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15 Jan 2003

Volume 118, Issue 3, pp. 999-1574

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Time-resolved photoelectron imaging of the photodissociation of I2−

Alison V. Davis, Roland Wester, Arthur E. Bragg, and Daniel M. Neumark

J. Chem. Phys. 118, 999 (2003); http://dx.doi.org/10.1063/1.1536617 (4 pages) | Cited 45 times

Online Publication Date: 6 January 2003

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Time-resolved photoelectron imaging is presented as a new method for the study of anion dynamics. Time-dependent photoelectron energy spectra and angular distributions are extracted from images taken during the dissociation of I2− at 793 nm, and used to follow in detail the dissociation dynamics from 0–1 ps. © 2003 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
33.80.Eh Autoionization, photoionization, and photodetachment
33.60.+q Photoelectron spectra
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment

Oxygen adsorption on graphite and nanotubes

P. Giannozzi, R. Car, and G. Scoles

J. Chem. Phys. 118, 1003 (2003); http://dx.doi.org/10.1063/1.1536636 (4 pages) | Cited 86 times

Online Publication Date: 6 January 2003

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We study the binding of molecular oxygen to a graphene sheet and to a (8,0) single walled carbon nanotube, by means of spin-unrestricted density-functional calculations. We find that triplet oxygen retains its spin-polarized state when interacting with graphene or the nanotube. This leads to the formation of a weak bond with essentially no charge transfer between the molecule and the sheet or tube, as one would expect for a physisorptive bond. This result is independent on the approximation used for the exchange-correlation functional. The binding strength, however, depends strongly on the functional, reflecting the inability of current approximation functionals to deal correctly with dispersion forces. Gradient-corrected functionals yield very weak binding at distances around 4 Å, whereas local density functional results yield substantially stronger binding for both graphene and the nanotube at distances of less than 3 Å. The picture of oxygen physisorption is not substantially altered by the presence of topological defects such as 5–7 Stone–Wales pairs. © 2003 American Institute of Physics.
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68.43.Bc Ab initio calculations of adsorbate structure and reactions
68.43.Mn Adsorption kinetics
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.20.Hb Impurity and defect levels; energy states of adsorbed species
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back to top Theoretical Methods and Algorithms

A Lorentzian function based spectral filter for calculating the energy of excited bound states in quantum mechanics

Amrendra Vijay

J. Chem. Phys. 118, 1007 (2003); http://dx.doi.org/10.1063/1.1528895 (8 pages)

Online Publication Date: 6 January 2003

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In this paper, we study a Lorentzian function based spectral filter suitable for computing highly excited bound states of a quantum system. Using this filter, we have derived an expression for spectral intensities and also implemented a filter diagonalization scheme. We have used a Chebyshev polynomial based series expansion of the filter operator, and this allows us to accomplish a partial resummation of the double series analytically when computing the necessary matrix elements; this saves considerable computational effort. The exponential damping term in the Lorentzian provides a convenient control over the resolution of the computed spectrum in the spectral intensity plot. As a numerical test, we have computed eigenvalues and spectral intensities of a model Hamiltonian in an arbitrary energy window. For situations where eigenvalues are distributed nonuniformly we suggest a computational protocol, which judiciously combines the spectral intensity information with the filter diagonalization method. This protocol is efficient only with the Lorentzian filter studied here. © 2003 American Institute of Physics.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
42.50.-p Quantum optics

Quasirelativistic theory for the magnetic shielding constant. I. Formulation of Douglas–Kroll–Hess transformation for the magnetic field and its application to atomic systems

Ryoichi Fukuda, Masahiko Hada, and Hiroshi Nakatsuji

J. Chem. Phys. 118, 1015 (2003); http://dx.doi.org/10.1063/1.1528933 (12 pages) | Cited 56 times

Online Publication Date: 6 January 2003

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A two-component quasirelativistic theory based on the Douglas–Kroll–Hess (DKH) transformation has been developed to study magnetic properties of molecules. The proposed Hamiltonian includes the relativistic magnetic vector potential in the framework of the DKH theory, and is applicable to the calculations of magnetic properties without further expansion in powers of c−1. By combining with the finite-perturbation theory and the generalized-UHF method, new pictures of the magnetic shielding constant are derived. We apply the theory to calculations of the magnetic shielding constants of He isoelectronic systems, Ne isoelectronic systems, and noble gas atoms. The results of the present theory compare well with those of the four-component Dirac–Hartree–Fock calculations; the differences were within 3%. We note that the quasirelativistic theory that handles the magnetic vector potential at a nonrelativistic level greatly underestimates the relativistic effect. The so-called “picture change” effect is quite important for the magnetic shielding constant of heavy elements. The change in the orbital picture plays a significant role in the valence-orbital magnetic response as well as the core-orbital one. The effect of the finite nucleus is also studied using Gaussian nucleus model. The present theory reproduces the correct behavior of the finite-nucleus effect that has been reported with the Dirac theory. In contrast, the nonrelativistic theory and the quasirelativistic theory with the nonrelativistic vector potential underestimate the finite-nucleus effect. © 2003 American Institute of Physics.
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31.30.-i Corrections to electronic structure
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
31.15.xr Self-consistent-field methods

Quasirelativistic theory for magnetic shielding constants. II. Gauge-including atomic orbitals and applications to molecules

Ryoichi Fukuda, Masahiko Hada, and Hiroshi Nakatsuji

J. Chem. Phys. 118, 1027 (2003); http://dx.doi.org/10.1063/1.1528934 (9 pages) | Cited 61 times

Online Publication Date: 6 January 2003

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Quasirelativistic theory of magnetic shielding constants based on the Douglas–Kroll–Hess transformation of the magnetic potential presented in a previous paper is extended to molecular systems that contain heavy elements. The gauge-including atomic orbital method is adapted to the quasirelativistic Hamiltonian to allow origin-independent calculations. The present theory is applied to the proton and halogen magnetic shielding constants of hydrogen halides and the 199Hg magnetic shielding constants and chemical shifts of mercury dihalides and methyl mercury halides. While the relativistic correction to the magnetic interaction term has little effect on the proton magnetic shielding constants, this correction is a dominant origin of the heavy atom shifts of the magnetic shielding constants of heavy halogens and mercury. The basis set-dependence of mercury shielding constants is quite large in the relativistic calculation; it is important to use the basis functions that are optimized by the relativistic method to properly describe the relativistic effect. The relativistic correction to the magnetic interaction term is quite important for mercury dihalides in which the relativistic effects from mercury and halogen are strongly coupled. Without this correction, we obtain quite incorrect results. The origin of the 199Hg chemical shifts in mercury dihalides is the spin–orbit interaction from heavy halogens. In methyl mercury halides, the paramagnetic shielding term as well as the spin–orbit interaction from heavy halogens dominates the 199Hg chemical shifts. © 2003 American Institute of Physics.
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31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
31.30.-i Corrections to electronic structure

Angular momentum in solid-harmonic-Gaussian integral evaluation

Brett I. Dunlap

J. Chem. Phys. 118, 1036 (2003); http://dx.doi.org/10.1063/1.1528935 (8 pages) | Cited 6 times

Online Publication Date: 6 January 2003

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Solid-harmonic derivatives of generalized Gaussian functions—exponential functions of a scalar argument that has no third derivatives with respect to any nuclear coordinate—are evaluated for three, four, and five centers without coupling any of the original angular momenta. Generalized Gaunt coefficients arise in this approach. They represent scalar coupling of all angular momenta lost from cross differentiation. All formulas are independent of all original angular momenta, which aids the evaluation of all integrals involving n centers at one time. Recurrence relations are given for the 3-j generalized Gaunt coefficient. The methods of Racah are used to obtain the coefficients that transform the generalized Gaunt coefficients into a representation in which the angular momentum lost due to cross differentiation are arbitrarily coupled, and thus show directly that the generalized Gaunt coefficients always represent scalar coupling. More intermediate information can be reused if the coupled generalized Gaunt coefficients are used to evaluate all the integrals involving a given set of centers. © 2003 American Institute of Physics.
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31.15.A- Ab initio calculations

Application of time-dependent current-density-functional theory to nonlocal exchange-correlation effects in polymers

M. van Faassen, P. L. de Boeij, R. van Leeuwen, J. A. Berger, and J. G. Snijders

J. Chem. Phys. 118, 1044 (2003); http://dx.doi.org/10.1063/1.1529679 (10 pages) | Cited 54 times

Online Publication Date: 6 January 2003

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We provide a successful approach towards the solution of the longstanding problem of the large overestimation of the static polarizability of conjugated oligomers obtained using the local density approximation within density-functional theory. The local approximation is unable to describe the highly nonlocal exchange and correlation effects found in these quasi-one-dimensional systems. Time-dependent current-density-functional theory enables us to describe ultranonlocal exchange-correlation effects within a local current description. Recently a brief account was given of the application of the Vignale–Kohn current-functional [G. Vignale and W. Kohn, Phys. Rev. Lett. 77, 2037 (1996)] to the axial polarizability of oligomer chains [M. van Faassen, P. L. de Boeij, R. van Leeuwen, J. A. Berger, and J. G. Snijders, Phys. Rev. Lett. 88, 186401 (2002)]. With the exception of the model hydrogen chain, our results were in excellent agreement with best available wavefunction methods. In the present work we further outline the underlying theory and describe how the Vignale–Kohn functional was implemented. We elaborate on earlier results and present new results for the oligomers of polyethylene, polysilane, polysilene, polymethineimine, and polybutatriene. The adiabatic local density approximation gave good results for polyethylene, which were slightly modified by the Vignale–Kohn functional. In all other cases the Vignale–Kohn functional gave large improvements upon the adiabatic local density approximation. The Vignale–Kohn results were in agreement with best available data from wave function methods. We further analyze the hydrogen chain model for different bond length alternations. In all these cases the Vignale–Kohn correction upon the adiabatic local density approximation was too small. Arguments are given that further improvements of the functional are needed. © 2003 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Usefulness of the Colle–Salvetti model for the treatment of the nondynamic correlation

J. C. Sancho-García and F. Moscardó

J. Chem. Phys. 118, 1054 (2003); http://dx.doi.org/10.1063/1.1531102 (5 pages) | Cited 10 times

Online Publication Date: 6 January 2003

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In this work, the behavior of the Colle–Salvetti correlation functional is examined for strongly correlated systems with non-negligible nondynamic effects. Used with an appropriate multideterminantal wave function, it is able to reproduce accurately previous multireference coupled-cluster results for the problem of the automerization of cyclobutadiene, as well as to provide the correct energetical profiles for diatomic molecules under dissociation. The results confirm the current quality of the functional for complicated chemical problems, in spite of the fact that the functional does not satisfy some known exact properties. © 2003 American Institute of Physics.
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31.15.bw Coupled-cluster theory
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
31.15.V- Electron correlation calculations for atoms, ions and molecules

A general method for implementing vibrationally adiabatic mixed quantum-classical simulations

Ward H. Thompson

J. Chem. Phys. 118, 1059 (2003); http://dx.doi.org/10.1063/1.1528891 (9 pages) | Cited 7 times

Online Publication Date: 6 January 2003

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An approach for carrying out vibrationally adiabatic mixed quantum-classical molecular dynamics simulations is presented. An appropriate integration scheme is described for the vibrationally adiabatic equations of motion of a diatomic solute in a monatomic solvent and an approach for calculating the adiabatic energy levels is presented. Specifically, an iterative Lanczos algorithm with full reorthogonalization is used to solve for the lowest few vibrational eigenvalues and eigenfunctions. The eigenfunctions at one time step in a mixed quantum-classical trajectory are used to initiate the Lanczos calculation at the next time step. The basis set size is reduced by using a potential-optimized discrete variable representation. As a demonstration the problem of a homonuclear diatomic molecule in a rare gas fluid (N2 in Ar) has been treated. The approach is shown to be efficient and accurate. An important advantage of this approach is that it can be straightforwardly applied to polyatomic solutes that have multiple vibrational degrees-of-freedom that must be quantized. © 2003 American Institute of Physics.
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61.20.Ja Computer simulation of liquid structure

Local hybrid functionals

Juanita Jaramillo, Gustavo E. Scuseria, and Matthias Ernzerhof

J. Chem. Phys. 118, 1068 (2003); http://dx.doi.org/10.1063/1.1528936 (6 pages) | Cited 78 times

Online Publication Date: 6 January 2003

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We present a novel approach for constructing hybrid functionals by using a local mix of regular density functional theory (DFT) exchange and exact Hartree–Fock (HF) exchange. This local hybrid approach is computationally feasible for a wide range of molecules. In this work, the local mix of HF and DFT exchange is driven by the ratio of τW = ∣∇ρ∣2/8ρ, the Weizsäcker kinetic energy density, with τ, the exact kinetic energy density. This particular choice of local mix yields 100% of exact exchange in one-electron regions. Dissociation energy curves, binding energies, and equilibrium geometries for two-center, three-electron symmetric radical cations can be modeled accurately using this scheme. We also report encouraging results for reaction energy barriers, and somewhat disappointing atomization energies for the small G2 set. © 2003 American Institute of Physics.
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31.15.E- Density-functional theory
31.15.xr Self-consistent-field methods

Self-guided enhanced sampling methods for thermodynamic averages

Ioan Andricioaei, Aaron R. Dinner, and Martin Karplus

J. Chem. Phys. 118, 1074 (2003); http://dx.doi.org/10.1063/1.1528893 (11 pages) | Cited 29 times

Online Publication Date: 6 January 2003

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In the self-guided molecular dynamics (SGMD) simulation method, a continuously updated average force is used to bias the motions of the system. The method appears to sample the configuration space of a number of complex systems more efficiently than ordinary molecular dynamics, and it was argued that it yields canonical averages of observable quantities with only negligible errors. We analyze the dynamic mapping associated with the SGMD algorithm and find that the dynamics lacks reversibility because the effective potential that governs the motion is a functional of the trajectory rather than a function of the coordinates (i.e., the dynamics is not uniquely specified by the initial conditions but depends on past history as well). This irreversibility is shown to result in substantial errors in canonical averages for model systems. Motivated by this analysis, we introduce an alternative self-guided scheme (the momentum-enhanced hybrid Monte Carlo method) that does converge to the canonical distribution in principle. The method differs from the original SGMD algorithm in that momenta, rather than forces, are averaged to bias the initial choice of momenta at each step in a hybrid Monte Carlo procedure. The relation of the method to other enhanced sampling algorithms is discussed. © 2003 American Institute of Physics.
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05.70.Ce Thermodynamic functions and equations of state
82.60.-s Chemical thermodynamics
02.70.Ns Molecular dynamics and particle methods

Efficient thermal rate constant calculation for rare event systems

S. A. Corcelli, J. A. Rahman, and J. C. Tully

J. Chem. Phys. 118, 1085 (2003); http://dx.doi.org/10.1063/1.1529192 (4 pages) | Cited 8 times

Online Publication Date: 6 January 2003

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We present an efficient method for computing thermal reaction rate constants that can be applied to systems in which transitions from reactant to product are infrequent. The method can be applied to high-dimensional, disordered systems which exhibit too many transition states to be identified, and for which useful reaction coordinates cannot be easily defined. The focus of our method is the time correlation function C(t), the normalized partition function for trajectories that begin in the reactant region and end in the product region after a time t; the time derivative of C(t) is the reaction rate constant, k(t). We use an umbrella potential to select initial positions from improbable regions of the reactant configuration space. We then compute C(t) directly by choosing random thermal momenta and asking if the resulting dynamical trajectory reaches the product region in time t. Since dynamical trajectories are run on the true potential energy surface, without the umbrella, re-crossing effects are included correctly. The initial condition bias introduced by the umbrella is removed by a weighting factor. We test the method on a simple two dimensional model potential and on a model for the isomerization of a diatomic in a Weeks–Chandler–Andersen fluid, and show that it gives accurate and precise rates with substantial reduction in computer time. © 2003 American Institute of Physics.
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82.20.Db Transition state theory and statistical theories of rate constants
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Kh Potential energy surfaces for chemical reactions
82.30.Qt Isomerization and rearrangement

Ab initio molecular dynamics with a continuum solvation model

Hans Martin Senn, Peter M. Margl, Rochus Schmid, Tom Ziegler, and Peter E. Blöchl

J. Chem. Phys. 118, 1089 (2003); http://dx.doi.org/10.1063/1.1528890 (12 pages) | Cited 17 times

Online Publication Date: 6 January 2003

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We present an implementation of the conductor-like screening model (COSMO) within the framework of Car–Parrinello ab initio molecular dynamics. In order to obtain the accurate forces needed for energy-conserving dynamics, analytic derivatives with respect to the atomic positions are required for all energy terms. We use a steep, but continuous surface function that effectively switches the surface charges off when they are not exposed on the molecular surface. This allows us to construct the cavity surface in such a way that the required analytic derivatives of the surface charges and surface segments are always available. Furthermore, we treat the surface charges as fictitious dynamic variables within the extended Lagrangian approach, solving the electrostatic problem determining the charges “on the fly” as the system evolves in time. Our implementation makes it possible to perform energy-conserving ab initio molecular dynamics simulations in which continuum solvation is included. It provides solvation energies within the accuracy expected for a COSMO implementation at the density-functional level and allows one to study special features of reactivity that can only be observed at finite temperature in solution. © 2003 American Institute of Physics.
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61.20.Ja Computer simulation of liquid structure
82.30.Nr Association, addition, insertion, cluster formation

On the optimization of Gaussian basis sets

George A. Petersson, Shijun Zhong, John A. Montgomery, and Michael J. Frisch

J. Chem. Phys. 118, 1101 (2003); http://dx.doi.org/10.1063/1.1516801 (9 pages) | Cited 16 times

Online Publication Date: 6 January 2003

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A new procedure for the optimization of the exponents, αj, of Gaussian basis functions, Ylm(ϑ,φ)rle−αjr2, is proposed and evaluated. The direct optimization of the exponents is hindered by the very strong coupling between these nonlinear variational parameters. However, expansion of the logarithms of the exponents in the orthonormal Legendre polynomials, Pk, of the index, j: ln αj = ∑k = 0kmaxAkPk((2j−2)/(Nprim−1)−1), yields a new set of well-conditioned parameters, Ak, and a complete sequence of well-conditioned exponent optimizations proceeding from the even-tempered basis set (kmax = 1) to a fully optimized basis set (kmax = Nprim−1). The error relative to the exact numerical self-consistent field limit for a six-term expansion is consistently no more than 25% larger than the error for the completely optimized basis set. Thus, there is no need to optimize more than six well-conditioned variational parameters, even for the largest sets of Gaussian primitives. © 2003 American Institute of Physics.
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31.15.xr Self-consistent-field methods
31.15.A- Ab initio calculations
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
31.15.xt Variational techniques

Method for the ab initio calculation of intermolecular potentials of ionic clusters: Test on Rg–CO+, Rg=He, Ne, Ar

Victor F. Lotrich and Ad van der Avoird

J. Chem. Phys. 118, 1110 (2003); http://dx.doi.org/10.1063/1.1527570 (9 pages) | Cited 9 times

Online Publication Date: 6 January 2003

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The interaction energy of a cationic complex A–B+ can be computed as the sum of the interaction energy of the neutral complex A–B and the geometry dependent difference in the ionization potentials of the complex A–B and the molecule B, with ionization potentials calculated by the outer valence Green’s function method. We test this method by computing the intermolecular potential energy of the complexes He–CO+, Ne–CO+, and Ar–CO+ for linear and T-shaped geometries. One-dimensional potential energy cuts were analyzed with emphasis on the asymptotic behavior. Results obtained by this method have been compared to interaction energies of the A–B+ complex computed directly by the partially spin-restricted single and double excitation coupled cluster method with perturbative triples. For the weakly bound complexes He–CO+ and Ne–CO+ the differences are only a few percent at small intermolecular distances but become significant for separations around the equilibrium distance and larger. Scaling the long range induction coefficients to match accurately known values significantly improves the agreement: the resulting interaction potentials are accurate to within a few percent at all intermolecular separations. For the Ar–CO+ complex the method produces less accurate results for small intermolecular distances but the binding in Ar–CO+ is very strong and for small R this system cannot be considered a weakly bound complex anymore. © 2003 American Institute of Physics.
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34.20.Gj Intermolecular and atom-molecule potentials and forces
31.15.A- Ab initio calculations
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
31.15.bw Coupled-cluster theory

Many-body effects in nonadiabatic molecular theory for simultaneous determination of nuclear and electronic wave functions: Ab initio NOMO/MBPT and CC methods

Hiromi Nakai and Keitaro Sodeyama

J. Chem. Phys. 118, 1119 (2003); http://dx.doi.org/10.1063/1.1528951 (9 pages) | Cited 39 times

Online Publication Date: 6 January 2003

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We have investigated the many-body effects in a molecular theory to determine simultaneously nuclear and electronic wave functions without the Born–Oppenheimer (BO) approximation. We first apply the many-body perturbation theory using the electron–nucleus and nucleus–nucleus interactions to the non-BO theory and show the importance of the electron–nucleus correlation rather than the nucleus–nucleus one. We next combine the non-BO theory with the coupled cluster double and Brueckner double methods using the one-electron plus one-nucleus excitation operators. © 2003 American Institute of Physics.  
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
31.15.A- Ab initio calculations
31.15.bw Coupled-cluster theory

Equation-of-motion coupled cluster method with full inclusion of the connected triple excitations for ionized states: IP-EOM-CCSDT

Monika Musiał, Stanisław A. Kucharski, and Rodney J. Bartlett

J. Chem. Phys. 118, 1128 (2003); http://dx.doi.org/10.1063/1.1527013 (9 pages) | Cited 53 times

Online Publication Date: 6 January 2003

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The equation-of-motion (EOM) coupled cluster (CC) method with full inclusion of the connected triple excitations for ionization energies has been formulated and implemented. Using proper factorization of the three- and four-body parts of the effective Hamiltonian, an efficient computational procedure has been proposed for IP-EOM-CCSDT which at the EOM level requires no-higher-than nocc3nvir4 scaling. The method is calibrated by the evaluation of the valence vertical ionization potentials for CO, N2, and F2 molecules for several basis sets up to 160 basis functions. At the basis set limit, errors vary from 0.0 to 0.2 eV, compared to “experimental” vertical ionization potentials. © 2003 American Institute of Physics.
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31.15.bw Coupled-cluster theory
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Core shell excitation of 2-propenal (acrolein) at the O 1s and C 1s edges: An experimental and ab initio study

D. Duflot, J.-P. Flament, I. C. Walker, J. Heinesch, and M.-J. Hubin-Franskin

J. Chem. Phys. 118, 1137 (2003); http://dx.doi.org/10.1063/1.1527924 (9 pages) | Cited 10 times

Online Publication Date: 6 January 2003

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The carbon and oxygen K-shell spectra of gaseous 2-propenal (acrolein) have been measured using the inner-shell electron energy loss spectroscopy method. Large scale ab initio configuration interaction calculations have been carried out to enable firm assignments of the observed bands. The overall shapes of the spectra are similar to previous low resolution monolayer and multilayer phases NEXAFS spectra recorded by photoabsorption of synchrotron radiation, but the spectral bands are much better resolved than the earlier ones. The spectra are dominated by excitation of π∗ type states and by interaction between the C = C and C = O π∗ orbitals. © 2003 American Institute of Physics.
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34.80.-i Electron and positron scattering
33.20.Rm X-ray spectra

Understanding highly excited states via parametric variations

Aravindan Semparithi, Venkataraman Charulatha, and Srihari Keshavamurthy

J. Chem. Phys. 118, 1146 (2003); http://dx.doi.org/10.1063/1.1527922 (12 pages) | Cited 4 times

Online Publication Date: 6 January 2003

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Highly excited vibrational states of an isolated molecule encode the vibrational energy flow pathways in the molecule. Recent studies have had spectacular success in understanding the nature of the excited states mainly due to the extensive studies of the classical phase space structures and their bifurcations. Such detailed classical-quantum correspondence studies are presently limited to two- or quasi-two-dimensional systems. One of the main reasons for such a constraint has to do with the problem of visualization of relevant objects like surface of sections and Wigner or Husimi distributions associated with an eigenstate. This necessitates various alternative techniques which are more algebraic than geometric in nature. In this work we introduce one such method based on parametric variation of the eigenvalues of a Hamiltonian. It is shown that the level velocities are correlated with the phase space nature of the corresponding eigenstates. A semiclassical expression for the level velocities of a single resonance Hamiltonian is derived which provides theoretical support for the correlation. We use the level velocities to dynamically assign the highly excited states of a model spectroscopic Hamiltonian in the mixed phase space regime. The effect of bifurcations on the level velocities is briefly discussed using a recently proposed spectroscopic Hamiltonian for the HCP molecule. © 2003 American Institute of Physics.
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33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
05.45.-a Nonlinear dynamics and chaos
02.10.Ud Linear algebra
02.50.Ng Distribution theory and Monte Carlo studies

Infrared emission spectra of BeH and BeD

A. Shayesteh, K. Tereszchuk, P. F. Bernath, and R. Colin

J. Chem. Phys. 118, 1158 (2003); http://dx.doi.org/10.1063/1.1528606 (4 pages) | Cited 8 times

Online Publication Date: 6 January 2003

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High resolution infrared emission spectra of beryllium monohydride and monodeuteride have been recorded. The molecules were generated in a furnace-discharge source, at 1500 °C and 333 mA discharge current, with beryllium metal and a mixture of helium and hydrogen or deuterium gases. Approximately 160 BeH lines and 167 BeD lines for the vibrational bands v = 1→0 to v = 4→3 were observed in the spectra and spectroscopic constants were determined. The Dunham constants (Yl,m) and Born–Oppenheimer breakdown constants were obtained in a combined fit of the BeH and BeD data. The equilibrium rotational constants (Be) for BeH and BeD were found to be 10.319 59(3) cm−1 and 5.688 29(2) cm−1, respectively, while the equilibrium vibrational constants (ωe) are 2061.416(3) and 1529.956(3) cm−1. The equilibrium distance (Re) was determined to be 1.342 436(2) Å for BeH. © 2003 American Institute of Physics.
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33.20.Ea Infrared spectra
33.50.-j Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion)
33.15.Mt Rotation, vibration, and vibration-rotation constants

The dynamics of the H+D2O→OD+HD reaction at 2.5 eV: Experiment and theory

M. Brouard, I. Burak, D. Minayev, P. O’Keeffe, C. Vallance, F. J. Aoiz, L. Bañares, J. F. Castillo, Dong H. Zhang, and Michael A. Collins

J. Chem. Phys. 118, 1162 (2003); http://dx.doi.org/10.1063/1.1528896 (13 pages) | Cited 10 times

Online Publication Date: 6 January 2003

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The title reaction has been studied both experimentally and computationally at a mean collision energy of 2.48 eV. OD quantum state populations, rotational alignment parameters, rovibrational quantum state-resolved center-of-mass angular scattering distributions and HD co-product internal energy release distributions have been determined, along with OD quantum state averaged energy disposals. The experiments employ pulsed laser photolysis coupled with polarized Doppler-resolved laser induced fluorescence detection of the radical products. The OD angular scattering distributions show a preference for scattering in the forward direction, and are quite different from those observed previously at the lower collision energy of 1.4 eV. So too are the kinetic energy release distributions, which reveal that the HD co-products are born significantly more internally excited at 2.48 eV than at 1.4 eV. The HD internal energy distributions obtained from analysis of the Doppler resolved profiles are in reasonable accord with that derived from the direct HD population measurements performed by Zare and co-workers [J. Chem. Phys. 98, 4636 (1993)] at collision energies around 2.7 eV. The data are compared in detail with the results of new quasi-classical trajectory (QCT) calculations employing two alternative potential energy surfaces (PESs), as well as with the results from previous QCT studies of the title reaction by other workers. Refinements to the most recent of the PESs employed here, that developed using the iterative methods of Collins and Zhang and co-workers [J. Chem. Phys. 115, 174 (2001)], are also described. The theoretical results obtained using this refined PES agree very well with many of the experimental observables, and the surface appears to be a significant improvement on those previously developed. However, even with this new PES, the QCT calculations at 2.48 eV overestimate the internal excitation of the HD products. © 2003 American Institute of Physics.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Hf Product distribution

Velocity map imaging of the photodissociation of CF3I: Vibrational energy dependence of the recoil anisotropy

F. Aguirre and S. T. Pratt

J. Chem. Phys. 118, 1175 (2003); http://dx.doi.org/10.1063/1.1530582 (9 pages) | Cited 30 times

Online Publication Date: 6 January 2003

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The photodissociation of jet-cooled CF3I into CF3+I(2P3/2) and CF3+I∗(2P1/2) has been investigated between 304 and 277 nm by using velocity map ion imaging. The two-dimensional images provide detailed information on the partition of available energy into kinetic and internal energy of the photofragments. Vibrational structure with spacing of 695±100 cm−1 is resolved in both I and I∗ images, indicating excitation of the umbrella mode ν2 of the CF3 photofragment. The fragment recoil anisotropies β(I) and β(I∗) are determined as a function of the excitation wavelength and their variations are interpreted in terms of the crossing between the 3Q0 and 1Q1 dissociative electronic states. The high-resolution images allow the determination of the variation of the anisotropy parameter β as a function of the vibrational level of CF3 fragment, and provide a complementary method for the determination of the C–I bond energy. The vibrational dependence of the anisotropy values is discussed in terms of final-state interactions between the CF3 umbrella motion and the C–I dissociation coordinate, as discussed previously by Hennig et al. [J. Chem. Phys. 84, 544 (1986)]. © 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
82.37.Vb Single molecule photochemistry

Quantum dynamics study of the isotopic effect on capture reactions: HD, D2+CH3

Dunyou Wang

J. Chem. Phys. 118, 1184 (2003); http://dx.doi.org/10.1063/1.1529178 (5 pages) | Cited 9 times

Online Publication Date: 6 January 2003

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Time-dependent wave-packet-propagation calculations are reported for the isotopic reactions, HD+CH3 and D2+CH3, in six degrees of freedom and for zero total angular momentum. Initial-state-selected reaction probabilities for different initial rotational-vibrational states are presented in this study. This study shows that excitations of the HD(D2) enhances the reactivities, whereas the excitations of the CH3 umbrella mode have the opposite effects. This is consistent with the reaction of H2+CH3. The comparison of these three isotopic reactions also shows the isotopic effects in the initial-state-selected reaction probabilities. The cumulative reaction probabilities (CRPs) are obtained by summing over initial-state-selected reaction probabilities. Theenergy-shift approximation to account for the contribution of degrees of freedom missing in the six dimensionality calculation is employed to obtain approximate full dimensional CRPs. The rate constant comparison shows the H2+CH3 reaction has the biggest reactivity, then HD+CH3, and D2+CH3 has the smallest. © 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.)

Ab initio transition state theory calculation of the rate constant for the hydrogen abstraction reaction H2O2+H→H2+HO2

Y. Tarchouna, M. Bahri, N. Jaïdane, Z. Ben Lakhdar, and J. P. Flament

J. Chem. Phys. 118, 1189 (2003); http://dx.doi.org/10.1063/1.1527920 (7 pages) | Cited 4 times

Online Publication Date: 6 January 2003

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Large basis set and two levels of ab initio calculation (ROHF and MCSCF) are used to determine the electronic structure of reactants, products, and saddle point involved in the hydrogen abstraction reaction H2O2+H→H2+HO2. The calculated ROHF and MCSCF imaginary frequency ω ≠ corresponds to the motion of an hydrogen atom between H2O2 and H and has respectively, a magnitude of 6826.5 and 2909.9 cm−1. Calculated (MP2//ROHF and MP2//MCSCF) values of 8.92 and 7.92 Kcal/mol are, respectively, found for the barrier height of the title reaction. The ab initio results are used with the transition state theory (TST) to evaluate the rate constant kTST(T) over the range of temperature 200 ⩽ T ⩽ 2000 K. Tunneling corrections to kTST(T) are considered through the evaluation of the transmission coefficient by Wigner (W) and zero curvature tunneling (ZCT) methods. Our results show that the calculated rate constants based on the ROHF electronic structure results do not agree with the experimental values. The best agreement with the preferred experimental values measured by Baulch et al. for 300 ⩽ T ⩽ 800 K and with the values measured by Stang and Hampson for 850 ⩽ T ⩽ 2000 K is found for the calculation based on the MCSCF electronic structure results and using the ZCT method to account for tunneling correction to kTST. © 2003 American Institute of Physics.  
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82.20.Db Transition state theory and statistical theories of rate constants
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Xr Quantum effects in rate constants (tunneling, resonances, etc.)
31.15.A- Ab initio calculations

Intermolecular vibrations of the hydrogen bonded OH–CO reactant complex

Mark D. Marshall, Bethany V. Pond, and Marsha I. Lester

J. Chem. Phys. 118, 1196 (2003); http://dx.doi.org/10.1063/1.1527921 (10 pages) | Cited 13 times

Online Publication Date: 6 January 2003

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Intermolecular vibrations of the linear OH–CO reactant complex have been observed as combination bands in the OH overtone region using infrared action spectroscopy. Rotational analyses and simulations of the band structures have been carried out for transitions to geared bend, excited spin–orbit, and H-atom bend states with 50–250 cm−1 of intermolecular excitation. The projection quantum number associated with each of these upper states is identified through the intensity profile of the band contour, missing rotational lines, and/or parity splitting of individual rotational lines. Intermolecular states with projection quantum numbers P = 1/2 and 5/2 are observed for each of the two bending modes, arising from coupling of the unquenched angular momentum of OH with the vibrational angular momentum associated with the bending motion of the complex. An additional P = 1/2 state is attributed to spin–orbit excitation, which shifts to higher energy than in free OH and gains infrared transition strength through the spin-decoupling interaction. The intermolecular energy level pattern is also examined in the context of the Renner-Teller interaction and spin–orbit coupling. The intermolecular bends of the OH–CO complex are of special interest because they probe portions of the reaction path leading to trans-HOCO formation. © 2003 American Institute of Physics.
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33.20.Ea Infrared spectra
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
34.50.Ez Rotational and vibrational energy transfer
33.15.Fm Bond strengths, dissociation energies
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