Configuration interaction calculation of the potential curves for the C 3 molecule in its ground and lowest-lying Π u states

Abstract

Ab initio SCF and Cl calculations are reported for the C 3 molecule using a basis set of double-zeta plus polarization quality. Potential curves are obtained for the symmetric stretch and bending and antisymmetric stretch vibrational coordinates for the ground and 3σ u → l π g 3,1Π u excited states of this system in order to calculate the intensity distributions for the associated electronic transitions. The calculated T 0 value for the 1Π u ← X̃ 1 ∑ + g transition of 3.03 eV is in quite good agreement with the location of the origin of the 4050 Å (3.06 eV) band system in C 3, confirming its previous assignment to this electronic transition; the lifetime of the 1H u upper state is also obtained in the CI treatment. A value of 2.04 eV is calculated for the corresponding 3Π u ← X̃ 1 ∑ + g origin, which result in turn suggests that the weak feature starting at 2.10 eV (5900 Å) should be assigned thereto.