Constants of the 5s ^1Σg+ state of Na_2 from two-photon spectroscopy

Fluorescence spectroscopy is used as an aid in the identification of two-photon transitions in Na₂. Several methods are introduced and used to identify the transitions and analyze the spectra. By using these methods, the upper-level rotational quantum number, energy, and electronic character may be determined without any assumptions about the state to which the upper level belongs. Twenty-nine two-photon transitions were observed and analyzed. A Dunham expansion for the energy levels allowed 18 of the 29 to be associated with the ${{}^1\mathrm{\Sigma }}_g^{+}\hspace{0.17em}(3s+5s)$ state. They were used to calculate new values of the Dunham coefficients for that state. These were in close agreement with values obtained in polarization-labeling experiments.