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8 Dec 2002

Volume 117, Issue 22, pp. 9973-10428

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The naphthalene-benzene anion: Anion complex of aromatic hydrocarbons with the smallest electron affinity

Jae Kyu Song, Nam Ki Lee, Sang Yun Han, and Seong Keun Kim

J. Chem. Phys. 117, 9973 (2002); http://dx.doi.org/10.1063/1.1519002 (4 pages) | Cited 8 times

Online Publication Date: 19 November 2002

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The mixed cluster anions between naphthalene and benzene were studied by mass spectrometry, photoelectron spectroscopy, and theoretical calculations. We found clear evidence for a stable anion of the 1:1 complex, [(Np)1(Bz)1]−, which has the smallest electron affinity measured so far for complexes of aromatic hydrocarbons. The photoelectron spectrum of [(Np)1(Bz)1]− was identical in shape with those of (Np)2− and [(Np)1(H2O)1]−, implying the presence of a common ion core, (Np)−, in these systems. Thus [(Np)1(Bz)1]− is viewed to be (Np)1−(Bz)1, where Bz stabilizes the core anion, (Np)−, as a neutral solvent. The geometry of (Np)1−(Bz)1 was calculated to be T-shaped, with a strong character for the π-hydrogen bonding. An adiabatic electron affinity of 0.01 eV was determined from the measured vertical detachment energy of 0.03 eV and the theoretical estimate of the energy difference between the two neutral structures involved. © 2002 American Institute of Physics.
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33.60.+q Photoelectron spectra
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Ta Mass spectra
33.15.Bh General molecular conformation and symmetry; stereochemistry
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back to top Theoretical Methods and Algorithms

An extended Heisenberg model for conjugated hydrocarbons

Jian Wu, T. G. Schmalz, and D. J. Klein

J. Chem. Phys. 117, 9977 (2002); http://dx.doi.org/10.1063/1.1520133 (6 pages) | Cited 5 times

Online Publication Date: 19 November 2002

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An improved valence bond model, in the form of an extended Heisenberg model including next-nearest-neighbor transpositions and six-cyclic permutations, is developed to describe the low-lying “covalent” portion of the Hubbard model eigenspectrum (at half filling). The use of a cluster expansion including all diameter 1 and 2 subgraphs plus the diameter 3 six-membered ring allows the coefficients in the extended Heisenberg model to be determined from the results of accurate calculations of the Hubbard spectrum of benzene. The model is found to predict the lower energy states of two test molecules, styrene and naphthalene, rather accurately, and is thus expected to be generally applicable to benzenoid aromatic hydrocarbons. © 2002 American Institute of Physics.
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71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
75.10.Jm Quantized spin models, including quantum spin frustration

Orbital nonrelaxed coupled cluster singles and doubles with perturbative triples corrections calculations of first-order one-electron properties

Kasper Hald, Asger Halkier, Poul Jørgensen, and Sonia Coriani

J. Chem. Phys. 117, 9983 (2002); http://dx.doi.org/10.1063/1.1517991 (8 pages) | Cited 3 times

Online Publication Date: 19 November 2002

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The calculation of first-order one-electron molecular properties is discussed for an orbital nonrelaxed CCSD(T) (coupled cluster singles and doubles with perturbative triples corrections) wave function model. The conventional CCSD(T) triples amplitude equations have been generalized to contain terms that depend explicitly on the perturbation to compensate for the fact that the Hartree–Fock molecular orbitals are not allowed to relax. Results of sample calculations are presented, including the molecular electric quadrupole moment of benzene in the d-aug-cc-pVTZ basis set, which contains 564 contracted basis functions. © 2002 American Institute of Physics.
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31.15.bw Coupled-cluster theory
31.15.xr Self-consistent-field methods
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

The Jahn–Teller effect in the lower electronic states of benzene cation. I. Calculation of linear parameters for the e2g modes

Philip M. Johnson

J. Chem. Phys. 117, 9991 (2002); http://dx.doi.org/10.1063/1.1519006 (10 pages) | Cited 18 times

Online Publication Date: 19 November 2002

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Jahn–Teller (JT) coupling parameters can be simply derived from features of the potential energy surfaces of the JT active vibrational modes of a molecule subject to that effect. Potential energy curves representing cuts of D2h symmetry have been calculated using density functional theory for each of the four active e2g modes of benzene cation in each of the lowest three degenerate electronic states. From these curves and the vibrational frequencies, the JT coupling parameters can be found (vibrational numbering follows Wilson’s notation, coupling parameters are in Moffit’s notation). For the C6H6+math 2E1g state the largest JT coupling parameter is provided by mode 6 (D = 0.48), followed closely by mode 8 (0.30) and then mode 9 (0.10). Mode 7 provides almost no stabilization. For the math 2E2g state, calculated coupling parameters are very large, particularly for modes 8 (1.36) and 6 (0.93). Modes 7 (0.10) and 9 (0.07) are smaller but finite. For the math 2E1u state, mode 6 has an impressive linear coupling parameter of 4.12, able to support several vibrations below the JT cusp. Indications of a substantial quadratic stabilization for that mode result in the possibility of a completely static distortion in that state. Similar, but not identical, results are obtained for C6D6+. © 2002 American Institute of Physics.
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31.30.Gs Hyperfine interactions and isotope effects
33.20.Tp Vibrational analysis

The Jahn–Teller effect in the lower electronic states of benzene cation. II. Vibrational analysis and coupling constants of the math 2E2g state

Philip M. Johnson

J. Chem. Phys. 117, 10001 (2002); http://dx.doi.org/10.1063/1.1519007 (7 pages) | Cited 12 times

Online Publication Date: 19 November 2002

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The vibrational structure seen in photoinduced Rydberg ionization spectra of the math 2E2g state of benzene cation (C6H6+ and C6D6+) has been analyzed by fitting the vibrational patterns to energy levels derived from multimode Jahn–Teller calculations. Most of the structure can be ascribed to various combinations of modes 6 and 16, with minor contributions from 4, 17, and 18 (using Wilson’s numbering convention). In qualitative agreement with parameters derived from electronic structure calculations, the linear coupling parameter for mode 6 is very large (D = 1.39 in C6H6+ and 1.28 in C6D6+). This raises questions about certain angular momentum selection rules in the classical Jahn–Teller model. © 2002 American Institute of Physics.
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31.30.Gs Hyperfine interactions and isotope effects
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants

An L-shaped equilibrium geometry for germanium dicarbide (GeC2)? Interesting effects of zero-point vibration, scalar relativity, and core–valence correlation

Levent Sari, Kirk A. Peterson, Yukio Yamaguchi, and Henry F. Schaefer

J. Chem. Phys. 117, 10008 (2002); http://dx.doi.org/10.1063/1.1518966 (11 pages) | Cited 6 times

Online Publication Date: 19 November 2002

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The ground state potential energy surface of the GeC2 molecule has been investigated at highly correlated coupled cluster levels of theory. Large basis sets including diffuse functions and functions to describe core correlation effects were employed in order to predict the true equilibrium geometry for GeC2. Like the much-studied valence isoelectronic SiC2, the linear (1∑+), L-shaped (1A′), and T-shaped structures (1A1) must be investigated. The L-shaped Cs geometry is found to have real harmonic vibrational frequencies along every internal coordinate, and the linear stationary point has an imaginary vibrational frequency along the bending mode at every level of theory employed. The T-shaped geometry is found to have an imaginary vibrational frequency along the asymmetric stretching mode. At the coupled cluster with single and double excitations and perturbative triple excitations [CCSD(T)]/correlation consistent polarized valence quadrupole-ζ (cc-pVQZ) level, the nonrelativistic classical relative energies of the T-shaped and linear structures with respect to the L-shaped minimum are 0.1 and 2.8 kcal/mol, respectively. Including zero-point vibrational energy, scalar relativistic, and core-valence corrections, the T-L energy separation is shifted to 0.4 kcal/mol and the relative energy between the L-shaped and linear structures is still 2.8 kcal/mol. All nonrelativistic and relativistic computations predict that the L-shaped (1A′) structure is most favored for the ground state. The linear structure is predicted to be a transition state, as the case of SiC2. © 2002 American Institute of Physics.
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31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.bw Coupled-cluster theory

Vibrational predissociation of NeBr2 (X, v = 1) using an ab initio potential energy surface

Rita Prosmiti, Carlos Cunha, Alexei A. Buchachenko, Gerardo Delgado-Barrio, and Pablo Villarreal

J. Chem. Phys. 117, 10019 (2002); http://dx.doi.org/10.1063/1.1519001 (7 pages) | Cited 17 times

Online Publication Date: 19 November 2002

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Quantum mechanical calculations on the vibrational predissociation dynamics of NeBr2 are performed using an ab initio (coupled cluster using single and double excitations with a noniterative perturbation treatment of triple excitations) potential energy surface. Energy positions, lifetimes, and final rotational state distributions are determined for vibrational predissociation from the two lowest linear (n = 0) and T-shaped (n = 1) van der Waals levels of NeBr2 (X, v = 1). Comparison with the experimental assumption as regards the energy transfer to rotation provides information about the type of isomer involved in the experimental vibrational predissociation process, suggesting that it was the linear one. © 2002 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
33.15.Mt Rotation, vibration, and vibration-rotation constants

Relativistic effects on interaction-induced electric properties of weakly interacting systems: The HF…AuH dimer

Aggelos Avramopoulos, Manthos G. Papadopoulos, and Andrzej J. Sadlej

J. Chem. Phys. 117, 10026 (2002); http://dx.doi.org/10.1063/1.1520131 (13 pages) | Cited 8 times

Online Publication Date: 19 November 2002

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The relativistic effect on interaction-induced dipole moment and polarizability in the HF…AuH dimer is studied in the framework of the long-range perturbation theory model and by using the supermolecular approach. The perturbation treatment is limited to the lowest multipole-expanded form known as the dipole–induced-dipole (DID) approximation. Although the long-range DID model may be useful in elucidating the origin of the relativistic effect on interaction-induced electric properties, it fails to predict the correct magnitude of this effect for all but very large separations between the two subsystems. At intermediate monomer separations the supermolecular model predicts a substantial relativistic contribution to interaction-induced dipole moments and a rather moderate relativistic effect on induced polarizabilities. It has also been found that the vibrational contribution to the interaction-induced polarizability estimated in the double harmonic approximation may dominate over the changes in the pure electronic term. However, sufficiently accurate calculations of the vibrational contribution to electric properties of a weakly bound dimer, which would confirm this finding, appear to be unlikely at present. © 2002 American Institute of Physics.
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31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.xp Perturbation theory

Thermochemistry of small cationic iron–sulfur clusters

Konrad Koszinowski, Detlef Schröder, Helmut Schwarz, Rohana Liyanage, and P. B. Armentrout

J. Chem. Phys. 117, 10039 (2002); http://dx.doi.org/10.1063/1.1518004 (18 pages) | Cited 7 times

Online Publication Date: 19 November 2002

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The kinetic energy dependences of the reactions of Fen+ with COS (n = 2–6) and CS2 (n = 2–5) are studied in a guided-ion beam tandem mass-spectrometer. The main products arise from sulfur transfer and subsequent losses of Fe atoms. In the case of CS2, this reactant also formally replaces one Fe atom of the cluster to form Fen−1CS2+ with losses of further Fe atoms at elevated energies. In addition, the kinetic energy dependences of the reactions of FenS+ (n = 2–4) with Xe and CS2 are studied. The former system yields collision-induced dissociations, whereas the latter reagent effects sulfur transfer accompanied by subsequent losses of Fe atoms. Analyses of the cross sections for endothermic reactions yield the bond energies D0(Fen+–S), n = 2–5, D0(SFen−1+–Fe), n = 2–5, D0(SFen+−S), n = 1–3, and D0(S2Fen−1+–Fe), n = 2, 3, as well as the ionization energy IE(Fe2S2). These values are derived with explicit consideration of the lifetimes of the energized reaction intermediates. The binding between sulfur and the cluster core strengthens as the cluster size increases, which is rationalized by simple structural arguments. © 2002 American Institute of Physics.
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36.40.Jn Reactivity of clusters
82.33.Fg Reactions in clusters
33.15.Ta Mass spectra
82.60.-s Chemical thermodynamics

Vibrational structures of predissociating methylamines (CH3NH2 and CH3ND2) in states: Free internal rotation of CH3 with respect to NH2

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

J. Chem. Phys. 117, 10057 (2002); http://dx.doi.org/10.1063/1.1518005 (4 pages) | Cited 13 times

Online Publication Date: 19 November 2002

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Resonantly-enhanced one-color two-photon (1+1) ionization spectra of jet-cooled methylamines (CH3NH2 and CH3ND2) reveal the vibrational structures of these molecules in predissociative states. Rotational fine structure is clearly resolved for CH3ND2 at the origin and first wagging vibrational level in the excited state. The spectral linewidth becomes homogeneously broadened to give only vibrationally resolved spectral features for the higher vibrational energy levels of CH3ND2 (). From the spectral analysis of the –X transition of CH3ND2, it is found that the methyl moiety rotates nearly freely about the C–N axis with respect to the amino group in the state, indicating that the removal of an electron from the nonbonding orbital of N is responsible for the free internal rotation. Vibrational levels are only barely resolved in the –X excitation spectrum of CH3NH2 due to severe homogeneous line-broadening, indicating ultrashort lifetimes of ∼0.4 ps for predissociating CH3NH2 molecules in the state. Spectral interpretation of the –X excitation spectrum of CH3NH2 is carried out by the comparison with that of CH3ND2, giving the confirmative vibrational assignment of methylamines in states for the first time. The dramatic difference of CH3NH2 and CH3ND2 in their lifetimes in states suggests that the major dissociation channel of the excited methylamine may be the N–H (or D) bond dissociation. © 2002 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.20.Sn Rotational analysis
31.30.Gs Hyperfine interactions and isotope effects
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.-b Photon interactions with molecules
33.70.Jg Line and band widths, shapes, and shifts
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

A revised experimental absolute magnetic shielding scale for oxygen

Roderick E. Wasylishen and David L. Bryce

J. Chem. Phys. 117, 10061 (2002); http://dx.doi.org/10.1063/1.1518683 (6 pages) | Cited 39 times

Online Publication Date: 19 November 2002

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A revised absolute magnetic shielding scale for oxygen is established based on a recently reported highly precise experimental measurement of the 17O spin-rotation constant in carbon monoxide. The isotropic oxygen magnetic shielding constant for 12C17O at the equilibrium geometry, σe, is found to be −56.8±0.6 ppm. The experimental rovibrationally averaged value of the shielding constant at 300 K, 〈σ〉300 K, is −62.7±0.6 ppm, in excellent agreement with the ab initio value reported by Vaara et al. [J. Chem. Phys. 109, 8388 (1998)]. Based on the revised scale and on experimentally known oxygen chemical shifts, 〈σ〉300 K (H2O(l)) is 287.5±0.6 ppm and 〈σ〉300 K (H2O(g)) is 323.6±0.6 ppm. © 2002 American Institute of Physics.
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33.25.+k Nuclear resonance and relaxation
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Accuracy of the centrifugal sudden approximation in the H+H2O reaction and accurate integral cross sections for the H+H2O→H2+OH abstraction reaction

Dong H. Zhang, Minghui Yang, and Soo-Y. Lee

J. Chem. Phys. 117, 10067 (2002); http://dx.doi.org/10.1063/1.1519009 (6 pages) | Cited 16 times

Online Publication Date: 19 November 2002

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The initial state selected time-dependent wave packet method has been extended to calculate the total reaction probability for atom-triatom reactions with total angular momentum J>0 by treating both bonds in the triatom reagent reactively. The total exchange and abstraction reaction probabilities for the title reaction with J = 15 calculated with 2 K-blocks (the projection of the total angular momentum on the body-fixed axis) show that one has to treat both OH bonds in the H2O reagent reactively for the exchange reaction, but for the abstraction reaction one can treat one OH bond as a spectator bond to get accurate results. This is in accord with what had been found for the total reaction probabilities for J = 0 [Phys. Rev. Lett. 89, 103201 (2002)]. The J = 15 reaction probabilities also show that the CS (centrifugal sudden) approximation is inadequate for the title reaction, in particular for the abstraction reaction. The integral cross sections for the abstraction reaction, calculated without the CS approximation but by freezing one OH bond in the H2O reagent for the ground and first vibrationally excited states, are found to be substantially larger than the corresponding CS integral cross sections. However, the integral cross section for the ground vibrational state is still much smaller than the existing experimental result. Since the treatment of freezing OH bond is not expected to introduce any noticeable error, it is conceivable that the experiments overestimated the integral cross section for the abstraction reaction. © 2002 American Institute of Physics.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Pm Rate constants, reaction cross sections, and activation energies

Study of the stretching vibrational band intensities of XH4 molecules employing four-dimensional ab initio (X�C and Sn) and effective (X�C and Si) dipole moment surfaces

Sheng-Gui He, An-Wen Liu, Hai Lin, Shui-Ming Hu, Jing-Jing Zheng, Lu-Yuan Hao, and Qing-Shi Zhu

J. Chem. Phys. 117, 10073 (2002); http://dx.doi.org/10.1063/1.1520130 (8 pages)

Online Publication Date: 19 November 2002

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Stretching vibrational band intensities of XH4 molecules were investigated employing four-dimensional ab initio (X�C and Sn) and effective (X�C and Si) dipole moment surfaces (DMS) in combination with the local mode potential energy surfaces. The ab initio DMS of CH4 and SnH4 calculated at the coupled cluster CCSD(T) level of theory reproduced most of the observed intensities within a factor of 1.5. The effective DMS of CH4 and SiH4 were obtained by adjusting some selected high-order terms in the ab initio DMS to fit the observed intensities. They were applied to the corresponding deuterated isotopomers yielding better results than the ab initio DMS. The intensities of the combination bands are mainly due to the interbond cross terms in the DMS for SiH4, GeH4, and SnH4, while for CH4, both diagonal and cross terms are important. The relatively strong combination band that has comparable intensity with the pure overtone was predicted at the fourth local mode manifold for SnH4. © 2002 American Institute of Physics.
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33.20.Tp Vibrational analysis
31.15.A- Ab initio calculations
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.bw Coupled-cluster theory

Practical implementation of the instanton theory. II. Decay of metastable state through tunneling

Gennady V. Mil’nikov and Hiroki Nakamura

J. Chem. Phys. 117, 10081 (2002); http://dx.doi.org/10.1063/1.1520532 (7 pages) | Cited 4 times

Online Publication Date: 19 November 2002

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A new instanton theory for decay rate problem at zero temperature is presented. The canonically invariant expression for the lifetime of metastable state is derived. The theory is fully implemented by an effective numerical recipe to find the instanton trajectory and is applicable to any high dimensional systems. © 2002 American Institute of Physics.
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31.50.Df Potential energy surfaces for excited electronic states
73.40.Gk Tunneling
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

Catching the collision complex through a femtosecond coherently controlled pump/probe process

G. Grégoire, H. Kang, I. Dimicoli, C. Dedonder-Lardeux, S. Martrenchard, and C. Jouvet

J. Chem. Phys. 117, 10088 (2002); http://dx.doi.org/10.1063/1.1520533 (9 pages) | Cited 2 times

Online Publication Date: 19 November 2002

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We propose a very simple and efficient way to stabilize ions issued from a collision complex through a femtosecond coherently controlled pump/probe process. Starting from a van der Waals complex, one can initiate a collision at a well-defined time and with a restricted impact parameter. Formation of stable ionic complex can be achieved by ionizing the collision complex at the “right time.” We present in this paper its application to the NaI–(CH3CN)1–2 system. Na+–CH3CN ion formation is coherently controlled by ionization of colliding Na atom on CH3CN molecules issued from the dissociation of NaI within NaI–(CH3CN)1–2. Classical mechanic calculations using simple ionization/dissociation conditions can reproduce the experimental data and give an insight into the control of such a reaction. © 2002 American Institute of Physics.
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82.53.Eb Pump probe studies of photodissociation
82.53.Kp Coherent spectroscopy of atoms and molecules
82.50.-m Photochemistry
36.40.Jn Reactivity of clusters

Dynamics of OH formation in the dissociation of acrylic acid in its (n,π∗) and (π,π∗) transitions excited at 248 and 193 nm

Hari P. Upadhyaya, Awadhesh Kumar, Prakash D. Naik, Avinash V. Sapre, and Jai P. Mittal

J. Chem. Phys. 117, 10097 (2002); http://dx.doi.org/10.1063/1.1520534 (7 pages) | Cited 13 times

Online Publication Date: 19 November 2002

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The (n,π∗) and (π,π∗) transitions in acrylic acid (H2C�CHCOOH) are excited by KrF (248 nm) and ArF (193 nm) laser pulses, respectively, and the dynamics of its photodissociation to give OH fragments is studied using laser induced fluorescence technique. At both the photolysis wavelengths, the OH fragments produced are vibrationally cold, but have different rotational state distributions. To get an insight into the potential energy surface involved in the dissociation process, spin–orbit and Λ-doublets ratios are also measured. Average relative translational energy partitioned into the photofragments is determined using linewidth of the Doppler profiles to be 13.2±3.1 and 10.2±2.8 kcal/mol at 193 and 248 nm excitations, respectively. High percentage of translational energy released into the photofragments suggests the presence of an exit barrier for the dissociation. On 248 nm excitation, the OH radicals are formed instantaneously during the laser pulse, while on 193 nm excitation, a risetime of ∼2 μs is seen. Another difference between the photodissociation at 193 nm and 248 nm is the observation of an intense fluorescence in UV–visible region at the former, and no fluorescence at the later wavelength. Our experimental results are compared with those obtained by recent ab initio calculations by Fang and Liu. It is concluded that when (π,π∗) transition of acrylic acid is excited at 193 nm, the initially prepared S2 state undergoes nonradiative transitions to S1 and T2 states, and from where the molecule subsequently dissociates, while excitation to (n,π∗) transition at 248 nm leads to dissociation solely from the initially prepared S1 state. © 2002 American Institute of Physics.
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82.50.-m Photochemistry
33.80.-b Photon interactions with molecules
33.50.Dq Fluorescence and phosphorescence spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Sn Rotational analysis
33.70.Jg Line and band widths, shapes, and shifts

A new model of N2O quantum yield in the UV photolysis of O3/O2/N2 mixtures: Contributions of electronically excited O3 and O3⋅N2

Sheo S. Prasad

J. Chem. Phys. 117, 10104 (2002); http://dx.doi.org/10.1063/1.1516795 (5 pages) | Cited 3 times

Online Publication Date: 19 November 2002

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Electronically excited O3 and O3⋅N2 dimer are proposed as contributors to the N2O quantum yield, ϕN2O, following UV photolysis of O3 in O3/O2/N2 mixture. At 100 to 900 torr N2 pressures, ϕN2O is dominated by the electronically excited O3. In this pressure regime ϕN2O in the 310⩽λ⩽340 nm region could, potentially, exceed ϕN2O in the λ<310 nm region. The “classical” O(1D), N2 association predominates above 10 atm. The O3⋅N2+hν may dominate at high pressures (≳500 atm) if the temperature is very low (≲50 K). The atmospheric importance of N2O production via the classical mechanism is well known to be insignificant. In contrast, the production from excited O3 appears to have the potential to significantly affect our current understandings of stratospheric coupled NOx–O3 chemistry and the climatologically important N2O source-sink budget. It is therefore critical to determine the wavelength variation of ϕN2O in the 310⩽λ⩽340 nm region by gas phase experiments. Theoretical studies are needed to understand, at the quantum chemistry level, the mechanism of the suggested N2O formation from ultra-short-lived electronically excited O3. © 2002 American Institute of Physics.
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82.50.-m Photochemistry
82.33.Tb Atmospheric chemistry

Experimental and theoretical study of intramultiplet transitions in collisions of C(3P) and Si(3P) with He

S. D. Le Picard, P. Honvault, B. Bussery-Honvault, A. Canosa, S. Laubé, J.-M. Launay, Bertrand Rowe, D. Chastaing, and I. R. Sims

J. Chem. Phys. 117, 10109 (2002); http://dx.doi.org/10.1063/1.1518026 (12 pages) | Cited 3 times

Online Publication Date: 19 November 2002

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We present a combined theoretical and experimental study of intramultiplet transitions in collisions of C(3P) and Si(3P) with He. Relaxation rate constants have been measured using the CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) technique at 15 K for C(3P)+He and over the 15–49 K temperature range for Si(3P)+He. Three sets of interaction potentials have been generated for the 3∑− and 3∏ electronic states of CHe and SiHe systems. Quantum-mechanical calculations have been performed on these potential curves for the spin–orbit relaxation and excitation. Cross sections and rate constants are very sensitive to the interaction potential. For the Si(3P)+He system, an overall good agreement between the theoretical and experimental rate constants is found with the best quality interaction potential, while for the C(3P)+He system experimental rate constants are much smaller than the theoretical ones. © 2002 American Institute of Physics.
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34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
31.15.A- Ab initio calculations
31.15.xr Self-consistent-field methods
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Diffuse interface analysis of crystal nucleation in hard-sphere liquid

László Gránásy and Tamás Pusztai

J. Chem. Phys. 117, 10121 (2002); http://dx.doi.org/10.1063/1.1519862 (4 pages) | Cited 19 times

Online Publication Date: 19 November 2002

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We show that the increase of the interface free energy with deviation from equilibrium seen in recent Monte Carlo simulations [S. Auer and D. Frenkel, Nature (London) 413, 711 (2001)] can be recovered if the molecular scale diffuseness of the crystal–liquid interface is considered. We compare two models, Gránásy’s phenomenological diffuse interface theory, and a density functional theory that relies on the type of Ginzburg–Landau expansion for fcc nucleation, that Shih et al. introduced for bcc crystal. It is shown that, in the range of Monte Carlo simulations, the nucleation rate of the stable fcc phase is by several orders of magnitude higher than for the metastable bcc phase, seen to nucleate first in other fcc systems. The nucleation barrier that the diffuse interface theories predict for small deviations from equilibrium is in far better agreement with the simulations than the classical droplet model. The behavior expected at high densities is model dependent. Gránásy’s phenomenological diffuse interface theory indicates a spinodal point close to glass transition, while a nonsingular behavior is predicted by the density functional theory with constant Ginzburg–Landau coefficients. Remarkably, a minimum of the nucleation barrier, similar to the one seen in polydisperse systems, occurs if the known density dependence of the Ginzburg–Landau coefficients is considered. © 2002 American Institute of Physics.
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61.25.-f Studies of specific liquid structures
64.60.Q- Nucleation
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
65.20.-w Thermal properties of liquids
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
68.08.De Liquid-solid interface structure: measurements and simulations

Effects of anharmonicity and electronic coupling on photoinduced electron transfer in mixed valence compounds

Daren M. Lockwood, Mark A. Ratner, and Ronnie Kosloff

J. Chem. Phys. 117, 10125 (2002); http://dx.doi.org/10.1063/1.1519258 (8 pages) | Cited 10 times

Online Publication Date: 19 November 2002

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We develop a semigroup model of electron transfer (ET) dynamics in mixed valence compounds. This model is useful for investigating the effects of anharmonicity in inner sphere nuclear modes, as well as the dependence of the electronic dynamics on the nature of the electronic coupling. Two effective “subsystem” nuclear vibrations are treated explicitly in the model, to account for the rapid electronic energy gap fluctuations induced by the inner sphere vibrations. The essentially Markovian effects of the remaining “bath” modes are approximated by semigroups. We find that including the anharmonicity in inner sphere vibrations leads to a very small increase in the rate of ET. This effect is due to the change in reactant and product vibronic states when anharmonicity is included, as well as the rapid electronic dephasing induced by the bath. An assumption of strong electronic coupling is found to be sufficient to explain experimentally observed ET rates, but the possible role of conical intersections in ultrafast ET reactions is also noted. © 2002 American Institute of Physics.
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71.28.+d Narrow-band systems; intermediate-valence solids
71.70.-d Level splitting and interactions

Rotation of O2 molecules in solid D2 and HD: An electron spin resonance study

Takayuki Kumada

J. Chem. Phys. 117, 10133 (2002); http://dx.doi.org/10.1063/1.1520142 (6 pages) | Cited 3 times

Online Publication Date: 19 November 2002

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X-band electron spin resonance (ESR) spectroscopy has been applied to the study of molecular rotation of O2 molecules in isotopic solid hydrogen, D2 and HD. ESR signal of the O2 molecules in hindered rotational states has been observed, and its pressure dependence has been measured up to 19 MPa. Although molar volume of solid hydrogen decreases, the O2 rotation has become less hindered with the increase in pressure and isotope substitution from HD to D2. These effects of pressure and isotope substitution suggest that the potential barrier for the O2 rotation is mainly produced by distortion of O2 cages in D2 and HD. Since solid hydrogen becomes less compressible with the increase in pressure and the isotope substitution from HD to D2, the O2 rotation becomes less hindered in the less distorted O2 cages. © 2002 American Institute of Physics.
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33.35.+r Electron resonance and relaxation
33.15.Mt Rotation, vibration, and vibration-rotation constants

A time dependent density functional treatment of superfluid dynamics: Equilibration of the electron bubble in superfluid 4He

J. Eloranta and V. A. Apkarian

J. Chem. Phys. 117, 10139 (2002); http://dx.doi.org/10.1063/1.1520139 (12 pages) | Cited 29 times

Online Publication Date: 19 November 2002

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Time dependent density functionals are formulated and implemented in numerical simulations of the equilibration dynamics of an excess electron in superfluid helium. Previously developed density functionals that incorporate nonlocal potential and kinetic correlations and reproduce the dispersion curve of liquid 4He, are used. The electron–helium interaction is treated using pseudopotentials, after testing their accuracy in reproducing the static properties of the solvated electron bubble through its known spectroscopy. The dynamics initiated by the sudden compression of the bubble is dissected, and the results are favorably compared to classical hydrodynamics. In the near-field, the fast motion corresponds to interfacial compressional waves, followed by the slow breathing of the cavity. The far-field motion consists of a shock wave, followed by radiating sound waves. The solitonic shock wave propagates at speeds as high as 580 m/s, determined by the amplitude of excitation. The energy carried by the shock front ensures that the subsequent bubble dynamics occurs in the linear response regime. Dissipation occurs through radiation of sound during the acceleration stages of the bubble, carried by driven phonons of λ = cτ = 300 Å, where c = 240 m/s is the speed of sound, and τ=130 ps is the breathing period of the bubble. The interfacial waves generate traveling excitations at k = 2 Å−1, high on the positive roton branch. Excitations in the roton well are not observed. The time dependent spectroscopy of the trapped electron is shown to provide a sensitive probe of the evolving dynamics by tracking the damped oscillations of the bubble, which is damped in two periods. The results are consistent with the related time-resolved experiments on He2∗ Rydberg electrons, and significantly different from prior estimates of the electron-bubble relaxation dynamics. © 2002 American Institute of Physics.
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67.25.dg Transport, hydrodynamics, and superflow
67.25.dr Restricted geometries
31.15.E- Density-functional theory
47.40.Nm Shock wave interactions and shock effects

Specific heat anomaly at the glass transition

Takashi Odagaki, Takashi Yoshidome, Toshiaki Tao, and Akira Yoshimori

J. Chem. Phys. 117, 10151 (2002); http://dx.doi.org/10.1063/1.1519237 (5 pages) | Cited 11 times

Online Publication Date: 19 November 2002

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A general frame work is devised to obtain the specific heat of nonequilibrium systems described by the energy-landscape picture, where a representative point in the phase space is assumed to obey a stochastic motion which is governed by a master equation. The specific heat depends on the observation time and becomes quenched one for short observation time and annealed one for long observation time. In order to test its validity, the frame work is applied to a two-level system where the state goes back and forth between two levels stochastically. The specific heat is shown to increase from zero to the Schottky form as the observation time is increased from zero to infinity. The anomaly of specific heat at the glass transition is reproduced by a system with a model energy-landscape, where basins of the landscape form a one-dimensional array and jump rate between adjacent basins obeys a power-law distribution. It is shown that the glass transition can be understood as a transition from an annealed to a quenched system and that the glass transition temperature becomes lower when the observation time is increased. © 2002 American Institute of Physics.
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65.20.-w Thermal properties of liquids
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

Structures of hard-sphere fluids from a modified fundamental-measure theory

Yang-Xin Yu and Jianzhong Wu

J. Chem. Phys. 117, 10156 (2002); http://dx.doi.org/10.1063/1.1520530 (9 pages) | Cited 84 times

Online Publication Date: 19 November 2002

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We reformulate Rosenfeld’s fundamental-measure theory using the excess Helmholtz energy density from the Boublik–Mansoori–Carnahan–Starling–Leland equation of state instead of that from the scaled-particle theory. The new density functional theory yields improved density distributions, especially the contact densities, of inhomogeneous hard-sphere fluids as well as more accurate direct and pair correlation functions of homogeneous hard spheres including those of highly asymmetric mixtures. This new density functional theory will provide an accurate reference for the further development of a statistical-thermodynamic theory of complex fluids at uniform and at inhomogeneous conditions. © 2002 American Institute of Physics.
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61.20.Gy Theory and models of liquid structure
05.20.-y Classical statistical mechanics
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
05.70.Ce Thermodynamic functions and equations of state

Monte Carlo simulation for the hard-core two-Yukawa fluids and test of the two-Yukawa equation of state

Yang-Zheng Lin, Yi-Gui Li, Jiu-Fang Lu, and Wei Wu

J. Chem. Phys. 117, 10165 (2002); http://dx.doi.org/10.1063/1.1518687 (8 pages) | Cited 26 times

Online Publication Date: 19 November 2002

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A recently proposed analytical equation of state (EOS) for the hard-core two-Yukawa fluids is tested against the results of Monte Carlo (MC) simulation in six cases. One range parameter in the two-Yukawa potential is taken as 1.8 or 2.8647, and another is taken as 2.0, 4.0, 8.0, or 13.5485. Attractive and repulsive dominant cases of the potential outside the core are all considered. The simulation conditions selected ensure that, the interaction between two particles is attractive at enough long distance. Some of the cases can give the similar potential as that between charged colloid particles. The hard-core two-Yukawa fluid with parameters, which are obtained from fitting the Lennard-Jones potential, is also studied. The two-Yukawa EOS results fit very well with that of the MC simulation except for some points at high density (as ρ∗ = 0.9), which is found to be crystal state. It is found that the two-Yukawa EOS can be used to study the fluid–fluid equilibrium of hard-core two-Yukawa fluid. © 2002 American Institute of Physics.
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61.20.Ja Computer simulation of liquid structure
64.10.+h General theory of equations of state and phase equilibria
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
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