bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrafast nonexponential dynamics in a polymer glass forming liquid
Authors: Sengupta Abhijit , Fayer M. D.
Published: July 2002

The orientational dynamics of phenyl side groups in poly(methylphenylsiloxane) (PMPS) melts are examined over a broad range of viscosity/temperature (η/T) using subpicosecond transient grating optical Kerr effect (TGOKE) measurements. Measurements on poly(dimethylsiloxane) are also reported. Following ultrafast (hundreds) of fs librational dynamics, the phenyl side group orientational dynamics occur over a range of times from 2 ps to a few hundred ps. The experiments were performed from 25 to 143 °C, resulting in η/T changing by a factor of 40. In spite of the large change in η/T, the side group dynamics remain unchanged throughout the entire temperature range. Comparison of the dynamics of PMPS in the melt and PMPS in dilute CCl4 solution shows that chain–chain interactions influence the phenyl side group dynamics in the melt. The dynamics are described as local orientational relaxation of phenyl groups in the microenvironments defined by the backbone geometry and side group steric interactions rather than rotational diffusion. The dynamics exhibit power-law behavior, t−α, over two decades of signal decay. Two possible physical processes that can give rise to a power-law decay are discussed. The relationship of the observed dynamics to the β and α relaxations of glass forming liquids is also discussed.
Generation of pseudopotentials from correlated wave functions
Authors: Acioli Paulo H. , Ceperley David M.
Published: July 2002

The density matrix, or equivalently the natural orbitals play an essential role in determining the transferability of pseudopotentials to all orders of perturbation theory. In this work the one-particle density matrix and natural orbitals of Li, C, and Ne atoms are obtained using variational and diffusion Monte Carlo. Using these a pseudopotential is computed for the lithium atom.
On the performance of correlation consistent basis sets for the calculation of total atomization energies, geometries, and harmonic frequencies
Authors: Martin Jan M. L.
Published: July 2002

The total atomization energies (∑De values), geometries, and harmonic frequencies for a number of experimentally well-described molecules have been calculated at the CCSD(T) (coupled cluster) level using Dunning’s correlation-consistent cc-pVDZ([3s2p1d]), cc-pVTZ([4s3p2d1f]), and cc-pVQZ([5s4p3d2f1g]) basis sets. Additivity correction are proposed for binding energies and geometries. Using a three-term additive correction of the form proposed by Martin [J. Chem. Phys. 97, 5012 (1992)] mean absolute errors in ∑De are 0.46 kcal/mol for the cc-pVQZ, 0.93 for the cc-pVTZ, and 2.59 for the c-pVDZ basis sets. The latter figure implies that, although unsuitable for quantitatively accurate work, three-term corrected CCSD(T)/cc-pVDZ binding energies can still be used for a rough estimate when the cost of larger basis set calculations would be prohibitive. CCSD(T)/cc-pVQZ calculations reproduce bond lengths to 0.001 Å for single bonds, and 0.003 Å for multiple bonds; remaining error is probably partly due to core–core and core–valence correlation. CCSD(T)/cc-pVTZ calculations result in additional overestimates of 0.001 Å for single, 0.003 Å for double, and 0.004 Å for triple bonds. CCSD(T)/cc-pVDZ calculations result in further overestimates of 0.01 Å for single bonds, and 0.02 Å for multiple bonds.

CCSD(T)/cc-pVDZ harmonic frequencies are in surprisingly good agreement with experiment, except for pathological cases like the umbrella mode in NH3. Both CCSD(T)/cc-pVTZ and CCSD(T)/cc-pVQZ harmonic frequencies generally agree with experiment to 10 cm−1 or better; performance of cc-pVQZ is somewhat superior on multiple bonds or the umbrella mode in NH3. Again, a source of remaining error appears to be core correlation. The use of MP2/6-31G* reference geometries in the ∑De calculation can result in fairly substantial errors in the uncorrected ∑De values for systems with cumulated multiple bonds. These errors however appear to be largely absorbed by the three-term correction. Use of CCSD(T)/cc-pVDZ reference geometries appears to have no detrimental effect on computed ∑De values and is recommended for cases where only single-point calculations in the cc-pVTZ basis set are possible.
Large-scale ab initio calculations for C3
Authors: Mladenović M. , Schmatz S. , Botschwina P.
Published: July 2002

Large-scale calculations by the single, double, and perturbative triple excitation coupled cluster [CCSD(T)] method have been carried out for C3. A linear equilibrium geometry with Re=1.2945 Å was obtained. The use of large basis sets and the inclusion of connected triple substitutions is crucial for an accurate representation of the extremely shallow bending potential. Rovibrational term energies were calculated from a three-dimensional CCSD(T) potential (basis: 177 contracted Gaussian-type orbitals) by the discrete variable representation (DVR). Compared with the best previous ab initio calculations [P. Jensen et al., J. Chem. Phys. 97, 3399 (1992)] agreement with experiment is improved by almost an order of magnitude. The errors in the wave numbers of the fundamentals are −7.7 (ν1), 0.9 (ν2), and 0.6 (ν3) cm−1, respectively.
Line shapes and forced autoionization of the 8s and 9s, v=1 Rydberg states of NO
Authors: Nussenzweig A. , Eyler E. E.
Published: July 2002

We report line shapes for several rotational levels of the 9s, v=1 state of NO, lying just above the autoionization threshold, and the 8s state, just below threshold. The 8s levels exhibit unexpectedly large Stark shifts, giving way at higher fields to multiline Stark spectra, and eventually to Lorentzian autoionizing resonances. The large low-field shifts are tentatively attributed to an unusual ‘‘field-induced deperturbation’’ process. At zero field, the 8s states have lifetimes of at least 20 ns, indicating that predissociation does not play a major role for these states.
Study of the electronic states of the benzene molecule using spin-coupled valence bond theory
Authors: da Silva Edilson Clemente , Gerratt Joseph , Cooper David L. , Raimondi Mario
Published: July 2002

The spin-coupled VB method is used to study all the singlet and triplet valence excited states, as well as the n=3,4 singlet and triplet Rydberg states of benzene below the first ionization potential at 9.25 eV. The valence excited states are classified in an obvious physical way into covalent or ionic states, from which it follows at once that covalent states are well described using the approximation of σ/π separation and a frozen σ core, whereas the error in the computed transition energies to the ionic states is much larger and these states require additional σ/π correlation for their proper description. The Rydberg states are very well-described, provided that a suitable σ core, derived from a calculation on the C6H+6 ion, is used. The numerical accuracy of the final results for the transition energies is at least the same as that given by the largest MO-CI- or CASSCF-CI-based methods reported to date. The spin-coupled VB approach has the obvious advantage in providing a compact and clear picture of the various states.
A high resolution crossed molecular beam investigation of the absolute cross sections and product rotational states for the reaction F+D2 (v
i=0; j
i=0,1)→DF(v
f;j
f)+D
Authors: Faubel M. , Rusin L. , Schlemmer S. , Sondermann F. , Tappe U. , Toennies J. P.
Published: July 2002

High resolution time of flight spectra of DF products have been measured for 12 different center-of-mass angles in the range θc.m.=114° to 180° for the reaction F+D2→DF+D at a center-of-mass collision energy of Ec.m.=82.5±2.6 meV. The resolution is sufficient to clearly resolve the different final product vibrational states and to extract rotational product distributions for each of the vibrational states. Absolute reactive cross sections for the final vibrational states vf=1, 2, 3, and 4 were determined from a careful calibration of the beam source intensities and detector sensitivity. For all final vibrational states, nearly the same large rotational surprisal values of Θ̄R=5.3 were found. From the rotational distributions, it has also been possible to estimate opacity functions for these final vf states via the method of Elsum and Gordon [J. Chem. Phys. 76, 3009 (1982)]. The angular distributions for different vf states are compared to recent infinite order sudden approximation (IOSA) and classical trajectory calculations and the general trends with angle are in good agreement. The absolute values of the differential cross sections differ by as much as a factor of 10. The overall reactive cross section is smaller by about a factor of 2 than the most recent classical trajectory calculations, but the difference is barely within the large experimental errors. These new experiments provide critical data for further improving the parameters of the potential hypersurface.
Stationary points on the S1 potential energy surface of C2H2
Authors: Stanton John F. , Huang Chang-Ming , Szalay Péter G.
Published: July 2002

Recent theoretical developments that facilitate characterization of excited-state potential energy surfaces are applied to study five stationary points on the S1 surface of C2H2. Although previous calculations have focused on the acetylenic trans and cis forms, the present research predicts that the vinylidene isomer is the global minimum on the potential surface. However, a high activation barrier calculated for rearrangement to the trans isomer suggests that S1 vinylidene is not likely to be formed via photoexcitation of ground-state acetylene. The trans and cis acetylenic forms of the S1 state are shown to interconvert along an in-plane reaction coordinate with an activation energy of ∼4000 cm−1, a value which is significantly lower than usually assumed in spectroscopic analyses.
Counterpropagating pulsed molecular beam scattering of NH3–Ar. I. State resolved integral cross sections
Authors: Meyer Henning
Published: July 2002

A new approach to molecular beam scattering is described. The method uses counterpropagating molecular beam pulses to define a scattering geometry of cylindrical symmetry while resonance enhanced multiphoton ionization is applied for the state specific product detection. The simple correlation of laboratory and center-of-mass quantities allows a straightforward determination of differential cross sections from measured ion time-of-flight distributions. In addition, the short duration of the pulses causes a delay dependence of the scattering signal which is used as an additional control parameter to define the size of the scattering volume. The method is applied to the rotational excitation of NH3 in collisions with Ar at a collision energy of 158 meV. Delay and depletion studies yield an effective mean free path of 60 cm, confirming single collision condition. While parity averaged integral cross sections are determined for the para modification of NH3, fully state resolved integral cross sections are determined for o-NH3. The general behavior of the integral cross sections for both modifications is well described by an exponential energy gap law. Deviations of individual cross sections from the scaling law confirm the propensity for inelastic collisions with Δk=3. Transitions to parity levels, which are forbidden in the centrifugal sudden approximation, show significantly less intensity.
Novel model for calculating the intermolecular part of the infrared spectrum for molecular complexes
Authors: Åstrand P.-O. , Karlström G. , Engdahl A. , Nelander B.
Published: July 2002

An approach for including the intermolecular part of the zero-point vibrational energy in the calculations of intermolecular interactions is presented. The approach is applied to the water complexes of water, ammonia, dimethyl ether, formaldehyde, formamide, acetone and formic acid adopting a model potential. Effects on structure, interaction energy and intermolecular vibration frequencies are discussed. The model is successful in predicting the experimental far infrared spectra, and provides further insights in the assignment of these spectra.
A Monte Carlo study of the dielectric constant of the restricted primitive model of electrolytes on the vapor branch of the coexistence line
Authors: Caillol J. M.
Published: July 2002

We compute the wave number dependent dielectric constant ε(k) of the restricted primitive model of electrolytes along two isochores crossing the vapor branch of the coexistence curve. It is shown that, at low k, ε(k) is given by a Debye Hückel type law and therefore that ε−1(k)→0 as k→0. We conclude that the saturated vapor is conducting and that an insulator–conductor transition is unlikely. Earlier contradictory results by ourselves [J. Chem. Phys. 100, 2161 (1994)] are easily explained as a consequence of finite size effects.
Reactive scattering using the multiconfiguration time-dependent Hartree approximation: General aspects and application to the collinear H+H2→H2+H reaction
Authors: Jäckle A. , Meyer H.-D.
Published: July 2002

The recently developed multiconfiguration time-dependent Hartree approach (MCTDH) is for the first time applied to quantum reactive scattering. State-resolved reaction probabilities for the collinear H+H2(ν=0,1)→H2(ν=0,1)+H exchange-reaction are calculated and are found to be in excellent agreement with previous results obtained by time-independent methods. To compute the reaction probabilities the initial wavepacket is propagated forward and the final wave packet backwards in time. The Fourier transform at energy E of the time-dependent overlap of both wave packets is then proportional to the S-matrix element. Complex absorbing potentials are shown to be easily implemented in the MCTDH scheme. Fixed single-particle functions are introduced which result in a decrease in computational effort. The MCTDH algorithm requires the potential energy surface to be represented in a particular form. A new scheme for representing potential energy surfaces in a MCTDH adapted form is derived. This scheme can also be used for fitting multidimensional surfaces to given data points.
The shape of the ground and lowest two excited states of H2NO
Authors: Ricca A. , Weber J. , Hanus M. , Ellinger Y.
Published: July 2002

The structure of the ground and lowest two excited states of H2NO have been determined in large scale configuration interaction calculations using a multiconfiguration self-consistent description of the molecular orbitals. These treatments are based on a systematic building of the correlation contribution which has been designed to account for the characteristics of the nitroxide group. This approach shows that the aminoxyl functional group is more than a three electron group shared by two atoms, but, in fact, a nine electron entity. Our best estimate of the geometry of the ground electronic state, obtained after second-order configuration interaction using a large basis of atomic natural orbitals, is pyramidal. However, since the potential depth between 0° and 40° is lower or of the same order of magnitude as the estimated inversion frequency, the conclusion that this molecule behaves like a planar system is totally justified. The structure of the excited (n−π*) and (π−π*) states have been determined and the transitions energies are in accordance with the experimental results on the highly substituted stable nitroxide radicals.
Ab initio potential energy surface, infrared spectrum, and second virial coefficient of the He–CO complex
Authors: Moszynski Robert , Korona Tatiana , Wormer Paul E. S. , van der Avoird Ad
Published: July 2002

Symmetry-adapted perturbation theory has been applied to compute the intermolecular potential energy surface of the He–CO complex. The interaction energy is found to be dominated by the first-order exchange contribution and the dispersion energy. The ab initio potential has a single minimum of εm=−24.895 cm−1 for the linear CO–He geometry at Rm=6.85 bohr. The computed potential energy surface has been analytically fitted and used in converged variational calculations to generate bound rovibrational states of the He–CO molecule and the infrared spectrum, which corresponds to the simultaneous excitation of vibration and internal rotation in the CO subunit within the complex. The predicted positions and intensities of lines in the infrared spectrum are in good agreement with the experimental spectrum [C.E. Chuaqui et al., J. Chem. Phys. 101, 39 (1994)]. The theoretical potential was also checked by comparison of computed excess second virial coefficients with the experimental data. The ab initio interaction virial coefficients, including quantum corrections, lie within the experimental error bars over a wide range of temperatures.
Noise-free spectrum for time-dependent calculation of eigenenergies
Authors: Dai Jiqiong , Zhang John Z. H.
Published: July 2002

We explored and studied the use of several energy spectra for numerical applications in time-dependent calculation of bound state energies. Although all three types of the spectrum we studied, Sinc, Lorentzian, and Gaussian, approach the δ-function limit in the infinite time limit, their numerical properties at finite time limit are quite different. Our analysis, supported by numerical example, shows that by using Gaussian or Lorentzian spectrum, one can eliminate all the ‘‘noises’’ (extra peaks) present in the standard Sinc spectrum based on Fourier transform of autocorrelation function. The use of these two spectra enables us to obtain unambiguously all eigenvalues as long as the corresponding eigenfunctions have overlaps, albeit small, with the initial wavepacket. These small-component eigenstates are normally buried under the spectral ‘‘noise’’ in the standard Sinc spectrum. The Gaussian spectrum offers better resolution than Lorentzian spectrum and is recommended for use in time-dependent calculation of eigenenergies.
Accurate density functional theory study of cationic magnesium clusters and Mg+–rare gas interactions
Authors: Eriksson Leif A.
Published: July 2002

The equilibrium geometries, energetics, and hyperfine coupling constants for a number of charged magnesium clusters and magnesium–rare gas complexes are investigated using gradient corrected density functional theory. In the study of matrix effects, Mg+ and Mg+2 are embedded in matrices with up to 10 neon or argon atoms. For the magnesium ion, we calculate a shift in the isotropic hyperfine coupling constant of 10 G when changing the matrix from Ne to Ar (expt. value: 10.9 G), and for Mg+2 the calculated shift is −0.5 G (expt. value=1.1 G). In the second part of the paper, several different positively charged magnesium clusters with up to six magnesium atoms are optimized, and the resulting geometries, relative energies, and hyperfine coupling constants are compared with experimental data and with previous theoretical studies. Based on the computed averaged hyperfine coupling constants, a reassignment is proposed of the experimentally observed average values (in gauss), −222.5 (Mg+), −105.4 (Mg+2), −69.5 (linear Mg+3), −55.0 (triangular Mg+3), −48.5 (Mg+4), and −34.6 (Mg+5). The corresponding calculated values are −211.6, −100.0, −65.2, −58.7, −48.3, and −33.3 G, respectively. For the hexamer ion, we predict an average hfcc of −28.5 G.
Quantum scattering calculations of energy transfer and dissociation of HCO in collisions with Ar
Authors: Pan Baiyu , Bowman Joel M.
Published: July 2002

We report a quantum scattering calculation of energy transfer and collision-induced dissociation of HCO in collisions with Ar. The HCO rotation is treated in the infinite order sudden approximation, and the HCO vibrations are treated by the coupled-channel method. Sixty L2 HCO vibrational wave functions are included in the coupled-channel basis, of which 15 correspond to bound HCO states for zero HCO angular momentum, and the remainder represent a discretized continuum, which includes ten resonances. A simple ‘‘sum-of-pairs’’ potential is used to describe the Ar–HCO interaction, and the HCO intramolecular potential is the previous Legendre polynomial fit to ab initio calculations. Vibrational state-specific and state-to-state cross sections, averaged over the orientation of Ar relative to the CO-bond axis, are calculated over a range of translational energies. Collision-induced dissociation cross sections to form H+CO from all HCO bound states are presented, and decomposed into components corresponding to dissociation via HCO resonances and dissociation via nonresonance states. The energy transfer from selected initial states is also calculated as a function of initial relative translational energy.
Evidence for nonrigid HCCN
Authors: McCarthy M. C. , Gottlieb C. A. , Cooksy A. L. , Thaddeus P.
Published: July 2002

Rotational transitions from seven low-lying vibrational states of HCCN and five low-lying vibrational states of DCCN have been detected in the frequency range from 100 to 400 GHz with a sensitive millimeter-wave spectrometer. The CCH bending states ν5±1, 2ν5±2, and 3ν5±3, and the CCN bending state ν4±1 have been assigned. In addition, transitions from three vibrational states in HCCN and one in DCCN with zero orbital angular momentum (l) were also detected. These states in all likelihood originate from the three lowest l=0 excited states, i.e., (ν4+ν5)−0, (ν4+ν5)+0, and 2ν05. Analysis of the high-accuracy millimeter-wave frequency data establishes that HCCN is not a near-rigid bent molecule and intensity measurements confirm that the CCH bending states are much lower in energy than in typical well-behaved linear molecules. The low barrier to linearity in HCCN and DCCN of ∼235 cm−1, estimated from intensity measurements and the ab initio calculations of Malmquist et al. [Theor. Chim. Acta 73, 155 (1988)], confirms that HCCN is quasilinear.
Impulsive excitation of FeCp+2 and SiMe+3 during surface-induced dissociation at organic multilayers
Authors: Burroughs John A. , Wainhaus Samuel B. , Hanley Luke
Published: July 2002

These experiments scattered 20–90 eV FeCp+2 (Cp=cyclopentadiene) and SiMe+3 ions off multilayers of propylene (C3H6), hexafluoropropylene (C3F6), and tetrachloroethylene (C2Cl4) adsorbed on Ni(111). The ion internal energies following the surface collisions were estimated from the relative fragment ion intensities. The kinetic to internal energy transfer efficiencies varied as follows: C2Cl4 (∼15%)≥C3F6 (∼14%)≳C3H6 (∼10%). The scattered ion kinetic energies were less than 10% of the incident ion energy and did not depend upon the incident ion energy or angles, but did depend upon the chemical identity of the multilayer. The experimental data was analyzed in terms of a three step model of surface-induced dissociation which was previously described to explain the scattering of Cr(CO)+6 off organic monolayers [J. A. Burroughs, S. B. Wainhaus, and L. Hanley, J. Phys. Chem. 98, 10 913 (1994)]. Impulsive excitation is the first step of this model and it semiquantitatively predicted (within a factor of 2) the experimental kinetic to internal energy transfer efficiencies. Impulsive excitation was estimated to occur within 10–35 fs of the initial ion impact. Inelastic scattering and unimolecular dissociation were the latter steps of this model. Both FeCp+2 and SiMe+3 underwent the inelastic scattering step, with the surface dissipating ∼70% of the incident ion kinetic energy. Unlike the unimolecular dissociation observed for Cr(CO)+6 scattering off organic monolayers, both FeCp+2 and SiMe+3 were crudely estimated to dissociate at the surface within 3 ps of the initial ion impact.
Gaussian-2 theory: Use of higher level correlation methods, quadratic configuration interaction geometries, and second-order Mo/ller–Plesset zero-point energies
Authors: Curtiss Larry A. , Raghavachari Krishnan , Pople John A.
Published: July 2002

The performance of Gaussian-2 theory is investigated when higher level theoretical methods are included for correlation effects, geometries, and zero-point energies. A higher level of correlation treatment is examined using Brueckner doubles [BD(T)] and coupled cluster [CCSD(T)] methods rather than quadratic configuration interaction [QCISD(T)]. The use of geometries optimized at the QCISD level rather than the second-order Mo/ller–Plesset level (MP2) and the use of scaled MP2 zero-point energies rather than scaled Hartree–Fock (HF) zero-point energies have also been examined. The set of 125 energies used for validation of G2 theory [J. Chem. Phys. 94, 7221 (1991)] is used to test out these variations of G2 theory. Inclusion of higher levels of correlation treatment has little effect except in the cases of multiply-bonded systems. In these cases better agreement is obtained in some cases and poorer agreement in others so that there is no improvement in overall performance. The use of QCISD geometries yields significantly better agreement with experiment for several cases including the ionization potentials of CS and O2, electron affinity of CN, and dissociation energies of N2, O2, CN, and SO2. This leads to a slightly better agreement with experiment overall. The MP2 zero-point energies gives no overall improvement. These methods may be useful for specific systems.
Stabilization of barium dimers on clusters: Reactions of Ba2 with Cl2 and O2 on large argon clusters
Authors: Biquard X. , Sublemontier O. , Berlande J. , Gaveau M. A. , Mestdagh J. M. , Visticot J. P.
Published: July 2002

Barium dimers have been produced and stabilized by the successive pickup of two barium atoms on large argon clusters (average size of 8000). By adding chlorine and oxygen molecules, chemiluminescent reactions of these dimers have been observed. This technique of dimer formation can be extended to higher order clusters to study reactions of cold metallic clusters.
Quantum control of multidimensional systems: Implementation within the time-dependent Hartree approximation
Authors: Messina Michael , Wilson Kent R. , Krause Jeffrey L.
Published: July 2002

The exact formulation of quantum control is now well known and sufficiently general to describe multidimensional quantum systems. The implementation of this formalism relies on the solution of the time-dependent Schrödinger equation (TDSE) of the system under study, and thus far has been limited for computational reasons to simple quantum systems of very small dimensionality. To study quantum control in larger systems, such as polyatomic molecules and condensed phases, we explore an implementation of the control formalism in which the TDSE is solved approximately using the time-dependent Hartree (TDH) approximation. We demonstrate formally that the TDH approximation greatly simplifies the implementation of control in the weak response regime for multidimensional systems. We also present numerical examples to show that the TDH approximation for the weak response case is sufficiently accurate to predict the laser fields that best drive a quantum system to a desired goal at a desired time, in systems containing more than one degree of freedom, by considering a two-dimensional quantum system and comparing the optimal fields obtained by solving the TDSE exactly to those obtained using the TDH approximation.
The dynamics of Rydberg states of molecules in the intermediate regime: The role of the vibrations
Authors: Rabani Eran , Levine R. D.
Published: July 2002

The coupling of a Rydberg electron to the vibrational motion is discussed in the intermediate regime in which the orbital period is long on the scale of the vibrational motion but is still considerably faster than the rotation of the core. Two dimensionless variables characterize the dynamics: the ratio of time scales and the action exchanged between the electron and the core, per one revolution. The classical dynamics are reduced to a map which provides a realistic approximation in the limit when the action exchanged is larger than ℏ. There are two distinguishable time regimes, that of prompt processes where the corresponding spectrum is so broad that individual Rydberg states cannot be resolved and a much slower process, where the electron revolves many times around the core before it ionizes. The overall spectrum is that of a Rydberg series, where the lines are broadened by (the delayed) vibrational autoionization superimposed on a broad background. The semiclassical dynamics is quantitatively more accurate in the typical situation when the action exchanged is comparable or smaller than ℏ. Explicit analytical expressions are obtained for the width for vibrational autoionization including for the case when resonances are possible. The presence of resonances is evident in Rydberg lines which are broader. For low Rydberg states the present approach recovers the Herzberg–Jungen approximation in the weak coupling limit.
Nonlinear continuum approach to solvation in polar liquids
Authors: Georgievskii Yuri
Published: July 2002

A novel approach which allows one to treat the nonlinear dielectric response of the solvent in a general fashion is suggested to calculate the nonequilibrium solvation free energies along the reaction coordinate. A simple continuum model of the dielectric response of the solvent is used to investigate the effects of dielectric saturation on the solvation energies and on the activation energies of electron transfer reactions. A simple expression for the solvation energy of a lone spherical solute is obtained. To calculate the solvation energy of an ion pair the noninteracting redox centers approximation is used. This approximation is valid if the donor and acceptor are far enough from each other. The obtained expressions are in good agreement with the results of numerical simulations and allow one to explain the observed deviations from the linear response theory. The activation energies of the charge separation/recombination reaction A+B⇄A++B− are calculated. It is shown that the dependence of the activation energy on the driving force of the reaction must deviate from Marcus’ formula in the strong saturation regime. General relations for the solvation free energies are derived, which are valid for most of the molecular models used in numerical simulations.
Bending of bi-gels
Authors: Zhang Xiaomin , Hu Zhibing , Li Yong
Published: July 2002

The bending of bi-gels has been studied as a function of temperature, acetone concentration, and NaCl concentration. The bi-gels consist of acrylamide on one side, and the interpenetrating polymer networks of acrylamide and N-isopropylacrylamide on the other side. The maximum bending strain achieved by the bi-gel is about 0.85. The bending mechanism of the bi-gels reported here is due to the engineered structure heterogeneity, in contrast with previous homogeneous gel bending which is induced by external gradient fields. The kinetic behavior of the bi-gel is discussed. A theoretical model is used to estimate the collective diffusion coefficient Dc of the IPN side of the bi-gels in pure water and in salt solution. The results agree with those obtained by the light-scattering method.
Fast and slow fluorescence decays in pyrazine under nanosecond excitation conditions: A resolution of the enigma
Authors: Medvedev Emile S. , Pratt David W.
Published: July 2002

We study the fluorescence decay behavior of the S1(1B3u) electronic state of pyrazine following its excitation from the ground S0(1A1g) electronic state with a few nanoseconds light pulse. Our probe of the dynamics is the time-dependent Schrödinger equation. We form superpositions of the eight strongest S1 molecular eigenstates (MEs) of pyrazine with the light pulse, and then compute the total spontaneous emission as a function of time using the known optical properties of the MEs. Both coherent and incoherent contributions to the fluorescence decay have been observed. We find that single exponential decays exist at selected frequencies in the spectrum, corresponding to exact ME resonances. However, most decays are biexponential owing to the off-resonant excitation of many nearby MEs. Even resonant excitation decays become biexponential at high power. Thus, the ‘‘enigma’’ is apparently resolved; the fast component (and its J dependence) in the nanosecond excited fluorescence decay of pyrazine has its origin in the nonlinear light scattering properties of the isolated molecule.
Experimental study of the rotational relaxation of electronically excited NH/ND(c 1Π) radicals in collisions with He and Ar
Authors: Hohmann J. , Stuhl F.
Published: July 2002

We present a comprehensive set of state-to-state rate constants for the relaxation of isolated rotational levels of NH and ND in their (c 1Π,v=0, J) states in the presence of colliding He and Ar. The rotational states were populated in pulsed photolysis experiments by excitation on single (c,v′=0, J′←a,v″=1, J″) transitions. Fluorescence spectra of the (c,v′=0→a,v″=0) transitions were recorded to determine the relative populations caused by inelastic collisions. The master equation of the relaxation processes was solved iteratively to yield single collision rate constants. Additionally, time profiles were recorded. Rate data on the 8 and 12 lowest rotational levels are furnished for NH(c) and ND(c), respectively. These data are compared with previous results on BH(A 1Π) and NH and PH in their (A 3Π) states. The rate constants for rotational energy transfer can be represented by the exponential gap law.
Observation of the spin-forbidden O(1D)+O2(X 3Σg−) channel in the 317–327 nm photolysis of ozone
Authors: Takahashi Kenshi , Kishigami Masahiro , Matsumi Yutaka , Kawasaki Masahiro , Orr-Ewing Andrew J.
Published: July 2002

The photofragment excitation spectra for O(1D) production from the 317–327 nm photolysis of ozone under supersonic free-jet and low-temperature flow conditions show structure superimposed on an underlying continuum. Doppler profiles of the nascent O(1D) photofragments confirm that the O(1D) formed by photolysis at the wavelengths of the peaks in the photofragment excitation spectrum arises from the hitherto unobserved spin-forbidden predissociation to O(1D)+O2(X 3Σg−) products.
Femtosecond investigation of charge carrier dynamics in CdSe nanocluster films
Authors: Ai Xicheng , Jin Rong , Ge Changbao , Wang Jingjing , Zou Yinghua , Zhou Xiaowen , Xiao Xurui
Published: July 2002

The charge carrier dynamics in the novel CdSe nanocluster films fabricated by a chemical deposition method was studied by the femtosecond pump–probe measurements. The intensity dependent signals can be well described by a rate equation model. The overall kinetic process is listed as follows: a rapid electron trapping (<1 ps), the Auger recombination, the recombination of electrons in the surface states (∼46 ps) and the long-lived trapped electron–hole recombination. When the cluster radius is as large as 27 nm, an induced transient absorption can be observed. We attribute the induced transient absorption to the formation of the biexcitons or the trapped-carrier-induced Stark effect.
Dynamics of dissociative scattering: Hyperthermal energy collisions of state-selected OCS+ on Ag(111)
Authors: Morris J. R. , Kim G. , Barstis T. L. O. , Mitra R. , Jacobs D. C.
Published: July 2002

The dynamics of dissociation and negative ion formation have been investigated for the hyperthermal energy scattering of state-selected OCS+(X 2Πx, υ1, υ2, υ3) on Ag(111). Experiments reveal the effect that collision energy and internal energy have on the formation of scattered ionic products. An analysis of the appearance threshold and fragment velocity distribution for each scattered product channel [S−(2P), O−(2P), and SO−(X 2Π)] suggests that three distinct fragmentation mechanisms compete. Prompt impulsive dissociation of neutralized OCS+(X 2Π), followed by electron attachment to the nascent O fragment, is responsible for O−(2P) emergence. The production of SO−(X 2Π) relies on a collisionally activated distortion of OCS, forcing the O and S atoms close together while ejecting the central carbon atom. Finally, a comparison between the scattering of state-selected OCS+(X 2Πx, υ1, υ2, υ3) and S+(4S) on Ag(111) provides strong evidence that dissociative neutralization of OCS+(X 2Πx, υ1, υ2, υ3) leads to S−(2P) fragments. A discussion of time scales for the various dissociation mechanisms is presented.
Resonance Raman study of solvent dynamics in electron transfer. II. Betaine-30 in CH3OH and CD3OD
Authors: Zong Yaping , McHale Jeanne L.
Published: July 2002

Raman excitation profiles for twelve vibrational modes of the solvatochromic dye betaine-30 have been measured in CH3OH and CD3OD solutions at wavelengths that span the S0→S1 charge transfer transition. Though the absorption spectra of the dye are the same in the protonated and deuterated forms of the solvent, Raman cross-sections for all modes were found to be generally lower in the CH3OH solution than inCD3OD. The time-dependent theory of Heller was applied to model the absorption and Raman profiles, and both mono- and bi-exponential solvent relaxation were considered in order to account for solvent induced electronic dephasing. The two models lead to different physical pictures for the relevant solvent dynamics, but in either case the amplitude of solvent dephasing is reduced in deuterated compared to protonated methanol. The effect is interpreted in terms of stronger solvent–solute and solvent–solvent hydrogen bonding in deuterated methanol solution. Comparing to previous results for betaine-30 Raman cross-sections in acetonitrile [Y. Zong and J. L. McHale, J. Chem. Phys. 106, 4963 (1997)], it is concluded that slower solvent dynamics and perturbations to the electronic structure of betaine-30 lead to larger Raman intensities in methanol. The data suggest that solvent dynamics depend strongly on the electronic state of betaine-30.
Quantum state-resolved dynamics study for the reaction O(1D)+H2→OH+H(J=0)
Authors: Dai Jiqiong
Published: July 2002

This paper presents an exact quantum state-to-state dynamics calculation for the prototype insertion reaction O(1D)+H2→OH+H with the total angular momentum J=0. By extending the Peng et al. previous study of total reaction probabilities [Chem. Phys. Lett. 248, 37 (1996)], the state-to-state reaction probabilities from the initial ground rovibrational state (v=j=0) have been obtained for 500 evenly spaced energy points covering the total energy from 0.3 to 0.8 eV. An individual state-to-state reaction probability is heavily oscillatory as a function of the collision energy, while the total reaction probability remains flat in the high-energy region, which implies that the reaction is predominantly direct. In the low-energy region, several possible resonance energies have been identified and compared to the reduced-dimension counterpart. The product-state distribution clearly demonstrates an inverted rotational distribution in which highly excited rotational states are excessively populated. The vibrational distribution is also in good agreement with the three-dimensional trajectory calculations as well as the reduced-dimension calculation.
Many-body perturbation theory for quasiparticle energies
Authors: Sun Jun-Qiang , Bartlett Rodney J.
Published: July 2002

Quasiparticle energies are defined as ionization potentials (IP) for occupied orbitals and as electron affinities (EA) for unoccupied orbitals. They correspond to band energies in extended systems. As many-body perturbation theory (MBPT) readily provides energies of any order, we extend the theory to give any order corrections to IPs and EAs for finite and infinite systems, which permits a direct evaluation of correlation corrections. The diagrams for IPs and EAs can be classified into two types. The first type are linked diagrams which can be further separated into two sets. One set consists of the diagrams having one and only one bubble with a fixed index. They mainly account for orbital relaxation effects that are shown to have a finite contribution in infinite periodic systems. The other diagrams are derived from the diagrams for the total energy. In each of those diagrams, there is one and only one line with a fixed index. The second type of diagrams are the diagrams which have two or more lines with fixed indices. Because of mutual cancellations among the contributions of the orbital relaxation and electron correlation, the only remaining diagrams are those which fall apart by switching any two ending vertices of the lines that have fixed indices. These diagrams can be expressed as unlinked diagrams, of which each separated part is a diagram of the first type. Since each unlinked part has one line with a fixed index, these unlinked diagrams are size intensive. The rules to interpret these diagrams are explained. The connection between the first type of diagrams for the MBPT correction and the total self-energy with the diagonal approximation for E=εp(0) in propagator or Greens function methods is explicitly established for any order.
Spectroscopy and structure of the open-shell complex O2–N2O
Authors: Qian Hai-Bo , Seccombe Dominic , Howard Brian J.
Published: July 2002

The high-resolution spectrum of O2–N2O, the first for a complex containing more than one unpaired electron, has been studied in the region of the ν3 N2O monomer vibrational band using a molecular beam diode laser absorption spectrometer. The spectrum has been completely analyzed using a newly developed effective Hamiltonian. The rotational constants are accurately determined for both ground and excited vibrational states. The equilibrium structure of the complex is planar, with a separation between the centers of the mass of two monomers of 3.423 Å. The structural angles have been experimentally determined as: either θO2=58° and θN2O=77°, or θO2=122° and θN2O=100°. The large amplitude motion of the monomers leads to the complex having an effective out-of-plane root mean square angle of φ=φ1−φ2≈23°. In addition, an interpretation of the structure of the complex is given in terms of an intermolecular potential using a model described by Muenter.
Mixed-order semiclassical dynamics in coherent state representation: The connection between phonon sidebands and guest–host dynamics
Authors: Ovchinnikov M. , Apkarian V. A.
Published: July 2002

The formalism of mixed-order semiclassical molecular dynamics in coherent state representation is developed and applied to calculations of quantum time correlation functions in extended systems. The method allows the consistent treatment of a selected number of degrees of freedom to second order in the stationary phase approximation, through the Herman and Kluk propagator, while the rest of the system is treated to zeroth order, using frozen Gaussians. The formulation is applied to calculate the absorption spectrum, of the B←X transition of Cl2 isolated in solid Ar a spectrum that shows zero-phonon lines and phonon sidebands with relative intensities that depend on the excited state vibrational level. The explicit simulation of quantum time correlation functions of the system consisting of 321 degrees of freedom, reproduces the spectrum and allows its interpretation in terms of the underlying molecular motions. Details of the dynamics of a chromophore coupled to lattice phonons are discussed.
Critical properties of the self-consistent Ornstein–Zernike approximation for three-dimensional lattice gases with varying range of interaction
Authors: Borge A. , Ho/ye J. S.
Published: July 2002

The self-consistent Ornstein–Zernike approach (SCOZA) is solved numerically, and its properties in the critical region are investigated for the lattice gas or Ising model in three dimensions. We especially investigate how critical properties depend upon the inverse range of interaction. We find effective critical indices that depend upon this range. However, the SCOZA does not fulfill scaling. Nevertheless, comparing with experimental results for fluids and magnets we find good agreement. Away from the critical point we find that SCOZA yields deviations from scaling that seem similar to experiments.
Optical-field-induced pendular states and pendular band contours in symmetric tops
Authors: Kim Wousik , Felker Peter M.
Published: July 2002

The pendular states that arise from the interaction between a polarizable symmetric top and a strong, polarized optical field are investigated. Analytical solutions to the Schrödinger equation for this situation are presented corresponding to the limit of large field-polarizability interaction. The eigenfunctions and eigenvalues obtained are used to explore the manifestations of pendular states in nonlinear Raman and electric-dipole-allowed spectroscopies—that is, pendular band contours. The theoretical expectations regarding pendular band contours are compared with direct numerical simulations of the contours and with experimental results from nonlinear Raman spectroscopy on benzene–Ar and naphthalene trimer.
Very high resolution spectroscopy of high Rydberg states of the argon atom
Authors: Merkt F. , Schmutz H.
Published: July 2002

Very high resolution spectra of high Rydberg states of the argon atom with principal quantum numbers in the range n=60–200 have been measured in double-resonance experiments using a high resolution vacuum ultraviolet laser and frequency stabilized millimeter waves. The 250 kHz resolution achieved in the double-resonance spectra enables the determination of accurate effective quantum numbers and the precise measurement of fine-structure intervals in l=0–3 Rydberg states at n values much beyond 50. The high resolution is also used to detect spectral shifts induced by small electric fields. Analysis of these spectral shifts allows the determination of stray electric fields with uncertainties of less than 1 mV/cm and their compensation to less than 1 mV/cm. The spectra of high Rydberg states are very strongly influenced by experimental conditions and the highest resolution can only be obtained when the stray electric fields are reduced to less than 1 mV/cm and the intensity of the millimeter waves are reduced to much less than 1 μW/cm2. High resolution measurements on the very high Rydberg states probed by pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectroscopy are also reported. These spectra are strongly influenced by the inhomogeneous electric field of ions and other Rydberg states located in the photoexcitation region. These fields induce a strong mixing of the optically accessible low-l Rydberg states with nonpenetrating high-l Rydberg states. These results conclusively demonstrate the important role played by ions in PFI-ZEKE spectroscopy.
Closed-shell interaction in silver and gold chlorides
Authors: Doll Klaus , Pyykkö Pekka , Stoll Hermann
Published: July 2002

Hartree–Fock and coupled-cluster calculations have been performed for cubic AgCl and for AuCl having a cubic or the observed structure with space group I41/amd. Cohesive energies and lattice constants are in excellent agreement with experiment for AgCl; for AuCl we find good agreement, and the experimental structure is correctly predicted to be lower in energy than the cubic one. Electron-correlation effects on lattice constants are very large, of up to 0.8 Å for cubic AuCl. We especially discuss the strength of the closed-shell interactions, and for the first time a quantitative analysis of the so-called “aurophilic” Au(I)–Au(I) interaction is presented in solids.