Double Differential Cross Sections and Generalized Oscillator Strength Distributions of Ammonia

The absolute double differential cross section (DDCS), the generalized oscillator strength distribution (GOSD), and the ionization efficiency of ammonia (NH3) were investigated from the threshold to 40 eV under the condition of 200 and 400 eV incident electron energies and 6 and 8 degree scattering angles using electron energy-loss spectroscopy and electron- ion coincidence techniques. To determine the absolute values, we used a mixture of helium (He) and NH3 and normalized the measured relative DDCS spectrum by the differential cross section for 21P excitation of He. Our results are in close agreement with previous dipole (e, e) spectroscopy, although the incident electron energy is lower. The ionization efficiency curve obtained from coincidence measurements indicated the existence of doubly excited states that cause neutral dissociation.