Figure 4
From: Aqueous Solution Chemistry of Ammonium Cation in the Auger Time Window
(A) Nitrogen 1s Auger/autoionization spectra from 2 M NH4Cl (blue curve) and 2 M ND4Cl (red circles) aqueous solution measured at 500 eV photon energy. Details as well as all labels in the figure are explained in the text. (B) Illustration of the double-proton transfer of \({{\rm{NH}}}_{4}^{+}\) in aqueous solution upon core ionization; only two water molecules are shown. (I) Auger process forming core-excited \({({{\rm{N}}{\rm{H}}}_{4}^{3+})}^{\ast }\) (aq) and Auger electron eAuger. (II) Auger decay and ICD of proton-transferred structure transients. (III) The complete transfer of the first proton from \({({{\rm{NH}}}_{4}^{2+})}^{\ast }\) (aq) to a neighbor water molecule forms \({{(\text{NH}}_{3}^{+})}^{\ast }\) (aq) + H3O+ (aq) within 7 fs. Subsequent local Auger decay is depicted. (IV) \({{(\text{NH}}_{3}^{+})}^{\ast }\) also releases a proton which travels only half way to another water molecule, forming a Zundel-analogue complex where the proton is shared between the remaining \({{\rm{NH}}}_{2}^{\ast }\) (aq) and a water molecule. Depiction of the subsequent autoionization processes of the transient structures by Auger decay (IV.1) and ICD and PTM-Auger (IV.2). These latter processes are the same as for NH3 aqueous solution. The vertical arrow indicates the temporal succession of processes I to IV, with IV being completed within 7 fs.
