High‐Resolution UV Spectroscopy of Molecular Complexes

Information on the structure, the rigidity and the intermolecular potential of molecular complexes is essential to our understanding of the physical and chemical properties of molecular complexes. In this work we would like to demonstrate that rotationally resolved UV spectroscopy provides precise new information on these topics. In particular, the structure and van der Waals bond length of benzene‐X complexes (X = Ne, Ar, Kr, Xe, N 2 ) have been experimentally determined. In the benzene‐N 2 complex with its parallel‐stacked configuration, the two constituents, benzene and N 2 , can rotate against each other. Rotationally resolved vibronic van der Waals bands allow the clear assignment of the excited van der Waals vibrations. Their anharmonicity and the vibrationally averaged rotational constants provide basic information on the intermolecular potential. For the example of the benzene‐Ar 2 trimer it is shown that isomeric structures exist that are rigid on the nanosecond time scale.