Quantum-chemical calculation of spectroscopic parameters for rotational spectroscopy: Application to astrophysics and atmospherical systems

Quantum-chemical calculations are a powerful tool for assisting experimental investigations in the field of rotational spectroscopy. High-level calculations can provide reliable values for the corresponding spectroscopic parameters (rotational constants, centrifugal distortion constants, etc.), thus significantly facilitating observations and assignments. Theoretical predictions for the hyperfine parameters (quadrupole coupling constants, spin-rotation tensors, spin-spin couplings, etc.) are often essential for a detailed analysis of the hyperfine structure of the measured rotational spectra. The theoretical and computational backgrounds for the required quantum-chemical calculations will be reviewed with an emphasis on the adequate treatment of electron correlation (using coupled-cluster techniques), the calculation of molecular properties using analytic derivative techniques, and the treatment of vibrational effects within a perturbational approach. Examples of astrophysical as well as atmospherical interest will be presented to illustrate the succesfull interplay of theory and experiment in the field of rotational spectroscopy.