bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of resonant excitation and shakeoff contributions to the C K
V
V Auger line shapes of several gas phase hydrocarbons
Authors: Hutson F. L. , Ramaker D. E.
Published: July 2002

We have consistently interpreted the C KVV Auger line shapes of five hydrocarbons (methane, ethane, cyclohexane, benzene, and ethylene) and compared the results with those previously reported for three different solids (polyethylene, diamond, and graphite). We show that an interpretation procedure normally used for solids, namely, a self-fold of the one-electron DOS and incorporation of hole–hole correlation effects utilizing the Cini expression, is also adequate for molecules, and thus direct comparison of the gas phase and solid phase results is possible. In contrast to the solids, the normal kvv line shape accounts for only about half of the total experimental intensity for the gas phase molecules. The remaining part of the experimental line shape can be attributed to three different satellite contributions; namely resonant excitation (ke–vve), initial-state–shake (kv–vvv), and final-state–shake (k–vvv) satellites. The normal kvv Auger line shapes are seen to reflect delocalized holes, however correlation effects are evident. In contrast, the three-hole final state of the kv–vvv process reflects holes localized primarily on a single methyl group. The results indicate that long range polarization effects are not important in the extended solids; short range π electron screening is important in the alkenes and in graphite.
The harmonic force field for PF5 from a
b i
n
i
t
i
o calculations and experimental data. Comparisons with SiF4, PF3, and SF6
Authors: Marsden Colin J.
Published: July 2002

Force constants have been obtained for PF5 from ab initio SCF calculations, using a basis set of double zeta plus polarization quality for phosphorus, and nearly triple zeta for fluorine. Parallel calculations have been performed for SiF4, PF3, and SF6, to obtain optimum scale factors for PF5. SCF scale factors are different for stretching and bending motions, and also for interaction constants. Scale factors for SiF4 and SF6 differ substantially; intermediate values seem appropriate for PF5. The scaled ab initio force field for PF5 predicts all available spectroscopic data satisfactorily, with an average discrepancy of only 1.2 times the estimated uncertainty. A refined force field has been obtained by least-squares fitting, constraining three of the off-diagonal force constants. The normal modes of PF5 are described, with particular emphasis on the E′ bending motion and pseudorotation. Trends in force constants of SiF4, PF3, PF5, and SF6 are discussed.
Algebraic resonance quantization of strongly chaotic coupled oscillators
Authors: Kellman Michael E. , Lynch Eric D.
Published: July 2002

The algebraic resonance quantization (ARQ) method has previously been investigated for coupled Morse oscillators with moderate coupling and a substantial degree of classical chaos. This method is investigated here for strong coupling with the transition to global chaos and a Wigner distribution of level spacings in the quantum spectrum. A sparse matrix multiresonance approximation (SMRA) is found to give good results even when there is global chaos. A truncated basis set approximation (TMRA) is successful for moderate coupling but breaks down for strong coupling. Implications of these results for calculation of rotation–vibration levels of polyatomics in the regime of global chaos are discussed. Prospects for nonlinear least-squares fitting of experimental spectra in the regime of global chaos are also discussed.
Photodissociation of methyl nitrite: Angular distributions in one- and two-photon dissociations
Authors: Inoue Gen , Kawasaki Masahiro , Sato Hiroyasu , Kikuchi Toshiyuki , Kobayashi Shuichiro , Arikawa Tatsuo
Published: July 2002

The photodissociation of methyl nitrite in the molecular beam has been studied by laser irradiation at 348–364 nm. The NO photofragments were analyzed by MPI analysis in a one-color experiment. The translational energy distribution for the photofragment indicates that there are two distinct paths by which CH3O and NO radicals are produced; one is a one-photon dissociation, and the other is a two-photon dissociation. The angular distribution of fragment intensities peaks in a direction orthogonal to the electric vector of the photolysis light indicating that the transition moments for both the first and the second one-photon absorptions lie perpendicular to the O–N bond that breaks.
Laser induced thermal desorption: A theoretical study
Authors: Zeiri Yehuda
Published: July 2002

The simulation of desorption caused by rapid surface heating, due to irradiation by a laser or electron beam pulse, is described. A stochastic trajectory technique has been used to calculate the translational energy, angular, and residence time distributions of Xe atoms desorbing from a W(100) surface. The relationship between these distribution functions and different parameters used for the heating pulse and the nature of the simulated system are discussed. In particular, the dependence on heating rate, maximum surface temperature, and pulse temporal shape together with the effect of adsorbate–surface potential corrugation and initial surface coverage were studied. In general, it was found that the mean desorbate translational energy is much lower than the surface temperature at the instant of desorption and that the angular distribution is highly peaked towards the surface normal. It is also shown that high adsorbate–surface potential corrugation and attractive adsorbate–adsorbate interaction tends to broaden the desorbate angular distribution.
UV multiphoton excitation: An access to the energy dependence of unimolecular reactions and collisional energy transfer
Authors: Damm M. , Hippler H. , Troe J.
Published: July 2002

Repetitive absorption of UV (or visible) photons followed by fast internal conversions allows to deposit large amounts of vibrational energy in polyatomic molecules. Intra- and intermolecular processes with relatively weak energy dependences can be studied by this excitation over broad energy ranges. The technique is illustrated for the unimolecular isomerization azulene → naphthalene and collisional energy transfer of vibrationally excited azulene. With ns excimer laser pulses, up to three photons at λ=308 nm were deposited in the molecule, and collisional quenching competing with isomerization was studied. The results can be modeled conveniently by a multistep mechanism.
Analytic solution of the stochastic-Liouville model of spin exchange
Authors: Adrian Frank J.
Published: July 2002

An analytic solution is obtained for the stochastic-Liouville model of spin exchange between a pair of radicals undergoing isotropic diffusion in solution and interacting via an exchange interaction that decays exponentialy with radical separation. The resulting spin exchange cross section is the sum of a ‘‘strong encounter’’ term that is approximately equal to the biomolecular reaction cross section and a ‘‘grazing encounter’’ term that is due to encounters in the tail of the exchange interaction. The latter term may range from negligible to twice the former term for plausible values of the diffusion rate and the range of the exchange interaction. It is shown that the theory combined with experimental data on the spin-exchange contribution to spin–lattice relaxation can provide an estimate of the range of the exchange interaction between two radicals.
Reaction of barium atoms with N2O clusters
Authors: Visticot J. P. , Mestdagh J. M. , Alcaraz C. , Cuvellier J. , Berlande J.
Published: July 2002

The chemiluminescence of the reaction of barium atoms and N2O molecules is observed in a crossed molecular beam experiment. The conditions of the molecular N2O beam are varied so that this beam contains no, or many large, N2O clusters. No additional chemiluminescence occurs when the cluster concentration is increased. The large difference in electronic structure between monomers and polymers, which has been shown by Echt et al. by measurement of electron attachment, suggests that a different reaction channel yielding BaO solvated in a N2O cluster is responsible for this absence of chemiluminescence.
Analysis of the 4f, v=3 state of NO
Authors: Eyler E. E. , Biernacki D. Therese
Published: July 2002

The long-range force model has been used to analyze high resolution spectra of the nearly nonpenetrating 4f, v=3 state of NO. The energy levels are described to an accuracy of 0.03 cm−1 by a fit with four adjustable parameters. The quantum defects are predicted to better than 0.1%, showing that the 4f state is almost completely unperturbed. Implications for previously reported measurements of the autoionization rates are discussed.
Inversion transition frequencies in the v=5 state of NH3 measured by millimeter wave-optical double resonance
Authors: Matsuo Yukari , Endo Yasuki , Hirota Eizi , Shimizu Tadao
Published: July 2002

Eight new frequencies of inversion transitions in the v=5 state of NH3 have been determined by millimeter wave-optical double resonance method. The transitions are definitely assigned and the accuracy in frequency determination has been improved by more than two digits.
Structure of hard particle fluids near a hard wall. II. y
w(z) for hard spheres
Authors: Labik S. , Smith William R. , Speedy Robin J.
Published: July 2002

Predictions of the wall–cavity correlation function yw(z) for hard spheres against a hard wall are tested using the treatment that Smith and Speedy developed and examined for the case of hard disks in part I of this series, as well as an extension of this approach using an alternative procedure. yw(z) in the range 0≤z≤1 may be accurately predicted using only the thermodynamic properties of the bulk fluid, for which precise expressions are available. These predictions are tested by determining yw(z) and the cavity concentration profile nwo(z) in a computer simulation study. We also derive a new integral equation relating yw(z) near the wall to its values just outside the wall and illustrate this in examining the consistency of our computer simulation results.
Interrelations among overlap, kinetic energy, and nuclear attraction integrals over hydrogenic orbitals
Authors: Koga Toshikatsu , Matsuhashi Toshiyuki
Published: July 2002

In addition to the sum rules and relations reported recently for one-, two-, and three-center nuclear attraction integrals, we show that there also exist exact interrelations among the overlap, kinetic energy, and nuclear attraction integrals over hydrogenic orbitals. The present results together with the previous ones establish the internal structure of the three types of hydrogenic one-electron integrals.
Ultraviolet laser photodesorption of NO from condensed films: Translational and internal energy distributions
Authors: Natzle W. C. , Padowitz D. , Sibener S. J.
Published: July 2002

In this paper we report that ultraviolet laser induced desorption from the surface of a thin nitric oxide film proceeds via two mechanisms which are present simultaneously. One mechanism is attributed to laser induced thermal desorption while the other is due to a nonthermal, single photon process. A film of 1–2000 ML (layers) of NO condensed on a Ag(111) substrate under UHV conditions at 25–50 K was irradiated by 5 ns pulses of 220–270 nm laser light (4.6–5.5 eV) with 0.5–5 mJ/cm2 (0.1–1 MW/cm2 ) power density at the surface. Translational energies of desorbed molecules were measured from time-of-flight (TOF) spectra taken with a mass spectrometer, while the internal energy distribution of molecules desorbed in the nonthermal channel was determined by a (1+1) resonance enhanced multiphoton ionization (REMPI) probe. NO monomer in the 2Π3/2,1/2 electronic ground states was the only significant product. There were two distinct characteristic TOF components, which we associate with different desorption mechanisms. Each component had a different velocity and angular distribution, and their relative yields varied with laser pulse energy and NO layer thickness. Under conditions where both mechanisms gave comparable desorption yields, we obtained TOF distributions which were bimodal. A ‘‘slow’’ peak with an average translational energy up to 0.06 eV was Maxwellian with temperatures between 160 and 280 K and a broad angular distribution. Yield in this peak increased strongly with layer thickness and exponentially with laser pulse energy. A ‘‘fast’’ TOF peak with average energy of 0.22 eV was non-Maxwellian, with an angular distribution peaked toward normal, and yield increasing linearly with laser pulse energy. REMPI of the fast peak showed a vibrational population ratio v=3:v=2 of 0.85. A Boltzmann plot of the rotational population distribution of v=2 molecules, if fit with a single line, gave a temperature of 2500 K. We use these angular, velocity, rotational, and vibrational distributions to suggest mechanisms for the nonthermal desorption. We also discuss factors determining the relative extent of thermal and photochemical effects, which control the morphology of ablated surfaces.
Analysis of Fermi resonances in CH2Cl2 and CD2Cl2 using an internal coordinate Hamiltonian
Authors: Halonen Lauri
Published: July 2002

A curvilinear internal coordinate Hamiltonian is used to analyze Fermi resonances between CH (CD) stretching and CH2 (CD2) scissoring vibrations in CH2Cl2 and CD2Cl2. Eigenvalues of the Hamiltonian are obtained variationally using a Morse oscillator basis set for the stretching vibrations and a harmonic oscillator basis set for the scissoring vibration. The least-squares method is used to optimize the potential energy parameters. The observed vibrational levels of CH2Cl2 and CD2Cl2 are reproduced well with a single potential energy surface.
Application of finite element and boundary integral methods in molecular collision theory. I. Introduction and model calculations
Authors: Sethuraman V. , Hunt P. M.
Published: July 2002

The adaptive multigrid technique in the finite element method of the solution of partial differential equations is examined in the context of model problems in atom–atom and collinear atom–diatom collisions. For the problem leading to scattering along an L-shaped region, it yields accurate results for regions of energy far from threshold for excitation of a new channel without inclusion of virtual states. Close to threshold, the cusp-like structure of the transition probability (vs energy) and the time delay associated with the onset of a resonance are recovered only by inclusion of the new (closed) channel in the finite element solution. For atom–diatom collinear collisions, use of an orthogonal coordinate system facilitates discretization and adds no extra labor in the finite element method, compared to the usual mass-weighted system. In such collisions, where the threshold behavior of the transition probability resembles the presence of a bound-state resonance below the threshold, the no-virtual-state solution is shifted in energy relative to the converged one-virtual-state solution. Under certain circumstances, transition probabilities from the former solution are found to deviate substantially from those determined from the latter in energy regions well below threshold. The multigrid method of solution of the finite element equation is found to be accurate provided a sufficiently fine grid is employed for the coarsest level of the multigrid adaptive solution process. However, for the problems studied, when the solution obtained from the coarsest grid does not yield a sufficiently accurate interpolated initial approximation for the relaxation method of solution of the finer grid levels, this method was found to converge to erroneous solutions. In future work, techniques examined herein will be applied to molecular scattering problems involving collisional dissociation.
Sensitivity analysis of mass effects in rotational energy transfer
Authors: Kreutz Thomas G. , Eno Larry , Rabitz Herschel
Published: July 2002

This paper examines the sensitivity of rotationally inelastic integral state-to-state cross sections to variations in the masses of the collision partners. We investigate the helium-hydrogenic scattering system with its many physical isotopes and excellent ab initio potential. The collision dynamics are approximated by coupled states-exponential distorted wave (CS-EDW) theory and both cross sections and elementary sensitivity coefficients (partial derivatives of the cross sections with respect to the mass parameters) are calculated. In order to be able to properly interpret these results, we first generate conceptually and computationally simpler distorted wave (CS-DW) cross sections and elementary sensitivities. These perturbative results are analyzed using simple collisional concepts and models. In addition, we present functional forms which predict (or scale) the global behavior of DW cross sections through the mass parameter space. As a quantitative aid in linking EDW cross sections with the DW results, a new type of sensitivity coefficient is introduced which measures the sensitivity of a given EDW cross section to the variation of a single DW cross section or combination thereof.
Vacuum ultraviolet fluorescence excitation spectrum of I2
Authors: Hiraya A. , Shobatake K. , Donovan R. J. , Hopkirk A.
Published: July 2002

A detailed study of the vacuum ultraviolet fluorescence excitation spectrum of I2 in the region 110–210 nm is reported. Both absorption and fluorescence excitation spectra were recorded simultaneously using continuously tunable synchrotron radiation. At long wavelengths (176–210 nm) the fluorescence excitation spectrum is dominated by the D(0+u) ion-pair state. Perturbations between the D(0+u) state and isoenergetic levels of the c6 Rydberg state lead to pronounced resonances (dips) in the fluorescence excitation spectrum. Weaker absorption to the F(0+u) and F′(0+u) ion-pair states is identified at 170 and 150 nm, respectively. Below 149 nm electronically excited iodine atoms (I 6s 4P5/2 and I 6s 2P3/2) are formed by predissociation of high-lying Rydberg and ion-pair states.
Nonadiabatic unimolecular reactions. III. Dissociation mechanisms of methylnitrite and deuterated methylnitrite ions
Authors: Leyh-Nihant B. , Lorquet J. C.
Published: July 2002

At low energies, methylnitrite ions dissociate via two channels giving rise to CH3O+NO+ or to [CH3O+]+NO fragments. Peculiar characteristics have been detected in the dissociation of energy-selected parent ions, viz., remarkably low rate constants, one of which is found to remain insensitive to an increase of the internal energy, and large isotope effect. These peculiarities are accounted for by a statistical, nonadiabatic model. Ab initio calculations, confirmed by multipolar expansions reveal that the potential energy curves which correlate to these two dissociation asymptotes cross. The crossing takes place at a large value along the reaction coordinate R, indicating a long-range interaction. Production of the CH3O+NO+ fragments results from a simple bond cleavage taking place on a single diabatic surface. On the other hand, production of [CH3O+]+NO fragments is brought about by a transition from one diabatic surface to the other. It leads to deformed methoxy ions which immediately rearrange to the much more stable H2COH+ structure. The nonadiabatic rate constant has been calculated by a statistical method. The contribution of each channel is weighted by a transmission coefficient which is equal to the nonadiabatic transition probability. Implementation of this statistical treatment requires partitioning

the set of degrees of freedom as follows: {R, y, d, v}. It is necessary to withdraw the isomerization mode y from the statistical treatment, because the equilibrium positions along this coordinate are very different in each electronic state. Physically, this means that the reaction involves tunneling from one surface to the other along the displaced degree of freedom y. The large isotope effect has a double origin: part of it (a factor of ∼9) results from tunneling along y; the remainder (an additional factor of 3) comes from the usual RRKM-like effect on the densities of states. The degrees d constitute a set of four low-energy bending modes which form a sink for the internal energy. The nonadiabatic transition probability is determined by the off-diagonal matrix element V12(Rc). Effective potential energy curves have been calculated by extending the Quack and Troe method to nonadiabatic reactions. It turns out that the excitation of the set d leads to a decrease of V12(Rc) and hence to a decrease of the nonadiabatic transmission coefficient. This accounts for the weak dependence of the rate constants kCH3O+ and kCD3O+ vs the energy (at least above a certain energy threshold).
Theory of multiple quantum dynamic NMR spectroscopy
Authors: Gamliel D. , Luz Z. , Vega S.
Published: July 2002

A formalism for calculating dynamic multiple quantum NMR line shapes obtained by the time proportional phase increment (TPPI) method from spin-1/2 systems is developed. The formalism is essentially an extension of the related formalism in Liouville space used in the theory of conventional dynamic NMR of strongly interacting spin systems. It is subsequently used to calculate the expected multiple quantum proton NMR line shapes of a number of (hypothetical and real) systems consisting of compounds dissolved in liquid crystalline solvents and undergoing intramolecular rearrangement. These include cyclobutadiene, cyclohexatriene, and cyclooctatetraene undergoing bond shifts and s-trioxane undergoing ring inversion. Since the computations involve diagonalization of high-dimensional matrices extensive use is made of symmetry factorization. It is shown that the resulting line shapes depend on the mechanism and rate of the dynamic processes, and may therefore be used to derive kinetic parameters from multiple quantum experiments. The high-quantum order spectra are particularly useful because for intermediate and large spin systems they are much simpler than the corresponding conventional single quantum spectra. Approximate expressions for the multiple quantum line shapes are also derived for the slow and fast exchange limits. It is found that except for an intermediate dynamic region these equations faithfully reproduce the exact line shapes in the appropriate limits.
Probing director fluctuations in liquid crystals. 2H relaxation dispersion of deuterated toluene and p-xylene
Authors: Plomp L. , Schreurs M. , Bulthuis J.
Published: July 2002

Deuterium spin-lattice relaxation rates in toluene-d8 and p-xylene-d10, dissolved in nematic Phase V, have been measured at five different field strengths. The frequency-dependent relaxation behavior can be satisfactorily described by a model in which the molecules undergo small step rotational diffusion in an axially symmetric orienting potential, with contributions from slow director fluctuations. The parameters defining the model are fitted to the relaxation rates of para and methyl deuterons, using a least-squares parameter estimation program. Parameter values obtained are consistent with a physically acceptable set of values of the associated hydrodynamic properties of the solutions, and are in agreement with results obtained previously on 14N relaxation in methylisocyanide. Relaxation rates of ortho and meta deuterons in toluene, and of the ring deuterons in p-xylene lead to a J1/J2 ratio smaller than unity. Moreover, both J1 and J2 are weakly frequency dependent. The former effect may turn up as a consequence of the assumption of axially symmetric diffusion; the frequency dependence of J2 is probably due to second order effects of the director fluctuations.
Optimized virtual orbital space for high-level correlated calculations. II. Electric properties
Authors: Adamowicz Ludwik , Bartlett Rodney J. , Sadlej Andrzej J.
Published: July 2002

The optimized virtual orbital space (OVOS) technique recently proposed for high-level correlated calculations of energy surfaces, is shown to be nearly as efficient for electric field properties. In particular, the polarizability of F−, and the dipole moment and polarizability of FH as a function of internuclear separation are studied. A reduction of the virtual space to about one-half has a negligible effect on the dipole moment and polarizabilities for FH and F− examples. A further reduction to one-quarter is reliable when augmented with the exact second-order result, obtained as a by-product of the OVOS generation. This enables the extension of high-level correlated methods to systems at least 2–4 times larger than those that could be accurately studied using the full space of virtual orbitals.
Mean spherical approximation (MSA) for a simple model of electrolytes. I. Theoretical foundations and thermodynamics
Authors: Ho/ye Johan S. , Lomba Enrique
Published: July 2002

A simple electrolyte in a polar solvent is modeled by a mixture of polar hard spheres and equal diameter charged hard spheres. The solution of the mean spherical approximation for this model is rederived to its full extent. Explicit expressions for thermodynamic quantities in terms of the MSA solution are established. A nice property of this MSA approach is the possibility to express quantities of physical interest in terms of a set of three parameters, which represent nothing but the excess internal energies due to charge–charge, charge–dipole, and dipole–dipole interactions, respectively.
Numerical simulations of electron spin resonance spectra: Unified description and comparison of the Lanczos algorithm, the generalized Mori method, and Padé approximants
Authors: Dammers A. J. , Levine Y. K. , Tjon J. A.
Published: July 2002

A comprehensive study of the various related methods for the solution of the stochastic Liouville equation is presented. The methods are essentially based on moment expansions and continued fraction representations and lead to efficient algorithms for carrying out numerical simulations of electron spin resonance (ESR) spectra. The convergence, stability, and error propagation are discussed and compared using the model system of an axially symmetric nitroxide molecule tumbling isotropically in solution.
Shape resonance and non-Franck–Condon behavior in the photoelectron spectra of O2 produced by (2+1) multiphoton ionization via 3sσ Rydberg states
Authors: Miller Paul J. , Li Leping , Chupka William A. , Colson Steven D.
Published: July 2002

Photoelectron spectra produced by (2+1) MPI via the v=0–3 levels of the (3sσg ) C 3 Πg Rydberg state of O2 show large deviations from the Franck–Condon principle. These deviations are attributed largely to a shape resonance in the σu ionization channel and probably a ‘‘window’’ resonance in the 3 Σ−u part of the πu channel.
Study of chemical gelation dynamics of acrylamide in water by real-time pulsed nuclear magnetic resonance measurement
Authors: Tanaka Hajime , Fukumori Kenzo , Nishi Toshio
Published: July 2002

Chemical gelation process of acrylamide monomers in water has been studied by a real-time pulsed nuclear magnetic resonance (NMR) measurement. The temporal change of molecular mobility has been detected by a real-time observation of the spin–spin relaxation time T2. The influence of the concentration of crosslinker and acrylamide on gelation dynamics has been studied, and it becomes clear that these factors have strong effects on the gelation dynamics. The effects of linear polymerization and network formation on the motional state of water have been studied. The formation of three-dimensional cages drastically reduces the mobility of water. In low acrylamide concentration, the results of NMR measurement mainly reflect the state of water. In high acrylamide concentration, on the other hand, they reflect both polymer network and water, and furthermore, in high crosslinker concentration the spatial heterogeneity of gels is observed. In this paper, we demonstrate that a real-time NMR measurement is a useful tool for a direct observation of the temporal change of molecular mobility during polymerization and gelation process.
[3+2] resonance enhanced multiphoton ionization of I and Br formed from the infrared multiphoton decomposition of CF3I and CF3Br
Authors: Robertson Robert M. , Golden David M. , Rossi Michel J.
Published: July 2002

Resonance enhanced multiphoton ionization (REMPI) has been used to study the products of the infrared multiphoton decomposition (IRMPD) of CF3I in a very low-pressure photolysis (VLPΦ) cell. The strongest REMPI signals are due to the ground state I(2P3/2) and the spin–orbit excited state I*(2P1/2). The origins of I and I* were determined from the time and IR laser fluence dependences of the REMPI signal. I* is formed by visible single photon dissociation of vibrationally excited CF3I and by visible multiphoton dissociation of I2 and thermal CF3I. The ionization efficiency of I has been determined relative to NH3 for our probe laser conditions, and the sticking coefficient of I with gold surfaces has been determined. The REMPI spectra of the products of the IRMPD of CF3Br is also presented.
Many-body effects in tetrahedral water clusters
Authors: Hermansson Kersti
Published: July 2002

Many-body contributions to the energies, forces, electron densities, dipole moments, and Mulliken charges for a water molecule bound in a tetrahedral environment have been calculated by ab initio SCF methods. An (H2O)5 and two ⊕2+2⋅H2O complexes have been investigated. Nonadditive effects in the energies can to a large part be explained on the basis of the electron redistribution for interacting pairs, while nonadditive effects in the electron rearrangement were found to be small. Four- and five-body corrections to all the pentamer properties calculated were found to be small.
Effect of heterogeneity on the lag time in one-dimensional diffusion
Authors: Chen Jenn-Shing , Fox Jeffrey L.
Published: July 2002

A new general equation has been developed for the lag time for a dilute diffusant permeating through a one-dimensional membrane in which both diffusivity D and partition coefficient K are dependent on position. The lag time is given by tL=∫h0K(x)[∫x0 R(y)dy][∫hxR(y)dy] ×dx/ ∫h0R(x)dx, where h is the membrane thickness and R(x)=1/[D(x)K(x)]. Formulas derived from this equation include those for: lag time in the presence of an electrical potential gradient; lag time in a multilaminar periodic membrane; and an upper bound for lag time given by tL <(h2/ 4Deff), where Deff is the effective diffusivity as deduced from steady-state partitioning and permeability measurements. The lag time is shown to be independent of the direction of diffusion. A computational technique is presented in which the equation for tL is rearranged to a system of two differential equations, which are readily solvable by numerical integration, even when the system has discontinuities in D and K which would increase the difficulty of evaluating the double integral directly.
An electronegativity model for vibrational intensities of substituted methanes
Authors: Neto B. B. , Scarminio I. S. , Bruns R. E.
Published: July 2002

The mean dipole moment derivatives of the carbon polar tensors of the halogenated methanes are shown to be linearly related to the carbon partial charges calculated using the equalization of the electronegativity principle. The relationship is quantitative and allows the calculation of mean dipole derivatives of carbon atoms from valence state ionization potentials and electron affinities of the atoms in the halogenated methanes. The methyl group electronegativity in ethane calculated from the carbon mean dipole derivative is in excellent agreement with the previously reported value obtained from electronic transition data. Ab initio charge, charge flux, and overlap contributions to the carbon mean dipole derivatives are shown to be useful in the interpretation of the relation between the derivatives and the partial charges.
Hyper-quasielastic light scattering of liquid CCl4 due to the rotational motions of molecules and the intermolecular interactions
Authors: Shin S. , Ishigame M.
Published: July 2002

Hyper-quasielastic light scattering of liquid carbon tetrachloride CCl4 is measured in the temperature range between −9 and 68 °C. The spectra consist of two different Lorentzians, narrow and broad ones. By the measurements of the polarization ratio and the temperature dependence of the spectra, the narrow Lorentzian spectrum is found to arise from the rotational Brownian motion of a CCl4 molecule. This spectrum is inactive for both Raman and infrared measurements but is only active for the hyper-Raman measurement. The broad Lorentzian spectrum mainly comes from the temporary dipole moment induced by the intermolecular interactions between the molecules. The intermolecular interaction becomes strongest around 40 °C. The temperature dependences of the half-width and the integrated intensity of the narrow Lorentzian are strongly affected by the intermolecular interactions.
Photophysics of atomic magnesium isolated in solid methane and perdeuteromethane. I. Optical absorption of an impurity species in a quantum solid
Authors: McCaffrey John G. , Ozin Geoffrey A.
Published: July 2002

Optical absorption spectra recorded at 12 K for the 1 P–1 S transition of atomic magnesium isolated in solid methane and perdeuteromethane exhibit significant differences in their spectral positions and bandwidths. The greater blue shift in CD4 relative to CH4 was found to be unchanged upon sample annealing. Shifts in the spectral position of the resonance transition in the two solids are discussed in the context of mass related differences in the lattice parameters of these light solids which is a manifestation of their behavior as quantum solids. From the blue shift observed in CD4 , the isotope having the smaller cage size, it is proposed that repulsive forces dominate in the interaction of the atomic magnesium guest species with its host. The greater bandwidth of the absorption profile in CH4 , relative to CD4 is discussed in terms of a Jahn–Teller model where the effective frequency of the phonon modes coupling with the electronic transition of the optically active impurity are higher in the former solid.
Sub-Doppler resolution infrared spectra of the isoelectronic pair: N2–HCN and OC–HCN
Authors: Jucks K. W. , Miller R. E.
Published: July 2002

Sub-Doppler resolution infrared spectra have been obtained for the ν1 bands of N2 –HCN and OC–HCN using the opto-thermal detection method, from which accurate ground and excited state molecular constants are determined. Vibrational predissociation lifetimes are estimated from the homogeneous broadening of the observed transitions, giving lifetimes of 80 and 2.6 ns for N2 –HCN and OC–HCN, respectively. These lifetimes are considerably longer than those obtained previously for N2 –HF and OC–HF. This difference can be understood in terms of the strength of the coupling between the intra- and intermolecular motions, which is also reflected in the vibrational frequency shift associated with complex formation.
Cluster volume and surface area in dispersions of penetrable particles or pores
Authors: Fanti Lisa A. , Glandt Eduardo D. , Chiew Yee C.
Published: July 2002

The complete description of a homogeneous, multiphase dispersion is contained within the infinite set of n-body density distribution functions g(rn) which have been used to calculate macroscopic properties such as interfacial area and specific volume. Certain quantities of interest, however, must take the connectedness of the individual phases into account. This requires the introduction of a complete set of n-body connectedness functions g+n(rn). Until now, only the pair-connectedness function g+2(r2) has been computed. Here, a formalism for the estimation of higher-order connectedness functions from lower order ones is presented. Results are given for the average volume and interfacial area per cluster for a dispersion of randomly placed spheres.
Mean spherical approximation for a simple model of electrolytes. II. Correlation functions and thermodynamics: Numerical results
Authors: Ho/ye J. S. , Lomba E. , Stell G.
Published: July 2002

We investigate various properties of Blum’s solution of the MSA for a mixture of dipolar hard spheres and equal-diameter charged hard spheres, fully rederived in a former publication. Numerical results for thermodynamic quantities, phase equilibria, and osmotic pressure are presented together with results for the ion–ion and ion–dipole correlation functions obtained via a simple integral-equation procedure. A generalization of the MSA results to a system of polarizable dipolar hard spheres and charged hard spheres is also given.
The kinetics of nucleation of adamantane crystals from the vapor
Authors: Lubetkin S. D.
Published: July 2002

Carefully purified adamantane was sublimed under controlled conditions of temperature and supersaturation onto a clean optically flat glass substrate. The nucleation which took place was found not to be entirely random in position, but rather, took place at certain sites more readily than at others. The times (τ) taken under various conditions for a crystal to appear at a particularly active site were measured. After an allowance had been made for the time taken for the crystal to grow to a visible size, the reciprocals of these times were assumed to be proportional to J, the rate of nucleation on this site. The assumption of proportionality between τ−1 and J, is justified theoretically, and the results of the kinetic measurements were compared with classical nucleation theory, which was found to provide a broadly satisfactory description of the data. When the experiments on the pure material were completed, known amounts of impurity were added, and the kinetic effects of this impurity were studied. It was found that the impurity had a much more marked effect on the kinetics of nucleation at low than at high temperatures.
Sedimentation and dispersion of Brownian particles in spatially periodic potential fields
Authors: Nitsche Johannes M. , Brenner Howard
Published: July 2002

A generalized Taylor dispersion analysis is presented of the combined diffusion and sedimentation of a Brownian particle subjected to a spatially periodic potential plus a uniform force. At long times this transport process is macroscopically characterized by a uniform mean drift velocity vector of the Brownian particle, and by a dispersion dyadic that quantifies stochastic ‘‘spreading’’ about the (traveling) mean position. A general explicit integral formula is derived for the dispersion coefficient in the one-dimensional case, which supplements known results for the mean velocity. Illustrative calculations show that, for sufficiently large values of the drift force, the dispersivity exceeds the molecular diffusivity, which characterizes dispersion in the absence of any potential barriers. These calculations also lead to the surprising conclusion that an increase in the height of the potential barriers can sometimes lead to an increase in the dispersivity. A general asymptotic analysis is developed for the limiting case where the drift force tends to infinity. Although in one dimension the dominance of the drift force over the potential leads to a spatially uniform, steady-state, periodic distribution, the same behavior does not generally obtain in higher-dimensional cases. Asymptotic expressions are derived for the mean velocity and dispersivity characterizing one-dimensional systems and a class of two-dimensional systems. The analysis is subsequently applied to the related problem of sedimentation and dispersion of a particle within a medium for which its molecular diffusivity is a periodic function of position (in the absence of any potential). Although a periodic potential and a periodic diffusivity lead to equivalent mathematical problems in the absence of a sedimentation force, the presence of drift leads to important qualitative differences.
Emission spectra and electronic structure of group IIIa monohalide cations
Authors: Glenewinkel-Meyer Th. , Kowalski A. , Müller B. , Ottinger Ch. , Breckenridge W. H.
Published: July 2002

Optical spectra of ten AX+ ions (A=B, Al, Ga, In; X=F, Cl, Br) have been observed in the visible and near UV; a total of 18 band systems were newly discovered. The emission was produced by chemiluminescent reactions A++X2 at low (2–10 eVCM) kinetic energy in a beam-gas arrangement. A position-sensitive photon counting detector with large surface area and very low dark count rate was employed, the resolution was mostly 5–50 Å FWHM. Three types of band systems were observed: (1) For all AX+ combinations except BCl+ and BBr+, a very broad quasicontinuum with undulatory structure appears. On the basis of electronic state correlation arguments, photoelectron data, some ab initio calculations and, in one case, a known emission spectrum (InCl+) these band systems were identified as B 2Σ+–X 2Σ+ transitions. It is concluded that the excited state potentials are considerably displaced against the ground state, and their energetics are given. (2) For six species AX+, narrow band systems were observed in the 2500 Å region. They could be clearly identified as being due to C 2Π–X 2Σ+ transitions by means of comparison with the systematics of the analogous A 2Π–X 2Σ+ transitions of the isoelectronic alkaline earth halides, by the resolved fine structure, and, in the case of AlF+, by an ab initio calculation. (3) In the GaCl+, GaBr+, and InBr+ spectra, narrow features accompany the C–X transitions. They are attributed to D 2Σ+–X 2Σ+ transitions, analogous to the alkaline earth halide B 2Σ+–X 2Σ+ band systems. Qualitative electronic state correlations are discussed, and the expected dominant configurations in different regions of the AX+ ground and excited states are given. These are in accord with recent ab initio results on AlF+.
Nuclear magnetic resonance determination of the CF2 order parameter tensor in a lyotropic liquid crystal
Authors: Post Jan F. M. , Simplaceanu Virgil
Published: July 2002

1 9F nuclear magnetic resonance (NMR) experiments on 8,8-F2-K-myristate/H2O (77:23, w/w) in the liquid crystalline Lα phase were carried out over the temperature range 29–70 °C. While only one Saupe order parameter is obtainable by 2H-NMR or electron spin resonance (ESR) spin–label methods, 19F-NMR line shape analysis yields the complete Saupe order parameter tensor for the CF2 segment. In contrast with the usual assumption of axial symmetry of the Saupe tensor for lyotropic lamellar liquid crystals, it appears that there is asymmetry in the motional freedom of the lipid chains. The asymmetry in the order parameters was found to be in quantitative agreement with molecular dynamics results published for a similar system.
State-resolved ultrafast internal conversion in chromyl chloride
Authors: Xie Y. J. , Kwok H. S.
Published: July 2002

The technique of infrared multiphoton ionization was used to obtain state specific internal conversion rates in CrO2 Cl2. Using tunable 10 ps dye laser pulses, different vibrational states in the B1 manifold were excited and the energy relaxation was monitored by an IR ps laser pulse. The relaxation can be characterized by a fast component, which is due to internal conversion to the 1 A1 state, and a slow component, which is due to cooling of the vibrationally hot 1 A1 ground state. The nonradiative energy transfer rate changes by almost three orders of magnitude for an excess vibrational energy change of merely 550 cm−1. The possibility of state specific pumping of 1 A1 is also pointed out.
Rotationally resolved electronic spectroscopy of tryptamine conformers in a supersonic jet
Authors: Philips Laura A. , Levy Donald H.
Published: July 2002

We have observed the high resolution fluorescence excitation spectrum of the molecule tryptamine in the gas phase. At low resolution the spectrum contains six features which have been assigned as the origins of different conformers of the tryptamine molecule. At high resolution the rotational structure in each of these features has been resolved, and the rotational structure of five of the features has been analyzed. This analysis has provided information about the geometries of the different conformers. Two conformers, labeled A and F, have the amino group of the molecule gauche to the indole ring, while conformer D has the amino group nearly eclipsed by the indole ring. Conformer B has a rotational structure identical to that of conformer A, while the rotational structure of conformer E is identical to that of conformer D. It is suggested that the pairs of conformers with identical rotational structure are related to each other by rotation about the Cα–N bond, such a rotation moving only hydrogen atoms. Feature C consists of two overlapped conformers, and it is suggested that these conformers have the amino group trans to the indole ring. The direction of the transition moment is measured for five of the conformers and is found to be identical for all conformers within the precision of the measurement. The direction of the transition moment indicates that the transition is to the 1Lb excited electronic state.
Projection methods for obtaining intramolecular energy transfer rates from classical trajectory results: Application to 1,2-difluoroethane
Authors: Raff Lionel M.
Published: July 2002

A general method for analyzing the results of classical trajectory calculations to obtain the details of intramolecular energy transfer is described. The method is based on the determination of the time dependence of the normal mode velocities by projection of the instantaneous Cartesian velocities onto the normal mode vectors. It is shown that the method obviates the need to arbitrarily define a ‘‘bond’’ or ‘‘mode’’ energy as a means of following the energy flow. Average mode energies are computed using the virial theorem. For a given potential surface, the results are exact within the framework of the classical approximation. The method is applied to a study of intramolecular energy transfer in 1,2-difluoroethane. Decay rates and pathways of energy flow for initial excitation of each of the 18 vibrational modes are reported. The results obtained from the time variation of the normal mode velocities are used to extract a first-order, mode-to-mode energy transfer rate coefficient matrix. The mode-to-mode coefficients are shown to provide an excellent means of collating the energy transfer information. Their values yield a quantitative description of the energy transfer rates and a clear picture of the relative importance of the available pathways for energy flow in the system.