Experimental and BE f -scaled cross sections for electron-impact excitation of ammonia molecules from near threshold to high-intermediate energy

olute differential and integral cross sections (DCSs and ICSs) for the lowest-lying singlet excitations in ammonia (NH 3 ) molecules have been measured from near threshold to 400 eV using angle-revolved electron energy loss spectroscopy. Normalizing the angular distributions of inelastically scattered electrons to the absolute DCS of He as the reference, the reliable absolute cross sections for the A^1A^''_2 excitation were obtained in a wider impact energy range. The BE f -scaled ICS was also derived as a function of incident electron energy from the generalized oscillator strengths analysis using the corresponding DCS measured at higher impact energies. The experimental ICS of the singlet excitation in the present study has reasonably reproduced the BE f -scaled ICS in the energy of not only higher impact energies but also near the threshold energy within the experimental uncertainties. The present absolute measurement has suggested that the BE f -scaling law was confirmed to be quite useful to NH 3 molecules even towards the threshold energy. Graphic abstract