Rotationally resolved ultraviolet spectra of benzene-noble gas van der Waals clusters

Sub-Doppler electronic spectra with hundreds of resolved rotational
lines are now available for benzene-Ar dimers and trimers. From
their analysis the structure of these clusters is precisely
determined. The analysis of two bands, 6 0 1 and 16 0 2 , of C6H6 ·
Ar is presented in detail. It leads to accurate values of the van
der Waals bond length in the electronic ground and excited state.
The change in frequency upon clustering is found to be a factor of
17 larger for the overtone of the out-of-plane modev 16 than for
the in-plane vibrationv 1. This can be tentatively explained by an
interaction of the low frequency out-of-plane motion of the ring
with the van-der-Waals motion of the Ar atom.