Ab initio investigation of the vibronic structure and the spin–orbit coupling in the XΠu state of C2D2

Results of an ab initio study of the Renner–Teller effect in the X²Π_u state of C₂D₂⁺ are presented. Potential curves for the trans- and cis-bending vibrations calculated by means of the internally contracted multireference configuration interaction method are employed. Vibronic energy levels and their splitting upon spin–orbit coupling are computed by means of a variational approach.