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22 Jun 2001

Volume 114, Issue 24, pp. 10569-10986

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Electron transfer to oriented molecules: Surprising steric effect in t-butyl bromide

Sean A. Harris and Philip R. Brooks

J. Chem. Phys. 114, 10569 (2001); http://dx.doi.org/10.1063/1.1380233 (4 pages) | Cited 6 times

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Collisions between neutral K atoms and oriented t-butyl bromide molecules produce the ions K+ and Br− at energies high enough to separate charged particles (≳4 eV). Ions are detected by coincidence tof mass spectrometry for orientation of the t-butyl bromide such that the K atom attacks either the Br end or the t-butyl end of the molecule. At high energies the steric asymmetry factor is larger than that for CH3Br. But at energies near threshold, the steric asymmetry factor reverses sign and attack at the t-butyl end becomes more reactive than attack at the Br end. The electron is apparently transferred into different orbitals at different ends. © 2001 American Institute of Physics.
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
34.70.+e Charge transfer
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
33.15.Ta Mass spectra

Thermodynamic regulation of actin polymerization

Priya S. Niranjan, Jeffrey G. Forbes, Sandra C. Greer, Jacek Dudowicz, Karl F. Freed, and Jack F. Douglas

J. Chem. Phys. 114, 10573 (2001); http://dx.doi.org/10.1063/1.1380693 (4 pages) | Cited 23 times

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A Flory–Huggins-type lattice model of actin polymerization under equilibrium conditions is employed to analyze new spectroscopic measurements for the extent of actin polymerization Φ as a function of temperature T, salt concentration [KCl], and the initial concentration of actin monomers [G0]. The theory subsumes existing mechanisms for actin monomer initiation, dimerization, and chain propagation. The extent of polymerization Φ increases with T to an unanticipated maximum, and the calculations explain this unusual effect as arising from a competition between monomer activation, which diminishes upon heating, and propagating chain growth, which increases upon heating. The actin polymerization is described as a rounded phase transition, and the associated polymerization temperature Tp depends strongly, but nearly linearly on [G0] and [KCl] over the concentration regimes investigated. Our findings support the suggestion that physicochemical changes can complement regulatory proteins in controlling actin polymerization in living systems. © 2001 American Institute of Physics.
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87.15.R- Reactions and kinetics
82.35.Pq Biopolymers, biopolymerization
87.14.E- Proteins

Relationship between kinetics and thermodynamics of supercooled liquids

Udayan Mohanty, Nathaniel Craig, and John T. Fourkas

J. Chem. Phys. 114, 10577 (2001); http://dx.doi.org/10.1063/1.1381060 (2 pages) | Cited 10 times

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We show that a single, reasonable assumption about the probability of rearrangements in a supercooled liquid necessarily implies a direct connection between kinetic and thermodynamic observables in these media. The prediction is tested against available experimental data for supercooled liquids spanning the range of observed kinetics. © 2001 American Institute of Physics.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
65.20.-w Thermal properties of liquids

Stability and production of positron–diatomic molecule complexes

Massimo Mella, Dario Bressanini, and Gabriele Morosi

J. Chem. Phys. 114, 10579 (2001); http://dx.doi.org/10.1063/1.1381009 (4 pages) | Cited 9 times

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The energies at geometries close to the equilibrium for the e+LiF and e+BeO ground states were computed by means of diffusion Monte Carlo simulations. These results allow us to predict the equilibrium geometries and the vibrational frequencies for these exotic systems, and to discuss their stability with respect to the various dissociation channels. Since the adiabatic positron affinities were found to be smaller than the dissociation energies for both complexes, we propose these two molecules as possible candidates in the challenge to produce and detect stable positron–molecule systems. Moreover, low-energy positron scattering on LiF and BeO targets may show vibrational Feshbach resonances as fingerprints of the existence of stable ground states of e+LiF and e+BeO. © 2001 American Institute of Physics.
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34.80.Uv Positron scattering
33.20.Tp Vibrational analysis
33.15.Fm Bond strengths, dissociation energies
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back to top Theoretical Methods and Algorithms

Scaling of classical rate constants on scaled potential-energy surfaces

Myung Soo Kim, Sang Tae Park, Bong June Sung, and Jeong Hee Moon

J. Chem. Phys. 114, 10583 (2001); http://dx.doi.org/10.1063/1.1374938 (8 pages) | Cited 3 times

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The scaling relation for the classical rate constants on the scaled potential-energy surfaces has been derived using the scaling theorem in classical dynamics reported previously. This applies to the classical rate constants, both for unimolecular and for bimolecular reactions, that can be obtained by the classical trajectory method and the transition state theory. Validity of the theory has been tested for the prototype reactions, H2CO→H2+CO and Cl+H2→HCl+H. Exact scaling of the rate constants obtained by the classical trajectory calculations has been demonstrated. The rate-energy relations for the former reaction calculated with the statistical Rice–Ramsperger–Kassel–Marcus theory also displayed excellent scaling in the high-energy limit. The scaling relation does not hold rigorously near the reaction threshold due to the quantum mechanical zero-point energy effect. Regardless, the order of magnitude prediction of the threshold rate constant by scaling was possible even in extreme cases. The present method may allow reliable prediction of the classical rate constant by using potential energy data obtained at moderately high levels of electronic structure calculation. © 2001 American Institute of Physics.
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82.20.Kh Potential energy surfaces for chemical reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.30.-b Specific chemical reactions; reaction mechanisms
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

Exchange energy functionals based on the full fourth-order density matrix expansion

Sergey N. Maximoff and Gustavo E. Scuseria

J. Chem. Phys. 114, 10591 (2001); http://dx.doi.org/10.1063/1.1373432 (7 pages) | Cited 11 times

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We have derived the fourth-order generalized density matrix expansion and used it to construct various exchange-energy functionals. The fourth-order terms depend on several quantities containing invariants of the second-order derivative matrices of the orbitals and the electron density. The impact of these variables on the accuracy of exchange functionals has never been studied before and we here demonstrate their importance. The new exchange functionals show excellent accuracy (as compared to Hartree–Fock exchange energies) surpassing those of our previously developed exchange functionals. © 2001 American Institute of Physics.
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31.15.E- Density-functional theory

Vibration–rotation kinetic energy operators: A geometric algebra approach

Janne Pesonen

J. Chem. Phys. 114, 10598 (2001); http://dx.doi.org/10.1063/1.1374577 (10 pages) | Cited 9 times

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The elements of the reciprocal metric tensor g(qiqj), which appear in the exact internal kinetic energy operators of polyatomic molecules can, in principle, be written as the mass-weighted sum of the inner products of measuring vectors associated to the nuclei of the molecule. In the case of vibrational degrees of freedom, the measuring vectors are simply the gradients of the vibrational coordinates. It is more difficult to find these vectors for the rotational degrees of freedom, because the components of the total angular momentum operator are not conjugated to any rotational coordinates. However, by the methods of geometric algebra, the rotational measuring vectors are easily calculated for any geometrically defined body-frame, without any restrictions to the number of particles in the system. In order to show that the rotational measuring vectors produced by the present method agree with the known results, the general formulas are applied to the triatomic bond-z, and to the triatomic angle bisector frame. All the rotational measuring vectors are also explicitly derived for a new triatomic body frame defined in terms of two Jacobi vectors. As a final application, all the rotational measuring vectors are presented for a new N-atomic frame defined in terms of N−1 Jacobi vectors, and for a simple N-atomic frame defined in terms of N nuclear position vectors (N = 3,4,5,6,…). © 2001 American Institute of Physics.
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33.20.Vq Vibration-rotation analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
02.10.-v Logic, set theory, and algebra

Direct semiclassical simulation of photochemical processes with semiempirical wave functions

G. Granucci, M. Persico, and A. Toniolo

J. Chem. Phys. 114, 10608 (2001); http://dx.doi.org/10.1063/1.1376633 (8 pages) | Cited 51 times

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We describe a new method for the simulation of excited state dynamics, based on classical trajectories and surface hopping, with direct semiempirical calculation of the electronic wave functions and potential energy surfaces (DTSH method). Semiempirical self-consistent-field molecular orbitals (SCF MO’s) are computed with geometry-dependent occupation numbers, in order to ensure correct homolytic dissociation, fragment orbital degeneracy, and partial optimization of the lowest virtuals. Electronic wave functions are of the MO active space configuration interaction (CI) type, for which analytic energy gradients have been implemented. The time-dependent electronic wave function is propagated by means of a local diabatization algorithm which is inherently stable also in the case of surface crossings. The method is tested for the problem of excited ethylene nonadiabatic dynamics, and the results are compared with recent quantum mechanical calculations. © 2001 American Institute of Physics.
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82.50.-m Photochemistry
82.20.Kh Potential energy surfaces for chemical reactions
31.15.xr Self-consistent-field methods
31.15.V- Electron correlation calculations for atoms, ions and molecules

Self-consistent field algorithms for Kohn–Sham models with fractional occupation numbers

Eric Cancès

J. Chem. Phys. 114, 10616 (2001); http://dx.doi.org/10.1063/1.1373430 (7 pages) | Cited 20 times

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The calculations of electronic ground state energies, following either the Hartree–Fock or the Kohn–Sham schemes, are major issues in quantum chemistry. In a recent publication, we have proposed a new numerical method, namely the relaxed constrained algorithms (RCA), to solve the Hartree–Fock problem. The purpose of the present paper is to discuss the extension of this method to the case of the Kohn–Sham problem. It is shown that RCA seems to be more robust than other self-consistent field algorithms currently used and that they provide in addition a natural way to solve the extended Kohn–Sham problem, obtained by allowing fractional occupancy of the single-particle orbitals. © 2001 American Institute of Physics.
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31.15.xr Self-consistent-field methods

Quantum dissipative master equations: Some exact results

Y. Zhao and G. H. Chen

J. Chem. Phys. 114, 10623 (2001); http://dx.doi.org/10.1063/1.1374537 (15 pages) | Cited 4 times

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With the help of quantum characteristic functions some exact results are found for two quantum dissipative master equations which contain dissipative Liouvillian operators of the Lindblad-type corresponding to two forms of dissipation mechanisms. Population relaxation is used to demonstrate how dynamic information can be retrieved from these solutions. © 2001 American Institute of Physics.
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03.67.Lx Quantum computation architectures and implementations
02.30.-f Function theory, analysis

Problematic p-benzyne: Orbital instabilities, biradical character, and broken symmetry

T. Daniel Crawford, Elfi Kraka, John F. Stanton, and Dieter Cremer

J. Chem. Phys. 114, 10638 (2001); http://dx.doi.org/10.1063/1.1373433 (13 pages) | Cited 52 times

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The equilibrium geometry, harmonic vibrational frequencies, and infrared transition intensities of p-benzyne were calculated at the MBPT(2), SDQ-MBPT(4), CCSD, and CCSD(T) levels of theory using different reference wave functions obtained from restricted and unrestricted Hartree-Fock (RHF and UHF), restricted Brueckner (RB) orbital, and Generalized Valence Bond (GVB) theory. RHF erroneously describes p-benzyne as a closed-shell singlet rather than a singlet biradical, which leads to orbital near-instabilities in connection with the mixing of orbital pairs b1u-ag (HOMO–LUMO), b2g-ag (HOMO-1-LUMO), and b1g-ag (HOMO-2-LUMO). Vibrational modes of the corresponding symmetries cause method-dependent anomalous increases (unreasonable force constants and infrared intensities) or decreases in the energy (breaking of the D2h symmetry of the molecular framework of p-benzyne). This basic failure of the RHF starting function is reduced by adding dynamic electron correlation. However RHF-MBPT(2), RHF-SDQ-MBPT(4), RHF-CCSD, RB-CCD, and RHF-CCSD(T) descriptions of p-benzyne are still unreliable as best documented by the properties of the b1u-, b2g-, and b1g-symmetrical vibrational modes. The first reliable spin-restricted description is provided when using Brueckner orbitals at the RB-CCD(T) level. GVB leads to exaggerated biradical character that is reduced at the GVB-MP2 level of theory. The best results are obtained with a UHF reference wave function, provided a sufficient account of dynamic electron correlation is included. At the UHF-CCSD level, the triplet contaminant is completely annihilated. UHF-CCSD(T) gives a reliable account of the infrared spectrum apart from a CCH bending vibrational mode, which is still in disagreement with experiment. © 2001 American Institute of Physics.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Ea Infrared spectra
33.70.Fd Absolute and relative line and band intensities
31.15.xp Perturbation theory
31.15.bw Coupled-cluster theory
31.15.xr Self-consistent-field methods
31.15.xw Valence bond calculations
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Exact three-dimensional quantum mechanical calculation of ozone photodissociation in the Hartley band

Shi Ying Lin, Ke Li Han, and Guo Zhong He

J. Chem. Phys. 114, 10651 (2001); http://dx.doi.org/10.1063/1.1374580 (11 pages) | Cited 17 times

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Exact three-dimensional time-dependent wave packet calculation for ozone photodissociation in the Hartley band has been carried out for total angular momentum J = 0. Fully converged absorption spectrum, autocorrelation function, and O2(a 1Δg) photofragment rovibrational state distributions over wide range of wavelengths are obtained using the Sheppard–Walker potential energy surface (PES). Excellent agreements as well as some deviations have been found in comparison to the various experimental results. From these successes and failings, the ways for further improving the PES have been suggested, and the dynamics has been discussed in some detail in conjunction with time-dependent pictures of the wave packet. © 2001 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
82.50.-m Photochemistry
33.20.Vq Vibration-rotation analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.50.-x Potential energy surfaces
82.20.Kh Potential energy surfaces for chemical reactions

Experimental and theoretical differential cross sections for the reactions Cl+H2/D2

Dimitris Skouteris, Hans-Joachim Werner, F. Javier Aoiz, Luis Bañares, Jesus F. Castillo, Marta Menéndez, Nadia Balucani, Laura Cartechini, and Piergiorgio Casavecchia

J. Chem. Phys. 114, 10662 (2001); http://dx.doi.org/10.1063/1.1372764 (11 pages) | Cited 27 times

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Experimental and theoretical differential cross sections for the reactions between Cl atoms and two isotopic variants of molecular hydrogen (H2 and D2) are presented. The experimental results have been obtained by using the crossed molecular beam method with mass spectrometric detection. The theoretical results have been computed using both the quasiclassical trajectory and quantum mechanical (QM) methods. The potential energy surface employed for the calculations is the ab initio BW2 surface by Bian and Werner [J. Chem. Phys. 112, 220 (2000)]. The theoretical results have been directly compared to the experiments in the laboratory frame at a collision energy (Ec) of 4.25 and 5.85 kcal/mol for the Cl+H2 reaction and of 4.9 and 6.3 kcal/mol for the Cl+D2 reaction. The agreement between QM results and experiment is quite satisfactory for the Cl+D2 reaction, especially for the low collision energy, while for Cl+H2 is less good, especially when considering data at the lower Ec. © 2001 American Institute of Physics.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Tr Kinetic isotope effects including muonium
82.20.Kh Potential energy surfaces for chemical reactions
31.15.A- Ab initio calculations

An ab initio study of the betaine anion–dipole-bound anionic state of a model zwitterion system

Janusz Rak, Piotr Skurski, and Maciej Gutowski

J. Chem. Phys. 114, 10673 (2001); http://dx.doi.org/10.1063/1.1373689 (9 pages) | Cited 23 times

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The electron binding to a model zwitterionic molecule, betaine, is studied at the coupled cluster level of theory with single, double, and noniterative triple excitations as well as at the density functional theory level. Our results indicate that there is only one stable conformer of betaine with a dipole moment of 11.5 D. This dipole moment supports a relatively strongly bound anionic state and the vertical electron detachment energy was found to be 2261 cm−1. Furthermore, we predict the excess electron binding energy for the betaine analog with a blocked canonical structure (N,N-dimethylglycine methyl ester) to be less than 100 cm−1. This significant difference in electron binding energies suggests that the gas phase instability of zwitterions of some common naturally occurring amino acids with respect to their canonical forms may be reversed by the excess electron attachment. The calculated Franck–Condon factors for the betaine’s anion/neutral pair suggest that the photoelectron spectrum of the anion will display only a very weak vibrational structure. © 2001 American Institute of Physics.
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31.15.A- Ab initio calculations
31.15.E- Density-functional theory
31.15.bw Coupled-cluster theory
34.50.Gb Electronic excitation and ionization of molecules
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.60.+q Photoelectron spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants

The math 2B1, 2B2, 2A1, and 2A2 states of oxygen difluoride cation (F2O+): High-level ab initio calculations and simulation of the ultraviolet photoelectron spectrum of F2O

De-Chao Wang, Foo-Tim Chau, Daniel Kam-Wah Mok, Edmond P. F. Lee, Levi Beeching, J. Steven Ogden, and John M. Dyke

J. Chem. Phys. 114, 10682 (2001); http://dx.doi.org/10.1063/1.1373690 (13 pages) | Cited 11 times

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The ultraviolet photoelectron spectrum of F2O was recorded with a higher resolution than previously published. New vibrational structure was observed in the second and third bands. Near state-of-the-art molecular orbital calculations were performed on the math 1A1 state of F2O and the math 2B1, 2B2, 2A1, and 2A2 state of F2O+, and their potential energy functions were computed. Spectral simulations based on Franck–Condon factor calculations including the Duchinsky effect were carried out within the harmonic oscillator model and also with the inclusion of anharmonicity, in order to assist spectral assignment. Based on the computed ionization energies obtained with the coupled cluster and multireference configuration interaction methods with basis sets of up to quintuple zeta quality, the order of the low-lying cationic states of F2O+ has been firmly established. However, the detailed assignment of the overlapping second and third photoelectron bands was only achieved with the aid of spectral simulation. The iterative Franck–Condon analysis (IFCA) procedure was carried out for the first band {F2O+ (math 2B1)←F2O (math 1A1)} in the photoelectron spectrum. With the geometrical parameters of F2O (math 1A1) being fixed at the available experimental values, geometrical parameters of the math 2B1 state of F2O+ were derived. Based on anharmonic Franck–Condon factor calculations, the recommended IFCA geometrical parameters for the ground state of F2O+ are R(FO) = 1.323±0.002 Å and ∠FOF = 107.3±0.2°. © 2001 American Institute of Physics.
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31.15.A- Ab initio calculations
33.60.+q Photoelectron spectra
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
31.15.bw Coupled-cluster theory
31.15.vq Electron correlation calculations for polyatomic molecules

Electronic structure studies of six-atom gold clusters

Mohammad A. Omary, Manal A. Rawashdeh-Omary, Charles C. Chusuei, John P. Fackler, and Paul S. Bagus

J. Chem. Phys. 114, 10695 (2001); http://dx.doi.org/10.1063/1.1373431 (7 pages) | Cited 16 times

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Combined theoretical and experimental studies of the hexagold phosphine-stabilized complex [Au6(PPh3)6][BF4]2 (1) and of related systems are reported. The goal of these studies is to gain a better understanding of how 1 interacts with the TiO2(110) substrate to yield finely dispersed supported Au particles that are effective for practical catalytic reactions. The experimental efforts involved the measurement of the visible-ultraviolet (UV) absorption spectra of 1 and Au(PPh3)Cl in solution. The theoretical efforts involved the determination of the electronic structure of molecular models of 1 based on density functional theory (DFT), Hartree–Fock (HF), and configuration interaction (CI) methods. The CI wave functions and energies were obtained for a range of excited states and were used to simulate the absorption spectra of Au6 and Au62+ clusters. The theoretical CI absorption spectra for Au6 can be correlated with the visible-UV absorption spectra while the theoretical spectra for Au62+ cannot be correlated with the experiments. This suggests, even though the [Au6(PPh3)6] unit of 1 carries a +2 charge, that the Au6 portion is essentially neutral. More direct evidence for this distribution of the ionized charge has been obtained from HF and DFT calculations of the double ionization energies of models of 1. It is found that the energy required to remove two electrons from a bare Au6 cluster is much larger than that from an Au6 cluster with phosphine ligands present; this is again consistent with the +2 charge in 1 being delocalized onto the triphenylphosphine ligands. It is possible that this delocalization of positive charge is responsible for facilitating the adhesion of the gold cluster as finely dispersed particles onto the metal oxide support. © 2001 American Institute of Physics.
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36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Cg Electronic and magnetic properties of clusters
31.15.E- Density-functional theory
31.15.vq Electron correlation calculations for polyatomic molecules
31.15.xr Self-consistent-field methods
33.20.Kf Visible spectra
33.20.Lg Ultraviolet spectra

Isomerizations and relative kinetic stability of LJn clusters in a carrier gas

E. Curotto

J. Chem. Phys. 114, 10702 (2001); http://dx.doi.org/10.1063/1.1375025 (9 pages) | Cited 10 times

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A number of simulations of LJ7He(ρ) and LJ28He(ρ), for several values of the density of the carrier gas ρ are carried out. Heat capacity data demonstrate that the cluster becomes kinetically more stable at higher values of ρ. Using a structural characterization strategy, it is found that the isomeric distributions are affected by changes in ρ. The relative isomer probability curves are integrated over the simulation temperature range. The resulting quantities increase as a function of ρ monotonically but nonlinearly for Ar7. The patterns for the integrated probabilities for Ar28 are less obvious. © 2001 American Institute of Physics.
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36.40.Jn Reactivity of clusters
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
82.30.Qt Isomerization and rearrangement

Interpolated potential-energy surface and reaction dynamics for BH++H2

Rebecca O. Fuller, Ryan P. A. Bettens, and Michael A. Collins

J. Chem. Phys. 114, 10711 (2001); http://dx.doi.org/10.1063/1.1377602 (6 pages) | Cited 7 times

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An ab initio potential-energy surface for the ground doublet state of BH3+ has been constructed at the QCISD(T)/6-311G(d,p) level of theory. Classical simulations of the collision between BH+ and H2(D2) and isotopic analogs show that the deep BH3+ well gives rise to substantial “scrambling” of the hydrogen and deuterium atoms leading to BHD++D, BD++HD, and BD2++H products. © 2001 American Institute of Physics.
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82.20.Kh Potential energy surfaces for chemical reactions
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

A Drude-model approach to dispersion interactions in dipole-bound anions

F. Wang and K. D. Jordan

J. Chem. Phys. 114, 10717 (2001); http://dx.doi.org/10.1063/1.1376630 (8 pages) | Cited 28 times

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A one-electron model potential for calculating the binding energy of an excess electron interacting with polar molecules and their clusters is described. The unique feature of this potential is the treatment of polarization and dispersion effects by means of a Drude model. The approach is tested by calculating the energies for binding an excess electron to HCN, (HCN)2, HNC, and (HNC)2. The model potential results are found to be in good agreement with the predictions of high-level all-electron calculations. © 2001 American Institute of Physics.
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33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
31.15.A- Ab initio calculations
31.15.xr Self-consistent-field methods
31.15.bw Coupled-cluster theory

The E1Σg+ state of lithium dimer revised

W. Jastrzȩbski, A. Pashov, and P. Kowalczyk

J. Chem. Phys. 114, 10725 (2001); http://dx.doi.org/10.1063/1.1374927 (3 pages) | Cited 9 times

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This article describes the use of the inverted perturbation approach method for construction of an accurate potential energy curve of the E1Σg+ “shelf” state in Li2. Contrary to previous reports the applied method provides a potential curve free of unphysical oscillations and reproduces energies of all the levels known from previous experiments. Our results confirm the possibility of describing the E state within the Born–Oppenheimer approximation. © 2001 American Institute of Physics.
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31.50.-x Potential energy surfaces
31.15.xp Perturbation theory

Single vibronic level emission spectroscopy of jet-cooled HSiF and DSiF

David A. Hostutler, Dennis J. Clouthier, and R. H. Judge

J. Chem. Phys. 114, 10728 (2001); http://dx.doi.org/10.1063/1.1374956 (5 pages) | Cited 12 times

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Using the technique of single vibronic level emission spectroscopy, the ground state vibrational manifolds of jet-cooled HSiF and DSiF have been studied. The radicals were produced in a pulsed electric discharge jet using trifluorosilane (HSiF3 or DSiF3) as the precursor. The gas phase ground state harmonic vibrational frequencies of both isotopomers have been determined for the first time. A normal coordinate analysis using the vibrational frequencies and literature values for the centrifugal distortion constants allowed the determination of all six ground state force constants. Our previous ground state rotational constants have been combined with the calculated harmonic contributions to the α constants to obtain an average (rz) structure and an estimate of the equilibrium (rez) structure. The reliability of the force constants has been evaluated by Franck–Condon simulations of the emission spectra and comparisons of the calculated and experimentally determined inertial defects. © 2001 American Institute of Physics.
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33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
31.30.Gs Hyperfine interactions and isotope effects

A theoretical study of the nitrogen clusters formed from the ions N3−, N5+, and N5−

Laura Gagliardi, Giorgio Orlandi, Stefano Evangelisti, and Björn O. Roos

J. Chem. Phys. 114, 10733 (2001); http://dx.doi.org/10.1063/1.1370063 (5 pages) | Cited 15 times

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The results of a theoretical study on the formation of the nitrogen cluster N10 from the ionic species N5+ and N5− are presented. The possibility to form N8 from N5+ and N3− has also been studied but no stable form was found. Structural and vibrational data are given for the different clusters. It is suggested that the anion N5− might be stable enough to be synthesized. The calculations have been carried out using multiconfigurational self-consistent-field wave functions and second-order perturbation theory. © 2001 American Institute of Physics.
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36.40.Jn Reactivity of clusters
82.30.Nr Association, addition, insertion, cluster formation
31.15.xr Self-consistent-field methods
31.15.xp Perturbation theory
31.15.vq Electron correlation calculations for polyatomic molecules

Electronic structure and chemical bonding of 3d-metal dimers ScX, X=Sc–Zn

G. L. Gutsev, P. Jena, B. K. Rao, and S. N. Khanna

J. Chem. Phys. 114, 10738 (2001); http://dx.doi.org/10.1063/1.1373693 (11 pages) | Cited 20 times

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The electronic and geometrical structures of the ground and excited states of the homonuclear Sc2, mixed ScTi, ScV, ScCr, ScMn, ScFe, ScCo, ScNi, ScCu, and ScZn 3d-metal dimers and their anions have been calculated using the density functional theory with generalized gradient approximation for the exchange-correlation potential. The ground states of the neutral dimers are found to be 5Σu− (Sc2), 6Σ+ (ScTi), 7Σ+ (ScV), 4Σ+ (ScCr), 3Σ+ (ScMn), 2Δ(ScFe), 1Σ+ (ScCo), 2Σ+ (ScNi), 3Δ(ScCu), and 4Σ+ (ScZn). A natural bond analysis reveals an antiferrimagnetic spin coupling in the ground states of ScCr, ScMn, and ScFe. This is due to the electron transfer from Sc to the opposite atom and specific bond formations. While each dimer has a unique chemical bonding pattern, most curious is the localization of two 4s electrons at both atomic sites in the ground 5Σu− state of Sc2, which leads to formation of two lone pairs and the bonding scheme: (3d+3d)α3(4s+4s)β1. No appreciable sd hybridization is found for the ground states of the ScX dimers except for ScNi. Even though the electron affinities of the ScX dimers are relatively low and do not exceed 1 eV, each ScX− (except ScCo−) possesses at least two states stable towards detachment of an extra electron. © 2001 American Institute of Physics.
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33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.E- Density-functional theory
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Structures, energies, and vibrational spectra of water undecamer and dodecamer: An ab initio study

Han Myoung Lee, Seung Bum Suh, and Kwang S. Kim

J. Chem. Phys. 114, 10749 (2001); http://dx.doi.org/10.1063/1.1374926 (8 pages) | Cited 24 times

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Ab initio calculations have been carried out to study the water clusters of undecamer [(H2O)11] and dodecamer [(H2O)12]. At the level of Møller–Plesset second-order perturbation theory using TZ2P++ basis set, the lowest-energy conformer of the undecamer has the skeletal structure of Prism56 that a cyclic pentamer and a cyclic hexamer are fused into a prism shape with 16 hydrogen bonds (HBs). In this case, there are quite a number of nearly isoenergetic conformers with different hydrogen orientations. Among these, more stable conformers tend to have dangling H atoms separated (i.e., less clustered). The lowest energy conformer of the undecamer is different in hydrogen orientation from any previously suggested structure (including the ones obtained from various minimization algorithms). A second lowest energy skeletal structure is of Prism56B that a cyclic pentamer and an open-book hexamer are fused into a prism shape with 17 HBs. The most stable dodecamer is a fused cubic or tetragonal prism skeletal structure (Prism444) with 20 HBs. The lowest energy structure among these skeletal conformers has HB orientations with opposite helicities between adjacent tetragonal rings. The second lowest-energy skeletal structure is the hexagonal prism structure (Prism66) with 18 HBs fused by two cyclic water hexamers. The OH stretching vibrational spectra and electronic properties of several low energy conformers of (H2O)11,12 are also reported. © 2001 American Institute of Physics.
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36.40.Mr Spectroscopy and geometrical structure of clusters
33.20.Tp Vibrational analysis
31.15.A- Ab initio calculations
31.15.xp Perturbation theory
33.15.Fm Bond strengths, dissociation energies

Ground state electronic structures and spectra of zinc complexes of porphyrin, tetraazaporphyrin, tetrabenzoporphyrin, and phthalocyanine: A density functional theory study

Kiet A. Nguyen and Ruth Pachter

J. Chem. Phys. 114, 10757 (2001); http://dx.doi.org/10.1063/1.1370064 (11 pages) | Cited 68 times

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Density functional theory (DFT) electronic structure calculations were carried out to predict the structures and ground-state spectra for zinc complexes of porphyrin (ZnP), tetraazaporphyrin (ZnTAP), tetrabenzoporphyrin (ZnTBP), and phthalocyanine (ZnPc). All four porphyrins are found to have stable D4h structures. Structurally, meso-tetraaza substitutions significantly reduce the central hole in ZnTAP and ZnPc compared to ZnP. The excitation energies and oscillator strengths, computed by time-dependent DFT, provide a good account of the observed spectra of all four compounds. The TDDFT spectrum of ZnPc has a number of bands in the Soret region, in agreement with the experimental spectra that have been determined through spectral deconvolution. The low energy n→π∗ transition (Q′) reported for ZnPc, however, was not found in the computed spectrum. The effects of meso-tetraaza substitutions and tetrabenzo annulations on the spectrum of ZnP are discussed. © 2001 American Institute of Physics.
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31.15.E- Density-functional theory
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
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