INVESTIGADORES
ROMANO Rosana Mariel
congresos y reuniones científicas
Título:
Total ion yield spectra and photofragmentation in CH3OC(O)SCl, under VUV and soft-X-Ray Irradiation
Autor/es:
M. GERONÉS; M. F. ERBEN; R. M. ROMANO; C. O. DELLA VÉDOVA
Lugar:
Campinas, Brasil
Reunión:
Workshop; IWP International Workshop on Photoionization; 2005
Institución organizadora:
Laboratório Nacional de Luz Síncrotron
Resumen:
We report here results concerning the S 2p, Cl 2p and O 1s ionization edges of CH3OC(O)SCl, that include the measurement of the Total Ion Yield (TIY) spectra around each ionization edge and the use of multicoincidence techniques, such as Photoelectron-Photoion-Coincidence (PEPICO) and Photoelectron-Photoion-Photoion-Coincidence (PEPIPICO) time of flight (TOF) mass spectrometry achieved by using the TGM (12-300 eV) and SGM (240-1000 eV) beamlines available at the LNLS (Campinas, Brazil) facilities. Below the S 2p threshold, at around 171 eV, the spectrum shows a rather complex feature, characterized by a group of six signals. The TIY spectra around the O 1s region is dominated by two signals and the O 1s threshold is located at approximately 540 eV. On the other hand, the Cl 2p threshold is located at approximately 211eV. The TOF mass spectrum of CH3OC(O)SCl around the sulfur 2p edge shows peaks corresponding to the following ions: H+, CHx + (x=0,1,2,3), O+ or S+2, CO+, COH+, S+, Cl+ (35 and 37), CO2 + or CS+, CH3Cl+, CH3OC(O)+, OCS+, OCS+2, SCl+, CH3OC(O)S+, C(O)SCl+. The parent ion, CH3OC(O)SCl+, can be observed in this energy range and shows the characteristic chlorine isotopic distribution. The molecular ion has a negligible contribution above this region. The signals of both CH3OC(O)S+ and C(O)SCl+ ions are not observed above this energy range. The signal assignable to the Cl+2 ion is observed in the TOF mass spectrum of CH3OC(O)SCl around the chlorine 2p edge and oxygen 1s edge. Therefore, a site site-specific fragmentation behaviour is observed. This result is rather interesting because in the previously studied XC(O)SY molecules FC(O)SCl and ClC(O)SCl, a lose memory effect or non specific fragmentation after an Auger decay, promoted by the delocalization of the valence orbitals over the whole planar molecule, where invoked in order to explain the almost nonvariation of the PEPICO spectra in the range of 100-1000 eV [1], [2]. The analysis of the PEPIPICO spectra results useful to identify several molecular dissociation mechanisms followed by Auger decays. Thus, two-body and three-body mechanisms dissociation channels were found. Some of the most important coincidences are = CO+/O+, S+/CHx (x:0,1,2,3), Cl+(35 and 37)/ CHx (x:0,1,2,3),  /C+, Cl+(35 and 37)/CO+. A coincidence between S+ and O+ was found originated by the rupture of C-O double bond. 3OC(O)SCl, that include the measurement of the Total Ion Yield (TIY) spectra around each ionization edge and the use of multicoincidence techniques, such as Photoelectron-Photoion-Coincidence (PEPICO) and Photoelectron-Photoion-Photoion-Coincidence (PEPIPICO) time of flight (TOF) mass spectrometry achieved by using the TGM (12-300 eV) and SGM (240-1000 eV) beamlines available at the LNLS (Campinas, Brazil) facilities. Below the S 2p threshold, at around 171 eV, the spectrum shows a rather complex feature, characterized by a group of six signals. The TIY spectra around the O 1s region is dominated by two signals and the O 1s threshold is located at approximately 540 eV. On the other hand, the Cl 2p threshold is located at approximately 211eV. The TOF mass spectrum of CH3OC(O)SCl around the sulfur 2p edge shows peaks corresponding to the following ions: H+, CHx + (x=0,1,2,3), O+ or S+2, CO+, COH+, S+, Cl+ (35 and 37), CO2 + or CS+, CH3Cl+, CH3OC(O)+, OCS+, OCS+2, SCl+, CH3OC(O)S+, C(O)SCl+. The parent ion, CH3OC(O)SCl+, can be observed in this energy range and shows the characteristic chlorine isotopic distribution. The molecular ion has a negligible contribution above this region. The signals of both CH3OC(O)S+ and C(O)SCl+ ions are not observed above this energy range. The signal assignable to the Cl+2 ion is observed in the TOF mass spectrum of CH3OC(O)SCl around the chlorine 2p edge and oxygen 1s edge. Therefore, a site site-specific fragmentation behaviour is observed. This result is rather interesting because in the previously studied XC(O)SY molecules FC(O)SCl and ClC(O)SCl, a lose memory effect or non specific fragmentation after an Auger decay, promoted by the delocalization of the valence orbitals over the whole planar molecule, where invoked in order to explain the almost nonvariation of the PEPICO spectra in the range of 100-1000 eV [1], [2]. The analysis of the PEPIPICO spectra results useful to identify several molecular dissociation mechanisms followed by Auger decays. Thus, two-body and three-body mechanisms dissociation channels were found. Some of the most important coincidences are = CO+/O+, S+/CHx (x:0,1,2,3), Cl+(35 and 37)/ CHx (x:0,1,2,3),  /C+, Cl+(35 and 37)/CO+. A coincidence between S+ and O+ was found originated by 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.