Alkali metal vapors ionization energy

Equation (1) is possible because of the binding energy of the molecular ion, Cs2, which is 0.64 eV (3). Similar associative ionization processes exist for other alkali metal vapors. While Eq. (1) is energetically possible only for a sufficiently high... 

Potassium, a soft, low density, silver-colored metal, has high thermal and electrical conductivities, and very low ionization energy. One useful physical property of potassium is that it forms liquid alloys with other alkali metals such as Na, Rb, and Cs. These alloys have very low vapor pressures and melting points. 

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. 

Until now detailed experiments on Rydberg atoms in crossed electric and magnetic fields have been performed on alkali atoms [568] and on Rydberg states of the H atom [573], which are excited either by direct two-photon transitions or by stepwise excitation via the 2 p state. Since the ionization energy of H is 13.6 eV, one needs photon energies above 6.7 eV (1 < 190 nm), which can be produced by frequency doubling of UV lasers in gases or metal vapors [574, 575]. 

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