Dissociative attachment and predissociation in ammonia

Abstract

The dissociative attachment cross sections of NH3 and ND3 in the 5.0-6.0 eV region are found to consist of a series of overlapping peaks characteristic of the nu 2 (inversion mode) vibrational quanta. The total scattering cross section is also structured at these energies as observed by electron transmission spectroscopy. Comparison of the results with optical absorption and electron energy loss data for excitation of the lowest Rydberg state of NH3 suggests that fragment ions are produced through the negative-ion analogue of the predissociation process known to occur in this state. The authors assign the electronic state of the relevant temporary negative ion to the configuration ((. . .)(la2)1NH3+)(3sa'1)*(3sa'1)'2A2(D3h). The relative vibrational spacings in the cation, the Rydberg state of the neutral and the anion provide evidence for the nature of the electron correlation in the latter.