Potential energy surfaces for the electronic states of the CCCH radical correlating at linear nuclear arrangement with the X (2)Pi state are calculated by means of an extensive ab initio approach. They are used to compute the vibronic and spin-orbit structure of this electronic state by means of a variational approach based on the use of normal bending coordinates. The results of calculations enable a reliable interpretation of the available experimental data and offer explanation for several apparently peculiar features observed. (C) 2003 American Institute of Physics.