[en] The rotational eigenvalues of isotopically substituted hydrogen molecules adsorbed into single-walled carbon nanotubes are calculated using a semiclassical method and using a model potential. The resulting eigenvalues are used to calculate the separation factors due to rotational confinement between different isotopic species as a function of temperature and nanotube size. The results show that even for small shifts in the eigenvalues, significant fractionations should occur, suggesting possible application as an isotope-separation technique

[en] We show that fourth-order dispersion functions of solid-phase polymers can be determined by multicolor optical diffraction. Electrodynamically trapped microparticles of polyethylene glycol with different molecular weights were probed by two-dimensional optical diffraction with four different laser wavelengths (632.8, 514.5, 488.0, and 457.9 nm); subsequent Mie analysis of one-dimensional scattering patterns yielded size and refractive index (both real and imaginary parts). Using a single wavelength as a size reference, the nonlinear dependence of the refractive index of solid (nonevaporating) polymer microparticles was determined by finding the refractive index for a given wavelength that best matched a Mie calculation subject to the reference size constraint. The experimentally determined refractive index values were fit to a standard fourth-order Cauchy function to obtain values for n₀, n₁, and n₂

[en] The Energy Sciences Network (ESnet) is the primary provider of network connectivity for the US Department of Energy Office of Science (SC), the single largest supporter of basic research in the physical sciences in the United States. In support of the Office of Science programs, ESnet regularly updates and refreshes its understanding of the networking requirements of the instruments, facilities, scientists, and science programs that it serves. This focus has helped ESnet to be a highly successful enabler of scientific discovery for over 20 years.

[en] The structures and photophysical properties of single molecule MEH-PPV (2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylenevinylene) and CN-PPV (2,5,2' ,5'-tetrahexyloxy-7,8'-dicyano-p-phenylenevinylene) nanoparticles are investigated using electronic structure theory and high resolution fluorescence experiments. It is shown that electron withdrawing substituents, such as CN, on the vinyl group of the PPV polymer backbone cause substantial change in the π electronic structure which subsequently decreases the inter-chain distance. Not only does CN-PPV have a smaller inter-chain separation compared to MEH-PPV, but also an increased binding energy and more efficient charge transport (carrier mobility) due to larger electronic coupling (charge transfer integrals). These changes help explain the enhanced luminescence quantum yield, photo-stability, and lifetime for CN-PPV versus MEH-PPV observed in experimental high resolution fluorescence imaging of individual single molecule nanoparticles