An ab initio study of the vibronic, spin–orbit and hyperfine coupling in the X2Π electronic state of the CCCD radical

The results of an ab initio study of the vibronic, spin–orbit and magnetic hyperfine structure in the X2Π electronic state for the various isotopomers of the CCCD radical are reported. The bending vibronic energy levels and their splitting due to the spin–orbit coupling are calculated by means of a variational approach. The electronically averaged hyperfine coupling constants of D and 13C are obtained as functions of two bending vibrational modes by the density functional theory method. The results of this study help to reliably interpret the available experimental data and predict yet unobserved features in the ground and excited vibronic states.