CF2Cl at laser energy fluences up to 8 J/cm2. Center-of-mass product translational energy distributions were obtained for both dissociation channels. In agreement with previous work, the products of reaction (1) are found to have a statistical translational energy distribution. The products of reaction (2) are formed with a mean translational energy of 8 kcal/mol, and the distribution peaks rather sharply about this value, indicating a sizeable exit barrier to molecular elimination. The product branching ratio was directly determined. Reaction (2) accounts for roughly 10% of the total dissociation yield in the fluence range 0.3–8 J/cm2. These results provide an additional test of the statistical theory of unimolecular reactions.
Experimental verification of the breakdown of the electric dipole rotational selection rule in electron impact ionization–excitation of N2
Authors: Hernandez S. P. , Dagdigian P. J. , Doering J. P.
Published: February 2003

Variable energy (60–1500 eV) electron impact excitation of cold (∼10 K) N2 supersonic beams has been used to produce excited N+2 B 2Σ+u ions whose rotational energy distribution has been determined by spectroscopic examination of N2+ first negative system (B 2Σ+u→X 2Σ+g) emissions. For energies ≳800 eV, the rotational state distribution is found to be constant with electron energy. The distribution is non-Boltzmann with a peak at the N′=1 rotational state and a long tail to higher energies. At high electron energies, the electric dipole selection rule (‖ΔJ‖=1) is expected to be obeyed in the ionization–excitation process. Above 800 eV, this rule is followed, and the non-Boltzmann B 2Σu+ rotational distribution arises from the non-Boltzmann rotational distribution in the neutral supersonic N2 beam. Below 800 eV, however, breakdown of the ‖ΔJ‖=1 selection rule occurs with ‖ΔJ‖=3 transitions observed first, followed by much larger ΔJ transitions at low electron energies (<100 eV). Implications of this effect for geophysics and supersonic beam diagnostics, as well as the theoretical questions involved, are discussed.
Laser photolysis of benzene. V. Formation of hot benzene
Authors: Nakashima Nobuaki , Yoshihara Keitaro
Published: February 2003

Flash photolysis of gaseous benzene has been carried out with a KrF laser (248.4 nm) as an excitation source. Two new transients have been detected, one of which has a structured absorption in the wavelength region from 235 to 260 nm. It has a rise time of 80 ns and a long decay time (≳25 μs). The precursor of this transient has also been detected. It appears as a shoulder at 225 nm and has a lifetime of 80 ns. This species is postulated to be a highly excited vibrational state of the ground electronic state, namely, a hot benzene molecule. This species is quenched by ground state benzene as well as by 12 different foreign gases, including oxygen and nitrogen, which have similar quenching rates. The decay of the hot benzene is accompanied by an increase in the temperature of the sample, which leads in turn to formation of the species with the structured absorption. The temperature of the equilibrated sample was determined by comparing the thermalized spectra in the nanosecond time scale with the steady-state absorption spectra at higher temperatures. The temperature rises by about 50° when 20 Torr of benzene are excited with an energy of 33 mJ/cm2. This temperature increase indicates that the yield of hot benzene is 0.6±0.2. The Tn←T1 absorption spectrum has been measured and the intersystem crossing yield is estimated to be 0.2±0.1. The major nonradiative channel in benzene is internal conversion.
Isomeric structures of CH2LiF, the prototype carbenoid
Authors: Vincent Mark A. , Schaefer Henry F.
Published: February 2003

Molecular electronic structure theory has been used to investigate the geometrical and energetic characteristics of CH2LiF the simplest halolithiocarbenoid. The structures of three isomers were predicted using self-consistent field (SCF) theory in conjunction with a basis set of better than double zeta plus polarization quality, namely, C(9s5p1d/4s2p1 d), H(4s1p/2s1p), Li(9s4p/4s2p), and F (9s6p1d/4s3p1d). At this level of theory there are three minima on the potential energy hypersurface: I, which may be roughly described as the ion pair H2CLi+⋅⋅⋅F−; II, for which the description H2C⋅⋅⋅LiF is suitable; and III, where the picture H2C⋅⋅⋅FLi (and to a lesser degree H2CF−⋅⋅⋅Li+) is pertinent. Vibrational frequencies have been predicted for each of these structures. The part of the potential surface connecting structures II and I is initially extremely flat, but a transition state connecting them has been located. Explicitly correlated wave functions (22 366 configurations) confirm the SCF prediction that I is the lowest energy isomer with II lying at ∼27 kcal and structure III at ∼25 kcal.
Second-order cascading in third-order nonlinear optical processes
Authors: Meredith Gerald R.
Published: February 2003

Because cascaded second-order processes make substantial qualitative and quanitative differences to the results of third-order nonlinear optical experiments, a formalism for their treatment is presented. The symmetry dictates concerning the occurrence and relationships of magnitudes of cascading are tabulated for the higher symmetry crystal classes. Angular momentum considerations are applied to the situations allowing circularly polarized light waves.
High orbital angular momentum states in H2 and D2
Authors: Herzberg G. , Jungen Ch.
Published: February 2003

A characteristic group of lines observed in the infrared emission spectrum of H2 has been identified as representing the transitions between the 5g and the 4f group of levels. Because of nearly complete uncoupling of l from the molecular axis the appearance of this group of lines is very different from a normal band spectrum. An analysis was possible on the basis of ab initio computations of the spectrum using the knowledge of the vibrational levels, quadrupole moment, and the polarizability of the H+2 core. The validity of the assignments was further corroborated by agreement of the predicted spectra of D2 with the observed spectra. In addition, similar transitions corresponding to 4f–3d have been observed.
Concentration dependence of the self-diffusion coefficient of hard, spherical particles measured with photon correlation spectroscopy
Authors: Kops-Werkhoven M. M. , Pathmamanoharan C. , Vrij A. , Fijnaut H. M.
Published: February 2003

The concentration dependence of the self-diffusion coefficient Ds has been measured with photon correlation spectroscopy (PCS) from a mixture of two optically distinct hard spherical silica particles in cycloheptane. In the long wavelength limit (K=0), we have found that Ds is a linear function of the particle volume fraction φ in the range of 0<φ<0.10: Ds(K=0)=D0(1+kD,sφ). Here, D0 is the diffusion coefficient at infinite dilution and the constant kD,s has an experimental value of −2.7±0.3. Away from the optical matching point of one of the components and close to that of the other component, we have shown that the theories of optical polydispersity can be applied in light scattering and it is found that the result of the PCS measurements is in accordance with that obtained from time-averaged light scattering. With the ultracentrifugation techique, it was possible to obtain information about the sedimentation velocity of a few ‘‘tracer’’ particles in the presence of other particles. Here, we found that the experimental data are not consistent with the available theories.
Steady absorption of Brownian particles by a sphere
Authors: Harris S.
Published: February 2003

The problem of steady Brownian motion in the presence of an absorbing sphere is studied in the full Brownian particle position, velocity phase space. Approximate solutions are found for the Brownian particle distribution function by solving the Fokker–Planck equation subject to the boundary condition that the solution for emergent particles vanish on the surface of the sphere. Comparisons are made with results from the macroscopic theory based on the diffusion equation. We find that the macroscopic theory is not valid in a boundary layer of extent depending on the radius of the Brownian particle and absorber and the viscosity and temperature of the host fluid in a fairly complicated manner. Close to the boundary, Fick’s law only holds if the diffusion coefficient is taken to be space dependent. One significant consequence of our results is that the macroscopic theory of diffusion-controlled rate constants is shown not to be generally valid. The corrected values for the rate constant that we find for aerosol particles are in good agreement with the values found by Fuchs based on an ad hoc semiempirical theory.
A nonclassical thermodynamic description of heat conducting viscous fluids
Authors: Lebon G. , Jou D.
Published: February 2003

Classically, the description of a fluid is assumed to be governed by the usual variables: density, temperature, and velocity. Here it is postulated that such a system requires supplementary variables, namely, the heat flux vector and the viscous part of the pressure tensor. Starting from this hypothesis, a general theory of thermoviscous fluids is proposed. Balance equations and constitutive equations necessary to its description are given. Restrictions on the form of the constitutive equations are placed by the second law. The relaxation times associated with the various dissipative fluxes are interpreted in terms of the theory of fluctuations. This is achieved by extending Einstein’s theory of fluctuations. The corresponding expressions for the second moments and the time correlations of the fluctuations of the dissipative fluxes are derived. In the limit of vanishing relaxation times, the classical results are recovered.
The 1B2u←←1A
l
g two-photon spectra of several isotopes of benzene by supersonic beam–multiphoton ionization spectroscopy
Authors: Sur Abha , Knee Joseph , Johnson Philip
Published: February 2003

The two-phonon spectra of the 1B2u←←1Alg transitions of benzene, perdeuterobenzene, sym-C6H3D3, p-C6H4D2, and C6H5D have been recorded in a supersonic beam–multiphoton ionization experiment. A thorough assignment of these spectra includes a number of new bands as well as some reassignments of features seen in previous room temperature studies, notably in transitions concerning the ν12 vibration. Efficient rotational cooling has allowed the direct measurement of rotationless band origins with better than 0.5 cm−1 accuracy, uncovering structure due to naturally occurring 13C substituted molecules and to dimers created in the expansion.
Brillouin spectra of the solid electrolyte Li2SO4
Authors: Aronsson Robert , Gunilla Knape H. E. , Torell Lena M.
Published: February 2003

Brillouin spectra of single crystals of the solid electrolyte Li2SO4 were obtained for various crystal orientations in the temperature range 899–1120 K. The spectra contained one longitudinal component and at least one and sometimes both transverse components. The frequency shifts varied between 14.5 and 17.4 GHz for the longitudinal and between 4.1 and 9.0 GHz for the transverse component, the shift being strongly dependent on crystal orientation. The observed frequency shifts correspond to values of the elastic constants typical for plastic materials.
Defect chemistry in CaF2:Eu3+
Authors: Hamers R. J. , Wietfeldt J. R. , Wright J. C.
Published: February 2003

Site selective spectroscopy has been performed for CaF2:Eu3+ samples as a function of annealing temperature and dopant concentration. The Eu3+ lines have been classified into five sites, two of which correspond with Eu3+ clusters. High annealing temperatures dissociate the clusters and leave Eu3+ ions in cubic and tetragonal sites. The relative concentrations of these sites change anomalously as the Eu3+ concentration is raised. Absolute concentration measurements of all the sites eliminates competing equilibria as a possible explanation. These results confirm the conclusions reached in an earlier paper for a more complex system.
Origin and effects of orientational correlations in chemical reactions
Authors: Steiger Ulrich Robert , Keizer Joel
Published: February 2003

The effects of translational and rotational diffusion on chemical reactions are examined based on the theory of nonequilibrium thermodynamics. Density distributions of the reactants are obtained for various models as a function of their separation and their relative orientation, in two and three dimensions. These models are used to calculate the chemical rate constant for bimolecular reactions based on the shape of the molecules and the reactivity as a function of separation and relative orientation (which can be obtained from molecular calculations). It is shown that effects due to rotational diffusion become important especially for high densities and for fast chemical reactions. In three dimensions, the calculated reaction rate depends on the particular form of the reactivity function. In two dimensions, if the concentration of the reactants is low and the reactions are diffusion controlled, the same rate constant is obtained for a large class of models.
Fall-off behavior of models of thermal unimolecular reactions
Authors: Snider Neil
Published: February 2003

Aspects of fall-off behavior for thermal unimolecular reactions were investigated theoretically. The starting point for this investigation was the master equation which describes the generally accepted picture of collisional excitation and reaction. Deviations from simple Lindemann behavior were analyzed in terms of deviations from linearity of the reciprocal of the rate coefficient as a function of reciprocal concentration (or pressure) of collider gas. This function was shown to be always either linear or concave downward under conditions for which the rate of chemical reaction is slow compared to the rate of relaxation of the internal state distribution of the reacting molecules. Analytic results were obtained for two collision models of interest, the stepladder model and the separable exponential model. The strong collision limits for these models were carefully defined, and it was shown that the fall-off behavior becomes more Lindemann-like as the strong collision limit is approached. It was further shown how this characteristic of the approach to the strong collision limit is related to the pressure dependence of weak collision effects.
Modeling of the charge transfer afterglow excited by intense electrical discharges in high pressure helium nitrogen mixtures
Authors: Pouvesle J. M. , Bouchoule A. , Stevefelt J.
Published: February 2003

In this work, we report the study of bimolecular and termolecular charge transfer and Penning ionization reactions in He–N2 mixtures excited by repetitive 3 kA, 7 ns duration discharges. He(2 3S) destruction frequencies have been determined from measurements of the optical absorption of the 2 3S→3 3P helium transition and were found to correlate with the late-time decay rate of the N2+(B 2Σu→X 2Σg) fluorescence. The much more intense early-time fluorescence was ascribed to charge transfer from He2+. The values found for the bimolecular and termolecular charge transfer reactions were, respectively, (1.1±0.1)×10−9 cm3 s−1 and (1.36±0.20)×10−29 cm6 s−1, while the corresponding values for the Penning reactions were (7.6±0.4)×10−11 cm3 s−1 and (3.3±0.3)×10−30 cm6 s−1. Branching ratios for producing the N2+(B 2Σu) state in these reactions are discussed. A comprehensive kinetic model of the He–N2 afterglow has been formulated which was able to reproduce all the experimental data obtained as functions of helium pressure over the range 310–760 Torr and as functions of the partial pressure of nitrogen from 5–500 mTorr.
Force field calculations for formamide, acetamide, and urea using the CNDO/force method
Authors: Annamalai A. , Singh Surjit
Published: February 2003

CNDO/force calculations are employed to evaluate theoretical force fields for formamide, acetamide, and urea. Since the stretching force constants are overestimated and other diagonal as well as off-diagonal force constants are predicted reasonably well by these calculations, the initial force fields are set up by transferring the stretching force constants from structurally related molecules and by including the other force constants from the CNDO force field. The experimental force fields are obtained for the condensed phases as well as monomeric species using vibrational frequencies by carrying out least squares refinement. Frequencies of HCONH2, HCOND2, DCONH2, DCOND2, HCONHD, and DCONHD for formamide, CH3CONH2, CH3COND2, CD3CONH2, CD3COND2, CH3CONHD, CD3CONHD, and CH3CO 15NH2 for acetamide, and NH2CONH2, ND2COND2, 15NH2CO 15NH2, 15ND2CO 15ND2, and NH2C 18ONH2 for urea are employed in refining the force fields. The force fields obtained are found to be reliable on the basis of the force constants for chemically related molecules, frequency fits, and potential energy distributions.
The propagation of basis set error and geometry optimization in a
b i
n
i
t
i
o calculations. A statistical analysis of the sulfur d-orbital problem
Authors: Mezey Paul G. , Haas Ernst -C.
Published: February 2003

By generating a sample of 100 random molecular basis sets from a normal distribution centered on the best-energy, fully variational AO basis sets, a statistical analysis has been carried out on the distributions and pair correlations of calculated Hartree–Fock total energies, optimum bond lengths, energy components, and formal atomic charges. Dimethylsulfoxide (DMSO), the calculated geometry of which has been found extremely sensitive to basis variations in an earlier study, has been selected as model compound. The results provide a clear answer to the sulfur d-orbital problem, since no simultaneous reproduction of experimental geometry and an adequate approximation to the variationally optimum total energy have been possible without including d-polarization functions on sulfur.