Spectroscopy and photodissociation dynamics of weakly bound rare gas-bromine complexes

This dissertation presents experimental investigations of van der Waals forces and the chemical dynamics that occur as a result of these forces, using as a model system clusters consisting of one or more rare gas atoms weakly bound to diatomic bromine. Three pump-probe spectroscopic studies of these RgNBr2 clusters are reported.;First, the vibrational predissociation (VP) dynamics of the T-shaped isomer of ArBr2 is characterized. The formation rate of the product free Br2 from the dissociation of the complex is measured in real-time as a function of initial Br-Br stretching levels 16 ≤ nu' ≤ 25. These rates vary erratically with the initial nu' state of the complex, indicating that the transfer of vibrational energy from the halogen to the van der Waals bond occurs via intramolecular vibrational energy redistribution (IVR) in the sparse regime.;The second study examines the excitation spectra of the linear isomers He-, Ne-, and Ar-Br2. Unlike the discrete X→B spectra for the T-shaped isomers, the linear isomer spectra are broad continua due to the repulsive nature of the B-state intermolecular potential energy surface. These broad continua change dramatically as a function of the rare gas atom, becoming increasingly broadened and blue-shifted as the rare gas atom is changed from He to Ar due to the increasingly attractive intermolecular interaction in the ground state and increasingly repulsive interaction in the excited B state.;Finally, the VP of the Ne2Br2 complex is characterized. After pumping the Br2 within the complex to a vibrational level ∣nu', the flow of halogen vibrational energy to the van der Waals modes is monitored in real-time ∣by recording the time-dependent behavior of the Ne 2Br2 (nu'), NeBr2 (nu' -- n) intermediates, and Br2 (nu' -- m) products. The results indicate the dynamics depends strongly on the size of the halogen vibrational quanta. When the vibrational quanta are large, the dissociation mechanism is sequential direct VP: Ne2Br2 (nu') → NeBr2 (nu' -- 1) → Br2 (nu' -- 2). IVR mechanisms become important when the vibrational quanta are smaller at higher nu', as evidenced by the observation of multiple NeBr 2 (nu' -- n) intermediates and Br2 (nu' -- m) products.