Proton affinity of SO311In memory of Robert R. Squires, mentor and friend.

AbstractCollision-induced dissociation (CID) of the radical cation H2SO4+ gives the product pairs H2O+ + SO3 and HO + HSO3+ 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 SO3. This can be used to derive PA(SO3) = 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 < PA(SO3) < PA(CO) = 594 kJ/mol. The threshold of 152 ± 16 kJ/mol for formation of H2O+ + SO3 indicates that the barrier to CID is small or nonexistent, in contrast to the substantial barriers to decomposition for H3SO4+ and H2SO4