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1 Nov 2005

Volume 123, Issue 17, Articles (17xxxx)

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Observation of fragile-to-strong liquid transition in surface water in CeO2

E. Mamontov

J. Chem. Phys. 123, 171101 (2005); http://dx.doi.org/10.1063/1.2125729 (4 pages) | Cited 27 times

Online Publication Date: 28 October 2005

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A quasielastic neutron-scattering experiment carried out on a backscattering spectrometer with sub-μeV resolution in the temperature range of 200–250 K has revealed the dynamics of surface water in cerium oxide on the time scale of hundreds of picoseconds. This slow dynamics is attributed to the translational mobility of the water molecules in contact with the surface hydroxyl groups. The relaxation function of this slow motion can be described by a slightly stretched exponential with the stretch factor exceeding 0.9, which indicates almost a Debye-type dynamics. Down to about 220 K, the temperature dependence of the residence time for water molecules follows a Vogel-Fulcher-Tamman law with the glass transition temperature of 181 K. At lower temperatures, the residence time behavior abruptly changes, indicating a fragile-to-strong liquid transition in surface water at about 215 K.
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64.70.Ja Liquid-liquid transitions
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
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back to top Theoretical Methods and Algorithms

Energy band gaps and lattice parameters evaluated with the Heyd-Scuseria-Ernzerhof screened hybrid functional

Jochen Heyd, Juan E. Peralta, Gustavo E. Scuseria, and Richard L. Martin

J. Chem. Phys. 123, 174101 (2005); http://dx.doi.org/10.1063/1.2085170 (8 pages) | Cited 132 times

Online Publication Date: 28 October 2005

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This work assesses the Heyd-Scuseria-Ernzerhof (HSE) screened Coulomb hybrid density functional for the prediction of lattice constants and band gaps using a set of 40 simple and binary semiconductors. An extensive analysis of both basis set and relativistic effects is given. Results are compared with established pure density functionals. For lattice constants, HSE outperforms local spin-density approximation (LSDA) with a mean absolute error (MAE) of 0.037 Å for HSE vs 0.047 Å for LSDA. For this specific test set, all pure functionals tested produce MAEs for band gaps of 1.0–1.3 eV, consistent with the very well-known fact that pure functionals severely underestimate this property. On the other hand, HSE yields a MAE smaller than 0.3 eV. Importantly, HSE correctly predicts semiconducting behavior in systems where pure functionals erroneously predict a metal, such as, for instance, Ge. The short-range nature of the exchange integrals involved in HSE calculations makes their computation notably faster than regular hybrid functionals. The current results, paired with earlier work, suggest that HSE is a fast and accurate alternative to established density functionals, especially for solid state calculations.
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61.66.Fn Inorganic compounds
61.66.Bi Elemental solids
73.20.At Surface states, band structure, electron density of states
71.20.Mq Elemental semiconductors
71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Rf Relativistic effects

Density-functional calculations of relativistic spin-orbit effects on nuclear magnetic shielding in paramagnetic molecules

Teemu O. Pennanen and Juha Vaara

J. Chem. Phys. 123, 174102 (2005); http://dx.doi.org/10.1063/1.2079947 (10 pages) | Cited 16 times

Online Publication Date: 31 October 2005

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Terms arising from the relativistic spin-orbit effect on both hyperfine and Zeeman interactions are introduced to density-functional theory calculation of nuclear magnetic shielding in paramagnetic molecules. The theory is a generalization of the former nonrelativistic formulation for doublet systems and is consistent to O(α4), the fourth power of the fine structure constant, for the spin-orbit terms. The new temperature-dependent terms arise from the deviation of the electronic g tensor from the free-electron g value as well as spin-orbit corrections to hyperfine coupling tensor A, the latter introduced in the present work. In particular, the new contributions include a redefined isotropic pseudocontact contribution that consists of effects due to both the g tensor and spin-orbit corrections to hyperfine coupling. The implementation of the spin-orbit terms makes use of all-electron atomic mean-field operators and/or spin-orbit pseudopotentials. Sample results are given for group-9 metallocenes and a nitroxide radical. The new O(α4) corrections are found significant for the metallocene systems while they obtain small values for the nitroxide radical. For the isotropic shifts, none of the three beyond-leading-order hyperfine contributions are negligible.
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31.15.E- Density-functional theory
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
33.25.+k Nuclear resonance and relaxation
33.70.Jg Line and band widths, shapes, and shifts
33.15.Pw Fine and hyperfine structure

Nucleation-controlled multiphase transitions

Andrzej Ziabicki

J. Chem. Phys. 123, 174103 (2005); http://dx.doi.org/10.1063/1.2038807 (11 pages) | Cited 2 times

Online Publication Date: 31 October 2005

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Thermodynamics and kinetics of phase transitions in multiphase systems have been discussed. Thermodynamically admissible transitions have been identified and transition kinetics described in terms of the extended Kolmogoroff-Avrami-Evans model. Different combinations of transitions have been described as directed graphs. Graph nodes represented individual phases, graph edges—transitions. Superposition of parallel transitions in various mother phases, simultaneous transition of the same mother phase into different target phases, and successive (chain) transitions have been analyzed. Detailed solutions for a three-phase system consisting of one liquid phase and two polymorphic solid phases have been presented.
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64.60.Q- Nucleation
64.70.-p Specific phase transitions

Orbital-free embedding applied to the calculation of induced dipole moments in CO2⋯X (X = He, Ne, Ar, Kr, Xe, Hg) van der Waals complexes

Christoph R. Jacob, Tomasz A. Wesolowski, and Lucas Visscher

J. Chem. Phys. 123, 174104 (2005); http://dx.doi.org/10.1063/1.2107567 (11 pages) | Cited 20 times

Online Publication Date: 1 November 2005

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The orbital-free frozen-density embedding scheme within density-functional theory [ T. A. Wesolowski and A. Warshel, J. Phys. Chem. 97, 8050 (1993) ] is applied to the calculation of induced dipole moments of the van der Waals complexes CO2⋯X (X = He, Ne, Ar, Kr, Xe, Hg). The accuracy of the embedding scheme is investigated by comparing to the results of supermolecule Kohn-Sham density-functional theory calculations. The influence of the basis set and the consequences of using orbital-dependent approximations to the exchange-correlation potential in embedding calculations are examined. It is found that in supermolecular Kohn-Sham density-functional calculations, different common approximations to the exchange-correlation potential are not able to describe the induced dipole moments correctly and the reasons for this failure are analyzed. It is shown that the orbital-free embedding scheme is a useful tool for applying different approximations to the exchange-correlation potential in different subsystems and that a physically guided choice of approximations for the different subsystems improves the calculated dipole moments significantly.
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31.15.E- Density-functional theory

Calculation of specific, highly excited vibrational states based on a Davidson scheme: Application to HFCO

Christophe Iung and Fabienne Ribeiro

J. Chem. Phys. 123, 174105 (2005); http://dx.doi.org/10.1063/1.2101457 (9 pages) | Cited 7 times

Online Publication Date: 2 November 2005

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We present the efficiency of a new modified Davidson scheme which yields selectively one high-energy vibrationally excited eigenstate or a series of eigenstates. The calculation of a highly vibrationally excited state ψ located in a dense part of the spectrum requires a specific prediagonalization step before the Davidson scheme. It consists in building a small active space P containing the zero-order states which are coupled with the zero-order description of the eigenstate of interest. We propose a general way to define this active space P which plays a crucial role in the method. The efficiency of the method is illustrated by computing and analyzing the high-energy excited overtones of the out-of-plane mode ∣6,8,10ν6〉 in HFCO. These overtone energies correspond to the 234th, 713th, and 1774th energy levels in our reference basis set which contains roughly 140 000 states. One of the main advantages of this Davidson scheme comes from the fact that the eigenstate and eigenvalue convergence can be assessed during the iterations by looking at the residual ∥(H−EM)ψM∥. The maximum value ϵ allowed for this residual constitutes a very sensitive and efficient parameter which sets the accuracy of the eigenvalues and eigenstates, even when the studied states are highly excited and are localized in a dense part of the spectrum. The physical analysis of the eigenstates associated with the 5th, 7th, and 9th out-of-plane overtones in HFCO provides some interesting information on the energy localization in this mode and on the role played by the in-plane modes. Also, it provides some ideas on the numerical methods which should be developed in the future to tackle higher-energy excited states in polyatomics.
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33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
34.50.-s Scattering of atoms and molecules

Coherent excitation of a two-state system by a linearly chirped Gaussian pulse

G. S. Vasilev and N. V. Vitanov

J. Chem. Phys. 123, 174106 (2005); http://dx.doi.org/10.1063/1.2090260 (10 pages) | Cited 3 times

Online Publication Date: 2 November 2005

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This work presents an analytic description of coherent excitation of a two-state quantum system by an external field with a Gaussian temporal shape and a linear frequency sweep. A very accurate analytic approximation to the transition probability in terms of the Lambert function is derived by using the Dykhne-Davis-Pechukas approach. This approximation provides analytic expressions for the frequency and the amplitude of the probability oscillations and for the ranges of interaction parameters where high transition probability is obtained.
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32.70.Cs Oscillator strengths, lifetimes, transition moments

Transition probabilities of a string oscillator subject to impulsive collisions with a heavy mass point

Max Teubner

J. Chem. Phys. 123, 174107 (2005); http://dx.doi.org/10.1063/1.2084946 (5 pages)

Online Publication Date: 2 November 2005

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Impulsive linear collisions between a string oscillator (a one-dimensional particle in a box) and a mass point are studied quantum mechanically. In the limit of a very heavy mass point (which corresponds classically to many collisions during a single encounter) the transition probabilities are determined exactly. The result permits a discussion of the mixed quantum-classical regime where the collider becomes almost classical while the oscillator remains quantum mechanical. While the average transition probabilities Pm→n are well reproduced by the Ehrenfest mean-field approximation, the prediction for the superimposed high-frequency resonance structure is qualitatively wrong for a genuine quantum oscillator. Only if the oscillator is also almost classical and if (m−n)2math⪡m, where μ is the mass ratio collider∕oscillator, this structure is correctly predicted by the Ehrenfest approximation.
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03.65.Ge Solutions of wave equations: bound states

Semiclassical nonadiabatic dynamics using a mixed wave-function representation

Sophya Garashchuk, Vitaly A. Rassolov, and George C. Schatz

J. Chem. Phys. 123, 174108 (2005); http://dx.doi.org/10.1063/1.2099547 (10 pages) | Cited 4 times

Online Publication Date: 2 November 2005

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Nonadiabatic effects in quantum dynamics are described using a mixed polar/coordinate space representation of the wave function. The polar part evolves on dynamically determined potential surfaces that have diabatic and adiabatic potentials as limiting cases of weak localized and strong extended diabatic couplings. The coordinate space part, generalized to a matrix form, describes transitions between the surfaces. Choice of the effective potentials for the polar part and partitioning of the wave function enables one to represent the total wave function in terms of smooth components that can be accurately propagated semiclassically using the approximate quantum potential and small basis sets. Examples are given for two-state one-dimensional problems that model chemical reactions that demonstrate the capabilities of the method for various regimes of nonadiabatic dynamics.
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82.20.Gk Electronically non-adiabatic reactions
82.20.Wt Computational modeling; simulation
82.30.-b Specific chemical reactions; reaction mechanisms

Pair potentials from diffraction data on liquids: A neural network solution

Gergely Tóth, Norbert Király, and Attila Vrabecz

J. Chem. Phys. 123, 174109 (2005); http://dx.doi.org/10.1063/1.2102887 (8 pages) | Cited 2 times

Online Publication Date: 3 November 2005

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The inverse theorem of liquids states a one to one correspondence between classical mechanical pair potentials and structural functions. Molecular-dynamics and Monte Carlo simulations provide exact structural functions for known pair interactions. There is no exact or widespread method in the opposite direction, where the pair interactions are to be determined from a priori known pair-correlation functions or structure factors. The methods based on the integral equation theories of liquids are approximate and the iterative refinements of pair potentials with simulations take a long time. We applied artificial neural networks to get pair interactions from known structure factors in this study. We performed molecular-dynamics simulations on one-component systems with different pair potentials and the structure factors were calculated. To optimize (train) the weights of neural networks 2000 pair interaction-structure factor pairs were used. The performance of the method was tested on further 200 data pairs. The method provided reasonable potentials for the majority of the systems opening a “quick and dirty” method to determine pair interactions.
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61.20.Ja Computer simulation of liquid structure

Theory and method for calculating resonance Raman scattering from resonance polarizability derivatives

L. Jensen, L. L. Zhao, J. Autschbach, and G. C. Schatz

J. Chem. Phys. 123, 174110 (2005); http://dx.doi.org/10.1063/1.2046670 (11 pages) | Cited 31 times

Online Publication Date: 3 November 2005

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We present a method to calculate both normal Raman-scattering (NRS) and resonance Raman-scattering (RRS) spectra from the geometrical derivatives of the frequency-dependent polarizability. In the RRS case, the polarizability derivatives are calculated from resonance polarizabilities by including a finite lifetime of the electronic excited states using time-dependent density-functional theory. The method is a short-time approximation to the Kramers, Heisenberg, and Dirac formalism. It is similar to the simple excited-state gradient approximation method if only one electronic excited state is important, however, it is not restricted to only one electronic excited state. Since the method can be applied to both NRS and RRS, it can be used to obtain complete Raman excitation profiles. To test the method we present the results for the S2 state of uracil and the S4, S3, and S2 states of pyrene. As expected, the results are almost identical to the results obtained from the excited-state gradient approximation method. Comparing with the experimental results, we find in general quite good agreement which enables an assignment of the experimental bands to bands in the calculated spectrum. For uracil the inclusion of explicit waters in the calculations was found to be necessary to match the solution spectra. The calculated resonance enhancements are on the order of 104–106, which is in agreement with experimental findings. For pyrene the method is also able to distinguish between the three different electronic states for which experimental data are available. The neglect of anharmonicity and solvent effects in the calculations leads to some discrepancy between theory and experiment.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
31.15.E- Density-functional theory
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Information entropy, information distances, and complexity in atoms

K. Ch. Chatzisavvas, Ch. C. Moustakidis, and C. P. Panos

J. Chem. Phys. 123, 174111 (2005); http://dx.doi.org/10.1063/1.2121610 (10 pages) | Cited 45 times

Online Publication Date: 3 November 2005

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Shannon information entropies in position and momentum spaces and their sum are calculated as functions of Z(2 ⩽ Z ⩽ 54) in atoms. Roothaan-Hartree-Fock electron wave functions are used. The universal property S = a+b ln Z is verified. In addition, we calculate the Kullback-Leibler relative entropy, the Jensen-Shannon divergence, Onicescu’s information energy, and a complexity measure recently proposed. Shell effects at closed-shell atoms are observed. The complexity measure shows local minima at the closed-shell atoms indicating that for the above atoms complexity decreases with respect to neighboring atoms. It is seen that complexity fluctuates around an average value, indicating that the atom cannot grow in complexity as Z increases. Onicescu’s information energy is correlated with the ionization potential. Kullback distance and Jensen-Shannon distance are employed to compare Roothaan-Hartree-Fock density distributions with other densities of previous works.
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31.15.xr Self-consistent-field methods
32.50.+d Fluorescence, phosphorescence (including quenching)
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Isomers of NCO2: IR-absorption spectra of ONCO in solid Ne

Yu-Jong Wu and Yuan-Pern Lee

J. Chem. Phys. 123, 174301 (2005); http://dx.doi.org/10.1063/1.2062267 (6 pages) | Cited 2 times

Online Publication Date: 28 October 2005

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Irradiation of a Ne matrix sample containing NO and CO near 4 K with an ArF excimer laser at 193 nm yielded new lines at 2045.1 and 968.0 cm−1 that were depleted upon secondary photolysis at 308 nm. These lines are assigned to CO stretching and mixed stretching modes of ONCO, based on results of math-, math-, and math-isotopic experiments and quantum-chemical calculations. These calculations using density-functional theory (B3LYP and PW91PW91/aug-cc-pVTZ) predict five stable isomers of NCO2: ONCO, NCOO, N-cyc-CO2, CNOO, and cyc-CNOO, listed in order of increasing energy. According to B3LYP calculations, ONCO has a trans configuration, with bond angles of ∠ONC ≅ 136.3° and ∠NOC ≅ 160.7°. Calculated vibrational wave numbers, IR intensities, math-, math-, and math-isotopic shifts for ONCO agree satisfactorily with experimental results. ONCO was formed from reaction of CO with NO in its excited state.
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33.20.Ea Infrared spectra
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.E- Density-functional theory
82.50.Bc Processes caused by infrared radiation
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
33.15.Dj Interatomic distances and angles
33.70.Jg Line and band widths, shapes, and shifts

The vibrational energy pattern in acetylene VII: mathmathH2

S. Robert, A. Fayt, G. Di Lonardo, L. Fusina, F. Tamassia, and M. Herman

J. Chem. Phys. 123, 174302 (2005); http://dx.doi.org/10.1063/1.2056538 (6 pages) | Cited 6 times

Online Publication Date: 28 October 2005

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In mathmathH2 129 vibrational term values up to 10 000 cm−1 are merged, about 60% of which are newly reported. They are fitted using an effective Hamiltonian with a standard deviation of 0.22 cm−1. The vibrational assignments and vibrational constants are listed and discussed. The energy pattern is found to be very similar to the one in mathH2 with additional anharmonic resonances arising from the lack of u/g character in the asymmetric isotopolog.
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33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis

The UV photodissociation dynamics of ClO radical using velocity map ion imaging

Hahkjoon Kim, Jiho Park, Tracy C. Niday, and Simon W. North

J. Chem. Phys. 123, 174303 (2005); http://dx.doi.org/10.1063/1.2083487 (11 pages) | Cited 16 times

Online Publication Date: 28 October 2005

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We have studied the wavelength-dependent photodissociation dynamics of jet-cooled ClO radical from 235 to 291 nm using velocity map ion imaging. We find that Cl(math)+O(math) is the dominant channel above the O(math) threshold with minor contributions from the Cl(math)+O(math) and Cl(math)+O(math) channels. We have measured the photofragment angular distributions for each dissociation channel and find that the A math state reached via a parallel transition carries most of the oscillator strength above the O(math) threshold. The formation of O(math) fragments with positive anisotropy is evidence of curve crossing from the A math state to one of several dissociative states. The curve crossing probability increases with wavelength in good agreement with previous theoretical calculations. We have directly determined the O(math) threshold to be 38 050±20 cm−1 by measuring O(math) quantum yield in the wavelength range of 260–270 nm. We also report on the predissociation dynamics of ClO below the O(math) threshold. We find that the branching ratio of Cl(math)/Cl(math) is 1.5±0.1 at both 266 and 291 nm. The rotational depolarization of the anisotropy parameters of the Cl(math) fragments provides predissociation lifetimes of 1.5±0.2 ps for the 9-0 band and 1.0±0.4 ps for the 8-0 band, in reasonable agreement with previous spectroscopic and theoretical studies.
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82.50.Hp Processes caused by visible and UV light
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

Ab initio relativistic calculation of the RbCs molecule

S. Kotochigova and E. Tiesinga

J. Chem. Phys. 123, 174304 (2005); http://dx.doi.org/10.1063/1.2107607 (11 pages) | Cited 26 times

Online Publication Date: 28 October 2005

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We apply the relativistic configuration-interaction valence-bond method to calculate various characteristics of the alkali-metal RbCs dimer. These include the electronic potentials and transition dipole moments between the ground and first excited states and permanent dipole moments of the X math and a math states of the ground configuration. In addition, we estimate the lifetime of the rovibrational levels of the X state due to blackbody radiation. These data can help experimentalists to optimize photoassociative formation of ultracold RbCs molecules and their longevity in a trap or in an optical lattice. Extended basis sets, constructed from Dirac-Fock and Sturm’s orbitals, have been used to ensure convergence of our calculations. We compare our data with other theoretical and experimental results when they were available.
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31.15.A- Ab initio calculations
31.15.V- Electron correlation calculations for atoms, ions and molecules
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.20.Vq Vibration-rotation analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants

SiH2Cl2: Ab initio anharmonic force field, dipole moments, and infrared vibrational transitions

An-Wen Liu, Shui-Ming Hu, and Qing-Shi Zhu

J. Chem. Phys. 123, 174305 (2005); http://dx.doi.org/10.1063/1.2090267 (9 pages)

Online Publication Date: 28 October 2005

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The vibrational spectra of SiH2Cl2 have been recorded in the 1000–13 000 cm−1 region, utilizing the Fourier-transform spectroscopy and Fourier-transform intracavity laser absorption spectroscopy. Totally 61 band centers and intensities are derived from the infrared spectra. An ab initio quartic force field is obtained by applying the second-order Møller-Plesset perturbation theory and correlation-consistent polarized valence triplet-zeta basis sets [ J. Chem. Phys. 90, 1007 (1989); 98, 1358 (1993) ]. Most observed bands are assigned by the vibration analysis based on the second-order perturbation theory. Reduced-dimensional ab initio dipole moment functions (two dimensional and three dimensional) have also been calculated to investigate the absolute band intensities of the SiH2 chromophore. The calculated values agree reasonably with the observed ones.
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33.20.Ea Infrared spectra
31.15.A- Ab initio calculations
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.70.Fd Absolute and relative line and band intensities
31.15.xp Perturbation theory

State-resolved collisional quenching of vibrationally excited pyrazine (Evib = 37 900 cm−1) by D35Cl(v = 0)

Ziman Li, Ekaterina Korobkova, Kathryn Werner, Lawrence Shum, and Amy S. Mullin

J. Chem. Phys. 123, 174306 (2005); http://dx.doi.org/10.1063/1.2098647 (9 pages)

Online Publication Date: 31 October 2005

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Supercollision relaxation of highly vibrationally excited pyrazine (Evib = 37 900 cm−1) with D35Cl is investigated using high-resolution transient IR diode laser absorption spectroscopy at 4.4 μm. Highly excited pyrazine is prepared by pulsed UV excitation at 266 nm, followed by rapid radiationless decay to the ground electronic state. The rotational energy distribution of the scattered DCl (v = 0,J) molecules with J = 15–21 is characterized by Trot = 755±90 K. The relative translational energy increases as a function of rotational quantum number for DCl with Trel = 710±190 K for J = 15 and Trel = 1270±240 K for J = 21. The average change in recoil velocity correlates with the change in rotational angular momentum quantum number and highlights the role of angular momentum in energy gain partitioning. The integrated energy-transfer rate for appearance of DCl (v = 0,J = 15–21) is k2int = 7.1×10−11 cm3 molecule−1 s−1, approximately one-eighth the Lennard-Jones collision rate. The results are compared to earlier energy gain measurements of CO2 and H2O.
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33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Ea Infrared spectra
33.80.-b Photon interactions with molecules
34.50.Gb Electronic excitation and ionization of molecules
33.20.Sn Rotational analysis

Lifetime and yield of metastable Ar2+ ions

V. Lepère, I. M. Ismail, M. Barat, J. A. Fayeton, Y. J. Picard, K. Wohrer, C. Jouvet, and S. Martrenchard

J. Chem. Phys. 123, 174307 (2005); http://dx.doi.org/10.1063/1.2085168 (5 pages) | Cited 8 times

Online Publication Date: 31 October 2005

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Ar2+ ions produced in a cooled supersonic expansion by electron-impact ionization are accelerated at 2.5 keV and kept during few milliseconds inside a linear electrostatic trap. The lifetime of the metastable Ar2+ ion is determined from the measurement of the rate of the argon atoms escaping the trap. The lifetime and the relative metastable populations are measured as a function of the pressure and temperature in the supersonic expansion, i.e., of the mean cluster size. Possible mechanisms responsible for the metastable formation are discussed.
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36.40.Wa Charged clusters
36.40.Cg Electronic and magnetic properties of clusters
32.70.Cs Oscillator strengths, lifetimes, transition moments
34.80.Dp Atomic excitation and ionization

Three-isotope plot of fractionation in photolysis: A perturbation theoretical expression

M. K. Prakash and R. A. Marcus

J. Chem. Phys. 123, 174308 (2005); http://dx.doi.org/10.1063/1.2102908 (6 pages) | Cited 6 times

Online Publication Date: 31 October 2005

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The slope of the three-isotope plot for the isotopomer fractionation by direct or nearly direct photodissociation is obtained using a perturbation theoretical analysis. This result, correct to first order in the mass difference, is the same as that for equilibrium chemical exchange reactions, a similarity unexpected a priori. A comparison is made with computational results for N2O photodissociation. This theoretical slope for mass-dependent photolytic fractionation can be used to analyze the data for isotopic anomalies in spin-allowed photodissociation reactions. Earlier work on chemical equilibria is extended by avoiding a high-temperature approximation.
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82.20.Tr Kinetic isotope effects including muonium
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.50.-m Photochemistry
82.60.Hc Chemical equilibria and equilibrium constants

Rare-gas insertion compounds of perfluorobenzene: Aromaticity of some unstable species

Jon Baker, Patrick W. Fowler, Alessandro Soncini, and Mark Lillington

J. Chem. Phys. 123, 174309 (2005); http://dx.doi.org/10.1063/1.2069867 (9 pages) | Cited 1 time

Online Publication Date: 31 October 2005

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Calculations on the novel argon insertion compounds C6F6Arn, n = 1–6, where the argon atoms are inserted into the C–F bonds in perfluorobenzene, suggest that all possible species, with one to six inserted argon atoms, occupy minima on their respective potential energy surfaces. Ring-current plots using the ipsocentric model indicate that there is no disruption of the aromatic π system upon argon insertion, and consequently all insertion compounds are aromatic according to the magnetic criterion. The barrier height for decomposition of the single-insertion compound, C6F6Ar, into C6F6+Ar is 19.5 kcal/mol at HF/6-311G** and 29.5 kcal/mol at B3LYP/6-311G**, suggesting that, although clearly thermodynamically unstable, argon-perfluorobenzene insertion compounds may be stable kinetically. Preliminary calculations indicate that other rare gas-perfluorobenzene insertion compounds may also be metastable. Both C6F6Ne and C6F6He are predicted to occupy minima on their respective potential energy surfaces.
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31.15.E- Density-functional theory
31.15.xr Self-consistent-field methods
31.50.-x Potential energy surfaces
33.15.Fm Bond strengths, dissociation energies

Mass-analyzed threshold ionization study of vinyl bromide cation in the first excited electronic state using vacuum-ultraviolet radiation generated by four-wave mixing in Hg

Mina Lee and Myung Soo Kim

J. Chem. Phys. 123, 174310 (2005); http://dx.doi.org/10.1063/1.2104530 (7 pages) | Cited 5 times

Online Publication Date: 31 October 2005

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The vibrational spectrum of the vinyl bromide cation in the first excited electronic state math math was obtained by one-photon mass-analyzed threshold ionization (MATI) spectroscopy. The use of an improved vacuum-ultraviolet radiation source based on four-wave sum frequency mixing in Hg resulted in excellent sensitivity for MATI signals. From the MATI spectrum, the ionization energy to the math math state of the cation was determined to be 10.9150±0.0006 eV. Nearly complete vibrational assignments for the MATI peaks were possible by utilizing the vibrational frequencies and Franck-Condon factors calculated at the density-functional theory (DFT) and time-dependent DFT/B3LYP levels with the 6-311+G(df,p) basis set.
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31.15.E- Density-functional theory
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Ta Mass spectra
33.20.Tp Vibrational analysis
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.80.Eh Autoionization, photoionization, and photodetachment

Rotational excitation cross sections of para-H2+para-H2 collisions. A full-dimensional wave-packet propagation study using an exact form of the kinetic energy

Fabien Gatti, Frank Otto, Suren Sukiasyan, and Hans-Dieter Meyer

J. Chem. Phys. 123, 174311 (2005); http://dx.doi.org/10.1063/1.2085167 (13 pages) | Cited 25 times

Online Publication Date: 1 November 2005

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A full-dimensional quantum dynamical study of the rotational excitation in para-para H2+H2 collisions using the potential-energy surface of Boothroyd et al. [J. Chem. Phys. 116, 666 (2002)] is reported. The multiconfiguration time-dependent Hartree algorithm is utilized to propagate wave packets and the cross sections for collision energies up to 1.2 eV are determined by a flux analysis through the interaction of the wave packet with a complex absorbing potential. Calculations for a collection of total angular momenta up to J = 70 are performed; the missing channels are obtained with a J-interpolation algorithm.
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34.50.Gb Electronic excitation and ionization of molecules
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
31.15.xr Self-consistent-field methods

Cross sections of the O++H2→OH++H ion-molecule reaction and isotopic variants (D2, HD): Quasiclassical trajectory study and comparison with experiments

Rodrigo Martínez, José Daniel Sierra, and Miguel González

J. Chem. Phys. 123, 174312 (2005); http://dx.doi.org/10.1063/1.2098667 (7 pages) | Cited 8 times

Online Publication Date: 1 November 2005

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A dynamics study [cross section and microscopic mechanism versus collision energy (ET)] of the reaction O++H2→OH++H, which plays an important role in Earth’s ionosphere and interstellar chemistry, was conducted using the quasiclassical trajectory method, employing an analytical potential energy surface (PES) recently derived by our group [ R. Martínez et al., J. Chem. Phys. 120, 4705 (2004) ]. Experimental excitation functions for the title reaction, as well as its isotopic variants with D2 and HD, were near-quantitatively reproduced in the calculations in the very broad collision energy range explored (ET = 0.01–6.0 eV). Intramolecular and intermolecular isotopic effects were also examined, yielding data in good agreement with experimental results. The reaction occurs via two microscopic mechanisms (direct and nondirect abstraction). The results were satisfactorily interpreted based on the reaction probability and the maximum impact parameter dependences with ET, and considering the influence of the collinear [OHH]+ absolute minimum of the PES on the evolution from reactants to products. The agreement between theory and experiment suggests that the reaction mainly occurs through the lowest energy PES and nonadiabatic processes are not very important in the wide collision energy range analyzed. Hence, the PES used to describe this reaction is suitable for both kinetics and dynamics studies.
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.20.Fd Collision theories; trajectory models
82.20.Ln Semiclassical theory of reactions and/or energy transfer
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Tr Kinetic isotope effects including muonium
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Pm Rate constants, reaction cross sections, and activation energies

A diffusion quantum Monte Carlo study on the lowest singlet and triplet electronic states of BN molecule

Shih-I Lu

J. Chem. Phys. 123, 174313 (2005); http://dx.doi.org/10.1063/1.2104347 (5 pages) | Cited 3 times

Online Publication Date: 1 November 2005

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Ab initio calculation of both the lowest singlet and triplet electronic states of BN has been performed by the fixed-node Ornstein-Uhlenbeck diffusion quantum Monte Carlo method with the floating spherical Gaussian orbitals and spherical Gaussian geminals. The Monte Carlo calculation gives equilibrium bond lengths and equilibrium harmonic frequencies of 1.3317(7) Å and 1529(7) cm−1, respectively, for the lowest triplet state and 1.2751(7) Å and 1709(8) cm−1, respectively, for the lowest singlet state. Also, the Monte Carlo calculation reports an energy separation of 178(83) cm−1 between the two electronic states and recommends the ground state is the lowest triplet state.
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31.15.A- Ab initio calculations
33.15.Dj Interatomic distances and angles
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