Laser-induced fluorescence of a fast beam is obtained for a triatomic molecular ion. We use ${\mathrm{CO}}_2^{+}$ in its (0,0,0)Ã ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{\mathit{u}–}^{}{}_{}{}^{}$(0,0,0)X̃ ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{\mathit{g}}^{}{}_{}{}^{}$ electronic transition to show the feasibility of the experimental method. The high resolution (0.008 ${\mathrm{cm}}^{\mathrm{-}1}$) allows us to improve the accuracy of the molecular parameters of the upper (0,0,0) ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{\mathit{u}}^{}{}_{}{}^{}$ vibronic state. Fourier-transform emission spectroscopy was used to confirm the calibration in wave numbers and the rotational analysis.

• Received 18 September 1992

DOI:https://doi.org/10.1103/PhysRevA.48.471