Investigation of the predissociation of SO2: state selective detection of the SO and O fragments Original Research Article

A detailed investigation of the predissociation of SO2 in the electronically excited C̃ 1B2 state is presented. The photodissociation of SO2 from selectable single quantum states is determined in all electronic and rovibrational quantum numbers for its fragments SO and O. This could be achieved with cooled SO2 parent molecules generated in a supersonic jet and detection of the fragments SO and O using REMPI-TOF technique. The dissociation energy D0 for fragmentation SO2(C̃ 1B2) → SO(X 3Σ−, ν″ = 0) + O(3P2) is determined with high accuracy to the value of D0 = 45725.3(1) cm−1. The dissociation rate is very slow at this threshold. Observed rotational distributions of the SO(X 3Σ−, ν″ = 0) fragment for excess energies Eexc = 0–20 cm−1 are in good agreement with simulations from phase-space theory. The analysis indicates no reaction barrier, but proves the existence of a rotational barrier, i.e. the predissociation is caused by a coupling to a bound potential surface with an asymptote correlating to the ground states of the fragments. Possible mechanisms of the predissociation process are discussed.