Theoretical prediction of the potential curves for the lowest-lying states of the C2+ molecular ion

Abstract

Ab initio MRD–CI potential curves have been calculated for C₂⁺ in its first 16 electronic states and vertical transition energies T_v have been computed for a number of higher‐lying species, all of which correlate with the first dissociation limit C(³P_g)+C⁺(²P_u). The ground state of this molecular ion is found to be X ⁴Σ_g⁻ while the first excited state is 1 ²Π_u, with a calculated T_e value of 0.84 eV. On the basis of this work the C₂ I.P. value known experimentally is ascribed to the a ³Π_u→1 ²Π_u process while the transition involving both ground states appears to be difficult to detect experimentlly. Thus, the measured D_e value for C⁺₂ should involve fragmentation of the 1 ²Π_u states as well. A comparison with previous calculations which attempt to estimate the correlation energies of the various C⁺₂ states in a semiempirical manner shows very large discrepancies, both in the transition energies themselves and in the ordering of these states. Finally the assignment for the Meinel experimental band system at 4.98 eV as a ²Σ⁻_g←²Π_u transition in C⁺₂ is not supported by the present theoretical study.