Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.
J Mass Spectrom. 2010 Mar;45(3):306-12. doi: 10.1002/jms.1717.
Fragmentation of the pyridine ring upon K-shell excitation/ionization has been studied with gaseous 2-, 3- and 4-methylpyridine by the electron-impact method. Ab initio molecular orbital (MO) calculations were also carried out to explore electronic states correlating with specific fragments. Some specific fragmentation channels were identified from the ionic fragments enhanced characteristically at the N 1s edge. Yields of the C(2)HN(+) and C(5)H(5)(+)/C(5)H(6)(+) ions show that the fission of the N-C2 and C4-C5/C5-C6 bonds of the ring is likely to occur after the N 1s excitation and ionization. Ab initio MO calculations for the 2-methylpyridine molecule indicate that the dissociation channels to produce these ions are only accessible through the excited states of the parent molecular dication, which can be formed by Auger decays after the N 1s ionization. Fragment ions via hydrogen rearrangement are produced as well, but the rearrangement is not a phenomenon specific to the K-shell excitation/ionization.
用电子冲击法研究了气态 2-、3-和 4-甲基吡啶的吡啶环在 K 壳层激发/电离时的碎裂情况。还进行了从头算分子轨道 (MO) 计算，以探索与特定片段相关的电子态。从 N 1s 边缘增强的特征离子碎片中确定了一些特定的碎裂通道。C(2)HN(+) 和 C(5)H(5)(+)/C(5)H(6)(+) 离子的产率表明，N-C2 和 C4-C5/C5-C6 键的裂解可能发生在 N 1s 激发和电离之后。对于 2-甲基吡啶分子的从头算 MO 计算表明，产生这些离子的解离通道只能通过母体分子二价阳离子的激发态来实现，而母体分子二价阳离子可以通过 N 1s 电离后的俄歇衰变形成。也产生了通过氢重排的碎片离子，但重排不是 K 壳层激发/电离特有的现象。
