Fine and hyperfine structure of the triplet states 1 3Σu+ and 1 3Σg+ of the Na2 molecule

The 1 3Σg+ ← 1 3Σu+ absorption spectrum of Na2 has been measured with sub-Doppler resolution in a collimated cold argon beam seeded with sodium vapor, using resonant two-photon ionization with a cw single mode Ti-sapphire laser and a cw argon laser. The spectrally resolved fine and hyperfine structure of the rotational lines allowed the determination of the spin-spin interaction constants λ″ = - 1294 MHz, λ′ = - 529 MHz, the spin-rotation constants γ″ = 42 MHz, γ′ =2.6 MHz and the Fermi contact constants b ′ = 293 MHz, b′ = 22MHz. All the molecular constants of both electronic states obtained from this and from former work are compiled and compared with theoretical values.