bluuebunny/crossref_metadata_2025 huggingface dataset:
The statistical mechanics of a liquid of two-state molecules
Authors: Stratt Richard M.
Published: February 2003

The question of how the internal degrees of freedom of molecules are influenced by, and themselves influence, a condensed phase is taken up for the special case of a liquid of two-state molecules. It is well known that this model, in its classical version, is immediately solvable within a number of many-body approximations when the system is treated as a mixture. However, by using an internal-degree-of freedom diagrammatic approach, the fact that one can remove the internal dynamics and consider the system either as if it had an effective density or as if it were subject to effective interactions is made manifest. Further, by considering the analogy to magnetic systems, one is forced to predict, at least formally, the existence of a phase transition which implies a cooperative condensation into one particular internal state. The quantum mechanical version of the problem is then solved similarly (with a discretized path integral method) but the effective density and interaction are generalized to matrices and the classical phase transition becomes that of a quantal spin system. In the course of the discussion, both the classical and quantal ideas are shown to have some relevance to a number of physical problems; including the behavior of polarizable molecules, the structure of molten salts, and the symmetrization of hydrogen bonds.
Surface self-diffusion constants at low temperature: Monte Carlo transition state theory with importance sampling
Authors: Voter Arthur F. , Doll Jimmie D.
Published: February 2003

We present an importance-sampling method which, when combined with a Monte Carlo procedure for evaluating transition state theory rates, allows computation of classically exact, transition state theory surface diffusion constants at arbitrarily low temperature. In the importance-sampling method, a weighting factor is applied to the transition state region, and Metropolis steps are chosen from a special distribution which facilitates transfer between the two important regions of configuration space: the binding site minimum and the saddle point between two binding sites. We apply the method to the diffusion of Rh on Rh(111) and Rh on Rh(100), in the temperature range of existing field ion microscope experiments.
Polymer migration phenomena based on the general bead-spring model for flexible polymers
Authors: Brunn Peter O.
Published: February 2003

This paper is concerned with the migration of general bead spring model macromolecules in inhomogeneous flows. The corresponding diffusion equation is derived. In order to obtain the translational diffusion tensor 𝒟 and the polymer migration velocity vm, respectively, some special models are considered. For Zimm coils, 𝒟 is isotropic with a constant diffusivity D. This implies that these molecules do not migrate across streamlines in unidirectional flows. For Zimm coils, the forms of D and vm, respectively, are obtained and explicit results are provided in the limit of no hydrodynamic interaction (Rouse coils). For more general models, the tensorial character of 𝒟 comes into play. For the simplest model (dumbbell with nonaveraged Oseen tensor), the predictions for channel flow seem unacceptable, which this author associates with an inadequacy of the dumbbell model.
Transition state theory description of surface self-diffusion: Comparison with classical trajectory results
Authors: Voter Arthur F. , Doll Jimmie D.
Published: February 2003

We have computed the surface self-diffusion constants on four different crystal faces [fcc(111), fcc(100), bcc(110), and bcc(211)] using classical transition state theory methods. These results can be compared directly with previous classical-trajectory results which used the same Lennard-Jones 6-12 potential and template model; the agreement is good, though dynamical effects are evident for the fcc(111) and bcc(110) surfaces. Implications are discussed for low-temperature diffusion studies, which are inaccessible to direct molecular dynamics, and the use of ab initio potentials rather than approximate pairwise potentials.
Comment on ‘‘Three photon resonance ionization of H2’’ [J. Chem. Phys. 7
7, 877 (1982)]
Authors: Dixit S. N. , McKoy V.
Published: February 2003

Ritchie et al’s1 Paper on three photon resonance ionization of hydrogen is commented upon. Their three-photon angular distribution relation based on the extended two−level rate theory of Eberly and O’Neil2, is found to be incorrect. (AIP)
Mode-to-mode energy transfer in collisions between S1 state aniline and Ar, CO, CO2, C2H2, C3H4, OCS, Xe, and N2O
Authors: Pineault Richard L. , Crackel Robert L. , Hedstrom John F. , Struve Walter S.
Published: February 2003

SVL fluorescence spectroscopy was used to study V-T,R processes in collisions of 00 aniline with Ar, Xe, CO, CO2, OCS, N2O, acetylene, and allene. Populations were monitored in eight aniline vibronic levels. To first order, the experimental propensity rules for single-collision up pumping of 00 aniline to these levels are identical for all collision gases. An exception is the unusually large rate constant for population of the 11 level in collisions with allene, whose 111 level is nearly degenerate with the I1 level in aniline; this may be evidence of an important V–V process. The endoergic up-pumping probabilities correlate well with μ1/2 for rare gas partners, but poorly for the other collision gases. No evidence is found that V-R processes contribute substantially to the rate constants for aniline in collision with CO or the polyatomic gases. The quantitative propensity rules provide a basis for a mode-to-mode collisional energy transfer theory, developed by Freed, in which the observed large V-T,R cross sections arise as a direct consequence of the intramolecular intermode coupling within large molecules such as aniline.
The interaction of a water molecule with an ion at a distance
Authors: Dacre Peter D.
Published: February 2003

The interaction of an ion with a water molecule at intermediate separation is considered. It is shown that the SCF interaction energy in the small overlap region can be calculated as the sum of the electrostatic and induction terms. For the electrostatic interaction multipoles up to hexadecapoles must be included. The induction term, which is appreciable, may be accurately obtained from the α, A, and C tensors.
Molecular structure of the hydroperoxyl anion (HO−2 )
Authors: Cohen Drora , Basch Harold , Osman Roman
Published: February 2003

The equilibrium geometry of ground state HO−2 (1A′) has been determined by an ab initio multiconfiguration self-consistent field gradient optimization method using 14 active space molecular orbitals in a double zeta+polarization+(two different) diffuse Gaussian function basis sets. The calculated geometry is R(O–O)=1.498 Å, R(O–H)=0.962 Å, and ∠HOO=99.8°. For comparison purposes, parallel results were also obtained for the ground states of O, O−, O2, O−2 , and HO2. For a given basis set the calculated adiabatic electron affinities of O, O2, and HO2 are all found to differ by a constant value ±0.05 eV relative to their respective experimental values, suggesting that the errors in the molecular cases are essentially atomic in nature.
Variation-perturbation theory within a time-dependent Kohn–Sham formalism: An application to the determination of multipole polarizabilities, spectral sums, and dispersion coefficients
Authors: Bartolotti Libero J.
Published: February 2003

The variation-perturbation method within time-dependent Kohn–Sham theory is used to calculate atomic multipole polarizabilities, spectra sums, and multipole–multipole two-body dispersion coefficients. The first-order corrections to Kohn–Sham amplitudes and phases were obtained from a direct variational approach and from the method of Cauchy moments. The multipole Cauchy moments were used to construct Padé approximants, which gave us upper and lower bounds to the two-body dispersion coefficients. Four approximations to the exchange-correlation energy were investigated in the present work and the gradient expansion for atoms proved to be most satisfactory.
Computer simulation of muonium in water
Authors: De Raedt Bart , Sprik Michiel , Klein Michael L.
Published: February 2003

The structure of water molecules surrounding an isolated hydrogen atom (H) or muonium (Mu) is investigated using computer simulation. The water solvent is treated using classical mechanics and a simple effective two body potential that is designed to yield a reasonable solvent structure. Feynman’s path integral approach is used to treat the single quantum impurity (H or Mu). Both the H and Mu atoms are found to be clathrated with average coordination numbers of 18 and 23 water molecules, respectively. The value for the H atom differs little from the results of a purely classical calculation. It is suggested that the lack of isotope effect in certain diffusion controlled reactions of H and Mu is due to the enclathration of  both species.
Hopping transport on a randomly substituted lattice for long range and nearest neighbor interactions
Authors: Loring Roger F. , Andersen Hans C. , Fayer M. D.
Published: February 2003

A theoretical study of hopping transport of excitations or charge carriers among particles randomly distributed on a lattice is presented. The method used is an extension of the diagrammatic technique applied by Gochanour, Andersen, and Fayer to hopping transport in a continuum. We present an exact diagrammatic analysis of the configuration averaged Green function of the Pauli master equation. We obtain a self-consistent approximation to the Green function from which transport properties such as the mean squared displacement may be calculated for any transfer rate, any lattice type and any concentration. For a three dimensional lattice, the results are shown to be accurate in the low concentration limit and for the filled lattice, and are expected to be accurate at intermediate concentration. This is the first theory of hopping transport on a randomly substituted lattice, which is not restricted to low concentration, that can be applied in the case of a long range transfer rate. Results are presented for a Förster dipole–dipole transfer rate and for a transfer rate limited to nearest neighbors for a simple cubic lattice. The latter has a percolation threshold that is described in a qualitatively correct manner by our approximation.
Velocity dependence of rotational rainbow structure in Na2–Ar
Authors: Moskowitz W. P. , Stewart B. , Bilotta R. M. , Kinsey James L. , Pritchard David E.
Published: February 2003

We present level-to-level differential cross sections for the rotationally inelastic process Na2( ji=7)+Ar→Na2( jf)+Ar at center of mass energies 0.49 and 1.1 eV, with Na2 in its lowest vibronic state. The energy was varied by seeding Na2 in noble gas mixtures of varying atomic mass. The range of the final rotational quantum number  jf is 9≤ jf ≤47, corresponding to 2≤Δj≤40. The measurements were made in crossed molecular beams. The initial rotational level was selected using optical pumping, and the final rotational level was detected by laser induced fluorescence. The angular distribution was determined by a new Doppler technique that gives good small angle resolution, and whose indifference to the direction of the initial relative velocity of the collision simplifies measurements at different energies.
A new rigid-rotor H2–CO potential energy surface from accurate a
b i
n
i
t
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o calculations and rotationally inelastic scattering data
Authors: Schinke R. , Meyer H. , Buck U. , Diercksen G. H. F.
Published: February 2003

We determined a new rigid-rotor potential energy surface for H2–CO by combining large basis set SCF calculations with damped long range dispersion coefficients. The damping function contains two parameters which were determined by comparison of experimental and calculated cross sections for oD2–CO scattering at E=87.2 meV. The dynamical calculations were performed within the coupled states approximation because neither a classical nor an energy sudden description of the CO rotation are accurate enough. It is found that the rotational rainbow structures of the energy transfer cross sections determine the relative anisotropy of the interaction potential, while the diffraction oscillations of the total differential cross section determine the absolute range of the effective spherically averaged potential. For a unique potential determination both sets of experimental data have to be fitted simultaneously.
Kinetic theory of the depolarized light scattering R parameter. I. Formal theory
Authors: Cole R. G. , Hoffman D. K. , Evans G. T.
Published: February 2003

The R parameter, which measures the magnitude of the Rytov dip observed in light scattering spectra, is calculated using kinetic theory for a dense, neat fluid of hard ellipsoids (rotors). The kinetic theory truncates the BBGKY hierarchy at the Enskog level and ignores chattering events when determining two body dynamics. As such, this theory represents an extension of our earlier work on the collective and single particle orientational correlation times of rotor-like molecules.
Mean square torques and correlation functions of the ν3 vibration of N2O mixed in argon at variable temperature
Authors: Dreyfus C. , Cartigny J.
Published: February 2003

The second and fourth spectral moments of the ν3 vibration of N2O mixed in compressed argon are reported for five temperatures. The ratio of the mean square torque to the density is deduced and it is found to increase with the temperature, thus showing the major role of the repulsive potential in the formation of the torque. Comparison of experimental correlation functions with models shows that the assumption of instantaneous collisions is too crude. The Steele memory function theory yields instead a satisfactory agreement with the experimental data.
Optical and magnetic properties of uranium borohydride and tetrakismethylborohydride
Authors: Rajnak K. , Gamp E. , Shinomoto R. , Edelstein N.
Published: February 2003

The U(BD4)4/Hf(BD4)4 optical spectrum reported by Bernstein and Keiderling has been reanalyzed. All 19 allowed transitions have been identified. The crystal field is ∼2.5 times as strong as that of  U4+/ThBr4, but the values of the Fk and ζ parameters are nearly the same. The magnetic susceptibility of the structurally related molecule U(BH3CH3)4 has been measured from 2–330 K. Using the eigenvectors from the optical analysis, the magnetic data can be fit with an orbital reduction factor k=0.85. For U(BD4)4/Hf(BD4)4 k=ζ/ζfree ion=0.91.
Intermolecular vibrations of two 1:1 complexes between CH3CN and HCN in solid Ar
Authors: Knözinger Erich , Wittenbeck Rüdiger
Published: February 2003

The far IR spectra of mixtures of acetonitrile and hydrogen cyanide isolated in solid argon have been measured over the range 200–10 cm−1. Depending on the physical conditions and on the sample preparation, absorption patterns of two different 1:1 complexes have been observed: (a) a predominantly antiparallel structure giving rise to four far IR bands and (b) a more stable linear hydrogen bonded structure exhibiting only two far IR bands.
Cold jet infrared absorption spectroscopy: The ν3 band of WF6
Authors: Takami Michio , Kuze Hiroaki
Published: February 2003

The ν3 band of WF6 is studied at a low rotational and vibrational temperature by using a tunable diode laser. Infrared absorption in a pulsed supersonic free jet of WF6 is observed by phase sensitive detection synchronized with the pulse frequency. Absorption lines of four isotopic species, 182WF6, 183WF6, 184WF6, and 186WF6 are measured between 711.5 and 716.6 cm−1 with a Doppler limit resolution. Five molecular constants, ν3, B3, Bζ3, F110, and α224 are determined for each isotopic species and α220 for 186WF6. Isotope shift for the ν3 band is determined to be −0.316 cm−1/amu.
The excited states of 1, 3-butadiyne determined by electron energy loss spectroscopy
Authors: Allan Michael
Published: February 2003

Dipole forbidden electronic transitions in butadiyne were studied in the range 2–12 eV using a trochoidal electron spectrometer. The lowest observed feature is weak, structureless, with an onset sround 2.7 eV, and is probably due to the lowest excited state 3Σ+u . The second triplet state 3Δu is observed at 3.216 ±0.01 eV(000), respectively 4.2±0.2 eV (vertical). It exhibits long progressions in the ν′2 C≡C stretch and ν6 C–H bend vibrations. The latter indicates a bent equilibrium configuration. The UV inactive 000 transition of the 1Δu state is observed at 5.06±0.01 eV with low electron energies. This value is in excellent agreement with the prediction of Jungen et al. based on the interpretation of the UV absorption. At higher electron energies only the UV active vibronic transitions of this state are observed. With low electron energies a number of narrow bands corresponding to dipole forbidden transitions are observed above 7 eV. They are tentatively grouped into three new Rydberg series with δ=0.46, 0.5, and 0.87. Finally, three narrow anion states (Feshbach resonances) are observed at 6.71, 6.82, and 7.00±0.04 eV. They decay preferentially by emission of a slow (≤0.3 eV) electron.
Collisional dissociation and chemical relaxation of alkali halide molecules: 2000–4200 K
Authors: Milstein Richard , Berry R. Stephen
Published: February 2003

Shock-induced dissociation and the subsequent chemical relaxation processes of diatomic alkali halide molecules have been studied by time-resolved absorption spectrometry of alkali atoms, halide ions, and alkali halide molecules. The salts studied in detail are NaCl, KBr, RbCl, RbBr, CsCl, CsBr, and CsI. Rate coefficients have been determined in the temperature range2000–4200 K for these processes: collisional detachment by argon Ar+X−→Ar+X+e; ionization of alkali atoms by thermal electron impact e+M0→2e+M+; ion–ion neutralization M++X−→M0+X0; collisional dissociation to ions Ar+MX→Ar+M++X−; and finally, collisional dissociation to atoms Ar+MX→Ar+M0+X0. The branching ratio (probability of dissociation to atoms)/(probability of dissociation to ions) is, in all cases studied, favorable to formation of ion pairs, relative to the equilibrium distribution of atom pairs/ion pairs. However, in every case except CsI, the primary collisional dissociation process gives a significant fraction of atom pairs.
Explodator: A new skeleton mechanism for the halate driven chemical oscillators
Authors: Noszticzius Z. , Farkas H. , Schelly Z. A.
Published: February 2003

In the first part of this work, some shortcomings in the present theories of the Belousov–Zhabotinskii oscillating reaction are discussed. In the second part, a new oscillatory scheme, the limited Explodator, is proposed as an alternative skeleton mechanism. This model contains an always unstable three-variable Lotka–Volterra core (the ‘‘Explodator’’) and a stabilizing limiting reaction. The new scheme exhibits Hopf bifurcation and limit cycle oscillations. Finally, some possibilities and problems of a generalization are mentioned.
Microwave spectrum and internal rotation of 2-butyne-1, 1, 1-d3 (dimethylacetylene), CH3C≡CCD3
Authors: Nakagawa Jun , Hayashi Michiro , Endo Yasuki , Saito Shuji , Hirota Eizi
Published: February 2003

The rotational transitions of CH3C≡CCD3 have been observed for J=13←12, 15←14, 18←17, 19←18, 20←19, 22←21, 23←22, and 26←25 using a source-frequency modulation microwave spectrometer with a 3.7 m long free space absorption cell maintained at −50 to −60 °C. The observed spectrum clearly shows the effect of internal rotation with a small potential barrier. The expression for the rotational transition frequency derived by Kirchhoff and Lide [J. Chem. Phys. 43, 2303 (1965)] using a second-order perturbation theory for the contributions of the internal rotation was employed in analyzing the observed spectrum, and the least-squares analysis has yielded the rotational constant B=2982.4980±0.0011 MHz and a few centrifugal distortion constants. The barrier height to internal rotation has been estimated to be 5.62±0.16 cm−1.
Hidden correlations and the behavior of the dynamic structure at short times
Authors: Phillies George D. J.
Published: February 2003

Reexamination of methods for calculating the initial slope of the dynamic structure factor demonstrates the importance of covert correlations between the motions and subsequent positions of interacting colloidal particles. These correlations, whose existence has hitherto not been explicitly emphasized, explain the numerical discrepancies between one- and two-time derivative methods for calculating dS(k,t)/dt. A method for avoiding artifacts due to these correlations is presented.
Vibrational relaxation of highly excited diatomics. VI. DF(9≤v≤12)+N2, CO, CO2, and N2O and HF(v=5–7)+CO
Authors: Dzelzkalns L. S. , Kaufman F.
Published: February 2003

Vibrational relaxation rate constants are determined for DF(v=9–12) by Q=N2, CO, CO2, and N2O and for HF(v=5–7) by CO using the fast flow infrared chemiluminescence technique. The rate constants range from 0.6 to 35×10−11 cm3 s−1, and with the exception of Q=N2, the energy transfer probabilities P per gas-kinetic (Lennard-Jones) collision are large 0.4<P<1.0. The vibrational energy gap ΔE is small for the DF(v) relaxation processes and the v dependence of kQv, v−1 is much weaker than that for HF(v). The data suggest independent effects based on ΔE and on v which partially cancel each other for DF, but not for HF. The initial, unrelaxed v distribution for the D+F2→DF(v≤13)+F reaction is found to peak at v=9, in disagreement with earlier experimental studies but in agreement with recent theoretical work.
Studies of vibrational relaxation in OCS and CF4 by pulsed photoacoustic techniques
Authors: Smith Nicholas J. G. , Davis Christopher C. , Smith Ian W. M.
Published: February 2003

We have used the pulsed photoacoustic technique to measure the effective collisional probabilities for relaxation of the lowest vibrational modes of OCS and CF4 by several collision partners. The measured probabilities at 300 K are OCS by OCS—(3.7±0.7)×10−4; He—(8.0±0.3) ×10−4; Ar—(0.96±0.3)×10−4; H2—(12.0±7.0)×10−4; D2—(12.9±2.5) ×10−4; N2—(2.5±0.5)×10−4; CO—(3.0±0.7)×10−4; CF4 by CF4—(3.4 ±0.2)×10−4; He—(8.6±1.0)×10−4; Ar—(1.6±0.2)×10−4. We also consider in some detail the acoustic waves generated by cylindrically symmetric laser excitation of a weakly absorbing gas in a cylindrical tube and how the signals produced by a microphone in the tube wall reflect the V-R,T relaxation of the gas.
Electron attachment to the perfluoroalkanes n-CNF2N+2 (N=1–6) using high pressure swarm techniques
Authors: Hunter S. R. , Christophorou L. G.
Published: February 2003

The electron attachment rate constants and negative ion formation mechanisms for six perfluoroalkanes [n-CNF2N+2(N=1–6)] have been studied in a high pressure swarm experiment within the mean electron energy range from thermal energy (≊0.04 eV) to ≊4.9 eV. These experiments were performed over a total gas number density range of 3.2×1019 to 3.9×1020 cm−3 using N2 and argon as buffer gases. Dissociative electron attachment was found to be the only negative ion formation process for CF4 and C2F6. For C3F8, n-C4F10, and n-C5F12 the electron attachment rate constant measurements exhibited a large total pressure dependence which was strongest for C3F8 and decreased with increasing size of the perfluoroalkane molecule. These measurements have been interpreted as electron attachment by parent negative ion formation due to three-body stabilization processes of the initially excited, short-lived (5×10−11 s <τ<10−8 s) parent anion. The lifetimes of these transient parent anions have been found to depend on the nature of the parent ion and on the electron energy. The electron attachment rate constants are largest for the n-C6F14 molecule and decrease with decreasing size of the perfluoroalkane molecule. Furthermore, the peak in the attachment rate constants occurs at the lowest mean energy (∼1.1 eV) for n-C6F14 and shifts to higher mean energy with decreasing size of the molecule (to ≥5 eV for CF4). The electron attachment cross sections for all of these molecules have been calculated using the swarm-unfolding method and calculated electron energy distribution functions in argon. These measurements are compared with relative negative ion cross sections, determined previously using mass spectrometric techniques. The negative ion formation mechanisms are discussed and the effect of molecular size on the electron attachment properties of these molecules is indicated using the present measurements in conjuction with the results of a recent single collision negative ion study.
Dynamic analysis of electron density in the course of the internal motion of molecular system
Authors: Tachibana Akitomo , Hori Kenzi , Asai Yoshihiro , Yamabe Tokio
Published: February 2003

The general dynamic aspect of electron density of a molecular system is studied on the basis of the general equation of the electron orbital which is formulated for the dynamic study of electronic motion. The newly defined electron orbital incorporates the dynamics of molecular vibration into the electronic structures. In this scheme, the change of electron distribution caused by excitation of vibrational state is defined as the ‘‘dynamic electron transfer.’’ The dynamic electron density is found to have the remarkable ‘‘additive’’ property. The time-dependent aspect of the dynamic electron redistribution is also analyzed on the basis of the ‘‘coherent state.’’ The new method relates the classical vibrational amplitude to the quantum number of the vibrational state. As a preliminary application of the present treatment, the dynamic electron densities of H2, HD, HT, HF, and HCl molecules are calculated by use of ab initio molecular orbital method.
Electron density and intermolecular interactions in NaHC2O4 ⋅ H2O
Authors: Lunell Sten
Published: February 2003

The electron density in the NaHC2O4 ⋅ H2O crystal has been studied by quantum mechanical ab initio MO-LCAO-SCF calculations. Calculations have been performed on one hand for the free HC2O−4 and H2O molecules/ions, and on the other hand, for these molecular units in the crystalline surrounding. The main effects of the intermolecular interactions on the electron density can be summarized as follows: (1) The polarity of the intramolecular bonds is increased in the crystal, as compared to the free state. (2) The deviation from spherical symmetry around the oxygen atoms is smaller in the crystal than in the free molecules/ions. In particular, this implies a decrease of lone pair density at these atoms. (3) The experimental observation that lone pairs accepting stronger hydrogen bonds, in general, show less intense peaks in the deformation density than those which accept weaker hydrogen bonds is explained as being primarily a superposition effect between donor and acceptor deformation densities.
X-ray diffraction and calorimetric phase study of a binary paraffin: C23H48–C24H5
Authors: Denicolo I. , Craievich A. F. , Doucet J.
Published: February 2003

The phase diagram of the binary paraffin system C23H48–C24H50 was determined by calorimetric and x-ray diffraction methods. The present experimental results and previous work on pure C23H48 and C24H50 paraffins allow us to identify all the phases of the binary system. The composition and temperature dependences of the lattice parameters were also investigated.
Near infrared spectra and the disrupted network model of normal and supercooled water
Authors: Angell C. A. , Rodgers V.
Published: February 2003

The near IR (overtone) spectra of water, H2O–D2O solutions, and a glass-forming glycerol +D2O solution have been measured in the temperature range 80 to −30 °C (−120 °C for the glycerol +D2O solution) using emulsion samples to gain access to the deep supercooling range. At −30 °C the intensity attributed to weakly hydrogen bonded –OH is greatly diminished and a small extrapolation in the latter case leads to a spectrum closely similar to that of the vitreous glycerol +D2O solution. This is a very broad spectrum, extending from 1.4–1.65 μm, which we associate with a fully bonded and immobile quasilattice in which there is a distribution of hydrogen bond strengths. The changes in intensity which occur with rise in temperature are seen to be consistent with an ‘‘exciting across the centroid’’ model (a weak bond⇄strong bond exchange) suggested by Stillinger and Rahman on the basis of MD calculations. The enthalpy change for this process is found to be 3.0 kcal/mol, consistent with light-scattering data for the hydrogen bond-breaking energy.
Lithium doping of (CH)x molecular diffusion of the dopant
Authors: Rachdi F. , Bernier P. , Faulques E. , Lefrant S. , Schué F.
Published: February 2003

We have studied the kinetics of the n-type doping process of cis-(CH)x using lithium–benzophenone solutions in THF. For short doping times the distribution of the dopant in the film is strongly inhomogeneous. The diffusion of the dopant in the material is characterized by two processes with very different kinetics corresponding to the interfibrillar and intrafibrillar diffusions, whose coefficients could be determined by studying the evolution of the EPR spectra. Raman spectroscopy shows that during the doping process, isomerization from cis to trans occurs, in a time scale very short compared with the time needed by the dopant to diffuse in the fibrils.
Optical and magneto-optical rotation due to transverse electronic motion in thick helices of nonintegral turns
Authors: Brown Samuel H. , Chiu Ying-Nan
Published: February 2003

The induction of time-oscillating (and radiating) dipoles in a helical structure is first discussed from a classical, geometrical viewpoint. It is shown that not only the longitudinal but also the transverse component of the helix can contribute to this dipole moment. The transverse contribution is also chiral in that it can give rise to opposite signs for optical rotation for the left vs right helices. Such transverse effects cannot be accounted for by the existing treatment of a free electron in a one-dimensional helix. We used a nonorthogonal curvilinear arc coordinate system to represent a three-dimensional helix and computed general transverse excitation matrix elements for optical rotation based on a free electron in a three-dimensional potential box. As a rough comparison of transverse vs longitudinal effect, the parameters in the conjugated hexahelicene molecule are used as examples. It is suggested that the transverse effect will be present not only in the optical rotation of inherently asymmetric molecules in random systems, but also in Rayleigh and Raman optical activity and in the optical rotation of oriented helices. It may also some day be useful for the determination of the absolute configuration of optical isomers.
Forces in molecular systems: Effect of nuclear motion on chemical binding
Authors: García-Sucre M. , Dohnert A. , Lo Russo A. , Reif I.
Published: February 2003

We have used nuclear coordinate scalings to treat the problem of forces in molecular systems in such a way that nuclei are quantum mechanically described throughout. We first examined the case in which only one of the nuclei is considered to occupy successive fixed positions. We have shown that the force acting on such a nucleus can be exactly described in terms of an electrostatic field which results from the electronic charge density and from the nuclear charge density of all other nuclei. We propose a definition of the force acting on a nucleus which remains valid when all the nuclei in the molecule are quantum mechanically described and we examined modifications of the Berlin’s binding and antibinding regions due to the effect of quantum motion of the nuclei. Thus, we describe the effect of nuclear motion on chemical binding.
Acetone impurity effects on the binary fluid mixture methanol–cyclohexane
Authors: Cohn R. H. , Jacobs D. T.
Published: February 2003

Measurements on the coexistence curves of the binary fluid mixture methanol–cyclohexane with increasing amounts of acetone impurity showed essentially linear changes in the critical temperature and critical concentration with impurity. Adding 1.0% acetone impurity caused the critical temperature to decrease by 3.4 K, the effective critical exponent β to increase and the critical concentration, as measured by volume fraction methanol, to decrease by 0.005.
Theta point (‘‘tricritical’’) region behavior for a polymer chain: Transition to collapse
Authors: Kholodenko A. L. , Freed Karl F.
Published: February 2003

The conformational space renormalization group method is generalized further to describe excluded volume effects in finite molecular weight polymers in the theta point region where contributions from effective three-body interactions become appreciable. The theory builds upon our previous description of the good solvent region and uses t’Hooft-Veltman style dimensional regularization along with the renormalization group (RG) to determine the general analytic structure of measurable quantitites of interest. Our formalism is compared in detail with that employed in field theory to describe tricritical behavior. Although many results are in qualitative agreement between the two approaches, there are some numerical differences. Our method considers renormalization for chains with fixed length, and this introduces differences into the renormalization scheme from that used in field theory, differences dictated by the physical differences in the types of systems considered. Our treatment of finite length chains contrasts with the field theoretical expansions about the unphysical limit of infinitely long polymers; thus it entirely avoids the use of the method of insertions. The RG theory is used to calculate the mean square end-to-end distance 〈R2〉 and the second and third virial coefficients A2 and A3 in the theta region as a function of both the two- and three-body interactions and of the chain length. We compute the temperature difference between the point at which A2 vanishes and at which 〈R2〉 is the pure Gaussian limiting value. The virial coefficients are used to evaluate the dilute solution portion of the coexistence curve, providing an estimate of the collapse transition temperature. The presence of essential logarithmic dependences of the coexistence curve on chain length implies that mean field theory is not valid for describing measurable quantities in this region.
NiNO. A model for NO on a metal surface
Authors: Bauschlicher Charles W. , Bagus Paul S.
Published: February 2003

Two different mechanisms for the bonding of NO to Ni have been found; the first is for a linear geometry and involves a 3d-2π* bond and has a short Ni–N bond length. The second mechanism, the more weakly bound, involves a Ni4s–N2p bond in a bent structure. The relationship of these two states to NO chemisorbed on metals is discussed. For both mechanisms, there are no open shell electrons on NO, consistent with the fact that multiplet splitting is not definitely observed in the photoemission spectra of adsorbed NO.
1
3C NMR spectrum analysis of electrochemically prepared polythienylene films
Authors: Hotta Shu , Hosaka Tomiharu , Shimotsuma Wataru
Published: February 2003

The 13C NMR spectrum analysis of electrochemically prepared polythienylene films has been investigated. Both a film doped with ClO−4 ions (PT–ClO4) and an undoped film (PT0) through the electrochemical reduction of PT–ClO4 give only two sharp absorption bands. The spectra of PT–ClO4 and PT0 are remarkably similar to each other in shape. These results demonstrate that both polythienylene are well-defined polymers with only two kinds of carbon atoms which are compatible with dominance of the α–α′ linkage. The upfield shift of the absorption band for PT0 compared with PT–ClO4 is consistent with the increase in electron density through the electrochemical reduction.
Lattice theory of reaction efficiency in compartmentalized systems. II. Reduction of dimensionality
Authors: Lee Pil H. , Kozak John J.
Published: February 2003

The timing and efficiency of a diffusion-controlled kinetic process in a compartmentalized system can be enhanced by reducing the dimensionality of the reaction space of the system. This idea, introduced by Adam and Delbrück and referred to as ‘‘reduction of dimensionality,’’ is explored quantitatively in this paper using a lattice theory of reaction efficiency developed in our earlier work. In particular, we study the interplay between system geometry and reaction efficiency using an approach in which group theoretic arguments are used within the framework of the theory of finite Markov processes to determine the average number 〈n〉 of steps required for a diffusing coreactant A to undergo an irreversible reaction with a stationary target molecule B. We study in detail three classes of problems in this paper. First, we study as a function of the position of the reaction center how the efficiency of the underlying, irreversible, reaction-diffusion process A+B → C changes with increase in system size for symmetrical geometries. We show how reducing the dimensionality of the flow of the diffusing co-reactant leads to a crossover in reaction efficiency with increase in the size of the system, and document this effect as a function of N (the total number of sites characterizing the reaction space of the system), d (the dimensionality of the system), and ν (the valency or connectivity between adjacent sites in the reaction space). Secondly, we study how the calculated value of 〈n〉, and hence the efficiency of the process, changes when the compartmentalized system is characterized by tubular or platelet geometries, and show how the process of reduction of dimensionality is dependent on the further geometrical characteristics of eccentricity ε and the surface-to-volume ratio S/V. Finally, we study the consequences of reduction of dimensionality for (two) consecutive (say, enzymatic) reactions taking place in a compartmentalized system and demonstrate the advantages of a further collapse in the dimensionality of the flow from d=3 → 2 to d=2 →1 for tubular geometries. The (exact) results presented in these studies provide a detailed and comprehensive picture of the role of system morphology in influencing the efficiency of diffusion-controlled irreversible processes involving a single reaction center in organized molecular assemblies (micelles, vesicles, microemulsions). Our results also cast light on the geometrical factors which may govern the optimal configuration of (two) reaction centers when consecutive enzymatic reactions take place in evolving cellular systems.
Extended analysis of the 5g→4f emissions in H2
Authors: Chang Edward S. , Pulchtopek Stanley , Eyler E. E.
Published: February 2003

An analysis starting from Hund’s case d has been used to extend the work of Herzberg and Jungen on the 5g→4f emissions in H2. A simple analytical expression for the line intensities is presented that agrees with their calculations is about 1%. All of the experimentally observed lines have been accounted for by including higher vibrational levels in our calculations.
Depolarized light scattering from shear wave in a viscoelastic liquid: α-phenyl o-cresol
Authors: Wang C. H. , Ma R.-J. , Liu Q.-L.
Published: February 2003

Polarized and depolarized Rayleigh–Brillouin spectra of α-phenyl o-cresol are studied as a function of temperature and scattering angle. The frequency of the longitudinal wave as measured in the polarized spectra displays kinks at the glass transition temperature and at 325 K (TK). TK is above the melting temperature. The shear wave frequency increases linearly with decreasing temperature below TK and is vanishingly small above TK. Over the temperature region that the shear wave can be resolved, the shear wave frequency is proportional to q and the linewidth is proportional to q2. Comparison of the experimental results with the available theory is provided.
The Raman study on the rotation of the C≡N− ion in the triethylamine–hydrogen cyanide system at 77 K
Authors: Kanesaka Isao , Kiyokawa Yoshinobu , Kawai Kiyoyasu
Published: February 2003

The Raman spectrum of the C≡N stretching region in the triethylamine–hydrogen cyanide-d1 system is reported, where there are some structures. They are analyzed on the basis of a rotation-vibration coupling model and it is confirmed that the C≡N− ion with the band center at 2068 cm−1 rotates, interacting with the translational mode. The values of parameters obtained are: ν=70 cm−1 and b=1.1. The Raman study on CO in the Ar matrix is discussed with the present calculation.
Trajectory studies of model H–C–C → H+C=C dissociation. III. Details of the lifetime distribution following chemical activation
Authors: Hase William L. , Duchovic Ronald J. , Swamy Kandadai N. , Wolf Ralph J.
Published: February 2003

Classical trajectories are used to study the unimolecular decomposition of H–C–C* radicals formed by the H+C=C chemical activation step. The lifetime distribution of the H–C–C* radicals is strongly nonexponential. A long time exponential tail to the lifetime distribution has a unimolecular rate constant ten times smaller than that for a microcanonical ensemble. The relationship between the lifetime distribution and the collision averaged unimolecular rate constant is considered. A discussion is presented on the effect of quasiperiodic trajectories in the molecular phase space on the quantum mechanical unimolecular rate constant.
On the photofragmentation of Fe(CO)5. II. Molecular orbital studies of Fe(CO)n, 1≥n≥5
Authors: Guenzburger Diana , Baggio-Saitovitch Elisa , De Paoli Marco A. , Manela Henrique
Published: February 2003

Self-consistent molecular orbital calculations were performed for Fe(CO)5 and its photofragments Fe(CO)n, 1≤n<5. The discrete variational method was employed, with the Xα local approximation for the exchange interaction. In the case of Fe(CO)5, photoelectron and optical spectra are analyzed, and photochemical behavior is discussed. The Mössbauer isomer shifts and quadrupole splittings are investigated. In the case of Fe(CO)5 and Fe(CO)4, the values derived for these hyperfine interactions are compared to experimental measurements reported in a polyethylene matrix.
The competition of Penning ionization and ion pair formation in fast collisions of metastable rare gas atoms with O2 and Cl2 molecules
Authors: Alvariño J. M. , Hepp C. , Kreiensen M. , Staudenmayer B. , Vecchiocattivi F. , Kempter V.
Published: February 2003

Integral ionization cross sections have been measured for collisions of the metastable rate gas atoms He(2 3S), Ne(2p53s), and Ar(3p54s) with the molecular targets O2 and Cl2 in the energy range 30 to 1000 eV by collecting the slow mass-analyzed target ions X+,X+2 and X−,X−2, where X stands for O and Cl. The cross sections for ion pair formation yielding X− and X−2 ions are found to be strongly influenced by the presence of continuum and energy transfer channels. The energy dependence of the cross sections for Penning ionization leading to the formation of X+ and X+2 ions is, on the other hand, strongly altered by the presence of low-lying ionic states of the type Rg+–X−2, where Rg stands for a rare gas atom. The energy dependence of the efficiency for secondary electron emission by the metastable rare gas atom He*(2 3S), Ne*(2p53s), Ar*(3p54s), and Kr*(4p55s) is presented for kinetic energies between 80 and 1000 eV.
Numerical inversion of symmetric well ring-puckering energy levels
Authors: Pajunen Petri
Published: February 2003

By applying higher-order RKR method, the experimental energy level pattern of symmetric well ring-puckering potentials of small ring molecules is inverted to yield very accurate, flexible, nonparametric (numerical) potential function. The method is tested with model potentials and applied to the ring-puckering spectra of oxetanone-3 and thietanone-3.
Integrated infrared intensities in cyanogen
Authors: Kim Kwan , King W. T.
Published: February 2003

The integrated intensities of the fundamental modes in cyanogen have been measured by the Wilson–Wells–Penner–Weber method. The results are 4.55±0.04 km mol−1 for the fundamental at 2149 cm−1 and 36.28±0.32 km mol−1 for the fundamental at 226 cm−1. The dipole moment derivative for the Πu mode obtained from these measurements and that obtained from ab initio calculations using a STO-NG basis set are found to be in essentially exact agreement with each other, although there is some disagreement in magnitude for the Σ−u mode.
Theoretical study of competing photoionization and photodissociation processes in the NO molecule
Authors: Giusti-Suzor A. , Jungen Ch.
Published: February 2003

The multichannel quantum defect theory of dissociative recombination is reviewed and adapted to treat simultaneous vibrational preionization and electronic predissociation in NO. The photoionization, photodissociation, and photoabsorption cross sections of NO corresponding to 2Π excited states are computed in the range from the N(2D)+O(3P) dissociation limit up beyond the second vibrational level of NO+(X 1Σ+). The calculations are based on the 2Π Rydberg and valence state potential curves and Rydberg-valence state interaction energies extracted by Gallusser and Dressler from the high-resolution spectroscopic data of Miescher and co-workers. These data pertain to the discrete range and furnish precise information on numerous spectral perturbations involving levels of the npπ Rydberg series and the B and L valence states. The calculated cross section profiles reproduce with reasonable accuracy the observed absorption and photoionization curves, and in particular the widths of the Rydberg resonances. The coexistence of Δv=1 and Δv≳1 preionization mechanisms is demonstrated. While the Δv=1 process is related to the R dependence of the quantum defect, the Δv≳1 preionization is shown to be induced by the strong electronic Rydberg-valence state coupling which primarily (and simultaneously) is responsible for predissociation. This result is generalized to the competition between any different decay mechanisms affecting a discrete excited level, and several limiting cases of competition are characterized. The relative contributions of different partial waves lλ to the photoionization spectrum of NO are estimated on the basis of the medium-resolution Rydberg absorption spectrum.
Temperature dependent libron relaxation in naphthalene
Authors: Schosser Claire L. , Dlott Dana D.
Published: February 2003

The Raman linewidths of librons in naphthalene and perdeuteronaphthalene measured over a wide temperature range are compared with the recent calculation of Della Valle et al. [Chem. Phys. 74, 179 (1983)]. Excellent agreement with the Della Valle calculation is observed up to ∼60 K. The inclusion of an additional up-conversion pathway, not considered by Della Valle, involving scattering to the ∼175 cm−1 ‘‘butterfly’’ vibration extends the range of agreement to ∼200 K. The temperature dependence over the range 1.5 to 200 K can be entirely explained by energy relaxation via cubic anharmonic coupling. Picosecond Raman results on several other materials with the naphthalene crystal structure are in good agreement with a simplified version of the Della Valle calculation which assumes the cubic anharmonic matrix elements are equal for each possible decay pathway.