HIGH-RESOLUTION SPECTROSCOPY OF THE 1(3)SIGMA(-1(3)SIGMA(+)(U)(X) TRANSITION OF NA-2()(G)(B)[)

Rotational-vibrational transitions of the triplet system 1(3) Sigma(g) (+) <-- 1(3) Sigma(u)(+) of the Na-2 molecule have been investigated a round <(nu)over bar> = 13970 cm(-1) by Doppler-free polarization spect roscopy in a heat pipe and by resonant two-step photoionization in a c ollimated cold argon beam, seeded with sodium vapor. The fine- and hyp erfine structure of the transitions is partly resolved. The analysis o f the measured spectra and a theoretical discussion of the expected mu ltiplet structure yields the rotational constants B-upsilon'(upsilon' = 17) = 0.0866(4) cm(-1) for the upper and B-upsilon''(upsilon '' = 0) = 0.0533(4) cm(-1) for the lower state. The difference Delta b = b((3 ) Sigma(u))- b((3) Sigma(g)) of the hyperfine coupling constants b tur ns out to be Delta b = 80 MHz.