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22 Dec 2003

Volume 119, Issue 24, pp. 12697-13179

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Relationship between long-range charge-transfer excitation energy error and integer discontinuity in Kohn–Sham theory

David J. Tozer

J. Chem. Phys. 119, 12697 (2003); http://dx.doi.org/10.1063/1.1633756 (3 pages) | Cited 147 times

Online Publication Date: 18 December 2003

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Charge-transfer (CT) electronic excitation energies are known to be very poorly predicted by time-dependent density functional theory (TDDFT) using local exchange-correlation functionals. Insight into this observation is provided by a simple analysis of intermolecular CT excitations at infinite separation. It is argued that the first TDDFT CT excitation energy approximately underestimates the experimental excitation by the average of the integer discontinuities of the donor and acceptor molecules; errors are of the order of several electron volts. © 2003 American Institute of Physics.
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34.70.+e Charge transfer
31.15.E- Density-functional theory
34.20.Gj Intermolecular and atom-molecule potentials and forces

Formation and photodepletion of cluster ion–messenger atom complexes in a cold ion trap: Infrared spectroscopy of VO+, VO2+, and VO3+

Mathias Brümmer, Cristina Kaposta, Gabriele Santambrogio, and Knut R. Asmis

J. Chem. Phys. 119, 12700 (2003); http://dx.doi.org/10.1063/1.1634254 (4 pages) | Cited 23 times

Online Publication Date: 18 December 2003

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A novel experimental technique is described in which radiation from a free electron laser is used to measure infrared spectra of gas-phase cluster ions via vibrational predissociation of the corresponding ion–messenger atom complexes. The weakly bound complexes are formed in a temperature-controllable, radio frequency ion trap. This technique is applied to the study of the vibrational spectroscopy of the monovanadium oxide cluster cations VO+, VO2+, and VO3+. © 2003 American Institute of Physics.
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36.40.Cg Electronic and magnetic properties of clusters
82.30.Nr Association, addition, insertion, cluster formation
33.20.Ea Infrared spectra
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.15.Mt Rotation, vibration, and vibration-rotation constants
37.20.+j Atomic and molecular beam sources and techniques

An interaction energy decomposition approach for the supermolecule density functional theory calculations

Sławomir M. Cybulski and Christopher E. Seversen

J. Chem. Phys. 119, 12704 (2003); http://dx.doi.org/10.1063/1.1635351 (4 pages) | Cited 7 times

Online Publication Date: 18 December 2003

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A method is proposed for partitioning the supermolecule interaction energy obtained from density functional theory calculations. Exploratory calculations for Ar2 reveal serious shortcomings of several commonly used correlation functionals. There are also problems with exchange functionals resulting in unphysical behavior at long range. These findings clearly demonstrate the limitations of some commonly used functionals. © 2003 American Institute of Physics.
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31.15.E- Density-functional theory
31.15.A- Ab initio calculations
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back to top Theoretical Methods and Algorithms

A super-linear minimization scheme for the nudged elastic band method

Jhih-Wei Chu, Bernhardt L. Trout, and Bernard R. Brooks

J. Chem. Phys. 119, 12708 (2003); http://dx.doi.org/10.1063/1.1627754 (10 pages) | Cited 44 times

Online Publication Date: 18 December 2003

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In this article, we present a superlinear minimization scheme for the nudged elastic band (NEB) method, which determines a minimum-energy path (MEP) of a reaction via connecting intermediate “replicas” between the reactant and the product. The minimization scheme is based on a quasi-Newton method: the adopted basis Newton–Raphson (ABNR) minimization scheme. In each step of ABNR minimization, the Newton–Raphson procedure is performed in a subspace of a user-defined dimension. The tangent directions of the path at a new Newton–Raphson step are determined self-consistently in the subspace. The acceleration of the proposed scheme over the quenched molecular-dynamic minimization, the current practice for minimizing a path using NEB, is demonstrated in three nontrivial test cases: isomerization of an alanine dipeptide, α-helix to π-helix transition of an alanine decapeptide, and oxidation of dimethyl sulfide. New features are also added such that the distances between replicas can be defined in the root of mean squared (RMS) best-fit space with flexible weighting options. This offers a way to incorporate the effects of a mobile solvent in the process with a finite number of replicas. MEPs obtained from various initial structures can be used to investigate different proposed reaction mechanisms, and the speedup of minimizing a path enhances the applicability of the NEB method. The combination of NEB force projection procedures, the flexible distance definition in the RMS best fit space with arbitrary weighting options, and the superlinear minimization scheme provides a framework to aid in the study of transition processes of biological molecules as such proteins. © 2003 American Institute of Physics.
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87.14.E- Proteins
87.15.-v Biomolecules: structure and physical properties

Equilibration of long chain polymer melts in computer simulations

Rolf Auhl, Ralf Everaers, Gary S. Grest, Kurt Kremer, and Steven J. Plimpton

J. Chem. Phys. 119, 12718 (2003); http://dx.doi.org/10.1063/1.1628670 (11 pages) | Cited 91 times

Online Publication Date: 18 December 2003

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Several methods for preparing well equilibrated melts of long chains polymers are studied. We show that the standard method in which one starts with an ensemble of chains with the correct end-to-end distance arranged randomly in the simulation cell and introduces the excluded volume rapidly, leads to deformation on short length scales. This deformation is strongest for long chains and relaxes only after the chains have moved their own size. Two methods are shown to overcome this local deformation of the chains. One method is to first pre-pack the Gaussian chains, which reduces the density fluctuations in the system, followed by a gradual introduction of the excluded volume. The second method is a double-bridging algorithm in which new bonds are formed across a pair of chains, creating two new chains each substantially different from the original. We demonstrate the effectiveness of these methods for a linear bead spring polymer model with both zero and nonzero bending stiffness, however the methods are applicable to more complex architectures such as branched and star polymer. © 2003 American Institute of Physics.
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61.25.H- Macromolecular and polymers solutions; polymer melts
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

Fast, scalable master equation solution algorithms. III. Direct time propagation accelerated by a diffusion approximation preconditioned iterative solver

Terry J. Frankcombe and Sean C. Smith

J. Chem. Phys. 119, 12729 (2003); http://dx.doi.org/10.1063/1.1628213 (12 pages) | Cited 1 time

Online Publication Date: 18 December 2003

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In this paper we propose a novel fast and linearly scalable method for solving master equations arising in the context of gas-phase reactive systems, based on an existent stiff ordinary differential equation integrator. The required solution of a linear system involving the Jacobian matrix is achieved using the GMRES iteration preconditioned using the diffusion approximation to the master equation. In this way we avoid the cubic scaling of traditional master equation solution methods and maintain the low temperature robustness of numerical integration. The method is tested using a master equation modelling the formation of propargyl from the reaction of singlet methylene with acetylene, proceeding through long lived isomerizing intermediates. © 2003 American Institute of Physics.
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05.60.-k Transport processes
02.30.-f Function theory, analysis
82.20.-w Chemical kinetics and dynamics
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

Fast, scalable master equation solution algorithms. IV. Lanczos iteration with diffusion approximation preconditioned iterative inversion

Terry J. Frankcombe and Sean C. Smith

J. Chem. Phys. 119, 12741 (2003); http://dx.doi.org/10.1063/1.1628214 (8 pages) | Cited 4 times

Online Publication Date: 18 December 2003

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In this paper we propose a second linearly scalable method for solving large master equations arising in the context of gas-phase reactive systems. The new method is based on the well-known shift-invert Lanczos iteration using the GMRES iteration preconditioned using the diffusion approximation to the master equation to provide the inverse of the master equation matrix. In this way we avoid the cubic scaling of traditional master equation solution methods while maintaining the speed of a partial spectral decomposition. The method is tested using a master equation modeling the formation of propargyl from the reaction of singlet methylene with acetylene, proceeding through long-lived isomerizing intermediates. © 2003 American Institute of Physics.
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82.40.-g Chemical kinetics and reactions: special regimes and techniques
82.30.Qt Isomerization and rearrangement

Transition path sampling with a one-point boundary scheme

L. Y. Chen and Patrick L. Nash

J. Chem. Phys. 119, 12749 (2003); http://dx.doi.org/10.1063/1.1628219 (4 pages) | Cited 6 times

Online Publication Date: 18 December 2003

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Studying the motion of Lennard-Jones clusters in an external potential having a very narrow channel passage at the saddle point, we present a one-point boundary scheme to numerically sample transition (reaction) paths. This scheme does not require knowledge of the transition states (saddle points) or that of the final states. A transition path within a given time interval (0,tf) consists of an activation path during (0,tM) and a deactivation path during (tM,tf) (0<tM<tf) joined at an intermediate time tM. The activation path is a solution to a Langevin equation with negative friction, while the deactivation path is that to a regular Langevin equation with positive friction. Each transition path so generated carries a determined statistical weight. Typical transition paths are found for two-particle and three-particle clusters. A two-particle cluster adjusts its orientation to the direction of the narrow channel and then slides through it. A three-particle cluster completes a transition by openning one of its three bonds, becoming linear, and sliding through the channel. © 2003 American Institute of Physics.
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36.40.Jn Reactivity of clusters
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
82.30.Nr Association, addition, insertion, cluster formation

Gaussian basis sets of quadruple zeta valence quality for atoms H–Kr

Florian Weigend, Filipp Furche, and Reinhart Ahlrichs

J. Chem. Phys. 119, 12753 (2003); http://dx.doi.org/10.1063/1.1627293 (10 pages) | Cited 200 times

Online Publication Date: 18 December 2003

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We present Gaussian basis sets of quadruple zeta valence quality with a segmented contraction scheme for atoms H to Kr. This extends earlier work on segmented contracted split valence (SV) and triple zeta valence (TZV) basis sets. Contraction coefficients and orbital exponents are fully optimized in atomic Hartree–Fock (HF) calculations. As opposed to other quadruple zeta basis sets, the basis set errors in atomic ground-state HF energies are less than 1 mEh and increase smoothly across the Periodic Table, while the number of primitives is comparably small. Polarization functions are taken partly from previous work, partly optimized in atomic MP2 calculations, and for a few cases determined at the HF level for excited atomic states nearly degenerate with the ground state. This leads to basis sets denoted QZVP for HF and density functional theory (DFT) calculations, and for some atoms to a larger basis recommended for correlated treatments, QZVPP. We assess the performance of the basis sets in molecular HF, DFT, and MP2 calculations for a sample of diatomic and small polyatomic molecules by a comparison of energies, bond lengths, and dipole moments with results obtained numerically or using very large basis sets. It is shown that basis sets of quadruple zeta quality are necessary to achieve an accuracy of 1 kcal/mol per bond in HF and DFT atomization energies. For compounds containing third row as well as alkaline and earth alkaline metals it is demonstrated that the inclusion of high-lying core orbitals in the active space can be necessary for accurate correlated treatments. The QZVPP basis sets provide sufficient flexibility to polarize the core in those cases. All test calculations indicate that the new basis sets lead to consistent accuracies in HF, DFT, or correlated treatments even in critical cases where other basis sets may show deficiencies. © 2003 American Institute of Physics.
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31.15.xr Self-consistent-field methods
31.15.E- Density-functional theory
33.15.Dj Interatomic distances and angles
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

The effect of grid quality and weight derivatives in density functional calculations of harmonic vibrational frequencies

Massimo Malagoli and Jon Baker

J. Chem. Phys. 119, 12763 (2003); http://dx.doi.org/10.1063/1.1627291 (6 pages) | Cited 5 times

Online Publication Date: 18 December 2003

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We investigate the accuracy of harmonic vibrational frequencies computed with and without the inclusion of quadrature weight derivatives in our recently completed initial implementation of density functional theory (DFT) analytical second derivatives. Unlike the situation with analytical DFT gradients, second derivatives are much more sensitive to the inclusion of weight derivatives, and omitting them can produce nonsensical results unless the numerical grid is of sufficiently high quality. Results are presented for the homonuclear diatomics F2, Cl2, Br2, and I2 and for a number of larger molecules. Errors introduced by excluding weight derivatives increase with increasing atomic number and increasing basis set size. The origin of the error is the difficulty of accurately integrating high-order derivatives of basis functions with large exponents around their own atomic center, and it is not the weight derivatives themselves that eliminate this error but the fact that proper allowance for atom-centered grids that “move” with the atom means that basis functions no longer directly contribute to derivative quantities evaluated on their own grid. © 2003 American Institute of Physics.
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31.15.E- Density-functional theory
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis

Grand canonical molecular dynamics

Sharada Boinepalli and Phil Attard

J. Chem. Phys. 119, 12769 (2003); http://dx.doi.org/10.1063/1.1629079 (7 pages) | Cited 13 times

Online Publication Date: 18 December 2003

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A hybrid molecular dynamics-Monte Carlo grand canonical simulation technique is developed for systems with constant chemical potential and temperature. The method ensures that the particle number and energy fluctuate according to the standard grand canonical probability distribution. Partial coupling and fractional particles are used to enhance the success of insertion and deletion attempts, and the method is shown to be feasible in dense liquids. The method is applied to a Lennard-Jones fluid and it gives the density as a function of chemical potential in agreement with known results. It is demonstrated that the transport coefficients can be obtained with the method by analyzing the influence of the stochastic perturbation on the diffusion constant for an isothermal system. © 2003 American Institute of Physics.
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61.43.Bn Structural modeling: serial-addition models, computer simulation
02.70.Ns Molecular dynamics and particle methods
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
02.70.Uu Applications of Monte Carlo methods
02.50.Ng Distribution theory and Monte Carlo studies

Nonadiabatic reaction rates for dissipative quantum-classical systems

Alessandro Sergi and Raymond Kapral

J. Chem. Phys. 119, 12776 (2003); http://dx.doi.org/10.1063/1.1627752 (8 pages) | Cited 14 times

Online Publication Date: 18 December 2003

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The dynamics of a quantum system which is directly coupled to classical degrees of freedom is investigated. The classical degrees of freedom are in turn coupled to a classical bath whose detailed dynamics is not of interest. The resulting quantum-classical evolution equations are dissipative as a result of coupling to the classical heat bath. The dissipative quantum-classical dynamics is used to study nonadiabatic chemical reactions and compute their rates. The reactive flux correlation formalism for the calculation of nonadiabatic rate constants is generalized to dissipative quantum-classical dynamics and implemented in terms of averages over surface-hopping Langevin trajectory segments. The results are illustrated for a simple quantum-classical two-state model. The techniques developed in this paper can be applied to complex classical environments encountered, for example, in proton and electron transfer processes in the condensed phase where local environmental degrees of freedom must be treated explicitly but the remainder of the environment can be treated simply as a heat bath. © 2003 American Institute of Physics.
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82.20.-w Chemical kinetics and dynamics
82.30.-b Specific chemical reactions; reaction mechanisms

Stiffness in stochastic chemically reacting systems: The implicit tau-leaping method

Muruhan Rathinam, Linda R. Petzold, Yang Cao, and Daniel T. Gillespie

J. Chem. Phys. 119, 12784 (2003); http://dx.doi.org/10.1063/1.1627296 (11 pages) | Cited 69 times

Online Publication Date: 18 December 2003

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We show how stiffness manifests itself in the simulation of chemical reactions at both the continuous-deterministic level and the discrete-stochastic level. Existing discrete stochastic simulation methods, such as the stochastic simulation algorithm and the (explicit) tau-leaping method, are both exceedingly slow for such systems. We propose an implicit tau-leaping method that can take much larger time steps for many of these problems. © 2003 American Institute of Physics.
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82.20.Uv Stochastic theories of rate constants
82.20.Wt Computational modeling; simulation
82.30.-b Specific chemical reactions; reaction mechanisms
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Absorption, resonance, the preresonance Raman study of the 1,3-dicyanomethylene croconate dianion using complete active space self-consistent field and density functional theory methods

M. Makowski and M. T. Pawlikowski

J. Chem. Phys. 119, 12795 (2003); http://dx.doi.org/10.1063/1.1626544 (10 pages) | Cited 6 times

Online Publication Date: 18 December 2003

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The electronic structures of the 11B2 and 21A1 excited electronic states of the 1,3-dicyanomethylene croconate dianion are studied in the framework of complete active space self-consistent field (CASSCF) and Becke’s three-parameter hybrid method with a Lee–Yang–Parr correlation functional methods applied on the level aug-cc-pVDZ basis set. The CASSCF/aug-cc-pVDZ treatment provides the ground (11A1) and the excited 11B2 and 21A1 states geometries, which are then used to evaluate the Franck–Condon parameters in the 11B2 and 21A1 states. The quality of the numerical results is verified on the bases of experimental near-resonance and resonance Raman data available in the vis-UV excitation region. The analysis is done in terms of the vibronic model, which treats the totally symmetric vibrations as displaced harmonic oscillators. Under the resonance with the 11A1→11B2 electronic transition, that somewhat simplified vibronic model leads to excellent agreement between the theoretical and empirical excitation profiles for the ν2 = 2234 cm−1, ν9 = 911 cm−1, ν13 = 376 cm−1, and ν14 = 318 cm−1 fundamentals. At preresonance with the 11A1→11B2 electronic excitation the agreement with the experimental Raman spectrum is reasonable but some discrepancies are noticed for the ν4 = 1620 cm−1 and ν5 = 1546 cm−1 fundamental lines. We argue that the observed discrepancies can be removed when mode-mixing (Duszynski) effects between ν4 and ν5 vibrations in the 11B2 state are taken into account. © 2003 American Institute of Physics.
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31.15.xr Self-consistent-field methods
33.20.Lg Ultraviolet spectra
33.20.Kf Visible spectra
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
31.15.E- Density-functional theory
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Influence of electronic transitions on the collision-induced multifragmentation dynamics of Na4+ cluster ions

Muriel Sizun, François Aguillon, and Victor Sidis

J. Chem. Phys. 119, 12805 (2003); http://dx.doi.org/10.1063/1.1628211 (14 pages) | Cited 2 times

Online Publication Date: 18 December 2003

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The collision-induced multifragmentation of Na4+ alkali metal cluster ions by He impact in the 100 eV (center of mass) collision energy range is investigated theoretically using a DIM-based nonadiabatic molecular dynamics method. Compared to our earlier adiabatic molecular dynamics calculations new fragmentation channels are populated and new relaxation processes of excited electronic states to the ground state take place. The mechanisms of the different processes are analyzed. Comparisons with experiments are presented and discussed. © 2003 American Institute of Physics.
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34.50.-s Scattering of atoms and molecules
02.70.Ns Molecular dynamics and particle methods
31.15.xv Molecular dynamics and other numerical methods

The kinetic energy dependence of association reactions. A new thermokinetic method for large systems

Hideya Koizumi and P. B. Armentrout

J. Chem. Phys. 119, 12819 (2003); http://dx.doi.org/10.1063/1.1627758 (11 pages) | Cited 10 times

Online Publication Date: 18 December 2003

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The reactions of bare alkali metal ions (M+ = Li+, Na+, or K+) with dimethoxyethane (CH3OCH2CH2OCH3, DXE) are studied using guided ion beam tandem mass spectrometry. The bimolecular reaction forms an associative M+(DXE) complex that is long-lived and dissociates back to the reactants. The kinetic energy dependences of the cross sections for formation of the complexes are interpreted with several different models (including rigorous phase space theory) that assume that the complex lifetimes are limited by dissociation over a loose, orbiting transition state. After accounting for the effects of multiple ion–molecule collisions, internal energy of the reactant ions, Doppler broadening, and dissociation lifetimes, the analyses yield 0 K bond energies as the only adjustable parameter. These values are compared with bond energies obtained from previous collision-induced dissociation (CID) studies of the M+(DXE) complexes and found to be self-consistent for all models studied. Association and CID form the same energized M+(DXE) complex in two distinct ways, such that a comparison of these results allows an assessment of the models used to interpret CID thresholds and test the limits of statistical theories such as RRKM and phase space theory. © 2003 American Institute of Physics.
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82.30.Nr Association, addition, insertion, cluster formation
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
33.15.Ta Mass spectra
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Characterization of the three lowest-lying singlet electronic states of AlOH

Se Li, Kurt W. Sattelmeyer, Yukio Yamaguchi, and Henry F. Schaefer

J. Chem. Phys. 119, 12830 (2003); http://dx.doi.org/10.1063/1.1627294 (12 pages) | Cited 4 times

Online Publication Date: 18 December 2003

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Two linear (1Σ+ and 1Π) and three bent (1 1A′, 2 1A′, and 1 1A″) lowest-lying electronic singlet states of AlOH have been systematically investigated employing ab initio self-consistent-field, configuration interaction with single and double excitations, coupled cluster with single and double excitations (CCSD), CCSD with perturbative triple excitations [CCSD(T)], and CCSD with iterative partial triple excitations (CCSDT-3 and CC3) quantum mechanical methods with basis sets up to augmented correlation consistent polarized valence quadruple zeta (aug-cc-pVQZ). The linear 1Σ+ state is found to be a remarkably low-energy transition state between the two equivalent bent 1 1A′ structures, while the linear 1Π state is a second-order saddle point, which leads to the bent 2 1A′ and 1 1A″ states. The bent ground (math 1A′) state of AlOH is predicted to have a bond angle of 157° at the aug-cc-pVQZ CC3 level of theory and is classified as a quasilinear molecule, confirming previous studies. Employing the equation-of-motion coupled cluster method, the first singlet excited state ( 1A′) is predicted to have a bond angle of 110° and to lie 114 kcal/mol (39 900 cm−1, 4.94 eV) above the ground state, whereas the second singlet excited state (math 1A″) is predicted to have a bond angle of 116° and to be located 119 kcal/mol (41 700 cm−1, 5.17 eV) above the ground state. These theoretical energy separations are in excellent agreement with the experimental values T0 ( 1A′) = 114.57 kcal/mol (40 073 cm−1, 4.968 eV) and T0 (math 1A″) = 119.36 kcal/mol (41 747 cm−1, 5.176 eV). The barriers to linearity for the two bent singlet excited states are determined to be 11.6 kcal/mol for the  1A′ state and 6.2 kcal/mol for the math 1A″ state. © 2003 American Institute of Physics.
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31.15.A- Ab initio calculations
31.15.xr Self-consistent-field methods
31.15.vn Electron correlation calculations for diatomic molecules
31.15.bw Coupled-cluster theory

Propyne and allene photolysis at 193.3 nm and at 121.6 nm

Rafay H. Qadiri, Emma J. Feltham, N. Hendrik Nahler, Rodrigo Pérez García, and Michael N. R. Ashfold

J. Chem. Phys. 119, 12842 (2003); http://dx.doi.org/10.1063/1.1627761 (10 pages) | Cited 21 times

Online Publication Date: 18 December 2003

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The fragmentation dynamics of allene and propyne molecules following photoexcitation at 193.3 nm and at 121.6 nm have been investigated by H(D) Rydberg atom photofragment translational spectroscopy. The total kinetic energy release (TKER) spectra of the H (and D) atoms resulting from H2CCCH2, H3CCCH, and D3CCCH photolysis at 193.3 nm are found to be essentially identical. The results contradict conclusions reached in several previous studies of propyne photochemistry at this wavelength. The observed energy disposal, and the isomer independence, are most readily rationalized by assuming that the fragmentation of both molecules following excitation at 193.3 nm is preceded by internal conversion to the ground (S0) state potential energy surface, and that the isomerization rate of the resulting highly vibrationally excited S0 molecules is faster than their unimolecular decay rate. The time-of-flight (TOF) and TKER spectra of the H and D atoms resulting from 121.6 nm photolysis of allene, propyne and propyne-d3 show significant differences, however. The differences can be reconciled by assuming two competing pathways for forming H(D) atoms following photoexcitation of propyne. One, involving selective cleavage of the acetylenic H3CCC–H bond, is assumed to occur from the excited electronic state prepared by photon absorption or from a recognizably “propynelike” state to which it couples efficiently. The other, which yields a slower distribution of H(D) atoms, is considered to arise via radiationless transfer to a lower electronic state, isomerization, and subsequent unimolecular decay. The TOF and TKER spectra of the H atoms resulting from 121.6 nm photolysis of allene are indistinguishable from those associated with this second, “statistical” fragmentation channel in propyne. © 2003 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
82.50.Bc Processes caused by infrared radiation
82.37.Vb Single molecule photochemistry
82.30.Qt Isomerization and rearrangement
82.20.Kh Potential energy surfaces for chemical reactions

Rational classification of a series of aromatic donor–acceptor systems within the twisting intramolecular charge transfer model, a time-dependent density-functional theory investigation

Christine Jödicke Jamorski and Hans-Peter Lüthi

J. Chem. Phys. 119, 12852 (2003); http://dx.doi.org/10.1063/1.1627292 (14 pages) | Cited 13 times

Online Publication Date: 18 December 2003

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The goal of this paper is to rationalize the fluorescence activity, experimentally observed for 21 molecules of the same family as the 4-(N,N-dimethyl)anilines, based on their potential energy surfaces calculated within the twisting intramolecular charge transfer model. A classification in four groups is proposed according to the sign of two parameters, ΔEgap, characterizing the energy difference between the vertical locally and charge transfer excited states, and ΔE1S (or Δmath1S for pretwisted systems), representing the energy gain of the charge transfer excited state with a perpendicular conformation compared to the first vertical excited state. In this study, the time-dependent density-functional theory has been used to calculate the potential energy surfaces of the ground and excited states along the twisting angle. Computed excitation energies and optimized ground state geometries have been obtained with both B3LYP and MPW1PW91 functionals using a 6-311+G(2d,p), and a 6-31G(d) basis set, respectively. From this study, it follows that ΔEgap and ΔE1S are the main parameters necessary to understand the fluorescence activity of these molecules. The fact that the same fluorescence activity is observed for the members of each group (or subcategory for the particular case of group II), reveals the underlying twisting mechanism as a common process for all the investigated molecules, which explains their experimental dual and nondual emission. © 2003 American Institute of Physics.
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33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
34.70.+e Charge transfer
33.50.Dq Fluorescence and phosphorescence spectra

Theoretical study of the electronic states of niobium trimer (Nb3) and its anion (Nb3−)

D. Majumdar and K. Balasubramanian

J. Chem. Phys. 119, 12866 (2003); http://dx.doi.org/10.1063/1.1626594 (12 pages) | Cited 8 times

Online Publication Date: 18 December 2003

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Geometries and energy separations of the various low-lying electronic states of niobium trimer (Nb3) and its anion (Nb3−) with triangular and linear structural arrangements have been investigated. The complete active space multiconfiguration self-consistent field method followed by multireference singles plus doubles configuration interaction (MRSDCI) that included up to 48 million configuration spin functions have been used to compute several electronic states of these clusters. The geometries of ground and excited states of Nb3 and Nb3− are triangular. The ground states of both Nb3 (2B1) and Nb3− (1A1) have been found to be of low spin. The low-lying electronic states with degenerate symmetries in the D3h group are distorted to the C2v structure (from the ideal D3h) due to the Jahn–Teller effect. On the basis of the energy separations of our computed electronic states of Nb3, we have assigned the observed photoelectron spectrum of Nb3−. We have also compared our MRSDCI results with density functional calculations. The electron affinity, ionization potential, dissociation and atomization energies of Nb3 have been calculated and the results have been found to be in excellent agreement with the experiment. © 2003 American Institute of Physics.
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36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Cg Electronic and magnetic properties of clusters
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.xr Self-consistent-field methods
31.15.vq Electron correlation calculations for polyatomic molecules

Theoretical calculation of vibronic levels of C2H and C2D to 10 000 cm−1

Riccardo Tarroni and Stuart Carter

J. Chem. Phys. 119, 12878 (2003); http://dx.doi.org/10.1063/1.1627755 (12 pages) | Cited 22 times

Online Publication Date: 18 December 2003

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The rovibronic levels for the X 2Σ+,A 2Π electronic system of C2H, C2D and all 13C substituted isotopomers are calculated using a recently developed variational method [Carter et al., Mol. Phys. 98, 1967 (2000)] and high level ab initio diabatic potential energy surfaces. Energies, rotational constants and spin–orbit splittings of all levels of Σ, Π, Δ, Φ symmetry are reported up to 6400 cm−1 for C2H and up to 5500 cm−1 for C2D. Computed energies of Σ, Π levels up to 10 000 cm−1 are also reported for all 13C substituted isotopomers. Experimental data are reviewed in the light of the present results. © 2003 American Institute of Physics.
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33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Dipole-bound negative ions: Collisional destruction and blackbody-radiation-induced photodetachment

L. Suess, Y. Liu, R. Parthasarathy, and F. B. Dunning

J. Chem. Phys. 119, 12890 (2003); http://dx.doi.org/10.1063/1.1628215 (5 pages) | Cited 8 times

Online Publication Date: 18 December 2003

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The lifetimes and collisional destruction of dipole-bound negative ions formed by electron transfer in collisions between K(np) Rydberg atoms and acetonitrile, deuterated acetonitrile, acrylonitrile, dimethylsulfoxide, and pyridazine are studied using a Penning ion trap. The data show that the rate constants for destruction of these ions by rotational energy transfer in collisions with residual target gas present in the trap are large, ∼ 10−7 cm3 s−1, consistent with the behavior to be expected for weakly bound species. Ion decay in the trap is characterized by a single exponential. When corrected for collision-induced destruction, the observed decay rates correspond to ion lifetimes that lie in the range ∼60 to 100 μs. These relatively short lifetimes are attributed to photodetachment induced by background thermal blackbody radiation. © 2003 American Institute of Physics.
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32.80.Gc Photodetachment of atomic negative ions
33.80.Eh Autoionization, photoionization, and photodetachment
44.40.+a Thermal radiation

A rigorous test of the statistical model for atom–diatom insertion reactions

Edward J. Rackham, Tomas Gonzalez-Lezana, and David E. Manolopoulos

J. Chem. Phys. 119, 12895 (2003); http://dx.doi.org/10.1063/1.1628218 (13 pages) | Cited 43 times

Online Publication Date: 18 December 2003

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The statistical model of atom–diatom insertion reactions is combined with coupled-channel capture theory and used to calculate differential cross sections for the reactions of C(1D), N(2D), O(1D) and S(1D) with H2. In the case of C(1D) and S(1D), the resulting statistical differential cross sections are found to be in excellent agreement with the recent quantum reactive scattering calculations of Honvault and Launay. They are therefore also in good agreement with molecular beam experiments for the S(1D)+H2 reaction, in contrast to the results of earlier calculations based on a less rigorous statistical theory. However, because the exact quantum mechanical differential cross sections for N(2D) and O(1D) exhibit a slight forward–backward asymmetry, the agreement with the statistical model for these reactions is not quite so good. The difference between the two cases can be rationalized in terms of the greater exoergicities of the N(2D) and O(1D) reactions, which lead to broader resonances and hence to shorter lifetimes of the H2O and NH2 collision complexes than those of CH2 and H2S. © 2003 American Institute of Physics.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Nr Association, addition, insertion, cluster formation

The effect of conformation on the ionization energetics of n-butylbenzene. I. A threshold ionization study

Xin Tong, Mark S. Ford, Caroline E. H. Dessent, and Klaus Müller-Dethlefs

J. Chem. Phys. 119, 12908 (2003); http://dx.doi.org/10.1063/1.1626622 (6 pages) | Cited 7 times

Online Publication Date: 18 December 2003

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Conformational isomers of the aromatic hydrocarbon n-butylbenzene have been studied using two-color REMPI (resonance enhanced multiphoton ionization) and MATI (mass analyzed threshold ionization) spectroscopy to explore the effect of conformation on ionization dynamics. Gauche- and anti-cationic conformers were selectively produced by two-color excitation via the respective S1 origins. Adiabatic ionization potentials of the gauche- and anti-conformations were determined to be 70 148 and 69 955±5 cm−1, respectively. Analysis of the REMPI and MATI spectra allowed the determination of the S0 (38 cm−1), S1 (100 cm−1), and D0 (−155 cm−1) gauche- and anti-conformer energy differences. Spectral features and vibrational modes are interpreted with the aid of MP2/cc-pVDZ ab initio calculations, and ionization-induced changes in the molecular conformations discussed. © 2003 American Institute of Physics.
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34.50.Gb Electronic excitation and ionization of molecules
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.A- Ab initio calculations
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

The effect of conformation on the ionization energetics of n-butylbenzene. II. A zero electron kinetic energy photoelectron spectroscopy study with partial rotational resolution

Mark S. Ford, Xin Tong, Caroline E. H. Dessent, and Klaus Müller-Dethlefs

J. Chem. Phys. 119, 12914 (2003); http://dx.doi.org/10.1063/1.1626623 (7 pages) | Cited 12 times

Online Publication Date: 18 December 2003

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Rotationally resolved zero electron kinetic energy (ZEKE) spectra of n-butylbenzene have been investigated using a spectator orbital model to compare the ionization energetics of two molecular conformers. A new ZEKE electron detection scheme was employed to record ZEKE excitation spectra as a function of the S1←S0 excitation laser photon energy, with fixed photon energy of the ionization laser. These ZEKE excitation spectra are a sensitive probe of the rotational constants of all three states involved, the S0 and S1 of the neutral and the D0 of the cation. For gauche-conformer I, the rotational constants of the cation have been determined as A+ = 2330.6±2.3 MHz, B+ = 772.4±1.5 MHz, and C+ = 741.61±0.72 MHz. The rotational constants for the anti-conformer, V, were determined as A+ = 3410.4±3.3 MHz, B+ = 577.7±1.9 MHz, and C+ = 524.79±0.50 MHz. This is the first time that the geometric structures of two cationic conformers have been identified using a rotational analysis. The inertial defects derived from the rotational constants provide detailed information relating to the geometric changes experienced by the conformers upon S1←S0 excitation and D0←S1 ionization. Despite the relatively small difference in geometry between the two conformers, they are observed to display dramatically different ionization cross sections. The differences in ionization dynamics of the conformers are interpreted in terms of conformationally dependent electronic structure changes, with reference to excess charge delocalization from the aromatic ring to the side chain in the cations, resulting in higher angular momentum contributions in the spectator orbital of conformer V compared to conformer I. These higher spectator electron orbital angular momentum components result in a reduced ionization cross section for conformer V compared to conformer I. © 2003 American Institute of Physics.
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34.50.Gb Electronic excitation and ionization of molecules
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.60.+q Photoelectron spectra
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