No abstract

The proton distribution in the upper portion of the F2 region must follow a chemical equilibrium distribution up to a critical level, hc, which is determined by the condition λΛ = H2, where Λ is the mean free path for the scattering of protons by oxygen ions, A is the charge‐exchange mean free path for protons among oxygen atoms, and H is the scale height of atomic oxygen. Above this critical level, the distribution of protons is governed by diffusion. The number of protons in the whistler medium (that is, the protonosphere) is large enough, and the rate of diffusion of protons through oxygen ions slow enough, so that no large diurnal changes in whistler‐region ion concentrations can be expected. This is in agreement with observation. The weak coupling between the oxygen ions in the normal F2 region and the protons in the protonosphere lends support to the position that the protonosphere should be considered separately from the heavy ion region which constitutes the normal ionosphere; the protonosphere can be thought of, in large degree, as floating on top of the normal ionosphere.

R6sum6.-Les calculs relativistes de bandes par la methode des ondes planes orthogonaliskes ont ktk menks A bien aux points de symetrie simple dans la zone rkduite de Brillouin pour plusieurs composCs IV-VI. La structure de bande dans le reste de la zone a et6 deduite par interpolation. A notre connaissance, ce sont les premiers calculs de bandes pour Ies composb IV-V1 qui se basent au depart sur des principes relativistes (contrairement aux calculs non relativistes affines par des corrections relativistes et de couplage spin-orbite). Nos calculs conduisent A des modkles de bandes ayant une rkalitk physique, qui sont suffisamment prkcis pour tenir compte de la plupart des singularitks des spectres expkrimentaux de rkflectivitk. 11 est difficile #interpreter les spectres d'kectroreflectivite sans ambigufte a l'aide de ces modeles de bande mais un certain nombre de recoupements plausibles dans les spectres peuvent &re faits. Des calculs des bandes d'energie et de spectre optique plus Claborks se poursuivent et seront publies ailleurs. Abstract.-Relativistic OPW band calculations have been carried out at key points in the reduced zone for several IV-V1 compounds. The band structure in the remainder of the zone has been filled in with the aid of an interpolation scheme. To our knowledge, these are the first fully relativistic first-principles band calculations for IV-V1 compounds (in contrast to non-relativistic calculations supplemented by relativistic and spin-orbit coupling corrections). Our first-principles band calculations lead to physically realistic energy band models which are sufficiently accurate to account for most of the characteristic features of the experimental reflectivity spectra. It is difficult to interpret the electroreflectivity spectra unambiguously in terms of these band models but a number of plausible spectral assignments can be made. Refined energy band and optical spectrum calculations are in progress and will be reported elsewhere.

The E 1 c reflectivity has been measured up to 10 eV for hexagonal, single-crystal GaN.The band structure and reflectivity have been computed by the empirical pseudopotential method and used to identify the observed spectral peaks.La rBflectivit6 E 1 c d'un monocristal de GaN hexagonal a 6t6 measure6 jusqu'8 10 eV.La structure de bande et la r6flectivitk ont 6t6 calculkes par la mkthode du pseudopotentiel empirique et ont 8th utiliseks pour identifier les cretes du spectre observ6.

The empirical pseudopotential method is used to compute the band structure, density of states, and reflectivity of hexagonal zinc oxide. The local approximation is assumed, on the basis of recent photoemission experiments which showed that the zinc core 3d band lies deep below the valence band. The calculation succeeds in identifying the reflectivity peaks, but gives stronger amplitudes than are observed, and these identifications are shown to fit well into the systematics of the other three zinc chalcogenides. Reasonable agreement is also obtained with the experimental locations of the maxima in the density of states and with the large value of the valence bandwidth.La methode des pseudopotentiels empiriques a Bt6 utilisee pour calculer la structure des bandes, la densit6 des 6tats et la reflectivit6 de l'oxide de zinc hexagonal. On suppose une approximation locale, car les resultats recents en photo-6mission ont montre que la bande 3d du zinc est beaucoup plus profonde que la bande de valence. Le calcul reussit B identifier la structure de reflectivite, mais donne des amplitudes plus grandes que celles qui sont observbes, e t ces identifications sont en bon accord avec le systeme des autres trois chalcogenides de zinc. Un accord raisonable est aussi obtenu avec la position des maxima de densite d'btats determinee experimentalement e t avec la grosse largeur de la bande de valence.