| Abstract
| - The photodissociation of homogeneous methyl nitrite clusters,[CH3ONO]n with n≈ 400−1000, wasinvestigated in a supersonic jet using excitation mainly at 365 nm,which corresponds to S0 →S1 (nπ*)excitation in the monomer. Besides the two types ofNO(X̃2II) photofragment distributions, arotationallyrelaxed one (Trot ∼ 250 K) and a nonthermally“hot” one (〈J‘‘〉 = 35.5) which result from theprimarydissociation step CH3ONO → CH3O + NOof cluster-bound CH3ONO, we observed the productsHNO(X̃A‘) andH2CO(X̃1A1) bystate-selected LIF spectroscopy. Their product−yield excitationspectra andtheir formation dependence on the backing pressure revealed that HNOand H2CO originate exclusively fromcluster photodissociation and not from primary photodissociation of themonomer. The mechanism of theirformation was found to be the disproportionation reaction of theprimary photofragments, CH3O + NO →HNO + H2CO, mediated by caging of the clusterenvironment. The fragments collide with, and recoil at,thesolvent shell followed by subsequent recombination, disproportionation,or escape from the evaporating solventcage. The present results are consistent with previous findings onthe photolysis of isolated CH3ONOmoleculesin solid noble gas matrices where exclusively the products HNO andH2CO were found.
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