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28 Nov 2007

Volume 127, Issue 20, Articles (20xxxx)

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Coherent control of bond breaking in amino acid complexes with tailored femtosecond pulses

T. Laarmann, I. Shchatsinin, P. Singh, N. Zhavoronkov, M. Gerhards, C. P. Schulz, and I. V. Hertel

J. Chem. Phys. 127, 201101 (2007); http://dx.doi.org/10.1063/1.2806029 (4 pages) | Cited 7 times

Online Publication Date: 30 November 2007

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Intense femtosecond laser pulses, judiciously tailored in an adaptive, optimal control feedback loop were used to break preferentially the acyl-N (“peptide”) bond of Ac-Phe-NHMe that may be regarded as a dipeptide model. We show that coherent excitation of complex wave packets in the strong-field regime allows to cleave strong backbone bonds in the molecular system preferentially, while keeping other more labile bonds intact. These results show the potential of pulse shaping as a powerful complementary analytical tool for protein sequencing of large biopolymers in addition to the well-known mass spectrometry and chemical analysis.
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82.35.Pq Biopolymers, biopolymerization
82.53.Ps Femtosecond probing of biological molecules
82.53.Eb Pump probe studies of photodissociation
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back to top Theoretical Methods and Algorithms

Circular dichroism of helical structures using semiempirical methods

Edith Botek and Benoît Champagne

J. Chem. Phys. 127, 204101 (2007); http://dx.doi.org/10.1063/1.2805395 (9 pages) | Cited 7 times

Online Publication Date: 26 November 2007

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A general semiempirical scheme has been elaborated to simulate circular dichroism (CD) spectra of supramolecular systems. This approach adopts the analytical method of Beck and Hohlneicher [Theor. Chem. Acc. 101, 297 (1999).] to evaluate the one- and two-center integrals over Slater atomic orbitals. The performance of the method, employing INDO/S and CNDO/S semiempirical parametrizations, has been assessed by considering (i) the effect of the size of the singly excited states manifold, (ii) the origin invariance, and (iii) comparisons with the experimental and other theoretical spectra of several helicenes as well as pyridine-pyrimidine oligomers, which can adopt helical conformations. The main results are (i) the INDO/S parametrization with rather small excitation manifolds is able to reproduce, at low computational costs, the experimental CD spectra of several helicenes as well as CD simulations performed at ab initio and time-dependent density functional theory level of approximation; (ii) in the series of homohelicenes, the rotatory strength of the lowest-energy band increases almost linearly with the size of the helix; (iii) as evidenced by the study of tetradodecyloxy helicene bisquinone, packing effects can change the sign of remarkable CD bands, which are used to assign the structure configuration.
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33.55.+b Optical activity and dichroism
33.57.+c Magneto-optical and electro-optical spectra and effects
31.15.bu Semi-empirical and empirical calculations (differential overlap, Hückel, PPP methods, etc.)
31.15.E- Density-functional theory
31.15.vj Electron correlation calculations for atoms and ions: excited states

New implementation of a combined quantum mechanical and molecular mechanical method using modified generalized hybrid orbitals

Jaewoon Jung, Cheol Ho Choi, Yuji Sugita, and Seiichiro Ten-no

J. Chem. Phys. 127, 204102 (2007); http://dx.doi.org/10.1063/1.2801988 (12 pages) | Cited 10 times

Online Publication Date: 26 November 2007

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Two new techniques are introduced in the generalized hybrid orbital (GHO) method [ Pu et al., J. Phys. Chem. A 108, 632 (2004) ] and tested on small molecules. The first is a way to determine occupation numbers dependent on the molecular mechanical (MM) atoms linked to the boundary. The method takes account of the inhomogeneity in the occupation numbers of the auxiliary orbitals from different types of MM atoms in such a way that the formal charge condition is fulfilled. The second technique is a rigorous orthogonalization procedure of auxiliary orbitals for more than two boundary atoms. It is shown that the new implementation widens the realm of the GHO method with flexible quantum mechanical/MM partitionings.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
31.10.+z Theory of electronic structure, electronic transitions, and chemical binding

A density matrix-based method for the linear-scaling calculation of dynamic second- and third-order properties at the Hartree-Fock and Kohn-Sham density functional theory levels

Jörg Kussmann and Christian Ochsenfeld

J. Chem. Phys. 127, 204103 (2007); http://dx.doi.org/10.1063/1.2794033 (12 pages) | Cited 15 times

Online Publication Date: 27 November 2007

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A density matrix-based time-dependent self-consistent field (D-TDSCF) method for the calculation of dynamic polarizabilities and first hyperpolarizabilities using the Hartree-Fock and Kohn-Sham density functional theory approaches is presented. The D-TDSCF method allows us to reduce the asymptotic scaling behavior of the computational effort from cubic to linear for systems with a nonvanishing band gap. The linear scaling is achieved by combining a density matrix-based reformulation of the TDSCF equations with linear-scaling schemes for the formation of Fock- or Kohn-Sham-type matrices. In our reformulation only potentially linear-scaling matrices enter the formulation and efficient sparse algebra routines can be employed. Furthermore, the corresponding formulas for the first hyperpolarizabilities are given in terms of zeroth- and first-order one-particle reduced density matrices according to Wigner’s (2n+1) rule. The scaling behavior of our method is illustrated for first exemplary calculations with systems of up to 1011 atoms and 8899 basis functions.
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42.65.-k Nonlinear optics

Optimization of replica exchange molecular dynamics by fast mimicking

Jozef Hritz and Chris Oostenbrink

J. Chem. Phys. 127, 204104 (2007); http://dx.doi.org/10.1063/1.2790427 (13 pages) | Cited 3 times

Online Publication Date: 27 November 2007

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We present an approach to mimic replica exchange molecular dynamics simulations (REMD) on a microsecond time scale within a few minutes rather than the years, which would be required for real REMD. The speed of mimicked REMD makes it a useful tool for “testing” the efficiency of different settings for REMD and then to select those settings, that give the highest efficiency. We present an optimization approach with the example of Hamiltonian REMD using soft-core interactions on two model systems, GTP and 8-Br-GTP. The optimization process using REMD mimicking is very fast. Optimization of Hamiltonian-REMD settings of GTP in explicit water took us less than one week. In our study we focus not only on finding the optimal distances between neighboring replicas, but also on finding the proper placement of the highest level of softness. In addition we suggest different REMD simulation settings at this softness level. We allow several replicas to be simulated at the same Hamiltonian simultaneously and reduce the frequency of switching attempts between them. This approach allows for more efficient conversions from one stable conformation to the other.
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31.15.xv Molecular dynamics and other numerical methods
33.15.Bh General molecular conformation and symmetry; stereochemistry

An analytical derivative procedure for the calculation of vibrational Raman optical activity spectra

Vincent Liégeois, Kenneth Ruud, and Benoît Champagne

J. Chem. Phys. 127, 204105 (2007); http://dx.doi.org/10.1063/1.2801986 (6 pages) | Cited 29 times

Online Publication Date: 28 November 2007

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We present an analytical time-dependent Hartree-Fock algorithm for the calculation of the derivatives of the electric dipole–magnetic dipole polarizability with respect to atomic Cartesian coordinates. Combined with analogous procedures to determine the derivatives of the electric dipole–electric dipole and electric dipole–electric quadrupole polarizabilities, it enables a fully analytical evaluation of the three frequency-dependent vibrational Raman optical activity (VROA) invariants within the harmonic approximation. The procedure employs traditional non-London atomic orbitals, and the gauge-origin dependence of the VROA intensities has, therefore, been assessed for the commonly used aug-cc-pVDZ and rDPS:3-21G basis sets.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.55.+b Optical activity and dichroism
33.57.+c Magneto-optical and electro-optical spectra and effects

Automatic generation of potential energy and property surfaces of polyatomic molecules in normal coordinates

D. Toffoli, J. Kongsted, and O. Christiansen

J. Chem. Phys. 127, 204106 (2007); http://dx.doi.org/10.1063/1.2805085 (14 pages) | Cited 30 times

Online Publication Date: 29 November 2007

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A procedure for the automatic construction of Born-Oppenheimer (BO) potential energy and molecular property surfaces in rectilinear normal coordinates is presented and its suitability and accuracy when combined with vibrational structure calculations are assessed. The procedure relies on a hierarchical n-mode representation of the BO potential energy or molecular property surface, where the n-mode term of the sequence of potentials/molecular properties includes only the couplings between n or less vibrational degrees of freedom. Each n-mode cut of the energy/molecular property surface is first evaluated in a grid of points with ab initio electronic structure methods. The ab initio data are then spline interpolated and a subsequent polynomial fitting provides an analytical semiglobal representation for use in vibrational structure programs. The implementation of the procedure is outlined and the accuracy of the method is tested on water and difluoromethane. Strategies for improving the proposed algorithm are also discussed.
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31.50.-x Potential energy surfaces
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Bh General molecular conformation and symmetry; stereochemistry

A first principles theory of nuclear magnetic resonance J-coupling in solid-state systems

Siân A. Joyce, Jonathan R. Yates, Chris J. Pickard, and Francesco Mauri

J. Chem. Phys. 127, 204107 (2007); http://dx.doi.org/10.1063/1.2801984 (9 pages) | Cited 19 times

Online Publication Date: 29 November 2007

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A method to calculate NMR J-coupling constants from first principles in extended systems is presented. It is based on density functional theory and is formulated within a planewave-pseudopotential framework. The all-electron properties are recovered using the projector augmented wave approach. The method is validated by comparison with existing quantum chemical calculations of solution-state systems and with experimental data. The approach has also been applied to the silicophosphate, Si5O(PO4)6, giving 31P–29Si-couplings which are in excellent agreement with experiment.
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76.60.-k Nuclear magnetic resonance and relaxation
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Block correlated coupled cluster theory with a complete active-space self-consistent-field reference function: The formulation and test applications for single bond breaking

Tao Fang and Shuhua Li

J. Chem. Phys. 127, 204108 (2007); http://dx.doi.org/10.1063/1.2800027 (12 pages) | Cited 16 times

Online Publication Date: 30 November 2007

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Block correlated coupled cluster (BCCC) theory with a complete active-space self-consistent-field (CASSCF) reference function is presented. This theory provides an alternative multireference coupled cluster framework to describe the multireference characters of the ground-state wave functions. In this approach, a multireference block is defined to incorporate the nondynamic correlation, and all other blocks involve just a single spin orbital. The cluster operators are truncated up to the four-block correlation level, leading to the BCCC4 scheme. For a single bond breaking problem, the present CAS-BCCC4 approach with a CASSCF(2,2) reference function computationally scales as the traditional single-reference coupled cluster singles and doubles. We have applied the present approach to investigate the electronic structures of several model systems including H4, P4, and BeH2, and the single bond breaking processes in small systems such as F2, HF, BH, and CH4. A comparison of our results with those from full configuration interaction calculations shows that the present approach can provide quantitative descriptions for all the studied systems. The size-consistency error is found to be quite small in the dissociation limit of diatomic molecules F2, HF, and BH.
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31.15.bw Coupled-cluster theory
31.15.xr Self-consistent-field methods
31.15.ve Electron correlation calculations for atoms and ions: ground state
31.15.vn Electron correlation calculations for diatomic molecules
33.15.Fm Bond strengths, dissociation energies
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Accurate ab initio potential energy curve of F2. II. Core-valence correlations, relativistic contributions, and long-range interactions

L. Bytautas, N. Matsunaga, T. Nagata, M. S. Gordon, and K. Ruedenberg

J. Chem. Phys. 127, 204301 (2007); http://dx.doi.org/10.1063/1.2801989 (12 pages) | Cited 14 times

Online Publication Date: 26 November 2007

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The nonrelativistic, valence-shell-only-correlated ab initio potential energy curve of the F2 molecule, which was reported in the preceding paper, is complemented by determining the energy contributions that arise from the electron correlations that involve the core electrons as well as the contributions that are due to spin-orbit coupling and scalar relativistic effects. The dissociation curve rises rather steeply toward the energy of the dissociated atoms because, at larger distances, the atomic quadrupole-quadrupole repulsion and spin-orbit coupling counteract the attractive contributions from incipient covalent binding and correlation forces including dispersion.
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31.15.A- Ab initio calculations
31.50.-x Potential energy surfaces
31.15.vn Electron correlation calculations for diatomic molecules
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Kh Potential energy surfaces for chemical reactions

Effect of the Gouy phase on the coherent phase control of chemical reactions

Robert J. Gordon and Vishal J. Barge

J. Chem. Phys. 127, 204302 (2007); http://dx.doi.org/10.1063/1.2787011 (8 pages) | Cited 2 times

Online Publication Date: 26 November 2007

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We show how the spatial phase of a focused laser beam may be used as a tool for controlling the branching ratio of a chemical reaction. Guoy discovered [Acad. Sci., Paris, C. R. 110, 1250 (1890) ] that when an electromagnetic wave passes through a focus its phase increases by π. In a coherent control scheme involving the absorption of n photons of frequency ωm and m photons of frequency ωn, the overall phase shift produced by the Gouy phase is (n−m)π. At any given point in space, this phase shift is identical for all reaction products. Nevertheless, if the yields for different reaction channels have different intensity dependencies, the Gouy phase produces a net phase lag between the products that varies with the axial coordinate of the laser focus. We obtain here analytical and numerical values of this phase as the laser focus is scanned across the diameter of the molecular beam, taking into account the Rayleigh range and astigmatism of the laser beam and saturation of the transition. We also show that the modulation depth of the interference pattern may be increased by optimizing the relative intensities of the two fields.
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82.50.Nd Control of photochemical reactions
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Be Level crossing and optical pumping
32.80.-t Photoionization and excitation

Nuclear quadrupole moment of 139La from relativistic electronic structure calculations of the electric field gradients in LaF, LaCl, LaBr, and LaI

Christoph R. Jacob, Lucas Visscher, Christian Thierfelder, and Peter Schwerdtfeger

J. Chem. Phys. 127, 204303 (2007); http://dx.doi.org/10.1063/1.2787000 (7 pages) | Cited 5 times

Online Publication Date: 26 November 2007

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Relativistic coupled cluster theory is used to determine accurate electric field gradients in order to provide a theoretical value for the nuclear quadrupole moment of 139La. Here we used the diatomic lanthanum monohalides LaF, LaCl, LaBr, and LaI as accurate nuclear quadrupole coupling constants are available from rotational spectroscopy by Rubinoff et al. [J. Mol. Spectrosc. 218, 169 (2003)] . The resulting nuclear quadrupole moment for 139La (0.200±0.006 barn) is in excellent agreement with earlier work using atomic hyperfine spectroscopy [0.20(1) barn].
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33.25.+k Nuclear resonance and relaxation
31.15.bw Coupled-cluster theory
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
33.20.Sn Rotational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants

Photodissociation spectroscopy of stored CH+ and CD+ ions: Analysis of the b 3Σ−-a 3Π system

U. Hechtfischer, J. Rostas, M. Lange, J. Linkemann, D. Schwalm, R. Wester, A. Wolf, and D. Zajfman

J. Chem. Phys. 127, 204304 (2007); http://dx.doi.org/10.1063/1.2800004 (13 pages)

Online Publication Date: 27 November 2007

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We have measured the photodissociation spectrum of CH+ and CD+ molecular ions, stored as fast (MeV) ion beams in the heavy-ion storage ring TSR. Several b 3Σ−-a 3Π bands were observed as strong resonances because a large fraction of the ions in the metastable a 3Π(v = 0) state were pumped to b 3Σ− levels and predissociated via the c 3Σ+ state into C+ and H(D) fragments. From a rotational analysis of the 2-0, 3-0, and 4-0 bands in CH+ and the 3-0 and 4-0 bands in CD+, we derive spectroscopic constants for these levels and also revise a previous analysis of the 0-0 and 1-0 bands in CH+. Combining all data delivers new, significantly adjusted equilibrium constants for the b 3Σ− and a 3Π electronic states. Apart from the spectroscopic analysis, we estimate the predissociation rates of the upper b 3Σ− vibrational levels in CH+ and compare them to a model. For the initial rovibrational distribution of the stored metastable CH+ molecules, the data indicate a faster vibrational cooling than derived before, and rotational cooling at a rate similar to the X 1Σ+ ground state. New aspects of the spin-forbidden a 3Π-X 1Σ+ radiative decay are discussed. Finally, we predict b 3Σ−-a 3Π absorption and a 3Π-X 1Σ+ emission lines through which CH+ in the metastable a 3Π(v = 0) state might be detectable in astrophysical environments.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis
33.20.Vq Vibration-rotation analysis

Wave packet driven dissociation and concerted elimination in CH2I2

Dominik Geißler, Brett J. Pearson, and Thomas Weinacht

J. Chem. Phys. 127, 204305 (2007); http://dx.doi.org/10.1063/1.2805186 (4 pages) | Cited 11 times

Online Publication Date: 27 November 2007

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We follow the evolution of a vibrational wave packet in a highly excited state of the halogenated methane CH2I2. We observe how the wave packet modulates both dissociation and concerted elimination to form CH2I+ and I2+, respectively. We present a simple and intuitive interpretation of the molecular dynamics leading to the formation of the products.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
31.50.Df Potential energy surfaces for excited electronic states

New insights in the formation of thioxophosphine: A quantum chemical study

Rommel B. Viana and André S. Pimentel

J. Chem. Phys. 127, 204306 (2007); http://dx.doi.org/10.1063/1.2800012 (8 pages) | Cited 4 times

Online Publication Date: 27 November 2007

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The investigation of the thioxophosphine (PS) formation from different reaction paths is successfully performed and presented in this paper. The PH3+SH1 reaction is likely to yield the intermediates PH22+H2S through an energy barrier of 2.8 kcal mol−1. However, the next step is the H2PS2 formation, which has a too high energy barrier, 52.6 kcal mol−1. The PH3+S1 reaction path is the likely source of the HPS1 molecule. The other possibilities are the PH1+H2S, PH22+SH1, and PH3+H2S reactions, but they are spin forbidden and energetically unfavorable for the HPS1 and PSH1 formations. On the other hand, the PS2 formation is more likely to happen by the PH1+SH1 reaction. The PH22+S1, PH3+SH1, P2+H2S, and P4+H2S reactions are also favorable in terms of energetics; however, these reactions are spin forbidden. The chemical mechanism for the PS2 formation is now presented in more details, which is of great importance in the atmosphere of Jupiter and Saturn, and in interstellar medium.
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82.20.-w Chemical kinetics and dynamics
82.30.Nr Association, addition, insertion, cluster formation
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
95.30.Ft Molecular and chemical processes and interactions

The permanent electric dipole moment of chromium monodeuteride, CrD

Jinhai Chen, Timothy C. Steimle, and Anthony J. Merer

J. Chem. Phys. 127, 204307 (2007); http://dx.doi.org/10.1063/1.2800003 (6 pages) | Cited 2 times

Online Publication Date: 28 November 2007

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A number of low-N lines of the X 6Σ+←A 6Σ+(0,0) band of chromium monodeuteride, CrD, have been recorded at near the natural linewidth limit by high resolution laser excitation spectroscopy of a supersonic molecular beam sample. The shifts and splitting of these lines caused by a static electric field have been analyzed to give the permanent electric dipole moments of the X 6Σ+(υ = 0) and A 6Σ+(υ = 0) states as 3.510(33) and 1.153(3) D, respectively. The dipole moment of the A 6Σ+(υ = 0) state can be measured with higher precision because of some interesting near degeneracies in its level structure. The trends in the observed dipole moments for the first-row transition metal monohydrides are rationalized and compared with theoretical predictions.
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33.57.+c Magneto-optical and electro-optical spectra and effects
33.70.Jg Line and band widths, shapes, and shifts
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Reinvestigation of the electronic spectroscopy of the Au–Ar complex

Richard J. Plowright, Victoria L. Ayles, Mark J. Watkins, Adrian M. Gardner, Rossana R. Wright, Timothy G. Wright, and W. H. Breckenridge

J. Chem. Phys. 127, 204308 (2007); http://dx.doi.org/10.1063/1.2800006 (8 pages) | Cited 12 times

Online Publication Date: 28 November 2007

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The Au–Ar complex is reinvestigated employing resonance-enhanced multiphoton ionization spectroscopy. Spectra are reported, corresponding to the atomic transition Au(6p←6s). This electronic excitation yields 2Π and 2Σ+ states of Au–Ar, which interact under the influence of spin-orbit coupling. The spectra are consistent with strong σ-π mixing induced by the large spin-orbit coupling of Au, leading to strong interaction of the two Ω = 1/2 states, which arise from the Ar(1S0)+Au(2P1/2,3/2) asymptotes, and the consequent formation of a “shelf” on the outer wall of the lowest Ω = 1/2 state. In addition, high-level ab initio calculations are reported on the ground electronic state, math 2Σ+, including extrapolation to the basis set limit.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.80.Eh Autoionization, photoionization, and photodetachment
31.15.A- Ab initio calculations

Temperature and heat capacity of atomic clusters as estimated in terms of kinetic-energy release of atomic evaporation

Mikiya Fujii and Kazuo Takatsuka

J. Chem. Phys. 127, 204309 (2007); http://dx.doi.org/10.1063/1.2800995 (7 pages) | Cited 1 time

Online Publication Date: 29 November 2007

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The temperature and heat capacity of isolated atomic clusters are studied in terms of an ab initio statistical theory of kinetic energy distribution by atomic evaporation. Two definitions of canonical temperature are examined and numerically compared: One is based on the most probable kinetic energy release (KER), whereas the other is determined with use of the entire distribution of the KER. The mutual relationship and their advantages are discussed.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
36.40.-c Atomic and molecular clusters
31.50.-x Potential energy surfaces

An experimental and theoretical study of the S1←S0 transition of p-ethynyltoluene

John G. Philis and Vasilios S. Melissas

J. Chem. Phys. 127, 204310 (2007); http://dx.doi.org/10.1063/1.2804865 (9 pages) | Cited 2 times

Online Publication Date: 29 November 2007

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The one photon and the two photon S1←S0 spectra of jet-cooled p-ethynyltoluene have been measured for the first time, and a detailed vibronic analysis for both spectra has been attained. Mass analyzed resonance enhanced multiphoton ionization spectroscopy is the employed technique. In the one photon spectrum, the allowed component (origin and Franck-Condon bands) is much weaker than the forbidden component, and the same mechanisms as in the one photon spectrum of phenylacetylene are observed. The methyl torsional transitions are active. The 000 band is at 35 483 cm−1. The two photon spectrum is very strong and bears a resemblance to the two photon spectrum of phenylacetylene. The potential barrier of the methyl rotor in the S1 state has been determined as V6 = −12 cm−1 with BCH3 = 5.55 cm−1. Ab initio calculations, MP2(full)/cc-pVTZ and CAS/cc-pVTZ, have been implemented for the geometry optimization and the normal mode vibration computation in the S0 and S1 states.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
32.80.Rm Multiphoton ionization and excitation to highly excited states
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.20.Tp Vibrational analysis

Coriolis coupling effects on the initial-state-resolved dynamics of the N(2D)+H2→NH+H reaction

Paolo Defazio and Carlo Petrongolo

J. Chem. Phys. 127, 204311 (2007); http://dx.doi.org/10.1063/1.2798105 (4 pages) | Cited 10 times

Online Publication Date: 29 November 2007

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We present Coriolis coupling effects on the initial-state-resolved dynamics of the insertion reaction N(2D)+H2(math 1Σg+)→NH(math 3Σ− and math 1Δ)+H(2S), without and with nonadiabatic Renner-Teller (RT) interactions between the NH2 math 2B1 and math 2A1 electronic states. We report coupled-channel (CC) Hamiltonian matrix elements, which take into account both Coriolis and RT couplings, use the real wave-packet and flux methods for calculating initial-state-resolved reaction probabilities, and contrast CC with centrifugal-sudden (CS) results. Without RT interactions, Coriolis effects are rather small up to J = 40, and the CS approximation can be safely employed for calculating initial-state-resolved, integral cross sections. On the other hand, RT effects are associated with rather large Coriolis couplings, mainly near the linearity of NH2, and the accuracy of the CS approximation thus breaks down at high collision energies, when the reaction starts on the excited math 2A1 surface. We also present the CC-RT distribution of the math 3Σ− and math 1Δ electronic states of the NH products.
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82.30.Nr Association, addition, insertion, cluster formation
82.20.Wt Computational modeling; simulation
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Kh Potential energy surfaces for chemical reactions
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)

Evidence for cluster shape effects on the kinetic energy spectrum in thermionic emission

F. Calvo, F. Lépine, B. Baguenard, F. Pagliarulo, B. Concina, C. Bordas, and P. Parneix

J. Chem. Phys. 127, 204312 (2007); http://dx.doi.org/10.1063/1.2804861 (5 pages) | Cited 2 times

Online Publication Date: 30 November 2007

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Experimental kinetic energy release distributions obtained for the thermionic emission from Cn− clusters, 10 ⩽ n ⩽ 20, exhibit significant non-Boltzmann variations. Using phase space theory, these different features are analyzed and interpreted as the consequence of contrasting shapes in the daughter clusters; linear and nonlinear isomers have clearly distinct signatures. These results provide a novel indirect structural probe for atomic clusters associated with their thermionic emission spectra.
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79.40.+z Thermionic emission
36.40.-c Atomic and molecular clusters

Accurate ab initio potential energy curve of F2. III. The vibration rotation spectrum

L. Bytautas, N. Matsunaga, T. Nagata, M. S. Gordon, and K. Ruedenberg

J. Chem. Phys. 127, 204313 (2007); http://dx.doi.org/10.1063/1.2805392 (19 pages) | Cited 14 times

Online Publication Date: 30 November 2007

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An analytical expression is found for the accurate ab initio potential energy curve of the fluorine molecule that has been determined in the preceding two papers. With it, the vibrational and rotational energy levels of F2 are calculated using the discrete variable representation. The comparison of this theoretical spectrum with the experimental spectrum, which had been measured earlier using high-resolution electronic spectroscopy, yields a mean absolute deviation of about 5 cm−1 over the 22 levels. The dissociation energy with respect to the lowest vibrational energy is calculated within 30 cm−1 of the experimental value of 12 953±8 cm−1. The reported agreement of the theoretical spectrum and dissociation energy with experiment is contingent upon the inclusion of the effects of core-generated electron correlation, spin-orbit coupling, and scalar relativity. The Dunham analysis [Phys. Rev. 41, 721 (1932) ] of the spectrum is found to be very accurate. New values are given for the spectroscopic constants.
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31.50.-x Potential energy surfaces
33.20.Tp Vibrational analysis
33.20.Sn Rotational analysis

Quantum optimal control of electron ring currents in chiral aromatic molecules

Manabu Kanno, Kunihito Hoki, Hirohiko Kono, and Yuichi Fujimura

J. Chem. Phys. 127, 204314 (2007); http://dx.doi.org/10.1063/1.2806180 (9 pages) | Cited 12 times

Online Publication Date: 30 November 2007

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We report the results of optimal control simulations of π-electron rotation (ring current) in a six-membered chiral aromatic molecule, 2,5-dichloro[n](3,6)pyrazinophane (DCP), attached at a surface and excited by a linearly polarized UV laser. DCP has a pair of optically allowed, quasidegenerate π-electronic excited states. The laser pulse to generate an approximate angular momentum eigenstate consisting of the quasidegenerate states was designed using the global optimal control theory. For both counterclockwise and clockwise π-electron rotations, the calculated objective functional and target yield as a function of the angle of the photon polarization vector show two maxima and two minima. The origin of the two minima is coherent excitation to only one of the quasidegenerate states. The two maxima arise from creation of a superposition of the quasidegenerate states. The optimal control pulse at the maxima is a two-color laser field resonant with the quasidegenerate states. The electric field of the optimal control pulse consists of two parts: a slowly oscillating part with phase φenv and a rapidly oscillating one. The phase φenv is a crucial parameter for determination of the rotation direction of π electrons at the end of control. The results of the optimal control simulations suggest that π-electron rotation can be controlled by applying a two-color laser field with adjusted phases.
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33.20.Lg Ultraviolet spectra
33.80.-b Photon interactions with molecules
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Sn Rotational analysis
31.15.-p Calculations and mathematical techniques in atomic and molecular physics

Microwave spectra of O2–HF and O2–DF: Hyperfine interactions and global fitting with infrared data

Shenghai Wu, Galen Sedo, Erik M. Grumstrup, and Kenneth R. Leopold

J. Chem. Phys. 127, 204315 (2007); http://dx.doi.org/10.1063/1.2804770 (11 pages) | Cited 2 times

Online Publication Date: 30 November 2007

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Spectra of the open shell complexes O2–HF and O2–DF were recorded using Fourier transform microwave spectroscopy. A complete analysis of the hyperfine structure and a global fit including microwave and infrared frequencies [ W. M. Fawzy, C. M. Lovejoy, D. J. Nesbitt, and J. T. Hougen, J. Chem. Phys. 117, 693 (2002) ] are reported. The Fermi contact interaction between the electron and nuclear spins, the electron spin-nuclear spin dipolar interaction, the nuclear spin-nuclear spin dipolar interaction, and the nuclear electric quadrupole interaction (for O2–DF) were considered in the analysis. The correspondence between the magnetic hyperfine constants and the two nuclei of the H(D)F is unambiguously established. In both O2–HF and O2–DF, the Fermi contact parameter is larger for the fluorine than for the hydrogen, while for the nuclear spin-electron spin dipolar hyperfine constants, the reverse is true. The effective angle between the HF bond and the a axis of the complex, determined from the nuclear spin-nuclear spin interaction constant, is 38(4)°. The same angle for the DF complex, derived from the deuterium nuclear quadrupole coupling constant, is 31(4)°.
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33.25.+k Nuclear resonance and relaxation
33.20.Bx Radio-frequency and microwave spectra
33.15.Pw Fine and hyperfine structure
33.20.Ea Infrared spectra
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Observation of slow charge redistribution preceding excited-state proton transfer

D. B. Spry and M. D. Fayer

J. Chem. Phys. 127, 204501 (2007); http://dx.doi.org/10.1063/1.2803188 (10 pages) | Cited 4 times

Online Publication Date: 28 November 2007

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The photoacid 8-hydroxy-N,N,N′,N′,N′,N′-hexamethylpyrene-1,3,6-trisulfonamide (HPTA) and related compounds are used to investigate the steps involved in excited-state deprotonation in polar solvents using pump-probe spectroscopy and time correlated single photon counting fluorescence spectroscopy. The dynamics show a clear two-step process leading to excited-state proton transfer. The first step after electronic excitation is charge redistribution occurring on a tens of picoseconds time scale followed by proton transfer on a nanosecond time scale. The three states observed in the experiments (initial excited state, charge redistributed state, and proton transfer state) are recognized by distinct features in the time dependence of the pump-probe spectrum and fluorescence spectra. In the charge redistributed state, charge density has transferred from the hydroxyl oxygen to the pyrene ring, but the OH sigma bond is still intact. The experiments indicate that the charge redistribution step is controlled by a specific hydrogen bond donation from HPTA to the accepting base molecule. The second step is the full deprotonation of the photoacid. The full deprotonation is clearly marked by the growth of stimulated emission spectral band in the pump-probe spectrum that is identical to the fluorescence spectrum of the anion.
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82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.50.-m Photochemistry
82.30.Rs Hydrogen bonding, hydrophilic effects
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