Ionization and fragmentation of CH3C(O)SH after photoexcitation around the sulfur 2p edge and oxygen 1s edge

M. GERONÉS; M. F. ERBEN; R. M. ROMANO; C. O. DELLA VÉDOVA

Campinas, Brasil

Workshop; IWP International Workshop on Photoionization; 2005

Laboratório Nacional de Luz Síncrotron

The excitation of core electrons in a molecule leads to multiple ionic fragmentation of the molecule after electronic de-excitation like the Auger decay. Tunable synchrotron radiation enables a selective excitation of core electrons in the specified atom. For this reason, ionization and fragmentation of CH3C(O)SH after photoexcitation around the sulfur 2p edge and oxygen 1s edge have been studied by using the TGM (12-300 eV) and SGM (240-1000 eV) beamlines available at the LNLS (Campinas, Brazil) facilities. A similar study was made for others molecules corresponding to the sulfenylcarbonyl family of compounds XC(O)SY, such as FC(O)SCl and ClC(O)SCl [1,2]. 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. S 2p and O 1s ionisation energies have been extracted from the TIY spectra and compared with those predicted based on the equivalent-core approximation taking 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 TOF mass spectra of CH3C(O)SH around the sulfur 2p edge and oxygen 1s edge show peaks corresponding to the ions H+, S+, CHx + (x=0,1,2,3 ), CH3CO+, CO+, COH+, S+, SH+, OCS+, COSH+, among others. The intensity of the m/z=12 and m/z=16 signals is incremented by going from S 2p to the O 1s region. The analysis of the 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 coincidence between S+ and O+ was found which means the rupture of C-O double bond. 3C(O)SH after photoexcitation around the sulfur 2p edge and oxygen 1s edge have been studied by using the TGM (12-300 eV) and SGM (240-1000 eV) beamlines available at the LNLS (Campinas, Brazil) facilities. A similar study was made for others molecules corresponding to the sulfenylcarbonyl family of compounds XC(O)SY, such as FC(O)SCl and ClC(O)SCl [1,2]. 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. S 2p and O 1s ionisation energies have been extracted from the TIY spectra and compared with those predicted based on the equivalent-core approximation taking 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 TOF mass spectra of CH3C(O)SH around the sulfur 2p edge and oxygen 1s edge show peaks corresponding to the ions H+, S+, CHx + (x=0,1,2,3 ), CH3CO+, CO+, COH+, S+, SH+, OCS+, COSH+, among others. The intensity of the m/z=12 and m/z=16 signals is incremented by going from S 2p to the O 1s region. The analysis of the 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 coincidence between S+ and O+ was found which means the rupture of C-O double bond. References [1] M. F. Erben, R. M. Romano, and C. O. Della Védova, J. Phys. Chem. A. 108 (18), 3938 (2004). [2] M. F. Erben, R. M. Romano, and C. O. Della Védova, J. Phys. Chem. A. 109 (2), 304 (2005).108 (18), 3938 (2004). [2] M. F. Erben, R. M. Romano, and C. O. Della Védova, J. Phys. Chem. A. 109 (2), 304 (2005).109 (2), 304 (2005). Acknowledgements This work has been largely supported by LNLS. The authors are indebted to UNLP, CONICET, Fundación Antorchas, DAAD and CIC for financial support. The authors wish to thank Arnaldo Naves de Brito and his research group for fruitful discussions and generous collaboration during their stay in Campinas and the TGM and SGM beamlines staff for their assistance throughout the experiments.