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

Abstract

We study vibrationally-resolved resonant Auger (RAS) spectra of ammonia recorded in coincidence with the NH+2 fragment, which is produced in the course of dissociation either in the core-excited 1s−14a1 intermediate...

Dynamics of core-excited ammonia: disentangling fragmentation pathways by complementary spectroscopic methods

“…From the fit analysis we can also conclude that higher vibrational levels of the initial coreexcited state are practically not populated since the observed Poisson-like intensity distribution of the vibrational progression is typical for a transition starting at the vibrational ground state v'' = 0. This agrees with the conclusions also derived in our previous work [24]. Indications for the populations of higher vibrational levels in the initial state are expected at higher kinetic energies, namely at ≅ 382.5 eV for v'' = 1 and ≅ 383 eV for v'' = 2; obviously such lines are absent in the spectrum.…”

“…One can notice that the width of the individual peaks within the vibrational progression of the 3a 1 -1 is significantly narrower from that of the vibrationally resolved 1 A 1 state of the NH 2 + fragment. This is 𝑎 owing to the contribution of the lifetime broadening (Γ ~130 meV) in Auger decay process occurring in the fragments after UFD, while molecular Auger decay does not include lifetime broadening of core-excited state in resonant Raman conditions [24].…”

“…Since the lifetime broadening of coreexcited NH 2 is not known, we applied Γ = 120 meV, which is the average of the N 1 N 1 u -1 levels of N 2 . These lineshapes were convoluted with a Gaussian to describe the experimental resolution and the Doppler broadening due to the dissociation of NH 3 [24]. The width of the Gaussian function was a free parameter and resulted in ΔE = 130 (5) meV.…”

Multireference Approach to Normal and Resonant Auger Spectra Based on the One-Center Approximation

“…The high sensitivity of AES/RAES to electronic and nuclear dynamics encouraged experimentalists to explore it to unravel underlying electron and nuclear dynamics of photoexcited molecules. − In the case of halogen-containing molecules, the photoexcited repulsive σ* states expose the competition between nuclear dynamics and resonant Auger electron emission, because of the fact that both Auger decay and direct dissociation occur on the femtosecond time scale. − In a series of recent studies, it was also demonstrated that ultrafast dissociation, distinguished by means of its fingerprint in the RAES, is a practical mechanism of distributing the molecular internal energy of the L -edge photoexcited systems in small molecules like HCl as well as in heavier ones, such as CH 2 Cl 2 and CHCl 3 . , Moreover, the Auger decay around the Cl 1s threshold of HCl has been recently simulated, considering the evolution of the relaxation process, including both electron and nuclear dynamics . Adding to that is the fact that AES does not obey the same dipole transition rules as XAS does, so AES/RAES can be used as a powerful tool to probe dark states and couple to nuclear dynamics. − However, from the computational point of view, for AES/RAES to be used effectively as a probe of (excited-state) nuclear dynamics, one should efficiently deal with one of the major complications in the computation of Auger spectra, namely the description of the electron in the continuum.…”

Multi-Reference Approach to Normal and Resonant Auger Spectra Based on the One-Center Approximation

“…2 The high sensitivity of AES/RAES to electronic and nuclear dynamics encouraged experimentalists to explore it to unravel underlying electron and nuclear dynamics of photoexcited molecules. [11][12][13][14][15][16] In the case of halogen-containing molecules, the photoexcited repulsive σ * states expose the competition between nuclear dynamics and resonant Auger electron emission owing to the fact that both Auger decay and direct dissociation take place in the fs time scale. [17][18][19] In a series of recent studies, it was also demonstrated that ultrafast dissociation, distinguished by means of its fingerprint in the RAES, is a practical mechanism of distributing the molecular internal energy of the L-edge photoexcited systems in small molecules like the relaxation process, including both electron and nuclear dynamics.…”