Ammonia cluster anions and their relationship to ammoniated (solvated) electrons: The photoelectron spectra of (NH3)n=41–1100−

We report the negative ion photoelectron spectra of (NH3)n=41–1100−, recorded using 2.540 eV photons. The largest cluster anion in this series has a diameter of approximately 4.3 nm. The vertical detachment energies (VDEs) of these cluster anions increase smoothly from 0.55 eV for n=41 to 1.05 eV for n=1100. The VDEs throughout this size range are linear with n−1/3 and extrapolate to a VDE (n=∞) value, which is very close to the measured photoelectric threshold energy of condensed phase ammoniated electrons. The linear extrapolation of this data to an analogous condensed phase property implies that these cluster anions are gas-phase counterparts to ammoniated electrons, i.e., they are embryonic forms of ammoniated electrons which will mature with increasing cluster size to become condensed phase-solvated electrons. The VDE data further implies that these embryonic ammoniated electrons were generated in solid ammonia environments, consistent with the source conditions under which they were produced.