The d 3Πg-c 3Σu+ band system of C2

A two-dimensional fluorescence (excitation/emission) spectrum of C-2 produced in an acetylene discharge was used to identify and separate emission bands from the d (3)Pi(g)<- c (3)Sigma(+)(u) and d (3)Pi(g)<- a (3)Pi(u) excitations. Rotationally resolved excitation spectra of the (4 <- 1), (5 <- 1), (5 <- 2), and (7 <- 3) bands in the d (3)Pi(g)<- c (3)Sigma(+)(u) system of C-2 were observed by laser-induced fluorescence spectroscopy. The molecular constants of each vibrational level, determined from rotational analysis, were used to calculate the spectroscopic constants of the c (3)Sigma(+)(u) state. The principal molecular constants for the c (3)Sigma(+)(u) state are B-e=1.9319(19) cm(-1), alpha(e)=0.018 55(69) cm(-1), omega(e)=2061.9 cm(-1), omega(e)x(e)=14.84 cm(-1), and T-0(c-a)=8662.925(3) cm(-1). We report also the first experimental observations of dispersed fluorescence from the d (3)Pi(g) state to the c (3)Sigma(+)(u) state, namely, d (3)Pi(g)(v=3)-> c (3)Sigma(+)(u)(v=0,1).