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Pion elastic scattering on 4He was calculated within the second-order optical model. The roles of pion double isospin and spin flip in intermediate states and of recoil correlation were investigated in some detail. A second-order term, which represents the effects of true pion absorption, is also included in the optical potential. A comparison was made between the results obtained using the Kerman-McManus-Thaler and Watson formulations of multiple scattering theory.

We present a semi-analytical line transfer model, (SALT), to study the absorption and re-emission line profiles from expanding galactic envelopes. The envelopes are described as a superposition of shells with density and velocity varying with the distance from the center. We adopt the Sobolev approximation to describe the interaction between the photons escaping from each shell and the remainder of the envelope. We include the effect of multiple scatterings within each shell, properly accounting for the atomic structure of the scattering ions. We also account for the effect of a finite circular aperture on actual observations. For equal geometries and density distributions, our models reproduce the main features of the profiles generated with more complicated transfer codes. Also, our SALT line profiles nicely reproduce the typical asymmetric resonant absorption line profiles observed in starforming/starburst galaxies whereas these absorption profiles cannot be reproduced with thin shells moving at a fixed outflow velocity. We show that scattered resonant emission fills in the resonant absorption profiles, with a strength that is different for each transition. Observationally, the effect of resonant filling depends on both the outflow geometry and the size of the outflow relative to the spectroscopic aperture. Neglecting these effects will lead to incorrect values of gas covering fraction and column density. When a fluorescent channel is available, the resonant profiles alone cannot be used to infer the presence of scattered re-emission. Conversely, the presence of emission lines of fluorescent transitions reveals that emission filling cannot be neglected.

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Observations of two photon absorption in gaseous CaCl. A study of theIn the wavelength region, 616-623nm, two photon processes have been observed in diatomic calcium chloride. The D 'E-X 'E transitions of both Ca35C1 and Ca3'C1 were obtained. Rotational and vibrational constants have been derived for the D ' E and X states of Ca35Cl.