title: Unexpected methyl migrations of ethanol dimer under synchrotron VUV radiation.
abstract: While methyl transfer is well known to occur in the enzyme- and metal-catalyzed reactions, the methyl transfer in the metal-free organic molecules induced by the photon ionization has been less concerned. Herein, vacuum ultraviolet single photon ionization and dissociation of ethanol dimer are investigated with synchrotron radiation photoionization mass spectroscopy and theoretical methods. Besides the protonated clusters cation (C2H5OH)⋅H(+) (m/z = 47) and the β-carbon-carbon bond cleavage fragment CH2O⋅(C2H5OH)H(+) (m/z = 77), the measured mass spectra revealed that a new fragment (C2H5OH)⋅(CH3)(+) (m/z = 61) appeared at the photon energy of 12.1 and 15.0 eV, where the neutral dimer could be vertically ionized to higher ionic state. Thereafter, the generated carbonium ions are followed by a Wagner-Meerwein rearrangement and then dissociate to produce this new fragment, which is considered to generate after surmounting a few barriers including intra- and inter-molecular methyl migrations by the aid of theoretical calculations. The appearance energy of this new fragment is measured as 11.55 ± 0.05 eV by scanning photoionization efficiency curve. While the signal intensity of fragment m/z = 61 starts to increase, the fragments m/z = 47 and 77 tend to slowly incline around 11.55 eV photon energy. This suggests that the additional fragment channels other than (C2H5OH)⋅H(+) and CH2O⋅(C2H5OH)H(+) have also been opened, which consume some dimer cations. The present report provides a clear description of the photoionization and dissociation processes of the ethanol dimer in the range of the photon energy 12-15 eV.
authors.affiliation: MOE Key Laboratory of Laser Life Science and Institute of Laser Life Science, College of Biophotonics, South China Normal University, Guangzhou 510631, People's Republic of China.
authors.forename: Weizhan
authors.initials: W
authors.lastname: Xiao
authors.affiliation: MOE Key Laboratory of Laser Life Science and Institute of Laser Life Science, College of Biophotonics, South China Normal University, Guangzhou 510631, People's Republic of China.
authors.forename: Yongjun
authors.initials: Y
authors.lastname: Hu
authors.affiliation: MOE Key Laboratory of Laser Life Science and Institute of Laser Life Science, College of Biophotonics, South China Normal University, Guangzhou 510631, People's Republic of China.
authors.forename: Weixing
authors.initials: W
authors.lastname: Li
authors.affiliation: MOE Key Laboratory of Laser Life Science and Institute of Laser Life Science, College of Biophotonics, South China Normal University, Guangzhou 510631, People's Republic of China.
authors.forename: Jiwen
authors.initials: J
authors.lastname: Guan
authors.affiliation: National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029, People's Republic of China.
authors.forename: Fuyi
authors.initials: F
authors.lastname: Liu
authors.affiliation: National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029, People's Republic of China.
authors.forename: Xiaobin
authors.initials: X
authors.lastname: Shan
authors.affiliation: National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029, People's Republic of China.
authors.forename: Liusi
authors.initials: L
authors.lastname: Sheng
mesh_terms: D019281:Dimerization; D000431:Ethanol / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D055668:Photochemical Processes; D017356:Synchrotrons; D014466:Ultraviolet Rays
chemical_list: D000431:Ethanol