Molecules in the cold environment of a supersonic free-jet beam: from spectroscopy of neutral–neutral interactions to a test of Bell's inequality

The supersonic free-jet expansion technique has been used in different fields of research in physics, physical chemistry and chemistry to study vibrational and rotational molecular structures in ground and excited electronic energy states as well as in cold chemistry to study chemical reactions in a unique environment. The supersonic beam technique, as a widely used method in laser spectroscopy of molecules, exploits a source of monokinetic, rotationally and vibrationally cold molecules, that are very weakly bound in their ground electronic states (van der Waals molecules). In experiments at Jagiellonian University the supersonic free-jet beam serves as a source of ground-state van der Waals objects in studies of neutral-neutral interactions between group 12 metal (M = Zn, Cd, Hg) and noble gas (NG) atoms. Recently, the method has been applied as a source of entangled 199Hg atom pairs in order to test Bell's inequality in an experiment at Texas A&M University.