Laser excitation of the 1s-hyperfine transition in muonic hydrogen

The CREMA collaboration is pursuing a measurement of the ground-state hyperfine splitting (HFS) in muonic hydrogen ($\mu$p) with 1 ppm accuracy by means of pulsed laser spectroscopy to determine the two-photon-exchange contribution with $2\times10^{-4}$ relative accuracy. In the proposed experiment, the $\mu$p atom undergoes a laser excitation from the singlet hyperfine state to the triplet hyperfine state, {then} is quenched back to the singlet state by an inelastic collision with a H$_2$ molecule. The resulting increase of kinetic energy after the collisional deexcitation is used as a signature of a successful laser transition between hyperfine states. In this paper, we calculate the combined probability that a $\mu$p atom initially in the singlet hyperfine state undergoes a laser excitation to the triplet state followed by a collisional-induced deexcitation back to the singlet state. This combined probability has been computed using the optical Bloch equations including the inelastic and elastic collisions. Omitting the decoherence effects caused by {the laser bandwidth and }collisions would overestimate the transition probability by more than a factor of two in the experimental conditions. Moreover, we also account for Doppler effects and provide the matrix element, the saturation fluence, the elastic and inelastic collision rates for the singlet and triplet states, and the resonance linewidth. This calculation thus quantifies one of the key unknowns of the HFS experiment, leading to a precise definition of the requirements for the laser system and to an optimization of the hydrogen gas target where $\mu$p is formed and the laser spectroscopy will occur.Comment: 21 pages, 4 figure

Two-Dimensional Solid State NMR and Separation of 7Li Quadrupolar Interactions in Paramagnetic Compounds

Ln layered paramagnetic compounds, such as La2Li0.5Ni0.5O4 with a perovskite structure, the Li-7 NMR spectrum is broadened by anisotropic quadrupolar as well as paramagnetic dipolar interactions. We have used a two-dimensional spin echo (SE) experiment to separate the quadrupolar interaction and obtain a clean quadrupolar spectrum along the wi dimension. This is demonstrated in La2Li0.5B0.5O4 (B = Cu, Ni), through 2D SE experiments conducted in static samples as well as those in spinning at the magic angle. A quadrupole coupling constant of 92 kHz is estimated from the Wi spectrum for paramagnetic La2Li0.5Ni0.5O4

The nature of vanadium in vanado-silicate (MFI) molecular sieves: influence of synthesis methods

The influence of synthesis in acidic or alkaline media on the incorporation of vanadium in the MFI (ZSM-5) lattice has been studied. An alkaline gel favors the incorporation of vanadium in the MFI framework, while an acidic gel does not. EPR and analytical data indicate that mostly V4+species are present in an octahedral (Oh) environment in the as-synthesized V-MFI prepared in acidic media, which latter transform into polymeric V5+species on calcination. In the alkaline media, vanadium is incorporated mostly as V5+in a distorted Td environment. Thermal analysis and XRD data indicate that phase transformation from orthorhombic to monoclinic takes place during the calcination process only when the sample is prepared from acidic medium. It is found that the sample prepared from alkaline medium contains Si-OH groups from defect centers while such groups are absent in the sample prepared in acidic medium. It appears that V-ions are present in the defect sites in the MFI framework in the sample prepared from alkaline medium

A study of the structure of poly(hexene-1) prepared by nickel(α-diimine)/MAO catalyst using high resolution NMR spectroscopy

Homopolymerization of hexene-1 with nickel(α-diimine) catalyst forms poly(hexene-1) containing different types of branches and varying number of methylene units in the backbone. Types of branches identified by NMR spectroscopy include, butyl (C<SUB>4</SUB>), longer than butyl (&gt;C<SUB>4</SUB>) and methyl (isolated and meso and racemic head-to-head). Formation of ethyl (C<SUB>2</SUB>) and propyl (C<SUB>3</SUB>) branches were not observed. The migration of the nickel during polymerization not only causes the formation of branches other than C<SUB>4</SUB>, but also the runs of methylene units in the backbone due to complete 1,6-enchainment (chain running). The formation of regio-irregular methyl branches required an insertion of hexene-1 in the nickel-secondary carbon. Formation of methyl branches and (1, ω) enchainment has also been observed during the polymerization of octene-1, decene-1, tetradecene-1 using the same catalyst system. The extent formation of these subunits in the polymer depends on polymerization temperature. A plausible explanation for the formation of different branches is discussed

Selective hydrogenation of chloronitrobenzenes with an MCM-41 supported platinum allyl complex derived catalyst

A platinuin precatalyst (1) has been prepared by reacting [(eta(3)-C(3)H(5))(4)Pt(4)Cl(4)] with surface functionalized MCM-41 with pendant -(CH(2))(3)NH(CH(2))(2)NH(2) groups. For the hydrogenation of o-, m- and p-chloronitrobenzenes to the corresponding chloroanilines, 1 is found to be a highly active catalyst with good selectivities for them-and p-isomers. Its performance is superior to that of its palladium analogue and far superior to that of commercial (5%) Pt/C or (5%) Pt/Al(2)O(3). Comparison of solid state and solution NMR data and other evidences indicate that on treatment with the functionalized MCM-41 support; [(eta(3)-C(3)H(5))(4)Pt(4)Cl(4)] loses the ally! ligand. XPS data show that in the fresh catalyst Pt is present in the 2+ oxidation state. Based on these and analytical data, co-ordination by surface diamine and hydroxo groups to Pt(2+) in 1 is suggested. In the used catalyst both Pt(2+) and Pt are present but the amount of metallic platinum is similar to 16% of the total. (C) 2011 Elsevier B.V. All rights reserved

Hydration in polymer studied through magic angle spinning nuclear magnetic resonance and heteronuclear <SUP>13</SUP>C{<SUP>1</SUP>H} Overhauser enhancement spectroscopy: cross-relaxation and location of water in poly(acrylamide)

A combination of magic angle spinning (MAS) and heteronuclear 13C{1H} Overhauser enhancement spectroscopy (HOESY) is shown to be a powerful technique for studying hydration in polymers. This is demonstrated in poly(acrylamide)-water system. The increased spectral resolution due to MAS is shown to resolve polymer-polymer and polymer-water dipolar correlations in the two dimensional HOESY experiment. The 2D experiment is thus shown to lead to an indirect detection of water interacting with the polymer. The one dimensional transient Overhauser experiment involving selective inversion of water allows the study of cross-relaxation between water protons and carbonyl carbon in the polymer side chain. The cross-relaxation rate is rationalized in terms of a direct dipole-dipole interaction between the carbonyl carbon and the hydrated bound water. Based on temperature dependent 17O spin-lattice relaxation time measurements and a two-step motional model for water, we gather that water molecules close to the observed polymer site reorient anisotropically, typically an order of magnitude slower than in pure water. The correlation time for bound water mobility has been estimated to be 0.58&#215;10-10 s at 298 K, and, in turn, has been used to locate hydrated water at a distance of 3.45 &#197; from amide carbonyl. This is the first time such an estimate has been made for hydrated water in a polymer using HOESY data

Evidence for multiple M sites in AMO<SUB>2</SUB> compounds: <SUB>59</SUB>Co solid state NMR studies on LiCoO<SUB>2</SUB>

The layered AMO2 compounds (A = alkali metal, M = trivalent octahedral site cations) derived from the simple rock-salt structure have always been considered to have only one crystallographic site for the A and the M atoms. These structures are described in terms of close-packed oxygen layers with interstitial A and M atoms, especially when A = Li. This gives a layer sequence (AO)- and (MO)+. The AMO2 compounds are part of the compounds in the A-M-O systems such as A2MO3 and A5MO6, which are derived from the rock-salt structure with alternating layers of pure (AO)- and mixed [(A,M)O]+ layers with multiple interstitial octahedral sites in the (A,M)O layer for occupation by the different A and M cations. Evidence is presented from 59Co NMR experiments on LiCoO2 for the existence of at least two sites in the (CoO)+ layer. Several NMR methodologies, such as the use of various pulse sequence, nutation experiments, and magic angle sample spinning (MASS) are employed. Magic-angle-sample-spinning experiments show only one isotropic peak. However, an analysis of spinning sidebands envelope at various spinning speeds clearly shows the presence of at least two sites. One of these has orthorhombic symmetry and another has axial symmetry, with closely related chemical shift anisotropy components that result in the observation of nearly identical isotropic chemical shifts. The possible importance of the absence or presence of holes on oxygen has been discussed in accounting for the two sites

MCM-41-supported organometallic-derived nanopalladium as a selective hydrogenation catalyst

Palladium nanocatalysts have been prepared by anchoring (eta(3)-C3H5)(2)Pd2Cl2 onto dian-tine-functionalized MCM-41 supports followed by reaction with hydrogen under catalytic conditions. The catalyst precursor and used catalyst have been studied by solid-state NMR (C-13, Si-29), XPS, and TEM. The organometallic-derived catalyst exhibits the best performance (activity and selectivity) to date toward the selective hydrogenation of industrially relevant o- and m-chloronitrobenzene to the corresponding chloroaniline derivatives and is distinctly superior to 5% Pd/C. Grazing angle XPS studies reveal that conversion of the tethered molecular species to the nanoparticles of palladium produces a core-shell nanostructure

Preferential hydration in superabsorbing polymers by solid-state carbon-13 NMR spectroscopy

This article does not have an abstract