Diamond infrared emission bands in circumstellar media

Since the discovery of small diamond grains in meteorites, the presence of such grains in the interstellar medium has been suspected. Here we report w hat we think to be the first unambiguous evidence of the presence of small crystallites of diamond in the dusty envelopes surrounding stars. Thanks to experimental results obtained in different laboratories on the diamond gro wth process, we identify two peculiar unidentified infrared emission bands at 3.43 and 3.53 mu m as the vibrational modes of hydrogen-terminated cryst alline facets of diamond. The intensities of these two strong features obse rved in the envelope of HD 97048 correspond to a mass of 10(-10) to 10(-9) M. of diamond dust at an equilibrium temperature of similar to 1000 K.