An ionization-induced multistage reaction of ionized diethylether (DEE) dimer involving isomerization, proton transfer, and dissociation is investigated by combination of infrared (IR) spectroscopy, tandem mass spectrometry, and theoretical reaction path search. The vertically-ionized DEE dimer isomerizes to a hydrogen-bonded cluster of protonated DEE and the [DEE - H] radical through the barrierless intermolecular proton transfer from the CH bond of the ionized moiety. This isomerization process is confirmed by the IR spectroscopy and theoretical reaction path search. The multiple dissociation pathways following the isomerization are analyzed by the tandem mass spectrometry. The isomerized cluster stepwisely dissociates to the [protonated DEE-acetaldehyde (AA)] cluster, protonated DEE, and protonated AA. The structure of the fragment ion is also analyzed by the IR spectroscopy. The reaction map of the multistage processes is revealed through a harmony of these experimental and theoretical methods.

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