Fragmentation of methylphenylsilane and trimethylphenylsilane: A combined theoretical and experimental study

• Electron impact ionization of methylphenylsilane and trimethylphenylsilane was measured and compared with previously published experimental data of dimethylphenylsilane.
• The density functional theory calculations are performed to support the experimental data.
• The fragmentation pattern of selected ionic fragments was explained by use of quantum chemical calculations.

The electron impact ionization (EII) of methylphenylsilane (MPS), dimethylphenylsilane (DMPS) and trimethylphenylsilane (TMPS) was investigated using the mass spectrometry technique. The composition of fragmentation products from MPS and TMPS measured in this work is interpreted with respect to the ionization energy, appearance energies of fragments and bond dissociation energies of selected bonds. The results are compared to the previously published experimental data for DMPS. Comparison with the theoretical bond dissociation energies calculated using the density functional theory (DFT) calculations is presented. Using the combined experimental and theoretical approaches, we have focused our recent studies on the common features as well as basic differences of the fragmentation schemes of all three molecules. The elimination of the H2 molecule, specific for MPS but rarely observed in the other two compounds, was also of high interest in our studies. It can run in two mechanisms: (i) loss of two hydrogens one-by-one and (ii) elimination of H2 in one step. We can predict which mechanism is more probable according to the DFT calculated energy profile of reaction. The calculated predictions were in correlation with the composition of fragmentation products determined experimentally from mass spectra.

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