The oxidation of Fe(111)

The oxidation of Fe(111) was studied using Auger electron spectroscopy (AES), low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS) and scanning tunnelling microscopy (STM). Oxidation of the crystal was found to be a very fast process, even at 200 K, and the Auger O signal saturation level is reached within ~ 50 × 10^? 6 mbar s. Annealing the oxidised surface at 773 K causes a significant decline in apparent surface oxygen concentration and produces a clear (6 × 6) LEED pattern, whereas after oxidation at ambient temperature no pattern was observed. STM results indicate that the oxygen signal was reduced due to the nucleation of large, but sparsely distributed oxide islands, leaving mainly the smooth (6 × 6) structure between the islands. The reactivity of the (6 × 6) layer towards methanol was investigated using temperature programmed desorption (TPD), which showed mainly decomposition to CO and CO₂, due to the production of formate intermediates on the surface. Interestingly, this removes the (6 × 6) structure by reduction, but it can be reformed from the sink of oxygen present in the large oxide islands simply by annealing at 773 K for a few minutes. The (6 × 6) appears to be a relatively stable, pseudo-oxide phase, that may be useful as a model oxide surface.     

Sub-200 fs microjoule pulses from a monolithic linear fiber CPA system

An all-fiber-integrated linear chirped-pulse amplifier system generating microjoule pulse energies is reported. It is seeded by an all-fiber dissipative-soliton laser and incorporates a newly developed fiber stretcher, whose dispersive properties match that of the grating compressor. Pulse durations of 189 fs with energies of 2.2 μJ were achieved after compression. The average power was 9.8 W at the repetition rate of 4.5 MHz.     

Flow-field measurements of liquid and gaseous phases in the ultra-dense region of diesel sprays

The velocities of both the liquid and the gaseous phases in a diesel spray are determined for the first time simultaneously via laser flow tagging (LFT). The experimental setup and uncertainties introduced by seeding particles in the gas phase are greatly reduced by using phosphorescent tracer molecules, i.e. acetone and biacetyl, for the gaseous phase. In addition, simultaneous droplet velocimetry is achieved by doping the liquid fuel with a lanthanide–chelate complex.The relative velocity of gas and liquid phases can be determined from the data on the spray axis close to the nozzle for the first time. This is an important quantity for modeling droplet break-up and evaporation in ultra-dense sprays.PACS 42.62.-b; 47.61.Jd     

Sliding-induced decoupling and charge transfer between the coexisting Q1 and Q2 charge density waves in NbSe3

Using high-resolution x-ray scattering in the presence of an applied current, we report evidence for a dynamical decoupling between the two NbSe3 charge-density waves (CDWs), Q1 (T(C1)=145 K) and Q2 (T(C2)=59 K), coexisting below T(C2). Simultaneous and oppositely directed shifts of the relevant CDW superlattice spots develop above a threshold current which we identify as the depinning threshold I(C1) for the more strongly pinned upper CDW Q1 (I(C1) approximately 10I(C2)). In contrast with shifts induced by current conversion processes, the present effect is not current polarized and is not limited to the current-contact regions. We propose a model which explains this instability through a sliding-induced charge transfer between the two electronic reservoirs corresponding to the Q1 and Q2 CDWs.     

Study of 19Na at SPIRAL

The excitation function for the elastic-scattering reaction p( ¹⁸Ne, p) ¹⁸Ne was measured with the first radioactive beam from the SPIRAL facility at the GANIL laboratory and with a solid cryogenic hydrogen target. Several broad resonances have been observed, corresponding to new excited states in the unbound nucleus ¹⁹Na. In addition, two-proton emission events have been identified and are discussed.     

Polarometrische bestimmung von zirkonium(IV) mit tartrazin

A new polarimetric procedure has been developed for the rapid determination of zirconium in the presence of tartrazin as reagent This determination is possible in the presence of uranium.     

Phosphaketenes as Building Blocks for the Synthesis of Triphospha Heterocycles

Unsaturated phosphorus compounds, such as phosphaalkenes and phosphaalkynes, show a versatile reactivity in cycloadditions. Although phosphaketenes (R?P?C?O) have been known for three decades, their chemistry has remained limited. Herein, we show that heteroatom‐substituted phosphaketenes, R₃E?P?C?O (E=Si, Sn), are building blocks for silyl‐ and stannyl‐substituted five‐membered heterocycles containing three phosphorous atoms. The structure of the heterocyclic anion depends on the nature of the tetrel atom involved. Although the silyl analogue [P₃C₂(OSiR₃)₂]^? is an aromatic 1,2,4‐triphospholide, the stannyl compound [P(CO)₂(PSnR₃)₂]^? is a 1,2,4‐triphosphacyclopenta‐3,5‐dionate with a delocalized OCPCO fragment. Because of their anionic character, these compounds can easily be used as building blocks, for example, in the preparation of a silyl‐functionalized hexaphosphaferrocene or the parent 1,2,4‐triphosphacyclopenta‐3,5‐dionate [P(CO)₂(PH)₂]^?. NMR spectroscopic investigations and computations have shown that the heterocycle‐formation reactions presented herein are remarkably complex.