On the question of interstellar diamonds

Abstract

The evidence to support the recent proposal that interstellar extinction may be caused by small diamond crystals is open to substantial criticism. Wickramasinghe has shown that the optical properties of diamond do not readily provide an explanation of the observed interstellar curve. Similar calculations made by us support and extend Wickramasinghe's results. It may be possible to modify the form of the size distribution until the interstellar extinction curve is reproduced as Greenberg and Shah have done for "dirty ice" grains. For diamond, however, considerable variation in the slope occurs in the infrared and it is not obvious that it will be possible simultaneously to fit the infrared, visible and ultraviolet regions.