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22 Dec 2002

Volume 117, Issue 24, pp. 10917-11405

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Anomalous charge-transfer behavior in the scattering of hyperthermal Br+(3P2) on Pt(111)

M. Maazouz, P. L. Maazouz, and D. C. Jacobs

J. Chem. Phys. 117, 10917 (2002); http://dx.doi.org/10.1063/1.1529687 (4 pages) | Cited 2 times

Online Publication Date: 11 December 2002

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In contrast to conventional charge-transfer theory, the scattering of state-selected Br+(3P2) on Pt(111) shows a dramatic enhancement in the yield of Br−(1S0) at an impact energy of 26 eV. Coincident with this resonance, the Br−(1S0) product scatters with additional translational energy. The observed scattering behavior is consistent with a collision-induced deformation of the lattice that evolves in phase with the departing projectile. The experimental data demonstrate the strong coupling between the motion of the platinum lattice and the surface electronic states responsible for charge transfer. © 2002 American Institute of Physics.
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34.35.+a Interactions of atoms and molecules with surfaces
34.70.+e Charge transfer
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
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Single-molecule optical spectroscopy of autofluorescent proteins

W. E. Moerner

J. Chem. Phys. 117, 10925 (2002); http://dx.doi.org/10.1063/1.1521150 (13 pages) | Cited 31 times

Online Publication Date: 11 December 2002

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Several genetically encoded autofluorescent proteins are now available, in which the emission arises from the formation of a fluorophore directly from the amino acids of the protein sequence. These proteins are heavily used in cellular biology to assess gene expression and protein localization. The optical behavior of such proteins has recently been described in vitro at the single-molecule level. These investigations have explored several yellow-emitting mutants of the green fluorescent protein (GFP), the red-emitting DsRed protein, and the dual-GFP cameleon construct designed for fluorescence resonant energy transfer sensing of calcium ion binding. A variety of blinking, switching, and fluctuation effects have been observed, showing that several dark states are accessible after optical excitation, arising from variations in charge state, isomerization state, and photobleaching. The single-molecule spectroscopy of these systems will be surveyed by describing several illustrative examples. Although the autofluorescent proteins available at present need improvement in order to reach the performance of laser dye fluorophores, the novelty of these systems and their ease of use in biological contexts requires a continuing effort to understand the photophysical behavior. © 2002 American Institute of Physics.
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87.15.M- Spectra of biomolecules
87.14.E- Proteins
87.15.Ya Fluctuations
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
33.50.Dq Fluorescence and phosphorescence spectra

Single-molecule spectroscopy: The road ahead

Michel Orrit

J. Chem. Phys. 117, 10938 (2002); http://dx.doi.org/10.1063/1.1521152 (9 pages) | Cited 34 times

Online Publication Date: 11 December 2002

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The spectroscopy of single molecules in frozen matrices at liquid helium temperatures reveals very narrow lines, often with lifetime-limited widths. The sensitivity of such sharp lines provides a wealth of information about the molecules, their environment, and their interaction with electromagnetic fields. As compared to more conventional bulk investigations, single molecules reveal the full extent of inhomogeneity at small scales, in the static or structural sense as well as in the time-resolved or dynamical sense. A few examples from the recent literature, on single molecules as sources of single photons, as probes for molecular or electronic motion, or as beacons in structural studies of biological molecules, illustrate these general features of the technique. The author’s best hopes for advances in the field include bridging between room and liquid helium temperatures, investigating structural problems on frozen biomolecules, using a single molecule as a tip for near-field optics, or as an input or output gate for quantum cryptography and quantum computing, and probing and exploiting the multiple possible interactions between single molecules. © 2002 American Institute of Physics.
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33.20.-t Molecular spectra
03.67.Dd Quantum cryptography and communication security
03.67.Lx Quantum computation architectures and implementations

Vibrational spectroscopy and imaging of single molecules: Bonding of CO to single palladium atoms on NiAl(110)

N. Nilius, T. M. Wallis, and W. Ho

J. Chem. Phys. 117, 10947 (2002); http://dx.doi.org/10.1063/1.1521151 (6 pages) | Cited 7 times

Online Publication Date: 11 December 2002

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A low temperature scanning tunneling microscope (STM) was used to probe the bonding of CO on NiAl(110) and the formation of PdCO and Pd(CO)2 at the single molecule level. While tilting of the two ligands is expected for Pd(CO)2, the observed bending of the CO molecule in PdCO is surprising. The combination of real space topographic imaging and spatially resolved vibrational spectroscopy in a STM provides a unique method in revealing internal bonding configuration and vibrational properties of individual metal carbonyls. © 2002 American Institute of Physics.
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68.43.Mn Adsorption kinetics
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
33.15.Mt Rotation, vibration, and vibration-rotation constants
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Fluorescent probes and bioconjugation chemistries for single-molecule fluorescence analysis of biomolecules

Achillefs N. Kapanidis and Shimon Weiss

J. Chem. Phys. 117, 10953 (2002); http://dx.doi.org/10.1063/1.1521158 (12 pages) | Cited 40 times

Online Publication Date: 11 December 2002

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Fluorescence-based detection of single biomolecules in solution and at room temperature has opened new avenues for understanding biological mechanisms. Single-molecule fluorescence spectroscopy (SMFS) of biomolecules requires careful selection of fluorophores, sites of incorporation, and labeling chemistries. SMFS-compatible fluorophores should permit extended, uninterrupted observations of fluorescence with high signal-to-noise ratios; more stringent considerations apply for specific methodologies, such as fluorescence resonance energy transfer and fluorescence anisotropy. Strategies for site-specific in vitro labeling of small proteins exploit the reactivity of the amino acid cysteine (Cys), allowing incorporation of one or more fluorophores; labeling of closely spaced Cys residues using bis-functionalized fluorophores allows probing of the orientation of individual protein domains. For in vitro labeling of large proteins, the options include peptide ligation, intein-mediated labeling, puromycin-based labeling, unnatural amino acid mutagenesis, and reconstitution from individual subunits or subunit fragments. For in vivo analysis, one can use proteins that are labeled in vitro and then incorporated in cells; genetic encoding of specific protein sequences can also lead to in vivo labeling, either by in vivo targeting by fluorophores or by biosynthesis of protein fusions with natural fluorophores such as the green fluorescent protein. The existing methods, along with others under development, will bring SMFS to the mainstream and advance significantly our understanding of vital biological processes. © 2002 American Institute of Physics.
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87.15.M- Spectra of biomolecules
87.15.R- Reactions and kinetics
33.50.Dq Fluorescence and phosphorescence spectra

Probing single-molecule dynamics photon by photon

Haw Yang and X. Sunney Xie

J. Chem. Phys. 117, 10965 (2002); http://dx.doi.org/10.1063/1.1521154 (15 pages) | Cited 61 times

Online Publication Date: 11 December 2002

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We present the theoretical rationales for data analysis protocols that afford an efficient extraction of conformational dynamics on a broad range of time scales from single-molecule fluorescence lifetime trajectories. Based on correlation analyses, a photon-by-photon approach on one hand provides the highest time resolution, whereas a minimal-binning method on the other hand is most suitable for experiments experiencing external fluorescence intensity variations. Applications of the two methods are illustrated via computer simulations. In cases where fluorescence quenching is either due to Förster fluorescence resonance energy transfer or due to the excited-state electron transfer, the fluorescence lifetime is dependent on donor-acceptor distance, thereby providing a window through which conformational dynamics are revealed. To assist in interpreting experimental data derived from the new protocols, analytical expressions relating fluorescence lifetime fluctuation correlations to a Brownian diffusion model and to an anomalous diffusion model are discussed. © 2002 American Institute of Physics.
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33.50.Dq Fluorescence and phosphorescence spectra
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.70.Fd Absolute and relative line and band intensities

Current status of single-molecule spectroscopy: Theoretical aspects

YounJoon Jung, Eli Barkai, and Robert J. Silbey

J. Chem. Phys. 117, 10980 (2002); http://dx.doi.org/10.1063/1.1521157 (16 pages) | Cited 33 times

Online Publication Date: 11 December 2002

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We survey the current status of single-molecule spectroscopy in the view point of theoretical aspects. After an explanation of basic concepts in single-molecule spectroscopy, we focus on the following topics: (1) line shape phenomena in disordered media, (2) photon counting statistics for time-dependent fluctuations in single-molecule spectroscopy, (3) fluorescence intensity fluctuations for nonergodic systems, (4) time-resolved single-molecule fluorescence for conformational dynamics of single biomolecules, (5) single-molecule reaction dynamics at room temperature, and (6) quantum jump method of single quantum system. We conclude this paper with some open questions and perspectives of single-molecule spectroscopy. © 2002 American Institute of Physics.
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07.60.-j Optical instruments and equipment
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
33.50.Dq Fluorescence and phosphorescence spectra
33.70.Jg Line and band widths, shapes, and shifts
33.70.Fd Absolute and relative line and band intensities
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
01.30.Rr Surveys and tutorial papers; resource letters
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Direct measurements of memory effects in single-molecule kinetics

Shilong Yang and Jianshu Cao

J. Chem. Phys. 117, 10996 (2002); http://dx.doi.org/10.1063/1.1521155 (14 pages) | Cited 31 times

Online Publication Date: 11 December 2002

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Statistics and correlations of single-molecule sequences of modulated reactions are explicitly evaluated in the stochastic rate representation. The memory function, introduced through the Gaussian approximation of the stochastic rate expression, characterizes the correlation in single-molecule rate processes in a formalism similar to the stochastic line shape theory. Within this formalism, the on-time correlation is shown to approximate the memory function of the fluctuating rate at discretized effective time separations. A new measurement, the two-event number density, is proposed as a means to map out the memory function over the complete time range. Confirmed by numerical calculations, these relations quantify dynamic disorder caused by conformational fluctuations and hence are useful for analyzing single-molecule kinetics. © 2002 American Institute of Physics.
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82.30.-b Specific chemical reactions; reaction mechanisms
82.40.-g Chemical kinetics and reactions: special regimes and techniques
02.50.Ey Stochastic processes
05.10.Gg Stochastic analysis methods (Fokker-Planck, Langevin, etc.)

Single-molecule dynamics of semiflexible Gaussian chains

Shilong Yang, James B. Witkoskie, and Jianshu Cao

J. Chem. Phys. 117, 11010 (2002); http://dx.doi.org/10.1063/1.1521156 (14 pages) | Cited 11 times

Online Publication Date: 11 December 2002

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A semiflexible Gaussian chain model is used to determine the statistics and correlations of single-molecule fluorescence resonant energy transfer (FRET) experiments on biological polymers. The model incorporates a persistence length in a Rouse chain and describes single-chain dynamics with normal modes. The hydrodynamic interaction is included in the dynamics of the semiflexible Gaussian chain on the preaveraging level. The distribution functions of the fluorescence lifetime and the FRET efficiency provide direct measures of the chain stiffness, and their correlation functions probe the intrachain dynamics at the single-molecule level. When measured with finite time resolution, the instantaneous diffusion coefficient for FRET is much smaller in the collapsed structure than in the coiled structure, and the variation has a quadratic dependence on the donor–acceptor distance. In the fast reaction limit, single-molecule FRET lifetime measurements can be used to map out the equilibrium distribution function of interfluorophore distance. As an example of microrheology, the intrinsic viscoelasticity can be extracted from single-molecule tracking of the Brownian dynamics of polymers in solution. © 2002 American Institute of Physics.
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61.25.H- Macromolecular and polymers solutions; polymer melts
87.15.H- Dynamics of biomolecules
83.60.Bc Linear viscoelasticity
78.55.Bq Liquids
33.50.Dq Fluorescence and phosphorescence spectra

Single-molecule approach to dispersed kinetics and dynamic disorder: Probing conformational fluctuation and enzymatic dynamics

X. Sunney Xie

J. Chem. Phys. 117, 11024 (2002); http://dx.doi.org/10.1063/1.1521159 (9 pages) | Cited 59 times

Online Publication Date: 11 December 2002

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This article reviews our efforts in understanding dynamical fluctuations of both conformation and enzymatic reactivity in single biomolecules. The single-molecule approach is shown to be particularly powerful for studies of dispersed kinetics and dynamic disorder. New single-molecule observations have revealed conformational transitions occurring on a broad range of timescales, 100 μs–10 s, offering new clues for understanding energy landscape of proteins, as well as the structural and chemical dynamics therein. © 2002 American Institute of Physics.
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82.39.-k Chemical kinetics in biological systems
82.37.Rs Single molecule manipulation of proteins and other biological molecules
87.14.E- Proteins
33.50.Dq Fluorescence and phosphorescence spectra
82.30.-b Specific chemical reactions; reaction mechanisms

Single-molecule chemistry

W. Ho

J. Chem. Phys. 117, 11033 (2002); http://dx.doi.org/10.1063/1.1521153 (29 pages) | Cited 214 times

Online Publication Date: 11 December 2002

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The ability to probe individual atoms and molecules have made it possible to reveal properties which otherwise would be hidden in the study of an ensemble of atoms and molecules. The scanning tunneling microscope (STM) with its unmatched spatial resolution and versatility literally allows us to touch atoms and molecules one at a time and to carry out experiments which previously were only imagined. One of the great attributes of the STM is that it provides a real space view of the individual molecules and the atomic landscape of their environment, thus removing many of the uncertainties surrounding the nature of the system under study. Combining its imaging, manipulation, spectroscopic characterization, and chemical modification capabilities, the STM has enabled direct visualization of chemistry by revealing the fundamental properties of atoms and molecules and their interactions with each other and the environment. While femtosecond lasers have made it possible to study chemistry at the temporal limit, the STM provides an understanding of chemistry at the spatial limit. © 2002 American Institute of Physics.
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82.37.Gk STM and AFM manipulations of a single molecule
back to top Theoretical Methods and Algorithms

Image charges in spherical geometry: Application to colloidal systems

René Messina

J. Chem. Phys. 117, 11062 (2002); http://dx.doi.org/10.1063/1.1521935 (13 pages) | Cited 51 times

Online Publication Date: 11 December 2002

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The effects of image charges (i.e., induced surface charges of polarization) in spherical geometry and their implication for charged colloidal systems are investigated. We study analytically and exactly a single microion interacting with a dielectric sphere and discuss the similarities and discrepancies with the case of a planar interface. By means of extensive Monte Carlo simulations, we study within the framework of the primitive model the effects of image charges on the structure of the electrical double layer. Salt-free environment as well as salty solutions are considered. A remarkable finding of this study is that the position of the maximum in the counterion density (appearing at moderately surface charge density) remains quasi-identical, regardless of the counterion valence and the salt content, to that obtained within the single-counterion system. © 2002 American Institute of Physics.
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82.70.Dd Colloids
82.45.-h Electrochemistry and electrophoresis
61.20.Ja Computer simulation of liquid structure

Quantum-classical Liouville approach to molecular dynamics: Surface hopping Gaussian phase-space packets

Illia Horenko, Christian Salzmann, Burkhard Schmidt, and Christof Schütte

J. Chem. Phys. 117, 11075 (2002); http://dx.doi.org/10.1063/1.1522712 (14 pages) | Cited 52 times

Online Publication Date: 11 December 2002

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In mixed quantum-classical molecular dynamics few but important degrees of freedom of a molecular system are modeled quantum mechanically while the remaining degrees of freedom are treated within the classical approximation. Such models can be systematically derived as a first-order approximation to the partial Wigner transform of the quantum Liouville-von Neumann equation. The resulting adiabatic quantum-classical Liouville equation (QCLE) can be decomposed into three individual propagators by means of a Trotter splitting: (1) phase oscillations of the coherences resulting from the time evolution of the quantum-mechanical subsystem, (2) exchange of densities and coherences reflecting non adiabatic effects in quantum-classical dynamics, and (3) classical Liouvillian transport of densities and coherences along adiabatic potential energy surfaces or arithmetic means thereof. A novel stochastic implementation of the QCLE is proposed in the present work. In order to substantially improve the traditional algorithm based on surface hopping trajectories [J. C. Tully, J. Chem. Phys. 93, 1061 (1990)], we model the evolution of densities and coherences by a set of surface hopping Gaussian phase-space packets (GPPs) with variable width and with adjustable real or complex amplitudes, respectively. The dense sampling of phase space offers two main advantages over other numerical schemes to solve the QCLE. First, it allows us to perform a quantum-classical simulation employing a constant number of particles; i.e., the generation of new trajectories at each surface hop is avoided. Second, the effect of nonlocal operators on the exchange of densities and coherences can be treated beyond the momentum jump approximation. For the example of a single avoided crossing we demonstrate that convergence towards fully quantum-mechanical dynamics is much faster for surface hopping GPPs than for trajectory-based methods. For dual avoided crossings the Gaussian-based dynamics correctly reproduces the quantum-mechanical result even when trajectory-based methods not accounting for the transport of coherences fail qualitatively. © 2002 American Institute of Physics.
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61.20.Ja Computer simulation of liquid structure
31.15.xv Molecular dynamics and other numerical methods

Correlated line broadening in multidimensional vibrational spectroscopy

Ravindra Venkatramani and Shaul Mukamel

J. Chem. Phys. 117, 11089 (2002); http://dx.doi.org/10.1063/1.1518001 (13 pages) | Cited 26 times

Online Publication Date: 11 December 2002

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The third-order optical response of two coupled anharmonic vibrations interacting with a Brownian oscillator bath that induces energy level fluctuations with arbitrary time scales and degree of correlation is calculated. Two-dimensional correlation plots show distinct signatures of these fluctuations in the various possible three pulse, infrared, femtosecond techniques. © 2002 American Institute of Physics.
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07.60.Rd Visible and ultraviolet spectrometers
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
42.65.-k Nonlinear optics

Effects of dipole alignment and channel interference on two-photon absorption cross sections of two-dimensional charge-transfer systems

Peter Cronstrand, Yi Luo, and Hans Ågren

J. Chem. Phys. 117, 11102 (2002); http://dx.doi.org/10.1063/1.1522408 (5 pages) | Cited 31 times

Online Publication Date: 11 December 2002

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The relationship between two-photon absorption cross sections and the architecture of donor–acceptor substitutions in two-dimensional charge-transfer cumulene-containing aromatic molecules is analyzed. It is shown that a molecular design strategy proposed for one-dimensional charge-transfer molecules must be considerably altered for two-dimensional systems. It is found that the maximal two-photon cross section of such two-dimensional systems can often be well described by a four state model. The importance of the alignment of the transition dipole moments and of channel interference on the two-photon absorption cross sections is emphasized. © 2002 American Institute of Physics.
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31.15.E- Density-functional theory
34.70.+e Charge transfer
33.80.-b Photon interactions with molecules
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Optimization of density matrix functionals by the Hartree–Fock–Bogoliubov method

Viktor N. Staroverov and Gustavo E. Scuseria

J. Chem. Phys. 117, 11107 (2002); http://dx.doi.org/10.1063/1.1523060 (6 pages) | Cited 17 times

Online Publication Date: 11 December 2002

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It is demonstrated that the “corrected Hartree–Fock” (CHF) density matrix functional proposed by Csányi and Arias is identical with the Hartree–Fock–Bogoliubov (HFB) functional of the generalized density matrix up to the sign of the pairing energy term. Using this analogy, variational CHF calculations can be performed much more efficiently by solving the HFB equations for the generalized density matrix than by optimizing separately the natural orbitals and their occupations numbers. A family of CHF-type functionals with a scaled pairing energy is introduced and compared to the closely related antisymmetrized geminal power method. © 2002 American Institute of Physics.
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31.15.xr Self-consistent-field methods
31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.xt Variational techniques
02.60.Pn Numerical optimization

Helium dimer dispersion forces and correlation potentials in density functional theory

Mark J. Allen and David J. Tozer

J. Chem. Phys. 117, 11113 (2002); http://dx.doi.org/10.1063/1.1522715 (8 pages) | Cited 52 times

Online Publication Date: 11 December 2002

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The dispersion interaction in the helium dimer is considered from the viewpoint of the force on a nucleus. At large internuclear separations, Brueckner coupled cluster BD(T) forces agree well with near-exact dispersion forces. The atomic density distortion associated with the dispersion force is quantified by comparing the BD(T) dimer density with a superposition of atomic densities. For density functional theory calculations in the Hartree–Fock–Kohn–Sham (HFKS) formalism, the accuracy of the dispersion force is governed by the correlation potential. Calculations using the conventional Lee–Yang–Parr [Phys. Rev. B 37, 785 (1988)] potential only generate a small density distortion, giving forces significantly smaller than BD(T). The BD(T) electron densities are therefore used to determine improved correlation potentials using a modified Zhao–Morrison–Parr (ZMP) approach [Phys. Rev. A 50, 2138 (1994)]. HFKS calculations using these ZMP potentials quantitatively reproduce the distortion, giving dispersion forces in good agreement with BD(T). The dimer ZMP correlation potential is partitioned into two parts, one equal to the sum of two unperturbed spherical atomic correlation potentials and the other representing an interaction potential. HFKS calculations using the former do not generate the distortion; forces are close to Hartree–Fock. Calculations using the latter do generate the distortion, giving forces essentially identical to those from the full dimer potential. The origin of the distortion is traced to the asymmetric structure of the interaction correlation potential in the vicinity of each nucleus. © 2002 American Institute of Physics.
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34.20.Gj Intermolecular and atom-molecule potentials and forces
31.15.E- Density-functional theory
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

The 248 nm photolysis of NO2/N2O4: Time-resolved Fourier transform infrared emission from NO and NO2, and quenching of NO (v = 5–8)

Claire Morrell, Ciara Breheny, Vanessa Haverd, Aimee Cawley, and Gus Hancock

J. Chem. Phys. 117, 11121 (2002); http://dx.doi.org/10.1063/1.1521724 (10 pages) | Cited 13 times

Online Publication Date: 11 December 2002

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The photolysis of NO2 and N2O4 has been studied at 248 nm by observations of time-resolved Fourier transform infrared emission from the photofragments. The photolysis of NO2 produces emission in the Δv = −1 and −2 fundamental and overtone bands of NO(X 2Π), and spectral analysis yields a broad Gaussian-type distribution in the vibrational levels v = 2–8, in good agreement with one of two previously reported initial nascent quantum state distributions. Quenching of the higher levels (v = 5–8) of NO in collisions with NO2 produces rate constants which increase with increasing v with values between 0.91 and 3.5×10−11 cm3 molecule−1 s−1. The process is shown to have a larger component of resonance energy transfer from NO(v) to NO2(0,0,1) than previously reported values for the rate constants at lower v which are further from resonance. A fast component of IR emission from the nascent excited states of NO2 is observed, together with slower decaying emissions near 1450 and 2750 cm−1, assigned as Δν3 = −1 and Δν1 = Δν3 = −1 transitions from high vibrational levels of the ground state formed by quenching of electronically excited NO2 produced from the photolysis of N2O4. A comparison is made of these IR bands with similar features seen in the IR emission from NO2 following electronic excitation in the visible region below its dissociation limit. Further emission near 1880 cm−1 accompanies the photolysis of N2O4, and is tentatively assigned to the direct formation of NO as a photolysis product, with a non-negligible quantum yield in low vibrational levels. © 2002 American Institute of Physics.
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82.50.Hp Processes caused by visible and UV light
82.53.Eb Pump probe studies of photodissociation
33.80.Gj Diffuse spectra; predissociation, photodissociation

Role of isomerization channel in unimolecular dissociation reaction H2CO→H2+CO: Ab initio global potential energy surface and classical trajectory analysis

Takehiro Yonehara and Shigeki Kato

J. Chem. Phys. 117, 11131 (2002); http://dx.doi.org/10.1063/1.1523058 (8 pages) | Cited 22 times

Online Publication Date: 11 December 2002

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We constructed a full dimensional potential energy function of H2CO that can describe both the dissociation and isomerization channels by the modified Shepard interpolation method. Ab initio calculations at the MP2/cc-pVTZ level were carried out to obtain the local potential functions at about 4700 points. The interpolant points were sampled by classical trajectory calculations and by the grid searches in the internal coordinate space. Classical trajectory calculations were performed to examine the intramolecular dynamics associated with the dissociation as well as the product state distributions. The time scale of intramolecular vibrational energy randomization was much faster than that of the dissociation reaction. The dissociation rate was obtained from the classical trajectory results and the effect of the isomerization channel on the dissociation was estimated. The calculated rate constants were compared with those by Rice–Ramsperger–Kassel–Marcus theory. © 2002 American Institute of Physics.
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82.30.Qt Isomerization and rearrangement
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.37.Np Single molecule reaction kinetics, dissociation, etc.
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Fd Collision theories; trajectory models

Quantum dynamics of the photoinitiated unimolecular dissociation of HOCO

Hua-Gen Yu and James T. Muckerman

J. Chem. Phys. 117, 11139 (2002); http://dx.doi.org/10.1063/1.1522711 (7 pages) | Cited 16 times

Online Publication Date: 11 December 2002

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The photodissociation dynamics of HOCO in the overtone νOH = 3 are studied using a time-dependent wave packet dynamics approach. The dynamics calculations are carried out using a four-dimensional planar model in which the terminal C☒O bond (spectator) is fixed at its equilibrium bond distance in the trans-HOCO conformer based on an empirical potential energy surface for HOCO fit to accurate ab initio calculations of the stationary point energies. The branching fraction into the H+CO2 products, and the resonance states associated with νOH = 3 are investigated in detail. © 2002 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
82.37.Vb Single molecule photochemistry
31.15.A- Ab initio calculations
82.20.Kh Potential energy surfaces for chemical reactions

Vibronic spectroscopy of the H-bonded aminophenol–water complex

P. S. Meenakshi, N. Biswas, and S. Wategaonkar

J. Chem. Phys. 117, 11146 (2002); http://dx.doi.org/10.1063/1.1523059 (6 pages) | Cited 9 times

Online Publication Date: 11 December 2002

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In this work, the vibronic spectroscopy of the p-aminophenol–water 1:1 complex is presented. The S1 vibrational energy levels of the complex were characterized by REMPI spectroscopy up to 2500 cm−1 above the band origin. The dispersed fluorescence spectra were recorded for the B.O., 6a01 and I02 excitations to characterize the vibrational levels in the S0 state of the complex. Stimulated ion depletion spectroscopy was carried out to determine the higher vibrational levels of the ground state all the way up to ∼3075 cm−1. The structure and the vibrational levels of the AP–W1 complex were calculated ab initio at the HF level and DFT with B3LYP functional for S0, and CIS level for S1 using 6-31G∗∗ basis set. The structure of the AP–W1 complex compared well with the earlier calculations for this case as well as the other ROH–water (R=aromatic group) complexes reported in the literature. However, the redshift in the electronic band origin was almost half of that observed in other cases. A good correlation was shown to exist between the electronic red shifts and the respective pKa∗ values (the pKa in the excited state). © 2002 American Institute of Physics.
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33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.15.Fm Bond strengths, dissociation energies
33.50.Dq Fluorescence and phosphorescence spectra

Fate of isolated CH(B2Σ−,v = 0,J) states in inelastic collisions with CO

M. Kind, P. Meden, and F. Stuhl

J. Chem. Phys. 117, 11152 (2002); http://dx.doi.org/10.1063/1.1522714 (6 pages) | Cited 2 times

Online Publication Date: 11 December 2002

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The kinetic fate of the single rotational states 0 ⩽ N ⩽ 7 of electronically excited CH(B2Σ−,v = 0) radicals has been studied in the gas phase at room temperature in the presence of CO. Rate constants of the state-to-state relaxation are presented. Further, rate constants were determined for the electronic quenching of single-N states and are compared with the corresponding data for CH(A2Δ,v = 0). The radiative lifetimes of the rotational levels are given, too. All these processes were found to be more efficient for the B state than those for the A state. Further, collisional mixing of the B with the A state is described quantitatively. © 2002 American Institute of Physics.
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34.50.Ez Rotational and vibrational energy transfer
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.50.Dq Fluorescence and phosphorescence spectra
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

On the theoretical determination of the static dipole polarizability of intermediate size silicon clusters

Víctor E. Bazterra, María C. Caputo, Marta B. Ferraro, and Patricio Fuentealba

J. Chem. Phys. 117, 11158 (2002); http://dx.doi.org/10.1063/1.1521761 (8 pages) | Cited 19 times

Online Publication Date: 11 December 2002

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The B3PW91 method of the density functional theory has been applied to the study of the dipole polarizability of medium size silicon clusters employing pseudopotential on all of them. All electron calculations have been performed for those clusters with less than nine atoms. In addition, we have optimized the structures of the clusters with less than ten atoms. On using the modified genetic algorithm, fourteen conformers of silicon isomers with nine atoms have been determined. The corresponding geometry of these clusters was optimized and their relative stability determined. The calculated polarizabilities are compared with experimental data and previous theoretical results. © 2002 American Institute of Physics.
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36.40.-c Atomic and molecular clusters
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.E- Density-functional theory

Elastic and rotationally inelastic differential cross sections for He+H2O collisions

Jesko Brudermann, Christof Steinbach, Udo Buck, Konrad Patkowski, and Robert Moszynski

J. Chem. Phys. 117, 11166 (2002); http://dx.doi.org/10.1063/1.1521726 (9 pages) | Cited 10 times

Online Publication Date: 11 December 2002

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Elastic and rotationally inelastic cross sections have been measured for He+H2O scattering at two collision energies, 66.3 and 99.0 meV, using the crossed molecular beam technique. The inelastic events are detected by time-of-flight analysis of the scattered He atoms. The data are converted to elastic differential cross sections and inelastic angular-dependent energy loss spectra in the center-of-mass system. They are compared with averaged, full close-coupling calculations of state-to-state cross sections for rotational excitation based on a newly calculated ab initio potential using symmetry-adapted perturbation theory. The agreement with the elastic differential cross sections is excellent. The energy loss spectra are reproduced satisfactorily and among the largest differential cross sections that contributed to the measurements are excitations around all three possible axes for ΔJ = 1 but a preference of the excitation around the in-plane C axis for ΔJ = 2 transitions. © 2002 American Institute of Physics.
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34.50.Ez Rotational and vibrational energy transfer
31.15.A- Ab initio calculations
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
31.15.xp Perturbation theory

Heats of formation of phosphorus compounds determined by current methods of computational quantum chemistry

Naomi L. Haworth and George B. Bacskay

J. Chem. Phys. 117, 11175 (2002); http://dx.doi.org/10.1063/1.1521760 (13 pages) | Cited 12 times

Online Publication Date: 11 December 2002

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The heats of formation of a range of phosphorus containing molecules (P2, P4, PH, PH2, PH3, P2H2, P2H4, PO, PO2, PO3, P2O, P2O2, HPO, HPOH, H2POH, H3PO, HOPO, and HOPO2) have been determined by high level quantum chemical calculations. The equilibrium geometries and vibrational frequencies were computed via density functional theory, utilizing the B3LYP/6-31G(2df,p) functional and basis set. Atomization energies were obtained by the application of ab initio coupled cluster theory with single and double excitations from (spin)-restricted Hartree–Fock reference states with perturbative correction for triples [CCSD(T)], in conjunction with cc-pVnZ basis sets (n = T, Q, 5) which include an extra d function on the phosphorus atoms and diffuse functions on the oxygens, as recommended by Bauschlicher [J. Phys. Chem. A 103, 11126 (1999)]. The valence correlated atomization energies were extrapolated to the complete basis limit and corrected for core–valence (CV) correlation and scalar relativistic effects, as well as for basis set superposition errors (BSSE) in the CV terms. This methodology is effectively the same as the one adopted by Bauschlicher in his study of PO, PO2, PO3, HPO, HOPO, and HOPO2. Consequently, for these molecules the results of this work closely match Bauschlicher’s computed values. The theoretical heats of formation, whose accuracy is estimated as ranging from ±1.0 to ±2.5 kcal mol−1, are consistent with the available experimental data. The current set of theoretical data represent a convenient benchmark, against which the results of other computational procedures, such as G3, G3X, and G3X2, can be compared. Despite the fact that G3X2 [which is an approximation to the quadratic CI procedure QCISD(T,Full)/G3Xlarge] is a formally higher level theory than G3X, the heats of formation obtained by these two methods are found to be of comparable accuracy. Both reproduce the benchmark heats of formation on the average to within ±2 kcal mol−1 and, for these molecules at least, they are superior to the basic G3 method. The performance of G3X2 is further improved, however, by the incorporation of BSSE corrections in the CV component of the energies. All the G3n methods have difficulties, however, with molecules which have multiple or highly strained P–P bonds, such as P2 and P4.© 2002 American Institute of Physics.
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82.60.Cx Enthalpies of combustion, reaction, and formation
31.15.A- Ab initio calculations
31.15.bw Coupled-cluster theory
31.15.E- Density-functional theory
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