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1 Nov 2004

Volume 121, Issue 17, pp. 8175-8660

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back to top Theoretical Methods and Algorithms

Formally exact quantization condition for nonrelativistic quantum systems

Y. C. Ou, Zhuangqi Cao, and Qishun Shen

J. Chem. Phys. 121, 8175 (2004); http://dx.doi.org/10.1063/1.1799015 (4 pages) | Cited 21 times

Online Publication Date: 26 October 2004

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Based on the standard transfer matrix, a formally exact quantization condition for arbitrary potentials, which outflanks and unifies the historical approaches, is derived. It can be used to find the exact bound-state energy eigenvalues of the quantum system without solving an equation of motion for the system wave functions.© 2004 American Institute of Physics.
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03.65.Ge Solutions of wave equations: bound states
03.65.Nk Scattering theory
02.10.Yn Matrix theory
02.10.Ud Linear algebra

The Kawasaki identity and the Fluctuation Theorem

D. M. Carberry, S. R. Williams, G. M. Wang, E. M. Sevick, and Denis J. Evans

J. Chem. Phys. 121, 8179 (2004); http://dx.doi.org/10.1063/1.1802211 (4 pages) | Cited 5 times

Online Publication Date: 26 October 2004

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In this paper we show that the Fluctuation Theorem of Evans and Searles [D. J. Evans, D. J. Searles, Phys. Rev. E 50, 1645 (1994)] implies that the Kawasaki function 〈exp(−Ωt)〉 is unity for all time t. We confirm this relationship using experimental data obtained using optical tweezers, and show that the Kawasaki function is a valuable diagnostic tool.© 2004 American Institute of Physics.
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05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
02.30.Sa Functional analysis

Calculation of single-beam two-photon absorption rate of lanthanides: Effective operator method and perturbative expansion

Chang-Kui Duan, Gang Ruan, and Michael F. Reid

J. Chem. Phys. 121, 8183 (2004); http://dx.doi.org/10.1063/1.1802791 (4 pages) | Cited 1 time

Online Publication Date: 26 October 2004

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Perturbative contributions to single-beam two-photon transition rates may be divided into two types. The first, involving low-energy intermediate states, require a high-order perturbation treatment, or an exact diagonalization. The other, involving high-energy intermediate states, only require a low-order perturbation treatment. We show how to partition the effective transition operator into two terms, corresponding to these two types, in such a way that a many-body perturbation expansion may be generated that obeys the linked cluster theorem and has a simple diagrammatic representation.© 2004 American Institute of Physics.
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32.80.-t Photoionization and excitation
31.15.xp Perturbation theory

Effect of the Perdew–Zunger self-interaction correction on the thermochemical performance of approximate density functionals

Oleg A. Vydrov and Gustavo E. Scuseria

J. Chem. Phys. 121, 8187 (2004); http://dx.doi.org/10.1063/1.1794633 (7 pages) | Cited 44 times

Online Publication Date: 26 October 2004

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The Perdew–Zunger self-interaction-corrected density functional theory (SIC-DFT) was implemented self-consistently using a quasi-Newton direct minimization method. We calculated SIC-DFT energies for a number of atoms and molecules using various approximate density functionals, including hybrids. Self-interaction errors (SIE) of these functionals were compared and analyzed in terms of contributions from valence and core orbitals. We also calculated enthalpies of formation of the standard G2-1 set of 55 molecules and found that self-interaction-correction (SIC) improves agreement with experiment only for the LSDA functional, while all other functionals show worse performance upon introducing SIC. This is the first systematic study of the effect of SIC on thermochemical properties. We found no direct connection between the magnitude of the SIE contained in a functional and its performance for thermochemistry. Approximate functionals with large self-interaction errors can accurately reproduce enthalpies of formation. Our results do not support the popular belief that a smaller SIE of hybrid functionals is the main reason for their higher accuracy. © 2004 American Institute of Physics.
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82.60.Cx Enthalpies of combustion, reaction, and formation
31.15.E- Density-functional theory
31.15.xr Self-consistent-field methods
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

A theoretical study of the excited states of CrH: Potential energies, transition moments, and lifetimes

Giovanni Ghigo, Björn O. Roos, P. C. Stancil, and P. F. Weck

J. Chem. Phys. 121, 8194 (2004); http://dx.doi.org/10.1063/1.1794631 (7 pages) | Cited 5 times

Online Publication Date: 26 October 2004

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Ab initio calculations of low-lying electronic states of CrH are presented, including potential energies, dipole and transition dipole moment (TDM) functions, and radiative lifetimes for X 6Σ+, A 6Σ+, 3 6Σ+, 1 6Π, 2 6Π, 3 6Π, and 6Δ. Calculation of dynamic correlation effects was performed using the multistate complete active space second-order perturbation method, based on state-averaged complete active space self-consistent-field reference wave functions obtained with seven active electrons in an active space of 16 molecular orbitals. A relativistic atomic natural orbital-type basis set from the MOLCAS library was used for Cr. Good agreement is found between the current calculations and experiment for the lowest two 6Σ+ states, the only states for which spectroscopic data are available. Potential curves for the 3 6Σ+ and 2 6Π states are complicated by avoided crossings with higher states of the same symmetry, thus resulting in double-well structures for these two states. The measured bandhead T0 = 27 181 cm−1, previously assigned to a 6Π←X 6Σ+ transition, is close to our value of T0 = 28 434 cm−1 for the 2 6Π state. We tentatively assign the ultraviolet band found experimentally at 30 386 cm−1 to the 3 6Π←X 6Σ+ transition for which the computed value is 29 660 cm−1. The A 6Σ+←X 6Σ+ TDM and A 6Σ+ lifetimes are found to be in reasonable agreement with previous calculations. © 2004 American Institute of Physics.
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31.50.Df Potential energy surfaces for excited electronic states
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
31.50.-x Potential energy surfaces
31.15.A- Ab initio calculations
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.xr Self-consistent-field methods
33.20.Lg Ultraviolet spectra

Mass-independent isotope effect in the earliest processed solids in the solar system: A possible chemical mechanism

R. A. Marcus

J. Chem. Phys. 121, 8201 (2004); http://dx.doi.org/10.1063/1.1803507 (11 pages) | Cited 26 times

Online Publication Date: 26 October 2004

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A major constraint is described for a possible chemical origin for the “mass-independent” oxygen isotope phenomenon in calcium-aluminum rich inclusions (CAIs) in meteorites at high temperatures (∼1500–2000 K). A symmetry-based dynamical η effect is postulated for O atom-monoxide recombination on the surface of growing CAIs. It is the surface analog of the volume-based η effect occurring in a similar phenomenon for ozone in the gas phase [Y. Q. Gao, W. C. Chen, and R. A. Marcus, J. Chem. Phys. 117, 1536 (2002), and references cited therein]: In the growth of CAI grains an equilibrium is postulated between adsorbed species XO (ads)+O (ads)⇄XO2∗ (ads), where XO2∗ (ads) is a vibrationally excited adsorbed dioxide molecule and X can be Si, Al, Ti, or other metals and can be C for minerals less refractory than the CAIs. The surface of a growing grain has an entropic effect of many order of magnitude on the position of this monoxide-dioxide equilibrium relative to its volume-based position by acting as a concentrator. The volume-based η effect for ozone in the earlier study is not applicable to gas phase precursors of CAIs, due to the rarity of three-body recombination collisions at very low pressures and because of the high H2 and H concentration in solar gas, which reduces gaseous O and gaseous dioxides and prevents the latter from acting as storage reservoirs for the two heavier oxygen isotopes. A surface η effect yields XO2∗ (ads) that is mass-independently rich in 17O and 18O, and yields XO (ads)+O (ads) that is mass-independently poor in the two heavier oxygen isotopes. When the XO2∗ (ads) is deactivated by vibrational energy loss to the grain, it has only one subsequent fate, evaporation, and so undergoes no further isotopic fractionation. After evaporation the XO2 again has only one fate, which is to react rapidly with H and ultimately form 16O-poor H2O. The other species, O (ads)+XO (ads), are 16O rich and react with Ca (ads) and other adsorbed metal atoms or metallic monoxides to form CAIs. The latter are thereby mass-independently poor in 17O and 18O. Some O (ads) used to form the minerals are necessarily in excess of the XO (ads), because of the stoichiometry of the mineral, and modify the fractionation pattern. This effect is incorporated into the mechanistic and mathematical scheme. A merit of this chemical mechanism for the oxygen isotope anomaly is that only one oxygen reservoir is required in the solar nebula. It also does not require a sequestering of intermediate products which could undergo isotopic exchange, hence undoing the original isotopic fractionations. The gas phase source of adsorbed O atoms in this environment is either O or H2O. As inferred from data on the evaporation of Mg2SiO4 taken as an example, the source of O (ads) is primarily H2O rather than O and is accompanied by the evolution of H2. Nonisotopic kinetic experiments can determine more sharply the mechanism of condensed phase growth of these minerals. Laboratory tests are proposed to test the existence of a surface η effect on the growing CAI surfaces at these high temperatures. © 2004 American Institute of Physics.
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96.30.Za Meteors, meteorites and tektites
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.20.Tr Kinetic isotope effects including muonium
61.72.Qq Microscopic defects (voids, inclusions, etc.)
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Hf Product distribution
61.66.Bi Elemental solids
61.66.Dk Alloys

Structure, stability, and spectra of C9H3, C11H3, and C13H3 radicals

Congjie Zhang

J. Chem. Phys. 121, 8212 (2004); http://dx.doi.org/10.1063/1.1804176 (9 pages) | Cited 5 times

Online Publication Date: 26 October 2004

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Density functional theory has been used to investigate the geometries, vibrational frequencies, rotational constants, and dipole moments of the C9H3, C11H3, and C13H3 radicals. Vertical electronic transition energies of C9H3, C11H3, and C13H3 are calculated by the time-dependent density functional theory. Present results show that the most stable arrangements of C9H3, C11H3, and C13H3 are H2C9H, H2C11H, and H2C13H with a C2v symmetry, respectively. Such lowest-energy isomers have an obvious single and triple bond alternation carbon chain. Their isomers HC4(HC)C4H, HC4[C(C2H)]C4H, and C(C4H)3 are predicted to have vibrational frequencies and vertical excitation energies in good agreement with experimental observations. HC4(HC)C4H, HC4[C(C2H)]C4H, and C(C4H)3 have similar trigonal structure, which gives rise to the remarkably similar spectroscopic features as obtained experimentally. On the basis of present calculations, the isomers HC4(HC)C4H, HC4[C(C2H)]C4H, and C(C4H)3 of C9H3, C11H3, and C13H3 radicals are most likely the carriers of the observed spectra. © 2004 American Institute of Physics.
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31.15.E- Density-functional theory
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
33.20.Sn Rotational analysis
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Fm Bond strengths, dissociation energies

An Anderson impurity model for efficient sampling of adiabatic potential energy surfaces of transition metal complexes

M. X. LaBute, R. G. Endres, and D. L. Cox

J. Chem. Phys. 121, 8221 (2004); http://dx.doi.org/10.1063/1.1795152 (10 pages) | Cited 3 times

Online Publication Date: 26 October 2004

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We present a model intended for rapid sampling of ground and excited state potential energy surfaces for first-row transition metal active sites. The method is computationally inexpensive and is suited for dynamics simulations where (1) adiabatic states are required “on-the-fly” and (2) the primary source of the electronic coupling between the diabatic states is the perturbative spin-orbit interaction among the 3d electrons. The model Hamiltonian we develop is a variant of the Anderson impurity model and achieves efficiency through a physically motivated basis set reduction based on the large value of the d-d Coulomb interaction Ud and a Lánczos matrix diagonalization routine to solve for eigenvalues. The model parameters are constrained by fits to the partial density of states obtained from ab initio density functional theory calculations. For a particular application of our model we focus on electron transfer occurring between cobalt ions solvated by ammonium, incorporating configuration interaction between multiplet states for both metal ions. We demonstrate the capability of the method to efficiently calculate adiabatic potential energy surfaces and the electronic coupling factor we have calculated compares well to previous calculations and experiment. © 2004 American Institute of Physics.
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31.50.Bc Potential energy surfaces for ground electronic states
31.50.Df Potential energy surfaces for excited electronic states
31.15.A- Ab initio calculations
31.15.E- Density-functional theory

Observation of Au2H− impurity in pure gold clusters and implications for the anomalous Au-Au distances in gold nanowires

Hua-Jin Zhai, Boggavarapu Kiran, and Lai-Sheng Wang

J. Chem. Phys. 121, 8231 (2004); http://dx.doi.org/10.1063/1.1802491 (6 pages) | Cited 11 times

Online Publication Date: 26 October 2004

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Au2H− was recognized and confirmed as a minor contamination to typical photoelectron spectra of Au2−, produced by laser vaporization of a pure Au target using an ultrahigh purity helium carrier gas. The hydrogen source was shown to be from trace H impurities present in the bulk gold target. Carefully designed experiments using H2- and D2-seeded helium carrier gas were used to study the electronic structure of Au2H− and Au2D− using photoelectron spectroscopy and density functional calculations. Well-resolved photoelectron spectra with vibrational resolution were obtained for Au2H− and Au2D−. Two isomers were observed both experimentally and theoretically. The ground state of Au2H− turned out to be linear with a terminal H atom [Au-Au-H]− (1A1,C∞v), whereas a linear [Au-H-Au]− (1A1,D∞h) structure with a bridging H atom was found to be a minor isomer 0.6 eV higher in energy. Calculated electron detachment energies for both isomers agree well with the experimental spectra, confirming their existence in the cluster beam. The observation and confirmation of H impurity in pure gold clusters and the 3.44 Å Au-Au distance in the [Au-H-Au]− isomer presented in the current work provide indirect experimental evidence that the anomalous 3.6 Å Au-Au distances observed in gold nanowires is due to an “invisible” hydrogen impurity atom. © 2004 American Institute of Physics.
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36.40.Cg Electronic and magnetic properties of clusters
61.46.-w Structure of nanoscale materials
33.60.+q Photoelectron spectra
31.15.E- Density-functional theory
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.80.Eh Autoionization, photoionization, and photodetachment

Infrared depletion spectra of 2-aminopyridine⋅2-pyridone, a Watson–Crick mimic of adenine⋅uracil

Jann A. Frey, Andreas Müller, Hans-Martin Frey, and Samuel Leutwyler

J. Chem. Phys. 121, 8237 (2004); http://dx.doi.org/10.1063/1.1795673 (9 pages) | Cited 14 times

Online Publication Date: 26 October 2004

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The 2-aminopyridine⋅2-pyridone (2AP⋅2PY) dimer is linked by N–H⋯O�C and N–H⋯N hydrogen bonds, providing a model for the Watson–Crick hydrogen bond configuration of the adenine⋅thymine and adenine⋅uracil nucleobase pairs. Mass-specific infrared spectra of 2AP⋅2PY and its seven N–H deuterated isotopomers have been measured between 2550 and 3650 cm−1 by IR laser depletion combined with UV two-color resonant two-photon ionization. The 2PY amide N–H stretch is a very intense band spread over the range 2700–3000 cm−1 due to large anharmonic couplings. It is shifted to lower frequency by 710 cm−1 or ≈ 20% upon H bonding to 2AP. On the 2AP moiety, the “bound” amino N–H stretch gives rise to a sharp band at 3140 cm−1, which is downshifted by 354 cm−1 or ≈ 10% upon H bonding to 2PY. The amino group “free” N–H stretch and the H–N–H bend overtone are sharp bands at ≈ 3530 cm−1 and 3320 cm−1. Ab initio structures and harmonic vibrations were calculated at the Hartree–Fock level and with the PW91 and B3LYP density functionals. The PW91/6-311++G(d,p) method provides excellent predictions for the frequencies and IR intensities of all the isotopomers.© 2004 American Institute of Physics.
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33.20.Ea Infrared spectra
33.15.Ta Mass spectra
33.15.Fm Bond strengths, dissociation energies
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.30.Gs Hyperfine interactions and isotope effects
33.20.Lg Ultraviolet spectra
33.80.Eh Autoionization, photoionization, and photodetachment
31.15.A- Ab initio calculations
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
31.15.xr Self-consistent-field methods
31.15.E- Density-functional theory
33.70.Fd Absolute and relative line and band intensities

Normal Auger spectra of Br in alkali bromide molecules

Zhengfa Hu, Antonio Caló, Juha Nikkinen, Tommi Matila, Edwin Kukk, Helena Aksela, and Seppo Aksela

J. Chem. Phys. 121, 8246 (2004); http://dx.doi.org/10.1063/1.1797732 (7 pages) | Cited 2 times

Online Publication Date: 26 October 2004

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Molecular Auger electron spectra following the bromine 3d ionization in gas-phase alkali bromides and in HBr were studied both experimentally and theoretically. The AES for HBr and CsBr were measured using photoexcitation, and for LiBr, NaBr, and KBr by using electron impact. These results are compared with the theoretical spectra from nonrelativistic ab initio calculations and one-center approximation and with the spectra of Br−, computed with the multiconfiguration Dirac–Fock method. © 2004 American Institute of Physics.
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33.80.Eh Autoionization, photoionization, and photodetachment
31.15.xr Self-consistent-field methods
31.15.A- Ab initio calculations
34.80.Gs Molecular excitation and ionization

One- and two-photon absorption of three-coordinate compounds with different centers (B,Al,N) and a 2,2′-dipyridylnitrogen functional group

Xiao-Juan Liu, Ji-Kang Feng, Ai-Min Ren, Hong Cheng, and Xin Zhou

J. Chem. Phys. 121, 8253 (2004); http://dx.doi.org/10.1063/1.1798975 (8 pages) | Cited 8 times

Online Publication Date: 26 October 2004

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A series of three-coordinate octupolar compounds with varied centers (boron, aluminum, and nitrogen), which exhibit very large effective two-photon absorption cross sections have been theoretically studied. The ground state geometries and electronic structures are obtained using the density functional theory with the B3LYP functional and 6-31G(d) basis set, and the results are comparable to the available experimental determinations. Based on the correct geometrical and electronic structures, the one- and two-photon absorptions are predicted by the ZINDO-SOS method. Among these compounds, the boron (B) and aluminum (Al) centers act as acceptors, while the nitrogen center acts as donor according to the net charge changes during the excitation. It is found that (i) the compounds with boron and aluminum centers show two large two-photon absorption peaks, while the molecule with nitrogen center show only one two-photon absorption peak; (ii) the cross sections of the molecules with B or Al as centers are larger than that of the molecule with nitrogen as center; furthermore, the two-photon absorption cross section of the molecule with Al center is larger than that of the molecule with B center, from this point of view, our theoretical prediction provides for the experiment a good new candidate with large two-photon absorption cross section for further research; (iii) lengthening the conjugation bridge by inserting a benzene ring on the organoborane compounds (forming the investigated molecule B-2) enhances the two-photon absorption cross section, and keeping good transparency at the same time. © 2004 American Institute of Physics.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
31.15.bu Semi-empirical and empirical calculations (differential overlap, Hückel, PPP methods, etc.)
31.15.E- Density-functional theory
33.15.Bh General molecular conformation and symmetry; stereochemistry

Potential energy surface, bound states, and rotational inelastic cross sections of the He-CH4 system: A theoretical investigation

G. Calderoni, F. Cargnoni, R. Martinazzo, and M. Raimondi

J. Chem. Phys. 121, 8261 (2004); http://dx.doi.org/10.1063/1.1791111 (10 pages) | Cited 8 times

Online Publication Date: 26 October 2004

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We determined two potential energy surfaces (PES) for the He-CH4 system by means of MP4 and Valence Bond (VB) calculations. The MP4 potential is similar to the one commonly adopted for this system [U. Buck, K. H. Kohl, A. Kolhase, M. Faubel, and U. Staemmler, Mol. Phys. 55, 1255 (1985)], while the VB PES is slightly more attractive. To evaluate the reliability of these potentials, we investigated the scattering properties by performing close coupling calculations, and concluded that: (i) the available experimental data do not permit the ranking among the PES considered; (ii) some theoretical predictions differ considerably from the experimental data, and these discrepancies cannot entirely be ascribed to the inaccuracy of the ab initio calculations; (iii) the scattering properties at low energy might discriminate between the MP4 and VB potentials. © 2004 American Institute of Physics.
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34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
31.15.xw Valence bond calculations
34.50.Ez Rotational and vibrational energy transfer
33.20.Sn Rotational analysis
03.65.Ge Solutions of wave equations: bound states

Experimental and theoretical investigations of rate coefficients of the reaction S(3P)+O2 in the temperature range 298–878 K

Chih-Wei Lu, Yu-Jong Wu, Yuan-Pern Lee, R. S. Zhu, and M. C. Lin

J. Chem. Phys. 121, 8271 (2004); http://dx.doi.org/10.1063/1.1792611 (8 pages) | Cited 6 times

Online Publication Date: 26 October 2004

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Rate coefficients of the reaction S+O2 with Ar under 50 Torr in the temperature range 298–878 K were determined with the laser photolysis technique. S atoms were generated by photolysis of OCS with a KrF excimer laser at 248 nm; their concentration was monitored via resonance fluorescence excited by atomic emission of S produced from microwave-discharged SO2. Our measurements show that k(298 K) = (1.92±0.29)×10−12 cm3 molecule−1 s−1, in satisfactory agreement with previous reports. New data determined for 505–878 K show non-Arrhenius behavior; combining our results with data reported at high temperatures, we derive an expression k(T) = (9.02±0.27)×10−19T2.11±0.15 exp[(730±120)/T] cm3 molecule−1 s−1 for 298 ⩽ T ⩽ 3460 K. Theoretical calculations at the G2M (RCC2) level, using geometries optimized with the B3LYP/6-311+G(3df) method, yield energies of transition states and products relative to those of the reactants. Rate coefficients predicted with multichannel RRKM calculations agree satisfactorily with experimental observations; the reaction channel via SOO(1A′) dominates at T<500 K, whereas channels involving formation of SOO(3A″) followed by isomerization to SO2 before dissociation, and formation of SOO(1A″) followed by direct dissociation, become important at high temperatures, accounting for the observed rapid increase in rate coefficient. © 2004 American Institute of Physics.
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82.20.Pm Rate constants, reaction cross sections, and activation energies
82.50.-m Photochemistry
82.30.Qt Isomerization and rearrangement
42.55.Lt Gas lasers including excimer and metal-vapor lasers
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Potential energy curves of diatomic molecular ions from high-resolution photoelectron spectra. II. The first six electronic states of Xe2+

P. Rupper, O. Zehnder, and F. Merkt

J. Chem. Phys. 121, 8279 (2004); http://dx.doi.org/10.1063/1.1804953 (12 pages) | Cited 15 times

Online Publication Date: 26 October 2004

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The pulsed-field-ionization zero-kinetic-energy photoelectron spectrum of Xe2 has been measured between 90 000 and 109 000 cm−1 following single-photon excitation from the ground neutral state. Transitions to five of the six low-lying electronic states of Xe2+ could be observed. Whereas extensive vibrational progressions were observed for the X0g+→I(1/2u), I(3/2g), and II(1/2u) photoelectron transitions, only the lowest vibrational levels of the I(3/2u) and II(1/2g) states could be detected. Unambiguous assignments of the vibrational quantum numbers were derived from the analysis of the isotopic shifts of the vibrational bands and of the intensity distribution and from the modeling of the potential energy curves. Analytical potential energy curves of spectroscopic accuracy (i.e., ∼ 1 meV) were determined for all six low-lying electronic states using a global model, which includes the first (charge-induced dipole, ∝1/R4) member of the long-range interaction series and treats the spin-orbit interaction explicitely. The assumption of an R-independent spin-orbit coupling constant was tested and found to be an excellent approximation.© 2004 American Institute of Physics.
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33.60.+q Photoelectron spectra
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
33.70.Jg Line and band widths, shapes, and shifts

Organo-noble-gas hydride compounds HKrCCH, HXeCCH, HXeCC, and HXeCCXeH: Formation mechanisms and effect of 13C isotope substitution on the vibrational properties

Hanna Tanskanen, Leonid Khriachtchev, Jan Lundell, and Markku Räsänen

J. Chem. Phys. 121, 8291 (2004); http://dx.doi.org/10.1063/1.1799611 (8 pages) | Cited 15 times

Online Publication Date: 26 October 2004

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We investigate the formation mechanism of HXeCCXeH in a Xe matrix. Our experimental results show that the HXeCCXeH molecules are formed in the secondary reactions involving HXeCC radicals. The experimental data on the formation of HXeCCXeH is fully explained based on the model involving the HXeCC+Xe+H→HXeCCXeH reaction. This reaction is the first case when a noble-gas hydride molecule is formed from another noble-gas molecule. In addition, we investigate the 12C/13C isotope effect on the vibrational properties of organo-noble-gas hydrides (HKrCCH, HXeCCH, HXeCC, and HXeCCXeH) in noble-gas matrixes. The present experimental results and ab initio calculations on carbon isotope shifts of the vibrational modes support the previous assignments of these molecules. Upon 12C to 13C isotope substitution, we observed a pronounced effect on the H-Kr stretching mode of HKrCCH (downshift of 1.0–3.6 cm−1, depending on the matrix site) and a small anomalous shift (+0.1 cm−1) of the H-Xe stretching mode of HXeCCH and HXeCCXeH. © 2004 American Institute of Physics.
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33.70.Jg Line and band widths, shapes, and shifts
82.20.Tr Kinetic isotope effects including muonium
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
33.20.Tp Vibrational analysis
31.15.A- Ab initio calculations
33.15.Fm Bond strengths, dissociation energies
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)

A first principles study on the solvation and structure of SO42−(H2O)n, n = 6–12

Bing Gao and Zhi-feng Liu

J. Chem. Phys. 121, 8299 (2004); http://dx.doi.org/10.1063/1.1802011 (8 pages) | Cited 14 times

Online Publication Date: 26 October 2004

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The structures of hydrated sulfate clusters, SO42−(H2O)n with n = 6–12, are obtained by density functional theory calculations. For SO42−(H2O)12, two structures with symmetric distribution of H2O molecules around the sulfate group are favored in energy. The structures for the smaller clusters, SO42−(H2O)n with n = 6–11, are obtained by taking away one H2O molecule successively from the two symmetric SO42−(H2O)12 isomers. The hydrogen bonding between the sulfate O atoms and H2O molecules are strong. So are the hydrogen bonds among H2O molecules, which are facilitated by the structure of the polyatomic sulfate group. The solvation energy is quite large (often exceeding 15 kcal/mol). The patterns for structural and energy changes as the cluster size increases are very different from the well studied hydrated halide ions, although the competition between solute-solvent and solvent-solvent interactions is again an important factor. Ab initio molecular dynamics simulations also show “crowding” effects in the first solvation of SO42−(H2O)12 at raised temperature.© 2004 American Institute of Physics.
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82.30.Nr Association, addition, insertion, cluster formation
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
31.15.E- Density-functional theory
31.15.A- Ab initio calculations
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.xv Molecular dynamics and other numerical methods
33.15.Fm Bond strengths, dissociation energies
36.40.Mr Spectroscopy and geometrical structure of clusters
82.33.Hk Reactions on clusters

The mechanism of proton exchange: Guided ion beam studies of the reactions, H(H2O)n+ (n = 1–4)+D2O and D(D2O)n+ (n = 1–4)+H2O

Kenji Honma and P. B. Armentrout

J. Chem. Phys. 121, 8307 (2004); http://dx.doi.org/10.1063/1.1802391 (14 pages) | Cited 8 times

Online Publication Date: 26 October 2004

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Reactions of protonated water clusters, H(H2O)n+ (n = 1–4) with D2O and their “mirror” reactions, D(D2O)n+ (n = 1–4) with H2O, are studied using guided-ion beam mass spectrometry. Absolute reaction cross sections are determined as a function of collision energy from thermal energy to over 10 eV. At low collision energies, we observe reactions in which H2O and D2O molecules are interchanged and reactions where H-D exchange has occurred. As the collision energy is increased, the H-D exchange products decrease and the water exchange products become dominant. At high collision energies, processes in which one or more water molecules are lost from the reactant ions become important, with simple collision-induced dissociation processes, i.e., those without H-D exchange, being dominant. Threshold energies of endothermic channels are measured and used to determine binding energies of the proton bound complexes, which are consistent with those determined by thermal equilibrium measurements and previous collision-induced dissociation studies. A kinetic scheme that relies only on the ratio of isomerization and dissociation rate constants successfully accounts for the kinetic energy dependence observed in the branching ratios for H-D and water exchange products in all systems. Rice–Ramsperger–Kassel–Marcus theory and ab initio calculations confirm the feasibility and establish the details of this kinetic model. © 2004 American Institute of Physics.
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82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.30.Nr Association, addition, insertion, cluster formation
31.15.A- Ab initio calculations

Observation of rotamers of m-aminobenzoic acid: Zero kinetic energy photoelectron and hole-burning resonantly enhanced multiphoton ionization spectroscopy

Yonggang He, Chengyin Wu, and Wei Kong

J. Chem. Phys. 121, 8321 (2004); http://dx.doi.org/10.1063/1.1802551 (8 pages) | Cited 12 times

Online Publication Date: 26 October 2004

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We report studies of supersonically cooled m-aminobenzoic acid using two-color resonantly enhanced multiphoton ionization (REMPI) and two-color zero kinetic energy (ZEKE) photoelectron spectroscopy. Two conformers have been identified and characterized using the hole-burning method in the REMPI experiment. With the aid of ab initio and density functional calculations, vibrational modes of the first electronically excited state (S1) of the neutral species and those of the ground state cation (D0) have been assigned, and the adiabatic ionization potentials have been determined for both conformers. The REMPI spectra are dominated by in-plane motions of the substituents and ring deformation modes. A propensity of Δv = 0, where Δv is the change in vibrational quantum number from the S1 to the D0 state, is observed in the ZEKE spectra. The origin of this behavior is discussed in the context of electron back donation from the two substituents in the excited state and in the cationic state. Comparisons of these results with those of p-aminobenzoic acid will be analyzed. © 2004 American Institute of Physics.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.60.+q Photoelectron spectra
31.15.A- Ab initio calculations
31.15.E- Density-functional theory
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Electron and nuclear dynamics of molecular clusters in ultraintense laser fields. IV. Coulomb explosion of molecular heteroclusters

Isidore Last and Joshua Jortner

J. Chem. Phys. 121, 8329 (2004); http://dx.doi.org/10.1063/1.1802554 (14 pages) | Cited 38 times

Online Publication Date: 26 October 2004

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In this paper we present a theoretical and computational study of the temporal dynamics and energetics of Coulomb explosion of (CD4)n and (CH4)n (n = 55–4213) molecular heteroclusters in ultraintense (I = 1016–1019 W cm−2) laser fields, addressing the manifestation of electron dynamics, together with nuclear energetic and kinematic effects on the heterocluster Coulomb instability. The manifestations of the coupling between electron and nuclear dynamics were explored by molecular dynamics simulations for these heteroclusters coupled to Gaussian laser fields (pulse width τ=25 fs), elucidating outer ionization dynamics, nanoplasma screening effects (being significant for I ⩽ 1017 W cm−2), and the attainment of cluster vertical ionization (CVI) (at I = 1017 W cm−2 for cluster radius R0 ⩽ 31 Å). Nuclear kinematic effects on heterocluster Coulomb explosion are governed by the kinematic parameter η = qCmA/qAmC for (CA4)n clusters (A = H,D), where qj and mj (j = A,C) are the ionic charges and masses. Nonuniform heterocluster Coulomb explosion (η>1) manifests an overrun effect of the light ions relative to the heavy ions, exhibiting the expansion of two spatially separated subclusters, with the light ions forming the outer subcluster at the outer edge of the spatial distribution. Important features of the energetics of heterocluster Coulomb explosion originate from energetic triggering effects of the driving of the light ions by the heavy ions (C4+ for I = 1017–1018 W cm−2 and C6+ for I = 1019 W cm−2), as well as for kinematic effects. Based on the CVI assumption, scaling laws for the cluster size (radius R0) dependence of the energetics of uniform Coulomb explosion of heteroclusters (η=1) were derived, with the size dependence of the average (Ej,av) and maximal (Ej,M) ion energies being Ej,av = aR02 and Ej,M = (5a/3)R02, as well as for the ion energy distributions P(Ej)∝Ej1/2; Ej ⩽ Ej,M. These results for uniform Coulomb explosion serve as benchmark reference data for the assessment of the effects of nonuniform explosion, where the CVI scaling law for the energetics still holds, with deviations of the a coefficient, which increase with increasing η. Kinematic effects (for η>1) result in an isotope effect, predicting the enhancement (by 9%–11%) of EH,av for Coulomb explosion of (C4+H4+)η (η=3) relative to ED,av for Coulomb explosion of (C4+D4+)η (η=1.5), with the isotope effect being determined by the ratio of the kinematic parameters for the pair of Coulomb exploding clusters. Kinematic effects for nonuniform explosion also result in a narrow isotope dependent energy distribution (of width ΔE) of the light ions (with ΔE/EH,av ≃ 0.3 and ΔE/ED,av ≃ 0.4), with the distribution peaking at the high energy edge, in marked contrast with the uniform explosion case. Features of laser-heterocluster interactions were inferred from the analyses of the intensity dependent boundary radii (R0)I and the corresponding average D+ ion energies (ED,av)I, which provide a measure for optimization of the cluster size at intensity I for the neutron yield from dd nuclear fusion driven by Coulomb explosion (NFDCE) of these heteroclusters. We infer on the advantage of deuterium containing heteronuclear clusters, e.g., (CD4)n in comparison to homonuclear clusters, e.g., (D2)n/2, for dd NFDCE, where the highly charged heavy ions (e.g., C4+ or C6+) serve as energetic and kinematic triggers driving the D+ ions to a high (10–200 keV) energy domain. © 2004 American Institute of Physics.  
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36.40.Jn Reactivity of clusters
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
34.80.Gs Molecular excitation and ionization
82.20.Tr Kinetic isotope effects including muonium
33.80.Eh Autoionization, photoionization, and photodetachment
31.15.xv Molecular dynamics and other numerical methods
31.30.Gs Hyperfine interactions and isotope effects

Cluster size effects in core excitons of 1s-excited nitrogen

R. Flesch, N. Kosugi, I. L. Bradeanu, J. J. Neville, and E. Rühl

J. Chem. Phys. 121, 8343 (2004); http://dx.doi.org/10.1063/1.1804180 (8 pages) | Cited 6 times

Online Publication Date: 26 October 2004

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Cluster size effects in core excitons below the N 1s ionization energy of nitrogen clusters are reported in the energy regime 405–410 eV. These results are compared to the molecular Rydberg states as well as the corresponding bulk excitons of condensed nitrogen. The experimental results are assigned using ab initio calculations. It is found that the lowest excitons (N 1s→3sσ and N 1s→3pπ) are blueshifted relative to the molecular Rydberg transitions, whereas others (N 1s→3dπ and N 1s→4pπ) show a redshift. Results from ab initio calculations on (N2)13 clearly indicate that the molecular orientation within a cluster is critical to the spectral shift, where bulk sites as well as inner- and outer-surface sites are characterized by different inner-shell absorption energies. These results are compared to the experimental spectra as well as previous work on site-selectively excited atomic van der Waals clusters, providing an improved spectral assignment of core exciton states in weakly bound molecular clusters and the corresponding condensed phase.© 2004 American Institute of Physics.
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36.40.Mr Spectroscopy and geometrical structure of clusters
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
31.15.A- Ab initio calculations
33.70.Jg Line and band widths, shapes, and shifts

Fourier transform microwave spectroscopy and Fourier transform microwave–millimeter wave double resonance spectroscopy of the ClOO radical

Kohsuke Suma, Yoshihiro Sumiyoshi, and Yasuki Endo

J. Chem. Phys. 121, 8351 (2004); http://dx.doi.org/10.1063/1.1792591 (9 pages) | Cited 7 times

Online Publication Date: 26 October 2004

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Pure rotational spectra of the ClOO radical for the 35Cl and 37Cl isotopomers have been observed using Fourier transform microwave and Fourier transform microwave–millimeter wave double resonance spectroscopy. The rotational, centrifugal, spin-rotation coupling, and hyperfine coupling constants have been determined by least-squares fits of the observed transition frequencies. The molecular constants indicate that the electronic ground state is 2A″. The r0 structure is determined to be r0(ClO) = 2.075 Å, r0(OO) = 1.227 Å, and θ0(ClOO) = 116.4°. Several highly accurate ab initio calculations have also been performed. Some of them turned out to be inaccurate because it is necessary to take into account both static and dynamic electronic correlations. Only multireference (single and double) configuration interaction calculations with large basis sets reproduce the present experimental results. The anharmonic force constants obtained by the ab initio calculations are used to determine the re structure, re(ClO) = 2.084(1) Å, re(OO) = 1.206(2) Å, and θe(ClOO) = 115.4(1)°. Unique features of the ClOO radical have become clear by the present experiment and the ab initio calculations. © 2004 American Institute of Physics.
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33.20.Bx Radio-frequency and microwave spectra
33.20.Sn Rotational analysis
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
31.30.Gs Hyperfine interactions and isotope effects
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.15.Pw Fine and hyperfine structure
31.15.A- Ab initio calculations
31.15.V- Electron correlation calculations for atoms, ions and molecules

Characterizing the later 3d cyanides: The submillimeter spectrum of CoCN(X 3Φi)

P. M. Sheridan, M. A. Flory, and L. M. Ziurys

J. Chem. Phys. 121, 8360 (2004); http://dx.doi.org/10.1063/1.1791091 (9 pages) | Cited 14 times

Online Publication Date: 26 October 2004

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The pure rotational spectrum of the CoCN radical has been recorded in the frequency range 350–500 GHz using direct absorption techniques. This study is the first spectroscopic observation of this molecule by any experimental technique. Spectra of Co 13CN have been measured as well. These data indicate that this species is linear in its ground electronic state and has the cyanide, as opposed to the isocyanide, geometry. The ground state term has been assigned as 3Φi, based on the measurement of three spin components (Ω=4, 3, and 2) and in analogy to other isovalent cobalt-bearing species. Hyperfine splittings resulting from the 59Co nuclear spin of I = 7/2 were observed in every transition, each of which exhibited an octet pattern. For the lowest energy spin component, Ω=4, vibrational satellite features were also identified arising from the first quantum of the Co-C (v1 = 1) stretch and the v2 = 1 and v2 = 2 quanta of the bending mode, which were split by Renner-Teller interactions. The ground state measurements of CoCN were analyzed with a case aβ Hamiltonian, establishing rotational, fine structure, and hyperfine parameters. The vibrational and Co 13CN spectra for the Ω=4 component were fit as well. An r0 structure was also calculated, providing estimates of the Co-C and C-N bond distances, based on the Ω=4 transitions. CoCN is the fourth molecule in the 3d transition metal series to exhibit the linear cyanide structure, along with the Zn, Cu, and Ni analogs. The preference for this geometry, as opposed to the isocyanide form, may indicate a greater degree of covalent bonding in these species. © 2004 American Institute of Physics.
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33.20.Sn Rotational analysis
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.30.Gs Hyperfine interactions and isotope effects
33.20.Tp Vibrational analysis
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.15.Dj Interatomic distances and angles

Icosahedral gold cage clusters: MAu12− (M=V, Nb, and Ta)

Hua-Jin Zhai, Jun Li, and Lai-Sheng Wang

J. Chem. Phys. 121, 8369 (2004); http://dx.doi.org/10.1063/1.1799574 (6 pages) | Cited 40 times

Online Publication Date: 26 October 2004

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We report the observation and characterization of a series of stable bimetallic 18-valence-electron clusters containing a highly symmetric 12-atom icosahedral Au cage with an encapsulated central heteroatom of Group VB transition metals, MAu12− (M = V,Nb,Ta). Electronic and structural properties of these clusters were probed by anion photoelectron spectroscopy and theoretical calculations. Characteristics of the MAu12− species include their remarkably high binding energies and relatively simple spectral features, which reflect their high symmetry and stability. The adiabatic electronic binding energies of MAu12− were measured to be 3.70±0.03, 3.77±0.03, and 3.76±0.03 eV for M = V, Nb, and Ta, respectively. Comparison of density-functional calculations with experimental data established the highly symmetric icosahedral structures for the 18-electron cluster anions, which may be promising building blocks for cluster-assembled nanomaterials in the form of stoichiometric [MAu12−]X+ salts. © 2004 American Institute of Physics.
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36.40.Qv Stability and fragmentation of clusters
36.40.Cg Electronic and magnetic properties of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
61.46.-w Structure of nanoscale materials
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.60.+q Photoelectron spectra

Spectroscopy and reactivity of size-selected Mg+-ammonia clusters

James I. Lee, David C. Sperry, and James M. Farrar

J. Chem. Phys. 121, 8375 (2004); http://dx.doi.org/10.1063/1.1802498 (10 pages) | Cited 7 times

Online Publication Date: 26 October 2004

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Photodissociation spectra for mass-selected Mg+(NH3)n clusters for n = 1 to 7 are reported over the photon energy range from 7000 to 38 500 cm−1. The singly solvated cluster, which dissociates primarily via a N–H bond cleavage, exhibits a resolved vibrational structure corresponding to two progressions in the intracluster Mg+–NH3 modes. The addition of the second, third, and fourth solvent molecules results in monotonic redshifts that appear to halt near 8500 cm−1, where a sharp feature in the electronic spectrum is correlated with the formation of a Mg+(NH3)4 complex with Td symmetry and the closing of the first solvation shell. The spectra for the clusters with 5 to 7 solvent molecules strongly resemble that for the tetramer, suggesting that these solvent molecules occupy a second solvation shell. The wavelength-dependent branching-ratio measurements show that increasing the photon energies generally result in the loss of additional solvent molecules but that enhancements for a specific solvent number loss may reveal special stability for the resultant fragments. The majority of the experimental evidence suggests that the decay of these clusters occurs via the internal conversion of the initially excited electronic states to the ground state, followed by dissociation. In the case of the monomer, the selective cleavage of a N–H bond in the solvent suggests that this internal-conversion process may populate regions of the ground-state surface in the vicinity of an insertion complex H–Mg+–NH2, whose existence is predicted by ab initio calculations. © 2004 American Institute of Physics.
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36.40.Jn Reactivity of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
33.20.Tp Vibrational analysis
33.50.Hv Radiationless transitions, quenching
82.50.-m Photochemistry
82.30.Nr Association, addition, insertion, cluster formation
31.70.Dk Environmental and solvent effects
33.70.Jg Line and band widths, shapes, and shifts
33.15.Fm Bond strengths, dissociation energies
31.15.A- Ab initio calculations
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