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8 Jun 2002

Volume 116, Issue 22, pp. 9559-10029

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back to top Theoretical Methods and Algorithms

New exchange-correlation density functionals: The role of the kinetic-energy density

A. Daniel Boese and Nicholas C. Handy

J. Chem. Phys. 116, 9559 (2002); http://dx.doi.org/10.1063/1.1476309 (11 pages) | Cited 93 times

Online Publication Date: 22 May 2002

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New density functionals, using the kinetic-energy density Tau are reported. The newly introduced variable enhances the performance of previous functionals, leading to highly accurate functionals with and without the use of exact exchange. All these functionals are compared to commonly used functionals for a large test set, looking also at reactions and hydrogen bonded systems. Furthermore, their physical plausibility is discussed. © 2002 American Institute of Physics.
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31.15.E- Density-functional theory
33.15.Fm Bond strengths, dissociation energies

A correlation of exchange energy-exchange potential at the nucleus in atoms

K. D. Sen

J. Chem. Phys. 116, 9570 (2002); http://dx.doi.org/10.1063/1.1476013 (4 pages) | Cited 3 times

Online Publication Date: 22 May 2002

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We report the results of numerical tests on atom He–Lu, which suggest that the exchange energy calculated within the spin-polarized exchange-only optimized potential model for atoms can be expressed as a power-law in terms of the local effective exchange potential evaluated at the nucleus. The total effective exchange potential increases linearly with the atomic number. These results are useful in improving the energy density functionals at the small r region where most of the popularly used energy functionals provide rather poor functional derivatives. The significance of the present results in obtaining detailed information on the correlation-kinetic energy of the Kohn–Sham model is discussed.© 2002 American Institute of Physics.
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31.15.E- Density-functional theory

Kinetics of escape through a small hole

Igor V. Grigoriev, Yurii A. Makhnovskii, Alexander M. Berezhkovskii, and Vladimir Yu. Zitserman

J. Chem. Phys. 116, 9574 (2002); http://dx.doi.org/10.1063/1.1475756 (4 pages) | Cited 59 times

Online Publication Date: 22 May 2002

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We study the time dependence of the survival probability of a Brownian particle that escapes from a cavity through a round hole. When the hole is small the escape is controlled by an entropy barrier and the survival probability decays as a single exponential. We argue that the rate constant is given by k = 4Da/V, where a and V are the hole radius and the cavity volume and D is the diffusion constant of the particle. Brownian dynamics simulations for spherical and cubic cavities confirmed both the exponential decay of the survival probability and the expression for the rate constant for sufficiently small values of a. © 2002 American Institute of Physics.
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05.40.Jc Brownian motion
02.50.Cw Probability theory

Simple one-electron quantum capping potentials for use in hybrid QM/MM studies of biological molecules

Gino A. DiLabio, Margaret M. Hurley, and Phillip A. Christiansen

J. Chem. Phys. 116, 9578 (2002); http://dx.doi.org/10.1063/1.1477182 (7 pages) | Cited 44 times

Online Publication Date: 22 May 2002

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Calculations demonstrate that with a minor modification conventional ab initio effective potentials can be employed in place of link atoms to truncate quantum regions in hybrid quantum mechanics/molecular mechanics calculations. Simple quantum capping potentials are formed by replacing excess valence electrons in conventional effective potentials by spherical shielding and Pauli terms chosen to duplicate all-electron molecular structures and charge distributions. Tests involving truncated histidine show errors in charge and protonation energy to be reduced as compared to the link atom approach. Because of the use of conventional effective potential expansions, this approach can be implemented with minimal or no program modifications. Indeed, in its simplest form it requires the addition of only a single Gaussian and adjustable parameter to a conventional effective potential expansion. The parametrization requires little effective potential expertise or effort. © 2002 American Institute of Physics.
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87.15.A- Theory, modeling, and computer simulation
31.15.A- Ab initio calculations

Four-component relativistic configuration-interaction calculation using the reduced frozen-core approximation

Yoshihiro Watanabe and Osamu Matsuoka

J. Chem. Phys. 116, 9585 (2002); http://dx.doi.org/10.1063/1.1476694 (6 pages) | Cited 13 times

Online Publication Date: 22 May 2002

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The reduced frozen-core approximation (RFCA) is a kind of frozen-core approximation (FCA). In our previous study [J. Chem. Phys. 109, 8182 (1998)], we found that Dirac–Fock–Roothaan calculations using RFCA had some desirable features compared to the all-electron and usual FCA calculations. In this study, in addition to these features, we found that they also describe well unoccupied as well as occupied orbitals. We developed a fully relativistic multireference configuration-interaction (CI) program that incorporates these features of RFCA, and report CI calculations for ThO and AuH. The calculated spectroscopic constants agree well with experimental values. © 2002 American Institute of Physics.
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31.15.V- Electron correlation calculations for atoms, ions and molecules
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions

On the required shape corrections to the local density and generalized gradient approximations to the Kohn–Sham potentials for molecular response calculations of (hyper)polarizabilities and excitation energies

Myrta Grüning, Oleg V. Gritsenko, Stan J. A. van Gisbergen, and Evert Jan Baerends

J. Chem. Phys. 116, 9591 (2002); http://dx.doi.org/10.1063/1.1476007 (11 pages) | Cited 56 times

Online Publication Date: 22 May 2002

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It is well known that shape corrections have to be applied to the local-density (LDA) and generalized gradient (GGA) approximations to the Kohn–Sham exchange–correlation potential in order to obtain reliable response properties in time dependent density functional theory calculations. Here we demonstrate that it is an oversimplified view that these shape corrections concern primarily the asymptotic part of the potential, and that they affect only Rydberg type transitions. The performance is assessed of two shape-corrected Kohn–Sham potentials, the gradient-regulated asymptotic connection procedure applied to the Becke–Perdew potential (BP–GRAC) and the statistical averaging of (model) orbital potentials (SAOP), versus LDA and GGA potentials, in molecular response calculations of the static average polarizability α, the Cauchy coefficient S−4, and the static average hyperpolarizability β. The nature of the distortions of the LDA/GGA potentials is highlighted and it is shown that they introduce many spurious excited states at too low energy which may mix with valence excited states, resulting in wrong excited state compositions. They also lead to wrong oscillator strengths and thus to a wrong spectral structure of properties like the polarizability. LDA, Becke–Lee–Yang–Parr (BLYP), and Becke–Perdew (BP) characteristically underestimate contributions to α and S−4 from bound Rydberg-type states and overestimate those from the continuum. Cancellation of the errors in these contributions occasionally produces fortuitously good results. The distortions of the LDA, BLYP, and BP spectra are related to the deficiencies of the LDA/GGA potentials in both the bulk and outer molecular regions. In contrast, both SAOP and BP-GRAC potentials produce high quality polarizabilities for 21 molecules and also reliable Cauchy moments and hyperpolarizabilities for the selected molecules. The analysis for the N2 molecule shows, that both SAOP and BP–GRAC yield reliable energies ωi and oscillator strengths fi of individual excitations, so that they reproduce well the spectral structure of α and S−4.© 2002 American Institute of Physics.
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31.15.E- Density-functional theory
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Flexible constraints: An adiabatic treatment of quantum degrees of freedom, with application to the flexible and polarizable mobile charge densities in harmonic oscillators model for water

Berk Hess, Humberto Saint-Martin, and Herman J. C. Berendsen

J. Chem. Phys. 116, 9602 (2002); http://dx.doi.org/10.1063/1.1478056 (9 pages) | Cited 20 times

Online Publication Date: 22 May 2002

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In classical molecular simulations chemical bonds and bond angles have been modeled either as rigid constraints, or as nearly harmonic oscillators. However, neither model is a good description of a chemical bond, which is a quantum oscillator that in most cases occupies the ground state only. A quantum oscillator in the ground state can be represented more faithfully by a flexible constraint. This means that the constraint length adapts itself, in time, to the environment, such that the rotational and potential forces on the constraint cancel out. An accurate algorithm for flexible constraints is presented in this work and applied to study liquid water with the flexible and the polarizable “mobile charge densities in harmonic oscillators” model. The iterations for the flexible constraints are done simultaneously with those for the electronic polarization, resulting in negligible additional computational costs. A comparison with fully flexible and rigidly constrained simulations shows little effect on structure and energetics of the liquid, while the dynamics is somewhat faster with flexible constraints. © 2002 American Institute of Physics.
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61.25.Em Molecular liquids
61.20.Ja Computer simulation of liquid structure

Calculation of third-rank molecular hypermagnetizabilities by continuous transformation of the origin of the current density

M. C. Caputo and P. Lazzeretti

J. Chem. Phys. 116, 9611 (2002); http://dx.doi.org/10.1063/1.1477458 (5 pages) | Cited 3 times

Online Publication Date: 22 May 2002

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The third-rank hypermagnetizabilities of three small molecules have been evaluated at the Hartree–Fock level of accuracy within the conventional common-origin approach as well as alternative procedures formally based on continuous transformation of the origin of the electronic current density induced by a perturbing electromagnetic field. Gaugeless basis sets of increasing size and flexibility have been employed in a numerical test (i) to assess the practicality of distributed origin methods whereby the diamagnetic contribution to the current density is formally annihilated, and (ii) to estimate the degree of convergence of diamagnetic and paramagnetic contributions to tensor components. It is shown that two nice features characterize the computational scheme adopted in this study: (i) the results depend only linearly on a shift of origin; (ii) a permutational symmetry condition of tensor indices yields a natural criterion for the near-Hartree–Fock quality of computed values. © 2002 American Institute of Physics.
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33.15.-e Properties of molecules
31.15.xr Self-consistent-field methods

Stochastic molecular dynamics: A combined Monte Carlo and molecular dynamics technique for isothermal simulations

Phil Attard

J. Chem. Phys. 116, 9616 (2002); http://dx.doi.org/10.1063/1.1478057 (4 pages) | Cited 12 times

Online Publication Date: 22 May 2002

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A hybrid Monte Carlo molecular dynamics technique is developed that gives equations of motion for an isothermal system. Test results for a Lennard-Jones fluid are shown to be in good agreement with the known equation of state. The physical interpretation of the procedure and the extension to isothermal–isobaric systems is also discussed. © 2002 American Institute of Physics.
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61.20.Ja Computer simulation of liquid structure

A critical note on density functional theory studies on rare-gas dimers

Tanja van Mourik and Robert J. Gdanitz

J. Chem. Phys. 116, 9620 (2002); http://dx.doi.org/10.1063/1.1476010 (4 pages) | Cited 95 times

Online Publication Date: 22 May 2002

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In recent literature, some authors claim to have successfully applied density functional theory (DFT) methods to the attractive interaction between rare-gas atoms. In this note, we make a critical survey of these works and come to the conclusion that, in contrast to the claims made, state-of-the-art DFT methods are incapable of accounting for dispersion effects in a quantitative way. © 2002 American Institute of Physics.
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31.15.E- Density-functional theory

Efficient methods to calculate dynamic hyperpolarizability tensors by time-dependent density-functional theory

Habbo Hait Heinze, Fabio Della Sala, and Andreas Görling

J. Chem. Phys. 116, 9624 (2002); http://dx.doi.org/10.1063/1.1476014 (17 pages) | Cited 12 times

Online Publication Date: 22 May 2002

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A derivation of density-functional response theory is presented which is based directly on the Runge–Gross theorem and does not invoke the action formalism and thus does not violate causality requirements in time. Working equations to treat linear and nonlinear response properties of electronic systems by time-dependent density-functional theory in the frequency domain are given. Efficient noniterative methods to calculate dynamic hyperpolarizability tensors of molecules for arbitrary frequency combinations are presented. With the introduced methods, hyperpolarizabilities of benzene and stilbene derivatives are investigated. The results show that the influence of substituents on the frequency-dependent hyperpolarizability is well described by time-dependent density-functional theory at the adiabatic local density level. Inspection of the linear and nonlinear response of the electron density shows the importance of screening effects for the response properties of larger molecules on electric fields and electromagnetic radiation. © 2002 American Institute of Physics.
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31.15.E- Density-functional theory
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Wavelet approximation of correlated wave functions. I. Basics

Heinz-Jürgen Flad, Wolfgang Hackbusch, Dietmar Kolb, and Reinhold Schneider

J. Chem. Phys. 116, 9641 (2002); http://dx.doi.org/10.1063/1.1476008 (17 pages) | Cited 23 times

Online Publication Date: 22 May 2002

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We suggest an alternative approach to electronic structure calculations based on numerical methods from multiscale analysis. By this we are aiming to achieve a better description of the various length- and energy-scales inherently connected with different types of electron correlations. Taking a product ansatz for the wave function Ψ = FΦ, where Φ corresponds to a given mean-field solution like Hartree–Fock or a linear combination of Slater determinants, we approximate the symmetric correlation factor F in terms of hyperbolic wavelets. Such kinds of wavelets are especially adapted to high dimensional problems and allow for local refinement in the region of the electron–electron cusp. The variational treatment of the ansatz leads to a generalized eigenvalue problem for the coefficients of the wavelet expansion of F. Several new numerical features arise from the calculation of the matrix elements. This includes the appearance of products of wavelets, which are not closed under multiplication. We present an approximation scheme for the accurate numerical treatment of these products. Furthermore the calculation of one- and two-electron integrals, involving the nonstandard representation of Coulomb matrix elements, is discussed in detail. No use has been made of specific analytic expressions for the wavelets, instead we employ exclusively the wavelet filter coefficients, which makes our method applicable to a wide class of different wavelet schemes. In order to illustrate the various features of the method, we present some preliminary results for the helium atom. © 2002 American Institute of Physics.
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31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.xt Variational techniques
02.10.Yn Matrix theory
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

The influence of internal degrees of freedom on the unimolecular decay of the molecule–cluster compound Au8+CH3OH

M. Vogel, K. Hansen, A. Herlert, L. Schweikhard, and C. Walther

J. Chem. Phys. 116, 9658 (2002); http://dx.doi.org/10.1063/1.1476934 (5 pages) | Cited 7 times

Online Publication Date: 22 May 2002

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Time-resolved photodissociation measurements of the sequential reaction Au8+CH3OH→Au8+→Au7+ and the direct reaction Au8+→Au7+ have been performed for several excitation energies. The production rates and yields of the final state Au7+ in the sequential process are strongly influenced by the excitation energy deposited into the evaporated methanol molecule during the initial fragmentation step. Both the rate constants and yields can be fitted with a single parameter, the cluster–methanol binding energy. © 2002 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
82.50.-m Photochemistry
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment
36.40.Cg Electronic and magnetic properties of clusters

Microsolvation of small anions by aromatic molecules: An exploratory study

K. Le Barbu, J. Schiedt, R. Weinkauf, E. W. Schlag, J. M. Nilles, S.-J. Xu, O. C. Thomas, and K. H. Bowen

J. Chem. Phys. 116, 9663 (2002); http://dx.doi.org/10.1063/1.1475750 (9 pages) | Cited 16 times

Online Publication Date: 22 May 2002

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This work was motivated by the experimental finding that the O2−/benzene interaction energy is unexpectedly large. To further explore the interactions of small anions with aromatic molecules, anion photoelectron spectroscopy was utilized to measure interaction strengths of the seed anions, O2− and NO−, complexed with several aromatic molecules, including benzene, naphthalene, pyridine, and pyrimidine. As in the case of O2−(benzene), the anion(aromatic)1 binding energies for the other complexes studied were also higher than one might have anticipated. In addition, the interaction energy of O2− complexed with a given aromatic molecule was, in every case studied, higher (by a factor of ∼1.5) than that of NO− complexed with the same aromatic. While the dependence of interaction strengths on solvent dipole moments and/or polarizabilities implied a substantial electrostatic component to the binding in these complexes, differences in the binding of O2− and NO− with these aromatic molecules showed that there is a distinct covalent aspect to the interaction as well. A significant portion of this interaction was attributed to the fact that O2− and NO− are both open-shell anions that are interacting with closed-shell aromatic molecules. In the accompanying paper [J. Chem. Phys. 116, 9672 (2002)] calculations on O2−(benzene)1 by Jalbout and Adamowicz shed additional light on the nature of small anion–aromatic molecule interactions. Last, results are also presented comparing the interaction energies of several multisolvent, anion–molecule complexes. © 2002 American Institute of Physics.
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82.30.Nr Association, addition, insertion, cluster formation
34.50.-s Scattering of atoms and molecules
34.20.Gj Intermolecular and atom-molecule potentials and forces
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Anion–aromatic molecule complex. Ab initio study of the benzene⋅O2 anion

A. F. Jalbout and L. Adamowicz

J. Chem. Phys. 116, 9672 (2002); http://dx.doi.org/10.1063/1.1476012 (5 pages) | Cited 11 times

Online Publication Date: 22 May 2002

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A series of ab initio calculations were carried out for the O2⋅benzene complex and its anions to determine their structures and the O2⋅benzene adiabatic electron affinity. The calculations revealed interesting differences between the electronic and molecular structures of the anion and the neutral complex, and between the free and complexed O2−. While for O2⋅benzene the calculations predict two equilibrium structures, one planar and one with O2 located above the benzene and interacting with its π electrons, for [O2⋅benzene]− only the planar structure was predicted to be stable. Analysis of the [O2⋅benzene]− wave function shows some delocalization of the excess electron from O2− to the region of the σ electrons in benzene. This delocalization may explain the predicted increase of the adiabatic electron affinity (A.E.A) by 0.59 eV upon O2 complexation with benzene. This increase is consistent with A.E.A. shift reported in the accompanying paper by Le Barbu et al. [J. Chem. Phys. 116, 9663 (2002)]. © 2002 American Institute of Physics.
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31.15.A- Ab initio calculations
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Bh General molecular conformation and symmetry; stereochemistry

Theoretical studies of the vibrational states of Ne2SH and Ne2OH ( 2Σ+)

Hee-Seung Lee and Anne B. McCoy

J. Chem. Phys. 116, 9677 (2002); http://dx.doi.org/10.1063/1.1471238 (13 pages) | Cited 6 times

Online Publication Date: 22 May 2002

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Variational calculations of the 25 lowest energy vibrational states of the Ne2SH and Ne2OH ( 2Σ+) complexes are performed using potentials that are obtained by the pairwise addition of accurate neon dimer and Ne⋅XH potentials. The Ne2XH complexes are able to sample several local minima in their respective potentials at relatively low internal energies. Consequently, both complexes display average densities of states that exceed one vibrational state per cm−1 in the energy regime covered by this study. In spite of this, all of the calculated states are assigned to specific vibrational excitations, based on a structure of the complex that corresponds to one of the minima on the potential, and all of the minima are found to support progressions of bending states. In most cases, it is found that the wave functions have most of their amplitude in one of the potential minima, but the couplings between zero-order states that are localized in different minima increase as the internal energy is increased. The extent of mixing is found to depend on the symmetry of the wave functions with respect to the interchange of the two neon atoms. Effects of the differences in the anisotropies of the Ne⋅OH and Ne⋅SH potentials on the vibrational energies and wave functions are also investigated. © 2002 American Institute of Physics.
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31.50.-x Potential energy surfaces
31.15.xt Variational techniques
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis

Photo-induced intra-complex reactions in Mg+-2,2,2-trifluoroethanol

Wenyue Guo, Haichuan Liu, and Shihe Yang

J. Chem. Phys. 116, 9690 (2002); http://dx.doi.org/10.1063/1.1475755 (7 pages) | Cited 9 times

Online Publication Date: 22 May 2002

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We induced the intra-complex reactions in Mg+-2,2,2-trifluoroethanol by photons in the spectral region of 240–410 nm. We observed the nonreactive channel product Mg+ and a number of reactive channel products throughout the whole excitation region. The reactive photoproducts originate from the scission of the C–O or C–F bond, as well as from the simultaneous rupture of both bonds. The action spectrum consists of two broad peaks between the atomic transition of Mg+(3 2P←3 2S). Ab initio calculations show a minimum-energy structure, in which Mg+ attaches to the O atom and one of the three F atoms of 2,2,2-trifluoroethanol, forming a five-membered ring. The calculated absorption spectrum corresponding to the minimum-energy structure agrees nicely with the experimental action spectrum. The branching fractions of the photoproducts are approximately constant in a given spectral range, but they change significantly across the spectral ranges. The constant branching fractions point to the ground state reactions following traversals from the initially accessed excited states through conical intersections. On the other hand, the observation of the electronic state-specific branching fractions is explained by the orbital alignments of the excited electron, which is dictated by the five-membered ring structure of the complex. © 2002 American Institute of Physics.
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82.50.Hp Processes caused by visible and UV light
33.20.Lg Ultraviolet spectra
31.15.A- Ab initio calculations

Suppression of decomposition of aniline cation in intense laser fields by cluster formation with ammonia molecules

Jun Watanabe, Ryuji Itakura, Akiyoshi Hishikawa, and Kaoru Yamanouchi

J. Chem. Phys. 116, 9697 (2002); http://dx.doi.org/10.1063/1.1475753 (6 pages) | Cited 7 times

Online Publication Date: 22 May 2002

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Mass-selected aniline cations and [aniline-(NH3)n]+ (n = 1 and 2) cluster ions are exposed to the femtosecond laser fields (λ ∼ 395 nm,I ∼ 4×1015 W/cm2) and the nanosecond laser fields (λ = 532 nm,I ∼ 2.7×1010 W/cm2) by using a tandem type time-of-flight mass spectrometer. In the case of the bare aniline cation, the decomposition forming the five-membered ring compound, cyclopentadienyl cation (C5H6+), dominantly proceeds in both the femtosecond and nanosecond laser fields. When one or two ammonia molecules are attached to the aniline cation, the decomposition is significantly suppressed. This suppression was interpreted in terms of an intermolecular energy flow through the hydrogen bonding. © 2002 American Institute of Physics.
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36.40.Wa Charged clusters
36.40.Qv Stability and fragmentation of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
33.80.Gj Diffuse spectra; predissociation, photodissociation
36.40.Jn Reactivity of clusters
82.30.Nr Association, addition, insertion, cluster formation
78.47.-p Spectroscopy of solid state dynamics
33.15.Ta Mass spectra
82.50.Hp Processes caused by visible and UV light

Nickel clusters: The influence of adsorbates on magnetic moments

Mark B. Knickelbein

J. Chem. Phys. 116, 9703 (2002); http://dx.doi.org/10.1063/1.1477175 (9 pages) | Cited 38 times

Online Publication Date: 22 May 2002

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Magnetic moments have been measured for bare, isolated nickel clusters Nin and their association complexes with carbon monoxide, oxygen, and hydrogen using a molecular beam deflection method. The moments measured for bare Nin are in general agreement with those previously reported by Apsel et al. [Phys. Rev. Lett. 76, 1441 (1996)], lying slightly lower overall. It is found that adsorbed carbon monoxide and hydrogen decrease magnetic moments of Nin. The reduction in moments can be substantial for smaller clusters: the moment of Ni8 is decreased by approximately 6 bohr magnetons by a single absorbed CO molecule. In general, the adsorbate-induced changes in magnetic moments diminish with increasing cluster size. The present results are in qualitative accord with previous measurements of the magnetization quenching effects of CO and H on nickel nanoparticles and thin nickel films. Atomic oxygen decreases cluster moments of some nickel clusters and increases those of others, an effect attributed to adsorbate-induced reconstruction. The experimental results are compared to detailed electronic structure calculations of nickel cluster–adsorbate complexes and to the predictions of the semiempirical bond order-rigid band model of Fourier and Salahub [Surf. Sci. 238, 330 (1990)]. © 2002 American Institute of Physics.
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75.30.Cr Saturation moments and magnetic susceptibilities
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
36.40.Jn Reactivity of clusters
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Mono-halobenzenes anion fragmentation induced by atom–molecule electron-transfer collisions

R. F. M. Lobo, P. Limão Vieira, S. S. M. C. Godinho, and M. J. Calhorda

J. Chem. Phys. 116, 9712 (2002); http://dx.doi.org/10.1063/1.1476697 (9 pages) | Cited 2 times

Online Publication Date: 22 May 2002

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The crossed molecular beam technique is used to study the formation of negative ions in monosubstituted halobenzenes, by electron transfer collisions, using potassium atoms as electron donor projectiles, in a collision energy range from 10 up to 500 eV. The negative ions are detected by time-of-flight mass spectrometry and a quasidiatomic dynamical behavior in the fragmentation is found. A minor negative fragmentation of the phenyl ring is also reported. The parent negative ion is not observed for the range of collision energies in use. Density functional theoretical calculations support the major abundance of the halogen negative ions and explain the completely different behavior in the negative fragmentation of these aromatic systems compared to the one previously observed with the three fluoro-iodo-benzene isomers. © 2002 American Institute of Physics.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.40.-g Chemical kinetics and reactions: special regimes and techniques
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
37.20.+j Atomic and molecular beam sources and techniques
31.15.E- Density-functional theory
33.15.Ta Mass spectra

Unimolecular decomposition of nitrooxyalkyl radicals from NO3–isoprene reaction

Dan Zhang and Renyi Zhang

J. Chem. Phys. 116, 9721 (2002); http://dx.doi.org/10.1063/1.1476695 (8 pages) | Cited 6 times

Online Publication Date: 22 May 2002

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The unimolecular decomposition of the nitrooxyalkyl radicals arising from the NO3-initiated reaction of isoprene is investigated. Density functional theory and ab initio molecular orbital calculations have been employed to determine the structures and energies of the transition states of decomposition of the nitrooxylalkyl radicals and the corresponding oxirane products. Geometry optimizations were performed using density functional theory at the B3LYP/6-31G(d,p) level and the single-point energies were computed using second-order Møller–Plesset perturbation theory and the coupled-cluster theory with single and double excitations including perturbative corrections for the triple excitations (CCSD(T)). At the CCSD(T)/6-31G(d) level of theory, the decomposition barriers range from 13 to 21 kcal mol−1, and the decomposition products (i.e., the separated oxirane and NO2) are 9 to 25 kcal mol−1 more stable than the nitrooxylalkyl radicals. The rate constants of decomposition of the nitrooxylalkyl radicals and the pressure-dependent oxirane yields have been calculated using the transition state theory and master equation formalism. © 2002 American Institute of Physics.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
31.15.E- Density-functional theory
31.15.A- Ab initio calculations
31.15.bw Coupled-cluster theory

Vibration and two-photon absorption

David M. Bishop, Josep M. Luis, and Bernard Kirtman

J. Chem. Phys. 116, 9729 (2002); http://dx.doi.org/10.1063/1.1477179 (11 pages) | Cited 27 times

Online Publication Date: 22 May 2002

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A treatment of nuclear vibrational motions in two-photon absorption is laid out in detail. Perturbation theory is used to develop working formulas for diatomic molecules and tested for the X 1Σ+–A 1Π transition of carbon monoxide. The results are compared with the exact numerical values. Certain vibrational contributions, not previously recognized, are found to make an important contribution to the two-photon absorption probability. © 2002 American Institute of Physics.
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33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.80.Wz Other multiphoton processes

A theoretical study of the azide (N3) doublet states. A new route to tetraazatetrahedrane (N4): N+N3→N4

Martina Bittererová, Henric Östmark, and Tore Brinck

J. Chem. Phys. 116, 9740 (2002); http://dx.doi.org/10.1063/1.1476310 (9 pages) | Cited 30 times

Online Publication Date: 22 May 2002

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The potential energy surfaces for the low-lying doublet states of the azide radical (N3) have been computed at the complete active space self-consistent field (CASSCF) level with the CAS(15,12) active space. The cc-pVTZ and aug-cc-pVTZ basis sets have been employed throughout the present work. Energies, geometries and harmonic frequencies were determined for the N3 linear ground electronic state (2Πg), a stable C2v ring structure (2B1), and a Cs transition state (2A″) connecting the ring and linear structures. Other N3 (C2v) stationary points (2A2, 2B1, and 2A1) have been characterized, as well. The vertical excitation energies for the doublet excited states of the N3 linear (2Πg) and stable ring (2B1) isomers were calculated using CASSCF and multireference configuration interaction [MRCI-SD(Q)] methods. A new route to tetraazatetrahedrane [N4(Td)] has been proposed on the N4 singlet potential energy surface within Cs symmetry. MRCI-SD(Q) calculations predict that N4 (Td) can be formed from atomic nitrogen in the 2D state and N3 (C2v, 2B1) in a barrierless exothermic reaction. The energy difference (D0) is 135.4 kcal/mol at the MRCI-SD(Q) level. © 2002 American Institute of Physics.
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31.50.-x Potential energy surfaces
82.20.Kh Potential energy surfaces for chemical reactions
31.15.xr Self-consistent-field methods
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.V- Electron correlation calculations for atoms, ions and molecules
82.30.Nr Association, addition, insertion, cluster formation

The vibrational energies of ozone up to the dissociation threshold: Dynamics calculations on an accurate potential energy surface

Rüdiger Siebert, Paul Fleurat-Lessard, Reinhard Schinke, Martina Bittererová, and S. C. Farantos

J. Chem. Phys. 116, 9749 (2002); http://dx.doi.org/10.1063/1.1473664 (19 pages) | Cited 82 times

Online Publication Date: 22 May 2002

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We present an ab initio potential energy surface for the ground electronic state of ozone. It is global, i.e., it covers the three identical C2v (open) minima, the D3h (ring) minimum, as well as the O(3P)+O2(3Σg−) dissociation threshold. The electronic structure calculations are performed at the multireference configuration interaction level with complete active space self-consistent-field reference functions and correlation consistent polarized quadruple zeta atomic basis functions. Two of the O–O bond distances, R1 and R2, and the O–O–O bending angle are varied on a regular grid (ca. 5000 points with R1 ≥ R2). An analytical representation is obtained by a three-dimensional cubic spline. The calculated potential energy surface has a tiny dissociation barrier and a shallow van der Waals minimum in the exit channel. The ring minimum is separated from the three open minima by a high potential barrier and therefore presumably does not influence the low-temperature kinetics. The dissociation energy is reproduced up to 90% of the experimental value. All bound states of nonrotating ozone up to more than 99% of the dissociation energy are calculated using the filter diagonalization technique and employing Jacobi coordinates. The three lowest transition energies for 16O3 are 1101.9 cm−1 (1103.14 cm−1), 698.5 cm−1 (700.93 cm−1), and 1043.9 cm−1 (1042.14 cm−1) for the symmetric stretch, the bending, and the antisymmetric stretch modes, respectively; the numbers in parentheses are the experimental values. The root-mean-square error for all measured transition energies for 16O3 is only 5 cm−1. The comparison is equally favorable for all other isotopomers, for which experimental frequencies are available. The assignment is made in terms of normal modes, despite the observation that with increasing energy an increasing number of states acquires local-mode character. At energies close to the threshold a large fraction of states is still unambiguously assignable, particularly those of the overtone progressions. This is in accord with the existence of stable classical periodic orbits up to very high energies. © 2002 American Institute of Physics.
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31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.xr Self-consistent-field methods
33.15.Mt Rotation, vibration, and vibration-rotation constants

Velocity modulation laser absorption spectroscopy of the A 2Πi←X 2Σ+ transition of the CS+ cation

Yuyan Liu, Chuanxi Duan, JinJun Liu, Ling Wu, Chaoxiong Xu, Yangqin Chen, P. A. Hamilton, and P. B. Davies

J. Chem. Phys. 116, 9768 (2002); http://dx.doi.org/10.1063/1.1470201 (8 pages) | Cited 8 times

Online Publication Date: 22 May 2002

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The laser absorption spectrum of the (5,0) and (6,0) bands of the A 2Πi←X 2Σ+ transition of CS+ has been recorded using velocity modulation spectroscopy enhanced by optical heterodyne and magnetic rotation effects. First, improved molecular constants for the ground state of the ion were determined by a global linear least-squares fit of combination differences from the (1,0) (5,0), and (6,0) bands. Then a standard model was used to analyze the perturbations between the vibrational levels of the A 2Πi state and high vibrational levels of the X 2Σ+ state, leading to molecular constants and perturbation parameters for the υA = 5 ∼ υX = 13 and υA = 6 ∼ υX = 14 complexes. A new set of equilibrium parameters has been derived for the A and X states by combining all the available spectroscopic data, weighted according to the accuracy of the input parameters. The equilibrium internuclear distances from the new analysis are X 2Σ+re = 1.492 156(78) Å and A 2Π re = 1.639 55(10) Å. The Rydberg–Klein–Rees potential energy curves for the A 2Πi and X 2Σ+ states were constructed using the improved equilibrium constants, and the Franck–Condon factors calculated for all vibrational bands up to υ″ = 11 and υ′ = 10 of the A 2Πi−X 2Σ+ system. The overlap integrals calculated from the RKR turning points were used to find the interaction parameters a and b from the experimental perturbation parameters ξ and η. The r dependence of the a and b values relevant to the perturbations in the (1,0), (5,0), and (6,0) bands is discussed. © 2002 American Institute of Physics.
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33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
31.50.Bc Potential energy surfaces for ground electronic states
33.15.Dj Interatomic distances and angles
33.20.Kf Visible spectra
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