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7 Mar 2006

Volume 124, Issue 9, Articles (09xxxx)

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Theoretical evidence for nonadiabatic vibrational deexcitation in H2(D2) state-to-state scattering from Cu(100)

A. C. Luntz, M. Persson, and Greg O. Sitz

J. Chem. Phys. 124, 091101 (2006); http://dx.doi.org/10.1063/1.2177664 (4 pages) | Cited 13 times

Online Publication Date: 1 March 2006

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Dynamical calculations are presented for electronically nonadiabatic vibrational deexcitation of H2 and D2 in scattering from Cu(111). Both the potential energy surface and the nonadiabatic coupling strength were obtained from density functional calculations. The theoretically predicted magnitude of the deexcitation and its dependence on incident energy and isotope are all in agreement with state-to-state scattering experiments [on Cu(100)], and this gives indirect evidence for a nonadiabatic mechanism of the observed deexcitation. Direct evidence could be obtained by measuring the chemicurrent associated with the deexcitation, and its properties have been predicted.
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34.35.+a Interactions of atoms and molecules with surfaces
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
31.15.E- Density-functional theory
33.15.Mt Rotation, vibration, and vibration-rotation constants

Self-interaction-free exchange-correlation functional for thermochemistry and kinetics

Paula Mori-Sánchez, Aron J. Cohen, and Weitao Yang

J. Chem. Phys. 124, 091102 (2006); http://dx.doi.org/10.1063/1.2179072 (4 pages) | Cited 69 times

Online Publication Date: 3 March 2006

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We develop a self-interaction-free exchange-correlation functional which is very accurate for thermochemistry and kinetics. This is achieved by theoretical construction of the functional form and nonlinear fitting. We define a simple interpolation of the adiabatic connection that uses exact exchange, generalized gradient approximation (GGA) and meta-GGA functionals. The performance is optimized by fitting a small number of empirical parameters. Overall the new functional improves significantly upon hybrids and meta-GGAs while correctly describing one-electron systems. The mean absolute error on a large set of reaction barriers is reduced to 1.99 kcal/mol.
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82.60.-s Chemical thermodynamics
82.20.-w Chemical kinetics and dynamics
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back to top Theoretical Methods and Algorithms

High precision variational calculations for the Born-Oppenheimer energies of the ground state of the hydrogen molecule

James S. Sims and Stanley A. Hagstrom

J. Chem. Phys. 124, 094101 (2006); http://dx.doi.org/10.1063/1.2173250 (7 pages) | Cited 22 times

Online Publication Date: 1 March 2006

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Born-Oppenheimer approximation Hylleraas variational calculations with up to 7034 expansion terms are reported for the math ground state of neutral hydrogen at various internuclear distances. The nonrelativistic energy is calculated to be −1.174 475 714 220(1) hartree at R = 1.4 bohr, which is four orders of magnitude better than the best previous Hylleraas calculation, that of Wolniewicz [J. Chem. Phys. 103, 1792 (1995) ]. This result agrees well with the best previous variational energy, −1.174 475 714 216 hartree, of Cencek (personal communication), obtained using explicitly correlated Gaussians (ECGs) [ Cencek and Rychlewski, J. Chem. Phys. 98, 1252 (1993); Cencek et al., ibid. 95, 2572 (1995); Rychlewski, Adv. Quantum Chem. 31, 173 (1998) ]. The uncertainty in our result is also discussed. The nonrelativistic energy is calculated to be −1.174 475 931 399(1) hartree at the equilibrium R = 1.4011 bohr distance. This result also agrees well with the best previous variational energy, −1.174 475 931 389 hartree, of Cencek and Rychlewski [ Rychlewski, Handbook of Molecular Physics and Quantum Chemistry, edited by S. Wilson (Wiley, New York, 2003), Vol. 2, pp. 199–218; Rychlewski, Explicitly Correlated Wave Functions in Chemistry and Physics Theory and Applications, edited by J. Rychlewski (Kluwer Academic, Dordrecht, 2003), pp. 91–147. ], obtained using ECGs.
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31.15.xt Variational techniques
33.15.Mt Rotation, vibration, and vibration-rotation constants

The quantum defect: The true measure of time-dependent density-functional results for atoms

Meta van Faassen and Kieron Burke

J. Chem. Phys. 124, 094102 (2006); http://dx.doi.org/10.1063/1.2173252 (9 pages) | Cited 8 times

Online Publication Date: 1 March 2006

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Quantum defect theory is applied to (time-dependent) density-functional calculations of Rydberg series for closed shell atoms: He, Be, and Ne. The performance and behavior of such calculations are much better quantified and understood in terms of the quantum defect rather than transition energies.
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31.15.E- Density-functional theory

Explicitly correlated local second-order perturbation theory with a frozen geminal correlation factor

Frederick R. Manby, Hans-Joachim Werner, Thomas B. Adler, and Andrew J. May

J. Chem. Phys. 124, 094103 (2006); http://dx.doi.org/10.1063/1.2173247 (6 pages) | Cited 54 times

Online Publication Date: 1 March 2006

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The recently introduced MP2-R12/2*A(loc) and LMP2-R12/2*A(loc) methods are modified to use a short-range correlation factor expanded as a fixed linear combination of Gaussian geminals. Density fitting is used to reduce the effort for integral evaluation, and local approximations are introduced to improve the scaling of the computational resources with molecular size. The MP2-F12/2*A(loc) correlation energies converge very rapidly with respect to the atomic orbital basis set size. Already with the aug-cc-pVTZ basis the correlation energies computed for a set of 21 small molecules are found to be within 0.5% of the MP2 basis set limit. Furthermore the short-range correlation factor leads to an improved convergence of the resolution of the identity, and eliminates problems with long-range errors in density fitting caused by the linear r12 factor. The DF-LMP2-F12/2*A(loc) method is applied to compute second-order correlation energies for molecules with up to 49 atoms and more than 1600 basis functions.
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31.15.xp Perturbation theory

Multiple time step update schemes for dissipative particle dynamics

Ask F. Jakobsen, Gerhard Besold, and Ole G. Mouritsen

J. Chem. Phys. 124, 094104 (2006); http://dx.doi.org/10.1063/1.2167645 (6 pages) | Cited 5 times

Online Publication Date: 1 March 2006

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In dynamical simulations of coarse-grained models of soft matter in a solvent a considerable amount of the total simulation time is generically spent on updating the solvent particles, although their dynamics is in most cases not of primary interest. In order to speed up such simulations and as a consequence allow to extend them to cover larger system sizes, we propose and examine various multiple, specifically dual, time step update algorithms for dissipative particle dynamics simulations that are based on the velocity-Verlet scheme [ Phys. Rev. 159, 98 (1967) ]. Common to all update variants is that the solvent beads are updated with a lower frequency than the bonded interactions within the solute. As a test case we consider a coarse-grained model of a lipid bilayer in water. Our results demonstrate that a considerable saving of simulation time can be gained, while the obtained simulation data are within error brackets virtually identical to those obtained for the reference single time step update scheme.
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87.14.Cc Lipids
87.16.D- Membranes, bilayers, and vesicles
87.16.A- Theory, modeling, and simulations

Time-dependent density functional theory calculations for core-excited states: Assessment of standard exchange-correlation functionals and development of a novel hybrid functional

Ayako Nakata, Yutaka Imamura, Takao Otsuka, and Hiromi Nakai

J. Chem. Phys. 124, 094105 (2006); http://dx.doi.org/10.1063/1.2173987 (9 pages) | Cited 23 times

Online Publication Date: 2 March 2006

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A new hybrid functional for accurate descriptions of core and valence excitations, the core-valence Becke's three-parameter exchange (B3)+Lee-Yang-Paar (LYP) correlation functional (CV-B3LYP), is proposed. The construction of the new hybrid functional is based on the assessment that B3LYP performs well for properties concerning valence electrons and Becke's half-and-half exchange+LYP functional (BHHLYP), which includes 50% portion of Hartree-Fock exchange, performs well for core excitations. By using the appropriate portions of Hartree-Fock exchange for core and valence regions separately, CV-B3LYP overcomes the disadvantages of BHHLYP and B3LYP, which give inferior descriptions of valence and core excitations, respectively. Density functional theory (DFT) calculations with the CV-B3LYP functional reproduce core- and valence-orbital energies close to those of BHHLYP and B3LYP, respectively. Time-dependent DFT calculations with the CV-B3LYP functional yield both core- and valence-excitation energies with reasonable accuracy.
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31.15.E- Density-functional theory
31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.xr Self-consistent-field methods

Simulation of x-ray absorption near-edge spectra and x-ray fluorescence spectra of optically excited molecules

R. K. Pandey and Shaul Mukamel

J. Chem. Phys. 124, 094106 (2006); http://dx.doi.org/10.1063/1.2173243 (10 pages) | Cited 3 times

Online Publication Date: 2 March 2006

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The x-ray absorption near-edge spectra (XANES) and fluorescence spectra of molecules in the ground state and optically excited states are computed using time-dependent density functional theory and time-dependent Hartree-Fock theory. The calculated XANES spectra of optically excited methanol, benzonitrile, hydrogen sulphide, and titanium tetrachloride and the fluorescence spectra of optically excited methanol can be used to simulate ultrafast optical pump/x-ray probe experiments.
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33.20.Rm X-ray spectra
33.50.Dq Fluorescence and phosphorescence spectra
31.15.E- Density-functional theory
31.15.xr Self-consistent-field methods

Geometries and properties of excited states in the gas phase and in solution: Theory and application of a time-dependent density functional theory polarizable continuum model

Giovanni Scalmani, Michael J. Frisch, Benedetta Mennucci, Jacopo Tomasi, Roberto Cammi, and Vincenzo Barone

J. Chem. Phys. 124, 094107 (2006); http://dx.doi.org/10.1063/1.2173258 (15 pages) | Cited 117 times

Online Publication Date: 3 March 2006

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In this paper we present the theory and implementation of analytic derivatives of time-dependent density functional theory (TDDFT) excited states energies, both in vacuo and including solvent effects by means of the polarizable continuum model. The method is applied to two case studies: p-nitroaniline and 4-(dimethyl)aminobenzonitrile. For both molecules PCM-TDDFT is shown to be successful in supporting the analysis of experimental data with useful insights for a better understanding of photophysical and photochemical pathways in solution.
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31.15.E- Density-functional theory
31.70.Dk Environmental and solvent effects
33.15.Bh General molecular conformation and symmetry; stereochemistry

Scaling down the Perdew-Zunger self-interaction correction in many-electron regions

Oleg A. Vydrov, Gustavo E. Scuseria, John P. Perdew, Adrienn Ruzsinszky, and Gábor I. Csonka

J. Chem. Phys. 124, 094108 (2006); http://dx.doi.org/10.1063/1.2176608 (8 pages) | Cited 29 times

Online Publication Date: 3 March 2006

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Semilocal density functional approximations (DFAs) for the exchange-correlation energy suffer from self-interaction error, which is believed to be the cause of many of the failures of common DFAs, such as poor description of charge transfer and transition states of chemical reactions. The standard self-interaction correction (SIC) of Perdew and Zunger mends some of these failures but spoils such essential properties as thermochemistry and equilibrium bond lengths. The Perdew-Zunger SIC seems to overcorrect many-electron systems. In this paper, we propose a modified SIC, which is scaled down in many-electron regions. The new SIC has an improved performance for many molecular properties, including total energies, atomization energies, barrier heights of chemical reactions, ionization potentials, electron affinities, and bond lengths. The local spin-density approximation (LSDA) benefits from SIC more than higher-level functionals do. The scaled-down SIC has only one adjustable parameter. Rationalization of the optimal value of this parameter enables us to construct an almost-nonempirical version of the scaled-down SIC-LSDA, which is significantly better than uncorrected LSDA and even better than the uncorrected generalized gradient approximation. We present an analysis of the formal properties of the scaled-down SIC and define possible directions for further improvements. In particular, we find that exactness for all one-electron densities does not guarantee correct asymptotics for the exchange-correlation potential of a many-electron system.
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31.15.E- Density-functional theory
33.15.Fm Bond strengths, dissociation energies
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Dj Interatomic distances and angles

Efficient computation of the exchange-correlation contribution in the density functional theory through multiresolution

Jing Kong, Shawn T. Brown, and Laszlo Fusti-Molnar

J. Chem. Phys. 124, 094109 (2006); http://dx.doi.org/10.1063/1.2173244 (7 pages) | Cited 11 times

Online Publication Date: 6 March 2006

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A new algorithm is presented to improve the efficiency of the computation of exchange-correlation contributions, a major time-consuming step in a density functional theory (DFT) calculation. The new method, called multiresolution exchange correlation (mrXC), takes advantage of the variation in resolution among the Gaussian basis functions and shifts the calculation associated with low-resolution (smooth) basis function pairs to an even-spaced cubic grid. The cubic grid is much less dense in the vicinity of the nuclei than the atom-centered grid and the computation on the former is shown to be much more efficient than on the latter. MrXC does not alter the formalism of the current standard algorithm based on the atom-centered grid (ACG), but instead employs two fast and accurate transformations between the ACG and the cubic grid. Preliminary results with local density approximation have shown that mrXC yields three to five times improvement in efficiency with negligible error. The extension to DFT functionals with generalized gradient approximation is also briefly discussed.
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31.15.E- Density-functional theory

A surface hopping method for chemical reaction dynamics in solution described by diabatic representation: An analysis of tunneling and thermal activation

Atsushi Yamada and Susumu Okazaki

J. Chem. Phys. 124, 094110 (2006); http://dx.doi.org/10.1063/1.2172595 (11 pages) | Cited 2 times

Online Publication Date: 6 March 2006

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We present a surface hopping method for chemical reaction in solution based on diabatic representation, where quantum mechanical time evolution of the vibrational state of the reacting nuclei as well as the reaction-related electronic state of the system are traced simultaneously together with the classical motion of the solvent. The method is effective in describing the system where decoherence between reactant and product states is rapid. The diabatic representation can also give a clear picture for the reaction mechanism, e.g., thermal activation mechanism and a tunneling one. An idea of molecular orbital theory has been applied to evaluate the solvent contribution to the electronic coupling which determines the rate of reactive transition between the reactant and product potential surfaces. We applied the method to a model system which can describe complex chemical reaction of the real system. Two numerical examples are presented in order to demonstrate the applicability of the present method, where the first example traces a chemical reaction proceeded by thermal activation mechanism and the second examines tunneling mechanism mimicking a proton transfer reaction.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Xr Quantum effects in rate constants (tunneling, resonances, etc.)
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Ej Quantum theory of reaction cross section

Singularities of Møller-Plesset energy functions

Alexey V. Sergeev and David Z. Goodson

J. Chem. Phys. 124, 094111 (2006); http://dx.doi.org/10.1063/1.2173989 (11 pages) | Cited 7 times

Online Publication Date: 7 March 2006

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The convergence behavior of Møller-Plesset (MP) perturbation series is governed by the singularity structure of the energy, with the energy treated as a function of the perturbation parameter. Singularity locations, determined from quadratic approximant analysis of high-order series, are presented for a variety of atoms and small molecules. These results can be used as benchmarks for understanding the convergence of low-order methods such as MP4 and for developing and testing summation methods that model the singularity structure. The positions and types of singularities confirm previous qualitative predictions based on functional analysis of the Schrödinger equation.
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31.15.xp Perturbation theory

Theoretical scheme for the shear viscosity of Lennard-Jones fluids

M. Robles and L. I. Uruchurtu

J. Chem. Phys. 124, 094112 (2006); http://dx.doi.org/10.1063/1.2176676 (6 pages) | Cited 3 times

Online Publication Date: 7 March 2006

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We use the shear viscosity expression from the Enskog theory of dense gases in a perturbative scheme for the Lennard-Jones (LJ) fluid. This perturbative scheme is formulated by combining the analytic rational function approximation method of Bravo Yuste and Santos [ Phys. Rev. A 43, 5418 (1991) ] for the radial distribution function of hard-sphere fluids and the well known Mansoori-Canfield/Rasaiah-Stell perturbation theory to determine an effective diameter for the LJ fluid. The scheme is reliable on a wide range of temperatures and densities, and is very accurate around the critical point. Using this information, we build an accurate empirical formula for the shear viscosity in the liquid phase, which fits the recent data [ K. Meier et al., J. Chem. Phys. 121, 3671 (2004) ] in the whole simulation range.
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66.20.-d Viscosity of liquids; diffusive momentum transport
61.20.Gy Theory and models of liquid structure
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Internal motions in a complex consisting of a rare gas atom and a C2v molecule: Theoretical formulations and their applications to Fourier transform microwave spectra of Ne-dimethyl ether and Ar-dimethyl ether

Yasumasa Morita, Nobukimi Ohashi, Yoshiyuki Kawashima, and Eizi Hirota

J. Chem. Phys. 124, 094301 (2006); http://dx.doi.org/10.1063/1.2172609 (14 pages) | Cited 4 times

Online Publication Date: 1 March 2006

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The internal motion of the rare gas atom, i.e., the relative motion of the two constituents, in a complex shown in the title was discussed by paying special attention to its effect on the rotational motion of the complex in order to extract as much precise information on this motion as possible from the observed rotational spectra. We have set up two theoretical formulations. One is based on a coordinate axis system attached to the C2v molecule, but its origin is floating with the motion of the rare gas atom, while keeping the orientation parallel to the original C2v molecule-fixed coordinate system. The second approach starts with counting the number of equivalent potential minima, which are well separated from the others by high potential barriers, and then collects all permutation-inversion operations, which transform the system from one minimum to another, to set up a group appropriate for the complex. By using the symmetry properties thus derived, a phenomenological Hamiltonian is set up to fit the observed spectra. The two formulations result in alike rotational energy matrices, and we have applied them to analyze the internal motions in the two complexes of present concern: neon-dimethyl ether (Ne–DME) and argon-dimethyl ether (Ar–DME). Some of the transitions observed by the present study exhibited additional splittings, which were interpreted as due to an internal rotation of the methyl groups in DME and were analyzed by the second formulation. For Ar–DME the splittings appeared only in high-K transitions, yielding the V3 potential barrier to be 778(1) cm−1, whereas those observed for Ne–DME were ascribed to the effects of the CH3 internal rotation on the inversion splitting.
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33.20.Bx Radio-frequency and microwave spectra
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

A theoretical investigation of hyperpolarizability for small GanAsm (n+m = 4–10) clusters

Y.-Z. Lan, W.-D. Cheng, D.-S. Wu, J. Shen, S.-P. Huang, H. Zhang, Y.-J. Gong, and F.-F. Li

J. Chem. Phys. 124, 094302 (2006); http://dx.doi.org/10.1063/1.2173993 (8 pages) | Cited 11 times

Online Publication Date: 1 March 2006

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In this paper, the second and third order polarizabilities of small GanAsm (n+m = 4–10) clusters are systematically investigated using the time dependent density functional theory (TDDFT)/6-311+G* combined with the sum-over-states method (SOS//TDDFT/6-311+G*). For the static second order polarizabilities, the two-level term (βvec.2) makes a significant contribution to the βvec for all considered GanAsm clusters except for the Ga3As4 cluster. And, for the static third order polarizabilities, the positive channel (〈γ〉II) makes a larger contribution to 〈γ〉tot than the negative channel (〈γ〉I). Similar to the cubic GaAs bulk materials, the small GanAsm cluster assembled materials exhibit large second order (1×10−6 esu) and third order susceptibilities (5×10−11 esu). The dynamic behavior of β(−2ω;ω,ω) and γ(−3ω;ω,ω,ω) show that the small GanAsm cluster will be a good candidate of nonlinear optical materials due to the avoidance of linear resonance photoabsorption.
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36.40.-c Atomic and molecular clusters
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.E- Density-functional theory
42.70.-a Optical materials
42.65.An Optical susceptibility, hyperpolarizability

Calculations of partial cross sections for photofragmentation processes using complex absorbing potentials

T. P. Grozdanov, L. Andric, and R. McCarroll

J. Chem. Phys. 124, 094303 (2006); http://dx.doi.org/10.1063/1.2174014 (8 pages) | Cited 3 times

Online Publication Date: 1 March 2006

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We investigate the use of complex absorbing potentials for the calculation of partial cross sections in multichannel photofragmentation processes. An exactly solvable, coupled-two-channel problem involving square-well potentials is used to compare the performance of various types of absorbing potentials. Special emphasis is given to the near-threshold regions and the conditions under which the numerical results are able to reproduce the Wigner threshold laws. It was found that singular, transmission-free absorbing potentials perform better than those of power or polynomial form.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
82.50.-m Photochemistry
82.20.Pm Rate constants, reaction cross sections, and activation energies

On the influence of microsolvation by argon atoms on the electron affinity properties of water dimer

Pawel Wielgus, Robert W. Gora, Borys Szefczyk, Szczepan Roszak, and Jerzy Leszczynski

J. Chem. Phys. 124, 094304 (2006); http://dx.doi.org/10.1063/1.2173994 (10 pages)

Online Publication Date: 1 March 2006

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This work provides a comparison of neutral (H2O)2Arn and negatively charged (H2O)2−Arn complexes. The excess electron stabilizes the complexes and leads to the trans to cis rearrangement within the water dimer core. In the case of small complexes (n ⩽ 4) the microsolvation of the dimer by argon atoms arises on the trans side with respect to the donor water molecule. The stabilization of an excess electron is enhanced by the delocalization of the electronic charge density due to microsolvation. The process of cis to trans rotation is induced by the electric field of the approaching negative charge. The interaction energy decomposition suggests a more ionic character of binding in the negatively charged complexes. The attachment of an electron is controlled by the correlation energy.
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82.30.Nr Association, addition, insertion, cluster formation
82.30.Qt Isomerization and rearrangement
82.20.-w Chemical kinetics and dynamics

Velocity map imaging study of BrCl photodissociation at 467 nm: Determination of all odd-rank (K = 1 and 3) anisotropy parameters for the Cl(math) photofragments

Andrey G. Smolin, Oleg S. Vasyutinskii, Olivier P. J. Vieuxmaire, Michael N. R. Ashfold, Gabriel G. Balint-Kurti, and Andrew J. Orr-Ewing

J. Chem. Phys. 124, 094305 (2006); http://dx.doi.org/10.1063/1.2168149 (11 pages) | Cited 11 times

Online Publication Date: 2 March 2006

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Resonance-enhanced multiphoton ionization and velocity map imaging of the Cl(math) fragments of BrCl photolysis at 467.16 nm have been used to obtain a complete set of orientation parameters (with ranks K = 1 and 3) describing the polarization of the electronic angular momentum. The experiments employ two geometries distinguished only by the circular or linear polarization of the photolysis laser beam. Normalized difference images constructed from the data accumulated using a right or left circularly polarized probe-laser beam, counterpropagating with the photolysis laser, were fitted to basis images corresponding to contributions from various odd-rank anisotropy parameters. Expressions are given for the difference images in terms of the K = 1 and 3 anisotropy parameters, which describe coherent and incoherent parallel and perpendicular excitation and dissociation mechanisms. The nonzero values of the anisotropy parameters are indicative of nonadiabatic dissociation dynamics, with likely contributions from flux on the A math(1),B math(0+),C math(1), and X math(0+) states as well as one further Ω = 1 state, all of which correlate adiabatically to Cl(math)+Br(math) photofragments. The magnitudes of the parameters depend both on the amplitudes of dissociative flux in these states, and also on the phases accumulated by the nuclear wave functions for different dissociation pathways.
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82.50.Pt Multiphoton processes
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Kh Potential energy surfaces for chemical reactions

A dispersed fluorescence and ab initio investigation of the math math and math math electronic states of the PH2 molecule

Z. J. Jakubek, P. R. Bunker, M. Zachwieja, S. G. Nakhate, B. Simard, S. N. Yurchenko, W. Thiel, and Per Jensen

J. Chem. Phys. 124, 094306 (2006); http://dx.doi.org/10.1063/1.2168155 (5 pages) | Cited 4 times

Online Publication Date: 3 March 2006

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In this work, the math math and math math electronic states of the phosphino (PH2) free radical have been studied by dispersed fluorescence and ab initio methods. PH2 molecules were produced in a molecular free-jet apparatus by laser vaporizing a silicon rod in the presence of phosphine (PH3) gas diluted in helium. The laser-induced fluorescence, from the excited math math electronic state down to the ground electronic state, was dispersed and analyzed. Ten (υ1υ2υ3) vibrationally excited levels of the ground electronic state, with υ1 ⩽ 2, υ2 ⩽ 6, and υ3 = 0, have been observed. Ab initio potential-energy surfaces for the math math and math math electronic states have been calculated at 210 points. These two states correlate with a math state at linearity and they interact by the Renner-Teller coupling and spin-orbit coupling. Using the ab initio potential-energy surfaces with our RENNER computer program system, the vibronic structure and relative intensities of the math math→math math emission band system have been calculated in order to corroborate the experimental assignments.
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31.15.A- Ab initio calculations
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.50.Dq Fluorescence and phosphorescence spectra

Reaction dynamics of CN+O2→NCO+O(math)

Mark F. Witinski, Marívi Ortiz-Suárez, and H. Floyd Davis

J. Chem. Phys. 124, 094307 (2006); http://dx.doi.org/10.1063/1.2173261 (6 pages) | Cited 3 times

Online Publication Date: 3 March 2006

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We have used oxygen Rydberg time-of-flight spectroscopy to carry out a crossed molecular beam study of the CN+O2 reaction at collision energies of 3.1 and 4.1 kcal/mol. The O(math) products were tagged by excitation to high-n Rydberg levels and subsequently field ionized at a detector. The translational energy distributions were broad, indicating that the NCO is formed with a wide range of internal excitation, and the angular distribution was forward-backward symmetric, indicating the participation of NCOO intermediates with lifetimes comparable to or longer than their rotational periods. Rice-Ramsperger-Kassel-Marcus modeling of the dissociation of NCOO to NCO+O suggests that Do(NC–OO) ≥ 38 kcal/mol, which is consistent with several theoretical calculations. Implications for the competing CO+NO channel are discussed.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.40.-g Chemical kinetics and reactions: special regimes and techniques
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Electric field effects on water clusters (n = 3–5): Systematic ab initio study of structures, energetics, and transition states

Young Cheol Choi, Chaeho Pak, and Kwang S. Kim

J. Chem. Phys. 124, 094308 (2006); http://dx.doi.org/10.1063/1.2173259 (4 pages) | Cited 25 times

Online Publication Date: 6 March 2006

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The structures, energetics, and transition states of water clusters (trimer to pentamer, n = 3–5) are investigated as a function of electric field by using ab initio calculations. With an increasing strength of the field, the most stable cyclic structures of trimer, tetramer, and pentamer open up to align their dipole moments along the direction of the field. For the lower strength (below 0.3 V/Å) of the electric field, the dipole moment of each water monomer is along the same direction with the field, while it retains the cyclic structure. For the higher strength of the field, to have a higher dipole moment for the cluster along the field direction, each cyclic structure opens up to form a linear chain or “water wire.” We have investigated the transition state structures between the cyclic and linear forms for the field strengths of 0.3–0.4 V/Å where both cyclic and linear forms are energetically comparable.
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36.40.Mr Spectroscopy and geometrical structure of clusters
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.A- Ab initio calculations
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Theoretical calculation of the excited states of the KCs molecule including the spin-orbit interaction

M. Korek, Y. A. Moghrabi, and A. R. Allouche

J. Chem. Phys. 124, 094309 (2006); http://dx.doi.org/10.1063/1.2173239 (10 pages) | Cited 8 times

Online Publication Date: 7 March 2006

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For the molecule KCs the potential energy has been calculated for the 72 lowest molecular states Ω. Using an ab initio method the calculation is based on nonempirical pseudopotentials within the range of 5.0a0–34.0a0 of the internuclear distance R. Gaussian basis sets have been used for both atoms and spin-orbit effects have been taken into account through a semiempirical spin-orbit pseudopotential added to the electrostatic Hamiltonian. The spectroscopic constants for 60 states have been calculated by fitting the calculated energy values to a polynomial in terms of the internuclear distance R. The components of the spin-orbit splitting for (1,2,5,6) math and (1) math have been identified. The comparison of the present results with those available in the literature shows a very good agreement, while the other results, to the best of our knowledge, are given here for the first time.
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31.15.A- Ab initio calculations
31.50.Df Potential energy surfaces for excited electronic states

Effects of conjugation length, electron donor and acceptor strengths on two-photon absorption cross sections of asymmetric zinc-porphyrin derivatives

Òscar Rubio-Pons, Yi Luo, and Hans Ågren

J. Chem. Phys. 124, 094310 (2006); http://dx.doi.org/10.1063/1.2178790 (5 pages) | Cited 17 times

Online Publication Date: 7 March 2006

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Exceptionally large two-photon absorption cross sections at the infrared region have been revealed by time-dependent density functional theory calculations for asymmetric charge-transfer conjugated zinc-porphyrin derivatives. The largest two-photon cross section is found to be more than one order of magnitude larger than for the conventional two-photon active organic molecules. The calculations show that the formation of strong charge-transfer states depends on the length of the conjugation bridge between the zinc-porphyrin core and the electron donor∕acceptor. The two-photon absorption cross section can be greatly enhanced by increasing the strengths of the electron donor∕acceptor.
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31.15.E- Density-functional theory
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
34.70.+e Charge transfer
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Application of a two-length-scale field theory to the solvation of neutral and charged molecules

G. Sitnikov, M. Taran, A. Muryshev, and S. Nechaev

J. Chem. Phys. 124, 094501 (2006); http://dx.doi.org/10.1063/1.2172603 (15 pages) | Cited 2 times

Online Publication Date: 1 March 2006

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We develop a continuous self-consistent theory of solute-water interactions that allows determination of the hydrophobic layer around a solute molecule of any geometry, with an explicit account of solvent structure described by its correlation function. We compute the mean solvent density profile n(r) surrounding the solute molecule as well as its solvation free energy ΔG. We compare the two-length-scale field theory to the numerical data of Monte Carlo simulations found in the literature for spherical molecules and discuss the possibility of self-consistent adjustment of the free parameters of the theory. In the framework of this approach, we compute the solvation free energies of alkane molecules and the free energy of interaction of two spheres of radius R separated by the distance D. We describe the general setting of the self-consistent account of electrostatic interactions in the framework of our model where the water is considered not as a continuous medium but as a gas of dipoles. We analyze the limiting cases where the proposed theory coincides with the electrostatics of a continuous medium.
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82.30.Nr Association, addition, insertion, cluster formation
82.60.Lf Thermodynamics of solutions
65.20.-w Thermal properties of liquids
61.20.Ja Computer simulation of liquid structure
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