Sub-Doppler UV spectroscopy by resonance-enhanced two-photon ionization: the structure of the benzene20,22Ne 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-20Ne and benzene-22Ne 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 Å with a slight difference for the two isotopes.
This distance decreases by 40 mÅ when benzene is electronically
excited. The influence of the large amplitude van der Waals
vibrations on the average bond length is discussed.