bluuebunny/crossref_metadata_2025 huggingface dataset:
Fourier transform spectrum of the in-plane CH3-rocking fundamental and vibrational coupling in C-13 methanol
Authors: Predoi Adriana , Lees R. M. , Johns J. W. C.
Published: July 2002

The Fourier transform infrared spectrum of the in-plane CH3-rocking fundamental of CH313OH has been investigated at 0.002 cm−1 resolution. The rocking band is principally of parallel character and has a double-peaked Q branch and relatively wide spread subbands indicative of a substantial change in torsional barrier height. All A subbands from K=0 to 11 and all but one E subband from K=0 to 9 have been assigned in the n=0 torsional state and fitted to J(J+1) power-series expansions to obtain the subband origins and excited-state energy structure. The effects of vibrational interactions between the CH3-rocking and CO-stretching modes are prominent in the spectrum. Coriolis coupling between rocking (K−1) and CO-stretching K levels is observable for K⩾6, and makes significant contributions to the subband origins and effective B values. Several J-localized perturbations due to level-crossing resonances with CO-stretch states have been observed and characterized. Two reported strong far-infrared laser lines optically pumped by the 10R(26) CO2 laser line have been found to arise through such a ΔK=3 level-crossing resonance. Modeling of the rocking-state torsion-K-rotation energies yields a height of V3r=469.2(38) cm−1 for the torsional potential barrier, a 26% increase over the ground state. The asymmetry K-doubling pattern in the excited state is qualitatively consistent with this barrier for K=2 to 4, but the K=5 rocking substate displays strongly enhanced splitting.
Reactions of laser-ablated chromium atoms with dioxygen. Infrared spectra of CrO, OCrO, CrOO, CrO3, Cr(OO)2, Cr2O2, Cr2O3 and Cr2O4 in solid argon
Authors: Chertihin George V. , Bare William D. , Andrews Lester
Published: July 2002

Reactions of laser-ablated Cr atoms with O2 gave a very strong, sharp 965.4 cm−1 band and weak, sharp 1869.7, 984.3, 914.4, 846.3, 716.2, and 643.1 cm−1 bands. The 1869.7, 965.4, and 914.4 cm−1 bands track together on annealing, show 52Cr, 53Cr, 54Cr isotopic splittings appropriate for a single Cr atom and triplets with statistical 16,18O2 for two equivalent O atoms, and are assigned to the ν1+ν3, ν3 and ν1 modes of the bent (128°±4°) chromium dioxide OCrO molecule. The 984.3 cm−1 band shows chromium isotopic splittings for two Cr atoms and 16,18O2 components for two O atoms, and is attributed to the bent CrOCrO molecule. The weak 846.3 cm−1 band exhibits proper oxygen isotopic behavior for CrO and is redshifted 39 cm−1 from the gas-phase value, the maximum shift observed for a first row transition metal monoxide. The sharp 716.2 and 643.1 cm−1 bands track together; the former reveals Cr isotopic splittings for two Cr atoms and the latter 16,18O2 splittings for two sets of dioxygen subunits; the branched-puckered-ring dimer O(Cr2O2)O is identified. Annealing produces new bands due to CrOO, CrO3, Cr(OO)2 and the ring dimers (Cr2O2) and (Cr2O2)O, which are identified from isotopic shifts and splitting patterns.
Determination of structural parameters for the half-sandwich compounds cyclopentadienyl thallium and cyclopentadienyl indium and indium quadrupole coupling for cyclopentadienyl indium using microwave spectroscopy
Authors: Drouin B. J. , Cassak P. A. , Briggs P. M. , Kukolich S. G.
Published: July 2002

Microwave rotational transitions for J′←J=2←1 and 3←2 were measured in the 7–11 GHz range for three isotopomers of (C5H5)In. Similar transitions (up to J′←J=5←4) for eight isotopomers of (C5H5)Tl were measured in the 5–15 GHz range. The rotational constants of the most abundant isotopomers are B(Cp 203Tl)=1467.9730(11) MHz, B(Cp 205Tl) =1465.0723(14) MHz, B(Cp 113In)=1809.9785(30) MHz, and B(Cp 115In)=1800.8199(18) MHz (Cp=C5H5). The quadrupole coupling strengths for the indium compounds are eQq(Cp 113In)=−118.397(69) MHz and eQq(Cp 115In)=−119.981(31) MHz. Spectra for single-substitution C13 isotopomers were seen in natural abundance. Deuterated samples of CpTl were prepared to obtain spectra for deuterium-substituted isotopomers. Analysis of the spectra allowed the determination of the following structural parameters; for (C5H5)Tl, r(Tl–C5)=2.413(3) Å, r(C–C)=1.421(10) Å, r(C–H)=1.082(9) Å and ∠C5–H=0.9(2)° (C5 represents the planar, 5-carbon ring of C5H5), and for (C5H5)In, r(In–C5)=2.314(4) Å and r(C–C)=1.426(6) Å. A Kraitchman analysis was performed on the available isotopomers for comparison of r0 and rs values. Both structural analyses indicate that the hydrogen atoms in (C5H5)Tl are bent slightly out of the carbon plane away from the coordinated metal atom.
Extracting polarizabilities of organic molecules at their optical absorption regions from the enhanced reflection of a submonolayer of organic molecules at air-quartz interface
Authors: Xu Zhi , He Gregory , Elking Mark D.
Published: July 2002

It has been demonstrated in this paper that polarizabilities of organic molecules at their optical absorption regions can be extracted from the experimental data of the enhanced reflection for s-polarized electromagnetic radiation caused by a submonolayer of organic molecules physisorbed on quartz surface. Experiments have been carried out with Rhodamine-6G and D289 molecules. For each molecule, the polarizability increases dramatically in the wavelength region where the electronic transition takes place. For Rhodamine-6G, the polarizability is about 980 Å3 at its peak absorption wavelength 530 nm, and for D289, the value is about 392 Å3 at its peak absorption wavelength 470 nm. The perfect match between the reflection and transmission spectra of Rhodamine-6G indicates that the polarizability of a molecule at its absorptive region is proportional to its molar absorptivity.
Quantitative calculation of spontaneous polarization in ferroelectric liquid crystals
Authors: Terzis Andreas F. , Photinos Demetri J. , Samulski Edward T.
Published: July 2002

We compute the spontaneous polarization, P, exhibited by a class of ferroelectric liquid crystals (FLCs) with systematically varying structures in an effort to critically test a recently proposed model [D. J. Photinos and E. T. Samulski, Science 270, 783 (1995)] which implies that polarity is indigenous to tilted smectic phases. We evaluate the first and second rank segmental order parameters of the FLC compounds by taking into account the essential features of molec-ular structure and conformation subjected to the general stratification constraints in the model smectic FLC. The results compare favorably with available experimental values of P and bond order parameters obtained from NMR measurements.
Molecular dynamics simulations of free energy and conformational transition rates of calix[4]arene in chloroform
Authors: den Otter W. K. , Briels W. J.
Published: July 2002

In a previous article we introduced a reaction coordinate based on the unstable normal mode at the saddle point of the potential energy surface. We here calculate the free-energy distribution along this coordinate for the isomerization of calix[4]arene in vacuo and in chloroform using umbrella sampling, with one umbrella covering the entire range of the reaction coordinate. An excellent first guess at this umbrella is obtained by performing a normal-mode analysis at various points along the reaction path. The isomerization rate constant of this reaction is determined using the reactive flux method and is found to be in good agreement with experimental data. The rate was found to be independent of the location of the transition state, as it should be.
Fluorescence following electron impact on argon clusters
Authors: Kedzierski W. , McConkey J. W.
Published: July 2002

A detailed study has been made of electron impact induced fluorescence from Ar clusters. Use of suitable filters in the vacuum ultraviolet spectral region together with time-resolved techniques has enabled the dimer emission from the clusters to be investigated in detail. Excitation function measurements have revealed a number of processes leading to exciton production. Two-center collisions within the cluster appear to be significant. A close parallel to what is observed with solid Ar targets is noted.
Photoelectron imaging spectroscopy for (2+1) resonance-enhanced multiphoton ionization of atomic iodine produced from A-band photolysis of CH3I
Authors: Jung Young-Jae , Shin Kim Yong , Kyung Kang Wee , Jung Kyung-Hoon
Published: July 2002

Photoelectron imaging spectroscopy has been applied to study on two-photon resonant third photon ionization of two states of atomic iodine (5p5 P23/2 and P21/2) in the wavelength region 277–313 nm. The technique has yielded simultaneously both relative branching ratios to the four levels of I+(3P2, P30,1, D12 and S10) with 5p4 configuration and the angular distributions of outgoing photoelectrons. The product branching ratios reveal a strong propensity to populate particular levels in many cases. Several pathways have been documented for selective formation of I+(3P2), I+ (3P0,1) and I+(1D2) ions. In general, the final ion level distributions are dominated by the preservation of the ion core configuration of resonant excited state defined by the Jcl coupling scheme. Some deviations from this simple picture are discussed in terms of the configuration interaction of resonant states and the autoionization in the continuum. The photoelectron angular distributions are qualitatively similar, with a positive A2 anisotropy coefficient of 1.0–2.0 and negligible A4 in most cases, which suggests that higher-order Legendre terms are suppressed by the restriction of a maximum orbital angular momentum of ejected electron, 2.
The coil–globule transition of polymers of long rigid monomers connected by flexible spacers
Authors: Sear Richard P.
Published: July 2002

A simple model of a polymer with long rigid segments which interact via excluded volume repulsions and short ranged attractions is proposed. The coil–globule transition of this model polymer is strongly first order, the globule is crystalline and the coil which coexists with the globule is swollen. A virial expansion truncated at low order is shown to provide a very poor approximation to the free energy and so a cell theory is used to calculate the free energy of the globule.
Experimental and theoretical angular and translational energy distributions for the reaction CN+D2→DCN+D
Authors: Wang Jeng-Han , Liu Kopin , Schatz George C. , ter Horst Marc
Published: July 2002

This paper presents new measurements of angular and translational energy distributions for the title reaction at a reagent kinetic energy of 5.8 kcal/mol, and compares them with the corresponding results from quasiclassical trajectory calculations based on an accurate global potential energy surface. The comparison of theory and experiment is generally good; however, the minor deviations that we find provide valuable information concerning errors in the potential energy surface. Both experiment and theory indicate that CN+D2 is a simple abstraction reaction, with predominantly backward-scattered angular distributions and about 37% of the available energy ending up in product translation. Strong dependence of the calculated angular and translational energy distributions on reagent kinetic energy is noted.
Kinetic oscillations in the catalytic CO oxidation on Pt single crystal surfaces: Theory and simulation
Authors: Kuzovkov V. N. , Kortlüke O. , von Niessen W.
Published: July 2002

A simple lattice gas model is studied for the description of the kinetic oscillations in the CO oxidation on the Pt(100) and Pt(110) surfaces. It takes CO diffusion and surface reconstruction into account and exhibits very interesting phenomena such as synchronized oscillations and mesoscopic pattern formation. The model uses only few parameters, the CO gas phase concentration y, the CO diffusion constant D, the surface phase propagation velocity V, and the ratio of the O2 sticking coefficients on the two surface phases. This enables the study of the whole parameter regime and the theoretical stability analysis for the kinetic oscillations. It can be shown that it is only the ratio of the O2 sticking coefficients on the reconstructed and non–reconstructed surfaces which determines the type of oscillations and the parameter range where these oscillations exist.
The coupling of electron thermalization and electron attachment in CCl4/Ar and CCl4/Ne mixtures
Authors: Kowari Ken-ichi , Leung Ki , Shizgal Bernie D.
Published: July 2002

The relaxation of a nonequilibrium distribution of electrons in a mixture of CCl4 with either Ar or Ne is studied. In this paper, electron-CCl4 and electron-inert gas elastic collisions, vibrationally inelastic collisions between electrons and CCl4, as well as the electron attachment reaction with CCl4, are included in the analysis. The time dependent electron energy distribution function is determined from the Boltzmann equation and the energy relaxation times are determined. The coupling of the thermalization process and the attachment process are discussed in detail. The results from the calculations are analyzed analogous to experimental studies, and the methodology of the experimental reduction of the data is studied.
The boundary between liquidlike and solidlike behavior in magnetic resonance
Authors: Warren Warren S. , Ahn Sangdoo
Published: July 2002

Recent experimental work in two-dimensional solution NMR (nuclear magnetic resonance) has demonstrated anomalous cross-peaks and additional resonances due to dipolar couplings between distant nuclei. These spectra have been analyzed either classically, using Bloch equations which include a mean-field approximation to the demagnetizing field, or quantum mechanically, using a full density matrix picture which shows that the peaks correspond to intermolecular multiple-quantum coherences (iMQCs). Here we use a density matrix treatment to predict intensities in solution for dipolar effects conventionally seen in solids; we also explore in detail the fundamental differences between dipolar effects in solids and liquids. For example, even though polarization transfer via the dipolar Hamiltonian in solution is not possible, indirect detection with substantial signal enhancement is possible. We find that, even for high-γ nuclei such as H1 or He3, solidlike dipolar effects are quite small unless the diffusion constant is roughly one million times smaller than that of water—which means that deviations between the quantum and classical treatments are barely observable in solution NMR, and that even solid He3 has liquidlike dipolar effects in agreement with experiment. However, the dipolar correlation function has an extremely unusual functional form—the long time falloff is proportional to t−3/2, not the exponential one commonly encounters. Because of this long falloff, solidlike dipolar effects can be substantial in solution electron spin resonance, and the classical picture of the demagnetizing field would fail in that case.
Ab initio calculation for potential energy surfaces relevant to the microscopic reaction pathways for Mg(3s3p1P1)+H2→MgH(2Σ+)+H
Authors: Ou Yaw-Ren , Liu Dean-Kuo , Lin King-Chuen
Published: July 2002

Two ab initio methods have been employed to calculate the dynamical potential energy surfaces (PES’s) for the excited (B21 or A'1) and the ground (A11 or A'1) states in the Mg(3s3p1P1)–H2 reaction. The obtained PES’s information reveals that the production of MgH in the Σ+2 state, as Mg(1P1) approaches H2 in a bent configuration, involves a nonadiabatic transition. The MgH2 intermediate around the surface crossing then elicits two distinct reaction pathways. In the first one, the bent intermediate, affected by a strong anisotropy of the interaction potential, decomposes via a linear HMgH geometry. The resulting MgH is anticipated to populate in the quantum states of rotational and vibrational excitation. In contrast, the second pathway produces MgH in the low rotational and vibrational states, as a result of the intermediate decomposition along the stretching coordinate of the Mg–H elongation. These two tracks may account for the previous experimental findings for the MgH distribution, which the impulsive model has failed to comprehend. By far, different interpretations have been proposed especially for the low-N MgH product. The supply of a detailed PES’s information in this work helps to clarify the ambiguity. It is also conducive to an interpretation of the isotope and temperature effects on the product rotational distribution.
An ab initio investigation of spin-allowed and spin-forbidden pathways of the gas phase reactions of O(3P)+C2H5I
Authors: Stevens Jonathan E. , Cui Qiang , Morokuma Keiji
Published: July 2002

The singlet and triplet potential energy surfaces involved in the gas phase reactive collisions of O(3P) and C2H5I have been studied with ab initio electronic structure computations. The collisions produce both spin-forbidden HOI+C2H4 and spin-allowed OI+C2H5 products. The calculations indicate that HOI is formed via a triplet complex and through a triplet/singlet intersystem crossing, followed by passage through a singlet intermediate and transition state for the intramolecular abstraction of β-hydrogen. All the relevant structures for this pathway are lower in energy than the reactants, and this pathway is accessible even at low impact energies. The calculations also indicate that OI may be formed by two channels. One is the same to the above singlet pathway up to the singlet intermediate, which now dissociates endothermically without barrier to give the products. The second channel is the direct dissociation of the triplet intermediate, and is open only when an enough excess energy to surmount a triplet transition state is provided. The product energy distribution is also discussed based on the structures of transition states. © 1998 American Institute of Physics.
Evaluation of coherent-state path integrals in statistical mechanics by matrix multiplication
Authors: Burghardt Bernd , Eicke Joachim , Stolze Joachim
Published: July 2002

The numerical evaluation of coherent-state path-integral representations for partition functions and other quantities in equilibrium quantum statistical mechanics is discussed. Several coherent-state path-integral schemes are introduced, which differ from each other by the order of approximation and by the operator ordering employed in the high-temperature approximation of the density operator. Simple one-dimensional systems are used to test these schemes. For the harmonic oscillator, finite-dimensional approximations to the coherent-state path integral are calculated analytically and compared to each other and to the real-space path integral. For anharmonic systems, integrations must be approximated by quadrature formulas. This leads to a matrix multiplication scheme which is tested for the double-well potential. The results obtained are accurate from zero temperature way up into the high-temperature regime where quantum effects become negligible. This is a significant advantage over traditional real-space path integral schemes which break down at low temperatures.
Improved analytical investigation of the hard particle system: Two- and three-dimensional cases
Authors: Edgal U. F. , Huber D. L.
Published: July 2002

We present new results for the hard particle system (2D and 3D cases) in the low density branch of the equation of state that provide substantial improvement over results given by us in an earlier work. The well known low density limit of the equation of state allows an accurate determination of a parameter m(η), a function of the packing fraction η, which then allows an accurate computation of the equation of state at higher densities throughout the low density branch. Our approach therefore provides an extrapolation scheme in which the known behavior of the hard particle fluid in some density regime provides a “signature” via the parameter m(η) from which the fluid behavior at other densities is predictable. We note that the developments in this paper apply as well to arbitrary equilibrium systems provided “m” may be appropriately chosen as a function of density and temperature. Also, unlike most other extrapolation schemes, our approach is of a systematic nature, not involving ad hoc approximations or assertions that are not rigorously founded. Extensions of our approach to the high density branch of the equation of state, as well as computations of error bounds for our results are also discussed.
Freezing of compact random heteropolymers with correlated sequence fluctuations
Authors: Chakraborty Arup K. , Shakhnovich Eugene I. , Pande Vijay S.
Published: July 2002

Random heteropolymers (RHPs) with uncorrelated sequence fluctuations on the segmental scale can undergo a transition wherein, below a certain temperature, the thermodynamics is determined by a few dominant conformations. We study this “freezing” transition for RHPs with correlated sequence fluctuations. Specifically, we apply our theory to the case where the correlations decay with a single correlation length; a pragmatically realizable example is provided by random block copolymers. Our results show that the temperature at which freezing occurs grows with the block length of such polymers. Freezing also occurs on the scale of the correlation length, thus making experimental observation of this phenomenon (a consequence of frustration coupled with quenched disorder) more accessible. The results are rationalized on physical grounds.
Photo-induced changes in the complex index of refraction in conjugated polymer/fullerene blends
Authors: Kirk Miller E. , Lee Kwanghee , Hasharoni Kobi , Hummelen J. C. , Wudl Fred , Heeger Alan J.
Published: July 2002

We report steady-state photo-induced absorption (PIA) and photo-induced reflectance (PIR) in films of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) and poly[2,5-bis cholestanoxy-1,4 phenylene vinylene] (BCHA-PPV) blended with fullerenes. Absorption from the metastable charge-transferred state is probed by PIA; the modulated absorption spectrum causes changes in the real part of the index of refraction, Δn, which can be measured directly by PIR. The charge transfer gives rise to pronounced features in Δn, including vibrational structure in the mid-infrared, and broad spectral windows with negative Δn in the mid- and near-infrared. Our measurements over a wide spectral range (0.05 eV–1.9 eV) allow quantitative comparison of Δn obtained from PIR with that obtained from Kramers–Kronig transformation of the PIA data. We find good agreement throughout the infrared, indicating that our method for measuring Δn is useful as an analytical tool for optical characterization and for prediction of optical spectral ranges for nonlinear optical response.
Double-resonance spectroscopy of the high Rydberg states of HCO. II. Mode specificity in the dynamics of vibrational autoionization via CO stretch versus bend
Authors: Mayer Eric E. , Hedderich Hartmut G. , Grant Edward R.
Published: July 2002

We report ionization-detected absorption spectra of vibrationally autoionizing high Rydberg states of formyl radical. Steps of uv–visible double resonance with selected rovibrational levels of the 3pπ 2Π Rydberg state of HCO promote Franck–Condon vertical transitions that isolate series converging to (010) (bend) and (001) (CO stretch) excited states of HCO+. Final state energies in these spectra exceed the threshold for production of the cation ground state. Intensities and linewidths of observed resonances convey information on the dynamics of electron ejection driven by the vibronic relaxation of specific normal modes of the linear triatomic core. Many resonances in (010) and (001) autoionization spectra exhibit widths that approach the resolution of our laser. Other resonances in series converging to both limits are noticeably broadened, with linewidths that display an inverse cubic dependence on principal quantum number. Among these broader resonances, those in series that decay by relaxation of CO stretch exhibit a scaled width that is about a factor of two larger than that of the broadest resonances in series that relax via the bending fundamental. This trend mirrors to some degree one which has been seen in similar experiments on NO2. We consider these dynamics in the light of a multichannel quantum defect theory picture for the autoionization of polyatomic molecules.
Number-dependence concerns in Gibbs-ensemble Monte Carlo
Authors: Valleau John P.
Published: July 2002

The Gibbs-ensemble Monte Carlo method is a powerful tool for estimating the location of the coexistence curves of model fluids. This note points out, however, some annoying consequences of the fact that in general there may be different numbers of particles in the two phases simulated. If so, the shape of the coexistence curve may be quite unphysical; for example, there will be no critical point. We conclude that it is only with extreme care in this regard that reliable information on critical parameters or the shapes of coexistence curves may be obtained from Gibbs-ensemble computations.
The interfacial thickness of symmetric diblock copolymers: Theory and experiment
Authors: McCoy John D. , Nath Shyamal K. , Curro John G. , Saunders Randall S.
Published: July 2002

A recent application of density functional theory to the structure and thermodynamics of the ordering of symmetric, tangent hard site, diblock copolymers [S. K. Nath et al., J. Chem. Phys. 106, 1950 (1997)] predicted an interfacial thickness larger than would be expected from previous self-consistent-field studies of thread chains. Here we compare the theoretical predictions with the few experimental measurements of interfacial thickness in symmetric diblocks. It is observed that predictions of the thickness of the interface are sensitive to the details of the monomer structure included in the underlying model, and that the range of the experimental measurements is spanned by the two theoretical models.
Dynamical quenching of field-induced dissociation of H2+ in intense infrared lasers
Authors: Châteauneuf F. , Nguyen-Dang T.-T. , Ouellet N. , Atabek O.
Published: July 2002

The dynamics of dissociation of the hydrogen molecular ion H2+ in an intense infrared (IR) field is studied by a series of wave packet simulations. In these simulations, the molecular ion is assumed to be instantly prepared at the initial time by a sudden ionization of the ground-state H2 parent molecule, and a variety of frequency and intensity conditions of the laser field are considered. A new stabilization mechanism, called dynamical dissociation quenching, is found operative in the IR spectral range. In a time-resolved picture, this effect is shown to arise when a proper synchronization between the molecular motions and the laser field oscillations is ensured. In the Floquet, dressed molecule picture, the effect is related to interferences between the Floquet resonances that are excited initially by the nonadiabatic, sudden preparation of the ion. The Floquet analysis of the wave packets in this low frequency regime reveals important intersystem couplings between Floquet blocks, reflecting the highly multiphoton character of the dynamics.
Surface diffusion of K on Pd{111}: Coverage dependence of the diffusion coefficient determined with the Boltzmann–Matano method
Authors: Šnábl M. , Ondřejček M. , Cháb V. , Chvoj Z. , Stenzel W. , Conrad H. , Bradshaw A. M.
Published: July 2002

The surface diffusion of potassium on Pd{111} has been studied with photoelectron emission microscopy (PEEM) for coverages up to one monolayer. The coverage dependence of the chemical diffusion coefficient is determined by analysis of the concentration profiles obtained from the PEEM images with the Boltzmann–Matano method. The diffusion coefficient, D, decreases with increasing coverage but a local maximum is found at a coverage of Θ≈0.5 ML. The values of D at low coverages (Θ<0.3 ML) agree well with those obtained in a previous investigation for Θ≈0.12 ML. The maximum in D is interpreted in terms of an order–disorder phase transition in the adsorbed layer.
Two-photon absorption spectrum of 3-butoxycarbonylmethylurethane polydiacetylene thin films
Authors: Banfi GianPiero , Fortusini Davide , Dainesi Paolo , Grando Daniela , Sottini Stefano
Published: July 2002

We report the two-photon absorption (TPA) spectrum of a film of poly[4,6-dacadiyne-1,10-diolbis(3-butoxycarbonyl-methyl-urethane)]—commonly known as poly(3-BCMU)—in the wavelength range λ=1.6–0.7 μm. We find that the TPA coefficient of the film, which was prepared by spin coating, increases from ≈2 cm/GW at 1.45 μm to 170 cm/GW at 0.8 μm. The main features of the spectrum can be accounted for by a three-level model with a two-photon state positioned at 2.8 eV.
The quantum threshold behavior of the Na+HF reaction
Authors: Gargano R. , Crocchianti S. , Laganà A. , Parker G. A.
Published: July 2002

Full three dimensional quantum calculations of reactive properties of the Na+HF system have been performed at zero total angular momentum (J=0) to investigate the energy dependence of the reactive probability of this reaction. The effect of increasing the vibrational excitation of reactants is also discussed.
Primitive models of chemical association. IV. Polymer Percus–Yevick ideal-chain approximation for heteronuclear hard-sphere chain fluids
Authors: Kalyuzhnyi Yu. V. , Lin C.-T. , Stell G.
Published: July 2002

We continue here our series of studies in which integral-equation theory is developed and used for the monomer-monomer correlation functions in a fluid of multicomponent freely jointed hard-sphere polymers. In this study our approach is based on Wertheim’s polymer Percus–Yevick (PPY) theory supplemented by the ideal-chain approximation; it can be regarded as a simplified version of Wertheim’s four-density PPY approximation for associating fluids considered in the complete-association limit. The numerical procedure of this simplified theory is much easier than that of the original Wertheim’s four-density PPY approximation, but the degree of accuracy is reduced. The theory can also be regarded as an extension of the PPY theory for the homonuclear polymer system proposed by Chang and Sandler [J. Chem. Phys. 102, 437 (1995)]. Their work is based upon a description of a system of hard-sphere monomers that associate into a polydisperse system of chains of prescribed mean length. Our theory instead directly describes a multicomponent system of associating monomers that form monodisperse chains of prescribed length upon complete association. An analytical solution of the PPY ideal-chain approximation for the general case of a multicomponent mixture of heteronuclear hard-sphere linear chain molecules is given. Its use is illustrated by numerical results for two models of copolymer fluids, a symmetrical diblock copolymer system, and an alternating copolymer system. The comparison with Monte Carlo simulations is given to gauge the accuracy of the theory. We find for the molecules we study here that predictions of our theory for heteronuclear chain systems have the same degree of accuracy as Chang and Sandler’s theory for homonuclear chain systems.
The nuclear quadrupole moment of 133Cs: Accurate relativistic coupled cluster calculations for CsF within the point-charge model for nuclear quadrupole moments
Authors: Pernpointner Markus , Schwerdtfeger Peter , Hess Bernd A.
Published: July 2002

The nuclear quadrupole moment (NQM) of the 133 isotope of Cs is not accurately known. This is due to the fact that the electric field gradient (EFG) of Cs for the 6p1 2P3/2 excited state was only estimated from the 6p〈r−3〉 expectation value using Hartree–Slater calculations. CsF microwave data yield a very accurate nuclear quadrupole coupling constant (NQCC). We therefore decided to perform relativistic coupled cluster calculations for CsF in order to obtain a more accurate value for the Cs EFG. At the highest level of theory we obtain a NQM for the first vibrational-rotational state of −3.43(10) mb which should be more accurate than the previously estimated value of −3.7(1.6) mb or −9(4) mb.
Kinetic isolation of persistent radicals and application to polymer–polymer reactions
Authors: Karatekin Erdem , O’Shaughnessy Ben , Turro Nicholas J.
Published: July 2002

We analyze the transient kinetics of a mixture of two radicals (M and P), one of which (P) has very low, or zero self-reactivity (i.e., P is a “persistent” radical). For the case where the self-reactivity of the persistent radical is zero, we find a critical value for the initial concentration ratio r≡P0/M0, above which the persistent radicals are isolated at long reaction times after all of the M’s react. If r is below its critical value the surviving fraction of P is zero. An experiment employing virtually zero self-reactivity nitroxide radicals is proposed to test the predicted critical behavior. If the self-reactivity of the M is stronger than the cross-coupling reactivity, then the critical value of the ratio r is negative, and a finite fraction of the persistent P radicals are always isolated, regardless of the initial concentration ratio r. For the case where the self-reactivity of the persistent radicals is finite but small, we find similar behavior, except now the P radicals react with one another on a much longer time scale following their isolation. The isolation process facilitates the measurement of P–P reaction kinetics in situations where it is difficult to generate the P radicals by themselves. An experiment to measure fundamental polymer–polymer reaction kinetics in concentrated solutions or melts is proposed based on these ideas.
Electronic states of linear polyenes: High resolution spectroscopy of cis- and trans-1,3,5,7,9-decapentaene
Authors: Kohler Bryan E. , Terpougov Victor
Published: July 2002

High resolution fluorescence, one-photon excitation and two-photon excitation spectra of cis- and trans-1,3,5,7,9,-decapentaene have been measured in n-alkane matrices at 4.2 K and vibronic progressions have been analyzed. Trans-decapentaene in decane occupies a centrosymmetric site and one-photon transition occurs via mixing with a low frequency promoting vibrational mode. Cis-decapentaene can occupy two different sites in the crystal lattice of heptane with comparable probabilities. Some vibrations associated with the cis-double bond are observed in the emission spectra of cis-decapentaene. The totally symmetric double bond stretch vibration has a higher frequency in the excited 2 1Ag state (≈1790 cm−1) than in the ground 1 1Ag state (≈1600 cm−1). The appearance of another double bond vibrational band around 1530 cm−1 in the excitation spectra of trans-decapentaene may be evidence of substantial mixing of normal vibrational modes in the first excited 2 1Ag electronic state. The two-photon excitation spectra of the 1 1Ag→2 1Ag electronic transition of trans-decapentaene in n-decane and n-heptane exhibit vibronic progressions based on overtones of the totally symmetric double bond stretch vibrational mode. Five overtones of this mode are observed in the region 24 700–33 000 cm−1 and the vibronic progression appears to be nearly harmonic. No other Ag electronic states with an appreciable two-photon cross section have been observed in the region below 40 000 cm−1.
Theoretical study on the mechanism of CH4+C2H2+ reaction: Mode-enhancement effect
Authors: Cui Qiang , Liu Zhiwei , Morokuma Keiji
Published: July 2002

High level ab initio calculations have been performed to investigate the mechanism of the ion–molecule reaction of CH4+C2H2+. Except for some subtle differences, the profile for the H-abstraction channel obtained here at the G2M//B3PW91/6-311G(d,p) level is very similar to that found in a previous study at the G2//MP2/6-31G(d) level. For the complex formation channel, however, a different transition state has been located; the geometry and energetics of which are more consistent with experimental findings. Calculations of a few direct trajectories have been carried out to investigate the possible reason for the significant mode enhancement observed experimentally for the H-abstraction channel. Although none of them is reactive, a trajectory with an asymmetric C2H bend excitation exhibits a clear signature for being more reactive than those without vibrational excitation or with a symmetric bend excitation.
Generalized ballistic deposition of small buoyant particles
Authors: Csúcs G. , Ramsden J. J.
Published: July 2002

The adsorption kinetics of the protein bee venom phospholipase A2 to a smooth, planar metal oxide surface has been measured under controlled hydrodynamic conditions using optical waveguide lightmode spectroscopy (OWLS). Adsorption follows the generalized ballistic deposition (GBD) model, except at low bulk protein concentrations, where Langmuir kinetics are observed.
6-31G* basis set for atoms K through Zn
Authors: Rassolov Vitaly A. , Pople John A. , Ratner Mark A. , Windus Theresa L.
Published: July 2002

Medium basis sets based upon contractions of Gaussian primitives are developed for the third-row elements K through Zn. The basis functions generalize the 6-31G and 6-31G* sets commonly used for atoms up to Ar. They use six primitive Gaussians for 1s, 2s, 2p, 3s, and 3p orbitals, and a split-valence pair of three and one primitives for valence orbitals, which are 4s and 5p for atoms K and Ca, and 4s, 4p, and 3d for atoms Sc through Zn. A 6-31G* set is formed by adding a single set of Gaussian polarization functions to the 6-31G set. They are Cartesian d-functions for atoms K and Ca, and Cartesian f-functions for atoms Sc through Zn. Comparison with experimental data shows relatively good agreement with bond lengths and angles for representative vapor-phase metal complexes.
Electronic coupling matrix element for electronic excitation energy transfer: S1+S1→S2+S excited state annihilation
Authors: Harcourt Richard D. , Ghiggino Kenneth P. , Scholes Gregory D. , Steer Ronald P.
Published: July 2002

For the singlet–singlet annihilation process S1+S1→S2+S0, an expression is derived for the electronic coupling matrix element involved in electronic excitation energy transfer (EET) between two equivalent chromophores. Allowance is made for vibronic coupling to occur between the S1 and S2 states of the chromophores, for each of which the S1←S0 and S2←S0 excitations are, respectively, electric-dipole forbidden and allowed. Attention is also given to aspects of the theory for singlet–singlet (πDπ*D)(nAnA)→(πDπD)(nAπ*A) EET with vibronic coupling. The theory for S1+S1→S2+S0 is illustrated via the results of some model calculations for two C=S chromophores. For each chromophore, the calculations treat explicitly the valence-shell pπ atomic orbitals and a sulphur lone-pair atomic orbital. The results of the calculations highlight the nature of the primary contributors to the vibronic coupling component of the electronic EET matrix element, namely Coulombic-type terms. The theory also shows that a Coulombic term is the primary contributor to the vibronic coupling component for singlet–singlet (πDπ*D)(nAnA)→(πDπD)(nAπ*A) EET.
Vibrationally resolved threshold photoelectron–photoion coincidence spectra of ArKr
Authors: Morioka Y. , Tanaka T. , Yoshii H. , Hayaishi T.
Published: July 2002

Threshold photoelectron–photoion coincidence (TPEPICO) spectra of ArKr were measured between the ionization threshold and 16.0 eV by using the penetrating field technique and synchrotron radiation. The ground state (X 1/2 state) vibrational progression of ArKr+ was observed from v′=2 to 27 and the first ionization energy was estimated to be 108 703±12 cm−1 by extrapolation to v′=0. The other excited states constructed from the ground state atom and ion were also observed. The ionization energies to the A1 3/2, A2 1/2, C1 3/2, B 1/2, and C2 1/2 states from the neutral ground state were 112 274, 117 388, 126 211, 126 614, and 127 952 cm−1, respectively.
Intersystem crossing rate constants from the (0,4,1) and (1,2,1) levels of the Ã 1A2 to ã 3B1 state of SO2
Authors: Bae S. C. , Yoo H. S. , Ku J. K.
Published: July 2002

Collision-induced intersystem crossing rate constants from the (0,4,1) and (1,2,1) levels of the Ã 1A2 to ã 3B1 state and rovibronic relaxation rate constants in the Ã 1A2 state of SO2 have been studied. The laser wavelength was set at 335.86 and 334.09 nm for the (0,4,1) and (1,2,1) excitation, respectively. When a few rotational levels belonging to the (0,4,1) and (1,2,1) vibrational levels were populated by a narrow bandwidth laser, both the fluorescence from the Ã 1A2 state and the phosphorescence from the ã 3B1 state were observed from the time resolved emission spectra. The decay behavior of the fluorescence signal showed fast and slow components. The radiative lifetimes and apparent quenching rate constants obtained from the fast component analysis are 38±5 and (9.8±0.2)×10−10 for (0,4,1) excitation and 33±5 μs and (1.0±0.1)×10−9 cm3 mol−1 s−1 for (1,2,1) excitation, respectively. The effective lifetimes and quenching rate constants for the slow component are 280±100 and (1.5±0.1)×10−10 for (0,4,1) excitation and they are 220±100 μs and (1.6±0.1)×10−10 cm3 mol−1 s−1 for (1,2,1) excitation. Based on the measured rate constants, kinetic simulations of the emission profiles were done to obtain the magnitudes of intersystem crossing and rovibronic relaxation rate constants. The magnitudes of the rovibronic relaxation and the intersystem crossing rate constants are found to be in the range of 8.5–10.0×10−10 and 1.3–1.5×10−10 cm3 mol−1 s−1, respectively.
Semiclassical initial value approach for chaotic long-lived dynamics
Authors: Campolieti G. , Brumer Paul
Published: July 2002

A time-dependent initial value semiclassical propagator approach is developed and applied to the propagation of a two-dimensional quantum system whose classical counterpart is highly chaotic. The energy spectrum of a quartic oscillator, obtained from the propagated wavefunction, is shown to be accurately and simply computed by application of stationary-phase Monte Carlo integration. Chaotic trajectories are handled naturally, without giving rise to the singularities seen in other methods.
Interaction potentials for He–F− and Ne–F−
Authors: Archibong Edet F. , Hu Ching-Han , Thakkar Ajit J.
Published: July 2002

Ab initio potential energy curves for the interaction of a fluoride anion with a He atom and a Ne atom are obtained by supermolecular CCSD(T) calculations, that is, coupled cluster calculations in the space of single and double substitutions corrected noniteratively for triple substitutions. The computations include full counterpoise corrections and employ large basis sets with bond functions. The CCSD(T) potential energy curves have significantly deeper wells than their many-body perturbation theory counterparts. Fits to functional forms that reproduce the CCSD(T) points with an average absolute error less than 0.3% are reported.
The Hartree–Fock calculation of the magnetic properties of molecular solutes
Authors: Cammi R.
Published: July 2002

In this paper we set the formal bases for the calculation of the magnetic susceptibility and of the nuclear magnetic shielding tensors for molecular solutes described within the framework of the polarizable continuum model (PCM). The theory has been developed at self-consistent field (SCF) level and adapted to be used within the framework of some of the computational procedures of larger use, i.e., the gauge invariant atomic orbital method (GIAO) and the continuous set gauge transformation method (CSGT). The numerical results relative to the magnetizabilities and chemical shielding of acetonitrile and nitrometane in various solvents computed with the PCM-CSGT method are also presented.
Theory of ion solvation dynamics in mixed dipolar solvents
Authors: Yoshimori Akira , Day Tyler J. F. , Patey G. N.
Published: July 2002

Time dependent density functional theory in its “extended linear” or “surrogate” form is used to investigate the dynamics of selective ion solvation in binary dipolar solvents. It is shown that simple analytical approximations that trap the basic physics of the solvation process can be obtained. In particular, it is found that the relaxation of the solvent number densities about a charged solute is governed by two distinct modes clearly associated with electrostriction and redistribution processes. This is consistent with the physical picture suggested by molecular dynamics (MD) simulations. The solvent polarization relaxation is also dominated by two modes associated with the two rotational diffusion constants of the binary solvent. In addition to the analytical approximations, full numerical solutions of the extended linear theory are obtained and the dependence of the relaxation on solvent density and solute charge is discussed. Detailed comparisons of the theory with MD simulations for a closely related model indicate that the theory is qualitatively correct, but quantitatively poor generally predicting relaxation rates which are too fast. This is due mainly to the neglect of inertial or non-Markovian effects in the theoretical approach.
Microscopic analysis of the coarsening of an interface in the spinodal decomposition of a binary fluid
Authors: Kumaran V.
Published: July 2002

The coarsening of a random interface in a fluid of surface tension γ and viscosity μ is analyzed using a curvature distribution function A(Km,Kg,t) which gives the distribution of the mean curvature Km and Gaussian curvature Kg on the interface. There is a variation in the area distribution function due to the rate of change of Km, Kg and the compression of the interface due to tangential motion. The rates of change of mean and Gaussian curvature at a point are related to the rate of change of the normal velocity in the tangential directions along the interface. The fluid velocity is governed by the Stokes equation for a viscous flow, and the velocity field at a point is determined as an integral of the product of the Oseen tensor and the normal force at other points on the interface. Using a general form for this integral, it is shown that there is a characteristic variable K*=Kg/(Km2−4Kg)1/2 which is independent of time even as Km and Kg decrease proportional to t−1 and t−2, respectively. In the late stages, analytical forms for the distribution function are determined in the limit Km≪K* using a similarity variable η=(γKmt/μ). Two reasonable approximations are used for the characteristic length for the correlation of the curvature and normal along the interface, and the results for these two approximations are quadratic polynomials in |η| which are nonzero for a finite interval about η=0. It is expected that the actual distribution function is in between these two limiting cases.