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We used the electron impact ([EI.sup.+]) mode at 70 eV electron energy in a mass range of 10-650 atomic mass units (amu).
Fortunately, the SSIMS spectrum for dimethyl silicone has strong peaks at 73 and 147 atomic mass units (AMU) from ([CH.sub.3])[sup.3.Si.sup.+] and its dimen which are absent in the spectrum of [SiO.sub.2].
Furthermore, the weights of different elements will not accord exactly with the number of atomic mass units they possess.