bluuebunny/crossref_metadata_2025 huggingface dataset:
Static hyperpolarizabilities and polarizabilities of linear polyynes
Authors: Maroulis George , Thakkar Ajit J.
Published: July 2002

The dipole polarizability(α) and second dipole hyperpolarizability(γ) tensors are calculated, by finite-field methods, for the ground states of butadiyne, hexatriyne, and octatetrayne. The effects of varying one-particle basis sets and molecular geometry, and the effects of including electron correlation at the fourth-order many-body perturbation theory level, are examined for butadiyne. The hyperpolarizabilities are more sensitive to geometry changes than to electron correlation. Coupled self-consistent-field calculations on hexatriyne and octatetrayne indicate that the longitudinal components αzz and γzzzz, grow as n1.5 and n3.0, respectively, and that the mean values ᾱ and γ̄ grow as n1.2 and n2, respectively, as the chain length increases in the C2nH2 series.
Electron affinities, shake-up affinities, and ionization energies of S4 isomers
Authors: von Niessen W.
Published: July 2002

Nine isomers of S4 (D∞h,D2h,D4h,D3h,D2i,C2v, C2h,C3v,Cs) have been studied with large basis sets in Green function, CASSCF, and single and multi reference CI approaches. The C2v and D2h isomers are found to be nearly equally stable with the C2v isomer 1 kcal/mol below the D2h form and the C2h isomer about 10 kcal/mol higher in energy. All isomers have an appreciable electron affinity and some have several bound negative ion states. Besides normal electron affinities they have shake-up affinities, which may also be strongly positive. The lowest ionization energies of the isomers range from 7.5 to 9 eV.
Molecular dynamics in systems with multiple time scales: Systems with stiff and soft degrees of freedom and with short and long range forces
Authors: Tuckerman Mark E. , Berne Bruce J.
Published: July 2002

When there are high and low frequency motions in systems with long and short range forces a judicious choice of reference system leads to very large accelerations in molecular dynamic (MD) simulations. Building on our previous work where we have developed reference system methods for systems with high frequency oscillators, disparate masses, or long range forces, we present a double reference system method which leads to acceleration of as much as 20 in systems consisting of 864 molecules with Lennard-Jones (12-6) forces. Much larger savings should be achieved when this method is applied to longer range forces and larger systems.
Excitation of CO2 by energy transfer from highly vibrationally excited benzene derivatives
Authors: Toselli Beatriz M. , Barker John R.
Published: July 2002

The time-resolved infrared fluorescence technique has been used to study V–V and V–T/R energy transfer to carbon dioxide from highly excited benzene, benzene-d6, toluene, and toluene-d8. The highly vibrationally excited aromatics in the electronic ground state are obtained by radiationless transitions after pumping with a KrF laser at 248 nm to the S1 excited electronic level. The V–V energy transfer from the excited parent to the asymmetric stretch mode of CO2 was measured by observing the characteristic emission of CO*2 near 4.3 μm. From these measurements, the probability per collision of formation of CO*2 was determined as a function of the internal energy in the excited aromatic. In all cases investigated, this probability is ≤0.1% at the initial excitation energy of 40 000 cm−1 and it is approximately directly proportional to the vibrational energy of the excited aromatic. The total concentration of CO*2 produced as a result of the many collisions needed to totally deactivate the excited aromatic amounted to >5% of the initial concentration of the excited aromatic and the quantitative values obtained are in excellent agreement with other work.

A simple dipole–dipole interaction model is shown to explain the observed magnitude of V–V energy transfer and it is used to predict the amount of energy transferred to the bending mode of CO2. A key feature of this model is that the states of the highly vibrationally excited polyatomic are assumed to be broadened by rapid intramolecular vibrational redistribution of energy. In addition to the V–V energy-transfer measurements, the average energy lost per collision by the excited aromatic was determined as a function of the vibrational energy of the aromatic, and the rate constants were determined for CO*2 deactivation by the nondeuterated species. For the deuterated species, the results implicated a contribution from resonant V–V transfer between the C–D stretch modes and the asymmetric stretch mode of CO2. The overall results for the CO2 collider gas indicate that V–V energy transfer contributes a relatively small portion of the total energy transfer, and that portion can be described with the dipole–dipole interactions model.
A coupled cluster study of the classical barrier height of the F+H2→FH+H reaction
Authors: Scuseria Gustavo E.
Published: July 2002

Basis sets as large as F[7s7p5d4f2g]/H[6s5p4d2f] have been used in connection with the coupled cluster method including all single, double, and perturbative triple excitations [CCSD(T)] to predict the classical barrier height of the F+H2→FH+H reaction. Employing transition state geometries optimized at the seven- and nine-electron CCSD(T) level with a [5s5p3d2f1g/4s3p2d1f] basis set, the calculated nine-electron barrier of 2.05 kcal/mol exhibits a 0.20 kcal/mol correlation contribution from the fluorine 2s electrons. Comparison with full configuration interaction (FCI) calculations in smaller basis sets for the electron affinity (EA) of fluorine, the energy of FH at stretched bond lengths, and the barrier height itself, demonstrate that the CCSD(T) method is capable of accurately reproducing the exact benchmark results. Employing large atomic natural orbital basis sets and correlating the F 2s electrons, the CCSD(T) predictions for the electron affinity (EA) of F (3.36 eV), the spectroscopic constants of FH (re=0.917 Å, ωe=4146 cm−1, and De=140.9 kcal/mol), and the exothermicity of F+H2→FH+H (31.6 kcal/mol), are in excellent agreement with the experimental values of 3.40 eV, 0.917 Å, 4138 cm−1, and 141.2 and 31.7 kcal/mol, respectively. The present CCSD(T) results are also in good agreement with previous seven-electron [5s5p3d2f1g/4s3p2d] predictions for the barrier height and exothermicity obtained at the multireference configuration interaction level of theory including the Davidson correction (MRCI+Q). They are also consistent with the seven- and nine-electron MRCI results, but do not support the +Q correction when the F 2s electrons are correlated. The largest CCSD(T) calculation in this work employs 209 basis functions in C2v symmetry and indirectly accounts for more than twenty-nine million connected triple excitations.
Thermal energy reactions of N+2 (ν=1) with SF6, H2, D2, H, and D
Authors: Schwarzer M. , Hansel A. , Freysinger W. , Oberhofer N. , Lindinger W. , Ferguson E. E.
Published: July 2002

The very fast charge transfer of N+2 with SF6 and the H abstraction from H2 by N+2 are found not to be detectably diminished by vibrational excitation of N+2 to ν=1. No vibrational quenching was observed in either case, establishing an upper limit of ≊5% to the vibrational quenching efficiency. No reaction of N+2 with H or D was observed, k<10−11 cm3 s−1, and no vibrational quenching was observed in either case, kq<3×10−11 cm3 s−1.
Rotationally resolved photoionization of H2O
Authors: Tonkyn Russell G. , Wiedmann Ralph , Grant Edward R. , White Michael G.
Published: July 2002

A rotationally resolved one-photon threshold photoionization spectrum of jet-cooled water (H2O and D2O) has been obtained by pulsed field ionization of extremely high-n Rydberg states. Observed spectral intensities for both vibrationless (0,0,0) and vibrationally excited (1,0,0) water cation show a strong propensity for ΔN=0, ±1 transitions. In contrast to earlier work on O2 and HCl, the lack of large ΔN transitions suggests that ionization occurs with only small angular momentum transfers between the core and photoelectron. The presence of both type A and type C ‘‘symmetric top’’ transitions varies from the conclusions of a recent MQDT analysis of H2O photoionization, which predicts only type C transitions. Rotational analysis of the spectra yields improved ionization potentials for both H2O and D2O. The ionization potential of the (1,0,0) vibrational level provides a direct measurement of the symmetric stretch fundamental in H2O+ which is in excellent agreement with an earlier indirect determination. Room temperature spectra are presented for ionization into the (0,0,0), (0,1,0), and (1,0,0) vibrational levels of H2O+.
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o calculations on the structure, stabilization, and dipole moment of benzene⋅⋅⋅Ar complex
Authors: Hobza P. , Selzle H. L. , Schlag E. W.
Published: July 2002

The potential energy surface (PES) of the benzene⋅⋅⋅Ar complex was investigated ab initio using the second-order Moller–Plesset theory demonstrating the practical use of such calculations for these complexes. Among five structures studied, the highest symmetry C6v structure for the Ar appeared to be most stable (stabilization energy: 429 cm−1; distance of molecular centers: 3.526 Å). The PES is much more isotropic than was found in previous papers using an empirical potential. The calculated intermolecular distance is in excellent agreement with recent high resolution measurements—also the dipole moment is in excellent agreement with known data.
Adsorbed state of benzene on the Si(100) surface: Thermal desorption and electron energy loss spectroscopy studies
Authors: Taguchi Y. , Fujisawa M. , Takaoka T. , Okada T. , Nishijima M.
Published: July 2002

The adsorbed state of benzene on the Si(100) surface at 90 and 300 K has been investigated by the use of thermal desorption spectroscopy (TDS) and high resolution electron energy loss spectroscopy (EELS). Benzene is chemisorbed nondissociatively on Si(100) at 300 K, and the fractional saturation coverage corresponds to 0.27 benzene molecule per surface Si atom. It is proposed that chemisorbed benzene is di-σ bonded to two adjacent Si atoms saturating the dangling bonds on Si(100). At 90 K, physisorbed multilayers of benzene molecules are formed in addition to the chemisorbed layer. The multilayers consist of the metastable transition layer (α2) and ‘‘bulk’’ multilayers (α3). These results are markedly different from those of benzene on the Si(111)(7×7) surface, and the origin of the crystal-face specificity is discussed.
Time-resolved measurement of the stimulated emission Stokes shift in LDS750: Evidence for inhomogeneous relaxation kinetics
Authors: Blanchard G. J.
Published: July 2002

The fluorescence spectrum of LDS750, a polar organic molecule, is measured as a function of time subsequent to its excitation using transient stimulated emission spectroscopy. At early time, the emission profile of LDS750 is dependent on the excitation energy, while at long times it is not. The evolution of the steady-state fluorescence spectrum is seen to occur as a result of inhomogeneous relaxation kinetics in the emission band rather than via a uniform red shift of a single feature. The individual features giving rise to the observed spectral dynamics are a consequence of an end-group photoisomerization of LDS750.
Dispersion formula for the average first hyperpolarizability β̄
Authors: Bishop David M.
Published: July 2002

It is shown that the asymptotic formula for the dispersion in the average value of the first electronic hyperpolarizability (β̄e) is exactly β̄e( − ωσ;ω1,ω2) = β̄e(0;0,0)(1 + Aω2L) where ω2L = ω2σ + ω21 + ω22.
Doppler spectroscopy of hydrogen atoms from the photodissociation of saturated hydrocarbons and methyl halides at 157 nm
Authors: Tonokura Kenichi , Matsumi Yutaka , Kawasaki Masahiro , Kasatani Kazuo
Published: July 2002

Hydrocarbons (CnH2n+2, n=3, 4, and 6) and methyl halides (CH3X, X=Cl, Br, I) are photodissociated at 157 nm. The hydrogen atom photofragments are detected by a resonance-enhanced multiphoton ionization technique. The Doppler profiles of the hydrogen atoms from hydrocarbons are well represented by a Gaussian profile, while those from methyl halides by a mixture of a Gaussian and a non-Gaussian profiles. These Doppler profiles are interpreted assuming that (a) hot ethyl photofragments from hydrocarbons result in the formation of hydrogen atoms and (b) methyl halides undergo both direct and indirect photolytic scissions of the C—H bonds at 157 nm.
Selective product channels in the reactions of NH(a 1Δ) and NH(X 3Σ−) with NO
Authors: Yamasaki Katsuyoshi , Okada Satoru , Koshi Mitsuo , Matsui Hiroyuki
Published: July 2002

Reactions of imidogen, NH, in the electronically excited a 1Δ and ground X 3Σ− states with NO have been studied at 300±2 K and at 20 Torr (Ar). NH(a 1Δ) and NH(X 3Σ−) were produced in the 193 nm photolysis of HNCO and CHBr3/NO, respectively, and detected by the laser-induced fluorescence (LIF) technique. Rate constants have been measured under pseudo-first-order conditions by scanning the time delay between the photolysis and probe laser pulses. Overall rate constants were determined: [4.8±0.1(2σ)]×10−11 cm3 molecule−1 s−1 for NH(a 1Δ)+NO; [4.7±0.6(2σ)]×10−11 cm3 molecule−1 s−1 for NH(X 3Σ−)+NO. The ratio of electronic quenching, NH(a 1Δ)+NO→NH(X 3Σ−) +NO, to the overall reaction has been obtained to be 0.53±0.1. An interesting specificity for the products from different spin states of the reactants has been found from observation of OH concentration profiles. NH(X 3Σ−)+NO produces OH+N2 exclusively, while NH(a 1Δ)+NO is over five times less effective in producing OH+N2. Profiles of H atoms detected by the vuv LIF technique indicated that H atoms are directly produced in the reaction NH(a 1Δ)+NO but not in the reaction NH(X 3Σ−)+NO.
Molecular dynamics of a model S
N1 reaction in water
Authors: Keirstead W. P. , Wilson Kent R. , Hynes James T.
Published: July 2002

Results are presented from a computer simulation of the dynamics of a model SN1 reaction in water, very loosely based on the reaction t-BuCl→t-Bu++Cl−. Two diabatic electronic states are considered, covalent and ionic, which cross in the presence of the polar solvent. The curve crossing is treated in the electronically adiabatic limit, which gives rise to coupled reagent and solvent dynamics involving a mixed covalent/ionic adiabatic potential surface. The reaction dynamics are analyzed in terms of a simple solute reaction coordinate defined to be the t-Bu to Cl separation distance. By employing constraint dynamics techniques, the potential of mean force is determined as a function of this reaction coordinate. The time evolution of the reaction is followed in terms of the full molecular dynamics of all reagent and solvent atoms. Beginning with the largely covalently bound reactant t-BuCl, the following was observed: (i) how energy flows out of the water solvent bath into a solvent–reactant fluctuation driving the system to the top of the barrier, (ii) how barrier recrossings lower the reaction rate below the transition state theory prediction, and (iii) how the products slide down the barrier toward separated t-Bu+ and Cl−, dissipating their excess energy back into the solvent. The calculated transmission coefficient measuring the departure of the rate constant from its transition state theory value is 0.53±0.04. This is found to agree with the Grote–Hynes theory prediction, and also with its nonadiabatic solvation, frozen solvent limit, to within the estimated error bars. By contrast, Kramers’ theory incorrectly predicts a much smaller value.
Electronic absorption spectra in a polar fluid: Theory and simulation
Authors: Shemetulskis Norah E. , Loring Roger F.
Published: July 2002

We present calculations of the inhomogeneously broadened absorption line shape associated with a single vibronic transition in a polar chromophore at infinite dilution in a polar solvent. The permanent electric dipole moment of the solute is assumed to change upon electronic excitation. The line shape is related to the dipolar solvation free energy of a fictitious solute with a complex-valued dipole moment. This relation allows methods of equilibrium fluid theory to be applied to the line shape calculation. In order to assess the accuracy of theoretical predictions, we determine line shapes from Monte Carlo simulations for a dipolar hard sphere solute in a dipolar hard sphere solvent. Simulated line shapes are compared to predictions of the mean spherical approximation (MSA) and to a simplified nonlinear solvation theory. The MSA is found to show semiquantitative agreement with simulation results, despite the large value of the solute’s ground-state dipole moment and of its dipole moment change upon excitation. Simulation results are also compared to the relation between the first and second moments of the spectrum that is predicted by any linearized solvation theory. The comparison suggests that an ‘‘exact’’ linearized theory would provide accurate predictions for absorption spectra in polar solutions.
New simulation method for grafted polymeric brushes
Authors: Dickman Ronald , Hong Daniel C.
Published: July 2002

We present the first Monte Carlo simulation method for determining the force between two surfaces due to the interaction of end-grafted polymers. The method is an elaboration of recently devised techniques for measuring the pressure by introducing hard or repulsive walls. The approach is applied to the usual self-avoiding-walk lattice model, as well as to the fluctuating bond model devised by Carmesin and Kremer. The latter is found to offer very significant computational advantages. Our results are in qualitative agreement with recent theoretical predictions.
Localized and nonlocalized polymer chains interacting with a surface
Authors: Stratouras G. , Kosmas M.
Published: July 2002

The conformational properties of a polymer chain interacting with a surface are studied and new features for the cases of a chain free to move in the whole space and for a localized chain fixed with one of its ends at a point are clearly illustrated. The progress achieved is based on exact solutions given in the frame of the continuous model by means of integral equations and Laplace transforms. They permit the study of the behavior of the chain at any distance from the surface as a function of its length, the intensity of the polymer-surface interactions, and the size L of the available space perpendicular to the surface for the nonlocalized chain or the localization position for the localized chain, respectively. The necessary attractions for the gathering of the nonlocalized chains at the surface are larger for larger freedom of the chains which increases with L. From the dependence on the surface-polymer interactions, density profiles are determined for both the depletion and adsorption cases. The behavior of the localized chains is governed by both, the localization constraint and the interactions with the surface.
Ab initio calculation of the vibrational frequencies and the equilibrium geometry of SiH3+
Authors: Botschwina Peter , Oswald Melanie
Published: July 2002

Ab initio calculation of the vibrational frequencies and equilibrium geometry of SiH+ is carried out in this paper.In the computation of the 2−D PEF,only valence electrons are correlated in the CEPA−1 calculations and canonical molecular orbitals are employed in the construction of the electron pairs. (AIP)
Final-state interactions in the zero-kinetic-energy-photoelectron spectrum of H2
Authors: Merkt F. , Softley T. P.
Published: July 2002

A rotationally resolved zero-kinetic-energy (ZEKE) photoelectron spectrum has been recorded for the lowest energy valence band of H2. A coherent laser-based extreme ultraviolet (XUV) source, tuned from 128 200–128 900 cm−1 excites the molecules to the ionization limit, and near-threshold electrons, in a narrow energy bandwidth (a few cm−1 ) just below the ionization limit, are detected by field ionization as a function of laser wavelength. The rotational components for the H2+X  2Σ+g–H2 X 1Σ+g (2–0) vibrational band show different relative intensities, compared to the conventional photoelectron spectrum and to the predictions of theoretical calculations. The perturbed intensities of the N+=0←J″=0 and the 0←2 rotational lines are shown to be attributable to an interaction of the pseudocontinuum of near-threshold N+=0 np J′=1 Rydberg states, with the interloper N+=2, 26p J′=1 state. The enhanced intensity of the 2←0 rotational line is attributable to a ‘‘complex resonance’’ involving the v+=3 R(0) 8p0 transition.
Fourier-transform infrared observation of the ν4 stretching mode of C5 in Ar at 10 K
Authors: Kranze Richard H. , Graham W. R. M.
Published: July 2002

The vibrational spectrum of the C5 carbon cluster produced by trapping the products of the vacuum-ultraviolet photolysis of 2-methyl-1,3-butadiene, or the high-temperature evaporation of graphite in Ar at ∼10 K, has been analyzed by Fourier-transform spectroscopy and has resulted in the identification for the first time of the second infrared-active stretching mode, ν4(σu), at 1446.6 cm−1. The assignment is supported by extensive 13C isotopic data, and is in good agreement with the results of ab initio calculations.
A reexamination of the Rydberg–Klein–Rees potential of the a 3Σ+u state of Na2
Authors: Friedman-Hill Ernest J. , Field Robert W.
Published: July 2002

The ∼0.1 Å error in the inner wall of the experimental Rydberg–Klein–Rees (RKR) potential for the Na2 a 3Σ+u state [L. Li, S. F. Rice, and R. W. Field, J. Chem. Phys. 82, 1178 (1985)], detected by Jenč and Brandt using the reduced potential curve (RPC) method [F. Jenč and B. A. Brandt, J. Chem. Phys. 91, 3287 (1989)], was due to neglect of centrifugal distortion effects and not due to a fundamental flaw in the LeRoy–Bernstein near-dissociation expansion (NDE) G(v) and B(v) fitting expressions used to generate it. The NDE expressions, in fact, are preferable to the more traditional Dunham expansions of B(v) and G(v) for the fitting of sparse data sets. We have refined the previously published RKR curve to include centrifugal distortion effects without including additional data. The results are in excellent agreement with theoretical predictions, and are probably accurate to ±0.01 Å up to energies within 5 cm−1 of dissociation. The principal constants are Te+Y00=5848.48(22) cm−1, ωe=24.15(2) cm−1, Be=0.0562(1) cm−1, re=5.011(9) Å, and De=175.76(35) cm−1.
Structural, thermodynamic, and electrical properties of polar fluids and ionic solutions on a hypersphere: Results of simulations
Authors: Caillol J. M. , Levesque D.
Published: July 2002

The reliability and the efficiency of a new method suitable for the simulations of dielectric fluids and ionic solutions is established by numerical computations. The efficiency depends on the use of a simulation cell which is the surface of a four-dimensional sphere. The reliability originates from a charge–charge potential solution of the Poisson equation in this confining volume. The computation time, for systems of a few hundred molecules, is reduced by a factor of 2 or 3 compared to this of a simulation performed in a cubic volume with periodic boundary conditions and the Ewald charge–charge potential.
The gas phase reaction of C2H+2 with H2 below 3 K: The reopening of the bimolecular C2H+3 channel at low energy
Authors: Hawley Michael , Smith Mark A.
Published: July 2002

The bimolecular reaction of C2H+2 with H2 is found to undergo a surprising change of mechanism to one of inverse energy dependence below temperatures of 3 K as observed in a free jet flow reactor. The observed rate coefficient for C2H+3 production is found to be k=5.6×10−11 T−2 cm3/s in this energy regime. Contrary to previous belief, the reaction is exothermic and results are described regarding kinetic isotope effects, the competitive three body association process and internal C2H+2 vibrational state dependency of the chemistry. A mechanism is suggested which involves a low temperature switching to a tunneling process through a small barrier and is intimately coupled to the long lived complex properties of very low energy collisions.
Deviation from mean-field behavior in a low molecular weight critical polymer blend
Authors: Hair D. W. , Hobbie E. K. , Nakatani A. I. , Han C. C.
Published: July 2002

A deviation from mean-field behavior is observed in the static susceptibility and correlation length measured with small angle neutron scattering as a function of temperature near the phase boundary of a relatively low molecular weight critical polymer mixture. The possibility of a fluctuation influenced crossover from mean-field to nonmean-field behavior is considered.
Solvent-electronic state interactions measured from the glassy to the liquid state. II. Fluorescence line narrowing spectroscopy in glycerol
Authors: Yu Jongwan , Earvolino Patrick , Berg Mark
Published: July 2002

Fluorescence line narrowing spectroscopy is extended to the study of liquid state dynamics. Measurements are made on solutions of dimethyl-s-tetrazine in glycerol from room temperature to below the glass transition. The structural broadening identified in the preceding paper is related to a relaxation function by the use of a simple configuration coordinate model. This relaxation function is ∼150 times faster than the structural relaxation function measured by other experiments, showing that electronic state solvation is sensitive to a unique aspect of the structural dynamics of the liquid.
Thermally activated processes in Li doped Ar matrices studied by electronic spin–lattice relaxation
Authors: Schrimpf A. , Rosendahl R. , Bornemann T. , Stöckmann H.-J. , Faller F. , Manceron L.
Published: July 2002

Optical absorption and ESR spectra were taken simultaneously of Li doped Ar matrices. The measurements showed that the broad absorption near the free atom D1, D2 transitions is in reality a superposition of two spectra, the so-called blue and red triplet, well known from other alkali rare gas systems. Both triplets could be correlated with corresponding ESR spectra. Longitudinal and transversal electronic relaxation times T1 and T2 were determined by carefully analyzing the saturation of the ESR signal amplitudes and the line broadening. The temperature dependence of T1 and T2 suggests that the relaxation is caused by thermally activated local structural changes with an extremely low activation enthalpy of the order of 1 meV. Similar results were obtained in K, Ag, and Au doped Ar matrices.
Vibrationally resolved shape resonant photoionization of SiF4
Authors: Kakar Sandeep , Poliakoff E. D. , Rosenberg R. A.
Published: July 2002

We have measured vibrationally resolved fluorescence from SiF+4(D̃ 2A1) photoions to determine the vibrational branching ratio σ[v=(1,0,0,0)]/σ[v=(0,0,0,0)] in the excitation energy range 22<hν<70 eV. The branching ratio shows pronounced enhancements at hν=25 and 45 eV. The deviation from Franck–Condon behavior at higher energy (hν=45 eV) is attributed to a shape resonance and it appears that a shape resonance is also responsible for the lower energy feature (hν=25 eV). However, the present results in this lower energy region conflict with interpretations of previous vibrationally unresolved work. Applications of these results to general problems in polyatomic photoionization are discussed.
Dynamics of ozone photoabsorption: A theoretical study of the Chappuis band
Authors: Banichevich Antonio , Peyerimhoff Sigrid D. , Beswick J. Alberto , Atabek Osman
Published: July 2002

The first two excited singlet states of ozone are discussed in light of recent ab initio MRD-CI calculations. In the asymmetric pathway for O2+O fragmentation, the two 1 1A2 and 1 1B1 states undergo an avoided crossing resulting in the C 1A″ and D 1A″ states. The D 1A″ state has bound vibrational levels in the Franck–Condon region while the C 1A″ is repulsive (towards O2+O fragmentation) in that area and is found to possess a local minimum away from the Franck–Condon area at small bond angles. A one-dimensional cut along the dissociation reaction coordinate was extracted from the three-dimensional calculated potential surfaces. Quantum mechanical calculations of the absorption spectrum based on these one-dimensional ab initio potentials and of the corresponding ab initio transition moments were undertaken. The present work assigns the distinct features of the Chappuis band to the bound levels of the D 1A″ state superimposed on the C 1A″ state continuum as an alternative interpretation of the second absorption band in the ozone spectrum.
Scattering studies of self-assembling processes of polymer blends in spinodal decomposition. II. Temperature dependence
Authors: Takenaka Mikihito , Hashimoto Takeji
Published: July 2002

Our previous work on time evolution of the interfacial structure for a near critical mixture of polybutadiene and polyisoprene undergoing the spinodal decomposition (SD) [T. Hashimoto, M. Takenaka, and H. Jinnai, J. Appl. Crystallogr. 24, 457 (1991)] was extended to explore the behavior as a function of temperature T, again using the time-resolved light scattering method. The study involved the investigation of the time evolutions of various characteristic parameters such as the wave number qm(t;T ) of the dominant mode of the concentration fluctuations, the maximum scattered intensity Im(t;T ), the scaled structure factor F(x;T ), the interfacial area density Σ(t;T ), and the characteristic interfacial thickness tI(t;T ) from the early-to-late stage SD, where t refers to time after the onset of SD and x refers to the reduced scattering vector defined by x=q/qm(t;T ); q is the magnitude of the scattering vector. The results confirm the model previously proposed at a given T over a wider temperature range corresponding to the quench depth ΔT=T−Ts =5.5–34.5 K, or εT=(χ−χs)/χs =4.50×10−2 to 2.79×10−1, where Ts is the spinodal temperature, and χ and χs are the Flory interaction parameters at T and Ts, respectively. This blend is noted to have a phase diagram of the lower critical solution temperature type.
Calculations on the rate of the ion–molecule reaction C2H+2+H2→C2H+3+H
Authors: Yamashita Koichi , Herbst Eric
Published: July 2002

The minimum energy pathway for the ion–molecule reaction C2H+2+H2→C2H+3+H has been calculated via ab initio quantum chemical techniques. The reactants first form a weakly bound entrance channel complex with H2 in a bridged position perpendicular to the C2H2 linear structure. A transition state is then encountered with an asymmetric structure in which H2 favors one of the two carbon atoms as it begins to come apart. After proceeding through a weakly bound exit channel complex, once again of bridged structure, the system produces the product ion C2H+3 in the nonclassical (bridged) position. The reactants do not access the deep potential well of C2H+4. At our highest level of calculation, the reaction is determined to be endothermic by approximately 2 kcal mol−1, in good agreement with thermochemical values. However, phase space calculations on the reaction dynamics, including tunneling, using the calculated potential energy surface are not in good agreement with measurements of the rate coefficient at both 300 and in the vicinity of 2 K. A revised potential energy surface, in which the products and intermediate stationary points are lowered in energy by 2 kcal mol−1, making the reaction thermoneutral and reducing the barrier over the transition state, leads to better agreement with measured rate coefficients. With the reduced energies, the calculated rate coefficient shows a temperature dependence similar to that obtained previously for the reaction between NH+3 and H2.
Photodissociation of HNO3 at 193, 222, and 248 nm: Products and quantum yields
Authors: Turnipseed Andrew A. , Vaghjiani Ghanshyam L. , Thompson John E. , Ravishankara A. R.
Published: July 2002

The quantum yields for OH, O(3P), O(1D), and H(2S) from the photolysis of HNO3 have been determined at 248, 222, and 193 nm at 298 K. The quantum yield for OH was observed to be near unity at 248 [Φ(OH)=0.95±0.09] and 222 nm [Φ(OH)=0.90±0.11]. However, at 193 nm the quantum yield for OH was found to be 0.33±0.06. The quantum yield for O atoms [O(3P)+O(1D)], Φ(O), was observed to be 0.031±0.010, 0.20±0.03, 0.81±0.13, at 248, 222, and 193 nm, respectively. Both O(3P) and O(1D) were observed at 222 and 193 nm, but only O(3P) was detected at 248 nm. It was observed that 40% of the O atoms formed at both 193 and 222 nm were O(1D) atoms. The upper limits for H(2S) quantum yields: Φ(H)≤0.002 at 248 nm, ≤0.01 at 222 nm, and ≤0.012 at 193 nm were also determined. This present work quantifies the photolysis channel producing HONO+O and show that it accounts for a large fraction at HNO3 photolysis at 193 nm.
Structure of a dipolar hard sphere fluid near a neutral hard wall
Authors: Tang Zixiang , Scriven L. E. , Davis H. T.
Published: July 2002

The position-orientation distribution of a dipolar hard sphere fluid in contact with a neutral hard wall is studied using a density functional theory. Effects of hard sphere exclusions are incorporated in the excess hard sphere free energy density functional. Orientational correlations between the dipoles are taken into account through approximating the pair correlation function of the inhomogeneous dipolar fluid by that of the homogeneous one of the same chemical potential and dipole moment. The latter is obtained by solving reference quadratic hypernetted chain equation. Theoretical results agree well with those of computer simulations which are available at high density. The theory predicts a qualitatively different interfacial structure at low density and high dipole moments from that at high density; the former is very similar to the liquid/vapor interface of dipolar fluids with regard to both the density distribution and orientational order. The theory also demonstrates that different density distributions correspond closely to different orientational orderings of the dipoles at the interface.
Classical trajectory studies of the molecular dissociation dynamics of formaldehyde: H2CO→H2+CO
Authors: Chang Yan-Tyng , Minichino Camilla , Miller William H.
Published: July 2002

Classical trajectory calculations have been carried out to simulate the unimolecular decomposition of formaldehyde in the ground electronic state (S0). Global potential-energy surfaces were constructed using the empirical valence-bond (EVB) approach. Two sets of ab initio input were used to characterize two different EVB potential-energy surfaces, and trajectory calculations using one of these gives excellent agreement with experimental data for the product-state distributions of H2 and CO. The trajectory study of vector correlations with prompt dissociation of the parent molecule provides understanding of the dissociation dynamics in the molecular frame. From comparison with some of the experimental results and information from a few ab initio calculations, some improvements for the current potential surfaces are suggested.
Three particle hydrodynamic interactions in suspensions
Authors: Clercx H. J. H. , Schram P. P. J. M.
Published: July 2002

We present an outline of a method to determine the components of the grand mobility matrix of a system of three hydrodynamically interacting spherical particles with arbitrary particle configuration. We present the results of a study of some components of the grand mobility matrix in the case of two special configurations. The results derived for one configuration, with the three particles on a line, are compared with some results from the literature. In the other configuration, we have put the particles on the corners of an equilateral triangle. Besides the study of the mobility matrix, we have derived virial expansions for the translational and rotational self-diffusion coefficients up to quadratic order in φ, the volume fraction. Three particle contributions are incorporated in these expressions. We also present virial expansions, where three particle hydrodynamic interactions are included, for the translational and rotational sedimentation velocities. There are some results available in the literature in the case of the translational self-diffusion coefficient and the translational sedimentation velocity, which are different from our results. We discuss these differences. As far as we know, the results of the three particle contribution to the virial expansions of the rotational self-diffusion coefficient and the rotational sedimentation velocity are new. All the virial expansions mentioned above are compared with experimental results and simulation data from the literature.
State selective reactions prepared through the excitation of orbital states in van der Waals complexes of Ca–HX*
Authors: Soep B. , Abbès S. , Keller A. , Visticot J. P.
Published: July 2002

We have observed the chemiluminescent reaction Ca*+HX→CaX*+H, where the reactants are prepared in a van der Waals complex formed in a supersonic expansion. This preparation, combined with tunable laser excitation, allows access to well-defined electronic states of the reaction complex corresponding to different orientations of the calcium excited orbital. In the case of the Ca–HBr complex, a remarkable effect of this preparation is observed on the branching ratio to the final excited states A 2Π and B 2Σ of CaBr: Depending upon the selected state of the complex, the A/B ratio varies by a factor of 2. This is interpreted by the conservation of the orbital orientation during the reaction involving the departure of the hydrogen.
Spectroscopy and photodissociation of chlorine monomers and clusters in argon matrices
Authors: McCaffrey J. G. , Kunz H. , Schwentner N.
Published: July 2002

Steady-state and time-resolved emission spectroscopy of the A–X system of Cl2 is used to distinguish molecular chlorine isolated as monomers and clusters in solid argon samples. The lifetime of the metastable A′ 3Π2u state is measured to be an order of magnitude less, when chlorine is present as clusters, than when it is truly isolated. Photodissociation of molecular chlorine clusters was found to be insignificant as monitored by the emission of Ar2Cl at 260 nm. Measurement of the dissociation threshold of molecular chlorine in the 9 eV region as a function of temperature showed little variation. Using spectroscopic data it is concluded that dissociation is occurring by an impulsive mechanism involving curve-crossing from the initially populated Ar+(Cl2)− charge transfer state to repulsive potentials correlating with ground state atomic chlorine and not via a harpooning mechanism. A simple microscopic model, drawn from experimental data and pairwise addition of ArCl potential terms, is constructed to describe the steps involved in this dissociation process in the solid lattice.
Electronic spectroscopy of oxygen atoms trapped in solid xenon
Authors: Lawrence W. G. , Apkarian V. A.
Published: July 2002

The electronic spectroscopy of oxygen atoms trapped in solid xenon are reported. Excitation of the solid between 220 and 260 nm leads to two main emissions centered at 3.35 and 1.65 eV, both of which arise from the same upper state. The excitations are assigned to charge-transfer absorptions in interstitial Oh sites; the emitting state, which has a lifetime of 227 ns, is assigned to Xe+O−(1Σ+). An avoided crossing between the ionic and covalent 1Σ+ states, and differential solvation of these states, explains the main trends of the spectroscopy of XeO in the gas and condensed phases. Implications regarding ionic and covalent many-body surfaces are discussed.
Electronic spectroscopy and vibrational predissociation dynamics of OH–Kr and OD–Kr
Authors: Fei Suli , Zheng Xiaonan , Heaven Michael C.
Published: July 2002

OH/D–Kr complexes have been characterized via laser excitation of the A–X system. Progressions of the OH/D–Kr stretch were seen in conjunction with the OH/D 0–0 and 1–0 transitions. Rotational analyses of 17 bands provided ground state rotational constants of B″=0.0835 (OH–Kr) and 0.0806 cm−1 (OD–Kr). These constants correspond to an intermolecular separation of 3.78±0.01 Å. Assignment of the A state vibrational levels was accomplished by means of the 84Kr/86Kr isotope effect. A lower limit for the dissociation energy of OH(A,v=0)–Kr of De ≳ 1840 cm−1 was derived from the vibrational constants. Extrapolation of the rotational constants yielded an equilibrium intermolecular separation of 2.67±0.12 Å. The properties defined by the spectroscopic analysis indicated weak, van der Waals bonding in the ground state, and incipient chemical bonding in the excited state. Vibrational predissociation of OH/D–Kr was observed through homogeneous broadening of the rotational lines. The predissociation rates ranged from <1×1010 to 4×1011 s−1, with a general trend of decreasing decay rate with increasing excitation of the intermolecular stretch. Wavelength resolved fluorescence spectra showed that predissociation of OH–Kr partitioned ∼40% of the available energy into OH(A,v=0) rotation. Predissociation of OD–Kr released ≊25% of the energy to OD(A,v=0) rotation.
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o determination of the nonlinear optical properties of HCl
Authors: Hammond Brian L. , Rice Julia E.
Published: July 2002

A b initio calculations of the static- and frequency-dependent dipole polarizability α and first and second hyperpolarizabilities β and γ of HCl are presented. Static polarizabilities are determined using the self-consistent field (SCF), second-order Mo/ller–Plesset perturbation theory (MP2), the coupled-cluster single and double excitation method (CCSD), and CCSD with a perturbative estimate of triple excitations [CCSD(T)]. The effect of basis set expansion, particularly the addition of diffuse functions up to g type, is explored. It is found that for highly accurate calculations, f functions are necessary on Cl, but g functions have a much smaller effect. The frequency-dependent hyperpolarizabilities for wavelengths of 694.3 and 1319 nm are determined at the SCF and MP2 levels of theory. The CCSD(T) static values, scaled using MP2 dispersion, are found to be in good agreement with experiment. Electron correlation is found to play a significant role in both the static and dynamic quantities. Use of the SCF dispersion as a percentage correction to the static MP2 hyperpolarizability, however, is found to be a good approximation to the total MP2 frequency-dependent hyperpolarizability at the frequencies studied. The effects of vibrational contributions to the polarizabilities are discussed.
Comparison of the Rg+(2P1/2)/Cl−/He and Rg+(2P3/2)/Cl−/He three-body ionic-recombination reactions for the formation of RgCl*, Rg*, and Cl*
Authors: Tsuji Masaharu , Muraoka Toshihiko , Kouno Hiroyuki , Nishimura Yukio
Published: July 2002

Three-body ionic-recombination reactions of Rg++Cl−+He (Rg=Kr or Xe) leading to RgCl* excimers and their predissociation products (Rg* and Cl*) have been studied by observing emission spectra in the flowing afterglow. The branching ratios of KrCl(B,C,D):Kr(5s 3P1):Cl(4p) are 0.13:0.014:0.86 in the Kr+(2P1/2) reaction, while those of KrCl(B,C):Kr(5s 3P1):Cl(4s) are 0.64:0.23:0.13 in the Kr+(2P3/2) reaction. Although the Xe+(2P1/2) reaction gives only XeCl(D), the Xe+(2P3/2) reaction provides XeCl(B,C) and Xe(3P1) with branching ratios of 0.98:0.02, respectively. The preferential formation of the Rg(3P1) level by the Rg+(2P3/2) reaction can be explained as being due to the conservation of ion configuration with J=3/2. The electronic state distribution of Cl(4p) in the Kr+(2P1/2) reaction is nonstatistical providing any preference for doublet, quartet, or for particular J states, while the J=3/2 levels of Cl(4s) are favored channels relative to the J=1/2 and 5/2 ones in the Kr+(2P3/2) reaction. It is predicted that the dominant predissociation product in the Xe+(2P1/2) reaction is the metastable Xe(3P0) atom.
The influence of electron correlation on anisotropic electron intracule and extracule densities
Authors: Wang Jiahu , Tripathi Awadh N. , Smith Vedene H.
Published: July 2002

The electron intracule and extracule densities of the neon atom, the hydrogen molecule, and lithium hydride have been studied using both correlated and self-consistent-field (SCF) wave functions. For the first time, the effects of electron correlation on the anisotropic intracule and extracule densities are simultaneously displayed and analyzed.
Time-dependent methods for calculating thermal rate coefficients using flux correlation functions
Authors: Thachuk Mark , Schatz George C.
Published: July 2002

In this paper we study numerical methods for calculating thermal rate coefficients using flux correlation functions, with the goal of determining optimal methods for producing values with a specified accuracy. In all cases we employ grid based methods for solving the time-dependent Schrödinger equation in one mathematical dimension for a simple barrier potential function. The solutions are used to determine the propagator matrix elements needed to evaluate the flux correlation functions. Within this framework, we examine (1) several time-dependent methods for propagating the wave packets, (2) several procedures for evaluating the action of the Hamiltonian on the wave function, (3) the choice of complex time contours for evaluating the rate coefficient expression, (4) alternatives for estimating the initial short-time evolution of the wave packet (which starts as a δ function), (5) quadrature methods for evaluating the spatial and time integrals appearing in the flux correlation function, and (6) special numerical strategies which can dramatically improve the accuracy of the calculation, particularly at low temperatures. We find that several methods yield rate coefficients accurate to 1% or 0.1% using about the same computational effort.

These include (a) split-operator time propagators combined with fast-Fourier-transform evaluations of the wave-function derivatives, and (b) the Chebyshev time propagator combined with either an eleventh-order finite-difference or fifth-order spline evaluation of the wave-function derivatives. These finite-difference and spline methods can also be used competitively with the split-operator approach provided that a Crank–Nicholson approximation is utilized in evaluating the action of the kinetic-energy propagator. It was also found that inaccuracies in estimating the initial short-time behavior of the wave function could limit the effectiveness of the more accurate methods. A multigrid approach based on the split-operator/Fourier transform method is developed for treating this, and provides results with sufficient accuracy. However, for some choices of grid parameters this initialization process determines the overall computational efficiency of the calculation, independent of the numerical efficiency of methods used after the initialization.