IN SITU INFRARED MEASUREMENTS OF FREE-FLYING SILICATE DURING CONDENSATION IN THE LABORATORY

We developed a new experimental system for infrared (IR) measurements on free-flying nucleating nanoparticles in situ and applied it to studies on silicate particles. We monitored the condensation of magnesium-bearing silicate nanoparticles from thermally evaporated magnesium and silicon monoxide vapor under an atmosphere of oxygen and argon. The IR spectrum of newly condensed particles showed a spectral feature for non-crystalline magnesium-bearing silicate that is remarkably consistent with the IR spectrum of astronomically observed non-crystalline silicate around oxygen-rich evolved stars. The silicate crystallized at <500 K and eventually developed a high crystallinity. Because of the size effects of nanoparticles, the silicate would be expected to be like a liquid at least during the initial stages of nucleation and growth. Our experimental results therefore suggest decreasing the possible formation temperature of crystalline silicates in dust formation environments with relatively higher pressure.