Reactions of microhydrated ozonide with methyl chloride

Abstract Size selected O 3 − (H 2 O) n and O 2 − (H 2 O) n clusters with n  = 0–4, produced by electrospray ionization in a corona discharge, were reacted with CH 3 Cl in the collision cell of a quadrupole-time-of-flight mass spectrometer under near thermal conditions. The ozonide–water clusters react primarily by ligand exchange, substituting CH 3 Cl for H 2 O; dehydration due to collisionally induced dissociation is also observed. Only extremely weak signals are observed for the S N 2 reaction between O 3 − (H 2 O) n and CH 3 Cl, yielding Cl − (H 2 O) n−m , also for the naked ozonide ( n  = 0). This is in contrast to superoxide–water clusters, where the S N 2 reaction with CH 3 Cl occurs readily. High level quantum chemical computations predict energy barriers in accord with the experimental observations, and the difference in nucleophilicity between O 3 − and O 2 − is discussed in light of quantum chemical calculations and Marcus theory.