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

抄録

We have studied the fragmentation of four lower alkylsilanes (CH₃SiH₂C₂H₅, CH₃SiH_2-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.