Optical properties of likely constituents of interstellar dust

Abstract

Optical properties of polyoxymethelene (POM) at room temperature have been measured from the near ultra-violet to infra-red as an initial stage of a line between interstellar dust and organic matter, and we report our results which are particularly relevant to interstellar extinction. There is a strong possibility of a more complex organic component which could significantly contribute to the interstellar extinction. Measurements have also been made of the effect of fast neutron bombardment on the optical properties of quartz (SiO). At a high total flux of neutrons the crystalline quartz will change to its amorphous form which has extinction properties that resemble the interstellar extinction. Extinction due to small particles of several forms of SiO.2 have been measured and among them the hydrated mineral, opal, behaved like an amorphous silica. Neutron irradiated olivine showed a stronger and a broader lOym band in addition to weaker bands towards the longer wavelengths which indicated that atomic damage has been produced. At high fluxes more atomic damage is expected to change the crystalline structure and there by cause changes in the infra-red absorption properties. Extinction measurements were also made for smoke particles of MgO in the infra-red. When the measurements Were made with the particles deposited on substrates, in addition to a very broad surface mode absorption feature around 20ym an extinction maximum was observed typical of the bulk mode at 25ym. Extinction measurements for MgO smoke particles in air also showed similar results. However when the particles were dispersed in a non-absorbing medium, the bulk absorption mode was not observed. This implies that the appearance of the bulk mode is due to clumping. It was also observed that the width of the band reduced significantly with decreasing powder density f in the medium. Hence it is concluded that considerable broadening is due to interactions which is not properly accounted for in the single particle theory.