The 584 Å photoelectron spectrum of mercury vapor exhibits weak peaks corresponding to formation of the excited (5d)10 (6p) 2P1/2,3/2 ionic states, in addition to the one-electron transitions, which produce the (5d)10 (6s) 2S1/2 and (5d)9 (6s)2 2D5/2,3/2 states of Hg+. Although the 2P1/2,3/2 states are forbidden by the usual shakeup mechanism, they can occur either by a ``conjugate'' shakeup process or by configuration interaction (CI) in the initial state. We present calculations which indicate that the latter is responsible for ∼80% of the 2P1/2,3/2 intensity observed. The 304 Å photoelectron spectrum provides evidence for formation of additional excited ionic states which may have the configuration (5d)9 (6p)2 and/or (5d)9 6s 7s. Our calculations show that the energies of these states are in the region of peaks experimentally observed. The (5d)9 (6p)2 states can be formed by the initial-state CI mechanism, whereas the (5d)9 6s 7s states are attainable via the shakeup process. The probabilities for these two transitions are comparable.