Theory

The main research direction of our group on the theory side is ab initio quantum scattering. We are primarily interested in collisional processes for simple diatomic molecules that can be described in a fully quantum way starting from first principles. A model example is molecular hydrogen colliding with noble-gas atoms [15, 22, 23, 38] and with itself [67, 79].

These studies are motivated both by testing quantum-chemical calculations [15, 22] and by understanding collisional physics at the molecular level [3, 5, 15, 38], as well as by astrophysical [67, 69] and atmospheric [45, 46, 61, 64] applications. Depending on the context, the collision energy spans from the ultracold regime [68], where a single partial wave can dominate, through intermediate energies relevant to astrophysics [67, 69], up to room temperature and higher, where more than a hundred partial waves may be needed [45].

Our quantum scattering calculations are strongly related to molecular spectrum simulations, where collision-induced line-shape effects often play an important role [67]. We also calculate molecular structure and properties to support our experimental projects.

Examples include calculations of hyperfine structure in molecular hydrogen [31, 49] and its isotopologues [32, 33, 47, 48], general studies of hyperfine interactions [57, 62], calculations of magic wavelengths in molecules [56], molecular transition intensities [72] and concepts for enhancing the sensitivity of optical cavities to variations in the fine-structure constant [54].