Reactions of H₃O⁺(H₂O)n with Formaldehyde and Acetaldehyde

Rate constants were measured as a function of temperature for the reactions of H 3 O + (H 2 O) 0 - 4 with CH 3 CHO and H 3 O + (H 2 O) 0 - 5 with CH 2 O. The CH 3 CHO reactions all occur at the collision rate to within the experimental error. The n = 0 ion reacts via proton transfer, while the clusters react via ligand switching. In the CH 2 O reactions, n = 0 reacts at 90% of the collision rate and proceeds by proton transfer. The n = 1 reaction is somewhat less efficient and proceeds by ligand exchange. The efficiencies for both reactions are independent of temperature. The n = 2−5 reactions are progressively slower, except for the point at the highest temperature at which a particular cluster has been studied for n = 3−5. Thermal dissociation is postulated to be the reason for the upturn at higher temperatures. Otherwise, the reactions involve mostly ligand exchange with some association occurring at low temperature. The use of these results in model calculations of particle formation in jet engine exhaust is discussed.