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1 Jul 2003

Volume 119, Issue 1, pp. 1-639

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Kohn–Sham equations for nanowires with direct current

D. S. Kosov

J. Chem. Phys. 119, 1 (2003); http://dx.doi.org/10.1063/1.1584661 (5 pages) | Cited 17 times

Online Publication Date: 18 June 2003

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The paper describes the derivation of the Kohn–Sham equations for a nanowire with direct current. A value of the electron current enters the problem as an input via a subsidiary condition imposed by pointwise Lagrange multiplier. Using the constrained minimization of the Hohenberg–Kohn energy functional, we derive a set of self-consistent equations for current carrying orbitals of the molecular wire. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials

Infrared-active vibron bands associated with substitutional impurities in solid parahydrogen

Robert J. Hinde

J. Chem. Phys. 119, 6 (2003); http://dx.doi.org/10.1063/1.1584662 (4 pages) | Cited 14 times

Online Publication Date: 18 June 2003

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We present a model for the line shapes of infrared-active Q1(0) vibron bands observed in solid parahydrogen doped with low concentrations of spherical substitutional impurities. The line shapes are highly sensitive to the H2 vibrational dependence of the dopant–H2 interaction. When this vibrational dependence is strong, the dopant can trap the infrared-active vibron in its first solvation shell; in this case, the trapped vibron manifests itself in the absorption spectrum as a narrow feature to the red of the pure solid’s vibron band. © 2003 American Institute of Physics.
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82.30.Nr Association, addition, insertion, cluster formation
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.70.Jg Line and band widths, shapes, and shifts
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Ea Infrared spectra

Tunneling splitting in polyatomic molecules: Application to malonaldehyde

Gennady V. Mil’nikov, Kiyoshi Yagi, Tetsuya Taketsugu, Hiroki Nakamura, and Kimihiko Hirao

J. Chem. Phys. 119, 10 (2003); http://dx.doi.org/10.1063/1.1586252 (4 pages) | Cited 38 times

Online Publication Date: 18 June 2003

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We report an accurate and efficient full dimensional semiclassical ab initio method for calculation of energy level splitting due to tunneling in polyatomic system. The method is applied to 21-dimensional 9-atomic malonaldehyde molecule. The tunneling splittings obtained are ΔE(H) = 21.2 cm−1 for hydrogen atom transfer and ΔE(D) = 3.0 cm−1 for deuterium atom transfer, which are in excellent agreement with the experimental values of 21.6 cm−1 and, 2.9 cm−1 respectively. We believe that the present analysis gives the final solution to the longstanding problem. © 2003 American Institute of Physics.
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31.15.xp Perturbation theory
31.15.vq Electron correlation calculations for polyatomic molecules
31.15.bw Coupled-cluster theory
73.40.Gk Tunneling
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back to top Theoretical Methods and Algorithms

A potential energy surface construction scheme for accurate reaction rate calculations: General approach and a test for the H+CH4→H2+CH3 reaction

Tao Wu and Uwe Manthe

J. Chem. Phys. 119, 14 (2003); http://dx.doi.org/10.1063/1.1577328 (10 pages) | Cited 20 times

Online Publication Date: 18 June 2003

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An approach for the construction of accurate potential energy surfaces for reaction rate calculations is presented. It employs Shepard interpolation with reference points randomly selected from range of geometries relevant for the reaction rate. Quantum dynamics calculations, which use the multiconfigurational time-dependent Hartree approach and flux correlation functions to obtain thermal rate constants, monitor the convergence of the potential energy surface with increasing number of reference points. As a test of the approach, the H+CH4→H2+CH3 reaction is studied and the analytic Jordan–Gilbert potential energy surface is reproduced by the interpolation scheme. About 40 reference points are required in the interpolation to obtain a converged interpolated surface which reproduces the thermal rate constants with errors smaller than 20%. © 2003 American Institute of Physics.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Kh Potential energy surfaces for chemical reactions

Dissipative quantum dynamics of anharmonic oscillators with the multiconfiguration time-dependent Hartree method

M. Nest and H.-D. Meyer

J. Chem. Phys. 119, 24 (2003); http://dx.doi.org/10.1063/1.1576384 (10 pages) | Cited 39 times

Online Publication Date: 18 June 2003

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We investigate the dissipative dynamics of a Morse oscillator coupled nonlinearly to a heat bath. To this end, we compare several reduced equations of motion with the dynamics of a full-dimensional wave packet with up to 61 spatial degrees of freedom. The discretized bath is converged for the relevant times considered in this paper. The propagations are done with a general purpose implementation of the multiconfiguration time-dependent Hartree method. © 2003 American Institute of Physics.
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03.65.Ge Solutions of wave equations: bound states
31.15.xr Self-consistent-field methods

Restricted density functional theory of linear time-dependent properties in open-shell molecules

Zilvinas Rinkevicius, Ingvar Tunell, Paweł Sałek, Olav Vahtras, and Hans Ågren

J. Chem. Phys. 119, 34 (2003); http://dx.doi.org/10.1063/1.1577329 (13 pages) | Cited 32 times

Online Publication Date: 18 June 2003

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In this paper we report the derivation and the performance of a spin-restricted density functional formalism for linear time-dependent properties in open-shell molecules. The formalism is based on an exponential parameterization of the density operator with the response functions defined through Ehrenfest’s principle. In addition to the derivation of formulas, details of implementation are given as well as a discussion of numerical results for excitation energies and dynamic polarizabilities for a selected set of radicals. © 2003 American Institute of Physics.
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31.15.E- Density-functional theory

The parallel implementation of a full configuration interaction program

Zhengting Gan, Yuri Alexeev, Mark S. Gordon, and Ricky A. Kendall

J. Chem. Phys. 119, 47 (2003); http://dx.doi.org/10.1063/1.1575193 (13 pages) | Cited 19 times

Online Publication Date: 18 June 2003

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Both the replicated and distributed data parallel full configuration interaction (FCI) implementations are described. The implementation of the FCI algorithm is organized in a hybrid strings-integral driven approach. Redundant communication is avoided, and the network performance is further optimized by an improved distributed data interface library. Examples show linear scalability of the distributed data code on both PC and workstation clusters. The new parallel implementation greatly extends the hardware on which parallel FCI calculations can be performed. The timing data on the workstation cluster show great potential for using the new parallel FCI algorithm in expanding applications of complete active space self-consistent field applications. © 2003 American Institute of Physics.
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31.15.V- Electron correlation calculations for atoms, ions and molecules

Bohmian versus semiclassical description of interference phenomena

Yi Zhao and Nancy Makri

J. Chem. Phys. 119, 60 (2003); http://dx.doi.org/10.1063/1.1574805 (8 pages) | Cited 11 times

Online Publication Date: 18 June 2003

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The origin of quantum interference characteristic of bound nonlinear systems is investigated within the Bohmian formulation of time-dependent quantum mechanics. By contrast to time-dependent semiclassical theory, whereby interference is a consequence of phase mismatch between distinct classical trajectories, the Bohmian, fully quantum mechanical expression for expectation values has a quasiclassical appearance that does not involve phase factors or cross terms. Numerical calculations reveal that quantum interference in the Bohmian formulation manifests itself directly as sharp spatial/temporal variations of the density surrounding kinky trajectories. These effects are most dramatic in regions where the underlying classical motion exhibits focal points or caustics, and crossing of the Bohmian trajectories is prevented through extremely strong and rapidly varying quantum mechanical forces. These features of Bohmian dynamics, which constitute the hallmark of quantum interference and are ubiquitous in bound nonlinear systems, represent a major source of instability, making the integration of the Bohmian equations extremely demanding in such situations. © 2003 American Institute of Physics.
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03.65.Sq Semiclassical theories and applications
05.45.Mt Quantum chaos; semiclassical methods

Torsional path integral Monte Carlo method for calculating the absolute quantum free energy of large molecules

Thomas F. Miller and David C. Clary

J. Chem. Phys. 119, 68 (2003); http://dx.doi.org/10.1063/1.1568727 (9 pages) | Cited 14 times

Online Publication Date: 18 June 2003

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A new technique for evaluating the absolute free energy of large molecules is presented. Quantum-mechanical contributions to the intramolecular torsions are included via the torsional path integral Monte Carlo (TPIMC) technique. Importance sampling schemes based on uncoupled free rotors and harmonic oscillators facilitate the use of the TPIMC technique for the direct evaluation of quantum partition functions. Absolute free energies are calculated for the molecules ethane, n-butane, n-octane, and enkephalin, and quantum contributions are found to be significant. Comparison of the TPIMC technique with the harmonic oscillator approximation and a variational technique is performed for the ethane molecule. For all molecules, the quantum contributions to free energy are found to be significant but slightly smaller than the quantum contributions to internal energy. © 2003 American Institute of Physics.
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31.15.xt Variational techniques
33.20.Tp Vibrational analysis

Semiclassically optimized complex absorbing potentials of polynomial form. II. Complex case

Bill Poirier and Tucker Carrington

J. Chem. Phys. 119, 77 (2003); http://dx.doi.org/10.1063/1.1573631 (13 pages) | Cited 21 times

Online Publication Date: 18 June 2003

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In a previous paper [J. Chem. Phys. 118, 17 (2003)], we presented an optimal, pure imaginary complex absorbing potential (CAP) of polynomial form, for use with resonance and scattering calculations. The optimal CAP was derived by minimizing reflection and transmission, and was found to greatly reduce CPU time. In this paper, the previous analysis is extended to more general complex polynomial functional forms, and new CAPs are developed which are even more efficient than those of the previous work, especially for highly accurate calculations. © 2003 American Institute of Physics.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
02.10.De Algebraic structures and number theory
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Exploiting both C3v symmetry and sparsity in vibrational calculations for methanelike molecules

Bill Poirier

J. Chem. Phys. 119, 90 (2003); http://dx.doi.org/10.1063/1.1573193 (4 pages) | Cited 7 times

Online Publication Date: 18 June 2003

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In a recent article [J. Chem. Phys. 118, 6946 (2003)], X.-G. Wang and T. Carrington, Jr. presented an efficient method for computing the vibrational bend levels of five-atom molecules. The method is particularly useful if four of the five atoms are identical, in which case G4 symmetry may be exploited in conjunction with the iterative symmetry-adapted Lanczos method. In this paper, we demonstrate how to extend the group of exploitable symmetry operations to G12, without compromising any of the desirable numerical features of the Wang and Carrington approach. This reduces total CPU effort by at least a factor of 3. © 2003 American Institute of Physics.
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33.20.Tp Vibrational analysis
02.60.-x Numerical approximation and analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants

Using C3v symmetry with polyspherical coordinates for methane

Xiao-Gang Wang and Tucker Carrington

J. Chem. Phys. 119, 94 (2003); http://dx.doi.org/10.1063/1.1559479 (7 pages) | Cited 8 times

Online Publication Date: 18 June 2003

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It is well known that the group of operators that commutes with the Hamiltonian operator can be used to facilitate the calculation of energy levels. Due to numerical errors in the computation of Hamiltonian matrix elements, it may happen that the matrix representation of a group operator does not commute with the Hamiltonian matrix although the group operator does commute with the Hamiltonian operator. We demonstrate that it is possible, even in this case, to use the single-symmetry and multisymmetry symmetry-adapted Lanczos (SAL) methods to efficiently compute energy levels. The two SAL methods are applied to the calculation of the bend levels of methane using the G6 symmetry group and polyspherical angles. We show that although potential matrix elements are corrupted by quadrature error, it is nonetheless possible to take advantage of the full symmetry of the polyspherical basis. For a CX3Y-type molecule the symmetry-adapted method of this paper would enable one to exploit all of the symmetry of the molecule. © 2003 American Institute of Physics.
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31.15.V- Electron correlation calculations for atoms, ions and molecules

A contracted basis-Lanczos calculation of vibrational levels of methane: Solving the Schrödinger equation in nine dimensions

Xiao-Gang Wang and Tucker Carrington

J. Chem. Phys. 119, 101 (2003); http://dx.doi.org/10.1063/1.1574016 (17 pages) | Cited 66 times

Online Publication Date: 18 June 2003

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We present a contracted basis-iterative method for calculating numerically exact vibrational energy levels of methane (a 9D calculation). The basis functions we use are products of eigenfunctions of bend and stretch Hamiltonians obtained by freezing coordinates at equilibrium. The basis functions represent the desired wavefunctions well, yet are simple enough that matrix-vector products may be evaluated efficiently. We use Radau polyspherical coordinates. The bend functions are computed in a nondirect product finite basis representation [J. Chem. Phys. 118, 6956 (2003)] and the stretch functions are computed in a product potential optimized discrete variable (PODVR) basis. The memory required to store the bend basis is reduced by a factor of ten by storing it on a compacted grid. The stretch basis is optimized by discarding PODVR functions with high potential energies. The size of the primitive basis is 33 billion. The size of the product contracted basis is six orders of magnitude smaller. Parity symmetry and exchange symmetry between two of the H atoms are employed in the final product contracted basis. A large number of vibrational levels are well converged. These include almost all states up to 8000 cm−1 and some higher local mode stretch bands. © 2003 American Institute of Physics.
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33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
03.65.Ge Solutions of wave equations: bound states

Infrared action spectroscopy and time-resolved dynamics of the OD–CO reactant complex

Ilana B. Pollack, Maria Tsiouris, Helen O. Leung, and Marsha I. Lester

J. Chem. Phys. 119, 118 (2003); http://dx.doi.org/10.1063/1.1577320 (13 pages) | Cited 5 times

Online Publication Date: 18 June 2003

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The infrared action spectrum of the linear OD–CO reactant complex has been recorded in the OD overtone region near 1.9 μm using an infrared pump-ultraviolet probe technique. The pure overtone band of OD–CO (2νOD) is observed at 5148.6 cm−1 and combination bands involving the simultaneous excitation of OD stretch and D-atom bend are identified 160.0 and 191.2 cm−1 to higher energy. Band assignments and spectroscopic constants are derived from the rotationally resolved structure of the spectra. The change in the ground state rotational constant upon deuteration demonstrates that the H/D-atom of the hydroxyl radical points toward CO in the OH/D-CO complex. Direct time-domain measurements yield a lifetime of 37(4) ns for OD–CO (2νOD) prior to decay via inelastic scattering or chemical reaction. This is significantly longer than the laser-limited lifetime of ⩽5 ns observed for OH–CO (2νOH), and is attributed in part to the closing of a near-resonant vibration to vibration energy transfer channel upon deuteration. Vibrational predissociation of OD–CO (2νOD) proceeds by a vibration to rotation and/or translation mechanism that yields highly rotationally excited OD (v = 1) fragments. Intermolecular D-atom bend excitation, which drives the structural transformation from the reactant complex to the transition state for reaction, results in a dramatic shortening of the lifetime to ⩽6 ns (laser-limited). Excitation of the D-atom bend also supplies sufficient energy to reopen the near-resonant vibrational energy transfer channel, resulting in minimal rotational excitation of the OD (v = 1) fragments. Finally, a ground state binding energy for OD–CO of D0 ⩽ 456 cm−1 is established from the OD (v = 1) product state distribution. © 2003 American Institute of Physics.
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36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Sx Diffusion and dynamics of clusters
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.20.Ea Infrared spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
34.20.Gj Intermolecular and atom-molecule potentials and forces
34.50.Ez Rotational and vibrational energy transfer

Singlet–triplet excitation spectrum of the CO–He complex. I. Potential surfaces and bound–bound CO(a 3Π←X 1Σ+) transitions

W. B. Zeimen, G. C. Groenenboom, and A. van der Avoird

J. Chem. Phys. 119, 131 (2003); http://dx.doi.org/10.1063/1.1577334 (10 pages) | Cited 15 times

Online Publication Date: 18 June 2003

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The interaction of He with metastable CO(a 3Π) gives rise to two adiabatic potential surfaces of reflection symmetry A′ and A″ which were calculated with the partially spin-restricted open-shell single and double excitation coupled cluster method with perturbative triples, RCCSD(T). Two diabatic potentials were constructed and fitted analytically; the appropriate form of the angular expansion functions was derived from general invariance properties. From variational calculations on these diabatic potential surfaces we obtained the quasibound vibration-rotation-spin levels of the CO–He complex in its lowest triplet state. Only the lower spin–orbit levels of this complex with approximate quantum number Ω = 0 of the CO(a 3Π) monomer were found to be stable with respect to dissociation into He and triplet CO. The potential and the bound van der Waals levels of the ground state CO(X 1Σ+)–He complex were recalculated and used in combination with the triplet excited state wave functions to compute the line strengths and the bound–bound part of the singlet–triplet excitation spectrum of the CO–He complex. The spin-forbidden singlet–triplet transitions access mainly the higher spin–orbit levels with ∣Ω∣ = 1, but these were found to undergo rapid predissociation. The companion Paper II explicitly studies this process, predicts the excited state lifetimes, and generates the bound-continuum part of the CO–He singlet–triplet spectrum. © 2003 American Institute of Physics.
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33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.15.Mt Rotation, vibration, and vibration-rotation constants
34.20.Gj Intermolecular and atom-molecule potentials and forces
31.50.-x Potential energy surfaces

Singlet–triplet excitation spectrum of the CO–He complex. II. Photodissociation and bound-free CO(a 3Π←X 1Σ+) transitions

W. B. Zeimen, G. C. Groenenboom, and A. van der Avoird

J. Chem. Phys. 119, 141 (2003); http://dx.doi.org/10.1063/1.1577335 (8 pages) | Cited 7 times

Online Publication Date: 18 June 2003

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The dissociating states of the triplet–excited CO–He complex are studied by means of scattering calculations on ab initio diabatic potential energy surfaces produced in the preceding paper (Paper I). With the aid of an effective transition dipole function and the bound states of the CO–He complex in the ground singlet state we obtain the photoabsorption cross section as a function of the excitation energy and generate the full UV spectrum of the singlet–triplet transition. It was found that the dominant contributions to the spectrum, in the energy range from −5 to +10 cm−1 relative to the band origin at 48 473.201 cm−1, originate from resonances that correspond to higher spin–orbit levels of the excited CO(a 3Π)–He complex with approximate quantum number ∣Ω∣ = 1. Rapid predissociation, with the triplet CO fragment decaying into its lower spin–orbit levels with Ω = 0, limits the lifetime of these excited levels to, typically, 10–700 ps. We also predict the rotational and spin–orbit state distribution of the triplet CO fragment and the maximum deflection angle of the photodissociation products in a molecular beam experiment. © 2003 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
82.50.Hp Processes caused by visible and UV light
33.20.Ni Vacuum ultraviolet spectra
82.37.Vb Single molecule photochemistry

Two-pulse atomic coherent control spectroscopy of Eley–Rideal reactions: An application of an atom laser

Solvejg Jørgensen and Ronnie Kosloff

J. Chem. Phys. 119, 149 (2003); http://dx.doi.org/10.1063/1.1576383 (12 pages) | Cited 4 times

Online Publication Date: 18 June 2003

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A spectroscopic application of the atom laser is suggested. The spectroscopy termed 2PACC (two-pulse atomic coherent control) employs the coherent properties of matter waves from a two-pulse atom laser. These waves are employed to control a gas–surface chemical recombination reaction. The method is demonstrated for an Eley–Rideal reaction of a hydrogen or alkali atom-laser pulse where the surface target is an adsorbed hydrogen atom. The reaction yields either a hydrogen or alkali hydride molecule. The desorbed gas-phase molecular yield and its internal state is shown to be controlled by the time and phase delay between two atom-laser pulses. The calculation is based on solving the time-dependent Schrödinger equation in a diabatic framework. The probability of desorption which is the predicted 2PACC signal has been calculated as a function of the pulse parameters. © 2003 American Institute of Physics.
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03.75.Pp Atom lasers
03.75.Be Atom and neutron optics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Dynamical tunneling in molecules: Role of the classical resonances and chaos

Srihari Keshavamurthy

J. Chem. Phys. 119, 161 (2003); http://dx.doi.org/10.1063/1.1577313 (4 pages) | Cited 6 times

Online Publication Date: 18 June 2003

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The influence of classical phase space structures on the dynamical tunneling splittings is studied using an effective spectroscopic Hamiltonian for water. It is argued that the enhancements in the splittings due to resonances and chaos are best understood away from the fluctuations associated with avoided crossings. The essential differences between various mechanisms are investigated using perturbation theory. © 2003 American Institute of Physics.
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33.80.Be Level crossing and optical pumping
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
03.65.Xp Tunneling, traversal time, quantum Zeno dynamics
05.45.-a Nonlinear dynamics and chaos

The strongest bond in the universe? Accurate calculation of compliance matrices for the ions N2H+, HCO+, and HOC+

Jörg Grunenberg, Rainer Streubel, Gerd von Frantzius, and Wolfgang Marten

J. Chem. Phys. 119, 165 (2003); http://dx.doi.org/10.1063/1.1576756 (5 pages) | Cited 18 times

Online Publication Date: 18 June 2003

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Compliance matrices of protonated CO and N2 are calculated using coupled cluster methods and basis sets of quadruple zeta quality. Diagonal elements of the compliance matrices are used as unique bond strength descriptors. Going from CO (0.052 Å/mdyn) to CO–H+ the C–O bond is weakened (0.062 Å/mdyn), while the C–O bond in H–CO+ is getting stronger (0.045 Å/mdyn). After protonation, the N–N bond strength is getting stronger (from 0.043 to 0.042 Å/mdyn), too. The invariance of compliance matrix elements Cij under completion of (xi,xj) to a complete set (…,xi,…,xj,…) of internal coordinates is demonstrated. © 2003 American Institute of Physics.
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33.15.Fm Bond strengths, dissociation energies
31.15.bw Coupled-cluster theory
02.10.Yn Matrix theory

Millimeter-wave spectroscopy and coupled cluster calculations for a new phosphorus–carbon chain: HC5P

L. Bizzocchi, C. Degli Esposti, and P. Botschwina

J. Chem. Phys. 119, 170 (2003); http://dx.doi.org/10.1063/1.1576380 (6 pages) | Cited 7 times

Online Publication Date: 18 June 2003

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The linear, unstable HC5P molecule has been detected for the first time in the pyrolysis products of phosphorus trichloride and toluene mixtures. Its rotational spectrum has been investigated in the millimeter-wave region (78–195 GHz) for the ground and v11 = 1 excited state of both normal and deuterated species. Accurate values of rotational, centrifugal distortion and q11 l-type doubling constants have been obtained. The experimental work was assisted by coupled-cluster single double triple [CCSD(T)] calculations, which provided accurate predictions for the equilibrium structure and the dipole moment of this new carbon chain, phosphorus bearing molecule. © 2003 American Institute of Physics.
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33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Sn Rotational analysis
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.20.Bx Radio-frequency and microwave spectra
31.15.bw Coupled-cluster theory
31.15.A- Ab initio calculations
31.15.xr Self-consistent-field methods
33.70.Jg Line and band widths, shapes, and shifts

Photodissociation dynamics of ethyl ethynyl ether: A new ketenyl radical precursor

M. J. Krisch, J. L. Miller, L. J. Butler, H. Su, R. Bersohn, and J. Shu

J. Chem. Phys. 119, 176 (2003); http://dx.doi.org/10.1063/1.1577318 (11 pages) | Cited 4 times

Online Publication Date: 18 June 2003

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The work presented here investigates the dynamics of the photodissociation of ethyl ethynyl ether at 193.3 nm with photofragment translational spectroscopy and laser-induced fluorescence. The data from two crossed laser-molecular beam apparatuses, one with vacuum ultraviolet photoionization detection and one with electron bombardment detection, showed that only cleavage of the C–O bond to form a C2HO radical and a C2H5 (ethyl) radical occurs. We observed neither cleavage of the other C–O bond nor molecular elimination to form C2H4+CH2CO (ketene). The C2HO radical is formed in two distinct product channels, with 37% of the radicals formed from a channel with recoil kinetic energies extending from about 10 to 70 kcal/mole and the other 63% formed from a channel with lower average recoil energies ranging from 0 to 40 kcal/mole. The measurements using photoionization detection reveal that the C2HO radical formed in the higher recoil kinetic-energy channel has a larger ionization cross section for photon energies between 10.3 and 11.3 eV than the radical formed in the lower recoil kinetic-energy channel, and that the transition to the ion is more vertical. The radicals formed in the higher recoil kinetic-energy channel could be either math(2A″) or (2A′) state ketenyl (HCCO) product and the shape of the recoil kinetic-energy distribution fitting this data does not vary with ionization energy between 10.3 and 11.3 eV. The C2HO formed in the channel with the lower kinetic-energy release is likely the spin forbidden (4A″) state of the ketenyl radical, reached through intersystem crossing. The math state of ketenyl is energetically inaccessible. We also consider the possibility that the lower kinetic-energy channel forms two other C2HO isomers, the CCOH (hydroxyethynyl) radical or the cyclic oxiryl radical. Signal from laser-induced fluorescence of the HCCO photofragment was detected at the electronic origin and the 510 band. The fluorescence signal peaks after a 20 μs delay, indicating that HCCO is formed with a significant amount of internal energy and then subsequently relaxes to the lowest vibrational level of the ground electronic state. The data show that the photodissociation of ethyl ethynyl ether produces C2HO with unit quantum yield, establishing it as the first clean photolytic precursor of the ketenyl radical, a key species in combustion reactions. © 2003 American Institute of Physics.
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82.50.Hp Processes caused by visible and UV light
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.50.Dq Fluorescence and phosphorescence spectra

Structures, energetics, and spectra of electron–water clusters, e−–(H2O)2–6 and e−–HOD(D2O)1–5

Han Myoung Lee, Sik Lee, and Kwang S. Kim

J. Chem. Phys. 119, 187 (2003); http://dx.doi.org/10.1063/1.1576757 (8 pages) | Cited 55 times

Online Publication Date: 18 June 2003

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Although various low-lying energy structures of electron–water clusters, e−–(H2O)2–6, have been reported, some of the global minimum energy structures (in particular, for the tetramer and pentamer) are still not clearly characterized yet. Therefore, using high-level ab initio calculations, we have investigated several new low-lying energy conformers in addition to previously reported ones. The lowest energy conformer for the pentamer is found to have a wedge-like structure which has never been studied before. Based on the experimental vertical electron-detachment energies and OH vibrational spectra of the electron–water clusters, we report the most probable structures and their nearly isoenergetic structures. The OH vibrational frequencies of e−(H2O)2–6 and e−HOD(D2O)1–5 are investigated, and are found to be in excellent agreement with the available experimental data. Their O–H stretch frequency shifts are classified in terms of the types of water molecules. © 2003 American Institute of Physics.
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31.15.A- Ab initio calculations
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Ea Infrared spectra
33.80.Eh Autoionization, photoionization, and photodetachment
33.70.Jg Line and band widths, shapes, and shifts

Quantum mechanical investigation of the O+H2→OH+H reaction

N. Balakrishnan

J. Chem. Phys. 119, 195 (2003); http://dx.doi.org/10.1063/1.1576532 (5 pages) | Cited 15 times

Online Publication Date: 18 June 2003

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We report quantum mechanical calculations of cross sections and rate coefficients for the O+H2→OH+H reaction using the chemically accurate potential energy surfaces of 3A′ and 3A″ geometry by Rogers et al. [J. Phys. Chem. A 104, 2308 (2000)]. Calculations were performed for total angular momentum quantum number J = 0 and the J-shifting approximation was applied to obtain cumulative reaction probabilities, initial state selected reaction cross sections, and thermal rate coefficients. The reliability of the J-shifting approximation was tested by performing accurate calculations for selected values of nonzero J. We obtain thermal rate coefficients in good agreement with experimental data at temperatures lower than 500 K but our calculations predict rate coefficients that are smaller than the experimental values at higher temperatures. © 2003 American Institute of Physics.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Xr Quantum effects in rate constants (tunneling, resonances, etc.)
82.20.Kh Potential energy surfaces for chemical reactions

Reaction of formaldehyde cation with methane: Effects of collision energy and H2CO+ and methane vibrations

Jianbo Liu, Brian Van Devener, and Scott L. Anderson

J. Chem. Phys. 119, 200 (2003); http://dx.doi.org/10.1063/1.1577312 (15 pages) | Cited 11 times

Online Publication Date: 18 June 2003

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The effects on the title reaction of collision energy (Ecol), five H2CO+ vibrational modes, and deformation vibrations of methane have been studied, including the measurement of product integral and differential cross sections over a center-of-mass Ecol range from 0.09–3.3 eV. Electronic structure and RRKM calculations are reported, providing an additional mechanistic insight. The total reaction efficiency is well below unity, despite there being two exoergic reaction pathways with no activation barriers. The energetically more favorable channel corresponds to H elimination (HE) from an intermediate complex, however, this channel accounts for only ∼15% of the total reaction cross section at low Ecol and is negligible at high energies. The dominant channel, hydrogen abstraction (HA) by H2CO+ from methane, is dominated by a complex-mediated mechanism at low Ecol, switching over to a direct hydrogen-stripping mechanism at high Ecol. Both HA and HE are inhibited in a strongly mode-specific fashion by H2CO+ vibrational excitations, and greatly enhanced by excitation of methane deformation vibrations. The strong mode specificity indicates that the reaction-limiting step occurs early in the collisions. © 2003 American Institute of Physics.
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
33.15.Mt Rotation, vibration, and vibration-rotation constants

Vacuum ultraviolet mass-analyzed threshold ionization spectroscopy of benzene: Vibrational analysis of C6H6+ and C6D6+ in the math 2E1g state

Chan Ho Kwon, Hong Lae Kim, and Myung Soo Kim

J. Chem. Phys. 119, 215 (2003); http://dx.doi.org/10.1063/1.1577317 (9 pages) | Cited 9 times

Online Publication Date: 18 June 2003

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Vibrational spectra of C6H6+ and C6D6+ in the ground electronic state have been measured by one-photon mass-analyzed threshold ionization (MATI) spectroscopy using coherent vacuum ultraviolet radiation generated by four wave mixing in Kr gas. The ionization energies of C6H6 and C6D6 determined by one-photon MATI, 74551±5 and 74579±5 cm−1, respectively, are similar to those reported previously. Vibrational spectra are much simpler than the previous zero kinetic energy photoelectron and MATI spectra obtained by two-photon excitation. Almost complete vibrational assignments for the cations have been possible, which will be useful for future theoretical studies of the Jahn-Teller effect in these cations. Implication from the present one-photon spectra agrees with the previous suggestion that the geometry of benzene cation in the ground electronic state belongs to the D6h symmetry. © 2003 American Institute of Physics.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.20.Ni Vacuum ultraviolet spectra
33.20.Tp Vibrational analysis
33.60.+q Photoelectron spectra
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
33.15.Ta Mass spectra
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