The photodetachment spectroscopy of the ClO2- ion is studied theoretically with the aid of a time-dependent wave packet method. The theoretical findings in conjunction with the experimental observations unambiguously established the existence of a conical intersection in the excited B-2(2)-(2)A(1) electronic manifold of ClO2. The highly diffused vibrational structure of this electronic manifold observed in the experimental recording is attributed to the nonadiabatic effects associated with this conical intersection. In our study we employed the near-equilibrium potential energy surfaces reported by Peterson and Werner [J. Chem. Phys. 96, 8948 (1992)] along the symmetric stretching and bending vibrations of ClO2. The potential energy surfaces along the asymmetric stretching vibration are assumed to be harmonic. The dynamics of the system is studied within a linear vibronic coupling scheme, and the strength of the coupling is explicitly determined by ab initio methods. The effect of the next higher (2)A(2) electronic state of ClO2 on the above photoelectron band is also discussed. The nonradiative decay dynamics of the system mediated by the vibronic coupling is examined, and the findings are correlated with the femtosecond time-resolved experiment. (C) 2003 American Institute of Physics.