Production and ionization energies of K_nF (n = 2–6) clusters by thermal ionization mass spectrometry

RATIONALE

The very small clusters of the type K_nF 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_nF (n >2) clusters.

METHOD

K_nF (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_nF (n = 3–6) were detected for the first time. The order of the ion intensities was K₂F⁺> > K₄F⁺> > K₃F⁺K₆F⁺ > K₅F⁺. The determined IEs were 3.99 ± 0.20 eV for K₂F, 4.16 ± 0.20 eV for K₃F, 4.27 ± 0.20 eV for K₄F, 4.22 ± 0.20 eV for K₅F, and 4.31 ± 0.20 eV for K₆F. The IEs of K_nF 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_nF (n = 2–6) clusters belong to the group of 'superalkali' species. Copyright © 2012 John Wiley & Sons, Ltd.