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1 Feb 2005

Volume 122, Issue 5, Articles (05xxxx)

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Chemisorption sites of CO on small gold clusters and transitions from chemisorption to physisorption

Hua-Jin Zhai and Lai-Sheng Wang

J. Chem. Phys. 122, 051101 (2005); http://dx.doi.org/10.1063/1.1850091 (4 pages) | Cited 40 times

Online Publication Date: 18 January 2005

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Gold clusters adsorbed with CO, Aum(CO)n− (m=2–5; n=0–7), were studied by photoelectron spectroscopy (PES). The first few CO adsorptions were observed to induce significant redshifts to the PES spectra relative to pure gold clusters. For each Au cluster, a critical CO number (nc) was observed, beyond which the PES spectra of Aum(CO)n− change very little with increasing n. nc was shown to correspond exactly to the available low coordination apex sites in each Au cluster. CO first chemisorbs to these sites and additional CO then only physisorbs to the chemisorption-sautrated Aum(CO)n− complexes. © 2005 American Institute of Physics.  
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68.43.Mn Adsorption kinetics
79.60.Dp Adsorbed layers and thin films
82.33.Hk Reactions on clusters
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back to top Theoretical Methods and Algorithms

Gaussian split Ewald: A fast Ewald mesh method for molecular simulation

Yibing Shan, John L. Klepeis, Michael P. Eastwood, Ron O. Dror, and David E. Shaw

J. Chem. Phys. 122, 054101 (2005); http://dx.doi.org/10.1063/1.1839571 (13 pages) | Cited 33 times

Online Publication Date: 13 January 2005

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Gaussian split Ewald (GSE) is a versatile Ewald mesh method that is fast and accurate when used with both real-space and k-space Poisson solvers. While real-space methods are known to be asymptotically superior to k-space methods in terms of both computational cost and parallelization efficiency, k-space methods such as smooth particle-mesh Ewald (SPME) have thus far remained dominant because they have been more efficient than existing real-space methods for simulations of typical systems in the size range of current practical interest. Real-space GSE, however, is approximately a factor of 2 faster than previously described real-space Ewald methods for the level of force accuracy typically required in biomolecular simulations, and is competitive with leading k-space methods even for systems of moderate size. Alternatively, GSE may be combined with a k-space Poisson solver, providing a conveniently tunable k-space method that performs comparably to SPME. The GSE method follows naturally from a uniform framework that we introduce to concisely describe the differences between existing Ewald mesh methods. © 2005 American Institute of Physics.
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87.15.A- Theory, modeling, and computer simulation
87.15.H- Dynamics of biomolecules
87.14.E- Proteins
36.20.-r Macromolecules and polymer molecules
02.30.Jr Partial differential equations
02.60.Lj Ordinary and partial differential equations; boundary value problems
02.30.Nw Fourier analysis
02.50.Ng Distribution theory and Monte Carlo studies
02.70.Ns Molecular dynamics and particle methods

van der Waals interactions of polycyclic aromatic hydrocarbon dimers

Svetla D. Chakarova and Elsebeth Schröder

J. Chem. Phys. 122, 054102 (2005); http://dx.doi.org/10.1063/1.1835956 (5 pages) | Cited 20 times

Online Publication Date: 14 January 2005

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Density functional theory is in principle exact and includes also long-range interactions, such as the van der Waals interactions. These are, however, part of the exchange-correlation energy functional that needs to be approximated, and are absent in the local and semilocal standard implementations. Recently a density functional which includes van der Waals interactions for planar systems has been developed [Phys. Rev. Lett. 91, 126402 (2003)], which we show can be extended to provide a treatment of planar molecules. We use this functional to calculate binding distances and energies for dimers of three of the smallest polycyclic aromatic hydrocarbons (PAHs)—naphthalene, anthracene, and pyrene.© 2005 American Institute of Physics.
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31.15.E- Density-functional theory
34.20.Gj Intermolecular and atom-molecule potentials and forces
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Fm Bond strengths, dissociation energies
33.15.Dj Interatomic distances and angles

Accurate hybrid stochastic simulation of a system of coupled chemical or biochemical reactions

Howard Salis and Yiannis Kaznessis

J. Chem. Phys. 122, 054103 (2005); http://dx.doi.org/10.1063/1.1835951 (13 pages) | Cited 64 times

Online Publication Date: 14 January 2005

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The dynamical solution of a well-mixed, nonlinear stochastic chemical kinetic system, described by the Master equation, may be exactly computed using the stochastic simulation algorithm. However, because the computational cost scales with the number of reaction occurrences, systems with one or more “fast” reactions become costly to simulate. This paper describes a hybrid stochastic method that partitions the system into subsets of fast and slow reactions, approximates the fast reactions as a continuous Markov process, using a chemical Langevin equation, and accurately describes the slow dynamics using the integral form of the “Next Reaction” variant of the stochastic simulation algorithm. The key innovation of this method is its mechanism of efficiently monitoring the occurrences of slow, discrete events while simultaneously simulating the dynamics of a continuous, stochastic or deterministic process. In addition, by introducing an approximation in which multiple slow reactions may occur within a time step of the numerical integration of the chemical Langevin equation, the hybrid stochastic method performs much faster with only a marginal decrease in accuracy. Multiple examples, including a biological pulse generator and a large-scale system benchmark, are simulated using the exact and proposed hybrid methods as well as, for comparison, a previous hybrid stochastic method. Probability distributions of the solutions are compared and the weak errors of the first two moments are computed. In general, these hybrid methods may be applied to the simulation of the dynamics of a system described by stochastic differential, ordinary differential, and Master equations. © 2005 American Institute of Physics.
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82.20.Wt Computational modeling; simulation
82.40.-g Chemical kinetics and reactions: special regimes and techniques
87.15.R- Reactions and kinetics

The E⊗e dynamic Jahn-Teller problem: A new insight from the strong coupling limit

Tohru Sato, Liviu F. Chibotaru, and Arnout Ceulemans

J. Chem. Phys. 122, 054104 (2005); http://dx.doi.org/10.1063/1.1836758 (13 pages) | Cited 6 times

Online Publication Date: 14 January 2005

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Correct boundary conditions for the E⊗e dynamic Jahn-Teller problem are considered explicitly for the first time to obtain approximate analytical solutions in the strong coupling limit. Numerical solutions for the decoupled equations using the finite difference method are also presented. The numerical solutions for the decoupled equations exhibit avoided crossings in the weak coupling region, which explains the oscillating behavior of the solutions obtained by Longuet-Higgins et al. for the coupled equations. The obtained analytical energy expressions show improved agreement with the numerical calculations as compared with the previous treatment in which the potentials were assumed to be harmonic. We demonstrate that the pseudorotational energy j2/(2g2), where g is the dimensionless vibronic coupling constant, and j total angular momentum: j=±1/2,±3/2,…, in the conventional strong coupling expression for the vibronic levels of the lower sheet is exact. Non-Hermitian first-order perturbation theory gives the energy which is correct up to 1/g4. The asymptotic behavior of the wave function at the origin does not influence the corrected energy up to order of 1/g4. At the same time the treatment of the upper sheet with correct boundary conditions gives solutions which are entirely different from the corresponding Slonczewski’s solutions. Besides, the correct boundary conditions enable us to evaluate the nonadiabatic coupling between the lower and upper potential sheets. The energy correction due to the nonadiabatic coupling is estimated to be of order 1/g6. © 2005 American Institute of Physics.
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33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
31.15.xp Perturbation theory
31.30.Gs Hyperfine interactions and isotope effects
02.70.Bf Finite-difference methods
02.10.Ud Linear algebra

Fast centroid molecular dynamics: A force-matching approach for the predetermination of the effective centroid forces

Tyler D. Hone, Sergei Izvekov, and Gregory A. Voth

J. Chem. Phys. 122, 054105 (2005); http://dx.doi.org/10.1063/1.1836731 (7 pages) | Cited 16 times

Online Publication Date: 18 January 2005

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A fast centroid molecular dynamics (CMD) methodology is proposed in which the effective centroid forces are predetermined through a force-matching algorithm applied to a standard path integral molecular dynamics simulation. The resulting method greatly reduces the computational cost of generating centroid trajectories, thus extending the applicability of CMD. The method is applied to the study of liquid para-hydrogen at two state points and liquid ortho-deuterium at one state point. The static and dynamical results are compared to those obtained from full adiabatic CMD simulations and found to be in excellent agreement for all three systems; the transport properties are also compared to experiment and found to have a similar level of agreement. © 2005 American Institute of Physics.
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61.20.Ja Computer simulation of liquid structure
66.10.C- Diffusion and thermal diffusion

Finite bias conductance of an Anderson level: A source-Liouville Hartree–Fock study

Igor V. Ovchinnikov and Daniel Neuhauser

J. Chem. Phys. 122, 054106 (2005); http://dx.doi.org/10.1063/1.1835261 (5 pages)

Online Publication Date: 19 January 2005

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We address the problem of stationary conductance through an Anderson spin-degenerate level at finite bias. Just as in the Anderson solution, for a finite bias in parameter space (bias, gate voltage, interaction constant, and the couplings to the leads) there exist spin-polarized and non-spin-polarized regions. The transition curve between them is found analytically for the case of symmetric coupling to the left and right leads. We approach the problem by a non-Markovian source-Liouville equation where the two-body interaction self-energies are taken in the Hartree–Fock approximation.© 2005 American Institute of Physics.
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72.60.+g Mixed conductivity and conductivity transitions
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.30.+h Metal-insulator transitions and other electronic transitions
72.25.-b Spin polarized transport

Cubic response functions in time-dependent density functional theory

Branislav Jansik, Paweł Sałek, Dan Jonsson, Olav Vahtras, and Hans Ågren

J. Chem. Phys. 122, 054107 (2005); http://dx.doi.org/10.1063/1.1811605 (19 pages) | Cited 34 times

Online Publication Date: 19 January 2005

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We present density-functional theory for time-dependent response functions up to and including cubic response. The working expressions are derived from an explicit exponential parametrization of the density operator and the Ehrenfest principle, alternatively, the quasienergy ansatz. While the theory retains the adiabatic approximation, implying that the time-dependency of the functional is obtained only implicitly—through the time dependence of the density itself rather than through the form of the exchange-correlation functionals—it generalizes previous time-dependent implementations in that arbitrary functionals can be chosen for the perturbed densities (energy derivatives or response functions). In particular, general density functionals beyond the local density approximation can be applied, such as hybrid functionals with exchange correlation at the generalized-gradient approximation level and fractional exact Hartree–Fock exchange. With our implementation the response of the density can always be obtained using the stated density functional, or optionally different functionals can be applied for the unperturbed and perturbed densities, even different functionals for different response order. As illustration we explore the use of various combinations of functionals for applications of nonlinear optical hyperpolarizabilities of a few centrosymmetric systems; molecular nitrogen, benzene, and the C60 fullerene. Considering that vibrational, solvent, and local field factors effects are left out, we find in general that very good experimental agreement can be obtained for the second dynamic hyperpolarizability of these systems. It is shown that a treatment of the response of the density beyond the local density approximation gives a significant effect. The use of different functional combinations are motivated and discussed, and it is concluded that the choice of higher order kernels can be of similar importance as the choice of the potential which governs the Kohn–Sham orbitals. © 2005 American Institute of Physics.
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31.15.E- Density-functional theory
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Bh General molecular conformation and symmetry; stereochemistry

Multiconfiguration self-consistent-field theory based upon the fragment molecular orbital method

Dmitri G. Fedorov and Kazuo Kitaura

J. Chem. Phys. 122, 054108 (2005); http://dx.doi.org/10.1063/1.1835954 (10 pages) | Cited 43 times

Online Publication Date: 19 January 2005

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The fragment molecular orbital (FMO) method was combined with the multiconfiguration self-consistent-field (MCSCF) theory. One- and two-layer approaches were developed, the former involving all dimer MCSCF calculations and the latter limiting MCSCF calculations to a small part of the system. The accuracy of the two methods was tested using the six electrons in six orbitals complete active space type of MCSCF and singlet spin state for phenol+(H2O)n, n=16,32,64 (6-31G∗ and 6-311G∗ basis sets); α helices and β strands of phenylalanine-(alanine)n, n=4,8,16 (6-31G∗). Both double-ζ and triple-ζ quality basis sets with polarization were found to have very similar accuracy. The error in the correlation energy was at most 0.000 88 a.u., the error in the gradient of the correlation energy was at most 6.×10−5 a.u./bohr and the error in the correlation correction to the dipole moment was at most 0.018 D. In addition, vertical singlet-triplet electron excitation energies were computed for phenol+(H2O)n, (n=16,32,64), 6-31G∗, and the errors were found to be at most 0.02 eV. Approximately linear scaling was observed for the FMO-based MCSCF methods. As an example, an FMO-based MCSCF calculation with 1262 basis functions took 98 min on one 3.0 GHz Pentium4 node with 1 Gbyte RAM.© 2005 American Institute of Physics.
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31.15.xr Self-consistent-field methods
31.15.E- Density-functional theory
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.vj Electron correlation calculations for atoms and ions: excited states

Intramolecular energy transfer through charge transfer state in lanthanide compounds: A theoretical approach

W. M. Faustino, O. L. Malta, and G. F. de Sá

J. Chem. Phys. 122, 054109 (2005); http://dx.doi.org/10.1063/1.1830452 (10 pages) | Cited 14 times

Online Publication Date: 19 January 2005

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A theoretical approach for the intramolecular energy transfer process involving the ligand-to-metal charge transfer (LMCT) state in lanthanide compounds is developed. Considering a two-electron interaction, both the direct Coulomb and exchange interactions are taken into account, leading to expressions from which selection rules may be derived and transfer rates may be calculated. These selection rules show that the direct Coulomb and exchange mechanisms are complementary, in the same way as obtained in previous works for the case of ligand-lanthanide ion energy transfer processes. An important result from numerical estimates is that the channel ligand–LMCT state is by far the dominant case, leading to transfer rates higher than for the channel lanthanide ion–LMCT state by several orders of magnitude. The analysis of the emission quantum yield as a function of the relative energy position of the LMCT state in a typical Eu3+ compound allows the identification of two quenching regions, the most pronounced one occurring close to the lower ligand triplet level. © 2005 American Institute of Physics.
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33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
31.15.vj Electron correlation calculations for atoms and ions: excited states

Coupled cluster methods including triple excitations for excited states of radicals

Christopher E. Smith, Rollin A. King, and T. Daniel Crawford

J. Chem. Phys. 122, 054110 (2005); http://dx.doi.org/10.1063/1.1835953 (8 pages) | Cited 26 times

Online Publication Date: 20 January 2005

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We report an extension of the coupled cluster iterative-triples model, CC3, to excited states of open-shell molecules, including radicals. We define the method for both spin-unrestricted Hartree–Fock (UHF) and spin-restricted open-shell Hartree–Fock (ROHF) reference determinants and discuss its efficient implementation in the PSI3 program package. The program is streamlined to use at most O(N7) computational steps and avoids storage of the triple-excitation amplitudes for both the ground- and excited-state calculations. The excitation-energy program makes use of a Löwdin projection formalism (comparable to that of earlier implementations) that allows computational reduction of the Davidson algorithm to only the single- and double-excitation space, but limits the calculation to only one excited state at a time. However, a root-following algorithm may be used to compute energies for multiple states of the same symmetry. Benchmark applications of the new methods to the lowest valence 2B1 state of the allyl radical, low-lying states of the CH and CO+ diatomics, and the nitromethyl radical show substantial improvement over ROHF- and UHF-based CCSD excitation energies for states with strong double-excitation character or cases suffering from significant spin contamination. For the allyl radical, CC3 adiabatic excitation energies differ from experiment by less than 0.02 eV, while for the 2Σ+ state of CH, significant errors of more than 0.4 eV remain. © 2005 American Institute of Physics.
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31.15.bw Coupled-cluster theory
31.15.vn Electron correlation calculations for diatomic molecules
02.60.Gf Algorithms for functional approximation

Propagator corrections to adiabatic time-dependent density-functional theory linear response theory

Mark E. Casida

J. Chem. Phys. 122, 054111 (2005); http://dx.doi.org/10.1063/1.1836757 (9 pages) | Cited 42 times

Online Publication Date: 20 January 2005

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It has long been known that only one-electron excitations are available from adiabatic time-dependent density functional theory (TDDFT). This is particularly clear in Casida’s formulation of TDDFT linear response theory [M. E. Casida, in Recent Advances in Density Functional Methods, Part I, edited by D. P. Chong (World Scientific, Singapore, 1995), p. 155]. Nevertheless the explicit inclusion of two- and higher-electron excitations is necessary for an adequate description of some excited states, notably the first excited singlet states of butadiene and quartet excited states of molecules with a doublet ground state. The equation-of-motion superoperator approach is used here to derive a Casida-like propagator equation which can be clearly separated into an adiabatic part and a nonadiabatic part. The adiabatic part is identified as corresponding to Casida’s equation for adiabatic TDDFT linear response theory. This equivalence is confirmed by deriving a general formula which includes the result that Gonze and Scheffler derived to show the equivalence of TDDFT and Görling-Levy adiabatic connection perturbation theory for the exchange-only optimized effective potential [X. Gonze and M. Scheffler, Phys. Rev. Lett. 82, 4416 (1999)]. The nonadiabatic part explicitly corrects adiabatic TDDFT for two- and higher-electron excitations. The “dressed TDDFT” of Maitra, Zhang, Cave, and Burke is obtained as a special case where the ground state is closed shell [N. T. Maitra, F. Zhang, R. J. Cave, and K. Burke, J. Chem. Phys. 120, 5932 (2004)]. The extension of dressed TDDFT to the case where the ground state is an open-shell doublet is presented, highlighting the importance of correctly accounting for symmetry in this theory. The extension to other ground state spin symmetries is a straightforward consequence of the present work.© 2005 American Institute of Physics.
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31.15.E- Density-functional theory
31.15.V- Electron correlation calculations for atoms, ions and molecules

Targeted Car–Parrinello molecular dynamics: Elucidating double proton transfer in formic acid dimer

Phineus R. L. Markwick, Nikos L. Doltsinis, and Dominik Marx

J. Chem. Phys. 122, 054112 (2005); http://dx.doi.org/10.1063/1.1842049 (8 pages) | Cited 12 times

Online Publication Date: 20 January 2005

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The targeted molecular dynamics method, making possible the study of rare events, has been assessed in the framework of Car–Parrinello ab initio molecular dynamics. As a test case, we have studied the staggered–eclipsed rotation of ethane. The technique has subsequently been applied to investigate the nature of double proton transfer in formic acid dimer. The latter is found to follow a concerted transfer mechanism involving an essentially planar transition state. A “funnel-like region” of the potential energy surface is identified, where floppy intermolecular modes stiffen upon approaching the transition state. © 2005 American Institute of Physics.
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31.15.A- Ab initio calculations
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Wt Computational modeling; simulation
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
33.15.Mt Rotation, vibration, and vibration-rotation constants
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

An investigation of valence shell orbital momentum profiles of difluoromethane by binary (e,2e) spectroscopy

G. L. Su, C. G. Ning, S. F. Zhang, X. G. Ren, H. Zhou, B. Li, F. Huang, G. Q. Li, and J. K. Deng

J. Chem. Phys. 122, 054301 (2005); http://dx.doi.org/10.1063/1.1839851 (8 pages) | Cited 5 times

Online Publication Date: 13 January 2005

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The electron binding energy spectra and momentum profiles of the valence orbitals of difluoromethane, also known as HFC32 (HFC—hydrofluorocarbon) (CH2F2), have been studied by using a high resolution (e,2e) electron momentum spectrometer, at an impact energy of 1200 eV plus the binding energy, and by using symmetric noncoplanar kinematics. The experimental momentum profiles of the outer valence orbitals and 4a1 inner valence orbital are compared with the theoretical momentum distributions calculated using Hartree–Fock and density functional theory (DFT) methods with various basis sets. In general, the shapes of the experimental momentum distributions are well described by both the Hartree–Fock and DFT calculations when large and diffuse basis sets are used. However, the result also shows that it is hard to choose the different calculations for some orbitals, including the methods and the size of the basis sets employed. The pole strength of the ionization peak from the 4a1 inner valence orbital is estimated. © 2005 American Institute of Physics.
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34.80.-i Electron and positron scattering
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
31.15.xr Self-consistent-field methods
31.15.E- Density-functional theory

Multireference configuration interaction calculations for positronium halides

Shiro L. Saito

J. Chem. Phys. 122, 054302 (2005); http://dx.doi.org/10.1063/1.1839853 (8 pages) | Cited 10 times

Online Publication Date: 13 January 2005

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Multireference configuration interaction (MRCI) calculations of the positronium halides, PsF, PsCl, PsBr, and PsI, are carried out, to give positron ionization energies, positronium binding energies, and two-photon annihilation rates. All CI calculations consider only valence correlation effect with a frozen-core approximation, and use the orbitals with angular momentum up to 8. To incorporate the effects of many-body correlations in the energies and two-photon annihilation rates, the MRCI calculations are repeated with increasing reference configurations, and the full CI limits of these energies and annihilation rates are estimated. The contribution from orbitals having angular momentum greater than 8 to those values is also estimated. Relative to our previous single reference CI calculations, many-body correlation effects significantly increase the positron ionization energies, positronium binding energies, and two-photon annihilation rates. The structures of the positronium halides are also discussed. © 2005 American Institute of Physics.
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31.15.vn Electron correlation calculations for diatomic molecules
36.10.Dr Positronium
33.80.Wz Other multiphoton processes
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Theoretical investigation of the SO2+ dication and the photo-double ionization spectrum of SO

A. Ben Houria, Z. Ben Lakhdar, M. Hochlaf, F. Kemp, and I. R. McNab

J. Chem. Phys. 122, 054303 (2005); http://dx.doi.org/10.1063/1.1834513 (10 pages) | Cited 10 times

Online Publication Date: 14 January 2005

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Highly correlated ab initio methods were used in order to generate the potential energy curves of the electronic states of the SO2+ dication and of the electronic ground state of the neutral SO molecule. These curves were used to predict the spectroscopic properties of this dication and to perform forward calculations of the double photoionization spectrum of SO. In light of spin-orbit calculations, the metastability of this doubly charged ion is discussed: for instance, the rovibrational levels of the X 1Σ+ and A 3Σ+ states are found to present relatively long lifetimes. In contrast, the other electronic excited states should predissociate to form S+ and O+ in their electronic ground states. The simulated spectrum shows structures due to transitions between the v=0 vibrational level of SO (X 3Σ−) and the vibrational levels below the barrier maximum of 11 of the calculated electronic states. The 2 1Σ+ electronic state of SO2+ received further treatment: in addition to vibrational bands due to the below barrier energy levels of this electronic state, at least nine continuum resonances were predicted which are responsible for the special shape of the spectrum in this energy region. This work is predictive in nature and should stimulate future experimental investigations dealing with this dication. © 2005 American Institute of Physics.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Gj Diffuse spectra; predissociation, photodissociation
31.50.Df Potential energy surfaces for excited electronic states
31.50.Bc Potential energy surfaces for ground electronic states
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
33.20.Vq Vibration-rotation analysis
33.70.Jg Line and band widths, shapes, and shifts
31.15.A- Ab initio calculations

Time-dependent quantum mechanical wave packet study of the He+H2+(v,j)→HeH++H reaction

Aditya Narayan Panda and N. Sathyamurthy

J. Chem. Phys. 122, 054304 (2005); http://dx.doi.org/10.1063/1.1839866 (7 pages) | Cited 20 times

Online Publication Date: 14 January 2005

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A detailed three-dimensional time-dependent quantum dynamical study of the He+H2+(v=0–3,j=0)→HeH++H reaction is reported for different vibrational v states of H2+ in its ground rotational (j=0) state over a range of translational Etrans energies on an accurate ab initio potential energy surface published by Palmieri et al. Plots of reaction probability as a function of total energy E reveal a large number of oscillations indicating the presence of a number of reactive scattering resonances. When averaged over total angular momentum J, some of the oscillations survive, indicating that they may be amenable to experimental observation. A comparison of our present results with our earlier results on the McLaughlin–Thompson–Joseph–Sathyamurthy surface and the experimental results from different research groups reveal a good deal of agreement as well as some discrepancies between theory and experiment at the level of state-selected gas phase dynamics. © 2005 American Institute of Physics.
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51.10.+y Kinetic and transport theory of gases
51.30.+i Thermodynamic properties, equations of state

Ab initio potential energy surfaces, total absorption cross sections, and product quantum state distributions for the low-lying electronic states of N2O

Mohammad Noh Daud, Gabriel G. Balint-Kurti, and Alex Brown

J. Chem. Phys. 122, 054305 (2005); http://dx.doi.org/10.1063/1.1830436 (9 pages) | Cited 7 times

Online Publication Date: 18 January 2005

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Adiabatic potential energy surfaces for the six lowest singlet electronic states of N2O (X 1A′, 2 1A′, 3 1A′, 1 1A″, 2 1A″ and 3 1A″) have been computed using an ab initio multireference configuration interaction (MRCI) method and a large orbital basis set (aug-cc-pVQZ). The potential energy surfaces display several symmetry related and some nonsymmetry related conical intersections. Total photodissociation cross sections and product rotational state distributions have been calculated for the first ultraviolet absorption band of the system using the adiabatic ab initio potential energy and transition dipole moment surfaces corresponding to the lowest three excited electronic states. In the Franck–Condon region the potential energy curves corresponding to these three states lie very close in energy and they all contribute to the absorption cross section in the first ultraviolet band. The total angular momentum is treated correctly in both the initial and final states. The total photodissociation spectra and product rotational distributions are determined for N2O initially in its ground vibrational state (0,0,0) and in the vibrationally excited (0,1,0) (bending) state. The resulting total absorption spectra are in good quantitative agreement with the experimental results over the region of the first ultraviolet absorption band, from 150 to 220 nm. All of the lowest three electronically excited states [1Σ−(1 1A″), 1Δ(2 1A′), and 1Δ(2 1A″)] have zero transition dipole moments from the ground state [1Σ+(1 1A′)] in its equilibrium linear configuration. The absorption becomes possible only through the bending motion of the molecule. The 1Δ(2 1A′)←X 1Σ+(1A′) absorption dominates the absorption cross section with absorption to the other two electronic states contributing to the shape and diffuse structure of the band. It is suggested that absorption to the bound 1Δ(2 1A″) state makes an important contribution to the experimentally observed diffuse structure in the first ultraviolet absorption band. The predicted product rotational quantum state distribution at 203 nm agrees well with experimental observations.© 2005 American Institute of Physics.
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31.15.A- Ab initio calculations
31.50.Bc Potential energy surfaces for ground electronic states
31.50.Df Potential energy surfaces for excited electronic states
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis
31.15.vn Electron correlation calculations for diatomic molecules
33.20.Lg Ultraviolet spectra
33.70.Jg Line and band widths, shapes, and shifts
33.15.Bh General molecular conformation and symmetry; stereochemistry

New CO–CO interaction potential tested by rovibrational calculations

G. W. M. Vissers, A. Heßelmann, G. Jansen, P. E. S. Wormer, and A. van der Avoird

J. Chem. Phys. 122, 054306 (2005); http://dx.doi.org/10.1063/1.1835262 (11 pages) | Cited 8 times

Online Publication Date: 18 January 2005

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A four-dimensional potential energy surface (PES) for the CO dimer consisting of rigid molecules has been calculated, using a scheme that combines density functional theory to describe the monomers and symmetry adapted perturbation theory for the interaction energy (DFT-SAPT). The potential is fitted in terms of analytic functions, and the fitted potential is used to compute the lowest rovibrational states of the dimer. The quality of the PES is comparable to that of a previously published surface [G. W. M. Vissers, P. E. S. Wormer, and A. van der Avoird, Phys. Chem. Chem. Phys., 5, 4767 (2003)], which was calculated with the coupled cluster single double and perturbative triples [CCSD(T)] method. It is shown that a weighted average of the DFT-SAPT and the CCSD(T) potential gives results that are in very good agreement with experimental data, for both (12CO)2 and (13CO)2. The relative weight was determined by adjusting the energy gap between the origins of the lowest two stacks of rotational levels of (12CO)2 to the measured value.© 2005 American Institute of Physics.
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31.50.Df Potential energy surfaces for excited electronic states
31.15.E- Density-functional theory
31.15.xp Perturbation theory
31.15.bw Coupled-cluster theory
33.20.Sn Rotational analysis
34.50.-s Scattering of atoms and molecules
33.20.Vq Vibration-rotation analysis

Photodissociation dynamics of IBr−(CO2)n, n<15

Todd Sanford, Sang-Yun Han, Matthew A. Thompson, Robert Parson, and W. Carl Lineberger

J. Chem. Phys. 122, 054307 (2005); http://dx.doi.org/10.1063/1.1839178 (11 pages) | Cited 18 times

Online Publication Date: 18 January 2005

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We report the ionic photoproducts produced following photoexcitation of mass selected IBr−(CO2)n, n=0–14, cluster ions at 790 and 355 nm. These wavelengths provide single state excitation to two dissociative states, corresponding to the A′ 2Π1/2 and B 2 2Σ1/2+ states of the IBr− chromophore. Excitation of these states in IBr− leads to production of I−+Br and Br−+I∗, respectively. Potential energy curves for the six lowest electronic states of IBr− are calculated, together with structures for IBr−(CO2)n, n=1–14. Translational energy release measurements on photodissociated IBr− determine the I–Br− bond strength to be 1.10±0.04 eV; related measurements characterize the A′ 2Π1/2←X 2Σ1/2+ absorption band. Photodissociation product distributions are measured as a function of cluster size following excitation to the A′ 2Π1/2 and B 2 2Σ1/2+ states. The solvent is shown to drive processes such as spin-orbit relaxation, charge transfer, recombination, and vibrational relaxation on the ground electronic state. Following excitation to the A′ 2Π1/2 electronic state, IBr−(CO2)n exhibits size-dependent cage fractions remarkably similar to those observed for I2−(CO2)n. In contrast, excitation to the B 2 2Σ1/2+ state shows extensive trapping in excited states that dominates the recombination behavior for all cluster sizes we investigated. Finally, a pump-probe experiment on IBr−(CO2)8 determines the time required for recombination on the ground state following excitation to the A′ state. While the photofragmentation experiments establish 100% recombination in the ground electronic state for this and larger IBr− cluster ions, the time required for recombination is found to be ∼5 ns, some three orders of magnitude longer than observed for the analogous I2− cluster ion. Comparisons are made with similar experiments carried out on I2−(CO2)n and ICl−(CO2)n cluster ions. © 2005 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
31.50.Bc Potential energy surfaces for ground electronic states
31.70.Dk Environmental and solvent effects
34.50.Ez Rotational and vibrational energy transfer
34.70.+e Charge transfer
36.40.Jn Reactivity of clusters
36.40.Wa Charged clusters
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light

Photoelectron anisotropy and channel branching ratios in the detachment of solvated iodide cluster anions

Richard Mabbs, Eric Surber, and Andrei Sanov

J. Chem. Phys. 122, 054308 (2005); http://dx.doi.org/10.1063/1.1839861 (9 pages) | Cited 21 times

Online Publication Date: 18 January 2005

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Photoelectron spectra and angular distributions in 267 nm detachment of the I−⋅Ar, I−⋅H2O, I−⋅CH3I, and I−⋅CH3CN cluster anions are examined in comparison with bare I− using velocity-map photoelectron imaging. In all cases, features are observed that correlate to two channels producing either I(2P3/2) or I(2P1/2). In the photodetachment of I− and I−⋅Ar, the branching ratios of the 2P1/2 and 2P3/2 channels are observed to be ≈0.4, in both cases falling short of the statistical ratio of 0.5. For I−⋅H2O and I−⋅CH3I, the 2P1/2 to 2P3/2 branching ratios are greater by a factor of 1.6 compared to the bare iodide case. The relative enhancement of the 2P1/2 channel is attributed to dipole effects on the final-state continuum wave function in the presence of polar solvents. For I−⋅CH3CN the 2P1/2 to 2P3/2 ratio falls again, most likely due to the proximity of the detachment threshold in the excited spin-orbit channel. The photoelectron angular distributions in the photodetachment of I−, I−⋅Ar, I−⋅H2O, and I−⋅CH3CN are understood within the framework of direct detachment from I−. Hence, the corresponding anisotropy parameters are modeled using variants of the Cooper-Zare central-potential model for atomic-anion photodetachment. In contrast, I−⋅CH3I yields nearly isotropic photoelectron angular distributions in both detachment channels. The implications of this anomalous behavior are discussed with reference to alternative mechanisms, affording the solvent molecule an active role in the electron ejection process. © 2005 American Institute of Physics.
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34.50.Rk Laser-modified scattering and reactions
36.40.Mr Spectroscopy and geometrical structure of clusters
33.60.+q Photoelectron spectra
33.70.Jg Line and band widths, shapes, and shifts
82.50.Kx Processes caused by X-rays or γ-rays

Molecules in high spin states III: The millimeter/submillimeter-wave spectrum of the MnCl radical (X 7Σ+)

D. T. Halfen and L. M. Ziurys

J. Chem. Phys. 122, 054309 (2005); http://dx.doi.org/10.1063/1.1824036 (10 pages) | Cited 3 times

Online Publication Date: 18 January 2005

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The pure rotational spectrum of the MnCl radical (X 7Σ+) has been recorded in the range 141–535 GHz using millimeter–submillimeter direct absorption spectroscopy. This work is the first time the molecule has been studied with rotational resolution in its ground electronic state. MnCl was synthesized by the reaction of manganese vapor, produced in a Broida-type oven, with Cl2. Transitions of both chlorine isotopomers were measured, as well as lines originating in several vibrationally excited states. The presence of several spin components and manganese hyperfine interactions resulted in quite complex spectra, consisting of multiple blended features. Because 42 rotational transitions were measured for Mn35Cl over a wide range of frequencies with high signal-to-noise, a very accurate set of rotational, fine structure, and hyperfine constants could be determined with the aid of spectral simulations. Spectroscopic constants were also determined for Mn37Cl and several vibrationally excited states. The values of the spin-rotation and spin–spin parameters were found to be relatively small (γ=11.2658 MHz and λ=1113.10 MHz for Mn35Cl); in the case of λ, excited electronic states contributing to the second-order spin–orbit interaction may be canceling each other. The Fermi contact hyperfine term was found to be large in manganese chloride with bF(Mn35Cl)=397.71 MHz, a result of the manganese 4s character mixing into the 12σ orbital. This orbital is spσ hybridized, and contains some Mn 4pσ character, as well. Hence, it also contributes to the dipolar constant c, which is small and positive for this radical (c=32.35 MHz for Mn35Cl). The hyperfine parameters in MnCl are similar to those of MnH and MnF, suggesting that the bonding in these three molecules is comparable. © 2005 American Institute of Physics.
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33.20.Sn Rotational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Bx Radio-frequency and microwave spectra
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.20.Tp Vibrational analysis
31.30.Gs Hyperfine interactions and isotope effects
33.15.Pw Fine and hyperfine structure
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.15.Fm Bond strengths, dissociation energies

Femtosecond dynamics of Cu(H2O)2

Mark S. Taylor, Jack Barbera, Claus-Peter Schulz, Felician Muntean, Anne B. McCoy, and W. Carl Lineberger

J. Chem. Phys. 122, 054310 (2005); http://dx.doi.org/10.1063/1.1836759 (11 pages) | Cited 10 times

Online Publication Date: 18 January 2005

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The ultrafast relaxation dynamics of Cu(H2O)2 is investigated using femtosecond photodetachment-photoionization spectroscopy. In addition, stationary points on the Cu(H2O)2 anion, neutral, and cation potential energy surfaces are characterized by ab initio electronic structure calculations. Electron photodetachment from Cu−(H2O)2 initiates the dynamics on the ground-state potential energy surface of neutral Cu(H2O)2. The resulting Cu(H2O)2 complexes experience large-amplitude H2O reorientation and dissociation. The time evolution of the Cu(H2O)2 fragmentation products is monitored by time-resolved resonant multiphoton ionization. The parent ion, Cu+(H2O)2, is not detected above background levels. The rise to a maximum of the Cu+ signal from Cu−(H2O)2, and the decay of the Cu+(H2O) signal from Cu−(H2O)2 have similar τ≈10 ps time dependences to the corresponding signals from Cu−(H2O), but display clear differences at very short and long times. The experimental observations can be understood in terms of the following picture. Prompt dissociation of H2O from nascent Cu(H2O)2 gives rise to a vibrationally excited Cu(H2O) complex, which dissociates to Cu+H2O due to coupling of H2O internal rotation to the dissociation coordinate. This prompt dissociation removes all intra-H2O vibrational excitation from the intermediate Cu(H2O) fragment, which quenches the long time vibrational predissociation to Cu+H2O previously observed in analogous experiments on Cu−(H2O). © 2005 American Institute of Physics.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
33.80.Eh Autoionization, photoionization, and photodetachment
34.50.Gb Electronic excitation and ionization of molecules
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
82.20.Kh Potential energy surfaces for chemical reactions
31.15.A- Ab initio calculations
33.80.Gj Diffuse spectra; predissociation, photodissociation
82.53.Kp Coherent spectroscopy of atoms and molecules
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
82.20.Hf Product distribution

Electronic effect on protonated hydrogen-bonded imidazole trimer and corresponding derivatives cationized by alkali metals (Li+, Na+, and K+)

Shihai Yan, Yuxiang Bu, and Ping Li

J. Chem. Phys. 122, 054311 (2005); http://dx.doi.org/10.1063/1.1839855 (10 pages) | Cited 5 times

Online Publication Date: 19 January 2005

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The electronic effects on the protonated hydrogen-bonded imidazole trimer (Im)3H+ and the derivatives cationized by alkali metals (Li+, Na+, and K+) are investigated using B3LYP method in conjunction with the 6-311+G∗ basis set. The prominent characteristics of (Im)3H+ on reduction are the backflow of the transferred proton to its original fragment and the remoteness of the H atom from the attached side bare N atom. The proton transfer occurs on both reduction and oxidation for the corresponding hydrogen-bonded imidazole trimer. For the derivatives cationized by Li+, (Im)3Li+, the backflow of the transferred proton occurs on reduction. The electron detachment from respective highest occupied molecular orbital of (Im)3Na+ and (Im)3K+ causes the proton transferring from the fragment attached by the alkali metal cation to the middle one. The order of the adiabatic ionization potentials of (Im)3M+ is (Im)3H+>(Im)3Li+>(Im)3Na+>(Im)3K+; the order of (Im)3M indicates that (Im)3H is the easicst complex to be ionized. The polarity of (Im)3M+ (M denotes H, Li, Na, and K) increases on both oxidation and reduction. The (Im)3M+ complexes dissociate into (Im)3 and M+ except (Im)3H+, which dissociates preferably into (Im)3+ and H atom, while the neutral complexes [(Im)3M] dissociate into (Im)3 and M. The stabilization energy of (Im)3Li2+, (Im)3Na2+, and (Im)3K2+ indicate that their energies are higher as compared to those of the monomers. © 2005 American Institute of Physics.
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31.15.E- Density-functional theory
33.15.Fm Bond strengths, dissociation energies
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
33.80.Eh Autoionization, photoionization, and photodetachment
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

First principles study of the diatomic charged fluorides MF±, M=Sc, Ti, V, Cr, and Mn

Stavros Kardahakis, Constantine Koukounas, and Aristides Mavridis

J. Chem. Phys. 122, 054312 (2005); http://dx.doi.org/10.1063/1.1834912 (22 pages) | Cited 10 times

Online Publication Date: 20 January 2005

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Employing multireference configuration interaction and coupled-cluster methods in conjunction with quantitative basis sets, we have explored the electronic structure of the charged diatomic fluorides MF±, where M=Sc, Ti, V, Cr, and Mn. In addition, and in order to complete our recently published work on the neutral diatomic fluorides MF, M=Ti–Mn [C. Koukounas, S. Kardahakis, and A. Mavridis, J. Chem. Phys. 120, 11500 (2004)], we have also examined the ground (X 1Σ+) and the first excited state (α 3Δ) of neutral ScF. For the entire anionic MF− series and the cations ScF+, VF+, and MnF+, no experimental or theoretical results of any kind have been reported so far in the literature. For the charged MF± sequence we have investigated a total of 43=29(MF+)+14(MF−) states, reporting potential energy curves, energetics, and common spectroscopic parameters. Two are the most interesting conclusions of the present work. (a) The Coulombic binding character of MF+ cations, i.e., the conformity of their equilibrium description to M2+F− and (b) the atypical bonding of the MF− anions and their surprisingly high dissociation energies (up to 85 kcal/mol for the X 2Δ state of ScF−). Considering the complexities of these chemically “simple” systems, our results on ScF, TiF+, and CrF+ are in very good agreement with the limited experimental findings.© 2005 American Institute of Physics.
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31.15.A- Ab initio calculations
31.15.bw Coupled-cluster theory
31.50.Bc Potential energy surfaces for ground electronic states
31.50.Df Potential energy surfaces for excited electronic states
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Fm Bond strengths, dissociation energies
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