Single-photon double and triple ionization of acetaldehyde (ethanal) studied by multi-electron coincidence spectroscopy

Abstract

PostprintThis is the accepted version of a paper published in Chemical Physics. This paper has been peerreviewed but does not include the final publisher proof-corrections or journal pagination.Citation for the original published paper (version of record):Zagorodskikh, S., Zhaunerchyk, V., Mucke, M., Eland, J H., Squibb, R J. et al. (2015) Single-photon double and triple ionization of acetaldehyde (ethanal) studied by multi-electron coincidence spectroscopy. Single-photon multiple ionization processes of acetaldehyde (ethanal) have been experimentally investigated by utilizing a multi-particle coincidence technique based on the time-of-flight magnetic bottle principle, in combination with either a synchrotron radiation source or a pulsed helium discharge lamp. The processes investigated include double and triple ionization in the valence region as well as single and doubleAuger decay of core-ionized acetaldehyde. The latter are studied site-selectively for chemically different carbon core vacancies, scrutinizing early theoretical predictions specifically made for the case of acetaldehyde. Moreover, Auger processes in shake-up and core-valence ionized states are investigated. In the cases where the processes involve simultaneous emission of two electrons, the distributions of the energy sharing are presented, emphasizing either the knock-out or shake-off mechanism.a)

Mechanisms of site-specific photochemistry following core-shell ionization of chemically inequivalent carbon atoms in acetaldehyde (ethanal)

“…in the Auger spectra) or by a dependence of the fragmentation from particular energy levels of the doubly-charged molecule on the initial charge position. As it is known already for the case of acetaldehyde 24 , there is indeed a substantial difference in the Auger spectra from 1s ionisation at the two carbon atoms. The lowest internal energy states of the doubly ionised products are not significantly populated in formylic Auger decay, while higher internal energy states around 60 eV are populated more strongly 24 .…”

“…Triple ionisation by double Auger decay might also cause the PIPICO and mass spectra to represent different events. This could be significant as we have previously estimated the double to single Auger ratio to be about 29%, 27% and 21.5% for the oxygen, formylic and methylic carbon 1s core hole respectively 24 . Table II presents a comparison of integrated intensities of the three groups of flight time differences in Fig.…”

“…To allow for the non-linearity of this formula, conversion of flight time spectra to energy spectra with a fixed bin size has been done by redistribution of the intensity information from the time bins, as described before 24,37 .…”

“…If the breakdown pattern depends only on the ions' total internal energy content (as assumed in the statistical theory of mass spectra for a molecule of this size), then differences in mass spectra can be caused by differences in the energy deposition, that is by differences in the Auger spectra from vacancies on different atoms, defined by the overlap between the core hole and the valence orbital 6 . As known from the very recently investigated cases of acetone 22 , ethyl trifluoracetate 23 and acetaldehyde 24 , the Auger spectra from holes on different C atoms can be significantly different. At the other extreme, if Auger decays from different atoms produce exactly the same total energy distribution in the ions, then differences in ion behavior could still arise if the same amount of energy is deposited in different quantum states (including location) which decay in different ways.…”

“…The energy-selected fragmentation of singly ionised acetaldehyde was studied by Golovin et al 34 , Bombach et al 35 and by Johnson et al 36 . Very recently, we have investigated multi-electron emission processes in acetaldehyde 24 with emphasis on double and triple valence ionisation and site-specific single and double Auger decay. We also investigated core-valence double ionisation of acetaldehyde for direct comparison to theoretical modelling.…”