The size of interstellar nanodiamonds revealed by infrared spectra of CH on synthetic diamond nanocrystal surfaces

Infrared spectra of CH stretches have been investigated on the surfaces of synthetic diamond crystallites (5, 100, and 700 nm in diameter) to provide insights into the mid-infrared emission bands of stardusts in interstellar media. While the spectrum of 5-nm diamonds fails to display the distinct 2835 cm(-1) (or 3.53 mum) band. a remarkably good match of the absorption bands of larger diamond grains with the emission observed for the stars Elias 1 and HD 97048 is obtained. Suggested by this study, the nanodiamonds that can display such characteristic emission bands at 3.53 mum in these two interstellar systems have a size significantly larger than 5 nm. (C) 2002 American Institute of Physics.