Stable Stoichiometry of Gas-Phase Manganese Oxide Cluster Ions Revealed by Temperature-Programmed Desorption

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• 作者：Kohei Koyama ; Satoshi Kudoh ; Ken Miyajima ; Fumitaka Mafun茅
• 刊名：Journal of Physical Chemistry A
• 出版年：2015
• 出版时间：August 6, 2015
• 年：2015
• 卷：119
• 期：31
• 页码：8433-8442
• 全文大小：830K
• ISSN：1520-5215

文摘

Temperature-programmed desorption (TPD) experiments were performed on gas-phase manganese oxide cluster ions, namely, Mn_nO_m⁺ (n = 3鈥?0) and Mn_nO_m^{鈥?/sup> (n = 3鈥?8). These cluster ions were prepared by laser ablation of a manganese rod in the presence of oxygen gas, and their composition was investigated using mass spectrometry. The composition of Mn_nO_m卤 distribution lies above the m = (4/3)n line. When the cluster ions were heated to 1000 K, Mn_nO_m+ (m = (4/3)n + 未, with 未 = 鈭?, 0) and Mn_nO_m鈥?/sup> (m = (4/3)n + 未, with 未 = 0, 1) was found to be the predominant species, formed by thermal dissociation. These experimental findings indicate that the nascent manganese oxide clusters comprise robust Mn_nO_m卤 (m/n 鈮?4/3) and weakly bound excess oxygen atoms. On the basis of the TPD experiments, the oxygen-molecule release was identified as the main dissociation channel. The temperature dependence of O₂ desorption was found to be similar among the clusters with the same oxygen excess or deficiency regardless of the number of Mn atoms. The threshold energy of O₂ desorption was estimated for Mn₄O_m+ (m = 6鈥?1) and compared with bond dissociation energies calculated by density functional theory.}