AB INITIO THEORETICAL STUDY ON STRUCTURES AND ELECTRONIC STATES OF C2H+

The structure of C2H+ in the ground state and low-lying excited states have been optimized using the complete active space self-consistent field (CASSCF) method. The C2H+ ion has a linear geometry with C∞v symmetry, a bent geometry with Cs symmetry and triangle geometry with C2v symmetry. For each of these geometries with certain symmetry, different electronic states exist. For the linear structure, the X3Π, 13Σ−, 11Π, 11Δ, 11Σ+ and 21Σ+ states were optimized with cc-pVQZ basis set at the CASSCF level and vibrational frequencies were determined. Electronic states with bent and triangle structures of the ion have been studied with the same method and basis sets. The electronic states 13A′, 13A″, 11A′, 11A″ and 21A′ with bent structure and 11A1, 13B1, 11B1, 13B2, 13A2, 13A1, 11A2, 23B1, 11B2 and 21B1 with triangle structure were optimized. In order to accurately determine the electronic transition energy Te, with these optimized structures, calculation were performed with the multi-reference configuration interaction (MRCI) method and the cc-pV5Z basis set.