Formation of positive cluster ions LinBr (n=2-7) and ionization energies studied by thermal ionization mass spectrometry

Clusters of the type LinX (X = halides) can be considered as potential building blocks of cluster-assembly materials. In this work, LinBr (n = 2-7) clusters were obtained by a thermal ionization source of modified design and selected by a magnetic sector mass spectrometer. Positive ions of the LinBr (n = 4-7) cluster were detected for the first time. The order of ion intensities was Li2Br+ Li4Br+ > Li5Br+ > Li6Br+ > Li3Br+. The ionization energies (IEs) were measured and found to be 3.95 +/- 0.20 eV for Li2Br, 3.92 +/- 0.20 eV for Li3Br, 3.93 +/- 0.20 eV for Li4Br, 4.08 +/- 0.20 eV for Li5Br, 4.14 +/- 0.20 eV for Li6Br and 4.19 +/- 0.20 eV for Li7Br. All of these clusters have a much lower ionization potential than that of the lithium atom, so they belong to the superalkali class. The IEs of LinBr (n = 2-4) are slightly lower than those in the corresponding small Li-n or LinH clusters, whereas the IEs of LinBr are very similar to those of Li-n or LinH for n = 5 and 6. The thermal ionization source of modified design is an important means for simultaneously obtaining and measuring the IEs of LinBr (n = 2-7) clusters (because their ions are thermodynamically stable with respect to the loss of lithium atoms in the gas phase) and increasingly contributes toward the development of clusters for practical applications. Copyright (C) 2012 John Wiley & Sons, Ltd.