The Absorption Spectrum of Atomic Sodium

Using a long optical path attained by the method of Kratz and Mack, the wave-lengths of the principal series of sodium in absorption have been measured to $n=73$, and observed to $n=79$. The members to $n=9$ have been resolved. The series limit has been computed to be 41449.65±{}0.02 cm^-1 from the center of gravity or 41449.69±{}0.02 cm^-1 from the lower hyperfine structure component, of the 3s²S1/2 term. Forbidden 3s²S1/2-nd²D3/2,5/2 were found up to $n=13$. A critically compiled table to all known levels, including np²P1/2,3/2 to $n=73$ and nd²D3/2,5/2 to $n=13$, is given. The pressure shift from a foreign gas is less than reported by some earlier observers.