SUB-DOPPLER UV SPECTROSCOPY BY RESONANCE-ENHANCED 2-PHOTON IONIZATION - THE STRUCTURE OF THE BENZENE-NE-20, NE-22 CLUSTER

In this work it is demonstrated that mass selected multiphoton ionization is a powerful technique for high resolution spectroscopy, isotope cluster separation and investigation of the structure of van der Waals clusters. The rotationally resolved UV spectra of the benzene-Ne-20 and benzene-Ne-22 clusters are selectively measured in a natural isotopic mixture of benzene and benzene-Ne clusters in a cooled supersonic jet. The analysis of these spectra yields accurate values for the rotational constants of both species. From this data it is found that the Ne atom is located on the C6 rotational axis of the benzene ring at an average distance of 3.46 angstrom with a slight difference for the two isotopes. This distance decreases by 40 m-angstrom when benzene is electronically excited. The influence of the large amplitude van der Waals vibrations on the average bond length is discussed.