Vacuum ultraviolet (VUV) photoionization of small water clusters
Vacuum ultraviolet (VUV) photoionization of small water clusters
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DOI：
10.1021/jp075263v
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发表时间：
2007-10-11
影响因子：
2.9
通讯作者：
Ahmed, Musahid
中科院分区：
文献类型：
--
作者：
Belau, Leonid;Wilson, Kevin R.;Ahmed, Musahid
利用10- 14 eV同步辐射对水团簇进行了可调谐真空紫外光电离研究，并通过反射飞行时间质谱进行了分析。测量了质子化水团簇（H_2O）（n）H ~+的光电离效率（PIE）曲线，能量分辨率为50 meV。一系列质子化水团簇的出现能量由光电离阈值确定的集群组成的多达79个分子。这些表观能量代表了超音速分子束中相应母体中性水团簇绝热电离能的上限。实验结果表明，小的中性水团簇的表观能量急剧下降（从12.62 +/- 0.05到10.94 +/- 0.06 eV，分别为H2O和（H2O）（4）），然后逐渐减少的集群（H2O）（23）收敛到10.6 eV（+/- 0.2 eV）的值。从相应的中性水团簇中除去水分子的解离能是通过热力学循环利用文献中先前报道的质子化水团簇的解离能导出的。实验结果表明，对于小的中性水团簇，去除一个水分子的解离能逐渐减小（3
Tunable vacuum ultraviolet (VUV) photoionization studies of water clusters are performed using 10- 14 eV synchrotron radiation and analyzed by reflectron time-of-flight (TOF) mass spectrometry. Photoionization efficiency (PIE) curves for protonated water clusters (H2O)(n)H+ are measured with 50 meV energy resolution. The appearance energies of a series of protonated water clusters are determined from the photoionization threshold for clusters composed of up to 79 molecules. These appearance energies represent an upper limit of the adiabatic ionization energy of the corresponding parent neutral water cluster in the supersonic molecular beam. The experimental results show a sharp drop in the appearance energy for the small neutral water clusters (from 12.62 +/- 0.05 to 10.94 +/- 0.06 eV, for H2O and (H2O)(4), respectively), followed by a gradual decrease for clusters up to (H2O)(23) converging to a value of 10.6 eV (+/- 0.2 eV). The dissociation energy to remove a water molecule from the corresponding neutral water cluster is derived through thermodynamic cycles utilizing the dissociation energies of protonated water clusters reported previously in the literature. The experimental results show a gradual decrease of the dissociation energy for removal of one water molecule for small neutral water clusters (3