Probes for electronic and geometrical shell structure effects in alkali-metal clusters. Photoionization measurements on KxLi, KxMg and KxZn(x < 25)
✍ Scribed by Manfred M. Kappes; Peter Radi; Martin Schär; Ernst Schumacher
- Publisher
- Elsevier Science
- Year
- 1985
- Tongue
- English
- Weight
- 465 KB
- Volume
- 119
- Category
- Article
- ISSN
- 0009-2614
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✦ Synopsis
as well as ionization potential determinations for K6Mg-K9Mg and K,Zn. Li/K beams manifest abundance maxima in agreement with results for Ns, K, and Na,Ky beams [1,2] *. K/Mg and K/Zn expansions yielded new abundance maxima and couplmg of structural and electronic stabilities which contradict the predictions of the jellium model of metal clusters. 2. Experimental Clusters were generated in supersonic molecular beams by expansion of metal vapor(s) from a hightemperature oven They were detected using one-photon iomzation mass spectroscopy_ For rough neutral abundance measurements, the molecular beam was crossed with radiation from a 1 kW Xe/Hg arc lamp, within the ion source of a quadrupole mass spectrometer mounted perpendicular to both molecular and light beams. Apart from the loss of ions with high precursor IPs. insertion of W-cut-off filters between lamp and beam had little effect on ion distributions_ Vertical ionization potentials were obtained using an arc-lamp/monochromator configuration_ Instrumentation and procedures used have been described [5,8,9] _ Corncal nozzles were used to maximize the generation of "large" clusters [5] _ Of highest utility were nozzles with 0.4 X 0.5 mm cyhndrical channels leading into the throat of a 30" cone. Mass spectra and photoiomzation efficiency curves were measured at oven temperatures of 750°C. This temperature was chosen to maximize the vapor pressure of the minority metal and allow for reasonable measurement perrods before loss of potassmm occurs. Vapor pressures (calculated from ref. [lo]) were 706, 1,12,and121 TorrforK,Li,MgandZn,respectively. Experiments were carried out with initial excess potassium_ Beam cornpositron changed slbwly with time, potassium being preferentially removed from the oven. This affected the ratio of pure to mixed potassium clusters at constant oven temperature; relative abundance maxima within a set of K, or K,M clusters remained unchanged_ Changes in beam com-* Prehminary Na/K data were reported both by us and Knight et al. at the Interlaken workshcp on metal clusters. October 1984_ Knight et al_ have anus pubhshed their fiidings in ref. [3] _