Renner–Teller effect in linear tetra-atomic molecules. II. Rovibronic levels analysis of the X 2Πu electronic state of HCCH+.

The variational approach detailed in the previous paper (Paper I) for the treatment of the Renner–Teller effect in linear tetra-atomic molecules including all degrees of freedom and couplings between angular momenta is applied for HCCH⁺. The accurate six-dimensional potential energy surfaces of the X ²Π_u electronic state, presented in Paper I is incorporated in the variational treatment in order to obtain all rovibronic levels including the spin-orbit coupling for 1/2≤J≤7/2 and up to 2600 cm^-1 above the global zero point energy. The “pure” stretching levels are calculated up to 11 000 cm^-1 from the stretching zero point energy. The calculated rovibronic energies are compared with previous theoretical and experimental data. The mean agreement with the zero kinetic energy photoelectron measurements of Tang et al. [J. Chem. Phys. 125, 133201 (2006)] is of 16.7 cm^-1. The Renner–Teller parameters have been determined at ν_trans=690.0 cm^-1, ε_trans=0.30, ν_cis=715.0 cm^-1, and ε_cis=-0.063. A detailed analysis of the rovibronic Hund’s cases is presented and the rotational structures of some vibronic bands recorded by Yang and Mo [J. Phys. Chem. A 110, 11001 (2006)] are given. [ABSTRACT FROM AUTHOR]