2-PHOTON DISSOCIATION OF SULFUR-DIOXIDE AT 248-NM AND 308-NM

The photodissociation of SO2 after two-photon excitation at 248 and 308 nm has been studied by means of photofragment translational spectroscopy (PTS). With 308 nm excitation, the time-of-flight distributions of the SO photofragments exhibit high kinetic-energy thresholds which are assigned to the formation of SO(X 3Σ-) +O (3P), SO(X 3Σ-) +O (1D), and SO(a 1Δ) +O (3P). A weak vibrational structure indicates the production of SO(a 1Δ) molecules in vibrational states up to at least ν=8. After excitation at 248 nm, nine different primary processes are clearly identified leading to SO+O as well as to S+O2 fragments in various electronic states. All observed kinetic energy thresholds conform to a dissociation energy Do=543 kJ/mol (45400 cm-1) for the reaction SO2→SO+O and Do= 569 kJ/mol (47600 cm-1) for the reaction SO2→S+O2. Evidence was found for the formation of higher SO electronic states in the energy region 28000-31000 cm-1, in particular for the previously not observed SO (A″ 3Σ+) state which possesses a term energy To close to 30000 cm-1. Furthermore, the PTS method, in providing a direct way to determine the electronic states of each individual fragment of a fragment pair, revealed that the spin is not conserved in the SO2→SO+O dissociation. © 1990.