The highly overlapping (A) over tilde B-2(2)-(B) over tilde (2)A(1) photoelectron bands of Cl2O molecule are studied theoretically with the aid of ab initio quantum dynamical methods. The theoretical results are compared with the high-resolution 58.4 nm He I recording of Motte-Tollet [Chem. Phys. 284, 452 (1998)]. The theoretical findings reveal the existence of a conical intersection in the (A) over tilde B-2(2)-(B) over tilde (2)A(1) electronic manifold of the radical cation (Cl2O+) and the highly overlapping photoelectron bands originate from the associated nonadiabatic interactions. A diabatic vibronic Hamiltonian for the (A) over tilde B-2(2)-(B) over tilde (2)A(1) interacting manifold of Cl2O+ is constructed in terms of the dimensionless normal coordinates of the neutral Cl2O employing a linear vibronic coupling scheme. The coupling parameters of the Hamiltonian are derived from ab initio electronic structure results. The photoelectron bands are then calculated with this Hamiltonian by solving the eigenvalue equation using a quantum dynamical method and the Lanczos algorithm. The photoelectron bands reveal a prominent progression of the bend vibrational mode and a weak progression of the symmetric stretch vibrational mode of the cation. The vibronic fine structures of the photoelectron bands are carefully examined and an adiabatic ionization energy value of 12.171 eV is estimated for the (B) over tilde (2)A(1) band. The impact of nonadiabatic coupling between the (A) over tilde B-2(2) and (B) over tilde (2)A(1) electronic states of Cl2O+ on the photoelectron dynamics is also explicitly discussed.