Ionization energies of beryllium in strong magnetic fields: a frozen core approximation

An effective frozen core approximation has been developed and applied to the calculation of energy levels and ionization energies of the beryllium atom in magnetic field strengths up to 2.35 x 10(5) T. Systematic improvement over the existing results for the beryllium ground and low-lying states has been accomplished by taking into account most of the correlation effects in the four-electron system. To our knowledge, this is the first calculation of the electronic properties of the beryllium atom in a strong magnetic field carried out using a configuration interaction approximation and thus allowing a treatment beyond that of Hartree-Fock. Differing roles played by strong magnetic fields in intrashell correlation within different states are observed. In addition, possible ways to gain further improvement in the energies of the states of interest are proposed and discussed briefly.

Fragmentation of metastable SF6−* ions with microsecond lifetimes in competition with autodetachment

Fragmentation of metastable SF6-* ions formed in low energy electron attachment to SF₆has been investigated. The dissociation reaction SF6-*?SF5-+F has been observed ~ 1.5–3.4 µs and ~ 17–32 µs after electron attachment in a time-of-flight and a double focusing two sector field mass spectrometer, respectively. Metastable dissociation is observed with maximum intensity at ~ 0.3 eV between the SF6-* peak at zero and theSF5- peak at ~ 0.4 eV. The kinetic energy released in dissociation is low, with a most probable value of 18 meV. The lifetime of SF6-* decreases as the electron energy increases, but it is not possible to fit this decrease with statistical Rice–Ramsperger–Kassel/quasiequilibrium theory. Metastable dissociation of SF6-* appears to compete with autodetachment of the electron at all electron energies.

Seasonal patterns of singing activity vary with time of day in the nightingale (Luscinia megarhynchos)

Seasonal patterns of singing activity of male birds have been thoroughly studied, but little is known about how those patterns vary with time of day. Here, we censused mated and unmated male Nightingales (Luscinia megarhynchos) at four different hours of the day throughout the breeding cycle. In unmated males, singing activity increased until the young hatched in their neighborhood, and the seasonal variation was similar at each of the four hours of the day. In mated males, however, the seasonal patterns of singing activity differed between hours of the day. In morning (about the hour of egg-laying) and during the dusk chorus, the singing activity of mated males was strongly influenced by the females' reproductive state: singing activity was low before egg-laying and during incubation, but high during the egg-laying period. In the dawn chorus, however, singing activity showed a similar seasonal pattern in mated and unmated males and was high until late stages of the breeding cycle. Our results suggest that the social context influences singing behavior to a varying degree across the season, and that this variation also depends on time of day. The hour of data collection thus is an important but often neglected factor when seasonal changes of singing activity are studied.

Laser-Induced Fluorescence Measurements of Absolute Atomic Densities: Concepts and Limitations

The potential of laser-induced fluorescence spectroscopy of atoms is reviewed with emphasis on the determination of absolute densities. Examples of experiments with single-photon and two-photon excitation are presented. Calibration methods applicable with the different schemes are discussed. A new method is presented that has the potential to allow absolute measurement in plasmas of elevated pressure where collisional depletion of the excited state is present.