Stimulated-emission pumping spectroscopy of jet-cooled C_3: antisymmetric stretch–bend levels

We present a study of jet-cooled C₃ in which stimulated-emission pumping spectroscopy is used to probe rovibrational levels at energies up to 8930 cm⁻¹ in the ground state. Stimulated-emission pumping spectra are reported for pump bands in the $\tilde{A}{}^1{\Pi }_u-\tilde{X}{}^1{\Sigma }_g^{+}$ system and for dump transitions that terminate in the bending progressions of states with two and four quanta of antisymmetric stretch. These spectra are used to determine the rovibrational term energies over the range J = 2 to J = 12 for the antisymmetric stretch–bend levels, 0υ2 (υ = 0 to υ = 8) and 0υ4 (υ = 0 to υ = 14). These data clearly illustrate that the effective bending potentials in the 002 and the 004 states have substantial barriers to linearity.