Triplet states of ammonia excited by low-energy electrons

Abstract

A low-energy crossed-beam electron spectrometer is used to investigate excitation of ammonia. Spectra obtained at low residual energies and large scattering angles in both constant residual energy mode and energy loss mode show excitation of two triplet states of ammonia, labelled a and b. A triplet b state is observed for the first time in the present work, while for the a state several lower, previously unobserved vibrational levels are detected. The threshold electron spectrum obtained by detecting zero residual energy electrons reveals a strong influence of threshold resonance in the excitation of he lowest Rydberg a state. Also a very large threshold peak in the excitation of the v=1 level of the symmetric stretch mode (v1) of the ground electronic state suggests a resonant process at very low energies.