Charge delocalization dynamics of ammonia in different hydrogen bonding environments: free clusters and in liquid water solution

Abstract

Valence and core level photoelectron spectra and Auger electron spectra of ammonia in pure clusters have been measured. The Auger electron spectra of gas-phase ammonia, pure ammonia clusters and ammonia in aqueous solution are compared and interpreted via ab initio calculations of the Auger spectrum of the ammonia monomer and dimer. The calculations reveal that the final two-hole valence states can be delocalized over both ammonia molecules. Features at energies pertaining to delocalized states involving one, or more, hydrogen bonding orbitals can be found in both the ammonia cluster Auger electron spectrum and in that of the liquid solvated molecule. The lower Coulombic repulsion between two delocalized valence final state holes gives higher kinetic energy of the Auger electrons which is also observed in the spectra. This decay path--specific to the condensed phase--is responsible for more than 5% of the total cluster Auger intensity. Moreover, this interpretation is also applicable to the solid phase since the same features have been observed, but not assigned, in the Auger spectrum of solid ammonia.

On the nature and origin of dicationic, charge-separated species formed in liquid water on X-ray irradiation

“…The final product is a doubly charged species, but with the two positive charges located on different water units, i.e., a [H 2 O + ··H 2 O + ](aq) complex is formed. Computational work suggests that the ICD process is a rather general mechanism for electronic deactivation in hydrogen-bonded molecules in water such as hydrated biomolecules, 19 ammonia, [20][21] or water molecules interacting with a protein residue. 21 More recently ICD-like processes have also been observed for core-ionization and core-excitation of aqueous solutions.…”

“…21 More recently ICD-like processes have also been observed for core-ionization and core-excitation of aqueous solutions. 20,[22][23][24][25][26] The coreionization induced processes of ICD type have been also observed and thoroughly discussed for water [27][28] and ammonia clusters. 29 An important difference between relaxation of coreholes and inner-valence holes is that single core-ionization energies are greater than the 3 lowest valence double-ionization energies; thus the Auger channel is always open upon coreionization whereas it might be energetically forbidden upon inner-valence ionization.…”

Probing RbBr solvation in freestanding sub-2 nm water clusters

“…Water clusters were then doped with RbBr using a pick-up oven located downstream along the water cluster beam path. Further details of the cluster source 12,[15][16][17] and the cluster formation process 17,18 can be found elsewhere.…”

The role of charge and proton transfer in fragmentation of hydrogen-bonded nanosystems: the breakup of ammonia clusters upon single photon multi-ionization

“…Above the N1s edge, we mostly produce two-hole states localized on one molecule. 15 However, we do not observe any photon energy dependence in the dissociation dynamics with the present statistics, indicating that the same efficient charge separation mechanism dominates below and above the N1s edge. Further charge transfer in a hydrogen bonded system implies a complex nuclear and structural rearrangement.…”

“…[12][13][14] Photoabsorption and -ionization studies have also proven useful in providing information on the mechanisms of charge solvation, as well as on the electronic properties of various ionic species. 15,16 The advances in spectroscopic methods based on the multi-coincident detection of particles have opened up new avenues for studying multiply charged clusters, leading for instance to the discovery of inter-molecular decay (ICD), a mechanism that transfers the electronic excess energy between neighboring molecules. 17,18 In this work, we study for the first time the fragmentation dynamics of multiply-charged ammonia clusters combining coincidence and 3D momentum imaging techniques with synchrotron radiation.…”