Laboratory production of magnesium sulfide grains and their characteristic infrared spectra due to shape

• Published in: Astronomy and astrophysics (Berlin) 2005-11, Vol.442 (2), p.507-512
• Main Authors: Kimura, Y., Kurumada, M., Tamura, K., Koike, C., Chihara, H., Kaito, C.
• Format: Article
• Language: English
• Subjects: infrared: ISM; infrared: stars; methods: laboratory; stars: AGB and post-AGB
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361:20052757

Nanosized MgS grains, which have been considered the origin of the 30 μm emission feature of carbon-rich evolved objects, were produced from the gas phase using an advanced gas evaporation method. The far-infrared spectrum of cubic MgS grains showed a characteristic absorption peak at 311 cm-1 (32.1 μm) with three shoulders at 460, 400 and 262 cm-1 (21.7, 25.0 and 38.2 μm). On the other hand, when the grains were roundish or network-like, the absorption peak at 250 cm-1 became predominant. The cubic MgS grains were produced by direct nucleation from the gas phase. In the case of production via a gas-solid reaction, the MgS grains were network-like. Therefore, the formation environments of MgS grains around carbon-rich evolved objects may be predicted from the intensity of 310 and 250 cm-1 bands. We suggest that the origins of the absorption band at 310 and 250 cm-1 are (100), (110) and/or (111) surfaces of MgS grains, respectively.