From interstellar systems to terrestrial organic and biomolecules: a synergetic theoretical and experimental rotational study

Abstract

The hunt for new complex organic molecules (COMs) in the interstellar medium (ISM) based on the synergy between radio astronomy and rotational spectroscopy is among the most coveted targets in current Astronomy and Astrophysics. Recent improvements in sensitivity, bandwidth, and spatial resolution in instrumentation at existing telescopes, together with the construction of new observational facilities, have opened a new window of possibilities for studying rich astronomical sources, awaiting the detection of entirely new species. Furthermore, understanding their formation pathways and their corresponding intricate chemical networks remains some of the key challenges for Astrochemistry. In this context, the scientific community is constantly pushing the limits of the complexity of interstellar chemistry, highlighting the recent detection of systems of unparalleled degrees of complexity, such as cyanonaftalene or ethanolamine. Nevertheless, many molecules that are reasonable interstellar candidates remain unexplored even in the laboratory because they are solid and labile molecules with very low vapor pressure, which usually decompose during conventional experiments. To overcome the urgent need for rotational data, in the first part of the present Thesis, we have carried out a combinational theoretical and laboratory rotational study of several COMs as a prerequisite to search for them in the ISM. Hence, we have used a battery of state-of-the-art rotational spectroscopic techniques to characterize the rotational spectrum of several relevant glycine isomers: acetohydroxamic acid and glycolamide; two cyano bearing compounds: cyanoacetamide and cyanoacetic acid; as well as two aldehydes: n- and i-butyraldehyde, together with a purely computational study of amino acetaldehyde. Moreover, we have explored the potential energy surfaces (PES) on the gas-phase formation of several protonated glycine isomers along with protonated cyanoacetamide, finding for each case a feasible interstellar formation process. Our precise laboratory measurements have been subsequently used to search for some of the studied molecular systems toward the giant molecular cloud complex Sagittarius B2 (Sgr B2) using different ALMA line surveys and toward the cold molecular cloud G+0.693-0.027 employing IRAM 30-m and Yebes 40-m observations. Regardless of the differences in their physical-chemical properties, both astronomical sources stand among the richest chemical inventories in the ISM. To date, we have not achieved any positive identification of the studied molecules. Nevertheless, the experimental data reported in this thesis will also enable eventual searches for the yet undetected species in the ISM using new and more sensitive astronomical line surveys. These future identifications in space should establish a road map that will help to understand the levels of chemical complexity reached in the ISM, as well as to decipher the link between interstellar chemistry and the rich chemical reservoir found in comets and meteorites. In the second part of this Thesis, we have taken advantage of the excellent sensitivity and specificity of our laser ablation Fourier transform microwave techniques to unleash the conformational panorama and molecular shape of several organic and biomolecules for the first time. Herein, we report a comprehensive microwave study of the amino acid L-DOPA and unveil the three-dimensional structure of two organic synthons of significant relevance: squaric acid and its water clusters and a “shape-shifting” (fluxional) substituted barbaralone. The latest exhibit an interesting valence tautomerism, which has been conclusively deciphered in the gas phase using rotational spectroscopy. We also analyze the role of the intramolecular interactions that modulate the conformational behavior of these systems using a combination of precise experimental data, such as the analysis of the 14N hyperfine structure in the case of N-bearing species (i.e., L-DOPA) and quantum chemical computations.