title: Competitive fragmentation pathways of acetic acid dimer explored by synchrotron VUV photoionization mass spectrometry and electronic structure calculations.
abstract: In present study, photoionization and dissociation of acetic acid dimers have been studied with the synchrotron vacuum ultraviolet photoionization mass spectrometry and theoretical calculations. Besides the intense signal corresponding to protonated cluster ions (CH(3)COOH)(n)·H(+), the feature related to the fragment ions (CH(3)COOH)H(+)·COO (105 amu) via β-carbon-carbon bond cleavage is observed. By scanning photoionization efficiency spectra, appearance energies of the fragments (CH(3)COOH)·H(+) and (CH(3)COOH)H(+)·COO are obtained. With the aid of theoretical calculations, seven fragmentation channels of acetic acid dimer cations were discussed, where five cation isomers of acetic acid dimer are involved. While four of them are found to generate the protonated species, only one of them can dissociate into a C-C bond cleavage product (CH(3)COOH)H(+)·COO. After surmounting the methyl hydrogen-transfer barrier 10.84 ± 0.05 eV, the opening of dissociative channel to produce ions (CH(3)COOH)(+) becomes the most competitive path. When photon energy increases to 12.4 eV, we also found dimer cations can be fragmented and generate new cations (CH(3)COOH)·CH(3)CO(+). Kinetics, thermodynamics, and entropy factors for these competitive dissociation pathways are discussed. The present report provides a clear picture of the photoionization and dissociation processes of the acetic acid dimer in the range of the photon energy 9-15 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: Jiwen
authors.initials: J
authors.lastname: Guan
authors.forename: Yongjun
authors.initials: Y
authors.lastname: Hu
authors.forename: Hao
authors.initials: H
authors.lastname: Zou
authors.forename: Lanlan
authors.initials: L
authors.lastname: Cao
authors.forename: Fuyi
authors.initials: F
authors.lastname: Liu
authors.forename: Xiaobin
authors.initials: X
authors.lastname: Shan
authors.forename: Liusi
authors.initials: L
authors.lastname: Sheng
mesh_terms: D019342:Acetic Acid / Q000737:chemistry*; D019281:Dimerization; D004583:Electrons; D007700:Kinetics; D013058:Mass Spectrometry; D015394:Molecular Structure; D055668:Photochemical Processes; D011789:Quantum Theory; D017356:Synchrotrons; D013816:Thermodynamics; D014466:Ultraviolet Rays
chemical_list: D019342:Acetic Acid