Using radio astronomical receivers for molecular spectroscopic characterization in astrochemical laboratory simulations: A proof of concept

Abstract

We present a proof of concept on the coupling of radio astronomical receivers and spectrometers with chemical reactors and the performances of the resulting setup for spectroscopy and chemical simulations in laboratory astrophysics. Several experiments including cold plasma generation and UV photochemistry were performed in a 40 cm long gas cell placed in the beam path of the Aries 40 m radio telescope receivers operating in the 41-49 GHz frequency range interfaced with fast Fourier transform spectrometers providing 2 GHz bandwidth and 38 kHz resolution. The impedance matching of the cell windows has been studied using different materials. The choice of the material and its thickness was critical to obtain a sensitivity identical to that of standard radio astronomical observations. Spectroscopic signals arising from very low partial pressures of CH 3 OH, CH 3 CH 2 OH, HCOOH, OCS, CS, SO 2 (<10 −3 mbar) were detected in a few seconds. Fast data acquisition was achieved allowing for kinetic measurements in fragmentation experiments using electron impact or UV irradiation. Time evolution of chemical reactions involving OCS, O 2 and CS 2 was also observed demonstrating that reactive species, such as CS, can be maintained with high abundance in the gas phase during these experiments.

Broad-band high-resolution rotational spectroscopy for laboratory astrophysics

“…The vibrationally excited states of HC 3 N ν 4 , ν 5 , ν 6 , ν 7 , 2 ν 7 , 3 ν 7 , 4 ν 7 , ν 5 + ν 7 , ν 6 + ν 7 and 2 ν 6 + ν 7 are detected with very good S/N. As in other plasmas studied with the GACELA setup the vibrational temperature seems to be 100-150 K above the ambient temperature (see also Tanarro et al (2018)).…”

“…A prototype chamber was built at the ICMM mechanical work-shop to test the concept. Results from this protoype have been published by Tanarro et al (2018), together with detailed formulae describing the data calibration process (see also Appendix B), and how to derive physical parameters of the gas inside the chamber (partial pressures, temperatures, collisional broadening coefficients, etc. ).…”

“…Except the experiment of Wehres et al (2018a,b), most of these experimental setups were focused on the pre-launch characterization of receivers onboard satellites and not on the possibility of using them for laboratory spectroscopy and chemical reactivity. A proof of concept experiment (Tanarro et al 2018) was developed in the period 2015-2017 using a small prototype chamber placed in the beam path of a receiver covering the 42-50 GHz band installed on the 40 m ARIES radio telescope at the Yebes Observatory (Spanish National Geographic Institute; hereafter referred to as IGN). These experiments showed that radioastronomical receivers can be used to perform simulations (photochemistry, cold plasma discharges) addressing chemical compositions similar to those of interstellar clouds.…”

“…Thermal emission provides, in addition, partial pressures derived from the intensity and linewidth of the observed lines in the same way radio astronomers do to derive volume and column densities when observing interstellar clouds. A comparison with other techniques, such as the chirped pulse Fourier transform microwave spectroscopy, has been done by Tanarro et al (2018).…”

New laboratory techniques using heterodyne receivers

“…Both spectrometers have been described elsewehere (Wehres et al (2018a,b)). For similar efforts at lower frequencies see also the publication by Tanarro et al (2018).…”