Photoionization of highly charged ions using an ECR ion source and undulator radiation

Photoionization of Xe4+ to Xe7+ ions was studied by combining an electron cyclotron resonance ion source with synchrotron radiation. Multiconfiguration Dirac-Fock calculations were performed to interpret the data. Many autoionization lines were measured and identified, resulting from excitation of a 4d electron into nf and np orbitals followed by Auger decay of the excited states. Continuum photoionization is negligible for the higher members of the isonuclear series.     

Polarizing the Nazarov cyclization: the impact of dienone substitution pattern on reactivity and selectivity

The impact of dienone substitution on the Nazarov cyclization has been examined in detail. Substrates bearing different substituents at each of four positions on the dienone backbone were systematically probed in order to identify trends leading to higher reactivity and better selectivity. Desymmetrization of the pentadienyl cation and oxyallyl cation intermediates through placement of polarizing groups at both the C-2 and C-4 positions was found to be particularly effective. These modifications allowed cyclizations to occur in the presence of catalytic amounts of mild Lewis acids. It was also found that stereoconvergent cyclization of mixtures of E and Z isomers of alkylidene beta-ketoesters occurred via an efficient isomerization process that occurred under the reaction conditions.     

Uptake of Ba2+ ions by natural bentonite and CaCO3: A radiotracer, EDXRF and PXRD study

Ba²⁺ uptake by natural bentonite, CaCO₃ in addition to a number of bentonite-CaCO₃ mixtures with variable compositions as a function of pH and Ba²⁺ concentration was studied. Radiotracer method, EDXRF, and PXRD were used. The results of radiotracer experiments showed that the uptake of Ba²⁺ by CaCO₃ was larger than its uptake by natural bentonite samples, particularly at low initial concentrations of Ba²⁺ and higher pH values. This finding was supported by the EDXRF results. According to the sorption data, the apparent DG° values of sorption were in the range -9±1 to -13±3 kJ/mol. The PXRD studies revealed the formation of BaCO₃ upon sorption of Ba²⁺ on pure CaCO₃ and on some of the bentonite-CaCO₃ mixtures.     

Small exponent asymptotics

We study the surprisingly complicated asymptotic character ofa simple first-order differential equation, which involves aterm with a low exponent of the dependent variable. While numericalsolutions and straightforward asymptotic expansions indicatea clearly defined boundary layer type transition, we find thatthe correct asymptotic structure involves a 'hidden' boundarylayer, and that a straightforward approach cannot discern this.