Bound orbiting states of benzene-Ar and evidence for reversible intramolecular vibrational energy redistribution within the complex

We have explored the proposition that emission from bound orbiting states of aromatic van der Waals complexes occurs where the free aromatic emits. Pumping 61¯ in benzene-Ar is predicted to lead, via intramolecular vibrational energy redistribution (IVR), to excitation in van der Waals modes associated with 161¯ that are above the barrier to bound orbital motion. The 61¯ dispersed fluorescence spectrum shows a red-shaded, broad band with a maximum 21 cm−1 to the blue of the expected 6101611¯ transition, where the 6101611 band of free benzene occurs. The time dependence of the parent and growth bands in the 61¯ spectrum suggests that IVR from this level is reversible.