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Asfandiarov NL Fal'ko VS Lukin VG Nafikova EP Pshenichnyuk SA Fokin AI Lomakin GS Chizhov YV 《Rapid communications in mass spectrometry : RCM》2001,15(19):1869-1878
A series of halogenated anthraquinone (AQ) derivatives has been studied by means of electron capture negative ion (NI) mass spectrometry (ECNI-MS). 1Cl-AQ and 2Br-AQ display dramatically steep positive temperature dependencies of Hal(-) ion abundance in the low electron energy region. Molecular NI intensity decreases rapidly with increasing temperature in the case of 1I-AQ. In the case of 2Br-AQ, a metastable NI peak (m/z 22.9) corresponding to the process BrAQ(-) --> Br(-) + AQ(0) was recorded. This means that the characteristic dissociation lifetime of the molecular NI Br-AQ(-) is at least approximately 25 micros at the energy approximately 0.67 eV in the low-temperature spectrum (T approximately 80 degrees C), and at the energy approximately 0.13 eV in the hot spectrum (T approximately 290 degrees C). Together with the observed temperature dependence of the 2Br-AQ curves of effective yield (CEY), this proves that this anion dissociates according to Coulson's model. The same halogen anion behavior is observed in the case of 1Cl-AQ. There are three consecutive stages in the process of molecular NI dissociation of Cl- and Br-substituted AQ, namely, electron capture into the empty pi-orbital by means of the shape resonance mechanism, followed by a radiationless transition into the ground electronic pi-state of the anion, as predicted by Compton in the case of the parabenzoquinone molecule, and, finally, a fluctuative dissociation of the molecular NI accompanied by the transition from the pi-term into the sigma-term, so-called predissociation. Calculations show reasonable agreement with the experimental data. In the case of 1I-AQ, an effect of inversion of empty levels in the process of electron capture by the molecule takes place, a violation of the so-called frozen shell approximation. The phenomenon found may be of significance not only in the case of ECNI-MS, but also in other experimental investigations using low-energy electron-molecule and ion-molecule collisions. 相似文献
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The lifetimes of long-lived negative molecular ions SF6−-, C6H5NO2−, and C6F6− are measured with a static mass spectrometer. A great spread in published data for the lifetimes of these ions is explained
using a concept of multiexponential decay of molecular ions. The influence of the Boltzmann distribution of neutral target
molecules over vibrational states on the lifetime of negative molecular ions is studied in terms of the Illenberger-Smirnov-Kompaneits
simple statistical model. It is shown that this distribution has a profound effect on the multiexponential decay of molecular
anions and, as a consequence, on the lifetime of negative molecular ions measured on different mass spectrometers. 相似文献
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V. E. Vildeman E. V. Lomakin T. V. Tret’yakova M. P. Tret’yakov 《Mechanics of Solids》2016,51(5):612-618
The paper deals with experimental studies of inhomogeneous strain fields in the “neck” region in extension of plane and cylindrical specimens at the postcritical stage, which directly precedes the fracture, by using a video system and a digital image correlation method. We consider the problems of interpretation of extension diagrams obtained for specimens of various length with strain inhomogeneity in the working section of the specimen with a “neck.”We obtain experimental data about the distribution of longitudinal, transverse, and shear strain fields and the displacement fields in the region of the plane specimen localization by using the digital image correlation method. 相似文献