Extinction by interstellar radicals.
Abstract
Summary. In this paper we calculate the scattering by interstellar free radicals (Platt's particles). The results are applied to interpret recent data on the farultraviolet extinction, which apparently is due to scattering rather than absorption processes. The calculation is based on two onedimensional models of free electrons confined to a small box with size R, the first with an infinite and the second with a finite binding potential U0. An exact analytic treatment is given for the first model and an approximative treatment for the second model based on a perturbation calculation. We derive transition frequencies and  probabilities between the ground  and the first excited state as a function of the model parameters R and U0. Using two plausible distribution functions for the size of interstellar radicals we calculate continuous extinction spectra, made up of distinct quantum transitions within individual radicals. A possible fit is shown to extinction data for Per below 1600 A. From this fit follows a mean radical size of about 10 A and a density of 10 m 3, which appear reasonable numbers. We conclude that scattering by free electrons in rather small radicals can account for the observed farultraviolet extinction and the high albedo. We conjecture that bonding electrons in the same particles are responsible for the visual and nearultraviolet extinction. Key words: interstellar radicals  farultraviolet extinction
 Publication:

Astronomy and Astrophysics
 Pub Date:
 January 1974
 Bibcode:
 1974A&A....30...51A