Infrared Photodissociation Spectroscopy of Cationic Nitric Oxide Clusters, [(NO)_<i>n</i>]⁺, and [NO₂(NO)_<i>n</i>]⁺

Photofragmentation spectroscopy provides a powerful method for the determination of structures and bonding in isolated gas-phase clusters. Here we report infrared action spectra of mass-selected cationic nitric oxide clusters, (NO)_<i>n</i>⁺ (<i>n</i> = 3-8), and mixed NO₂(NO)_<i>n</i>⁺ clusters which are interpreted with the help of quantum chemical calculations. Despite the rich potential energy landscape which exhibits very many calculated low-energy isomers, clear structural motifs are observed. Important differences between our (NO)_<i>n</i>⁺ spectra and others published previously are interpreted in terms of the qualitatively different experimental techniques employed in the initial formation of the clusters in each study. Finally, spectra recorded in different fragmentation channels provide clear evidence for intracluster chemistry leading to the formation of mixed nitrous oxide/nitrogen dioxide/nitric oxide complexes, (N₂O)(NO₂)(NO)_<i>n</i>⁺.