Ionization potentials of large sodium doped ammonia clusters

Abstract

In a continuous neat supersonic expansion ammonia clusters are generated and doped with sodium atoms in a pickup cell. Thus clusters of the form Na(NH(3))(n) are produced that are photoionized by a tunable dye laser system. The ions are mass analyzed in a reflectron time-of-flight mass spectrometer, and the wavelength dependent ion signals serve for the determination of the ionization potentials (IP) of the different clusters in the size range 10< or =n< or =1500. Aside from a plateau for 10< or =n< or =17 and smaller steps at n=24, 35, and 59 on the average a continuous decrease of the IP with cluster size is observed. The IPs in this size range are linear with (n+1)(-13) and extrapolate to IP(n=infinity)=1.66+/-0.01 eV. The slope is consistent with a dielectric continuum model of the solvated electron and the dielectric constant of the solid. The extrapolated IPs are compared with results obtained for negative ammonia cluster ions and metallic solutions in liquid ammonia. Differences are explained by the presence of counterions and their various distances from the solvated electron.

A sodium atom in a large water cluster: Electron delocalization and infrared spectra

“…[19][20][21][22][23] They reveal a reduction of the IP for the first four or six solvent molecules. The results are available for water, ammonia, and very recently also for methanol.…”

Communications: Observation of two classes of isomers of hydrated electrons in sodium-water clusters

“…The IPs of Na͑H 2 O͒ n clusters decrease from n =1-4 and stay constant for n Ն 4, while the Na͑NH 3 ͒ n IPs decrease from n = 1 to 11, stay constant up to n = 19, and drop further in steps for n Ն 20 matching the macroscopic binding energies of ammoniated electrons, when scaled and extrapolated to infinity. 6,11 These observations stimulated significant theoretical efforts for understanding the nature of the sodium-water and sodium-ammonia microsolutions. [12][13][14][15] Early studies tried to rationalize the IP evolutions of small ͑n =1-6͒ Na͑NH 3 ͒ n and Na͑H 2 O͒ n clusters assuming a direct vertical ionization, while more recent work also discussed adiabatic contributions.…”

“…With respect to the standard IP assignment of 2.8 eV based on the steepest gradient extrapolation, one should keep in mind that the gradual signal increase and transition to saturation may reflect a spectrum of cluster geometries and contributions of autoionization. 11,17 However, the scarceness of ion yield signals below 3.05 eV for n Յ 10 and the distinguishable regions of significant signal increase show the coexistence of two cluster groups with different IPs. For isomer I in our measurement the size range is extended to about n = 500.…”

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

“…These can be either size-selected anionic clusters (NH 3 ) − n [7,8] or neutral clusters doped with an alkali metal atom M(NH 3 ) n [9][10][11]. The ion-pair (M + · e − ) in the M(NH 3 ) n clusters may take different forms depending on the cluster size.…”