[{(CH3)3Si}3C–Li–C{Si(CH3)3}3][Li · 3(OC4H8)] und {(CH3)3Si}3C–Li · O=C(Si(CH3)3)2, zwei neue Addukte des Lithium‐trisylmethanids

[{(CH₃)₃Si}₃C–Li–C{Si(CH₃)₃}₃][Li · 3(OC₄H₈)] and {(CH₃)₃Si}₃C–Li · O=C(Si(CH₃)₃)₂, two New Adducts of Lithium Trisylmethanide Sublimation of (Tsi–Li) · 2 THF (Tsi = –C(Si(CH₃)₃)₃) at 180 °C and 10^–4 hPa gives (Tsi–Li) · 1.5 THF in very low yield. The X‐ray structure determination shows an almost linear [Tsi–Li–Tsi]^– anion connected by short agostic Li…C contacts with the threefold THF‐coordinated Li‐cation. Base‐free Tsi–Li, solved in toluene is decomposed by oxygen, forming the strawberry‐colored ketone O=C(SiMe₃)₂, which forms an 1 : 1 adduct with undecomposed Tsi–Li. The X‐ray structure elucidation of this compound is also discussed.     

Towards laser spectroscopy of antihydrogen

The development of the first continuous coherent source at 121.56 nm is described. Radiation at this wavelength of Lyman α can be used for laser cooling of antihydrogen on the strong 1S–2P transition. It also opens up a possibility for precision spectroscopy that requires just a few antihydrogen atoms. This revised version was published online in August 2006 with corrections to the Cover Date.     

Combined trap for laser stimulated recombination

We present a combined Paul-Penning trap to study CO₂ laser stimulated recombination of protons and electrons. The trap is located in the center of an optical resonator for 11 μm radiation. In this manner the available laser intensity is enhanced for stimulated recombination to the n=1 state of hydrogen. This revised version was published online in August 2006 with corrections to the Cover Date.     

350-fold improved measurement of the antiproton magnetic moment using a multi-trap method

We summarize our recent 1.5 parts per billion measurement of the antiproton magnetic moment using the multi Penning-trap system of the BASE collaboration. The result was achieved by combining the detection of individual spin-transitions of a single antiproton with a novel two-particle spectroscopy technique, which dramatically improved the data sampling rate. This measurement contributes to improve the test of the fundamental charge, parity, time reversal (CPT) invariance in the baryon sector by a factor of 350 compared to our last measurement, and by a factor of 3000 compared to the best competing measurement. We review the measurement technique and discuss the improved limits on CPT-violating physics imposed by this measurement.     

Trapped antihydrogen in its ground state

Antihydrogen atoms (Hˉ) are confined in an Ioffe trap for 15-1000 s-long enough to ensure that they reach their ground state. Though reproducibility challenges remain in making large numbers of cold antiprotons (pˉ) and positrons (e(+)) interact, 5±1 simultaneously confined ground-state atoms are produced and observed on average, substantially more than previously reported. Increases in the number of simultaneously trapped Hˉ are critical if laser cooling of trapped Hˉ is to be demonstrated and spectroscopic studies at interesting levels of precision are to be carried out.     

Mode shaping in mixed ion crystals of 40Ca2+ and 40Ca+

We present studies of mixed Coulomb crystals of ⁴⁰Ca⁺ and ⁴⁰Ca²⁺ ions in a linear Paul trap. Doubly charged ions are produced by photoionization of trapped ⁴⁰Ca⁺ with a vacuum ultraviolet laser source and sympathetically cooled via Doppler cooled ⁴⁰Ca⁺ ions. We investigate experimentally and theoretically the structural configurations and the vibrational modes of these mixed crystals. Our results with ⁴⁰Ca²⁺ are an important step towards experimental realization of the proposals for mode shaping in a linear crystal and spin-dependent configuration changes from zigzag to linear as proposed by Li et al. (Phys Rev A 87:052304, 2013) and Li and Lesanovsky (Phys Rev Lett 108:023003, 2012) using ions excited to Rydberg states.     

Direct measurement of the free cyclotron frequency of a single particle in a Penning trap

A measurement scheme for the direct determination of the free cyclotron frequency ν(c) of a single particle stored in a Penning trap is described. The method is based on the dressed states of mode coupling. In this novel measurement scheme both radial modes of the single trapped particle are simultaneously coupled to the axial oscillation mode.     

Identities for trigonometric B-splines with an application to curve design

In this paper we investigate some properties of trigonometric B-splines. We establish a complex integral representation for these functions, which is in certain analogy to the polynomial case, but the proof of which has to be done in a different and more complicated way. Using this integral representation, we can prove some identities concerning the evaluation of a trigonometric B-spline, its derivative and its partial derivative w.r.t. the knots. Finally we show that—in the case of equidistant knots—the trigonometric B-splines of odd order form a partition of a constant, and therefore the corresponding B-spline curve possesses the convex-hull property. This is illustrated by a numerical example.     

Baumaterialien

Ohne Zusammenfassung