Ionic Fragmentation and Dissociation Channels in Methoxycarbonylsulfenyl Chloride; CH3OC(O)SCl, and Thioacetic Acid; CH3C(O)SH, under soft-X-Ray Irradiation

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

Laboratório Nacional de Luz Síncrotron, Campinas, Brasil

Otro; 15ª Reunião Anual de Usuários (RAU); 2005

Laboratório Nacional de Luz Síncrotron

Recently we have started with the study of shallow and inner shell electron structure and the dynamic of the ionic dissociation following photon absorption on the carbonylsulfenyl family of compounds XC(O)SY.  Thus, halogenocarbonylsulfenyl derivatives, such as FC(O)SCl and ClC(O)SCl, have been extensively studied [1], [2]. Following with this general project by increasing the molecular complexity, we have reported in the 14 RAU a study concerning to the photodissociation channels in CH3OC(O)SCl and CH3C(O)SH under VUV irradiation [3]. Neither spectroscopic nor photodissociation studies exist so far in the literature for these species. We report here preliminary results concerning the C 1s and O 1s ionisation edges of these molecules, that include the measurement of the Total Ion Yield (TIY) spectra around each ionisation edge and the use of multicoincidence techniques, such as PhotoElectron-PhotoIon-Coincidence (PEPICO) and PhotoElectron-PhotoIon-PhotoIon-Coincidence (PEPIPICO) time of ight mass spectrometry achieved by using the SGM beamline facility available at the LNLS. Furthermore, the C 1s and O 1s ionisation energies have been extracted from the TIY spectra and compared with those predictions 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 spectrum of CH3C(O)SH measured at a photon energy of 529.2 eV (at the O 1s resonance) shows important peaks at around 15 a.m.u./q, which are characteristics for methyl group CHx+ (x= 0,1,2,3), and at 43 a.m.u./q assigned to a CH3CO+ fragment. The parent ion is present at 76 a.m.u./q. The most intense peaks appear at 32 and 33 a.m.u./q, corresponding to mass/charge ratios for the S and SH simple charged ions, respectively. Out of the resonant energies, the spectra show broad and less resolved peaks, denoting the importance of Resonant Auger process. On the other hand, PEPICO spectra of CH3OC(O)SCl measured in the O 1s resonance at 532.9 eV show important contributions of atomic charged ions, such as carbon, oxygen, sulfur and chlorine. The spectrum is dominated by an intense signal at 28 a.m.u./q assigned to the CO+. Other intense signals are observed at mass/charge ratio of 15 and 44 a.m.u./q originated by CH3 and CO2 single charged fragments. Results arising from both TGM and SGM beamlines are currently under study in order to elucidate the following questions: Site speci c fragmentation: through the analysis of the PEPICO spectra, the evaluation of the study of state-selective fragmentation in molecules possessing diferent geometrical structure, size and substituents is quite likely. Fragmentation Dynamics: Branching ratios at diferent energy regions and double coincidences (PEPIPICO spectra) between ions produced in each event allow us to explain the dissociation mechanisms originated by electron excitation. Acknowledgements.This work was supported by LNLS under proposal D08A-SGM, UNLP, CONICET, CIC, and Fundación Antorchas. References 1. Erben, M. F.; Romano, R. M.; Della Vedova, C. O., J. Phys. Chem. A. 108, 3938 (2004) 2. Erben, M. F.; Romano, R. M.; Della Vedova, C. O.; to be submitted to J. Phys. Chem. A 3. Erben, M. F.; Romano, R. M.; Della Vedova, C. O.; 14 RAU, LNLS Campinas, 2004 2. Erben, M. F.; Romano, R. M.; Della Vedova, C. O.; to be submitted to J. Phys. Chem. A 3. Erben, M. F.; Romano, R. M.; Della Vedova, C. O.; 14 RAU, LNLS Campinas, 2004