More than 290 molecules have been detected in the interstellar medium (ISM), including simple and complex organic molecules such as ethylene glycol, benzene, indene, and fullerene.1 Due to the prevailing ultra-low temperature-pressure conditions in ISM, these molecules exist in solid form on the interstellar dust. The chemical evolution of such molecular solids is largely governed by thermal and photochemical processes. These diverse processes include phase transition, diffusion, crystallization, clathrate hydrate formation, and chemical reactions. Such phenomena can be understood by mimicking the laboratory's temperature, pressure conditions of ISM. In this regard, we are studying several molecular solids with the help of reflection absorption infrared spectroscopy (RAIRS), temperature programmed desorption mass spectrometry (TPD-MS), secondary ion mass spectrometry (SIMS) under ultrahigh vacuum (UHV) (5×10-10 mbar) and cryogenic conditions (10-160 K).2 Our primary focus is to explore the complex chemistry of several molecular solids, including ethane, dimethyl ether, methyl chloride etc., upon thermal annealing and photo-irradiation processing under UHV and cryogenic conditions. In our recent work, we showed the formation of ethane clathrate hydrate at 60 K by thermal annealing in simulated ISM conditions.3 We have also studied the photochemistry of methyl chloride4 (recently detected in ISM) in its three phases: amorphous crystalline and polycrystalline.
References:
1. Arumainayagam, C. R. et al. Extraterrestrial prebiotic molecules: photochemistry vs. radiation chemistry of interstellar ices. Chem. Soc. Rev. 48, 2293–2314 (2019).
2. Bag, S. et al. Development of ultralow energy (1-10 eV) ion scattering spectrometry coupled with reflection absorption infrared spectroscopy and temperature programmed desorption for the investigation of molecular solids. Rev. Sci. Instrum. 85, 1–7 (2014).
3. Malla, B. K., Vishwakarma, G., Chowdhury, S., Selvarajan, P. & Pradeep, T. Formation of Ethane Clathrate Hydrate in Ultrahigh Vacuum by Thermal Annealing. J. Phys. Chem. C 2022, 17983–17989 (2022).
4. Gombosi, Fayolle, E. C. et al. Protostellar and cometary detections of organohalogens. Nat. Astron. 1, 703–708 (2017).