Resonant Auger electron-ion-coincidence spectroscopy of N -methyltrifluoroacetamide: Site-specific fragmentation studies

Abstract

We present a theoretical and experimental study of the electronic structure of N-methyltrifluoroacetamide (FNMA) and examine the resonant Auger (RA) decay upon site-and state-specific excitation at the C 1s, N 1s, and O 1s edges. Based on the calculated energies for cationic states of 1h and 2h-1p configurations, we assign the peaks of recorded VUV photoelectron and RA spectra. Specifically, we identify the spectral features associated with participator and spectator RA decay. To aid in a deeper understanding of previous observations of limited site-specific bond breaking in FNMA, the influence of the site-specific excitation and the character of the Auger decay on the fragmentation is investigated using Auger electron ion coincidence experiments. Moreover, to investigate the potentially different capacity for selective bond cleavage of participator and spectator Auger states, we apply this technique to the spectator Auger state with the main electronic configuration of (31a) −1 (32a) −1 (34a) 1 , which is well resolved in the experimental spectrum. Finally, the influence of the molecular excess energy and the electronic character of the RA final states on fragmentation is addressed. Based on our findings, we argue that the excess energy the FNMA molecule gains upon RA decay is the dominant factor determining the fragmentation pattern.

Coincidence study of core-ionized adamantane: site-sensitivity within a carbon cage?

“…Thus we have studied the dissociation of adamantane molecules in the gas phase after C-1s core-ionization using synchrotron X-ray radiation and explore site-sensitive dissociation. In fact, K-shell ionization by synchrotron radiation has been extensively used to probe the chemical environment of many molecular and cluster systems [25][26][27][28][29][30][31][32][33] even though site-specific dissociation is often considered as weak 34 and that fragmentation dynamics is mostly driven by internal energy 35,36 . The fact that adaman-tane is a saturated hydrocarbon implies that the detection of siteselective dissociation (using the direct photoelectron) is highly challenging due to small energy difference between the two different carbon sites (similar chemical environment) and the effect is expected to be rather small.…”

“…In fact, K-shell ionization by synchrotron radiation has been extensively used to probe the chemical environment of many molecular and cluster systems 25–33 even though site-specific dissociation is often considered as weak 34 and that fragmentation dynamics is mostly driven by internal energy. 35,36 The fact that adamantane is a saturated hydrocarbon implies that the detection of site-selective dissociation (using the direct photoelectron) is highly challenging due to small energy difference between the two different carbon sites (similar chemical environment) and the effect is expected to be rather small. Nevertheless, multi-coincidence tools using Auger electron and ion spectroscopy can reveal such processes as we will show in the following.…”