Partial cation and anion-yield experiments in ammonia around the N 1s ionization threshold

We report partial cation and anion-yield measurements around the N K edge in isolated ammonia molecules. Due to the dominance of spectator electronic decay following Rydberg excitations, fragmentation was found to be more extensive following excitation to intermediate states of Rydberg character compared to excitation of states with molecular-orbital character. Unusual stability of the NH32+ fragment produced directly above threshold by normal-Auger decay is attributed to a stable planar geometry induced by a specific electronic configuration. Hydrogen anions are not detected above threshold except following the decay of resonant doubly excited neutral states embedded in the K-shell ionization continuum.