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14 Jul 2006

Volume 125, Issue 2, Articles (02xxxx)

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Quantum-state resolved reaction dynamics at the gas-liquid interface: Direct absorption detection of HF(v,J) product from F(math)+Squalane

Alexander M. Zolot, Warren W. Harper, Bradford G. Perkins, Paul J. Dagdigian, and David J. Nesbitt

J. Chem. Phys. 125, 021101 (2006); http://dx.doi.org/10.1063/1.2217016 (4 pages) | Cited 8 times

Online Publication Date: 11 July 2006

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Exothermic reactive scattering of F atoms at the gas-liquid interface of a liquid hydrocarbon (squalane) surface has been studied under single collision conditions by shot noise limited high-resolution infrared absorption on the nascent HF(v,J) product. The nascent HF(v,J) vibrational distributions are inverted, indicating insufficient time for complete vibrational energy transfer into the surface liquid. The HF(v = 2,J) rotational distributions are well fit with a two temperature Boltzmann analysis, with a near room temperature component (TTD ≈ 290 K) and a second much hotter scattering component (THDS ≈ 1040 K). These data provide quantum state level support for microscopic branching in the atom abstraction dynamics corresponding to escape of nascent HF from the liquid surface on time scales both slow and fast with respect to rotational relaxation.
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68.03.-g Gas-liquid and vacuum-liquid interfaces
78.30.-j Infrared and Raman spectra
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.Bc State selected dynamics and product distribution

Spin-orbit mechanism of predissociation in the Wulf band of ozone

S. Yu. Grebenshchikov, Z.-W. Qu, H. Zhu, and R. Schinke

J. Chem. Phys. 125, 021102 (2006); http://dx.doi.org/10.1063/1.2219444 (4 pages) | Cited 3 times

Online Publication Date: 12 July 2006

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Previously calculated resonance widths of the ground vibrational levels in the electronic states 1 math (math) and 1 math (math), which belong to the Wulf band system of ozone, are significantly smaller than observed experimentally. We demonstrate that predissociation is drastically enhanced by spin-orbit coupling between 1 math/X math and 1 math/1 math. Multistate quantum mechanical calculations using ab initio spin-orbit coupling matrix elements give linewidths of optically bright components of the right order of magnitude.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
31.15.A- Ab initio calculations
33.15.Mt Rotation, vibration, and vibration-rotation constants

Charge transport in disordered films of non-redox proteins

P. P. Pompa, A. Della Torre, L. L. del Mercato, R. Chiuri, A. Bramanti, F. Calabi, G. Maruccio, R. Cingolani, and R. Rinaldi

J. Chem. Phys. 125, 021103 (2006); http://dx.doi.org/10.1063/1.2221693 (4 pages)

Online Publication Date: 12 July 2006

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Electrical conduction in solid state disordered multilayers of non-redox proteins is demonstrated by two-terminal transport experiments at the nanoscale and by scanning tunneling microscopy (STM/STS experiments). We also show that the conduction of the biomolecular films can be modulated by means of a gate field. These results may lead to the implementation of protein-based three-terminal nanodevices and open important new perspectives for a wide range of bioelectronic/biosensing applications.
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87.14.E- Proteins
82.39.Jn Charge (electron, proton) transfer in biological systems
87.15.H- Dynamics of biomolecules

Design of infrared laser pulses for the deexcitation of highly excited homonuclear diatomic molecules

Qinghua Ren, Gabriel G. Balint-Kurti, Frederick R. Manby, Maxim Artamonov, Tak-San Ho, and Herschel Rabitz

J. Chem. Phys. 125, 021104 (2006); http://dx.doi.org/10.1063/1.2221932 (2 pages) | Cited 4 times

Online Publication Date: 12 July 2006

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We explore the possibility of using shaped infrared laser pulses to deexcite a homonuclear diatomic molecule from its highest vibrational state down to its ground vibrational state. The motivation for this study arises from the need to deexcite alkali metal dimers in a similar way so as to stabilize molecular Bose–Einstein condensates. We demonstrate that for the case of the H2 molecule, where it is possible to evaluate all the necessary high accuracy ab initio data on the interaction of the molecule with an electric field, we are able to successfully design a sequence of infrared laser pulses to accomplish the desired deexcitation process in a highly efficient manner.
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37.10.Mn Slowing and cooling of molecules
37.10.Pq Trapping of molecules
33.20.Tp Vibrational analysis
31.15.A- Ab initio calculations

Counter-ion perturbation of the fragmentation pathways of multiply charged anions: Evidence for exit channel complexes on the fragmentation potential energy surfaces

Ruth M. Burke, William E. Boxford, and Caroline E. H. Dessent

J. Chem. Phys. 125, 021105 (2006); http://dx.doi.org/10.1063/1.2219116 (4 pages) | Cited 6 times

Online Publication Date: 13 July 2006

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We report the first low-energy collisional excitation measurements and density functional theory calculations to characterize the ground state potential energy surfaces of contact ion-pair complexes that contain multiply charged anions (MCAs). Excitation of K+∙Pt(CN)42− and K+∙Pt(CN)62− result in fragmentation products associated with decay of the isolated constituent dianions, revealing that the ground state ion-pair surfaces are dominated by the intrinsic characteristics of the MCA. This observation is important since it indicates that counter-ion complexation only weakly perturbs the electronic structure of an MCA. For K+∙Pt(CN)42−, where the Pt(CN)42− dianion decays with production of two ionic fragments, we observe evidence for the existence of a novel exit-channel complex corresponding to a polar KCN salt unit bound to the Pt(CN)3− anion. The results described provide a basis for understanding the potential energy surfaces and fragmentation characteristics of other ion-pair complexes that involve MCAs.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Kh Potential energy surfaces for chemical reactions
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back to top Theoretical Methods and Algorithms

Evaluation of alternative sum-over-states expressions for the first hyperpolarizability of push-pull π-conjugated systems

Benoît Champagne and Bernard Kirtman

J. Chem. Phys. 125, 024101 (2006); http://dx.doi.org/10.1063/1.2206181 (7 pages) | Cited 19 times

Online Publication Date: 10 July 2006

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A dipolar-free sum-over-states expression for the diagonal components of the first hyperpolarizability (β) tensor has been proposed by Kuzyk [Phys. Rev. A 72, 053819 (2005) ] as an alternative to the traditional expression. We examine both alternatives for the longitudinal β of four typical push-pull π-conjugated systems using the ab initio CIS and CIS(D) schemes to approximate the excited state properties. Since they are each evaluated approximately the two SOS expressions yield different values for β and it is found that (i) they evolve symmetrically as the number of excited states is increased so that their average is nearly constant; (ii) in the static limit, the two values agree better with one another when their average is close to the “exact” correlated result; and (iii) frequency dispersion can affect the agreement between the alternative expressions. On the basis of (i) and (ii) it appears best for typical push-pull π-conjugated systems to estimate the static β, and the error in the value so obtained, by averaging the Kuzyk and traditional results.
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42.65.An Optical susceptibility, hyperpolarizability
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.A- Ab initio calculations

A second-quantization framework for the unified treatment of relativistic and nonrelativistic molecular perturbations by response theory

Trygve Helgaker, Alf Christian Hennum, and Wim Klopper

J. Chem. Phys. 125, 024102 (2006); http://dx.doi.org/10.1063/1.2198527 (17 pages) | Cited 10 times

Online Publication Date: 13 July 2006

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A formalism is presented for the calculation of relativistic corrections to molecular electronic energies and properties. After a discussion of the Dirac and Breit equations and their first-order Foldy-Wouthuysen [Phys. Rev. 78, 29 (1950)] transformation, we construct a second-quantization electronic Hamiltonian, valid for all values of the fine-structure constant α. The resulting α-dependent Hamiltonian is then used to set up a perturbation theory in orders of α2, using the general framework of time-independent response theory, in the same manner as for geometrical and magnetic perturbations. Explicit expressions are given to second order in α2 for the Hartree-Fock model. However, since all relativistic considerations are contained in the α-dependent Hamiltonian operator rather than in the wave function, the same approach may be used for other wave-function models, following the general procedure of response theory. In particular, by constructing a variational Lagrangian using the α-dependent electronic Hamiltonian, relativistic corrections can be calculated for nonvariational methods as well.
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31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
33.15.Pw Fine and hyperfine structure
31.15.xp Perturbation theory
31.15.xr Self-consistent-field methods
31.15.xt Variational techniques
31.10.+z Theory of electronic structure, electronic transitions, and chemical binding

First-principles calculations of zero-field splitting parameters

Dmitry Ganyushin and Frank Neese

J. Chem. Phys. 125, 024103 (2006); http://dx.doi.org/10.1063/1.2213976 (11 pages) | Cited 35 times

Online Publication Date: 13 July 2006

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In this work, an implementation of an approach to calculate the zero-field splitting (ZFS) constants in the framework of ab initio methods such as complete active space self-consistent field, multireference configuration interaction, or spectroscopy oriented configuration interaction is reported. The spin-orbit coupling (SOC) contribution to ZFSs is computed using an accurate multicenter mean-field approximation for the Breit-Pauli Hamiltonian. The SOC parts of ZFS constants are obtained directly after diagonalization of the SOC operator in the basis of a preselected number of roots of the spin-free Hamiltonian. This corresponds to an infinite order treatment of the SOC in terms of perturbation theory. The spin-spin (SS) part is presently estimated in a mean-field fashion and appears to yield results close to the more complete treatments available in the literature. Test calculations for the first- and second-row atoms as well as first-row transition metal atoms and a set of diatomic molecules show accurate results for the SOC part of ZFSs. SS contributions have been found to be relatively small but not negligible (exceeding 1 cm−1 for oxygen molecule). At least for the systems studied in this work, it is demonstrated that the presented method provides much more accurate estimations for the SOC part of ZFS constants than the emerging density functional theory approaches.
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31.15.A- Ab initio calculations
33.15.Pw Fine and hyperfine structure
31.15.xr Self-consistent-field methods
31.15.vn Electron correlation calculations for diatomic molecules
31.15.xp Perturbation theory
31.15.E- Density-functional theory

Dynamically screened local correlation method using enveloping localized orbitals

Alexander A. Auer and Marcel Nooijen

J. Chem. Phys. 125, 024104 (2006); http://dx.doi.org/10.1063/1.2209685 (14 pages) | Cited 27 times

Online Publication Date: 13 July 2006

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In this paper we present a local coupled cluster approach based on a dynamical screening scheme, in which amplitudes are either calculated at the coupled cluster level (in this case CCSD) or at the level of perturbation theory, employing a threshold driven procedure based on MP2 energy increments. This way, controllable accuracy and smooth convergence towards the exact result are obtained in the framework of an a posteriori approximation scheme. For the representation of the occupied space a new set of local orbitals is presented with the size of a minimal basis set. This set is atom centered, is nonorthogonal, and has shapes which are fairly independent of the details of the molecular system of interest. Two slightly different versions of combined local coupled cluster and perturbation theory equations are considered. In the limit both converge to the untruncated CCSD result. Benchmark calculations for four systems (heptane, serine, water hexamer, and oxadiazole-2-oxide) are carried out, and decay of the amplitudes, truncation error, and convergence towards the exact CCSD result are analyzed.
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31.15.bw Coupled-cluster theory
31.15.xp Perturbation theory

Phase control in the vibrational qubit

Meiyu Zhao and Dmitri Babikov

J. Chem. Phys. 125, 024105 (2006); http://dx.doi.org/10.1063/1.2220039 (6 pages) | Cited 19 times

Online Publication Date: 14 July 2006

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In order to use molecular vibrations for quantum information processing one should be able to shape infrared laser pulses so that they can play the role of accurate quantum gates and drive the required vibrational transitions. In this paper we studied theoretically how the relative phase of the optimized transitions affects accuracy of the quantum gates in such a system. Optimal control theory and numerical propagation of laser-driven vibrational wave packets were employed. The dependencies observed for one-qubit gates NOT, π-rotation, and Hadamard transform are qualitatively similar to each other. The results of the numerical tests agree well with the analytical predictions.
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03.67.Lx Quantum computation architectures and implementations
03.65.Ta Foundations of quantum mechanics; measurement theory
33.20.Tp Vibrational analysis

String method in collective variables: Minimum free energy paths and isocommittor surfaces

Luca Maragliano, Alexander Fischer, Eric Vanden-Eijnden, and Giovanni Ciccotti

J. Chem. Phys. 125, 024106 (2006); http://dx.doi.org/10.1063/1.2212942 (15 pages) | Cited 75 times

Online Publication Date: 14 July 2006

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A computational technique is proposed which combines the string method with a sampling technique to determine minimum free energy paths. The technique only requires to compute the mean force and another conditional expectation locally along the string, and therefore can be applied even if the number of collective variables kept in the free energy calculation is large. This is in contrast with other free energy sampling techniques which aim at mapping the full free energy landscape and whose cost increases exponentially with the number of collective variables kept in the free energy. Provided that the number of collective variables is large enough, the new technique captures the mechanism of transition in that it allows to determine the committor function for the reaction and, in particular, the transition state region. The new technique is illustrated on the example of alanine dipeptide, in which we compute the minimum free energy path for the isomerization transition using either two or four dihedral angles as collective variables. It is shown that the mechanism of transition can be captured using the four dihedral angles, but it cannot be captured using only two of them.
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82.30.Qt Isomerization and rearrangement
82.20.Db Transition state theory and statistical theories of rate constants
82.60.-s Chemical thermodynamics

An analysis of the accuracy of an initial value representation surface hopping wave function in the interaction and asymptotic regions

Alexey Sergeev and Michael F. Herman

J. Chem. Phys. 125, 024107 (2006); http://dx.doi.org/10.1063/1.2218332 (8 pages) | Cited 2 times

Online Publication Date: 14 July 2006

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The behavior of an initial value representation surface hopping wave function is examined. Since this method is an initial value representation for the semiclassical solution of the time independent Schrödinger equation for nonadiabatic problems, it has computational advantages over the primitive surface hopping wave function. The primitive wave function has been shown to provide transition probabilities that accurately compare with quantum results for model problems. The analysis presented in this work shows that the multistate initial value representation surface hopping wave function should approach the primitive result in asymptotic regions and provide transition probabilities with the same level of accuracy for scattering problems as the primitive method.
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03.65.Ge Solutions of wave equations: bound states
03.65.Sq Semiclassical theories and applications
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Electron localization function at the correlated level

Eduard Matito, Bernard Silvi, Miquel Duran, and Miquel Solà

J. Chem. Phys. 125, 024301 (2006); http://dx.doi.org/10.1063/1.2210473 (9 pages) | Cited 22 times

Online Publication Date: 11 July 2006

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The electron localization function (ELF) has been proven so far a valuable tool to determine the location of electron pairs. Because of that, the ELF has been widely used to understand the nature of the chemical bonding and to discuss the mechanism of chemical reactions. Up to now, most applications of the ELF have been performed with monodeterminantal methods and only few attempts to calculate this function for correlated wave functions have been carried out. Here, a formulation of ELF valid for mono- and multiconfigurational wave functions is given and compared with previous recently reported approaches. The method described does not require the use of the homogeneous electron gas to define the ELF, at variance with the ELF definition given by Becke. The effect of the electron correlation in the ELF, introduced by means of configuration interaction with singles and doubles calculations, is discussed in the light of the results derived from a set of atomic and molecular systems.
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31.15.V- Electron correlation calculations for atoms, ions and molecules
33.15.Fm Bond strengths, dissociation energies
82.30.-b Specific chemical reactions; reaction mechanisms
82.20.Db Transition state theory and statistical theories of rate constants

Semiclassical wave packet study of ozone forming reaction

Evgeny Vetoshkin and Dmitri Babikov

J. Chem. Phys. 125, 024302 (2006); http://dx.doi.org/10.1063/1.2213252 (11 pages) | Cited 6 times

Online Publication Date: 12 July 2006

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We have applied the semiclassical wave packet method (SWP) to calculate energies and lifetimes of the metastable states (scattering resonances) in a simplified model of the ozone forming reaction. All values of the total angular momentum up to J = 50 were analyzed. The results are compared with numerically exact quantum mechanical wave packet propagation and with results of the time-independent WKB method. The wave functions for the metastable states in the region over the well are reproduced very accurately by the SWP; in the classically forbidden region and outside of the centrifugal barrier, the SWP wave functions are qualitatively correct. Prony’s method was used to extract energies and lifetimes from the autocorrelation functions. Energies of the metastable states obtained using the SWP method are accurate to within 0.1 and 2 cm−1 for under-the-barrier and over-the-barrier states, respectively. The SWP lifetimes in the range of 0.5<τn<100 ps are accurate to within 10%. A three-level model was used to investigate accuracies of different approximations for the reaction rate constant. It was shown that the majority of the metastable states in this system are either long lived (narrow resonances) which can be treated as stable, or short lived (broad resonances) which can be treated without the knowledge of their lifetimes. Only a few metastable states fall into the intermediate range where both energies and lifetimes are needed to model the kinetics. The recombination rate constant calculated with the SWP method at room temperature and pressure is in good agreement with available experimental data.
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82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Hf Product distribution
82.20.Ln Semiclassical theory of reactions and/or energy transfer

Ab initio nonadiabatic dynamics study of ultrafast radiationless decay over conical intersections illustrated on the Na3F cluster

Roland Mitrić, Vlasta Bonačić-Koutecký, Jiří Pittner, and Hans Lischka

J. Chem. Phys. 125, 024303 (2006); http://dx.doi.org/10.1063/1.2209233 (7 pages) | Cited 16 times

Online Publication Date: 13 July 2006

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We present a theoretical approach for the ultrafast nonadiabatic dynamics based on the ab initio molecular dynamics carried out “on the fly” in the framework of the configuration interaction method combined with Tully’s surface hopping algorithm for nonadiabatic transitions. This approach combined with our Wigner distribution approach allows us to perform accurate simulations of femtosecond pump-probe spectra in the systems where radiationless transitions among electronic states take place. In this paper we illustrate this by theoretical simulation of ultrafast processes and nonradiative relaxation in the Na3F cluster, involving three excited states and the ground electronic state. Furthermore, we show that our accurate simulation of the photoionization pump-probe spectrum is in full agreement with the experimental signal. Based on the nonadiabatic dynamics at high level of accuracy and taking into account all degrees of freedom, the nonradiative lifetime for the 1 math excited state of Na3F has been determined to be ∼ 900 fs.
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36.40.-c Atomic and molecular clusters
31.15.A- Ab initio calculations
31.15.xv Molecular dynamics and other numerical methods
31.15.vq Electron correlation calculations for polyatomic molecules
33.50.Hv Radiationless transitions, quenching
33.80.Eh Autoionization, photoionization, and photodetachment

Nonstatistical effects in the dissociation of ethyl radical: Finding order in chaos

Andreas Bach, Jonas M. Hostettler, and Peter Chen

J. Chem. Phys. 125, 024304 (2006); http://dx.doi.org/10.1063/1.2217744 (8 pages) | Cited 11 times

Online Publication Date: 14 July 2006

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How does one identify order in complex dynamical systems? A Born-Oppenheimer molecular dynamics simulation of the dissociation of ethyl radical, C2H5, produces an ensemble of classical trajectories which are decomposed in the time-frequency domain using wavelets. A time-dependent scalar metric, the normalized instantaneous orbital complexity, is constructed and shown to correlate not only to the more conventional Lyapunov exponents but also to the dissociation time for an individual trajectory. The analysis of the ensemble of trajectories confirms that the long-lived trajectories are associated with a low degree of ergodicity. While the analysis of molecular dissociation dynamics is the narrow focus of the present work, the method is more general for discovery and identification of ordered regimes within large sets of chaotic data.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

Conformational identification of tryptamine embedded in superfluid helium droplets using electronic polarization spectroscopy

Linsen Pei, Jie Zhang, Chengyin Wu, and Wei Kong

J. Chem. Phys. 125, 024305 (2006); http://dx.doi.org/10.1063/1.2217948 (8 pages) | Cited 6 times

Online Publication Date: 14 July 2006

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We report electronic polarization spectroscopy of tryptamine embedded in superfluid helium droplets. In a dc electric field, dependence of laser induced fluorescence from tryptamine on the polarization direction of the excitation laser is measured. Among the three observed major conformers A, D, and E, conformers D and E display preference for perpendicular excitation relative to the orientation field, while conformer A is insensitive to the polarization direction of the excitation laser. We attribute the behavior of conformer A to the fact that the angle between the permanent dipole and the transition dipole is close to the magic angle. Using a linear variation method, we can reproduce the polarization preference of the three conformers and determine the angle between the transition dipole and the permanent dipole. Since the side chain exerts small effect on the direction of the transition dipole in the frame of the indole chromophore, all three conformers have a common transition dipole more or less in the indole plane at an angle of ∼ 60° relative to the long axis of the chromophore. The orientation of the side chain, on the other hand, determines the size and direction of the permanent dipole, thereby affecting the angle between the permanent dipole and the transition dipole. For conformer D in the droplet, our results agree with the Anti(ph) structure, rather than the Anti(py) structure. Our work demonstrates that polarization spectroscopy is effective in conformational identification for molecules that contain a known chromophore. Although coupling of the electronic transition with the helium matrix is not negligible, it does not affect the direction of the transition dipole.
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33.50.Dq Fluorescence and phosphorescence spectra
33.80.-b Photon interactions with molecules
33.15.Bh General molecular conformation and symmetry; stereochemistry

Electronic states and potential energy curves of molybdenum carbide and its ions

Pablo A. Denis and K. Balasubramanian

J. Chem. Phys. 125, 024306 (2006); http://dx.doi.org/10.1063/1.2216700 (9 pages) | Cited 1 time

Online Publication Date: 14 July 2006

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The potential energy curves and spectroscopic constants of the ground and 29 low-lying excited states of MoC with different spin and spatial symmetries within 48 000 cm−1 have been investigated. We have used the complete active space multiconfiguration self-consistent field methodology, followed by multireference configuration interaction (MRCI) methods. Relativistic effects were considered with the aid of relativistic effective core potentials in conjunction with these methods. The results are in agreement with previous studies that determined the ground state as X math. At the MRCISD+Q level, the transition energies to the 1 math and 4 math states are 3430 and 8048 cm−1, respectively, in fair agreement with the results obtained by DaBell et al. [J. Chem. Phy. 114, 2938 (2001) ], namely, 4003 and 7834 cm−1, respectively. The three band systems located at 18 611, 20 700, and 22 520 cm−1 observed by Brugh et al. [J. Chem. Phy. 109, 7851 (1998) ] were attributed to the excited 11 math, 14 math, and 15 math states respectively. At the MRCISD level, these states are 17 560, 20 836, and 20 952 cm−1 above the ground state respectively. We have also identified a math state lying 14 309 cm−1 above the ground state. The ground states of the molecular ions are predicted to be math and math for MoC− and MoC+, respectively.
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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.ve Electron correlation calculations for atoms and ions: ground state
31.15.vj Electron correlation calculations for atoms and ions: excited states
31.15.xr Self-consistent-field methods
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions

Ab initio studies on (H2O)14− clusters: Existence of surface and interior-bound extra electrons

Arshad Khan

J. Chem. Phys. 125, 024307 (2006); http://dx.doi.org/10.1063/1.2216705 (4 pages) | Cited 14 times

Online Publication Date: 14 July 2006

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A recent paper by Turi et al. [Science 309, 914 (2005)] suggests that the anionic water clusters smaller than (H2O)45− (at a low temperature) will only have surface-bound extra electrons and no internally bound electrons. Accordingly, (H2O)14− cluster isomers should only have surface-bound extra electrons. The ab initio results presented here, however, suggest that the (H2O)14− cluster isomers can have two distinct types of isomers with almost the same energy. The one type of isomer (type 1) has all the non-H-bonding H atoms (NHB H) directed outward and surface-bound extra electron while the other type (type 2) has a number of NHB H atoms directed toward cavity and has an interior-bound electron, and thus, contradicts the earlier quantum simulation results of Turi et al.
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36.40.Mr Spectroscopy and geometrical structure of clusters
31.15.A- Ab initio calculations
33.15.Bh General molecular conformation and symmetry; stereochemistry

Relativistic correction to the 1sσ and 2pσ electronic states of the H2+ molecular ion and the moleculelike states of the antiprotonic helium He+math

Ts. Tsogbayar and V. I. Korobov

J. Chem. Phys. 125, 024308 (2006); http://dx.doi.org/10.1063/1.2209694 (4 pages) | Cited 4 times

Online Publication Date: 14 July 2006

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Effective potentials of the relativistic Breit-Pauli corrections for the 1sσg and 2pσu electron states of the H2+ molecular ion and the 1sσ, 2sσ, and 3pσ states of the antiprotonic helium atom He+math are calculated within the Born-Oppenheimer approximation. The variational expansion with randomly chosen exponents has been used for numerical studies. The results obtained for the Breit-Pauli effective potentials are accurate up to ten significant digits for the H2+ molecular ion and eight digits for the He+math atom.
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31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
36.10.Gv Mesonic, hyperonic and antiprotonic atoms and molecules
31.15.xt Variational techniques
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Host-assisted intramolecular vibrational relaxation at low temperatures: OH in an argon cage

H. K. Shin

J. Chem. Phys. 125, 024501 (2006); http://dx.doi.org/10.1063/1.2212412 (10 pages) | Cited 3 times

Online Publication Date: 11 July 2006

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The vibrational relaxation of hydroxyl radicals in the A math (v = 1) state has been studied using the semiclassical perturbation treatment at cryogenic temperatures. The radical is considered to be trapped in a closest packed cage composed of the 12 nearest argon atoms and undergoes local translation and hindered rotation around the cage center. The primary relaxation pathway is towards local translation, followed by energy transfer to rotation through hindered-to-free rotational transitions. Free-to-free rotational transitions are found to be unimportant. All pathways are accompanied by the propagation of energy to argon phonon modes. The deexcitation probability of OH(v = 1) is 1.3×10−7 and the rate constant is 4.7×105 s−1 between 4 and 10 K. The negligible temperature dependence is attributed to the presence of intermolecular attraction (⪢kT) in the guest-host encounter, which counteracts the T2 dependence resulting from local translation. Calculated relaxation time scales are much shorter than those of homonuclear molecules, suggesting the importance of the hindered and free motions of OH and strong guest-host interactions.
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34.50.Ez Rotational and vibrational energy transfer
34.20.Gj Intermolecular and atom-molecule potentials and forces
31.15.xp Perturbation theory

Dynamic light scattering in mixed alkali metaphosphate glass forming liquids

B. V. Rodenburg and D. L. Sidebottom

J. Chem. Phys. 125, 024502 (2006); http://dx.doi.org/10.1063/1.2210936 (5 pages) | Cited 4 times

Online Publication Date: 11 July 2006

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We report the first ever photon correlation spectroscopy performed on single alkali and mixed alkali metaphosphate glasses at refractory temperatures above the glass transition. We find not only a significant decrease in the glass transition temperature but also a decrease in fragility for the mixed alkali composition as compared with the single akali glasses. We argue that structural relaxation in these polymeric oxide glasses is largely controlled by the cross linking cations and that the changes in fragility that we observed are a reflection of changes in the cooperativity of structural relaxation wrought by the substantial decrease in the ion mobility that accompanies the mixing of alkali ions.
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61.43.Fs Glasses
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Symmetrized correlation function for liquid para-hydrogen using complex-time pair-product propagators

Akira Nakayama and Nancy Makri

J. Chem. Phys. 125, 024503 (2006); http://dx.doi.org/10.1063/1.2209682 (10 pages) | Cited 14 times

Online Publication Date: 13 July 2006

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We present a simple and efficient method for calculating symmetrized time correlation functions of neat quantum fluids. Using the pair-product approximation to each complex-time quantum mechanical propagator, symmetrized correlation functions are written in terms of a double integral for each degree of freedom with a purely positive integrand. At moderate temperatures and densities, where the pair-product approximation to the Boltzmann operator is sufficiently accurate, the method leads to quantitative results for the early time part of the correlation function. The method is tested extensively on liquid para-hydrogen at 25 K and used to obtain accurate quantum mechanical results for the initial 0.2 ps segment of the symmetrized velocity autocorrelation function of this system, as well as the incoherent dynamic structure factor at certain momentum transfer values.
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61.20.Ja Computer simulation of liquid structure
61.20.Lc Time-dependent properties; relaxation
61.25.Em Molecular liquids

Solvent response and dielectric relaxation in supercooled butyronitrile

Naoki Ito, Kalyan Duvvuri, Dmitry V. Matyushov, and Ranko Richert

J. Chem. Phys. 125, 024504 (2006); http://dx.doi.org/10.1063/1.2212420 (8 pages) | Cited 6 times

Online Publication Date: 13 July 2006

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We have measured the dynamics of solvation of a triplet state probe, quinoxaline, in the glass-forming dipolar liquid butyronitrile near its glass transition temperature Tg = 95 K. The Stokes shift correlation function displays a relaxation time dispersion of considerable magnitude and the optical linewidth changes along the solvation coordinate in a nonmonotonic fashion. These features are characteristic of solvation in viscous solvents and clearly indicate heterogeneous dynamics, i.e., spatially distinct solvent response times. Using the dielectric relaxation data of viscous butyronitrile as input, a microscopic model of dipolar solvation captures the relaxation time, the relaxation dispersion, and the amplitude of the dynamical Stokes shift remarkably well.
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77.22.Gm Dielectric loss and relaxation
82.30.Nr Association, addition, insertion, cluster formation
82.20.Yn Solvent effects on reactivity
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

Global phase diagram for the honeycomb potential

Antti-Pekka Hynninen, Athanassios Z. Panagiotopoulos, Mikael C. Rechtsman, Frank H. Stillinger, and Salvatore Torquato

J. Chem. Phys. 125, 024505 (2006); http://dx.doi.org/10.1063/1.2213611 (5 pages) | Cited 7 times

Online Publication Date: 13 July 2006

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We calculate the global phase diagram using classical statistical mechanics for an isotropic pair potential that has been previously [ Rechtsman et al., Phys. Rev. Lett. 95, 228301 (2005) ] shown to produce the low-coordinated two-dimensional honeycomb crystal as the ground-state structure. Low-coordinated crystals are of practical interest because they have desirable photonic band-gap properties. The phase diagram is obtained from Helmholtz free energies calculated using thermodynamic integration and Monte Carlo simulations. Our results show that the honeycomb crystal remains stable in the global phase diagram even after temperature effects are taken fully into account. Other stable phases in the phase diagram are high and low density triangular phases and a fluid phase. We find no evidence of gas-liquid or liquid-liquid phase coexistence.
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64.60.Cn Order-disorder transformations
42.70.Qs Photonic bandgap materials
65.40.G- Other thermodynamical quantities
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