title: Conformation-specific pathways of beta-alanine: a vacuum ultraviolet photoionization and theoretical study.
abstract: We report a photoionization and dissociative photoionization study of beta-alanine using IR laser desorption combined with synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry. Fragments at m/z = 45, 44, 43, and 30 yielded from photoionization are assigned to NH(3)CH(2)CH(2)(+), NH(2)CHCH(3)(+), NH(2)CHCH(2)(+), and NH(2)CH(2)(+), respectively. Some new conformation-specific dissociation channels and corresponding dissociation energies for the observed fragments are established and determined with the help of ab initio G3B3 calculations and measurements of photoionization efficiency (PIE) spectra. The theoretical values are in fair agreement with the experimental results. Three low-lying conformers of the beta-alanine cation, including two gauche conformers G1+, G2+ and one anti conformer A+ are investigated by G3B3 calculations. The conformer G1+ (intramolecular hydrogen bonding N-H...OC) is found to be another precursor in forming the NH(3)CH(2)CH(2)(+) ion, which is complementary to the previously reported formation pathway that only occurs with the conformer G2+ (intramolecular hydrogen bonding O-H...N). Species NH(2)CHCH(2)(+) may come from the contributions of G1+, G2+, and A+ via different dissociation pathways. The most abundant fragment ion, NH(2)CH(2)(+), is formed from a direct C-C bond cleavage. Intramolecular hydrogen transfer processes dominate most of the fragmentation pathways of the beta-alanine cation.
authors.affiliation: National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui230029, PR China.
authors.forename: Lidong
authors.initials: L
authors.lastname: Zhang
authors.forename: Yang
authors.initials: Y
authors.lastname: Pan
authors.forename: Huijun
authors.initials: H
authors.lastname: Guo
authors.forename: Taichang
authors.initials: T
authors.lastname: Zhang
authors.forename: Liusi
authors.initials: L
authors.lastname: Sheng
authors.forename: Fei
authors.initials: F
authors.lastname: Qi
authors.forename: Po-Kam
authors.initials: PK
authors.lastname: Lo
authors.forename: Kai-Chung
authors.initials: KC
authors.lastname: Lau
mesh_terms: D013058:Mass Spectrometry; D008958:Models, Molecular; D008968:Molecular Conformation; D055668:Photochemical Processes; D017785:Photons; D013237:Stereoisomerism; D014466:Ultraviolet Rays; D015091:beta-Alanine / Q000737:chemistry*
chemical_list: D015091:beta-Alanine