Chemical bond elongation following core-excitation of ammonia: resonant Auger spectra calculation

Abstract

Theoretical resonant Auger decay spectra of ammonia with core-hole excited state dynamics simulation were investigated and some specific features of the experiment except for a vibrational structure were reproduced. A power spectral analysis with short-time maximum entropy method has been applied, and an obtained vibrational spacing assigned to NH stretching mode was 340 meV, which was consistent with the experiment of 390 ± 10 meV. Proton dynamics of ammonia on the first core-excited state was discussed. 1. Introduction Auger decay [1, 2] is one of the de-excitation processes in atoms and molecules after core-excitation. The processes are classified based on the excitation energy as "normal" or "resonant" Auger decay for autoionization of a state created through ionization of an inner-shell electron and through resonant excitation of an inner-shell electron to an unoccupied valence orbital. Depending on the potential energy surface of the excited state the molecule may undergo dynamics during the core-hole lifetime, which depends on the specific element and is in the range of femtoseconds for the second-row atoms. Even if the core-excited state is dissociative, the Auger decay transition in most cases takes place before a bond scission. For some special cases, however, the repulsive character of the potential energy surface in the core-excited state can induce bond scissions within the core-hole lifetime; this is usually referred to as ultra-fast dissociation. Ultra-fast dissociation upon resonant core-excitation into dissociative states has indeed been observed by several researchers through effects on the subsequent Auger decay [3-8] and X-ray emission [9-11]. The ammonia molecule is the simplest molecule including an N atom and has been studied for a long time experimentally and theoretically. It is also interested from a viewpoint of periodicity because HF, H 2 O, NH 3 , and CH 4 are isoelectronic with neon. Recent developments of soft X-ray

Characterization of vibrational wave packets by core-level high-harmonic transient absorption spectroscopy

“…1 and the resulting transition energies in Fig. 2, which is consistent with the bond order of a system with a 3d core hole and an additional electron in a σ * orbital [24]. At large R's, the XUV transition energy to the core-hole excited states is less than at small R's.…”

Ultrafast dissociation of ammonia: Auger Doppler effect and redistribution of the internal energy

“…Therefore, the Raman line narrowing below the core–hole lifetime width, which takes place for the molecular band, does not hold for the fragment band. 24,26 The variation of the line widths can be used as a tool to distinguish molecular and fragment bands in RAS, which allows us confirming the fragment nature of the lines in the 381–382 eV region and removing the doubts in their attribution, raised in the theoretical work by Takahashi et al 27…”

“…One can distinguish two qualitatively different spectral regions: the band below 382 eV, related to the first spectator molecular state (3a 1 ) −2 (4a 1 ) 1 , see ref. 27; and the kinetic energy region comprising Auger decays to X̃ and à participator final states with valence electron vacancy in the HOMO (3a 1 ) and HOMO−1 (1e) molecular orbitals of NH 3 , respectively. The sharp lines, which are seen in the electron kinetic energy region of 380 < E e < 382 eV, correspond to the N–H symmetric stretching vibrations of the ã + final state ((1a 1 ) 2 (2a 1 ) 2 (1b 2 ) 2 (3a 1 ) 2 ) of the NH 2 + ion reached after Auger decay in the core-excited N*H 2 fragment.…”

Fast Padé transform in the theory of resonances: exact solution of the harmonic inversion problem

“…This is a completely different methodology from fitting estimators that require the envelope spectrum from the FFT before attempting to quantify the encoded time signals. These two distinct approaches, the FFT followed by ambiguous fittings versus unambiguous and self-contained estimation by the FPT, are anticipated to give substantially different results, especially with respect to closely overlapping resonances that are often of critical importance in applications across interdisciplinary fields, including atomic and molecular spectroscopy [18,19].…”