The 4(3)Pi(g) state of Na-2: Vibrational numbering and hyperfine structure

The Na-2 4(3)Pi(g) state has been studied by continuous-wave (cw) perturbat ion-facilitated optical-optical double resonance (PFOODR) fluorescence exci tation and resolved fluorescence spectroscopy. The absolute vibrational num bering was determined by resolved fluorescence to the a(3)Sigma(u)(+) state . The OODR excitation lines of the 4(3)Pi(g) (v, N) <-- b(3)Pi(u) (v(b)', J ') similar to A(1)Sigma(u)(+) (v(A)', J'), <-- X(1)Sigma(g)(+) (v ", J ") t ransitions show hyperfine splittings, and the hyperfine coupling scheme of the upper 4(3)Pi(g) levels is case b(beta S). Although this 4(3)Pi(g) state dissociates to the 3p + 3p atomic limit, it is a Rydberg state at a small internuclear distance, and the hyperfine splitting is caused mainly by the Fermi contact interaction of the sigma(g)3s valence electron with the nucle i. The Fermi contact constant was determined to be b(F) = 218.3 +/- 3.9 MHz . (C) 1999 Academic Press.