排序方式: 共有70条查询结果,搜索用时 343 毫秒
11.
Köhler J Hemberger P Fischer I Piani G Poisson L 《The journal of physical chemistry. A》2011,115(50):14249-14253
The ultrafast dynamics of isolated 9-fluorenone was studied by femtosecond time-resolved photoionization and photoelectron spectroscopy. The molecule was excited around 264-266 nm into the S(6) state. The experimental results indicate that the excitation is followed by a multistep deactivation. A time constant of 50 fs or less corresponds to a fast redistribution of energy within the initially excited manifold of states, i.e., a motion away from the Franck-Condon region. Internal conversion to the S(1) state then proceeds within 0.4 ps. The S(1) state is long-lived, and only a lower bound of 20 ps can be derived. In addition, we computed excited state energies and oscillator strengths by TD-DFT theory, supporting the interpretation of the experimental data. 相似文献
12.
To be able to meet the demands of low emissions and fuel consumption ofmodern combustion engines, new ways have to be found to control thecombustion. We use new sensors to measure the pressure in the combustionchamber and analyze this signal with a neural network in order to receiveseveral form factors which can be used to control the ignition timing. Theneural network is trained off line with measured data and used on line toderive the form factors. The proposed algorithm can be computed in real timeon conventional digital signal processors and adapted to new engines withvery little effort. 相似文献
13.
Staresinić D Lunkenheimer P Hemberger J Biljaković K Loidl A 《Physical review letters》2006,96(4):046402
We report on broadband dielectric spectroscopy on the one-dimensional semiconductor (NbSe4)3I. Below the structural phase transition close to 270 K, which is accompanied by complex charge-order processes, we observe colossal dielectric constants with a frequency and temperature dependence very similar to what is observed in charge-density wave systems. 相似文献
14.
Engelbert Reusch Dr. Fabian Holzmeier Marius Gerlach Prof. Dr. Ingo Fischer Dr. Patrick Hemberger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(72):16652-16659
The reaction products of the picolyl radicals at high temperature were characterized by mass-selective threshold photoelectron spectroscopy in the gas phase. Aminomethylpyridines were pyrolyzed to initially produce picolyl radicals (m/z=92). At higher temperatures further thermal reaction products are generated in the pyrolysis reactor. All compounds were identified by mass-selected threshold photoelectron spectroscopy and several hitherto unexplored reactive molecules were characterized. The mechanism for several dissociation pathways was outlined in computations. The spectrum of m/z=91, resulting from hydrogen loss of picolyl, shows four isomers, two ethynyl pyrroles with adiabatic ionization energies (IEad) of 7.99 eV (2-ethynyl-1H-pyrrole) and 8.12 eV (3-ethynyl-1H-pyrrole), and two cyclopentadiene carbonitriles with IE′s of 9.14 eV (cyclopenta-1,3-diene-1-carbonitrile) and 9.25 eV (cyclopenta-1,4-diene-1-carbonitrile). A second consecutive hydrogen loss forms the cyanocyclopentadienyl radical with IE′s of 9.07 eV (T0) and 9.21 eV (S1). This compound dissociates further to acetylene and the cyanopropynyl radical (IE=9.35 eV). Furthermore, the cyclopentadienyl radical, penta-1,3-diyne, cyclopentadiene and propargyl were identified in the spectra. Computations indicate that dissociation of picolyl proceeds initially via a resonance-stabilized seven-membered ring. 相似文献
15.
Pulsed dielectric spectroscopy is introduced as a technique for selectively emphasizing specific components of the non-exponential
dielectric response of matter. Samples studied include supercooled liquid propanol, propylene carbonate, and poly(lauryl-methacrylate).
It is shown that particular sequences of pulses can be used to emphasize the fast response regime, to produce a cross-over
or memory effect, or to eliminate the response of selected components. Furthermore, for materials characterized by broad distributions
of relaxation times, the technique facilitates the investigation of a relatively narrow band from that distribution. It is
also shown that the time domain spectroscopy can be combined with conventional frequency domain techniques to provide the
characterization of dielectric response over an extraordinarily broad spectral range. 相似文献
16.
Engelbert Reusch Dr. Fabian Holzmeier Philipp Constantinidis Dr. Patrick Hemberger Prof. Dr. Ingo Fischer 《Angewandte Chemie (International ed. in English)》2017,56(27):8000-8003
Nitrogen-containing resonance-stabilized radicals such as the picolyl radical are important in combustion chemistry and astrochemistry. They have only been scarcely studied because an isomer-selective generation is often difficult. Herein, we present threshold photoelectron spectra of the three picolyl radical isomers, C6H6N, that were obtained with synchrotron radiation. The radicals were selectively generated by flash pyrolysis from aminomethylpyridine precursors through deamination. Ionization energies of 7.70, 7.59, and 8.01 eV were determined for 2-, 3-, and 4-picolyl, respectively. The observed vibrational structure was assigned to an in-plane deformation mode of the aromatic ring. The spectroscopic insight gained in this study can be used to distinguish different picolyl isomers in on-line combustion analysis, for example. 相似文献
17.
Dr. Domenik Schleier Marius Gerlach Dr. Deb Pratim Mukhopadhyay Emil Karaev Dorothee Schaffner Dr. Patrick Hemberger Prof. Ingo Fischer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(42):e202201378
We have investigated the photoionization of ammonia borane (AB) and determined adiabatic ionization energy to be 9.26±0.03 eV for the X+ 2E←X 1A1 transition. Although the threshold photoelectron spectrum appears at first glance to be similar to the one of the isosteric ethane, the electronic situation differs markedly, due to different orbital energies. In addition, an appearance energy AE0K(NH3BH3, NH3BH2+)= 10.00±0.03 eV has been determined, corresponding to the loss of a hydrogen atom at the BH3-site. From the data, a 0 K bond dissociation energy for the B−H bond in the cation of 71.5±3 kJ mol−1 was derived, whereas the one in the neutral compound has been estimated to be 419±10 kJ mol−1. 相似文献
18.
A. W. Garrett P. H. Hemberger N. S. Nogar 《Spectrochimica Acta Part B: Atomic Spectroscopy》1995,50(14):1889-1895
The ion storage capacity (<106) of ion trap mass spectrometers (ITMS) can sometimes limit the ability to analyze trace components in complex mixtures. We demonstrate here that resonant laser ablation (RLA) can offer a degree of selectivity in the ionization process, thus allowing the preferential accumulation of analyte ions in the trap. Selectivities of 75 and 50, for chromium and iron, respectively, are reported here for RLA of stainless steel in an ITMS. We offer suggestions to improve both the selectivity and the ionization efficiency, relative to the results reported here. 相似文献
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20.
Fichtl R Tsurkan V Lunkenheimer P Hemberger J Fritsch V von Nidda HA Scheidt EW Loidl A 《Physical review letters》2005,94(2):027601
Low-temperature specific heat measurements and dielectric spectroscopy have been performed on polycrystalline and single-crystalline FeCr2S4, the single crystals showing a transition into a low-temperature orbital glass phase. The freezing of the orbital moments is revealed by a glasslike specific heat anomaly and by a clear relaxational behavior of the dielectric permittivity, exhibiting several hallmark features of glassy dynamics. The orbital relaxation dynamics continuously slows down over six decades in time, before at the lowest temperatures the glass transition becomes suppressed by quantum tunneling. 相似文献