Ammonia Borane, NH 3 BH 3 : A Threshold Photoelectron-Photoion Coincidence Study of a Potential Hydrogen-Storage Material.

We have investigated the photoionization of ammonia borane (AB) and determined adiabatic ionization energy to be 9.26±0.03 eV for the X + 2 E←X 1 A 1 transition. Although the threshold photoelectron spectrum appears at first glance to be similar to the one of the isosteric ethane, the electronic situation differs markedly, due to different orbital energies. In addition, an appearance energy AE 0K (NH 3 BH 3 , NH 3 BH 2 + )= 10.00±0.03 eV has been determined, corresponding to the loss of a hydrogen atom at the BH 3 -site. From the data, a 0 K bond dissociation energy for the B-H bond in the cation of 71.5±3 kJ mol -1 was derived, whereas the one in the neutral compound has been estimated to be 419±10 kJ mol -1 .