Dissociative electron attachment to the silane derivatives trichlorovinylsilane (SiCl3C2H3), tetravinylsilane (Si(C2H3)(4)) and trimethylvinylsilane (Si(CH3)(3)C2H3)
Abstrakt
The formation of negative ions following low energy (0-12 eV) electron attachment to the title compounds is studied in a crossed electron-molecular beam experiment applying mass spectrometric detection of the anions. All silane derivatives presently studied are weak electron scavengers which also holds for trichlorovinylsilane.
The behaviour in the silanes is hence in strong contrast to the hydrocarbons where chlorination usually results in a strong increase of the cross section for dissociative electron attachment (DEA) yielding intense Cl- signals already at very low electron energies (near 0 eV). The different behaviour can be explained by the appreciably stronger Si-Cl binding energy compared to that of C-Cl making the DEA reaction leading to Cl- endothermic for trichlorovinylsilane while the corresponding reaction is exothermic for most chlorinated hydrocarbons.
Trichlorovinylsilane and tetravinylsilane undergo various further DEA reactions via different resonances at higher energy (in the range between 4 and 10 eV) leading to a variety of ionic fragments. These reactions range from simple bond cleavages to considerably more complex unimolecular decompositions involving multiple bond cleavages, hydrogen transfer in the temporary negative ion and formation of new bonds.
Trimethylvinylsilane yields only one single fragment due to the loss of a neutral hydrogen atom ((M-H)(-)).