bluuebunny/crossref_metadata_2025 huggingface dataset:
A quantitative technique for revealing the usefulness of experimental data in refining a potential surface
Authors: Lazarides A. A. , Rabitz H. , McCourt F. R. W.
Published: July 2002

A singular value decomposition is used to determine how much and what kind of information about a potential surface is obtainable from a given set of measurements. From the functional sensitivities which relate a set of observable cross sections to the potential, an orthogonal set of potential variations is produced which provides a basis set for describing errors in the potential model. Corresponding to each basis function is an image vector representing a linear combination of cross sections which is the observable response to that particular correlated potential variation. The inclusion of realistic models of measurement uncertainties and potential model uncertainties in the analysis makes possible the division of the potential variation space spanned by the potential variation basis into (i) a subspace of measurable model errors and (ii) a complementary subspace of model errors which the proposed measurements will be unable to estimate. The analysis procedure may be used to assess the value of proposed measurements for inversion, and the technique is compatible with an allied inversion method under development. The method is illustrated for the He–H2 rigid rotor system using as observables a candidate set of generalized cross sections which could be obtained from measurements of viscosity and thermal conductivity in the presence and absence of a magnetic field. The set of observables considered here is found to be capable of providing five distinguishable pieces of information, primarily about the repulsive potential wall and its anisotropy. Field effect measurements of the quality now available are thus shown to offer a means for refining existing models of the anisotropy of the rare-gas-diatom interaction.
New anionic states of the lithium trimer
Authors: Gutowski Maciej , Simons Jack
Published: July 2002

Anionic states of Li3 were studied theoretically using a full-valence complete active space (CAS) self-consistent field (SCF) approach to explore their potential energy surfaces followed by quadratic configuration interaction with single, double, and approximate triple excitations calculations to more accurately determine relative energies and electron detachment energies. In addition to the known 1Σ+g state, one triplet (3A2′) and two quintet (5A1″ and 5A2′) states were found to be relatively low lying and electronically and geometrically stable in D3h geometries. All of these states remain electronically stable in C2v and D∞h geometries. Hence, they are amenable to photoelectron spectroscopy detection. Preliminary CAS SCF results for the valence isoelectronic Na−3 are also reported.
Analysis of the absorption spectrum (1 1B
u←1 1A
g) and resonance Raman excitation profiles of trans-1,3,5-hexatriene based on ab initio molecular orbital calculations
Authors: Torii Hajime , Tasumi Mitsuo
Published: July 2002

The electronic absorption spectrum, the relative Raman intensities upon 0-0 excitation, and the resonance Raman excitation profiles of trans-1,3,5-hexatriene in the region of the 1 1Bu←1 1Ag transition are analyzed on the basis of the structures and vibrational force fields obtained from ab initio molecular orbital (MO) calculations. The second-order Mo/ller–Plesset perturbation (MP2) and the configuration interaction singles (CIS) methods are employed to describe the 1 1Ag and 1 1Bu states, respectively. The vibrational force fields obtained from ab initio MO calculations are scaled in order to fit the calculated frequencies to the observed. The Duschinsky rotation among all the modes of ag symmetry is fully taken into account. Both the calculated absorption spectrum and resonance Raman intensities are in agreement with the observed. This shows the usefulness of the CIS method for estimating the structure and vibrational force field in the 1 1Bu state of trans-1,3,5-hexatriene. On this basis, some refinements are made on the structure and force field in the 1 1Bu state in order to obtain a better fit between the observed and calculated results for the absorption spectrum and resonance Raman intensities. Effects of the frequency changes and Duschinsky rotation upon the electronic excitation are significant in the resonance Raman excitation profiles of some bands. The structure and vibrational force field obtained for the ground electronic state by the simple Hartree–Fock method do not give an appropriate set of parameters for calculating the absorption spectrum and resonance Raman intensities.
A site selective luminescence excitation and Raman scattering study of Eu(CF3SO3)3-PPO; ion association and ionic exchange rate
Authors: Brodin A. , Mattsson B. , Torell L. M.
Published: July 2002

The luminescence of Eu3+ in a salt–polymer complex, poly(propylene oxide) containing Eu(CF3SO3)3 salt, was studied using broad band and site-selective excitation. Two distinctly different types of local structure around Eu3+ were detected. To investigate and compare the local structure around the SO3CF−3 anions with that around the Eu3+ cations, a Raman scattering study of the SO3 symmetric stretch vibration was performed in the same system. The vibrational data clearly reveal that also the anions are subject to two types of local environment. It is found that neither of the two states can be attributed to ‘‘free’’ (completely solvated) ions, which implies the existence of two different anion–cation configurations. Temperature and concentration dependent studies of the site-selective Eu3+ luminescence and the SO3 vibrational spectrum show that the relative amount of ions in the two states is, within the experimental accuracy, constant. However at elevated temperatures there is a rapid exchange between the two states not found at lower temperatures. The characteristic time scale for the ionic exchange is found to be closely related to the structural relaxation time of the polymer segmental mobility. The findings support the idea that ionic diffusion in salt–polymer complexes is assisted by the local polymer chain mobility which is used in models to explain polymer electrolyte performance.
Investigation of the rotational spectrum of the hydrogen-bonded dimer formed between methylenecyclopropane and HCl
Authors: Kisiel Z. , Fowler P. W. , Legon A. C.
Published: July 2002

The rotational spectrum of the hydrogen bonded dimer formed between methylenecyclopropane and hydrogen chloride has been obtained with pulsed-supersonic nozzle Fourier-transform microwave spectroscopy. Analysis of rotational constants and quadrupole coupling constants for three isotopic species of the dimer shows that HCl is attached to the C=C bond of methylenecyclopropane in a T-type configuration. The HCl monomer lies in or very near the plane that bisects the cyclopropyl ring, with the Cl atom lying 3.569 Å from the center of the C=C bond. The HCl axis is bent towards the three membered ring and there are experimental indications of a near 20° bend in the hydrogen bond. The observed dimer geometry is consistent with an electrostatic model which predicts the alternative configuration with HCl T bonded to the edge of the ring (as in cyclopropane–HCl) to be less stable when the base is methylenecyclopropane.
Microscopic theory of ion solvation dynamics in liquid methanol
Authors: Roy Srabani , Bagchi Biman
Published: July 2002

A microscopic study of the solvation dynamics of a rigid ion in liquid methanol is presented. The theory is in good agreement with the available computer simulation results. We further find that the collective and single particle dissipative kernels (that is, the memory functions) show rather similar dynamics at ultrashort times.
Site-selective fragmentation in core-excited bromo-chloro-alkanes [Br(CH2)nCl]
Authors: Schmelz H. C. , Reynaud C. , Simon M. , Nenner I.
Published: July 2002

We report strong site-selective ionic fragmentation of the core-excited bromo-chloro-alkanes [Br(CH2)nCl] (n=1,...,3), using time-of-flight mass spectrometry in the multicoincidence mode and monochromatized synchrotron radiation to excite the vicinity of the bromine 3d (65–150 eV) and chlorine 2p edge (150–220 eV), respectively. We observe strong differences between the fragmentation after excitation of the two edges, where for all three molecules the bond between the excited halogen atom and the rest of the molecule is broken preferentially. This site selectivity is discussed in terms of a fast two- and three-body fragmentation which takes place after the primary Auger decay of the core vacancy but on the same time scale as further autoionization.
Thermally induced fragmentation in an ice lattice
Authors: Sonwalkar Nishikant , Yip Sidney , Shyam Sunder S.
Published: July 2002

Molecular dynamics simulation of isobaric heating of an H2O lattice with diamond cubic structure reveals a distinct two-step sequence of hydrogen-bond breaking in a temperature range clearly below the melting point. Partial breakage, signaled by an abrupt increase in local atomic coordination and the coupling of intermolecular torsions with intramolecular angle bending, first occurs and leaves the lattice in a fragmented but still ordered state. This is then followed by full breakage at a temperature about 20–30 K higher, bringing the lattice to an orientationally disordered state characterized by a vibrational spectrum similar to that of water.
A simple method for quantitative comparisons of mode specific chemistry using stimulated Raman excitation
Authors: Ravichandran K. , Yorgancioglu Maxim , Fletcher T. Rick
Published: July 2002

Stimulated Raman excitation (SRE) of polyatomic molecules provides an efficient and general means for studies of mode specific chemistry. Here we present a simple method for quantifying the amount of vibrationally excited polyatomic molecules that can be created using SRE and demonstrate that excitation of vibrational overtones in polyatomics is also possible.
Quantum reactive scattering: Diabatic approach to the dynamics of chemical reactions
Authors: Shin Seokmin , Light John C.
Published: July 2002

We present a diabatic approach to the dynamics of electronically adiabatic chemical reactions. A method is proposed for constructing diabatic surfaces from a single adiabatic potential surface. By using diabatic surfaces we can choose natural coordinate systems for both the reactant and product arrangements. The diabatic approach can be easily adapted to exact quantum mechanical calculations based on variational scattering formulations. The square integrable basis functions are obtained by diagonalizing the total Hamiltonian matrix which is constructed from the separate eigenfunctions on the reactant and product diabatic surfaces. Applications to one-dimensional barrier problems and the collinear H+H2→H2+H reaction demonstrate the feasibility of the diabatic approach. At low total energies, reaction probabilities for adiabatic reactions can be reproduced by the present method. Moderately accurate results can be obtained at high total energies for the collinear H+H2→H2+H reaction, which may be improved by the optimal construction of diabatic surfaces.
Potential energy surface of the H+3 ground state in the neighborhood of the minimum with microhartree accuracy and vibrational frequencies derived from it
Authors: Röhse Robert , Kutzelnigg Werner , Jaquet Ralph , Klopper Wim
Published: July 2002

The potential energy surface (PES) of the H+3 ground state is computed by means of the single and double excitation configuration interaction with an explicit linear r12 term in the wave function (CISD-R12) developed recently by the present authors, with a nearly saturated basis set. The points of the PES suggested by Meyer, Botschwina, and Burton (MBB) were chosen and the fitting procedure of the same authors was followed. The present PES has both on an absolute and a relative scale (i.e., relative to the minimum) an error of a few microhartrees (μEh) in the relevant region, an accuracy that has never before been achieved in a quantum chemical calculation for a triatomic molecule. From the fit the vibrational term values for the fundamental bands and some overtones of H+3, H2D+, HD+2, and D+3 were computed by means of the TRIATOM package of Tennyson and Miller. The computed frequencies are in better agreement with experiment (maximum error ∼0.5 cm−1) than those of all previous ab initio calculations (without empirical adjustment). To achieve this accuracy, it is necessary to go beyond the Born–Oppenheimer approximation and to take care of the finite mass ratio between nuclei and electrons.
Ab initio potential and variational transition state theory rate constant for H-atom association with the diamond (111) surface
Authors: de Sainte Claire Pascal , Barbarat Philippe , Hase William L.
Published: July 2002

High-level ab initio calculations were performed to determine accurate analytic potential energy functions for interactions a gas-phase H-atom has with H-atoms attached to the diamond (111) surface and with C-atom radical sites on this surface. The nonbonded potential between the gas-phase H-atom and H-atoms attached to the surface was determined from coupled-cluster ab initio calculations, including single, double, and perturbatively applied triple excitations [CCSD(T)], with the 6-311++G(2df,p) basis set. The resulting nonbonded potential is nearly identical to that found previously from both theory and experiment for interactions between H-atoms on different hydrocarbon molecules. In the ab initio calculations, a C-atom radical site on the diamond surface is represented by a constrained tert-butyl radical. Radial and small-displacement angular potentials for a H-atom interacting with this radical were determined from unrestricted quadratic configuration interaction calculations, with single, double and perturbatively applied triple excitations [UQCISD(T)], with the 6-31G** basis set. UQCISD(T) calculations were performed on the H+CH3→CH4 reaction system with both the 6-31G** and 6-311++G(3df,3pd) basis sets to calibrate the accuracy of the 6-31G** basis set results for the H-atom plus constrained tert-butyl radical.

The above information was used to construct an analytic potential energy function for H-atom association with a radical site on the (111) surface of diamond, which was then employed in a canonical variational transition state theory (CVTST) calculation of the association rate constant. The resulting rate constant is 1.8–2.1×1013 cm3 mol−1 s−1 for the 1000–2000 K temperature range. It is insensitive to the gas-phase H-atom/surface H-atom nonbonded potential and the potential for the diamond lattice. The H+diamond (111) CVTST rate constant is used to estimate a rate constant of 4×1013 cm3 mol−1 s−1 for H+tert-butyl association at 298 K. The UQCISD(T)/6-31G* calculations give a H—C(CH3)3 bond dissociation energy which is only 1 kcal/mol lower than the experimental value.
Remark concerning the theory of the tilting transition in expanded Langmuir monolayers
Authors: Shin Seokmin , Rice Stuart A.
Published: July 2002

We report calculations, based on the Cai–Rice theory [J. Chem. Phys. 96, 6229 (1992)], of the relative importance of chain–surface and chain–chain interactions for the occurrence of the tilting transition in expanded Langmuir monolayers. The interaction between amphiphile molecules, and that between an amphiphile molecule and the surface, are described by Lennard-Jones potentials. It is found that for a reasonable set of interaction parameters the structure of the expanded monolayer supports a collective tilt, and that the existence of a nonzero amphiphile chain–surface interaction plays an important role in determining the collective tilt. However, over much of the range of surface density of interest, an expanded monolayer with nonzero collective tilt is unstable with respect to one with zero collective tilt and a smaller separation of the molecules. The existence or nonexistence of a collective tilt in the monolayer is very sensitive to the relative magnitude of the amphiphile chain–amphiphile chain and amphiphile chain–surface interactions; only a modest increase in the latter is sufficient to drive the collective tilt in the monolayer toward 90°. Our results are in accord with the observed behavior of monolayers of perfluorinated amphiphiles and ordinary amphiphiles if the ratio of chain–surface to chain–chain interactions is allowed to vary.
Three-dimensional variable-angle nuclear magnetic resonance exchange spectroscopy without rotor axis hopping
Authors: Lee Y. K. , Emsley L. , Larsen R. G. , Schmidt-Rohr K. , Hong M. , Frydman L. , Chingas G. C. , Pines A.
Published: July 2002

Slow, large-amplitude chain motions play an important role in determining the macroscopic mechanical properties of polymers. Although such motions have been studied quantitatively by two-dimensional (2D) nuclear magnetic resonance (NMR) exchange experiments, overlapping anisotropic patterns hamper spectral analysis, and limit applications. Variable angle correlation spectroscopy (VACSY) has proven useful in resolving such problems for rapidly spinning samples by separating anisotropic spectral patterns according to isotropic chemical shifts. In a previous study [J. Am. Chem. Soc. 115, 4825 (1993)], we described a three-dimensional (3D) NMR experiment that incorporates the VACSY method and a hop of the rotor axis to correlate the isotropic chemical shifts to 2D anisotropic exchange patterns. The hop of the rotor axis, however, presents experimental difficulties and limits the range of motional rates that may be studied. We present in this paper a new 3D VACSY exchange experiment that obtains the same correlations without the need for the rotor axis hop. A series of 2D exchange spectra are recorded with the sample spinning at different rotation axis angles. Then using the scaling of the anisotropic frequency at the different angles, we construct the data onto a 3D matrix so that a Fourier transformation directly yields the desired correlations. The technique is applied to 13C exchange NMR to study the slow molecular motion of ordered isotactic polypropylene.
Stationary approaches for solving the Schrödinger equation with time-dependent Hamiltonians
Authors: Yao Guanhua , Wyatt Robert E.
Published: July 2002

Accurate and efficient computational schemes are utilized for solving the Schrödinger equation with time-dependent Hamiltonians. These schemes, based on an extended Hilbert space in which time is treated like a space coordinate, allow essentially all of the computational strategies for stationary problems to be equally applicable to explicitly time-dependent problems. In particular, variational principles, the discrete variable representation in time, the fast Fourier transform in time, the recursive residue generation method (RRGM), and the Chebyshev propagator can be employed. Some of these methods are implemented and tested for a rigid rotor interacting with various laser pulses. The fast exponential convergence with respect to the number of time grid points is illustrated, which accounts for the high accuracy of the methods (limited only by the precision of computer), a feature which is hardly achievable by other methods.
Symmetry demand in polar excited state formation of 9,9′-bianthryl in clusters with some ketones
Authors: Honma Kenji , Kajimoto Okitsugu
Published: July 2002

Laser-induced fluorescence (LIF) and dispersed fluorescence (DF) spectra have been studied for clusters of 9,9′-bianthryl (BA) with acetone, diethyl ketone, and methyl–ethyl ketone. Two different kinds of clusters have been observed in clusters containing the symmetric ketones. One shows broad LIF and DF spectra which are characteristic to the polar excited state of BA. The other shows sharp LIF bands and short lifetime which indicate the absence of the electron transfer.
A spherical top or a symmetric top? A photoacoustic titanium:sapphire ring laser spectrum of the sixth stretching vibrational overtone band system of 116SnH4
Authors: Halonen Marjo , Zhan Xiaowei
Published: July 2002

A Doppler limited high resolution photoacoustic titanium:sapphire ring laser spectrum of the sixth stretching vibrational overtone band system of monoisotopic stannane, 116SnH4, has been measured in the wave-number region 11 970–12 130 cm−1. The spectrum has been rotationally analyzed both using a spherical top and a symmetric top model. The results obtained by both approaches are compared with each other. In addition, the degree of localization of the sixth stretching vibrational overtone of stannane is compared with that of the first and second stretching vibrational overtones. No perturbations due to the bending vibrations are found, which demonstrates the suitability of stannane as a model molecule for studying vibrational localization.
Spectroscopy of a chromophore coupled to a lattice of dynamic two-level systems. I. Absorption line shape
Authors: Reilly Philip D. , Skinner J. L.
Published: July 2002

Frequency modulation of a dilute chromophore’s transition is a common mechanism of line broadening in condensed phases. In many different physical situations this frequency modulation arises from coupling of the chromophore to a collection of flipping two-level systems. In this paper we calculate the absorption line shape for such a chromophore when the two-level systems occupy the sites of a regular lattice. We consider both general and specific (dipolar) two-level system/chromophore interactions. We present both exact (numerical) and approximate (analytical) expressions for the line shape as a function of the two-level system excitation probability, p, and the flip rate. We find that when p≪1 the line shape is Lorentzian for any value of the flip rate, and that when p=1/2 the chromophore’s fluctuating frequency is described approximately by a Gaussian random process, and that therefore the seminal stochastic model of Anderson and Kubo is applicable.
Hybrid Monte Carlo simulation of polymer chains
Authors: Irbäck A.
Published: July 2002

We develop the hybrid Monte Carlo method for simulations of single off-lattice polymer chains. We discuss implementation and choice of simulation parameters in some detail. The performance of the algorithm is tested on models for homopolymers with short- or long-range self-repulsion, using chains with 16≤N≤512 monomers. Without excessive fine tuning, we find that the computational cost grows as N2+z′ with 0.64<z′<0.84. In addition, we report results for the scaling of the end-to-end distance, r1N∼Nν(ln N)−α.
Equilibrium determination of H2O desorption kinetic parameters of H2O/K/Ni(111)
Authors: Kuch W. , Schnurnberger W. , Schulze M. , Bolwin K.
Published: July 2002

Equilibrium measurements in a dynamic equilibrium of adsorption and desorption were performed to obtain coverage-dependent kinetic parameters of water desorption from K/Ni(111) with K coverages in the submonolayer regime. A H2O particle beam was employed which enabled beam fluxes up to 8×1019 m−2 s−1 while the water equilibrium coverage in the temperature range from 155 to 175 K was determined using x-ray photoelectron spectroscopy (XPS). On the clean sample water desorbs with two different sets of desorption kinetic parameters, for water coverages below 0.42 monolayers (ML) a desorption energy of (52±3) kJ/mol and a pre-exponential factor of 1016±1 s−1 were found, whereas for higher coverages values of Eγ=(38.6±0.3) kJ/mol and νγ=8×1012±0.1 s−1, characteristic for desorption from ice multilayers, were determined. The effect of preadsorbed K manifested itself in a dissociation of one H2O molecule per K atom to OH and H and in the presence of a more strongly bound molecular water species. No K induced changes of the desorption kinetics of the further adsorbed water could be observed for ΘK≤0.15 ML, and the water coverage of 0.42 monolayers, at which the icelike state is initially observed, also remains unchanged. This implies that the structure of the first layer of adsorbed water is similar for potassium precoverages lower than 0.15 ML.
Hyperfine structure of first negative system (B 2Σ+u–X 2Σ+g) of 14N+2 and 15N+2 from laser-induced fluorescence measurements
Authors: Boudjarane K. , Lacoursière J. , Larzillière M.
Published: July 2002

In this work, we present a study of the hyperfine structure of the (1,2) band of the first negative system (B 2Σ+u–X 2Σ+g) of 14N+2 and 15N+2 using laser-induced fluorescence with the fast ion beam laser spectroscopy technique. The hyperfine structure of 14N+2 and 15N+2 have been observed in 30 rotational lines (5≤N″≤19) of the (1,2) band of this system. The Fermi-contact (bF′,bF″) and dipolar (t′,t″) hyperfine parameters are given with their evolutions versus the vibrational quantum numbers. Furthermore, the hyperfine structure of 15N+2 led to the revision of the preliminary spin–rotation (γ′,γ″) constants. The hyperfine parameters for the (1,2) band in the B 2Σ+u–X 2Σ+g system have been determined for the first time.
Theoretical study of the S1↔S spectroscopy of anthracene
Authors: Gruner Daniel , Nguyen An , Brumer Paul
Published: July 2002

Dispersed fluorescence spectra for S0 to S1 vibronic transitions in anthracene are computed using the semiempirical QCFF/PI approach plus corrections resulting from fits to experimental spectral intensities. Extensive comparisons are made with the experimental jet spectra. The nature and assignment of low lying levels are clarified within the normal mode picture, whereas higher energy spectra are shown to be considerably broadened by low order anharmonic corrections.
The Ar–O2 anisotropic interaction from a global analysis of dynamical properties
Authors: Gianturco F. A. , Storozhev A.
Published: July 2002

The existing potential energy surfaces (PES) which have been previously suggested for the title system are analyzed in terms of their behavior in reproducing experimental data for some of the transport coefficients (diffusion and viscosity) and of total differential cross sections from crossed beam measurements. The insufficient anisotropy of the earliest of the surfaces is modified by carrying out a preliminary sensitivity study on the transport properties and then a further global optimization using the molecular beam data. The final potential function is found to be markedly more anisotropic in the well region and at the onset of the repulsive wall, and it is shown to reproduce very well both the existing scattering data and the available transport coefficients. The simple optimization procedure discussed here could therefore be used profitably with a broad range of van der Waals (vdW) molecular mixtures and thus allow us to improve on some initial description of their anisotropic interactions by means of direct computational comparisons with existing scattering data.
Nonlocal electrodynamics of weakly confined excitons in semiconductor nanostructures
Authors: Belleguie Loys , Mukamel Shaul
Published: July 2002

The third order nonlinear optical response of semiconductor quantum dots is calculated in the limit of weak exciton confinement. We treat exactly the nonlocal photon–exciton interaction using Green function techniques, without invoking the long wavelength approximation. This procedure provides a unified treatment of systems with arbitrary size compared with the optical wavelength. Geometric confinement gives rise to quantized polariton modes with a finite radiative lifetime. The variation of optical nonlinearities with size, and the role of local field effects are analyzed.
Rotation–vibrational states of H+3 computed using hyperspherical coordinates and harmonics
Authors: Wolniewicz L. , Hinze Juergen
Published: July 2002

The rotation–vibrational states of H+3 are calculated, using the Meyer–Botschwina–Burton interaction potential surface. The Schrödinger equation of the three particle system is expressed in hyperspherical coordinates, and the wave functions are expanded in hyperspherical harmonics. All states are computed up to a total angular momentum of J=4 and an energy of less than 10 000 cm−1. The mean difference between the calculated and experimental transition energies is less than 0.5 cm−1. We expect a numerical uncertainty of less than 0.01 cm−1 in our computed term values for the given potential surface.
Phase diagram of the hard-sphere/attractive-Yukawa system
Authors: Mederos L. , Navascués G.
Published: July 2002

A density functional approximation is used to study the phase diagram of a hard sphere-attractive Yukawa system. We pay special attention to the dependence of the liquid phase stability on the range of the attractive tail. When this is sufficiently short-ranged, the liquid phase is not present in the phase diagram. The transition to the usual behavior with a phase diagram showing vapor, liquid, and solid phases takes place for a value of the range of the attractive part which is in reasonable agreement with recent Monte Carlo simulations and theoretical results.
Optimal squeezing of vibrational wave packets in sodium dimers
Authors: Abrashkevich D. G. , Averbukh I. Sh. , Shapiro M.
Published: July 2002

We present an application of ‘‘optimal squeezing’’ theory to the design of laser pulses for generation of squeezed states of material waves (states whose localization in some variable exceeds that of the ground state) in Na2. Spatiotemporal evolution of the squeezed states during and after the laser pulse is studied. We show that the optimized laser pulses can affect squeezing via three basic scenarios whose realizations depend on the desired position of the wave packet and target squeezing times. These scenarios are alternations between momentum-space and coordinate-space squeezing, interfering collisions between wave packets, and overtaking of a slow front by a fast tail.
Exciton induced decay of krypton clusters
Authors: de Vries J. , Kamke B. , Steger H. , Hielscher A. , Holzapfel J. , Mische U. , Kamke W.
Published: July 2002

Krypton clusters are ionized and excited with synchrotron radiation in the energy range 22.0–28.5 eV. In threshold photoelectron photoion coincidence spectra (TPEPICO) resonancelike structures are observed and can be attributed to excitations of valence excitons (additional to ionization) as well as core excitons. Metastable decay is also detected and is found to be initiated by excitation of the valence levels only.
Radiative lifetimes of the a 3Σ+ metastable state of NO+
Authors: Calamai Anthony G. , Yoshino Kouichi
Published: July 2002

Radiative lifetimes for the v′=0, 1, and 2 vibrational levels of the a 3Σ+ metastable state of NO+ have been measured by counting for equal time intervals the UV photons emitted as the metastable ions decay to various ro-vibrational levels of the NO+(X 1Σ+) electronic ground state. A metastable NO+ ion population was produced inside a cylindrical radio frequency ion trap by electron bombardment of NO vapor at pressures ranging from 3.2 to 12.0×10−8 Torr. After the ions were created, the radiative decay of the a 3Σ+ population was monitored versus time by focusing a geometric-fraction of the light emitted by the decaying metastable ions onto a narrow-bandwidth (∼10 nm FWHM) interference filter in front of a photomultiplier tube operated in photon-counting mode. Several filters with differing transmittance envelopes were used during the experiment to resolve different lifetimes for the lowest, three, vibrational levels of the a 3Σ+ metastable state. Previous ‘‘indirect’’ measurements of the NO+(a 3Σ+) lifetime produced results that differed by about an order of magnitude, as have attempts to calculate the a 3Σ+ lifetime. Our experiment resolves the uncertainty associated with the radiative lifetime of the a 3Σ+ metastable state, and the improved resolution of our method, relative to previous measurements, allowed us to observe a significant vibrational-state dependence of the a 3Σ+ lifetime. Our results for the radiative lifetimes of the v′=0, 1, and 2 vibrational levels of the a 3Σ+ metastable state of NO+ are 720±70, 465−90+50, and 330−60+30 ms, respectively.
The formation, photodissociation, and bond structure of cobalt–sulfur cluster ions
Authors: Shi Yang , Zhang Nan , Gao Zhen , Kong Fanao , Zhu Qihe
Published: July 2002

The formation and photodissociation of cobalt–sulfur cluster ions (ConS+m) produced by laser ablation on a tablet of well-mixed cobalt and sulfur powder were studied with a home-built tandem time-of-flight (TOF) mass spectrometer. In the mass spectrum, there are many intense peaks of more stable cluster ions ConS+m signified as follows: n=2–5,7, m=n−1; n=6,8–11, m=n−2; n=12–13, m=n−3; n=14–16, m=n−4. The photolysis of the mass-selected cluster ions was performed with a 248 nm excimer laser. The dissociation patterns support the above composition results. Previous theories about clusters do not explain the experimental results. A relationship between the electron number and orbital number of more stable clusters was recognized. Ab initio calculations were performed on two small cluster ions to determine stable geometries.
Non-Arrhenius behavior in the initial rate of a catalytic-surface reaction: Theory and Monte Carlo simulation
Authors: Fichthorn Kristen A. , Balan Prakash G.
Published: July 2002

We have identified the factors contributing to the compensation effect in the initial rate of a bimolecular surface reaction, the kinetics of which are influenced by adsorbate lateral interactions. A simple theory, based on the quasichemical approximation, can predict the temperature ranges over which compensation is the most pronounced in Monte Carlo simulations of the initial rate. Both the simulations and the theory reveal an interesting phenomenon—apparent negative activation energies, which occur when the activation energy for reaction increases with increasing temperature faster than kBT. This phenomenon could contribute to experimentally observed decreases seen in the rate of the CO oxidation reaction on several single-crystal metal surfaces.
Threshold photoelectron spectrum of HOBr
Authors: Ruscic B. , Berkowitz J.
Published: July 2002

The threshold photoelectron spectrum (TPES) of HOBr has been obtained in the wavelength regions corresponding to the first and second ionization bands. The adiabatic ionization potential (IP) is 10.642±0.005 eV; the O–Br stretching frequency in this X 2A″ state is found to be 730±20 cm−1. The adiabatic IP for the first excited state (A 2A′) of HOBr+ is 11.448±0.005 eV. The latter value confirms an earlier, tentative conclusion based on the interpretation of autoionizing structure in the photoionization mass spectrum (PIMS). There is a slight difference in the TPES and PIMS values of the first adiabatic IP, whose origin is still somewhat ambiguous.
An application of minimax analysis to robust optimal control of molecular dynamics
Authors: Zhang Hong , Rabitz Herschel
Published: July 2002

Recent theoretical research has shown that a molecule can be manipulated and controlled by an optical field designed through optimal control theory. In practice, a number of disturbances/uncertainties arise, e.g., in the laboratory generated control field, in the molecular Hamiltonian, or in the interaction term (i.e., the dipole moment). It is, therefore, important to design an optimal control field which is robust to such disturbances. In this paper, we apply minimax analysis to design optimal control fields in the presence of disturbances having finite magnitude. The minimax analysis seeks the best control field in the presence of the worst disturbance of bounded magnitude, thus, the minimax solution gives a conservative estimate of the extent to which a physical objective can be achieved under the possed disturbances. As an example, we consider a diatomic molecule modeled as a Morse oscillator. The control objective is to achieve either selective excitation of a particular energy state or to transform an initial wave packet to an arbitrary nonstationary wave packet, in the presence of the three aforementioned disturbances. For the former objective, the results for the bounded worst disturbances and robust optimal control fields are similar to that of previous perturbation calculations. For the second objective, however, the results significantly differ from analogous perturbation calculations. Under certain severe conditions useful minimax solutions may be difficult to find or simply do not exist.
Initial state-selected reaction probabilities for OH+H2→H+H2O and photodetachment intensities for HOH−2
Authors: Thompson Ward H. , Miller William H.
Published: July 2002

We have used a discrete variable representation (DVR) with absorbing boundary conditions (ABC) to calculate initial state-selected reaction probabilities and photodetachment intensities. We apply this method to the OH+H2 reaction constrained to a plane with the OH bond frozen. The calculated reaction probabilities have all the qualitative features observed in full dimensional calculations. We have similarly computed arrangement-selected photodetachment intensities for one geometry of the HOH−2 anion. The resulting spectrum has a dominant peak which will present a test of the neutral potential energy surface upon comparison with experimental results.
Electron spin polarization in radical pair recombination in micelles. Cage and supercage models
Authors: Shushin A. I.
Published: July 2002

Characteristic features of chemically induced dynamic electron polarization (CIDEP) in radical pair (RP) recombination in micelles are analyzed theoretically. The confinement effect of micelles is modeled by the spherical stepwise potential well for the radicals. The accurate and rigorous analytical expression for the multiplet CIDEP at long times is derived by solution of the stochastic Liouville equation (SLE) for the RP spin density matrix. It is shown that in the limits of weak and strong hyperfine interactions in the radicals, the rigorous analytical results can be interpreted within the simple exponential models which are called the cage and supercage models, respectively. These models enable us to reduce the complicated SLE describing diffusive motion of radicals within the potential well to the Bloch-type equations. The cage and supercage models are applied to the analysis of the CIDEP generation kinetics and the electron-spin resonance (ESR) line shape of spin correlated RPs in micelles. The models make it possible to predict simple relations of characteristic parameters of kinetics and the line shape with the parameters of the general problem: diffusion coefficients, the size and depth of the potential well, etc.
A mean radius for the first coordination shell in lanthanides
Authors: Carlos L. D. , Videira A. L. L.
Published: July 2002

A mean radius R̄ for the first coordination shell of lanthanides in solids is defined in terms of Morrison’s local polarizability model, substituting the shifts of the Slater and spin–orbit parameters by their observed phenomenological values. The results obtained agree within 10% with the measured ion-nearest neighbors’ distances in rare-earth compounds. We used our definition of a mean radius to predict the average Eu3+-nearest ligand’s distance in new luminescent polymer electrolytes. The values found for different concentrations of Eu3+ (2.3–2.7 Å) are compatible with known data for europium.
ArnH2O (n=1–14) van der Waals clusters: Size evolution of equilibrium structures
Authors: Liu Suyan , Bačić Zlatko , Moskowitz Jules W. , Schmidt Kevin E.
Published: July 2002

Size evolution of the equilibrium structures of ArnH2O van der Waals clusters with n=1–14 has been investigated. Pairwise additive intermolecular potential energy surfaces (IPESs) for ArnH2O clusters were constructed from the spectroscopically accurate Ar–Ar and anisotropic 3D Ar–H2O potentials. For each cluster size considered, we determined the global minimum of the respective IPES and several other lowest-lying ArnH2O isomeric structures. This was accomplished by using simulated annealing followed by a direct minimization scheme. The minimum-energy structures of all ArnH2O clusters considered in this work are fully solvated; up to n=12, the Ar atoms fill a monolayer around H2O. For n=12, the optimal Ar12H2O structure has the Ar atoms arranged in a highly symmetrical icosahedron, with H2O in its center. The icosahedral Ar12H2O structure is exceptionally stable; the energy gap separating it from the next higher n=12 isomer (289.55 cm−1) exceeds that for any other cluster in this size range. The observed preference for solvated ArnH2O structures was carefully analyzed in terms of the relative energetic contributions from Ar–Ar and Ar–H2O interactions. For n≤9, the monolayer, cagelike geometries are favored primarily by providing optimal Ar–H2O interactions, significantly larger than for alternative ArnH2O structures. For n≳9, the solvated ArnH2O isomers offer the best Ar–Ar packing, in addition to the strongest total Ar–H2O interactions. A detailed comparison was made with the minimum-energy structures of ArnHF clusters, determined by us recently [J. Chem. Phys. 100, 7166 (1994)], revealing interesting differences in the growth patterns of the optimal cluster structures.
Calculations of magnetic properties. V. Electron-correlated hypermagnetizabilities (Cotton–Mouton effect) for H2, N2, HF, and CO
Authors: Cybulski Sl/awomir M. , Bishop David M.
Published: July 2002

Calculations of the hypermagnetizabilities (η) at the self-consistent-field (SCF) and second-order Mo/ller–Plesset perturbation theory (MP2) levels of theory are reported for H2, N2, HF, and CO. Electron correlation is found to be unimportant for H2, but very important for the other three molecules. The individual components of η are more affected by correlation effects than the hypermagnetizability anisotropy (Δη) which mediates the birefringence of a material in the presence of a magnetic field (the Cotton–Mouton effect). The zero-point-vibrational averaging, pure vibrational corrections, and frequency dependence are important for the individual components, but are less important for Δη due to cancellation between the various contributions. Excellent agreement is found with the previous theoretical results for H2, but only fair agreement with the experimental results for N2 and CO.
Multiphoton ionization spectroscopy of hydrogen iodide
Authors: Wright Scott A. , McDonald J. Douglas
Published: July 2002

The spectroscopy of hydrogen iodide Rydberg states is investigated by resonantly enhanced multiphoton ionization (REMPI), utilizing time-of-flight mass spectrometry for detection. A (2+1) REMPI excitation mechanism provides access to electronic states in the region 64 641–71 352 cm−1. Two-photon selection rules allow the observation of transitions forbidden in the HI absorption experiments. Many of the assigned Rydberg states contain underlying, unassigned structure with anomalous intensity fluctuations and apparent breaking off of branches. Additionally, we observe autoionized levels, most likely accessed by either a (3+1) or a direct four-photon excitation. Molecular constants are calculated for all HI bands observed. Also included is the first REMPI study of iodine atoms coming from photolyzed HI precursor.
Vibration–rotation–tunneling spectroscopy of Ar–NH3
Authors: Schmuttenmaer C. A. , Loeser J. G. , Saykally R. J.
Published: July 2002

Eight new intermolecular vibrational states of Ar–NH3 have been observed by tunable far infrared laser vibration–rotation–tunneling spectroscopy (FIRVRTS) between 28 and 45 cm−1. These states provide a detailed measure of the angular-radial coupling in the intermolecular potential energy surface (IPS) and permit the dependence of the IPS on rotation about the NH3 symmetry axis to be quantitatively assessed for the first time. The determination of a complete three-dimensional IPS for the complex is described in the accompanying paper.
Kinetic-energy release in the dissociation of CO2+
Authors: Masuoka Toshio
Published: July 2002

The kinetic-energy release distributions of the fragment ions (C+ and O+) produced in dissociative double photoionization of carbon monoxide have been determined by analyzing the photoion–photoion coincidence (PIPICO) spectra measured in the region hν=39–100 eV by use of a time-of-flight (TOF) mass spectrometer and synchrotron radiation. At low excitation energies (39–46.5 eV), low kinetic-energy components were observed, which cannot be explained by a simple framework whereby a doubly charged molecular ion is directly produced on single photon absorption which then dissociates into two ionic fragments. The majority of the ion pairs are produced through indirect processes in which highly excited CO*+ and CO** (double Rydberg) converging to the high-lying CO2+ electronic states autoionize before and after dissociation.
Laser-induced fluorescence detection of ClO radicals at 167–180 nm
Authors: Matsumi Yutaka , Shamsuddin Sayed Mohammed , Kawasaki Masahiro
Published: July 2002

ClO radicals are detected by a laser-induced fluorescence technique, using the C 2Σ–X 2Π transition with a tunable vacuum ultraviolet laser system. Predissociation in the C 2Σ state is discussed in terms of the fluorescence lifetime and excitation spectra. The vibrational distribution of ClO produced by the reaction between O1D and HCl is measured.
Stratification-induced order–disorder phase transitions in molecularly thin confined films
Authors: Schoen Martin , Diestler Dennis J. , Cushman John H.
Published: July 2002

By means of grand canonical ensemble Monte Carlo simulations of a monatomic film confined between unstructured (i.e., molecularly smooth) rigidly fixed solid surfaces (i.e., walls), we investigate the mechanism of molecular stratification, i.e., the tendency of atoms to arrange themselves in layers parallel with the walls. Stratification is accompanied by a heretofore unnoticed order–disorder phase transition manifested as a maximum in density fluctuations at the transition point. The transition involves phases with different transverse packing characteristics, although the number of layers accommodated between the walls remains unchanged during the transition, which occurs periodically as the film thickens. However, with increasing thickness, an increasingly smaller proportion of the film is structurally affected by the transition. Thus, the associated maximum in density fluctuations diminishes rapidly with film thickness.
Counterpropagating pulsed molecular beam scattering of NH3–Ar. II. State resolved differential cross sections
Authors: Meyer Henning
Published: July 2002

State resolved differential cross sections (DCSs) for the rotational excitation of NH3 in collisions with Ar for various final states at a collision energy of 158 meV have been determined in a counterpropagating pulsed molecular beam scattering experiment. Simultaneous state and velocity specific detection of scattered products is achieved through resonance enhanced multiphoton ionization with subsequent ion time-of-flight analysis. The supersonic expansion ensures the preparation of well-defined initial states in both nuclear spin modifications. While measured DCSs for para-NH3 are parity averaged, state resolved cross sections could be determined for ortho-NH3. All DCSs are dominated by small or intermediate angle scattering, indicating the importance of the anisotropy in the long range part of the potential surface. The maxima in the DCSs are shifted towards larger scattering angles with increasing energy transfer, a behavior characteristic of a rotational rainbow. Excitation probabilities to states which are forbidden in the centrifugal sudden approximation are characterized by a significant decrease in intensity in the backward direction as well as a steeper exponential fall off at small angles.
Single hop diffusion of CO from bridge to top sites on Pt(111)
Authors: Nekrylova J. V. , Harrison I.
Published: July 2002

The isothermal kinetics of single hop diffusion of CO from bridge sites to top sites of Pt(111) have been examined by reflection absorption infrared spectroscopy over the temperature range from 37–42 K.