Ionic Fragmentation and Dissociation Channels in Sulfenylcarbonyl compounds –SC(O)–

CARLOS OMAR DELLA VEDOVA; ERBEN, M.; GERONÉS, M.; ROMANO, R. M.

Campinas

Congreso; Actas del IWP2005 International Workshop on Photoionization; 2005

Recently, we have started with the study of the different processes occurring as result of the interaction between photons with energies in the range of 12-1000 eV and molecules corresponding to the sulfenylcarbonyl family of compounds XC(O)SY, such as FC(O)SCl, ClC(O)SCl, CH3C(O)SH, CH3C(O)SCH3 and CH3OC(O)SCl. The energy range selected for this study corresponds to the ionization energies of the S  2p and O 1s electrons of the –SC(O)– moiety. Total Ion Yield spectra (TIY) and multicoincidence techniques, such as Photoelectron-Photoion-Coincidence (PEPICO) and Photoelectron-Photoion- Photoion-Coincidence (PEPIPICO) time of flight (TOF) mass spectrometry were applied by using the TGM and SGM beamlines available at the LNLS (Campinas, Brazil) facilities. The TIY spectra below the S 2p edge a complex behaviour. Two of these signals may correspond to a spin-orbit split of the 2p term of the sulfur in 2p1/2 and 2p3/2 levels present in the excited species. In the case of the SH2 molecule, this splitting was reported to be 1.201 eV [1]. The TIY spectra around the O 1s region are dominated in all cases by an intense resonance and by a second signal with much smaller intensity. These signals may correspond to excitations to vacant p*CO and s*CO orbitals, respectively.The experimental S 2p and O 1s ionisation energies were compared with those predicted on the basis of equivalent-core approximation using OCS as the reference compound. Calculations were performed by using the Density Functional Theory (DFT) at the B3LYP level of approximation and the 6-311++G** basis sets, as implemented in the Gaussian 98 suite of programs. The analysis of the PEPICO spectra suggests the possibility of site-specific fragmentation. For example, preliminary results show that important changes occurs in the branching ratios of the ions derived from CH3OC(O)SCl with the incident photon energy. In the molecules FC(O)SCl and ClC(O)SCl only minor changes were observed. The analysis of PEPIPICO spectra results useful to identify several molecular dissociation mechanisms followed by Auger decays. Thus, two-body and three-body mechanism dissociation channels were found. A new three-body dissociation mechanism defined as Secondary Decay after an Ion Rearrange (SD-IR) was proposed in order to explain the dissociation process involving two double coincidences, namely F+/Cl+ and CO+/S+ in FC(O)SCl. The equivalent pairs of ions for this mechanism in ClC(O)SCl are the CO+/S+ coincidence on one hand and the Cl+/Cl+ coincidence on the other hand [2, 3]. Furthermore, the existence of processes leading to atomization can be identified by the appearance of atomic species like carbon and oxygen, among others. Multi-body dissociation dynamics should be involved in these processes. Moreover in FC(O)SCl, ClC(O)SCl and CH3OC(O)SCl compounds, triple charged molecular ions should be considered in order to explain the appearance in the PEPIPICO spectra of S+2 and CO+ ions in coincidence.