Results 1 - 10 of 6966
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[en] The fragmentation of tryptophan (Trp) - metal complexes [Trp+M]+, where M = Cs, K, Na, Li and Ag, induced by 22 eV energy electrons was compared to [Trp+H]+. Additional insights were obtained through the study of collision-induced dissociation (CID) of [Trp+M]+ and through deuterium labelling. The electron-induced dissociation (EID) of [Trp+M]+ resulted in the formation of radical cations via the following pathways: (i) loss of M to form Trp+, (ii) loss of an H atom to form [(Trp-H)+M]+, and (iii) bond homolysis to form C2H4NO2M+. Deuterium labelling suggests that H atom loss can occur from hetero-atom and/or C-H positions. Other types of fragment ions observed include: C9H7NM+, C9H8N+, M+, C2H3NO2M+, CO2M+, C10H11N2M+, C10H9NOM+. Formation of C2H4NO2M+ and C9H7NM+ cations suggests that the metal interacts with both the backbone and aromatic side chain, thus implicating π-interactions for all M. CID of [Trp+M]+ resulted in: loss of metal cation (for M = Cs and K); successive loss of NH3 and CO as the dominant channel for M = Na, Li and Ag; formation of C2H3NO2M+. Preliminary DFT calculations were carried out on [Trp+Na]+ and [(Trp-H)+Na]+ which reveal that: the most stable conformation involves chelation by the backbone together with a π-interaction with the indole side chain; loss of H atom from α-CH of the side chain is thermodynamically favoured over losses from other positions, with the resultant radical cation maintaining a (N, O, ring) chelated structure which is stabilized by conjugation. (authors)
[en] In the present paper we shall discuss the mechanism of the etching, in particular the origin of the anisotropy and selectivity. We shall also present data offering the explanation why the electrons impinging at the anode with a relatively low energy of approximately 20 eV can facilitate the etching with a remarkably high reaction yield. (Author)
[en] The spectrum of visible emission from photofragments of acetylene excited by single 16.85 eV photons has been recorded for the first time. The spectrum is dominated by the Swan and Deslandres-d'Azambuja bands of C2 and the 431.5 nm band of CH. The yields of these emissions are of the order 10-3 photons per absorbed incident photon. The experimental conditions suggest that the emission results from primary C*2 and CH* photofragments
[en] Using the technique of electron spectrometry and the synchrotron radiation of the storage ring ACO, the photoionization of helium has been investigated between 69 and 150 eV. The probability to leave the residual ion in the n = 2 excited state has been measured as a function of photon energy. The absolute partial photoionization cross section for this process has been determined and found to be in good agreement with recent Multiconfigurational Many-Body Calculations
[en] The fragmentations of iodine cyanide ions created with 2 to 8 positive charges by photoionization from inner shells with binding energies from 59 eV (I 4d) to ca. 900 eV (I 3p) have been examined by multi-electron and multi-ion coincidence spectroscopy with velocity map imaging ion capability. The charge distributions produced by hole formation in each shell are characterised and systematic effects of the number of charges and of initial charge localisation are found.
[en] In recent years, a series of opacity diagnostics have been developed at the Research Center of Laser Fusion in China. Two types of cavities (a conical cavity called a type I target, and a cylindrical cavity with foam baffles called a type II target) were designed to convert the eight-beam laser into x-ray radiation to efficiently heat the sample and to prevent the sample from irradiation of the reflected laser and plasmas on the Shengguang II laser facility. Typical opacity experiments have been carried out using the two target designs, respectively. The results show that a sample temperature of about 95 eV has been reached using the type II target which is the highest obtained on the high power laser facility.
[en] Using 10.7 m and 3 m normal-incidence vacuum ultraviolet spectrographs, we investigated the spectrum of singly ionized potassium in the regions 495-612 A and 1247-2150 A. More than 120 new K II lines were identified. The previous study on this spectrum was revised and extended. All levels of the 3p5 4f and 5f configurations as well as the levels of 3p5 6f based on the 3p52P3/2 core state have now been located. Several new levels of 3p5 3d were also located. The ionization limit was determined from the 3p5nf 1.5[4.5]5 (n=4-6) series as 255072.8±1.5 cm-1 (31.6250±0.0002 eV)
[en] New structures in the Kr 4s photoionization cross section were observed. Closely above threshold the cross section shows a stepwise decline. At somewhat higher energies, the cross section reveals strong dips, which correlate with maxima in cross sections for satellite production, measured too. (orig.)