In trap fragmentation and optical characterization of rotaxanes.

The first experiments on trapped rotaxanes are presented, combining collision induced fragmentation and in-trap laser spectroscopy. The intrinsic optical properties of three rotaxanes and their non-interlocked building blocks (thread and macrocycle) isolated in a quadrupolar ion trap are investigated. The excitation and relaxation processes under thermal activation as well as under photo-activation are addressed.

Properties of broadband depth-graded multilayer mirrors for EUV optical systems.

The optical properties of a-periodic, depth-graded multilayer mirrors operating at 13.5 nm wavelength are investigated using different compositions and designs to provide a constant reflectivity over an essentially wider angular range than periodic multilayers. A reflectivity of up to about 60% is achieved in these calculation in the [0, 18 degrees] range of the angle of incidence for the structures without roughness.

The structure of deprotonated tri-alanine and its a3- fragment anion by IR spectroscopy.

We present the first infrared spectra of a mass-selected deprotonated peptide anion (AlaAlaAla) and its decarboxylated fragment anion formed by collision induced dissociation. Spectra are obtained by IRMPD spectroscopy using an FTICR mass spectrometer in combination with the free electron laser FELIX. Spectra have been recorded over the 800-1800 cm(-1) spectral range and compared with density functional theory calculated spectra at the B3LYP/6-31++G(d,p) level for different isomeric structures.

Single shot damage mechanism of Mo/Si multilayer optics under intense pulsed XUV-exposure.

We investigated single shot damage of Mo/Si multilayer coatings exposed to the intense fs XUV radiation at the Free-electron LASer facility in Hamburg - FLASH. The interaction process was studied in situ by XUV reflectometry, time resolved optical microscopy, and "post-mortem" by interference-polarizing optical microscopy (with Nomarski contrast), atomic force microscopy, and scanning transmission electron microcopy. An ultrafast molybdenum silicide formation due to enhanced atomic diffusion in melted silicon has been determined to be the key process in the damage mechanism.

Intensity-resolved IR multiple photon ionization and fragmentation of C60.

The sequential absorption of multiple infrared (IR) photons by isolated gas-phase species can lead to their dissociation and/or ionization. Using the newly constructed "Free-Electron Laser for IntraCavity Experiments" (FELICE) beam line at the FELIX facility, neutral C(60) molecules have been exposed to an extremely high number (approximately 10(23)) of photons/cm(2) for a total time duration of up to 5 micros. At wavelengths around 20 microm, resonant with allowed IR transitions of C(60), ionization and extensive fragmentation of the fullerenes are observed.

Scattering of hyperthermal nitrogen atoms from the Ag(111) surface.

Measurements on scattering of hyperthermal N atoms from the Ag(111) surface at temperatures of 500, 600, and 730 K are presented. The scattered atoms have a two-component angular distribution. One of the N components is very broad.

Development and testing of a fast Fourier transform high dynamic-range spectral diagnostics for millimeter wave characterization.

A fast Fourier transform (FFT) based wide range millimeter wave diagnostics for spectral characterization of scattered millimeter waves in plasmas has been successfully brought into operation. The scattered millimeter waves are heterodyne downconverted and directly digitized using a fast analog-digital converter and a compact peripheral component interconnect computer. Frequency spectra are obtained by FFT in the time domain of the intermediate frequency signal.

Molecular dynamics simulations of amorphous hydrogenated carbon under high hydrogen fluxes.

We study the flux dependence of the carbon erosion yield and the hydrogen enrichment of the surface in the high flux regime at 10(28) ions per m(2) s and higher by using molecular dynamics (MD). We simulate an amorphous hydrogenated carbon sample exposed to high flux hydrogen bombardment with a hydrogen energy of 10 eV at surface temperatures of 700 and 1000 K. As interaction potential the reactive empirical bond order potential of Brenner-Beardmore is taken and energy dissipation is simulated with the Berendsen thermostat.

Strong scattering of high power millimeter waves in tokamak plasmas with tearing modes.

In tokamak plasmas with a tearing mode, strong scattering of high power millimeter waves, as used for heating and noninductive current drive, is shown to occur. This new wave scattering phenomenon is shown to be related to the passage of the O point of a magnetic island through the high power heating beam. The density determines the detailed phasing of the scattered radiation relative to the O-point passage.

Detection and characterization of carbon contamination on EUV multilayer mirrors.

In this paper, we detect and characterize the carbon contamination layers that are formed during the illumination of extreme ultraviolet (EUV) multilayer mirrors. The EUV induced carbon layers were characterized ex situ using spectroscopic ellipsometry (SE) and laser generated surface acoustic waves (LG-SAW). We show that both LG-SAW and SE are very sensitive for measuring carbon layers, even in the presence of the highly heterogeneous structure of the multilayer.

Gas-phase deprotonation of p-hydroxybenzoic acid investigated by IR spectroscopy: solution-phase structure is retained upon ESI.

The gas-phase structure of the conjugate base of p-hydroxybenzoic acid (and related compounds) and the influence of the solvent used in its generation by electrospray ionization have recently been under debate. While the phenoxide structure is known to be lower in energy in the gas phase, the carboxylate structure is favored in aqueous solution, fuelling the controversy. Here we probe the structure of this gas-phase anion by IR spectroscopy and show that its structure is determined by the protic or aprotic nature of the solvent, which suggests that it is the solution-phase structure that is transferred to the gas phase.

Action spectroscopy of gas-phase carboxylate anions by multiple photon IR electron detachment/attachment.

We report on a form of gas-phase anion action spectroscopy based on infrared multiple photon electron detachment and subsequent capture of the free electrons by a neutral electron scavenger in a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. This method allows one to obtain background-free spectra of strongly bound anions, for which no dissociation channels are observed. The first gas-phase spectra of acetate and propionate are presented using SF(6) as electron scavenger and a free electron laser as source of intense and tunable infrared radiation.

Infrared spectroscopy and structures of cobalt carbonyl cations, Co(CO)n+ (n = 1-9).

Cobalt carbonyl cations of the form Co(CO)(n)(+) (n = 1-9) are produced in a molecular beam by laser vaporization in a pulsed nozzle source. These ions, and their corresponding "argon-tagged" analogues, Co(CO)(n)(Ar)(m)(+), are studied with mass-selected infrared photodissociation spectroscopy in the carbonyl stretching region. The number of infrared-active bands, their frequency positions, and their relative intensities provide distinctive patterns allowing determination of the geometries and electronic structures of these complexes.

Gas-phase IR spectroscopy of deprotonated amino acids.

Gas-phase infrared multiple photon dissociation (IRMPD) spectra have been recorded for the conjugate bases of a series of amino acids (Asp, Cys, Glu, Phe, Ser, Trp, Tyr). The spectra are dominated by strong symmetric and antisymmetric carboxylate stretching modes around 1300 and 1600 cm(-1), respectively. Comparison of the experimental spectra with spectra calculated at the DFT level suggests a carboxylate structure for all species investigated, which is in contrast with what has recently been suggested in this journal for deprotonated cysteine [J.

Microstructure of Mo/Si multilayers with B4C diffusion barrier layers.

The growth behavior of B(4)C interlayers deposited at the interfaces of Mo/Si multilayers was investigated using x-ray photoemission spectroscopy, x-ray reflectivity, and x-ray diffraction measurements. We report an asymmetry in the formation of B(4)C at the B(4)C-on-Mo interface compared to the B(4)C-on-Si interface. X-ray photoelectron spectroscopy (XPS) depth profiling shows that for B(4)C-on-Mo the formed stoichiometry is close to expectation (4:1 ratio), while for B(4)C-on-Si it is observed that carbon diffuses from the B(4)C interfaces into the multilayer, resulting in nonstochiometric growth (>4:1).

Spectroscopic evidence for an oxazolone structure of the b(2) fragment ion from protonated tri-alanine.

Infrared multiple photon dissociation (IRMPD) spectroscopy is used to identify the structure of the b(2)(+) ion generated from protonated tri-alanine by collision induced dissociation (CID). The IRMPD spectrum of b(2)(+) differs markedly from that of protonated cyclo-alanine-alanine, demonstrating that the product is not a diketopiperazine. Instead, comparison of the IRMPD spectrum of b(2)(+) to spectra predicted by density functional theory provides compelling evidence for an oxazolone structure protonated at the oxazolone N-atom.

Rotation of a strongly magnetized hydrogen plasma column determined from an asymmetric Balmer-beta spectral line with two radiating distributions.

A potential buildup in front of a magnetized cascaded arc hydrogen plasma source is explored via E x B rotation and plate potential measurements. Plasma rotation approaches thermal speeds with maximum velocities of 10 km/s. The diagnostic for plasma rotation is optical emission spectroscopy on the Balmer-beta line.

Tautomerism of uracil probed via infrared spectroscopy of singly hydrated protonated uracil.

Tautomerism of the nucleobase uracil is characterized in the gas phase through IR photodissociation spectroscopy of singly hydrated protonated uracil created with tandem mass spectrometric methods in a commercially available Fourier transform ion cyclotron resonance mass spectrometer. Protonated uracil ions generated by electrospray ionization are re-solvated in a low-pressure collision cell filled with a mixture of water vapor seeded in argon. Their structure is investigated by IR photodissociation spectroscopy in the NH and OH stretching region (2500-3800 cm(-1)) with a tabletop IR laser source and in the 1000-2000 cm(-1) range with a free-electron laser.

CO blocking of D2 dissociative adsorption on Ru(0001).

The influence of pre-adsorbed CO on the dissociative adsorption of D(2) on Ru(0001) is studied by molecular-beam techniques. We determine the initial dissociation probability of D(2) as a function of its kinetic energy for various CO pre-coverages between 0.00 and 0.

High sensitivity imaging Thomson scattering for low temperature plasma.

A highly sensitive imaging Thomson scattering system was developed for low temperature (0.1-10 eV) plasma applications at the Pilot-PSI linear plasma generator. The essential parts of the diagnostic are a neodymium doped yttrium aluminum garnet laser operating at the second harmonic (532 nm), a laser beam line with a unique stray light suppression system and a detection branch consisting of a Littrow spectrometer equipped with an efficient detector based on a "Generation III" image intensifier combined with an intensified charged coupled device camera.

Benchmarking of electro-optic monitors for femtosecond electron bunches.

The longitudinal profiles of ultrashort relativistic electron bunches at the soft x-ray free-electron laser FLASH have been investigated using two single-shot detection schemes: an electro-optic (EO) detector measuring the Coulomb field of the bunch and a radio-frequency structure transforming the charge distribution into a transverse streak. A comparison permits an absolute calibration of the EO technique. EO signals as short as 60 fs (rms) have been observed, which is a new record in the EO detection of single electron bunches and close to the limit given by the EO material properties.

Temperature gradients in fast collisionless magnetic reconnection.

Temperature gradients are shown to deform and shift the magnetic islands that grow during fast collisionless reconnection when electron inertia decouples the plasma motion from the magnetic field. A kinetic electron model describes the collisionless processes during the reconnection of field lines originating in regions with different temperatures. Using a novel model of the reconnecting instability as a surface mode, the kinetic effects are treated analytically in the linear and nonlinear stages of the instability of a current-carrying low-beta plasma slab in a strong magnetic guide field.