TeraHertz time domain spectroscopy (THz TDS) of molecular ices

Abstract

In mol. clouds and protoplanetary disks, water-dominated ices comprise the bulk of the condensible CNO-elements that can ultimately be delivered to planetary surfaces. Such ices have long been studied by IR spectroscopy, but in the very densest cloud cores or in the disks around young stars such studies are exceedingly difficult. Yet, any grains warm enough to emit at mid-IR wavelengths are too hot to retain icy mantles. We have developed a coherent TeraHertz (THz) time domain instrument that can measure the optical consts. of solid materials and mol. ices from temps. of 10-300 K. Such an instrument probes the intermol. degrees of freedom in ices, and provides the possibility of studying the dominant org. and volatile reservoirs in forming planetary systems with instruments such as the HIgh Resoln. Mid-IR Spectrometer (HIRMES) onboard the Stratospheric Observatory for IR Astronomy (SOFIA). In our latest generation instrument, we have implemented a single shot multi-channel detection system that permits the entire THz waveform to be detected with each laser pulse, resulting in an approach that can study thin samples down into the several to several tens of monolayer regime. We will report on THz TDS studies of single component and mixed ices of relevance to star- and planetformation, with a view toward upcoming studies with SOFIA and the James Webb Space Telescope (JWST).