JCP Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

You Tube Flickr Twitter UniPHY Group iResearch App Facebook

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue Next Issue

14 Jul 2011

Volume 135, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

J. Chem. Phys. 135, 024203 (2011); http://dx.doi.org/10.1063/1.3598959 (12 pages)

D. Segale and V. A. Apkarian
Enlarge Image | Read More
Page 1 of 3 Pages Next Page | Jump to Page
back to top
RSS Feeds
FREE

Perspective: Water cluster mediated atmospheric chemistry

Veronica Vaida

J. Chem. Phys. 135, 020901 (2011); http://dx.doi.org/10.1063/1.3608919 (8 pages) | Cited 4 times

Online Publication Date: 14 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The importance of water in atmospheric and environmental chemistry initiated recent studies with results documenting catalysis, suppression and anti-catalysis of thermal and photochemical reactions due to hydrogen bonding of reagents with water. Water, even one water molecule in binary complexes, has been shown by quantum chemistry to stabilize the transition state and lower its energy. However, new results underscore the need to evaluate the relative competing rates between reaction and dissipation to elucidate the role of water in chemistry. Water clusters have been used successfully as models for reactions in gas-phase, in aqueous condensed phases and at aqueous surfaces. Opportunities for experimental and theoretical chemical physics to make fundamental new discoveries abound. Work in this field is timely given the importance of water in atmospheric and environmental chemistry.
Show PACS
82.33.Tb Atmospheric chemistry
82.50.-m Photochemistry
82.30.Vy Homogeneous catalysis in solution, polymers and zeolites
82.30.Rs Hydrogen bonding, hydrophilic effects
82.20.Db Transition state theory and statistical theories of rate constants
back to top
RSS Feeds
FREE

Communication: Interfacial water structure revealed by ultrafast two-dimensional surface vibrational spectroscopy

Zhen Zhang, Lukasz Piatkowski, Huib J. Bakker, and Mischa Bonn

J. Chem. Phys. 135, 021101 (2011); http://dx.doi.org/10.1063/1.3605657 (3 pages)

Online Publication Date: 8 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Knowledge of the interfacial water structure is essential for a basic understanding of the many environmental, technological, and biophysical systems in which aqueous interfaces appear. Using ultrafast two-dimensional surface-specific vibrational spectroscopy we show that the structure of heavy water at the water-air interface displays short-lived heterogeneity and is very different from that at the water-lipid interface.
Show PACS
68.35.Ja Surface and interface dynamics and vibrations
FREE

Communication: First observation of ground state I(2P3/2) atoms from the CH3I photodissociation in the B-band

M. G. González, J. D. Rodríguez, L. Rubio-Lago, and L. Bañares

J. Chem. Phys. 135, 021102 (2011); http://dx.doi.org/10.1063/1.3613656 (4 pages) | Cited 1 time

Online Publication Date: 12 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The photodissociation of CH3I in the second absorption band (the B-band) has been studied at the wavelength 199.11 nm, coincident with the 301 3R1(E)←math(1A1) CH3I vibronic transition, using a combination of slice imaging and resonance enhanced multiphoton ionization detection of the CH3 fragment. The kinetic energy and angular distributions of the recoiling CH3 fragment confirm a major predissociation dynamics channel as a result of the interaction between the bound 3R1 Rydberg state and the repulsive 3A1(E) state − ascribed to the A-band − yielding CH3 fragments in correlation with spin-orbit excited I*(2P1/2) atoms. In addition, first evidence of a non-negligible population of ground state I(2P3/2) atoms in the CH3 fragment slice images, suggests a secondary predissociation mechanism via interaction between the 3R1 Rydberg state and the repulsive A-band 1Q1 state.
Show PACS
82.50.-m Photochemistry
31.15.es Applications of density-functional theory (e.g., to electronic structure and stability; defect formation; dielectric properties, susceptibilities; viscoelastic coefficients; Rydberg transition frequencies)
31.50.Bc Potential energy surfaces for ground electronic states
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
back to top
RSS Feeds
back to top Theoretical Methods and Algorithms

Phase-corrected surface hopping: Correcting the phase evolution of the electronic wavefunction

Neil Shenvi, Joseph E. Subotnik, and Weitao Yang

J. Chem. Phys. 135, 024101 (2011); http://dx.doi.org/10.1063/1.3603447 (7 pages) | Cited 1 time

Online Publication Date: 8 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this paper, we show that a remarkably simple correction can be made to the equation of motion which governs the evolution of the electronic wavefunction over some prescribed nuclear trajectory in the fewest-switches surface hopping algorithm. This corrected electronic equation of motion can then be used in conjunction with traditional or modified surface hopping methods to calculate nonadiabatic effects in large systems. Although the correction adds no computational cost to the algorithm, it leads to a dramatic improvement in scattering probabilities for all model problems studied thus far. We show that this correction can be applied to one of Tully's original one-dimensional model problems or to a more sophisticated two-dimensional example and yields substantially greater accuracy than the traditional approach.
Show PACS
73.20.At Surface states, band structure, electron density of states
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)

The kinetics of homogeneous melting beyond the limit of superheating

D. Alfè, C. Cazorla, and M. J. Gillan

J. Chem. Phys. 135, 024102 (2011); http://dx.doi.org/10.1063/1.3605601 (8 pages)

Online Publication Date: 8 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Molecular dynamics simulation is used to study the time-scales involved in the homogeneous melting of a superheated crystal. The interaction model used is an embedded-atom model for Fe developed in previous work, and the melting process is simulated in the microcanonical (N, V, E) ensemble. We study periodically repeated systems containing from 96 to 7776 atoms, and the initial system is always the perfect crystal without free surfaces or other defects. For each chosen total energy E and number of atoms N, we perform several hundred statistically independent simulations, with each simulation lasting for between 500 ps and 10 ns, in order to gather statistics for the waiting time τw before melting occurs. We find that the probability distribution of τw is roughly exponential, and that the mean value 〈τw〉 depends strongly on the excess of the initial steady temperature of the crystal above the superheating limit identified by other researchers. The mean 〈τw〉 also depends strongly on system size in a way that we have quantified. For very small systems of ∼100 atoms, we observe a persistent alternation between the solid and liquid states, and we explain why this happens. Our results allow us to draw conclusions about the reliability of the recently proposed Z method for determining the melting properties of simulated materials and to suggest ways of correcting for the errors of the method.
Show PACS
64.70.dj Melting of specific substances
61.20.Ja Computer simulation of liquid structure
02.50.-r Probability theory, stochastic processes, and statistics

New method of accurate estimation of the electron–phonon coupling constants in fractionally charged incommensurate electronic states in molecular systems

Takashi Kato

J. Chem. Phys. 135, 024103 (2011); http://dx.doi.org/10.1063/1.3600066 (13 pages)

Online Publication Date: 8 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The electron–phonon interactions in the fractionally positively charged incommensurate tetrathiafulvalene (TTF) molecular systems are investigated. In particular, since there are fractionally positive charges per TTF molecule, it is very difficult to estimate the vibronic and electron–phonon coupling constants, and thus there have been no reports of the exact calculations in the electron–phonon coupling constants in such fractionally positively charged incommensurate systems. Therefore, in this paper, we suggest new method of accurate estimation of the electron–phonon coupling constants in the fractionally positively charged systems. Total electron–phonon coupling constants for the monocation (l+100) of TTF is compared with that for the monoanion (l−100) of tetracyanoquinodimethanide (TCNQ). Furthermore, logarithmically averaged phonon frequency for the monocation (νln , +1.00) of TTF is compared with that for the monoanion (νln , −1.00) of TCNQ. The C–C and C–S stretching mode of 1599 cm−1 and the C–S–C and C–C–S bending mode of 472 cm−1 strongly couple to the b3u highest occupied molecular orbital (HOMO) in TTF molecule. The l+100 value for TTF molecule is estimated to be 0.274 eV, and the νln , +1.00 value for TTF molecule is estimated to be 926 cm−1. The density of states at the Fermi level (NNM, crystal(εF)+0.59, +0.59) values for TTF0.59+, which are essential physical values in order to investigate the mechanisms of the non-Ohmic current–voltage characteristics excellently suggested by Cohen and Heeger et al., are also estimated. By comparing the NNM, crystal(εF)+0.59, +0.59 values estimated by us with those estimated from the experimental results of the Pauli susceptibility and the current–voltage characteristics in TTF0.59+ suggested by Cohen and Heeger et al., and from the band calculations, we show that the l+0.59, νln , +1.00, RE+0.59, and NNM, crystal(εF)+0.59, +0.59 values estimated by our new calculation method are very accurate and reliable.
Show PACS
63.20.kd Phonon-electron interactions
71.15.-m Methods of electronic structure calculations
71.20.Rv Polymers and organic compounds
71.38.-k Polarons and electron-phonon interactions
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Time-dependent importance sampling in semiclassical initial value representation calculations for time correlation functions

Guohua Tao and William H. Miller

J. Chem. Phys. 135, 024104 (2011); http://dx.doi.org/10.1063/1.3600656 (9 pages)

Online Publication Date: 11 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
An efficient time-dependent importance sampling method is developed for the Monte Carlo calculation of time correlation functions via the initial value representation (IVR) of semiclassical (SC) theory. A prefactor-free time-dependent sampling function weights the importance of a trajectory based on the magnitude of its contribution to the time correlation function, and global trial moves are used to facilitate the efficient sampling the phase space of initial conditions. The method can be generally applied to sampling rare events efficiently while avoiding being trapped in a local region of the phase space. Results presented in the paper for two system-bath models demonstrate the efficiency of this new importance sampling method for full SC-IVR calculations.
Show PACS
31.15.-p Calculations and mathematical techniques in atomic and molecular physics

Comparison of enveloping distribution sampling and thermodynamic integration to calculate binding free energies of phenylethanolamine N-methyltransferase inhibitors

Sereina Riniker, Clara D. Christ, Niels Hansen, Alan E. Mark, Pramod C. Nair, and Wilfred F. van Gunsteren

J. Chem. Phys. 135, 024105 (2011); http://dx.doi.org/10.1063/1.3604534 (13 pages)

Online Publication Date: 11 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The relative binding free energy between two ligands to a specific protein can be obtained using various computational methods. The more accurate and also computationally more demanding techniques are the so-called free energy methods which use conformational sampling from molecular dynamics or Monte Carlo simulations to generate thermodynamic averages. Two such widely applied methods are the thermodynamic integration (TI) and the recently introduced enveloping distribution sampling (EDS) methods. In both cases relative binding free energies are obtained through the alchemical perturbations of one ligand into another in water and inside the binding pocket of the protein. TI requires many separate simulations and the specification of a pathway along which the system is perturbed from one ligand to another. Using the EDS approach, only a single automatically derived reference state enveloping both end states needs to be sampled. In addition, the choice of an optimal pathway in TI calculations is not trivial and a poor choice may lead to poor convergence along the pathway. Given this, EDS is expected to be a valuable and computationally efficient alternative to TI. In this study, the performances of these two methods are compared using the binding of ten tetrahydroisoquinoline derivatives to phenylethanolamine N-transferase as an example. The ligands involve a diverse set of functional groups leading to a wide range of free energy differences. In addition, two different schemes to determine automatically the EDS reference state parameters and two different topology approaches are compared.
Show PACS
87.15.Fh Bonding; mechanisms of bond breakage
87.15.R- Reactions and kinetics
87.19.Pp Biothermics and thermal processes in biology
36.20.Hb Configuration (bonds, dimensions)
87.14.ej Enzymes
87.15.H- Dynamics of biomolecules

Seeking for parameter-free double-hybrid functionals: The PBE0-DH model

Eric Brémond and Carlo Adamo

J. Chem. Phys. 135, 024106 (2011); http://dx.doi.org/10.1063/1.3604569 (6 pages) | Cited 4 times

Online Publication Date: 11 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A new double hybrid functional is herein presented, in which the ratio of the Hartree-Fock, Kohn-Sham, and perturbation terms (MP2) is determined on the basis of physical considerations. This functional, denominated PBE0 Double Hybrid (PBE0-DH), contains a small MP2 contribution (12.5%) and it has been tested on a number of different molecular properties, including atomization energies, weak interactions, and reaction energies. From the obtained results, PBE0-DH seems to represent a significant improvement with respect to the parent PBE0 functional, a parameter-free hybrid. Overall its performances are comparable to the ones found using other parameterized double hybrids. From a more general point of view, our work points out that, already showed for classes of other functionals, reliable and general-purpose double hybrids can be obtained on purely theoretical bases, without the use of any empirical fitting.
Show PACS
31.15.xr Self-consistent-field methods
31.15.E- Density-functional theory
31.15.xp Perturbation theory

Photoexcited conversion of gauche-1,3-butadiene to bicyclobutane via a conical intersection: Energies and reduced density matrices from the anti-Hermitian contracted Schrödinger equation

James W. Snyder, Jr. and David A. Mazziotti

J. Chem. Phys. 135, 024107 (2011); http://dx.doi.org/10.1063/1.3606466 (8 pages)

Online Publication Date: 12 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The photoexcited reaction pathway from gauche-1,3-butadiene to bicyclobutane via a conical intersection is analyzed through the direct calculation of two-electron reduced density matrices (2-RDMs) from solutions to the anti-Hermitian contracted Schrödinger equation (ACSE). The study utilizes the recent generalization of the ACSE method for the treatment of excited states [G. Gidofalvi and D. A. Mazziotti, Phys. Rev. A 80, 022507 (2009)10.1103/PhysRevA.80.022507]. We computed absolute energies of the critical points as well as various intermediate points along the ground-and excited-state potential energy surface of gauche-1,3-butadiene and bicyclobutane. To treat multi-reference correlation, we seeded the ACSE with an initial 2-RDM from a multi-configuration self-consistent field (MCSCF) calculation. The ACSE, MCSCF, and second-order multi-reference many-body perturbation theory (MRPT2) all demonstrate that there exists a family of pathways from gauche-1,3-butadiene to bicyclobutane via a conical intersection that are monotonically decreasing in energy, confirming a conjecture by Sicilia et al. [J. Phys. Chem. A 111, 2182 (2007)10.1021/jp067614w]. The ACSE recovers more single-reference correlation energy than MRPT2 and more multi-reference correlation energy than comparable single-reference wave function methods. The 2-RDMs from the ACSE nearly satisfy all necessary N-representability conditions.
Show PACS
33.80.-b Photon interactions with molecules
31.50.Df Potential energy surfaces for excited electronic states
31.50.Bc Potential energy surfaces for ground electronic states
31.15.xr Self-consistent-field methods
31.15.xp Perturbation theory
31.15.vq Electron correlation calculations for polyatomic molecules

A generalized mathematical framework for thermal oxidation kinetics

Zhijie Xu, Kevin M. Rosso, and Stephen M. Bruemmer

J. Chem. Phys. 135, 024108 (2011); http://dx.doi.org/10.1063/1.3607984 (7 pages)

Online Publication Date: 12 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a generalized mathematical model for thermal oxidation and the growth kinetics of oxide films. The model expands long-standing classical models by taking into account the reaction occurring at the interface as well as transport processes in greater detail. The standard Deal-Grove model (the linear-parabolic rate law) relies on the assumption of quasi-static diffusion that results in a linear concentration profile of, for example, oxidant species in the oxide layer. By relaxing this assumption and resolving the entire problem, three regimes can be clearly identified corresponding to different stages of oxidation. Namely, the oxidation starts with the reaction-controlled regime (described by a linear rate law), is followed by a transitional regime (described by a logarithmic or power law depending on the stoichiometry coefficient m), and ends with the well-known diffusion-controlled regime (described by a parabolic rate law). The theory of Deal-Grove is shown to be the lower order approximation of the proposed model. Various oxidation rate laws are unified into a single model to describe the entire oxidation process.
Show PACS
82.20.Nk Classical theories of reactions and/or energy transfer
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Sb Correlation function theory of rate constants and its applications
82.20.Uv Stochastic theories of rate constants

Complete optimisation of multi-configuration Jastrow wave functions by variational transcorrelated method

Hongjun Luo

J. Chem. Phys. 135, 024109 (2011); http://dx.doi.org/10.1063/1.3607990 (7 pages) | Cited 1 time

Online Publication Date: 12 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We investigate the performance of the newly developed variational transcorrelated (VTC) method (H. Luo, J. Chem. Phys. 133, 154109 (2010)10.1063/1.3505037) on the overall optimisation of the multi-configuration Jastrow wave function. Similar to the standard multi-configuration self consistent field methods, optimisations of orbitals are realized by iterative unitary transformations, where the skew-symmetric matrix elements are determined by using Newton-Raphson scheme. Third order density matrices are introduced to deal with the three-body VTC potential. Test calculations are performed for the C2 molecule on several small complete active spaces, and the results are compared with those of variational quantum Monte Carlo calculations. The results demonstrate that with the VTC method one can practically recover the results of highly non-linear variational calculations.
Show PACS
31.15.vn Electron correlation calculations for diatomic molecules
31.15.xt Variational techniques

On effective electric field nano-octupoling in two dimensions

A. C. Mitus, G. Pawlik, and J. Zyss

J. Chem. Phys. 135, 024110 (2011); http://dx.doi.org/10.1063/1.3605602 (9 pages)

Online Publication Date: 13 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Conditions towards effective electric field poling in two dimensions (2D) of octupolar molecules which can be achieved are being addressed, based on a lattice model which mimics the basic features of poling. The model is studied using the complementary approaches of analytical methods in statistical mechanics and Monte Carlo simulations. The poling field is imparted by a system of adequately shaped cylindrical electrodes. A topologically rich structure of local and global inhomogeneous octupolar order, including octupolar vortices, is present in the system. The poling criteria are shown to vary strongly throughout the cell: in close proximity to the contact points of neighboring electrodes, a high quality local octupolar order appears at temperature T ≃ 0.1 K while octupoling in the center of the cell requires temperatures as low as 10−4 K. The highly demanding octupoling criteria are ascribed to symmetry-driven effects which decrease the quality of the octupolar phase even in the ground state, as well as to thermal fluctuations and numerical factors at above zero temperatures. Based on our results and using plausible conjectures related to the generalization of the model, it is argued that a weak global octupolar order can be reached at liquid Helium temperatures (a few Kelvins), based on current advances in optical techniques and nanotechnologies.
Show PACS
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.bt Statistical model calculations (including Thomas-Fermi and Thomas-Fermi-Dirac models)

Rigorous non-Born-Oppenheimer theory: Combination of explicitly correlated Gaussian method and nuclear orbital plus molecular orbital theory

Minoru Hoshino, Hiroaki Nishizawa, and Hiromi Nakai

J. Chem. Phys. 135, 024111 (2011); http://dx.doi.org/10.1063/1.3609806 (13 pages)

Online Publication Date: 14 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The present study proposes a rigorous non-Born-Oppenheimer theory combining between the explicitly correlated Gaussian (ECG) method and the nuclear orbital plus molecular orbital (NOMO) method. The new method, called ECG-NOMO, adopts the ECG functions between the electronic and nuclear coordinates and, therefore, is capable of describing the nucleus-electron correlation effect accurately. The basic formalism of the ECG-NOMO method is close to the NOMO method, which starts with the Hartree-Fock type equations for NOs and MOs. The present method requires more computational cost than the original NOMO method. However, its cost is significantly smaller than that of the ECG method. The numerical tests was performed for hydrogen-like atoms (H-Ne9+) and dihydrogen cations (H2+, D2+ and T2+), and clarified that the ECG-NOMO method shows the sufficient accuracy.
Show PACS
31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.xr Self-consistent-field methods

Comparison of standard and damped response formulations of magnetic circular dichroism

Thomas Kjærgaard, Kasper Kristensen, Joanna Kauczor, Poul Jørgensen, Sonia Coriani, and Andreas J. Thorvaldsen

J. Chem. Phys. 135, 024112 (2011); http://dx.doi.org/10.1063/1.3607991 (16 pages)

Online Publication Date: 14 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We apply damped response theory to the phenomenon of magnetic circular dichroism (MCD), and we investigate how the numerical instability associated with the simulation of the MCD spectrum from individually calculated A and B terms for close lying states can be remedied by the use of damped response theory. We also present a method for calculating the Faraday A term, formulated as a double residue of the quadratic response function.
Show PACS
33.57.+c Magneto-optical and electro-optical spectra and effects
31.15.E- Density-functional theory
33.55.+b Optical activity and dichroism

A weak second order tau-leaping method for chemical kinetic systems

Yucheng Hu, Tiejun Li, and Bin Min

J. Chem. Phys. 135, 024113 (2011); http://dx.doi.org/10.1063/1.3609119 (15 pages)

Online Publication Date: 14 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Recently Anderson and Mattingly [Comm. Math. Sci. 9, 301 (2011)] proposed a method which can solve chemical Langevin equations with weak second order accuracy. We extend their work to the discrete chemical jump processes. With slight modification, the method can also solve discrete chemical kinetic systems with weak second order accuracy in the large volume scaling. Especially, this method achieves higher order accuracy than both the Euler τ-leaping and mid-point τ-leaping methods in the sense that the local truncation error for the covariance is of order τ3V−1 when τ = V−β (0 < β < 1) and the system size V → ∞. We present the convergence analysis, numerical stability analysis, and numerical examples. Overall, in the authors’ opinion, the new method is easy to be implemented and good in performance, which is a good candidate among the highly accurate τ-leaping type schemes for discrete chemical reaction systems.
Show PACS
82.20.Uv Stochastic theories of rate constants
back to top Advanced Experimental Techniques

Stark-induced adiabatic Raman passage for preparing polarized molecules

Nandini Mukherjee and Richard N. Zare

J. Chem. Phys. 135, 024201 (2011); http://dx.doi.org/10.1063/1.3599711 (10 pages) | Cited 1 time

Online Publication Date: 8 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We propose a method based on Stark-induced adiabatic Raman passage (SARP) for preparing vibrationally excited molecules with known orientation and alignment for future dynamical stereochemistry studies. This method utilizes the (J, M)-state dependent dynamic Stark shifts of rovibrational levels induced by delayed but overlapping pump and Stokes pulses of unequal intensities. Under collision-free conditions, our calculations show that we can achieve complete population transfer to an excited vibrational level (v > 0) of the H2 molecule in its ground electronic state. Specifically, the H2 (v = 1, J = 2, M = 0) level can be prepared with complete population transfer from the (v = 0, J = 0, M = 0) level using the S(0) branch of the Raman transition with visible pump and Stoke laser pulses, each polarized parallel to the math axis (uniaxial π − π Raman pumping). Similarly, H2 (v = 1, J = 2, M = ±2) can be prepared using SARP with a left circularly polarized pump and a right circularly (or vice versa) polarized Stokes wave propagating along the math axis (σ± − σ∓ Raman pumping). This technique requires phase coherent nanosecond pulses with unequal intensity between the pump and the Stokes pulses, one being four or more times greater than the other. A peak intensity of ∼16 GW/cm2 for the stronger pulse is required to generate the desirable sweep of the Raman resonance frequency. These conditions may be fulfilled using red and green laser pulses with the duration of a few nanoseconds and optical energies of ∼12 and 60 mJ within a focused beam of diameter ∼0.25 mm. Additionally, complete population transfer to the v = 4 vibrational level is predicted to be possible using SARP with a 355-nm pump and a near infrared Stokes laser with accessible pulse energies.
Show PACS
33.57.+c Magneto-optical and electro-optical spectra and effects
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.20.Kf Visible spectra
33.20.Ea Infrared spectra
33.80.Be Level crossing and optical pumping
33.70.Jg Line and band widths, shapes, and shifts

Design and evaluation of a pulsed-jet chirped-pulse millimeter-wave spectrometer for the 70–102 GHz region

G. Barratt Park, Adam H. Steeves, Kirill Kuyanov-Prozument, Justin L. Neill, and Robert W. Field

J. Chem. Phys. 135, 024202 (2011); http://dx.doi.org/10.1063/1.3597774 (10 pages)

Online Publication Date: 8 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Chirped-pulse millimeter-wave (CPmmW) spectroscopy is the first broadband (multi-GHz in each shot) Fourier-transform technique for high-resolution survey spectroscopy in the millimeter-wave region. The design is based on chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy [G. G. Brown, B. C. Dian, K. O. Douglass, S. M. Geyer, S. T. Shipman, and B. H. Pate, Rev. Sci. Instrum. 79, 053103 (2008)]10.1063/1.2919120, which is described for frequencies up to 20 GHz. We have built an instrument that covers the 70–102 GHz frequency region and can acquire up to 12 GHz of spectrum in a single shot. Challenges to using chirped-pulse Fourier-transform spectroscopy in the millimeter-wave region include lower achievable sample polarization, shorter Doppler dephasing times, and problems with signal phase stability. However, these challenges have been partially overcome and preliminary tests indicate a significant advantage over existing millimeter-wave spectrometers in the time required to record survey spectra. Further improvement to the sensitivity is expected as more powerful broadband millimeter-wave amplifiers become affordable. The ability to acquire broadband Fourier-transform millimeter-wave spectra enables rapid measurement of survey spectra at sufficiently high resolution to measure diagnostically important electronic properties such as electric and magnetic dipole moments and hyperfine coupling constants. It should also yield accurate relative line strengths across a broadband region. Several example spectra are presented to demonstrate initial applications of the spectrometer.
Show PACS
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
32.30.Bv Radio-frequency, microwave, and infrared spectra
33.20.Bx Radio-frequency and microwave spectra
32.70.Jz Line shapes, widths, and shifts
33.70.Jg Line and band widths, shapes, and shifts
Author Select

Dissipative quantum coherent dynamics probed in phase-space: Electronically resonant 5-color 4-wave mixing on I2(B) in solid Kr

D. Segale and V. A. Apkarian

J. Chem. Phys. 135, 024203 (2011); http://dx.doi.org/10.1063/1.3598959 (12 pages) | Cited 2 times

Online Publication Date: 8 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Spectrally resolved, 4-wave mixing measurements in five resonant colors are used to interrogate vibronic quantum coherences in phase-space. We highlight the principles through measurements on the B-state of I2 in solid Kr – a prototype of a system strongly coupled to its environment. The measurements consist of preparing a superposition of wavepackets on the B-state and interrogating their cross-coherence as they get entangled with the environment. The study provides direct realizations of fundamental quantum principles in the mechanics of molecular matter, among them: the distinction between quantum and classical coherent dynamics of a system entangled with the environment, coherent dissipation, event-driven decoherence, environment selected coherent states, and non-local mechanics.
Show PACS
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.80.Wz Other multiphoton processes

Temperature dependences of rate coefficients for electron catalyzed mutual neutralization

Nicholas S. Shuman, Thomas M. Miller, Jeffrey F. Friedman, Albert A. Viggiano, Satoshi Maeda, and Keiji Morokuma

J. Chem. Phys. 135, 024204 (2011); http://dx.doi.org/10.1063/1.3605631 (8 pages)

Online Publication Date: 12 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The flowing afterglow technique of variable electron and neutral density attachment mass spectrometry (VENDAMS) has recently yielded evidence for a novel plasma charge loss process, electron catalyzed mutual neutralization (ECMN), i.e., A+ + B− + e− → A + B + e−. Here, rate constants for ECMN of two polyatomic species (POCl3− and POCl2−) and one diatomic species (Br2−) each with two monatomic cations (Ar+and Kr+) are measured using VENDAMS over the temperature range 300 K–500 K. All rate constants show a steep negative temperature dependence, consistent with that expected for a three body process involving two ions and an electron. No variation in rate constants as a function of the cation type is observed outside of uncertainty; however, rate constants of the polyatomic anions (∼1 × 10−18 cm6 s−1 at 300 K) are measurably higher than that for Br2− [(5.5 ± 2) × 10−19 cm6 s−1 at 300 K].
Show PACS
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.20.Pm Rate constants, reaction cross sections, and activation energies
52.80.Hc Glow; corona
52.70.Ds Electric and magnetic measurements
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Potential energy surface and rotational cross sections for methyl formate colliding with helium

Alexandre Faure, Krzysztof Szalewicz, and Laurent Wiesenfeld

J. Chem. Phys. 135, 024301 (2011); http://dx.doi.org/10.1063/1.3607966 (10 pages) | Cited 1 time

Online Publication Date: 8 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A potential energy surface for helium interacting with methyl formate has been computed using high-level electronic structure methods. The interaction energies obtained on a three-dimensional grid have been fitted by an analytic function of interatomic distances with correct asymptotic behavior for large intermonomer separations. This potential has then been refitted using partial wave expansion in terms of the distance between centers of mass and spherical angles. The latter potential has been used to compute cross sections for the rotational excitations of methyl formate at the full quantum close-coupling level. Collisional propensity rules and astrophysical implications are discussed.
Show PACS
31.15.bw Coupled-cluster theory
31.50.Df Potential energy surfaces for excited electronic states
33.20.Sn Rotational analysis
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
34.50.-s Scattering of atoms and molecules

Study of RgS− and RgS (Rg = Ne, Ar, and Kr) via slow photoelectron velocity-map imaging spectroscopy and ab initio calculations

Etienne Garand and Daniel M. Neumark

J. Chem. Phys. 135, 024302 (2011); http://dx.doi.org/10.1063/1.3605595 (8 pages)

Online Publication Date: 8 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
High-resolution photoelectron spectra of RgS− (Rg = Ne, Ar, and Kr) were obtained using slow electron velocity-map imaging (SEVI). The SEVI spectra reveal well-resolved vibrational transitions between multiple spin-orbit states of RgS− and RgS, both of which are open-shell species. Detailed assignments are made by comparison with theoretical simulations based on high level ab initio calculations and a atoms-in-molecule model that accounts for spin-orbit coupling in the anion and neutral. Several RgS− and RgS vibrational frequencies and excited-state term energies are accurately determined from the analysis of the experimental spectra and are found to be in excellent agreement with the calculated values.
Show PACS
33.20.Tp Vibrational analysis
33.60.+q Photoelectron spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure

Joint analysis of the Cs2 a3Σu+ and 1g (33Π1g) states

F. Xie, Li Li, D. Li, V. B. Sovkov, K. V. Minaev, V. S. Ivanov, A. M. Lyyra, and S. Magnier

J. Chem. Phys. 135, 024303 (2011); http://dx.doi.org/10.1063/1.3606397 (7 pages)

Online Publication Date: 8 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Sets of experimental data on the Cs2 a3Σu+ and 1g (33Π1g) states, including the bound-bound and bound-free fluorescence spectra, are analyzed simultaneously to produce the potential energy curves of both states in the form of the Morse long range multiparameter function. The attractive branch of the a3Σu+ state potential is improved relative to the one reported in our earlier work [F. Xie, V. B. Sovkov, A. M. Lyyra, D. Li, S. Ingram, J. Bai, V. S. Ivanov, S. Magnier, and L. Li, J. Chem. Phys. 130, 051102 (2009)]10.1063/1.3075580, in which the data on this state alone were analyzed. Besides, the new potential of this state also includes the repulsive branch in the range spanned by the bound-free fluorescence spectra. We have not found experimental evidence of the double minimum character of the 33Π1g state potential, predicted by ab initio calculations, at least up to v = 8. This fact testifies that the upper state observed is better described by the Hund coupling case (c), in which the case (a) electronic basis states are intermixed by the strong spin-orbit interaction.
Show PACS
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure
31.50.-x Potential energy surfaces
33.50.Dq Fluorescence and phosphorescence spectra

Relaxation of energetic S(1D) atoms in Xe gas: Comparison of ab initio calculations with experimental data

S. Bovino, P. Zhang, V. Kharchenko, and A. Dalgarno

J. Chem. Phys. 135, 024304 (2011); http://dx.doi.org/10.1063/1.3600352 (7 pages)

Online Publication Date: 11 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this paper, we report our investigation of the translational energy relaxation of fast S(1D) atoms in a Xe thermal bath. The interaction potential of Xe-S was constructed using ab initio methods. Total and differential cross sections were then calculated. The latter have been incorporated into the construction of the kernel of the Boltzmann equation describing the energy relaxation process. The solution of the Boltzmann equation was obtained and results were compared with those reported in experiments [G. Nan, and P. L. Houston, J. Chem. Phys. 97, 7865 (1992)]10.1063/1.463461. Good agreement with the measured time-dependent relative velocity of fast S(1D) atoms was obtained except at long relaxation times. The discrepancy may be due to the error accumulation caused by the use of hard sphere approximation and the Monte Carlo analysis of the experimental data. Our accurate description of the energy relaxation process led to an increase in the number of collisions required to achieve equilibrium by an order of magnitude compared to the number given by the hard-sphere approximation.
Show PACS
34.50.Cx Elastic; ultracold collisions
34.20.Cf Interatomic potentials and forces
31.15.A- Ab initio calculations

Isomerization reaction between linear AlNC and AlCN including the math 1Σ+ and math 1Π states studied by three-dimensional wave packet propagation

Ikuo Tokue and Shinkoh Nanbu

J. Chem. Phys. 135, 024305 (2011); http://dx.doi.org/10.1063/1.3608915 (9 pages)

Online Publication Date: 11 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Excitation transfers between linear AlNC and AlCN via the math 1Π (1 1A″, 2 1A′)−math 1Σ+ transition were studied by a wave packet propagation method as applied to a simple system for an isomerization reaction. The photoabsorption and fluorescence spectra calculated in this work are in good agreement with Einstein's A and B coefficients reported in our previous paper [I. Tokue and S. Nanbu, J. Chem. Phys. 124, 224301 (2006)]10.1063/1.2207611. In the 2 1A′−math 1Σ+ excitation of linear AlNC, both isomerization to linear AlCN and dissociation to Al + CN can occur; the probability of both decay channels strongly depends on the vibrational modes of the initial wave packet. The 1 1A″−math 1Σ+ excitation of linear AlNC results primarily in dissociation with isomerization being found to be a relatively minor phenomenon. For the linear AlCN excitation, vibrational levels above 1000 cm−1 occur for both isomerization and dissociation. The isomerization of AlNC ↔ AlCN was found to occur after the math 1Π−math 1Σ+ fluorescence of AlNC and AlCN, with even the initial wave packet being made with the vibrational ground level of the math 1Π state, whereas no dissociation was recognized for any of the cases calculated in this study using lower vibrational levels as initial wave packets. The procedure for wave packet propagation employed in this study is concluded to be very effective for analyzing in detail the reaction dynamics of isomerization for triatomic molecules.
Show PACS
82.30.Qt Isomerization and rearrangement
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.50.Bc Processes caused by infrared radiation
82.20.-w Chemical kinetics and dynamics
Page 1 of 3 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Your Recent History Recent History Help

Recently Viewed

  1. Binary systems from quantum cluster equilibrium theory
  2. A combination of the tree-code and IPS method to simulate large scale systems by molecular dynamics
  3. Large-scale symmetry-adapted perturbation theory computations via density fitting and Laplace transformation techniques: Investigating the fundamental forces of DNA-intercalator interactions
  4. Optimization of a genetic algorithm for searching molecular conformer space
  5. Computer simulation of bottle-brush polymers with flexible backbone: Good solvent versus theta solvent conditions
Go to AIP Home
Copyright © American Institute of Physics
close