Ab initio calculations are performed to study the molecular equilibrium structure and the vibrational levels of the low-lying five ionic states, 1 2B1, 1 (2)2B2, 2 2B1, 2 2B2, and 2A1 of ketene (C2H2O and C2D2O.) The theoretical intensity curve obtained by the Franck-Condon factors for the ionization transitions are also reported and compared with the photoelectron spectrum of C2H2O and C2D2O. A number of new assignments of the vibrational levels of the photoelectron spectrum are proposed.