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22 Jun 2002

Volume 116, Issue 24, pp. 10571-11040

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back to top Theoretical Methods and Algorithms

New correlation energy functionals with explicit dependence on the number of electrons

Ángel J. Pérez-Jiménez, José M. Pérez-Jordá, Luis Pastor-Abia, and Juan C. Sancho-García

J. Chem. Phys. 116, 10571 (2002); http://dx.doi.org/10.1063/1.1480870 (6 pages) | Cited 4 times

Online Publication Date: 7 June 2002

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Based upon the idea of effective number of electrons, we develop simple but accurate correlation energy functionals to be used for density functional theory calculations. We derive both a spin-independent and a spin-dependent functional. The spin-dependent one, used in conjunction with Becke’s exchange functional [A. D. Becke, Phys. Rev. A 38, 3098 (1988)], yields excellent results for thermochemistry calculations, giving an average absolute error of 2.9 kcal/mol for a test set comprised of the enthalpies of formation of the 148 molecules in the extended G2 set [L. A. Curtiss, K. Raghavachari, P. C. Redfern, and J. A. Pople, J. Chem. Phys. 106, 1063 (1997); L. A. Curtiss, P. C. Redfern, K. Raghavachari, and J. A. Pople, ibid. 109, 42 (1998)] plus the total energies of the atoms H through Ar. We also discuss the problem of fractional occupation number, and we show that the corresponding principle of integer preference can be fulfilled by the procedure that we propose to build correlation energy functionals. © 2002 American Institute of Physics.
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31.15.E- Density-functional theory
82.60.Cx Enthalpies of combustion, reaction, and formation

Semiclassical IVR treatment of reactive collisions

Y. Elran and K. G. Kay

J. Chem. Phys. 116, 10577 (2002); http://dx.doi.org/10.1063/1.1479137 (12 pages) | Cited 16 times

Online Publication Date: 7 June 2002

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We generalize a recently-developed semiclassical uniform initial value representation (IVR) treatment of the S-matrix [Y. Elran and K. G. Kay, J. Chem. Phys. 114, 4362 (2001)] to chaotic nonreactive and reactive collinear scattering. The present modifications allow one to determine the phase of the complex IVR integrand in a unique and practical manner even when the integrand is discontinuous or rapidly varying. The method is applied to the collinear H+H2 exchange reaction on the Porter–Karplus surface. A strategy is introduced for adapting the integration over the chaotic chattering zones to the fractal nature of the integrand. The results indicate that the technique is capable of good accuracy while requiring a relatively small number of trajectories per energy. © 2002 American Institute of Physics.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Ln Semiclassical theory of reactions and/or energy transfer

Prediction of trapping rates in mixtures of partially absorbing spheres

Anuraag R. Kansal and Salvatore Torquato

J. Chem. Phys. 116, 10589 (2002); http://dx.doi.org/10.1063/1.1479718 (9 pages) | Cited 10 times

Online Publication Date: 7 June 2002

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The combined effects of diffusion and reaction in heterogeneous media govern the behavior of a wide variety of physical and biological phenomena, including the consumption of nutrients by cells and the study of magnetic relaxation in tissues. We have considered the so-called “trapping problem,” in which diffusion takes place exterior to a collection of fixed traps while reaction occurs at their surface. A simulation technique for predicting the overall trapping rate for systems of partially absorbing spherical traps based on the first-passage spheres method is presented. Using data obtained by applying this simulation technique, we then consider the problem of mixtures of partially absorbing traps. By hypothesizing a method for reducing a general mixture of traps to a mixture of perfect absorbers and perfect reflectors (i.e., reducing the dimensionality of the space of variables), we are able to accurately predict the effective surface rate constant and the trapping rate for an arbitrary mixture of partially absorbing traps. Remarkably, we find that a single, nearly universal curve allows accurate predictions to be made over a wide range of trap volume fractions and even for different trap distributions. © 2002 American Institute of Physics.
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05.60.-k Transport processes
82.20.-w Chemical kinetics and dynamics
87.16.Uv Active transport processes

Solution of phase space diffusion equations using interacting trajectory ensembles

Arnaldo Donoso and Craig C. Martens

J. Chem. Phys. 116, 10598 (2002); http://dx.doi.org/10.1063/1.1479138 (8 pages) | Cited 22 times

Online Publication Date: 7 June 2002

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In this paper, we present a new method for simulating the evolution of the phase space distribution function describing a system coupled to a Markovian thermal bath. The approach is based on the propagation of ensembles of trajectories. Instead of incorporating environmental perturbations as stochastic forces, however, the present method includes these effects by additional deterministic interactions between the ensemble members. The general formalism is developed and tested on model systems describing one-dimensional diffusion, relaxation of a coherently excited harmonic oscillator coupled to a thermal bath, and activated barrier crossing in a bistable potential. Excellent agreement with exact results or approximate theories is obtained in all cases. The method provides an entirely deterministic trajectory-based approach to the solution of condensed phase dynamics and chemical reactions. © 2002 American Institute of Physics.
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82.20.-w Chemical kinetics and dynamics
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

Novel generalized Born methods

Michael S. Lee, Freddie R. Salsbury, and Charles L. Brooks

J. Chem. Phys. 116, 10606 (2002); http://dx.doi.org/10.1063/1.1480013 (9 pages) | Cited 135 times

Online Publication Date: 7 June 2002

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The generalized Born (GB) model is a simple continuum dielectric model for the calculation of molecular electrostatic solvation energies. It is a pairwise approximation to the solution of the Poisson equation for continuum electrostatic solvation. Key to the GB method is the calculation of Born radii for every atom in the system. We introduce two new methods for determining Born radii. The first is a two-parameter grid-based method that uses nearly the same molecular volume that is used in conventional Poisson calculations. The second is a five-parameter analytical method that utilizes a molecular volume built from a superposition of atomic functions. The analytical method, distinct from the grid-based algorithm, is amenable to force-based calculations, e.g., energy minimization and molecular dynamics. Unlike other Born radii methods, both algorithms employ a new empirically determined correction term that includes energetic effects beyond the Coulomb field approximation. With this correction term, the grid-based algorithm generally yields Born radii with greater than 0.99 correlation versus converged numerically derived Poisson Born radii. The analytical method reproduces Born radii with approximately 0.95 correlation versus Poisson-derived Born radii. With respect to absolute solvation energies, the grid-based method achieves an overall 1.3% error versus converged Poisson solutions for a set of 3029 single-chain proteins obtained from the Brookhaven Protein Data Bank. On the other hand, the analytic method delivers modest 2–4 % errors versus the Poisson solutions for the same data set. Results concerning absolute solvation energies of RNA and relative solvation energies in two sets of protein conformations are also presented. © 2002 American Institute of Physics.
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82.30.Nr Association, addition, insertion, cluster formation
87.15.N- Properties of solutions of macromolecules
82.39.Pj Nucleic acids, DNA and RNA bases
87.14.E- Proteins
87.15.R- Reactions and kinetics
36.20.Ey Conformation (statistics and dynamics)
36.20.Hb Configuration (bonds, dimensions)
33.15.Bh General molecular conformation and symmetry; stereochemistry

Time-resolved x-ray diffraction: Statistical theory and its application to the photo-physics of molecular iodine

S. Bratos, F. Mirloup, R. Vuilleumier, and M. Wulff

J. Chem. Phys. 116, 10615 (2002); http://dx.doi.org/10.1063/1.1477923 (11 pages) | Cited 25 times

Online Publication Date: 7 June 2002

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A theory is proposed to study time-resolved x-ray diffraction on the pico- and subpicosecond time scales. Electromagnetic fields are treated in the frame of Maxwellian electrodynamics, whereas the molecular system is treated by using quantum mechanics. An expression is given for the time-resolved x-ray signal; it involves a three-time correlation function of the Fourier transformed electronic density and of the electric dipole moment of the system. This theory is applied to the study of the recombination of photodissociated iodine molecules in solution. Both geminate and nongeminate recombination are considered. The feasibility of the real time visualization of atomic motions is discussed. © 2002 American Institute of Physics.
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07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Theoretical study of predissociation dynamics of HCN/DCN in their first absorption bands

Dingguo Xu, Daiqian Xie, and Hua Guo

J. Chem. Phys. 116, 10626 (2002); http://dx.doi.org/10.1063/1.1480874 (10 pages) | Cited 11 times

Online Publication Date: 7 June 2002

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Predissociation dynamics of HCN and DCN in the α absorption band is studied using a newly calculated ab initio potential energy surface of the first excited singlet (1 1A″) state and the corresponding transition dipole surface. The recently proposed complex-symmetric single Lanczos propagation method is applied to generate absorption spectra and fragment internal state distributions for the photodissociation of both HCN and DCN. The absorption spectra of both molecules are dominated by bending progressions, thanks to the linear-to-bent transition. For most low-lying resonances, the CN fragment is found predominantly in its ground vibrational state even when significant energy is available. The absence of fragment vibrational excitation is attributed to the coincidence of the C–N distance at the exit barrier and the dissociation asymptote, and to the lack of final-state interaction outside the barrier. On the other hand, the CN rotational distribution is found to be highly oscillatory and depend on the vibrational quanta of the resonance. The exit barrier plays a role in restricting rotational excitation in the CN fragment. The calculated results provide detailed information about the dissociation dynamics. © 2002 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
31.50.Df Potential energy surfaces for excited electronic states

Selective dissociation of the stronger bond in HCN using an optical centrifuge

R. Hasbani, B. Ostojić, P. R. Bunker, and M. Yu. Ivanov

J. Chem. Phys. 116, 10636 (2002); http://dx.doi.org/10.1063/1.1478696 (5 pages) | Cited 7 times

Online Publication Date: 7 June 2002

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Using the example of the HCN molecule, we study theoretically the possibility of selectively breaking the stronger bond in a triatomic molecule by rotationally accelerating it in an optical centrifuge using a combination of two oppositely chirped and counter-rotating strong laser fields. In our simulation the resultant field forces rotational acceleration of the HCN molecule to a point where the centrifugal force between the two heavy atoms (C and N) exceeds the strength of their (triple) bond. The effects of bending, rovibrational coupling, and the Coriolis force, which conspire to prevent the molecule from rotational dissociation into HC+N, can be efficiently counteracted by simple optimization of the frequency chirp. © 2002 American Institute of Physics.
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33.15.Fm Bond strengths, dissociation energies
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Vq Vibration-rotation analysis
33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis

Reaction cross sections for the H+D2(ν0=1)→HD+D and D+H2(ν0=1)→DH+H systems. A multiconfiguration time-dependent Hartree (MCTDH) wave packet propagation study

S. Sukiasyan and H.-D. Meyer

J. Chem. Phys. 116, 10641 (2002); http://dx.doi.org/10.1063/1.1479346 (7 pages) | Cited 28 times

Online Publication Date: 7 June 2002

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Cumulative initial-state-selected reaction cross sections of the H+D2 and D+H2 systems are computed for collision energies up to 1.6 eV and initial vibrational and rotational quantum numbers ν0 = 1 and j0 = 0–4. The Boothroyd–Keogh–Martin–Peterson (BKMP2) potential energy surface is taken as interaction potential. For comparison the Liu–Siegbahn–Truhlar–Horowitz (LSTH) potential energy surface is also considered, however, for j0 = 0 only. The cross sections are computed by propagating wave packets employing the multiconfiguration time-dependent Hartree scheme. The reactive flux, which determines the integral cross section, is evaluated through the interaction of the wave packet with a complex absorbing potential. A new approach of J-interpolation for the reaction probabilities has been developed. This approach allows to skip about every second of the individual propagations. The presence of weak oscillations appearing in the total integral cross sections has been observed. As in our previous calculations [J. Phys. Chem. 105, 2604 (2001)] on ν0 = 0, we attribute them to transition state resonances associated with excitations of the bending motion. Some of the present results are compared with previous results obtained by using the coupled states approximation. © 2002 American Institute of Physics.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Tr Kinetic isotope effects including muonium
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Db Transition state theory and statistical theories of rate constants

Photoabsorption spectra of icosahedral fullerenes: A semiempirical approach

S. Iglesias-Groth, A. Ruiz, J. Bretón, and J. M. Gomez Llorente

J. Chem. Phys. 116, 10648 (2002); http://dx.doi.org/10.1063/1.1479347 (8 pages) | Cited 8 times

Online Publication Date: 7 June 2002

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A semiempirical model has been used to predict the electronic photoabsorption spectra of five icosahedral fullerenes in the range C60–C720. The model parameters are first fixed in C60 by fitting its calculated spectrum to the available experimental data, and then conveniently adjusted to describe the larger fullerenes. The structures observed in the calculated spectra show a tendency to smooth π and σ plasmons as the fullerene size increases; however other finite-size features related to the particular geometry of these molecules are still visible at higher resolution. Some consequences of the strong electron screening effects on these spectra are discussed. © 2002 American Institute of Physics.
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36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Gk Plasma and collective effects in clusters
33.20.Lg Ultraviolet spectra
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.30.-i Corrections to electronic structure
31.15.bu Semi-empirical and empirical calculations (differential overlap, Hückel, PPP methods, etc.)

Vector properties of S(3P) and S(1D) in the photodissociation of SH: Quantum interference and overlapping resonance

Sungyul Lee, Hosung Sun, Bongsoo Kim, and Karl F. Freed

J. Chem. Phys. 116, 10656 (2002); http://dx.doi.org/10.1063/1.1480005 (8 pages) | Cited 7 times

Online Publication Date: 7 June 2002

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A quantal analysis is presented for the vector properties of the S(3P) and S(1D) fragments produced in the photodissociation of SH. We find that several different kinds of effects influence the angular distributions and the alignments of the sulfur atoms. At energies between the thresholds to the S(3P) and S(1D) terms, the vector properties are constant near the isolated Lorentzian resonances. The vector properties for the overlapping resonances, show rapid changes due to the difference of the geometrical factors characterizing the individual resonance. For the highest levels (v′ = 6,N′ ≥ 6), quantum interference between the predissociative (via the bound A 2Σ+ state) and the direct (by the repulsive 2Σ− state) pathways produces strong variations in the values of vector properties across the asymmetric resonances, suggesting a convenient means of angular control of the different atomic terms or the fine structure components of a given atomic term. At energies above the threshold to the S(1D) term, the interference between the two direct dissociating routes [through the A 2Σ+ and 2Σ− states for the S(3P) product, and through the 2Δ and 22Π states for the S(1D) product] is shown to yield highly oscillatory variations of the vector properties. © 2002 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
82.37.Vb Single molecule photochemistry

New analytical potential energy surface for the CH4+H hydrogen abstraction reaction: Thermal rate constants and kinetic isotope effects

J. Espinosa-García

J. Chem. Phys. 116, 10664 (2002); http://dx.doi.org/10.1063/1.1480273 (10 pages) | Cited 35 times

Online Publication Date: 7 June 2002

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A modified and recalibrated potential energy surface for the gas-phase CH4+H→CH3+H2 reaction and its deuterated analogs is reported and tested, which is completely symmetric with respect to the permutation of the four methane hydrogen atoms, and is calibrated with respect to updated experimental and theoretical stationary point (reactants, products, and saddle point) properties, and experimental forward thermal rate constants. The forward and reverse rate constants are calculated using variational transition-state theory with multidimensional tunneling effect over a wide temperature range, 300–2000 K. The theoretical results reproduce the available experimental data, with a small curvature of the Arrhenius plot which indicates the role of the tunneling in this reaction. Five sets of kinetic isotope effects are also calculated. In general, they agree with experimental values within the experimental errors. This surface is then used to analyze dynamical features, such as reaction-path curvature, the coupling between the reaction-coordinate and vibrational modes, and the effect of the vibrational excitation on the rate constants. It is found qualitatively that excitation of the CH4 stretching and umbrella modes enhance the forward rate constants, and only the CH3 umbrella mode in the product appear vibrationally excited. © 2002 American Institute of Physics.
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82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Tr Kinetic isotope effects including muonium

Computational studies on the infrared vibrational spectra, thermodynamic properties, detonation properties, and pyrolysis mechanism of octanitrocubane

Ji Zhang and Heming Xiao

J. Chem. Phys. 116, 10674 (2002); http://dx.doi.org/10.1063/1.1479136 (10 pages) | Cited 40 times

Online Publication Date: 7 June 2002

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The molecular geometries, infrared vibrational spectra, and thermodynamic properties of octanitrocubane (ONC) are calculated using the density functional theory (DFT) method at the B3LYP/6-31G∗ level. The IR frequency scaling factor 0.9501 suitable for polynitrocubanes is obtained at the B3LYP/6-31G∗ level, and the calculated IR frequencies of ONC are scaled. The accurate heat of formation 726.47 kJ/mol of ONC in gas phase is obtained via designed isodesmic reaction in which the cubane cage skeleton has been kept. The sublimation enthalpy, density, and heat of formation for ONC crystal are also calculated, and they are 220.63 kJ/mol, 2.189 g/cm3, and 505.84 kJ/mol, respectively. In addition, the estimated detonation velocity and detonation pressure of ONC are 10.26 mm/ms and 520.86 kbar, respectively. Finally, the pyrolysis mechanism of ONC is studied using various theoretical methods, i.e., MP2, DFT, and selected MINDO/3 semiempirical MO, based on the unrestricted Hartree–Fock model. The calculated results show that the pyrolysis initiation reaction of ONC, i.e., rate-controlling step, is to form a diradical by the single C–C bond breaking in the cube. The second C–C bond breaking is easily followed to form a nitrocyclooctatetraene. The calculated activation energy for the pyrolysis initiation reaction of ONC, obtained from B3LYP/6-31G∗ method, is 155.30 kJ/mol, which this rather large activation energy indicates that ONC is a new type of energetic material with less sensitivity and better thermal stability, and has highly exploitable values. © 2002 American Institute of Physics.
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33.20.Ea Infrared spectra
33.20.Tp Vibrational analysis
47.40.-x Compressible flows; shock waves
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.60.Cx Enthalpies of combustion, reaction, and formation

Nature of the interaction of paramagnetic atoms (A=4N,4P,3O,3S) with π systems and C60: A theoretical investigation of A⋅⋅⋅C6H6 and endohedral fullerenes AC60

Jung Mee Park, P. Tarakeshwar, Kwang S. Kim, and Tim Clark

J. Chem. Phys. 116, 10684 (2002); http://dx.doi.org/10.1063/1.1479135 (8 pages) | Cited 18 times

Online Publication Date: 7 June 2002

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The nature of the interaction of paramagnetic atoms A ( = 4N,4P,3O,3S) with π systems and C60 in the A⋅⋅⋅C6H6 complexes and endohedral fullerenes (AC60) has been investigated employing second-order Møller–Plesset perturbation level of theory and density functional theory calculations. The coupled cluster theory with single and double excitations, and with perturbed triplet excitations have also been carried out for the A⋅⋅⋅C6H6 complexes. The calculated geometries indicate that the paramagnetic N and P atoms lie on the C6 axis of benzene in the A⋅⋅⋅C6H6 complex and at the center of the C60 cage in AC60. On the other hand, the O and S atoms are slightly shifted towards the C–C bond of benzene in the A⋅⋅⋅C6H6 complex. A comparison of the calculated binding energies (BEs) of these paramagnetic complexes and the corresponding rare gas complexes like He⋅⋅⋅C6H6 and HeC60 indicate that the BEs of the former are much larger than those of the latter. For both the rare gas and paramagnetic atom complexes dispersive interactions dominate the BEs. The energy barriers of the penetration of the O atom through a [6,6] bond are lower than the penetration of the helium atom and higher than the penetration of a N atom. © 2002 American Institute of Physics.
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33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.E- Density-functional theory
36.40.Mr Spectroscopy and geometrical structure of clusters
31.15.bw Coupled-cluster theory
31.15.xp Perturbation theory

The O(1D)+H2 reaction at 56 meV collision energy: A comparison between quantum mechanical, quasiclassical trajectory, and crossed beam results

F. J. Aoiz, L. Bañares, J. F. Castillo, V. J. Herrero, B. Martínez-Haya, P. Honvault, J. M. Launay, X. Liu, J. J. Lin, S. A. Harich, C. C. Wang, and X. Yang

J. Chem. Phys. 116, 10692 (2002); http://dx.doi.org/10.1063/1.1478693 (12 pages) | Cited 49 times

Online Publication Date: 7 June 2002

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Quantum mechanical and quasiclassical trajectory reactive scattering calculations have been performed for the O(1D)+H2 (v = 0,j = 0) reaction on the Dobbyn–Knowles ab initio 1 1A′ and 1 1A″ potential energy surfaces (PES) at the mean collision energy Ecol = 56 meV (1.3 kcal/mol) of a crossed beam experimental study based on H-atom Rydberg “tagging” time-of-flight detection. Novel data from this latter experiment are presented and compared with the theoretical results at the level of state-resolved integral and differential cross sections and product recoil energy distributions. A good overall agreement with small discrepancies is found between the experimental data and the results of the two theoretical approaches. The main conclusion of the present work is that the contribution of the ground state 1 1A′ PES to the global reactivity accounts for the experimental observations and that, at the title collision energy, the participation of the 1 1A″ PES in the reaction is negligible for all practical purposes. © 2002 American Institute of Physics.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Hf Product distribution

Hyperfine structure of the 13Δg, 2 3Πg, and 33Σg+ states of 6Li7Li

Li Li, Angelos Lazoudis, Peng Yi, Yaoming Liu, John Huennekens, Robert W. Field, and A. Marjatta Lyyra

J. Chem. Phys. 116, 10704 (2002); http://dx.doi.org/10.1063/1.1478692 (9 pages) | Cited 8 times

Online Publication Date: 7 June 2002

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The hyperfine splittings of the 1 3Δg, 2 3Πg, and 3 3Σg+ states of 6Li7Li have been resolved by sub-Doppler, continuous wave, perturbation facilitated optical–optical double resonance excitation spectroscopy through newly identified A 1Σu+ (vA′ = 5, J′ = 24) ∼ b 3Πu (vb′ = 12, N′ = 23, J′ = 24) mixed window levels. The 3 3Σg+ and 1 3Δg states follow the case bβS coupling scheme. The Fermi contact interaction between the 7Li nucleus and the electron spin is the dominant term for the observed hyperfine splittings. The Fermi contact constants for the 7Li nucleus in the 6Li7Li molecule have been determined to be 110 MHz for the 3 3Σg+ state and 107 MHz for the 1 3Δg state. The 2 3Πg state has doubly excited character and its hyperfine coupling is different from that of the 3 3Σg+ and 1 3Δg states. The Fermi contact constants of triplet Rydberg states of 6Li7Li versus 7Li2 are discussed, and insights into the physical basis for case bβS coupling are illustrated. © 2002 American Institute of Physics.
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31.30.Gs Hyperfine interactions and isotope effects
33.15.Pw Fine and hyperfine structure
33.40.+f Multiple resonances (including double and higher-order resonance processes, such as double nuclear magnetic resonance, electron double resonance, and microwave optical double resonance)

Fourier transform millimeter-wave spectroscopy of the deuterated vinyl radical, C2D3

Eunsook Kim and Satoshi Yamamoto

J. Chem. Phys. 116, 10713 (2002); http://dx.doi.org/10.1063/1.1480270 (6 pages) | Cited 5 times

Online Publication Date: 7 June 2002

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The 101–000 rotational transition of the C2D3 radical in the ground electronic state has been detected for the first time with the Fourier transform millimeter-wave spectrometer. The C2D3 radical is produced by discharging the C2D3Br gas diluted in Ar. Thirty-two fine and hyperfine components of the 101–000 transition are measured in the frequency region around 44.4 GHz. The rotational constant (B+C)/2, the spin-rotation interaction constant, and the hyperfine interaction constants for the s and a states split by the tunneling motion associated with the CDα rocking mode are determined by a least-squares analysis. The energy splitting due to the tunneling motion is discussed on the basis of the hyperfine interactions. The angle between the CDα bond and the a-axis is estimated to be 148.5° from the nuclear quadrupole interaction constant χaa. © 2002 American Institute of Physics.
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33.20.Bx Radio-frequency and microwave spectra
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Ab initio theory and rotational spectra of linear carbon chains SiCnS

Peter Botschwina, M. Eugenia Sanz, Michael C. McCarthy, and Patrick Thaddeus

J. Chem. Phys. 116, 10719 (2002); http://dx.doi.org/10.1063/1.1473807 (11 pages) | Cited 8 times

Online Publication Date: 7 June 2002

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On the basis of extensive coupled cluster calculations, the rotational spectra of the linear silicon- and sulfur-containing carbon chains SiC2nS (n = 1–3) in their singlet electronic ground state and SiC3S in its triplet electronic ground state have been detected and characterized by means of molecular beam Fourier transform microwave spectroscopy. Rotational and centrifugal distortion constants have been determined to high accuracy as well as the spin-spin coupling constant for triplet SiC3S. In addition, the 29Si, 34S, and both 13C isotopic species of SiC2S have been detected, allowing the determination of both an effective r0 structure, as well as a mixed experimental–theoretical structure resulting from the combination of the measured rotational constants with the vibration–rotation coupling constants calculated ab initio. Several rotational satellite lines have also been observed for SiC2S and, on the basis of their predicted vibration–rotation and l-type doubling constants, were assigned to the two highest-frequency stretching modes v1 and v2, and to a progression in the second lowest-frequency bending mode v4 up to 3v4. Equilibrium structures and various spectroscopic properties are predicted for all SiCnS species with n = 1–8. © 2002 American Institute of Physics.
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31.15.A- Ab initio calculations
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.bw Coupled-cluster theory
33.20.Bx Radio-frequency and microwave spectra
31.30.Gs Hyperfine interactions and isotope effects
33.20.Vq Vibration-rotation analysis

Electric dipole moments and polarizabilities of single excess electron sodium fluoride clusters: Experiment and theory

D. Rayane, I. Compagnon, R. Antoine, M. Broyer, Ph. Dugourd, P. Labastie, J. M. L’Hermite, A. Le Padellec, G. Durand, F. Calvo, F. Spiegelman, and A. R. Allouche

J. Chem. Phys. 116, 10730 (2002); http://dx.doi.org/10.1063/1.1480595 (9 pages) | Cited 7 times

Online Publication Date: 7 June 2002

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In this article we present the first measurement of the electric dipole susceptibility of one excess electron NanFn−1 clusters. The static electronic polarizability and the permanent electric dipole of these clusters have been calculated with a one-electron model. Experimental values for the susceptibility are clearly related to the calculated values of the permanent dipole. The size evolution of the dipole moments is interpreted in terms of the interplay between the lattice and electron properties. This study outlines that the response of the cluster to the electric field cannot be fully understood with only equilibrium structure calculations and that the coupling between the permanent dipole and the vibrational motion of the cluster has to be taken into account. © 2002 American Institute of Physics.
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36.40.Cg Electronic and magnetic properties of clusters

Nuclear spin selection rule in the photochemical reaction of CH3 in solid parahydrogen

Mizuho Fushitani and Takamasa Momose

J. Chem. Phys. 116, 10739 (2002); http://dx.doi.org/10.1063/1.1480003 (5 pages) | Cited 7 times

Online Publication Date: 7 June 2002

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Photolysis of a methyl radical CH3 in solid parahydrogen produces a methane molecule CH4 via the reaction between an intermediate singlet methylene 1CH2 and a parahydrogen molecule H2. Conservation of nuclear spin during the reaction has been investigated by the intensity distribution of the rotation-vibration spectrum of methane produced by the reaction. It was found that the population of each nuclear spin state of methane just after the reaction was different from that of the statistical ratio, which indicates that a nuclear spin selection rule does exist in the reaction. However, the observed population was significantly different from the theoretically predicted ratio. The discrepancy between the experiment and the theory may indicate a breakdown of the nuclear spin conservation during the reaction, if the reaction mechanism in solid parahydrogen is the same as in the gas phase. © 2002 American Institute of Physics.
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82.50.Hp Processes caused by visible and UV light
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Hf Product distribution
82.20.Rp State to state energy transfer
33.20.Vq Vibration-rotation analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants

The relative reactivity of the stretch–bend combination vibrations of CH4 in the Cl (2P3/2)+CH4 reaction

Sangwoon Yoon, Sarah Henton, Aleksandar N. Zivkovic, and F. Fleming Crim

J. Chem. Phys. 116, 10744 (2002); http://dx.doi.org/10.1063/1.1476318 (9 pages) | Cited 39 times

Online Publication Date: 7 June 2002

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Direct infrared absorption prepares CH4 in two nearly isoenergetic vibrationally excited states, the symmetric stretch–bend combination (ν1+ν4) and the antisymmetric stretch–bend combination (ν3+ν4), for a study of the effect of stretching vibrations of CH4 on the reaction, CH4+Cl(2P3/2)→CH3+HCl. Comparison of intensities in the action spectra with those in the simulated absorption spectra shows that vibrational excitation of methane to the ν1+ν4 state promotes the reaction more efficiently than excitation to the ν3+ν4 state by a factor of 1.9±0.5. The reaction of methane in both vibrational states produces a substantial fraction (35%) of the CH3 products with the umbrella mode (ν2) excited, which we attribute to the presence of the bending vibration (ν4) in the combination states. The similarity of the vibrational population distributions of the products for the two excitations implies that the differences in the action spectra arise from the relative reactivity of the states rather than from population of different product states. This result is consistent with theoretical calculations that predict a stronger coupling of the symmetric stretching vibration to the reaction coordinate than the antisymmetric stretch. Analyzing the infrared laser power dependence of the signal with a simple two state model shows that the reaction cross section of the ν1+ν4 state of methane is 19±5 times larger than that of methane molecules in their ground or thermally populated vibrational states. © 2002 American Institute of Physics.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
33.15.Mt Rotation, vibration, and vibration-rotation constants

Pump–probe dissociative ionization of NaI and CsI aggregated with CH3CN

Darian T. Stibbe, Eric Charron, Valerie Brenner, Philippe Millié, and Annick Suzor-Weiner

J. Chem. Phys. 116, 10753 (2002); http://dx.doi.org/10.1063/1.1478697 (7 pages) | Cited 3 times

Online Publication Date: 7 June 2002

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Recent experiments have investigated the dissociative ionization of NaI and CsI, each aggregated with a molecule of acetonitrile CH3CN, using two femtosecond laser pulses. The first, the pump pulse, excites the NaI or CsI diatom to a dissociative state. The second, the probe pulse, then ionizes the sodium or cesium atom after a variable delay time, and the resulting ion is detected. In the case of NaI, the ion signal is characterized by a single maximum. For CsI, however, an oscillatory signal is observed. By performing two-dimensional wave packet propagations, we are able to reproduce this behavior, which can be explained using simple physical arguments. © 2002 American Institute of Physics.
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82.50.Hp Processes caused by visible and UV light
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.-b Photon interactions with molecules

Vector correlations and alignment parameters in the photodissociation of HF and DF

G. G. Balint-Kurti, A. J. Orr-Ewing, J. A. Beswick, Alex Brown, and O. S. Vasyutinskii

J. Chem. Phys. 116, 10760 (2002); http://dx.doi.org/10.1063/1.1476937 (12 pages) | Cited 45 times

Online Publication Date: 7 June 2002

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Orientation and alignment parameters have been computed from first principles for the photodissociation of the HF and DF diatomic molecules. The calculations are entirely ab initio and the break-up dynamics of the molecule is treated rigorously taking account of the electronically nonadiabatic dynamics on three coupled adiabatic electronic potential energy curves. The potential energy curves and spin–orbit interactions, which have been previously reported [J. Chem. Phys. 113, 1870 (2000)], are computed using ab initio molecular electronic structure computer codes. These are then used to compute photofragmentation T matrix elements using a time-dependent quantum mechanical wave packet treatment and from these a complete set of anisotropy parameters with rank up to K = 3 is computed. The predicted vector correlations and alignment parameters are presented as a function of energy for HF and DF initially in both their ground and first excited vibrational states. The parameters predicted for the molecules which are initially in their excited vibrational states display a pronounced sharp energy dependence arising from the nodal structure of the initial vibrational wavefunction. The theoretical results are analyzed using a simple model of the dynamics and it is demonstrated how the magnitude and relative phases of the photofragmentation T matrix elements can be deduced from the experimentally measured alignment parameters. No experimental measurements have yet been made of alignment parameters for hydrogen halide diatomics and the present results provide the first predictions of these quantities which may be compared with future experimental observations. © 2002 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
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Laboratory measurement of water nucleation using a laminar flow tube reactor

Vladimir B. Mikheev, Patricia M. Irving, Nels S. Laulainen, Stephan E. Barlow, and Viktor V. Pervukhin

J. Chem. Phys. 116, 10772 (2002); http://dx.doi.org/10.1063/1.1480274 (15 pages) | Cited 20 times

Online Publication Date: 7 June 2002

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A Laminar Flow Tube Reactor (LFTR) was used to study the nucleation of water vapor. Computational analysis was carried out to define the operating conditions of the LFTR suitable for water nucleation measurements. An interface between the LFTR and a mass spectrometer was developed to analyze the chemical content of the freshly nucleated water particles. Contaminants were detected in the initial configuration of the LFTR. As a result, improvements were made to the LFTR to achieve ultrahigh purity conditions in the system. The nucleation rate of water vapor as a function of supersaturation was measured over the temperature range 210–250 K. The first measurement of the nucleation rate of water at a temperature of 210 K was obtained. Reasonable agreement with the classical theory predictions is observed for temperatures in the range 230–250 K. However, below 220 K, classical theory begins to overestimate nucleation rates compared to experimental data and the disagreement grows with decreasing temperature. The experimental data obtained provide an excellent benchmark for further nucleation studies of binary, ternary, and more complex systems. © 2002 American Institute of Physics.
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82.60.Nh Thermodynamics of nucleation
64.60.Q- Nucleation
64.70.F- Liquid-vapor transitions

Elastic properties of the rotator phases of pentacosane C25H52

Prabir K. Mukherjee

J. Chem. Phys. 116, 10787 (2002); http://dx.doi.org/10.1063/1.1479711 (7 pages) | Cited 10 times

Online Publication Date: 7 June 2002

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Pentacosane C25H52 exhibits two different rotator to rotator phase transitions. A phenomenological theory of the elastic properties of the rotator phases is developed on the basis of a free energy expansion. The temperature dependence of the elastic constants is calculated for the various rotator phases. We discuss the temperature variation of the heat capacity in the rotator phases in terms of the elastic constants. The theoretical predictions are found to be in good qualitative agreement with available experimental results. © 2002 American Institute of Physics.
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62.20.D- Elasticity
65.40.G- Other thermodynamical quantities
65.40.Ba Heat capacity
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