A simple diagnostic is developed for the purpose of determining when a third state must be considered to calculate the electronic coupling element for a given pair of diabatic states within the context of the generalized Mulliken-Hush approach (Chem. Phys. Lett. 1996, 275, 15-19). The diagnostic is formulated on the basis of Löwdin partitioning theory. In addition, an effective 2-state GMH expression is derived for the coupling as it is modified by the presence of the third state. Results are presented for (i) a model system involving charge transfer from ethylene to methaniminium cation, (ii) a pair of donor-acceptor-substituted acridinium ions, and (iii) (dimethylamino)benzonitrile, and the diagnostic is shown to be a useful indicator of the importance of multistate effects. The effective 2-state GMH expression is also shown to yield excellent agreement with the exact 3-state GMH results in most cases. For cases involving more than three interacting states a similar diagnostic is presented and several approximations to the full n-state GMH result are explored.

A technique for determining the size of microscopic spherical particles using light scattering is presented as an undergraduate physics lab. Scatterer size is determined from angular scattering distribution measurements of laser light scattered from a dilute suspension of latex spheres with diameters of 4.99Ϯ0.05 and 6.038Ϯ0.045 m. Previous experiments of this type used approximate theoretical corrections and required the construction of specialized sample cells to minimize complicating effects. As a significant improvement to these, we generate angular scattering distributions from Mie theory and, using an accurate numerical procedure, correct these distributions for Snell's law and foreshortening effects. Scatterer size is then determined using a fast, robust fitting algorithm to compare these corrected angular scattering distributions to measured angular scattering distributions. We fit the scatter from a solution of 6.04-m-diam spheres to spheres of 5.95Ϯ0.11 m diameter, and that from a solution of 4.99-m spheres to 4.85 Ϯ0.15 m. Additionally, scattering data for a 2:1 mixture of spheres of diameters 4.99 and 6.04 m are taken, and after numerical adjustment for Snell's law and foreshortening effects, good agreement with theory is obtained.

We have examined the production of hard x-rays from the irradiation of ∼1 µm diameter water droplets with a 35 fs laser at an intensity of up to 7×10 17 W cm −2. We observe substantial x-ray production in the photon energy range above 100 keV and find that the implied hot electron temperatures from these micronscale targets are significantly higher than electron temperatures observed from irradiation of solid planar plastic targets under nearly identical irradiation conditions. The observed enhancement of the hot electron temperature from droplets is consistent with hot electron spectra calculated from particle-in-cell simulations.

Collective Thomson scattering (CTS) of electromagnetic radiation from thermal plasma fluctuations in principle allows the velocity distribution of plasma ions and its composition in the plasma to be measured. The use of powerful microwave radiation from gyrotrons opens new perspectives for the application of CTS, which is considered to be a promising candidate for alpha-particle diagnostics in reactor-size tokamaks with D/T operation.We have performed the first experiments at W7-AS with different scattering geometries to prove the applicability of gyrotrons for CTS. The experiments were performed with a 140 GHz gyrotron which is routinely used for ECRH, delivering a power of 0.45 MW. The receiver antenna and detection system for the registration of CTS spectra were especially designed for the scattering experiment. In backscattering experiments, which have inherently no spatial resolution, we have measured a transversely propagating, non-thermal lower-hybrid turbulence, which is driven by perpendicularly injected fast particles from a diagnostic neutral beam. The instability is excited by the beam ions under double-resonance conditions, where the LH frequency coincides with some harmonic of the beam ion gyrofrequency. For scattering geometries with the scattering wavevector not perpendicular to the magnetic field, thermal density fluctuations in the plasma were experimentally detected. The ion temperatures derived from these thermal spectra agree well with other diagnostics.A modified scattering geometry (90 • scattering) allows local measurements of the ion temperature and is considered a prototype for the design of a routine diagnostic for iontemperature measurements.

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