RIGS: Radiofrequency Interstellar Gas System for Molecular Spectroscopy

Abstract

The astrophysical interpretation of molecular line surveys at millimeters and submillimeter wavelengths is based on molecular spectroscopy of gas phase species, so modelling of this data requires a large amount of laboratory information concerning the reactivity of these species in the gas phase. Consequently we have designed and developed a RIGS dedicated to laboratory simulations guided by targeted astrophysical observations. RIGS mainly consists of a cylindrical shaped chamber with broad band radiofrequency receivers on the outside. The chamber is a stainless steel cylinder of 90 cm length and 50 cm of diameter giving a total volume of 177 liters approximately, built with numerous mounting and access ports to allow a range of instrumentation, pumping systems, sensors and measurement instrumentation to be coupled to the chamber (figure 1). The main evacuation system is a 950 l/s turbomolecular pump, which provides several advantages as wide pressure range operation for different experiments and fast partial chamber cleaning between experiments. The photochemical studies will be carried out by UV lamps with emissions peaked at 185 and 254 nm and mounted parallel to the cylinder principal axis. The chamber is designed with non-parallel entrance windows (made of pure or hybrid polymer materials) to avoid multiple reflections at their surfaces during the spectra acquisition with the radiofrequency receivers. The versatility of RIGS lies on a design that allows not only further coupling of other systems (gas/radiation sources, detection instrumentation¿) but also its integration as a module of the Stardust machine (see K. Lauwaet et al. and G. Santoro et al. abstracts). Regarding the detection and analysis systems, new radiofrequency receivers based on high electron mobility transistors (HEMT) with high sensitivity in 30-50GHz and 70-110 GHz bands will be developed and a quadrupole mass spectrometer with a 0-200 amu range will be used as a tool for better control of the chemical processes during experiments. The fact that these HEMT receivers are suitable for a gas phase simulation chamber has been successfully proved by a set of experiments performed with a prototype chamber in the 40 m radiotelescope of Yebes Observatory (Guadalajara, Spain) where methanol and OCS were detected (see I.Tanarro et al. abstract) In conclusion, RIGS has been designed to simulate the origin and evolution of interstellar molecules under UV illumination, by their emission in the 30-50 GHz and 70-115 GHz domains with the new developed HEMT receivers, which will contribute to interpret radiofrequency observations and develop instrumentation in the radioastronomy laboratory scope.