Magnetic Rotation Spectrum and Heat of Dissociation of the Potassium Molecule

Abstract

The magnetic rotation spectrum of the near red, $^{1}\ensuremath{\Pi}\ensuremath{-}^{1}\ensuremath{\Sigma}$ band system of ${\mathrm{K}}_{2}$ has been photographed with the apparatus previously used for ${\mathrm{Li}}_{2}$. In this way the series of upper vibrational levels has been extended from the 16th, the last one observed by Crane and Christy, to the 27th. This permits an accurate extrapolation to convergence, which is estimated to occur at ${v}^{\ensuremath{'}}=31.6$, the corresponding energy being 17160 ${\mathrm{cm}}^{\ensuremath{-}1}$ = 2.12 volts. It follows that the heat of dissociation of the normal molecule is 0.51\ifmmode\pm\else\textpm\fi{}0.02 volt. From this and other data the percentage of molecules in the vapor at various temperatures is calculated. An improved Franck-Condon diagram for the red and infrared systems of ${\mathrm{K}}_{2}$ has been constructed. It gives a good representation of the observed distribution of bands and predicts the existence of an infrared edge. This is confirmed by observation. Magnetic rotation spectra have been found in the regions of the infrared and blue $^{1}\ensuremath{\Sigma}\ensuremath{-}^{1}\ensuremath{\Sigma}$ systems. They are probably analogous to the red magnetic rotation spectrum of sodium, and like it, are not yet understood.