Knowledge Bank

We report the observation and analysis of the fluorescence excitation spectra (FES) of the van der Waals complex of argon weakly bound to all-trans-1,4-diphenyl-1,3-butadiene (DPB). The data include a vibronically resolved FES, recorded using a supersonic jet, and a rovibronically resolved FES, recorded using a molecular beam. The low resolution data allow us to determine the difference between the ground and excited state binding energies of Ar to DPB. The high resolution data allow us to determine the rigid-rotor Hamiltonian parameters for both the ground and excited electronic states of the complex. These parameters combined with those previously determined for bare DPB allow us to determine the position of the attached argon substituent in the bare DPB inertial frame. The derived argon position is interpreted as resulting from vibrational averaging effects associated with large amplitude DPB-Ar intermolecular motions.