アルキルシラン類のマススペクトル1．エチルメチルシラン，メチルプロピルシラン，ジエチルシラン，ブチルメチルシラン

概要

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We have studied the fragmentation of four lower alkylsilanes (CH3SiH2C2H5, CH3SiH2-C3 H7, (C2H5)2SiH2, CH3SiH2C4H9) appeared in EIMS. The main fragment ions of m/z 45 (CH3 SiH2+) of ethylmethylsilane and methylpropylsilane were produced by the cleavage of the Si-C bond on the longer alkyl chain side, respectively, and the large fragment ion of m/z 59 (C2H5 SiH2+) of diethylsilane was also produced by the cleavage of Si-C bond. The base peak of butylmethylsilane was m/z 73 (CH3SiH2CH2CH2+). The H-loss ions [M-H]+ and the H2-loss ions [M-H2]+ of CH3SiH2C2H5 and CH3SiH2C3H7 were very abundant, especially at low ionization energies. The optimized geometries of neutral molecules and molecular cations of methylpropylsilane and butylmethylsilane were calculated by using ab initio MO method. The Si-C bond on the larger alkyl group side of molecular cation was lengthened from 1.87Å to 2.17Å and the net charge on Si-atom was positive. This showed that the Si-C bond was easy to cleavage and the fragment containing Si-atom to have a positive charge.