Conformation-Specific Pathways of β-Alanine: A Vacuum Ultraviolet Photoionization and Theoretical Study

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• 作者：Lidong Zhang ; Yang Pan ; Huijun Guo ; Taichang Zhang ; Liusi Sheng ; Fei Qi ; Po-Kam Lo ; Kai-Chung Lau
• 刊名：Journal of Physical Chemistry A
• 出版年：2009
• 出版时间：May 21, 2009
• 年：2009
• 卷：113
• 期：20
• 页码：5838-5845
• 全文大小：300K
• 年卷期：v.113,no.20(May 21, 2009)
• ISSN：1520-5215

文摘

We report a photoionization and dissociative photoionization study of β-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 NH₃CH₂CH₂⁺, NH₂CHCH₃⁺, NH₂CHCH₂⁺, and NH₂CH₂⁺, 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 β-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 NH₃CH₂CH₂⁺ ion, which is complementary to the previously reported formation pathway that only occurs with the conformer G2+ (intramolecular hydrogen bonding O−H···N). Species NH₂CHCH₂⁺ may come from the contributions of G1+, G2+, and A+ via different dissociation pathways. The most abundant fragment ion, NH₂CH₂⁺, is formed from a direct C−C bond cleavage. Intramolecular hydrogen transfer processes dominate most of the fragmentation pathways of the β-alanine cation.