bluuebunny/crossref_metadata_2025 huggingface dataset:
Inverse polarization of asymmetric hyper-Raman lines
Authors: Kozierowski M. , Ożgo Z. , Kielich S.
Published: July 2002

Index asymmetry in the scattering tensor bijk, related to permutation of i and whichever of the indices j or k, makes active vibrations inactive in the case of a completely symmetric tensor leading to new selection rules for hyper-Raman scattering and to the emergence of new vibrational lines in the scattered spectrum. These purely asymmetric lines correspond to the asymmetric irreducible part of weight 2 of the tensor bijk. This scattering, similarly to antisymmetric Raman, is shown to exhibit the phenomenon of inverse polarization. A detailed discussion of angular distribution and of various polarization parameters for all polarization states of the incident light is given in terms of Stokes parameters.
Effects of Coriolis interaction on the rotational line intensities of symmetry-forbidden electronic transitions
Authors: Nanes Roger , Lee Edward K. C.
Published: July 2002

The effect of Coriolis coupling on intensities in infrared rotation–vibration bands is here extended to vibronically allowed transitions between electronic states of a nearly symmetric top. Within the framework of the Herzberg–Teller treatment of vibronic interaction, equations are developed which describe the intensity distribution in the p- and r-form branches of a vibronic transition in the cases where Coriolis interaction perturbs one or both vibrational levels associated with the transition. The Ã 1A2–X̃ 1A1 transition in H2CO is used as an example to illustrate the theory.
Ionic force field of vibrational spectra of symmetrical hydrogen bonds
Authors: Matsui Yoshiki , Ezumi Kiyoshi , Iwatani Kouji
Published: July 2002

The ionic force field for analysis of the vibrational spectra of symmetrical hydrogen bonds, X–H–X, is described. The force field has a stretching force constant K and a force constant kc derived from the Coulombic force. One characteristic of this force field is that the frequency of the symmetric stretching vibration, νs, can be calculated from the values observed for out-of-plane bending and antisymmetric stretching bands of X–H–X. The agreement between the calculated and observed frequencies of the νs is excellent. The νs vibrations are treated as intermolecular vibrations such as those of carboxylic acid dimers.
Dynamics of unimolecular dissociation of silylene
Authors: NoorBatcha I. , Raff Lionel M. , Thompson Donald L. , Viswanathan R.
Published: July 2002

The semiempirical valence-bond surface formulated by Viswanathan et al. [J. Phys. Chem. 89, 1428 (1985)] for the unimolecular dissociation of SiH2 has been fitted to an analytical function of the type suggested by Murrell and co-workers [J. Phys. Chem. 88, 4887 (1984)]. The fitted surface accurately represents most of the experimental and CI results. The dynamics of the unimolecular dissociation of SiH2 to form Si and H2 have been investigated by classical trajectory methods on this fitted surface. The effect of describing the initial state of the molecule using normal and local mode approximations has been studied. In spite of the presence of the heavier atom, no bond or mode specificity is observed. The product energy distribution is found to be statistical. Using the RRK model, the high-pressure limiting rate coefficient is found to be k(T,∞)=3.38×1012 exp[−61.6 kcal mol−1/RT] s−1, which is less than the dissociation rate for SiH4. This has been attributed to the higher activation energy for SiH2 and to a statistical factor.
Emission of phosphorescence from biacetyl surface by collision of N2(A 3Σ+u)
Authors: Kume Hiroshi , Kondow Tamotsu , Kuchitsu Kozo
Published: July 2002

A supersonic beam of nitrogen molecules was excited to the A 3Σ+u state by electron impact and was allowed to collide with a biacetyl surface cooled at 77 K. The spectrum of the emission from the surface observed in the 500–580 nm region was assigned to the phosphorescence of biacetyl. Its lifetime, 1.0±0.1 ms, measured from the time dependence of the phosphorescence is found to be shorter than that measured by use of laser excitation (308 and 380 nm) from the same surface, 1.30±0.02 ms. These results are interpreted by a mechanism of triplet–triplet energy transfer from N2(A) (gas) to biacetyl (solid). The quantum yield of the phosphorescence is estimated to be about 1×10−3. The applicability of this method for detection of N2(A) or other low-lying metastable states is discussed.
A test of the intrinsic nature of the shallow proton traps in ice
Authors: Wooldridge Paul J. , Devlin J. Paul
Published: July 2002

Electron beam radiolysis of ice and the ion pair defects it generates in ice are discussed. The FI-IR spectra of thin films of ice are recorded both before and after irradiation. (AIP)
Temperature dependence of the zero-field splitting of Ni2+ in ZnSiF6 ⋅ 6H2O and ZnSiF6 ⋅ 6D2O at low temperatures
Authors: Rubins R. S. , Hutton Stuart L. , Drumheller John E.
Published: July 2002

EPR measurements at 9.25 GHz were made on single crystals of Ni2+ in ZnSiF6 ⋅ 6H2O and ZnSiF6 ⋅ 6D2O at small temperature intervals from 4 K to above 100 K. Least-squares fits of the zero-field splitting data below 70 K for the two crystals to a theoretical model of Shrivastava, based on the interaction in the long wavelength approximation, yielded values for the Debye temperature θD of 130 K for ZnSiF6 ⋅ 6H2O and 99 K for ZnSiF6 ⋅ 6D2O. The value of θD for the hydrated salt is roughly 30% larger than the more direct estimate of Vasyukov et al. from measurements of the stress coefficients. The deviations from the theoretical curves for both crystals are appreciable above 75 K.
Light induced and ‘‘dark’’ rotamerization of simple ethers and thioethers in solid neon
Authors: Rasanen M. , Schwartz G. P. , Bondybey V. E.
Published: July 2002

Several simple ethers and thioethers are examined in solid neon matrix by FTIR and Raman spectroscopy. In each compound several rotational isomers are observed and their infrared induced and ‘‘dark’’ interconversions occurring in the matrix investigated. New information is obtained about the spectra and torsional potentials of the compounds studied.
Deterministic modeling and computations for the states of two-electron systems with an explicit formula for the excited states of helium
Authors: Greenspan Donald
Published: July 2002

A new, semiclassical approach is developed for the states of two-electron systems. The theory incorporates a classical interpretation of electron pairing and requires simple computer methodology for its implementation. Computer results are described and discussed. Special emphasis is given to helium, for which an explicit formula for excited states is developed.
Spin-coupling in ferric metalloporphyrin radical cation complexes: Mössbauer and susceptibility studies
Authors: Lang George , Boso Brian , Erler Brian S. , Reed Christopher A.
Published: July 2002

The ferric metalloporphyrin π-radical cation complexes Fe(III) (OClO3)2 (TPP.) and [Fe(III) Cl (TPP.)] [SbCl6] were examined in microcrystalline form by Mössbauer spectroscopy and magnetic susceptometry over a range of temperatures and applied fields. All measurements on the six-coordinate Fe(OClO3)2 (TPP.) were consistent with isolated molecules having an S=5/2 iron site with zero field splitting (12 cm−1) S2z that is ferromagnetically coupled to the S=1/2 porphyrin radical by an energy term (−110 cm−1) S⋅s. Thus the ground state is overall spin-3. In the five-coordinate [FeCl (TPP.)] [SbCl6] the susceptibility is in reasonable agreement with the results of a calculation based on zero field splitting (12 cm−1) S2z for the S=5/2 iron and antiferromagnetic coupling (200 cm−1) S⋅s with the radical to give an overall spin-2 ground state. However, the Mössbauer measurements require a more complicated model having the same large intramolecular iron–radical coupling, a smaller zero field splitting (3 cm−1) S2z, and weak intermolecular antiferromagnetic coupling between heme pairs given by (32 cm−1) s1⋅s2 or, equivalently, (0.65 cm−1) S1⋅S2. A slightly improved correspondence with the measured susceptibility results. The intermolecular antiferromagnetic coupling probably results from crystallization of the [FeCl (TPP.)]+ cations in face-to-face dimers as observed in other closely related five-coordinate iron (III) porphyrins.
Direct correlation function in the 2D one-component plasma at Γ=2
Authors: Hernando J. A.
Published: July 2002

The two-body direct correlation function for the two-dimensional one-component plasma with coupling constant Γ=2 is evaluated. It is analytically shown that its long-range behavior is identical with that of the interaction potential and the remainder is explicitly evaluated in closed form. The dependence of the distribution functions and correlation functions with the size of the system is considered and it is concluded that they are size independent in the thermodynamic limit. The bridge function, which is of interest in the MHNC approximation, is evaluated and discussed in terms of a recent universality ansatz. The relevance of these results for the mean spherical approximation is also pointed out.
Base deuteration effects on HF complexes in solid argon
Authors: Patten Kenneth O. , Andrews Lester
Published: July 2002

FTIR matrix studies of ethylene–hydrogen fluoride complexes have shown that the base ν7 mode is perturbed slightly more by DF than by HF complexation, and that the νs (HF) mode is displaced more in C2D4--HF than in C2H4--HF. The νl (HF) mode perpendicular to the C=C bond increases while the νl (HF) mode parallel to the C=C bond decreases with deuteration of the ethylene base. These trends are explained by decreases in electrostatic repulsions in the deuterium species owing to reduced amplitudes of zero-point motion.
Electronic excitation energy transfer in organic liquid scintillators
Authors: Mathad R. D. , Chikkur G. C. , Umakantha N.
Published: July 2002

The rate constant for transfer of electronic excitation energy from the first excited singlet state of the solvent toluene to two indoles, 1-p-chlorophenyl-5-benzyloxy-2-phenylindole and 5-methyl-3-phenylindole-1-propionitrile, as solutes in three types of solvent media, pure toluene, 1:9 mixture of toluene and cyclohexane, and 1:9 mixture of toluene and liquid paraffin is determined as a function of temperature in the range 293–353 K under oxygen-free conditions. The diffusion coefficients of the interacting molecules are measured in situ at ambient temperature. The rate constant is found to vary, in the case of each of the six systems, linearly with the sum of the diffusion coefficients of the two interacting molecules; from this linear variation the contributions of molecular diffusion and excitation energy migration to the rate constant are quantitatively estimated. The results indicate that energy migration involves weak multipole–multipole interaction between an excited and an unexcited solvent molecule, and not successive excimer formation and dissociation. Unique values of the energy migration coefficient and the effective distance at which the solvent–solute energy transfer takes place in the final step, are evaluated in the case of all the six systems; these values are model independent. The final step in energy transfer essentially involves long-range interaction. Dependence of energy migration coefficient and the effective energy transfer distance on environment is discussed.
Self-consistent lattice dynamics investigation of small neon crystallites
Authors: Spornick L. B. , Danilowicz R. L. , Helmy A. A. , Etters R. D.
Published: July 2002

A self-consistent phonon (SCP) approximation is used to calculate the structural and dynamic properties of neon crystallites consisting of N=2–7, 13 atoms. It is shown that the large zero-point oscillations have a dramatic effect on the predicted properties which include the lattice parameters, thermal expansion, free energies, specific heats, entropy, excitation frequencies, and the rms fluctuations of the atoms about their equilibrium positions. These positions are determined by first performing Monte Carlo calculations and the resulting symmetry coordinates are then refined by relaxing them in the SCP calculation until the forces on each atom are zero and the free energy is minimized. The resulting structures are qualitatively identical to those predicted previously for classical rare gas clusters.
Fitting form for rotational transitions of large inelasticity
Authors: Brechignac Ph. , Whitaker B. J.
Published: July 2002

The A over N (AON) fitting form for rotational transfer in diatomic molecules relies on the energy sudden approximation. We show that by making the proper choice of the sudden kinetic energy (the lowest value of the entrance and exit channels), the energy dependent expression [AON(E)] of this model: σl→0(εl) =(αγ/n)[ln(α/n(εl)1/2) −1+n(εl)1/2/α] can be used to interpret experimental data involving transitions of large inelasticity. This is illustrated using the CsH–H2 system which Ferray et al. have experimentally investigated [M. Ferray, J. P. Visticot, and B. Sayer, J. Chem. Phys. 81, 3009 (1984)]. Very good agreement is found with the experiment both in the case of selecting the initial level J=0 and J=10.
Ionic pairing in binary liquids of charged hard spheres with nonadditive diameters
Authors: Pastore G. , Giaquinta P. V. , Thakur J. S. , Tosi M. P.
Published: July 2002

We examine types of short range order that arise in binary liquids from a combination of Coulombic interactions and nonadditivity of excluded volumes, the initial motivation being observations of complex formation by hydrated ions in concentrated aqueous solutions. The model is a fluid of charged hard spheres with contact distances σ+−≠ 1/2 (σ+++σ−−), its structural functions being evaluated in the mean spherical approximation and in the hypernetted chain approximation. Cation–anion pairing is clearly seen in the calculated structural functions for negative deviations from additivity (σ+−<σ++=σ−−), though the absence of true chemical bonding in the model does not allow long-lived complexes. Positive deviations from additivity (σ+−>σ++=σ−−) favor long-wavelength concentration fluctuations and demixing in a neutral mixture: these are suppressed by Coulombic interactions in favor of microscopic intermixing of the two species in the local liquid structure, up to like-ion pairing. Comparison is made with diffraction from concentrated aqueous solutions of cadmium sulphate and other instances of possible applicability of the model are pointed out.
Molecular overlap integrals with exponential-type orbitals
Authors: Bhattacharya A. K. , Dhabal S. C.
Published: July 2002

A fast and accurate method for the calculation of molecular overlap integrals involving exponential-type orbitals is discussed on the basis of the Fourier transform convolution theorem. The overlap integrals are related to a one-dimensional integral for which an exact analytical expression is given in a computationally convenient form. The numerical stability of the analytical expression is examined over a wide range of values of relevant parameters. Alternative procedures for evaluating the one-dimensional integral in regions of the parameter space where the analytical expression becomes unreliable are examined. The speed, accuracy, and the range of applicability of the method for the evaluation of overlap integrals are discussed in the light of recent work by other authors.
Energetic consideration of the vibrational potential function in the effective nuclear charge model. V
Authors: Ohwada Ken
Published: July 2002

Two homogeneity hypotheses of the total molecular and electronic energies proposed by Parr and Gadre are examined through derivation of the harmonic as well as anharmonic force constants for diatomic molecules by making use of the intramolecular potential function in the effective nuclear charge model. The results suggest that the homogeneity postulate of the total molecular energy may be compared favorably with that of the electronic energy. Inhomogeneous linear first-and second-order differential equations for diatomic molecules, which are derivable from the homogeneity assumption of the total molecular energy, are solved and their solutions are used for elucidating the correlation between two hypotheses as described above. Finally, an approximate Hartree–Fock method with a homogeneity constraint of the total molecular energy is developed and discussed in detail.
The applicability of a percolation model to photoconductivity in guest–host thermotropic nematic liquid crystal systems
Authors: Chapoy L. Lawrence
Published: July 2002

Photoconductivity is investigated for a thermotropic nematic low molar mass liquid crystal which has been doped with carbazole, a known photoconductor. The dopant is oriented by a guest–host mechanism and is studied as a function of concentration. Threshold levels of photoconductivity occur at levels three orders of magnitude below that predicted from simple percolation theory. Some possible explanations for this as well as its implications are proposed.
Extra resonances in four-wave mixing as a probe of exciton dynamics: The steady-state analog of the transient grating
Authors: Loring Roger F. , Mukamel Shaul
Published: July 2002

We present a microscopic theory of the nonlinear susceptibility χ(3) of a crystal composed of interacting two-level absorbers. The relationship between the signals in a steady-state four-wave mixing experiment and in a time-resolved transient grating experiment is established. In general, the steady-state signal is not simply the Fourier transform of the time-resolved signal, although such a relationship does hold under certain experimental conditions. We evaluate χ(3) for the Haken–Strobl model. χ(3) displays a dephasing-induced extra resonance, whose intensity and line shape are sensitive to the degree of exciton coherence. We also calculate χ(3) for a crystal of interacting three-level absorbers, under the assumption that population in the higher excited state relaxes rapidly to the lower excited state. We propose steady-state four-wave mixing as an alternative to the transient grating experiment in investigating the nature of exciton motion.
Picosecond laser study of the quasicontinuum of C2F5Cl
Authors: Mukherjee P. , Kwok H. S.
Published: July 2002

The quasicontinuum of the vibrationally hot (∼10 CO2 laser photons) C2F5Cl molecule was investigated using a two-laser pulse arrangement. The first laser pulse preheated the molecules into the QC (quasicontinuum) while the second picosecond CO2 laser was employed to probe the absorption characteristics of the excited molecules. The second laser could be tuned either in frequency or in pulse duration. Several experiments were performed. In the first experiment, the small signal absorption spectrum of C2F5Cl was measured and compared with the dissociation spectrum obtained by Borsella et al.1 The same ν6+ν10 hot band was observed with a considerably narrower linewidth. In the second experiment, the saturation properties of the hot band were investigated. It was found that the absorption line could be characterized as inhomogeneously broadened with no evidence for any broadening due to intramolecular damping. In a third series of experiments, the absorption of C2F5Cl at low as well as high laser energy fluences was measured as a function of the laser pulse duration between 22 and 120 ps. It was found that (i) the absorption can be characterized as predominantly intensity dependent and (ii) the small signal absorption cross section increased considerably as the pulse duration was decreased. These observations were discussed using the multitier energy level classification scheme in the QC. It was concluded that within the laser pulse duration, individual states within the first tier which interacted with the laser were not coupled to each other. The change in the absorption cross section as a function of the pulse duration is consistent with the picture that under laser irradiation, a rapid equilibrium was achieved with the final state populations remaining relatively constant in time. The final populations were dependent almost entirely on the laser intensity. Increasing the laser pulse duration had little effect on the final state distribution and the total energy absorbed by the molecule.
Branching ratios for quenching and reaction in the interaction of S(1D2) with various gases
Authors: Black Graham
Published: July 2002

Resonance-enhanced photoionization has been used to monitor the time evolution of S(3 3P2) produced by the interaction of S(3 1D2) with various gases. The S(3 3P2) signals have been used to calculate the branching ratios for quenching by these gases. The rate coefficients for reaction of S(3 3PJ) with O2, C2H4, and C3H6 were determined and used to correct the branching ratios for these gases.
Rayleigh linewidth and thermal conductivity of SF6 in the supercritical range
Authors: Letaief A. , Tufeu R. , Garrabos Y. , Le Neindre B.
Published: July 2002

The Rayleigh linewidth of SF6 along the critical isochore and its thermal conductivity coefficient as a function of temperature and pressure have been measured. The decay rate of the density fluctuations is asymptotically well described by the Kawasaki mode–mode coupling theory without any adjustable parameters, and a small systematic deviation between theory and experiment is observed away from the critical point.
Nonequilibrium electronic polarization of the solvent in photoionization
Authors: Delahay Paul , Dziedzic Andrew
Published: July 2002

The energetics of photoionization in condensed phases includes a significant contribution from nonequilibrium processes arising from dielectric dispersion of the solvent at the prevailing photon energy. The solvent is polarized by the varying electric field caused by the change of ionic valence as a result of photoionization. This ionic field varies in a time interval determined by the frequency of incident radiation. The following contributions from nonequilibrium processes to the energetics of photoionization are calculated for transparent and absorbing solvents: electronic polarization, London dispersion, and Born repulsion energies for a discrete model of coordinated solvent molecules in the inner-sphere solvation shell of anions and cations; electronic polarization of the outer-sphere region for a continuous medium model. The losses resulting from the rapid variation of the ionic field for an absorbing solvent are calculated for the inner- and outer-sphere regions, respectively, from a discrete model and a continuous medium. Damping of the ionic field resulting from solvent absorption is negligible. The theory is applied to aqueous solutions in the 7–10.4 eV range of photon energies by using dielectric data from reflectance spectroscopy of liquid water. Experimental dispersion spectra for photoelectron emission have the shape predicted by theory and display all the extrema at the photon energies of the calculated curves. The very pronounced effect of ionic strength on the balance between inner- and outer-sphere contributions predicted by theory (inner–outer sphere splitting) is fully confirmed by experiment. Dispersion spectra of inorganic ions in the range of each of the two absorption bands of liquid water (maxima at ∼8.2 and 10.0 eV) therefore exhibit a double maximum for normal dispersion and a double minimum for anomalous dispersion (12 extrema between 7.2 and 10.4 eV). Specific effect of the nature of anions is evident above 9.0 eV in inner–outer sphere

splitting. The present study provides a way of probing the response of liquids and solutions to the rapidly varying intense ionic field resulting from the process of photoionization.
Third-order nonlinear optical interaction and conformational transition in poly-4-BCMU polydiacetylene studied by picosecond and subpicosecond degenerate four wave mixing
Authors: Rao D. Narayana , Chopra Pratibha , Ghoshal Suniti K. , Swiatkiewicz Jacek , Prasad Paras N.
Published: July 2002

The electronic third-order nonlinear optical interaction in a solution cast film of a polydiacetylene has been studied by degenerate four wave mixing. The results demonstrate a subpicosecond response and a very high χ(3) value. The χ(3) value changes considerably during the thermally induced conformational transition in the film in which the effective π-electron conjugation is reduced.
About the overestimation of the basis set superposition error on interaction energy calculations for van der Waals systems
Authors: Olivares del Valle F. J. , Tolosa S. , Esperilla J. J. , Ojalvo E. A. , Requena A.
Published: July 2002

A procedure to estimate the basis set superposition error is proposed avoiding the overestimation of the counterpoise correction in the van der Waals interactions. Numerical calculations were carried out in the Ne ⋅⋅⋅ Ne complex at the SCF level.
Excited singlet state absorption spectra and relaxation kinetics of the azanaphthalenes
Authors: Boldridge David W. , Scott Gary W.
Published: July 2002

Picosecond excited-state singlet–singlet absorption spectra (Sn ← S1) and excited-state decay kinetics are reported for several diazanaphthalenes and a triazanaphthalene in room temperature solution. New Sn (1nπ*) state energies are obtained empirically from these spectra. INDO-PSDCI molecular orbital calculations are used to confirm the Sn ← S1 nature of the excited state transitions observed. Decay rates are calculated from models based on a semiempirical molecular orbital formalism, and these calculated rates are compared with the observed ones. Agreement of the calculated and observed rates are good except in cases of substantial nπ*–ππ* mixing of the actual excited states and in a particular case of high molecular symmetry (1,5-naphthyridine).
The time-dependent variational description of one-dimensional inelastic scattering
Authors: de Aguiar M. A. M. , Malta C. P.
Published: July 2002

The time-dependent variational principle is applied to generate semiclassical approximations in the description of inelastic collisions in one dimension. This is acheived by using appropriately parametrized trial wave functions. The method is applied to an exactly solvable model and the results are fairly good, in general much better than other approximate calculations.
Quenching of I*(5 2P1/2) by halogen fluorides
Authors: Chowdhury M. A. , Pritt A. T. , Patel D. , Benard D. J.
Published: July 2002

Absolute rate constants of the collisional decay of I(5 2P1/2) by the halogen fluorides F2, ClF, and IF have been determined using the technique of time-resolved, laser-initiated infrared fluorescence, as well as atomic absorption spectroscopy (in the case of IF only). The room temperature rate constants, kF2<8.7×10−14, kCIF=1.3±0.3×10−13, and kIF (∼400 K) =1.3±0.6×10−11 cm3 molecule−1 s−1, along with other reported quenching rate constants for the other halogen diatomics have been explained in terms of correlations based on the symmetry of the relevant potential energy surfaces.
Decoupling transformation approach to the lattice vibrations of molecular crystals: Hexamethylenetetramine
Authors: Yeung Y. Y.
Published: July 2002

The decoupling transformation method as applied to lattice vibrations is reformulated in terms of the concept of partitioning crystals into regions with periodic boundary conditions—cyclic regions. Values of force constants for the hexamethylenetetramine system are determined using the decoupling transformation scheme which are consistent with results in the literature. An interpolation formula and its modification are established for constructing the lattice dynamical maxtix of molecular crystals and applied successfully to the above physical system as well. More aspects of the decoupling transformation are pointed out in detail.
The limiting concentration dependence of the heat of transport in electrolyte solutions
Authors: Thacher Thomas S. , Mou C. Y. , Mohanty Udayan , Lin Jeong-long
Published: July 2002

The limiting concentration dependence of the heat of transport of electrolyte solutions has been investigated. The ionic contribution to the Onsager phenomenological coefficients for heat-matter coupling Lqi have been calculated by the time-correlation function method using the Fokker–Planck operator as the time-evolution operator. It is shown that the limiting slope due to the direct ion–ion electrostatic effect obtained in the present work agrees with the result in the literature. It is also shown that the contribution to the limiting slope due to ion–solvent interaction may be written in terms of the differences in the Stokes law radii of the ions as well as the reduced ionic heats of transport at infinite dilution. Although our result resembles Agar’s result based on a hydrodynamic theory, we point out that there exist substantial differences in the implications of the two results. Finally, an error in the theory of Kahana and Lin [J. Chem. Phys. 75, 5043 (1981)] has been uncovered and corrected.
Effects of bond bending on the electronic structure of silane
Authors: Wilner Martin , Adler David , Eberhart Mark E. , Johnson Keith H.
Published: July 2002

We have calculated the one-electron orbital energies and the total ground-state energy of a distorted silane molecule as a function of bond angle, using the SCF-Xα-SW technique. We find significant increases in the energy of the highest occupied molecular orbital as the bond angle deviates from its tetrahedral value in either direction. The total energy exhibits a shallow minimum for tetrahedral symmetry.
On the problem of assigning electronic transitions in diketonate complexes. Polarized crystal spectra of tin(IV) and antimony(V) mono(acetylacetonate) and -(tropolonate) complexes
Authors: Teutsch Ursula , Schmidtke Hans-Herbert
Published: July 2002

Polarized crystal spectra of some (mono acetylacetonate) and -(tropolonate) complexes were recorded in the visible and ultraviolet region. The intense internal ligand π–π* transitions of the diketonates were measured for the first time on extremely thin single crystals (0.1–1 μm). All crystal spectra exhibit high dichroic ratios due to favorable alignment of the molecules. Since no Davydov splitting is evident, the observed absorption bands in the crystals belong to electronic transitions localized on the individual complexes. For those cases where the complete crystal structures are known, the spectra polarized, to a good approximation, parallel to the molecular axes x,y,z were obtained as well. Several problems concerning the assignment of internal ligand transitions were solved. In (diketonato)tetrachlorostannates the y-polarized π–π* bands are not superimposed on other transitions of appreciable intensity, therefore their absorption profiles can be measured directly. The lowest, x-polarized n–π* transition of the acetylacetonates is very weak and is located for Sb(acac)Cl4 at an energy lower than that of the π–π* absorption. Some new evidence has been obtained on acetylacetonate-to-metal charge-transfer transitions: two peaks observed in Sb(acac)Cl4 are most probably π(acac)-Sb and O(acac)-Sb charge-transfer in origin. These types of transitions should be considered in the interpretation of electronic spectra of acetylacetonate complexes when optical electronegativities of the central ion are larger than 1.6–1.7.
Classical response theory propagators: An illustrative example
Authors: Holian B. L.
Published: July 2002

Time-ordered exponential propagators, introduced in the derivation of classical response theory, are illustrated for the case of the driven harmonic oscillator.
The scattering matrix for randomly oriented particles
Authors: Singham M. K. , Singham Shermila B. , Salzman Gary C.
Published: July 2002

An efficient numerical method is derived for evaluation of the scattering properties of randomly distributed particles described by the coupled dipole approximation. An exact analytic average for these properties is also derived. All elements of the scattering matrix for a collection of randomly oriented particles can be obtained by either method. The results are applicable to model calculations of the scattering matrix for realistic particles. The analytic average also allows qualitative interpretation of the dependence of the matrix elements on dipolar interactions.
A 23Na NMR study of the structure of Na β-alumina conduction plane at 5 K
Authors: Carduner Keith R. , White David
Published: July 2002

From measurements of the angularly dependent second order quadrupole shift of the central transition of the 23Na spectrum in Na β-alumina at 5 K, it is possible to conclude that sodium resides in three distinct kinds of sites in the conduction plane. Calculation of the electric field gradients (efg) consistent with experiment indicate that these sites are localized around a structural defect in the conduction plane that changes the local symmetry away from that of the average unit cell. Independent calculation of the efg’s with a point charge model reveals (1) that the sodiums in one of the three sites, called site 1, are closely associated with the BR position in the conduction plane, (2) sites 2 and 3 are nearby the mO positions clustered around the charge compensating oxygen, and (3) site 3 is closer to this oxygen than site 2. The NMR results agree with the Roth–Reidinger model of the conduction plane as modified by Wang.
Minimum cross-entropy inference of molecular momentum densities
Authors: Koga Toshikatsu , Hayashi Masahiko , Hoshina Hideo
Published: July 2002

The principle of minimum cross entropy, instead of the principle of maximum entropy, of information theory is employed to estimate a molecular radial momentum density I(p) under the constraint of a given moment 〈pn〉. An application to the ground-state H2 system shows that the minimum cross-entropy inference is superior to the maximum entropy inference.
Higher excited electronic states in clusters of ZnSe, CdSe, and ZnS: Spin-orbit, vibronic, and relaxation phenomena
Authors: Chestnoy N. , Hull R. , Brus L. E.
Published: July 2002

Metal selenide clusters have been made and characterized, using the arrested precipitation colloidal technique. A comparison of sulfide and selenide spectra enables observation of the effect of changes in the highest occupied molecular orbitals upon cluster electronic properties. The first and second excited electronic states are both observed as a function of size in ZnSe clusters. The systematic dependence of the spectra lead to assignment of the higher state to a 1S-type hole based upon the split-off valence band. It is shown that the energy spectrum of discrete hole states is controlled by the spin-orbit energy and the isotropic hole mass in small, highly symmetrical clusters. This result contrasts with the heavy hole and light hole states observed for planar confinement. In ≂ 20 Å diameter ZnS clusters, there is a strong vibronic temperature dependence in the excited state spectra, while in clusters of smaller gap materials such vibronic effects are very minor. We conjecture that lifetime broadening is severe in clusters of small gap materials.
Laser induced fluorescence and phosphorescence of matrix isolated glyoxal: Evidence for exciplex formation in the Ã 1A
u and ã 3A
u states
Authors: van IJzendoorn L. J. , Allamandola L. J. , Baas F. , Körnig S. , Greenberg J. M.
Published: July 2002

Laser-induced fluorescence (Ã 1Au→X̃ 1Ag) and phosphorescence (ã 3Au→X̃ 1Ag) as well as absorption and excitation spectra of glyoxal in Ar, N2, and CO matrices have been measured at 12 K. Supplementary infrared absorption spectra have also been taken. Although the dominant band in the absorption and excitation spectra is the 000 transition, it is absent in both the fluorescence and phosphorescence spectra leading to the hypothesis that glyoxal forms an exciplex with its nearest neighbor(s) in both the Ã 1Au and ã 3Au states. The equilibrium configuration of the nuclei is distorted in the exciplex producing, after fluorescence or phosphorescence, ground state glyoxal molecules born vibrationally excited while the Franck–Condon factors for the 000 transition vanish. In argon the fundamentals ν7 and ν12 are preferentially excited, corresponding to two different isomers of the complex, while in N2 and CO an unambiguous assignment for the preferentially excited modes cannot be given. The rule of mutual exclusion still holds in the IR spectra, in agreement with the formation of an excited rather than a ground state complex. Fluorescence and phosphorescence lifetimes place limits on the quantum yields of the various deexcitation channels and show that localized phonon modes play a dominant role in coupling to the matrix.
Tunneling flip flops and spin-lattice relaxation in solid CH4
Authors: Glättli Hans , Calvani Paolo , Bouchet Brigitte
Published: July 2002

Measurements of T1 in solid CH4 at T=4.2 K as a function of frequency up to 200 MHz and at lower temperatures as a function of the spin isomer populations are reported. A model is proposed, based on simultaneous tunneling transitions of nearest neighbors. These tunneling flip flops are able to account quantitatively for the whole set of observed relaxation times. The contributions of the different pairs of tunneling levels could be separated.
Intensities in the ν7, ν8, and ν9 bands of CH2NH and the harmonic force field of methyleneimine
Authors: Halonen L. , Deeley C. M. , Mills I. M.
Published: July 2002

A high resolution Fourier transform infrared spectrum of methyleneimine, HN=CH2, has been obtained in the gas phase in the region 700 to 1300 cm−1. The rovibrational line intensities of the three lowest fundamentals ν7 (A′), ν8 (A″), and ν9 (A″) have been simulated including all Coriolis interactions between the three bands, and by fitting the observed spectrum the relative signs and magnitudes of the vibrational transition moments have been determined. All of the available spectroscopic data have been used to determine the harmonic force field of methyleneimine.
Stimulated Raman amplification spectra in a four-level atomic system interacting with a strong bichromatic field
Authors: Mavroyannis Constantine
Published: July 2002

We have considered the stimulated Raman spectra arising from interaction of a four-level atom with a strong bichromatic field and a weak signal field simultaneously. The atomic system consists of two upper excited states ‖3〉 and ‖4〉 and two lower states ‖1〉 and ‖2〉, where the metastable state ‖2〉 is depleted through the action of two strong laser fields operating between the states ‖2〉↔‖4〉 and ‖2〉↔‖3〉, respectively. Using a model Hamiltonian, where all the free and interacting fields are quantized, and the Green function method in the limit of high photon densities of both laser fields, we have studied stimulated two-photon processes near the frequencies ±ω≊ω21≊ω41 −ωa≊ω31 −ωb for the ‖1〉→‖2〉 electric dipole forbidden transition describing physical processes, where one photon of the signal field with frequency ω41(ω31) is absorbed while a photon of the laser field with frequency ωa(ωb) is emitted and vice versa; ωij refers to an atomic transition frequency between the states ‖i〉 and ‖j〉. The spectral function for the stimulated two-photon processes consists of a central peak at the frequency ω=ω21, which has a delta function distribution indicating the stability of the mode in question, and three pairs of sidebands, where one pair of sidebands is induced by each laser field, respectively, while the third pair of sidebands is induced by both laser fields simultaneously. The intensities of the sidebands are always negative indicating that strong amplification (stimulated emission) takes place at the corresponding frequencies. The computed resonance and off-resonance spectra are graphically presented and discussed. When a classical description for both laser fields is used, the spectral function is found to describe one pair of sidebands, which is induced by both laser fields simultaneously; this classical result is graphically presented and compared with those obtained when the fields are quantized. It is shown that the results obtained when the fields are quantized and in the limit of high photon densities describe the classical

as well as the quantum nature of the photon fields which is lost in the classical picture. The effect of the quantum nature or, equivalently, the boson character of the photon is to split the ‘‘classical’’ spectrum described by one pair of sidebands into three pairs, whose sum of relative intensities is equal to that of the original pair derived classically.
High pressure study of changes in energy and intensity of excitations in crystalline metal glyoximes
Authors: Tkacz M. , Drickamer H. G.
Published: July 2002

The effect of high pressure has been measured on the energy and integrated intensity of electronic excitations of several layered crystals of glyoximes containing Ni, Pd, or Pt. Large changes in both energy and intensity were observed, both of which were completely reversible. The shifts in energy with pressure, are explained in terms of the relative spatial extent of the outer d and p orbitals of Ni, Pd, and Pt. The effects of back donation from the ligands and intensity borrowing from the higher energy charge transfer excitations are considered as possible causes of the observed intensity changes. It was concluded that intensity borrowing was the major cause of the observed changes.
Temperature dependence of the rate of the electronic-to-electronic energy transfer from NF(b 1Σ+) to IF
Authors: Pritt A. T. , Benard D. J.
Published: July 2002

The temperature dependence of the rate of transfer of electronic energy from NF(b 1Σ+) to ground state IF(X 1Σ+) to form IF[B 3Π(O+)] has been determined using a chemiluminescence flowtube apparatus. The energy transfer rate depends on the vibrational distribution of the IF(X 1Σ+), but is independent of the vibrational distribution of the NF(b 1Σ+). The vibrational temperature of the IF[B 3Π(O+)] product was also greater than or equal to the vibrational temperature of the IF(X 1Σ+) reagent. These results are explained in terms of an energy transfer model requiring that the individual state-to-state rates are proportional to the corresponding Franck–Condon factors.
An exchange energy functional based on the Dirac and the Fermi–Amaldi approximations
Authors: Cedillo Andrés , Ortiz Elba , Gázquez José L. , Robles Juvencio
Published: July 2002

The exchange energy density functional of an N electron atom is approximated by a combination of the Dirac and the Fermi–Amaldi approximations. The unknown coefficients of the combination are estimated by requiring that the sum of the Coulombic and exchange energies vanish when evaluated with the exact one-electron density. Evaluating the present functional with the Hartree–Fock densities of 1785 atoms and ions, and comparing the resulting exchange energies with the corresponding Hartree–Fock values gave an average error of 2%. The functional derivative has the correct long-range behavior, and leads to an Euler–Lagrange equation whose solutions gave energies which were in very good agreement with the Hartree–Fock values.
A virial expansion of the pressure in a quantum system within the local thermodynamic transcription of density functional theory
Authors: Robles Juvencio
Published: July 2002

The concept of local pressure in an electronic system is extended and developed, starting from an integral relation of Bartolotti and Parr (Ref. 11) and using the local thermodynamic language of Ghosh, Berkowitz, and Parr (GBP) (Ref. 3), who have shown that for an ideal, noninteracting microscopic system the internal pressure at a point r is purely kinetic and given by ps=ρ(r)kT̃(r), where T̃(r) is an appropriately defined local temperature. In the present paper, we show that this equation, exact for the noninteracting, ideal system within the local thermodynamic transcription is a first order truncation of the real, interacting system pressure density functional, which contains explicit correlation and exchange pressure contributions, which act as ‘‘deviations from ideality’’ in the real system. From analogy with the macroscopic situation, the pressure density functional is written as a virial expansion in terms of the density.
NMR pulse response and measurement of the quadrupole coupling constant of I=3/2 nuclei
Authors: Pandey Lakshman , Towta S. , Hughes D. G.
Published: July 2002

The rf pulse response of a system of I=3/2 nuclei which experience identical first-order quadrupole splitting is investigated using the density matrix method. A general expression is derived for the time evolution of the in-phase magnetization following a rectangular pulse applied at the center line frequency. The maximum amplitude of the magnetization associated with the center line, and the length of pulse that gives rise to it, are calculated as a function of the ratio of the quadrupole splitting to the amplitude of the rf field. Data obtained for 23Na in a single crystal of NaNO3 are in fairly good agreement with the theoretical form. The theory has been extended to the case where the nuclei are situated at equivalent sites in a polycrystalline sample. The length of pulse that maximizes the amplitude of the FID of 23Na in a powder sample of NaNO3 has been measured as a function of the amplitude of the rf field. The quadrupole coupling constant, found by fitting the data to the theoretical form, is in very good agreement with the accepted value. It is proposed that this method can be widely used to measure the quadrupole coupling constants of I=3/2 nuclei.
Classical, diatomic molecule, kinetic theory cross sections. IV. A perturbation series
Authors: Curtiss C. F.
Published: July 2002

Classical mechanical expressions for the generalized or kinetic theory cross sections associated with collisions between nonvibrating diatomic molecules which were developed earlier are reformulated in such a manner that the effects of the anisotropy of the intermolecular potential are isolated as ‘‘correction’’ terms to the expressions which arise in the treatment of collisions between atoms. The expansion of these correction terms in perturbation series in which the anisotropic portion of the interaction potential is the perturbation is then discussed. The first order terms are obtained explicitly as integrals over the classical trajectories associated with the unperturbed (spherical) potential and it is shown that the first order contribution to the first average generalized opacity function, may be written as a sum of two terms, each a product of two factors. In each term the first is a constant independent of the details of the collisions which depends only on the indices q, q′, and κ. The details of the collision determine the second factors which depend on the indices l, l′, and κ only. The numerical evaluation of these functions leads to results which are consistant with those obtained from full, nonperturbative calculations and indicates that the first order results are probably sufficiently accurate to investigate the convergence of the perturbation series for the molecular distribution functions and the validity of various ‘‘truncation’’ approximations which have been suggested.
Floquet theoretic approach to sensitivity analysis for periodic systems
Authors: Larter Raima
Published: July 2002

The mathematical relationship between sensitivity analysis and Floquet theory is explored. The former technique has been used in recent years to study the parameter sensitivity of numerical models in chemical kinetics, scattering theory, and other problems in chemistry. In the present work, we derive analytical expressions for the sensitivity coefficients for models of oscillating chemical reactions. These reactions have been the subject of increased interest in recent years because of their relationship to fundamental biological problems, such as development, and because of their similarity to related phenomena in fields such as hydrodynamics, plasma physics, meteorology, geology, etc. The analytical form of the sensitivity coefficients derived here can be used to determine the explicit time dependence of the initial transient and any secular term. The method is applicable to unstable as well as stable oscillations and is illustrated by application to the Brusselator and to a three variable model due to Hassard, Kazarinoff, and Wan. It is shown that our results reduce to those previously derived by Edelson, Rabitz, and others in certain limits. The range of validity of these formerly derived expressions is thus elucidated.