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921.
Naphthalene was ionized with 130 fs pulses of different polarizations at 1.4 microm. In contrast to the results of ionization by 0.8 microm pulses, fragmentation was dramatically suppressed and naphthalene molecular ions of up to 3+ were produced. The use of this simple model of ionization and large electron kinetic energy enabled us to study the electron-recollision-induced fragmentation and/or double ionization more precisely. The failure of the theoretical prediction of ion yield for the case of naphthalene prevented us from judging the electron recollision solely by a comparison with theoretical curves. Therefore, the effects of laser polarization on the ratios between differently charged states and between molecular and total ions were compared at the same effective (peak) intensity instead of average intensity. Comparison under the same effective intensity enabled us to identify the effects of ellipticity clearly. Evidence of the electron recollision was found in the doubly charged molecular ion formation but not in the fragmentation. The single-electron recollision event was not sufficient to induce fragmentation because of its low energy transfer efficiency. We concluded that the fragmentation originated in the unstable nature of the highly charged molecular ion itself and in the Coulomb explosion in the case of naphthalene. 相似文献
922.
923.
A nucleophilic addition reaction to N-methylaldimines without acid or metal species is described. A novel reagent, dicyanomethyl acetate, is used as a nucleophile to give alpha-(N-methyl-N-acetyl)amino acid methyl esters in excellent yield. 相似文献
924.
Tomoyuki Watanabe Susumu HasegawaNaoki Wakiyama Fusao UsuiAkira Kusai Tetsuhiko IsobeMamoru Senna 《Journal of solid state chemistry》2002,164(1):27-33
A composite of indomethacin (IM) and SiO2 was prepared in a solid state by cogrinding. Dehydration was observed as a consequence of a chemical reaction between silanol groups of SiO2 and carboxyl groups of IM. Several specific radical species found on separately ground SiO2 disappeared preferentially after cogrinding as a result of their recombination. These chemical interactions under mechanical stress bring about a charge transfer, as confirmed by X-ray photoelectron spectroscopy, leading to Si-O-C bridging bond formation at the IM/SiO2 interface. 相似文献
925.
Fostriecin, a potent protein phosphatase inhibitor and antitumor agent, has been enantioselectively synthesized in naturally occurring form via a versatile route, which also allows one to secure all possible stereoisomeres of the C1-C13 fragment including the C11 stereocenter and the geometry of the delta 12-double bond. 相似文献
926.
927.
Takeshi Murata Tomoyuki TeraiTakashi Fukuda Tomoyuki Kakeshita 《Journal of magnetism and magnetic materials》2006
We have examined magnetizations as a function of temperature and magnetic field in layered perovskite manganites La2−2xSr1+2xMn2O7 single crystals (x=0.313, 0.315, 0.318, 0.320 and 0.350) in order to determine the phase boundary between two ferromagnets (one is an uniaxial ferromagnet whose easy axis is parallel to the c-axis and the other is a planar ferromagnet whose easy axis is within the ab-plane) and following results are obtained: (i) all the present manganites exhibit magnetic transitions from a ferromagnet to a paramagnet at 76, 107, 116, 120 and 125 K for x=0.313, 0.315, 0.318, 0.320 and 0.350, respectively; (ii) for x=0.318, 0.320 and 0.350, the magnetic structure is a planar ferromagnet below Curie temperature; (iii) for x=0.313 and 0.315, the magnetic structure changes from an uniaxial to a planar ferromagnet at 66 and 85 K, respectively. From the results described above we have constructed the magnetic phase diagram of layered perovskite manganite La2−2xSr1+2xMn2O7 (0.313?x?0.350). 相似文献
928.
929.
Fulton B. Gonzalez Tomoyuki Kakehi 《Transactions of the American Mathematical Society》2004,356(10):4161-4180
Fix , and let and denote the affine Grassmann manifolds of - and -planes in . We investigate the Radon transform associated with the inclusion incidence relation. For the generic case and n$">, we will show that the range of this transform is given by smooth functions on annihilated by a system of Pfaffian type differential operators. We also study aspects of the exceptional case .
930.