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 Dec 1999

Volume 111, Issue 24, pp. 10747-11239

Page 1 of 3 Pages Next Page | Jump to Page
back to top
RSS Feeds

Intracluster hydrogen transfer followed by dissociation in the phenol–(NH3)3 excited state: PhOH(S1)–(NH3)3→PhO•+(NH4)(NH3)2

G. A. Pino, C. Dedonder-Lardeux, G. Grégoire, C. Jouvet, S. Martrenchard, and D. Solgadi

J. Chem. Phys. 111, 10747 (1999); http://dx.doi.org/10.1063/1.480437 (3 pages) | Cited 44 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The study of the phenol–(NH3)3 cluster with two-color two-photon ionization shows that the main ion observed with delays between the lasers up to a few hundred nanoseconds is the (NH4)+(NH3)2 fragment, resulting from direct ionization of the (NH4)(NH3)2 product coming from the reaction: PhOH(S1)–(NH3)3→PhO•+(NH4)(NH3)2. © 1999 American Institute of Physics.
Show PACS
36.40.Jn Reactivity of clusters
31.50.Df Potential energy surfaces for excited electronic states
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
33.80.-b Photon interactions with molecules
33.80.Eh Autoionization, photoionization, and photodetachment

The infrared spectrum of the benzene–Ar cation

Rob G. Satink, Hans Piest, Gert von Helden, and Gerard Meijer

J. Chem. Phys. 111, 10750 (1999); http://dx.doi.org/10.1063/1.480438 (4 pages) | Cited 32 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The infrared (IR) absorption spectra of the jet-cooled C6H6 and C6D6 cations, complexed with Ar, are measured throughout the 450–1500 cm−1 region via IR-laser-induced vibrational dissociation spectroscopy. The IR spectrum of the C6H6–Ar cation is dominated by a Fermi resonance between the IR active ν11 mode and two components of the combination mode of the lowest frequency modes ν6 and ν16. A stringent upper limit of 316 cm−1 is found for the value of the dissociation limit D0 of the neutral C6D6–Ar complex. © 1999 American Institute of Physics.
Show PACS
33.20.Ea Infrared spectra
33.20.Tp Vibrational analysis
31.30.Gs Hyperfine interactions and isotope effects
33.20.Vq Vibration-rotation analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants

Infrared photodissociation spectra of the C–H stretch vibrations of C6H6+–Ar, C6H6+–N2, and C6H6+–(CH4)1–4

Otto Dopfer, Rouslan V. Olkhov, and John P. Maier

J. Chem. Phys. 111, 10754 (1999); http://dx.doi.org/10.1063/1.480492 (4 pages) | Cited 29 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Vibrational infrared photodissociation spectra of mass selected C6H6+–Ar, C6H6+–N2, and C6H6+–(CH4)1–4 ionic complexes are recorded in the spectral range of the C–H stretching vibrations. Transitions at 3095±15 cm−1 occur in all spectra and are assigned to C–H stretch fundamentals of the benzene cation in its 2E1g electronic ground state. In the case of the C6H6+–(CH4)1–4 complexes, additional transitions at 2904±7 and 3010±24 cm−1 are observed and attributed to the symmetric and antisymmetric C–H stretch vibrations of the CH4 ligands, ν1 and ν3. The deduced C–H stretching vibrations of C6H6+ in the 2E1g ground state are roughly 30 cm−1 higher than the corresponding frequencies in the 1A1g electronic ground state of the neutral species, indicating that the C–H bonds become stronger upon removal of an electron from the highest occupied e1g orbital of C6H6. © 1999 American Institute of Physics.
Show PACS
33.80.Gj Diffuse spectra; predissociation, photodissociation
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
33.20.Ea Infrared spectra
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
36.40.Qv Stability and fragmentation of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters

Dynamics of Y+H2CO reactions

Hans U. Stauffer, Ryan Z. Hinrichs, Jonathan J. Schroden, and H. Floyd Davis

J. Chem. Phys. 111, 10758 (1999); http://dx.doi.org/10.1063/1.480439 (4 pages) | Cited 8 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The reactions of ground state yttrium atoms (Y) with formaldehyde (H2CO) have been studied in crossed molecular beams as a function of collision energy (Ecoll). The potential energy barrier for C–H insertion is found to lie below 12 kcal/mol. It is proposed that the reaction is initiated by C–H insertion, producing HYCHO followed by H atom migration forming H2YCO. Although Y–CO bond fission leading to YH2+CO is dominant, a secondary minor channel also leads to the production of YCO+H2. Formation of YCHO+H is not observed at 16 kcal/mol, but is clearly seen at 31 kcal/mol, indicating that D0(Y–CHO) lies between 58 and 73 kcal/mol. © 1999 American Institute of Physics.
Show PACS
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Kh Potential energy surfaces for chemical reactions
34.50.Lf Chemical reactions
37.20.+j Atomic and molecular beam sources and techniques

Ground state and vertical electron detachment energies of icosahedral and D5h Al13−

O. Dolgounitcheva, V. G. Zakrzewski, and J. V. Ortiz

J. Chem. Phys. 111, 10762 (1999); http://dx.doi.org/10.1063/1.480440 (4 pages) | Cited 21 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Al13− clusters are studied with ab initio, many-body methods. Coupled-cluster theory places the icosahedral structure 0.54 eV lower than the D5h isomer. Electron propagator predictions on the photoelectron spectrum of Al13− are in close agreement with the observed bands and attribute shakeup character to features at higher energy. © 1999 American Institute of Physics.
Show PACS
31.15.bw Coupled-cluster theory
34.50.Gb Electronic excitation and ionization of molecules
31.15.A- Ab initio calculations
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.15.Bh General molecular conformation and symmetry; stereochemistry

A simplified force field for describing vibrational protein dynamics over the whole frequency range

Konrad Hinsen and Gerald R. Kneller

J. Chem. Phys. 111, 10766 (1999); http://dx.doi.org/10.1063/1.480441 (4 pages) | Cited 19 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The empirical force fields used for protein simulations contain short-ranged terms (chemical bond structure, steric effects, van der Waals interactions) and long-ranged electrostatic contributions. It is well known that both components are important for determining the structure of a protein. We show that the dynamics around a stable equilibrium state can be described by a much simpler midrange force field made up of the chemical bond structure terms plus unspecific harmonic terms with a distance-dependent force constant. A normal mode analysis of such a model can reproduce the experimental density of states as well as a conventional molecular dynamics simulation using a standard force field with long-range electrostatic terms. This finding is consistent with a recent observation that effective Coulomb interactions are short ranged for systems with a sufficiently homogeneous charge distribution. © 1999 American Institute of Physics.
Show PACS
87.15.H- Dynamics of biomolecules
87.15.B- Structure of biomolecules
87.14.E- Proteins
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
36.20.Ng Vibrational and rotational structure, infrared and Raman spectra
33.15.Fm Bond strengths, dissociation energies
34.20.Gj Intermolecular and atom-molecule potentials and forces
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.15.Bh General molecular conformation and symmetry; stereochemistry
36.20.Hb Configuration (bonds, dimensions)
36.20.Ey Conformation (statistics and dynamics)

Grand canonical ensemble Monte Carlo simulation of a lipid bilayer using extension biased rotations

Pál Jedlovszky and Mihaly Mezei

J. Chem. Phys. 111, 10770 (1999); http://dx.doi.org/10.1063/1.480442 (4 pages) | Cited 17 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The cavity-biased grand-canonical ensemble method was applied to the simulation of a lipid bilayer using an enhanced Monte Carlo sampling technique. The enhancements include controlling the torsion and molecular rotation step size based on the lipid’s conformation and controlling the order of torsion change attempts. It was found that the proposed sampling technique significantly enhances the rate of sampling of the lipid conformations while the grand-canonical ensemble implementation ensures that the water can both penetrate and escape pockets in the bilayer. The latter will be particularly important for simulating bilayers with embedded molecules. © 1999 American Institute of Physics.
Show PACS
87.14.Cc Lipids
87.16.D- Membranes, bilayers, and vesicles
61.20.Ja Computer simulation of liquid structure
back to top
RSS Feeds

Configuration interaction singles, time-dependent Hartree–Fock, and time-dependent density functional theory for the electronic excited states of extended systems

So Hirata, Martin Head-Gordon, and Rodney J. Bartlett

J. Chem. Phys. 111, 10774 (1999); http://dx.doi.org/10.1063/1.480443 (13 pages) | Cited 77 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A general formalism for time-dependent linear response theory is presented within the framework of linear-combination-of-atomic-orbital crystalline orbital theory for the electronic excited states of infinite one-dimensional lattices (polymers). The formalism encompasses those of time-dependent Hartree–Fock theory (TDHF), time-dependent density functional theory (TDDFT), and configuration interaction singles theory (CIS) (as the Tamm–Dancoff approximation to TDHF) as particular cases. These single-excitation theories are implemented by using a trial-vector algorithm, such that the atomic-orbital-based two-electron integrals are recomputed as needed and the transformation of these integrals from the atomic-orbital basis to the crystalline-orbital basis is avoided. Convergence of the calculated excitation energies with respect to the number of unit cells taken into account in the lattice summations (N) and the number of wave vector sampling points (K) is studied taking the lowest singlet and triplet exciton states of all-trans polyethylene as an example. The CIS and TDHF excitation energies of polyethylene show rapid convergence with respect to K and they are substantially smaller than the corresponding Hartree–Fock fundamental band gaps. In contrast, the excitation energies obtained from TDDFT and its modification, the Tamm–Dancoff approximation to TDDFT, show slower convergence with respect to K and the excitation energies to the lowest singlet exciton states tend to collapse to the corresponding Kohn–Sham fundamental band gaps in the limit of K→∞. We consider this to be a consequence of the incomplete cancellation of the self-interaction energy in the matrix elements of the TDDFT matrix eigenvalue equation, and to be a problem inherent to the current approximate exchange–correlation potentials that decay too rapidly in the asymptotic region. © 1999 American Institute of Physics.
Show PACS
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
31.15.E- Density-functional theory
31.15.xr Self-consistent-field methods
31.50.Df Potential energy surfaces for excited electronic states
71.10.Li Excited states and pairing interactions in model systems
02.60.-x Numerical approximation and analysis

Application of the forward–backward initial value representation to molecular energy transfer

David E. Skinner and William H. Miller

J. Chem. Phys. 111, 10787 (1999); http://dx.doi.org/10.1063/1.480444 (7 pages) | Cited 15 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
It is shown how the forward–backward (FB) approximation to the semiclassical initial value representation (IVR) can be used to calculate the probability (or cross section) for molecular energy transfer. Specifically, the probability P(ΔEA) for a molecule A to gain (or lose) an amount of internal energy ΔEA by collision with a bath molecule B is given by the Fourier transform of a time correlation function C(t), which is in turn given by a single phase space average over the initial conditions of classical trajectories of the A+B collision system. Application to energy transfer of H2 by collision with He is carried out to demonstrate that the FB-IVR provides a good description of quantum effects in P(ΔEA). © 1999 American Institute of Physics.
Show PACS
34.50.-s Scattering of atoms and molecules
02.30.-f Function theory, analysis
82.20.-w Chemical kinetics and dynamics

Time propagation and spectral filters in quantum dynamics: A Hermite polynomial perspective

Amrendra Vijay, Robert E. Wyatt, and Gert D. Billing

J. Chem. Phys. 111, 10794 (1999); http://dx.doi.org/10.1063/1.480483 (12 pages) | Cited 7 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present an investigation of Hermite polynomials as a basic paradigm for quantum dynamics, and make a thorough comparison with the well-known Chebyshev method. The motivation of the present study is to develop a compact and numerically efficient formulation of the spectral filter problem. In particular, we expand the time evolution operator in a Hermite series and obtain thereby an exponentially convergent propagation scheme. The basic features of the present formulation vìs a vìs Chebyshev scheme are as follows: (i) Contrary to the Chebyshev scheme Hamiltonian renormalization is not needed. However, an arbitrary time scaling may be necessary in order to avoid numerical hazards, and this time scaling also provides a leverage to accelerate the convergence of the Hermite series. We emphasize the final result is independent of the arbitrary scaling. (ii) As with the Chebyshev scheme the method is of high accuracy but not unitary by definition, and thus any deviation from unitarity may be used as a guideline for accuracy. The calculation of expansion coefficients in the present scheme is extremely simple. To contrast the convergence property of present method with that of the Chebyshev one for finite time propagation, we have introduced a time–energy scaling concept, and this has given rise to a unified picture of the overall convergence behavior. To test the efficacy of the present method, we have computed the transmission probability for a one-dimensional symmetric Eckart barrier, as a function of energy, and shown that the present method, by suitable time–energy scaling, can be very efficient for numerical simulation. Time–energy scaling analysis also suggests that it may be possible to achieve a faster convergence with the Hermite based method for finite time propagation, by a proper choice of scaling parameter. We have further extended the present formulation directed toward the spectral filter problem. In particular, we have utilized the Gaussian damping function for the purpose. The Hermite propagation scheme has allowed all the time integrals to be done fully analytically, a feature not completely shared by the Chebyshev based scheme. As a result, we have obtained a very compact and numerically efficient scheme for the spectral filters to compute the interior eigenspectra of a large rank eigensystem. The present formulation also allows us to obtain a closed form expression to estimate the error of the energies and spectral intensities. As a test, we have utilized the present spectral filter method to compute the highly excited vibrational states for the two-dimensional LiCN (J = 0) system and compared with the exact diagonalization result. © 1999 American Institute of Physics.
Show PACS
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
03.65.Fd Algebraic methods
02.10.De Algebraic structures and number theory
02.10.Ud Linear algebra
02.10.Xm Multilinear algebra

Methods for optimizing large molecules. II. Quadratic search

Ödön Farkas and H. Bernhard Schlegel

J. Chem. Phys. 111, 10806 (1999); http://dx.doi.org/10.1063/1.480484 (9 pages) | Cited 71 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Geometry optimization has become an essential part of quantum-chemical computations, largely because of the availability of analytic first derivatives. Quasi-Newton algorithms use the gradient to update the second derivative matrix (Hessian) and frequently employ corrections to the quadratic approximation such as rational function optimization (RFO) or the trust radius model (TRM). These corrections are typically carried out via diagonalization of the Hessian, which requires O(N3) operations for N variables. Thus, they can be substantial bottlenecks in the optimization of large molecules with semiempirical, mixed quantum mechanical/molecular mechanical (QM/MM) or linearly scaling electronic structure methods. Our O(N2) approach for solving the equations for coordinate transformations in optimizations has been extended to evaluate the RFO and TRM steps efficiently in redundant internal coordinates. The regular RFO model has also been modified so that it has the correct size dependence as the molecular systems become larger. Finally, an improved Hessian update for minimizations has been constructed by combining the Broyden–Fletcher–Goldfarb–Shanno (BFGS) and (symmetric rank one) SR1 updates. Together these modifications and new methods form an optimization algorithm for large molecules that scales as O(N2) and performs similar to or better than the traditional optimization strategies used in quantum chemistry. © 1999 American Institute of Physics.
Show PACS
31.15.bu Semi-empirical and empirical calculations (differential overlap, Hückel, PPP methods, etc.)
33.15.Bh General molecular conformation and symmetry; stereochemistry

Combining coupled cluster and perturbation theory

Marcel Nooijen

J. Chem. Phys. 111, 10815 (1999); http://dx.doi.org/10.1063/1.480445 (12 pages) | Cited 9 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Single reference coupled cluster (CC) singles and doubles theory is combined with low-order perturbation theory (PT) to treat ground state electron correlation. Two variants of the general scheme are discussed that differ in the type of amplitudes that are approximated perturbatively and which are treated to infinite order. The combined CC/PT methods to include ground state correlation are merged with equation-of-motion (EOM) and similarity transformed EOM methods to describe excitation spectra of the highly correlated s-tetrazine, MnO4− and Ni(CO)4 systems. It is shown that the computationally efficient CC/PT schemes can reproduce full CCSD results even if perturbation theory by itself is a very poor approximation, as is the case for many transition metal compounds. In a second test CC/PT is applied to determine ground state equilibrium molecular structures and harmonic vibrational frequencies for a set of small molecules. Using either variant of CC/PT, full CCSD geometries are easily recovered, while vibrational frequencies can be more sensitive to details of the approximation. © 1999 American Institute of Physics.
Show PACS
31.15.bw Coupled-cluster theory
31.15.xp Perturbation theory
31.15.vq Electron correlation calculations for polyatomic molecules
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
33.15.Bh General molecular conformation and symmetry; stereochemistry

High order finite difference algorithms for solving the Schrödinger equation in molecular dynamics

Raul Guantes and Stavros C. Farantos

J. Chem. Phys. 111, 10827 (1999); http://dx.doi.org/10.1063/1.480446 (9 pages) | Cited 11 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The view of considering global Pseudospectral methods (Sinc and Fourier) as the infinite order limit of local finite difference methods, and vice versa, finite difference as a certain sum acceleration of the pseudospectral methods is exploited to investigate high order finite difference algorithms for solving the Schrödinger equation in molecular dynamics. A Morse type potential for iodine molecule is used to compare the eigenenergies obtained by a Sinc Pseudospectral method and a high order finite difference approximation of the action of the kinetic energy operator on the wave function. Two-dimensional and three-dimensional model potentials are employed to compare spectra obtained by fast Fourier transform techniques and variable order finite difference. It is shown that it is not needed to employ very high order approximations of finite differences to reach the numerical accuracy of pseudospectral techniques. This, in addition to the fact that for complex configuration geometries and high dimensionality, local methods require less memory and are faster than pseudospectral methods, put finite difference among the effective algorithms for solving the Schrödinger equation in realistic molecular systems. © 1999 American Institute of Physics.
Show PACS
61.20.Ja Computer simulation of liquid structure
61.43.Bn Structural modeling: serial-addition models, computer simulation
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
03.65.Ge Solutions of wave equations: bound states
02.70.Bf Finite-difference methods
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
02.10.Ud Linear algebra
02.10.Xm Multilinear algebra

Periodic orbit–Quantum mechanical investigation of the inversion mechanism of Ar3

Raul Guantes, Anastasios Nezis, and Stavros C. Farantos

J. Chem. Phys. 111, 10836 (1999); http://dx.doi.org/10.1063/1.480447 (7 pages) | Cited 4 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The inversion mechanism of a T-shaped Ar3 is studied both classically and quantum mechanically. Regular states, localized in the region of the transition state for the inversion of the axial argon atom are found and are assigned by the symmetric stretch stable periodic orbits which emanate from the saddle point of the potential. These states inhibit the inversion process. States which promote the inversion are mainly irregular, but a few of them are localized and they have their nodes perpendicularly arranged along periodic orbits which originate from saddle node bifurcations. The two types of periodic orbits, inhibiting and isomerizing, are used to produce distinctly different spectra and to extract the corresponding eigenfunctions by solving the time dependent Schrödinger equation using a variable order finite difference method [J. Chem. Phys. 111, 10827 (1999), preceding paper]. © 1999 American Institute of Physics.
Show PACS
82.30.Qt Isomerization and rearrangement
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
02.10.Ud Linear algebra
02.10.Xm Multilinear algebra
03.65.Ge Solutions of wave equations: bound states
02.70.Bf Finite-difference methods
31.15.xf Finite-difference schemes

Semiclassical dynamics of nonadiabatic transitions in discrete-state systems using spin coherent-state path integrals

Andreas Lucke, C. H. Mak, and Jürgen T. Stockburger

J. Chem. Phys. 111, 10843 (1999); http://dx.doi.org/10.1063/1.480448 (9 pages) | Cited 6 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a semiclassical method for simulating the dynamics of nonadiabatic transitions in a discrete-state quantum system coupled to a bath of explicit continuous coordinates. This method employs a coherent-state formulation of the path integrals for the discrete system whose dynamics is described by spin operators. This spin coherent-state formulation allows the discrete system to be mapped onto a continuous coordinate. Stationary approximations of the resulting coherent-state path integrals of the system plus bath lead to quasiclassical equations of motion which can be solved numerically by direct integration. This algorithm reduces the problem to a number of simple classical trajectory calculations and does not require calculating any fluctuation determinants. © 1999 American Institute of Physics.
Show PACS
03.65.Sq Semiclassical theories and applications

A simple semiclassical approach to the Kramers’ problem

Jyotipratim Ray Chaudhuri, Bidhan Chandra Bag, and Deb Shankar Ray

J. Chem. Phys. 111, 10852 (1999); http://dx.doi.org/10.1063/1.480449 (7 pages) | Cited 24 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We show that the Wigner–Leggett–Caldeira equation for Wigner phase space distribution function which describes the quantum Brownian motion of a particle in a force field in a high temperature, ohmic environment can be identified as a semiclassical version of Kramers’ equation. Based on an expansion in powers of ℏ, we solve this equation to calculate the semiclassical correction to Kramers’ rate. © 1999 American Institute of Physics.
Show PACS
03.65.Sq Semiclassical theories and applications
03.65.Ge Solutions of wave equations: bound states
05.40.Jc Brownian motion
42.50.Lc Quantum fluctuations, quantum noise, and quantum jumps
02.50.Cw Probability theory
02.50.Ga Markov processes
back to top
RSS Feeds

FT-ICR study on hydrogenation of niobium cluster cations Nbn+ (n = 2–15) in seeded supersonic jet and multiple-collision-induced dissociation of NbnHm+ hydrides

Andrei B. Vakhtin and Ko-ichi Sugawara

J. Chem. Phys. 111, 10859 (1999); http://dx.doi.org/10.1063/1.480450 (7 pages) | Cited 10 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Hydrogenation of niobium cluster cations Nbn+ (n = 2–15) in a seeded supersonic jet of H2/He and multiple-collision-induced dissociation (MCID) of the resulting NbnHm+ hydrides have been studied using a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The nascent NbnHm+ hydrides trapped in the FT-ICR cell have broad m distributions with no apparent prevalence of odd or even m. A pulse of argon applied to the trapped clusters causes a dramatic squeezing of the initial m distribution (through the collision-induced removal of weakly bound H2 molecules), favoring several particular hydrides for each cluster size n, e.g., Nb7H8+, Nb7H11+, and Nb7H12+ for n = 7. The maximum m values of these stable hydrides are close to the stoichiometric composition of NbH2 for the clusters with n<13, and approach that of NbH at larger n. The hydrides observed in our experiments are different from the products of the Nbn++H2 reactions performed in the FT-ICR cell at room temperature, which show only even and strongly n-dependent m values. The MCID of the NbnHm+ clusters occurs through the sequential desorption of H2 molecules yielding NbnH+ and Nbn+ as final dissociation products for odd and even m, respectively. Based on the experiments on the MCID of Nb12H18+, an explanation is suggested for different reactivities of the Nb12+ clusters toward H2 in the ICR and fast-flow-reactor experiments. © 1999 American Institute of Physics.
Show PACS
36.40.Jn Reactivity of clusters
36.40.Wa Charged clusters
36.40.Qv Stability and fragmentation of clusters
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
33.15.Ta Mass spectra

Quantum Monte Carlo simulation of intermolecular excited vibrational states in the cage water hexamer

Mark W. Severson and Victoria Buch

J. Chem. Phys. 111, 10866 (1999); http://dx.doi.org/10.1063/1.480451 (10 pages) | Cited 21 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Rigid-body diffusion Monte Carlo simulations of the ground state and ten low-lying intermolecular excited vibrational states for the cage form of (H2O)6 are reported. The excited states are found by a nodal optimization procedure in which the fundamental excited-state nodes are constructed from the harmonic normal coordinates. The anharmonic effects in the excited states are found to be large. One of the states with relatively large transition intensity involves primarily flipping motions of the free OH bonds on the doubly bound monomers, and is assigned to the vibration–rotation–tunnelling band observed experimentally by Liu et al. [Nature 301, 501–503 (1996)]. © 1999 American Institute of Physics.
Show PACS
36.40.Cg Electronic and magnetic properties of clusters
31.50.Df Potential energy surfaces for excited electronic states
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Vq Vibration-rotation analysis
34.20.Gj Intermolecular and atom-molecule potentials and forces
33.15.Fm Bond strengths, dissociation energies

Laser-induced fluorescence and Optical/Stark spectroscopy of PtC

S. A. Beaton and T. C. Steimle

J. Chem. Phys. 111, 10876 (1999); http://dx.doi.org/10.1063/1.480452 (7 pages) | Cited 12 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Optical/Stark measurements have been performed on the (0,0) bands of both the A″ 1Σ+–X 1Σ+ system (ν0 ≈ 12 643 cm−1) and the A′ 1Π–X Σ+ system (ν0 ≈ 13 196 cm−1) of platinum monocarbide. The PtC molecules were produced in a pulsed supersonic molecular beam source following the reaction of laser ablated platinum vapor with a mixture of a few percent of methane in argon. The newly determined permanent electric dipole moments obtained are 1.94(2)D (A″ 1Σ+) and 1.919(9)D (A′ 1Π). These results are discussed in terms of a proposed molecular orbital correlation diagram for platinum containing diatomics. The laser-induced fluorescence spectrum of the (0,0)A″ 1Σ+–X 1Σ+ transition of PtC has been re-recorded at high resolution (full width of half-maximum ∼40 MHz) and analyzed to yield rotational constants for the four most abundant isotopomers of PtC, extending the previous analysis [Appelblad, Nilsson, and Scullman, Phys. Scr. 7, 65 (1973)]. The anomalously large value (∼15 MHz) for the newly derived nuclear-spin rotation parameter, CI(195Pt), for the A″ 1Σ+ state is discussed. © 1999 American Institute of Physics.
Show PACS
33.50.Dq Fluorescence and phosphorescence spectra
33.20.Kf Visible spectra
33.57.+c Magneto-optical and electro-optical spectra and effects
37.20.+j Atomic and molecular beam sources and techniques
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.30.Gs Hyperfine interactions and isotope effects
33.15.Bh General molecular conformation and symmetry; stereochemistry

Spin polarization of zero kinetic energy electrons from HBr

M. Drescher, R. Irrgang, M. Spieweck, U. Heinzmann, N. A. Cherepkov, and H. Lefebvre-Brion

J. Chem. Phys. 111, 10883 (1999); http://dx.doi.org/10.1063/1.480405 (4 pages) | Cited 1 time

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The range of observables in zero kinetic energy (ZEKE) electron spectroscopy of molecules, previously restricted to the total electron intensity, was extended by measuring the integral spin polarization of ZEKE electrons at the HBr Ω+ = 3/2 thresholds after single-photon excitation with narrow-band circularly polarized light. A comparison with calculated values from multichannel quantum defect theory underlines the importance of autoionization for the decay dynamics. © 1999 American Institute of Physics.
Show PACS
33.60.+q Photoelectron spectra

An ab initio molecular dynamics study of the SN2 reaction Cl−+CH3Br→CH3Cl+Br−

Simone Raugei, Gianni Cardini, and Vincenzo Schettino

J. Chem. Phys. 111, 10887 (1999); http://dx.doi.org/10.1063/1.480490 (8 pages) | Cited 8 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
An ab initio molecular dynamics study of the SN2 reaction Cl−+CH3Br→CH3Cl+Br− has been performed at the Becke, Lee, Yang, and Parr (BLYP) level of theory by the blue-moon method. The potential energy and the free energy profile along the reaction coordinate have been determined and compared with the available experimental and calculated data. An analysis of the structural parameters along the reaction pathway is presented. Results of impact studies are also reported. It is shown that, depending on impact velocity, recrossing of the barrier can occur. Strong polarization effects are reported. © 1999 American Institute of Physics.
Show PACS
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
02.70.Ns Molecular dynamics and particle methods
31.15.xv Molecular dynamics and other numerical methods
31.15.A- Ab initio calculations

Magnetic field effects on the dynamics of a Rydberg electron: The residence time near the core

Hirohiko Kono, Takayuki Tazaki, Isao Kawata, and Yuichi Fujimura

J. Chem. Phys. 111, 10895 (1999); http://dx.doi.org/10.1063/1.480453 (8 pages) | Cited 1 time

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Using symplectic integrator schemes, we calculate the classical trajectory of a Rydberg electron in external electric and magnetic fields. We also solve the equation of motion obtained by taking the mean values over one revolution of the electron in the undisturbed motion. The resulting secular motion is periodic. When only an electric field F is applied, as long as the modulation period in the orbital angular momentum l is longer than the revolution period, the motion agrees with the secular one and the duration for which l is much larger than its low initial value is stretched. The residence time (RT), namely, the probability of finding the electron at the distance r, is hence smaller than that at F = 0. In crossed electric and magnetic fields, the secular motion predicts that an additional time stretching due to a magnetic field occurs up to the critical value of magnetic field strength, Bc = 3mathnF (n is the principal action). In the actual simulations, the RT near the core is smaller than that at B = 0 even beyond Bc, regardless of the magnitude of the non-Coulombic interaction C2/r2. Slow modulations in l are generated by transitions to secular motions that maintain high l, in addition to the fast modulation originating from the secular motion. When the magnetic field is so strong as to induce chaotic motion (∼4000 G for the energy of −5 cm−1), the RT is one order of magnitude as large as those in weak field cases around 40 G. In the intermediate region (> a few hundred Gauss), without a non-Coulombic interaction, the RT monotonically increases as B increases. In the presence of C2/r2, transitions from low l states to high l states occur: the RT decreases. The motions in high l states can be explained by the well-known model in which an electron bound to the core by a harmonic force moves in a magnetic field. © 1999 American Institute of Physics.
Show PACS
31.50.Df Potential energy surfaces for excited electronic states
02.50.Cw Probability theory
05.10.-a Computational methods in statistical physics and nonlinear dynamics

One- and two-body densities for the beryllium isoelectronic series

F. J. Gálvez, E. Buendía, and A. Sarsa

J. Chem. Phys. 111, 10903 (1999); http://dx.doi.org/10.1063/1.480485 (7 pages) | Cited 16 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
One- and two-body densities in position space have been calculated for the atomic beryllium isoelectronic series starting from explicitly correlated multideterminant wave functions. The effects of electronic correlations have been systematically studied by comparing the correlated results with the corresponding Hartree–Fock ones. Some expectation values such as 〈δ(r)〉, 〈rn〉, 〈δ(r12)〉, 〈r12n〉, 〈δ(R)〉, and 〈Rn〉, where r, r12, and R stand for the electron–nucleus, interelectronic, and two electron center of mass coordinates, respectively, have been obtained. All the calculations have been carried out by using the Monte Carlo algorithm. © 1999 American Institute of Physics.
Show PACS
31.15.ve Electron correlation calculations for atoms and ions: ground state

Isotopic branching in (He, HD+) collisions: A time-dependent quantum mechanical study in three dimensions

C. Kalyanaraman, David C. Clary, and N. Sathyamurthy

J. Chem. Phys. 111, 10910 (1999); http://dx.doi.org/10.1063/1.480454 (9 pages) | Cited 23 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A time-dependent quantum mechanical approach has been used to investigate the reaction He+HD+(v = 0–4,j = 0–3)→HeH++D; HeD++H in three dimensions for total angular momentum J = 0. The vib-rotation (v,j) state-selected reaction probability (Pv,jR) is shown to increase with v over the collision energy (Etrans) range (0.95–2.25 eV) investigated for both the exchange channels, in accord with the experimental results. The isotopic branching ratio Γ = PR(HeH+)/PR(HeD+) generally remains less than unity for different v states at different Etrans in agreement with experiment. But at Etrans = 1.0 eV, for v = 4, Γ obtained from our calculations for j = 0 of HD+ is ∼ 0.8, in excellent agreement with the earlier quasiclassical trajectory calculations, but a factor of 2 less than that obtained from experiment. This difference could arise from the inclusion of nonzero j states in the experimental study, as Pv,jR is found to be j dependent for both the channels. While Pv,jR (HeH+) decreases initially with increase in j from 0 to 2 and then increases when j is increased further to 3, Pv,jR (HeD+) reveals an unusual j dependence; it is larger for even j states of HD+ than for odd j. As a result, Γ is strongly dependent on j, in contrast to the marginal dependence shown by the earlier quasiclassical trajectory calculations. © 1999 American Institute of Physics.
Show PACS
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Tr Kinetic isotope effects including muonium

High resolution spectroscopy of MgOH (X 2Σ+) in its V2 mode: Further evidence for quasilinearity

A. J. Apponi, M. A. Anderson, and L. M. Ziurys

J. Chem. Phys. 111, 10919 (1999); http://dx.doi.org/10.1063/1.480455 (7 pages) | Cited 17 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Pure rotational spectra of the MgOH and MgOD radicals have been recorded in the v2 bending vibration of their X 2Σ+ ground electronic states using millimeter-wave direct absorption spectroscopy. Multiple rotational transitions arising from the v2l = 11, 22, 20, 31, 33, 42, and 44 substates have been measured in the frequency range 240–520 GHz for these species. Both the spin-rotation and l-type doubling interactions have been resolved in the spectra. The complete data sets for MgOH and MgOD have been analyzed using a linear model for the Hamiltonian which takes into account higher order (l = ±4) l-type interactions. The global analyses were adequate, but anomalous behavior was apparent in both molecules. In particular, the Bv vs v2 relation was found to be highly nonlinear, large variations in the l-type doubling constant q were observed with vibrational level, and r0, rs, and mathe structures determined differed substantially. Such findings suggest that MgOH is highly quasilinear, comparable to HNCO. The competition between ionic and covalent bonding is therefore becoming apparent in the lighter alkaline earth hydroxide species. © 1999 American Institute of Physics.
Show PACS
33.20.Bx Radio-frequency and microwave spectra
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.20.Sn Rotational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
31.30.Gs Hyperfine interactions and isotope effects
Page 1 of 3 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close