Ab initio calculations of lower resonant states of two-electron systems

The complex scaling and the stabilization methods are applied to calculating the parameters of the lowest resonance states of He and Li⁺. The results obtained by both methods are in a good agreement with the published data. It is shown that the wave functions constructed using the restricted configuration interaction approximation provide fairly accurate estimates of the resonance parameters. The possibility of using the stabilization method for calculating the phase shift function is also discussed.     

Electronic and medium effects on the rate of arene C [bond] H activation by cationic Ir(III) complexes

A detailed mechanistic study of arene C [bond] H activation in CH(2)Cl(2) solution by Cp(L)IrMe(X) [L = PMe(3), P(OMe)(3); X = OTf, (CH(2)Cl(2))BAr(f); (BAr(f) = B[3,5-C(6)H(3)(CF(3))(2)](4))(-)] is presented. It was determined that triflate dissociation in Cp(L)IrMe(OTf), to generate tight and/or solvent-separated ion pairs containing a cationic iridium complex, precedes C [bond] H activation. Consistent with the ion-pair hypothesis, the rate of arene activation by Cp(L)IrMe(OTf) is unaffected by added external triflate salts, but the rate is strongly dependent upon the medium. Thus the reactivity of Cp(PMe(3))IrMe(OTf) can be increased by almost 3 orders of magnitude by addition of (n-Hex)(4)NBAr(f), presumably because the added BAr(f) anion exchanges with the OTf anion in the initially formed ion pair, transiently forming a cation/borate ion pair in solution (special salt effect). In contrast, addition of (n-Hex)(4)NBAr(f) to [CpPMe(3)Ir(Me)CH(2)Cl(2)][BAr(f)] does not affect the rate of benzene activation; here there is no initial covalent/ionic pre-equilibrium that can be perturbed with added (n-Hex)(4)NBAr(f). An analysis of the reaction between Cp(PMe(3))IrMe(OTf) and various substituted arenes demonstrated that electron-donating substituents on the arene increase the rate of the C [bond] H activation reaction. The rate of C(6)H(6) activation by [Cp(PMe(3))Ir(Me)CH(2)Cl(2)][BAr(f)] is substantially faster than [Cp(P(OMe)(3))Ir(Me)CH(2)Cl(2)][BAr(f)]. Density functional theory computations suggest that this is due to a less favorable pre-equilibrium for dissociation of the dichloromethane ligand in the trimethyl phosphite complex, rather than to a large electronic effect on the C [bond] H oxidative addition transition state. Because of these combined effects, the overall rate of arene activation is increased by electron-donating substituents on both the substrate and the iridium complex.     

Laser-induced breakdown spectroscopy at a water/gas interface: A study of bath gas-dependent molecular species

Single-pulse laser-induced breakdown spectroscopy has been performed on the surface of a bulk water sample in an air, argon, and nitrogen gas environment to investigate emissions from hydrogen-containing molecules. A microplasma was formed at the gas/liquid interface by focusing a Nd:YAG laser beam operating at 1064 nm onto the surface of an ultra-pure water sample. A broadband Echelle spectrometer with a time-gated intensified charge-coupled device was used to analyze the plasma at various delay times (1.0–40.0 μs) and for incident laser pulse energies ranging from 20–200 mJ. In this configuration, the dominant atomic spectral features at short delay times are the hydrogen H-alpha and H-beta emission lines at 656 and 486 nm, respectively, as well as emissions from atomic oxygen liberated from the water and air and nitrogen emission lines from the air bath gas. For delay times exceeding approximately 8 μs the emission from molecular species (particularly OH and NH) created after the ablation process dominates the spectrum. Molecular emissions are found to be much less sensitive to variations in pulse energy and exhibit a temporal decay an order of magnitude slower than the atomic emission. The dependence of both atomic hydrogen and OH emission on the bath gas above the surface of the water was studied by performing the experiment at standard pressure in an atmospheric purge box. Electron densities calculated from the Stark broadening of the H-beta and H-gamma lines and plasma excitation temperatures calculated from the ratio of H-beta to H-gamma emission were measured for ablation in the three bath gases.     

Reactions C<Subscript>2</Subscript>H<Subscript>2</Subscript> + OH and C<Subscript>2</Subscript> + H<Subscript>2</Subscript>O: Ab initio study of the potential energy surfaces

The stationary points of the potential energy surfaces for the reactions C₂H₂ + OH and C₂ + H₂O are calculated using density functional theory and the coupled cluster method. The relative energies and geometric parameters of the stable intermediates and transition states are in good agreement with the results of independent studies. In most cases, the relative energies differ from the earlier published values by no more than 3 kcal/mol, whereas the rotational constants, by 1–2%. The mechanism of the reaction CCOH₂ → C₂ + H₂O is studied in detail. The possible sources of errors in the calculation methods are examined.     

Proton transfer reactions of hydrazine‐boranes

Hydrazine‐borane and hydrazine‐diborane contain, respectively, 15.4 and 16.9 wt% of hydrogen and are potential materials for hydrogen storage. In this work we present the gas‐phase complexation energies, acidities, and basicities of hydrazine‐borane and hydrazine‐bisborane calculated at MP2/6‐311 + G(d,p) level. We also report the release of dihydrogen from both protonated complexes (ΔG_{hydrazine‐borane} = ?20.9 kcal/mol and ΔG_{hydrazine‐bisborane} = ?27.2 kcal/mol) which is much more exergonic than from analogues amine‐boranes. The addition of the first BH₃ to the hydrazine releases 17.1 kcal/mol, and the second addition releases 15.8 kcal/mol. The attachment of BH₃ also increases the N―H acidity of hydrazine by 46.3 kcal/mol. It was found that the B―H deprotonation leads to intramolecular rearrangement. The basicity values for hydrazine‐borane and ‐bisborane are 180 and 172.8 kcal/mol, respectively. For both complexes the protonation centres are located at the boron moiety. The protonated structure of hydrazine‐bisborane is cyclic and can be described as H₂ captured between a negatively charged B―H hydrogen and positive boron (B―H??H2??B). Atoms in molecules analysis are used to investigate bond paths in concerning structures. Copyright © 2015 John Wiley & Sons, Ltd.     

Improved search for Muon-neutrino to electron-neutrino oscillations in MINOS

We report the results of a search for ν(e) appearance in a ν(μ) beam in the MINOS long-baseline neutrino experiment. With an improved analysis and an increased exposure of 8.2 × 10(20) protons on the NuMI target at Fermilab, we find that 2 sin(2) (θ(23))sin(2)(2θ(13))<0.12(0.20) at 90% confidence level for δ = 0 and the normal (inverted) neutrino mass hierarchy, with a best-fit of 2sin(2) (θ(23))sin(2)(2θ(13)) = 0.041(-0.031)(+0.047) (0.079(-0.053) (+0.071)). The θ(13) = 0 hypothesis is disfavored by the MINOS data at the 89% confidence level.     

Ellipsometry of anisotropic graphene-like two-dimensional materials on transparent substrates

New possibilities for determining anisotropic properties of the dielectric constants of two-dimensional materials by ellipsometry are developed. Graphene-like 2D materials are considered within the framework of macroscopic electrodynamics as ultrathin absorbing anisotropic films where the optical axis is perpendicular to the film surface. The ellipsometric inversion problem is resolved analytically. The resulting inversion formulas are very fast because they allow you to directly calculate the complex anisotropic dielectric constants without the use of sophisticated regression analysis or iterative root-finding procedures. In particular, the method offers an interest in graphene and related 2D materials because the anisotropic properties of such materials have not been studied to date.     

Correlation‐free reflection diagnostics of graphene‐like surface layers in the infrared region

New diagnostics possibilities for graphene‐like (two‐dimensional absorbing) ultrathin films on dielectric substrates by integrating ellipsometric and reflectance measurements are analyzed. The analysis is based on the analytical theory which has been developed in the framework of a long‐wavelength approximation. Importantly, the new method allows simultaneously (without correlation) to determine the thickness and optical constants of two‐dimensional materials in the infrared region. Another interesting feature of this reflection technique lies in the fact that for data handling the traditional model‐based regression analysis is not in use. The inversion problem is resolved on the basis of an analytical approach which has no need of initial guesses for the desired parameters. The results are also of interest as suitable starting points for non‐approximated numerical iterative methods where the proper choice of the initial data plays a crucial role. The presented method is tested using a numerical simulation. Copyright © 2015 John Wiley & Sons, Ltd.     

Multiparticle state tomography: hidden differences

We address the problem of completely characterizing multiparticle states including loss of information to unobserved degrees of freedom. In systems where nonclassical interference plays a role, such as linear-optics quantum gates, such information can degrade interference in two ways, by decoherence and by distinguishing the particles. Distinguishing information, often the limiting factor for quantum optical devices, is not correctly described by previous state-reconstruction techniques, which account only for decoherence. We extend these techniques and find that a single modified density matrix can completely describe partially coherent, partially distinguishable states. We use this observation to experimentally characterize two-photon polarization states in single-mode optical fiber.     

Use of stabilization by uniformly charged sphere for the resonance states calculations

The possibility of using the uniformly charged sphere with the variable charge and constant radius for accurate phase shift and resonance states parameters calculations is investigated. It is demonstrated on the example of the Hazy-Taylor model problem that the proposed numerical technique provides the relative errors about 1% for the phase shift function and resonance state parameters (energy and width). The choice of the optimal basis set for such calculations is discussed also.