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28 Mar 2013

Volume 138, Issue 12, Articles (12xxxx)

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J. Chem. Phys. 138, 124701 (2013); http://dx.doi.org/10.1063/1.4794685 (9 pages)

Luying Wang, Randall S. Dumont, and James M. Dickson
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Vibrational and electronic excitations in fluorinated ethene cations from the ground up

Jonelle Harvey, Patrick Hemberger, Andras Bodi, and Richard P. Tuckett

J. Chem. Phys. 138, 124301 (2013); http://dx.doi.org/10.1063/1.4795428 (12 pages)

Online Publication Date: 22 March 2013

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Valence threshold photoelectron spectra of four fluorinated ethenes; C2H3F, 1,1-C2H2F2, C2HF3, and C2F4 were recorded at the Swiss Light Source with 0.002 eV resolution. The adiabatic ionization energies were found to be 10.364 ± 0.007, 10.303 ± 0.005, 10.138 ± 0.007, and 10.110 ± 0.009 eV, respectively. The electronic ground state of each cation shows well-resolved multi-component vibrational progressions, the dominant transitions being in the C=C stretching mode. Density functional theory based Franck–Condon simulations are used to model the vibrational structure and assign the spectra, sometimes revising previous assignments. An additional vibrational progression in the first photoelectron band of 1,1-C2H2F2 indicates that the ground electronic state of the molecular ion is no longer planar. It is shown that ab initio vibrational frequencies together with the observed vibrational spacings do not always suffice to assign the spectra. In addition to symmetry rules governing the transitions, it is often essential to consider the associated Franck–Condon factors explicitly. Ionization to higher lying excited valence electronic states were also recorded by threshold ionization up to 23 eV photon energy. Equation-of-motion coupled cluster with single and double substitutions for ionization potential (EOM-IP-CCSD/cc-pVTZ) calculations confirmed historic electronic state assignments, and untangled the ever more congested spectra with increasing F-substitution. Previous attempts at illuminating the intriguing dissociative photoionization mechanism of fluorinated ethenes are reconsidered in view of new computational and experimental results. We show how non-statistical F-atom loss from C2H3F+ is decoupled from the ground state dissociation dynamics in the energy range of its math state. Both the statistical and the non-statistical dissociation processes are mediated by a plethora of conical intersections.
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33.20.Tp Vibrational analysis
33.80.Gj Diffuse spectra; predissociation, photodissociation
31.15.ae Electronic structure and bonding characteristics
31.15.E- Density-functional theory
33.60.+q Photoelectron spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants

Ab initio studies of atomic properties and experimental behavior of element 119 and its lighter homologs

A. Borschevsky, V. Pershina, E. Eliav, and U. Kaldor

J. Chem. Phys. 138, 124302 (2013); http://dx.doi.org/10.1063/1.4795433 (5 pages)

Online Publication Date: 22 March 2013

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Static dipole polarizabilities of element 119 and its singly charged cation are calculated, along with those of its lighter homologs, Cs and Fr. Relativity is treated within the 4-component Dirac-Coulomb formalism and electron correlation is included by the single reference coupled cluster approach with single, double, and perturbative triple excitations (CCSD(T)). Very good agreement with available experimental values is obtained for Cs, lending credence to the predictions for Fr and element 119. The atomic properties in group-1 are largely determined by the valence ns orbital, which experiences relativistic stabilization and contraction in the heavier elements. As a result, element 119 is predicted to have a relatively low polarizability (169.7 a.u.), comparable to that of Na. The adsorption enthalpy of element 119 on Teflon, which is important for possible future experimental studies of this element, is estimated as 17.6 kJ/mol, the lowest among the atoms considered here.
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31.15.ap Polarizabilities and other atomic and molecular properties
31.15.bw Coupled-cluster theory
31.15.vj Electron correlation calculations for atoms and ions: excited states
31.30.jc Relativistic corrections to atomic structure and properties
32.30.-r Atomic spectra
68.43.Mn Adsorption kinetics

Photoelectron spectroscopy of the aluminum hydride anions: AlH2−, AlH3−, Al2H6−, Al3H9−, and Al4H12−

Xinxing Zhang, Haopeng Wang, Evan Collins, Alane Lim, Gerd Ganteför, Boggavarapu Kiran, Hansgeorg Schnöckel, Bryan Eichhorn, and Kit Bowen

J. Chem. Phys. 138, 124303 (2013); http://dx.doi.org/10.1063/1.4796200 (4 pages)

Online Publication Date: 25 March 2013

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We report measurements of the negative ion photoelectron spectra of the simple aluminum hydride anions: AlH2−, AlH3−, Al2H6−, Al3H9−, and Al4H12−. From these spectra, we measured the vertical detachment energies of the anions, and we estimated the electron affinities of their neutral counterparts. Our results for AlH2−, AlH3−, and Al2H6− were also compared with previous predictions by theory.
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33.60.+q Photoelectron spectra
33.20.Xx Spectra induced by strong-field or attosecond laser irradiation
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Fm Bond strengths, dissociation energies

Ion imaging study of dissociative charge transfer in the N2+ + CH4 system

Linsen Pei and James M. Farrar

J. Chem. Phys. 138, 124304 (2013); http://dx.doi.org/10.1063/1.4796205 (5 pages)

Online Publication Date: 25 March 2013

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The velocity map ion imaging method is applied to the dissociative charge transfer reactions of N2+ with CH4 studied in crossed beams. The velocity space images are collected at four collision energies between 0.5 and 1.5 eV, providing both product kinetic energy and angular distributions for the reaction products CH3+ and CH2+. The general shapes of the images are consistent with long range electron transfer from CH4 to N2+ preceding dissociation, and product kinetic energy distributions are consistent with energy resonance in the initial electron transfer step. The branching ratio for CH3+:CH2+ is 85:15 over the full collision energy range, consistent with literature reports.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
34.70.+e Charge transfer
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

Vibrational Raman spectra of hydrogen clathrate hydrates from density functional theory

K. R. Ramya and Arun Venkatnathan

J. Chem. Phys. 138, 124305 (2013); http://dx.doi.org/10.1063/1.4795610 (6 pages)

Online Publication Date: 25 March 2013

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Hydrogen clathrate hydrates are promising sources of clean energy and are known to exist in a sII hydrate lattice, which consists of H2 molecules in dodecahedron (512) and hexakaidecahedron (51264) water cages. The formation of these hydrates which occur in extreme thermodynamic conditions is known to be considerably reduced by an inclusion of tetrahydrofuran (THF) in cages of these hydrate lattice. In this present work, we employ the density functional theory with a dispersion corrected (B97-D) functional to characterize vibrational Raman modes in the cages of pure and THF doped hydrogen clathrate hydrates. Our calculations show that the symmetric stretch of the H2 molecule in the 51264H2·THF cage is blueshifted compared to the 51264H2 cage. However, all vibrational modes of water molecules are redshifted which suggest reduced interaction between the H2 molecule and water molecules in the 51264H2·THF cage. The symmetric and asymmetric O–H stretch of water molecules in 512H2, 51264H2, and 51264H2·THF cages are redshifted compared with the corresponding guest free cages due to interactions between encapsulated H2 molecules and water molecules of the cages. The low frequency modes contain contributions from contraction and expansion of water cages and vibration of water molecules due to hydrogen bonding and these modes could possibly play an important role in the formation of the hydrate lattice.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
65.40.G- Other thermodynamical quantities
61.50.Lt Crystal binding; cohesive energy
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
78.30.Jw Organic compounds, polymers
63.50.-x Vibrational states in disordered systems

Ionization of large homogeneous and heterogeneous clusters generated in acetylene–Ar expansions: Cluster ion polymerization

J. Kočišek, J. Lengyel, and M. Fárník

J. Chem. Phys. 138, 124306 (2013); http://dx.doi.org/10.1063/1.4796262 (8 pages)

Online Publication Date: 26 March 2013

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Pure acetylene and mixed Ar-acetylene clusters are formed in supersonic expansions of acetylene/argon mixtures and analysed using reflectron time-of-flight mass spectrometer with variable electron energy ionization source. Acetylene clusters composed of more than a hundred acetylene molecules are generated at the acetylene concentration of ≈8%, while mixed species are produced at low concentrations (≈0.7%). The electron energy dependence of the mass spectra revealed the ionization process mechanisms in clusters. The ionization above the threshold for acetylene molecule of 11.5 eV results in the main ionic fragment progression (C2H2)n+. At the electron energies ⩾21.5 eV above the CH+CH+ dissociative ionization limit of acetylene the fragment ions nominally labelled as (C2H2)nCH+, n ⩾ 2, are observed. For n ⩽ 7 these fragments correspond to covalently bound ionic structures as suggested by the observed strong dehydrogenation [(C2H2)n − k × H]+ and [(C2H2)nCH − k × H]+. The dehydrogenation is significantly reduced in the mixed clusters where evaporation of Ar instead of hydrogen can stabilize the nascent molecular ion. The C3H3+ ion was previously assigned to originate from the benzene molecular ion; however, the low appearance energy of ≈13.7 eV indicates that a less rigid covalently bound structure of C6H6+ ion must also be formed upon the acetylene cluster electron ionization. The appearance energy of Arn(C2H2)+ fragments above ≈15.1 eV indicates that the argon ionization is the first step in the fragment ion production, and the appearance energy of Ar n ≥ 2(C2H2)m ≥ 2+ at ≈13.7 eV is discussed in terms of an exciton transfer mechanism.
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36.40.Jn Reactivity of clusters
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
34.80.Gs Molecular excitation and ionization
33.15.Ta Mass spectra
36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Qv Stability and fragmentation of clusters

Morphology of collisional nonlinear spectra in H2-Kr and H2-Xe mixtures

Waldemar Głaz, Tadeusz Bancewicz, Jean-Luc Godet, George Maroulis, and Anastasios Haskopoulos

J. Chem. Phys. 138, 124307 (2013); http://dx.doi.org/10.1063/1.4795438 (7 pages)

Online Publication Date: 26 March 2013

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This article reports new results of theoretical and numerical studies of spectral features of the collision-induced hyper-Rayleigh light scattered in dihydrogen-noble gas (H2-Rg) mixtures. The most massive and polarizable scattering supermolecules with Rg = Kr and Xe have been added to the previously considered systems in order to gain a more complete insight into the evolution of the spectral properties. The symmetry adapted components of the first collisional hyperpolarizabilities are obtained by means of the quantum chemistry numerical routines supplemented with appropriate theoretical methods. Roto-translational spectral lines are calculated on the grounds of the quantum-mechanical as well as semi-classical approach. The role of particular hyperpolarizability components in forming the line shapes is discussed. The intensities of the lines are compared with those obtained for less massive scatterers. Advantages of prospective application of the new scattering systems for experimental detection of the nonlinear collisional effects are indicated.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.70.Fd Absolute and relative line and band intensities
33.70.Jg Line and band widths, shapes, and shifts
34.50.-s Scattering of atoms and molecules
31.15.xv Molecular dynamics and other numerical methods
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

High temperature reaction kinetics of CN(v = 0) with C2H4 and C2H6 and vibrational relaxation of CN(v = 1) with Ar and He

Ghassen Saidani, Yulia Kalugina, Aline Gardez, Ludovic Biennier, Robert Georges, and François Lique

J. Chem. Phys. 138, 124308 (2013); http://dx.doi.org/10.1063/1.4795206 (13 pages)

Online Publication Date: 27 March 2013

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The investigation of the chemical complexity of hot environments, ranging from combustion flames to circumstellar envelopes of evolved stars, relies on the determination of the reaction kinetics and product branching ratio. We have designed a chemical reactor for the exploration of high temperature chemistry. This apparatus is employed in the present study to measure the reaction kinetics of the CN radical with C2H4 and C2H6 over the 300–1200 K temperature range. In our setup and in some environments, the CN radical is partially produced in a vibrationally excited state, before relaxing by collision with the surrounding gas. We complement the experimental kinetic studies of hydrocarbons reactions with CN(v = 0) with a theoretical study of vibrational relaxation of CN(v = 1) by He and Ar atoms, the main collisional partners in our apparatus. Calculations are carried out to determine the collisional elastic and inelastic cross sections versus the kinetic energy as well as the corresponding vibrationally elastic and inelastic rate coefficients. The results are compared with empirical calculations and with a few experimental observations. The range of validity of the empirical model is discussed and potential applications sketched.
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82.20.Rp State to state energy transfer
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.33.Vx Reactions in flames, combustion, and explosions
33.15.Mt Rotation, vibration, and vibration-rotation constants
34.50.Ez Rotational and vibrational energy transfer

Full-dimensional quantum calculations of the vibrational states of H5+

Hongwei Song, Soo-Ying Lee, Minghui Yang, and Yunpeng Lu

J. Chem. Phys. 138, 124309 (2013); http://dx.doi.org/10.1063/1.4797464 (10 pages)

Online Publication Date: 28 March 2013

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Full-dimensional quantum calculations of the vibrational states of H5+ have been performed on the accurate potential energy surface developed by Xie et al. [J. Chem. Phys. 122, 224307 (2005)10.1063/1.1927529]. The zero point energies of H5+, H4D+, D4H+, and D5+ and their ground-state geometries are presented and compared with earlier theoretical results. The first 10 low-lying excited states of H5+ are assigned to the fundamental, overtone, and combination of the H2–H3+ stretch, the shared proton hopping and the out-of-plane torsion. The ground-state torsional tunneling splitting, the fundamental of the photon hopping mode and the first overtone of the torsion mode are 87.3 cm −1, 354.4 cm −1, and 444.0 cm −1, respectively. All of these values agree well with the diffusion Monte Carlo and multi-configuration time-dependent Hartree results where available.
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33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.xr Self-consistent-field methods
31.50.Bc Potential energy surfaces for ground electronic states
31.50.Df Potential energy surfaces for excited electronic states

Resonance Regge poles and the state-to-state F + H2 reaction: QP decomposition, parametrized S matrix, and semiclassical complex angular momentum analysis of the angular scattering

J. N. L. Connor

J. Chem. Phys. 138, 124310 (2013); http://dx.doi.org/10.1063/1.4794859 (21 pages)

Online Publication Date: 28 March 2013

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Three new contributions to the complex angular momentum (CAM) theory of differential cross sections (DCSs) for chemical reactions are reported. They exploit recent advances in the Padé reconstruction of a scattering (S) matrix in a region surrounding the Re J axis, where J is the total angular momentum quantum variable, starting from the discrete values, J = 0, 1, 2, …. In particular, use is made of Padé continuations obtained by Sokolovski, Castillo, and Tully [Chem. Phys. Lett. 313, 225 (1999)10.1016/S0009-2614(99)01016-7] for the S matrix of the benchmark F + H2(vi = 0, ji = 0, mi = 0) → FH(vf = 3, jf = 3, mf = 0) + H reaction. Here vi, ji, mi and vf, jf, mf are the initial and final vibrational, rotational, and helicity quantum numbers, respectively. The three contributions are: (1) A new exact decomposition of the partial wave (PW) S matrix is introduced, which is called the QP decomposition. The P part contains information on the Regge poles. The Q part is then constructed exactly by subtracting a rapidly oscillating phase and the PW P matrix from the input PW S matrix. After a simple modification, it is found that the corresponding scattering subamplitudes provide insight into the angular-scattering dynamics using simple partial wave series (PWS) computations. It is shown that the leading n = 0 Regge pole contributes to the small-angle scattering in the centre-of-mass frame. (2) The Q matrix part of the QP decomposition has simpler properties than the input S matrix. This fact is exploited to deduce a parametrized (analytic) formula for the PW S matrix in which all terms have a direct physical interpretation. This is a long sort-after goal in reaction dynamics, and in particular for the state-to-state F + H2 reaction. (3) The first definitive test is reported for the accuracy of a uniform semiclassical (asymptotic) CAM theory for a DCS based on the Watson transformation. The parametrized S matrix obtained in contribution (2) is used in both the PW and semiclassical parts of the calculation. Powerful uniform asymptotic approximations are employed for the background integral; they allow for the proximity of a Regge pole and a saddle point. The CAM DCS agrees well with the PWS DCS, across the whole angular range, except close to the forward and backward directions, where, as expected, the CAM theory becomes non-uniform. At small angles, θR ≲ 40°, the PWS DCS can be reproduced using a nearside semiclassical subamplitude, which allows for a pole being close to a saddle point, plus the farside surface wave of the n = 0 pole sub-subamplitude, with the oscillations in the DCS arising from nearside-farside interference. This proves that the n = 0 Regge resonance pole contributes to the small-angle scattering.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Ln Semiclassical theory of reactions and/or energy transfer
33.20.Tp Vibrational analysis
33.20.Sn Rotational analysis

Carbon X-ray absorption spectra of fluoroethenes and acetone: A study at the coupled cluster, density functional, and static-exchange levels of theory

Thomas Fransson, Sonia Coriani, Ove Christiansen, and Patrick Norman

J. Chem. Phys. 138, 124311 (2013); http://dx.doi.org/10.1063/1.4795835 (12 pages)

Online Publication Date: 29 March 2013

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Near carbon K-edge X-ray absorption fine structure spectra of a series of fluorine-substituted ethenes and acetone have been studied using coupled cluster and density functional theory (DFT) polarization propagator methods, as well as the static-exchange (STEX) approach. With the complex polarization propagator (CPP) implemented in coupled cluster theory, relaxation effects following the excitation of core electrons are accounted for in terms of electron correlation, enabling a systematic convergence of these effects with respect to electron excitations in the cluster operator. Coupled cluster results have been used as benchmarks for the assessment of propagator methods in DFT as well as the state-specific static-exchange approach. Calculations on ethene and 1,1-difluoroethene illustrate the possibility of using nonrelativistic coupled cluster singles and doubles (CCSD) with additional effects of electron correlation and relativity added as scalar shifts in energetics. It has been demonstrated that CPP spectra obtained with coupled cluster singles and approximate doubles (CC2), CCSD, and DFT (with a Coulomb attenuated exchange-correlation functional) yield excellent predictions of chemical shifts for vinylfluoride, 1,1-difluoroethene, trifluoroethene, as well as good spectral features for acetone in the case of CCSD and DFT. Following this, CPP-DFT is considered to be a viable option for the calculation of X-ray absorption spectra of larger π-conjugated systems, and CC2 is deemed applicable for chemical shifts but not for studies of fine structure features. The CCSD method as well as the more approximate CC2 method are shown to yield spectral features relating to π*-resonances in good agreement with experiment, not only for the aforementioned molecules but also for ethene, cis-1,2-difluoroethene, and tetrafluoroethene. The STEX approach is shown to underestimate π*-peak separations due to spectral compressions, a characteristic which is inherent to this method.
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33.20.Rm X-ray spectra
31.15.E- Density-functional theory
31.15.bw Coupled-cluster theory
31.15.eg Exchange-correlation functionals (in current density functional theory)

Vibrational and vibronic spectra of tryptamine conformers

Nitzan Mayorkas, Amir Bernat, Shay Izbitski, and Ilana Bar

J. Chem. Phys. 138, 124312 (2013); http://dx.doi.org/10.1063/1.4798218 (12 pages)

Online Publication Date: 29 March 2013

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Conformation-specific ionization-detected stimulated Raman spectra, including both Raman loss and Raman gain lines, along with visible-visible-ultraviolet hole-burning spectra of tryptamine (TRA) conformers have been measured simultaneously, with the aim of obtaining new data for identifying them. The slightly different orientations of the ethylamine side chain relative to the indole lead to unique spectral signatures, pointing to the presence of seven TRA conformers in the molecular beam. Comparison of ionization-loss stimulated Raman spectra to computationally scaled harmonic Raman spectra, especially in the alkyl C–H and amine N–H stretch regions together with the retrieved information on the stabilities of the TRA conformers assisted their characterization and structural identification. The prospects and limitations of using these spectroscopic methods as potential conformational probes of flexible molecules are discussed.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.20.Tp Vibrational analysis
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Mt Rotation, vibration, and vibration-rotation constants

The molecular frame electric dipole moment and hyperfine interactions in hafnium fluoride, HfF

Anh Le, Timothy C. Steimle, Leonid Skripnikov, and Anatoly V. Titov

J. Chem. Phys. 138, 124313 (2013); http://dx.doi.org/10.1063/1.4794049 (9 pages)

Online Publication Date: 29 March 2013

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The (1,0) [17.9]2.5−X2Δ3/2 band of hafnium monofluoride (HfF) has been recorded using high-resolution laser-induced fluorescence spectroscopy both field-free and in the presence of a static electric field. The field-free spectra of 177HfF, 179HfF, and 180HfF were modeled to generate a set of fine and hyperfine parameter for the X2Δ3/2(v = 0) and [17.9]2.5 (v = 1) states. The observed optical Stark shifts for the 180HfF isotopologue were analyzed to produce the molecular frame electric dipole moments of 1.66(1) D and 0.419(7) D for the X2Δ3/2 and [17.9]2.5 state, respectively. Both the generalized effective core potential and all-electron four component approaches were used in ab initio calculations to predict the properties of ground state HfF including equilibrium distance, dipole moments, quadrupole coupling, and magnetic hyperfine constants.
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31.30.Gs Hyperfine interactions and isotope effects
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Pw Fine and hyperfine structure
33.50.Dq Fluorescence and phosphorescence spectra
33.70.Jg Line and band widths, shapes, and shifts
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure
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