Total Ion Counts

POLYDIMETHYLSILICONE (OV-1) see insert in spectrum Supelco, USA

solution in toluene; 10 ug

Teq 510°C; ty 5s; tj 10s; Eei 12eV; expansion chamber removed (Extranuclear 5000-1 Py-MS system)

2 X 103

REMARKS - The low ion intensity may be caused by condensation losses of large fragments on the reaction chamber wall, by incomplete pyrolysis, by lower ion transmission in the high mass range or by a combination of these factors. The large peak at m/z 207 must represent the (M-15) electron impact fragment of the trimer although no trimer parent ion is observed at m/z 222. This is due to the presence of six methyl groups in the trimer, each of which has a significant chance of being lost in the electron impact ionisation process in spite of the low electron energy. Note the unusual isotope peak distribution around m/z 207, due to the presence of three Si atoms. The absence of obvious monomer or dimer peaks as well as of thermal degradation products indicates a strong dominance of backbiting mechanisms. A peak occurring at m/z 281 (not shown) points at the occurrence of tetramer formation, b-monomer

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