Fragmentation of doubly charged ammonia cations NH ⁺⁺₃ studied by the photoion-photoion coincidence (PIPICO) method

Abstract

Doubly charged NH ⁺⁺₃ cations were produced by double photoionization of neutral ammonia molecules by using the synchrotron radiation from ACO as a photon source of variable energy in the 35–49 eV energy range. The fragmentation of NH ⁺⁺₃ was studied by the photoion-photoion coincidence (PIPICO) method. NH ⁺⁺₃ cations were produced in the$\tilde X^1$ A ₁ and$\tilde B^1$ electronic states of which the onset energies were measured at, respectively, 35.4±0.5 eV and 44.5±0.5 eV. It was shown that the NH ⁺⁺₃ ions, initially produced in their$\tilde X^1$ A ₁ state, rapidly dissociate (in less than 50 ns), into NH ⁺₂ + H⁺. Furthermore, the comparison with results obtained by other methods indicates that NH ⁺⁺₃ ions can either be long-lived (τ>10 µs) or slowly dissociating (1 µs<τ<10 µs) or rapidly dissociating (τ<50 ns), depending on their geometry and/or internal energy in their$\tilde X^1$ E A ₁ electronic state.