JCP Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

You Tube Flickr Twitter iResearch App Facebook

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue

22 Jun 2005

Volume 122, Issue 24, Articles (24xxxx)

Page 1 of 4 Pages Next Page | Jump to Page
back to top
RSS Feeds

Reaction of SO2 with Au/CeO2(111): Importance of O vacancies in the activation of gold

J. A. Rodriguez, M. Pérez, J. Evans, G. Liu, and J. Hrbek

J. Chem. Phys. 122, 241101 (2005); http://dx.doi.org/10.1063/1.1946748 (4 pages) | Cited 21 times

Online Publication Date: 27 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Synchrotron-based high-resolution photoemission was used to study the adsorption and chemistry of SO2 on Au/CeO2(111) and AuOx/CeO2 surfaces. The heat of adsorption of the molecule on Au nanoparticles supported on stoichiometric CeO2(111) was 4–7 kcal/mol larger than on Au(111). However, there was negligible dissociation of SO2 on the Au/CeO2(111) surfaces. The full decomposition of SO2 was observed only after introducing O vacancies in the ceria support. AuOx/CeO2 surfaces were found to be much less chemically active than Au/CeO2(111) or Au/CeO2−x(111) surfaces. The active sites in {Au+AuOx}/ceria catalysts should involve pure gold nanoparticles in contact with O vacancies.
Show PACS
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.35.Dv Composition, segregation; defects and impurities
68.35.Md Surface thermodynamics, surface energies
79.60.Jv Interfaces; heterostructures; nanostructures

Observation of resonant Interatomic Coulombic Decay in Ne clusters

S. Barth, S. Joshi, S. Marburger, V. Ulrich, A. Lindblad, G. Öhrwall, O. Björneholm, and U. Hergenhahn

J. Chem. Phys. 122, 241102 (2005); http://dx.doi.org/10.1063/1.1937395 (4 pages) | Cited 25 times

Online Publication Date: 29 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We have measured the electron spectra of Ne clusters after excitation with photon energies around the 2s inner valence threshold. At two photon energies below threshold, a resonantly enhanced surplus of low kinetic-energy electrons is observed. The kinetic energy of the peak does not vary with the photon energy and is slightly larger than the transition energy of Interatomic Coulombic Decay (ICD) above threshold. This leads us to assume that an ICD-like process is present. In analogy to the Auger and the resonant Auger decay this new phenomenon is termed resonant ICD.
Show PACS
36.40.Mr Spectroscopy and geometrical structure of clusters
33.80.-b Photon interactions with molecules

Relating kinetic rates and local energetic roughness by accelerated molecular-dynamics simulations

Donald Hamelberg, Tongye Shen, and J. Andrew McCammon

J. Chem. Phys. 122, 241103 (2005); http://dx.doi.org/10.1063/1.1942487 (4 pages) | Cited 26 times

Online Publication Date: 1 July 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We show that our accelerated molecular-dynamics (MD) approach can extend the time scale in all-atom MD simulations of biopolymers. We also show that this technique allows for the kinetic rate information to be recaptured. In deducing the kinetic rates, the relationship between the local energetic roughness of the potential-energy landscape and the effective diffusion coefficient is established. These are demonstrated on a very slow but important biomolecular process: the dynamics of cis–trans-isomerization of Ser–Pro motifs. We do not only recapture the slow kinetic rates, which is difficult in traditional MD, but also obtain the underlying roughness of the energy landscape of proteins at atomistic resolution.
Show PACS
87.14.E- Proteins
87.15.R- Reactions and kinetics
87.15.H- Dynamics of biomolecules
82.35.Pq Biopolymers, biopolymerization
82.39.Rt Reactions in complex biological systems
82.30.Qt Isomerization and rearrangement
82.20.Pm Rate constants, reaction cross sections, and activation energies

Different chemical dynamics for different conformers of biological molecules: Photoionization of glycine

D. Shemesh and R. B. Gerber

J. Chem. Phys. 122, 241104 (2005); http://dx.doi.org/10.1063/1.1937407 (4 pages) | Cited 6 times

Online Publication Date: 6 July 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Single-photon ionization dynamics of two conformers of glycine is studied by classical trajectory simulations using the semiempirical PM3 potential surface in “on the fly” calculations. Initial conditions for the trajectories are weighted according to the Wigner distribution function computed for the initial vibrational ground state. Vertical ionization in the spirit of the classical Franck–Condon principle is assumed. The dynamics of the two conformers are compared during the first 10 ps. The comparison shows very different dynamical behavior for the two conformers. In particular, the chemical fragmentation pathways differ in part. Also, one of the conformers gives much higher rates of conformational transitions, while the other conformer gives larger chemical fragmentation yields. The example shows significantly different chemical dynamics for two conformers close in energy and separated by a low barrier.
Show PACS
87.15.H- Dynamics of biomolecules
87.15.M- Spectra of biomolecules
87.15.R- Reactions and kinetics
33.80.Eh Autoionization, photoionization, and photodetachment
82.20.Kh Potential energy surfaces for chemical reactions
33.80.Gj Diffuse spectra; predissociation, photodissociation
82.20.Fd Collision theories; trajectory models
82.20.Nk Classical theories of reactions and/or energy transfer
back to top
RSS Feeds
back to top Theoretical Methods and Algorithms

An efficient approach for the calculation of Franck–Condon integrals of large molecules

Marc Dierksen and Stefan Grimme

J. Chem. Phys. 122, 244101 (2005); http://dx.doi.org/10.1063/1.1924389 (9 pages) | Cited 45 times

Online Publication Date: 24 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A general and efficient approach for the calculation of Franck–Condon integrals (FCIs) of large molecules is presented. In a first step, by exploiting the diagonally dominant and sparse structure of the Duschinsky matrix, a model system is constructed for which the Duschinsky matrix takes a block-diagonal form. For each of these blocks separately, the FCIs are calculated discarding all below a certain threshold. From those integrals retained the FCIs of the model system are obtained by simple multiplication. These serve as an estimate for the FCIs of the exact system which are calculated for those integrals which lie above a certain threshold. By systematically decreasing the threshold, the simulation can be reliably converged to the exact result with an arbitrary accuracy. Using this scheme, a considerable reduction of the number of FCIs which have to be calculated is achieved which leads to an improved scaling behavior of the computational effort with system size. The approach has been tested thoroughly for a set of molecules including difficult cases. For the larger systems a speedup of up to three orders of magnitude compared to an exact calculation is observed while the errors can be kept negligible. With this approach accurate calculations of FCIs are feasible also for large molecules encountered in “real-life” chemistry, especially biochemistry and material science.
Show PACS
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
31.15.xv Molecular dynamics and other numerical methods

Open-shell localized Hartree–Fock method based on the generalized adiabatic connection Kohn–Sham formalism for a self-consistent treatment of excited states

Vincenzo Vitale, Fabio Della Sala, and Andreas Görling

J. Chem. Phys. 122, 244102 (2005); http://dx.doi.org/10.1063/1.1938868 (17 pages) | Cited 11 times

Online Publication Date: 24 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
An effective exact-exchange Kohn–Sham approach for the treatment of excited electronic states, the generalized adiabatic connection open-shell localized Hartree–Fock (GAC-OSLHF) method is presented. The GAC-OSLHF method is based on the generalized adiabatic connection Kohn–Sham formalism and therefore capable of treating excited electronic states, which are not the energetically lowest of their symmetry. The method is self-interaction free and allows for a fully self-consistent computation of excited valence as well as Rydberg states. Results for atoms and small- and medium-size molecules are presented and compared to restricted open-shell Hartree–Fock (ROHF) and time-dependent density-functional results as well as to experimental data. While GAC-OSLHF and ROHF results are quite close to each other, the GAC-OSLHF method shows a much better convergence behavior. Moreover, the GAC-OSLHF method as a Kohn–Sham method, in contrast to the ROHF approach, represents a framework which allows also for a treatment of correlation besides an exchange by appropriate functionals. In contrast to the common time-dependent density-functional methods, the GAC-OSLHF approach is capable of treating doubly or multiply excited states and can be easily applied to molecules with an open-shell ground state. On the nodal planes of the energetically highest occupied orbital, the local multiplicative GAC-OSLHF exchange potential asymptotically approaches a different, i.e., nonzero, value than in other regions, an asymptotic behavior which is known from exact Kohn–Sham exchange potentials of ground states of molecules.
Show PACS
31.15.xr Self-consistent-field methods
31.15.E- Density-functional theory
33.15.Bh General molecular conformation and symmetry; stereochemistry

Electronic quantum Monte Carlo calculations of atomic forces, vibrations, and anharmonicities

Myung Won Lee, Massimo Mella, and Andrew M. Rappe

J. Chem. Phys. 122, 244103 (2005); http://dx.doi.org/10.1063/1.1924690 (6 pages) | Cited 13 times

Online Publication Date: 24 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Atomic forces are calculated for first-row monohydrides and carbon monoxide within electronic quantum Monte Carlo (QMC). Accurate and efficient forces are achieved by using an improved method for moving variational parameters in variational QMC. Newton’s method with singular value decomposition (SVD) is combined with steepest-descent (SD) updates along directions rejected by the SVD, after initial SD steps. Dissociation energies in variational and diffusion QMC agree well with the experiment. The atomic forces agree quantitatively with potential-energy surfaces, demonstrating the accuracy of this force procedure. The harmonic vibrational frequencies and anharmonicity constants, derived from the QMC energies and atomic forces, also agree well with the experimental values.
Show PACS
34.20.Cf Interatomic potentials and forces
31.15.xt Variational techniques
33.15.Fm Bond strengths, dissociation energies
31.50.-x Potential energy surfaces
33.15.Mt Rotation, vibration, and vibration-rotation constants

Two-photon absorption in solution by means of time-dependent density-functional theory and the polarizable continuum model

Luca Frediani, Zilvinas Rinkevicius, and Hans Ågren

J. Chem. Phys. 122, 244104 (2005); http://dx.doi.org/10.1063/1.1944727 (12 pages) | Cited 27 times

Online Publication Date: 28 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present the first study of two-photon absorption (TPA) of solvated molecules based on direct evaluation of TPA cross sections from the quadratic response of time-dependent perturbations. A set of prototypical two-photon (TP) chromophores has been selected and analyzed: a pure π system (t-stilbene) and its substituted homologs obtained employing a donor (D) and an acceptor (A) group to probe the solvent effects along the series π, D−π−D, A−π−D, and A−π−A. For the selected systems we have calculated the TPA cross sections in different environments by means of the polarizable continuum model. The data have been analyzed to evaluate how the structural and environmental parameters contribute to the final two-photon absorption cross section. These include molecular structure, geometry relaxation in solution, polarity, and refractive index of the solvent. The performances of the three common functionals SVWN, BLYP, and B3LYP have been compared. The results show a significant solvent dependence of the TPA cross section and an unusual trend when passing from cyclohexane to water. The data have also been rationalized in terms of the main orbital excitations leading to the transitions. Finally, trends along the series have been described and comparison with experiments and previous calculations has been drawn.
Show PACS
61.20.Lc Time-dependent properties; relaxation
61.20.Gy Theory and models of liquid structure
61.25.Em Molecular liquids
31.15.E- Density-functional theory
31.15.xp Perturbation theory
33.80.-b Photon interactions with molecules
31.70.Dk Environmental and solvent effects
33.15.Bh General molecular conformation and symmetry; stereochemistry

Statistical mechanical theory for steady-state systems. III. Heat flow in a Lennard-Jones fluid

Phil Attard

J. Chem. Phys. 122, 244105 (2005); http://dx.doi.org/10.1063/1.1942491 (11 pages) | Cited 8 times

Online Publication Date: 28 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A statistical mechanical theory for heat flow is developed based upon the second entropy for dynamical transitions between energy moment macrostates. The thermal conductivity, as obtained from a Green–Kubo integral of a time correlation function, is derived as an approximation from these more fundamental theories, and its short-time dependence is explored. A new expression for the thermal conductivity is derived and shown to converge to its asymptotic value faster than the traditional Green–Kubo expression. An ansatz for the steady-state probability distribution for heat flow down an imposed thermal gradient is tested with simulations of a Lennard-Jones fluid. It is found to be accurate in the high-density regime at not too short times, but not more generally. The probability distribution is implemented in Monte Carlo simulations, and a method for extracting the thermal conductivity is given.
Show PACS
61.20.Ja Computer simulation of liquid structure
65.20.-w Thermal properties of liquids
47.27.T- Turbulent transport processes

Novel Monte Carlo scheme for systems with short-ranged interactions

Georgios C. Boulougouris and Daan Frenkel

J. Chem. Phys. 122, 244106 (2005); http://dx.doi.org/10.1063/1.1931652 (8 pages) | Cited 8 times

Online Publication Date: 29 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We propose a Monte Carlo (MC) sampling algorithm to simulate systems of particles interacting via very short-ranged discontinuous potentials. Such models are often used to describe protein solutions or colloidal suspensions. Most normal MC algorithms fail for such systems because, at low temperatures, they tend to get trapped in local potential-energy local minima due to the short range of the pair potential. To circumvent this problem, we have devised a scheme that changes the construction of trial moves in such a way that the potential-energy difference between initial and final states drops out of the acceptance rule for the Monte Carlo trial moves. This approach allows us to simulate systems with short-ranged attraction under conditions that were unreachable up to now.
Show PACS
61.20.Ja Computer simulation of liquid structure
02.70.Uu Applications of Monte Carlo methods

Computing resonance energies, widths, and wave functions using a Lanczos method in real arithmetic

Jean Christophe Tremblay and Tucker Carrington

J. Chem. Phys. 122, 244107 (2005); http://dx.doi.org/10.1063/1.1942494 (11 pages) | Cited 5 times

Online Publication Date: 30 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We introduce new ideas for calculating resonance energies and widths. It is shown that a non-Hermitian–Lanczos approach can be used to compute eigenvalues of H+W, where H is the Hamiltonian and W is a complex absorbing potential (CAP), without evaluating complex matrix-vector products. This is done by exploiting the link between a CAP-modified Hamiltonian matrix and a real but nonsymmetric matrix U suggested by Mandelshtam and Neumaier [ J. Theor. Comput. Chem. 1, 1 (2002) ] and using a coupled-two-term Lanczos procedure. We use approximate resonance eigenvectors obtained from the non-Hermitian–Lanczos algorithm and a very good CAP to obtain very accurate energies and widths without solving eigenvalue problems for many values of the CAP strength parameter and searching for cusps. The method is applied to the resonances of HCO. We compare properties of the method with those of established approaches.
Show PACS
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
02.10.Ud Linear algebra
02.10.Yn Matrix theory

Local correlation potentials from Brueckner coupled-cluster theory

A. Heßelmann

J. Chem. Phys. 122, 244108 (2005); http://dx.doi.org/10.1063/1.1947167 (8 pages) | Cited 6 times

Online Publication Date: 30 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Local correlation potentials have been obtained from the nonlocal Brueckner coupled-cluster correlation potentials for the rare-gas atoms He, Ne, and Ar and the CO molecule. It is shown that the local correlation potential can mainly be expressed as a sum of two components: a “pure” correlation part and a relaxation contribution. While the total correlation potentials show an oscillating behavior near the nuclei, indicating the atomic shell structure, their components decrease rather monotonously, with a step structure in case of Ne and Ar. By looking at the determinantal overlap and one-electron properties it has been found that the orbitals obtained from these local potentials form a determinant which very well corresponds with the Brueckner determinant. Thus the previously found closeness between the Hartree–Fock determinant and the exchange-only Kohn–Sham determinant [ Della Sala and Görling, J. Chem. Phys. 115, 5718 (2001) ] is confirmed also for the correlated case.
Show PACS
31.15.bw Coupled-cluster theory

Gradient-corrected density-functional potential with correct asymptotic behavior: Application to interconfigurational energies in transition-metal atoms

Chung-Yuan Ren

J. Chem. Phys. 122, 244109 (2005); http://dx.doi.org/10.1063/1.1938188 (5 pages) | Cited 2 times

Online Publication Date: 5 July 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Based upon the optimized effective potential with the self-interaction correction, we present in this paper an alternative gradient-corrected density-functional approximation with the proper long-range behavior of the effective potential. As applied to the study of the interconfigurational energies of the whole transition-metal atoms, the present combination of the gradient-corrected contribution and the modified optimized effective potential lead the s ionization to the excellent agreement with the experiment. The calculated d ionizations and s–d transition energies are also discussed.
Show PACS
31.15.E- Density-functional theory
34.20.Cf Interatomic potentials and forces
32.50.+d Fluorescence, phosphorescence (including quenching)

Density functional energy decomposition into one- and two-atom contributions

Sergei F. Vyboishchikov, Pedro Salvador, and Miquel Duran

J. Chem. Phys. 122, 244110 (2005); http://dx.doi.org/10.1063/1.1935511 (13 pages) | Cited 16 times

Online Publication Date: 6 July 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The present work provides a generalization of Mayer’s energy decomposition for the density-functional theory (DFT) case. It is shown that one- and two-atom Hartree–Fock energy components in Mayer’s approach can be represented as an action of a one-atom potential VA on a one-atom density ρA or ρB. To treat the exchange-correlation term in the DFT energy expression in a similar way, the exchange-correlation energy density per electron is expanded into a linear combination of basis functions. Calculations carried out for a number of density functionals demonstrate that the DFT and Hartree–Fock two-atom energies agree to a reasonable extent with each other. The two-atom energies for strong covalent bonds are within the range of typical bond dissociation energies and are therefore a convenient computational tool for assessment of individual bond strength in polyatomic molecules. For nonspecific nonbonding interactions, the two-atom energies are low. They can be either repulsive or slightly attractive, but the DFT results more frequently yield small attractive values compared to the Hartree–Fock case. The hydrogen bond in the water dimer is calculated to be between the strong covalent and nonbonding interactions on the energy scale.
Show PACS
31.15.E- Density-functional theory
31.15.xr Self-consistent-field methods
33.15.Fm Bond strengths, dissociation energies

Coarse graining using pretabulated potentials: Liquid benzene

Nikolas Zacharopoulos, Niki Vergadou, and Doros N. Theodorou

J. Chem. Phys. 122, 244111 (2005); http://dx.doi.org/10.1063/1.1948370 (11 pages) | Cited 7 times

Online Publication Date: 7 July 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The large length and time scales involved in polymer simulation render the atomistic representation of polymer systems a computationally expensive and unnecessarily detailed procedure. We present a novel coarse-graining method for the description of nonbonded interactions between moieties composing the monomeric units of polymers, phenyl rings in particular. The method is based on the determination of the interactions between pairs of moieties from precalculated and tabulated values of the energy between the moieties in their atomistic representation. Validation of the method is performed by carrying out coarse-grained and fully atomistic simulations of a benzene liquid, where structural and thermodynamic properties at various state points are compared. The effects of the coarse grained model assumptions and of the energy table dimension and discretization are investigated. Results are also presented for the reverse mapping from the coarse grained to the fully atomistic representation.
Show PACS
61.25.H- Macromolecular and polymers solutions; polymer melts
61.20.-p Structure of liquids
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

The vibrational predissociation spectra of the H5O2+∙RGn(RG = Ar,Ne) clusters: Correlation of the solvent perturbations in the free OH and shared proton transitions of the Zundel ion

Nathan I. Hammer, Eric G. Diken, Joseph R. Roscioli, Mark A. Johnson, Evgeniy M. Myshakin, Kenneth D. Jordan, Anne B. McCoy, Xinchuan Huang, Joel M. Bowman, and Stuart Carter

J. Chem. Phys. 122, 244301 (2005); http://dx.doi.org/10.1063/1.1927522 (10 pages) | Cited 73 times

Online Publication Date: 24 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
 Predissociation spectra of the H5O2+∙RGn(RG = Ar,Ne) cluster ions are reported in energy regions corresponding to both the OH stretching (3350–3850 cm−1) and shared proton (850–1950 cm−1) vibrations. The two free OH stretching bands displayed by the Ne complex are quite close to the band origins identified earlier in bare H5O2+ [ L. I. Yeh, M. Okumura, J. D. Myers, J. M. Price, and Y. T. Lee, J. Chem. Phys. 91, 7319 (1989) ], indicating that the symmetrical H5O2+ “Zundel” ion remains largely intact in H5O2+∙Ne. The low-energy spectrum of the Ne complex is simpler than that observed previously for H5O2+∙Ar, and is dominated by two sharp transitions at 928 and 1047 cm−1, with a weaker feature at 1763 cm−1. The H5O2+∙Arn,n = 1–5 spectra generally exhibit complex band structures reflecting solvent-induced symmetry breaking of the Zundel core ion. The extent of solvent perturbation is evaluated with electronic structure calculations, which predict that the rare gas atoms should attach to the spectator OH groups of H5O2+ rather than to the shared proton. In the asymmetric complexes, the shared proton resides closer to the more heavily solvated water molecule, leading to redshifts in the rare gas atom-solvated OH stretches and to blueshifts in the shared proton vibrations. The experimental spectra are compared with recent full-dimensional vibrational calculations (diffusion Monte Carlo and multimode/vibrational configuration interaction) on H5O2+. These results are consistent with assignment of the strong low-energy bands in the H5O2+∙Ne spectrum to the vibration of the shared proton mostly along the O–O axis, with the 1763 cm−1 band traced primarily to the out-of-phase, intramolecular bending vibrations of the two water molecules.
Show PACS
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
36.40.Mr Spectroscopy and geometrical structure of clusters
33.70.Jg Line and band widths, shapes, and shifts

Two-color resonantly enhanced multiphoton ionization and zero-kinetic-energy photoelectron spectroscopy of jet-cooled indan

Yonggang He and Wei Kong

J. Chem. Phys. 122, 244302 (2005); http://dx.doi.org/10.1063/1.1938927 (6 pages) | Cited 5 times

Online Publication Date: 24 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We report studies of supersonically cooled indan using two-color resonantly enhanced multiphoton ionization and two-color zero-kinetic-energy photoelectron spectroscopy. With the aid of ab initio and density-functional calculations, vibrational modes of the first electronically excited state of the neutral species and those of the cation have been assigned, and the adiabatic ionization energy has been determined to be 68458±5 cm−1. Similar to the ground state and the first electronically excited state of the neutral molecule, the ground state of the cation is also proven to be nonplanar, with an estimated barrier of 213 cm−1 and a puckering angle of 15.0°. These conclusions will be discussed in comparison with a previous study of an indan derivative 1,3-benzodioxole.
Show PACS
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
31.15.A- Ab initio calculations
31.15.E- Density-functional theory
31.50.Bc Potential energy surfaces for ground electronic states
31.50.Df Potential energy surfaces for excited electronic states
33.60.+q Photoelectron spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis

Valence photoionization dynamics in circular dichroism of chiral free molecules: The methyl-oxirane

S. Stranges, S. Turchini, M. Alagia, G. Alberti, G. Contini, P. Decleva, G. Fronzoni, M. Stener, N. Zema, and T. Prosperi

J. Chem. Phys. 122, 244303 (2005); http://dx.doi.org/10.1063/1.1940632 (6 pages) | Cited 23 times

Online Publication Date: 27 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The dynamical behavior of circular dichroism for valence photoionization processes in pure enantiomers of randomly oriented methyl-oxirane molecules has been studied by circularly polarized synchrotron radiation. Experimental results of the dichroism coefficient obtained for valence photoionization processes as a function of photon energy have been compared with theoretical values predicted by state-of-the-art ab initio density-functional theory. The circular dichroism measured at low electron kinetic energies was as large as 11%. Trends in the experimental dynamical behavior of the dichroism coefficients Di(ω) have been observed. Agreement between experimental and theoretical results permits unambiguous identification of the enantiomer and of the individual orbitals.
Show PACS
33.55.+b Optical activity and dichroism
33.80.Eh Autoionization, photoionization, and photodetachment
31.15.A- Ab initio calculations
31.15.E- Density-functional theory
33.15.Bh General molecular conformation and symmetry; stereochemistry

Effect of rotational energy on the reaction Li+HF(υ = 0,j)→LiF+H: An experimental and computational study

Rolf Bobbenkamp, Alessandra Paladini, Andrea Russo, H. J. Loesch, Marta Menéndez, Enrique Verdasco, F. J. Aoiz, and H.-J. Werner

J. Chem. Phys. 122, 244304 (2005); http://dx.doi.org/10.1063/1.1942496 (18 pages) | Cited 6 times

Online Publication Date: 27 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In a crossed molecular-beam study we have measured angular and time-of-flight distributions of the product LiF from the reaction Li+HF(υ = 0)→LiF+H at various collision energies ranging from 97 to 363 meV for three markedly different rotational state distributions of HF obtained at nozzle temperatures close to 315, 510, and 850 K. Particularly, for the low and intermediate collision energies we observe significant effects of the varying j-state populations on the shape of the product angular distributions. At 315 K an additional feature appears in the angular distributions which is interpreted as being due to scattering from HF dimers. The experimental data are compared with simulations of the monomer reaction based on extensive quasiclassical trajectory calculations on a new state-of-the-art ab initio potential energy surface. We find an overall good agreement between the theoretical simulations and the experimental data for the title reaction, especially at the highest HF nozzle temperature.
Show PACS
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Hf Product distribution
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Fd Collision theories; trajectory models
34.50.Lf Chemical reactions
33.20.Sn Rotational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

A new ab initio potential-energy surface of HO2(X2A″) and quantum studies of HO2 vibrational spectrum and rate constants for the H+O2↔O+OH reactions

Chuanxiu Xu, Daiqian Xie, Dong Hui Zhang, Shi Ying Lin, and Hua Guo

J. Chem. Phys. 122, 244305 (2005); http://dx.doi.org/10.1063/1.1944290 (8 pages) | Cited 41 times

Online Publication Date: 27 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A new global potential-energy surface for the ground electronic state of HO2(X2A″) has been developed by three-dimensional cubic spline interpolation of more than 15 000 ab initio points, which were calculated at the multireference configuration-interaction level with Davidson correction using the augmented correlation-consistent polarized valence quadruple zeta basis set. Low-lying vibrational states were obtained in this new potential using the Lanczos method and assigned. The calculated vibrational frequencies are in much better agreement with the available experimental band origins than those obtained from a previous potential. In addition, rate constants for the H+O2↔O+OH reactions were obtained using a wave-packet-based statistical model. Reasonably good agreement with experimental data was obtained. These results demonstrate the accuracy of the potential.
Show PACS
31.50.Bc Potential energy surfaces for ground electronic states
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.A- Ab initio calculations
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Pm Rate constants, reaction cross sections, and activation energies

HF in clusters of molecular hydrogen. I. Size evolution of quantum solvation by parahydrogen molecules

Hao Jiang and Zlatko Bačić

J. Chem. Phys. 122, 244306 (2005); http://dx.doi.org/10.1063/1.1927528 (10 pages) | Cited 9 times

Online Publication Date: 27 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a theoretical study of the quantum solvation of the HF molecule by a small number of parahydrogen molecules, having n = 1–13 solvent particles. The minimum-energy cluster structures determined for n = 1–12 have all of the H2 molecules in the first solvent shell. The first solvent shell closes at n = 12 and its geometry is icosahedral, with the HF molecule at the center. The quantum-mechanical ground-state properties of the clusters are calculated exactly using the diffusion Monte Carlo method. The zero-point energy of (p-H2)nHF clusters is unusually large, amounting to 86% of the potential well depth for n>7. The radial probability distribution functions (PDFs) confirm that the first solvent shell is complete for n = 12, and that the 13th p-H2 molecule begins to fill the second solvent shell. The p-H2 molecules execute large-amplitude motions and are highly mobile, making the solvent cage exceptionally fluxional. The anisotropy of the solvent, very pronounced for small clusters, decreases rapidly with increasing n, so that for n ∼ 8–9 the solvent environment is practically isotropic. The analysis of the pair angular PDF reveals that for a given n, the parahydrogen solvent density around the HF is modulated in a pattern which clearly reflects the lowest-energy cluster configuration. The rigidity of the solvent clusters displays an interesting size dependence, increasing from n = 6 to 9, becoming floppier for n = 10, and increasing again up to n = 12, as the solvent shell is filled. The rigidity of the solvent cage appears to reach its maximum for n = 12, the point at which the first solvent shell is closed.
Show PACS
36.40.Mr Spectroscopy and geometrical structure of clusters
31.70.Dk Environmental and solvent effects
82.30.Nr Association, addition, insertion, cluster formation
31.50.Bc Potential energy surfaces for ground electronic states
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.15.Bh General molecular conformation and symmetry; stereochemistry

Ab initio study of small acetonitrile cluster anions

Toshiyuki Takayanagi

J. Chem. Phys. 122, 244307 (2005); http://dx.doi.org/10.1063/1.1944722 (8 pages) | Cited 6 times

Online Publication Date: 27 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Ab initio electronic structure calculations have been performed for (CH3CN)2− and (CH3CN)3− cluster anions using a diffuse basis set. We found both the dipole-bound structures and internal structures, where in the former structure an excess electron is mainly distributed on the surface of the cluster while an excess electron is internally trapped in the latter configuration. The optimized structures found for cluster anions were compared to those for neutral clusters. Potential-energy surfaces were also plotted as a function of appropriate internal coordinates in order to understand the interconversions of the optimized structures of clusters. The relative stabilities of the optimized confirmers have been discussed on the basis of the characteristics of these potential surfaces, relative energies, and electron vertical detachment energies.
Show PACS
31.15.A- Ab initio calculations
36.40.Qv Stability and fragmentation of clusters
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.50.-x Potential energy surfaces

The 4051-Å band of C3 (math math−math math, 000-000): Perturbed low-J lines and lifetime measurements

Guiqiu Zhang, Kan-Sen Chen, Anthony J. Merer, Yen-Chu Hsu, Wei-Jan Chen, S. Shaji, and Yean-An Liao

J. Chem. Phys. 122, 244308 (2005); http://dx.doi.org/10.1063/1.1928827 (8 pages) | Cited 6 times

Online Publication Date: 28 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Rotational analyses have been carried out at high resolution for the 000-000 and 000-100 bands of the math math−math math transition of supersonic jet-cooled C3. Two different spectra have been recorded for each band, using time gatings of 20–150 and 800–2300 ns. At the shorter time delay the spectra show only the lines observed by many previous workers. At the longer time delay many extra lines appear, some of which have been observed previously by [ McCall et al.Chem. Phys. Lett. 374, 583 (2003) ] in cavity ring-down spectra of jet-cooled C3. Detailed analysis of these extra lines shows that at least two long-lived states perturb the math math, 000 state. One of these appears to be a math vibronic state, which may possibly be a high vibrational level of the math math state, and the other appears to be a P = 1 state with a low rotational constant B. Our spectra also confirm the reassignment by McCall et al. of the R(0) line of the 000-000 band, which is consistent with the spectra recorded towards a number of stars that indicate the presence of C3 in the interstellar medium. Fluorescence lifetimes have been measured for a number of upper-state rotational levels. The rotational levels of the math math state have lifetimes in the range of 230–190 ns, decreasing slightly with J; the levels of the perturbing states have much longer lifetimes, with some of them showing biexponential decays. An improved value has been obtained for the ν1 vibrational frequency of the ground state, ν1 = 1224.4933±0.0029 cm−1.
Show PACS
33.20.Sn Rotational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.20.Tp Vibrational analysis
33.50.Dq Fluorescence and phosphorescence spectra
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Structure and energy difference of two isomers of He–CH3F

Kelly J. Higgins and William Klemperer

J. Chem. Phys. 122, 244309 (2005); http://dx.doi.org/10.1063/1.1940633 (12 pages) | Cited 8 times

Online Publication Date: 28 June 2005

Full Text: Read Online (HTML) | Download PDF


See Also: Publisher's Note

Show Abstract
The intermolecular potential surface of He–CH3F is investigated through ab initio calculations and microwave and millimeter-wave spectroscopies. The intermolecular potential is calculated at the fourth-order Møller–Plesset level with a large basis set including bond functions. Three minimums exist, the deepest of which is at the carbon end of the C–F axis and has a depth of 46.903 cm−1, the second deepest is in a T-shaped position relative to the C–F axis with a depth of 44.790 cm−1, and the shallowest is at the fluorine end of the C–F axis with a depth of 30.929 cm−1. The barrier to internal rotation of the CH3F subunit about its C–F axis is very low, thus leading to essentially free internal rotation and two separate sets of bound states correlating to ortho-CH3F (∣K∣ = 3n) for the ground, or A, internal rotor state upon which this study focuses, and to para-CH3F (∣K∣ = 3n±1) for the excited, or E, internal rotor state. Bound-state calculations of the A state performed using two different techniques show the lowest-energy state to have the helium localized in the T-shaped well with an energy of −11.460 cm−1, while two excited configurations of the A state have the helium localized either in the well at the carbon end (“linear”) with an energy of −7.468 cm−1 or in the well at the fluorine end (“antilinear”) with an energy of −4.805 cm−1. Spectroscopic observations confirm the predicted energy-level structure of the ground and first excited states. Sixteen transitions between 12 distinct energy levels have been observed, including pure rotational transitions of both the T-shaped ground state and the linear excited state, as well as rovibrational transitions between the ground state and the linear excited state. The energy difference between the T-shaped state and the linear state is measured to be 132 374.081(16) MHz. There is significant Coriolis mixing of the ground state JKaKc = 220 and the linear JK = 20 levels which aided in the observation of the T to linear transitions. This mixing and the T to linear energy difference are sensitive probes of the relative well depths of the two lowest minimums and are well predicted by the ab initio potential. Improved agreement between experiment and theory is obtained by morphing the correlation energy of the potential. He–CH3F is one of just a few atom-molecule complexes for which the ground-state geometry does not coincide with the global potential minimum.
Show PACS
34.20.Cf Interatomic potentials and forces
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.A- Ab initio calculations
33.20.Bx Radio-frequency and microwave spectra
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
31.15.ve Electron correlation calculations for atoms and ions: ground state
33.20.Sn Rotational analysis
33.20.Vq Vibration-rotation analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants

Decomposition of nitramine energetic materials in excited electronic states: RDX and HMX

Y. Q. Guo, M. Greenfield, and E. R. Bernstein

J. Chem. Phys. 122, 244310 (2005); http://dx.doi.org/10.1063/1.1929741 (6 pages) | Cited 24 times

Online Publication Date: 28 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Ultraviolet excitation (8-ns duration) is employed to study the decomposition of RDX (1,3,5-trinitro-1,3,5-triazacyclohexane) and HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane) from their first excited electronic states. Isolated RDX and HMX are generated in the gas phase utilizing a combination of matrix-assisted laser desorption and supersonic jet expansion techniques. The NO molecule is observed as one of the initial dissociation products by both time-of-flight mass spectroscopy and laser-induced fluorescence spectroscopy. Four different vibronic transitions of NO are observed: A math(v′ = 0)←X math(v″ = 0,1,2,3). Simulations of the NO rovibronic intensities for the A←X transitions show that dissociated NO from RDX and HMX is rotationally cold ( ∼ 20 K) and vibrationally hot ( ∼ 1800 K). Another potential initial product of RDX and HMX excited state dissociation could be OH, generated along with NO, perhaps from a HONO intermediate species. The OH radical is not observed in fluorescence even though its transition intensity is calculated to be 1.5 times that found for NO per radical generated. The HONO intermediate is thereby found not to be an important pathway for the excited electronic state decomposition of these cyclic nitramines.
Show PACS
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.-w Chemical kinetics and dynamics
Page 1 of 4 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close