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1.
Bruno Hasiak Guy Ricart Didier Barbry Daniel Couturier Michel Hardy 《Journal of mass spectrometry : JMS》1981,16(1):17-20
The ammonia chemical ionization desorption spectra of N,N-dimethyl quaternary ammonium iodides in addition to high protonated molecular ion [M + H]+ intensity, show signals for an ion radical composed of N-methyl abstracted salt cation and ammonia [C + NH3? CH3]+˙. These ions corresponding to the cation +2 show increased importance in the chemical ionization mode, using the same reagent gas. The technique of chemical ionization desorption appears suitable for the analysis of salts, and thus for the determination of the molecular weight of both anion and cation. 相似文献
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A comparative and systematic ab initio study of different models simulating the Si (111) surface has been carried out for a variety of embedding hydrogen atoms including unmodified hydrogen atoms and modified hydrogen atoms described with a STO-4G basis set and a Slater exponent optimized to have the cluster atoms as neutral as possible. The study has been extended to some chemisorption processes as Ag and Al on Si (111). The main conclusion of the present work is that neither the electronic structure of the isolated cluster models nor the nature of the chemisorption bond depend on the kind of embedding hydrogen atoms used to saturate the free valences of the cluster edge atoms. © John Wiley & Sons, Inc. 相似文献
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Hichem Eloussifi Jordi Farjas Pere Roura Jaume Camps Mohamed Dammak Susagna Ricart Teresa Puig Xavier Obradors 《Journal of Thermal Analysis and Calorimetry》2012,108(2):589-596
A detailed analysis of the thermal decomposition of yttrium trifluoroacetate under different atmospheres is presented. Thermogravimetry,
differential thermal analysis, and evolved gas analysis have been used for this in situ analysis. Solid residues at different
stages have been characterized by means of X-ray diffraction, elemental analysis, Fourier transform infrared spectroscopy,
and scanning electron microscopy. The first decomposition stage (310 °C) is exothermic and involves the complete removal of
carbon (organic part) and the formation of yttrium fluoride. This process is characterized by a fast mass loss rate. Afterwards,
yttria (Y2O3) is formed at 1200 °C through a slow process controlled by the out diffusion of fluorine that involves the formation of yttrium
oxyfluoride as an intermediate. The evolution of the mass during the decomposition and the structure of the yttria particles
is not affected by the presence of oxygen or water. However, when the oxygen (water) partial pressure is as low as 0.02% (<0.002%),
the kinetics and final particle structure are strongly affected. 相似文献
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The possible Cs, C2v, and C∞v structures of AlO2 corresponding to the two lowest electronic states which dissociate into the neutral Al(2P) and O2(3Σg?) fragments have been investigated at the ab initio self-consistent field (SCF) and CI levels using nonempirical pseudopotentials. The most stable structure corresponds to a C2v symmetry in the 2A2 electronic state. However, this structure presents the three-center three-electron Hartree-Fock instability and CASSCF calculations were necessary to unequivocally characterize it as true minimum. Moreover, only another stable structure, of C2v geometry, was found to be a minimum, corresponding to a low-lying excited state of 2A1 symmetry. The optimized C∞v structures were not minima on the corresponding potential energy surfaces and no evidence of any stable Cs structure was found. Calculating values are compared with the different experimental data obtained from the reaction of Al and O2 in frozen gas inert matrices. 相似文献
6.
Davy L S Nieskens Francisco Ample-Navarro Maarten M M Jansen Daniel Curulla-Ferré Josep Ricart Hans Niemantsverdriet 《Chemphyschem》2006,7(5):1068-1074
The decomposition of acetylene on a Rh(100) single crystal was studied by a combination of experimental techniques [static secondary ion mass spectrometry (SSIMS), temperature-programmed desorption (TPD), and low-energy electron diffraction (LEED)] to gain insight into the reaction pathway and the nature of the reaction intermediates. The experimental techniques were combined with a computational approach using density functional theory (DFT). Acetylene adsorbs irreversibly on the Rh(100) surface and eventually decomposes to atomic carbon and gas-phase hydrogen. The combination of experimental and computational results enabled us to determine the most likely reaction pathway for the decomposition process. 相似文献
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Susagna Ricart Dr. Josep M. Moretó Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(30):9193-9202
From a practical synthetic point of view, the nickel‐mediated carbonylative cycloaddition of alkynes and allyl halides is a straightforward method for obtaining the cyclopentane skeleton in high yields and with controlled stereochemistry, especially when considering the efficiency of the intermolecular version of the reaction. The efforts to make the previously stoichiometric process catalytic in nickel, after experimental mechanistic observations, are reported herein. The unexpected intervention of iron as a reductant and the isolation of a final dimeric species that exhibits interesting tautomeric behavior are also presented. An extension of the reaction to new substrates has led to the conclusion that, although the steric and electronic effects of the alkyne substituents are generally irrelevant in relation to the adducts and their yields, those of the allylic counterpart may have a significant influence on the outcome of the reaction. However, the presence of the amine moiety in the alkyne completely inhibited the reaction. The feasibility of a multicentered reaction was verified with a triacetylene in which up to 12 bonds were created at once and in good yield. 相似文献
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J. M. Piot Q. Zhao D. Guillochon P. Dhulster G. Ricart D. Thomas 《Chromatographia》1990,30(3-4):205-210
Summary An important goal of previous high-performance liquid chromatography (HPLC) studies was the development of a simple procedure for the purification of peptides from very complex haemoglobin enzymatic hydrolysates. This report demonstrates that the separation system described can be used for large sample loadings at laboratory preparative scale (more than 50 mg) without loss of resolution. The efficiency of peptide purification was shown by fast atom bombardment-mass spectrometry (FAB-MS) and tandem mass spectrometry (tandem M S). The procedure described will be of interest in the biotechnology area for the extensive preparation of peptides for fine applications from complex enzymatic hydrolysates. 相似文献
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Antonietta Artillo Marco De Santis Susagna Ricart Aldo Spinella 《Journal of organometallic chemistry》2007,692(6):1277-1284
Mono and disubstituted ureas react with alkynyl Fischer carbene complexes to give mono and di N,N-substituted organometallic uracil analogues. An optimization of the process using different starting metal carbene complexes and variously substituted ureas under conventional heating (with and without solvent) and microwave irradiation techniques is reported. The synthesis of the metal-carbene analog of the commercially available dimethyl uracil is reported. 相似文献