bluuebunny/crossref_metadata_2025 huggingface dataset:
Microwave spectrum, barrier to internal rotation, and dipole moment of 1,2,3-pentatriene
Authors: Ogata Teruhiko , Mochizuki Akiyoshi , Yamashita Eiichi
Published: July 2002

The microwave spectrum of 1,2,3-pentatriene, CH2=C=C=CHCH3, has been studied in the frequency region from 8 to 40 GHz. A-type R-branch transitions from J=3←2 to J=9←8 were assigned. Most of the observed lines are split slightly as a result of internal rotation. Analysis of the splittings by PAM leads to an internal barrier of 1341±14 cal/mol (or 56.1±0.6 kJ/mol). The effective rotational constants are A0=29 802(20) MHz, B0=2212.646(7) MHz, and C0=2085.023(4) MHz. The value of Ic−Ia−Ib shows the molecule is planar except for the hydrogen atoms in the methyl group. A new method has been developed for the determination of the electric dipole moment of a molecule from high-J transitions in which individual Stark components are not resolved. The dipole moments of 1,2,3-pentatriene are determined to be μa=0.50±0.05 D, μb=0.122±0.003 D, and μtotal=0.51±0.05 D. Comparison of obtained molecular constants with those for propene and 1,2-butadiene revealed that increase in the cumulative double bonds lowers the potential barrier to internal rotation and increases the dipole moment.
Stimulated surface ionization of alkali metals from alkali aluminum silicates in the presence of F2 or Cl2
Authors: Fujii Toshihiro
Published: July 2002

The mechanism of the well-known ‘‘stimulated surface ionization’’ has been investigated, employing fluorine or chlorine gases on alkali aluminum silicate surfaces. Alkali atoms contained in this compound are stimulated into surface ionization in the presence of these halogen gases at thermal energy. All the observations of this study are consistent with the mechanism suggested by Herschbach’s group: the alkali ions emitted result from surface-catalyzed reaction of halogen atoms with the alkali oxide contained as a main component in the aluminum silicate over the limited surface temperature range. This interpretation is consistent with thermodynamic considerations; the energy required to eject alkali ions can be supplied by the energy released from the formation of strong bonds of alkali halide molecules.
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o approach to the interaction of CF4 and CH4 with O2, CO2, N2, and CO. The nature of the interaction force in perfluorochemical artificial blood
Authors: Mack Hans-Georg , Oberhammer Heinz
Published: July 2002

Interaction potentials for complexes of CF4 and CH4 with O2, N2, CO, and CO2 have been calculated by ab initio methods. The geometries of the interacting molecules were optimized at various interacting distances in the HF approximation using 6-31G* (for CF4) and 6-31G** (for CH4) basis sets. Electron correlation effects were included by the MP2 approximation and the basis set superposition errors (BSSE) were corrected by the full function counterpoise method. Various geometric arrangements were considered for the complexes containing oxygen and the structure with O2 along a C3 axis of CF4 (C3v symmetry) was found to be most stable. In all cases the interactions are stronger in the CF4 complexes as compared to the CH4 complexes.
Theory of thermomagnetic effects in the transition regime
Authors: Cole R. G. , Mason E. A. , Mazur E.
Published: July 2002

A simple model is presented that describes the complex behavior of the magnetic field dependence of the thermal conductivity of a polyatomic gas as a function of the Knudsen number. The model treats the solid surface as one component of a gas mixture, and a first-order Chapman–Enskog solution is adequate to account for the thermomagnetic effects in single gases. The results provide an interpolation scheme between the continuum and Knudsen regimes, in the form of scaling rules in which the Knudsen number appears in the coefficients and arguments of the functions that describe the limiting cases. Good agreement is obtained with the available experimental data, and leads to the conclusion that different surface accommodation coefficients are needed for the translational and internal energies of the gas molecules. This conclusion is consistent with analysis of independent field-free conductivity data, and with independent vibrating-surface measurements.
Valence photoionization of hydrogen fluoride with synchrotron radiation
Authors: Banna M. S. , Malutzki R. , Schmidt V.
Published: July 2002

Photoionization from hydrogen fluoride has been studied with synchrotron radiation in the 30–130 eV photon energy range. Relative photoelectric cross sections have been obtained for the 1π (ionization energy of 16.1 eV) MO, the 3σ MO (19.9 eV ionization energy), and in some cases the inner 2σ valence MO (I.E.=39.6 eV). Comparison is made with other measurements such as quasiphotoionization results and with one-center calculations. Angular distribution asymmetry parameters have also been measured for the 1π and 3σ MO’s and compared with those of Ne2p. In the inner valence region, satellites have been observed; this is in accord with most theoretical calculations which predict the breakdown of the one-particle description in this region.
A modified Boltzmann kinetic equation for line shape functions
Authors: Blackmore Robert
Published: July 2002

The shape of an isolated spectral transition is analyzed in terms of an approximation to the Waldmann–Snider kinetic equation. This equation is written in the form of a drift and collision operator acting on a density matrix. With the use of the spherical approximation, the collision operator is subdivided into an elastic Boltzmann-like collision term, an inelastic loss term, and a dephasing term. The Boltzmann-like term is responsible for Dicke narrowing of spectral lines, the inelastic loss term leads to line broadening and the dephasing term may contribute both to line broadening and shifting. Simple approximations to these terms are powerful enough to account for some of the details of experimental line shapes such as asymmetrical deviations from a Lorentzian line shape. Model numerical calculations are carried out assuming classical scattering potentials of the form 1/rn in the Boltzmann-like term and single complex frequencies for the other two. It was found that as long as the density was scaled to give the same diffusion constant, the exact form of the scattering cross section had little effect on the final line shape.
Kinetic theory and irreversible thermodynamics of dense fluids subject to an external field
Authors: Eu Byung Chan
Published: July 2002

A formal theory of dense fluids subject to an external electric field is developed as an extension of the kinetic theory of dense fluids reported previously. The present formulation also refines and modifies the previous theory wherever deemed necessary and especially in the part related to the renormalization. The extended Gibbs relation and a theory of irreversible thermodynamics are developed. A generalized Kirkwood integral equation for correlation functions and a generalized equation for local nonequilibrium chemical potentials are also derived for nonequilibrium mixtures.
The orientation and bonding of CO on Mo(100) using angle-resolved photoelectron spectroscopy and near-edge x-ray absorption fine structure
Authors: Fulmer J. P. , Zaera F. , Tysoe W. T.
Published: July 2002

The nature of the species formed by CO chemisorption of Mo(100) has been investigated using angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) and near-edge x-ray absorption spectroscopy. High-resolution electron energy loss spectroscopy (HREELS) indicates the formation of two distinct types of CO. At coverages greater than 50% of saturation, chemisorbed CO exhibits a CO stretching frequency of ∼2100 cm−1 corresponding to a CO molecule chemisorbed in an atop site. ARUPS indicates that at these coverages CO chemisorbs with its axis perpendicular to the surface in an analogous manner to that commonly observed on transition metal surfaces. At coverages less than 50% of saturation, CO exhibits an extraordinarily low stretching frequency of ∼1200 cm−1. Both NEXAFS and ARUPS measurements unequivocally indicate that at low coverages CO is tilted at ∼40° to the surface normal. Since CO is tilted with respect to the surface at low coverages, this effect cannot be ascribed to adatom–adatom interactions, and a careful measurement of the positions of the photoelectron peaks of the tilted molecule indicates that both the 1π and the 5σ orbitals participate in surface bonding. A bonding model is proposed that is in accord with these observations in which the CO molecule chemisorbs into a fourfold hollow site.
Triplet (T1) state and radical cation resonance Raman spectroscopy of N,N,N′,N′-tetramethyl- and N,N,N′,N′-tetraethyl-p-phenylenediamines
Authors: Poizat O. , Bourkba A. , Buntinx G. , Deffontaine A. , Bridoux M.
Published: July 2002

The time-resolved resonance Raman spectra of the first triplet state and the cw resonance Raman spectra of the radical cation are reported for various isotopic derivatives of the N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) and of the N,N,N′,N′-tetraethyl-p-phenylenediamine (TEPD). Vibrational assignments and structural implications are discussed. The radical cation spectra are consistent with a semiquinoidal conformation of the ionized species. They are characterized by a significant frequency increase of the in-phase ν(N–ring) mode with respect to the ground state spectra (Δν≥120 cm−1) and by the high resonance enhancement of various bands assigned to vibrations of the N(alkyl)2 groups, resulting from couplings of these vibrations with modes of the π chromophore. The triplet spectra display almost only bands due to vibrations of the N(alkyl)2 groups, implying that similar couplings take place in the T1 state. Two signals characterize the N–ring–N framework: one is assigned to the Wilson ring mode 9a (CH bending ); the second one, a strong signal around 1500 cm−1, corresponds to a vibration involving a large contribution of the N–ring stretching motion and possibly also of the ring mode 8a.
Gradient theory of the electric double layer at hydrocarbon–water interfaces
Authors: Sweeney J. B. , Scriven L. E. , Davis H. T.
Published: July 2002

Gradient theory of inhomogeneous fluids is used to model the electric double layer at a hydrocarbon–aqueous electrolyte interface. It is applied to a four-component regular solution (two solvent components and two ionic species) in which the dielectric permittivity is also inhomogeneous. The permittivity is determined by a Clausius–Mossotti constitutive equation based on the local densities of the solvent species. The gradient equations are coupled to Poisson’s equation and are solved using a Galerkin/finite element scheme. The results indicate that in dilute solution, the dependence of the interfacial tension on bulk electrolyte concentration is linear, and the sign and magnitude of the deviation of the tension from the pure solvent value depends strongly on the degree of ion partitioning between the two phases. In more concentrated solutions, the deviation becomes nonlinear and can change sign as the electrolyte concentration is increased.
Response to the paper: ‘‘Conformation kinetics of methyl nitrite. IV’’
Authors: Bauer S. H.
Published: July 2002

Our measurements of the relaxation times for the syn–anti isomerization of CH3ONO have been criticized by True et al. However, their recounting of the flaws in our procedure was based on distortions. Furthermore, the basic disagreement concerns the interpretation of the pressure dependence of the relaxation times they reported which differed insignificantly from our initial observations. The clear increase with decreasing pressure of the bimolecular rate constant (at low pressures) is not consistent with any RRKM model which has yet been proposed contrary to the claim by True. It is consistent with the limited phase space model proposed by Bauer and Lazaar.
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o study of H2 dissociation and vibrational relaxation in mixtures of He and Ar: Implications for the linear mixture rule
Authors: Raynor Susanne , Burke Kathleen
Published: July 2002

The master equation for the thermal dissociation and vibrational relaxation of H2 infinitely dilute in mixtures of He and Ar was solved using rotationally averaged rate constants from previous ab initio studies on H2/He and H2/Ar. The calculated rate constants for dissociation, kd, vibrational relaxation times, τ, and induction times for dissociation, ti, for the mixtures were compared to those predicted by the linear mixture rule: kLMR=Σixiki, where xi is the mole fraction of gas i and ki is the rate constant for the process in pure component i. Substantial deviations were found to occur, with the greatest deviations occurring for kd. Further analysis indicates that the deviations arise due to differing efficiencies for multiquantum transitions in H2/He and H2/Ar.
A computer ‘‘experiment’’ on the microstructure of amorphous Cr
Authors: Lai S. K. , Wang S. , Wang K. P.
Published: July 2002

We present a computer experiment for simple monatomic amorphous Cr. Contrasted to the widely used Lennard-Jones or Morse potential function, a first-principles metallic pair potential is employed. Starting from this latter potential, a temperature-quench Monte Carlo simulation procedure is applied to study (a) the liquid–glass transitions and (b) the amorphous states for Cr element. It is found that the pair distribution functions exhibit general short-range order features characteristic of real metallic glasses. Further, by examining the pair potential used and with due attention paid to the Friedel oscillation, we obtain interesting structural results for the amorphous Cr.
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o quantum chemical study of the hydrogen- and ‘‘anti’’-hydrogen-bonded HF/ClF and HF/Cl2 dimers
Authors: Rendell Alistair P. L. , Bacskay George B. , Hush Noel S.
Published: July 2002

A b initio electronic structure calculations at the SCF and coupled pair functional (CPF) level have been carried out for the hydrogen- and ‘‘anti’’-hydrogen-bonded isomers of the ClF/HF and Cl2/HF complexes. The stability of each isomer with respect to its constituent monomers has been calculated at the appropriate optimized geometry, paying particular attention to correlation effects, zero point energies, and basis set superposition errors. The differences between the latter quantities for a given pair of isomers, all calculated to be ≲0.5 kcal mol−1, are comparable in magnitude to the difference in stabilities, hence in a quantitative description of bonding in these dimers all these effects must be considered. The dipole moments and the 35Cl and 2H nuclear quadrupole coupling constants for the dimers have also been evaluated and compared with the available experimental data. In agreement with the results of recent molecular beam measurements, in both systems the anti-hydrogen-bonded isomers are found to be the more stable ones.
Resonances in molecular photoionization. II. Autoionization effects in the NO molecule
Authors: Sobolewski A. L.
Published: July 2002

Near-threshold autoionization features in the photoionization spectroscopy of nitric oxide are studied by the use of the Feshbach projection-operator formalism of scattering theory. The complex autoionization structure in the photoionization spectrum of NO in the wavelength region of 1140–950 Å is described by assuming one valence state interacting with the ionization continuum and the converging Rydberg series. The strong non-Condon effects observed in the photoelectron spectra of this molecule are also discussed.
Reaction kinetics of the solid state polymerization in diacetylene crystals
Authors: Kollmar C. , Sixl H.
Published: July 2002

We report on experimental and theoretical studies concerning the reaction kinetics of the solid state polymerization in diacetylene crystals. The individual reaction steps of the short-chain reaction intermediates (dimer, trimer, tetramer, ...) have been investigated by time resolved ESR and optical spectroscopy. In a microscopic theory energy barriers of molecular translations and rotations as well as the mismatch of the oligomer molecules in the crystal matrix are taken into account. The ‘‘molecular-mechanical’’ model gained in this way is successful in describing the experimentally observed dependencies of the activation energy of the addition reaction on chain length, temperature, and conversion. It also explains the time-conversion behavior of the reaction. Moreover, we gain information about the activation energy of the total reaction and can anticipate the temperature dependency of the chain length.
Accurate evaluation of quantal saddles and Regge pole positions and residues for calculation of elastic differential cross section by the Prüfer phase function method
Authors: Pajunen Petri
Published: July 2002

The Prüfer phase function method for calculation of differential cross section by Regge pole theory is described and tested. The approach provides a procedure for exact quantal calculation of Regge pole positions and residues, quantum saddles and other quantities required for evaluation of the differential cross section to virtually any desired accuracy and with realistic error control. Applications to a complex optical potential and to rainbow scattering are presented.
The excited states of barrelene: An absorption and magnetic circular dichroism study in the gas phase
Authors: Gedanken A. , de Meijere A.
Published: July 2002

The absorption and magnetic circular dichroism (MCD) spectra of barrelene in the gas phase have been investigated in the wavelength region of 2600–1500 Å. The 3s, 3p, and 3d Rydberg transitions have been identified and assigned. A strong valence band is observed at 1780 Å and is assigned as a 1A′1→1A″2 transition in accordance with theoretical predictions. The vibrational structure and the intensity distribution of the vibrational progressions indicate that only minor conformational changes occur in the excited electronic states of barrelene.
Theory of distortion-induced IR and Raman intensities of different modes of molecular units adsorbed onto metal surfaces
Authors: Bhattacharjee R.
Published: July 2002

A quantitative theory of distortion-induced IR and Raman intensities due to different modes of molecular units adsorbed on metal surfaces is formulated. This theory not only classifies the vibrational modes into categories of those attaining AI, AII, AIII, DIA-I(μ), DIA-II(μ), etc., but also gives a better understanding of the mechanism which activates the modes. In addition, it helps in deciding the effective symmetry of the adsorbed molecular unit onto metal surfaces. This point has been demonstrated by discussing an example of surface Raman spectroscopy of benzene-d6 molecule adsorbed onto (111) and (110) faces of silver single crystal. It is concluded that this molecule attains polar type of distortion of C1 symmetry on these surfaces.
Vibrational adiabaticity and infrared multiphoton dynamics
Authors: Parson Robert P.
Published: July 2002

The classical dynamics of a vibrating, rotating diatomic molecule in a strong laser field resonant with the vibration is examined. Particular attention is given to vibrational adiabaticity and its breakdown near resonance. The strong nonadiabatic effects seen in an earlier quantum calculation are explained in terms of the structure of the classical phase space. A connection between the breakdown of the vibrational adiabatic approximation and the onset of extensive intramolecular dephasing is explored.
Optimization of dynamic structuring in a reaction cell
Authors: Corbet Aaron B.
Published: July 2002

A simple model reaction cell is examined, with an intrinsic reaction dynamic, coupled to exchange with environment. As the concentration of a single input species is monotonically increased, the attractor of the cell dynamics increases in complexity from a zero-dimensional point to a limit cycle, through a subharmonic cascade to chaos, then hyperchaos with a minimal embedding dimension of four, and decreases in complexity back through a reverse cascade. A two-variable subsystem has the lowest order kinetics of any system known to display limit cycle oscillations. A three-variable subsystem has the lowest order kinetics of any chemically realistic system known to display a chaotic attractor.
An effect of antiphase boundaries on the kinetics of short-range ordering by a vacancy mechanism
Authors: Fultz B.
Published: July 2002

In Monte Carlo simulations of chemical short-range ordering on a square lattice, the number of single-atom domains was found to depend on the presence of antiphase boundaries and on the mechanism by which ordering occurred. When antiphase boundaries were present and the ordering occurred by a vacancy mechanism, the number of single-atom domains was found to increase with decreasing temperature, in contrast to thermodynamic predictions. This is understood as a consequence of highly correlated vacancy motions in those regions of the lattice away from antiphase boundaries.
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7O NQR study of the antiferroelectric phase transition in TlH2PO4
Authors: Seliger J. , Žagar V. , Blinc R. , Schmidt V. H.
Published: July 2002

The temperature dependence of the 17O NQR spectra in TlH2PO4 has been measured using a proton-17 O nuclear quadrupole double resonance technique. The results show that the protons in the short one-dimensionally linked O1–H1--O1 and O2–H2--O2 hydrogen bonds are moving between two equilibrium sites above Tc and freeze into one of the off-center sites below Tc. The protons in the asymmetric O3–H3--O4 hydrogen bonds are static and ordered above and below Tc.
Collisional broadening of CO2 IR lines. I. Diode laser measurements for CO2–N2 mixtures in the 295–815 K temperature range
Authors: Rosenmann L. , Perrin M. Y. , Taine J.
Published: July 2002

We present first diode–laser measurements of N2-broadened linewidths and strengths of 12C16O2 at high temperature. A T−N dependence of linewidths on temperature is deduced from measurements in the 295–815 K temperature range for the R38, R42, and R54 lines of the ν3 band. The measured line strengths are 21.48±0.49, 12.84±0.28, and 1.82±0.04 cm−2 atm−1 at 300 K for the R38, R42, and R54 lines, respectively. The corresponding half-widths are 71.02, 70.05, and 67.81×10−3 cm−1 atm−1. The N exponent takes the values 0.73±0.05, 0.72±0.02, and 0.72±0.04.
Hartree–Fock study of polysulphur nitride II. Three-dimensional structures and interchain interactions
Authors: Causà M. , Dovesi R. , Pisani C. , Roetti C. , Saunders V. R.
Published: July 2002

The electronic structure and stability of three-dimensional polysulphur nitride are studied using the same SCF-HF-LCAO computational technique as previously used for the isolated infinite polymeric chain [J. Chem. Phys. 81, 2839 (1984)]. A minimal basis set is adopted, supplemented with d functions on sulphur atoms. Interchain interactions are shown to have almost negligible influence on electron density and bond populations, but are important in determining the electronic properties of the system. The calculated HF energy of the polymer is slightly less than that of the molecular precursor, contrary to experimental evidence; the introduction of correlation corrections according to the Colle and Salvetti method reduces the disagreement but does not reverse the order of stabilities.
Photophysical properties of matrix-isolated Mg2: Evidence for efficient predissociation
Authors: McCaffrey John G. , Ozin Geoffrey A.
Published: July 2002

Optical absorption and excitation profiles recorded for emission of magnesium dimer in argon and krypton matrices allow identification of the A 1Σ+u and B 1Πu states. The radiative lifetime measured for the lowest vibrational levels of the A 1Σ+u state is 1.0 ± 0.25 ns in Ar consistent with a strongly allowed A 1Σ+u–X 1Σ+g transition. Excitation into the higher vibrational levels produces a rise time of 0.5 ± 0.25 ns in the A→X emission, indicating the rate of vibrational relaxation under solid state conditions. Photoexcitation into the higher vibrational levels of the A 1Σ+u state also produces atomic triplet emission by a mechanism of homogeneous predissociation occuring via coupling of this bound, optically active state with the repulsive, optically inactive 3Πu state. The enhancement of predissociation in solid krypton compared with argon is interpreted in terms of the greater overlap of the coupling states in the former solid which is facilitated by the differential shifting of the bound and repulsive dimer states in the two solids. From the observations that the bound A 1Σ+u state is stabilized while predissociation occurs for lower vibrational levels in Kr relative to Ar, it is concluded that the repulsive 3Πu state crosses the bound state on its inner limb.
Trap avoiding walk: A model for polymer growth
Authors: Narasimhan S. L. , Goyal P. S. , Dasannacharya B. A.
Published: July 2002

To describe the irreversible growth of a linear polymer chain, we introduce a random walk called trap avoiding walk (TAW). This walk is strictly self-avoiding, can grow successfully to any specified length, and does not have the restriction that it should not end inside a cage. This has been achieved by allowing a TAW to avoid only those cages which prevent it from growing to its full length. The physical justification for such a walk is that a polymer can, in general, grow inside a cage and get chemically terminated there. Monte Carlo results of the TAW on a square lattice for lengths up to N=105 are presented. The critical exponents ν, ν0, νI of the mean square end-to-end distance for the total ensemble of TAWs and for its subensembles of walks ending outside and inside cages are found to have the values 0.571±0.005, 0.578±0.007, and 0.61±0.05, respectively.
Extension of a general potential-energy function for diatomic molecules
Authors: Ogilvie J. F.
Published: July 2002

The conditions applicable at the limits of the united atom and the separate atoms may be applied to any radial function for diatomic molecules based on the argument z≡2(R−Re)/ (R+Re) so as to generate further coefficients in a polynomial representation that thus has the correct asymptotic behavior in the approach to these limits. The appropriate conditions are given for the potential-energy and dipole-moment functions, and the results are illustrated by application to HCl. This type of representation is compared with rational functions.
Prediction and experimental comparison of deuterium quadrupole coupling constants in some bifluoride salts: An extreme example of symmetric hydrogen bonding in different crystalline environments
Authors: Bacskay George B. , Gready Jill E.
Published: July 2002

The electric field gradient (EFG) at the deuterium nucleus of the bifluoride ion, a linear symmetrically H-bonded system, has been calculated using ab initio Hartree–Fock SCF, singles and doubles CI, and coupled pair functional methods using basis sets ranging from double zeta to the [7,5,2,1;5,4,2] contracted Gaussian set. For the free DF−2 ion, the EFG and the resulting nuclear quadrupole coupling constant (nqcc) are found to be very low and positive in sign, and to display marked dependences on basis set, and the effects of electron correlation and vibrational averaging. In particular, we note a peculiarly extreme basis-set limit problem for deuterium EFGs in symmetric H-bonded molecules. The effects of the crystal lattice on the nqcc have been calculated for the sodium, potassium, and ammonium bifluorides taking into account: the direct contribution of the lattice to the EFG as modeled by a point-charge distribution; its polarizing effect on an individual DF−2 ion using two different methods; and also the effects of librational averaging. The predicted deuterium nqccs and asymmetry parameters (η) in the bifluoride salts are compared with the free-ion values (η necessarily zero). While our predicted nqcc in KDF2 of 55±3 kHz is consistent with the only reported experimental value of 58±10 kHz [R. Blinc et al., Chem. Phys. Lett. 48, 596 (1977)], the calculated η value of 0.07±0.01 is at serious variance with the experimental value of 0.4±0.1. As our treatment of the crystal lattice effects is quite comprehensive this disagreement requires further investigation. We have predicted a significantly higher nqcc for NaDF2 of 83±3 kHz, but, again, with a very small η value of 0.04±0.01.
Microwave spectrum of the boron monosulfide radical BS
Authors: Tanimoto Mitsutoshi , Saito Shuji , Yamamoto Satoshi
Published: July 2002

The microwave spectrum of the most abundant isotopic species of the boron monosulfide radical 11B32S in the ground electronic state X 2Σ+ has been observed with a glow discharge cell spectrometer. Boron monosulfide was produced in an absorption cell by a glow discharge through a gaseous mixture of boron trichloride and hydrogen sulfide. The transitions were observed for N=2–1 to N=7–6 which fell in the frequency region up to 332 GHz. The molecular parameters were derived by a least-squares analysis: these included the rotational and centrifugal distortion constants, the spin–rotation interaction constant, the magnetic hyperfine interaction constants, and the nuclear quadrupole interaction constant. The nuclear spin-rotation interaction constant was also determined.
Dual Lanczos vector space. III. Generalized polynomials and polynomial operators in the investigation of spectral and temporal properties of globally linear dynamical systems
Authors: Wassam W. A. , Torres-Vega Go.
Published: July 2002

Dual Lanczos transformation theory is further developed by incorporating generalized polynomials and polynomial operators into its mathematical infrastructure. With the aid of these quantities, we obtain a number of new and useful results for understanding and determining the spectral and temporal properties of globally linear dynamical systems. Among these results are powerful practical tools for (i) investigating generalized Langevin equations and memory function hierarchies; (ii) making mathematically rigorous statements about expected temporal character, including the possible existence of separations in time scales and memory effects; and (iii) extracting and utilizing dynamically embedded information to determine the time evolution or spectral densities of dynamical variables and their ensemble averages, autocorrelation functions, and cross correlation functions. The reported results apply to any time evolution and spectral density problem associated with a globally linear dynamical system, including problems that are inaccessible by matrix diagonalization techniques and those that may not be given the usual continued fraction representation.
Knudsen diffusion through thin porous films
Authors: Faley Timothy L. , Strieder William
Published: July 2002

Upper and lower bounds on Knudsen flow rates through a random porous film of finite thickness are applied to a bed of randomly overlapping spheres. This extension of Clausing’s original work on short tubes, to random porous media, yields estimates of the Knudsen flow as a function of film thickness. Insights into the collision paths for gas membrane transport are obtained.
Short-time behavior of diffusion with random traps
Authors: Schotland John
Published: July 2002

A field theory is developed for diffusion with high density, partially absorbing random traps. Instanton techniques are used to derive the short-time properties of S(t), the average fraction of surviving particles. In three dimensions it is shown that S(t)∼t−3/2e−ρu0t[1+O(t1/2)], where ρ is the trap density and u0 is the absorption rate of a single trap. This result provides corrections to the mean field survival function. The above form of S(t) is valid for t≪D−1ρ−2/d, where D is the diffusion constant.
Microwave spectra, structure, and dipole moment of trifluoromethyl silane
Authors: Durig J. R. , Attia G. , Groner P. , Beckers H. , Bürger H.
Published: July 2002

The microwave spectra in the region from 18.5 to 39.0 GHz have been measured and assigned for the following isotopic species of trifluoromethyl silane: CF328SiH3, CF329SiH3, CF330SiH3, CF328SiD3, CF329SiD3, CF330SiD3, CF328SiDH2, CF329SiDH2, CF328SiD2H, and CF329SiD2H. In addition to the vibrational ground state, two torsionally excited states were assigned for some of the asymmetrically substituted molecules whereas as many as thirteen states involving multiple excitation of the torsional and/or CF3 rocking modes were assigned for some of the symmetric rotor species. From a least squares adjustment to fit 18 rotational constants for the vibrational ground state, the following r0 structural parameters were obtained: r(C–F) =1.3600±0.0029 Å, r(C–Si)=1.8997±0.0071 Å, r(Si–H)=1.4600±0.0007 Å, r(Si–H) =1.4600±0.0007 Å, CSiH=107.15±0.03°, and FCSi=113.28±0.30°. The rs structural parameters were obtained for the SiH3 moiety and were found to be r(Si–H) =1.4598±0.0033 Å and CSiH=107.17±0.09°. The dipole moment was obtained from the ground state Stark effect measurements on CF328SiDH2 and was found to be ‖μa‖=2.32±0.02 D. The barrier to internal rotation is estimated from relative intensity measurements to be 403±20 cm−1 (1.15±0.06 kcal/mol). These results are compared to the corresponding parameters of some similar molecules.
Thermal roughening on stepped tungsten surfaces. II. The zone (011)–(001)
Authors: Gong Y. M. , Gomer R.
Published: July 2002

Self-diffusion measurements by the field emission fluctuation method have been extended to the (011)–(001) zone. Some evidence for roughening at 700–900 K is seen on (023), (012), and (017). On (013) there is much less indication of roughening. In all cases diffusion appears to be one dimensional below 900 K where it becomes two dimensional. These results are in contrast to those obtained on the zone (011)–(112), where steps are better defined and close packed, so that a sharper transition is observed at higher temperature.
Measurement of the resonantly enhanced quasielastic light scattering cross sections of heme proteins
Authors: Chiarello Ron , Reinisch Lou
Published: July 2002

We have measured the absolute cross sections for resonantly enhanced quasielastic light scattering in the heme proteins: cytochrome-c and metmyoglobin. Measurements of the scattered intensity were made as a function of protein concentration using the Brillouin scattering of the solvent as an internal standard. Our choice of scattering standard permits the measurement of absolute cross sections without employing correction factors for the reabsorption of scattered light. Incident laser excitation was on the red edge of the ‘‘Soret’’ absorption band of these proteins (21 839–23 529 cm−1). Scattering cross sections are nearly a factor of 3 larger than predicted with the Kramers–Kronig transform for both cytochrome-c and metmyoglobin.
Spatially inhomogeneous structures in a one-dimensional array of Brussellators
Authors: Lahiri A. , Ghosal S. S.
Published: July 2002

Considering a one-dimensional array of diffusively coupled Brussellators, we examine the bifurcations of the steady homogeneous solution to steady but spatially inhomogeneous structures. Several important aspects of such bifurcations are related to branching (see below) of the fixed point of a four-dimensional conservative map. In addition to the usual period doubling (‘‘wavelength doubling’’ in our terminology) observed in case of two-dimensional maps, the four-dimensional map is seen to exhibit a new type of branching, namely, giving rise to an invariant curve in phase space. In case of subthreshold branching of either type, the steady homogeneous solution bifurcates to either a ‘‘wavelength-two’’ or a quasiperiodic solution. In case of superthreshold branching, on the other hand, bifurcations involving more complicated spatial and temporal behavior are possible. Other relevant questions are dealt with.
A theoretical evaluation of the vinyl torsional potential in protoporphyrins
Authors: Findsen Leonore A. , Bocian David F. , Birge Robert R.
Published: July 2002

The potential surfaces for the vinyl torsion in 2,4-divinyl porphyrins are calculated by using semiempirical [INDO (intermediate neglect of differential overlap) and INDO-PSDCI (partial single and double excitation configuration interaction)] molecular orbital theory. Calculations are carried out on the two pyrrole hydrogen tautomers of the free base porphyrin as well as on the porphyrin dianion. The calculated potential surfaces are predicted to have energy maxima at 0° and 180° due to steric hindrance. A third maximum near 70° (approximately perpendicular) is predicted due to electronic destabilization associated with the loss of conjugation and a decrease in dispersive stabilization energy. The torsional surface associated with the porphyrin dianion is qualitatively different from that calculated for the free base porphyrin due primarily to more effective conjugation of the vinyl group into the porphyrin macrocycle in the dianion. Neither pyrrole hydrogen tautomerization nor internal rotation of the second vinyl group have any significant effect on the torsional potential surface of the first vinyl group. The latter result indicates that the vinyl groups are effectively ‘‘uncoupled’’ in 2,4-divinyl porphyrins. A complete vibronic analysis is carried out by calculating the torsional energy levels using a free internal rotor basis set containing 201 basis functions. A Boltzmann analysis of level occupation and numerical evaluation of the individual torsional expectation values are used in conjunction to calculate average dihedral angles as a function of temperature. We predict that the average torsional angle of the vinyl group is 114.2° in the free base porphyrin and 121.2° in the porphyrin dianion at ambient temperature. In order to compare these results with NMR studies, we also calculate the average angle by evaluating the expectation value of sin2 Φ. This expectation function, when transformed into an angular measurement (〈Φ*〉=sin−1〈sin2 Φ〉), restricts angular expectation values to lie within the first quadrant. Calculations of 〈Φ*〉 yield average angles of 46.3° for the free base porphyrin and 47.5° for the porphyrin dianion. These values are in good agreement with the NMR experimental

value of 51° which is based on a 〈sin2 Φ〉 measurement. The origins of the nonplanarity of the vinyl substituents are analyzed in terms of repulsive, dispersive, and electrostatic nonbonding interactions as well as bonding and electron correlation effects. We demonstrate that many of the predictive limitations associated with the use of INDO semiempirical procedures to calculate potential surfaces are improved by the inclusion of electron correlation embodied in double excitation configuration interaction.
Comment on: Accuracy of a
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o C–H bond length differences and their correlation with isolated C–H stretching frequencies
Authors: Schäfer Lothar , Siam Khamis
Published: July 2002

Relative C–H bond distances in n-alkanes, obtained from ab initio geometry optimizations with the 4-31G, 4-21G, and 5-31G** basis sets, are compared with experimental isolated C–H stretching frequency data. It is found that results from different calculations all give essentially linear frequency-bond length correlations, but with different slopes. For each of the sets of calculated C–H bonds investigated, the slope of the frequency-bond correlation is too small compared to the equation given by McKean [J. Mol. Struct. 116, 313 (1984)] for correlations between isolated C–H stretching frequencies and experimental r0 bonds. Thus it is concluded that, in contrast to work previously published by Aljibury et al. [J. Chem. Phys. 84, 6872 (1986)] and Snyder et al. [J. Chem. Phys. 81, 5352 (1984)], precise correlation between calculated bond lengths and isolated C–H stretching frequencies does not determine the relative differences between the various C–H bonds in n-alkanes to ±0.0001 Å.
Differential force law and related integral theorems for a system of N identical interacting particles. I. General geometries
Authors: Baltin R.
Published: July 2002

Starting from the stationary Schrödinger equation for a system of identical interacting particles, the three-dimensional differential force law (DFL) is derived in terms of the kinetic energy density tensor with components tαβ(x), the particle density n(x), and the potential. The most general vector field h(x) is given such that integrating the scalar product of h with the DFL over an arbitrary volume Ω yields theorems involving in their volume integrals the tensor components only in the form t≡∑3α=1tαα (if at all) t being the positive definite density of kinetic energy. The procedure results in four integral theorems: (i) balance equation of forces, (ii) balance equation of torques, (iii) the generalized virial theorem, and (iv) a new exact theorem which can be regarded as vector theorem on the first moment of the kinetic energy density. The new theorem is shown to imply validity of the other three, and therefore is more comprehensive than they.
Excited state absorption of Sm2+ in SrF2 and SrCl2
Authors: Payne Stephen A. , Chase L. L. , Krupke William F. , Boatner L. A.
Published: July 2002

The excited state absorption spectrum of Sm2+ diluted as an impurity in the single crystal hosts SrF2 and SrCl2 has been observed. The absorption peaks associated with the 5D0(4f6) excited state were found to be displaced by approximately 3000 cm−1 from the absorption bands arising from the 7F0(4f6) ground state when the 5D0–7F0 energy was taken into account. The observed peak separation is ascribed to the 4f–5d exchange interaction. From the measured peak positions and band intensities, the exchange energy for the Sm2+ impurity in the two host crystals was determined to be about the same order of magnitude as that expected for the free ion. The implications of the properties of the excited state absorption bands for the performance of CaF2:Sm2+ and SrF2:Sm2+ lasers are considered.
Classical and quantal pseudoergodic regions of the Henon–Heiles system
Authors: Kay Kenneth G. , Ramachandran B.
Published: July 2002

This work describes an approximate and temporary form of ergodicity, called pseudoergodicity. This is a classical phenomenon that is of particular interest since it has a straightforward quantum analog and can be expected to influence the dynamics of a quantum system more directly than rigorous ergodicity. A procedure is described for locating phase space regions where classical motion is pseudoergodic (pe) and this technique is applied to the Henon–Heiles system excited to near its escape energy. Certain pe zones containing chaotic trajectories appear to coincide with the vague tori of Reinhardt and co-workers while other such zones have less familiar forms. When the Henon–Heiles system is observed for long times, a single pe region becomes larger than others, thus marking incipient ergodicity on much of the energy shell. The classical pe regions are compared to quantum pe zones, calculated by a slight modification of a technique presented in an earlier paper. It is found that certain classical pe regions have close quantum analogs while others do not, for reasons probably related to the short time scale for quantum-classical correspondence. Among the classical regions that do not have quantum analogs is the aforementioned dominant pe zone. The implication is that the present quantum system does not display behavior similar to the truly large-scale ergodicity that occurs in the classical system.
Heat production in steady states and oscillations
Authors: Roelofs M. G.
Published: July 2002

Measurements were made of the rate of heat production in three oscillatory systems: benzaldehyde oxidation, the Briggs–Rauscher reaction, and the Belousov–Zhabotinsky reaction. In cases where a stable steady state coexists with a limit cycle oscillation or where the steady state undergoes a hard loss of stability to oscillations, the heat production in the oscillatory state was quite different from that of the steady state, varying from 50% less to 210% greater. Bifurcations to oscillations involving a soft loss of stability showed no discontinuity in the heat production, as expected. Consideration of the thermodynamics of these reactions indicates that the contribution to the rate of entropy production due to enthalpy changes dominates that due to differences in the entropies of the products and reactants. In the benzaldehyde oxidation, the changes in heat production are due to a change in the average rate of the reaction, and not due to a change in the distribution of products.
X-ray study of Kr and Xe adsorbed on the basal plane of nickel chloride
Authors: Morishige K. , Hanayama M. , Kittaka S.
Published: July 2002

X-ray scattering has been used to investigate the structures and phase transitions of Xe and Kr films adsorbed on the basal plane of NiCl2. The x-ray scattering measurements were carried out both as a function of temperature at fixed coverage and as a function of coverage at fixed temperature in the monolayer and bilayer coverage regimes. The results indicate that both the monolayers of Xe and Kr adsorbed on the basal plane of NiCl2 form a 2D solid of the simple triangular structure incommensurate with the substrate and 2D melting is first order in the incommensurate solid of Xe but continuous in that of Kr. With the addition of the second-layer atoms the interparticle distance of the adsorbed atoms reduces and the crystallinity of the incommensurate solid improves.
Level excitation cross sections of Si I fragments produced by 100 eV electron impact on SiH4
Authors: Sato Toshihiko , Kono Akihiro , Goto Toshio
Published: July 2002

The fluorescence decay Si i atomic lines after electron impact excitation of SiH4 molecular gas was observed, and the level excitation cross sections (LECS) of Si i fragments were determined by separating the contribution from cascade transitions to line emissions. Observed transitions were 4s 1P–3p2 1D, 4s 3P–3p2 3P, 3d 1P–3p2 1S, 3d 1D–3p2 1D, 3d 1F–3p2 1D, 3d 3P–3p2 3P, and 3p3 3D–3p2 3P, for which the LECSs of the upper levels were determined at 100 eV excitation energy. The contribution of the direct excitations to these line emissions were found to range from 37% to 80%. Analysis of the 4s 1P–3p2 1D decay curve also gave the LECSs of the cascading levels 4p 1P, 4p 1S, and 4p 1D. Also obtained were some radiative lifetimes not reported before.
Global order parameters and Antonoff’s rule in multicomponent regular and related solutions
Authors: Teubner Max
Published: July 2002

The global phase diagram of multicomponent mixtures is obtained in mean field theory from minimizing a function Φ of many variables. It is shown that by subjecting the variational parameters (global order parameters) in Φ to linear transformations, the number of parameters can often be greatly reduced. Simple criteria are constructed that guarantee the reduction to a single global order parameter. In this case the mixture is globally equivalent to the Landau theory with a single order parameter, and Antonoff ’s rule is often valid in these mixtures. Examples are furnished by regular solutions, multicomponent van der Waals mixtures, and Flory–Huggins mixtures if the interaction energies aij approximately satisfy the geometric mean rule aij=(aiiajj)1/2.
Probe-frequency dependence of the resonant inverse Raman band shape
Authors: Takayanagi Masao , Hamaguchi Hiro-o , Tasumi Mitsuo
Published: July 2002

Dependence of the inverse Raman band shape on the probe frequency was observed in detail in the region of a single photon resonance with a structured electronic absorption band of rhodamine 640 (a highly fluorescent molecule). Three parameters were introduced to represent an inverse Raman band shape which is strongly dependent on the probe frequency. The band-shape parameters derived from the observed data could be simulated using a vibronic treatment based on a Herzberg–Teller expansion. The simulation is shown to be potentially useful for obtaining information on the excited electronic states of fluorescent molecules whose spontaneous Raman spectra are difficult to observe.