Excited Electronic States of Lithium and Sodium Molecules

Abstract

THE electronic spectra of the alkali metal molecules are of interest for several reasons: for example, (1) Li₂ is sufficiently simple to be the subject of quantitative wave-mechanical calculations^1,2, and (2) these spectra may be expected to be somewhat similar to that of H₂, for which reliable analyses of many systems are now available^3,4. Furthermore, the excited singlet ungerade states of the alkali metals are readily accessible, since they may be observed in combination with the ground states at λ > 2300 Å. It is therefore surprising that for Li₂ and Na₂ only the lowest excited singlet states, A ¹Σ⁺ _u and B ¹II_u, have been well characterized⁵: several systems at shorter wave-lengths have been reported^5,6, but the vibrational analyses of some of these are uncertain, and only for the system C—X of Na₂ has a rotational analysis been attempted⁷.