bluuebunny/crossref_metadata_2025 huggingface dataset:
Saturation effects on the hole shapes produced by photochemical hole burning: Application to the anthracene–tetracene photoadduct
Authors: Iannone Mark A. , Scott Gary W.
Published: July 2002

The kinetics of photochemical spectral hole burning are modeled considering low temperature photochemical mechanisms requiring both one and two photons. The calculated results are compared with experimental results on photochemical hole burning in the anthracene–tetracene photoadduct (AT) using single color irradiation. Better agreement is obtained for the two photon mechanism while assuming the second photon is absorbed by the lowest triplet state of AT. The effects of irradiation source bandwidth and polarization are included in the analysis. Photochemical and transient saturation effects are evident in the calculated hole shapes.
Electronic structure and photoelectron spectra of substituted anilines
Authors: LaFemina John P. , Duke C. B. , Paton A.
Published: July 2002

The spectroscopically parametrized CNDO/S3 model is used to provide a quantitative description of the valence electron photoemission spectra of a series of substituted anilines. The CNDO/S3 density of valence states was used to determine the twist angles in these molecules via analysis of gas-phase photoemission spectra. These twist angles are compared with prior estimates. Finally, a discussion of the use of photoelectron spectroscopy in the determination of molecular geometries is presented.
A density of states transformation Monte Carlo method: Thermodynamics of the Lennard-Jones fluid
Authors: Shaw M. S.
Published: July 2002

The standard NVT ensemble Metropolis Monte Carlo method is modified to include uniformly weighted steps in ln β as well as weighted steps in U, the total potential energy. This simulation is used to sample a soft sphere (r−12 potential) fluid over a very wide range of energies. For each r−12 energy U12, the corresponding r−6 energy U6 is also recorded. Information from the simulation is used to determine relative values of the configurational density of states γ12(U12 ) (i.e., the number of configurations with total potential energy between U12 and U12+dU12) for the soft sphere fluid over a large range in energy. Then using the distribution of U6 at each U12, the configurational density of states for arbitrary linear combinations of U12 and U6 is determined and the equation of state for the Lennard-Jones fluid is evaluated for a wide range of densities and temperatures in a very efficient manner. The generalization to simulations of other linear combinations of potentials is discussed.
Model Hamiltonian approach to chemisorption: Treatment of diffuse virtual adorbitals
Authors: Drakova D. , Doyen G. , Hübner R.
Published: July 2002

A model Hamiltonian approach to chemisorption is described which is a development of the model described previously for the cases of larger overlaps SA between metal wave functions and adorbitals. Inconsistencies due to basis set overcompleteness are cured. Nonorthogonality between adsorbate projected metal wave functions on different adorbitals is accounted for by explicitly evaluating the overlap integrals between them as well as the hopping terms in the metal part of the Hamiltonian due to coupling of metal wave functions through the adorbitals. Physically adequate hopping between adatom and metal through the core potentials is introduced for high overlap situations. The core hopping terms merge smoothly into the Wolfsberg–Helmholz approximation to core hopping, established earlier to lead to a reasonable description of chemisorption interactions at small overlaps. For the limiting case SA =1, due to completeness of the metal basis set, the adorbitals will be represented by the metal wave functions. k–k state scattering between metal electrons in the overlap region is introduced explictly. Electron repulsions between metal electrons in the overlap region are estimated subject to conditions of hybridizational and rotational invariance and requirements imposed by overcompleteness. The model Hamiltonian is applied to Li adsorption on the (100) surface of copper. The numerical results obtained are discussed extensively and compared to other theoretical work and to experiment.
Short range order in AgI–AgPO3 glasses by x-ray diffraction
Authors: Musinu A. , Piccaluga G. , Pinna G.
Published: July 2002

A structural investigation by x-ray diffraction is presented on ionic conducting glasses of composition (AgI)x (AgPO3)1−x, with x=0.0, x=0.45, and x=0.55. The radial distribution functions of the AgI-doped glasses, calculated from the experimental diffracted intensities, are dominated by a peak centered at about 2.80–2.85 Å, which can be ascribed to Ag–I pairs. According to this, model interpretations showed that the diffraction effects are essentially due to the shortest and heaviest pair interactions (Ag–I and Ag–O), while there is no evidence of important structural details at medium range. The compatibility of the results obtained with current models of AgI–AgPO3 glasses is examined.
New method for numerical integration of the radial electronic Schrödinger equation
Authors: Koures Antonios G. , Harris Frank E.
Published: July 2002

We present a new method for numerical integration of the radial electronic Schrödinger equation with these characteristics: (i) it uses a quantity directly related to the logarithmic derivative of the wave function, thereby facilitating the matching of solutions obtained for different radial regions; (ii) it avoids difficulty from the singularity of the logarithmic derivative at the nodes of the wave function; and (iii) it takes appropriate cognizance of the asymptotic form of the wave function at infinite radius. Examples are presented showing that eigenvalues can be obtained by the new method by outward integration alone, but that a combination of inward and outward integration leads to efficiencies which compare favorably with those achievable by the most popular previously existent method, that of Numerov.
Quenched random strain fields and lattice mediated interactions in K(CN)x Br1−x and K(CN)xCl1−x
Authors: Fossum J. O. , Garland C. W.
Published: July 2002

Static c44 elastic constant data for K(CN)x Br1−x and K(CN)x Cl1−x single crystals are analyzed using an extended mean-field model. This model includes quenched random strain fields in terms of an Edwards–Anderson order parameter as an additional fitting variable. Good fits are obtained with no significant systematic deviations between the data and the theoretically predicted temperature behavior. The composition dependences of the resulting fitting parameters are also in good agreement with the predictions of the model. As expected from ionic radii arguments, the width of the distribution of the random strain field is considerably larger in K(CN)x Cl1−x than in K(CN)x Br1−x .
Two-photon excitation of dense sodium vapor near the n
d 2D5/2, 3/2 (n=3, 4, 5) levels: Na2 1 3Σ+g→1 3Σ+u excimer emission
Authors: Bajic S. J. , Compton R. N. , Stockdale J. A. D. , Konowalow Daniel D.
Published: July 2002

Laser excitation and ionization processes in dense (1–10 Torr) sodium vapor have been studied for laser wavelengths near the two-photon allowed nd 2D(n=3, 4, 5) and ns 2S(n=4, 5, 6) states. In particular, the 1 3Σ+g→1 3Σ+u excimer emission in Na2, predicted in 1980 by Konowalow and Julienne and observed recently by Dinev et al, was studied here in greater detail. Strong excimer emission (∼830 nm) was observed for two-photon pumping to both sides of the unresolved 4D states, and weak excimer emission was seen when pumping near the 5D levels. The excimer emission exhibits a complicated pump laser profile with a pronounced ‘‘dip’’ at the 4d 2D two-photon resonance. Similarly, [2+1] photon ionization via the 3d 2D and 4d 2D states shows a dramatic decrease as the sodium density increases. These results can be attributed either to depleted 3d 2D or 4d 2D population due to stimulated electronic Raman scattering (SERS) or to the interference effects recently reported by Malcuit et al. and Krasnikov et al. and treated theoretically by Manykin and Afanas’ev and by Agarwal. It is argued that both mechanisms are operative. Strong ionization and SERS signals were observed at the hybrid resonances corresponding to 3p 2P3/2, 1/2 →4d 2D transitions; however, no excimer lasing at 830 nm was detected. No excimer emission was detected upon two-photon pumping near or at the 3d 2D or ns 2S(n=4, 5, 6) states. Based on these and other observations, the 1 3Σ+g→1 3Σ+u excimer emission is attributed to a molecular Raman process involving stimulated emission or six-wave mixing via a pathway of the type 1 3Σ+u→2hν 3Δu→

j 3Πg→(k 3Πu, l 3Σ +u)→1 3Σ+g→1 3Σ +u .
Theoretical calculations of XeF ground state kinetics
Authors: Wilkins Roger L.
Published: July 2002

Rate coefficients were calculated for collision-induced vibrational and rotational relaxation and for dissociation processes that occur when He atoms collide with XeF(v, J) ground state molecules. These coefficients were calculated using a pairwise additive potential energy surface, which consists of a Morse function for the XeF interaction and Lennard-Jones functions for the HeXe and HeF interactions. It is found that the relaxation and dissociation processes occur by multiquanta (v,J) transitions and that dissociation is greatly enhanced if the total internal energy of the XeF molecule is near the rotationless dissociation limit of XeF. Dissociation can be achieved with either an initial high rotational quantum number and an initial low vibrational quantum number or vice versa. The effectiveness of initial energy in promoting dissociation increases in the order translation–rotation–vibration. Both the temperature and v dependences of the rate coefficients were calculated for collision-induced vibrational and rotational relaxation and dissociation. Strong vibration–rotation coupling in both vibrational relaxation and in the dissociation processes is demonstrated.
Comment on: The instabilities of mixed stack organic charge transfer crystals
Authors: Girlando Alberto , Painelli Anna
Published: July 2002

The dimeric model proposed by Luty to investigate the phase transitions in mixed regular stack charge transfer crystals is shown to be not correct due to some formal inconsistencies. Moreover, it is shown that the model cannot account, at least without further extension, for a collective phenomenon like a phase transition.
Electron correlation described by extended geminal models
Authors: Ro/eggen I.
Published: July 2002

Within the framework of the general extended geminal models, two new approximate models are introduced. Compared with previous models, the double pair correction terms {εKL} are given a more accurate representation. The models are tested against full CI calculations on the beryllium atom, the neon atom, and the beryllium dimer.
Comment on ‘‘Analytic solution of relaxation in a system with exponential transition probabilities’’
Authors: Lim Kieran F.
Published: July 2002

The relaxation of a system of highly excited molecules can be described by a reaction/(de)activation master equation. Much work has been concentrated on the functional form of q(x,y), the probability of a reactant molecule starting with energy y and having final energy x after collision with a bathgas molecule. A recent study [J. Chem. Phys. 86, 1269 (1987)] suggests that an exponential q(x,y) is neccessary for linear decay. This Comment shows that such an exponential transition probability is merely sufficient. The linear decay is also predicted by a step-ladder model for q(x,y).
Optical spectra of Yb atoms and dimers in rare gas matrices
Authors: Suzer Sefik , Andrews Lester
Published: July 2002

Matrix isolated Yb vapor spectra show absorptions due to atoms, dimers, and higher aggregates. The atomic spectrum reveals strong 395 and 344 nm bands and very sharp weaker 267 and 255 nm absorptions in solid argon. The spectrum of Yb2 shows extensive vibrational stucture around 550 nm both in Ar and Kr matrices with a spacing of 48 cm−1. This absorption is assigned to a 6s2(1S0)6s2(1S0)(1Σ+g) →6s2(1S0)6s6p(1P1)(1Σ+u) transition similar to the one observed for group IIA metal dimers. Higher aggregate spectra overlap with the 550 nm dimer and weak atomic band.
Study on YAG:Nd3+ spectra. I. Absorption spectra
Authors: Hua Dao-hong , Song Zeng-fu , Wang Shu-kun , Rong Zu-xiu
Published: July 2002

Absorption spectra of YAG:Nd3+ in the region 28 000–39 500 cm−1 at liquid helium temperature (LHeT) and liquid nitrogen temperature (LNT) have been studied. The whole absorption spectra of YAG:Nd3+ at room temperature (RT) has been measured. Based upon the present and earlier measurements the data at three temperatures are listed. By using the irreducible tensor method, we diagonalized the parametrized D2 Hamiltonian in a free-ion wave function space involving the whole J multiplets, fitting the eigenvalues to the experiment data at LNT, we assigned the whole Stark levels by using the eigenvectors obtained.
Discretization of a continuum coupled to a discrete state by tridiagonalizing the Schrödinger equation
Authors: Schek Israel , Wyatt Robert E.
Published: July 2002

A new approach to discretization of a continuous band coupled to a discrete state is provided by the Lanczos tridiagonalization procedure, which uses linked moments of the continuum with respect to the discrete state. Numerical convergence of this scheme is shown for two models of the line-shape function.
Electromotive force measurements in liquid K–Te solutions with a potassium β alumina electrolyte
Authors: Petric Anthony , Pelton Arthur D. , Saboungi Marie-Louise
Published: July 2002

Thermodynamic properties and phase relations of K–Te alloys were measured over a temperature range of 573–873 K and over the composition range 0–55 at. % K. An electromotive force (emf) technique was used in which potassium-substituted beta alumina served as the solid electrolyte. Partial and integral values of Gibbs energy, entropy, enthalpy, excess stability, and excess heat capacity are reported. The excess stability function exhibits maxima near 12 and 50 at. % K which can be interpreted as an indication of maximum short-range ordering near these compositions. Liquidus points on the phase diagram are also reported as are the Gibbs energies of formation of the compounds K2Te3 and KTe.
Perturbation treatment of electronically nonadiabatic collisions
Authors: Cross R. J.
Published: July 2002

The electronically inelastic two-state problem is solved by using a double perturbation theory. The wave function is expressed as a set of coupled differential equations in a diabatic representation, and the elastic wave functions are removed from the exact wave functions to give a set of coupled differential equations for the coefficients of the elastic functions. These are then linearized about the crossing point in the potential-energy curves and solved as in the Landau–Zener approximation. The approximate, Landau–Zener coefficients are then removed from the exact coefficients to give a set of differential equations for the resulting second-level coefficients. Having removed most of the problem in these two steps, the resulting second-level equations can usually be solved accurately by an exponential perturbation theory. The theory is designed as a prototype for more complicated inelastic and spectroscopic problems for which a computer solution of the Schrödinger equation is impractical.
Picosecond solvation dynamics of S1 t
r
a
n
s-stilbene by nanosecond transient Raman spectroscopy with ‘‘optical depletion timing’’
Authors: Hamaguchi Hiro-o
Published: July 2002

The laser-power dependent Raman spectral changes observed for S1 trans-stilbene in hexane are analyzed in terms of the competition between a picosecond solvation process occurring immediately after the S1←S0 photoexcitation (by the pump laser) and the optical depletion of the S1 state caused by the Sn←S1 photoexcitation (by the probe laser). Such spectral changes were not observed in acetonitrile, indicating that the solvation process is absent in a polar solvent. The scheme of ‘‘optical depletion timing’’ is demonstrated to be useful as an effective means to study picosecond phenomena by nanosecond spectroscopic measurements.
Conformational stability, barriers to internal rotation, vibrational assignment, and a
b i
n
i
t
i
o calculations of chloroacetyl fluoride
Authors: Durig J. R. , Zhao Wenyun , Lewis Durig , Little T. S.
Published: July 2002

The far infrared spectrum of gaseous chloroacetyl fluoride, CH2ClC(O)F, has been recorded at a resolution of 0.10 cm−1 in the 350 to 35 cm−1 region. The fundamental asymmetric torsional frequencies of the more stable trans (two halogen atoms oriented trans to one another) and high energy gauche (Cl–C–C=O torsional dihedral angle of 122°) have been observed at 86.5 and 48.8 cm−1, respectively, each with excited states falling to lower frequency. From these data the asymmetric torsional potential function governing internal rotation about the C–C bond has been determined. This potential function is consistent with torsional potential coefficients of: V1=350±12, V2=306±6, V3=420±1, V4=44±1, and V6=2±1 cm−1. The trans to gauche, gauche to gauche, and gauche to trans barriers have been determined to be 796, 245, and 271 cm−1, respectively, with an energy difference between the conformations of 525±24 cm−1 (1.50±0.07 kcal/mol). From studies of the Raman spectrum at variable temperatures the conformational energy difference has been determined to be 445±80 (1.27±0.2 kcal/mol) and 534±68 cm−1 (1.53±0.2 kcal/mol) for the gaseous and liquid phases, respectively. A complete assignment of the vibrational fundamentals observed from the infrared (3500 to 50 cm−1) spectra of the gaseous and solid states and Raman (3200 to 10 cm−1) spectra of the gaseous, liquid, and solid states is proposed. All of these data are compared to the corresponding quantities obtained from ab initio Hartree–Fock gradient calculations employing both the 3-21G* and 6-31G* basis sets. Additionally, complete equilibrium geometries have been determined for both rotamers. The results are discussed and compared with the corresponding quantities obtained for some similar molecules.
Stern–Gerlach deflection spectra of nitrogen oxide radicals
Authors: Gedanken A. , Kuebler N. A. , Robin M. B. , Herrick D. R.
Published: July 2002

Magnetic deflection spectra of beams of pure NO2 and NO2 seeded into rare gases have been determined using a Stern–Gerlach apparatus. Using He as carrier, a simple two-line deflection pattern is observed, indicating the breakdown of spin–rotation coupling in fields of 10 kG or more. Use of the other rare gases as carriers yields the two satellites at positions dictated by the beam velocities, and in addition, a more-or-less intense component at zero deflection which we hold to be due to diamagnetic or weakly paramagnetic (NO2)x clusters. The deflection amplitudes and line shapes are in good agreement with calculations. Additional weak bands observed in the spectra are likely due to van der Waals clusters such as NO2 ⋅ Ar and NO2 ⋅ Ne. 14N/15N isotope effects in NO2 were visible as changes of line shape. Zeeman level anticrossings are calculated quantum mechanically to occur for NO2 in the 20–30 kG regime, however their effects are small and were not observed. Deflection spectra of NO in its 2Π3/2 thermally excited state were obtained showing satellites at the positions predicted assuming pure Hund’s case-a coupling. Modeling of the observed spectra shows that both the electronic and rotational temperatures of the NO in the beam are rather high (20–125 K). The observed magnetic deflection spectra of the dialkyl nitroxide TEMPO when combined with line-profile calculations do not support the suggestion of Amirav and Navon [Chem. Phys. 82, 253 (1983)] that this molecule undergoes significant intramolecular spin relaxation while in the magnetic gap. In contrast, the SG spectra of the related radical di-t-butyl nitroxide shows no magnetic deflection, suggesting a spin lifetime of 0.5 μs or less.
Flow measurement by ‘‘Doppler shift’’ nuclear magnetic resonance
Authors: Wang Zhiyue , Leigh John S.
Published: July 2002

A nuclear magnetic resonance (NMR) 1D flow measurement technique is described and demonstrated experimentally. The technique uses a ‘‘meander coil’’ in the NMR probe for the radio frequency (rf) excitation and detection. The meander coil gives rise to highly inhomogeneous B1 field, whose direction varies linearly as a function of spatial coordinates. The detected NMR signal acquires a frequency shift which is proportional to the speed of the nuclear spin. In a sense, this frequency shift is similar to the Doppler shift. The flow speed can be measured by one free induction decay (FID) without applying B0 field gradient.
The Hubbard transition and unsaturated hydrocarbons
Authors: Lee Stephen
Published: July 2002

We contrast a simple molecular orbital theory (Hückel) with a simple valence bond theory (Heisenberg–Dirac). We find for alternant systems in which both models have nondegenerate ground states that both models have ground states belonging to the most symmetrical irreducible representation of the molecular point group. We also find there exist nonalternant systems which have ground states with different irreducible representations. In these latter systems neither the Hückel nor the Heisenberg–Dirac model is sufficient to give a qualitative picture of the molecule. Instead a combined Hückel–Heisenberg–Dirac model (the Hubbard model) must be used. Finally we list some organic unsaturated hydrocarbons, whose ground state changes from one irreducible representation to another as the Hubbard parameters vary.
A
b i
n
i
t
i
o molecular orbital and resonance Raman studies of the structure of the lowest triplet state of N,N,N′,N′-tetramethyl-p-phenylenediamine
Authors: Abe Jiro , Miyazaki Tomo-o , Takahashi Hiroaki
Published: July 2002

A b initio STO-3G and semiempirical modified neglect of diatomic overlap (MNDO) calculations have been performed for the ground state, the radical cation, and the lowest triplet state of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD). The geometry of each state optimized by the ab initio calculation is not much different from that optimized by the MNDO calculation. The optimized structures of the ground state and the radical cation are both in good agreement with the structures determined by x-ray diffraction. It is concluded based on the molecular-orbital calculations as well as on our previously reported time-resolved resonance Raman spectra that the lowest triplet state of TMPD takes a ‘‘softened’’ 1,4-quinoid-like structure in the planar configuration with the C=C bonds of the phenyl ring being lengthened while the N–Ph bonds shortened.
The comparative role of potential structure in classical, semiclassical, and quantum mechanics
Authors: Judson R. S. , Shi S. , Rabitz H.
Published: July 2002

The corresponding effects of features in the potential on classical, semiclassical, and quantum mechanics are probed using the technique of functional sensitivity analysis. It is shown that the classical and quantum functional sensitivities are equivalent in the classical (small ℏ) and harmonic limits. Classical and quantum mechanics are known to react in qualitatively similar ways provided that features on the potential are smooth on the length scale of oscillations in the quantum wave function. By using functional sensitivity analysis, we are able to show in detail how the classical and quantum dynamics differ in the way that they sense the potential. Two examples are given, the first of which is the harmonic oscillator. This problem is well understood by other means but is useful to examine because it illustrates the detailed information about the interaction of the potential and the dynamics which can be provided by functional sensitivity analysis, simplifying the analysis of more complex systems. The second example is the collinear H+H2 reaction. In that case there are a number of detailed and striking differences between the ways that classical and quantum mechanics react to features on the potential. For features which are broad compared to oscillations in the wave function, the two react in qualitatively the same way. The sensitivities are oscillatory, however, and there are phasing differences between the classical and quantum sensitivity functions. This means that using classical mechanics plus experimental data in an inversion scheme intended to find the ‘‘true’’ potential will necessarily introduce sizeable errors.
A comparison between the sensitivity behavior of direct and long-lived classical trajectories and quantum wave packets
Authors: Judson R. S. , Shi S. , Rabitz H.
Published: July 2002

We compare the sensitivities to initial conditions for both direct (regular) and long-lived (chaotic) trajectories in classical scattering calculations with the corresponding properties of trajectories of position and momentum expectation values for quantum wave packets. The collinear H+H2 reaction is used as an example. The results show that the high sensitivity seen in chaotic trajectories is not reflected in the quantum dynamics. We conclude that it is possible for a classical ensemble consisting of only regular trajectories to respond trajectory by trajectory to perturbations in much the same way as a quantum wave packet. (There will of course be cases that are exceptions to this rule.) The response of an ensemble consisting of chaotic trajectories may on the average be similar to that of a wave packet, but not at the level of individual trajectories. In addition, the sensitivities of these trajectories to variations in the potential are analyzed. We conclude that the large contributions to the sensitivities from particular long-lived trajectories must approximately cancel when an exact ensemble average is taken. An algorithm is presented to smoothly account for the contributions to the sensitivities from these trajectories.
The effect of an external electric field on dynamic scattering from a polymer chain
Authors: Lipson J. E. G. , Stockmayer W. H.
Published: July 2002

We derive the quasielastic scattering function for a neutral Gaussian chain incorporating a charge distribution along its backbone and interacting with an externally applied electric field. Both free-draining and non-free-draining conditions are investigated. For the practically important case in which the distribution results in a series of dipoles oriented along the chain contour, we obtain expressions for the first cumulant Γ(q), and particle scattering factor P(q) and make use of these results to predict the effects of dipole-field interactions on quasielastic light scattering (QELS) under experimentally realizable conditions.
Extent of the correlation between the squared radius of gyration and squared end-to-end distance in random flight chains
Authors: Mattice Wayne L. , Sienicki Krzysztof
Published: July 2002

Manipulation of generator matrix equations permits the evaluation of exact closed-form analytical expressions for 〈r4〉, 〈s4〉, and 〈r2s2〉 for freely jointed chains comprised of n bonds of length l. The squared end-to-end distance and squared radius of gyration for a specified conformation are denoted by r2 and s2, respectively. The expression for 〈r4〉, and the limit for 〈s4〉, agree with results in the literature that were obtained by other methods. The results are used to formulate the three dimensionless ratios, 〈r4〉/〈r2〉2, 〈s4〉/〈s2〉2, and 〈r2s2〉/〈r2〉〈s2〉, that are necessary for evaluation of the correlation coefficient for s2 and r2 in a freely jointed chain. The three dimensionless ratios have asymptotic limits of 5/3, 19/15, and 4/3, respectively. The value of the correlation coefficient decreases from 1 to (5/8)1/2 as n increases from 2 to infinity. In the limit as n goes to infinity, the best linear relationship between s2 and r2 is s2=(〈r2〉+r2)/12. The nature of the deviation of s2 and r2 for specified conformations from the best straight line is documented by an illustrative numerical calculation.
Molecular dynamics of a liquid crystal in decalin glass at radio and far infrared frequencies
Authors: Murthy U. M. S. , Vij J. K.
Published: July 2002

Dielectric loss spectra of 4-cyano-4-n-heptyl biphenyl liquid crystal (7CB), in decalin glass and in the frequency range 100 Hz–10 MHz, have been measured. Two distinct loss processes, namely β1 and β2 have been observed below Tg. The β2 process is analyzed further in terms of a stretched exponential decay function and the β1 process is fitted to a single exponential decay function. A multioscillator model is used to fit the far infrared spectrum of 7CB in decalin glass.
The C–H infrared stretching bands of ordered and disordered phases of adamantane
Authors: Salmon David , Shannon Victoria L. , Strauss Herbert L.
Published: July 2002

The C–H stretching bands of perdeuteroadamantane molecules containing one hydrogen atom have been taken in a number of condensed phases. Calculation of the effects of intermolecular interactions are compared to the observations. The ordered phases are used to validate the calculations and the observed bands are assigned. Comparison of experiment and calculation shows that the wide bands seen in both the disordered crystal phase and in solution are due to inhomogeneous broadening. The broadening in the disordered crystal is calculated accurately. The methine C–H bonds sample a wider range of environments than do the methylene C–H bonds.
Contact theorems for models of the sticky electrode
Authors: Blum L. , Rosinberg M. L. , Badiali J. P.
Published: July 2002

A contact theorem for the interface between a hard, flat, smooth wall with an arbitrary distribution of sticky sites and a fluid containing charged hard spheres is derived.
Selective excitation of Ti2+Mn2+ and Mn2+Ti2+Mn2+ spin clusters in MgCl2
Authors: Herren Markus , Jacobsen Stuart M. , Güdel Hans U. , Briat Bernard
Published: July 2002

Ti2+Mn2+ dimers and three types of Mn2+Ti2+Mn2+ trimers obtained by codoping MgCl2 with Ti2+ and Mn2+ were studied by site-selective dye-laser spectroscopy. Very high selectivity was achieved by using the 6A1g→4A1g,4Eg excitation on Mn2+, which does not coincide with any Ti2+ single-ion excitation. Sharp-line 1Eg(T2g)→3Ta1g luminescence from Ti2+ was observed in the near infrared (NIR). Electronic ground-state splittings resulting from Ti2+–Mn2+ exchange interactions were observed for the various spin clusters and, as a result, accurate exchange parameters could be obtained. The luminescence behavior of Ti2+Mn2+ pairs was investigated as a function of temperature and compared with the behavior of Ti2+ single ions in MgCl2. As in Ti2+:MgCl2 luminescence from Ti2+Mn2+ clusters was not only observed in the NIR but also in the visible, it corresponds to 3Tb1g→3Ta1g transitions.
Vibrational relaxation of HCl(v=1) in hydrogen gaseous mixtures at low temperatures
Authors: Papadimitriou D. , Schramm B.
Published: July 2002

Vibrational relaxation of HCl(v=1) has been measured in mixtures with H2, HD, and D2 in the temperature range between 300 and 140 K using laser-induced fluorescence. Relaxation in mixtures with n-H2 and with hydrogen enriched with its para modification is a pure vibration–translation, rotation (V–T,R) process. In mixtures with HD and D2 both vibration–vibration (V–V) and V–T,R relaxation rates could be determined separately.
On the effects of an isomerization chemical reaction upon the sound velocity
Authors: Palomares F. , Veguillas J. , Diaz M. A.
Published: July 2002

The more general hydrodynamic equations (including viscosity, heat conduction and diffusion effects) for a reactive system, in which the isomerization reaction A+A⇄B+B occurs, are used to find the influence of the reaction upon the sound velocity in the extreme cases of fast and slow reactions. A Monte Carlo simulation, based on the Boltzmann equation, has been carried out in order to verify the theoretical expressions of the sound velocity.
Deconvolution of the luminescence and magnetic circularly polarized luminescence spectra of the lowest excited states of Ru(bpy)2+3
Authors: Krausz Elmars , Moran Grainne
Published: July 2002

The luminescence and magnetic circular polarized luminescence (MCPL) spectra of Ru(bpy)2+3 in poly-(vinyl-alcohol) solid solutions are analyzed in terms of a three level model of the lowest excited states. The individual luminescence and MCPL profiles of the three states are obtained, for the first time, by careful deconvolution of the temperature dependent spectra. The temperature dependence of the MCPL spectra in the 1.5–60 K range can be quite accurately accounted for by the superposition of strong (temperature independent) B terms from each of the states of relative magnitudes ≈4:1:−0.1. A comparison of the very different luminescence and MCPL spectral profiles of the transitions arising from the three individual states provides insights into the unusual and apparently vibronically induced processes dominant in Ru(bpy)2+3 luminescence for all three electronic states.
Variational principles for a nonreacting, nonviscous mixture
Authors: Greco F.
Published: July 2002

Integral variational principles for the statics of a nonreacting, nonviscous fluid mixture are presented, both for open and closed systems. It is demonstrated that the use of Gibbs’ free energy as ‘‘density function’’ gives the appropriate field equations only if a peculiar choice for constitutive equations is made: mass and heat fluxes must be linear in gradients of chemical potential and temperature.
Phase equilibrium in a special class of polydisperse fluid models
Authors: Kincaid J. M. , Azadi M. , Fescos G. , Pellizzi L. , Shon K. B.
Published: July 2002

For a special class of polydisperse fluid models we have developed methods for obtaining (numerically) exact solutions to the equilibrium conditions. The models considered are special in the sense that the functional dependence of thermodynamic properties on the mole–fraction distribution density F(I) and microscopic parameter functions is restricted. For example, the pressure may depend only on a single moment of F(I). For our special class of models, we show how the dew/bubble conditions can be given a simple two-dimensional geometric representation, and the dew/bubble conditions are reduced to solving two equations in two unknowns. The solution of the full equilibrium conditions can be obtained by an iterative procedure given the solutions of the dew/bubble equations. Three specific models, based on the van der Waals and Soave–Redlich–Kwong equations of state, are examined in detail. We also show how to implement these new solution techniques when the mixture contains a finite number of chemical species.
Nematic behavior of reversibly polymerizing proteins
Authors: Hentschke R. , Herzfeld J.
Published: July 2002

The nematic behavior exhibited by a variety of amphiphiles is driven by the coupling between the growth and alignment of elongated aggregates. We have previously studied these systems using a model derived from lattice combinatorics, with attendant restriction of particle orientations to the three mutually orthogonal lattice axes. In this work we present a generalization of the above model for rod-like aggregates with a continuum of orientations. Overall, the calculated phase diagrams are similar to those obtained earlier for discrete orientations. This includes the second order isotropic-to-nematic transition in the weak aggregation regime. However, the nematic-to-nematic transition, obtained previously for intermediate aggregation strength, is not reproduced. We also consider the consequences of solvent filled spaces in the aggregates. Increasing the effective excluded volume of the solute by this mechanism causes the isotropic-to-nematic transition to shift to lower concentrations. This response of the phase behavior to the incorporation of solvent in the aggregate is important for the interpretation of experimental data.
Semiempirical determination of intermolecular anharmonicity in molecular crystals: The case of 1,2,4,5-tetrabromobenzene
Authors: Dye R. C. , Eckhardt C. J.
Published: July 2002

The molecular crystal 1,2,4,5-tetrabromobenzene (TBB) has been studied using Brillouin scattering and lattice dynamical calculations. A method for mapping acoustic mode anharmonicity is developed that exhibits substantial directional behavior and correlates well with the directions of the molecular movements associated with the phase transition. It is shown that by comparing the calculated sound velocities with the experimental values, insight can be gained into the displacive phase transition and the lattice dynamics of TBB. The sound velocities are plotted for three crystallographic planes containing the crystal axes. The relationships between sound velocities and lattice dynamics are discussed. The phonon dispersion curves for three directions are also presented.
Spectroscopic analysis of Nd3+ pairs in CsCdBr3
Authors: Barthem R. B. , Buisson R. , Cone R. L.
Published: July 2002

In Nd3+-doped CsCdBr3 crystals, most of the Nd3+ ions form pairs. A detailed analysis of the optical spectroscopy of these pairs has been carried out using both absorption and luminescence spectra. Due to the low value of the Debye cutoff frequency for the phonons, many excited levels are luminescent, thus giving a lot of spectroscopic information and allowing the assignment of 65 levels to their associated irreducible representations. These results have been used to deduce, through a fitting procedure, the free-ion and crystal-field parameters. The results are discussed and compared with those found in other compounds.
Electron-spin-resonance studies of 12CH3F+, 13CH3F+, and 12CH2DF+ in neon matrices at 4 K: Comparison with theoretical calculations
Authors: Knight Lon B. , Gregory Brian W. , Hill Devon W. , Arrington C. A. , Momose Takamasa , Shida Tadamasa
Published: July 2002

Various isotopic forms of the methyl fluoride cation 12CH3F+, 13CH3F+, and 12CH2DF+ have been generated by photoionization at 16.8 eV and separately by electron bombardment at 50 eV. The first electron-spin-resonance (ESR) results are reported for this radical cation which was isolated in neon matrices at 4 K. The measured A tensors or nuclear hyperfine parameters were compared with the results obtained from various computational approaches. Surprising observations were the large amounts of spin density on the methyl group, especially the hydrogen atoms, and the extreme differences in the deuterated spectra compared to the nondeuterated case. The presence of a single D atom apparently acts to prevent dynamic Jahn–Teller averaging which makes the methyl hydrogens equivalent on the ESR time scale. Such a dramatic Jahn–Teller effect has been previously observed for the similar methane cations CH+4 and CH2D+2. The magnetic parameters for CH2DF+ in neon at 4 K are gX=2.0032(5), gY=2.0106(8), and gZ=2.0120(5); for H: AX = 483(1), AY=476(1), and AZ=483(1) MHz; for D: ‖AX‖=5.0(3), ‖AY‖<3, and ‖AZ‖=7.1(3) MHz; for 19F : AX=965(1), AY=−130(2), and AZ=−166(1) MHz. For CH3F+, the g tensor and 19F A tensor were similar to those above but the H atoms were equivalent with values of AX=317(1), AY=323(2), and AZ=312 MHz.
Monte Carlo investigations of Coulombic correlations in lattice gas models
Authors: Lonergan Mark C. , Perram John W. , Ratner Mark A. , Shriver Duward F.
Published: July 2002

Monte Carlo simulations were performed on lattice gas systems with Coulombic interactions. Emphasis was placed on two lattice gases. The first consists of both mobile anions and cations while the second is composed of mobile anions and a random distribution of fixed cations. Comparisons are made to a strictly repulsive lattice gas. The addition of attractive forces is shown to significantly retard particle motion relative to the repulsive system. In the mobile-anion, mobile-cation system, at temperatures high enough to suppress ion clustering, the effect of backward correlations on the particle diffusivity is found to be similar to that for the strictly repulsive system. In the mobile-anion, fixed-cation system, however, backward correlations are much stronger due to the presence of immobile Coulomb traps. Both systems deviate from Nernst–Einstein behavior. The mobile-anion, mobile-cation system exhibits diminished conductivity (Haven ratio ≳1) due to the migration of neutral ion pairs, whereas the mobile-anion, fixed-cation system exhibits slightly enhanced conductivity (Haven ratio <1) due to the mutual repulsions between mobile charge carriers. The results of these simulations are discussed in terms of multiple timescale behavior, specifically including Funke’s jump relaxation model, and observations on relaxation times are reported.
A statistical model for activated dissociative adsorption: Application to methane dissociation on Pt(111)
Authors: Ukraintsev V. A. , Harrison I.
Published: July 2002

A statistical model of activated dissociative adsorption is developed using microcanonical, unimolecular rate theory. Dissociation is treated as occurring through energy randomizing collisions between incident molecules and local clusters of surface atoms. The predictions of the statistical model are found to be in remarkable accord with existent experimental data for methane dissociative adsorption and the thermal hydrogenation of methyl radicals on Pt(111). Perhaps surprisingly, the ‘‘over the barrer’’ statistical model adequately describes the known kinetics of these reactions without any explicit provision for quantum tunneling.
The shape of the nonlocal dielectric function of polar liquids and the implications for thermodynamic properties of electrolytes: A comparative study
Authors: Kornyshev Alexei A. , Sutmann Godehard
Published: July 2002

Consequences of different forms of the nonlocal dielectric function ε(k) of a polar solvent in thermodynamics of electrolytes are studied. This is done with the help of an analytical approximation which covers, as particular cases, different types of results obtained by several groups on the basis of molecular theories or computer simulations. It is shown that the forms of ε(k) which include a range of negative values may not contradict experimental data for hydration energies (in contrast to which was argued before) when one goes beyond the simple Born model of an ion and accounts for higher frequency mode contributions. A study of the implications for the activity coefficents shows that oscillations of the interaction energy between ions, following from such forms of ε(k), lead to a compensation effect which brings the results closer to the prediction of classical electrostatics and to experimental data.
Determination of the molecular constants of interacting bright and dark states: Analysis of the high-resolution infrared spectrum of the S–O stretching fundamental of thionylimide, HNSO
Authors: Joo Duck-Lae , Clouthier Dennis J.
Published: July 2002

The S–O stretching fundamental, ν2, of thionylimide has been recorded at high resolution and rotationally analyzed for the first time. This strong A-type band with origin at 1257.5808 cm−1 is extensively perturbed by the 5161 state at 1206.58 cm−1 through a- and b-axis Coriolis interactions. Even though no ν5+ν6 band transitions could be found, a complete analysis of the perturbed rotational structure has been achieved. Accurate molecular constants for the ‘‘bright’’ 21 state and the ‘‘dark’’ 5161 state have been obtained, using a Hamiltonian that includes both types of Coriolis interactions. Further small perturbations at high Ka and J have been identified as higher-order interactions with the ν3 band at much lower energy.
Ionization energy and electron affinity of a metal cluster in the stabilized jellium model: Size effect and charging limit
Authors: Seidl Michael , Perdew John P. , Brajczewska Marta , Fiolhais Carlos
Published: July 2002

We report the first reliable theoretical calculation of the quantum size correction c which yields the asymptotic ionization energy I(R)=W+(12+c)/R+O(R−2) of a simple-metal cluster of radius R. Restricted-variational electronic density profiles are used to evaluate two sets of expressions for the bulk work function W and quantum size correction c: the Koopmans expressions, and the more accurate and profile-insensitive ΔSCF expressions. We find c≈−0.08 for stabilized (as for ordinary) jellium, and thus for real simple metals. We present parameters from which the density profiles may be reconstructed for a wide range of cluster sizes, including the planar surface. We also discuss how many excess electrons can be bound by a neutral cluster of given size. Within a continuum picture, the criterion for total-energy stability of a negatively charged cluster is less stringent than that for existence of a self-consistent solution.
Arrhenius and non-Arrhenius conductivities in intercalated polymer electrolytes
Authors: Jeevanandam P. , Vasudevan S.
Published: July 2002

Intercalated polymer electrolytes (IPEs), Cd0.75PS3A0.5(PEO) [A=Li, Na, K, Cs], formed by the insertion of alkali metal ions solvated by polyethylene oxide (PEO) into the interlamellar space of the layered insulating cadmium thio-phosphate form an interesting class of materials. Their ambient temperature dc conductivities are comparable to that of the corresponding solid polymer electrolytes (SPEs) formed by dissolving alkali-metal salts in PEO. The conductivity of the intercalated materials, irrespective of the cation, exhibits a change in conduction mechanism with temperature. At low temperatures (T<225 K) the dc conductivity values are small and exhibit an Arrhenius temperature dependence. Above 225 K the dc conductivity rises sharply and in this temperature regime its temperature variation depends on the alkali-cation. The dc conductivity of the Li and Na containing IPEs follow the non-Arrhenius Vogel–Tamann–Fulcher (VTF) relation, σdc=σ0T−0.5 exp(−B/(T−T0)), while the K and Cs IPEs follow an Arrhenius dependence. The origin of the Arrhenius and non-Arrhenius conductivity of the IPEs, Cd0.75PS3A0.5(PEO) [A=Li, Na, K, Cs], have been investigated by analyzing the frequency-dependent conductivity in the dielectric and electrical modulus representations. We show that the difference in behavior is related to differences in the coupling of ionic motion and polymer segmental modes. In the Li and Na containing IPEs the motions are coupled and the conductivity exhibits a VTF temperature dependence. In the K and Cs compounds these motions are decoupled, consequently, although the mean relaxation time associated with segmental motion of the intercalated PEO exhibits a VTF dependence, ionic conductivity has an Arrhenius temperature dependence.
Dissociation of water on the surface of galena (PbS): A comparison of periodic and cluster models
Authors: Wright Kate , Hillier Ian H. , Vincent Mark A. , Kresse G.
Published: July 2002

The adsorption and dissociation of molecular water on the defective (001) surface of galena (PbS) have been investigated using both periodic and embedded cluster electronic structure methods. The results show that in the periodic calculations, the energies are particularly sensitive to the thickness of the simulated slab. The predicted activation and reaction energies from the different approaches are in good agreement given the different levels of theory used, and show that water will easily dissociate at a surface step site, with the product structure being the more stable in such an environment.
Adiabatic connection from accurate wave-function calculations
Authors: Frydel Derek , Terilla William M. , Burke Kieron
Published: July 2002

An extremely easy method for accurately calculating the adiabatic connection of density functional theory is presented, and its accuracy tested on both Hooke’s atom and the He atom. The method is easy because calculations are needed only for different values of parameters in the external potential, which can be achieved with almost any electronic structure code. Application of the method to accurate calculations on small systems should lead to benchmark adiabatic connection curves.