Photochemical deactivation pathways of microsolvated hydroxylamine

• The excited states of hydroylamine with 1–4 water molecules are investigated.
• First nonadiabatic dynamics study of hydroylamine and hydroxylamine–water clusters.
• OH bond dissociation is the primary process in NH2OH photolysis.
• Complexation with water suppresses the primary process.
• In the hydrates excited state proton transfer is the main deactivation pathway.

Hydroxylamine is a prototypical molecule displaying OH and NH bond interactions. Despite the early interest in the photolysis of NH2OH the primary mechanism of photodissociation remained unclear. Here we perform nonadiabatic trajectory-surface-hopping dynamics simulations based on the algebraic diagrammatic construction method to the second order (ADC(2)) together with reaction path calculations based on the multi-state complete active space second-order perturbation theory (CASPT2) method to identify the dominant deactivation channel of NH2OH. By considering the photoinduced dynamics of hydroxylamine hydrates, ranging from monohydrates to tetrahydrates we show how this channel is modified by site-specific addition of water.