LIF of C2 (A 1Πu) via the Freymark band (E1Σ6+ ← A 1Πu)

C2 (A 1Πu) produced from multi-photon dissociation of C2H2 at 193 nm was probed via the Δν = −2 sequence of the Freymark band system (EΣg+ ← A1πu) using laser induced fluorescence. The (ν′ = 0, ν″ = 2), (νv′ = 1, ν″ = 3) and a few lines of the (ν′ = 2, ν″ = 4) vibrational progressions were observed under nascent conditions. The intensity of the (ν′ = 0, ν″ = 2) and (ν′ = 1, ν″ = 3) bands are comparable but the (ν′ = 2, ν″ = 4) band is much weaker, implying that the vibrational population of the ν″ = 2 and 3 levels are approximately equal while that of ν″ = 4 is much smaller.