15 research outputs found
Mehr Chancen als Risiken - Südkorea als Markt der Zukunft: Acht Fragen an Klaus F. Zimmermann
No full textA combined neutralization-reionization mass spectrometric and theoretical study of oxyallyl and other elusive [C(3),H(4),O] neutrals
No full textFive different anionic [C3′H4′O]•- isomers, i.e. the radical anions of acrolein, acetyl carbene, formyl methyl carbene, methoxy vinylidene, and oxyallyl are generated in an ion beam mass spectrometer and subjected to neutralization-reionization (NR) mass spectrometric experiments including neutral and ion decomposition difference (NIDD) mass spectrometry; the latter allows for the examination of the neutrals' unimolecular reactivity. Further, the anionic, the singlet and triplet neutral, and the cationic [C3′H4′O] •-/0/•+ potentialenergy surfaces are calculated at the B3LYP/6-311++G(d,p) level of theory. For some species, notably the singlet state of oxyallyl, the theoretical treatment is complemented by G2, CASSCF, and MR-CI calculations. Theory and experiment are in good agreement in that at the neutral stage (i) acrolein does not react within the μsec timescale, (ii) acetyl and formyl methyl carbenes isomerize to methyl ketene, (iii) methoxy vinylidene rearranges to methoxy acetylene, (iv) singlet 1A1 oxyallyl undergoes ring closure to cyclopropanone, and (v) triplet 3B2 oxyallyl may have a lifetime sufficient to survive a NR experiment.Christoph A. Schalley, Stephen Blanksby, Jeremy N. Harvey, Detlef Schröder, Waltraud Zummack, John H. Bowie and Helmut Schwar
Mass spectrometric fragmentation of isomeric 2-alkyl-substituted 1,3-indandiones and 3-alkylidenephthalides: a seven-step consecutive isomerization of regular and distonic molecular radical cations
No full textKuck D. Mass spectrometric fragmentation of isomeric 2-alkyl-substituted 1,3-indandiones and 3-alkylidenephthalides: a seven-step consecutive isomerization of regular and distonic molecular radical cations. Organic Mass Spectrometry. 1994;29(3):113-125.The electron impact-induced fragmentation of 2,2-dimethyl- and 2-ethyl-1,3-indandione, 1 and 2, and their isomers, 3-isopropylidene- and 3-propylidenephthalide, 3 and 4, respectively, was studied in detail by mass-analysed ion kinetic energy (MIKE) and collision-induced dissociation (CID-MIKE) spectrometry, including H-2 and C-13-labelled analogues of 1 and 2. In all regimes of internal energy, the molecular ions 1+. - 4+. interconvert by up to seven consecutive, reversible isomerization steps prior to the main fragmentation processes, viz. loss of CH3. and C2H4 . 1,3-Indandione and 3-methylenephthalide ions with identical alkylidene moieties (i.e. 1+. half arrow right over half arrow left 3+. and 2+. half arrow right over half arrow left 4+.) equilibrate rapidly and completely prior to fragmentation, whereas these pairs of isomers interconvert only slowly via a five-step rearrangement of the indandione ions 1+. half arrow right half arrow left 2+.. Distinct from the behaviour of simpler ionized carbonyl species, a 1,2-C shift of a (formally) neutral carbonyl group is found to occur along with that of a protonated one. Also distinct from simpler cases, methyl loss does not take place from the ionized enol intermediates formed within the interconversion 1+. half arrow right over half arrow left 2+. of the diketone ions but rather from the n-propylidenephthalide ions 4+.. This follows from CID-MIKE spectrometry of the [M - CH3]+ ions of 1-4 and two reference C10H7O2+ (m/z 159) ions of authentic structures (protonated 2-methylene-1,3-indandione and protonated 1,4-naphthoquinone). The characteristic CID fragmentation of the C10H7O2+ ions is rationalized. Finally, the multistep isomerization of ionized 1,3-indandiones apparently also extends to higher homologues [eg. 5+. from 2-ethyl-2-methyl-1,3-indandione (5) and 6+. from 2,2-diethyl-1,3-indandione (6)]: the ionized phthaloyl group of 1,3-indandione radical cations 1+., 2+., 5+. and 6+., originally attached with its two acyl functionalities to the same carbon of the aliphatic chain, performs, in fact, a 'multi-step migration'
All-Optical Synchronization of Pulsed Laser Systems at FLASH and XFEL
No full textThe all-optical laser synchronization at FLASH and XFEL provides femtosecond-stable timing of the FEL X-ray photon pulses and associated optical laser pulses (photo-injector laser, seed laser, pump-probe laser, etc.). Based on a two-color balanced optical cross-correlation scheme a high-precision measure of the laser pulse arrival time is delivered, which is used for diagnostic purposes as well as for the active stabilization of the laser systems. In this paper, we present the latest installations of our all-optical synchronization systems at FLASH and the recent developments for the upcoming European XFEL that will ensure a reliable femtosecond-stable timing of FEL and related pulsed laser systems
Large-Scale Optical Synchronization System of the European XFEL
No full textAt the European XFEL, a facility-wide optical synchronization system providing a femtosecond-stable timing reference at more than 40 end-stations had been developed and installed. The system is based on an ultra-stable, low-noise laser oscillator, whose signals are distributed via actively length-stabilized optical fibers to the different locations across the accelerator and experimental areas. There, it is used to locally re-synchronize radio frequency signals, to precisely measure the arrival time of the electron beam for fast beam-based feedbacks, and to phase-lock optical laser systems for electron bunch generation, beam diagnostics and user pump-probe experiments with femtosecond temporal resolution. In this paper, we present the system's architecture and discuss design choices to realize an extensible, large-scale synchronization infrastructure for accelerators that meets reliability, maintainability as well as the performance requirements. Furthermore, the latest performance result of an all-optically synchronized laser oscillator is shown
STATUS OF THE FIBER LINK STABILIZATION UNITS AT FLASH
No full textAbstract State-of-the-art X-ray photon science with modern freeelectron lasers (FEL) like FLASH (free-electron laser in Hamburg) and the upcoming European X-ray Free-Electron Laser Facility (XFEL) requires timing with femtosecond accuracy. For this purpose a sophisticated pulsed optical synchronization system distributes precise timing via lengthstabilized fiber links throughout the entire FEL. Stations to be synchronized comprise bunch arrival time monitors (BAM's), RF stations and optical cross-correlators (OXC) for external lasers. The different requirements of all those stations have to be met by one optical link stabilization unit (LSU) design, compensating drifts and jitter in the distribution system down to a fs-level. Five years of LSU operation at FLASH have led to numerous enhancements resulting in an elaborate system. This paper presents these enhancements, their impact on synchronization performance and the latest state of the LSUs
First Results on Femtosecond Level Photocathode Laser Synchronization at the SINBAD Facility
No full textSINBAD, the "short-innovative bunches and accelerators at DESY" is an accelerator research and development facility which will host various experiments. SINBAD-ARES linac is a conventional S-band linear accelerator which will be capable of producing ultra-short electron bunches with duration of few femtoseconds and energy of up to 100 MeV. In order to fully utilize the potential of ultra-short electron bunches while probing the novel acceleration techniques (e.g. external injection in LWFA), it is crucial to achieve femtosecond level synchronization between photocathode laser and RF source driving the RF gun of the ARES linac. In this paper we present the first results on the synchronization of the near-infrared photocathode laser to the RF source with the residual timing jitter performance of ~10 fs rms. These results were obtained using a conventional laser-to-RF synchronization setup employing heterodyne detection of an RF signal generated by impinging the laser pulses to a fast photodetector. In addition, we describe an advanced laser-to-RF phase detection scheme as a future upgrade; promising even lower timing jitter and most importantly the long-term timing drift stability
Femtosecond Timing Distribution at the European XFEL
No full textAccurate timing synchronization on the femtosecond timescale is an essential installation for time-resolved experiments at free-electron lasers (FELs) such as FLASH and the upcoming European XFEL. To date the required precision levels can only be achieved by a laser-based synchronization system. Such a system has been successfully deployed at FLASH and is based on the distribution of femtosecond laser pulses over actively stabilized optical fibers. For time-resolved experiments and for special diagnostics it is crucial to synchronize various laser systems to the electron beam with a long-term stability of better than 10 fs. The upcoming European XFEL has raised the demands due to its large number of stabilized optical fibers and a length of 3400 m. Specifically the increased lengths for the stabilized fibers had necessitated major advancement in precision to achieve the requirement of less than 10 fs precision. This extensive rework of the active fiber stabilization has led to a system exceeding the current existing requirements and is even prepared for increasing demands in the future. This paper reports on the laser-based synchronization system focusing on the active fiber stabilization for the European XFEL, discusses major complications, their solutions and the most recent performance results
Reactions Of Gaseous Halocarbonyl Cations With Aromatic Compounds: Ionic Carbonylation Of Inert C-h Bonds
No full textThe mass-selected halocarbonyl cations FCO+, ClCO+, and BrCO+ were reacted with benzene, thiophene, pyrrole, and furan and a few of their alkyl derivatives to evaluate the ability of XCO+ ions to promote C-H bond activation of aromatic compounds (M-H) via gas-phase ionic carbonylation. This novel reaction occurs via electrophilic addition followed by prompt HX elimination, forms the respective acylium ions (M-CO+), and competes with electron abstraction and X+ transfer. The intrinsic gas-phase reactivity order observed for ionic carbonylation was: FCO+>ClCO+>BrCO+. The ability of the fluorosulfinyl cation (FSO+) to promote analogous ionic sulfonylation of aromatic compounds was also tested, but owing to its high recombination energy, FSO+ acts as a potent oxidizing agent and electron abstraction dominates. A novel, highly efficient and nearly exclusive O-abstraction reaction of FC+ and SF+ with N2O was used to the straightforward preparation of gaseous FCO+ and SFO+. 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Author Correction: A MHz-repetition-rate hard X-ray free-electron laser driven by a superconducting linear accelerator
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