Experiment and computation: a combined approach to study the van der Waals complexes

A review of recent results on the millimetre-wave spectroscopy of weakly bound van der Waals complexes, mostly those which contain H₂ and He, is presented. In our work, we compared the experimental spectra to the theoretical bound state results, thus providing a critical test of the quality of the M–H₂ and M–He potential energy surfaces (PESs) which are a key issue for reliable computations of the collisional excitation and de-excitation of molecules (M = CO, NH₃, H₂O) in the dense interstellar medium. The intermolecular interactions with He and H₂ play also an important role for high resolution spectroscopy of helium or para-hydrogen clusters doped by a probe molecule (CO, HCN). Such experiments are directed on the detection of superfluid response of molecular rotation in the He and p-H₂ clusters.