Doubly excited states of ammonia produced by photon and electron interactions

Abstract

The formation and decay of doubly excited ammonia produced by photon and electron interactions have been investigated through measuring (i) the cross sections for the emission of the Lyman-α fluorescence in the photoexcitation of NH3 as a function of incident photon energy in the range 15–60 eV and (ii) the electron-energy-loss spectrum of NH3 tagged with the Lyman-α photons at 100 eV incident electron energy and 8° electron scattering angle in the range of the energy loss 15–48 eV. Six superexcited states have been found, four of which are doubly excited states with one being a singly excited state and the other being a state including electron configurations of a single excitation and double excitations. There exist two forbidden doubly excited states whose widths are approximately 1 eV, i.e. much sharper than the allowed superexcited states in the electron-energy-loss spectrum tagged with the Lyman-α photons. It is remarkable that the electron interaction with NH3 at 100 eV incident electron energy and 8° electron scattering angle promotes the ratio of the oscillator strength for the double excitation to that for the single excitation as compared with the photon interaction.

Bond angle variations in XH3[X = N, P, As, Sb, Bi]: the critical role of Rydberg orbitals exposed using a diabatic state model

“…Bands in the one-photon absorption spectrum observed at 18.4 eV and at 30-33 eV previously assigned to double excitations involving Rydberg transitions are reassigned to the valence single-excitation resonances ns* E and a combination of s Es* E and s Es* A , respectively. The 18.4 eV band had been previously assigned 114 as n -3s, n -? and presumed to be associated with the IP observed at 24 eV that is assigned 119 to the double excitation n -3s, n -N. Properties of the diabatic model are key to this reassignment as the n -3s, n -3s excitation dr is found to be counter-intuitively at higher energies than n -3s, n -N and ca.…”

“…Absorption at 16.3 eV and 25.3 eV is also observed to Rydberg bands leading up to the ionization potentials for s E -N and s A -N at 16.4 and 27.3 eV, respectively. 114 Two other broad bands are also observed centred at 18.4 eV and 31.5 eV, although originally only part of the 18.4 eV band was in the observable range and so this band was first assigned at 22 eV whilst the higher-energy band was observed partially resolved into components at 30 eV and 33 eV. 64 Both systems were attributed to double excitations, despite the typically low oscillator strength for such bands in one-photon spectroscopy.…”

“…64 Both systems were attributed to double excitations, despite the typically low oscillator strength for such bands in one-photon spectroscopy. 64,114 The 18.4 eV band was assigned to the dr-type series transitions n -3s, n -? leading up to an observed very weak ionization process at 24 eV involving r excitation plus ionization, n -3s, n -N. 119 This would appear feasible as the isolated ionization process n -N occurs at 10.9 eV whilst the r absorption n -3s occurs at 6.5 eV, summing to 17.4 eV, amidst the observed band.…”

“…63 Both systems were attributed 80 to double excitations, despite the typically low oscillator strength for such bands in one-photon spectroscopy. 63,109 The 18.4 eV band was assigned to the dr-type series transitions n3s,n? leading up to an observed very weak ionization process at 24 eV involving r excitation plus ionization, 85 n3s,n.…”

Three-body neutral dissociations of a multiply excited water molecule around the double ionization potential

“…In our previous studies, it has been shown that the multiply excited states are well probed by fluorescence photons emitted by fragments produced through the neutral dissociations (process (4)). Several doubly excited states of CH 4 , NH 3 and H 2 O were revealed in photoexcitation by measuring the cross sections for the emission of the Lyman-α, Balmer series and radical fluorescences as a function of the incident photon energy [7][8][9][10][11][12]. These authors found much larger cross sections due to doubly excited states than those expected within the independent electron model.…”