Molecular dynamics of NH₃ induced by core-electron excitation

Abstract

Nuclear motion in the N1s(-1)4a core-excited state of ammonia is investigated by studying the angular anisotropy of fragments produced in the decay of the highly excited molecule and compared with predictions from ab initio calculations. Two different fragmentation channels (H(+)/NH2(+) and H(+)/NH(+)/H) reveal complex nuclear dynamics as the excitation photon energy is tuned through the 4a1 resonance. The well-defined angular anisotropy of the fragments produced in the dissociation of the molecular dication species suggests a very rapid nuclear motion and the time scale of the nuclear dynamics is limited to the low fs timescale.

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

“…The two arrows denote the excitation energies at which the Auger electron–ion coincidence measurements were performed – at the maximum of the 1s → 4a 1 resonance and at about +230 meV detuning. The energy for the positive detuning was chosen to be above the barrier which is present on the N 1s −1 4a 1 potential energy surface of NH 3 (170 meV 23 ).…”

“…The core-excited NH 3 molecule is pyramidal in its equilibrium geometry with the angle α ∼ 108°, similar to the one of its ground state. 19,23 We can assume that it may decay to the final state with the planar equilibrium geometry, which is dissociative along the H 2 N–H bond. When the planar final state is reached after the Auger decay, the NH 2 group rotates from pyramidal to planar geometry at the same time as the H 2 N–H bond elongation starts to proceed.…”

Highly Accurate Prediction of Core Spectra of Molecules at Density Functional Theory Cost: Attaining Sub-electronvolt Error from a Restricted Open-Shell Kohn–Sham Approach

“…As a simple proof of principle, Figure 2 presents the potential energy surface (PES) of core excited NH 3 (1s → 4a 1 ) against NH stretching. This state can relax to a shallow local minimum, but ultrafast dissociation to NH 2 + H is energetically more favorable (after crossing a small barrier 118 ). ROKS is able to reproduce this behavior, which is a significant advantage over TDDFT (as the latter is completely incapable of modeling excited-state bond dissociation 119 ).…”

Inner-shell X-ray absorption spectra of the cationic series NHy+ (y = 0–3)

“…[16][17][18], enabling us to probe the changes in the electronic structure of the respective molecular ions by performing a XAS-experiment. Whereas there is plenty of previous work on the neutral species of the series NH y , [19][20][21][22][23][24][25][26][27][28][29][30] little work on the cations NH y + ( y = 1-3) has been published. Theoretical work on the electronic structure of NH + 31,32 and NH 2 + 33 has been done calculating molecular potential curves and bonding angles.…”