The mechanism and photodissociation dynamics of the (S·SO2)+ cluster at 308 nm

Abstract A pulsed laser technique has been developed ofr studying the photodissociation of ions and ion clusters in a fast ion beam. The experiments were conducted using a reverse geometry double focusing mass spectrometer. Ions were produced via multiphoton ionization by crossing a continuous supersonic jet with a 20 nm pulse of a XeCI excimer laser. These ions were accelerated to 8 keV, mass selected by a magnet, and brought to a spatial focus where they were intercepted by the focused 308 nm output of a second pulsed XeCI excirem laser. The major ions produced in the ions source were S + , SO + and clusters of these ion SO 2 . Photodissociation of the (S·SO 2 ) + cluster ion was investigated. The predominant product channel leads to SO + + SO products, but small amounts of S + + SO + 2 + S products were also observed. Photofragment kinetic energy distributions were measured for each product channel. Production of S + SO + 2 products in their ground electronic states is favored. In contrast, S + + SO 2 products are formed with S + in electronically excited spin-orbit states. The observation of a strong SO + + SO photodissociation channel is a surprising result. Photodissociation of an isomeric form of (S·SO 2 ) + , the SO + 2 dimer ion, is postulated to explain this result. The photofragment angular distributions and kinetic energy distribution for SO + products lend support to this structural assignment.