Laser-induced Fluorescence Excitation Spectrum of C₃ Cooled in a Supersonic Free Jet

The Laser-induced fluorescence （LIF） excitation vibronically resolved spectrum of gas-phase C₃ radical cooled in a supersonic free jet has been observed in the wavelength range 367. 5 -408.0nm. The C₃ radical was produced in the DC discharge of the mixture of Ar and C₂H₄. About 79 vibronic bands were assigned. Twenty-two bands of those were first assigned. The assignment demonstrates the A¹Πu-X¹∑_g⁺ transition of C₃ resulting from excitation of the v’2 mode which has a stronger Renner effect. The molecular constants of A¹Πu, v₁, v₂, T₀ and Renner parameter ∈, were obtained from the assigment. All conclusion from this work is consistent with the references. The frequencies of the vibronic-band transitions we calculated by the Renner-Teller formulae with the constant and parameter we obtained are basically in agreement with those of the experimental.