Mechanistic Insights into the Delayed Fragmentation of Photoionized Ethanol

decay profiles reveal that the metastability arises from statistical fragmentation of vibrationally hot ground states of dehydrogenated ions. Ultrafast hydrogen loss is found to stabilize intermediates by dissipating excess energy and introducing moderate energy barriers, thereby restricting subsequent bond cleavage. These findings establish a clear mechanistic picture of how ethanol ions redistribute excess energy and undergo delayed fragmentation. The combined experiment-theory approach presented here provides a broadly applicable framework for disentangling barrier-mediated delayed fragmentation in polyatomic molecular ions.