Shape-controlled Synthesis of Gold Nanoparticles from Gold(III)-chelates of β-diketones

Chelating ligands with β-diketone skeleton have been employed for the first time as reductant to produce ligand stabilized gold nanoparticles of different shapes out of aqueous HAuCl₄ solutions. Evolution of stable gold nanoparticles happens to be first order with respect to gold particles having rate constants ∼ ∼10⁻² min⁻¹ and subsequent chlorine insertion in the β-diketone skeleton is reported as a general feature. Spherical or triangular or hexagonal particle evolution goes selectively under the influence of different β-diketones in terms of capping and reducing capabilities of the reductants.     

Probing Balitsky-Fadin-Kuraev-Lipatov dynamics in the dijet cross section at large rapidity intervals in pp collisions at sqrt[s]=1800 and 630 GeV

Inclusive dijet production at large pseudorapidity intervals (Deltaeta) between the two jets has been suggested as a regime for observing Balitsky-Fadin-Kuraev-Lipatov (BFKL) dynamics. We have measured the dijet cross section for large Deltaeta in pp collisions at sqrt[s]=1800 and 630 GeV using the D0 detector. The partonic cross section increases strongly with the size of Deltaeta. The observed growth is even stronger than expected on the basis of BFKL resummation in the leading logarithmic approximation. The growth of the partonic cross section can be accommodated with an effective BFKL intercept of alphaBFKL(20 GeV)=1.65+/-0.07.     

Measurement of the W-->taunu production cross section in pp collisions at square root s=1.8 TeV

We report on a measurement of sigma(pp-->W+X)B(W-->taunu) in pp collisions at sqrt[s]=1.8 TeV at the Fermilab Tevatron. The measurement is based on an integrated luminosity (lum) of 18 pb-1 of data collected with the D0 detector during 1994-1995. We find that sigma(pp-->W+X)B(W-->taunu)=2.22+/-0.09 (stat)+/-0. 10 (syst)+/-0.10 (lum) nb. Lepton universality predicts that the ratio of the tau and electron electroweak charged current couplings to the W boson, gWtau/gWe, be unity. We find gWtau/gWe=0.980+/-0.031, in agreement with lepton universality.     

Yield and enrichment studies of C-13 isotope by multi-photon dissociation of Freon-22 at low temperatures

Multi-photon dissociation of Freon-22 (CF₂HC1) at low temperatures has been carried out to separate the C-13 isotope using a TEA CO₂ laser. Yield and enrichment of C-13 isotope in the product C₂F₄ are studied at 9P(22) laser line as a function of temperature (−50°C to 30°C). It is observed that at a given fluence when the temperature is lowered the yield decreases and the enrichment factor of C-13 increases. Room temperature irradiation of CF₂HC1 towards the blue edge of C-13 absorption (i.e. at 9P(20) laser line) gives low yield of the product (C₂F₄) at a fluence, which produces the desired enrichment factor of 100. An increase in fluence gives very high yield of C₂F₄ but the enrichment factor is very low. Irradiating CF₂HC1 at a temperature of −10°C enhances the enrichment factor to 100 and the yield obtained is comparable to that towards the red edge of C-13 absorption (i.e. at 9P(26) laser line). At a given enrichment factor higher enrichment efficiency is achieved when CF₂HC1 is irradiated at lower temperature.     

Synthesis of Iron(III)-Doped Titania Nanoparticles and its Application for Photodegradation of Sulforhodamine-B Pollutant

Iron(III)-doped titania nanoparticles were prepared by modified sol-gel method using titanium (IV) butoxide and inorganic precursor iron(III) nitrate nonahydrate. Spectroscopic measurements show the onset of the band-gap transition to be red-shifted (~λ = 475 nm) to the visible region with increasing iron(III) ion content. Characterizations were preformed by X-ray diffractometry, electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Photocatalysis experiments were performed with dye pollutant sulforhodamine-B in aqueous environment. Direct photocatalytic effect was observed in the dye degradation experiments when irradiated with visible light into the band gap of the iron(III)-doped titania.     

Effect of hydrogenation on the electrical conductivity of amorphous silicon carbide

The d.c. conductivity of RF sputtered hydrogenated amorphous SiC films have been studied in the temperature range of 350–130 K. High temperature data yield activation energy gap which increases significantly with hydrogen content, while the low temperature conductivity is explained by hopping between localized states.     

Behaviour of a bz oscillating system at low temperatures

The BZ oscillating reaction has been studied at low temperatures and it was noted that strangely enough the oscillation period itself showed some sort of periodicity.     

The optical absorption and emission spectra of Cs2NaSmCl6

Optical absorption and emission spectra are reported for single crystals of the cubic elpasolite Cs₂NaSmCl₆. The variable temperature spectra obtained at high resolution are assigned using energies and relative intensities. Transitions from the ground level, ⁶H_{$\text{5}\text{2}$} to cystal fi levels of ⁶H_{$\text{7}\text{2}$-$\text{15}\text{2}$}, ⁶F_{$\text{1}\text{2}$-$\text{11}\text{2}$}, ⁴G_{$\text{5}\text{2}$-$\text{9}\text{2}$}, ⁴F_{$\text{3}\text{2}$,$\text{5}\text{2}$}, ⁴I_{$\text{9}\text{2}$}, and ⁶P_{$\text{3}\text{2}$, $\text{5}\text{2}$} are located and characterized. Intensity calculations are reported for magnetic dipole allowed transitions. The dominance of vibronic intensity in ⁶H_{$\text{5}\text{2}$}→⁶F _{$\text{1}\text{2}$-$\text{9}\text{2}$} and ⁶P_{$\text{3}\text{2}$, $\text{5}\text{2}$} transitions is accounted for qualitatively through the ligand polarization model involving quadrupole metal (Sm³⁺)-ligand (Cl^?) interaction mechanisms. The E_u″(⁶H_{$\text{5}\text{2}$})→E′(⁶H_{$\text{1}\text{2}$}) E_u′(⁶F_{$\text{1}\text{2}$}) no-phonon transition is postulated to be pure electric quadrupole allowed. The ground state magnetic moment is determined to be very small from magnetic circular dichroism (MCD) spectra.This study has led to the assignment of nearly all of the crystal field levels in the visible and IR region for Cs₂NaSmCl₆. A total of 27 such levels were identified, 17 from no-phonon transitions and the rest from vibronic transitions. The magnetic dipole intensity calculated using intermediate coupling O_h wavefunctions along with a crystal field analysis of the splitting pattern was used in the assignment of the levels. Vibronic bands were observed for all transitions and their vibrational symmetries were tentatively assigned. MCD data were used to determine the magnet moment of the ground state.     

Infrared and high energy fixed angle domains of scattering and the role of eikonal approximation

We examine the infrared structure and fixed angle behaviour of generalised ladder diagrams in spinor electrodynamics. The external line rules for infrared divergence is proved within the framework of parametric representation of the amplitudes. We derive a set of rules for computing the precise form of the leading infrared behaviour of any generalised ladder diagram. The same set of rules is shown to yield the leading term in the high energy fixed angle limit. Our analysis shows that both in the infrared and in the fixed-angle high energy limits the usual propagator eikonal approximation fails even in the leading order. The deficiencies of eikonal approximation can be partially removed if one also makes the small angle approximation. Leading corrections of relative $\text{O(}\text{|t}\text{|}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{/s}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}$ to the small-angle eikonal amplitude are calculated.