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91.
92.
Spectral ellipsometry has developed into a routine method applicable to the infrared spectral range. It can give both the refractive index (n) and the absorption index (k), which has so far only been determined for a limited number of compounds. It turns out that vibrations that have a dispersion with an interval of n<1 are by no means restricted to crystals, but occur with numerous compounds including polymers and liquids. In conventional infrared spectroscopy, one usually is not aware of such a situation and so the consequences are disregarded. These include the so-called reststrahlen (residual rays) bands and specific phenomena that occur when n matches the absorption index (the Berreman effect) or the refractive index of ambient air (vanishing reflection, the Christiansen effect). These and some typical applications are discussed, including model calculations and experimental data.Dedicated to the memory of Wilhelm Fresenius 相似文献
93.
Arnulf P. Hagen Shelly J. Hodge Bruce B. Randolph John L. Laing 《Journal of mass spectrometry : JMS》1994,29(6):326-328
Metastable ion scanning was used to investigate the fragmentation patterns of ethyl(trimethoxy)silane, ethyl(dimethoxy)chlorosilane and ethyl(methoxy)dichlorosilane, their deuterated counterparts and ethyltrichlorosilane. For these compounds the molecule ion has a low abundance using 70 eV electron impact ionization. In all cases the base peak corresponds to the loss of neutral C2H5. When chemical ionization is employed with isobutane, usable peaks representative of the molecule ions are observed. 相似文献
94.
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96.
Arnulf Materny 《Chemie in Unserer Zeit》2006,40(4):226-237
Femtochemistry is about the investigation and control of ultrafast elementary molecular dynamics, which are the basis of every chemical reaction. The processes finally resulting in breaking of chemical bonds or molecular structure changes take place on a time scale of only femto to picoseconds. Solely femtosecond laser pulses are fast enough to resolve these fast processes. Different techniques were developed, which make use of a combination of femtosecond pulses having a relative temporal delay, in order to get access to the dynamics even in complex molecules. The knowledge of the elementary processes allows for a better understanding of the reaction mechanisms and their dependence on environmental conditions. The interaction with the molecules even before the final reaction path is entered, opens up new exciting possibilities for the control of chemical processes. A specific manipulation of the molecular dynamics using adapted pulse shapes appears to be realistic also for complex reactions and systems. The evolutionary optimization strategies, which exploit the experimental results as feedback, make selective chemistry come true even without knowledge of all system parameters. 相似文献
97.
98.
Snehasis Bhunia Rasha Hassanein Arnulf Materny Animesh K. Ojha 《Journal of Raman spectroscopy : JRS》2015,46(12):1191-1199
The interaction of K+ with the zwitterionic form of alanine (ZAla) is investigated using Raman spectroscopy and density functional theory calculations. The Raman spectra of an aqueous solution of Ala and its mixture with KOH at different molar concentrations [ZAla + xKOH, x = 1–5 M] have been recorded in the spectral region 400–1800 cm−1. The wavenumber position of the band at ~529 cm−1 shows a red shift of 14 cm−1, while the Raman band at ~634 cm−1 shows a blue shift of 10 cm−1 with the increasing x from 1 to 5 M. The intensity ratio I634/I529 is increased with increasing x, and it could be because of the increase in concentration of the [ZAla + K+] complex in the solution. The new Raman band appeared at ~1079 cm−1 in the Raman spectra of [ZAla + xKOH, x = 1–5] complex. To determine the most probable site for the interaction of K+ with ZAla, the structures of ZAla and the [ZAla + K+] were optimized at B3LYP/6‐311++G(d,p) level of theory. The electrostatic potential calculation carried out for ZAla reveals that the maximum density of electron is lying over COO−, and therefore, COO− would be the most probable site for the interaction of K+ with ZAla. The theoretically calculated Raman spectra of ZAla, [ZAla + K+] and the [ZAla− + K+] are in good agreement with experimentally observed Raman spectra. Thus, the Raman bands at ~529, 634, and 1079 cm−1 may be used as the Raman fingerprint for the interaction of K+ with COO− of the ZAla and ZAla−. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
99.
Arnulf Soltys 《Mikrochimica acta》1930,8(1):275-279
Ohne Zusammenfassung 相似文献
100.
Dr. Soroush Naseri Dr. Inès Taarit Dr. Hélène Bolvin Prof. Dr. Jean-Claude Bünzli Dr. Alexandre Fürstenberg Dr. Laure Guénée Dr. Giau Le-Hoang Dr. Mohsen Mirzakhani Dr. Homayoun Nozary Dr. Arnulf Rosspeintner Prof. Dr. Claude Piguet 《Angewandte Chemie (International ed. in English)》2023,62(50):e202314503
Previously limited to highly symmetrical homoleptic triple-helical complexes [Er( Lk )3]3+, where Lk are polyaromatic tridentate ligands, single-center molecular-based upconversion using linear optics and exploiting the excited-state absorption mechanism (ESA) greatly benefits from the design of stable and low-symmetrical [ Lk Er(hfa)3] heteroleptic adducts (hfa−=hexafluoroacetylacetonate anion). Depending on (i) the extended π-electron delocalization, (ii) the flexibility and (iii) the heavy atom effect brought by the bound ligand Lk , the near-infrared (801 nm) to visible green (542 nm) upconversion quantum yield measured for [ Lk Er(hfa)3] in solution at room temperature can be boosted by up to three orders of magnitude. 相似文献