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Nigel Stothard Robert Humpfer Horst-Henning Grotheer 《Chemical physics letters》1995,240(5-6):474-480
NH2 profiles were measured in a discharge flow reactor at ambient temperature by monitoring reactants and products with an electron impact mass spectrometer. At the low pressures used (0.7 and 1.0 mbar) the gas-phase self-reaction is dominated by a ‘bimolecular’ H2-eliminating exit channel with a rate coefficient of k3b(300 K) = (1.3 ± 0.5) × 10−12 cm3 molecule−1 s−1 and leading to N2H2 + H2 or NNH2 + H2. Although the wall loss for NH2 radicals is relatively small (kw ≈ 6–14 s−1), the contribution to the overall NH2 decay is important due to the relatively slow gas-phase reaction. The heterogeneous reaction yields N2H4 molecules. 相似文献
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Premixed laminar flat ethylene flames were investigated for nascent nanoparticles through photoionization mass spectrometry
(PIMS). Using an atmospheric McKenna burner and ethylene air flames coupled to an atmospheric sampling system, within a relatively
narrow C/O range two modes of these particles were found, which can be clearly distinguished with regard to their temperature
dependence, their reactivity, and their ionization behaviour. Behind a diesel engine the same particles were observed. 相似文献
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Horst-Henning Grotheer Johann Wolfgang Hammer Klaus-Werner Hoffmann 《Zeitschrift für Physik A Hadrons and Nuclei》1969,225(4):293-302
The electron capture decay of85Sr and55Y has been investigated using NaI(Tl)-detectors. Spectroscopic-coincidence techniques have been employed to examine theK-electron capture rates. The experimental results areP K ω K (Sr)=.5959 ± 0.0035 andP K ω K (Y)=0.6340± 0.0032. Using theK-capture probabilities, derived from the capture ratios ofBrysk andRose with the exchange correction ofBahcall:P K (Sr)=0.880± 0.008 andP K (Y)=0.883 ± 0.008, one can derive from these results the fluorescence yieldsω K (Rb)=0.677± 0.009 andω K (Sr)=0.712± 0.010. Functions ofω K (Z) were fitted to recent experimental data and tabulated forZ=5–90. In addition to these results the half life of the 514 keV state of85Rb and the branching ratios and the positron rate of the88Y-decay have been measured with the same techniques. The data obtained partly disagree from measurements of other authors. 相似文献
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Baquet TG Grotheer HH Aigner M 《Rapid communications in mass spectrometry : RCM》2007,21(24):4060-4064
The soot precursor particles reported in the literature to date may be roughly divided into two classes. Some of their features are very different. Using photoionization mass spectrometry behind premixed atmospheric ethylene/air flames, particle mass distribution functions were measured for these precursor particles. Within a limited C/O range bimodality was found, i.e. two types of particles are formed simultaneously. Through analysis of the photoionization behaviour it was found that the ionization order (IO) is different for these two modes as is the stability of the respective particles. In accordance with earlier measurements, particles with IO = 1 are interpreted as polyaromatic hydrocarbon (PAH) stacks whereas the IO = 2 particles rather seem to be large molecules. This is consistent with the different particle classes mentioned above. Their potential role in soot formation is briefly addressed. Copyright (c) 2007 John Wiley & Sons, Ltd. 相似文献
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The complementary REMPI (resonance-enhanced multi-photon ionisation) techniques using either a tuneable laser or a fixed-frequency
laser are compared. Our Jet-REMPI apparatus, consisting of a tuneable laser unit (Nd:YAG pump laser and OPO) and a reflectron
mass spectrometer, is briefly introduced. This machine has been upgraded to cope with the difficult conditions (such as vibrations,
temperature fluctuations and dust) prevailing in an incinerator. On-line measurements of the raw gas have been carried out
at the municipal waste incinerator (MWI) in Stuttgart. Although this test series could not be completed the results are encouraging.
They show that wavelength resolution can provide valuable information beyond that which can be obtained by fixed-frequency
REMPI. Examples discussed include identification of phenanthrene as major constituent of the isomeric pair phenanthrene/anthracene
and the structural identification of xylene isomers in the incinerator raw gas. Both examples are also of more general interest,
the former with regard to investigation of soot precursors and the latter for quality assessment of refinery products. Spectra
of some deuterated aromatics are reported for use of these compounds as standards. In addition, a mass spectrum containing
DDT is shown and a chlorobenzene profile measured earlier in a pilot scale incinerator as demonstration of the sensitivity
of the instrument. As is to be discussed, significant further sensitivity gains through increase of the beam density are limited
because of ion collisions within the sample beam.
Received: 23 February 2000 / Revised version: 9 June 2000 / Published online: 5 October 2000 相似文献
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In an extension of our earlier studies at lower temperatures [4,5] the title reaction was measured directly in a flow reactor at temperatures of 600 and 700 K. The pressure of 0.65 mb was chosen that low in order to reduce the contribution of the stabilization channel. OH was used in an excess over CH3. Both reactants along with the reaction products were monitored by mass spectrometry. CH3 profiles served as the major observable quantity for the extraction of rate data. This had to be done by using computer simulation since it was impossible to work under pseudo-first-order conditions. The obtained total rate coefficients were divided into channel rate coefficients by means of branching ratios as determined by the mass spectrometric measurement of the reaction products. For CH3 + OH, this led to a rate coefficient, k1a into the stabilization channel, and another one, k1e + f referring to the sum of two H2-eliminating channels yielding the biradical HCOH and to a minor extent H2CO. These latter channels have not been measured before. In order to distinguish between them we switched over from OH to OD to get so that the biradical and/or aldehyde channels could be determined by their by-products H2 and HD, respectively. The use of OD makes it also possible to measure the channel through its by-product, HDO. A comparison of the rate coefficients of both systems, i.e., CH3 + OH and CH3 + OD, indicates that within our error limits no significant isotope effect takes place. For the rate coefficient into the HCOH channel, we arrive at a preliminary Arrhenius expression in units of cm, molec, and s: . The H2CO channel could not be detected at our lower temperature rendering us with a rate coefficient at 700 K: . Since simulation is needed for the deduction of the total rate coefficients as well as of the branching ratios, an uncertainty factor of 1.5 has to be attributed to these numbers. © 1995 John Wiley & Sons, Inc. 相似文献
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Happold J Grotheer HH Aigner M 《Rapid communications in mass spectrometry : RCM》2007,21(7):1247-1254
Samples were drawn from sooting premixed low-pressure ethylene oxygen flames and investigated through photoionization mass spectrometry using either KrF or ArF lasers as the radiation source. With the former, mass spectra were obtained as described in the literature and characterized through a series of signal groups, one for each C-number and extending to about m/z 1000, assigned as a PAH series. When the ArF laser was used the same series was observed with a somewhat higher sensitivity. In addition, a new series was observed overlaid on the PAH series and starting at about m/z 680. The new series exhibited abundant ions and it completely dominated the spectrum beyond m/z 1000. This series was identified as being the spectrum of soot precursor particles. Through measurement of the ionization order it was concluded that at least two photons are needed for ionization of PAHs whereas the particles need only one photon. Consequently, they can be measured with high sensitivity when an ArF laser is used as the radiation source. Furthermore, the discrimination of soot precursor molecules and soot precursor particles becomes possible through photoionization and this enables an improved understanding of the mass spectra. This should allow a particle growth mechanism to be deduced in the near future. 相似文献
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