Trapping and Structural Characterization of the XNO 2 ·NO 3 - (X = Cl, Br, I) Exit Channel Complexes in the Water-Mediated X - + N 2 O 5 Reactions with Cryogenic Vibrational Spectroscopy

The heterogeneous reaction of N O with sea spray aerosols yields the ClNO molecule, which is postulated to occur through water-mediated charge separation into NO and NO ions followed by association with Cl . Here we address an alternative mechanism where the attack by a halide ion can yield XNO by direct insertion in the presence of water. This was accomplished by reacting X (D O) (X = Cl, Br, I) cluster ions with N O to produce ions with stoichiometry [XN O ] . These species were cooled in a 20 K ion trap and structurally characterized by vibrational spectroscopy using the D messenger tagging technique. Analysis of the resulting band patterns with DFT calculations indicates that they all correspond to exit channel ion-molecule complexes based on the association of NO with XNO , with the NO constituent increasingly perturbed in the order I > Br > Cl. These results establish that XNO can be generated even when more exoergic reaction pathways involving hydrolysis are available and demonstrate the role of the intermediate [XN O ] in the formation of XNO .