Renner–Teller effect in six-atomic molecules: Ab initio investigation of the vibronic spectrum of

Theoretical investigation of the vibronic spectrum in the XΠu2 electronic state of C6+

“…22 The atomic orbital basis set ͑276 functions͒ might seem to be unnecessarily large, but we employed it to obtain the results consistent with those in our recent study on the anionic species C 6 − . 1 The geometry optimization gives linear equilibrium nuclear arrangement, with the bond lengths of C 1 -C 2 =C 5 -C 6 = 1.3345 Å, C 2 -C 3 =C 4 -C 5 = 1.2553 Å and C 3 -C 4 = 1.3039 Å. These values reasonably agree with those obtained by Giuffreda et al 23 ͑1.347, 1.268, 1.315 Å͒ who used a smaller ͑cc-pVDZ͒ basis set.…”

“…Table III includes the results obtained in the zero-, first-, and secondorder perturbation theory by means of the formulas presented in Ref. 1. The complete ͑second-order͒ results are given for the cases when the spin quantum number takes the values ⌺ = Ϯ 1 / 2, as well as for the ͑hypothetical͒ case of ⌺ = 0.…”

“…Finally, the reader can easily compute such levels by employing the perturbative formulas presented in Ref. 1. As seen, the second-order perturbative formulas given in Ref.…”

“…12,14,1 Further simplification of the Hamiltonian is made by introducing dimensionless normal bending coordinates q j . Assuming the basis functions in the form of Eq.…”

“…In a recent study 1 we introduced a perturbative approach for handling the Renner-Teller ͑RT͒ effect 2 combined with the spin-orbit coupling in symmetric six-atomic molecules with linear equilibrium geometry ͑D ϱh point group͒. In the present study we present the results of ab initio calculations for the X 2 ⌸ u state of C 6 + .…”