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41.
Maul J Strachnov I Eberhardt K Karpuk S Passler G Trautmann N Wendt K Huber G 《Analytical and bioanalytical chemistry》2006,386(1):109-118
A combined setup for spatially resolved mass analysis of trace amounts of elements and macromolecules is presented. Using
a MALDI-TOF mass spectrometer, a laser spectroscopic setup for resonant ionization of neutral atoms has been implemented.
This allows for an efficient and selective detection of trace elements by means of resonance ionization mass spectrometry
(RIMS). The instrumental scheme is described, and methodological developments are presented. In a first application pure,
laser desorption/ionization with TOF-MS was used to measure mass distributions of cosmic nanodiamonds. For further applications
regarding the spatially resolved ultra-trace analysis of elements in solid samples, an implanted target was used to characterize
both laser desorption/ionization and laser desorption/resonance ionization for the detection of trace elements within. A perspective
of the setup is given and future investigations are outlined. 相似文献
42.
The (free) electron transfer (FET) from electron donor molecules to parent solvent radical cations of alkanes and alkyl chlorides exhibits mechanistic peculiarities that are conditioned by the low polarity of these solvents. Because of the negligible solvation of ions in such systems and the almost complete lack of an activation barrier, the electron jump takes place at the very first encounter of the reactants and, as such, in extremely short times of 相似文献
43.
Roland Duduchava Ralf Kirsch Sergej Rjasanow 《Journal of Mathematical Fluid Mechanics》2006,8(2):242-266
We present new estimates of the Boltzmann collision operator in weighted Lebesgue and Bessel potential spaces. The main focus
is put on hard potentials under the assumption that the angular part of the collision kernel fulfills some weighted integrability
condition. In addition, the proofs for some previously known
-estimates have been considerably shortened and carried out by elementary methods. For a class of metric spaces, the collision
integral is seen to be a continuous operator into the same space.
Furthermore, we give a new pointwise lower bound as well as asymptotic estimates for the loss term without requiring that
the entropy is finite. 相似文献
44.
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46.
Pradnya Nalawade Sergej Naumov Sudhir Kapoor 《Journal of Physical Organic Chemistry》2013,26(11):870-878
The bimolecular electron transfer from p‐amino benzhydrazide (PABH) and its meta‐derivative (m‐amino benzhydrazide (MABH)) to specific one‐electron oxidant results in the formation of anilino radical. In case of PABH, reaction with ?OH radicals results in the synchronous formation of adduct as well as anilino radical. The interesting observation is that the yield of the anilino radical increases with increase in pH. The effect of substitution also has a significant effect on the formation of adduct. In case of MABH, significant yield of anilino radical gets form on reaction with ?OH radical. The free radical electron transfer from PABH and MABH to parent radical cation of non‐polar solvent also results in the formation of anilino radical only suggesting that the radical cation of PABH and MABH has short life time. The above results were supported by quantum chemical calculations. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
47.
Silicon based deposits were prepared by TEA CO2 pulsed laser ablation (PLA) of SiO and SiO2 targets in the atmosphere of selected gases (N2, He, Ne, Ar, Kr). These deposits possess high specific area of several hundreds m2 per gram. Owing to the high specific area, some chemical groups and hydrogen related radical were detected by means of FTIR and EPR analyses and theoretical calculations: silyl (E′ center) Si, silylen Si:, silanon SiO, POL (peroxy linkage) SiOOSi and/or NBOHC (non-bridging oxygen hole center) SiO, POR (peroxy radical) SiOO and dioxysilirane Si(O)2. In SiO2 deposits the concentration of silyl Si resp. POR SiOO was determined to be 5.8 × 1018/g resp. 6.2 × 1019/g. In SiO deposits the ratio [Si:]:[Si] = (3.1-5.7) × 1019/g: (5.3-9.8) × 1019/g was measured. Estimated concentration of [Si] in deposits was increased nearly five times in comparison with SiO target. After exposure of the SiO deposits to H2 EPR doublet with hyperfine splitting of 7.7 mT was observed. The best agreement between calculated theoretical and experimental values was found for the model [(HO)3SiO]2HSi. FTIR measurements and calculations of the silanol theoretical model clusters enabled us to discuss the chemical surroundings of the silanol and to determine the defects in the deposits. 相似文献
48.
Tom Scherzer Wolfgang Knolle Sergej Naumov Christian Elsner Michael R. Buchmeiser 《Journal of polymer science. Part A, Polymer chemistry》2008,46(14):4905-4916
Brominated aromatic acrylates were found to polymerize rapidly upon exposure to UV light. Moreover, they are able to initiate the UV‐induced polymerization of acrylic formulations that do not contain a conventional photoinitiator. In contrast, the corresponding unbrominated homologues are not effective as initiators. Investigations by real‐time FTIR spectroscopy have shown that the addition of only 1 wt % of a brominated acrylate is sufficient for an efficient initiation. Fast photopolymerization is achieved even if irradiation is carried out at λ > 300 nm where most acrylates do not absorb. Short‐lived transients were studied by laser flash photolysis. The triplet was found to show low sensitivity to oxygen which is because of its very short lifetime. Bromine radicals split of from the acrylates were trapped with bromine ions from tetraethyl ammonium bromide and detected as Br. The resulting quantum yields for the formation of bromine radicals are in the range of up to 0.3. Quantum chemical modeling was carried out to establish a mechanism for the release of bromine radicals. Both bromine and bromophenyl radicals are able to initiate the polymerization reaction. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4905–4916, 2008 相似文献
49.
Joshi R Ghanty TK Naumov S Mukherjee T 《The journal of physical chemistry. A》2007,111(51):13590-13594
Ab initio molecular orbital calculations have been employed to characterize the structure and bonding of the (HO2-H2O)+ radical cation system. Geometry optimization of this system was carried out using unrestricted density functional theory in conjunction with the BHHLYP functional and 6-311++G(2df,2p) as well as 6-311++G(3df,3p) basis sets, the second-order M?ller-Plesset perturbation (MP2) method with the 6-311++G(3df,3p) basis set, and the couple cluster (CCSD) method with the aug-cc-pVTZ basis set. The effect of spin multiplicity on the stability of the (HO2-H2O)+ system has been studied and also compared with that of oxygen. The calculated results suggest a proton-transferred hydrogen bond between HO2 and H2O in H3O3+ wherein a proton is partially transferred to H2O producing the O2...H3O+ structure. The basis set superposition error and zero-point energy corrected results indicate that the H3O3+ system is energetically more stable in the triplet state; however, the singlet state of H3O3+ is more stable with respect to its dissociation into H3O+ and singlet O2. Since the resulting proton-transferred hydrogen-bonded complex (O2...H3O+) consists of weakly bound molecular oxygen, it might have important implications in various chemical processes and aquatic life systems. 相似文献
50.
Prager L Dierdorf A Liebe H Naumov S Stojanović S Heller R Wennrich L Buchmeiser MR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(30):8522-8529
The photochemical conversion of 200-500 nm layers of perhydropolysilazane --(SiH2-NH)n-- (PHPS) in the presence of oxygen into an SiOx network was studied. Different UV sources in the wavelength range of 160-240 nm, that is, 172 nm Xe2* and 222 nm KrCl* excimer, and 185 nm Hg low-pressure (HgLP) lamps were used for these purposes. The role of both ozone and O(1D) as well as of catalytic amounts of tertiary amines in the degradation process of PHPS and the formation of SiOx were studied. In this context, the kinetics of the entire reaction were elucidated and allowed both a continuous and discontinuous process to be established for the production of fully transparent, flexible barrier coatings. Barrier improvement factors (BIFs) of 400 were achieved with one single layer on 23 microm poly(ethyleneterephthalate) (PET), which translated into oxygen transmission rates (OTRs) of 0.20 cm3 m(-2) day(-1) bar(-1). Double layers prepared by this technique allowed the realization of OTRs of or=800. 相似文献