Photodissociation of sulfur dioxide clusters: Excitation to the e state

Due to its ubiquitous nature, SO₂ has been a chromophore of spectroscopic interest for some time. However, its potential energy surface is very complex and many details of SO₂ photolysis remain unknown. A femtosecond pump-probe technique was used to elucidate the temporal evolution of photoinduced wavepacket motion of this chromophore. The monomer transient rapidly decayed, exhibiting an excited state lifetime of 230 fsec. The corresponding product, SO, displayed a growth of 225 fsec in accord with the proposed mechanism resulting in S-O cleavage. The addition of sequential SO₂ molecules to the cluster significantly altered the lifetime associated with the E state, resulting in an increase from 230 to 435 fsec for one to four SO₂ units, respectively. This trend was consistent with the proposed dissociation mechanism. Molecular SO₂ clusters were formed through van der Waals forces and as additional units are accommodated a steric force was exerted on the bending SO₂, thereby impeding its achievement of a linear geometry. Dissociation of the molecular clusters proceeded differently than the SO₂ molecule itself. This is an abstract of a paper presented at the 228th ACS National Meeting (Philadelphia, PA 8/22-26/2004).