巴豆酸甲酯的光电离实验与理论研究

Dissociative photoionization of methyl crotonate:experimental and theoretical insights

利用可调谐同步辐射与飞行时间质谱实验,研究巴豆酸甲酯在9.0~14.5 eV能量范围内的真空紫外光电离和光解离过程。通过光电离效率曲线测定巴豆酸甲酯的电离能以及主要碎片离子C4H5O+2、C4H5O+、C4H4O+、C2H3O+2、C3H+5和C2H+5的出现势,分别为10.11、10.73、10.88、12.2、11.93(12.77)和12.44 eV。通过实验结果和G3B3计算结果的比较,分析主要碎片C4H5O+2+CH3、C4H5O++CH3O、C4H4O++CH4O、C2H3O+2+C3H5、C3H+5+C2H3O2(CO+CH3O)和C2H+5+C3H3O2的可能解离通道以及解离通道上经历的过渡态和中间体。在巴豆酸甲酯的光电离和光解离过程中,大多数碎片是母体离子异构化之后形成的,氢转移和开闭环是主要的过程。

The photoionization and dissociation of methyl crotonate have been studied by tunable vacuum ultraviolet synchrotron radiation coupled with time-of-flight mass spectrometer in the photon energy region 9.0-14.5 eV.The ionization energy of methyl crotonate and the appearance energies for major fragments C4H5O+2,C4H5O+,C4H4O+,C2H3O+2,C3H+5,and C2H+5 are determined to be 10.11,10.73,10.88,12.2,11.93(12.77),and 12.44 eV,respectively,according to the photoionization efficiency curves.Based on the experimental AEs and energies predicted by ab initio G3B3 calculations,possible formation channels for the major fragments C4H5O+2+CH3,C4H5O++CH3O,C4H4O++CH4O,C2H3O+2+C3H5,C3H+5+C2H3O2(CO+CH3O),and C2H+5+C3H3O2 are proposed.Transition states and intermediates involved in the dissociation channels are also located.The majority of the proposed channels occur through isomerization processes prior to dissociations.Hydrogen shift and ring closing/opening are found to be the dominant processes during photoionization and dissociation of methyl crotonate.