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14 Jun 2008

Volume 128, Issue 22, Articles (22xxxx)

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Announcement: Online manuscript submission and peer review via Peer X-Press

Mark M. Cassar

J. Chem. Phys. 128, 220201 (2008); http://dx.doi.org/10.1063/1.2952646 (1 page)

Online Publication Date: 13 June 2008

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Abstract Unavailable
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01.10.Cr Announcements, news, and awards
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Free energy and structure of calcium carbonate nanoparticles during early stages of crystallization

D. Quigley and P. M. Rodger

J. Chem. Phys. 128, 221101 (2008); http://dx.doi.org/10.1063/1.2940322 (4 pages) | Cited 18 times

Online Publication Date: 10 June 2008

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We introduce a metadynamics based scheme for computing the free energy of nanoparticles as a function of their crystalline order. The method is applied to small nanoparticles of the biomineral calcium carbonate to determine the preferred structure during early stages of crystal growth. For particles 2 nm in diameter, we establish a large energetic preference for amorphous particle morphologies. Particles with partial crystalline order consistent with vaterite are also observed with substantially lower probability. The absence of the stable calcite phase and stability of the amorphous state support recent conjectures that calcite formation starts via the deposition of amorphous calcium carbonate.
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65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.43.-j Disordered solids

Efficient linear-scaling calculation of response properties: Density matrix-based Laplace-transformed coupled-perturbed self-consistent field theory

Matthias Beer and Christian Ochsenfeld

J. Chem. Phys. 128, 221102 (2008); http://dx.doi.org/10.1063/1.2940731 (4 pages) | Cited 12 times

Online Publication Date: 13 June 2008

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A density matrix-based Laplace reformulation of coupled-perturbed self-consistent field (CPSCF) theory is presented. It allows a direct, instead of iterative, solution for the integral-independent part of the density matrix-based CPSCF (D-CPSCF) equations [ J. Kussmann and C. Ochsenfeld, J. Chem. Phys. 127, 054103 (2007) ]. In this way, the matrix-multiplication overhead compared to molecular orbital-based solutions is reduced to a minimum, while at the same time, the linear-scaling behavior of D-CPSCF theory is preserved. The present Laplace-based equation solver is expected to be of general applicability.
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31.15.xr Self-consistent-field methods
31.15.E- Density-functional theory
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.xp Perturbation theory
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back to top Theoretical Methods and Algorithms

New torsion potential expression for molecules without rotational symmetry

Xiaobo Ji, Liuming Yan, and Wencong Lu

J. Chem. Phys. 128, 224101 (2008); http://dx.doi.org/10.1063/1.2929828 (9 pages)

Online Publication Date: 9 June 2008

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A new torsion potential function for bond rotations without rotational symmetry is proposed. This function is composed of a few Gaussian-type terms each corresponding to an eclipsed conformation of the 1,2 substituents of the C–C bonds. Different from the truncated Fourier series or the truncated cosine polynomial, it is easy to determine how many terms are needed to represent any type of torsion potential barrier at a glance using the Gaussian-type function. It could also intuitively deduce the physical meaning of the expansion parameters of the new torsion potential function, which corresponds to the barrier height, the dihedral defining the eclipsed conformations, and the size of the substituents, respectively. The new torsion potential function is also applied to the 1, 2-substituted haloethanes with satisfactory results, where three Gaussian-type terms corresponding to the fully eclipsed and the partially eclipsed conformations are needed.
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33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Bh General molecular conformation and symmetry; stereochemistry

Coupled-cluster dynamic polarizabilities including triple excitations

Jeff R. Hammond, Wibe A. de Jong, and Karol Kowalski

J. Chem. Phys. 128, 224102 (2008); http://dx.doi.org/10.1063/1.2929840 (11 pages) | Cited 6 times

Online Publication Date: 10 June 2008

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Dynamic polarizabilities for open- and closed-shell molecules were obtained by using coupled-cluster (CC) linear response theory with full treatment of singles, doubles, and triples (CCSDT-LR) with large basis sets utilizing the NWChem software suite. By using four approximate CC methods in conjunction with augmented cc-pVNZ basis sets, we are able to evaluate the convergence in both many-electron and one-electron spaces. For systems with primarily dynamic correlation, the results for CC3 and CCSDT are almost indistinguishable. For systems with significant static correlation, the CC3 tends to overestimate the triples contribution, while the PS(T) approximation [ J. Chem. Phys. 127, 164105 (2007) ] produces mixed results that are heavily dependent on the accuracies provided by noniterative approaches used to correct the equation-of-motion CCSD excitation energies. Our results for open-shell systems show that the choice of reference (restricted open-shell Hartree–Fock versus unrestricted Hartree–Fock) can have a significant impact on the accuracy of polarizabilities. A simple extrapolation based on pentuple-zeta CCSD calculations and triple-zeta CCSDT calculations reproduces experimental results with good precision in most cases.
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31.15.bw Coupled-cluster theory
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Numerical integration of exchange-correlation energies and potentials using transformed sparse grids

Juan I. Rodríguez, David C. Thompson, Paul W. Ayers, and Andreas M. Köster

J. Chem. Phys. 128, 224103 (2008); http://dx.doi.org/10.1063/1.2931563 (10 pages) | Cited 11 times

Online Publication Date: 12 June 2008

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A new numerical integration procedure for exchange-correlation energies and potentials is proposed and “proof of principle” results are presented. The numerical integration grids are built from sparse-tensor product grids (constructed according to Smolyak’s prescription [Dokl. Akad. Nauk. 4, 240 (1963)] ) on the unit cube. The grid on the unit cube is then transformed to a grid over real space with respect to a weight function, which we choose to be the promolecular density. This produces a “whole molecule” grid, in contrast to conventional integration methods in density-functional theory, which use atom-in-molecule grids. The integration scheme was implemented in a modified version of the DEMON2K density-functional theory program, where it is used to evaluate integrals of the exchange-correlation energy density and the exchange-correlation potential. Ground-state energies and molecular geometries are accurately computed. The biggest advantages of the grid are its flexibility (it is easy to change the number and distribution of grid points) and its whole molecule nature. The latter feature is potentially helpful for basis-set-free computational algorithms.
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31.15.eg Exchange-correlation functionals (in current density functional theory)
31.50.Bc Potential energy surfaces for ground electronic states
33.15.Bh General molecular conformation and symmetry; stereochemistry
02.60.Jh Numerical differentiation and integration
02.10.Ud Linear algebra

First-order exchange energy of intermolecular interactions from coupled cluster density matrices and their cumulants

Tatiana Korona

J. Chem. Phys. 128, 224104 (2008); http://dx.doi.org/10.1063/1.2933312 (14 pages) | Cited 9 times

Online Publication Date: 12 June 2008

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A new method for the calculation of the first-order intermolecular exchange energy is proposed. It is based on the partition of two-particle density matrices of monomers into the antisymmetrized product of one-particle density matrices and the remaining cumulant part. This partition is used to modify the formula for the first-order exchange energy developed by Moszynski et al. [J. Chem. Phys. 100, 5080 (1994)] . The new expression has been applied for the case of monomer density matrices derived from the expectation value expression for the coupled cluster singles and doubles wave function. In this way an accurate method of calculation of the first-order exchange energy for many-electron systems has been obtained, where both monomers are described on the coupled cluster level. Numerical results are presented for several benchmark van der Waals systems to illustrate the performance of the new approach.
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34.20.Gj Intermolecular and atom-molecule potentials and forces

Accurate calculations of free-energy differences by the distribution method

Di Wu

J. Chem. Phys. 128, 224105 (2008); http://dx.doi.org/10.1063/1.2936987 (9 pages) | Cited 4 times

Online Publication Date: 12 June 2008

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We employ the strategy used in the successive umbrella sampling method [ P. Virnau and M. Müller, J. Chem. Phys. 120, 10925 (2004) ] to obtain the energy-difference distribution over its desired range. This is very helpful in calculating free-energy differences, where the source of the error is well recognized as the insufficient sampling over the relevant tail region in the energy-difference distribution. The distribution method proposed here employs the idea of restricting the sampling within an appropriate energy range, as was presented by Shing and Gubbins in their restricted umbrella sampling method [ Mol. Phys. 46, 1109 (1982) ]. We demonstrate the efficiency of the distribution method by calculating the free-energy difference of a model of harmonic oscillators where the systems exhibit nonoverlap features in their important phase spaces through the original Metropolis sampling. For this particular case, we show that the distribution method outperforms the free-energy perturbation method and even the Bennett’s acceptance ratio method [ J. Comput. Phys. 22, 245 (1976) ] with the fastest convergence and the smallest relative errors. We further demonstrate the application of the distribution method with a simple point charge water model.
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64.10.+h General theory of equations of state and phase equilibria
05.70.Ce Thermodynamic functions and equations of state

Linear scaling multireference singles and doubles configuration interaction

Tsz S. Chwee, Andrew B. Szilva, Roland Lindh, and Emily A. Carter

J. Chem. Phys. 128, 224106 (2008); http://dx.doi.org/10.1063/1.2937443 (9 pages) | Cited 19 times

Online Publication Date: 13 June 2008

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A linear scaling multireference singles and doubles configuration interaction (MRSDCI) method has been developed. By using localized bases to span the occupied and virtual subspace, local truncation schemes can be applied in tandem with integral screening to reduce the various bottlenecks in a MRSDCI calculation. Among these, the evaluation of electron repulsion integrals and their subsequent transformation, together with the diagonalization of the large CI Hamiltonian matrix, correspond to the most computationally intensive steps in a MRSDCI calculation. We show that linear scaling is possible within each step. The scaling of the method with system size is explored with a system of linear alkane chains and we proceed to demonstrate this method can produce smooth potential energy surfaces via calculating the dissociation of trans-6-dodecene (C12H24) along the central C=C bond.
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31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
31.50.-x Potential energy surfaces

Block correlated coupled cluster method with a complete-active-space self-consistent-field reference function: The formula for general active spaces and its applications for multibond breaking systems

Tao Fang, Jun Shen, and Shuhua Li

J. Chem. Phys. 128, 224107 (2008); http://dx.doi.org/10.1063/1.2939014 (8 pages) | Cited 12 times

Online Publication Date: 13 June 2008

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The block correlated coupled cluster (BCCC) theory is developed for a general complete-active-space (CAS) self-consistent-field reference function. By truncating the cluster operator up to the four-block correlation level, we derive the spin orbital formulation of the CAS-BCCC4 approach. The CAS-BCCC4 approach is invariant to separate unitary transformation within active, occupied, and virtual orbitals. We have implemented the approach and applied this approach to describe the potential energy surfaces for bond breaking processes in C2 and N2 and for a simultaneous double bond dissociation in H2O. Numerical results show that the CAS-BCCC4 approach provides quite accurate descriptions for the entire dissociation process in each of the studied systems. The overall performance of the present approach is found to be better than that of the internally contracted multireference configuration interaction singles and doubles or complete-active-space second-order perturbation theory. The size-extensivity error is found to be relatively small for N2.
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31.15.bw Coupled-cluster theory
31.15.xr Self-consistent-field methods
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
31.15.xp Perturbation theory
31.50.-x Potential energy surfaces
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Electron paramagnetic resonance spectrum of the FCO2 radical isolated in noble gas matrices

H. Beckers, H. Willner, D. Grote, W. Sander, and J. Geier

J. Chem. Phys. 128, 224301 (2008); http://dx.doi.org/10.1063/1.2933462 (7 pages) | Cited 5 times

Online Publication Date: 10 June 2008

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The EPR spectra of the fluoroformyloxyl radical FCO2 isolated in noble gas matrices at temperatures from 5 to 30 K have been investigated. This study provides principal g values and 19F hyperfine coupling constants of FCO2 measured in Ar matrices at 5 K, and yields isotropic values at 30 K. A detailed analysis of the coupling parameters obtained from the EPR and a concomitant high resolution spectroscopic MMW study supported by quantum chemical calculations rationalized the fine and hyperfine interactions of this simple fluorooxyl radical.
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76.30.Rn Free radicals
71.70.Jp Nuclear states and interactions

Detailed study of fine and hyperfine structures in rotational spectra of the free fluoroformyloxyl radical FCO2⋅

Lucie Kolesniková, Juraj Varga, Helmut Beckers, Marie Šimečková, Zdeněk Zelinger, Lucie Nová Stříteská, Patrik Kania, Helge Willner, and Štěpán Urban

J. Chem. Phys. 128, 224302 (2008); http://dx.doi.org/10.1063/1.2933499 (8 pages) | Cited 6 times

Online Publication Date: 10 June 2008

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More than 160 new hyperfine components of rotational transitions of the free fluoroformyloxyl radical FCO2⋅ have been measured using the Prague millimeter wave high resolution spectrometer. The frequencies of these transitions together with the previously measured data were analyzed in detail and precise values of magnetic hyperfine and fine parameters were obtained. These new parameters significantly improve the values of previously determined hyperfine parameters which were rather unreliable. The new fine and hyperfine parameters obtained in this study are compatible with those of the simultaneously electron paramagnetic resonance study. Besides that, significantly improved ground state rotational and centrifugal distortion constants of the fluoroformyloxyl radical were derived.
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33.15.Pw Fine and hyperfine structure
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Sn Rotational analysis
33.20.Bx Radio-frequency and microwave spectra
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Structure and bonding of the MCN molecules, M = Cu,Ag,Au,Rg

Patryk Zaleski-Ejgierd, Michael Patzschke, and Pekka Pyykkö

J. Chem. Phys. 128, 224303 (2008); http://dx.doi.org/10.1063/1.2937148 (5 pages) | Cited 9 times

Online Publication Date: 10 June 2008

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High-precision calculations are reported for the title series with M = Cu, Ag, Au, using CCSD(T) with the latest pseudopotentials and basis sets up to cc-pVQZ. The bond lengths for M = Cu, Ag, Au agree with experiment within better than 1 pm. The role of deep-core excitations is studied. The second-order spin-orbit effects are evaluated at the density functional theory level, including M = Rg. A qualitative bonding analysis suggests multiple M–C bonding. The calculated vibrational frequencies are expected to be more accurate than the available experimental estimates. The M–C bond lengths obey Cu<Rg<Au<Ag.
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33.15.Dj Interatomic distances and angles
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Bh General molecular conformation and symmetry; stereochemistry
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)

Cold and ultracold chemical reactions of F+HCl and F+DCl

Goulven Quéméner and Naduvalath Balakrishnan

J. Chem. Phys. 128, 224304 (2008); http://dx.doi.org/10.1063/1.2928804 (11 pages) | Cited 17 times

Online Publication Date: 10 June 2008

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We report quantum dynamics calculations of F(2P)+HCl(v,j)→HF(v′,j′)+Cl(2P) and F+DCl(v,j)→DF(v′,j′)+Cl reactions at cold and ultracold temperatures. The effect of rotational and vibrational excitations of the HCl molecule on the reactivity is investigated. It is found that, in the ultracold regime, vibrational excitation of the HCl molecule from v = 0 to v = 2 enhances the reactivity by four orders of magnitude. The rotational excitation from j = 0 to j = 1 decreases the reactivity while the rotational excitation from j = 0 to j = 2 increases the reactivity. The overall effect of rotational excitation was found to be much smaller than vibrational excitation. The reactivity of the F+DCl system is significantly lower than that of the F+HCl case indicating the importance of quantum tunneling at low energies. For both reactions, Feshbach resonances corresponding to F⋯ HCl or F⋯DCl triatomic states occur at low energies. We also explored the validity of the coupled-states approximation for cold collisions taking the F+HCl(v = 0,j = 0) reaction as an illustrative example. It is found that the coupled-states approximation is generally valid for the background scattering even at low energies but it is inadequate to accurately describe the rich resonances in the energy dependence of the cross section resulting from the decay of van der Waals complexes. It is further shown that the coupled-states approximation cannot be used for scattering in the Wigner threshold regime when the molecule is initially in a rotationally excited level.
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.20.Rp State to state energy transfer
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.50.Df Potential energy surfaces for excited electronic states

State-selective predissociation dynamics of methylamines: The vibronic and H/D effects on the conical intersection dynamics

Doo-Sik Ahn, Jeongmook Lee, Jeong-Mo Choi, Kyoung-Seok Lee, Sun Jong Baek, Kunhye Lee, Kyoung-Koo Baeck, and Sang Kyu Kim

J. Chem. Phys. 128, 224305 (2008); http://dx.doi.org/10.1063/1.2937451 (7 pages) | Cited 12 times

Online Publication Date: 11 June 2008

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The photodissociation dynamics of methylamines (CH3NH2 and CD3ND2) on the first electronically excited state has been investigated using the velocity map ion imaging technique probing the H or D fragment. Two distinct velocity components are found in the H(D) translational energy distribution, implying the existence of two different reaction pathways for the bond dissociation. The high H(D) velocity component with the small internal energy of the radical fragment is ascribed to the N–H(D) fragmentation via the coupling of S1 to the upper-lying S2 repulsive potential energy surface along the N–H(D) bond elongation axis. Dissociation on the ground S0 state prepared via the nonadiabatic dynamics at the conical intersection should be responsible for the slow H(D) fragment. Several S1 vibronic states of methylamines including the zero-point level and nν9 states (n = 1, 2, or 3) are exclusively chosen in order to explore the effect of the initial quantum content on the chemical reaction dynamics. The branching ratio of the fast and slow components is found to be sensitive to the initial vibronic state for the N–H bond dissociation of CH3NH2, whereas it is little affected in the N–D dissociation event of CD3ND2. The fast component is found to be more dominant in the translational distribution of D from CD3ND2 than it is in that of H from CH3NH2. The experimental result is discussed with a plausible mechanism of the conical intersection dynamics.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
31.50.Df Potential energy surfaces for excited electronic states
82.20.Kh Potential energy surfaces for chemical reactions
33.80.Gj Diffuse spectra; predissociation, photodissociation

Water line lists close to experimental accuracy using a spectroscopically determined potential energy surface for H216O, H217O, and H218O

Sergei V. Shirin, Nikolay F. Zobov, Roman I. Ovsyannikov, Oleg L. Polyansky, and Jonathan Tennyson

J. Chem. Phys. 128, 224306 (2008); http://dx.doi.org/10.1063/1.2927903 (10 pages) | Cited 15 times

Online Publication Date: 11 June 2008

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Line lists of vibration-rotation transitions for the H216O, H217O, and H218O isotopologues of the water molecule are calculated, which cover the frequency region of 0–20 000 cm−1 and with rotational states up to J = 20 (J = 30 for H216O). These variational calculations are based on a new semitheoretical potential energy surface obtained by morphing a high accuracy ab initio potential using experimental energy levels. This potential reproduces the energy levels with J = 0, 2, and 5 used in the fit with a standard deviation of 0.025 cm−1. Linestrengths are obtained using an ab initio dipole moment surface. That these line lists make an excellent starting point for spectroscopic modeling and analysis of rotation-vibration spectra is demonstrated by comparison with recent measurements of Lisak and Hodges [J. Mol. Spectrosc. (unpublished)]: assignments are given for the seven unassigned transitions and the intensity of the strong lines are reproduced to with 3%. It is suggested that the present procedure may be a better route to reliable line intensities than laboratory measurements.
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33.70.Jg Line and band widths, shapes, and shifts
33.20.Vq Vibration-rotation analysis
31.50.-x Potential energy surfaces
31.15.A- Ab initio calculations
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Nonadiabatic electron dynamics in the exit channel of Na-molecule optical collisions

F. Rebentrost, C. Figl, R. Goldstein, O. Hoffmannn, D. Spelsberg, and J. Grosser

J. Chem. Phys. 128, 224307 (2008); http://dx.doi.org/10.1063/1.2928716 (9 pages)

Online Publication Date: 11 June 2008

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We study optical collisions of Na atoms with N2, CO, C2H2, and CO2 molecules in a crossed-beam experiment. Excited electronic states of the collision complex are selectively populated during the collision. We measure the relative population of the Na(3p) fine-structure levels after the collision and observe in this way the nonadiabatic transitions occuring in the final phase of the collision process. For the NaCO, NaC2H2, and NaCO2 systems new ab initio potential surfaces were generated. The theoretical analysis of the nonadiabatic electron dynamics on the excited potential surfaces is made within the classical-path formalism. The results are in good qualitative agreement with the experimental data and provide insight into the nonadiabatic mechanisms prevailing during the evolution in the upper 3p manifold. The differences between the different collisional systems are related to the presence and system-specific locations of conical intersections and avoided crossing seams in the excited potential surfaces.
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34.50.-s Scattering of atoms and molecules
31.50.Df Potential energy surfaces for excited electronic states
32.10.Fn Fine and hyperfine structure
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure
31.50.Gh Surface crossings, non-adiabatic couplings

Low-temperature inelastic collisions between hydrogen molecules and helium atoms

G. Tejeda, F. Thibault, J. M. Fernández, and S. Montero

J. Chem. Phys. 128, 224308 (2008); http://dx.doi.org/10.1063/1.2938366 (11 pages) | Cited 2 times

Online Publication Date: 11 June 2008

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Inelastic H2:He collisions are studied from the experimental and theoretical points of view between 22 and 180 K. State-to-state cross sections and rates are calculated at the converged close-coupling level employing recent potential energy surfaces (PES): The MR-PES [J. Chem. Phys. 100, 4336 (1994) ], and the MMR-PES and BMP-PESs [J. Chem. Phys. 119, 3187 (2003) ]. The fundamental rates k2→0 and k3→1 for H2:He collisions are assessed experimentally on the basis of a master equation describing the time evolution of rotational populations of H2 in the vibrational ground state. These populations are measured in the paraxial region of supersonic jets of H2+He mixtures by means of high-sensitivity and high spatial resolution Raman spectroscopy. Good agreement between theory and experiment is found for the k2→0 rate derived from the MR-PES, but not for the BMP-PES. For the k3→1 rate, which is about one-third to one-half of k2→0, the result is less conclusive. The experimental k3→1 rate is compatible within experimental error with the values calculated from both PESs. In spite of this uncertainty, the global consistence of experiment and theory in the framework of Boltzmann equation supports the MR-PES and MMR-PESs, and the set of gas-dynamic equations employed to describe the paraxial region of the jet at a molecular level.
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34.50.Ez Rotational and vibrational energy transfer
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
33.15.Mt Rotation, vibration, and vibration-rotation constants

Spectroscopy, dissociation dynamics, and potential energy surfaces for CN(A)−Ar

Jiande Han, Michael C. Heaven, and Udo Schnupf

J. Chem. Phys. 128, 224309 (2008); http://dx.doi.org/10.1063/1.2936123 (9 pages) | Cited 3 times

Online Publication Date: 12 June 2008

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The A 2Π-X 2Σ+ band system of CN–Ar has been examined using fluorescence depletion and action spectroscopy techniques. Eight vibronic bands of the complex were observed in association with the monomer 3-0 transition. Pump-probe measurements were used to characterize CN(A 2Π3/2,ν = 3) fragments from direct photodissociation of CN(A 2Π,ν = 3)−Ar and CN(X 2Σ+,ν = 7) fragments from CN(A 2Π,ν = 3)−Ar predissociation. The latter showed a marked preference for population of positive parity diatomic rotational levels. Bound state calculations were used to assign the A-X bands and to obtain fitted potential energy surfaces for the A state. The average potential obtained from fitting had a well depth of De = 137.8 cm−1. High-level ab initio calculations were used to obtain equilibrium Jacobi coordinates of θe = 94° and Re = 7.25 bohr. The near-symmetric character of the fitted potential energy surface was consistent with the symmetry preference observed in the predissociation dynamics.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
34.20.Gj Intermolecular and atom-molecule potentials and forces
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.50.Dq Fluorescence and phosphorescence spectra
31.15.A- Ab initio calculations

Resonance Raman and theoretical investigation of the photodissociation dynamics of benzamide in S3 state

Ke-Mei Pei, Yufang Ma, and Xuming Zheng

J. Chem. Phys. 128, 224310 (2008); http://dx.doi.org/10.1063/1.2938373 (10 pages) | Cited 3 times

Online Publication Date: 12 June 2008

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Resonance Raman spectra were obtained for benzamide in methanol and acetonitrile solutions with excitation wavelengths in resonance with the S3 state. These spectra indicate that the Franck–Condon region photodissociation dynamics have multidimensional character with the motions mainly along the benzene ring C=C stretch ν9, the Ph–CO–NH2 and ring benzene stretch ν14, the CCH in plane bend ν17, the Ph–CO–NH2 stretch and NH2 rock ν19, the ring trigonal bend ν23, and the ring deformation and Ph–CO–NH2 stretch ν29. A preliminary resonance Raman intensity analysis was done, and the results were compared to those previously reported for acetophenone to examine the substituent effect. Solvent effect on the short-time photodissociation dynamics of benzamide was also examined. A conical intersection point S2/S3 between S3 and S2 potential energy surfaces of benzamide was determined by using a complete active space self-consistent field theory computations. The structural differences and similarities between S3/S2 point and S0 were examined, and the results were used to correlate to the Franck–Condon photodissociation dynamics of benzamide in S3 state.
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82.50.-m Photochemistry
78.30.Jw Organic compounds, polymers
82.80.Gk Analytical methods involving vibrational spectroscopy
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Wt Computational modeling; simulation

Effective method for the computation of optical spectra of large molecules at finite temperature including the Duschinsky and Herzberg–Teller effect: The Qx band of porphyrin as a case study

Fabrizio Santoro, Alessandro Lami, Roberto Improta, Julien Bloino, and Vincenzo Barone

J. Chem. Phys. 128, 224311 (2008); http://dx.doi.org/10.1063/1.2929846 (17 pages) | Cited 37 times

Online Publication Date: 12 June 2008

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The authors extend their recent method for the computation of vibrationally resolved optical spectra of large molecules, including both the Duschinsky rotation and the effect of finite temperature in the framework of the Franck–Condon (FC) approximation, to deal with the more general case of the Herzberg–Teller (HT) model, where also the linear dependence of the transition dipole moment on the nuclear coordinates is taken into account. This generalization allows us to investigate weak and vibronically allowed transitions by far extending the range of application of the method. The calculation of the spectra of sizable molecules is computationally demanding because of the huge number of final vibrational states that must be taken into account, and the inclusion of HT terms further increases the computational burden. The method presented here automatically selects the relevant vibronic contributions to the spectrum, independent of their frequency, and it is able to provide fully converged spectra with a modest computational requirement. The effectiveness of the method is illustrated by computing the HT absorption and fluorescence Qx spectra of free-base porphyrin both at T = 0 K and at room temperature, performing for the first time an exact treatment of vibrations in harmonic approximation. Qx spectra are compared to experiments and FC/HT interferences are analyzed in detail.
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33.20.Kf Visible spectra
33.20.Lg Ultraviolet spectra
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.20.Tp Vibrational analysis
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.50.Dq Fluorescence and phosphorescence spectra

Vibrational cooling of spin-stretched dimer states by He buffer gas: Quantum calculations for Li2(a 3Σu+) at ultralow energies

S. Bovino, E. Bodo, E. Yurtsever, and F. A. Gianturco

J. Chem. Phys. 128, 224312 (2008); http://dx.doi.org/10.1063/1.2933405 (6 pages) | Cited 5 times

Online Publication Date: 12 June 2008

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The interaction between the triplet state of the lithium dimer, 7Li2, with 4He is obtained from accurate ab initio calculations where the vibrational dependence of the potential is newly computed. Vibrational quenching dynamics within a coupled-channel quantum treatment is carried out at ultralow energies, and large differences in efficiency as a function of the initial vibrational state of the targets are found as one compares the triplet results with those of the singlet state of the same target.
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31.15.A- Ab initio calculations
31.50.Df Potential energy surfaces for excited electronic states
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.50.-x Potential energy surfaces
34.50.Ez Rotational and vibrational energy transfer
34.20.Gj Intermolecular and atom-molecule potentials and forces
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Directional states of symmetric-top molecules produced by combined static and radiative electric fields

Marko Härtelt and Bretislav Friedrich

J. Chem. Phys. 128, 224313 (2008); http://dx.doi.org/10.1063/1.2929850 (19 pages) | Cited 6 times

Online Publication Date: 12 June 2008

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We show that combined electrostatic and radiative fields can greatly amplify the directional properties, such as axis orientation and alignment, of symmetric top molecules. In our computational study, we consider all four symmetry combinations of the prolate and oblate inertia and polarizability tensors, as well as the collinear and perpendicular (or tilted) geometries of the two fields. In, respectively, the collinear or perpendicular fields, the oblate or prolate polarizability interaction due to the radiative field forces the permanent dipole into alignment with the static field. Two mechanisms are found to be responsible for the amplification of the molecules’ orientation, which ensues once the static field is turned on: (a) permanent-dipole coupling of the opposite-parity tunneling doublets created by the oblate polarizability interaction in collinear static and radiative fields and (b) hybridization of the opposite parity states via the polarizability interaction and their coupling by the permanent dipole interaction to the collinear or perpendicular static field. In perpendicular fields, the oblate polarizability interaction, along with the loss of cylindrical symmetry, is found to preclude the wrong-way orientation, causing all states to become high-field seeking with respect to the static field. The adiabatic labels of the states in the tilted fields depend on the adiabatic path taken through the parameter space comprised of the permanent and induced-dipole interaction parameters and the tilt angle between the two field vectors.
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33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.-p Calculations and mathematical techniques in atomic and molecular physics

Full-dimensional quantum calculations of ground-state tunneling splitting of malonaldehyde using an accurate ab initio potential energy surface

Yimin Wang, Bastiaan J. Braams, Joel M. Bowman, Stuart Carter, and David P. Tew

J. Chem. Phys. 128, 224314 (2008); http://dx.doi.org/10.1063/1.2937732 (9 pages) | Cited 26 times

Online Publication Date: 12 June 2008

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Quantum calculations of the ground vibrational state tunneling splitting of H-atom and D-atom transfer in malonaldehyde are performed on a full-dimensional ab initio potential energy surface (PES). The PES is a fit to 11 147 near basis-set-limit frozen-core CCSD(T) electronic energies. This surface properly describes the invariance of the potential with respect to all permutations of identical atoms. The saddle-point barrier for the H-atom transfer on the PES is 4.1 kcal/mol, in excellent agreement with the reported ab initio value. Model one-dimensional and “exact” full-dimensional calculations of the splitting for H- and D-atom transfer are done using this PES. The tunneling splittings in full dimensionality are calculated using the unbiased “fixed-node” diffusion Monte Carlo (DMC) method in Cartesian and saddle-point normal coordinates. The ground-state tunneling splitting is found to be 21.6 cm−1 in Cartesian coordinates and 22.6 cm−1 in normal coordinates, with an uncertainty of 2–3 cm−1. This splitting is also calculated based on a model which makes use of the exact single-well zero-point energy (ZPE) obtained with the MULTIMODE code and DMC ZPE and this calculation gives a tunneling splitting of 21–22 cm−1. The corresponding computed splittings for the D-atom transfer are 3.0, 3.1, and 2–3 cm−1. These calculated tunneling splittings agree with each other to within less than the standard uncertainties obtained with the DMC method used, which are between 2 and 3 cm−1, and agree well with the experimental values of 21.6 and 2.9 cm−1 for the H and D transfer, respectively.
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82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Kh Potential energy surfaces for chemical reactions

Density functional study of CO adsorption on Scn (n = 2–13) clusters

Guangfen Wu, Jinlan Wang, Yiming Lu, and Mingli Yang

J. Chem. Phys. 128, 224315 (2008); http://dx.doi.org/10.1063/1.2938377 (10 pages) | Cited 6 times

Online Publication Date: 13 June 2008

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The adsorption properties of a single CO molecule on Scn (n = 2–13) clusters are studied by means of a density functional theory with the generalized gradient approximation. Two adsorption patterns are identified. Pattern a (n = 3, 4, 6, 8, 11, and 12), CO binds to hollow site while Pattern b (n = 5, 7, 9, 10, and 13), CO binds to bridge site accompanied by significantly lengthening of the Sc–Sc bond. The adsorption energy exhibits clear size-dependent variation and odd-even oscillation for n<10 and reach the peak at n = 5, 7, and 9, implying their high chemical reactivity. Similar variations are noted in C–O bond length, vibrational frequency, and charge transferred between CO and the clusters. This can be understood in light of the adsorption pattern, the atomic motif, and the relative stability of the bare Sc clusters. Compared with the free Sc clusters, the magnetic nature remains upon adsorption except n = 2, 4, 12, and 13. Particularly, the moments of n = 13 reduce significantly from 19 to 5μB, implying the adsorption plays an attenuation influence on the magnetism of the cluster.
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68.43.Mn Adsorption kinetics
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
75.30.Cr Saturation moments and magnetic susceptibilities
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