Photofragmentation of Isoleucine by Vacuum Ultraviolet Photoionization

• Published in: Chinese journal of chemical physics Vol. 25; no. 4; pp. 379 - 388
• Main Authors: Xie, Yang, Cao, Lan-lan, Zhang, Qiang, Chen, Jun, Chu, Gen-bai, Zhao, Yu-jie, Shan, Xiao-bin, Liu, Fu-yi, Sheng, Liu-si
• Format: Journal Article
• Language: English
• Published: 01.08.2012
• Subjects: Vacuum ultraviolet; Photoionization mass spectroscopy; Dissociation pathway; Synchrotron radiation; Isoleucine
• ISSN: 1674-0068; 2327-2244
• DOI: 10.1088/1674-0068/25/04/379-388

Vacuum ultraviolet photon-induced ionization and dissociation of isoleucine are investigated with synchrotron radiation photoionization mass spectroscopy and theoretical calculations. 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 C5H12N+ (m/z=86), C2H5NO2 + (m/z=75), C5H9 + (m/z=69), C4H9 + (m/z=57), and CH4N+ (m/z=30) are determined to be 8.84±0.07, 9.25±0.06, 10.20±0.12, 9.25±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.