Double-Minimum(2)Σu+1State ofNa2

A new double-minimum state, $\mathrm{}\left(2\right)\mathrm{}{}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{u}}_{}^{+}{}_{}{}^{}$, of ${\mathrm{Na}}_2$ has been characterized by infrared fluorescence recorded at high resolution by Fourier-transform spectrometry. A ring dye laser populates ${}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{g}}_{}^{+}{}_{}{}^{}$ Rydberg levels in the two-photon process ${}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{g}}_{}^{+}{}_{}{}^{}\leftarrow A{}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{u}}_{}^{+}{}_{}{}^{}\leftarrow X{}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{g}}_{}^{+}{}_{}{}^{}$, and ${}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{g}}_{}^{+}{}_{}{}^{}\to \mathrm{}\left(2\right)\mathrm{}{}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{u}}_{}^{+}{}_{}{}^{}$ fluorescence is analyzed. The two potential minima lie at 28 454.6 ${\mathrm{cm}}^{-1\mathrm{}}$, 3.688 Å, and 27 870.4 ${\mathrm{cm}}^{-1\mathrm{}}$, 6.739 Å, respectively, and the energy at the top of the barrier is about 29 150 ${\mathrm{cm}}^{-1\mathrm{}}$ (relative to the minimum in $X{}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{g}}_{}^{+}{}_{}{}^{}$).