New identification of the visible bands of the C2 Swan system

The well known Swan system (d(3)Pi(g)-a(3)Pi(u)) of C-2 has been observed in absorption in a hollow cathode discharge in a mixture of C2H2 and helium. Three bands, (v', v") = (5, 7), (6, 8), and (7, 9), of the Swan system have been identified and rotationally analyzed. However, the transition wavenumbers are found not to be quite consistent with the literature values compiled by Phillips and Davis. The (7, 9) band has been observed and identified for the first time. New identifications of the (5, 7) and (6, 8) bands are presented. The observed wavenumbers are fit to the effective Hamiltonian derived by Brown and Meter for (3)Pi states. The molecular constants for both the upper and lower electronic states have been determined from the least squares fitting. (C) 2002 Elsevier Science (USA).