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 2003

Volume 118, Issue 24, pp. 10821-11336

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

Low temperature single molecule spectroscopy using vibronic excitation and dispersed fluorescence detection

Alper Kiraz, Moritz Ehrl, Christoph Bräuchle, and Andreas Zumbusch

J. Chem. Phys. 118, 10821 (2003); http://dx.doi.org/10.1063/1.1582845 (4 pages) | Cited 26 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF


See Also: Publisher's Note

Show Abstract
We demonstrate vibronic excitation combined with spectrally resolved zero phonon line detection of single terrylenediimide (TDI) molecules in both the Shpol’skii matrix hexadecane and the polymer PMMA at cryogenic temperatures. Spectral jumps as large as 80 cm−1 are recorded with a 1 s time resolution. This technique does not require a weak electron–phonon coupling, and promises applications in spectroscopy of a wide-range of single nanostructures in amorphous hosts including fluorescing proteins. Vibronic excitation is also used to determine vibrational spectra of the excited state of single TDI molecules. © 2003 American Institute of Physics.
Show PACS
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.50.Dq Fluorescence and phosphorescence spectra
back to top
RSS Feeds
back to top Theoretical Methods and Algorithms

Two interacting electrons confined within a sphere: An accurate solution

J. Jung and J. E. Alvarellos

J. Chem. Phys. 118, 10825 (2003); http://dx.doi.org/10.1063/1.1574786 (10 pages) | Cited 17 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present highly accurate configuration interaction results for two nonrelativistic electrons confined within a sphere and interacting via a Coulomb force. In such a system, the radius of the sphere R can be considered as a measure of the strenght of the electronic repulsion. So, distinct correlation regimes, from the noninteracting limit to a high correlated regime, can be achieved by varying R. The results clearly show how very high correlation effects might appear in the system. Energies, density distributions, conditional probabilities and the exchange–correlation hole have been evaluated for different values of R. The essentially exact results here presented can be used as benchmarks for new exchange–correlation functionals and/or other approximate methods. © 2003 American Institute of Physics.
Show PACS
31.15.V- Electron correlation calculations for atoms, ions and molecules
02.50.Cw Probability theory
03.65.-w Quantum mechanics

N-representability and variational stability in natural orbital functional theory

John M. Herbert and John E. Harriman

J. Chem. Phys. 118, 10835 (2003); http://dx.doi.org/10.1063/1.1574787 (12 pages) | Cited 32 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Several “reconstructive” proposals for density matrix functional theory are investigated, each of which expresses the two-electron density matrix, and therefore the electronic energy, as a functional of the natural orbitals and their occupation numbers. It is shown that for each of these functionals, half of the parallel-spin eigenvalues of the reconstructed two-electron density matrix are necessarily negative. Illustrative all-electron calculations for Be and LiH, in a variety of Gaussian basis sets, demonstrate that these spurious negative eigenvalues lower the electronic energy substantially. In spite of this, there is no indication that the variationally optimized energy diverges as the basis set approaches completeness, as has been suggested based on calculations with a small number of active orbitals. The apparent variational instability reported previously is attributed to qualitative differences between the minimal-basis and extended-basis potential curves, for certain functionals. However, we identify one functional that yields accurate LiH potential curves—comparable to full configuration interaction results—in both minimal and extended basis sets. Explicitly antisymmetric reconstructions are recommended as a remedy for the positivity problem. © 2003 American Institute of Physics.
Show PACS
31.15.E- Density-functional theory
31.15.xt Variational techniques
31.15.V- Electron correlation calculations for atoms, ions and molecules

A fast multipole method combined with a reaction field for long-range electrostatics in molecular dynamics simulations: The effects of truncation on the properties of water

Gerald Mathias, Bernhard Egwolf, Marco Nonella, and Paul Tavan

J. Chem. Phys. 118, 10847 (2003); http://dx.doi.org/10.1063/1.1574774 (14 pages) | Cited 20 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a combination of the structure adapted multipole method with a reaction field (RF) correction for the efficient evaluation of electrostatic interactions in molecular dynamics simulations under periodic boundary conditions. The algorithm switches from an explicit electrostatics evaluation to a continuum description at the maximal distance that is consistent with the minimum image convention, and, thus, avoids the use of a periodic electrostatic potential. A physically motivated switching function enables charge clusters interacting with a given charge to smoothly move into the solvent continuum by passing through the spherical dielectric boundary surrounding this charge. This transition is complete as soon as the cluster has reached the so-called truncation radius Rc. The algorithm is used to examine the dependence of thermodynamic properties and correlation functions on Rc in the three point transferable intermolecular potential water model. Our test simulations on pure liquid water used either the RF correction or a straight cutoff and values of Rc ranging from 14 Å to 40 Å. In the RF setting, the thermodynamic properties and the correlation functions show convergence for Rc increasing towards 40 Å. In the straight cutoff case no such convergence is found. Here, in particular, the dipole–dipole correlation functions become completely artificial. The RF description of the long-range electrostatics is verified by comparison with the results of a particle-mesh Ewald simulation at identical conditions. © 2003 American Institute of Physics.
Show PACS
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
61.20.Ja Computer simulation of liquid structure
02.70.Ns Molecular dynamics and particle methods
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations

Density functional response approach for the linear and nonlinear electric properties of molecules

K. B. Sophy and Sourav Pal

J. Chem. Phys. 118, 10861 (2003); http://dx.doi.org/10.1063/1.1576213 (6 pages) | Cited 4 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
This is a preliminary study toward implementation of analytic density functional response approach for molecules to obtain linear and nonlinear electric properties. The Kohn–Sham framework has been used with Gaussian basis sets. We propose a fully variational approach to obtain the response of electronic density in terms of the atomic orbital basis (contracted Gaussians). As a first step, this derivative of the Kohn–Sham operator is obtained by a finite field method using five different values of electric field. Using this, we obtain the energy derivatives up to third order using fully analytic expressions. We calculate the dipole moment, polarizability, and hyperpolarizability of the hydrogen fluoride (HF) molecule as a test case using different exchange–correlation functionals and basis sets within the present methodology. We also explore the feasibility of this response approach by studying the properties of the HF molecule for different H–F distances. © 2003 American Institute of Physics.
Show PACS
31.15.E- Density-functional theory
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.xt Variational techniques

Correlations between structure and optical properties in Jahn–Teller Mn3+ fluorides: A study of TlMnF4 and NaMnF4 under pressure

Fernando Rodriguez and Fernando Aguado

J. Chem. Phys. 118, 10867 (2003); http://dx.doi.org/10.1063/1.1569847 (9 pages) | Cited 13 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
This work investigates the Jahn–Teller (JT) distortion in different Mn3+ fluoride series by optical absorption (OA) spectroscopy. The aim is to establish correlations between the local structure of the formed MnF63− derived from x-ray diffraction and the JT splitting associated with the parent octahedral 5Eg(3z2−r2,x2−y2) and 5T2g(xy,xz,yz) states, Δe and Δt, obtained from the OA spectrum. A salient feature is the linear relation exhibited by both Δe and Δt with the tetragonal coordinate Qθ along the whole series. From these relations we derive suitable electron-ion coupling coefficients related to the 5Eg and 5T2g states whose values play a key role in the e⊗E and e⊗T JT theory, respectively. The results of these correlations are applied to investigate the structural variations undergone by the two-dimensional compounds NaMnF4 and TlMnF4 under pressure using OA spectroscopy. Interestingly, the analysis carried out is relevant since it provides useful information on the Mn3+ local structure, a task that is difficult to achieve using extended x-ray-absorption fine structure under pressure due to the high absorption of the diamond anvils. We conclude that the effect of pressure in NaMnF4 is to reduce progressively the JT distortion of the complex, keeping its tetragonal symmetry. The pressure effects in TlMnF4 are more drastic, leading to pressure-induced structural phase transitions of low symmetry. At variance with NaMnF4, the high-pressure Mn3+ local structure seems to have significant rhombic distortions. © 2003 American Institute of Physics.
Show PACS
78.40.Ha Other nonmetallic inorganics
62.50.-p High-pressure effects in solids and liquids
61.66.Fn Inorganic compounds
78.70.Dm X-ray absorption spectra
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Continuous transition between Brillouin–Wigner and Rayleigh–Schrödinger perturbation theory, generalized Bloch equation, and Hilbert space multireference coupled cluster

Jiří Pittner

J. Chem. Phys. 118, 10876 (2003); http://dx.doi.org/10.1063/1.1574785 (14 pages) | Cited 80 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A continuous transition between the Rayleigh–Schrödinger and Brillouin–Wigner perturbation theories is constructed and the Bloch equation for the corresponding wave operator is derived. Subsequently it is applied to the Hilbert space multireference coupled cluster theory and used to investigate relationships between several versions of multireference coupled cluster methods. Finally, based on those continuous transitions, new size extensivity corrections for the Brillouin–Wigner coupled cluster method are suggested. Numerical tests of size-extensivity and separability of a supermolecule to closed- and open-shell fragments are also presented. Equivalence of some of the multireference coupled cluster methods with single and double excitations to full configuration interaction for two-electron systems is investigated, both theoretically and numerically. © 2003 American Institute of Physics.
Show PACS
31.15.xp Perturbation theory
31.15.bw Coupled-cluster theory
31.15.V- Electron correlation calculations for atoms, ions and molecules
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Near-infrared spectroscopy of H3+ above the barrier to linearity

Jennifer L. Gottfried, Benjamin J. McCall, and Takeshi Oka

J. Chem. Phys. 118, 10890 (2003); http://dx.doi.org/10.1063/1.1575737 (10 pages) | Cited 13 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The first H3+ transitions above the barrier to linearity have been observed in absorption in the near infrared using a highly sensitive dual-beam, double-modulation technique with bidirectional optical multipassing. A total of 22 rovibrational transitions of H3+ have been detected and assigned to the fourth and fifth overtone and combination bands (5ν21, 5ν25, 2ν1+2ν22, 3ν1+ν21, ν1+4ν22, 2ν1+3ν21, and 6ν22). These transitions, which are more than 4600 times weaker than the fundamental band, probe energy levels above 10 000 cm−1, the regime in which H3+ has enough energy to sample linear configurations. Experimentally determined energy levels above the barrier to linearity provide a critical test of ab initio calculations in this challenging regime. The comparison between experimental energy levels and theoretical energy levels from ab initio calculations in which the adiabatic and relativistic corrections are incorporated reveals the extent of higher-order effects such as nonadiabatic and radiative corrections. We compare our results with several recent theoretical calculations.© 2003 American Institute of Physics.
Show PACS
33.20.Ea Infrared spectra
33.20.Vq Vibration-rotation analysis
31.15.A- Ab initio calculations

Electronic structures, vibrational spectra, and revised assignment of aniline and its radical cation: Theoretical study

Piotr M. Wojciechowski, Wiktor Zierkiewicz, Danuta Michalska, and Pavel Hobza

J. Chem. Phys. 118, 10900 (2003); http://dx.doi.org/10.1063/1.1574788 (12 pages) | Cited 43 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Comprehensive studies of the molecular and electronic structures, vibrational frequencies, and infrared and Raman intensities of the aniline radical cation, C6H5NH2+ have been performed by using the unrestricted density functional (UB3LYP) and second-order Møller–Plesset (UMP2) methods with the extended 6-311++G(df,pd) basis set. For comparison, analogous calculations were carried out for the closed-shell neutral aniline. The studies provided detailed insight into the bonding changes that take place in aniline upon ionization. The natural bond orbital (NBO) analysis has revealed that the pπ-radical conjugative interactions are of prime importance in stabilizing the planar, quinoid-type structure of the aniline radical cation. It is shown that the natural charges calculated for aniline are consistent with the chemical properties of this molecule (an ortho- and para-directing power of the NH2 group in electrophilic substitutions), whereas Mulliken charges are not reliable. The theoretical vibrational frequencies of aniline, calculated by the B3LYP method, show excellent agreement with the available experimental data. In contrast, the MP2 method is deficient in predicting the frequencies of several modes in aniline, despite the use of the extended basis set in calculations. The frequencies of aniline radical cation, calculated at the UB3LYP/6-311++G(df,pd) level, are in very good agreement with the recently reported experimental data from zero kinetic energy photoelectron and infrared depletion spectroscopic studies. The clear- cut assignment of the IR and Raman spectra of the investigated molecules has been made on the basis of the calculated potential energy distributions. Several bands in the spectra have been reassigned. It is shown that ionization of aniline can be easily identified by the appearance of the very strong band at about 1490 cm−1, in the Raman spectrum. The redshift of the N–H stretching frequencies and the blueshift of the C–H stretching frequencies are observed in aniline, upon ionization. As revealed by NBO analysis, the frequency shifts can be correlated with the increase of electron density (ED) on the antibonding orbitals (σNH∗) and decrease of ED on σCH∗, respectively. These effects are associated with a weakening of N–H bonds and strengthening of C–H bonds in the aniline radical cation. The simulated theoretical Raman and infrared spectra of aniline and its radical cation, reported in this work, can be used in further spectroscopic studies of their van der Waals clusters and hydrogen bonded complexes. © 2003 American Institute of Physics.
Show PACS
33.20.Tp Vibrational analysis
33.20.Ea Infrared spectra
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.60.+q Photoelectron spectra
33.70.Jg Line and band widths, shapes, and shifts

Electronic structure of the π-bonded Al–C2H4 complex: Characterization of the ground and low-lying excited states

Ana-Maria C. Cristian and Anna I. Krylov

J. Chem. Phys. 118, 10912 (2003); http://dx.doi.org/10.1063/1.1576212 (7 pages) | Cited 2 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The equilibrium properties of the π-bonded Al–ethylene complex in its ground state are calculated by coupled-cluster theory. Significant changes in the geometry of the ethylene molecule upon complexation (elongation of the CC bond, pyramidalization of the CH2 groups) are consistent with the formation of a chemical bond between fragments. The overall interaction is rather weak because bonding is derived from the overlap between: (i) a singly occupied p orbital of Al and the antibonding π∗ orbital of ethylene and (ii) a vacant Al sp hybrid and π of C2H4. Electronically excited states are studied by the equation-of-motion coupled-cluster method. The covalent nature of the interaction between fragments is reflected in the excited-state delocalization over both fragments (as opposed to the corresponding van der Waals complex). In the examined energy range (0–5.18 eV) both valence and Rydberg excited states are found. Bonding in the valence states is explained in terms of a simple molecular orbital picture. Two very intense transitions at 3.50 eV and at 3.79 eV can be used as a probe in experimental studies. © 2003 American Institute of Physics.
Show PACS
31.15.bw Coupled-cluster theory
33.15.Bh General molecular conformation and symmetry; stereochemistry

Free ion formation in K(np)/SF6 collisions at low-to-intermediate n: Velocity dependence of the number and lifetime of the product ions

L. Suess, R. Parthasarathy, and F. B. Dunning

J. Chem. Phys. 118, 10919 (2003); http://dx.doi.org/10.1063/1.1574804 (5 pages) | Cited 13 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The rates for free ion production through electron transfer in K(np)/SF6 collisions are measured as a function of Rydberg atom velocity for low-to-intermediate values of n, together with the lifetime of the product SF6− ions against autodetachment. The data show that postattachment interactions between the K+–SF6− product ion pair become increasingly important as n, and the Rydberg atom velocity, are decreased. These result in the conversion of internal energy from the SF6− ion into translational energy of the ion pair and in a dramatic increase in SF6− ion lifetimes. Analysis of the data using a Monte Carlo collision model suggests that the energy transfer is sizable, and is more than sufficient to stabilize the product SF6− ions against autodetachment. © 2003 American Institute of Physics.
Show PACS
34.50.-s Scattering of atoms and molecules

Experimental verification of line- and band-shape asymmetry in the Schumann–Runge system of O2

M. Kono, B. R. Lewis, K. G. H. Baldwin, and S. T. Gibson

J. Chem. Phys. 118, 10924 (2003); http://dx.doi.org/10.1063/1.1574512 (5 pages) | Cited 1 time

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
High-resolution, laser-based photoabsorption cross-section measurements in the weakly absorbing windows between the (11,0) and (16,0) Schumann–Runge bands of O2 have been performed at liquid-nitrogen temperature and the results compared with corresponding coupled-channel Schrödinger-equation (CSE) and line-by-line model calculations. While the symmetric-line- shape-based line-by-line model cross sections differ significantly from experiment, the excellent agreement found between the CSE and experimental window cross sections serves to confirm clearly for the first time the CSE-model predictions of band shape asymmetry and quantum-mechanical interference effects, especially in the (11,0)–(14,0) band region. © 2003 American Institute of Physics.
Show PACS
33.70.Jg Line and band widths, shapes, and shifts

Six-dimensional ab initio potential energy surfaces for H3O+ and NH3: Approaching the subwave number accuracy for the inversion splittings

Timo Rajamäki, Andrea Miani, and Lauri Halonen

J. Chem. Phys. 118, 10929 (2003); http://dx.doi.org/10.1063/1.1574784 (10 pages) | Cited 28 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
New potential energy surfaces are calculated for the hydronium ion using high-order coupled cluster ab initio methods. Large basis sets are used especially for the inversion part of the full surface. Electronic energies obtained with different correlation consistent basis sets are extrapolated to the infinite basis set limit. Core-valence and first order relativistic effects are also included. The influence of these two contributions and basis set sizes on both the inversion barrier height and equilibrium geometry are investigated thoroughly. The same methods are also adopted for ammonia in order to further improve a recently published surface [J. Chem. Phys. 118, 6358 (2003)]. The vibrational eigenvalues are calculated variationally both for the symmetric and asymmetric isotopomers using exact six-dimensional kinetic energy operators and successive basis set contractions. With the new surfaces, the mean absolute deviations obtained for all experimentally observed inversion splittings for different isotopomers of H3O+ (8 states) and 14NH3 (17 states) are 0.78 and 0.25 cm−1, respectively. Inversion levels are calculated with almost similar accuracy. These results indicate that the calculated inversion barrier heights for H3O+ and NH3, 650 and 1792 cm−1, respectively, are close to the real values. The value for ammonia is also close to the height determined from published experimental data in our previous work. The lowest energies for the high-frequency modes are computed with the mean absolute deviation being less than 2 cm−1 for isotopomers of H3O+ and less than 4.5 cm−1 for 14NH3 with respect to experimental energies. © 2003 American Institute of Physics.
Show PACS
31.15.A- Ab initio calculations
31.15.bw Coupled-cluster theory
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions

The evolution of the monoelectron dihydrogen bond H⋯e⋯H in the symmetric and asymmetric cluster anions (FH)n{e}(HF)m

Xi-Yun Hao, Zhi-Ru Li, Di Wu, Ze-Sheng Li, and Chia-Chung Sun

J. Chem. Phys. 118, 10939 (2003); http://dx.doi.org/10.1063/1.1574783 (5 pages) | Cited 7 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Using the aug-cc-pVDZ basis set supplemented with diffuse bond functions (BF), the evolution of the monoelectron dihydrogen bond H⋯e⋯H in the symmetric (n = m = 2–5) and asymmetric (n,m:3,1;3,2;4,2;4,3) cluster anions (FH)n{e}(HF)m have been studied. When n = m = 3, 4, 5, and n, m: 3, 2 the H⋯e⋯H bond evolves into the FH–e–HF monoelectron bimolecular bond. While in some asymmetric cluster anions (n,m:4,2;4,3) the FH–e–HF bond changes to H–e–HF bond, and some bond rearrangements occur in the larger subunit (HF)4 at the same time. This evolution shows a size effect of the subunits on the structure and the bond for the molecular cluster anions. © 2003 American Institute of Physics.
Show PACS
36.40.Mr Spectroscopy and geometrical structure of clusters
33.15.Fm Bond strengths, dissociation energies
33.15.Bh General molecular conformation and symmetry; stereochemistry

Spectroscopy and dynamics of excited states in maleimide and N-methyl maleimide: Ionic projection and ab initio calculations

D. H. A. ter Steege and W. J. Buma

J. Chem. Phys. 118, 10944 (2003); http://dx.doi.org/10.1063/1.1574803 (12 pages) | Cited 7 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The state that is responsible for the strong one-photon absorption around 200 nm in the vapor absorption spectrum of maleimide and N-methyl maleimide has been investigated using excited-state photoelectron spectroscopy in combination with ab initio calculations. The projection of the wave function of the excited state on the ionic manifold done in this way reveals multiple, vibrationally resolved, ionization pathways to ground- and excited states of the radical cation, which provide direct evidence for electronic couplings with other, lower-lying states. From a comparison of the experimental intensity distribution over the ionic vibrational states with ab initio calculated Franck–Condon factors, we are able to elucidate the role of the various electronically excited states in the ionization process. The experiments also provide the first determination of adiabatic ionization energies in the two molecules. For maleimide values of 10.330 and 10.903 eV are found for D0 and D1, respectively; for N-methyl maleimide D0 is found at 9.897 or, in an alternative interpretation of the spectrum, at 9.676 eV. Calculations and experiment demonstrate that in this molecule the ground ionic state changes its character with respect to maleimide from a lone pair to a π orbital ionization. © 2003 American Institute of Physics.
Show PACS
33.20.Lg Ultraviolet spectra
31.15.A- Ab initio calculations
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis

The stability of free and oxidized silver clusters

M. Schmidt, Ph. Cahuzac, C. Bréchignac, and Hai-Ping Cheng

J. Chem. Phys. 118, 10956 (2003); http://dx.doi.org/10.1063/1.1575738 (7 pages) | Cited 19 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The stability and the structure of small silver and silver-oxide particles are investigated by a comparison between experimentally deduced intensity relations in the evaporative ensemble limit and theoretical results of a Born–Oppenheimer local spin density molecular dynamics calculation. We have found two-dimensional (2D) structures for pure small silver particles up to seven atoms and three-dimensional (3D) above. In contrast, we found 3D structures for all oxidized clusters even the small ones. Small silver cluster therefore undergo a 2D-to-3D structural transition by oxidation. The electronic shell structure of the metallic part still persists, when the oxygen atoms are added, taking into account that each oxygen atom reduces the number of valence electrons by 2. The enhanced stability at electronic shell closings presents some unusual evaporation channels like the ejection of a single oxygen atom from Ag3O+ leading to Ag3O+→Ag3++O as the preferential decay channel. © 2003 American Institute of Physics.
Show PACS
36.40.Cg Electronic and magnetic properties of clusters
61.46.-w Structure of nanoscale materials
31.15.xv Molecular dynamics and other numerical methods
31.15.E- Density-functional theory
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations

Revisiting the stationary points on the potential energy surface of tetramethylene at the MR-AQCC level using analytic gradients

Elizete Ventura, Michal Dallos, and Hans Lischka

J. Chem. Phys. 118, 10963 (2003); http://dx.doi.org/10.1063/1.1575191 (10 pages) | Cited 3 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The stationary points on the potential energy surface (PES) of tetramethylene have been investigated using highly correlated multireference methods and extended basis sets. Full geometry optimization using analytic gradients as well as systematic scans of the PES employing different basis sets show that all minima and most of the saddle points found at the lower computational level (mostly CASSCF) cease to exist. Finally, only the G2 (gauche cyclization with conrotatory double CH2 twist) and the CT (cis–trans isomerization) saddle points have been confirmed. Activation and reaction enthalpies have been computed and are within 1–2 kcal/mol in agreement with experimental results. © 2003 American Institute of Physics.
Show PACS
31.50.-x Potential energy surfaces
31.15.bw Coupled-cluster theory
31.15.xr Self-consistent-field methods
82.30.Qt Isomerization and rearrangement

Glycine-Zn+/Zn2+ and their hydrates: On the number of water molecules necessary to stabilize the switterionic glycine-Zn+/Zn2+ over the nonzwitterionic ones

Hongqi Ai, Yuxiang Bu, and Keli Han

J. Chem. Phys. 118, 10973 (2003); http://dx.doi.org/10.1063/1.1575192 (13 pages) | Cited 18 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Several interaction modes of glycine with one Zn+ or Zn2+ and further with one and even two H2O molecules in the gas phase are studied at the hybrid three-parameter B3LYP and Hartree–Fock level, respectively. On the basis of these optimized geometries, single point calculations are performed using different theoretical methods and larger basis sets. The calculated results imply that the most stable glycine-Zn+ isomer is a five-membered ring with Zn+ bound to both amino nitrogen and carbonyl oxygen (NO) of glycine, and the next most stable glycine-Zn+ species is a four-membered ring with Zn+ coordinated at both oxygen ends (OO) of the zwitterionic glycine. The binding energy of the most stable glycine-Zn+ is 68.5 kcal/mol calibrated at the BHLYP/6-311+G∗//6-311+G∗ level. On the contrary with glycine-Zn+ isomers, the most stable glycine-Zn2+ species holds the similar coordination mode to that of next most stable glycine-Zn2+ complex, while the next most stable glycine-Zn2+ exhibits the similar coordination mode to that of the most stable glycine-Zn+. The binding strength of these glycine-Zn2+ isomers are all far more than those of their corresponding counterparts of glycine-Zn+ isomers, such as the binding energy of the most stable glycine-Zn2+ being 234.4 kcal/mol, showing stronger electrostatic interaction. The reoptimization for the two most stable modes with the different valent states (+1,+2) to combine a H2O molecule at their each end of Zn ion show that the relative energy ordering does not change, and also resembles their no-H2O-combined counterparts. However, an interesting and important observation has been first obtained that single hydration effect can strikingly strengthen the stability of the monovalent OO form though it is still higher by 0.1 kcal/mol in energy than the NO counterpart. Hydration effect of double waters can reverse their relative stability due to the strong hydrogen bond effect in the OO form. Different from the case of the two monovalent hydrated complexes, calculated results for the divalent zinc ion chelated complexes show that with or without single hydration hardly change the value of their relative energy, and hydration strength and glycine deformation difference induced with or without hydration in the two different modes display surprising similarity. So we predict that the further hydration basically do not yield any effect on the relative stability. The prediction for the hydration effect on the glycine-Zn+/Zn2+ system would be also suitable for its analogs, such as glycine-Cu+/Cu2+ and glycine-Ni+/Ni2+ systems, and even suitable for other similar transition metal ion-chelated glycine systems. © 2003 American Institute of Physics.
Show PACS
82.30.Nr Association, addition, insertion, cluster formation
31.15.xr Self-consistent-field methods
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Dual-level direct dynamics studies for the reactions of CH3OCH3 and CF3OCH3 with the OH radical

Jia-yan Wu, Jing-yao Liu, Ze-sheng Li, and Chia-chung Sun

J. Chem. Phys. 118, 10986 (2003); http://dx.doi.org/10.1063/1.1575197 (10 pages) | Cited 6 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The reactions of CH3OCH3+OH (R1) and CF3OCH3+OH (R2) via two hydrogen abstraction channels are investigated theoretically using the dual-level direct dynamics approach. The minimum energy path calculation is carried out at the MP2/6-311G(d,p) level, and energetic information is further refined by the G3 theory. For each reaction hydrogen abstraction is favored for the out-of-plane hydrogen, while the abstraction from the in-plane hydrogen is a minor channel. Hydrogen-bonded complexes are present on the reactants and products sides of the primary channel, indicating that the reactions may proceed via an indirect mechanism. By means of variational transition state theory with interpolated single-point energies method the dynamic results of all channels are obtained, and the small-curvature tunneling is included. The total rate constants calculated from the sum of the individual rate constants are in good agreement with the experimental data and are fitted to be k1 = 3.33×10−20 T2.91 exp(−409.7/T) and k2 = 1.23×10−24 T3.93exp(−188.2/T) cm3 molecule−1 s−1 over the temperature range 230–2000 K. The calculation indicates the CH3OCH3+OH reaction may proceed much easier than the CF3OCH3+OH reaction and fluorine substitution decreases the reactivity of the C–H bond. © 2003 American Institute of Physics.
Show PACS
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
31.15.xp Perturbation theory
31.15.xt Variational techniques

An experimental and theoretical study of the reaction of ethynyl radicals with nitrogen dioxide (HC�C+NO2)

Shaun A. Carl, Hue Minh Thi Nguyen, Minh Tho Nguyen, and Jozef Peeters

J. Chem. Phys. 118, 10996 (2003); http://dx.doi.org/10.1063/1.1573192 (13 pages) | Cited 9 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A pulsed laser photolysis/chemiluminescence (PLP/CL) technique was used to determine absolute rate constants of the reaction C2H+NO2→products over the temperature range 288–800 K at a pressure of 5 Torr (N2). The reaction has a large rate constant that decreases with increasing temperature. It may be expressed in simple Arrhenius form as k1(T) = (7.6±1.0)×10−11 exp[(130±50) K/T], although there is an indication of a downward curvature for T>700 K. A three-parameter Arrhenius fit to the data, which takes this into account gives k1(T) = (9.7±1.5)×10−9T−0.68 exp[(158±65) K/T]. Our experiments also show that the 293 K rate constant is invariant to pressure between 2 and 11 Torr (N2). We have also characterized the C2H+NO2 reaction theoretically. A large portion of the potential energy surface (PES) of the [C2,H,N,O2] system has been investigated in its electronic (singlet) ground-state using DFT with the B3LYP/6-311++G(3df,2p) method and MO computations at the CCSD(T)/6-311++G(d,p) level of theory. Seventeen isomers and thirty-two transition structures were found to connect reactants to products following eighteen different channels. Hydroxyl cyano ketone 11 and formylisocyanate 16 were found to be the most stable intermediates, although the reaction flux through them, as a fraction of the total, is likely to be small over the temperature range studied. A part of the PES corresponds with that of the HCCO+NO reaction [I. V. Tokmakov, L. V. Moskaleva, D. V. Paschenko, and M. C. Lin, J. Phys. Chem. A 167, 1066 (2003)], and the dominant product channels for C2H+NO2 proceed via the same nitrosoketene intermediate that is formed initially in the HCCO+NO reaction. However, unlike in the latter reaction, the fate of the much more highly excited nitrosoketene formed by C2H+NO2 is likely to be governed dynamically. We present arguments as to the likely product channels for C2H+NO2 based on both statistical and dynamical considerations. A statistical description overwhelmingly favors the product set HCCO+NO. Dynamical considerations on the other hand favor both the HCN+CO2 and HCCO+NO product sets. Formation of HCNO+CO appears unlikely. Energetically allowed paths, leading to five other product sets, namely, HNCO+CO, HOCN+CO, HOCC+NO, HONC+CO, and HNC+CO2, have also been identified, and are discussed. © 2003 American Institute of Physics.
Show PACS
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.50.Hp Processes caused by visible and UV light
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Db Transition state theory and statistical theories of rate constants

Isotropic and anisotropic collision-induced light scattering by gaseous sulfur hexafluoride at the frequency region of the ν1 vibrational Raman line

Y. Le Duff, J.-L. Godet, T. Bancewicz, and K. Nowicka

J. Chem. Phys. 118, 11009 (2003); http://dx.doi.org/10.1063/1.1575733 (8 pages) | Cited 6 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Experimental binary isotropic and anisotropic Stokes spectra of the collision-induced light scattered by gaseous sulfur hexafluoride are measured at the frequency region of the ν1 vibrational Raman line. They are compared to theoretical intensities due to dipole–multipole interactions. Taking into account the results of a previous study on the interaction-induced intensities in the Rayleigh wings of gaseous sulfur hexafluoride, an experimental value of the derivative of the dipole–octopole polarizability associated with the ν1 vibrational mode is provided and compared to the result of a recent ab initio calculation. © 2003 American Institute of Physics.
Show PACS
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

First observation of autodetachment lifetimes of methide, CH3−

Stephen E. Mitchell, Philip M. Conklin, and John W. Farley

J. Chem. Phys. 118, 11017 (2003); http://dx.doi.org/10.1063/1.1574017 (9 pages)

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The methide ion, CH3−, has been studied in a mass-selected ion beam. Two autodetachment lifetimes were observed that differ by three orders of magnitude. Infrared laser excitation near 3 micrometers reveals a vibrationally excited state with an autodetachment lifetime of 9–12 ns. This is the first resonant vibrational–rotational transition observed in methide. In addition, metastable ions were observed with a much longer autodetachment lifetime. For simplicity in the data analysis, all metastable ions are assumed to have a single autodetachment lifetime. This is an oversimplification, because the metastable ions decay by rotational autodetachment, and the metastable lifetime will therefore vary with rotational quantum number. The data analysis yields two possible values for the autodetachment lifetime: either 1.59±0.35 μs or 0.42±0.28 ms. The longer lifetime is much more plausible. The metastable states are attributed to rotationally excited states, which can only decay by channels with ΔJ ≥ 5. This interpretation is supported by modeling the energy manifold and populations of ions and neutrals. In contrast, the nanosecond lifetime arises from a vibrationally excited state. There are presently no theoretical calculations of the autodetachment mechanism or lifetimes for the methide ion. © 2003 American Institute of Physics.
Show PACS
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.-b Photon interactions with molecules
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis

Spectroscopy and dynamics of methylamine. I. Rotational and vibrational structures of CH3NH2 and CH3ND2 in states

Sun Jong Baek, Kyo-Won Choi, Young S. Choi, and Sang Kyu Kim

J. Chem. Phys. 118, 11026 (2003); http://dx.doi.org/10.1063/1.1575734 (14 pages) | Cited 17 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Rovibrational structures of methylamines (CH3NH2 and CH3ND2) in predissociative states (3s–n) are investigated using (1+1) resonant-enhanced two-photon ionization (R2PI) spectroscopy. A part of experimental results was briefly reported earlier [J. Chem. Phys. 117, 10057 (2002)], and full detailed results and analyses are given here. Spectral origins are determined to be 41 669 and 42 038 cm−1 for CH3NH2 and CH3ND2, respectively. Amino wagging and CH3 rocking modes are optically active, giving their respective fundamental frequencies of 636 (487) and 1008 (1012) cm−1 for CH3NH2 (CH3ND2). The CH3 moiety is found to rotate nearly freely about the C–N axis with respect to the amino group with an accurately determined torsional barrier of 5.0±0.5 cm−1 at the zero-point level of CH3ND2(). The torsional barrier increases to 19.0±0.5 cm−1 at the v (ND2-wag) = 1 level due to wagging-torsional mode coupling. Both internal and overall rotational fine structures are clearly resolved for the first few vibrational levels of CH3ND2(), providing accurate values of vibrational frequencies and associated internal and overall rotational constants. Broad spectral features of the CH3NH2 excitation spectrum are unambiguously assigned by using the internal rotor Hamiltonian established in the analysis of the CH3ND2 excitation spectrum. Linewidths of spectral bands provide lifetimes of corresponding quantum states excited at particular rovibrational levels, giving, for example, ∼8.8 and ∼1.8 ps for zero-point and v (ND2-wag) = 2 levels of the CH3ND2 () state, respectively. The lifetime of CH3NH2() is estimated to be much shorter, giving τ∼0.38 ps at the origin band. The large H/D isotope effect in lifetimes of excited states indicates that the primary dissociation channel is the N–H(D) bond dissociation and it proceeds via tunneling through a reaction barrier. Lifetimes are found to be mode specific, showing the experimental fact that energy deposition to a certain vibrational mode, which is perpendicular to the reaction coordinate, may modify the reaction barrier along the N–H(D) reaction coordinate. Ab initio results for structures and vibrational frequencies of methylamines at excited states are compared with the experiment. © 2003 American Institute of Physics.
Show PACS
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.70.Jg Line and band widths, shapes, and shifts
33.80.Gj Diffuse spectra; predissociation, photodissociation

Spectroscopy and dynamics of methylamine. II. Rotational and vibrational structures of CH3NH2 and CH3ND2 in cationic D0 states

Sun Jong Baek, Kyo-Won Choi, Young S. Choi, and Sang Kyu Kim

J. Chem. Phys. 118, 11040 (2003); http://dx.doi.org/10.1063/1.1575735 (8 pages) | Cited 12 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Accurate and precise ionization energies of methylamines (CH3NH2 and CH3ND2) are determined to be 9.0422±0.0012 and 9.0532±0.0012 eV, respectively, by (1+1′) two-photon mass-analyzed threshold ionization (MATI) spectroscopy. From selective ionizations from specified intermediate quantum states, fundamental frequencies of amino-wagging and CH3-rocking modes of CH3NH2+ (CH3ND2+) in D0 states are determined to be 738 (573) and 1013 (1024) cm−1, respectively. The frequency of the amino wag is largely blueshifted from that of the neutral S1 state, while the CH3-rocking frequency is little shifted from that of S1. Internal rotational constants associated with the nearly free internal rotation of the top (amino group) with respect to the frame (methyl group) about the C–N axis are accurately determined, from which the geometries of methylamine ions are revealed. Barrier heights for torsional motion in CH3ND2+ are determined to be 25±5 and 34±5 cm−1 at the origin and first ND2-wagging bands, respectively. Mode-resolved spectroscopy using the MATI signal for resolving overlapped spectral features in the intermediate state is employed for clarifying the vibrational assignment of the intermediate state. An ab initio calculation at the QCISD level is carried out, giving good agreement with the experiment. © 2003 American Institute of Physics.
Show PACS
31.15.A- Ab initio calculations
31.30.Gs Hyperfine interactions and isotope effects
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.80.-b Photon interactions with molecules
33.80.Eh Autoionization, photoionization, and photodetachment
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
33.20.Sn Rotational analysis
31.15.vq Electron correlation calculations for polyatomic molecules
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Viscoelasticity of fluids with steeply repulsive potentials

G. Rickayzen, J. G. Powles, and D. M. Heyes

J. Chem. Phys. 118, 11048 (2003); http://dx.doi.org/10.1063/1.1575204 (9 pages) | Cited 11 times

Online Publication Date: 9 June 2003

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We consider the infinite frequency moduli and time correlation functions of fluids composed of particles that interact through a steeply repulsive potential of the general analytic form, ϕ(r) = kBT exp[−αf(r)], where α is a measure of the steepness or stiffness of the potential. Although these potentials have different analytical forms, in the steeply repulsive limit of α→∞, the derived properties become almost identical and are only dependent on the value of α and other basic variables. All the infinite frequency moduli which we study are proportional to α and the interaction part of the pressure is only weakly dependent on α. For the force and other configurational property time functions C(t), time t can be replaced by αt, i.e., C(t) = 1−T∗(αt∗)2+O[(αt∗)4], where T∗ = kBT/ϵ, is the reduced temperature, kB is Boltzmann’s constant, where ϵ is a characteristic energy for the potential, and t∗ is a reduced time. We proved this in earlier publications for an inverse power, r−n potential (where α ≡ n), and show here this more general relationship. The effective hard-sphere diameter by the Barker–Henderson equation, and an alternative prescription derived here, give to first order in α−1 the same formula for the effective hard-sphere diameter for these potentials. We have carried out molecular-dynamics simulations that confirm the equivalence in the steeply repulsive limit of both the static and dynamical properties of two such potentials, which have an inverse power r−n and exponential potential exp(−κr) form. We consider that the theory for the infinite frequency shear rigidity modulus presented here could be usefully applied to predict the infinite frequency storage modulus of colloidal liquids. © 2003 American Institute of Physics.
Show PACS
83.60.Bc Linear viscoelasticity
83.60.Df Nonlinear viscoelasticity
61.20.Ja Computer simulation of liquid structure
Page 1 of 3 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close