The photoionization and fragmentation of octadecane were investigated with infrared laser desorption/tunable synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (IRLD/VUV PIMS) and theoretical calculations. Mass spectra of octadecane were measured at various photon energies. The fragment ions were gradually detected with the increase of photon energy. The main fragment ions were assigned to radical ions (C _n H ⁺_2n+1 , n = 4–11) and alkene ions (C _n H ⁺_2n , n = 5–10). The ionization energy of the precursor and appearance energy of ionic fragments were obtained by measuring the photoionization efficiency spectrum. Possible formation pathways of the fragment ions were discussed with the help of density functional theory calculations.

中文翻译：

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十八烷的真空紫外光碎裂：光电离质谱法和理论研究。

用红外激光解吸/可调谐同步加速器真空紫外（VUV）光电离质谱（IRLD / VUV PIMS）研究了十八烷的光电离和裂解过程，并进行了理论计算。在各种光子能量下测量十八烷的质谱。随着光子能量的增加，碎片离子逐渐被检测到。主要碎片离子被分配为自由基离子（C _n H ⁺ _{2 n +1}，n  = 4-11）和烯烃离子（C _n H ⁺ _{2 n}，n  = 5-10）。通过测量光电离效率谱来获得前体的电离能和离子碎片的出现能。借助密度泛函理论计算，讨论了碎片离子的可能形成途径。