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22 Jan 2004

Volume 120, Issue 4, pp. 1667-2070

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Scaling of the memory function and Brownian motion

G. R. Kneller and G. Sutmann

J. Chem. Phys. 120, 1667 (2004); http://dx.doi.org/10.1063/1.1642599 (3 pages) | Cited 4 times

Online Publication Date: 23 January 2004

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It has been recently shown that the velocity autocorrelation function of a tracer particle immersed in a simple liquid scales approximately with the inverse of its mass [J. Chem. Phys. 118, 5283 (2003)]. With increasing mass the amplitude is systematically reduced and the velocity autocorrelation function tends to a slowly decaying exponential, which is characteristic for Brownian motion. We give here an analytical proof for this behavior and comment on the usual explanation for Brownian dynamics which is based on the assumption that the memory function is proportional to a Dirac distribution. We also derive conditions for Brownian dynamics of a tracer particle which are entirely based on properties of its memory function. © 2004 American Institute of Physics.
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05.40.Jc Brownian motion
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back to top Theoretical Methods and Algorithms

Sigma–pi separation of the electron localization function and aromaticity

J. C. Santos, W. Tiznado, R. Contreras, and P. Fuentealba

J. Chem. Phys. 120, 1670 (2004); http://dx.doi.org/10.1063/1.1635799 (4 pages) | Cited 34 times

Online Publication Date: 23 January 2004

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The electron localization function (ELF) has been separated in its sigma and pi components. The topological analysis of the new ELFσ and ELFπ functions has been used to quantify the concept of resonance. The highest bifurcation values of these functions describe in a correct way the aromaticity of classical ring molecules and some new aromatic compounds as B6CO6, Al42−, and N5−. In the case of Al42−, an important σ delocalization contribution has been found, which is in agreement with previous interpretation. © 2004 American Institute of Physics.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics

A global investigation of excited state surfaces within time-dependent density-functional response theory

M. Wanko, M. Garavelli, F. Bernardi, T. A. Niehaus, T. Frauenheim, and M. Elstner

J. Chem. Phys. 120, 1674 (2004); http://dx.doi.org/10.1063/1.1635798 (19 pages) | Cited 64 times

Online Publication Date: 23 January 2004

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This work investigates the capability of time-dependent density functional response theory to describe excited state potential energy surfaces of conjugated organic molecules. Applications to linear polyenes, aromatic systems, and the protonated Schiff base of retinal demonstrate the scope of currently used exchange-correlation functionals as local, adiabatic approximations to time-dependent Kohn–Sham theory. The results are compared to experimental and ab initio data of various kinds to attain a critical analysis of common problems concerning charge transfer and long range (nondynamic) correlation effects. This analysis goes beyond a local investigation of electronic properties and incorporates a global view of the excited state potential energy surfaces. © 2004 American Institute of Physics.
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31.50.Df Potential energy surfaces for excited electronic states
31.15.E- Density-functional theory
31.15.vj Electron correlation calculations for atoms and ions: excited states

Size extensive modification of local multireference configuration interaction

Arun Venkatnathan, Andrew B. Szilva, Derek Walter, Robert J. Gdanitz, and Emily A. Carter

J. Chem. Phys. 120, 1693 (2004); http://dx.doi.org/10.1063/1.1635796 (12 pages) | Cited 21 times

Online Publication Date: 23 January 2004

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We recently developed a reduced scaling multireference configuration interaction (MRCI) method based on local correlation in the internal (occupied) and external (virtual) orbital spaces. This technique can be used, e.g., to predict bond dissociation energies in large molecules with reasonable accuracy. However, the inherent lack of size extensivity of truncated CI is a disadvantage that in principle worsens as the system size grows. Here we implement an a priori size-extensive modification of local MRCI known as the averaged coupled pair functional (ACPF) method. We demonstrate that local MR-ACPF recovers more correlation energy than local MRCI, in keeping with trends observed previously for nonlocal ACPF. We test the size extensivity of local ACPF on noninteracting He atoms and a series of hydrocarbons. Basis set and core correlation effects are explored, as well as bond breaking in a variety of organic molecules. The local MR-ACPF method proves to be a useful tool for investigating large molecules and represents a further improvement in predictive accuracy over local MRCI. © 2004 American Institute of Physics.
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31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.A- Ab initio calculations
31.50.-x Potential energy surfaces

Mapping the interaction energy surfaces of cyclic alkanes: Evaluating the transferability of an ab initio based potential model

Jukka-Pekka Jalkanen, Tapani A. Pakkanen, and Richard L. Rowley

J. Chem. Phys. 120, 1705 (2004); http://dx.doi.org/10.1063/1.1636152 (10 pages) | Cited 5 times

Online Publication Date: 23 January 2004

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Detailed interaction energy maps are computed for symmetric cyclopropane and tetrahedrane dimer systems using ab initio methods. Interaction energies of cubane and cyclohexane dimers are also reported. The global minimum energy structures of cyclopropane and tetrahedrane systems are both D3d structures with energies of −1.850 and −2.171 kcal mol−1. The ability of NIPE potential model, based on ab initio nonbonding data of neopentane (N), isobutane (I), propane (P), ethane (E) and all their combinations [J.-P. Jalkanen, T. A. Pakkanen, Y. Yang, and R. L. Rowley, J. Chem. Phys. 118, 5474 (2003)] to predict the pair interaction energies of these strained cyclic hydrocarbons is also investigated. The difference between the energies predicted by NIPE and those obtained from the ab initio calculations increases with ring strain In general, NIPE values are in close agreement with the ab initio results for alkane ring structures having low ring strain. © 2004 American Institute of Physics.
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34.20.Gj Intermolecular and atom-molecule potentials and forces
31.15.A- Ab initio calculations

New coupled-cluster methods with singles, doubles, and noniterative triples for high accuracy calculations of excited electronic states

Karol Kowalski and Piotr Piecuch

J. Chem. Phys. 120, 1715 (2004); http://dx.doi.org/10.1063/1.1632474 (24 pages) | Cited 102 times

Online Publication Date: 23 January 2004

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The single-reference ab initio methods for high accuracy calculations of potential energy surfaces (PESs) of excited electronic states, termed the completely renormalized equation-of-motion coupled-cluster approaches with singles, doubles, and noniterative triples [CR-EOMCCSD(T)], are developed. In the CR-EOMCCSD(T) methods, which are based on the formalism of the method of moments of coupled-cluster equations [P. Piecuch et al., Int. Rev. Phys. Chem. 21, 527 (2002)], the suitably designed corrections due to triple excitations are added, in a state-selective manner, to the excited-state energies obtained in the standard equation-of-motion coupled-cluster calculations with singles and doubles (EOMCCSD). It is demonstrated that the CR-EOMCCSD(T) approaches, which can be regarded as the excited-state analogs of the ground-state CR-CCSD(T) theory [K. Kowalski and P. Piecuch, J. Chem. Phys. 113, 18 (2000)], provide a highly accurate description of excited states dominated by double excitations, excited states displaying a manifestly multireference character, and PESs of excited states along bond breaking coordinates with the ease of the ground-state CCSD(T) or CR-CCSD(T) calculations. The performance of the CR-EOMCCSD(T) methods is illustrated by the results of calculations for the excited states of CH+, HF, N2, C2, and ozone. © 2004 American Institute of Physics.
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31.15.bw Coupled-cluster theory
31.50.Df Potential energy surfaces for excited electronic states
31.15.A- Ab initio calculations
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Energy transfer in Li(4p)+(Ar,H2,CH4) collisions

Brian C. Hattaway, Solomon Bililign, Lionel Uhl, Vincent Ledentu, and Gwang-Hi Jeung

J. Chem. Phys. 120, 1739 (2004); http://dx.doi.org/10.1063/1.1634557 (7 pages) | Cited 3 times

Online Publication Date: 23 January 2004

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The direct collisional energy transfer processes of the excited states of Li(4p) by several gases are investigated under gas cell conditions. The nonreactive absorption profiles of the collision complex are monitored as a function of laser detuning from the Li(2s–4p) resonances. Pronounced structures in the absorption spectra along with high level ab initio calculations of the relevant potential energy surfaces are used to understand the experimental results. © 2004 American Institute of Physics.
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34.50.-s Scattering of atoms and molecules
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

Resonances in three-dimensional H+HLi scattering: A time-dependent wave packet dynamical study

R. Padmanaban and S. Mahapatra

J. Chem. Phys. 120, 1746 (2004); http://dx.doi.org/10.1063/1.1634559 (10 pages) | Cited 5 times

Online Publication Date: 23 January 2004

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This paper examines the resonances in H+HLi scattering. The signature of these resonances is obtained from the oscillations in its reaction probability versus energy curves. They are identified here from a set of pseudospectra calculated for different initial locations of a stationary Gaussian wave packet on the ab initio potential energy surface (PES) reported by Dunne, Murrel, and Jemmer [Chem. Phys. Lett. 336, 1 (2001)]. The nuclear motion on this PES is monitored with the aid of a time-dependent wave packet method and the pseudospectrum are calculated by Fourier transforming the time autocorrelation function of the initial wave packet. The resonances are further examined and assigned by computing their eigenfunctions through spectral quantization algorithm. Both the linewidth as well as decay lifetimes of the resonances are reported. © 2004 American Institute of Physics.
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34.50.-s Scattering of atoms and molecules

Vacuum ultraviolet-infrared photo-induced Rydberg ionization spectroscopy: C–H stretching frequencies for trans-2-butene and trichloroethene cations

H. K. Woo, P. Wang, K.-C. Lau, X. Xing, and C. Y. Ng

J. Chem. Phys. 120, 1756 (2004); http://dx.doi.org/10.1063/1.1634561 (5 pages) | Cited 13 times

Online Publication Date: 23 January 2004

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We have demonstrated the two-color vacuum ultraviolet (VUV)-infrared (IR) photoinduced Rydberg ionization (PIRI) experiment. Trichloroethene (ClCH�CCl2) and trans-2-butene (trans-CH3CH�CHCH3) were prepared in Rydberg states in the range of effective principal quantum number n∗ ≈ 7–93 by VUV excitation prior to IR-induced autoionization. The observed VUV-IR-PIRI spectra are found to be independent of n∗, suggesting that the electron Rydberg orbital is conserved, i.e., the Rydberg electron is behaving as a spectator during the excitation process. The observed IR active C–H stretching vibrational frequencies ν12+ = 3072±5 cm−1 for ClCH�CCl2+ and ν23+ = 2908±3 cm−1, ν25+ = 2990±10 cm−1 and ν30+ = 3022±10 cm−1 for trans-CH3CH�CHCH3+ are compared with predictions based on ab initio quantum-chemical procedures and density functional calculations. © 2004 American Institute of Physics.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.20.Ni Vacuum ultraviolet spectra
33.20.Ea Infrared spectra

Ionization from a double bond: Rovibronic photoionization dynamics of ethylene, large amplitude torsional motion and vibronic coupling in the ground state of C2H4+

S. Willitsch, U. Hollenstein, and F. Merkt

J. Chem. Phys. 120, 1761 (2004); http://dx.doi.org/10.1063/1.1635815 (14 pages) | Cited 26 times

Online Publication Date: 23 January 2004

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Rotationally resolved pulsed-field-ionization zero-kinetic-energy photoelectron spectra of the math→math+ transition in ethylene and ethylene-d4 have been recorded at a resolution of 0.09 cm−1. The spectra provide new information on the large amplitude torsional motion in the cationic ground state. An effective one-dimensional torsional potential was determined from the experimental data. Both C2H4+ and C2D4+ exhibit a twisted geometry, and the lowest two levels of the torsional potential form a tunneling pair with a tunneling splitting of 83.7(5) cm−1 in C2H4+ and of 37.1(5) cm−1 in C2D4+. A model was developed to quantitatively analyze the rotational structure of the photoelectron spectra by generalizing the model of Buckingham, Orr, and Sichel [Philos. Trans. R. Soc. London, Ser. A 268, 147 (1970)] to treat asymmetric top molecules. The quantitative analysis of the rotational intensity distributions of allowed as well as forbidden vibrational bands enabled the identification of strong vibronic mixing between the math+ and + states mediated by the torsional mode ν4 and a weaker mixing between the math+ and math+ states mediated by the symmetric CH2 out-of-plane bending mode ν7. The vibrational intensities could be accounted for quantitatively using a Herzberg–Teller-type model for vibronic intensity borrowing. The adiabatic ionization energies of C2H4 and C2D4 were determined to be 84 790.42(23) cm−1 and 84 913.3(14) cm−1, respectively. © 2004 American Institute of Physics.
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33.60.+q Photoelectron spectra
33.80.Eh Autoionization, photoionization, and photodetachment
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Double ionization of fluorinated benzenes: Hole localization and delocalization effects

Cristian Villani and Francesco Tarantelli

J. Chem. Phys. 120, 1775 (2004); http://dx.doi.org/10.1063/1.1634562 (17 pages) | Cited 5 times

Online Publication Date: 23 January 2004

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The dense double ionization spectra of all the twelve fluoro-substituted benzene molecules are investigated in great detail by Green’s function ADC(2) calculations and a two-hole density mapping. Double ionization is shown to provide an extremely sensitive tool of electronic structure analysis. The calculations evidence and measure quantitatively how the charge distribution is dictated by the complex interplay between the resilience of the aromatic ring electronic structure and the disruptive effect of the electronegative halogen substituents. Successive substitutions are found not to have any synergic effect, but affect the spectra in very identifiable ways. The Auger spectra of the fluorobenzenes are interpreted in the light of the charge distribution results, using the foreign-imaging model. The double charge transfer spectra are also analyzed and discussed. © 2004 American Institute of Physics.
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33.80.Eh Autoionization, photoionization, and photodetachment

Reaction dynamics of Cl+CH3SH: Rotational and vibrational distributions of HCl probed with time-resolved Fourier-transform spectroscopy

Shin-Shin Cheng, Yu-Jong Wu, and Yuan-Pern Lee

J. Chem. Phys. 120, 1792 (2004); http://dx.doi.org/10.1063/1.1634558 (9 pages) | Cited 3 times

Online Publication Date: 23 January 2004

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Rotationally resolved infrared emission spectra of HCl(v = 1–3) in the reaction of Cl+CH3SH, initiated with radiation from a laser at 308 nm, are detected with a step-scan Fourier-transform spectrometer. Observed rotational temperature of HCl(v = 1–3) decreases with duration of reaction due to collisional quenching; a short extrapolation to time zero based on data in the range 0.25–4.25 μs yields a nascent rotational temperature of 1150±80 K. The rotational energy averaged for HCl(v = 1–3) is 8.2±0.9 kJ mol−1, yielding a fraction of available energy going into rotation of HCl, 〈fr〉 = 0.10±0.01, nearly identical to that of the reaction Cl+H2S. Observed temporal profiles of the vibrational population of HCl(v = 1–3) are fitted with a kinetic model of formation and quenching of HCl(v = 1–3) to yield a branching ratio (68±5):(25±4):(7±1) for formation of HCl(v = 1):(v = 2):(v = 3) from the title reaction and its thermal rate coefficient k2a = (2.9±0.7)×10−10 cm3 molecule−1 s−1. Considering possible estimates of the vibrational population of HCl(v = 0) based on various surprisal analyses, we report an average vibrational energy 36±6 kJ mol−1 for HCl. The fraction of available energy going into vibration of HCl is 〈fv〉 = 0.45±0.08, significantly greater than a value 〈fv〉 = 0.33±0.06 determined previously for Cl+H2S. Reaction dynamics of Cl+H2S and Cl+CH3SH are compared; the adduct CH3S(Cl)H is likely more transitory than the adduct H2SCl. © 2004 American Institute of Physics.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Rp State to state energy transfer
33.20.Ea Infrared spectra

Isotopic effect on the cage-induced quenching of OH(A)/OD(A) inside small argon clusters

A. Kanaev, L. Museur, F. Edery, T. Laarmann, and T. Möller

J. Chem. Phys. 120, 1801 (2004); http://dx.doi.org/10.1063/1.1636457 (5 pages) | Cited 1 time

Online Publication Date: 23 January 2004

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In this paper we report on the isotopic effect on the cage-induced excited-state quenching inside small Arm clusters (m<102) solvated in large NeN clusters (N ≈ 7.5×103). Excited OH(A)/OD(A) fragments are produced by photodissociation of H2O and D2O molecules and the quenching agents are correspondingly H or D atoms. The decrease of the fluorescence yield with the size of the cluster m>m0 is observed in both cases and it is attributed to the formation of the cage of argon atoms around the doped molecule. Interestingly, more atoms are needed to induce the fluorescence quenching of OD∗(A) fragments, m0 = 21±3, compared to the electronically excited state quenching of OH∗(A) molecules, 11±2. A diffusion model containing two free parameters, the quenching cross section σq and the number of argon atoms forming the cage m0, explains the effect in terms of the residence time of the hydrogen atom inside the cage. We suggest that the melting of the doped rare gas clusters is responsible for the different predissociation dynamics. The quenching cross section obtained from the experimental data is in good agreement with former experiments. © 2004 American Institute of Physics.
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33.50.Hv Radiationless transitions, quenching
33.50.Dq Fluorescence and phosphorescence spectra
33.80.Gj Diffuse spectra; predissociation, photodissociation
31.30.Gs Hyperfine interactions and isotope effects

Electron-spin polarization of photoions produced through photoionization from the laser-excited triplet state of Sr

Nobuaki Yonekura, Takashi Nakajima, Yukari Matsuo, Tohru Kobayashi, and Yoshimitsu Fukuyama

J. Chem. Phys. 120, 1806 (2004); http://dx.doi.org/10.1063/1.1635818 (7 pages) | Cited 5 times

Online Publication Date: 23 January 2004

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We report the detailed experimental study on the production of electron-spin-polarized Sr+ ions through one-photon resonant two-photon ionization via laser-excited 5s5p 3P1 (MJ = +1) of Sr atoms produced by laser-ablation. We have experimentally confirmed that the use of laser-ablation for the production of Sr atoms prior to photoionization does not affect the electron-spin polarization. We have found that the degree of electron-spin polarization is 64±9%, which is in good agreement with our recent theoretical prediction. As we discuss in detail, we infer, from a simple analysis, that photoelectrons, being the counterpart of electron-spin-polarized Sr+ ions, have approximately the same degree of electron-spin polarization. Our experimental results demonstrate that the combined use of laser-ablation technique and pulsed lasers for photoionization would be a compact and effective way to realize a pulsed source for spin-polarized ions and electrons for the studies of various spin-dependent dynamics in chemical physics. © 2004 American Institute of Physics.
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32.80.Fb Photoionization of atoms and ions
32.80.Rm Multiphoton ionization and excitation to highly excited states

On symmetry breaking in BNB: Real or artifactual?

Apostolos Kalemos, Thom H. Dunning, and Aristides Mavridis

J. Chem. Phys. 120, 1813 (2004); http://dx.doi.org/10.1063/1.1635797 (7 pages) | Cited 13 times

Online Publication Date: 23 January 2004

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The ground state of the linear BNB molecule has been examined with multireference-based ab initio methods coupled with quantitative basis sets. Previous computational studies on BNB, even those using highly correlated single reference-based methods, e.g., the CCSD(T) and BDT methods, suggested that the two BN bond lengths were unequal. In this paper, the BN(X 3Π)+B(2Pu) potential energy curve is constructed using a state-averaged multireference-based correlated method (SA-CASSCF+PT2). The four lowest states of BN were included in the state averaging procedure. These calculations reveal no symmetry breaking along the antisymmetric stretching mode of the molecule. © 2004 American Institute of Physics.
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31.15.A- Ab initio calculations
31.50.Bc Potential energy surfaces for ground electronic states
31.15.ve Electron correlation calculations for atoms and ions: ground state
31.15.xp Perturbation theory
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

The mutual diffusion coefficient for (meth)acrylate monomers as determined with a nuclear microprobe

Christian M. Leewis, Peter H. A. Mutsaers, Arthur M. de Jong, Leo J. van IJzendoorn, Martien J. A. de Voigt, Min Q. Ren, Frank Watt, and Dirk J. Broer

J. Chem. Phys. 120, 1820 (2004); http://dx.doi.org/10.1063/1.1635800 (6 pages) | Cited 5 times

Online Publication Date: 23 January 2004

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The value of the mutual diffusion coefficient DV of two acrylic monomers is determined with nuclear microprobe measurements on a set of polymer films. These films have been prepared by allowing the monomers to diffuse into each other for a certain time and subsequently applying fast ultraviolet photo-polymerization, which freezes the concentration profile. The monomer diffusion profiles are studied with a scanning 2.1 MeV proton microprobe. Each monomer contains a marker element, e.g., Cl and Si, which are easily detected with proton induced x-ray emission. From the diffusion profiles, it is possible to determine the mutual diffusion coefficient. The mutual diffusion coefficient is dependent of concentration, which is concluded from the asymmetry in the Cl- and Si-profiles. A linear dependence of the mutual diffusion coefficient on the composition is used as a first order approximation. The best fits are obtained for a value of b = (0.38±0.15), which is the ratio of the diffusion coefficient of 1,3-bis(3-methacryloxypropyl)-1, 1,3,3-tetramethyldisiloxane in pure 2-chloroethyl acrylate and the diffusion coefficient of 2-chloroethyl acrylate in pure 1,3-bis(3-methacryloxypropyl)-1,1,3,3-tetramethyldisiloxane. Under the assumption of a linear dependence of the mutual diffusion coefficient DV on monomer composition, it follows that DV = (2.9±0.6)⋅10−10 m2/s at a 1:1 monomer ratio. With Flory–Huggins expressions for the monomer chemical potentials, one can derive approximate values for the individual monomer diffusion coefficients. © 2004 American Institute of Physics.
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82.35.-x Polymers: properties; reactions; polymerization
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
82.60.-s Chemical thermodynamics
82.50.-m Photochemistry

Molecular dynamics study of atomic transport properties in rapidly cooling liquid copper

F. F. Chen, H. F. Zhang, F. X. Qin, and Z. Q. Hu

J. Chem. Phys. 120, 1826 (2004); http://dx.doi.org/10.1063/1.1636452 (6 pages) | Cited 16 times

Online Publication Date: 23 January 2004

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Based on Mei’s embedded atom model [Mei et al., Phys. Rev. B 43, 4653 (1991)] molecular dynamics simulations have been performed to investigate the rapidly cooling processes of Cu. The atomic transport property, namely the self-diffusion coefficient, is computed in the liquid state, and the results near the melting point of Cu are in good agreement with experimental data and other computational values. The atom diffusion movements during the long period of relaxation have been also studied around the solidification temperature Tc. To describe the complex microstructural evolutions during the rapidly cooling processes and the long relaxation processes, the pair correlation function and the pair analysis technique are used. It is demonstrated that the crystallization of amorphous Cu is caused by the atomic diffusion. © 2004 American Institute of Physics.
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66.10.C- Diffusion and thermal diffusion
61.25.Mv Liquid metals and alloys
61.20.Ja Computer simulation of liquid structure
64.70.D- Solid-liquid transitions

Orientational order in binary mixtures of hard Gaussian overlap molecules

Xin Zhou, Hu Chen, and Mitsumasa Iwamoto

J. Chem. Phys. 120, 1832 (2004); http://dx.doi.org/10.1063/1.1634954 (5 pages) | Cited 10 times

Online Publication Date: 23 January 2004

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Based on a standard constant-pressure Monte Carlo molecular simulation, we have studied liquid crystal phases of binary mixtures of nonspherical molecules. The components of the mixtures are two types of hard Gaussian overlap (HGO) molecules. The first type of molecule has a small molecularelongation parameter (short HGO molecules) and cannot form stable liquid crystal phase in the bulk by themselves. The second type of molecule has a large elongation parameter (long HGO molecules) and can form a liquid crystal phase easily. In the mixtures, the short HGO molecules can form an orientationally ordered phase because the long HGO molecules form confining surfaces to induce the alignment of the short molecules. We also study the isotropic–nematic phase transition in different mixtures composed of short and long HGO molecules with different elongations and concentrations. The obtained result implies that small anisotropic molecules can show liquid crystal behavior. © 2004 American Institute of Physics.
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61.30.-v Liquid crystals

Precipitate pattern formation in fluctuating media

Ferenc Izsák and István Lagzi

J. Chem. Phys. 120, 1837 (2004); http://dx.doi.org/10.1063/1.1635354 (4 pages) | Cited 2 times

Online Publication Date: 23 January 2004

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Simulation of the Liesegang pattern formation in low concentration gradient is presented using concentration perturbation in a deterministic model. The precipitation process is based on ion-product supersaturation theory (Ostwald’s model). In the classical experiments with high initial concentration gradients, appearance time and locations of the band formation are well reproducible. Decreasing initial concentration gradients results in a more stochastic pattern structure; this means that the reproducibility of the experiments becomes worse. The presented model and the results of the simulations exhibit the same trend, which were demonstrated and investigated experimentally by Kai et al. [S. Kai, S. C. Müller, and J. Ross, J. Phys. Chem. 87, 806 (1983)] and Kai and Müller [S. Kai and S. C. Müller, Sci. Form 1, 9 (1985)]. © 2004 American Institute of Physics.
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05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
82.40.Ck Pattern formation in reactions with diffusion, flow and heat transfer

Conformation of p-terphenyl under hydrostatic pressure

K. K. Zhuravlev and M. D. McCluskey

J. Chem. Phys. 120, 1841 (2004); http://dx.doi.org/10.1063/1.1634560 (5 pages) | Cited 7 times

Online Publication Date: 23 January 2004

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The conformation of p-terphenyl (C18H14) and deuterated p-terphenyl (C18D14) has been investigated, using high-pressure infrared spectroscopy at liquid-helium temperatures. First-principles calculations, together with the experimental results, were performed to determine the structure of p-terphenyl in the twisted conformation. At low temperatures and pressures, p-terphenyl belongs to the C2 point group of symmetry. In this configuration, the central ring is twisted with respect to the plane of the outer rings. The symmetry of the molecule is nearly C2h, consistent with previous x-ray diffraction measurements. © 2004 American Institute of Physics.
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33.15.Bh General molecular conformation and symmetry; stereochemistry
33.20.Ea Infrared spectra

Statistico-probabilistic approach to taking account of the vapor depletion in the kinetics of homogeneous nucleation: A free-molecular regime of droplet growth

A. P. Grinin, F. M. Kuni, and Y. S. Djikaev

J. Chem. Phys. 120, 1846 (2004); http://dx.doi.org/10.1063/1.1630958 (9 pages) | Cited 3 times

Online Publication Date: 23 January 2004

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We propose a statistico-probabilistic approach to investigate the process of homogeneous formation of droplets in a vapor phase in the presence of an already formed and growing droplet under free-molecular regime of droplet growth after the instantaneous creation of initial vapor supersaturation. We find the probability density for the formation of a new, nearest (neighbor) droplet in the vicinity of an initially formed droplet. The mean distance between two neighboring droplets is also determined, as well as the average time lag for the formation of the nearest (neighbor) droplet; the latter quantity serves as an estimate for the duration of the nucleation stage. An estimate for the average number of droplets forming in unit volume by the end of the nucleation stage is also given. Our results are compared with the predictions of classical nucleation theory which assumes the density uniformity of a metastable phase. Where the proposed appoach is applicable, there is observed qualitative agreement between the results. The underlying cause of this agreement is analyzed and the limits of applicability of the uniformity approximation are clarified. © 2004 American Institute of Physics.
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64.60.Q- Nucleation
47.55.D- Drops and bubbles

Structure of ionic liquids of 1-alkyl-3-methylimidazolium cations: A systematic computer simulation study

Sérgio M. Urahata and Mauro C. C. Ribeiro

J. Chem. Phys. 120, 1855 (2004); http://dx.doi.org/10.1063/1.1635356 (9 pages) | Cited 118 times

Online Publication Date: 23 January 2004

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Molecular dynamics simulations of room temperature molten salts (ionic liquids) containing imidazolium cations have been performed. Ten different systems were simulated at 323 K by using united atom force fields, in which the anion size (F−, Cl−, Br−, and PF6−) and the length of the alkyl chain of 1-alkyl-3-methylimidazolium cations (1-methyl-, 1-ethyl-, 1-butyl-, and 1-octyl-) were systematically varied. It is shown that the resulting equilibrium structures account for the observed features of experimental static structure factors when available. A detailed analysis of the simultaneous effect of changing the anion and the alkyl chain on the preferential location of nearest-neighbor anions around the cations is provided. It is shown that regions above and below the imidazolium ring are the preferential ones in case of large anions. By increasing the length of the alkyl chain, nearest-neighbor anions are pushed away from the volume occupied by the flexible alkyl chain. Partial structure factors of 1-butyl- and 1-octyl- derivatives display a peak at a wave vector smaller than the main peak, indicating the occurrence of an intermediate range order in these ionic liquids due to the presence of long alkyl chains. © 2004 American Institute of Physics.
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61.20.Ja Computer simulation of liquid structure

On the ordering of the first two excited electronic states in all-trans linear polyenes

J. Catalán and J. L. G. de Paz

J. Chem. Phys. 120, 1864 (2004); http://dx.doi.org/10.1063/1.1634556 (9 pages) | Cited 17 times

Online Publication Date: 23 January 2004

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Reported experimental evidence of the relative position of the first two excited electronic states in linear polyenes was carefully examined and compared with that derived from time dependent density functional theory (TDDFT) theoretical calculations performed at the B3LYP level on optimized geometries. The energy values for the first two triplet states 3Bu and 3Ag, obtained from TDDFT calculations, were found to be highly strongly correlated with the experimental values. Also, the theoretical calculations for the electronic transition 1 1Ag→1 1Bu were also extremely well correlated with their experimental counterparts; even more important, the three reported experimental data for 1 1Ag→2 1Ag transitions in these systems conformed to the correlation for the TDDFT 1 1Ag→1 1Bu transition. The first excited electronic state in the linear polyenes studied (from ethene to the compound consisting of 40 ethene units, P40) was found to be 1Bu. The energy gap between the excited states 2 1Ag and 1 1Bu decreased with increasing length of the polyene chain, but not to the extent required to cause inversion, at least up to P40. In the all-trans linear polyenes studied, the widely analyzed energy gap from the ground electronic state to the first excited singlet state for infinitely long chains may be meaningless as, even in P40, it is uncertain whether the ground electronic state continues to be a singlet. © 2004 American Institute of Physics.
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36.20.Kd Electronic structure and spectra
31.15.E- Density-functional theory

Multipole induced splitting of metal-cage vibrations in crystalline endohedral D2d-M2C84 dimetallofullerenes

M. Krause, V. N. Popov, M. Inakuma, N. Tagmatarchis, H. Shinohara, P. Georgi, L. Dunsch, and H. Kuzmany

J. Chem. Phys. 120, 1873 (2004); http://dx.doi.org/10.1063/1.1632899 (8 pages) | Cited 1 time

Online Publication Date: 23 January 2004

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Metal-carbon cage vibrations of crystalline endohedral D2d-M2C84 (M = Sc,Y,Dy) dimetallofullerenes were analyzed by temperature dependent Raman scattering and a dynamical force field model. Three groups of metal-carbon cage modes were found at energies of 35–200 cm−1 and assigned to metal-cage stretching and deformation vibrations. They exhibit a textbook example for the splitting of molecular vibrations in a crystal field. Induced dipole–dipole and quadrupole–quadrupole interactions account quantitatively for the observed mode splitting. Based on the metal-cage vibrational structure it is demonstrated that D2d-Y2C84 dimetallofullerene retains a monoclinic crystal structure up to 550 K and undergoes a transition from a disordered to an ordered orientational state at a temperature of approximately 150 K. © 2004 American Institute of Physics.
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63.20.-e Phonons in crystal lattices

Probing lattice distortions in mixed CH3I1−cBrc by methyl rotational tunneling

M. Prager

J. Chem. Phys. 120, 1881 (2004); http://dx.doi.org/10.1063/1.1635817 (5 pages)

Online Publication Date: 23 January 2004

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Methyl iodide alloyed with methyl bromide is studied for low methyl bromide concentrations c ⩽ 0.3 by rotational tunneling spectroscopy with neutrons. The appearance of three tunneling bands, their shift with respect to the pure materials and their broadening is explained semiquantitatively on the basis of the crystal structure and global and local changes of interatomic distances based on the r-dependence of intermolecular interactions. Besides the overall reduction of the lattice parameter local free volume around guest molecules is important. A local relaxation of the atomic position by 1.3% towards guest molecules is found. © 2004 American Institute of Physics.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
61.66.Hq Organic compounds
78.70.Nx Neutron inelastic scattering
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