JCP Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

You Tube Flickr Twitter iResearch App Facebook

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue

22 Dec 2000

Volume 113, Issue 24, pp. 10835-11399

Page 1 of 3 Pages Next Page | Jump to Page
back to top
RSS Feeds

The nuclear spin–spin coupling constant in He2

Magdalena Pecul

J. Chem. Phys. 113, 10835 (2000); http://dx.doi.org/10.1063/1.1332994 (2 pages) | Cited 15 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The scalar nuclear spin–spin coupling constant was calculated for the helium dimer using full configuration interaction (FCI) and EOM-CCSD methods. The Fermi-contact was found to have nonnegligible value of 1.3 Hz at R = 5.6 a.u., while the other contributions are zero. This suggests that the nuclear spin–spin coupling constants transmitted through van der Waals interactions are a much more common phenomenon than previously thought. All contributions exhibit sharp exponential decay with the internuclear distance. © 2000 American Institute of Physics.
Show PACS
33.25.+k Nuclear resonance and relaxation
31.15.vn Electron correlation calculations for diatomic molecules
31.15.bw Coupled-cluster theory
33.15.Dj Interatomic distances and angles
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Electronic instability of isolated SO42− and its solvation stabilization

Xue-Bin Wang, John B. Nicholas, and Lai-Sheng Wang

J. Chem. Phys. 113, 10837 (2000); http://dx.doi.org/10.1063/1.1333703 (4 pages) | Cited 43 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Despite its ubiquity in nature, SO42− as an isolated dianion has never been detected because of its electronic instability as a result of the two negative charges. This study shows how the first few waters solvate and stabilize an isolated SO42−, molecule-by-molecule, using photodetachment spectroscopy and theoretical calculations. We find that the minimum number of water required to stabilize a free SO42− is three. The first four waters bind tightly to SO42−, each forming two H-bonds with SO42− without inter-water H-bonding. The charges of the dianion are stabilized sufficiently that additional waters form only single H-bonds with SO42− and that inter-water H-bonding is observed starting at n = 5. © 2000 American Institute of Physics.
Show PACS
82.30.Nr Association, addition, insertion, cluster formation
33.80.Eh Autoionization, photoionization, and photodetachment
33.15.Fm Bond strengths, dissociation energies
33.15.Ta Mass spectra
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.60.+q Photoelectron spectra
33.15.Bh General molecular conformation and symmetry; stereochemistry
back to top
RSS Feeds
back to top Theoretical Methods and Algorithms

Incorporating physical implementation concerns into closed loop quantum control experiments

J. M. Geremia, Wusheng Zhu, and Herschel Rabitz

J. Chem. Phys. 113, 10841 (2000); http://dx.doi.org/10.1063/1.1326905 (8 pages) | Cited 59 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In quantum control experiments, it is desirable to build features into the field that address physical concerns such as simplicity, robustness, dynamical coherence, power expenditure, etc. With a judicious choice for the cost functional, it is possible to incorporate such secondary features into the field, often without altering the experimental procedure or apparatus. Through simulated closed-loop population transfer experiments, we demonstrate the benefit of carefully designed cost functionals. As specific examples, we address two common physical concerns: removing extraneous structure from the control pulse and finding robust fields. Removing unnecessary field components is critical if information about the mechanism is to be interpreted from the structure of the optimal pulse. Robust fields produce a stable outcome despite noise in the field and, perhaps, environmental inhomogeneities in the quantum system as is typical of condensed phase experiments. © 2000 American Institute of Physics.
Show PACS
03.65.Ta Foundations of quantum mechanics; measurement theory

Spectral decomposition and Bloch equation of the operators represented by fixed-centroid path integrals

Telesforo López-Ciudad and Rafael Ramírez

J. Chem. Phys. 113, 10849 (2000); http://dx.doi.org/10.1063/1.1327293 (12 pages) | Cited 15 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Interesting approaches to study statical and dynamic properties of quantum systems, e.g., the quantum transition state theory and the centroid molecular dynamics, have been previously derived using fixed centroid path integrals. We show that these constrained propagators can be alternatively defined using an operator formalism. An interesting result is the finding of the differential equations that determine the temperature dependence of these propagators. One equation applies to path integrals with fixed-centroid position (i.e., those used in quantum transition state theory), and the other one to path integrals with fixed-centroid position and momentum (i.e., those used in centroid molecular dynamics). Both equations are solved for a harmonic oscillator, so that the spectral decomposition of the operators represented by fixed-centroid path integrals is derived for this particular case. Their eigenvalues build an alternating geometric series, showing explicitly the impossibility of considering such operators as true density operators, i.e., some eigenfunctions are associated to “negative probabilities.” The eigenfunctions are shown to be a generalization of the coherent and squeezed states of the harmonic oscillator. The physical meaning of centroid molecular dynamics, an approximation to study the time evolution of these mixed states, is clarified by considering the time evolution of the corresponding eigenfunctions. The mixed states constructed with “negative probabilities” display vanishing small position and momentum dispersion in the high temperature limit. © 2000 American Institute of Physics.
Show PACS
03.65.Ge Solutions of wave equations: bound states
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
42.50.Dv Quantum state engineering and measurements

Some relationships within the nonlocal (pair–site) chemical reactivity formalism of density functional theory

E. Chamorro, R. Contreras, and P. Fuentealba

J. Chem. Phys. 113, 10861 (2000); http://dx.doi.org/10.1063/1.1327265 (6 pages) | Cited 11 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
General and exact relationships within the nonlocal (pair–site) reactivity context are explicitly derived in the framework of density functional theory. The equations are expressed in terms of linear response functions and associated kernels of the Fukui function and its derivatives with respect to the electron number at constant external potential. It is shown that under a local approximation for the general nonlocal pair–site kernels, the nonlocality character of the chemical response must appear only implicitly through the changes in the chemical potential of the system. In the framework of a more general nonlocal reactivity theory, new relations can be written through the incorporation of more spatial coordinates. The case of a three-site equation between Fukui functions has been explored. © 2000 American Institute of Physics.
Show PACS
82.20.Wt Computational modeling; simulation

Extended kinetic models with waiting-time distributions: Exact results

Anatoly B. Kolomeisky and Michael E. Fisher

J. Chem. Phys. 113, 10867 (2000); http://dx.doi.org/10.1063/1.1326912 (11 pages) | Cited 35 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Inspired by the need for effective stochastic models to describe the complex behavior of biological motor proteins that move on linear tracks, exact results are derived for the velocity and dispersion of simple linear sequential models (or one-dimensional random walks) with general waiting-time distributions. The concept of “mechanicity” is introduced to conveniently quantify departures from simple “chemical,” kinetic rate processes, and its significance is briefly indicated. The results are extended to more elaborate models that have finite side branches and include death processes (to represent the detachment of a motor from the track). © 2000 American Institute of Physics.
Show PACS
87.16.Nn Motor proteins (myosin, kinesin dynein)
87.15.-v Biomolecules: structure and physical properties

Quantum codes for controlling coherent evolution

Yehuda Sharf, Timothy F. Havel, and David G. Cory

J. Chem. Phys. 113, 10878 (2000); http://dx.doi.org/10.1063/1.1326071 (8 pages) | Cited 2 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Control over spin dynamics has been obtained in nuclear magnetic resonance (NMR) via coherent averaging, which modifies the effective internal Hamiltonian, and via quantum codes, which can protect against decoherent evolution. Here, we discuss the design and implementation of quantum codes that enable modification of the internal Hamiltonian. A detailed example is given of a quantum code for protecting two data spins from evolution under a weak coupling term in the Hamiltonian, using an “isolated” ancilla that does not evolve on the experimental time scale. The code is realized in a three-spin system by liquid-state NMR spectroscopy on 13C-labeled alanine, and tested for two initial states. It is also shown that with internal interactions and isolated ancillae, codes exist that do not require the ancillae to initially be in a (pseudo-) pure state. Finally, it is shown that even with nonisolated ancillae, quantum codes exist which can protect against evolution under weak coupling. An example is presented for a six-qubit code that protects two data spins to first order. © 2000 American Institute of Physics.
Show PACS
03.67.Lx Quantum computation architectures and implementations

Atoms in molecules, an axiomatic approach. I. Maximum transferability

Paul W. Ayers

J. Chem. Phys. 113, 10886 (2000); http://dx.doi.org/10.1063/1.1327268 (13 pages) | Cited 37 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Central to chemistry is the concept of transferability: the idea that atoms and functional groups retain certain characteristic properties in a wide variety of environments. Providing a completely satisfactory mathematical basis for the concept of atoms in molecules, however, has proved difficult. The present article pursues an axiomatic basis for the concept of an atom within a molecule, with particular emphasis devoted to the definition of transferability and the atomic description of Hirshfeld. © 2000 American Institute of Physics.
Show PACS
31.15.-p Calculations and mathematical techniques in atomic and molecular physics

A mobile charge densities in harmonic oscillators (MCDHO) molecular model for numerical simulations: The water–water interaction

Humberto Saint-Martin, Jorge Hernández-Cobos, Margarita I. Bernal-Uruchurtu, Iván Ortega-Blake, and Herman J. C. Berendsen

J. Chem. Phys. 113, 10899 (2000); http://dx.doi.org/10.1063/1.1324711 (14 pages) | Cited 60 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this work we present a new proposal to model intermolecular interactions and use it for water molecules. The parameters of the model were fitted to reproduce the single molecule’s electrostatic properties, a sample of 352 points in a refined ab initio single molecule deformation potential energy surface (PES), and the theoretical limit of the dimerization energy, −20.8 kJ/mol. The model was able to reproduce a sample of 180 additional points in the single molecule deformation PES, and 736 points in a pair-interaction surface computed at the MP2/aug-cc-pVQZ′ level with the counterpoise correction. Though the model reproduced the diagonal of the polarizability tensor, it could account for only 60% of the three-body nonadditive contributions to the interaction energies in 174 trimers computed at the MP2/6-311++(2d,2p) level with full counterpoise correction, but reproduced the four-body nonadditivities in 34 tetramers computed at the same level as the trimers. The model’s predictions of the structures, energies, and dipoles of small clusters resulted in good agreement with experimental data and high quality ab initio calculations. The model also reproduced the second virial coefficient of steam at various temperatures, and the structure and thermodynamical properties of liquid water. We found that the short-range water–water interactions had a critical influence on the proper performance of the model. We also found that a model based on the proper intermolecular interactions requires the inclusion of intramolecular flexibility to be adequate. © 2000 American Institute of Physics.
Show PACS
34.20.Gj Intermolecular and atom-molecule potentials and forces
31.15.A- Ab initio calculations

Efficient particle-mesh Ewald based approach to fixed and induced dipolar interactions

Abdulnour Toukmaji, Celeste Sagui, John Board, and Tom Darden

J. Chem. Phys. 113, 10913 (2000); http://dx.doi.org/10.1063/1.1324708 (15 pages) | Cited 85 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We have implemented classical Ewald and particle-mesh Ewald (PME) based treatments of fixed and induced point dipoles into the sander molecular dynamics (MD) module of AMBER 6. During MD the induced dipoles can be propagated along with the atomic positions either by iteration to self-consistency at each time step, or by a Car–Parrinello (CP) technique using an extended Lagrangian formalism. In this paper we present the derivation of the new algorithms and compare the various options with respect to accuracy, efficiency, and effect on calculated properties of a polarizable water model. The use of PME for electrostatics of fixed charges and induced dipoles together with a CP treatment of dipole propagation in MD simulations leads to a cost overhead of only 33% above that of MD simulations using standard PME with fixed charges, allowing the study of polarizability in large macromolecular systems. © 2000 American Institute of Physics.
Show PACS
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
61.20.Ja Computer simulation of liquid structure
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

The electronic structure and electron affinities of higher chlorine oxide radicals ClOx (x = 2–4) from photoelectron spectroscopy of ClOx− anions

Xue-Bin Wang and Lai-Sheng Wang

J. Chem. Phys. 113, 10928 (2000); http://dx.doi.org/10.1063/1.1326067 (6 pages) | Cited 14 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The electronic structure of ClOx (x = 2–4) radicals were experimentally investigated using anion photoelectron spectroscopy of the respective anions at several photon energies. The electron affinities of ClO3 and ClO4 were obtained for the first time and were found to be very high, 4.25±0.10 and 5.25±0.10 eV, respectively. Three low-lying excited states were observed for ClO2 with excitation energies of 2.10 eV (2B2), ∼ 2.60 eV (2A1 and 2A2). The 2A1 and 2A2 states were found to be nearly degenerate. Two low-lying states were observed for ClO3 at ∼ 1.20 eV (2A2) and ∼ 2.65 eV (2E), whereas no excited state was observed for ClO4 even at our highest photon energy of 157 nm (7.866 eV). The photoelectron spectra were assigned and compared with available theoretical calculations. The excellent agreement between the experimental and theoretical results confirmed the previous calculations. © 2000 American Institute of Physics.
Show PACS
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.60.+q Photoelectron spectra

Transient resonance Raman spectroscopy and density functional theory investigation of iso-polyhalomethanes containing bromine and/or iodine atoms

Xuming Zheng, Wei-Hai Fang, and David Lee Phillips

J. Chem. Phys. 113, 10934 (2000); http://dx.doi.org/10.1063/1.1326064 (13 pages) | Cited 27 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We report additional transient resonance Raman spectra and density functional theory computations for the products formed following ultraviolet photoexcitation of solution phase polyhalomethanes containing bromine and/or iodine atoms. We show that the iso-polyhalomethane photoproduct is responsible for the intense transient absorption band observed in the 350–470 nm region after ultraviolet excitation of polyhalomethanes in the solution phase. We examine the trends and correlation in the density functional theory optimized geometry and intense electronic absorption transition in the 350–470 nm region for the iso-polyhalomethanes containing bromine and/or iodine atoms. We explore the chemical reactivity of the iso-polyhalomethane species using density functional theory computations for the reaction of iso-CH2Br–Br with ethylene as an example. Our results and comparison with experimental data in the literature indicate that the iso-polyhalomethane species is most likely the methylene transfer agent in the cyclopropanation reactions of olefins using ultraviolet photoexcitation of polyhalomethanes in the solution phase. We briefly discuss the possibility that the photochemistry and chemistry of the iso-polyhalomethanes may give significant release of reactive halogens to the atmosphere. © 2000 American Institute of Physics.
Show PACS
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
31.15.E- Density-functional theory
33.80.-b Photon interactions with molecules
33.20.Lg Ultraviolet spectra

Vibration–rotation transfer in molecular super rotors

Anthony J. McCaffery

J. Chem. Phys. 113, 10947 (2000); http://dx.doi.org/10.1063/1.1326072 (5 pages) | Cited 8 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The collisional behavior of (X)6Li2 molecules in very high rotational levels of v = 0 is considered. Highly efficient vibration–rotation transfer is predicted in these “super rotors” particularly when the conditions for quasiresonant transfer are fulfilled. This requires simultaneous near-resonance in energy and in angular momentum. Values of Δj for which quasiresonant vibration–rotation transfer (QRT) occurs become smaller as initial rotor state increases and transfer is likely to become particularly fast for Δj = 2, predicted to occur when ji = 130. This behavior is contrasted with the inefficiency of pure rotational transfer within the v = 0 level for fast-rotating molecules. QRT will take place for quite cold collisions and thus will provide competition for the spinning-up process used to create the super rotors. © 2000 American Institute of Physics.
Show PACS
34.50.Ez Rotational and vibrational energy transfer
33.15.Mt Rotation, vibration, and vibration-rotation constants

The ←math(1+1)REMPI spectrum and high-level ab initio calculations of the complex between NO and N2

Jérôme Lozeille, Sophia E. Daire, Stuart D. Gamblin, Timothy G. Wright, and Edmond P. F. Lee

J. Chem. Phys. 113, 10952 (2000); http://dx.doi.org/10.1063/1.1326068 (10 pages) | Cited 14 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The results of two separate studies of the complex between NO and N2 are reported. The (1+1) REMPI spectrum of the ←math transition of the complex between NO and N2 is presented of improved quality over that reported previously, and the appearance of the spectrum is discussed. The results of high-level ab initio calculations [RCCSD(T)/aug-cc-pVQZ//QCISD/6-311+G(2d)] on the math 2Π state are also reported. The indications are that the NO moiety is more freely rotating in the complex than is N2, and that a wide angular space is sampled in the zero-point energy level. The appearance of the REMPI spectrum suggests that the  2Σ+ state is (close to) linear, and RCCSD(T)//QCISD calculations on the state, using Rydberg-function-augmented basis sets, suggest that the lowest energy linear isomer is the ON⋅N2 linear orientation. It is clear, however, that the understanding of this complex, and its spectroscopy, is far from complete, and will be challenging. © 2000 American Institute of Physics.
Show PACS
31.15.A- Ab initio calculations
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Wz Other multiphoton processes

Cluster photofragmentation dynamics: Quasiclassical trajectory studies of Arn–H2S and Arn–SH (n = 1,2)

Joanna R. Fair and David J. Nesbitt

J. Chem. Phys. 113, 10962 (2000); http://dx.doi.org/10.1063/1.1326066 (11 pages) | Cited 7 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Quasiclassical trajectory calculations with model potential energy surfaces have been used to elucidate the formation dynamics of open-shell radical clusters by “gentle-recoil” photolysis of closed-shell hydride clusters. Specifically, model surfaces for Ar–H2S and Ar2–H2S have been constructed and used to explore photofragmentation dynamics at 193 and 248 nm for comparison with previous experimental results. A remarkable efficiency (as high as 25%) for forming highly excited radical Ar–SH and Ar2–SH clusters is calculated, despite photolysis recoil energies more than 100-fold in excess of the dissociation limit. This surprisingly high survival probability is traced to two dynamical sources. First, ejection of the light H atom from Arn–H2S effectively removes all but a small fraction of the excess photolysis energy from the nascent radical cluster in the center-of-mass frame. Second, although trajectory calculations indicate that nearly 50% of the surviving clusters contain energies up to two-fold higher than the dissociation limit, these clusters are classically bound due to novel angular momentum barriers predicted by Pollak [J. Chem. Phys. 86, 1645 (1987)] for a polyatomic system. Finally, an analysis is presented that indicates the “gentle-recoil” photolysis mechanism may permit efficient formation of highly internally excited, chemically reactive radical clusters of OH and SH with light species such as H2 and D2. © 2000 American Institute of Physics.
Show PACS
33.80.Gj Diffuse spectra; predissociation, photodissociation
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
82.20.Fd Collision theories; trajectory models
82.20.Kh Potential energy surfaces for chemical reactions

Dipole bound and valence state coupling in argon-solvated nitromethane anions

F. Lecomte, S. Carles, C. Desfrançois, and M. A. Johnson

J. Chem. Phys. 113, 10973 (2000); http://dx.doi.org/10.1063/1.1326476 (5 pages) | Cited 26 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The coupling between the dipole bound and valence electronic states of the nitromethane anion has been investigated via Rydberg electron transfer spectroscopy and field detachment spectroscopy of the bare and argon-solvated anions. The unique aspects of the nitromethane system are highlighted by comparing the solvation behavior of nitromethane anion with that of acetonitrile, a system in which the dipole bound state is well-isolated from the resonance arising from excess electron occupation of its high lying lowest unoccupied molecular orbital. © 2000 American Institute of Physics.
Show PACS
31.50.Df Potential energy surfaces for excited electronic states
33.20.-t Molecular spectra

Thermodynamic study of the gaseous molecules Al2N, AlN, and Al2N2 by Knudsen cell mass spectrometry

G. Meloni and K. A. Gingerich

J. Chem. Phys. 113, 10978 (2000); http://dx.doi.org/10.1063/1.1326848 (5 pages) | Cited 6 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The Knudsen effusion mass spectrometric method has been employed to measure the equilibrium partial pressures of the Al2N molecule over the AlN–Au–graphite system. Theoretical computations were carried out to determine the structure, molecular parameters, and thermodynamic properties of Al2N. The partial pressures have been combined with the calculated thermal functions to determine the atomization enthalpy, ΔaH0o, and enthalpy of formation, ΔfH298.15o, in kJ mol−1, of 783.2±15 and 342.7±15 for Al2N, respectively. Upper values for the dissociation energy of AlN, D0o(AlN,g) ⩽ 368±15 kJ mol−1, and for the atomization enthalpy of Al2N2, ΔaH0o(Al2N2,g) ⩽ 1402 kJ mol−1 have been obtained. These results are discussed and compared with recent theoretical literature values. © 2000 American Institute of Physics.
Show PACS
65.20.-w Thermal properties of liquids
65.40.gd Entropy
82.60.-s Chemical thermodynamics
33.15.Ta Mass spectra
33.15.Fm Bond strengths, dissociation energies

Ab initio and quasiclassical trajectory study of the N(2D)+NO(X 2Π)→O(1D)+N2(X 1Σg+) reaction on the lowest 1A′ potential energy surface

Miguel González, R. Valero, and R. Sayós

J. Chem. Phys. 113, 10983 (2000); http://dx.doi.org/10.1063/1.1327263 (16 pages) | Cited 16 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this work we have carried out ab initio electronic structure calculations, CASSCF/CASPT2 with the Pople’s 6-311G(2d) basis set on the ground singlet potential energy surface (1 1A′ PES) involved in the title reaction. Transition states, minima and one 1 1A′/2 1A′ surface crossing have been characterized, obtaining three NNO isomers with the energy ordering: NNO (1Σ+)<cyclic−C2v NON(1A1)<NON(1Σg+). Approximately 1250 ab initio points have been used to derive an analytical PES which fits most of the stationary points, with a global root-mean-square deviation of 1.12 kcal/mol. A quasiclassical trajectory study at several temperatures (300–1500 K) was performed to determine thermal rate constants, vibrational and rovibrational distributions and angular distributions. The dynamics of this barrierless reaction presents a predominant reaction pathway (96% at 300 K) with very short-lived collision complexes around the NNO minimum, which originate backward scattering and a similar fraction of vibrational and translational energy distributed into products. At higher temperatures other reaction pathways involving NON structures become increasingly important as well as the N-exchange reaction (3.02% of the branching ratio at 1500 K), this latter in accord with experimental data. It is concluded that the physical electronic quenching of N(2D) by NO should be negligible against all possible N(2D)+NO reaction channels. © 2000 American Institute of Physics.
Show PACS
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Kh Potential energy surfaces for chemical reactions
31.15.xr Self-consistent-field methods
31.15.A- Ab initio calculations

Severely perturbed vibrational structure in the 266–310 nm electronic transition of C3

Mitsuaki Izuha and Kaoru Yamanouchi

J. Chem. Phys. 113, 10999 (2000); http://dx.doi.org/10.1063/1.1326070 (10 pages) | Cited 3 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The laser induced fluorescence (LIF) spectra of C3 are measured under jet-cooled conditions in the wide UV region of 266–310 nm, and 173 vibronic bands are identified. Among them, 77 and 68 vibronic bands were found to exhibit Σ–Σ type and Π–Σ type rotational structures, respectively. From the rotational analysis, the band-origin wave numbers and the rotational constants of the upper Σ and Π vibronic levels and K-type doubling parameters for the Π vibronic levels are determined. The rotational constants for the Σ and Π vibronic levels exhibit, respectively, similar distributions with almost the same mean values, math′ = 0.395(14) and 0.398(17) cm−1, indicating that the Σ and Π vibronic levels have the same electronic origin and that the average C–C bond distance of the upper electronic state in the observed energy range is about 1.331(25) Å, which is longer than the electronic ground math 1Σg+ state by 0.054(25) Å. The convolution and Fourier-transform analyses are performed separately for the spectra composed only of Σ–Σ type and Π–Σ type vibronic bands to derive estimates of the vibrational fundamentals in the upper electronic state. The low ν1 fundamental of 940(60) cm−1 derived from these analyses and the seemingly regular ν1 progression in the convoluted spectra indicate that the bright character is carried primarily by the transitions to the vibrational levels in the 1Δu electronically excited state and is distributed into a large number of the originally dark transitions to the vibrational levels in the 1Πg electronically excited state, resulting in the exceedingly complex vibronic band system. © 2000 American Institute of Physics.
Show PACS
33.50.Dq Fluorescence and phosphorescence spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Dj Interatomic distances and angles

Vibrational wave packets in the B 1Πu and D 1Σu+ states of Cs2: Determination of improved Cs2+(X) and Cs2(B) spectroscopic constants

A. L. Oldenburg, P. C. John, and J. G. Eden

J. Chem. Phys. 113, 11009 (2000); http://dx.doi.org/10.1063/1.1326065 (10 pages) | Cited 5 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Vibrational wave packets in the B 1Πu and D 1Σu+ excited states of Cs2 have been studied on the ∼100 fs time scale by pump–probe laser spectroscopy. The temporal behavior of the wave packets was monitored by photoionizing the electronically excited molecule with a time-delayed probe pulse and recording the time and energy-integrated photoelectron signal as a function of time delay between the pump and probe pulses. For the B 1Σu+ experiments, wave packets were produced by exciting the B 1Σu+←X 1Σg+ transition in the ∼740–790 nm region and subsequently detected by photoionizing the molecule at wavelengths between 565 nm and 600 nm. By simulating the experimentally observed transients with the density matrix formalism (and explicitly accounting for laser chirp and ∣Δv∣>1 coherences), improved values for the equilibrium internuclear separation for the Cs2(B 1Πu) state and Te for the Cs2+(X) state were determined to be Re(B 1Πu) = 4.93±0.03 Å and Te[Cs2+(X)] = 29 930±100 cm−1, respectively. Similar experiments were conducted for the D 1Σu+ state. Wave packets composed of vibrational levels (v′ ≈ 40–50) perturbed by the bound 2 3Πou state were produced on the D 1Σu+ potential surface by driving the D 1Σu+←X 1Σg+ transition in the 575–610 nm spectral interval. © 2000 American Institute of Physics.
Show PACS
33.20.Kf Visible spectra
33.20.Ea Infrared spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants

Statistical rate theory for the HO+O⇔HO2⇔H+O2 reaction system: SACM/CT calculations between 0 and 5000 K

L. B. Harding, A. I. Maergoiz, J. Troe, and V. G. Ushakov

J. Chem. Phys. 113, 11019 (2000); http://dx.doi.org/10.1063/1.1314374 (16 pages) | Cited 49 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The potential energy surface of the HO+O⇔HO2⇔H+O2 reaction system is characterized by ab initio calculations. The complex-forming bimolecular reaction is then treated by statistical rate theory, using statistical adiabatic channel and classical trajectory calculations for the HO+O⇔HO2 and HO2⇔H+O2 association/dissociation processes. Specific rate constants k(E,J) of both reactions as well as thermal rate constants are calculated over wide ranges of conditions. Open shell quantum effects are important up to room temperature. The good agreement with experimental results suggests that the ab initio potential is of sufficient accuracy. There is no evidence for non-statistical effects or for a significant contribution from electronically excited states. The comparison with rate data for the H+O2→HO+O reaction, because of the remaining uncertainty in the heat of formation of HO, is somewhat inconclusive. Apart from this problem, the calculated rate constants appear reliable between 0 and 5000 K. © 2000 American Institute of Physics.
Show PACS
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Nr Association, addition, insertion, cluster formation
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies

Effect of pressure and temperature on the competition between nondissociative and dissociative electron attachment to POCl3

D. H. Williamson, C. A. Mayhew, W. B. Knighton, and E. P. Grimsrud

J. Chem. Phys. 113, 11035 (2000); http://dx.doi.org/10.1063/1.1311800 (9 pages) | Cited 9 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Branching between the nondissociative, POCl3−, and dissociative, POCl2−, products of the POCl3 electron attachment reaction has been examined as a function of buffer gas pressure and temperature. A strong positive pressure dependence is observed for the nondissociative channel, where at 303 K, the %POCl3− increases from 31% at 1 Torr to 94% at 675 Torr total pressure. Conversely, the dissociative channel displays a strong positive temperature dependence. The effect of pressure and temperature on the relative amounts of POCl3− and POCl2− observed is discussed in terms of the competition between the collisional stabilization and dissociation rates of the POCl3−∗ excited intermediate. The decomposition of POCl3−∗ is modeled with Rice–Ramsperger–Kassel decomposition kinetics weighted by the vibrational energy distribution of POCl3 neutrals. This model provides an excellent simulation of the experimental pressure and temperature dependencies of the electron attachment process. © 2000 American Institute of Physics.
Show PACS
34.80.Lx Recombination, attachment, and positronium formation
34.80.Ht Dissociation and dissociative attachment

Ab initio/spectroscopic interaction potential for He+Ne+

M. F. Falcetta, M. J. Dorko, and P. E. Siska

J. Chem. Phys. 113, 11044 (2000); http://dx.doi.org/10.1063/1.1327267 (11 pages) | Cited 12 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
High-level ab initio calculations have been carried out on the lowest Σ and Π states of HeNe+. These have been used to construct a new interaction potential in a Hund’s case (e) representation, by fitting spectroscopic vibrational spacings ΔGv+1/2 and rotational constants Bv using a close-coupling method and a potential function whose form is established by the ab initio data and a long-range analysis. The characteristics of the resulting Born–Oppenheimer potential curves, particularly for the X state, where only the higher vibrational levels were observed, differ considerably from those derived by extrapolation of the experimental spectroscopic constants. A new set of constants is proposed, and functions for the X-state G(v) and Bv are given that are well-behaved from the bottom of the well to the dissociation limit. The asymptotic formula for Bv of Le Roy is extended to improve its accuracy. The X state of 4HeNe+ is predicted to support 15 bound vibrational states, the A2 state 7. Good agreement with experiment in magnitude and trends is found for spin-splitting and Ω-doubling constants. Comparison is made between energy levels calculated in the close-coupling formalism and in the customary case (c) Born–Oppenheimer approximation; the largest differences, which are readily resolved spectroscopically, are reflected in Bv for high vibrational levels of the X state, including those observed. © 2000 American Institute of Physics.
Show PACS
34.20.Cf Interatomic potentials and forces
34.50.-s Scattering of atoms and molecules
31.15.A- Ab initio calculations
33.20.Tp Vibrational analysis
33.20.Sn Rotational analysis

Time-dependent quantum mechanical calculations on H+O2 for total angular momentum J>0. III. Total cross sections

Evelyn M. Goldfield and Anthony J. H. M. Meijer

J. Chem. Phys. 113, 11055 (2000); http://dx.doi.org/10.1063/1.1326904 (8 pages) | Cited 35 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The H+O2→OH+O reaction has been studied with a time-dependent wave packet method for total angular momentum J = 15, 20, 25, 35. This work is a continuation of previous studies for J ⩽ 10. The calculations were performed combining a real wave packet method with the Coriolis coupled method on parallel computers. We find that for most energies there is a monotonic decrease of reaction probability with increasing J. Nevertheless, due to the 2J+1 degeneracy, higher angular momentum states contribute significantly to the total reaction cross section. A smoothing/interpolation/extrapolation scheme is employed to compute total reaction cross sections. These cross sections are compared with quasiclassical results on the same potential energy surface, and the most recent experimental cross sections. Comparisons with quasiclassical results show the significance of zero-point energy constraints. The quantum mechanical theoretical cross sections are smaller than the experimental ones everywhere, suggesting that a more accurate potential energy surface is required. There is also some possibility that nonadiabatic effects play a role in this reaction. © 2000 American Institute of Physics.
Show PACS
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Wt Computational modeling; simulation

Negative ion formation from low energy (0–15 eV) electron impact to CF2Cl2 under different phase conditions

Judith Langer, Sara Matt, Martina Meinke, Petra Tegeder, Aleksandar Stamatovic, and Eugen Illenberger

J. Chem. Phys. 113, 11063 (2000); http://dx.doi.org/10.1063/1.1326849 (8 pages) | Cited 14 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Negative ion formation following low energy (0–10 eV) electron attachment to free and bound CF2Cl2 molecules is studied in (1) a molecular beam experiment (single molecules, homogeneous clusters, and mixed CF2Cl2/NH3 clusters) and (2) a UHV surface experiment where desorption of negative ions from condensed CF2Cl2 is observed. From single gas phase CF2Cl2 molecules we observe Cl− and F− generated via dissociative electron attachment from a resonance near 0 eV and 3 eV, respectively, as the most abundant ions. From homogeneous clusters (CF2Cl2)n, we additionally detect undissociated complexes of the form (M)n−(M=CF2Cl2) including the stabilized monomer CF2Cl2− and also “solvated fragment ions” of the form Mn⋅X−(X=Cl, F). Their relative abundance vs size (n) of the final product varies in a significant different way between (M)n− and Mn⋅X− reflecting the different relaxation probabilities in the initial cluster. In the desorption spectra, the dominant low energy Cl− gas phase resonance is strongly suppressed in favor of a significant resonant feature appearing near 8 eV. These last results are discussed in light of previously reported giant enhancements of electron induced desorption of Cl− and F− from CF2Cl2 on Ru coadsorbed with water or ammonia ices under 250 eV electron impact [Q. B. Lu and T. E. Madey, Phys. Rev. Lett. 82, 4122 (1999); J. Chem. Phys. 111, 2861 (1999)]. © 2000 American Institute of Physics.
Show PACS
34.80.Gs Molecular excitation and ionization
34.80.Ht Dissociation and dissociative attachment
Page 1 of 3 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close