Microsolvation of Li⁺in Water Analyzed by Ionization and Double Ionization

Abstract

The microsolvation of Li + in water is investigated. The ionization and double-ionization spectra of the series of (H 2 O) n Li + (n ) 1-5) clusters are calculated ab initio by Green's function methods and discussed in detail. The impact of the solvation of the lithium cation with an increasing number of water molecules on the spectral characteristics is revealed. In the context of microsolvation, the discussion of the results for the (H 2 O) 5 Li + cluster is particularly important because the second solvation shell is accessed. Ionization-and double-ionization spectra may be considered to be very useful for the study of microsolvation clusters.

Tracing electron solvation in Li−(NH3)n clusters with K-shell photodetachment spectroscopy

“…Having essentially only two peaks, the main line and a very strong low-energy satellite separated by 2.84 eV, the spectrum of the tetra-ammoniated lithium anion thus differs significantly from both the spectra of the smaller clusters and that of the bare Li − . If it were not this strong satellite peak, the spectrum of Li − surrounded by four ammonia molecules would resemble the core-level spectrum of a microsolvated Li + cation [32]. We ascribe these strong spectral changes to the transition from a contact ion-pair of the two excess electrons and the cationic metal Li + core to a solvent-separated ion-pair (see below).…”

“…In Li − , like in many negative ions [31], electron correlation plays an extremely important role and is responsible for the appearance of several intense resonance peaks in the corresponding K-shell photodetachment spectrum. Contrastingly, the K-shell photoionization spectrum of the isolated Li + exhibits only one dominant peak, the main line, and no strong satellites [32]. The Li − (NH 3 ) 4 cluster where the two outermost electrons of Li − are detached from the ionic metal core and delocalized beyond the solvation shell has the spectrum which is reminiscent of the spectrum of Li + except for a strong satellite peak appearing due to excitation of one of these electrons.…”

Soft-x-ray fragmentation studies of molecular ions

“…The energy region of double valence-vacancy levels (uppermost box) is estimated with the help of Ref. [42], which also indicates that the single inner-valence excitation 2a −1 should dissolve into several energy levels around the indicated dashed line. Correlation plot of the longitudinal and radial relative momenta (∆p…”

“…Water clusters carrying vacancies are model systems for investigating electrostatic electron-electron interactions between distant molecular sites, notably intermolecular Coulombic decay (ICD) [46] and related processes. Recent theoretical work [42,47] was devoted to the vacancy level energies of in small water clusters near a positive charge; here, the case of solvated Li + was treated in detail, and some indicative information can be derived for solvated H + structures [42], although the internuclear (O-H + -O) distances in the equilibrium geometries of protonated water clusters [48] are expected to be considerably smaller when compared to the O-Li + -O distances assumed in Ref. [42].…”

“…Recent theoretical work [42,47] was devoted to the vacancy level energies of in small water clusters near a positive charge; here, the case of solvated Li + was treated in detail, and some indicative information can be derived for solvated H + structures [42], although the internuclear (O-H + -O) distances in the equilibrium geometries of protonated water clusters [48] are expected to be considerably smaller when compared to the O-Li + -O distances assumed in Ref. [42]. Experimentally, both valence vacancy levels and dissociation following photoabsorption of positive water cluster ions are essentially unexplored.…”