Proton affinity of SO3

Abstract Collision-induced dissociation (CID) of the radical cation H 2 SO 4 + gives the product pairs H 2 O + + SO 3 and HO + HSO 3 + with a 1:3 ratio that is essentially independent of collision energy. Statistical analysis of the two channels indicates that the proton affinity of HO is 3 ± 4 kJ/mol lower than that of SO 3 . This can be used to derive PA(SO 3 ) = 591 ± 4 kJ/mol at 0 K and 596 ± 4 kJ/mol at 298 K. Previously, Munson and Smith bracketed the proton affinity as PA(HBr) = 584 kJ/mol 3 ) 2 O + + SO 3 indicates that the barrier to CID is small or nonexistent, in contrast to the substantial barriers to decomposition for H 3 SO 4 + and H 2 SO 4 .