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28 Dec 2007

Volume 127, Issue 24, Articles (24xxxx)

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Evidence for an energy level substructure of molecular states in helium droplets

Rudolf Lehnig, Nicholas V. Blinov, and Wolfgang Jäger

J. Chem. Phys. 127, 241101 (2007); http://dx.doi.org/10.1063/1.2822041 (4 pages) | Cited 8 times

Online Publication Date: 28 December 2007

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The pure tunneling inversion transition of ammonia embedded in 4He droplets was investigated in the microwave frequency range. We observed a spectrum that consists of a sharp peak, only 15 MHz wide, on top of a broad feature. The peculiar line shape could be simulated with an empirical model and is a clear experimental evidence for an energy level substructure of molecular states in doped helium droplets.
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33.15.Bh General molecular conformation and symmetry; stereochemistry
33.20.Bx Radio-frequency and microwave spectra
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back to top Theoretical Methods and Algorithms

The electronic nonadiabatic coupling term: Can it be ignored in dynamic calculations?

G. J. Halász, A. Vibók, S. Suhai, and M. Baer

J. Chem. Phys. 127, 244101 (2007); http://dx.doi.org/10.1063/1.2806167 (8 pages) | Cited 8 times

Online Publication Date: 27 December 2007

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Whereas the search for the degeneracy points which are better known as conical intersections (or ci-points) is usually carried out with a lot of devotion, the nonadiabatic coupling terms (NACTs) which together with the adiabatic potential energy surfaces appear in the nuclear Born-Oppenheimer-Schrödinger equation are ignored in most dynamical calculations. In the present article we consider two well known frameworks, namely, the semiclassical surface hopping method and the vibrational coupling model Hamiltonian that avoid the NACTs and examine to what extent, this procedure is justified.
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31.50.Gh Surface crossings, non-adiabatic couplings
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis

Calculation of the magnetic circular dichroism B term from the imaginary part of the Verdet constant using damped time-dependent density functional theory

Mykhaylo Krykunov, Michael Seth, Tom Ziegler, and Jochen Autschbach

J. Chem. Phys. 127, 244102 (2007); http://dx.doi.org/10.1063/1.2806990 (16 pages) | Cited 15 times

Online Publication Date: 27 December 2007

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A time-dependent density functional theory (TDDFT) formalism with damping for the calculation of the magnetic optical rotatory dispersion and magnetic circular dichroism (MCD) from the complex Verdet constant is presented. For a justification of such an approach, we have derived the TDDFT analog of the sum-over-states formula for the Verdet constant. The results of the MCD calculations by this method for ethylene, furan, thiophene, selenophene, tellurophene, and pyrrole are in good agreement with our previous theoretical sum-over-states MCD spectra. For the π→π* transition of propene, we have obtained a positive Faraday B term. It is located between the two negative B terms. This finding is in agreement with experiment in the range of 6–8 eV.
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33.57.+c Magneto-optical and electro-optical spectra and effects
33.55.+b Optical activity and dichroism

Two-photon absorption of [2.2]paracyclophane derivatives in solution: A theoretical investigation

Lara Ferrighi, Luca Frediani, Eirik Fossgaard, and Kenneth Ruud

J. Chem. Phys. 127, 244103 (2007); http://dx.doi.org/10.1063/1.2814168 (10 pages) | Cited 8 times

Online Publication Date: 27 December 2007

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The two-photon absorption of a class of [2.2]paracyclophane derivatives has been studied using quadratic response and density functional theories. For the molecules investigated, several effects influencing the two-photon absorption spectra have been investigated, such as side-chain elongation, hydrogen bonding, the use of ionic species, and solvent effects, the latter described by the polarizable continuum model. The calculations have been carried out using a recent parallel implementation of the polarizable continuum model in the DALTON code. Special attention is given to those aspects that could explain the large solvent effect on the two-photon absorption cross sections observed experimentally for this class of compounds.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.70.Jg Line and band widths, shapes, and shifts

Uniqueness of the iterative solution of the optimized effective potential equation

D. P. Joubert

J. Chem. Phys. 127, 244104 (2007); http://dx.doi.org/10.1063/1.2821122 (5 pages) | Cited 5 times

Online Publication Date: 27 December 2007

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The optimized effective potential (OEP) equation can be used in a numerically efficient self-consistent form to solve for the density functional exchange and correlation potentials, as shown in a recent paper of Kümmel and Perdew [Phys. Rev. Lett. 90, 43004 (2003) ]. The uniqueness of an iterative solution of the OEP equation has not yet been adequately addressed. In this paper, it is shown that no nonconstant multiplicative potentials that can contaminate an iterative solution of the OEP equation exist and, hence, that formally the exact exchange-correlation potential determined form of the OEP equation is unique to within a constant.
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31.15.eg Exchange-correlation functionals (in current density functional theory)
31.15.xr Self-consistent-field methods

Multireference self-consistent-field energies without the many-electron wave function through a variational low-rank two-electron reduced-density-matrix method

Gergely Gidofalvi and David A. Mazziotti

J. Chem. Phys. 127, 244105 (2007); http://dx.doi.org/10.1063/1.2817602 (6 pages) | Cited 7 times

Online Publication Date: 28 December 2007

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The variational two-electron reduced-density-matrix (2-RDM) method allows for the computation of accurate ground-state energies and 2-RDMs of atoms and molecules without the explicit construction of an N-electron wave function. While previous work on variational 2-RDM theory has focused on calculating full configuration-interaction energies, this work presents the first application toward approximating multiconfiguration self-consistent-field (MCSCF) energies via low-rank restrictions on the 1- and 2-RDMs. The 2-RDM method with two- or three-particle N-representability conditions reduces the exponential active-space scaling of MCSCF methods to a polynomial scaling. Because the first-order algorithm [ Mazziotti, Phys. Rev. Lett. 93, 213001 (2004) ] represents each form of the 1- and 2-RDMs by a matrix factorization, the RDMs are readily defined to have a low rank rather than a full rank by setting the matrix factors to be rectangular rather than square. Results for the potential energy surfaces of hydrogen fluoride, water, and the nitrogen molecule show that the low-rank 2-RDM method yields accurate approximations to the MCSCF energies. We also compute the energies along the symmetric stretch of a 20-atom hydrogen chain where traditional MCSCF calculations, requiring more than 17×109 determinants in the active space, could not be performed.
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31.50.Bc Potential energy surfaces for ground electronic states
31.15.xr Self-consistent-field methods
31.15.xt Variational techniques
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Cavity ring-down spectroscopy of jet-cooled silane isotopologues in the Si–H stretch overtone region

R. Bisson, T. T. Dang, M. Sacchi, and R. D. Beck

J. Chem. Phys. 127, 244301 (2007); http://dx.doi.org/10.1063/1.2819072 (6 pages) | Cited 1 time

Online Publication Date: 26 December 2007

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Absorption spectra of silane in the region of the first overtone of the Si–H stretch vibration have been recorded in a seeded supersonic jet expansion by cavity ring-down spectroscopy as well as in a static gas cell at room temperature by photoacoustic spectroscopy. Spectral simplification due to strong rotational cooling in the jet expansion enables us to clearly resolve and assign the rovibrational transitions of the (2000) and (1100) bands of the three isotopologues, 28SiH4, 29SiH4, and 30SiH4, in their natural isotopic abundance. Interconversion between different nuclear spin species of SiH4 is found to be absent during the jet expansion. Isotope shifts for 29SiH4 and 30SiH4 relative to 28SiH4 are measured and found to be suitable for selective vibrational excitation of any of three silane isotopologues by pulsed laser excitation in a jet expansion.
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78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
78.40.Ha Other nonmetallic inorganics

Interactions of transition metal atoms in high-spin states: Cr2, Sc–Cr, and Sc–Kr

Łukasz Rajchel, Piotr S. Żuchowski, Jacek Kłos, Małgorzata M. Szczȩśniak, and Grzegorz Chałasiński

J. Chem. Phys. 127, 244302 (2007); http://dx.doi.org/10.1063/1.2805390 (10 pages) | Cited 6 times

Online Publication Date: 26 December 2007

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The high-spin van der Waals states are examined for the following dimers: Cr2 (13Σg+), Sc–Cr (8Σ+, 8Π, 8Δ), and Sc–Kr (2Σ+, 2Π, 2Δ). These three systems offer a wide range of van der Waals interactions: anomalously strong, intermediate, and typically weak. The single-reference [coupled cluster with single, double, and noniterative triple excitations, RCCSD(T)] method is used in the calculations for all three systems. In addition, a range of configuration-interaction based methods is applied in Cr2 and Sc–Cr. The three dimers are shown to be bound by the dispersion interaction of varying strength. In a related effort, the dispersion energy and its exchange counterpart are calculated using the newly developed open-shell variant of the symmetry-adapted perturbation theory (SAPT). The restricted open-shell time-dependent Hartree-Fock linear response function is used in the calculations of the dispersion energy in Sc–Cr and Sc–Kr calculations, while the restricted open-shell time-dependent density functional linear response function is used for Cr2. A hybrid method combining the repulsive restricted open-shell Hartree-Fock (or complete active space self-consistent field) interaction energy with the dispersion and exchange-dispersion terms is tested against the RCCSD(T) results for the three complexes. The Cr2 (13Σg+) complex has the well depth of 807.8 cm−1 at the equilibrium distance of 6.18a0 and the dissociation energy of 776.8 cm−1. The octet-state Sc–Cr is about four times more strongly bound with the order of well depths of 8Δ>8Π>8Σ+ and a considerable anisotropy. The enhanced bonding is attributed to the unusually strong dispersion interaction. Sc–Kr (2Σ+, 2Π, 2Δ) is a typical van der Waals dimer with well depths in the range of 81 cm−1 (2Δ), 84cm−1 (2Σ+), and 86 cm−1 (2Π). The hybrid model based on SAPT leads to results which are in excellent qualitative agreement with RCCSD(T) for all three interactions.
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34.20.Gj Intermolecular and atom-molecule potentials and forces

Low-energy electron attachment to SF6. I. Kinetic modeling of nondissociative attachment

Jürgen Troe, Thomas M. Miller, and Albert A. Viggiano

J. Chem. Phys. 127, 244303 (2007); http://dx.doi.org/10.1063/1.2804761 (12 pages) | Cited 22 times

Online Publication Date: 26 December 2007

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Low-energy electron-molecule collisions are analyzed by kinetic modeling within the framework of statistical unimolecular rate theory. Nondissociative electron attachment to SF6 is used to illustrate the approach. An internally consistent representation is provided for attachment cross sections and rate coefficients in relation to detachment lifetimes, and both thermal and specific rate coefficients for detachment. By inspecting experimental data, the contributions of intramolecular vibrational redistribution and vibrationally inelastic collisions can be characterized quantitatively. This allows for a prediction of attachment rate coefficients as a function of electron and gas temperature as well as gas pressure over wide ranges of conditions. The importance of carefully controlling all experimental parameters, including the carrier gas pressure, is illustrated. The kinetic modeling in Part II of this series is extended to dissociative electron attachment to SF6.
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34.80.Ht Dissociation and dissociative attachment
34.50.Gb Electronic excitation and ionization of molecules
33.15.Mt Rotation, vibration, and vibration-rotation constants

Low-energy electron attachment to SF6. II. Temperature and pressure dependences of dissociative attachment

Jürgen Troe, Thomas M. Miller, and Albert A. Viggiano

J. Chem. Phys. 127, 244304 (2007); http://dx.doi.org/10.1063/1.2804762 (13 pages) | Cited 25 times

Online Publication Date: 26 December 2007

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Low-energy electron-molecule collisions, leading to dissociative attachment through metastable anionic states, are kinetically modeled within the framework of statistical unimolecular rate theory. The reaction e−+SF6→SF5−+F is used as an illustrative example. The modeling is applied to new measurements of branching fractions for SF5− formation in the bath gas He between 360 and 670 K at 1 and 2 Torr, and between 490 and 620 K over the range of 0.3–9 Torr. The analysis of the data follows the previous kinetic modeling of the nondissociative electron attachment, e−+SF6→SF6−, from Part I of this series. Experimental results from the present work and the literature on branching fractions and total cross sections for anion formation as functions of electron energies, bath gas temperatures and pressures, as well as observation times are analyzed. The assumption of a participation of the electronic ground state of SF6− alone suffices to model the available experimental data. A value of the dissociation energy of SF6− into SF5−+F of E0,dis = 1.61(±0.05) eV is determined, which may be compared to the electron affinity of SF6, EA = 1.20(±0.05) eV, such as derived in Part III of this series.
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34.80.Ht Dissociation and dissociative attachment
33.15.Fm Bond strengths, dissociation energies

Low-energy electron attachment to SF6. III. From thermal detachment to the electron affinity of SF6

Albert A. Viggiano, Thomas M. Miller, Jeffrey F. Friedman, and Jürgen Troe

J. Chem. Phys. 127, 244305 (2007); http://dx.doi.org/10.1063/1.2804764 (8 pages) | Cited 24 times

Online Publication Date: 26 December 2007

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The thermal attachment of electrons to SF6 is measured in a flowing-afterglow Langmuir-probe apparatus monitoring electron concentrations versus axial position in the flow tube. Temperatures between 300 and 670 K and pressures of the bath gas He in the range of 0.3–9 Torr are employed. Monitoring the concentrations of SF6− and SF5−, the latter of which does not detach electrons under the applied conditions, an onset of thermal detachment and dissociation of SF6 at temperatures above about 530 K is observed. Analysis of the mechanism allows one to deduce thermal detachment rate coefficients. Thermal dissociation rate coefficients for the reaction SF6−→SF5−+F can only be estimated by unimolecular rate theory based on the results from Part I and II of this series. Under the applied conditions they are found to be smaller than detachment rate coefficients. Combining thermal attachment and detachment rates in a third-law analysis, employing calculated vibrational frequencies of SF6 and SF6−, leads to the electron affinity (EA) of SF6−. The new value of EA = 1.20(±0.05) eV is significantly higher than previous recommendations which were based on less direct methods.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
34.80.Ht Dissociation and dissociative attachment
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Mt Rotation, vibration, and vibration-rotation constants

Stability of small Pdn (n = 1–7) clusters on the basis of structural and electronic properties: A density functional approach

Bulumoni Kalita and Ramesh C. Deka

J. Chem. Phys. 127, 244306 (2007); http://dx.doi.org/10.1063/1.2806993 (10 pages) | Cited 13 times

Online Publication Date: 26 December 2007

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Density functional calculations within the generalized gradient approximation have been used to investigate the lowest energy electronic and geometric structures of neutral, cationic, and anionic Pdn (n = 1–7) clusters in the gas phase. In this study, we have examined three different spin multiplicities (M = 1, 3, and 5) for different possible structural isomers of each neutral cluster. The calculated lowest energy structures of the neutral clusters are found to have multiplicities, M = 1 for Pd1, Pd3, Pd5, Pd6, and Pd7, while M = 3 for Pd2 and Pd4. We have also determined the lowest energy states of cationic and anionic Pdn (n = 1–7) clusters, formed from the most stable neutral clusters, in three spin multiplicities (M = 2, 4, and 6). Bond length, coordination number, binding energy, fragmentation energy, bond dissociation energy, ionization potential, electron affinity, chemical hardness, and electric dipole moment of the optimized clusters are compared with experimental and other theoretical results available in the literature. Based on these criteria, we predict the four-atom palladium cluster to be a magic-number cluster.
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36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Cg Electronic and magnetic properties of clusters
33.15.Dj Interatomic distances and angles
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Quantum wave packet dynamics of N(2D)+H2 reaction

B. Jayachander Rao and S. Mahapatra

J. Chem. Phys. 127, 244307 (2007); http://dx.doi.org/10.1063/1.2806031 (11 pages) | Cited 8 times

Online Publication Date: 27 December 2007

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The quantum wave packet dynamics of the title reaction within the coupled state approximation is examined here and initial state-selected reaction probabilities, integral reaction cross sections, and thermal rate constants are reported. The ab initio potential energy surface of the electronic ground state (1 2A″) of the system recently reported by Ho et al. [J. Chem. Phys., 119, 3063 (2003)] is employed in this investigation. All partial wave contributions up to the total angular momentum J = 55 were necessary to obtain converged integral reaction cross sections up to a collision energy of 1.0 eV. Thermal rate constants are calculated from the reaction cross sections and compared with the available theoretical and experimental results. Typical resonances formed during the course of the reaction and elucidating the insertion type mechanism for the product formation are calculated. Vibrational energy levels supported by the deep well ( ∼ 5.5 eV) of the 1 2A″ potential energy surface of NH2 are also calculated for the total angular momentum J = 0. A statistical analysis of the spacing between the adjacent levels of this energy spectrum is performed and the extent of irregularity in the spectral sequence is assessed.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.30.Nr Association, addition, insertion, cluster formation
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Bc State selected dynamics and product distribution
82.20.Ej Quantum theory of reaction cross section

Analogy of silicon clusters with deltahedral boranes: How far can it go? Reexamining the structure of Sin and Sin2−, n = 5–13 clusters

Aristides D. Zdetsis

J. Chem. Phys. 127, 244308 (2007); http://dx.doi.org/10.1063/1.2816138 (6 pages) | Cited 15 times

Online Publication Date: 27 December 2007

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Silicon clusters of 5 up to 13 atoms, Sin, n = 5–13, and their dianions are studied in the light of an anticipated analogy with the corresponding isoelectronic boranes suggested recently by Zdetsis [J. Chem. Phys. 127, 014314 (2007) ]. It is demonstrated that this analogy is a fruitful and powerful concept which allows the straightforward determination of the structures of silicon clusters, based on the structure of corresponding closo-boranes, meeting the requirements of well known structural rules. All lowest-lying structures of Sin, n = 5–13 clusters, have been obtained through a systematic way on the basis of this analogy. For magic clusters, such as Si6 and Si10, characterized by special stability, the analogy to boranes seems to be much stronger.
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36.40.Sx Diffusion and dynamics of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Cg Electronic and magnetic properties of clusters

Boron 1s photoelectron spectrum of 11BF3: Vibrational structure and linewidth

T. Darrah Thomas, Ralph Püttner, Hironobu Fukuzawa, Georg Prümper, Kiyoshi Ueda, Edwin Kukk, Rami Sankari, James Harries, Yusuke Tamenori, Takahiro Tanaka, Masamitsu Hoshino, and Hiroshi Tanaka

J. Chem. Phys. 127, 244309 (2007); http://dx.doi.org/10.1063/1.2820772 (6 pages) | Cited 2 times

Online Publication Date: 27 December 2007

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The boron 1s photoelectron spectrum of 11BF3 has been measured at a photon energy of 400 eV and a resolution of about 55 meV. The pronounced vibrational structure seen in the spectrum has been analyzed to give the harmonic and anharmonic vibrational frequencies of the symmetric stretching mode, 128.1 and 0.15 meV, as well as the change in equilibrium BF bond length upon ionization, −5.83 pm. A similar change in bond length has been observed for PF3 and SiF4, but a much smaller change for CF4. Theoretical calculations for BF3 that include the effects of electron correlation give results that are in reasonable accord with the experimental values. The Lorentzian (lifetime) width of the boron 1s core hole in BF3 is found to be 72 meV, comparable to the value of 77 meV that has been reported for CF4.
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33.15.Dj Interatomic distances and angles
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.80.Eh Autoionization, photoionization, and photodetachment
33.20.Tp Vibrational analysis
33.70.Jg Line and band widths, shapes, and shifts

Infrared spectra of SF6−∙(H2O)n (n = 1–3): Incipient reaction and delayed onset of water network formation

Holger Schneider and J. Mathias Weber

J. Chem. Phys. 127, 244310 (2007); http://dx.doi.org/10.1063/1.2815808 (7 pages) | Cited 3 times

Online Publication Date: 27 December 2007

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We present data on the microsolvation of an extended charge distribution with SF6− as a model system. Infrared spectroscopy, aided by ab initio calculations, shows that the first two water molecules attach to the ion by a combination of single ionic H bonds, sharing one of the F atoms, and weak electrostatic interactions with other F atoms in the ion. No water-water bonds are formed at the dihydrate level, which is an unusual observation, given the strong propensity of water to form H-bonded networks. The onset of water networks occurs with the addition of the third water molecule. Moreover, the attachment of the first two water molecules considerably weakens the SF bond of the F atom involved in bonding to both ligands, indicating a possible mechanism for water-induced reactions.
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82.30.Nr Association, addition, insertion, cluster formation
82.30.Rs Hydrogen bonding, hydrophilic effects
33.20.Ea Infrared spectra
33.15.Fm Bond strengths, dissociation energies
82.20.Hf Product distribution

Nonadiabatic dynamics of charge transfer in diatomic anion clusters

Eunseog Cho and Seokmin Shin

J. Chem. Phys. 127, 244311 (2007); http://dx.doi.org/10.1063/1.2812543 (7 pages)

Online Publication Date: 27 December 2007

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We have studied the photodissociation and recombination dynamics of the diatomic anions X2− and XY− designed to mimic I2− and ICl−, respectively, by using a one-electron model in size-selected N2O clusters. The one-electron model is composed of two nuclei and an extra electron moving in a two-dimensional plane including the two nuclei. The main purpose of this study is to explain the salient features of various dynamical processes of molecular ions in clusters using a simple theoretical model. For heteronuclear diatomic anions, a mass disparity and asymmetric electron affinity between the X and Y atoms lead to different phenomena from the homonuclear case. The XY− anion shows efficient recombination for a smaller cluster size due to the effect of collision-mediated energy transfer and an inherent potential wall on excited state at asymptotic region, while the recombination for the X2− anion is due to rearrangement of solvent configuration and faster nonadiabatic transitions. The results of the present study illustrate the microscopic details of the electronically nonadiabatic processes which control the photodissociation dynamics of molecular ions in clusters.
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82.30.Nr Association, addition, insertion, cluster formation
36.40.Jn Reactivity of clusters
82.33.Fg Reactions in clusters
33.80.Gj Diffuse spectra; predissociation, photodissociation
82.50.-m Photochemistry

Absolute asymmetric synthesis from an isotropic racemic mixture of chiral molecules with the help of their laser orientation-dependent selection

Dmitry V. Zhdanov and Victor N. Zadkov

J. Chem. Phys. 127, 244312 (2007); http://dx.doi.org/10.1063/1.2801640 (16 pages) | Cited 7 times

Online Publication Date: 28 December 2007

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We analyzed the absolute asymmetric synthesis (AAS) of enantiomers from an isotropic racemic mixture of chiral molecules, which employs the laser electrodipole interaction, and revealed a set of basic symmetry-based conditions on the parameters of field-molecule interaction. Using these conditions, we developed a novel scenario of the AAS (through selective photodestruction of the enantiomers of a given type) based on the joint action of the strong multicomponent femtosecond and picosecond laser pulses. Key mechanism of this scenario is the partly modified scheme of laser orientation-dependent selection of molecules proposed by us earlier [ D. V. Zhdanov et al., JETP 130, 387 (2006) ]. Calculations made on example of chiral molecule SiHNaClF show rather high efficiency and stability of the proposed AAS scenario with respect to the parameters of the incident laser pulses and even feasibility of its realization at room temperature.
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33.80.-b Photon interactions with molecules
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Multireference theoretical investigation on selectivity of the bond fissions in photodissociation of acetyl cyanide

Hong-Yan Xiao, Ya-Jun Liu, and Wei-Hai Fang

J. Chem. Phys. 127, 244313 (2007); http://dx.doi.org/10.1063/1.2814169 (7 pages) | Cited 2 times

Online Publication Date: 28 December 2007

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The selectivity of the C–CH3 and C–CN bond fissions upon excitation of acetyl cyanide at 193 nm has been investigated at the theoretical level of multistate complete active space self-consistent field second order perturbation. The calculated results indicated that the initially excited S3 state relaxes to S2 via ultrafast internal conversion. The S2 state could dissociate via two pathways. One, adiabatically dissociates to CH3CO(math)+CN(math). The other one internally converts to S1 before S1 intersystem crossing to T1. The T1 state subsequently dissociates to two groups of products: CH3(math)+OCCN(math) and CH3CO(math)+CN(math). The experimentally observed preference branching of CN elimination over CH3 one and bond selectivity are the results of the competition between the adiabatic and nonadiabatic dynamics of the S2 state.
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82.50.Hp Processes caused by visible and UV light
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Wt Computational modeling; simulation

Microwave spectrum of the H2DO+ ion: Inversion-rotation transitions and inversion splitting

Takashi Furuya, Shuji Saito, and Mitsunori Araki

J. Chem. Phys. 127, 244314 (2007); http://dx.doi.org/10.1063/1.2813352 (6 pages) | Cited 2 times

Online Publication Date: 28 December 2007

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Inversion-rotation spectral lines of the monodeuterated hydronium ion, H2DO+, have been observed by a source-modulation spectrometer in the millimeter- to submillimeter-wave region. The ion was generated by a hollow-cathode discharge in a gas mixture of H2O and D2O. Nine inversion-rotation lines were measured precisely for the lowest pair of inversion doublets in the frequency region from 210 to 720 GHz. The measured lines were analyzed to derive rotational constants in the inversion-doublet states and inversion splitting. The inversion splitting in the ground state was determined to be 1 215 866(410) MHz, that is, 40.5569(137) cm−1, where the numbers in parentheses give probable uncertainties estimated from the Jacobian matrix of the assumed centrifugal distortion constants of the inversion-doublet states. The determined inversion splitting is off by −0.58 cm−1 from the predicted value of 41.14 cm−1 by Rayamäki et al. using high-order coupled cluster ab initio calculations [J. Chem. Phys. 118, 10929 (2003) ], and by 0.039 cm−1 from the observed value of 40.518(10) cm−1 by Dong and Nesbitt using high-resolution jet-cooled infrared spectroscopy [J. Chem. Phys. 125, 144311 (2006) ] beyond the quoted uncertainty. The most astronomically important transition 000−-10+ for the ortho species was measured at 673 257.024(31) MHz, which could be used as a radioastronomical probe investigating interstellar chemistry of deuterium fractionation in space.
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33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Bx Radio-frequency and microwave spectra

Collisional quenching of rotations in lithium dimers by ultracold helium: The Li2(a 3Σu+) and Li2+(X 2Σg+) targets

L. González-Sánchez, E. Bodo, and F. A. Gianturco

J. Chem. Phys. 127, 244315 (2007); http://dx.doi.org/10.1063/1.2803190 (8 pages) | Cited 5 times

Online Publication Date: 28 December 2007

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Quantum coupled-channel scattering calculations have been carried out at ultralow energies (down to 10−5 K) for rotational quenching of ionic and spin-stretched states of the lithium dimer in collision with He atoms. Marked cross section differences, to be related to changes in their interactions with He, have been observed with respect to the singlet case while little changes in the collisional behavior are seen to occur upon ionization when the spin-stretched target is considered. Both effects originate from an interplay of structural and dynamical features of the colliding partners which are analyzed in detail.
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34.50.Ez Rotational and vibrational energy transfer
34.50.Gb Electronic excitation and ionization of molecules
33.15.Mt Rotation, vibration, and vibration-rotation constants

An approximate theory of the ozone isotopic effects: Rate constant ratios and pressure dependence

Yi Qin Gao and R. A. Marcus

J. Chem. Phys. 127, 244316 (2007); http://dx.doi.org/10.1063/1.2806189 (8 pages) | Cited 5 times

Online Publication Date: 28 December 2007

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The isotopic effects in ozone recombination reactions at low pressures are studied using an approximate theory which yields simple analytic expressions for the individual rate constant ratios, observed under “unscrambled” conditions. It is shown that the rate constant ratio between the two competing channels XYZ→X+YZ and XYZ→XY+Z is mainly determined by the difference of the zero-point energies of diatomic molecules YZ and XY and by the efficiency of the deactivation of the newly formed excited ozone molecules, whereas the mass-independent fractionation depends on a “nonstatistical” symmetry factor η and the collisional deactivation efficiency. Formulas for the pressure effects on the enrichment and on the rate constant ratios are obtained, and the calculated results are compared with experiments and more exact calculations. In all cases, ratios of isotope rates and the pressure dependence of enrichments, the agreement is good. While the initial focus was on isotope effects in the formation of O3, predictions are made for isotope effects on ratios of rate constants in other reactions such as O+CO→CO2, O+NO→NO2, and O+SO→SO2.
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82.20.Pm Rate constants, reaction cross sections, and activation energies
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Tr Kinetic isotope effects including muonium
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Nature of the metal–nonmetal transition in metal–ammonia solutions. I. Solvated electrons at low metal concentrations

Gennady N. Chuev, Pascal Quémerais, and Jason Crain

J. Chem. Phys. 127, 244501 (2007); http://dx.doi.org/10.1063/1.2812244 (17 pages) | Cited 9 times

Online Publication Date: 27 December 2007

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Using a theory of polarizable fluids, we extend a variational treatment of an excess electron to the many-electron case corresponding to finite metal concentrations in metal–ammonia solutions (MAS). We evaluate dielectric, optical, and thermodynamical properties of MAS at low metal concentrations. Our semianalytical calculations based on a mean-spherical approximation correlate well with the experimental data on the concentration and temperature dependencies of the dielectric constant and the optical absorption spectrum. The properties are found to be mainly determined by the induced dipolar interactions between localized solvated electrons, which result in the two main effects: the dispersion attractions between the electrons and a sharp increase in the static dielectric constant of the solution. The first effect creates a classical phase separation for the light alkali metal solutes (Li, Na, K) below a critical temperature. The second effect leads to a dielectric instability, i.e., polarization catastrophe, which is the onset of metallization. The locus of the calculated critical concentrations is in a good agreement with the experimental phase diagram of Na-NH3 solutions. The proposed mechanism of the metal–nonmetal transition is quite general and may occur in systems involving self-trapped quantum quasiparticles.
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71.30.+h Metal-insulator transitions and other electronic transitions
77.22.Ch Permittivity (dielectric function)
78.20.-e Optical properties of bulk materials and thin films

Electronic polarization effect on low-frequency infrared and Raman spectra of aprotic solvent: Molecular dynamics simulation study with charge response kernel by second order Møller–Plesset perturbation method

Miho Isegawa and Shigeki Kato

J. Chem. Phys. 127, 244502 (2007); http://dx.doi.org/10.1063/1.2813421 (11 pages) | Cited 4 times

Online Publication Date: 27 December 2007

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Low-frequency infrared (IR) and depolarized Raman scattering (DRS) spectra of acetonitrile, methylene chloride, and acetone liquids are simulated via molecular dynamics calculations with the charge response kernel (CRK) model obtained at the second order Møller–Plesset perturbation (MP2) level. For this purpose, the analytical second derivative technique for the MP2 energy is employed to evaluate the CRK matrices. The calculated IR spectra reasonably agree with the experiments. In particular, the agreement is excellent for acetone because the present CRK model well reproduces the experimental polarizability in the gas phase. The importance of interaction induced dipole moments in characterizing the spectral shapes is stressed. The DRS spectrum of acetone is mainly discussed because the experimental spectrum is available only for this molecule. The calculated spectrum is close to the experiment. The comparison of the present results with those by the multiple random telegraph model is also made. By decomposing the polarizability anisotropy time correlation function to the contributions from the permanent, induced polarizability and their cross term, a discrepancy from the previous calculations is observed in the sign of permanent-induce cross term contribution. The origin of this discrepancy is discussed by analyzing the correlation functions for acetonitrile.
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78.30.C- Liquids
61.20.Ja Computer simulation of liquid structure
61.25.Em Molecular liquids

When is H2O not water?

Chris J. Pickard and R. J. Needs

J. Chem. Phys. 127, 244503 (2007); http://dx.doi.org/10.1063/1.2812268 (7 pages) | Cited 8 times

Online Publication Date: 28 December 2007

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We have combined a computational search strategy with first-principles density-functional-theory calculations to identify metastable phases of H2O under pressure. The most stable structures consist of water molecules, while the most energetic metastable phases consist of oxygen and hydrogen molecules. In between lie many other metastable phases, consisting of various combinations of a few small molecules. It may be possible to synthesize some of these metastable phases, and we use our results to understand the nature of the crystalline metastable phase of H2O recently synthesized by Mao et al. [Science 314, 636 (2006) ].
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64.60.My Metastable phases
61.25.Em Molecular liquids
61.20.Gy Theory and models of liquid structure
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