Oxygen (O6+) ion beam irradiation effects on etching parameter in lexan polymeric track detector

The polymer Lexan was irradiated to 80MeV O⁶⁺ ion beam using the 15UD pelletron at Inter University Accelerator Centre, New Delhi. The ion fluence ranging from 10¹¹ to 3 × 10¹² ions/cm² has been used to study the dose effects of irradiation on Lexan. By using the etching technique, it is observed that the bulk etch rate of the sample increases with increasing the ion influence, while the activation energy associated with it show a decreasing trend which can be explained on the basis of polymer degradation.      

Modification of the omega-meson lifetime in nuclear matter

Information on hadron properties in the nuclear medium has been derived from the photoproduction of omega mesons on the nuclei C, Ca, Nb, and Pb using the Crystal Barrel/TAPS detector at the ELSA tagged photon facility in Bonn. The dependence of the omega-meson cross section on the nuclear mass number has been compared with three different types of models: a Glauber analysis, a Boltzmann-Uehling-Uhlenbeck analysis of the Giessen theory group, and a calculation by the Valencia theory group. In all three cases, the inelastic omega width is found to be 130-150 MeV/c(2) at normal nuclear matter density for an average 3-momentum of 1.1 GeV/c. In the rest frame of the omega meson, this inelastic omega width corresponds to a reduction of the omega lifetime by a factor approximately 30. For the first time, the momentum dependent omegaN cross section has been extracted from the experiment and is in the range of 70 mb.     

Efficient synthesis of spirooxindole-pyrrolizidines and dispirooxindole-piperazines

A simple and efficient approach for the construction of spirooxindole-pyrrolizidines and dispirooxindole-piperazines by cycloaddition reaction of azomethine ylide generated by isatin and proline has been demonstrated successfully. The formation of two different types of frameworks by two different modes of cycloaddition is explored. The developed protocol highlights simple reaction conditions, easy workup processes, and very good yields of products.     

Internal heavy atom effect on the radiative and non-radiative rate constants in xanthene dyes

Flourescence quantum yield (ø_f), phosphorescence and fluorescence quantum yield ratio (ø_p/ø_f) and the observed triplet decay time (τ_po) of fluorescein and its halogen derivatives have been measured. On halogen substitution an increase in ø_p/ø_f and a decrease in ø_f and τ_po is observed in the sequence of Cl, Br, and I. The increase in ø_p/ø_f is not in the same proportion as the decrease in τ_po. Although ø_p/ø_f is higher for cations than for dianions, it increases more for dianions on halogen substitution. However, the increase in 1/τ_po is about 10³ times more for cations than for dianions. The radiative and non-radiative rate constants viz., k_is, k_p and k_qp have been calculated. On halogen substitution k_f remains almost constant, whereas an increase in k_p, k_is and k_qp is observed. For dianions the increase occurs in the order k_qp> k_is> k_p while for cations the order is k_qp> k_p> k_is. The deuterium solvent effect on triplet decay time and intensity is also observed.     

Red-edge effect in excited state reaction in β-naphthylamine

Alkaline aqueous solutions of β-naphthylamine show the edge effect; a decrease in the relative intensity or emission from the anion (RNH^?) and the neutral molecule (RNH₂) on red-edge excitation (REE) is observed. The nature of quenching of the neutral molecule by OH^? ions also changes on REE. It is suggested that on REE, participation of some non-promoting out-of-plane modes slows down the proton-transfer rate in the excited state.     

Capillary zone electrophoresis in phosphate buffer--known or unknown?

It has been shown recently that the analysis records in capillary electrophoresis may involve regions with extremely strong electromigration dispersion of peaks. Such a fundamental effect is due to the existence of more centers of symmetry in a given electrolyte system. This paper shows that even such a simple and frequently used electrolyte system as phosphate buffer may exhibit more than one center of symmetry. By using the peak shape diagram approach we have revealed that neutral and alkaline phosphate buffers have two centers of symmetry and one center of extreme dispersion. Model experiments confirmed this new important discovery.     

Buildup of the acceptor emission as a result of energy transfer from Tb3+ to Sm3+ in barium borate glass

Intensity and lifetime data indicate that the self-quenching of Sm³⁺ fluorescence in barium borate glass matrix is by direct dipole-quadrupole interactions. The quenching of Tb³⁺ fluorescence by Sm³⁺ has been found due to direct dipole-dipole interactions. However, at relatively low Sm³⁺ concentrations, energy transfer through migration among Tb³⁺ ions also occurs. Further at low Sm³⁺ concentrations, there is an enhancement of Sm³⁺ emission due to energy transfer to an Sm³⁺ that is not coupled to a second Tb³⁺ or Sm³⁺ ion. At high Sm³⁺ concentrations, no enhancement of Sm³⁺ emission occurs and is attributed to transfer to Sm³⁺Sm³⁺ or Sm³⁺Tb³⁺ couples that take up the energy by simultaneous transitions that lie well below the ${}^4\text{G}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ manifold of Sm³⁺.     

Ferrofluid catalyzed water gas shift reaction to give carbon-dioxide and hydrogen

A ferrofluid consisting of colloidally dispersed magnetite particles in water was found to be an efficient selective catalyst for water gas shift reaction at 15–25 atmosphere of CO pressure in the temperature range of 423–553 K where the products obtained were only CO₂ and H₂. The reaction was studied as a function of variation of the concentration of catalyst, pressure of CO gas and temperature. Kinetic parameters suggested a mechanism involving first order dependence in CO and catalyst concentrations.