摘要
Vacuum ultraviolet photon-induced ionization and dissociation of isoleucine are investi- gated with synchrotron radiation photoionization mass spectroscopy and theoretical cal- culations. The main fragment ions at m/z=86, 75, 74, 69, 57, 46, 45, 44, 41, 30, 28, and 18 from isoleucine are observed in the mass spectrum at the photon energy of 13 eV. From the photoionization efficiency curves, appearance energies for the principal fragment ions CsH12N＋ （rn/z=86）, C2H5NO2＋ （m/z=75）, C5H9＋ （rn/z=-69）, C4H9＋ （m/z=57）, and CH4N＋ （m/z=30） are determined to be 8.844-0.07, 9.254-0.06, 10.20-4-0.12, 9.254-0.10, and 11.05＋0.07 eV, respectively, and possible formation pathways are established in detail by the calculations at the B3LYP/6-31＋＋G（d, p） levels. These proposed channels include simple bond cleavage reactions as well as reactions involving intermediates and transition structures. The experimental and computational appearance energies or barriers are in good agreement.
基金
V. ACKNOWLEDGMENTS This work is supported by the National Natural Science Foundation of China （No.10875126 and No.10979048） and the Specialized Research Fund for the Doctoral Program of Higher Education, SRF for ROCS, SEM.
