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28 Aug 2008

Volume 129, Issue 8, Articles (08xxxx)

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Quantum anharmonic densities of states using the Wang–Landau method

M. Basire, P. Parneix, and F. Calvo

J. Chem. Phys. 129, 081101 (2008); http://dx.doi.org/10.1063/1.2965905 (4 pages) | Cited 10 times

Online Publication Date: 25 August 2008

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The Wang–Landau sampling method is adapted to the calculation of quantum densities of states for fully coupled anharmonic systems. The accuracy of the method is illustrated against exact counting for two molecules with separable oscillators, namely, the Zundel complex H5O2+ and the Na11 cluster. Application to the fully coupled naphthalene molecule (C10H8) reveals significant deviations in the finite temperature thermodynamical properties that are not captured by simple perturbation theory. There are no limitations in the size of the molecules that can be treated with this method.
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71.20.Rv Polymers and organic compounds
65.40.G- Other thermodynamical quantities
71.15.-m Methods of electronic structure calculations

Anomaly of the rotational nonergodicity parameter of glass formers probed by high field electron paramagnetic resonance

V. Bercu, M. Martinelli, C. A. Massa, L. A. Pardi, E. A. Rössler, and D. Leporini

J. Chem. Phys. 129, 081102 (2008); http://dx.doi.org/10.1063/1.2973660 (5 pages) | Cited 3 times

Online Publication Date: 26 August 2008

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Exploiting the high angular resolution of high field electron paramagnetic resonance measured at 95, 190, and 285 GHz we determine the rotational nonergodicity parameter of different probe molecules in the glass former o-terphenyl and polybutadiene in a model-independent way. Our results clearly show a characteristic change in the temperature of the nonergodicity parameter proving a rather sharp dynamic crossover in both systems, in contrast to previous results from other techniques.
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76.30.-v Electron paramagnetic resonance and relaxation
64.70.P- Glass transitions of specific systems
61.43.Fs Glasses

Vibrational activation in direct and precursor-mediated chemisorption of SiH4 on Si(100)

Régis Bisson, Tung T. Dang, Marco Sacchi, and Rainer D. Beck

J. Chem. Phys. 129, 081103 (2008); http://dx.doi.org/10.1063/1.2976563 (4 pages) | Cited 6 times

Online Publication Date: 26 August 2008

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The quantum state-resolved reactivity S0 of SiH4 on Si(100)-2×1 has been measured for the first time for two vibrationally excited Si–H stretch local mode states (|2000〉 and |1100〉) as well the ground state S0 as a function of translational energy En and surface temperature Ts. We observe evidence for both direct and precursor-mediated chemisorption pathways. As expected, increasing En (or Ts) decreases S0 for the precursor-mediated reaction and increases S0 for the direct chemisorption. However, vibrational excitation of the incident SiH4 increases S0 for both the direct and the precursor-mediated pathway with a higher S0 for the |2000〉 state than for the |1100〉 state, indicating a nonstatistical reaction mechanism.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
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back to top Theoretical Methods and Algorithms

Symmetry-adapted perturbation theory utilizing density functional description of monomers for high-spin open-shell complexes

Piotr S. Żuchowski, Rafał Podeszwa, Robert Moszyński, Bogumił Jeziorski, and Krzysztof Szalewicz

J. Chem. Phys. 129, 084101 (2008); http://dx.doi.org/10.1063/1.2968556 (17 pages) | Cited 10 times

Online Publication Date: 22 August 2008

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We present an implementation of symmetry-adapted perturbation theory (SAPT) to interactions of high-spin open-shell monomers forming high-spin dimers. The monomer spin-orbitals used in the expressions for the electrostatic and exchange contributions to the interaction energy are obtained from density functional theory using a spin-restricted formulation of the open-shell Kohn–Sham (ROKS) method. The dispersion and induction energies are expressed through the density-density response functions predicted by the time-dependent ROKS theory. The method was applied to several systems: NH⋯He, CN⋯Ne, H2O⋯HO2, and NH⋯NH. It provides accuracy comparable to that of the best previously available methods such as the open-shell coupled-cluster method with single, double, and noniterative triple excitations, RCCSD(T), with a significantly reduced computational cost.
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31.15.xp Perturbation theory
31.15.bw Coupled-cluster theory
31.15.E- Density-functional theory
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure

Quantum-classical Liouville dynamics in the mapping basis

Hyojoon Kim, Ali Nassimi, and Raymond Kapral

J. Chem. Phys. 129, 084102 (2008); http://dx.doi.org/10.1063/1.2971041 (6 pages) | Cited 4 times

Online Publication Date: 25 August 2008

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The quantum-classical Liouville equation describes the dynamics of a quantum subsystem coupled to a classical environment. It has been simulated using various methods, notably, surface-hopping schemes. A representation of this equation in the mapping Hamiltonian basis for the quantum subsystem is derived. The resulting equation of motion, in conjunction with expressions for quantum expectation values in the mapping basis, provides another route to the computation of the nonadiabatic dynamics of observables that does not involve surface-hopping dynamics. The quantum-classical Liouville equation is exact for the spin-boson system. This well-known model is simulated using an approximation to the evolution equation in the mapping basis, and close agreement with exact quantum results is found.
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05.30.Jp Boson systems
03.65.Ta Foundations of quantum mechanics; measurement theory
03.65.Db Functional analytical methods
02.60.Nm Integral and integrodifferential equations

Reconciling semiclassical and Bohmian mechanics. VI. Multidimensional dynamics

Bill Poirier

J. Chem. Phys. 129, 084103 (2008); http://dx.doi.org/10.1063/1.2969102 (18 pages) | Cited 8 times

Online Publication Date: 26 August 2008

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In previous articles [ J. Chem. Phys. 121, 4501 (2004) ; J. Chem. Phys. 124, 034115 (2006) ; J. Chem. Phys. 124, 034116 (2006) ; J. Phys. Chem. A 111, 10400 (2007) ; J. Chem. Phys. 128, 164115 (2008) ] an exact quantum, bipolar wave decomposition, ψ = ψ++ψ−, was presented for one-dimensional stationary state and time-dependent wavepacket dynamics calculations, such that the components ψ± approach their semiclassical WKB analogs in the large action limit. The corresponding bipolar quantum trajectories are classical-like and well behaved, even when ψ has many nodes or is wildly oscillatory. In this paper, both the stationary state and wavepacket dynamics theories are generalized for multidimensional systems and applied to several benchmark problems, including collinear H+H2.
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03.65.Pm Relativistic wave equations
03.65.Ca Formalism

Gaussian-based techniques for quantum propagation from the time-dependent variational principle: Formulation in terms of trajectories of coupled classical and quantum variables

Dmitrii V. Shalashilin and Irene Burghardt

J. Chem. Phys. 129, 084104 (2008); http://dx.doi.org/10.1063/1.2969101 (9 pages) | Cited 6 times

Online Publication Date: 27 August 2008

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In this article, two coherent-state based methods of quantum propagation, namely, coupled coherent states (CCS) and Gaussian-based multiconfiguration time-dependent Hartree (G-MCTDH), are put on the same formal footing, using a derivation from a variational principle in Lagrangian form. By this approach, oscillations of the classical-like Gaussian parameters and oscillations of the quantum amplitudes are formally treated in an identical fashion. We also suggest a new approach denoted here as coupled coherent states trajectories (CCST), which completes the family of Gaussian-based methods. Using the same formalism for all related techniques allows their systematization and a straightforward comparison of their mathematical structure and cost.
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31.15.xr Self-consistent-field methods
03.65.Ge Solutions of wave equations: bound states
03.65.Db Functional analytical methods
31.15.xt Variational techniques

Second-order, two-electron Dyson propagator theory: Comparisons for vertical double ionization potentials

T. Ida and J. V. Ortiz

J. Chem. Phys. 129, 084105 (2008); http://dx.doi.org/10.1063/1.2973533 (11 pages) | Cited 4 times

Online Publication Date: 28 August 2008

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The second-order, two-electron Dyson propagator is derived using superoperator theory with a spin-adapted formulation. To include certain ladder diagrams to all orders, the shifted-denominator (SD2) approximation is made. Formal and computational comparisons with other approximations illustrate the advantages of the SD2 procedure. Vertical double ionization potentials (DIPs) for a set of closed-shell molecules are evaluated with the second-order propagator and the SD2 method. The results of the SD2 approximation are in good agreement with experiment. To systematically examine the quality of the results, we compared SD2 and equation-of-motion, coupled-cluster predictions. The average absolute discrepancy is 0.26 eV for 36 doubly ionized states.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Investigation of the O+allyl addition/elimination reaction pathways from the OCH2CHCH2 radical intermediate

Benjamin L. FitzPatrick, Kai-Chung Lau, Laurie J. Butler, Shih-Huang Lee, and Jim Jr-Min Lin

J. Chem. Phys. 129, 084301 (2008); http://dx.doi.org/10.1063/1.2966004 (12 pages) | Cited 5 times

Online Publication Date: 22 August 2008

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These experiments study the preparation of and product channels resulting from OCH2CHCH2, a key radical intermediate in the O+allyl bimolecular reaction. The data include velocity map imaging and molecular beam scattering results to probe the photolytic generation of the radical intermediate and the subsequent pathways by which the radicals access the energetically allowed product channels of the bimolecular reaction. The photodissociation of epichlorohydrin at 193.3 nm produces chlorine atoms and c-OCH2CHCH2 radicals; these undergo a facile ring opening to the OCH2CHCH2 radical intermediate. State-selective resonance-enhanced multiphoton ionization (REMPI) detection resolves the velocity distributions of ground and spin-orbit excited state chlorine independently, allowing for a more accurate determination of the internal energy distribution of the nascent radicals. We obtain good agreement detecting the velocity distributions of the Cl atoms with REMPI, vacuum ultraviolet (VUV) photoionization at 13.8 eV, and electron bombardment ionization; all show a bimodal distribution of recoil kinetic energies. The dominant high recoil kinetic energy feature peaks near 33 kcal/mol. To elucidate the product channels resulting from the OCH2CHCH2 radical intermediate, the crossed laser-molecular beam experiment uses VUV photoionization and detects the velocity distribution of the possible products. The data identify the three dominant product channels as C3H4O (acrolein)+H, C2H4+HCO (formyl radical), and H2CO (formaldehyde)+C2H3. A small signal from C2H2O (ketene) product is also detected. The measured velocity distributions and relative signal intensities at m/e = 27, 28, and 29 at two photoionization energies show that the most exothermic product channel, C2H5+CO, does not contribute significantly to the product branching. The higher internal energy onset of the acrolein+H product channel is consistent with the relative barriers en route to each of these product channels calculated at the CCSD(T)/aug-cc-pVQZ level of theory, although a clean determination of the barrier energy to H+acrolein is precluded by the substantial partitioning into rotational energy during the photolytic production of the nascent radicals. We compare the measured branching fraction to the H+acrolein product channel with a statistical prediction based on the calculated transition states.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.50.Hp Processes caused by visible and UV light
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)

Time-dependent configuration-interaction calculations of laser-driven dynamics in presence of dissipation

Jean Christophe Tremblay, Tillmann Klamroth, and Peter Saalfrank

J. Chem. Phys. 129, 084302 (2008); http://dx.doi.org/10.1063/1.2972126 (8 pages) | Cited 9 times

Online Publication Date: 22 August 2008

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Correlated, multielectron dynamics of “open” electronic systems within the fixed-nuclei approximation are treated here within explicitly time-dependent configuration-interaction schemes. Specifically, we present simulations of laser-pulse driven excitations of selected electronic states of LiCN in the presence of energy and phase relaxation. The evolution of the system is studied using open-system density matrix theory, which embeds naturally in the time-dependent configuration-interaction singles (doubles) formalism. Different models for dissipation based on the Lindblad semigroup formalism are presented. These models give rise to lifetimes for energy relaxation ranging from a few hundreds of femtoseconds to several nanoseconds. Pure dephasing is treated using a Kossakowski-like Gaussian model, proceeding on similar time scales. The pulse lengths employed range from very short (tens of femtoseconds) to very long (several nanoseconds). To make long-time propagations tractable, the quasiresonant approximation is used. The results show that despite the loss of efficiency, selective dipole switching can still be achieved in the presence of dissipation when using appropriately designed laser pulses.
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31.15.vj Electron correlation calculations for atoms and ions: excited states
31.15.ee Time-dependent density functional theory
33.80.-b Photon interactions with molecules
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

An eight-degree-of-freedom quantum dynamics study of the isotopic effect on the reaction: HD+C2H

Dunyou Wang and Winifred M. Huo

J. Chem. Phys. 129, 084303 (2008); http://dx.doi.org/10.1063/1.2971184 (6 pages) | Cited 3 times

Online Publication Date: 22 August 2008

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An eight-dimensional time-dependent quantum dynamics calculation is reported to study the isotopic reaction, HD+C2H, on a new modified potential energy surface. Initial-state-selected reaction probability, integral cross section, and rate constants are presented in this isotopic reaction study. Initial-state-selected reaction probability is obtained by summing over all the possible product’s arrangements in this isotopic reaction study. This study shows that vibrational excitations of HD enhance the reactivity, whereas stretching excitations of C2H only have a small effect on the reactivity. Furthermore, the bending excitations of C2H, compared to the ground-state reaction probability, hinder the reactivity. The present results are consistent with those obtained for the H2+C2H reaction. The comparison of these two reactions also shows the isotopic effect in the initial-state-selected reaction probability, integral cross section, and rate constants. The rate constant comparison shows that the HD+C2H reaction has a smaller reactivity than the H2+C2H reaction.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Ej Quantum theory of reaction cross section
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies

Infrared photodissociation spectroscopy and density-functional calculations of protonated methanol cluster ions: Solvation structures of an excess proton

Kensuke Tono, Jer-Lai Kuo, Masanori Tada, Koudai Fukazawa, Naoya Fukushima, Chiharu Kasai, and Koichi Tsukiyama

J. Chem. Phys. 129, 084304 (2008); http://dx.doi.org/10.1063/1.2963499 (8 pages) | Cited 1 time

Online Publication Date: 22 August 2008

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Solvation structures of an excess proton in protonated methanol cluster ions, H+(CH3OH)n (n = 5–8), were investigated by photodissociation spectroscopy in the middle infrared region (900–2300 cm–1) and by using density-functional theory. This work indicates that the excess proton is delocalized between two methanol molecules. Spectral features observed in the range 1400–1800 cm–1 are attributed to vibrational modes involving collective motion of the shared proton and the two ligand molecules. At n = 6–8, broad spectral features in the region above 1800 cm–1 suggest coexistence of isomers in which the excess proton and a methanol molecule are tightly bound to form an ion core, CH3OH2+.
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36.40.Mr Spectroscopy and geometrical structure of clusters
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.20.Ea Infrared spectra
33.20.Tp Vibrational analysis
31.15.es Applications of density-functional theory (e.g., to electronic structure and stability; defect formation; dielectric properties, susceptibilities; viscoelastic coefficients; Rydberg transition frequencies)

Characteristics of the interaction of azulene with water and hydrogen sulfide: A computational study

Enrique M. Cabaleiro-Lago, Jesús Rodríguez-Otero, and Ángeles Peña-Gallego

J. Chem. Phys. 129, 084305 (2008); http://dx.doi.org/10.1063/1.2973632 (8 pages) | Cited 7 times

Online Publication Date: 22 August 2008

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A computational study was carried out for studying the characteristics of the interaction between azulene and water or hydrogen sulfide. In azulene ⋯ water complex the water molecule is located with both hydrogen atoms pointing toward the aromatic cloud but displaced to the five-membered ring. Hydrogen sulfide adopts a similar arrangement but located roughly over the central C–C bond of azulene. Calculations show that hydrogen sulfide interacts with azulene more strongly (−4.19 kcal/mol) than water (−3.76 kcal/mol), although this is only revealed at the highest levels of calculation. The nature of the interaction is electrostatic and dispersive in the same percentage for water cluster, whereas for hydrogen sulfide dispersion is the dominant contribution. Clusters containing two water molecules are controlled by the possibility of establishing an O–H⋯O hydrogen bond. As a consequence, the most stable structure corresponds to the interaction between a water dimer and azulene, with an interaction energy amounting to −11.77 kcal/mol. Hydrogen sulfide interaction is stronger with azulene than with itself, so structures with S–H⋯S contact and others, where H2S only interacts with azulene, present similar interaction energies (−8.02 kcal/mol for the most stable one).
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36.40.Jn Reactivity of clusters
36.40.Sx Diffusion and dynamics of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
34.20.Gj Intermolecular and atom-molecule potentials and forces
31.15.E- Density-functional theory
31.15.xp Perturbation theory

Toward spectroscopic accuracy for organic free radicals: Molecular structure, vibrational spectrum, and magnetic properties of F2NO

Cristina Puzzarini and Vincenzo Barone

J. Chem. Phys. 129, 084306 (2008); http://dx.doi.org/10.1063/1.2969820 (7 pages) | Cited 14 times

Online Publication Date: 26 August 2008

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The structure, harmonic frequencies, and hyperfine couplings of F2NO have been computed by the coupled cluster ansatz using a hierarchical series of basis sets and, in some cases, extrapolation procedures to reach the complete basis set limit. Methods rooted into the density functional theory have been used to estimate anharmonic and environmental effects. The remarkable agreement with experimental hyperfine coupling constants and most of vibrational frequencies confirms the reliability of the computational approach and suggests that one of the observed frequencies probably refers to a different species.
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33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Pw Fine and hyperfine structure
31.15.bw Coupled-cluster theory
31.15.E- Density-functional theory
33.15.Bh General molecular conformation and symmetry; stereochemistry

The H3+ rovibrational spectrum revisited with a global electronic potential energy surface

Luis Velilla, Bruno Lepetit, Alfredo Aguado, J. Alberto Beswick, and Miguel Paniagua

J. Chem. Phys. 129, 084307 (2008); http://dx.doi.org/10.1063/1.2973629 (11 pages) | Cited 16 times

Online Publication Date: 27 August 2008

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In this paper, we have computed the rovibrational spectrum of the H3+ molecule using a new global potential energy surface, invariant under all permutations of the nuclei, that includes the long range electrostatic interactions analytically. The energy levels are obtained by a variational calculation using hyperspherical coordinates. From the comparison with available experimental results for low lying levels, we conclude that our accuracy is of the order of 0.1 cm−1 for states localized in the vicinity of equilateral triangular configurations of the nuclei, and changes to the order of 1 cm−1 when the system is distorted away from equilateral configurations. Full rovibrational spectra up to the H++H2 dissociation energy limit have been computed. The statistical properties of this spectrum (nearest neighbor distribution and spectral rigidity) show the quantum signature of classical chaos and are consistent with random matrix theory. On the other hand, the correlation function, even when convoluted with a smoothing function, exhibits oscillations which are not described by random matrix theory. We discuss a possible similarity between these oscillations and the ones observed experimentally.
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33.20.Vq Vibration-rotation analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.50.-x Potential energy surfaces

A benchmark theoretical study of the electron affinities of benzene and linear acenes

B. Hajgató, M. S. Deleuze, D. J. Tozer, and F. De Proft

J. Chem. Phys. 129, 084308 (2008); http://dx.doi.org/10.1063/1.2967182 (15 pages) | Cited 13 times

Online Publication Date: 28 August 2008

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A benchmark theoretical determination of the electron affinities of benzene and linear oligoacenes ranging from naphthalene to hexacene is presented, using the principles of a focal point analysis. These energy differences have been obtained from a series of single-point calculations at the Hartree–Fock, second-, third-, and partial fourth-order Møller–Plesset (MP2, MP3, and MP4SDQ) levels and from coupled cluster calculations including single and double excitations (CCSD) as well as perturbative estimates of connected triple excitations [CCSD(T)], using basis sets of improving quality, containing up to 1386, 1350, 1824, 1992, 1630, and 1910 basis functions in the computations, respectively. Studies of the convergence properties of these energy differences as a function of the size of the basis set and order attained in electronic correlation enable a determination of the vertical electron affinities of the four larger terms of the oligoacene (C2+4nH2+2n) series within chemical accuracy (0.04 eV). According to our best estimates, these amount to +0.28, +0.82, +1.21, and +1.47 eV when n = 3, 4, 5, and 6. Adiabatic electron affinities have been further calculated by incorporating corrections for zero-point vibrational energies and for geometrical relaxations. The same procedure was applied to determine the vertical electron affinities of benzene and naphthalene, which are found to be markedly negative ( ∼ −1.53 and ∼ −0.48 eV, respectively). Highly quantitative insights into experiments employing electron transmission spectroscopy on these compounds were also amenable from such an approach, provided diffuse atomic functions are deliberately removed from the basis set, in order to enforce confinement in the molecular region and enable a determination of pseudoadiabatic electron affinities (with respect to the timescale of nuclear motions). Comparison was made with calculations employing density functional theory and especially designed models that exploit the integer discontinuity in the potential or incorporate a potential wall in the unrestricted Kohn–Sham orbital equation for the anion.
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31.15.xr Self-consistent-field methods
31.15.xp Perturbation theory
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.bw Coupled-cluster theory
33.20.Tp Vibrational analysis

Quasiclassical trajectory study of the SiH4+H→SiH3+H2 reaction on a global ab initio potential energy surface

Manhui Wang, Xiaomin Sun, and Wensheng Bian

J. Chem. Phys. 129, 084309 (2008); http://dx.doi.org/10.1063/1.2973626 (8 pages) | Cited 2 times

Online Publication Date: 28 August 2008

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The SiH4+H→SiH3+H2 reaction has been investigated by the quasiclassical trajectory (QCT) method on a recent global ab initio potential energy surface [ M. Wang et al., J. Chem. Phys. 124, 234311 (2006) ]. The integral cross section as a function of collision energy and thermal rate coefficient for the temperature range of 300–1600 K have been obtained. At the collision energy of 9.41 kcal/mol, product energy distributions and rovibrational populations are explored in detail, and H2 rotational state distributions show a clear evidence of two reaction mechanisms. One is the conventional rebound mechanism and the other is the stripping mechanism similar to what has recently been found in the reaction of CD4+H [ J. P. Camden et al., J. Am. Chem. Soc. 127, 11898 (2005) ]. The computed rate coefficients with the zero-point energy correction are in good agreement with the available experimental data.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Fd Collision theories; trajectory models
82.20.Hf Product distribution
82.20.Pm Rate constants, reaction cross sections, and activation energies

The vibronic level structure of the cyclopentadienyl radical

Takatoshi Ichino, Scott W. Wren, Kristen M. Vogelhuber, Adam J. Gianola, W. Carl Lineberger, and John F. Stanton

J. Chem. Phys. 129, 084310 (2008); http://dx.doi.org/10.1063/1.2973631 (19 pages) | Cited 11 times

Online Publication Date: 28 August 2008

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The 351.1 nm photoelectron spectrum of the cyclopentadienide ion has been measured, which reveals the vibronic structure of the math 2E1″ state of the cyclopentadienyl radical. Equation-of-motion ionization potential coupled-cluster (EOMIP-CCSD) calculations have been performed to construct a diabatic model potential of the math 2E1″ state, which takes into account linear Jahn–Teller effects along the e2′ normal coordinates as well as bilinear Jahn–Teller effects along the e2′ and ring-breathing a1′ coordinates. A simulation based on this ab initio model potential reproduces the spectrum very well, identifying the vibronic levels with linear Jahn–Teller angular momentum quantum numbers of ±1/2. The angular distributions of the photoelectrons for these vibronic levels are highly anisotropic with the photon energies used in the measurements. A few additional weak photoelectron peaks are observed when photoelectrons ejected parallel to the laser polarization are examined. These peaks correspond to the vibronic levels for out-of-plane modes in the ground math 2E1″ state, which arise due to several pseudo-Jahn–Teller interactions with excited states of the radical and quadratic Jahn–Teller interaction in the math 2E1″ state. A variant of the first derivative of the energy for the EOMIP-CCSD method has been utilized to evaluate the strength of these nonadiabatic couplings, which have subsequently been employed to construct the model potential of the math 2E1″ state with respect to the out-of-plane normal coordinates. Simulations based on the model potential successfully reproduce the weak features that become conspicuous in the 0° spectrum. The present study of the photoelectron spectrum complements a previous dispersed fluorescence spectroscopic study Miller and co-workers [J. Chem. Phys. 114, 4855 (2001); 4869 (2001) Miller and co-workers [J. Chem. Phys.114, 4869 (2001)] to provide a detailed account of the vibronic structure of math 2E1″ cyclopentadienyl. The electron affinity of the cyclopentadienyl radical is determined to be 1.808±0.006 eV. This electron affinity and the gas-phase acidity of cyclopentadiene have been combined in a negative ion thermochemical cycle to determine the C–H bond dissociation energy of cyclopentadiene; D0(C5H6,C–H) = 81.5±1.3 kcal mol−1. The standard enthalpy of formation of the cyclopentadienyl radical has been determined to be ΔfH298(C5H5) = 63.2±1.4 kcal mol−1.
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33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.60.+q Photoelectron spectra
33.50.Dq Fluorescence and phosphorescence spectra
82.60.Cx Enthalpies of combustion, reaction, and formation
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
31.15.bw Coupled-cluster theory

Neutral and charged excitations in carbon fullerenes from first-principles many-body theories

Murilo L. Tiago, P. R. C. Kent, Randolph Q. Hood, and Fernando A. Reboredo

J. Chem. Phys. 129, 084311 (2008); http://dx.doi.org/10.1063/1.2973627 (7 pages) | Cited 11 times

Online Publication Date: 28 August 2008

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We investigate the accuracy of first-principles many-body theories at the nanoscale by comparing the low-energy excitations of the carbon fullerenes C20, C24, C50, C60, C70, and C80 with experiment. Properties are calculated via the GW–Bethe–Salpeter equation and diffusion quantum Monte Carlo methods. We critically compare these theories and assess their accuracy against available photoabsorption and photoelectron spectroscopy data. The first ionization potentials are consistently well reproduced and are similar for all the fullerenes and methods studied. The electron affinities and first triplet excitation energies show substantial method and geometry dependence. These results establish the validity of many-body theories as viable alternative to density-functional theory in describing electronic properties of confined carbon nanostructures. We find a correlation between energy gap and stability of fullerenes. We also find that the electron affinity of fullerenes is very high and size independent, which explains their tendency to form compounds with electron-donor cations.
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71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Tx Fullerenes and related materials; intercalation compounds
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Preparation of oriented and aligned H2 and HD by stimulated Raman pumping

Nate C. M. Bartlett, Daniel J. Miller, Richard N. Zare, Dimitris Sofikitis, T. Peter Rakitzis, and Andrew J. Alexander

J. Chem. Phys. 129, 084312 (2008); http://dx.doi.org/10.1063/1.2973628 (6 pages) | Cited 9 times

Online Publication Date: 28 August 2008

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Stimulated Raman pumping has been used to prepare oriented and aligned samples of H2(ν = 1,J = 1,2,3) and HD(ν = 1,J = 2) under collision-free conditions using the (1,0) S(0), S(1), Q(1), Q(2), and O(3) lines. The M-sublevel anisotropies were interrogated by polarized [2+1] resonance-enhanced multiphoton ionization via the (0,1) O(2), O(3), and S(1) lines of the E,F 1Σg+−X 1Σg+ system. The optical excitation schemes employed in this study generate highly oriented and aligned molecular ensembles. We show that the H2(ν = 1,J = 2,M = 0) and H2(ν = 1,J = 2,M = 2) samples retain their initial polarization for greater than 100 ns and are therefore suitable candidates for targets or projectiles in future scattering experiments.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.80.Eh Autoionization, photoionization, and photodetachment
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

High pressure study on molecular mobility of leucrose

K. Kaminski, E. Kaminska, S. Hensel-Bielowka, S. Pawlus, M. Paluch, and J. Ziolo

J. Chem. Phys. 129, 084501 (2008); http://dx.doi.org/10.1063/1.2969816 (5 pages) | Cited 5 times

Online Publication Date: 22 August 2008

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Broadband dielectric measurements on leucrose were performed under ambient and high pressure. We showed that in this disaccharide, there are two secondary relaxation modes, a slower one sensitive to pressure and a faster one that is not. This finding clearly indicates that the faster secondary relaxation originates from the intramolecular motion. This conclusion contradicted previous interpretations of this mode observed for trehalose and maltitol, systems very closely related to leucrose. In addition, pressure sensitivity of the slower relaxation confirms our recent interpretation about the character of this process. Furthermore, we discovered that unlike the faster relaxation, the slower secondary relaxation is sensitive to the thermodynamic history of measurements. Finally, monitoring the changes in maximum loss of the slower secondary relaxation measured at the same pressure and temperature conditions for glasses obtained via different thermodynamic routes enabled us to draw a conclusion about the density of the formed glasses. Our observations may be helpful in establishing a new method of suppressing crystallization of amorphous drugs.
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61.43.Fs Glasses
62.50.-p High-pressure effects in solids and liquids
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

Diffraction and IR/Raman data do not prove tetrahedral water

Mikael Leetmaa, Kjartan Thor Wikfeldt, Mathias P. Ljungberg, Michael Odelius, Jan Swenson, Anders Nilsson, and Lars G. M. Pettersson

J. Chem. Phys. 129, 084502 (2008); http://dx.doi.org/10.1063/1.2968550 (13 pages) | Cited 23 times

Online Publication Date: 25 August 2008

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We use the reverse Monte Carlo modeling technique to fit two extreme structure models for water to available x-ray and neutron diffraction data in q space as well as to the electric field distribution as a representation of the OH stretch Raman spectrum of dilue HOD in D2O; the internal geometries were fitted to a quantum distribution. Forcing the fit to maximize the number of hydrogen (H) bonds results in a tetrahedral model with 74% double H-bond donors (DD) and 21% single donors (SD). Maximizing instead the number of SD species gives 81% SD and 18% DD, while still reproducing the experimental data and losing only 0.7–1.8 kJ/mole interaction energy. By decomposing the simulated Raman spectrum we can relate the models to the observed ultrafast frequency shifts in recent pump-probe measurements. Within the tetrahedral DD structure model the assumed connection between spectrum position and H-bonding indicates ultrafast dynamics in terms of breaking and reforming H bonds while in the strongly distorted model the observed frequency shifts do not necessarily imply H-bond changes. Both pictures are equally valid based on present diffraction and vibrational experimental data. There is thus no strict proof of tetrahedral water based on these data. We also note that the tetrahedral structure model must, to fit diffraction data, be less structured than most models obtained from molecular dynamics simulations.
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61.20.Ja Computer simulation of liquid structure
61.25.Em Molecular liquids
78.30.C- Liquids

Multilevel vibrational coherence transfer and wavepacket dynamics probed with multidimensional IR spectroscopy

Matthew J. Nee, Carlos R. Baiz, Jessica M. Anna, Robert McCanne, and Kevin J. Kubarych

J. Chem. Phys. 129, 084503 (2008); http://dx.doi.org/10.1063/1.2969900 (11 pages) | Cited 15 times

Online Publication Date: 25 August 2008

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Multidimensional infrared (MDIR) spectroscopy of a strongly coupled multilevel vibrational system Mn2(CO)10 (dimanganese decacarbonyl) in cyclohexane solution reveals fully resolved excited vibrational state coherences that exhibit slow 0.25–0.50 ps−1 decay constants. Detailed analysis of the waiting-time dependence of certain cross-peak amplitudes shows modulation at multiple frequencies, providing a direct signature of excited vibrational coherences resulting from coherence transfer. A new signature of coherence transfer is observed as temporally modulated cross-peak amplitudes with more than one modulation frequency. The relative importance of different coherence transfer paths is considered in the context of the orientational response of a system which includes two vibrational modes with parallel dipole moments. Since MDIR spectroscopy enables spectral isolation of individual excited vibrational coherences (i.e., coherences between fundamental excitations), these experiments report directly on the frequency-frequency correlation functions of the excited states relative to each other as well as relative to the ground state. These results highlight the rich information contained in fully exploring three-dimensional third-order spectroscopy, particularly regarding chemically relevant slower dynamics and the importance of intramolecular interactions leading to dephasing by optically dark or low-frequency modes of the molecule.
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33.20.Ea Infrared spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
31.15.vj Electron correlation calculations for atoms and ions: excited states

Short- and medium-range structure of multicomponent bioactive glasses and melts: An assessment of the performances of shell-model and rigid-ion potentials

Antonio Tilocca

J. Chem. Phys. 129, 084504 (2008); http://dx.doi.org/10.1063/1.2972146 (9 pages) | Cited 11 times

Online Publication Date: 25 August 2008

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Classical and ab initio molecular dynamics (MD) simulations have been carried out to investigate the effect of a different treatment of interatomic forces in modeling the structural properties of multicomponent glasses and melts. The simulated system is a soda-lime phosphosilicate composition with bioactive properties. Because the bioactivity of these materials depends on their medium-range structural features, such as the network connectivity and the Qn distribution (where Qn is a tetrahedral species bonded to n bridging oxygens) of silicon and phosphorus network formers, it is essential to assess whether, and up to what extent, classical potentials can reproduce these properties. The results indicate that the inclusion of the oxide ion polarization through a shell-model (SM) approach provides a more accurate representation of the medium-range structure compared to rigid-ion (RI) potentials. Insight into the causes of these improvements has been obtained by comparing the melt-and-quench transformation of a small sample of the same system, modeled using Car–Parrinello MD (CPMD), to the classical MD runs with SM and RI potentials. Both classical potentials show some limitations in reproducing the highly distorted structure of the melt denoted by the CPMD runs; however, the inclusion of polarization in the SM potential results in a better and qualitatively correct dynamical balance between the interconversion of Qn species during the cooling of the melt. This effect seems to reflect the slower decay of the fraction of structural defects during the cooling with the SM potential. Because these transient defects have a central role in mediating the Qn transformations, as previously proposed and confirmed by the current simulations, their presence in the melt is essential to produce an accurate final distribution of Qn species in the glass.
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87.85.J- Biomaterials
61.43.Fs Glasses
61.43.Bn Structural modeling: serial-addition models, computer simulation

Reversible geminate recombination of hydrogen-bonded water molecule pair

Omer Markovitch and Noam Agmon

J. Chem. Phys. 129, 084505 (2008); http://dx.doi.org/10.1063/1.2968608 (13 pages) | Cited 5 times

Online Publication Date: 27 August 2008

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The (history independent) autocorrelation function for a hydrogen-bonded water molecule pair, calculated from classical molecular dynamics trajectories of liquid water, exhibits a t−3/2 asymptotic tail. Its whole time dependence agrees quantitatively with the solution for reversible diffusion-influenced geminate recombination derived by Agmon and Weiss [J. Chem. Phys. 91, 6937 (1989) ]. Agreement with diffusion theory is independent of the precise definition of the bound state. Given the water self-diffusion constant, this theory enables us to determine the dissociation and bimolecular recombination rate parameters for a water dimer. (The theory is indispensable for obtaining the bimolecular rate coefficient.) Interestingly, the activation energies obtained from the temperature dependence of these rate coefficients are similar, rather than differing by the hydrogen-bond (HB) strength. This suggests that recombination requires displacing another water molecule, which meanwhile occupied the binding site. Because these activation energies are about twice the HB strength, cleavage of two HBs may be required to allow pair separation. The autocorrelation function without the HB angular restriction yields a recombination rate coefficient that is larger than that for rebinding to all four tetrahedral water sites (with angular restrictions), suggesting the additional participation of interstitial sites. Following dissociation, the probability of the pair to be unbound but within the reaction sphere rises more slowly than expected, possibly because binding to the interstitial sites delays pair separation. An extended diffusion model, which includes an additional binding site, can account for this behavior.
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66.10.C- Diffusion and thermal diffusion
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