Electronic Properties of Fluorosulfonyl Isocyanate, FSO₂NCO: A Photoelectron Spectroscopy and Synchrotron Photoionization Study

Abstract

The electronic properties of fluorosulfonyl isocyanate, FSO2NCO, were investigated by means of photoelectron spectroscopy and synchrotron based techniques. The first ionization potential occurs at 12.3 eV and was attributed to the ejection of electrons formally located at the π NCO molecular orbital (MO), with a contribution from nonbonding orbitals at the oxygen atoms of the SO2 group. The proposed interpretation of the photoelectron spectrum is consistent with related molecules reported previously and also with the prediction of OVGF (outer valence green function) and P3 (partial third order) calculations. The energy of the inner- and core-shell electrons was determined using X-ray absorption, measuring the total ion yield spectra, and the resonances before each ionization threshold were interpreted in terms of transitions to vacant molecular orbitals. The ionic fragmentation mechanisms in the valence energy region were studied using time-of-flight mass spectrometry as a function of the energy of the incident radiation. At 13 eV the M(+) was the only ion detected in the photoion-photoelectron-coincidence spectrum, while the FSO2(+) fragment, formed through the breaking of the S-N single bond, appears as the most intense fragment for energies higher than 15 eV. The photoion-photoion-photoelectron-coincidence spectra, taken at the inner- and core-levels energy regions, revealed several different fragmentation pathways, being the most important ones secondary decay after deferred charge separation mechanisms leading to the formation of the O(+)/S(+) and C(+)/O(+) pairs.

Electronic properties and photofragmentation mechanisms of pyrosulfuryl chloride, ClSO2OSO2Cl

“…The ionization threshold of the Cl 2p electrons occurs close to 211.5 eV. The ionization energy of S 2s electrons is located at 234.9 eV (see Figure 6), in agreement with the observed for related molecules [7,8].…”

“…The ionization energies of the outer valence electrons were determined, and the characters of the molecular orbitals involved were assigned according to the B3LYP calculations. The interpretation and assignment of the photoelectron spectrum was performed with the aid of different theoretical calculations, OVGF/6-311+G(d) and P3/6-311+G(d), which correlated well with the experimental values for compounds containing the XSO2 group, with X = halogen [7]. The vertical ionization energies, as well as the approximate character of the molecular orbitals involved in each ionization, were calculated for the optimized most stable molecular structure.…”

“…The study presented here is part of a general project aimed to photochemical studies of species with atmospheric interest, as for example fluorinated alcohols (CF3CH2OH) [5], perfluorocarbons (CF3CF2CF2C(O)Cl) [6], compounds containing the SO2 group (FSO2NCO [7], ClSO2NCO) [8], among others. The main objective of these studies is the determination of the photochemical mechanisms through the detection of the photoproducts and reactive intermediates, allowing the modeling of possible atmospheric process.…”

“…Below the first ionization potential, in the region of visible and UV light, the fragmentation process occurring through free radicals and producing neutral species are followed mainly by IR spectroscopy [9,10]. When ionizing radiation is used, in the VUV and X ray region, electron and ionic species are detected [5][6][7][8].…”

Photofragmentation Mechanisms of Chlorosulfonyl Isocyanate, ClSO2NCO, Excited with Synchrotron Radiation between 12 and 550 eV

“…The same mechanism was proposed for this coincidence in the study of the fragmentation of FSO 2 NCO in similar conditions, for which the experimental slope of also −0.7 was observed. 6 → +…”