Study of small chlorine-doped potassium clusters by thermal ionization mass spectrometry.

The theoretical calculations have predicted that nonmetal-doped potassium clusters can be used in the synthesis of a new class of charge-transfer salts which can be considered as potential building blocks for the assembly of novel nanostructured material. In this work, K(n)Cl (n = 2-6) and K(n)Cl(n-1) (n = 3 and 4) clusters were produced by vaporization of a solid potassium chloride salt in a thermal ionization mass spectrometry. The ionization energies (IEs) were measured, and found to be 3.64 ± 0.20 eV for K(2)Cl, 3.67 ± 0.20 eV for K(3)Cl, 3.62 ± 0.20 eV for K(4)Cl, 3.57 ± 0.20 eV for K(5)Cl, 3.69 ± 0.20 eV for K(6)Cl, 3.71 ± 0.20 eV for K(3)Cl(2) and 3.72 ± 0.20 eV for K(4)Cl(3). The K(n)Cl(+) (n = 3-6) clusters were detected for the first time in a cluster beam generated by the thermal ionization source of modified design. Also, this work is the first to report experimentally obtained values of IEs for K(n)Cl(+) (n = 3-6) and K(n)Cl(n-1) (+) (n = 3 and 4) clusters. The ionization energies for K(n)Cl(+) and K(n)Cl(n-1) (+) clusters are much lower than the 4.34 eV of the potassium atom; hence, these clusters should be classified as 'superalkali' species.

Production and ionization energies of K(n)F (n = 2-6) clusters by thermal ionization mass spectrometry.

RATIONALE: The very small clusters of the type K(n)F are of particular importance since their first ionization energies (IEs) are lower than those of the alkali metal atoms. Theoretical calculation has demonstrated that this kind of cluster represents a potential 'building block' for cluster-assembly materials with unique structural, electronic, optical, magnetic, and thermodynamic properties. To date, however, there have been no experimental results on the IEs of K(n)F (n >2) clusters. METHOD: K(n)F (n = 2-6) clusters were produced by the evaporation of a solid potassium fluoride salt using a modified thermal ionization source of modified design, and mass selected by a magnetic sector mass spectrometer where their IEs were determined. RESULTS: Clusters K(n)F (n = 3-6) were detected for the first time. The order of the ion intensities was K(2)F(+)> > K(4)F(+)> > K(3)F(+)K(6)F(+)> K(5)F(+). The determined IEs were 3.99 ± 0.20 eV for K(2)F, 4.16 ± 0.20 eV for K(3)F, 4.27 ± 0.20 eV for K(4)F, 4.22 ± 0.20 eV for K(5)F, and 4.31 ± 0.20 eV for K(6)F. The IEs of K(n)F increase slightly with the increase in potassium atom number from 2 to 6. We also observed that the presence of a fluorine atom leads to increasing ionization energy of bare metal potassium clusters. CONCLUSIONS: The modified thermal ionization source provides an efficient way of obtaining the fluorine-doped potassium clusters. These results also present experimental proof that K(n)F (n = 2-6) clusters belong to the group of 'superalkali' species.

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

Clusters of the type Li(n)X (X = halides) can be considered as potential building blocks of cluster-assembly materials. In this work, Li(n)Br (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 Li(n)Br (n = 4-7) cluster were detected for the first time. The order of ion intensities was Li(2)Br(+) > Li(4)Br(+) > Li(5)Br(+) > Li(6)Br(+) > Li(3)Br(+). The ionization energies (IEs) were measured and found to be 3.95 ± 0.20 eV for Li(2)Br, 3.92 ± 0.20 eV for Li(3)Br, 3.93 ± 0.20 eV for Li(4)Br, 4.08 ± 0.20 eV for Li(5)Br, 4.14 ± 0.20 eV for Li(6)Br and 4.19 ± 0.20 eV for Li(7)Br. 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 Li(n)Br (n = 2-4) are slightly lower than those in the corresponding small Li(n) or Li(n)H clusters, whereas the IEs of Li(n)Br are very similar to those of Li(n) or Li(n)H for n = 5 and 6. The thermal ionization source of modified design is an important means for simultaneously obtaining and measuring the IEs of Li(n)Br (n = 2-7) clusters (because their ions are hermodynamically stable with respect to the loss of lithium atoms in the gas phase) and increasingly contributes toward the development of clusters for practical applications.

Formation and ionization energies of small chlorine-doped lithium clusters by thermal ionization mass spectrometry.

RATIONALE: Theoretical calculations have shown that the first ionization energy of clusters of the type Li(n) Cl (n ≥2), with more than eight valent electrons, is lower than that of alkali metal atoms; hence they are named superalkali. Superalkali clusters can mimic the chemical behavior of alkali metals and may be used as building blocks of new cluster-assembled materials. There is currently no reliable experimental proof of this kind of clusters and such proof is required. METHODS: The Li(n) Cl (n = 2-6) clusters were produced by a thermal ionization source of modified design, and mass selected by a magnetic-sector mass spectrometer. The modification pertains to the replacement of the side filaments by a cylinder in the triple-filament thermal ionization source. The sample, which is LiCl salt, was pressed into a ring and placed on the inner wall of the cylinder. RESULTS: It was observed that the ions of clusters with an even number of lithium atoms (Li(2) Cl(+) , Li(4) Cl(+) , Li(6) Cl(+) ) are more stable than the odd-numbered ones (Li(5) Cl(+) , Li(3) Cl(+) ). The ionization energies were determined to be 3.98 ± 0.25 eV for Li(2) Cl, 4.10 ± 0.25 eV for Li(3) Cl, 3.90 ± 0.25 eV for Li(4) Cl, 4.01 ± 0.25 eV for Li(5) Cl, and 4.09 ± 0.25 eV for Li(6) Cl. The presence of a halogen atom reduces the ionization energy of the metal clusters. CONCLUSIONS: The thermal ionization source of modified design presents a suitable simple way to obtaining and measuring the ionization energies of very small lithium monochloride clusters. Clusters Li(n) Cl, n = 4 to 6, were detected for the first time.

Ionization energies of K2X (X=F, Cl, Br, I) clusters.

The electronic structure and properties of dipotassiummonohalides are important for understanding the unique physical and chemical behavior of M(n)X systems. In the present study, K(2) X (here X=F, Cl, Br, I) clusters were generated in the vapor over salts of the corresponding potassium halide, using a magnetic sector thermal ionization mass spectrometer. The ionization energies obtained for K(2)F, K(2)Cl, K(2)Br, and K(2)I molecules were 3.82 ± 0.1 eV, 3.68 ± 0.1 eV, 3.95 ± 0.1 eV, and 3.92 ± 0.1, respectively. These experimental values of ionization energies for K(2) X (X=F, Br, and I) are presented for the first time. The ionization energy of K(2)Cl determined by thermal ionization corresponds to previous results obtained by photoionization mass spectrometry, and it agrees with the theoretical ionization energy calculated by the ab initio method. The presently obtained results support previous theoretical predictions that the excess electron in dipotassiummonohalide clusters is delocalized over two potassium atoms, which is characteristic for F-center clusters.