The 5v 3 bands of 18O enriched ozone: line positions of 16O16O18O, 16O18O16O, 16O18O18O and 18O16O18O

The four 5v ₃ bands of ¹⁸O enriched ozone have been observed and analysed for the first time. Two species (¹⁶O¹⁸O¹⁶O and ¹⁸O¹⁶O¹⁸O) belong to the C_2v symmetry group and two other (¹⁸O¹⁸O¹⁶O and ¹⁶O¹⁶O¹⁸O) to the C_s symmetry group. They have been recorded at a resolution of 0.008 cm^?1 with a pathlength of 32.16 m. Despite the very weak absorptions observed, almost 250 energy levels have been derived for each of the 4 species, with J ? 35 and K _a ? 13, and suitable sets of Hamiltonian parameters have been determined. For 3 species it has been necessary to account for the resonance between the (005) and (311) states to correctly reproduce the spectra observed. These resonances, anharmonic for C_2v, and hybrid (both anhar-monic and Coriolis) for C_s symmetry confirm the accidentally extremely strong coupling between the (005) and (311) states for ¹⁶O₃, due in that case to the very close distance between unperturbed energy levels. This work also confirms the excellent prediction of band centres of these four species derived from the recently determined isotopically invariant molecular potential function.     

A new search for the allowed decay π0→4γ

A new search with increased detection efficiency has been made for the decay of the neutral pion into four photons, an allowed decay which is expected to be rare. We have observed no events, placing an upper limit on the branching ratio of 4.4 × 10^?6 at 90% confidence level.     

Three-dimensional nanofabrication with elastomeric phase masks

This Feature Article reviews recent work on an optical technique for fabricating, in a single exposure step, three-dimensional (3D) nanostructures with diverse structural layouts. The approach, which we refer to as proximity field nanopatterning, uses conformable, elastomeric phase masks to pattern thick layers of transparent, photosensitive materials in a conformal contact mode geometry. Aspects of the optics, the materials, and the physical chemistry associated with this method are outlined. A range of 3D structures illustrate its capabilities, and several application examples demonstrate possible areas of use in technologies ranging from microfluidics to photonic materials to density gradient structures for chemical release and high-energy density science.     

A photolyticallyQ-switched photolytic iodine laser

A novel, repetitively pulsed, photolyticQ-switching scheme has been demonstrated on a 1.315 m (² P _1/2² P _3/2) cw photolytic iodine laser using an intracavity cell containing either IBr or ICl. When the cell is irradiated with a KrF laser (=248 nm), I(² P _3/2) atoms are produced and lasing ceases due to the introduction of loss into the laser cavity. Lasing resumes, however, following recombination of the atoms into the parent molecule. Experimental evidence is presented which indicates that the laser's shut-off time is a function of excimer laser energy and the pressure of buffer gas in the cell.