Photoionization of hypervalent molecular clusters: electronic structure and stability of NH 4 (NH 3) n

Abstract

Ammoniated NH 4 radicals produced by an ArF excimer laser photolysis of ammonia clusters are studied by one-photon ionization and time-of-flight mass spectroscopy. The ionization potentials (IPs) of NH 4(NH 3) n ( n = 0–35) are determined by the photoionization threshold measurements. The binding energies of NH 4 (NH 3) n−1 -NH 3 ( n = 1–6) are estimated from IPs. The results indicate that the bonding between NH 4 and NH 3 is semi-ionic. The IPs for larger clusters are found to decrease monotonically with increasing n to a limit of 1.33 eV, which coincides with the photoemission threshold of liquid NH 3. This feature is similar to those found recently for alkali atoms-ammonia clusters.