Dissociative photoionization of chloromethylsilanes using VUV synchrotron radiation

Dissociative photoionization of Si(CH3)Cl3 and Si(CH3)2Cl2 has been investigated with photoionization mass spectrometry (PIMS) and a synchrotron as source of vacuum ultraviolet (VUV) radiation. We determined appearance energies (AE) of the parent cations, Si(CH3)Cl3+ and Si(CH3)2Cl2+, and various ionic fragments. The appearance energy of Si(CH3)Cl3+ is 11.18 eV and that of Si(CH3)2Cl2+ is 10.41 eV, in agreement with measurements of the photoelectron spectrum. Molecular electronic calculations of structures and energies of the radical cations and various fragment cations are made with Gaussian-2 and Gaussian-3. Results of these calculations are applied to establish dissociative photoionization channels of Si(CH3)Cl3 and Si(CH3)2Cl2 near the ionization threshold. A comparison of Si(CH3)Cl3 and Si(CH3)2Cl2 provides insight and understanding of fragmentation processes on dissociative photoionization of gaseous chloromethylsilanes.