Fragmentation of the C̃ 2T2 and D̃ 2A1 states of CCl+4 and SiCl+4 studied by threshold photoelectron—photoion coincidence spectroscopy

Threshold photoelectron—photoion coincidence (TPEPICO) spectroscopy has been used to study the decay pathways of the C̃2T2 and D̃2A1 excited electronic states of CCl+4 and SiCl+4 in the range 14–23 eV. Vacuum UV photons from a synchrotron radiation source ionise the parent neutral molecule, and the electrons and ions are detected by threshold electron analysis and time-of-flight mass spectrometry, respectively. TPEPICO spectra are recorded continuously as a function of photon energy, allowing ion yield curves to be obtained. The C̃ and D̃ states of CCl+4 fragment exclusively to CCl+2 and CCl+ respectively, corresponding to non-statistical routes. Radiative decay from the C̃ state of SiCl+4 is an important process and this state fragments indirectly to SiCl+3 by fluorescence from the C̃ state, followed by dissociation from lower-lying repulsive states. The D̃ state of SiCl+4fragments exclusively to SiCl+2. Kinetic energy releases into CCl+2 + Cl2 and SiCl+3 + Cl have been measured at the Franck—Condon maximum of the C̃2T2 states of the two parent ions.