Rotational spectroscopy and astrophysical investigations: the role of quantum-chemical calculations

Among the various spectroscopic research fields, the investigation of the phenomena that allow to understand the chemistry of the interstellar medium plays a particularly relevant role. The need of laboratory, experimental as well as computational, investigations in this field is due to the fact that astronomical observations require the knowledge of the spectroscopic parameters involved. Among the various spectroscopic techniques, thanks to its intrinsic high resolution, rotational spectroscopy is a powerful tool for studying the chemistry and physics of the atmosphere and interstellar medium. Of interest to this talk is the complementarity of theory and experiment. By means of a few exemplificative cases it will be shown how quantum-chemical calculations can guide and support experiment in the field of astrophysical investigations. For these high-level calculations the requirements are efficient treatment of electron correlation via coupled-cluster theory, basis-set extrapolation techniques, incorporation of core correlation, relativistic as well as vibrational effects together with the use of suitable additivity schemes. The species of interest are here organic molecules, like formic acid and uracil, as well as ionic species and radicals.