The Continuous Radiative Absorption Cross-Section of Singly Ionized Potassium

After obtaining exchange wave functions of K III the continuous absorption cross-section of K II is calculated over the energy range o to 13.53 e.V. of the ejected electron, using both the dipole length and the dipole velocity formulae and allowing for the effect of electron exchange. The recommended mean value is taken to be $${\alpha }_{\nu }=3.2\times {10}^{-17}{\nu }_{1}/\nu \,\text{cm}.^{2}$$, where ν₁ is the frequency at the spectral head. The cross-section data are used to evaluate the “modified dilution factor” introduced by Strömgren in considering the ionization balance in interstellar space. The possibility of captures to excited states introduces a correction factor of 430 $$({T}_{e}={10}^{2}),\,290\,({T}_{e}={10}^{3}),\,160\,({T}_{e}={10}^{4})$$, where T_e is -the electron temperature (deg. K.). The abundance of interstellar potassium is briefly discussed.