Potassium clusters

Adduct ions are quite frequent in the mass spectra. In positive ion mode, sodium or potassium cluster ions are commonly found. Mineral compounds often lead to multiple cluster ions. For example, spectra of FeCl3 in negative ion mode lead to several peaks from m/z 35 (Cl ) to m/z 487 ([(FeCl3)2FeCl3] ) [Van Ham et al. 2004],... 

Takai, K., S. Eto, M. Inaguma, T. Enoki, H. Ogata, M. Tokita, and J. Watanabe. 2007. Magnetic potassium clusters in the nanographite host system. Phys. Rev. Lett. 98 017203-1-4. 

In Reference 3, two distinct ESR spectra were identified for potassium clusters in argon matrices. Both spectra have doublet ground states (S = h) and a well resolved hyperfine (hf) structure arising from the Fermi contact interaction of the unpaired electron spin with three I = h nuclei. Seven groups of four transitions each were assigned to a potassium trimer of 62 symmetry whose apical and two equivalent terminal atoms have hf splitting... 

This is a severe drawback in the case of equilibrium studies of metal molecules since, as a rule, such molecules are minor vapor components and maximum sensitivity is required for their thermodynamic evaluation. However, very precise ionization potentials can be measured using photoionization spectroscopy (5,28). Berkowltz (28) reviewed early work concerning alkali metal dimers. Herrmann et al. ( ) have measured the ionization potentials of numerous sodium, potassium and mixed sodium-potassium clusters. For most of these clusters the atomization energies of the neutral molecules are not known. Therefore, the dissociation energies of the corresponding positive ions cannot be calculated. 

Figure 9.6 Cluster crystals formed by Na43+ clusters located in the sodalite cages of zeolites with different structures, (a) Sodalite (SOD), (b) Zeolite Y (FAU). (c) Zeolite A (LTA). Although the array shown in (c) has not been prepared, the analogous potassium clusters shown in (d) is indeed available in (d) the cluster crystal is actually composed of K43+ clusters in all the sodalite cages and the larger K,24+ clusters in every other a-cages. Reproduced from [4], Copyright (2002) Springer-Verlag...

In the intermediate regime one can try to smoothly extrapolate from the limit of the monomer to that of the bulk. An example of such interpolation is shown in Fig. 1 for the ionization potentieil (IP) of potassium clusters. 

It is well known that the experimental cohesive energies of neutral sodium and potassium clusters agree remarkably well with the classical spherical droplet model. The model can be represented by the equation... 

Extended Energy-Level Model. The real-time spectra - performed with femtosecond time resolution - of the Naa system, as well as of the larger sodium and potassium clusters (see Sects. 4.2, 4.3 and 4.4), reveal a nonexponential decay which cannot be explained within the simple energy-level model introduced above. It seems reasonable that this different behavior is caused by clusters in the beam which are larger than those of interest. Therefore, the simple model has to be slightly extended. This extended energy-level model has the following features. 

This type of ultrafast dynamics will now be investigated in detail for several alkali aggregates, beginning with the model molecule Nas excited to its C state (Sect. 4.1) and D state (Sect. 4.2). The ultrafast fragmentation of sodium clusters (Sect. 4.3) and potassium clusters (Sect. 4.4) rounds off these studies. 

While the dipole absorption features [114, 124] and photodissociation dynamics of small sodium clusters are rather well known [112, 113, 126, 127, 407-409], there is very little knowledge about potassium clusters larger than the dimer. The lack of experimental data might be caused by ultrafast fragmentation processes within the potassium clusters, so that conventional stationary spectroscopic techniques might fail. Hence, the goal of this section is to determine the photodissociation probability of small potassium clusters as a function of cluster size as well as excitation energy. 

Special Features of the Experimental Setup. Brechnignac s investigations [111] encouraged the study of the photodissociation dynamics of K for three different excitation energies. Employing a two-color TPI experiment, the potassium clusters were excited at 1.47 eV and 2.94 eV, while with one-color TPI spectroscopy these clusters were excited at 2eV. Therefore, two... 

When molecular ions have spherical or near spherical stereochemistry they often pack in a similar way to classical ionic solids. For example, in the fulleride KgCgo the spherical Cgo" ions pack in a standard body-centered cubic structure with potassium clusters located in the interstitial sites. ... 

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