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Session 51 - Interstellar Medium II.
Display session, Thursday, January 08
Exhibit Hall,

[51.22] Does Surface Disorder Influence Light Scattering by Small Particles?

Crystalline particles have a surface layer roughly 3 atoms/molecules thick whose structure is not periodic. This is due to the asymmetric distribution of ionic and covalent bonds that occur at any free surface. The effect is called surface reconstruction (Somorjai, G.A "Surface Reconstruction and Catalysis", Annual Review of Physical Chemistry , 45, 721751, 1994). and is analogous to surface tension in liquids. In amorphous material like glass the it is called the gel layer. As the particle size decreases, the volume fraction of the outer layers increases. The optical properties of this layer are slightly different than those of the interior. Thus the particle acts like a coated sphere and can be treated using Mie theory (Johnson, B.R. "Light scattering from a multilayered sphere," Applied Optics, 35, 3286-3296, 1996). To study the effect we have computed the extinction cross sections, differential scattering cross sections and single scattering albedos for both highly absorbing (m = 1.6 + i 0.5) and purely scattering (m=1.6) particles in the 0.01 - 1 micron radius range. Optical constants of the outer layers were derived using the continuous distribution of oscillators approximation (Lynch, D.K. “A New Model for the Infrared Dielectric Function of Amorphous Materials”, Astrophys. J., 467, 894-898, 1996). We found that changes in the single scattering albedoes can be as large as 40particles with a 0.001 micron coating compared to uncoated sphere. More complete results and their significance to astrophysical situations will be presented at the meeting.

Program listing for Thursday