Unusual photofragmentation mechanisms of chlorinated species elucidated by a combination of double and triple ionic coincidences spectra

YANINA B. BAVA; ROSANA M. ROMANO; REINALDO L. CAVASSO FILHO; YANINA BERRUETA MARTÍNEZ

Campinas

Otro; 26th RAU Annual Users Meeting LNLS; 2016

Laboratório Nacional de Luz Síncrotron

Photofragmentation mechanisms of small molecular compounds after shallow- or core-electron ionization can be determined by using coincidence techniques (Photoelectron-Photoion-PhotoionCoincidences, PE2PICO), as presented for example in reference 1 and references cited therein. In this work we discuss the importance of the combined study of the PE2PICO and PE3PICO spectra to understand some unusual photofragmentation mechanisms of chlorinated species, trichloroethylene (HClC=CCl2, 3CE), deuterotrichloroethylene (DClC=CCl2, D3CE) and tetrachloroethylene (Cl2C=CCl2, 4CE), after ionization of Cl 2p and C 1s electron. The studies were performed in the TGM and SGM beamlines at LNLS, with the experimental station for gaseous samples and coincidence techniques (PEPICO, PE2PICO and PE3PICO) using a WileyMac Laren time-of-flight mass spectrometer. The pressure of the sample inside the chamber was mantained below 5.10-6 mbar, which guarantees the study of only unimolecular fragmentation mechanisms. Different fragmentation mechanisms were proposed by the analysis of the bidimensional PE2PICO spectra, being the most important Cl+/C2Cl2+/Cl⋅ and CCl2+/CCl2+ for 4CE, and Cl+/XC2Cl2+ and XC2Cl+/Cl2+ (with X = H or D) for 3CE and D3CE. However, some of the islands with positive slopes, as for example the H+/C+ coincidence presented in Figure 1, could not be interpreted in terms of any fragmentation mechanisms of M2+. In these cases, the analysis of the PE3PICO projections, also shown in Figure 1 for the selected example, are needed for the correct evaluation of the PE2PICO spectra. Clearly, the fragments were produce after a triple ionization, giving H+, C+, Cl+ and neutral fragments. This behaviour was also observed for the deuterated sample, corroborating the proposed fragmentation channel.