Multiphoton ionization photoelectron spectroscopy of acetaldehyde via the Ã 1A″, B, C, and D states

REMPI spectra are reported for the acetaldehyde à 1A″, B̃, C̃, and D̃ states. Photoelectron spectroscopy is used to probe the nature of the intermediate states, measure the cation vibrational frequencies, and to identify useful routes for preparing state-selected ions. Ab initio calculations of neutral and cation vibrational frequencies are also reported. The B̃ state is found to be a well-behaved Rydberg state, but with some distortion relative to the cation geometry along the ν10 and ν15 coordinates. There are B̃ state REMPI transitions that produce well state-selected cations, with vibrational energies of up to 0.4 eV, and several new cation frequencies are observed. The à 1A″ state gives structured, if somewhat broadened, REMPI transitions, but ionizes to produce a broad population of vibrationally hot ions. Only the origin band of the C̃ state is observed in REMPI, despite high intensity for this state in absorption. A few D̃ state transitions are sharp, and ionize to produce cold cations, as expected for a good Rydberg state. Most D̃ state levels are strongly mixed and broadened, however, and ionize to hot cations. Inconsistencies in the literature are discussed in light of the photoelectron spectra and ab initio results.