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28 Dec 2011

Volume 135, Issue 24, Articles (24xxxx)

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J. Chem. Phys. 135, 244701 (2011); http://dx.doi.org/10.1063/1.3660673 (22 pages)

Max C. Watson, Evgeni S. Penev, Paul M. Welch, and Frank L. H. Brown
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Communication: Manipulating the singlet-triplet equilibrium in organic biradical materials

Ö. Günaydın-Şen, J. Fosso-Tande, P. Chen, J. L. White, T. L. Allen, J. Cherian, T. Tokumoto, P. M. Lahti, S. McGill, R. J. Harrison, and J. L. Musfeldt

J. Chem. Phys. 135, 241101 (2011); http://dx.doi.org/10.1063/1.3672101 (4 pages)

Online Publication Date: 27 December 2011

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We investigated the tunability of the singlet-triplet equilibrium population in the organic biradical 1,4-phenylenedinitrene via magneto-optical spectroscopy. A rich magnetochromic response occurs because applied field increases the concentration of the triplet state species, which has a unique optical signature by comparison with the singlet biradical and the precursor molecule. A Curie-like analysis of the magneto-optical properties allows us to extract the spin gap, which is smaller than previously supposed. These measurements establish the value of local-probe photophysical techniques for magnetic property determination in open-shell systems such as biradicals where a traditional electron paramagnetic resonance Curie law analysis has intrinsic limitations.
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82.50.Hp Processes caused by visible and UV light
33.80.Eh Autoionization, photoionization, and photodetachment
33.57.+c Magneto-optical and electro-optical spectra and effects
31.15.vj Electron correlation calculations for atoms and ions: excited states
31.15.vq Electron correlation calculations for polyatomic molecules
31.15.ee Time-dependent density functional theory
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Communication: Spectroscopic phase and lineshapes in high-resolution broadband sum frequency vibrational spectroscopy: Resolving interfacial inhomogeneities of “identical” molecular groups

Luis Velarde, Xian-yi Zhang, Zhou Lu, Alan G. Joly, Zheming Wang, and Hong-fei Wang

J. Chem. Phys. 135, 241102 (2011); http://dx.doi.org/10.1063/1.3675629 (4 pages)

Online Publication Date: 29 December 2011

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The ability to achieve sub-wavenumber resolution (0.6 cm−1) and a large signal-to-noise ratio in high-resolution broadband sum-frequency generation vibrational spectroscopy (HR-BB-SFG-VS) allows for the detailed SFG spectral lineshapes to be used in the unambiguous determination of fine spectral features. Changes in the structural spectroscopic phase in SFG-VS as a function of beam polarization and experimental geometry proved to be instrumental in the identification of an unexpected 2.78 ± 0.07 cm−1 spectral splitting for the two methyl groups at the vapor/dimethyl sulfoxide (DMSO, (CH3)2SO) liquid interface as well as in the determination of their orientational angles.
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33.70.Jg Line and band widths, shapes, and shifts
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Mt Rotation, vibration, and vibration-rotation constants
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Communication: The reason why +c ZnO surface is less stable than −c ZnO surface: First-principles calculation

Seitaro Ito, Tomomi Shimazaki, Momoji Kubo, Hideomi Koinuma, and Masatomo Sumiya

J. Chem. Phys. 135, 241103 (2011); http://dx.doi.org/10.1063/1.3675680 (4 pages) | Cited 1 time

Online Publication Date: 29 December 2011

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It has been experimentally shown that an O(−c)-polar ZnO surface is more stable than a Zn(+c)-polar surface in H2 ambient. We applied first-principles calculations to investigating the polarity dependence on the stability at the electronic level. The calculations revealed that the −c surface terminated with H atom was stable maintaining a wurtzite structure, whereas the +c surface was unstable due to the change of coordination numbers of Zn at the topmost surface from four (wurtzite) to six (rock salt). This causes the generation of O2 molecules, resulting in instability at the +c surface.
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68.35.bg Semiconductors
68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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back to top Theoretical Methods and Algorithms

Localization scheme for relativistic spinors

J. Ciupka, M. Hanrath, and M. Dolg

J. Chem. Phys. 135, 244101 (2011); http://dx.doi.org/10.1063/1.3670415 (11 pages)

Online Publication Date: 22 December 2011

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A new method to determine localized complex-valued one-electron functions in the occupied space is presented. The approach allows the calculation of localized orbitals regardless of their structure and of the entries in the spinor coefficient matrix, i.e., one-, two-, and four-component Kramers-restricted or unrestricted one-electron functions with real or complex expansion coefficients. The method is applicable to localization schemes that maximize (or minimize) a functional of the occupied spinors and that use a localization operator for which a matrix representation is available. The approach relies on the approximate joint diagonalization (AJD) of several Hermitian (symmetric) matrices which is utilized in electronic signal processing. The use of AJD in this approach has the advantage that it allows a reformulation of the localization criterion on an iterative 2 × 2 pair rotating basis in an analytical closed form which has not yet been described in the literature for multi-component (complex-valued) spinors. For the one-component case, the approach delivers the same Foster-Boys or Pipek-Mezey localized orbitals that one obtains from standard quantum chemical software, whereas in the multi-component case complex-valued spinors satisfying the selected localization criterion are obtained. These localized spinors allow the formulation of local correlation methods in a multi-component relativistic framework, which was not yet available. As an example, several heavy and super-heavy element systems are calculated using a Kramers-restricted self-consistent field and relativistic two-component pseudopotentials in order to investigate the effect of spin-orbit coupling on localization.
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31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
31.15.xr Self-consistent-field methods

Unambiguous optimization of effective potentials in finite basis sets

Christoph R. Jacob

J. Chem. Phys. 135, 244102 (2011); http://dx.doi.org/10.1063/1.3670414 (16 pages)

Online Publication Date: 23 December 2011

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The optimization of effective potentials is of interest in density-functional theory (DFT) in two closely related contexts. First, the evaluation of the functional derivative of orbital-dependent exchange-correlation functionals requires the application of optimized effective potential methods. Second, the optimization of the effective local potential that yields a given electron density is important both for the development of improved approximate functionals and for the practical application of embedding schemes based on DFT. However, in all cases this optimization turns into an ill-posed problem if a finite basis set is introduced for the Kohn–Sham orbitals. So far, this problem has not been solved satisfactorily. Here, a new approach to overcome the ill-posed nature of such finite-basis set methods is presented for the optimization of the effective local potential that yields a given electron density. This new scheme can be applied with orbital basis sets of reasonable size and makes it possible to vary the basis sets for the orbitals and for the potential independently, while providing an unambiguous potential that systematically approaches the numerical reference.
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31.15.eg Exchange-correlation functionals (in current density functional theory)

Exact on-lattice stochastic reaction-diffusion simulations using partial-propensity methods

Rajesh Ramaswamy and Ivo F. Sbalzarini

J. Chem. Phys. 135, 244103 (2011); http://dx.doi.org/10.1063/1.3666988 (17 pages)

Online Publication Date: 23 December 2011

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Stochastic reaction-diffusion systems frequently exhibit behavior that is not predicted by deterministic simulation models. Stochastic simulation methods, however, are computationally expensive. We present a more efficient stochastic reaction-diffusion simulation algorithm that samples realizations from the exact solution of the reaction-diffusion master equation. The present algorithm, called partial-propensity stochastic reaction-diffusion (PSRD) method, uses an on-lattice discretization of the reaction-diffusion system and relies on partial-propensity methods for computational efficiency. We describe the algorithm in detail, provide a theoretical analysis of its computational cost, and demonstrate its computational performance in benchmarks. We then illustrate the application of PSRD to two- and three-dimensional pattern-forming Gray-Scott systems, highlighting the role of intrinsic noise in these systems.
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82.20.Wt Computational modeling; simulation
82.20.Fd Collision theories; trajectory models

Analytic second derivatives for the spin-free exact two-component theory

Lan Cheng and Jürgen Gauss

J. Chem. Phys. 135, 244104 (2011); http://dx.doi.org/10.1063/1.3667202 (8 pages) | Cited 1 time

Online Publication Date: 23 December 2011

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The formulation and implementation of the spin-free (SF) exact two-component (X2c) theory at the one-electron level (SFX2c-1e) is extended in the present work to the analytic evaluation of second derivatives of the energy. In the X2c-1e scheme, the four-component one-electron Dirac Hamiltonian is block diagonalized in its matrix representation and the resulting “electrons-only” two-component Hamiltonian is then used together with untransformed two-electron interactions. The derivatives of the two-component Hamiltonian can thus be obtained by means of simple manipulations of the parent four-component Hamiltonian integrals and derivative integrals. The SF version of X2c-1e can furthermore exploit available nonrelativistic quantum-chemical codes in a straightforward manner. As a first application of analytic SFX2c-1e second derivatives, we report a systematic study of the equilibrium geometry and vibrational frequencies for the bent ground state of the copper hydroxide (CuOH) molecule. Scalar-relativistic, electron-correlation, and basis-set effects on these properties are carefully assessed.
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31.15.vq Electron correlation calculations for polyatomic molecules
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.20.Tp Vibrational analysis

Computing the energy of a water molecule using multideterminants: A simple, efficient algorithm

Bryan K. Clark, Miguel A. Morales, Jeremy McMinis, Jeongnim Kim, and Gustavo E. Scuseria

J. Chem. Phys. 135, 244105 (2011); http://dx.doi.org/10.1063/1.3665391 (9 pages)

Online Publication Date: 27 December 2011

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Quantum Monte Carlo (QMC) methods such as variational Monte Carlo and fixed node diffusion Monte Carlo depend heavily on the quality of the trial wave function. Although Slater-Jastrow wave functions are the most commonly used variational ansatz in electronic structure, more sophisticated wave functions are critical to ascertaining new physics. One such wave function is the multi-Slater-Jastrow wave function which consists of a Jastrow function multiplied by the sum of Slater determinants. In this paper we describe a method for working with these wave functions in QMC codes that is easy to implement, efficient both in computational speed as well as memory, and easily parallelized. The computational cost scales quadratically with particle number making this scaling no worse than the single determinant case and linear with the total number of excitations. Additionally, we implement this method and use it to compute the ground state energy of a water molecule.
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31.15.ep Variational particle-number approach

Rigorous formulation of two-parameter double-hybrid density-functionals

Emmanuel Fromager

J. Chem. Phys. 135, 244106 (2011); http://dx.doi.org/10.1063/1.3671384 (8 pages) | Cited 1 time

Online Publication Date: 28 December 2011

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A two-parameter extension of the density-scaled double hybrid approach of Sharkas et al. [J. Chem. Phys. 134, 064113 (2011)] is presented. It is based on the explicit treatment of a fraction of multideterminantal exact exchange. The connection with conventional double hybrids is made when neglecting density scaling in the correlation functional as well as second-order corrections to the density. In this context, the fraction ac of second-order Møller-Plesset (MP2) correlation energy is not necessarily equal to the square of the fraction ax of Hartree-Fock exchange. More specifically, it is shown that ac ≤ ax2, a condition that conventional semi-empirical double hybrids actually fulfill. In addition, a new procedure for calculating the orbitals, which has a better justification than the one routinely used, is proposed. Referred to as λ1 variant, the corresponding double hybrid approximation has been tested on a small set consisting of H2, N2, Be2, Mg2, and Ar2. Three conventional double hybrids (B2-PLYP, B2GP-PLYP, and PBE0-DH) have been considered. Potential curves obtained with λ1- and regular double hybrids can, in some cases, differ significantly. In particular, for the weakly bound dimers, the λ1 variants bind systematically more than the regular ones, which is an improvement in many but not all cases. Including density scaling in the correlation functionals may of course change the results significantly. Moreover, optimized effective potentials based on a partially-interacting system could also be used to generate proper orbitals. Work is currently in progress in those directions.
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31.15.E- Density-functional theory
31.15.xr Self-consistent-field methods
31.50.-x Potential energy surfaces

A novel method to describe the interaction pressure between charged plates with application of the weighted correlation approach

Zhao Wang, Longcheng Liu, and Ivars Neretnieks

J. Chem. Phys. 135, 244107 (2011); http://dx.doi.org/10.1063/1.3672001 (14 pages)

Online Publication Date: 29 December 2011

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Based on the Euler–Lagrange equation for ion density distribution in an inhomogeneous, charged, and hard-sphere fluid, a novel method is proposed to determine the interaction pressure between charged plates. The resulting expression is a sum of distinct physical contributions to the pressure, which involves different contributions to the single-particle direct correlation function. It can, therefore, be conveniently used in any density functional approach to facilitate analysis of the pressure components. In this study, the so-called fundamental measure theory (FMT)/weighted correlation approach (WCA) approach is applied to estimate both the hard-sphere and the electric residual contributions to the single-particle direct correlation function, upon the calculation of the ionic density profiles between charged plates. The results, against the Monte Carlo simulations, show that the FMT/WCA approach is superior to the typical FMT/mean spherical approximation approach of the density functional theory in predicting the interaction pressure between charged plates immersed in an electrolyte solution upon various conditions in the primitive model. The FMT/WCA approach can well capture the fine features of the pressure-separation dependence, to reproduce not only the shoulder shape and the weak attractions in monovalent electrolytes but also the strongly oscillatory behavior of pressure in divalent electrolytes where pronounced attractions are observed. In addition, it is found that the FMT/WCA approach even has an advantage over the anisotropic, hyper-netted chain approach in that it agrees with the Monte Carlo results to a very good extent with, however, much less computational effort.
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05.20.-y Classical statistical mechanics
05.10.Ln Monte Carlo methods
02.50.-r Probability theory, stochastic processes, and statistics
82.45.Gj Electrolytes

Anisotropy effect on global minimum structures of clusters: Two-center Lennard-Jones model

Yan Feng, Jing Wu, Longjiu Cheng, and Haiyan Liu

J. Chem. Phys. 135, 244108 (2011); http://dx.doi.org/10.1063/1.3672237 (7 pages)

Online Publication Date: 29 December 2011

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Using a two-center Lennard-Jones (2CLJ) model, the simplest anisotropic case, we investigated how anisotropy affects global minimum structures of clusters and obtained some interesting results. The anisotropy parameter, R, is defined as the ratio of the bond length of 2CLJ dimer to the LJ equilibrium pair separation, where a larger R value means higher anisotropy. For low R values, the structures resemble those of the Lennard-Jones atomic clusters. However, as the pairwise interaction becomes more anisotropic, the “magic numbers” change, and several novel cluster patterns emerge as particularly stable structures, and the global minima change from icosahedral, to polyicosahedral and to novel irregular structures. Moreover, increasing the anisotropy effectively softens the 2CLJ potential. Given the general importance of the LJ cluster as a simple model cluster, 2CLJ model can provide a straightforward and useful analysis of the effect of molecular shape on the structures of clusters.
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33.15.Dj Interatomic distances and angles
34.20.Gj Intermolecular and atom-molecule potentials and forces
36.40.-c Atomic and molecular clusters
33.15.Bh General molecular conformation and symmetry; stereochemistry

On a relationship between molecular polarizability and partial molar volume in water

Ekaterina L. Ratkova and Maxim V. Fedorov

J. Chem. Phys. 135, 244109 (2011); http://dx.doi.org/10.1063/1.3672094 (5 pages)

Online Publication Date: 30 December 2011

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We reveal a universal relationship between molecular polarizability (a single-molecule property) and partial molar volume in water that is an ensemble property characterizing solute-solvent systems. Since both of these quantities are of the key importance to describe solvation behavior of dissolved molecular species in aqueous solutions, the obtained relationship should have a high impact in chemistry, pharmaceutical, and life sciences as well as in environments. We demonstrated that the obtained relationship between the partial molar volume in water and the molecular polarizability has in general a non-homogeneous character. We performed a detailed analysis of this relationship on a set of ∼200 organic molecules from various chemical classes and revealed its fine well-organized structure. We found that this structure strongly depends on the chemical nature of the solutes and can be rationalized in terms of specific solute-solvent interactions. Efficiency and universality of the proposed approach was demonstrated on an external test set containing several dozens of polyfunctional and druglike molecules.
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33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.70.Dk Environmental and solvent effects

Quantum entanglement between electronic and vibrational degrees of freedom in molecules

Laura K. McKemmish, Ross H. McKenzie, Noel S. Hush, and Jeffrey R. Reimers

J. Chem. Phys. 135, 244110 (2011); http://dx.doi.org/10.1063/1.3671386 (11 pages)

Online Publication Date: 30 December 2011

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We consider the quantum entanglement of the electronic and vibrational degrees of freedom in molecules with tendencies towards double welled potentials. In these bipartite systems, the von Neumann entropy of the reduced density matrix is used to quantify the electron-vibration entanglement for the lowest two vibronic wavefunctions obtained from a model Hamiltonian based on coupled harmonic diabatic potential-energy surfaces. Significant entanglement is found only in the region in which the ground vibronic state contains a density profile that is bimodal (i.e., contains two separate local maxima). However, in this region two distinct types of density and entanglement profiles are found: one type arises purely from the degeneracy of energy levels in the two potential wells and is destroyed by slight asymmetry, while the other arises through strong interactions between the diabatic levels of each well and is relatively insensitive to asymmetry. These two distinct types are termed fragile degeneracy-induced entanglement and persistent entanglement, respectively. Six classic molecular systems describable by two diabatic states are considered: ammonia, benzene, BNB, pyridine excited triplet states, the Creutz-Taube ion, and the radical cation of the “special pair” of chlorophylls involved in photosynthesis. These chemically diverse systems are all treated using the same general formalism and the nature of the entanglement that they embody is elucidated.
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33.20.Tp Vibrational analysis
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
31.50.-x Potential energy surfaces

An algebraic operator approach to electronic structure

Neil Shenvi and Weitao Yang

J. Chem. Phys. 135, 244111 (2011); http://dx.doi.org/10.1063/1.3671388 (14 pages)

Online Publication Date: 30 December 2011

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In this paper, we introduce an algebraic approach to electronic structure calculations. Our approach constructs a Jordan algebra based on the second-quantized electronic Hamiltonian. From the structure factor of this algebra, we show that we can calculate the energy of the ground electronic state of the Hamiltonian operator. We apply our method to several generalized Hubbard models and show that we can usually obtain a significant fraction of the correlation energy for low-to-moderate values of the electronic repulsion parameter while still retaining the O(L3) scaling of the Hartree-Fock algorithm. This surprising result, along with several other observations, suggests that our algebraic approach represents a new paradigm for electronic structure calculations which opens up many new directions for research.
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31.15.xr Self-consistent-field methods
02.10.-v Logic, set theory, and algebra

Efficient electron dynamics with the planewave-based real-time time-dependent density functional theory: Absorption spectra, vibronic electronic spectra, and coupled electron-nucleus dynamics

Seung Kyu Min, Yeonchoo Cho, and Kwang S. Kim

J. Chem. Phys. 135, 244112 (2011); http://dx.doi.org/10.1063/1.3671952 (8 pages)

Online Publication Date: 30 December 2011

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The electron dynamics with complex third-order Suzuki-Trotter propagator (ST3) has been implemented into a planewave (PW) based density functional theory program, and several applications including linear absorption spectra and coupled electron-nucleus dynamics have been calculated. Since the ST3 reduces the number of Fourier transforms to less than half compared to the fourth-order Suzuki-Trotter propagator (ST4), more than twice faster calculations are possible by exploiting the ST3. We analyzed numerical errors of both the ST3 and the ST4 in the presence/absence of an external field for several molecules such as Al2, N2, and C2H4. We obtained that the ST3 gives the same order of numerical errors (10−5 Ry after 100 fs) as the ST4. Also, the time evolution of dipole moments, hence the absorption spectrum, is equivalent for both ST3 and ST4. As applications, the linear absorption spectrum for an ethylene molecule was studied. From the density difference analysis, we showed that the absorption peaks at 6.10 eV and 7.65 eV correspond to the π → 4ag and π → π* excitation bands, respectively. We also investigated the molecular vibrational effect to the absorption spectra of an ethylene molecule and the dynamics of a hydrogen molecule after the σ → σ* transition by formulating coupled electron-nucleus dynamics within the Ehrenfest regime. The trajectory of nuclei follows the excited state potential energy curve exactly.
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31.15.ee Time-dependent density functional theory
33.20.Tp Vibrational analysis
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.50.Df Potential energy surfaces for excited electronic states
33.20.Lg Ultraviolet spectra
33.20.Kf Visible spectra
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

High-resolution Fourier-transform extreme ultraviolet photoabsorption spectroscopy of 14N15N

A. N. Heays, G. D. Dickenson, E. J. Salumbides, N. de Oliveira, D. Joyeux, L. Nahon, B. R. Lewis, and W. Ubachs

J. Chem. Phys. 135, 244301 (2011); http://dx.doi.org/10.1063/1.3672165 (11 pages)

Online Publication Date: 22 December 2011

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The first comprehensive high-resolution photoabsorption spectrum of 14N15N has been recorded using the Fourier-transform spectrometer attached to the Desirs beamline at the Soleil synchrotron. Observations are made in the extreme ultraviolet and span 100 000–109 000 cm−1 (100–91.7 nm). The observed absorption lines have been assigned to 25 bands and reduced to a set of transition energies, f values, and linewidths. This analysis has verified the predictions of a theoretical model of N2 that simulates its photoabsorption and photodissociation cross section by solution of an isotopomer independent formulation of the coupled-channel Schrödinger equation. The mass dependence of predissociation linewidths and oscillator strengths is clearly evident and many local perturbations of transition energies, strengths, and widths within individual rotational series have been observed.
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33.20.Lg Ultraviolet spectra
33.70.Jg Line and band widths, shapes, and shifts
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
31.15.bw Coupled-cluster theory

Multiphoton dissociative ionization of tert-pentyl bromide near 265 nm

Rui Mao, Qun Zhang, Jianzheng Zang, Chao He, Min Chen, and Yang Chen

J. Chem. Phys. 135, 244302 (2011); http://dx.doi.org/10.1063/1.3671368 (6 pages)

Online Publication Date: 22 December 2011

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We report on the photodissociation dynamics of tert-pentyl bromide near 265 nm investigated by time-sliced velocity map imaging. The speed and angular distributions have been analyzed for both the ground-state Br(2P3/2) atom (denoted Br) and the spin–orbit excited-state Br(2P1/2) atom (denoted Br*). The speed distributions of Br and Br* atoms are all found to consist of three Gaussian components, which correlate to three independent dissociation pathways on the excited potential energy surfaces: (1) the high translational energy (ET) component from the prompt dissociation along the C–Br stretching mode, (2) the middle ET component from the repulsive mode along the C–Br stretching coupled with some bending motions, and (3) the low ET component from the repulsive mode along the C–Br stretching coupled with more bending motions. More interestingly, we have also observed the tert−C5H11+ ions in 263–267 nm. The near-zero kinetic energy distributions extracted from the three tert−C5H11+ images near 265 nm show the typical characteristics that are attributable to multiphoton dissociative ionization, suggesting the existence of a neutral superexcited state of the parent tert-pentyl bromide molecule. The contribution of bromine atoms formed in this dissociative ionization channel adds in the total relative distribution of low ET component in the Br*(Br) formation channel, which reasonably explains the abnormal distributions observed in between the middle and low ET components in the Br*(Br) formation channel.
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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)
31.50.Bc Potential energy surfaces for ground electronic states
31.50.Df Potential energy surfaces for excited electronic states

Ab initio calculations of the electronic states of AsH2 including dissociation characteristics

Aleksey B. Alekseyev, Robert J. Buenker, and Heinz–Peter Liebermann

J. Chem. Phys. 135, 244303 (2011); http://dx.doi.org/10.1063/1.3671374 (8 pages)

Online Publication Date: 23 December 2011

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Multireference configuration interaction calculations have been carried out for low-lying electronic states of AsH2. Bending potentials for the ten lowest states of AsH2 are obtained in C2v symmetry for As–H distances fixed at the the ground state equilibrium value of 2.845 a0, as well as for the minimum energy path constrained to R1 = R2. The calculated equilibrium geometries for the math2B1 ground state and the math2A1 excited state agree very well with the previous experimental and theoretical results, whereas the data for the higher-lying states are obtained for the first time. Asymmetric potential energy surface (PES) cuts (at R1 = 2.845 a0, θ = 90.7°) and two-dimensional (2D) PESs for the lowest three states are also new. The calculated ab initio data are used for analysis of possible AsH2 photodissociation channels and predissociation effects. It is shown that the math2A1−math2B1 transition dipole moment decreases with increasing bending angle, which influences the intensity distribution in the math(0,0,0)→math emission spectrum (v2′′ bending series), shifting its maximum to smaller v2′′ quantum numbers.
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31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.50.Df Potential energy surfaces for excited electronic states
33.80.Gj Diffuse spectra; predissociation, photodissociation

Rotational and vibrational energy transfer in vibrationally excited acetylene at energies near 6560 cm−1

Jiande Han, Keith Freel, and Michael C. Heaven

J. Chem. Phys. 135, 244304 (2011); http://dx.doi.org/10.1063/1.3671459 (11 pages)

Online Publication Date: 23 December 2011

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Collisional energy transfer kinetics of vibrationally excited acetylene has been examined for states with internal energies near 6560 cm−1. Total population removal rate constants were determined for selected rotational levels of the (1,0,1,00,00) and (0,1,1,20,00) states. Values in the range of (10–18) × 10−10 cm3 s−1 were obtained. Measurements of state-to-state rotational energy transfer rate constants were also carried out for these states. The rotational energy transfer kinetics was found to be consistent with simple energy gap models for the transfer probabilities. Vibrational transfer out of the (0,1,1,20,00) state accounted for no more than 16% of the total removal process. Transfer from (1,0,1,00,00) to the u-symmetry (0,2,0,31,1−1), (0,1,1,20,00), and (1,1,0,11,1−1) states was observed. Applying the principle of detailed balance to these data indicated that vibrational transfer to (1,0,1,00,00) accounted for ∼0.1% of the population loss from (0,2,0,31,1−1) or (0,1,1,20,00), and 3% of the loss from (1,1,0,11,1−1). Relative rotational transfer probabilities were obtained for transfer to the g-symmetry (1,1,0,20,00)/(0,0,2,00,00) dyad. These results are related to recent studies of optically pumped acetylene lasers.
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33.15.Mt Rotation, vibration, and vibration-rotation constants
33.80.Be Level crossing and optical pumping
31.15.vj Electron correlation calculations for atoms and ions: excited states

HNO3−NHx, H2SO4−NHx, CH(O)OH−NHx, and CH3C(O)OH−NHx complexes and their role in the formation of condensation nuclei

Jared Clark, Sambhav Kumbhani, Jaron C. Hansen, and Joseph S. Francisco

J. Chem. Phys. 135, 244305 (2011); http://dx.doi.org/10.1063/1.3664302 (11 pages)

Online Publication Date: 27 December 2011

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The formation of sulfuric acid (H2SO4), nitric acid (HNO3), acetic acid (CH3C(O)OH), and formic acid (HC(O))H) complexes with ammonia (NH3), amidogen radical (NH2), and imidogen radical (NH) was studied using natural bond orbital calculations. The equilibrium structures, binding energies, and harmonic frequencies were calculated for each acid-NHx complex using hybrid density functional (B3LYP) and second-order Møller-Plesset perturbation approximation methods with the 6-311++G(3df,3pd) basis set. The results presented here suggest that the effect of NH2 on the formation of new condensation nuclei will be similar to that of NH3, but to a lesser degree and confined primarily to complexes with H2SO4 and HNO3. The NH radical is not expected to play a significant role in the formation of new atmospheric condensation nuclei.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
31.15.E- Density-functional theory
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations

Zero kinetic energy photoelectron spectroscopy of jet cooled benzo[a]pyrene from resonantly enhanced multiphoton ionization

Jie Zhang, Colin Harthcock, Fangyuan Han, and Wei Kong

J. Chem. Phys. 135, 244306 (2011); http://dx.doi.org/10.1063/1.3672161 (7 pages)

Online Publication Date: 28 December 2011

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We report zero kinetic energy (ZEKE) photoelectron spectroscopy of benzo[a]pyrene (BaP) via resonantly enhanced multiphoton ionization (REMPI). Our analysis concentrates on the vibrational modes of the first excited state (S1) and those of the ground cationic state (D0). Similar to pyrene, another peri-condensed polycyclic aromatic hydrocarbon we have investigated, the first two electronically excited states of BaP exhibit extensive configuration interactions. However, the two electronic states are of the same symmetry, hence vibronic coupling does not introduce any out-of-plane modes in the REMPI spectrum, and Franck-Condon analysis is qualitatively satisfactory. The ZEKE spectra from the in-plane modes observed in the REMPI spectrum demonstrate strong propensity in preserving the vibrational excitation of the intermediate state. Although several additional bands in combination with the vibrational mode of the intermediate state are identifiable, they are much lower in intensity. This observation implies that the molecular structure of BaP has a tremendous capability to accommodate changes in charge density. All observed bands of the cation are IR active, establishing the role of ZEKE spectroscopy in mapping out far infrared bands for astrophysical applications.
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33.60.+q Photoelectron spectra
33.20.Tp Vibrational analysis
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.Eh Autoionization, photoionization, and photodetachment
95.30.Ft Molecular and chemical processes and interactions

Long-range interactions between like homonuclear alkali metal diatoms

Jason N. Byrd, Robin Côté, and John A. Montgomery, Jr.

J. Chem. Phys. 135, 244307 (2011); http://dx.doi.org/10.1063/1.3671371 (7 pages)

Online Publication Date: 28 December 2011

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Long-range electrostatic and van der Waals coefficients up to terms of order R−8 have been evaluated by the sum over states method using ab initio and time-dependent density functional theory. We employ several widely used density functionals and systematically investigate the convergence of the calculated results with basis set size. Static electric moments and polarizabilities up to octopole order are also calculated. We present values for Li2 through K2 which are in good agreement with existing values, in addition to new results for Rb2 and Cs2. Interaction potential curves calculated from these results are shown to agree well with high level ab initio theory. Preliminary results are reported that demonstrate the applicability of the method to larger alkali clusters.
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31.15.ee Time-dependent density functional theory
31.15.ap Polarizabilities and other atomic and molecular properties
34.20.Gj Intermolecular and atom-molecule potentials and forces
31.50.-x Potential energy surfaces
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

The ab initio ground-state potential energy function of beryllium monohydride, BeH

Jacek Koput

J. Chem. Phys. 135, 244308 (2011); http://dx.doi.org/10.1063/1.3671610 (7 pages)

Online Publication Date: 28 December 2011

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The accurate ground-state potential energy function of beryllium monohydride, BeH, has been determined from large-scale ab initio calculations using the multi-reference averaged coupled-pair functional (MR-ACPF) method in conjunction with the correlation-consistent core-valence basis sets up to septuple-zeta quality. The effects of electron correlation beyond the MR-ACPF level of approximation were taken into account. The scalar relativistic and adiabatic (the diagonal correction) effects, as well as some of the nonadiabatic effects, were also discussed. The vibration-rotation energy levels of three isotopologues, BeH, BeD, and BeT, were predicted to sub-cm−1 accuracy.
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31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure
31.15.eg Exchange-correlation functionals (in current density functional theory)
31.50.Bc Potential energy surfaces for ground electronic states
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis

Theoretical characterization of intermolecular vibrational states through the multi-configuration time dependent Hartree approach: The He2,3ICl clusters

Álvaro Valdés, Rita Prosmiti, Pablo Villarreal, and Gerardo Delgado-Barrio

J. Chem. Phys. 135, 244309 (2011); http://dx.doi.org/10.1063/1.3671611 (9 pages)

Online Publication Date: 28 December 2011

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Benchmark, full-dimensional calculations on the ground and excited vibrational states for the tetra-, and penta-atomic weakly bound He2,3ICl complexes are reported. The representation of the potential energy surfaces includes three-body HeICl potentials parameterized to coupled-cluster singles, doubles, and perturbative triples ab initio data. These terms are important in accurately describing the interactions of such highly floppy systems. The corresponding 6D/9D computations are performed with the multi-configuration time dependent Hartree method, using natural potential fits, and a mode combination scheme to optimize the computational effort in the improved relaxation calculations. For these complexes several low-lying vibrational states are computed, and their binding energies and radial/angular probability density distributions are obtained. We found various isomers which are assigned to different structural models related with combinations of the triatomic isomers, like linear, T-shaped, and antilinear ones. Comparison of these results with recent experimental data is presented, and the quantitative deviations found with respect to the experiment are discussed.
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36.40.Mr Spectroscopy and geometrical structure of clusters
31.15.bw Coupled-cluster theory
31.15.xr Self-consistent-field methods
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.20.Tp Vibrational analysis

Accurate ab initio quartic force fields of cyclic and bent HC2N isomers

Natalia Inostroza, Xinchuan Huang, and Timothy J. Lee

J. Chem. Phys. 135, 244310 (2011); http://dx.doi.org/10.1063/1.3671389 (13 pages)

Online Publication Date: 29 December 2011

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Highly correlated ab initio quartic force fields (QFFs) are used to calculate the equilibrium structures and predict the spectroscopic parameters of three HC2N isomers. Specifically, the ground state quasilinear triplet and the lowest cyclic and bent singlet isomers are included in the present study. Extensive treatment of correlation effects were included using the singles and doubles coupled-cluster method that includes a perturbational estimate of the effects of connected triple excitations, denoted as CCSD(T). Dunning's correlation-consistent basis sets cc-pVXZ, X = 3,4,5, were used, and a three-point formula for extrapolation to the one-particle basis set limit was used. Core-correlation and scalar relativistic corrections were also included to yield highly accurate QFFs. The QFFs were used together with second-order perturbation theory (PT) (with proper treatment of Fermi resonances) and variational methods to solve the nuclear Schrödinger equation. The quasilinear nature of the triplet isomer is problematic, and it is concluded that a QFF is not adequate to describe properly all of the fundamental vibrational frequencies and spectroscopic constants (though some constants not dependent on the bending motion are well reproduced by PT). On the other hand, this procedure (a QFF together with either PT or variational methods) leads to highly accurate fundamental vibrational frequencies and spectroscopic constants for the cyclic and bent singlet isomers of HC2N. All three isomers possess significant dipole moments, 3.05 D, 3.06 D, and 1.71 D, for the quasilinear triplet, the cyclic singlet, and the bent singlet isomers, respectively. It is concluded that the spectroscopic constants determined for the cyclic and bent singlet isomers are the most accurate available, and it is hoped that these will be useful in the interpretation of high-resolution astronomical observations or laboratory experiments.
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31.15.bw Coupled-cluster theory
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure
33.20.Tp Vibrational analysis
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.xp Perturbation theory
31.15.xt Variational techniques
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